Patent Publication Number: US-6336235-B1

Title: Chair bed

Description:
RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 09/018,542, filed Feb. 4, 1998, now U.S. Pat. No. 6,163,903, which is a continuation of U.S. patent application Ser. No. 08/511,711, filed Aug. 4, 1995, now U.S. Pat. No. 5,715,548, which is a continuation in part of application Ser. No. 08/186,657, filed Jan. 25, 1994, now U.S. Pat. No. 5,479,666. 
    
    
     BACKGROUND AND SUMMARY OF THE INVENTION 
     The present invention relates to a bed, and particularly to a chair bed that can be manipulated to achieve both a conventional bed position having a horizontal sleeping surface upon which a person lies in a supine position and a sitting position having the feet of the person on or adjacent to the floor and the head and back of the person supported above a seat formed by the bed. More particularly, the present invention relates to a hospital bed or a patient-care bed which is convertible to a chair and which is configured to facilitate several activities that may be performed by a caregiver for a person on the sleeping surface of the bed. 
     Many hospital beds are positionable to a configuration having the sleeping surface of the bed at a predetermined height above the floor and having side rails positioned to restrain the movement of a person lying on the sleeping surface past sides of the sleeping surface and off of the bed. The sleeping surfaces of many such hospital beds can typically be lowered to reduce the distance between the sleeping surface and the floor, and the sleeping surfaces of such beds can often be manipulated to adjust the position of the person on the sleeping surface. In addition, the side rails of these hospital beds can typically be moved to a position away from the sleeping surface to facilitate movement of the person on the sleeping surface from the supine position on the sleeping surface to a standing position on the floor near the bed. 
     According to the present invention, a patient support apparatus is provided including a support and a platform. The support includes a base and a strut coupled to the base. The platform includes a seat portion and a head portion pivotably coupled to the seat portion. The head portion is pivotably coupled to the strut. The patient support apparatus further includes at least one pair of bars pivotably coupled to the support and pivotably coupled to the seat portion. The at least one pair of bars and the strut are configured to automatically coordinate pivoting movement of the head portion relative to the seat portion as the seat portion moves downward toward the base. 
     According to another embodiment of the present invention, a patient support is provided including a base and a patient support platform positioned above the base. The patient support platform includes a seat portion and a head portion pivotably coupled to the seat portion. The patient support further includes a plurality of links coupled to the patient support platform and coupled to the base. The head portion is pivotably coupled to at least one of the plurality of links. The plurality of links being configured to automatically coordinate pivoting movement of the head portion relative to the seat portion during upward and downward movement of the seat portion relative to the base. 
     According to yet another embodiment of the present invention, a patient support is provided including a base and a patient support platform including a seat portion and a head portion pivotably coupled to the seat portion. The patient support further includes a plurality of links coupled to the support platform and coupled to the base. The head portion is pivotably coupled to at least one of the plurality of links. The plurality of links is configured to automatically coordinate upward pivoting movement of the head portion relative to the seat portion as the seat portion moves downward toward the base. 
     Additional features of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments exemplifying the best mode of carrying out the invention as presently perceived. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The detailed description particularly refers to the accompanying figures in which: 
     FIG. 1 is a perspective view of a chair bed in accordance with the present invention showing a side rail exploded away from the chair bed, head side rails and foot side rails positioned along longitudinal sides of the deck, and a swinging foot gate in a closed position; 
     FIG. 2 is a view similar to FIG. 1 showing the chair bed in the sitting position having a head section of an articulating deck moved upwardly to a back-support position, a thigh section of the deck inclined slightly upwardly, a foot section of the deck moved to a generally vertical downwardly extending down position, a foot portion of the mattress being deflated, and swinging gates moved to an open position with one swinging gate folded next to the chair bed; 
     FIG. 3 is a diagrammatic view of the chair bed of FIG. 1 showing the chair bed in a bed position including a mattress having an upwardly-facing sleeping surface held a predetermined first distance above the floor, the deck being in an initial position supporting the sleeping surface in a generally planar configuration, and the foot section being a first length; 
     FIG. 4 is a diagrammatic view showing the chair bed in a low position; 
     FIG. 5 is a diagrammatic view showing the chair bed in a Trendelenburg position; 
     FIG. 6 is a diagrammatic view showing the chair bed in a reverse Trendelenburg position; 
     FIG. 7 is a diagrammatic view showing the chair bed in an intermediate position having a head end of a head section of the deck pivoted slightly upward from the initial position of the deck, a seat section positioned to lie in the horizontal plane defined by the seat section in the initial position of the deck, and the foot section being inclined slightly so that the foot end of the foot section lies below the position of the foot section when the deck is in the initial position of the deck; 
     FIG. 8 is a diagrammatic View showing the chair bed in a sitting or chair position with the head end of the head section pivoted upwardly away from the seat section to a back-support position, the seat section lying generally horizontal as in the initial deck position, the thigh section being raised upwardly, the foot section extending downwardly from the thigh section and being a second shorter length, and the portion of the mattress over the foot section being deflated; 
     FIG. 9 is a perspective view of a first embodiment of a step deck and a mattress in accordance with the present invention; 
     FIG. 10 is a sectional view taken along line  10 — 10  of FIG. 9 showing the bottom of the step deck beneath the projection; 
     FIG. 11 is an exploded perspective view of the chair bed of FIG. 1 with portions broken away; 
     FIG. 12 is a perspective view of the base frame of the chair bed of FIG. 1 showing portions of the hydraulic system module mounted on the base frame; 
     FIG. 12 a  is a perspective view of the power unit for supplying power to move the portions of the chair bed; 
     FIG. 13 is a fluid circuit diagram of a hydraulic system module of the chair bed of FIG. 1; 
     FIG. 14 is an exploded perspective view of the intermediate frame and the weigh frame of the chair bed of FIG. 1; 
     FIG. 14 a  is a sectional view taken along line  14   a — 14   a  of FIG. 14 showing a load beam cantilevered to the intermediate frame; 
     FIG. 15 is a sectional view taken along line  15 — 15  of FIG. 1 having the chair bed in the intermediate position similar to the position shown in FIG. 7; 
     FIG. 16 is a view similar to FIG. 15 showing portions of the head section of the articulating deck and the reduced-shear pivot assembly in the down position shown in FIG. 3; 
     FIG. 17 is a view similar to FIG. 16 showing portions of the head section and the reduced-shear pivot assembly in the back-support position shown in FIG. 8; 
     FIG. 18 is a perspective view of a second embodiment of a chair bed in a generally horizontal bed position; 
     FIG. 19 is a perspective view of chair bed of FIG. 18 showing the chair bed in a sitting position; 
     FIG. 20 is a sectional view taken along line  20 — 20  of FIG. 18 showing the chair bed of FIG. 18 in the bed position; 
     FIG. 21 is a view similar to FIG. 20 showing the chair bed in an intermediate position; 
     FIG. 22 is a view similar to FIG. 21 showing the chair bed in the sitting position; 
     FIG. 23 is an enlarged view similar to FIG. 20 of the second embodiment of the chair bed showing a telescoping member received by a sheath and riding on a roller while in the fully retracted position; 
     FIG. 24 is a sectional view taken along line  24 — 24  of FIG. 1 showing the deck foot section in an expanded position; 
     FIG. 25 is a view similar to FIG. 24 showing the deck foot section and the pivoting member in the contracted position; 
     FIG. 25 a  is a view similar to FIG. 24 of a second embodiment of a deck foot section in an expanded position; 
     FIG. 26 is a view taken along line  26 — 26  of FIG. 25 showing a first tongue and groove connection between the pivoting member and the sliding member; 
     FIG. 27 is a view taken along line  27 — 27  of FIG. 25 showing a second tongue and groove connection between the pivoting member and the sliding member; 
     FIG. 28 is an exploded perspective view of a second embodiment of a step deck and the mattress of the chair bed; 
     FIG. 29 is a sectional view taken along line  29 — 29  of FIG. 28 of the step deck and the mattress and showing a C-arm (in phantom) for holding medical equipment such as fluoroscopic equipment; 
     FIG. 30 is an exploded perspective view of a third embodiment of the mattress and the deck showing the foot section of the deck and the foot portion of the mattress in a minimized condition having the foot section of the deck contracted and the foot portion of the mattress contracted longitudinally and deflated so that the foot portion of the mattress is thinner and shorter than when foot portion is inflated; 
     FIG. 31 is a diagrammatic side elevation view of the chair bed of FIG. 1 showing the chair bed in the bed position of FIG.  3  and showing a head section side rail and a body section side rail; 
     FIG. 32 is a diagrammatic view similar to FIG. 31 showing the head section of the articulating deck of the chair bed raised to an intermediate position of FIG. 7; 
     FIG. 33 is a diagrammatic view similar to FIG. 31 showing the head section in the back-support position of FIG. 8; 
     FIG. 34 is a sectional view taken along line  34 — 34  of FIG. 31 of a side rail in a patient-restraining position; 
     FIG. 35 is a view similar to FIG. 34 of the side rail intermediate the patient-restraining position of FIG. 34 and a down-out-of-the-way position (in phantom) having a top of the side rail beneath the sleeping surface; 
     FIG. 36 is an exploded view of a head section of an articulating deck of the chair bed of FIG. 1 including a breakaway side rail; 
     FIG. 37 is a front elevation view from outside of the bed of a head section side rail in accordance with the present invention having a mechanical angle indicator; 
     FIG. 38 is a sectional view taken along line  38 — 38  of FIG. 37 showing the mechanical angle indicator; 
     FIG. 39 is a perspective view from outside of the bed of a body section side rail in accordance with the present invention having a mechanical angle indicator and a pivotable display; 
     FIG. 40 is a sectional view taken along line  40 — 40  of FIG. 39 showing the pivotable display; 
     FIG. 41 is a sectional view taken along line  41 — 41  of FIG. 39 showing the patient control buttons on the inside of the side rail; 
     FIG. 42 is a sectional view taken along line  42 — 42  of FIG. 41 showing the patient control buttons; 
     FIG. 43 is a block diagram illustratively showing major functional components of the chair bed and some of the mechanical and fluid connections therebetween; 
     FIG. 44 is a block diagram of the base module and portions of the hydraulic module illustratively showing some components of the base module and illustrating some of the mechanical, fluid, and electrical interconnections therebetween; 
     FIG. 45 is a block diagram of the intermediate frame module and portions of the hydraulic module illustratively showing some components of the intermediate frame module and illustrating some of the mechanical, fluid, and electrical interconnections therebetween; 
     FIG. 46 is a block diagram of the articulating deck/weigh frame module and portions of the hydraulic module illustratively showing some components of the articulating deck/weigh frame module and illustrating some of the mechanical, fluid, and electrical interconnections therebetween; 
     FIG. 47 is a block diagram of the side rail assemblies illustratively showing some components of the side rail assemblies and illustrating some of the mechanical, fluid, and electrical interconnections therebetween; 
     FIG. 48 is a block diagram illustrating the electronic control modules of the present invention connected in a peer-to-peer network configuration and illustrating the additional system components which are coupled to the various modules by discrete electrical connections; 
     FIG. 49 is a diagrammatical view illustrating the electrical connection from the communication network cable to a selected module and illustrating a coupler between a pair of network connectors to facilitate adding another module to the network; 
     FIG. 50 is a schematic block diagram illustrating the electronic components of a bed articulation control module; 
     FIG. 51 is a schematic block diagram illustrating the electrical components of the scale instrument module; 
     FIG. 52 is a schematic block diagram illustrating the mechanical and electrical components of the bed position sense and junction module; 
     FIG. 53 is a schematic block diagram illustrating the components of the left and right standard caregiver interface module for either the left siderail or the right siderail; 
     FIG. 54 is a diagrammatical view of the lockout switches on the siderail control panel to prevent movement of selected sections of the bed; and 
     FIG. 55 is a schematic block diagram illustrating the mechanical and electrical components of the graphical caregiver interface module; 
     FIGS. 56 and 57 are flow charts illustrating details of the automatic module recognition feature of the graphical caregiver interface module; 
     FIG. 58 is a flow chart illustrating the steps performed by the communications module for automated data collection from the other modules connected to the communication network of the bed; 
     FIG. 59 is a diagrammatical view illustrating a patient status module and a gateway module of the present invention; 
     FIG. 60 is a diagrammatical view illustrating details of a patient charting module of the present invention; 
     FIG. 61 is a block diagram illustrating the modular therapy and support surface system of the present invention including a plurality of control modules for controlling various air therapy devices and surface sections of a support surface and illustrating an air supply module for controlling an air handling unit and a switching valve to selectively supply air pressure and a vacuum to the various therapy devices and surface sections; 
     FIG. 62 is a diagrammatical illustration of the configuration of an air therapy control module; 
     FIG. 63 is an exploded perspective view illustrating a foam surface foundation with side bolsters configured to be positioned on a deck of the bed, an upper foam support surface, and an inflatable and deflatable surface foot section; 
     FIG. 64 is a perspective view illustrating the surface foot section in an inflated configuration when the bed is in a normal bed position and illustrating the surface foot section in a retracted and collapsed configuration when the bed is in a chair position; 
     FIG. 65 is a diagrammatical view further illustrating how the surface foot section retracts or shortens and collapses or thins as the bed moves from the bed position to the chair position; 
     FIG. 66 is a diagrammatical view of the control module and bladder configuration of the surface foot section; 
     FIG. 67 is a partial perspective view with portions broken away illustrating another embodiment of the surface foot section; 
     FIG. 68 is an exploded perspective view of another embodiment of the present invention illustrating a pulmonary therapy rotational bladder located between a deck of the bed and the surface foundation and illustrating an upper air bladder support surface located above the surface foundation in place of the upper foam support surface of FIG. 61; 
     FIG. 69 is a diagrammatical end view illustrating the configuration of the modular therapy and support surface of the present invention when the pulmonary bladders are all deflated; 
     FIG. 70 is a diagrammatical view similar to FIG. 66 illustrating inflation of left side pulmonary bladders to rotate a patient to the right; 
     FIG. 71 is a diagrammatical view similar to FIGS. 66 and 67 illustrating inflation of the right side pulmonary bladders to rotate the patient to the left; 
     FIG. 72 is a block diagram illustrating another embodiment of the present invention illustrating separate exchangeable surfaces or therapy devices which are each coupled to a control module including pneumatic control valves and sensors, an electrical connection, and a processor for communicating with an air and power handling unit on the bed and with a graphical interface display on the bed through the electrical communication network of the bed; and 
     FIG. 73 is a block diagram illustrating the support surface system of the present invention including a plurality of a bed articulation control module controlling movement of the articulating deck sections and illustrating a surface instrument module and an air supply module for controlling an air handling unit and a switching valve to selectively supply air pressure and a vacuum to control inflation and deflation of zones of the support surface. 
    
    
     DETAILED DESCRIPTION OF THE ILLUSTRATIVE AND PREFERRED EMBODIMENTS 
     A chair bed  50  in accordance with the present invention having a head end  52 , a foot end  54 , and sides  56 ,  58  is illustrated in FIG.  1 . As used in this description, the phrase “head end  52 ” will be used to denote the end of any referred-to object that is positioned to lie nearest head end  52  of chair bed  50 . Likewise, the phrase “foot end  54 ” will be used to denote the end of any referred-to object that is positioned to lie nearest foot end  54  of chair bed  50 . 
     Chair bed  50  includes a base module  60  having a base frame  62  connected to an intermediate frame module  300  by lift arms  320 ,  322 ,  324 ,  326  as shown in FIGS. 1,  11  and  43 . An articulating deck/weigh frame module  400  is coupled to intermediate frame module  300  by load beams  330 ,  336 ,  342 ,  348 . Side rail assemblies  800 ,  802 ,  804 ,  806  and an extended frame module  610  having a swinging foot gate  622  are coupled to articulating deck/weigh frame module  400 . A mattress  550  is carried by articulating deck/weigh frame module  400  and provides a sleeping surface or support surface  552  configured to receive a person (not shown). 
     Chair bed  50  can be manipulated by a caregiver or by a person (not shown) on sleeping surface  552  using hydraulic system module  100  so that mattress  550 , an intermediate frame  302  of intermediate frame module  300 , and an articulating deck  402  of articulating deck/weigh frame module  400  assume a variety of positions, several of which are shown diagrammatically in FIGS. 3-7. 
     Articulating deck  402  includes a head section  404 , a seat section  406 , a thigh section  408 , and a foot section  410 . Mattress  550  rests on deck  402  and includes a head portion  558 , a seat portion  560 , a thigh portion  562 , and a foot portion  564 , each of which generally corresponds to the like-named portions of deck  402 , and each of which is generally associated with the head, seat, thighs, and feet of the person on sleeping surface  552 . Details of deck  402  and mattress  550  will be explained hereinafter. 
     Chair bed  50  can assume a bed position having deck  402  configured so that sleeping surface  552  is planar and horizontal, defining an initial position of deck  402  as shown in FIG.  1  and as shown diagrammatically in FIG.  3 . In the bed position, sleeping surface  552  is a predetermined first distance  566  above the floor. Chair bed  50  can also be manipulated to assume a low position shown diagrammatically in FIG. 4 having deck  402  in the initial position and having sleeping surface  552  a predetermined second distance  568  above the floor, the second distance  568  being smaller than first distance  566 . The foot section  410  of the articulating deck  402  has a first length  465  when the deck  402  is in the initial position. 
     Chair bed  50  can be moved to a Trendelenburg position shown diagrammatically in FIG. 5 having deck  402  in a planar configuration and tilted so that head end  52  of sleeping surface  552  is positioned to lie closer to the floor than foot end  54  of sleeping surface  552 . Chair bed  50  can also achieve a reverse Trendelenburg position shown diagrammatically in FIG. 6 having deck  402  in a planar configuration and tilted so that foot end  54  of sleeping surface  552  is positioned to lie closer to the floor than head end  52  of sleeping surface  552 . 
     As described above, chair bed  50  is convertible to a sitting position shown in FIG.  2  and shown diagrammatically in FIG.  8 . In the sitting position, head end  52  of head section  404  of deck  402  is pivoted upwardly away from intermediate frame  302  to a back-support position providing a pivotable backrest so that head section  404  and intermediate frame  302  form an angle  512  generally between  55  and  90  degrees. Seat section  406  of deck  402  is positioned to lie generally horizontally as in the initial position, foot end  54  of thigh section  408  is slightly upwardly inclined, and foot section  410  of deck  402  extends generally vertically downwardly from thigh section  408  and has a length  464  that is shorter than when deck  402  is in the initial position. Foot portion  564  of mattress  550  is inflatable and is in a deflated condition when chair bed  50  is in the sitting position. Foot portion  564  of mattress  550  is thinner and shorter when deflated than when inflated. 
     Chair bed  50  is capable of assuming positions in which head, thigh, and foot sections  404 ,  408 ,  410  of deck  402  are in positions intermediate to those shown in FIGS. 3 and 8. For example, chair bed  50  can assume an intermediate position shown diagrammatically in FIG.  7  and also shown in FIG. 15, having head end  52  of head section  404  of deck  402  pivoted slightly upwardly from the initial position, seat section  406  positioned to lie in the same generally horizontal plane as in the initial position, foot end  54  of thigh section  408  raised slightly upwardly from the initial position, and foot section  410  being inclined so that foot end  54  of foot section  410  lies below head end  52  of foot section  410 . 
     Additionally, articulating deck  402  of chair bed  50  is configured as a step deck  412  as shown illustratively along with illustrative step mattress  550  in FIGS. 9,  10 , and  28 - 30 . The step deck and mattress of FIGS. 28-30 are those illustrated in FIGS. 3-8. Step deck  412  includes an upper deck  414  and a central, longitudinally extending recess  456  defined by a lower deck  430  of step deck  412  and a wall  438  surrounding recess  456  and connecting lower deck  430  to upper deck  414 . Upper deck  414  includes longitudinally extending upper deck side portions  417 , a head end upper deck end portion  416 , and a foot end upper deck end portion  460 . 
     Mattress  550  includes a generally upwardly-facing sleeping surface  552  and a bottom surface  586  that is generally parallel to sleeping surface  552  and that is positioned to lie beneath sleeping surface  552 . A perimetral side  578  connects sleeping surface  552  and bottom surface  586 . A projection  576  is appended to bottom surface  586  and extends downwardly therefrom. Preferably, projection  576  is spaced-apart from sides  578  of mattress  550  and nests in recess  456 . Projection  576  may engage wall  438  of step deck  412  to prevent movement of mattress  550  relative to step deck  412  and to maintain the generally central position of mattress  550  on deck  412 . 
     Preferably, mattress  550  is provided with a thick zone  582  adjacent to recess  456  and projection  576 , and a thin zone  580  engaging upper deck  414  as shown in FIG.  10 . For example, thick zone  582  can be one and one-half times the thickness of thin zone  580 . In one preferred embodiment, the thick zone is approximately 7½ inches (19 cm) thick and the thin zone is 5 inches (12.7 cm) thick. Thick zone  582  is positioned to carry the majority of the weight of a person (shown in phantom) supported on sleeping surface  552  to maximize the comfort of the person. Having perimetral thin zone  580  provides a perimetral portion of mattress  550  that appears to the person on sleeping surface  552  to be firmer than thick zone  582 , facilitating entry onto and exit from sleeping surface  552  along sides  578  of mattress  550 . 
     As can be seen, step deck  414  and mattress  550  can be used in many applications requiring a support surface for supporting a person. For example, step deck  414  and mattress  500  can be configured for use as a stretcher to be carried by caregivers and as a gurney having step deck  414  mounted on a frame with wheels for transporting the person supported by the gurney. 
     A general overview of the system architecture will be followed by a description of the general operation of chair bed  50 . 
     System Architecture 
     Base module  60 , intermediate frame module  300 , articulating deck/weigh frame module  400 , and side rail assemblies  800 ,  802 ,  804 ,  806  are illustratively shown in FIG.  11  and are shown diagrammatically in FIGS. 43-47. The solid lines of FIGS. 43-47 represent mechanical connections, the thick short dashed lines represent fluid connections, the thin long dashed lines represent electrical connections, and the double lines represent connections to the electronic network. Base module  60 , intermediate frame module  300 , and articulating deck/weigh frame module  400  cooperate with a hydraulic system module  100  to manipulate mattress  550  in accordance with commands from the caregiver or from the person supported by sleeping surface  552 . These modules and some connections therebetween are described below. 
     BASE MODULE  60   
     Base Module  60  includes a base frame  62  on which the components of the chair bed  50  are mounted as shown in FIGS. 11 and 12, and diagrammatically in FIG.  14 . Base module  60  includes a lifting mechanism  130  that raises and lowers sleeping surface  552  of chair bed  50  relative to base frame  62 . Much of the electrical, air, and hydraulic components of chair bed  50  are located in or on base frame  62 . 
     Head end casters  70 ,  72 , and foot end casters  74 ,  76  coupled to the base frame  62 . A brake/steer linkage  80  couples the casters  70 ,  72 ,  74 ,  76  to brake/steer pedals  78  that are connected to base frame  62 . Brake/steer pedals  78  are butterfly wheel pedals that can move between a braking position locking casters  70 ,  72 ,  74 ,  76  so that casters  70 ,  72 ,  74 ,  76  do not rotate, a middle neutral position that allows casters  70 ,  72 ,  74 ,  76  to rotate freely, and a steering position having foot end casters  74 ,  76  locked into steer and head end casters  70 ,  72  free to swivel. 
     Head end casters  70 ,  72  are positioned to lie adjacent to head end  52  of chair bed  50  and foot end casters  74 ,  76  are spaced-apart from foot end  54  of chair bed  50  as shown in FIGS. 11 and 15 to facilitate articulation of chair bed  50  to the sitting position. Additionally, this inward positioning of foot end casters  74 ,  76  closer to the center of gravity of chair bed  50  maximizes the maneuverability of chair bed  50  in the steering condition. 
     Struts  64  are appended to sides  66  of base frame  62  to provide mounting surfaces for portions of hydraulic system module  100  as shown in FIGS. 11-13 and  44 . As shown best in FIGS. 12 and 13, illustrative hydraulic system module  100  includes lifting mechanism  130  having actuators  132  and  142  for individually raising and lowering head end  52  and foot end  54  of intermediate frame  302  relative to base frame  62 , actuators  150 ,  158 ,  168 ,  176  for raising and lowering the head, thigh, and foot sections  404 ,  408 ,  410  of articulating deck  402  relative to intermediate frame  302 , control manifold  186  for selectively controlling actuators  132 ,  142 ,  150 ,  158 ,  168 ,  176 , power unit  112  for providing energy to drive actuators  132 ,  142 ,  150 ,  158 ,  168 ,  176 , and conduit  122  for connecting power unit  112  and control manifold  186  to actuators  132 ,  142 ,  150 ,  158 ,  168 ,  176 . 
     Power unit  112  is preferably a hydraulic power unit and actuators  132 ,  142 ,  150 ,  158 ,  168 ,  176  are preferably hydraulic cylinders. It will be appreciated, however, that in accordance with the present invention, various mechanical and electromechanical actuators and drivers may be used to raise and lower intermediate frame  302  on base frame  62  as well as to raise and lower individual deck sections  404 ,  406 ,  408 ,  410  relative to intermediate frame  302 . As will be explained below, fluid actuators are preferred since they are capable of manual operation with a battery to provide power for electrical control. 
     It is well known in the hospital bed art that electric drive motors with various types of transmission elements including lead screw drives and various types of mechanical linkages may be used to cause relative movement of portions of hospital beds. It is also well known to use pneumatic actuators to actuate and/or move individual portions of hospital beds. The terms “means for raising or lowering” in the specification and in the claims, therefore, are intended to cover all types of mechanical, electromechanical, hydraulic, and pneumatic mechanisms, including manual cranking mechanisms of all types, for raising and lowering portions of chair bed  50  of the present invention. 
     The caregiver can adjust the height and angle of inclination of sleeping surface  552  as shown in FIGS. 3-6 by activating a hydraulically powered lifting mechanism  130  to control intermediate frame  302  by lift arms  320 ,  322 ,  324 ,  326  connected to cylinders  132 ,  142 . A CPR foot pedal  250  and emergency Trendelenburg actuator  254  are mounted on base frame  62  to manually control control manifold  186 . In addition, CPR foot pedal  250  shown in FIG. 12 may be used as the emergency Trendelenburg actuator  254  when pivoted upwardly to a raised position. 
     If chair bed  50  is plugged into an AC outlet (not shown), the caregiver activates the lifting function with the push of a button. When not plugged in, the caregiver may raise chair bed  50  by pumping one of the hydraulic foot pump pedals  252  located on either side of the base frame  64 . The caregiver may also place chair bed  50  in the Trendelenburg position when chair bed  50  is not plugged in or in an emergency by activating the emergency Trendelenburg actuator  254  located on base frame  62 . If chair bed  50  is equipped with a battery  92 , the caregiver may operate any functions of chair bed  50  by pumping the hydraulic foot pump pedal  252  and simultaneously pressing the desired function switch. The electrical control of the valves is supported by a battery  92  on base frame  62 . 
     Base frame  62  also serves as a mounting location for other modules or components such as well as a bed articulation control module  1018 , surface electronics, a bed-side communications interface, components of the electronic network, bed exit electronics, a night light  1073 , a power supply AC/DC converter  1062 , and a battery/charge circuit  88 . 
     HYDRAULIC SYSTEM MODULE  100   
     Hydraulic System Module  100  provides the mechanical power required to move articulating deck  402  and to raise and lower chair bed  50 . Hydraulic system module  100  includes hydraulic cylinders  132 ,  142 ,  150 ,  158 ,  168 ,  176  that cooperate with linkages to provide these movements. 
     Movements of head, thigh, and foot sections  404 ,  408 ,  410  of articulating deck  402  and the raising and lowering of intermediate frame  302  of chair bed  50  illustratively shown in FIGS. 3-8 are accomplished with hydraulic system module  100 . The illustrative system comprises a hydraulic power unit  112 , conduit  122 , a valve or control manifold  186 , and cylinders  132 ,  142 ,  150 ,  158 ,  168 ,  176  as shown in FIG.  13 . Hydraulic power unit  112  comprises an electric motor  124 , a pump  116  driven by electric motor  124 , a manual pump  118 , and a reservoir  120  containing hydraulic oil. 
     Pump  116  pressurizes hydraulic oil when chair bed  50  is connected to AC power, which in turn moves piston rods  134 ,  144 ,  152 ,  160 ,  170 ,  178  inside of cylinders  132 ,  142 ,  150 ,  158 ,  168 ,  176  to articulate chair bed  50 . When chair bed  50  is not connected to AC power, manual pump  118  can be used, via a foot pump pedal  250  mounted on base frame  62  and coupled to manual pump  118 , to pressurize the hydraulic oil and cause piston rods  134 ,  144 ,  152 ,  160 ,  170 ,  178  to move. Manually activated valves  212 ,  214  in valve manifold  162  make it possible for the caregiver to rapidly lower head section  404  to a horizontal CPR position and to take advantage of a manual Trendelenburg feature to manually move chair bed  50  to the Trendelenburg position, illustratively shown in FIG. 5, when AC power is not available. 
     For chair beds  50  equipped with a battery  92 , the caregiver may use any of the nurse control functions by pumping foot pump pedal  252  and simultaneously pressing the desired nurse control function on the side rail assemblies  800 ,  802 ,  804 ,  806 . The caregiver supplies the hydraulic power via the foot pump pedal  252 , and battery  92  supplies electrical power to open or close the valves on valve manifold  186  in illustrative chair bed  50 . 
     INTERMEDIATE FRAME MODULE  300   
     Intermediate Frame Module  300  includes intermediate frame  302  which is supported and positioned via lift arms  320 ,  322 ,  324 ,  326  of lifting mechanism  130  of base frame  62 . Intermediate frame  302  in turn supports articulating deck/weigh frame module  400  and thus couples articulating deck/weigh frame module  400  to lifting mechanism  130  as shown in FIG.  11  and shown diagrammatically in FIG.  45 . 
     Intermediate frame  302  includes four load beams  330 ,  336 ,  338 ,  342  that movably couple weigh frame  506  of articulating deck/weigh frame module  400  to intermediate frame  302 . Each load beam  330 ,  336 ,  342 ,  348  includes a housing  334 ,  340 ,  346 ,  352  and a sensing end  332 ,  338 ,  344 ,  350  that is movable relative to housing  334 ,  340 ,  346 ,  352 . The details of load beam  330  is discussed herein with reference to FIG. 14 a.  Each load beam  330 ,  336 ,  342 ,  348  additionally comprises a transducer (not shown) connected to sensing ends  332 ,  338 ,  344 ,  350  that provides an electrical signal in response to movement of sensing end  332 ,  338 ,  344 ,  350  relative to housing  334 ,  340 ,  346 ,  352 . The extent of the movement of sensing ends  332 ,  338 ,  344 ,  350  depends upon the amount of weight supported by load beams  330 ,  336 ,  342 ,  348 , so that the electrical signal provided by load beams  330 ,  336 ,  342 ,  348  varies in response to the weight supported by weigh frame  506 . 
     Load beams  330 ,  336 ,  342 ,  348  can be replaced by dummy beams (not shown) that support weigh frame  506  on intermediate frame  302  but that do not provide for any movement of weigh frame  506  relative to intermediate frame and that do not provide any electrical signals. When chair bed  50  has dummy beams instead of load beams  330 ,  336 ,  342 ,  348 , weigh frame  506  is fixed to intermediate frame  302  and cooperates therewith to provide a common frame (not shown). The common frame is used with chair beds  50  that do not include weigh scales  368  but that include other features of chair beds  50  described herein. 
     Intermediate frame  302 , illustratively shown in FIG. 14, includes permanent IV poles  376 , an oxygen tank holder  380 , a mount  310  having openings  312  for caregivers to mount added-on IV poles (not shown), mounting locations  304  for bumpers, mounting locations  316  for headboard  318  adjacent to head end  52  of intermediate frame  302  as shown in FIG. 1, and a drainage bag mount  306  for holding drainage bags (not shown) adjacent to foot end  54  of intermediate frame  302  so that the weight of added-on oxygen tanks, IV poles, and drainage bags is not included in the weight measurement of the person (assuming the chair bed  50  is equipped with weigh scales  368 ). Intermediate frame  302  is the fixed platform on which load beams  330 ,  336 ,  342 ,  348 , which are weight sensing components of the weigh scales  368 , are mounted and weigh frame  506  is mounted to intermediate frame  302  by load beams  330 ,  336 ,  342 ,  348 . Any equipment (not shown) mounted to the intermediate frame  302  will not be weighed. 
     Intermediate frame  302  moves upwardly and downwardly relative to base frame  62 , so that weigh frame  506 , articulating deck  402 , mattress  550 , and extended frame module  610  connected to weigh frame  506 , which are supported thereon as shown in FIG. 11, also move upwardly and downwardly relative to base frame  62 . The movable head, thigh, and foot sections  404 ,  408 ,  410  of articulating deck  402  move upwardly and downwardly relative to weigh frame  506 , and seat section  406  is fixed relative to weigh frame  506 . 
     Intermediate frame  302  provides a place off of weigh frame  506  for mounting equipment. For chair beds  50  equipped with weigh scales  368 , the caregiver may wish to exclude the weights of added-on components such as IV bags (not shown) and drainage bags (not shown) from the weight of the patient. Mounting drainage bag mount  306  and IV pole mount  310  on intermediate frame  302  makes this possible. 
     ARTICULATING DECK/WEIGH FRAME MODULE  400   
     Articulating Deck/Weigh Frame Module  400  includes mattress  550  that rests on four sections, head section  404 , seat section  406 , thigh section  408 , and foot section  410  of articulating deck  402  as shown in FIGS. 11,  28 - 30 , and  46 . The sections  404 ,  406 ,  408 ,  410  of articulating deck  402  are movable to change the position of a person supported on sleeping surface  552  of mattress  550 . For chair beds  50  equipped with weigh scales  368 , deck  402  and a weigh frame  506 , which supports deck  402  and is interposed between deck  402  and intermediate frame  302 , are equivalent to a weigh platform of a platform scale, i.e., anything resting on deck  402  will be weighed when the weigh scales  368  are used. For chair beds  50  that are not equipped with weigh scales  368 , deck  402  and weigh frame  506  are fixed together by dummy beams (not shown) to form a common frame (not shown). 
     Articulating deck  402  is the surface upon which the mattress  550  rests. Deck  402  is illustratively segmented into head, seat, thigh, and foot sections  404 ,  406 ,  408 ,  410 , three of which, head section  404 , thigh section  408 , and foot section  410 , may be rotated to change the angle of inclination of the back, thighs, and lower legs of the person (not shown) with respect to seat section  408 . Head section  404  has a special “reduced-shear pivot” which is the movement produced by a reduced-shear pivot assembly  650  to be described hereinafter that causes head section  404  to pivot about an effective pivot axis  652  that is positioned to lie above lower deck section  510  and that is preferably at upper deck  414  as shown in FIGS. 16 and 17. Seat section  406  of deck  402  remains horizontal and the head, thigh, and foot sections  404 ,  408 ,  410  of deck  402  can move relative to the seat section  406  and relative to each other, thereby moving the head, thigh, and foot portions  558 ,  562 ,  564  of mattress  550  relative to seat portion  560  of mattress  550  and relative to each other. 
     Articulating deck  402  is mounted to weigh frame  506 . Actuators or cylinders  150 ,  158 ,  168 ,  176 , that power the movement of head, thigh, and foot sections  404 ,  408 ,  410  of deck  402 , are also mounted to weigh frame  506  as shown in FIGS. 11,  14 , and  15 . Articulating deck/weigh frame module  400  is, in turn, supported by intermediate frame module  300 . The interface between articulating deck/weigh frame module  400  and intermediate frame module  300  is illustratively limited to four attachments as shown in FIG.  14 . For beds equipped with weigh scales  368 , load beams  330 ,  336 ,  342 ,  348  are located at these points. For chair beds that are not equipped with weigh scales  368 , or “non-scale chair beds,” the modules are rigidly coupled. 
     Articulating deck/weigh frame module  400  may also carry other components of chair bed  50 . For example, details  304  on the articulating deck  402 , shown in FIG. 11, make it possible for caregivers to tie restraint straps (not shown) to deck  402  when required. While head section side rails  808 ,  810  are mounted to head section  404 , body section side rails  812 ,  814  are mounted to weigh frame  506  by brackets  816 ,  818 . In a preferred embodiment, head side rails  808 ,  810  are mounted to breakaway mounting brackets or collateral deck portions  922 ,  924 . Other modules or components that may be attached to articulating deck/weigh frame module  400  include, for example, a removable foot prop  646  for supporting the feet of the person on sleeping surface  552  during movement between the bed position and the sitting position, a foot safety switch  648 , and extended frame module  610 . 
     EXTENDED FRAME MODULE  610   
     Extended Frame Module  610 , shown in FIG.  11  and shown diagrammatically in FIG. 46, includes an extended U-shaped frame  612  at the foot end  54  of the chair bed  50  and mounted to weigh frame  506 , extended frame  612  providing a location for mounting caregiver controls, traction equipment (not shown), handles for transport (not shown), a utility shelf  644 , and bumpering (not shown). The design of chair bed  50  provides for egress or ingress of the person at foot end  54  of chair bed  50 , particularly when chair bed  50  is converted to the sitting position shown in Fig. and diagrammatically in FIG.  8 . 
     Extended frame module  610  includes a foot gate  622  having swinging gates  626 ,  634 , one swinging gate  626 ,  634  mounted on either side of chair bed  50  as shown in FIGS. 1,  2 , and  11 . Gates  626 ,  634  can swing outwardly away from chair bed  50  to provide the person a clear path out of chair bed  50  for easy egress from the sitting position while also providing the caregiver clear access to the patient. Foot section  410  of articulating deck  402  and foot portion  564  of mattress  550  rotate through the U-shaped extended frame  612  when foot section  410  moves between the up position and the down position. 
     SIDE RAIL ASSEMBLIES  800 ,  802 ,  804 ,  806   
     Side Rail Assemblies  800 ,  802 ,  804 ,  806  include side rails  808 ,  810 ,  812 ,  814 , which are passive restraint devices mounted on both sides of chair bed  50  as shown in FIGS. 1,  2 ,  11 ,  31 - 38 , and diagrammatically in FIG.  47 . In the upward patient-restraining position, side rails  808 ,  810 ,  812 ,  814  are vertical barriers extending above sleeping surface  552  to restrain movement of the person past sides  554 ,  556  of sleeping surface  552 , thereby preventing the person from rolling out of chair bed  50 . Side rails  808 ,  810 ,  812 ,  814  may also be lowered below sleeping surface  552  of mattress  550  to permit the person to move past sides  554 ,  556  of sleeping surface  552  when entering and exiting chair bed  50  or to give the caregiver clear access to the patient. 
     Lowering each side rail  808 ,  810 ,  812 ,  814  is accomplished by pulling a release handle  862 . After pulling release handle  862 , the caregiver may let go of release handle  862  and allow side rail  808 ,  810 ,  812 ,  814  to rotate downwardly and tuck into the tucked position under deck  402 . The rate at which each side rail  808 ,  810 ,  812 ,  814  rotates downwardly is preferably controlled by a mechanical damper  868 . To raise side rails  808 ,  810 ,  812 ,  814 , the caregiver pulls upwardly on side rails  808 ,  810 ,  812 ,  814  until they lock in the patient-restraining position. 
     Illustratively, there are four side rails  808 ,  810 ,  812 ,  814  on chair bed  50 . Two head section side rails  808 ,  810  are mounted to head section  404  of articulating deck  402 , and two body section side rails  812 ,  814  are mounted to move or stay with seat section  406  of deck  402 , seat section  406  and side rails  812 ,  814  being fixed relative to weigh frame  506 . 
     Side rails  808 ,  810 ,  812 ,  814  can be provided with mechanical angle indicators  938  that provide a visual indication of the angular orientation of side rails  808 ,  810 ,  812 ,  814  relative to the floor. Head section side rails  808 ,  810  move with head section  404  of deck  402  as head section  404  pivots between the down position and the back-support position, so that angle indicators  938  mounted to head section side rails  808 ,  810  generally indicate the angular orientation of head section  404 . Likewise, body section side rails  812 ,  814  are generally fixed in an angular orientation relative to intermediate frame  302  so that angle indicators  938  mounted to body section side rails  812 ,  814  generally indicate the angular orientation of intermediate frame  302 . 
     Body section side rails  812 ,  814  can also be provided with a hip pivot guide  694  shown in FIGS. 31-33 to help the caregiver to properly position the hip (not shown) of the person (not shown) on sleeping surface  552 . Proper positioning of the hip operates to maximize the effectiveness of the reduced-shear pivot. 
     Besides serving as passive restraints, side rails  808 ,  810 ,  812 ,  814  also serve as a mounting location for nurse controls  1028 ,  1030 , patient controls  1156 ,  1160  and entertainment modules. These modules are referred to as human interface control modules. These interface control modules output the occurrence of any switch activation into the electronic network. In addition, side rails  808 ,  810 ,  812 ,  814  may preferably contain the necessary hardware to allow patient-to-nurse communications (not shown) and entertainment audio output (not shown). 
     Detailed Description of Modules and Systems 
     Hydraulic System Module  100   
     Actuators  132 ,  142 ,  150 ,  158 ,  168 ,  176  are preferably hydraulic actuators. For example, head end actuator  132  is a lift cylinder as shown in FIG. 12 having an interior region  133  shown diagrammatically in FIG. 13 and a piston rod  134  slidably received by interior region  133 . Head end lift cylinder  132  is formed to include a front port  136  and a rear port  138 , each of which are in fluid communication with interior region  133 . When pressurized fluid such as hydraulic oil is received by rear port  138 , the pressurized fluid pushes piston rod  134  toward front port  136  and causes an end  135  of piston rod  134  to extend out of and move away from lift cylinder  132 . At the same time, non-pressurized fluid escapes from front port  136  and is received by a return conduit  185  in fluid communication with a reservoir  120 . Likewise, if pressurized fluid were to be received by front port  136 , it would act on piston rod  136  to slide piston rod  136  toward rear port  138 , thereby retracting end  135  into lift cylinder  132  and releasing non-pressurized fluid into return line  185  and reservoir  120 . This allows actuators  132 ,  142 ,  150 ,  158 ,  168 ,  176  to be hydraulically locked. 
     Hydraulic power unit  112  is mounted on base frame  62  and includes reservoir  120 , pump  116  which is driven by electric motor  124 , and manual pump  118  which is driven by foot pump pedal  252  as shown in FIGS. 12,  12   a,  and  13 . Hydraulic power unit  112  operates to pressurize a fluid such as hydraulic oil which is stored at atmospheric pressure in reservoir  120 . The pressurized hydraulic oil is supplied to control manifold  186  which in turn selectively supplies the pressurized hydraulic oil to actuators  132 ,  142 ,  150 ,  158 ,  168 ,  176 . 
     Pump  116  receives the hydraulic oil from reservoir  120 , pressurizes the hydraulic oil, and supplies the pressurized hydraulic oil to a pressurized oil manifold  184  of control manifold  186  as shown in FIG.  13 . Control valves of control manifold  186  receive the pressurized hydraulic oil and each control valve either supplies the pressurized hydraulic oil to the actuator or blocks the flow of the hydraulic oil to the actuator, depending upon the state of the control valve. The control valves are typically either three-way valves or they are two-way valves that cooperate with companion two-way valves to supply pressurized hydraulic oil to the actuators or to receive hydraulic oil from the actuators and divert the hydraulic oil from the actuators to return conduit  185  that returns non-pressurized hydraulic oil to reservoir  120 . Thus, the control valves operate to control the flow of pressurized hydraulic oil between hydraulic power unit  112  and actuators  132 ,  142 ,  150 ,  158 ,  168 ,  176 . 
     Lifting mechanism  130  includes head end actuator  132  to raise and lower head end  52  of intermediate frame  302  and foot end actuator  142  to raise and lower foot end  54  of intermediate frame  302  as shown in FIG. 13. A head end rear first valve  188 , a head end rear second valve  190 , and an emergency Trendelenburg valve  214  control the flow of fluid between rear port  138  of head end actuator  132  and hydraulic power unit  112 . A head end front pilot operated check valve  220  controls the flow of fluid between front port  136  of head end actuator  132  and hydraulic power unit  112 . The raising and lowering of head end  52  of intermediate frame  302  will provide the most satisfactory results when the operation of valves  188 ,  190 ,  214 ,  220  is coordinated as described below. 
     First valve  188  is a two-way valve interconnecting pressurized oil manifold  184  and conduit  122  that is in fluid communication with rear port  138  of head end lift cylinder  132  as shown in FIG.  13 . In addition, a head end lift pilot line  236  is in fluid communication with rear port  138  so that when first valve  188  is activated, as shown in FIG. 13, first valve  188  blocks the flow of pressurized hydraulic oil from pressurized oil manifold  184  to both pilot line  236  and rear port  138 . When first valve  188  is deactivated, fluid communication is restored between pressurized oil manifold  184  and both pilot line  236  and rear port  138  so that pressurized hydraulic oil can flow to both rear port  138  and pilot line  236 . 
     Second valve  190  is a two-way valve coupled to return conduit  185  and coupled by conduit  122  to rear port  138  of head end lift cylinder  132 . When second valve  190  is deactivated as shown in FIG. 13, second valve  190  blocks the flow of hydraulic oil between rear port  138  and return conduit  185 . When second valve  190  is activated, fluid communication is restored between rear port  138  and return conduit  185  to allow hydraulic oil to flow from rear port  138  of head end lift cylinder  132  to reservoir  120 . Typically when first valve  188  is deactivated to restore fluid communication between pressurized oil manifold  184  and rear port  138 , second valve  190  is also deactivated to block fluid communication between rear port  138  and return conduit  185 . 
     Emergency Trendelenburg valve  214  is a two-way valve coupled to return conduit  185  and coupled by conduit  122  to rear port  138  of head end lift cylinder  132 . When emergency Trendelenburg valve  214  is deactivated as shown in FIG. 13, emergency Trendelenburg valve  214  blocks the flow of hydraulic oil from rear port  138  to return conduit  185 . When emergency Trendelenburg valve  214  is activated, fluid communication between rear port  137  and return conduit  185  is restored so that hydraulic oil can flow from rear port  138  to reservoir  120  bypassing second valve  190 . Unlike first and second valves  188 ,  190  which are typically electronically activated, emergency Trendelenburg valve  214  is activated by a manual actuator  254  such as an emergency Trendelenburg lever, shown diagrammatically in FIG.  13 . Emergency Trendelenburg valve can also be activated by pulling CPR pedal  250  upwardly. Typically, when emergency Trendelenburg valve  214  is activated to restore fluid communication between rear port  138  and return conduit  185 , first valve  188  is activated to block fluid communication between pressurized oil manifold  184  and rear port  138 . 
     Pilot operated check valve  220  is a two-way valve coupled to return conduit  185  and coupled by conduit  122  to front port  136  of head end lift cylinder  132 . Check valve  220  is deactivated when head end lift pilot line  236  is not in fluid communication with pressurized oil manifold  184  as shown in FIG.  13 . When pilot line  236  is in fluid communication with pressurized oil manifold  184 , pilot operated check valve  220  is activated. Thus, check valve  220  is activated when first valve  188  is deactivated to restore the fluid communication between pilot line  236  and pressurized oil manifold  184 , and check valve  220  is deactivated when first valve  188  is activated to block the fluid communication between pilot line  236  and pressurized oil manifold  184 . 
     When pilot operated check valve  220  is deactivated, hydraulic oil can flow through check valve  220  only in a direction from return conduit  185  to front port  136  as shown in FIG.  13 . When check valve  220  is activated, hydraulic oil can flow through check valve  220  either from front port  136  to return conduit  185  or from return conduit  185  to front port  136 . Thus, when first valve  188  is deactivated to restore fluid communication between pressurized oil manifold  184 , pilot line  236 , and rear port  138 , hydraulic oil can flow from front port  136 , through check valve  220 , to return conduit  185  and reservoir  120 . 
     To raise the head end  52  of intermediate frame  302 , first valve  188  is deactivated to restore fluid communication between pressurized oil manifold  184 , pilot line  236 , and rear port  138 , second valve  190  and emergency Trendelenburg valve  214  are deactivated to block fluid communication between rear port  138  and return conduit  185 , and pilot operated check valve  220  is activated to allow the flow of hydraulic oil from front port  136  to return conduit  185 . As pressurized hydraulic oil flows from pressurized oil manifold  184 , through first valve  188 , through rear port  138 , and into interior region  133 , piston rod  134  is pushed toward front port  136  and end  135  of piston rod  134  extends from lift cylinder  132  lifting head end  52  of intermediate frame  302  through linkages between head end  52  of intermediate frame  302  and end  135  of piston rod  134  described below. As piston rod  134  is pushed toward front port  136 , hydraulic oil flows out of interior region  133  through front port  136 , through check valve  220 , through return conduit  185 , to reservoir  120 . 
     To lower head end  52  of intermediate frame  302 , first valve  188  is activated to block the fluid communication between pressurized oil manifold  184  and both pilot line  236  and rear port  138 . Blocking fluid communication between pressurized oil manifold  184  and pilot operated check valve  220  deactivates check valve  220  so that check valve  220  blocks the flow of hydraulic oil from front port  136  to return conduit  185  but allows the flow of hydraulic oil from return conduit  185  to front port  136 . Either one or both of second valve  190  and emergency Trendelenburg valve  214  are activated to restore fluid communication between rear port  138  and return conduit  185 . The weight of intermediate frame  302  and articulating deck/weigh frame module  400  is sufficient to push piston rod  134  toward rear port  138  to retract end  135  of piston rod  134  into head end lift cylinder  132  and to push hydraulic oil from interior region  133 , through rear port  138 , through either one or both of second valve  190  and emergency Trendelenburg valve  214 , and to return conduit  185  and reservoir  120 . The retraction of piston rod  134  into head end lift cylinder  132  lowers head end  52  of intermediate frame  302  through linkages between head end  52  of intermediate frame  302  and end  135  of piston rod  134  described below. 
     Lifting mechanism  130  also includes foot end actuator  142  to raise and lower foot end  54  of intermediate frame  302  as shown in FIG. 13. A foot end rear first valve  192 , a foot end rear second valve  194 , and a bleed-off valve  216  control the flow the fluid between rear port  146  of foot end actuator  142  and hydraulic power unit  112 . Unlike head end actuator  132 , foot end actuator  142  includes no front port. 
     First valve  192  is a two-way valve coupled to pressurized oil manifold  184  and coupled by conduit  122  to rear port  146  of foot end lift cylinder  142 . When first valve  192  is activated, as shown in FIG. 13, first valve  192  blocks the flow of pressurized hydraulic oil from pressurized oil manifold  184  to rear port  146 . When first valve  192  is deactivated, fluid communication is restored between pressurized oil manifold  184  and rear port  146  allowing pressurized hydraulic oil to flow thereto. 
     Second valve  194  is a two-way valve coupled to return conduit  185  and coupled by conduit  122  to rear port  146  of foot end lift cylinder  142 . When second valve  194  is deactivated as shown in FIG. 13, second valve  194  blocks the flow of hydraulic oil from rear port  146  to return conduit  185 . When second valve  194  is activated, fluid communication is restored between rear port  146  and return conduit  185  so that hydraulic oil can flow from rear port  146  of foot end lift cylinder  142  to return conduit  185  and to reservoir  120 . 
     Bleed-off valve  216  is a two-way valve coupled to return conduit  185  and coupled by conduit  122  to rear port  146  of foot end lift cylinder  142  as shown in FIG.  13 . When bleed-off valve  216  is closed the flow of hydraulic oil from rear port  146  to return conduit  185  through bleed-off valve  216  is blocked. When bleed-off valve  216  is open, fluid communication is restored between return conduit  185  and rear port  146  to allow hydraulic oil to flow from rear port  146  of foot end lift cylinder  142 , through bleed-off valve  216 , to return conduit  185  and to reservoir  120 . Unlike first and second valves  192 ,  194  which are typically electronically activated, bleed-off valve  216  is activated manually such as by turning a member (not shown) of bleed-off valve  216  to move bleed-off valve  216  between the open and closed positions. 
     To raise the foot end  54  of intermediate frame  302 , first valve  192  is deactivated to restore fluid communication between pressurized oil manifold  184  and rear port  146 , and second valve  194  is deactivated and bleed-off valve  216  is closed to block fluid communication between rear port  146  and return conduit  185 . As pressurized hydraulic oil flows into lift cylinder  142  from pressurized oil manifold  194 , through first valve  192 , and through rear port  146 , piston rod  144  is pushed forward to extend therefrom and acts through linkages between foot end  54  of intermediate frame  302  and piston rod  144  described below to lift foot end  54  of intermediate frame  302 . 
     To lower foot end  54  of intermediate frame  302 , first valve  192  is activated to block the fluid communication between pressurized oil manifold  184  and rear port  146  of foot end lift cylinder  142 . Either second valve  194  can be activated or bleed-off valve  216  can be opened to restore fluid communication between rear port  146  and return conduit  185 . The weight of intermediate frame  302  and articulating deck/weigh frame module  400  is sufficient to push piston rod  144  toward rear port  146  thereby retracting piston rod  144  into foot end lift cylinder  142 , and to push hydraulic oil out of foot end lift cylinder  142 , through rear port  146 , and through either one or both of second valve  194  and bleed-off valve  216  to return conduit  185  and reservoir  120 . The retraction of piston rod  144  into foot end lift cylinder  142  lowers foot end  54  of intermediate frame  302  through linkages between foot end  54  of intermediate frame  302  and piston rod  144  described below. 
     Head section  404  is movable between a generally horizontal down position and an upward back-support position providing a pivotable backrest. Head section pivot cylinder  150  is pivotably coupled to weigh frame  506  as shown in FIGS. 15-17 and has a piston rod  152  pivotably coupled to head section  404  as described below. A head section rear first valve  196 , a head section rear second valve  198 , and a CPR valve  212  shown in FIG. 13 control the flow of fluid between rear port  154  of head section pivot cylinder  150  and hydraulic power unit  112 . 
     First valve  196  is a two-way valve coupled to pressurized oil manifold  184  and coupled by conduit  122  to rear port  154  of head section pivot cylinder  150 . When first valve  196  is deactivated, as shown in FIG. 13, fluid communication is restored between pressurized oil manifold  184  and rear port  154  allowing pressurized hydraulic oil to flow thereto. When first valve  196  is activated, first valve  196  blocks fluid communication between pressurized oil manifold  184  and rear port  154 . 
     Second valve  198  is a two-way valve coupled to return conduit  185  and coupled by conduit  122  to rear port  154  of head section pivot cylinder  150 . When second valve  198  is deactivated, as shown in FIG. 13, second valve  198  blocks the flow of hydraulic oil between rear port  154  and return conduit  185 . When second valve  198  is activated, fluid communication is restored between rear port  154  and return conduit  185  to allow hydraulic oil to flow from rear port  154  of head section pivot cylinder  150  to return line  185  and to reservoir  120 . Typically, when first valve  196  is deactivated to restore fluid communication between pressurized oil manifold  185  and rear port  154 , second valve  198  is also deactivated to block fluid communication between rear port  154  and return conduit  185 . 
     CPR valve  212  is a two-way valve coupled to return conduit  185  and coupled by conduit  122  to rear port  154  of head section pivot cylinder  150 . When CPR valve  212  is deactivated, as shown in FIG. 13, CPR valve  212  blocks the flow of hydraulic oil from rear port  154  to return conduit  185 . When CPR valve  212  is activated, fluid communication between rear port  154  and return conduit  185  is restored so that hydraulic oil can flow from rear port  154  to reservoir  120 . Unlike first and second valves  196 ,  198  which are typically electronically activated, CPR valve  212  is activated by a manual activator such as CPR foot pedal  250 , shown in FIG.  12  and shown diagrammatically in FIG.  13 . Typically when CPR valve  212  is activated to restore fluid communication between rear port  154  and return conduit  185 , first valve  196  is activated to block fluid communication between pressurized oil manifold  184  and rear port  154 . Preferably, conduit  122  coupling CPR valve  212  to return conduit  185  has a sufficiently large diameter to cause the hydraulic oil to drain rapidly from head section pivot cylinder  150  resulting in rapid movement of head section  404  from the back-support position to the down position when CPR valve  212  is activated. 
     To move head section  404  from the down position to the back-support position, first valve  196  is deactivated to restore fluid communication between pressurized oil manifold  184  and rear port  154  of head section pivot cylinder  150 . Second valve  198  and CPR valve  212  are deactivated to block fluid communication between rear port  154  and return conduit  185 . As pressurized hydraulic oil flows from pressurized oil manifold  184  through first valve  196  and then through rear port  154  into head section pivot cylinder  150 , piston rod  152  is pushed outwardly to extend from head section pivot cylinder  150 , thereby lifting head section  404  as the result of connections between piston rod  152  and head section  404  described below. 
     To lower head section  404 , first valve  196  is activated to block the fluid communication between pressurized oil manifold  184  and rear port  154 , and either one or both of second valve  198  and CPR valve  212  are activated to restore fluid communication between rear port  154  and return conduit  185 . The weight of head section  404  is sufficient to push piston rod  152  toward rear port  154  thereby retracting piston rod  152  into head section pivot cylinder  150 . As piston rod  152  retracts into head section pivot cylinder  150 , hydraulic oil is pushed through rear port  154 , through either one or both of second valve  198  and CPR valve  212 , and to return conduit  185  and reservoir  120 . The retraction of piston rod  152  into head section pivot cylinder  150  lowers head section  404  as the result of the linkages connecting piston rod  152  and head section  404  described below. 
     Thigh section  408  of articulating deck  402  is movable between a generally horizontal down position and a slightly inclined up position shown diagrammatically in FIG.  7  and shown in FIGS. 2 and 15. Thigh section pivot cylinder  158  is coupled to thigh section  408  as shown in FIG. 13 to move thigh section  408  between the up position and the down position. A thigh section front valve  200  and a thigh section front pilot operated check valve  222  control the flow of fluid between a front port  162  and hydraulic power unit  112 . A thigh section rear valve  202  and a thigh section rear pilot operated check valve  224  control the flow of fluid between a rear port  164  and hydraulic power unit  112 . The raising and lowering of thigh section  408  of articulating deck  402  will provide the most satisfactory results when the operation of valves  200 ,  202 ,  222 ,  224  is coordinated as described below. 
     Rear valve  202  is a three-way valve coupling pressurized oil manifold  184  and return manifold  185  to rear port  164  of thigh section pivot cylinder  158 . In addition, rear valve  202  couples a thigh section front pilot line  238  to pressurized oil manifold  184  so that when rear valve  202  is activated, as shown in FIG. 13, rear valve  202  restores the flow of pressurized hydraulic oil from pressurized oil manifold  184  to both rear port  164  and to pilot line  238 , thus activating pilot operated check valve  222 . When rear valve  202  is deactivated, fluid communication between pressurized oil manifold  184  and both rear port  164  and pilot line  238  is blocked, and fluid communication is restored between rear port  164  and return conduit  185  and reservoir  120  through check valve  224 . 
     Front valve  200  is a three-way valve coupling front port  162  of thigh section pivot cylinder  158  to return conduit  185  when front valve  200  is in a deactivated position shown in FIG. 13, and to pressurized oil manifold  184  when front valve  200  is in an activated position. When front valve  200  is deactivated, front valve  200  blocks the fluid communication between front port  162  and pressurized oil manifold  184  while restoring the fluid communication between front port  162  and return conduit  185 . When front valve  200  is activated, fluid communication is restored between front port  162  and pressurized oil manifold  184 , while fluid communication between front port  162  and return conduit  185  is blocked. In addition, front valve  200  couples a thigh section rear pilot line  240  to pressurized oil manifold  184  so that when front valve  200  is activated fluid communication is restored between pressurized oil manifold  184  and pilot line  240  allowing pressurized hydraulic oil to flow to pilot operated check valve  224  to activate check valve  224 . 
     Thigh section rear pilot operated check valve  224  is a two-way valve coupled to rear port  164  and rear valve  202 . Check valve  224  is deactivated when fluid communication between thigh section rear pilot line  240  and pressurized oil manifold  184  is blocked as shown in FIG.  13 . When pilot line  240  is in fluid communication with pressurized oil manifold  184 , pilot operated check valve  224  is activated. Thus check valve  224  is activated when front valve  200  is activated and check valve  240  is deactivated when front valve  200  is deactivated as shown in FIG.  13 . 
     When check valve  224  is deactivated, hydraulic oil can flow through check valve  224  only in a direction from rear valve  202  to rear port  164  as shown in FIG.  13 . When check valve  224  is activated, hydraulic oil can flow through check valve  224  either from rear port  162  to rear valve  202  or from rear valve  202  to rear port  162 . Thus, when front valve  200  is activated to restore fluid communication between pressurized oil manifold  184 , pilot line  240 , and front port  162  so that pressurized hydraulic oil flows from manifold  184  to front port  162 , hydraulic oil can also flow from rear port  164 , through check valve  224 , to rear valve  202 . If rear valve  202  is deactivated at the same time that front valve  202  is activated, then the hydraulic oil from rear port  264  can flow through rear valve  202  to return conduit  185  and reservoir  120 . 
     Likewise, thigh section front pilot operated check valve  222  is a two-way valve coupled to front port  162  and to front valve  200 . Check valve  222  is activated when rear valve  202  is activated so that thigh section front pilot line  238  is in fluid communication with pressurized oil manifold  184  as shown in FIG.  13 . When rear valve  202  is deactivated, pilot line  238  is not in fluid communication with pressurized oil manifold  184  and pilot operated check valve  222  is deactivated. Thus, check valve  222  is activated when rear valve  202  is activated and check valve  222  is deactivated when front valve  202  is deactivated. 
     When pilot operated check valve  222  is deactivated, hydraulic oil can flow through check valve  222  only in a direction from front valve  200  to front port  162 . When check valve  222  is activated, hydraulic oil can flow through check valve either from front port  162  to front valve  200  or from front valve  200  to front port  162 . Thus, when rear valve  200  is activated to restore fluid communication between pressurized oil manifold  184 , pilot line  238 , and rear port  164  so that pressurized hydraulic oil flows from manifold  184  to rear port  164 , hydraulic oil can also flow from front port  162 , through check valve  222 , to front valve  200 . If front valve  200  is deactivated when rear valve  202  is activated, then hydraulic oil from front port  162  can pass through front valve  200  to return conduit  185  and reservoir  120 . 
     To raise thigh section  408  of articulating deck  402 , rear valve  202  is activated to restore fluid communication between pressurized oil manifold  184 , pilot line  238 , and rear port  164 . Front valve  200  is deactivated to block fluid communication between pressurized oil manifold  184  and front port  162  and to restore fluid communication between front port  162  and return conduit  185 . As pressurized hydraulic oil flows from pressurized oil manifold  184 , through rear valve  282 , through rear port  164 , and into thigh section pivot cylinder  158 , piston rod  160  is pushed toward front port  162  and extends from thigh section pivot cylinder  158  to lift thigh section  408  through linkages between thigh section  408  and piston rod  160  described below. As piston rod  160  is pushed toward front port  162 , hydraulic oil flows through front port  162 , through activated check valve  222 , through front valve  200 , and to return conduit  185  and reservoir  120 . 
     To lower thigh section  408  of articulating deck  402 , front valve  200  is activated to restore the fluid communication between pressurized oil manifold  184 , pilot line  240 , and front port  162  of thigh section pivot cylinder  158 . Rear valve  202  is deactivated to block the fluid communication between pressurized oil manifold  184 , pilot line  238 , and rear port  164 , and to restore fluid communication between rear port  164  and return conduit  185 . As pressurized hydraulic oil flows from pressurized oil manifold  184 , through front valve  200 , through front port  162 , and into thigh section pivot cylinder  158 , piston rod  160  is pushed toward rear port  164  and is retracted into thigh section pivot cylinder  158 , lowering thigh section  408  through linkages between piston rod  160  and thigh section  408  that are described below. As piston rod  160  is pushed toward rear port  164 , hydraulic oil flows through rear port  164 , through activated check valve  224 , through rear valve  202 , and to return conduit  185 . 
     Foot section  410  of articulating deck  402  is movable between the generally horizontal up position shown in FIGS. 1,  11 , and  24  and the generally vertically downwardly extending down position shown diagrammatically in FIG.  8  and shown in FIGS. 2 and 25. Foot section pivot cylinder  168  is coupled to foot section  410  as shown in FIG. 13 to move foot section  410  between the up position and the down position. A foot pivot front valve  204  and a foot pivot front pilot operated check valve  226  control the flow of fluid between a front port  172  and hydraulic power unit  112 . A foot pivot rear valve  206  and a foot pivot rear pilot operated check valve  228  control the flow of fluid between a rear port  174  and hydraulic power unit  112 . The raising and lowering of foot section  410  of articulating deck  402  provides the most satisfactory results when the operation of valves  204 ,  206 ,  226 ,  228  is coordinated as described below. 
     Rear valve  206  is a three-way valve coupling pressurized oil manifold  184  and return manifold  185  to rear port  174  of foot section pivot cylinder  168 . In addition, rear valve  206  couples a foot pivot front pilot line  242  to pressurized oil manifold  184  so that when rear valve  206  is activated, as shown in FIG. 13, rear valve  206  restores the flow of pressurized hydraulic oil from pressurized oil manifold  184  to both rear port  174  and to pilot line  242 , thus activating pilot operated check valve  226 . When rear valve  206  is deactivated, fluid communication between pressurized oil manifold  184  and both rear port  174  and pilot line  242  is blocked, and fluid communication is restored between rear port  174  and return conduit  185  and reservoir  120  through check valve  228 . 
     Front valve  204  is a three-way valve coupling front port  172  of foot section pivot cylinder  168  to return conduit  185  when front valve is in a deactivated position, and to pressurized oil manifold  184  when front valve  204  is in an activated position shown in FIG.  13 . When front valve  204  is deactivated, front valve  204  blocks the fluid communication between front port  172  and pressurized oil manifold  184  while restoring the fluid communication between front port  172  and return conduit  185 . When front valve  204  is activated, fluid communication is restored between front port  172  and pressurized oil manifold  184 , while fluid communication between front port  172  and return conduit  185  is blocked. In addition, front valve  204  couples a foot pivot rear pilot line  244  to pressurized oil manifold  184  so that when front valve  204  is activated fluid communication is restored between pressurized oil manifold  184  and pilot line  244  allowing pressurized hydraulic oil to flow to pilot operated check valve  228  to activate check valve  228 . 
     Foot pivot rear pilot operated check valve  228  is a two-way valve coupled to rear port  174  and rear valve  206 . Check valve  228  is deactivated when fluid communication between foot pivot rear pilot line  244  and pressurized oil manifold  184  is blocked. When pilot line  244  is in fluid communication with pressurized oil manifold  184 , pilot operated check valve  228  is activated as shown in FIG.  13 . Thus check valve  228  is activated when front valve  204  is activated and check valve  228  is deactivated when front valve  204  is deactivated. 
     When check valve  228  is deactivated, hydraulic oil can flow through check valve  228  only in a direction from rear valve  206  to rear port  174  as shown in FIG.  13 . When check valve  228  is activated, hydraulic oil can flow through check valve  228  either from rear port  174  to rear valve  206  or from rear valve  206  to rear port  174 . Thus, when front valve  204  is activated to restore fluid communication between pressurized oil manifold  184 , pilot line  244 , and front port  172  so that pressurized hydraulic oil flows from manifold  184  to front port  172 , hydraulic oil can also flow from rear port  174 , through check valve  228 , to rear valve  206 . If rear valve  206  is deactivated at the same time that front valve  204  is activated, then the hydraulic oil from rear port  264  can flow through rear valve  206  to return conduit  185  and reservoir  120 . 
     Likewise, foot pivot front pilot operated check valve  226  is a two-way valve coupled to front port  172  and to front valve  204 . Check valve  226  is activated when rear valve  206  is activated and foot pivot front pilot line  242  is in fluid communication with pressurized oil manifold  184 . When rear valve  206  is deactivated, pilot line  242  is not in fluid communication with pressurized oil manifold  184  and pilot operated check valve  226  is deactivated as shown in FIG.  13 . Thus, check valve  226  is activated when rear valve  206  is activated and check valve  226  is deactivated when rear valve  206  is deactivated. 
     When pilot operated check valve  226  is deactivated, hydraulic oil can flow through check valve  226  only in a direction from front valve  204  to front port  172 . When check valve  226  is activated, hydraulic oil can flow through check valve either from front port  172  to front valve  204  or from front valve  204  to front port  172 . Thus, when rear valve  206  is activated to restore fluid communication between pressurized oil manifold  184 , pilot line  242 , and rear port  174  so that pressurized hydraulic oil flows from manifold  184  to rear port  174 , hydraulic oil can also flow from front port  172 , through check valve  226 , to front valve  204 . If front valve  204  is deactivated when rear valve  206  is activated, then hydraulic oil from front port  172  can pass through front valve  204  to return conduit  185  and reservoir  120 . 
     To raise foot section  410  of articulating deck  402 , rear valve  206  is activated to restore fluid communication between pressurized oil manifold  184 , pilot line  242 , and rear port  174 . Front valve  204  is deactivated to block fluid communication between pressurized oil manifold  184  and front port  172 , and to restore fluid communication between front port  172  and return conduit  185 . As pressurized hydraulic oil flows from pressurized oil manifold  184 , through rear valve  282 , through rear port  174 , and into foot section pivot cylinder  158 , piston rod  160  is pushed toward front port  172  and extends from foot section pivot cylinder  158  to lift foot section  410  through linkages between foot section  410  and piston rod  160  described below. As piston rod  160  is pushed toward front port  172 , hydraulic oil flows through front port  172 , through activated check valve  226 , through front valve  204 , and to return conduit  185  and reservoir  120 . 
     To lower foot section  410  of articulating deck  402 , front valve  204  is activated to restore the fluid communication between pressurized oil manifold  184 , pilot line  244 , and front port  172  of foot section pivot cylinder  168  as shown in FIG.  13 . Rear valve  206  is deactivated to block the fluid communication between pressurized oil manifold  184 , pilot line  242 , and rear port  174 , and to restore fluid communication between rear port  174  and return conduit  185 . As pressurized hydraulic oil flows from pressurized oil manifold  184 , through front valve  204 , through front port  172 , and into foot section pivot cylinder  168 , piston rod  160  is pushed toward rear port  174  and is retracted into foot section pivot cylinder  168 , lowering foot section  410  through linkages between piston rod  160  and foot section  410  that are described below. As piston rod  160  is pushed toward rear port  174 , hydraulic oil flows through rear port  174 , through activated check valve  228 , through rear valve  206 , and to return conduit  185 . 
     In addition to pivoting between the up and down positions, foot section  410  of articulating deck  402  is also movable between the expanded position, shown best in FIGS. 11 and 24, and the contracted position, shown best in FIG.  25 . Foot section contracting cylinder  176  is coupled to foot section  410  to move foot section  410  between the expanded position and the contracted position. A foot contracting front valve  208  and a foot contracting front pilot operated check valve  230  control the flow of fluid between a front port  180  and hydraulic power unit  112  as shown in FIG. 13. A foot contracting rear valve  210  and a foot contracting rear pilot operated check valve  232  control the flow of fluid between a rear port  182  and hydraulic power unit  112 . The raising and lowering of foot section  410  of articulating deck  402  will provide the most satisfactory results when the operation of valve  208 ,  210 ,  230 ,  232  is coordinated as described below. 
     Rear valve  210  is a three-way valve coupling pressurized oil manifold  184  and return manifold  185  to rear port  182  of foot section contracting cylinder  176 . In addition, rear valve  210  couples a foot contracting front pilot line  246  to pressurized oil manifold  184  so that when rear valve  210  is activated the flow of pressurized hydraulic oil from pressurized oil manifold  184  is restored to both rear port  182  and to pilot line  246 , thus activating pilot operated check valve  230 . When rear valve  210  is deactivated, as shown in FIG. 13, fluid communication between pressurized oil manifold  184  and both rear port  182  and pilot line  246  is blocked, and fluid communication is restored between rear port  182  and return conduit  185  and reservoir  120  through check valve  232 . 
     Front valve  208  is a three-way valve coupling front port  180  of foot section contracting cylinder  176  to return conduit  185  when front valve  208  is in a deactivated position and to pressurized oil manifold  184  when front valve  208  is in an activated position shown in FIG.  13 . When front valve  208  is deactivated, front valve  208  blocks the fluid communication between front port  180  and pressurized oil manifold  184  while restoring the fluid communication between front port  180  and return conduit  185 . When front valve  208  is activated, fluid communication is restored between front port  180  and pressurized oil manifold  184 , while fluid communication between front port  180  and return conduit  185  is blocked. In addition, front valve  208  couples a foot contracting rear pilot line  248  to pressurized oil manifold  184  so that when front valve  208  is activated fluid communication is restored between pressurized oil manifold  184  and pilot line  248  allowing pressurized hydraulic oil to flow to pilot operated check valve  232  to activate check valve  232 . 
     Foot contracting rear pilot operated check valve  232  is a two-way valve coupled to rear port  182  and rear valve  210 . Check valve  232  is deactivated when fluid communication between foot contracting rear pilot line  248  and between pressurized oil manifold  184  is blocked. When pilot line  248  is in fluid communication with pressurized oil manifold  184  as shown in FIG. 13, pilot operated check valve  232  is activated. Thus check valve  232  is activated when front valve  208  is activated and check valve  232  is deactivated when front valve  208  is deactivated. 
     When check valve  232  is deactivated, hydraulic oil can flow through check valve  232  only in a direction from rear valve  210  to rear port  182  as shown in FIG.  13 . When check valve  232  is activated, hydraulic oil can flow through check valve  232  either from rear port  182  to rear valve  210  or from rear valve  210  to rear port  182 . Thus, when front valve  208  is activated to restore fluid communication between pressurized oil manifold  184 , pilot line  248 , and front port  180  so that pressurized hydraulic oil flows from manifold  184  to front port  180  so that pressurized hydraulic oil flows from manifold  184  to front port  180 , hydraulic oil can also flow from rear port  182 , through check valve  232 , to rear valve  210 . If rear valve  210  is deactivated at the same time that front valve  208  is activated, then the hydraulic oil from rear port  264  can flow through rear valve  210  to return conduit  185  and reservoir  120 . 
     Likewise, foot contracting front pilot operated check valve  230  is a two-way valve coupled to front port  180  and to front valve  208 . Check valve  230  is activated when rear valve  210  is activated so that foot contracting front pilot line  246  is in fluid communication with pressurized oil manifold  184 . When rear valve  210  is deactivated as shown in FIG. 13, pilot line  246  is not in fluid communication with pressurized oil manifold  184  and pilot operated check valve  230  is deactivated. Thus, check valve  230  is activated when rear valve  210  is activated and check valve  230  is deactivated when front valve  208  is deactivated. 
     When pilot operated check valve  230  is deactivated, hydraulic oil can flow through check valve  230  only in a direction from front valve  208  to front port  180 . When check valve  230  is activated, hydraulic oil can flow through check valve either from front port  180  to front valve  208  or from front valve  208  to front port  180 . Thus, when rear valve  210  is activated to restore fluid communication between pressurized oil manifold  184 , pilot line  246 , and rear port  182  so that pressurized hydraulic oil flows from manifold  184  to rear port  182 , hydraulic oil can also flow from front port  180 , through check valve  230 , to front valve  208 . If front valve  208  is deactivated when rear valve  210  is activated, then hydraulic oil from front port  180  can pass through front valve  208  to return conduit  185  and reservoir  120 . 
     To expand foot section  410  of articulating deck  402 , rear valve  210  is activated to restore fluid communication between pressurized oil manifold  184 , pilot line  246 , and rear port  182 . Front valve  208  is deactivated to block fluid communication between pressurized oil manifold  184  and front port  180 , and to restore fluid communication between front port  180  and return conduit  185 . As pressurized hydraulic oil flows from pressurized oil manifold  184 , through rear valve  282 , through rear port  182 , and into foot section contracting cylinder  176 , piston rod  160  is pushed toward front port  180  and extends from foot section contracting cylinder  176  to expand foot section  410  through linkages between foot section  410  and piston rod  160  described below. As piston rod  160  is pushed toward front port  180 , hydraulic oil flows through front port  180 , through activated check valve  230 , through front valve  208 , and to return conduit  185  and reservoir  120 . 
     To contract foot section  410  of articulating deck  402 , front valve  208  is activated to restore the fluid communication between pressurized oil manifold  184 , pilot line  248 , and front port  180  of foot section contracting cylinder  176 . Rear valve  210  is deactivated to block the fluid communication between pressurized oil manifold  184 , pilot line  246 , and rear port  182 , and to restore fluid communication between rear port  182  and return conduit  185 . As pressurized hydraulic oil flows from pressurized oil manifold  184 , through front valve  208 , through front port  180 , and into foot section contracting cylinder  176 , piston rod  160  is pushed toward rear port  182  and is retracted into foot section contracting cylinder  176 , contracting foot section  410  through linkages between piston rod  160  and foot section  410  that are described below. As piston rod  160  is pushed toward rear port  182 , hydraulic oil flows through rear port  182 , through activated check valve  232 , through rear valve  210 , and to return conduit  185 . 
     Illustratively, the control valves can be configured to selectively operate actuators  132 ,  142 ,  150 ,  158 ,  168 ,  176  to move chair bed  50  to various positions including the sitting position shown diagrammatically in FIG.  13 . To move chair bed  50  to the sitting position, the valves are configured so that piston rod  134  is retracted into head end lift cylinder  132 , piston rod  144  is retracted into foot end lift cylinder  142 , piston rod  152  is extended from head section pivot cylinder  150 , piston rod  160  is extended from thigh section pivot cylinder  158 , piston rod  170  is retracted into foot section pivot cylinder  168 , and piston rod  178  is retracted into foot section contracting cylinder  176 . As described above with respect to each individual actuator  132 ,  142 ,  150 ,  158 ,  168 ,  176  and as shown diagrammatically in FIG. 13, to attain the sitting position requires that head end rear first valve  188  is activated, foot end rear first valve  192  is activated, foot retractor front valve  208  is activated, foot section front valve  204  is activated, thigh section rear valve  202  is activated, and head section rear first valve  196  is activated. In addition, all other valves are maintained in the deactivated position. As can be seen, then, the positions of the head, thigh, foot sections  404 ,  408 ,  410  of articulating deck  402 , and the position of intermediate frame  302  relative to base frame  62  can be manipulated by manipulating the control valves of control manifold  186 . 
     Of note, in preferred embodiments, only two valves—head end rear first valve  188  and foot end rear first valve  192 —are normally open, the other valves being normally closed as shown in FIG. 13, so that when all of the control valves are deactivated, pressurized hydraulic oil flows only through valve  188  and valve  192 . When pressurized hydraulic oil flows through valve  188 , piston rod  134  extends from head end lift cylinder  132  to lift head end  52  of intermediate frame  302 . When pressurized hydraulic oil flows through valve  192 , piston rod  144  extends from head end lift cylinder  142  to lift foot end  54  of intermediate frame  302 . Therefore, if hydraulic oil is pressurized when all control valves are deactivated, intermediate frame  302  will move to the raised position. 
     In case of an emergency when intermediate frame  302  is in the low position, caregiver can simply pump foot pump pedal  252  to raise intermediate frame  302  even when chair bed  50  is away from an AC power source. If intermediate frame  302  is not level when caregiver starts pumping foot pump pedal  252 , hydraulic system  100  will continue to raise intermediate frame as long as caregiver pumps foot pump pedal  252  until both head end  52  and foot end  54  of intermediate frame  302  are in the raised positions. 
     In addition, conduit  122  connecting pump  116  to each of the control valves includes a variable restrictive orifice  234  as shown in FIG.  13 . Each restrictive orifice  234  widens and narrows to maintain the pressure drop across restrictive orifice  234  at a preselected value. This “pressure compensation” operates to cause uniform articulation of intermediate frame  302  and head, thigh, and foot sections  404 ,  408 ,  410  of deck  402  irrespective of the distribution of the weight load on deck  402 . For example, pressure compensation will cause head end  52  and foot end  54  of intermediate frame  302  to raise or lower at the same rate even if the center of gravity of the person (not shown) on sleeping surface  552  is positioned to lie near one of the ends  52 ,  54  of intermediate frame  302 . 
     Further, it can be seen that by bringing, for example, rear port  154  of head section pivot cylinder  150  into fluid communication with pressurized oil manifold  184 , that head section  404  can be secured in the back-support position. In addition, by opening, for example, CPR valve  212 , head section  404  can be released and can move downwardly toward the bed position. Additionally, by closing CPR valve  212  after head section  404  has moved away from the back-support position but before head section  404  has moved to the down position, head section  404  can be secured in an intermediate position between the back-support position and the down position. The ability to secure head section  404  in an intermediate position is a characteristic of actuator  150  that likewise holds true for actuators  132 ,  142 ,  158 ,  168 ,  176  so that when the actuators cooperate with lifting mechanism  130  and with the linkages connecting the actuators to the head, thigh, and foot sections  404 ,  408 ,  410  of articulating deck  402 , chair bed  50  can be secured in many positions between the bed position and the sitting position providing a full range of positions of chair bed  50  to meet the needs of many different people. 
     Remote Operation of the Chair Bed (away from an Electrical Power Source) 
     Foot pump pedal  252  shown in FIG. 12 can be pumped by the caregiver to operate manual pump  118 , shown best in FIG. 12 a,  to pressurize the hydraulic oil. Foot pump pedal  252  can be used, for example, when electrical power is not available to electric motor  124  and pump  116  is, therefore, not operating to pressurize the hydraulic oil. Foot pump pedal  252  is pivotably coupled to base frame  62  for movement between an up position and a down position relative to base frame  62 . A lever  253  is coupled to foot pump pedal  252  so that when foot pump pedal  252  is in the down position, lever  253  is pulled to a forward position toward foot end  54  of chair bed  50 , and when foot pump pedal  252  is in the up position, lever  253  is pushed to a back position toward head end  52  of chair bed  50 . 
     Manual pump  118  is mounted to control manifold  186  of hydraulic power unit  112  as shown in FIG. 12 a.  Manual pump  118  includes two cylinders  104 , each cylinder  104  carrying a piston rod  106 . Rods  106  are configured to pressurize hydraulic oil when rods  106  are pushed to a retracted position toward foot end  54  of chair bed  50 , forcing pressurized hydraulic oil out of cylinders  104  and into pressurized oil manifold  184 . As rods  106  move from the retracted position to an extended position toward head end  52  of chair bed  50 , unpressurized hydraulic oil from reservoir  120  moves into cylinders  104 . 
     Manual pump  118  also includes a bar  108  connecting head end  52  of rods  106  together as shown in FIG. 12 a  and a block  114  coupled to control manifold  186 . Block  114  is formed to include guide openings  115  that are positioned to lie so that rods  106  are received by guide openings  115  and travel therethrough as rods  106  reciprocate between the retracted and extended positions. A cable  126  has a first end  127  connected to lever  253  as shown in FIG. 12 and a second end  129  connected through a third guide opening  115  formed in block  114  to bar  108  as shown in FIG. 13 a.    
     Control manifold  186  is formed to include an opening  187  that extends through control manifold  186  so that cable  126  can be configured to lie in a generally straight line without having cable  126  between first and second ends  127 ,  129  engaging any portion of chair bed  50 . Cable  126  runs from bar  108 , through third guide opening  115  formed in block  114 , through opening  187  formed in control manifold  186 , and to lever  253  of foot pump pedal  252 . Forming opening  187  through control manifold  186  additionally allows for compact placement of hydraulic power unit  112  and other components on base frame  62  of chair bed  50 . A cylindrical return spring  110  is received by cable and is positioned to act against bar  108  and block  114  to yieldably bias bar  108  toward head end  52  of chair bed  50 . 
     When foot pump pedal  252  is moved downwardly pulling lever  253  toward foot end of chair bed  50 , lever  253  pulls cable  126  toward foot end  54  of chair bed and cable  126  pulls bar  108  and rods  106  toward foot end  54  of chair bed  50  so that rods  106  retract into cylinders  104  and pressurize hydraulic oil, forcing the hydraulic oil into pressurized oil manifold  184 . When foot pump pedal  252  is released, return spring  110  pushes bar  108  toward head end  52  of chair bed  50 , pulling rods  106  to their extended positions and drawing hydraulic oil from reservoir  120  into cylinders  104 . At the same time, bar  108  pulls cable  126  through openings  115 ,  187 , pulling lever  253  toward head end  52  of chair bed  50  and moving foot pump pedal  252  upwardly to the up position. Repeated pumping of foot pump pedal  252  causes manual pump  118  to pressurize the hydraulic oil so that the hydraulic oil can operate the head and foot end lift cylinders  132 ,  142 , as well as head, thigh, and foot section pivot cylinders  150 ,  158 ,  168 , and foot section contracting cylinder  176 . 
     Typically, the control valves are moved between various configurations using electrical power. Chair bed  50  includes a battery  92  configured to provide electrical power to operate the control valves when electrical power is not available from a source outside of chair bed  50 . Use of foot pump pedal  186  to pressurize the hydraulic oil and the availability of electrical power from battery  92  to operate the control valves allows a caregiver to manipulate lifting mechanism  130  and articulating deck  402  to move chair bed  50  to any desired position within its range of movement when there is no electrical power supplied to the chair bed  50 . 
     In addition, depressing CPR foot pedal  250  manually moves head section  404  from the back-support position to the down position for performing CPR on a person on sleeping surface  552 , and the emergency Trendelenburg lever  254  manually activates emergency Trendelenburg valve  214  to move sleeping surface  552  to the Trendelenburg position. Both of the CPR foot pedals  250  and the emergency Trendelenburg lever  254  operate to change the position of chair bed  50  when chair bed  50  is away from a power source, and both operate without the need to pump foot pump pedal  252 . 
     Lifting Mechanism 
     Lifting mechanism  130  includes a head end axle  258  rotatably mounted to brackets  260  that are fixed to sides  66  of base frame  62  as shown in FIGS. 11 and 12. A lever  256 , and lift arms  320 ,  322  are fixed to axle  258  and piston rod  134  of head end lift cylinder  132  is coupled to lever  256 . Foot end  54  of base frame  62  carries levers  214  fixed to brackets  212 , a foot end cross bar  276  fixed to distal ends  294  of levers  214 , and piston rod  144  of foot end lift cylinder  142  coupled to foot end cross bar  276 . 
     Head end connector members  262 ,  264  couple lift arms  320 ,  322  to intermediate frame  302 . Each connector member  262 ,  264  has a first end  266 ,  268  that is pivotably connected to lift arms  320 ,  322 . Second ends  270 ,  272  of head end connector members  262 ,  264  are pivotably coupled to intermediate frame  302 . Foot end connector members  282 ,  284  each have a first end  286 ,  288  that is pivotably connected to lift arms  324 ,  326 . Second ends  290 ,  292  of foot end connector members  262 ,  264  are fixed to intermediate frame  302 . 
     Head end lift cylinder  132  and foot end lift cylinder  142  are each pivotably mounted to struts  64  of base frame  62  as shown in FIGS. 11 and 15. Piston rod  134  of head end lift cylinder  132  is pivotably coupled to distal end  274  of lever  256 . When head end lift cylinder  132  is activated by supplying pressurized hydraulic oil to interior region  133  through rear port  138 , the pressurized hydraulic oil pushes piston rod  134  so that piston rod  134  slides outwardly to extend from head end lift cylinder  132 , pushing distal end  274  of lever  256  toward head end  52  of chair bed  50  and rotating head end axle  258  so that lift arms  320 ,  322  rotate upwardly. As lift arms  320 ,  322  rotate upwardly, connecting members  262 ,  264  push head end  52  of intermediate frame  302  upwardly relative to base frame  62 . 
     Likewise, piston rod  144  of foot end lift cylinder  142  is pivotably coupled to foot end cross bar  276 . When foot end lift cylinder  142  is activated by supplying pressurized hydraulic oil to foot end lift cylinder  142  through rear port  146 , the pressurized hydraulic oil pushes piston rod  144  so that piston rod  144  slides outwardly to extend from foot end lift cylinder  142 , pushing cross bar  276  and thus distal ends  294  of levers  214  toward foot end  54  of chair bed  50 , thereby rotating lift arms  324 ,  326  upwardly. As lift arms  324 ,  326  rotate upwardly, connecting members  282 ,  284  push foot end  54  of intermediate frame  302  upwardly relative to base frame  62 . 
     When chair bed  50  is in the standard bed position with articulating deck  402  configured to provide a planar sleeping surface  552 , lifting mechanism  130  is in the raised position shown in FIG. 15 having lift cylinders  132 ,  142  activated and piston rods  134 ,  144  extended therefrom, axle  258  and lift arms  320 ,  322  rotated upwardly, and cross bar  276  pushed toward foot end  54  of chair bed  50  with lift arms  324 ,  326  rotated upwardly, so that lift arms  320 ,  322 ,  324 ,  326  and connecting members  262 ,  264 ,  282 ,  284  hold sleeping surface  552  first distance  566  above the floor as illustratively shown in FIG.  3 . When chair bed  50  is in the low position, lifting mechanism  130  is in the low position shown in FIG. 12 having lift cylinders  132 ,  142  deactivated and piston rods  134 ,  144  retracted into lift cylinders  132 ,  142 , axle  258  and lift arms  320 ,  322  rotated downwardly, and cross bar  276  pulled toward head end  52  of chair bed  50  with lift arms  324 ,  326  rotated downwardly, so that lift arms  320 ,  322 ,  324 ,  326  and connecting members  262 ,  264 ,  282 ,  284  hold sleeping surface  552  second distance  568  above the floor as illustratively shown in FIG.  4 . 
     Lifting mechanism  130  can also be used when chair bed  50  is in the sitting position to help a person (not shown) on sleeping surface  552  to stand up. When chair bed  50  is in the sitting position, head section  404  of articulating deck  402  is in the back-support position, thigh section  408  is in the up position, foot section  410  is in the down position, and intermediate frame  302  is in the low position as shown in FIGS. 2 and 7. Typically, the person on sleeping surface  552  can place their feet (not shown) on the floor when chair bed  50  is in the sitting position. after the feet of the person are on the floor, lifting mechanism  130  can be moved from the low position to the raised position to help the person to stand up. Additionally, chair bed  50  can be provided with grip handles  632 ,  640 , described below and shown in FIG. 2, that are mounted to move with intermediate frame  302  to provide additional support for the person standing up with the aid of chair bed  50 . 
     Reduced-Shear Pivot 
     Head section  404  is coupled to weigh frame  506  by reduced-shear pivot assembly  650  shown in FIGS.  11  and  14 - 17 . Reduced-shear pivot assembly  650  mounts head section  404  to weigh frame  506  for both translational movement and pivoting movement of head section  404  relative to seat section  406  of deck  402  and relative to weigh frame  506 . The pivoting and translational movements combine to produce a motion in which head section  404  pivots relative to weigh frame  506  about an effective pivot axis positioned to lie above lower deck  430  and immediately adjacent upper deck  414 . The shear between the back of the person and the sleeping surface  552  caused by movement of head section  404  is reduced, thereby reducing scrubbing of the sleeping surface  552  against the person. 
     Reduced-shear pivot assembly  650  includes brackets  654  mounted to each side  656  of head section  404  as shown in FIGS.  11  and  15 - 17 . Brackets  654  connect flattened U-shaped struts  658  that span head section  404  to sides  656  as shown in FIG. 11. A lever arm  660  having a cap  662  is fixed to struts  658  and extends longitudinally in a direction parallel to the sides  656  of head section  404  toward foot end  54  of chair bed  50 , terminating in a tip  664  as shown best in FIGS. 15-17. Two spacer rods  666  each have a first end  668  pivotably coupled to struts  658  adjacent to brackets  654  and a second end  670  pivotably connected to weigh frame  506  so that spacer rods  666  pivot about a spacer pivot axis  672 . Spacer rods  666  maintain the separation between spacer pivot axis  672  and struts  658  as head section  404  moves between the back-support position of FIG.  15  and the down position of FIG.  16 . 
     Slotted brackets  674  are fixed to sides  676  of seat section  406  adjacent to foot end  54  of head section  404  as shown in FIGS. 15-17. Each slotted bracket  674  is formed to include a horizontal longitudinal slot  678 . Foot end  54  of head section  404  includes pins  680  that are received by slots  678 . Pins  680  and slots  678  cooperate to guide the movement of foot end  54  of head section  404  so that foot end  54  of head section  404  translates horizontally or longitudinally toward head end  52  of chair bed  50  when head section  404  pivots upwardly to the back-support position. 
     Head section pivot cylinder  150  operates to pivot head section  404  between the down position and the back-support position as shown in FIGS.  11  and  15 - 17 . A bracket  682  having a distal end  684  is fixed to an upper deck end portion  460  of thigh section  408 . Bracket  682  is generally centrally located along weigh frame end portion  460 . Head section pivot cylinder  150  is pivotably coupled to distal end  684  of bracket  682  and piston rod  152  of head section pivot cylinder  150  is pivotably coupled to tip  664  of lever arm  660  so that head section pivot cylinder  138  and lever arm  660  act between struts  658  of head section  404  and weigh frame  506 . 
     When head section  404  is in the down position shown, for example, in FIG. 16, head end pivot cylinder  150  is in a deactivated configuration having piston rod  152  in the retracted position. Head section  404  and lever arm  660  are generally parallel to weigh frame  506  when head section  404  is in the down position. 
     When head end pivot cylinder  150  moves to the extended position, piston rod  152  pushes tip  664  of lever arm  660  toward head end  52  of chair bed  50 . Lever arm  660  pushes against struts  658  to pivot head section  404  upwardly to the back-support position as shown in FIG.  17 . Pins  680  cooperate with slots  678  so that foot end  54  of head section  404  moves longitudinally toward head end  52  of chair bed  50  a distance  686 . At the same time, spacer rods  666  swing upwardly forcing head section  404  to engage in the motion illustratively shown by arc  688  in FIG. 17 combining the pivoting movement of head section  404  and the translating movement of head section  404  to provide the reduced-shear pivot. Since pivot pins  680  are located immediately adjacent the top of side walls  438  of step deck  412 , the pivot is between sleeping surface  552  and bottom  586  of mattress  550 . This reduces the travel required to reduce shear between the person (not shown) and sleeping surface  552 . 
     The longitudinal displacement of the pivot is selected to prevent a crease in mattress  550  between head and seat portions  558 ,  560 . The effective point of contact on mattress back portion  558  extends as it pivots upwardly as does the corresponding point on the person on sleeping surface  552  as the person pivots about his or her hip. As a result of the reduced-shear pivot assembly  650 , the point of contact on mattress back portion  558  and the corresponding point on the person move together, thus reducing the sliding of the person relative to sleeping surface  552 . 
     Although the surface of the person&#39;s back expands when the person pivots upwardly to a sitting position, the surface of the back legs of the person contract as the back legs pivot downwardly. As will be explained with respect to FIGS. 24-28 and  30 , foot section  410  of deck  402  and foot portion  564  of mattress  550  are mounted and constructed to shorten in length and mattress  550  thins and shortens in length when pivoting to the sitting position to effect a reduced-shear pivot. 
     Chair bed  50  can be provided with hip pivot guide  694  shown in FIGS. 31-33 to help the caregiver accurately position the hip (not shown) of the person (not shown) on sleeping surface  552 . Hip pivot guide  694  indicates the position of the hip of the person that will minimize the distance between effective pivot axis and the axis (not shown) about which the person&#39;s hip pivots, thereby maximizing the effectiveness of the reduced-shear pivot. Caregivers providing care to people using conventional beds having movable head sections typically attempt to place the hip of the person at the pivot joint of the head section to the bed. Typically, the only available method for the caregiver to estimate this placement is by viewing the distance between the top of the person&#39;s head and the head end of the mattress. Providing hip pivot guide  694  on body section side rails  804 ,  806  of chair bed  50  maximizes the ability of the caregiver to properly locate the hip of the person on sleeping surface  552 . 
     A reduced-shear pivot assembly  714  is shown in included on an examination table  700  having a head end  702 , a foot end  704 , and an articulating deck/patient support platform  706 , including a head section  708 , a seat section  710 , and a foot section  712  as shown in FIGS. 18-23. Examination table  700  is convertible between an examination position having deck  706  in a generally planar configuration as shown in FIGS. 18,  20  and a sitting position as shown in FIGS. 19,  22 . Head section  708  moves between a generally horizontal down position shown in FIG.  18  and an upward back-support position shown in FIG. 19, and foot section  712  moves between a generally horizontal up position shown in FIG. 18 and a generally vertically downwardly extending down position shown in FIG.  19 . 
     Head section  708  and foot section  712  are both provided with a reduced shear pivot assembly  714 , shown best in FIGS. 20-23, that operates to pivot head section  708  relative to seat section  710  about an effective pivot axis  720  that is positioned to lie above an examination or support surface  722  and that also operates to pivot foot section  712  relative to seat section  710  about an effective pivot axis  778  that is positioned to lie above examination or support surface  722 . 
     Although the reduced shear pivot assembly  714  is described with respect to an examination table, it can also be used in a bed, a chair bed, a stretcher, a gurney or any other device having an articulated deck including one or more articulated deck sections wherein the pivot corresponds to the pivoting of a person on the deck. 
     Examination table  700  includes a base platform/base  724  having upstanding posts/struts/links  726  fixed thereto and extending upwardly therefrom. The upstanding posts  726  are secured to the base  724  by diagonal braces  725 . The base platform  724  is shown resting on the ground. Wheels  723  are provided at the back end of the base  724  displaced from the ground when the base  724  is in its horizontal position. To move the table, the table is rotated up such that the base  724  pivots back onto the wheel  723 . Then, the table can be moved to any desired location. This movement is preferable when in the chair position of FIG. 19 with an occupant therein. It is not recommended to transport the table in its supine position of FIG. 18 on wheel  723  with an occupant thereon. Alternatively, wheels may be provided at the four ends of the base  724  so as to make the table portable without titling. This will allow the table to be used as a gurney in an emergency department wherein the patient is brought in from the ambulance, moved into an emergency bay, then moved out to a room or surgery center without moving from one conveyance to another. 
     Reduced-shear pivot assembly  714  includes a frame/head frame member  716  pivotably attached to a pair of spaced upstanding posts  726  for pivoting movement relative thereto about a pivot axis  718 . A drive motor  728  is pivotably attached to base platform  724  by bracket  727  for pivoting movement about a pivot axis  780 . Drive motor  728  is configured to rotatably drive a lead screw  730  that angles upwardly from drive motor  728  to a sheath  732  that is coupled to frame  716  for pivoting movement about a pivot axis  734 . 
     Sheath  732  is formed to include an interior region (not shown) that threadably receives lead screw  730  as shown in FIG.  20 . Extension of lead screw  730  from sheath  732  by rotating causes frame  716  to pivot relative to base platform  724  about pivot axis  718  with foot end  704  of frame  716  pivoting upwardly and head end  702  of frame  716  pivoting downwardly. Likewise, retraction of lead screw  730  into sheath  732  cause frame  716  to pivot about pivot axis  718  with foot end  704  of frame  716  pivoting downwardly and head end  702  of frame  716  pivoting upwardly. 
     Head section  708  of articulating deck  706  is fixed to frame  716  by flanges  717  as shown in FIGS. 20-23. As frame  716  pivots from a generally horizontal initial position shown in FIG. 20 to an inclined position shown in FIG. 22 having head end  702  of frame  716  positioned above foot end  704  of frame  716 , head section  708  pivots from a generally horizontal down position of FIG. 18 to an upward back-support position of FIG.  19 . 
     The head end of seat section  710  is connected to upstanding posts  726  by transverse upper struts/bars/links  740 , transverse lower struts/bars/links  742 , and brackets  746 . Bracket  746  includes a first end  748  fixed to head end of seat section  710  and extends downward to terminate at a second end  750 . Each upper strut  740  has a first end  752  pivotably coupled to seat section  710  adjacent to first end  748  of bracket  746  and a second end  754  pivotably coupled to one of upstanding posts  726 . Each lower strut  742  has a first end  756  pivotably coupled to second end  750  of bracket  746  and a second end  758  pivotably coupled to one of upstanding posts  726  beneath second end  754  of upper strut  740 . 
     As can best be seen in FIGS. 20 and 22, the connection of the struts  740  and  742  at ends  754  and  758  respectfully to the upstanding post  726  are offset with respect to a vertical. The connection of the strut  740  and  742  at ends  752  and  756  to the bracket  746  are aligned vertically. The lengths of the struts  740  and  742  are substantially equal. As an alternative, the strut  740  and  742  may be of unequal length and their connection to the outstanding post  26  may be aligned vertically. As a further alternative, the connections may be offset and the struts lengths different. The lengths of the struts  740  and  742  and their connections to the upstanding posts  726  and to the bracket  726  are selected such that the seat section  710  is horizontal in the planar or horizontal position of the articulate deck  6  as shown in FIGS. 18 and 20 and the foot end of seat section  710  is raised with respect to the head end of seat section  710  in the chair position as illustrated in FIGS. 19 and 22. Thus, the struts  740 ,  742  do not form a true parallelogram with the upstanding post  726  and bracket  746 . The raising of the knee with respect to the hip secures the occupant to the chair and prevents sliding out. 
     First telescoping members  744  are slidably received by a sheath  760  appended to head section  708  and flange  717  of frame  716  as shown best in FIG. 23 for movement over rollers  762  between a retracted position shown in FIGS. 20 and 23, and an extended position shown in FIGS. 21 and 22. Each first telescoping member  744  includes a foot end  764  that is pivotably coupled to seat section  710  adjacent to first end  748  of bracket  746  and a head end (not shown) received by sheath  760 . As first telescoping members  744  move between the retracted position and the extended position, seat section and head section translates relative to each other. Thus, the pivot point  764  of the seat and head sections moves alone a plane parallel to the frame  716 . 
     Foot section  712  is pivotably coupled at head end  702  of foot section  712  to second telescoping members  766  at  776  as shown in FIGS. 20-22. Seat section  770  is formed to include sheaths  770  and each second telescoping member  766  is slidably received by a sheath  770  of the seat section  710  for movement over rollers  768  between an extended position shown in FIG. 20 and a retracted position shown in FIG.  22 . As second telescoping members  766  move between the retracted position and the extended position, foot section  712  translates relative to seat section  710 . Thus, the pivotal connection of the foot section  712  to the seat section  710  moves in a plane parallel to the seat section transfers to the plane of the frame  716 . A link  782  is pivotably connected at a first end  784  to frame  716  and at a second end  786  to a bracket  788  extending from foot section  720  pivoting of the frame  716  pivots the foot section  712 . 
     A cable  772  has a first end  776  fixed to head end of foot section  712  and a second end  774  fixed to flange  717  of head section  708 . The length of cable  772  is fixed so that second telescoping members  766  move from the extended position to the retracted position when first telescoping members  744  move from the retracted position to the extended position. Consequently, cable  772 , frame  716  and link  782  act to coordinate the movement of head section  708  and foot section  712  relative to seat section  710  so that as head section  708  translates and pivots upwardly relative to seat section  710 , foot section  712  simultaneously translates and pivots downwardly relative to seat section  710 . 
     Seat section  710  translates relative to head section  708  as head section  708  pivots from the down position to the back-support position as shown in FIGS. 19-22. The pivoting movement of head section  708  and the translational movement of seat section  710  combine to produce a motion in which head section  8  pivots relative to seat section  710  about effective pivot axis  720  positioned to lie above support surface  722  and coincident with a hip (not shown) of a person on the support surface  722 . 
     Likewise, seat section  710  translates relative to foot section  712  as foot section  712  pivots from the up position to the down position as shown in FIGS. 19-22. The pivoting movement of foot section  712  and the translational movement of seat section  710  combine to produce a motion in which foot section  712  pivots relative to seat section  710  about a second effective pivot axis  778  positioned to lie above support surface  722  and coincident with a knee (not shown) of a person (not shown) on support surface  722 . 
     The head section  708  is fixed to the frame  716  which pivots about a fixed pivot point  718  adjacent the foot end of head section  708  fixed to the base platform  724  and the seat section  710  moves relative to the head section  722  and frame  716 . Thus, when the frame  716  pivots from the planar position of FIG. 18 to the sixty degree position of FIG. 19, the seat  722  is moved closer to the ground. This allows easy egress. 
     As can be seen both in bedchair  50  and table  700 , head section  404 ,  708  translates relative to seat section  406 ,  710  when head section  404 ,  708  pivots from the down position to the back-support position. This relative translation effectively expands the length of deck  402 ,  706  and support surface  552 ,  722  at the junction of the head and seat sections  404 ,  708  and  406 ,  710 , during the articulation of deck  402 ,  706 . The effective expansion of deck  402 ,  706  and support surface  552 ,  722  at the seat and head juncture conforms to the lengthening of the back of the person to minimize the shear that could take place between the person and surface  552 ,  722 . For the foot-seat juncture, the surface  552 ,  722  contracts when moving from a lying position to a sitting position which corresponds to the concentration of the back of the legs. 
     In other words, the expansion of deck  402 ,  706  and surface  552 ,  722  at the back and contraction of the foot allows the lower body of the person to remain stationary relative to surface  552 ,  722  when tilting the upper body of the person, which also remains stationary relative to surface  552 ,  722 , in order to minimize the scrubbing between the person and surface  552 ,  722  during articulation of deck  402 ,  706 . 
     Thus, the translational movement of seat section  710  of examination table  700  illustratively shown in FIGS. 18-23 relative to head and foot sections  708 ,  712  and contemporaneous with the pivoting movement of head and foot sections  708 ,  712  results in a reduced-shear pivoting movement of head and foot sections  708 ,  712 . The effective pivot axes  720 ,  778  of head and foot sections  708 ,  712  to lie above support surface  722 . If effective pivot axes  720 ,  778  are approximately co-linear with axis of rotation of hip and knee respectively, then the scrubbing of support surface  722  against the person (not shown) supported by support surface  722  will be minimized. 
     As can be seen in both chair bed  50  and examination table  700 , head section  404 ,  708  translates relative to seat section  406 ,  710  when head section  404 ,  708  pivots from the down position to the back-support position. This relative translation effectively expands the length of deck  402 ,  706  at the junction of the back and seat during the articulation of deck  402 ,  706 . When the upwardly-facing person (not shown) supported by surface  552 ,  722  moves from a lying position to a sitting position, the back (not shown) of the person lengthen. The effective expansion of deck  402 ,  706  at the juncture of seat section  406 ,  710  and head section  404 ,  708  and the consequent expansion of surface  552 ,  722  conforms to the lengthening of the back of the person to reduce the shear that could take place between the person and surface  552 ,  722 . For the foot-seat juncture, surface  552 ,  722  contracts when moving from a lying position to a sitting position. 
     In other words, the expansion of deck  402 ,  706  and surface  552 ,  722  at the back and contraction at the foot allows the lower body of the person to remain stationary relative to surface  552 ,  722  when tilting the upper body of the person, which also remains stationary relative to surface  552 ,  722 , in order to minimize the scrubbing between the person and surface  552 ,  722  during articulation of deck  402 ,  706 . The reduced-shear pivot also minimizes the migration of the person on sleeping surface  552  toward foot end  54  of chair bed  50  as head section  404  is repeatedly raised and lowered and minimizes “bunching” of mattress  550  and the potential corresponding pressure on the hip and shoulder of the person. 
     CPR Foot Pedal 
     CPR foot pedals  250  are coupled to hydraulic system module  100  as shown in FIGS. 11 and 12 and are positioned to be operable by the foot of the caregiver. As described above, hydraulic system module  100  includes CPR valve  212  shown in FIG. 13 that can be activated to restore fluid communication between rear port  154  of head section pivot cylinder  150  and return conduit  185  so that hydraulic oil can be released from cylinder  150  and head section  404  can move from the back-support position to the down position. CPR foot pedals  250  are movable between an up position and a downward releasing position. When CPR foot pedals  250  are in the releasing position, CPR valve  212  is activated and head section  404  moves from the back-support position to the down position. 
     CPR foot pedals  250  and CPR valve  212  are configured so that CPR foot pedals  250  can be moved from the releasing position to the up position when head section  404  is in an intermediate position after head section  404  has moved away from the back-support position but before head section  404  has reached the down position. CPR valve  212  can thus be deactivated when head section  404  is in the intermediate position to block the fluid communication between rear port  154  of head section pivot cylinder  150  and return conduit  185 . Blocking the fluid communication locks head section  404  in the intermediate position. CPR foot pedals  250  can thereafter be moved back to the releasing position so that CPR valve is once again activated to restore fluid communication between rear port  154  and return conduit  185  allowing movement of head section  404  toward the down position. Providing this capability to the caregiver in an actuator designed as a foot pedal keeps the hands of the caregiver free to conduct other activities while CPR foot pedals  250  are depressed and head section  404  moves to the down position. 
     Thigh Section 
     The first embodiment of a chair bed  50  in accordance with the present invention additionally includes thigh section  408  of articulating deck  402  which is configured to pivot relative to weigh frame  506  as shown in FIG.  15 . Thigh section  408  pivots about a pivot axis  602  adjacent to head end  52  of thigh section  408  between a down position in which thigh section  408  is generally horizontal and parallel to weigh frame  506  and an upward position in which foot end  54  of thigh section  408  is elevated above weigh frame  506 . Thigh section pivot cylinder  158  is connected to weigh frame  506  as shown in FIGS. 14 and 15. Although thigh section  408  can move independently of the head and foot sections  404 ,  410 , thigh section  408  preferably moves to the upward position when head section  404  moves to the back-support position so that the head and thigh sections  404 ,  408  cooperate to cradle the person (not shown) on sleeping surface  552  therebetween. Thigh section  408  preferably moves to the down position when head section  404  moves to the down position. 
     Foot Section 
     Foot section  410  of articulating deck  402  is movable from a generally horizontal up position parallel to intermediate frame  302  as shown in FIGS. 1 and 3 to a generally vertically downwardly extending down position to permit the lower legs and feet of the person (not shown) to be lowered to the sitting position as shown in FIGS. 2 and 8. Foot section  410  can also be contracted from an expanded position having a longitudinal length  465  as shown in FIGS. 3,  24 , and  30  to a contracted position having foot end  54  of foot section  410  drawn inwardly toward head end  52  of chair bed  50  so that foot section  410  has a longitudinal length  464  that will “clear” the floor when foot section  410  moves to the down position as shown in FIGS. 8 and 25. Preferably, length  464  of foot section  410  when foot section  410  is contracted is such that foot end  54  of foot section  410  clears the floor and is spaced-apart therefrom sufficiently to permit a base (not shown) of an over bed table (not shown) to fit therebetween. 
     Foot section  410  is pivotably coupled to an upper deck end portion  460  of thigh section  408  by hinge  468  as shown in FIGS. 12,  15 ,  24 ,  25 , and  30 . Consequently, foot section  410 , when in the down position, can be longer by an amount equal to a vertical offset  514  between lower deck  430  and upper deck  414  than it could be if there were no step deck  412 , and foot section  410  were instead connected to lower deck  430 . Thus, for foot section  410  to clear the floor when foot section  410  pivots from the up position to the down position, foot section  410  can contract a lesser amount than would be required if there were no step deck  412 . 
     Foot section  410  includes a pivoting member  466  that is pivotably coupled to thigh section  408  and a contracting member  462  that can be drawn inwardly toward head end  52  of foot section  410  from an expanded position to the contracted position. Foot section pivot cylinder  168  and foot section contracting cylinder  176  cooperate to move pivoting member  466  between the up position and the down position and to move contracting member  462  between the expanded position shown in FIG.  24  and the contracted position shown in FIG.  25 . 
     Contracting member  462  is positioned to slide across top surface  470  of pivoting member  466  as shown in FIGS. 11 and 15. A folding bracket  472  has a first end  474  pivotably coupled to weigh frame  506  and a second end  476  pivotably coupled to pivoting member  466  as shown in FIGS. 15,  24 , and  25 . Piston rod  170  of foot section pivot cylinder  168  is pivotably coupled to bracket  472 . Piston rod  170  pushes against bracket  472  as piston rod  170  extends from foot section pivot cylinder  168  causing bracket  472  to pivot upwardly from a folded position about a pivot axis  478  adjacent to weigh frame  506  and to push pivoting member  466  upwardly to the up position. When piston rod  170  is in the extended position, bracket  472  is generally unfolded, horizontal, and parallel to pivoting member  466 . 
     Foot section  410  further includes first and second linkages  480 ,  482  and a thruster strut  484  as shown in FIGS. 24 and 25. First linkage  480  has a first end  486  pivotably coupled to pivoting member  466 . A second end  488  of first linkage  480  is pivotably coupled to a first end  490  of second linkage  482  and a second end  492  of second linkage  482  is pivotably coupled to foot end  54  of contracting member  462 . Thus, first and second linkages  480 ,  482  couple pivoting member  466  and contracting member  462 . 
     Thruster strut  484  has a first end  494  that is pivotably coupled to pivoting member  466  and a second end  496  that is pivotably coupled to second linkage  482  between the first and second ends  490 ,  492  of second linkage  482  as shown in FIGS. 24 and 25. Foot section contracting cylinder  176  is pivotably coupled to pivoting member  466  near head end  52  of pivoting member  466  and piston rod  178  is pivotably coupled to thruster strut  484  between the first and second ends  494 ,  496  of thruster strut  484 . First and second linkages  480 ,  482 , thruster strut  484 , and foot section contracting cylinder  176  are generally coplanar and generally operate in a plane that is parallel to foot section  410 . 
     As piston rod  178  moves from the retracted position, shown in FIG. 25, to the extended position, shown in FIG. 24, thruster strut  484  pivots about a pivot axis  498  so that second end  496  of thruster strut  484  swings toward foot end  54  of chair bed  50 . As thruster strut  484  swings toward foot end  54  of chair bed  50 , second linkage  482  is pushed by thruster strut  484  toward foot end  54  of chair bed  50  and second linkage  482  pulls second end  488  of first linkage  480  toward foot end  54  of chair bed  50 . 
     Second end  492  of second linkage  482  pushes contracting member  462  toward foot end  54  of chair bed  50  when thruster strut  484  pushes second linkage  482  toward foot end  54  of chair bed  50  as shown in FIGS. 24 and 25. Likewise, when piston rod  178  moves from the extended position shown in FIG. 24 to the retracted position shown in FIG. 25, thruster strut  484  pulls second linkage  482  toward head end  52  of chair bed  50  and second linkage  482  pulls foot end  54  of contracting member  462  toward head end  52  of chair bed  50 , causing contracting member  462  to contract and reducing the length of foot section  410  by a distance  500  as shown in FIG.  25 . 
     Contracting member  462  is formed to include downwardly extending longitudinal tabs  502  and pivoting member is formed to include longitudinal channels  504  as shown in FIGS. 24-27. Longitudinal tabs  502  are received by longitudinal channels  504  as shown best in FIGS. 26 and 27. Tabs  502  cooperate with channels  504  to maintain the transverse position of contracting member  462  relative to pivoting member  466  as contracting member  462  slides longitudinally relative to pivoting member  466 . 
     As foot section  410  pivots from the up position to the down position, inflatable foot portion  564  of mattress  550  deflates as shown in FIG.  30  and shown diagrammatically in FIG. 8 so that foot section  410  of articulating deck  402  can move to the down position without interference from foot portion  564  of mattress  550 . Deflating foot portion  564  also allows the person (not shown) carried by chair bed  50  to sit on chair bed  50  when chair bed  50  moves to the sitting position without having the thickness of foot portion  564  of mattress  550  pull the knees and shins of the person forward as foot section  410  of articulating deck  402  pivots to the down position. In addition, the deflating action of deflating foot portion  564  prevents scrubbing between sleeping surface  552  and the legs (not shown) of the person (not shown) on sleeping surface  552  by allowing sleeping surface  552  adjacent foot portion  564  to move with the legs of the person. 
     A second embodiment of a contracting mechanism  520  for expanding and contracting the length of foot section  410  can illustratively be operated using an air control system  522  that also operates to inflate and deflate foot portion  564  of mattress  550  as shown in FIG. 25 a.  Air control system  522  includes an air supply  524  for supplying pressurized air and a controller  526  for controlling the flow of air through conduit  528  to inflatable foot portion  564  and to contracting mechanism  520 . 
     Contracting mechanism  520  includes a bellows  530  that is received between a first wall  534  that is fixed to pivoting member  466  and a second wall  536  that is fixed to contracting member  462  as shown in FIG. 25 a.  Contracting member  462  is slidably connected to pivoting member so that second wall  536  can slide relative to first wall  534 . As second wall  536  moves toward first wall  534 , contracting member is drawn inwardly to contract foot section  410 . As second wall is pushed away from first wall  534 , contracting member extends from foot section  410  and expands the length of foot section  410 . Contracting mechanism  520  also includes two extension springs  538  connected to pivoting member  466  and contracting member  462  to yieldably bias contracting member  462  to the contracted position. 
     As air control system  522  supplies pressurized air to bellows  530 , bellows expands and pushes against first and second walls  534 ,  536  moving second wall  536  away from first wall  534  and causing contracting member to extend from foot section  410  thereby expanding the length of foot section  410 . As air control system  522  withdraws air from bellows  530 , bellows stops pushing against first and second walls  534 ,  536 , and springs  538  pull contracting member  462  inwardly toward pivoting member  466 , thus contracting the length of foot section  410 . 
     As described above, illustrative air control system  522  operate to control both the inflation of foot portion  564  and the inflation of bellows  530  as shown in FIG. 25 a.  The illustrative system provides a satisfactory method for coordinating the inflation and deflation of foot portion  564  with the contraction and expansion of the length of foot section  410 . 
     STEP DECK AND MATTRESS 
     The head, seat, thigh, and foot sections  404 ,  406 ,  408 ,  410  of articulating deck  402  cooperate to define a step deck  412  as shown best in FIGS. 11, and  28 - 30 . Step deck  412  includes an upper deck  414  having a head end upper deck portion  416  appended to head end  52  of head section  404 , side upper deck portions  418 ,  420 ,  422 ,  424 ,  426 ,  428  appended to sides of the head, seat, and thigh sections  404 ,  406 ,  408 , and a foot end upper deck portion  460  appended to foot end  54  of weigh frame  506  adjacent to thigh section  408 . The upper deck portions  416 ,  418 ,  420 ,  422 ,  424 ,  426 ,  428 ,  460  and a top surface  411  of foot section  410  are coplanar when articulating deck  402  is in the initial position and cooperate to form upper deck  414  which is generally parallel to weigh frame  506 . 
     Step deck  412  also includes a lower deck  430  having a head slat  432 , a seat slat  434 , and a thigh slat  436 . Head, seat, and thigh slats  432 ,  434 ,  436 , are coplanar when articulating deck  402  is in the initial position and they cooperate to form lower deck  430  which is generally parallel to weigh frame  506  and to upper deck  414  when articulating deck  402  is in the initial position. 
     Lower deck  430  is connected to upper deck  414  by a wall  438  including a head end wall  440  connecting head slat  432  to head end upper deck portion  416 , side walls  442 ,  444 ,  446 ,  448 ,  450 ,  452  connecting head, seat, and thigh slats  432 ,  434 ,  436  to side upper deck portions  418 ,  420 ,  422 ,  424 ,  426 ,  428 , and a foot end wall  454  connecting thigh slat  436  to foot end upper deck portion  460  as shown in FIGS. 11 and 28. Step deck  412 , then, comprises upper deck  414  and is formed to include a central, longitudinally extending recess  456  defined by lower deck  430  and by wall  438  connecting lower deck  430  to upper deck  414 . In the preferred embodiment, foot section  410  of step deck  412  is displaced from recess  456  and forms part of upper deck  414 , as shown in FIGS. 28 and 30. 
     In preferred embodiments, head section  404  of articulating deck  402  is coupled to weigh frame  506  by reduced-shear pivot assembly  650  immediately adjacent upper deck  414  which causes head section  404  of articulating deck  402  to pivot relative to weigh frame  506  between the down position and the back-support position. 
     Combining step deck  412  and reduced-shear pivot assembly  650  in chair bed  50  allows reduced-shear pivot assembly  650  to be mounted to wall  438  rather than to a bottom of a conventional deck. Consequently, the vertical distance between sleeping surface  552  and reduced-shear pivot assembly  650  is minimized. This minimizing the extent that reduced-shear pivot assembly  650  is required to raise effective pivot axis above reduced-shear pivot assembly  650 . 
     Mattress  550  is received by articulating deck  402  and includes a projection  576  sized to be received by recess  456  as shown in FIGS. 28 and 29. Consequently, mattress  550  is thinner along sides  580  of mattress  550  where mattress  550  engages upper deck  414  of step deck  412 . Conversely, mattress  550  is thicker in portions adjacent to projection  576 . Preferably, projection  576  is positioned directly beneath portions of mattress  550  carrying a majority of the weight of the person on sleeping surface  552 . The thick portion of mattress  550  including the thickness of mattress  550  between sleeping surface  552  and a bottom surface  586  engaging upper deck  414  plus the thickness of projection  576  provides greater comfort for the person on sleeping surface  552 . Mattress  550 , then, has a thinner perimetral zone  580  and a thicker body-support zone  582  adjacent to projection  576 . Preferably, body support zone is 1½ times the thickness of perimetral zone  580 . For example, perimetral zone can be 5 inches (12.7 cm) thick and body-support zone  582  can be 7½ inches (19 cm) thick. 
     Thinner perimetral zone  580  and upper deck side portions  417  cooperate to define “rammed” edges that provide greater firmness around the edges of sleeping surface  552  as the result of sleeping surface  552  being in close proximity to upper deck  414 . This increased firmness is advantageous when the person enters and exits the bed along the sides of the bed. 
     Additionally, the rammed edges provide a firm edge that cooperates with side rail assemblies  800 ,  802 ,  804 ,  806  to minimize the potential for side rail entrapment, in which an object becomes wedged between sleeping surface  552  and one of side rails  808 ,  810 ,  812 ,  814 . Also, step deck  412  cooperates with side rail assemblies  800 ,  802 ,  804 ,  806  to maximize the height relative to sleeping surface  552  at which side rails  808 ,  810 ,  812 ,  814  are mounted as shown in FIGS. 34 and 35. Tops of side rails  808 ,  810 ,  812 ,  814  can be higher when in the patient-restraining position for improved coverage and protection of the person (not shown) on sleeping surface  552  and bottoms  814  can be higher when in the tucked position for improved access to base frame  62  and to the space beneath intermediate frame  302 . 
     Projection  576  includes a side wall  584  that can be configured to engage at least portions of the wall  438  of step deck  412  as shown in FIG. 29, thereby preventing lateral and longitudinal sliding of mattress  550  relative to step deck  412 . Also, mattress  550  includes sides  578  connecting sleeping surface  552  and bottom surface  586 . Mattress  550  and step deck  412  are configured so that sides  578  of mattress  550  are exposed above deck  402  as shown in FIGS. 28 and 29 providing the caregiver greater and easier access to mattress  550 , rather than engaging a portion of a frame or upstanding walls of a deck as is found with conventional mattress and deck systems. 
     In preferred embodiments, sleeping surface  550  is generally planar and projection  576  is centrally located beneath sleeping surface  550  to form thick body support zone  582  of mattress  550  surrounded by perimetral zone  580  engaging upper deck  414 . Mattress  550  may be provided in more than one piece, for example, mattress  550  may comprise a first mattress piece fit into recess  456  and a second mattress piece surrounding and abutting sides of the first mattress piece and engaging upper deck  414 , or a first mattress piece could fit into recess  456  and a second mattress piece having a planar bottom surface could fit over the first mattress piece so that the bottom of the second mattress piece engages the first mattress piece and upper deck  414 . However, a one-piece mattress  550  including both body-support zone  582  and perimetral zone  580  is preferred. 
     Inflatable Mattress Portion—minimizing the Foot Section 
     Additionally, mattress  550  can include an inflatable portion  574  that can assume both an inflated position and a deflated position. Preferably, inflatable portion  574  is positioned to lie in foot portion  564  as shown in FIG. 30 so that inflatable portion  574  can be inflated to serve as sleeping surface  552  when foot section  410  of deck  402  is in the up position and so that inflatable portion  574  can be deflated and inclined downwardly when the foot section  410  is lowered to the down position to provide room for the lower legs of the person when chair bed  50  is in the sitting position. Foot portion  564  is thinner and shorter when deflated than when foot portion  564  is inflated. 
     Foot portion  564  of mattress  550  and foot section  410  of articulating deck  402  cooperate to minimize the length of the foot of chair bed  50  as shown in FIG.  30 . Foot section  410  and foot portion  564  are a first length  465  when foot section  410  is in the-up position and a second length  464  when foot section  410  is in the down position, first length  465  being greater than second length  464 . Also, foot portion  564  is a first thickness  608  when foot section  410  is in the up position and a second thickness  609  when foot section  410  is in the down position, first thickness  608  being greater than second thickness  609 . 
     In addition, the width  604  of foot portion  564  of mattress  550  is less than the width  606  of head portion  558  of mattress  550 , the width  606  of head portion  558  typically being a standard mattress width as shown in FIGS. 28 and 30. This difference between the widths  604 ,  606  permits a standard fitted sheet (not shown) to be tightly installed onto mattress  550  while remaining loose adjacent to foot portion  564  so that pressure relief can be maintained in the section of foot portion  564  receiving the heels (not shown) of the person (not shown) supported on sleeping surface  552 . The smaller width  604  of foot portion  564 , the contraction of foot section  410  and the corresponding contraction of foot portion  564 , and the deflation of inflatable portion  574  when inflatable portion  574  is positioned to lie in foot portion  564 , all act to minimize the foot of chair bed  50  when the foot section  410  moves from the up position to the down position so that the feet of the person supported on the sleeping surface  552  can reach the floor (not shown) or foot prop  646 . The narrow foot section  410  of deck  402  and foot portion  564  of mattress  550  minimizes the width of foot end  54  of deck  402  so that the width of bed  50  adjacent to extended frame  610  is no greater than the width of bed  50  adjacent to body section side rails  812 ,  814 . 
     C-arm Access 
     Use of step deck  412  can additionally improve access of equipment to portions of chair bed  50  as shown in FIG. 29. A C-arm  588  carrying equipment  590 ,  592  aid having equipment  590  positioned to lie above sleeping surface  552  and equipment  592  positioned to lie below step deck  412  can be positioned near chair bed  50 . C-arm  588  is C-shaped having an inner surface  594  and a point  596  on inner surface  594  that is the maximum lateral distance on inner surface  594  away from equipment  590 ,  592 . An edge  598  of upper deck  414  is positioned to lie a distance  600  above lower deck  430  of step deck  412 . While a conventional deck bottom (not shown) would have an edge (not shown) engaging C-arm  588  away from point  596 , edge  598  of step deck  412  engages C-arm adjacent to point  596 , thereby maximizing the area of sleeping surface  552  across which equipment  590 ,  592  can be located. 
     Additionally, head slat  432  can have a radiolucent portion  510  made from a radiolucent material that is transparent to X-rays thereby permitting X-rays to pass therethrough as shown in FIGS. 28 and 29. Equipment  590 ,  592  can be radiography equipment used to produce images such as X-ray images or photographs of the person (not shown) on sleeping surface  552 . Having step deck  412  arranged to engage point  596  of C-arm  588  maximizes the area of sleeping surface  552  away from edge  598  that equipment  590 ,  592  can be positioned, thereby maximizing the area of sleeping surface  552  on which the person can be positioned to lie while fluoroscopic procedures are performed on the person. 
     EXTENDED FRAME 
     An extended frame module  610  can be provided for chair bed  50 . Extended frame module  610  includes an extended frame  612  at foot end  54  of chair bed  50  as shown in FIG.  11 . Extended frame  612  comprises frame-extender members  614 , each frame-extender member  614  having a first end  616  fixed to foot end  54  of weigh frame  506  on each side of chair bed  50 . Frame-extender members  614  each extend outwardly away from head end  52  of chair bed  50  and terminate in a second end  618  positioned to lie longitudinally between thigh section  408  and foot end  54  of foot section  410  and along sides  508  of foot section  410 . 
     Extended frame  612  further comprises swing members  620 , each swing member  620  having a first end  624  pivotably coupled to second end  618  of frame-extender members  614 . Swing members  620  can swing between a tucked position beside frame-extender members  614  and an extended position beside foot section  410  of articulating deck  402  as shown in FIG.  2 . Each swing member  620  is preferably provided with a foot safety switch  648  as shown in FIGS. 2 and 11 to prevent entrapment of objects under swing members  620  during movement of intermediate frame  302 . 
     Extended frame  612  additionally comprises a foot gate  622  including swinging gates  626 ,  634 , each swinging gate  626 ,  634  having a first end  628 ,  636  rotatably coupled to swing members  620  as shown in FIG.  11 . Gates  626 ,  634  can rotate a full 360 degrees relative to swing members  620 . Gates  626 ,  634  cooperate with swing members  620  to move gates  626 ,  634  to several positions relative to weigh frame  506 . For example, gates  626 ,  634  can “close” foot end  54  of chair bed  50  as shown in FIG. 1 by moving to a closed position in which gates  626 ,  634  are positioned to lie transversely across foot end  54  of chair bed  50  having second ends  630 ,  638  of gates  626 ,  634  in juxtaposition. Gates  626 ,  634  provide a protective “crib-like” perimeter when gates  626 ,  634  are closed and chair bed  50  is in the sitting position. 
     Foot gate  622  can also be moved to a side-grip position shown in FIG. 2 by first swinging gates  626 ,  634  inwardly along arc  642  as shown in FIG. 11 so that gates  626 ,  634  are positioned to lie directly above swing members  620  and then swinging swing members  620  along arc  732  so that swing members  620  and gates  626 ,  634  are positioned to lie beside frame-extender members  614 . Including both fixed frame-extender members  614  and swing members  620  in extended frame  612  allows gates  626 ,  634  to both close foot end  54  of chair bed  50  while at the same time reducing the radius through which swing members  620  swing when moving from the closed position to the side-grip position. As a result, the space required around chair bed  50  to permit the movement of gates  626 ,  634  is minimized. Gates  626 ,  634  are provided with grip handles  632 ,  640  that provide support for a person on sleeping surface  552  moving from a seated position to a standing position when chair bed  50  is in the sitting position and foot gate  622  is in the side-grip position as shown in FIG.  2 . 
     Gates  626 ,  634  perform the function of a conventional footboard when gates  626 ,  634  are closed and chair bed  50  is in the bed position. Gates  626 ,  634  can swing outwardly from the closed position to an open position having each gate  626 ,  634  positioned to lie away from foot end  54  of chair bed  50 . When gates  626 ,  634  are in the open position, the caregiver has clear access to foot section  410  of chair bed  50 . Additionally, gates  626 ,  634  act as support aids for the person (not shown) supported by sleeping surface  552  when the person stands or is transferred to a wheelchair (not shown) or other equipment (not shown) when chair bed  50  is in the sitting position, swing members  620  are extended, and gates  626 ,  634  are angled back toward the person. Also, gates  626 ,  634  can be removed entirely from foot end  54  of chair bed  50  to clear foot end  54  of chair bed  50  for caregivers and equipment (not shown) when swing members  620  are folded back and gates  626 ,  634  are folded back. Safety switches (not shown) can be included to limit the articulation of deck  402  and intermediate frame  302  when gates  626 ,  634  are in selected positions to prevent limb entrapment between gates  626 ,  634  and either deck  402  or intermediate frame  302 . 
     Typically, extended frame  612  is carried by weigh frame  506 . For embodiments of chair bed  50  that do not include weighing capability, extended frame  612  is carried by the common frame, which typically includes intermediate frame  302  and weigh frame  506  fixed together. Weigh frame  506  and the common frame also carry articulating deck  402 . Carrying extended frame  612  on weigh frame  506  or the common frame causes extended frame  612  to move with articulating deck  402  when intermediate frame  302  is raised and lowered relative to base frame  62 . Consequently, extended frame  612  and gates  626 ,  634  remain stationary relative to the person (not shown) supported by sleeping surface  552 . For example, when chair bed  50  is in the sitting position and extended frame  612  is in the side-grip position, intermediate frame  302  can be raised from the low position to the raised position to help the person to stand. Extended frame  612  is stationary relative to sleeping surface  552  so that the person can use grip handles  632 ,  640  for support. 
     SIDE RAIL ASSEMBLIES 
     Chair bed  50  is typically provided with side rail assemblies  800 ,  802 ,  804 ,  806  as shown in FIGS.  11  and  31 - 38  and shown diagrammatically in FIG.  47 . Side rail assemblies  800 ,  802 ,  804 ,  806  include head section side rails  808 ,  810  mounted to head section  404  of articulating deck  402 , and body section side rails  812 ,  814  mounted to weigh frame  506  adjacent to thigh section  408  of deck  402 . 
     Head section side rails  808 ,  810  are mounted to move with head section  404  as head section  404  pivots relative to weigh frame  506  between the down position and the back-support position as shown in FIGS.  11  and  31 - 33 . Body Section side rails  812 ,  814  are mounted to weigh frame  506  and do not move relative to weigh frame  506  and seat section  406  when head, thigh, and foot sections  404 ,  408 ,  410  of articulating deck  402  move. Head section side rails  808 ,  810  are shorter than body section side rails  812 ,  814  and extend only adjacent head section  404 , whereas body section side rails  812 ,  814  extend adjacent head and body (seat and thigh) sections  404 ,  406 ,  408 . Both of the head section and body section side rails  808 ,  810 ,  812 ,  814  are configured to maintain a between-rail gap  866  of approximately 2-3 inches as head section  404  moves between the back-support position and the down position. 
     In addition, having short head section side rails  808 ,  810  ideally positions head section side rails  808 ,  810  to provide support to a person (not shown) entering or exiting chair bed  50  on one of sides  554 ,  556  when appropriate head section side rail  808 ,  810  is in the patient-restraining position and body section side rail  812 ,  814  is in the tucked position. This configuration allows the person to enter and exit by sitting on sleeping surface  552  while holding head section side rail  808 ,  810  for support, and pivoting off of or onto sleeping surface  552  so that the person does not have to “scoot” along sleeping surface  552 . Also, a hip pivot guide  694  on body section side rails  812 ,  814  helps to optimize the positioning of the hip (not shown) of the person on chair bed  50  after entering chair bed  50  from one of sides  554 ,  556 . 
     Side rails  808 ,  810 ,  812 ,  814 , are passive restraint devices mounted on both sides of chair bed  50  as shown in FIGS. 11,  34 , and  35 . In the upward patient-restraining position shown in FIGS. 31-34, side rails  808 ,  810 ,  812 ,  814  are vertical barriers that can abut sides  554 ,  556  of mattress  550  and extending above sleeping surface  552  to restrain movement of the person past sides  554 ,  556  of sleeping surface  552 , thereby preventing the person from rolling out of chair bed  50 . Side rails  808 ,  810 ,  812 ,  814  may also be lowered below sleeping surface  552  of mattress  550  to a tucked position shown in phantom in FIG. 35 beneath side portions  418 ,  420 ,  422 ,  424 ,  426 ,  428  of upper deck  414  to permit the person to move past sides  554 ,  556  of sleeping surface  552  when entering or exiting chair bed  50 . Lowering side rails  808 ,  810 ,  812 ,  814  also provides the caregiver with clear access to the patient. 
     Lowering each side rail  808 ,  810 ,  812 ,  814  is accomplished by pulling release handle  862  as shown in FIGS. 34 and 35. After pulling release handle  862 , the caregiver may let go of release handle  862  and allow side rail  808 ,  810 ,  812 ,  814  to rotate downwardly into the tucked position. The rate at which each side rail  808 ,  810 ,  812 ,  814  rotates downwardly is preferably controlled by a mechanical damper  868 . To raise side rails  808 ,  810 ,  812 ,  814 , the caregiver pulls up on side rails  808 ,  810 ,  812 ,  814  until they lock in the patient-restraining position. Side rail assemblies  800 ,  802 ,  804 ,  806  are configured so that side rails  808 ,  810 ,  812 ,  814  are generally vertical and generally parallel to the sides of chair bed  50  at all positions between the tucked position and the patient-restraining position as shown in FIGS. 34 and 35. 
     Side rail assemblies  800 ,  802 ,  804 ,  806  are of similar construction. The principles discussed below with respect to body section side rail assembly  806  pertains to each side rail assembly  800 ,  802 ,  804 ,  806  unless the description herein specifically states otherwise. 
     Side rail assembly  806  includes body section side rail  814 , a side rail mounting mechanism  816 , and a mounting bracket  818  connecting mounting mechanism  816  to sides  508  of weigh frame  506  as shown in FIGS. 34 and 35. Mounting bracket  818  is positioned to lie beneath upper deck  414  and is attached to weigh frame  506  as shown in FIGS. 34 and 35. Similarly, head section side rail assemblies  800 ,  802  are connected to walls  442 ,  444  of head section  404 , and body side rail assembly  804  is connected to side  508  of weigh frame  506  as shown in FIG.  11 . 
     Mounting bracket  818  includes an upstanding support wall  820  attached to wall  508  of weigh frame  506  and outwardly extending walls  822  attached thereto and attached to weigh frame  506  as shown in FIGS. 34 and 35. Walls  822  of mounting bracket  818  are formed to include upper openings  824  and lower openings  826 . Side rail mounting mechanism  816  is a parallelogram connecting mechanism that connects side rail  814  to mounting bracket  818  for movement between the patient-restraining position and the tucked position while maintaining side rail  814  in a generally vertical orientation. Side rail mounting mechanism  816  includes three curved parallel bars  828 ,  830 ,  832  having first ends  834 ,  836 ,  838 , and second ends  840 ,  842 ,  844 . Curved bar  830  is laterally positioned to lie between curved bars  828 ,  832  and vertically positioned to lie above curved bars  828 ,  832 . Bracket mounting pins  848  are appended to a first end  836  of curved bar  830  and are rotatably received by upper openings  824  of walls  822 . Bracket mounting pins  846 ,  850  are appended to first ends  834 ,  838  of curved bars  828 ,  832  and are rotatably received by lower openings  826  of walls  822 . Curved bars  828 ,  830 ,  832  are mounted to pivot relative to weigh frame  506 . 
     Curved bars  828 ,  830 ,  832  each include a first section extending perpendicular to and above upper deck section  428  and a second section extending transverse to the first bar section below upper deck section  428  when side rail  814  is in the patient-restraining position as shown in FIG.  34 . This curved structure in combination with the raised pivot connection to step deck  412  allows side rail  814  to be raised above bottom surface  586  of mattress  550  while being immediately adjacent sides  578  with minimum gap. 
     Side rail  814  is also formed to include upper openings  852  and lower openings  854  as shown in FIGS. 34 and 35. Side rail mounting pins  858  are appended to second end  842  of curved bar  830  and are received by upper openings  852  of side rail  814 . Side rail mounting pins  856 ,  860  are appended to second ends  840 ,  844  of curved bars  828 ,  832  and are received by lower openings  854  of side rail  814 . Curved bars  828 ,  830 ,  832  are mounted to pivot relative to side rail  814 . Upper and lower openings  824 ,  826  of mounting bracket  818  are spaced apart and upper and lower openings  852 ,  854  of side rail  814  are spaced apart an equal amount so that curved bars  828 ,  830 ,  832  are positioned in parallel relation between side rail  814  and mounting bracket  818 . 
     Side rail  814  can thus rotate between an upper patient-restraining position abutting side  556  of mattress  550  as shown in FIG. 34 to a tucked position beneath section  428  of upper deck  414  shown in FIG. 35 (in phantom). Parallel curved bars  828 ,  830 ,  832  cooperate with upper and lower openings  824 ,  826  of mounting bracket  818  and upper and lower openings  852 ,  854  of side rail  814  to keep side rail  814  generally parallel to wall  452  of step deck  412  and generally perpendicular to sleeping surface  552  as side rail  814  rotates between the patient-restraining position and the tucked position. 
     Side rail assembly  806  also includes a latching mechanism  870  including a release handle  862  rotatably mounted to curved bars  828 ,  832  for movement between a forward latched position shown in FIG. 34 and a rearward released position shown in FIG. 34 (in phantom). Latching mechanism additionally includes links  872  and latches  878 , each link having a first end  874  pivotably connected to release handle  862  and a second end  876  that is pivotably connected to a latch  878 . Each latch  878  is formed to include a first end  880  that is pivotably connected to curved bars  828 ,  832 , a second end  882  spaced apart from first end  880 , a rod-gripper recess  884  adjacent to second end  882 , and a spring-receiving opening  886  spaced apart from both ends  880 ,  882  of latch  878 . 
     Tension springs  888  each have a first end  890  connected to spring-receiving openings  886  of latches  878  and a second end  892  connected to brackets  894  fixed to curved bars  828 ,  832  as shown in FIG.  34 . As release handle  862  is pulled outwardly by the caregiver, release handle  862  pulls links  872  outwardly and upwardly which in turn pull latches  878  upwardly to pivot latches  878  against the bias of springs  888 . 
     A rod  896  is connected to walls  822  of mounting bracket  818  and is arranged to be received by rod-gripper recesses  884  when side rail  814  is in the patient-restraining position shown in FIG. 34 so that rod  896  and latches  878  cooperate to retain side rail  814  in the patient-retraining position. When release handle  862  is pulled outwardly, as shown in phantom in FIG. 34, latches  878  disengage from rod  896 , thereby allowing side rail  814  to rotate downwardly as shown in FIG. 35 until side rail  814  reaches the tucked position beneath upper deck  414  of articulating deck  402 , as shown for side rail  808  in FIG.  1  and side rail  814  in FIG. 35 (in phantom). 
     To raise side rail  814 , the caregiver simply lifts side rail  814  to rotate side rail  814  upwardly to the patient-restraining position. Each latch  878  has second end  882  having a camming surface  898  as shown in FIGS. 34 and 35 that engages rod  896 . As side rail  814  advances toward the patient-restraining position, camming engagement of camming surfaces  898  and rod  896  forces latches  878  to pivot upwardly against the bias of springs  888 . Latches  878  ride over rod  896  as side rail  814  advances to the patient-restraining position until rod  896  is adjacent to rod-gripper recesses  884 . Springs  888  then pull latches  878  downwardly to capture rod  896  in rod-gripper recesses  884 , thereby holding side rail  814  in the patient-restraining position. 
     Side rail  814  cooperates with side rail mounting mechanism  816  to control the gap between mattress  550  and side rail  814 . Because side rail  814  rotates upwardly from the tucked position to the patient-restraining position toward side  556  to abut side  556  of mattress  550 , a gap that could form between mattress  550  and side rail  814  is minimized. Additionally, side rail  814  cooperates with step deck  412  to minimize the distance between a bottom  864  of side rail  814  and section  428  of upper deck  414 , further maximizing the effectiveness of side rail  814  as a passive restraint. In addition, side rail mounting mechanism  816  provides a one-step release and auto-tuck movement as side rail  814  rotates from the patient-restraining position to the tucked position. 
     Each side rail assembly  800 ,  802 ,  804 ,  806  operates in a manner similar to side rail assembly  806  described above to move side rails  808 ,  810 ,  812 ,  814  between the tucked position and the patient-restraining position. Head section side rails  808 ,  810  can additionally be provided with breakaway side rails  920  that move from the tucked position to a generally vertically downwardly extending down-out-of-the-way position described below. 
     Breakaway Side Rails 
     Breakaway side rails  920  allow the caregiver to move the side rail assemblies from the generally horizontal tucked position to a generally vertically downwardly extending down-out-of-the-way position to provide clear access to chair bed  50  beneath intermediate frame  302  as shown in FIG.  36  and also to provide clear access beneath intermediate frame  302  for equipment mounted on a C-arm. Breakaway side rails  920  accomplish this by moving the side rail to a down-out-of-the-way position away from the side of chair bed  50  and by narrowing the width of the section of chair bed  50  adjacent to the side rail for deeper C-arm insertion. 
     When chair bed  50  is provided with breakaway side rails  920 , head section upper deck side portions  418 ,  420  include collateral head frames  922 ,  924  as shown in FIG.  36 . Each collateral head frame  922 ,  924  is pivotably mounted to upper deck side portion  418 ,  420  by a hinge  926 ,  928 . Each collateral head frame  922 ,  924  can swing between an up position, as shown, for example, by collateral head frame  924  in FIG. 36, and a generally vertically downwardly extending down-out-of-the-way position, as shown, for example, by collateral head frame  922  in FIG.  36 . Preferably, hinges  926 ,  928  are connected to head end  52  of collateral head frames  922 ,  924  so that collateral head frames  922 ,  924  are adjacent to head end  52  of chair bed  50  when collateral head frames  922 ,  924  are in the down-out-of-the-way position. Each collateral head frame  922 ,  924  can be locked into the up position by a pin  930  configured to be received by an opening (not shown) in upper deck side portion  418 ,  420  and an opening  932  in collateral head frame  922 ,  924 . 
     Mounting brackets  818  are fixed to collateral head frame  922 ,  924  and are configured to move with collateral head frames  922 ,  924  so that side rails  808 ,  810  swing between the generally horizontal tucked position and the generally vertically downwardly extending down-out-of-the-way position when collateral head frames  922 ,  924  move between the up position and the down-out-of-the-way position as shown in FIG.  36 . When a caregiver wishes to move head section side rails  808 ,  810  to the down-out-of-the-way position, such as when preparing chair bed  50  for use during a procedure including the use of equipment mounted on a C-arm, the caregiver can raise intermediate frame  302  to the raised position, rotate the appropriate head section side rail  808 ,  810  to the tucked position, remove pin  930  from opening  932  in collateral head frame  922 ,  924  and from the opening (not shown) in upper deck side portions  418 ,  420 , and swing side rail  808 ,  810  from the tucked position to the down-out-of-the-way position. 
     Mechanical Angle Indicators 
     Side rails  808 ,  810 ,  812 ,  814  can additionally be provided with angle indicators  938  as shown, for example, in FIGS. 37-39. Head section side rails  808 ,  810  include indicators  938  as shown in FIG. 37 that generally indicate the angular orientation of head section  404  of deck  402 , and body section side rails include angle indicators  938  as shown in FIG. 39 that generally indicate the angular orientation of intermediate frame  302  relative to base frame  62 . Thus, angle indicators  938  on body section side rails  812 ,  814  are sometimes referred to as Trendelenburg indicators or Trend indicators. Mounting angle indicators  938  on side rails  808 ,  810 ,  812 ,  814  prominently displays angle indicators  938  so that the caregiver can quickly and easily judge the status of chair bed  50 . 
     Each angle indicator  938  includes a housing  940  having an interior region  942  defined by a rear wall  944  formed in side rail  808 ,  810 ,  812 ,  814  and a front wall  946  connected to side rail  808 ,  810 ,  812 ,  814  as shown in FIG.  38 . An indicator member  948  is received by interior region  942  for movement therein relative to housing  940  as the angular orientation of side rail  808 ,  810 ,  812 ,  814  and angle indicator  938  changes. The position of indicator member  948  relative to housing  940  indicates the angular orientation of angle indicator  938 . Housing  940  can be formed so that rear wall  944  is arcuate across the face of side rail  808 ,  810 ,  812 ,  814  as shown in FIG.  37  and indicator member  948  can be spherical and can be positioned to lie on and to roll along arcuate rear wall  944  as the angular orientation of angle indicator  938  changes. 
     Preferably, indicator member  948  includes an indicator surface  950  that is visible through front wall  946  of housing  940 . Markings  952  that are stationary relative to housing  940  can be positioned to lie adjacent to front wall  946  so that markings  952  and indicator member  948  cooperate to indicate the position of indicator member  948  relative to housing  940 , thus indicating the angular orientation of side rails  808 ,  810 ,  812 ,  814 . 
     Angle indicator  938  mounted to head section side rail  808 ,  810  includes a first end  954  positioned to lie toward head end  52  of side rail  808 ,  810  and a second end  956  positioned to lie toward foot end  54  of side rail  808 ,  810  and positioned vertically higher than first end  954  as shown in FIG.  37 . When head section  404  is in the down position, shown in FIG. 37, indicator member  948  is toward first end  954 . When head section  404  moves from the down position to the back-support position, indicator member  948  moves from first end  954  toward second end  956 . Indicator member  948  is infinitely positionable relative to housing  940  between first end  954  and second end  956  and the positions of indicator member  948  correspond to positions of head section  404  between the down position and the back-support position. 
     Angle indicator  938  mounted to body section side rail  812 ,  814  is substantially identical to angle indicator  938  on head section side rail  808 ,  760 , except that first and second ends  954 ,  956  are positioned to lie on generally the same horizontal plane as shown in FIG.  39 . When intermediate frame  302  is generally horizontal, body section side rail  812 ,  814  is generally horizontal and indicator member  948  is positioned to lie generally half-way between first end  954  and second end  956 . When intermediate frame  302  moves to the Trendelenburg position, intermediate frame  302 , body section side rail  812 ,  814 , and angle indicator  938  move so that indicator member moves toward first end  954  of housing  940 . When intermediate frame  302  moves to the reverse Trendelenburg position, body section side rail  812 ,  814  and angle indicator  938  move so that indicator member moves toward second end  956  of housing  940 . Indicator member  948  is infinitely positionable relative to housing  940  between first end  954  and second end  956  and the positions of indicator member  948  correspond to positions of intermediate frame  302  between the Trendelenburg position and the reverse Trendelenburg position. 
     Alternatively, an angle indicator can be a spirit level having a housing filled with a fluid to form a liquid-filled bulb type bubble spirit level. In such a spirit levels the position of the bubble relative to the housing changes as the angular orientation of the spirit level changes, the position of the bubble relative to the housing indicating the angular orientation of the spirit level. 
     Controls on Side Rails 
     Side rails  808 ,  810 ,  812 ,  814  can additionally be provided with controls for operating bed  50  and moving bed  50  to various positions. Controls can include control buttons  960  on a bed side of the side rail  960  for use by a person (not shown) on sleeping surface  550  as shown in FIGS. 40 and 41. Typically, the person&#39;s head will rest on head end  52  of sleeping surface  550 . To accommodate the person on sleeping surface and allow the person to easily locate and view control buttons  960 , control buttons  960  can be angled toward head end  52  of deck  402  as shown in FIGS. 40 and 41 so that faces  961  of buttons  960  are toward head end  52  of deck  402 . Bed  50  can also be provided with a second plurality of control buttons (not shown) on an outside of the side rail for use by a person outside of bed  50  as described below. 
     Side rail  812  is coupled to the side of deck  402  for movement between the patient-restraining position and the tucked position. A pad  962  having a display screen  964  can be provided on a side of side rail  812  outside of bed  50  as shown in FIGS. 39 and 42 for use by the caregiver. Preferably, pad  962  is mounted to side rail  812  to pivot outwardly for easy viewing of display screen  964  as shown in FIG.  42 . For example, pad  962  can be mounted to the outside of side rail  812  and can be configured to pivot upwardly about a pivot axis  966  adjacent to the top of pad  962 . This movement of pad  962  particularly allows for easy viewing of display screen  964  by a person standing next to the bed  50  even when side rail  812  is in the tucked position. 
     FIG. 48 is a block diagram illustrating the plurality of electronic control modules for controlling operation of the hospital bed. As discussed above, the plurality of modules are electrically coupled to each other using a twisted pair network channel in a peer-to-peer configuration. The peer-to-peer network extends between first and second network terminators  1012  and  1013 . The network connections are illustrated by the solid black lines in FIG.  48 . Discrete connections to each of the modules are illustrated by the dotted lines in FIG.  48 . The bold line of FIG. 48 illustrates an AC power connection. 
     Network terminator  1012  is coupled to an air supply module  1014 . Air supply module  1014  is coupled via the network cable to accessory port module  1016 . Accessory port module  1016  is coupled to the bed articulation control module (BACM)  1018 . BACM  1018  is coupled to a communications module  1020 . Communications module  1020  is coupled to scale instrument module  1022 . Scale instrument module  1022  is coupled to surface instrument control module  1024 . Surface instrument module  1024  is coupled to position sense and junction module  1026 . Position sense module  1026  is coupled to the network terminator  1013 . A left side standard caregiver interface module  1028  is also coupled to the network by a connection in position sense module  1026 . The right side standard caregiver interface module  1030  and the graphic caregiver interface module  1032  are also coupled to the network using a connection in the position sense module  1026 . 
     It is understood that the modules can be rearranged into a different position within the peer-to-peer network. The modules are configured to communicate with each other over the network cable without the requirement of a master controller. Therefore, modules can be added or removed from the network without the requirement of reprogramming or redesigning a master controller. The network recognizes when a module is added to the network and automatically enables a control interface such as graphic caregiver interface module  1032  to display specific module controls for the added module. This eliminates the requirement for controls on individual modules. The module recognition feature is discussed in detail below. 
     Each module is connected to its appropriate sensors and actuators so that it can perform its dedicated function. The following is a brief description of each electronic module: 
     Power for the communication network is supplied by a power supply and battery charge module  1062 . Power supply  1062  is coupled to a power entry module  1063  and an AC main plug  1065 . Power Supply/Battery charge module (PSB)  1062  converts the AC Mains input  1065  to DC levels to be used by the electronic modules. PSB  1062  contains filtering for the AC Mains  1065  at the Mains entry point  1063 . The PSB  1062  also provides power for limited bed functionality upon removal of the AC Mains power input via a battery  1067 . The PSB  1062  contains an automatic battery charging circuit with output to indicate battery status (i.e., battery dead, battery low, battery OK). PSB  1062  also controls the hydraulic pump  1055 . 
     Bed Articulation Control Module (BACM)  1018 —The BACM  1018  primarily controls the hydraulic system used to articulate the bed. BACM  1018  accepts inputs from various user interfaces located throughout the bed to control bed articulations. This control input is qualified with a position sensing input representing the actual locations of the bed deck sections, along with patient lockout controls, to determine whether the bed should articulate. The BACM  1018  is present in every bed. BACM includes a real time clock circuit to set the time for various other modules. 
     Position Sense module  1026  detects the angles of all the appropriate bed deck sections. In addition, it interfaces to the bed exit detect, and the four (4) side rail UP sensors. The position sense module  1026  outputs this information to the network. These functions may be incorporated into the BACM  1018  and Bed-Side Communications Interface module  1020 . The position sense module  1026  also provides the interconnections of the bed network and hospital communications links to the siderail standard caregiver interface  1028  and  1030  modules. 
     Siderails (SIDE)—The siderails will contain standard caregiver interface modules  1028  and  1030  consisting of input switch controls, output status indicators, and an audio channel. The standard caregiver interface modules  1028  and  1030  are coupled to patient control mechanisms for bed articulations, entertainment, surface, lighting, Bed Exit, and Nurse Call. 
     Scale Instrument Module  1022  translates the signals from the embedded load beams into actual weight measured on the weigh frame. Scale module  1022  outputs this weight to the Graphic Caregiver Interface Module (GCI)  1032  for display purposes. This weight is also available to the communications module  1020  for transmittal to the hospital information network. Scale module  1022  includes Bed Exit and weight gain/loss alarm detection capability. 
     Surface Instrument Module  1024  controls the dynamic air surface. It will accept input from the GCI  1032  to dictate system performance characteristics. Surface module  1024  uses the GCI  1032  to display outgoing system information. Surface instrument module  1024  also interfaces with the air supply module  1014  to control the air handling unit  1046 . 
     Sequential Compression Device (SCD)—This module will control the optional compression boots. It will use the GCI  1032  for interfacing to the caregiver. 
     Graphic Caregiver Interface Module (GCI)  1032  controls the scale  1022  and surface module  1024  (including SCDs). In addition, GCI  1032  provides control input and text and graphic output capability for future design considerations. GCI  1032  utilizes a graphic display along with a software menu structure to provide for full caregiver interaction. 
     Communications module  1022  is the gateway between the patient&#39;s environment controls and bed status information residing on the bed, and the hospital information/control network. 
     Bed Exit Sensor (BES)  1069  exists on non-scale beds. The BES connects to the position sense module  1026  to detect a patient bed exit. 
     Brake-Not-Set Sensor (BNS)  1056  detects the state of the Brake/Steer Pedal. It is connected to the BACM  1018 . 
     Bed-Not-Down Sensor (BND)  1058  detects if the bed is fully down (both Head and Foot Hilo). It is connected to the BACM  1018 . 
     Side Rail Up Detect Sensors (SUD)  1071  consists of four switches to detect the secure UP position of the side rails. The SUD  1071  is connected to the position sense module  1026 . 
     Night Light  1073  is a stand alone unit providing the night light function. It is powered by low voltage AC coming from the Power Supply/Battery module  1062 . 
     Pendant  1048  provides for bed articulation control input through accessory port module  1016 . 
     Patient Assist Arm Control  1050  is a functional equivalent of the standard caregiver interface modules  1028  and  1030  controls in a different physical embodiment. The assist arm includes a control pad coupled to the accessory module  1016 . 
     The air supply module  1014 , the bed articulation control module  1018 , the power supply module  1062 , and the power entry module  1063  are all coupled to the base frame of the hospital bed. The communications module  1020 , the scale instrument  1022 , and the remote information interface  1124  are all coupled to the intermediate frame. The left standard caregiver interface  1028  and patient interfaces  1154  and  1156  are all coupled to the left siderail. The right standard caregiver interface  1030  and patient interfaces  1158  and  1160  are all coupled to the right siderail. Graphical caregiver interface module  1032  may either be coupled to the left siderail or the right siderail. The position sense module  1026  and surface module  1024  are each coupled to the weigh frame. It is understood that the position of each module can be changed. 
     FIG. 49 diagrammatically illustrates how the various modules are added and removed from the network. The electronic network uses an Echelon LonTalk serial communications protocol for module to module communication in the bed. The cable  1034  illustrated in FIG. 49 contains power and a twisted pair connection. The preferred protocol is RS-485 with a transmission speed of 78 kbs. The cable  1034  is provided with connectors  1036 . Extra connectors  1036  are provided for module additions. When the connectors  1036  are not coupled to a module, a coupler  1038  is provided to interconnect adjacent connectors  1036 . In order to connect a particular module  1040  to the network, the coupler  1038  is removed and connectors  1036  are coupled to mating connectors  1042  of the module  1040 . Connectors  1042  are electrically coupled within the module  1040  as illustrated by dotted line  1044 . 
     Referring again to FIG. 48, air supply module  1014  is coupled to an air handling unit  1046  by a discrete electrical connection. Air supply module  1014  controls compressor  1046  to inflate and deflate the mattress surface of the bed as discussed in detail below (or in main application). 
     The accessory port module  1016  provides connections to the network for a pendant  1048 , an assist arm control  1050 , or a diagnostic tool  1052 . Pendant  1048  is a hand held control unit which is movable from bed to bed. Therefore, pendant  1048  may be coupled and uncoupled from accessory port module  1016  to control various functions of the bed. For example, the accessory port module  1016  can communicate with BACM  1018  to control movement of the bed. Assist arm controls  1050  provide input to accessory port module  1016  from a control pad coupled to an assist arm extending out over the patient support surface of the bed. The assist arm  1050  can be used to control movement of the bed, as well as for other desired functions. The pendant  1048  and assist arm control  1050  may include all the controls of the right and left standard caregiver interface modules discussed below. 
     Diagnostic tool  1052  is used for servicing the bed, either at the bed site or from a remote location. A modem is coupled to accessory port module  1016  to provide a telephone line connection to the hospital bed. This permits information related to the bed from any module to be retrieved from the peer-to-peer network at a remote location. For instance, the amount of time that the surface of the bed is in use may be detected at the remote location through the modem for billing purposes. The diagnostic tool  1052  permits a remote operator to interrogate every module of the electrical control network. The diagnostic tool  1052  checks application dependent parameters, runs each of the modules through a test procedure, and fully accesses all network information. Diagnostic tool  1052  may be a hand held tool such as a lap top computer which is coupled directly to accessory port module  1016 . In addition, a remote computer can be coupled to accessory port  1016  with the modem link to provide a data link to the network. A Voice Mate™ control system available from Hill Rom, Inc. may also be coupled to accessory port module  1016  to control the bed. 
     The bed articulation control module (BACM)  1018  is the module that controls movement of the bed. BACM  1018  controls actuation of a plurality of solenoids  1054  which open and close valves coupled to hydraulic cylinders to move the articulating deck sections of the hospital bed relative to each other. BACM  1018  is also coupled to a Break Not Set sensor  1056  and a Bed Not Down sensor  1058 . When BACM  1018  receives an input signal from the network requesting movement of the bed to a predetermined position, the BACM  1018  first reads the position of the bed provided from position sense module  1026 . If movement of a portion of the bed is necessary, BACM  1018  checks for a lockout signal from the left and right standard caregiver interface modules  1028  and  1030 . If the lockouts are not set, BACM  1018  controls activation of the selected solenoid  1054  and then BACM  1018  turns on the hydraulic pump  1055  (gravity may also be used if appropriate) to actuate a selected cylinder if necessary. 
     Details of the BACM  1018  are illustrated in FIG.  50 . BACM  1018  includes a neuron controller  1060 . Illustratively, neuron controller  1060  is a MC143150FU echelon neuron networking microprocessor available from Motorola. Controller  1060  is coupled to the network through an RS-485 transceiver  1061 . BACM  1018  operates to move a plurality of solenoids  1054  in a hydraulic manifold to open and close control valves coupled to the hydraulic cylinders and articulate the bed based on various network commands received from the peer-to-peer network. Neuron controller  1060  receives commands from the right and left siderail standard caregiver interface modules  1028  and  1030 , the graphic caregiver interface  1032 , or from another input device to articulate the bed. Neuron controller  1060  also receives other information from the network regarding the position of the head, seat, thigh, and foot deck sections of the articulating deck of the bed. Therefore, neuron controller  1060  controls the solenoids and pump to stop articulating the bed as a limit is reached or when the particular bed section reaches its desired or selected position. 
     Both the articulating deck of the bed and the height of the deck are controlled by the BACM  1018 . Upon receiving a bed function command from the network, the BACM  1018  energizes the appropriate solenoids and provides a control signal to the Power Supply/Battery Module  1062  illustrated in FIG. 48 to power the hydraulic pump, if necessary. BACM  1018  may use bed position information provided by the remotely mounted bed position transducers. Alternatively, the position of the various sections of the articulating deck may be supplied to BACM  1018  by the position sense module  1026 . BACM  1018  also instructs air supply module  1014  and surface control module  1024  via the network to partially deflate a seat section and a foot section of the mattress when the bed moves to a chair position. BACM  1018  also receives lockout information from the siderail standard caregiver interface modules  1026  and  1028  to determine whether or not a particular section of the articulating deck should move. 
     Neuron controller  1060  executes code stored in EPROM  1064 . Illustratively, EPROM  1064  is a 27C256-70 EPROM available from AMD. In order to conserve power, BACM  1018  uses a pulse width modulation (PWM) control system to minimize the current draw required to actuate the solenoids  1054 . Conventional control systems simply turn the solenoid  1054  full on or full off and, as the voltage varies, current consumption goes up and down accordingly. With the PWM control design of the present invention, as the voltage varies BACM  1018  controls the power that is applied to the solenoid  1054  to maintain substantially the same current level to minimize power consumption. Neuron controller  1060  controls a timing generator  1066  through a memory map address decoder  1068 . Memory map address decoder  1068  provides a signal to timing generator  1066  on line  1070  to start PWM and provides a signal on line  1072  to timing generator  1066  to stop PWM. Neuron controller  1060  provides a 5 or 10 MHz clock signal to timing generator  1066  on line  1074 . 
     Timing generator  1066  provides six different time periods in which to actuate one of six pairs of solenoids  1054  used to control the valves of the hydraulic cylinders. Each time period is about 50 milliseconds. Only one solenoid  1054  can be pulled during any one time period. This minimizes the maximum current draw on the power supply or battery at any given time. It is understood that a different number of solenoid pairs may be controlled in accordance with the present invention. The number of time periods and the time period intervals may be changed, if desired. In the illustrated embodiment, six pairs of solenoids are controlled by the BACM  1018 . One solenoid of each pair is used to open a first valve to control movement of a deck section in a first direction, and the other solenoid of each pair is used to open a second valve to control movement of the particular section in an opposite direction. Therefore, a pair of solenoids is provided for the head section cylinder, the foot section cylinder, the foot Hi Lo cylinder, the head Hi Lo cylinder, the knee section cylinder, and the foot retracting section cylinder. 
     Timing generator  1066  supplies a PWM enable signal on line  1076  to a solenoid PWM select logic control circuit  1078 . Timing generator  1066  also provides time division terms to PWM control circuit  1078  on line  1080 . 
     Illustratively, there are twelve different solenoids  1054  powered by FET drivers  1090 . Neuron controller  1060  can provide three separate commands for each solenoid. The commands include an extend command, a retract command, and a pull-in command. The extend command is used to select the correct solenoid which when energized will extend the appropriate cylinder. Steady-state control of the FET which powers the solenoids is pulsed ON and OFF at the PWM rate. The retract command is used to select the opposing solenoid which when energized retracts the cylinder. It too is turned ON and OFF at the PWM rate. When a solenoid is initially activated or turned on, it is desirable to actuate the selected solenoid at “full on” for a predetermined time. Therefore, the pull-in command overrides the PWM control circuit. 
     Data including the control commands (pull-in, extend, or retract) for a selected solenoid  1054  transmitted from the neuron controller  1060  is written to buffer register  1084 . To synchronize the commands stored in the buffer register  1084  with the timing pulses from timing generator  1066 , the commands are shifted into a holding register  1088 . Therefore, asynchronous information is received in buffer register  1084 . This asynchronous information is synchronized into the holding register  1088  using a timing generator pulse on line  1094 . The timing signal  1094  synchronizes the pull-in latch  1082  in buffer register  1084  and the pull-in latch  1086  in the holding register  1088  with the timing generator  1066 . Timing signal  1094  also synchronizes the solenoid “extend” latches  1096  and  1098  and the solenoid  1054  “retract” latches  1100  and  1102  with the timing generator  1066 . 
     The PWM select logic control circuit  1078  receives commands from the holding register  1088  and provides signals to drive a discrete FET through FET drivers  1090  during each timing interval of the PWM timing generator  1066 . Driver  1090  pulls the selected solenoid  1054  down to ground and applies a voltage across the selected solenoid  1054  to control the solenoid. A voltage clamp  1104  is coupled to each of the solenoids  1054 . When power is removed from a particular FET an inductive signal is supplied to the solenoids  1054 . Voltage clamp  1104  clamps the inductive signal to the voltage rail. 
     Therefore, voltage clamp  1104  provides voltage spike suppression. 
     A diagnostic block  1106  also receives current signals related to each pair of solenoids  1054  from voltage clamp  1104  on line  1105 . Only one solenoid  1054  in each pair can be controlled or actuated at any given time. Diagnostic block  1106  also receives a data command signal from neuron controller  1060  on line  1108  indicating the particular solenoids  1054  which are designated by the controller  1060  for activation. Therefore, diagnostic block  1106  compares the actual information received from the solenoid  1054  pairs to the data received on lines  1108 . If the actual solenoid  1054  current does not match the desired solenoid  1054  activation data from controller  1060 , diagnostic block  1106  sends a signal to neuron controller  1060  on line  1110 . A signal on line  1110  actuates a signal on supervisory line  1112  coupled to a master FET  1114  to turn off the master FET  1114  and shut off power to all the solenoids  1054 . The master FET  1114  is coupled in line with all twelve solenoids  1054 . Therefore, supervisory FET must be turned on to provide power to any one of the solenoids  1054 . 
     A current sense resister  116  is coupled to the FET drivers  1090 . The current sense resister  116  is coupled to the first input terminal of a comparator  1118 . A second input terminal of comparator  1118  is coupled to a reference voltage. The output of comparator  1118  provides PWM feedback signal to timing generator  1066  on line  1120 . In order to provide PWM, the current must be measured in each solenoid  1054 . Therefore, the current sense resister  116  measures the current in each of the six time slots used for controlling the solenoids  1054 . Depending on the measured current, the signal on line  1120  adjusts the timing generator  1066  to control the pulse width of the driver signal. Therefore, if too much current is being drawn, then timing generator  1066  shortens the width of the driver pulse in order to bring the current down. 
     Referring again to FIG. 48, communications module  1020  provides an interface needed for bed-to-hospital or hospital-to-bed information transfer. Communications module  1020  is a gateway between the bed network and the hospital information/control network. Communications module  1020  is connected to a standard side-com interface  1122 . Interface  1122  also provides direct hard wired links between the nurse call switches on the side rails of the bed and the hospital priority nurse call network. signals from these nurse call switches can also be sent over the network. On beds without a scale, a switch input port is provided to accept a bed exit signal coming from a bed exit sensor. 
     Interface  1122  supports all existing discrete wire protocols. Interface  1124  will support newly defined serial protocols, both to hospital network and other hospital room equipment. Any other hospital room equipment can use the GCI module  1032  as its user interface control module. 
     Communications module  1020  also provides entertainment functions. Television, radio, or the like may be controlled by communications module  1020  based on input/output signals received/sent from the left or right siderail standard caregiver interface modules  1028  and  1030  over the network or via discrete connections. 
     Communications module  1020  is directly coupled to the hospital information electrical network to transmit and receive signals from a remote location. Communications module  1020  receives weight information from scale instrument module  1022 . Communications module also receives surface setting information, including pressures and other parameters from surface instrument module  1024 . Communications module  1020  also receives bed position information from position sensing module  1026 . In addition, communications module  1020  can receive all information travelling on the network. 
     The hospital network can drive a display on the graphic caregiver interface  1032  using signals transmitted from the remote location through a remote information interface  1124 , to communications module  1020 , and then to graphic caregiver interface  1032  over the network. Therefore, communications module  1020  provides an interactive data link between the remote location and the graphic caregiver interface module  1032 . Requests for weight acquisition can be automatically sent from a remote location through remote information interface  1124  and communications module  1020 . Communications module  1020  then communicates with scale instrument  1022  to determine the weight and then transmits the weight to the remote location via the remote information interface  1124 . 
     The scale instrument module  1022  receives input signals from load beams coupled to a weigh frame of the bed. Specifically, scale instrument module  1022  receives input signals from a left head load beam  1126 , a right head load beam  1128 , a right foot load beam  1130 , and a left foot load beam  1132 . The scale module  1022  transmits weight information and operation parameters to the GCI module  1032  and communications module  1020 . Load beams  1126 ,  1128 ,  1130 , and  1132  are bolted to the intermediate frame. The articulating deck and weigh frame module is then bolted to the load bearing ends of the load beams. Any item attached to or resting on the articulating deck and weigh frame will be weighed by the load beams. Scale instrument module  1022  receives information from the network via a nurse caregiver interface unit or a graphic caregiver interface module  1032 . The scale acquires data from the load beam transducers  1126 ,  1128 ,  1130 , and  1132  and automatically factors in the tare weight to calculate a patient weight. Scale module  1022  transmits an output signal to the network representing the patient weight. Scale module  1022  can detect bed exit and alert the hospital via the communications module  1020  and remote information interface  1124 . 
     Scale module  1022  also provides a weight change alarm. Scale module  1022  accepts a set point weight from the network. Scale module  1022  detects if a patient&#39;s weight change has exceeded or dropped below a preset level from the initial set point weight. If a preset weight change has occurred, scale module  1022  provides an alarm message to the network. Scale module  1022  stores all data critical to the functioning of the scale in non-volatile memory. Scale module  1022  has built in diagnostic capability to detect hardware integrity and data integrity. 
     Details of scale module  1022  are illustrated in FIG.  51 . The four load cells  1126 ,  1128 ,  1130 , and  1132  are coupled to a four channel analog to digital converter  134 . Illustratively, analog to digital converter is a CS5516,4 MHz analog to digital converter available from Crystal Semiconductor. Analog to digital converter  134  converts analog signals from the load cells  1126 ,  1128 ,  1130 , and  1132  into digital signals and inputs the signals into the echelon neuron controller  1136 . Neuron controller  1136  is a MC143150,10 MHz networking microprocessor available from Motorola. Controller  1136  executes code stored in an EPROM  1138 . Illustratively, EPROM  1138  is a 32K×8, model 27HC256 EPROM available from AMD. 
     Neuron controller  1136  stores calibration data related to each of the load cells  1126 ,  1128 ,  1130 , and  1132  either in its internal memory or in external EEPROM  1140 . Calibration data is necessary because each load beam  1126 ,  1128 ,  1130 , and  1132  has slightly different gain or offset constant associated with it. Calibration/excitation relay  1142  transmits the calibration data from neuron controller  1136  to analog to digital converter  1134 . Two connectors  1148  and  1150  are provided to couple scale module  1022  to the peer-to-peer communication network. Connector  1148  is hard wired to connector  1150 . An RS-485 transceiver  1149  is coupled between connectors  1148  and  1150  and controller  1136 . Transceiver  1149  takes logic inputs and outputs and converts them to RS-485 level signals for the network. For each of the modules on the peer-to-peer network, a connecter such as connector  1148  is hard wired to another connector such as connector  1150  that goes onto the next node or module in a daisy chain configuration. Scale module  1022  also includes a +5 VDC regulated power supply  1152 . 
     Referring again to FIG. 48, the surface instrument module  1024  is provided for controlling operation of the mattress or support surface. Details of this module are discussed below with reference to the surface design (or in main application). 
     The bed includes position transducers mounted throughout the bed to sense any needed positions of individual bed sections for articulation and caregiver interface purposes. The position sense module  1026  also interfaces a Side Rail Up Detect Sensor, and a Bed Exit Sensor. 
     Details of the position sense module  1026  are illustrated in FIG.  52 . Illustratively, the position transducers are discrete tilt sensors on various deck sections of the bed. The sensors include a trendelenburg limit sensor at 13° relative to earth, a reverse trendelenburg sensor at −13° relative to earth, and a bed-level at 0° relative to earth. In addition, the articulating deck sections include position transducers which are also discrete tilt sensors. Illustratively, the tilt sensors are model A½ sensors available from AEC. The patient head limit sensor detects the head section at 55° relative to earth. The head contour limit sensor detects the head section at 30° relative to earth. The knee contour limit detects the knee section at 12° relative to earth. The patient foot limit detects the position of the foot section at 30° relative to earth. 
     The sensor inputs are coupled to the position sense module  1026 . The sensor input signals are signed conditioned using a RC filter  1154 . The output of RC filter  1154  is coupled to a neuron controller networking microprocessor  1156 . An output from controller  1156  drives a local alarm  1158 . Input power on line  1160  is coupled to a regulated power supply  1162  which produces a +5V output. The output from power supply  1162  is coupled to neuron controller  1156  and to a network transceiver  1164 . The position transducers illustratively switch from a logic high to a logic low upon detection of the particular angle relative to earth. 
     Controller  1156  transmits and receives network information through transceiver  1164 . Network transceiver  1164  is coupled to a first network connector  1165  via lines  1166 . Position sense module  1126  also provides the connection points to the network for the left and right standard caregiver interface modules  1028  and  1030 . Network connector  1165  also coupled to a left siderail network connector  1170  which is coupled to the left siderail standard caregiver interface module  1128 . Left siderail connector  1170  is coupled to a right siderail connector  1172  by lines  1171 . Connector  1172  is coupled to a right siderail standard caregiver interface module  1030 . Connector  1172  is also coupled to a second network connector  1173  by lines  1175 . Therefore, position sense module  1026  is also a junction module for connection to the left and right side rail standard care giver interface modules  1028  and  1030 . 
     During operation, neuron controller  1156  interprets the sensor signals received from RC filter  1154  and sends an output signal indicative of the state of each sensor to the network through network transceiver  1164 . Network transceiver  1164  is a RS-485 protocol transceiver. Alarm  1158  contains a piezo device so that any alarms on the bed that are transmitted through the network turn on the piezo alarm on the position sense module  1026 . These alarms may include bed exit, patient weight gain, weight loss, surface pressure loss, or other desired alarms. Alarm  1158  can also be used to alert an operator when catastrophic failures are detected in the bed by the diagnostic tools. 
     The left and right standard caregiver interface modules  1028  and  1030  are substantially identical. The left standard caregiver interface module  1028  is coupled to patient controls including an articulation and entertainment interface in the left siderail as illustrated at block  1154  of FIG.  48 . Standard caregiver interface module  1028  is also coupled to a surface patient interface on the left side rail as illustrated at block  1156 . The standard caregiver interface module  1030  for the right side is coupled to articulation and entertainment patient interface module on the right siderail as illustrated at block  1158 . The right standard caregiver interface module  1030  is also coupled to a surface patient interface caregiver interface on the right side rail as illustrated at block  1160 . 
     Details of the left standard caregiver interface module  1028  is illustrated in FIG.  53 . The standard caregiver interface module includes an echelon controller  1162  which is a networking microprocessor. Echelon controller  1162  is coupled to a +5.0V supply voltage from power supply  1164 . Echelon controller  1162  is also coupled to a network transceiver  1166 . Transceiver  1166  is an RS-485 protocol transceiver. Transceiver  1166  couples controller  1162  to the peer-to-peer communication network as illustrated at line  1168 . A network connection for the graphic caregiver interface module  1032  is provided at line  1170  for both the left and right standard caregiver interface modules  1128  and  1030 . Graphic caregiver interface module  1032  can be connected on either the left or right side of the bed. Echelon controller  1162  interprets the network messages. Network controller  1162  also detects switch activation from the articulation and entertainment patient interface  1154  and the surface patient interface  1156  and transmits output signals to the network on line  1168 . The switches can be dead function switches, lockout switches, bed exit switches, nurse call backlit switches, and so on. Controller  1162  drives a LED driver  1172  to light indicator LEDS  1174  related to various bed status functions, such as bed-not-down, brake-not-set, battery low, and service required. 
     The LED driver  1172  is also coupled to a backlighting switch  1176  of the articulation and entertainment patient interface  1154 . Backlighting switch  1176  is coupled to backlighting LEDs  1178 . Backlighting switch  1176  is also coupled to backlighting LEDs  1180  on the surface patient interface  1156 . 
     The standard caregiver modules  1028  and  1030  connect all the caregiver interfaces switches in a row/column type architecture to provide a 4×10 matrix. A keyboard row selection logic circuit is used to detect switch presses as illustrated at block  1182 . 
     The standard caregiver interface (SCI) modules  1028  and  1030  include the network circuitry for interfacing all caregiver and patient siderail caregiver interfaces to the communication network. The patient caregiver interfaces are separated into modules which can be connected to the SCI module  1028  or  1030  in a modular fashion. 
     Each SCI module  1028  and  1030  includes bed articulation switches  1184 . These include head up, head down, knee up, knee down, foot up, foot down, bed up, bed down, chair in, chair out, trendelenburg, and reverse trendelenburg. In the case of a switch closure, a signal is periodically output to the network until the opening of the switch occurs. The SCI modules  1028  and  1030  further include lockout switches  1186  as discussed below, bed exit switches  1188 , nurse call switches  1190 , and backlighting switches  1192 . Control buttons for the switches  1184 ,  1186 ,  1188 ,  1190 , and  1192  are typically on an outside portion of the siderail for use by a nurse. 
     The articulation and entertainment patient interface  1154  also includes a nurse call switch  1194 , interactive TV switches and a light switch  1196 , and bed articulation switches  1198 . Surface patient interface  1156  includes nurse call LEDs  1200 , mattress switches  1202 , and a nurse call switch  1204 . 
     As discussed above, the lockout control switches are located on the left and right siderail control interfaces. As illustrated in FIG. 54, the lockout control includes a global enable lockout activation switch  1205  which must be pressed in order to activate any of the other lockout toggle switches for the foot control lockout  1207 , the knee control lockout  1209 , the head control lockout  1211 , or the lockout for all controls at  1213 . This double lockout activation reduces the likelihood of the accidental deactivation of one of the lockout control switches. Therefore, the global enable switch  1205  must be pressed in order to turn any of the other lockout controls on or off. The global enable switch  1205  automatically deactivates after about 5 seconds of inactivity. After the global enable is deactivated, the lockout status cannot be changed. Since the caregiver controls are within reach of a patient, the global enable switch may be used to enable and disable both the patient and caregiver bed articulation control switches. 
     A graphic caregiver interface (GCI) module  1032  is illustrated in detail in FIG.  55 . The GCI module  1032  provides an enhanced menu-driven caregiver input and output for bed articulation, scale, surface caregiver interface, and sequential compression device controller, and all other modules needing this type of user interface. The GCI module  1032  includes a LCD display  1206 , which is illustratively a 320×240, model DMF 50081 available from Optrex. Display  1206  may also be a 320×240,model G321EX available from Seiko. Display  1206  outputs graphical information to the caregiver. A switch panel  1208  permits the caregiver to input information into the GCI module  1032 . Switch panel  1208  may be a series of discrete switches or an alpha/numeric keypad. Switch panel  1208  is coupled to a connector  1210 . Connector  1210  is coupled to an input of CPU  1212 . CPU  1212  is illustratively an 80C188XL, 10 MHz CPU available from Intel. The input device for the caregiver may also be an encoder  1214  which is coupled to a connector  1216 . Connector  1216  is coupled to CPU  1212 . Illustratively, encoder  1214  is a rotary encoder. 
     Connection to the peer-to-peer communication network is provided at terminal  1218 . The network connection is made to a RS-485 transceiver  1220 . Transceiver  1220  is coupled to a +5 VDC regulated power supply  1222 . Transceiver  1220  is also coupled to a +12 VDC regulated power supply  1224 . Transceiver  1220  is coupled to an echelon neuron controller networking microprocessor  1226 . Controller  1226  is illustratively an AMC143120, 10 MHz networking microprocessor available from Motorola. Neuron controller  1226  is coupled to an I/O test port  1228 . Controller  1226  is also coupled to CPU  1212 . Software code for operating CPU  1212  is stored in an EPROM memory  1230 . Illustratively, memory  1230  is a 512 K×8 flash EPROM memory. Data is stored in static RAM memory  1232 . Illustratively, memory  1232  is a 128 K×8 memory chip. Additional memory is provided in a 2 K×8 EEPROM  1234 . An output from CPU  1212  is coupled to a LCD backlight inverter  1236 . Backlight inverter  1236  is coupled to LCD display  1206  by connector  1238 . Backlight inverter facilitates viewing of display  1206  in all types of room lighting. Inverter  1236  is configured to match the particular display  1206  selected. 
     CPU  1212  is also coupled to a LCD controller  1240 . LCD controller  1240  drives the display  1206  through a connector  1242 . Controller  1240  is coupled to a 32 K×8 static video RAM  1244 . As the CPU  1212  writes an image to LDC controller  1240 , the controller  1240  stores the image in VRAM  1244  and then continuously refreshes the display screen  1206  with the image stored in the VRAM  1244 . 
     Contrast of the display  1206  is controlled by software contrast adjustment as illustrated at block  1246 . A LCD bias supply voltage at block  1248  is coupled to connector  1242 . Supply  1248  converts a +5V input or a +12V input into a −22V output. An external watchdog timer  1250  monitors CPU  1212 . If the CPU  1212  does not pulse the particular line on a periodic basis, timer  1250  resets the system. 
     GCI module  1032  also includes a diagnostic port  1252 . Diagnostic port  1252  is coupled to CPU  1212  through a serial port  1254 . Serial port  1254  is a RS-232 UART. Therefore, a laptop may be connected at port  1252  to interrogate the CPU  1212 . CPU  1212  can access and send information to the network through controller  1226 . 
     The GCI module  1032  provides an enhanced menudriven caregiver input and output control for bed articulation, scale, surfaces, sequential compression devices, and all other modules needing this user interface capability. The GCI module  1032  is intended to be a drop in replacement for Scale/Surface Nurse Control Unit. GCI module  1032  interacts with scale module  1022 . Specifically, GCI module  1032  can transmit a request for patient weight to the scale module  1022 . In addition, the GCI module  1032  can also zero the scale and perform other scale module functions. 
     GCI module  1032  stores predetermined graphics data and caregiver interface data in memory  1230 . This predetermined graphics data is stored in the GCI module  1032  at the time of production. Additionally, other modules on the peer-to-peer communication network can download screen formats to the GCI module into static RAM  1232 . The GCI module then retrieves the stored graphic screen formats either from memory  1230  or static RAM  1232  and displays the output on display  1206 . By providing stored built-in graphics in memory  1230 , the GCI module  1032  can support products or other modules that may later be connected to the peer-to-peer communication network. By providing the stored predetermined graphic formats, the GCI module  1032  does not have to be updated each time a new module is added to the system. If the desired graphics format is not present in memory  1230 , then the newly added module must download the desired graphic formats into RAM  1232  at run time. 
     The specific graphic formats stored in the GCI module  1032  can include charting formats such as bar graphs, X-Y graphs, pie charts, etc., icons or pictures representing each of the modules in the communication network, or any other type of graphical format desired. Graphic formats for use by the modules are stored in two different ways in the GCI module  1032 . Typically, these various graphic formats are stored in EPROM  1230  at the time of manufacture. In other words, these graphical formats are typically designed into the GCI module  1032 . If a particular GCI module  1032  does not include the desired graphic format stored in memory  1230 , then the particular graphic format for the new module added to the system is downloaded into the static RAM  1232  of GCI module  1032  after the bed is powered up. For instance, if GCI module  1032  does not include a X-Y graphic format in memory  1230 , this graphic format can be downloaded into RAM  1232  after the bed is powered up. Once a particular graphic format is stored in GCI module  1032 , in either memory  1230  or RAM  1232 , the new module transmits only data to the GCI module  1032  during operation. The GCI module  1032  uses the received data and the stored graphic format to produce an appropriate screen output on display  1206 . For instance, after the X-Y graphic format is stored in either memory  1230  or RAM  1232 , the particular module transmits only the X-Y data to the GCI module  1032  over the network. The GCI module  1032  then uses this data along with the stored X-Y graphic format to provide an output to display  1206 . Each new module will also download a particular icon representative of the new module for the menu-driven display  1206  of GCI module  1032  as discussed below. 
     Updating of the graphic formats and menu information of the GCI module  1032  can be accomplished in one of three ways. The particular graphic format and menu information can be downloaded into static RAM  1232  at power up of the bed. The graphic format and menu information can also be downloaded to EEPROM  1234  during installation of a new module. Finally, EPROM  1232  can be changed to include the new graphic format and menu information at the time the new module is installed. 
     Details of the operation of GCI module  1032  for automatically recognizing and controlling newly added modules on the communication network are illustrated in FIGS. 56 and 57. Bed power up is illustrated at block  1260 . A graphics status flag and a menu saved status flag are both cleared at block  1262 . These flags provide an indication of whether a particular graphic format or menu information for the module must be downloaded to the GCI module  1032 . For each module on the network, menu screens will be provided on display  1206 . Therefore, if a particular module is selected using the GCI module  1032 , control options for that module will appear as menu items on display  1206 . Once a particular control option is selected, additional menu items for the selected control option may appear, and so on. 
     GCI module  1032  performs a system query at block  1264 . GCI module  1032  first determines whether any modules are present on the communication network which use the GCI module  1032  as illustrated at block  1266 . If no modules are present on the network which use the GCI module  1032 , the GCI module  1032  returns to block  1264 . The system query is carried out at predetermined time intervals. 
     If modules are present which use the GCI module  1032  at block  1266 , the GCI module  1032  determines whether any of the modules need to download graphic formats to the GCI module  1032  as indicated at block  1268 . If no modules need to download graphic information, GCI module  1032  advances to block  1274 . If any of the modules need to download graphic formats, the graphic formats are downloaded to static RAM  1232  of GCI module  1032  as illustrated at block  1270 . The graphics status flag for the module is then updated as illustrated at block  1272 . The graphics status flag is initially generated at block  1266  during detection of any modules which use the GCI module. Therefore, after step  1270  the status flag  1272  indicates that all the graphic format data for the particular module is now stored on the GCI module  1032 . 
     GCI module  1032  next determines whether any of the modules need to download menu structure information to the GCI module. If not, GCI module  1032  advances to block  1280  in FIG.  57 . If any of the modules need to download menu structure information, the appropriate menu structure information is downloaded to the static RAM  1232  of GCI module  1032 . This menu structure information provides the appropriate menu-driven control for each module. For instance, once the module icon is selected using the switch panel  1208  or encoder  1214  of the GCI module  1032 , the GCI module  1032  automatically displays a menu screen of options on display  1206  associated with the particular module. Once a particular option is selected, another menu screen may be provided to display  1206  giving further options. Button sizes and text fonts are included in the graphics format data stored in the GCI module  1032 . The menu structure information provides the actual textural material to be included with the menu-screen buttons. 
     The GCI module  1032  next updates a menu saved status flag at block  1278 . This status flag provides an indication that all the menu structure information for the particular module has been downloaded. GCI module  1032  then proceeds to block  1280  of FIG.  57 . 
     GCI module determines whether this particular loop is the first time through after power up or if a new module has been added as illustrated at block  1280 . If not, GCI module  1032  proceeds to block  1286 . If it is the first time through or a new module has been added, GCI module  1032  reconfigures an opening menu to include icons of all the modules present as illustrated at block  1282 . In other words, the main menu initial display screen of display  1206  is updated to include an icon representing each of the controllable modules. GCI module  1032  then reconfigures existing menus to include the new options of added modules as illustrated at block  1284 . The code stored in the GCI module  1032  is altered, in real time, to merge new menu information for the newly added modules with existing menu information of the previous modules. 
     GCI module  1032  then performs an integrity check on RAM  1232  based saved information as illustrated at block  1286  (i.e. checksum). If the integrity of the stored information in RAM  1232  is not correct at block  1288 , GCI module  1032  changes an appropriate saved status flag at block  1290 . GCI module  1032  then proceeds back to block  1268  to download the appropriate graphical format information or menu structure information for the particular module again. 
     If the integrity of the information saved in RAM  1232  is correct at block  1288 , GCI module  1032  determines whether an input switch from switch panel  1208  or encoder  1214  has been pressed at block  1292 . If no input has been pressed, GCI module returns to block  1264  of FIG. 56 to perform another system query at the next predetermined time interval. 
     If an input switch has been pressed at block  1292 , GCI module  1032  updates the display screen  1206  as illustrated at block  1294 . The GCI module  1032  then transmits an appropriate network command to the particular module to perform any selected application or specific function as illustrated at block  1296 . For instance, GCI module  1032  can transmit a signal to scale module  1022  to weigh a patient, to surface instrument module  1024  and air supply module  1014  to adjust the pressure within a particular bladder of the bed surface, or to perform any other module function. 
     It is understood that the hospital network can use the GCI module  1032  in an identical way to the other network modules. The hospital network can send menu driven control options to the GCI if desired. Either the patient or the caregiver can use the GCI module  1032  to control bed functions and interact with the hospital network or another remote location. 
     The automated data collection feature of communications module  1020  is illustrated in further detail in FIG. 58. A request for bed information and/or bed control is received as illustrated at block  1300 . The request is either from the hospital information network or from a remote data acquisition system. In other words, the hospital bed may be connected to the hospital network through wiring in a wall as discussed above. In addition, the bed may be connected to another piece of equipment in the room which can be connected to a remote location through the hospital network, a modem, or other data link. Finally, the request for information and/or control can be from an on-board bed data acquisition system. 
     The particular command or status request is then mapped to a network variable or value as illustrated at block  1302 . In other words, the received request or command is changed to a usable network format at block  1302 . Illustratively, a table is used to transform the received request for information and/or control to an appropriate and understandable network command. 
     A message is then issued to the bed modules over the communication network as illustrated at block  1304 . Communications module  1020  determines whether the particular module responded over the network with an acknowledgement of the message at block  1306 . Once a particular module receives a message, an acknowledgement of the message is transmitted back over the network before the particular function is carried out by the module. If the acknowledgement is not received, the communication module  1020  sets an error status indicator as illustrated at block  1308 . If the acknowledgement is received at block  1306 , communications module  1020  next determines whether the module responds over the network with a particular status that was requested or with an acknowledgement that a particular control has been implemented as illustrated at block  1310 . If not, communications module  1020  sets the error status indicator as illustrated at block  1308 . If the module did respond over the network with the particular status requested or with the acknowledgement that the control was implemented, the network response is mapped to the off bed network as illustrated at block  1310 . The communications module  1020  transforms the response received from the bed network format to the off-bed network format for transmission at block  1312 . The communications module  1020  then sends the off-bed network command or an error message to the remote network as illustrated at block  1314 . An error message sent to the hospital network or other remote location provides an indication that something went wrong with the particular request for status information or control. This request can then be retransmitted. A persistent error message indicates problems with one of the modules. Therefore, corrective action to repair the module can be implemented. 
     Each of the modules on the hospital bed can store specific status information related to operation and control of the bed or related to the module functions in an internal memory present on each module. For instance, the BACM  1018  can store all bed articulations and positions in a memory of the BACM  1018 . In addition, the surface instrument module  1024  can store all surface positions and settings or therapy module usages in memory on the surface instrument module  1024 . This information can be retrieved using the automated data collection feature discussed above to indicate patient activity. The standard caregiver interface modules  1028  and  1030  can store all entertainment patient control interactions in memory. These interactions can be retrieved via the automated data collection feature for billing or other monitoring purposes. Each module has a capability of storing all patient interaction with controls on the module. This stored information is available to the GCI module  1032  and to the off bed information system via the automated data collection feature. 
     As discussed above, the hospital network can retrieve status information through the communications module  1020 . In addition, status information can be retrieved from a remote location through a data link coupled to accessory port module  1016 . This status information may be bed status information stored in any of the modules. Each module can store status information related to switch presses, and specific movements, controls, or functions performed by the module. 
     Another module which can be coupled to the peer-to-peer communication network is a patient status module  1320 . This patient status module  1320  is illustrated in FIG.  59 . The patient status module  1320  monitors and records vital statistics from the patient received from a selected patient monitoring device  1322 . Such body monitors may include, for example, temperature sensors, blood pressure detectors, heart rate monitors, or any other body monitor. Data from these monitors  1322  is stored in memory of the patient status module  1320  and can be transmitted over the network to the hospital network or to a remote location through a data link coupled to accessory port  1016 . Patient monitoring devices  1322  are discretely coupled to the patient status module  1320 . 
     Another module coupled to the bed peer-to-peer communication network is a gateway module  1324 . The gateway module  1324  provides an interface to the network for an application specific module  1326 . Specifically, gateway module  1324  provides echelon network interface circuitry for communicating with the peer-to-peer network of the hospital bed. Gateway module  1324  also includes application specific interface circuitry for communicating with the application specific module  1326  for performing a dedicated function on the bed or elsewhere. Therefore, gateway module  1324  provides a format change for the data so that understandable information and commands are transmitted and received by both the bed network and the application specific module  1326 . 
     Another feature of the present invention is that each of the bed modules can be upgraded over the network using a data link through accessory port  1016  or using communications module  1020 . Upgrade information can be transmitted from the remote location to the peer-to-peer network. In other words, a remote location can be used to download new software to all the modules connected to the communication network of the bed. This permits an operator to reprogram the bed modules from a remote location over the peer-to-peer communication network. 
     Yet another feature of the present invention is that each module is able to perform internal diagnostics. After a module performs its dedicated function, a diagnostic check can be performed to make sure that the module is functioning correctly. If an error is detected, an error message can be transmitted over the network to another module or to a remote location through communications module  1020  or accessory port  1016 . 
     Another module of the present invention is illustrated in FIG.  60 . FIG. 60 illustrates an automatic charting module  1330 . The automatic charting module  1330  includes an echelon controller  1332  which is a networking microprocessor. Controller  1332  accesses memory  1334 . Memory  1334  includes an EEPROM, and EPROM, and a static RAM. Controller  1332  is coupled to a RS-485 transceiver  1336 . Transceiver  1336  is coupled to first and second network connectors  1338  and  1340 . Module  1330  includes an internal power supply  1342  coupled to a power input. Illustratively, power supply  1342  supplies a +5 V supply voltage to controller  1332  on line  1344 . Power supply  1342  also supplies power to a bar code interface  1346 , a display interface  1348 , and a keyboard interface  1350 . Display interface  1348  and keyboard interface  1350  are optional elements of charting module  1330 . 
     Bar code interface  1346  receives an input from bar code scanner  1352 . An output of bar code interface  1346  is coupled to controller  1332  on line  1354 . Controller supplies information to display interface  1348  on line  1356 . An output from display interface  1348  is coupled to a suitable display  1358 . Keyboard interface  1350  receives an input from a keyboard  1360 . An output of keyboard interface  1350  is coupled to controller  1332  by line  1362 . 
     Charting module  1330  provides an apparatus for automatically charting patient information. Bar code scanner  1352  and keyboard  1360  provide input devices for inputting information into charting module  1330 . It is understood that any type of input device can be used in connection with the present invention. The patient or caregiver can input information to the network using the bar code scanner  1352  or keyboard  1360 . This information can remain locally on the peer-to-peer communication network of the hospital bed. In addition, the information can be sent to the hospital network through transceiver  1336  and communication module  1020  or to another remote location via accessory module  1016 . 
     An output device such as display  1358  is provided to display information to the user. The display  1359  can be a series of LEDS or a display panel, such as a LCD display. 
     The memory of  1334  of charting module  1330  is loaded in a manner similar to the GCI module  1032  discussed above. Memory  1334  contains code that translates raw bar code scanner information and keyboard input information from keyboard  1360  into specific network commands, either for local on-bed use or for hospital network off-bed use. For instance, the nurse can scan bar codes directly from prescription medicine or input various information into keyboard  1360  related to the patient. This input is used to generate an internal chart of the medical history of the patient for use on the hospital bed. This chart data can be displayed on display  1358 . In addition, this chart can be transmitted over the hospital network or transmitted to a remote location using a data link coupled to accessory port  1016 . 
     It is understood that the GCI module  1032  discussed above may be modified to include an input interface such as bar code interface  1346 . The functionality of charting module  1330  is similar to the GCI module  1032  except for the scanning device  1352  and the bar code interface  1346 . 
     Another use of charting module  1330  is for inputting a control sequence used to control a module to perform a dedicated function on the bed. For instance, a doctor can prescribe a certain surface therapy for pulmonary or other type of treatment of the patient on the bed. This treatment prescription can specify a period of time for percussion and vibration therapy or for rotational therapy of the patient on the bed. The prescription can include a specific period of time for the therapy with varying rates of rotation or a varying frequency of percussion and vibration. This specific control sequence or prescription is encoded onto a bar code or other appropriate input scanning device format and scanned or otherwise input into charting module  1330 . Charting module  1330  then automatically executes the prescribed control sequence by transmitting appropriate commands at appropriate times through transceiver  1336  to the network and to the selected modules to control the selected modules in the prescribed control sequence. 
     As discussed above, each of the network modules includes a echelon neuron networking microprocessor or controller. Each of the networking controllers has a unique serial number which is different from the serial number on any other controller. At manufacturing time, a data base is created to associate each unique serial number with the module type and manufacturing date. Any other desired information related to the particular module may also be stored in the data base. Therefore, the hospital bed of the present invention provides an inventory control feature both in the plant prior to shipment of the beds and in the field at remote customer locations. A diagnostic tool coupled to accessory port module  1016  through a data link or the hospital network coupled to communications module  1020  can instantly query a bed over the peer-to-peer communication network to retrieve the unique serial number associated with all the modules on the network of the bed. Therefore, an operator has access to an instantaneous inventory of all the modules and associated features of a particular bed from a remote location for maintenance, repairs, recalls, upgrades, etc. An operator at a remote location can quickly determine the exact modules on the bed at any time. 
     The apparatus of the present invention can automatically poll beds at a remote location over the network by providing a query to all modules and retrieving all the serial numbers over the network. Therefore, by using the stored data base, an operator can determine an inventory of all bed modules present in a hospital or other remote location. 
     Details of the modular therapy and support surface apparatus of the present invention are illustrated in FIG.  61 . The support surface of the present invention is configured to be positioned over a bed deck  1596  of a hospital bed. The support surface includes a surface foundation  1500  located on the bed deck. An inflatable and deflatable surface foot section  1502  is located adjacent surface foundation  1500 . For certain applications, an upper foam support surface  1504  is located on foundation  1500 . Upper foam support  1504  is typically used for short hospital stays. An upper air bladder  1506  can also be positioned over surface foundation  1500 . A rotation bladder  1508  is located between the surface foundation and the bed deck. An optional percussion bladder  1510  may be inserted in place of a section of upper air bladder  1506 . A sequential compression device  1512  for venous compression therapy of a patient is also provided. 
     A plurality of separate treatment and surface control modules are provided for interconnecting the various treatment devices and support surface bladders to the communication network of the bed and to on-board air handling unit  1046 . Specifically, the present invention includes a foot section control module  1014 , a decubitus prevention control module  1516 , and a decubitus treatment control module  1518 . The modular therapy apparatus further includes a pulmonary rotation control module  1520 , a sequential compression device air control module  1522 , and a pulmonary percussion and vibration control module  1524 . An auxiliary air port control module  1526  is also provided. The air port control module  1526  provides for auxiliary air output for manual filling of auxiliary bladder systems for positioning, safety barriers, clinical treatments such as burn contractures, and other purposes. 
     Each of the modules is designed to physically and functionally connect the various bladders and treatment devices to both the communication network of the hospital bed through the surface instrument module  1024  and to the air handling unit  1046  which is controlled by air supply module  1014 . Air supply module  1014  is coupled to the peer-to-peer communication network. Air supply electronics  1528  are connected to air supply module  1014  for controlling air handling unit  1046  and switching valve  1530  based on network commands for controlling the various surface and treatment modules illustrated in FIG.  61 . 
     Air handling unit  1046  is configured to supply air under pressure to switching valve  1530  on line  1532 . Air handling unit  1046  also applies a vacuum to switching valve  1530  through line  1534 . An output of switching valve  1530  is coupled to a connector block  1536 . Connector block  1536  provides an air and vacuum supply line to each of the surface control and treatment control modules as illustrated in block  1538  of FIG.  61 . It is understood that dual control lines for both air and vacuum can be supplied to each of the surface control and treatment control modules of FIG.  61 . This dual control allows each module to apply pressure and vacuum simultaneously to different zones of a bladder or treatment device. 
     The surface instrument module  1024  which is also coupled to the peer-to-peer communication network is electrically coupled to each of the surface control modules and treatment control modules as illustrated in block  1540  of FIG.  61 . This network connection permits all the modules to receive input commands from other network modules and to output information to the network. 
     Details of a therapy or support surface control module  1542  are illustrated in FIG.  62 . It is understood that the details of foot section module  1514 , prevention module  1516 , treatment module  1518 , pulmonary rotation module  1520 , SCD air module  1522 , pulmonary percussion/vibration module  1524 , and air port module  1526  include the same or similar structural components as module  1542  illustrated in FIG.  62 . The FIG. 62 embodiment illustrates the air handling unit  1046  coupled directly to connector block  1536  by both an air pressure supply line  1544  and a vacuum supply line  1546 . As discussed above, lines  1549  and  1546  from air handling unit may be coupled to a switching valve  1530  and only a single pressure/vacuum tube may be coupled to connector block  1536  as illustrated in FIG.  61 . 
     The connector block  1536  is coupled to module connector  1548  located on the hospital bed. Specifically, connector block  1536  is coupled to module connector  1548  by a pressure supply line  1550  and a vacuum supply line  1552 . It is understood that a single supply line for both pressure and vacuum could also be used. 
     Module connector  1548  is also coupled to one of the surface or therapy devices as illustrated by a block  1554  by a pressure supply line  1556 , a vacuum supply line  1558 , and a sensor supply line  1560 . Depending upon the particular surface or therapy device, more than one pressure, vacuum, and sensor lines may be connected between the connector block  1548  and the surface or therapy device  1554 . Typically, each separate air zone of the surface or therapy device will have its own pressure, vacuum, and sensor lines. For illustration purposes, however, only a single set of supply lines will be discussed. 
     The bed also includes an electrical connector  1562  coupled to surface instrument module  1024  of the peer-to-peer communication network of the bed by suitable cable  1564 . The therapy or surface control module  1542  illustrated in FIG. 62 is designed to facilitate coupling of the control module  1542  to the bed. Each of the surface and treatment options illustrated in FIG. 61 is provided in the bed with a pneumatic connector such as connector  1548  and an electrical connector such as connector  1562  provided for each of the surface and therapy devices. The module  1542  is easily installed by coupling connector  1548  on the bed to a mating connector  1566  of module  1542 . In addition, a mating electrical connector  1568  is provided on module  1542  for coupling to electrical connector  1562  on the hospital bed. The configuration of module  1542  permits a simple “slide in” connection to be used to install the module  1542  and activate the surface of therapy device  1554 . 
     An air pressure input from pneumatic connector  1566  is coupled to an electrically controlled valve  1570  by a supply line  1572 . An output of valve  1570  is coupled to a pressure output port  1571  by line  1574 . Port  1571  is coupled to the surface or therapy device  1554  by pressure supply line  1556 . 
     The vacuum supply line  1552  from connector block  1536  is coupled to an electrically controlled valve  1576  by line  1578  of control module  1542 . An output of valve  1576  is coupled to a vacuum port  1577  of connector  1566  by line  1580 . Vacuum port  1577  is coupled to the surface or therapy device  1554  by the vacuum supply line  1558 . The electrically controlled valves  1570  and  1576  are controlled by output signals on lines  1582  and  1584 , respectively, from a control circuit  1586  of module  1542 . Control circuit includes a microprocessor or other controller for selectively opening and closing valves  1570  and  1576  to control surface or treatment device  1554 . 
     It is understood that several valves may be used for each surface or treatment device. For instance, the upper air bladder  1506  may have a plurality of different air zones which are independently controlled. In this instance, separate pressure and vacuum and sensor lines are coupled to each zone of the air bladder. A electrically controlled valve is provided for each pressure and sensor line in each zone to provide independent controls for each zone. 
     Module  1542  also includes a pressure sensor  1588 . Pressure sensor  1588  is coupled to sensor supply line  1560  by line  1590 . Pressure sensor  1588  generates an output signal indicative of the pressure in the particular zone of the surface or therapy device  1554 . This output signal from pressure sensor  1588  is coupled to the control circuit  1586  by line  1592 . 
     Control circuit  1586  is also coupled to an electrical connector  1568  by a suitable connection  1594  to couple the control circuit  1586  of module  1542  to the surface instrument module  1024 . Therefore, control circuit  1586  can receive instructions from the other modules coupled to the peer-to-peer communications network illustrated in FIG.  48 . Control circuit  1586  can also output information related to the particular surface or therapy device  1554  to the network. Specifically, the graphical interactive display  1664  or the graphic caregiver interface module  1032  is coupled to the electrical communication network for transmitting command signals for the plurality of air therapy devices over the electrical communication network to control operation of the plurality of air therapy devices. The graphical interactive display includes a display and a user input. Each control module transmits display commands to the display related to the corresponding air therapy device. The display commands from the control modules provide a menu driven list of options to the display to permit selection of control options for the plurality of air therapy devices from the user input. 
     Details of the structural features of the modular therapy and support surface are illustrated in FIGS. 63-72. FIG. 63 illustrates a deck portion  1596  of a hospital bed. Illustratively, deck portion  1596  is a step deck having a cross-sectional shape best illustrated in FIGS. 69-71. Illustratively, deck  1596  includes a head section  1598 , a seat section  1600 , and a thigh section  1602 . Sections  1598 ,  1600 , and  1602  are all articulatable relative to each other. 
     The modular therapy and support surface system of the present invention includes surface foundation  1500  including a foundation base  1606  and side bolsters  1608  and  1610 . Preferably, side bolsters  1608  and  1610  are coupled to opposite sides of foundation base  1606 . Foundation base  1606  includes foldable sections  1612  and  1614  to permit the foundation  1500  to move when the step deck  1596  articulates. 
     The hospital bed also includes an expanding and retracting foot section  410  to facilitate movement of the hospital bed to the chair position. Surface foot section  1502  is located over the retracting mechanical foot portion  410 . Surface foot section  1502  is described in detail below with reference to FIGS. 64-67. 
     The FIG. 63 embodiment includes an upper foam surface insert  1504  configured to the positioned on the foam foundation base  1606  between side bolsters  1608  and  1610 . Foam surface  1504  provides a suitable support surface for a patient who is mobile and whose length of stay is expected to be less than about two days. 
     The surface foot section  1502  is particularly designed for use with the chair bed of the present invention. The foot section  1502  includes a first set of air bladders  1618  and a second set of air bladders  1620  alternately positioned with air bladders  1618 . Air bladders  1618  and  1620  are configured to collapse to a near zero dimension when air is withdrawn from the bladders  1618  and  1620 . The first set of bladders  1618  are oriented to collapse in a first direction which is generally parallel to the foot section  410  of the bed deck as illustrated by double headed arrow  1622 . The second set of bladders  1620  are configured to collapse in a second direction generally perpendicular to the foot deck section  410  as illustrated by double headed arrow  1624 . This orientation of bladders  1618  and  1620  in foot section  1502  causes the foot section  1502  to retract or shorten and to collapses or thin as the bladders  1618  and  1620  are deflated by the foot section control module  1514  as the hospital bed moves from a bed orientation to a chair orientation. In the chair orientation, the foot deck section  410  and surface foot section  1502  move from a generally horizontal position to a generally vertical, downwardly extending position. Preferably, the foot deck section  410  moves from a retracted position to an extended position to shorten the foot deck section as the articulating deck of the bed moves to a chair configuration. 
     The minimizing foot section  1504  is further illustrated in FIG.  65 . The surface foot section  1502  deflates as it moves from the bed position to the chair position in the direction of arrow  1626 . In the bed position, the surface foot section  1502  has a length of about 27 inches (68.6 cm) and a thickness of about 5 inches (12.7 cm) when the bladders  1618  and  1620  are fully inflated. When in the downwardly extended chair position illustrated at location  1628  in FIG. 65, the surface foot section is fully deflated and has a length of about 14 inches (35.6 cm) and a thickness of preferably less than one inch (2.54 cm). The length of the surface foot section is preferably reduced by at least 40% and the thickness of the surface foot section is preferably reduced by at least 80% as the bed moves to the chair configuration. The width of the surface foot section  1502  remains substantially the same in both the bed orientation and the chair orientation. 
     Pressure control in the surface foot section  1502  is illustrated diagrammatically in FIG.  66 . Each of the vertically collapsible bladders  1620  are separately coupled to foot section control module  1514  by pressure/vacuum supply lines  1630  and sensor lines  1632 . Therefore, each of the three bladders  1620  are independently coupled to and controlled by foot section control module  1514 . Each of the three horizontally collapsing bladders  1618  are commonly connected to a common pressure/vacuum source of the foot section control module as illustrated line  1634 . A single sensor line  1636  is used to determine the pressure in the common zone of the interconnected bladders  1618 . The control configuration illustrated in FIG. 66 permits independent inflation and deflation of bladders  1620  to provide heel pressure relief in foot section  1502 . Details of the heel pressure management apparatus are illustrated in copending U.S. patent application Ser. No. 08/367,829 filed Jan. 3, 1995, owned by the assignee of the present application, the disclosure of which is hereby expressly incorporated by reference into the present applications. 
     Another embodiment of the foot section  1502  is illustrated in FIG.  67 . In this embodiment, bladders  1618  have been replaced by diamond shaped bladders  1640 . It is understood that any shape which collapses in a specified direction upon deflation may be used in foot section  1502  of the present invention to provide the shortening or retracting and thinning or collapsing features discussed above. 
     Additional surface and treatment options of the modular air therapy and support surface apparatus are illustrated in FIG.  68 . In FIG. 68, an upper air bladder  1506  is located on foam foundation base  1606  between side bolsters  1608  and  1610 . Upper air bladder  1506  includes a plurality of adjacent air tubes or bladders  1642  oriented transverse to a longitudinal axis of the bed. Illustratively, bladders  1642  are connected in three commonly controlled zones  1644 ,  1646 , and  1648 . It is understood that more zones may be provided. If desired, each bladder  1642  may be controlled independently. 
     The surface instrument module  1024  receives commands from the BACM  1018  and the position sense module  1026  to reduce the pressure in a seat section defined by zone  1644  of the upper air bladder  1506  as the bed moves to the chair configuration in order to distribute a patient&#39;s weight. A thigh section of the deck is angled upwardly to help maintain the patient in a proper position on the seat when the bed is in the chair configuration. 
     For the upper surface decubitus prevention, the three supply tubes  1650  of upper air bladder  1506  are all connected to a common pressure source through prevention module  1516 . For the upper surface decubitus treatment, the three supply lines  1650  are coupled to three separate valves in treatment module  1518  to control each of the zones  1644 ,  1646 , and  1648  of upper air bladder  1506  independently. 
     A pulmonary rotation bladder  1508  is located between foundation base  1606  and step deck  1596 . It is understood that rotation bladder  1508  may be positioned between foundation base  1606  and upper air bladder  1506  if desired. Rotation bladder  1508  includes separate bladders  1650  which are oriented to run parallel to a longitudinal axis of the hospital bed. Illustratively, three separate pressure zones  1652 ,  1654 , and  1656  are provided in rotation bladder  1508 . In the illustrated embodiment, each of the pressure zones  1652 ,  1654 , and  1656  are independently controlled by pressure supply lines  1658 . Each pressure supply line is coupled to a separate valve in pulmonary control module  1520  illustrated in FIG. 61. A separate sensor line (not shown) for each zone  1652 ,  1654 , and  1656  is also coupled to pulmonary rotation control module  1520 . 
     Pulmonary rotation bladder  1508  is stored in a deflated position within the bed until it is desired to treat the patient with rotational therapy. In this embodiment, the rotation bladder  1508  does not provide a support surface for the patient. The support surface is provided by either upper foam mattress  1504  or upper air bladder  1506 . Therefore, rotation bladder  1508  can be stored flat in the bed during normal operation of the bed as illustrated in FIG.  69 . It is understood that in another embodiment of the invention, the rotation bladder  1508  may be normally inflated to provide a support surface for the patient. 
     When it is desired to provide rotational treatment to the patient, a pulmonary rotation control module  1520  is coupled to the bed. The graphical interactive display  1664  of the bed or the graphic caregiver interface module  1032  automatically recognizes that the pulmonary rotation control module  1520  is attached to the bed. Therefore, controls for the pulmonary rotation therapy device can be actuated from the graphical interactive display  1664  or the graphic caregiver interface  1032 . 
     FIG. 69 illustrates the configuration of rotation bladder  1508  in its deflated position during normal operation of the bed with the upper foam mattress  1504  in place of upper air bladder  1506 . In FIG. 69, all three zones  1652 ,  1654 , and  1656  of rotation bladder  1508  are deflated or flat. 
     FIG. 70 illustrates actuation of the rotation bladder  1508  to rotate a patient situated on foam mattress  1504  to the right. Pulmonary rotation control module  1520  controls airflow to fully inflate zone  1656  to partially inflate zone  1654 , and to deflate zone  1652  of rotation bladder  1508 . FIG. 71 illustrates actuation of the rotation bladder  1508  to rotate the patient to the left. Pulmonary rotation control module  1520  fully inflates zone  1652 , partially inflates zone  1656 , and deflates zone  1654  to rotate the patient. 
     Another embodiment of the modular therapy and support surface invention is illustrated in FIG.  72 . In this embodiment, separate exchangeable surfaces are provided. The bed is illustrated by dotted line  1660 . As discussed above, the bed includes a peer-to-peer communication network  1662  which is coupled to a graphical interactive display  1664 . It is understood that graphical interactive display  1664  may be the graphic caregiver interface module  1032  discussed above. In addition, graphical interface display  1664  may be a display with control switches embedded in a foot board or at another location of the bed to provide a user control for all therapy and surface options. As discussed above, the network  1662  automatically recognizes when a specific therapy module is connected to the bed  1660  and automatically provides control options to the graphical interactive display  1664 . The open architecture of the electrical communication network  1662  allows interaction between the added module and the graphical interactive display  1664  without redesigning the system. Bed  1660  includes a surface header connector  1664  coupled to the air handling unit  1046  and to the electrical communication network  1662  by line  1668 . In addition, bed  1660  includes therapy header connectors illustrated at block  1670  which are connected to the air and power handling unit  1046  and to the electrical communication network  1662  as illustrated by line  1672 . 
     In this embodiment of the present invention, separate surfaces are provided, including a decubitus treatment surface  1674  and a separate decubitus prevention surface  1676 . The decubitus treatment surface  1674  has its own attached control module  1678  for connecting to surface header  1666 . Decubitus prevention surface  1676  has its own control module  1680  configured to be coupled to surface header connector  1666 . Header connector  1666  is connected to modules  1678  or  1680  in a manner similar to module  1542  in FIG.  62 . 
     Separate therapy modules are also provided. A pulmonary rotation therapy surface  1682  can be added to bed  1660 . Rotation therapy surface  1682  is coupled to its own control module  1684  which is configured to be connected to therapy header connector  1670 . A sequential compression therapy device  1686  is also provided. Sequential compression device  1686  is coupled to its own control module  1688  which is configured to be connected to therapy header connector  1670 . The present invention permits the sequential compression device to use an on board air handling unit  1046  and control system. This eliminates the requirement for a separate air pump and control panel which takes up valuable floor space near the bed and makes the bed difficult to move. 
     A separate pulmonary percussion and vibration therapy surface  1690  is also provided. Pulmonary percussion and vibration therapy surface is added to bed  1660  in place of a portion of the support surface of the bed. Pulmonary percussion and vibration therapy surface  1690  is coupled to its own control module  1692 . Control module  1692  is configured to be coupled to a therapy header connector  1670 . 
     The separate control modules are used to control power and air distribution, and to control user options displayed on the graphical interactive display  1664  for each therapy or surface option. As discussed above in detail with reference to FIG. 62, each control module  1678 ,  1680 ,  1684 ,  1688  and  1692  contain valves, sensors, and electronic control circuits specific to the particular surface or therapy application. All control features are implemented as a menu driven interactive control for the selected therapy or surface module of the present invention on the graphical interface display  1664  or on the graphic care giver interface  1023 . 
     All surface related parameters can be transmitted from surface instrument module  1024  to communications module  1020  and then to a remote location via the hospital network. Surface instrument  1024  can be interrogated by a diagnostic tool coupled to accessory port  1016  if desired. Information related to the surface modules can also be received via modem from a remote location through accessory port  1016 . 
     Further details of the air support surfaces, the articulating deck, and the control modules of the present invention are illustrated in FIG.  73 . The support surface of the present invention is configured to be positioned over a bed deck  402  of a hospital bed. The support surface includes a surface foundation  1500  located on the bed deck  402 . An inflatable and deflatable surface foot section  1502  is located adjacent surface foundation  1500 . An upper air bladder  1506  is positioned over surface foundation  1500 . 
     As discussed above, the articulating deck includes separate, independently movable deck sections. Specifically, deck  402  includes a head deck section  404 , a seat deck section  406 , a thigh deck section  408 , and a foot deck section  410 . Upper air bladder  1506  includes a plurality of separate air bladders. The air bladders are preferably connected in three independently controlled air zones corresponding to the different sections of deck  402 . Specifically, air bladder  1506  is divided into a head air zone  1648 , a seat air zone  1646 , and a air thigh zone  1644 . The separate surface foot section  1502  which overlies foot deck section  410  is also independently controlled. 
     An air surface control module  1517  is provided for selectively coupling the various air zones  1644 ,  1646 , and  1648  to the air handling unit  1046 . Air surface control module  1517  includes separate valves and pressure sensors for each air zone  1644 ,  1646 , and  1648  of air bladder  1506 . When a command to move the bed deck is transmitted to the network from a user input control on one of the standard caregiver interface modules  1028  and  1030 , the graphic caregiver interface module  1032 , or from another control device, the BACM  1018  actuates appropriate cylinders to articulate the deck  402 . The BACM  1018  also provides signals to surface instrument module  1024  and air supply module  1014  for controlling inflation and deflation of the surface foot section  1502  and the independent air zones  1644 ,  1646 , and  1648  of upper air bladder  1506  automatically as the bed articulates. 
     The surface instrument module  1024  sends signals to a controller inside the air surface control module  1517  to open and close valves at predetermined intervals to control inflation and deflation of the air zones  1649 ,  1646 , and  1648 . The surface instrument module  1024  and the air supply module  1014  also receive signals over the network from the position sense module  1026  to indicate the position of the articulating deck sections  409 ,  406 ,  408  and  410 . 
     As discussed above, the surface foot section  1502  is deflated as the deck  402  moves to the chair position. In addition, seat air zone  1646  and thigh air zone  1644  are partially deflated to distribute the weight of the person in the chair. When in the chair position, the surface thigh bladder  1644  and the thigh deck section  408  support most of a patient&#39;s weight. This partial deflation of the chair seat section is controlled automatically by surface instrument module  1024 , air supply module  1014 , and air surface control module  1517  as the bed deck moves from the bed position of FIG. 1 to the chair position of FIG.  2 . In some instances, a single air bladder may be provided for seat air zone  1646  and thigh air zone  1644 . In other instances, a plurality of individual air zones may be all separately controlled. In other words, each of the air zones of air bladder  1506  may have several independently controlled air bladders  1642 . 
     Separate valves and pressure sensors in air surface control module  1517  are provided for interconnecting the various air zones  1644 ,  1646 , and  1648  to the communication network of the bed and to on-board air handling unit  1046 . The present invention also includes a foot section control module  1514  which includes valves and pressure sensors for each air zone of the surface foot section  1502 . 
     Each of the control modules  1514 ,  1517  is designed to physically and functionally connect the various air zone bladders and to both the communication network of the hospital bed through the surface instrument module  1024  and to the air handling unit  1046  which is controlled by air supply module  1014 . Air supply module  1014  is coupled to the peer-to-peer communication network. Air supply electronics  1528  are connected to air supply module  1014  for controlling air handling unit  1046  and switching valve  1530  based on network commands for controlling the various surface and treatment modules illustrated in FIG.  73 . 
     Air handling unit  1046  is configured to supply air under pressure to switching valve  1530  on line  1532 . Air handling unit  1046  also applies a vacuum to switching valve  1530  through line  1534 . An output of switching valve  1530  is coupled to a connector block  1536 . Connector block  1536  provides an air and vacuum supply line  1515  to the foot section control module  1514  and provides an air and vacuum supply line  1519  to the air surface control module  1517 . It is understood that dual control lines for both air and vacuum can be supplied to each of the foot section control module  1514  and the air surface control module  1517 . This dual control allows each module to apply pressure and vacuum simultaneously to different zones of a bladder or treatment device. 
     The surface instrument module  1024  receives commands from the BACM  1018  and the position sense module  1026  to control the air surface control module  1517  to reduce the pressure in a seat section defined by zones  1644  and  1646  of the upper air bladder  1506  automatically as the bed moves to the chair configuration in order to distribute a patient&#39;s weight. An end of the thigh deck section  408  closest to foot end  54  is angled upwardly automatically as illustrated in FIG. 8 to help maintain the patient in a proper position on the seat when the bed is in the chair configuration. 
     Although the invention has been described in detail with reference to preferred embodiments, variations and modifications exist within the scope and spirit of the invention as described and defined in the following claims.