Patent Publication Number: US-2005125899-A1

Title: Hospital bed mechanisms

Description:
The present application is a divisional of U.S. patent application Ser. No. 10/338,558, filed Jan. 8, 2003 which is a continuation of U.S. patent application Ser. No. 09/458,780, filed Dec. 10, 1999, now U.S. Pat. No. 6,505,365 which is based upon U.S. provisional patent application Ser. No. 60/118,850, filed Dec. 11, 1998 and U.S. provisional patent application Ser. No. 60/112,149, filed Dec. 14, 1998, the complete disclosures of which are hereby expressly incorporated herein by reference. 
    
    
     BACKGROUND AND SUMMARY OF THE INVENTION  
      The present invention relates to various mechanisms for hospital beds. More particularly, the present invention relates to hospital bed mechanisms that move a patient support deck of the bed between a high position and a low position. The present invention further relates to an articulating patient support mechanism that includes a perimeter frame. In addition, the present invention relates to a pivotal handle/tray mechanism that can be provided at either or both ends of a hospital bed.  
      According to other features, characteristics, embodiments and alternatives of the present invention which will become apparent as the description thereof proceeds below, the present invention provides a bed assembly having a height-adjustable patient support surface which bed includes a head end and a foot end, a pair of hollow support tubes at each of the head end and the foot end, a first carriage movably coupled to the pair of hollow support tubes at the head end and a second carriage movably coupled to the pair of hollow support tubes at the foot end, a frame for supporting a patient support surface, said frame having opposite ends that are coupled to the first and second carriages, and a mechanism for raising and lowering the first and second carriages and the frame with respect to the pairs of hollow support tubes, the mechanism including a rotatable threaded shaft having a pulley support coupled thereto for movement along the shaft.  
      The present invention further provides a patient support assembly for an articulating bed which includes a bed frame that is supported at opposite ends, a perimeter frame that includes a head section, a seat section, and a foot section, the seat section being coupled to the head section by a pair of first hinges and coupled to the foot section by a pair of second hinges, a support bar that is coupled to the bed frame and to each of the pair of first hinges, and head, seat, and foot inserts which are received within the respective head, seat, and foot sections of the perimeter frame.  
      The present invention also provides a pivotal push handle assembly for hospital beds which includes spaced apart posts at an end of a bed, corner connectors provided on tops of the spaced apart post, and a push handle pivotally coupled between the corner connectors.  
      The present invention also further provides a hospital bed which includes a head end and a foot end, a pair of hollow support tubes at each of the head end and the foot end, a first carriage having a pair of spaced apart outer tubes and being movably coupled to the pair of hollow support tubes at the head end and a second carriage having a pair of spaced apart outer tubes and being movably coupled to the pair of hollow support tubes at the foot end, a frame for supporting a patient support surface, said frame having opposite ends that are coupled to the first and second carriage, a hi/lo mechanism for raising and lowering the first and second carriages and the frame with respect to the pairs of hollow support tubes, a perimeter frame that includes a head section, a seat section, and a foot section, the seat section being coupled to the head section by a pair of first hinges and coupled to the foot section by a pair of second hinges, a support bar that is coupled to the frame and to each of the pair of first hinges, head, seat, and foot inserts which are received within the respective head, seat, and foot sections of the perimeter frame, corner connectors provided on tops of at least one of the pair of spaced apart outer tubes, and a push handle pivotally coupled between the corner connectors.  
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
      The present invention will be described hereafter with reference to the attached drawings that are given as non-limiting examples only, in which:  
       FIG. 1  is a perspective view of a hospital bed according to one embodiment of the present invention;  
       FIG. 2  is a side elevational view of the hospital bed of  FIG. 1  that illustrates how the patient support surface moves between a low position close to the floor and an elevated position (shown in phantom lines);  
       FIG. 3  is a perspective view with portions broken away illustrating a headboard having a hi/lo mechanism mounted therein for moving the intermediate support frame up and down and illustrating a pivotable push handle and tray combination coupled to the headboard;  
       FIG. 4  is a perspective view with portions broken away illustrating the hi/lo mechanism and the intermediate support frame in lowered positions.  
       FIG. 5  illustrates an optional manual drive handle for controlling the hi/lo mechanism according to one embodiment of the present invention;  
       FIG. 6  illustrates an alternative embodiment of the hi/lo mechanism according to the present invention;  
       FIG. 7  illustrates a locking mechanism that is used for positioning the push handle and tray in a pre-selected position relative to the headboard or footboard;  
       FIG. 8   a  is a perspective view illustrating details of the intermediate frame that is coupled between the headboard and a footboard of the hospital bed;  
       FIG. 8   b  is an enlarged, partially exploded perspective view of a rack assembly according to one embodiment of the present invention;  
       FIGS. 9-11  illustrate an adjustable knee carriage control mechanism coupled to the intermediate frame for controlling articulation between a seat section and a foot section of a perimeter frame that provides a support deck;  
       FIG. 12  is an exploded perspective view illustrating details of the perimeter frame for supporting radiolucent panels, sleep surface inserts and mattress sections to support a patient;  
       FIG. 13  is a sectional view taken along plane XIII-XIII of  FIG. 1  illustrating additional details of the perimeter frame, the radiolucent panel, the sleep surface insert, and the mattress of  FIG. 10 ;  
       FIG. 14  is a side elevational view of a caster assembly and braking mechanism of the present invention;  
       FIG. 15  illustrates a brake pad that is moved downwardly by a pedal to engage the floor and brake the caster;  
       FIG. 16  is a perspective view of a hospital bed according to one embodiment of the present invention which includes a pair of optional full length siderails;  
       FIG. 17  is a perspective view of a hospital bed according to another embodiment of the present invention which includes optional half length siderails;  
       FIG. 18  is a perspective view of a pendant control according to another embodiment of the present invention which is configured to be located within a recessed portion of the perimeter frame;  
       FIG. 19  is a perspective view of another embodiment of a hospital bed in accordance with the present invention;  
       FIG. 20  is a perspective view illustrating movement of the bed about a transverse axis to move a patient support surface between a Trendelenburg and a reverse Trendelenburg position;  
       FIG. 21  is a side elevational view, with portions broken away, illustrating a drive mechanism for articulating a patient support deck with a deck in a generally planar position; and  
       FIG. 22  is a side elevational view similar to  FIG. 17  in which the drive mechanism has been actuated to articulate the patient support deck. 
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION  
       FIG. 1  is a perspective view of a hospital bed according to one embodiment of the present invention.  FIG. 1  illustrates a hospital bed  10  that includes a head end  12  and a foot end  14 . Head end  12  and Foot end  14  each include spaced-apart, hollow support tubes  16 . A curved support member  17  is coupled between tubes  16  at both head end  12  and foot end  14 . Support members  17  provide stability for tubes  16 . Support members  17  are curved inwardly as shown in  FIG. 1  to reduce the likelihood that support members  17  will be in the way of a caregiver pushing the bed or in the way of equipment located near either end of the bed. Each support tube  16  has a caster assembly  18  coupled to its lower end. Movable covers  20  slide up and down in the direction of double headed arrows  22  on tubes  16  in response to movement of a hi/lo mechanism  24  discussed below with reference to  FIG. 3 . Covers  20  are coupled to tubes  77  so as to move up and down together with tubes  77  that are positioned over tubes  16  as discussed below.  
      A push handle  26  is pivotably coupled to top end of tubes  77  at both head end  12  and foot end  14 . In  FIG. 1 , push handle  26  at head end  12  is shown in a downwardly pivoted, generally vertical orientation adjacent head end  12 . Push handle  26  coupled to tubes  77  at foot end  14  is shown in its outwardly pivoted position to permit a caregiver to push bed  10 . When push handle  26  is in the outwardly pivoted, generally horizontal position as shown adjacent foot end  14 , push handle  26  may also be used as a tray to support items near hospital bed  10 . A raised outer perimeter edge  27  of handle  26  defines a recessed central portion to help hold items on handle  26 .  
       FIG. 2  is a side elevational view of the hospital bed of  FIG. 1  that illustrates how the patient support surface is moved between a low position close to the floor and an elevated position (shown in phantom lines). A hand control pendant  30  ( FIG. 1 ) is coupled to a controller located in a controller housing  33  ( FIG. 1 ) for controlling hi/lo motors  32  (indicated in  FIG. 3 ) located at head end  12  and foot end  14  and articulation motor  151  ( FIG. 2 ). Hand control pendant  30  is used to control the elevation of the patient support surface and articulation of a perimeter frame  34  discussed below. Another embodiment of a hand control pendant is illustrated in  FIG. 18  discussed below.  
      An intermediate frame  36  is configured to support perimeter frame  34 . Intermediate frame  36  is coupled to hi/lo mechanisms  24  located within covers  20  adjacent both head end  12  and foot end  14  by mounting brackets  38 . Therefore, intermediate frame  36  moves up and down with covers  20 , tubes  77 , and push handles  26  as hi/lo mechanisms  24  move bed  10  between a low position shown in solid lines in  FIG. 2  and an elevated position shown in phantom lines in  FIG. 2 .  
      Perimeter frame  34  includes a head frame section  40 , a seat frame section  42 , and a leg frame section  44 . A mattress  46  located on perimeter frame  34  also includes a separate head mattress section  48 , seat mattress section  50 , and leg mattress section  52  as discussed in detail below.  
       FIG. 3  is a perspective view with portions broken away illustrating a headboard having a hi/lo mechanism  24  mounted therein for moving intermediate support frame  36  up and down and illustrating a pivotable push handle  26  and tray combination coupled to the headboard.  FIG. 4  is a perspective view with portions broken away illustrating hi/lo mechanism  24  and intermediate support frame  36  in lowered positions. As illustrated in  FIG. 3 , tubes  16  are each formed to include an elongated slot  54 . Hi/lo mechanisms  24  are located at both head end  12  and foot end  14  of bed  10 . Motors  32  adjacent the head end  12  and foot end  14  are separately controllable so that hi/lo mechanisms  24  at head end  12  and foot end  14  operate independently. Hi/lo mechanisms  24  can be operated simultaneously in the same direction to raise or lower intermediate frame  36 . In addition, hi/lo mechanisms  24  at opposite ends of bed  10  may be operated in opposite directions to move the intermediate frame  36  to either a Trendelenburg or a reverse Trendelenburg position, if desired. Of course, if one of hi/lo mechanisms  24  is at either its maximum high position or its minimum low position, the other hi/lo mechanism  24  is operated by itself to move intermediate frame  36  to the Trendelenburg position or the reverse Trendelenburg position.  
      Hi/lo mechanisms  24  each have a carriage  56  that includes first and second outer tubes  77  that slide over support tubes  16 . A top cross bar  60  and a bottom cross bar  62  extend between tubes  77 . Top cross bar  60  and bottom cross bar  62  include U-shaped cross sections or other shapes that define a channel therein. Vertical support bars  64  and  66  extend between cross bars  60  and  62 . Mounting brackets  38  for intermediate frame  36  are coupled to vertical support bars  64  and  66 . Covers  20  are located over the lower portion of carriage  56  to conceal and shield hi/lo mechanisms  24  ( FIG. 1 ).  
      A threaded shaft  68  is rotatably coupled to carriage  56 . Specifically, shaft  28  is coupled to a top support plate  70  and a bottom support plate  72  by suitable bearings  74 . Top support plate  70  is coupled to top cross bar  60  in the channel  65  therein, and bottom support plate  72  is coupled to bottom cross bar  62  in the channel  67  therein. Threaded shaft  68  is coupled to motor  32  that rotates the threaded shaft  68  in either direction about its longitudinal axis  84 .  
       FIG. 5  illustrates an optional manual drive handle for controlling the hi/lo mechanism according to one embodiment of the present invention. A hex nut  76  is formed on top of threaded shaft  68  to provide a manual overdrive using a manually operated crank  78  shown in  FIG. 5 . A removable cover  75  can be provided to cover nut  76  if desired. Crank  78  includes a hex opening  80  and a handle  82  to permit rotation of threaded shaft  68  about axis  84  in either direction as illustrated by arrow  86  in  FIG. 5 . It is to be understood that shapes other than hexagonal could be used for nut  76  and opening  80  so long as such shapes allow crank  78  to engage and rotate threaded shaft  68 .  
      Referring back to  FIG. 3 , a chain  86  is securely coupled to an upper portion or top end  88  of each support tubes  16 . Chain  86  extends downwardly through each tube  16  and around rollers  90 . Each chain  86  then extends inwardly within channel  67  to rollers  92  and upwardly over upper pulleys or rollers  94  that are rotatably coupled to a movable support  96 . Each chain  86  then extends downwardly and is securely coupled to lower support  72  by fastener  98 . Movable support  96  includes a pair of spaced-apart plates  100  and an internally threaded member  102  located over threaded shaft  68 . Rollers  90 ,  92 , and  94  are illustratively made from a plastic material that provides quieter operation of hi/lo mechanism  24 . Rollers  90 ,  92  are rotatably coupled between opposing side support plates  63  of bottom cross bar  62 .  
      It is to be understood that a cable, belt or similar flexible link element may be used in place of chain  86 , if desired. In addition, sprockets that engage chain  86  may be used in place of rollers  90 ,  92 , and  94 , if desired.  
      As threaded shaft  68  is rotated by motor  32  or by manual crank  78 , movable support  96  moves up or down on threaded shaft  68 . Limit switches (not shown) are mounted to cross bars  60  and  62 . Movable support  96  is configured to engage the limit switches (not shown) that in turn control operation of motors  32  to limit movement of support  96 .  
      Chains  86  that loop over rollers  94  on support  96  provide twice the amount of movement of carriage  56  relative to tubes  16  as the amount of movement of support  96  relative to shaft  68 . Carriage  56  is shown in its high position in  FIG. 3 . When shaft  68  is rotated by motor  32  or crank  78  to move movable support  96  downwardly in the direction of arrow  104 , carriage  56  moves downwardly twice the distance in the direction of arrow  106 . Hi/lo mechanism  24  permits the patient support surface hospital bed to move from a low position shown in solid lines in  FIG. 2  wherein a top of perimeter frame  34  is about 33 cm. above the floor  108 . When threaded shafts  68  are rotated so as to move movable support  96  upwardly on shafts  68 , carriages  56  at head end  12  and foot end  14  move upwardly in the direction of arrow  110  in  FIG. 2  to the elevated position shown in dashed lines. The range of movement of intermediate frame  36  is illustratively about 50 cm.  
      In the illustrated embodiment, the placement of rollers  92  on bottom cross bar  62  is selected so that plates  100  and rollers  94  are configured to nest between rollers  92  within channel  67  of bottom cross bar  62  when movable support  96  moves to its low position. In other words, plates  100  and rollers  94  enter channel  67  of bottom cross bar  62  as depicted best in  FIG. 4 .  
       FIG. 6  illustrates an alternative embodiment of hi/lo mechanism  24  according to the present invention. Those numbers referenced by numbers similar to  FIGS. 3-5  perform the same or similar function. In the embodiment of the invention depicted in  FIG. 6 , movable support  112  is coupled to threaded shaft  68  by bearing  114 . Each chain  86  extends downwardly over an outer roller  116  coupled to bottom cross members  62 . Chain  86  then extends upwardly over outer rollers  118  coupled to movable support  112 . Chains  86  then extend downwardly over inner rollers  120  coupled to cross bars  62 , upwardly over inner rollers  122  coupled to movable support  112 , and downwardly to fasteners  98 . The chain configuration illustrated in  FIG. 6  provides movement of carriage  56  relative to tubes  16  that is four times greater than the amount of movement of movable support  112  relative to threaded shaft  68 .  
      As discussed above in reference to  FIG. 3 , push handles  26  are pivotably coupled to tubes  77  that extend upwardly from carriage  56 . Corner connectors  79  are coupled to tubes  77  and push handles  26  are pivotably coupled to corner connectors  79  so as to rotate about axis  81 . Push handles  26  include a generally rectangular body portion  83  configured to define an interior region  85 . Grip apertures  87  are formed at opposite corners of rectangular body portion  83 .  
       FIG. 7  illustrates a locking mechanism that is used for positioning push handle  26  in a pre-selected position relative to the headboard or footboard. As shown in  FIG. 7 , corner connectors  79  include a locking member  89  formed to include spaced apart notches  91 ,  93 , and  95 . A locking arm  97  coupled to push handle  26  includes a tab  99  that is normally biased into one of notches  91 ,  93 , or  95  by a spring  101  adjacent each end of locking arm  97 . Locking arm  97  is coupled to a support  103  by a pin  105  that extends into an opening  107  formed in support  103 .  
      An actuator portion  109  extends through rectangular body portion  83  so that a caregiver has access to actuator  109  as best illustrated in  FIGS. 1 and 3 . When actuator  109  is pressed in the direction of arrow  111  toward handle  26 , locking arm  97  also moves in the direction of arrow  111  to release locking tab  99  from one of slots  91 ,  93 , or  95 . When locking tab  99  is released, push handle  26  can be rotated about axis  81  as illustrated by double headed arrow  113  in  FIG. 7 . Therefore, push handle  26  can be rotated to the generally horizontal position shown adjacent foot end  14  of bed  10  in  FIG. 1 . A caregiver can then grip push handle  26  adjacent apertures  87  to push bed  10 . Push handles  26  also provide a tray for supporting articles adjacent bed  10  when the push handles  26  are in the horizontal position. When actuator  109  is released, springs  101  automatically force locking tab  99  into the next slot  91 ,  93 , or  95  to lock push handles  26  in position. Push handle  26  adjacent head end  12  is easily removable to provide access to the head of a patient. Illustratively, removable fasteners or a latch assemblies (not shown) can be provided so that corner connectors  79  are quickly removable from tubes  77  adjacent head end  12 .  
       FIG. 8  is a perspective view illustrating details of intermediate frame  36  that is coupled between the headboard and a footboard of bed  10 . As illustrated in  FIG. 8 , intermediate frame  36  includes a pair of rails  124  that extend longitudinally between hi/lo mechanisms  24  at the head end  12  and foot end  14  of the bed  10 . Rails  124  include channels  125 . According to one embodiment, rails  124  have a U-shaped cross sections which defines channels  125 . The ends of rails  124  are coupled to brackets  38 . A fixed support bar  126  extends transversely between rails  124  and is coupled to rails  124  by brackets  128 . End plates  130  are coupled to opposite ends of support bar  126 . Each end plate  130  is pivotably coupled to a hinge  132  including first and second hinge members  134 ,  136  by a pivot connection  138 . Hinges  132  are coupled to perimeter frame  34  as discussed below with reference to  FIG. 12 .  
      A head carriage  140  is movably coupled to intermediate frame  36 . Head carriage  140  includes plates  142  having rollers  143  ( FIG. 9 ) located within rails  124 . A cross bar  144  extends between plates  142 . A cylinder  146  is pivotably coupled to a cross bar  148  by a connector  150 . Cross bar  148  is rigidly coupled to rails  124  by brackets  152 . Cylinder  146  includes a movable piston  154  that is pivotably coupled to cross bar  144  by a pivot connection  156 .  
      Head lift arms  158  are also pivotably coupled to each end of cross bar  144  by pivot connections  160 . Opposite ends  159  of head lift arms  158  are coupled to the head section  40  of perimeter frame  34  by pivot connections  162  as best shown in  FIG. 2 . Head section pivot hinge  132  is fixed relative to intermediate frame  36  by support bar  126 , brackets  128 , and end plates  130 . When piston  154  is extended from cylinder  146  in the direction of arrow  164  by actuation of motor  151 , head carriage  140  moves in the direction of arrow  164 , thereby causing the lift arms  158  to move head section  40  of perimeter frame  34 , along with head section  48  of mattress  46 , upwardly to the inclined position shown in  FIG. 1 .  
      It should be understood that other types of drive mechanisms may be used to provide movement of plates  142  and cross bar  144  if desired. 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 and stretchers. As a result, the term “drive mechanism” is intended to cover all types of mechanical, electromechanical, hydraulic, and pneumatic mechanisms for raising and lowering portions of bed  10 , including manual cranking mechanisms of all types, and including combinations thereof such as hydraulic cylinders in combination with electromechanical pumps for pressurizing fluid received by the hydraulic cylinders.  
      A knee carriage  170  is provided and includes plates  172  having rollers (not shown) located within rails  124  for movement relative to the longitudinal axis of bed  10 . A cross bar  174  extends between plates  172 . A link arm  176  is pivotably coupled to each of the plates  172  of head carriage  140  by a pivot connection  178 . Each arm  176  extends over a pin  180  coupled to plate  172  of knee carriage  170 . Arm  176  includes a plurality of angled notched portions  182 ,  184 ,  186  ( FIG. 10 ) that are configured to slide over and engage pin  180  and couple knee carriage  170  to the head carriage  140 .  
      Intermediate frame  36  includes a knee elevation adjustment mechanism  188  having a rack  190  located in each rail  124 . Racks  190  include a plurality of teeth  192  that are configured to be engaged by a gear or pinion  194 . Pinions  194  are connected by a cross bar  196 . Pinions  194  are rigidly coupled to cross bar  196 . In an alternative embodiment, if pinions  194  are not used, racks  190  can be coupled together by cross bars  198  and  200 . Teeth on racks  190  are not required in this alternative embodiment. An angle indicator  202  ( FIGS. 9-11 ) is coupled to each rack  190  and configured to point to various angle settings the knee articulation that are marked on the outside of channels  124  as indicated by markings  204 .  
       FIG. 8   b  is an enlarged, partially exploded perspective view of a rack assembly according to one embodiment of the present invention. Rack  190  in  FIG. 8   b  includes a central portion  191  having teeth  192  formed in an upper surface. Central portion  191  is secured between side plates  193  and  195 . As shown, side plates  193 ,  195  have a height that is taller than the top edges of teeth  192  so that teeth  192  are recessed between side plates  193  and  195 . Central portion  191  can be made of any suitable strong material such as metals, plastics, etc. Side plates  193 ,  195  are made from metal or other suitable material that will resist wear from tabs  218  which slide along ramp  216  of rack  190  and upper surfaces  197  of side plates  193 ,  195  as discussed below. As depicted, side plates  193 , 195  are coupled together or are coupled to central portion  191  by threaded fasteners  199 . In an alternative embodiment, central portion  191  is an insert which is received in a U-shaped channel that includes, in addition to side plates  193 ,  195 , a bottom (not shown).  
      The location of racks  190  is adjustable to control which of notches  182 ,  184 ,  186 , if any, engage pins  180  on knee carriage  170 . In one embodiment, an operator can rotate wheels  206  that are coupled to shaft  196  on either side of intermediate frame  36  to move racks  190  to a different location along rails  124 . In other words, rotation of wheels  206  moves racks  190  relative to stationary pinions  194 . In another alternative embodiment, pinions  194  are replaced by any suitable mechanical connection for moving racks  190  relative to intermediate frame  36  to adjust the point at which notches  182 ,  184 , and  186  in arms  176  engage pins  180  to control knee articulation. Adjustment knobs  206  outside intermediate frames  36  are optional.  
      In another embodiment, pinions  194  cooperate to move racks  190  on opposite sides of intermediate frame  36  without adjustment knob  206 . In this embodiment, an operator uses angle indicator  202  to slide racks  190  longitudinally. As an operator moves angle indicator  202  on one side of intermediate frame  36 , rack  190  coupled to angle indicator  202  also moves which causes pinions  194  to rotate on both sides of intermediate frame  36 . Therefore, both the racks  190  move longitudinally relative to intermediate frame  36  in response to the operator moving only one of angle indicators  202 .  
      In another alternative embodiment, pinions  194  can be replaced by a suitable mechanical connection for moving racks  190  relative to intermediate frame  36  to adjust the point at which notches  182 ,  184  and  186  in arms  176  engage pins  180  to control knee articulation. For instance, cross bars  198 ,  200  can be used to interconnect racks  190  in this embodiment. The operator again moves angle indicator  202 . Since racks  190  are interconnected by cross bars  198 ,  200  in this embodiment, movement of one of angle indicator  202  and rack  190  on one side of frame  36  causes corresponding movement of rack  190  and angle indicator  200  on the opposite side of the frame.  
      A knee lift arm  210  is coupled to each end of cross bar  174  of knee carriage  170  on opposite sides of intermediate frame  36  by pivot connections  212 . Opposite ends of knee lift arms  210  are coupled to seat section  42  of perimeter frame  34  by pivot connections  214  as shown in  FIG. 2 .  
       FIGS. 9-11  illustrate an adjustable knee carriage control mechanism coupled to intermediate frame  36  for controlling articulation between a seat section and a foot section of a perimeter frame that provides a support deck. As depicted in  FIGS. 9-11 , when motor  151  is actuated to extend piston  154  from cylinder  146  ( FIG. 8   a ), plates  142  and rollers  143  move within rails  124  in the direction of arrow  164  shown in  FIG. 9 . The position of racks  190  determine which of notches  182 ,  184 , or  186 , if any, engage the pins  180 . Racks  190  include a leading ramp  216  and lift arms  176  include a tab  218 . Tab  218  is positioned to contact and slide along ramp  216  and the upper surface of one or both side plates  193 ,  195  of rack  190 , so as to pass over teeth  192  in central portion  191  of rack  190 .  
      When racks  190  are positioned as shown in  FIG. 9 , indicators  202  are at the 20° knee articulation position. In this instance, as head carriage  140  moves in the direction of arrow  164 , arms  176  move over ramp  216  so that first angled notch  182  catches pins  180  and pulls knee carriage  170  in the direction of arrow  164 . Therefore, lift arms  210  begin lifting seat section and leg sections  42  and  44  of the perimeter frame  34  upwardly to provide a 20° knee articulation angle.  
      When racks  190  are moved so that indicator  202  is aligned with the 15° mark, arms  176  move down ramps  216  later so that second notch  184  engages pins  180 . This causes delayed movement of knee plates  172  and lift arms  210 . Therefore, when piston  154  is fully extended, the knee articulation angle is only about 15°.  
       FIG. 10  shows the indicator  202  at the 10° position with racks  190  moved upwardly in the direction of arrow  164 . In this rack position, arms  176  do not move downwardly over ramp  216  until third notch  186  is aligned with pins  180 . Therefore, the knee only articulates 10° upon full extension of piston  154 .  
      Finally, when indicator  202  is located at the 0° position, end portions  221  of arms  176  remain on racks  190  until all of notches  182 ,  184 ,  186  have passed pins  180 . Therefore, lift arms  210  are not moved to lift the seat section  42  and foot section  44  upwardly.  
       FIG. 11  illustrates an automatic reset feature of the knee elevation adjustment mechanism  188 . Illustratively, in  FIG. 11 , the 10° knee articulation setting was initially made so that notches  186  on arms  176  engage pins  180  to articulate the knee about 10°. Before piston  154  was retracted, however, the rack was moved to the 0° position. As piston  154  is retracted, head carriage  140  moves in the direction of arrow  220  of  FIG. 10  and pushes arms  176  and knee carriage  170  in the direction of arrow  220 . As arms  176  move in the direction of arrow  220 , arms  176  push racks  190  in the direction of arrow  220 . Once seat frame section  42  and leg frame section  44  are in the horizontal position, knee carriage  170  stops moving in the direction of arrow  220 . At that point, arms  176  have pushed racks  190  to the proper location for the 10° knee articulation (or the other knee articulation setting that was initially set). Further retraction of piston  154  causes arms  176  to move upwardly in the direction of arrow  222  over ramps  216  of racks  190  due to the angle of notches  182 ,  184 , and  186 .  
      As shown in  FIGS. 2 and 8 , a roller  224  is rotatably coupled to leg section  44  of frame  34  by bracket  226 . Rollers  224  ride on top of rails  124  as foot section  44  of frame  34  moves toward head end  12  during knee articulation. Stops  225  shown in  FIG. 2  provide support for head frame section  40  in its horizontal position.  
       FIG. 12  is an exploded perspective view illustrating details of perimeter frame  34  for supporting radiolucent panels, sleep surface inserts and mattress sections to support a patient.  FIG. 13  is a sectional view taken along plane XIII-XIII of  FIG. 1  illustrating additional details of perimeter frame  34 , the radiolucent panel, the sleep surface insert, and the mattress of  FIG. 10 . As illustrated, perimeter frame  34  is formed from lengths of an extruded member  230  having a cross section best illustrated in  FIG. 13 . Illustratively, extruded member  230  includes an outer semi-circular shaped portion  232  and an inner rectangular shaped portion  234 . It should be understood that other shapes are possible in accordance with the present invention. Rectangular portion  234  includes an inwardly extending flange  236  and a notched top ledge  238 . Extrusion member  230  may be formed from a suitable metal or plastic material.  
      Head section  40 , seat section  42 , and leg section  44  of perimeter frame  34  are all formed from the same extruded members  230  that are cut to different lengths. Corner portions  240  include ends  242  having the same cross sectional configuration as semi-circular portion  232  and rectangular portion  234  of extruded frame members  230 . Therefore, ends  242  of corner portions  240  slide into the openings of extruded members  230  to secure corner portions  240  to frame sections  40 ,  42 , and  44 . Head frame section  40  and foot frame section  44  of perimeter frame  34  have identical shapes to facilitate manufacturing of hospital bed  10 .  
      Hinge members  134  extend into rectangular portions  234  of both head frame section  40  and seat frame section  42  in order to pivotably couple head frame section  40  to seat frame section  42 . A flexible cover  244  surrounds each hinge  132 .  
      Similar hinges  246  are located between seat frame section  42  and foot frame section  44 . Hinges  246  include a first hinge member  248  configured to be inserted into rectangular portion  234  of seat frame section  42 . A second hinge member  250  is configured to be inserted into rectangular portion  234  of foot frame section  44 . Flexible covers  252  are configured to surround hinges  246 . Hinge members  134 ,  136 ,  248 , and  250  are all identically shaped. Therefore, the configuration of hinges  132 ,  246  also facilitates manufacture of bed  10 .  
      Radiolucent panels  254 ,  256 , and  258  are coupled to head section  40 , seat section  42 , and foot section  44 , respectively, of perimeter frame  34 . Support surface inserts  260 ,  262 , and  264  are located on head section  40 , seat section  42 , and foot section  44  of perimeter frame  34 , respectively. Each of the support surface inserts  260 ,  262 , and  264  includes a bottom surface  266 , an upwardly extending sidewall  268 , and an outwardly extending flange  270 . Flanges  270  of inserts  260 ,  262 , and  264  are located on ledges  238  of extruded members  230  as depicted in  FIG. 13 . Sidewalls  268  extend downwardly along the periphery of the support surface and bottom surfaces  266  extend over radiolucent panels  254 ,  256 , or  258 . Illustratively, support surface inserts  260 ,  262 , and  264  are formed from a molded plastic material. Inserts  260 ,  262 , and  264  facilitate cleaning by providing a wipable surface that catches fluids or other contaminants. Mattress sections  48 ,  50 , and  52  are located in inserts  260 ,  262 , and  264 , respectively. Velcro strips (not shown) can be provided between mattress sections  48 ,  50 , and  52  and inserts  260 ,  262 , and  264  to secure mattress sections  48 ,  50  and  52  in place. As best shown in  FIG. 12 , seat mattress section  50  includes an inclined edge surface  274  located adjacent foot section  52 . This inclined edge  274  facilitates movement during knee articulation.  
      In an alternative embodiment, mattress sections  48 ,  50 , and  52  may sit directly on radiolucent panels  254 ,  256 , and  258 , respectively. In yet another embodiment, mattress  48 ,  50 , and  52  sections can be formed with suitable rigid bottom portions  272  as depicted in  FIG. 13 . Such reinforced mattress sections  48 ,  50 , and  52  may sit directly on head section  40 , seat section  42 , and leg section  44 , respectively, of perimeter frame  34  with rigid support portions  272  engaging flanges  236 . When reinforced bottom  272  is used, inserts  260 ,  262 , and  264  may be used without radiolucent panels  254 ,  256 , and  258  to facilitate cleaning of bed  10 .  
      In yet another embodiment of the invention, a stronger material can be used for support surface inserts  260 ,  262 , and  264 . In this embodiment, mattress sections  48 ,  50 , and  52  can be located directly over inserts  260 ,  262 , and  264 , respectively, without radiolucent panels  254 ,  256 , and  258 .  
      Flexible portions (not shown) or other suitable retainers are used to hold panels  254 ,  256 , and  258  and inserts  260 ,  262 , and  264  in a proper position on perimeter frame  34 .  
       FIG. 14  is a side elevational view of a caster assembly and braking mechanism of the present invention.  FIG. 15  illustrates a brake pad that is moved downwardly by a pedal to engage the floor and brake the caster. Each caster assembly  18  includes an outer cylindrical portion  280  rotatably coupled to support tubes  16 . A washer  282  is located between support members  17  and cylindrical portion  280 . Caster  284  is coupled to lateral support members  286  extending away from cylindrical portion  280  about an axis  288  of rotation of casters  284 . Axis  288  is spaced apart from a central axis  290  of cylindrical portion  280  and tubes  16  by a sufficient distance so that an outer edge  292  of caster  284  is spaced apart from axis  290  and from an edge  281  of cylindrical portion  280 . This offset caster  284  permits cylinder  280  and tubes  16  to be located closer to floor  108  to achieve a lower position of intermediate frame  36  relative to the floor  108 .  
      A brake pad  294  is coupled to a shaft  296  by a fastener  298 . The brake pad  294  is movable from a retracted position shown in  FIG. 14  to an extended position illustrated in  FIG. 15  to engage floor  108  and brake bed  10 . A brake pedal  300  is coupled to post  296 . When brake pedal  300  is moved downwardly in the direction of arrow  302 , brake pad  294  moves to its extended position depicted in  FIG. 15 . A spring  304  is configured to assist downward movement of brake pad  294 . When an operator moves pedal  300  upwardly, a latch (not shown) secures brake pad  294  in the retracted position.  
       FIG. 16  is a perspective view of a hospital bed according to one embodiment of the present invention that includes a pair of optional full length siderails. The full length siderails  306  include siderail frames  317  having support arms  319  that support tubular rails  321 . Siderail frames  317  are either pivotably or non-pivotably coupled to perimeter frame  34  or intermediate frame  36  on opposite sides of bed  10 . Support arms  319  extend upward and can optionally curve slightly inward as shown.  
       FIG. 17  is a perspective view of a hospital bed according to another embodiment of the present invention which includes optional half length siderails. The half length siderails  307 ,  308  are coupled to opposite sides of bed  10  adjacent head section  40  and foot section  44 , respectively, of perimeter frame  34 .  FIG. 17  also shows a pair of patient assist devices  309  that have handles to assist a patient getting into and out of bed  10 . Patient assist devices  309  include telescoping legs to compensate for variations in height of intermediate frame  36  off floor  108 . Illustratively, patient assist devices  309  are coupled to one of siderails  307 ,  308 , perimeter frame  34 , or intermediate frame  36 . An overbed table  311  is also illustrated in  FIG. 18 . The overbed table  311  may include a stand located on floor  108 . Overbed table  311  may also be coupled to one of perimeter frame  34  or intermediate frame  36 .  
      Another embodiment of a hand pendant control  313  is illustrated in  FIG. 18 . In the  FIG. 18  embodiment, pendant  313  is configured to be located within a recessed portion  315  formed in perimeter frame  34 . Pendant  313  may be pivotably coupled to perimeter frame  34 , or pendant  313  may be removable from perimeter frame  34  for use by an operator. Pendant  313  includes a stand  313   a  pivotably coupled to pendant  313  to permit pendant  313  to rest in an inclined position shown in  FIG. 18 . Stand  313   a  is pivotably coupled to pendant  313  so that pendant  313  can nest within recessed portion  315  of perimeter frame  34  when stand  313   a  is folded against pendant  313 .  
      Another embodiment of the invention is illustrated in  FIGS. 19-22 . A hospital bed  310  includes base  312  having a plurality of casters  314 . The base includes a curved bearing portions  316  configured to receive side support members  318 . Side support members  318  each include a curved bearing surface  320  that engages a bearing surface  316  of base  312 . A support frame  322  includes a pair of spaced apart side frame members  324  that are coupled to support members  318 . A headboard  326  and a footboard  328  are coupled to opposite ends of frame members  324 .  
      An articulating deck  330  is also coupled to frame members  324 . Deck  330  includes a head section  332 , a seat section  334 , a thigh section  336 , and a foot section  338 . Each of deck sections  332 ,  334 ,  336 , and  338  are pivotably coupled to an adjacent deck section by suitable hinges. Seat section  334  includes guide posts  340  that extend outwardly from both side portions of seat section  334 . A guide bar  342  is coupled to each of frame members  324 . Guide bars  342  define a slot  334  for receiving posts  340  coupled to seat frame section  334 .  
      A suitable drive mechanism (not shown) is coupled between base  312  and support frame  322  to pivot support frame  322  and deck  330  about a transverse pivot axis so that deck  330  can be moved between a Trendelenburg position and a reverse Trendelenburg position.  
      Referring to  FIGS. 21 and 22 , a threaded drive shaft  346  is pivotably coupled to head frame section  332  by connector  348 . A motor  350  is coupled to drive shaft  346 . Motor  350  is pivotably coupled to support frame  322  by connector  352 . Opposite sides of thigh sections  336  of deck  330  are pivotably coupled to link arms  354  by pivot connections  356 . Opposite ends of link arms  354  are pivotably coupled to side frame members  324  by pivot connection  357 . Opposite sides of head section  332  of deck  330  are coupled to link arms  358  by pivot connections  360 . Opposite ends of link arms  358  are pivotably coupled to side frame members  324  by pivot connections  362 .  
       FIG. 21  illustrates deck  330  in a generally planar configuration. When motor  350  is actuated, threaded shaft  346  moves in the direction of arrow  364 . This causes deck  330  to move in the direction of arrow  364  to the position shown in  FIG. 22 . Since head section  334  is linked to frame members  324 , head section  334  pivots upwardly in the direction of arrow  366  of  FIG. 21 . Thigh section  336  pivots upwardly in the direction of arrow  368  and foot section  338  pivots upwardly in the direction of arrow  370  so that deck  330  moves to its articulated position shown in  FIG. 22  as threaded shaft  346  moves in the direction of arrow  364 . A support post  372  coupled to foot section  338  slides over frame members  324  as deck  330  moves to its articulated position. It should be understood that rollers could be used in place of posts  372 . In addition, slot  344  is preferably formed by a track in a side frame member so that slot  334  is not exposed. Link arms  354  and  358  are moved inwardly toward a center of bed  10  in another embodiment.  
      Although the present invention has been described with reference to particular means, materials and embodiments, from the foregoing description, one skilled in the art can easily ascertain the essential characteristics of the present invention and various changes and modifications may be made to adapt the various uses and characteristics without departing from the spirit and scope of the present invention as described by the claims which follow.