Patent Publication Number: US-11044996-B2

Title: Medical support apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 15/680,290 filed Aug. 18, 2017, by inventors Anish Paul et al. and entitled MEDICAL SUPPORT APPARATUS, which in turn is a continuation of U.S. patent application Ser. No. 14/801,167 filed Jul. 16, 2015, by inventors Anish Paul et al. and entitled MEDICAL SUPPORT APPARATUS, and claims priority to U.S. provisional patent application Ser. No. 62/029,142 filed Jul. 25, 2014 by inventors Anish Paul et al. and entitled MEDICAL SUPPORT APPARATUS, the complete disclosures of all of which are hereby incorporated herein by reference. 
    
    
     TECHNICAL FIELD AND BACKGROUND 
     The present disclosure relates to a patient support apparatus, and more particularly to a medical recliner chair. 
     It is well known in the medical field that a patient&#39;s recovery time can be improved if the patient becomes more mobile. To that end, it is desirable for a patient to move in and out of the hospital bed on which he or she is most typically positioned. Providing a chair for the patient encourages movement from the bed to the chair and vice versa. The present disclosure relates to a chair that can comfortably support the patient and that better accommodates the patient&#39;s and/or the caregiver&#39;s needs. 
     SUMMARY 
     According to one embodiment, a chair is provided that includes a base, a seat, a seat actuator, a backrest, a backrest actuator, a leg rest, a leg rest actuator, a memory, and a controller. The seat actuator changes a tilt of the seat. The backrest actuator changes an angular orientation of the backrest with respect to the seat. The leg rest changes an orientation of the leg rest with respect to the seat. The memory has stored therein first, second, and third states wherein each of the first, second, and third states define positions for each of the seat actuator, backrest actuator, and leg rest actuator. The controller moves the seat actuator, backrest actuator, and leg rest actuator from the first state to the second state and from the second state to the third state. The controller also coordinates movement of the seat actuator, backrest actuator, and leg rest actuator such that they all arrive at the second state substantially simultaneously and such that they all arrive at the third state substantially simultaneously. 
     According to other aspects of the disclosure, the first state includes a first position of the backrest actuator that causes the backrest to be oriented generally upright and a first position of the leg rest actuator that causes the leg rest to be retracted. The second state includes a second position of the leg rest actuator that causes the leg rest to be extended and a second position of the backrest actuator that causes the backrest to be oriented generally horizontally. 
     In some embodiments, the first state further includes a first position of the seat actuator that causes the seat to be tilted at a first orientation and the second state includes a second position of the seat actuator that causes the seat to be tilted at a second orientation. 
     In some embodiments, the first orientation of the seat is defined by a forward end of the seat being lower than a rear end of the seat, and the second orientation of the seat is generally horizontal. 
     The chair may further include a lift actuator adapted to simultaneously change a height of the seat, the backrest, and the leg rest. When included, the first state may include a first position of the lift actuator and the second state may include a second position of the lift actuator. 
     In various embodiments, the seat actuator, the backrest actuator, and the leg rest actuator move different distances when moving between the first state and the second state. 
     The controller, in some embodiments, determines which of the seat actuator, backrest actuator, and the leg rest actuator needs to move the farthest when moving from the first state to the second state. The controller activates at a maximum speed the actuator needing to move the farthest when moving from the first state to the second state, and the controller activates the other two of the seat actuator, backrest actuator and leg rest actuator at a fraction of the speed of the actuator needing to move the farthest. The fractions are selected in order to result in the substantially simultaneous arrival of the seat actuator, backrest actuator, and leg rest actuator at the second and third states. 
     In some embodiments, the first state corresponds to a configuration adapted to assist an occupant into a standing position, and the second state corresponds to a configuration adapted to support the occupant in a Trendelenburg position. 
     The memory may include a fourth state defining positions of the seat actuator, backrest actuator, and leg rest actuator. When so included, the controller is further adapted to coordinate movement of the seat actuator, backrest actuator, and leg rest actuator from the third state to the fourth state such that they all arrive at the fourth state substantially simultaneously. 
     In some embodiments, the chair further comprises a control panel having a first icon and a first light positioned adjacent to each other, a second icon and a second light positioned adjacent to each other, and a plurality of intermediate lights positioned between the first and second lights. The first icon corresponds to the first state and the second icon corresponds to the second state. The control panel illuminates the first light when the chair is in the first state, illuminates the second light when the chair is in the second state; and illuminates one of the intermediate lights when the chair is transitioning between the first state and the second state. 
     The first icon, in some embodiments, is positioned at or near a first control on the control panel that, when pressed, moves the chair to the first state. Similarly, the second icon is positioned at or near a second control on the control panel that, when pressed, moves the chair to the second state. 
     According to another embodiment of the present disclosure, a chair is provided that includes a base, a seat, a seat actuator, a lift actuator, a backrest, a backrest actuator, a leg rest, a leg rest actuator, a memory, and a controller. The seat actuator changes a tilt of the seat. The lift actuator changes a height of the seat. The backrest actuator changes an angular orientation of the backrest with respect to the seat. The leg rest actuator changes an orientation of the leg rest with respect to the seat. The memory has stored therein first, second, and third states wherein each of the first, second, and third states define positions for each of the seat actuator, lift actuator, backrest actuator, and leg rest actuator. The controller automatically coordinates movement of all of the seat actuator, lift actuator, backrest actuator, and leg rest actuator from the first state to the second state, and coordinates movement of only the seat actuator, backrest actuator, and leg rest actuator when moving from the second state to the third state. 
     According to other aspects, the controller does not activate the lift actuator when moving from the second state to the third state. The first state may correspond to a stand assist state in which a front end of the seat is lower than a rear end of the seat, and the second state may correspond to a seated state in which the front end of the seat is higher than the rear end of the seat. The backrest is tilted backward a greater extent when in the seated state than when in the stand assist state. 
     The third state may correspond to another seated state in which the front end of the seat is higher than the rear end of the seat, the leg rest is retracted, and the backrest is tilted backward a greater extent than when the backrest is in the seated state. 
     Alternatively, the first state may correspond to a flat state in which the backrest, the seat, and the leg rest are all oriented generally horizontally, and the second state may correspond to a recline state in which the backrest it tilted upwardly, a front end of the seat is higher than a rear end of the seat, and the leg rest remains oriented generally horizontally. 
     The third state may alternatively corresponds to another recline state in which the backrest is tilted upwardly to a greater extent than in the recline state, the seat is oriented at a different angle with respect to horizontal than in the recline state, and the leg rest remains oriented generally horizontally. 
     In some embodiments, the chair also includes a control panel having first, second, and third icons and a plurality of lights positioned therebetween. The first icon is illuminated when the chair is in the first state and unilluminated when the chair is in the second or third state. The second icon is illuminated when the chair is in the second state and unilluminated when the chair is in the first or third state. The third icon is illuminated when the chair is in the third state and unilluminated when the chair is in the first or second state. The lights are selectively illuminated to indicate progress of the chair when moving between the first and second states and between the second and third states. 
     Before the various embodiments disclosed herein are explained in detail, it is to be understood that the claims are not to be limited to the details of operation or to the details of construction and the arrangement of the components set forth in the following description or illustrated in the drawings. The embodiments described herein are capable of being practiced or being carried out in alternative ways not expressly disclosed herein. Also, it is to be understood that the phraseology and terminology used herein are for the purpose of description and should not be regarded as limiting. The use of “including” and “comprising” and variations thereof is meant to encompass the items listed thereafter and equivalents thereof as well as additional items and equivalents thereof. Further, enumeration may be used in the description of various embodiments. Unless otherwise expressly stated, the use of enumeration should not be construed as limiting the claims to any specific order or number of components. Nor should the use of enumeration be construed as excluding from the scope of the claims any additional steps or components that might be combined with or into the enumerated steps or components. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view of a chair according to one embodiment of the present disclosure; 
         FIG. 2  is a set of side elevational views showing the chair of  FIG. 1  in a series of six different states; 
         FIG. 3  is a side, sectional view of many of the structural components the chair of  FIG. 1 , including multiple actuators; 
         FIG. 4  is a diagram of one embodiment of a control system that can be incorporated into the chair of  FIG. 1 ; 
         FIG. 5  is a plan view of a control panel of the chair of  FIG. 1  showing a full set of controls that are available and active; 
         FIG. 5A  is a plan view of the control panel of  FIG. 5  showing a reduced set of controls that are available and active; 
         FIG. 6  is a side elevational view of various structural components of the chair of  FIG. 1  shown in a Trendelenburg state; 
         FIG. 7  is a side elevational view of the chair of  FIG. 6  shown in a flat state; 
         FIG. 8  is a side elevational view of the chair of  FIG. 6  shown in a recline state; 
         FIG. 9  is a side elevational view of the chair of  FIG. 6  shown in a second upright state; 
         FIG. 10  is a side elevational view of the chair of  FIG. 6  shown in a first upright state; 
         FIG. 11  is a side elevational view of the chair of  FIG. 6  shown in a stand state; 
         FIG. 12  is a set of diagrams illustrating the backrest angles, seat angles, footrest angles, and seat heights of the chair when the chair moves between the states illustrated in  FIGS. 6-11 ; 
         FIG. 13  is a set of diagrams illustrating the position of the backrest actuator, seat actuator, footrest actuator, and seat actuator of the chair when the chair moves between the states illustrated in  FIGS. 6-11 ; 
         FIG. 14  is a chart illustrating a range of permitted seat height adjustments when the chair moves between the states illustrated in  FIGS. 6-11 ; 
         FIG. 15  is a perspective view of an alternative embodiment of a backrest that may be incorporated into the chair of  FIG. 1 ; and 
         FIG. 16  is a side elevational view of a linkage between the backrest and seat frame of  FIG. 15 . 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Referring to  FIG. 1 , a chair  20  according to one embodiment is shown. Although the following written description will be made with respect to a chair, it will be understood by those skilled in the art that the principles disclosed herein may also be incorporated into other types of person support apparatuses besides chairs, such as, but not limited to, beds, stretchers, cots, surgical tables, or the like. 
     Chair  20  includes a seat  22 , a backrest  24 , a leg rest  26 , a pair of armrests  28 , and a plurality of wheels  30 . Chair  20  is constructed such that both the height and tilt of seat  22  is adjustable. Further, chair  20  is constructed such that backrest  24  is pivotable between a generally upright position, such as shown in  FIG. 1 , and a rearwardly reclined position, such as shown in  FIG. 6 . Leg rest  26  is constructed such that it is able to be moved between a retracted position, such as shown in  FIG. 1 , and an extended position, such as shown in  FIG. 8 . Armrests  28  may be constructed such that a user can raise and lower their height relative to seat  22 . Several manners in which chair  20  may be constructed in order to carry out these various motions of the seat, backrest, and leg rest are described in greater detail below. It will also be understood, however, that in other embodiments, chair  20  may be constructed in accordance with any of the embodiments disclosed in commonly assigned, copending U.S. patent application Ser. No. 14/212,253 filed Mar. 14, 2014 by inventors Christopher Hough et al. and entitled MEDICAL SUPPORT APPARATUS, the complete disclosure of which is incorporated herein by reference. 
       FIG. 2  illustrates in greater detail six states that chair  20  can be moved to according to one embodiment. As shown therein, chair  20  is movable to any of a Trendelenburg state  32 , a flat state  34 , a recline state  36 , a second upright state  38 , a first upright state  40 , and a stand state  42 . Further, although not shown in  FIG. 2 , chair  20  is movable to a virtually infinite number of states that are in between the six states shown in  FIG. 2 . That is, as will be discussed in greater detail below, a user may operate chair  20  to move it to a state, for example, in which the backrest  24  is positioned at an angle between the backrest angles shown in the flat state  34  and the recline state  36 . Once the user moves the chair to such a desired state, the chair remains fixed in that state until the user decides to move the chair to a different state. The manner in which chair  20  is controlled in order to achieve these different states will be described in greater detail below. 
       FIG. 3  shows various internal components of chair  20 , including a seat actuator  44 , a backrest actuator  46 , a leg rest actuator  48 , and a lift actuator  50 . Each of actuators  44 ,  46 ,  48 , and  50  are motorized linear actuators that are designed to linearly extend and retract under the control of a controller. Seat actuator  44  includes a stationary end  52  that is pivotally mounted to a chassis  54 . Seat actuator  44  further includes an extendible end  56  that is pivotally mounted to a seat frame  58 . When seat actuator  44  extends or retracts, extendible end  56  causes seat frame  58  to pivot about a seat pivot axis  60 . The extension of seat actuator  44  therefore causes seat frame  58  to tilt in such a manner that a forward end of seat  22  moves downward relative to a backward end of seat  22  (i.e. seat frame  58  will rotate in a counterclockwise direction as shown in  FIG. 3 ). The retraction of seat actuator  44  will, in contrast, cause seat frame  58  to tilt in the opposite manner (i.e. seat frame  58  will rotate in a clockwise direction as shown in  FIG. 3 ). 
     Backrest actuator  46  includes a stationary end  62  that is mounted to backrest  24  and an extendible end  64  that is mounted to seat frame  58 . The extension and retraction of backrest actuator  46  will therefore cause backrest  24  to pivot with respect to seat frame  58 . More specifically, when backrest actuator  46  extends, backrest  24  will rotate in a counterclockwise direction in  FIG. 3 . In contrast, when backrest actuator  46  retracts, backrest  24  will rotate in a clockwise direction in  FIG. 3 . Because backrest  24  is coupled to seat frame  58 , the rotation of seat frame  58  by seat actuator  44  will also cause backrest  24  to rotate with respect to the floor as seat frame  58  rotates. This rotation, however, will be independent of the rotation of backrest  24  caused by backrest actuator  46 . In other words, the relative angle between backrest  24  and seat  22  will only change when backrest actuator  46  is actuated (and not when seat actuator  44  extends or retracts while backrest actuator  46  does not change length). The angle of backrest  24  with respect to the floor (or another fixed reference), however, will change as seat frame  58  pivots about seat pivot axis  60 . 
     Leg rest actuator  48  includes a stationary end  66  that is mounted to seat frame  58  and an extendible end  68  that is mounted to leg rest  26 . The extension of leg rest actuator  48  therefore will pivot leg rest  26  from a retracted position (e.g.  FIG. 1 ) to an extended position, such as shown in  FIG. 3 . The physical construction of leg rest  26  may take on any of the forms disclosed in the commonly assigned U.S. patent application Ser. No. 14/212,253 mentioned above, whose disclosure is incorporated completely herein by reference. Other physical constructions of leg rest  26  are also possible. The extension and retraction of leg rest actuator  48  will change the orientation of leg rest  26  with respect to seat frame  58 . The orientation of leg rest  26  with respect to seat frame  58  will not change based on the extension or contraction of any other actuators  44 ,  46 , or  50 . The orientation of leg rest  26  with respect to the floor (or some other fixed reference), however, will change when seat frame  58  is pivoted about seat pivot axis  60  by seat actuator  44 . In summary, then, the pivoting of seat frame  58  about its pivot axis  60  will therefore change the orientations of all of seat  22 , backrest  24 , and leg rest  26  with respect to the floor (or other fixed reference), but will not, by itself, change the orientations of any of these components (seat  22 , backrest  24 , and leg rest  26 ) with respect to each other. 
     Lift actuator  50  includes a stationary end  70  that is coupled to a base  74  and an extendible end  72  that is coupled to an X-frame lift  76 . X-frame lift  76  includes two legs  78  that are pivotally coupled to each other about a center axis  79 . When lift actuator  50  extends or retracts, the relative angle between each of the legs  78  changes, which changes the overall height of X-frame lift  76 . Further, because chassis  54  is mounted on a top end of X-frame lift, the changing height of X-frame lift changes the height of chassis  54 . Lift actuator  50  therefore raises the height of chassis  54  when it extends and lowers the height of chassis  54  when it retracts. Because seat frame  58  is mounted (pivotally) on chassis  54 , and because backrest  24  and leg rest  26  are both mounted to seat frame  58 , raising and lowering the height of chassis  54  simultaneously raises and lowers the height of seat  22 , backrest  24 , and leg rest  26 . However, extending and retracting lift actuator  50  does not, by itself, change the angular orientations of any of leg rest  26 , backrest  24 , and/or seat  22 , either with respect to each other or with respect to the floor. 
     The operation and coordinated movement of actuators  44 - 50  is carried out via a control system  80 . One example of such a control system  80  is depicted in  FIG. 4 . Control system  80  includes a controller  82  that is in communication with seat actuator  44 , backrest actuator  46 , leg rest actuator  48  and lift actuator  50 . Controller  82  is further in communication with a right control panel  84   a , a left control panel  84   b , an occupant control panel  86 , a brake  88 , a sensor  90 , a safety mechanism  92 , an indicator  94 , an exit detection system  96 , and a memory  100 . Controller  82  is constructed of any electrical component, or group of electrical components, that are capable of carrying out the functions described herein. In many embodiments, controller  82  is microprocessor based, although not all such embodiments need include a microprocessor. In general, controller  82  includes any one or more microprocessors, microcontrollers, field programmable gate arrays, systems on a chip, volatile or nonvolatile memory, discrete circuitry, and/or other hardware, software, or firmware that is capable of carrying out the functions described herein, as would be known to one of ordinary skill in the art. Such components can be physically configured in any suitable manner, such as by mounting them to one or more circuit boards, or arranging them in other manners, whether combined into a single unit or distributed across multiple units. The instructions followed by controller  82  in carrying out the functions described herein, as well as the data necessary for carrying out these functions are stored in memory  100 . 
     In one embodiment, controller  82  communicates with individual circuit boards contained within each control panel  84   a ,  84   b , and  86  using an I-squared-C communications protocol. It will be understood that, in alternative embodiments, controller  82  could use alternative communications protocols for communicating with control panels  84   a ,  84   b , and/or  86  and/or with the other components of control system  80 . Such alternative communications protocols includes, but are not limited to, a Controller Area Network (CAN), a Local Interconnect Network (LIN), Firewire, one or more Ethernet switches, such as disclosed in commonly assigned, copending U.S. patent application Ser. No. 14/622,221 filed Feb. 13, 2015 by inventors Krishna Bhimavarapu et al. and entitled COMMUNICATION METHODS FOR PATIENT HANDLING DEVICES, the complete disclosure of which is incorporated herein by reference. Still other forms of communication are possible. 
     Sensor  90 , brake  88 , safety mechanism  92 , indicator  94 , and exit detection system  96  are described in greater detail in the aforementioned copending U.S. patent application Ser. No. 14/212,253 filed Mar. 14, 2014 and incorporated herein by reference. Accordingly, a detailed description of these components is not provided herein. In general, however, brake  88  is adapted to selectively brake and unbrake wheels  30  (prevent and allow both the swiveling and rotation of wheels  30 ) so that chair  20  may be moved to different locations. Indicator  94 , which may be a light or other device, provides a visual indication to a user of chair  20  when brake  88  is activated. Sensor  90  is adapted to detect when chair  20  is in motion and forward that information to controller  82 , which then automatically prevents brake  88  from braking wheels  30  while the chair  20  is in motion. This helps avoid damage to the brake  88  and/or sudden jerks to an occupant of chair  20 . Safety mechanism  92  is adapted to detect if an obstruction lies beneath a bottom edge of armrests  28  and prevent movement of armrests  28  when such an obstruction is present. Exit detection system  96  is adapted, when armed, to provide an audio and/or visual alarm when an occupant leaves chair  20 . 
     One embodiment of a control panel  84  is shown in greater detail in  FIG. 5 . Because right control panel  84   a  and left control panel  84   b  look the same and provide the same functionality, the following description of control panel  84  will apply to both control panels  84   a  and  84   b . Control panel  84  includes a plurality of controls  98   a - 98   i . In the embodiment shown in  FIG. 5 , each control  98  is a dedicated button that, when pushed, carries out a specific function (described below). In an alternative embodiment, controls  98  may be implemented as one or more areas on a touch screen that is incorporated into control panel  84  such that, when touched, the control  98  carries out the corresponding function. Other configurations are also possible. 
     In the embodiment shown in  FIG. 5 , control panel  84  includes a stand state control  98   a , a first upright state control  98   b , a second upright state control  98   c , a recline state control  98   d , a flat state control  98   e , a Trendelenburg state control  98   f , an arm/disarm control  98   g , a brake control  98   h , a patient lockout control  98   i , a lift up control  98   j , and a lift down control  98   k . When a user presses on any of state controls  98   a - f , controller  82  will activate the necessary ones of actuators  44 ,  46 ,  48 , and/or  50  to move the chair  20  to the corresponding state. That is, stand state control  98   a  will move chair to stand state  42 ; first upright state control  98   b  will move chair to first upright state  40 ; second upright state control  98   c  will move chair  20  to second upright state  38 ; recline state control  98   d  will move chair  20  to recline state  36 ; flat state control  98   e  will move chair  20  to flat state  34 ; and Trendelenburg state control  98   f  will move chair  20  to Trendelenburg state  32 . 
     In the embodiment illustrated in  FIG. 5 , a user must press on one of state controls  98   a - f  and continue to press on the corresponding state control  98   a - f  until the actuators bring chair  20  into the state corresponding to the pressed control. If the user stops pressing on the corresponding control  98  prior to the chair reaching the commanded state, controller  82  will cease movement of all of the actuators and chair  20  will stop in whatever position and orientation (i.e. state) it is currently in. Thus, for example, if a user wishes to change chair  20  to the stand state  42 , the user must press and hold stand state control  98   a  until actuators  44 ,  46 ,  48 , and  50  have finished moving seat  22 , backrest  24 , and leg rest  26  into the positions and orientations corresponding to stand state  42 . In an alternative embodiment, controller  82  may be modified such that pressing on one of state controls  98   a - f  and thereafter releasing the corresponding control will cause controller  82  to move the chair to the commanded state automatically without requiring the user to continue to press the corresponding state control  98   a - f.    
     When a user presses arm/disarm control  98   g , controller  82  toggles between arming and disarming exit detection system  96 . As noted, when exit detection system  96  is armed, controller  82  will issue an alert if an occupant leaves chair  20 . When disarmed, no such alarm will be issued when the occupant leaves chair  20 . 
     When a user presses brake control  98   h  ( FIG. 5 ), controller  82  will toggle brake  88  on and off. This toggling is carried out electrically by a powered brake actuator (not shown) under the control of controller  82 . Chair  20  may further include a plurality of brake pedals  104  (e.g.  FIG. 3 ) that are adapted to manually engage the brake  88  when pressed downwardly and manually disengage the brake  88  when lifted upwardly. This manual engagement and disengagement works in coordination with the electric activation and deactivation of the brake by controller  82  under the control of control panel  84 . That is, regardless of what state the brake is currently in (braked or unbraked), pressing on brake control  98   h  will electrically toggle the brakes to the other state, as well as physically move pedal  104  to the other state by moving it either up (brakes disengaged) or down (brakes engaged). Similarly, regardless of what state the brake is currently in, manually moving pedal  104  to its other position (either up or down) will manually change the state of the brakes. Still further, anytime brake control  98   h  is pressed for the first time after the state of the brakes was previously changed manually, controller  82  will automatically change the state of the brakes electrically. A user is therefore completely free to change the state of the brakes manually via pedals  104  or electrically via brake control  98   h  in any order or sequence. 
     When a user presses patient lockout control  98   i , controller  82  toggles between enabling and disabling occupant control panel  86 . When occupant control panel  86  is disabled, pressing on any of the controls thereon (e.g. buttons, knobs, switches, or the like) does not cause chair  20  to do anything. When occupant control panel  86  is enabled, pressing on any of the controls thereon will cause chair  20  to carry out the corresponding function of the control that has been pressed. In some embodiments, occupant control panel includes a smaller subset of controls than that shown on control panel  84  of  FIG. 5 . For example, in one embodiment, occupant control panel  86  includes upright state control  98   b , second upright state control  98   c , and recline state control  98   d , but does not include any of the other controls  98   a ,  98   e ,  98   f ,  98   g ,  98   h , or  98   i.    
     When a user presses on lift up control  98   j , controller  82  will cause lift actuator  50  to extend such that the height of seat  22  is raised. When a user presses on lift down control  98   k , controller  82  will cause lift actuator  50  to retract such that the height of seat  22  is lowered. This lifting or lowering of seat  22  via controls  98   j  and  98   k  will continue for as long as controls  98   j  or  98   k  are pressed, or until seat  22  reaches its upper or lower limits. 
     Control panel  84  further includes an exit icon  106   a  that is illuminated in a first manner when exit detection system  96  is armed and that is illuminated in a second and different manner when exit detection system  96  is disarmed. The difference between the first and second manners of illumination may take on a variety of different forms. In one embodiment, the first manner of illumination is brighter than the second manner. In another embodiment, the first manner of illumination is a different color than the second manner. In general, the second manner of illumination provides just enough illumination for a user to be able to see icon  106   a , but not so much so as to cause the user to believe that exit detection system  96  is armed. In contrast, the first manner of illumination provides illumination of a greater intensity and/or different color such that a user knows that exit detection system  96  is armed. 
     Control panel  84  also includes a brake enabled icon  106   b , a brake disabled icon  106   c , a patient control lockout enabled icon  106   d , and a patient control lockout disabled icon  106   e . Brake enabled icon  106   b  is illuminated when brake  88  is activated (either manually or electrically) and is not illuminated when brake  88  is deactivated. Brake disabled icon  106   c  is illuminated when brake  88  is deactivated (either manually or electrically), and is not illuminated when brake  88  is activated. Patient control lockout enabled icon  106   d  is illuminated when occupant control panel  86  is enabled, and is not illuminated when occupant control panel  86  is disabled. Patient control lockout disabled icon  106   e  is illuminated when occupant control panel  86  is disabled, and is not illuminated when occupant control panel  86  is enabled. 
     In an alternative embodiment, all of icons  106   b ,  106   c ,  106   d , and  106   e  remain illuminated regardless of the brake and patient lockout status, but simply change their manners of illumination based on the status of these two features. That is, similar to icon  106   a , each of icons  106   b - e  have at least two different manners of illumination, and controller  82  switches between these two based upon the brake status and the status of the occupant control panel  86  (enabled or disabled). In this manner, a user is always able to see all of icons  106   b - e  and is made aware of the status of corresponding to these icons by the differences in illumination between icons  106   b  and  106   c , and the differences in illumination between icons  106   d  and  106   e . Still other variations are possible. 
     Control panel  84  further includes a plurality of progress indicators  108  that are arranged in a curved line on control panel  84  ( FIG. 5 ). In the embodiment shown in  FIG. 5 , progress indicators  108  are light emitting diodes (LEDs). In alternative embodiments, progress indicators  108  may include one or more graphics on a display that change based on the movement of chair  20  through the states. Still other forms of indicators  108  are possible. Regardless of form, indicators  108  provide a visual indication to a user of the current state of chair  20 . That is, controller  82  changes which one of indicators  108  is illuminated based on the current state of chair  20 . For example, indicators  108  include indicators  108   a ,  108   b ,  108   c ,  108   d ,  108   e , and  108   f  that correspond to states  32 ,  34 ,  36 ,  38 ,  40 , and  42 , respectively. Whenever chair  20  is in one of these states ( 32 - 42 ), controller  82  will illuminate the indicator  108   a - f  that corresponds to that state. Further, as chair  20  moves between any of states  42 ,  40 ,  38 ,  36 ,  34 , and/or  32 , controller  82  will illuminate corresponding ones of indicators  108  that are in between indicators  108   a - f , thereby providing a user a visual indication of how far or near the chairs current state is from one of the six states  32 ,  34 ,  36 ,  38 ,  40 , and  43 . 
     For example, if chair  20  is currently in first upright state  40 , indicator  108   b —which is the indicator  108  that is closest to first upright state control  98   b  on control panel  84 —will be illuminated. All of the other indicators  108  will be unilluminated. If a user then presses, say, flat state control  98   e  in order to move chair  20  to flat state  34 , controller  82  will selectively turn on and turn off the indicators  108  as the chair progresses from first upright state  40  to flat state  34 . In other words, shortly after flat state control  98   e  is pressed and chair  20  has begun to move toward flat state  34 , controller  82  will turn off indicator  108   b  and turn on indicator  108   g . After chair  20  has moved an even greater amount toward flat state  34 , controller  82  will turn off indicator  108   g  and turn on indicator  108   h . This pattern of turning on and off indicators  108  will continue as chair  20  progresses toward flat state  34  such that when chair  20  finally reaches flat state  34 , indicator  108   e  will be illuminated, while none of the other indicators  108  will be illuminated. Controller  82  will therefore control the illumination of indicators  108  in a manner that provides a visual indication of what state chair  20  is currently in vis-a-vis the six states  32 ,  34 ,  36 ,  38 ,  40 , and  42 . 
     In the example above where chair  20  initially starts in first upright state  40  and is moved to flat state  34 , chair  20  will pass through second upright state  38  and recline state  36  before eventually reaching flat state  34 . This is because all of the six states  32 ,  34 ,  36 ,  38 ,  40 , and  42  are arranged sequentially and controller  82  is configured to coordinate the control of actuators  44 ,  46 ,  48 , and  50  such that chair  20  is only able to move from one state to another in the sequence defined on control panel  84 . That is, a user cannot move chair  20  from state  32  to state  42  without passing through states  34 ,  36 ,  38 , and  40 , and vice versa. Similarly, regardless of chair  20 &#39;s initial state, it will always move sequentially from its initial state to its final commanded state by moving through whatever intermediate states, if any, that lie between the initial and final states. In one embodiment, the movement of chair  20  through these intermediate states, if any, happens without pause or interruption. That is, controller  82  continues to move the appropriate actuators without stopping as the chair passes through any intermediate states. 
     However, in at least one embodiment, controller  82  is configured to pause for a brief moment whenever chair  20  passes through one of states  34 ,  36 ,  38 , or  40  while on its way to another state. Such pausing may also be accompanied by an aural indication to the user. The pausing and/or aural indication provides notification to the user that the chair has reached one of these intermediate states. Movement toward the final desired state will resume automatically after this short pause (so long as the user continues to press on the state control  98  that corresponds to the final desired state). 
     Controller  82  is further configured to automatically remove and/or disable one or more of the controls  98  on control panel  84  based upon the current state of chair  20 . That is, when chair  20  is in some states, it may be undesirable to allow a user to access certain functionality of chair  20 . Controller  82  will therefore disable and/or remove the controls  98  from control panel  84  corresponding to those functions when chair  20  is in the particular states for which such functions are not desired. For example, in one embodiment, controller  82  is configured to disable the exit detection system  96  whenever the chair is in the stand state  42 , flat state  34 , or Trendelenburg state  32 . Accordingly, in one embodiment, whenever chair  20  is in one of these three states, controller  82  will both disable and cease to illuminate arm/disarm control  98   g.    
     An example of this disabling and terminated illumination is shown in  FIG. 5A  where it can be seen that control  98   g  is no longer visible. Indeed, controller  82  has also ceased to provide any back illumination to the chair exit icon  106   a , thereby rendering it virtually invisible to a user. Were a user to press on control panel  84  in the area of arm/disarm control  98   g  while it was in the unilluminated state of  FIG. 5A , controller  82  would take no action in response. That is, turning on the exit detection system  96  while the chair is in any one of the stand state  42 , flat state  34 , or Trendelenburg state  32  is not possible. By removing the back illumination for arm/disarm control  98   g  and chair exit icon  106   a , a user will know that this function is disabled. This helps avoid the possibility—which could happen if control  98   g  and/or icon  106   a  were to remain illuminated in any of these states—of the user attempting to turn on the exit detection and becoming frustrated that this functionality appeared to be broken in these states, when in fact this functionality had been deliberately disabled in these states. 
     Another example of the automatic disabling of a function and the visual removal of its corresponding control  98  from control panel  84  is the lift up and lift down controls  98   j  and  98   k , respectively. In one embodiment, chair  20  is configured such that the height of chair  20  cannot be changed by controls  98   j  and  98   k  when chair  20  is in certain states. Specifically, in one embodiment, controller  82  disables controls  98   j  and  98   k , as well as turns off the illumination of these controls on control panel  84 , whenever chair  20  is in the Trendelenburg state  32  or the stand state  42 .  FIG. 5A  illustrates how control panel  84  appears when chair  20  is in either of these states. As can be seen in  FIG. 5A , lift up and lift down controls  98   j  and  98   k  have disappeared from view on control panel  84 . This is accomplished by controller  82  ceasing to provide back illumination for these controls. In addition to removing this back illumination, controller  82  has also disabled these controls such that, were a user to press on the areas of control panel  84  where controls  98   j  and  98   k  otherwise appear, controller  82  will take no action. Thus, whenever chair  20  is in the Trendelenburg state  32  or stand state  42 , a user cannot adjust the height of chair  20  via controls  98   j  and  98   k.    
     It will be understood that, in other embodiments, different ones of controls  98  may be automatically disabled than the ones described above when chair  20  is in one or more specific states. Further, the specific states in which exit detection system  96  and lift controls  98   j  and  98   k  are disabled may be varied from the states described above. Still other variations are possible. 
     Control panel  84  shown in  FIGS. 5 and 5A  is constructed, in one embodiment, in the same manner as the control panel described in commonly assigned, copending application Ser. No. 14/282,383 filed May 20, 2014 by applicants Christopher Hopper et al. and entitled THERMAL CONTROL SYSTEM, the complete disclosure of which is incorporated herein by reference. When constructed in this manner, the background of control panel  84  is generally black and when controller  82  ceases to provide back illumination to any one of controls  98  (e.g.  98 ,  98   j , and/or  98   k ) or icons  106  (e.g.  106   a ), the lack of back illumination causes the area of the control  98  or icon  106  to appear black, thereby blending in with the adjacent black background of the control panel and making the control  98  or icon  106  virtually, if not completely, invisible. 
     In other embodiments, control panel  84  may be physically constructed to include, or to be made entirely of, a liquid crystal display, or other type of display that is capable of selectively displaying one or more graphics thereon. When constructed in this manner, the display is preferably incorporated into a touch screen configuration such that pressing on different areas of the screen will cause controller  82  to react accordingly. When control panel  84  is constructed in this manner, controller  82  disables a selected function in certain states by simply ceasing to display the graphic corresponding to that function and ignoring any pressing by the user on the area of the touch screen that is otherwise aligned with the graphic for that function. 
       FIGS. 6, 7, 8, 9, 10, and 11  illustrate in greater detail chair  20  in each of the states  32 ,  34 ,  36 ,  38 ,  40 , and  42 , respectively. As with  FIG. 2 , one of the armrests  28  has been removed in order to provide a clear view of the interior of chair  20  and its internal structure in each of these states. 
       FIG. 12  shows four charts  110  that graph the seat  22  angles, the backrest  24  angles, the leg rest  26  angles, and the seat  22  height in each of the six different states  32 ,  34 ,  36 ,  38 ,  40 , and  42 . More specifically, chart  110   a  shows the angles of backrest  24  (with respect to horizontal) for each of the six states  32 - 42 , as well as the angles of backrest  24  between each of these six states  32 - 42 . Chart  110   b  shows the angles of seat  22  (with respect to horizontal) for each of the six states  32 - 42 , as well as the angles of seat  22  between each of these six states. Chart  110   c  shows the angles of leg rest  26  (with respect to horizontal) for each of the six states  32 - 42 , as well as the angles of leg rest  26  between each of these six states  32 - 42 . Finally, chart  110   d  shows the height in inches (measured from the floor on which chair  20  is positioned) of seat  22  for each of the six states  32 - 42 , as well as the height of seat  22  between each of these six states. 
       FIG. 13  shows four charts  112  that graph the position of the four actuators  44 ,  46 ,  48 , and  50  in each of the six states  32 - 42 , as well as in between each of these states. More specifically, chart  112   a  shows the position of backrest actuator  46  in each of the six states  32 - 42 , as well as its position in between these states. Chart  112   b  shows the position of seat actuator  44  in each of the six states  32 - 42 , as well as its position in between these states. Chart  112   c  shows the position of leg rest actuator  48  in each of the six states  32 - 43 , as well as its position in between these states. And chart  112   d  shows the position of lift actuator  50  in each of the six states  32 - 42 , as well as its position in between these states. 
     With specific reference to lift actuator  50  and its height and position information shown in charts  110   d  and  112   d , respectively, it can be seen that no height or position information is shown between recline state  36  and first upright state  40 . This is because lift actuator  50  does not have a controlled height or position in the second upright state  38 . That is, controller  82  does not power lift actuator  50  when moving from first upright state  40  to second upright state  38 , nor does controller  82  power lift actuator  50  when moving from recline state  36  to second upright state  38 . Instead, whatever position lift actuator  50  is currently in when chair  20  starts out from either first upright state  40  or recline state  36 , controller  82  leaves it in that position when moving to second upright state  38 . 
     As can been seen from  FIG. 14 , lift actuator  50  is also independently movable by a user between the limits shown in the graph of  FIG. 14  whenever chair  20  is in the flat, recline, second upright, or first upright states  34 ,  36 ,  38 , and  40 , respectively. For example, as shown in  FIG. 14 , when chair  20  is in the recline state  36 , a user is free to change the height of seat  22  (by pressing on controls  98   j ,  98   k , or the height controls on occupant control panel  86 ) to any height that is within the range of about 17.5 inches to 25 inches above the floor. Although a user is free to adjust the height of seat  22  within the ranges shown in  FIG. 14 , controller  82  will control lift actuator  50  so that it attempts to reach the target heights for the Trendelenburg state  32 , the flat state  34 , and the stand state  42  shown in chart  110   d  ( FIG. 12 ) whenever chair  20  is moved to any of these states. Further, controller  82  will control lift actuator  50  so that it attempts to reach the target height for the recline state  36  shown in chart  110   d  when chair  20  starts from any state to the left of recline state  36  in chart  110   d . Finally, controller  82  will control lift actuator  50  so that it attempts to reach the target height for first upright state  40  shown in chart  110   d  when chair  20  starts from any state to the right of first upright state  40  in chart  110   d.    
     Each actuator  44 ,  46 ,  48 , and  50  includes an internal position sensor that sends a signal to controller  82  that is indicative of its current position. Controller  82  uses these position signals as feedback signals in the control of actuators  44 ,  46 ,  48 , and  50 . That is, controller  82  controls each of actuators  44 ,  46 ,  48 , and  50  in a closed-loop manner based upon the position feedback signals coming from actuators  44 ,  46 ,  48 , and  50 . 
     Controller  82  uses one of the pre-defined positions of states  32 ,  34 ,  36 ,  38 ,  40 , and  42  as the target values for controlling actuators  44 ,  46 ,  48 , and  50 . More specifically, chair  20  has stored in memory  100  the desired positions of each of actuators  44 - 50  for each of the six states  32 - 42 . Whenever chair  20  is commanded by a user to move from its current position to a different one of these six states, controller  82  will use the stored position information for whichever one of states  32 - 42  is the next state in the sequence of states that leads to the final desired state as the target positions in the closed-loop control of each of the actuators  44 - 50 . 
     For example, if chair  20  is initially in flat state  34  and a user presses on stand state control  98   a , controller  82  will first retrieve from memory  100  the positions of each actuator  44 - 50  that correspond to recline state  36 . Controller  82  choses the positions of recline state  36  because recline state  36  is the first one of the six states in the sequence of states between flat state  34  (chair  20 &#39;s initial state) and stand state  42  (chair  20 &#39;s final desired state in this example). Once the positions of each actuator  44 - 50  for recline state  36  are retrieved, controller  82  uses these positions as the target positions for moving each of the actuators  44 - 50 . Thus, with specific reference to backrest actuator  46 , controller  82  selects a position of approximately 15 inches as its target position (see chart  112   a  of  FIG. 13  and the value of backrest actuator  46  for the recline state  36 ). Controller  82  then controls backrest actuator  46  so that it extends from the approximately 12.5 inches of its current initial position (flat state  34 ) to the 15 inches corresponding to recline state  36 . Controller  82  does the same for each of the other actuators using the positions shown in charts  112   a ,  112   c , and  112   d  of  FIG. 13 . 
     As will be described in more detail below, controller  82  controls each of actuators  44 - 50  such that they all arrive at recline state  36  simultaneously, or substantially simultaneously. After each of the actuators  44 - 50  reaches recline state  36 , controller  82  then retrieves the position values for each of the actuators  44 - 50  that correspond to the next one of the six states in the sequence of movement. Thus, in this example, where the final desired state is stand state  42 , controller  82  then retrieves the position values for second upright state  38 . Once these are retrieved, controller  82  controls each of the actuators  44 - 50  such that they simultaneously arrive at each of their positions that correspond to second upright state  38 . Thereafter, controller  82  proceeds in a similar manner and moves each of the actuators  44 - 50  toward their positions that correspond to first upright state  40 . Finally, after the actuators have arrived at their positions for first upright state  40 , controller  82  retrieves from memory  100  the values corresponding to stand state  42  and moves the actuators to these values. This movement, as with all movement to one of the six states  32 - 42 , is coordinated by controller  82  such that all of the actuators stop at the desired state (stand state  42  in this example) simultaneously, or substantially simultaneously. The phrase “substantially simultaneously” refers to arrivals that are not precisely simultaneously, but are not otherwise readily discernable by a user as occurring at separate times. 
     Because controller  82  moves actuators  44 - 50  toward the positions corresponding to each of the six states  32 - 42 , controller  82  does not store in memory the positions identified in  FIG. 13  that are between these six states. Thus, for example, controller  82  does not store point A in chart  112   a  of  FIG. 13  and does not ever utilize point A as a target value for backrest actuator  46 . This can be better understood by way of an example. Suppose, for instance, that chair  20  initially starts in a position where backrest actuator  46  has the value defined by point B. Suppose further that a user presses on flat state control  98   e . Controller  82  will not, in that case, attempt to control backrest actuator  46  such that it follows a path from point B to point A, and then from point A to point C ( FIG. 13 ). Instead, controller  82  will control backrest actuator  46  such that it follows a path directly from point B to point C (where point C corresponds to flat state  34 ). Similarly, if backrest actuator  46  starts out at point B and a user presses recline state control  98   d , controller  82  will control actuator  46  such that it follows a path directly from point B to point D (the point corresponding to the recline state), rather than a path from point B to point A, and then from point A to point D. Thus, not only for backrest actuator  46 , but for all of the actuators  44 - 50 , controller  82  moves them such that they are directed toward whatever one of the six states is next in the sequence of states between their initial position and their final user-chosen position. 
     As was noted earlier, controller  82  controls each of the actuators  44 - 50  such that they all arrive simultaneously at each of the six states  32 - 42  on their journey from their current initial position to their final user-chosen position (with the sole exception of the lift actuator which, as noted, does not have a target position and is therefore not moved for certain states, such as the second upright state  38 ). Thus, for example, if chair  20  is initially in Trend state  32  and a user presses on stand state control  98   a , controller  82  will moves each of the actuators  44 - 50  in a manner such that they all simultaneously (or substantially simultaneously) arrive first at flat state  34 . Controller  82  will then continue to move actuators  44 - 50  such that they all simultaneously arrive at recline state  36 . Controller  82  will continue in this manner to move actuators  44 - 50  such that they all arrive simultaneously at second upright state  38  (except for lift actuator  50  which does not change position between recline state  36  and second upright state  38 ), and then all arrive simultaneously at first upright state  40  (with the exception again of lift actuator  50 ), and then all arrive simultaneously at stand state  42 . 
     In one embodiment, the manner in which controller  82  achieves this simultaneous arrival is accomplished as follows. Whenever a user presses on a state control  98   a - g , controller  82  identifies which one of the six states  32 - 42  is the first one that chair  20  will proceed to on its journey to the user-chosen final state. Once that first state is identified, controller  82  compares the current position of each of the actuators  44 - 50  with the desired positions for each of the actuators corresponding to that first state. Controller  82  then identifies as a pacing actuator whichever one of the actuators  44 - 50  has the greatest difference between its current position and its desired position at the first state. Controller  82  then determines the ratio of the distances the other actuators (the non-pacing actuators) have to travel to the first state compared to the distance that the pacing actuator has to travel to this first state. Thus, for example, if backrest actuator  46  is the pacing actuator and it has to move  120  units to the first state and seat actuator  44  has to move thirty units to the first state, controller  82  will calculate a ratio of 0.25 ( 30/120=0.25). Controller  82  will do a similar ratio calculation for the other two non-pacing actuators (leg rest and lift, in this example). 
     Once all of the ratios are determined, controller  82  controls the pacing actuator such that it moves at a first speed, and controls the other non-pacing actuators to move at speeds that are equal to the first speed multiplied by the calculated ratios. Thus, in the example above, controller  82  sends control signals to the seat actuator  44  to move at a speed equal to one fourth of the commanded speed of the pacing actuator. Further, as noted above, controller  82  uses feedback during the movement of the actuators  44 - 50 . Consequently, controller  82  will repetitively re-calculate the distances of each of the actuators from their desired first state positions, re-calculate the ratios, and send out revised speed commands, if necessary, to ensure that the actuators arrive at the first state substantially simultaneously. 
     Once the actuators arrive at the first state, controller  82  will repeat the same procedure for moving chair  20  to the second state (assuming that the first state is not the user-chosen final state). In repeating this procedure, controller  82  may or may not choose the same actuator as the pacing actuator that is chosen for movement to the first state. The selection of the pacing actuator for movement to the second state is based on the actuator having the greatest distance to travel from the first state to the second state, which may or may not be the same actuator that had the greatest distance to travel from the initial state to the first state. Once the pacing actuator is chosen for movement to the second state, the distance ratios for the other actuators are computed and used for generating speed commands. 
     In some cases, due to the feedback received by controller  82  from each of the actuators  44 - 50 , the selection of which of the four actuators  44 - 50  is the pacing actuator for movement to the next state may change before chair  20  arrives at that next state. This can happen, for example, if one of the non-pacing actuators ends up moving slower than commanded (due to, for example, excessive loading) such that its distance to the next state ends up surpassing the pacing actuator&#39;s distance to the next state at some point during the movement to that next state. 
       FIG. 15  illustrates one manner in which backrest  24  may be joined to seat  22 . More specifically,  FIG. 15  illustrates one embodiment of a backrest frame  113  pivotally coupled to seat frame  58 . Seat frame  58  is pivotally coupled to backrest frame  113  by a pair of links  114  that are joined to each other by way of a crossbar  115 . Crossbar  115  helps with stabilizing the pivotal connection of backrest frame  113  to seat frame  58 . Each link  114  has a first end  116  that is pivotally coupled to seat frame  58  and a second end  118  that is pivotally coupled to backrest frame  113 . The pivotal coupling at first end  116  defines a first pivot axis  120  and the pivotal coupling at second ends  118  defines a second pivot axis  122 . As will be discussed in greater detail below, seat frame  58  pivots about axes  120  and  122  (sometimes simultaneously and sometimes individually) as backrest  24  pivots with respect to respect to seat  22 . 
     Seat frame  58  further includes a pair of channels  124  defined in it that are positioned adjacent a rear end of either side of seat frame  58 . A roller  126  that is rollingly mounted to a backrest bracket  128  rides in each of channels  124  as backrest frame  113  pivots with respect to seat frame  58  ( FIG. 16 ). The shape of channel  124  guides the movement of each roller  126  during pivoting of backrest frame  113  with respect to seat frame  58 , which in turn determines when and to what extent backrest frame  113  pivots about first pivot axis  120  relative to second pivot axis  122 , as will be discussed below in greater detail with respect to  FIG. 16 . 
     As shown in  FIG. 16 , channel  124  includes a generally upright upper portion  130  and a generally arcuate lower portion  132 . When roller  126  is in the generally upright upper portion  130 , the sides of channel  124  constrain roller  126  from left-to-right movement (as viewed in  FIG. 16 ). This constraining of roller  126  against left-to-right movement in  FIG. 16  while positioned in upper portion  130  prevents backrest frame  113  from pivoting about second pivot axis  122 . However, when roller  126  is positioned in the generally upright upper portion  130  of channel  124 , it is free to move in a generally up and down direction. This vertical freedom of movement permits backrest frame  113  to pivot with respect to seat frame  58  about first pivot axis  120 . 
     As backrest frame  113  tilts backwardly from an initially upright position toward a more reclined position, roller  126  moves from upper portion  130  toward lower portion  132 . As roller  126  moves closer to lower portion  132 , the side-to-side movement constraints (as viewed in  FIG. 16 ) on roller  126  in channel  124  become more relaxed, thereby permitting backrest frame  113  to start pivoting more and more about second pivot axis  122 . When roller  126  eventually reaches lower portion  132 , backrest frame  113  will pivot exclusively about second pivot axis  122  and cease to pivot about first pivot axis  120 . This exclusive pivoting about second pivot axis  122  is due to the shape of lower portion  132 , which has a curve that is coaxial with respect to second pivot axis  122  (as viewed in  FIG. 16 ). 
     In summary, when reclining backrest frame  113  from an initially upright position to a fully reclined position, backrest frame  113  initially pivots backward about first pivot axis  120  for a first angular range, then begins to pivot simultaneously about both first and second pivot axes  120  and  122  for a second angular range, and finally pivots exclusively about second pivot axis  122  for a third angular range. The relative amount of pivoting of backrest frame  113  about each of axes  120  and  122  during the second angular range is not static, but changes as the backrest pivots. This change in the location of the pivot axis/axes when backrest frame  113  pivots with respect to seat frame  58  helps to reduce the shear forces that are created between chair  20  and the back and buttocks of an occupant of chair  20  as backrest frame  113  pivots. This, in turn, alleviates the discomfort experienced by a patient during pivoting of backrest  24  and/or the need of a patient to re-position himself or herself on chair  20  during pivoting of backrest  24 . 
     Various additional alterations and changes beyond those already mentioned herein can be made to the above-described embodiments. This disclosure is presented for illustrative purposes and should not be interpreted as an exhaustive description of all embodiments or to limit the scope of the claims to the specific elements illustrated or described in connection with these embodiments. For example, and without limitation, any individual element(s) of the described embodiments may be replaced by alternative elements that provide substantially similar functionality or otherwise provide adequate operation. This includes, for example, presently known alternative elements, such as those that might be currently known to one skilled in the art, and alternative elements that may be developed in the future, such as those that one skilled in the art might, upon development, recognize as an alternative. Any reference to claim elements in the singular, for example, using the articles “a,” “an,” “the” or “said,” is not to be construed as limiting the element to the singular.