Abstract:
A wheelchair is provided, having a recline mechanism for the chair back and wherein the seat is repositioned forward in response to recline to reposition the user&#39;s weight relative to the supporting wheels. The chair is also independently equipped with a weight-shifting tilt mechanism. Moreover, a bilateral tracking mechanism (i.e., controlled motion is transmitted to both sides) is used to reposition the seat. This avoids torque due to uneven loading of the chair. Back canes of the chair and/or brackets on the chair back are slotted to enable infinite adjustment of chair arms, ventilator trays, and other accessories.

Description:
FIELD OF THE INVENTION 
     The invention relates to wheelchair seats, and in particular to a reclining and tilting wheelchair seat. The invention also relates to a reclining and tilting wheelchair seat having weight-shifting capability for maintaining the stability of an occupied chair during these repositioning actions. This is accomplished by minimizing the change in the center of gravity of the occupant of the wheelchair relative to the wheelchair supporting chassis. Further, the wheelchair utilizes a bilateral linkage with a single linear actuator to synchronize the forward movement of the seat relative to the base during recline in order to achieve weight-shift. This linkage also keeps the back from torquing in response to uneven loading. Further, the wheelchair has both weight-shift recline and weight-shift tilt features. Wheelchair canes are provided which permit infinite height adjustment for accessories by providing a longitudinal mounting slot. 
     BACKGROUND OF THE INVENTION 
     The market for wheelchairs is constantly changing. As the average age of the world&#39;s population continues to increase due to advances in health care, so does the need for health care appliances such as wheelchairs to serve an aging population. Further, the health care industry constantly strives to address the needs of individuals disabled by trauma and illness. While some wheelchair users may have their needs met by basic, manually operated chairs, many other wheelchair users require chairs with increasing numbers of features including electrical locomotion, shock absorption, and more comfortable seating. 
     Advances in seating have included features such as upholstered seats, tilting seats and reclining seats. However, features such as tilting and reclining seats, while desirable, can also be problematic. More specifically, when the seat of an occupied wheelchair is tilted or reclined, the center of gravity of the occupant of the chair relative to the wheelchair supporting chassis changes. In many cases the occupant is unable to reposition himself or herself so as to compensate for these changes. Although prior art wheelchairs have addressed the problem of changing center of gravity for a tilting-seat, similar problems associated with reclining seats have proven more difficult to overcome. 
     Prior art wheelchairs have attempted to solve the changing center of gravity problem upon seat recline, primarily in one of two ways. One common way to attempt to solve this problem has been to locate the wheelchair seat forward relative to the chassis of the chair. Thus, when the occupied seat is reclined by the occupant, the risk of the entire wheelchair overturning in a rearward direction is minimized. However, locating the seat toward the front of the wheelchair places too much weight on the front casters of the chair, thereby lowering the efficiency of the wheelchair motor and making it more difficult to maneuver. 
     An alternate prior art mode of solving the foregoing problem has been to increase the front-to-back length of the supporting chassis of the wheelchair, and locating the seat generally in the center of that chassis. Such a structure overcomes both problems associated with locating the chair toward the front of the wheelchair chassis as described immediately above. That is, the front casters of the wheelchair are free of undue loading, and upon recline of the chair seat the rear portion of the elongated chassis prevents rearward tipping of the chair. However, such a solution causes other problems. More particularly, providing an elongated chassis on the wheelchair adds unwanted weight and expense to the chair. Moreover, the elongated chassis, due to its added weight, requires more powerful and expensive motors to move the chair. Also, such an elongated chassis causes some loss of maneuverability of the wheelchair, such as in tight spots like an entryway, when compared to wheelchairs having a more compact chassis. 
     SUMMARY OF THE INVENTION 
     Objectives of the present invention include providing a reclining seat for a wheelchair, in which the center of gravity of the occupant of the chair shifts in a frontward direction relative to the chassis of the chair to maintain the stability of the wheelchair chair as the seat reclines. The invention relates to “weight shift” which is used herein to mean the repositioning of the chair members in order to maintain a relatively constant center of gravity of a hypothetical chair occupant and in turn to maintain the stability of the chair. The object of maintaining the stability of the wheelchair upon recline is met by providing a mechanism for shifting the chair seat forward in response to a backward recline of the seat back. More specifically, a curved link is provided which is connected to the back portion of the seat back and which retracts the seat back about an axis offset vertically upward from the rearward bottom edge of the seat cushion. A single linear actuator acts upon a lateral tie bar extending across the length of the seat and includes a toothed gear which engages a rack below the seat cushion to bilaterally transmit the motion of the actuator to both lateral edges of the seat cushion during the forward shifting. This bilateral effect inhibits torque which could result from uneven loading while minimizing the expense of the actuator. 
     Another objective of the present invention is to provide such a reclining seat for a wheelchair, in which the seat can optionally be capable of tilting. The tilting aspect is also provided with weight-shift capabilities in order to maintain the center of gravity of the occupant of the chair with regard to the supporting chassis. 
     This is accomplished by shifting the seat forward as the seat back and seat bottom are tilted relative to the supporting chassis. It is within the scope of the invention to provide for a rearward and/or sideways shifting of the seat relative to the chassis if this is necessary to maintain the stability of the chair. Further, the weight-shifting, tilt option is provided along, but independent of, a weight-shift, recline option. 
     An additional object of the invention is to provide stiffer wheelchair canes having a longitudinal slot which give the ability to mount accessories such as a ventilator tray or handles with infinite height adjustment while eliminating traditional double half clamps. 
     A further objective of the present invention is to provide a reclining seat for a wheelchair, which is relatively inexpensive to manufacture and maintain, relatively lightweight, and durable and reliable in use. 
     These objectives and advantages are obtained by the weight-shifting reclining wheelchair seat of the present invention, the general nature of which may be stated as including a reclinable back which desirably includes a back-shear feature; and a seat base frame which is projected forward an appropriate amount as the seat back is reclined. The recline mechanism may include a power actuator and a controller having a user interface. Further, the chair may include an independent seat tilt mechanism which preferably also includes a weight shift feature so as to stabilize the wheelchair during use. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The preferred embodiment of the invention, illustrative of the best mode in which applicants have contemplated applying the principles, is set forth in the following description and is shown in the drawings and is particularly and distinctly pointed out and set forth in the appendede claims. 
     FIG. 1 is a perspective view of one type of wheelchair on which the weight-shifting, reclining seat of the present invention can be utilized; 
     FIG. 2 is a right-elevation view of the wheelchair of FIG. 1; 
     FIG. 3 is an enlarged top plan view of the seat bottom, with hidden parts represented by broken lines, and with the seat bottom upholstery removed, showing the manner of operative connection of the seat bottom to the chair chassis; 
     FIG. 4 is a fragmentary right-elevation view of the seat bottom shown in FIG. 3 with portions in section, and further showing a seat back operatively connected to the seat bottom and in a fully upright position. 
     FIG. 5 is an enlarged view similar to FIG. 4 showing the seat back in an initial position. 
     FIG. 6 is a view similar to FIG. 5, but showing the seat back in a first partially reclined position. 
     FIG. 7 is a view similar to FIGS. 5 and 6, but showing the seat back in a second partially reclined position. 
     FIG. 8 is a view similar to FIGS. 5 through 7, but showing the seat back in a fully reclined position. 
     FIG. 9 is a view similar to FIGS. 5 through 7, but showing the manner in which the wheelchair seat of the present invention can be optionally tilted. 
    
    
     Similar numerals refer to similar parts throughout the drawings. 
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     It is understood that weight-shifting reclining wheelchair seat of the present invention can be used in other applications or environments besides a wheelchair without affecting the overall concept of the present invention. These other applications or environments include but are not limited to seat recline applications. 
     The invention is illustrated with a basic power wheelchair  10 , which includes a chassis  11  having a pair of drive wheels  13 , and a pair of front casters  15 , and a pair of rear anti-tip assemblies  16 . A carriage frame  18  is supported by the various wheels. The chassis optionally includes intermediate suspension structure. The recline mechanism of the present invention is shown with respect to a power wheelchair having a drive motor  14 , but it should be understood that the mechanism could also be used for a manual wheelchair. 
     The carriage frame  18  includes on either side a pivot assembly  21 , which supports a rectangular chair seat frame  22 . The seat frame  22  has a front member  23 , a rear member  24 , and opposing side member  25  which are operatively connected to pivot assembly  21 , which comprises pivot links  26  extending upward at pivot points  27  carried on the carriage  18 . In accordance with the recline mechanism of the present invention, the seat frame  22  can be longitudinally displaced relative to the pivot assembly  21 . 
     Each drive wheel  13  is powered respectively by one of a pair of motors  14  mounted on chassis  11  adjacent to and operatively connected to its respective drive wheel. A pair of caster wheels  15  each is rotatably and movably mounted on a front end of chassis  11  forwardly of drive wheels  13 . A pair of spaced-apart, anti-tip wheels  16 , of a type which is well known to those skilled in the wheelchair art, each is movably mounted on a rear end of chassis  11  rearwardly of drive wheels  13 . It is understood that wheelchair shown and described to this point commonly is referred to as a rear-wheel drive wheelchair due to the location of the axis of the drive wheels  13  generally behind the center of gravity of the wheelchair when it is occupied and being operated. However, it is further understood that seat  12  could be utilized on what are conventionally referred to as front and mid-wheel drive wheelchairs without affecting the overall concept of the present invention. 
     As seen in FIGS. 5 through 8, on both sides of the chair, a C-shaped link  44  is connected to the chair canes  40  by means of a rear bracket  45 . The other end of the link  44  is pivotally mounted to tie member  46 . The seat frame  22  includes an inner-assembly  60  having opposing racks  61 , which are united by means of the tie member  46  for controlled forward and rearward engagement by a series of toothed gears  63  (i.e., two on either side). The actuator  35  driven by motor  31  acts by means of the inner assembly  60  to drive tie member  46  forward which both causes recline of the seat back shown in FIGS. 6,  7  and  8 , and causes the seat to travel forward to cause weight shift during recline. 
     Tilt is the action of the seat back and bottom rotating relative to the chassis while maintaining a constant angle between the seat back and bottom. The present invention provides for tilt independently of recline (i.e., the rotation of the seat back relative to the seat bottom). Further, the present invention addresses the change in the center of gravity of a hypothetical user (an individual who is of average height and weight) during repositioning of the seat or seat components. 
     The tilt mechanism is accomplished using a three-bar linkage where one side has a variable length. Two such linkages are used on either side of the seat frame. Further, one of the links is defined by two members having a fixed angle there between. The first link  28  extends between the seat frame  22  and a laterally extending bracket  32  (including parallel mount plates  34  and a pivot point  29  fixed to the carriage frame  18 ,) which enables the seat frame member to be slid longitudinally forward in response to the movement of a second linear actuator  30  driven by motor  33  so as to provide the weight-shift feature. The second link is defined by a portion of the seat frame  22  and the rear pivot link  26  which is at a fixed angle relative to the seat frame  22 . Pivot link  26  is a member of the pivot assembly  21  also including pivot point  27 . The third bar of the linkage includes a linear actuator  30  which provides for a variable length. The actuator  30  is pivotally mounted at one end to the bracket  32  at point  53 , and at its other end to a point  83  which is part of a slide assembly  80 . The slide assembly  80  further includes a rectangular frame having a rear bar  81  and lateral side members  82  which are carried on rails  84  by means of ball bearing containing mounts  85 . A front bar  86  extends from a first mount  85  on a first side member  82  to the opposing mount  85  on the second side member  82 . The pivot assembly  21  is carried on the front bar  86 . Thus, the third link would extend between the pivot point  53  and the pivot point  83 . 
     The seat back support members or canes  92  are pivotally supported by back brackets  41 , which extend at a 90° angle relative to the seat frame at an axis offset from the rear edge of the seat. This hinge connection  42  provides for pivoting of the back canes relative to the seat frame at an axis offset from the rear edge of the seat. This vertical offset (i.e., a distance from the seat base) is meant to provide more anatomically correct pivoting action. Further, the chair is provided with a back-shear assembly  50 , which permits readjustment of the chair back rest  51  relative to the chair seat during recline in order to avoid frictional forces to which the user&#39;s back would be otherwise subjected, and to help reduce the possibility of back sores which stress and friction could cause. 
     In this case, the canes  92  carry a slide mounted  52  (see FIG. 8) back rest  51 , which may include a linear actuator (see FIG.  4 ), such as a ball screw, to actuate the seat back relative to the chair seat. Alternatively, other means of actuator may be used. Thus, as the chair seat is slid longitudinally forward, the seat back may be slid longitudinally downwardly to accommodate the relative change in a person&#39;s back relative to the chair back. Further, a microprocessor may be used to control the linear actuator for the back-shear to link the relative position of the back to the seat as it is pushed forward during recline. Alternatively, other mechanical linking means can be used. 
     The chair further includes arm rest  64  which are pivotally linked to the back and seat bottom to permit repositioning of the arm rests  64  in response to recline. 
     Further, the back canes  40  are slotted along their longitudinal axis to permit infinite adjustment of rear handles or the like. 
     Back support  50  comprises a pair of upright lateral supports  92  which include an extension or bracket member  94  having one or more longitudinal slot  95  which will accommodate an accessory such as a lateral stabilizer  96  a push handle, or a ventilation tray. 
     This provides for infinite vertical adjustment of the accessory relative to the back. 
     While in accordance with the patent statutes the best mode and preferred embodiment have been set forth, the scope of the invention is not limited thereto, but rather by the scope of the attached claims.