Patent Publication Number: US-7585019-B2

Title: Seat reclining mechanism for power wheelchair

Description:
BACKGROUND OF THE INVENTION 
   1. Technical Field 
   The present invention relates to seats of power wheelchairs, and more particularly, to a seat reclining mechanism for a power wheelchair. 
   2. Description of Related Art 
   Power wheelchairs, such as electric wheelchairs or motorized wheelchairs are mobility assistive devices commonly provided to disabled people or bed-bound patients for allowing them to move self-reliantly. Thus, good adaptability and maneuverability are obviously important in wheelchairs. For meeting such need, some wheelchairs may be equipped with reclining chairs for providing the users with comfortable and convenient usage. 
   As everyone knows, a chair is basically composed of a seat portion and a back portion, which is settled roughly perpendicular to the seat portion. A pair of arm rests and footrests may be also attached for the user&#39;s comfort. Further, the seat is preferable to possess position angle variability for providing convenience to the user for his movement between the wheelchair and a bed under or without others&#39; assistance. Thus, it is desirable that a seat of a wheelchair can be reclined into a flat shape. To form such flat shape, the back portion has to perform a pivot motion with about a 90-degree pivot angle and the arm rests as well as footrests have to move toward an altitude approximately close to the seat. 
   Since the center-of-gravity position of a human body can consequently shift from hips toward the lumbar and back regions during reclining, person sitting on a reclining chair designed without consideration of gravity adjustment may fall down therefrom during operation of the reclining mechanism. Thus, a need exists for a seat reclining mechanism, which is capable of reclining the back portion and shifting the seat portion thereof in harmony with the center-of-gravity position of the wheelchair it is attached to synchronously. 
   SUMMARY OF THE INVENTION 
   The present invention has been accomplished under the circumstances in view and provides a seat reclining mechanism comprising an actuator and a plurality of linkages mechanistically connected mutually. 
   It is one object of the present invention to provide a seat reclining mechanism for a power wheelchair which can be adjusted from an initial seat position to a reclined flat position to provide a horizontal carrying surface for facilitating a user&#39;s riding or alighting from the wheelchair. 
   It is another object of the present invention to provide a seat reclining mechanism for a power wheelchair, which keeps the center-of-gravity positions of both the wheelchair user and the wheelchair coincided through the reclining motions thereof, so that a safe and steady change of posture of the wheelchair user can be ensured. 
   It is still another object of the present invention to provide a seat reclining mechanism for a power wheelchair which accomplishes a smooth seat-reclining movement by implementing a single actuator and an ingenious linkage system with small costs and mechanical loading. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention as well as a preferred mode of use, further objectives and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein: 
       FIG. 1  is a perspective view of a seat reclining mechanism assembled with a power wheelchair according to the present invention; 
       FIG. 2  is an exploded view illustrating the fabrication of the stationary bracket, seat frame and back frame of the disclosed seat reclining mechanism; 
       FIG. 3  is an assembly drawing depicting the fabrication of the stationary bracket, seat frame and back frame of the disclosed seat reclining mechanism; 
       FIG. 4  is a lateral view depicting the stationary bracket, seat frame and back frame of the disclosed seat reclining mechanism at an initial seat position; 
       FIG. 5  is a lateral view depicting the stationary bracket, seat frame and back frame of the disclosed seat reclining mechanism at a reclined flat position; 
       FIG. 6  is an assembly drawing depicting the fabrication of the stationary bracket and leg support linkage of the disclosed seat reclining mechanism; 
       FIG. 7  is an applied view showing the link motion of the leg support linkage with regard to the stationary bracket according to the disclosed seat reclining mechanism; 
       FIG. 8  is an assembly drawing depicting the fabrication of the stationary bracket, back frame and back cushion of the disclosed seat reclining mechanism; 
       FIG. 9  is an enlarged drawing describing partial assembly according to  FIG. 8 ; 
       FIG. 10  is a lateral view depicting the disclosed seat reclining mechanism at the initial seat position; and 
       FIG. 11  is a lateral view depicting the disclosed seat reclining mechanism at the reclined flat position. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   According to a concept of the present invention, the disclosed seat reclining mechanism can be applied to a mobility assistive device, such as a power wheelchair  100 . As shown in  FIG. 1 , according to one embodiment of the present invention, a power wheelchair  100  may include a power source  102 , a plurality of wheels  104  and a stationary bracket  90  mounted onto the wheels  104  and functioning as a chassis whereon the disclosed seat reclining mechanism is installed, wherein the seat reclining mechanism primarily comprises an actuator  10 , a seat frame  20 , and a back frame  40 . The structural relationship among the stationary bracket  90 , seat frame  20 , and the back frame  40 , as shown in  FIGS. 2 ,  3  and  4 , will be explained below. 
   The orientation related to the seat reclining mechanism is firstly defined for further description. In following description, alleged front is referred to an end thereof corresponding to the actuating direction of the actuator  10 , while the opposite end is defined as the rear. 
   The details of the seat reclining mechanism according to the present invention are to be elaborated in the following description. First, four junction points  92  on the stationary bracket  90  and four junction points  222  on the bottom of the seat frame  20  are arranged correspondingly and between each pair of the corresponding junction points  92 ,  222 , a first bracket link  242  is provided to hold the seat frame  20  above the stationary bracket  90 . 
   The back frame  40  is pivotably arranged at the rear end of the seat frame  20  and has a pair of junction points  422  positioned respectively at the lower ends of both sides thereof. To link up the stationary bracket  90  with each junction point  422  of the back frame  40 , a second bracket link  442  is provided therebetween. 
   A connecting portion  226  is extended form the central bottom of the seat frame  20  and drivably connected to the actuator  10 . 
   Through foresaid structure, when the seat reclining mechanism is at its initial seat position, as shown in  FIG. 4 , the seat frame  20  and back frame  40  are approximately perpendicular to each other, and the four junction points  222  of the seat frame  20  are at the rear top of the four junction points  92  of stationary bracket  90  correspondingly. At this point, each first bracket link  242  is reclined with respect to the relevant junction point  92  on the stationary bracket  90 . 
   When the actuator  10  is started, the connecting portion  226  at the bottom of the seat frame  20  is pushed forward and renders the four first bracket links  242  oscillating forward synchronously. Such oscillations in turn cause the seat frame  20  to move forward smoothly and stably and stop at a predetermined advanced position. At this point, each first bracket link  242  is reclined with respect to the relevant junction point  92  on the stationary bracket  90 . 
   As the seat frame  20  is pushed forward, the back frame  40  that is mounted at the rear end thereof is pulled forward proceedingly. Since the back frame  40  is further fastened to the stationary bracket  90  by the second bracket links  442 , it is restrained from moving forward vertically and pulled to recline gradually along moving forward. Eventually, the back frame  40  is brought into a level position, as shown in  FIG. 5 . 
   The disclosed seat reclining mechanism still comprises a pair of leg support linkages  60 , as shown in  FIG. 6 , each having a footrest  622 , a leg rests  624  and a linkage system wherein the linkage system includes a third bracket link  646  having one end pivotly connected to the stationary bracket  90  and the other end pivotly connected to one end of an intermediate link  644 , of which the other end is immovably affixed by the leg rest  624  as well as the footrest  622  and a bent link arm  642  fastened to the seat frame  20  and the middle portion of the intermediate link  644  at both ends thereof respectively. 
   According to foregoing structure, when the seat reclining mechanism is at its initial seat position, the third bracket links  646  are approximately perpendicular to the stationary bracket  90 , and the intermediate links  644  are also positioned approximately perpendicular to the stationary bracket  90  so that the footrest bars  648  as well as the footrests  622  are consequently oriented toward the ground. 
   When the actuator  10  is started, the seat frame  20  is pushed forward as previously discussed and in turn presses the bent link arm  642  forward to give an impetus to the intermediate link  644 . At this point, the advancement of the intermediate link  644  lifts up the third bracket link  646  which is further fastened to the stationary bracket  90  and cause the intermediate link  644  to pivot on the bent link arm  642  and stop at an approximate level position. Thereby, the third bracket links  646 , the intermediate link  644 , leg rest  624  as well as the footrest  622  are relatively spread in a horizontal direction, as shown in  FIG. 7 . 
   Also, referring to  FIGS. 8 and 9 , a pair of armrests  80  may be provided to the disclosed mechanism, wherein each armrest  80  has one end connected with a linkage system which comprises an armrest link  842 , a back frame link  844 , and an intermediate link  846 . Specifically, the back frame link  844  is pivotally connected to the back frame  40 ; the armrest link  842  is attached to the outer side of the back frame link  844 ; and the intermediate link  846  has one end pivotally connected to the back frame link  844  while has the other end pivotally connected to the second bracket link  442  provided between the stationary bracket  90  and the back frame  40 . Further, each the armrest  80  has an L-shaped crutch  802  extended therefrom before the armrest link  842  for propping the armrest link  842  from pivoting downward. 
   Through said structure, when the disclosed seat reclining mechanism is at its initial seat position, the armrests  80  can be propped up by the L-shaped crutch  802  and maintained at a position horizontal to the seat frame  20 , as shown in  FIG. 8 . Accordingly, when the actuator  10  is started, the back frame  40  and second bracket links  442  are pulled forward as described above, and such movements in turn cause the intermediate links  846  reclining to bring the armrests  80  descending toward the seat frame  20 . 
   Furthermore, a seat cushion  26  may be fixed to the seat frame  20  while a back cushion  48  is slidably attached to the back frame  40 . As can be seen in  FIGS. 7 ,  8  and  9 , the back cushion  48  is installed so as to automatically shift along the back frame  40  according to the reclining motion of the disclosed mechanism by means of a sliding device. 
   For achieving above shifting motion of the back cushion  48 , according to the present embodiment, the back cushion  48  having a height smaller than that of the back frame  40  includes two sets of clamping pieces  482  for holding a pair of vertical bars  426  provided on the back frame  40 , a reversed U-shaped frame  464  having a height similar to that of the back cushion  48  which is fixedly attached to the clamping pieces  482  beyond the vertical bars  426  and a pair of elongated guide slots  262  are provided at the lower back side of the back cushion  48  to receive a pair of extensible rods  468  each having a sleeve part fixed to the inner side of each back frame link  844  and thus the back cushion  48  with the sliding device is accomplished. In addition, the reversed U-shaped frame  464  may comprise a headrest holder  466  whereon a headrest  49  can be mounted in an adjustable way. 
   By the disclosed structure, when the seat reclining mechanism of the present invention is at the initial seat position, as the extensible rod  468  is now retracted, the back cushion  48  can be positioned at the upper portion of the back frame  40 . When the actuator  10  is started, as the back frame  40  and back frame links  844  are pulled to move as previously described, the extensible rod  468  is therefore inclined and elongated to push the back cushion  48  to shift forward along the reclining back frame  40 . Thus, when the seat reclining mechanism finally comes to the reclined flat position, the distance between the seat cushion  26  and the back cushion  48  as well as the headrest  49  are closer than the distance therebetween at the initial seat position so as to respond to the changes of the positions of a user&#39;s head and back when he has a posture change from setting to laying. 
   According to the presently discussed embodiment, a power wheelchair equipped with the disclosed seat reclining mechanism can be seen at the initial seat position in  FIG. 10 . When the actuator  10  is started, a user sitting on the wheelchair has a posture change from setting to laying gradually while the center of gravity of the body is shifting from the hips toward the lumbar and back regions. At this time, since the seat cushion  26  fixed on the seat frame  20  moves forward under the operation of the seat reclining mechanism, the user&#39;s center of gravity of the body can keep reduplicated to the center of gravity of the wheelchair  100  throughout the reclining movement. Further, due to the ingenious linkage system, the disclosed seat reclining mechanism can achieve a reliable and approximately horizontal carrying surface through moving the seat cushion  26  forward, drawing the back cushion  48  and head rest  49  toward the seat cushion  26 , lifting and extending the leg rests  624  and footrests  622  to an altitude similar to the seat cushion  26  and descending the armrests  80  to a position close to the seat cushion  26  by efficiently implementing the only actuator  10 . 
   Whereas, when the actuator  10  is operated reversely, the seat reclining mechanism has all the components driven to move reversely according to foresaid motions and returns to the initial seat position from the reclined position as shown in  FIG. 11 . 
   Although a particular embodiment of the invention has been described in detail for purposes of illustration, it will be understood by one of ordinary skill in the art that numerous variations will be possible to the disclosed embodiments without going outside the scope of the invention as disclosed in the claims.