Patent Publication Number: US-7905504-B2

Title: Seat

Description:
TECHNICAL FIELD 
     The present invention relates to seating, in particular but not exclusively a seat for a wheelchair. 
     BACKGROUND ART 
       FIG. 1  shows a wheelchair  10  of the kind known from WO2006/106324 and EP1348414 and comprising a chassis  12  with a seat framework  14  mounted thereon, the seal framework  14  comprising base plates  60  and a pair of upright elongate frame members  18 . Base plates  60  carry a bottom rest  13  and leg rests  15 , while frame members  18  carry inter alia a head rest  20 , a back rest  22 , armrests  23  and thoracic supports  24 . The rest elements  13 , 15 , 20 , 22 , 23  and  24  together form a postural management system, the thoracic supports  24  supporting a child&#39;s upper torso to assist prevention, if not correction, of spinal deformities. 
       FIGS. 2 and 3  are side and detail views of the wheelchair disclosed in EP1348414. 
       FIG. 2  shows schematically how the seat framework  14  is attached to a chassis  12 . Plates  60  are rotatably mounted on a support beam  16 , a mounting bracket  62  being provided to centre the seat framework  14  on the chassis  12 . 
     Plates  60  extend rearwardly of the support beam  16  and a rearward portion  64  of each is coupled to a respective end of a tube  66 . The tube  66  is supported by a variable length strut  68  which is mounted on bracing member  32 . The strut  68  is pivotally mounted at each end and comprises a rod  70  which is a sliding lit in housing  72 . A foot pedal  74  operates a locking mechanism (not shown) in housing  72  which allows the rod  70  to move relative to the housing  72  when the foot pedal  74  is operated. With the foot pedal  74  depressed, the seat framework  14  is free to rotate in direction arrow A around the support member  16 . 
       FIG. 2  shows schematically some detail of the backrest  130  of seat member  14 , the position of which may he adjusted from an upright position to an inclined position (shown in phantom lines). The back rest  130  is adjustably mounted via bracket  132  to the rearward portion  64  of plates  60 . The rearward portion  64  includes three arcuate slots each for receiving a bolt (not shown) securing bracket  132  to the tube  66  extending between plates  60 . The position of each bolt within its respective slot  134  is determined by the position of arm  136  relative to the rearward portion  64  of plates  60 . A plurality of apertures  138  is provided in the rearward portion  64  which are selectably registrable with apertures  140  in arm  136 . The inclination of the back rest  130  is thus determined by selecting which of apertures  138  are registered with apertures  140  in the arm  136 . Once the appropriate apertures are registered, a locking pin (not shown) may be used to secure the desired back rest inclination. Such adjustment is typically carried out by a healthcare professional rather than when the chair is in use. 
     However, the present inventors have established mat if aback rest is reclined relative to a seat member (i.e. when the angle between the back rest and the seat member increases) when the seat is occupied, the seat occupant&#39;s clothing is pulled upwards at the back, making the occupant uncomfortable. This will be referred to hereafter as the ‘shirt pull effect’. Where the seat incorporates a thoracic support, this also moves upwards relative to the occupant&#39;s body, spoiling the positioning of the support and the associated postural management. 
     The present invention has as an objective the mitigation of the aforementioned problems. 
     DISCLOSURE OF INVENTION 
     According to the present invention, there is provided a: 
     seat comprising: 
     a bottom rest, 
     a back rest support rotatable relative to the bottom rest about an axis of rotation, the back rest support and bottom rest defining an angle therebetween; and 
     a back rest slidably mounted on the back rest support and moveable therealong to vary its position relative to the bottom rest; 
     the back rest being kinematically linked to the bottom rest such that the back rest moves nearer to the axis of rotation as the angle between the back rest support and the bottom rest 
     increases. 
     Kinematic linkage of tire back rest to the bottom rest means that movement of the bottom rest relative to the back rest support will result in movement of the back rest relative to the back rest. A back rest that moves downwards (i.e. nearer to the axis of rotation) as it reclines (i.e. as the angle between the back rest and the bottom rest increases) reduces or even offsets completely the increase in separation between the point of contact of the occupant with the bottom rest and the point of contact of the occupant with the back rest as the back rest is inclined relative to the bottom rest. Such an increase in separation would otherwise result in the aforementioned shirt-pull effect. Where, for example, the seat occupant was wearing a shirt tucked into trousers, such an increase would result in the shirt being pulled out of the trousers. 
     According to one embodiment, the back rest may be kinematically linked to the bottom rest by a rigid link pivotally attached at a first end to the back rest and at a second end to the bottom rest. 
     According to another embodiment, the back rest may be kinematically linked to the bottom rest, by a jointed linkage. The jointed linkage may comprise a lower link, attached at a first end to the bottom rest, and an upper link, pivotally attached at a first end to the back rest and at a second end to the second end of the lower link. 
     The seat may comprise a locking mechanism configured to releasably fix the angle between the back rest support and the bottom rest. The locking mechanism may comprise an adjustable length strut attached at a first end to the bottom rest and at a second end to the back rest support. The first end of the adjustable length strut may be attached to the bottom rest by a coupling configured to be releasable in the course of normal operation of the seat. 
     In another embodiment, the aforementioned lower link may be kinematically linked to the back rest support and the locking mechanism may comprise an adjustable length strut pivotally attached at a first end to the bottom rest and a second end to the lower link. The lower link may be kinematically linked to the back rest support by a further link pivotally attached at a first end to the lower link and at a second end to an arm rigidly attached to the back rest support and extending radially from the axis of rotation. 
     The rigid link or jointed linkage may be configured to pass underneath the axis of rotation. 
     The seat may comprise a leg rest pivotable relative to the bottom rest, the seat being configured to decrease the angle of the leg rest relative to the bottom rest as the angle between the back rest and the bottom rest increases. The leg rest may be kinematically linked to the back rest support via the rigid link or jointed linkage. 
     According to another aspect of the present invention, there is provided a seat having a back rest and a bottom rest, the back rest being rotatable relative to the bottom rest about an axis of rotation; the seat being configured to move the back rest nearer to the axis of rotation as the angle between the back rest and the bottom rest increases. The seat may comprise a back rest support for said back rest, the back rest support being rotatable relative to the bottom rest about the axis of rotation and the back rest being moveable along the back rest support in a radial direction relative to said axis. The back rest may be kinematically linked to the bottom rest, i.e. movement of the bottom rest relative to the back rest support results in movement of the back rest relative to the back rest support. 
     The invention also provides a wheelchair comprising a chassis with ground-engaging wheels and, mounted thereon, a seat as set out above. The seat may be pivotable relative to the chassis. The wheel chair may have a handle for pushing the wheelchair along, the handle being attached to the back rest of the seat such that the handle moves nearer to the axis of rotation of the back rest as the angle between the back rest and the bottom rest increases. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       An embodiment of the invention will now be described by way of example with reference to the accompanying drawings, in which: 
         FIG. 1  is a side view of a wheelchair of the kind known from WO2006/106324 and EP1348414; 
         FIG. 2  is a schematic sectional view of a wheelchair according to EP1348414: 
         FIG. 3  shows detail of backrest tilt adjustment of the wheelchair of  FIG. 2 ; 
         FIG. 4  is a side view of an embodiment of a seat according to the present invention; 
         FIG. 5  is a diagram showing the operation of a seat according to the present invention; 
         FIG. 6  is a side view of the embodiment of  FIG. 4  including additional detail; 
         FIG. 7  is a side view of the embodiment of  FIGS. 4 and 6  when in a fully reclined position. 
         FIG. 8  is a side view of a second embodiment of the invention; 
         FIG. 9  is a side view of a third embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS 
       FIG. 4  is a side view of a first embodiment of a seat according to the present invention when in a first, upright position. The seat is mounted on a chassis of the kind shown in  FIGS. 1 and 2  to form a wheelchair. The seat may be pivoted relative to the chassis about a mounting bracket as indicated at  62  in  FIG. 2 . 
     As in the embodiments of  FIGS. 1-3 , seat framework  14  comprises base plates  60  (shown in dashed lines) and a pair of upright elongate frame members  18 . Base plates  60  carry a bottom rest  13  while frame members  18  carry a back rest  22  and, typically, a head rest and thoracic supports (not shown). 
     Frame members  18  are mounted to the rear of the base plates  60  by means of a pivot  100 , thereby allowing the back rest  22  to be reclined relative to the bottom rest  13  and increasing the angle T between the back rest  22  and the bottom rest  13 . A handle  23  for pushing the wheelchair is also attached to the back rest. 
     To reduce the ‘shirt pull effect’, back rest  22  is provided with upper and lower guides  110  and  111  which slidably engage the frame members  18 , allowing the back rest  22  and handle  23  to slide up and down the frame members  18 . Although not shown, thoracic supports of the kind discussed above with regard to the prior art wheelchair of  FIG. 1  may also he attached to the back rest  22  or handle  23  such that they also slide up and down. 
     The position of the back rest  22  along the frame members  18  is determined by a linkage  120  connected between the base plates  60  and the back rest  22 . In the example shown, the linkage is connected via pivot  112  to the lower guide  111  of the backrest  22 . 
     As illustrated by the diagram of  FIG. 5 , attachment of the lower end of a linkage  120  to a pivot  121  on the seat framework in front of the pivot  100  results in the back rest  22  being pulled on its guides  110 , 111  down the frame members  18  in a radial direction D when the frame members  18  are reclined backwards (as indicated by arrow B), thereby reducing the ‘shirt pull effect’. 
     Such a linkage whereby movement of one end of the linkage (in this case movement of the base plates  60  relative to the frame members  18 ) results in movement of the other end of the linkage (in this case the back rest  22  relative to the frame members  18 ) is known as a kinematic linkage and elements at either end of the linkage are said to be kinematically linked. It will be appreciated that such kinematic linking can be effected by means other than the rigid links used in the described embodiment, for example gear trains, chains or belts. 
     It will be appreciated that, particularly when the seat is fully reclined, a straight linkage  120  of the kind shown in  FIG. 5A  might encroach into the space between the back rest  22  and bottom rest  13 , spoiling the comfort of the seat occupant. 
     Accordingly, in the particular embodiment of  FIG. 4 , linkage  120  comprises upper and lower links  122  and  124  pivoted together at pivot  126 . Upper link  122  is attached to the seat back guide  111  at pivot  112 , while lower link  124  is attached to the base plates  60  at pivot  130 . Such a linkage  120  adopts a dog leg or ‘V’ shape, allowing it to sit behind the bottom and back rests  13  and  22  and out of the way of the seat occupant, especially if lower pivot  130 , in addition to being located forward of the Same member pivot  100 , is also located below the pivot  100 . 
     Lower link  124  is also connected to the frame members  18  via a further linkage  134  comprising a second lower link  136  connected at one end  137  to lower link  124  and at the other end (via pivot  138 ) to an arm  140  rigidly fixed to the frame members  18 . 
     The angular position of the frame members  18  is controlled by a lockable strut  150  pivotally attached at one end  152  to the link  124  and at the other end  154  to the base plates  60 . As is well known and thus not illustrated, a control (e.g. a press brake style lever on the handle  23 ) allows the length of the strut  150  to be locked, thereby preventing rotation of the lower link  124 . Unlocking the strut allows the length of the strut to be increased or decreased, typically under the action of a gas spring, allowing the lower link  124  to rotate and the angular position of the frame members  18  to change. 
     In addition to varying the inclination of the back rest, it may also be desirable to vary the inclination of the leg rests in a complementary manner and  FIG. 6  shows an embodiment having such functionality. 
     A leg rest  15  is attached to a support member  200  which itself is pivotally mounted to the front of the base plates  60  by pivot  210 . The inclination of the leg rest is controlled by a further link  220  attached at one end to the support member via a bracket  230  and at the other end to lower link  124  at pivot  235 . It will be evident that, in locking the rotational position of the link  124 , the strut  150  also locks the rotational position of support member  200  and thus the angle of inclination of the leg rest  15 . 
     The further link  220  is shaped, e.g. with multiple dog legs, so as to avoid other seat components. The further link may also comprise two parts  240 , 250 , joined by fasteners passing through slots  260  in each part, so as to allow the length of the further link to be adjusted as is known per se. Adjusting the length allows the angle of the leg rest relative to the back rest to be varied, while adjusting the position of the bracket along the support member allows the rate of variation of leg rest angle to the changed. It will be understood that right and left leg rests are individually variable in both angle and rate. The further link  220  is connected to the bracket by means of a latch  280  which can be released to allow the leg rest  15  to swing away. 
     As shown in  FIG. 6 , link  124  is advantageously pivoted around the wheelchair main support beam  300 , with the pivots  132 ,  152  and  235  being located on a flange  310  of the link  124  surrounding that beam. 
       FIG. 7  is a side view of the seat of  FIGS. 4 and 6  in a fully reclined position. Compared to the upright position of  FIGS. 4 and 6 , it will be seen that back rest  22  has slid down frame members  18  towards bottom rest  13 . Leg rest  15  has correspondingly rotated upwards. 
       FIG. 8  shows a second embodiment of the invention in which the back rest  22  is kinematically linked to the bottom rest and supporting base plates  60  by a rigid link  120  attached at first and second ends thereof by pivots  122  and  121  respectively. To avoid the mechanism encroaching into fee space between the back rest  22  and bottom rest  13 , as mentioned above with regard to  FIG. 5 , rigid link  120  is shaped in the form of a “U” such that it passes beneath the axis about which back rest support frame members  18  rotate relative to the bottom rest base plates  60 . 
     In the embodiment of  FIG. 8 , the rotation of the back rest is controlled by a lockable strut  150  mounted between the seat base frame (specifically a cross member  400  extending between the rear of the base plates  60 ) and the seat back frame (specifically a cross member  410  extending between upright elongate frame members  18 ). Cross member  410  is releasably attached to the elongate frame members  18 , e.g. by releasable clamps, such that the position of the cross member  410  along the length of the frame members may be adjusted. This in turn allows the maximum recline angle of the members  18  of the seat back frame—corresponding to the minimum contracted position of the stmt  150 —to be adjusted. 
     The lower end of the strut  150  may be attached to cross member  400  by means of a coupling  410  which can be released during normal operation of the seat, allowing the entire seat back (including frame members  18 , handle  23  and backrest  22 ) to be folded forward against the seat base frame (including base frame members  60  and bottom rest  13 ), thereby facilitating storage or transport of the wheelchair. 
       FIG. 9  shows a further embodiment incorporating the mechanism of  FIG. 8  and additionally enabling variation of the angle of the leg rests with variation of the angle of the back rest, in the manner of the embodiments of  FIGS. 6 and 7 . Specifically, leg rest  15  is kinematically linked to rigid link  120  by means of further link  220  via pivots  230 ,  235 .