Abstract:
A seat supporting assembly ( 24 ) for supporting a seat ( 18 ), the assembly comprising a base ( 25 ) including a substantially elongated guiding rod ( 58 ), a seat support ( 36 ), a seat support-to-base linking member ( 56 ) pivotally coupled to the seat support ( 36 ) and sliding on the base guiding rod ( 58 ), a substantially elongated tilting member ( 60 ) having a guiding groove ( 66 ) and being pivotally attached to the seat support ( 36 ) and to the base ( 25 ). An actuating assembly ( 44 ) is coupled to the base ( 25 ) and includes a motion transmitting member ( 68 ) mounted within the guiding groove ( 60 ). The force from the actuating assembly moves the tilting member ( 60 ) according to the geometry of the guiding groove ( 66 ), which causes the seat supporting assembly ( 24 ) to move between tilted and upright configurations by pivoting the tilting member ( 60 ) relative to the seat support ( 36 ) and the base ( 25 ) and substantially simultaneously moving the seat support-to-base linking member ( 56 ) longitudinally relative to the guiding rod ( 58 ). The assembly is designed to maintain the location of the center of gravity of a user as the seat tilts rearwardly by automatically moving the seat forwardly during tilting. The guiding groove ( 66 ) in the tilting member ( 60 ) may be curved such that the tilting motion occurs with a constant angular velocity The seat assembly is particularly useful for wheelchairs.

Description:
FIELD OF THE INVENTION 
     The present invention relates to the general field of mobility assistance and is particularly concerned with a seat supporting assembly and a wheelchair including same. 
     BACKGROUND OF THE INVENTION 
     Wheelchairs have been used for many years in order to provide assistance in transportation of handicapped persons. In some cases, the handicapped person may be a paraplegic or a quadriplegic. In such cases, the wheelchair constitutes an invaluable source of individual transportation. 
     Whether manually operated or motor-driven, wheelchairs typically include a wheel-supported base for rollably supporting a seat. The seat, in turn, typically includes a bottom portion for supporting the gist of the weight of the intended user and a backrest portion for supporting the back of the intended user. Over the passed recent years, powered wheelchairs in particular have incorporated various features aimed at assisting the handicapped individual in his or her pursuit of independent operation and movement. Accordingly, some individuals, such as paraplegics and quadriplegics may spend a considerable amount of time sitting in their wheelchairs. 
     One of the major problems encountered by wheelchair users, especially paraplegics and quadriplegics, is the necessity to shift or move the body weight with respect to the support provided by the wheelchair. Indeed, the continuous pressure of the body&#39;s weight on certain specific locations of the body such as that provided by the skeletal structure causes the supporting skin to lose circulation. 
     If a person sits in the same position in a wheelchair for a long period of time, pressure is continuously applied to the tissue on the buttocks, legs and/or back that is bearing the person&#39;s weight in that position. This not only leads to discomfort and even pain but may also lead to medical complications such as sores, ulcers or the like. 
     In order to provide shifting of their body weight from time to time, some paralysed individuals may have to resort to using a nurse or attendant to manually tilt the entire wheelchair or the seat portion of the latter backwards so that the occupant&#39;s weight is shifted and the pressure points on the occupant&#39;s body is moved. However, body weight shifting is recommended at intervals of at least every 20 minutes. 
     This may prove to be a considerable task for a nurse or attendant. Furthermore, it would be more desirable to provide the wheelchair user with a means to make this shift of position on their own without assistance from an attendant. 
     It would, hence, be desirable to provide a reclining wheelchair in which the seat of the wheelchair is pivotally supported on the base of the wheelchair. The pivoting of an occupant with respect to the base would facilitate blood circulation, thereby providing relief for the occupant. 
     To address this problem, wheelchairs are sometimes provided with a movable pivot point upon which the wheelchair seat is mounted. Typically, a linear-type actuator is provided to raise the front end of the seat and tilt the seat back. However, prior art structures typically suffer from numerous drawbacks. One such drawback is that some prior art structures require the seat of the wheelchair be elevated to meet this demand since the actuating mechanism and associated linkage structures are relatively bulky. Wheelchair occupants typically disfavor this increase in elevation of the seat. 
     Another disadvantage associated with some prior art wheelchair tilting assemblies is that their configuration is such that, as the seat is reclined, the center of gravity for the occupied wheelchair shifts rearwardly. This shift of the center of gravity increases the tendency of the wheelchair towards rearward overturn. A significant shift in the center of gravity may even result in an unstable condition in which the force of gravity alone acting on the occupant is sufficient to overturn the wheelchair. 
     Accordingly, there exists a need in the industry for an improved seat supporting assembly and wheelchairs including same. 
     OBJECT OF THE INVENTION 
     An object of the present invention is therefore to provide an improved seat supporting assembly and wheelchairs including same. 
     SUMMARY OF THE INVENTION 
     In a first broad aspect, the invention provides a seat supporting assembly for supporting a seat, the seat supporting assembly comprising:
         a base, the base including a substantially elongated base guiding member;   a seat support for supporting the seat;   a seat support-to-base linking member, the seat support-to-base linking member being operatively coupled to the seat support and to the base guiding member with the seat support being tiltable relatively to the base and the seat support-to-base linking member being substantially longitudinally movable relatively to the base guiding member;   a substantially elongated tilting member defining a tilting member first end section, a substantially longitudinally opposed tilting member second end section and a tilting member intermediate section extending therebetween, the tilting member intermediate section defining a guiding groove extending generally longitudinally relatively to the tilting member, the tilting member first end section being pivotally attached to the seat support in a substantially spaced apart relationship relatively to seat support-to-base linking member, the tilting member second end section being pivotally attached to the base; and   an actuating assembly operatively coupled to the base and to the tilting member for moving the seat supporting assembly between an upright configuration and a tilted configuration, a seat support-to-base angle between the seat support and the base being larger in the tilted configuration than in the upright configuration, the actuating assembly including a motion transmitting member mounted to the guiding groove so as to be substantially slidably movable relatively thereto, the motion transmitting member being movable relatively to the base along a predetermined path;   wherein moving the motion transmitting member along the predetermined path slides the motion transmitting member relatively to the guiding groove, which causes the seat supporting assembly to move between the tilted and upright configurations by pivoting the tilting member relatively to the seat support and the base and substantially simultaneously moving the seat support-to-base linking member substantially longitudinally relatively to the base guiding member.       

     Advantages of the present invention include that the proposed seat supporting assembly is usable to support a seat, such as for example the seat of a wheelchair, so that the seat is reclinable and therefore allows an occupant thereof to independently and ergonomically pivot the seat of the wheelchair relative to its base. The proposed seat supporting assembly is designed so as to be relatively compact so as to reduce the need for increasing the spacing between the base of the wheelchair and the seat of the wheelchair. 
     Furthermore, the proposed seat supporting assembly is designed so as to reduce shifting of the center of gravity of the wheelchair as the seat is pivoted relative to its base, hence reducing the risk of the wheelchair being overturned by gravity. 
     Still furthermore, the proposed seat supporting assembly is designed so as to provide a relatively smooth pivoting motion with a relatively constant rotational speed throughout the pivotal range of motion. 
     Yet, still furthermore, the proposed seat supporting assembly is designed so as to be relatively mechanically simple, hence providing a structure that will be relatively reliable and require minimal maintenance. Also, the proposed seat supporting assembly is designed so as to be manufacturable using conventional forms of manufacturing so as to provide a seat supporting assembly that will be economically feasible. 
     In another broad aspect, the invention provides a tiltable seat assembly, the tiltable seat assembly comprising the proposed seat supporting assembly and a seat mounted to the seat supporting assembly. 
     In yet another broad aspect, the invention provides a wheelchair for supporting an intended user, the wheelchair comprising:
         a wheelchair frame;   at least three wheels rotatably mounted to the wheelchair frame;   the proposed seat supporting assembly attached to the wheelchair frame; and   a seat mounted to the proposed seat supporting assembly.       

     Other objects, advantages and features of the present invention will become more apparent upon reading of the following non-restrictive description of preferred embodiments thereof, given by way of example only with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the appended drawings: 
         FIG. 1 , in a front perspective view, illustrates a wheelchair in accordance with an embodiment of the present invention, the wheelchair including a seat supporting assembly supporting a seat, the seat being partially shown in phantom lines, the seat supporting assembly being shown in an upright configuration; 
         FIG. 2 , in a side elevational view, illustrates the wheelchair shown in  FIG. 1  with its seat supporting assembly in an upright configuration; 
         FIG. 3 , in a side elevational view, illustrates the wheelchair shown in  FIGS. 1 and 2  with its seat supporting assembly in the tilted configuration; 
         FIG. 4 , in a top plan view, illustrates the seat supporting assembly shown in  FIGS. 1 through 3  with the seat supporting assembly in the upright configuration; 
         FIG. 5 , in a top plan view, illustrates the seat supporting assembly shown in  FIGS. 1 through 4  with the seat supporting assembly in the tilted configuration; 
         FIG. 6 , in a side cross-sectional view, illustrates the seat supporting assembly shown in  FIGS. 1 through 5  with the seat supporting assembly in the tilted configuration; and 
         FIG. 7 , in a side cross-sectional view, illustrates the seat supporting assembly shown in  FIGS. 1 through 6  with the seat supporting assembly in a configuration intermediate the tilted and upright configurations. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , there is shown a wheelchair in accordance with an embodiment of the present invention, generally indicated by the reference numeral  10 . The wheelchair  10  typically includes a wheelchair frame, also referred to as a wheelchair base, shown in phantom lines and generally indicated by the reference numeral  12 . At least three wheels are rotatably mounted to the wheelchair frame  12 , the at least three wheels define a sustentation polygon. In the specific embodiment of the invention shown in the drawings, the wheelchair frame  12  is rollably mounted on a pair of front wheels  14  and a pair of rear wheels  16 . 
     The wheel chair  10  also includes a seat generally indicated by the reference numeral  18 . The seat  18  includes a seat frame defining a bench section  20  and a backrest section  22 . The bench and backrest sections  20 ,  22  are adapted to support cushioning means (not shown in the drawings) for respectively bearing the gist of the weight of the intended user and acting as a backrest for the latter. 
     The wheelchair  10  further includes a seat supporting assembly generally indicated by the reference numeral  24  for mounting the seat  18  thereto and for pivoting the seat  18  between an upright configuration shown in  FIGS. 1 ,  2  and  4  and a tilted configuration shown in  FIGS. 3 ,  5  and  6 . The seat supporting assembly  24  is mounted to the wheelchair frame  12  and operatively coupled to the seat  18 . It should be understood that the wheelchair frame  12 , its associated set of wheels  14 ,  16  and the seat  18  shown throughout the drawings are only illustrated by way of example and that the wheelchair frame  12  and the seat  18  could vary in configuration, size and other parameters without departing from the scope of the present invention. 
     Referring now more specifically to  FIGS. 2 through 7 , there is shown in greater details some of the features of the seat supporting assembly  24 . The seat supporting assembly  24  includes a base  25 , the base  25  including a base frame generally indicated by the reference numeral  26 . The base frame  26  is adapted to be secured to the wheelchair frame  12  by suitable fastening means. 
     Referring to  FIGS. 4 and 5 , in the embodiment shown throughout the drawings, the base frame  26  includes a pair of longitudinally opposed base frame end walls  28  and a pair of transversally opposed base frame peripheral walls  30 . The base frame peripheral walls  30  are provided with attachment apertures  32  extending therethrough, as better seen in  FIG. 3 . The attachment apertures  32  may be used for securing the base frame  26  to the wheelchair frame  12  using conventional fastening means such as screws, bolts, rivets or the like. The base frame  26  typically further includes a base frame reinforcement members  34  for improving the structural rigidity of the seat supporting assembly  24 . For example, the base frame reinforcement member  34  is substantially T-shaped and is secured to one of the base frame end walls  28  and to the two base frame peripheral walls  30 . This configuration of the frame reinforcement member  34  is relatively lightweight and allows to reinforce the base frame  26  without unduly increasing its height. 
     The seat supporting assembly  24  also includes a seat support generally indicated by the reference numeral  36 . The seat support  36  is adapted to be secured to the seat  18  of the wheelchair  10  for selectively inducing the pivotal movement thereof. As seen in  FIGS. 6 and 7 , a seat support-to-base angle  71  between the seat support  36  and the base  25  is larger in the tilted configuration than in the upright configuration 
     In the embodiment shown throughout the Figures, the seat support  36  includes a pair of elongated pivoting members  38  maintained in a spaced apart relationship relative to each other by two substantially longitudinally spaced apart transversal rods  40 . The pivoting members  38  are typically provided with attachment apertures  42  extending therethrough adapted to be used for attachment to the bench component  20  of the seat  18  by conventional fastening means such as screws, bolts, rivets or the like. It should be understood that both the base frame  26  and the seat support  36  could vary in shape, configuration, size and construction without departing from the scope of the present invention. 
     The seat supporting assembly  24  further includes an actuating assembly, generally indicated by the reference numeral  44 , and substantially elongated tilting members  60  both for together pivoting the seat support  36  relative to the base frame  26 . As better seen in  FIG. 5 , the actuating assembly  44  typically includes an actuator, such as a linear-type actuator  46 . The linear-type actuator  46  may be of any suitable type such as the endless screw type or the like. The linear actuator  46  includes an actuator piston or rod  48  adapted to be selectively extended and retracted. The distal end of the actuator piston or rod  48  is solidly anchored to an anchoring wall  50  extending across the base frame  26 . The body of the linear-type actuator  46  is secured to an actuating assembly frame generally indicated by the reference numeral  52 . 
     The actuating assembly frame  52  is, in turn, slidably mounted to the base frame  26  for substantially longitudinal slidable movement relative thereto. In other words, the actuating assembly frame  52  is mounted to the base  25  so as to be movable relatively thereto over a substantially rectilinear path. Typically, the actuator mounting frame  52  includes a pair of actuator mounting bracket longitudinal arms  54 . The actuator bracket longitudinal arms  54  are each provided with a corresponding sliding cursor or block  53  adjacent a longitudinal end thereof, each of the sliding cursors  53  being slidably mounted to a respective guiding rod  51  extending, at least partially, longitudinally across the base frame  26 . For example, the guiding rods  51  each extend between the anchoring wall  50  and a base frame end wall  28 . 
     The linear-type actuator  46  includes first and second end portions  47  and  49 , the actuator first and second end portions  47  and  49  being attached respectively to the base  25  and to the actuating assembly frame  52 . The linear-type actuator  46  is selectively movable between a retracted configuration, shown in  FIG. 4 , and an extended configuration, shown in  FIG. 5 . The actuator first and second end portions  47  and  49  are closer to each other in the retracted configuration than in the extended configuration. 
     The base  25  includes a substantially elongated base guiding member, for example taking the form of a guiding rod  58 . Typically, the guiding rods  58  extend between the anchoring wall  50  and a corresponding base frame end wall  28 . The seat supporting assembly also includes a seat support-to-base linking member, for example taking the form of sliding cursors  56 . The seat support-to-base linking member is operatively coupled to the seat support  36  and to the base guiding member with the seat support  36  being tiltable relatively to the base  25  and the seat support-to-base linking member being substantially longitudinally movable relatively to the base guiding member. In the specific embodiment of the invention shown in the drawings, two sliding cursors  56  are each slidably mounted on a corresponding guiding rod  58  extending, at least partially, longitudinally across the base frame  26 . More specifically, as seen for example in  FIG. 6 , the sliding cursors  56  each includes a collar  57  defining a collar aperture  59 , the guiding rods  58  being slidably mounted into the collar apertures  59 . 
     As seen in  FIGS. 6 and 7 , each tilting member  60  defines a tilting member first end section  61 , a substantially longitudinally opposed tilting member second end section  63  and a tilting member intermediate section  65  extending therebetween. Each tilting member intermediate section  65  defines a guiding groove  66  extending generally longitudinally relatively to the tilting member  60 . 
     Each tilting member first end section  61  is pivotally attached to the seat support  36  in a substantially spaced apart relationship relatively to seat support-to-base linking member by a suitable tilting member-to-seat support pivotal link  64 . The tilting member-to-seat support pivotal links  64  typically take the form of a corresponding pivoting axle extending between the tilting member  60  and a corresponding pivoting member  38 . 
     Each tilting component second end section  63  is pivotally attached to the base frame  26  by a suitable tilting member-to-base frame pivotal link  62 . The tilting member-to-base frame pivotal link  62  typically takes the form of a corresponding axle extending between the tilting member  60  and an adjacent base frame peripheral wall  30 . 
     The actuating assembly  44  is operatively coupled to the base frame  26  and to the tilting members  60  for moving the seat supporting assembly  24  between the upright and tilted configurations. To that effect, the actuating assembly includes a motion transmitting member  68  mounted to the guiding groove  66  so as to be substantially slidably movable relatively thereto, the motion transmitting member  68  being movable relatively to the base along a predetermined path. In the embodiment of the invention shown in the drawings, the motion transmitting member  68  take the form of transmitting pins  68  and the predetermined path is substantially rectilinear and substantially parallel to the base guiding member  58 . This allows to assemble a seat supporting assembly that is relatively simple and relatively compact. 
     In these embodiments, each guiding groove  66  is configured, sized and positioned for substantially fittingly and slidably receiving therein a corresponding transmitting pin  68 . Each transmitting pin  68  is mechanically coupled to the actuating assembly frame  52 . For example, each transmitting pin  68  extends from the actuating assembly frame  52 . Typically, the transmitting pins  68  extend substantially laterally from the actuator mounting bracket  52  adjacent a corresponding longitudinal end thereof. Typically, the guiding slots  66  are formed on a corresponding inner surface of the motion converting component  60 . 
     The configuration of the tilting member  60  and the manner in which it is coupled to the seat support  36 , the actuating assembly  44  and the base  25  minimizes undesirable movements of the seat support  36  relatively to the base  25  that may caused by small spacings present between linked components, these small spacings being caused by manufacturing imperfections. This ensures a relatively smooth operation of the seat supporting assembly  24 . 
     As illustrated more specifically in  FIGS. 6 and 7 , each guiding groove  66  is typically at least in part curved. For example, the guiding groove  66  has the general configuration of an arc segment. The guiding groove  66  is configured, sized and located so that the seat support-to-base angle  71  varies at a substantially constant angular speed as the seat supporting assembly  24  moves between the upright and tilted configurations in response to the motion transmitting member  68  moving at a substantially constant speed along the predetermined path. In other words, in the embodiment of the invention shown in the drawings, the configuration of the guiding groove  66  is designed so as to convert the linear movement of the linear-type actuator  46  into a pivoting movement of the seat support  36  with the pivoting speed of the seat support  36  remaining substantially constant throughout the pivoting range thereof as the linear-type actuator  46  translates at a relatively constant linear speed. In yet other words, the substantially arc-shape configuration of the guiding slots  66  provide a compensation for the change in the angular relationship between the seat support  36  and the base frame  26  such that the relatively constant translational movement of the linear-type actuator  46  is converted into a substantially constant speed rotational movement of the seat support  36 . 
     In order to achieve such a compensation, the guiding groove  66  includes a substantially arc segment shaped portion. More specifically, in the specific embodiment of the invention shown in the drawings, the guiding groove  66  includes a guiding groove first section  69  located substantially adjacent the tilting member first end section  61  and a guiding groove second section  73  located substantially adjacent the tilting member second end section  63 . The guiding groove first and second sections  69  and  73  are each substantially arc segment shaped and have respectively a first radius of curvature and a second radius of curvature, the second radius of curvature being substantially smaller than the first radius of curvature. The precise configuration of the guiding slots  66  could vary depending on the configuration and size of the other components of the seat supporting assembly and their respective relationship therebetween. 
     In some embodiments of the invention, the seat supporting assembly  24  is located, configured and sized so that a combined center of gravity of the seat supporting assembly  24 , the seat  18  and the intended user (not shown) remains substantially within the sustentation polygon defined by the wheels  14  and  16  of the wheelchair  10  with the intended user sitting in the seat and the seat supporting assembly  24  being moved between the upright and tilted configurations. This is caused, at least in part, by the pivoting and slidable link between the seat support  36  and the base frame  26 . 
     In use, moving each of the motion transmitting member, in other words the transmitting pins  68 , along the predetermined path slides the motion transmitting member relatively to the guiding groove  66 , which causes the seat supporting assembly  24  to move between the tilted and upright configurations by pivoting the tilting member  60  relatively to the seat support  36  and the base  25  and substantially simultaneously moving the seat support-to-base linking member  56  substantially longitudinally relatively to the base guiding member  58 . 
     Although the present invention has been described hereinabove by way of preferred embodiments thereof, it can be modified, without departing from the spirit and nature of the subject invention as defined in the appended claims.