Patent Publication Number: US-11389351-B2

Title: Wheelchair footrest assembly

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims the priority of U.S. Patent Application No. 62/690,463, filed on Jun. 27, 2018 and incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present application relates to wheelchairs and, more particularly, to wheelchair footrest assemblies. 
     BACKGROUND OF THE ART 
     Wheelchairs have evolved over the years to become increasingly ergonomic, lightweight, easy to maneuver and to use. However, there remains room for improvement to add additional adjustment possibilities to wheelchairs, and to render them even more convenient to use, notably in the maneuverability, stiffness, balance, but also for moving into or out of the wheelchair, and folding or unfolding the wheelchair for storage. 
     For example, footplate assemblies, also known as footplate, footplate mechanism, footrest, among other possible names, must often be foldable if used in a foldable wheelchair. Some footplates and footrests are designed to extend from side to side, thereby adding rigidity to the front of the wheelchair. However, by adding a foldable footplate mechanism, the wheelchair has yet another mechanism that may add weight and oppose its forces against the folding and deployment of the chair. Moreover, the addition of another mechanism such as a footrest assembly to the wheelchair may complicate the assembly of the wheelchair due to the precise length of such mechanism to extend from side to side of the wheelchair. 
     SUMMARY 
     It is therefore an aim of the present disclosure to provide a wheelchair footrest assembly that addresses issues associated with the prior art. 
     Therefore, in accordance with a first embodiment of the present disclosure, there is provided a footrest assembly for wheelchair of the type having a structure expandable from a contracted condition to an expanded position, the footrest assembly comprising: a beam assembly having a structural member having a first end and a second end, a first joint with at least one rotational degree of freedom adapted to interface the first end of the structural member to a first side of a frame of the wheelchair, a linkage assembly connected to the structural member by a central joint with at least a rotational degree of freedom and a lockable translational degree of freedom joint, a second joint with at least one rotational degree of freedom adapted to interface the linkage assembly to a second side of the frame of the wheelchair, and a connector interface releasably engaging the beam assembly to the linkage assembly and/or to the second joint when the wheelchair is deployed for use. 
     Further in accordance with the first embodiment, a rotational axis of the central joint is for instance higher than a rotational axis of the first joint and of the second joint relative to a ground when the wheelchair is deployed for use. 
     Still further in accordance with the first embodiment, projections on a horizontal plane of the rotational axis of each of the first joint, the central joint and the second joint are for instance parallel to one another. 
     Still further in accordance with the first embodiment, the connector interface includes for instance a hook unit at or adjacent to the second end of the structural member. 
     Still further in accordance with the first embodiment, the structural member is for instance a tube, and the hook unit has for instance a quill and wedge assembly to be secured inside the second end of the tube. 
     Still further in accordance with the first embodiment, the first joint is for instance part of a pivot clamp unit having a clamp configured to be connected to the first side of the frame of the wheelchair. 
     Still further in accordance with the first embodiment, the clamp forms for instance a cylindrical joint with the first side of the frame. 
     Still further in accordance with the first embodiment, the second joint is for instance part of a mating clamp unit having a clamp configured to be connected to the second side of the frame of the wheelchair. 
     Still further in accordance with the first embodiment, the clamp forms for instance a cylindrical joint with the second side of the frame. 
     Still further in accordance with the first embodiment, the mating clamp unit has for instance a male member of the connector interface, for mating engagement with a female member of the connector interface on the structural member. 
     Still further in accordance with the first embodiment, the central joint is for instance part of a carriage clamp connected to the structural member. 
     Still further in accordance with the first embodiment, the carriage clamp forms for instance a cylindrical joint with the structural member, the cylindrical joint including the lockable translational degree of freedom joint and a lockable rotational degree of freedom joint about a longitudinal axis of the structural member. 
     Still further in accordance with the first embodiment, the beam assembly includes for instance a footplate. 
     Still further in accordance with the first embodiment, the footplate is for instance connected to the structural member by at least one clamp forming a lockable cylindrical joint with the structural member. 
     In accordance with a second embodiment of the present disclosure, there is provided a footrest assembly for wheelchair of the type having a structure expandable from a contracted condition to an expanded position, the footrest assembly comprising: a beam assembly having a structural member having a first end and a second end, a pivot clamp unit including a first joint with at least one rotational degree of freedom adapted to interface the first end of the structural member to a first side of a frame of the wheelchair, and a first clamp forming a cylindrical joint with the first side of the frame, a linkage assembly connected to the structural member by a central joint with at least a rotational degree of freedom, a mating clamp unit including a second joint with at least one rotational degree of freedom adapted to interface the linkage assembly to a second side of the frame of the wheelchair, and a second clamp forming a cylindrical joint with the second side of the frame, and a connector interface releasably engaging the beam assembly to the linkage assembly and/or to the mating clamp unit when the wheelchair is deployed for use. 
     Further in accordance with the second embodiment, a rotational axis of the central joint is for instance higher than a rotational axis of the first joint and of the second joint relative to a ground when the wheelchair is deployed for use. 
     Still further in accordance with the second embodiment, projections on a horizontal plane of the rotational axis of each of the first joint, the central joint and the second joint are for instance parallel to one another. 
     Still further in accordance with the second embodiment, the connector interface includes for instance a hook unit at or adjacent to the second end of the structural member. 
     Still further in accordance with the second embodiment, the structural member is for instance a tube, and the hook unit has for instance a quill and wedge assembly to be secured inside the second end of the tube. 
     Still further in accordance with the second embodiment, the mating clamp unit has for instance a male member of the connector interface, for mating engagement with a female member of the hook unit. 
     Still further in accordance with the second embodiment, the central joint is for instance part of a carriage clamp connected to the structural member. 
     Still further in accordance with the second embodiment, the carriage clamp forms for instance a cylindrical joint with the structural member, the cylindrical joint including the lockable translational degree of freedom joint and a lockable rotational degree of freedom joint about a longitudinal axis of the structural member. 
     Still further in accordance with the second embodiment, the beam assembly includes for instance a footplate. 
     Still further in accordance with the second embodiment, the footplate is for instance connected to the structural member by at least one clamp forming a lockable cylindrical joint with the structural member. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a wheelchair with a footrest assembly in accordance with the present disclosure; 
         FIG. 2  is an underside perspective view of a footplate on a beam assembly in the footrest assembly of the present disclosure; 
         FIG. 3  is a perspective view of the footrest assembly of the present disclosure; 
         FIG. 4  is a top view of a joint between the beam assembly and a pivot clamp unit, in accordance with the present disclosure; 
         FIG. 5  is an exploded view of a hook unit of the beam assembly of  FIG. 3 ; 
         FIG. 6  is a perspective view of the hook unit in directing for mating with a mating clamp unit, in accordance with the present disclosure; 
         FIG. 7  is an elevation view of the mating clamp unit, in accordance with the present disclosure; and 
         FIG. 8  is a perspective view of an interface between a linkage assembly and the beam assembly in accordance with the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to the drawings and more particularly to  FIG. 1 , there is illustrated a wheelchair assembly at  10 , also simply referred to as wheelchair. The wheelchair assembly  10  is of the type having a plurality of other components, including a seat frame  20 , a pair of front caster assemblies  30 , a footrest assembly  40 , a backrest frame  50 , bracket assemblies  60  and rear wheel units  70 . 
     The seat frame  20  forms the structure of the wheelchair assembly  10 , and forms a structure for a seat  20 A to be supported by the seat frame  20 . The seat frame  20  may have a pair of tube assemblies  21 , a right-side tube assembly and a left-side tube assembly, for instance mirror images of one another. The seat frame  20  can be made of other components, i.e., not necessarily tubes, such as plates, beams, etc. The tube assemblies  21  are shown as having a L-shape. The L-shape is one possible embodiment of the tube assemblies  21 , and other shapes include a generally polygonal shape, a U-shape, etc. Although the expression “L-shape” is used, the tube assemblies  21  may appear to be a L rotated by 90 degrees clockwise or counterclockwise, depending on the point of view of the observer of the wheelchair  10  of  FIG. 1 . Moreover, although a right-angle bend is shown in  FIG. 1 , other angles may be used. 
     The tube assemblies  21  may each include a tubular member made in any appropriate material, such as carbon fiber, composites, metals (e.g., aluminum, titanium, steel, etc), and combinations thereof. According to an embodiment, the tubular member is a monolithic tube. The tubular member may have a first portion  21 A and a second portion  21 B. The first portion  21 A is generally horizontal when the wheelchair  10  is on its wheels, as in  FIG. 1 . The expression “generally horizontal” is well depicted in  FIG. 1 , in that the first portion  21 A may or may not be substantially parallel to the ground, e.g., it may be at an angle of up to 20 degrees relative to the ground. It is observed that the first portion  21 A is in the seating zone of the wheelchair  10 , and may even support a seat of the wheelchair  10 , as described hereinafter. The first portion  21 A may also support the bracket assemblies  60  and the rear wheel units  70 . The second portion  21 B is generally vertical or generally upright when the wheelchair  10  is on its wheels, as in  FIG. 1 . The expression “generally vertical” is also well depicted in  FIG. 1 , in that the second portion  21 B may or may not be substantially perpendicular to the ground. The second portion  21 B is in the bottom front zone of the wheelchair  10 , and may even support the front caster assemblies  30  and the footrest assembly  40 , as described hereinafter. The sectional shape of the second portion  21 B may be circular as in  FIG. 1 . The second portions  21 B may be parallel to one another, but may also be in a non-parallel relation. For example, the second portions  21 B may converge toward one another in a downward direction. 
     The backrest frame  50 , bracket assemblies  60  and rear wheel units  70  are connected to the seat frame  20  in any appropriate manner. Moreover, these components often include mechanisms so as to be foldable or removable from the seat frame  20 , for stowing the wheelchair  10 . It is pointed out that the backrest frame  50 , bracket assemblies  60  and rear wheel units  70  can have any appropriate configuration, beyond the configuration shown in the figures. For example, the seat frame  20 , the front caster assemblies  30 , the backrest frame  50 , the bracket assemblies  60  and/or the rear wheel units  70  may be as in any of U.S. Pat. Nos. 8,628,108, 9,844,479, U.S. patent application Ser. No. 15/811,073, U.S. Pat. No. 10,123,922, U.S. patent application Ser. No. 16/081,459, U.S. Pat. No. 10,155,414, and/or US patent application Ser. No. 16/081,315. 
     Referring to  FIGS. 2 and 3 , the footrest assembly  40  is shown in greater detail. Although the expression “footrest assembly” is used, other expressions may be used to identify the assembly, including footrest, footrest system, footrest unit, footrest mechanism, for example. Moreover, the expression “footplate” and “footrest” may be used interchangeably. The footrest assembly  40  may have a footplate  400 , a beam assembly  410 , a pivot clamp unit  420 , a mating clamp unit  430 , and/or a linkage assembly  440 :
         The footplate  400  is the part of the footrest assembly  40  upon which the user of the wheelchair  10  lays his/her feet. It is the interface between the user&#39;s feet and the wheelchair  10 .   The beam assembly  410  is one of the structural components of the footrest assembly  40 , and extends from side to side of the wheelchair  10 . Accordingly, the beam assembly  410  provides stiffness to the wheelchair  10 , especially when connected at opposed ends to the seat frame  20 , or other frame member of the wheelchair  10 . Moreover, the beam assembly  410  supports the footplate  400 . Although not shown, the beam assembly  410  and the footplate  400  may be integrated to one another, for instance by having plates integral with the beam assembly  410 .   The pivot clamp unit  420  interfaces the beam assembly  410  to one of the tube assemblies  21 , for instance. The pivot clamp unit  420  defines a rotational joint with the beam assembly  410  for the folding of the footrest assembly  40 .   The mating clamp unit  430  interfaces the beam assembly  410  to the other one of the tube assemblies  21 , when the wheelchair  10  is in a use condition (i.e., rolling condition, deployed condition, etc). The mating clamp unit  430  defines a releasable connector joint with the beam assembly  410  for allowing the folding of the footrest assembly  40 , such that the beam assembly  410  is releasably clamped to the mating clamp unit  430 .   The linkage assembly  440  is another one of the structural components of the footrest assembly  40 , and extends from the mating clamp unit  430  to the beam assembly  410 . The linkage assembly  440  assists in the folding of the footrest assembly  40  by interfacing the beam assembly  410  to the beam assembly  410  when the footrest assembly  40  is folded or in the process of being folded.       

     Referring to  FIG. 2 , the footplate  400  is shown in greater detail. The footplate  400  may have a plate member  401 , with one or more clamps  402  on the underside of the plate member  401 . A top side of the plate member  401  may be substantially planar, but may also have surface features like ribs, or added grip components, such as sandpaper like surface features, etc. Moreover, additional items such as foot straps may also be present. The clamps  402  may be of the type having a bore of adjustable size (e.g., by a set screw), the bore being for example of circular shape. Accordingly, if mounted on a cylindrical component of the beam assembly  410 , such as beam member  411 , a rotational and translational joint may be formed, allowing an adjustment of the position of the footplate  400  in a direction parallel to an elongated axis X of the beam member  411 , and an adjustment of the orientation of the footplate  400  relative to the elongated axis X of the beam member  411 . Once a desired position and orientation is reached, the clamp(s)  402  may be tightened (e.g., set screws) to lock the footplate  400  in position and orientation on the beam member  411 . 
     The configuration of the footplate  400  in  FIG. 2  is one of the numerous contemplated configurations. There may be one footplate  400  per foot or one footplate  400  for both feet. The footplate  400  may have a single clamp  402  or more than two clamps  402 . The footplate  400  may be fixed directly to the beam assembly  410  without adjustment possibility, for example without any clamp  402 , or with only one of the translational or rotational adjustment possibility, e.g., such as by way of cylindrical joint (a lockable cylindrical joint). The footplate  400  may be made of any appropriate material such as metal(s), composites and/or plastics, and may have additional components such as an anti-slip top surface, anti-slip adhesive, surface formations (e.g., ribs), etc. 
     Referring to  FIGS. 2 to 4 , the beam assembly  410  is illustrated as having the beam member  411 , or like elongated structural member with its elongated axis X. The beam member  411  may be a hollow tube of circular cross-section, although it may be solid (e.g., a rod), non-tubular, non-circular, etc. The beam member  411  may be made of any appropriate material such as metal(s), composites and/or plastics. In the illustrated embodiment, the beam member  411  is a tube, and the ends of the tube forming the beam member  411  may be open to accommodate connection components, such as those of a pivot unit  412  and of a connection interface such as a hook unit  413 . According to an embodiment, a length of the beam member  411  is cut in plant as a function of the desired width of the wheelchair  10 , and/or cut in situ to retrofit the footplate  400  on an existing wheelchair  10 . The pivot unit  412  and the hook unit  413  may then be mounted to the opposed ends of the beam member  411 . 
     The pivot unit  412  defines a support for pivot  412 A shared with the pivot clamp unit  420 . The pivot unit  412  may have an end press-fitted into the beam member  411  (e.g., force fit, interference fit, etc) or may be secured to the beam member  411  by a set screw, adhesive, among possibilities. As shown in  FIG. 4 , the pivot  412 A may be a bolt and nut assembly as one of numerous possibilities. Other possibilities include a screw, a pin with lock washers, safety pins, etc. The pivot  412 A has a rotational axis Y 2 . As observed in  FIG. 3 , the pivot unit  412  has an end projecting out of the beam member  411  that dips downwardly. Consequently, as shown in  FIG. 3 , the axis Y 2  is below the axis X when the wheelchair  10  has its wheels to the ground (i.e., as in the orientation shown in  FIG. 3 ). Stated differently, the axes X and Y 2  are in a transverse relation, with the axis Y 2  below axis X. 
     Referring to  FIG. 5 , an exploded view of the hook unit  413  is provided. The hook unit  413  is one of numerous connection interfaces by which the beam member  411  may be releasably connected to mating clamp unit  430  or to the linkage assembly  440 . Other embodiments may include a snap-fit system, with biased balls, a C-shaped clamp of resilient material, etc. The connection interface, such as hook unit  413  may be at various locations along the beam member  411  or on the linkage assembly  440  or on the seat frame  20 , and may be between the second end and a carriage clamp described hereinafter for example. The hook unit  413  is mounted to the end of the beam member  411  opposite the end of the beam member  411  featuring the pivot unit  412 . The hook unit  413  may have various components including a hook  413 A by which the beam assembly  410  releasably connects to the mating clamp unit  430 . The hook  413 A may define a female slot  413 B for being releasably connected to the mating clamp unit  430  in a manner described in more detail below. The female slot  413 B may be a truncated circle for snuggly receiving therein a cylindrical component as explained below, but it may also be elongated to allow some play with the component is received in the female slot  413 B. Alternatively, the hook  413 A could have a male member for mating engagement with the mating clamp unit  430 . Other coupling pairs could be used between the hook unit  413  and the mating clamp unit  430 , including magnetic pairs, complementary pairs, etc. 
     The hook unit  413  may be connected to the beam member  411  in any appropriate way, including force fit, interference fit, set screw, adhesive.  FIG. 5  shows one contemplated arrangement, with a quill  413 C received in the open end of the beam member  411 . As such, the quill  413 C may have a circular cross-section. The quill  413 C has a central bore  413 D such that an expander bolt or screw  413 D may extend from an exterior of the beam member  411  to an interior thereof, in which the expander bolt  413 E is operatively coupled to a wedge  413 F. The rotational axis of the expander bolt  413 E is not normal to the plane of the surfaces  413 G of the quill  413 C and wedge  413 F such that a screwing action will cause a slide of the wedge  413 F relative to the quill  413 C. The hook unit  413  may consequently be wedged into the beam member  411 , by the cooperative action of the quill  413 C and wedge  413 F. Therefore, the position and/or orientation of the hook unit  413  at the end of the beam member  411  may be finely adjusted. This may allow a user to readily adjust the length of the beam assembly  410  to fit the wheelchair  10 . A similar quill arrangement may be provided to connect the pivot unit  412  to the beam member  411 . In an embodiment, only one of the pivot unit  412  and hook unit  413  has a quill assembly, as it may be required to adjust the position and/or orientation only at one end. 
     The pivot clamp unit  420  and the mating clamp unit  430  are now described. While the clamp units  420  and  430  are convenient in allowing an adjustment of position and/or orientation on the seat frame  20  when the footrest assembly  40  is installed, other connection units, interfaces or joints may be used as alternatives to the clamp units  420  and  430 , to interface the footrest assembly  40  to the seat frame  20 . For example, there may not be any clamping as other connection configurations are contemplated, depending for instance on the nature of the seat frame  20 . The clamp units  420  and  430  are interfaces among others that may be used as part of the footrest assembly  40 . 
     Referring to  FIG. 4 , the pivot clamp unit  420  is shown from a top point of view relative to the pivot unit  412 . The pivot clamp unit  420  may have a clamp  421  by which it may be fixed to one of the tube assemblies  21  of the seat frame  20 . The clamp  421  may be of the same type as the clamp  402  described above, i.e., with a bore of adjustable diameter, such that a position and orientation of the clamp  421  may be adjusted relative to the tube assembly  21 , with the clamp  421  then locked into place by a set screw or the like tightening the assembly. In an embodiment, with the second portion  21 B having a round cross-section, the clamp  421  and second portion  21 B may form a two degree-of-freedom (DOF) joint—a cylindrical joint—, with a rotational DOF about a central axis of the second portion  21 B, and a translation in a direction parallel to the central axis of the second portion  21 B. The pivot clamp unit  420  may be mounted in other ways to the seat frame  20 , such as at a bottom open end of the tube assembly  21  (a male portion received in the tube assembly  21 , indexed holes in the tube assembly  21 , etc.). The pivot clamp unit  420  may also be an integral part of the tube assembly  21 . 
     A U-shaped bracket  422  projects from the clamp  421  and supports the pivot  412 A. Accordingly, the pivot unit  412  may rotate about axis Y 2  via the pivot  412 A. In an embodiment, one or more wave washers (or curved washers)  423  are located on the pivot  412 A, between the bracket  422  and the pivot unit  412 . The washers  423  apply some biasing force therebetween, which biasing force may be of sufficient magnitude to be felt by a user during the folding or deployment of the wheelchair  10 . The footrest assembly  40  may be without the washer(s)  423 . 
     Referring to  FIGS. 6 and 7 , the mating clamp unit  430  is on the other side of the wheelchair  10 . The mating clamp unit  430  may also have one or more clamps  431  (two shown in  FIG. 6 ) by which it may be fixed to the other of the tube assemblies  21  of the seat frame  20 . The clamp  431  may be of the same type as the clamps  402  and  421  described above, such that a position and orientation of the clamp  431  may be adjusted relative to the tube assembly  21 , with the clamp  431  then locked into place by a set screw or the like (two independent set screws may be present for the double clamps  431 ). In an embodiment, with the second portion  21 B having a round cross-section, the clamp  431  and second portion  21 B may form a two DOF joint—a cylindrical joint—, with a rotational DOF about a central axis of the second portion  21 B, and a translation in a direction parallel to the central axis of the second portion  21 B. The mating clamp unit  430  may also be mounted in other ways to the seat frame  20 , such as at a bottom open end of the tube assembly  21 , etc., e.g., manners described for the pivot clamp unit  420 . The mating clamp unit  430  may also be an integral part of the tube assembly  21  as well. 
     The mating clamp unit  430  may also have a U-shaped bracket  432  projecting from the clamp  431 , to support the ends of pin  433 . Accordingly, the pin  433  has an elongated axis. The pin  433  is the male connector that will be matingly received in the female slot  413 B of the hook unit  413 . The pin  433  is therefore sized for snug engagement with the female slot  413 B, for instance with some resistance against the release of one from the other once matingly engaged. However, if the female slot  413 B is elongated as opposed to being circular, the female slot  413 B may receive the pin  433  with some play. As the beam assembly  410  rotates in the direction shown by R 1  in  FIG. 6 , the pin  433  is one example of a male connector, and is located in the path of the hook unit  413  to matingly engage with the female slot  413 B, another example among possible female connectors. The pin  433  may be a bolt with nut, etc, in similar fashion to the pivot  412 A. A connector  434  is provided on one side of the bracket  432 . The connector  434  may be a set screw, a bolt, etc. The connector  434  serves as interface for the linkage assembly  440 , and may allow pivoting motion of the linkage assembly  440  relative to the mating clamp unit  430 . The connector  434  is located below the pin  433  may or may not extend from side to side of the U-shaped bracket  432 . 
     Referring to  FIGS. 3 and 6-8 , the linkage assembly  440  has a rod member  441 . The rod member  441  may be a rigid rod, such as a metal, plastic or composite rod. It may be a tube as well. In an embodiment, the rod member  441  has a smaller diameter than the beam member  411 . A carriage clamp  442  of the linkage assembly  440  is secured to the beam member  411 . The carriage clamp  442  may be of the same type as the clamps  402 ,  421  and  431  described above, such that a position and/or orientation of the carriage clamp  442  may be adjusted relative to the beam member  411 , with the carriage clamp  442  then locked into place by a set screw  442 A or the like. The carriage clamp  442  may hence form a central cylindrical joint with the beam member  411 . The rod member  441  may be pivoted to the beam member  411  in other ways, such as by a through pivot received in a pivot hole in the beam member  411 . In an embodiment, the carriage clamp  442  is convenient as it allows position and/or orientation adjustment. According to an embodiment, the carriage clamp  442  may lie over a center point of the beam member  411 . Moreover, as shown in  FIG. 8 , the carriage clamp  442  may be lodged between the clamps  402  of the footplate  400 . Hence, the spacing between the clamps  402  may be determined as a function of the presence of the carriage clamp  442 . A nipple  443  is mounted to the side of the carriage clamp  442  and is held by a pivot  444 , in such a way that the nipple  443  may rotate relative to the carriage clamp  442 , along axis Y 4 , with axis Y 4  being generally parallel to axis Y 2  when projected onto a horizontal plane. The rod member  441  has a first end received in the nipple  443 , whereby the rod member  441  is in a rotational relation with the carriage clamp  442 . The rod member  441  and nipple  443  may be screwed to one another, force fitted together, integral, etc. The nipple  443  could also be entered into a hollow end of the rod member  441  according to another embodiment. In an embodiment, the nipple  443  acts a female component of a male-female connector, though it may also be a male component. 
     The linkage assembly  440  may have another clamp at the other end of the rod member  441 , such as in the form of a clip  445 . The clip  445  may operate under the same principle as the previously described clamps (passage of variable size), such that a position and orientation of the clip  445  may be adjusted relative to the rod member  441 , with the clip  445  then locked into place by a set screw  445 A or the like. The orientation of the clip  445 , with its passage parallel to the rod member  441 , is such that the positon of the clip  445  along the rod member  441  does not impose a precise length constraint to the rod member  441 . 
     A tab  446  may extend from clip  445 . The tab  446  may define a hole  447 , for receiving the connector  434  of the mating clamp unit  430  therein. According to an embodiment, the hole  447  may be elongated in shape as shown in  FIG. 7 , to allow some play during the folding/deployment of the wheelchair  10 . The tab  446  and connector  434  thereby form a rotational joint about an axis Y 3 , that may also allow some translational movement in one particular embodiment. The axis Y 3  may be generally parallel to axes Y 2  and Y 4  when all are projected onto a horizontal plane. 
     To summarize, the footrest assembly  40  and its components, i.e., the beam assembly  410 , the pivot clamp unit  420  and the mating clamp unit  430  (or like frame interfaces), and the linkage assembly  440 , form a foldable mechanism with numerous DOF joints. For example, when assembled and ready for use, the beam assembly  410  and the linkage assembly  440  have a rotational DOF joint therebetween, about axis Y 4 . In an embodiment, another rotational DOF joint and a translation DOF joint may also be present, respectively about the X axis and in a direction parallel to the X axis of the beam member  411 , with these other DOF joints being lockable by the carriage clamp  442  or like interface component. The interface between the beam assembly  410  and the seat frame  20 , shown in an embodiment as the pivot clamp unit  420 , provides one rotational DOF joint (about axis Y 2 ). The pivot clamp unit  420  may also define another rotational DOF joint and a translation DOF joint about or in a direction parallel to an axis of the tube assembly  21 , these additional DOF joints being lockable by the clamping of the pivot clamp unit  420 . Accordingly, if the second portions  21 B on opposite sides of the frame  20  are not parallel to one another, the configuration of the clamps  421  and  431  allows an installation of the footrest assembly  40  to the seat frame  20 . Finally, the interface between the linkage assembly  440  and the seat frame  20 , shown in an embodiment as the mating clamp unit  430 , has a rotational DOF joint about axis Y 3 . There may also be translational DOF joint if the hole  447  has the form of an elongated slot, though such translational DOF joint provides a limited range of movement. The mating clamp unit  430  may also define another rotational DOF joint and a translation DOF joint about or in a direction parallel to an axis of the tube assembly  21 , these additional DOF joints being lockable by the clamping of the mating clamp unit  430 . The rod member  441  may also be in a lockable translational DOF joint relation with the clip  445 . Once assembled in the manner shown in  FIG. 3 , the total number of DOFs may be reduced by the constraints concurrently imposed by the components of the footrest assembly  40 .