Abstract:
A tilt seat mechanism for a wheelchair that includes a base frame and a seat frame that are nested and parallel in a first position and separated and angled in a second position. The seat frame is rotated about a pivot on the base frame by an electrically driven jackscrew. The drive linkage comprises a crossbar connected to the end of the jackscrew and a pair of tee-head connecting links that move with the crossbar. The ends of the crossbar move in channels on the base frame and pivotally connect to the tee-head links. The connecting links are pivotally attached to a bracket fixed on the seat frame. As the jackscrew turns it moves the crossbar and connecting links out from a closed position. This movement results in the lifting of the seat platform to a reclining position with respect to the horizontal base frame.

Description:
RELATIONSHIP TO PRIOR APPLICATIONS 
     The present application claims the benefit of the filing date of U.S. Provisional Patent Application Serial No. 60/192,302 filed Mar. 27, 2000. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to components and structures for wheelchairs. The present invention relates more specifically to mechanisms for retaining, supporting and tilting the seat platform of a wheelchair. 
     2. Description of the Related Art 
     It is desirable in many uses of a wheelchair to be able to move the seat platform of the chair to a reclining position. Efforts to achieve this capability have frequently failed to provide both a durable tilting framework and a low profile structure. Effective mechanisms typically have excessive structural requirements while low profile systems typically fail to operate very effectively. 
     It would be desirable to have a low profile seat tilting mechanism that operated smoothly and efficiently without the need for excessive power motor requirements. It would be desirable if such a low profile seat tilting mechanism could move the seat platform of the wheelchair through at least sixty (60) degrees of effective rotation or tilt. It would be desirable if such a mechanism could be implemented in a minimal amount of space below or within the seat platform of the wheelchair. Finally it would be desirable if such a tilt system provided stability to the seat platform throughout the range of motion possible. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a tilt mechanism for a wheelchair seat platform that is both durable and low in profile. 
     It is an object of the present invention to provide a tilt seat mechanism for a wheelchair that provides a stabile range of motion of at least sixty (60) degrees from the horizontal to the inclined. 
     It is a further object of the present invention to provide a tilt seat mechanism for a wheelchair that incorporates a linkage system that minimizes the motorized power required to effect tilting movement of the seat platform. 
     It is a further object of the present invention to provide a tilt seat mechanism for a wheelchair that is rugged and durable in the face of repeated use and yet does not require excessively heavy linkage members and frame supports. 
     In fulfillment of these and other objectives the present invention provides an improved tilt seat mechanism for a wheelchair that is structurally durable, operationally effective, and yet low in profile, adding very little to the overall framework of the chair platform. The mechanism structure includes a base frame and a seat platform frame that are nested and parallel in a first position and separated and at an angle of sixty (60) degrees or more in a second position. The seat platform component is rotated about a pivot point on and with respect to the base frame, by an electrically driven jack-screw with a unique linkage between the frame components. The linkage comprises a movable cross bar connected to the end of the jack-screw as well as a pair of tee-head connecting links that move with the crossbar. The ends of the cross bar move in channels on the base frame and pivotally connect to the tee-head connecting links. The connecting links are each pivotally attached to a transverse lever bracket fixed on the seat platform frame. As the jack-screw turns it moves the cross bar and connecting links forward or out from a “closed” position. Due to the placement of the pivot point for the seat platform frame, the movement of the connecting links outward pulls on the lever bracket of the platform frame and rotates the seat platform frame around the pivot point. This rotation results in the lifting of the seat platform to a reclining position with respect to the typically horizontal base frame. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a top plan view of the assembly of the present invention in a lowered condition. 
     FIG. 2 is a perspective view of the seat platform frame component of the present invention. 
     FIGS. 3 a - 3   b  are detailed perspective and detailed side views respectively of the base frame component of the present invention. 
     FIGS. 4 a - 4   d  are detailed side views of the connecting link components of the present invention. 
     FIGS. 5 a - 5   c  are partial cross sectional side views of the assembly of the present invention in three different tilt configurations. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference is made first to FIG. 1 for a general description of the complete assembly of the present invention and the various linkages that implement its tilting motion. Initially it is understood that the assembly of the present invention as shown in FIG. 1 would be positioned on a wheelchair frame in support of a seat structure for receiving the occupant of the wheelchair. The present invention would typically be used in conjunction with an electric motorized wheelchair powered by batteries or the like. The structure of the present invention would be fixed to the wheelchair carriage in a manner well known in the art and would receive and fix the chair or seat structure of the wheelchair, again in a manner well known in the art. 
     The assembly of the present invention as shown in FIG. 1 is comprised primarily of seat platform frame  10  and base frame  12 . In the closed or horizontal condition shown in FIG. 1, base frame  12  is nested within and parallel to seat platform frame  10 . The two frames are pivotally attached to each other at pivot points  16 . These pivot points  16  allow seat platform frame  10  to be raised in a rotational manner to an inclined position with respect to generally horizontal base frame  12 . 
     Seat platform frame  10  incorporates a transverse component that extends over and across base frame  12  and incorporates two lever brackets  14 . This transverse component of seat platform frame  10  receives most of the torsional forces involved in tilting the seat platform and is therefore constructed of a relatively rugged grade metal stock or the like. Lever brackets  14  are rigidly fixed to the transverse component of seat platform frame  10  and move with platform frame  10  during the tilting process. Lever brackets  14  are each pivotally linked to tee-head connecting links  18   a  and  18   b  in a manner described in more detail below. 
     At the opposite end of each of tee-head connecting links  18   a  and  18   b  are additional pivoting connection points to cross bar  20 . Cross bar  20  is essentially a moveable axle that pivotally engages tee-head connecting links  18   a  and  18   b  adjacent opposing ends of cross bar  20 . At the extreme ends of cross bar  20  are positioned channel bushings  11  which permit the sliding movement of the ends of cross bar  20  within channels  22 . Channels  22  are positioned on and fixed to base frame  12  and remain horizontal (coplanar with base frame  12 ) during the tilting operation. 
     Cross bar  20  is linked at its center to jack screw  24  which extends parallel to tee-head connecting links  18   a  and  18   b,  back towards the drive mechanism for the assembly. The end of jack screw  24  that is connected to cross bar  20  is the movable end of the jack screw, serving to move cross bar  20  along channels  22  as shown. The fixed end of jack screw  24  is attached to base frame  12  at jack screw fixed yoke  25 . Intermediate to this fixed end of jack screw  24  is worm gear  26  which couples electric motor  28  to jack screw  24 . 
     The assembly described above operates in the following manner. Activation of electric motor  28  (by an appropriate electrical switch) turns worm gear  26  which drives jack screw  24 . Movement of jack screw  24  displaces cross bar  20  “forward” in channels  22  by means of channel bushings  11 . As a result, cross bar  20  pulls tee-head connecting links  18   a  and  18   b  forward with it. As tee-head connecting links  18   a  and  18   b  move forward, they pull on lever brackets  14  which are fixed to the transverse component of platform frame  10 . This lever action on seat platform frame  10  causes a rotation of the platform about pivot points  16  thus raising the platform to an inclined angle with respect to base frame  12 . 
     Reference is now made to FIG. 2 for a brief description of the structure of seat platform frame  10 . As shown in FIG. 2, seat platform frame  10  is essentially a rectangular metal frame adjustable in a number of aspects and suitable for the retention of the seat platform for a typical electric wheelchair. Pivot points  16  are shown constructed from yoke configurations that serve to receive matching pivot points on base frame  12 . The transverse component of seat platform frame  10  is shown in this perspective view connecting pivot points  16  on either side. Positioned behind the transverse component of seat platform frame  10  are lever brackets  14 , partially hidden in this view. 
     FIGS. 3 a  and  3   b  show in greater detail the structure of base frame  12 . In FIG. 3 a,  pivot points  16 , positioned on either side of base frame  12 , are shown appropriately aligned to insert into the pivot point yokes shown on seat platform frame  10  in FIG.  2 . Open channels  22  are shown positioned to receive channel bushings  11  and the associated cross bar  20 . Jack screw yoke  25  is positioned on a rear transverse component of base frame  12  where it suitably fixes one end of jack screw  24 . 
     Once again, base frame  12  is to be permanently mounted or fixed to the carriage of the electric wheelchair. Appropriate apertures and plates for such a mounting are provided. 
     Reference is now made to FIGS. 4 a  through  4   d  for a brief description of the structural components of tee-head connecting links  18   a  and  18   b.  FIGS. 4 a  through  4   c  disclose in a number of views the structure of bar component  17  of connecting link  18 . At one end of bar component  17  is cross bar aperture  19  which is a cylindrical aperture sized and shaped to receive cross bar  20  as described above. At an opposite end of bar component  17  is threaded aperture  21  which serves to receive adjustable link eye  23  shown in FIG. 4 d.  Adjustable link eye  23  may be adjustably screwed into threaded aperture  21  and held fixed at a specific length. Lever bracket aperture  15  on adjustable link eye  23  is then positioned to engage lever bracket pins that pivotally connect connecting links  18   a  and  18   b  to lever brackets  14  shown in FIG.  1 . 
     Reference is now made to FIGS. 5 a  through  5   c  for a description of the functioning of the tilt seat mechanism of the present invention and its configuration in a lowered, a middle, and a raised position. FIG. 5 a  shows in a partial cross sectional side view the configuration of the assembly in a lowered position. In this view, seat platform frame  10  is generally parallel to and coplanar with base frame  12 . Pivot point  16  matches the respective pivot point components on seat platform frame  10  and base frame  12  and provides the rotational pivot point for the rotational movement of seat platform frame  10  with respect to base frame  12 . Lever bracket  14  is shown fixed on seat platform frame  10  and connected to connecting link  18   b  (in this view). Similar connections would be made to connecting link  18   a  on an opposite side of the assembly. 
     Cross bar  20  is seen in its diametrical cross section, positioned to travel along channel  22  at the urging of jack screw  24  positioned at its center. Jack screw  24  is driven by electric motor  28  through the linkages described above. Movement of cross bar  20  in channel  22  draws connecting link  18   b  forward (to the left in FIG. 5 a ) which in turn draws lever bracket  14  downward and forward in a clockwise rotational direction in this view. This tends to force seat platform frame  10  upward with respect to base frame  12 . 
     In FIG. 5 b  the tilting process has been carried out through approximately half of its range. In this view, connecting link  18   b  is shown directed forward and pulling on lever bracket  14  in the process. Jack screw  24  has forced cross bar  20  forward in channel  22  in base frame  12 . This causes the clockwise rotation (in this view) of seat platform frame  10  about pivot point  16  connected to base frame  12 . 
     Finally, in FIG. 5 c  the assembly is shown in its most extreme tilting position (approximately 60 degrees from horizontal). In this view, connecting link  18   b  has been pulled completely forward with cross bar  20  reaching its limit in channel  22 . In this manner, lever bracket  14  has been rotated from a nearly horizontal orientation (FIG. 5 a ) to a nearly vertical orientation. Jack screw  24  has reached its fullest extent forcing cross bar  20  forward, guided by channel bushings  11  which move within channels  22 . 
     Many features and advantages of the present invention are discernable from the detailed specification and the attached figures. It is therefore intended by the appended claims to cover all such features and advantages of the invention that fall within the spirit and scope of the invention. Furthermore, since numerous modifications and variations will readily occur to those skilled in the art, it is not desired that the present invention be limited to the exact construction and operation illustrated and described herein. Accordingly therefore, all suitable modifications and equivalents that may be resorted to are intended to fall within the scope of the claims. Although the invention has been described with reference to specific embodiments, this description should not be construed as limiting. Various modifications of the disclosed embodiments, as well as alternative embodiments of the inventions will become apparent to persons skilled in the art upon reference to the description of the invention. It is, therefore, contemplated that the appended claims will cover such modifications that fall within the scope of the invention.