Anti-tip assembly for power wheelchair

0001The invention relates to an anti-tip assembly for power wheelchairs in which a pair of drive wheels are operatively driven by one or more motors powered by an onboard battery assembly. Although the invention is particularly described with reference to a power wheelchair, it may also find application in related environments such as scooters or the like.

0002Power drive wheelchairs incorporating an anti-tip assembly are well known in the art. For example, our U.S.A. Patent No. 5,575,348, is representative of an earlier generation and shows and describes a spring dampener secured at one end to a frame and at an opposite end to an anti-tip assembly. The anti-tip assembly extends from an arm that also supports the drive motor so that the dampener acts as both a suspension for the wheelchair, as well as a portion of the anti-tip assembly that effectively resists tipping forces imposed by initial acceleration of the wheelchair.

0003In an effort to improve upon this commercially successful arrangement, and isolate the anti-tip assembly from the suspension during most tipping action, consideration is given to providing a separate anti-tip force resistance and using the dampener only through a latter part of a tipping action, if necessary. Because the anti-tip assembly is always connected through the suspension mechanism in the prior arrangement, there may be situations where the anti-tip mechanism of the prior arrangement lifts the drive wheels off the ground. The wheelchair could be stuck until the obstacle is overcome.

0004Simultaneously, it is desired to use as much of the structure of the commercially successful version as possible. This, of course, reduces inventory, and also provides for easy modification of an existing design.

0005Consequently, it has been considered desirable to develop a new and improved anti-tip assembly for a power wheelchair that can overcome the noted problems and achieve these various objectives.

0006According to one aspect of the invention there is provided a wheelchair comprising: <ul id="ul0001" list-style="none" compact="compact"><li>a frame;</li><li>first and second drive wheels operably mounted to the frame;</li><li>at least one driven wheel operably mounted to the frame;</li><li>at least one motor to power the first and second drive wheels;</li><li>a seat received on the frame;</li><li>an anti-tip assembly having a plate extending from the frame and an arm extending from the plate having an end with a smooth surface to engage the ground surface, first and second pins extending from the arm and received in corresponding first and second slots in the plate for respective non-parallel movement in the slots, and a biasing member having a first end secured to the plate and a second end operatively engaging the arm for opposing tipping forces imposed on the wheelchair.</li></ul>

0007According to another aspect of the invention there is provided a power wheelchair comprising: <ul id="ul0002" list-style="none" compact="compact"><li>a frame;</li><li>a drive assembly mounted on the frame;</li><li>a pair of drive wheels rotatably mounted to the frame and operably connected to the drive assembly;</li><li>at least one driven wheel mounted to the frame;</li><li>a seat secured to the frame to receive a user;</li><li>an anti-tip assembly extending from the frame and including a plate secured to the frame via a dampening mechanism, a first arm extending from the plate and mounted thereto for a limited amount of movement relative thereto, a ground engaging wheel disposed on a distal end of the first arm, a biasing member interposed between the first arm and the plate for urging the ground engaging wheel toward the ground surface, whereby initial anti-tip forces are provided by the biasing member until the first arm completes its travel relative to the plate and then the anti-tip forces are provided by the dampening mechanism.</li></ul>

0008According to a further aspect of the invention there is provided an anti-tip assembly for a power wheelchair, wherein the wheelchair includes drive wheels powered by a drive mechanism mounted on the frame, and first and second driven wheels rotatably connected to the frame that supports a seat, the anti-tip assembly comprising: <ul id="ul0003" list-style="none" compact="compact"><li>a plate secured to the frame via a dampening mechanism, a first arm mounted to the plate for limited relative movement, a smoothly curved, ground engaging surface disposed on a distal end of the first arm, a biasing member interposed between the first arm and the plate to urge the smoothly curved surface toward the ground, whereby initial anti-tip forces are provided by the biasing member until the first arm completes its travel relative to the plate and then the anti-tip forces are provided by the dampening mechanism.</li></ul>

0009Thus a power wheelchair may include first and second drive wheels secured to a frame and powered by a motor. An anti-tip assembly includes a plate extending from the frame and an arm extending from the plate for relative movement thereto. A ground engaging surface is defined at a distal end of the arm and is urged toward the ground surface by a biasing member connected at one end to the plate, and at the other end to an intermediate portion of the arm. Thus, initial anti-tip forces are provided by the biasing member resisting movement of the arm relative to the plate, and subsequently by the dampener when the relative movement between the arm and the plate has ceased.

0010Preferably, a pair of diverging slots are provided in the plate to allow a rotational and translational movement of the arm relative to the plate. Once pins associated with the arms engage opposite or upper ends of the slots, the anti-tip forces are then generated by the dampener.

0011Advantageously, a smooth surface on the distal end of the arm is provided by a rotating wheel.

0012Advantages that can be gained include a simplified structure that provides effective anti-tip forces and an improved anti-tip assembly achieved by modifying an existing structure.

0013The invention is diagrammatically illustrated by way of example in the accompanying drawings, in which:-

0014Figure 1 is a perspective view of a prior art power wheelchair of the kind under consideration.

0015Figure 2 is an elevational view of a power wheelchair incorporating the new anti-tip assembly and with selected features of the power wheelchair removed for ease of illustration.

0016Figure 3 is an enlarged view of the new anti-tip assembly.

0017Figure 4 is a perspective view of the new anti-tip assembly.

0018Figure 5 is a graphical representation of resistive forces generated by the new anti-tip assembly.

0019Referring now to the drawings wherein the showings are for the purposes of illustrating the preferred embodiment of the invention only and not for purposes of limiting the invention, the Figures show a power wheelchair A of the type shown and described in our U.S.A. Patent No. 5,575,348. More particularly, the wheelchair A includes a frame 10, such as a conventional H-shaped frame defined by a pair of longitudinal frame members that extend fore and aft and an interconnecting cross-frame member. Secured to the frame is a drive assembly that includes a pair of motors 12a,12b. The motors are powered by an on-board battery 14. A seat defined by seat portion 16 and a seat back 18 is also mounted to the frame. The seat may adopt a number of different configurations, including a non-adjustable standard seat, a tilt and/or recline seat, a van style seat, or a customized cushion mounted on a rigid seat pan that may include pelvic, head, or thigh pads/bolsters as desired by the user.

0020Preferably mounted on one of the arm rests 20a,20b is a motor controller such as a joystick controller 22. As is well known in the art, movement of the joystick in forward, rearward, leftward and rightward directions selectively powers the drive wheels, here shown as enlarged drive rear drive wheels 30, for desired steering of the wheelchair. Typically, a pair of driven wheels such as the illustrated small diameter front wheels 32 are provided on the chair. The front wheels are caster mounted 34 at front end portions of the longitudinal frame members, allowing the front wheels to rotate about respective vertical axes.

0021Although not shown or described herein for purposes of brevity, it will be understood that still other customized features may be incorporated into the power wheelchair, such as front riggings, footplates, leg rests, etc., without departing from the scope and intent of the present invention.

0022For purposes of consistency, like reference numerals will be used in Figures 2-4 to refer to like elements already described with regard to the power wheelchair of Figure 1. Likewise, new elements will be described by new numerals. Shown in Figure 2, an elongate arm 40 is pivotally secured by a pin 42 at a first end to an intermediate region of the frame. On a second or distal end of the elongate arm 40, is provided a plate 44, which is preferably defined by U-shaped channel structure that includes a pair of parallel plates disposed on opposite sides of a dampener 46. The dampener 46 is secured at a first end 48 to one end of the frame, preferably an end of the frame opposite the frame end where the driven wheels 32 are mounted. A second end 50 of the dampener is secured to the plate 44. Since the drive motors and driven wheels all are secured to the elongate arm 40, it will be appreciated that the dampener 46 also acts as a suspension shock absorber for the wheelchair.

0023With continued reference to Figure 2 and additional reference to Figure 3, a rigid metal arm 52 is mounted for limited movement relative to the plate 44. In the preferred arrangement, the arm is a U-shaped configuration (Figure 4). The arm is received between the parallel portions of the plate 44 for limited movement relative to the plate. The movement is defined by a pair of slots 54, 56 formed in the parallel plate portions. Each slot 54, 56 receives a pin 64,66, respectively, and the pins also extend through lower and upper portions of the arm, respectively. As will be appreciated, the pins 64,66 can move within the slots, and are shown in their normal at-rest position in Figure 3. This at-rest position is a result of the force imposed by a biasing member 68 that forms another key portion of the anti-tip assembly. The biasing member 68, illustrated in the preferred embodiment as a coil spring 68, is secured at a first end about a pin 70 to the frame. The pin 70 does not move relative to the frame so that the first or lower end of the spring 68 is fixed thereto. A second end of the spring is received about the pin 64 received in the groove 54 in the plate. Since the pin 64 is engaged in the arm 52, the spring 68 urges the arm toward its downward, counterclockwise position shown in Figure 3. There, the pin 66 is disposed against a lower end of the slot 56 while the pin 64 is likewise engaging a lower end of the slot 54.

0024Mounted on a distal end of the arm is a smoothly curved, ground-engaging surface defined by the peripheral surface of a rotating wheel 72. The wheel 72 has an axis 74 at an end of the first arm 52 and can engage the ground surface when the wheelchair begins to tip.

0025Referring again to Figure 2, initial resistive or anti-tip forces are provided by the biasing spring 68. That is, the wheel engages the ground surface and the movement of the first arm is dictated by the movement of the pins (54,56) in the associated slots (64,66). In essence, the wheel 72 moves upwardly and toward the left as viewed in Figures 2 and 3, this movement being resisted by the linear force imposed by the spring 68. During this relative movement of the first arm 52 relative to the plate 44, it is only the biasing spring 68 which opposes the tipping action of the wheelchair.

0026Ultimately, the pin 64 reaches the opposite or upper end of the associated slot 54. Likewise, the pin 66 reaches the opposite or upper end of the slot 66. When this occurs, further movement of the first arm 52 relative to the plate 44 in this direction is precluded. Thus, if tipping motion is still occurring, the anti-tipping forces are then generated by the dampener 46 that extends between the plate 44 and the frame 10. Again, this provides a linear anti-tip force that is associated with the dampener 46.

0027These resisting forces are generally illustrated in the graph of Figure 5. The spring 68 has an initial preload so that until the tipping forces reach this preload, no anti-tipping or resisting forces are provided. Thereafter, the first arm 52 begins to move relative to the plate 44 and is resisted by the spring force 68. This is represented by portion 80 of the curve. It will be appreciated that a different spring having a different spring rate could be is substituted if desired. Thus, even though the resisting force will still be linear, it will be defined by a different spring rate or constant associated with the new spring.

0028Once the first arm 52 has completed its movement relative to the plate, the dampener 46 then takes over. This changeover is represented at point 82 on the graph. The increase in the resisting force for a small amount of change in vertical displacement is then represented by the portion 84 in the graph. This is associated with the resisting force provided by the dampener 46.

0029Still another adjustment that may be made is represented by a slot 90 in the plate 52. The slot 90 is parallel to the slot 54 but is located closer to the slot 56 in the plate. By inserting the pin 64 in the slot 90, the movement of the arm 52 will be altered. The operation of the anti-tip assembly, though, is substantially as described above and allows the wheelchair to overcome small obstacles because of the arm 52 that is movable relative to the suspension assembly.