WO2013095501A1

WO2013095501A1 - Obstacle crossing wheelchair and method of use

Info

Publication number: WO2013095501A1
Application number: PCT/US2011/066795
Authority: WO
Inventors: Shin-Min SONG
Original assignee: Northern Illinois Research Foundation
Priority date: 2011-12-22
Filing date: 2011-12-22
Publication date: 2013-06-27

Abstract

An apparatus for crossing obstacles in a wheelchair comprises a frame, a seat and a seat back, and a gearbox configured to raise the front and rear wheels. At least one support leg may move horizontally and vertically along the frame to support the wheelchair when the front or rear wheels are raised. The apparatus may be used to ascend steps or cross thresholds. As the obstacle crossing wheelchair ascends a step or crosses a threshold, the seat is maintained substantially parallel to the travelling surface below the step or threshold, and the wheelchair frame is not raised with respect to the travelling surface below the step or threshold when the wheelchair ascends the step or crosses the threshold.

Description

Attorney Docket No.23973WO01

TITLE

Obstacle Crossing Wheelchair And Method Of Use

RELATED APPLICATIONS

[0001] [Not Applicable]

FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] [Not Applicable]

[MICROFICHE/COPYRIGHT REFERENCE]

[0003] [Not Applicable]

BACKGROUND OF THE INVENTION

[0004] The present obstacle crossing wheelchair generally relates to the field of wheelchairs. More specifically, the present obstacle crossing wheelchair relates to apparatus and methods that enable a wheelchair operator to cross an obstacle in the wheelchair without assistance from another person.

[0005] Wheelchairs are an important transportation tool for millions of disabled persons throughout the world. A typical manually operated wheelchair includes a cross-brace frame to facilitate folding of the chair for transportation when not in use, built-in or removable armrests, swing-away footrests, a seat, two small diameter front wheels, two relatively large drive rear wheels, and push handles for persons other than the operator to use for assisting the operator in moving the wheelchair. Some manual wheelchairs are specially modified for the particular needs of their users. For example, some manual wheelchairs are designed to be heavy duty wheelchairs, which are useful for users who are hard on their wheelchair or weigh in excess of approximately 160 kilograms. Other wheelchairs are designed to place the operator in a reclined position. This recliner design is useful for operators who cannot readily shift their weight. Still other wheelchairs are pediatric wheelchairs designed for children. [0006] Wheelchairs may also be motorized. The motor of a typical motor- operated wheelchair is powered by a battery. Motorized wheelchairs are typically heavier than manual wheelchairs, and require battery charging and maintenance. However, a motorized wheelchair may be necessary for an individual having limited arm and/or torso strength, or situations where the user must travel up significant inclines. Similar to the manual wheelchairs, motorized wheelchairs frequently employ rear drive wheels that are larger than the front wheels, although not usually as large as the rear wheels on manual wheelchairs. Also similar to the manual wheelchairs, some motorized wheelchairs are specially modified for the particular needs of their users. Examples include heavy duty wheelchairs, pediatric wheelchairs, and mid-drive wheel wheelchairs. Mid-drive wheel chairs typically have two sets of small idler wheels, one set in front of the mid-drive wheels, and one set behind. This design increases the maneuverability of the wheelchair, making it well-suited for small apartments.

[0007] While traditional wheelchairs may perform adequately on smooth surfaces, they have limited obstacle crossing capability. However, many of the walkways of our world include structures that present obstacles for those operating a traditional wheelchair. Traditional wheelchairs cannot cross, for example, a small step or a door threshold up to 20 centimeters high without assistance from someone other than the wheelchair operator. These structures may not be considered obstacles to non-disabled individuals walking across them.

[0008] Of the millions of wheelchairs in use throughout the world, only a fraction have a significant obstacle crossing capability. These specialty wheelchairs may employ additional drive wheels, or even tracks to cross obstacles. Some specialty wheelchairs can even maneuver up and down a stairway. However, the cost of these wheelchairs may many times more than that of a conventional wheelchair. For example, an IBOT power wheelchair can cross many obstacles but may cost over $26,000 U.S. dollars. As a result, the majority of wheelchair users cannot afford a wheelchair with obstacle crossing capabilities.

[0009] Existing specialty wheelchairs that possess significant obstacle-crossing capabilities typically jostle the wheelchair operator while traversing obstacles. The seat of these wheelchairs are frequently raised and tilted during the crossing of obstacles. In fact, the operator may sometimes be placed at awkward or even dangerous angles to the otherwise level surface while crossing obstacles. In any case, such jostling and tilting does not promote user comfort, and may aggravate existing injuries of the user, if any.

[0010] To accommodate the majority of wheelchair users, buildings and walkways must often be designed or modified to eliminate obstacles for wheelchair users. These designs and modifications may result in high costs for eliminating, for example, a small step or steps that present no significant obstacle for the majority of the people using the buildings or walkway. Even small, individual obstacles, such as a single step 20 centimeters high, can be costly to design around, and may even involve the construction of a separate, inclined pathway to facilitate the use of a typical wheelchair. Moreover, in many parts of the world, doorways to buildings include a substantial threshold that may be costly to design around.

[0011] Obstacles, such as small steps, thresholds, etc., may be found on walkways throughout the world today. In light of the above, wheelchair users needing to cross these obstacles such as steps, thresholds, etc. may not be able to do so, or may not be able to do so safely, or without incurring a high monetary cost.

BRIEF SUMMARY OF THE INVENTION

[0012] One embodiment of the present obstacle crossing wheelchair comprises a pair of front wheels and a pair of rear wheels movably connected to a frame, a seat and a seat back connected to the frame, a gearbox configured to raise the rear wheels by rotating the rear wheels around a rear wheel driven sprocket offset from a center axis of the rear wheels, the gearbox also configured to raise the front wheels by rotating a linkage attached to a front wheel driven sprocket and the frame, at least one support leg, the at least one support leg horizontally and vertically moveable along the frame, the at least one support leg further comprising at least one roller at a bottom end of the support leg, a locking mechanism for vertically locking the at least one support leg to the frame, and a locking mechanism for locking the at least one roller.

[0013] The obstacle crossing wheelchair may be configured to maintain the seat substantially parallel to a travelling surface as the wheelchair crosses an obstacle. The pair of rear wheels and the pair of front wheels may be raised at least twenty centimeters above a travelling surface. The at least one support leg may be comprised of two support legs. The gearbox may be configured to be manually operated or motor operated. The linkage may be configured to move the front wheels in a substantially vertical direction when the front wheel driven sprocket is rotated. The at least one support leg may be configured to move along the frame horizontally using a horizontal sliding mechanism, a rotary joint in combination with a sliding mechanism, or another suitable mechanism. The wheelchair may be configured to maintain the frame at a fixed crossing height when the wheelchair crosses an obstacle. The wheelchair may further comprise a front wheel drive chain connecting a front wheel drive sprocket in the gearbox with the front wheel driver sprocket, and a rear wheel drive chain connecting a rear wheel drive sprocket in the gearbox with the rear wheel driver sprocket. The gearbox may comprise a clutch to selectively engage the gearbox with the front wheel drive sprocket or the rear wheel drive sprocket.

[0014] A method of ascending a step with an obstacle crossing wheelchair may comprise: positioning a wheelchair having a center of gravity such that a pair of rear wheels are on a lower travelling surface adjacent to the bottom of a step, a center axis of the pair of rear wheels at a travelling height above the lower travelling surface, lowering at least one support leg to contact the lower travelling surface below the step at a position between the step and the center of gravity, vertically locking the at least one support leg with a locking mechanism, operating a gearbox to rotate the pair of rear wheels around a driven sprocket offset from the center axis of the rear wheels to raise the pair of rear wheels into contact with a top edge of the step, rolling the wheelchair backwards towards the step to position the pair of rear wheels on an upper travelling surface away from the top edge of the step to provide stability, unlocking and raising the at least one support leg above the step, vertically locking the at least one support leg with a locking mechanism, rolling the wheelchair further backwards to position a pair of front wheels on the lower travelling surface adjacent the step, a center axis of the pair of front wheels at a travelling height above the lower travelling surface, unlocking and lowering the at least one support leg to contact the upper travelling surface between the step edge and the center of gravity, vertically locking the at least one support leg with a locking mechanism, operating the gearbox to rotate a linkage attached to a front wheel driven sprocket and the frame to raise a lowermost point on the pair of front wheels substantially vertically to a height above a height of the upper travelling surface, rolling the wheelchair still further backwards to position the pair of front wheels above the top surface of the step away from the top edge of the step to provide stability, and operating the gearbox to rotate a linkage attached to a front wheel driven sprocket and the frame to lower the pair of front wheels into contact with the upper travelling surface.

[0015] Another method of ascending a step with an obstacle crossing wheelchair may comprise: positioning a wheelchair having a center of gravity such that a pair of front wheels are on a lower travelling surface adjacent to the bottom of a step, a center axis of the pair of front wheels at a travelling height above the lower travelling surface, lowering at least one support leg to contact the lower travelling surface below the step at a position between the step and the center of gravity, vertically locking the at least one support leg with a locking mechanism, operating a gearbox to rotate a linkage and raise the pair of front wheels substantially vertically to a height greater than the height of the step, rolling the wheelchair towards the step to position the pair of front wheels over an upper travelling surface away from the top edge of the step to provide stability, unlocking and raising the at least one support leg above the step, vertically locking the at least one support leg with a locking mechanism, rolling the wheelchair further to position a pair of rear wheels on the lower travelling surface adjacent the step, a center axis of the pair of rear wheels at a travelling height above the lower travelling surface, unlocking and lowering the at least one support leg to contact the upper travelling surface between the step edge and the center of gravity, vertically locking the at least one support leg with a locking mechanism, operating the gearbox to rotate a rear wheel driver sprocket and raise the rear wheels into contact with a top edge of the step, rolling the wheelchair still further to position the pair of rear wheels on a top surface of the step away from the top edge of the step to provide stability, and operating the gearbox to rotate a rear wheel driver sprocket and lower the pair of rear wheels into contact with the upper travelling surface.

[0016] The above-described methods may further comprise unlocking and raising the at least one support leg, vertically locking the at least one support leg with a locking mechanism, and operating the gearbox to simultaneously return the center axis of both the rear wheels and the front wheels to their respective travelling heights. The upper travelling surface in the methods may be 20 centimeters above the lower travelling surface.

[0017] A method of crossing a threshold with an obstacle crossing wheelchair may comprise: positioning a wheelchair such that a pair of rear wheels are on a travelling surface adjacent to a first side of the threshold, a center axis of the pair of rear wheels at a travelling height above the travelling surface, lowering at least one support leg to contact the travelling surface at a position between the threshold and the center of gravity, vertically locking the at least one support leg with a locking mechanism, operating a gearbox to rotate a driven sprocket offset from the center axis of the pair of rear wheels to raise the pair of rear wheels into contact with a top edge of the threshold, rotating the pair of rear wheels backwards over the top surface of the threshold, further operating the gearbox to lower the pair of rear wheels onto the travelling surface on a second side of the threshold and pull the wheelchair backwards, unlocking and raising the at least one support leg to a height above the height of the threshold, vertically locking the at least one support leg with a locking mechanism, rolling the wheelchair further backwards to position a pair of front wheels on the travelling surface adjacent the first side of the threshold, a center axis of the front wheels at a travelling height above the travelling surface, lowering the at least one support leg to contact the travelling surface on the second side of the threshold at a position between the threshold and the center of gravity, vertically locking the at least one support leg with the locking mechanism, operating the gearbox to rotate a linkage attached to a front wheel driven sprocket and the frame to raise a lowermost point of the pair of front wheels substantially vertically to a height greater than the height of the threshold, rolling the wheelchair still further backwards to position the pair of front wheels on the second side of the threshold, and operating the gearbox to lower the pair of front wheels onto the travelling surface on the second side of the threshold.

[0018] Another method of crossing a threshold with an obstacle crossing wheelchair may comprise: positioning a wheelchair such that a pair of front wheels are on a travelling surface adjacent to a first side of the threshold, a center axis of the pair of front wheels at a travelling height above the travelling surface, lowering at least one support leg to contact the travelling surface at a position between the threshold and the center of gravity, vertically locking the at least one support leg with a locking mechanism, operating the gearbox to rotate a linkage attached to a front wheel driven sprocket and the frame to raise a lowermost point of the pair of front wheels substantially vertically to a height greater than the height of the threshold, rolling the wheelchair forward to position the pair of front wheels on a second side of the threshold, operating the gearbox to lower the pair of front wheels onto the travelling surface on the second side of the threshold, unlocking and raising the at least one support leg to a height above the height of the threshold, vertically locking the at least one support leg with a locking mechanism, further rolling the wheelchair forward to position a pair of rear wheels adjacent to the first side of the threshold, lowering the at least one support leg to contact the travelling surface on the second side of the threshold at a position between the threshold and the center of gravity, vertically locking the at least one support leg with the locking mechanism, operating the gearbox to rotate a driven sprocket offset from the center axis of the rear wheels to raise the rear wheels into contact with a top edge of the threshold on the first side of the threshold, rotating the pair of rear wheels forwards over a top surface of the threshold to a top edge of the threshold on the second side of the threshold, further operating the gearbox to lower the pair of rear wheels onto the travelling surface on the second side of the threshold and pull the wheelchair further forwards.

[0019] The top surface of the threshold may be 20 centimeters from the travelling surface below the threshold in the above-described methods of crossing a threshold with an obstacle crossing wheelchair. In the above-described methods of ascending a step or crossing a threshold with an obstacle crossing wheelchair, the wheelchair seat may be maintained substantially parallel to the travelling surface below the step or threshold as the wheelchair ascends the step or crosses the threshold, and the wheelchair frame may not be raised with respect to the travelling surface below the step or threshold when the wheelchair ascends the step or crosses the threshold.

[0020] Objects and advantages of the present obstacle crossing wheelchair and method of use are set forth in, or will be apparent to those of ordinary skill in the art from the detailed description herein. Also, it should be further appreciated that modifications and variations to the specifically illustrated and discussed features or materials hereof may be practiced in various embodiments and uses of this invention without departing from the spirit and scope thereof, by virtue of present reference thereto. Such variations may include, but are not limited to, substitution of equivalent means and features or materials for those shown or discussed, and the functional or positional reversal of various parts, features or the like.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

[0021] A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which:

[0022] Figure 1 depicts a side view of the present obstacle-crossing wheelchair;

[0023] Figure 2 depicts a front perspective view of the present obstacle-crossing wheelchair;

[0024] Figure 3 depicts a rear perspective view of the present obstacle-crossing wheelchair;

[0025] Figure 4 depicts a left front perspective view showing details of the gearbox illustrated in Figures 2 and 3 for the present obstacle-crossing wheelchair;

[0026] Figure 5 depicts a right front perspective of the gearbox illustrated in Figures 2 and 3 for the present obstacle crossing wheelchair;

[0027] Figure 6 depicts a right front view of a supporting leg;

[0028] Figure 7 depicts a right front view of a variation of the supporting leg illustrated in Figure 6;

[0029] Figure 8 depicts a right rear view of a supporting leg and an exemplary locking mechanism;

[0030] Figure 9 depicts a side view of the present obstacle-crossing wheelchair with the front and rear wheels in a travel position and the rear wheels in a positioned adjacent to a step; [0031] Figure 10 depicts a side view of the present obstacle-crossing wheelchair of Figure 9 with support legs lowered onto the surface below the step;

[0032] Figure 11 depicts a side view of the present obstacle-crossing wheelchair of Figure 10 with the rear wheels raised from the travel position to the level of the step;

[0033] Figure 12 depicts a side view of the present obstacle-crossing wheelchair of Figure 11 with the rear wheels positioned on the step;

[0034] Figure 13 depicts a side view of the present obstacle-crossing wheelchair of Figure 12 with the support legs raised;

[0035] Figure 14 depicts a side view of the present obstacle-crossing wheelchair of Figure 13 with the front wheels positioned adjacent to the step and the rear wheels on the step;

[0036] Figure 15 depicts a side view of the present obstacle-crossing wheelchair of Figure 14 with the support legs lowered onto the step surface;

[0037] Figure 16 depicts a side view of the present obstacle-crossing wheelchair of Figure 15 with the front wheels raised from the travel position to the level of the step;

[0038] Figure 17 depicts a side view of the present obstacle-crossing wheelchair of Figure 16 positioned with the front and rear wheels on the step;

[0039] Figure 18 depicts a side view of the present obstacle-crossing wheelchair of Figure 17 with the support legs raised and the rear wheels returned to the travel position on the step;

[0040] Figure 19 depicts a side view of the present obstacle-crossing wheelchair of Figure 18 with the front wheels returned to the travel position on the step;

[0041] Figure 20 depicts a side view of the present obstacle-crossing wheelchair with the front and rear wheels in a travel position and the rear wheels in a positioned adjacent to a first side of a threshold;

[0042] Figure 21 depicts a side view of the present obstacle-crossing wheelchair of Figure 20 with support legs lowered onto the surface on the second side of the threshold; [0043] Figure 22 depicts a side view of the present obstacle-crossing wheelchair of Figure 21 with the rear wheels raised from the travel position to a level above the threshold;

[0044] Figure 23 depicts a side view of the present obstacle-crossing wheelchair of Figure 22 positioned with the raised rear wheels positioned on a second side of a threshold;

[0045] Figure 24 depicts a side view of the present obstacle-crossing wheelchair of Figure 23 with the rear wheels positioned on the surface on the second side of the threshold;

[0046] Figure 25 depicts a side view of the present obstacle-crossing wheelchair of Figure 24 with the support legs raised;

[0047] Figure 26 depicts a side view of the present obstacle-crossing wheelchair of Figure 23 with the front wheels positioned adjacent to the first side of the threshold;

[0048] Figure 27 depicts a side view of the present obstacle-crossing wheelchair of Figure 26 with the support legs lowered onto the surface on the second side of the threshold;

[0049] Figure 28 depicts a side view of the present obstacle-crossing wheelchair of Figure 27 with the front wheels raised from the travel position to a level above the threshold;

[0050] Figure 29 depicts a side view of the present obstacle-crossing wheelchair of Figure 28 positioned with the front wheels raised over the surface on the second side of the step;

[0051] Figure 30 depicts a side view of the present obstacle-crossing wheelchair of Figure 29 with the front wheels lowered onto the surface on the second side of the step;

[0052] Figure 31 depicts a side view of the present obstacle-crossing wheelchair of Figure 30 with the rear wheels returned to the travel position;

[0053] Figure 32 depicts a side view of the present obstacle-crossing wheelchair of Figure 31 with the front wheels returned to the travel position;

[0054] Figure 33 depicts a side view of the present obstacle-crossing wheelchair of Figure 32 with the support legs raised. [0055] Repeat use of reference characters throughout the present specification and appended drawings is intended to represent same or analogous features or elements of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0056] Reference now will be made in detail to the embodiments of the invention, one or more examples of which are set forth below. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment, can be used on or with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention cover such modifications and variations. Other objects, features and aspects of the present invention are disclosed in or are apparent from the following detailed description. It is to be understood by one of ordinary skill in the art that the present discussion is a description of exemplary embodiments only, and is not intended as limiting the broader aspects of the present invention.

[0057] Turning now to Figure 1, an embodiment of the present obstacle crossing wheelchair 10 includes a pair of front wheels 12 and a pair of rear wheels 14 (see also Figs. 2 and 3). The wheelchair 10 also includes a seat 16 and a seat back 18. The X in figure 1 represents the center of gravity of the wheelchair 10. A gearbox 20 may be used to drive front wheel driven sprocket 24 using front wheel chain 22 and rear wheel driven sprocket 40 using rear wheel chain 38, individually or simultaneously. One embodiment of the gearbox 20 is described in detail in association with Figures 4 and 5. Gearbox 20 may also be comprised of a wormgear or other suitable mechanism for rotating the front and rear driver sprockets. Gearbox 20 is depicted as manually operated by crank 60 in Figure 4, but may also be motor powered (not shown). In that case, wheelchair 10 may include a control apparatus (not shown) to automate the obstacle crossing process. The apparatus may be programmable or preprogrammed to cross various obstacles. [0058] Front wheel 12 is movably attached to the obstacle crossing wheelchair frame (see Figs. 2 and 3) using a linkage comprised of first link 26, which is attached to and rotates with front wheel driven sprocket 24 at a first end and pivotally attached to a first end of second link 30 at pivot point 28 at a second end. The second end of the second link, in turn, is pivotally connected to a first end of a third link 34 at pivot point 32. The second end of the third link is pivotally connected to the wheelchair frame at pivot point 36. The linkage essentially forms a parallelogram configuration for raising the front wheels. The front wheel 12 may be raised or lowered by turning sprocket 24 by cranking gearbox 20. The front wheel should be raised to be slightly over the maximum height of the step and threshold to be crossed by the wheelchair.

[0059] When support legs 46 are locked in a supporting position and rear wheels are supported on surface 50, the front wheel driver sprocket may be driven to rotate in a clockwise direction. This linkage configuration in the embodiment shown lifts front wheels 12 above surface 50 to a position that is slightly above the step or threshold, up to 20 centimeters. Other contemplated configurations of the front wheel linkage and rear wheel offsets permit the crossing of even higher obstacles. The lifting of front wheel 12 is more fully described in association with Figures 9-33.

[0060] Rear wheel 14 is movably attached to the obstacle crossing wheelchair frame (see Figs. 2 and 3) using a rear-wheel sprocket 40 offset from the rear wheel center axis 44. The rear-wheel sprocket is in turn connected to the rear wheel center axis 44 by a connecting member 42. Connecting member 42 is pivotally connected to the rear wheel 14 at central axis 44. The connecting member provides the offset that is longer than the maximum height of the step or the threshold to be crossed. The rear wheel 14 may be raised or lowered by turning sprocket 40 by cranking gearbox 20.

[0061] When support legs 46 are locked in a supporting position, and rear wheels are supported on surface 50, the rear wheel driven sprocket 40 may be driven to rotate in a clockwise direction, thus linkage configuration lifts rear wheels 14 above surface 50 to a position that is slightly above the step or threshold. The lifting of rear wheel 14 is more fully described in association with Figures 9-33. [0062] The design is such that when the front wheels 12 or rear wheels 14 are lifted, the bottom seat portion 16, and the obstacle crossing wheelchair 10 generally, remains stable and substantially level with respect to surface 50. To that end, a pair of support legs 46 are configured to support the obstacle crossing wheelchair 10 in conjunction with front wheels 12 or rear wheels 14 when the opposite pair of wheels is lifted (see also Figs. 6-8). Each support leg 46 may include one or more rollers 48. Support legs 46 further include a locking mechanism for locking the support legs 46 in position vertically. This locking mechanism may comprise, for example and without limitation, a rack 61 and a lockable pinion 63 by a paw 65, a ratchet lock design (see, e.g., Figure 8), a simple friction lock, or other suitable locking mechanisms (not shown). It should be noted that while support legs 46 may comprise the vertical slide with the rack-pinion-lock mechanism shown, other embodiments that can generate linear motion may be employed, including for example and not by way of limitation, a self-lock screw and nut system with linear guides or a ball screw and nut system with linear guides and a locking device (not shown).

[0063] When the rollers 48 are on the ground surface 50, the roller 48 directly under the support leg 46 may be locked by releasing a remotely controlled spring mechanism that extends two paws 51 into the teeth of the two pinions 47 alongside the roller (see Figure 8). The mechanism may be operated by a remote linkage or cable, for example a cable (not shown) passing through the inside of supporting legs 46. The user can lock the roller 48 and push against the support legs to move the wheelchair frame 52 horizontally with respect to the support leg 46 when the rear wheels 14 are not in contact of any surface. This horizontal movement of wheelchair may be needed when the height of the step or threshold is close to the maximum height that the rear wheels can be raised. Under such circumstances, the rear wheels may not be raised sufficiently to contact the top edge of a step or threshold at a desired height in one movement. In that case, they may be held at their highest position and the wheelchair moved horizontally to be closer to the top edge or threshold. The user can lock the support leg roller 48 and push against the support legs to move the wheelchair horizontally. The rear wheels are then placed in contact with the top edge of the step or threshold. This case is further discussed below in conjunction with Figure 22. [0064] Support legs 46 may be mounted to wheelchair frame 18 through a vertical slide mechanism and a horizontal slide mechanism as shown, for example, in Figure 6. The vertical and horizontal slide mechanisms allow the support legs 46 to move vertically and horizontally, respectively, with respect to the wheelchair frame 52. The user can move rollers 48 to a desired position along surface 50 to support wheelchair 10 and keep it above surface 50 at a desired height when a pair of front or rear wheels are raised above surface 50. As seen in Figure 6, support leg guide 57 guides support leg 46 while permitting vertical movement of the leg 46 in the guide 57. Horizontal movement of the support leg 46 in the guide is not permitted, but the guide 57 itself is configured to slide horizontally along upper guide rail 55 and lower guide rail 53. Guide rails 53 and 55 are attached to wheelchair frame 52.

[0065] After each roller 48 of support leg 46 is placed on the surface 50, a vertical locking mechanism such as the one depicted in Figure 8 may be used to vertically lock the support leg 46 in support leg guide 57 to prevent the wheelchair 10 from falling due to gravity when the rear wheels 14 or front wheels 12 are raised above the ground surface 50. A horizontal lock is not employed such that horizontal motion of the frame 52 relative to the support legs 46 may be achieved when rollers 48 are locked on surface 50. However, at least one roller 48 may be locked to allow the user to push against support legs 46 to move wheelchair 10 into a desired position when traversing an obstacle. This is discussed in greater detail with reference to Figure 23.

[0066] It should be appreciated that the design of support legs 46 may be varied and still achieve the desired movement of the wheelchair wheels. For example, and not by way of limitation, the two rollers in a support leg may be reduced to one roller, or a pivot ratchet clutch 59 mounted on wheelchair frame 52 (see Figure 7) may be used in place of the horizontal slide mechanism depicted in Figure 6. In that case, a combination of a turning motion of a rotary joint, such as pivot ratchet clutch 59, and a sliding motion of leg 46 in leg guide 57 allows the user to move roller 48 to a desired position, both vertically and horizontally with respect to surface 50. [0067] Frame 52 of wheelchair 10 is shown in Figures 2 and 3. Frame 52 may be comprised of tube steel or another metal or alloy, such as aluminum. In this embodiment, support legs 46 each include a single wheel 48. In this embodiment, support legs 46 are slidably mounted to frame 52 on rails 58 such that support legs 46 may be moved towards the front 54 or rear 56 of wheelchair 10. Although two rails are depicted and preferred, one may suffice.

[0068] Turning now to Figures 4 and 5, an exemplary manual gearbox 20 includes a housing 90 and crank 60 that is inserted in crank shaft 62 through a square hole. Rotating crank 60 rotates shaft 62, which includes pinion 64. Pinion 64 engages gear 66, which in turn rotates associated shaft 68. Shaft 68 includes pinion 70 and pinion 71. Pinion 70 controls the raising or lowering of front wheel 12 through sprocket 76 where as pinion 71 controls the raising or lowering of rear wheel 14 through sprocket 77. Pinion 70 engages gear 72 which in turn rotates associated shaft 74. Sliding clutch 78 may be used to engage gear 72 with front wheel drive sprocket 76 that is engaged with rotary ratcheted clutch 80. Rotary clutches 80 and 81 are bi-directional, ratcheted clutches with a neutral position. If rotary clutch 80 is at the position to prevent sprocket 76 from turning due to gravity, front wheel 12 can be hold at a fixed height. If the user wants to raise or lower front wheel 12, it can be done by switching sliding clutch 78 to engage sprocket 76 to gear 72 and switching rotary clutch 80 to the neutral or opposite position.

[0069] Similarly, pinion 71 engages gear 73 which in turn rotates associated shaft 75. Sliding clutch 79 may be used to engage gear 73 with rear wheel drive sprocket 77 that is engaged with rotary ratcheted clutch 81. If rotary clutch 81 is at the position to prevent sprocket 77 from turning due to gravity, rear wheel 14 can be hold at a fixed height. If the user wants to raise or lower rear wheel 14, it can be done by switching sliding clutch 79 to engage sprocket 77 to gear 73 and switching rotary clutch 81 to the neutral or opposite position. By switching the two sliding clutches and two rotary clutches, the user can raise or lower the front pair and rear pair of wheels independently or simultaneously. Under no load condition, crank 60 can be inserted to shaft 68 through its square hole to rotate shaft 68 to speed up the lowering and raising of front pair and rear pair of wheels. Note that there are variations of the design of the gearbox. One variation is to replace the two-step pinion and gear transmission with a wormgear. Other mechanical arrangements are also known in the art.

[0070] The wheelchair can cross a step by facing forward or backward. Figures 9 - 19 illustrate the presently preferred method of ascending a step using the present obstacle crossing wheelchair 10. The present obstacle crossing wheelchair 10 is first positioned with the rear wheels 14 adjacent to the step 100. At this point, the wheelchair is in a travel position wherein the driver sprockets 24 and 40 are positioned such that the front 12 and rear wheels 14 are at a suitable height for travelling. The seat bottom 16 is thus at a normal travelling height of, for example, approximately 50 centimeters above the travelling surface. The vertical line topped by the X represents the horizontal center of gravity of the wheelchair 10.

[0071] Once wheelchair 10 is positioned as shown in Figure 9, support legs 46 are lowered such that support leg rollers 48 contact travelling surface 50 at a position between the step 100 and the horizontal center of gravity of wheelchair 10 as shown in Figure 10. This lowering is indicated in Figure 9 by the dotted arrow pointing down over support legs 46. Support legs 46 are then locked in this vertical position with a locking mechanism such as that described in association with Figure 8. With wheelchair 10 thus stabilized, the rear wheels 14 of obstacle crossing wheelchair 10 may now be raised to a height approximately level with step 100 and placed in contact with step 100 as shown in Figure 11.

[0072] To lift rear wheels 14, clutch 60 is positioned to engage pinion 62 with rear wheel drive sprocket 64. Crank 66 is then rotated, which in turn rotates shaft 68 and associated pinion 70. Pinion 70 drives gear 72, and thus associated shaft 74 having pinion 62. Pinion 62 in turn drives rear wheel drive sprocket 64, rotating rear wheel drive chair 38 and rear wheel driven sprocket 40 in a clockwise direction as viewed in Figures 9-19. Rear wheels 14 then rotate around rear wheel drive sprocket 40 (see dotted arrow in Figure 10).

[0073] When rear wheels 14 are raised to a height approximately level with the height of step 100 and placed in contact with the edge of step 100, wheelchair 10 is then rolled in the direction of the solid arrow in Figure 12 onto step 100 to position rear wheels 14 on travelling surface 50 away from the edge of step 100 as depicted in Figure 12. Support legs 46 slide towards the front 54 of wheelchair 10 during this step. Support legs 46 may then be unlocked and raised as represented by the dotted arrow in Figure 12 to the position seen in Figure 13, and wheelchair 10 rolled in the direction of the solid arrow in Figure 13 to position front wheels 12 adjacent to step 100 as shown in Figure 14.

[0074] To ascend the step 100 with front wheels 12, support legs 46 are lowered as shown by the dotted arrow in Figure 14 to contact travelling surface 50 beyond step 100 at a position between the step and the horizontal center of gravity of wheelchair 10 as shown in Figure 15. With wheelchair 10 thus stabilized, front wheels 12 may be raised to a height above the height of step 100 as seen in Figure 16.

[0075] To raise front wheels 12, clutch 60 is positioned to engage pinion 62 with front wheel drive sprocket 78. Crank 66 is then rotated, which in turn rotates shaft 68 and associated pinion 70. Pinion 70 drives gear 72, and thus associated shaft 74 having pinion 62. Pinion 62 in turn drives front wheel drive sprocket 78, rotating front wheel drive chain 22 and front wheel driver sprocket 24 in a clockwise direction represented by the dotted arrow in Figure 15. Front wheel 12 is raised vertically as the linkage comprised of first link 26, second link 30 and third link 34 is operated in conjunction with front wheel driver sprocket 24.

[0076] When front wheels 12 are raised to a height above step 100, wheelchair 10 is then rolled in the direction of the solid arrow in Figure 16 (towards step 100) to position front wheels 12 over travelling surface 50 as seen in in Figure 17, and the front wheel driver sprocket rotated as shown by the dotted arrow around front wheels 12 in Figure 17 to lower front into contact with travelling surface 50. Once both front wheels 12 and rear wheels 14 are on travelling surface 50 beyond step 100, the front and rear wheel driver sprockets 24, 40 may be operated to return the front 12 and rear wheels 14 to their travel position as seen in Figure 18 and support legs 46 may be raised and moved in the direction of the dotted arrow in Figure 17 to the position seen in Figure 18. Finally, as shown in Figure 18, the support legs 46 may be moved in the direction of dotted arrow to the position as shown in Figure 19, and wheelchair 10 is ready to travel along upper travelling surface 50. [0077] It is important to note that seat bottom 16 is maintained substantially level to the travelling surface 50 as wheelchair 10 ascends step 100. As a result, the person sitting in wheelchair 10 is not significantly jostled or placed at unsafe angles while wheelchair 10 traverses the step.

[0078] Wheelchair 10 may also be used to ascend a step with the front wheels 12 initially facing the step. In that case, the motion sequence of the front wheels 12 and the rear wheels 14 are exchanged. That is, the front wheels 12 are raised and placed on the step with the support of the supporting legs 46 followed by the raising and placing the rear wheels 14 on the step 100 with the support of the supporting legs 46. The user may choose either moving forward or backward to ascend a step, which may turn on the particular preference of the user. Further, wheelchair 10 may also be used to descend a step by essentially reversing the method used to ascend a step.

[0079] Figures 20-33 illustrate the presently preferred method of crossing a threshold using the present obstacle crossing wheelchair 10. Threshold 104 has a first side 106 and a second side 108. Similar to the method described above of crossing a step, wheelchair 10 is first positioned with the rear wheels 14 adjacent to the first side of threshold 106 as seen in Figure 20. At this point, the wheelchair 10 is in a travel position wherein the driven sprockets 24 and 40 are positioned such that the front wheels 12 and the rear wheels 14 are at a suitable height for travelling. Seat bottom 16 is thus at a normal travelling height of approximately 50 centimeters above the travelling surface 50. In addition, support legs 46 are in a raised position above travelling surface 50. Note that gearbox 20 is shown as a crank and single sprocket for simplicity, but may actually be configured as shown in Figures 4 and 5.

[0080] Once wheelchair 10 is positioned as shown in Figure 20, support legs 46 are lowered (represented by the dotted arrow over the support legs 46) such that support leg rollers 48 contact travelling surface 50 at a position between the threshold and the horizontal center of gravity of wheelchair 10 as shown in Figure 21. Support legs 46 are then locked in this vertical position with a locking mechanism, such as that depicted in Figure 8. The rear wheels 14 of obstacle crossing wheelchair 10 may now be raised to contact the edge of threshold 104 as seen in Figure 22.

[0081] Referring to Figures 4 and 22, rear wheels 14 may be lifted by operating clutch 60 to engage pinion 62 with rear wheel drive sprocket 64. Crank 66 is then rotated, which in turn rotates shaft 68 and associated pinion 70. Pinion 70 drives gear 72, and thus associated shaft 74 having pinion 62. Pinion 62 in turn drives rear wheel drive sprocket 64, rotating rear wheel drive chair 38 and rear wheel driven sprocket 40 in a clockwise direction shown by the dotted arrow in Figure 21. Rear wheels 14 are therefore rotated around rear wheel drive sprocket 40.

[0082] When rear wheels 14 are raised contact with the leading edge of step 100, wheelchair 10 is then rolled in the direction of the solid arrow in Figure 22 (towards threshold 104) to position rear wheels 14 at the far edge of the threshold 108 as depicted in Figure 23. If the rear wheels 14 is too low and slips at the contact of the threshold 104 during the rolling over motion, the user may correct this problem by raising the rear wheels higher, locking the support leg rollers 48 and pushing the support legs so that his/her body pushes against the seat back 18 and moves the wheelchair 10 backward until the rear wheels 14 are in contact with the threshold 104 at a higher position. The user then unlocks the rollers 48.

[0083] During the rolling motion of rear wheels 14, support legs 46 slide horizontally towards the front 54 of wheelchair 10. The gearbox 20 is then operated to rotate the rear wheel driver sprocket in the direction of the dotted arrow in Figure 23 to pull the wheelchair further toward the second side of the threshold 108 and lower the rear wheels 14 onto travelling surface 50 on the second side of the threshold 108 as depicted in Figure 24. Support legs 46 may now be unlocked and raised to the position as seen in Figure 25, and wheelchair 10 rolled in the direction of the solid arrow in Figure 25 (further towards threshold 104) to position front wheels 12 adjacent to the first side 106 of threshold 104 as shown in Figure 26.

[0084] To step over threshold 104 with front wheels 12, support legs 46 are once again lowered (see dotted arrow in Figure 26) to contact travelling surface 50 on the second side 108 of the threshold 104 at a position between the threshold and the horizontal center of gravity of wheelchair 10 as shown in Figure 27. With wheelchair 10 thus stabilized, front wheels 12 may be raised to a height above the height of threshold 104 as seen in Figure 28.

[0085] Referring to Figures 4 and 28, front wheels 12 may be lifted by operating clutch 60 is positioned to engage pinion 62 with front wheel drive sprocket 78. Crank 66 is then rotated, which in turn rotates shaft 68 and associated pinion 70. Pinion 70 drives gear 72, and thus associated shaft 74 having pinion 62. Pinion 62 in turn drives front wheel drive sprocket 78, rotating front wheel drive chair 22 and front wheel driver sprocket 24 in a clockwise direction as represented by the dotted arrow in Figure 27. Front wheel 12 is raised substantially vertically as the linkage comprised of first link 26, second link 30 and third link 34 is operated in conjunction with front wheel driver sprocket 24.

[0086] When front wheels 12 are raised to a height above the top of threshold 104, wheelchair 10 is then rolled in the direction of the solid arrow in Figure 28 (towards threshold 104) to position front wheels 12 beyond the second side 108 of threshold 104 as seen in Figure 29. Gearbox 20 may then be operated to rotate front driver sprocket 24 in the direction of the dotted arrow in Figure 29 and lower front wheels 12 into contact with travelling surface 50 on the second side 108 of threshold 104 as seen in Figure 30.

[0087] Once both front wheels 12 and rear wheels 14 are on travelling surface 50 on the second side 108 of threshold 104, rear wheel driven sprocket 40 may be operated in the direction of the dotted arrow in Figure 30 (counterclockwise) to return rear wheels 14 to their travel position as seen in Figure 31. Support legs 46 may now be raised (dotted arrow in Figure 31), and returned to their travelling position by sliding them horizontally in the direction of the dotted arrow in Figure 32 (towards the back 56 of wheelchair 10) to the position shown in Figure 33. Wheelchair 10 may now travel along travelling surface 50 on the second side of threshold 104.

[0088] It is important to note that seat bottom 16 is maintained substantially level to travelling surfaces 50 and 102 as wheelchair 10 crosses step 100. As a result, the person sitting in wheelchair 10 is not significantly jostled or placed at unsafe angles while wheelchair 10 traverses the step. [0089] Wheelchair 10 may also be used to cross a threshold with the front wheels 12 initially facing the threshold. In that case, the motion sequence of the front wheels 12 and the rear wheels 14 are exchanged. That is, supporting legs 46 are lowered onto traveling surface 50 between the threshold and the horizontal center of gravity, and vertically locked to support the wheelchair 10, and the front wheels 12 are raised above the height of the threshold. The wheelchair 10 is then rolled towards the threshold to position the front wheels 12 on the second side of the threshold 104, and then lowered to contact the travelling surface 50. Supporting legs 46 are then unlocked, raised and vertically locked, and wheelchair 10 rolled further to position rear wheels 14 adjacent to the first side of threshold 104.

[0090] Supporting legs 46 are then unlocked, lowered into contact with travelling surface 50 between the threshold and the horizontal center of gravity of wheelchair 10, and vertically locked again. Gearbox 20 is then operated to raise rear wheels 14 into contact with the edge on the first side of the threshold 104. Wheelchair 10 may then be rolled to position the rear wheels 14 on the top edge of the second side of the threshold 104, and the gearbox 20 further operated to lower the rear wheels onto the travelling surface on the second side of the threshold, simultaneously pulling the wheelchair 10 further towards the second side of the threshold. The user may then unlock and raise the supporting legs 46 and position them horizontally as desired, and operate the gearbox to return the rear wheels to their travelling position. The user may choose either moving forward or backward to cross a threshold, which may turn on the particular preference of the user.

[0091] Although preferred embodiments of the invention have been described using specific terms, devices, and methods, such description is for illustrative purposes only. The words used are words of description rather than of limitation. It is to be understood that changes and variations may be made by those of ordinary skill in the art without departing from the spirit or the scope of the present invention, which is set forth in the following claims. In addition, it should be understood that aspects of the various embodiments may be interchanged either in whole or in part. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred versions contained therein.

Claims

CLAIMS What is claimed is:

1. An obstacle crossing wheelchair comprising:

a pair of front wheels and a pair of rear wheels movably connected to a frame;

a seat and a seat back connected to the frame;

a gearbox configured to raise the rear wheels by rotating the rear wheels around a rear wheel driven sprocket offset from a center axis of the rear wheels, the gearbox also configured to raise the front wheels by rotating a linkage attached to a front wheel driven sprocket and the frame;

at least one support leg, the at least one support leg horizontally and vertically moveable along the frame, the at least one support leg further comprising at least one roller at a bottom end of the support leg;

a locking mechanism for vertically locking the at least one support leg to the frame; and

a locking mechanism for locking the at least one roller.

2. The obstacle crossing wheelchair of claim 1, wherein the wheelchair is configured to maintain the seat substantially parallel to a travelling surface as the wheelchair crosses an obstacle.

3. The obstacle crossing wheelchair of claim 1, wherein the pair of rear wheels and the pair of front wheels may be raised at least twenty centimeters above a travelling surface.

4. The obstacle crossing wheelchair of claim 1, wherein the at least one support leg is comprised of two support legs.

5. The obstacle crossing wheelchair of claim 1, wherein the gearbox is configured to be manually operated.

6. The obstacle crossing wheelchair of claim 1, wherein the gearbox is configured to be motor operated.

7. The obstacle crossing wheelchair of claim 1, wherein the linkage is configured to move the front wheels in a substantially vertical direction when the front wheel driven sprocket is rotated.

8. The obstacle crossing wheelchair of claim 1, wherein the at least one support leg is configured to move along the frame horizontally using a horizontal sliding mechanism.

9. The obstacle crossing wheelchair of claim 1, wherein the at least one support leg is configured to move along the frame horizontally using a rotary joint in combination with a sliding mechanism.

10. The obstacle crossing wheelchair of claim 1, wherein the wheelchair is configured to maintain the frame at a fixed crossing height when the wheelchair crosses an obstacle.

11. The obstacle crossing wheelchair of claim 1, further comprising a front wheel drive chain connecting a front wheel drive sprocket in the gearbox with the front wheel driver sprocket.

12. The obstacle crossing wheelchair of claim 1, further comprising a rear wheel drive chain connecting a rear wheel drive sprocket in the gearbox with the rear wheel driver sprocket.

13. The obstacle crossing wheelchair of claim 1, wherein the gearbox further comprises a clutch to selectively engage the gearbox with the front wheel drive sprocket or the rear wheel drive sprocket.

14. A method of ascending a step with an obstacle crossing wheelchair, the method comprising:

positioning a wheelchair having a center of gravity such that a pair of rear wheels are on a lower travelling surface adjacent to the bottom of a step, a center axis of the pair of rear wheels at a travelling height above the lower travelling surface;

lowering at least one support leg to contact the lower travelling surface below the step at a position between the step and the center of gravity;

vertically locking the at least one support leg with a locking mechanism;

operating a gearbox to rotate the pair of rear wheels around a driven sprocket offset from the center axis of the rear wheels to raise the pair of rear wheels into contact with a top edge of the step;

rolling the wheelchair backwards towards the step to position the pair of rear wheels on an upper travelling surface away from the top edge of the step to provide stability;

unlocking and raising the at least one support leg above the step;

vertically locking the at least one support leg with a locking mechanism;

rolling the wheelchair further backwards to position a pair of front wheels on the lower travelling surface adjacent the step, a center axis of the pair of front wheels at a travelling height above the lower travelling surface;

unlocking and lowering the at least one support leg to contact the upper travelling surface between the step edge and the center of gravity;

vertically locking the at least one support leg with a locking mechanism;

operating the gearbox to rotate a linkage attached to a front wheel driven sprocket and the frame to raise a lowermost point on the pair of front wheels substantially vertically to a height above a height of the upper travelling surface;

rolling the wheelchair still further backwards to position the pair of front wheels above the top surface of the step away from the top edge of the step to provide stability; and operating the gearbox to rotate a linkage attached to a front wheel driven sprocket and the frame to lower the pair of front wheels into contact with the upper travelling surface.

15. A method of ascending a step with an obstacle crossing wheelchair, the method comprising:

positioning a wheelchair having a center of gravity such that a pair of front wheels are on a lower travelling surface adjacent to the bottom of a step, a center axis of the pair of front wheels at a travelling height above the lower travelling surface;

vertically locking the at least one support leg with a locking mechanism;

operating a gearbox to rotate a linkage and raise the pair of front wheels substantially vertically to a height greater than the height of the step;

rolling the wheelchair towards the step to position the pair of front wheels over an upper travelling surface away from the top edge of the step to provide stability;

unlocking and raising the at least one support leg above the step;

vertically locking the at least one support leg with a locking mechanism;

rolling the wheelchair further to position a pair of rear wheels on the lower travelling surface adjacent the step, a center axis of the pair of rear wheels at a travelling height above the lower travelling surface;

vertically locking the at least one support leg with a locking mechanism;

operating the gearbox to rotate a rear wheel driver sprocket and raise the rear wheels into contact with a top edge of the step;

rolling the wheelchair still further to position the pair of rear wheels on a top surface of the step away from the top edge of the step to provide stability; and

operating the gearbox to rotate a rear wheel driver sprocket and lower the pair of rear wheels into contact with the upper travelling surface.

16. The method of ascending a step with an obstacle crossing wheelchair of claims 14 or 15, further comprising unlocking and raising the at least one support leg, vertically locking the at least one support leg with a locking mechanism; and operating the gearbox to simultaneously return the center axis of both the rear wheels and the front wheels to their respective travelling heights.

17. The method of ascending a step with an obstacle crossing wheelchair of claims 14 or 15, wherein the upper travelling surface is 20 centimeters above the lower travelling surface.

18. A method of crossing a threshold with an obstacle crossing wheelchair, the method comprising:

positioning a wheelchair such that a pair of rear wheels are on a travelling surface adjacent to a first side of the threshold, a center axis of the pair of rear wheels at a travelling height above the travelling surface;

lowering at least one support leg to contact the travelling surface at a position between the threshold and the center of gravity;

vertically locking the at least one support leg with a locking mechanism;

operating a gearbox to rotate a driven sprocket offset from the center axis of the pair of rear wheels to raise the pair of rear wheels into contact with a top edge of the threshold; rotating the pair of rear wheels backwards over the top surface of the threshold;

further operating the gearbox to lower the pair of rear wheels onto the travelling surface on a second side of the threshold and pull the wheelchair backwards;

unlocking and raising the at least one support leg to a height above the height of the threshold;

vertically locking the at least one support leg with a locking mechanism;

rolling the wheelchair further backwards to position a pair of front wheels on the travelling surface adjacent the first side of the threshold, a center axis of the front wheels at a travelling height above the travelling surface;

lowering the at least one support leg to contact the travelling surface on the second side of the threshold at a position between the threshold and the center of gravity;

vertically locking the at least one support leg with the locking mechanism; operating the gearbox to rotate a linkage attached to a front wheel driven sprocket and the frame to raise a lowermost point of the pair of front wheels substantially vertically to a height greater than the height of the threshold;

rolling the wheelchair still further backwards to position the pair of front wheels on the second side of the threshold; and

operating the gearbox to lower the pair of front wheels onto the travelling surface on the second side of the threshold.

19. A method of crossing a threshold with an obstacle crossing wheelchair, the method comprising:

positioning a wheelchair such that a pair of front wheels are on a travelling surface adjacent to a first side of the threshold, a center axis of the pair of front wheels at a travelling height above the travelling surface;

vertically locking the at least one support leg with a locking mechanism;

operating the gearbox to rotate a linkage attached to a front wheel driven sprocket and the frame to raise a lowermost point of the pair of front wheels substantially vertically to a height greater than the height of the threshold;

rolling the wheelchair forward to position the pair of front wheels on a second side of the threshold;

operating the gearbox to lower the pair of front wheels onto the travelling surface on the second side of the threshold;

vertically locking the at least one support leg with a locking mechanism;

further rolling the wheelchair forward to position a pair of rear wheels adjacent to the first side of the threshold;

lowering the at least one support leg to contact the travelling surface on the second side of the threshold at a position between the threshold and the center of gravity; vertically locking the at least one support leg with the locking mechanism;

operating the gearbox to rotate a driven sprocket offset from the center axis of the rear wheels to raise the rear wheels into contact with a top edge of the threshold on the first side of the threshold;

rotating the pair of rear wheels forwards over a top surface of the threshold to a top edge of the threshold on the second side of the threshold; and

further operating the gearbox to lower the pair of rear wheels onto the travelling surface on the second side of the threshold and pull the wheelchair further forwards.

20. The method of crossing a threshold with an obstacle crossing wheelchair of claims 18 or 19, wherein the top surface of the threshold is 20 centimeters from the travelling surface below the threshold.

21. The method of ascending a step or crossing a threshold with an obstacle crossing wheelchair of claims 14, 15, 18 or 19, wherein the wheelchair seat is maintained substantially parallel to the travelling surface below the step or threshold as the wheelchair ascends the step or crosses the threshold.

22. The method of ascending a step or crossing a threshold with an obstacle crossing wheelchair of claims 14, 15, 18 or 19, wherein the wheelchair frame is not raised with respect to the travelling surface below the step when the wheelchair ascends the step or crosses the threshold.