Abstract
A caster wheel arrangement for a powered wheelchair, the caster wheel arrangement comprising: a caster wheel module comprising: a wheel rotatably connected to a first linkage member, wherein the wheel is rotatably arranged about a first axis of rotation of the wheel; and a support element rotatably connected to the first linkage member through a joint configured to allow a rotation of the first linkage member relative to the support element around a second axis of rotation perpendicular to the first axis of rotation; a second linkage member connected to the support element at a third axis of rotation, wherein the third axis of rotation is essentially perpendicular to the second axis of rotation of the first linkage member, to allow rotation of the caster wheel module about the third axis of rotation, wherein the third axis of rotation passes adjacent to the second axis of rotation.
Claims
1. A caster wheel arrangement for a powered wheelchair, said caster wheel arrangement comprising: a caster wheel module comprising: a wheel rotatably connected to a first linkage member, wherein said wheel is rotatably arranged about a first axis of rotation of said wheel; and a support element rotatably connected to said first linkage member through a joint configured to allow a rotation of said first linkage member relative to said support element around a second axis of rotation perpendicular to said first axis of rotation; a second linkage member connected to said support element at a third axis of rotation, wherein said third axis of rotation is essentially perpendicular to said second axis of rotation of said first linkage member, to allow rotation of said caster wheel module about said third axis of rotation, wherein said third axis of rotation passes adjacent to said second axis of rotation.
2. The caster wheel arrangement according to claim 1, wherein said second linkage member is rotatably connected to said support member.
3. The caster wheel arrangement according to claim 1, further comprising an engaging element for engaging to a surface, wherein said engaging element is arranged to be rotatable around said third axis of rotation.
4. The caster wheel arrangement according to claim 3, wherein said engaging element is rotatably arranged to said support element, wherein said engaging element is rotatable about said third axis or rotation independent of said support element.
5. The caster wheel arrangement according to claim 1, wherein said support element comprises a compartment for housing a part of the wheel, wherein a portion of said wheel extends outside said compartment through an open end of said compartment.
6. The caster wheel arrangement according to claim 5, wherein said third axis of rotation passes adjacent to a center of said compartment.
7. The caster wheel arrangement according to claim 5, wherein said open end extends in a plane and is arranged opposite said joint with respect to said wheel.
8. The caster wheel arrangement according to claim 5, wherein said engaging element is a rough outside surface of said support element.
9. The caster wheel arrangement according to claim 1, wherein said caster wheel module comprises a gear wheel for enabling a rotation of said caster wheel module, said gear wheel arranged such that a centre axis of said gear wheel defines said third axis of rotation of said caster wheel module.
10. The caster wheel arrangement according to claim 9, wherein said second linkage member comprises a rotation member, wherein said gear wheel is connected to said rotation member arranged on said second linkage member and configured to transfer a rotation of said second linkage member into a rotation of said caster wheel module via said gear wheel and said rotation member.
11. The caster wheel arrangement according to claim 1, wherein said wheel is a first wheel, said caster wheel arrangement further comprising a second wheel rotatably arranged about said first axis of rotation to said first linkage member adjacent to said first wheel.
12. A powered wheelchair comprising a caster wheel arrangement according to claim 1, wherein said wheel is arranged as a rear wheel of said powered wheelchair.
13. The powered wheelchair according to claim 12, comprising a control unit configured to control said caster wheel module to rotate around said third axis of rotation such that said second axis of rotation is tilted towards a driving direction of said powered wheelchair.
14. The powered wheelchair according to claim 13, wherein said control unit is configured to position said caster wheel module to a rotational angle by rotation about said third axis or rotation depending on a driving speed of said powered wheelchair.
15. The powered wheelchair according to claim 12, further comprising a gyroscope and/or an accelerometer configured to determine a signal indicative of a slope angle of a ground supporting said powered wheelchair, wherein said tilt angle of said caster wheel module depends on said slope angle.
16. A method of controlling a caster wheel module arranged as a rear wheel arrangement on a powered wheelchair, said caster wheel module comprising: a wheel rotatably connected to a first linkage member, wherein said wheel is rotatably arranged about a first axis of rotation of said wheel; and a support element rotatably connected to said first linkage member through a joint configured to allow a rotation of said first linkage member relative to said support element around a second axis of rotation perpendicular to said first axis of rotation; a second linkage member connected to said support element at a third axis of rotation, wherein said third axis of rotation is essentially perpendicular to said second axis of rotation of said first linkage member, to allow rotation of said caster wheel module about said third axis of rotation, wherein said third axis of rotation passes adjacent to said second axis of rotation, wherein said method comprises the steps of: controlling said caster wheel module to rotate about said third axis of rotation.
17. The method according to claim 16, further comprising: acquiring a driving speed of said powered wheel chair; and controlling said caster wheel module to rotate about said third axis of rotation a rotational angle depending on said driving speed of said powered wheelchair.
18. The method according to claim 16, further comprising: determining a slope angle of a ground supporting the caster wheel module, and controlling said caster wheel module to rotate about said third axis of rotation a rotational angle depending on said slope angle.
19. The method according to claim 16, further comprising a step of: controlling said rotation about the third axis of rotation of said caster wheel module such that said second axis of rotation maintains vertical to a plane parallel to a ground in contact with said wheel.
Description
BRIEF DESCRIPTION OF DRAWINGS
[0045] These and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing currently preferred embodiments of the invention, wherein:
[0046] FIG. 1 schematically shows an exemplary caster wheel arrangement according to an embodiment of the invention mounted on a powered wheel chair;
[0047] FIG. 2a-b schematically show an exemplary caster wheel arrangement according to an embodiment of the invention:
[0048] FIG. 3 schematically shows a perspective cross-section of an exemplary caster wheel arrangement according to an embodiment of the invention:
[0049] FIG. 4a-b show an exemplary function of an exemplary embodiment of the invention;
[0050] FIG. 5a-b show an exemplary function of an exemplary embodiment of the invention; and
[0051] FIG. 6 is a flow-chart illustrating a method according to an exemplary embodiment of the invention.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
[0052] In the following description, the present invention is mainly described with reference to a caster wheel arrangement to be arranged on a wheelchair. However, the invention is equally applicable to other vehicles, trolleys, or similar.
[0053] FIG. 1 shows a powered wheelchair according to an exemplary embodiment of the invention. The powered wheelchair 100 may be powered by an electrical motor (not shown) and may further comprise a control unit (not shown). The powered wheelchair 100 comprises a caster wheel arrangement 102 according to an embodiment of the invention. The control unit may for example be arranged under the seat 103 of the wheelchair 100. The caster wheel arrangement 102 comprises a caster wheel module 104 and a second linkage member 101 as will be described with reference to subsequent drawings. The caster wheel module 104 may be connected to a chassis (for example at a location under the seat 103) of the wheelchair via for example a servo motor for controlling the position of the caster wheel module 104 with respect to the ground and/or the chassis. The second linkage member 101 may be rotatably connected to the chassis via e.g. the servo motor. The control unit here is configured to control the caster wheel arrangement 102 such that the caster wheel module 104 is rotated about a third axis 106 of rotation in a direction 108 towards a driving direction 110 of the wheel chair 100. The rotation of the caster wheel module 104 provides improved control of the powered wheel chair when turning. By rotating the caste wheel module 104 an amount depending on speed during the turning action of the powered wheel chair 100, oversteering may be reduced. The term oversteering means that the wheelchair turns more (with a smaller radius of curvature) than expected by a driver operating the wheelchair. Furthermore, the control unit may be configured to increase the angle (or amount of) of rotation as a response to an increased driving speed of the wheelchair. As an example, the motor providing power to the powered wheel chair may be arranged in the hub 112 of the wheels of the powered wheel chair 100. For example, the electrical motor may have rotor and stator elements arranged coaxially with the circumference of the wheel rim and adjacent to a bearing allowing the wheel to rotate. The design and layout of the wheelchair as depicted in FIG. 1 is only for illustrative purposes and is thus only an example. The location of certain parts such as wheels or the control unit is not limiting the scope of the invention but is only to be considered as an example.
[0054] FIG. 2a illustrates an exemplary caster wheel arrangement 202 according to an embodiment of the invention. The caster wheel arrangement 202 may be implemented on a powered wheelchair as described in FIG. 1. FIG. 2a shows a second linkage member 204 and a caster wheel module 206 comprising a wheel 208, a first linkage member 210, a joint 212 and a support element 214. FIG. 2a shows the non-powered wheel 208 connected to the first linkage member 210. The wheel 208 here is non-powered which means that no power from a motor or similar is supplied to drive the wheel 208. Furthermore, the wheel 208 is connected in a rotatable manner to the first linkage member 210 at the center of rotation of the wheel, the center of rotation is along the first axis 216 of rotation. Hence, the wheel may rotate about the first axis of rotation 216. Moreover, the support element 214 is connected to the first linkage member 210 via the joint 212. The joint 212 is configured to allow the first linkage member 210 to rotate about a second axis 218 of rotation with respect to the support member 214. Preferably the rotation about the second axis 218 of rotation is the only degree of freedom of the joint 212. In other words, the joint 212 may typically not allow rotation about any other axis than the second axis 218 of rotation. Furthermore, the second axis 218 of rotation is perpendicular to the first axis 216 of rotation, or at least an axis parallel to the second axis 218 of rotation is perpendicular to the first axis 216 of rotation. For example, the second axis of rotation 218 may be offset from the first axis of rotation, which means the first axis of rotation 216 and the second axis of rotation 218 do not intersect. In such case, an axis parallel to the second axis 218 of rotation is perpendicular to the first axis 216 of rotation. The second linkage member 204 is connected to the support element 214 at a third axis 220 of rotation. The third axis 220 of rotation is essentially perpendicular to the second axis 218 of rotation, or at least an axis parallel to the third axis 220 of rotation is essentially perpendicular to the second axis 218 of rotation. The provision of essentially perpendicular should be interpreted as that a small deviation from perpendicular is fine as long as the function of the caster wheel arrangement 202 is not substantially affected. Hereby, the second linkage member 204 is arranged to allow rotation of the caster wheel module 206 about the third axis 220 of rotation. Furthermore, the third axis of rotation 220 passes adjacent to the second axis 218 of rotation. In other words, the second linkage member 204 is arranged such that the third axis of rotation 220 passes adjacent to the second axis of rotation 220. Furthermore, in the depicted embodiment, the third axis of rotation 220 passes adjacent to the first linkage member 210.
[0055] FIG. 2b shows the caster wheel arrangement 202 in FIG. 2a, with the caster wheel module 206 rotated about the third axis or rotation 220. Thus, as is shown in FIG. 2b, the second axis of rotation 218 has been tilted compared to what is shown in FIG. 2a. The second axis of rotation 218 has been tilted by a rotation about the third axis 220 of rotation. Thereby, the support element 214, the first linkage member 210, and the joint 212 have also been rotated about the third axis 220 of rotation. By tilting about the third axis of rotation 220, oversteering may be reduced in a turning situation with the caster wheel arrangement 202 mounted as e.g. a rear wheel on a powered wheelchair. A consequence of tilting the second axis of rotation 218 by a rotation about the third axis of rotation 220 is that the rotation of the wheel 208, the first linkage member 210, and the joint 212 (e.g. the caster wheel module 206) about the second axis of rotation is limited when the wheel 208 is rolling on the ground. In FIG. 2a, the rotation (allowed by the joint 212) about the second axis 218 is less limited due to the vertically positioned second axis 212 (see also FIG. 4) which means the weight supported by the wheel is perpendicular to the ground (see FIG. 4) in contrast to the situation in FIG. 2a. The rotation about the third axis of rotation 220 may be controlled by a control unit as a function of speed of the wheelchair.
[0056] In some exemplary embodiments, the wheel 208 is a first wheel and there is a second wheel arranged adjacent to the first wheel 208. The second wheel is rotatably arranged to the first linkage member 210 about the first axis of rotation 216. Thus, the fork-like shape of the first linkage member 210 is wider such that the second wheel fits inside the fork-shape. However, other configurations are possible, for example having a similar second fork-shaped linkage member next to the first linkage member 210 as long as the first and second wheels share the same first axis of rotation 216.
[0057] The rotation (only shown in one direction, however in both directions are possible) depicted in FIGS. 2a-b may further be used for controlling the second axis of rotation 218 to be vertical to a plane parallel to the ground. For example, at low speeds when oversteering may not have to be reduced, it is advantageous for the second axis of rotation 218 to be vertical with the ground in order for the wheel 208 and the first linkage member 210 to easily rotate about the second axis of rotation. A situation where the second axis of rotation 218 may not be vertical to the ground, thus a rotation may be desired, is for example when driving over a bump, or an otherwise uneven surface. In this way, the wheel easily turns about the second axis or rotation 218 and thereby aligns with a driving direction 110.
[0058] It should be noted that the rotations mentioned above may be in two opposite directions. For example, although the rotation about the third axis of rotation 220 is depicted to be in one direction (e.g. indicated by the arrow about axis 220), the rotation is also possible in the other direction.
[0059] In FIG. 2a-b the third axis of rotation 220 passes through the wheel 208 in the depicted position of the wheel 208. Naturally the third axis of rotation 220 may not pass through the wheel in some positions of the wheel 208, for example, at some position of the wheel 208 if the wheel 208 is rotated about the second axis of rotation 218 a full turn. Moreover, the third axis of rotation 220 passes adjacent to the second axis of rotation 218.
[0060] Furthermore, if the caster wheel arrangement 202 is mounted on a powered wheelchair 100 as a rear wheel, the caster wheel arrangement 202 is arranged such that if the caster wheel module is rotated about the third axis of rotation 220 the second axis of rotation 218 is tilted towards a driving direction 110 of the powered wheel chair 100. Thus, the third axis of rotation 220 is essentially perpendicular to the driving direction 110 of the powered wheel chair 100.
[0061] FIG. 3 schematically illustrates perspective cross-section of a caster wheel arrangement 300 according to an exemplary embodiment of the present invention. FIG. 3 shows a second linkage member 302 and a caster wheel module 304 comprising a wheel 306, a first linkage member 308, a joint 310 and a support member 312. Similar to the depicted exemplary embodiment in FIG. 2a-b, the first linkage member 308 is rotatably connected to the wheel 306 at a first axis 314 of rotation. The first linkage member 308 is connected to the support member 312 via the joint 310 such that the first linkage member 308 may rotate about a second axis 316 of rotation with respect to the support member 312. Moreover, the second linkage member 302 is rotatably connected to the support member 312 at a third axis 318 of rotation substantially perpendicular to the second axis 316 of rotation. One difference between the embodiment in FIG. 3 and the embodiment in FIGS. 2a-b is that in FIG. 3, the support member 312 is in the form of a housing 312 forming a compartment 320 for the wheel 306. In addition, the third axis of rotation 318 passes adjacent to a center of the compartment 320. This allows the caster wheel module to rotate about the third axis of rotation 318 without substantially interfering with a position in a vertical direction of a wheelchair having the caster wheel module 304. In addition, the third axis of rotation 318 passes adjacent to the second axis of rotation 316. Furthermore, the first linkage member 308 and the joint 310 are located in the compartment 320 and the joint 310 is connected, for example via a bolt or screw, to an inner surface 322 of the support element 312. In addition, a portion 324 of the wheel 306 here extends outside the compartment 320 through an open end (more clearly seen in FIGS. 4a-b) of the support element 312. In the depicted exemplary embodiment, the open end is located substantially opposite the joint 310 with respect to the wheel 306. On the outside surface of the support element, there are provided engaging elements 326, 328 in the form of grooves 326 and ribs 328. The engaging elements 326, 328 may be similar to the engaging features of a terrain tire. The support member 312 may be made from a plastic material, such as for example abs-plastic (Acrylonitrile butadiene styrene) or glass fiber reinforced plastic.
[0062] Furthermore, on the support element 312 there is arranged a gear wheel 330 with a centre axis of the gear wheel 330 determining the third axis 318 of rotation. Thus, by rotating the gear wheel 330 about the centre axis, the caster wheel module 304 rotates about the third axis 318 of rotation. For example, as shown in FIG. 3, the second linkage member 302 comprises a rotatable shaft 332 having a rotation member 334 in the form of a second gear wheel 334. If the rotatable shaft 332 is rotated, the second gear wheel 334 causes the first gear wheel 330 to rotate and thereby the caster wheel module 304 is also rotated about the third axis 318 of rotation. In the depicted embodiment in FIG. 3, a bevel gear arrangement 334,330 is shown as an example.
[0063] FIG. 4a-b illustrate the caster wheel arrangement 300 in FIG. 3 in two different positions. Similar to what is shown in FIG. 3, in FIG. 4a-b the caster wheel module 304 comprises the wheel 306 having the first axis of rotation 314, and via the joint a rotation of the wheel 306 about a second axis 316 of rotation is possible. A portion of the wheel 306 extends through on open end such that the wheel 306 may touch the ground 340. There is further indicated a third axis 318 of rotation of the caster wheel module 304. In FIG. 4a, the caster wheel module 304 is in an upright position, thus non-rotated. For example, as illustrated, the second axis of rotation 316 is substantially perpendicular to the ground 340. In FIG. 4b, the caster wheel module 304 has been rotated about the third axis 318 of rotation compared to what is depicted in FIG. 4a. In FIG. 4b, the second axis 316 of rotation is not perpendicular to the ground 340, instead the second axis 316 of rotation is tilted an angle with respect to an axis perpendicular to the ground 340. Assuming a driving direction 342 indicated in FIG. 4a-b, the second axis 316 of rotation is tilted towards the driving direction 342. A consequence of tilting the second axis of rotation 318 by a rotation about the third axis of rotation 318 is that the rotation of caster wheel module 304 comprising the wheel 306, about the second axis of rotation is limited when the wheel 306 is rolling on the ground 340. This is due to that the weight supported by the wheel 306 is not aligned with the second axis of rotation 316 leading to a more constraint ability for a rotation about the second axis of rotation 316. Thereby, when the wheelchair (e.g. as shown in FIG. 1) turns, the caster wheel module 304 being rotated an angle may not rotate about the second axis of rotation 316 as easily. A typical angle of rotation is in the interval of 0-10. Furthermore, the angle of rotation is proportional to a driving speed of a wheelchair comprising the caster wheel arrangement, for example as depicted in FIG. 1. For example, at a driving speed of 15 km/h, may be approximately 10.
[0064] FIG. 5a-b Illustrates a caster wheel arrangement 500 is shown. In FIG. 5a-b the caster wheel arrangement 500 is shown as it climbs over an obstacle in the form of a curb. The caster wheel arrangement 500 is similar to the caster wheel arrangement in FIG. 3 and FIG. 4a-b. The caster wheel arrangement 500 may be mounted on e.g. a powered wheelchair. As the caster wheel arrangement 500 approaches the curb 502, the caster wheel module 504 is rotated about the third axis of rotation (316 in FIG. 4a-b). This way, the engaging elements 506 (not all are numbered in order to avoid cluttering in the drawing) engage with the curb 502, and as the caster wheel module 504 rotates about the third axis (316) of rotation, the caster wheel arrangement 500 climbs up to the upper surface 508 of the curb 502 as is shown in FIG. 5b. Furthermore, with the caster wheel module rotated, for example as shown in FIG. 5b, the caster wheel module effectively works as a hand-break for a powered wheelchair.
[0065] FIG. 6 shows a flow-chart describing an exemplary method according to an embodiment of the invention. The method is for controlling a caster wheel arrangement 202, 300 arranged as a rear wheel arrangement on a powered wheelchair 100. A caster wheel module 206, 304 of the caster wheel arrangement is rotatable about a third axis of rotation 220, 318 as described in e.g. FIG. 2a-b, FIG. 4a-b, and/or FIG. 5a-b. The method comprises an optional first step S101 of acquiring a driving speed of the powered wheelchair. In a subsequent step S103, the caster wheel module 206, 304 is rotated a rotational angle about the third axis 220, 318 of rotation depending on the driving speed of the powered wheelchair, for example, the higher the speed the larger the rotational angle.
[0066] Thanks to the present invention, there is provided a system and method capable of an improved control of a powered wheel chair. In particular, there is provided a system and method capable of reducing the effect of oversteering of a powered wheelchair when turning at a high speed.
[0067] In each of the above exemplary embodiments in FIGS. 1-6 and in other embodiments, a typical size of the wheel is in the interval between 150 mm and 250 mm in diameter and a wheel width in the interval between 50 mm and 70 mm, however, these measures may be different and are only for exemplary purposes. The rim of the wheel is commonly made from aluminum and the tire is typically a rubber tire, although other materials may also be used.
[0068] Furthermore, powered wheel chair 100 may also be equipped with sensors such as e.g. a gyroscope and/or an accelerometer. As mentioned (e.g. with reference to FIG. 4a-b) the caster wheel tilt angle may be controlled between e.g. 0-10 proportionally with actual speed of the powered wheel chair 100. However, it may be advantageous to include more signals which affect tilt angle, other than speed. For example, when ground is downhill, uphill or slanted, the signals from the accelerometer and/or gyroscope may also be used to influence tilt angle , in order to enhance driving characteristics. In one exemplary embodiment, an accelerometer measuring the acceleration in three perpendicular directions (e.g. axes X, Y, Z) and a gyroscope measuring rotational speed about the axes X, Y, Z, of the powered wheel chair 100 are arranged to provide measurements for determining the slope angle of the ground. The measurements from the accelerometer and the gyroscope are combined with e.g. the geometry of the powered wheel chair 100 in order to determine the slope angle of the ground.
[0069] Furthermore, powered wheel chairs 100 typically have some type of steering device, usually a joystick. When traveling at high speed, which would suggest a high tilt angle , a steering command from e.g. the joystick indicating a sharp turn, may require the tilt angle to be temporarily reduced in order to obtain the desired turn
[0070] Additionally, variations to the disclosed embodiments can be understood and effected by the skilled person in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims.
[0071] It should be understood that the inventive concept is not limited to the described exemplary embodiments; rather the scope being generally defined by the accompanying claims.
[0072] In the claims, the word comprising does not exclude other elements or steps, and the indefinite article a or an does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage.
