Spherical wheel intended for moving a vehicle and vehicle using the wheel

Abstract

A spherical wheel to move a vehicle comprises two caps, the surface of which follows the spherical surface of the wheel, the caps being articulated by means of a pivot link relative to a shaft. The wheel further comprises two casters each arranged in an opening of each of the caps, the opening centered about the axis of the corresponding pivot link, each caster arranged in the extension of the pivot link of the cap concerned. Each caster ensures a rolling at the level of the spherical surface. Radii S of the opening of each cap and r of the corresponding caster are defined to substantially balance forces needed to drive a cap and the corresponding caster when the wheel goes from bearing on the ground on a cap at the edge of the opening to bearing on the ground on the corresponding caster.

Claims

1. A spherical wheel configured to move a vehicle and be driven in rotation by a shaft rotating about an axis, the wheel comprising: first and second caps, each of the first and second caps having a surface that follows a spherical surface of the wheel and delimited by a plane, each of the first and second caps being articulated a pivot link relative to the shaft about an axis at a right angles to the plane of the each of the first and second caps; and first and second casters, each of the first and second casters arranged in an opening of the first and second caps, the openings being circular and centered about the axis of the corresponding pivot link, each of the first and second casters being arranged in an extension of the pivot link of one of the first and second caps, each of the first and second casters being free to rotate about an axis at right angles to the axis of the shaft, each of the first and second casters ensuring that the spherical wheel rolls, wherein a radius of the openings of each of the first and second caps and a radius of each of the first and second casters are defined to substantially balance forces needed to drive the first and second caps and the first and second casters when the spherical wheel goes from bearing on one of the first and second caps to bearing on one of the first and second casters.

2. The spherical wheel of claim 1, wherein a rolling line of the casters occupies an angular sector centered on the center of the spherical wheel and wherein the angular sector is greater than 35?.

3. The spherical wheel of claim 2, wherein the angular sector is less than 125?.

4. The spherical wheel of claim 2, wherein the angular sector is between 45? and 50?.

5. The spherical wheel of claim 1, wherein a greater radius of each of the first and second casters about its respective axis is greater than a quarter of the radius of the spherical wheel.

6. The spherical wheel of claim 5, wherein a greater radius of each of the first and second casters about its respective axis is greater than a third of the radius of the spherical wheel.

7. The spherical wheel of claim 6, wherein a greater radius of each of the first and second casters about its respective axis is equal to half the radius of the spherical wheel.

8. The spherical wheel of claim 1, wherein, for each of the first and second caps, a friction torque Cf.sub.c is defined at a level of the pivot link between each of the first and second caps and the shaft, wherein, for each of the first and second casters, a friction torque Cf.sub.r is defined in its freedom to rotate relative to the shaft, and wherein the radii S of the opening of the first and second caps and r of the first and second casters are defined so that the following equality is substantially observed:
Cf.sub.c/S=Cf.sub.r/r.

9. The spherical wheel of claim 1, wherein the first and second caps and the first and second casters are defined to substantially balance kinetic energies of one the first and second caps and of the one of the first and second casters when the spherical wheel goes from bearing on the one of the first and second caps at an edge of the opening to bearing on the one of the first and second casters.

10. The spherical wheel of claim 9, wherein, for each of the first and second caps, a moment of inertia I.sub.c is defined about an axis of the pivot link between the first and second caps and the shaft, wherein, for each of the first and second casters, a moment of inertia I.sub.r is defined about a rotating axis relative to the shaft, and wherein dimensions and materials of the first and second caps and of the first and second casters are defined for the following equality to be substantially observed: $\frac{\mathrm{Ic}.?c}{2}=\frac{\mathrm{Ir}.?r}{2}$ ?.sub.c representing a speed of rotation of the cap when the spherical wheel is bearing on one of the first and second caps at the edge of the opening, ?.sub.r representing the speed of rotation of the caster when the wheel goes from bearing on the first and second caps at the edge of the opening to bearing on the caster.

11. The spherical wheel of claim 1, further comprising first and second covers associated with each of the first and second casters and fixed to the shaft, wherein the first and second covers form a portion of the spherical surface coming into the extension of the spherical surface of the first and second caps at the level of the opening through which said caster is arranged, wherein the first and second covers partly cover said first and second casters from said opening and wherein the first and second covers extend symmetrically relative to a rolling line of the first and second casters.

12. A vehicle, comprising at least three spherical wheels of claim 1, wherein axes of the shafts of at least two of the spherical wheels are not arranged in a same plane.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be better understood and other advantages will become apparent on reading the detailed description of an embodiment given by way of example, the description being illustrated by the attached drawing in which:

(2) FIGS. 1 and 2 represent a first variant spherical wheel according to the invention;

(3) FIG. 3 represents a second variant spherical wheel according to the invention;

(4) FIG. 4 represents, in partial cross section, the wheel of FIGS. 1 and 2;

(5) FIG. 5 represents another external view of the wheel of FIGS. 1 and 2;

(6) FIG. 6 represents, in perspective and in partial cross section, the wheel of FIGS. 1 and 2;

(7) FIG. 7 represents an example of a vehicle equipped with a number of wheels of FIGS. 1 and 2.

(8) For clarity, the same elements will bear the same references in the different figures.

DETAILED DESCRIPTION

(9) FIGS. 1 and 2 represent a spherical wheel 10 of radius R intended to move a vehicle 11. FIG. 1 is a profile representation and FIG. 2 a perspective representation. The wheel 10 is driven in rotation by a shaft 12. The vehicle 11 is represented by its shell and the shaft 12 is linked to the shell by a pivot link 13. The axis of rotation of the shaft 12 bears the reference 14.

(10) The wheel 10 comprises two caps 15 and 16, the outer surface of which follows the spherical surface of the wheel 10. The cap 15 is delimited by a plane 17 and the cap 16 is delimited by a plane 18. The caps 15 and 16 are each articulated by means of a pivot link, respectively 19 and 20, relative to the shaft 12. The axis 21 of the pivot link 19 is at right angles to the plane 17 of the cap 15 and the axis 22 of the pivot link 20 is at right angles to the plane 18 of the cap 16. The two pivot links 19 and 20 are arranged inside their respective cap and will be detailed later.

(11) It is possible to produce caps 15 and 16 that are different, but, advantageously, the latter are identical and arranged symmetrically relative to the shaft 12. In other words, the planes 17 and 18 are secant along a line having a point of intersection 23 with the axis 14 of the shaft 12. In this configuration, the axes 21 and 22 of the two pivot links 19 and 20 are secant and form a non-zero angle between them.

(12) The wheel 10 is intended to roll on the ground referenced 25 in FIGS. 1 and 2. One of the two caps 15 or 16 is in contact with the ground 25. When the shaft 12 drives the wheel 10, the latter maintains a contact with the ground 25 according to a circle 26 of the spherical surface of the wheel 10. In this movement, the vehicle has a speed vector at right angles to the axis 14 at the point of intersection 27 between the axis 14 and a plane containing the circle 26. When the speed vector of the vehicle 11 applied at the point 27 is not at right angles to the axis 14, the cap which is in contact with the ground starts to revolve freely about its pivot link.

(13) In other words, the cap in contact with the ground 25 can be driven by two movements: a first driving rotation about the axis 14 and a second rotation about the axis of its pivot link. The two rotations can of course be combined depending on the direction of the speed vector of the vehicle at the point 27.

(14) FIG. 3 represents a variant spherical wheel 30 driven in rotation by a shaft 12 leaving a vehicle 11. The wheel 30 comprises two caps 31 and 32, the surface of which follows the spherical surface of the wheel 30. The cap 31 is delimited by a plane 33 and the cap 32 is delimited by a plane 34. Unlike the wheel 10, the planes 33 and 34 are parallel to one another and parallel to the axis 14 of the shaft 12. In this variant, the axis 12 is parallel to the ground 25, assuming that the ground 25 is flat.

(15) In the operation of the wheels 10 and 30, a singularity occurs when the cap in contact with the ground 25, the cap 16 in FIG. 1 or the cap 32 in FIG. 3, has its plane, respectively 18 and 34, horizontal.

(16) In this configuration, if the vehicle of FIG. 1 has a vector applied at the point 27 that is not at right angles to the axis 14, then the cap 16 cannot revolve about its pivot link 20 and slips on the ground 25. To avoid this slip, the wheel 10 comprises two casters 28 and 29, a caster being associated with each of the caps. Each caster is arranged in the extension of the pivot link of the cap concerned and ensures a rolling on the spherical surface of the wheel 10. More specifically, the cap 15 is equipped with the caster 28 and the cap 16 with the caster 29. The casters 28 and 29 can have a single degree of freedom in rotation about an axis at right angles to the axis 14. This rotational movement is sufficient to avoid the slip of the wheel in a singularity configuration. The casters each have a rolling line which follows the spherical surface of the wheel 10.

(17) The same applies for the wheel 30 which comprises two casters 37 and 38, a caster associated with each of the caps, respectively 31 and 32.

(18) The rest of the description is given in relation to the variant wheel 10 represented in FIGS. 1 and 3. The features presented apply also to the wheel 30.

(19) FIG. 4 represents, in partial cross section, the wheel 10 in a plane containing the axes of rotation of the two casters 28 and 29. Only the cap 15 is cut. The wheel 10 comprises a support 40 secured to the shaft 12. The support 40 revolves around the axis 14 with the shaft 12.

(20) The pivot link 19 links the support 40 and the cap 15. The pivot link 19 is formed by a bearing 42. Similarly, the pivot link 20, concealed in FIG. 4, links the support 40 and the cap 16. It is of course possible to use a number of bearings for each cap depending on the rigidity sought for the wheel 10. In this embodiment, the bearing 42 is formed by means of a spacer 43 interposed between the support 40 and the cap 15. The spacer 43 is for example produced in a material that makes it possible to obtain a low friction coefficient. It is for example possible to use polytetrafluoroethylene. The two pivot links 19 and 20 are advantageously identical. Other embodiments of the bearings are possible. It is for example possible to use rolling bearings to limit the resisting torque in the rotation of the pivot links 19 and 20.

(21) A pivot link 44 links the caster 28 and the shaft 12 via the support 40. The pivot link 44 allows the caster 28 to revolve freely about an axis 47. The pivot link 44 is for example produced by means of a shaft 45 borne at its two ends by the support 40. The caster 28 is passed through by the shaft 45. The caster 28 revolves freely relative to the shaft 45. Bushes can be placed between the shaft 45 and the caster 28. As for the spacer 43, the bushes can be produced in a material with low friction coefficient such as, for example, polytetrafluoroethylene.

(22) Similarly, a pivot link 48, similar to the pivot link 44 and concealed in FIG. 4, links the caster 29 and the shaft 12 via the support 40. This pivot link enables the caster 29 to revolve freely about an axis 49.

(23) The casters 28 and 29 are barrel-shaped so that their respective rolling link 51 and 52, visible in FIG. 4, follows the spherical form of the wheel 10. A rolling line 51 or 52 is a curve formed on the surface of a caster 28 or 29, a curve that is furthest away from the axis 14. On a caster, the rolling line moves on the surface of the caster according to its rotation. The rolling line of a caster is a circle portion formed on the spherical surface of the wheel 10. The rolling line 51 is situated in a plane at right angles to the plane 17 delimiting the cap 15. Similarly, the rolling line 52 is situated in a plane at right angles to the plane 18 delimiting the cap 16.

(24) FIG. 5 represents a view of the wheel 10, the view being centered on one of the casters, for example the caster 28. The caster 28 appears in a circular opening 54 produced in the cap 15 and centered on the axis 21. The opening of each cap has a radius S about the axis of its corresponding pivot link.

(25) To avoid abrupt changes of speed for the cap 15 when the bearing of the wheel 10 on the ground leaves the cap 15, moves to the caster 28 and finally returns to the cap 15, the length of the rolling line 51, and consequently the diameter S of the opening 54, is increased. The rolling line 51 or 52 of each of the casters 28 and 29 occupies an angular sector ? centered on the center of the spherical wheel. Advantageously, the angular sector ? is greater than 35?. Tests in-house have shown that an optimum angular sector value lies between 45? and 50?. By construction, it is possible to produce a maximum angular sector of 130?. The value retained depends on the inertias of the different moving parts and the frictions between these different parts.

(26) The greatest radius of each of the casters 28 and 29 about their axis, respectively 47 and 49, is denoted r. In order to limit the speed of rotation of the casters 28 and 29, it is possible to increase the radius r of the casters 28 and 29. Tests in-house have shown that when the radius r of each of the casters 28 and 29 is greater than a quarter of the radius R of the spherical wheel 10, the reduction in speed of the casters is already notable.

(27) It is possible to achieve a radius r equal to half the radius R of the spherical wheel 10 by means of a particular arrangement of the shaft 12 and of the support 40. The shaft 12 would then have an end that does not reach the center of the sphere. In the configuration where the radius r is equal to half the radius R, the two casters 28 and 29 touch. This makes it possible to increase the inertia of the caster which is in contact with the ground 25. More specifically, when one of the casters enters into contact with the ground, its rotation drives the other caster. The inertia obtained is substantially doubled compared to the inertia of just one caster.

(28) Other intermediate values of proportions between the radii r and R can also be envisaged. While, from a radius r equal to a quarter of the radius R of the sphere, the reduction in the speed of rotation of the caster is already advantageous, it has been found that, when the maximum radius r of each of the casters 28 and 29 about its respective axis 47 and 49 is greater than a third of the radius R, the reduction in the speed of rotation of the caster is particularly advantageous.

(29) It is of course possible to produce this same structure for the casters 27 and 38 of the spherical wheel 30.

(30) The radius r of the casters and the angular sector ? occupied by the rolling line of the casters can be optimized independently of one another. Moreover, the radius S of the opening 54 is linked to the angular sector ? in order to reduce to the maximum the functional play between the caster and its opening. It is advantageous to balance the forces needed to drive a cap and a corresponding caster when the wheel 10 goes from a cap bearing on the ground at the edge of its opening to a bearing on the ground on the corresponding caster and vice-versa. That makes it possible to avoid abrupt variations of the force between the wheel 10 and the ground at the moment of transition, such a variation of force being reflected in a jerk on the shaft 12 and therefore on the vehicle equipped with the wheel 10.

(31) Once the materials are chosen, the balancing of the forces is done mainly by means of the relative dimensions of the radius S of the opening and the radius r of the corresponding caster. To be more concise, the radii S of the opening of each cap and r of the corresponding caster are defined so as to substantially balance forces needed to drive a cap and the corresponding caster when the wheel goes from bearing on the ground on a cap at the edge of the opening to bearing on the ground on the corresponding caster.

(32) For each cap, it is possible to define a friction torque Cf.sub.c at the level of the pivot link between the cap concerned and the shaft 12 and, more specifically, with the support 40. Similarly, it is possible to define, for each caster, a friction torque Cf.sub.r in its freedom to rotate relative to the shaft 12.

(33) It is advantageous to obtain a static balancing of the friction forces due to the two pivot links 19 and 44 or 20 and 48. The static balancing is obtained by defining the radii S of the opening of the cap and r of the corresponding caster so that the following equality is substantially observed:
Cf.sub.c/S=Cf.sub.r/r

(34) Moreover, it is advantageous to obtain a dynamic balancing of the forces. The forces are a function of the inertia of the cap and of the corresponding caster. These two inertias are a function of the materials and of the dimensions of the cap and of the corresponding caster. The caps and the casters are defined so as to substantially balance the kinetic energies of a cap and of the corresponding caster when the wheel goes from bearing on the ground on the cap at the edge of the opening to bearing on the ground on the caster.

(35) More specifically, for each cap, a moment of inertia is defined about the axis of its pivot link between the cap concerned and the shaft. For each caster, a moment of inertia I.sub.r is defined about the axis its freedom to rotate relative to the drive shaft 12 of the wheel 10. The dimensions and the materials of the caps 15 and 16 and of the casters 28 and 29 are defined for the following equality to be substantially observed:

(36) $\frac{\mathrm{Ic}.?c}{2}=\frac{\mathrm{Ir}.?r}{2}$
?c representing the speed of rotation of the cap when the wheel is bearing on the ground on the cap at the edge of the opening and ?r representing the speed of rotation of the caster when the wheel goes from bearing on the ground on the cap at the edge of the opening to bearing on the ground on the caster.

(37) Advantageously, the wheel comprises two covers 56 associated with each caster and fixed to the shaft 12 via the support 40. FIGS. 5 and 6 illustrate the two covers 56 associated with the caster 28. The covers 56 each have the form of a flat crescent parallel to the plane 17. The covers 56 partly cover the caster 28 from the opening 54. The covers 56 both extend symmetrically relative to the rolling line 51. The covers 56 are secured to the support 40. The covers 56 make it possible to limit the ingress of particles into the wheel 10 through the opening 54. Nevertheless, a functional play is provided between the covers 56 and the cap 15 to allow the rotation of the cap 15 about its pivot link 19 without rubbing against the covers 56.

(38) FIG. 7 represents a vehicle 11 equipped with three wheels 10 according to the invention. This vehicle is for example a robot. It is also possible to apply the invention for vehicles comprising more than three wheels. For example, for a vehicle with four wheels, the axes of opposing wheels are situated in a same vertical plane relative to a horizontal ground, thus forming two pairs of wheels. The planes containing the axes of the two pairs of wheels are at right angles. More generally, the axes of the shafts of at least two wheels are not arranged in a same plane, which makes it possible for the vehicle to be moved in all the directions by keeping its wheels 10 on the ground 25 by means of suitable control.