Wheel, and friction drive device and omni-directional vehicle using the same

In a wheel for use in an omni-directional vehicle, gravel and other foreign matters are prevented from being trapped between free rollers forming the wheel, and traveling vibrations and noises are minimized at the same time. The wheel includes an annular member and a plurality of free rollers each rotatably supported by the annular member around a corresponding tangential line of the annular member, and a gap member is placed between each adjacent pair of the free rollers to fill a gap defined between the free rollers.

TECHNICAL FIELD

The present invention relates to a wheel, and a friction drive device and an omni-directional vehicle using the same, and in particular to an omni-wheel, and a friction drive device and an omni-directional vehicle using the same.

BACKGROUND OF THE INVENTION

A friction drive device for an omni-directional vehicle that can freely move about on a floor is known. This device comprises a main wheel including an endless annular member and a plurality of free rollers rotatably supported along the outer circumference of the annular member, and a plurality of drive rollers engaging the outer circumferential surfaces of the free rollers at the outer circumferential surfaces thereof so that the rotation of the drive rollers may be frictionally transmitted to the free rollers. See the third embodiment illustrated in FIGS. 17 and 18 of Japanese patent publication No. 3820239B, for instance.

Also is known a wheel for an omni-directional vehicle including two kinds of barrel-shaped free rollers having large and small diameters arranged along the periphery of the wheel in an alternating fashion. Each large diameter barrel-shaped free roller is provided with a recess in which the bearing and a part of the adjacent small diameter barrel-shaped free roller is received, and the curvatures of the two kinds of free rollers are selected such that the overall profile of the barrel-shaped free rollers, and hence the overall profile of the wheel may be highly close to a true circle. See Japanese patent publication No. 3421290B, for instance.

BRIEF SUMMARY OF THE INVENTION

Task to be Achieved by the Invention

In the wheels of the friction drive devices mentioned above, wedge shaped gaps are created between adjacent free rollers (or on axial ends thereof), and foreign matters such as gravel could be trapped in such gaps while the wheel travels over a road surface. Should such a foreign matter is trapped in any of the gaps, the free rollers are prevented from rotating around the respective axial lines, and this prevents the vehicle actuated by the friction drive deice from cornering or traveling obliquely as designed.

Also, the gaps between adjacent free rollers cause irregularities in the outer profile of the wheel (with respect to a circular profile centered around the central axial line of the wheel), and this may cause rattling or other vibrations and noises as the wheel rotates around the central axial line thereof, and rolls over the road surface.

In view of such problems of the prior art, a primary object of the present invention is to provide a friction drive device that can avoid intrusion of gravel and other foreign matters into gaps between the free rollers, and minimize the vibrations and noises when the wheel rolls over the road surface.

Means to Achieve the Task

The wheel of the present invention comprises a wheel including an annular member and a plurality of free rollers each rotatably supported by the annular member around a corresponding tangential line of the annular member, and is characterized by that a gap member is placed between an adjacent pair of the free rollers to fill a gap defined between the free rollers.

The gap member is required not to obstruct the rotation of the free rollers. The gap member may be given with a wedge shape tapering toward a central axial line of the wheel, and configured to be moveable in a same direction as a rotational movement of the free rollers at least in a part of the gap member facing a road surface. The gap member may also be given with a wedge shape complementary to the gap defined between the free rollers, and secured to the annular member in a rotational fast manner. Alternatively, the gap member may include a plurality of vane members extending radially from the annular member like a brush.

The friction drive device of the present invention may comprise a wheel as defined above, a pair of rotatable members rotatably supported on either side of the wheel around a central axial line of the annular member; and a plurality of drive rollers arranged on each rotatable member along a circle concentric to a rotational center of the rotatable member such that each drive roller is rotatable around a rotational center line in a skewed relationship to the rotational center line of the rotatable member, and engages an outer circumferential surface of the corresponding free roller.

The friction drive device of the present invention may also comprise a wheel as defined above, a wheel supporting rotatable member rotatably supported on one side of the wheel around a central axial line of the annular member and supporting the annular member of the wheel, a rotatable member rotatably supported on another side of the wheel around the central axial line of the annular member, and a plurality of drive rollers arranged on each rotatable member along a circle concentric to a rotational center of the rotatable member such that each drive roller is rotatable around a rotational center line in a skewed relationship to the rotational center line of the rotatable member, and engages an outer circumferential surface of the corresponding free roller.

The omni-directional vehicle of the present invention includes a friction drive device as defined above, and is configured to travel by a wheel as defined above.

Effect of the Invention

In the wheel of the present invention, the gap member fills the gap between the adjacent free rollers, and prevents any foreign matter from being trapped in the gap. Also, as the irregularities in the outer profile of the wheel are reduced, vibrations and noises that are generated as the wheel rolls over the road surface can be minimized.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Referring toFIGS. 1 to 4, a friction drive device embodying the present invention and an omni-directional vehicle1using the same are described in the following.

As shown inFIGS. 1 and 2, the omni-directional vehicle1of the illustrated embodiment comprises a lower vehicle body7of a yoke configuration that supports, although in an indirect manner, a main wheel (road wheel)2in a rotatable manner.

The lower vehicle body7includes a pair of leg members7R and7L that are hinged to each other via a hinge pin11. Each leg member7R,7L is provided with a step32R,32L extending substantially in the horizontal direction. To the left leg member7L is affixed a lower end of a pole33which extends vertically upward and provided with a horizontally extending handle bar34at the upper end thereof. A compression coil spring8is interposed between the right and left leg members7R and7L of the lower vehicle body7so that the two leg members7R and7L are resiliently urged toward each other.

The lower vehicle body7, two steps32R and32L, pole33and handle bar34are integrally joined to each other, and jointly form a vehicle body of the omni-directional vehicle1.

The lower vehicle body7is fitted with an auxiliary wheel35via an arm36having an upper end pivotally supported by a rear part of the of the lower vehicle body7so as to be raised and lowered as required. The auxiliary wheel35is supported by the free end (lower end) of the arm36so as to be located behind the main wheel2and rotatable around a horizontal axial line. The handle bar34is provided with a grip lever37that is connected to the arm36via a per se known Bowden cable (not shown in the drawings) so that the arm36may be raised by squeezing the grip lever37by hand.

A right rotatable member4R is rotatably supported by the right leg member7R via a support shaft6R, and a left rotatable member4L is rotatably supported by the left leg member7L via a support shaft6L so that the right and left rotatable members4R and4L are supported by the vehicle body7so as to be rotatable around a common central axial line (A) in an axially spaced apart relationship.

Each rotatable member4R,4L is integrally and coaxially provided with a pulley (or sprocket)9R,9L. Each leg member7R,7L is provided with an electric motor5R,5L in such a manner that each rotatable member4R,4L is rotatively actuated around the central axial line (A) of the support shaft6R,6L by drivingly connecting the output end of the corresponding electric motor5R,5L with the corresponding pulley9R,9L via an endless belt (or link chain)10R,10L. Thereby, the two rotatable members4R and4L can be individually actuated by the corresponding electric motors5R and5L.

The vehicle body7and/or the pole33are incorporated with a rechargeable battery for powering the electric motors5R and5L and a control unit for the inverted pendulum control and travel control of the omni-directional vehicle1which are not shown in the drawings.

Each rotatable member4R,4L is formed with a frusto-conical tapered outer circumferential surface12R,12L opposing the other rotatable member. To the frusto-conical tapered outer circumferential surface12R of the right rotatable member4R are mounted a plurality of drive rollers (second free rollers)3R which are arranged circumferentially or along the direction of the movement of the right rotatable member4R, each via a bracket13R and a pivot pin14R, at a regular angular interval. To the frusto-conical tapered outer circumferential surface12L of the left rotatable member4L are likewise mounted a plurality of drive rollers (second free rollers)3L which are arranged circumferentially or along the direction of the movement of the left rotatable member4L, each via a bracket13L and a pivot pin14L, at a regular angular interval.

The main wheel2is located between the right and left rotatable members4R and4L, and is rotatably supported around a central axial line (B) (axis of symmetry) coaxial with the central axial line (A) of the right and left rotatable members4R and4L by being interposed between the right drive rollers3R of the right rotatable member4R and left drive rollers3L of the left rotatable member4L.

The main wheel2is interposed between the right and left rotatable members4R and4L, and is rotatably supported by being held between the right drive rollers3R of the right rotatable member4R and left drive rollers3L of the left rotatable member4L around the central axial line (B) (axis of symmetry) coaxial with the central axial line (A) of the right and left rotatable members4R and4L. In other words, the right and left rotatable members4R and4L are rotatably supported on either side of the main wheel2around an axial center line coaxial with the axial center line of the main wheel2.

The main wheel2comprises an annular member22, a plurality of free rollers (first free rollers)25rotatably supported thereby so as to be rotatable around an axial line tangential to the corresponding point of the annular member22, and gap members53.

More specifically, as shown inFIG. 3, the annular member22is formed by a metallic rod having a hexagonal cross section. A plurality of inner sleeves23each having a hexagonal bore23A curved at a same curvature as the annular member22, and complementary in cross section with the annular member22are fitted onto the annular member22so as to be rotatively and circumfenetically immobile relative to the annular member22. The outer circumferential surface23B of each inner sleeve23defines a true cylindrical surface. The annular member22may consist of a polygonal ring or a combination of arcuate segments.

Each free roller25comprises a metallic cylindrical sleeve25A and a cylindrical outer peripheral member25B fixedly fitted on the inner sleeve25A and defining an outer circumferential surface25C of the free roller25. The outer peripheral member25B s made of rubber-like elastomeric material. The inner circumferential surface of each free roller25is rotatably fitted on the outer circumferential surface23B of the corresponding inner sleeve23via a needle bearing51.

Each free roller25is configured to engage an object to which a drive force is to be transmitted or applied, and is fitted around the annular member22like beads of a rosary. More specifically, each free roller25is rotatable around the tangential direction of the annular member22or the cross sectional center line (C) of the annular member22. In other words, each free roller25is rotatable around the axial center line thereof, and this rotational movement may be compared to a rotation of a planet around the rotation axis thereof.

The outer circumferential surface of each drive roller3R,3L engages the outer circumferential surface25C of the corresponding free roller25under the biasing force of the compression coil spring8, and power is frictionally transmitted from the drive rollers3R and3L to the free rollers25. In other words, the outer circumferential surface of each drive roller3R,3L engages the outer circumferential surface25C of the corresponding free roller25in a torque transmitting relationship so that the rotation of the rotatable members4R and4L is transmitted to the main wheel2.

The number of the drive rollers3R,3L on each rotatable member4R,4L in relation with the number of the free rollers25is selected in such a manner that the free roller25engaging the floor surface or road surface is engaged by at least one of the drive rollers3R,3L, and thereby receives a drive force at all times.

In this case, the cross sectional center line of the main wheel2is defined by connecting the central axial lines of the free rollers25into a ring, and the rotation of the main wheel2around the cross sectional center line (C) is given by the rotation of each free roller25around the central axial line thereof.

Between each adjacent pair of free rollers25is inserted a gap member53having a wedge shape tapering toward the central axial line of the main wheel2. Preferably, as shown inFIG. 4, the wedge shape of each gap member53is substantially complementary to the shape of the gap between the adjacent free rollers25. Each gap member53is provided with a circular central bore53A that circumscribes the hexagonal cross section of the annular member22, and defines an outer circumferential surface (ground contact surface)53B that is substantially coaxial with the outer circumferential surfaces of the adjoining free rollers25and has an outer diameter equal to or slightly smaller than that of the free rollers25. The gap member53may be made of material such as plastic, rubber-like elastomer, elastomer and foamed material.

On an imaginary plane perpendicular to the central axial line (B) of the main wheel2, or as seen inFIG. 3, each gap member53tapers toward the central axial line (B), and is rotatably fitted on the outer circumferential surface of the annular member22by the circular bore53A so as to be rotatable. In other words, each gap member53is supported by the annular member22so as to be rotatable around the cross sectional center line (C) thereof, and substantially entirely fills the gap between the adjacent free rollers25.

In particular, the outer circumferential surface53B of each gap member53that could engage the road surface is rotatable in the same direction as the adjacent free rollers25. In the case where the main wheel2engages the outer circumferential surface of a ball to cause the ball to roll, the outer circumferential surface53B of each gap member53could engage the outer circumferential surface of the ball.

By thus filling the gap between each adjacent pair of free rollers25with the gap member53, the irregularities of the circumferential contour centered around the central axial line (B) can be reduced or can even be eliminated.

Each gap member53is linearly cut off at the side having the least thickness (inner peripheral side of the main wheel2) into the shape of letter-D in front view to avoid interference with the free rollers25. The part of each gap member53having the least thickness is also provided with a slit53C so that the gap member53may be replaceably fitted on the annular member22by pushing the two parts of the gap member53adjoining the slit53C away from each other in the thickness-wise direction of the gap member53.

The outer circumferential surface3Ra,3La of each drive roller3R,3L engages the outer circumferential surface25C of the corresponding free roller25under the biasing force of the compression coil spring8so that rotative force (propelling force) is frictionally transmitted from the drive rollers3R and3L to the free rollers25. In other words, the outer circumferential surface3Ra,3La of each drive roller3R,3L engages the outer circumferential surface25C of the corresponding free roller25in a torque transmitting relationship so that the rotation of the rotatable members4R and4L is transmitted to the main wheel2.

Each of the drive rollers3R and3L is supported so as to be rotatable around a central axial line (D) which is neither perpendicular nor parallel to the rotational direction of the main wheel2around the central axial line (B) (which is the same as the central axial line (A) of the rotatable members4R and4L) or, more accurately, the tangential direction of the circle centered around the central axial line (B) at the point corresponding to the point of contact. In other words, each of the drive rollers3R,3L has a central axial line (D) which is tilted with respect to the rotational direction of the main wheel2around the central axial line (B), and is in a skewed relationship to the central axial line (A) of each rotatable member4R,4L.

When seen in a projected plane perpendicular to the central axial line (A), the central axial line of each drive roller3R,3L tilts by a certain angle with respect to the central axial line of the corresponding free roller25. The central axial line of each drive roller3R,3L tilts with respect to the radial line of the annular member22corresponding to the center of the corresponding free roller25, and, at the same time, tilts with respect to an imaginary plane tangential to the cross sectional central line of the annular member22. This three dimensional tilting of the two axial lines is similar to the tilting of the teeth of a pair of helical conical gears meshing with each other.

Owing to this geometrical relationship, the right and left drive rollers3R and3L transmit the rotation of the rotatable members4R and4L as a side force to the free rollers25via the frictional engagement between the outer circumferential surfaces of the drive rollers3R and3L and free rollers25.

Owing to the engagement between the right and left drive rollers3R and3L that rotate with the respective rotatable members4R and4L and the free rollers25, the main wheel2of the illustrated embodiment is able to apply a lateral drive force to the road surface by causing the free rollers25to rotate around the cross sectional center line (C) of the annular member22, and to apply a fore-and-aft drive force to the road surface by causing the main wheel2to rotate around the central axial line (B) thereof (or causing the free rollers25to move circumferentially around the central axial line (B) of the main wheel2).

When the rotatable members4R and4L rotate in the same direction at the same rotational speed powered by the corresponding electric motors5R and5L, the drive rollers3R and3L turn around the central axial line (A) of the rotatable members4R and4L without each drive roller3R,3L rotating around the central axial line thereof, and the resulting side force of each drive roller3R,3L includes a component that actuates each free roller25of the main wheel2along the cross sectional center line thereof (tangential direction). Thereby, the main wheel2rotates around the central axial line (B) without each free roller25rotating around the central axial line (C) thereof.

If the rotatable members4R and4L are made to rotate in opposite directions and/or at different speeds powered by the corresponding electric motors5R and5L, the drive rollers3R and3L turn around the central axial line (A) of the rotatable members4R and4L while each drive roller3R,3L rotates around the central axial line thereof, and the resulting side force of each drive roller3R,3L includes a component that actuates each free roller25of the main wheel2along the outer circumference of the free roller25or around the axial center line thereof. Thereby, the free roller25rotates around the cross sectional center line (C) or tangential line.

The rotation of each free roller25around the cross sectional center line (C) thereof or the tangential line depends on the difference between the rotational speeds of the two rotatable members4R and4L. For instance, when the two rotatable members4R and4L are rotated at the same speed in opposite directions, the main wheel2does not rotate around the central axial line (B) while each free roller25is rotated around the central axial line (C) thereof. Thereby, the main wheel2is actuated in the direction of the central axial line (B) thereof or receives a lateral drive force, and is propelled in the lateral direction.

In this manner, by individually controlling the rotational speeds and rotational directions of the rotatable members4R and4L via the two electric motors5R and5L, the omni-directional vehicle1can be propelled on the road surface in any desired direction.

When the free rollers25of the main wheel2are rotated around the respective central axial lines (C) by appropriately driving the electric motors5R and5L while the auxiliary wheel35is caused to engage the road surface, as the auxiliary wheel35produces a lateral side force (in the direction of the central axial line (B) of the main wheel2), and restricts the movement thereof, the main wheel2receives a yaw moment around a vertical yaw axis, and the lower vehicle body7(of the omni-directional vehicle1) is caused to turn around this yaw axis. In other words, by producing a frictional force at an angle to the line connecting the ground contact point of the main wheel2and the ground contact point of the auxiliary wheel35, a yaw moment around the yaw axis can be created. Thereby, the omni-directional vehicle1is enabled to make a turn with a relatively small turning radius.

The wedge shaped gaps defined between the free rollers25are filled by the gap members53so that the outer profile of the main wheel2centering around the central axial line (B) is free from or substantially free from irregularities. Therefore, vibrations and noises that are generated as the main wheel2rotates around the central axial line (B) and the omni-directional vehicle1travels over the road surface can be minimized.

The wedge shaped gaps defined between the free rollers25are filled with the gap members53, and foreign matters such as gravel are prevented from being trapped between the free rollers25so that the free rollers25are allowed to freely rotate around the respective central axial lines (C) thereof without being hindered by foreign matters, and the omni-directional vehicle1is allowed to turn as designed.

Each gap member53preferably contacts the adjoining free rollers25via contact surfaces that involve a low frictional resistance. In the illustrated embodiment, each gap member53is fitted on the annular member22via a circular bore53A so that the gap member53is allowed to rotate with the adjoining free rollers25to a certain extent. If each gap member25is made of material such as foamed material that is capable of compressive deformation in the thickness-wise direction, the gap member25may even be able to rotate around the central axial line (C) thereof by 360 degrees. This helps the omni-directional vehicle1to make a turn as designed when the gap member53engages the road surface.

Alternatively, as shown inFIG. 5, the gap member53may be provided with a hexagonal bore53that fits on the annular member22having a hexagonal cross section so that the gap member53may be held rotationally fast by the annular member22.

In this case, the gap member53is prevented from rotating with the adjoining free rollers25, and remains immobile with respect to the free rollers25. When the gap members53are prevented from rotating around the respective axial center lines (C), the outer diameter of the outer circumferential surface53B of each gap member53may be smaller than that of the free rollers25(by an extent that does not essentially compromise the function of the gap member53to prevent the intrusion of foreign matters) so that the gap member53does not engage the road surface.

FIG. 6shows yet another embodiment of the gap member55. The gap member55of this embodiment comprises a hexagonal annular member55B made of metallic or plastic material having a hexagonal bore55A fitted onto the annular member22having a hexagonal cross section and a plurality of vane members55C extending radially from the annular member55B like bristles of a brush. Each vane member55C is made of metallic plate, plastic plate or fiber material, and is highly stiff against a laterally applied force (in the direction of the movement of the free rollers25around the central axial line of the main wheel2) but is capable of resiliently deforming against a small thickness-wise force (in the direction of the rotation of the free rollers25around the respective central axial lines).

The gap member55is fitted onto the annular member22by the hexagonal bore55in a rotationally fast manner, and is thereby fixedly supported by the annular member22. The vane members55C extend from the annular member22in radial direction centered at the central axial line of the gap member22. The envelope circular line (a) defined by the tips of the vane members55C is coaxial with the outer circumferential surface25C of the free roller25, and has an outer diameter which is the same as or slightly smaller than that of the free roller25.

The wedge shaped gaps defined between the adjacent free rollers25are filled by the vane members55C of the gap members55that demonstrate a high stiffness in the lateral direction (direction of the cross sectional center line (C)). The vane members55C reduce or remove the irregularities in the outer profile of the main wheel2, and this minimizes vibrations and noises that are generated as the main wheel2rotates around the central axial line (B) and the omni-directional vehicle1travels over the road surface.

As the gaps between the adjacent vane members55C are narrow, foreign matters are prevented from being trapped in the gaps between the adjacent vane members55C. Therefore, the rotation of each free roller25around the central axial line (C) thereof is not impeded by the trapping of any foreign matters in the gaps between the adjacent vane member55C, and the omni-directional vehicle1is enabled to make a turn as designed without fail.

As the gap members55engage the free rollers25only at the lateral edges of the vane members55C, the free rollers25do not encounter any substantial frictional resistance as they rotate around their respective axial center lines. When the free rollers25rotate while the gap members55engage the road surface, as the vane members55C are configured to resiliently bend under a relatively small force directed in the thickness-wise direction of the vane members55C, the vane members55C undergo resilient bending deformation. Thereby, the gap members55engaging the road surface do not substantially prevent the omni-directional vehicle1from making a turn as designed.

Another embodiment of the main wheel of the present invention is described in the following with reference toFIGS. 7 and 8.

In this embodiment, an annular member61having an octagonal cross section is used for the main wheel2. A plurality of flanged inner sleeves62each having a central bore62A curved at a same curvature as the annular member61are fitted onto the annular member61so as to be rotatively and circumferentially immobile relative to the annular member61.

Each free roller25is similar to that of the previous embodiment, and comprises a metallic cylindrical sleeve25A and a cylindrical outer peripheral member25B fixedly fitted on the sleeve25A and defining an outer circumferential surface25C of the free roller25. The inner circumferential surface of each free roller25is rotatably fitted on the outer circumferential surface23B of the cylindrical main part of the corresponding flanged inner sleeve62via a ball bearing63.

The flanged inner sleeves62are provided so as to individually correspond to the particular free rollers25, and are arranged continuously along the circumference of the annular member61. A radial flange64is provided in an axial end (circumferential direction of the annular member61) of each inner sleeve62, and serves as a standoff member or a spacer member that determines the gap between the adjacent free rollers. In other words, each flange64is located in the wedge shaped gap defined between the adjacent free rollers25. The radial flange64is linearly cut off at diametrically opposing parts thereof as shown inFIG. 8.

To each radial flange64is secured a gap member65that straddles on the radial flange64from the radially outer part of the main wheel2. The gap member65is wedge shaped so that the wedge shaped gap between the adjacent free rollers25is filled as seen inFIG. 7(or as seen from side). The gap member65is provided with a pair of bifurcated parts that interpose the radial flange64from the linearly cut off sides as seen inFIG. 8(or as seen from front). Each bifurcated part of the gap member65is provided with a projection66that fits into a recess67formed in the corresponding cut off part of the radial flange64so that the gap member65is positively retained by the radial flange64.

The gap member65may be made of plastic material such as ABS resin or rubber-like elastomer material so that each projection66may be engaged by and disengaged from the recess67of the radial flange64by means of the resilient deformation of the gap member65. This simplifies the attachment and detachment of the gap member65to and from the radial flange64.

In this embodiment also, the gap member65fills the gap between the adjacent free rollers25, and prevents any foreign matter from being trapped in the gap.

A second embodiment of the main wheel, the friction drive device and the omni-directional vehicle using the same of the present invention is described in the following with reference toFIG. 9. InFIG. 9, the parts corresponding to those inFIG. 2are denoted with like numerals without repeating the description of such parts.

In this embodiment, the lower vehicle body7is provided with a pair of leg members7L and7R which rotatably support frusto-conical rotatable members71and72via support shafts73and74, respectably, in a coaxial relationship to a common central axial line (A).

The left leg member7L of the lower vehicle body7is provided with an electric motor75. The left rotatable member71is integrally and coaxially provided with a pulley (or a sprocket)76. The electric motor75is drivingly coupled with the pulley76via an endless belt (or a link chain)77so that the rotatable member71can be rotatively actuated around the central axial line (A) of the support shaft73.

The right leg member7R of the lower vehicle body7is provided with another electric motor78. The right rotatable member72is integrally and coaxially provided with a pulley (or a sprocket)79. The electric motor78is drivingly coupled with the pulley79via an endless belt (or a link chain)80so that the rotatable member72can be rotatively actuated around the central axial line (A) of the support shaft74.

A plurality of arms82extend from the tapered outer circumferential surface81of the rotatable member71toward the other rotatable member72(to the right as seen inFIG. 9), and a main wheel2including an annular member22and free rollers25similar to the main wheel of the previous embodiment is fixedly supported by the free ends of the arms82at the annular member22thereof. Therefore, the main wheel2is rotatably supported by the lower vehicle body7around the central axial line (A) jointly with the rotatable member71. In other words, the lower vehicle body7supports the main wheel2via the rotatable member71so as to be rotatable around the central axial line (A).

A plurality of drive rollers84are mounted on the tapered outer circumferential surface83of the other rotatable member72at a regular interval along the circumference of the rotatable member72each via a bracket85and a pivot pin86in a freely rotatable manner.

The outer circumferential surface of each drive roller84engages the outer circumferential surface of the corresponding free roller25under the biasing force of the compression coil spring8that resiliently urges the right and left leg members7R and7L toward each other, and torque is frictionally transmitted from the drive rollers84to the free rollers25. Each drive roller84is freely rotatable around a central axial line (D) thereof which is in a skewed relationship to the central axial line (C) of the corresponding free roller25. Therefore, the rotational center line of each drive roller84is in a skewed relationship to the rotational center line of the free roller25with which the particular drive roller84engages.

When seen in a projected plane perpendicular to the central axial line (A), the central axial line of each drive roller84tilts by a certain angle with respect to the central axial line of the corresponding free roller25. The central axial line of each drive roller84tilts with respect to the radial line of the annular member22corresponding to the center of the corresponding free roller25, and, at the same time, tilts with respect to an imaginary plane tangential to the cross sectional central line of the annular member22. This three dimensional tilting of the two axial lines is similar to the tilting of the teeth of a pair of helical conical gears meshing with each other.

Owing to this geometrical relationship, as the right and left rotatable members71and72are rotated relative to each other, each free roller25receives a frictional force (side force) including a force component directed tangentially around the rotational center line of the free roller25and a force component directed in the axial center line (or along the generatrix line) of the free roller25from the corresponding drive roller84at the point of contact between the two rollers.

Therefore, when the rotatable members75and78rotate in the same direction at the same rotational speed powered by the corresponding electric motors75and78, the drive rollers84turn around the central axial line (A) of the rotatable members75and78without each drive roller84rotating around the central axial line thereof, and the resulting side force of each drive roller64acts upon the corresponding free roller25along the axial center line thereof. As a result, the main wheel2rotatively actuated by the rotatable member71around the central axial line (B) thereof without the free rollers25rotating around the respective central axial lines thereof.

If the rotatable members71and72are made to rotate in opposite directions and/or at different speeds powered by the corresponding electric motors75and78, the drive rollers84turn around the central axial line (A) of the rotatable member72while each drive roller84rotates around the central axial line thereof so that the resulting side force of each drive roller84includes a component that actuates each free roller25of the main wheel2along the outer circumference of the free roller25or around the axial center line thereof. Thereby, the free roller25rotates around the cross sectional center line (C) or tangential line of the main wheel2.

In this manner, by individually controlling the rotational speeds and rotational directions of the rotatable members71and72via the two electric motors75and78, the omni-directional vehicle1can be propelled on the road surface in any desired direction.

In this embodiment also, the number of the drive rollers84and the number of the free rollers25are selected in such a manner that the free roller25engaging the floor surface or road surface is engaged by at least one of the drive rollers84, and thereby receives a drive force at all times.

As the main wheel2of this embodiment is essentially not different from the main wheel of the previous embodiment, this embodiment provides the advantages of preventing gravel and other foreign matters from being trapped between the free rollers25, and minimizing the traveling vibrations and noises similarly as the previous embodiment.

GLOSSARY