Patent ID: 8408339

Claim:
A frictional drive device, comprising a frame; a pair of drive disks each rotatably supported by the frame around a central axial line in a mutually opposing relationship; a pair of actuators supported by the frame for individually rotatively actuating the drive disks; a plurality of drive rollers arranged along an outer periphery of each drive disk so as to be rotatable along a prescribed plane of rotation at a certain angular relationship with the central axial line; and an annular main wheel disposed at least approximately coaxially with respect to the central axial line and engaged by the drive rollers of the drive disks, the main wheel comprising an annular member and a plurality of driven rollers supported along the annular member so as to be rotatable around a tangential line of the annular member; wherein each drive roller includes at least a pair of individually rotatable disk members coaxially stacked upon one another in a mutually freely rotatable manner and having different diameters so as to jointly define a substantially hourglass shaped outer profile, the diameters being selected so that the disk members engage the corresponding driven roller at outer peripheral parts thereof, and wherein each disk member is given with an axially straight outer peripheral surface so that the disk members jointly define an hourglass shaped outer contour in an axially stepwise fashion.