US Patent 7566102 Multiple roller wheel

A wheel 100 rotatable about a main axis 106a, including: (a) a frame 111 including multiple supports 114; (b) a first series 150 of rollers 140 radially spaced from the main axis and aligned with a first plane 160a normal to the main axis, the first series of rollers spaced to form a first discontinuous rim; and (c) a second series 152 of rollers radially spaced from the main axis and aligned with a second plane 160c normal to the main axis. The second series of rollers are spaced to form a second discontinuous rim. The first and second planes are aligned parallel to and spaced from one another. Each roller 140 is: (i) rotatable about an axis normal 117 to the main axis; (ii) mounted between a pair of the supports 115; and (iii) has a lateral central cross-sectional diameter greater than the diameter of its end portions. When viewed in side elevation, the effective ground contacting surface of each of the rollers of the first series of rollers overlaps with the effective ground contacting surface of at least one diagonally adjacent roller of the second series of rollers so that the wheel is adapted to make effective ground contact through at least two of the rollers at any one time for effective travel in directions having a component parallel to the main axis. The frame is furthermore incapable of flexing sufficiently to permit the rollers from being removed or dislodged from the frame, but capable of flexing sufficiently under high loads to redistribute load stress throughout the frame.