Patent ID: 6953086

Claim:
A traction apparatus comprising: a body incorporating at least two traction members spaced apart along the body for engaging an inner traction surface at locations spaced apart along the traction surface in the direction in which the apparatus is to be moved, each traction member having a plurality of outwardly extending legs substantially equiangularly distributed about a central axis, wherein: each traction member is mounted on an outer surface of a rotary bearing member which is rotatable to bias each of the legs in turn against the traction surface; and each rotary bearing member has a recess in one end for receiving an opposite end of an adjacent rotary bearing member; and propulsion means for operating the traction members to move the body along the traction surface, wherein: the propulsion means acts in a first phase to move one of the legs of the first traction member in one direction relative to the body whilst in contact with the traction surface to impart the required propulsion force at the same time as one of the legs of the second traction member is moved in the opposite direction relative to the body whilst out of contact with the traction surface, and the propulsion means acts in a second phase, which alternates with the first phase, to move one of the legs of the second traction member in said one direction whilst in contact with the traction surface to impart the required propulsion force at the same time as one of the legs of the first traction member is moved in said opposite direction whilst out of contact with the traction surface.