Designing Noncircular Pulleys to Realize Target Motion Between Two Joints

Many mechanisms reduce the number of inputs for their target motions by restricting the motions of pairs of joints. This study designs a novel constraint mechanism using a pair of noncircular pulleys and a wire. The wire restricts the motion of the joints to the target motion while enabling a compact structure. We analytically derive the shape of the noncircular pulleys using the desired relation between the joints and the lengths of their moment arms. The usability of the proposed mechanism is evaluated on a robotic leg, which maintains the height and posture of its upper body under the constraints.