Design of Planar 1-DOF Cam-Linkages for Lower-Limb Rehabilitation Via Kinematic-Mapping Motion Synthesis Framework

When designing linkage mechanisms for motion synthesis, many examples have shown that the optimal kinematic constraint on the task motion contains too large deviation to be approximately viewed as a single rotational or translational pair. In this paper, we seek to adopt our previously established motion synthesis framework for the design of cam-linkages for a more accurate realization, while still maintaining a 1-degree-of-freedom (DOF) mechanism. To determine a feasible cam to lead through the task motion, first a kinematic constraint is identified such that a moving point on the given motion traces a curve that is algebraically closest to a circle or a line. This leads to a cam with low-harmonic contour curve that is simple and smooth to avoid the drawbacks of cam mechanisms. Additional constraints could also be imposed to specify the location and/or size of the cam linkages. An example of the design of a lower-limb rehabilitation device has been presented at the end of this paper to illustrate the feasibility of our approach. It is shown that our design could lead the user through a normal walking motion.