Combined function based trajectory planning for a novel ankle rehabilitation robot
                                            LIAO Zhi wei, ZHANG Jun, LU Zong xing, YAO Li gang
                      （School of Mechanical Engineering and Automation, Fuzhou University, Fuzhou 350116, China）

Abstract: Aiming at the trajectory planning problems of the proposed hybrid ankle rehabilitation robot, the inverse kinematics, trajectory planning and the displacement of the pushrods were analyzed. A new trajectory for a novel patented ankle rehabilitation robot was proposed, which is composed of a cycloid function and a rectangular function. The kinetic characteristics i.e., the acceleration, the velocity and the displacement of the trajectory were derived and compared with those of a traditional cycloid trajectory. The influences of two types of trajectories on the stability, the maximum speed, the maximum acceleration and the rigid impact of the rehabilitation robot were compared. Finally, an inverse kinematic analysis was conducted to yield the displacements of three pushrods in the rehabilitation robot when it takes a planter/dorsal flexion motion. The displacements of three pushrods were imported into the ADAMS to analyze the parameters of the pushrods and the trajectory of the reference point. The results indicate that the proposed combined function based trajectory can provide a rehabilitation motion with better stability and less impact on the ankle.

Key words: ankle rehabilitation; inverse kinematics; trajectory planning; cycloid function; combined function