Kinematic analysis of a 3SPS+1PS parallel hip joint simulator based on Rodrigues parameters

Abstract

To overcome defects in complex motion simulation and variable dynamic loading of hip joint simulators available in literature, a parallel hip joint simulator with a spatial parallel manipulator as core module is proposed. The simulator has four degrees of freedom (DOFs) including three rotational freedoms which replicate abduction/adduction (AA), flexion/extension (FE) and internal/external rotation (IER) motions in various human motion states and one translational freedom designed for specimen replacement. First, the mobility properties of the simulator were analyzed based on screw theory. Second, its kinematics was analyzed and its active/constrained forces were solved based on Rodrigues parameters. Some analytic formulae were derived for solving the inverse/forward displacements, velocities, accelerations and forces. Third, according to ISO 14242-1:2002(E), a numerical simulation of the inverse kinematics was conducted, the motion configuration scheme of the simulator was determined and the selection of actuators was validated. Then the numerical simulation was validated by an experiment. Finally, higher calculation efficiency of the Rodrigues parameters against the Quaternion was proved. It is shown that the simulator proposed here can replicate motions of a natural hip joint under various motion states via changing control programs but mechanical structure.