Study on Workspace Optimization of 3SPS+1PS Parallel Hip Joint Simulator

Abstract

In order to evaluate kinematics performance of an artificial hip joint, a novel hip joint simulator has been proposed, and the workspace analysis is necessary to ensure the capacity of simulating various activities and their motion ranges in daily human life. Comparing with the current simulators established by some serial manipulators, 3SPS+1PS parallel manipulator is designed as the key component of the hip joint simulator. Based on Quaternion method, the formulae for solving the inverse/forward kinematics equations are derived. The homogeneous velocity Jacobian matrix of 3SPS+1PS parallel manipulator has been established by constructing three related points on moving platform. Comparing the condition number variations in different workspace areas and structure parameters respectively, the structure parameters of the manipulator are optimized by analyzing the relationships among the mean values of the condition number and the design size ratio of base and moving platform, the allowable angles of spherical joints, the central height of moving platform are obtained. Furthermore, the suitable workspace to meet with the bionic essentiality of the hip joint has been obtained. The workspace optimization provided has great significance for trajectory planning, dynamic analysis and control design of the simulator.