Workspace analysis of 3SPS+1PS bionic parallel test platform for hip joint simulator

Abstract

In order to evaluate the movement performance of a human hip joint, a novel parallel manipulator called 3SPS+1PS bionic parallel test platform is proposed in this article. SPS denotes the spherical-prismatic-spherical leg, and PS the prismatic-spherical leg where only the prismatic joint is actuated and hence underlined. For the 3SPS+1PS bionic parallel test platform with four degrees of freedom including three rotations and one translation, the formulae for solving the inverse kinematics equations are derived based on the quaternion method. Unit quaternion is used to represent the position and orientation of a moving platform, and singularities caused by Euler angles are avoided. Combining the topological structure characteristics of the parallel manipulator, the orientation workspace of the moving platform at a given translation position is constructed. Moreover, the procedures to solve and evaluate the orientation workspace of the parallel manipulator are obtained. In order to ensure dexterity and obtain more workspace, the condition index is studied by the condition number and singular values analysis of the dimensionally homogeneous Jacobi matrix. The parallel manipulator has three rotations about the Z-axis, the Y-axis, and the X-axis applied to represent three rotation motions (flexion/extension (FE), abduction/adduction (AA), and internal/external (IE) rotation motion) of a human hip joint, respectively. The numerical results illustrate that the 3SPS + 1PS bionic parallel test platform generates ±25° to ±108° in FE, −20° to 20° in AA, and −21° to 21° in IE rotation where the maximum permissible condition numbers of Jacobi matrix are set within the range 15–20 and the parallel manipulator can provide full-scale friction motion for hip joint simulator. In the dexterous orientation workspace, the slide track on the friction counterface of hip joint prostheses can be varied consistently. By verifying the lengths of the SPS-type active legs, the parallel manipulator can provide cross-path multidirectional slide motion for hip joint prostheses. The three-dimensional model and kinematics simulation of the manipulator are established and analysed. The simulation results prove that the 3SPS + 1PS bionic parallel test platform can accurately represent human hip joint motion and provide more reliable experimental data for hip joint prostheses in clinical application. The research builds the theoretical basis for its bionic motion simulation in practical application.