Study On Parallel Bionic Test Mechanism For Hip Prosthesis

In order to evaluate friction and wear characteristics of hip joint prosthesis biomaterials as well as to verify the coincidence between its theoretical results and test results, a tribology test for the biomaterials is primarily important. However, the accuracy of the tribology test largely depends on test simulators. Therefore, the hip joint simulators intend to simulate the actual working conditions of the human hip joint. In this dissertation, as the key component of a novel hip joint simulator, a bionic parallel mechanism is proposed. The hip joint simulator should provide the movement and dynamic alternating load between the joint and acetabular. Therefore, the parallel mechanism should at least have three rotations movement and one translation which produces load, i.e. the degree of freedoms of the bionic parallel mechanism are more than or equal to 4. Moreover, taking kinematic and dynamic performance of the mechanism and its manufacture cast into consideration, the degree of freedoms of the bionic parallel mechanism are set as 4, i.e. 4-DOF parallel mechanism which has one translation and three rotations. In order to make sure the parallel mechanism can accurately represent bionic motion and dynamic, it need to analyze the mechanism type- synthesis, kinematics, singular configurations, and workspace optimization, and so on. Finally, a 3SPS+1PS bionic parallel mechanism as a novel hip joint simulator is developed. The main study works in this paper are as follows:20 healthy young adults are randomly recruited for gait analysis of the human hip joint. 3D movement kinematics parameters of all kinds of gait are captured using an Optotrak Certus motion capture system, and then used to create a model from which kinematics is determined. Through the statistically analysis of the interested kinematic variables, experimental data are obtained for planning trajectory of the parallel hip joint test mechanism.Based on the quaternion method, the kinematic model of the 3SPS+1PS parallel mechanism is built, the position/orientation is depicted, and the inverse/forward displacement kinematics, inverse/forward velocity, inverse/forward acceleration and Jacobi matrix are derived. According to the gait trajectory of the human hip joint, trajectory of the moving platform of the 3SPS+1PS parallel mechanism is planned. Based on inverse kinematics analysis, the corresponding displacement, velocity and acceleration carves of the active legs are derived. Therefore, the parallel mechanism can represent the planned trajectory by driving the active legs with their inverse numerical data.For the 3SPS+1PS bionic parallel mechanism, the static mechanics of the mechanism is analyzed, and the static mechanics conversion matrix P is obtained. Six matrix column vectors can be presented by six Plücker vectors which associate with six analytical lines for Grassmann analysis. The analysis of the forward singularities by studying the linear dependency of six analytical lines using Grassmann geometry yielded to 32 singular configurations. The lower rank singular configurations are rich and complex, but their distributions are easily understood and their singular surfaces or carves are simple enough to plan the trajectory of the parallel mechanism. And the simple higher rank singular configurations are advantage for planning trajectory.For the 3SPS+1PS bionic parallel mechanism, the inverse position/orientation equations and the corresponding dimensionally Jacobi matrix are derived based on the quaternion method. In order to avoid the singularities caused by Euler angles and allow the orientation workspace to be depicted intuitively, the sets of the three-dimensional orientation workspace of the parallel manipulator are clearly depicted by Euler angles according to the relationship between the quaternion and Euler angles. By simulating the corresponding reachable orientation workspace with different architectures, the optimized architectures are derived. In addition, the workspace volume largely depends on the permissible rotation angles of spherical joints, particularly the permissible rotation angle of the spherical joints on the moving platform. In order to obtain a larger and well-conditioned orientation workspace, the maximum permissible condition numbers of the Jacobi matrix are set as 15~20. Regions of the dexterous orientation workspaces corresponding to the Jacobi matrix singular values, where either high output velocities may be achieved or where fine accuracy over the manipulator orientation exists are derived by constraining the Jacobi matrix condition number and its singular value.The 3D model of the 3SPS+1PS bionic parallel mechanism is conducted in UG NX. And inverse/forward kinematics of the parallel mechanism is simulated in ADAMS. To prove the numerical results, six extreme motions of the simulation manipulator are conducted in UG NX. From the simulating results, it can be derived that the 3SPS+1PS bionic parallel mechanism can produce enough workspace for simulating gait movement of the human hip joint. After verifying the correctness of the parallel mechanism's kinematics, dynamic of the mechanism is analyzed by loading a force on the moving platform. Statics and dynamics performance of the parallel mechanism are analyzed based on ANSYS. Stress and strain, natural frequency and vibration modes of the parallel mechanism are derived. This can make sure parallel mechanism avoids the interference of vibration source which frequency closes to the parallel mechanism's natural frequency.The general design scheme is derived based on the previous kinematics and dynamics analysis. And combining with the design requirements of the hip joint simulator, a prototype mechanism of the hip joint simulator is developed by designing machining and agency processes of the mechanism in detail. The key parts of control system include computer, control cabinet, electric cylinder and hydraulic loading modularity. With the based trajectory and the supplemented bulk transfer, the method of data transmission improves stability and expedited the response velocity of system. Finally, some suggestions are proposed for the mechanical structure and control.