Study On Structure Design And Dynamic Performance Of The Parallel Bionic Robot Leg

Parallel manipulators have been intensively studied for over a decade. The manipulators have more advantages including good system rigidity, rapid motion velocity, not-accumulative error, high nominal load to weight ratio, and flexible end position-stance. One kind of symmetrical parallel manipulators with two rotational and one translational degree of freedom was designed as the key part of rescue robots in coal mines. After the structures of the parallel manipulators with 2R1T DOF were synthesized, the dissertation was focused on the theoretical analysis in terms of singular configures, error modeling and kinematics calibration, optimization of kinematic characters, dynamic modeling and stiffness optimization. As a result, the experimental system of single parallel bionic robot leg has been developed.Subsequent research contents and conclusions are presented as follows:The parallel manipulators with 2R1T DOF were synthesized by the reciprocal screw theory. Especially, the design rules and the combinations of revolute and prismatic joints with only one pure wrench force in one limb have been obtained. Based on principal screw theory and imaginary mechanism method, the kinematic characters of a three DOF symmetrical spatial parallel manipulator with three UCR limbs were validated. It is proved that the matrices of influence coefficient are only dependent on input parameters and dimension parameters, mechanical structures. When the moving platform is parallel to the base, the results of the pitches principal screws validate the kinematic characters of the parallel manipulator.A new method with Rodrigues parameters was proposed to describe the position-stance of the parallel manipulator. By analyzing the topologic structure of the parallel manipulator, the kinematic model with Rodrigues parameters was established. By the geometrical constraints and elimination, the forward kinematic model was obtained. The numerical solutions of forward kinematic model were analyzed by using the Newton-Raphson method and the corresponding numerical simulation proved the validity of iterative steps. According to the relation of spatial vectors, the velocity and the acceleration of every part of the manipulator were deduced.The static equilibrium equations of the parallel manipulators are developed. The forward singular configures were studied from their geometric essence by means of Grassmann theory. And singular configures of different line dimensions from 1 to 6 were concluded. The numerical simulation showed the singular trajectories and the change of every Rodrigues parameters. It is essential to design the kinematic layouts aiming at avoiding the singular configures.By the means of the complete differential-coefficient matrix theory, we established the mechanical position-stance error model including the main errors of the parallel manipulators. By normalizing all error sources in reachable workspace, the statistical model of sensitivity coefficients was obtained. Based on successive approximation algorithm, the kinematic parameters can be calibrated. Considering the analytical results of sensitivity coefficients, the operation steps have concrete directivity.The numerical analysis of workspace showed that the end effector can improve the workspace effectively. The whole workspace along Z axis which is perpendicular to the base can be described as a quasi-ellipsoid. The scope of singular values setting as 0.3≤δ≤3 can get more workspace. By the analysis of global condition index, in order to get more workspace and ensure dexterity of the whole manipulator, the radius ratio of the base and the moving platform can be set as 1.0≤η≤1.4.Based on principle of virtual work, the dynamic model of the symmetrical parallel manipulators with three RPS limbs was established. Moreover, the forces and the moments of the limbs, the joints, the base, the moving platform and the end effector have been presented analytically. The joint forces of the moving platform in axial direction and the base in normal direction changed greatly. Because the motion along Z axis caused in great change of the joint forces, it is stated that the translational motion have more influence on the joints, relatively to the rotational motions.Considering geometrical deformation of the parallel manipulator causing by outside forces, the conservative stiffness matrix was deduced on the basis of the conservative congruence transformation (CCT). Moreover, the element units of stiffness Jacobi matrix have been uniformed. The average of eigenvalue extremum of workspace stiffness was proposed for optimizing the whole stiffness of the parallel manipulator. When the radius ratio is set as 1.2≤η≤1.4, the whole performance of stiffness is better comparatively.For the purpose of guaranteeing the design targets of the single parallel bionic robot leg, the high precision digital display instrument has been developed. The key parts of control system include PC, multi-axis control modularity and comprehensive evaluation modularity of workspace. The tracks are designed ahead for the kinematic control. The method of data transmission improves stability and expedited the response velocity of system. The position limits of the parallel bionic robot leg are measured by Optotrak Position Sensor. According to gaits of human being, the elementary track is programmed. The suggestions are proposed to improve the mechanical structure and control policy.