Research On Control And Assembly For Target Plate Of 7-DOF Space Manipulator

With the rapid development of aerospace technology,the manipulators have been used more and more in space missions.This paper completed the control and assembly task for target plate using 7-DOF space redundant manipulator in a small space.The main research is on the forward and backward kinematics and inverse dynamics,motion control and kinematics optimization,force control and assembly strategy for the target plate of the redundant manipulator.In order to avoid the self-motion of the 7-DOF manipulator,this paper uses the "arm angle" parameterized the redundancy to obtain all the inverse solutions at position level.For the singularity of the arm angle,this paper improves the definition of the arm angle reference plane.The reference plane is defined using fixed vector when the arm angle singularity is not generated,otherwise the reference plane is defined by the arm plane with the joint 3 being zero.The simulation results show that all the inverse solutions of the 7-DOF manipulator can be obtained even when the arm angle is singular.For the problem of the expensive computation of multi-degree-of-freedom manipulator dynamics,this paper uses the Space Notation tool to study the Newton-Euler dynamic recursive algorithm of the 7-DOF manipulator and express it as the linear equation of the inertial parameter of the manipulator.Based on this linear equation,this paper improves the inertia parameter update rate in adaptive control which calculated directly from the forward kinematics.To verify the feasibility of the algorithm,a set of numerical experiments have been carried out by ADAMS/Simulink co-simulation.The joint torque output by ADAMS is exactly the same as the joint torque calculated by the inverse dynamics model,which verifies the effectiveness of the dynamic algorithm.To enable the 7-DOF manipulator to move in a small space,this paper plans trajectory of arm angle to realize optimization tasks such as obstacle and joint limits avoidance.The main task(tracking trajectory of the end-effort)and the additional task(tracking trajectory of the arm angle)are combined to design the adaptive control algorithm in task space based on augmented Jacobian matrix.The ADAMS and Simulink co-simulation shows that the method can not only ensure the tracking accuracy of the end-effort of the manipulator,but also realize the control of the arm angle,so as to realize the optimization tasks of obstacle and joint limits avoidance.In order to complete the target plate assembly task,this paper studies the 6DOF impedance control in task space and both position and orientation compliance are achieved.And the direct force control is realized based on hybrid impedance control.For the problem of complexity of the contact states and additional contact moment caused by the contact force,this paper proposes an assembly strategy so-called the varying active compliance center for large workpiece.This strategy reduces the additional contact moment by calculating and updating the active compliance center on-line.Then the directed force control is implemented to ensure that the contact state is unchanged during the assembly process and complete the assembly task smoothly.To verify the proposed assembly strategy,the KUKA 7-DOF manipulator is used to construct the ground experimental platform,then the target plate assembly experiments are carried out under the given 8 sets of position and orientation errors.The experimental results show that the proposed strategy can complete the assembly task under the given pose errors,and verify the correctness of the assembly strategy of the varying compliance center.