Research On Active Compliant Control Of Redundant Robot Manipulators

Due to the unique self-motion,redundant manipulators can obtain better flexibility and interaction capabilities.While the complexity of motion and the uncertainty of environment make it difficult for redundant manipulators to achieve motion and force compliance when satisfying the actual motion capability limitations.Aiming at this problem,this paper makes a detailed analysis and research on the motion and force compliance based on the self-motion character of redundant manipulators,considering the actual motion capability limitations.This paper constructs a coordinate optimization function for joint angles,velocities and torques according to actual motion capability limitations.Their coordinate optimization is achieved by constructing the weighted matrix.The compliant control system is established based on self-motion planning,and position controller and force controller are designed respectively.To obtain motion compliance,singular configurations and their avoidance capability are analyzed,so are the joints that are about to fall into singularity.To obtain force compliance,the contact force model is built and situations that single or multiple forces act at different positions of the manipulator are considered.Based on different compliant control objectives,selection principle and velocity planning and solving methods of redundant joints are given.Thus,the self-motion planning based compliant controller is designed.To unify motion and force compliance,the decoupling of torques arising from operation space and null space motion is carried out.The stability proof of this decoupling control method is given based on Lyapunov stability criterion.Force compliance is achieved in the extended operation space based on impedance control and motion compliance is achieved by optimizing null space velocity.Thus,the motion and force hybrid compliant controller is designed.Finally,considering the advantages and limitations of different compliant control methods,the application and switching conditions of each control method are given.The transition between the proposed compliant control methods are realized by force estimation and cubic polynomial interpolation.Thus,the total compliant control system for redundant manipulators is established.To verify the proposed compliant control methods,an 8-DOF manipulator is selected for kinematics and dynamics analysis.Singular configurations of the manipulator are calculated using the suppression spin method,and the avoidancecapability of them is judged.The position and force error of force compliant control is derived,and the influence of impedance parameters on the control process is also analyzed.Finally,an optimization function is constructed to optimize the force compliant control process and impedance parameters are chosen from this.The proposed compliant control methods are verified by the co-simulation of Matlab and Adams.The simulation results show that the self-motion planning based motion and force compliant control methods can respectively realize singularity and force avoidance without disturbing end effectors and influencing main tasks.And the proposed motion and force hybrid compliant control method can decline the force greatly and improve the flexibility of the manipulator at the same time while the main work is being performed.