Research On The Force Control Method Of Manipulator In Uncertain Environment

The implementation of the ’ Made in China 2025 ’ strategic plan has promoted the development of the intelligent manufacturing industry.As an indispensable part of the intelligent manufacturing industry,the robotic arm is widely used in all walks of life.In the past,manipulators were widely used in tasks such as painting,welding,and palletizing that can be achieved only through position control.However,today ’s manipulators are required to be used in tasks that require interaction with the environment,such as grinding and polishing,workpiece assembly,and medical rehabilitation.However,when the working surface environment of the manipulator is unknown,the traditional force control can not meet the performance.Therefore,how to realize the force control of the manipulator under the condition of unknown environment is a hot issue in the current research of manipulator force control.In view of the above scenarios,this paper takes the SD7-700 manipulator in the laboratory as the research object,and studies the kinematics,impedance control and force control method of the manipulator in unknown environment.The main research contents are as follows :(1)The kinematics model of the manipulator is established by using the improved D-H method,and the analytical solution of the inverse kinematics of the manipulator is obtained by using the geometric method and the inverse transformation method,and the optimal solution of the inverse solution is determined according to the shortest stroke method.(2)The principle of impedance control is introduced,and the steady-state error formula of impedance control is derived.Aiming at the phenomenon that the force tracking error increases and the tracking force changes suddenly in the traditional impedance control under the change of environmental stiffness,an impedance control based on recursive least squares method is proposed,and a forgetting factor is introduced according to the data saturation phenomenon.The simulation of traditional impedance control and impedance control based on recursive least squares method is completed.The simulation results are compared and analyzed.(3)Aiming at the phenomenon that the tracking force error of the manipulator increases with the increase of surface curvature in the unknown surface environment,an impedance control based on adaptive variable damping algorithm is proposed,and the stability and convergence of the algorithm are proved.Aiming at the phenomenon that the system oscillation intensifies and the force tracking error decreases with the increase of the adaptive law,an adjustment method of the adaptive law changing with the change of force and force error is proposed.The simulation of traditional impedance control and adaptive variable damping impedance control is completed,and the simulation results are compared and analyzed.(4)The experimental platform of manipulator force tracking is built.The software environment of the upper computer of the manipulator is configured,and the communication between the upper computer,the lower computer,the manipulator and the force sensor is established.The encoder values of the position sensor and force sensor of each axis of the manipulator are transformed into the actual position and force values.The hardware interface of the manipulator is debugged to make the manipulator move in position mode.The experiments of plane fixed stiffness force tracking,plane variable stiffness force tracking and surface force tracking of the manipulator are completed.