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Compliant control based on impedance principle under unknown environmental stiffness

Constant force control plays a very important role in the flexible operation of industrial robots. The difficulty lies in how to use the existing methods to track the force during the robot motion. In this paper, the traditional impedance control method is improved for the case where the accurate information of the environment stiffness is unknown. Firstly, the principle of position-based impedance control is analyzed. By establishing the dynamic relationship between the contact force of the robot and its end position, the contact force in the end of the robot can be controlled indirectly by adjusting the position of the robot. When considering that the reference position is uncertain due to the unknown environmental stiffness information, the reference position in the impedance model is replaced with the environmental position, and by analyzing the steady-state error of the system, When the stiffness coefficient of the impedance model is set to 0, the steady-state error of the system can be made zero as long as the appropriate inertia and damping coefficient are selected. Simulation and experimental results demonstrate the feasibility and effectiveness of the proposed method.