PD-adaptive variable impedance constant force control of macro-mini robot for compliant grinding and polishing

In order to realize the compliant grinding and polishing of complex surfaces, the traditional impedance control cannot adjust the system impedance, so the force tracking deviation is large, the adaptive variable impedance control can adapt to the environmental changes to adjust the system impedance and realize the stable tracking of the contact force, but the overshoot is too large. In this paper, the constant force control of compliant grinding and polishing processing is studied on the designed macro-mini robotic system, and an adaptive variable impedance control algorithm with pre-PD adjustment is proposed. The control law is used to update the damping term in the impedance parameters of the system, and realize the constant force control process in which the grinding and polishing head is approximately perpendicular to the machined surface, and the stability and convergence of the force control algorithm are proved. Through simulation and experiment, the four algorithms of impedance control, adaptive impedance control, adaptive variable impedance control and the proposed PD-adaptive variable impedance control are compared and analyzed in the force tracking performance of plat surface, sloped surface and curved surface, and then in the grinding and polishing experiments to verify the grinding and polishing force tracking error, the force tracking errors of the other three control algorithms are controlled within 2.08 N, 1.30 N, and 1.34 N, and the overshoot amounts to 19.2%, 56.3%, and 11.1%. The proposed algorithm can control the force tracking error within 0.78 N, the overshoot is less than 4.5%, which verifies that the proposed force control algorithm is more superior in force control performance and is suitable for force control scenarios of actual grinding and polishing.