Robotic normal constant force polishing of unknown-model workpieces using variable impedance control

Maintaining a constant normal contact force during the polishing process is essential for consistent material removal. However, achieving automated robotic polishing for workpieces without prior models necessitates considerable flexibility in both position and force control, which presents significant challenges. To address this issue, the force tracking error is examined, revealing that force fluctuations primarily result from the effects of posture adjustments on the end-effector position and workpiece perturbations. Accordingly, a robot attitude smoothing scheme based on contact moments and quaternion interpolation is proposed. Furthermore, the quadratic programming variable impedance control method (QPIC) is introduced, transforming the variable impedance design problem into a constrained optimization problem. This approach adaptively adjusts the impedance parameters to accommodate workpiece perturbations. Finally, experiments on robotic metal polishing demonstrate that this framework can effectively adapt to unknown-model workpieces profiles and achieve high-quality surfaces.