Force Control Based on Acceleration and Spindle Speed for Robotic Milling

The in-situ machining mode of industrial robots is expected to significantly improve the machining efficiency of large parts. Milling force is a critical parameter during robotic milling. The force control for robotic milling can improve the machining performance, protect the tool and the workpiece, among others. In this article, a novel force control framework based on acceleration and spindle speed is proposed for robotic milling. First, the predicted spindle speed corresponding to the peak milling force is obtained based on the milling force model. The milling force identified by the acceleration is used to obtain the parameter and coefficient in the milling force model. Next, the reference spindle speed, based on the predicted spindle speed and the reference generator, is used to avoid overshooting of the milling force. Then, the spindle speed controller is proposed with a computation time of about 0.012 s for each input, based on the reference spindle speed and the machine model with time delay. The stability of the proposed controller is proved theoretically. Finally, a force control system is constructed and applied to robotic milling. The effectiveness of the proposed force control framework is verified by robotic milling experiments and applications. The results show that the percentage error between the measured peak milling force and the reference peak milling force is less than 5% after applying the proposed force control framework to robotic milling.