Dynamic Compliant Force Control Strategy for Suppressing Vibrations and Over-Grinding of Robotic Belt Grinding System

Abstract

This work develops a dynamic compliant force control (DCFC) strategy for the robotic belt grinding system to suppress the vibrations and over-grinding phenomenon. First, the vibration mechanism is investigated, and the corresponding vibration models before and after contact are constructed, both of which can decompose the vibrations into three components: free, accompanying and forced vibrations. Next, the extra compliant hardware is equipped to the grinder to realize the dynamic adjustment of equivalent damping. The DCFC strategy considering mechanical compliance accompanied by the dynamic closed-loop control of the grinder damping is presented based on the empirical wavelet transform and multi-scale permutation entropy. Moreover, the cutting fluctuation ratio index is proposed to evaluate the severity of the over-grinding together with over-grinding time. Experiments demonstrate that compared with the general force control, the DCFC strategy can reduce the vibration amplitude from 3.01 mm/s <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^2$</tex-math> </inline-formula> to 0.97 mm/s <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^2$</tex-math> </inline-formula> , and the over-grinding time/cutting fluctuation ratio from 1.05 s/24.71% to 0.54 s/13.18%, consequently enhancing the grinding stability and quality. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Note to Practitioners</i> —This work is motivated by the need to maintain the grinding stability and suppress the over-grinding phenomenon for the robotic belt grinding system. The vibrations and over-grinding phenomenon caused by the weak rigidity and poor precision of the robot always result in incomplete grinding of the workpiece that needs partially manual regrinding. The proposed DCFC strategy enables a dynamic compliant contact force between the grinding tool and the robot, thus effectively suppressing the over-grinding phenomenon and enhancing the consistency of grinding quality, which is particularly suitable for considering material removal consistency in cut-in and cut-out areas. This method can be implemented by the user as described or be acquired as a standalone device, but some extra hardware needs to be equipped with the grinding tool to use this method.