Robotic grinding of curved parts with two degrees of freedom active compliant force-controlled end-effector using decoupling control algorithm

Abstract

This paper proposes a novel two degrees of freedom (2-DOF) active compliant force-controlled end-effector (EE) using decoupling control algorithm to improve grinding efficiency, material removal accuracy, and surface quality of the curved parts for robotic grinding. First, a robotic grinding system is described, which consists of an industrial robot for tool-path control and a novel 2-DOF compliant EE to improve grinding efficiency and compliance. Second, the dynamic relationship between the friction coefficient and the normal force is established to develop an online prediction model for the normal force. The tangential tool tip displacement model is also established. A force-position decoupling control algorithm, which comprises force–position decoupling and fuzzy force–position switching controllers, is then proposed to improve the normal force and the tangential tool tip displacement control accuracy of the 2-DOF compliant EE. Finally, the developed methodology is validated through grinding experiments to confirm its effectiveness. The grinding results show that under the premise of ensuring the neglectable tangential tool tip displacement error to the original grinding process, the developed 2-DOF compliant EE with decoupling control demonstrates similar high force control accuracy and grinding depth accuracy to the 1-DOF compliant EE, and the machining efficiency is improved by approximately 30 % compared to that of the 1-DOF compliant EE. Compared with the traditional 2-DOF rigid EE using hybrid control, the normal force and tangential tool tip displacement control errors of the developed 2-DOF compliant EE with decoupling control are reduced by approximately 60 % and 33 %, respectively, and the overshoot is reduced from 30 % to almost 0. The developed 2-DOF compliant EE with decoupling control improves the grinding depth accuracy and surface quality compared to the traditional 2-DOF rigid EE with hybrid control.