Force controller design and evaluation for robot-assisted die and mould polishing

Abstract

A significant portion of the total manufacturing time for a die or a mould, both used extensively in producing complex shaped parts, is spent on surface finishing operations following the primary machining of the die or mould cavity. Hence, there is considerable incentive in pursuing even partial automation of die or mould surface finishing operations. This paper concentrates on the control issues that arise during automation of die and mould surface finishing using industrial robot held tools, with particular attention being devoted to the design and evaluation of force controllers to maintain the desired tool-workpiece interaction. Simplified models of the polishing process including the effect of robot structural compliance are presented first, for analysing and designing controllers. A through-the-arm robot force control implementation using off-the-shelf tooling is discussed next. However, the major focus of this paper is on active end effector force control since there are limitations in the performance of the through-the-arm force control loop. Active end effector force controller design requirements and a simple robust stability test in the face of model uncertainty are given and applied to several design examples. Results of force controller analysis and design are verified by experiments where force regulation during polishing and trajectory tracking are demonstrated.