Gantry type Lapping Manipulator toward Unmanned Lapping Process for a Large Work Surface

Abstract

This paper presents a developed manipulator and control method for automatic lapping process applied to a large work surface. A lapping machine consists of a newly designed parallelogram-type 5-axis manipulator and a conventional 3-axis gantry machine. The gantry machine is utilized to precision positioning over a large work area, and the manipulator is controlled by a separate controller for lapping operation in the local surface area which is provided by the CNC controller of gantry machine. The lapping process is, as a first step, needed to remove milling tool marks without injuring original shape, and then to correct the shape error. Wheel compliance becomes different in accordance with the special purpose such as tool mark removal and shape correction. Both processes require high stiffness of the manipulator. In this study, newly designed joints are adopted to secure the stiffness of the joints in both normal and lateral directions. Deadweight of manipulator including wheel motor as well as feed-forward torque control are adopted to suppress the vibration caused by abruptly dynamic cutting force. It was confirmed that the lapping operation was successful in wiping the curved contour without the structural vibration, and that the feed-forward torque control produces twice higher machining efficiency as well as 30% higher surface quality in comparison with the existing compliance control method. The experiment investigated the effects of the abrasive wheel compliance and the dynamic cutting force. In results, the smooth surface was achieved within a satisfied quality level of less than Rz 0.5 μm. It is considered that the proposed manipulator has great potential to be applied in unmanned lapping systems for a large work surface.