Development of a desktop NC machine tool with compliant motion capability and its application to LED lens finishing process

In this paper, a novel desktop NC machine tool with compliance controllability is presented for finishing metallic molds with small curved surface. The NC machine tool consists of a robot with three axes. A small ball-end abrasive tool is attached to the tip of 2-axis of the robot. The control system of the NC machine tool is composed of a force feedback loop, a position feedback loop and a position feedforward loop. The force feedback loop controls the polishing force consisting of tool contact force and kinetic friction force. The position feedback loop controls the position in pick feed direction. Also, the position feedforward loop leads the tool tip along cutter location data. It is expected that the NC machine tool delicately removes small surface cusps on a mold, and finishes the surface with high quality. In order to first confirm the application limit of a conventional industrial robot to a finishing task, we evaluate the backlash which causes the position inaccuracy at the tip of the abrasive tool, through a simple position/force measurement. The basic position/force controllability of the proposed NC machine tool is demonstrated by a similar position/force measurement and by a surface-following-control experiment along a lens mold. Finally, the proposed NC machine tool is applied for finishing a LED lens mold to evaluate its performance qualitatively.