Basic performance of a desktop NC machine tool with compliant motion capability

In this paper, a new desktop NC machine tool with compliance controllability is presented for finishing metallic molds with small curved surface. The NC machine tool consists of three single-axis robots with high position resolution. A tool attached to the tip of the z-axis has a small ball-end shape. Also, the control system of the NC machine tool is composed of a force feedback loop, position feedback loop and 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. Further, the position feedforward loop leads the tool tip along cutter location data. It is expected that the NC machine tool delicately removes surface cusps with under about 0.3 mm height 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 that causes the position inaccuracy at the tip of the abrasive tool, through a simple position/force measurement. Through a similar position/force measurement and a surface following control experiment along a lens mold, the basic position/force controllability of the proposed NC machine tool is demonstrated.