Intelligent desktop NC machine tool with compliant motion capability

In this paper, a new desktop NC machine tool with compliance control capability is presented for finishing metallic molds with small curved surface. The NC machine tool consists of three single-axis robots. Tools attached to the tip of the z-axis are ball-end abrasive tools. The control system of the NC machine tool is composed of a force feedback loop, position feedback loop and position feed-forward 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 feed-forward loop leads the tool tip along cutter location data. 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 an abrasive tool, through a simple position/ force measurement. Through a similar measurement and a surface following control experiment along a lens mold, the basic position/force controllability with high resolutions is demonstrated.