“Rigid Press Device (RPD)” for Robotic Stack Drilling in Aircraft Assembly

In this paper, a Rigid Press Device (RPD) is proposed for robotic stack drilling in aircraft assembly. Although robots have widened their applicability, robot machining is rarely applied, mainly due to their low stiffness. Meanwhile, the interlayer gap problem occurs during the stack drilling of plates, e.g., chips entering the interlayer gap caused by the drilling thrust force. Although systems such as a pressure foot and/or a dedicated end effector may be utilized for the latter problem, they are generally not designed to increase rigidity. To solve these problems simultaneously, a Rigid Press Device is developed, where pressing is intended to eliminate the gap and its small closed compliance loop is intended to increase the rigidity of the machining system. The effectiveness of the developed device is clarified through the hammering of the system and drilling experiments of a two-layer aluminum stack mounted on a robot-imitating compliant structure, where the rigidity-increase effect (e.g., an 88% decrease in the magnitude of the dynamic compliance) is confirmed; the interlayer chip/burr and vibration are suppressed (e.g., the suppression of chatter vibration of 870 μm amplitude); and the hole accuracy is increased.