Pose optimization and path improvement in robotic drilling through minimization of joint reversals

Abstract

Industrial robots have been increasingly adopted in precision manufacturing applications such as aerospace drilling. However, achieving the strict tolerance requirements of the aerospace industry has been a major challenge due to the relatively poor accuracy of robots. One of the major sources of error which has a detrimental effect on the quality and circularity of drilled holes is the static friction in robot joints. These errors are particularly pronounced when one or more joints reverse direction. To improve robot motion for better hole quality, this paper proposes an optimization framework to eliminate or minimize joint reversals throughout a drilling motion. A general robotic drilling motion with a redundant degree of freedom due to the twist of the tool is first modeled. Particle Swarm Optimization (PSO) is then used for strategic pose selection considering the entire drilling motion. Experimental tests performed on a KUKA KR 6 R700-2 show a 40% reduction in the tool deviation envelope. The proposed technique can be readily implemented on any commercial robotic drilling cell without interfering with the controller.