Characterization of Tool-Specimen Interaction in Non-Repetitive Mechanical Micro-Drilling Tasks Performed by Collaborative Robot Manipulators

Abstract Mechanical micro-drilling finds widespread use in diverse applications ranging from advanced manufacturing to medical surgery. Our work is focused on developing methods enabling robots to perform non-repetitive micro-drilling tasks effectively. Achieving this goal encounters many challenges. Even small variations in drill process parameters cause the micro-drills to break frequently. In this paper, an experimental approach is proposed to conduct a systematic characterization of the interactions between the micro-drill tool and the specimen, which is crucial to understanding the underlying processes and developing effective methods of robotic micro-drilling. Specifically, we carry out an experimental investigation of the relationship between drill feed-rate and reaction forces experienced by the micro-drill as it contacts and penetrates the specimen. The Sawyer and KUKA collaborative robots were used as the test beds during experimental validation as they were found to be suitable candidates for implementing the micro-drilling strategies proposed in this work. The Photron Fastcam Nova S6 high-speed camera was used for video-based observation of microdrilling, revealing the temporal details of interaction between the microdrill tool and the specimen, with a high time-resolution of a few microseconds to milliseconds between successive frames. The experimental results consisted of characterization studies that involved the execution of several micro-drill plans and analyzing the drill tool-surface interactions. In particular, graphs of temporal and spatial variations of feedrate and reaction forces were obtained and used to identify and characterize different stages — approach, touchdown, penetration, drill-through, coming-to-a-halt, and retraction — of each executed micro-drill plan. A regression analysis revealed a relationship between feed rate and reaction forces involved in the micro-drilling process that matched the underlying mathematical model of the tool-specimen interactions. Experimental results show that the Sawyer and KUKA robots can use the developed strategies to drill micro-holes of diameters up to a minimum of 0.6 mm and 0.2 mm, respectively.