Quantifying Tool Path Deviations in Robotic Continuous Ultrasonic Welding of Thermoplastic Composites

Abstract

This study investigates the positional accuracy and deformation behaviour of a robotic system performing simulated Continuous Ultrasonic Welding of thermoplastic composites. Thermoplastic composites are attractive due to their high specific properties and can be processed with lower-cost and faster assembly methods. Using a custom-developed end effector on a KUKA KR560 robot, a series of welding motion tests were conducted to analyse lateral deviation and tilt errors during CUW, without activating ultrasonic vibrations. High forces involved in the process result in consistent horizontal slip and tilt at motion initiation, attributed to static friction and stored mechanical energy in the system. Measurements from a laser tracker, force/torque sensors, and triangulation sensors revealed that robot pose and weld-line distance significantly influence these deflections. Notably, deflections were consistent and repeatable, suggesting potential for compensation via calibration or feedback control. Additionally, internal deformation within the end-effector structure and Force Torque sensor assembly contributed to the observed positioning errors. Recommendations include improving frame symmetry and stiffness to reduce mechanical distortion. These findings aim to support more accurate and reliable Continuous Ultrasonic Welding implementation in aerospace-grade composite manufacturing.