High-Accuracy Online Circular Path Compensation for Coordinated Hexapod Industrial Robots

This article presents a novel online path-correction framework for a pair of coordinated FANUC F-200iB hexapods. The robotic machining cell was designed to extend the workspace by assigning one robot to hold the tool and the other to hold the workpiece. The proposed framework integrates cooperative Dynamic Path Modification (DPM)-based trajectory correction with a hybrid PID-Active Disturbance Rejection Control (ADRC) strategy and real-time feedback. The controller combines PID and ADRC and uses real-time distance measurements, obtained from a Renishaw telescoping ballbar, to adjust the commanded robot positions. With this online correction, the radial error along 100 mm, 150 mm, and 300 mm circular paths is kept within 0.15 mm at feed rates of up to 40 mm/s, which represents roughly an 85% reduction compared to the uncompensated open-loop motion. A discrete-time Extended State Observer rapidly estimates and rejects multirobot synchronization disturbances, abrupt payload changes, and spindle-induced vibrations, achieving subsecond settling and minimal overshoot. Because no explicit kinematic or dynamic model is required, the proposed approach can be implemented through FANUCś DPM.