A model free cascade control for backlash compensation in multi drive systems

This article presents a study focused on devising a control methodology for managing multiple motors operating along a shared axis. The research proposes a novel velocity control of a model-free cascade-based control system. The control system is characterized by velocity synchronization loops that utilize the output velocity from other loops, referred to as root loops, to replicate the velocity of a reference signal. This process takes into account backlash compensation and aims to prevent the occurrence of the fighting phenomenon. A novel aspect of this system is the proposed ladder structure, where the loops are arranged sequentially, allowing the error from one driver to be mitigated by the contributions of other loops, termed agent loops. Additionally, a straight structure is proposed in which a single motor acts as the primary root for tracking, while the remaining loops function to distribute load and minimize chattering. In both configurations, the tracking process remains uninterrupted even after the removal of any driver, thanks to an online adaption feature in the control algorithm that updates equations. The algorithm is designed to support any even number of motors and drives across the two proposed configurations. Finally, simulation tests were carried out on 2, 4, and 6 drive structures, the proposed method was also implemented on a dual-drive experimental setup. The results show that the root mean square of velocity error in different tracking scenarios is below 0.2°/s, which is an appropriate result for the performance of the velocity controller.