A Robust Position Control System Based on Load Force Observer for RotLin Machine

In this paper, a robust position control system was designed specifically for the RotLin Machine, a radialgap magnetic-screw type direct-drivable linear actuator. The RotLin Machine, as a 2-mass system, is insufficient in accuracy and robustness. To ensure system accuracy under load side disturbance, firstly, a load force estimator with a similar structure of Disturbance Observer (DOB) was designed based on a spring force estimation. Secondly, a deflection compensator, which can adjust the rotor angle according to load side disturbance and thereby ensure accuracy of position control, was designed. Besides, to further enhance response speed against a sudden change load force, a feedback loop with an adjustable parameter was designed inside of speed control loop. Under an appropriate parameter design, this inner loop reacts to load force sudden change before outer loops and thus increase response speed. Finally, the proposed system was tested comparing with the conventional system in both simulation and experiment. The results show superiority of the proposed control system in robustness and accuracy over the conventional system.