Flux-controlled Hybrid Reluctance Actuator for High-precision Scanning Motion

To achieve highly precise and linear scanning motion by a hybrid reluctance actuator (HRA), this paper proposes a flux-controlled mode that uses regulated magnetic flux as the control input for the actuator operation and evaluates its performance in comparison with the conventional current-controlled mode. In the conventional case, HRAs exhibit magnetic nonlinearities (e.g. hysteresis) and position-dependent force that can make the system unstable. A model-based analysis reveals that they are included in the variable magnetic flux of a HRA. Thus, they are captured by flux estimation and rejected by flux feedback control for high quality scanning motion. For the estimation, sensor fusion with a current monitor and a search coil is used. PI controllers are used for the flux feedback control, as well as for current feedback control of the benchmarking current-controlled mode. During scanning, feedforward control is used to compensate linear dynamics. When sine motions are experimentally tested at 60-300Hz, the current-controlled mode exhibits a nonlinearity between 6% and 23%, which is decreased to less than 5% by the flux-controlled mode. For a +75μm triangular motion at 100Hz, the flux-controlled mode decreases the tracking error by a factor of 19 to 3.2μm, successfully demonstrating its high-quality linear scanning motion.