Masato Koyama

Control of an Interior Permanent-Magnet Screw Motor With Power-Saving Axial-Gap Displacement Adjustment

This paper proposes position and force control of a screw motor with power-saving axial-gap displacement adjustment. The motor has a helical-shape mover, which moves in a helical-shape stator without contact. Due to the fabrication process, the actual helical shapes of the mover and the stator are not completely uniform, and the air-gap length between the mover and the stator slightly changes, depending on the mover rotation angle. The d-axis current remains a finite value, and copper loss arises even when the mover is located at the center between the stator cores. A power-saving axial-gap displacement adjustment method is proposed to solve this problem. The proposed control is experimentally verified.

Validation of spiral motor parameters by FEA and experimental identification

This paper validates parameter identification of a spiral motor by FEA and experiments with least square method. Validity of the identification is discussed in simulations and experiments. Parameters of the spiral motor is utilized to design controller so as to achieve a maximum performance of the spiral motor. In this paper, the parameters are analyzed and compared between FEA and experiments. As results of the simulations and the experiments, the experimentally obtained parameters are close to FEA results and the accuracy of the identification is confirmed.

Comparison between zero power control methods of spiral motor

This paper investigates two zero power control methods for a spiral motor, which are current integral type and external force feedback type. A spiral motor is a linear motor having helical mover and stator that can realize a high thrust force density and high back-drivability. In latest researches, the magnetic levitation control, position control and force control were archived. Additionally, power-saving magnetic levitation is successful by a zero power control. However, a response time of the force control is delayed by the zero-power controller. This paper presents a comparison between zero power control methods through simulations and experiments. As a result, on the force control, external force feedback type zero power control is able to improve the transition time than the conventional method.

Proposal of current integral zero power control with force feedforward for helical motor

This paper investigates three zero power control methods for a helical motor, which are current integral type, external force feedback type, and current integral with feedforward type. A helical motor is a linear motor having helical mover and stator that can realize a high thrust force density and high back-drivability. The magnetic levitation control, position control and force control were archived. Additionally, power-saving magnetic levitation by a zero power control was successfully realized. However, a gap response with current-integral type and external-force-feedback type has an undershoot on a force control. This paper proposes a current-integral zero-power control with force feedforward to suppress the undershoot, and compare it with current-integral and external-force-feedback. As a result, on the force control, we confirm the proposed method suppresses the undershoot and improve the transition time compared with the conventional methods.

Improvement of position tracking and magnetic-levitation control based on optimal-control for helical motor

For various assistive devices, safe and compact high output actuators are desired. The authors have proposed a helical motor that consists of a helical mover and stator. In the latest study, a motion controller of a helical motor is based on PD-control law and disturbance observer. However, the performance of the conventional controller is not enough to achieve more high preciesion motion and robustness. Therefore, this paper presents a comparison between new controllers based on optimal-control theorem and the conventional controller. Through simulations and experiments, an optimal servo with feedfoward for a helical motor has the best performance compared with the others.