Current Research Projects
Novel magnetically-suspended sample stage for next-generation X-ray microscopes
Self-sensing bearingless hysteresis motors for next-generation ultra-high-speed drives
High-acceleration over-actuated magnetically levitated linear stages for improved throughput in semiconductor manufacturing
Selected Past Projects
Magnetically Levitated Linear Stage for In-vacuum Transportation Tasks
This work focuses on the modeling, design, building, and testing for a novel magnetically-levitated linear stage driven by linear hysteresis motors. The stage is targeting at the in-vacuum reticle transportation tasks in EUV photo-lithography machines, where the reticle needs to be transported from the storage position to the scanning position through a channel in high vacuum, and the transporation mechanism needs to satisfy the ultra-tight contamination requirements. Here, the stage is driven along the motion direction, and is magnetically levitated in the other five degrees of freedom (DOFs). The magnetic suspension of the system shows a linear slice motor design, where the vertical, pitch, and roll DOFs of the stage are levitated passively using a permanent magnet bias flux. The levitation in the lateral and yaw DOFs are actively controlled. To our knowledge, this work presents the first linear bearingless slice motor design, and is the first reported study on linear hysteresis motors.
Magnetically Suspended Reaction Sphere with One-axis Hysteresis Drive (1D-MSRS)
This project focuses on the design, modeling, and testing of a magnetically suspended reaction sphere driven by an one-axis hysteresis motor (1D-MSRS). The goal of this work is twofold: (a) exploring the possible design of a magnetically suspended reaction sphere driven about three-axes for spacecraft’s attitude control; and (b) evaluating the performance of a hysteresis motor for the reaction wheel/sphere application. The novel 1D-MSRS demonstrates a hysteresis motor with a solid steel spherical rotor, which is magnetically suspended in all translational directions by a combination of an electromagnetic actuator and a bearingless motor. Modeling of the magnetic suspension of the sphere is demonstrated, and its motor dynamics is analyzed by an equivalent circuit model. This study also demonstrated that the hysteresis motor has a good potential for being used for high speed, low vibration reaction wheels.
Position Control for Hysteresis Motors using Field-oriented Control
This work studies the modeling and field-oriented control (FOC) for hysteresis motors, with the goal of achieving position control of hysteresis motors for servo applications. Hysteresis motors include a wide range of machines with solid cylindrical steel rotors, which generate torque via the magnetic hysteresis effect of the rotor material. Previously, hysteresis motors have been mainly used under open-loop operation. However, they are also attractive for position control in some special applications such as in-vacuum operation or when smooth running and high speed is required.
In this work, an equivalent circuit model for hysteresis motors that describes its transient-time dynamics is introduced, and a state space model for hysteresis motors is developed. This model is used to construct a rotor flux orientation observer for the FOC for hysteresis motors. The proposed FOC-based position control method was tested with three hysteresis motors. Experimental results show that position control for all three hysteresis motors can reach a bandwidth of 130 Hz with the proposed methods. To our best knowledge, this is the first experimental study on FOC and position control for hysteresis motors.