Magnetically Levitated Linear Stage with Linear Bearingless Slice Hysteresis Motors

This article presents the design, construction, modeling, and testing of a novel magnetically levitated linear stage using a linear bearingless slice motor design, targeting in-vacuum transportation tasks in precision manufacturing systems. The stage is driven by novel linear hysteresis motors, where the motor secondaries are made of magnetically semihard material exhibiting magnetic hysteresis. The suspension of the stage in three degrees of freedom, including vertical, pitch, and roll, is achieved passively through permanent magnet bias flux. The suspension in the lateral and yaw directions is actively controlled. This compact design effectively reduces the number of sensors and actuators needed for stabilizing the levitation. The prototype stage has been successfully levitated with a maximum thrust force of 5.8 N under 2.5-A current amplitude, which generates a stage acceleration of 1200 mm/ $\text{s}^2$ . The stage position control loop has a bandwidth of 30 Hz. The stage is tested to track a reference trajectory of the target application, and the maximum position tracking error is $50\,\mu \text{m}$ . The stage's lateral displacement during motion is below 50  ${\mu \text{m}}$ , which is well below making mechanical contact to the side walls. To our knowledge, this article presents the first linear bearingless slice motor design, and also the first study on linear versions of hysteresis motors.