Rotor Position Tracking Control of a Bearingless Motor with Oscillating Motion Function

Machines with oscillating movement function are applied to agitating machines for food processing, power transmission mechanisms of automobiles, and so on. The oscillating movement is a motion which a reciprocating motion is added to a rotary motion with a constant stroke. However, there are some problems: the mechanical bearings, cams, and other fixtures are subjected to a large load, which may lead to wear and tear on them, and the size of the entire system expands because of the mechanism for converting the motor rotational motion into oscillating motion. To solve these problems, the authors have studied and developed a built-in motor for machines with oscillating movement function, in which bearingless drive technique is applied. The target is an application to machine tools. In the previous study, it has revealed that the rotor trajectory control can be achieved at high speed when the rotor rotation and the trajectory motion speeds are synchronized. However, it has not been possible to separate between the speeds of the oscillatory motion and the rotor rotation because the rotor position is fluctuated with the rotation frequency. It is better to be able to perform oscillatory motion and rotation at different speeds for machine tools that perform trochoidal machining. In this paper, the suppression method of rotor fluctuation during the trajectory control is proposed. The rotor fluctuation is successfully suppressed by the proposed method while the rotor trajectory control is performed. It is confirmed by the experimental test results using a prototype machine that the rotor position is followed on the reference trajectory, and the high rotational speed can be realized even when the rotational and the trajectory motion speeds are not synchronized.