Rotation Control and Characterization of High-Speed Variable-Capacitance Micromotor Supported on Electrostatic Bearing

This paper presents the rotation control design and experimental performance of a micro-electromechanical systems (MEMS) variable-capacitance motor where a free-spinning rotor is suspended and centered in an evacuated vacuum cavity by a contactless electrostatic bearing. The micromachined device is based on a glass/silicon/glass bonding structure, fabricated by bulk micromachining, driven by a three-phase electrostatic motor, and used as an angular rate gyroscope by spinning-up the rotor rate over $\text{10}^{\text{4}}\;\text{r/min}$ . A closed-loop phase commutation scheme is proposed in our rotation design where three-phase drives are switched depending on one channel of the rotor’s angular position. The design of the micromotor spin-up and constant-speed operation is described based on the proposed electronic commutation. Experimental results of the motor spin-up process under different vacuum settings, static, and dynamic characteristics of the constant-speed control loop together with scale factor of the spinning-rotor gyroscope are described for the device operated in vacuum. It is indicated that the rotor can be spun up to $\text{2.5}\times\text{10}^{\text{4}}\;\text{r/min}$ within 400 s, and up to $\text{2.96}\times\text{10}^{\text{4}}\;\text{r/min}$ in steady state under a drive voltage of 11.8 V. Measurement data in constant-speed control mode show that the standard deviation of the spin rate error is 0.07 r/min at a rated speed of $\text{1.5}\times\text{10}^{\text{4}}\;\text{r/min}$ .