Research On The Levitation System Of An Electrostatic Silicon Micromotor

Electrostatically levitated micromotor is a type of microactuator, which combines the features of electrostatic levitation and the micro machining technology. With non-contact support, the electrostatic suspension can eliminate the frication torque usually occurred in mechanical-contact bearing and prolong the motor's lifetime. The typical applications of electrostatically levitated micromotors include multi-axis electrostatic accelerometer/gyro and optical switch.This paper presents an electrostatic micromotor based on a ring-shaped rotor levitated electrostatically in five degrees of freedom (DoFs), variable-capacitance drive and silicon bulk microfabrication. The design and analysis of the electrostatic levitation system are described and the principles of the rotation of the motor are introduced.To fabricate the glass-silicon-glass stack structure, two micro fabrication methods, sand blasting and Al-sacrificing layer, are described and compared. The fabrication procedures are given and problems during the fabrication are listed and analyzed. Some proposals to improve the fabrication are also given.A set of micro-capacitance detecting circuits, based on frequency multiplexing method, is presented with an aim to detect the motion of the rotor in six DOFs. The experimental results showed that the sensitivity in the x axis is 23.3V/pF, the bandwidth is 10.58 kHz and the output stability is less than 0.1mV. A digital sinusoidal-wave generator is designed based on the technology of direct digital synthesization (DDS) and DSP in the control unit is used as the digital controller. A functional chip AD9834 is chosen and communicated with the SPI of DSP and generates sinusoidal waves with a high frequency from 1MHz to 2MHz and a resolution of 0.186Hz.The model of the levitation system is analyzed and the lag-lead compensation is applied. Simulation results show that some key indexes, including the open-loop and closed-loop frequency characteristics, step response and the suspension stiffness, are satisfied with the design requirement. The closed-loop bandwidth of the five-DoF levitation system ranges from 1.1 kHz to 1.47 kHz, the dynamic stiffness in the axial dimension is greater than 7.58×10~2N/mwhile in the radial dimension is10.96N/m . An electrostatic levitation experiment system based on the frequency multiplexing is set and the experiments of position sensing, electrostatic forcing and electrostatic stimulation are completed.