Capacitive Micromachined Electrostatic Servo Accelerometer System Analysis

The tendency of morden inertial accelerometer is micromation and integration. And MEMS technology just meets this possibility. The principal needs of realization on strategic inertial accelerometer are large measurement range(higher than 70g) and high stability. In this paper aimed at a most basic and typical "sandwich" structure with easy realization in techniques,the system of micromachined electrostatic servo-accelerometer is analyzed in detail on static and dynamic state, mainly including:the influence on the z-component of the center of mass, lateral accelerations disturbance and the applied bias voltage on the stability of the sensor. The solutions of maximum measurement range and the methods to increase the measurement are given in the condition of stable state and the restricted parameters. How to compensate dynamic performance of servo-system and the analysis of response of system in different inputs are given, too.In this paper the movement equations of the seismic mass of inertial sensor are derived by the known models of the accelerometer. The influence on the parameters of the measurement range and stability and its mutual relations are analyzed. It is pointed out that the key parameters are the weight of seismic mass and the critical voltage. Dynamic response of closed-loop servo-system of the accelerometer and the method to adjust dynamic parameters are studied by the second-order method. Finally, the visual diagrams and verifications are given by MATLAB tools.The closed-loop servo principle ensure that micro inertial accelerometer has larger measurement, and a series of transformations of closed-loop system can be approximately linear relation. Because of the design of central suspension beams structure, the stability of the sensor is mainly determined to the value of critical bias voltage. Whenthe applied bias voltage is smaller than the critical bias voltage or electronical stiffness is smaller than mechanical stiffness, the sensor can be the stable state. The design of maximum measurement range on the accelerometer is largely restricted by definite micro-process techniques. At that time the decrease in the weight of mass is the most useful method to increase the measurement range, and the desired dynamic behaviors of closed-loop system is much easily achieved by adjusting the parameters of serco-circuit.In a word the designed accelerometer with four central suspension beams structure(Figure 2-5) and the parameters(section 3.2.4) has the maximum measurable acceleration of 70 g. When the z-component of the center of mass is 5 (m, the maximum allowable lateral acceleration is 4542 g. This meets the fundmental needs to the realization of micro inertial accelerometer with large measurement range.