Research On Detection And Control System Of Capacitive Micro-accelerometer With Round Proof Mass Supported By Multi-Beam

Accelerometer is a typical inertial sensor. With the development of micro-electro mechanical system (MEMS), MEMS acceleration sensor is more and more important and has a wide range of applications in aerospace, weapons and equipment, automotive, consumer electronics, etc. In high impact load measurement, ammunition fuze and other fields, a high overload micro-accelerometer, having tens of thousands to hundreds of thousands of G(G is gravity acceleration) range, wide frequency bandwidth and harsh working conditions, is in great demand. Based on the well developed MEMS technology, it is urgent to develop the micro-accelerometers with high precision, high G range, low power consumption and low cost. Capacitive accelerometer is one important developing direction of high overload MEMS micro-accelerometer, for its high measurement sensitivity and accuracy, good working stability, small temperature drift, extremely low power consumption and strong overload protection ability. In addition, by implementing feedback loop control, the performance of the capacitive micro-accelerometer can be significantly improved.This thesis studies a kind of capacitive micro-accelerometer with round proof mass supported by multi-beam and its main structural materials is metal, for the fracture toughness of metal is far higher than that of silicon, which can prevent the rupture and improve the shock resistance ability largely. In order to improve the ability of overload, the proof mass in round-disc shape is supported by multi-beam to reduce the stress distribution at edges, and compared with the square-palte shape, its structure deformation distribution is more uniformity. By increasing the number of the suporting beams, to some extent, the stress distribution will be more uniformity, and the impact resistant ability of the proof mass will beincreased, that is, the measurement range of the micro-accelerometerwill improved.The main research contents of the thesis are as follows:1,The equivalent electrical model of the accelerometer is studied. According to the dynamic model of the accelerometer, the equivalent electrical model and differential capacitance model of capacitive micro-accelerometer is set up using PSpiceTM tools and the simulation is carried out to analysize the displacements and differential capacitances of the accelerometer under the different appilied accelerations.2,The microfabrication of the micro-accelerometer is presented. The microfabrication scheme of the accelerometer employed in this thesis is: a top stator and a bottom stator, which has movable beams and proof mass structures integrated, are fabricated sepearately, then they are solder bonded to form capactive gaps. Based on UV-LIGA technology of ourlaboratory, microfabrication processes of two stators have been experimented. And the key processes, such as wet etching of Pyrex glass pits and releasing of sacrificial Layer, have been well developed. With the fabricated, bottom stator and top stator areassembled and solder bonded, a prototype of the designed micro-accelerometer is obtained.3,The detection and control system is designed. The detection channel is studied, which includes the pre-amplifier charge integral, high-pass filter, four order band-pass filter, phase sensitive demodulating, low pass filtering and electrical level transform circuit. System simulation of detection channel is carried on based on PSpiceTM tools.To complete the closed-loop control, the digital controller is designed based on SEED-DSP28335 platform, which includes A/D conversion, PID control and D/A conversion. The feedback channel is designed, which mainly includes low pass filter circuit and high voltage amplifier circuit. The offset voltage and feedback voltage are added up to the feedback electrode of the micro-accelerometer to complete the closed-loop control.The calibrated accelerometer circuit based on the accelerometer MMA1200 is designed.4,The capacitance calibration, self-test of the device and static capacitance experiments are carried on. The range of the detection channel is±6pF, the sensitivity is 89.3mV/pF, and the linearity is 2.59%, which meets the measurement accuracy of the micro-accelerometer control system. The left and right structure is basic symmetrical from the self-test experiment. These experimental results lay the foundation of measurement and control system for the next step.