Study On Self-organizing Design Methodology Of Structural Topology Of A Tuning Fork Vibratory Micromachined Gyroscope

Topology design of microstructure is a hot research topic as well as the most challenging and difficult problem in structural design. Topology design of microstructure is also one of the key technologies that limit the practical application of micro-electro-mechanical system (MEMS). Design and fabrication of MEMS device with high performance and high sensitivity is an important assurance of the practical application of MEMS. However, it is very difficult to set out from the topology of microstructure and consider microstructure topology, internal connection and working environment synthetically to build the behavioral model of MEMS device. That is, in the mechanism of the scale effects and complex dynamics, it is difficult to build the high-precision mapping relationship (high-precision behavior model of MEMS device) between elastic deformation and the output performance (electrical signal). In seeking of high-performance MEMS, it is necessary to describe the high degree of freedom and solve the problem of large calculation amount in structural topology design.For the solving of the key problem in topology design of high-performance and high-sensitivity microstructure, this paper focuses on a tuning fork vibratory micromachined gyroscope fabricated by the bulk silicon micromachining procedures. The self-organizing structural topology design methodology using Cellular Automata (CA) is presented for the design and optimization of the micromachined gyroscope. The down-top self-organizing theory with the features of complex dynamics mechanism is applied in the design and optimization of the structural topology of the micromachined gyroscope. To increase the sensitivity and bandwidth of the micromachined gyroscope, the structural topology design methodology for the micromachined gyroscope is researched systemically and in depth. The contents of this paper are as follows:(1) Several issues about the basic working principle, the air damping characteristics, the driving and sensing method, the design of elastic beam are discussed based on the rigid body model of micronmachined gyroscope. And then, the merits and some defects of rigid body model in the concept design are profoundly discussed. The necessity of the high-performance and high-sensitivity structural topology model for MEMS device based on elastic theory is presented.(2) To improve the analytical and design precision of the detection capacitance and solve the problem of long computation time in structural analysis and optimization of the micromachined gyroscope, the detection capacitance analysis method based on the substructuring model is first proposed by employing the dynamic finite element theory of multi-degree of freedom. The high-precision mapping relationship (high-precision behavior model of MEMS device) between elastic deformation and the output performance is therefore built. The performance-oriented analysis and calculation of the dynamics and detecting characteristics for the micromachined gyroscope is realized. Since the working environment cannot be ignored, the nonlinear finite element method for mechanical-thermal coupled field is employed to analysis the influence of environmental temperature on the natural frequencies, the output of detection capacitance and bandwidth of the micromachined gyroscope.(3) To increase the sensitivity (output performance) and bandwidth of the micromachined gyroscope, a procedure for design of microstructure with high degree of freedom is presented. The Cellular Automata is applied in the expression of self-organizing design model of the high degree of freedom, nonlinear and complex microstructure topology. Considering the practical structure and dynamic characteristics of the micromachined gyroscope, the indirect local rule for topology evolution is built to drive the self-organizing evolution process. A performance evaluation function is derived based on the output performance. The high-sensitivity substructuring model for the topology design of the micromachined gyroscope is established to conduct analysis and optimization with a reasonable accuracy and a reduced computational cost. The optimization of the spring beams is processed as a numerical example, and the proposed method is applied in the topology optimization of the spring beams. The self-organizing topology optimization of the micromachined gyroscope is achieved. The optimization result shows that the performance of micromachined gyroscope is promoted greatly without change in the high Q-factors.(4) To test the performance of the optimized structure in practice, the improved micromachined gyroscope is fabricated and tested according to the optimization results. The testing results show that the improved micromachined gyroscope has much promotion on sensitivity and bandwidth, which proves the validity of the self-organizing topology design methodology. The self-organizing topology design provides an effective method to shorten the design period for micromachined gyroscope.