| The Voice Coil Motor (VCM), an electromagnetic actuator driven by Lorentz force, can be applied widely in precise active isolators, with simple structure, small size, low noise, fast response time, good current-thrust linearity, and so on. Due to strict requirements on the overall dimensions, thrust and structure, in precise active isolators, and the common VCM can’t satisfy these demands. This dissertation focuses on the key issues, the accurate modeling of flux density distribution and current-thrust of the VCM, to study the VCM for Precise Active Isolators. A decoupling magnetic equivalent circuit (MEC) method and model are proposed for VCM. Considering some of the demands of precision instruments such as temperature and overall dimensions, the cost function and the related restraint condition are proposed and the optimization of VCM is conducted. The corresponding software and hardware of VCM driver are also designed and implemented; a simple and effective control strategy is proposed to restrain the step overshoot of VCM. The proposed methods are validated by simulations and experiments. Simultaneously, the VCM, as the actuator, is applied successfully in active vibration absorber systems. Contents and results of this dissertation are as follows.Under the constraints of the overall dimensions, thrust, temperature etc., the electromagnetic structure optimization of VCM is conducted. The higher magnetic flux density (MFD) distribution of the air-gap in the proposed electromagnetic structure is validated by comparison with finite element (FE) simulation results. To solve the cooling problem of VCM, design, analysis and validation of a forced water cooling system are also performed. The permanent magnet material and the coil are analyzed, and the restraint conditions are obtained. The cost function of thrust is proposed and the related restraint conditions are analyzed.To predict accurately MFD distribution of the air-gap in a VCM, the decoupling MEC model of VCM is proposed, which is based on independent flux sources and loops. In the proposed model, every PM flux source and corresponding loops are divided into three sub-sections (the outer, the middle and the inner). The middle sub-MEC can be treated as an ideal MEC and solved accurately. Based on the further decoupled analysis of outer and inner MECs, MFD distribution in the air-gap can be approximated by a quadratic curve. Combining the cost function and the related restraint conditions, the optimization of VCM is completed. The effectiveness of proposed decoupling MEC method is demonstrated by comparison with FE results, conventional MEC and experimental results. Considering the principle of economy and performance, an architecture based on micro-controller and various analog circuit modules is proposed in the design of the driver. The micro-controller circuit, H full-bridge driving circuit, current measurement circuit, rectifier and filter circuit and various protection circuits are designed. By simulation and experimental results, the validity of the driver is verified successfully.As the thrust of the actuator (VCM and its driver) acts directly on the object, thrust overshoot of VCM will appear in the payload. To depress the overshoot of the actuator, a simple and effective control strategy is investigated which is based on the method of restraining mutually by response. The system transfer function of the actuator is identified firstly. Then, based on the transfer function, a novel method of trajectory overlay planning is presented to solve effectively the step overshoot, in which the original step input is divided into two step inputs with different amplitudes. An analytical formula is derived to express the relationship between the two step inputs, and the output error. The effectiveness of the proposed method is verified by simulation and experimental results.The designed VCM is applied successfully to a system of ultra-precision active isolator. Tests about active and passive isolators are performed, and the results show that the system of active isolator has obvious advantages. Optimization and analysis of the actuator is tested in active isolator to show the validity. |
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