A New 3D Analytical Design Model of an Electrostatic Micromotor using Multi-objective Approach

摘要

This paper presents a new design technique for finding the optimal structures of small size variable capacitance (VC) side-drive micromotors, based on a new 3D analytical micromotor design model. Two objective functions in mutual contrast, depending on the most important design parameters have been considered, giving rise to a multi-criteria design problem. In order to obtain as many optimal solutions as possible a non-dominated sorting algorithm (NSA) has been set up; different solutions are distributed both in the objective space and variable space giving rise to different possible optimal geometries. On one hand, these solutions are characterized by equal values of rotor and stator pole widths and by small values of bearing clearance to air gap spacing in order to maximize the net-average torque; on the other hand, the solutions found are featured by a small value of rotor pole widths in order to minimize the torque ripple. Due to the huge number of objective functions evaluation requested by the NSA we adopted the idea of using a 3D analytical simulation that has the advantage of a low computational cost and the drawback of smaller precision as compared with 3D finite element numerical solution. This new model has been considered to simulate the net-drive torque and torque ripple as two objective functions of the design process. This type of simulation takes into account the effect of both rotor-plane fringing fields and out-off axial fringing fields in actual estimation of total equivalent capacitance in the (r-θ-z) plane. Using such modeling in combination with the proposed design method provides a very powerful optimization tool to obtain many optimal solutions, distributed on the Pareto optimal front.