Simplified Numerical Model for Rapid Design of AF Module Spring Shape Parameters

Abstract

The autofocusing (AF) performance of cell phone cameras is critically dependent on the design of the voice-coil motor (VCM) used to drive the lens module. Also, the metal springs in the AF module should combine high stiffness with a good actuation response and a light weight. The present study utilizes a reverse engineering approach to construct three-dimensional finite element models of the top and bottom springs in the VCM mechanism. Simulations are then performed to investigate the von Mises stress distribution and stiffness characteristics of the two springs given horizontal and vertical orientations of the AF module, respectively. In performing the simulations, the actuation force is computed using two different analysis methods, namely a simplify structure method and a coupled electromagnetic-structural method. It is shown that the simplify structure method has the advantages of a lower computational complexity and a more comprehensive modeling capability. A further series of simulations is thus to examine the effects of the spring shape parameters on the reaction force developed by the spring stiffness. The results show that the spring stiffness increases with an increasing thickness and a decreasing rib length. The simulation results obtained for different spring shape parameter settings are summarized in the form of a parameter design chart for predicting the reaction force given known values of the spring rib length and spring thickness.