Design and Validation of the GA-based Sliding Mode Controller for a Two Degree-of-Freedom Translational Optical Image Stabilizer in Image Sensors

Jeremy H.-S. Wang, Paul C.-P. Chao

Optical Image Stabilizer, Equations of Motion (EOM), Genetic Algorithm, Sliding Mode Controller

This study proposes a genetic algorithm (GA) based sliding mode controller (SMC) for two degree-of-freedom (DOF) translational optical image stabilizer (OIS) of cell cameras installed in the mobile phone. Hand tremors vibrates the lens holder to causes the photographed object projected on different pixels of the image sensor while shooting a picture. The OIS can stabilize the lens holder and efficiently improve the blurring image. The OIS controls a two-DOF translational stage actuated by voice coil motors (VCMs) to stabilize the lens holder for up to four directions of involuntary vibrations. This study includes three main parts: (1) mechanism analysis, (2) establishments of the dynamic equation of motions (EOMs) of the two-DOF translational mechanism, and (3) designs and realizations of a sliding mode controller optimized by genetic algorithm. The first part shows the OIS four-parallel-wire suspension mechanism providing the two-DOF planar movement for the lens holder and magnets offering electro-magnetic force for actuation. In the second part, based on the Lagrange’s laws, the dynamics EOMs are derived and analyzed through considering kinetic and potential energy. The last parts include a GA-based SMC is designed to control the lens holder based on EOMs and associated simulations are conducted. According to the simulations, The GA-based SMC is forged and tested by a real-time system integrating a field programmable gate array (FPGA) module. The controllers containing the derived system is built up for anti-shake mechanism. After a series of experiments and verifications, the designed OIS can reduce the vibrations within 5-8 in 0.05 seconds. The setting time of experimental results are much less than 0.1 seconds of the previously report and the residual vibration is smaller than the pixel size of the most commercial image sensor. Thus, the prototype of the novel OIS is finally accomplished with satisfactory performance of vibration reduction.