Design of Sliding Mode Controller for Voice Coil Motor Using Nonlinear Observer

Abstract

Voice coil motors (VCM) are used in very small equipment such as mobile phone cameras and the use of a robust control feature as sliding mode control (SMC) is inevitable in them. The most important property of SMC is its invariant against matched disturbances and uncertainties which is due to the using of Sign function in input control signal. The invariant property is stronger than robustness. But, this method is not invariant with respect to the mismatched uncertainties i.e. is variant and sensitive. This is the challenge of SMC in VCM because of existents mismatched uncertainty in their models. To solve this problem in this paper, input control signal is calculated at first via SMC and then, coefficients of the sliding surface are determined in such a way that the effect of mismatched uncertainties or disturbances is removed in closed loop system and invariant property is retained. The proposed approach is simple in concept and realization. Moreover, due to the inaccessible system states, a new nonlinear observer is proposed for system model identification. In simulation, the electro-mechanical model of motor has been used which has both matched and mismatched uncertainties. Simulation results show the effectiveness of this approach.

Keywords

• voice coil motor
• nonlinear observer
• mismatched uncertainty
• sliding mode control