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The sliding mode controller is designed for a class of non linear dynamic systems to tackle the problems with model uncertainties, parameter fluctuations and external disturbances. By this design, the bounds of the uncertainties are not required to be known in advance. In this paper, we develop a sliding mode controller for the robust position control of synchronous motor. Also, the load torque disturbance affects directly the motor shaft. An observer is considered to overcome the problem of torque disturbance. An asymptotically stable observer gain can be obtained without affecting the overall system response. The simulation results show the effectiveness of the proposed control strategy with desired tracking accuracy and robustness.