Servo control system in CNC machine tools is crucial for machining accuracy. In order to obtain good dynamic precision, the in-depth analysis of the output torque of the servo motor should be a prerequisite. In this paper the servo control system including CNC, electromagnetic noise and feedback information disturbance, are analyzed in frequency domain, to study their individual influence on the frequency spectrum of the linear motor thrust. The following work has been done: 1) the control-related modules in CNC, i.e., the interpolator and the Acceleration/Deceleration Control (ADC) module are studied by analytic method to reveal their impact on the command signal used to control the servo motor. 2) The influence of the servo drive circuit on the frequency components of the motor current as well as the mechanism of PWM module & power amplifier is investigated. 3) The electromagnetic conversion inside the servo motor is analyzed to explore the energy flow of the motion inside the mechatronic system. 4) The influences of the electromagnetic noise and feedback information disturbance on the thrust spectrum are analyzed. The results show that, the frequency spectrum distribution of the motor thrust is decentralized and complicated, and each part is influenced by certain module of the servo control system respectively. It is also found that the thrust spectrum varies with the feed speeds.

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