A method has been developed to monitor the microassembly process of the shaft into the plate of the high-precision spindle motor. The plate is expanded to reduce the shaft low problem by using the preheating technique at the experimentally simulated temperature. The finite element method is utilized to simulate the expansion of the plate. The force sensor is utilized to monitor the pressing force. A proposed method to reduce the shaft high problem introduces the reference voltage as the threshold value, which is obtained by taking the differentiation of the in-process pressing force. A slope detector is developed to calculate the output voltage, and the motor driver of the machine is controlled when the obtained output voltage is larger than the reference voltage. It is proved that the shaft high and the shaft low are well controlled and reduced by the proposed preheating technique and the developed slope detector.
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