Quasi-stationary Initial Position Identification Method for Non-salient Motor with Incremental Position Sensor

For the motor in robot joint or servo systems, an incremental encoder is typically used as the position sensor. Considering the rotor's position may change after each power off, it is essential for the control system to re-determine the initial position after each power-on. Known as the most common method, the initial position detection scheme based on high-frequency injection will rely on the saliency of the motor and magnetic polarity detection is also required. To solve this problem, this paper proposes an initial position identification method based on incremental sensor capturing motor signals under quasi-stationary state, which is effective to non-salient joint motor. First, a current pulse is injected to obtain the range of the d-axis and a controller is used to perform feedback control on the encoder signal, so that the motor shaft moves to the nearest minimum resolution scale line. Then, a controller is applied to perform feedback control on the encoder signal to obtain the precise position of d-axis. This method achieves initial position identification without relying on the saliency of the motor, while ensuring the accuracy and rapidity of initial position detection, keeping the motor rotor in a quasi-stationary state and no magnetic pole detection is required.