hi all
i found this another forum then i understands all bldc commutation signal where use.
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At power up, the UVW signals are present and they provide a low resolution "absolute position" feedback that tells the servo drive the electrical position of the servo motor rotor (electrical position is different from mechanical position due to multiple pole pairs in most servo motors - if the motor was 2 pole then electrical position would be equal to mechanical position). No movement of the rotor is necessary to initialize the torque angle in the servo drive. The torque of the servo motor is proportional to the sin of the angle so there is plenty of torque to start the initial motion even if the torque was off by as much as 45 electrical degrees (70% of peak torque would be available in this case). After power-up, the UVW signals are automatically switched over to the high resolution quadrature "incremental position" data and the once per revolution reference marker signal. As soon as the servo drive detects the first occurrence of the encoder marker signal the torque angle is adjusted in the servo drive to the near perfect value. The servo motor manufacturer mechanically aligns the marker pulse to provide the near perfect torque angle during manufacturing of the motor. If the motor encoder were to be removed or replaced then this alignment process must be repeated.
With the SureServo system, the UVW encoder signals are present at power-up for about 0.5 seconds. This gives the servo drive enough time to detect rough position of the servo motor rotor. After about 1/2 second, the motor encoder automatically switches over to high resolution ABZ data signals which the servo drive uses for real-time commutation of the brush less servo motor. With the first occurrence of the Z signal (marker pulse) the rotor angle inside the drive is set to the exact value. Hope this answers your question.
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thanks
shabbir