Servo Motor Position Feedback Component Incremental Encoder And Absolute Encoder Phase Alignment

- Jul 19, 2018-

Servo motor position feedback component incremental encoder and absolute encoder phase alignment



The mainstream servo motor position feedback components include incremental encoders, absolute encoders, sine and cosine encoders, and rotary transformers.


Phase alignment of incremental encoders


In this discussion, the output signal of the incremental encoder is a square wave signal, which can be divided into an incremental encoder with a commutation signal and a conventional incremental encoder. The ordinary incremental encoder has two phase

 square wave pulse output signals A and B, and the zero bit signal Z; the incremental encoder with the phase change signal has the ABZ output signal, and each of the electronic commutation signals with 120 degrees difference ,each revolution the number of cycles is consistent with the number of pole pairs of the rotor of the motor. The phase of the UVW electronic commutation signal of the incremental encoder with the commutation signal is aligned with the rotor pole phase and the electrical angular phase is as follows


1. Use a DC power supply to pass the UV winding of the motor to a DC current less than the rated current, U in, V out, to orient the motor shaft to an equilibrium position;

2. Observe the U-phase signal and Z-signal of the encoder with an oscilloscope. Adjust the relative position of the encoder shaft and the motor shaft according to the convenience of operation, or the relative position of the encoder housing and the motor housing.

position;

3. While adjusting, observe the U-phase signal transition edge of the encoder, and the Z signal until the Z signal is stable at a high level (in this case, the default Z signal is normally low), locking the encoder and the motor.

Relative positional relationship; the motor shaft is twisted back and forth. After the hand is released, if the motor shaft is free to return to the equilibrium position each time, the Z signal can be stabilized at a high level, and the alignment is effective.


After removing the DC power supply, verify as follows:

Observe the U phase signal of the encoder and the UV back EMF waveform of the motor with an oscilloscope; turn the motor shaft, the rising edge of the U phase signal of the encoder and the UV back EMF waveform of the motor from low to high zero crossings coincide, and the Z signal of the encoder also appears at this zero crossing.

The above verification method can also be used as an alignment method. It should be noted that the phase zero point of the U-phase signal of the incremental encoder is aligned with the phase zero of the motor UV back-EM potential, due to electricity.

The U potential of the machine is different from the backlash of the UV line by 30 degrees. Therefore, after this alignment, the phase zero of the U-phase signal of the incremental encoder is aligned with the -30 degree phase point of the opposite potential of the motor U.

The phase angle of the motor electrical angle is the same as the phase of the U potential waveform, so the phase zero point of the U-phase signal of the incremental encoder is aligned with the -30 degree point of the motor electrical angle phase.


Some servo companies are accustomed to directly aligning the zero point of the encoder's U-phase signal with the zero point of the motor's electrical angle. To achieve this, you can:

1. Connect three stars with the same resistance to form a star, and then connect the three resistors connected to the star to the UVW three-phase winding of the motor;

2. Observe the U-phase input of the motor and the midpoint of the star-shaped resistor with an oscilloscope to approximate the U-potential waveform of the motor. Adjust the phase of the encoder shaft and the motor shaft according to the convenience of operation.

The position, or the relative position of the encoder housing to the motor housing;

3. While adjusting, observe the rising edge of the U-phase signal of the encoder and the zero-crossing point of the opposite potential waveform of the motor U from the low to the high, and finally make the rising edge and the zero-crossing point coincide, locking the encoder and the motor.

Relative positional relationship, complete alignment. Since the ordinary incremental encoder does not have UVW phase information, and the Z signal can only reflect one point within one circle, there is no direct phase alignment potential.Therefore, it is not a topic of this discussion.


Phase alignment of absolute encoders

The phase alignment of absolute encoders is not much different for single and multiple turns. In fact, the phase and motor of the encoder are aligned in one revolution.

The phase of the electrical angle. Early absolute encoders gave the highest level of the single-turn phase as a separate pin. With this level of 0 and 1 flipping, encoders and motors can also be implemented.

The phase alignment is as follows: 

1.a DC power supply is used to pass the DC winding of the motor to a DC current less than the rated current, U in, V out, and the motor shaft is oriented to an equilibrium position;

2. Observe the highest count bit level signal of the absolute encoder with an oscilloscope; adjust the relative position of the encoder shaft and the motor shaft according to the convenience of operation, or the encoder housing and motor housing

While adjusting the relative position, observe the edge of the highest count bit signal until the edge of the jump appears exactly at the directional equilibrium position of the motor shaft, and lock the relative position of the encoder to the motor.


3. Reverse the motor shaft back and forth, after the hand is released, if the motor shaft is free to return to the equilibrium position each time, the jump edge can be accurately reproduced, and the alignment is effective.


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