Zero adjustment method of incremental servo motor encoder

Mainstream servo motor position feedback components include incremental encoders, absolute encoders, sin-cos encoders, resolvers and so on.

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 an ordinary incremental encoder. The ordinary incremental encoder has two Phase quadrature square wave pulse output signals A and B, and zero signal Z; Incremental encoder with commutation signal in addition to ABZ output signal, also has 120 degrees of mutual difference of electronic commutation signal each revolution The number of cycles is consistent with the number of pole pairs of the motor rotor. The alignment method between the phase of the UVW electronic commutation signal of the incremental encoder with commutation signal and the phase of the rotor magnetic pole, electrical angle phase is as follows:

1. Use a DC power supply to pass a DC current less than the rated current to the UV winding of the motor, U input, V output, and orient the motor shaft to a balanced 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, or the relative position of the encoder housing and the motor housing according to the ease of operation;

3. While adjusting, observe the encoder's U-phase signal transition edge and Z signal until the Z signal is stable at a high level (here the normal state of the Z signal is low by default), lock the encoder and the motor relative Position relationship: after twisting the motor shaft back and forth, after letting go, if the Z signal can be stabilized at a high level every time the motor shaft freely returns to the equilibrium position, the alignment is valid.

After removing the DC power supply, verify as follows:

Use an oscilloscope to observe the U-phase signal of the encoder and the UV back-EMF waveform of the motor; rotate the motor shaft, the rising edge of the U-phase signal of the encoder coincides with the zero-crossing point of the UV back-EMF waveform of the motor from low to high, the encoder’s The Z signal also appears at this zero crossing.

The above verification method can also be used as an alignment method. It should be noted that at this time, the phase zero of the U-phase signal of the incremental encoder is aligned with the phase zero of the UV line back EMF of the motor. Because the U reverse potential of the motor is 30 degrees different from the UV line back EMF, After this alignment, the phase zero point of the U-phase signal of the incremental encoder is aligned with the -30 degree phase point of the motor U opposite potential, and the electrical angle phase of the motor is consistent with the phase of the U opposite potential waveform, so at this time the incremental encoding The phase zero point of the U phase signal of the motor is aligned with the -30 degree point of the electrical angle phase of the motor.

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

1. Connect 3 resistors of equal resistance value into a star shape, and then connect the 3 resistors connected in the star shape to the UVW three-phase winding leads of the motor;

2. Observe the midpoint of the motor's U-phase input and star resistance with an oscilloscope, and you can approximate the motor's U opposite potential waveform; according to the convenience of operation, adjust the relative position of the encoder shaft and the motor shaft, or the encoder housing and The relative position of 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 reverse potential waveform of the motor U from low to high, and finally make the rising edge coincide with the zero-crossing point, lock the relative position relationship between the encoder and the motor, and complete the alignment .

Since ordinary incremental encoders do not have UVW phase information, and the Z signal can only reflect one point within a circle, it does not have the potential for direct phase alignment, so it is not the topic of this discussion.

Phase alignment of absolute encoder:

The phase alignment of the absolute encoder is not much different for single-turn and multi-turn. In fact, the phase alignment of the encoder is aligned with the phase of the electrical angle of the motor within one turn. Early absolute encoders will give the highest level of the single-turn phase with a separate pin. Using this level of 0 and 1 inversion, the phase alignment of the encoder and the motor can also be achieved. The method is as follows: A DC power supply supplies a DC current less than the rated current to the UV winding of the motor, U input, V output, and orient the motor shaft to a balanced position;

4. Use an oscilloscope to observe the highest count level signal of the absolute encoder;

According to the ease of operation, adjust the relative position of the encoder shaft and the motor shaft, or adjust the relative position of the encoder housing and the motor housing while observing the transition edge of the highest counting bit signal until the transition edge accurately appears on the motor shaft At the directional balance position, lock the relative position relationship between the encoder and the motor;

5. Twist the motor shaft back and forth, and after letting go, if the jumping edge can accurately reappear every time the motor shaft returns to the equilibrium position freely, the alignment is effective.