I have a 3 phase ac servo motor. I wrote a foc algorithm suitable for this motor (I think!), but I need to determine the zero rotation angle to get the starting commutation of the rotor. I asked this question in another forum, but could not get the answer.
There is a sincos encoder on the motor (SRS50). This encoder works with 8 v input voltage. and the output signal has an offset voltage of around 2.5V. output signal has 1V peak to peak voltage with 90 degree phase difference. The encoder has 1024 periods in 1 turn. There is no index output on the encoder. Below is the datasheet file.
There are REFCOS, REFSIN outputs in the encoder information in the datasheette. Since REFSIN output connection is problematic, I couldn't observe it, but he could observe the RESCOS output after energizing it. According to the oscilloscope image, it has a constant 2.88V dc voltage. This is the offset value of the cos output signal I mentioned above.
How do I know the zero degree position of the motor shaft? I really need your help in this matter? Thank you.
Datasheet: bergerlahr ser368/3l7ss0co
Best Answer
If you were using the Resolver version, it would simply be when the amplitude of the SIN output was 0 and the COS amplitude was peak. Demodulate these using REF as a reference carrier.
With the sensor you have, clearly it does some processing which will be documented elsewhere. So find that document and consult it. It may be that the SIN and COS outputs work as though they came from a resolver and REFSIN/REFCOS are the DC components (compare with SIN/COS to find zero crossings etc) but without the databook that is mere speculation.
It may also be there is a direct positional indication on the RS485 outputs, in which case it's easier to use that instead.
As the datasheet says,