Trying to align and encoder with hall sensors to the motor phases...

[Hypersonic]

Hi I am using an oscilloscope to try to properly align an encoder to the servo motor phases.
I can get one channel to read one of the hall sensor outputs well.
I can get another channel on the scope to read the back emf between 2 legs of the motor phases well also.
I read on the "Kolmorgen" site how to do this, so I think it is a valid method.

When I spin the servo motor using a cordless drill motor, the two signals seem to drift i.e. can't align anything if they won't synch up.

This may be just not properly use of the oscilloscope, but I don't know.

I have tried setting "trigger" to both channels and don't get any better result regardless of what channel I use for the trigger.

Anyone have any insight on this?

Thanks!

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[he1957]

It's unlikely the speed of the cordless drill is anywhere near constant - perhaps at full speed with lower gearbox ratios. If you have a tacho see if you can see if it's anywhere near consistent.

[Al_The_Man]

I usually back feed the motor about 200rpm.
You should be able to use the hall pulses for the trigger, For the 3 phases I create a virtual neutral by connecting a 1K resistor to each phase and connect the 3 ends together and use as the scope gnd reference.
Never had to regulate the rpm so far.
Al.

[Hypersonic]

I usually back feed the motor about 200rpm.
You should be able to use the hall pulses for the trigger, For the 3 phases I create a virtual neutral by connecting a 1K resistor to each phase and connect the 3 ends together and use as the scope gnd reference.
Never had to regulate the rpm so far.
Al.

Thank you both, I will give this a try.
I didn't have resistors the other day to do the star setup like you recommended so I probably wasn't getting a good signal anyways.
Have a new 4 channels scope coming today and one of those cheaper ones you hook to a pc that is 8 channels so hopefully can see everything that is going on.

This one has me stumped. I have some experience with servo motors and drives etc as I have put a few systems together, but never had this much trouble.
Hopefully this will get me pointed in the right direction or possible let me know if something is bad in the system.

Thank you!