DC Servo motor and resolver testing


Thread Starter


Good day.

Newbie with a question about testing a servo motor and a resolver. The motor is a DC, permanent magnet, has a tach and a resolver. I do not have the motor connected to the E-beam welder at this time. I have the two motor leads, two wires for the tach, and the 6 or so wires to the resolver. I tried taking my bench top power supply and put the +/- 12VDC across the two motor leads and it does nothing. This power supply will provide up to 3 Amps, which should be plenty for this test. This is an old motor that has been working inside a vacuum chamber of an E-beam welder since 1982 so all of the faceplate info was gone a long time ago and I don't know how to determine any of the information without it. All I know is that the resolver attaches to an Allen-Bradley 8000 CNC Control and the tach and motor leads are driven by another servo board. It uses +/- 12VDC for the armature voltage (I think is what it is called). Any help would be greatly appreciated. I do have a 2- Channel Storage Scope if needed to test the resolver. The main reason I want to test the resolver is a different problem with the same machine. What happens is this: the operator moves the work piece from one end of the weld, and then moves it to the other end of the weld. The computer calculates the lead-in and lead out, then the gun fires and the part moves. The problem is that X and Y do not appear to be staying in synch. At the end of the weld it appears as though the control realizes it is in the wrong place and then will rapid to where it was supposed to end. The weld itself is not a straight line. It arc's out and then back in, at the end, as mentioned before, it rapids to where it is supposed to be. I would like to use my scope and check the resolver but don't know how. I have googled it but I don't understand what I have read. I thought maybe someone here could explain it so I could understand as I am not the sharpest tool in the shed. Thank you.
The right way for your test could be using any digital servo controller with resolver feedback - for example from Elmo -

That can you possibility to test all components separately and even together.

But in any case +/-12VDC must move your motor in both directions as well. And for resolver's connection you must define one reference coil and two sin and cose ones with the same resistance. The reference signal may be sine with 1...3V amplitude and 2...5 kHz frequency. The sin and cose coils must produce the same frequency sin and cos signals with amplitudes depended from resolver (i.e. motor's) shaft position.