Galil 2280 issue

[battwell]

interesting fault!

[mjanne65]

Just a follow-up on this in case someone else runs into the same problem.

1) The encoder pulses look very good on the scope, but if you go up to higher frequencies, there is some noise overlay.  The noise is from the servo drives and is a sine wave that dies and then repeats.  It looks like it might get one cycle that would be of sufficient amplitude to be read as a pulse.  I'm still not sure how this is seen as quadrature, but it is. This was not an issue on the Dynapath for some reason, perhaps the frequency is too high for it to read or the threshold voltage is higher.

2) I had the same error on the X & Y axes and with two different make/model encoders on the Y.  The cable on both is three twisted pairs with shield and drain wire on each pair. There is no outer shield.  Both originally had the shields tied to case ground on the encoder and floating at the control.  The A & B channels are on different pairs.  The cable was run in the same conduit as the tach and power cables, but removing it did not solve the problem.

3) To completely solve the problem, I had to tie the shield wires to case ground on the encoder AND ground them on the Galil. Grounding on one side or the other would not eliminate the noise.

Mike

[HillBilly]

There should be a ground wire ran with the armature wires. Check its integrity or install one, then disconnect the shield at the encoder because it is doing what the ground wire should. This could also be an indication of insulation breakdown in the motor.

Darek