VFD interference problem

[Graeme]

I was helping (well trying) to help Geoffroy over the weekend with his "noise" issue. His current problem is that when he runs the spindle all the steppers start making random moves. It is these rapid random stepper moves that is the noise he is hearing.
We started looking into the shielding of the spindle cable and he managed to improved it, but no change to the random stepper movements. He then removed the VFD unit and all VFD wiring from his control cabinet -still the same issue. So it does not look like it is caused by the cable radiating noise into the BOB.
The last thing we tried was to disconnect the parallel port cable from the BOB. This did seem to stop the steppers from moving when the VFD was run.
The reason I suggested he disconnected his slaved X axis motors was when the spindle was run these motors were sometimes going in opposite directions causing his gantry to twist. Removing them kept his machine safe, but did lower the "noise" from the steppers.
It looks like the BOB is seeing noise on the signals from the PC when the spindle is run, which is then being used to send random STEP and DIR pulses to the stepper drivers. This could be caused by an earth loop between PC and control cabinet or by a poor 0v connection between the two. More testing will be required to find out which.
Hope that clears up the meaning of the "noise", any suggestions welcome as to how to solve this one.

[eurikain]

Thanks Graeme, you couldn't explain it better :)

[cropwell]

You may well have a ground loop, however you would do well to relocate your BoB so that the PP cable from the computer plugs directly into it (get rid of the unshielded flat form cable).

A good principle to follow when wiring up a cabinet is to put signal cables on one side of the cabinet and power cables on the other.

Cheers,

Rob

[eurikain]

This is how the cabinet is set. All hight voltage power cables are on one side of the cabinet. Signal cables are close to the BOB, there is only 5V power cables that run next to them.

I'll get rid of the ribbon cable, but that doesn't solve my ground loop. Why would I have a ground loop while other don't ? Is it the computer that's the problem ?

[komatias]

This is how the cabinet is set. All hight voltage power cables are on one side of the cabinet. Signal cables are close to the BOB, there is only 5V power cables that run next to them.

I'll get rid of the ribbon cable, but that doesn't solve my ground loop. Why would I have a ground loop while other don't ? Is it the computer that's the problem ?

I think it is down to the fact that many use metal cabinets to house the electronics and also for the machine frame. Spurious currents then have an easier path to earth.

[eurikain]

I confirm that it is a ground loop. I changed the parallel port today using a PCI card I have. Same noise issue. Disconnecting the PC fixes the issue.

[komatias]

I confirm that it is a ground loop. I changed the parallel port today using a PCI card I have. Same noise issue. Disconnecting the PC fixes the issue.

have you got an oscilloscope to probe the parallel port?

[Clive S]

I confirm that it is a ground loop. I changed the parallel port today using a PCI card I have. Same noise issue. Disconnecting the PC fixes the issue.

How can you confirm that it is a ground loop problem!! Have you confirmed that your PP cable is not just a printer cable (not all printer cables are the straight though type) You can check it with a multi meter

[magicniner]

Is there a reason why you don't have an RFI filter on the VFD power lines close to the VFD?

[JAZZCNC]

The last thing we tried was to disconnect the parallel port cable from the BOB. This did seem to stop the steppers from moving when the VFD was run.

Does the BOB have Charge pump.? If so then disconnecting from PC will kill the Outputs so you won't get any movement.!!

Going to sound obvious but have you tried another parallel port cable.? Also you are using a proper straight thru cable not some Old printer cable.?