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motors lose steps after vfd install
« on: July 18, 2012, 10:17:28 PM »
Finally got my vfd step/dir working and ran a code and noticed that stepper motors are now losing steps. At one moment they faulted out both digital drivers. Shut down system restarted and went into motor tuning changed a few numbers vel. accel and same problem occurs. Whats going on? Can there be some kind of noise or interference causing this issue . Kernal speed is set to 25000k . Maybe debounce setting increased not sure any help out there would be great.

Offline Hood

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Re: motors lose steps after vfd install
« Reply #1 on: July 19, 2012, 03:02:09 AM »
If it is only when the VFD is running then it is very likely that the issue is noise. Debounce in Mach will not make a difference if it is losing steps as it would be external wiring to the stepper drives that is seeing the noise. You need to shield and properly ground all your wiring, especially any low voltage signalling wiring.
I use 24v on all my machines where possible to help eliminate the effects of noise and for signals that have to be 5v such as encoders or Step/Dir signals I have them via line drivers to make them differential (Step +, Step - , Dir + Dir -) This makes them very noise immune. My servo drives accept differential step/dir so I dont have to convert it back to single ended for them but if you went down that route then you could easily convert back just before the drives with a line receiver.
 As said though properly grounding and shielding all your wiring will help greatly with noise issue.
Hood
Re: motors lose steps after vfd install
« Reply #2 on: July 19, 2012, 04:25:11 PM »
Hood
Im currently using a shielded 6 conductor for the low voltage wiring from the C6 board to the vfd . Do I use the shield non insulated wire to to ground on one end or both ends.
I know at  work shielded pairs are normally grounded on one end but in this case im not sure. and would the controller case be a sufficient area to ground the wire.
Thanks Hood   

Offline Hood

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Re: motors lose steps after vfd install
« Reply #3 on: July 19, 2012, 04:42:09 PM »
Normally you would take the all of you shields to a single point in the cabinet and Gnd it. One end seems to be the way of thinking now for most things although my servo drives have both ends of the encoder cables connected. All other shielded wires just have one end connected.

Just to confirm, all is well when the VFD is not running the spindle?
Possibly some line filters on the VFD may help.
Hood
Re: motors lose steps after vfd install
« Reply #4 on: July 19, 2012, 07:05:10 PM »
Hood
Motors run abnormally in spindle on or off.I am currently using 570 oz. steppers and set to 2000 steps, step pulse set to 2, vel. =270, accel= 70. Iam using Digital drivers and was happy with the performance. I will definitely check the grounding issue to begin with.
 thanks

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Re: motors lose steps after vfd install
« Reply #5 on: July 19, 2012, 07:07:56 PM »
Ok it doesnt sound like the VFD is the issue then if it doesnt matter if its running or not, could it possible be the active state of the Step pulse that is the wrong way for your drives?
Hood
Re: motors lose steps after vfd install
« Reply #6 on: July 19, 2012, 08:16:15 PM »
Not real sure what you mean. Active hi or i suppose is what your saying
Re: motors lose steps after vfd install
« Reply #7 on: July 19, 2012, 10:22:07 PM »
Figured it out .. you were on the money on the active state.  Hood thanks again

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Re: motors lose steps after vfd install
« Reply #8 on: July 20, 2012, 02:54:59 AM »
Glad to hear your sorted :)
Hood