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Author Topic: smooth stepper works differently in different computers?  (Read 9529 times)

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Offline BarryB

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Re: smooth stepper works differently in different computers?
« Reply #10 on: April 14, 2010, 12:47:09 PM »
No problem, I'm happy to have the help.  The relay switching sends a DC signal to tell the VFD to turn on a off the spindle.  I also have it wired with low voltage DC to control the speed of the spindle.  Btw, I'm using the C23 card from CNC4PC which has inputs/outputs for all this stuff directly on the card.

Barry

Online Tweakie.CNC

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Re: smooth stepper works differently in different computers?
« Reply #11 on: April 14, 2010, 01:06:49 PM »
Hi Barry,

I have now looked at both my laptops and neither have a protective earth connection (they are both 'double insulated', as far as the regulations are concerned and do not have any connection to the incoming mains supply earth).
Assuming your laptop has no electrical connection between the mains earth pin and the USB or LPT port outer metal screens then this would explain the difference between the behavior of your PC and laptop.  One mystery solved I hope.

I will now go and look at my VFD setup and check how it is wired and report back with suggestions.

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.

Offline BarryB

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Re: smooth stepper works differently in different computers?
« Reply #12 on: April 14, 2010, 01:12:27 PM »
Hmm, I'm not sure I understand.  My laptop is connected via 3 prong power adapter.  The PC is powered via a 3 prong cord to the wall.  Aren't those the same then?

Online Tweakie.CNC

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Re: smooth stepper works differently in different computers?
« Reply #13 on: April 14, 2010, 01:36:38 PM »
Not quite the same thing Barry, as the laptop uses an adapter.

If you have a multimeter, with your laptop switched off and disconnected from the mains, measure the continuity between the mains earth pin and the metal part on the outside of your USB connection or the metal part on the outside of your LPT port - Is it an open circuit ?.

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.

Offline BarryB

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Re: smooth stepper works differently in different computers?
« Reply #14 on: April 14, 2010, 01:38:46 PM »
I'll have to check tonight.  I'm at my day job currently;)

Online Tweakie.CNC

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Re: smooth stepper works differently in different computers?
« Reply #15 on: April 14, 2010, 01:42:29 PM »
OK Barry, back in communication tomorrow. This means I can go home now  ;D. As long as you have the patience we will sort this !!.

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.

Offline BarryB

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Re: smooth stepper works differently in different computers?
« Reply #16 on: April 14, 2010, 01:44:06 PM »
sounds cool, I'd really like to get that machine running the mill, rather than my lappy.

Barry

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Re: smooth stepper works differently in different computers?
« Reply #17 on: April 15, 2010, 11:16:50 AM »
Hi Barry,

After much thought I have compiled a list of things for you to check. I have probably forgotten something important but that's life.

1)   All exposed metal parts forming part of a ‘mains operated machine’ must be connected to Earth. [this is more for your own personal safety than anything else].
2)   All input devices such as limit switches, estop etc.should be connected with screened cable.
3)   The screen of all screened cables must be connected to Earth and only at one end (preferably to one single Earthing point at the controller end).
4)   The VFD frequency control input cable should preferably be screened or at least a ‘twisted pair’.
5)   The VFD forward/reverse – on/off switching cables should preferably be screened or comprise of ‘twisted pairs’.
6)   The cable between the VFD and the spindle motor should ideally be screened and not routed, for any great distance, alongside wiring for inputs (limit switches, estop etc.). [ideally the screen should be connected at the VFD earth terminal only but if the spindle motor is metal bodied the cable should contain a fourth wire for the earth connection to the motor body but the motor itself must then only be fitted to the machine using an insulated mounting to avoid creating an Earth loop].
7)   There must be no Earth loops. [typical examples are where the machine frame is connected to Earth via the incoming supply and the VFD is also connected to Earth via the incoming supply and  then these two items are fitted in electrical contact with each other thus an Earth loop is formed. The same thing applies with the PC which is also earthed via the incoming supply, if its metal casing parts or its cable screens/shields (LPT / USB etc) come into electrical contact with the machine frame an Earth loop is again formed].
8)   Any forms of Radio Frequency Interference (RFI) or Electro Magnetic Interference (EMI) must be traced and eliminated by fitting screening, filters etc. [the EMI is relatively short range but the generation of RFI can be just as much of a problem for your systems as it is to your neighbors computer, TV and radio systems].
9)   You should not make any direct electrical connection between ‘the computers Ground wires (pins 18 – 25) or the LPT cable screen/shield’ and ‘Earth’. [the computer ‘Ground’ and ‘Earth’ are to be considered as two separate circuits].
10)   If anything here conflicts with any product manufacturer’s recommendations then their instructions take precedence. [they should be a lot smarter than I].


Hope this helps.

Tweakie.
« Last Edit: April 15, 2010, 11:18:57 AM by Tweakie.CNC »
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.

Offline BarryB

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Re: smooth stepper works differently in different computers?
« Reply #18 on: April 15, 2010, 12:12:51 PM »
I'll fix the deficiencies in my box compared to this list with the 2nd control box I build.  The first one I have here is temporary 'proof of service' type thing.  I think comparing what's different between the lappy and the desktop will be the key though.  I'll be doing that this weekend, as I'm getting an art opening ready.

Barry

Offline rcaffin

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Re: smooth stepper works differently in different computers?
« Reply #19 on: October 07, 2010, 06:56:17 PM »
My laptop is connected via 3 prong power adapter.  The PC is powered via a 3 prong cord to the wall.  Aren't those the same then?
Certainly NOT! The output of the laptop charger is very likely floating. The PC is not.

Yes, this sounds very much like a noise problem, and my guess is that the noise source is associated with whatever earthing you have set up between the PC and the machine. Earthing sounds simple, but it AIN'T!
Set up a single central earth bolt somewhere. Make all earth connections radial, direct to this bolt. Do NOT allow any earth loops; do not earth screens at both ends, etc. Use opto-isolation between SS and machine. Twinkie's list is good.

Cheers