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Author Topic: PWM Spindle Fluctuation  (Read 7208 times)

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Offline SScnc

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PWM Spindle Fluctuation
« on: August 01, 2012, 05:42:47 PM »
I have my spindle setup with PWM output to a Digispeed XL and finally to a GS3 VFD. The problem is the spindle fluctuates only when an axis is moving. If the machine is still the spindle is stable. As soon as it makes a move on any axis, the speed drops. Any ideas?

Thanks

Offline Hood

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Re: PWM Spindle Fluctuation
« Reply #1 on: August 01, 2012, 05:53:32 PM »
I have never used PWM or indeed any VFD spindle control from Mach but I have something in the back of my mind about pulse width, try setting 5 in motor tuning and see if that makes a difference.
Hood

Offline SScnc

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Re: PWM Spindle Fluctuation
« Reply #2 on: August 01, 2012, 09:09:10 PM »
Just tried it. No change.

It's worse the higher up in RPM. Very strange. It only does it when I move an axis.
Re: PWM Spindle Fluctuation
« Reply #3 on: August 02, 2012, 12:59:46 AM »
Hi,

Step pulse width has nothing to do with the PWM output.

On the surface it sounds like EMI is getting into the PWM signal. What PWM base frequency are you using? It should be set to 50Hz.

Cheers,

Peter.

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Homann Designs
http://www.homanndesigns.com
email: peter at homanndesigns.com

Offline SScnc

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Re: PWM Spindle Fluctuation
« Reply #4 on: August 02, 2012, 05:12:58 AM »
That was my next assumption. I have the frequency set at 50hz.

Offline SScnc

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Re: PWM Spindle Fluctuation
« Reply #5 on: August 02, 2012, 06:04:19 PM »
Well I don't think noise is the issue. I put a 1uF cap on the output and I have the same result. Any other ideas? Any settings on the Digispeed I'm possibly missing?

Offline SScnc

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Re: PWM Spindle Fluctuation
« Reply #6 on: August 02, 2012, 06:12:29 PM »
If I were to use the Digispeed XL as STEP/DIR instead of PWM, what motor tuning values should I use?
Re: PWM Spindle Fluctuation
« Reply #7 on: August 02, 2012, 06:36:59 PM »
Hi,

The DigiSpeed Step/Dir is not compatible with Mach3. It is for TurboCNC

The inputs to the DigiSpeed are filtered on board. The are no settings on the DigiSpeed that could be causing a fluctuation

I'm wondering if there is something with Mach3 that is causing it?

Have you done a Mach3 driver test to see if it is fluctuating?

Also do you have an oscilloscope to look at the PWM signal?

Cheers,

Peter

----------------------------------------------------
Homann Designs
http://www.homanndesigns.com
email: peter at homanndesigns.com

Offline SScnc

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Re: PWM Spindle Fluctuation
« Reply #8 on: August 02, 2012, 09:42:10 PM »
Hi,

The DigiSpeed Step/Dir is not compatible with Mach3. It is for TurboCNC

The inputs to the DigiSpeed are filtered on board. The are no settings on the DigiSpeed that could be causing a fluctuation

I'm wondering if there is something with Mach3 that is causing it?

Have you done a Mach3 driver test to see if it is fluctuating?

Also do you have an oscilloscope to look at the PWM signal?

Cheers,

Peter



That would explain why I couldn't get the step/dir to work. I'll have to run the driver test. I've done it in the past and everything looked okay IIRC. I don't have an o-scope unfortunately.

I emailed you a few weeks ago about the Digispeed and how I can't get more then 7V back to my VFD. I still have that same issue and I wonder if it is somehow related to this issue. Maybe my Digispeed board is faulty?

I compensated for the lower voltage by programming the VFD Analog Input Gain. Which works but I'd really like to know why I can't get 10V out. 
Re: PWM Spindle Fluctuation
« Reply #9 on: August 02, 2012, 09:54:04 PM »
Hi,

It is unlikely that the DigiSpeed is faulty as I test them all myself. That said it is possible.

Can you take an image of the DigiSpeed so I can see if I can pick anything with the board and check the  up the jumper settings.

If the VFD is providing 10V to the Digispeed, you should be seeing a max of at least 9.4V

Cheers,

Peter.
----------------------------------------------------
Homann Designs
http://www.homanndesigns.com
email: peter at homanndesigns.com