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Author Topic: Smoothstepper PWM output has long ramp up  (Read 5184 times)

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Smoothstepper PWM output has long ramp up
« on: July 26, 2010, 05:10:19 PM »
I am using a smoothstepper, with plugin version Beta2 0.015ogx, along with Mach3 R3.042.040.

I am controllingf my spindle via PWM, through a Homann Designs Digispeed which converts the PWM to 0-10VDC, then to my Moeller/Eaton VFD.

Everthing is working as it should, except that when I first press "Spindle FWD" or type "M3" in MDI, the PWM takes about 60 seconds to slowly ramp up to the proper duty cycle for teh commanded speed. It seems to take teh same amout of time whether I am commanding a speed of 25%, 50% or 100% of the pulley Maximum.

Once I have run teh motor at commanded speed. turning the spindle off and on does not change the duty cycle seen on teh PWM signal(I should mention I am looking at the PWM square wave on a scope.

I started out using 1000Hz as teh PWM base frequency, but I now have it set at 200Hz, as it seems to work much better with teh Digispeed at that frequency.

Has anyone seen anything like this before?

ANdy
Re: Smoothstepper PWM output has long ramp up
« Reply #1 on: July 26, 2010, 05:23:20 PM »
Hi Andy,


When using the SmoothStepper to generate the PWM signal for the spindle speed you need to go to the Motor tuning tab and set an acceleration value for the Spindle axis. That should fix it.

Also, the optimum PWM base frequency for the DigiSpeed controllers is 50Hz.

Cheers,

Peter

----------------------------------------------------
Homann Designs
http://www.homanndesigns.com
email: peter at homanndesigns.com
Re: Smoothstepper PWM output has long ramp up
« Reply #2 on: July 26, 2010, 05:28:32 PM »
Thanks, Peter! I'll try that.

Andy
Re: Smoothstepper PWM output has long ramp up
« Reply #3 on: July 26, 2010, 08:34:35 PM »
Well, that did the trick! Thanks again, Peter!

Now if I could just getthis SS to stop locking up on noise.......

Offline Jeff_Birt

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Re: Smoothstepper PWM output has long ramp up
« Reply #4 on: July 27, 2010, 09:41:36 AM »
Make sure your wiring and earth grounding is proper. Also a good line filter on the spindle motor and arc snubbers on any relays that switch AC will work wonders.
Happy machining , Jeff Birt
 
Re: Smoothstepper PWM output has long ramp up
« Reply #5 on: July 27, 2010, 09:49:48 AM »
Hii Jeff:

i think my wiring, grounding, and shielding is done correctly, though I know from past experience that it is sometimes closer to voodoo than science.

I am venturing into new territory with my VFD and 3-phase motor. Can I still install aline filter on teh spindle motor when driven by a VFED?

And I am very familiar with switching DC with relays; not so much with AC. Where do you get an arc snubber? is it something I can build?

Thanks,

Andy

Offline Jeff_Birt

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Re: Smoothstepper PWM output has long ramp up
« Reply #6 on: July 27, 2010, 11:56:13 AM »
The key word here is 'VFD'. VFD's are VERY noisy critters. Look at the catalog for your manufacturers VFD and they will likely have line reactors (if it is a 3 phase input) to reduce noise problems. Mounting the VFD away from the rest of your controls is also helpful. If you have a VFD then likely you are using its build in on/off inputs? Are you using an isolated BOB?
Happy machining , Jeff Birt
 
Re: Smoothstepper PWM output has long ramp up
« Reply #7 on: July 27, 2010, 11:58:47 AM »
Jeff:

I had the noise problems before I installed teh VFD-and tehy don;t seem to have gotten worse with the VFD installed.

I am not using an isolated BOB-teh VFD control inputs are optoisolated though.