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Author Topic: Spindle Speed Feedback and Accuracy  (Read 3859 times)

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Spindle Speed Feedback and Accuracy
« on: September 17, 2017, 01:59:24 PM »
   Just got my other issues resolved ! Now on to the Spindle Speed .   Mach4 3481 and dspMC newest Pluggin.
When M3S1500 is commanded , My true Spindle Speed is 1530ish , I have Encoder feedback to Mach4 that is Dead On at the control screen. The VFD has an RPM Screen that Reads 1530ish.
   and I verified the Spindle RPM with a Laser and it is dead on . Analog Control Voltage is 0-10dc . Doesnt Mach4 provide Feedback to control Spindle Speed? What am I doing Wrong
Re: Spindle Speed Feedback and Accuracy
« Reply #1 on: September 17, 2017, 02:19:10 PM »
You have not done anything wrong. The Mach4 software does
not provide closed loop speed control. It is open loop just like
the motion commands. Any such control would require that
the motion device implement it, or perhaps you could do it
in a PMC script.

Steve Stallings
www.PMDX.com
Re: Spindle Speed Feedback and Accuracy
« Reply #2 on: September 17, 2017, 02:35:55 PM »
Hi,
and dead accurate speed control is important why?

Craig
'I enjoy sex at 73.....I live at 71 so its not too far to walk.'
Re: Spindle Speed Feedback and Accuracy
« Reply #3 on: September 17, 2017, 07:40:59 PM »
        I would like True Accurate Speed because , some of the tools i use at HSM . 15 to 40 Rpm can be a make or break deal , especially with Large diameter tools ( facemills ) .
Re: Spindle Speed Feedback and Accuracy
« Reply #4 on: September 17, 2017, 07:48:30 PM »
Hi,
your spindle is driven by a VFD, that is your spindle motor is an asynchronous induction motor. They, by definition,
have slip. Without tacho/encoder feedback precise speed control is not possible.

Craig
'I enjoy sex at 73.....I live at 71 so its not too far to walk.'
Re: Spindle Speed Feedback and Accuracy
« Reply #5 on: September 17, 2017, 08:25:24 PM »
Hi,
does your VFD have feedback inputs?

Many of the most recent made VDFs have sensorless vector control
which will give you speed control of about 1% accuracy over  about 10:1 maybe 20:1 range.

You use a Vital Systems motion controller. I know the HICON unit can be upgraded to do closed loop ops,
maybe your one can too.

Craig
'I enjoy sex at 73.....I live at 71 so its not too far to walk.'
Re: Spindle Speed Feedback and Accuracy
« Reply #6 on: September 18, 2017, 06:25:57 PM »
Hi dunnitagain,
I've been thinking about your spindle speed problem, I see five different solutions

1) Use Sensorlles Vector control if your VFD is capable.
2) Use a pulse generator, aka your encoder, to provide feedback for your VFD, if it is capable.
3) Use a F to V chip and opamps to close the loop electronically, fun if your electronically inclined.
4) Uprate your controller to give analogue output and use your controller to close the loop, costs of the upgrade?
5) Use Mach4s built in PMC, probably result in less control bandwidth than 2) or 3) but still probably tens of Hz,plenty enuf.

Craig.
'I enjoy sex at 73.....I live at 71 so its not too far to walk.'
Re: Spindle Speed Feedback and Accuracy
« Reply #7 on: September 18, 2017, 09:04:17 PM »
  My machine has a  25HP Spin motor with 1000 Line Encoder for Feedback to VFD , the VFD has encoder outputs which I hooked to the dspMC to provide Spin Speed Feedback to Mach.
I thought the Vital System dspMC would close the spindle speed loop . Isnt there a way to Scale the Analog output of the dspmc to synch up the speed of the spindle.
Re: Spindle Speed Feedback and Accuracy
« Reply #8 on: September 18, 2017, 10:22:41 PM »
HI.
I have no idea, its your controller and you have the manual not me.

I think in the first instance I would check that the VFD can't close the loop, I would suspect you can.

Then look at the controller closing the loop. If it has analogue outputs at all in absence of the board/software
activation then they are likely to be 12 or 14 bit resolution, probably adequate. If you want the best the system
has to offer then you will want the 16 bit resolution of the fullblown controller at whatever expense for the analogue
upgrade.

I suspect there will be an adjustment that you could sync the spindle but what happens under load? The speed will
fall as sure as God made little green apples, without a closed feedback loop you can't avoid it.

You could avoid the expense of the Vital Systems upgrade to close the loop by having Mach do it with PMC. Require
some trick programming particularly if you want PID control...sounds like SERIOUS FUN...you poor sick little puppy!

Craig
'I enjoy sex at 73.....I live at 71 so its not too far to walk.'
Re: Spindle Speed Feedback and Accuracy
« Reply #9 on: September 19, 2017, 08:00:45 AM »
  Maybe Ill just leave that till later.......