Machsupport Forum
Mach Discussion => Mach4 General Discussion => Topic started by: dunnitagain on September 17, 2017, 01:59:24 PM
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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
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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.
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Hi,
and dead accurate speed control is important why?
Craig
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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 ) .
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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
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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
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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.
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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.
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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
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Maybe Ill just leave that till later.......
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Hi,
as it stands you have speed within 2% fast of nominal and as the load comes on and slows down it will get better before the load slows it to the
extent that the error grows on the slow side. Most operators would be delighted with that.
You may have noted in other posts I've made the claim that many, myself included, have spent way too much time on precise spindle speed control
when it's not necessary. I agree, get some work done with what appears already to be a very good setup and then make a decision whether further
investment of time and money is warranted. In my case I realised that improving my coolant system would've been a better use of my dollars.
Craig