Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: keithmech on April 10, 2009, 05:53:00 PM
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Has any one checked the 0-10 volt signal output from a breakout board that has a speed control
for controlling a vfd?I checked mine and the output bounces around .It will change from say .105-.115.
This may not sound like much but at very slow speed it causes the spindle to pulse.At higher speeds it causes the gears to chatter.
This goes away at about 1 volt but at this point it is friction in the system , the voltage still bounces around.
Is this normal or can I have something set wrong?
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Hi Keith,
A couple of things. The reason that their is ripple on the 0-10V control signal is most probably due to ripple on the power supply feeding the 0-10V control circuity. Less ripple should produce a more stable signal.
More importantly, it sounds like the acceleration parameter the VFD is too hi. If you reduce the acceleration parameter, the speed fluxuations should be smoothed out and a steady peed should be the result.
Cheers,
Peter.
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You could also be seeing some issues with phase jitter from the pulse stream being generated by Mach. Some PCs will do better than others. You didn't say if you were using a Step/Direction signal to drive the VFD or PWM. If you have an O-scope you can take a look at the pulse stream from your LPT. If you don't have an O-Scope listen for small popping sounds as an axis accelerated. In my experience these are caused by phase jitter. If your LPT cable is really long it could cause problems like this too.
You could also have an issue with electrical noise. This could come from how cables are run etc.
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I tried adjusting the accel on the vfd.no real change.I'm using a smooth stepper.
The signal wire from the bob to the vfd is only about 12" and is shielded and grounded at one end.
I have a couple of other machines with Mach control so I'll see what happens if I lower there speed
real low.This may point to the pc.
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looks like Jeff maybe right.I tried lowering the speed way down on another machine
and no pulsing.I'm at .5-.8 hz.I'll order a new motherboard and go from there.
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You might try an add on PCI->USB card. They are pretty inexpensive...
I just saw you said you were using a SS. I seem to recall that some folks are having an issue with the SS and S/D or PWW spindle control. I would also take a look at the power supply like Peter suggested.
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Well I replaced the motherboard with a new one ,same as my other machines.Same thing.
Any way to "smooth out" the 0-10 vdc signal between the bob and the vfd?
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What make of VFD do you have? It should be possible to adjust the accel parameters in the VFD as long as the signal isn't too unstable.
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I'm using an AC Tech SMV.
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Ok. I'm not familiar with those. Danfoss VFD on the other hand....... ;)
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My first controller fluctuated all over the place. I gave up on it and got a board from Homann and it was better, but still fluctuated too mych to be usefull. I tried every suggestion to resolve it including setting up the breakout and speed controlers on a new computer in my office and just runing it with a voltmeter attached. The wires were literally only inches long and there were no machine tools anywhere around. Still fluctuated.
Peter was kind enough to send me one of his new design controllers and breakout boards to try.
These things are awesome! The controller is PWM and it the control voltage it puts out is dead steady . . at leaste in my nice quiet office on a new computer. Honestly I was afraid when I got it down on the old battle axe computer next to the mill, it would be fluctuating again.
I was just waiting for a second parallel port for the computer to arrive and and I just got it hooked up today on the machine tool. Still dead steady on the volt meter AND The spindle motor finally runs nice and steady!
Happy camper here. Highly recommend Homanns new stuff . . and I rarely endorse anything.