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How to use closed loop spindle rpm with SS
« on: October 20, 2010, 05:37:12 PM »
Hi guys,

I've got my spindle operating in PWM output mode from mach3 with SS, and I have an opto-interrupter reading from a single gap wheel for rpm feedback to mach3. I can control rpm from within mach3 and I see a readout show up. Currently I'm trying to setup closed loop operation but I'm unable to make it do anything (it's just ingoring any settings in the section). Any suggestions where I can try to look? or does the SS not support closed loop right now?

Thanks

Offline Jeff_Birt

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Re: How to use closed loop spindle rpm with SS
« Reply #1 on: October 21, 2010, 10:47:19 AM »
I suspect you really don't want closed loop operation. What you are likely after is Mach syncing with the spindle speed. Look at the Spindle tab in Ports&Pins.
Happy machining , Jeff Birt
 
Re: How to use closed loop spindle rpm with SS
« Reply #2 on: October 21, 2010, 11:58:00 AM »
Yeah, I've tried every combination of those checkboxes under spindle setup and mach just ignores them, or at least I see zero effect.
spindle rpm will show 2500 in the DRO for example but mach has been asked to do 2000 and I see zero adjustment in pwm to get it to match.

Eugene

Offline Jeff_Birt

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Re: How to use closed loop spindle rpm with SS
« Reply #3 on: October 21, 2010, 12:05:46 PM »
OK, that is not closed loop either :) It is just PWM output.

There was a post a few weeks ago here about getting PWM running properly. I'll see if I can find it later and link to it here.

Here is the link: http://www.cjh.com.au/PWM%20Spindle%20Control%20using%20Mach3.pdf

« Last Edit: October 21, 2010, 12:10:04 PM by Jeff_Birt »
Happy machining , Jeff Birt
 

Offline thosj

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Re: How to use closed loop spindle rpm with SS
« Reply #4 on: October 21, 2010, 12:23:44 PM »
So what this boils down to is there is no way in Mach to control spindle speed with the index signal? Or am I missing it?

The doc linked by Jeff talks about tuning spindle speed and stuff, but I don't think it mentions if we can actually adjust the spindle speed to the index signal. I guess that is "closed loop" and it simply doesn't work. It seems that if one has an index signal to Mach, Mach should adjust the spindle PWM to achieve the commanded S RPM.

My problem is if I have a pulley setup, say Pulley 7, to 300-3000 RPM, at 2000 I'm pretty close, but at 1000 I'm low and at 3000 I'm high. If we can't have index feedback for spindle speed, what's the correct way to adjust linearity? I've read to delete linearity.dat and not use Calibrate Spindle. Is there a way to get the linearity better?

All PWM control with SS is done in SS settings, right? Mach settings ignored?
Re: How to use closed loop spindle rpm with SS
« Reply #5 on: October 21, 2010, 12:30:11 PM »
That's precisely my problem, DC motors are by nature not linear. So there needs to be some way of adjusting pwm linearity not just max/min like the doc you linked to suggests. I tried to use the caibration screen but as soon as I click AutoCal my spindle turns off and mach goes into an EStop condition and calibration stops, not sure if that's because AutoCal thinks it's done and just powers off the spindle (having not done anything) or if something is screwy because i'm using an SS.

My original question was same as one from thosj, the index signal doesn't seem to "correct" mach 3's pwm output based on the actual rpm being reported vs rpm requested.

btw, thanks jeff, I've actually read that doc you've linked, and there was a lot of info in there that I needed to get this far. :)

Offline Jeff_Birt

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Re: How to use closed loop spindle rpm with SS
« Reply #6 on: October 21, 2010, 12:46:46 PM »
Actaully, DC motors ARE quite linear in speed w.r.t. input voltage. Speed controllers and/or PWM to voltage circuits are not linear many times though. If you set it up open circuit does mach's PWM output change in response to your commanded speed?
Happy machining , Jeff Birt
 
Re: How to use closed loop spindle rpm with SS
« Reply #7 on: October 21, 2010, 01:01:54 PM »
Yeah, well, they're pretty linear, but not perfectly, and that's true, my error could be anywhere in the system, as i'm using an SS -> G540 -> KBMM-125 (motor speed control)  -> motor.

I can control motor rpm within mach 3 with the S word, but the motor rpm is never what I actually want, it's correct at around 1800 rpm, but then at s3000 actual rpm is like 6k and at s1000 actual is like 340 so there seems to be a pretty epic curve. I'm using an ac/dc motor with a max rpm of 30k, i believe it was removed from a vacuum cleaner it doesn't have permanent magnets, but rather a coil.
Re: How to use closed loop spindle rpm with SS
« Reply #8 on: October 21, 2010, 01:06:20 PM »
Guess I should give a little more background here, I know for a fact that my G540 outputs its 0-10v vfd signal non linearly, as in when I request s2000 I get 2.4v and when I do s1000 i get 1.6 which is WAY off, and then when I do s3000 I get 3.8v.

I'm going to put a scope on my setup and try to determine if my PWM is possibly incorrect coming out of the SS, or maybe I have excessive noise feeding back from the KBMM-125.

My question was really a more theoretical, in a situation like this, true closed loop control would be able to adjust out all of this error and dial in the correct speed via the PID algorithm, but I've till now been unable to get the adjustment to happen at all.

Offline Jeff_Birt

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Re: How to use closed loop spindle rpm with SS
« Reply #9 on: October 21, 2010, 08:39:36 PM »
I think maybe you have configuration problems. I have had the G540 VFD out hooked up to a KBIC and I seem to recall it was not more than 100 RPM off all along the scale. Do you have the tach sensor on the motor or spindle?
Happy machining , Jeff Birt