Adding a 4th axis spindle to my mill, servo troubles

Hi all,

I'm adding a spindle to my mill, just for small turning parts etc. I'm using the chinese AASD servo and drive but cannot get it to run correctly on my controller. The controller is a CS Labs IP/A unit.

It will run ok as long as speed is below say 2900 rpm but if i ask for full speed the controller faults on max following error being exceeded.

In Pid tuning you can jog the spindle at various speeds and below 2900 rpm the following error is low <100 as you go over that speed the counter just runs away until it faults and stops

JazzCNC had the same setup here...
https://youtu.be/tW8knRAOr7s

and it seems to run ok.

I also have these motors/drives on all other axes but the big difference is that they never run flat out as i have the motion tuned pretty low. I did take a motor off of another axis and connected it to this drive and it did the same thing so that points to the drive or controller??

Four pictures below of encoder channel A, at the controller, three at different speeds and one taken direct from the drive output with cable to controller disconnected.

I have no idea if these are normal or bad??

Its not a ground loop as the signal does change if i remove the shield connection.

Attachment 25806

Attachment 25807

Attachment 25808

Attachment 25809

Totally baffled.

Any suggestions?

Its not encoder related as far as i can see :(

I had a spare 600ppr encoder so wired that in and connected it by clamping in the spindle.

It still suffers the same fault, just slower as there are only 2,400 pulses instead of 10,000 per rev - the error count just goes up slower.

It still worked ok until 2980rpm.

What's the drives max speed, and analogue input scaling set to?

I'd guess most drives will default to 3000rpm, and 3000rpm at 10v.

Exactly that - 3000rpm, 10v.

300rpm/v

Quote:

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Originally Posted by Davek0974

Its not encoder related as far as i can see :(

I had a spare 600ppr encoder so wired that in and connected it by clamping in the spindle.

It still suffers the same fault, just slower as there are only 2,400 pulses instead of 10,000 per rev - the error count just goes up slower.

It still worked ok until 2980rpm.

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I am not sure but I don't think the motors will go above 3K

Yes but i can't even reach 3k when it should??

A hand-tacho seems to think its doing 3k but the controller error says its not?

BTW, the motor and drive will do 5k but only 3k for manuf specs ;)

Quote:

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Originally Posted by Davek0974

Exactly that - 3000rpm, 10v.

300rpm/v

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The drive is probably not seeing the full 10v. Try bumping the rpm/v up a bit

Tried that now, apart from altering either the top speed or the acceleration ramp depending on which way i tweaked the ramp, it made no difference at all - still get the increasing error count above 2990 rpm

Ok,

Using my bench PSU it was giving 2965rpm one way and 2971rpm the other.

It was also creeping with the inputs shorted out.

I ran the auto zero speed set function which killed most of the creep.

Then adjusted the gain to 305rpm/V

It now gives 3000rpm forwards and backwards.

Did it fix the issue?

No :(

A short video of the Pid screen at 2990rpm and 3000rpm

https://youtu.be/i7GEe7jAoY4

Motor slip ;-)
Most servo spindle controllers have a switch-over speed from Positional to Speed between 2000rpm & 3000rpm

But what can i do about it?

It should be covered in the user manual, parameter manual or commissioning manual for the drive.

Quote:

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Originally Posted by magicniner

It should be covered in the user manual, parameter manual or commissioning manual for the drive.

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Not with these drives, manual is chinglish i'm afraid

Sorry Dave, I only buy stuff with well written English Language manuals ;-)

What happens if you up rpm/v to 400?

There may also be a setting somewhere for maximum motor frequency.

In fact, I've just had a scan of the manual I have and notice the following paramters-
PN020 - Rated speed setting
PN051 - Motor top running speed limit
PN198 - Torque Control speed limit (should only apply in torque mode, but I assume you are using Speed Control mode?)

Quote:

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Originally Posted by m_c

What happens if you up rpm/v to 400?

There may also be a setting somewhere for maximum motor frequency.

In fact, I've just had a scan of the manual I have and notice the following paramters-
PN020 - Rated speed setting
PN051 - Motor top running speed limit
PN198 - Torque Control speed limit (should only apply in torque mode, but I assume you are using Speed Control mode?)

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Yes speed mode, I have tweaked..
PN158 - Gain
PN159 - Zero offset
PN051 - Top Speed

Will check PN020 - rated speed.

I think i listed what happened when i tweaked RPM/V or Gain setting - it altered the acceleration ramp one way and lowered the top speed the other way, both expected results really, I have it on 305rpm/V now which was determined with a bench supply at 10v and tweaked gain to give 3000rpm. It made no difference though.

Maybe the rated speed AND the max speed need to be slightly above where i want to run say 3010rpm? Just guessing here as this is going way beyond my knowledge but could it be the controller calling for 3000 and the motor never quite giving it hence the following error rise????

I think I have fixed it :)

Two parameters -

PN020 - Motor rated speed - this is set by default motor settings
PN051 - Motor Max Speed - this is a user adjustable one

PN051 Max was set at 3000 - i had tweaked this before but not the other one as it's a default setup one.

I have now set both to 3050rpm and away she goes :)

My working theory is that the controller was calling for 3000 but the drive was maxing out somewhere around 2990 - where it faulted so it was stuck in an endless fault loop - controller saying "I want more” and the drive saying “you can't have it”

Short video…

https://youtu.be/ksGlgcCWO4s

I think it makes sense??

Also in the video you can see it runs with a error of about 1980 - is that god, bad, ugly??

I can tune it but have not idea of tuning spindles - as said above, they are nothing like axes drives.

Thanks for all the help BTW.

What I meant was set rpm/v to something like 350 or 400 rpm/v so there is plenty headroom, just to eliminate the drive not seeing the full 10 volts. Due to various factors, the drive might never see the full 10V, so if you set a higher rpm/V, then the drive should max out long before 10V is needed.

What you are saying is roughly correct.
Mach requests 3000rpm from the controller, which then increases the voltage to achieve that speed, however the speed maxes out at 2990rpm despite the controller outputting maximum voltage, meaning you then have an ever increasing following error of 10rpm.


Have you checked what speed the drive thinks the motor is doing?
You can normally configure the drive to show motor speed on the display, and if you have a discrepancy between the drive and the controller, then there could be a totally separate issue.


Regarding allowable following error. As long as you're not doing positional work, then I wouldn't be too concerned. Being a couple revolutions away from commanded destination isn't likely to cause any issues when turning (thread cutting would normally work of actual position, not destination so the lag shouldn't cause any problems), however I would expect to be able to get position within a few hundred counts reliably.

Thanks. I did et a reply from CS-Labs shortly after posting, they did confirm that you cannot expect to pid-tune a servo to 3000 if its limited internally to 3000, they also advised, for the same reason to increase the gain to 400rpm/V - this was again to increase headroom and allow Pid to do its thing.

Its working now, error is about 2500 but thats because i only have P value set - seems adding any I or D causes issues, adding I seems to lower the error, i can get it down to about 200, but it makes it wobble at zero point and very unstable at speeds < 800 rpm, it gets very jerky at low speeds with I values.

I have set a following error of 8000 IIRC and its still working well, i even made a batch of parts for the first time today :)


BTW, the drive does report speed correctly, verified with a hand-tacho but it did not show voltage correctly, 10v applied showed as something like 9.89v i think it was