AC Servo Drives - Driving me nuts!

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ashesman
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AC Servo Drives - Driving me nuts!

Post by ashesman »

So, I am now five months into my mill conversion and feel like I am banging my head against a wall! Everything has been easy enough except motor drives!!! It seems the problem is me not wanting to replace my perfectly fit for purpose AC servo motors, particularly my 6000RPM AC servo spindle motor.

I have chosen and purchased DYN4 drives with their special encoder adapters for the X, Y and Z motors. There have been some teething issues with them but support is good and they are getting it sorted.

I followed all the suggestions around using a VFD for the spindle motor. I have tried two VFDs, both designed for permanent magnet motors. Sure they can run the motor at high speed but that's about it. At low speed they stall and jerk, most likely due to lack of encoder input. They have so little torque at 200 RPM that you can stop the spindle with one finger! I have spent months with ABB support and in the end they finally said, no, you need an AC servo drive. I kind of knew that all along but the internet said a VFD that does PM motors would do. They are much cheaper so I gave it a go.

Anyways, so now I need a servo drive for the spindle motor. Seems easy enough but I just cant find one that suits. The biggest issue is that most use a proprietary serial encoder signal and don't support incremental encoder input.

They only option I have found is from Kollmorgan which is pretty pricey. More than the oak and all three DYN4s combined! Metronix might also be an option but I never get a reply to my request for quotes. ABB options are too small. Yaskawa, Delta, Mitsubishi all have special encoder interface. Digitax has no encoder ouptut to the Oak, but maybe I could share the signals.

Does anyone know of a servo drive that is at least 2.2kW output power, 15A output, 200V 1/3 phase input, incremental encoder input, emulated encoder output, analog input, analog output, min 400 Hz output???
cncsnw
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Re: AC Servo Drives - Driving me nuts!

Post by cncsnw »

Have you looked at Glentek?

You would have to research the specifics to see if they have one that meets your requirements, but I am pretty sure they make analog velocity-mode AC servo drives that work with incremental encoders.
BodeRacing
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Re: AC Servo Drives - Driving me nuts!

Post by BodeRacing »

I would not give up on the VFD yet. What model are you using? I worked on a sheeter one time that had a servo motor with a VFD on it. Maybe 150 hp. The VFD failed and we needed to replace it. The motor and original servo drive were originally a matched system from Indramat, and Indramat will NOT give you any motor information. They are known for not giving out information.

When the original servo drive died, some smart individual put a standard VFD on it and made it work. When this VFD died, the plant installed I think 3 or 4 different brand VFDs, and one more after I got there. After 2 days, we gave up and bought a Reliance RPM AC motor (low inertia AC induction motor).

But I'm a lot smarter now. And it was just that we did not have the proper magnetization in the motor.

Tell us what you have and how it is programmed and maybe we can make it work. I work with a couple ex-ABB drive field service engineers. Technically I'm a motor guy now, but still know a lot about drives.
ashesman
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Re: AC Servo Drives - Driving me nuts!

Post by ashesman »

I still have an ABB ACS355 at home. I spent a lot of time on it. I think it could do the job if I didnt want stable low speed performance and full torque at low RPM. It needs to be able to do rigid tapping. It has basically no setting for motor information except power, rpm etc.. It relies on the motor to do an ID run to characterise.

I have most of a full set of motor data from here and there.

The original controller was Mazak special. 75 Amp peak so quite grunty and large.

I may talk to the abb guy and see if they have an encoder interface I can borrow to test. To be honest I am getting over mucking around and want to buy one that will just work. I am really struggling to create a control system that is better than what mazak did 25 years ago. Although to be fair I am trying to keep costs down!

If I did it again I would definitely look into a modular common DC bus system rather than all the odd parts.
ashesman
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Re: AC Servo Drives - Driving me nuts!

Post by ashesman »

cncsnw wrote: Fri Apr 09, 2021 5:38 pm Have you looked at Glentek?

You would have to research the specifics to see if they have one that meets your requirements, but I am pretty sure they make analog velocity-mode AC servo drives that work with incremental encoders.
Never came across Glentek. I will look into it tonight. Thanks...
ashesman
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Re: AC Servo Drives - Driving me nuts!

Post by ashesman »

So, this is still driving me nuts!

I have come up with some more options. Still waiting to hear back from Glentek. They look promising. Dont know how I didn't fins them in a month of google searching!

So far Kollmorgan at $2000 USD is the only sure bet I have found. But then you come across things like this that look like they could possibly do the job! https://www.aliexpress.com/item/33054202186.html. But, no concrete technical specs available. Has all the right inputs and outputs (except analog out, but I could make something that uses the RS-485 to make an analog output!). I suspect based on the physical size that it is 'Chinese power' rated. They don't actually give the actual current ratings for it!

Anybody tried these low cost servo drives?
martyscncgarage
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Re: AC Servo Drives - Driving me nuts!

Post by martyscncgarage »

Could you please continue to post in your BUILD LOG. It keeps us from trying to remember who you are and what you are working on.
I would have probably pulled that spindle motor and replaced it with a 3 phase spindle motor and quality VFD with encoder input.
Easy to make 3 axis move, spindle motors followed by ATCs make these builds more complex....
Scary you are considering throwing $2k at it and not sure it will actually work.....
Continued luck!
Marty
Reminder, for support please follow this post: viewtopic.php?f=20&t=383
We can't "SEE" what you see...
Mesa, AZ
ashesman
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Re: AC Servo Drives - Driving me nuts!

Post by ashesman »

martyscncgarage wrote: Tue Apr 13, 2021 11:25 am Could you please continue to post in your BUILD LOG. It keeps us from trying to remember who you are and what you are working on.
I would have probably pulled that spindle motor and replaced it with a 3 phase spindle motor and quality VFD with encoder input.
Easy to make 3 axis move, spindle motors followed by ATCs make these builds more complex....
Scary you are considering throwing $2k at it and not sure it will actually work.....
Continued luck!
Marty
I dont want my build log full of general banter. I have left it on purpose so it will be a concise forum just about how i actually solved the problems related to that machine incase one day someone else needs to convert one.

This thread is specifically about drives and where to get them.

The 2k option is not a guess it will work for sure. But yeah, fricken expensive. I also couldnt find a suitable motor that does 6000 rpm and will fit in the gap on the machine for any less than that drive.
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Re: AC Servo Drives - Driving me nuts!

Post by slodat »

Have you looked at Yaskawa spindle motors? I know they are not cheap, but used ones are plentiful and they have the kind of characteristics you are looking for. I'm powering the one that came in my mill with a Hitachi SJ-P1 drive and it's working well.
ashesman
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Re: AC Servo Drives - Driving me nuts!

Post by ashesman »

slodat wrote: Tue Apr 13, 2021 5:08 pm Have you looked at Yaskawa spindle motors? I know they are not cheap, but used ones are plentiful and they have the kind of characteristics you are looking for. I'm powering the one that came in my mill with a Hitachi SJ-P1 drive and it's working well.
Thanks for the suggestion. I dont have my notes with me right now but I am pretty sure that Yaskawa drives require a special serial encoder protocol and dont support incremental encoders. I think the Hitachi drives were the same.

If you have a model number that does work with incremental encoders then I will definitely check it out.
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