Need Help! I cant seem to find a suitable AC servo drive!


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Thread: I cant seem to find a suitable AC servo drive!

  1. #1

    Default I cant seem to find a suitable AC servo drive!

    I am some months into a retrofit of a Mazak machining center with Centroid controller and have become stuck on driving the AC servo spindle motor.

    General googling suggested 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 an AC 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. DMM and ABB options are too small. Yaskawa, Delta, Mitsubishi all have special encoder interface. Digitax has no encoder ouptut to the Centroid controller, but maybe I could share the signals.

    The motor is a 200V,1.5kW nominal, 1.9kW 10 min 6000RPM Panasonic with 2500 PPM incremental encoder and hall commutation 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???

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  2. #2
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    Default Re: I cant seem to find a suitable AC servo drive!

    I don't know much on servos. I just bought a 1.8kw servo set for my benchtop mill.
    Anyway. Have a look at this manual to see if it's an ok match.
    http://servo.xlichuan.com/Private/Pr...6713131150.pdf
    Prob the 2.3kw version:
    https://www.aliexpress.com/item/33054202186.html




  3. #3
    Community Moderator Jim Dawson's Avatar
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    Default Re: I cant seem to find a suitable AC servo drive!

    Trying to mix & match servo motors and drives is more hassle than I would be willing to go through, especially one that is designed to be Hall commutated.

    I guess I would replace the motor with a 3HP standard 3 phase motor and just run it with a standard sensorless vector VFD. Many small 3 phase motors are rated up to 6000 RPM max, at least the 4 pole Baldor on my mill is, I have seen others that are rated at 4500 RPM max. And yes, you can rigid tap with that setup, I'm doing it on my lathe as I'm typing this. Indexing for a tool change, if needed, can be done with a shot pin.

    Jim Dawson
    Sandy, Oregon, USA


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    Default Re: I cant seem to find a suitable AC servo drive!

    Hi,
    bought a new old stock AC servo as a spindle motor a couple of years ago. It is a 3kW Vickers servo from the mid 90's, and is a perfect fit for what I want.
    Downside is that it has a resolver rather than an encoder. Resolvers are fine, they lack the angular accuracy that you might get with an encoder but they are very rugged.
    Like you, I found when I tried to find a drive to operate it, what few I could find were really expensive.

    Electronics is my thing and so I elected to make one. It has turned into a hobby project all on its own.

    The real point is that with modern micro-controllers like the Texas Instruments TMS320F28069M, which is a fast 32 bit uP with single cycle floating point maths
    and vast array of periphials tailored for Field Oriented Control of motors it not as hard as you might believe.

    Using the C2000 development board (that has the processor above) I've made my own resolver to digital converter and that feeds into the Field Control
    algorithm. I've had it running as a free running motor wit 0-10V analogue input. I was always going to make it position control capable....but have just never got around
    to that part.

    No doubt that if you wanted all the bells and whistles that come with a commercial drive....that would be a huge undertaking. But a simple PID controlled position capable
    Field Control is not out of the way.

    Craig



  5. #5

    Default Re: I cant seem to find a suitable AC servo drive!

    Quote Originally Posted by joeavaerage View Post
    Hi,
    bought a new old stock AC servo as a spindle motor a couple of years ago. It is a 3kW Vickers servo from the mid 90's, and is a perfect fit for what I want.
    Downside is that it has a resolver rather than an encoder. Resolvers are fine, they lack the angular accuracy that you might get with an encoder but they are very rugged.
    Like you, I found when I tried to find a drive to operate it, what few I could find were really expensive.

    Electronics is my thing and so I elected to make one. It has turned into a hobby project all on its own.

    The real point is that with modern micro-controllers like the Texas Instruments TMS320F28069M, which is a fast 32 bit uP with single cycle floating point maths
    and vast array of periphials tailored for Field Oriented Control of motors it not as hard as you might believe.

    Using the C2000 development board (that has the processor above) I've made my own resolver to digital converter and that feeds into the Field Control
    algorithm. I've had it running as a free running motor wit 0-10V analogue input. I was always going to make it position control capable....but have just never got around
    to that part.

    No doubt that if you wanted all the bells and whistles that come with a commercial drive....that would be a huge undertaking. But a simple PID controlled position capable
    Field Control is not out of the way.

    Craig
    Haha, I am also an electronics engineer. I did contemplate making one. I also have the original Mazak power amplifier that I could use as a base by throwing a micro or FPGA onto it. But the reality is for me that I don't want this project to take much longer, I just want my mill going again! I have other projects I would rather sink the time into. Although I did think that it would be a good project in the future to do and open source it for others that are stuck in this same hole!



  6. #6

    Default Re: I cant seem to find a suitable AC servo drive!

    Quote Originally Posted by Jim Dawson View Post
    Trying to mix & match servo motors and drives is more hassle than I would be willing to go through, especially one that is designed to be Hall commutated.

    I guess I would replace the motor with a 3HP standard 3 phase motor and just run it with a standard sensorless vector VFD. Many small 3 phase motors are rated up to 6000 RPM max, at least the 4 pole Baldor on my mill is, I have seen others that are rated at 4500 RPM max. And yes, you can rigid tap with that setup, I'm doing it on my lathe as I'm typing this. Indexing for a tool change, if needed, can be done with a shot pin.
    Swapping out the motor is a little tricky mechanically. I also have a perfectly working motor already mounted and wired so a waste to replace it. I have options for drives but they are much more expensive than I was hoping for! Hall commutation is not a problem, it is just there to allow the driver to know motor position before it moves. The position feedback is in incremental encoder.



  7. #7

    Default Re: I cant seem to find a suitable AC servo drive!

    Quote Originally Posted by dazp1976 View Post
    I don't know much on servos. I just bought a 1.8kw servo set for my benchtop mill.
    Anyway. Have a look at this manual to see if it's an ok match.
    http://servo.xlichuan.com/Private/Pr...6713131150.pdf
    Prob the 2.3kw version:
    https://www.aliexpress.com/item/33054202186.html
    After looking at the manual, these are pretty interesting. It has all the wiring connections I want except analog output and supports the encoder I have. Unfortunately the manual does not have an specs for actual current ratings or any settings for configuring the number of motor poles. It also doesn't say what the maximum output frequency it has. Seems odd that they offer 200 to 2600W in the same physical package. I am guessing it is the same hardware with different settings to suit the ratings of their motors. At the price it is almost worth buying one and seeing if it works! I suspect given the physical size that it is China rated and probably couldn't deliver 2.6kW but....

    I would be interested in hearing more about the specs of your motor, number off poles and max RPM you can get out of that drive if you have tested it.

    Thanks for the suggestion.



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I cant seem to find a suitable AC servo drive!

I cant seem to find a suitable AC servo drive!

I cant seem to find a suitable AC servo drive!