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Author Topic: AC servo for spindle  (Read 1618 times)

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Offline derek

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AC servo for spindle
« on: October 25, 2014, 11:01:32 AM »
Hi
I'm thinking that switching over to an AC servo for my spindle.
This is on my knee mill. The things I'm trying to accomplish are:
Spindle indexing for ATC
Rigid (tap to an accurate depth) tapping
Torque over a wider range than I currently get from my VFD.

If I do a straight conversion from the 2hp motor to KW it's 1.5KW. But since AC servos have more torque at a lower range do I really need 1.5KW.

Most of the AC servo drives and motors I see are in the 2000-3000 rpm range. I run spindle speeds up to 6000 RPM so there will be a loss of HP there.

I know a few of you run AC servos for spindles and I'm looking for real world feedback.

Thanks
Derek

Offline Hood

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Re: AC servo for spindle
« Reply #1 on: October 25, 2014, 02:03:17 PM »
Ok a few things to consider.
First is increasing the ratio will not change the HP but it will change the torque.
You say you have a 2HP motor at the moment, how is it geared? Do you change pulleys for different speeds or do you just use the VFD and keep the pulley ratio constant?
Is it powerful enough at the moment the way you use it?

Now spindle indexing, that will likely be possible but will depend on the controller you use, ie external or parallel port and if external which one.
Rigid tapping again will depend on the above.
Torque is more constant with an AC servo than an induction motor/VFD.

Hood

Offline derek

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Re: AC servo for spindle
« Reply #2 on: October 25, 2014, 02:32:30 PM »
Hi Hood
right now I'm overdriving the 1725 motor at 120hz with a 1.75:1 ratio so I get around 6000 rpm. Down low is where I need the most torque for drilling and tapping and that combo seems to work well. I never change the pulley.

I'm using the UC-300 motion controller and it doesn't offer rigid tapping so I figured on doing some sort of swap axis kludge. I would also do a swap axis for the indexing as well.

Thanks
Derek

Offline Hood

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Re: AC servo for spindle
« Reply #3 on: October 25, 2014, 02:39:26 PM »
Well if the motor you have at the moment has enough torque then a similar sized servo would be adequate.
I dont think I would go smaller if possible, I would try to keep things about the same.
On the Beaver mill I have a 4000RPM  3.5Kw SERVO and it does well, it is probably more than needed but I like to be safe.

Does the UC300 support SwapAxis()  ?
If it does then you should have no problems at all, if it doesnt then you will have to ask them if they would consider adding it as it is a function of the controller if not using the Parallel Port.

Hood

Offline derek

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Re: AC servo for spindle
« Reply #4 on: October 25, 2014, 02:52:14 PM »
Thanks hood I'll check into it.

Derek