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Unread September 13th, 2019, 01:16 PM   #1
ganutenator
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Anyone a permanent magnet motor expert here?

I can't seem to increase torque to the desired level w/o the motor just sitting there shaking itself to death.
I can only get 80 foot lbs after the 30:1 gear box.
1/4hp motor
1/2 hp Toshiba drive
Auto tuned
Yes, the motor is rated at 239 inch pounds of torque. And after the gear box that equals 80 foot lbs, but come on.
Why does it shake itself to death when I raise the torque limit of the drive up from 200%?
The asynchronous motor had much better torque.
I thought IPM motors were supposed to produce more torque.
Was I mis-informed?
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Unread September 13th, 2019, 01:42 PM   #2
Phil Buchanan
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Sounds like it's not producing a smooth output in response to torque command and that's normally a feedback problem.

Can you run a trace on the output using the drive/drive software to see it's response to torque command changes? I possible that may show a clear picture of what's happening.
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Unread September 13th, 2019, 01:43 PM   #3
AustralIan
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This may be why it is shaking itself to death http://www.plctalk.net/qanda/showthread.php?t=121963
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Unread September 13th, 2019, 03:21 PM   #4
jaden
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I would question that a 1/4 HP motor is capable of delivering 20 Ft. Lbs (239 Ft Lbs.)
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Unread September 13th, 2019, 07:08 PM   #5
kamenges
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If you are getting 80 lb-ft of torque after a 30:1 reducer you are producing 2.67 lb-ft at the motor, or 32 lb-in. Even that is high for a 1/4 HP motor unless it is a higher pole count motor, something like 8 or 12 poles.

Is this a PM synchronous motor that you are running open loop?

Keith
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Unread September 13th, 2019, 07:19 PM   #6
jraef
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Has the Tosh drive been qualified to operate a PM motor? All of their newest drives like the AS3 and S15 are, but if you go back just one generation, they are not.
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Unread September 13th, 2019, 09:13 PM   #7
ganutenator
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I'm running it in PM mode
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Unread September 13th, 2019, 10:25 PM   #8
ganutenator
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It is actually running quite smooth. But the customer is concerned about the lack of torque.
It only becomes unstable when I increase the torque limit above 200%.
But that seems weird, because, at 200% it is producing 100% torque.
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Unread September 15th, 2019, 05:33 PM   #9
Gene Bond
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1hp, 1800rpm = 3ftlbs (36inlbs) of torque, so 1/4hp = .75ftlb (9inlb)... (assuming 1800rpm base speed)

x30 (for the reducer) = 22.5ftlb (270inlb)
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Unread September 15th, 2019, 05:43 PM   #10
ganutenator
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You all crack me up
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Unread September 15th, 2019, 06:28 PM   #11
Gene Bond
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What's the base speed of the motor? or pole count?
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Unread September 16th, 2019, 10:35 AM   #12
kamenges
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Quote:
Originally posted by ganutenator:

But that seems weird, because, at 200% it is producing 100% torque.
The motor is only going to draw what is required to control the load, on average, regardless of the torque limit. The instability when the torque limit is 200% is likely the result of having the torque available to actually follow the output of the velocity controller, which is tuned too tightly. If you require 100% torque to move the load and you are applying a 100% torque limit the drive is probably buried in torque limit and the tops are getting chopped off the velocity loop output.

Keith
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Unread September 16th, 2019, 03:31 PM   #13
AustralIan
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Does figure 3 help you?
https://library.e.abb.com/public/886..._lowres_v2.pdf

Figure 1 is probably the dol curve they're used to.
Does your motor manual/specsheet tell you any points on the torque curve?
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Unread September 17th, 2019, 06:52 AM   #14
Gene Bond
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Apparently none of us understand where the problem actually happens.

Is it when you overload the motor, or is it while you are running within the motor continuous rating?

IMO, running an open loop PM motor above 100% torque is asking for trouble. Closing the loop with an encoder (servo motor), 300% is no biggie. Open loop, you are running the motor as a stepper, and we all know what happens when you overload a stepper motor.
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Unread September 17th, 2019, 08:09 AM   #15
ganutenator
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Quote:
Originally Posted by Gene Bond View Post
Apparently none of us understand where the problem actually happens.

Is it when you overload the motor, or is it while you are running within the motor continuous rating?

IMO, running an open loop PM motor above 100% torque is asking for trouble. Closing the loop with an encoder (servo motor), 300% is no biggie. Open loop, you are running the motor as a stepper, and we all know what happens when you overload a stepper motor.
I guess the only problem is that the customer is concerned that it produces only 80 ft/lbs of torque after the 30:1 gearbox when the torque limit is set at 200% of the drive rating. (p.s. the motor and gear box claim that 80 ft/lbs of torque is 100% for the motor and gearbox)

The drive defaults to 250% for the torque limiting parameter F441 (Toshiba is calling that as being disabled). But, when I run the motor that way, it just tries to shake itself to death. When I remove the run signal from the drive, it doesn't stop (w/ parameter F441 at 250%) the drive. I have to power down the drive to get it to stop. Customer is worried about that too.

What does happen when you overload a stepper motor?

1800 is the rated rpm
The ipm motor has 4 poles.
The drive is 1/2hp, the motor is 1/4hp.
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