Stop an AC motor an a specific position?

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Danny89

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Happy holidays everyone. I'm scratching my head wondering how to stop an AC motor at a certain point. Would an encoder accomplish this? If so what kind.
Another way I think this could be stopped is somehow with a drive

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Danny89 said:
Happy holidays everyone. I'm scratching my head wondering how to stop an AC motor at a certain point. Would an encoder accomplish this? If so what kind.
Another way I think this could be stopped is somehow with a drive

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Click to expand...

it might help if you explain what you are trying to accomplish.
 
Its a tumbler machine I want the motor to stop when the shaft is at a specific point so that I don't have to constantly jog the machine to load and unload the barrels.

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First thing I thought of:

the-price-is-right.jpg


Seriously, though, is there a way to do a clutch so after it stops you can manually (maybe even with a crank if needed) rotate the assembly to the desired point, instead of jogging?

What's your tolerance? Meaning, do you need to be very exact, or is there a window of several degrees where stopping anywhere in there is acceptable?
 
You need braking of some sort and a means to determine how far the drum will continue trying to turn from inertia in the system. With a VFD capable of dynamic or regenerative braking and the right information you might be able to pull it off with a simple limit switch and some ladder logic. An encoder would require some advanced motion control programming capability.

Without a VFD this could be extremely difficult to pull off consistently, which is why most people resort to jogging / inching it into position. But that also depends on the turn-down ratio involved. If for example your drum turns at 1.75RPM and the motor spins at 1750RPM (a 1000:1 turn-down ratio), it could be easier to pull off than with a 100:1 ratio.
 
It would really help if you described the whole thing instead of giving us bits and pieces.

We only know-
it's a tumbler, holds 100 pounds of ???, has an on/off switch (but we don't know if that's a simple switch or controls a motor starter)

among other things, we don't know-
motor size and gearing/turn-down ratio
drum size
how often it gets loaded/unloaded
does it need to stop in multiple positions (load and unload stops are different)?
does it always turn the same direction or does it need to reverse?
environment (dirt, dust, wet, etc) which could affect things like encoders or cams
 
zbang said:
It would really help if you described the whole thing instead of giving us bits and pieces.

We only know-
it's a tumbler, holds 100 pounds of ???, has an on/off switch (but we don't know if that's a simple switch or controls a motor starter)

among other things, we don't know-
motor size and gearing/turn-down ratio
drum size
how often it gets loaded/unloaded
does it need to stop in multiple positions (load and unload stops are different)?
does it always turn the same direction or does it need to reverse?
environment (dirt, dust, wet, etc) which could affect things like encoders or cams
Click to expand...
I agree. You can achieve very precise position control and the more precise the greater the cost generally.

My guess is that this application doesn't need the precision required by a machine tool drive if it can be jogged into position.
 
181226-1318 EST

Danny89:

You need to learn how to ask the correct question(s). Several posts have tried to stimulate your thought on questions to ask, and/or informa6tion to provide. Specific information is needed that you are not providing.

My guess is that an electro-mechanical brake with some control circuitry might do what you want.

From years ago a DC 1000 #-ft clutch could de-energize and release in about 100 milliseconds. Back then the clutch alone was about $1000. Clutches and brakes are about the same thing in function and timing.

Whether you can use a bang-bang system, on-off, or need a servo systems depends upon response time, and accuracy.

You need to think about details and provide more information.

.
 
How about a simple switch located on the drum or shaft that is set so that it opens the motor starter circuit when you put it in the auto-stop switch position and it coasts down to almost where you want it (to minimize the jogging). Possibly even a couple of set-ups like that so you could choose depending on the drum load (if it doesn't always have pretty much the same momentum).
 
Right now I have it programmed to mix for 15 minute once the maintained on off switch is turned to the on position. After the the 15 minutes the motor contactor opens and the motor stops turning.
I don't have motor nameplate data at the moment.

Just trying to find a simple solution to establish a home position so that I don't have to constantly jog the machine to get it in the correct position for loading and unloading the barrels.

Thought a rotary encoder could possibly work.

It's a polyphase ac motor.
Is it ok to put a drive on a motor if it is not a inverter duty motor?

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