Is Servomotor More Robust when compared to a normal motor? 2

[gustavosilvano]

Hello everyone,

I'm working on a project that requires the motor to reverse it's rotation over 20 times per minute. This will happen for over 5 minutes, but them it will stop for long time.

What I want to do is to untangle a bundle of rebar, where it wieghts of 2 tons.

My question is: is a servomotor with a servodriver more robust them using only a motor with a VFD?

Best regards.

Gustavo

 

[cswilson]

Many issues and questions here:

Can you even find a servo motor (permanent magnet brushless motor) large enough to provide the required torque for 5 minutes? This length of time gets you into the "continuous current" rating for a motor. A properly sized servo motor and drive should have the capability, but large (multi-kW) servo motors can be very expensive.

I don't see any way that a "traditional" (open-loop) VFD commanding an AC induction motor can come close to the required reversal every 3 seconds. At a minimum, you would need a VFD that is really a "sensorless vector" drive.

And it may very well require a full field-oriented control drive with a shaft encoder on the motor. This effectively controls an induction motor as if it were a large servo motor. Because your operation is high current and low speed, you would need a separately powered cooling fan in this situation.

Curt Wilson
Omron Delta Tau

 

[controlsdude]

So do you reverse directions based on a torque value(rebar jammed together causing some resistance on table)?
Maybe need some way to measure torque on the shaft of motor?

So oversize the motor by how much?
Then make the drive you use to be heavy duty rated drive.

 

[Compositepro]

From the video I cannot see much detail about the drive of the shaker. But from the motion, I would guess that there is a flywheel involved to store energy, and that the motion is reversed using clutches and gearing after the flywheel.

By the way, I just learned this little trick about YouTube videos from another post on Eng-Tips:
You can watch videos frame by frame by using the period to advance forward and the comma to go back. I've been wanting to be able to do that for years, and never realized that you could do that. Is this common knowledge?

 

[waross]

lps for the YouTube trick CP

Bill
--------------------
"Why not the best?"
Jimmy Carter