DIY Proof of Torque?

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W@ttson

W@ttson

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Torque proving is a common drive feature which helps with handling large loads. The drive senses and proves to itself that it can control the load and provide the sufficient torque, then it outputs a permissive saying that the torque proving function was complete and the brake can be released.

Is the drives built-in feature any better than just keeping the brake set, have the motor start up and take the current reading from the drive? Once the current gets to a certain threshold the brake is commanded to release?

They both accomplish the same thing, is one better than the other?
 
spraymax6 said:
Torque proving is a common drive feature which helps with handling large loads. The drive senses and proves to itself that it can control the load and provide the sufficient torque, then it outputs a permissive saying that the torque proving function was complete and the brake can be released.

Is the drives built-in feature any better than just keeping the brake set, have the motor start up and take the current reading from the drive? Once the current gets to a certain threshold the brake is commanded to release?

They both accomplish the same thing, is one better than the other?
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Current generally equates to torque, but there is a component of current that is used to magnetize the windings BEFORE any torque can be created. The Torque Proving algorithm in a Flux Vector Controlled VFD knows what that is and where in the sine wave that occurs, so it is separating the flux producing current from the torque producing current. Without that ability, you would be taking a shot in the dark.

Years ago I worked at Boeing on the overhead cranes that moved 747s, 767s and 777s around in the factory. We had a vendor come to us claiming that they could do torque proving for the hoist control without the need for an encoder feedback, which is what tells the drive the exact rotor position so that it knows how to flux the motor. Without that it's a SWAG, but they were claiming theirs could do it. We had 40 ton test weights that we used to test the hoist controls and drives (because using a 747 for a test was not a good plan), so we told this vendor that if they truly believed in it, we would lift the test weight, set the brakes, they could stand under it and we would release the brakes and see if their drive was going to work. They declined... Of course, Boeing would have NEVER let that happen, it was just a test of their confidence in it. But essentially when we were moving 747s down the assembly line, peoples lives and livelihoods were at stake whenever we released the brakes on the hoists. It's not something to fool with.
 
Jraef said:
Current generally equates to torque, but there is a component of current that is used to magnetize the windings BEFORE any torque can be created. The Torque Proving algorithm in a Flux Vector Controlled VFD knows what that is and where in the sine wave that occurs, so it is separating the flux producing current from the torque producing current. Without that ability, you would be taking a shot in the dark.

Years ago I worked at Boeing on the overhead cranes that moved 747s, 767s and 777s around in the factory. We had a vendor come to us claiming that they could do torque proving for the hoist control without the need for an encoder feedback, which is what tells the drive the exact rotor position so that it knows how to flux the motor. Without that it's a SWAG, but they were claiming theirs could do it. We had 40 ton test weights that we used to test the hoist controls and drives (because using a 747 for a test was not a good plan), so we told this vendor that if they truly believed in it, we would lift the test weight, set the brakes, they could stand under it and we would release the brakes and see if their drive was going to work. They declined... Of course, Boeing would have NEVER let that happen, it was just a test of their confidence in it. But essentially when we were moving 747s down the assembly line, peoples lives and livelihoods were at stake whenever we released the brakes on the hoists. It's not something to fool with.
Click to expand...
that is such a good point. magnetizing current could be something on the order of 30-40% FLA. On a 76A FLA motor, that is 23A - 30A, that is quite a bit of current to try and sense before releasing brakes.

So logistically, such an event where the motor gains its magnetization current but fails to produce its torque producing current is if there is a short in the cage or rotor windings of an induction motor. The stator would flux up and you would get your no load current but the interaction with the rotor would be diminished?
 
Jraef said:
We had 40 ton test weights that we used to test the hoist controls and drives (because using a 747 for a test was not a good plan), so we told this vendor that if they truly believed in it, we would lift the test weight, set the brakes, they could stand under it and we would release the brakes and see if their drive was going to work. They declined... Of course, Boeing would have NEVER let that happen, it was just a test of their confidence in it.
Click to expand...
Like having a bridge-maker stand under his work during the first load test.
 
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