Inverter drive oscilates holding a load

DickDV said:

Pierre, I've been watching this thread with interest and would like to help you find a solution to your problem. I suspect that the drive is not defective but maybe programmed less than optimal.

My first question about the data: Are you sure the winding drum is 6 inch circumference? Is it possibly 6 inch diameter?

Second question: You have 200 lbs you need to lower in a fixed period of time. Can you give us the distance traveled and the amount of time to make that move?

Third: Do you have a means of displaying or monitoring the DC bus voltage while lowering the load? If yes, can you tell us what the voltage is doing when the motor starts to oscillate?

Finally, just an observation. I suspect that you are bumping up against some kind of braking capacity limit. I say this because, as you increase descending speed, you also increase the braking hp. It seems that a limit is reached around 15hz and the oscillations begin.

Please advise above requested data.

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We are going there tonight for a try. This system works once a day. Goes down.... rotates for 3 minutes, then goes back up. The End.


Its really 6 inches cir. every turn the cable goes down 6 inches.

200 pounds going down 40 feet in 15 seconds. Thats what they want anyway... it might not be what the system can give them... its about 180 feet per minutes... 42 HZ ...

What the DC buss is doing while oscillating load... I will check this during our tests tonight.

''limit is reached around 15hz and the oscillations begin.'' Hard to tell... If we run this below 10 HZ... it slip to the floor BOOM!. With the resistors, we have not checked which is the failure limit. We only know that we need to go to 15 HZ fast... we tried a 30 seconds accel going up and it failed... no on DC Buss overvoltage... the load just slipped back down... we hit the EM switch hence cannot give any good data on what happened. We only know that we did not have a DC OV alarm.

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Tonight we will boost the Torq to 15% and switch its control mode to sensorless vector. We will do an auto-tune on the drive prior to testing the SV control.
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I have to mention that this system was sized by a major companie. The 2 HP was there idea. It was to be sufficent. But us we have notice that going UP at 15 HZ... we see 4 Amps... the motor should be pulling no more than 2.85

This is not a perfect setuyp but the limitation in siz and space was very hard to accomodate.

Yes we stress the motor but we do it only 30 seconds a day... the rest of the time it can sleep

So that you and others can see how I have analyzed the sizing of the components in this system, I present the following:

Max weight on the cable is 200lbs
Max speed on the cable is 40ft in 15sec.
40ft in 15sec is equal to 160ft in 1minute (multiply both by 4)
At 6in or .5ft per drum revolution 160ft/min equals 320 drum rpm.
At 6in circumference, the dia = 6/3.14 = 1.91in and the radius = .96in
.96in = .96/12ft = .08ft
200lbs on the cable equals 200lb x .08ft = 16ft-lb torque on the drum shaft
Max drum hp = t x rpm/5250 = 16 x 320/5250 = .98hp
Max torque at motor with gearbox ratio of 5 is 16/5 = 3.2ft-lb
Max speed at motor with gearbox ratio of 5 is 320 x 5 = 1600rpm
2hp 4 pole motor at 60hz produces 1750rpm which exceeds 1600rpm needed
2hp 4 pole motor produces 2 x 5250/1750 = 6ft-lbs torque which exceeds
3.2ft-lbs needed
Conclusion: Motor is big enough for the application

Now, looking at the brake resistors:
Max braking hp = drum hp/gearbox efficiency = .98/.94 = 1.04hp
1.04hp x 746 = braking power in watts = 776watts
Brake resistor is rated 300w continuous which equates to ten times that when cold and being heated less that 20 seconds.
Max watts possible in resistor = 740VDC x 740VDC/300ohm = 1825watts
Conclusion: Brake resistor adequate for application

It is clear to me that the motor and brake resistor are sized large enough to handle the application. As long as the drive covers the motor Full Load Amps plus at least 10%, that leaves the programming and drive control limitations.

Recommendations:
First, set up the drive for sensorless vector control and tune up the speed loop for reasonably tight speed regulation using P and I gains.
Second, be sure the DC bus overvoltage controller is turned OFF in the software. This feature automatically increases the speed or extends the decel ramp when the DC bus exceeds its voltage limit. When a brake resistor is used, this must be turned off.

Ignore my earlier comment about binding in the power train. It doesn't apply in this application.

Hope some of this helps.

Pierre said:

Please, being french ... I do not understand ''binding''.

Can you elaborate?

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Gears and other mechanism runs smooth and OK in one direction but not in the other direction. Double check to ensure the gearbox is reversible. If it is not a shaft may be rubbing against the housing.

Gear lash ie "looseness"?? in gear train problem would be seen when you stop lifting and reverse. You would see the drum "jump" ie move for say 1/8 turn suddenly. This does not fit your description.

The other thing Pierre is I wonder if you are winding the rope on the drum evenly. IF not then as you unwind the rope may come off a "lump" and be slack for half second. This does not sound like your problem though. But I would double check - with 200 pounds load you do not need excessive wire rope wear and uneven winding will result in this.

Dan Bentler

DickDV said:

Recommendations:
First, set up the drive for sensorless vector control and tune up the speed loop for reasonably tight speed regulation using P and I gains.
Second, be sure the DC bus overvoltage controller is turned OFF in the software. This feature automatically increases the speed or extends the decel ramp when the DC bus exceeds its voltage limit. When a brake resistor is used, this must be turned off.

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Very good points.

Ron

pierre, sounds like your end user changed things up on you:

Its not an ideal setup. We where first asked to be on a fast-track limited budget project and the poo it the fan.

At first the load was to be insignificant... but its not.

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have you thought about having them install some counter balance to the load?
I think line reactors would help some. I have no experince with your brand of drive but i have moved loads heavier with other drives without the use of brake resistors.
I hate it when I am given the wrong specs and a low budget.
also does the load change going up or down? I mean is weight added or subtracted
at the top. and is there a safety brake involved in the process? or is the motor and drive all that hold the load in place when stoped?

The end of the universe

OK, now the gran finale...

We where there last Friday. At 6PM. Waited 'till 9 to be able to access this system.

First, we checked the Torq boost setting. TYhey where at ZERO, so none of it. Then we had the Drive calibrate itself for Sensorless vectoring... at stop it analises what the motor shows.

That done, where entered the specs of the motor and initiated the control mode.

Then we tried it.

Its hard to see all there is to see but we did notice the DC bus being at 655 Volts at stop and climbing to 764-765 during the descent.

We lower this about 10 feet out of the 40 feet and stopped.

It looked to me that it was not improving anything yet.

To better observe the DC Buss, I tried one more time.

Thats when a cable snaped.

The mechanical adjustment to level a module was held in place by a 1/4 inch bolt. The kind you can purchase at Home Depot.

The module tilted side way. I hit the EM Stop standing as always just beside my mousepad. Thats when the second cable snaped.

The last cable was holding the complete swinging module 30 feet in mid air and everybody was yeling.

After a while it stop to balance sideway and we brought the complet unit down. The bolts where bent sideway and there attachment was crooked.

I was told that this happened in there shop too. They replaced one bolt with a new one. Guess which one prevented the module from falling and crashing down?

So we attached the whole thing securelt in place and packed or bags and whent home.

Mechanical guys and Ing. who stamped the drawings have explaining to do.

We shall see what the futur hold for this thing. Now we have no more work on it.

It is funny that you mention 1/4 bolts. That is what breaks on my Lane recliner chair. I must replace them about every 6 months because they shear. I get the bolts from Home Depot. The bolts are cheap but hassle of replacing them is too much. I rather pay $2 per bolt and get something that lasts.

I wonder where home depot gets its bolts from?

Peter Nachtwey said:

It is funny that you mention 1/4 bolts. That is what breaks on my Lane recliner chair. I must replace them about every 6 months because they shear. I get the bolts from Home Depot. The bolts are cheap but hassle of replacing them is too much. I rather pay $2 per bolt and get something that lasts.

I wonder where home depot gets its bolts from?

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Peter
I think an Engineering Design Review is needed on this critical machine.
Uhhh have you done a motion analysis? Throw a couple of Charpy V notches on the bolts while you are at it.

You can bet your sweet life that Home Depot buys the best bolt they can get AT least cost.

I am sure you have a Tacoma Screw in the area - go see them.
Grade 8 comes to mind or maybe hardened bolts.

Dan Bentler

And 2 minutes before the bolt broke I was laying back waiting for craftmen to get out from under that thing. I was told... why don't you engage the movement... I said because those guys are to close for my confort.

So we waited and then...

SCARRY to say the least.

My neigbour is a mechanic for a prestigious airplane manufacturer. Talknig to him about this on saturday I told him I was amazed that Ingeneers signed off on this system. He told me that to him, whatever was done is not relevant. The mechanic should have notice the flaws in the design. He said that in his trade no mechanic would work on something they believe is not well designed and built, that they raise a red flag whenever they don't feel confortable.

Of course he talks about airplanes. No second chances here.

Has for the bolt grade and all, I think this fast pace was just to much. A prototype needs to be tested seriously.

Now that the attachments broke its easy to point out errors and mistakes but it would not be the case only IF we had a real chance to test this thing in the shop.

And one thing I must also say. That is the most amazing piece of multimedia display I have seen in a VERY long time. It was is just fantastic, Beautiful.

I sure hope they release some more budget to make it solid and test it. I wet my pants looking at it.

Peter Nachtwey said:

...That is what breaks on my Lane recliner chair...

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I understand that humour Have you been taking Terry Wood's sarcasm 101 course.

I wasn't trying to be funny. 1x1/4 carriage bolts are what my recliner uses and they break all the time. They cost 9 cents apiece. Actually, I may have gotten them from Lowes but I am sure they both Lowes and Home Depot get them from the same cheap source in China.

Dan, I live south of you in Vancouver, WA. We have Vancouver Bolt here
http://www.vancouverbolt.com/
and yes I simply have to get serious about get good bolts.
One more thing. The new versions of my chair have two bolts on each side instead of one. Obviously someone recognized the design flaws.

Finally, from my experience, good mechanical engineer are rare.

Pierre said:

And 2 minutes before the bolt broke I was laying back waiting for craftmen to get out from under that thing. I was told... why don't you engage the movement... I said because those guys are to close for my confort.

So we waited and then...

SCARRY to say the least.

My neigbour is a mechanic for a prestigious airplane manufacturer. Talknig to him about this on saturday I told him I was amazed that Ingeneers signed off on this system. He told me that to him, whatever was done is not relevant. The mechanic should have notice the flaws in the design. He said that in his trade no mechanic would work on something they believe is not well designed and built, that they raise a red flag whenever they don't feel confortable.

Of course he talks about airplanes. No second chances here.

Has for the bolt grade and all, I think this fast pace was just to much. A prototype needs to be tested seriously.

Now that the attachments broke its easy to point out errors and mistakes but it would not be the case only IF we had a real chance to test this thing in the shop.

And one thing I must also say. That is the most amazing piece of multimedia display I have seen in a VERY long time. It was is just fantastic, Beautiful.

I sure hope they release some more budget to make it solid and test it. I wet my pants looking at it.

Click to expand...

Pierre,

Wow, that's amazing. Glad no one was hurt. Please keep us posted as this saga continues to unfold.

HJTRBO said:

I remember having a problem with a cheap drive and a scrap winder. It was funny feeling the motor shake it's little tits off with the rotor only turning 1/10 of what the field was trying to turn it. Turned out the slip compensation was set too high.

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I'm still having visions of your motor shaking it's tits.

If you slipped a couple bucks in her panel did she shake 'em harder?

I would suggest that you exit this project at your first opportunity. With management like this, you can only end up being party to a disaster and then being blamed for it.

Get out now unless you see new management coming in soon.

dickdv said:

i would suggest that you exit this project at your first opportunity. With management like this, you can only end up being party to a disaster and then being blamed for it.

Get out now unless you see new management coming in soon.

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+1