Not sure where to start. 1

[willhan]

So, we've installed this fancy new system with a dual motor driven chain, and the damned thing has had problems since day one. It slows down from time to time and interrupts production. We have considered a number of options to cure the problem, for example, we just changed the motors' encoders at the engineer's recommendation, and the problem is still occurring. We are not sure if the problem is one of controller programming, bad wiring, mechanical, or something else.

I have included some shots that may help to illustrate the issue further. There is an 8 hour time series of both of the motor's currents. When the chain is not loaded, you can see an oscillation with period of about 40 minutes, the time it takes for one complete chain cycle. When production starts, the current begins to rise, and peaks after about half an hour or so. Then the chain randomly jerks, slows down, and sometimes even fully stops then returns to it's normal operation.

I appreciate anyone who might be able to point me in the right direction. What other information should I provide to help mitigate the problem?

 

[willhan]

Strange, the chain seems to be running fine today. Thanks for all the input!

 

[LionelHutz]

So there is a master and a slave VFD. Both get a speed reference. The slave gets a motor torque signal from the master and trims or slightly adjusts it's speed to loosely match the torque of the master.

I still don't see where the encoders come into play but I expect the encoder is being used by the VFD for closed loop vector control. If this is true, you could try switching the VFD's to sensorless vector mode which eliminates using the encoders, assuming this speed-trim load sharing feature still works in sensorless vector mode.

It appears you have 2 encoders with 2 wire runs back to 2 different VFD's. In other words, 2 separate systems. Yet both seem to be exhibiting the same encoder issue. This would make me suspect a connection error. Both are wired wrong causing both to work incorrectly in the same manner.

 

[1gibson]

Running fine today is not strange, it is interesting. Figure out why! Change in humidity?

 

[willhan]

Spoke too soon! The problem has started again.