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rope tension across pulleys on a take up winch

rope tension across pulleys on a take up winch

rope tension across pulleys on a take up winch

(OP)
Hello All,

We have several conveyors onsite which have a takeup winch to keep the belt tension is a specific band. We get the feedback from a strain guage at the fixed end of the rope and a load pin on the pully closest to the take up winch drum. These two tension feedbacks are averaged which is then used by the control system to adjust the winch in and out accordinly.

The conveyors had only been commissioned for a few months, and we have four of them.

The issue we have is that the two tension feedbacks are different, and the size of the difference varies quite considerably. The load pin is generally higher then the strain guage, which to me makes sence as the tension is applied from the drum, and you would expect to lose efficiency over the 13 pulleys the ropes go through (please note that im a elec eng) before it gets to the fixed point where the strain guage is.

However the difference is sometimes only 4% or less, often the difference gets to 13%, and in some cases the variance can get to 20%. Often these changes in the differrence between the two tensions occur when the winch has moved. Sometimes is load pins tension which changes, sometimes the both diverge equally but oppisote. I have attached a trend to help explain.

I guess my questions are is 20% and resonable variance in the tension accros the length of the rope. why does this difference vary, is it just the nature of the system with so many pulleys. under each winch movement dooes each pulley just end up with a differnent loss due to a binding or similar?

The pulley are 800mm on the fixed end of the trolley and 1000mm on the moving end, the rope would be 30 or 40mm (cant find a spec for it at the moment).

Thanks

Allan

RE: rope tension across pulleys on a take up winch

Can you post a sketch of the system? Why the spikes in your calculated average?

RE: rope tension across pulleys on a take up winch

(OP)
Attached is a sketch of the plan view with some rough lengths.

the spikes are because the tension feedback is via a comms link and not hardwired. We have verified that the spikes are not actually occuring. We are hardwiring the feedbacks next shut.

RE: rope tension across pulleys on a take up winch

Suggest you consider consulting appropriate persons to review, though:

An elevation (mechanical) illustration may assist.

Suspect it is hysteresis as you have suggested, though if you superimpose winch speed with the trend it may assist (is it due to acceleration / inertia of the take up?).

The tensions need to be bought into check immediately to ensure safety (fatigue of components and if the conveyor has "significant" lift, to ensure sufficient T2 for hold back / brake (?) operation).

Off topic, though: Is this a large underground mine in central NSW (planned to be largest in AU)?

Regards,
Lyle

RE: rope tension across pulleys on a take up winch

What you are observing is to be expected. If you have only one percent tension loss over each pulley you will have 1.01^13=1.14, or 14% difference in tension. And the pin reading will always be higher than or equal to the strain gage reading.

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