Pay Off Reel Slowdown; encoder to PLC

Did the encoder fail? What was determined to be the reason for the fast tail?

Are you always loading the same material, same length, same thickness, etc...?

Without knowing many details, perhaps adding something that monitors the diameter of the spool. If you know the core size of your spool you could determine (roughly) how much material remains and slowdown the feed, primarily by looking at the encoder and as a secondary by looking at the diameter of the spool.

At those speeds, checking for a wire break (tail) with a limit switch would probably not help.

I have used sensors that measure distance to detect the end of a spool of a web for a tire machine, but that type of device will probably have to be set up with enough margin that you'd end up going into slow mode too early in order for it to do you any good.

The system you have is probably going to be as good as you can get, since you are definitively measuring linear speed and rotational speed with encoders.

It might be possible to tweak the existing logic and make it more sensitive, but we'd have to see what you have already in order to speculate further.

Using a vision system to monitor the payoff reel as a backup might be a good method, but that certainly isn't on my list of K.I.S.S. principles...

The encoders did not fail the system came up and worked for days without problems. There is no Data Acq. on this Line so I put a recorder on the signals after the failure and all has looked ok.
The inside diameter is always the say, or should be, the material grade, width, guage changes.

Currently researching laser but have never used one but have used ultarsonic but only for presents not for this application.

Not very familiar with your process, but checking the material on the Reel with any suitable sensor looks like the simplest back up option.

bbear said:

Currently researching laser but have never used one but have used ultarsonic but only for presents not for this application.

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My experience with Ultrasonic is that it would not be precise enough. It is fine for presence detection, but I doubt it would work for this applications. Laser Photo-Eyes are precise enough, but a bit of a pain to adjust, because they are so precise. Depending on your machine setup, it should work as a backup to the usual tail slow down. Only you know the exact setup, so all we can do is give you suggestions.

Stu....

Presumably, you know how many feet of material are on the reel at the start. Modify your system to have the operator enter that number into the PLC and then integrate running speed over time. That will give you cumulative feet. If the primary system hasn't commanded a slowdown by the time the calculation predicts some percentage of the reel has been depleted, the backup system will take over. You could also set up an alarm to tell when the backup system had to command the stop.

Good answer, Steve. The backup system could be set to 1 lap less than the encoder, so that it only kicks in when the normal encoder system fails to do the slow-down.

If the encoder did not fail, then something was different about that particular reel - maybe it had some metal folds at the end, or the reel core was larger, or someone accidently reset the encoder totalizer in the PLC,.....or something!

The Pay Off Reel has an encoder that feeds into a High Speed Counter GE Genius Block and the Processor, is used to pull the material off the Pay Off Reel, has an encoder that feeds into the same High Speed Counter GE Genius Block. These signals are passed to the PLC where calculations are made using these two inputs.

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Bbear,
There is something missing in the above description. I see TWO inputs described, as if there are TWO encoder inputs. I understand that one encoder input is from the Pay-Off Reel. Where and What is the other encoder input?

EDIT: I think I see what you mean now. The "Processor" you described is not the CPU in the PLC, but a Metal Processor that is using the metal being pulled off of the Pay-Off Reel. It appears to me that you already have a Main End-of-Reel detector and also a backup system (which would be the encoder for the Metal Processor). Steve's method of caluclating based on a start length and speed would then be a 3rd method?

It seems that the Metal Processor encoder calculation would be looking to see if this encoder is close to a labeled Starting Length for the reel. In which case if it ALSO did not detect the end, the reel may just have been shorter than labeled.

Can you verify the rate of change? Look at the line speed and count pulses if you know both of them and the gauge you can get surface speed. Right? Because the coiler is pulled off the real so the speed is known the rate of pulses ca be calculated.

Thanks all for the feedback. I will study this and get back. We are having breakdowns and breakins that does not allow me to followup at this time. But I will look this all over and report.