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Measuring the amount of cable in a drum
Sensor technologies. topic
Posted by ZAKI on 31 May, 2008 - 12:50 am
Hello to all,

Does anybody again to share about my new project.

We have 3 drums of welding cable and rotating with each 3 platforms (little bigger than drum dia.). Each drum cable goes into the 3 welding tips respectively. Now, Operators want to know the remaining welding cables inside each drum. The operators remind the machine that it cannot start again once remaining cables are less than to complete one whole welding cycle.

Are there any other sensors to monitor the welding cables inside the drum? Aside, I am planning to put load cell/strain gauge in each platform to measure the weight of the drum. Is my approach correct?

Please give me some ideas about how to measure these drums. Those people in welding industries
will be much appreciated.

Thanks in advance,

zaki


Posted by Michael Griffin on 31 May, 2008 - 9:43 am
I assume that you mean the electrode wire, and not the shunt cable. It is difficult to give a realistic answer without knowing the mechanical parameters in more detail.

However, sensing wire feed is a common application. The most straight forward methods all rely on the length of wire between the spool and the work piece being enough for at least one part. Thus, when the spool itself runs out, there is still enough wire in the system to finish the part. This means you are not trying to measure the wire while it is still on the spool. Instead you are detecting it after it has left the spool (which is much more practical to do).

You then just need to detect either if the wire is present, or if it is moving. Detecting the wire itself reliably is usually not easy. It is usually better to have the motion of the wire turn or move something else (e.g. around a pulley or between a wheel and pinch roller), and then detect that. This also tells you if the wire is broken or jammed somewhere in the system (the wire is not moving when it should be). You will need to make the logic tolerant of timing lags in the system or else you will get a lot of false triggers.

I doubt that weighing the spools would work. There just isn't enough weight difference between "almost empty" and "empty" to weigh accurately. Furthermore, you won't know what that particular spool weighs empty until you actually empty (at which time it is too late to care).


Posted by zaki on 1 June, 2008 - 3:43 pm
Hello Mr. Griffin,
Your idea is very much appreciated.

Yes, I am reffering to the welding electrodes rotating inside the invisible drums (not a naked spool which also commonly seen and used).

To add some flow of the process, we are welding for a 11 meters long max. continues welding with no stopping between 0-11 meters.
Otherwise repairs will be done and considered downgraded products if not properly repaired.

We are to avoid stopping between 0-11 meters without knowing electrodes present in the drum. Operators should know or automatilcally determine electrodes present in the drum that it is not possible for a complete 1 cycle (0-11 meters) welding. Otherwise change the drum if detects less than 1 complete cycle.

Welding speed, voltage, amperes base on the thickness welded object may affect the lenght of the electrodes. Distance from the drum to the welding tip is 20 meters and I assure this is not possible for a 1 complete welding cycle proceess.

I might be grateful if this will be done,

zaki


Posted by caculate on 3 June, 2008 - 12:11 am
You might try the simple approach first. Have the controller count how many meters are used. Add to your interface a reset for a new spool or where the new spool meters are entered manually. Then have the control count down or subtract how much you used plus a safety factor, and you shouldn't be having to do rework. You could add a manual input for operators in the event they waste the wire on start up, wire breaks, etc.

Just a thought for a simple approach.


Posted by zaki on 4 June, 2008 - 12:07 am
Thanks a lot Mr Griffin.

You contributed me great idea in economic way.

More power,

Zaki


Posted by Michael Griffin on 3 June, 2008 - 12:09 am
The first parameter you have to determine is how much wire is enough. If 20 metres of wire isn't enough, then what is?

You might consider modifying the feed system such that it gives you more length between the spool and the work piece. You could move the spools further away, or (likely more practical) you could run the wire through some guides to zig-zag it back and forth.

Alternatively, you could try weighing the spools as in your original idea, but I think you will end up throwing out a lot of wire at the end of the spool to avoid the risk of running out. Weighing the wire simply won't be as accurate as actually measuring it.

It is not really possible to make a recommendation though, as this comes down to a matter of economics. Your application is a bit unusual in that the length of your continuous weld is much longer than in typical manufacturing. In most applications people want to avoid wasting wire. You however have to balance a more complex feed system (and more time to change spools) versus wasting wire versus scrapping what sounds like a large and expensive part.

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