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Post by wvengineer on Mar 2, 2016 20:01:52 GMT
I've got an engineering problem that I am stuck on. I need to accurately measure the length of a roll of paper. The length should be about 3 and a half miles. (20,000 ft) I am suspecting the vendor is shorting us, but I need to prove it. Archimedes's spiral principle is not accurate enough here due to the thickness of paper varying. That throws off the calculation.
I am looking at some sort of wheel length measurement setup that can measure the length as the roll is used and unwound. A surveyor's wheel would be easy to use, but their accuracy is questionable. Can you get a Surveyor's wheel with a certificate of calibration?
Any one have any other ideas how to measure something that long to a high degree of accuracy? What ever I use I will have to be able to get a tool with a calibration certificate, otherwise the vendor will just throw the data out.
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Post by GTCGreg on Mar 2, 2016 22:00:01 GMT
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Post by the light works on Mar 3, 2016 0:41:44 GMT
of course, the other side of it is if you determine you are being shorted, you can still blacklist the vendor.
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Post by the light works on Mar 3, 2016 0:45:09 GMT
addendum: measure with a cheap uncalibrated device and it it IS significantly short, then you should be able to get a calibrated device to prove it.
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Post by GTCGreg on Mar 3, 2016 0:58:19 GMT
addendum: measure with a cheap uncalibrated device and it it IS significantly short, then you should be able to get a calibrated device to prove it. Good point. And then if it does come up short, call in the vendor and make THEM prove that it isn't. |
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Post by the light works on Mar 3, 2016 1:17:34 GMT
another option would be to put a revolution counter on a feed roller of a known circumference. - and a footage counter is a good idea, anyway.
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Post by silverdragon on Mar 3, 2016 7:24:27 GMT
I have a slightly strange idea....
Take a 10ft length of the paper, and weigh it.
I am presuming the paper is a certain quality and therefore uniform thickness....
Subtract the weight of the empty spindle its wound on, and then some maths should do to work out the weight of the roll divided by the weight of the 10ft length?...
Am I on to something here?...
[PS... give this post a thumbs up if you think it may work, just so I know?...]
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Post by GTCGreg on Mar 3, 2016 14:18:31 GMT
I have a slightly strange idea.... Take a 10ft length of the paper, and weigh it. I am presuming the paper is a certain quality and therefore uniform thickness.... Subtract the weight of the empty spindle its wound on, and then some maths should do to work out the weight of the roll divided by the weight of the 10ft length?... Am I on to something here?... [PS... give this post a thumbs up if you think it may work, just so I know?...] I think he already said the paper was not of uniform thickness. But given a large enough sample size, that may still work. |
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Post by OziRiS on Mar 3, 2016 23:28:02 GMT
I have a slightly strange idea.... Take a 10ft length of the paper, and weigh it. I am presuming the paper is a certain quality and therefore uniform thickness.... Subtract the weight of the empty spindle its wound on, and then some maths should do to work out the weight of the roll divided by the weight of the 10ft length?... Am I on to something here?... [PS... give this post a thumbs up if you think it may work, just so I know?...] I think he already said the paper was not of uniform thickness. But given a large enough sample size, that may still work. Should at least be a relatively easy way of getting a ballpark figure to tell if there's enough lacking to warrant more accurate measurements. Since the paper isn't of uniform thickness, maybe starting with a bit more than 10 feet might be a good idea. After all, there's 20,000 feet of the stuff in total, so getting a reasonable average weight is key. Maybe start with weighing 30 or 40 feet...? |
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Post by wvengineer on Mar 4, 2016 5:49:54 GMT
There have been examples in the past where we thought the vendor was shorting us, but when you produce your evidance, they claim that since you are not using certified equipment, then you can't accurately know. From there is turns into a big mess with the contacts managers. So to avoid the headache, just start with the certified tools.
I was thinking about a starting test using a surveyor's wheel for proof of concept, but I don't know if the one that maintenance has on hand will measure that far.
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Post by GTCGreg on Mar 4, 2016 5:53:41 GMT
There have been examples in the past where we thought the vendor was shorting us, but when you produce your evidance, they claim that since you are not using certified equipment, then you can't accurately know. From there is turns into a big mess with the contacts managers. So to avoid the headache, just start with the certified tools. I was thinking about a starting test using a surveyor's wheel for proof of concept, but I don't know if the one that maintenance has on hand will measure that far. If your company won't split for a $150 digital wheel, just give it up. |
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Post by the light works on Mar 4, 2016 14:51:33 GMT
as we said, first confirm using cheap tools. then once you know you're right, get the certified measurement.
also, start getting a certified weight of each roll and each core. if they all weigh the same, then you have the claim that they are all the same length. if they don't weigh the same, or even close, then you have your claim right there that the vendor isn't providing a consistent product.
big question is: are you stuck with this vendor?
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Post by GTCGreg on Mar 4, 2016 15:03:18 GMT
A question I have is what makes you think you are being shorted? Are you not getting the expected amount of end product? Again, put the proof back on the vendor. Call them in an tell them that you aren't getting the expected results. Ask THEM to explain why. They may actually have a valid reason beside "your results may vary."
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Post by c64 on Apr 17, 2016 8:55:59 GMT
In the industry this is done using scales, just as mentioned. You need to sample the paper by cutting many pieces of a known length out of the roll. This is usually done by taking pieces from the process, e.g. if the roll is cut to pages, take pages randomly out of the process. The more, the better. Then put them onto a calibrated "counting scale" and tell the scale how many feet or meters you put on as samples. Then put an empty spool onto the scale, hit "Tara" (to set the scale to zero) and then the scale will display how many feet (or meters) you got on any spool you put onto the scale. If the reading of a fresh spool is short, the manufacturer either made the product thinner or shorter which is bad in any case. A counting scale which can handle up to 40kg and is compliant to the demands of the German gauging office costs you about €350 and comes with a 1-year governmental approved calibration certificate. I have worked with those, they are amazing. Just drop 3mm LEDs on it and it tells you how many they are. When e.g. 500 LEDs were used in production, there never were more than 2 LEDs missing or left over.
In production machines, counters are used. They count "digits" and don't have any error since each electric impulse is counted as one digit. You can get them for €5!  All you need is a tachogenerator, this is the critical part. Look at your production machine and identify a roller which has no slip so it revolves exactly with the paper. Attach a magnet, a punched disc or a reflector so you can count the revolves of the roller using a magnetic (HAL) sensor or a (reflex or fork) light barrier. Attach it to the counter and you can measure how often the roller revolves feeding the spool. All you need to do is to calibrate the system. Use a long tape to measure a hallway and run the paper over this distance and cut it. Feed it to the machine and you can calculate how many feet (meters) of paper you get per impulse. More expensive industrial counters can sound an alarm if a threshold of impulses is reached. This can be used to sound a bell to the workers can prepare to change the spool of paper before it ran out so the machine doesn't have to be stopped for a longer time. Sometimes it is possible to exchange the spools without stopping the machine. |
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