math problem

I am trying to show the time till splice on a roll of unwinding paper.
The rolls are unwinding down to a core of 5" then the new roll will splice on the run. I know the speed of the paper and the RPM of the unwinding roll. I also know the caliper of the paper. I am using a slc503. Any Ideas?
I have a HSCE counting prox pulses on the roll shaft and another HSCE for a prox on one of the rollers to tell me the paper speed.Any Ideas?

Hi David,

If I was you, I would use a counter to count down the number of revolutions left on the paper roll (you should be able to work the total number of revs / roll) and then do a math function with the number of revs / minute against the number of revs left to give you a time. Its pretty simple if you put your maths first on paper so you know how you can work out what additions, subtractions etc you will do, and then adapt this to your plc!

After all this is more of a maths problem than a plc problem!

We have a prox located on the shaft of the pinch rollers that pull the paper off the roll. This prox measures the paper off the roll in a linear fashion, rather than us trying to calculate what's left based on roll diameter etc. I'm assuming you already know how many linear feet are on the roll when you start. We just use on/off transitions of a 15 tooth sprocket (30 transistions), sproket diameter of 10", therefore 10 * pi / 30 = Inches travel per pulse. You should be able to use the prox you are measuring speed with to measure length.

math

Assuming you can determine the total length of material on the roll:

Vetteboy's length method seems sound.

(total roll length - actual ) / speed = time to splice

Here in lies the problem
The paper rolls aren't always the same diameter.

Ok I do know the diameter of the roll using the paper speed and shaft speed but how do i use the diameter to find the amount of paper left on the roll?

You know the RPM of the core and the linear speed of the paper, so you can calculate the diameter of the roll. (Linear speed in IPM divided by rotational speed in RPM yields Inches per revolution which is the same as circumference. Circumference divided by PI equals diameter). With diameter, you can calculate cross-sectional area. Area divided by caliper equals length of paper on the roll. Length divided by linear speed equals time.

I wait before getting involved because the answers are so entertaining!

(MaxRadius-MinRadius)*( counts per second ) / ( Paper thinkness * counts per rev )

(Max Radius - Min Radius)/ Paper thinkness = number of revs.


Counts per second / counts per rev = revs / sec.


Number of revs / revs per sec = seconds.

Maybe you could just use some photoelectric eyes or high resolution optical guages to determine the minimum acceptable diameter to allow time to splice. Perhaps even some additional pre-warning photoelectric eyes at a slightly larger diameter to alert an operator.

Whatever the poster decides I have decided to print this thread and add it to my collection.

I work with unwinds and rewinders daily, most dont have any form of photoeyes etc but are fairly accurate at splicing when the roll gets to a certain size. Of course if the rolls are a different size (diameter) and a different mil (thickness) then the system has to know this. Ours are of a predetermined size and thickness.

There are many ways to do this. I appreciate the information I have obtained from the responses.

Thank you all.

BTW daved, AB has done alot of work in this area, talking to a local rep may not be a bad idea (if the rep is good or knows someone good).

Thanks for everyones input.
I think Steve Bailey pointed me in the direction I was looking for.

I've used the method Steve lists quite often and quite successfully. The thing to remember is you are slaved to the accuracy of your diameter calculation and the consistency of your caliper (if it's entered). Diameter is really the big wildcard so pay attention to that.
I have had more luck calculating diameter by looking at linear distance per product roll revolution as opposed to looking at linear versus rotational speed. If you are using the rate function of the HSCE this probably isn't as big a deal since you can get a large number of counts per sample period. But the distance method tends to forgive short time velocity burps.

Keith

Keith,

If daved is going to use the calculated time to alert the operator when the roll is getting down close to core, he'll probably be OK as long as he provides a generous margin. I wouldn't recommend using it to control when to trigger the splice without first doing some testing to verify the accuracy and consistency of the linear and rotational speed data. We don't know anything about the resolution of the count signals into the HSCE modules, nor do we know the time period that the HSCEs use when they calculate speed.

Dumb question

This is outside my normal area of expertise, so I'm going to ask a few stupid questions. Instead of working off the feed roll, which is a changing diameter and varying ft./revolution, isn't there a pinch roll or similar feed mechanism that is going to accurately indicate the fpm of the paper? And then, would it be easy to do one calcuation for ft per roll vs. caliper and diameter? Then his timing job get's easy, doesn't it?

reel splicer

daved is the unit a megdme splicer.if its a newspaper press i presume youll be using between 45/49gram paper,if its commercial its a bit more complicated because of the different types of substrate that can be used.i found in newspaper that more or less 2 or 3 minutes of error is sufficient for the operator.repeat that in newspaper its easier because the web speeds are more constant,(zero or top speed),
because you know the diameter and the web speed why dont you try a scale funcion x and y being the speed and diameter and where they meet on the graph is the time left in minutes.i dont know this plc,i
did a meg dme with a omron cpm2c and its working quite well.because
the tickets on the reels have the diameter and meters of paper you can use this data to calibrate the scale funcion,if your company is asking for the precise time of the next splice then you will have to do lots of maths and have lots of data to take into account.i feel its more important for the machine operator to know how many formats he has left so he can make the decision wether or not to cancel the splice.