Unrolling of paper calculation

[bbur147274]

I might be overthinking my problem, but I need some help. I am trying to write a formula in my plc to calculate the footage of paper being unrolled on a paper splicer machine. The total length of the rolled paper is 31,224 feet using the L=Pi(D^2/4-d^2/4)/thickness formula. The motor runs at 1450RPMs with a 2:1 gearbox. What is the formula to figuring out the amount of paper being unrolled every minute.

 

[Steve Bailey]

The motor runs at 1450RPMs with a 2:1 gearbox.

What is the motor driving? If it drives a pinch roll that pulls the paper, the line speed (Inches per minute) is the speed of the pinch roll (Rev per minute) times the circumference of the pinch roll (Inches per Rev). If the motor drives the roll of paper it will turn at a slower speed with a full roll and increase in speed as the diameter of the paper roll decreases.
For every rotation of the paper roll you get a length of paper equal to the circumference of the roll. For greatest accuracy you need to factor in the thickness of the material being unwound, but paper is generally thin enough that it doesn't matter.

 

[DarrylR]

We have ours in a 30ms periodic program using line speed in feet per minute.

Footage = Footage + (FPM/60*.03)

 

[drbitboy]

... What is the formula to figuring out the amount of paper being unrolled every minute.

That depends; what information do you have from the process? E.g.

• roll rotational speed (RPM?)
• current (instantaneous) roll diameter?
• anything else?

 

[robertmee]

If your motor is running constant 1450 RPM at 2:1, gotta believe that's the pull roll and the unwind is a brake controlled passive unwind? Does the speed never change? If as Ken asked, the motor is driving the Unwind, then the 1450 RPM is likely not constant.

In otherwords, you need to supply more information.

 

[SCADA_Joe]

TLDR: Use a Footage Counter Wheel

I have done a fair amount of attempts for a similar calculation in the metal industry and it ultimately ends up being far more successful to just install a footage wheel somewhere. It will be more accurate than a calculation and from what i have seen a far better feedback loop for the system if your controlling anything based on that information. if the material is easily torn then i would install the wheel in direct contact with a drive/pinch roll in the system with zero slip.

The biggest pro for this method is it can accommodate any thickness of material without user input. when selecting a counter keep in mind the max total run length and how you will reset the counter.

No PLC, No Problem:
You may be able to accomplish your needs without a PLC or its analog IO. I have had great success using a Automation Direct Counter and McMaster counter Wheel assembly. It can even give you a digital output for predefined increments for alarming or a PLC digital input.

Counter ($94):
https://www.automationdirect.com/ad...tion_digital_counter_-z-_timer_-z-_tachometer

Wheel Assembly ($413):
https://www.mcmaster.com/16695T47-16695T42/

 

[MaxK]

I think the forum is missing an emoticon...
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With PN face