Web Tension and Guiding
Web Tension for Measurement and Control
Why measure and control tension? It improves product quality, production speeds and reduce material waste.
H
owever, even today, we must remember the basics; rubbish data in means rubbish data out to the controller. Firstly, measure the tension as close as possible to the key production area or rewind / unwind. Next, ensure that you have sufficient wrap angle on the roller and keep the loadcell cables as short as possible to the amplifier.
The same rules apply for a new design or a retro fit, finding the best place to site your tension loadcells is key. As is knowing the expected material tension, ideally you want your run tension to be around midway for the total capacity of the loadcells. TTS Systems’ CRL and CRF loadcells have built in overload protection, as well as a floating bearing head to allow for some misalignment and end drift of the roller.
The wrap angle is also important, the golden rule is at least 60 degrees, but more is always better. It is also worth remembering the eff ects of gravity and the roller dead weight; if the wrap is below the roller, then you are lifting against gravity and roller dead weight. Wherever possible, across the top is your best option. Loadcell cables should be as short as possible, but the same length from each loadcell. We would recommend cable lengths up to 10m, with good earth / screening at the amplifi er. Now what to do with the loadcell outputs; the DCA-22 is a dual channel loadcell amplifi er, so we treat the left and right loadcells as individual inputs, amplify them individually and then digitally sum them to give a Total Tension Output as either 0 to 10VDC or 4 to 20mA. We also provide the individual 0 to 10VDC outputs for Tension Left and Tension Right, which is useful for alignment setup and fault fi nding. The analogue tension outputs can either be connected to your PLC system to give the machine control or to a standalone tension controller to link to your drive or braking systems. Today our customers are about 50 / 50 on which control solution they choose, we can help with both.
So, you have your Tension Measurement and Control system designed, the installation and alignment of the loadcells with rollers is very important to save the loadcell bearing head and quality of measured tension. Also, do not forget calibration of the tension loadcells and amplifi er; there are some very simple techniques that still work well today.
Our products are UK manufactured and extensively used with paper, foil, film, tape, plastics and rubber. In fact, any material on a roll or reel that is processed through an automated machine can have its tension measured and controlled.
When used in a closed loop control system, the measured signals can be used to regulate the speed of the drive, brake or clutch thereby ensuring constant material tension throughout the process.
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September 2024
www.convertermag.com
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