Industry Supplier Q&A | Web Guiding and Tension Control with MAGPOWR and Dover Flexo

Published: September 22, 2018, By Christine Pietryla Wetzler

Christine Pietryla Wetzler interviews Chris Harper, MAGPOWR Tension Control and Mark Breen, Dover Flexo Electronics, Inc.

Q: Explain how your company has impacted the web guiding and/or tension control industry? 

BREEN: As one of the pioneers in automatic tension control in the U.S., having started in 1974, Dover Flexo Electronics, Inc., has focused its operations exclusively on designing and manufacturing technology to improve web converting and printing output quality and to reduce material waste from industrial web processes like printing and converting.

Dover Flexo has lead innovation in the industry by introducing technology that simplifies the measurement and control of process web tension on every type of web-fed machine imaginable.

Three of the top innovations that have been unparalleled in the tension control segment of the converting industry have been:

• The advent of the Tension Roll transducer, an idler roll with built-in tension sensors;
• pneumatic brakes that don't squeal; and
• a steady evolution of controller technology that mirrors the state-of-the-art electronics advancements from the consumer electronics industry and includes Quick-Cal™ push-button Zero and Calibration technology.

Q: What are the most common quality issues you experience and how do you troubleshoot for those?

BREEN: If you’re talking about the typical web quality issues that our customers experience to know that they need better tension control in their processes, then those would be things like web breaks, web wrap ups, wrinkling, loss of color-to-color registration during splicing or speed changes, unwind or rewind core crushing, telescoping rolls, starred rolls, and hard or soft finished rolls. These flaws are all visible and indicate a need for consistent, repeatable tension.

Q: Describe an ideal system set-up and what are the key characteristics that make it work well?

BREEN: Using tension control on a machine unwind as an example, an ideal closed-loop system may include tension transducers, to accurately measure the web tension in that zone of the web path. It may also include a tensioning device, like a pneumatic brake, and a tension controller. The controller would be set for a predetermined prescribed tension that the machine operator would set, and the controller would compare the input signal from the tension transducers and send a compensated output signal to the brake to adjust the speed of the web to keep the tension constant at the chosen setpoint. Once everything is running smoothly, the machine operator should be able to increase the speed of the machine while the tension controller maintains the web tension by making small adjustments to the pneumatic output to the brake. That would be an ideal tension control system.

Q: How are tension controls evolving to meet the needs of converters who want to run bigger rolls at faster speeds?

HARPER: Although tension controls are getting faster due to processor speeds increasing, the main features needed to deal with larger rolls and faster line speeds include automatic control loop gain adjustment as well as inertia compensation features both based on roll diameter and/or line speed in addition to measuring tension. Machine designers also must consider which type of control schemes should be used based on the process, roll quality, roll size and line speeds. Tension controls for load cell-based control systems and dancer-based control systems should each have these compensation features to help gain control of these bigger and faster applications.

BREEN: Tension controllers are evolving incrementally in the sense that while they still take input from the tension transducers and they output a compensated control signal to a drive, or a clutch or a brake that’s determined by a tuned PID algorithm, we now can tweak the control algorithm with finer tuning. This is possible because we’ve moved the control from an analog to a digital platform that is software based. We can better control for the inertia present in larger rolls and for higher speed variations through algorithms in software that compensate for the inertia and rapid accelerations and decelerations. Before digital technology had become as advanced as it is today, the control outputs were less fluid in their dynamic capabilities.

Q: Do you feel tension control solutions are ubiquitous with converters or is there still a remaining reticence to understand the benefits completely?

HARPER: There is a mix between trying to understand completely and “tweaking” things to get the production runs finished. As materials get thinner, line speeds increase, and rolls get larger. Sometimes those who resist fully understanding control are forced into a change as it starts to get impossible to keep production consistent run to run.  Proper tension control can stabilize an application, allow a process to run that maybe could not run before with more consistency and less intervention of the operators which will result in higher production volume, with higher quality product and consistency shift to shift and operator to operator.

BREEN: We find that the more sophisticated the applications are of a converter or web printer, the more receptive they are to the fact that closed-loop tension control using direct tension measurement is the obvious best choice solution. There are many applications such as bag-making that may require less sophisticated solutions, such as our open-loop EasyWeb torque controller. The end-use quality expectation isn’t as high when the profit margins of a particular converted product line are lower. What we find is that the more expensive the web substrate is, and the thinner it is, the more ubiquitous tension control is. The need becomes obvious when wasting a few meters of substrate is costing the converter lost revenue.