While it wasn’t the case 30 years ago, most flexible packaging printers and converters today know that by retro-fitting their web-fed machinery with direct tension-sensing and control equipment they can control their overall process better while preventing poor quality in finished roll material.

Flexible packaging converting and printing – one of the manufacturing segments growing at a healthy pace globally – has been the leading industry force for innovation from the manufacturers of tension measurement and control equipment over the past two decades. Product development by the tension controls manufacturers has had to keep pace over that time, although the innovation required by them hasn’t been nearly as rapid or drastic as we’ve seen in some other industry segments.

Electronic tension amplification, indication and control devices shifted in the 1990s from using analog-based circuitry with analog meter-scale faces and toggle switch user interfaces to microprocessor-based boards with surface-mount technology and digital user interfaces. The user interfaces for today’s industrial digital controls have moved in sync with (or slightly lagging behind) the interfaces developed first for the consumer electronics’ markets.

Even tension controls producers migrated their component choices beyond the basic LED readouts with push-button interfaces through monochromatic LCD graphic user interfaces and into full-color graphics. Now they offer full-featured touch screens that match the user experience of smart devices from the consumer electronics world.

How Web Converters and Printers Drive Change

Some significant market forces on the flexible packaging industry also shape product developments coming from the tension controls manufacturers.

One trend is the intense level of business competition in many consumer packaged goods categories. This compe-tition manifests itself in the proliferation of retail-level brand segmentation and customized regional promotions for popular retail products, particularly in the food and beverage industries. Today’s product differentiation fever has forced increased demand for shorter print runs, faster time to market, brighter colors, more sparkle, longer shelf life and environmental-friendliness for packaging.

Producer cost-containment measures and environmental conservation (green) drivers have pushed the demand for thinner films, improved film barrier characteristics, embedded security technology and package size minimization.

Web machinery builders and press builders have responded by designing presses that yield faster turnarounds, greater process versatility, increasing sub-process and finishing capabilities, and the capability to print on a wider variety of substrates. Web printers and film converters are still seeking more economical methods for completing short print runs. 

Tension control equipment manufacturers have had to respond to the fast turnaround demands and substrate variety by developing and offering measurement and control devices that are quick to install, set up and easy to use. The tension sensors and electronics must operate over a wider substrate tension range for a broader selection of web widths in more challenging industrial environments and with more input and output capability.

For the tension control electronics, the setup storage and recall features of digital controls are needed by converters who run a wide variety of web substrates or even the same substrate at various thicknesses. Other programmable features, like automatic zero and calibration, auto-PID-tuning, gain scheduling, diameter compensation, variable wrap-angle technology and tension profiling offer benefits that allow flexible packaging converters to maintain high output quality at speed.

Changes in tension-sensing technology have been more incremental, with tension transducers and load cells still using the same tried-and-true foil or silicon strain gauge sensor technology that has been used for the past four decades. Development in tension-sensing has come about as the result of changes in web press technology. For instance, the advent of the single-sided frame for narrow web printing presses many years ago forced the introduction of cantilever-mounted tension transducers. These are available in all lengths, diameters and load ranges for the frames of today’s narrow web presses. Tension transducers have to be designed to physically accommodate the presses and machines that they mount on.

The (Near) Future for Tension Control

With no revolutionary changes expected in tension sensing or control algorithm technology over the next few years, real growth in tension measurement and control is now occurring in only a few ways: 

Individual manufacturers are working to drive down component and system costs in order to stay competitive. They must. With several tension equipment manufacturers operating competitively in North America alone, flexible packaging converters have a choice of many tension control solutions for their web machinery. As a consequence of relatively inexpensive components, the potential user base for tension equipment is expanding. Now, smaller printers and converters globally are starting to be able to afford tension management technology that was too expensive for them 20 years ago.  

Along with the new touch screens that allow operators and plant technicians to interact quickly and easily with their tension control electronics, manufacturers are adding remote communications features to controller outputs. Production managers who choose this option are often looking to integrate the sensor outputs from their various process parameters into a supervisory control center. This can allow for more efficient monitoring and control of multiple individual process variables from a central location. Additional advancements have come in the form of useful features added to digital control software and firmware. For instance, specific to control output tuning for improved tension control and web process consistency, DFE’s SteadyWeb5 Tension Controller includes a PID tuning feature, TuneView, that allows the machine operator to view a time-lapse line graph of fluctuations in tension on the unit’s graphic user display. The operator may change PID values on the fly to fine tune the process and achieve a flatter system response.

Competition to dedicated tension controllers is also growing from the DC drives manufacturers who have integrated a PID control function for tension control right into their drive packages. This solution may be more cost effective than to purchase a dedicated tension controller and a separate drive, but the downside is the difficulty in determining which part of the system needs to be tuned if the customer’s web process becomes unstable during operation. A dedicated tension control system with one supplier having technical support responsibility throughout may be preferable for customers with limited technical staff or experience.

Finally, there are recent regulatory and compliance demands that have forced electronics manufacturers to change the way they manufacture, but this is independent of the trends noted above. For instance, the RoHS Directive from the European Commission is having a strong impact on design and manufacture of products for many electronics manufacturers as they scramble to meet the regulatory compliance to remove lead solder and other hazardous materials from their products and their manufacturing environments. Compliance with the current directive is not optional for electronic device manufacturers selling into Europe.

Dover Flexo Electronics, www.dfe.com