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The Drive and Control Company
Case Studies and Technical Papers
roll-to-roll electronics printing Challenge:
Perform tension adjustments in one tension control zone of a roll-to-roll web process without causing web jitter that compromises ink registration and reduces yield.

Rexroth Solution:
Rexroth multi-axis tension control solution allows the web to be decoupled into separate tension control zones. Tension can be adjusted as required in one zone area without destabilizing the entire web.

Recommended Solution:
  • During acceleration, tension control decoupling ensures the web is stable as soon as full production speed is reached, compared to a delay of five seconds or longer with coupled control.
  • Rexroth multi-axis tension control increases standstill web tension accuracy by a factor of two to four
  • The Rexroth multi-axis tension controller initiates a response to step reduction in tension control in one-fourth the time compared to typical controllers
Download the complete Tech Paper (PDF – 457 KB)

Rexroth solution for digital roll-to-roll web processing is revolutionizing printed electronics production

One of the brightest developments in electronics is Organic Light Emitting Diode (OLED) TVs, which are attracting consumers with their eye-popping colors and super-thin designs. Unlike the components found in traditional flat-screen display technology, OLEDs use thin, flexible sheets of material that emit their own light and are produced using a technique similar to inkjet or sheet-feed printing.

OLEDs are still relatively costly to manufacture in large sizes due to limitations in both shadow-mask deposition methods, and in newer laser annealing and inkjet printing techniques. To scale up large area display production economically, printed electronics manufacturers are seeing the benefits of another production method -- namely, digital roll-to-roll web processing enabled by Rexroth multi-axis tension control solutions.

Originally developed for digital printing, Rexroth multi-axis tension control has been found to be an excellent solution for roll-to-roll manufacturing of printed electronics, such as large area OLEDs, e-paper media and integrated circuits. Like an inkjet printer deposits ink on sheets of paper, a digital roll-to-roll press patterns thin-film transistors and other devices directly onto large organic, flexible substrates.

But unlike slower sheet-fed digital printing, the substrate in a roll-to-roll press is supplied from an infeed reel through the printing section onto an outfeed reel in one continuous inline web. An array of piezoelectric printheads deposit the ink -- comprised of a conductive organic solution -- on the substrate at precise locations.

For high-quality productive manufacturing of printed electronics like OLEDs, tension control of the web must sustain extreme degrees of registration. Tolerances for applications such as Thin-Film Transistors (TFTs) or OLEDs require registration smaller than 10 microns. High-speed, high-resolution cameras measure registration accuracy and provide input to the control system. To ensure that degree of accuracy, precise web tension control is required.

From the experience gained as a market leader in digital printing, Rexroth developed web tension control technology that is now being implemented to address digital roll-to-roll processing's main challenge--running at high speeds while maintaining high registration accuracy.

tension control chart 1
Correcting for tension in one zone often leads to a cascaded disturbance in other zones.
tension control chart 2
Decoupling each tension zone allows each controller to operate independently.
Figure 1 shows how instability affects a web traveling at five meters per second with two successive tension controllers for two tension zones. A command for a step change tension reduction is sent to the green zone controllers. No change is required in the upstream blue zone. But because the web is continuous, the tension disturbance is carried back to the blue zone, which causes the blue controller to compensate.

In an ideal world, web instability would never occur because tension adjustment would never be needed. However, due to factors ranging from oscillations caused by mechanical misalignments to out-of-round unwind and tension rolls, real-time web tension control is necessary to achieve desired yields.

There is a solution: Decouple each tension zone, allowing each controller to operate independently.

This has been accomplished in digital printing applications using Bosch Rexroth controllers incorporating a unique tension decoupling function block. As the name implies, the function block allows tension control for each zone to operate independently. As a result, tension changes can be isolated in one zone without affecting tension change in other areas.

Download the complete Tech Paper (PDF – 457 KB)
Tech Paper Download
Tech Paper Download
Web Tension Motion Control
for Electronics Printing
(PDF – 457 KB)
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