Line/Contrast Guiding

Light source selection depends on your application:

• Infrared (880 nm): Best for most high-contrast applications including black lines on white, coating edges, and foil substrates. Works for both edge guiding and line guiding with the same sensor.
• White Light: Required for low-contrast patterns, subtle color differences, and applications where infrared cannot distinguish the feature.
• UV (385 nm): Required when the line is printed with UV-fluorescent ink that is invisible under normal lighting.

Contact Roll-2-Roll Technologies to discuss your specific material and line characteristics.

No. Traditional line sensors have narrow fields of view, requiring motorized positioning to physically move the sensor until it finds the line. Roll-2-Roll® Sensors have wide sensing ranges from 48 mm to 960 mm, allowing the sensor to see the entire potential line position area simultaneously. The sensor and controller automatically identify and track the line within this range—no mechanical movement required.

Roll-2-Roll® Sensors can detect and track lines with a minimum width of 2 mm (0.08 in). The sensors also support negative space guiding—tracking the gap between printed features (such as the white space between labels) rather than a printed line. This eliminates the need to print a dedicated registration line, saving ink costs and allowing closer trim to printed edges.

No. With Roll-2-Roll® Sensors, you do not need to purchase or install a separate sensor for line/contrast guiding. The same ODC Family or 1DC Series handles edge detection, line guiding, center guiding, and contrast guiding. For most high-contrast applications, the standard infrared light source works for both edge and line detection. For low-contrast or UV-printed lines, white light or UV light source options are available.

The Roll-2-Roll® Controller includes Loss of Contrast Inhibit specifically for this situation. When the sensor encounters a gap where the tracked feature disappears (such as the space between labels), the web guide holds its current position. When the sensor sees the same feature again—matching the width and hue characteristics taught during setup—tracking resumes automatically. Loss of Contrast Inhibit stops actuator movement until the feature is detected again.

Yes, the same sensor family does both. An infrared head handles edges and high-contrast printed lines; for most line and contrast work, order the white-light head. The light source is fixed at order. This dual capability reduces equipment cost and simplifies changeovers—operators don't need to swap sensors when switching between edge-guided and line-guided products.

Preventing Loss of Focus

In line or contrast guiding, optical sensors or cameras are used to track a printed feature or line. These sensors require a stable focal distance to operate accurately. However, as the web guide mechanism actuates (moves back and forth), it creates a "twisting" effect in the web span, causing the web plane to shift closer to or further away from the sensor. This movement, known as pass line variation, can cause the sensor to lose focus, affecting the amount of light reflected back and disrupting the "teaching" or tracking of the feature.

Web Stabilization

The dead bar acts as a stabilizer. By wrapping the web over this bar, the web is forced to maintain a fixed distance relative to the sensor, regardless of the guide's movement or the twisting happening in the span. The sensor is then mounted specifically to "look" at the web directly over this dead bar.

Installation Specifications

• Mounting: The sensor should be installed to view the web while it is in contact with the dead bar.
• Wrap Angle: To prevent the dead bar from influencing the lateral dynamics of the web too heavily (which could cause drag or steering issues), the wrap angle should be kept small.
  • Dead Bar (Stationary): Maximum of 5 degrees wrap.
  • Idler/Backup Roller (Rotating): Up to 15 degrees wrap.

Application in Terminal Guides

For unwind or rewind applications where line guiding is required, the setup is slightly different to accommodate the moving stands:

• Unwind: A shifting idler or dead bar must move with the unwind stand to support the web, but the sensor must be fixed to the machine frame,.
• Rewind: The sensor moves with the rewind stand (chasing the web), and a fixed idler or dead bar is placed in the span just before the rewind.