Quick Answer:
Short Answer
Narrow-range sensors lose tracking during sudden web wander. Roll-2-Roll's wide-range sensors (up to 960mm) maintain lock on the target, and the SCU5/SCU6x controllers include "Lock on Lost Edge" protection that inhibits the actuator if tracking is lost.
In chasing applications, process upsets can cause the web to wander significantly—due to splice passage, tension changes, or roll eccentricity. This exposes a critical weakness in narrow-range sensors:
- Narrow sensor problem: If the target (line, edge, or pattern) moves outside the sensor's field of view, the system loses tracking. With older controllers lacking edge-loss protection, the actuator continues driving in one direction until it reaches its limit—potentially damaging equipment or producing scrap.
- Roll-2-Roll® Sensors + SCU5/SCU6x advantage: Wide-range sensors (up to 960mm) provide a large capture window that maintains lock on the target during extreme wander events. Additionally, the SCU5 and SCU6x controllers include a "Lock on Lost Edge" feature that inhibits actuator movement if the edge is lost—preventing runaway conditions. For line/contrast guiding, loss of contrast also inhibits the actuator.
Example: An ODC 288 sensor provides 288mm of sensing range. If the web edge wanders ±100mm during a splice, the sensor never loses sight of it—and the controller keeps tracking smoothly.