Web Guiding

Sizing an unwind actuator requires more than knowing the total load weight. The key factors are:

1. Breakaway Force: The actuator must overcome static friction to start movement. This depends on the bearing type:
   • Low-friction linear rail bearings (coefficient ~0.01): A 10,000 lb load requires only ~100 lbf to start moving
   • Sliding shaft bearings (coefficient ~0.25): The same 10,000 lb load requires ~2,500 lbf
2. Acceleration Requirements: Higher acceleration for faster response requires proportionally more thrust
3. Safety Factor: Include 20-30% margin for binding, misalignment, and wear

Recommendation: Always use low-friction linear rail bearings. The cost savings on a smaller actuator typically exceeds the bearing cost difference, plus you get better dynamic response.

Roll-2-Roll Technologies RLA and BLA series actuators provide thrust from 50 lbf to 2,000 lbf, handling loads up to 30,000 lbs when paired with proper bearing systems.

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 or 1DC sensor family 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 Logic 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. This prevents the "hunting" or crashing behavior common with traditional line sensors.

Yes. Unlike competitor systems that require separate sensors for edge detection and line/contrast guiding, a single Roll-2-Roll® Sensor handles both functions. The same infrared sensor that detects physical material edges can also detect printed lines, coating edges, and contrast patterns. 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.

Location and Function

• Terminal Guides: These are located at the very entry (unwind) and exit (rewind) of a roll-to-roll machine. Their purpose is to manage the master roll—either ensuring the web feeds correctly into the machine (unwind) or ensuring the roll winds up straight out of the machine (rewind).
• Intermediate Guides: These are located within the interior of the machine, typically just before a critical process such as printing, coating, laminating, or slitting. Their job is to shift the running web to align it for that specific downstream process.

Mechanism of Movement

• Terminal (Moving the Roll): Terminal guides function by moving the entire roll of material laterally. They typically utilize a "shifting stand" or "shifting base" on linear bearings to position the heavy unwind or rewind rolls.
• Intermediate (Moving the Web): Intermediate guides function by twisting or bending the web itself while the machine frame stays stationary. Mechanisms like Displacement Guides or Steering Guides displace the web by rotating or translating rollers over which the web passes.

Dynamics and Application

• Unwind vs. Rewind Dynamics:
  • Unwind Guides: Function as true guides. They shift the unwind stand to ensure the web enters the machine at a predetermined position.
  • Rewind Guides: Function as chasing systems. They do not control the web's lateral position; instead, the rewind stand moves to align the winding roll with the incoming web edge to ensure a straight roll.
• Intermediate Dynamics: Most intermediate guides (specifically Displacement and Steering guides) rely on the Normal Entry Rule, which states that a web will align itself perpendicular to the axis of the roller it is approaching.

Sensor Placement

• Terminal Guides:
  • Unwind: The sensor must be fixed to the machine frame (it does not move with the stand) and positioned immediately downstream of the shifting idler,.
  • Rewind: The sensor must be attached to the moving rewind stand so it moves with the carriage to "chase" the web.
• Intermediate Guides: The sensor is always located in the exit span (the span immediately following the guide roller) and moves with the web, not the guide mechanism. It should be placed as close to the exit roller as possible.

Actuator Requirements

• Terminal Guides: Because they often move heavy master rolls (potentially thousands of pounds), they typically require high-thrust actuators and robust mechanical rigidity to avoid resonance.
• Intermediate Guides: These move lighter guide frames and rollers, focusing more on dynamic response and low friction than raw thrust.