Technical

In rewind chasing applications, the sensor must be mechanically attached to the shifting stand because the control system is designed to keep the sensor output at "zero." When the sensor moves with the roll, the system naturally drives the stand until the sensor aligns with the web edge.

If the sensor were fixed to the floor (like in intermediate guiding), the system would lose the relative position between the web and the roll face. The result would be telescoped or uneven rolls because the guide has no reference point for where the roll edge should be.

The sensor should observe the web at a fixed idler immediately upstream of the shifting stand. This provides a stable reference point while the stand—and sensor—move together.

The choice between edge guiding and line guiding depends on what defines "correct position" for your process:

Use Edge Guiding When:

• The physical web edge is your reference (e.g., die-cutting to edge, edge-aligned lamination)
• Material has consistent, clean edges
• Processing unprinted or solid-color materials

Use Line Guiding When:

• Processing pre-printed materials where print registration matters more than edge position
• Web edges are inconsistent (ragged, variable width) but printed marks are reliable
• Guiding to a coating edge rather than the substrate edge
• Running materials with printed registration marks or tracking lines

The Roll-2-Roll Technologies Advantage: With ODC 960 wide-aperture sensors, you can switch between edge and line guiding modes without changing hardware. This is particularly valuable for slitter rewinder applications that process both plain substrates (edge guide) and pre-printed materials (line guide) on the same machine.

The sensor automatically adapts to detect either the physical edge or a contrast line based on your selection in the SCU5 or SCU6x controller interface.

Roll-2-Roll Technologies actuators are specifically designed for hydraulic cylinder replacement in unwind and rewind guiding applications:

What You Eliminate:

• Hydraulic fluid and the risk of product contamination from leaks
• Filter changes and fluid maintenance (typically 2-4 times per year)
• Seal replacement and valve rebalancing
• Hydraulic power unit (HPU) maintenance and energy costs

What You Gain:

• Clean, dry operation—critical for food, pharmaceutical, and medical applications
• Full thrust at zero speed (hydraulics struggle with static positioning)
• Smooth response at variable speeds without the "stick-slip" behavior of hydraulics
• Digital communication via EtherNet/IP, PROFINET, or EtherCAT for integration with modern PLCs

Retrofit Options:

• RLA Series: Rotary stepper with belt/pulley and ball screw, thrust up to 2,000 lbf
• BLA Series: Inline stepper with external ball screw for terminal guide applications

Most hydraulic retrofits can be completed in a scheduled maintenance window without major mechanical modifications to the existing stand structure.

The "fixed sensor rule" is fundamental to unwind guiding physics and is the opposite of rewind chasing:

The Logic: In unwind guiding, you are positioning the web to enter the machine at a specific target location. The sensor acts as that target. The controller moves the shifting stand until the web edge aligns with the fixed sensor position.

The Common Mistake: If you mount the sensor on the moving stand (as you would in a rewind chasing application), the sensor moves with the error. When the stand shifts left, the sensor shifts left too—so from the sensor's perspective, nothing has changed. The system cannot detect or correct the misalignment relative to the machine frame.

Proper Configuration:

• Sensor: Fixed to the machine frame (floor or fixed structure)
• At least one idler roller: Mounted on the shifting stand (moves with it)
• Sensor position: Immediately downstream of the shifting idler

This configuration ensures the sensor sees true web position relative to the machine, while the shifting idler maintains a consistent web plane as roll diameter changes.

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.