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Rewind guiding with edge sensor

Rewind/Winder Chasing Systems

Perfect Rolls. Dynamic Tracking. The "Moving Sensor" Logic.

In most parts of a machine, you move the web to match the machine. In rewinding, you must do the opposite: move the machine to match the web. If a web arrives at the winder with a slight wander, holding the winder stationary will result in a "telescoped" or uneven roll edge. To fix this, the entire rewind stand must physically move back and forth to catch the incoming web. This is called "Chasing." The sensor is mounted directly to the moving stand, allowing it to lock onto the web edge and force the heavy roll to follow the web's every movement, ensuring a perfectly straight-sided finished product.

The Challenge: It's Not "Guiding," It's Physics

Rewind chasing presents unique challenges that standard web guides do not face:

  • The "Moving Target" Logic: Unlike an unwind or intermediate guide where the sensor is fixed to the floor, a rewind sensor must move with the stand. If the sensor were fixed to the floor, the system would lose the relative position between the web and the roll, making accurate winding impossible.
  • Variable Mass Dynamics: A rewind application is physically demanding because the load changes constantly. You start with an empty core (light) and end with a full roll (heavy). The actuator must be sized to handle the maximum roll weight (often thousands of pounds) while maintaining the agility to make small, fast corrections.
  • Hydraulic Headaches: Historically, moving these massive stands required hydraulic cylinders. These introduce oil leaks that contaminate products, require filter/seal maintenance, and suffer from "valve balancing" issues where extension and retraction speeds differ.

The Solution: Roll-2-Roll Technologies Electromechanical Chasing

We replace messy hydraulics and complex linkage systems with high-thrust, maintenance-free electromechanical precision.

The Roll-2-Roll Technologies "Heavy-Duty" Advantage

  • High-Thrust, Clean Operation: Our electromechanical actuators can move loads up to 30,000 lbs (with low-friction bearings) without a single drop of hydraulic fluid. This eliminates the risk of product contamination and the noise of hydraulic pumps.
  • Smart "Chasing" Logic: The Roll-2-Roll® Controller is pre-programmed with specific Rewind logic. It processes the feedback from the moving sensor to keep the relative distance between the web edge and the roll face constant, effectively "freezing" the web position relative to the roll.
  • Stiff Control Loop: By using stiff, zero-backlash actuators, we ensure the heavy stand reacts immediately to sensor signals, avoiding the "lag" that causes telescoping on the outer layers of the roll.

Verified Specifications

SpecificationValue
Maximum Thrust50–1,500 lbf (222–6,670 N)
Load CapacityUp to 30,000 lbs with low-friction bearings
Stroke Length1–12 in (25–300 mm)
Maximum SpeedUp to 2 in/sec (51 mm/sec)
Sensor Ranges48–960 mm (1.9–37.8 in)
Controller Frequency25–50 Hz typical
Industrial ProtocolsEtherNet/IP, PROFINET, EtherCAT, Modbus/TCP

Advanced Capability: Dual-Sensor Bidirectional Operation

For coating applications that run forward and backward: The SCU6x and SCU5 controllers can process two sensors simultaneously with independent enable/disable control. This opens up specialized configurations:

  • Sensor 1: Mounted on the rewind moving frame—active during forward winding
  • Sensor 2: Mounted on the fixed machine frame—active during reverse (unwind) direction

This dual-sensor approach is ideal for coating machines that reverse direction between passes. Instead of repositioning a single sensor, operators simply switch which sensor is active via the controller interface or PLC command.

Benefits of Dual-Sensor Configuration

  • No sensor repositioning between forward and reverse operations
  • Instant direction changes—switch active sensor with a single command
  • Reduced changeover time on bidirectional coating lines
  • Simplified machine design—no motorized sensor positioners needed

Engineering Guide: The "Moving Sensor" Rule

The most common failure in rewind designs is improper sensor placement. Follow these rules to ensure stability.

The Mounting Rule

  • The Sensor MUST Move. For rewind applications, the sensor must be mechanically attached to the shifting rewind stand. As the actuator moves the stand, the sensor must move with it.
  • Why? The control loop is trying to keep the sensor output at "zero." By moving the sensor with the roll, the system naturally drives the roll until the sensor aligns with the web edge.

The "Fixed Idler" Rule

The sensor should look at the web while it is wrapped over a Fixed Idler (attached to the floor/frame) immediately upstream of the shifting stand.

  • Placement: Install the sensor as close as possible to this last fixed idler.
  • Stability: The arm holding the sensor must be structurally stiff. If the sensor arm wobbles as the heavy stand shifts, it induces "false error" and causes the stand to oscillate.

Actuator Sizing: Breakaway Force

Sizing a rewind actuator isn't just about weight; it's about friction.

  • Formula: The actuator must overcome the Breakaway Force (Static Friction) of the linear bearings under full load.
  • Recommendation: Use low-friction linear rail bearings (coefficient ~0.01) rather than sliding shafts (coefficient ~0.25) to reduce the actuator size required.

System Configurations (Select Your Kit)

Standard Rewind Chasing Kit

Best for: Converting lines, slitters, and laminators rewinding rolls up to 10,000 lbs.

  • Sensor: ODC 192 or ODC 288 (mounted on the moving stand)—wide aperture accommodates multiple web widths without repositioning
  • Actuator: BLA Series electromechanical actuator (replaces hydraulic cylinder)
  • Controller: SCU6x with integrated motor driver—compact solution for most converting lines

Heavy-Duty Retrofit Kit

Best for: Metals, heavy paper, and large diameter film rolls exceeding 10,000 lbs.

  • Sensor: ODC 480 or ODC 768 for wider webs
  • Actuator: RLA Series ball screw actuator—thrust up to 1,500 lbf (6,670 N)
  • Controller: SCU6x with diameter-based gain scheduling via EtherNet/IP or PROFINET (adjusting response as the roll gets heavier)

Cost of Inaction: What Staying Put Is Costing You

Every week you continue operating with legacy hydraulic systems or undersized guides, you're accumulating hidden losses:

Hidden Costs (Untracked but Real)

  • Hydraulic maintenance labor: Typical plants report 10–20 hours annually on unwind/rewind guide maintenance alone—filter changes, seal replacements, valve adjustments
  • Sensor repositioning time: If your narrow-aperture sensor requires repositioning between web widths, you're adding 2–5 minutes per changeover × multiple changeovers per day
  • Troubleshooting valve balance issues: Unequal extension/retraction speeds cause "hunting" that's difficult to diagnose

Risk Costs (Probability × Severity)

  • Product contamination: In food, pharmaceutical, or medical applications, a single hydraulic oil leak can contaminate an entire production run—potentially costing $50,000+ in recalls or rejected batches
  • Telescoped rolls: Rolls that telescope during shipping may be rejected by customers, requiring rework or scrapping
  • Slip/fall hazards: Hydraulic fluid on the production floor creates safety liability—average slip/fall claims cost $54,000

Opportunity Costs (Value You're Leaving on the Table)

  • Bidirectional coating capability: Without dual-sensor configuration, machines that reverse direction require manual sensor repositioning—limiting your ability to run complex coating processes
  • Speed limitations: Hydraulic response lag forces operators to run slower to prevent telescoping—often 10–20% below machine capability
  • Multi-width flexibility: Narrow-aperture sensors limit your ability to run varied SKU widths without frequent adjustments

The bottom line: The "cheaper" hydraulic system isn't cheaper when you factor in maintenance, contamination risk, and lost production capability. Typical customers report payback within 12–18 months from maintenance savings alone.

Results: Stop Telescoping. Stop Leaks.

Replacing a hydraulic shifting stand with Roll-2-Roll Technologies electromechanical systems solves three problems instantly:

  • Quality: Elimination of "spongy" or telescoped roll edges caused by hydraulic valve lag or seal friction
  • Maintenance: 100% elimination of hydraulic fluid, filter changes, and seal replacements
  • Safety: No high-pressure lines or slip hazards on the production floor

Frequently Asked Questions

Actuator sizing starts with one question: how much force does the actuator need to produce to move your guide or shifting stand reliably? The answer depends on more than just the weight on the bearings.

Roll-2-Roll Technologies uses a 6-term force model that accounts for every significant resistance the actuator must overcome:

  • Bearing friction — the dominant term for heavy loads on linear bearings
  • Inertia — force to accelerate the mass at your target correction rate
  • Web tension lateral component — the sideways pull from web wrap angle on guide rollers
  • Umbilical drag — hoses, cables, and air lines that resist carriage motion
  • Floor grade — gravity component if the travel axis is not perfectly level
  • Misalignment friction — additional drag from rail or bearing misalignment

Our actuator sizing calculator offers two approaches:

  • Simple mode — enter load weight and bearing type for a quick estimate. Uses a factor of safety of 2.0 or higher to compensate for forces not explicitly modeled.
  • Detailed mode — model all six force terms individually for a precise result, typically with a factor of safety of 1.5 to 1.75.

If you want a reality check before running the calculator, try a spring-scale pull test: attach a calibrated spring scale to the carriage and pull horizontally at a steady, slow rate. The peak reading gives you the actual installed friction force — often 2 to 5 times the catalog bearing friction value.

For a deeper walkthrough of the force model and worked examples, see the full actuator sizing technical article.

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.

This question highlights an important distinction that causes confusion: load weight is not the same as thrust force.

The RLA Series supports loads up to 30,000 lb on precision linear bearings. That is the weight sitting on the bearings — the roll, the chuck, the shifting stand structure. The actuator does not lift this weight. It pushes the carriage sideways along the bearings, overcoming friction and other resistance forces.

The actual thrust force required to move a 30,000 lb load is typically 120 to 600 lbf, depending on bearing type, rail condition, and secondary forces like web tension and umbilical drag. The RLA Series provides thrust across three models:

  • RLA-050 — 500 lbf thrust
  • RLA-100 — 1,000 lbf thrust
  • RLA-200 — 2,000 lbf thrust

To illustrate with rough numbers: a 20,000 lb load on profiled linear rails with a friction coefficient of 0.005 (installed, not catalog) produces approximately 100 lbf of friction force. Add inertia, web tension lateral component, umbilical drag, and a factor of safety — and the required thrust might be 250 to 400 lbf. An RLA-050 handles that with margin.

The key takeaway: do not select an actuator based on load weight alone. Run the force calculation to determine actual thrust demand. Our actuator sizing calculator does exactly this.

Roll-2-Roll Technologies RLA actuators are deployed in hundreds of installations across converting, printing, and packaging lines, reliably guiding loads from a few thousand pounds up to the rated 30,000 lb capacity — many running continuously for years.

Roll-2-Roll Technologies electromechanical rewind guides can handle loads up to 30,000 lbs (13,600 kg) when paired with low-friction linear rail bearings (coefficient ~0.01).

Key specifications:

  • Maximum thrust: 50–1,500 lbf (222–6,670 N)
  • Stroke length: 1–12 in (25–300 mm)
  • Maximum speed: Up to 2 in/sec (51 mm/sec)

The critical factor for sizing is breakaway force—the static friction the actuator must overcome to start moving the loaded stand. Using low-friction linear rail bearings dramatically reduces the required actuator size compared to sliding shaft designs (coefficient ~0.25).

For extremely heavy loads, the RLA Series ball screw actuators provide thrust up to 1,500 lbf while maintaining precision positioning.

Let us be direct: servo motors are excellent. They offer smooth torque delivery, high bandwidth, and precise closed-loop control. For many motion control applications, they are the right choice. The question is whether web guiding is one of those applications — and for OEM-shipped actuators, the answer favors steppers for specific, defensible reasons.

The OEM shipping problem: Roll-2-Roll Technologies builds actuators that ship to converting, printing, and packaging facilities worldwide. Servo drives require load-dependent tuning — reflected inertia ratio, friction characterization, and mechanical resonance all depend on the installed machine, not the actuator alone. A stepper motor sized conservatively at design time requires no field tuning. It works out of the box regardless of what it is bolted to.

The web sensor outer loop: This is the key enabler. In web guiding, position feedback comes from a Roll-2-Roll® Sensor observing the actual web edge — not from an encoder on the motor shaft. Every source of actuator imprecision (lost steps, backlash, drivetrain compliance) is corrected by the sensor on the next correction cycle. The actuator does not need to be a precision positioning device. It needs to move reliably in the commanded direction.

What we give up — honestly:

  • Efficiency — steppers draw current at rest to hold position; servos draw only what the load demands
  • Speed — stepper torque drops off faster at higher speeds than servo torque
  • Noise — steppers are audibly louder during motion, especially at certain speeds
  • High duty cycle — continuous rapid cycling favors servo thermal characteristics

For web guiding — where corrections are slow (0.5 to 2 Hz), the motor is at rest most of the time, and field simplicity matters — these tradeoffs are acceptable. The result is a reliable, zero-tuning actuator that has performed across hundreds of installations.

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