Unwind station
Record the roll direction, brake or regenerative-drive interface, core and full-roll diameter, and the first driven nip that closes the zone.
Resources / Unwind and Rewind Tension Control
Unwind and Rewind Tension Control
Unwind and rewind stations face opposite diameter changes but the same engineering requirement: coordinate roll speed, torque, feedback and compensation so the web remains within its intended tension range from core to full roll.
Winding control engineering guide
Control the complete roll, not one diameter
A stable winding zone accounts for changing radius, speed, torque, inertia, friction and the chosen feedback architecture.
1. Separate the unwind and rewind control zones
An unwind restrains the supply roll as its diameter decreases, while a rewind applies winding torque as its diameter increases. Each station must be bounded by a driven or nipped element that can isolate its web span; otherwise a controller cannot treat the span as an independent tension zone.
Rewind station
Record the winding direction, drive or clutch interface, core and finished-roll diameter, and whether the roll-build target requires a diameter-dependent tension reference.[1][3]
Process boundary
Identify which driven roll or nip separates winding tension from printing, coating, laminating, inspection or slitting tension.
Draw the real web path before selecting settings. Roll names alone do not define the mechanical boundary, and changing one station can disturb an adjacent zone when the line does not isolate them as expected.
2. Relate roll diameter, shaft speed and torque
For the centre-driven winding architecture documented by ABB, the basic tension-producing motor torque is calculated from the tension reference and actual roll radius. The same web tension therefore requires a different torque as radius changes. At a given web speed, shaft speed also changes with diameter, so the control system needs a dependable diameter value or calculation.[2]
Unwind from full roll to core
Radius falls and shaft speed rises. The resisting torque required for the same ideal web tension falls with radius, subject to the actual brake, drive and mechanical losses.[1][2]
Rewind from core to full roll
Radius rises and shaft speed falls. The ideal tension-producing torque rises with radius, while the drive must also operate within its speed and torque limits.[1][2]
Diameter information
A controller may calculate diameter from web and shaft motion, infer it from material build, or accept an external diameter signal. The usable method depends on the available machine signals and operating sequence.[1]
Treat the simple radius relationship as the starting model, not a complete machine command. Friction, acceleration, roll inertia, gearing and actuator response add terms that must be handled by the selected control implementation.[1][2]
3. Choose feedback for the real winding problem
The controller can schedule torque without direct tension feedback, regulate measured web force from a load cell, or regulate dancer position. Siemens documents these as different winding and tension-control methods, each with different signals, mechanics and disturbance behaviour.[1]
Indirect or open-loop
Use a machine model and diameter information to generate the winding command. Its accuracy depends on the model and compensation because actual web tension is not the controlled feedback variable.[1][2]
Load-cell feedback
Measure web force at a sensing roll and let the tension controller trim the command from the measured error. The load cell, wrap geometry, signal conditioning and installation must suit the machine.[1][2]
Dancer-position feedback
Regulate dancer position while the dancer mechanics establish the resulting web tension. Its travel can buffer short web-length disturbances, but the moving mechanism and applied force remain part of the control system.[1]
Do not select a method only by the desired accuracy label. Confirm the available drive mode, brake or clutch interface, feedback installation, dancer mechanics and operating cases before choosing the architecture.
4. Apply rewind taper tension deliberately
Taper tension changes the rewind tension reference as roll diameter builds. Siemens provides diameter-based linear, hyperbolic and breakpoint-table taper functions; Rockwell documents a centre-winder routine that reduces the reference between a selected start diameter and full roll.[1][3]
ABB describes taper as a way to influence roll hardness and help prevent roll starring or core crushing. These are documented functions of the cited winder implementation, not a universal setting: the required direction and amount depend on the material, winding method and finished-roll acceptance criteria.[2]
- Establish an acceptable core tension and confirm that the core, shaft and first layers can tolerate it.
- Choose the diameter at which taper begins and define the intended full-roll reference or reduction according to the controller's documented parameter convention.[1][3]
- Inspect roll hardness, layer movement, core condition, telescoping and downstream unwinding instead of judging the setting only from the controller display.
- Store the validated settings with the material, width, thickness, roll dimensions, speed range and winding method so they are not copied blindly to a different product.
5. Account for friction, inertia and speed changes
Steady-speed performance does not prove that a winding zone is correctly commissioned. Siemens separates tension-producing torque from friction and acceleration pre-control, while ABB calculates inertia compensation from roll diameter and material data to add torque during acceleration and deceleration.[1][2]
- Test an almost empty and an almost full roll because inertia, shaft speed and available torque differ across the winding cycle.[1][2]
- Check startup, acceleration, steady speed, deceleration and controlled stop separately; record both tension feedback and drive or brake command.
- Verify diameter initialization and reset behaviour after a roll change, splice, web break or manual jog.[1]
- Investigate mechanical friction, backlash, brake release, roll balance and dancer motion before using controller gain to hide a mechanical disturbance.
Compensation values are machine-specific. Use the current drive and controller documentation, confirm units and signal direction, and validate changes with the actual production material under controlled conditions.
6. Commission and troubleshoot with evidence
Use a repeatable test matrix instead of changing several parameters after each visible defect. Capture the material, roll diameter, line speed, setpoint, feedback, diameter value, actuator command and the exact stage of the machine cycle.
Tension changes with diameter
Check diameter scaling, core and full-roll values, torque direction, gear ratio, actuator range and whether the command includes the required radius relationship.[1][2]
Spike during speed change
Compare the feedback trace with acceleration and deceleration, inertia compensation, friction compensation, ramp timing and brake or drive response.[1][2]
Poor finished-roll build
Review taper settings together with nip loading, alignment, core condition, cross-machine tension profile and the material recipe; tension control alone cannot correct every roll defect.[2][3]
For a KRD engineering review, provide the web-path drawing, material and width, target tension range, core and maximum diameter, roll mass or inertia, full speed range, winding direction, present brake, clutch or drive, feedback signals and a short trend or video showing when the problem occurs.
Sources & References
- Siemens AG. SIMATIC Winder and Tension Control Back
- ABB. ACS880 Winder Control Program Firmware Manual Back
- Rockwell Automation. Drive Application Software - Tension Control Function Module Back
FAQ
Why does unwind tension change as the roll gets smaller?
In a centre-driven or braked unwind, the torque required to create a given ideal web tension changes with roll radius. Shaft speed also rises as diameter falls at the same web speed. Diameter calculation, feedback and machine-specific compensation are therefore important across the full roll.
What is the main control difference between unwind and rewind?
An unwind restrains or regeneratively controls the supply roll as diameter decreases. A rewind applies winding torque as diameter increases and may also use taper tension to manage the finished roll build. Both still require a defined mechanical tension zone and compatible actuator or drive.
Does every rewind need taper tension?
No. Taper is a diameter-dependent reference function used when the roll-build objective requires tension to change as the roll grows. Its direction, starting diameter and amount must be matched to the material, winding method, controller convention and finished-roll acceptance tests.
What data should be recorded during winding commissioning?
Record material and width, core and actual diameter, line and shaft speed, tension setpoint and feedback, diameter value, actuator command, acceleration state, taper state and the observed roll or web defect. Repeat the test near core and near full roll.
Ask KRD to review your unwind or rewind zone
Send the web-path drawing, material and width, tension range, core and maximum diameter, roll mass, speed range, winding direction, present actuator or drive, feedback signals and a trend or video of the problem. KRD can help narrow the controller, sensor and actuator shortlist for engineering review.