Unwind
Record the brake, clutch or regenerative-drive interface; the core and maximum roll diameter; roll mass; web direction; and the first driven nip that closes the supply zone.
Resources / Tension Control for Slitting Machines
Tension Control for Slitting Machines
A slitter-rewinder has to manage the supply roll, the web path through the knives and the finished rolls as one coordinated system. The usable tension strategy depends on the real control zones, changing roll diameter, feedback method, mechanical limits and the material being converted.
Slitter-rewinder engineering guide
Specify the tension zones before selecting a controller
A stable slitting line combines the unwind, web path, drives, feedback and finished-roll requirements rather than treating the rewind as an isolated setting.
1. Map the actual tension zones in the slitter
Start with the web path, not the controller label. On a typical slitter-rewinder, an unwind zone supplies the master section, intermediate driven or nipped sections establish process boundaries, and one or more rewind sections build finished rolls. A zone is only independently controllable where the mechanics and driven elements actually isolate the web span.
Knife and process span
Identify every driven roll, nip, draw ratio and dancer between the unwind and rewind. Those details determine whether a tension change can reach the slit web without disturbing an adjacent span.
Rewind shafts
For each finished roll, record the winding direction, shaft or differential-rewind arrangement, core size, full-roll diameter, speed range and roll-quality acceptance criteria.
The final number of control zones comes from the machine layout and process requirements. Do not assume that a narrow slit lane can be tuned independently until the web path, drive arrangement and mechanical isolation have been confirmed.
2. Account for changing roll diameter, speed and torque
A winder or unwinder has to keep web tension within its target while roll diameter changes. Siemens documents that diameter must be detected or calculated so motor speed can be adjusted, and that a centre winder's maximum speed is associated with minimum diameter while maximum torque is associated with maximum diameter.[1]
Unwind build-down
As the supply roll runs down, verify the diameter value, shaft-speed range and braking or drive capability from full roll to core. Treat friction, windage and acceleration as machine-specific terms, not constants copied from another line.[1][2]
Rewind build-up
As a finished roll builds, verify the torque capability, speed limit, core engagement and the way the winding reference changes with diameter. The result must be checked against the material and finished-roll acceptance criteria.[1][2]
Multiple rewinds
Where the machine has multiple rewind shafts or differential winding hardware, collect the mechanical arrangement and each roll's operating limits before assuming one tension setting applies to all lanes.
For indirect torque-based control, the accuracy of the calculated tension depends on compensation for friction and accelerating torque. Siemens and Rockwell both document the relevance of diameter and load compensation in open-loop winding control.[1][2]
3. Choose feedback for the process requirement
The feedback method should follow the process requirement and available mechanics. Siemens documents indirect tension-control modes, load-cell control modes and dancer control as distinct approaches; none should be selected only because it is familiar on another machine.[1]
Indirect control
A model and drive information generate a tension-related command without direct web-force measurement. It requires credible diameter and compensation inputs, and its attainable accuracy depends on the mechanical losses and model quality.[1][2]
Load-cell feedback
A load cell directly measures web tension and supplies the actual-value signal to the controller. Siemens notes that this can be used when open-loop torque accuracy is insufficient or disturbances need correction; the installation still needs suitable sensing-roll geometry and signal treatment.[1]
Dancer feedback
Dancer control regulates dancer position rather than directly regulating the web-force signal. Its mechanical storage can absorb short disturbances, but the dancer force, travel, geometry and position sensing become part of the tension system.[1]
For a slitter retrofit, confirm the existing sensor locations, available drive command interface, web path, material range and commissioning access before choosing a feedback architecture. A controller alone cannot correct a missing mechanical boundary or an unsuitable sensor installation.
4. Use taper as a tested finished-roll setting
Taper is a diameter-dependent change to the winding tension reference, not a universal cure for every rewind defect. Siemens documents a taper function that calculates a reduction factor for a winder tension setpoint as a function of diameter. Rockwell likewise documents that a constant current reference creates inherent taper as diameter changes and that taper profiling can be used when that result is not acceptable.[1][2]
- Define the material, core, finished-roll diameter, winding method and acceptance test before setting any taper start point or magnitude.
- Verify the controller's exact parameter convention: whether it expects a tension reduction factor, a final reference, a start diameter or another profile definition.[1][2]
- Run the full diameter range and inspect the finished rolls for the defects relevant to that material and product rather than judging the setting only from the HMI trend.
A change to taper can alter the roll build while also interacting with torque, acceleration and mechanical losses. Keep it as a documented, material-specific commissioning result.[1][2]
5. Commission across the whole roll and speed range
A steady-speed test at one diameter is not enough to qualify a slitter tension system. The commissioning plan should cover thread-up, acceleration, deceleration, splice or roll change where applicable, both ends of the diameter range and each representative material family.
- Trend the tension reference, actual tension or dancer position, diameter, shaft speed, torque command, line speed, acceleration state and relevant actuator or brake command.[1]
- Record material, width, thickness, core and full-roll diameter, roll mass, knife or process configuration and the observed defect together with the operating condition.
- Verify sensor direction, scaling and filtering before changing gains. Siemens' commissioning guidance explicitly calls for checking control sense, diameter and signal treatment for load-cell and dancer implementations.[1]
Use the collected evidence to separate sensing, control, drive, brake, web-path and mechanical-roll problems. If a change improves one product but degrades another, preserve both test conditions instead of treating the new setting as a general default.
6. Prepare a specification package before selecting equipment
A practical specification starts with the machine evidence: a web-path drawing, roll and material data, drive and actuator interfaces, sensor locations, operating speed range, target tension range, existing defects and the required commissioning access.
Machine data
Collect web width and thickness, material family, line speed, core and maximum diameters, roll mass or inertia where available, shaft configuration, brake or drive type and the driven/nipped elements that form each zone.
Control data
Collect tension setpoints, feedback type and signal range, diameter method, torque or speed command interface, taper profile, alarms and trend captures from both acceptable and unacceptable runs.[1]
Acceptance data
Define the finished-roll and process checks that matter to the application, then validate the proposed settings through the full operating range before standardizing them.
KRD can use this application package to narrow a controller, load-cell, actuator, brake or integrated tension-control solution for further engineering review. Final sizing and commissioning remain machine- and material-specific.
Sources & References
- Siemens AG. SIMATIC Winder and Tension Control Back
- Rockwell Automation. WebPak 3000 Drive Application Workbook Back
FAQ
What data is needed to specify tension control for a slitter-rewinder?
Start with the web path, material and width, speed range, core and full-roll diameters, roll mass where available, unwind and rewind hardware, driven or nipped elements, feedback signals, tension range, existing defects and trend captures. This lets the control zones and interfaces be reviewed before a component is selected.
Does every slitter-rewinder need load-cell feedback?
No. A load cell directly measures web tension and can be appropriate where the required accuracy or disturbances justify it, but the right architecture depends on the web path, sensing-roll installation, drive interface, material and mechanical arrangement. Indirect and dancer-based approaches are different engineering choices.
Is taper tension always required on the rewind?
No. Taper changes the winding tension reference with diameter. Its profile, direction and amount must be tested against the material, core, winding method, controller convention and finished-roll acceptance criteria.
Why test tension at both the core and full-roll conditions?
Roll diameter changes the speed and torque conditions. Testing only one diameter can miss behaviour during build-up or build-down, acceleration, deceleration and the material-specific conditions that define the actual production result.
Ask KRD to review your slitter-rewinder tension application
Send the web-path drawing, material and width, target tension range, speed range, core and maximum diameters, rewind arrangement, existing feedback, actuator or drive interface, and a trend or video of the defect. KRD can help prepare a controller, sensor and actuator shortlist for engineering review.