Feedback or process input
A load cell can measure web tension directly. A dancer-position sensor can report dancer movement, while an indirect system can estimate the required torque from machine variables such as roll diameter.[1][3]
Resources / Web Tension Control System
What Is a Web Tension Control System?
A web tension control system regulates the pulling force applied to a continuous material as it moves through unwind, process and rewind sections. A practical system coordinates sensing, control logic, an actuator or drive, and the machine mechanics instead of treating the controller as a stand-alone component.
Tension control fundamentals
Stable feedback starts with the complete machine loop
Sensors, control logic, actuators and the web path must work together to regulate material tension through each machine zone.
What web tension control means
Web tension is the force applied to a continuous material in the machine direction. Tension control is the process of regulating that force while the material is transported, processed or wound. The required value and allowable variation depend on the material, machine and process rather than on one universal setting.[2]
A tension controller does not act on the web by itself. It receives a measured or calculated process value, compares that value with the target, and commands a brake, clutch or drive. The resulting tension also depends on roll radius, inertia, friction, roller geometry and other machine conditions.[1][2]
The main parts of a tension control system
Controller
The controller evaluates the selected process value against the target and produces the command needed by the selected actuator or drive. Its configuration must match the feedback method and machine architecture.[1]
Actuator or drive
A brake, clutch or motor drive changes torque or speed so the machine can correct the controlled zone. The available control mode and mechanical transmission affect which method is practical.[1][2]
Machine and web path
Roll diameter, inertia, gearing, friction, roller layout and material behaviour are part of the control problem. Component selection and tuning therefore require the actual machine context.[1]
Tension zones in a roll-to-roll line
Roll-to-roll equipment is commonly considered as separate unwind, intermediate or process, and rewind tension zones. Driven or nipped sections can isolate one zone from another, allowing different parts of the line to use different tension targets or control methods.[2][3]
- The unwind zone controls material leaving the supply roll as its radius changes.[1][2]
- The process zone supports stable transport through printing, coating, laminating, slitting or another operation.[3]
- The rewind zone coordinates tension and winding torque as the finished roll builds.[1][2]
The physical boundaries must be confirmed from the real web path. Adding a controller cannot create an independent zone if the machine does not mechanically isolate that section.
Load-cell, dancer and indirect control methods
The three methods below solve different control problems. None is automatically the best choice for every line; selection depends on the required controlled variable, mechanical layout, disturbances, drive capability and commissioning constraints.[1]
Load-cell feedback
A load cell measures web tension directly and provides the actual value to the controller. This supports direct tension regulation but does not add the material-storage function of a dancer.[1]
Dancer feedback
A dancer uses a preloaded moving roller assembly. A position sensor reports movement so the controller can adjust speed or torque; the available travel can also absorb short changes in web length.[1][3]
Indirect or open-loop control
An indirect method calculates the command without measuring the controlled tension directly. Roll diameter, gear ratio and compensation terms become important because the required torque changes as the roll builds or unwinds.[1][2]
For a deeper comparison, see the related guide to open-loop and closed-loop tension control. The final method should be verified against the machine drawings, drive functions and commissioning tests.
Why roll diameter and disturbances matter
For a centre-driven roll, the relationship between applied torque, roll radius and web tension means the torque command must change as the roll diameter changes. Indirect control therefore needs a reliable diameter calculation or measurement and suitable compensation for the machine.[1][2]
Published roll-to-roll research treats web tension and velocity as a dynamic, nonlinear control problem in which disturbances affect regulation. A separate multispan study used load cells with an active dancer and observed tension spikes associated with roll-radius changes in that experimental system. These studies illustrate engineering mechanisms; they do not establish a universal performance result for every production line.[4][5]
Engineering information to collect before selection
KRD uses the complete application context to narrow the controller, sensor and actuator options. Final sizing and settings require engineering review and commissioning; a model number alone does not define the behaviour of the complete loop.
- Material type, width, thickness and whether it stretches, wrinkles, slips or is easily marked.
- Minimum and maximum line speed, target tension range and the zone where the problem occurs.
- Core diameter, maximum roll diameter, roll mass or inertia, shaft arrangement and web-path drawing.
- Existing brake, clutch or drive model; available torque or speed mode; PLC and analogue or fieldbus interfaces.
- Available sensor and actuator mounting space, environmental conditions, and photos or short operating videos.
- Observed symptoms during startup, acceleration, steady running, deceleration and roll change.
This information helps separate feedback, actuator, drive and mechanical questions before equipment is selected. It is a project-scoping checklist, not a remote diagnosis or a performance guarantee.
Sources & References
- Siemens AG. SIMATIC Winder and Tension Control Back
- Montalvo Corporation. Web Tension Control Basics Back
- Montalvo Corporation. Dancer Roll Tension Control Basics Back
- Japan Society of Mechanical Engineers. Back-Stepping Controller Based Web Tension Control for Roll-to-Roll Web Printed Electronics System Back
- Chinese Journal of Mechanical Engineering. Web Tension Regulation of Multispan Roll-to-Roll System Using Integrated Active Dancer and Load Cells for Printed Electronics Applications Back
FAQ
What does a web tension control system control?
It regulates the pulling force applied to a continuous web within a defined machine zone. The system coordinates a process input or feedback signal, controller logic, a brake, clutch or drive, and the machine mechanics.
Is a load cell always required for tension control?
No. A system may use direct load-cell feedback, dancer-position feedback or an indirect calculation. The suitable method depends on the controlled variable, accuracy requirement, machine layout, disturbances and available drive or actuator functions.
How do I choose between load-cell and dancer feedback?
A load cell directly measures tension, while a dancer regulates position and provides some material storage through its travel. Selection requires review of the web path, transient behaviour, available mounting space, mechanics and commissioning requirements.
What information should I send KRD for tension-control selection?
Send the material, width, thickness, speed, tension range, core and roll diameters, roll mass, zone, web-path drawing, existing brake or drive details, interface requirements, mounting space, and a description of when the problem occurs.
Discuss your tension-control application with KRD
Share your material, speed, tension range, roll dimensions, machine layout and existing drive or brake details. KRD can help identify controller, sensor and actuator families for further engineering evaluation.