The Automation of Winding and Unwinding Applications in Industrial Machinery

Winding and unwinding mechanisms form the backbone of material handling across diverse manufacturing sectors. From paper mills producing rolls for printing presses and packaging lines to steel processors handling coiled sheet metal, plastic film manufacturers, and textile operations, these systems ensure precise material control and quality throughout production.

This article examines the automation architecture behind industrial winding applications, with particular emphasis on motor selection, variable frequency drive (VFD) configuration, and control system design.

Understanding these components and their integration is essential for engineers tasked with specifying, implementing, or optimizing winder systems that demand consistent tension control, accurate speed regulation, and reliable performance under varying load conditions.

The Basics of Winders and Unwinders

At its core, a winding system takes continuous web material, whether paper, film, metal, or fabric and spools it onto a cylindrical core. The finished roll offers compelling advantages: compact form factor, efficient storage and transportation, and convenient dispensing for downstream operations.

However, high-speed winding without proper control leads to immediate quality problems. Insufficient tension produces loose, telescoping rolls with layers that shift during handling. These adverse results render the product unusable. Conversely, excessive tension risks breaking delicate webs or inducing permanent deformation, stretching film beyond recovery or ruining the structural integrity.

Unwinding is the reverse process. We start with a roll of material, and we unwind it in a controlled way. When the material is unwound, it is used in some other processes like printing, stamping, welding, perforating, cutting, etc. But the same principles hold true, we typically want to unwind at high speeds so we can process more finished goods, but we want to do it under control without damaging the product.

The Importance of Tensioning the Material

Every material has an optimal tension level that should be maintained during the winding process. If the tension is insufficient, the material may bunch up or wrinkle. Conversely, applying too much tension can lead to the material breaking, tearing, or stretching.

There are various methods to apply tension to the material. Traditionally, this tension could be managed using an adjustable spring-loaded mechanical device. Another option is to use a clutch that allows for adjustable opposing torque. Lastly, a motor roller that resists the winding or unwinding process can be utilized. The latter configuration is the focus of this article.

The demand for accurate tensioning often means the control system should be closed loop. Load cells can be used to accurately measure tension through a dancer roller and provide feedback to a controller which has an optimal ‘setpoint’. These sensors are particularly useful if additional rollers are required to prepare and smooth the material before winding. It is possible to have many different load cells if there are different processing zones during production. When a motor is acting directly on a roller or on the main core, a motor feedback device like a resolver or encoder, will allow the accurate measurement of torque and speed at the motor shaft.

Center-driven Winders and Material Build

Most winders, commonly found in the paper and metal coil industries, are center-driven types. In these systems, material is wound onto a central core that is powered by a motor.

 
As the material is wound, it builds up on itself, causing the diameter of the roll to increase. As the radius grows, the motor speed decreases to maintain a constant rate of material flow. This increase in radius leads to a higher required torque at the shaft to keep the web tension stable, creating an inverse relationship between the motor’s winding speed and torque. Additionally, the mass and inertia of the growing roll increase, which can lead to potential control issues.

 
As the roll approaches being fully wound, the motor operates at a low speed while requiring the highest torque. Controllers for center-driven winders must incorporate some form of build compensation to account for the changing radius of the wind and the corresponding torque requirement to command the variable frequency drive. Some VFDs have this functionality built in, while increasingly compensation algorithms can also be implemented in the programmable logic controller (PLC). This PLC approach offers the most flexibility, especially if adjustments need to be made or if the machine is managing multiple winding zones.

Surface-driven Winders

Surface-driven or drum winders differ from center-driven winders in that they operate through friction between a motorized secondary roller and the core roll. From a motor control perspective, these winders require constant torque, regardless of the amount of material buildup. While they are simpler to control from the motor’s standpoint, the quality of the finished roll may not be as high as that produced by center-driven winders, since the motorized roller comes into direct contact with the material.

Full Torque at 0 Speed

One of the key requirements for center-driven winders is the need for precise torque control at low speeds, including operation down to 0 RPM. To achieve this, the induction or servo motor must be equipped with an encoder feedback device.

While TEFC (totally enclosed fan-cooled) induction motors are commonly used in many industrial applications, they are less suitable for these specific applications since they need to operate at higher RPMs for the fan to effectively cool the motor.

KEB offers two excellent motor options for winding applications that require sustained operation of full torque at 0 speed. The first option is the DL4 PM servo motor, which can deliver full torque indefinitely. This motor is fully enclosed and does not rely on fans or forced cooling by default.

 
The second option is the AL4 asynchronous series motor. These motors were originally developed to replace the older style DC motors so they work great for retrofitting older machines. However, they combine all the advantages of an AC motor, including the maintenance-free brushless design so they are perfect for new machine designs as well.

 
These motors can be equipped with forced ventilation if the application requires it and the torque demands are high – in this case, consult with a KEB application engineer to discuss the application requirements and they can help size and select the correct motor.

Regenerative Energy and DC Bus Load Sharing

Motors can operate in two different modes depending on the direction of motor rotation and the torque at the motor shaft. These are called Motoring and Regenerating motor modes. The motor that is winding the material against tension will be operating in Motoring mode and will be consuming electrical energy.

 
The motor that resists and applies tension to the material is in Regenerating mode. A VFD controlled motor that is in Regen mode will have electrical energy flowing into the drive. Something must be done with this excess regenerated energy and the most straightforward option is to bleed the energy across a brake resistor. However, this system energy is lost as heat.

Furthermore, some applications like textiles might have fibers that should not be around hot elements like a hot resistor. A much better solution is to connect the DC buses of the 2 VFDs together. This allows current to flow between the two drives. The net result is far less energy consumption overall.

KEB’s S6 and F6 drives have DC bus terminals that can be connected with appropriate UL-rated fusing. Care should be taken when sizing the motors and drives to ensure they can handle the required current.

If there are additional motorized axes on the machine, it is even possible to tie more than one drive’s DC bus together. In this case, using a common rectifier like the R6 to power the system could save wiring will providing energy sharing to the entire machine.

Compact 3: Machine Controller for Motor Control and Build Compensation

This article has discussed motors and drives, but what about the controller responsible for the winding application? KEB’s industrial embedded controls are well-equipped to manage the entire machine, including the winding axes. In certain machines, such as printing presses, the winder is just a small component of the overall system. However, there is significant complexity in coordinating the various motor axes.

KEB’s C6 Compact 3 PLC simplifies multi-axis control through IEC-61131 Function Blocks. Each motor axis utilizes a dedicated KEB Motor Control function block, enabling straightforward velocity or torque control. These function blocks streamline axis synchronization and allow flexible cascading of control loops to meet application requirements.

 
The Compact 3 also supports in Structured Text (ST) through KEB’s Combivis Studio 6 Software. ST would be a great option to program any custom build compensation equations that are needed to manage the winding/unwinding process.

In this case, Tension profiles can be programmed that are customized to the requirements and sensitivities of the material or film being wound. When programming a machine, it is even possible to mix and match ST and FB programming languages – giving the best of both worlds and providing a very powerful and flexible control platform.

KEB Solutions: Optimizing Your Winding Application

Successful winding and unwinding automation requires careful integration of motors, drives, and controls to achieve the precise tension management and speed regulation that modern manufacturing demands. From selecting between servo and asynchronous motors to implementing DC bus sharing for energy efficiency, to programming sophisticated build compensation algorithms, each decision impacts both product quality and operational costs.

The complexity of these systems means that one-size-fits-all solutions rarely deliver optimal results. Material properties, production speeds, roll dimensions, and quality requirements all influence the ideal configuration for your specific application. Whether you’re designing a new machine, retrofitting existing equipment, or troubleshooting performance issues, the details matter.

KEB’s application engineers specialize in solving these challenges. With decades of experience across paper, film, textile, and metal processing industries, we can help you:

• Size motors and drives accurately for your torque and speed profiles
• Design energy-efficient systems with DC bus sharing or common rectifiers
• Develop custom build compensation algorithms tailored to your materials
• Integrate winding axes seamlessly with your broader machine control architecture
• Troubleshoot existing systems to improve tension control and product quality

Contact a KEB application engineer to discuss your specific requirements. Our team is ready to provide technical guidance, recommend the optimal component selection, and ensure your system delivers consistent, high-quality results from day one.