Digital strip guiding control Systems
Components for strip guiding control
We’ll take care of that… Everything used to be better! Who hasn’t heard that saying?
But if you look at how simple controls were implemented 30 years ago with complex analog circuits and controls, you have to admit: Many things have changed for the better! Even if the means used today for strip guiding controls are more modern – the task has remained the same, to control the strip flow in your different production lines by means of
- Pay-off reels
- Control rollers
- Control frames
- Tension reels
With the introduction of the digital controllers, Nireco created a flexible software platform early on and developed task-related different controllers itself.
These devices convince by their simple parameterisation, their functionality, their precision and their reliability. However, their hardware usually offers only a limited number of interfaces, so that additional modules have to be added to extend the range of functions. Our MGC1000 and SGA3000 controllers are examples of this.
Control unit NIGcon
Our most modern control unit NIGcon differs from its predecessors by:
- its modularity,
- its adaptability to the required interfaces
- and its simple expandability.
The same platform can therefore be used in different applications. The hardware is no longer manufactured in-house, but instead we use proven components from world-renowned manufacturers.
By taking this step, we are fulfilling the wishes of our customers so that our systems can be connected or integrated more easily to or into third-party systems.
By using only the hardware necessary for the task and the modular design of the hardware components, the spare parts inventory is greatly simplified and costs are reduced. Operation and visualization is carried out via the high-performance industrial computer and the touch operating panel.
Our hardware compactly summarized
- High performance industrial computer
- Touch operating panel
- Digital input and output modules
- Analog input and output modules (14 bit)
- Encoder modules
- Use without additional cooling up to 55 °C ambient temperature
- Power supply 18-30 V DC
- Almost all fieldbus systems can be coupled
- Hardware mountable on top-hat rails
All systems for strip guiding control are based on a simple closed control loop.
In strip guiding and strip guiding controls, a basic distinction is made between strip edge control and strip centre control.
Whether the position of the strip edge or that of the strip center has to be controlled depends on whether the strip is fed in edge position controlled or center position controlled for the subsequent process
Depending on the respective strip guiding method, measuring systems are used which either measure only one strip edge (strip edge control) or both strip edges (strip center control).
The challenge is to use the full line speed with exact positioning and to be able to start up all units integrated in the production lines (e.g. trimming shears) exactly – from the decoiler to the strip guidance through the production process to the coiler.
The different control methods
The positioning of pay-off reels
Both strip edge and strip centre controls are used on decoilers. The measuring device is located in the immediate vicinity of the pay-off reel in front of the first deflection roller.
If the measuring device can only be installed at a distance behind the deflection roller, a dead time compensation must be taken into account in the control loop so that the control runs stable.
If there is an trimming shear directly behind the pay-off reel, the measuring device must be installed directly in front of the trimming shear. In order to guarantee good strip guidance through the trimming shears, the deflection roller behind the pay-off reel and the pay-off reel must be mechanically coupled. This ensures that the border does not tear off.
Positioning with swivel frame
Pivoting frames with one or more deflection rollers influence the strip position not only at the exit but also at the entry. The measuring device is placed behind the swivel frame (seen in the strip running direction).
Positioning with control rollers
The control rollers rotate around a pivot point located in the level of the arriving strip. Turning the control roller(s) causes the strip behind the control roller to move laterally, the strip position in front of the control roller is not affected. The measuring device is located behind the control roller (view in the direction of strip flow).
The positioning of tension reels
Strip edge control is usually used with tension reels. This ensures that coils with a flat side surface are discharged.
If coils are fed to further production lines, which require a central feed of the material, a strip center control system must be used.
In the case of coated strip, the thickness of the coating may be higher at the strip edges than over the rest of the strip width. If such coils were wound with a flat side surface, they would not have a firm stand and in extreme cases would collapse. In such cases, the coil must be wound in a staggered manner, this is known as staggered winding. With staggered winding, a uniformly toothed strip edge is always achieved, even at different strip speeds, taking into account the current winding speed and the strip thickness.
For the tension reel control, the position of the measurement must follow the current tension reel position. This can be done by a mechanical or electrical coupling (synchronization control) between the reel and the measuring device. The strip must be fed to the reel via a deflection pulley, and care must be taken to ensure good wrap (correspondingly large wrap angle, high strip tension, large pulley diameter) of the pulley. The measuring device must be located in the immediate vicinity of the deflection roller in order to achieve a good control result.
Hydraulic units or electromechanical cylinders are used as actuators for positioning the final control elements (pay-off reels, control rollers, swivel frame, tension reels).
Videos for edge and center control
Nireco offers strip guiding systems for many production lines in the metal industry with the appropriate
- Measuring equipment
- Actuators for positioning the final control elements
- Control strategies
The strip guiding systems take into account special requirements such as
- Cascade control (integration of several measuring systems into the control loop)
- Dead time compensation (dead time within the controlled system)
- End product related control strategies, such as staggered winding for coated strips