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?
Considering how simple controls had to be realised with complex analogue circuits and controls 30 years ago, we can atest today: Some 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 run by means of pay-off reels, swivel frames, control frames and tension reels in your various production lines.
Nireco created a flexible software platform early on with the introduction of digital controllers. It also developed different controllers based on the task.
Since then, these devices have impressed with their simple parameterisation, functionality, precision and reliability. However, their hardware usually offers only a limited number of interfaces. This means that additional modules have to be added to expand the range of functions accordingly. Our MGC1000 and SGA3000 controllers are examples of this.
Control unit NIGcon
However, our most modern control unit NIGcon differs from its predecessors by its
- adaptability to the required interfaces,
- simple expandability.
The same hardware platform is used in different applications. We use proven components from globally based world-renwned manufacturers.
We thus fulfil the wishes of our customers to be able to connect or integrate the systems more easily with or into third-party systems.
The spare parts inventory is decisively simplified through the use of only the hardware necessary for the task and the modular design of the hardware modules. Costs are reduced.
Operation and visualisation are 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
- Analogue input and output modules (16 bit)
- Encoder modules
- No cooling necessary 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 loop control.
In the case of strip guiding systems and strip guiding controls, a distinction is made between strip edge and strip centre control. The specified type of control depends on whether the strip is fed to the subsequent process with edge or centre position control.
Accordingly, measuring systems are used which either measure only one (edge position control) or both strip edges (center position control).
The challenge is to be able to utilise the full line speed with exact positioning and to approach all units integrated in the production line (e.g. trimming shears) precisely – from the decoiler to the strip guidance through the production process to the coiler.
Different control methods
Positioning of pay-off reels
Both strip edge and strip centre controls are used on uncoilers. The measuring device is located in the immediate vicinity of the pay-off reel in front of the first deflection roller.
Otherwise, dead time compensation must be taken into account in the control loop if the measuring device is located at a distance behind the deflection roller. This is the only way to achieve stable control in this constellation.
The measuring device is to be installed directly in front of the trimming shear if there is a trimming shear directly behind the pay-off reel. The deflection roller behind the pay-off reel and the pay-off reel must be mechanically coupled in order to guarantee good strip guidance through the trimming shear. Finally, it must be ensured that the border does not tear off at the trimming shear.
Positioning with swivel frame
Swivel frames with one or more deflection rollers not only influence the belt position at the outlet, but also at the inlet. 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 plane of the incoming strip. As a result of the rotation of the control roller(s), the strip in the outlet of the control roller is shifted laterally. The strip position in front of the control roller is not affected. The measuring device is therefore sensibly located behind the control roller (seen in the strip running direction).
Positioning of tension reels
A strip edge control is usually used on coilers. This ensures that coils are discharged with a flat side surface.
If coils are fed to further production lines that require the material to be fed centrally, a strip center control is 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. As a result, the coil must be wound in a staggered manner. 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.
The position of the measurement is tracked to the current tension reel position. This is done by a mechanical or electrical coupling (synchronisation control) of the reel and the measuring device. For electrical coupling, the cameras do not necessarily have to be moved. The strip is fed to the reel via a deflection roller. It is important to ensure a good wrap (correspondingly large wrap angle, high strip tension, large roll diameter) of the roll. 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 for positioning the actuators (pay-off reels, control rollers, swivel frame, tension reels).
Videos for edge and center position 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