Equipment Layout line Left and centre: Width control sensors Right: Thickness control sensor
algorithmic format. With this approach, a fast, precise and robust controller could be developed. A further requirement was adaptivity. This means, the controller realises if process parameters change and adapts its behaviour to the new situation. For instance, it learns the relation of product shrinking between the extruder exit and the end of the line. This allows fastest reaction time if the product changes its characteristic due to raw material or environmental condition changes. The measurements input for the multi-loop approach is done with 3D laser measuring devices. Depending on the requirements of speed, product dimensions and accuracy, the system can be equipped with more or less sophisticated devices. The item list contains analogue sensors as well as 3D cameras.
The tuning of the line has various options and the controller decides which parameter has to be adjusted to change the behaviour. This could mean to adjust the extruder speed, a roller gap or a cutting roller speed, whatever is more useful to reach the goal in the shortest time.
This auto controlling tool ‘Safe-Ident Slab Control’ can be used to control all dimensions of slabs or sheets such as width, length and thickness. The results are tighter geometrical tolerances and a fast and automatic readjustment of the line to keep the geometrical dimensions always according to the specification. If individual slabs are out of tolerance or having damages which could happen (e.g. if a hopper runs empty, too much
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rework is added or an individual batch is not properly mixed) an optional removal unit takes those products out of the process – in order to guarantee that 100% good products are fed into the wrapping machine.
So far we could see that the process control has the ability to react in two speed categories: 1) immediate reactions are taking individual products which exceeds tolerance limits out of the process and 2) a closed loop control is reacting within seconds and optimises the process in order to achieve products which are as tight as possible within the permitted geometrical range. In addition to these real time control options, there is a third opportunity to optimise the behaviour of a chewing gum process
line, the long term optimisation with respect to the improvement of the overall equipment effectiveness (OEE). The optimisation of the overall equipment effectiveness means also to eliminate disturbing factors and achieve long term improvements. At the beginning of an OEE improvement project, collecting information about the factors of a production process is necessary. Here, Safe-Ident also assists since it collects automatic data of the production process, it counts products within a time range, good vs. bad products and categorises waste products by means of different criteria. This information is saved in a database for longer term observations and optimisation strategies. Graphics for trends or distributions can be created with an integrated analysis tool, but also exporting data in order to support the optimisation specialists at their daily work.
‘Safe-Ident Slab Control’ was introduced at the beginning of 2012 and first installations were made in March. The system operates on extrusion lines from Gabler GmbH + Co. KG that were shipped to large producers in Japan and Korea.
Above: Sensors and camera for sheet layer control (schematic) Below: Analysis of geometrical data in real time: A gaussian distribution
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