Developing PLC Control Rules

Indesit Company are a leading household appliance manufacturer, employing 20,000 people worldwide.

SIMUL8 software has been used within Indesit Company since 2002 to assess proposed production facility changes and to design and develop manufacturing systems.

Automatic allocation of product types to assembly lines was required to improve performance

The existing production line at a Cooker manufacturing facility relied on human product allocation from 8 assembly lines into a 14 lane sortation area. Due to the complicated product mix in the factory, it proved very difficult for a human to assess which item should go to which lane and change lane allocations in a quick and accurate manner. Getting the lane allocation wrong or not changing it in time for new models easily caused a bottleneck, possible production losses and extra work for the distribution department.

To maximize the efficiency of the process a £50,000 PLC conveyor system that automatically allocated a range of unique products to sortation tracks at the end of these assembly lines was to be installed. SIMUL8 was used to design and test the control rules of the system before installing.

SIMUL8 software simulated the sortation process and communicated with existing software

Martyn Hogg of Indesit used SIMUL8 Standard to simulate the system in conjunction with a specific tool for tracking product types.

The simulation was configured to run on actual data collected from barcode scanners in factory production lines. This enabled a validation exercise to take place, giving conclusive evidence that the simulation was behaving as the system would do under general working conditions. After this, it was possible to experiment with a series of different control rules to find the best automated allocation system before this was implemented in the real factory.

Martyn developed a Visual Basic program to communicate with SMUL8 and the existing Lane Allocation Software simultaneously. In the simulation, when a product arrives at the sortation system, SIMUL8 sends a COM message to the Visual Basic program. Then, when a product arrives at a lane, SIMUL8 checks if the model matches the model allocated to that lane. If they match a COM message is sent, representing the lane delivery signal that is sent in the factory. This updates a text file containing lane allocation data.

SIMUL8 then loads this text file which controls routing logic for the lanes. SIMUL8 sends lane delivery data when a product is delivered to a lane and also barcode information when a product arrives at the Sortation system.

The simulation allowed quick and easy testing of different rules options

The simulation tested a wide range of control rules in order to find the one that best optimized performance, so that this could be used in the real factories.

An example of one lane allocation rule is where a model is only allocated a lane if more than four units of that model are available for sortation. This leads to the build up of models at this point in the process until each of these units are available.

As the simulation worked with actual production data it was able to provide results with an added level of accuracy. The solution given by SIMUL8 was used to communicate proposals to company management and the simulation was used to train personnel in sortation and distribution procedures.

SIMUL8 found the optimal set of control rules to be implemented in the real factories

Once the selection of possible rule sets had been tested, SIMUL8 proved which setup performed best and used its output data dynamically through the Lane Allocation software to dictate routing decisions though barcodes within the real factory.

Practical benefits of using SIMUL8 software for this work include:

• The new system can better manage the complex product mix more effectively
• Increased understanding of the whole system was realized through use of the simulation
• SIMUL8 provided confidence that the solution would work prior to installation
• The COM functionality of SIMUL8 enabled it to be easily linked to Visual Basic to simulate communications between different equipment within the factory.

SIMUL8 software is still being used regularly within Indesit Company to test assembly line and manufacturing “what-if” scenarios like this one.

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