PLCs control complex bakery production demands

A Manchester (UK) manufacturer of bread improvers has increased total plant production capacity by 60 per cent by adding an additional range of cake mixes to its product lines.

A Manchester (UK) manufacturer of bread improvers has increased total plant production capacity by 60 per cent by adding an additional range of cake mixes to its product lines.

The Bakemark (UK) plant was already producing 17,500 tonnes of bread improver per annum but can now handle an additional 10,000 tonnes of cake mix as well.

The system performs mixing and batching processes, drawing its raw materials from 16 silos each capable of holding between 10 tonnes and 50 tonnes of raw material.

The weighing has to be exact, the mixing thorough, batch changeovers clean and plant utilisation high.

On top of that there are rigorous requirements for hygiene, quality and traceability.

Advanced Technical Software (ATS), who worked on the original system installed around 10 years ago, undertook development and installation of the new control system.

The old system was based on Mitsubishi PLCs.

An A3A model was used as a master and six smaller A1S units provided emergency back up facilities.

Although that system had served the plant well ATS realised that it would not have the facilities to cope with the increased production, nor the flexibility to encompass the new cake mix lines.

A site inspection showed that the existing plant cabling, panels and input and output devices were still in excellent condition and were retained intact.

The Mitsubishi A3A was upgraded to a Q series PLC, which although able to offer like-for-like facilities to the A3A, benefits from more processing power and capabilities.

A further Q series PLC was added to control the new equipment and was connected on the plant wide ethernet network.

Although the existing system software was completely redesigned, ATS was able to reduce the programming time by using Mitsubishi's GX IEC developer software.

The IEC61131-3 certified software is said to allow a library of standard program blocks to be developed and deployed multiple times within the application.

As the plant runs on a continuous three-shift pattern ATS realised that a high integrity control system was needed in order to avoid potentially costly stoppages, and that reliability of the main server was crucial.

Therefore, redundancy was built in by fitting dual power supplies and memory, plus additional hard disc drives installed as two raid arrays.

The simple serial communications were also upgraded to ethernet for high-speed two-way data transfer and to provide a distributed systems architecture instead of the centralised structure used beforehand.

That increases the redundancy within the system to an even higher level and thus reduces the possibilities of breakdowns even further.

During the planning stage it was decided that the distributed system architecture should divide the control operations into two distinct areas, administration and plant control.

Each production line has its own PC, which runs a local SCADA (supervisory control and data acquisition) programme developed by ATS from a standard Citect package.

A facility is also provided so that any of the PCs can be switched to control any of the other lines.

For the central control functions, ATS developed bespoke software for controlling the raw material movements from the storage hoppers to the mixing lines.

One of the most sophisticated routines in the programme is the weighing algorithm, which not only takes the input from precision scales but also makes precise allowances for the amount of material 'in flight' along the screw augers and pneumatic conveyors between each individual silo and mixer and adjusts them automatically after every batch.

It also provides recipe management, materials tracking and admin and enterprise information collation.

In addition to plant control and production flexibility, the system ATS has designed and commissioned provides Bakemark with reporting and product tracing.

For materials already used in production the reports allow backwards tracing from an individual product batch code.

A diagnostics and alarm function is operated centrally and ATS made a point of ensuring that it is straightforward so even even the most inexperienced operator can use it.

Before bringing the new control system on-line ATS ran exhaustive tests on a plant simulation programme called Trial Run it has developed in-house.

It was also used to train all operators prior to installation, and as a result change over from the old control system to the new was achieved in less than 48 hours.

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