Manufacturing system to treble screen output

A manufacturing system has been designed to treble flat screen production volumes, reduce production costs by one-third and has been realised without compromising quality.

Automating the manufacture of flat panel display screens for computers, TVs and mobile phones involved consideration of the fact that, like all consumer electronics, sales price was guaranteed to fall month on month as sales volume grew.

As the world's premier manufacturer of thin film transistor (TFT) displays, Swiss company Unaxis, which employs 6500 people and turns over around GBP 1bn, knew that the solution had to be multifaceted.

The most important issue was to design a manufacturing system that could easily treble production volumes: this had to be achievable without compromising quality while simultaneously reducing production costs by one-third.

It turned to Mitsubishi Electric when it began to work on the plant, designated KAI 1200, which would allow the production engineers' dreams to be realised and make flat screen technology as common in the average household as the video recorder or microwave oven.

Manufacturing thin film transistors is a complex process using many highly advanced technologies, with several steps needing to take place in high vacuum, where multiple layers of special coatings are applied to glass substrates with microscopic precision.

Unaxis knew that KAI 1200 would have to be fully automated, with no human intervention anywhere in the production process because the glass from which the screens are cut is 1.3m by 1.1m but less than 1mm thick.

The plant is equipped with two parallel process chambers, each fitted with 10 vapour deposition reactors arranged in vertical stacks.

It is 8m wide, 10m long and 3m high and can turn out a completed glass substrate every minute on a continuous running basis, the highest throughput of any plant anywhere in the world.

For automating the processes Unaxis engineers opted for a Melsec System Q automation platform from Mitsubishi Electric and integrated all functions from loading the blanks to unloading the finished TFT screens.

They cited Q's multi-processor technology as their main reason for the choice, as it could handle the demands of KAI 1200's advanced program structure while maintaining high speed program execution.

The Q PLCs (programmable logic controllers) can handle over 8000 I/O, with processing spread over four CPUs (central processor units) for speed and integrity.

Two motion control, two PC and eight logic CPUs are available, allowing the Q series to be finely tuned to the need of each application.

The multiple processors can be used to simultaneously control different processes or functions.

This innate power within the Q series often means that a single PLC can be used instead of having to network together several less powerful controllers.

The savings in programming, installing and commissioning can be considerable, as can subsequent reconfiguration costs.

KAI 1200 was a development from a previous system, which worked with glass substrates of half the size, yet cost 30 percent more to run.

It is designed so that it can work with substrates of 2m by 2m without alteration as soon as demand increases sufficiently, which is predicted to happen within months of commissioning.

It is also expected that the depositional processes can be refined so that fewer steps are required to complete a TFT.

And finally plans have already been laid down to add further parallel lines to keep up with increasing demand.

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