Quality control

4 min read

When manufacturing companies look to increase productivity, the first port of call is usually to investigate automation of some part of their process.

However, automation can cover the entire spectrum of factory systems, from a simple robot palletiser at the end of the production line to a complete door-to-door automation system that controls every aspect of production.

For Swiss company Oerlikon it was an entire process for manufacturing flat panel displays that required automating. This involved taking into consideration the fact that, like all consumer electronics, sales price was guaranteed to fall month-on-month as sales volume grew, so 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 reducing production costs by a third.

When the company began 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 VCR or microwave oven, it turned to Mitsubishi Electric.

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

Oerlikon 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 x 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. They are 8m wide x 10m long x 3m highand can turn out a completed glass substrate a minute on a continuous running basis, claimed to be the highest throughput of any plant anywhere in the world.

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

The Q programmable logic controllers (PLCs) can handle over 8,000 I/O, with processing spread over four central processor units (CPUs) 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.

For Envases (UK), a leading manufacturer of aluminium aerosol cans, the solution was a SCADA system. Among many other things, this was to monitor mission-critical process equipment and maintain compliance with local government regulations for atmospheric pollution.

About five years ago the company began to investigate methods of improving its productivity. The firm realised that it must first be capable of measuring its own overall equipment effectiveness (OEE) an established way of measuring and improving overall business performance.

'We examined the market, but at first could not find anything that could do this for us automatically,' said project engineer Owen Davies. 'As a result we wrote our own software but it wasn't overly successful, largely because the connectivity to our hardware was unreliable. It was subsequently pointed out to us that SCADA systems inherently exhibit extremely robust hardware connectivity, so this became our next port of call.'

Again Envases 'dipped its toe' into the market, this time investigating available SCADA systems — and eventually creating a shortlist of three. 'We selected WinCC because it offered the best application, both in terms of flexibility and power,' said Davies.

WinCC, part of Siemens' 'Totally Integrated Automation' concept, includes a high-performance database ideal for collection and analysis of OEE-orientated data.

At the same time, when linked with open communications, it makes it easier to present the analysed OEE data and other key performance indicators to those who need to act on it, in a form in which they can use it.

This might be at machine level on HMIs or mobile web pads (at work or home), at management level in the form of trend analysis data, or even on large displays on the plant floor giving a performance overview.

Installed in 2002 at Envases UK, WinCC is being used to measure the company's OEE and to deliver an indication of performance. The system is also being deployed to monitor mission critical processes. One example involves the disposal of volatile organic compounds (VOCs) produced by the company's aerosol can printing processes.

Finally, at Berwin Polymer Processing Group in Manchester a Smart Cart minor ingredients weighing system is being expanded to double the number of feeder stations from 20 to forty. A start/finish station is also being added, where bags will be formed prior to filling and subsequently sealed and dispatched. The system was originally developed to overcome the constraints of conventional minor ingredients systems, which typically are labour intensive and therefore costly to run and prone to error.

The system consists of static feeders arranged around a monorail track circuit, which carries intelligent mobile weigh carriages, or Smart Carts. In use, a bag is formed and clamped on to a carriage and a set of instructions (known as a recipe) is fed from the main control system to the carriage's on-board controller.

This initiates the carriage's journey around the track to the required feeder stations, where specified quantities of each ingredient are collected in accordance with the recipe. At each station a weight-tolerance check is automatically carried out after filling and before the carriage is allowed to advance to the next station.

At the final feeder station a double check ensures that the recipe has been accurately fulfilled, after which the carriage completes the circuit back to the start/finish station for sealing and unloading. Once unloaded, a new bag is formed and clamped on to the carriage ready for a new set of instructions.

The system was developed and installed by John P Waterhouse of Nottingham, which is now undertaking the expansion. The control system is based on hardware from Mitsubishi, with communication involving two separate CC-Link fieldbus networks.

In the original installation the twin network architecture and Mitsubishi hardware were attractive because of the simplicity and connectivity, attributes which paid dividends when it was decided to expand the system.