Pallet transfer system boosts output by 2million units/year

Schrader Electronics provides electronic products and systems to the automotive industry and is a market and technology leader in Remote Tyre Pressure Monitoring Systems. RTPMS allows drivers to monitor their vehicle's tyre pressures by using electronic sensors attached to the tyre valves to transmit pressure data from each wheel to displays on the dashboard or rear view mirror. Schrader's RTPMS includes four tyre valve-mounted pressure sensors and an on board receiver. The sensors send tyre pressure information at regular intervals via radio-frequency to an on-board central receiver and to the instrument cluster in the car to ensure tyre safety.

In recent years, the safety of automobiles has continuously increased. Nevertheless, in 30 per cent of the serious accidents that occur due to technical flaws of the vehicle, the cause can be attributed to the tyres. A number of tragic accidents in the USA, for example, were the result of a specific tyre model having too little pressure. In the coming years, all vehicles up to five tons must therefore be equipped with a tyre-pressure monitoring system (TPMS) in the USA. Direct measuring systems with sensor technology are expected to gain the upper hand in the market. In addition to tyre pressure, tyre temperature and acceleration are also transmitted to the central control unit in the vehicle.

The tyre-pressure sensor is a cast, LSI module and essentially contains a sensor chip with a microcontroller and an ISM transmitter that generates the RF signal. It is powered by a lithium battery with a lifetime of up to 100,000 miles. The European Union already supports this technology with research programs and tyre-pressure sensors are expected to become standard equipment in all vehicles within the next ten years.

Rising demand

Tyre pressure monitoring is the subject of a great deal of debate, especially in the USA where it is being seen as crucial in the battle to make vehicles safer. It is increasingly expected that legislation will be passed to make RTPMS mandatory and demand for the product is thus increasing fast.

In order to meet this expected demand Paul Gardner, manufacturing director at Schrader's Antrim site in Northern Ireland, wished to upgrade the first automated production line that was installed in 1999. He wanted to increase the capacity of the production line from 3million to 5million units per year by installing more automation along with a new workpiece pallet transfer system, moving the existing Bosch Rexroth equipment to expand the product testing facility and installing a VSP HMI controller. Schrader has also recently commissioned its sixth automated production line developed around similar principles used in the re-tooling of line one.

As well as the need to support a growing market there were also other reasons for Schrader Electronics to upgrade its production facility, including low-cost economy competitors. Paul Gardner was looking for improvements, not only in the volume of product being made, but also in the product's quality. Bosch Rexroth's input was part of an overall rationalisation of the production process that saw the PCB population process redesigned and the quality testing facility vastly expanded.

Transfer and control systems

Working with Rexroth's sales manager for Northern Ireland, Derek Wood, and its local sales partner, Schrader specified a system that included the Rexroth TS2plus Transfer system and a Rexroth IndraControl VSP 40 HMI controller. The operating principle of the RexrothTS2plus is that on an assembly line workpieces have to be transported from one station to another using a transfer system. Workpiece pallets, which hold the workpieces, are conveyed by friction on two constantly moving belts, enabling the workpiece to be transported through all the processing stages. Information about which destination and processing stages are required is carried in the workpiece pallet memory and the pallet is halted by stop gates at stations (areas for manual work or automatic stations), while the conveyor continues moving.

Several workpiece pallets can be built up in front of certain stations to form small buffers. Once the processing stage at a station is completed, the workpiece pallet is released to travel onto the next work station. At the same time, the pneumatic stop gate is opened, either manually or with a station control, and at the end of the assembly process the workpiece is removed from the workpiece pallet.

One of the main advantages for Schrader of the Rexroth TS2plus system is its flexibility. With different products required for different automotive manufacturers it is vital that Schrader is able to switch between makes and models very easily. The four systems available from Rexroth are the TS1, MTS2, TS 2 plus, TS 4plus, all of which differ in size and permissible load (the letters TS stand for flexible transfer system). The transfer systems are constructed from standard components that can be combined as desired to construct a system. This permits the construction of numerous variants and enables systems to be tailored to the particular assembly task.

Rexroth transfer systems are made with high-quality materials to ensure they are suitable for continuous use. They are resistant to lubricating and cleansing agents, plus almost all of the components and parts in Rexroth transfer systems are ESD (electro static discharge) compatible or available in ESD-compatible design. They can therefore be safely used in electrostatically sensitive areas.

Apart from the different types of conveying media, the Rexroth TS2plus also provides an abundance of specific units including curves, transverse conveyors, positioning and drive units. In addition to this, the time and effort spent on planning and designing can also be reduced to a minimum thanks to the range of pre-defined macro modules.

Panel PC with touchscreen

The other major investment in Rexroth technology is in the specification of the Rexroth IndraControl VSP 40, a compact 15inch panel PC with touch screen operation. This controls a robot performing a task that involves the separation of good and bad parts.

Reject information is then fed from the IndraControl and interfaces with the intelligent control on the production line. The Rexroth IndraControl VSP is economical for PC-based control, operation and monitoring. They are suitable for a variety of industries and applications that demand high performance, operation in standard environmental conditions and industrial capability. The unit offers a high level of investment protection due to its standardised hardware and software. It also has a high production safety level due to EMV certified design (the EMC/EMV mark demonstrates compliance with electromagnetic compatibility (emissions and immunity) law as well as the EMC requirements specified in the European EMC Directive 89/336/EEC).

The installation of the new equipment at Schrader Electronics was a good example of how Bosch Rexroth works effectively with its sales partners and customers. Re-tooling took place over one month (meaning one month of down time). Paul Gardner says: "This one month took five months to prepare for in terms of making sure we had the new equipment prepared and enough stock to supply our customers. In total the whole process has taken less than a year from concept to delivery."

Paul Gardner fully expected the new production line to run smoothly: "The new Rexroth product has proved to be robust and reliable. Our original line of Rexroth product has been running since 1999, so it was proven in use."

Rapid changeovers

One of the main advantages of the Rexroth TS2plus system is that it offers Schrader Electronics the flexibility to change between products very quickly with the minimum of lost production time. Schrader now supplies all the World's major car manufacturers and usually schedules a 10,000-piece build when it switches to producing a different product. Because of the flexibility of the Rexroth system, this switch between products can take as little as half an hour.

Because everything that Schrader Electronics makes is subject to 100 per cent functional testing, it was obvious that if they were to expand the capacity of the production line they would need to expand the capacity of the testing facility. Tony Davenport, senior sales engineer, comments: "We used the original Rexroth line to develop the testing facility and were able to use 48 per cent of the original capital equipment - a fact that gave us a significant saving. There was no point in getting rid of the original equipment when it could be perfectly well re-used."

Global competitiveness

Schrader's story is an enlightening one. It demonstrates that, with investment in automation (brought about by a rigorous pursuit of lean manufacturing techniques and continual improvement), Western European manufacturers can compete against the low-cost economies of Eastern Europe and the Far East, even in the intensely competitive electronics market.

As for Bosch Rexroth's relationship with Schrader, that looks set to continue profitably into the future. Paul Gardner says: "The relationship with Bosch Rexroth has been great in the last few years; we have even been able to use Bosch Rexroth's sales partners to help solve some of our other engineering problems." Going on to summarise the main reasons why the company has continued to trust in Bosch Rexroth, Paul says: "We looked at other equipment and suppliers but it would have meant a great deal of investment in training and spares and we would not have got any benefit. With Bosch Rexroth the reliability and robustness of the equipment is key."