RFID beats the heavy metal bluesAccurate tracking of high-value, costly items through a production or warehouse process is becoming an increasingly common requirement. Tim Stokes of SICK UK looks at what this means in practice.
Tracking errors are the gremlins that can undermine the logistics of a bespoke manufacturing operation. For car manufacturers who are compelled by marketing pressure to offer many choices to attract customers, it can be months or years before the same combination is requested again, so a wrongly kitted-out car could be an expensive mistake.
Luxury cars, for example, are supplied to specific customer preferences such as optional equipment, colour ways and trim. Tracking each vehicle to deliver exactly the right customer choices means knowing, in real time, the exact specification of each individual vehicle and the stage it has reached in the production process.
Tracking errors are the gremlins that can undermine the logistics of a bespoke manufacturing operation. Attaching a unique identifier early in manufacture, such as during installation of the floor pan, is therefore essential to avoid identification mix-ups. It enables the vehicle to be recognised throughout production to final assembly and completion.
RFID systems, with transponders on the work piece and read/write interrogators at the appropriate points in the product flow, offer many advantages in complex manufacture and assembly. The transponders are capable of holding large amounts of information which can be added at each stage.
The information stored provides traceability and quality assurance data, details the exact processes undergone and the components added to meet the required final specification. The data can even remain attached and accessible throughout the vehicle's lifetime for full accessibility, even aiding eventual recycling. Although more expensive per item, RFID is more reliable than 1D/2D barcoding and part-marking systems which are frequently obscured by dirt, paint or tape, damage and lack of line-of-sight visibility. For expensive goods RFID can be an alternative worth the investment. But the 'Achilles heel' of RFID has traditionally been its tendency to become inaccurate in locations with extensive metal surfaces and mass, or volumes of fluids, which may distort and reflect the radio signal.
Of course, these potential barriers are present in many manufacturing environments. So manufacturers are keen to find ways around them - especially those with high-value products with a large number of components and product variants. One customer of Sick, a prestige automotive manufacturer at a production plant in Germany, was experiencing difficulties with consistency of operation through the paint shop. Use of standard RFID had resulted in frequent line downtime from null reads, as well as some specification errors when the wrong car was selected. There had even been collisions where a car body became 'invisible'. As a result, some cars had to be rejected. Paper label identification did not survive the paintshop drying process, and attempts to use RFID after the paint shop, combined with additional barcoding, had also not delivered the accuracy needed for efficient manufacturing operations.
The Sick engineering team was called in and recommended new Sick RFU630 UHF read/write interrogators, which were installed at 24 points in the paint shop. These rugged and compact devices were required to operate under very unfriendly conditions including metal walls, ceiling and floor, heavy metal machinery such as the conveyor, other car bodies and a temperature of up to 180°C.
Reader location was important. For instance, by ensuring that the actual reading point was located where the car body stopped briefly before it entered the drying kiln, optimum transmission conditions were obtained. To match the RFID device, a rugged and long-life UHF transponder tag developed by Sick especially for the automotive industry was attached to each car body, designed to withstand conditions inside the kilns of 230°C. Despite the 'high noise' metal environment, the RFID system was found to operate with better than 99.98% accuracy over approximately 350,000 scans a day.
Following the paint drying, the bodies are loaded in any order onto a skid conveyor section for the next processing stages, such as seam sealing by robot. As these processes proceeded down three parallel lines and on to the complexities of engine and interior fit out, accuracy of the individual on-vehicle records is crucial. With the transponder, the on-car records are always available to the manufacturer, at any stage of the vehicles life.
The RFU630 is able to accommodate up to three external aerials, and has a reading range of between 0.4 and 1.2 metres, delivering excellent coverage. Operating on the Sick IDpro platform, it is easily integrated with a wide range of SCADA/Ethernet systems, as well operating easily with other Sick ident technologies such as 1D/2D barcodes for a factory-wide automated ident system. Configuration is very simple using the Sick SOPAS tool with its auto-ID function, and as well as application specific software, freely definable outputs, for example operating actuators, can be incorporated.
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