The MPA Stuttgart State Materials Testing Institute recently introduced advanced controller technology from Mitsubishi Electric for certification testing of passive safety systems for motor vehicles. As part of the modernisation programme for the crash test sled system (that has been in operation since 1975), the Melsec System Q automation platform was chosen to replace the existing conventional control system.
Passive safety devices tested on the system include child seats, airbags, safety belts and motorcycle helmets. The decisive factor for the choice of the MELSEC System Q controller was its high processing speed. Acquisition of test data (rpm rates, travel distances and acceleration rates, etc), calculation of speeds and the derivation of responses are all performed within an interval of just one millisecond (0,001 sec). Other factors favouring the Mitsubishi Electric solution included ease of integration with the existing IT systems, the modular architecture of the system and the cost-optimised implementation of the new components. The project was handled by Mitsubishi system partner Computec GmbH Computertechnik from Murrhardt, working in close collaboration with MPA Stuttgart. The new system was officially inaugurated on 6 June 2002 in a ceremony attended by top representatives of the motor industry and its suppliers.
In this high-speed application the MELSEC System Q automation platform controls a drive system with a motor and controlled brake and clutch combinations, and also handles the data acquisition and the calculation and derivation of the responses. Hans Wohlfarth, technical director at Computec, explains the stringent data reproducibility standards imposed by MPA Stuttgart for the controller in this application: "In this type of safety equipment tests it is very important to obtain as much data for the analysis as possible within a very short period. This means that the controller must be able to acquire the measured values extremely quickly, and initiate responses. The CPU of the selected Q02H-CPU system has a cycle period of just 34 nanoseconds per logical instruction, and this makes it possible to achieve the required execution time of one millisecond."
The PLC system is said to be the fastest on the market, and the only one suitable for applications requiring such brief processing times. In addition to this, the MELSEC System Q can also be expanded with up to a total of four CPUs in a single base unit for faster execution times, thus meeting another important project specification: "The modular systems design of the MELSEC System Q also has the additional performance reserves required for the future expansion of the testing system planned by MPA Stuttgart," explains Hans Wohlfarth.
Easy integration with existing IT systems
The Mitsubishi Electric PLC system earned further points with its simple integration in the existing Ethernet network system and the connected office systems at MPA Stuttgart. Since the system communicates via TCP/IP it is possible to transfer process and quality data at high speed - effectively online - to the organisation's own computer systems for further analysis and documentation. The pre-configured software tool MX Change makes this process simple, handling the export of the PLC data to Microsoft Excel. The process does not require any PLC programming skills.
Fast system installation and cost-optimised deployment
Another key requirement was the ability to modernise the test installation quickly to minimise idle time. "Thanks to Computec's many years of experience with Mitsubishi Electric PLC systems and the excellent collaboration with the institute we were able to run the first tests with the new controller just five working days after dismantling the old system," says Dieter Bosch, Computec's project manager for the MPA contract.
"Overall, the entire modernisation of the test system was smooth and trouble-free. Completion of the entire contract, including electrical engineering, assembly of the switchgear cabinets and installation, took just three months. The excellent value for money of the solution - which consisted entirely of Mitsubishi Electric components, from the controller CPU to the control units - also helped to optimise the cost of the project. Adds Hans Wohlfarth, "As a result, we were able to complete the entire project within the limits of the available budget."
For more information contact Eddie Milne, CBI, 011 928 2000, [email protected], www.cbi.co.za
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