Measurement technology specialist, measX, has developed a flexible automation solution for the endurance testing environment of world-leading power tool manufacturer STIHL. Efficient interaction between the Beckhoff TwinCAT automation software and LabVIEW plays a crucial role in the success of the solution.
measX, based in Mönchengladbach, Germany, has been designing and implementing customer-specific measurement, test and evaluation systems for applications in a wide range of industries since 1981. STIHL commissioned the measurement technology specialist to create an efficient automation solution for a large endurance testing facility featuring the EtherCAT and Bus Terminal I/O systems as well as TwinCAT PLC from Beckhoff. The endurance testing automation solution ‘Dauerlaufautomatisierung’ (DLA) was implemented using a combination of LabVIEW and TwinCAT software.
“The DLA application is designed to ensure reliable, high-performance testing of all types of different equipment with varying configurations,” explains Marco Tiskens, the measX engineer responsible for the STIHL project. A standardised operating concept makes it easy to define, perform and monitor each test session. It is also very simple to switch between different test sequences.”
Wide-ranging tests require high flexibility
The test systems are controlled by a C6015 ultra-compact Industrial PC with TwinCAT, which uses an EK1100 EtherCAT Coupler to collect the measurement data acquired by numerous terminals in real-time. The terminal systems provide the flexibility required for development test rigs. Tiskens explains: “There is no need for a separate measurement system and the data can be acquired synchronously with the control outputs without any additional effort. Furthermore, measurement channels can easily be used to alter the test sequence. Additional or alternative terminals can simply be integrated as required. The stability and robustness of the I/O terminals are a particular advantage for endurance testing. And they also offer attractive cost benefits.”
Different parameters need to be measured and controlled or regulated on all test specimens. However, it should also be possible to carry out the same test on a different test rig or even in a different location, despite the different hardware used in each case. This is achieved by defining the measurement technology and channels as well as the test sequence separately and only bringing them together to form a test program at the start of each measurement run as required for the task in question.
Seamless integration of measurement and control technology
For every endurance test, the channels to be measured and all necessary test parameters are defined precisely in the STIHL test database. The relevant measurement and sequential program is generated automatically and in a generic form suitable for the TwinCAT environment in the DLA via a LabVIEW framework. It is then compiled and only when the process is complete is it transferred to the PLC. No in-depth knowledge of TwinCAT is required to implement test sequences. The actual sequence is created once for every test type in Sequential Function Chart (SFC) programming and then reused with new parameters each time. This results in an entire library of templates for test sequences.
Automation interface as the linchpin
Configuring and creating the measurement and control programs from within the DLA is only possible with the TwinCAT Automation Interface. This open interface for automatic code generation supports complex applications such as the DLA, which uses predefined templates for configuration. “The reuse of tested program sections and the automated compilation of the different sections to form test-specific sequential software applications save time and minimises errors,” says Tiskens. “This method also helps to standardise the tests, making it easier to compare them.”
All test rigs can be operated and monitored via the same graphical user interface. The spectrum ranges from setting an individual variable, for example, in order to start the test sequence, to reading out over 100 measurement channels. The latter is carried out via multiple ring buffers that are generated dynamically when the program starts and temporarily store the data.
The DLA saves the data files provided by TwinCAT during testing to the test rig computer and transfers them to a central file server at configurable intervals, or when the files reach a certain size. The data packets are automatically consolidated and are immediately available for further offline evaluation. Important formulas and parameters are calculated while the data is still being prepared and PDF reports with basic evaluations are generated.
Future-proof: precise EtherCAT measurement technology and LabVIEW
Flexible test rig automation is essential for accommodating the wide range of different test requirements. In cases like this, it is worth establishing partnerships with experienced system integrators such as measX, which has a wealth of expertise. The results are high-performance, future-proof test rigs that can be quickly adapted to new products and technologies. With the new TwinCAT 3 Interface for LabVIEW (TF3710), Beckhoff has simplified the connection of the control level to the LabVIEW application. The Interface provides VIs that have been developed for high-performance reading and writing of ADS symbols and for configuring I/O terminals.
Together with the ultra-precise EtherCAT measurement terminals from the ELM series, Beckhoff provides all of the tools needed to implement high-performance test rig applications. “Our customers working in the field of test rig construction particularly appreciate the wide selection of I/O terminals: from the simple 12-bit voltage measurement terminal to the highly precise, calibrated 24-bit multi-functional terminal with LEMO connector, our range provides the right terminal to ensure projects can be implemented cost-effectively,” concludes Christian Lindemann, sales specialist for measurement analytics at Beckhoff. “We offer suitable EtherCAT Terminals for all key measurement variables, from standard signals to temperatures, speeds, vibrations, torques and shifts. Furthermore, all measurement data is perfectly synchronised via EtherCAT and provides comprehensive diagnostic information – vital for ensuring reliable test rig operation.”
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