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Virtual sensors enable self-maintaining machines

Posted: 04 Nov 2014 ?? ?Print Version ?Bookmark and Share

Keywords:iMAIN? virtual sensors? industrial machines?

Editor's Note: Scientists at Fraunhofer IWU in Germany stepped closer to the ideal of a self-maintaining machine. A technology developed as part of the iMAIN project provides real-time online monitoring of unprecedented quality.

Metal forming machines have to withstand considerable forces and yet remain in operation for a long time. When cold forming parts for automobiles, washing machines, refrigerators and the like, the exerted pressure can easily amount to several thousand metric tons. This operation has to be repeated hundreds of thousands of times in the complete lifetime of a machine. If the machine fails, it can cause substantial damage. Worse still, because the machine is usually integrated in a series of production steps, the failure can cause the entire production process to come to a standstill.

Depending on the extent of the damage, the repairs could take up to a monthaccompanied by a loss of revenues in the six-digit region. If it were possible to predict such failures, either of the entire machine or a single component, companies would know precisely when they ought to maintain the machine or replace specific components, preferably in coordination with the production schedule.

Researchers at the Fraunhofer Institute for Machine Tools and Forming Technology IWU in Chemnitz aim to change this situation. In the future, the machines themselves will be capable of detecting problems and predicting failures. As part of the EU-sponsored iMAIN project, the scientists have developed a prototype of an information-based predictive maintenance system that enables operators to determine when a component or entire plant is likely to fail.

The distinctive feature of this technology is its use of virtual sensors. These receive input both from computer-simulated models of the machine and from real sensors that provide information on the strain occurring in individual components. "Using mathematical models and a minimum of actually installed, real sensors, it is possible to realistically simulate strain scenarios for the entire machine in real time. This in turn provides the basis for an entirely new and innovative approach to predictive maintenance," said Markus Wabner of Fraunhofer IWU.

Virtual sensors

Trained workers at Gorenje install sensors in the tool components of a press used to produce parts for household appliances. (Source: Gorenje Group)

Until now, it has been customary to carry out plant maintenance according to a fixed schedule or on an ad-hoc basis in response to failures. Certain manufacturers already equip their machines with (real) sensors, but solutions that rely exclusively on these devices are not ideal: They are expensive and complicated to implement, require their own error monitoring system, and measure stress and strain only at the points where they are installedand nowhere else.

"In our option, the use of virtual sensors is the only conceivable and economical way to obtain a complete picture of the forces acting on the material," said Wabner. While algorithms, simulations and mathematical models can often provide a reasonably good image of reality, even the most precise calculations are subject to errors. This is why the researchers constantly compare the virtual data with real measurements recorded while the machine is in operation. "If there is a wide discrepancy between them, we modify the model accordingly," he added.

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