Aimed at providing a reliable and self-powered means of remote monitoring, the Smart Screw Connection from the Fraunhofer Cluster of Excellence Cognitive Internet Technologies (CCIT) in Germany combines sensors and radio technology to increase safety and reduce inspection time.
Found everywhere in structures including cranes, scaffolding, buildings, bridges and wind turbines, screws can loosen because of wear and tear, temperature fluctuations or vibrations, with potentially deadly results. Regular inspections are needed as a result.
The new system from CCIT is aimed at updating that approach with smart technology. The kit includes a screw fitted with a washer that is equipped with a piezoresistive DiaForce thin film, also developed at Fraunhofer. When the screw is tightened, the pressure-sensitive sensors register the preload force at three points. Any change in the preload force changes the electrical resistance in the DiaForce thin film.
“When a screw comes loose, the resulting change in resistance is reported to a radio module located on the screw head. The radio module, in turn, sends the data to a base station, which collects the information from all relevant screws in the object,” said project manager Dr Peter Spies.
Fraunhofer’s Mioty network protocol shares the warnings using minimal energy, enabling more than 100,000 sensors to transmit via one base station, which could be up to a few kilometres away. A software program then displays the data for each individual screw in a graphical overview. Depending on the configuration and application, the status of the screw connections can be transmitted permanently, to coincide with particular events, or at specified intervals.
“This remote monitoring system allows us, for the first time, to keep an eye on the stability of safety-critical infrastructures at all times, even remotely, and to carry out a proper check on every single relevant screw. This is a major asset in terms of safety. When inspecting a bridge or wind turbine, no engineer is required to be on site and check each screw individually, as all the data are transmitted via radio to the service station,” said Dr Spies.
The Smart Screw Connection can be adapted for a wide variety of applications, the developers said.
“No matter whether it’s for flange connections in industry, for the bolts in steel girders in high-rise buildings, for the load-bearing parts of bridges or for attaching rotors to wind turbines – the system can be individually configured for each scenario and adapted to the relevant load profile,” an announcement said.
The connections are self-powered by thermoelectric generators that generate electricity from the minute differences in temperature between the screw head and the environment. Solar cells could also be used, Fraunhofer said.
The screws are given individual encryption keys during installation, and transmissions are also encrypted to prevent sabotage.
The technology is designed for commercially available DIN screws and is ready to use for M18 screws. Versions will soon be available for M20 and M36 screws, Fraunhofer said. A demonstration version will be exhibited at the Hannover Messe 2022 event between 30 May and 2 June.
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