Screw connections are fundamental to the construction of machines, structures and vehicles. They secure bridges and buildings, keep flange connections tight and ensure that wheels and rotors are firmly positioned. But inspecting them as part of maintenance routines is complex and costly.
Making screws smart enough to report any problems at an early stage before any damage occurs was the aim of a research project on the Q-Bo® smart screw connection. This project was conducted by the cross-institute research team in the Fraunhofer Cluster of Excellence for Cognitive Internet Technologies CCIT, consisting of Fraunhofer IIS and the Fraunhofer Institutes for Surface Engineering and Thin Films IST, for Structural Durability and System Reliability LBF, and for Applied and Integrated Safety AISEC.
A piezoresistive, pressure-sensitive thin film on a washer measures a screw connection’s pretension at three points. Using three measuring points ensures that even a tilting of the screw connection will be detected. The measurement is then sent via a radio transmitter. An addi-
tional temperature reading on the washer takes into account and corrects any temperature effects on the measurement.
To enable many of these Q-Bo® smart screw connections to be energy-efficient or self-powered, the experts at Fraunhofer IIS integrated energy harvesting technologies into their radio transmitters. A thermoelectric energy converter generates sufficient current to operate the wireless sensor even when temperature differences are only small. The wireless sensor’s energy requirements can also be met completely using small solar cells. This eliminates the need to replace or recharge batteries. The mioty® LPWAN technology, also developed at Fraunhofer IIS, can be used to reliably send data across several kilometers using the robust telegram splitting method. That means a base station can receive and forward more than 3.5 million data packets per day. The mioty® protocol is so resistant to interference that even if 50 percent of the transmitted data packets are lost, all relevant information will safely reach its destination. Thanks to cryptographic encryption, each screw’s data transmission is tamper-proof.
Q-Bo® is already in the evaluation phase at several companies.