Wireless stress sensor based on piezoelectric energy harvesting for a rotating shaft

A shaft is a mechanical component which transmits mechanical power and torque. A failure of the shaft may result in serious damage to machine in operation. Contact or noncontact monitoring techniques of rotating shaft have been developed in order to prevent this damage. The application of contact monitoring techniques requires the use of additional devices. First of all, a slip ring assembly, which enables a sensor supply and a sending of measurement data from a rotating shaft to some receivers. The use of the slip ring assembly, which requires an access to the front of the rotating shaft and an additional channel located in an inside of this shaft, are the most important weaknesses of contact techniques. In contrast to these approaches, the article presents a contact technique of stress monitoring in the rotating shaft, in which the slip ring assembly is not required. Presented contact technique consists of a wireless sensor based on piezoelectric energy harvester and a radio transmission system. The piezoelectric energy harvester consists of Macro Fiber Composite (MFC) patch and a system of energy storage and energy transfer control. MFC patch is directly glued to the rotating shaft surface and product an amount of electric energy which is enough to supply only a radio transmitter. Such built wireless sensor based on piezoelectric energy harvester was tested in laboratory stand which contained a rotating shaft with a system of force generation, a belt transmission with a system of generation of rotational motion, and a measurement system. The time between radio signals was measured for selected values of the rate of rotation of the shaft and for selected values of stress in the shaft in laboratory experiments. The experiments showed that dependence between the value of stress in the shaft and the number of radio signals per second can be approximated by a straight line. A method of measurement of stress in the rotating shaft was elaborated on the basis of the experiments. The method is based on the number of radio signals per second, which is linearly correlated with an average value of stress in the shaft, for the known value of the rate of rotation of the monitored shaft. The elaborated piezoelectric wireless sensor of stress were tested as a main part of sensor of cracks in the shaft surface in the last experiments. The time, after which the crack was detected, depended on a sampling period of such piezoelectric wireless sensor. The sampling period in turn depended on the three parameters: an average value of stress in a place where MFC patch is glued, the rate of rotation of shaft, a capacity of capacitor in a system of energy storage in a piezoelectric energy harvester. (C) 2019 Elsevier B.V. All rights reserved.