Research On Frequency Up-conversion Energy Harvesting System For Railway Track Vibration

With the rapid development of rail transportation,it has become significantly important to guarantee the operation of large-scale transportation system,among which monitoring of rail structure and surrounding environment is still challenging since a large number of wireless sensor network nodes needs continuous power supply to gather information and transmit data in real time.Due to the development of integration and miniaturization of sensors as well as low power consumption technology,harvesting energy from rail vibrations and making wireless sensors dependent from batteries has become feasible to realize self-power.In this paper,an electromagnetic-piezoelectric hybrid harvester utilizing frequency up-conversion method by flexible hinge amplification mechanism was proposed based on the research of vertical vibration response characteristics of rail.The harvester can work and keep power output under low frequency and micro-displacement excitation input.The main work of this paper is presented as follows:1.Vertical vibration response characteristics of rail under action of high-speed train are studied in detail for designing suitable vibration energy harvester.Concretely,the vehicle and the rail are simplified to the multi-rigid body model and the three-layer discrete point supporting beam model respectively to establish the dynamic equations.Based on it,the vertical displacement curve is obtained by using the new display integral method.From the results,it can be concluded that the rail vibration had characteristics of low-frequency,lowamplitude and large load response,providing reference for later design of harvester.2.Three-stage displacement amplification and frequency up-conversion technologies are introduced to design of the harvester.Initially,since the low-amplitude characteristic is detrimental for power output,flexible hinge amplification mechanism is adopted to realize the primary amplification of input displacement and to reduce influence of working gap during the process of gear transmission.Subsequently,the secondary displacement amplification is realized by the usage of ball screw,which transforms motion form at the same time.Last,rapid rotation of the flywheel is achieved by gear transmission.Profit from the large load characteristics,the high displacement amplification is available.Additionally,the steel ball installed on the outer edge of the ball screw would generate impact to the side-mounted piezoelectric beam,which transforms the low-frequency motion of the rail into the high-frequency vibration of the piezoelectric beam and realize frequency upconversion.The experiment results showed that flexible hinge primary amplification effect was obvious when the input excitation amplitude was lower than 0.6 mm.Especially,when the excitation frequency increased to 4 Hz to 5 Hz,flexible hinge mechanism could significantly reduce the influence of working gap during the process of gear transmission,which proved the correctness of the designed model.3.The performance of the designed energy harvester is studied under rail vibration excitations.To begin with,the system was assumed to be a multi-rigid body model,and the electromechanical coupling equation is established.Then,simulations of power generation performance are conducted under the four different configurations.The results verify correctness of the established model by comparing with experiment results.Meanwhile,it is also found that the larger the flywheel mass is,the more energy can be collected,however,too large flywheel mass would reduce total magnification multiple of the device,resulting in decreasing the maximum speed as well as increasing the mechanical damper,and thus increasing energy loss.In addition,the electromagnetic coupling coefficient would reduce when adopting magnetic materials for the flywheel,which would affect the energy conversion efficiency.To study the influence of flexible hinge and shaft deformation during accelerating stage of the device,the dynamics equation considering elastic deformation of the parts is established to conduct numerical simulation in which rail vibration displacement signal is used as excitation input.According to the simulation results,the flexible hinge and the shaft are optimized for ensuring the reliability of the device and the allowable maximum moment of inertia for flywheel is obtained.4.The practical application of the designed harvester in wireless sensor network is explored.It is verified that the harvester can meet the energy demand of low-power sensor for normal work through the experiment that harvester powers the temperature and humidity sensor.Subsequently,the applications of the harvester to power wireless sensor node in rail transportation is further explored.