Research Of Piezoelectric Stack Energy Harvester For The Wireless Self-supply Energy Monitoring System Used In Coal Mining Machinery

The high-impact,strong-vibration characteristics of coal machines pose stringent demands on the reliability of the monitoring system.In particular,for rotary heavy-duty coal mining machinery,wired monitoring systems will not work properly due to wiring problems.This paper proposes a wireless,self-powered sensing test system based on piezoelectric stacks.The influence of the structure parameters of the energy harvester on its power generation performance was studied through theoretical modeling,simulation and loading experiments.The power generation experiment of the energy collection circuit was performed.The on-site installation and commissioning of the wireless self-powered monitoring system were performed on the coal mining machinery and equipment.The specific work is as follows:First,a single-degree-of-freedom model for piezoelectric stacks was established based on the first-type piezoelectric equations and its theoretical analysis was performed.Then the equivalent circuit model of the harvester under non-resonance state was studied.Based on this model,the theoretical analysis of output voltage,output power and energy conversion efficiency was carried out.The research results showed that the transmission efficiency of energy generated inside the harvester to the load resistor could be up 70% when the dielectric loss could be neglected.Furthermore,the finite element analysis of the load amplitude and the structural parameters such as the cross-sectional area,the thickness of the piezoelectric sheet,the number of piezoelectric layers that affected the energy generation performance of the piezoelectric stack energy harvester were performed,by which the theoretical analysis results were verified.Secondly,based on the experimental test platform,the energy output characteristics of the piezoelectric stacks under the periodic coal-rock cutting load were studied.The influence of the load amplitude,frequency,load resistance and structural parameters of the energy harvester such as cross-sectional area,thickness of the piezoelectric sheet,and number of stack layers on its power generation performance was studied.Based on the experimental test data,the theoretical and simulation models were verified and optimized.The results showed that the open-circuit voltage of the piezoelectric energy harvester was proportional to the load amplitude;under low frequency conditions,the load frequency had little effect on its open-circuit voltage.Moreover,the power output of the piezoelectric energy harvester had a negative correlation with its cross-sectional area;the larger the cross-sectional area of the energy harvester,the easier it is to match the impedance.Besides,the power output of the piezoelectric energy harvesters was positively correlated with the thickness of the piezoelectric sheet;the thinner the thickness of the piezoelectric sheet was,the easier it was to match the impedance.The power output was positively related to the number of piezoelectric sheets in the harvesters;the more numbers of piezoelectric sheets the harvesters had,the easier it was to match the impedance.Therefore,under the premise of guaranteeing the mechanical structure and feasibility of technical process,the more layers of the piezoelectric sheets,the more beneficial to output its electric energy and to perform impedance matching to achieve the maximum power output.Then the energy output characteristics and impact resistance characteristics of the piezoelectric stack energy harvester under the coal rock cutting impact load were studied.The results showed that when the hammer weight was 27.4 kg,impact height was 250 mm,the output power of the harvester can be up to 35 W with the impedance matching achieved,and the impact load resistance can be up to 5.023 MPa.Finally,according to the operating characteristics of the piezoelectric stack energy harvester,the energy management module based on the LTC3588 chip and the LTC4071 chip was designed and processed.The field commissioning and installation of the wireless and self-supplying energy monitoring system on the coal mining machine,the emulsion pump station and the mine hoist were realized.The experiment conclusion showed that the ZigBee wireless module can collect the signal of the acceleration sensor and temperature sensor in the system and display the signal on the upper computer software.