Vibration Performance Testing Of MDF Based On Piezoelectric Sensing Technology

With the rapid development of information technology,the production method of wood industry also gradually tends to be automated.Because of the low requirements for raw materials and simple production process,fiberboard industry has become the highest degree of automated production and the most industry-intensive man-made board industry.However,the finished product inspection stage of fiberboard is still using manual sampling and testing.In order to realize the automatic production process as soon as possible and improve the testing efficiency of fiberboard products,it is important to explore a convenient and effective method for testing the mechanical properties of fiberboard.In this paper,we propose a method for testing the vibration properties of MDF using piezoelectric sensing technology.The test method uses the piezoelectric effect of the piezoelectric chip to apply an excitation signal to the specimen,and adjusts the signal frequency to detect whether the specimen reaches the resonance state,so as to obtain the vibration properties such as the intrinsic frequency,elastic modulus and damping ratio of the specimen.The innovation of this method lies in the use of a single frequency and small amplitude equal-spoke signal to excite the specimen,which is more consistent with the basic assumption of small and medium deformation in elastodynamics;from the perspective of mechanical vibration,this method makes the response of vibration more similar to the steady-state response.In this paper,a compact,low-cost and easy-to-operate piezoelectric actuator is designed to drive a piezoelectric chip to generate a sinusoidal signal.The main contents and results of the research in this paper are as follows:1)Combined with the research of scholars at home and abroad,this paper analyzes several main mechanical detection methods of wood-based panels.Among them,the force hammer tapping method has the disadvantage that the force can not be effectively controlled,and the hammer material will also produce errors in the measurement,and then the method of using piezoelectric sensing technology to excite vibration is proposed.(2)Through the derivation of mathematical equations for single-degree-offreedom undamped and damped vibration systems,the relationship between the intrinsic frequency and damping and other vibration performance parameters in single-degree-of-freedom systems is pointed out,and the conclusion that the closer the vibration system is to the steady-state response,the closer the resonant frequency generated is to its own intrinsic frequency is drawn.The transverse vibration model of the beam is derived from the theoretical model of the single-degree-of-freedom vibration system,which lays a theoretical foundation for the vibration performance test of MDF by piezoelectric sensing technology.(3)From the overall requirements of the device to the functional requirements of each module,the device is divided into four parts: microcontroller,display and keypad module,signal generation module and power supply module.The hardware design of the device mainly focuses on the peripheral circuit design of these four parts,such as the anti-interference circuit of the key and display frequency,the low-pass passive filter and automatic gain amplification circuit of the signal generation module,and the power supply circuit of the device as a whole.The software design of the device is to realize the overall function of the device,from the bottom driver to the human-machine interface,to achieve the device output frequency,sweep time,adjustable output voltage and other functions.In order to facilitate the testers to quickly get started with the device,a concise human-machine interface is designed at the software application level.Finally,the overall functionality of the device was tested and the test results showed that the device met the expected standards.(4)In order to further verify the feasibility of using piezoelectric vibration method,the natural frequency,elastic modulus and damping ratio of medium density fiberboard with seven different thicknesses were measured by this method.The method is compared with the hammer tapping method specified in the national standard.The measurement results show that the three vibration performances measured by the two vibration methods have a high correlation.The natural frequency measured by the piezoelectric vibration method is smaller than that measured by the hammer tapping method,and the degree of dispersion is lower.The elastic modulus measured by the two methods has a high consistency on the whole,and the correlation coefficient value fluctuates around 0.9.The two dynamic elastic modulus detection methods are also compared with the static elastic modulus detection method.It is found that the correlation between the piezoelectric vibration method and the static elastic modulus is more significant.The correlation coefficient of the first-order damping ratio measured by the two methods is as high as 0.865,while the higher-order damping ratio is different due to external interference.