Study On Techniques For Measurement Of Mechanical Vibration Using Continuous Ultrasonic Beam

Non-contact vibration detection method is an important mechanical vibration detection method,which plays an irreplaceable role in the field of vibration detection.In this non-contact vibration detection method,the ultrasonic sensor is isolated from the object and the sensor can detect the vibration and do not interfere with the object.This non-contact vibration detection method particularly suitable for the vibration detection of the flexible structure,lightweight structure and fine structure.In the non-contact vibration detection method,the technique of vibration detection with a continuous ultrasonic beam owns unique advantages,such as high accuracy,simple measuring circuit,low cost and strong versatility.This technique can be used in the smog,opaque gas,strong corrosion,strong light and other harsh environments,and can detect the vibration of the surface,which have good ultrasonic reflection feature and its surface roughness shorter than the wavelength of the ultrasonic.Therefore,it is necessary to do a deep research on the technique of vibration detection with a continuous ultrasonic beam.Firstly,this paper makes a review of the vibration measurement technique using a continuous ultrasonic beam and the demodulation method of the vibration-modulated ultrasonic.Based on the Doppler effect and parametric effect,the principle of vibration measurement with a continuous ultrasonic beam is introduced in detail.The mathematical model of the vibration-modulated ultrasonic is established.According to this mathematical model and the principle of ultrasonic vibration detection,three main factors affecting the accuracy of vibration detection are obtained,it contains the ultrasonic velocity,the position of the sensor and the frequency of the ultrasonic.The factors affecting the ultrasonic velocity and the mounting position of ultrasonic sensor are studied deeply.The method modifying the ultrasonic velocity is proposed,the reasonable mounting position of ultrasonic sensor is determined in this paper.Then,based on the previous research results,considering the propagation characteristics of different frequency ultrasonic waves,40 KHz ultrasonic signal is selected for vibration detection.The sound field and the directivity of the ultrasonic sensor with different diameter are researched.According to this research result and considering the price of sensor,the ultrasonic sensor is selected.The vibration speed of the object was obtained from the simulation signal by using the energy operator demodulation method and the Hilbert transform demodulation method.The vibration velocity curve obtained by the Hilbert transform demodulation method has obvious end effect.Because of the error term of the energy operator demodulation method,the vibration frequency range can be measured is limited and the demodulation accuracy is affected.So an improved normalized complex teager energy operator demodulation method is proposed in this paper and is used to demodulate the vibration-modulated ultrasonic signal.The demodulation result of the improved normalized complex teager energy operator demodulation method be compared with the demodulation result of the Hilbert transform demodulation method and the demodulation result of the energy operator demodulation method.The comparison result show that improved normalized complex teager energy operator demodulation method can get better demodulation effect.Finally,based on the research above,the ultrasonic vibration measurement system is designed and the experiment table is built.The vibration detection experiment is carried out by using this experiment table built above.The vibration speed obtained from the vibration-modulated ultrasonic signal is compared with the speed obtained from the integral results of acceleration sensor signals,and the comparison result shows the correctness of the above theoretical research.