Research On Automatic Noise Analysis System Based On Sound Intensity Technology

Aiming at noise reduction and fault diagnosis of vehicle and other mechatronicsproducts an automatic noise analysis system is studied based on sound intensity technologyin this paper. The research of the paper includes scheme design, hardware design, softwaredesign, sound intensity processing algorithm, engineering application and so on. Theautomatic noise analysis system provides a tool for noise control, quality monitoring andfault diagnosis of vehicle and other mechatronics products.The automatic noise analysis system is a mechatronics equipment used to analyzeand monitor noise of vehicle and other mechatronics products in working. It comes downto sound intensity, virtual instrument, computer control and analysis, signal processing andartifical intelligent technologies. Existing noise analysis equipments have insufficiencieson automatization and intelligentization. So the automatic noise analysis system usescomputer as the central workbench. By a computer controlled planar robot sound intensityprobe can be drived to scan measurement plane automatically with high moving speed.Then the sound intensity probe can scan the measurement plane automatically and measurenoise signals simultaneously. The measured noise signals are transmited into computerafter conditioned and acquired by the dynamic signal acquisition card. In the computer themeasured noise signals are analyzed and processed by the software algorithm such assound intensity computing and analyzing, plotting equal intensity contour plans, noisesource identification, distinguishing abnormal sound, fault diagnosis and so on. Hige speed,exact location precision and accurate sound computing are characteristic of the system. Thesystem can be used for noise source identification and fault diagnosis with automatizationand intelligentization.The goal of the scheme design of the automatic noise analysis system is to realizeautomatization and intelligentization. Based on above scheme the hardware and thesoftware of the system are designed detailedly. Calibratation and debugging is alsocompleted. Consequently the whole system is realized. The realization of the automaticnoise analysis system lay the foundation for the further research.Using cross spectrum based sound intensity processing algorithm noise monitoringand main noise source identification is studied in the paper. On the aspect of noisemonitoring the automatic noise analysis system has the ability to scan noise source fleetlyand automatically. Using multiple model optimization algorithm the system can search for main noise source controlled by computer and the location precision is high.Cross spectrum based sound intensity processing algorithm is effective on stationarynoise signals. But it can't deal with nonstationary noise signals. Aiming at this problem ajoint time—frequency analysis method is studied in the paper based on STFT spectrum.This method can express noise signals as time—frequency form. The variety characteristicof noise signals along with time—frequency can be extracted by this method. Soundintensity joint time—frequency analysis method based on STFT spectrum provides a toolto analyze nonstationary characteristic of noise signals. The acceleration noise of an engineis analyzed with the method.Nonstationary instantaneous shock noise signals is ubiquitous in vehicle and othermechatronics products. Aiming at this problem a single wavelet packet reconstructionalgorithm is studied in the paper based on theory of wavelet transform. Using thisalgorithm a simulated instantaneous shock signal is analyzed to extract its instantaneouscharacteristic. Upon above work a sound intensity computing algorithm is studied based onwavelet packets analysis and the precision of this method is validated. The sound intensityalgorithm based on wavelet packets analysis incorporates sound intensity technology withwavelet packets technology so it can analyze abnormal phenomena of instantaneous shocknoise signals when faults take place. Meanwhile a tool for fault diagnosis is provided basedon noise signals. Using this method this paper analyzes the chosen of fault diagnosis indexof single cylinder misfire.In the sound intensity measurement the interference of background noise is a realmatter. From the aspects of software and harkware the anti-interference method is studiedfor sound intensity measurement. Using selective sound intensity technology the targetnoise source can be identified from strong background noise. An anti-interference shield isstudied, which can screen sound wave of background noise so the ability of sound intenstyto discriminate target noise source is improved.The research of the paper emphasizes on the engineering application. The feasibilityof researches in the paper is confirmed through experiments. To reduce exterior noise of aminibus the automatic noise analysis system is used to measure sound intensity of itssurface noise. According to the test result the maim noise source is separated, whichprovides reference for noise control of the minibus.