The component of gear vibration signal is very complex,when a localized tooth defect such as a tooth crack is pre- sent,the engagement of the cracked tooth will induce an impulsive change with comparatively low energy...The component of gear vibration signal is very complex,when a localized tooth defect such as a tooth crack is pre- sent,the engagement of the cracked tooth will induce an impulsive change with comparatively low energy to the gear mesh signal and the background noise.This paper presents a new comprehensive demodulation method which combined with amplitude envelop demodulation and phase demodulation to extract gear crack early fault.A mathematical model of gear vibration signal contain crack fault is put forward.Simulation results based on this model show that the new comprehensive demodulation method is more effective in finding fault and judging fault level then conventional single amplitude demodulation at present.展开更多
An improved variable cross‐section cantilever beam model for evaluating the time‐varying mesh stiffness(TVMS)of the perfect gear tooth is developed in which the tooth number of driving gear is less than 42 and that ...An improved variable cross‐section cantilever beam model for evaluating the time‐varying mesh stiffness(TVMS)of the perfect gear tooth is developed in which the tooth number of driving gear is less than 42 and that of driven is more than 42.The TVMS obtained by the proposed method is compared with the result without considering the misalignment between the base circle and gear root.Four types of root crack models and changes inTVMS of 13‐crack levels are presented.The fault vibration characteristic of a single‐stage spur gear reducer with root crack is ana-lyzed and the correctness is qualitatively verified by the vibration signals of an experimental gearbox with crack or missing failure.The results presented in this paper are of great significance for a deep understanding of the possible causes of vibration and noise of gears and provide a theoretical foundation for the fault diagnosis of the gearbox.展开更多
Background: There are challenges in detection and prevalence of cracked teeth, especially in asymptomatic cases. This underestimates the actual prevalence and possibility of preventive restorative treatment. Objective...Background: There are challenges in detection and prevalence of cracked teeth, especially in asymptomatic cases. This underestimates the actual prevalence and possibility of preventive restorative treatment. Objectives: To determine the prevalence and distribution of cracked posterior teeth among adult patients attending the dental clinic of OAUTHC, Ile-Ife, Osun State, Nigeria. Materials and Methods: A cross sectional study where consecutive patients aged 18 years and above were examined for the presence of cracked posterior teeth over a period of one year (May 2016-April 2017). The teeth were initially examined with the naked eye. Thereafter, transillumination, methylene blue dye and magnifying lens were used to aid detection of more cracks. Data was analyzed with the IBM Statistical Package for Social Sciences (SPSS) for Windows (version 21.0). Level of significance was set at p ≤ 0.05. Results: Out of the 64,370 posterior teeth examined for cracks in 3345 patients, 264 were diagnosed as cracked in 152 patients, giving a patient prevalence of 4.5% and tooth prevalence of 0.4%. Amongst the 152 patients, the prevalence was 9.1%. There was a slightly higher male preponderance while cracked tooth was observed to increase with age (p = 0.007). The skilled (56.6%) and those that attained tertiary education (77.6%, p = 0.023) had more cracked teeth. Mandibular first molar (19.7%) was the most frequently cracked tooth type. The cracks were usually centrally placed (91.7%) and run in a mesiodistal direction (61%). Transillumination (44.7%) detected more cracked teeth. Conclusion: Prevalence of cracked tooth was observed to be low with a slightly higher proportion in male and the figure increases with age. Mandibular first molar was the most frequently cracked tooth while transillumination was the most useful diagnostic tool. Most cracks ran in the mesiodistal direction and fracture lines were usually centrally placed.展开更多
文摘The component of gear vibration signal is very complex,when a localized tooth defect such as a tooth crack is pre- sent,the engagement of the cracked tooth will induce an impulsive change with comparatively low energy to the gear mesh signal and the background noise.This paper presents a new comprehensive demodulation method which combined with amplitude envelop demodulation and phase demodulation to extract gear crack early fault.A mathematical model of gear vibration signal contain crack fault is put forward.Simulation results based on this model show that the new comprehensive demodulation method is more effective in finding fault and judging fault level then conventional single amplitude demodulation at present.
基金National Natural Science Foundation of China,Grant/Award Numbers:11790282,12032017,11802184,11902205,12002221S&T Program of Hebei,Grant/Award Number:20310803DNatural Science Foundation of Hebei Province,Grant/Award Number:A2020210028。
文摘An improved variable cross‐section cantilever beam model for evaluating the time‐varying mesh stiffness(TVMS)of the perfect gear tooth is developed in which the tooth number of driving gear is less than 42 and that of driven is more than 42.The TVMS obtained by the proposed method is compared with the result without considering the misalignment between the base circle and gear root.Four types of root crack models and changes inTVMS of 13‐crack levels are presented.The fault vibration characteristic of a single‐stage spur gear reducer with root crack is ana-lyzed and the correctness is qualitatively verified by the vibration signals of an experimental gearbox with crack or missing failure.The results presented in this paper are of great significance for a deep understanding of the possible causes of vibration and noise of gears and provide a theoretical foundation for the fault diagnosis of the gearbox.
文摘Background: There are challenges in detection and prevalence of cracked teeth, especially in asymptomatic cases. This underestimates the actual prevalence and possibility of preventive restorative treatment. Objectives: To determine the prevalence and distribution of cracked posterior teeth among adult patients attending the dental clinic of OAUTHC, Ile-Ife, Osun State, Nigeria. Materials and Methods: A cross sectional study where consecutive patients aged 18 years and above were examined for the presence of cracked posterior teeth over a period of one year (May 2016-April 2017). The teeth were initially examined with the naked eye. Thereafter, transillumination, methylene blue dye and magnifying lens were used to aid detection of more cracks. Data was analyzed with the IBM Statistical Package for Social Sciences (SPSS) for Windows (version 21.0). Level of significance was set at p ≤ 0.05. Results: Out of the 64,370 posterior teeth examined for cracks in 3345 patients, 264 were diagnosed as cracked in 152 patients, giving a patient prevalence of 4.5% and tooth prevalence of 0.4%. Amongst the 152 patients, the prevalence was 9.1%. There was a slightly higher male preponderance while cracked tooth was observed to increase with age (p = 0.007). The skilled (56.6%) and those that attained tertiary education (77.6%, p = 0.023) had more cracked teeth. Mandibular first molar (19.7%) was the most frequently cracked tooth type. The cracks were usually centrally placed (91.7%) and run in a mesiodistal direction (61%). Transillumination (44.7%) detected more cracked teeth. Conclusion: Prevalence of cracked tooth was observed to be low with a slightly higher proportion in male and the figure increases with age. Mandibular first molar was the most frequently cracked tooth while transillumination was the most useful diagnostic tool. Most cracks ran in the mesiodistal direction and fracture lines were usually centrally placed.
