Host: The Japan Society of Mechanical Engineers
Name : [in Japanese]
Date : January 19, 2017 -
Low speed rotating bearing diagnosis for core mechanical parts, such as step chain sprockets and handrail driving wheels, of escalators in train stations is critical to maintain daily steady transportation of huge number of passengers. Since usual vibration diagnosis methods cannot be adapted because of its low sensitivity to low speed rotating machinery, we proposed the new diagnostic technique based on Acoustic Emission (AE) technology in order to detect failures of such low speed rotating bearings of the escalators before severe damages occur and to numerically record the results of diagnosis. A number of AE measurements at actual facilities of various train stations were carried out with the portable AE diagnosis instrument MK-560 (JFE Advantech Co., Ltd.). It was revealed that some damaged bearings indicated the high values of an AE parameter named E_area which was developed by some of the authors. There were, however, two major problems to be solved. First, meshing noise from the sprocket was frequently overlapped to the AE signal, which caused high values of E_area even for good bearings. The newly developed noise removal procedures were added to evaluation of E_area to greatly alleviate the situation. Its effectiveness was verified by AE measurements of actual facilities. Secondly, we found that E_area might not indicate high value for severe unlubricated bearings. This was because proper evaluation of E_area was difficult for the AE waveform showing large and gradual fluctuation caused by the unlubricated bearings. The new parameter E_sd based on width of the amplitude distribution of the AE waveform was introduced to overcome this problem. Finally, it was concluded that the low speed rotating bearings installed in escalators can be diagnosed by means of the newly developed AE technique. The damaged part of the bearings can be identified from the frequency analysis of the AE waveform.
