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Detection System for U-Shaped Bellows Convolution Pitches Based on a Laser Line Scanner

by Yutu Yang 1,†, Zengtao Chen 2,*,†, Ying Liu 1,†, Yuting Li 1, Zhongkang Hu 1 and Binli Gou 1
1
College of Mechanical and Electrical Engineering, Nanjing Forestry University, Nanjing 210037, China
2
Department of Mechanical Engineering, University of Alberta, Edmonton, AB T6G 1H9, Canada
*
Author to whom correspondence should be addressed.
These authors contributed equally to this work.
Sensors 2020, 20(4), 1057; https://doi.org/10.3390/s20041057
Received: 16 January 2020 / Revised: 12 February 2020 / Accepted: 12 February 2020 / Published: 15 February 2020
(This article belongs to the Section Optical Sensors)
An expansion joint is mainly composed of bellows and other components; it is attached on a container shell or pipe to compensate for the additional stress caused by temperature differences and mechanical vibrations. In China, the expansion joint fatigue tests are often used to assess the quality of products. After fatigue tests, convolution pitch will be changed. The amount of change is an important index that can be used to evaluate bellows expansion joints. However, the convolution pitch detection is mainly done manually and randomly by inspection agencies before shipping to the end users. This common practice is not efficient and is often subjective. This paper introduced a novel method for automatically detecting the change of the convolution pitch based on a laser line scanner and data processing technology. The laser line scanner is combined with a precision motorized stage to obtain the point cloud data of the bellows. After denoising and fitting, a peak-finding algorithm is applied to search for the crest of a convolution. The method to find the convolution pitch and the decision that needs to be made to ensure product eligibility are described in detail. A DN500 expansion joint is used as a sample to illustrate the efficiency of the system. The application of the technique intuitively allows a higher precision and relative efficiency in quality inspection of bellows expansion joints. It has also been implemented in the Special Equipment Safety Supervision and Inspection Institute of Jiangsu province with great success. View Full-Text
Keywords: bellows expansion joint; laser line scanner; S-G algorithm; convolution pitch detection bellows expansion joint; laser line scanner; S-G algorithm; convolution pitch detection
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Yang, Y.; Chen, Z.; Liu, Y.; Li, Y.; Hu, Z.; Gou, B. Detection System for U-Shaped Bellows Convolution Pitches Based on a Laser Line Scanner. Sensors 2020, 20, 1057.

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