Automatic Digital Inclinometer Calibration System Based on Image Recognition

doi:10.1007/s12204-023-2594-y

Abstract

Abstract: Traditional calibration method for the digital inclinometer relies on manual inspection, and results in its disadvantages of complicated process, low-efficiency and human errors easy to be introduced. To improve both the calibration accuracy and efficiency of digital inclinometer, an automatic digital inclinometer calibration system was developed in this study, and a new display tube recognition algorithm was proposed. First, a high-precision automatic turntable was taken as the reference to calculate the indication error of the inclinometer. Then, the automatic inclinometer calibration control process and the digital inclinometer zero-setting function were formulated. For display tube recognition, a new display tube recognition algorithm combining threading method and feature extraction method was proposed. Finally, the calibration system was calibrated by photoelectric autocollimator and regular polygon mirror, and the calibration system error and repeatability were calculated via a series of experiments. The experimental results showed that the indication error of the proposed calibration system was less than 4 , and the repeatability was 3.9 . A digital inclinometer with the resolution of 0.1 ◦ was taken as a testing example, within the calibration points’ range of [ − 90 ◦ , 90 ◦ ], the repeatability of the testing was 0.085◦, and the whole testing process was less than 90 s. The digital inclinometer indication error is mainly introduced by the digital inclinometer resolution according to the uncertainty evaluation.

Key words: digital inclinometer, automatic calibration, high-precision turntable, number recognition

摘要： 传统的数显倾角仪校准方法依赖于人工检测，存在操作复杂、效率低、易引入人为误差等缺点。为了提高数显倾角仪的校准精度和效率，本研究开发了一种全自动数显倾角仪校准系统，并提出一种新的数码管识别算法。首先，以高精度自动转台为基准，计算倾角仪的示值误差。其次，制定了全自动倾角仪校准控制流程和数显倾角仪调零功能。针对数码管识别，提出一种融合穿线法和特征提取法的数码管识别算法。最后，使用光电自准直仪和正多面棱体对校准系统进行标定，并通过一系列实验计算校准系统的误差和重复性。实验结果表明，该校准系统的示值误差小于4″，重复性为3.9″。以分辨率0.1°的数显倾角仪为测试示例，在[−90°，90°]范围内，测试的重复性为0.085°，同时整个测试过程耗时小于90 s。根据不确定度评定，数显倾角仪的示值误差主要由数显倾角仪分辨率引入。

关键词: 数显倾角仪，全自动校准，高精度转台，数字识别

CLC Number:

TH712

Feng Zheming, Chen Gang, Nan Zhuojiang, Tao Wei. Automatic Digital Inclinometer Calibration System Based on Image Recognition[J]. J Shanghai Jiaotong Univ Sci, 2025, 30(2): 280-290.

References

[1] CHEN W, SUN R S, FANG X P, et al. The analysis of positioning accuracy based on range and angle measurements [C]//2020 3rd International Conference on Unmanned Systems. Harbin: IEEE, 2020: 1030-1034.
[2] NAN Z J, TAO W, ZHAO H, et al. A fast laser adjustment-based laser triangulation displacement sensor for dynamic measurement of a dispensing robot [J]. Applied Sciences, 2020, 10(21): 7412.
[3] ZHAO J, ZHAO J W, WANG H, et al. Precision position measurement of linear motors mover based on temporal image correlation [J]. IEEE Transactions on Instrumentation and Measurement, 2019, 68(9): 3268- 3277.
[4] WANG Y Q, JING Y C, LU J F, et al. Discussion on the calibration method of angle instruments [J]. Shanghai Measurement and Testing, 2021(4): 16-19 (in Chinese).
[5] LIU Y L, HU H H, WANG H Z, et al. Research on the calibration method of dipincter [J]. Shanghai Measurement and Testing, 2020, 47(5): 51-53 (in Chinese).
[6] ZHANG W, LIANG H W, YANG X J, et al. Design of an auto-demarcation system of digital inclinometer [J]. Automation & Instrumentation, 2006, 21(1): 22-25 (in Chinese).
[7] FAN Z M. A calibration device for precision inclinometers [D]. Shanghai: Shanghai University of Engineering Science, 2015 (in Chinese).
[8] BIAN J J, CHENG W M, LI Y, et al. Auto-calibration system for digital display inclinometer based on angle encoder [J]. Control and Instruments in Chemical Industry, 2019, 46(1): 33-36 (in Chinese).
[9] HUANG Z Y, XIEWC, HUANG H R, et al. Overview of motion deblurring techniques for images [J]. Computer Engineering and Applications, 2020, 56(24): 28- 34 (in Chinese).
[10] ZHANG L, LIU B, GUI J G, et al. Location and recognition method of digital tube of digital display instrument under complex environment [J]. Industry and Mine Automation, 2018, 44(4): 85-89 (in Chinese).
[11] CHEN G, HU Z F, ZHENG C. Fast recognition algorithm for digital instruments based on feature detection [J]. China Measurement & Test, 2019, 45(4): 146-150 (in Chinese).
[12] ZHOU J J, YU J B. Online measurement of machining tool wear based on machine vision [J]. Journal of Shanghai Jiao Tong University, 2021, 55(6): 741-749 (in Chinese).
[13] GUO S. Study on automatic identification method of digital tube [J]. Communications Technology, 2012, 45(8): 91-93 (in Chinese).
[14] GOH T Y, BASAH S N, YAZID H, et al. Performance analysis of image thresholding: Otsu technique [J]. Measurement, 2018, 114: 298-307.
[15] LI Y Y. Product interface recognition system based on digital tube recognition [D]. Hangzhou: Hangzhou Dianzi University, 2018 (in Chinese).
[16] LIU W L. Research and implementation of number recognition in seven-segment numeric instrument [D]. Dalian: Dalian University of Technology, 2013 (in Chinese).
[17] HUANG S J, XU Y L, YANG X J, et al. ROI weld feature extraction algorithm of real-time tracking [J]. Journal of Shanghai Jiao Tong University, 2016, 50(12): 1877-1880 (in Chinese).
[18] LI Z M, LI J L, HAN B, et al. High precision angle indexing turntable and its error correction [J]. Journal of Mechanical & Electrical Engineering, 2021, 38(9): 1180-1184 (in Chinese).
[19] WANG Y Z. Optical system design and technology research of photoelectric autocollimator [D]. Chengdu: University of Electronic Science and Technology of China, 2020 (in Chinese).
[20] ZHANG J J. The study on improving resolution and indicating stability of photoelectric autocollimator [D]. Tianjin: Tianjin University, 2010 (in Chinese).
[21] ARA′UJO L M M, PAIVA R G N, PERUCHI R S, et al. New indicators for measurement error detection in GR&R studies [J]. Measurement, 2019, 140: 557-564.
[22] National Geometric Length Measurement Technical Committee. Calibration specification for inclinometers: JJF 1915—2021 [S]. Beijing: Standards Press of China, 2021 (in Chinese).
[23] National Legal Metrology Technical Committee. Evaluation and expression of uncertainty in measurement: JJF 1059—1999 [S]. Beijing: Measurement Press of China, 1999 (in Chinese).