Calibration of dial indicators using machine vision

Abstract

Using automatic machine vision-based systems, the calibration of measuring instruments can be extended. With machine vision it is possible to check hundreds of points on the scale of a dial indicator, giving new insight into its sources of error. This paper describes a machine vision-based system for the calibration of dial indicators developed at the Centre for Metrology and Accreditation in Finland, with emphasis on the calculation of measurement uncertainty.

Automatic Calibration System for Digital-Display Vibrometers Based on Machine Vision

“…According to the properties of the digital camera, the characteristics of the digital-display on the vibrometer and the selected ROI, there are 30 n  fps, 1 l  mm, Brought to you by | MIT Libraries Authenticated Download Date | 5/9/18 12:59 PM 1 a  mm. According to (9) and (10), the permissible maximum amplitudes of the exciter at different frequencies are calculated and shown in Table 2, which indicate that they are always much larger than the corresponding maximum displacements of the vibration exciter, so the vibration will not affect the recognition accuracy according to the analysis in section 3.4. Fig.…”

“…Most of the digital-display vibrometers could not be calibrated by the ordinary automatic calibration system directly because of no output or interface except the display on the vibrometers for cost considerations. In the recent years, machine vision technology has widely been applied in automatic systems [8][9][10][11][12][13][14][15][16][17]. A digital camera can be applied to replace human eyes to capture the images of digital or analog displays, and then the captured images are transmitted to a computer, in which the displays are recognized by some image recognition algorithms.…”

Segmentation-free approaches of computer vision for automatic calibration of digital and analog instruments

“…In the last years, many authors have proposed automatic calibration approaches using computer vision techniques [1][2][3][4][5][6][7].…”

“…Hemming et al presented a machine vision-based equipment for the calibration of dial indicators developed at the Centre for Metrology and Accreditation in Finland, with emphasis on the calculation of measurement uncertainty [5]. They also presented an updating of developed equipment into a calibration device for micrometers [6].…”

“…However, most of them, for example [1][2][3][4][5], firstly simplify the images using some operations to detection of edges, detection of interest points and segmentation/ binarization for after proceeding the digits recognition or pointer position detection. The problem is that these image-simplifying operations throw away the rich grayscale information, decreasing the robustness of the technique mainly when images are affected by illumination changes, noise and JPEG compression.…”