Research On Non-contact Measurement Technology Of Geometric Dimension Based On Virtual Instrument

Based on Virtual Instrument (VI) of non-contact measurement technology has high precision, high speed, low cost, and high reliability, it has become an important measurement technology. In the industrial processing, a non-contact visual inspection system for circular parts is very urgent, because it is difficult to measure the geometric dimension of the soft materials circular parts with contact tools. So, in this paper, a non-contact visual inspection system for circular parts is designed based on VI, machine vision and image processing technology.First, the principle of visual system and the configuration of the hardware parameters are studied. According to the system's technical target, the general structure design and the hardware configuration have been accomplished. Then, the image acquisition is carried out.Second, the image smoothing process and image edge sharpening are carried out by using the fast median filtering and Laplacian algorithm, respectively. Image segment is performed by using Otsu algorithm. The holes in the object are filled by area-filling method. To improve the accuracy of edge detection, the binary image is filtered by using the morphological algorithm. By comparing the traditional methods of edge detection, Sobel algorithm is chose to obtain continuous and single-pixel image edges as the rough edge position. And then sub-pixel edge detection based on the Zernike moments is chose to detect edge and get the more accurate target edge positioning.Third, Randomized Hough Transform (RHT) for circle feature detection is improved. The false edge and the computing time is reduced by using a regular hexagon window, respectively. The amount of invalid operation is reduced and the detection speed is faster by using the edge gradient direction information to limit the search scope.Finally, the software system is designed and debugged by using the LabVIEW software platform combined with MATLAB, IMAQ Vision. Different function programs are designed into separate sub-function modules to complete the image processing, the thickness of the circle, roundness, and concentricity measurements. Compared with the real value of GB3452.1-2005, the measurement error of the circle measurements are within tolerance scope. And the measurement error of the circle roundness and concentricity are measured. Last, the error of the system is analyzed. And then the non-contract measuring method of the soft materials circular parts has been achieved based on VI.