| In order to achieve real-time measurement of large-size parts in workshop, Amonocular vision measurement system with a light-pen is established. A new light pen isdesigned by lithography process. To the extraction of the feature point imaging centers onthe light pen, a method of sub-pixel edge extraction and fitting ellipse is applied in thispaper. According to the position distribution of the characteristic point on the light pen,an algorithm of image recognition is applied. The light pen features point’s image planecoordinates and the corresponding coordinates in the light-pen coordinate system iscorresponded. To lens’ irregular distortion in this system, a method of basis point weightscompensation is proposed. Then based on resection principle of single image space in theclose-range photogrammetry, conversion relationship between the light pen coordinatesystem and the camera coordinate system is established. At the same time based on thetransformation model, a method to optimize the camera focal length and stlylus locationcoordinates in the coordinate system of light pen is proposed. Experimental results showthat the present system has high measurement accuracy, and to a certain extent meet theneeds of the actual measurement. In this paper the studying key technologies consists ofthe following aspects:1. A new light pen is designed. The light pen is manufactured with photolithographyprocess, the error of the distance between every two centers of the feature points islimited within1micron. The coordinate system of light pen is established according tothe distribution characteristics of the light pen feature points. According to the positiondistribution of the characteristic point on the light pen, an algorithm of image recognitionis applied to match features point’s image plane coordinates and the correspondingcoordinates in the light-pen coordinate system.2. A method of grid compensation is proposed to compensate Lens’ distortion. First,based on the ideal imaging coordinates and the actual imaging coordinates of the targetpoints, a template database is created. Then compensating points are positioned in thetemplate database, peripheral points are based points and compensation point iscompensated according to the distances as weights.3. The extraction of the target feature points is shown. In this paper, based ongrayscale distribution of the bright round imaging edge obeys Gaussian distribution,firstly, sub-pixel edge is extracted, and then ellipse fitting is taken to make thecoordinates of the target point’s imaging center.4. Based on resection principle of single image space in the close-rangephotogrammetry, the transformation model between light pen coordinate system and thecamera coordinate system is established. Optimal exterior orientation elements of singleimage space are solved by loop iteration based on least squares adjustment method, and basic parameters of the transformation model are determined.5. The focal length’s impacts on the result of monocular vision measurement systemis analyzed.The relative accurate focus length and the position of light pen probe in thecoordinate system of the light pen are determined by optimization algorithm.The innovation of this paper is that a new type of light pen is made with thelithography process, a model of the conversion between the light-pen coordinate systemand the camera coordinate system is established, finally, at the basis of the transformationmodel, an optimization method of the camera focal length and position of the light penprobe in the light pen coordinate system is proposed. |
