Study On Large Section Geometric Shape Vision Measurement System

Section geometric shape and straightness measurement for large-scale part is performed by 3D measurement system consisted of theodolites or laser trackers, which evaluate the cross section geometric shape and the straightness of axis by measuring the coordinates of many characteristic points. Although the high precision result can be obtained, these systems are hard, tiring and time-consuming to be used by operators. In this dissertation, a large-scale cross section geometric shape vision system based on point structured-light scanning measurement is developed to accurately evaluate the cross section geometric shape and the straightness of axis. The major contributions and innovations of the dissertation are as follows:1. Various large-scale part 3D measurement techniques are deeply analyzed and large-scale 3D measurement instruments at home and abroad are introduced in detail. Applications in industry measurement of laser vision measurement techniques are summarized as well, such as white car body vision system, on-line measurement of seamless steel pipe straightness by laser vision etc.2. The mathematic model for point structured-light scanning measurement fixed on a rotation axis is built when the rotation and translation which relates the world coordinate system to the camera coordinate system is computed. The sensor's intrinsic unknown parameters are calibrated using the three-dimensional circularity drone and the measurement system parameter also is calibrated using a dual theodolites coordinate system.3. Various distributed network measurement techniques and system and relevant key techniques are introduced and analyzed. Because of the advantage in industry measurement, CAN field-bus technique is introduced into the large-scale cross section geometric shape vision system to transfer the signals between the computer and sensors. From this, the network control software of CAN field-bus and the hardware figure of system are shown in this paper.4. The laser point images are analyzed in detail and the center of light point is obtained by the method of such as ellipse fitting. All kinds of algorithm about ellipse fitting are compared to find out the good one for fitting the light point center into the section geometric shape. Straightness of axis is evaluated by using the line-fitting on the ellipse centers above computed. The section geometric shape can be acquired when the ellipse is projected to the plane perpendicular to the axis.5. The structure of sensor is analyzed in depth and the parameters are optimized excellently. The experiment is shown that the system has a good performance and deep potential for industry application.