Jinghao Yang

Improved camera calibration method based on perpendicularity compensation for binocular stereo vision measurement system

High-precision calibration of binocular vision systems plays an important role in accurate dimensional measurements. In this paper, an improved camera calibration method is proposed. First, an accurate intrinsic parameters calibration method based on active vision with perpendicularity compensation is developed. Compared to the previous work, this method eliminates the effect of non-perpendicularity of the camera motion on calibration accuracy. The principal point, scale factors, and distortion factors are calculated independently in this method, thereby allowing the strong coupling of these parameters to be eliminated. Second, an accurate global optimization method with only 5 images is presented. The results of calibration experiments show that the accuracy of the calibration method can reach 99.91%.

Precision calibration method for binocular vision measurement systems based on arbitrary translations and 3D-connection information

Binocular vision systems play an important role in computer vision, and high-precision system calibration is a necessary and indispensable process. In this paper, an improved calibration method for binocular stereo vision measurement systems based on arbitrary translations and 3D-connection information is proposed. First, a new method for calibrating the intrinsic parameters of binocular vision system based on two translations with an arbitrary angle difference is presented, which reduces the effect of the deviation of the motion actuator on calibration accuracy. This method is simpler and more accurate than existing active-vision calibration methods and can provide a better initial value for the determination of extrinsic parameters. Second, a 3D-connection calibration and optimization method is developed that links the information of the calibration target in different positions, further improving the accuracy of the system calibration. Calibration experiments show that the calibration error can be reduced to 0.09%, outperforming traditional methods for the experiments of this study.

A method for measuring the thermal geometric parameters of large hot rectangular forgings based on projection feature lines

The online dimensional measurement of large hot forging is an important procedure in the forging process. Because of different production demands, the final geometrical shapes of large forgings are usually different (e.g. cylindrical columns, rectangular prisms). Forgings of different geometric shapes need to be measured along different dimensions. For rectangular forgings, the lengths primarily need to be measured. A generalized measurement system for different geometric shapes of forgings cannot provide the accuracy of measurement systems targeted at measuring a known shape. Based on the characteristics of the rectangular forgings, a thermal dimensional measurement system is proposed in this paper. The localization, rapid extraction of feature points and method for measuring the dimensions of rectangular forgings are presented. The proposed methods can easily and efficiently extract the feature points of the forging. The experiment results show that the method proposed in this paper has the advantages of high precision and high efficiency, which is appropriate for online measurement.

A monocular vision 3D measurement method based on refraction of light

In this paper, a monocular vision measurement method based on refraction of light is proposed. A flat glass board is placed between the target and the camera, which causes light refraction during the measurement process. By analyzing images taken before and after light refraction, the 3D coordinates of the target can be obtained. Using this method, only the thickness and refractive index of the glass board is required to solve the problem of 3D measurement even if the glass board is placed at any angle. Besides, a novel method for calculating the normal vector of the glass board based on images before and after light refraction is proposed, which makes it easier to complete 3D measurement with a single camera. The measuring method proposed in this paper is simple, and the equipment required is low-costing. The 3D information of a target can be measured without requirement for a priori knowledge of feature points on the target or the location information of the glass board. Finally experiments are conducted in the laboratory, and results show that excellent accuracy can be obtained with proposed method.

Improved calibration method of binocular vision measurement system for large hot forging

Binocular vision measurement technology is widely used in large object measurement, such as large hot forging. However, the traditional method cannot satisfy the requirement of the binocular measurement system in the workshop, which is complex and fast-paced processing. Therefore, an improved binocular measurement system for large hot forging calibration method is proposed in this paper. The binocular measurement system in the severe workshop can be calibrated accurately by the proposed method. A stepwise accurate intrinsic parameter calibration method based on active vision is present. The strong coupling of these intrinsic parameters is eliminated. Besides an accurate global optimization method with multiple restrictions is presented in this paper. The calibration accuracy is further improved. The proposed method is applied for the binocular measurement system for large hot forging in the workshop. The experiment result shows that the proposed method is effective and the accuracy of the proposed method can reach 0.52%.

Image processing in dimensional measurement for hot large forgings based on laser-aided binocular machine vision system

Dimensional measurement for hot forgings is a key factor to improve the level of forging technology in industry field. However, the high temperature, large size and hostile environment increase difficulties to guarantee the robustness and speed of the measurement. In this paper, a robust real-time image processing method based on laser-aided binocular machine vision system is proposed. Firstly, images with clear laser stipes are acquired using spectral selection method, by which the influences of thermal radiation and ambient light can be reduced. Then, to improve the speed of extraction and the robustness of matching, an extraction method based on the information consistency of the images acquired by the system and a matching method based on sequential consistency and epipolar constraints are presented. Dimensional reconstruction models for square and axial forgings are built. Finally, the image processing results are used to reconstruct the feature dimensions of a ceramic plate in the laboratory as well as forgings in a forge. Experiments show that, the root-mean-square error of the reconstructed points is 0.002mm and the relative error for width reconstruction is 0.638% in a cold state. Lengths and diameters of hot large forgings are reconstructed robustly and in real time. It is verified that the method proposed in this paper can satisfy the requirements of precision, speed and robustness for measurement of large hot forgings in industrial field.