Geometric calibration method based on Euler transformation for a large field of view polarimetric imager

For the purpose of obtaining high-precision in stereo vision calibration, a large-size precise calibration target, which can cover more than half of the field of view is vital. However, large-scale calibration targets are very difficult to fabricate. Based on the idea of error tracing, a high-precision calibration method for vision system with large field of view by constructing a virtual 3-D calibration target with a laser tracker was proposed in this article. A virtual 3-D calibration target that covers the whole measurement space can be established flexibly and the measurement precision of the vision system can be traceable to the laser tracker. First, virtual 3-D targets by calculating rigid body transformation with unit quaternion method were constructed. Then, the high-order distortion camera model was taken into consideration. Besides, the calibration parameters were solved with Levenberg–Marquardt optimization algorithm. In the experiment, a binocular stereo vision system with the field of view of 4 × 3 × 2 m3 was built for verifying the validity and precision of the proposed calibration method. It is measured that the accuracy with the proposed method can be greatly improved comparing with traditional plane calibration method. The method can be widely used in industrial applications, such as in the field of calibrating large-scale vision-based coordinate metrology, and six-degrees of freedom pose tracking system for dimensional measurement of workpiece, as well as robotics geometrical accuracy detection and compensation.

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Calibration Method for Large Field of View Camera Based on Infinite Homography

Acta Optica Sinica ◽

10.3788/aos201232.0715002 ◽

2012 ◽

Vol 32 (7) ◽

pp. 0715002

Author(s):

苑云 Yuan Yun ◽

朱肇昆 Zhu Zhaokun ◽

张小虎 Zhang Xiaohu ◽

尚洋 Shang Yang ◽

于起峰 Yu Qifeng

Keyword(s):

Calibration Method ◽

Field Of View ◽

Large Field

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A Stereo-Vision System for Measuring the Ram Speed of Steam Hammers in an Environment with a Large Field of View and Strong Vibrations

Sensors ◽

10.3390/s19050996 ◽

2019 ◽

Vol 19 (5) ◽

pp. 996 ◽

Cited By ~ 4

Author(s):

Ran Chen ◽

Zhongwei Li ◽

Kai Zhong ◽

Xingjian Liu ◽

Yonghui Wu ◽

...

Keyword(s):

Stereo Vision ◽

High Speed ◽

Vision System ◽

Calibration Method ◽

Bundle Adjustment ◽

Field Of View ◽

Large Field ◽

Practical Applications ◽

Accuracy Of Measurements ◽

Ram Speed

The ram speed of a steam hammer is an important parameter that directly affects the forming performance of forgers. This parameter must be monitored regularly in practical applications in industry. Because of the complex and dangerous industrial environment of forging equipment, non-contact measurement methods, such as stereo vision, might be optimal. However, in actual application, the field of view (FOV) required to measure the steam hammer is extremely large, with a value of 2–3 m, and heavy steam hammer, at high-speed, usually causes a strong vibration. These two factors combine to sacrifice the accuracy of measurements, and can even cause the failure of measurements. To solve these issues, a bundle-adjustment-principle-based system calibration method is proposed to realize high-accuracy calibration for a large FOV, which can obtain accurate calibration results when the calibration target is not precisely manufactured. To decrease the influence of strong vibration, a stationary world coordinate system was built, and the external parameters were recalibrated during the entire measurement process. The accuracy and effectiveness of the proposed technique were verified by an experiment to measure the ram speed of a counterblow steam hammer in a die forging device.

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