Optimization of calibration method for scanning planar laser coordinate measurement system

This paper presents a high-resolution real-time 3D coordinate measurement system based on multi-angle intersection and cylindrical imaging. The measuring angle is detected by the linear camera equipped with cylindrical lenses, whose field of view is a 3D space rather than 2D plane. This camera has prominent advantages in precise coordinate measurement and dynamic position tracking due to the high resolution and outstanding frame rate of linear CCD. Each camera is a 1D angle measuring unit which confirms an angle thereby a plane passing through the light spot. With three cameras arrangement in front of the measurement field, the 3D coordinate of the light spot can be reconstructed by multi-angle intersection. An accurate and generic calibration method is introduced to calibrate this camera. The proposed calibration method is based on nonparametric ideas to find the mapping from incoming scene rays to photo-sensitive elements, and this method (black box calibration) is still effective even if the lens distortion is high and asymmetric. It is applicable to a central (single viewpoint) camera equipped with any lenses. The proposed calibration method is applied to the 3D coordinate measurement system. The coordinate measurement accuracy of the designed system is better than 0.49mm.

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Self-calibration Method and Pose Domain Determination of Light-Pen in a 3D Vision Coordinate Measurement System

10.20944/preprints202201.0054.v1 ◽

2022 ◽

Author(s):

Dongri Shan ◽

Chenglong Zhang ◽

Peng Zhang ◽

Xiaofang Wang ◽

Dongmei He ◽

...

Keyword(s):

Measurement System ◽

Absolute Error ◽

Calibration Method ◽

Measurement Range ◽

Experimental Results ◽

Auxiliary Equipment ◽

3D Vision ◽

Coordinate Measurement ◽

Self Calibration ◽

Light Pen

Light pen 3D vision coordinate measurement systems are increasingly widely used due to their advantages, such as small size, convenient carrying and wide applicability. The posture of the light pen is an important factor affecting accuracy. The pose domain of the pen needs to be given so that the measurement system has a suitable measurement range to obtain more qualified parameters. The advantage of the self-calibration method is that the entire self-calibration process can be completed at the measurement site without any auxiliary equipment. After the system camera calibration is completed, we take several pictures of the same measurement point with different poses to obtain the conversion matrix of the picture, and then use spherical fitting, the generalized inverse method of least squares, and the principle of position invariance within the pose domain range. The combined stylus tip center self-calibration method calculates the actual position of the light pen probe. The experimental results show that the absolute error is stable below 0.0737 mm and that the relative error is stable below 0.0025 mm. The experimental results verify the effectiveness of the method; the measurement accuracy of the system can meet the basic industrial measurement requirements.

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Study on Axis Calibration Method of the Coordinate Measurement System Based on Binocular Vision

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.989-994.3266 ◽

2014 ◽

Vol 989-994 ◽

pp. 3266-3269

Author(s):

Zi Miao Zhang ◽

Shi Hai Zhang ◽

Ya Nan Yu

Keyword(s):

Binocular Vision ◽

Measurement System ◽

Rotation Axis ◽

Vision System ◽

Calibration Method ◽

Reference Points ◽

Calibration Model ◽

Coordinate Measurement ◽

Rotation Stage ◽

Binocular Vision System

For a coordinate measurement system based on binocular vision, system calibration is an important factor for measurement accuracy. In this paper we present a flexible calibration method for the axis calibration of rotation stage which is installed in front of the binocular vision system to increase the system measurement range. By putting a standard ball in front of the binocular vision system, a sequence of pictures is taken by the two cameras with a few different rotation angles of the rotation stage. With the method of space intersection of two straight lines, the reference points (the ball centers at each rotation angles) for axis calibration are figured out. The trail of standard ball is a circle. Since all ball centers of rotation are on a plane perpendicular to the axis, the center of circle is on the axis of rotation stage. The rotation axis of stage is then calibrated according to the calibration model.

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Calibration of Large Scale Coordinate Measuring System Based on Scanning Laser Plane

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.503-504.1270 ◽

2012 ◽

Vol 503-504 ◽

pp. 1270-1275 ◽

Cited By ~ 2

Author(s):

Da Bao Lao ◽

Wei Hu Zhou ◽

Zi Li Zhang ◽

Xue You Yang ◽

Ji Gui Zhu

Keyword(s):

Large Scale ◽

Calibration Method ◽

Measurement Model ◽

Bundle Adjustment ◽

Measuring System ◽

Coordinate Frame ◽

Coordinate Measurement ◽

Global Calibration ◽

Planar Laser ◽

Measuring Network

To overcome the disadvantages of existing large-scale coordinate measurement systems about low level of automation and poor parallelism, this paper introduces a novel system which characters multi-sensor measuring network, while a single sensor measures angle via a couple of non-parallel planar laser beams rotating around a fixed shaft. The novel method for measuring angle improves automation in large-scale coordinate measurement. Furthermore, measuring network assures that measurement accuracy keeps to the same level even when the measuring range is enlarged. Measurement model and calibration are the key technologies of the system. They are the main sources of measuring errors. Therefore, to minimize the error, a practical global calibration method for the multi-sensor network system is proposed, with constructing a precise mathematical model. In this model, the parameters of the system are divided to inner and outer parts. While the inner parameters are obtained by aided instrument, the outer which means transform parameters between different sensors are figured out in spot calibration. Finally, the objective function based on transform coefficients between different sensor coordinate systems is defined and the outer parameters are optimized by bundle adjustment method. Thus, the whole system can finish global calibration by one time，and no medi-coordinate-frame is needed．Therewith，transformation time of coordinate frame decreases and calibration process is facilitated. Finally，measurement experiments are conducted with root mean square(RMS) error of not more than 0.1 mm.

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Location tracking scanning method based on multi-focus in confocal coordinate measurement system

Precision Engineering ◽

10.1016/j.precisioneng.2021.03.012 ◽

2021 ◽

Author(s):

Kang Gu ◽

Yifei Li ◽

Xiaoyu You ◽

Yuhang Wang ◽

Jianwei Cui ◽

...

Keyword(s):

Measurement System ◽

Location Tracking ◽

Scanning Method ◽

Coordinate Measurement

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A Self-Calibration Method for Robotic Measurement System

10.1115/imece1999-0753 ◽

1999 ◽

Author(s):

Chunhe Gong ◽

Jingxia Yuan ◽

Jun Ni

Keyword(s):

Coordinate System ◽

Measurement System ◽

Calibration Method ◽

Position Measurement ◽

Robot Calibration ◽

Robot System ◽

Self Calibration ◽

World Coordinate System ◽

Robot Accuracy ◽

Calibration Methods

Abstract Robot calibration plays an increasingly important role in manufacturing. For robot calibration on the manufacturing floor, it is desirable that the calibration technique be easy and convenient to implement. This paper presents a new self-calibration method to calibrate and compensate for robot system kinematic errors. Compared with the traditional calibration methods, this calibration method has several unique features. First, it is not necessary to apply an external measurement system to measure the robot end-effector position for the purpose of kinematic identification since the robot measurement system has a sensor as its integral part. Second, this self-calibration is based on distance measurement rather than absolute position measurement for kinematic identification; therefore the calibration of the transformation from the world coordinate system to the robot base coordinate system, known as base calibration, is not necessary. These features not only greatly facilitate the robot system calibration but also shorten the error propagation chain, therefore, increase the accuracy of parameter estimation. An integrated calibration system is designed to validate the effectiveness of this calibration method. Experimental results show that after calibration there is a significant improvement of robot accuracy over a typical robot workspace.

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