The hybrid iterative angular spectrum method is an effective approach for computing holograms with reduced interlayer crosstalk noise. However, the use of a random phase as the initial phase results in speckle noise across all reconstructed planes. We propose a hybrid iterative angular spectrum method based on the double-phase amplitude encoding method. This method eliminates the constraints of the initial phase by employing a quadratic phase instead of a random phase as the initial phase, successfully reducing speckle noise in the reconstructed images. Through simulation and experimental validation, the algorithm demonstrates superior reconstruction performance, making it applicable to various fields such as biology, medicine, and engineering design. It provides a robust solution to the challenges of multi-plane image reconstruction.
A data fusion attitude dynamic measurement method based on vision and Inertial Measurement Unit (IMU) was studied for attitude measurement in dynamic environment. Firstly, the composition and working principle of the attitude dynamic measurement system were introduced, and a mathematical model for attitude dynamic measurement was established. Secondly, a non-equal period Kalman data fusion algorithm was studied to address the differences in IMU and visual pose calculation cycles in measurement systems. Finally, an experimental platform was built, and a precision two-dimensional turntable was used as the standard value to evaluate the accuracy of the fused attitude. The experimental results show that the data update rate of the attitude measurement system can reach 100Hz. When the target rotates at 5°/s along the azimuth direction, the maximum absolute deviation of the azimuth angle at 3m is 0.49°, and the maximum absolute deviation of the azimuth angle at 15m is 1.05°. The proposed method can improve the dynamic performance of attitude measurement system and compensate for the limitation of visual solving which requires intervisibility.
KEYWORDS: Distance measurement, Cameras, Laser systems engineering, Prisms, Monte Carlo methods, Manufacturing, Laser applications, Imaging systems, 3D modeling
The Six-degree-of-freedom(6-DOF) measurement system based on laser tracking equipment provides a good solution for large-scale industrial measurement. However, there is no unified standard to evaluate the accuracy of attitude measurement system. At present, the accuracy evaluation method of attitude measurement mainly adopts the comparison method of standard parts, which is easily constrained by space dimensions. Aiming at this problems, a homogeneous coordinate transformation method based on spatial distance constraint is proposed to realize the on-site accuracy evaluation of attitude measurement. Firstly, a reasonable control field was arranged, and the distance constraints between the reference points and the measuring points were established. Secondly, the mathematical model which described the relationship between space distance and attitude was established by using homogeneous coordinate transformation matrix. Through the above evaluation method, the accuracy of attitude measurement can be evaluated by tracing the measurement results of attitude angle to the length measuring standards. The simulation results show that the accuracy of the evaluation model decreases linearly with the measurement distance of attitude measurement system. Assuming that the measurement accuracy of the distance constraint is 15μm+6μm/m, the size of the control field is 1.1m*6.4m*5.6m, and the attitude angle range is [-60°, 60°]. The accuracy of the evaluation model can be controlled within [0.34°,3.25°], when the working distance is 3 to 15 meters. This method provide an effective idea for the on-site evaluation of attitude measurement accuracy.
The angle-based intersection measurement system is a high-precision overall measurement network based on the perspective observation in space. However, when the target is moving, the angular intersection failure will cause dynamic error to limit its application in the field of dynamic measurement. Aiming at this problem, Firstly, this paper analyze the sources of dynamic error from the principle, studies the influencing factors of system dynamic error include :the motion state of the measured object, station deployment. Secondly, constructs a mathematical model to predict the dynamic error of the measurement system. Finally, design some simulation experiments to quantify the measurement dynamic error at different measure conditions. The results show that under the measurement conditions of the measurement area is 10m x 10m x 1m, observation angle uncertainty is 2′′, the measured target moves at 0.05m/s, the average dynamic error of the measured area under the 0_4 deployment is the minimum, and value is 0.25mm.
Aiming at the requirement of high precision real-time measurement of attitude angle in modern manufacturing industry, an attitude measurement system based on a Laser Tracker is constructed. A method of attitude measurement based on 2DPSD and monocular vision is proposed, and a target structure for realizing this method is proposed. Firstly, the rolling angle of the target relative to the camera is calculated by monocular vision, and the laser beam vector is obtained by Laser Tracker and 2DPSD. Then, the relative attitude between the Laser Tracker coordinate system and the camera coordinate system is calculated based on SVD. Finally, the transformation relations of unit vector of laser beam in different coordinate systems are established to calculate the attitude of target relative to Laser Tracker. Experiments show that the method can effectively measure the target attitude information, and the maximum error of attitude angle measurement can be less than 2° within the effective angle range of [- 25°, 25°] and distance range of 3m.
In the case of industrial field measurement, the present measuring instruments work with manual operation and collimation, which give rise to low efficiency for field measurement. In order to solve the problem, a new type industrial total station is presented in this paper. The new instrument can identify and trace cooperative target automatically, in the mean time, coordinate of the target is measured in real time. For realizing the system, key technology including high precision absolutely distance measurement, small high accuracy angle measurement, target automatic collimation with vision, and quick precise controlling should be worked out. After customized system assemblage and adjustment, the new type industrial total station will be established. As the experiments demonstrated, the coordinate accuracy of the instrument is under 15ppm in the distance of 60m, which proved that the measuring system is feasible. The result showed that the total station can satisfy most industrial field measurement requirements.
KEYWORDS: Transmitters, Calibration, Receivers, Control systems, 3D metrology, Optimization (mathematics), Head, Optical engineering, Time metrology, Computing systems
The workspace measurement and positioning system is a three-dimensional (3-D) coordinate system based on laser scanning, which is widely applied in large-scale metrology. As a core part ensuring measurement accuracy, the transmitter parameters’ calibration is the critical technique of the system. The present transmitter parameter calibration method relies on auxiliary measurement equipment, which is more error prone and less efficient. This paper will focus on the improvement of the transmitter parameters’ calibration by using a highly precise 3-D coordinate control network. Several calibration points with known coordinates are set in the workspace to establish the precise 3-D coordinate control network. After the new model of transmitter parameter calibration has been explained, both the calculation method for optimization and the production of the initial iteration value are given. As indicated by the results of the verifying experiment, the accuracy and efficiency of the transmitter calibration can be distinctly improved by using the proposed method. The experimental data show that the 3-D coordinate measurement error has obviously decreased from 0.3 to 0.15 mm as a merit of the proposed method.
As a novel network coordinate measurement system based on multi-directional positioning, workspace Measurement and Positioning System (wMPS) has outstanding advantages of good parallelism, wide measurement range and high measurement accuracy, which makes it to be the research hotspots and important development direction in the field of large-scale measurement. Since station deployment has a significant impact on the measurement range and accuracy, and also restricts the use-cost, the optimization method of station deployment was researched in this paper. Firstly, positioning error model was established. Then focusing on the small network consisted of three stations, the typical deployments and error distribution characteristics were studied. Finally, through measuring the simulated fuselage using typical deployments at the industrial spot and comparing the results with Laser Tracker, some conclusions are obtained. The comparison results show that under existing prototype conditions, I_3 typical deployment of which three stations are distributed in a straight line has an average error of 0.30 mm and the maximum error is 0.50 mm in the range of 12 m. Meanwhile, C_3 typical deployment of which three stations are uniformly distributed in the half-circumference of an circle has an average error of 0.17 mm and the maximum error is 0.28 mm. Obviously, C_3 typical deployment has a higher control effect on precision than I_3 type. The research work provides effective theoretical support for global measurement network optimization in the future work.
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