In order to raise the robustly of the automatic verification system of steel measuring tapes, a method on extracting the meter lines on steel measuring tapes image based on Gabor transformation is proposed in this paper. This method makes full use of the frequency and direction sensitivity of Gabor filters. Through the Gabor filtering, the particular direction and frequency line structures are filtered out. Based on these line structures, positions of the meter lines in the images can be located and an ROI with the lines in it can be created automatically. Furthermore, through the RANSAC calculation to fit the double edges in the ROI, this method is able to distinguish the broken and stain lines to improve the line detect accuracy and the robustness of the image processing system. Down sampling is used to improve the efficiency of the method. An experiment has been designed to test and verify the method. By standard steel measuring tapes and dual-frequency laser interferometer, the equivalence between pixel and the physical length can be calculated. The moving distance can be calculated with the equivalence and line marker center by the method proposed in the paper. Comparing the calculated value of moving distance with reference value of moving distance measured by dual-frequency laser interferometer, the method proposed in this paper has been proof with accuracy. With the capability of solving stain, complex background, uneven illumination problems, this method can raise the degree of automation of steel measuring tapes verification system.
The minimal-distance between aero-engine pipelines is a very important parameter that can ensure the normal operation of the aero-engine. The traditional measurement method by using the feeler gauge is inefficient. This paper introduces the calculating method by using optoelectronic measurement system. In this way we can get the point cloud data of all the pipelines. Firstly, the points belonged to the same pipeline is picked up and saved in a group. Secondly, a set of equal-interval grid is built along a coordinate direction in which the pipeline stretched longest. Thirdly, on each trend-line point, a projection plane is built vertically to a straight line connecting the point and its adjacent point. Fourthly, the projected points on each projection plane are fitted into a circle using least square fitting method. Finally, traversing method is used to calculate minimal-distance between two groups of center-line points. And minimal-distance of two pipeline surfaces is calculated by subtracting radii of two pipelines from the minimal-distance of center-line points. Four groups of pipelines are examined to verify the proposed strategy. The results show that the deviations of minimal-distance of two pipeline surfaces are within -0.35mm~0.46mm. And the deviations of pipeline radius are within-0.1mm~0.29mm. The proposed method is more robust than mostly used method for calculating center-line data of pipeline.
In order to solve the low precision and poor universality of the existing 6D sensors, a novel sensor is designed based on optical measurement. After the precision influence factor is analyzed, the numbers, layout and material of the target points on 6D sensor are especially considered. And then the structure of six points in the space by using infrared laser is designed. The double theodolites measurement network is used to calibrate the structure parameters of the sensor in order to improve precision. After the mathematic principle is given, both calculation methods for optimization based on Levenberg-Marquardt and the produce of the initial value based on lagrangian multiplier are stated. The experimental data show that the root-mean-square errors of three rotation angles are 0.017°,0.013°and 0.017°. The root-mean-square errors of three translation parameters are 0.077mm,0.095mm,0.079mm. The precision can meet the requirements and the 6D sensor can be successfully used in the manufacturing industry.
The dynamic envelope measurement plays very important role in the external dimension design for high-speed train. Recently there is no digital measurement system to solve this problem. This paper develops an optoelectronic measurement system by using monocular digital camera, and presents the research of measurement theory, visual target design, calibration algorithm design, software programming and so on. This system consists of several CMOS digital cameras, several luminous targets for measuring, a scale bar, data processing software and a terminal computer. The system has such advantages as large measurement scale, high degree of automation, strong anti-interference ability, noise rejection and real-time measurement. In this paper, we resolve the key technology such as the transformation, storage and calculation of multiple cameras’ high resolution digital image. The experimental data show that the repeatability of the system is within 0.02mm and the distance error of the system is within 0.12mm in the whole workspace. This experiment has verified the rationality of the system scheme, the correctness, the precision and effectiveness of the relevant methods.
The present scanning system consists of an industrial robot and a line-structured laser sensor which uses the industrial robot as a position instrument to guarantee the accuracy. However, the absolute accuracy of an industrial robot is relatively poor compared with the good repeatability in the manufacturing industry. This paper proposes a novel method using the workspace measurement and positioning system (wMPS) to remedy the lack of accuracy of the industrial robot. In order to guarantee the positioning accuracy of the system, the wMPS which is a laser-based measurement technology designed for large-volume metrology applications is brought in. Benefitting from the wMPS, this system can measure different cell-areas by the line-structured laser sensor and fuse the measurement data of different cell-areas by using the wMPS accurately. The system calibration which is the procedure to acquire and optimize the structure parameters of the scanning system is also stated in detail in this paper. In order to verify the feasibility of the system for scanning the large free-form surface, an experiment is designed to scan the internal surface of the door of a car-body in white. The final results show that the measurement data of the whole measuring areas have been jointed perfectly and there is no mismatch in the figure especially in the hole measuring areas. This experiment has verified the rationality of the system scheme, the correctness and effectiveness of the relevant methods.
Multi-task and real-time measurement of relative displacement is widely needed in the present industrial field. Existing measuring methods require complex preparation and data processing, or are unable meet the requirement of automation, multi-task and real-time. The instruments used to measure absolute coordinates are inefficiency because of the measured target is relative displacement. A new single-station wMPS (Workspace Measuring Position System) measurement method combined distance measurement is presented in this paper. It learns from measuring principle of total station, measures angle based on rotating scanning laser plane measuring method, and measures distance based on optoelectronic scanning multi-angle intersection location principle, uses the angle-length resection measuring method, builds a new mathematical model to measure the relative displacement of the target. The result of experiment proves that it increases measuring efficiency and achieves multi-task and real-time measurement of relative displacement.
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.
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