High precision photoelectric angle encoder is a key component of intelligent angle measuring with strategic significance. A special fixture and adjustment measurement method is proposed, which can effectively solve many problems such as eccentricity, tower difference error and rotation interference caused by the direct fixation of rotating shaft (mover) and driving shaft during measurement. An automatic calibration system is also setup, which can realize many measurement schemes, such as direct calibration of turntable, polyhedral prism calibration and permutation comparison calibration. The measurement accuracy of the system is verified by comparison experiments and repeatability experiments. The measurement uncertainty of the optimal angular division error can reach 0.15 "(k = 2).
KEYWORDS: Calibration, Interferometers, Data fusion, Detection and tracking algorithms, Testing and analysis, Visualization, Systems modeling, Standards development, Reliability, Manufacturing equipment
A traceable accuracy test method of multi-instrument cooperative measurement system is studied. Here a precise angle dividing table and a linear guide with a laser interferometer are used as standards to test the cooperative measurement’s external parameters. And the coordinates of common points and uncommon points are tested by the scale bars. This testing method is illustrated with a cooperative measurement system composed of two laser trackers. It is obvious that this method can intuitively test the accuracy of the multi-instrument cooperative measurement’s external parameters and coordinates. This method is not restricted by the measurement principle, the data fusion algorithm and the measurement targets of the cooperative system, and it is suitable for various non-fixed layout cooperative measurement system.
Nowadays most commercial measurement software only indirectly evaluates the accuracy of the cooperative measurement and lacks intuitiveness. Therefore an accuracy evaluation method of the cooperative measurement is studied so that the transformation parameters’ error and the final results’ error in the cooperative measurement are directly quantified. And customized software is developed which is used to quickly and easily evaluate and visually display the accuracy of the cooperative measurement in the industrial field. Finally an experiment with two laser trackers is conducted to prove the accuracy evaluation method and the software of cooperative measurement. It is obvious that the accuracy evaluation method is feasible and the accuracy evaluation software is user-friendly
Most 3D body scanners adopt a structure with multiple scanning sensors on the fixed frame to perform synchronous scanning from multiple directions of the human body. The position and attitude parameters of the multiple scanning sensors are the key to determining the 3D model stitching, and they are often calibrated when the scanner is installed. Any changes in these parameters of sensors will make model stitching errors and affect scanning accuracy. This paper studies a method for judging faults of 3D body scanner based on standard sphere. By scanning a standard sphere and observing the splicing deformation of the 3D model, it can determine whether the scanner's structure has changed, and identify which sensor has moved or rotated. Then the user can be guided to choose the appropriate calibration steps to compensate the scanner. Experiments prove that this method is a quick and effective intermediate check method of the 3D body scanner.
KEYWORDS: Standards development, Laser scanners, Calibration, Spherical lenses, Prisms, 3D metrology, Optical spheres, 3D acquisition, 3D scanning, Data centers
The spherical target is the standardization target of the laser scanner performance evaluation commonly used by international metrology institutions. How to obtain the spherical center coordinates of the target by using a higher precision class instrument is an important prerequisite for realizing the spatial performance calibration of the laser scanner. A split target set is proposed, which can be concentric with the laser scanner target by machining and adjusting. The extended uncertainty of the reference distance formed by the split target sets can reach 0.07 mm under the effective length of 3 m, which can be effectively applied to the spatial distance indication error calibration of the laser scanner.
Accurate and traceable reference coordinates in three-dimensional space is the key and difficult point for coordinate calibration of large-scale measurement instruments such as laser tracker and iGPS. This paper studies the application of multilateration with laser tracker in establishing reference coordinates. First, a reference coordinate network is established, which has good spatial scalability and is compatible with multiple targets. Then, multilateration with laser tracker is applied to calibrate the reference coordinate network. And the basic principle, measurement uncertainty evaluation and tracker layout optimization are studied in detail. So that the reference coordinates are traced to the laser interference. Finally, through the repeatability test, length test, and coordinate test, it is shown that the reference coordinates satisfy their measurement uncertainty range and can be used for coordinate calibration of the large-scale measurement instruments.
The network geometry strongly influences the performance of the distributed system, i.e., the coverage capability, measurement accuracy and overall cost. Therefore the network placement optimization represents an urgent issue in the distributed measurement, even in large-scale metrology. This paper presents an effective computer-assisted network placement optimization procedure for the large-scale distributed system and illustrates it with the example of the multi-tracker system. To get an optimal placement, the coverage capability and the coordinate uncertainty of the network are quantified. Then a placement optimization objective function is developed in terms of coverage capabilities, measurement accuracy and overall cost. And a novel grid-based encoding approach for Genetic algorithm is proposed. So the network placement is optimized by a global rough search and a local detailed search. Its obvious advantage is that there is no need for a specific initial placement. At last, a specific application illustrates this placement optimization procedure can simulate the measurement results of a specific network and design the optimal placement efficiently.
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