Steel tape is a commonly used length-measuring tool, which needs to be verified before using. In this paper, a method based on image processing for steel tape verification, which replaces the traditional eye detection, is proposed. Firstly, the camera is calibrated to get the pixel equivalent. Secondly, the standard steel tape and steel tape to be measured are arranged side by side on the calibration table, and the image of the integral meter is collected by the CCD camera. Thirdly, the acquired image is divided into regions, then the fine regions are further divided, and the area where the integral meter scale line locates is selected by the frame. Finally, the coordinates of the scale line at the integral meter are extracted and calculated by the method of pixel traversal and gray center of gravity. The error of the steel tape can be obtained by multiplying the difference between them by the pixel equivalent. The verification process is efficient and the results are reliable. The resolution of the measurement system can reach 0.04 mm, which meets the requirements of the measurement task.
With the continuous improvement of equipment measurement accuracy and production efficiency requirements, calibration method with external reference standard can no longer meet the quality and efficiency requirements. In order to solve the online calibration problem and effectively improve the calibration efficiency of the Articulated Arm Coordinate Measuring Machines (AACMMs) in practical application, a self-calibration system of circular grating angle sensor which is applied to joints of the AACMMs was established. Based on the harmonic analysis of the angle measurement error, this paper deduces and analyzes the error suppression principle of the layout of the scanning heads on the calibration result, and establishes a non-uniform layout of the scanning heads to eliminate more and higher order harmonic errors. The simulation and test results show that the self-calibration method using this layout form of multiple reading heads can effectively reduce the measurement angle error without increasing the number of scanning heads, and improve the calibration efficiency and measurement accuracy of AACMMs.
The precision of dimensional measurement plays an important role in guaranteeing the assembly accuracy of its internal components during the upgrading phase of EAST device. In this paper, the experimental research and analysis were done based on three dimensional combined measurement systems, combining Laser Tracker, flexible Measure ARM and measurement fiducials network, which are used for alignment and measurement of EAST components during the assembly process. The error sources were analyzed, e.g. temperature, gravity, welding, and so on. And the effective weight of each kind of error source was estimated by the simulation method. Then these results were used to correct and compensate the actual measured data, the stability and consistency of the measurement results was greatly improved in different measurement process, and the assembly precision of the EAST components was promised.
In order to obtain accurate position of the inner key components in the experimental advanced superconducting tokamak (EAST), a combined optical measurement method which is comprised of a laser tracker (LT) and articulated coordinate measuring machine (CMM) has been brought forward. LT, which is an optical measurement instrument and has a large measurement range and high accuracy, is employed for establishing the precision measurement network of EAST, and the articulated CMM is also employed for measuring the inner key components of EAST. The measurement uncertainty analyzed by the Unified Spatial Metrology Network (USMN) is 0.20 mm at a confidence probability of 95.44%. The proposed technology is appropriate for the inspection of the reconstruction of the EAST.
The combined measurement technology plays an increasingly important role in the digitalized assembly. This paper introduces a combined measurement system consists of a Laser tracker and a FACMM,with the applications in the inspection of the position of the inner parts in a large-scale device. When these measurement instruments are combined, the resulting coordinate data set contains uncertainties that are a function of the base data sets and complex interactions between the measurement sets. Combined with the characteristics of Laser Tracker and Flexible Articulated Coordinate Measuring Machine (FACMM),Monte-Claro simulation mothed is employed in the uncertainty evaluation of combined measurement systems. A case study is given to demonstrate the practical applications of this research.