A Novel Method for Measuring the Length of Hot Large Forgings Based on Machine Vision System

Large forgings can be applied to manufacture key parts in large equipment used in petrochemical, shipbuilding, aerospace, nuclear industry. At present, the size of hot large forgings is mainly measured by hand-hold calipers or mechanical gauges through contact measurement method. In order to realize non-contact length measurement of hot large forgings, a novel method for measuring the length of hot large forgings based on machine vision system is proposed. Firstly, the light strips are recognized according to the continuous characteristics of the light stripes in the image acquired by the hot forging dimension measurement system based on machine vision. Secondly, using the sub-pixel edge of light strips acquired by the improved sub-pixel edge detection algorithm, the three-dimension (3D) points of each edge of light strips are calculated, respectively. Lastly, the two-dimensional (2D) points projected from the 3D points onto the fitted plane are used for curve fitting, and the edge of hot part corresponding to each light strip edge is calculated according to the curvature of the fitted curves. The distance between the start point and the edge point on each light strip edge is considered as the length of hot forging at the corresponding edge of each light strip. The length measurement experiment shows that the method can be used to calculate the length of hot large forgings. The measurement error of the length measurement system when measuring part at room temperature is 0.547%. The time for measuring the length of hot forging is 6.8s.

Influencing factors of rotary table geometric error measurement using four-station laser tracers

The laser tracer multi-station measurement method has outstanding performance in computerized numerical control (CNC) rotary table geometric error measurement and separation. However, external factors, such as layout, selected distance between the target mirror and measurement coordinate system, uncertainty of the length measurement, selection of measuring radii for the rotary table, and installation deviation from the target mirror center to the rotary table surface, have negative effects on the results. In this research, the position dilution of precision in the global positioning system measurement process is introduced to evaluate the influence of the laser tracers’ positions on measurement errors. The optimal measurement layout of the laser tracer is used to select the distance between the target mirror and XY plane of the laser tracer measurement coordinate system for the simulation. Then, the influence of the length measurement uncertainty on the laser tracer self-calibration and point measurement results used for calibration is examined based on the Monte Carlo simulation method. Different measurement radii in the rotary table are selected, and four-station laser tracers are used to perform the virtual measurement and evaluate the maximum uncertainty in the X, Y, and Z directions to further determine the best measurement radii of the CNC rotary table. Finally, the effects of the deviation of the target mirror installation center on the geometric error items of the CNC rotary table are quantitatively examined through a simulation. The analysis of the influencing factors in the geometric error measurement and separation process of the CNC rotary table can help further understand how the final results are formed, so as to control the influencing factors during the measurement process and finally optimize them in practice.

Fried’s coherence length measurement of dynamic Kolmogorov type turbulence using autocorrelation function

A new method to find Fried’s coherence length of a dynamic Kolmogorov type turbulence in laboratory environment is reported in this paper. This method utilises autocorrelation function obtained from the quantitative characteristics of a rotating pseudo random phase plate in one of the arms of Mach-Zehnder interferometer. Theoretical formalism and experimental verification are presented.