Vision Measurement Technique Research Articles

Measurement of outer diameter parameters of manual grinding cable joints based on 3D point cloud processing

For the problems associated with low measurement accuracy caused by surface shrinkage, uneven grinding, and irregular shapes in manual grinding cable joints, as well as the limitations of existing machine vision measurement techniques for the outer diameter parameters, this paper proposes a non-contact outer diameter parameters measurement method of manual grinding cable joints based on three-dimensional (3D) point cloud processing. Firstly, statistical filtering is used to remove discrete noise, and coordinate transformation preprocessing is conducted to ordered the point cloud. Secondly, a bidirectional point cloud slicing method is proposed based on the cable joint structure and point cloud distribution to preserve the original features for effective measurement. Subsequently, the normalized mean curvature is utilized as the weight of point cloud coordinate averaging to construct key points for surface slices, which reduces the amount of data in the sliced point cloud and improves the matching efficiency. Finally, the key points are matched according to the position of the surface slices, and the distance of point pairs is calculated to complete the measurement of the outer diameter parameters. Experiments and error analysis are conducted on multiple manual grinding 110 kV and 500 kV real cable joints. The absolute error in the measurement of the outer diameter is less than 0.2 mm, with a relative error within 1 %. The absolute error of the XY-axis outer diameter deviation is less than 0.1 mm. The experiments demonstrate that the proposed method exhibits superior performance in cable joint outer diameter measurement.

A New Vision Measurement Technique with Large Field of View and High Resolution.

The three-dimensional (3D) displacement resolution of conventional visual measurement systems can only reach tens of microns in cases involving long measuring distances (2.5 m) and large fields of view (1.5 m × 1.5 m). Therefore, a stereo vision measurement technology based on confocal scanning is proposed herein. This technology combines macroscopic visual measurement technology with confocal microscopic measurement technology to achieve a long measuring distance, a large field of view, and micron-level measuring resolution. First, we analyzed the factors affecting the 3D resolution of the visual system and developed a 3D resolution model of the visual system. Subsequently, we fabricated a prototype based on the resolution model and the proposed stereo vision measurement technology. The 3D displacement resolution measurement results in the full field of view show that the displacement resolutions of the developed equipment in the x-, y-, and z-directions can reach 2.5, 2.5, and 6 μm, respectively.

Vision and Vibration Data Fusion-Based Structural Dynamic Displacement Measurement with Test Validation.

The dynamic measurement and identification of structural deformation are essential for structural health monitoring. Traditional contact-type displacement monitoring inevitably requires the arrangement of measurement points on physical structures and the setting of stable reference systems, which limits the application of dynamic displacement measurement of structures in practice. Computer vision-based structural displacement monitoring has the characteristics of non-contact measurement, simple installation, and relatively low cost. However, the existing displacement identification methods are still influenced by lighting conditions, image resolution, and shooting-rate, which limits engineering applications. This paper presents a data fusion method for contact acceleration monitoring and non-contact displacement recognition, utilizing the high dynamic sampling rate of traditional contact acceleration sensors. It establishes and validates an accurate estimation method for dynamic deformation states. The structural displacement is obtained by combining an improved KLT algorithm and asynchronous multi-rate Kalman filtering. The results show that the presented method can help improve the displacement sampling rate and collect high-frequency vibration information compared with only the vision measurement technique. The normalized root mean square error is less than 2% for the proposed method.

Vision measurement technique of model position and its widespread application on the ballistic range

In order to obtain the position changes of model flying freely with hypervelocity on the ballistic range, China Aerodynamics Research and Development Center (CARDC) applied the binocular vision technique to measure the model position. The binocular measurement stations were installed besides the room along the model flying direction, which would be calibrated and aligned to the global base reference coordinate system before the test. When the flying model with coded marking points on surface entered the measurement field, it would be illuminated by the extended laser beam with the pulse width of smaller than 10 ns, meanwhile, the two images of the target were obtained by the cameras. The model position was obtained by identifying and calculating coded marking points after the test. Based on solving the key technologies of obtaining clear images of the target, calibrating and aligning binocular measurement stations, dealing the model surface color and making marking points, the vision measurement system of the model position was accomplished on the 200 m free flight ballistic range of CARDC. The position changes of the 20° circular cone with the length of 165 mm were obtained by the vision measurement system, and the drag index and dynamic derivative of which were obtained by identifying, and the trend of the identified results were basic consistency with those on the G-Range of Arnold Engineering Development Center (AEDC). Meanwhile, the widespread application of vision imaging technique was validated by the test. Two new measurement technologies were developed. The first one was obtaining the image sequences, the other was obtaining the image of the target and shadow image at the same measurement field simultaneously. The image of the target for the debris cloud of aluminum sphere impacting aluminum plate at hypervelocity was obtained successfully.

Vision measurement technique of axle based on double beam

In order to improve the measurement efficiency and accuracy of axle diameter, this paper presents a new method for automatic measurement of axle. According to the data obtained from the scanned contour fitting and calculating the axle diameter. The system adopts the principle of double beam projection measurement. The precise measurement of large scale axis is accomplished by collimating beam and beam reflection. The system consists of two parts: the supporting device and the measuring sensor unit. Based on the scanning data acquisition, interpolation, fitting a straight, line fitting the entire axle contour, calculate the length and diameter of numerical train axle. Through the analysis of the experimental data, it can be seen that the double beam projection measurement sensor has the advantages of high measurement accuracy, large diameter measurement, good stability and so on. The repeatability error reaches 0.007 mm, and the measurement accuracy reaches 0.02 mm.The experimental results show that this method is feasible and it can solve the technical requirements for accurate inspection of axle size parameters in the process of production and processing of high-speed EMU.

An inkjet vision measurement technique for high-frequency jetting.

Inkjet technology has been used as manufacturing a tool for printed electronics. To increase the productivity, the jetting frequency needs to be increased. When using high-frequency jetting, the printed pattern quality could be non-uniform since the jetting performance characteristics including the jetting speed and droplet volume could vary significantly with increases in jet frequency. Therefore, high-frequency jetting behavior must be evaluated properly for improvement. However, it is difficult to measure high-frequency jetting behavior using previous vision analysis methods, because subsequent droplets are close or even merged. In this paper, we present vision measurement techniques to evaluate the drop formation of high-frequency jetting. The proposed method is based on tracking target droplets such that subsequent droplets can be excluded in the image analysis by focusing on the target droplet. Finally, a frequency sweeping method for jetting speed and droplet volume is presented to understand the overall jetting frequency effects on jetting performance.

Tracking based inkjet measurement for evaluating high frequency ink jetting

Inkjet technology has been used as a manufacturing tool for printed electronics. To increase productivity, the jetting frequency needs to be increased. When using high frequency jetting, the printed pattern quality can be non-uniform since jetting performance, including jetting speed and droplet volume, can vary significantly according to the jet frequency increase. Therefore, high frequency jetting behavior must be evaluated properly for performance improvement. However, it is difficult to measure high frequency jetting behavior using the previous vision analysis methods because subsequent droplets are very close and can even merge. In this paper, we present vision measurement techniques to evaluate the drop formation of high frequency jetting. The proposed method is based on the tracking of target droplets, and other subsequent droplets can therefore be excluded in the image analysis by focusing on the target droplet.

A Computer Vision Measurement System for Linear Deformation of Line Heating

Line heating is an important technique for processing hyperboloidal outside plate of ship hull. To realize the automation of the line heating, the deformation rule in line heating should be researched. In this paper, the computer vision measurement technique is applied to find out the disciplinarian of linear deformation in line heating. The principle of computer vision measurement is firstly introduced in this paper. The emphases are the images collection, camera calibration, edge detection, and 3D data reconstruction. Then some key techniques for ensuring the measurement precision are presented. At last, the result of experiments is given. The experiments showed that the measurement system was valid for measuring the linear deformation of line heating.

Investigation of pulse voltage shape effects on electrohydrodynamic jets using a vision measurement technique

In this paper, we present a vision measurement technique to evaluate electrohydrodynamic (EHD) inkjet behavior, and discuss the effects of the pulse voltage shape on the EHD jets for drop-on-demand printing, including the falling and rising time in the pulse voltage. Sequential images acquired by a charge-coupled device (CCD) camera with a strobe light-emitting diode (LED) were used to visualize EHD jet behavior with respect to time. A vision algorithm was implemented in an EHD jet system to enable in situ measurement and analysis of EHD jets. A guideline for selecting pulse shape parameters is also presented, to enable the achievement of high-frequency reliable jets for drop-on-demand printing. Printing results are presented to demonstrate the drop consistency of jets.

A Vision Measurement Technique for Evaluation of Pulse Voltage Effect on Electrohydrodynamic (EHD) Jet

In this paper, we present a vision measurement technique to evaluate electrohydrodynamic (EHD) inkjet behavior, and discuss the effects of the pulse voltage shape on the EHD jets for drop-on-demand printing, including the falling and rising time in the pulse voltage. Sequential images acquired by a charge-coupled device (CCD) camera with a strobe light-emitting diode (LED) were used to visualize EHD jet behavior with respect to time. A vision algorithm was implemented in an EHD jet system to enable in-situ measurement and analysis of EHD jets. A guideline for selecting pulse shape parameters is also presented, to enable the achievement of reliable jets for drop-on-demand printing.

전류 측정을 이용한 수력학적 잉크젯 토출 모니터링

The method for spraying of liquid through an electrical filed has become a printing method since it can make very small droplet. To increase the reliability using the electro-hydrodynamic (EHD) jet printing, the jetting status needs to be monitored. Vision measurement techniques using high speed camera has been used to visualize the jet images. However, it requires image processing of a lot of images after image acquisitions. So, it is difficult to understand jet behavior such as jetting frequency, jet repeatability etc. In this work, a low cost electrical current measurement method was developed to measure electrical current from EHD jet printing. To verify the jetting monitoring capability of developed circuit, images from high speed camera were processed for comparison purpose.

Measurement of Seedling Growth Rate by Machine Vision

Seed vigor and germination tests have traditionally been used to determine deterioration of seed samples. Vigor tests describe the seed potential to emerge and produce a mature crop under certain field conditions and one measure is seedling growth rate. A machine vision system was developed to measure root growth rate over the entire germination period. The machine vision measurement technique was compared to the manual growth rate technique. The vision system provided similar growth rate measurements as compared to the manual growth rate technique. The average error between the system and manual measurement was 0.13 cm for the lettuce test and 0.07 cm for the sorghum test. This technique also provided an accurate representation of the growth rate as well as percent germination.