From simple endoscopy to 3D phase measurement

The basis of nondestructive testing techniques is to see what the naked eye cannot see. Ultrasonics are used to identify defects and corrosion in metals, especially at welds. Radiographic techniques can be used to inspect castings and tubes for inclusions, delamination or other flaws. Eddy current can be used to detect hidden cracks in laminar surfaces. Industrial video endoscopes (RVI) are widely used in the aerospace industry to inspect aircraft components and structures, from engines to fuselages. In recent years, RVI has made great improvements in the imaging and measurement capabilities of the technology, which will be discussed in this article.

Industrial video endoscopes (RVI) are a long-standing inspection and nondestructive testing technology in the aviation field. Although traditional rigid rod scopes are still widely used for aircraft engine inspection, video endoscopes have become the preferred choice for military and civilian applications to inspect fuselages, auxiliary power units and engines. These are considered part of routine maintenance activities, and original equipment manufacturers also use video endoscopes when manufacturing engines. Use video endoscopes to check for leaks, corrosion and surface cracks, inspect internal gaps, identify blockages, and detect external objects. Understanding the wide range of potential applications for video endoscopy, videotapes have enabled the capture and storage of digital data. This technology has been further developed into CDs, DVDs, flash memory and solid-state memory cards, which enable the transfer of files to a PC for further evaluation or storage.

RVI 的演变

工业内窥镜起源于医疗业，1806年奥地利人研发出了第一个内窥镜，用于人体血管和体腔的检查。

二战后，工业内窥镜的发展才渐入佳境，早期的仪器由镜头和照明光源组成，连接到一个光传输扩展器，也就是目镜。这些基础内窥镜仅仅用于视觉检测，而不能测量。这样，人们就用它来检测由于结构或者组件的妨碍，难以接近或者正常情况无法访问的位置。

到60 年代，工业内窥镜才具有图像捕捉和测量能力，此时35mm 照相机添加了目镜。随之发展起来的还有：在光传输机理中引入了光纤，视频镜头成为图像捕捉的首选。与此同时，随着机载计算能力的引入，视频内窥镜的功能有了显著的改善，这使得内窥镜能保存和存储数字格式的视频图像。之前，软盘光盘和检测信息的共享是任何检测过程的重要环节，尤其在航空领域，出于安全和经济的考虑，经常要对发动机的正常运行进行专业评估。因此，共享信息的功能是最新一代RVI 仪器所特有的。

处理数据

将机载PC 植入RVI，即引入应用软件，从而确保对大量生成数据进行有效管理。这类软件能标记图像，并以逻辑文件的形式排列，允许快速简单读取。GE 检测控制技术推出的XLG3，在无损探伤中使用了数字成像和通信（DICONDE）格式，这是一种非专有格式，从医疗行业放射学使用的DICOM 发展起来，又纳入了许多纯粹的无损检测方面的特性。

此协议构成了GE Rhythm 软件平台的基础，可以获得、报告、审核和归档数据。它还是重要的应用工具，包括图像增强、操作和变焦。

航空业经常要处理与日俱增的大量检测信息，Archive 特性尤其与之息息相关。它接受来自任意连接的局域网、远程Rhythm Review 工作站的图像，使用各种不同的压缩技术来保存它们，在不牺牲图像质量的同时又节省了内存空间。DICONDE 简单的标记系统，使得信息的输入和检索快捷方便。而且，Rhythm Archive不仅存储原料检测数据，还会将Rhythm Review 工作站产生的增强图像存储下来。除此之外，还给用户带来了其他的效益。它能搜索更多的有效数据，因为可以在中央储存器得到同一网络里的所有工作站的全部信息。它还能控制图像信息流，所以数据可以发送到其他的RhythmReview 工作站作进一步分析。

Cursor positioning in phase detection[page]

Simplified

software can also be used to standardize inspection procedures to ensure consistency in inspection and description of inspection results. Menu-based inspection wizards (MDI) are software solutions that provide guided inspections and automatically add context. For example, when inspecting an engine, a drop-down menu will first allow the inspector to select the relevant manufacturer and specific engine. Before the inspector starts the inspection, all the certification data related to the task (inspector, location, date, etc.) is entered in the manner specified for the corresponding engine or component. The data image file is then marked with comments and fields in the endoscope's data capture system. Finally, a hard copy of the report is generated and the report can be reported at the click of a button.

Measure what you see

Today, the measurement of defects, differences, and gaps is as important as their detection and identification. To date, there are three main measurement systems: comparative measurement, stereo measurement, and shadow measurement.

Comparative measurement is based on a known reference dimension in the inspection image, and the measurement of other objects in the same view and plane (the reference dimension is often set in place by the instrument manufacturer or determined using a probe).

Stereo measurement uses a prism to split the image, allowing the camera to capture the left and right views with precise angular separation, and then a computer algorithm analyzes the position of the user's cursor to obtain precise measurements using triangulation.

Shadow measurement relies on measuring the distance to the target. A shadow lens projects a shadow onto the object being inspected, and the position of the resulting shadow shows the distance to the object. With this information, the shadow probe system can accurately calculate the size of the defect selected by the user. These methods can measure depth, length, area, point-to-line distance, length of multiple line segments, and circles.

Phase measurement can improve imaging and make measurements more accurate

. Although various measurement technologies exist today, measurement remains the most difficult problem in video endoscopy. Inspectors must be well trained and experienced to obtain stable, reliable, and repeatable results. This level of expertise is now called RVI, the official nondestructive testing standard for specialization, and is part of the testing and certification process of the American Society for Nondestructive Testing TC1A Level-III.

The accuracy, repeatability and ease of use of videoscopes have been greatly improved recently with the development of phase measurement methods.

3D phase measurement is a technology based on existing optical metrology. It projects a line of light onto a surface and captures this line pattern with a camera with high-quality optics. The image is then processed with a proprietary algorithm to produce a 3D point cloud of the entire surface. This is then used in conjunction with the measurement to obtain more precise information about the defect or object being measured. The measurement itself involves only the placement of a cursor on the full-screen image and does not require point matching, shadow identification or point selection, which are difficult to achieve with other technologies.

A major innovation of this measurement system is the 3D scan with rotation and zoom capabilities, which provides a strong indication of the size and shape of the object. The system's cross-section view feature provides further assistance in estimating the size and shape of the object. When the user places the cursor on either side of their area of ​​interest, the 3D phase measurement system draws a line between the two sides. Then select the cross-section view and the intersection along this line will be displayed, making the pit, crack or corrosion more clear. At the same time, the cross-section view can also be used to measure the depth of points in the cross-section section.

Improved Productivity through Greater Ease of Use

Measurement methods using stereo and shadow are time-consuming and require expertise. For example, with stereo measurement, you first identify the defect using the viewing lens, then switch to the stereo measurement lens, relocate the defect, lock the image, match the cursor, and finally measure. With phase measurement, once the defect is located and the image is locked, the measurement can begin without changing lenses.

Since there is no need for point matching, shadow identification, cursor matching, or point selection steps required by other measurement techniques, 3D phase measurement offers great ease of use. This means fewer operator errors and more repeatable and accurate results.

More Potential Applications

One important application of 3D phase measurement technology is measuring the gap from the tip of an aircraft engine to the shroud.

Aircraft engines and other shaft-type turbines are designed to reduce the diameter distance from the blade tip to the blade or casing. If there is a gap between the blade tip and the casing, fuel or air can leak into the downstream section, resulting in reduced efficiency. Therefore, it is important to check the gap both during production and during maintenance because the gap size changes during engine operation (high speed and high temperature cause elastic diameter growth of the blade and thermal expansion of the casing).

Previously, to measure the blade tip to casing clearance, a thin metal rod was inserted into the shaft bolt and the fitting was attached to the windbox so that the end of the rod was exactly where the blade tip was. After the engine was started, the wear of the metal rod was measured. Obviously, this is not a high-precision technique and often results in problems such as the metal rod releasing metal, which can cause damage to the engine.

Phase measurement provides a simple, non-contact, high-precision technique to measure the blade tip to casing clearance.

Conclusion

Industrial endoscopes have demonstrated many advances since their inception. Image quality has been significantly improved due to fully digital data streams and improved optical illumination technology. The integration of on-board processing has greatly expanded the capabilities of RVI and greatly facilitated data sharing through network connectivity. Application software (such as MDI) helps to increase the detection success rate while reducing the occurrence of detection errors. Software platforms for collecting, verifying, reporting and archiving complex data can effectively organize the accumulated data for optimal results. Now this innovative RVI measurement technology is easy to implement, can provide fast and accurate results, and has more comprehensive imaging information, improving the quality control level of the production process and making detection smarter and more effective. (end)