In the real application environment of field engineering, a large variety of metrology tools are required by the technician to inspect part profile features. However, some of these tools are burdensome and only address a sole application or measurement. In other cases, standard tools lack the capability of accessing irregular profile features. Customers of field engineering want the next generation metrology devices to have the ability to replace the many current tools with one single device. This paper will describe a method based on the ring optical gage concept to the measurement of numerous kinds of profile features useful for the field technician. The ring optical system is composed of a collimated laser, a conical mirror and a CCD camera. To be useful for a wide range of applications, the ring optical system requires profile feature extraction algorithms and data manipulation directed toward real world applications in field operation. The paper will discuss such practical applications as measuring the non-ideal round hole with both off-centered and oblique axes. The algorithms needed to analyze other features such as measuring the width of gaps, radius of transition fillets, fall of step surfaces, and surface parallelism will also be discussed in this paper. With the assistance of image processing and geometric algorithms, these features can be extracted with a reasonable performance. Tailoring the feature extraction analysis to this specific gage offers the potential for a wider application base beyond simple inner diameter measurements. The paper will present experimental results that are compared with standard gages to prove the performance and feasibility of the analysis in real world field engineering. Potential accuracy improvement methods, a new dual ring design and future work will be discussed at the end of this paper.
Service providers perform regular borescope inspection of field products to ensure system performance and prevent accidents. A full borescope inspection for large equipment usually takes several days to cover every region of interest in the turbine. One of the challenges that causes this long inspection time is the difficulty in navigating the borescope tip to some position of interest and aiming the view of the borescope in given direction. The image from the borescope tip is the only information available to the operator to judge the position of tip. In some cases, the operator can get lost due to the limited field-of-view and illumination provided by the borescope. It is very hard to tell the borescope tip position from one borescope image. This increases the difficulty of correlating the inspection results obtained at different times that might be used to predict potential machinery failure. This paper discusses various methods that have been investigated for 3D borescope tracking and presents a new approach using a shape sensor integrated in the borescope tube used with image based location determination to determine the position of the borescope tip during inspections. The shape sensor provides a real time estimate of the borescope tip position and orientation then the image based analysis uses the part CAD model to fine tune this position information. The tracking result can provide better information of the tip position for the operator. This enhanced position information can be used to better monitor defect changes over time by comparing the inspection result at different times in the parts lifetime.
Video borescopes are widely used for turbine and aviation engine inspection to guarantee the health of blades and
prevent blade failure during running. When the moving components of a turbine engine are inspected with a video
borescope, the operator must view every blade in a given stage. The blade counting tool is video interpretation software
that runs simultaneously in the background during inspection. It identifies moving turbine blades in a video stream,
tracks and counts the blades as they move across the screen. This approach includes blade detection to identify blades in
different inspection scenarios and blade tracking to perceive blade movement even in hand-turning engine inspections.
The software is able to label each blade by comparing counting results to a known blade count for the engine type and
stage. On-screen indications show the borescope user labels for each blade and how many blades have been viewed as
the turbine is rotated.
Optical coherence tomography (OCT), as an interferometric method, has been studied as a distance ranger. As a
technology capable of producing high-resolution, depth-resolved images of biological tissue, OCT had been widely used for the application of ophthalmology and has been commercialized in the market today. Enlightened by the emerging research interest in biomedical domain, the applications of OCT in industrial inspection were rejuvenated by a few groups to explore its potential for characterizing new materials, imaging or inspecting industrial parts as a service solution[3]. Benefiting from novel photonics components and devices, the industrial application of the older concepts in OCT can be re-visited with respect to the unique performance and availability. Commercial OCT developers such as Michelson Diagnostics (MDL; Orpington, U.K.) and Thorlabs (Newton, NJ) are actively exploring the application of OCT to industrial applications and they have outlined meaningful path toward the metrology application in emerging industry[3]. In this chapter, we will introduce the fundamental concepts of OCT and discuss its current and potential industrial applications.
Structured light based 3D measurement is a typical optic method used to detect surface profile. The primary system projects
a structured pattern onto the measured surface. Through the phase shifting analysis, the depth profile is extracted with a
high resolution. In this paper a portable device bases on structured light method is introduced. The tool is used to inspect
edge breaks and corrosion depth on the turbine system parts. In order to maintain the inspection accuracy under the portable
operation, a simple but reliable calibration process and enhancement algorithms are needed to mitigate the variations of
user operations and system noise. In this paper, an effective calibration method with simple process is introduced to
calculate the system parameters and minimize the measurement errors. A set of image enhancement algorithm designed
specially for the structured patterns are introduced that is able to mitigate the noise clearly but won't decrease the
measurement resolution. The results are demonstrated through the calibration of a prototype system. Measurement results
are presented for sample surface using the filtering. The results show that the calibration process and image enhancement
works effectively to maintain a good accuracy and data quality.
A method is proposed for surface defect analysis and evaluation. Good 3D point clouds can now be obtained through a variety of surface profiling methods such as stylus tracers, structured light, or interferometry. In order to inspect a surface for defects, first a reference surface that represents the surface without any defects needs to be identified. This reference surface can then be fit to the point cloud. The algorithm we present finds the least square solution for the overdetermined equation set to obtain the parameters of the reference surface mathematical description. The distance between each point within the point cloud and the reference surface is then calculated using to the derived reference surface equation. For analysis of the data, the user can preset a threshold distance value. If the calculated distance is bigger than the threshold value, the corresponding point is marked as a defect point. The software then generates a color-coded map of the measured surface. Defect points that are connected together are formed into a defect-clustering domain. Each defect-clustering domain is treated as one defect area. We then use a clustering domain searching algorithm to auto-search all the defect areas in the point cloud. The different critical parameters used for evaluating the defect status of a point cloud that can be calculated are described as: P-Depth,a peak depth of all defects; Defect Number, the number of surface defects; Defects/Area, the defect number in unit area; and Defect Coverage Ratio which is a ratio of the defect area to the region of interest.
Phase shift analysis sensors are popular in inspection and metrology applications. The sensor's captured image contains the region of interest of an object overlaid with projected fringes. These fringes bend according to the surface topography. 3D data is then calculated using phase shift analysis. The image profile perpendicular to the fringes is assumed to be sinusoidal. A particular version of phase shift analysis is the image spatial phase stepping approach that requires only a single image for analysis, but it is sensitive to noise. When noise, such as surface texture, appears in the image, the sinusoidal behavior is partially lost. This causes an inaccurate or noisy measurement. In this study, three digital de-noising filters are evaluated. The intent is to retrieve a smoother sine-like image profile while precisely retaining fringe boundary locations. Four different edge types are used as test objects. "Six Sigma" statistical analysis tools are used to implement screening, optimization, and validation. The most effective enhancement algorithms of the selection comprise (1) line shifting followed by horizontal Gabor filtration and vertical Gaussian filtering for chamfer edge measurement and (2) edge orientation detection followed by 2-D Gabor filter for round edges. These algorithms significantly improve the gauge repeatability.
In industry, there are needs to accurately measure the 3-D profile of edges parts in order to evaluate edge
condition. Optical methods are increasingly used for this purpose due to its advantages such as being non-contact,
fast, accurate, and easy to integrate with software for data acquisition and feature analysis. We
utilized structured line projection technology to measure edge's profile. In this method a structured light
distribution, created by the transmission of a sinusoidal grating, was projected onto the inspected parts at a
certain incidence angle. The projected light lines were deformed due to the depth change on the edge
surface. A CCD camera sitting at a different angle was used to record the deformed fringes. From the
deformed fringes the 3D surface profile was extracted based on triangulation principal. Because the
projected grating pattern can be interpreted as an interference pattern, we used the spatial carrier phase
shifting and phase unwrapping method as in classic interferometry to extract the phase information from
the intensity distribution of fringes. Due to the limited depth-of-range of the fringe image and depth-of-focus
of the imaging lens on the CCD camera, the observed deformed fringes have different widths and
frequencies at different depth. According to the definition of depth-of-focus, the fringe width out of focus
can be on the order of the square root of 2 wider than that which is in focus. The width change can also be
due to a tilt across the object. This width change affects the accuracy of the spatial carrier phase shifting
and subsequently the accuracy of extracted profile. In this paper, we proposed to monitor the change of the
fringe width with imaging depth. According to the width of the fringes, we defined a parameter called
compressing rate, to use in computing the edge profile. For different edge types, the compressing rate was
optimized in order to get the profile that can match the results from traditional the methods. By using this
method, the system repeatability can be improved significantly.
The measurements of refractive index and thickness of various transparent plates and films are very important for quality control. Additionally, the knowledge of refractive index, and thickness is significant in biomedicine for the treatment of many kinds of tumors. In this paper, we propose a new method for noninvasive and simultaneous measurement of refractive indices and physical thickness of specimens, which consist of surrounding and interior components with different refractive indices. In our experiment, we measure the refractive index and the physical thickness of a multimode fiber and a lotus root with a hollow hole, respectively. The experimental results verify the feasibility of this method.
An optical coherence tomography system capable of imaging subsurface objects in turbid media is described and the obtained cross-sectional image of a small region of lotus root by OCT is presented. The deconvolution algorithm with wiener filter was implemented to reconstruct this cross-sectional image. The imaging mechanism of OCT is investigated by Monte Carlo method.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.