Ernest A. Franke

Measurement of microdisplacements by machine vision photogrammetry (DISMAP)

An image processing system is described for use in micromechanics research on materials, such as for determining the displacements and strains surrounding crack tips. This vision system is a machine implementation of the stereoimaging technique that was developed for making submicron measurements of displacements under high resolution conditions. It uses a Cognex 2000 image processing system, cameras to obtain digital images from analog photographs, a graphics display terminal and track ball for operator interaction with the system, and a video display monitor for display of the measured displacements. Displacements are sent directly to an associated VAX that computes strains and permits their graphical display. The system is described in detail and examples of its use in micromechanics research are given.

Location of features of known height in the presence of reflective and refractive noise using a stereoscopic light-striping approach

A method for isolating three-dimensional features of known height in the presence of noisy data is presented. The approach is founded on observing the locations of a single light stripe in the image planes of two spatially separated cameras. Knowledge relating to the heights of sought features is used to define regions of interest in each image, which are searched to isolate the light stripe. This approach is advantageous because spurious features that may result from random reflections or refractions in the region of interest of one image usually do not appear in the corresponding region of interest of the other image. It is shown that such a system is capable of robustly locating features such as very thin vertical dividers even in the presence of spurious or noisy image data that would normally cause conventional single-camera light-striping systems to fail. The discussion that follows summarizes the advantages of the methodology in relation to conventional passive stereoscopic systems as well as light-striped triangulation systems. Results that characterize the approach in noisy images are also provided.

Reducing data distribution bottlenecks by employing data visualization filters

Between 1994 and 1997, researchers at Southwest Research Institute (SwRI) investigated methods for distributing parallel computation and data visualization under the support of an internally funded Research Initiative Program entitled the Advanced Visualization Technology Project (AVTP). A hierarchical data cache architecture was developed to provide a flexible interface between the modeling or simulation computational processes and data visualization programs. Compared to conventional post facto data visualization approaches, this data cache structure provides many advantages including simultaneous data access by multiple visualization clients, comparison of experimental and simulated data, and visual analysis of computer simulation as computation proceeds. However, since the data cache was resident on a single workstation, this approach did not address the issue of scalability of methods for avoiding the data storage bottleneck by distributing the data across multiple networked workstations. Scalability through distributed database approaches is being investigated as part of the Applied Visualization using Advanced Network Technology Infrastructure (AVANTI) project. This paper describes a methodology currently under development that is intended to avoid bottlenecks that typically arise as the result of data consumers (e.g. visualization applications) that must access and process large amounts of data that has been generated and resides on other hosts, and which must pass through a central data cache prior to being used by the data consumer.

3D precision surface measurement by dynamic structured light

This paper describes a 3-D imaging technique developed as an internal research project at Southwest Research Institute. The technique is based on an extension of structured light methods in which a projected pattern of parallel lines is rotated over the surface to be measured. A sequence of images is captured and the surface elevation at any location can then be determined from measurements of the temporal pattern, at any point, without considering any other points on the surface. The paper describes techniques for system calibration and surface measurement based on the method of projected quadric shells. Algorithms were developed for image and signal analysis and computer programs were written to calibrate the system and to calculate 3-D coordinates of points on a measured surface. A prototype of the Dynamic Structured Light (DSL) 3-D imaging system was assembled and typical parts were measured. The design procedure was verified and used to implement several different configurations with different measurement volumes and measurement accuracy. A small-parts measurement accuracy of 32 micrometers (.0012”) RMS was verified by measuring the surface of a precision-machined plane. Large aircraft control surfaces were measured with a prototype setup that provided .02” depth resolution over a 4’ by 8’ field of view. Measurement times are typically less than three minutes for 300,000 points. A patent application has been filed.

Bismap : A non-contact biaxial displacement measurement system

The development and validation of a prototype BISMAP (Biaxial Displacement Measurement by Machine Vision Processing) system is described. The non-contact biaxial displacement measurement system adapts machine vision technology to create a unique extensometer. The BISMAP system is built around a vision processing system that tracks and recognizes surface texture features around specific control points by using a normalized correlation technique. The system has numerous advantageous features including non-contact measurement in two-dimensions, variable gage length, direct surface measurement (no attached target) and real-time measurement of multiple, discrete points. The performance of the system is demonstrated with evaluations of the monotonic (and in some cases cyclic) stress-strain response for four different materials: aluminum, LEXAN, rubber and baboon tendon. The system has a measured accuracy of 370 μ∈ with ′50 μ∈ variability when compared to a strain gage. It is best-suited for measuring strains in excess of 5000 μ∈ and there is no practical upper limit on the measurable strain with retraining. The BISMAP system shows promise for development from prototype into a laboratory instrument capable of measuring strains in pliable or delicate materials.

Identification of flaws in metallic surfaces using specular and diffuse bispectral light sources

A computer vision based automated method for identifying and quantifying flaws in cast metal parts is presented. The specific defects to be isolated consist of small circular concavities in the surface (pits) and larger isolated regions (scratches) that may have been abraded due to cutting or handling operations. The approach taken identifies these anomalous features using two spatially separated light sources with different spectral characteristics to produce highly specular illumination at one wavelength and shallow diffuse illumination at a different wavelength. A bispectral image is processed to yield the sought flaws. This processing consists of identifying regions of interest in the original image that may contain potential flaws and applying a morphological region labelling operation to extract candidate pits and scratches. Geometric constraints are applied to the extracted regions in order to isolate the true flaws. The discussion that follows details the algorithmic approach used to identify flaws as well as characterizing the results obtained.

Novel Cam Mechanism for Core Sampling of Variable Density Materials

Project critical mission requirements often drive design decisions and processes. This was the case for National Aeronautics and Space Administration (NASA) funded DEep Phreatic THermal eXplorer (DepthX), an underwater robot designed to autonomously map, navigate, and acquire biological samples. Mission requirements led the authors to develop a novel core sampling mechanism for variable density materials. Preliminary testing was conducted on variable density materials simulating real world specimens to identify the series of motions to acquire an acceptable core and optimize the geometry of the coring tube. A geometric modeling approach with configuration functions was employed to design the overall mechanism and establish the cam profile. The design was tested and evaluated during multiple field expeditions to cenotes (sinkholes) in Mexico. The culmination of the preliminary testing and the selected design methodology resulted in a core sampling mechanism that is compact, has minimal operational torque requirements, and utilizes a single motor to complete a series of complex functions. Future applications are envisioned for space expeditions, underwater exploration, and medical sampling.© 2008 ASME

Machine vision applications of low-cost thermal infrared camera

Machine vision applications of thermal image sensors have been investigated under an Internal Research and Development Project at Southwest Research Institute. Initial investigations were conducted to determine response characteristics of a low-cost non-radiometric camera. Application investigations were conducted to develop defect detection capabilities for injection molded rubber parts. Various thermal excitation and material handling approaches were investigated. Image processing software was developed to detect anomalous temperature responses. Research findings, part inspection approaches, and image processing techniques are discussed.

Sensor-fusion-based approach for feature extraction in intelligent transportation system applications

The ability to extract useful and robust features from sensor data of vehicles in moving traffic is highly dependent on a number of factors. For imaging sensors that produce a two- dimensional representation of an observed scene such as a visible light camera, the principal factors influencing the quality of the acquired data include the ambient lighting and weather conditions as well the physical characteristics of the vehicles whose images are captured. Considerable variability in the ambient lighting conditions in combination with material characteristics may cause radically different appearances for various surfaces of a vehicle when viewed in the visible wavelengths. Infrared sensors, on the other hand, produce images that are far less sensitive to variations in ambient lighting conditions, but may not provide sufficient information that can be used to discriminate among vehicles. Combining information from these sensors provides the basis for exploiting the relative strengths of each sensor domain while attenuating the weaknesses that exist in single systems. This paper presents a basic framework for combining information from multiple sensor systems by describing methodologies for geometrically transforming between image spaces and extracting features using a multi-dimensional approach that exploits information gathered at different wavelengths. The potential use of point sensors (such as acoustic and microwave detectors) in combination with imaging sensors is also discussed.

Fiber optic sensor for characterization of surface coatings

A fiber optic sensor for determining the type and condition of aircraft coatings was originally developed to provide adaptive control of automated coating removal. The sensor, based on analysis of optical reflectance spectra, has also been found useful for determining the condition of other materials. Investigations have shown that artificial neural networks can be trained to recognize specific materials or material conditions from the sensor signals.