An introduction to the computer image processing and recognition techniques applied for accurately locating an object are presented in this paper. The accurate measurement of three dimensional position requires a camera calibration process as well as the determination of corresponding image points in two images. The accuracy of the three dimensional measurement depends upon the accuracy of the image matching solution. Since there are a variety of image matching techniques, the pattern recognition guidelines are reviewed which indicate that the optimum features are nonlinear, a posteriori probabilities of the measurements. These optimum features also maximize the trace of the between class scattermatrix normalized by the mixture scattermatrix. However, the theoretical guidelines do not indicate simple measurement methods for the optimum features. Therefore, some experimental examples are presented which illustrate some practical solutions to the problem.
In this paper a new digital interferometric output analyzer and display system (DIAD) is described. The functional characteristics of the DIAD measurement system is presented to illustrate the unique capabilities of the system. System performance characteristics are listed to provide an overview of the measurement capabilities of the system.
Colorimetry, as defined by the International Commission on Illumination, is the measurement of colors, made possible by the properties of the eye and based on a set of conventions. Instrumentation for measuring object color, therefore, must be based on a human observer. The intent is to design an instrument that in effect responds as a person would, so that research development, production control and quality control areas have some means of assessing the acceptability of the appearance of a product. Investigations of a human observer's psychological response to color, and the manner in which visual observations are made, give the instrument designer and manufacturer data necessary to answer two questions: a. How can we put numbers (instrument read-out) on a perception that occurs in the brain of the observer? b. What can we learn from examination of a visual observing situation that will guide us in our design of an instrumental simulation of this situation? Involving as it does our own daily, almost unconscious, practice of making judgments concerning the things we see, the design and manufacture of color measurement instruments is an exceedingly interesting field. The advances being made concurrently today in research concerning human color vision and in optical and electronic technology will make possible increasingly useful instrumentation for quality control of product color.
We present two approaches to rapid, single particle sizing for particles in the I to 20 μm diameter range. One method measures multiangle scattered light over a polar angular range of nearly 360 degrees. A second method is based on the analysis of the pulse shapes from small angle forward scattered light. In both cases the particles in liquid suspension are made to pass one at a time through a focused laser beam for analysis.
Direct-imaging and plane-projection instruments are mainstays for definitive calibration-quality measurements of small dimensions for industrial and clinical applications. Light-and electron-optical techniques span six orders of sizes, from millimeters through micrometers down to nanometers. A common assumption is that, above the resolution limit of a device, accurate measurements can be made based on the geometric optic relation of image size xi to object size xo: xi = Mx0, where M is the scalar magnification of the device. However, in measurements of lengths, widths or diameters, the relation fails long before the resolution limit of the device is approached. As a result, substantial systematic errors in dimensional measurements occur in industrial applications from particle sizing to photomask metrology. The causes of such difficulties and the techniques to overcome them are discussed in the context of work at the National Bureau of Standards (NBS) on the development of SEM and optical techniques for accurate measurements in the range 0.1 to 100 μm.
Some uses of photodiode detector arrays for on-line inferential measurement of process parameters are described in this paper. Optical considerations involving these arrays are discussed. High resolution camera lenses are not necessarily best in these applications since different lens design considerations apply when discrete arrays are used. Serious linearity and repeatability problems that were encountered with some commercially available solid state camera systems are discussed. The requirement of modest system cost, coupled with the need for high speed on line analysis, place stringent restrictions on the type and amount of computer analysis that can be carried out. A set of recognition algorithms which have worked well in the initial applications are described. Some of the remaining problems, and possible approaches to them, are presented.
A major emphasis is being placed on visual task automation in the aerospace industry. Computers and real-time hardware are performing image processing functions such as radiograph enhancement, non-contact mensuration and robotic vision. This paper discusses some of these visual task problems which exist in the manufacturing of aircraft and the types of image processing which can and are being applied to these problems.
Results of a program to experimentally evaluate existing techniques and develop new high-speed techniques for evaluation of optical distortion in aircraft windscreens are described. Present techniques for evaluation of aircraft windscreens' optical quality are based on grid board photography and point-by-point measurement of optical deviation errors. Experimental evaluation of the grid board techniques have shown them to be simple and easy to perform, but errors as large as 20 percent occur because of the associated data reduction. The approaches to point-by-point measurement of windscreen deviation errors provide high accuracy, but the time required to evaluate a single windscreen is typically 8 to 24 hours. New techniques were studied, developed, and evaluated in order to permit real-time evaluation of aircraft windscreens. Two approaches described will provide the capability for high speed evaluation of windscreen optical distortion. These techniques utilize raster scanned laser probe beams in conjunction with retro-reflecting screens and holographic lenses. In addition to high-speed scanning techniques, a speckle photographic technique is described that can be used to evaluate binocular disparity in a transparent aircraft windscreen.
Many aspherics can be tested using straightforward and simple methods that yield non-complex fringe patterns. The methods described are essentially null tests similar to those utilized for measuring large mirrors for astronomical work. The potential for such a test to exist for a given aspheric should always be explored prior to using more complicated and more costly techniques. This paper describes some of the analytical methods that are used to tackle the problem of determining which test may be used as well as the limitations of this approach. Experimental results are also presented.
For generations optical technicians have judged the accuracy of an optical surface by estimating the straightness of the fringes in an interference pattern. The eye, however, is not capable of estimating fringe straightness accurately enough to satisfy present-day demands for twentieth-wave or hundredth-wave accuracy. More rigorous quantitative methods must be used to attain the desired precision. Digital analysis of photographs is a help but the data obtained from photographs are noisy and such a method is greatly influenced by distortion in the imaging system and the problems associated with the necessity of providing many closely spaced fringes for analysis.
An optical method for measuring the percent of open area of perforated sheet materials is presented. The technique, which is based on Fourier optics, uses a detector to measure a small central portion of the light in the Fraunhofer diffraction pattern of-the perforated sheet. This approach offers accuracy and speed while avoiding diffraction problems associated with arrays of small holes. In addition it can be used with translucent materials. A brief theoretical analysis is presented as well as results obtained with a laboratory system. The system is being developed to inspect perforated materials fabricated for use on noise suppression systems for aircraft engines, however, it should be useful in the general noncontact determination of the open area of perforated materials.
We, at General Dynamics, are convinced that close-range industrial photogrammetry will play an increasingly important role as a basic metrology tool in support of airframe design, manufacture and quality control. A breakthrough in the use of software enabled us to gain initial success in the application of photogrammetry in the area of wind tunnel testing, then move to full-scale aircraft inspection and aircraft structural calibration. These successful applications have led to implementation of photogrammetry as the preferred method of periodic inspection on numerous planar type assembly tools. We are currently extending this technology to the more geometrically complex tools under an Air Force Material Laboratory Contract. In the future, we hope to go into such areas as aircraft control surface position, stereo-photogrammetry to eliminate the use of targets on locators, detail parts inspection, and structural testing, including proof load and deflection data, airworthiness of aircraft and service life.
Precise guidance of high energy laser beams is important in industrial laser machining to optimize the use of the available power and to assure high quality work. A crossed beam depth gauge has been designed that measures the distance to the workpiece surface with an accuracy of one part in two thousand over a range of 10 cm. The television camera based system is described along with an analysis of its performance.
The Inspectron is an instrument which will perform an automatic optical inspection of the etched circuitry on the individual layers of a multilayer printed circuit board. The concept of this instrument is unique in that it does not compare the PCB under test with a master or with computer-stored data. Instead, as the board is optically scanned, a small area is re-imaged onto a detector array. The detector signals, after digitization, are fed into high-speed logic circuitry which is programmed to distinguish between the appearance of a good board and an error. An 8 x 10 inch board can be inspected for line width, line spacing, line breaks, excess copper, and voids in about a minute. The Inspectron can also inspect pads for completeness and ground planes for shorts.
The need for fast, objective, and accurate measurement of several aspects of photomasks is clear. Photomask technology, on a production basis, is rapidly approaching the 1 pm geometries. In doing so, current automated inspection equipment becomes of limited usefulness. The following is a discussion of measurements made using a microdensitometer. These measurements are intended to show that the basis for an instrument that is capable of increasing high resolution measurements does exist.
Recent improvements to the Aerodyne Linear Microdensitometer have enabled the attainment of ensurational accuracies of 0.025-microns. This accuracy, coupled with optical resolution capabilities of 0.5 to 1.0-microns, permits computerized photomask inspection that allows submicron defect detection with outstanding mensurational accuracy. For photomask line widths on the order of 1-micron, mensurational accuracies of better than 5% of the line width are thus achieved.
A system was developed as part of a MICOM Manufacturing Methods and Technology (MM&T) contract to demonstrate the applicability of thermal scanning to testing electronic circuit boards and hybrid circuits on the production line. This paper presents a description of the test equipment outlining its hardware, software, test methodology, applications, capabilities, and limitations, and gives a summary of test results. A short discussion of the probable future of thermal scanning as an electronics test method for printed circuit boards and hybrids is also included.
We have shown that an electro-optical system can be used for automatic quality control inspection of thick-film hybrid circuits. This work was supported by the U.S. Army Electronics R&D Command under Contract No. DAAB07-77-C-0585 entitled "Automatic In-Process Microcircuit Evaluation." A high resolution (10,000 TVL/H) Return Beam Viaicon (RBV) is used to image an entire 2-inch by 2-inch substrate. The RBV is operated witn computer controlled electronic steering and zoom to provide an appropriate level of detail for rapid sequential frame inspection. Video from each frame is compared with that trom a referenced image stored on a video disc. Differences are displayed on a color TV monitor and processed by the computer to identify and characterize faults. Various manual ana automatic inspection sequences can be programmed readily. This technique can inspect hybrid substrates at rates of 750 per hour, and its efficiency makes 100% inspection an economical method for quality control at high through-put rates. This paper describes tree hardware instrumentation and reports functional inspection results achievea using sample hybrid circuits with built-in flaws.
In the manufacturing of printed circuit boards, microscopic analysis is an essential process control activity. An inspector microscopically analyzes board samples to deter-mine board lot quality and process conditions. Prior to computerizing, this sustained measurement-taking involved the tedious process of recording raw data, converting microscope filar readings, calculating averages, logging information in a job notebook, and completing detailed final lab reports. It is evident from this brief task description that this time-consuming repetitious data recording routine was an added burden to the already fatiguing visual inspection method and therefore was a prime candidate for automatic data capture and printout. Secondly, the creation of a permanent and easily accessible data base would improve process feedback and provide for a system with quick identification of any suspect boards if further assembly/testing exhibited board-related failures. This paper describes the evolution and implementation of a computer-aided microscopic inspection operation.
Considerable activities have been centered around the automation of manufacturing quality control and inspection functions. Several reasons can be cited for this development. The continuous pressure of direct and indirect labor cost increase is only one of the obvious motivations. With the drive for electronics miniaturization come more and more complex processes where control parameters are critical and the yield is highly susceptible to inadequate process monitor and inspection. With multi-step, multi-layer process for substrate fabrication, process defects that are not detected and corrected at certain critical points may render the entire subassembly useless. As a process becomes more complex, the time required to test the product increases significantly in the total build cycle. The urgency to reduce test time brings more pressure to improve in-process control and inspection. The advances and improvements of components, assemblies and systems such as micro-processors, micro-computers, programmable controllers, and other intelligent devices, have made the automation of quality control much more cost effective and justifiable.
This paper presents an overview of industrial robots, for those who work outside of robotics but are interested in robots and how they are used by industry. Areas to be discussed are: Basic robotics, definitinon of robot, composition of robots, types of robots; Current application of typical uses of each type of robot; Advanced robotics, systems, controls, vision, and future developments.
Nondestructive examination (NDE) can be defined as a technique or collection of tech-niques that permits one to determine some property of a material or object without damaging the object. There are a large number of such techniques and most of them use visual imaging in one form or another. They vary from holographic interferometry where displacements under stress are measured to the visual inspection of an objects surface to detect cracks after penetrant has been applied. The use of image processing techniques on the images produced NDE is relatively new and can be divided into three general categories.
An automatic inspector and product data system was developed by Du Pont specifically for the needs of nonwoven fabrics. The system detects defects, classifies them into five categories at high web speeds, and generates roll logs and 24-hour production summaries to assist in production record keeping and improved product flow through the finishing area. Techniques based on multiple feature-extraction and pattern-classification theory permit detection and classification of defects in the presence of product noise.
Optical gaging has evolved to a level where it can be applied in direct line with the production sequence. On-line, non-contact inspection of precision parts is now a factual occurrence and the concept is spreading. This paper discusses the optical system and discloses an actual application.