A method is described for performing non-contact optical gaging of complex parts in a production environment. The operational concept of the system, known as Gaging by Remote Image Tracking, relies upon an optical triangulation technique. A spot of light is projected from a gage head onto the surface of the part being gaged., an image of this spot is focused on the center of a tracking photodetector, mounted within the gage head. If the part is translated in a direction perpendicular to the projection axis, the focus spot on the surface of the photodetector will move as the surface curvature of the part changes. As a result of this movement, voltage signals are generated which provide: 1) a measure of the spot displacement on the photo-detector, and 2) a signal for driving the optical head in a direction which recenters the image spot on the photodetector. The first signal, with appropriate scaling, provides virtually an instantaneous measure of the dimensional change of the part. The second signal is used to drive the system to a known distance from the part (system null). By monitoring the motion of the entire system with a linear encoder and adding this measurement to the instantaneous measure of surface curvature, the result is a fast, non-contact optical gaging system with large dynamic range.

A noncontacting optical transducer, which measures the profile of machined surfaces, was constructed and tested. The profile transducer consists of a microscope objective, a point-source illuminator and two photo-detectors. The dynamic range of the instrument is typically 500 microinches with an accuracy of better than 10 microinches. The output of this transducer is a profile signal along a line on the surface under examination. The profile of a machined surface obtained by the optical-transducer correlates very well with that obtained by a mechanical Proficorder® which uses a diamond stylus. Principles of operation, results of various performance tests and potential applications of the optical-transducer are discussed.

In-process noncontact dimensional measurement and control systems incorporating laser sensors and microprocessor-based electronics provide higher levels of performance than heretofore possible using more conventional techniques. Because of their rugged construction, these systems can make measurements on the process line as well as have a substantial impact on process yields and scrap reduction. Many such systems have been produced and applied. This paper reviews the significant technical features and their impact on the production process. Several interesting applications are discussed.

A method for measuring the surface profile of a reflecting surface is presented. The technique involves comparing, in the time domain, a surface reflected laser beam to a reference beam. The comparison is made by alternately scanning both beams across an optical detector and measuring their phase relationship electronically. From this information and by scanning along a line, the surface profile in a plane can be determined. The accuracy of the method falls between mechanical contact techniques and more sophisticated interferometric schemes. Precision of microns with dynamic range of millimeters or more can be achieved. A brief theoretical analysis is presented as well as the result of several experimental tests. This method can be useful in such applications as measuring the profile of the human cornea and other delicate materials where non-contact is obligatory and in determining the surface contour of optical components or of any other reflecting surface. Precise monitoring of angular deflection is also possible with this technique.

Microdensitometers have already solved the problem of maintaining high spped and high accuracy across large regions of space. Modifications are needed to operate with much higher speed and in the reflection mode. Experimental results confirm accuracies better than 0.1 gm over areas over 40 cm.

The characteristics of reflectance patterns generated when a laser beam strikes a machined surface contain adequate information to determine the degree of surface finish. An 'extensive development endeavor has established equipment and procedures required to properly extract data from reflectance patterns to obtain a repeatable correlation between the gleaned information and surface finish. Two types of reflective patterns have been utilized: diffracted reflection from single-point-turned periodic surfaces, and diffuse reflection from random-ground or honed surfaces. Surface finishes ranging from 0.025 to 2 micrometers (1 to 80 microinches), AA, have been measured by using visible laser radiation on the finer surfaces and infrared lasers on rougher materials. Using this method to measure a surface finish provides a noncontact procedure and does not require critical alignment as is often the case when using a stylus instrument on curved surfaces. Data have been obtained by making full-pattern scans, then integrating the area under the curves and by measuring the intensity ratio at two predetermined points. Calibration curves rtave lbeen developed that produce straight lines on log-log graph paper. Also, production inspection equipment has been fabricated to measure the surface finish of parts by the ratio method.

A system was fabricated to demonstrate the utility of non-contact electro-optical switching to the testing of electronic circuit boards at the component level. This paper summarizes the results of tests on inventory avionics circuit boards and reviews the under-lying concepts for the new non-contact probing technique.

The fundamental measurement required for proof of quality of an optical system is the shape of its transmitted wavefront. A knowledge of wavefront error and the transmission characteristics of an optical system allow calculation (at the measurement wavelength) of all commonly used quality factors such as optical transfer function, point spread function, Strehl ratio, etc. This paper describes a recently developed shearing interferometer that is designed for general purpose laboratory use. Included is a description of the instrument characteristics and principle of operation as well as a comparison of measured and theoretical accuracy limits.

A step-by-step process for aligning an unequal path interferometer is given. The interferometer as an optical test tool is discussed as are configurations for evaluating a variety of optical components and systems.

At times the fabrication errors in test optics approach the magnitude of the desired residual errors in a finished optic. We discuss the problem of removing the rotationally asymmetric test optics errors from a composite wavefront of test optics errors and residual finished optics errors.

A versatile interferometer has been designed and built to evaluate infrared windows as large as 51 cm in diameter. Transmitted wavefront measurements may be made with an accuracy of 0.05λ peak-to-valley at 10.6 µm. Variations in refractive index of transmitting materials as small as 5 x 10-6 may be measured and mapped. Through the use of an auxiliary mirror, systems or components requiring a spherical wavefront at f/6 or slower may also be tested.

Utilizing the concept of Ronchi interferometry, a simple and inexpensive surface testing technique is described which allows the testing of large flat first surface optical mirrors. The system sensitivity is variable and responsive to a number of imaging defects introduced by imperfect mirrors. While easiest to use in a qualitative or semi-quantitative mode based on empirical measurements, the testing technique can be quantified to any required degree. When used qualitatively, the system functions best in a large volume testing environment as a screening comparator.

This is a tutorial paper showing how to use drafting equipment and a calculator to calculate the geometrical image of a point source and the profile plot along any part of the interferogram. Slope errors of geometrical rays are calculated by measuring the separation and angle of the fringes at each selected point on the interferogram. These angular errors are then plotted on a sheet of graph paper to represent the angular size of the geometrical point spread function. By integrating the angular errors multiplied by the distance be-tween points, a plot of the surface profile can easily be found.

Fourier Transform Spectrometers provide variable resolution spectra, rapid measurements and flexibility in data display. However, their high photometric accuracy can be destroyed by sampling requirements. Geometrical and index of refraction considerations must be taken into account to extract the inherent precision of the instrument.

The application of electro-optics to industrial metrology is discussed. Principles of operation and methods of implementation are illustrated by a detailed examination of two simple microprocessor-based gaging systems. One system measures the location an11 diameter of each of three fuel ports inside the bore of a diesel fuel injector barrel. The machine can handle any one of four different part numbers with an inspection cycle time of five seconds. The second system inspects and sorts precision springs. Features measured by the machine include spring rate, free length, and end squareness. The machine accommodates over 80 different springs and maintains a gross throughput of 1,000 pieces per hour.

A rapid and convenient method has been developed which uses electro-optical computer-based technology to capture the three-dimensional surface data of an object and to replicate the object from the data. In addition, the data may be used for automated mensuration or inspection. Conceived by Solid Photography, Inc. (SPI) it was developed initially for use in replicating portrait sculptures as well as for use in copying and scaling a variety of objects. The method, which uses patterns of white light projected onto the surface of an object, provides a quick and accurate means of recording the three-dimensional surface information in coded form either on film or by a "real time" TV camera.

This paper examines the use of speciallized silicon detectors in position and angle measurement systems. The operational characteristics of segmented position sensors are compared with those of lateral cell position sensors. Segmented position sensors of the quadrant and bi-cell variety exhibit the greater position sensitivity and resolution but have dynamic operating ranges which are limited to the dimensions of the optical image focused onto the detector. Segmented cells require uniform illumination intensity in the spot to achieve good linearity. They can operate at bandwidths of well over 100 megahertz as may be required in pulsed and high-speed tracking applications. Lateral cells are available in single and dual axis con-figurations. Their dynamic operating range is independent of spot size (excluding edge obscuration effects). Linearity and absolute measurement accuracy is also independent of spot size and uniformity characteristics to first order. Other advantages include excellent linearity, large operating range, and electronically adjustable null. Angle, x-y displacement and z-axis measuring schemes are discussed and two in-process measuring systems using lateral cells are described: an electronic auto-collimator for measuring tappet bore angles and an automatic "seam tracker" used to guide a TIG welding head.

Photo-optic measuring systems are presently utilized for automatic and continuous measurements of manufactured parts and subassemblies. Measurable parameters are physical dimensions such as bore diameters; flatness and concentricities; surface perturbations, such as microfinish, seams, pits and scratches; and finally, mechanical defects, such as cracks, mislocations, or unusual gaps in assemblies. The basic unit of these systems is the bifurcated fiber-optic probe which scans the surface of the object in question. The probe assembly utilizes reflected light from the object returning via the fiber optics to the detector for generation of the information signal. The information signal is processed electronically to yield the required values. The measurement is accomplished then in milliseconds instead of seconds.

This paper reviews a family of moire methods that are capable of generating contour fringes of in-plane displacement, out-of-plane deflection, slope, and curvature of displaced or deformed structures. The methods are real time techniques that can be applied to static and dynamic problems.

A quick review of the imaging problems encountered with rotating prism camera systems will be presented. The system performance of a diffraction limited objective when added to a rotating prism camera will be shown. The design considerations of a photographic objective designed specifically for use with rotating prisms will be briefly discussed. The methods of testing a lens and the rotating prism will be presented. Interference tests wilt be shown for a new rotating prism camera lens as will similar tests on a standard photographic objective when used on the rotating prism camera.

Using a heterodyne interferometer of unique design, high precision measurements of optical surfaces while undergoing deformation have been obtained. The device is described and results of various investigations are presented.

The interferometer described in this article combines a number of principles known for a long time in a system of unusual versatility. The operation modes range from classical interferometry for visual or photographic evaluation of apertures up to 150 mm diameter, to programmed scan heterodyne interferometry with fringe counting and to time and space resolved subfringe measurement with better than 10 nm resolution.

A prototype optical system is described incorporating a scanning lateral shearing interferometer, self-scanned photodiode array, electronic bandpass filter, a counter and a microprocessor for the rapid automatic testing of large area transparencies such as air-craft windscreens. Optical anomalies as small as 0.005 diopters and ranging to ± 0.2 diopters can be readily measured. The system also automatically compensates for beam deviation and displacement during the scanning process with an adaptive gimbaled mirror which provides a measure of prismatic deviation to an accuracy of about ± 0.02 degrees.

An automatic interference pattern processor has been developed for the purpose of rapidly and accurately evaluating either real time interference patterns or interferograms. The system has been designed to provide quick and easily interpretable feedback so that the operator can monitor the system's measurements. The system includes: (1) a semiautomatic mode to facilitate the measurement of difficult interference patterns and (2) an integral, easily used calibration mode. The results of the least squares evaluation are available in a variety of formats.

A vacuum rated Coaxial Reference Interferometer (CORI) has been designed that satisfies the data input requirements of Computer Controlled Polishing (CCP) methods. The instrument obtains wavefront data at very high sampling intervals (50 to 100 fringes per aperture) and maintains precise mirror to focal plane mapping fidelity. Realistic as manufactured design goals are a 0.010% rms wavefront quality at f/2.3 and the ability to locate positions on a 2.4 meter diameter mirror to within 0.6mm from interferogram coordinates. Internal calibration means have been provided to independently verify interferometer performance as required. The instrument can be used to test both uncoated and coated mirrors. Interferograms are recorded on 70-mm film but may be monitored visually or by means of a vidicon.