The measurement of aircraft jet engine turbine and compressor blades requires a high degree of accuracy. This paper will address the development and performance attributes of a noncontact electro-optical gaging system specifically designed to meet the airfoil dimensional measurement requirements inherent in turbine and compressor blade manufacture and repair. The system described consists of the following key components: a high accuracy, dual channel, laser based optical sensor, a four degree of freedom mechanical manipulator system and a computer based operator interface. Measurement modes of the system include point by point data gathering at rates up to 3 points per second and an 'on-the-fly' mode where points can be gathered at data rates up to 20 points per second at surface scanning speeds of up to 1 inch per second. Overall system accuracy is +/- 0.0005 inches in a configuration that is useable in the blade manufacturing area. The systems ability to input design data from CAD data bases and output measurement data in a CAD compatible data format is discussed.
The field of noncontact metrology is maturing as the video camera based and the laser probe based measurements are finding wide acceptance in the fields of semiconductor, micro electronics, disk drive, biomedical, chemical and aerospace industries. Some manufactures of conventional touch-probe based CMMs (Coordinated Measuring Machines) have started integrating video cameras and laser probes to compliment the measurements made by the touch-probe. The delicate nature of the parts and the extremely small feature sizes have fuelled the growing need for the multisensor technology to be incorporated into a single coordinate measuring machine. The laser probes compliment the video based metrology systems in providing the dynamic Z-height capabilities due to their faster data rate and increased resolution and accuracy. This paper highlights the pros and cons of different diode laser based sensors, drawn from the experience of applying them for measurements in different fields.
Built-in calibration of a range sensor may leave scaling and shifting errors in the scanner readings. A semiautomatic additional calibration procedure for a single-scanline range sensor is described. In the proposed procedure, a reference object located in the origin of the world coordinate system is utilized. A 3 X 3 mapping transformation matrix is used as a post-processor to correct scanner readings.
Usual commercial laser triangulation range sensor offers a noncontact means of measuring part dimensions for use with CMMs. However, there are several factors such as surface inclination and reflection variation which must be taken into account if accurate and reliable results are to be achieved. In this paper a precision laser triangulation range sensor with double detectors is proposed. The sensor can continuously and simultaneously detect the range of displacement and the surface inclination as well as generate a tracing signal to trace the surface normal. Using the summing signal processing method, the measurement error caused by surface inclination can be partly compensated. In this paper the derivation of the relation between the displacement of the surface and the centroid shift on the detector is presented. The computer simulation and experimental results show that the proposed sensor is able to provide the means with noncontact, high speed, high accuracy for profile measurement, even though for sculptured surface measurement on CMMs.
This paper described the experimental use of a new type of optical sensor to detect rolling element bearing defects for the purpose of condition monitoring. The incremental motion encoder (IME) is a patented development of the industrially proven technology of the optical shaft encoder. It combines the measurement of angular position with that of 2D shaft center position to submicron accuracy. The operational principle of the IME is explained. Its high resolution measurements allow shaft motion directly related to the condition of the supporting bearing to be sensed. This presents potential advantages over current bearing condition monitoring sensors which monitor transmitted vibration in the machine structure. A model explaining the effect of a bearing condition monitoring sensors which monitor transmitted vibration in the machine structure. A model explaining the effect of a bearing inner race defect on the IME signal is presented. Based on this model the statistical parameter kurtosis is proposed as a method of detecting such defects from the IME signal. The results of experiments comparing the IME signal from a new undamaged roller bearing with the signal from the same bearing with an induced defect are presented. These confirm the application of the model to defect detection.
Semiconductor position sensitive devices (PSD) enable to measure the position of a light spot using simple construction. A circular PSD, which has a circular photosensitive region, can be used for angular measurement. This paper presents a new type of circular PSD called Multi Electrode Circular PSD (ME-CPSD) and demonstrates its application for angular measurement. This device, constructed on Si substrate, has a photosensitive region, a resistor line and 16 output electrodes. The photosensitive region has the shape of a ring which is formed by a radial arrangement of long and narrow photodiodes. The outer end of the photodiodes are connected to the continuous resistor line. Photoexcited carriers which are generated in the photodiode by the incident light flow to the resistor line and are extracted by the multioutput electrode which divides the resistor into 16 equal parts. To measure the position of the light spot, a pair of electrodes is selected by switches connected to every electrode and the position of the light spot is calculated from the output current of the selected electrodes. Compared to conventional circular PSDs, the reliability of the angular measurement is improved, because the ME-CPSD does not have an undetectable region caused by the unavoidable discontinuity in the structure of conventional circular PSDs. This device can change its measuring range by selecting the pair of electrodes, making it not only capable of measuring any absolute angular position, but allows also a more precise angular measurement by selecting narrower electrode intervals. This device has the capability to realize a high precision noncontact angular measurement system with simple construction.
This paper will present the current status of the fiber optic gyroscope (FOG), a ring interferometric rotation sensor for commercial applications by industries and consumers. An open-loop FOG with all polarization-maintaining fiber components is being used in these applications. One primary application is in vehicle navigation systems for automobiles, and a mass-produced has already been installed in luxury automobiles in Japan. Another application is in sweeper robots, Other applications such as a route-measuring system for boreholes, an attitude-controlling system for industrial helicopters, and an optocompass or north-seeking instrument will also be described. These FOGs are compact and reliable and need only a +12 V or a +24 V DC power source. This bias error is determined by the electrical system rather than the optical system and varies between 0.01 and 36 deg/h depending on the design of the signal-processing unit. The scale factor error varies between 0.1% and 1% also depending on the design, however, it is stable over the temperature range from -30 to 85 degree(s)C.
With the increasing use of advanced materials in the aerospace, automotive, and medical industries, improved nondestructive evaluation techniques are needed to meet industry requirements for quality and product reliability. Both shearography and infrared thermography are noncontact, single-sided inspection techniques that can provide quantitative information about a material's characteristics by means of passive or active excitation techniques. An experiment was conducted using a focal plane array infrared camera and a traditional Michelson's shearing interferometric system. In this paper, the results of the experiment are discussed, and the advantages of using both shearography and thermography simultaneously for materials evaluation and nondestructive testing are presented.
The flight hardware in use for the Space Shuttle program is one of a kind equipment and therefore very costly. With safety as the number one concern, and quality following a close second, new and better ways to do nondestructive testing on flight hardware are always being sought. Research on laser shearography turned up a promising test method, and equipment was purchased. During the summer of 1994, the equipment was evaluated for use on various components and the equipment itself was checked out for reliability and ease of use. Work to date has shown that the equipment is difficult to use, but the staff feels that once the training hurdle is done, the equipment has great potential. A few of the areas where the equipment could be used are the external tank, the solid rocket boosters, and structural components of the orbiter itself. The primary goal is to use the equipment to test for debonds, and the secondary goal is to see if the equipment can detect corrosion.
The development of a holographic image processing computer has resulted in an exceptional quality display of both time average and real-time holographic interference patterns. The same processor, however, can be used for shearography, speckle correlation interferometry, and moire interferometry. This paper describes the various modules that have been developed for converting the standard electronic holography optical head into any of the other three modes of operation. The advantages of using a holographic image processing computer for these alternate forms of interferometry will be outlined.
We propose a new technique of AHI which combines the high speed operation advantages of dynamic holographic interferometry and a real- time, high resolution, high stability, Denisyuk's holograms. Based on a new high sensitive phototerfractive reversible crystals group 23 doped (P and Cu) a small power CW laser was used for continuously hologram read and read-out processing. Portable wariant of a small size AHI sensor and practical demonstration of this technique are described.
The purpose of this paper is to present an analysis of the interference of light scattered from different planes in a simple interferometer, in order to establish techniques for final output fringe contrast enhancement and spatial noise removal, which are simple to implement. The approach developed here involves modifying the spatial coherence of the illuminating wave. By controlling the correlation length of this wave, a time averaged interferogram along with another for which a (pi) phase shift has been introduced into the reference arm, provides the necessary information to retrieve the fringe pattern of interest without noise. The approach suggested allows the controlling parameters to be easily varied optically in order to deal with different spatial noise types and scales. The benefits of this method are to the case for which the long range and slowly varying surface or index profile under test, is to be accurately measured. Simulations are presented and an evaluation of the effectiveness of the proposed coherence degradation procedures is given.
When a low coherence light source is used in a multimode fiber linked interferometer, the level of the modal noise induced by the environmental perturbations on the fibers may be dramatically suppressed, provide the value of the coherence length, Lc, of the light source employed is less than that of the optical path differences (OPD) between the guided modes at the far end of the fiber. In this work, the results of an experimental study on the relationship between the modal noise and the length and diameter of fiber, and the coherence length of the source used are presented, illustrating the major considerations for the use of multimode fiber in a white light interferometer.
Absolute interferometry is based on the use of an optical synthetic wavelength generated by two beating lasers. To obtain high-resolution, absolute measurements over a wide range it is necessary to use multiple synthetic wavelengths. A tunable synthetic wavelength generator would be the ideal solution for this purpose. In this paper, two configurations based on the use of two diode lasers and two diode-pumped Nd:YAG lasers are discussed. The paper presents the optical set-up for the generation of the synthetic wavelength, the necessary frequency-locking electronics, and experimental results from two prototypes.
Although noncontacting instruments for the measurement of the 3D microtopography of surfaces are now widely available and are used on a routine basis in many branches of science and engineering, information on many aspects of their use, from measurement through characterization to interpretation, is still limited. One important area in which clear information is required is calibration. This paper sets out to breach some of the gap by proposing routines for the complete calibration of optical probe based instruments for the measurement of surface microtopography. It is suggested that contacting and noncontacting instruments can be calibrated in a very similar manner, but that a few subtle but relevant differences need to be borne in mind and the calibration routine modified accordingly. The calibration of stylus instruments using a calibrated sphere as practiced by some instrument manufacturers (and as is common practice with coordinate measurement machines - CMM) has been advocated with the observation that this technique might be of even greater relevance in optical probe based systems. A new technique based on optical sensors is also proposed for the calibration of the diameter of the optical probe.
In this paper, an optical stylus displacement sensing principle has been studied, which serving a composite holographic optical element as an off-focus detection element. The mathematical models of optical measuring system have been established by means of Operator Algebra. The analysis results show that: the displacement of the tested surface is proportional to the image spot size on the detector. The sensibility of the sensor is obviously affected by the ratio of the equivalent focus length of the holographic optical element to the focus length of the objective lenses. To improve the measuring resolution and S/N ratio, so called off-plane detection method has been adopted. With which the output of the measuring results have a better linearity with the displacement of the tested surface. No less than 0.01 micrometers high resolution with linear measuring range of 5 micrometers have been obtained. Some measuring experiments are given.
The present paper describes novel technique of optical fiber sensing on the basis of Mach-Zehnder interferometer. Proposed technique was realized in the sound pressure sensor. It has been demonstrated experimentally that the sensitivity of the developed sensor is equal to 12 Pa per 1 m length of w-lightguide in the measuring channel.
This paper describes a system for directly measuring and imaging fluorescent lifetimes of materials. The system has been prototyped and will be used to improve the detection and discrimination capabilities of our existing scanning systems. The fluorescence lifetimes are determined from the phase difference between a temporally modulated laser excitation source and the resulting fluorescence. Imaging is accomplished by scanning the laser spot across the sample.
This paper presents a new industrial sensor for measuring diameters of extreme thin objects. The system is divided in two parts. The first is the emitter and the second the receiver. It is possible to use this system for the automatic inspection of files and wires in the textile industries and wire works. Another application for the sensor is the control of production of chemical files in an extruder. Furthermore we can measure more than one object in the lightbeam because we get information not only about the dimensions also about the position of the objects in the beam. The innovation in this system is the using of a light emitting diode (LED) as emitter and the realization of a long distance of about two or more meters between the two sensorheads. The results of this development are a special kind of optical layout in the emitter to reduce the loss of intensity and minimize the divergence of the lightbeam. It is not necessary to develop an intensity distribution, which is equal over the complete width of the sensorhead. We can show that we have a better dynamic in the system with this feature. The experiments prove that we get the same resolution as a laserbeamsensor. Furthermore one advantage is the eye-safety.
An optical fractal image analysis system is being developed to permit the analysis of image texture in real time. This system could find application in real-time monitoring and control for high value processing, such as in the chemical process industry and medical laboratories, or where a quantitative measure of image texture is useful. This paper expands on previous presentations by discussing issues of optical versus digital implementation, the alternative interpretations of grayness, and the advantages of neural networks for the final analysis.
The regular particle counter presently works at string model. A new laser scattering particle counter which is working at concurrent model has been developed in China. Its counting principle and structure will be introduced in this paper. Its resulting measurement agrees with the Hica/Royce counter in experiment. CPC is suitable to the liquid which has higher particle density.
The design of an intelligent optical instrument for surface roughness measurement is given in this paper. The approach is obtainment of a profile image by light-sectioning method, digitization of the profile image with a camera and an image sampling board, and calculation of roughness parameters with a computer. Principles of measurement range design, camera choosing, thresholding, hardware design and software design etc. are discussed and calibration methods are analyzed. Based on these principles, a commercial optical instrument has been developed whose measurement height is in the range of 0.4 to 120 micrometers . Appearance of the instrument and measuring results are also provided in this paper.
The paper describes the present design of contact profile meters for evaluating of topography-roughness of machine part surfaces by the quality inspection in the manufacturing processes, including automated ones. Considerable attention is paid to the surfaces with a difficult or no access for the contact profile meter. In order to scan these surfaces of machine parts an experimental measuring device of module conception has been designed that works on the light principle and utilizes elements of laser technique. Interesting original experimental results are given that have been obtained by both, contact and light procedure. They explain in greater detail the given problems that are attractive especially from the standpoint of the quality inspection in the perspective automated production.
Upon diffusion of vapors in polymeric materials these change their optical properties in various forms. First, in diffused e.g. water increase the density and therefore the refractive index, due to the Lorentz Lorenz Equation. Second, in polymers with a high stress optical coefficient, birefringence can be detected. It occurs because of the swelling of such a material. Together with a fixed interface to a substrate clamped film, this leads to mechanical stress and therefore to birefringence. Depending on the choice of the polymer, one of these effects is dominant or can be neglected. In both cases however, it is possible to determine e.g. the humidity of the air or the concentration of other organic vapors in a certain gas flow. The behavior of such materials in contact to humid or other atmospheres is measured by wave guide techniques and ATR-spectroscopy. Both methods allow to realize real-time monitoring or online measurements.
This paper deals with the basic theory of a photoelectric type angular displacement measuring instrument, its design key pointers and measuring circuits. The test results of a prototype device have shown that the said photoelectric type angular displacement measuring device has the following technical characteristics: sensitivity, 1000 mv/1 degree(s); measurement range, +/- 5 degree(s); precision, 0.3%; resolution, 30".
In this work we have applied infrared camera techniques in a prototype of a quality control system for surface mount circuit board solder paste printing. The prototype system consists of a stepper motor controlled conveyor for board transportation and indexing, an infrared camera for paste pad temperature profile recording, a CCD camera for board and pad registration and recording, a pulse heating set-up, a video frame grabber and signal processor unit for preliminary image processing, and a PC for operator control, high level autonomous control and processing of preprocessed infrared and visual image data and communications with the other shop floor information and quality control systems. The operator interface is built on top of Windows 3.1, which makes it easy to operate and to connect to other programs at will. The prototype system was capable to process the locations and areas at over 100 solder paste pads per second speed and to evaluate the volumes of the pads within error tolerance of approximately equals 20%. The most severe obstacle in applying IR techniques in SMT product lines seems to be the current high cost of suitable IR scanning devices. Only slightly modified, the developed infrared quality control and testing system prototype can be used also in other electronics assembly line applications like solder checking and functional checking of boards by monitoring the thermal properties of solders and components correspondingly.
High-quality transformer winding requires precise measurement and control of the gapping between adjacent wires. We take a vision-based approach to the measurement subtask of determining the gaps between copper wires wound onto an oval transformer. The oval core shape, which can have an eccentricity as high as 2-to-1, leads to significant variations in surface normal and viewing distance. We use special lighting, a secondary mandrel shape sensor, and the specular reflection off the wires to give us an accurate model of the experimental geometry. We further exploit the vertical symmetry of the viewed region to condense our 2D image to a simple 1D signal containing reflectance peaks. after utilizing pattern recognition and some additional safety features to separate the wire peaks from background noise, we perform a least squares curve fit of the peaks to determine the subpixel maxima. the final algorithm is computationally fast and yields the desired wire gap in an absolute metric.
Ultraprecision machining is one of the most important developing branches of modern machine building, and it also forms the basis for the development of some of the most advanced technologies, such as the technology of electronics, the technology of aerospace, etc. This paper describes several chief aspects of how to increase the in-process measuring precision, which provides a basis for the development of ultraprecision turning machines.
Some aspects of the possible applications of new, nontraditional generation of the advanced photosensors having the inherent internal image processing for multifunctional optoelectronic systems such as machine vision systems (MVS) are discussed. The optical information in these solid-state photosensors, so-called photoelectric structures with memory (PESM), is registered and stored in the form of 2D charge and potential patterns in the plane of the layers, and then it may be transferred and transformed in a normal direction due to interaction of these patterns. PESM ensure high operation potential of the massively parallel processing with effective rate up to 1014 operation/bit/s in such integral operations as addition, subtraction, contouring, correlation of images and so on. Most diverse devices and apparatus may be developed on their base, ranging from automatic rangefinders to the MVS for furnishing robotized industries. Principal features, physical backgrounds of the main primary operations, complex functional algorithms for object selection, tracking, and guidance are briefly described. The examples of the possible application of the PESM as an intellectual 'supervideosensor', that combines a high-quality imager, memory media and a high-capacity special-purpose processor will be presented.
By analyzing the measuring principle of tool maker's microscope, the article presents a new method for thread measurement with a tool maker's microscope assisted by computer. Special real-time image sampler was developed. A new measuring system was established and relative software has been designed. For the hardware design, the technique of DMA transfer data was adopted and the real-time sampling of one field of image was realized. For the software design, both assembly language and high level language were used. Image sampling and edge detection were operated by assembly language rapidly and the thread parameters were calculated by high level language. Experiments show that the system can measure the thread parameters automatically and rapidly. The study of computer-aided measurement of thread accuracy with a tool maker's microscope is useful to realize the intelligent measurement of another shape accuracy with a tool maker's microscope.
A point diffraction interferometer with a liquid crystal filter is used to measure a phase object. A reference beam is locally generated by a microsphere embedded within the liquid crystal layer. Phase shifts between the object and reference beams are introduced by varying a voltage across the birefringent nematic liquid crystal layer. Periodic phase measurement errors caused by modulations in the average intensity distributions are discussed, and a normalization method is described to reduce the errors. Experimental results are compared to a computer simulation to verify that the periodic errors are caused by intensity variations in the object beam.