With increasing competition in the manufacturing industries product quality is becoming even more important. The shortcomings of human inspectors in many applications are well know, however, the eye/brain combination is very powerful and difficult to replace. At best, any system only simulates a small subset of the human's operations. The economic justification for installing automatic inspection is often difficult without previous applications experience. It therefore calls for confidence and long-term vision by those making the decisions. Over the last ten years the use of such systems has increased as the technology involved has matured and the risks have diminished. There is now a complete spectrum of industrial applications from simple, low-cost systems using standard sensors and computer hardware to the higher cost, custom-designed systems using novel sensors and processing hardware. The underlying growth in enabling technology has been in many areas; sensors and sensing techniques, signal processing and data processing have all moved forward rapidly. This paper will examine the currrent state of automatic inspection and look to the future. The use of expert systems is an obvious candidate. Parallel processing, giving massive increases in the speed of data reduction, is also likely to play a major role in future systems.

Real time in-situ optical measurements play a vital role in the monitoring and control of thin film deposition and etching. Techniques include single and multiwavelength monitoring of the reflectance and/or transmittance of the coating substrate, in-situ ellipsometry, and spectroscopic diagnostics of the vapour species. This paper will review these techniques and examine recent trends.

Ellipsometric measurement methods allow the characterization of interfaces or thin films between two media during deposition processes. The non-perturbing character combined with a remarkable sensitivity makes this optical technique suitable for in-situ measurements. The study of the complex refractive index as a function of the film thickness allows the control of inhomogeneous layers of dielectric and metallic materials. The present paper discusses the in-situ control of DC-sputtered silicon oxide, silicon nitride and titanium oxide films as well as electron-beam-gun evaporated films consisting of a mixture of different materials. The possibility of the production of preselected inhomogeneous layers by using oxide-nitride films will be demonstrated. The influences of different gas-control techniques on the optical properties will be shown.

The use of the smooth surface approximation to analyse light scattering from the surface of silicon wafers during epitaxial growth is described. Expressions for the time-dependent power spectral density function for isotropic and anisotropic surface textures are derived and compared with the experimental data for various stages of the epitaxial process. Additional quantitative information on epitaxial surface topography is provided by in-situ ellipsometry measurements, and by angle-resolved light scattering from wafers after removal from the growth reactor.

One of the most interesting techniques for in situ measurement of thin film optical properties and control of the coating deposition process is the wide wavelength band optical monitoring. This system allows the real time measurement of transmittance or reflectance of a sample during the film growth. In this paper a photometric monitoring system operating in the extended visible range (0.35- 1.1 μm) and connected to a r.f. sputtering apparatus is proposed. Real-time performances we-'e obtained by the use of 1K-diode array sensor positioned on the exit port of a grating monochromator. Optical fibers were used to obtain the required optical path inside the sputtering vacuum chamber. The instrument is computer controlled and the sample reflectance curve is displayed on a graphic monitor. An automatic control of the deposition process is obtained comparing this curve with expected reflectance values by the aid of a properly defined merit function. In the present configuration the monitoring equipment can be employed for single and multilayer dielectric coatings on transparent substrates.

For DC-reactive magnetron sputtering of different dielectric materials control algorithms have been derived to stabilize the discharge in the transition region between metallic and reactive mode. On-line measurement technology has been integrated to the large scale production machine concept to compensate long time effects and guarantee high reproducibility.

The new automatic PSZ-ellipsometer to be presented here is derived from known PSA/PSCA-arrangements. The usage of a double-beam polarizer for analyzing the reflected beam and of a new evaluation technique allow the compensation of main error sources. With the absolutely necessary optical elements only, our concept allows measurements with high precision, although a quasidynamic method is used. The actually presented realization is designed for measurements at multiple angles of incidence and wavelengths (MAI spectroscopic ellipsometry). The measuring process is dynamically computer guided for optimum performance. Our application is mainly the investigation of surface layers, not only for evaporated thin film coatings, but also for surface modifications due to polishing or cleaning processes. Instant experimental tests gave errors much less than 0.001 in refractive index and *lnm in film thickness while measuring MgF2 films on BK 7 glass. Investigations of "polishing films" resolved differen-ces in refractive indices between surface and substrate of only 0.0018 *0.0004 on BK 7 glass.

The current status and prospects for in-process optical sensors are examined in an international context. The global market for simple beam-interrupt sensors is contrasted with that developing for more complex analogue sensors. These are being encouraged internationally by both cooperative R&D groups and trade associations; examples in the UK and Japan are described. Japanese trade statistics and a survey of available product world-wide are outlined, allowing technology and product trends to be discerned.

For on-line control, the two alternatives of automatic sample transfert and in situ remote analysis are discussed. New concepts are emerging from the possibilities offered by optical fibers. Absorption in the visible, UV and IR, fluorescence and Raman spectrometric techniques are examined. The state of the art of optodes and devices in chemical process control are given, with some examples of applications in nuclear plants.

Fibre optic interferometric sensors (FOIS) are evolving as viable alternatives to alarge number of conventional sensors with extreme resolution coupled with very large dynamic ranges. This is particularly true when the measurand is periodic by nature, such as vibration for example. However, there still remain fundamental problems which must be solved before these new devices can be used routinely in process control measurements for quasi-steady state measurands such as temperature. One of these fundamental problems is associa-ted with the transfer function of the FOIS as its periodic nature can give rise to ambiguous outputs from the sensor on initial 'power up'. Special techniques have been developed for FOIS to solve this ambiguity problem based upon classical extended range interferometry. FOIS can be designed as contact sensors for many of the measurands important in the process control industry or as non-contact absolute measurement systems which can be used to calibrate conventional sensors such as those used for displacement or fluid flow. In this presentation the development of FOIS for temperature, pressure (displacement), flow and level will be discussed as these measurands are particularly important for 'in processing' measurements. In the case of the level measurement the system described is electronically rather than optically coherent.

Instrumentation systems employing optical-fibre links are under intensive development as they can offer features such as intrinsic safety, electrical isolation and freedom from electromagnetic interference. There are growing interests in the potential for such systems in military applications, process industries as well as general manufacturing. There are also requirements for optically-energized pneumatic and hydraulic actuation systems whereby a complete control system can be realised by optical means. This type of system may be referred to as an all-fibre control-by-light system. Examples of such control systems will be described.

Surface plasmon waves are perpendicularly polarised electro-magnetic waves which exist at boundaries between metals and dielectrics. The interest in surface plasmons from a measurement point of view arises from the fact that they can be excited optically and that their Oopagation is a sensitive function of the complex dielectric constants of the materials forming the interface. For chemical sensing, an interface is formed between the analyte (the dielectric) and a thin metal film. Surface plasmons are excited at this interface using a diverging laser beam which is reflected off the metal/analyte interface. Analysis of the reflected light shows a narrow dark line corresponding to energy being coupled to the surface wave. The position of this absorption line changes when the refractive index of the analyte changes. In our measurements, the analyte is a solution of acetone in water. By increasing the concentration of this solution its refractive index changes. By using an appropriate detector, the change in the position of the absorption line has been detected. Measurements made to deduce the concentration of the analyte by this technique are reported.

One of most important part of a total sensory system of a robot is a proximity sensing system, which must operate continuously during the work of the robot. In the paper a multiple optical fiber proximity sensing system developed for a robot gripper is described. The system performs a 3 - dimensional proximity sensing and is employed for the detection and localisation of an object before grasping it and then for the correct orientation of the gripper when grasping the object. In the paper conception of the system is presented. Some types of proximity sensor modules are described and they arrangement in robot grippers of different construction (2-and 3-fingered gripper) is suggested. Some remarks on the integration of multiple optical fiber proximity sensing system with the robot are given and the algorithm of the operation of the robot equipped with the sensor system is described. Although the multiple optical fiber proximity sensing system has been developed for robotics, it can also be used as multi point distance measuring system in other industrial automation systems.

A color sensing device has been developed for recognizing and measuring colors. The color sensor of the device consists of three photodiodes with double-cavity interference filters integrated on a single chip, each of them having a spectral response similar to each one of the 1931 CIE (Comission Internationale de l'Eclairage) color matching functions. The color sensing device is constructed with this color sensor, a light source of a tungsten halogen lamp and a micro processor. It illuminates an object through a plastic fiber, and detects scattered light from the object through another fiber. These fibers are set at 45° to each other, and one of them is set perpendicular to an object. The chromaticity coordinates of an object are calculated with the respective outputs of the photodiodes. The chromaticity coordinates that were measured for the sample chips with different colors (red to blue) do not vary more than 15% when the distance between the device and the sample chips varies within the range 4±1 mm, and not more than ±3% when the sample chips are inclined within as much as ±2° to the fiber plane.

This paper presents the effect of the positional error of metrological gratings on the contrast of Moire signals. The relationship between the positional error and the Moire fringe curvature has been discussed under different gap conditions. Theoretical expressions for the contrast of Moire signals have been deduced by means of geometrical approximation and diffraction principles. Agreement between the experimental results and the theoretical analysis is extremely good.

A method utilizing a visible-infrared interferometric technique has been developed to measure the thickness of ultra-thin films, the small spacing between two separated surfaces and the variations in the spacing. Successful measurements for the thickness of a thin magnetic film on a metallic substrate, the spacing between a magnetic head slider and a quartz disk, and the magnetic head slider fluctuations above a quartz disk are demonstrated. Specially designed single bounce reflectance attachment is used for the wavelength range from 400 nm to 700 nm and from 700 nm to 2500 nm. The wide range of the wavelength allows a vast variety of film material to be measured. Based on an intensity analysis of the reflection interference beams from the top and the bottom surfaces of the film over a wide spectrum, a relation of the intensity maximums and minimums vs. wavelength is obtained to calculate the film thickness, the spacing and the slider fluctuation. An optical thickness of L/10 (L is the wavelength) is obtained by a careful numerical analysis of the measured data which is significantly less than the limitation, L/4, by the conventional method for the first time.'

It is shown that the effect of attenuated total internal reflection (ATR) might be used for accelerometer design. Although the ATR-accelerometer will never outdate the conventional piezoelectrical accelerometer, it possesses some obvious advantages: Its performance is not limited by a Curie-Temperature, and since it is a purely optical device, it can be used in electrically noisy surroundings. Preliminary measurements on a prototype design are presented, and the performance with respect to optical, mechanical and thermal properties including noise-limitations are discussed.

The results obtained in the development of a laboratory prototype of intelligent spectrometric system with real time digital signal processing are shown in this paper. The system is acombination of visible range spectrophotometer and focussing holographic grid with photodiode linear structure, i.e.the sensor, real time digital signal processing controller and display processor for gray level visualization, together with PC/XT controlLing computer. The twodimesional adaptive differential pulse code modulator with simultaneous correction of sensor dark current introduced into the real time controller allows the registration of measurments with resolution of 10 bit/el and real time data compression 2.5 times. During computation of colorimetric estimations or wideband photo-metric compression the possibilities for express analysis increase together with the enhancement of the signal-to-noise ratio. The system control and the visualization of spectral and colorimetric features in the data flux is made with personal computer together with display processor with resolution 512x512x8 and interactive software. It may be used for ground-based and onboard complexes.

A novel technique has been developed for measuring the temperature of the burden inside an operating industrial lime kiln. In this technique, trace quantities of a rare earth element are introduced into the input stream to the kiln. Conditions inside the kiln cause the rare earth ions to become incorporated as substitutional impurities in the crystal lattice of the calcium oxide product. This results in a product which exhibits strong fluorescence under ultra-violet excitation. The decay time constant of this fluorescence, which is strongly temperature dependent, serves as a measure of burden temperature. The spectral and temporal characteristics of the fluorescence of several rare earths have been studied over a temperature range of 800 to 1150°C which is the range of interest in an operating kiln. This work has led to the selection of praseodymium as the most suitable rare earth element and to the development of techniques to permit temperature measurements with an accuracy of approximately ±20°C to be performed at rare earth concentrations in the parts per million range. A prototype sensor employing this fluorescence technique has been developed. This sensor, which has been designed to survive in the harsh lime kiln environment, utilizes a frequency tripled Nd:YAG laser to provide high energy UV pulses at 355 nm and a specially designed telescope and fiber-optic light collection system to detect the emitted fluorescence. This device will provide the first accurate, in-situ measurement of lime kiln burden temperature which can be made on a continuous basis.

In the last years more and more fibre optic transmission systems were used in the field of automation. This is because of the decisive advantages as - high protection against electromagnetic interference, - ground loop immunity between transmitter and receiver parts, - data rates which are independent of transmission distances. The present state of fibre optic transmission systems in Germany is shown in some examples of mainly installed point-to-point-links in short, medium and long distances, as well as bussystems. The situation of standardization activities and guideline works in Germany is shortly described. Finally, some future aspects and trends are given.

Light scattering techniques for velocity and particle size analysis are well established research and industrial tools. In general, light scattering instruments have been large and expensive, requiring skilled operation. We have constructed and tested a range of light scattering instruments in miniature form using the recently available range of new semiconductor laser diodes, avalanche and PIN photodiodes and optical fibres. Thus is has been possible to demonstrate laser Doppler and transit anemometers for turbulent flow analysis and dynamic light scattering instruments for particle size analysis all of which are small and cheap enough to be of value in on-line process monitoring and control. We describe the critically important features of the new technologies used, and how we have coupled new devices together into systems for industrial applications of importance eg biotechnology, pharmaceuticals, automobile, aerospace, chemicals, etc.

This presentation will discuss a novel sensing method for measuring fuel flow which was developed for the Ford Motor Co by Sira Ltd. The fuel flow sensor uses an optical technique based on detecting light scattered from particles carried in the flowing fuel. Two off axis light sources illuminate the fuel flow region. As particles move with the fuel some light is scattered normal to the fuel flow direction. The scattered light is focused onto a course beam splitter which then directs the light onto two matched detectors. The course beam splitter has 5 linear reflecting grooves per mm each with an included angle of 135₁. As a particle that is smaller than the groove width moves across the field of view the effect is to focus scattered light from the particle alternately onto each of the two detectors. Each detector therefore receives optical modulation which is in antiphase to that received by the other detector. The difference of the two detector signals is then used. Also presented will be a new design for an optically based steering wheel position. The sensor is now in full scale production and is manufactured by First Inertia Switch Ltd. An assembly consisting of a number of parallel light guides, each 0.25mm wide, views the light reflected from a black and white striped tape that is stuck to the steering column. The signals from the detectors that are mounted remotely at the end of the light guides are interpreted by a PLA device to give rotational information. The sensor offers a higher resolution than traditional similar sensors while maintaining a low manufacturing cost.

The optical and electro-optical requirements for on-line multi-component analysis of powder, granular and similar particulate solid materials are surveyed. The analysis is based on detecting small changes in weak nir absorption bands and the necessary photometric precision and spectral resolution are considered. Four alternative optical configurations are reviewed; filter wheel, tilting filters, spectral scanning and interferometer. Results obtained with the first of these are presented as a demonstration of the power of the technique and a number of possible applications presented.

This paper is a review of the applications of laser scanning in inspection. The reasons for the choice of a laser in flying spot scanning and the optical properties of a laser beam which are of value in a scanning instrument will be given. The many methods of scanning laser beams in both one and two dimensions will be described. The use of one dimensional laser scanners for automatic surface inspection for transmitting and reflective products will be covered in detail, with particular emphasis on light collection techniques. On-line inspection applications which will be mentioned include: photographic film web, metal strip products, paper web, glass sheet, car body paint surfaces and internal cylinder bores. Two dimensional laser scanning is employed in applications where increased resolution, increased depth of focus, and better contrast are required compared with conventional vidicon TV or solid state array cameras. Such examples as special microscope laser scanning systems and a TV compatible system for use in restricted areas of a nuclear reactor will be described. The technical and economic benefits and limitations of laser scanning video systems will be compared with conventional TV and CCD array devices.

A new sensor for measurement of micro profiles of fast running surfaces was developed, in which a fine Laser spot is created at the surface and the reflected light is received by photodiodes, arranged along an arc of 140 degrees perpendicular to the surface. These photodiodes are connected with resistors in the known manner of PSD's to realise an angle sensitive array to win the averaged angle of reflection of the asked surface-elements point by point. By calculating the local inclinations of these surface-elements and by integrating these values the micro profile is created, and by known calculations roughness parameters like Ra are determined. The distance of measuring points is 10 µm at a speed of the metal sheet up to 20 m/sec., thus the frequency of single measurements is 2 MHz. Results are shown and limitations are discussed.

An optical system for in-process sensing of tool wear is presented and discussed with application in a milling process. A strategy for automatic tool replacement is proposed on the basis of wear measurement feedback.

Oxide reflow, employed in IC technology to planarize the dielectric layers, is a critical step in multilevel CMOS processes. We have studied the control of the oxide reflow profile using laser beam diffraction by a line grating printed in the oxide film. Using an experimental set-up to record the diffracted light we found that a relation exists between the line profile and the diffraction pattern. In order to obtain a better understanding we developed a theoretical description of the full phenomenon : we first modelized the glass reflow as a purely viscous flow using numerical simulations. The diffraction was then analysed using a theory based on Maxwell equations and the corresponding equations were discretized. A good fit between theory and experiment was found showing a significant and sensitive correlation between the line profile and the diffraction pattern evolutions. These results lead to a new non-destructive in-line glass flow control method.

A method for the on-line analysis of liquid steel was developed. By focusing the light of a pulsed Nd:YAG laser on to the liquid surface, a plasma was produced and examined with a spectrometer and an optical multichannel analyser, respectively. As a result, calibra-tion curves were obtained for several elements. Typical lower detection limits were in the range between 10 and 100 ppm.

Under the conditions of many manufacturing processes the measurement and recognition of colours constitute an important task. The paper presents a reflectance spectrum analysis method for in-process colour recognition. In this method the reflectance spectra are analysed at different wavelengths by means of a set of narrow-band optical filters. The method constituted a basis for the development of an optical fiber colour sensor. The sensor necessitated an elaboration of a special method for selecting narrow-band optical filters. Thanks to this method the sensor has acquired good accuracy in colour recognition and can differentiate objects of very similar colours. The main advantages of the presented colour sensor include: the use of the whole spectrum instead of three coordinates, the speed of colour recognition, and the accuracy of colour recognition. Thanks to the application of optical fibers, the sensor head has small dimensions and a special construction which allows it to recognize objects of different degrees of glossiness. The second part of the paper describes a prototype of the optical fiber colour sensor and an experimental examination of the sensor. An example of an application of the sensor in robotics in recognizing and sorting coloured objects is also briefly presented.

A pencil beam incident on a translucent material causes a luminous circular spot of volume-reflected light. Its spectral radiance L (r) decreases with radius r. L_c, the value close to the centre is mainly determined by the scattering parameter s(1-g) of material. Le, the value at the edge of the spot, is determined by s(1-g) and the absorption coefficient a. The instrument (the CTM) employs three fibre bundles to measure L_c and L_e, both as a function of λ (400-700 nm). A central bundle (2 mm p) of - 1300 fibres each of 50 um g is randomly divided in a bundle for illumination and a bundle for measurement of L_c. A concentric ring (i.d. 4 mm, o.d. 5 mm) of - 2500 fibres is used to measure Le. This instrument was tested with aqueous suspensions of latex and a dissolved, non-latex adsorbing, red dye. Thus s(1-g) (scattering) and a (absorption) could be independently varied. For a=0, both L_c and L_e increased with s(1-g), reached a maximum and decreased. The maxima for L_c and L_e were at s(1 g) = 1 and 0.06 mm -1, respectively. At a constant scattering, increase of absorption decreased L_e much stronger than it did L_c. This absorption-caused decrease depended only weakly on the scattering coefficient: a variation of scattering of a factor 20 caused only a few percent change in absorption-caused decrease of Lc and only a factor 2 in absorption-caused decrease of L_e. At s(1-g) = 0.3 mm-1, Le depended much more strongly on a than did the overall regular reflection spectrum of the suspension as measured with a Hunter spectrophotometer under 0°/45° geometry. The readings of L_c and L_e with this instrument can be used to determine s(1-g) and a and the reflection spectrum. Only small samples are needed in comparison to the regular reflection spectrometry. To obtain absolute values the instrument has to be calibrated on the specific type of material under investigation.

A novel instrument based on the Laser-Doppler Velocimetry (LDV) principles has been developed for the in-field detection of torsional oscillations on rotating machinery. The LDV-probe permits the high sensitivity detection of the tangential velocity change on unprepared rough shafts. The probe is realized by means of the micro-optics and all-fiber technology in a compact assembly. E.M. immunity, easy handling and stoutness make the probe suitable for the in-field operation.

In recent years, increasing commercial and legislative pressure on automotive engine manufacturers, including increased oil drain intervals, cleaner exhaust emissions and high specific power outputs, have led to increasing demands on lubricating oil performance. Lubricant performance is defined by bench engine tests run under closely controlled conditions. After test, engines are dismantled and the parts rated for wear and accumulation of deposit. This rating must be consistently carried out in laboratories throughout the world in order to ensure lubricant quality meeting the specified standards. To this end, rating technicians evaluate components, following closely defined procedures. This process is time consuming, inaccurate and subject to drift, requiring regular recalibration of raters by means of international rating workshops. This paper describes two instruments for automatic rating of engine parts. The first uses a laser to determine the degree of polishing of the engine cylinder bore, caused by the reciprocating action of piston. This instrument has been developed to prototype stage by the NDT Centre at Harwell under contract to Exxon Chemical, and is planned for production within the next twelve months. The second instrument uses red and green filtered light to determine the type, quality and position of deposit formed on the piston surfaces. The latter device has undergone feasibility study, but no prototype exists.

Traditional high accuracy touch-trigger probing can now be complemented by high speed, non-contact, profile scanning to give another "dimension" to the three-dimensional Co-ordinate Measuring Machines (CMMs). Some of the features of a specially developed laser scanning probe together with the trade-offs involved in the design of inspection systems that use triangulation are examined. Applications of such a laser probe on CMMs are numerous since high speed scanning allows inspection of many different components and surfaces. For example, car body panels, tyre moulds, aircraft wing skins, turbine blades, wax and clay models, plastics, etc. Other applications include in-process surveillance in manufacturing and food processing, robotics vision and many others. Some of these applications are discussed and practical examples, case studies and experimental results are given with particular reference to use on CMMs. In conclusion, future developments and market trends in high speed non-contact measurement are discussed.