A very large percentage of the inspection tasks carried out by human inspectors in manufacturing plants rely primarily on visual examination. The reason for this is the fact that a large number of defects in mass produced parts can be spotted very quickly by a trained observer inspecting the product. Unlike other forms of inspection that may rely on a variety of sequential measurements, visual examination is in general very fast. This is due primarily to the fact that the eye and brain can acquire and process information regarding the exterior appearance of the part in parallel, and make a decision based on a multiplicity of features almost at once.
The basic components of an optical inspection system are considered from the point of view of their ability to perform the functions of optical data acquisition and preprocessing. The influence of the type of illumination source used is discussed and the data rate capabilities of both parallel and serial methods of acquiring the information from the object under inspection are described. The methods of coherent and incoherent spatial filtering as applied to the inspection of certain types of objects is described.
A review of image sensors suitable for application to industrial gaging and inspection will be presented. A description of operation as well as a comparison of performance will be made. Major emphasis will be on solid state image sensors, describing in detail the features which make them uniquely suited to industrial metrology and inspection.
Principles of operation of several optical gauging techniques are given including those of mature devices such as autocollimators, profile projectors, and conventional and moire interferometry as well as those of some of the newer techniques such as heterodyne interferometry, holographic and speckle interferometry, and optical probes. The range of measurements for which the different techniques are useful is given, and typical results are shown.
A laser scanning inspection gauge has been designed which enables quick objective assessment of optically polished surfaces to be carried out by relatively unskilled operators. The gauge is suitable for batch inspection of optical flats, windows, and lenses over a wide range of sizes and powers. It is capable of detecting and measuring surface defects such as scratches, digs, poor polish, surface contamination and inclusions in the body of the glass, or in a cement layer. It is possible to modify the gauge to permit inspection of lenses on the block, and reflecting surfaces, including semiconductor wafers.
Zinc plates used in the lithographic industry must be free from scratches and meet a stringent specification on surface finish (scratches under .002 inches wide and surface variations in the range of 400 ± 20 grit). Mechanical Technology Incorporated has developed an automated industrial machine for inspection of these zinc plates as part of the on-line processing system for a zinc plate manufacture. This paper describes the application briefly and the inspection system in detail. The inspection system uses a non-contacting fiber optic system, optical-to-electronic conversion and signal processing electronics.
High grazing-angle illumination interferometry is described. Two applications are discussed: microscopic surface profile measurement of machined surfaces (ground, one-dimensional), and observation of macroscopic surface deviations. In both applications it is shown that the grazing angle interferometry is applicable to objects having surface roughness up to 5-7pm (RMS).
Under the treaty of Paris the European Economic Community supports research and development related to the manufacture and processing of steel products. Optical methods have played an honourable part in this programme. They lend themselves especially to quality control during the manufacture of semi finished products and to inspection of finished material. Parallel with co-operative work sponsored by the Community, Steel Companies in the member countries of the EEC have carried out optical developments related to their own needs and instrument firms have developed equipment in response to meet market forces. This paper discusses optical developments in the European Steel Industry originating in each of these areas.
Diffraction and scattering allow subtle defects to be detected at the high rates required for industrial quality control applications. Flaw detection in textile, transparent plastic, and steel webs has been demonstrated. Similar techniques may also be applied to many non-web problems such as walnut meat inspection, blade sharpness, wire diameter, and small part measurement. Several of these systems are currently under development and will soon take their place on the factory floor. In each of these cases, the diffraction pattern provides all the information necessary to determine product quality so that relatively few samples of the diffraction intensity pattern may be analyzed at high speed to detect the defect. Thus, diffraction pattern analysis offers a significant advantage over video scanning systems (even those based on a laser scanner) by minimizing the amount of data presented to the system for decision making. In most applications, video systems can simply not keep up with the rates required for on-line inspection. On the other hand diffraction systems generally illuminate a relatively large area and are able to operate at speeds required for on-line inspection.
An Automatic Web Inspection System is described which is intended for the detection and classification of defects in the periodic cell structure of ceramic catalytic converter substrates. The system scans the cut ends of ceramic logs and optically processes the reflected light with spatial filtering in the image plane. The outputs of the optical detectors are then processed with electronic logic to classify and count the defects.
The efficiency of industrial quality control has greatly improved in the past decade through the application of the mini-computer and two major developments in optical systems, namely optical grating transducers and the c.w. gas laser. The paper describes a new automatic machine designed in collaboration by the SKF European Research Centre and the Cranfield Unit for Precision Engineering (CUPE), for not only gauging automotive engine cylinder bores, but also laser scanning the bore surfaces to evaluate surface quality, e.g. the presence of retained boring marks, porosity and blow hole defects and the existence of acceptable honing cross-hatch etc.. Thus, a previously labour intensive viewing type inspection process is replaced by an automatic QC system. A second automatic QC development for the automotive industry is the Horstmann-Cranfield CNC cam shaft measuring machine, which not only rapidly measures the rise errors on all lobes of a cam shaft, but also analyses and presents the derived errors of velocity, acceleration and "jerk". One such machine will provide quality audit services for a DNC manufacturing cell in the UK for high precision cam components. The cell will contain a group of new Adaptive-CNC cam grinding machines designed and developed by CUPE. These machines are "quality-adaptive" in that optical grating systems are used to ensure that irrespective of grinding wheel size, only cams of the correct profile and size are produced.
Infrared imaging devices can be used to view thermal characteristics in real time and to solve a wide variety of problems. An infrared microscanner originally introduced at SPIE in 1972 is shown applied to produce infrared signatures of beam lead devices . A number of other applications using other scanning techniques are also presented, including the examination of heat pipes, coatings, hybrid circuits and coils. Methods of using these thermal images in solving quality control and reliability problems are discussed.
Three systems for inspection of axially symmetric parts illustrate many characteristics of pure analog, hard-wired digital and computer controlled electro-optics. The optical, mechanical and electronic considerations of each are briefly reviewed to provide the quality control engineer, as well as the electro-optical engineer, with an overview of some basic design considerations.
The basic fundamentals of high speed automatic optical sorting equipment are reviewed with the emphasis on the electro-optical inspection aspect. Techniques described include monochromatic and bichromatic measurement of reflected light, measurement of transmitted light, ultra-violet fluorescence and X-ray fluorescence. Procedures for determining the configuration of illuminant, filters, detectors and viewing methods are described. Practical examples are given of the use of this equipment in the food, mineral and waste reclamation industries to control quality of the product at various stages. The problems of suiting this type of equipment to the industrial environment are discussed.
Three technologies are brought together to form a wide variety of electro-optical measurement and gauging systems. The discussion will cover how solid state image sensor technology combined with a variety of optical configurations and digital signal processing techniques provide a myriad of optical inspection systems. The discussion covers the various optical and part positioning parameters which must be evaluated in the design of an on-line optical gauging system. This is followed by a review of digital processing techniques which provide the outputs required. The .RS85.2 Button Inspection System is reviewed to provide an example of a 2 axis multiple parameter high speed part gauging system.
The process for manufacturing a major type of catalytic converter for exhaust pollution control depends upon the availability of a dimensionally precise honeycomb-like ceramic substrate upon which to plate the catalyst metal. Dimensions are important since the cylindrical shaped substrate is later placed within a rigid stainless steel container where close fit is necessary to prevent "blowby". This paper will present a multiple scanning laser technique which was employed to automatically measure diameter in several planes of the still soft ceramic cylinder during the extrusion process.
Functional descriptions of laser interferometers are presented. The specific application of a Hewlett-Packard Interferometer to the evaluation of the x axis motion of a scanning microdensitometer is detailed. Results of the analysis are discussed. Extensions to some other areas of metrology are given.
There is an increasing demand for inspection equipment that is designed or adapted to meet individual problems. This paper describes some of the solutions proposed or effected by the Special Projects Team of an instrument manufacturing company. The examples chosen are: (1) A method of assessing the straightness of long tubes using a steel ball and an alignment telescope, giving an accuracy of 0.001 inch. (2) A versatile photo-electric device for determining the position of a light - dark boundary. (3) Measurement of the positions of holes entering a cylindrical bore, by means of a profile projector and special fixtures. (4) A coarse alignment system for civil engineering in which a spot of light from a laser source is projected at constant diameter over a wide range of distances. (5) Presentation of turbine blade profiles on a CCTV monitor, using a modified Schmaltz light-sectioning technique.