Abstract:
A process for the detection of flaws in an article comprising infra-red scanning of the article as its temperatures changes and comparing the infra-red scans for regularity of cooling/heating pattern. Where the article is irregular, such as in marginal areas, thermodynamic modelling is performed to establish a hypothetic cooling/heating pattern for an unflawed article.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The invention relates to defect detection in articles using computer modelled dissipation correction differential time delay Far infra-red scanning. Especially the invention relates to such defect detection in articles such as fibre board panels, oriented strand board panels, medium density fibre board panels, metal panels, metal pipes, coated metal pipes and similar articles.  
           [0003]    2. Acknowledgement of the Prior Art  
           [0004]    Non-destructive testing inspection using Far IR scanning is well known in the detection of hot spots for example detecting where insulation is absent, where friction components are malfunctioning, or where cooling/exhaust systems are failing. However, flaws which do not cause local hot spots are more difficult to detect. Some of these flaws are very hard to detect.  
           [0005]    Various attempts have been made to overcome the difficulties which arise in this type of scanning for flaws. Examples of methods which have been used are set out in U.S. Pat. No. 5,357,112 issued Oct. 18, 1994 to Steele et al., U.S. Pat. No. 5,444,241 issued Aug. 22, 1995 to Del Grande et al., and U.S. Pat. No. 5,631,465 issued May 20, 1997 to Shepard.  
         SUMMARY OF THE INVENTION  
         [0006]    It has now been surprisingly discovered that in a large central area of an article it is not necessary to resort to various precautions to overcome difficulties. It is only necessary to utilize precautions in a marginal area where cooling of an unflawed article does not occur in such a set pattern as in a central area.  
           [0007]    The present invention provides a process for the detection of flaws in an article using Far infra-red scanning of its surface comprising changing the temperature of the surface of an article over a plurality of temperatures and making an infra-red scan at each of said temperatures during changing the temperature, the infra-red scans being separated one from another by equal time increments; characterized In the steps of allocating parts of said surface as central and marginal parts forming images from said infra-red scans, digitizing said infra-red scans, digitizing the images to provide a sequence of digitized scanned images; for said central part of the surface, comparing data directly from said digitized scanned images and noting variations and/or anisotropies from a general cooling pattern for the article and deducing the presence of flaws at locations in the article corresponding to the location of the variations and/or anisotropies in the comparison of the digitized scanned images; and for the marginal part of the surface, performing thermodynamic modelling on one of the digitized scanned images to provide an estimate of the temperature distribution for a hypothetic unflawed article after passage of one of said time increments, and comparing data from an adjacent digitized scanned image with said estimate and noting variations and/or anisotropies of the structure of the marginal part of the article.  
           [0008]    The present invention also provides a process for detection of flaws in an article. This process comprises changing the temperature of the surface of an article over a plurality of temperatures; making an infra-red scan at each of said temperatures during changing of temperature; said infra-red scans providing at least a first and a second scanned image and being separated one from the other by a time increment; digitizing the at least first and second scanned images to provide a sequence of at lease a first and a second digitized scanned image; performing thermodynamic modelling on the first digitized scanned image to provide an estimate of the temperature distribution for a hypothetic unflawed article after passage of said time increment; comparing data from said second digitized image with said estimate, noting variations and/or anisotropies of the structure of the article. Thereafter, quality decisions about the fitness of the article can be made.  
           [0009]    While first and second scans at first and second temperatures may be sufficient to provide data for flaw detection, a group of scans may be made at a series of three or more temperatures for greater accuracy. Said thermodynamic estimate may be made at any one of this series of temperatures and may be compared with data from scanned images obtained at higher or lower temperatures.  
           [0010]    The relative proportion of the central and marginal parts may be chosen in accordance with the shape and size of the article, the material from which it is made and the degree of accuracy required. For example, if the article is a circular metal plate of say 10 feet in diameter, the central portion may be a 9 foot circle within an annular marginal portion. If the plate is formed of a less thermally conductive material, the marginal portion may be smaller. If, however, the plate is square, the central portion may possibly still be circular, since the corners of the square cause irregularities. Many of the decisions will be within the skill of the operator once the general principle is appreciated may be made by a man skilled in the art. In very general terms the central portion may be of regular shape and may be from 10-90% of the surface area of the article.  
           [0011]    More particularly the central part may be from 20-80% or especially 75% of the surface area of the article.  
           [0012]    The process of specifically inducing, or introducing a heating or cooling transient, with the specific intention of creating a temporary temperature differential in what would have otherwise been a steady state situation is particularly important. The creation of, high speed monitoring of, image acquisition of, image processing of, enhancement of, and thermodynamic modelling of, these temporary temperature differences constitutes the essence of this invention.  
           [0013]    Conveniently the thermodynamic modelling and the comparison of data are performed by a suitably programmed computer.  
           [0014]    In the following specific detailed discussion, it is always assumed that a surface of the article to be tested is heated above ambient temperature and allowed to cool. In fact, it is within the scope of the invention to cool the article below ambient temperature and allow it to heat up to obtain two incremental temperature differences.  
           [0015]    While the following detailed discussion is limited to the scanning and comparison of only two images at different temperatures, it is clear that a much larger number of images may be scanned and compared.  
           [0016]    For example, the process may comprise the following steps:  
           [0017]    1. Central and marginal parts are designated if desired.  
           [0018]    2. The component to be inspected is heated so that its temperature rises significantly above ambient temperature. This heating is preferably uniform, and preferably of at least 50 degrees Celsius in magnitude.  
           [0019]    3. An IR image of the surface of the heated component to be analyzed is obtained with sufficient resolution (in temperature, spatial, and temporal domains) to allow for detection of defects. The spatial resolution required will depend on the defects in question (for example variation in oriented strand board (OSB) panels might require resolution of ¼″ square, variations in pipe wall thickness might require resolution of 0.5 mm square). The temperature resolution required from the Far IR image will typically be from 0.1 to 0.2 degrees Celsius. Typically the scanner will be a forward looking infra-red (FLIR) scanner using a cooled mercury cadmium telluride detector, or a cooled indium arsenide detector or even an uncooled micro-bolo metric array. The details of the scanner implementation are not important as long as:  
           [0020]    a) the resolution is adequate,  
           [0021]    b) the image acquisition speed is adequate  
           [0022]     (some thermal transients are of short duration)  
           [0023]    c) the image can be acquired in the appropriate setting (real time acquisition for in plant production monitoring, remote portable and field worthy acquisition for in-situ applications).  
           [0024]    d) the acquisition speed and mode is appropriate to the application (e.g. linear or flying spot scanning may be necessary for moving web processes, where as a real or snapshot acquisition may be necessary for quasi-stationary processes).  
           [0025]    4. The scanned Far IR (3-10 microns wavelength of peak sensitivity) image is digitized and stored. The pixel resolution of the digitization and the storage system must be adequate to preserve the spatial resolution of the original IR data.  
           [0026]    5. After a suitable time interval (this interval may vary from a fraction of a second in the case of a pipeline in use, to tens of minutes for large structures like the hulls of ships which have only been minimally heated), a second Far IR image of equivalent resolution is sampled and digitized. For the central part of the first and second images may be compared directly. For the marginal part thermodynamic modelling as described in the following steps may be used. If central and marginal parts are not designated then thermodynamic modelling is performed on the whole.  
           [0027]    6. Standard thermodynamic modelling involving specific heats, conductivities, temperature differentials from ambient, and rough convection and other loss estimates is applied to the component data for the first sample, and the temperature distribution for a “perfect homogeneous” component at the instant of the second sampled is modelled and estimated. Alternately, this estimate may be derived from images of “good” articles taken at the second sampling time. The main purpose of calculating this estimate is to account for the significant non-uniformity of heat loss that arises directly from thermodynamics of the situation, so that comparison of the estimated temperature distribution with the actual will not high light any local anomalies.  
           [0028]    7. The modelled radiant temperature profile estimate at the time of the second sampling is then compared with the actual profile data from the second sampling and the difference calculated, or high lighted.  
           [0029]    8. Significant variation or anisotropies from within three dimensional structure then become evident. Theses may correspond to flaws or other non-uniformities.  
           [0030]    9. The variations, and anisotropies evident in the image, can then be further enhanced using conventional image processing techniques, and:  
           [0031]    a) presented in the form of a visual spot  
           [0032]    b) quantified and used to make a pass/fail or grading decision.  
           [0033]    It is believed the process of the invention is especially applicable to:  
           [0034]    1. The inspection of pressed composite panel or laminated products, in a production environment for anisotropies, resin spots and delaminations or other defects.  
           [0035]    2. The in-situ inspection of structural panels on ships storage tanks, and other large structures; for external corrosion, paint or coating delamination, the buildup of layers or other defects.  
           [0036]    3. The in-situ inspection of wall thickness variations in pipelines. In this case no marginal part is designated, or the marginal part involves only the ends of the pipes. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0037]    Embodiments of the invention will now be described by way of example with reference to the drawings in which:  
         [0038]    [0038]FIG. 1 is a schematic representation of one embodiment of the invention;  
         [0039]    [0039]FIG. 1A shows exemplary central and marginal parts of the panel;  
         [0040]    [0040]FIG. 2 is another schematic representation of one embodiment of the invention;  
         [0041]    [0041]FIG. 3 is yet another schematic representation of one embodiment of the invention; and  
         [0042]    [0042]FIG. 4 is yet another schematic representation of one embodiment of the invention; and  
         [0043]    [0043]FIG. 5 is a flow chart. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0044]    Hot Pressed Composite Panel Inspection  
         [0045]    The production of oriented strand board (OSB), medium density fibre board (MDF), hot pressed laminated composites, and other pressed materials is a complex process. It is highly desirable to monitor process variability, e.g. to note variations in the placement of wood chips, fibre components, density, distribution of resin, local delamination, and other non-uniformities in the panel. Process variations from the mean intended usually result in a degradation of local properties (too brittle, too soft, too stiff, wrong colour, too weak, etc.).  
         [0046]    An embodiment of the invention will now be described which allows for a direct on-line measurement of these production variations.  
         [0047]    Since the panels undergo a hot pressing, they emerge from the press already uniformly heated. Therefore, apparatus used may be as follows:  
         [0048]    1. A first Far IR scanner capable of imaging the moving OSB with the required resolution.  
         [0049]    2. A digitization and storage unit that buffers and sequences the first images taken.  
         [0050]    3. A second independent Far IR scanner identical or similar resolution to the first that images the panels at a latter point in their transport and processing in the facility.  
         [0051]    4. Sufficient tachometers. broken beam sensors, and local ambient thermometers to allow for accurate and efficient tracking of the panels, and thermodynamic modelling of the associated heat loss in transport.  
         [0052]    5. An image processing computer system capable of performing the thermodynamic modelling calculations of the set of first images and computing the differences between these time forward modelled first temperature distributions, and actual second temperature distribution sampled.  
         [0053]    6. Image processing hardware and software capable of enhancing, identifying and quantifying the detected variations between the actual IR image samples, and the time forward modelled data from the earlier images.  
         [0054]    7. A process control interface to the PLC or control equipment which controls the sorting, marking, and grading of the panel products being produced.  
         [0055]    Panels are heated in a hot pressing step of their manufacture to high temperatures, e.g. 60 to 120 degrees Celsius above ambient. Panels are transported from the hot press typically at speeds of up to 400 ft. per minute. Temperature differences are large. In the ideal embodiment, the two IR scanners are placed as far apart as possible within a section of the production facility where motion of the panels is relatively uniform. The panels are scanned at different temperatures and the images are digitized.  
         [0056]    A central portion and a marginal portion may be designated for each panel. This designation is dependent on the accuracy required in the marginal area but for general purposes the central area may comprise between about 10 and 90% of the surface area. Usually the central area may be about 75% of the surface. For the rectangular panel shown in FIG. 1A, the marginal part is advantageously increased at the corners since irregularities in cooling or heating may occur. Thus the central area may have smoothed corners as shown or may even be circular.  
         [0057]    Spatial resolutions of on the order of ¼″ square are required, and image processing systems must store and process 400×200 pixels/image for 8′×4′ panels, and up to 1200×600 pixels/image for 24′×12′ panels.  
         [0058]    Thermodynamic modelling, for the marginal portion or when no central portion is designated, is calculated by means of a computer and the variations and anisotropies indicate flaws in the panels.  
         [0059]    Adequate image and mathematical processing must be provided (several billion operation per second) to perform image processing and thermodynamic modelling at rates up to 1 panel every 0.5 second.  
         [0060]    [0060]FIG. 1 generally illustrates schematically a process and apparatus for hot pressed panel inspection. In the drawing  10 A,  10 B,  10 C represent plywood panels in consecutive positions in their manufacture. Panel  10 A is located between the presses of hot press  12 . Panel  10 B is located for scanning by infra-red scanner  14  and temperature T 1  which is substantially the temperature at which the panel emerges from the hot press. Panel  10 C is shown in position for scanning by infra-red scanner  16  at temperature T 2  below the temperature T 1 . Each panel  10 A,  10 B and  10 C comprises a central part  11  (see FIG. 1A) and a marginal part  13  extending around it.  
         [0061]    The scanned data from scanner  14  is digitized in digitizer  18  and the scanned data from scanner  16  is digitized in digitizer  20 . Data from digitizer  18  together with data from thermodynamic sensors  22  to compute the thermodynamic model in computer  24 . Similarly data digitizer  20  together with data from sensors  26  are used to compute a second thermodynamic model by computer  24 . Computer  24  then compares the thermodynamic model to calculate significant variation in anisotropies.  
         [0062]    Large in-situ Panel Inspection  
         [0063]    Another example of the process of the invention is use for in-situ inspection of large panels, for example, metal panels.  
         [0064]    In this case, although the problem is different, the principle is the same.  
         [0065]    Large in-situ panels, iron or steel panels, must from time to time be inspected for corrosion. These panels might form part of the exterior hull of a ship above the water line, the exterior of a large storage tank or vessel, or in general the panel sheathing of some large structure already in place.  
         [0066]    In this case the apparatus may comprise:  
         [0067]    1. The single Far IR scanner capable of imaging the panel surface with the required resolution.  
         [0068]    2. A digitization and storage unit that buffers the images taken.  
         [0069]    3. Means to heat the panel such as a hose to produce a steam or hot water or hot fluid and direct it at the panel surface to induce significant local heating. The hose may be used to heat the panel just prior to the acquisition of the first image. Alternately if the panel has been heated by the sun, it may be sufficient to induce a thermal transient merely by pumping cool water against the hot surface. The second image may be taken after a suitable amount of time has passed. For empty tanks or ship&#39;s holds 20-40 minutes might be a suitable amount of time. For vessels or holds filled with dense liquids, a considerable shorter time would be appropriate.  
         [0070]    4. An image processing computer system capable of performing the thermodynamic modelling calculations on the set of first images and computing the differences between these time forward modelled first temperature distributions, and actual second temperature distribution sampled.  
         [0071]    5. Image processing hardware and software capable of enhancing, identifying and quantifying the detected variations between the later image sample, and the time forward modelled data from the earlier images.  
         [0072]    6. An output printing device capable of printing pseudo colour images, or contour map displays reproducing the Far IR images with areas of non uniformity enhanced, and marked.  
         [0073]    A first image is scanned at a first temperature and a second image is scanned at a second different temperature after the induction of a sudden thermal transient. The images are digitized.  
         [0074]    In this case panel temperature are high (50 to 70 degrees Celsius above ambient), a single Far IR scanner is used, and detailed knowledge of internal construction (nature of internal support and structure) is necessary.  
         [0075]    Spatial resolutions of on the order of ¼″ square are required, and image processing systems must store and process 400×200 pixels/image for 8′×4′ panels, and up to 1200×600 pixels/image for 24′×12′ panels.  
         [0076]    Adequate image and mathematical processing must be provided (up to several billion operations per seconds).  
         [0077]    Ideally an automatic azimuth and elevation control device for directing the Far IR imaging system will be used, and a large portion of the structure scanned using a long focal length imaging system, before the second set of identically located images is taken for differential comparison against the thermodynamically time forward modelled images from the first imaging pass.  
         [0078]    Similar considerations concerning central and marginal parts may be applied to these panels. Marginal heat/cooling effects may be, on the one hand, greater than those in FIG. 1 because the panel is metal, but, on the other hand, each panel may be bounded by other panels thus mitigating cooling irregularities. The final choice of the size and shape of the central part may be somewhat similar to that of FIG. 1.  
         [0079]    [0079]FIG. 2 generally illustrates schematically apparatus and process for inspection of a large in-situ panel.  
         [0080]    A panel  100  is heated (or cooled) by any suitable means  110 . The means  110  may suitably be a hose to deliver hot (or cold) water at a constant temperature. The water is delivered to a top surface of the panel  100  over a period sufficiently to provide relatively uniform surface temperature changes in the panel to bring it to a temperature T 10 . Temperature T 10  may be measured by heat sensors  114  distributed over the surface of the panel.  
         [0081]    At temperature T 10  infra-red scanner  116  forms an image of the top surface of the panel. The image is digitized in digitizer  118 . The digitized image together with information from the sensors  114  is fed to computer  120  where a thermodynamic model of the surface of panel  100  at temperature T 10  is made.  
         [0082]    The panel  100  is then allowed to change temperature to temperature T 12 . A second image is scanned by infra-red scanner  116 , digitized in digitizer  118  and fed to computer  120 . A second thermodynamic model is formed. The two thermodynamic models are compared in the computer to calculate significant variations in anisotropies between the images. The computer may conveniently be provided with a printer  122  for providing this information to the operator.  
         [0083]    In-situ Inspection of Pipe  
         [0084]    The invention may also be used to inspect pipe. The detailed inspection of buried pipelines, semi buried pipelines, surface pipelines as well as other in-service pipelines conventionally presents problems.  
         [0085]    In the case of pipelines transporting a liquid product, ultrasonic measures of exterior wall thickness are possible using internal pigging. This process is not so easy for pipelines transporting certain products, or for certain thick-walled pipelines transporting corrosive or abrasive slurries.  
         [0086]    In the case of gas pipelines, a pipeline might first be pigged with some sort of magnetic, dimensional or ultrasonic detector, and anomalous sections exposed for further examination.  
         [0087]    In the case of pipelines carrying corrosive, or abrasive slurries, or other materials difficult to pig, the pipes may already be exposed.  
         [0088]    In either case the application of the invention in this case is the detection of external surface corrosion internal surface corrosion, or wall thinning, in the pipe. Apparatus used is:  
         [0089]    1. An induction, or other heater (providing 500-10,000 watts of heat) is mounted on an external rolling frame which moves in a controlled linear (or spiral) fashion over the surface of the pipe, or alternately which can move beside the pipe as in a truck mounted system, or alternately a cooling system either frame or truck mounted for spraying cold water, if the pipe is already warm.  
         [0090]    2. A first and second IR scanner are also mounted on this external tracking unit, or alternately if transient bursts of heat are employed a single scanner used to capture he high speed progression of the transient.  
         [0091]    3. A digitization and storage unit that buffers and sequences the images taken is connected to allow the flow of data from the Far IR scanners.  
         [0092]    4. Sufficient tachometers, orientation measurement devices, and local ambient thermometers are provided to allow for accurate and efficient tracking of the external scanning frame or truck, and to allow accurate thermodynamic modelling of the associated heat loss in scanning, or alternately a second imaging system which acquires normal visible images of the affected pipe, which allows for later direct identification of the detected defects on the visual image.  
         [0093]    5. An image processing computer system capable of performing the thermodynamic modelling calculations on the set of first images and computing the differences between these time forward modelled first temperature distributions, and the actual second temperature distribution sampled, or alternately a high speed processing system which is capable of discriminating the presence of small anomalies in IR images as they are compared to “good” IR images.  
         [0094]    6. Image processing hardware and software capable of enhancing, identifying and quantifying the detected variations between the actual second image sample, and the time forward modelled data from the first image.  
         [0095]    7. An output printing device capable of printing out pseudo colour images, or contour map displays reporting the Far IR images with areas of non uniformity enhanced, and marked.  
         [0096]    A temperature transient is induced in the pipe, either heating, for example by using a heater or surface steaming, or by cooling, for example by using cold water. Images are acquired throughout the application of the transient change, and these images are digitized.  
         [0097]    In this case pipe surface temperatures are moderate (20 to 80 degrees Celsius above ambient), heat transfer is extremely rapid (depending upon the nature of the pipe contents being transported), and temperature differences are smaller. In a preferred embodiment, the IR scanner or scanners acquire(s) a large number of detailed images to completely document the transient.  
         [0098]    Spatial resolutions of on the order of 0.5 mm square or better may be required. Image processing systems must store and process very large amount of data (600×600 pixels or more for a 30 cm square patch of pipe surface).  
         [0099]    Adequate image and mathematical processing must be provided (up to several tens of billion operations per second) to perform image processing and thermodynamic modelling at rates adequate to keep up with the inspection of the pipe. Alternatively, mass storage devices may be employed to buffer “snap-shot” data, and computing may be performed in burst mode. In this case no central part and marginal part may be designated.  
         [0100]    A process and apparatus for in-situ inspection of pipe is generally illustrated schematically in FIG. 3. An indication heater  210  is mounted on a pipe  200  on a external rolling frame  212 . First and second IR scanners  214 ,  216  are also mounted on the external frame.  
         [0101]    The pipe is heated as the induction heater moves over the surface of the pipe and the surface of the pipe is scanned by scanner  214  at temperature T 20  and by infra-red scanner  216  at temperature T 22  which is lower than temperature T 20 . The scanned images from each of infra-red scanners  212 ,  216  are digitized respectively in digitizers  218 ,  220 .  
         [0102]    The digitized images from the digitizers are fed with respective temperative information from sensors  222 ,  224  to computer  226 . The computer first forms respective thermodynamic models of the images and then compares them to note any significant variations and an isotropies. These may be indicated to the operator by means of a printer  228 .  
         [0103]    [0103]FIG. 4 illustrates another process and apparatus for in situ pipe inspection for use on a pipe which is already hot, perhaps because it is carrying heated contents. Cooling means, for example a nozzle  310  for cold liquid such as water, is directed towards a pipe  300 . The nozzle  310 , which may be a spray nozzle, a jet nozzle, a hose outlet or specialist nozzle to produce a set liquid pattern, may be mounted on an external transport means (not shown) of any convenient type. An IR scanner  320 , is provided in the region of the pipe portion to be cooled by liquid from the nozzle  310 . The scanner  320  may be mounted on the same transport as the nozzle.  
         [0104]    The pipe  300  is cooled by liquid spray from the nozzle  310  and the surface of the pipe  300  is scanned by scanner  320 . The scanned images from the infra-red scanner  320  are digitized by digitizer  322 .  
         [0105]    The digitized images from the digitizer  322  are fed with respective temperature information from sensors  327 , via digitizer  328  to computer  324 . The computer stores the transient heat changes observed, notes and calculates models and highlights anomalies on a separate scanned image taken by an ordinary video camera  326  digitized by digitiser  328 .  
         [0106]    These highlighted anomalies can then be directly identified with normal image data and presented on any display or on printer  330 .  
         [0107]    [0107]FIG. 5 is a simplified flow chart defect detection by computer modelled dissipation correction time delayed Far IR scanning.