Abstract:
A spray monitoring device analyzes images obtained from a beam passing through a spray pattern applying a spray to a substrate, and identifies discontinuities in the image as indicative of a discontinuity in a spray pattern. The spray pattern is produced by a plurality of nozzles spaced apart across the substrate for applying a suitable coating thereto. The beam is produced by a laser, that preferably has a collimator for distributing the beam intensity. The beam is imaged by a camera that provides a constant image to a computers where the scattering of beam light by the spray pattern is processed by image processing software and optionally provided to a user interface for analysis. Discontinuities detected by the user or software indicate faulty spray nozzles and may trigger remedial action.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a Divisional of U.S. application Ser. No. 11/620,379, filed on Jan. 5, 2007, entitled “MONITOR SYSTEM FOR COATING APPARATUS,” which is a Continuation of PCTCA051123 filed on Jul. 18, 2005, the entirety of which are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to apparatus and methods of monitoring the application of a fluid to a substrate. 
       BACKGROUND 
       [0003]    It is frequently necessary to coat a substrate with a fluid during a manufacturing process. The application of the coatings may be for protective purposes or as part of the manufacturing process, and it is frequently essential that the fluid be applied in a uniform manner. Many manufacturing processes produce a substrate in a continuous manner as a web, and require the coating to be applied to the web as it is produced. A typical application for such coating is in the steel industry where an oil based lubricant is applied to a moving metal strip. The lubricant is required to assist in the further processing of the steel strip, and, accordingly, the film thickness of the lubricant must be uniform. Failure to provide a uniform coating will lead to inconsistencies in the further manufacturing process and the possibility of damage to the manufacturing equipment. 
         [0004]    The coating is frequently applied through an array of spray nozzles positioned in the path of the substrate. Each of the spray heads has a number of nozzles that in ideal circumstances will produce a uniform spray pattern and distribute the sprayed fluid evenly. There is a possibility that the nozzles may become blocked or experience wear, which can produce an uneven spray pattern, and consequently an uneven coating. When such a defect is discovered, it may be necessary to call back significant quantities of material that have been processed with a possibly defective coating. Therefore, the efficacy of the coating is typically inspected periodically, but usually by manual observation. This is both time consuming and inconsistent, and requires significant skill on the part of the operator to recognize the existence of a fault. 
         [0005]    It is therefore an object of the present invention to provide a method and apparatus in which the above disadvantages are obviated or mitigated. 
       SUMMARY OF THE INVENTION 
       [0006]    In general terms, the present invention provides a system or method in which a coherent light source, typically a laser, is directed through a spray pattern. A camera is positioned to record the image of a beam as it propagates through the spray pattern and analyze the image to determine spray uniformity and continuity of the spray pattern. 
         [0007]    Preferably the camera is integrated with the control system for the apparatus to provide an indication of inconsistent spraying and initiate remedial action. 
         [0008]    In one aspect, the present invention provides a method of monitoring the application of coating to a substrate from a plurality of nozzles spaced apart across the substrate. The method comprises the steps of projecting a beam of coherent radiation through a spray of coating from said nozzles, obtaining an image of the beam as it propagates through the spray, and processing the image to determine variations in a characteristic indicative of the presence of the spray. 
         [0009]    In another aspect, the present invention provides a system for monitoring the application of coating to a surface of a substrate, the coating being applied as a spray from a plurality of nozzles spaced apart across the substrate. The system comprises a coherent radiation source arranged to direct a beam of coherent radiation through the spray; an imaging device for obtaining an image of the beam as it propagates through the spray; and a computing device having a processor and being connected to the imaging device, the processor executing image processing software to process the image in order to determine variations in a characteristic indicative of the presence of the spray. 
         [0010]    In yet another aspect, the present invention provides an apparatus for monitoring the application of coating to a substrate, the coating being applied by a plurality of nozzles spaced apart across the substrate. The apparatus comprises a coating station having a feeder for continuously feeding the substrate through the apparatus; at least one sprayhead connected to the coating station and positioned a predetermined distance from the substrate, the sprayhead having a plurality of nozzles, the nozzles being connected to a source of coating to enable coating to be fed through the nozzles to produce a spray of coating, the spray of coating being applied to a surface of the substrate; at least one coherent radiation source arranged to direct a beam of coherent radiation through the spray as it is applied to the substrate; an imaging device for obtaining an image of the beam as it propagates through the spray; and a computing device having a processor for processing the image to determine variations in a characteristic indicative of the presence of the spray. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    An embodiment of the invention will now be described by way of example only with reference to the accompanying drawings in which: 
           [0012]      FIG. 1  is a perspective view of a coating apparatus; 
           [0013]      FIG. 2  is a view on the line II-II of  FIG. 1 ; 
           [0014]      FIG. 3A  and  FIG. 3B  are representations of images obtained from the apparatus of  FIG. 1  under different operating conditions; 
           [0015]      FIG. 4  is a screen shot of an interface showing the information obtained; and 
           [0016]      FIG. 5  is a flow chart indicating the processing of data obtained film the images shown in  FIG. 4 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0017]    Referring therefore to  FIG. 1 , a substrate  10 , for example a steel strip, is passed through a coating station  12  to obtain a coating from a fluid lubricant on one or both of oppositely directed surfaces  14 ,  16 . In the embodiment shown in  FIG. 1 , the coating station  12  includes sprayheads  18  arranged on opposite sides of the substrate  10  (only the upper sprayheads  18  are visible in  FIG. 1 ), although coating on only one side may be utilised where appropriate. A pair of sprayheads  18  are located at longitudinally spaced locations in the direction of movement of the substrate indicated by arrow A to provide successive coatings. 
         [0018]    As can best be seen in  FIG. 2 , each of the sprayheads  18  includes a manifold  20  connected to a pressurized supply  19  of fluid to be applied to the surfaces  14 ,  16 . A series of nozzles  22  are connected to the manifold  20  and each produce a generally conical spray pattern  24 . The form of the nozzles  22  is well known and need not be described in further detail. The nozzles  22  are spaced apart along the manifold  20 , and thus across the width of the substrate  10  creating a fluid plume, to produce a substantially uniform distribution of the coating fluid to the respective one of the surfaces  14 ,  16  of the substrate  10 . 
         [0019]    To monitor the uniformity of coating produced by the sprayheads  185  a laser  30  is located to the same side of the substrate as the manifold  20  that is being monitored. The laser  30  produces a beam  32  of coherent radiation of a particular wavelength, preferably in the direction parallel to the axis of the manifold  20 . The laser  30  is positioned such that the beam  32  passes through the overlapping spray patterns  24 . Where a plurality of sprayheads  18  are utilized as shown in  FIG. 1 , each of the sprayheads  18  has an associated laser  30 . A suitable laser  30  is one of the SNF Series lasers available from Lasiris.™. 
         [0020]    Preferably, the beam  32  is a non-Gaussian, uniform line, produced by a collimated line head  31 . A suitable collimated line head is also available from Lasiris.™. Particularly, model C-25 has shown particularly favourable results, having a collimated line length of 25 mm. However, model C-48 (48 mm line length) is also suitable. It will be appreciated that other line lengths may be used depending on the availability of components. A collimated beam  32  is beneficial as the collimator  31  transforms the traditional laser “dot” into a uniform intensity line, which retains a substantially uniform intensity across the beam width. This can be contrasted with the traditional Gaussian beam intensity distribution that has a central “hotspot” and where the intensity weakens towards the beam edges. Moreover, a collimator  31  is ideal for applications requiring a wide range of working distances. However, a traditional Gaussian beam may also be used if desired. 
         [0021]    A camera  40  ( FIG. 1 ) is positioned so as to be able to image the spray pattern  24  from the manifolds  20 . Where practical, the camera  40  is located above the substrate with a field of view in the direction of motion of the substrate  10 . Where this is impractical due to processing considerations, a camera  40  may be disposed to one side of the coating station but spaced from the lasers  30  so as to have a field of view including each spray pattern  24  from the respective sprayheads  18  (see “alternate location” in  FIG. 1 ). Where multiple beams  32  are to be imaged, the camera  40  is positioned out of the horizontal plane passing through the manifolds  20 . Typically a displacement of  5  cm to either side of the plane is sufficient to enable each beam to be imaged. Alternatively, the lasers  30  may be staggered in the vertical direction so that the respective beams  32  are vertically offset. Where manifolds  20  are located on both sides of the substrate  10  as shown in  FIG. 2 , a camera  40  is required on each side in order to image the respective spray patterns. 
         [0022]    The camera  40  provides a continuous image to an image processing computer  42  located either within the camera  40  or remotely from the coating apparatus  12 . The images obtained by the camera  40  may be processed such as by a narrow band optical filter (not shown) to enhance the contrast between the image produced by the beam  32  and the background The  28  computer  42  processes the images and produces an output to a user interface  46 , from which the uniformity of the plume can be determined. The output may be either a pass/fail signal and/or an image that can be viewed by the operator, as shown in more detail in  FIG. 4 . 
         [0023]    In operation, the beam  32  is propagated through the spray patterns  24 , and with each of the nozzles  22  functioning correctly, will be uniformly scattered as the beam  32  is propagated. The scattering is induced by the physical characteristics of the spray pattern  24  and the resultant scattering will be viewed by the camera  40  as a bright horizontal band  50  as indicated in  FIG. 3(   a ). 
         [0024]    The collimator  31  collimates the beam  32 , to provide a uniform intensity line. The uniform beam width is useful because regardless of where the plume crosses the beam  32  the incident light intensity, and thus the scattered light intensity, is substantially constant. This substantially constant scattering facilitates the setting of detection thresholds in the camera  40  and computer  42  for monitoring the spray patterns  24  and plume. A standard beam having a Gaussian intensity distribution may be used but it is sensitive to alignment. If the plume wanders off the axis of the laser beam  32 , the incident light intensity drops off. This can lead to increased error in detecting disruptions in the spray pattern  24 . 
         [0025]    The camera  40  therefore obtains images and checks the images for the presence of such a horizontal band  50 . As will be described in more detail below with reference to  FIG. 5 , the image processing isolates the horizontal band  50  and determines the uniformity of the intensity along the horizontal extent of the sprayheads  18 . Discontinuities in the image are indicative of discontinuities on the sprayhead and therefore these may be monitored and correlated with malfunction of the nozzles  22 . 
         [0026]    Wherever discontinuity is detected, remedial action may be taken and the uniformity of the spraying restored. 
         [0027]    The image obtained from the camera  40  is formed from a matrix of pixels each having a discrete value associated with the intensity of the pixel. This format of image allows information on the spray pattern  24  to be extracted and utilized in the production process. 
         [0028]    The signal processing is performed using selected procedures from commercially available imaging software such as that available from DVT Frameworks. As shown in  FIGS. 4 and 5 , after the image is captured, initially the region of interest is isolated by defining a window  60 , and the distribution of the intensities associated with pixels within the defined window  60  is assessed. The windows may be preset in regions of the image where a plume is to be expected to facilitate automatic monitoring. Using the intensity distribution, a threshold to accord a light pixel versus a dark pixel is set. For example, those regions where scattering is present would be considered a light pixel and those where no scattering is present would be considered a dark pixel. Adjustment of the threshold may also accommodate different operating conditions, spray densities and distance from the camera  40 . 
         [0029]    Having established the threshold, the image is processed to look for regions of continuous brightness, typically referred to a “blobs”. This can be performed using the blob tools available on the commercial software to identify a number of blobs present in the window  60 . If there is a uniform distribution of spray along the sprayhead then a single blob would be detected indicating a continuous region of brightness from one end of the sprayhead  18  to the other as shown in  FIG. 3(   a ) (i.e. the horizontal band  50 ). If however, there is a blocked nozzle or a reduced spray in certain areas, as shown in  FIG. 3(   b ), then two or more blobs (e.g.  52  and  54  shown in  FIG. 3(   b )) will be identified indicating a discontinuity in the spray pattern  24 . Similarly, if no blobs are observed then either the laser  30  is faulty or there is no spray. The detection of a plurality of blobs or no blobs can then be used to signal a fault and initiate remedial action. 
         [0030]    It will be seen therefore that a simple monitoring of the propagation of the beam  32  in a spray pattern  24  formed by successive spray nozzles  22  provides an effective indication of the uniformity of the spray between separate nozzles  22 , and allows the malfunction of a nozzle  22  to be detected and corrected. The identification may be done manually or may be used automated through image processing techniques that allow an claim to be initiated for corrective action. The imaging software is of course integrated with the spray control so that it is only responsive when the spray is to be delivered. 
         [0031]    The system works best with a fine spray, as produced by an electrostatic sprayer (charging of the spray drops causes them to break up into finer drops than initially emitted from the nozzle), or other misting-type applicator. 
         [0032]    The system functions best with a fine spray because the spray plume is “optically thin”. This allows most of the light to pass through the plume and only a small fraction is scattered. Therefore a segment at the far end of the plume sees about the same light intensity, and scatters about the same fraction, as a plume segment near the beginning of the plume. The device may be used with other sprays with suitable compensation of the threshold to accommodate light absorption in the spray. 
         [0033]    Although the invention has been described with reference to certain specific embodiments, various modifications thereof will be apparent to those skilled in the art without departing from the spirit and scope of the invention as outlined in the claims appended hereto.