Abstract:
A method and apparatus for detecting the presence of water on a surface of an object using infrared radiation. A surface area to be detected is illuminated with infrared radiation having a wavelength substantially absorbed by water. An optical system is employed to view images reflected from the surface area. An optical bandpass filter is disposed between the surface area and the sensor to limit transmission of infrared light to within a specific range of wavelengths known to be strongly absorbed by water. The sensor assembly produces a signal representative of the intensity of the reflected light. If the intensity signal is lower than a predetermined level water is detected and the signal may be used to trigger alarms, record the event or otherwise control the environment of the object. The present invention is particularly suited for detecting the presence of water on a moving sheet of metal during a manufacturing process.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention is directed to a method and apparatus of detecting water of the surface of an object, and more particularly, to the use of radiant energy, for example, infrared light, to detect water on a surface of a moving sheet of metal.  
         BACKGROUND OF THE INVENTION  
         [0002]    Within the steel industry, many different types of steel strips are produced, often with various coatings ranging from other metals such as for example, tin, zinc, and zinc alloy, to organic protective layers. The different processing steps involved in manufacturing such a variety of different coated steel sheet products requires the strip to be uncoiled and recoiled many times. The uncoiled strip is often deliberately exposed to water or water containing components during the manufacturing process. If water accidentally remains on the strip when it is recoiled, the remaining water will cause various types of oxides to form within the coil windings, the formed oxides reducing product quality and sometimes ruining the entire steel sheet coil. Therefore, the presence of water must be avoided in coiled steel sheet product because the presence of water will lead to product loss at a considerable cost to the manufacturer.  
           [0003]    [0003]FIG. 1, labeled Prior Art, shows the rinse section  1  of a typical continuous coating line. The steel sheet  3  is shown exiting a scrubber tank  5 , moving through hot air dryers  1  &amp;  13 , and entering a coiler  7  where the steel sheet product is coiled for further processing or packaged for customer shipping. In a high speed coating line, the steel sheet product  3  travels at speeds of up to 3000 feet per minute. The fast moving sheet exits the scrubber tank  5 , is sprayed with an oil/water emulsion at sprayer  9 , and the strip passes through a set of wringer rollers  11  where excess water is “squeezed off” or removed from the product surface. To further insure that all water is removed from the steel sheet surface, the sheet product  3  passes between a plurality of hot air dryers  1  &amp;  13  before reaching tension bridle rolls  7  of the coiler. At the higher speeds encountered in modem coating lines, the wringer rolls  11  are less effective at removing excess water from the product surface. As a result, there is a vary real possibility of having water present on the steel sheet surface when the strip  3  enters coiler (not shown).  
           [0004]    State-of-the-art systems employed to remove the water occasionally fail to operate properly resulting in inferior product. Thus, it is desirable to have a system that automatically and non-invasively detects the presence of water on the moving steel sheet or strip  3 , which heretofore has been void in the art. Previously, the only known method of detecting water was to manually hold a tissue or other water absorbent material on the surface of the steel sheet as it moved toward the coiler, and visually inspect the tissue for evidence of moisture. However, such a method is dangerous, inconsistent, and impractical.  
           [0005]    It is known in the prior art to detect defects on a moving body such as a cold rolled strip. U.S. Pat. No. 3,734,628 discloses a method and apparatus for detecting defects in strip product, and the 3,734,628 patent is incorporated herein by reference. The &#39;628 reference teaches coating the strip with a film of oil, and the apparatus scans the surface with infrared light, having a specified wavelength range capable of penetrating the oil to detect underlying defects. However, such a method and apparatus for detecting defects is not suited for detecting the presence of water on a steel sheet surface moving at high speed.  
           [0006]    U.S. Pat. No. 5,684,296 discloses using infrared light to detect the presence of a liquid, and the 5,684,296 patent is hereby incorporated herein by reference. However, this application is incompatible with the use of electronic sensors and requires the optical device to come into contact with the liquid. Therefore, the 296 patent does not have practical application as a non-invasive system for the detection of water, and in particular, for the detection of water on a continuous moving metal sheet.  
           [0007]    Additional methods and apparatus to detect water in other environments are also known in the art. However, these prior art applications have no practical application for detecting water on a surface of an object as in the present invention.  
           [0008]    Generic methods and apparatus to scan objects with infrared light or other light are well known in the art and are disclosed in various forms in the following references, U.S. Pat. Nos. 5,929,996; 5,835,220; 5,761,999; 4,005,926; and 3,825,351, all of which are incorporated herein by reference.  
           [0009]    Therefore, as clearly illustrated above, there is a long felt need within the industry to provide a non-invasive method and apparatus for detecting the presence of water on a surface of an object, and particular, there is a long felt need to provide a method and apparatus capable of detecting the presence of water on the surface of a continuous steel sheet moving at a high speed in a manufacturing operation.  
         SUMMARY OF THE INVENTION  
         [0010]    The present invention is directed to a method and apparatus for detecting the presence of water on a surface of an object using radiation. A surface area to be detected is illuminated with radiation having a wavelength substantially absorbed by water. An optical system is employed to view images reflected from the surface area. A bandpass filter is disposed between the surface area being monitored and the sensor to limit transmission of radiation to within a specific range of wavelengths known to be strongly absorbed by water. Thus, areas having no water will appear brightly illuminated and the reflected radiation more intense and areas where water is present will appear dark, the reflected radiation being less intense. The sensor assembly produces a signal representative of the intensity of the reflected radiation. If the intensity signal is lower than a predetermined level, water is detected and the signal may be used to trigger alarms or otherwise control the environment of the object. The present invention is particularly suited for detecting the presence of water on a moving strip of metal during a manufacturing process. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    The above and other objects and advantages and novel features of the present invention will become apparent from the following detailed description of the preferred embodiment of the invention illustrated in the accompanying drawings, wherein:  
         [0012]    [0012]FIG. 1 (Prior Art) is a schematic view showing the rinse section in a continuous coating line.  
         [0013]    [0013]FIG. 2 is similar to FIG. 1 and shows one embodiment of the water detection apparatus of the present invention.  
         [0014]    [0014]FIG. 3 is a view showing scanner assemblies employed to sense reflected light.  
         [0015]    [0015]FIG. 4 a view taken along the lines  4 - 4  of FIG. 2 showing an array of detectors to sense light reflected from the steel sheet surface.  
         [0016]    [0016]FIG. 5 is a circuit diagram of a high band pass filter amplifier.  
         [0017]    [0017]FIG. 6 is a closed loop circuit diagram of a thermoelectrically cooled sensor. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0018]    The present invention is directed to sensing the presence of water on the surface of an object by using reflected radiation, for example, light. In the preferred embodiment, the presence of water is detected by using reflected infrared light because infrared light has a wavelength substantially absorbed by water. However, it should be understood, that other energy sources and wavelengths that are similarly absorbed by water may be used to detect water without departing from the scope of this invention. The infrared light is directed onto the strip, and if water is present, a substantial amount of the infrared light will be absorbed. Consequently, the intensity of the infrared light reflected from the strip surface will be less than the irradiated infrared light. A “substantial amount” of infrared red light absorbed by water simply means that a sufficient amount of light is absorbed by the water to detect a noticeable change in the intensity between the irradiated and reflected light.  
         [0019]    Infrared light of different wavelengths has different transmittance and absorption rates through different mediums. For water, there are several strong absorption bands. Specifically, wavelength bands within a range from 1-2 microns, 2.5-3.5 microns and 6-7 microns are strongly absorbed by water. Therefore, infrared light having wavelengths within the cited ranges will have a reduced intensity after reflection through water. It has been demonstrated that infrared light having a wavelength in a range from 2.7-2.9 microns is particularly suited to detect the presence of water and is the preferred wavelength range for detecting water according to the present invention.  
         [0020]    The method of the present invention includes providing an infrared light source having a wavelength that is substantially absorbed by water, the infrared light being irradiated/directed onto a surface of the object being monitored for the presence of water. The infrared light is reflected off the surface is of the object and sensed. A signal is produced representative of reflected light intensity and compared to the irradiated/directed light intensity. If the reflected light intensity is less than the irradiated/directed light intensity by a predetermined amount, a presence of water is detected. If the reflected light intensity is substantially, for example, equal to or about the same as the directed/irradiated light intensity, no water is detected. The following apparatus, that also forms part of the present invention, provides means for carrying out the steps of the aforementioned method for detecting the presence of water on the surface of a moving object.  
         [0021]    [0021]FIG. 2 represents a steel sheet or strip  3  in a continuous high speed manufacturing line similar to the prior art described in FIG. 1, and a mechanism to automatically and non-invasively detect the presence of water on the steel sheet  3 . An energy source, and in particular, an infrared light source  21 , such as a quartz infrared heater, is positioned above a stabilized, for example, not fluttering portion of the strip proximate a roller  23  supporting a direction change in the conveyed strip  3 . In the preferred embodiment, a pair of longitudinally extending infrared heaters  21 , each having a parabolic reflector  25 , extend across the width of strip  3  so that the strip is sufficiently illuminate across its width. It is to be understood that one of ordinary skill in the art can employ other sources of infrared light within the pre-described wavelength range or other wavelength ranges, the details of which need not be further discussed.  
         [0022]    A sensor assembly  27  is positioned to receive light reflected from the surface area being monitored for the presence of water. In the preferred embodiment shown in FIG. 2, sensor assembly  27  is positioned between the infrared illuminators  21  and is disposed above the strip  3  to sense infrared light reflected off the surface of the steel sheet  3 . As the steel sheet  3  is conveyed beneath sensor assembly  27 , the entire width of the strip  3  is continuously illuminated by the infrared light source  21 . The sensor assembly  27  is adapted to sense light that is reflected across a width portion of the conveyed sheet  3 . Therefore, the system facilitates continuous monitoring to detect water on the entire surface area of the continuous moving sheet  3 . The sensor assembly  27  may be integrated with a computer system or other control device (not shown) for further processing or control to initiate an alarm, mark portions of the sheet where water is detected, control the speed of the conveyed strip  3 , record the frequency of water detection or even shut down strip movement. Other events are also contemplated by the present invention.  
         [0023]    [0023]FIG. 3 represents one embodiment of the sensor assembly according to the present invention. In the present embodiment, the surface of the steel sheet  3  is scanned with polyhedral rotating mirrors  51  that receive and direct reflected light into a detector box  53 . As the polyhedral mirror  51  rotates, each side or mirror surface will scan a portion of the strip width. Depending on the sheet in combination with the window size or scan width covered by a scanning mirror  51 , a plurality of rotating scanning mirrors  51  may be needed to scan the full sheet width. FIG. 3 depicts two such rotating polyhedral mirrors  51  driven by a motor  55  in coordination with the moving sheet  3 . The relationship of the lateral scanning of the rotating mirrors  51  and displacement of the strip  3  will cause each side  51   a  of each mirror  51  to scan an angled portion of the strip  3 . As each mirror  51  rotates exposing a subsequent side  51   b , an immediately adjacent parallel portion of the strip  3  is sensed. Thus, the entire length, as well as the width, of the moving steel sheet  3  is continuously scanned. The plurality of scanning mirrors  51  is arranged to slightly overlap a scan area to ensure that the entire width of the strip  3  is scanned. A screen  52  having openings or windows  54  may also be employed to limit the amount of reflected light reaching each scanning mirror  51 . Depending on the overall sheet, any number of scanning mirrors may be used to cover the fill sheet width. In the present embodiment, only two scanning mirrors are shown being used to scan the full width of sheet  3 , each scanning mirror  51  being attached to a motor and rotated at a speed of 3000 rpm. The combination of a five-sided polyhedral mirror rotated at 3000 rpm results in a scanning rate of 15000 scans per minute. The scanning mirrors receive and redirect reflected light from the sheet surface and onto a sensor  59  housed within detector box  53 . It is to be understood, however, that one of ordinary skill in the art may change the rotational speed and arrangement of the scanning mirrors  51  in response to the size and speed of a moving strip  3  so that the entire surface of a particular moving strip  3  is scanned and monitored to detect the presence of water.  
         [0024]    The detector box  53  includes a band pass filter  57  that selectively limits the light falling on sensor  59  to a pre-described wavelength range. As previously mentioned the preferred range of wavelengths is from 2.7-2.9 microns. A lens  61 , such as, for example but not limited to, an adjustable focus calcium fluoride lens, is employed in conjunction with a pinhole stop  63  to focus the reflected light onto the sensor  59 . An exemplary thermoelectrically cooled sensor such as the J12 series of Indium Arsenide photovoltaic infrared diodes produced by Judson Technologies, may be used to receive and convert the reflected light or radiation  56  to an electrical signal, the output signal being responsive to the reflected light intensity. An amplifying circuit, such as the exemplary circuit shown in FIG. 5, amplifies and converts the output signal from sensor  59  to a voltage signal suitable for communication with a computer or other control device. Sensor  59  is also preferably cooled as indicated in the circuit shown in FIG. 6.  
         [0025]    Referring to FIG. 4 showing an alternate embodiment of the present invention, instead of using rotating mirrors  51  to scan a target surface area, a linear array  150  of sensors  159  is arranged to receive radiation reflected from a target surface area  100  that extends across the entire width W of the sheet  3 . An image  101  of the target surface area is projected onto the linear array of sensors  159  using a suitable optical system known to one skilled in the art. Depending on the size of width W, and depending on the window area of each sensor  159  within array  150 , the number of sensors within an array will vary in order to monitor the entire sheet width. As in the previous embodiment, sensors  159  will receive reflected radiation through an optical system having an associated filter  160  to limit the transmission of light to a selected wavelength, and an optical lens  161 , stop  162  and pinhole aperture  163  arrangement capable of focusing the reflected light image  101  onto the linear array  150  and a filter (not shown) to limit the transmission of infrared light to within the aforementioned pre-described wavelength ranges.  
         [0026]    It should be understood that FIG. 4 is a schematic representation of the alternate embodiment as a detailed depiction of each of the many sensors and corresponding filters and optical lens is not practical. It is also to be understood that one of ordinary skill in the art can arrange an array  150  of sensors  159  to view or monitor the entire width W of the strip. For example, if a 30 inch wide steel sheet is being monitored to detect the presence of water, a suitable linear array should comprise 64 elements with each sensing element connected to an amplifying circuit in combination with an associated optical system including a filter and lens. Of course, two or more sensor arrays and optical systems may be used to improve image resolution without departing from the scope of this invention.  
         [0027]    While the foregoing invention has been shown and described with reference to a preferred embodiment, it will be understood by those possessing skill in the art that various changes and modifications may be made without departing from the spirit and scope of the invention.