Abstract:
An apparatus and method used to detect metallized containers or other objects in closed packages traveling in a conveyor stream. The apparatus includes a pair of coil units mounted in association with a packaging conveyor such that the closed packages will pass therebetween. Appropriate field generation circuitry are connected to the coil units for producing a magnetic field. When the metallized containers pass through the magnetic field, the impedance across the coils will vary. The varying impedance is measured continuously, thus giving an indication as to whether the metallized object has been detected. If the package is nonconforming, steps can be taken to automatically remove it from the conveyor stream.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates generally to quality control systems used with packaging conveyors in factory environments. More particularly, the invention relates to an apparatus and method for determining whether a closed package actually contains the desired contents.  
           [0002]    In the packaging of dry food products and the like, it is important to determine whether each box contains all of the desired contents. One approach used in industry to address this problem has been to weigh each closed package as it moves past a weighing station on a conveyor. If a particular package weighs less than a known threshold, it is assumed that all of the contents are not present. Appropriate action can then be taken, such as activation of an ejector mechanism to remove the defective product from the conveyor stream.  
           [0003]    While prior art weighing systems have been generally effective, they are not without disadvantages. For example, many dry food products, such as rice or pasta, will contain small seasoning packets having a weight less than the variance of the weighing system or the variance of the weight of one or more of the major components in the package. In this case, a weighing system would be unable to distinguish between a package with or without the small packet. In addition, it is often difficult to weigh individual packages that are constantly moving in a high-speed conveyor system. Weighing techniques are also unable to determine the position of the packed contents without opening the package.  
         SUMMARY OF THE INVENTION  
         [0004]    The present invention recognizes and addresses the foregoing disadvantages, and others of prior art constructions and methods. Accordingly, it is an object of the present invention to provide improvements in quality control techniques used with packaging conveyors.  
           [0005]    It is a further object of the present invention to provide an apparatus and method for use in detecting the contents of a closed package.  
           [0006]    It is an additional object of the present invention to provide an apparatus and method for detecting metallized containers in a closed package.  
           [0007]    It is a more particular object of the present invention to provide an apparatus and method for detecting metallized containers in closed packages moving rapidly in a conveyor stream.  
           [0008]    Some of these objects are achieved by providing an apparatus used in conjunction with a packaging conveyor to detect metallized objects in respective packages moving along a conveyor stream. The apparatus comprises at least one coil unit mounted in association with the packaging conveyor such that the respective packages pass adjacent thereto. Field generation circuitry is also provided, electrically connected to the coil unit. The field generation circuitry is operative to apply a signal to the coil unit for generating a magnetic field through which the respective packages will pass. Measurement circuitry is operative to measure electrical changes in the coil unit due to the metallized objects and produce an output indicative thereof.  
           [0009]    Other objects of the present invention are achieved by a method of detecting metallized objects in a closed package. One step of the method involves generating a magnetic field having a predetermined frequency. Next, the closed package is passed through the magnetic field. A change in the magnetic field due to presence of the metallized object is then detected. An output signal is then produced, indicative of the change in the magnetic field. In exemplary methodology, the output signal may be compared to predetermined levels. The results of the comparison can then be signaled for further use or processing.  
           [0010]    Still further objects of the present invention can be achieved by an apparatus for detection of a metallized object in a package. The apparatus comprises a pair of coil units mounted in parallel planes such that the packages can be passed therebetween. Field generation circuitry is also provided, electrically connected to the coil units. The field generation circuitry is operative to apply a signal thereto for generating a magnetic field in a region between the coil units. Measurement circuitry is operative to measure changes in an impedance of the coil units due to the metallized object.  
           [0011]    Other objectives, features and aspects of the present invention are provided by various combinations and subcombinations of the disclosed elements, as well as methods of practicing same, which are discussed in greater detail below.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    A full and enabling disclosure of the present invention, including the best mode thereof, to one of ordinary skill in the art, is set forth more particularly in the remainder of the specification, including reference to the accompanying figures, in which:  
         [0013]    [0013]FIG. 1 is a perspective view showing an apparatus for detecting metallized objects in a closed package in accordance with the present invention, installed in a packaging conveyor system;  
         [0014]    [0014]FIG. 2 is an elevational view taken along line  2 - 2  of FIG. 1;  
         [0015]    [0015]FIG. 3 is a cross-sectional view taken along line  3 - 3  of FIG. 1;  
         [0016]    [0016]FIG. 4 is an exploded view showing the construction of a single coil unit used in the apparatus of FIGS.  1 - 3 ;  
         [0017]    [0017]FIG. 5 is a perspective view of a detection apparatus in accordance with the present invention installed in an alternative conveyor system;  
         [0018]    [0018]FIG. 6 is a diagrammatic representation of a packaging conveyor system showing various additional features of the present invention;  
         [0019]    [0019]FIG. 7 is a block diagram of components of a detection system in accordance with a preferred embodiment of the invention; and  
         [0020]    [0020]FIG. 8 is a graph showing a continuous output of a detection system in accordance with a preferred embodiment of the invention. 
     
    
       [0021]    Repeat use of reference characters in the present specification and drawings is intended to represent same or analogous features or elements of embodiments of the invention.  
       DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0022]    It is to be understood by one of ordinary skill in the art that the present discussion is a description of exemplary embodiments only, and is not intended as limiting the broader aspects of the present invention, even though broader aspects are embodied in the present invention.  
         [0023]    [0023]FIG. 1 shows a stream of closed packages  10  moving down a conveyor  12  as in a typical factory setting. Often, each of the packages  10  may themselves includes several different types of contents. For example, dry food product such as rice or pasta will often be included within each of the packages  10 . Various metallized objects, such as metal cans  14  or foil seasoning packets  16 , may also be included.  
         [0024]    In order to ensure that adequate quality control standards are met, the conveyor includes an apparatus  18  for detecting whether the desired number of metallized objects are contained within each of the packages  10 . As will be described more fully below, packages  10  pass through a magnetic field generated by the apparatus  18  as they move down the conveyor (in the direction indicated by arrow A). The metallized objects cause known fluctuations in the magnetic field, the effects of which can be detected. If a particular package is found to be nonconforming, a suitable ejector mechanism, such as cylinder  20 , can be used to remove it from the product stream. In presently preferred embodiments, cylinder  20  may be a fluid-actuated cylinder, such as a hydraulic or pneumatic cylinder mechanism. It should be appreciated, however, that other suitable types of ejector mechanisms, such as magnetically and mechanically actuated cylinders, as well as various types of gates, may also be used to remove nonconforming product.  
         [0025]    Referring now also to FIG. 2, apparatus  18  may have a suitable device, such as a roller  24 , to determine whether a package  10  is physically present. Roller  24  pivots between a first lowered position and an upper raised position when a package  10  moves into the detection station of apparatus  18 . When roller  24  moves in this manner, a signal may be sent to indicate the presence of package  10 . One skilled in the art will appreciate that other mechanisms, such as a photoelectric cell, may also be used to signal the presence of an individual package.  
         [0026]    As can be seen in FIG. 3, apparatus  18  includes a pair of coil units  26  and  28  between which packages  10  will pass. As shown, the coil units are situated in parallel planes on opposite sides of conveyor  12 . Preferably, package  10  will pass approximately centered between coils  26  and  28 . As can be seen, coil units  26  and  28  will preferably have a size approximate to the size of packages  10 .  
         [0027]    In operation, coil units  26  and  28  generate a magnetic field  30  of a predetermined frequency. When the metallic object passes between coil units  26  and  28 , eddy currents are generated. The magnetic field produced by the eddy currents opposes the magnetic field produced by the coils  26  and  28 . These eddy currents cause a measurable fluctuation in the impedance of coil units  26  and  28 . Preferably, sensor electronics continuously measure the coil impedance to determine whether metallic objects have been detected.  
         [0028]    The use of two opposed and substantially identical coils in preferred embodiments of the invention will advantageously produce a magnetic field through package  10  that is nearly constant. As such, the output signal from apparatus  18  will show less dependence on the exact position of the package. Prior art metal detectors used by hobbyists, in contrast, have a single coil. These devices provide little information on the size, position or quantity of metallic objects.  
         [0029]    Referring to FIG. 4, one exemplary construction of coil unit  26  can be more easily explained. As can be seen, coil unit  26  includes a wire coil  32  wrapped around a core  34 . Often, it will be desirable to use a wire of at least 24 gauge, wound about core  34  by no more than about 200 turns. A pair of parallel plates  36  and  38  are situated on each axial end of core  34  to retain the coil  32  in position. Preferably, core  34 , as well as plates  36  and  38 , will be made from a suitable nonconductive and nonferrous material, such as LEXAN plastic or the like. The respective ends (collectively 40) of wire coil  32  are connected to appropriate circuitry to detect the presence of metal objects in packages  10  as they pass. While only coil unit  26  has been described in detail for purposes of brevity, it will be appreciated that coil unit  28  will be substantially identical.  
         [0030]    As used herein, the terms “conveyor” and “conveyor stream” should be construed broadly to include package travel paths generally, in addition to “conveyor belts” of the traditional type. For example, FIG. 5 illustrates an embodiment wherein coil units  26  and  28  are mounted on opposite sides of a vertical conveyor  42 . Vertical conveyor  42  moves packages  10  in the direction of arrow B, such that packages  10  pass between coil units  26  and  28 . As can be seen, conveyor  42  includes a pair of parallel belts  44  and  46  set apart from each other by a distance slightly less than the width of packages  10 . Belts  46  and  48  each have a plurality of deformable nubs, such as deformable nub  48 , which thus compress to retain packages  10  securely in position.  
         [0031]    [0031]FIG. 6 diagrammatically illustrates an overall control system constructed in accordance with the present invention. As shown, a weighing apparatus  50  measures the weight of package  10  and sends a signal to a control unit  52 . Weighing apparatus  50  is useful to determine whether the weight of package  10  is, within predetermined limits, what it should be. For example, dry food product, such as rice or pasta, will often constitute the bulk of the weight of package  10 . If the dry food product is not present, this will be detected immediately by weighing apparatus  50 .  
         [0032]    After being weighed, each of the packages  10  will travel along conveyor  12  to apparatus  18 . As described above, apparatus  18  will signal control unit  52  regarding the extent to which package  10  causes fluctuations in the magnetic field. If the particular package is found to be nonconforming, control unit  52  will send an actuation signal to ejector mechanism  20 . As a result, the package will be removed from the conveyor stream.  
         [0033]    [0033]FIG. 7 illustrates a block diagram of the electronics employed in an exemplary embodiment of apparatus  18 . As shown, apparatus  18  includes field generation circuitry  54  electrically connected to one or more coils  56  of the respective coil units. Field generation circuitry  54  applies a signal to coil  56  for generating a magnetic field through which the respective packages will pass.  
         [0034]    In this case, field generation circuitry  54  includes an oscillator  58  and a coil driver  60 . Oscillator  58  generates an electrical signal of the desired frequency of the magnetic field. Coil driver  60  receives the output of oscillator  58 , and applies it the coil units. The driving frequency, which will typically fall in a range from about 10 KHz to about 100 KHz, should preferably be optimized based on the specific characteristics of the coil unit and the packages to be detected. Coil driver  60  prevents the varying impedance of the coil unit from affecting the output frequency of oscillator  58 .  
         [0035]    As shown, apparatus  18  further includes measurement circuitry  62  for measuring electrical changes in the coil units due to the metallized objects. In the illustrated embodiment, measurement circuitry  62  includes an impedance measurement device  64  and an output driver  66 .  
         [0036]    Measurement circuitry  62  continuously measures impedance changes in the coil due to the generation of eddy currents in the metallized objects. Preferably, measurement circuitry  62  should respond rapidly to the change in impedance produced in the coils. Toward this end, numerous methods may be used. One example is an electronic bridge technique as used in proximity sensors. This technique generally requires a constant frequency, but high frequencies can be used. Another detection circuit is the Colpits oscillator which is often used in commercial metal detectors. Since the frequency in the absence of metal is fairly low, and the presence of metal is detected by a frequency shift, the response tends to be slow. By using a higher frequency, the Colpits oscillator can be made to respond more rapidly.  
         [0037]    Output driver  66  scales the output of impedance measurement device  64  to a convenient form for transmission to the control system. For example, output driver  66  may produce an output in the range of 0-10V or 4-20 ma, thus conforming to accepted industry standards. As described above, control unit  60  takes a continuous signal from the output driver  66  and determines whether the package is conforming or nonconforming to predetermined requirements.  
         [0038]    An example of a continuous output signal  68  from output driver  66  is depicted in FIG. 8. As can be seen, it has been predetermined that an output of less than about 8.270V (represented by line  70 ) corresponds to more than two foil seasoning packets. Fewer than two foil packets are present if the output is more than about 8.285V (represented by line  72 ). Output voltages between these thresholds correspond to exactly two foil packets.  
         [0039]    Each of the substantial peaks in signal  68  corresponds to the passage of one package  10 . As can be seen, this example recorded four packages of greater than two packets, as shown by the peaks  74 . Exactly two packets were also noted in four packages, as indicated by the peaks  76 . The remainder of the packages each contained fewer than two packets. While a negative peak was used in this example to note the presence of metallized objects, this is merely a matter of convention. It should be understood that positive peaks may also be used in accordance with the present invention to determine the presence or absence of various metallized objects.  
         [0040]    While preferred embodiments of the invention have been shown and described, modifications and variations may be made thereto by those of ordinary skill in the art. For example, the above example used a physical detector (e.g., roller) to determine whether a package was present in apparatus  18 . It should be understood, however, that the presence of a peak from an impedance measurement may also indicate the presence of a package to the system control unit.  
         [0041]    In addition, the apparatus of the preferred embodiment operates to detect the presence or absence of the metallized object. In other embodiments, however, it is contemplated that more sophisticated analysis of the impedance information can be performed. For example, it is believed that the techniques described herein can also determine whether a metallized object is in the correct orientation in the closed package.  
         [0042]    Accordingly, it should be understood that these and other variations of the disclosed embodiments are intended to be included within the scope of the appended claims. In addition, aspects of the various embodiments may be interchanged both in whole or in part. Furthermore, those of ordinary skill in the art will appreciate that the foregoing description is by way of example only, and is not intended to be limitative of the invention so further described in such appended claims.