Abstract:
An article handling system and method comprising a flow path along which articles travel and a metal detection system to detect the passage of metal items along the flow path. The system has a metal detector test system to support a metal test piece and positively move it along the flow path, and a metal detector to detect the metal test piece.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
         [0001]    This application claims the benefit of British Application No. 0012994.0, filed May 26, 2000, in the British Patent Office, the disclosure of which is incorporated herein by reference.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to an article handling system comprising a flow path along which articles travel and a metal detection system to detect the passage of metal items along the flow path. The invention also relates to a method to monitor the performance of a metal detection system.  
           [0004]    2. Description of the Related Art  
           [0005]    Metal detection systems are used in a wide range of article handling systems to monitor the presence of metal items, particularly those for handling foodstuffs. If a metal item is detected, the system must be stopped to enable the item to be extracted.  
           [0006]    It is important to check the sensitivity and performance of the metal detection system. In conventional weighing systems in which articles such as potato chips are dropped generally vertically from a weighing machine to a packaging machine, the sensitivity of the metal detection system provided around the flow path is checked by dropping a metal test piece along the flow path. Conventionally, this has been done by manually dropping the test piece, which may be an iron or a stainless steel sphere, and determining whether or not the metal detection system senses the passage of the item. This is then repeated with spheres of different sizes. In view of the need to introduce the metal test piece into the flow path, it is conventional to stop the article handling system while the sensitivity check is carried out.  
           [0007]    There are a number of problems with the conventional systems. One of the most significant is the need to recover the test piece after the test. This is often difficult to achieve and will result in significant waste of bags and the like while the test piece is located. It is therefore important to monitor the output from the article handling system to ensure that the metal piece can be retrieved.  
           [0008]    Furthermore, particularly in the case of combination weighing machines, since the metal test piece is dropped through a relatively narrow opening, there is a risk that the test piece may be caught in the machine and will require significant time to be recovered. It is also important that the test piece passes a predetermined position to ensure that the sensitivity of the metal detection system is correctly adjusted. This is difficult to achieve with the conventional systems.  
           [0009]    U.S. Pat. No. 4,726,434 describes a method of checking the sensitivity of a metal detection system provided around a discharge chute of a combination weighing machine. A metal test piece is supplied to one of the weighers of a combination weighing machine and the processor ensures that at the correct time, this particular weigher is involved in the combination which is released. Nevertheless, it is still necessary to recover the test piece and to stop the weighing machine following the test cycle.  
         SUMMARY OF THE INVENTION  
         [0010]    Accordingly, it is an object of the present invention to provide an article handling system that overcomes the above disadvantages of the prior system. Additional objects and advantages will be set forth in part in the description which follows, and, in part, will be obvious from the description, or may be learned by practice of the invention.  
           [0011]    The foregoing objects of the present invention are achieved by providing an article handling system comprising a flow path along which articles travel and a metal detection system having a metal detector to detect the passage of metal items along the flow path. A metal detector test system supporting a metal test piece is located relative to the flow path to move the test piece along the flow path past the metal detector in order to detect the sensitivity of the detector.  
           [0012]    The foregoing objects may also be achieved with a method to monitor the performance of a metal detection system having a metal detector to detect the passage of metal items along a flow path of an article handling system that comprises controllably moving a metal test piece along the flow path and determining whether the metal detection system detects the metal test piece.  
           [0013]    Unlike the known arrangements, the present metal detector test system supports the metal test piece and positively moves it along the flow path. The problem of recovery is eliminated since the metal test piece remains supported by the test system while the test piece is moved in a predetermined manner so that an accurate position of the test piece relative to the metal detection system is obtained.  
           [0014]    Although the present method could be implemented while the article handling system is not operational, the metal test piece is moved along the flow path during normal operation of the article handling system. The advantage of this method is that typically, the articles themselves have some metallic qualities and therefore it is important that the metal detection system is not sensitive to the normal articles, but is still sensitive to the passage of rogue metal items. If the test is carried out in the absence of articles, then the metal detection system could be set at too sensitive a level. Of course, where the articles comprise (unwrapped) foodstuffs, it may be necessary to dispose of those articles which have passed along the flow path at the same time as the metal test piece. However, the advantage achieved by on-line monitoring exceeds this disadvantage.  
           [0015]    The metal detector test system could be implemented in a number of different ways. For example, the test system may comprise a fluid operated cylinder coupled to a probe supporting the test piece, and a control system to control the supply of fluid to the cylinder to force the probe to move the test piece along the flow path. The cylinder could be pneumatically or hydraulically actuated.  
           [0016]    In a second embodiment, the system comprises a linkage assembly comprising a number of links, pivoted together in a concertina arrangement, the test piece being supported on one of the links; and a control system to extend the linkage assembly to move the test piece along the flow path.  
           [0017]    In a third embodiment, particularly where the flow path extends in a substantially vertical direction, the test system comprises an elongate flexible line which can be lowered along the flow path to carry the test piece and a control system to control the payout of the line.  
           [0018]    In some cases, the metal test piece could remain in the flow path when not in use, even though it may contact the articles being handled. However, in many cases, this is undesirable and therefore preferably the metal detection test system is operable to move the test piece to a retracted position where it does not interfere with articles flowing along the flow path. In the case of a vertical flow path, this can be achieved by retracting the metal test piece to a position upstream of the point at which articles enter the flow path.  
           [0019]    Typically, the parts of the metal detection test system which can be brought into the vicinity of the metal detection system are non-magnetic. This minimizes the risk that items other than the metal test piece are used to adjust the sensitivity of the metal detection system.  
           [0020]    In general, the article handling system has a single metal detector test system. However, in some cases, more than one such system of either the same or different construction is provided. This enables the metal detector to be tested under different conditions without having to replace the test piece. For example, test pieces of different materials (iron, stainless steel, etc.) or different sizes could be provided on the different test systems.  
           [0021]    The present invention is applicable to a wide variety of article handling systems, but is particularly suitable for use with weighing machines, and most particularly in combinational weighing apparatuses. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]    These and other objects and advantages of the invention will become apparent and more readily appreciated from the following description of the preferred embodiments, taken in conjunction with the accompanying drawings of which:  
         [0023]    [0023]FIG. 1 is a schematic side view, partially cut away, of a first embodiment of the present invention;  
         [0024]    [0024]FIGS. 2A and 2B illustrate the metal detector test system of FIG. 1 in more detail and in two different positions;  
         [0025]    [0025]FIG. 3 is a schematic view of a second embodiment of the present invention;  
         [0026]    [0026]FIG. 4 is a schematic diagram of the control system of the present invention; and  
         [0027]    [0027]FIG. 5 is a flow chart illustrating the operation of the system shown in FIGS.  1  to  3 .  
         [0028]    [0028]FIG. 6 is a schematic side view, partially cut away, of another embodiment of the present invention.  
         [0029]    [0029]FIG. 7 is a flow chart illustrating the operation of an alternate embodiment of the present invention.  
         [0030]    [0030]FIG. 8 is a flow chart illustrating the operation of still another embodiment of the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0031]    Reference will now be made in detail to the present preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout.  
         [0032]    A combination weighing and counting apparatus  10  utilizing vibrating feeders is shown in a schematic side sectional representation in FIG. 1. The combination weighing and counting apparatus  10  is supported on a machine base frame BF, and articles transported by a supply conveyor  22  are supplied onto a center portion of a dispensing feeder  25  of a vibrating type through a supply chute  24 . A number (n) of vibrating feeders  1  ( 1 - 1  to  1 -n) are radially disposed around and in the vicinity of an outer periphery of the dispensing feeder  25  and are mounted on a frame F, which is in turn supported by the machine base frame BF, to receive articles dispensed radially outwardly from the dispensing feeder  25  while it is vibrated. The vibrating feeders  1  when vibrated at a predetermined amplitude and a predetermined frequency, cause the articles to move radially outwardly and then fall downward onto corresponding pool hoppers  26  ( 26 - 1  to  26 -n) that are arranged in a circular row on the frame F at respective locations immediately below radially outer ends of the vibrating feeders  1 .  
         [0033]    The articles transported by the vibrating feeders  1  are, after having been temporarily pooled in pool hoppers  26  ( 26 - 1  to  26 -n) and after discharge gates  27  ( 27 - 1  to  27 -n) of some of the pool hoppers  26  that have been selected according to a weighing operation have been subsequently opened, supplied onto weighing hoppers  28  ( 28 - 1  to  28 -n) that are also mounted on the frame F at respective locations immediately below and in alignment with the pool hoppers  26 . The weight of the articles within each of the weighing hoppers  28  is measured by a corresponding weight detecting unit  30  ( 30 - 1  to  30 -n) such as a load cell, from which a weight detection signal can be outputted. Based on this weight detection signal, a combination calculation is performed by a combination selecting unit  20  built in a control device. Some of the weighing hoppers  28 , which result in the total weight of the articles in those weighing hoppers  28  that fall within a tolerance range determined based on a target weight, are selected, followed by opening of discharge gates  29  ( 29 - 1  to  29 -n) corresponding to the selected weighing hoppers  28 , with the articles consequently collected onto associated collecting chutes  32 . The articles collected in the collecting chutes  32  are then discharged through a central chute  33  to a bagging or packaging machine  34  where they are packaged in a bag containing the articles of a total weight equal to or substantially equal to the target weight.  
         [0034]    The weighing hoppers  28  that have been emptied as a result of the weighing operation perform subsequent weighing operations after the articles have been supplied from the pool hoppers  26  during the subsequent weighing, and the vibrating feeders  1  that have supplied the articles into the emptied pool hoppers  26  are simultaneously driven. After a predetermined quantity of articles have been supplied onto the pool hoppers  26 , the associated vibrating feeders  1  terminate their delivery operation and are held in a stand-by state. The foregoing operation of the weighing and counting apparatus  10  is executed under the control of the control device  31 . Located about a narrow portion of the central chute  33  is a metal detector  35  in the form of a coil coupled with detection electronics  45 . The detection electronics  45  are connected to the control device  31 .  
         [0035]    In order to test the sensitivity of the metal detector  35 , a test piece  36  comprising small metal sphere is controllably moved into the central chute  33  in the vicinity of the metal detector  35  as can be seen in FIGS. 2A and 2B. This is achieved by connecting the metal sphere to a non-magnetic (typically acetal) probe  37  connected to a piston  38  (shown in FIG. 4) of a double acting piston/cylinder arrangement  39 . As can be seen in FIG. 4, the cylinder  52  of the arrangement  39  is connected via tubes  40 ,  41  at respective ends to a valve  42  which in turn is connected to a compressed air source  43 . By suitably controlling the valve  42 , compressed air can be supplied either through the tube  40 , to extend the probe  37  (as shown in FIG. 2A), or through the tube  41 , to retract the probe  37  (as shown in FIG. 2B). The position of the valve  42  is controlled via a solenoid  44  connected to the control device  31 . Other arrangements are possible, for example, the arrangement  39  could have a spring to bias the piston  38  towards one end and a single compressed air supply to act against the bias.  
         [0036]    [0036]FIG. 3 illustrates a modified embodiment in which the probe  37  is replaced by a “magic hand” or concertina arrangement of pivoted links  50  shown in solid lines in FIG. 3 in their retracted position, and in chain dotted lines  50 ′ in their extended position, with the test piece  36  below the metal detector  35 . The position of the magic hand is controlled by a piston cylinder arrangement  51  of similar form to the arrangement  39 . The metal test piece  36  is held on an arm  60  connected to the magic hand. FIG. 6 illustrates another embodiment, in which an elongate flexible line  100  is lowered along the path to carry the test piece.  
         [0037]    The general operation of the embodiment shown in FIG. 1 is similar to the operation of the embodiment of FIGS. 3 and 6, and will now be described with reference to FIG. 5. Initially, various parameters must be set up (step  100 ). These include the time during which the test piece  36  is to be located in its extended position, the time to bring the test piece to the test position, and the frequency at which the test is to be carried out. Typically, this frequency will be based on either a specified time interval or, the case of a packaging machine, upon completion of a certain number of bags (or both). For example, the test might be run every 1000 bags in a typical potato chip weighing/packaging system. The system will then start and the following steps will be carried out by the control device  31 . Initially, the device  31  determines whether or not weighed articles are being discharged (step  105 ). If they are, a cycle counter is decreased (step  110 ) and a comparison is made to determine whether the number of cycles since the last test is equal to the preset parameter (step  115 ). If it does, then the control device  31  actuates the solenoid  44  to connect the compressed air source  43  with the tube  40  to cause the probe  37  to move to its extended position shown in FIG. 2A (step  120 ). The probe is maintained in this position for the predetermined time and then retracted.  
         [0038]    The control device  31  monitors the output from the electronics  45  to determine whether or not the presence of metal is detected (step  125 ). If it is, the control device  31  stops operation of the apparatus  10  (step  130 ). This is because at the same time the test piece  36  was brought to the extended position, another, rogue metal item may have been fed through the central chute  33 . For safety, therefore, it is important that the machine is stopped. Once the operator has confirmed that the apparatus  10  is clear, he will restart it and processing returns to step  105 .  
         [0039]    If no metal is detected in step  125 , then an error condition has arisen. Again, the machine will be stopped (step  135 ) allowing any rogue metal items to be removed while at the same time the control device  31  resets the sensitivity of the detection electronics  45  to a more sensitive setting (step  140 ) and processing returns to start step  102 .  
         [0040]    If a test cycle has not been reached in step  115 , then the system will operate in a conventional manner to monitor the electronics  45  to sense for the presence of metal items and, if detected, to stop the machine in the same way as steps  135 ,  130 . It will be noted that in this case, whenever the test  36  piece is detected, the packaging machine  34  stops.  
         [0041]    In the embodiment of FIG. 7, if metal is detected in step  125 , then there are two options A, B which could be followed depending upon how the control device  31  is set up. In option A, a divider (not shown) is inserted into the chute  33  to prevent articles and any metal objects from passing into the currently formed package. The divider is then removed and processing returns to step  102 .  
         [0042]    In another option, option B, the control device  31  prevents a cutter within the packaging machine from operating on the current bag so that a double length bag is created. The next cut is made so that the double size bag is removed from the packaging machine and fed in a conventional manner to a check weigher (not shown) which not only monitors the weight of the bag but also checks its length. On sensing a double length bag, this will then be removed by blowing or pushing the bag off the feed line.  
         [0043]    In a further option, the packaging machine could be stopped with the double length bag retained in its jaws. An operator can then remove the double length bag and then restart the packaging machine.  
         [0044]    In some cases, the manner in which the probe  37  is extended in step  120  needs to be considered. Two options A, B are illustrated in FIG. 8. In option A, the probe is extended at a speed which matches the timing of the falling articles and the speed of those articles. Alternatively, in option B, the probe  37  is extended at a predetermined time after a discharge signal so that the probe is extended between the passage of successive articles, thus reducing the risk of any damage to those articles. Following option A, or option B, processing returns to step  125 .  
         [0045]    Although a few preferred embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.