Abstract:
Foreign metal inspection equipment is provided with: a conveying device for conveying a sample to be subjected to inspection; electrodes positioned so as to face the surface of the sample; a measurement device for measuring the capacitance between the electrodes and the sample being conveyed by the conveying device; and a processing unit that inspects for foreign metal mixed in the sample on the basis of the change in capacitance measured by the measurement device.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to an inspection of a defect of a sample and, in particular, relates to an inspection equipment and an inspection method for a metallic foreign object on metal. 
       BACKGROUND ART 
       [0002]    It is known that, in the manufacturing process of a lithium battery, electrode materials are kneaded and, thereafter, a positive electrode medium such as lithium cobaltate is applied onto both sides of aluminum foil, which is a positive electrode, and dried and a negative electrode medium such as carbon material is applied onto both sides of copper foil, which is a negative electrode, and dried. 
         [0003]    Here, when a battery is manufactured from the positive electrode and the negative electrode each having a respective medium applied thereto and dried (hereinafter, referred to as battery sheets), micro short-circuit occurs to deteriorate the battery performance significantly if a metallic foreign object is mixed in the battery sheet. Moreover, while the lithium battery is recently expected to be applied to electric vehicles, short-circuit might occur due to a metallic foreign object to cause catching fire or explosion and, thus, from a view point of preventing accidents caused by the lithium battery and of improving reliability, the importance of a metallic foreign object inspection with regard to a battery sheet is heightened. 
         [0004]    As a prior art regarding a method for a foreign object inspection in an electrode material of a lithium battery, Patent Literature 1 (JP-A-2005-183142) discloses “a detection method for a foreign object causing magnetic turbulence in an electrode material for a lithium secondary battery, the method characterized in detecting existence of a foreign object causing magnetic turbulence in an electrode material for a lithium secondary battery formed in a thin film with use of a device that detects magnetic turbulence due to a magnetic impedance effect” (in CLAIMS). 
         [0005]    Further, Patent Literature 2 (JP-A-2003-75412) discloses “a method for a defect detection for a film, the method characterized in, while applying a voltage in the thickness direction of the film with the rise time thereof being delayed, determining that the film contains a defect when a current flowing at this time exceeds a prescribed value.” 
       CITATION LIST 
     Patent Literature   
       [0006]    Patent Literature 1: JP-A-2005-183142 
         [0007]    Patent Literature 2: JP-A-2003-75412 
       SUMMARY OF INVENTION 
     Technical Problem  
       [0008]    With the method described in Patent Literature 1, when a moving speed of a magnetoresistive element is increased in order to detect a finer foreign object, it exceeds the response speed of a magnetic impedance sensor and, thus, the foreign object cannot be detected. Moreover, with the method described in Patent Literature 2, the only way to detect a finer foreign object is to increase the voltage and, thus, there are concerns on the destruction of an object to be inspected due to discharge and on the danger caused by high voltage. 
         [0009]    Further, when there is a roughness in the surface of a manufactured metal or a non-uniformity in the thickness of an applied and dried medium or in the density of the medium, it results in a noise component in detecting a finer foreign object, thus making it difficult to detect the foreign object. In the methods described in Patent Literature 1 and Patent Literature 2, no specific methods are disclosed for detecting a foreign object in the state where this noise component is present, and there is a need to additionally provide a means to suppress the noise component so that a foreign object is detected.  
         [0010]    Also, the manufacturing process needs to be monitored in order to manufacture a high quality metal. In order to monitor the manufacturing process, the position of a foreign object needs to be detected in addition to the existence of the foreign object; in the methods described in Patent Literature 1 and Patent Literature 2, a specific method regarding detection of the position of a foreign object is not disclosed and, thus, there is a need to additionally provide a measure capable of monitoring the manufacturing process. 
         [0011]    An objective of the present invention is to provide an inspection equipment and an inspection method that contribute to achieving high reliability in metal manufacturing by providing a means to detect a fine metallic foreign object on metal with high accuracy. Also, by providing an inspection equipment and an inspection method that detect the existence of a metallic foreign object and the position thereof, it is to implement monitoring of mixing of a foreign object in the metal manufacturing process and to achieve reduction in costs due to reduction of manufacturing defects by early revision of the process. 
       Solution to Problem  
       [0012]    The following explains briefly the outlines of typical inventions among the inventions disclosed in the present application. 
         [0013]    (1) An inspection equipment for a metallic foreign object comprises: a moving device which moves a sample that is an object to be inspected; an electrode arranged at a position facing a surface of the sample; a measurement device which measures an electrostatic capacitance between the sample, which is in move by the moving device, and the electrode; and a processing part which inspects a metallic foreign object mixed in the sample based on a change in the electrostatic capacitance measured by the measurement device. 
         [0014]    (2) An inspection method for a metallic foreign object comprises the steps of: moving a sample that is an object to be inspected; measuring an electrostatic capacitance between the sample and an electrode arranged at a position facing with respect to a surface of the sample, which is in move in the moving step; and processing to inspect a metallic foreign object mixed in the sample based on a change in the electrostatic capacitance measured in the measuring step. 
       Advantageous Effects of Invention  
       [0015]    According to the present invention, an inspection equipment and an inspection method which implement detection of a metallic foreign object on metal with high accuracy can be provided. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0016]      FIG. 1  is a configuration diagram of a first embodiment of a foreign object inspection equipment according to the present invention; 
           [0017]      FIG. 2A  is a diagram illustrating a detection principle of the first embodiment of the foreign object inspection equipment according to the present invention; 
           [0018]      FIG. 2B  is a diagram illustrating the detection principle of the first embodiment of the foreign object inspection equipment according to the present invention; 
           [0019]      FIG. 2C  is a diagram illustrating the detection principle of the first embodiment of the foreign object inspection equipment according to the present invention; 
           [0020]      FIG. 3  is a monitor view showing a result of defect detection by the first embodiment of the foreign object inspection equipment according to the present invention; 
           [0021]      FIG. 4  is a diagram illustrating a detection principle of a second embodiment of the foreign object inspection equipment according to the present invention; 
           [0022]      FIG. 5  is a diagram showing a configuration of electrodes of a third embodiment of the foreign object inspection equipment according to the present invention; 
           [0023]      FIG. 6A  is a diagram illustrating a detection principle of a fourth embodiment of the foreign object inspection equipment according to the present invention; 
           [0024]      FIG. 6B  is a diagram illustrating the detection principle of the fourth embodiment of the foreign object inspection equipment according to the present invention; and 
           [0025]      FIG. 7  is a diagram illustrating an arrangement of electrodes of the first embodiment of the foreign object inspection equipment according to the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0026]    Hereinafter, the embodiments of the present invention will be described in detail based on the accompanying drawings. In all the drawings for illustrating the embodiments, incidentally, the same reference sign is attached to the same element and repeated explanation thereof is omitted. 
       Embodiment 1 
       [0027]    A first embodiment of a foreign object inspection equipment according to the present invention is described using  FIGS. 1 to 3 . 
         [0028]      FIG. 1  is a configuration diagram of a first embodiment of the foreign object inspection equipment according to the present invention. 
         [0029]    The foreign object inspection equipment of this embodiment is configured to comprise: rollers  2  and  3  for transferring a sample (metal  1 ) that is an object to be inspected; a plurality of electrodes  4   a ,  4   b , . . . ,  4   n  arranged at positions facing a surface of the metal  1  transferred by the rollers  2  and  3 ; a detection circuit  10  that detects the existence of a foreign object by an electrostatic capacitance between each of the plurality of electrodes  4   a ,  4   b , . . . ,  4   n  and the metal  1 ; a counter circuit  13  that counts the number of pulses based on encoder pulses  12  generated by rotation action of the roller  3 ; and a user interface  15  that outputs whether or not a foreign object is present on the metal  1  and at which position a foreign object is using foreign object existence information  11  output by the detection circuit  10  and a position signal (sweep coordinate)  14  output by the counter circuit  13 . 
         [0030]    Here, the metal  1  is an object to be inspected and the present invention relates to a foreign object inspection equipment which detects defects and/or foreign objects present in the metal  1 . Here, the defects include scratches, cracks, and the like. 
         [0031]    The rollers  2  and  3  rotate so as to sweep the metal  1 . 
         [0032]      FIG. 7  is a diagram illustrating an arrangement of electrodes of the first embodiment of the foreign object inspection equipment according to the present invention. The arrangement of the electrodes is described using  FIG. 7 . The plurality of the electrodes  4   a ,  4   b , . . . ,  4   n  are arranged so as to face a surface of the metal  1  and are arranged side by side in a direction normal to a direction of sweep by the roller  2 .  
         [0033]    The detection circuit  10  detects respective electrostatic capacitance values of the plurality of the electrodes  4   a ,  4   b , . . . ,  4   n . The electrostatic capacitance is described later; it is a capacitance C obtained in accordance with the distance between the metal  1  and each of the electrodes  4   a ,  4   b , . . . ,  4   n . Further, after detecting the electrostatic capacitance value, it processes the detection value and sends to the user interface  15  the foreign object existence information  11  indicating whether or not a defect or a foreign object is present in the metal  1 . 
         [0034]    The counter circuit  13  counts the number of pulses based on the encoder pulses  12  generated by the rotation action of the roller  3 . Thus, it determines a position in the surface of the metal  1 , at which the electrostatic capacitance is being detected with the plurality of the electrodes  4   a ,  4   b , . . . ,  4   n , and sends the sweep coordinate facing the plurality of the electrodes  4   a ,  4   b , . . . ,  4   n  to the user interface  15  as a position signal. 
         [0035]    The user interface  15  displays whether or not a defect or a foreign object is present in the metal  1  and also its position if present based on the foreign object existence information  11  transmitted from the detection circuit  10  and the position signal (sweep coordinate)  14  transmitted from the counter circuit  13 . Incidentally, the output device of the user interface  15  may be a display used with an ordinary computer or a touch panel or may be via a communication means; regardless of the type of the device, it is not illustrated. Moreover, in the configuration of the foreign object inspection equipment shown in  FIG. 1 , it is clear that a user may set conditions for foreign object determination in the detection circuit  10  via the user interface  15  and it is not illustrated here; furthermore, an input function in the user interface  15  may be a keyboard used with an ordinary computer or a touch panel or may be an input function via a communication means and regardless of the type of the device it is not illustrated. 
         [0036]      FIGS. 2A to 2C  are diagrams illustrating a detection principle of the first embodiment of the foreign object inspection equipment according to the present invention. 
         [0037]    For simplicity of description, out of the foreign object inspection equipment, in which the plurality of the electrodes  4   a ,  4   b , . . . ,  4   n  shown in  FIG. 1  are arranged, a schematic configuration of the detection circuit  10  for one electrode ( 4   a ) is shown in  FIGS. 2A to 2C . The side views of a metal  1 , a foreign object  5  present on the metal  1 , the electrode  4   a  arranged so as to face a surface of the metal  1 , and the detection circuit  10  are shown. 
         [0038]    The electrode  4   a  arranged facing the transferred metal  1  is connected to a voltage source  102  via a resistor  103  equipped in the detection circuit  10 . While the metallic foreign object  5  is present on the metal  1  and is passing under the electrode  4   a , the gap between the metal  1  connected to the earth potential and the electrode  4   a  changes and a capacitance C configured with the metal  1  and the electrode  4   a  changes to C+ΔC as shown in  FIG. 2B . As the capacitance C changes, a charging/discharging current  101  to/from the electrode  4   a  flows as shown in  FIG. 2C  and a voltage Vdet is induced between the both ends of the resistor  103 . 
         [0039]    In the detection circuit  10 , an amplifier circuit  104  is connected to the both ends of the resistor  103  and amplifies the voltage Vdet induced by the change in the capacitance; in a comparator circuit  105 , the output voltage of the amplifier circuit  104  and a comparison voltage  106  are compared with each other and, when the output voltage of the amplifier circuit  104  is higher than the comparison voltage  106 , for example, it is regarded that a foreign object is present and a signal indicative of presence of a foreign object is output as the foreign object existence information  11 . 
         [0040]    In  FIG. 2A , for simplify of the explanation of the detection principle, a configuration has been described in which the induced voltage Vdet of the resistor  103  is amplified by the amplifier circuit  104 ; it is needless to say, however, that it may be configured by a current-voltage conversion circuit. Moreover, although in  FIG. 2A  an example is illustrated in which one comparison voltage  106  and the output voltage of the amplifier circuit  104  are compared with each other in the comparator circuit  105 , the comparison with a plurality of voltages may be employed or the comparison operation may be performed with sampling data using an analog-to-digital-conversion circuit. 
         [0041]      FIG. 3  is a monitor view showing a result of defect detection by the first embodiment of the foreign object inspection equipment according to the present invention. 
         [0042]    The electrode coordinate of the abscissa corresponds to the electrode coordinate that is the position of each of the electrodes  4   a ,  4   b , . . . ,  4   n  and the sweep coordinate corresponds to the electrode position on the swept metal  1  based on the position signal (sweep coordinate)  14  from the counter circuit  13 . 
         [0043]    In the screen, a black portion is a portion in which it is determined by the detection circuit  10  that a foreign object is present, and a white portion is a portion in which it is determined that a foreign object is not present. In this manner, by the user interface  15 , the existence of a foreign object and a coordinate position of a foreign object in the metal  1  can be known. 
       Embodiment 2 
       [0044]    A second embodiment of the foreign object inspection equipment according to the present invention is described using  FIGS. 4A to 4C . 
         [0045]      FIGS. 4A to 4C  are diagrams illustrating a detection principle of the second embodiment of the foreign object inspection equipment according to the present invention. 
         [0046]    In the following, differences from the detection principle of the first embodiment described with  FIGS. 2A to 2C  are mainly explained. In the foreign object inspection equipment shown in  FIG. 4A , the electrode  4   a , the surface of which facing the metal  1  is formed in an uneven shape of a periodic interval, is arranged, and the output from the electrode  4   a  is connected to a current-voltage conversion circuit  107 . As a foreign object  1  passes under the electrode  4   a , the capacitance formed with the electrode  4   a  and the metal  1  periodically changes between C and C+ΔC as shown in  FIG. 4B  and the charging/discharging current  101  flowing between the electrode  4   a  and the current-voltage conversion circuits  107  results in a periodic signal shown in  FIG. 4C . 
         [0047]    In the detection circuit  10 , an output signal of the current-voltage conversion circuit  107  is sampled by an analog-to-digital-conversion circuit  108  and addition operations are performed in an addition circuit  111  via delay circuits  110   a ,  110   b , and  110   c  arranged in a signal processing circuit  109 . In the case of a fine foreign object, the charging/discharging current is very small and, thus, detection becomes difficult due to influences of noises. 
         [0048]    It is generally known that addition processing of signals is effective in order to suppress influences of noises; based on the periodic signal generated from one foreign object, influences of noises in signal detection can be suppressed by delaying the signal sequentially with the delay circuits  110   a ,  110   b , and  110   c  and performing addition processing. Subsequently, in a decision circuit  112 , the output of the addition circuit  111  is compared with a foreign object threshold value  16  from the user interface  15  (not shown) and the foreign object existence information  11  is output to the user interface  15 . 
       Embodiment 3 
       [0049]    A third embodiment of the foreign object inspection equipment according to the present invention is described using  FIG. 5 . 
         [0050]      FIG. 5  is a diagram showing a configuration of electrodes of the third embodiment of the foreign object inspection equipment according to the present invention. 
         [0051]    In the following, differences from the detection principle of the second embodiment described in  FIG. 4  are mainly explained. The electrode  4   a  shown in  FIG. 5  is made so that its side facing the metal  1  is formed in an uneven shape of a periodic interval and it is further formed in a ring shape, and the charging/discharging current  101  to/from the electrode  4   a  is converted into a voltage by the voltage-current conversion circuit  107 . Here, by letting a time for the foreign object  5  present on the metal  1  to pass under one of convex portions of the electrode  4   a  be Δt, a change in the capacitance configured with the metal  1  and the electrode  4   a  be ΔC, and a potential difference between the metal  1  and the electrode  4   a  be V, the charging/discharging current Δi flowing in the electrode  4   a  is expressed by the following Math. 1. 
         [0000]      [MATH. 1] 
         [0000]      Δ i=ΔCΔV/Δt.   (1)
 
         [0052]    Accordingly, when a foreign object is minute as it passes under the electrode  4   a , the change amount of the capacitance ΔC becomes small and, if the potential V and a time to pass Δt are constant, consequently, the charging/discharging current Δi becomes small so that detection of a foreign object becomes difficult. In the present embodiment, by rotating the electrode  4   a  formed in a ring shape in the direction opposite to the sweep direction of the metal  1  with a rotating mechanism (not shown) and reducing the time Δt for a foreign object to pass under one of convex portions of the electrode  4   a , the charging/discharging current Δi can be increased even when the foreign object is minute so that detection of a fine foreign object can be implemented. 
       Embodiment 4 
       [0053]    Using  FIGS. 6A and 6B , a fourth embodiment of the foreign object inspection equipment according to the present invention is described. 
         [0054]      FIGS. 6A and 6B  are diagrams illustrating a detection principle of the fourth embodiment of the foreign object inspection equipment according to the present invention. 
         [0055]    In the detection circuit  10  shown in  FIG. 6A , current-voltage conversion circuits  107   a ,  107   b , and  107   c  connected to a plurality of electrodes (not shown) are arranged and charging/discharging currents  101   a ,  101   b , and  101   c  are converted into voltages, respectively. Subsequently, in subtraction circuits  113   a ,  113   b , and  113   c , the output voltages of the current-voltage conversion circuits  107   a ,  107   b , and  107   c  are subject to subtraction processing. 
         [0056]    For example, in the subtraction circuit  113   b , a voltage Va is obtained from an output voltage V 1  of the current-voltage conversion circuit  107   a  and an output voltage V 2  of the current-voltage conversion circuit  107   b  through subtraction processing. In comparator circuits  114   a ,  114   b , and  114   c , the respective output voltages of the subtraction circuits  113   a ,  113   b , and  113   c  are compared with a comparison voltage  115 , the existence of a foreign object is determined in a foreign object determination part  116  based on the outputs of the comparator circuits  114   a ,  114   b , and  114   c , and the foreign object existence information  11  is output to the user interface  15  (not shown). 
         [0057]    When there is a roughness in the surface of the metal  1  or when there is a non-uniformity in the thickness or a non-uniformity in the density of the medium applied to the metal  1  and dried, the output voltages of the current-voltage conversion circuits  107   a ,  107   b , and  107   c  become signals as indicated by V 1 , V 2 , and V 3  of  FIG. 6B  and it thus becomes difficult to detect a fine foreign object. By taking differences of the detection signals V 1 , V 2 , and V 3  between adjacent electrodes in the subtraction circuits  113   a ,  113   b , and  113   c , signals Va and Vb with signal components other than that of a foreign object suppressed are generated, so that existence of a foreign object can be detected in the foreign matter determination part  116  from Vcmp_a and Vcmp_b, which are the results of comparison with the comparison voltage  115  in the comparator circuits  114   a ,  114   b , and  114   c.    
         [0058]    With the foreign object inspection equipment and the inspection method according to the present invention, detection of a fine metallic foreign object on a metal with high accuracy can be implemented and reliability of metal manufacturing can be improved. Also, monitoring of mixture of a foreign object in metal manufacturing process can be realized and cost reduction due to reduction of manufacturing defects by an early revision of the process can be implemented. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           1  metal to be inspected 
           2 ,  3  rollers 
           4   a ,  4   b , . . . ,  4   n  electrodes 
           5  foreign object 
           10  detection circuit 
           11  foreign object existence information 
           12  encoder pulses 
           13  counter circuit 
           14  position signal 
           15  user interface 
           16  foreign object threshold value 
           101 ,  101   a ,  101   b ,  101   c  charging/discharging currents 
           102  voltage source 
           103  resistor 
           104  amplifier circuit 
           105  comparator circuit 
           106  comparison voltage 
           107 ,  107   a ,  107   b ,  107   c  current-voltage conversion circuits 
           108  analog-to-digital-conversion circuit 
           109  signal processing circuit 
           110   a ,  110   b ,  110   c  delay circuits 
           111  addition circuit 
           112  decision circuit 
           113   a ,  113   b ,  113   c  subtraction circuits 
           114   a ,  114   b ,  114   c  comparator circuits 
           115  comparison voltage 
           116  foreign object determination part