Abstract:
A coin sensor is provided for more accurately assessing the authenticity of a coin passing through a vertical channel where the channel is sized to accommodate different diameter coins. In the present invention, magnetic coils are deployed on the side of the channel to measure magnetic flux, which is converted to digital signals and compared to stored values to assess the diameter, thickness, and material of the coin. To reduce the tolerances associated with the varying path of the coin, the sensors have been provided with cores having generally straight and parallel upper and lower surfaces aligned perpendicular to the path of the coin to remove the variances in the overlapping coin area as the coin.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates generally to coin sensors for validating a coin in a coin accepting machine, such as a vending machine, and more particularly to a sensor for evaluating the diameter of the coin. For purposes of the following disclosures, the term “coin” is used generally to refer to monetary coins, tokens, and the like.  
           [0003]    2. DESCRIPTION OF THE RELATED ART  
           [0004]    A coin sensor and a decision circuit of a coin selector are detailed with reference to FIGS. 18 and 19. The sensor is formed within a body  50  and includes a coin acceptance slot  51  leading to a coin passage  52 . The coin passage  52  is comprised of peripheral guidewalls  53 ,  54  and sideplates  55 ,  56 . The sideplates  55 ,  56  extend parallel to a diameter of the coin C, and the guidewalls  53 ,  54  are located at opposed ends of the sideplates as shown in FIG. 19 to form a rectangular profile. A line L illustrating the path of the coin C lies in the vertical direction.  
           [0005]    The distance between the peripheral guidewalls and between the sideplates are selected to accommodate several different sizes of coins. Accordingly, the space between the peripheral guidewalls  53 ,  54  is slightly larger than the largest diameter coin anticipated to be used in the sensor. Similarly, the space between the sideplates  55 ,  56  is slightly larger than the thickness of the largest coin that is to be used.  
           [0006]    A first coin sensor  57  is located on a horizontal line M that intersects the path line L in a perpendicular manner. The coin sensor  57  lies along the coin passage  52  adjacent the sideplate  55 . Sensor  57  comprises a wound coil  57 C about a cylindrical core  57 B. The core  57 B is preferably made of a ferromagnetic material, such as ferrite.  
           [0007]    A sensor  60  is fixed opposite the sensor  57  on sideplate  56 . Sensor  60  comprises a wound coil  60 C about a cylindrical core  60 B. Another sensor  61  is mounted on the sideplate  55  adjacent the peripheral guidewall  54 . The center of sensor  61  is also located on line M. Sensor  61  comprises a wound coil  61 C about a cylindrical core  61 B. Sensor  62  is mounted opposite sensor  61  at sideplate  56 . Sensor  62  comprises a wound coil  62 C about a cylindrical core  62 B. The sensor pair  57 ,  60  cooperate to form a coin left end sensor  63  used to determine the relative area of the left end of the portion of coin passing by sensor  63 . Similarly, the pair of sensors  61 ,  62 , cooperate to form a coin right end sensor  64  and is used to determine the relative portion of the coin passing by the right end sensor  64 .  
           [0008]    Sensors  65 ,  66  lie along path line L and is offset from line M. Sensors  65 ,  66  are similar in structure to sensor  61  in that each sensor  65 ,  66  includes a coil  65 C,  66 C, respectively, wound about a cylindrical core  65 B,  66 B, respectively. The sensors  65 ,  66  constitute a material sensor  67  and a thickness sensor  68 .  
           [0009]    A coil  65 D is wound around the outside of coil  66 C. The coil  65 D is connected to the coil  66 C. Similarly, the coil  65 D is connected to the coil  66 D. The thickness sensor  68  comprises the coil  65 C wound about the core  65 B and  66 B. The material sensor  67  comprises the coil  65 D and  66 D about the respective core  65 B and  66 B. A beginning end of coil  57 C is connected with a termination end of coil  61 C. The termination end of coil  57 C is connected with the termination end of coil  60 C. A starting end of the coil  60 C is connected with a termination end of coil  62 C. A starting end of the coil  62 C is connected to an oscillation circuit  70 , and a starting end of the coil  61 C is connected to the oscillation circuit  70 .  
           [0010]    The end of the coil  65 C of the thickness sensor  68  is connected to the oscillation circuit  71 . A starting end of the coil  65 C is connected to the termination end of the coil  66 C of the sensor  66 . A starting end of the coil  66 C is connected to the oscillation circuit  71 .  
           [0011]    A starting end of the coil  65 D of the material sensor  67  is connected to the oscillation circuit  69 . A termination end of the coil  65 D is connected with the termination end of the coil  66 D of sensor  66 . A starting end of the coil  66 D is connected to the oscillation circuit  69 . The oscillation circuit  69  if connected with a detection circuit  72 . An oscillation circuit  70  is connected to a detection circuit  73 . The oscillation circuit  71  is connected with the detection circuit  74 .  
           [0012]    The detection circuit  72 ,  73 ,  74  are respectively connected to a control circuit through AD connection circuits  75 ,  76 ,  77 . The control circuit comprises a microprocessor  78 . The unit also includes a reject board  80  which obliquely crosses the path line L of the coin passage  52 .  
           [0013]    The coin C is deflected by the reject board  80  when the reject board  80  protrudes in the pathway defined by the coin passage  52 . A coin return (not shown) is found at the end of the rejection passage  81 .  
           [0014]    The movement of the reject board  80  is controlled by a spring (not shown) generally, which biases the position of the reject board  80  into and out of the pathway of the coin passage  52 . The control is governed by a solenoid  82  excited by the signal of the microprocessor  78 , when the microprocessor determines that the coin is unacceptable. By the excitation of the solenoid  82 , the reject board  80  is withdrawn from the coin passage  52  when it is determined that the coin is acceptable. In this case, the coin falls past the reject board  80  into a coin collection unit (not shown).  
           [0015]    The foregoing describes a coin sensor which may be used, for example, in a vending machine. A coin C dropped into the receiving slot of a vending machine reaches the coin passage  52 . As the coin falls vertically, the coin passes left end sensor  63  and right end sensor  64  to varying extents depending on the path of the coin, i.e., whether the coin falls down the center or toward one side. As the coin passes the sensors, a high frequency is applied from the oscillation circuit  70  to the coil  57 C and  60 C of the left end sensor  63  and the coil  61 C and  62 C of the right end sensor  64 . A resultant magnetic flux is generated at the cores  57 B,  60 B,  61 B and  62 B. The magnetic flux from each core extends into the coin passage  52 . Eddy currents are generated in the coin C when the coin (an electrical conductor) passes through these magnetic flux. As a result, the magnetic flux of the coils  57 C,  60 C,  61 C and  62 C are reduced.  
           [0016]    The loss of flux due to the passing of the coin causes a change in the output of the oscillation circuit  70 . The flux loss is proportional to the relative area of the coin C adjacent the respective cores  57 B,  60 B, and  61 B,  62 B. The detection circuit  72  converts an output of the oscillation circuit into a voltage. The AD conversion circuit  75  output of the detection circuit  73  is converted into a digital value that is transmitted to microprocessor  78 .  
           [0017]    Similarly, a magnetic flux arising in the coil  65 C at the core  65 B is affected by the thickness of the coin C. A magnetic flux arising from the coil  66 C at the core  66 B is affected by the thickness of the coin C. As a result, an output of oscillation circuit  71  changes. The digital circuit  74  converts an output of the oscillation circuit  71  into a voltage. The AD conversion circuit  77  output of the detection circuit  74  is converted into a digital value, and is transmitted to the microprocessor  78 .  
           [0018]    A magnetic flux generated by the coil  65 D at core  65 B is affected by the material at the interior of the coin C. Similarly, a magnetic flux generated by the coil  66 D at the core  66 B is affected by the material at the interior of the coin C. As a result, the output of the oscillation circuit  69  varies. The detection circuit  72  converts an output of the oscillation circuit  69  into a voltage. The AD conversion circuit  76  output of the detection circuit  72  is converted into a digital value, and it is transmitted to the microprocessor  78 .  
           [0019]    The microprocessor  78  determines whether the coin C is of a particular acceptable diameter based on information stored in the memory  83 . That is, the voltage from the AD conversion circuit  75  is compared with a reference value to a known diameter coin determined beforehand and stored in the memory. The microprocessor  78  also distinguishes whether the material in the coin C is an acceptable material based on stored values. The voltage from the AD conversion circuit  76  is compared with reference values stored in memory  83  to evaluate the material. A microprocessor  78  also distinguishes whether the thickness of the coin C, based on the voltage from the AD conversion circuit  77 , is acceptable compared with reference values stored in memory  83 .  
           [0020]    When the microprocessor  78  determines that the diameter, material, and thickness of the coin C is acceptable, the microprocessor  78  excites the solenoid  82 . This excitation causes the reject board  80  to be withdrawn from the coin passage  52  such that the coin can fall into the retention reservoir (not shown).  
           [0021]    If the microprocessor determines that there is a deviation in the acceptable thickness material, or diameter from the provided reference values, then the solenoid  82  is not excited. The rejection board  80  remains in the pathway between the coin passage  52  and the retention reservoir. The coin is thus deflected by the rejection board  80  into the cancellation passage  81 , where it is led to a coin return.  
           [0022]    The width W (FIG. 18) of the coin passage  52  is selected to accommodate coins of various types. To accomplish this, the width is selected to be slightly bigger than the diameter of the largest coin anticipated to be used with the coin selector. As a result, the position of the coin passing along the coin passage  52  is unknown beforehand.  
           [0023]    For example, consider the case in which the coin C having the diameter shown in FIG. 20A travels along the central portion of the coin passage  52  as shown. At the point at which the coin falls directly and equally between the two sensors, the coin covers more than three quarters of the circular areas of cores  61 B,  62 B and of cores  57 B,  60 B. The covered portion of the two sensors is indicated by the hatched region, and the uncovered portion of the core&#39;s areas are unhatched.  
           [0024]    In the case illustrated in FIG. 20B, the coin passes closer to the sensors  57 ,  60 , than the sensors  61 ,  62 . In this case, the cores  57 B,  60 B are almost completely covered by the coin C, whereas about half of the cores  61 B,  62 B are covered by the coin C. As a result, the relative area for the coin C covering the portion of core  61 B,  62 B is decreased in comparison with the first case shown in FIG. 20A. To compare the areas left uncovered between FIG. 20A and FIG. 20B, the two slices of area from FIG. 20A is superimposed over the uncovered area of FIG. 20B in cross hatching. The difference in the total area left uncovered by the coin in FIG. 20B can be seen to be greater than the area left uncovered in FIG. 20A.  
           [0025]    As a result, the output of the detection circuit  75  becomes line v, as it is shown in FIG. 21 when the coin falls to the left as shown in FIG. 20B. When the coin falls down the center of the passage  52 , the output of the detection circuit  75  is shown by line V, and ΔV 1  is the voltage difference between the two cases. In FIG. 22, a similar case in which a smaller coin is explained with the same conditions as FIG. 20.  
           [0026]    In the case in which the small coin c falls to the left of the passageway as shown in FIG. 22B, the relative area of the cores  57 B,  60 B, and  61 B,  62 B covered up by the coin C increase and decrease, respectively, in comparison with the case in which the coin falls directly down the middle as shown in FIG. 22A. The superimposed cross-hatched area in FIG. 22B from the areas of coverage in FIG. 20A illustrates the difference between the two cases.  
           [0027]    As a result, the voltage is shown by line Y in FIG. 23 when the coin falls to the left side as shown in FIG. 22B. The voltage is shown by line y when the coin falls down the center of the passage  52 , and ΔV 2  is the voltage difference between the two cases. The potential difference of ΔV 1  and ΔV 2  arises from the size of the coin and the path that the coin travels down the passage.  
           [0028]    This tolerance associated with the voltage as a result of the path taken by the coin makes the threshold determination of the coin&#39;s verification difficult. That is, the evaluation that determines an acceptable coin as compared with a unacceptable coin is improved when the tolerance of ΔV is small. Conversely, the rate at which the sensor incorrectly judges the authenticity of the coin increases when the tolerance is large.  
         SUMMARY OF THE INVENTION  
         [0029]    The purpose of the present invention is to improve the selection performance of the coin sensor. This is achieved by the present invention in which the output of the sensor does not change regardless of the passage that the coin travels through the passageway.  
           [0030]    To achieve this objective, the coin selector of the present invention comprises a coin passage for guiding a coin, a first sensor and a second sensor adjacent the coin passage, both the first sensor and second sensor comprising a coil wound about a core, where the core of the first and second sensor is shaped to have substantially straight and parallel upper and lower boundaries, such as a rectangle or square.  
           [0031]    It is preferable that the coin passage is vertically oriented. In the present invention, it is preferable that the coin passes the core of the sensors such that the sensor reads the width of the coin. In reading the width of the coin, the area difference by the curvature of the circular arc of the coin is small. This allows for a common discrimination standard among multiple coins.  
           [0032]    Also in a preferred embodiment of the present invention, a coin passage in which a coin is guided includes a first sensor and a second sensor which are adjacent the coin passage, said first coin sensor laterally offset of the center of the coin passage, a third coin sensor that is located opposite the first coin sensor, said second coin sensor laterally offset from the center of the coin passage, a fourth coin sensor that is located opposite the second coin sensor, where the first, second, third and fourth coin sensors are each comprised of a coil wound about a core in the shape of a rectangle when viewed from the coin passage.  
           [0033]    When the coin passes the cores of the previously described sensors, an equal voltage output is derived, regardless of the passage path that the coin takes. Therefore, the detection accuracy of the coin is improved.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0034]    The exact nature of this invention, as well as its objects and advantages, will become readily apparent upon reference to the following detailed description when considered in conjunction with the accompanied drawings, in which like reference numerals designate like parts through the figures thereof, and wherein:  
         [0035]    [0035]FIG. 1 is a schematic diagram of a first embodiment;  
         [0036]    [0036]FIG. 2 is a plan view of a coin sensor of the first embodiment;  
         [0037]    [0037]FIG. 3 is the sectional view of FIG. 2 along line F-F;  
         [0038]    [0038]FIG. 4 is a sectional view of the embodiment in FIG. 2 along section line G-G;  
         [0039]    [0039]FIG. 5 is a explanatory circuit drawing of the first embodiment;  
         [0040]    [0040]FIG. 6 is a diagram illustrating the various passages of a large diameter coin across the sensors of the present invention;  
         [0041]    [0041]FIG. 7 is a diagram illustrating the various passages of a small diameter coin across the sensors of the present invention;  
         [0042]    [0042]FIG. 8 is an illustration of the cross-sectional area perceived by the sensors for two conditions;  
         [0043]    FIGS.  9 - 11  are second, third, and fourth embodiments of the coin sensor of the present invention;  
         [0044]    [0044]FIGS. 12 and 13 are voltage graphs for a large diameter coin and a small diameter coin, respectively, using the coin sensor of the fourth embodiment in FIG. 11;  
         [0045]    FIGS.  14 - 17  are examples of coil connections of the coin sensor of the present invention;  
         [0046]    FIGS.  18 - 23  illustrate the operation and problems of prior art coin sensors.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0047]    The following description is provided to enable any person skilled in the art to make and use the invention and sets forth the best modes contemplated by the inventors of carrying out his invention. Various modifications, however, will remain readily apparent to those skilled in the art, since general principles of the present invention have been defined herein specifically to provide a coin detecting mechanism.  
         [0048]    In FIGS. 1 and 5, sensors  1 ,  2 ,  3 , and  4  are the sensors which concern the present invention. Each of the sensors  1 ,  2 ,  3 , and  4  are identical in structure. FIG. 1 is explained for illustrative purposes, and the remaining sensors include like designations appended by common letters of the alphabet to indicate common elements.  
         [0049]    In FIG. 2, the main body of sensor  1  is formed of a ferromagnetic material such as ferrite. The cross-section of the main body  1 A is in the shape of an “E” as shown in FIG. 3. The face which is opposite to the coin passage  52  is a rectangle on the core  1 B which projects from the center of the main body  1 A as shown in FIGS. 2 and 3.  
         [0050]    A copper wire is wound about the core  1 B forming a coil  1 C. The coil  1 C may be circular. However, the efficiency of the magnetic flux generation is increased in the case where the coil  1 C conforms with the circumference of the core  1 B. An upper magnetic flux wall  1 U projects above the core  1 B, and a lower magnetic flux wall  1 D projects beneath the core  1 B.  
         [0051]    The sensor  1  is placed at the right end of the coin passage  52  as it is shown in FIGS. 1 and 5. The end face of the core  1 B, the upper magnetic flux wall  1 U, and the lower magnetic flux wall  1 D each oppose the coin passage  52  at sidewall  56 .  
         [0052]    With respect to the coin passage  52 , sensor  3  is opposite sensor  1 . The end face of core  3 B is disposed at the sidewall  55  in a position opposite the core  1 B. Combined, sensors  1  and  3  constitute the coin left end sensor.  
         [0053]    Sensor  2  is located at the right end of the coin passage  52 . The end face of the core  2 B faces the coin passage  52 , and is disposed at the sidewall  56 . Sensor  4  is positioned across the coin passage  52  opposite the sensor  2 . The end face of core  4 B is in contact with the sidewall  55 . Sensors  2  and  4  constitute the coin right end sensor.  
         [0054]    The starting end of the coil  2 C of the sensor  2  is connected to the oscillation circuit  70 . The termination end of the coil  2 C is connected with the starting end of the coil  1 C of the sensor  1 . The termination of the coil  1 C is connected with the termination of the coil  3 C of the sensor  3 .  
         [0055]    The starting end of the coil  3 C is connected with the termination of the coil  4 C of the sensor  4 . The starting end of the coil  4 C is connected to the oscillation circuit  70 .  
         [0056]    Sensor  66  is placed in between sensor  1  and sensor  2 . Sensor  65  is placed in between sensor  2  and sensor  4 .  
         [0057]    The connection of the coil  66 C,  66 D,  65 C, and  65 D is similar to that described above with respect to the prior art. The connection between the coil  66 C,  66 D,  65 C,  65 D, and the oscillation circuits  69 ,  71 , are also similar to that shown with respect to the prior art.  
         [0058]    The movement of the coin with respect to the sensors are now explained with reference to FIGS.  6 - 8 . FIG. 6 shows the relative position of the coin C with the core  3 B ( 1 B) and  4 B ( 2 B) with the large diameter coin C. FIG. 6A is the relative position of the coin as it passes down the central portion of the coin passage  52 . The portion of the sensors uncovered by the coin as it passes the sensors are shown by the unhatched areas.  
         [0059]    [0059]FIG. 6B is a relative position between the coin C and the core  3 B ( 1 B),  4 B ( 2 B) as the coin C passes along the left end of the passage  52 . The hatching of the core  3 B ( 1 B) and  4 B ( 2 B) shows the area adjacent the coin C.  
         [0060]    [0060]FIG. 7 is a similar illustration using the small diameter coin.  
         [0061]    [0061]FIG. 8 illustrates the relative areas of the coin C as perceived by the core  3 B and  4 B in the first embodiment. With the shape of the cores in a rectangular arrangement, the height “y” of the core  3 B and  4 B is substantially fixed. The width of the coin C overlapping the core  3 B and  4 B is identical “a” when the coin C passes down the center of the coin passage  52  as shown in FIG. 6A and FIG. 7A.  
         [0062]    The overlap of the coin C with the core of the sensors  3 B,  4 B, can be characterized as shown in FIG. 8A, 8B, as a rectangular portion and a rounded tip portion. This corresponds to the cross-hatched regions in FIGS. 6 and 7. Because the radius of the coin is unchanged, the rounded tip portion of the overlap is constant for sensors  3  and  4 , regardless of the path that the coin takes. Only the relative rectangular regions Sa, Sb, vary according to the path of the coin. Pursuant to FIG. 8A, when the coin travels down the middle of the passage, the respective portions of the coin seen by sensors  3  and  4  are identical. That is, rounded tip portion Sx is common for both sensors  3  and  4 , and rectangular portions Sa and Sb are identical in this case. The largest area of overlap of the coin with the combined areas of cores  3 B and  4 B of sensors  3 ,  4 , respectively, is given by the expression 1 for the case where the coin passes down the center of the passage  52 : 
           S   1 =Sa+Sb+2 Sx= 2 ay+ 2 Sx.   Expression 1) 
         [0063]    [0063]FIG. 8B represents the case where the coin passes down the left hand side of the coin passage  52 . The relative width of the area between the coin and the core  3 B, excluding the rounded tip portion Sx, is denoted “B” when the coin passes down the left hand side of the coin passage as shown in FIGS.  6 (B),  7 (B). The relative width of the overlap of the coin with sensor core  4 B is denoted by the letter “C”. Accordingly, the total area of overlap of the core  4 B is given by Expression 2: 
           S   2 = Sc+Sd+ 2 Sx=by+cy+ 2 Sx.   (Expression 2) 
         [0064]    However, the width is 
         2 a=b+c   (Expression 3) 
         [0065]    because the diameter of the coin is identical. Therefore, 
           by+cy= 2 ay   (Expression 4). 
         [0066]    Therefore, S 1 =2ay+2Sx=by+cy+2Sx=S2. This illustrates that the overlap of the coin with the sensor core  3 B and the sensor core  4 B is unchanging regardless of the path of the coin down the coin passage.  
         [0067]    The sum of the relative areas of the coin overlap with the two cores does not change regardless of the path taken by the coin down the coin passage. This phenomena is a result of the shape of the core which is opposite to the coin. The use of rectangle for the sensor core shape fixes the output voltage of the detection circuit.  
         [0068]    [0068]FIG. 9 is a second embodiment of the present invention. A plan view as shown in FIG. 9A illustrates a U-shaped core main body  11 A of a sensor  11  having a cross-sectional area in the shape of a rectangle. A sectional view of FIG. 9A taken along section lines H-H in FIG. 9B shows a double core sensor. Along the left end of the main body is a core  12 B with a coil  12 C wrapped around its circumference. The right side of the main body has a core  13 B with a coil  13 C wrapped around its circumference. In a preferred embodiment, the coils  12 B and  13 B are connected.  
         [0069]    In this embodiment, a second sensor opposed to the sensor shown in FIGS. 9A, 9B would be disposed across the coin passage, and cooperate with sensor  11 . The end faces for the core  12 B and  13 B is a rectangle in this embodiment. Because the core  12 A and core  13 B are integrated, the overlapping of the coin&#39;s two cores remains constant, regardless of the position of the coin within the coin passage  52 . The feature whereby the coils  12 C,  13 C are connected, reduces the labor where two coils must be connected to the sensor output.  
         [0070]    [0070]FIG. 10 is a third embodiment of the present invention. In FIG. 10A, a plan view shows that the core main body  14 A is identical with the core main body  11  of the previous embodiment shown in FIG. 9. Again, the core main body  14 A has a rectangular cross-section.  
         [0071]    [0071]FIG. 10B is a sectional view of FIG. 10A along sectional line J-J. Ends  15 B and  16 B of the core main body  14 A, which is connected to the central portion  14 B, adjoin the coin passage  52  at the sides. Here the coil  14 C has been ground around the central portion  14 B. In this embodiment, a single coil is used which reduces the cost to manufacture the sensor.  
         [0072]    [0072]FIG. 11 is a fourth embodiment of the present invention. Sensor  16  has an E-shaped profile with a rectangular core  16 B as shown in FIG. 11A. The sides of the core  16 B are somewhat convex. However, the end face of the core  16 B is substantially a rectangle. The upper edge of the main body  17  forms an upper magnetic flux wall  17 T. The lower edge of the substrate  17  forms a lower magnetic flux wall  17 U. The coil  16 C is wrapped around the core  16 B in a circular pattern. Alternatively, if the coil  16 C is wrapped tightly around the core  16 B, it will form a more rectangular pattern. Substituting sensor  16  in place of sensors  1 ,  2 ,  3 ,  4  in the first embodiment results in an output voltage of the detector circuit  72  as shown in FIG. 12. “P” represents the case of the large diameter coin passing down the central portion of the coin passage. “p” represents the case where the large diameter coin passes along the left end.  
         [0073]    A voltage difference of ΔV 3  results between the two outputs depending on the path of the coin. FIG. 13 is an output voltage of the detection circuit  72  using the small diameter coin. Here, when the small diameter coin passes through the center of the coin passage  52 , the output of the detection circuit is shown by “Q” whereas the output of the coin passing down the side of the coin passage  52  is shown by “q”. A voltage difference between the two curves is given by ΔV 4 . Note, ΔV 3  and ΔV 4  are much smaller in magnitude than the case of the prior art sensors using a circular core.  
         [0074]    As the cross-sectional area of core  16 B increases from a rectangular area to a circular area, the voltage differences of ΔV 3  and ΔV 4  increases. That is, there is a difference at the relative area of the coin for the pair of sensors as the cores become more rounded.  
         [0075]    [0075]FIG. 14 is a alternative embodiment of the coil connection. The starting end of coil  1 C of the sensor  1  constitutes the left end sensor  10  which is connected with the termination end of the coil  3 C of sensor  3 . The starting end of the coil  3 C is connected to the oscillation circuit  70 B. The termination end of the coil  1 C is connected to the oscillation circuit  70 B.  
         [0076]    The termination end of the coil  2 C of sensor  2  which constitutes the right end sensor  11  is connected with the starting end of the coil  4 C of sensor  4 . The starting end of coil  2 C and the termination end of coil  4 C are connected with the oscillation circuit  70 A. This embodiment combines the output of the oscillation circuit  70 A and  70 B, and it distinguishes the coin&#39;s diameter. This embodiment varies the oscillation circuit  70 A and  70 B in proportion with the left end sensor  10  and the right end sensor  11 . In this manner, the detection accuracy can be improved because the fluctuation of the relative area ratio rate of the coin for each of the cores  1 B,  2 B,  3 B,  4 B can be increased.  
         [0077]    [0077]FIG. 15 is an alternative embodiment of the oscillation circuit. Here the connection of the coils  1 C,  2 C,  3 C and  4 C is separate. That is, the starting end of the coil  1 C is connected with the starting end of the coil  3 C. The termination of coil  1 C and the termination of coil  3 C were connected to the oscillation circuit  70 B. The starting end of the coil  2 C is connected to the termination end of the coil  4 C. The termination of the coil  2 C and the termination of the coil  4 C are connected to the oscillation circuit  70 A.  
         [0078]    [0078]FIG. 16 is an alternate embodiment connection using a single oscillation circuit  70 . The termination of coil  2 C and the starting end of coil  4 C are connected with the oscillation circuit  70 . The starting end of the coil  2 C is connected with the termination end of coil  1 C. The starting end of the coil  1 C is connected with the termination of the coil  3 C. The starting end of the coil  3 C is connected to the termination end of the coil  4 C. Using this connection, a similar result to the first embodiment is obtained.  
         [0079]    [0079]FIG. 17 is yet another embodiment of a connection for the present invention. Sensors  1 ,  2  are located at the sidewall  56 . An output of the oscillation circuit  70  changes by the distance between the cores  1 B,  2 B and the coin C, when there is a single sensor (i.e., no sensor on the opposite side of the coin passage). Therefore, the distance between the coin C and the core  1 B,  2 B must be fixed.  
         [0080]    Therefore, the sidewall  56  is inclined so that the coin C may rest on the sidewall  56 . The configuration of sensor  1 ,  2  is otherwise identical with other embodiment. The termination of the coil  2 C and the termination of the coil C are connected with the oscillation circuit  70 . The starting end of the coil  1 C is connected with the starting end of the coil  2 C. This embodiment reduces costs because sensors are located at only one side of the coin passage.