Abstract:
A multifeed detection apparatus and method for use in a check processing terminal including a paper supply unit for individually feeding a plurality of checks from the paper supply unit along a check transportation path in a given direction; a MICR head having a non-movable contact surface on one side of the check transportation path; a pressure member disposed on another side of the check transportation path opposite the non-movable contact surface for pressing one or more transported checks between the pressure member and the MICR head; and a displacement detection sensor for detecting physical displacement of the pressure member from the non-movable contact surface to indicate check thickness.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of Technology 
   The present invention relates to a check multifeed detection apparatus for use in a check processing terminal and a multifeed detection method. 
   2. Description of Related Art 
   Payment systems using checks are widely used throughout Europe and North America, Asia (worldwide). This payment system enables businesses and consumers to use checks to make payments and financial transfers of many kinds. When a check is written, it is ultimately presented to the bank on which the check was drawn to either deposit or withdraw funds. 
   Bank tellers at each bank branch typically process many checks in a short time. The bank teller also typically confirms check validity, the check date, and the signature before completing the deposit or withdrawal. The teller also prints an endorsement on the back, and issues a transaction receipt as required. The teller may also require a driver license or other photo ID to check the identity of the person presenting the check, and in some situations may make a photocopy of the license or photo ID using a copying machine. A copy of the check is also captured and stored using a specialized check scanner. 
   Efforts to electromagnetically read information from checks have started in order to provide more efficient check processing. Part of this process is to electromagnetically read each check at the teller window using compact check processing terminals that can be installed at each teller window. 
   These check processing terminals have a magnetic ink character reader (MICR), scanner, and printing mechanism disposed along the check transportation path. When a check is received from a customer, the teller passes the check through the check processing terminal. The check processing terminal thus reads the magnetic ink characters printed on the check, captures an image of the check, and may print an endorsement on the back. See, for example, Japanese Unexamined Patent Appl. Pub. 2000-344428. 
   A common problem of check processing terminals with this type of medium transportation path is that two or more checks may unintentionally be conveyed simultaneously along the transportation path. This is called “multifeed,” and the problem is inherent. 
   To solve this problem, Japanese Patent 3421104 teaches a multifeed detection apparatus having a reflection sensor located near the paper guide defining the form transportation path. This reflection sensor detects light reflected by the surface of the transported medium to directly detect the thickness of the paper and thereby detect check multifeeding. 
   Japanese Unexamined Patent Appl. Pub. S60-144256 also teaches a multifeed detection apparatus having a lever disposed to the roller shaft of the paper transportation roller to detect multifeeding by using optical sensors, for example, to detect displacement of the lever due to the paper thickness. 
   A multifeed detection apparatus having such a lever is described more specifically below with reference to  FIG. 8 . 
   The multifeed detection apparatus  100  shown in  FIG. 8  has a detection lever  123  and a photodetector  140 . The detection lever  123  is disposed on end portion  122  of rotary shaft  105   a , which supports a pair of transportation rollers  105 . This detection lever  123  is pivotably displaceable on a pivot shaft  124  disposed to one end portion  123   c  of the detection lever  123 , is urged downward as seen in  FIG. 8  by a tension spring  125  hooked on a protrusion  123   a , and the force of this spring  125  holds the detection lever  123  applying downward pressure on the end portion  122  of the rotary shaft  105   a . The other distal end  123   b  of the detection lever  123  is thus located adjacent to the photodetector  140 , and the photodetector  140  detects displacement of this distal end  123   b  of the detection lever  123 . 
   When paper passes below the transportation rollers  105 , the transportation rollers  105  and rotary shaft  105   a  are pushed upward according to the thickness of the paper. The rotary shaft  105   a  therefore also pushes the detection lever  123  up in resistance to the force of the spring  125  while the paper passes below the transportation rollers  105 . The photodetector  140  detects this displacement of the detection lever  123 , and the paper thickness can then be detected based on the displacement of this detection lever  123 . 
   When the multifeed detection apparatus taught in Japanese Unexamined Patent Appl. Pub. 2000-344428 is used, the thickness difference between one and two sheets is extremely small, and the detection sensitivity of the reflection sensor used to detect light reflected from the medium must be sufficient to detect this slight difference. 
   Furthermore, when the multifeed detection apparatus that detects the displacement of the rotary shaft of the transportation rollers as taught in Japanese Patent 3421104 is used, the transportation rollers become compressed over time due to the applied pressure, or the center of the transportation rollers may become offset from the center of the rotary shaft so that the rollers turn eccentrically. The reference position of the rollers thus shifts, and the paper thickness cannot be accurately detected. 
   The present invention is therefore directed to the aforementioned problems, and an object of the present invention is to provide a multifeed detection apparatus capable of accurately detecting multifeed situations by means of a simple design, and to provide a hybrid processing apparatus having this multifeed detection apparatus. 
   SUMMARY OF THE INVENTION 
   To achieve the foregoing objects, the present invention provides a check multifeed detection apparatus for use in a check processing terminal which includes a paper supply unit for individually feeding a plurality of checks; a check transportation medium for conveying each check fed from said paper supply unit along a check transportation path in a given direction; and a reading unit disposed on one side of the check transportation path with the reading unit having a rigid member providing a rigid and stationary surface and an image sensor such as a MICR head for reading information from each check being transported along the check transportation path; 
   wherein the check multifeed detection apparatus comprises:
         a pressure member disposed on another side of the check transportation path opposite to and in alignment with the rigid member for pressing one or more transported checks passing therebetween against the rigid and stationary surface of the rigid member and a displacement detection sensor for detecting the displacement of the pressure member by the transported check(s);   wherein the displacement detection sensor detects multifeeding based on the displacement of the pressure member according to the thickness of the check(s) passed between said pressure member and said rigid stationary surface. The MICR head reads magnetic ink characters printed on each check.       

   Preferably, the pressure member has a pressure portion for pressing the check to the rigid surface, and a detection surface opposing the displacement detection sensor, in an arrangement such that the displacement of the detection surface is greater than the displacement of the pressure portion. 
   Further preferably, the pressure member is a lever that can pivot circularly on a rotary shaft. 
   Further preferably, the displacement detection sensor is an optical sensor for measuring displacement distance of the pressure member. 
   The present invention also embodies a check multifeed detection method comprising the steps of:
         individually feeding a plurality of checks from a paper supply unit;   conveying each check fed from the paper supply unit to a check transportation medium moving along a given transportation path;   locating a reading unit having a sensor such as an MICR head with a rigid stationary surface on one side of the transportation path for reading information from each check being transported along the check transportation path;   locating a pressure member on another side of the check transportation path opposite to and in alignment with said rigid stationary surface of said MICR head for pressing one or more transported checks passing therebetween against said rigid stationary surface; and   detecting the displacement of the pressure member according to the check thickness. Feeding more than one check at a time is detected while reading MICR characters using the MICR head for reading magnetic ink characters printed on the check.       

   Because the pressure member presses against a rigid surface of the MICR head which is stationary in a MICR reading apparatus according to the present invention, the MICR head cannot be displaced and the rigid surface cannot be deformed by pressure from the pressure member. The rigid and stationary surface of the reading apparatus can therefore be used as a stable reference surface for determining displacement of the pressure member such as lever  30 , and checks in a multifeed condition can be reliably detected based on this displacement reference surface. Check multifeeding can therefore be reliably detected by optically measuring the displacement of a pressure member that presses checks (a personal check or business check) to an MICR head having a rigid member used as a stationary reference surface. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an oblique view showing a check processing terminal including a check multifeed detection apparatus (MICR reading apparatus) according to the present invention; 
       FIG. 2  is a schematic diagram of the paper transportation path in the check processing terminal of  FIG. 1 ; 
       FIG. 3  is a schematic top view of the internal configuration of the check processing terminal of  FIG. 1 ; 
       FIG. 4  is an oblique view of check processing terminal of  FIG. 1  with the outside case removed; 
       FIG. 5  is another oblique view of the check processing terminal of  FIG. 1  with the outside case removed; 
       FIG. 6  schematically shows the multifeed detection apparatus according to the present invention for use in the check processing terminal of  FIG. 1 ; 
       FIG. 7  is divided into  FIGS. 7A , and  7 B with  FIG. 7A  showing one check S travelling through the middle transportation path (the normal position) of  FIG. 2 , and  FIG. 7B  showing two checks being fed at the same time through the middle transportation path (the multifeed position) of  FIG. 2 ; 
       FIG. 8  is an oblique view of a multifeed detection apparatus according to the prior art; 
       FIG. 9  is a plan view showing a variation of the check multifeed detection apparatus according to the present invention; 
       FIG. 10  shows the arrangement in  FIG. 9  in greater detail; and 
       FIG. 11  is an oblique view of an MICR reading apparatus incorporating the assembly shown in  FIG. 10 , shown with the first image scanning sensor  11  removed. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   A preferred embodiment of a check processing terminal incorporating a check multifeed detection apparatus (MICR reading apparatus) according to the present invention is described in detail below with reference to the accompanying figures. 
   The check processing terminal shown in  FIG. 1  can transport checks S through a first transportation path P 1  formed in the case  1   a , and can transport cards C through a second transportation path P 2  likewise formed in the case  1   a . The checks S are also referred to herein as a first scanning medium and are loaded into a paper supply section  3 . The cards C are inserted from a card insertion slot  20 , and are also referred to herein as a second scanning medium. 
   More specifically, the check processing terminal  1  shown in  FIG. 1  includes an image scanner such as an MICR reader, and a printer in an arrangement such that the image scanner can image each check S to read the magnetic ink characters printed on the check S, and print on the check S as needed while conveying the check S through the first transportation path P 1 . Likewise a card C can be imaged while conveying the card C through the second transportation path P 2 . 
   The check processing terminal shown in  FIG. 1  includes a first transportation path P 1  as is more clearly shown in  FIG. 2  which is basically U-shaped and a second transportation path P 2  which is straight for conveying cards C. The portion at the middle of the U-shaped path (shaded in  FIG. 2 ) is shared by the first transportation path P 1  and second transportation path P 2 , and this shared portion is referred to below as the middle transportation path M. Different reading devices are disposed to the check processing terminal  1  along this middle transportation path M. These reading devices are described in further detail below. 
   As shown in  FIG. 2 , the first transportation path P 1  is formed by an outside guide  2   a  and an inside guide  2   b  so that a check S is conveyed through space, referred to as the transportation portion  2   c  below, between the outside guide  2   a  and inside guide  2   b . A check S is inserted through the paper supply section  3  in the direction of arrow A in  FIG. 3  to the first transportation path P 1 . Multiple checks S can be stocked in the paper supply section  3 , which then supplies the checks individually into the first transportation path P 1 . 
   A first transportation roller pair  6  on the upstream side of the middle transportation path M, a middle transportation roller set  16  on the middle transportation path M, and a second transportation roller pair  7  on the downstream side of the middle transportation path M, are disposed to the first transportation path P 1  as the transportation mechanism for conveying checks S. 
   The first transportation, roller pair  6  includes a drive roller  6   a , and a pressure roller  6   b  disposed opposite the drive roller  6   a  with the first transportation path P 1  therebetween. 
   The second transportation roller pair  7  likewise includes a drive roller  7   a , and a pressure roller  7   b  disposed opposite the drive roller  7   a  with the first transportation path P 1  therebetween. 
   As shown in  FIG. 3  the middle transportation roller set  16  includes a lower pressure roller  16   b  disposed to the lower part of the first transportation path P 1 , an upper pressure roller  16   a  disposed above the lower pressure roller  16   b , and a drive roller  17  disposed opposite the upper pressure roller  16   a  and lower pressure roller  16   b  with the middle transportation path M therebetween. 
   A check S delivered into the first transportation path P 1  is conveyed through the middle transportation path M by the first transportation roller pair  6 , middle transportation roller set  16 , and second transportation roller pair  7  as shown in  FIG. 3 , and is then discharged from the paper exit  4  in the direction of arrow B by the discharge rollers  8 . As shown in  FIG. 4 , the bottom of the first transportation path P 1  is held at height L 1 , and checks S are conveyed referenced to this height L 1  along the bottom of the first transportation path P 1 , including through the middle transportation path M. 
   If the width (height) of the check S is less than a predefined height, the check S is conveyed by the lower pressure roller  16   b  and drive roller  17  of the middle transportation roller set  16 . If the check S width is equal to or greater than this predefined height, the check S is conveyed by the drive roller  17  and both upper pressure roller  16   a  and lower pressure roller  16   b.    
   As shown in  FIG. 2  and  FIG. 3 , the second transportation path P 2  includes the middle transportation path M and the card insertion slot  20  and card reversing path  21  that are contiguous to opposite ends of the middle transportation path M. 
   The card insertion slot  20  is an opening for inserting a card C to the middle transportation path M. As shown in  FIG. 3  and  FIG. 4 , bottom guides  24  and  24   a  are disposed below the card insertion slot  20 . These bottom guides  24  and  24   a  are part of the outside guide  2   a , and hold the bottom edge of the card C at a specific height L 2 . The card C is guided by bottom guide  24  and inserted to the middle transportation path M, and then transported at this height L 2 . More specifically, the bottom of the second transportation path P 2  is held at height L 2  referenced to bottom guides  24  and  24   a . Note that a check S conveyed through the first transportation path P 1  at height L 1  is guided by this bottom guide  24   a  so that the direction of check S travel bends and the check S is conveyed toward the paper exit  4 . 
   The upper pressure roller  16   a  is disposed to the second transportation path P 2  at a position above height L 2 . A card C conveyed into the middle transportation path M is transported through the middle transportation path M by the upper pressure roller  16   a  and drive roller  17 . 
   The card reversing path  21  is formed by straight guides  21   a ,  21   b  rendered as straight extensions of the middle transportation path M to the left side as seen in  FIG. 2 . Forward/reverse transportation rollers  22  are disposed near the end portion  21   c  of this card reversing path  21 . The forward/reverse transportation rollers  22  convey a card C transported from the middle transportation path M so that the card C overhangs a specific length from the end portion  21   c  of the card reversing path  21 , and then deliver the card C overhanging from the end portion  21   c  back into the middle transportation path M. 
   More specifically, when a card C is inserted from the card insertion slot  20  to the middle transportation path M, the card C is conveyed by the upper pressure roller  16   a  and drive roller  17  to the card reversing path  21 . The card C is then reversed by the forward/reverse transportation rollers  22  and conveyed from the card reversing path  21  through the middle transportation path M until the card C is discharged from the card insertion slot  20 . The card C is conveyed through the second transportation path P 2  with the bottom edge of the card C held at height L 2 . Note that in this embodiment of the invention height L 2  of the second transportation path P 2  is located at a position higher than height L 1  of the first transportation path P 1 . Cards C thus travel through the middle transportation path M at a height above the checks S. 
   By conveying checks S and cards C at different elevations, this embodiment of the invention can transport different types of media through a U-shaped first transportation path and a straight second transportation path without requiring special switching means to change the transportation path. This embodiment of the invention thus transports checks S and cards C as described above. 
   A first image scanning sensor  11  and a second image scanning sensor  12  for imaging media are disposed to the middle transportation path M. The first image scanning sensor  11  and second image scanning sensor  12  are contact image sensor (CIS) type image scanners, and thus illuminate the surface of a check S or card C travelling through the middle transportation path M and detect light reflected from the check S or card C. The first image scanning sensor  11  and second image scanning sensor  12  image the check S or card C travelling through the middle transportation path M one scan line at a time to acquire a two-dimensional image of the check S or card C. 
   A BOF (bottom of form) detector  9  and TOF (top of form) detector  10  for detecting the respective ends of a check S are disposed to the first transportation path P 1 . The BOF detector  9  is located between the paper supply section  3  and first transportation roller pair  6 , detects a check S inserted from the paper supply section  3 , and detects the trailing edge (bottom of form) of the check S by detecting when the check S passes the BOF detector  9 . 
   The TOF detector  10  is disposed between the first transportation roller pair  6  and first image scanning sensor  11  to detect the leading edge (top of form) of the check S. 
   The length of the check S can thus be accurately measured as a result of the BOF detector  9  and TOF detector  10  detecting the leading and trailing edges of the check S. 
   A hybrid processing apparatus  1  according to this embodiment of the invention is designed to operate according to detection of a check S by the BOF detector  9  and TOF detector  10 . More specifically, starting and stopping the image scanning sensors  11 ,  12  imaging a check S is controlled based on output from the BOF detector  9  and TOF detector  10 . It should be noted that either one of the image scanning sensors  11 ,  12  could be used to detect the leading edge of the check S, in which case the TOF detector  10  is unnecessary and can be omitted. 
   A print head  14  is also disposed to a straight portion of the first transportation path P 1  between the second transportation roller pair  7  and discharge rollers  8 . This print head  14  is for printing an endorsement on the check S, and prints to the check S as required. 
   A BOC (bottom of card) detector  25  and a TOC (top of card) detector  26  are also disposed to the second transportation path P 2 . The BOC detector  25  is disposed near the card insertion slot  20 , detects when a card C is inserted from the card insertion slot  20 , and detects when the card C has passed the BOC detector  25  to detect the trailing edge of the card C. 
   The TOC detector  26  is disposed between the middle transportation roller set  16  and second image scanning sensor  12 , and detects the leading edge of the card C. 
   The length of the card C can thus be accurately measured as a result of the BOC detector  25  and TOC detector  26  detecting the leading and trailing edges of the card C. 
   The check processing terminal  1  according to this embodiment of the invention also operates according to card C detection by the BOC detector  25  and TOC detector  26 . More specifically, starting and stopping scanning a card C by means of image scanning sensor  11  or  12  is controlled based on output from the BOC detector  25  and TOC detector  26 . It should be noted that either one of the image scanning sensors  11 ,  12  could be used to detect the leading edge of the card C, in which case the TOC detector  26  is unnecessary and can be omitted. 
   An MICR (magnetic ink character reader)  13  is disposed below the drive roller  17  on one side of the transportation path. This MICR  13  is a sensor for reading information written in magnetic ink on a check S. A pressure lever  30  as shown in  FIG. 9  is disposed on an opposite side of the transportation path and is aligned opposite to the position of the MICR  13  such that a check S fed along the middle transportation path M is pressed therebetween against the surface of the MICR  13  for reading. In the preferred embodiment of the present invention the MICR  13  represents a component of a multifeed detection apparatus  50  which also includes the pressure lever  30  and a sensor  40  as diagrammatically shown in  FIG. 6  and as shown in  FIG. 9 . 
   The pressure lever  30  has a long main portion  31  on one end of which is disposed a rotary shaft  32 . The pressure lever  30  pivots on this rotary shaft  32  in a plane perpendicular to the check transportation surface of the middle transportation path M. A pressure portion  33  is formed integrally to the main portion  31  projecting toward the middle transportation path side. This pressure portion  33  is urged toward a rigid surface  13   a  in the MICR  13  by the force of a pressure spring (not shown). When a check S is not present, the rigid surface  13   a  of the MICR  13  and the contact surface  33 a of the pressure portion  33  are in mutual engaging contact. 
   The contact surface  33   a  of the pressure portion  33  is rigid or is a rigid member that will not shift or deform due to pressure from the pressure portion  33  in this embodiment of the invention. When the contact surface  33   a  of the pressure portion  33  contacts the MICR  13 , the lengthwise direction of the main portion  31  is usually held substantially parallel to the middle transportation path M transporting the check S. 
   The detection apparatus  50  when used in a check processing terminal as shown e.g. in  FIG. 1  provides the following advantages: 
   (1) each check S will pass the MICR  13  without fail 
   (2) the MICR  13  does not move 
   (3) any check S which is wrinkled is mended by the large pressed load formed by the detection apparatus  50   
   The distal end portion of the main portion  31  has a bent portion  34  turned substantially  90  degrees away from the middle transportation path M. A displacement detection sensor  40  is located opposite the end face  34   a  of the bent portion  34  and is separated a specified distance from the end face  34   a.    
   This displacement detection sensor  40  is a sensor for detecting displacement of the detection surface, that is, the end face  34   a  of the bent portion  34 , and is, for example, an optical sensor that measures the distance to the end face  34   a  by illuminating the end face  34   a  and detecting light reflected from the end face  34   a  by means of photodetector  40   a . An Omron Z4D-B01 reflection-type optical microdisplacement sensor was used as the displacement detection sensor  40  in this embodiment of the invention. 
   Assuming that L 1  is the distance from the rotational axis of the rotary shaft  32  to a line passing through the end of the pressure portion  33  substantially parallel to the direction in which the pressure portion  33  protrudes, and L 2  is the distance from the rotational axis of the rotary shaft  32  to a line passing through the detection point of the end face  34   a  of the bent portion  34  parallel to the direction in which the pressure portion  33  protrudes, the pressure portion  33  is made so that the relationship between distance L 1  and distance L 2  shown in equations (1) and (2) is true.
 
 L 2= L 1× N ( N&gt; 1)  (1)
 
   That is,
 
L 2 &gt;L 1    (2)
 
   As shown in equation (2), the pressure lever  30  is made so that distance L 2  is greater than distance L 1 . As shown in  FIG. 6 , the MICR  13 , pressure lever  30 , and displacement detection sensor  40  form a multifeed detection apparatus  50  in this embodiment of the invention. The operation of this multifeed detection apparatus  50  is described further below with reference to  FIG. 7A  and  FIG. 7B . 
     FIG. 7A  shows the situation (normal position) when one check S is travelling through the middle transportation path M, and  FIG. 7B  shows the situation (multifeed position) when two checks S are fed at the same time through the middle transportation path M, that is, checks S 1  and S 2  overlap as they are conveyed through the middle transportation path M. 
   When one check S is transported from the left to right through the middle transportation path M as shown in  FIG. 7A  and travels between the MICR  13  and pressure portion  33  of the pressure lever  30 , the pressure portion  33  of the pressure lever  30  is pushed by the thickness d of the check S in resistance to the force acting thereon, and the pressure lever  30  therefore pivots upward (that is, moves rotationally in the clockwise direction as seen in  FIG. 7A ). 
   When the pressure lever  30  thus pivots, the end face  34   a  of the pressure lever  30  is displaced, and the displacement detection sensor  40  detects the distance between this end face  34   a  and the photodetector  40   a  of the displacement detection sensor  40 . Displacement D 1  of the end face  34   a  of the pressure lever  30  varies according to distances L 1  and L 2  as shown in the following equation.
 
 D   1   ≈d×L 2/ L 1 ( D   1  nearly equals  d×L 2/ L 1)  (3)
 
   This displacement D 1  of the end face  34   a  of the pressure lever  30  is thus greater than the thickness d of the check S located between the MICR  13  and the pressure portion  33  of the pressure lever  30 . The hybrid processing apparatus  1  can determine if only one check S is being transported as a result of the displacement detection sensor  40  detecting this displacement D 1 . 
   If two checks S 1  and S 2  overlap as they travel through the middle transportation path M as shown in  FIG. 7B  and pass between the MICR  13  and the pressure portion  33  of the pressure lever  30 , the pressure portion  33  of the pressure lever  30  is again pushed up against the spring pressure causing the pressure lever  30  to pivot (that is, move rotationally in the clockwise direction as seen in  FIG. 7B ) as described above. In this case, however, the pressure portion  33  is raised by thickness of the overlapping checks S, or thickness  2   d  in this example. The pressure lever  30  therefore pivots a greater distance than when only one check S is conveyed. 
   When the pressure lever  30  thus pivots, the end face  34   a  of the pressure lever  30  is displaced, and the displacement detection sensor  40  detects the distance between this end face  34   a  and the photodetector  40   a  of the displacement detection sensor  40 . Displacement D 2  of the end face  34   a  of the pressure lever  30  varies according to distances L 1  and L 2  as shown in the following equation.
 
 D   2 ≈2 d×L 2/ L 1   (4)
 
D 2 ≈2D 1    (5)
 
   Displacement D 2  of the end face  34   a  of the pressure lever  30  is thus greater than the overlapping thickness  2   d  of the checks S 1  and S 2  passing between the MICR  13  and the pressure portion  33  of the pressure lever  30 , and obviously greater than the displacement D 1  when only one check S is conveyed. When the displacement detection sensor  40  detects this displacement D 2 , the hybrid processing apparatus  1  can determine that two checks S are being conveyed, that is, can detect if more than one check S is being fed at a time, and can therefore call an appropriate error handling process such as stopping check S transportation, lighting a warning indicator, or outputting an alarm. 
   A hybrid processing apparatus  1  according to the foregoing embodiment of the invention thus has a multifeed detection apparatus  50  including a pressure lever  30  and a displacement detection sensor  40  for detecting displacement of the pressure lever  30 . The pressure lever  30  is a pressure member located on one side of the middle transportation path M (form transportation path) in order to press checks S to the surface  13   a  of an MICR  13  located on the other side of the middle transportation path M. The displacement detection sensor  40  detects multifeeding checks S by detecting the displacement of the pressure lever  30 , which is displaced according to thickness of the check or checks. 
   Because the MICR  13  is stationary and the surface  13   a  of the MICR  13  is a rigid surface, pressure by the pressure lever  30  does not cause displacement of the MICR  13  or deformation of the surface  13   a  of the MICR  13 . The surface  13   a  of the MICR  13  can therefore be used as a stable reference surface for determining displacement of the pressure lever  30 , and the thickness of the conveyed medium (checks S) can be reliably detected by detecting displacement of the pressure lever  30 . 
   Therefore, even if the paper supply section  3  feeds two checks S so that checks are multifeed as shown in  FIG. 7B , multifeeding of checks can be reliably detected by using the multifeed detection apparatus  50  to detect check thickness. Scanning and printing errors due to multifeeding can therefore be reliably prevented. 
   As also described above, the pressure lever  30  in this embodiment of the invention has a pressure portion  33  for pressing checks S to the surface  13   a  of the MICR  13 , an end detection face  34   a  opposite and detected by the displacement detection sensor  40 , and is constructed so that when the pressure lever  30  pivots, the displacement of the end face  34   a  is greater than the displacement of the pressure portion  33 . In other words, the pressure lever  30  of this embodiment of the invention is designed so that displacement of the end face  34   a , that is, the detection surface, actually amplifies the thickness of the check. Therefore, while checks are very thin and detecting check thickness requires corresponding precision, the displacement that is actually detected is the displacement that amplifies the actual check thickness. Overfeed detection is therefore simple compared with directly detecting check S thickness, and the reliability of check multifeed detection can be improved. 
   The displacement detection sensor  40  for measuring the distance to the end face  34   a  of the pressure lever  30  that is displaced according to the thickness of the check S is an optical sensor in this embodiment of the invention. Therefore, even if the check S sags or is wrinkled or creased, the check S is pressed by the pressure portion  33  to the MICR  13  while displacement is measured by illuminating a consistently flat end face  34   a , and check thickness can be reliably detected. 
   The pressure lever  30  is described as being pressed to the surface  13   a  of the MICR  13  in the foregoing embodiment, but the invention shall not be so limited. More particularly, the pressure lever  30  could press the scanning medium against any stationary fixed object that is not displaced or deformed. The pressure lever  30  could, for example, be rendered to press the medium to the inside wall of the middle transportation path M, or to one of the image scanning sensors  11  or  12 . 
   Furthermore, while the displacement detection sensor  40  is described in the foregoing embodiment as being an optical sensor, the invention shall not be so limited and any displacement sensor (including magnetic and potential detection sensors) capable of detecting displacement of the pressure lever  30  can be used. 
   The multifeed detection apparatus  50  is described in the foregoing embodiment as used for multifeed detection of checks S, but the invention shall not be so limited. This multifeed detection apparatus  50  could, for example, be used as a thickness detector for detecting the thickness of different media, such as thin paper and thick paper. 
     FIG. 9  shows a check thickness detector according to another implementation of the present invention. 
   Referring to  FIG. 9 , a check S inserted from the slip form transportation direction as indicated by the arrow at the top right in  FIG. 9  passes the first transportation roller pair  6  and TOF detector  10 , the back of the check S is scanned by the first image scanning sensor  11 , and the front of the check S (the side on which MICR text is printed) is read by the second image scanning sensor  12 . 
   The paper thickness sensor  40  is disposed opposite the end face  34   a  (detection face) of the MICR pressure lever  30  pressing the check S to the MICR head  13 . When a check (a slip form or check) S is conveyed and nipped between the MICR head  13  and MICR pressure lever  30 , the MICR pressure lever  30  is pushed away from the MICR head  13 . The MICR pressure lever  30  thus pivots on support shaft  32 , the detection face  34   a  of the MICR pressure lever  30  is displaced, and the distance from the detection face  34   a  to the paper thickness sensor  40  changes. The paper thickness sensor  40  in this implementation outputs a voltage according to the distance to the detection face  34   a.    
     FIG. 10  is a detailed view of the implementation shown in  FIG. 9 , specifically describing positioning the displacement detection sensor  40 . 
   The protrusion  300  at the distal end portion of the paper pressure lever  30  can be viewed through a window  410  rendered in a paper thickness detector positioning member  400 , inside of which the paper thickness detection sensor  40  is integrally disposed. The position of the paper thickness detector positioning member  400  can be moved forward and back, left and right, and firmly fastened with a screw  420  so that the protrusion  300  is accurately positioned to the window  410 . 
     FIG. 11  shows the paper thickness detector assembly shown in  FIG. 10  assembled in the MICR reader shown in  FIG. 4  and  FIG. 5  with the first image scanning sensor  11  and roller  12   a  opposite the second image scanning sensor  12  removed. 
   Although the present invention has been described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications will be apparent to those skilled in the art. Such changes and modifications are to be understood as included within the scope of the present invention as defined by the appended claims, unless they depart therefrom.