Abstract:
A paper multi-feed detection apparatus and a paper multi-feed detection method are provided for preventing the detection capability from being deteriorated by a noise factor and improving the detection precision even where an area around the feeding path has no extra space in terms of the shape and there are many noise-generating factors because of a demand for a smaller size of the device. An ultrasonic transmission opening formed in one of two feeding guide plates is large so as to discharge outside a reflected wave which returns through the ultrasonic transmission opening, and an ultrasonic receiving opening formed in the other feeding guide plate is smaller than a receiving face area of a receiver for receiving the ultrasonic wave.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a paper multi-feed detection apparatus applicable to office equipment such as, for example, copiers and scanners, and more specifically to a paper multi-feed detection apparatus and a paper multi-feed detection method for accurately detecting that sheets of paper such as blank or printed forms, banknotes, gift certificates, book coupons, checks, cards and the like are fed in an overlapped state. 
         [0003]    2. Description of the Prior Art 
         [0004]    Recently, as an apparatus for detecting multi-feed of sheets of paper which easily tend to be fed in an overlapped state, for example, sheets of thin paper or the like, a paper multi-feed detection apparatus using an ultrasonic sensor is known. When such an ultrasonic sensor is used to detect sheets of paper, the following detection capabilities unique to the ultrasonic sensor are provided. 
         [0005]    (1) Since detection is performed without any contact with the paper sheets, feeding of the paper sheets is not disturbed. 
         [0006]    (2) Since detection can be performed regardless of the thickness of the paper sheet, multi-feed can be detected even where paper sheets having different thicknesses are present. 
         [0007]    (3) Since detection can be performed regardless of the color of the paper sheet, no adjustment is necessary for different colors of the paper sheets. 
         [0008]      FIG. 4  shows an example of such a paper multi-feed detection apparatus using an ultrasonic sensor having the above-described features. The paper multi-feed detection apparatus shown in  FIG. 4  has the following structure. A feeding path  42  for feeding a paper sheet  41  two-dimensionally is interposed between a transmitter  44  of an ultrasonic sensor  43  and a receiver  45  of the ultrasonic sensor  43 . The transmitter  44  is provided above the feeding path  42 , and the receiver  45  is provided below the feeding path  42 . The transmitter  44  and the receiver  45  face each other. Transmitting and receiving directions of the transmitter  44  and the receiver  45  are set to be oblique with respect to the feeding path  42 . 
         [0009]    An ultrasonic wave  46  which is transmitted from the transmitter  44  is directed to a top surface of the paper sheet  41  via an entrance opening  48  for transmitting the ultrasonic wave. The entrance opening  48  is formed in an upper feeding guide plate  47  which covers a top surface of the feeding path  42 . The ultrasonic wave  46  directed to the paper sheet  41  is transmitted through the paper sheet  41  and is received by the receiver  45  via an exit opening  50  for transmitting the ultrasonic wave. The exit opening  50  is formed in a lower feeding guide plate  49  which covers a bottom surface of the feeding path  42 , and has the same size as that of the entrance opening  48 . The attenuation amount (transmission amount) of the ultrasonic wave  46  caused by the transmission through the paper sheet  41  is measured, and thus a control section detects whether one paper sheet  41  is being fed or a plurality of paper sheets are being fed in an overlapped state (see, for example, Patent Document 1). 
         [0010]    However, there may be an occasion that when the ultrasonic wave  46  is directed to the paper sheet  41 , a part of the ultrasonic wave  46  is reflected by a top face of the paper sheet  46  and the reflected wave is reflected diffusedly in a feeding space  42   a . For example, the paper sheet  41  may be bent in the feeding space  42   a . When being directed to the bent paper sheet  41 , the ultrasonic wave  46  is reflected diffusedly. The reflected wave generated as a result of the diffused reflection may occasionally be received by the receiver  45  as a noise component. Such a noise component may deteriorate the capability of the sensor and thus cause erroneous detection of the paper sheet  41 . 
         [0011]    In an attempt to solve this problem, the technology of Patent Document 1 directs the ultrasonic wave toward the face of the paper sheet obliquely so as to reduce the reflection of the ultrasonic wave by the top face of the paper sheet and also so as to reduce the reflection of the ultrasonic wave by a receiving face of the receiver. However, merely setting the transmitting direction of the ultrasonic wave to be oblique is not sufficient to obtain a sufficient sensor capability. 
         [0012]    In addition, devices such as copiers are desired to be reduced in size. Therefore, there is no extra space around the feeding path, which causes many factors generating noise components.  FIG. 5  shows another example of a paper multi-feed detection apparatus. This paper multi-feed detection apparatus has a structure in which a feeding path  52  for feeding a paper sheet  51  two-dimensionally is interposed between a transmitter  53  provided above the feeding path  52  and a receiver  56  provided below the feeding path  52 . Where there is a component surrounding the feeding path (reflecting object)  55  in or around a transmission section from the transmitter  53  to an upper feeding guide plate  54 , the transmission wave reflected by the paper sheet  51  may hit the component surrounding the feeding path  55  to be reflected diffusely and the resultant wave may be received by the receiver  56  as a noise component. 
         [0013]    For example, where an ultrasonic sensor and an optical sensor are both provided, a sensor opening  58  for the optical sensor may be formed in the upper feeding guide plate  54  or a lower feeding guide plate  57 . In such a case, before the paper sheet  51  which is being fed reaches the sensor opening  58 , a transmission wave  59  transmitted through the sensor opening  58  may directly reach the receiver  56  and may be added to the received component. Also, a reflected wave  60  may occasionally reach the receiver  56  from a space in the vicinity of the receiver  56  and act as a noise component. Such a noise component is likely to have an adverse influence on the performance of the paper multi-feed detection apparatus. 
         [0014]    According to another known multi-feed detection apparatus, a transmission area and a receiving area of an ultrasonic wave from the transmitter to the receiver are enclosed by a sound-absorbing material to absorb an external noise component and a noise component generated by the reflected wave (see, for example, Patent Document 2). 
         [0015]    However, such a structure requires the transmission and receiving areas to be enclosed air-tightly by the sound-absorbing material, and thus decreases the level of designing freedom because the arrangement and the shape of the sound-absorbing material are specified. This structure also has a problem that the ultrasonic sensor itself is costly. 
         [0016]    Patent Document 1: Japanese Laid-Open Patent Publication No. 6-72591 
         [0017]    Patent Document 2: Japanese Laid-Open Patent Publication No. 2005-82350 
         [0018]    In light of the above, the present invention has an object of providing a paper multi-feed detection apparatus and a paper multi-feed detection method capable of properly eliminating the reflected ultrasonic wave, which would otherwise become a noise component, to prevent the detection capability from being deteriorated by the noise component and thus to improve the detection precision. 
       SUMMARY OF THE INVENTION 
       [0019]    The present invention is directed to a paper multi-feed detection apparatus comprising a feeding path covered with one feeding guide plate and another feeding guide plate facing each other while having therebetween a feeding space for feeding a paper sheet two-dimensionally; and a transmitter of an ultrasonic sensor provided on one of two sides facing each other while having the feeding space therebetween, and a receiver of the ultrasonic sensor provided on the other of the two sides. An ultrasonic wave is incident on the feeding space from the transmitter via an entrance opening formed in the one feeding guide plate; the ultrasonic wave output via an exit opening formed in the another feeding guide plate is received by the receiver; paper multi-feed is detected by comparing attenuation information on the ultrasonic wave when the paper sheet passes between the transmitter and the receiver, against a threshold value for multi-feed detection; the entrance opening is formed to be large so as to discharge outside the ultrasonic wave incident thereon and then reflected, without making the reflected wave a noise component; and the exit opening is formed to be smaller than a receiving face area of the receiver for receiving the ultrasonic wave. 
         [0020]    In one embodiment of the present invention, the paper multi-feed detection apparatus comprises a feeding path covered with one feeding guide plate and another feeding guide plate facing each other while having therebetween a feeding space for feeding a paper sheet two-dimensionally; and a transmitter of an ultrasonic sensor provided on one of two sides facing each other while having the feeding space therebetween, and a receiver of the ultrasonic sensor provided on the other of the two sides. An ultrasonic wave is incident on the feeding space from the transmitter via an entrance opening formed in the one feeding guide plate; the ultrasonic wave output via an exit opening formed in the another feeding guide plate is received by the receiver; paper multi-feed is detected by comparing attenuation information on the ultrasonic wave when the paper sheet passes between the transmitter and the receiver, against a threshold value for multi-feed detection; an ultrasonic wave transmission area from the transmitter to the entrance opening is in a open state; and an ultrasonic wave receiving area from the exit opening to the receiver is enclosed by a noise shielding wall. 
         [0021]    In one embodiment of the present invention, according to a paper multi-feed detection method, where a transmitter and a receiver are provided to face each other while having a feeding path for a paper sheet therebetween, an entrance opening, on which an ultrasonic wave transmitted from the transmitter toward the receiver is incident via a feeding guide plate which covers an ultrasonic wave transmission side of the feeding path, is formed to be large so as to discharge a reflected wave outside; and an exit opening, for outputting the ultrasonic wave via a feeding guide plate which covers an ultrasonic receiving side of the feeding path facing the ultrasonic transmission side, is formed to be smaller than a receiving face area of the receiver. 
         [0022]    According to the present invention, a stable transmission capability is guaranteed because a noise component is avoided from being generated at the time of the ultrasonic wave transmission, and a receiving capability can be improved by properly blocking a noise component which is likely to enter the receiver at the time of the ultrasonic wave receiving. Especially, the structure of the present invention does not require any new parts, and can be easily obtained even where there is no ample extra space around the feeding path. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0023]      FIG. 1  is an operation illustration showing a detection state of a paper multi-feed detection apparatus according to Embodiment 1. 
           [0024]      FIG. 2  is a block diagram of a control circuit of an ultrasonic sensor which may be incorporated into the paper multi-feed detection apparatus according to Embodiment 1. 
           [0025]      FIG. 3  is an operation illustration showing a detection state of a paper multi-feed detection apparatus according to Embodiment 2. 
           [0026]      FIG. 4  is an operation illustration showing a detection state of a conventional paper multi-feed detection apparatus. 
           [0027]      FIG. 5  is an operation illustration showing a detection state of another conventional paper multi-feed detection apparatus. 
       
    
    
     DESCRIPTION OF THE REFERENCE NUMERALS 
       [0000]    
       
           11 ,  31  Paper multi-feed detection apparatus 
           13 ,  33  Feeding path 
           14 ,  15 ,  34 ,  35  Feeding guide plate 
           16 ,  36  Ultrasonic sensor 
           17 ,  37  Transmitter 
           18 ,  38  Receiver 
           19 ,  39  Entrance opening 
           20 ,  40  Exit opening 
           34   a , Noise shielding wall 
         U Ultrasonic wave 
         R Reflected wave 
       
     
       DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiment 1 
       [0039]    Hereinafter, one embodiment of the present invention will be described with reference to the figures. 
         [0040]    The figures show a paper sheet multi-feed detection apparatus which maybe built in a copier. As shown in  FIG. 1 , a paper sheet multi-feed detection apparatus  11  includes a main body  12  and a feeding path  13 , provided above the main body  12 , for feeding a paper sheet P in a horizontal direction two-dimensionally. A top surface of the feeding path  13  is covered with an upper feeding guide plate  14 , and a bottom surface of the feeding path  13  is covered with a lower feeding guide plate  15 . The upper feeding guide plate  14  and the lower feeding guide plate  15  face each other while having a two-dimensional feeding space  13   a  therebetween. 
         [0041]    A transmitter  17  of an ultrasonic sensor  16  is provided above the feeding path  13 , and a receiver  18  of the ultrasonic sensor  16  is provided below the feeding path  13 . The transmitter  17  and the receiver  18  also face each other while having the feeding path  13  therebetween. Transmitting and receiving directions of the ultrasonic sensor  16  are set to be oblique with respect to the feeding path  13 , so as to be suitable to transmit and receive an ultrasonic wave U. 
         [0042]    An entrance opening  19  is formed in the upper feeding guide plate  14 , more specifically at a position where the upper feeding guide plate  14  crosses the transmission wave advancing in the transmitting direction from the transmitter  17 . The ultrasonic wave U incident on the feeding space  13   a  from the transmitter  17  is reflected by the paper sheet P to become a reflected wave R, which could act as a noise component. The entrance opening  19  is formed to be large so as to discharge the reflected wave R outside the paper multi-feed detection apparatus  11 . For example, the entrance opening  19  may have a size sufficiently large to avoid multiple reflections. Herein, “multiple reflections” means that when the ultrasonic wave U is directed to a top surface of the paper sheet P, the reflected wave R directed upward at a certain angle hits the upper feeding guide plate  14  and is reflected again downward. The entrance opening  19  is circular around the center of the transmission area of the ultrasonic wave U from the transmitter  17  and has the largest possible size that does not disturb the feeding capability. 
         [0043]    An exit opening  20  is formed in the lower feeding guide plate  15 , more specifically at a position where the lower feeding guide plate  15  crosses the receiving wave advancing in the receiving direction toward the receiver  18 . The exit opening  20  is formed to be smaller than the size of a receiving face (receiving sensor head)  18   a  of the receiver  18  for receiving the ultrasonic wave U, which is output from the feeding space  13   a  toward the receiver  18 . The exit opening  20  is thus small so as to restrict the area through which the ultrasonic wave U passes to a certain size. This makes it difficult for noise to enter the receiving face  18   a , and the ultrasonic wave U is received by the receiver  18  stably. Preferably, the size of the exit opening  20  is equal to or smaller than the size of the receiving face  18   a  of the receiver  18  so as to prevent the noise from entering the receiver  18 , or is larger than half of the size of the receiving face  18   a  so as to maintain the receiving capability. 
         [0044]      FIG. 2  is a block diagram of a control circuit of the ultrasonic sensor  16  which may be incorporated into the paper multi-feed detection apparatus  11 . The ultrasonic sensor  16  includes, on the transmission side, an oscillation circuit  21  for generating a signal of a predetermined frequency (for example, 220 kHz) and an amplification circuit  22  for amplifying the signal of the predetermined frequency. 
         [0045]    The ultrasonic sensor  16  includes, on the receiving side, a filter/amplification circuit  23  for removing noise and amplifying the received signal, a rectification circuit  24  for detecting the amplified signal, and a determination circuit  25  for comparing the received signal against a reference value for determination. 
         [0046]    An electric signal of a predetermined frequency which is output from the oscillation circuit  21  is amplified by the amplification circuit  22  to a predetermined value, is input to the transmitter  17 , and is converted into an ultrasonic wave U by a piezoelectric element in the transmitter  17 . The resultant ultrasonic wave U is radiated toward the receiver  18  through the paper sheet P which is fed on the feeding path  13 . The ultrasonic wave U radiated from the transmitter  17  hits the paper sheet P which is being fed on the feeding path  13 , and is partially reflected. The ultrasonic wave U which is transmitted through the paper sheet P is received by the receiver  18 , is converted into an electric signal by a piezoelectric element in the receiver  18 , and is input to the control circuit on the receiving side. The attenuation degree of the ultrasonic wave U varies depending on whether one paper sheet P is being fed or a plurality of paper sheets P are being fed. The determination circuit  25  compares the transmission amount (attenuation degree) of the ultrasonic wave U against a reference value (threshold value) to detect whether the multi-feed of the paper sheets P is occurring or not. The detection result is transmitted to an upper-stage control section of the device, such as a copier or the like, which incorporates the paper multi-feed detection apparatus  11 . 
         [0047]    Now, with reference to the operation illustration in  FIG. 1 , the detection state of the paper multi-feed detection apparatus  11  will be described. 
         [0048]    The transmitter  17  of the ultrasonic sensor  16  directs the ultrasonic wave U in the obliquely downward transmitting direction. The ultrasonic wave U thus directed is incident on the feeding space  13   a  of the feeding path  13  via the entrance opening  19  formed in the upper feeding guide plate  14 . The ultrasonic wave U is directed toward the paper sheet P passing through the feeding space  13   a . At this point, a part of the ultrasonic wave U is reflected by the top surface of the paper sheet P, but goes outside as a reflected wave without hitting the upper feeding guide plate  14  owing to the large entrance opening  19 . Thus, the reflected wave does not cause multiple reflections and therefore does not become a noise factor. 
         [0049]    Meanwhile, the ultrasonic wave which advances linearly in the transmitting direction and is transmitted through the paper sheet P is received by the receiver  18  while being restricted in the amount by the small exit opening  20  facing the transmitting direction. The exit opening  20  is small so as to restrict the transmission amount of the ultrasonic wave U to a level appropriate for receiving. Therefore, noise is unlikely to enter the receiver  18 , and an appropriate amount of the ultrasonic wave U is received by the receiver  18  stably. 
         [0050]    Based on the determination result on the received ultrasonic wave U, it is detected on the receiving side whether one paper sheet P is being fed or a plurality of paper sheets P are being fed. When it is determined that one paper sheet P is being fed, normal feeding is confirmed. When it is determined that a plurality of paper sheets P are being fed, it is found that abnormal feeding has occurred and error information is output. 
         [0051]    As described above, when the ultrasonic sensor  16  is used for the paper multi-feed detection apparatus  11 , the reflected wave which would otherwise act as a noise component can be discharged outside by simply forming the entrance opening  19  for the ultrasonic wave U to be large. By simply forming the exit opening, for the ultrasonic wave U to be received, to be small, the noise can be prevented from entering the receiver  18  and the receiving capability can be improved. The capabilities of the ultrasonic wave can be significantly improved by simply changing the sizes of the entrance opening  19  and the exit opening  20 . 
       Embodiment 2 
       [0052]      FIG. 3  shows another paper multi-feed detection apparatus  31 . The paper sheet multi-feed detection apparatus  31  includes a main body  32  and a feeding path  33 , provided above the main body  32 , for feeding a paper sheet P in a horizontal direction two-dimensionally. A top surface of the feeding path  33  is covered with an upper feeding guide plate  34 , and a bottom surface of the feeding path  33  is covered with a lower feeding guide plate  35 . The upper feeding guide plate  34  and the lower feeding guide plate  35  face each other while having a two-dimensional feeding space  33   a  therebetween. 
         [0053]    A transmitter  37  of an ultrasonic sensor  36  is provided above the feeding path  33 , and a receiver  38  of the ultrasonic sensor  36  is provided below the feeding path  33 . The transmitter  37  and the receiver  38  also face each other while having the feeding path  33  therebetween. Transmitting and receiving directions of the ultrasonic sensor  36  are set to be oblique with respect to the feeding path  33 , so as to be suitable to transmit and receive an ultrasonic wave U. 
         [0054]    An entrance opening  39  is formed in the upper feeding guide plate  34 , more specifically at a position where the upper feeding guide plate  34  crosses the transmission wave advancing in the transmitting direction from the transmitter  37 . The ultrasonic wave transmission area from the transmitter  37  to the entrance opening  39  is in an open state without being enclosed. Since the ultrasonic wave transmission area is in an open state, when the ultrasonic wave U incident on the feeding space  33   a  from the transmitter  37  is reflected by the paper sheet P, the reflected wave R which would otherwise act as a noise component is discharged outside through the open area. Therefore, the multiple reflections in the transmission area can be avoided. An exit opening  40  is formed in the lower feeding guide plate  35 , more specifically at apposition where the lower feeding guide plate  35  crosses the receiving wave advancing in the receiving direction toward the receiver  38 . The ultrasonic wave receiving area from the exit opening  40  to the receiver  38  is enclosed by a cylindrical noise shielding wall  38   a . This structure prevents external disturbing noise R 1  or the reflected wave R from reaching the receiver  38 . This makes it difficult for noise to enter the receiver  38 , and the ultrasonic wave U is received by the receiver  18  stably. 
         [0055]    The elements of the above-described embodiments correspond to elements of the following claims as follows. 
         [0056]    The paper multi-feed detection apparatus according to the present invention corresponds to the paper multi-feed detection apparatuses  11  and  31  in the embodiments; 
         [0057]    the paper sheet corresponds to the paper sheet P; 
         [0058]    one feeding guide plate corresponds to the upper feeding guide plate  14 ; 
         [0059]    another feeding guide plate corresponds to the lower feeding guide plate  15 . 
         [0060]    The present invention is not limited to the above-described embodiments, and may be applied in various ways based on the technological idea defined by the claims.