Patent Publication Number: US-8991820-B2

Title: Paper conveying apparatus, jam detection method, and computer-readable, non-transitory medium

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority of prior Japanese Patent Application No. 2012-203466, filed on Sep. 14, 2012, the entire contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     Embodiments discussed in the present specification relate to paper conveying technology. 
     BACKGROUND 
     In a paper conveying apparatus of an image reading apparatus, image copying apparatus, etc., sometimes a jam occurs when the paper moves along the conveyance path. In general, a paper conveying apparatus is provided with the function of determining whether a jam has occurred by a paper being conveyed to a predetermined position inside the conveyance path within a predetermined time from the start of conveyance of the paper and of stopping the operation of the apparatus when a jam has occurred. 
     On the other hand, if a jam occurs, a large sound is generated in the conveyance path, so the paper conveying apparatus can determine whether a jam has occurred based on the sound which is generated on the conveyance path and thereby detect the occurrence of a jam without waiting for the elapse of the predetermined time. 
     A detection apparatus of printed matter which determines that a bill is normal if the level of an output signal of a filter which passes only a signal of a frequency band which is set in advance according to the type of the paper currency is higher than a preset detection level and determines that a bill is damaged if the level is lower than that, has previously been disclosed (see Japanese Laid-Open Patent Publication No. 61-169983). 
     SUMMARY 
     In the past, the conveyance sound of a paper which has wrinkles sometimes caused it to be mistakenly determined that a jam had occurred. 
     Accordingly, it is an object of the present invention to provide a paper conveying apparatus and a jam detection method that can suppress mistaken detection of the occurrence of a jam and a computer-readable, non-transitory medium storing a computer program for causing a computer to implement such a jam detection method. 
     According to an aspect of the apparatus, there is provided a paper conveying apparatus. The paper conveying apparatus includes a sound signal generator, provided with a sound detector near a conveyance path of a paper, for generating a sound signal, and a sound jam detector for determining whether a jam has occurred based on a variation of a component of the sound signal. 
     According to an aspect of the method, there is provide a jam detection method. The jam detection method includes acquiring a sound signal, and determining, by a computer, whether a jam has occurred based on a variation of a component of the sound signal. 
     According to an aspect of the computer-readable, non-transitory medium storing a computer program, the computer program causes a computer to execute a process, including acquiring a sound signal, and determining whether a jam has occurred based on a variation of a component of the sound signal. 
     The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view which shows a paper conveying apparatus  100  and image processing apparatus  10  according to an embodiment. 
         FIG. 2  is a view for explaining an example of a conveyance route at an inside of a paper conveying apparatus  100 . 
         FIG. 3  is an example of a block diagram which shows a schematic configuration of a paper conveying apparatus  100 . 
         FIG. 4  is a flow chart which shows an example of operation of overall processing of a paper conveying apparatus  100 . 
         FIG. 5  is a flow chart which shows an example of an abnormality detection of the paper conveyance. 
         FIG. 6  is a flow chart which shows an example of operation of sound jam detection processing. 
         FIG. 7  is a graph which shows an example of a frequency signal. 
         FIG. 8  is a flow chart which shows an example of operation of position jam detection processing. 
         FIG. 9  is a flow chart which shows an example of operation of multifeed detection processing. 
         FIG. 10  a view for explaining properties of an ultrasonic signal. 
         FIG. 11  is a flow chart which shows another example of operation of sound jam detection processing. 
         FIG. 12  is a block diagram which shows the schematic configuration of a paper conveying apparatus  200  corresponding to another embodiment. 
         FIG. 13  is a flow chart which shows still another example of the operations in sound jam detection processing. 
         FIG. 14  is a graph which shows an example of a frequency signal when another paper is conveyed. 
         FIG. 15  is a block diagram which shows the schematic configuration of a paper conveying apparatus  300  according to still another embodiment. 
         FIG. 16  is a view which shows an example of a screen for setting a resolution for reading a paper. 
         FIG. 17  is a graph which shows examples of frequency signals in the cases of difference conveyance speeds of a paper. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, a paper conveying apparatus, jam detection, and computer program according to an embodiment, will be described with reference to the drawings. However, note that the technical scope of the invention is not limited to these embodiments and extends to the inventions described in the claims and their equivalents. 
       FIG. 1  is a perspective view which shows a paper conveying apparatus  100  which are configured as an image scanner, and an information processing apparatus  10 , according to an embodiment. 
     The paper conveying apparatus  100  includes a lower housing  101 , an upper housing  102 , a paper tray  103 , an ejection tray  105 , an operation button  106 , etc., and is connected to an information processing apparatus (for example, personal computer, portable data terminal, etc.) 
     The upper housing  102  is arranged at a position which covers the top surface of the paper conveying apparatus  100  and is engaged with the lower housing  101  by hinges so as to be able to be opened and closed at the time of a paper jam, at the time of cleaning of the inside of the paper conveying apparatus  100 , etc. 
     The paper tray  103  is engaged with the lower housing  101  in a manner enabling a paper to be placed. The paper tray  103  is provided with side guides  104   a  and  104   b  which can be moved in a direction perpendicular to a conveyance direction of the paper, that is, to the left and right directions from the conveyance direction of the paper. By positioning the side guides  104   a  and  104   b  to match with the width of the paper, it is possible to limit the width direction of the paper. 
     The ejection tray  105  is engaged with the lower housing  101  by hinges so as to be able to pivot in the direction which is shown by an arrow mark A 1 . In the opened state as shown in  FIG. 1 , the ejected paper can be held. 
     The operation button  106  is arranged on the surface of the upper housing  102 . If pushed, it generates and outputs an operation detection signal. 
       FIG. 2  is a view for explaining an example of the conveyance route at the inside of the paper conveying apparatus  100 . 
     The conveyance route at the inside of the paper conveying apparatus  100  has a first paper detector  110 , a paper feed roller  111 , a retard roller  112 , a microphone  113 , a second paper detector  114 , an ultrasonic transmitter  115   a , an ultrasonic receiver  115   b , a first conveyor roller  116 , a first driven roller  117 , a third paper detector  118 , a first image capture unit  119   a , a second image capture unit  119   b , a second conveyor roller  120 , a second driven roller  121 , etc. 
     The top surface of the lower housing  101  forms the lower guide  107   a  of the conveyance path of the paper, while the bottom surface of the upper housing  102  forms the upper guide  107   b  of the conveyance path of the paper. In  FIG. 2 , the arrow mark A 2  shows the conveyance direction of the paper. Below, “upstream” means upstream of the conveyance direction A 2  of the paper, while “downstream” means downstream of the conveyance direction A 2  of the paper. 
     The first paper detector  110  has a contact detection sensor which is arranged at an upstream side of the paper feed roller  111  and the retard roller  112  and detects if a paper is placed on the paper tray  103 . The first paper detector  110  generates and outputs a first paper detection signal which changes in signal value between a state in which a paper is placed on the paper tray  103  and a state in which one is not placed. 
     The microphone  113  is an example of a sound detector, is provided near a conveyance path of a paper, and detects the sound generated by a paper during conveyance of the paper, and generates and outputs an analog signal corresponding to the detected sound. The microphone  113  is arranged at the downstream side of the paper feed roller  111  and the retard roller  112  while fastened to the frame  108  at the inside of the upper housing  102 . Note that, to enable the sound when papers are separated at the paper feed roller  111  and retard roller  112  to be detected better, the microphone  113  is preferably provided near to the paper feed roller  111  and retard roller  112  from near a side wall of the paper conveyance path. A hole  109  is provided in the upper guide  107   b  facing the microphone  113 , so that the sound generated by the paper during conveyance of the paper can be more accurately detected by the microphone  113 . 
     The second paper detector  114  has a contact detection sensor which is arranged at a downstream side of the paper feed roller  111  and the retard roller  112  and at an upstream side of the first conveyor roller  116  and first driven roller  117  and detects if there is a paper present at that position. The second paper detector  114  generates and outputs a second paper detection signal which changes in signal value between a state at which there is a paper at that position and a state where there is no paper there. 
     The ultrasonic transmitter  115   a  and the ultrasonic receiver  115   b  are an example of an ultrasonic detector, and are arranged near the conveyance path of the paper so as to face each other across the conveyance path. The ultrasonic transmitter  115   a  transmits an ultrasonic wave. On the other hand, the ultrasonic receiver  115   b  detects an ultrasonic wave which is transmitted by the ultrasonic transmitter  115   a  and passes through the paper or papers, and generates and outputs an ultrasonic signal comprised of an electrical signal corresponding to the detected ultrasonic wave. Below, the ultrasonic transmitter  115   a  and the ultrasonic receiver  115   b  will sometimes be referred to altogether as the “ultrasonic sensor  115 ”. 
     The third paper detector  118  has a contact detection sensor which is arranged at a downstream side of the first conveyor roller  116  and the first driven roller  117  and an upstream side of the first image capture unit  119   a  and the second image capture unit  119   b  and detects if there is a paper at that position. The third paper detector  118  generates and outputs a third paper detection signal which changes in signal value between a state where there is a paper at that position and a state where there is no such paper there. 
     The first image capture unit  119   a  has a CIS (contact image sensor) of an equal magnification optical system type which is provided with an image capture element using CMOS&#39;s (complementary metal oxide semiconductors) which are arranged in a line in the main scan direction. This CIS reads the back surface of the paper and generates and outputs an analog image signal. Similarly, the second image capture unit  119   b  has a CIS of an equal magnification optical system type which is provided with an image capture element using CMOS&#39;s which are arranged in a line in the main scan direction. This CIS reads the front surface of the paper and generates and outputs an analog image signal. Note that, it is also possible to arrange only one of the first image capture unit  119   a  and the second image capture unit  119   b  and read only one surface of the paper. Further, instead of a CIS, it is also possible to utilize an image capturing sensor of a reduced magnification optical system type using CCD&#39;s (charge coupled devices). Below, the first image capture unit  119   a  and the second image capture unit  119   b  will sometimes be referred to overall as the “image capture units  119 ”. 
     A paper which is placed on the paper tray  103  is conveyed between the lower guide  107   a  and the upper guide  107   b  toward the paper conveyance direction A 2  by rotation of the paper feed roller  111  in the direction of the arrow mark A 3  of  FIG. 2 . The retard roller  112  rotates in the direction of the arrow mark A 4  of  FIG. 2  at the time of paper conveyance. Due to the action of the paper feed roller  111  and the retard roller  112 , when the paper tray  103  has a plurality of papers placed on it, among the papers which are placed on the paper tray  103 , only the paper which is in contact with the paper feed roller  111  is separated. The conveyance of papers other than the separated paper is restricted (prevention of multifeed). The paper feed roller  111  and the retard roller  112  function as a paper separator. 
     A paper is fed between the first conveyor roller  116  and the first driven roller  117  while being guided by the lower guide  107   a  and the upper guide  107   b . The paper is sent between the first image capture unit  119   a  and the second image capture unit  119   b  by the first conveyor roller  116  rotating in the direction of the arrow mark A 5  of  FIG. 2 . The paper which is read by the image capture unit  119  is ejected onto the ejection tray  105  by the second conveyor roller  120  rotating in the direction of the arrow mark A 6  of the  FIG. 2 . 
       FIG. 3  is an example of a block diagram which shows the general configuration of a paper conveying apparatus  100 . 
     The paper conveying apparatus  100 , in addition to the above-mentioned configuration, further has a first image A/D conversion unit  140   a , a second image A/D conversion unit  140   b , a sound signal generator  141 , a drive unit  145 , an interface  146 , a storage unit  147 , a central processing unit  150 , etc. 
     The first image A/D conversion unit  140   a  converts an analog image signal which is output from the first image capture unit  119   a  from an analog to digital format to generate digital image data which it then outputs to the central processing unit  150 . Similarly, the second image A/D conversion unit  140   b  converts the analog image signal which is output from the second image capture unit  119   b  from an analog to digital format to generate digital image data which it then outputs to the central processing unit  150 . Below, these digital image data will be referred to as the “read image”. 
     The sound signal generator  141  includes a microphone  113 , a filter  142 , an amplifier  143 , a sound A/D conversion unit  144 , etc., and generates a sound signal. The filter  142  applies a bandpass filter which passes a predetermined frequency band of a signal to an analog signal which is output from the microphone  113  and outputs it to the amplifier  143 . The amplifier  143  amplifies the signal which is output from the filter  142  and outputs it to the sound A/D conversion unit  144 . The sound A/D conversion unit  144  converts the analog signal which is output from the amplifier  143  to a digital signal and outputs it to the central processing unit  150 . Below, a signal which is output by the sound signal generator  141  will be referred to as a “sound signal”. 
     Note that, the sound signal generator  141  is not limited to this. The sound signal generator  141  may include only the microphone  113 , while the filter  142 , the amplifier  143 , and the sound A/D conversion unit  144  may be provided outside of the sound signal generator  141 . Further, the sound signal generator  141  may include only the microphone  113  and the filter  142  or only the microphone  113 , the filter  142 , and the amplifier  143 . 
     The drive unit  145  includes one or more motors and uses control signals from the central processing unit  150  to rotate the paper feed roller  111 , the retard roller  112 , the first conveyor roller  116 , and the second conveyor roller  120  and operate to convey a paper. 
     The interface  146  has, for example, a USB or other serial bus-based interface circuit and electrically connects with the information processing apparatus  10  to send and receive a read image and various types of information. Further, it is also possible to connect a flash memory etc., to the interface  146  so as to store the read image. 
     The storage unit  147  has a RAM (random access memory), ROM (read only memory), or other memory device, a hard disk or other fixed disk device, or flexible disk, optical disk, or other portable storage device. Further, the storage unit  147  stores a computer program, database, tables, etc., which are used in various processing of the paper conveying apparatus  100 . The computer program may be installed on the storage unit  147  from a computer-readable, non-transitory medium such as a compact disk read only memory (CD-ROM), a digital versatile disk read only memory (DVD-ROM), or the like by using a well-known setup program or the like. Furthermore, the storage unit  147  stores the read images. 
     The central processing unit  150  is provided with a CPU (central processing unit) and operates based on a program which is stored in advance in the storage unit  147 . Note that, the central processing unit  150  may also be comprised of a DSP (digital signal processor), LSI (large scale integrated circuit), ASIC (application specific integrated circuit), FPGA (field-programming gate array), etc. 
     The central processing unit  150  is connected to the operation button  106 , first paper detector  110 , second paper detector  114 , ultrasonic sensor  115 , third paper detector  118 , first image capture unit  119   a , second image capture unit  119   b , first image A/D conversion unit  140   a , second image A/D conversion unit  140   b , sound signal generator  141 , drive unit  145 , interface  146 , and storage unit  147  and controls these units. 
     The central processing unit  150  control a drive operation of the drive unit  145 , control a paper read operation of the image capture unit  119 , etc., to acquire a read image. Further, the central processing unit  150  has a control module  151 , an image generator  152 , a sound jam detector  153 , a position jam detector  154 , a multifeed detector  155 , a frequency signal generator  156 , etc. These units are functional modules which are realized by software which operate on a processor. Note that, these units may be comprised of respectively independent integrated circuits, a microprocessor, firmware, etc. 
       FIG. 4  is a flow chart which shows an example of operation of overall processing of the paper conveying apparatus  100 . 
     Below, referring to the flow chart which is shown in  FIG. 4 , an example of the operation of the overall processing of the paper conveying apparatus  100  will be explained. Note that, the flow of the operation which is explained below is performed based on a program which is stored in advance in the storage unit  147  mainly by the central processing unit  150  in cooperation with the elements of the paper conveying apparatus  100 . 
     First, the central processing unit  150  stands by until a user pushes the operation button  106  and an operation detection signal is received from the operation button  106  (step S 101 ). 
     Next, the central processing unit  150  determines whether the paper tray  103  has a paper placed on it based on the first paper detection signal which was received from the first paper detector  110  (step S 102 ). 
     If the paper tray  103  does not have a paper placed on it, the central processing unit  150  returns the processing to step S 101  and stands by until newly receiving an operation detection signal from the operation button  106 . 
     On the other hand, when the paper tray  103  has a paper placed on it, the central processing unit  150  drives the drive unit  145  to rotate the paper feed roller  111 , retard roller  112 , first conveyor roller  116 , and second conveyor roller  121  and convey the paper (step S 103 ). 
     Next, the control module  151  determines whether an abnormality flag is ON or not (step S 104 ). This abnormality flag is set OFF at the time of startup of the paper conveying apparatus  100  and is set ON if a later explained abnormality detection processing determines that an abnormality has occurred. 
     When the abnormality flag is ON, the control module  151 , as an abnormal processing, stops the drive unit  145  to stop the conveyance of the paper, uses a not shown speaker, LED (light emitting diode), etc. to notify the user of the occurrence of an abnormality, sets the abnormality flag OFF (step S 105 ), and ends the series of steps. 
     On the other hand, when the abnormality flag is not ON, the image generator  152  makes the first image capture unit  119   a  and the second image capture unit  119   b  read the conveyed paper and acquires the read image through the first image A/D conversion unit  140   a  and the second image A/D conversion unit  140   b  (step S 106 ). 
     Next, the central processing unit  150  transmits the acquired read image through the interface  146  to a not shown information processing apparatus (step S 107 ). Note that, when not connected to an information processing apparatus, the central processing unit  150  stores the acquired read image in the storage unit  147 . 
     Next, the central processing unit  150  determine whether the paper tray  103  has a paper remaining thereon based on the first paper detection signal which was received from the first paper detector  110  (step S 108 ). 
     When the paper tray  103  has a paper remaining thereon, the central processing unit  150  returns the processing to step S 103  and repeats the processing of steps S 103  to S 108 . On the other hand, when the paper tray  103  does not have any paper remaining thereon, the central processing unit  150  ends the series of processing. 
       FIG. 5  is a flow chart which shows an example of an abnormality detection of the paper conveyance of the paper conveying apparatus  100 . 
     The flow of operation which is explained below is executed based on a program which is stored in advance in the storage unit  147  mainly by the central processing unit  150  in cooperation with the elements of the paper conveying apparatus  100 . 
     First, the sound jam detector  153  executes sound jam detection processing (step S 201 ). In the sound jam detection processing, the sound jam detector  153  determines whether a jam has occurred based on a variation of a component of a sound signal which is acquired from the sound signal generator  141 . The variation of the component of the sound signal means the magnitude of variation between specific components in a sound signal. Below, sometimes a jam which is determined to exist by the sound jam detector  153  based on a variation of a component of a sound signal will be called a “sound jam”. Details of the sound jam detection processing will be explained later. 
     Next, the position jam detector  154  performs position jam detection processing (step S 202 ). In the position jam detection processing, the position jam detector  154  determines the occurrence of a jam based on the second paper detection signal which is acquired from the second paper detector  114  and the third paper detection signal which is acquired from the third paper detector  118 . Below, sometimes a jam which is determined to exist by the position jam detector  154  based on the second paper detection signal and third paper detection signal will be called a “position jam”. Details of the position jam detection processing will be explained later. 
     Next, the multifeed detector  155  performs multifeed detection processing (step S 203 ). In the multifeed detection processing, the multifeed detector  155  determines the occurrence of a multifeed of papers based on the ultrasonic signal which was acquired from the ultrasonic sensor  116 . Details of the multifeed detection processing will be explained later. 
     Next, the control module  151  determines whether an abnormality has occurred in the paper conveyance processing (step S 204 ). The control module  151  determines that an abnormality has occurred if at least one of a sound jam, position jam, and paper multifeed has occurred. That is, it is determined that no abnormality has occurred when none of a sound jam, position jam, or paper multifeed has occurred. 
     The control module  151  sets the abnormality flag to ON (step S 205 ) and ends the series of steps when an abnormality occurs in the paper conveyance processing. On the other hand, when no abnormality occurs in the paper conveyance processing, it ends the series of steps without particularly performing any further processing. Note that, the flow chart which is shown in  FIG. 5  is repeatedly executed every predetermined time interval. 
       FIG. 6  is a flow chart which shows an example of operation of a sound jam judgment processing. 
     The flow of operation which is shown in  FIG. 6  is executed at step S 201  of the flow chart which is shown in  FIG. 5 . 
     First, the frequency signal generator  156  acquires a sound signal from the sound signal generator  141  (step S 301 ). 
     Next, the frequency signal generator  156  generates a frequency signal which is acquired by using a fast Fourier transform (FFT) to convert the sound signal which is acquired from the sound signal generator  141  to frequency (step S 302 ). 
     The sound A/D conversion unit  144  samples an analog signal which is output by the amplifier  143  at 22 kHz to convert it to a digital format and generate a sound signal. The frequency signal generator  156  acquires 1024 samples worth (46 msec worth) of the sound signal and samples it at 100 Hz to 600 Hz in range at 21.5 Hz intervals to acquire a signal converted to frequency. The frequency signal generator  156  converts the signal acquired by converting the sound signal to frequency to decibels based on the maximum possible volume so as to generate the frequency signal. 
       FIG. 7  is a graph which shows an example of frequency signals. In  FIG. 7 , the abscissa shows the frequency, while the ordinate shows the signal value of the frequency signal. The graph  700  of  FIG. 7  shows an example of a frequency signal  701  when a normal paper which does not have wrinkles (below, called “normal paper”) is conveyed, a frequency signal  702  when a paper which has wrinkles (below, called “wrinkled paper”) is conveyed, and a frequency signal  703  when a jam occurs. 
     As shown in  FIG. 7 , at the frequency signal  701  when normal paper is conveyed and the frequency signal  702  when wrinkled paper is conveyed, components of specific frequencies (170 Hz and 390 Hz) become larger than the components of other frequencies. On the other hand, in the frequency signal  703  when a jam occurs, the component of a specific frequency is not larger than the components of other frequencies as much as in the frequency signal  701  and frequency signal  702 . 
     Next, the sound jam detector  153  averages a plurality of values of the frequency signal which is generated by the frequency signal generator  156  at predetermined time periods to generate an averaged frequency signal (step S 303 ). The sound jam detector  153  averages the signal values at frequencies at 21.5 Hz intervals in six samples worth (276 msec worth) of the frequency signal to generate the averaged frequency signal. The sound jam detector  153  can average the frequency signal to thereby acquire stable results of detection in sound jam detection processing. 
     Next, the sound jam detector  153  calculates, as the fluctuation of a component of the sound signal, an unevenness of the frequency signal, that is, an unevenness of a frequency component of the sound signal (step S 304 ). The unevenness means the degree of change between specific components. 
     The sound jam detector  153  calculates the sum of the differences between the values of the frequency components at the averaged frequency signal and the values of the adjoining frequency components which respectively adjoin the frequency components as the unevenness of the frequency signal. The sound jam detector  153  calculates, for each frequency at 21.5 Hz intervals, the absolute value of the difference between the value of the averaged frequency signal at that frequency and the value of the averaged frequency signal at a frequency adjoining that frequency (frequency 21.5 Hz higher than that frequency). The sound jam detector  153  calculates the total sum of the absolute values of the differences which were calculated for each frequency of 100 Hz to 600 Hz as the unevenness of the frequency signal. 
     Next, the sound jam detector  153  determines whether the calculated unevenness is a predetermined value or more (step S 305 ). The predetermined value is set, by advance experiments, to a value which enables the unevenness when a jam occurs and the unevenness when no jam has occurred to be differentiated. In the present example, it is made 24. 
     Next, the sound jam detector  153  determines that no sound jam has occurred when the unevenness is a predetermined value or more (step S 306 ) and determines that a sound jam has occurred when the unevenness is less than the predetermined value (step S 307 ), then the series of steps is ended. 
     In the example which is shown in  FIG. 7 , the unevenness of the frequency signal  701  becomes 45 and the unevenness of the frequency signal  702  becomes 28, so for the frequency signal  701  and frequency signal  702 , it is determined that no sound jam has occurred. On the other hand, the unevenness of the frequency signal  703  becomes 19, so for the frequency signal  703 , it is determined that a sound jam has occurred. 
     Note that, at step S 304 , the sound jam detector  153  may calculate the deviation of unevenness of the frequency signal from the difference of the average values of the averaged frequency signal at adjoining frequency bands. In this case, the sound jam detector  153  divides the 100 Hz to 600 Hz frequency band into frequency bands of 64.5 Hz bandwidths including three frequencies at 21.5 Hz intervals. The sound jam detector  153  calculates, for each divided frequency band, the absolute value of the difference between the average value of the averaged frequency signal at that frequency band and the average value of the averaged frequency signal at a frequency band which adjoins that frequency bands. The sound jam detector  153  calculates the sum of the absolute values of the differences which were calculated for the respective frequency bands divided between 100 Hz and 600 Hz as the unevenness of the frequency signal. 
     Further, at step S 304 , the sound jam detector  153  may calculate the difference between the maximum value of the averaged frequency signal at 100 Hz to 600 Hz and the average value of the averaged frequency signal as the unevenness of the frequency signal. The predetermined value in this case may be made 5. 
     When calculating the difference between the maximum value of the averaged frequency signal at 100 Hz to 600 Hz and the average value of the averaged frequency signal as the unevenness of the frequency signal, in the example which is shown in  FIG. 7 , the unevenness of the frequency signal  701  becomes 10 and the unevenness of the frequency signal  702  becomes 7. Therefore, for the frequency signal  701  and frequency signal  702 , it is determined that no sound jam occurs. On the other hand, the unevenness of the frequency signal  703  becomes 3, so for the frequency signal  703 , it is determined that a sound jam has occurred. 
     Further, at step S 304 , the sound jam detector  153  may calculate the difference of the maximum value of the averaged frequency signal at 100 Hz to 600 Hz and the minimum value of the averaged frequency signal as the unevenness of the frequency signal. The predetermined value in this case may be made 9. 
     When calculating the difference of the maximum value of the averaged frequency signal at 100 Hz to 600 Hz and the minimum value of the averaged frequency signal as the unevenness of the frequency signal, in the example which is shown in  FIG. 7 , the unevenness of the frequency signal  701  becomes 16 and the unevenness of the frequency signal  702  becomes 11. Therefore, for the frequency signal  701  and frequency signal  702 , it is determined that no sound jam has occurred. On the other hand, the unevenness of the frequency signal  703  becomes 6, so for the frequency signal  703 , it is determined that a sound jam has occurred. 
     Further, at step S 304 , the sound jam detector  153  may calculate the difference of the signal value of the averaged frequency signal at a predetermined frequency (170 Hz) and the average value of the averaged frequency signal as the unevenness of the frequency signal. 
     Further, at step S 304 , the sound jam detector  153  may calculate the difference of the signal value of the averaged frequency signal at a predetermined frequency (170 Hz) and the minimum value of the averaged frequency signal as the unevenness of the frequency signal. 
     Further, at step S 304 , the sound jam detector  153  may calculate the unevenness of the frequency signal not from the averaged frequency signal, but from the frequency signal itself. 
     Regarding calculation of the unevenness, the values of the sampling frequency of the sound signal, the range of the frequency generating the frequency signal, the interval of frequencies which are sampled (resolution of frequency signal), etc., are not limited to the above-mentioned values and can be suitably changed. Further, the values of the number of frequency signals for generation of the averaged frequency signal, the predetermined value for comparison with the unevenness, the numbers of frequencies inside the respective divided frequency bands when dividing a frequency band, the predetermined frequency, etc., are not limited to the above-mentioned values and can be suitably changed. Further, the frequency signal may be made a signal which expresses the absolute quantity not converted to decibels. 
     When a plurality of papers are conveyed, when the papers are separated at the paper feed roller  111  and retard roller  112 , the papers rub against each other to thereby generate a rubbing sound. In the frequency signal which is generated from the sound signal at that time, due to this rubbing sound, specific frequency components will become larger than the other frequency components. On the other hand, if a jam occurs, the sound which is generated due to that jam masks that rubbing sound, so in the frequency signal which is generated from the sound signal at that time, no specific frequency components become larger than other frequency components as much as in a frequency signal when no jam has occurred. Therefore, as explained above, by utilizing the unevenness of a frequency signal, it is possible to precisely determine whether a jam has occurred. 
       FIG. 8  is a flow chart which shows an example of operation of a position jam detection processing. 
     The flow of operation which is shown in  FIG. 8  is executed at step S 202  of the flow chart which is shown in  FIG. 5 . 
     First, the position jam detector  154  stands by until the front end of the paper is detected by the second paper detector  114  (step S 401 ). The position jam detector  154  determines that the front end of the paper is detected at the position of the second paper detector  114 , that is, downstream of the paper feed roller  111  and retard roller  112  and upstream of the first conveyor roller  116  and first driven roller  117 , when the value of the second paper detection signal from the second paper detector  114  changes from a value which shows the state where there is no paper to a value which shows the state where there is one. 
     Next, when the second paper detector  114  detects the front end of a paper, the position jam detector  154  starts counting time (step S 402 ). 
     Next, the position jam detector  154  determines whether the third paper detector  118  has detected the front end of the paper (step S 403 ). The position jam detector  154  determines that the front end of the paper is detected at the position of the third paper detector  118 , that is, downstream of the first conveyor roller  116  and first driven roller  117  and upstream of the image capture unit  119 , when the value of the third paper detection signal from the third paper detector  118  changes from a value which shows the state where there is no paper to a value which shows the state where there is one. 
     When the third paper detector  118  detects the front end of a paper, the position jam detector  154  determines that no position jam has occurred (step S 404 ) and ends the series of steps. 
     On the other hand, if the third paper detector  118  detects the front end of the paper, the position jam detector  154  determines whether a predetermined time (for example, 1 second) has elapsed from the start of counting time (step S 405 ). If a predetermined time has not elapsed, the position jam detector  154  returns to the processing of step S 403  and again determines whether the third paper detector  118  has detected the front end of the paper. On the other hand, when a predetermined time has elapsed, the position jam detector  154  determines that position jam has occurred (step S 406 ) and ends the series of steps. Note that, when position jam detection processing is not required in the paper conveying apparatus  100 , this may be omitted. 
     Note that, when the central processing unit  150  detects that the front end of a paper is downstream of the first conveyor roller  116  and the first driven roller  117  by the third paper detection signal from the third paper detector  118 , it controls the drive unit  145  to stop the rotation of the paper feed roller  111  and retard roller  112  so that the next paper is not fed. After that, when the central processing unit  150  detects the rear end of the paper downstream of the paper feed roller  111  and the retard roller  112  by the second paper detection signal from the second paper detector  114 , it again controls the drive unit  145  to rotate the paper feed roller  111  and retard roller  112  and convey the next paper. Due to this, the central processing unit  150  prevents a plurality of papers from being superposed in the conveyance path. For this reason, the position jam detector  154  may start counting the time at the point of time when the central processing unit  150  controls the drive unit  145  to rotate the paper feed roller  111  and the retard roller  112  and determine that a position jam has occurred when the third paper detector  118  does not detect the front end of a paper within a predetermined time. 
       FIG. 9  is a flow chart which shows an example of operation of multifeed detection processing. 
     The flow of operation which is shown in  FIG. 9  is executed at step S 203  of the flow chart which is shown in  FIG. 5 . 
     First, the multifeed detector  155  acquires an ultrasonic signal from the ultrasonic sensor  115  (step S 501 ). 
     Next, the multifeed detector  155  determines whether the signal value of the acquired ultrasonic signal is less than the multifeed detection threshold value (step S 502 ). 
       FIG. 10  is a view for explaining properties of an ultrasonic signal. 
     In the graph  1000  of  FIG. 10 , the solid line  1001  shows the characteristic of the ultrasonic signal in the case where a single paper is conveyed, while the broken line  1002  shows the characteristic of the ultrasonic signal in the case where multifeed of papers has occurred. The abscissa of the graph  1000  shows the time, while the ordinate shows the signal value of the ultrasonic signal. Due to the occurrence of multifeed, the signal value of the ultrasonic signal of the broken line  1002  falls in the section  1003 . For this reason, it is possible to determine whether multifeed of papers has occurred by whether the signal value of the ultrasonic signal is less than the multifeed detection threshold value ThA. 
     On the other hand, the solid line  1004  shows the characteristic of the ultrasonic signal in the case where just one plastic card thicker than paper is conveyed. When a card is conveyed, the signal value of the ultrasonic signal becomes smaller than the multifeed detection threshold value ThA, so the multifeed detector  155  mistakenly determines that a multifeed of papers has occurred. Note that, even if sufficiently thick, high rigidity thick paper has been conveyed, an ultrasonic signal which has characteristics similar to the case where a plastic card is conveyed is detected, so the multifeed detector  155  is liable to mistakenly determine that a multifeed of papers has occurred. 
     The multifeed detector  155  determines that multifeed of the papers has occurred when the signal value of the ultrasonic signal is less than the multifeed detection threshold value (step S 503 ), determines that multifeed of the papers has not occurred when the signal value of the ultrasonic signal is the multifeed detection threshold value or more (step S 504 ), and ends the series of steps. 
     As explained in detail above, the paper conveying apparatus  100  operates in accordance with the flow charts which are shown in  FIG. 4 ,  FIG. 5 , and  FIG. 6  to thereby determine whether a jam has occurred based on the variation of a frequency signal which is generated from the sound generated by a paper during conveyance, in particular, the unevenness. There are no large peaks in the frequency spectrum of sound which is generated due to a jam, so the paper conveying apparatus  100  can precisely determine whether a jam has occurred. 
       FIG. 11  is a flow chart which shows another example of the operations in sound jam detection processing. 
     This flow chart can be used in the paper conveying apparatus  100  instead of the above-mentioned flow chart which is shown in  FIG. 6 . In the flow chart which is shown in  FIG. 11 , unlike the flow chart which is shown in  FIG. 6 , the sound jam detector  153  calculates a slant of the frequency signal as the variation of the components of the sound signal. The processing of steps S 601  to S 603  which are shown in  FIG. 11  is the same as the processing of steps S 301  to S 303  which are shown in  FIG. 6 , so explanations will be omitted. Below, only the processing of steps S 604  to S 607  will be explained. 
     At step S 604 , the sound jam detector  153  calculates the slant of the frequency signal, that is, the slant of the frequency components of the sound signal, as the variation of the components of the sound signal. The “slant” means the degree of reduction between specific components. 
     The sound jam detector  153  calculates the ratio of the average value of the frequency signal at 100 Hz to 600 Hz (second frequency band) to the average value of the frequency signal at 100 Hz to 200 Hz (first frequency band) as the slant of the frequency signal. Note that, the second frequency band is a frequency band where the lowest frequency is the same as the lowest frequency of the first frequency band and the highest frequency is higher than the highest frequency of the first frequency band. The signal value of a frequency signal is a negative value, so the tendency is shown of the signal value of a frequency signal greatly decreasing along with an increase in frequency the greater the slant. 
     Next, the sound jam detector  153  determines whether the calculated slant is a predetermined value or more (step S 605 ). The predetermined value is set by previous experiments to a value which enables the slant when a jam has occurred and the slant when a jam has not occurred to be differentiated. In the present case it was made 1.18. 
     Next, the sound jam detector  153  determines that a sound jam has not occurred when the slant is a predetermined value or more (step S 606 ) and determines that a sound jam has occurred when the slant is less than the predetermined value (step S 607 ), then the series of steps is ended. 
     In the example which is shown in  FIG. 7 , the slant of the frequency signal  701  becomes 1.24 and the slant of the frequency signal  702  becomes 1.23, so, for the frequency signal  701  and frequency signal  702 , it is determined that no sound jam has occurred. On the other hand, the slant of the frequency signal  703  becomes 1.13, so, for the frequency signal  703 , it is determined that a sound jam has occurred. 
     Further, at step S 604 , the sound jam detector  153  may calculate the ratio of the average value of the frequency signal at 200 Hz to 600 Hz (second frequency band) to the average value of the frequency signal at 100 Hz to 200 Hz (first frequency band) as the slant of the frequency signal. Note that, in this case, the second frequency band is a frequency band which is higher than the first frequency band. In this case, the predetermined value can be made 1.23. 
     When calculating the ratio of the average value of the frequency signal at 200 Hz to 600 Hz to the average value of the frequency signal at 100 Hz to 200 Hz as the slant, in the example which is shown in  FIG. 7 , the slant of the frequency signal  701  becomes 1.30 and the slant of the frequency signal  702  becomes 1.30. For the frequency signal  701  and frequency signal  702 , it is determined that no sound jam has occurred. On the other hand, the slant of the frequency signal  703  becomes 1.17, so for the frequency signal  703 , it is determined that a sound jam has occurred. 
     Further, at step S 604 , the sound jam detector  153  may also subtract from a first average value of the frequency signal at 100 Hz to 200 Hz (first frequency band) a second average value of the frequency signal at 200 Hz to 600 Hz (second frequency band) and calculate the difference as the slant of the frequency signal. 
     In the calculation of the slant, the above-mentioned values of the first frequency band, second frequency band, predetermined value for comparison with the slant, etc. are not limited to the above-mentioned values and may be suitably changed. 
     As explained above, in a frequency signal in the case where a plurality of papers are conveyed, specific frequency components will become larger than other frequency components due to the rubbing sound when the papers are separated, so at a frequency band higher than a specific frequency, there will be a tendency for the signal value to be decreased the higher the frequency. On the other hand, if a jam occurs, the sound which is generated due to that jam will mask the rubbing sound. Therefore, in a frequency signal in the case where a jam occurs, the tendency for the signal value to decrease the higher the frequency in a frequency band higher than a specific frequency will not be seen as much as with a frequency signal when a jam has not occurred. Therefore, as explained above, it is possible to precisely determine whether a jam has occurred by using the slant of a frequency signal. 
     As explained in detail above, the paper conveying apparatus  100  operates in accordance with the flow charts which are shown in  FIG. 4 ,  FIG. 5 , and  FIG. 11  to thereby determine if a jam has occurred based on the slant of a frequency signal which is generated from a sound generated by a paper during conveyance. The frequency spectrum of a sound which is generated due to a jam is small in slant, so the paper conveying apparatus  100  can precisely determine whether a jam has occurred. 
       FIG. 12  is a block diagram which shows the schematic configuration of a paper conveying apparatus  200  according to another embodiment. 
     The paper conveying apparatus  200  which is shown in  FIG. 12  has a sound signal generator  241  instead of the sound signal generator  141  of the paper conveying apparatus  100  which is shown in  FIG. 3 . Further, the central processing unit  250  does not have a frequency signal generator  156 . 
     The sound signal generator  241  includes a microphone  113 , a first filter  242   a , a second filter  242   b , a first amplifier  243   a , a second amplifier  243   b , a first sound A/D conversion unit  244   a , a second sound A/D conversion unit  244   b , etc. 
     The first filter  242   a  processes the analog signal which is output from the microphone  113  by applying a bandpass filter which passes a signal of a predetermined first frequency band and outputs it to the first amplifier  243   a . The first amplifier  243   a  amplifies the signal which is output from the first filter  242   a  and outputs it to the first sound A/D conversion unit  244   a . The first sound A/D conversion unit  244   a  converts the analog signal which is output from the first amplifier  243   a  to a digital signal and outputs it to the central processing unit  250 . Below, the signal which is output by the first sound A/D conversion unit  244   a  will be called the “first sound signal”. 
     The second filter  242   b  processes the analog signal which is output from the microphone  113  by applying a bandpass filter which passes a signal of a predetermined second frequency band and outputs it to the second amplifier  243   b . The second amplifier  243   b  amplifies the signal which is output from the second filter  242   b  and outputs it to the second sound A/D conversion unit  244   b . The second sound A/D conversion unit  244   b  converts the analog signal which is output from the second amplifier  243   b  to a digital signal and outputs it to the central processing unit  250 . Below, the signal which is output by the second sound A/D conversion unit  244   b  will be called the “second sound signal”. 
     The first frequency band is set to a frequency band where the components become larger due to the rubbing sound when papers are separated, while the second frequency band is set to a frequency band higher than the first frequency band. 
       FIG. 13  is a flow chart which shows still another example of the operations in sound jam detection processing. 
     This flow chart can be used instead of the above-mentioned flow chart which is shown in  FIG. 11  in the paper conveying apparatus  200 . In the flow chart which is shown in  FIG. 13 , unlike the flow chart which is shown in  FIG. 11 , the sound jam detector  153  calculates the slant of the frequency component of the sound signal based on the first sound signal and second sound signal instead of the slant of the frequency signal. The processing of steps S 703  to S 705  which are shown in  FIG. 13  is the same as the processing of steps S 605  to S 607  which are shown in  FIG. 11 , so the explanation will be omitted and, below, only the processing of steps S 701  to S 702  will be explained. 
     First, the sound jam detector  153  acquires the first sound signal and second sound signal from the sound signal generator  241  (step S 701 ). 
     Next, the sound jam detector  153  calculates the slant of the frequency component of the sound signal as the variation of a component of the sound signal. The sound jam detector  153  calculates the ratio of the signal value of the first sound signal to the signal value of the second sound signal as the slant of the frequency component of the sound signal (step S 702 ). 
     As explained above, when a jam has not occurred, due to the rubbing sound when papers are separated, the tendency becomes stronger for the signal value of the frequency signal to decrease along with an increase of the frequency in a frequency band higher than a specific frequency, while when a jam has occurred, that tendency becomes weaker. That is, for the frequency component of a sound signal, when a jam has not occurred, the tendency for the frequency component to decrease along with an increase in the frequency in a frequency band higher than a specific frequency becomes stronger, while when a jam has occurred, that tendency becomes weaker. Therefore, as explained above, it is possible to precisely determine whether a jam has occurred by utilizing the slant of the frequency component of the sound signal. 
     As explained in detail above, the paper conveying apparatus  200  calculates the slant of a frequency component of a sound signal based on the ratio of respective signals which were respectively processed using a filter for a frequency band where the components become larger due to the rubbing sound when papers are separated and a filter for a frequency band higher than that. Further, the paper conveying apparatus  200  determines whether a sound jam has occurred based on the calculated slant. Therefore, the paper conveying apparatus  200  becomes able to precisely determine whether a rubbing sound when papers are separated is masking a jam sound and becomes able to precisely determine whether a sound jam has occurred. 
     Furthermore, the paper conveying apparatus  200  determines whether a sound jam has occurred based on not the values of the sound signal itself, but the ratio of frequency components of the sound signal. In general, the output characteristics of microphones which are provided at different paper conveying apparatuses may vary, but no matter what the output characteristics of one microphone, the frequency components of the sound signal which is output by that microphone will fluctuate uniformly. Therefore, the paper conveying apparatus  200  can reduce the effects of variations in output characteristics of individual microphones and can more precisely determine whether a sound jam has occurred. 
       FIG. 14  is a graph which shows examples of frequency signals when papers of different thickness and paper quality than the case of  FIG. 7  are conveyed. 
     In  FIG. 14 , the abscissa shows the frequency, while the ordinate shows the signal value of the frequency signal. The graph  1400  of  FIG. 14  shows examples of a frequency signal  1401  when normal paper is conveyed, a frequency signal  1402  when wrinkled paper is conveyed, and a frequency signal  1403  when a jam has occurred. The frequency signal  701 , frequency signal  702 , and frequency signal  703  of  FIG. 7  showed the signals which were generated for thin paper of a ream weight of 22 kg. The frequency signal  1401 , frequency signal  1402 , and frequency signal  1403  of  FIG. 14  show signals which were generated for coated paper of a ream weight of 53 kg. 
     As shown in  FIG. 14 , the frequency bands where components become larger due to the rubbing sound when coated paper of a ream weight of 53 kg is separated are 170 Hz and 390 Hz or substantially the same as the frequency bands where the components become larger due to the rubbing sound when thin paper of a ream weight of 22 kg is separated. That is, the frequency bands where the components become larger due to the rubbing sound when papers are separated can be determined in advance without depending on the thickness and quality of a paper. 
       FIG. 15  is a block diagram which shows the schematic configuration of a paper conveying apparatus  300  according to still another embodiment. 
     The central processing unit  350  of the paper conveying apparatus  300  which is shown in  FIG. 15  has a conveyance speed information acquiring unit  357  in addition to the parts of the central processing unit  150  of the paper conveying apparatus  100  which is shown in  FIG. 3 . 
     The storage unit  147  stores scanning information input by a user. The scanning information includes information about a resolution for scanning a paper. Note that, the scanning information is set from the data processing apparatus  10  through the interface  146 . 
       FIG. 16  shows an example of the screen  1600  for setting the resolution for scanning a paper which the data processing apparatus  10  displays. 
     As shown in  FIG. 16 , the setting screen  1600  displays selection buttons for the resolution for scanning a paper to be selected by the user. When the resolution is selected by the user and the set button is pushed, the data processing apparatus  10  transmits resolution information which indicates the selected resolution to the paper conveying apparatus  100 . When the interface  146  of the paper conveying apparatus  100  receives the resolution information from the data processing apparatus  10 , it sends the received resolution information to the central processing unit  350 . The central processing unit  350  stores the resolution information which it received from the interface  146  as scanning information in the storage unit  147  and sets a rotational speed of the drive unit  145  in accordance with that resolution information so as to set the conveyance speed of the paper. The conveyance speed is set to become faster the smaller the resolution and to become slower the larger the resolution. The conveyance speed when the resolution is 200 dpi (dots per inch) is set to 60 ppm (page per minute), while the conveyance speed when the resolution is 600 dpi is set to 15 ppm. 
     The conveyance speed information acquiring unit  357  reads the resolution information in the scanning information from the storage unit  147  and acquires the conveyance speed information which shows the conveyance speed of the paper which was set by the central processing unit  350  based on the read resolution information. 
       FIG. 17  is a graph which shows examples of frequency signals when the conveyance speed of the paper differs from the case of  FIG. 7 . 
     In  FIG. 17 , the abscissa shows the frequency, while the ordinate shows the signal value of the frequency signal. The graph  1700  of  FIG. 17  shows examples of a frequency signal  1701  when normal paper is conveyed, a frequency signal  1702  when wrinkled paper is conveyed, and a frequency signal  1703  when a jam occurs. The frequency signal  701 , frequency signal  702 , and frequency signal  703  of  FIG. 7  showed the signals in the case where the resolution was set to 200 dpi and the paper conveyance speed was set to 60 ppm. The frequency signal  1701 , frequency signal  1702 , and frequency signal  1703  of  FIG. 17  show the signals in the case where the resolution is set to 600 dpi and the paper conveyance speed is set to 16 ppm. 
     As shown in  FIG. 17 , the frequency bands where the components become larger when the paper conveyance speed is set to 16 ppm are 215 Hz and 450 Hz or slightly higher than the frequency bands where the components become larger when the paper conveyance speed is set to 60 ppm (170 Hz and 390 Hz). That is, the slower the paper conveyance speed, the higher the frequency bands where the components become larger due to the rubbing sound when papers are separated. 
     Therefore, experiments are run in advance to investigate at each conveyance speed the frequency band where the components become larger due to the rubbing sound when papers are separated. The conveyance speed information acquiring unit  357  determines the frequency band where the components become larger due to the rubbing sound when papers are separated in accordance with the conveyance speed information. 
     When calculating the unevenness of a frequency signal by using the signal value of the averaged frequency signal at a predetermined frequency at step S 304  of  FIG. 6 , the sound jam detector  153  uses a signal of the frequency band which the conveyance speed information acquiring unit  357  determines. Similarly, the sound jam detector  153  uses a signal of the frequency band which the conveyance speed information acquiring unit  357  determines even when calculating the slant according to the flow chart of  FIG. 11  or the flow chart of  FIG. 13 . 
     As explained in detail above, the paper conveying apparatus  300  determines the frequency band where the components become larger due to the rubbing sound which is generated when papers are separated in accordance with the conveyance speed of the paper or the resolution for scanning the paper, so it becomes possible to more precisely determined whether a sound jam has occurred. 
     According to the paper conveying apparatus and the jam detection method, and the computer-readable, non-transitory medium, the paper conveying apparatus determines whether a jam has occurred based on a variation of a component of the sound generated by a paper during conveyance, so can suppress mistaken detection of the occurrence of a jam. 
     All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiment(s) of the present inventions have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.