Abstract:
A method for feeding sheets through a sheet transport path. Ultrasonic energy is directed toward a sheet in the transport path while an audio receiver detects audio data generated by the ultrasonic source and the mechanisms that transport the sheet. The audio data is processed to determine whether a multifeed or a misfeed condition exists in the transport path.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
       [0001]    The following U.S. patents and patent application are assigned to the same assignee hereof, Eastman Kodak Company of Rochester, N.Y., and contain subject matter related, in certain respect, to the subject matter of the present patent application. These patents and patent application are incorporated herein by reference in their entirety.
   U.S. Pat. No. 6,511,064 Method And Apparatus For Multiple Document Detection Using Ultrasonic Phase Shift Amplitude;   U.S. Pat. No. 7,025,348 Method And Apparatus For Detection Of Multiple Documents In A Document Scanner Using Multiple Ultrasonic Sensors;   U.S. Pat. No. 6,407,599 Method And Apparatus For Determining A Digital Phase Shift In A Signal;   U.S. Pat. No. 6,868,135 Method And Apparatus For Correcting For A Phase Shift Between A Transmitter And A Receiver;   U.S. Pat. No. 6,520,498 Method And Apparatus For Detection Of Wrinkled Documents In A Sheet Feeding Device;   U.S. Pat. No. 6,913,259 Apparatus For Detection Of Multiple Documents In A Document Transport;   U.S. Ser. No. 13/273,263, Filed: Oct. 14, 2011, entitled Jam Sensing At Document Feeding Station;   US patent application filed concurrently herewith, entitled “Combined Ultrasonic-Based Multifeed Detection Method and Sound-Based Damage Detection System”, and   US patent application filed concurrently herewith, entitled “Sound-Based Damage Detection”.   
 
     
    
     FIELD OF THE INVENTION 
       [0011]    The present invention is directed to devices and methods of detecting misfeeds and multifeeds in a document handling apparatus. In particular, to devices and methods utilizing ultrasonic transducers and sonic processing to detect jams and multifeeds. 
       BACKGROUND OF THE INVENTION 
       [0012]    Document scanners feed and transport paper documents past one or more imaging subsystems in order to create digital image files representative of the originals. When two or more documents or pieces of paper have inadvertently been delivered to the imaging portion of the scanner by the feeding mechanism (referred to herein as a “multifeed”) there is loss of information capture because of the overlap of the documents. This leads to the need to sort and rescan those documents and a loss of productivity. Most document scanners in the commercial arena utilize ultrasonic energy transmitted through the document to a receiver to detect when multifeeds occur. This technology is also employed in other paper transport devices when knowledge about whether more than one layer of paper is present is important, such as in ATM machines that dispense paper money. Most systems rely on a substantial drop in received amplitude of the ultrasonic energy due to destructive interference of the ultrasonic energy within the thin air gap or gaps between the multiple sheets of paper. Other systems use a combination of amplitude drops and the phase shift differential of multiple sheets vs. one sheet for detection of multifeed conditions as described in the U.S. Patents listed above. 
         [0013]    Additionally, systems have been described that detect excessive or unique sound energy using an audio frequency microphone, said energy created by the document being transported when the document or documents are being damaged, wrinkled, torn or otherwise deformed by the feeding and transport process (referred to herein as a “misfeed”). These sounds are differentiated from the normal sounds of the mechanisms via processing of the audio frequency sounds. The sounds are quantified, compared to a threshold (which may be adjustable), and then used to immediately stop the feeding and/or transport mechanism in order to prevent or substantially limit damage to the documents. 
         [0014]    Incorporating both a receiving device or devices for the ultrasonic energy (typically in the range of 40 KHz. to 300 KHz.) and an additional device or devices for receiving audio information (typically in the range of 1 KHz. to 10 KHz.) represents both a cost penalty and a packaging challenge given the position of drive rollers and other sensors within the document transport design. 
       SUMMARY OF THE INVENTION 
       [0015]    This invention combines both functions of ultrasonic-based multifeed detection and sound-based damage detection based on one receiving device (in the preferred method, an electret microphone), saving cost and enabling physical placement in paper transport systems where space may be at a premium. In addition, the electret microphone used here is substantially less expensive than dedicated ultrasonic receivers. 
         [0016]    The electret microphone operates over a wide frequency range and is capable of simultaneously detecting the sound patterns associated with document damage along with the 40 KHz. tone for multifeed detection. After buffering the signal with an amplifier, the spectrum of sound energy is split via two bandpass filters into a low frequency channel for damage detection and a high frequency channel for multifeed detection. Each subsystem, damage detection and multifeed detection, act independently on the information presented by their respective bandpass filters. It is important to keep the low frequency sound filtered out of the ultrasonic waveform used for multifeed detection as this sound modulates the high frequency ultrasonic tone in both amplitude and phase, degrading detection performance. Similarly it is important to filter out the ultrasonic tone before it is passed to the damage detection subsystem due to frequency aliasing by the analog-to-digital sampling process. This aliasing results in beat frequencies that can fall into the range of frequencies considered by the damage detection algorithm. 
         [0017]    Additionally, it has been found that mounting the sound detection device (microphone) in a compliant mount or rubber isolator helps to reduce the conduction of unwanted sounds, noise, and vibrations into the microphone from the scanner mechanisms. 
         [0018]    The electrical output amplitude of the sound detecting device, typically a microphone, at the ultrasonic frequency of the preferred embodiment (40 KHz.) is much lower than that of the piezoelectric receiver described in the prior art. This requires additional amplification of the microphone output compared to the conventional ultrasonic receiver. 
         [0019]    The ultrasonic-based multifeed detection determines when two or more documents overlap between the transmitter and receiver transducers. The output can be used to immediately stop the transport, or to allow the documents to be transported with a warning to the operator. There are several other options related to passing or not passing the document image to the host computer based on multifeed detection. 
         [0020]    A preferred embodiment of the present invention comprises a method for feeding a sheet, such as document, by urging the sheet through a sheet transport path using rollers, and directing ultrasonic energy toward the sheet and an audio receiver using an ultrasonic transducer. The audio receiver detects the audio data generated by the transducer and by mechanisms that transport the sheet. The audio data is recorded or otherwise converted to, and collected as, digital data frames and is processed to determine whether a multifeed or a misfeed condition exists in the transport path as indicated by the data frames. If so, sheet feeding is terminated. Part of the processing described above comprises filtering the audio data into two frequency bands. The first frequency band is used to determine the multifeed and the second is used to determine the misfeed. An energy level of the audio data is calculated in the second frequency band. 
         [0021]    Another preferred embodiment of the present invention comprises a method of determining a misfeed or multifeed in an article processing apparatus comprising placing a microphone in the article processing apparatus for receiving audio emanating from the apparatus, placing an ultrasonic energy source in the article processing apparatus directed toward the microphone to be received thereby, feeding an article into the article processing apparatus using devices for urging the articles forward through an article transport path in the apparatus. Sound detected by the microphone is converted to digital data frames and is processed to determine either a misfeed or a multifeed. False misfeed determinations are avoided by counting the number of data frames collected and reducing sensitivity of the processing if the count reaches a known threshold. The number of data frames collected represents a distance that the document has traveled. An energy level of the data frames is computed and compared to a known jam threshold corresponding to each data frame. The jam threshold for each data frame is determined according to the processing sensitivity setting. A jam count window is opened upon determining that the energy level of a current data frame exceeds its jam threshold, and the counting persists for data frames that exceed their corresponding jam threshold. A jam signal is issued if the jam count reaches a known jam count limit while the jam count window is open. Also, if a total number of frames that have been processed exceeds a known window size, the jam count window is closed and the jam count is then reset to zero. The data frames are filtered to distinguish intermittent amplitude peaks and continuous high amplitude data by use of cutoff frequencies. 
         [0022]    Another preferred embodiment of the present invention comprises a method of processing articles comprising holding the articles to be processed and feeding the first one into an article processing apparatus using a roller device configured to separate the first one of the articles from the rest, directing ultrasonic energy at the first article, collecting sound data generated by the ultrasonic energy and by the feeding mechanism, then separately processing the collected sound data. Based on processing the collected sound data, it is determined whether one or both of the following have occurred (i) that the collected sound data generated by the ultrasonic energy indicates a multifeed, (ii) that the collected sound data generated by the feeding indicates a misfeed and, if so, terminating processing the articles. 
         [0023]    It should be noted that in the present patent application preferred embodiments are described in terms of a scanner only for representative preferred embodiments. The present invention is not so limited, and the use of the term “scanner” is hereby intended to refer to any document or paper conveyance machine. These, and other, aspects and objects of the present invention will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following description, while indicating preferred embodiments of the present invention and numerous specific details thereof, is given by way of illustration and not of limitation. For example, the summary descriptions above are not meant to describe individual separate embodiments whose elements are not interchangeable. In fact, many of the elements described as related to a particular embodiment can be used together with, and possibly interchanged with, elements of other described embodiments. Many changes and modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications. The figures below are intended to be drawn neither to any precise scale with respect to relative size, angular relationship, or relative position nor to any combinational relationship with respect to interchangeability, substitution, or representation of an actual implementation. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]      FIG. 1  illustrates a document feed and transport path. 
           [0025]      FIGS. 2A-E  illustrate frequency domain band pass filtering. 
           [0026]      FIG. 3  illustrates a sonic processing circuit. 
           [0027]      FIG. 4  illustrates a pertinent frequency domain for detecting document damage. 
           [0028]      FIG. 5  illustrates a flowchart of an algorithm for implementing the present invention. 
           [0029]      FIG. 6  illustrates a timing diagram for processing document misfeeds. 
           [0030]      FIG. 7  represents the first frame where the energy level exceeds the Energy_Threshold. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0031]    With reference to  FIG. 1 , document  103  is moved forward by urging roller  101  into the feed and separation nip created by contact of rollers  105 . Not shown is a standard input tray holding a stack of documents wherein the urging roller is configured to separate the first one of the documents from the stack. One document at a time is sequentially pushed further into the transport rollers  107  by selective rotation of the feed mechanism rollers  105 . Ultimately the document is transported to an imaging station or stations to be converted into a digital image. Ultrasonic transmitter  109  is driven by signal generator  113  and emits sound energy which passes through document  103  to microphone receiver  111 . In addition, sound energy created by the physical transport of the document through the transport is also converted to an electrical signal by receiver  111 . This sound energy may be characteristic of normal, undamaged transport of the document including that of the scanner itself, or may contain sounds characteristic of a document undergoing damage as a result of the feed and/or transport process. The electrical signal from microphone  111  is representative of a composite of the ultrasonic energy used for multifeed detection as described by the prior art, and the lower frequency sounds associated with document transport. This composite signal is conveyed to amplifiers and signal conditioning block  115  which is described later. 
         [0032]    With reference to  FIGS. 2A-E , the electrical signal from microphone  211  is representative of a composite of the ultrasonic energy used for multifeed detection as described by the prior art and the lower frequency sounds associated with document transport including, potentially, those associated with document damage. This composite signal is conveyed to amplifiers and signal conditioning block  215  and is illustrated in the frequency domain in  FIG. 2A . The signal conditioning electronics separates the relatively low frequency signals associated with document transport, including the sounds of potential damage, using the bandpass filter in  FIG. 2B  that allows frequencies between the lower limit of F 1  and the upper limit of F 2  in the range of approximately 100 Hz to 10 KHz respectively to pass through while greatly attenuating the high frequency ultrasonic tone. The output of this filter is shown in  FIG. 2C . Similarly the bandpass filter illustrated in  FIG. 2D  has lower and upper limits of F 3  and F 4  in the range of approximately 30 KHz to 50 KHz respectively designed to pass the high frequency ultrasonic signal while greatly attenuating the lower frequency signals which would result in unwanted corruption of the ultrasonic signal used for multifeed detection. The output of the bandpass filter illustrated by  FIGS. 2B and 2C  is passed to an analog-to-digital converter, which receives analog audio data and converts these to digital data frames as described below, and further processing for damage detection while the output of the bandpass filter illustrated by  FIGS. 2D and 2E  is passed to processing for multifeed detection as described by the prior art. 
         [0033]    With reference to  FIG. 3 , the output of microphone  311  is amplified and filtered in the frequency domain by a split path. The output of amplifier and filter block  307  contains signals associated with ultrasonic-based multifeed detection and is passed to the scanner controller  301  for processing as described by the prior art. This processing can include continuing sheet feeding if the detected multifeed is acceptable, for example, a sticky-note intentionally attached to a document, and includes terminating sheet feeding if the multifeed is due to error. The output of amplifier and filter block  305  contains signals primarily associated with document transport, including those associated with possible damage as it is transported. These signals are converted to a digital representation by analog-to-digital converter  309  and then to the document damage processor  313  which makes a determination if the sound signals represent those of a document being damaged or not. Processor  313  receives signal  315  from the scanner controller when the feed mechanism is engaged. This prepares the damage detection processor  313  and initiates the detection algorithm which will be described later. If sounds associated with document damage are detected with sufficient energy and within timing windows as described below, then an output  317  from processor  313  is sent to the scanner controller which in turn quickly stops the transport and feed mechanisms to limit the damage to the document in question. 
       Damage Detection Algorithm 
       [0034]    The damage detection processor determines when document damage due to misfeeding, wrinkles, staples, adhesion or other factors is occurring and stops the document transport motors and feed mechanisms in a very brief time interval to prevent further damage to the documents. The document damage detection algorithm uses the idea of differentiating between the sound made by a normal document entering a document scanner and the sound of a document being wrinkled due to a jam. For a system to make this distinction, it is important to ignore or in some way isolate the background sounds of the scanner from the sounds coming from the document. The background sounds come from various moving parts of the scanner. The moving parts include, but are not limited to, the transport motors, transport rollers, feeder mechanism and possible cooling fans. These scanner background sounds are typically periodic and have low frequency components relative to that of documents being damaged. 
         [0035]    On the other hand, the sounds from a wrinkling or damaging document are a short duration signal in the time domain and have frequency components spread over a wide range in the frequency domain. In addition, the sound of a clean document being scanned typically has frequencies that overlap the frequencies that of a wrinkling document. Therefore, the algorithm can detect a jamming document by computing the energy of the audio signal by looking at a frequency band between F 5  and F 6  as shown in  FIG. 4 , where F 5  is the upper frequency limit of the background noise/clean document in the range of approximately 1 KHz. and where F 6  is the upper frequency of a jamming document in the range of approximately 4 KHz. This bandpass filter is in addition to the filter previously described that performs the first level of separation in the frequency domain between the damage detection sounds and the multifeed ultrasonic signal. The cut-off frequency F 5  is selected such that all the background sounds from different moving parts of the scanner and the sound associated with a clean document are substantially or detectably below this cut-off as shown below. This cut-off frequency selection can be based on test data collected and recorded from the scanners during normal operation. 
         [0036]    With reference to  FIG. 5 , when the feeder mechanism is enabled  501 , a document starts to enter the transport of the scanner. The damage detection processor uses a communicated feed enable signal generated at this point to determine when to start sampling the microphone. The algorithm for jam detection uses a frame-based processing technique. The system collects the digitized microphone data and processes the data in fixed data sets or frames that consist of N samples per frame  502 , for example, typically approximately 50 samples. The algorithm receives multiple frames of microphone data and then will determine if the data is indicative of a document jam as will be described below. These frames of data are non-overlapping and each frame consists of approximately a one millisecond duration of audio data. 
         [0037]    As the trail-edge of the document enters the document transport and passes over the point of feeding at the contact nip between rollers  105 , the trail edge of the document may make a snapping sound that creates a sharp impulse in the audio signal. To reduce the probability of false jam detection on the trail-edge, an additional check  503  needs to be performed to determine where the microphone frame was captured in relation to the lead-edge of the document. This is done by keeping track of how many frames have been processed since the feeder mechanism enable signal was asserted, and if the current frame number has passed the Sensitivity Switch Point (SSP). The Sensitivity Switch Point is dictated by the length of the shortest document that can be safely transported. The trail edge will pass by the point of feeding sooner for short documents and is therefore the limiting case for the need to switch to a lower sensitivity and avoid false jam detections. The number of frames counted to cross the SSP is equivalent to the time to transport the shortest document such that the trail edge passes over the point of feeding. 
         [0038]    If the frame count is greater than the Sensitivity Switch Point  505 , then the current frame for the microphone is susceptible to this trailing edge false detection and the low sensitivity settings are used  507  in a later stage for determining whether or not a document jam has occurred. If the frame count has not passed the SSP  509 , then the high sensitivity settings will be used  511 . 
         [0039]    Each frame of microphone output data is next processed by sending the digitized data through a band pass filter  513  with lower and upper cutoff frequencies F 5  and F 6  as previously described in  FIG. 4 . 
         [0040]    A 1D median filter  515  is next applied to the frame of data to help distinguish audio characteristics between a document that is merely wrinkled which exhibits intermittent high peak values, as opposed to a document in the process of being damaged which has relatively continuous high values of amplitude. The median filter, energy threshold calculations, and Jam Count window accumulation all combine to distinguish merely wrinkled documents from those being damaged during transport. 
         [0041]    After the median filter, the energy of the microphone frame of data is calculated  517 . The energy of the frame of data is calculated with the equation below, where N represents the number of data samples within a frame, and mic data  is a number correlated to a sound intensity of each individual digitized audio sample. 
         [0000]    
       
         
           
             ( 
             
               
                 ∑ 
                 1 
                 N 
               
                
               
                 
                   ( 
                   
                     mic 
                     data 
                   
                   ) 
                 
                 2 
               
             
             ) 
           
         
       
     
         [0042]    If the microphone frames are captured immediately after the feeder mechanism is enabled  520  then the algorithm completely ignores these frames of data by forcing the energy level to zero  521 . An example number of ignored frames is about thirty. This prevents the algorithm from falsely detecting the feeder mechanism noise as a potential jam. Otherwise  522  the energy calculation from  517  is compared against a sensitivity threshold  523  that is varied depending on whether we are in the low or high sensitivity mode as determined previously in  503 . A potential wrinkling document is detected when the energy level of the frame goes above the Energy_Threshold  524 . When this occurs, the algorithm initiates a jam count window if one has not been previously initiated and increments the Jam Count variable  525 . This window defines a block of frames where the energy level of some minimum number of frames must exceed the Energy_Threshold before an actual jam detection signal is issued. If the Jam Count exceeds the JamCount_Threshold  527 , then the jam signal is asserted  529  and the algorithm terminates  541 . Otherwise, if the Jam Count is below the JamCount_Threshold  543 , then the algorithm waits for next frame of data. 
         [0043]    If the energy level of this particular data frame is below the Energy_Threshold  533  then the algorithm increments the current position within the jam count window, assuming a jam had occurred on an earlier frame (jam count &gt;0) and a jam count window was open  535 . 
         [0044]    If a jam count window was opened by a previous frame exceeding the energy threshold, and the current frame position count reaches the end of the fixed window size  537  before the Jam Count exceeds the JamCount_Threshold, then the window is closed and the Jam Count is reset to zero  539  and the algorithm waits for the next frame of data  551 . Otherwise  549  the algorithm waits for the next frame of data  551 . 
         [0045]    In  FIG. 7 , “Jam # 1 ” represents the first frame where the energy level exceeds the Energy_Threshold and the jam count window opens. As each future frame is processed, the current position within the window is updated. Jam Detect #N represents the frame where the Jam Count exceeds the JamCount_Threshold before the window closes. 
         [0046]    With reference to  FIG. 6 , this timing diagram represents a single document traveling through the scanner. The damage detection algorithm commences when the feed mechanism enable signal is passed  601  from the main scanner controller to the damage detection processor. The delay period  603  is utilized to avoid false jam detection due to the sounds associated with the feed mechanism and a document entering the paper transport. At the end of this delay  605  the algorithm starts to actively look for sound signal data associated with document damage. The initial portion of the document is processed at high sensitivity in region  607  until there is the risk of false damage detection due to the trail edge of the document. At this point  609  the sensitivity drops to the lower sensitivity for the remainder of this document  611  until the end of the document is reached  613  and the algorithm terminates until the next document is fed. 
         [0047]    The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention. 
       PARTS LIST 
       [0000]    
       
           101  Roller 
           103  Document 
           105  Rollers 
           107  Rollers 
           109  Transmitter 
           111  Microphone 
           113  Signal Source 
           115  Signal Conditioner 
           211  Electric Circuit 
           215  Electric Circuit 
           301  Controller 
           303  Document 
           305  Electric Circuit 
           307  Electric Circuit 
           309  Converter 
           311  Microphone 
           313  Processor 
           315  Signal 
           317  Signal 
           319  Transmitter 
           501  Step 
           502  Step 
           503  Step 
           505  Branch 
           507  Step 
           509  Branch 
           511  Step 
           513  Step 
           515  Step 
           517  Step 
           519  Step 
           520  Branch
         521  Step     522  Branch     523  Step     524  Branch     525  Step     527  Branch     529  Step     533  Branch     535  Step     537  Step     539  Step     541  End     543  Branch     545  Branch     549  Branch     551  Step     601  Pointer     603  Document     605  Pointer     607  Document     609  Pointer     611  Document     613  Document