Abstract:
A method of scanning documents and moving such documents along a path such that during scanning a method of improving the documents velocity and the documents image quality is disclosed. The method includes providing a plurality of documents in an input tray and transporting each document along the path from the input tray at a transport velocity past the scanner to obtain scanned image data. By monitoring and controlling the velocity profile of the transport system, the scanning system may provide higher image quality, reduce slippage, misfeeds and jams, and provide alerts to an operator in the even slippage, misfeeds, or jams do occur.

Description:
FIELD OF THE INVENTION 
     The present invention relates to document scanning, and in particular to a system and method of providing an improved document velocity along a document transport and past an imaging camera to improve the scanned document image quality. 
     BACKGROUND OF THE INVENTION 
     Document image scanners typically include roller systems forming a transport path for a document fed into the scanner to move the document past imaging devices, such as a linear CCD (charged-coupled device) camera. The roller systems generally include multiple rollers, driven by a single motor or multiple motors, which serve to move the documents along the transport path within the scanner. Typically, when a stack of documents are fed into the entrance of a scanner, they first encounter an urging roller which urges a stack of documents to an adjacent feed roller, which mates with a separation device. The separation device provides a recessive force to the lead edge of a stack of documents and separates a single document from the stack and then advances the single document to transport rollers and past the camera. 
     However, documents fed through the scanner may cause the different rollers to turn at different velocities. This can lead to transport slippage, misfeeds, and a reduction in image quality. For example, when the trailing edge of a document leaves the separation device the scanner transport may speed up slightly due to the reduction in load on the drive system. These changes in transport speed cause the document to move past the cameras at different speeds, resulting in reductions in image quality. In typical document image scanners which utilize a linear CCD camera, a constant velocity of the document being imaged past the camera is desired, to achieve the best image quality. 
     What is needed is a system and method to monitor the velocity of the transport system, and in particular the velocity of the rollers within the system. The velocity of various rollers within the system may then be controlled at various times, such as when a document is entering or leaving a new set of rollers, in order to reduce slippage, jams, and improve image quality. 
     SUMMARY OF THE INVENTION 
     The invention provides systems and methods for scanning documents, including monitoring and controlling the velocity of the rollers that feed documents into a scanning system and transport the documents through the scanner. The velocity of the rollers may be monitored, and a controller may be provided to adjust the motors driving the rollers, thereby controlling the speed. By monitoring and controlling the velocity profile of the transport system, the scanning system may provide higher image quality and may reduce slippage, misfeeds and jams, and provide alerts to an operator in the event slippage, misfeeds, or jams do occur. 
     Sensors may be provided to detect the speed of the rollers, and to detect the position of documents transported within the system. For example, document detection sensors may be provided to sense the leading and trailing edges of documents as they move through the transport system. These sensors may detect when a document enters and leaves various rollers, or when it moves past certain components within the system. By tracking the leading and trailing edges of the documents, the scanner may know when to adjust the speed of the rollers or feed the next document from the stack into the scanner. 
     In addition, monitoring of the scanner transport speed may allow the system to predict when the leading edge of the document should be received at various locations. If the leading edge is not sensed at these locations at the expected time, an alert may be provided to the operator that there is a potential jam or misfeed within the scanning system. These early alerts may reduce the amount of jam damage done, and provide increased accuracy as to the location of the jam. Additional features of the scanner may be monitored and controlled based on the detected speeds along the transport path and detected document edges. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic of a scanning system in accordance with an embodiment of the invention that includes a block diagram of the control electronics. 
         FIG. 2  is a cross section perspective view of a scanning system in accordance with an embodiment of the invention. 
         FIG. 3  is view of the gear arrangement between the feeder roller and urging roller. 
         FIG. 4A  is a diagram illustrating the typical velocity of a document fed in a typical scanning system transport. 
         FIG. 4B  is a diagram illustrating the constant velocity of the transport drive motor in the typical scanning system transport. 
         FIG. 4C  is a diagram illustrating the resulting velocity of the document at the imaging camera being imaged in the typical scanning transport system. 
         FIG. 5A  is another diagram illustrating the typical velocity of a document fed in the scanning system transport. 
         FIG. 5B  is a diagram illustrating the adjusted velocity of the transport drive motor in a system implementing aspects of the present invention to monitor and control velocity within the scanning system. 
         FIG. 5C  is a diagram illustrating the resulting constant velocity of the document at the imaging camera being imaged by implementing the velocity control according to aspects of the present invention. 
         FIG. 6A  is a diagram illustrating another typical velocity of a document fed in the scanning system transport. 
         FIG. 6B  is a diagram illustrating the adjusted velocity of the transport drive motor in a system implementing aspects of the present invention to monitor and control velocity within the scanning system. 
         FIG. 6C  is a diagram illustrating the resulting improved velocity of the document at the imaging camera being imaged by implementing the velocity control according to aspects of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is directed to systems and methods for scanning documents, and for and controlling roller speed along the transport path. The scanning system  10 , shown in  FIGS. 1 and 2  includes an input tray  14  which supports a document stack  12  that will be separated and driven through the scanning system  10 . A motor  30  and clutch  34  are controlled by a motion controller  48  for feeding a document  52  from the document stack  12  and into a series of rollers configured to move the document  52  through the scanning system  10  and past imaging cameras  36 A and  36 B. As the document is fed past the cameras, its image data is captured and transferred by a control logic processor  28  and then to memory  50 . Typically, an urging roller  16  is the first roller at the entrance of the scanning system  10  and makes initial contact with all documents in the document stack  12  being fed along the transport path  22  for imaging. The urging roller  16  has a mating urging pinch roller  18  which provides a nip force against the document stack  12  and the urging roller  16 . The nip force helps to insure the urging roller  16  rotates without slippage on the document  52  being fed through this nip. The scanning system  10  includes an urging roller sensor  42  and an urging roller encoder wheel  44 , which is rigidly attached to the urging roller  16 , to monitor the velocity of the urging roller  16 . 
     The scanning system&#39;s motor  30  drives the clutch  34  which in turn drives the feed roller drive shaft  40  when the clutch  34  is energized. The feed roller  20  is pivotally mounted on the feed roller drive shaft  40  via a mechanical one-way clutch bearing (not shown), which allows the feed roller  20  to be driven by the clutch  34  as well as be pulled by the document  52  which is transported along the transport path  22 . The motor  30  also drives the first and exit transport rollers  24 ,  26  typically with a belt or gear arrangement (not shown). The urging roller  16  is also pivotally mounted on a mechanical one-way bearing (not shown) which is supported on the urging roller drive shaft  17 . The urging drive shaft  17  is driven via a gear arrangement  32 , shown in  FIG. 3 , which is in turn driven by the feed roller drive shaft  40 . This described configuration allows both the urging and feed rollers  16 ,  20  to be driven at different speeds by the motor  30  and gear arrangement  32 . Also this configuration allows the document  52  to pull both the urging and feed rollers  16 ,  20  at a faster rate of speed (than their motor driven speed) by the document  52  traveling in the transport rollers. 
     The urging roller encoder wheel  44  may be comprised of a small wheel with slots for the urging roller sensor  42  to optically detect. In this embodiment of the invention, the urging roller sensor  42  is a photoelectric thru beam sensor which looks thru the slots in the urging roller encoder wheel  44 . Other sensor types and wheel configurations may also be used to achieve the desired result, such as reflective sensors or magnetic sensors. The urging roller sensor  42 , with some signal amplification and conditioning, provides a number of positive and negative transitions, corresponding to the number of slots, per revolution. The urging roller  16  diameter and transport velocity may be considered in determining an encoder frequency. For example, the urging roller  16  may be approximately 1.06″ in diameter or 3.33″ in circumference, the urging roller encoder wheel  44  may have forty slots, and the transport velocity may 10.5″/second. Considering only the position transitions, the encoder frequency for this example is (10.5/3.33)×40=126 Hz. However, the urging roller sensor  42  frequency is not constant. It starts out slow (urging roller  16  speed), then speeds up when the lead edge of the document  52  enters the nip of feed roller  20 , then nearly doubles in speed when the lead edge of the document  52  enters the first transport roller  24  nip. The urging roller  16  tangential velocity is 67% of the feed roller  20 , which is in turn 52% of the first transport roller  24  and exit transport rollers  26 . 
     The nature of the construction of the urging roller encoder wheel  44  and possible contamination may lead to frequency flutter or occasional missing transitions. Therefore, it may be important to have a method to ignore frequency flutter or occasional missing transitions with a time domain filter. For example, an 8-bit counter may be used and a fixed clock may increment the counter. The encoder clock will reset the counter to zero. If the encoder clock stops, the counter will increment via the fixed clock to a terminal count, such as 4. This terminal count indicates that enough time has passed with no encoder clock to be interpreted as a stoppage of the urging roller. Reaching the terminal count will generate a signal to start the timer or distance counter to predict when the trail edge of the document reaches the feed nip. This time (in distance) is the urging roller to feed roller nip distance (29.0 mm), minus the latency of the counter filter. While the urging roller encoder wheel  44  is turning, the typical count sequence will be 0 1 0 1 0 1 as the fixed clock increments to 1 and the encoder resets to zero. If a few pulses are missing, the sequence will be 0 1 2 3 0 1 0 1. The fixed clock may be biased in a way that increments the counter to be lower than the urging encoder clock. The fixed clock may be unique for each transport speed used. 
     One or multiple motors  30  are provided to drive the various rollers in the system. The urging roller  16  is driven by a at a slower rotational speed than the next feed roller  20  via a gear arrangement  32  that is connected to the feed roller and urging roller shafts  40 ,  17 . For example, the urging roller  16  may be driven at 66% of speed of the feed roller  20 . Both the urging roller  16  and feed roller  20  are supported on one-way bearings (not shown), which allows both rollers to be driven forward by their mating shafts ( 40 , 17 ) and which also allows both rollers to rotate faster than their “driven” speeds when a document  52  in their associated nips is transported (pulled) at a faster transport speed. 
     The feed roller  20  may be engaged with a fixed elastomeric pad (known as a separation pad) or a separation roller (also known as a retard roller that provides a drag force on the document being transported), thereby creating one separation nip. Alternatively, the feed roller  20  may also be engaged with multiple separation devices  21 , such as a fixed pad and a separation roller, thereby creating two separation nips. These nips provide separation force on a stack of documents and are designed to allow only one of the documents  52  in contact with the feed roller  20  and urging roller  16  to be fed into the first transport roller  24  (also called the takeaway roller). 
     The third nip in the scanning system  10  is the first transport roller  24  and it&#39;s mating normal force roller, which is driven at the scanning system transport and cameras  36 A,  36 B scanning speed. The first transport roller  24  nip driven speed is faster than the feed roller  20  driven nip speed (for example the feed roller  20  nip speed may be 55% of the first transport roller  24  speed) and the feed roller  20  nip speed is faster than the urging roller  16  driven nip speed. 
     Imaging cameras  36 A,  36 B are included in the transport path after the first transport roller  24  nip, and are capable of detection of the document  52  lead and trailing edge. After the cameras  36 A,  36 B, there is an exit transport roller  26  nip that is driven at the same speed as the first transport roller  24  nip. This nip releases the fed documents  52  out of the scanning system  10  after the images are obtained. 
     In addition to the urging roller sensor  42 , the scanning system  10  may have additional sensors after the feed roller  20  nip which can detect the leading or trailing edge of the document  52  being transported. These sensors may be of many types, including ultrasonic sensors or photoelectric. 
     The urging roller sensor  42  can sense whether a fed document&#39;s  52  lead edge speeds up as it enters the feed roller  20  nip by monitoring the urging roller  16  velocity change. It can also sense whether the fed document&#39;s lead edge speeds up as it enters the first transport roller  24  nip by monitoring this velocity speed up. The urging roller sensor  42  may also monitor the amount of speed change, and the current speeds of the rollers within the scanning system  10 . In addition, the trailing edge of the document fed into the scanner can be sensed at the urging roller  16  nip when it is pulled out of this nip and the urging roller sensor  42  senses a stop in the rotation of the urging roller  16 . The urging roller sensor will issue a “roller stopped” signal to indicate that the roller has stopped rotating after a predetermined number of counts without a change in the sensed state of the urging roller. Alternatively, the “roller stopped” signal may be issued after a predetermined time period elapses without a change in the sensed state of the urging roller. This technique provides the capability of the urging roller sensor  42  to be a “document location sensor” by sensing the trailing edge of the fed document  52 . 
     The scanning system  10  includes an auto-document feeding (ADF) system, in which the feed roller  20  nip and urging roller  16  nip section of the scanning system  10  are driven by a main transport motor  30  through an electromagnetic clutch  34 . The clutch  34  is energized to drive the urging and feed roller  16 ,  20  and feed the document  52  to the first transport roller nip  24 . When the lead edge of the fed document  52  is in the first transport roller  24  nip, the clutch  34  can be disengaged. When the clutch  34  is disengaged the first transport roller  24  nip and then the exit transport roller  26  nip pull the trailing portion of the document  52  through the urging and feed nips. When the document location sensor  38  senses that the trailing edge of the fed document  52 , the clutch  34  can be re-energized to feed the next document  52  from the document stack  12 . 
     By monitoring the scanning system  10  with the urging roller sensor  42 , the systems and methods described herein allow for improved image quality, reduction in jams, reductions in slippage, reductions in misfeeds, and improved operator alerts identifying problems. 
     The scanning system  10  roller transport speed may be adjusted based on the detection of the trailing edge of the fed document  52 . Typically when the fed document&#39;s  52  trailing end leaves the separation device  21  nip, the scanning systems first and exit transport rollers  24 , 26  will speed up slightly, because of the reduction of separation drag force on the transported document  52  causes a slight increase in the actual velocity of the document  52 . For example, the scanning system transport may speed up by around 1% because of the sudden release of the separation drag force on the document  52  which was under tension. However, in order to maintain the best image quality, it is desired to keep the document  52  being imaged at a constant velocity within the scanning system  10 . In order to achieve this, the transport motor  30  velocity clock may be switched from a higher frequency that accounts for separation device  21  drag force to a lower speed at the time of the document  52  releases from the separation device  21  nip. The magnitude of this frequency change may be small, such as about 1.5%, but it is sufficient to provide a more uniform velocity profile for longer documents  52  and enhance magnification accuracy in the document travel direction by a significant amount. This function is beneficial for all transport speeds, which is often needed for different scanning resolutions. The end of the document  52  can be detected in advance of its release from the separation device  21  nip by using the urging roller sensor  42  and knowing the programmed transport speed and distance the urging roller  16  nip is from the separation device  21  nip. As mentioned above, this release may cause the scanning system  10  to speed up, resulting in a loss of image quality of the scanned document. Thus, the transport speed adjustment can be made near the time of the separation device  10  nip release to correct this velocity error for any length document. This adjustment can improve the document  52  captured image length to match the original document  52  length, thereby greatly reducing the effects of the separation device  21  on the velocity of the rollers, transport components, and documents  52 . This correction may be especially important for longer documents. 
     The systems and methods may also allow for jam detection of the fed document  52  based on lead edge detection. The lead edge of the fed document  52  may be detected at the feed roller nip by monitoring the urging roller sensor  42  speed up frequency. There is a known time in which the lead edge of the document should get to the document location sensor  38 , first transport roller  24  or imaging cameras  36 A,  36 B, because the nip speeds and distances are known between each component. Jams of the lead edge of fed documents can be sensed if the lead edge is not at one of these locations at a predetermined time. Thus, monitoring the velocity of the system and the location of the document within the system may increase the location accuracy of sensed jams, and may reduce the amount of jam damage done to the fed document  52 , by stopping the feeding process when a jam is sensed. The scanning system  10  may automatically stop the feeding process when such a jam is sensed, or provide an alert to an operator that a jam is present. 
     The present invention may also allow for detection if a document stack  12  is present in the scanning system input tray  14 , and detection of the last document being fed from a document stack  12 . The insertion of document stack  12  or a single document  52  into the scanner will rotate the urging roller  16  and provide a signal that documents have been inserted. After the last document  52  has left the scanning system  10  and the clutch  34  is turned on in an attempt to feed another document, the urging roller  16  will not begin to rotate at a faster speed at the predicted time as it would if a document was present in the urging roller nip. Therefore, the system can detect there are no more documents to feed, and the document stack  12  has been completely fed through the scanning system. This technique can be used for end of stack detection. 
     In addition to detection of documents, the present invention may detect transport roller slippage, which could impact image quality. If there is significant slippage of the document  52  in the first transport roller nip, which may be caused by non-carbon copy paper dirt for example on the rollers, the urging roller  16  speed will rotate at a slower rate than predicted based on the first transport roller  24  (also called the takeaway roller) driven nip speed. By detecting that urging roller  16  is rotating at a slower predicted rate, the scanning system will know that slippage of the document  52  is occurring, and can alert the operator. 
     The urging roller sensor  42  can also be used to monitor the clutch  34  engagement profile when the clutch  34  is energized to see if it is behaving according to specified parameters. For example, the clutch  34  engagement may be monitored to ensure it is not slipping. After the clutch  34  is energized, it should rotate the feed and urging rollers  20 ,  16  at the driven speed in an expected, repeatable manner over the life of the clutch  34 . Both initial installation evaluation and long term monitoring of this clutch  34  engage profile can be performed using the urging roller sensor  42 . 
     When the ADF clutch  34  is de-energized, the feed and urging roller drive shafts  40 , 17  should not rotate. If they rotate when the clutch is de-energized, some frictional driving torque is likely being transmitted to the feed and urging roller  20 , 16  by the clutch, which is not desirable. If this condition occurs, the trailing edge of the fed document  52  is pulled off the urging roller  16 , and the next document in the document stack  12  can be urged forward while the first fed document is still within the feeder roller nip. This condition will cause the lead section of the next fed document to buckle, which can cause jams for thin paper types (rice paper for example). Both initial installation evaluation and long term monitoring of this condition can be performed using the urging roller sensor  42 . 
       FIGS. 4A-4C  illustrate the velocity within a traditional scanning system. Referring to  FIG. 4A , the typical change in the document velocity from V 1  to V 2  can be seen. This change in document velocity occurs when the trailing end of the document is released from the separation device. The corresponding typical constant velocity V 3  of the scanning systems drive motor is shown in  FIG. 4B . Because of the release of the separation force on the document trailing end happens when the document&#39;s image is being captured, a change in the documents velocity from V 5  to V 6  at the imaging camera is typically seen (Refer to  FIG. 4C ). This small change in velocity (typically less than 2%) can impact the image length of the document as well as the geometric accuracy of the image. Therefore, scanned images from documents fed through traditional scanning systems using a constant motor velocity, as illustrated in  FIGS. 4A-4C , may experience distortion and loss of image quality due to the changes in velocity as the documents move past the image capturing devices. 
     As discussed above, aspects of the present invention monitor and control the velocity of the document scanning system to provide higher image quality and reduce slippage, misfeeds and jams.  FIGS. 5A-5C and 6A-6C  illustrate the improved, more constant document velocity at the image capture devices that may be obtained by controlling the motor velocity to account for expected velocity changes within the scanning device as the documents enter and leave the various rollers. 
     Referring to  FIG. 5A , the typical “expected” change in the document velocity from V 1  to V 2  is shown that occurs when the trailing end of the document is released from the separation device. In order to compensate for this expected change in velocity, adjustments to the motor velocity may be made as described above. An adjusted velocity V 3  to V 4  of the scanning systems drive motor is shown in  FIG. 5B . This change V 3  to V 4  in motor velocity coincides with the exact change in the document typical velocity change V 1  to V 2 . Also, because the magnitude of the motor velocity adjustment change is equal to that of the document in  FIG. 5A , the resulting “actual” document velocity at the imaging cameras is at an ideal constant velocity V 7 , which is seen in  FIG. 5C . These associated figures illustrate the ideal result of this embodiment of the invention, which is a constant document imaging velocity during the entire length of the document. 
     However, even if the magnitude or the exact timing of this scanning system drive motor adjustment is not ideal, it can still result in improved imaging velocities as illustrated in  FIGS. 6A, 6B, and 6C  as compared to no scanning system drive motor adjustment, as shown in  FIGS. 4A, 4B and 4C . Note that the improved change in velocity V 5 ′ to V 6 ′ as shown in  FIG. 6C , has been reduced as compared to the change in document velocity V 5  to V 6  being imaged as shown in  FIG. 4C  in a standard scanning transport with no velocity correction. Even if there are variations in the magnitude and timing of the document expected velocity change, the motor programmed velocity adjustment can greatly improve the document&#39;s resulting image quality by counter acting the change in scanning system transport speed that is typically seen when the document is released for the feed roller separation device nip. 
     PARTS LIST 
     
         
           10  scanning system 
           12  document stack 
           14  input tray 
           16  urging roller 
           17  urging roller drive shaft 
           18  urging pinch roller 
           20  feed roller 
           21  separation device 
           22  transport path 
           24  first transport roller 
           26  exit transport roller 
           28  control logic processor 
           30  motor 
           32  gear arrangement 
           34  clutch 
           36 A camera 
           36 B camera 
           38  document location sensor 
           40  feed roller drive shaft 
           42  urging roller sensor 
           44  urging roller encoder wheel 
           48  motion controller 
           50  memory 
           52  document