Patent Publication Number: US-2006012104-A1

Title: Automatic document feeder with anti-skew function

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
      This application claims the benefit of Korean Patent Application No. 2004-54941, filed on Jul. 14, 2004, the disclosure of which is hereby incorporated herein by reference in its entirety.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to an automatic document feeder with an anti-skew function and, more particularly, to an automatic document feeder for automatically feeding a plurality of documents to an image scanning device one by one.  
      2. Description of the Related Art  
      In a device for scanning and imaging, transmitting or duplicating contents of documents, such as a duplicator, a scanner, a facsimile or a multifunctional device having all functions of the aforementioned devices, an automatic document feeder (ADF) is used to feed a plurality of documents to an image scanning device (e.g., CCD module) mounted in the device one by one.  
      Referring to  FIG. 1 , an example of a typical automatic document feeder is illustrated. In this figure, the automatic document feeder is mounted in an image scanning device, which may be one of a scanner, a facsimile, a duplicator or a multifunctional device. Mounted in a main body  100  of an image scanning device is a charge coupled device (CCD) module  102  for digitally imaging light reflected from an illuminated surface of the document. The CCD module  102  is provided with a transparent window  104  at its upper portion to transmit the light to the CCD module  102 .  
      The automatic document feeder  110  is mounted on the main body  100 . The automatic document feeder  110  is provided with a tray  112  formed at a top surface of the automatic document feeder  110  for loading a plurality of documents P, which are to be inserted. A pick up roller  120  for inserting the documents one by one is installed at a position adjacent to the tray  112 . The pick up roller  120  is moved downward to the document by driving means (not shown) depending upon a signal from a controller (not shown) to transfer the document into the device by friction force. The transferred document is prevented from double feeding by an ADF roller  122 .  
      That is, a friction rubber  124  biased by a resilient spring  126  is located under the ADF roller  122  to come in contact with the ADF roller  122  to thereby supply only an uppermost document due to a difference of friction forces when the documents are double fed. The document P, which has passed through the ADF roller  122 , is transferred to a REGI roller  128 . The REGI roller  128  is rotated or stopped depending upon a signal from a controller to prevent the document from being double fed toward a feed roller  130  by transferring or temporarily stopping the document.  
      The document transferred by the REGI roller  128  is moved to an upper portion of the CCD module  102  by the feed roller  130  to be scanned. The feed roller  130  should have the strongest driving force of the aforementioned rollers to prevent the document from slipping in order to obtain a stable image, since the slip of the document may remarkably affect image quality. After scanning, the document is discharged to a discharge tray  114  by a discharge roller  132   
      In the case of the conventional automatic document feeder, the REGI roller  128  is set to have the same document feed speed on its surface as the feed roller  130 . That is, the document feed speed of the REGI roller  128  and the document feed speed of the feed roller  130  are set to have the same value. In reality, however, both of these feed speed values become different due to manufacturing and assembling tolerance.  
      For example, when the roller has an outer diameter of 22 mm, a gear train for driving the roller has a reduction ratio of 0.31, the number of rotations of the motor is 421.5 rpm, and the outer diameter of the roller has maximum and minimum tolerance of 0.05 mm, a linear velocity is calculated as follows: 
 
Vmax=π×Dmax(roller)×N(rpm)/60×l(reduction ratio)=22.05×421.5/60×0.31=150.78/sec 
 
Vmin=π×Dmax(roller)×N(rpm)/60×l(reduction ratio)=21.95×421.5/60×0.31=150.09/sec 
 
      Finally, the maximum and minimum velocities within the tolerance have a difference of about 0.7 mm/sec. When the REGI roller has an outer diameter at the maximum tolerance and the feed roller has an outer diameter at the minimum tolerance, it does not matter. By contrast, when the REGI roller has an outer diameter at the minimum tolerance and the feed roller has an outer diameter at the maximum tolerance, difficulties are presented since the feed roller has a velocity faster than that of the REGI roller.  
       FIG. 2  schematically illustrates when the feed roller is rotated faster than the REGI roller. Both rollers are illustrated in parallel with each other for illustrative purposes to facilitate a better understanding, but are actually positioned as illustrated in  FIG. 1 . As shown, when the feed roller  130  is faster, tensile strength is generated in a lateral direction of the document, and the feed roller  130  has larger document feeding pressure, thereby generating a slip of about 0.7 mm/sec on the REGI roller as the result calculated above. Therefore, the roller is subjected to load during the document feeding to generate skew, and driving means such as a motor is also subjected to load due to an increase of the document feeding pressure, as a result. Thereby, the motor may be stepped out.  
     SUMMARY OF THE INVENTION  
      Therefore, an object of the present invention is to provide an automatic document feeder capable of stably feeding documents by adjusting an RPM of a feed roller and an RPM of a roller disposed before the feed roller to prevent slip and skew from occuring.  
      According to an aspect of the present invention, an automatic document feeder includes: a pick up roller for feeding documents loaded on a tray; a feed roller for transferring the fed documents toward document scanning means; and an intermediate roller disposed just before the feed roller to transfer the documents toward the pick up roller, wherein the intermediate roller has a document feed speed on a surface thereof faster than that of the feed roller.  
      That is, the present invention intentionally makes the document feed speed on a surface of the feed roller slower than the document feed speed on a surface of the intermediate roller located just before the feed roller to prevent tensile strength from being transmitted to the document. In this connection, the intermediate roller may be a REGI roller for aligning the fed documents, which may be varied depending upon a type of the automatic document feeder.  
      At this time, the intermediate roller may be more rapidly rotated while outer diameters of the intermediate roller and the feed roller are remained as they were, the intermediate roller may have an outer diameter lager than the maximum tolerance of the feed roller to allow both rollers to be rotated at the same angular velocity, or both methods may be employed at the same time.  
      Meanwhile, preferably, the intermediate roller has a document feed speed on a surface thereof faster than that of the feed roller by about 1˜2%. When a speed difference becomes excessively large, the document may be sagging or rolled to cause jamming, and when the speed difference becomes excessively small, anti-slip and anti-skew effects become insignificant.  
      According to another aspect of the present invention, an automatic document feeder includes: a first pick up roller for feeding documents loaded on a tray; a feed roller transferring the fed documents toward document scanning means; a first intermediate roller disposed just before the feed roller to transfer the documents toward the pick up roller, a second pick up roller for refeeding the document that one surface was completely scanned, and a second intermediate roller for refeeding the document refed by the second pick up roller toward the feed roller, wherein the first and second intermediate rollers have a document feed speed on surfaces thereof faster than that of the feed roller.  
      That is, the present invention may be applied to the automatic document feeder for dual scanning, in this case, since the first and second intermediate rollers transfer the documents to the feed roller, the intermediate rollers have a document feed speed on the surfaces thereof faster than that of the feed roller.  
      In this connection, the first and second intermediate rollers have a document feed speed on the surfaces thereof faster than that of the feed roller by about 1˜2%. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The above and other features and advantages of the present invention will become more apparent to those of ordinary skill in the art by describing in detail preferred embodiments thereof with reference to the attached drawings in which:  
       FIG. 1  is a schematic side view illustrating a conventional automatic document feeder;  
       FIG. 2  is a perspective view illustrating a document fed in a poor manner due to a speed difference between a REGI roller and a feed roller in the automatic document feeder shown in  FIG. 1 ;  
       FIG. 3  is a perspective view illustrating improved operation of the automatic document feeder shown in  FIG. 1  in accordance with an embodiment of the present invention; and  
       FIG. 4  is a side view illustrating an automatic document feeder in accordance with another embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, the thickness of layers and regions are exaggerated for clarity. Like numbers refer to like elements throughout the specification.  
      Hereinafter, an embodiment of an automatic document feeder in accordance with the present invention will be described with reference to the accompanying drawings.  
      An automatic document feeder in accordance with an embodiment of the present invention will be described with reference to  FIG. 1 . The automatic document feeder of the present invention can comprise similar parts, however, it can be controlled differently. Thus, a basic structure of the embodiment may employ the structure of  FIG. 1 . However, in order to make a document feed speed on a REGI roller  128  (i.e., a linear velocity of the REGI roller  128 ) faster than that of a feed roller  130  by about 1%, the feed roller  130  has an outer diameter of 22 mm, and the REGI roller  128  has an outer diameter of 22.2 mm. When tolerance is 0.05 mm and the conditions in  FIG. 1  are applied, the maximum and minimum linear velocities of the REGI roller  128  and the feed roller  130  are calculated as follows: 
 
Vfeed-max=π× D max(roller)× N (rpm)/60 ×I (reduction ratio)=22.05×421.5/60×0.31=150.78/sec 
 
Vfeed-min=π× D max(roller)× N (rpm)/60 ×I(reduction ratio)= 21.95×421.5/60×0.31=150.09/sec 
 
Vregi-max=π× D max(roller)× N (rpm)/60 ×I(reduction ratio)= 22.25×421.5/60×0.31=152.14/sec 
 
Vregi-min=π× D max(roller)× N (rpm)/60 ×I(reduction ratio)= 22.15×421.5/60×0.31=151.46/sec 
 
      Viewing the calculated results, since the minimum velocity of the REGI roller  128  is faster than the maximum velocity of the feed roller  130  by about 0.7 mm/sec, i.e., the speed of document transferred toward the feed roller  130  by the REGI roller  128  is faster than the speed of document transferred toward a CCD module  102  by the feed roller  130 , tensile stress is not generated on the document.  
      That is, since the document feed speed of the REGI roller is faster than the linear velocity of the feed roller when the document is placed between the REGI roller and the feed roller, power of resistance is not generated by the REGI roller. Since the document is transferred by only the linear velocity and the feeding force of the feed roller, skew by the resisting force of the REGI roller is suppressed and a driving system has no load, thereby preventing a lifetime of the feeder from being shortened and improving document feeding performance.  
       FIG. 3  schematically illustrates the above-mentioned state. The REGI roller  128  and the feed roller  130  are disposed in parallel with each other for illustrative purposes. That is, since the REGI roller  128  has a linear velocity faster than that of the feed roller  130 , as shown, the document is fed loosely to prevent the slip or the skew from occurring. Of course, the released state of the document shown in  FIG. 3  is exaggerated for illustrative purposes and, in reality, the document is not so much separated from a predetermined feeding path.  
      While the automatic document feeder adjusts the linear velocity by increasing the outer diameter of the REGI roller, it may be desirable to adjust a reduction ratio of a gear train and maintain the outer diameter equally. In addition, it may be also desirable to adjust both the outer diameter and the reduction ratio of the gear train.  
      Referring to  FIG. 4 , another embodiment of an automatic document feeder in accordance with the present invention is illustrated. Like numbers as the embodiment in  FIG. 1  refer to like elements in the following description, so their descriptions will be omitted.  
      The embodiment in  FIG. 4  relates to an automatic document feeder for dual scanning, the document P′ primarily discharged to a discharge tray  114  by a discharge roller  132  is retransferred into the feeder by a second pick up roller  140 , and then the transferred document P′ is transferred toward the feed roller  130  by an intermediate roller  142  to be scanned. Therefore, the dual scanning of a single document may be performed. At this time, the REGI roller  128  awaits in the state that the document P is stopped while the scanning for the document is performed, and the REGI roller  128  initiates to transfer the document when the scanning for the document is completed, thereby preventing the document from overlapping on the feed roller.  
      Meanwhile, the intermediate roller  142  is also disposed just before the feed roller to have a linear velocity faster than that of the feed roller. In order to make the linear velocity of the intermediate roller  142  faster, the intermediate roller  142  may have an outer diameter larger than that of the feed roller  130 , similarly to the REGI roller  128 . In addition, it may be possible to adjust the reduction ratio, or adjust the reduction ratio and the outer diameter at the same time.  
      As can be seen from the foregoing, the present invention is capable of improving a document feed performance by preventing the skew from generating between the REGI roller or the intermediate roller and the feed roller by only adjusting the linear velocity of the REGI roller or the intermediate roller, and extending the lifetime of a device such as a motor since a driving system has no additional load.