Abstract:
A document feeder for multifunction printers or scanners offers high reliability and speedy paper-picking, -separating and -feeding functions. It comprises a picking module, a separating module and a feeding module. Since the three modules take turns to deliver paper, the paper can be picked at a lower speed, separated at a medium speed and then fed at a high speed. In addition, the separating module comprises a clutch. When the paper was fed by the feeding module, the clutch is activated to provide an interval between papers and to prevent papers from plucking.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit of Taiwan Patent Application No. 094137959, filed on Oct. 28, 2005, which is hereby incorporated by reference for all purposes as if fully set forth herein. 
   BACKGROUND OF THE INVENTION 
   1. Field of Invention 
   The invention relates to an automatic document feeder used in scanners, copiers, fax machines, or multifunction processors. It is used to separate paper in a pile and to feed it sheet by sheet into a machine for further processing. 
   2. Related Art 
     FIG. 1  shows a conventional paper picking/feeding mechanism used in fax machines. It mainly comprises a dynamic gear  11 , a paper-picking roller  10 , and a paper feeding roller  12 . The dynamic gear  11  is directly coupled to rotate the paper feeding roller  12 . A clutch (not shown) comprised of a spring is inserted between the dynamic gear  11  and the paper-picking roller  10 . The speed of the paper feeding roller  12  is designed to be greater than that of the paper-picking roller  10 . When this mechanism is in action, the dynamic gear  11  drives the paper-picking roller  10  (the clutch is closed at this moment), so that the paper  13  is pulled by the paper-picking roller  10  and sent to the paper feeding roller  12 . Since the paper feeding roller  12  has a higher speed than the paper-picking roller  10 , the paper  13  drives the paper-picking roller  10  to reach a higher rotating speed than the dynamic gear  11 . The clutch is thus in the open state without pulling the paper  13 . The above-mentioned conventional structure can be seen in U.S. Pat. No. 5,630,580, “FEED ROLL ASSEMBLY ADAPTED FOR DELIVERING SHEET OF clutch still produces a pulling force on the paper  13  even when the clutching gap is insufficient. This is disturbing for the operations of processors. 
   U.S. Pat. No. 6,024,357, “DOCUMENT SHEET FEEDING MECHANISM” discloses a mechanical clutch and paper separating design. Its primary goal is to solve the problems of separating and pulling paper. It uses a mechanical clutch and an appropriate gap design so that the paper is not pulled in this case. With the paper separating design, there is a higher reliability in picking a single sheet of paper. Even so, the paper separating design and the paper-picking roller are disposed at the same position. Therefore, the paper separating effect is still not reliable in practice. Therefore, U.S. Pat. No. 6,540,220, “PAPER FEEDING SYSTEM WITH BOTH PAPER ENGAGING AND PAPER SEPARATING MECHANISMS” proposed an automatic document feeder. It uses a swing-arm paper-picking roller to touch and move the paper to the paper-separating roller. The paper-separating roller is provided with a friction board. When the paper-picking roller picks more than one sheet of paper and feeds them to the paper-separating roller, only the sheet that is in contact with the paper-separating roller is passed on while the sheet in contact with the friction board is left behind because the friction of the friction board is greater than the paper-separating roller. To prevent paper from pulling after entering the paper-separating roller or overfeeding, the swing arm is controlled by a motor to increase/decrease its speed or even reverse its rotating direction. Therefore, the paper-picking roller is lifted without contacting the paper, providing a gap between two sheets of paper. 
   Even though the above-mentioned proposals have the paper picking/separating functions, paper pulling still happens. Moreover, current processors often need to process recycled paper. Such paper makes the paper picking/separating even more difficult. 
   SUMMARY OF THE INVENTION 
   In view of the foregoing, the paper picking/separating mechanisms in the prior art is not reliable enough for recycled paper. Secondly, there is a higher demand for faster processing speeds of the processors. In this case, the traditional designs often feed in more than one sheet of paper or have paper jams. Therefore, the invention provides an automatic document feeder to provide paper-picking, -separating, and -feeding functions with even higher speeds and reliability. 
   According to an embodiment of the invention, the automatic document feeder includes a paper-picking roller coupled to a paper-picking arm, a paper-separating roller coupled to the paper-picking arm, a driving shaft coupled to the paper-separating roller, and a paper-feeding roller. The speed of the paper-feeding roller is designed to be higher than that of the paper-separating roller, and the speed of the paper-separating roller is higher than that of the paper-picking roller. A clutch is provided between the driving shaft and the paper-separating roller. Therefore, paper is transferred from the paper-picking roller via the paper-separating roller to the paper-feeding roller. When paper reaches the paper-feeding roller, the paper-separating roller and the driving shaft are separated due to the clutch and the high speed of the roller. Therefore, the speeds of the paper-separating roller and the paper-feeding roller are the same, without pulling the paper. When the paper is moved out of the paper-separating roller, the clutch is still in the separate state. The driving shaft is not coupled to the paper-separating roller. In this case, both the paper-separating roller and the paper-feeding roller are not in action. That is, no paper is processed until the driving shaft catches up the gap of the clutch. 
   The invention uses the paper-picking roller to pick paper at a low speed, the paper-separating roller to separate paper at a medium speed, and the paper-feeding roller to feed paper at a high speed. The invention achieves three goals. Firstly, the speeds of the paper-feeding roller and the paper-picking roller do not need to be adjusted or reversed in direction. The speeds can be increased step by step. Therefore, the difference between the two speeds can be a factor of 2.5 or more. Secondly, the paper-picking roller and the paper-separating roller are designed to be separate, so that the reliability of separating paper is greatly enhanced. The invention can ensure that no more than one sheet of paper is being sent even when recycled paper is used. Thirdly, once the previous sheet of paper is sent out of the paper-separating roller, the paper-separating roller is immediately not in action until the driving shaft catches up with the gap of the clutch. Only after that can the driving shaft couples to the paper-picking roller to pick paper. This produces a gap between two consecutive sheets of paper. This also enables the process to count the sheets. 
   Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description given hereinbelow illustration only, and thus are not limitative of the present invention, and wherein: 
       FIG. 1  is a schematic view of the prior art; 
       FIG. 2  is a schematic view showing the structure of the invention; 
       FIG. 3  is a perspective view of the disclosed clutch; 
       FIG. 4  is a schematic view showing the structure of the paper-separating roller and the damping element in the invention; 
       FIGS. 5A to 5C  are schematic views showing the action of the clutch according to the invention; 
       FIG. 6  shows another embodiment of the disclosed paper-picking roller; and 
       FIG. 7  shows another embodiment of the disclosed damping element. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The automatic document feeder disclosed herein can be applied to multifunction processors (MFP), fax machines, copiers, and scanners. In the following description, we use the applications in scanners and MFP&#39;s as our preferred embodiments. 
   With reference to  FIG. 2 , the invention includes a paper-picking module  20 , a paper-separating module  30 , a paper-feeding module  40 , and a shell  50 . The paper  60  is transferred in sequence through a paper-transferring track  51  composed of the paper-picking module  20 , the paper-separating module  30 , and the shell  50 , and the paper-feeding module to reach the entrance  52  for the next process. 
   The paper-picking module  20  includes a paper-picking roller  21  disposed at one end of a paper-picking arm  22 . When the paper-picking module  20  functions, the arm  22  swings up and downs according to the thickness of each sheet of paper  60  in order to properly transfer a sheet of paper to the next stage. Since the outer surface of the paper-picking roller  21  is provided with a friction board  210  with a larger friction, the top sheet of paper  60  is moved out to the left of the drawing when the paper-picking roller  21  is in touch with the paper  60 . This is because the friction between each two sheets of paper is smaller than that between the friction board  210  and the top sheet of paper  60 . 
   With simultaneous reference to  FIGS. 2 and 3 , the paper-separating module  30  includes a damping element  31 , a paper-separating roller  32  in contact with the damping element  31 , a driving shaft  33 , and a clutch for coupling the driving shaft  33  and the paper-separating roller  32 . The clutch  34  is comprised of a first clutch element  340  fixed on the driving shaft  33  and a second clutch element  341  fixed on the paper-separating roller  32 . The first clutch element comprises a first tooth that projects in a radial direction from a surface of the driving shaft. The second clutch element comprises a second tooth that projects in an axial direction from an end of the paper-separating roller. When the first tooth abuts against the second tooth, the clutch is closed, and when the first tooth is separated from the second tooth, the clutch is separate. Apart from fixed installation of the clutch elements  340 ,  341 , they can be formed from extensions of the paper-separating roller  32  and the driving shaft  33 . The surface of the paper-separating roller  32  is disposed with a friction board  320  with a larger frictional coefficient than the paper. The frictional coefficient of the damping element  31  is designed to be smaller than that of the friction board  320 , but larger than that of the paper. Therefore, as shown in  FIG. 4 , when more than one sheet of paper is transferred to the paper separating module  30 , this design of frictional coefficients allows only the sheet  60  in contact with the paper-separating roller  32  to move on to the next step, the rest  60  remains at the damping element  31 . In this embodiment, the damping element  31  is designed as a board type element. However, the damping element  31  can be designed as a roller type element having the same function as the damping element  31 . Please refer to  FIG. 7 . It shows another embodiment of the damping element  31 , which is a damping roller  38  in constant contact with the paper-separating roller  32 . The damping roller comprises a torque limit roller  380  and a friction cover  381  fixed on the surface of the torque limit roller  380 . The torque limit roller  380  provides a continuous force to keep the friction cover  381  in constant contact with the paper-separating roller  32 . 
   The disposition of the first and second clutch elements  340 ,  341  is such that when the rotating speed of the paper-separating roller  32  is slower than that of the driving shaft  33 , the driving shaft  33  can rotate the paper-separating roller  32 . When the rotating speed of the paper-separating roller  32  is higher than that of the driving shaft  33 , the clutch elements  340 ,  341  depart so that the driving shaft  33  does not rotate the paper-separating roller  32 . Moreover, with reference to  FIG. 4 , the paper-separating roller  32  is coupled to the paper-picking roller  21  via a decelerating mechanism  23 . At the same time, the linear speed of the paper-separating roller  32  is designed to be higher than that of the paper-picking roller  21 . Therefore, when the paper  60  enters the paper-separating roller  32 , it proceeds with a larger linear speed. This design primarily slows down the paper-picking speed as much as possible. Therefore, not more than one sheet of paper is retrieved at a time. When the paper enters the paper-separating roller  32 , its speed can be increased to speed up its operation. 
   The paper-feeding module  40  has a paper-feeding roller  41  driven by an independent motor (not shown) and designed to have a linear speed larger than the paper-separating roller  32 . Therefore, when the paper  60  reaches the paper-feeding roller  41 , its speed is further increased. Driven via the paper  60 , the speed of the paper-separating roller  32  becomes the same as the paper-feeding roller  41  (the clutch  34  is separate). This action is illustrated in  FIGS. 5A to 5C .  FIG. 5A  shows that when more than one sheet of paper  60  is sent to the paper-separating roller  32 , the action of the paper-separating roller  32  and the damping element  31  separate the paper  60 , allowing only one sheet  60  to be transferred into the paper-transferring track  51 . In this case, the paper-separating roller  32  is driven by the driving shaft  33 . The clutch  34  is closed, as shown in  FIG. 5A . Secondly, as shown in  FIG. 5B , when the paper  60  is transferred to the paper-feeding roller  41 , the linear speed of the paper-separating roller  32  is increased to be the same as the paper-feeding roller  41 . Therefore, the transferring speed of the paper  60  increases without pulling the sheets. The clutch  34  at this moment is separate. As shown in  FIG. 5C , when the rear end of the sheet  60  is transferred out of the paper-separating roller  32 , the paper-separating roller  32  is not active because the clutch  34  is still separate and the paper-separating roller  32  is in contact with the damping element  31 . Since the driving shaft  33  is continuous working, the gap between the first and second clutch elements  340 ,  341  reduces. When the first and second clutch elements  340 ,  341  are closed, the driving shaft  33  starts to rotate the paper-separating roller  32  again. That is, the paper-picking roller  21  is driven to pick paper again. In this case, a gap is formed between the next sheet and the previous sheet for the convenience of counting and checking. 
   Moreover, when the paper  60  reaches the paper-feeding roller  41 , the speed of the paper-separating roller  32  becomes the same as the paper-feeding roller  41 . However, since the paper-picking roller  21  is driven by the paper-separating roller  32  at the moment, some pilling still exists. To prevent this phenomenon, another clutch  25  can be disposed between the paper-picking arm  22  and the paper-picking roller  21  (as shown in  FIG. 6 ). The first clutch element  251  is fixed on the paper-picking roller  21 , and the second clutch element  252  is directly driven by the decelerating mechanism  23  of the paper-picking arm. 22 , so that the linear speed of the paper-picking roller  21  becomes the same as the paper-separating roller  32 . This gives another embodiment of the invention. 
   To enhance the reliability of the invention, a spring  35  is provided below the damping element  31  (see  FIG. 2 ) to have continuous contact with the paper-separating roller  32 . Alternatively, one may select a rubber material for the damping element  31  and bend it to have continuous contact with the paper-separating roller  32 . 
   The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.