Patent Publication Number: US-7584912-B1

Title: Anti-jam device that restricts the number of paper sheets each time

Description:
BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The invention relates to a shredder. In particular, the invention relates to an anti-jam device for the shredder. In the AUTO mode, the passage width provided by the anti-jam device is exactly the maximum thickness of paper that can be fed each time. In the REV mode, the anti-jam device provides a larger passage width for the paper to be backed out easily. 
     2. Related Art 
     To prevent such documents as legal files, receipts, invoices, credit card numbers, research reports, or personal financial information (e.g., credit card and phone bills) from being released, it is common to destroy them using a shredder. Therefore, the shredder has become an indispensable device for both business and home applications. 
     The action principle of a shredder for shredding paper is to dispose several cutting blades on two rotary shafts with spacers in between. A motor and a gearbox are employed to drive the two parallel rotary shafts that rotate in opposite directions. They provide a shearing force on passing paper to cut it into small stripes. 
     The motor load and the strength of the cutting blades and rotary shafts limit the sheet capacity allowed by the shredder each time. That is, when many paper sheets need to be destroyed, the user has to limit the amount of paper each time. Otherwise, there may be paper jam occurring to the rotary shafts. Therefore, in order not for the user to put in too much paper at a time, it is necessary to provide an anti-jam device that automatically restricts the number of sheets. 
     SUMMARY OF THE INVENTION 
     An objective of the invention is to provide an anti-jam device that restricts the number of sheets each time. In the auto mode, the provided passage width is exactly the maximum thickness of paper that can be fed each time. In the rev mode, the anti-jam device provides a larger passage width for the paper to be backed out easily. 
     In accord with the above-mentioned objective, the disclosed anti-jam device comprises a movable element and a fixing element disposed above the rotary shafts of the shredder. The movable element is a pair of rod parallel to the rotary shafts, with both ends in the holes preformed on the fixing element. When the shredder is in its auto mode, the passage width provided by the rap between the rods is exactly the maximum thickness of paper that can be fed each time. In the rev mode, the rods are pushed upwards by the paper to render a larger passage width for the paper to be backed out easily. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will become more fully understood from the detailed description given herein below illustration only, and thus is not limitative of the present invention, and wherein: 
         FIG. 1  shows the appearance of the first embodiment according to the invention; 
         FIG. 2  is a locally enlarged view of  FIG. 1 ; 
         FIG. 3  shows the appearance of the second embodiment according to the invention; 
         FIG. 4  is a locally enlarged view of  FIG. 3 ; 
         FIG. 5  shows the appearance of the third embodiment according to the invention; and 
         FIG. 6  is a locally enlarged view of  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention will be apparent from the following detailed description, which proceeds with reference to the accompanying drawings, wherein the same references relate to the same elements. 
     The discloses shredder includes a housing  30 , a shredder opening  31  on the top surface of the housing for material such as paper to be fed in, and a shredder mechanism disposed inside the housing  30  for shredding the material. The shredder mechanism includes cutting blades mounted on the rotary shafts  40 . A motor and a gearbox drive the two parallel rotary shafts that run in opposite directions. The material being fed is then to cut into chips. The disclosed anti-jam device is disposed between the rotary shafts  40  and the shredder opening  31 , composed of a movable element  10  and a fixing element  20 . 
       FIG. 1  shows the appearance of a first embodiment of the invention.  FIG. 2  shows the local structure of  FIG. 1 . The movable element  10  is a pair of rods parallel to the rotary shafts  40 . Both ends of each rod fall into preformed holes  21  of the fixing element  20 . Normally, the movable element  10  is at the bottom of the hole  21 . As shown in the drawing, the hole  21  has an open space for the movable element  10  to move. When the shredder is in its auto mode, the passage width provided by the gap between the rods above the rotary shafts  40  is exactly the maximum thickness of paper that is allowed by the shredder each time. Therefore, only when the thickness of paper fed each time is smaller than the passage width can it pass through. When the shredder is in its rev mode, the rods of the movable element  10  are pushed upwards by the paper so that the rods move toward the open space in the upper part of the holes  21 . The passage width thus becomes larger for the paper to be backed out conveniently. 
     In the first embodiment, the rods in the movable element  10  can be metal or plastic hollow tubes or solid bars. To save the material, the second embodiment shown in  FIGS. 3 and 4  has rods  11  in smaller diameters and mounted with plastic rings  13 . The plastic rings  13  are provided in a symmetric way on the rods  11 . Therefore, the passage width provided by the gap between the plastic rings  13  is exactly the maximum thickness of paper allowed by the shredder each time. Only when the thickness of paper fed each time is smaller than the passage width can it pass through. When the shredder is in its rev mode, the plastic rings  13  in the movable element  10  are pushed upwards by the paper so that the rods  11  move towards the open space in the upper portion of the holes  21 . Consequently, the passage width between the plastic rings  13  becomes larger for the paper to be backed out conveniently. 
     The symmetrically disposed plastic rings  13  in the movable element  10  of the second embodiment can be replaced by plastic or metal rollers  12 , as shown in  FIGS. 5 and 6  of a third embodiment. In this case, the passage width provided by the gap between the rollers  12  is exactly the maximum thickness of paper allowed by the shredder each time. Only when the thickness of paper fed each time is smaller than the passage width can it pass through. When the shredder is in its rev mode, the rollers  12  in the movable element  10  are pushed upwards by the paper so that the rods  11  move towards the open space in the upper portion of the holes  21 . Consequently, the passage width between the rollers  12  becomes larger for the paper to be backed out conveniently. 
     Although the invention has been described with reference to specific embodiments, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiments, as well as alternative embodiments, will be apparent to persons skilled in the art. It is, therefore, contemplated that the appended claims will cover all modifications that fall within the true scope of the invention.