Patent Publication Number: US-6991227-B2

Title: Sheet feeder with stopper

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit of Korean Patent Application No. 2002-18024, filed Apr. 2, 2002, in the Korean Intellectual Property office, the disclosure of which is incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a sheet feeding apparatus, and more particularly, to a sheet feeding apparatus for a printing device to pick up sheets from a tray and deliver the sheets into a printing device sheet by sheet. 
   2. Description of the Related Art 
   A printing device  100 , such as a copying machine, includes a sheet feeding apparatus having a tray  11  for loading sheets S to be supplied into a printing device  10  and a pickup roller  12  introducing the sheets S on the tray  11  into a sheet feeding path (not shown) of the printing device  10  sheet by sheet as shown in  FIGS. 1 and 2 . The sheet feeding apparatus is used for feeding both sheets and documents. As an automatic document feeding (ADF) type printing device is known to automatically feed the documents, which are to be duplicated, as well as the sheets onto which images are printed, the sheet feeding apparatus has been applied to the printing device not only feeding the sheets but also feeding the documents. 
   Referring to  FIG. 2 , when a motor  13  rotates the pickup roller  12 , an uppermost sheet S stacked on the tray  11 , which is in contact with the pickup roller  12 , is inserted into the printing apparatus  10 . The sheet feeding apparatus includes a cover  14  that is closed during a printing process to protect the pickup roller  12  and an inlet of the printing device  10 , into which the sheets S are inserted as shown in  FIG. 2 . 
   In order to smoothly feed the sheets S into the printing device  10 , the pickup roller  12  must hold front ends of the sheets S disposed under the pickup roller  12 . When an excessive amount of sheets S is loaded on the tray  11 , it is difficult for the pickup roller  12  to hold the sheets S. Therefore, the amount of the sheets S that can be loaded on the tray  11  at one time is limited to about 20 sheets. Consequently, a user has to repeat to load the sheets S on the tray  11  to print a large amount of documents. In addition, according to the constitution of the sheet feeding apparatus as shown in  FIGS. 1 and 2 , an inclination of the tray  11  is angled as steep as possible toward the pickup roller  12  to smoothly slide the sheets S disposed under the pickup roller  12 . However, the constitution of the sheet feeding apparatus increases a height of the printing device  10 , so that the printing device  10  occupies a large space. In addition, according to the above constitution of the sheet feeding apparatus, more than two sheets may slide under the pickup roller  12 , which is referred to as double feeding of the sheets S. 
   SUMMARY OF THE INVENTION 
   To solve the above and other problems, it is an object of the present invention to provide an improved sheet feeding apparatus for a printing device to prevent double feeding of sheets and increase an amount of the sheets that can be loaded on a tray. 
   Additional objects and advantageous of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention. 
   To accomplish the above and other objects of the present invention, a sheet feeding apparatus for a printing device includes a pickup roller picking up sheets loaded on a tray to feed the sheets into a sheet feeding path, a feeding roller receiving the sheets picked up by the pickup roller to introduce the sheets into the sheet feeding path, a rotation member installed on a rotation shaft of the feeding roller to support and rotate the pickup roller at a free end of the rotation member, and a relay gear installed in the rotation member to engage the feeding roller and the pickup roller. 
   According to an aspect of the present invention, the sheet feeding apparatus includes a clutch unit selectively transferring a rotation force of the rotation shaft to the rotation member by blocking the rotation force between the rotation member and the rotation shaft so the pickup roller contacts a sheet on the tray by a weight of the pickup roller when the rotation shaft rotates in a sheet feeding direction and by connecting the rotation force between the rotation shaft and the rotation member to rotate the rotation member according to a rotation of the rotation shaft when the rotation shaft rotates in an opposite direction. 
   According to another aspect of the present invention, the sheet feeding apparatus includes a stopper installed in the rotation member to be elevated and lowered with respect to the rotation member according to the rotation of the rotation member so as to locate front ends of the sheets loaded on the tray to be disposed under the pickup roller while not reaching the feeding roller because the stopper blocks a path between the pickup roller and the feeding roller. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects and advantages of the present invention will become more apparent an embodiment thereof with reference to the attached drawings, in] and more readily appreciated from the following description of the preferred embodiment, taken in conjunction with the accompanying drawings of which: 
       FIG. 1  is a perspective view illustrating a printing device containing a conventional sheet feeding apparatus; 
       FIG. 2  is a view for explaining a sheet feeding process according to the conventional sheet feeding apparatus shown in  FIG. 1 ; 
       FIG. 3  is a perspective view illustrating a printing device containing a sheet feeding apparatus according to an embodiment of the present invention; 
       FIG. 4  is an exploded perspective view of the sheet feeding apparatus shown in  FIG. 3 ; 
       FIG. 5  is an exploded perspective view of a driving force connection unit of a feeding roller in the sheet feeding apparatus shown in  FIG. 3 ; 
       FIG. 6  is a perspective view of combined components of the sheet feeding apparatus shown in  FIGS. 4 and 5 ; and 
       FIGS. 7 and 8  are views explaining an operation of the sheet feeding apparatus shown in  FIG. 3 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Reference will now be made in detail to the present preferred embodiment of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiment is described in order to explain the present invention by referring to the figures. 
     FIGS. 3 through 8  illustrate a sheet feeding apparatus for a printing device according to an embodiment of the present invention. 
   With reference to  FIG. 3 , a printing device  100  includes a tray  110  on which sheets S are loaded, and a sheet feeding apparatus  200  driven by a driving source  130  to introduce the sheets S into a sheet feeding path in the printing device  100 . The printing device  100  further includes a cover  140  that covers the sheet feeding apparatus  200  while the sheet feeding apparatus  200  is in use. 
   Referring to  FIGS. 3 and 4 , the sheet feeding apparatus  200  includes a shaft  201  connected to the driving source  130 , a feeding roller  230  coaxially installed with the shaft  201 , a rotation member  220  rotating about a longitudinal center of the shaft  201 , a pickup roller  250  installed at a free end of the rotation member  220  so that the pickup roller  250  may rotate, and a stopper  260  engaged with a relay gear  240  to be elevated and lowered with respect to the rotation member  220 . In this case, the relay gear  240  connects the feeding roller  230  to the pickup roller  250 . In addition, in a case where the rotation member  220  does not receive a raising force for raising the pickup roller  250  in an upward direction with respect to the longitudinal center of the shaft  201 , the rotation member  220  rotates in a downward direction for the pickup roller  250  to contact the sheet S on the tray  110  by its own weight. 
   The sheet feeding apparatus  200  includes a clutch unit  210  selectively raising the rotation member  220  according to a rotating direction of the shaft  201 . When the shaft  201  rotates in a sheet feeding direction of the pickup roller  250 , such as a direction for introducing the sheets S into the sheet feeding path in the printing device  100 , the raising force between the shaft  201  and the rotation member  220  is disconnected to lower the rotation member  220  in the downward direction by its own weight. When the shaft  201  rotates in an opposite direction opposite to the sheet feeding direction, the raising force of the shaft  201  is connected to the rotation member  220  to raise the rotation member  220  in the upward direction according to the rotation of the shaft  201 . With reference to  FIG. 4 , the clutch unit  210  includes a coupling member  214  coupled on the shaft  201  of the rotation member  220 , a bushing  213  into which an external circumference of the coupling member  214  is inserted, a spring clutch  212  having both ends  212   b  and  212   a  respectively coupled to coupling grooves  213   a  and  214   a  of the bushing  213  and the coupling member  214 , and a driving member  211  fixed on the shaft  201  by a first fixing pin  211   a  while frictionally contacting an inner circumference of the spring clutch  212 . 
   The inner circumference of the spring clutch  212  contacts the driving member  211 , and an external circumference of the spring clutch  212  contacts an inner circumference of the bushing  213 . Therefore, when the shaft  201  rotates in a direction of an arrow A, the driving member  211  rotates by a friction in the same direction to rotate the spring clutch  212  in a direction of winding the spring clutch  212  upward. Accordingly, the driving member  211 , the spring clutch  212 , and the bushing  213  rotate simultaneously by the friction among these components to rotate the coupling member  214 , which is connected to the bushing  213  via the ends  212   a  and  212   b  of the spring clutch  212 . As a result, the rotation member  220  rotates in the upward direction or in the direction of the arrow A. In this case, the rotation member  220  rotates in the upward direction so that the pickup roller  250  is raised from the tray  110 . Although the shaft  201  stops rotating, the pickup roller  250  continues to be raised as long as the friction among the driving member  211 , the spring clutch  212 , and the bushing  213  is maintained. 
   When the shaft  201  rotates in a direction of an arrow B, which is opposite to the direction of the arrow A, the driving member  211  rotates in the same direction of the arrow B, in which the spring clutch  212  is unwound. Accordingly, the friction between the driving member  211  and the spring clutch  212  to raise the rotation member  220  is released to return the spring clutch  212 , the bushing  213 , the coupling member  214 , and the rotation member  220  to original positions by the weight of the rotation member  220 . Therefore, the pickup roller  250  contacts the sheet S on the tray  110 . In a case where the shaft  201  continues to rotate in the direction of the arrow B, the feeding roller  230  and the pickup roller  250  rotate to introduce the sheet S into the sheet feeding path. 
     FIG. 5  illustrates a connection unit transmitting a driving force between the feeding roller  230  and the shaft  201  to selectively rotate the feeding roller  230 . As shown in  FIG. 5 , a gear portion  231 , which is connected to the pickup roller  250  by the relay gear  240 , contains a slot  231   c  to which a second fixing pin  231   a  is coupled. The second fixing pin  231   a  is inserted into a coupling hole  203  formed in the shaft  201  and then coupled to the slot  231   c  of the gear portion  231 . Therefore, the shaft  201  rotates together with the gear portion  231 . An end of the feeding roller  230  contains a step surface  230   a  of a pinwheel shape, and a saw tooth member  232  with saw tooth portions  232   a  is installed between the step surface  230   a  and the gear portion  231 . Accordingly, the saw tooth portions  232   a  engages with the step surface  230   a.    
   The saw tooth member  232  also contains interference pieces  232   b , and the gear portion  231  contains interference projections  231   b , which interfere with the interference pieces  232   b . Consequently, when the gear portion  231  rotates, the interference projections  231   b  engage with the interference pieces  232   b  to rotate the saw tooth member  232 . According to the above constitution, when the shaft  201  rotates in the direction of the arrow B to rotate the gear portion  231  and the saw tooth member  232  in the same direction, vertical sections of the saw tooth portion  232   a  are coupled to the vertical sections of the step surface  230   a . As a result, the feeding roller  230  rotates with the shaft  201  in the same direction. 
   In contrast, when the shaft  201  rotates in the direction of the arrow A, first inclined sections of the saw tooth portion  232   a  slip off second inclined sections of the step surface  230   a  so as not to rotate the feeding roller  230 . As a result, when the shaft  201  rotates in the direction of the arrow A, the rotation member  220  rotates in the upward direction while the feeding roller  230  stops, and when the shaft  201  rotates in the direction of the arrow B, the rotation member  220  is lowered in the downward direction to allow the pickup roller  250  to contact the sheet S, and the feeding roller  230  rotates in the sheet feeding direction for feeding the sheets S. 
   Meanwhile, the pickup roller  250  does not require the above-described constitution, such as the connection unit, because the pickup roller  250  rotates by a gear connection with the feeding roller  230 . However, in order to firmly control a rotating direction of the pickup roller  250 , the pickup roller  250  may contain a unit transmitting the driving force between the gear portion  231  of the feeding roller  230  and a pickup gear  251  of the pickup roller  250  as described above, thereby the pickup roller  250  rotates only when the shaft  201  rotates in the direction of the arrow B. 
   Referring to  FIG. 4 , the stopper  260  with a rack gear portion  261  at an edge, coupled to an inner gear  241  of the relay gear  240 , is elevated and lowered with respect to the rotation member  220  according to a rotation of the relay gear  240 . With reference to  FIG. 8 , the stopper  260  is lowered to prevent the front ends of the sheets S on the tray  110  from reaching the feeding roller  230 . Accordingly, the stopper  260  prevents the front ends of the sheets S on the tray  110  from hitting the feeding roller  230  when an excessive force is applied to the pickup roller by a large amount of sheets S disposed under the pickup roller  250 . Consequently, the stopper  260  prevents the front ends of the sheets S from being crumpled. In other words, since the stopper  260  aligns the sheets S under the pickup roller  250 , one of the sheets S disposed on an upper portion of a stack of the sheets S is prevented from hitting the pickup roller  250  and being pushed back by the user before a printing operation. When the printing operation starts, the stopper  260  elevates as shown in  FIG. 7  to introduce the sheet S into the sheet feeding path through the feeding roller  230 . The sheet feeding apparatus  200  includes an elastic member that is installed on the tray  110  to apply an elastic force upward to the stopper  260  when the stopper  260  is lowered to push down the elastic member  111 . 
     FIG. 6  illustrates a perspective view of the sheet feeding apparatus  200 . When the shaft  201  rotates in the direction of the arrow B, the clutch unit  210  blocks the driving force from the shaft  201  to the rotation member  220 . Accordingly, the pickup roller  250  contacts the sheet S on the tray  110  as shown in  FIG. 7 . In this case, as the relay gear  240  rotates in the direction of the arrow A, the stopper  260  elevates to open the sheet feeding path. When the driving force is transmitted from the shaft  201  to the feeding roller  230 , the feeding roller  230  rotates in the direction of the arrow B by the saw tooth member  232 , which engages the step surface  230   a . Consequently, the pickup roller  250  connected to the feeding roller  230  by the relay gear  240  rotates in the direction of the arrow B to introduce the sheet S into the printing device  100 . In this case, a step portion  120  is formed between the pickup roller  250  and the feeding roller  230 , as the front end of the sheet S needs to pass over the step portion  120 . Therefore, since the sheet S picked up by the pickup roller  250  contacts and passes over the step portion  120  to be held by the feeding roller  230 , only the uppermost sheet S can pass over the step portion  120 . This constitution of the sheet feeding apparatus  200  is efficient in preventing a plurality of sheets S from being introduced into the sheet feeding apparatus  200  at the same time. 
   A sensor  150  of  FIG. 3  is installed in the printing apparatus  100  to detect whether there are no sheets S remaining in the tray  110 . When the sheets S are exhausted, the driving source  130  rotates the shaft  201  in the direction of the arrow A. Then, the driving member  211 , the spring clutch  212 , and the bushing  213  of the clutch unit  210  rotate by the friction to rotate the rotation member  220 , which is coupled to the coupling member  214 , with respect to the shaft  201 . Consequently, the pickup roller  250  is raised from the tray  110 , and the feeding roller  230  and the pickup roller  250  do not rotate as shown in  FIG. 8 . In this case, the stopper  260  located between the pickup roller  250  and the feeding roller  230  is lowered in accordance to the rotation of the relay gear  240  in the direction of the arrow B to prevent the sheets S from entering under the feeding roller  230 . By loading the sheets S on the tray  110  and pushing the sheets S toward the feeding roller  230 , the front ends of the sheets S reach the stopper  260  to be aligned. Then, the rotation member  220  rotates as shown in  FIG. 7  to continue a sheet feeding process. The sheet feeding apparatus  200  includes a stop projection  141  arranged in the cover  140  to prevent the rotation member  220  from rotating more than necessary. 
   According to the above-described constitution, when the sheets S on the tray  110  are exhausted, the pickup roller  250  is raised to allow the sheets S to be loaded on the tray  110  and then lowered after the sheets S are loaded. Consequently, the front ends of the sheets S are automatically inserted under the pickup roller  250 . Therefore, it is possible to decrease an inclination of the tray  110  and reduce a height of the printing device  100 , and the stack of the sheets S as high as a distance by which the pickup roller  250  is raised, may be loaded on the tray  110  at one time. In addition, since the front ends of the sheets S picked up by the pickup roller  250  contact and pass over the step portion  120  to be held by the feeding roller  230 , only an uppermost sheet S can be held by the feeding roller  230 . Accordingly, a plurality of the sheets S are prevented from being fed at once. Moreover, since the sheets S are aligned under the pickup roller  250  by the stopper  260  when the user pushes the sheets S between the tray  110  and the pickup roller  250 , the front ends of the upper portion of the stack of the sheets S are prevented from being crumpled by the feeding roller  230 . 
   The effects of the sheet feeding apparatus for the printing device according to the present invention are as follows. 
   First, since the pickup roller is raised to to allow the sheets to be loaded on the tray and then lowered after the sheets are loaded on the tray, the front ends of the sheets are automatically inserted under the pickup roller even when the inclination of the tray is not steep. 
   Second, since the step portion is arranged between the pickup roller and the feeding roller for only the uppermost sheet to pass over the step portion, a plurality of sheets are prevented from being fed at once. 
   Third, since the stopper aligns the sheets under the pickup roller when the user pushes the sheets toward the feeding roller, the front ends of the sheets are prevented from being crumpled by the feeding roller. 
   Although a few preferred embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in this embodiment without departing from the principles and sprit of the invention, the scope of which is defined in the claims and their equivalents.