Patent Publication Number: US-2006017212-A1

Title: Paper feeding unit for image forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application claims the benefit under 35 U.S.C. 119(a) of Korean Patent Application No. 2004-58075, filed Jul. 24, 2004, the entire disclosure of which is hereby incorporated by reference.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to an image forming apparatus. More particularly, the present invention relates to a paper feeding unit to transfer paper stacked in a paper supplying cassette or a secondary paper supplying tray to a printing engine of a image forming apparatus.  
      2. Description of the Related Art  
      Generally, an image forming apparatus comprises a paper supplying cassette, a paper feeding unit, a printing engine, and a paper ejecting unit. The paper supplying cassette contains pieces of paper. The paper feeding unit picks up paper in the paper supplying cassette and transfers the paper to the printing engine. The printing engine forms an image on the transferred paper. The paper ejecting unit ejects the paper with an image thereon.  
       FIG. 1  is a cross-sectional diagram showing a conventional paper feeding unit. The paper feeding unit  14  comprises a pickup roller  32 , a first transferring roller  10 , a second transferring roller  20 , a feeding roller  60 , and an idle roller  70 . The pickup roller  32  picks up paper P′ stacked in the paper supplying cassette  30 . The first and second transferring rollers  10  and  20  transfer the paper P′ picked up by the pickup roller  32  along a paper transferring path P. The feeding roller  60  transfers the paper P′ from the first and second transferring rollers  10  and  20  to the printing engine which includes a photosensitive medium  52 .  
      The feeding roller  60  is rotated by a motor, which is not illustrated in the drawing. Referring to  FIG. 2 , the idle roller  70  is rotated in contact with the feeding roller  60 . Due to the frictional force against the feeding roller  60 , the idle roller  70  is rotated in the opposite direction to the feeding roller  60 .  
      The paper P′ stacked in the paper supplying cassette  30  is picked up by the pickup roller  32 . Consequently, the paper P′ is transferred by engagement between the first and second transferred rollers  10  and  20  until it reaches the feeding roller  60 . A leading end of the paper P′ is aligned by colliding with the feeding roller  60  and the idle roller  70  in the contact area of the feeding roller  60  and the idle roller  70 . Herein, the front part of the paper P′ is bent, as shown in  FIG. 2 . The phenomenon that describes the front part  33  of the paper P′ being bent due to collision of the leading end of the paper P′ with the feeding roller  60  and the idle roller  70  is called a curl phenomenon.  
      The curl phenomenon is disadvantageous and inevitable in the process of aligning the paper P′ When the feeding roller  60  rotates to transfer the paper P′, the curled part  33  of the paper P′ straightens abruptly. Additionally, paper P′ is transferred at a rate (V 2 ) faster than the contact rate (V 1 ) of the feeding roller  60 . This is because, as the curl of the paper P′ (P) is straightened, the paper P′ slips into the feeding roller  60 . Consequently, the idle roller  70  abruptly rotates.  
      As described above, due to paper P′ movement, it is difficult to control the paper transferring rate by controlling the feeding roller. Moreover, it is difficult to control the margin of the leading end of the paper P′. Therefore, an error occurs in the margin of the leading end compared to the preset margin value. Thus, the printing quality of the image forming apparatus degrades.  
      Accordingly, there is a need for an image forming apparatus with an improved paper feeding unit to control a supply rate at which paper is transferred into a printing engine for directing the leading end margin of paper.  
     SUMMARY OF THE INVENTION  
      An aspect of the present invention is to solve at least the above problems and/or disadvantages and to provide at least the advantages described below. Accordingly, an aspect of the present invention is to provide a paper feeding unit to control the leading end margin of paper by controlling a paper supply rate at which the paper is transferred into a printing engine in an image forming apparatus.  
      In order to achieve the above-described aspects of the present invention, there is provided a paper feeding unit which comprises: a pickup roller for picking up contained paper; a paper feeding unit for aligning the paper picked up by the pickup roller and providing the paper to a printing engine, the paper feeding unit including a first feeding roller and a second feeding roller; a feeding sensor for sensing the paper transferred to the paper feeding unit; and at least one driving power source for operating the first feeding roller and the second feeding roller.  
      The driving power source is formed of a motor which operates the first feeding roller and the second feeding roller simultaneously.  
      The paper feeding unit of embodiments of the present invention further includes a gear unit for conveying power from the motor to the first feeding roller and the second feeding roller.  
      The gear unit includes a first gear for conveying the power from the motor to the first feeding roller; and a second gear which is connected to the first gear and conveys the power from the first gear to the second feeding roller in the paper feeding unit.  
      The gear unit comprises a gear for conveying the power from the motor to the first feeding roller; and a belt unit connected to the gear and conveying the power from the gear to the second feeding roller.  
      Herein, it is preferable that the belt unit comprises a first pulley formed in the first feeding roller, a second pulley formed in the second feeding roller, and a timing belt set up in the first pulley and the second pulley.  
      According to embodiments of the present invention of the above described structure, the top margin of the print on the paper can be controlled precisely by controlling the operating rates of the first and second feeding roller, even though the curl of the paper is straightened up abruptly.  
      Other objects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses preferred embodiments of the invention.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The above and other objects, and features, and advantages of certain embodiments of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings, in which:  
       FIG. 1  is a cross-sectional view showing a conventional paper feeding unit;  
       FIG. 2  is an enlarged cross-sectional view showing the feeding and idle rollers of the paper feeding unit of  FIG. 1 ;  
       FIG. 3  is a cross-sectional view showing a paper feeding unit in accordance with an embodiment of the present invention;  
       FIG. 4  is a plan view showing a paper feeding unit of  FIG. 3 ; and  
       FIG. 5  is a plan view showing a paper feeding unit in accordance with another embodiment of the present invention. 
    
    
      Throughout the drawings, the same drawing reference numerals will be understood to refer to the same elements, features, and structures.  
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS  
      The matters defined in the description such as a detailed construction and elements are provided to assist in a comprehensive understanding of the embodiments of the invention. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the invention. Also, descriptions of well-known functions and constructions are omitted for conciseness.  
       FIG. 3  shows a paper feeding unit  100  for an image forming apparatus in accordance with an embodiment of the present invention.  FIG. 4  shows a plan view of a paper feeding unit  150  of  FIG. 3 .  
      As illustrated in  FIG. 3 , the paper feeding unit  100  comprises a pickup roller, a first transferring roller  152 , a second transferring roller  154 , a feeding sensor  140 , and the paper feeding unit  150 .  
      The pickup roller includes a first pickup roller  132  for picking up pieces of paper stacked in a paper supplying cassette  170  one by one. A second pickup roller  142  is provided to pick up pieces of paper stacked in a secondary paper supplying tray.  
      The first and second transferring rollers  152  and  154  are arranged to rotate in contact with each other in a paper transferring path P over the first pickup roller  132 . The first and second transferring rollers  152  and  154  transfer the paper picked up by the first pickup roller  132  to the paper feeding unit  150 .  
      The feeding sensor  140  is formed in the front part of the paper feeding unit  150 . The feeding sensor  140  senses the paper transferred by the first and second transferring rollers  152  and  154  and the paper transferred by the second pickup roller  142 . Accordingly, the paper is sensed by the feeding sensor  140  before it reaches the paper feeding unit  150 . Thus, the feeding sensor  140  outputs a sensing signal to a control unit (not shown).  
      The paper feeding unit  150  is preferably located substantially above the first and second transferring rollers  152  and comprises a first feeding roller  110 , a second feeding roller  120 , and an elastic member  126 . The paper feeding unit  150  aligns the paper transferred from the first and second transferring rollers  152  and  154 . The paper feeding unit  150  also aligns the paper transferred from the second pickup roller  142  and supplies the aligned paper to a printing engine (not shown). The first and second feeding rollers  110  and  120  are configured to engage and rotate in contact with one another. One side of the elastic member  126  is supported by the body (not shown) of the image forming apparatus. The other side presses the second feeding roller  120  toward the first feeding roller  110 . Thus, the first and second feeding rollers  110  and  120  contact one another with a regular level of pressure.  
       FIG. 4  illustrates a plan view of the paper feeding unit  150 . As shown in the drawing, the first feeding roller  110  substantially surrounds a part of the first rotary shaft  111 . The second feeding roller  120  engages the first feeding roller  110  and surrounds a portion of the second rotary shaft  121 . In addition, a first gear  112  is preferably formed on one side of the first feeding roller  110 . A second gear  122  preferably engages with the first gear  112  and is formed on one side of the second feeding roller  120 . The first gear  112  and the second gear  122  are formed to have the same diameter so that the first gear  112  and the second gear  122  have the same rotation speed. Reference numeral  130  is a driving power source. A motor is preferably used for the driving power source in this embodiment. An axis  131  of the motor  130  is connected with a motor gear  132 . The motor gear  132  engages the first gear  112  and conveys rotation power to the first gear  112 . The paper feeding unit includes a plurality of elastic members, which are presented in the form of springs  126  in certain embodiments of the present invention, to press the second feeding roller  120  against the first feeding roller  110 . Although springs  126  are illustrated, other suitable elastic members may be used.  
      Hereafter, the operation of the paper feeding unit will be described with reference to  FIGS. 3 and 4 .  
      The first pickup roller  110  picks up the paper stacked in the paper supplying cassette  170  to provide the paper to the area between the first and second transferring rollers  152  and  154 . The transferring rollers  152  and  154  are set up in the paper transferring path P.  
      The paper is transferred to the paper feeding unit  150  by the rotation of the first and second transferring rollers  152  and  154 . Paper picked up by the second pickup roller  142  in the secondary paper supplying tray  160  is provided directly to the paper feeding unit  150 . Before the paper reaches the paper feeding unit  150 , a feeding sensor  140  senses the paper and aligns the paper with the paper feeding unit  150 .  
      When the paper contacts with the first and second feeding rollers  110  and  120 , which are in the state of suspension, the leading end of the paper is curled, which is called a curl phenomenon. The paper is aligned in good shape through the curl phenomenon. After the alignment, the control unit (not shown) operates the motor  130  to feed the paper to the printing engine. The first and second feeding rollers  110  and  120  are operated simultaneously through the first gear  112  and the second gear  122  which convey the driving power of the motor  130 .  
      Herein, the motor  130  is precisely rotated at a desired rotation speed suitable for controlling the leading end margin of the paper. Accordingly, the first and second feeding rollers  110  and  120  are rotated at a precise rotation speed. Also, since they are rotated by being engaged with one motor  130 , it is easy to rotate the first and second feeding rollers  110  and  120  at the same speed. Therefore, if the first and second feeding rollers  110  and  120  make an idle rotation, paper slips are avoided. Consequently, paper may be transferred precisely as much as a distance that corresponds to the rotation quantities of the first and second feeding rollers  110  and  120 . This way, the leading end margin of the paper may be controlled easily.  
       FIG. 5  is a plan view showing a paper feeding unit  150 ′ in accordance with another embodiment of the present invention. The configuration is very similar to that of the above described embodiment, except that the paper feeding unit  150 ′ of the present embodiment does not include the second gear installed on one side of the second rotary shaft  121  of the second feeding roller  120 . Moreover, the paper feeding unit  150 ′ includes a first pulley  113  in the first rotary shaft  111  and a second pulley  123  in the second rotary shaft  121 . In addition, the paper feeding unit  150 ′ of the embodiment includes a timing belt  125  set up in the first and second pulleys  113  and  123  to cooperate with the first rotary shaft  111  and the second rotary shaft  121 .  
      In the present embodiment, the rotation power of the motor  130  is conveyed to the first gear  112 . The first feeding roller  110  rotates as the first rotary shaft  111  connected to the first gear  112  is rotates. If the first rotary shaft  111  is rotated, the second feeding roller  120  is rotated at substantially the same rotation rate by the time belt  125 . Therefore, the frictional force between the first and second feeding rollers  110  and  120  is substantially the same.  
      As described above, the paper feeding unit suggested in the embodiments of the present invention may control the paper transferring rate at which the paper is transferred to the printing engine. The paper is transferred relatively easily by using two feeding rollers which are operated by the driving power source. The paper feeding unit minimizes a change in the paper transferring rate in the leading end. This is accomplished by passing the paper through the two feeding rollers to control the top margin of the paper easily. Therefore, it may secure stable printing quality.  
      The foregoing embodiments and advantages are merely exemplary and are not to be construed as limiting the present invention. The present teaching can be readily applied to other types of apparatuses.  
      While the invention has been shown and described with reference to certain embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.