Patent Publication Number: US-7584960-B2

Title: Registration device and image forming apparatus having the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims priority under 35 U.S.C. §119(a) from Korean Patent Application No. 10-2005-0116894, filed on Dec. 2, 2005, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present general inventive concept relates to a registration device to align a leading edge of a paper sheet and an image forming apparatus having the registration device. 
   2. Description of the Related Art 
     FIG. 1  is a view illustrating a conventional paper sheet registration method. Referring to  FIG. 1 , a paper sheet P is picked up from a cassette  5  by a pickup roller  1  and supplied to a registration roller  3 . The registration roller  3  conveys the paper sheet P according to a printing speed of a printing element  4 . Paper skew may take place in the process of conveying the paper sheet P from the cassette  5  to the registration roller  3 . Accordingly, to obtain a printed image with high quality, a registration process is performed to correct the paper skew. 
   A conventional registration method will now be briefly described with reference to  FIG. 1 . When the paper sheet P is conveyed to the registration roller  3 , the registration roller  3  is rotated in a reverse direction, i.e., a direction opposite to a direction in which the paper sheet P is fed. Thus, when a leading edge of the paper sheet P reaches the registration roller  3 , the paper sheet P is prevented from moving further toward the printing element  4 . If the pickup roller  1  continues to rotate, the paper sheet P is curled as illustrated by a broken line D in  FIG. 1 . As a result, the leading edge of the paper sheet P is aligned with respect to the registration roller  3 . Subsequently, the registration roller  3  is rotated in a forward direction, to make the paper sheet P move toward the printing element  4 . 
   This method of aligning a paper sheet through the reverse and forward rotation of the registration roller is problematic in the following aspects. First of all, the leading edge of the paper sheet may be damaged when the registration roller rotates in a reverse direction, thereby increasing the likelihood of a paper jam. Second, the registration roller must be stopped during the reverse rotation and then rotated in a forward direction, which is quite difficult due to an inertial resistance of the registration roller. Thus, a motor (not shown) that drives the registration roller may be overloaded. In a case of a high-speed printing image forming apparatus, it is even more difficult to change the rotational direction of the registration roller. Accordingly, it has been proposed to gently reduce the speed of the registration roller in order to stop the reverse rotation, and then to forwardly rotate the registration roller at a gradually increasing speed. However, such deceleration and acceleration process is time-consuming, and therefore reduces the printing speed of the image forming apparatus. Third, a power coupling device of a complicated structure has to be employed in order to rotate the registration roller in both the reverse and forward directions, which increases manufacturing costs of the image forming apparatus. 
   In addition, an alternate method may be used, wherein the registration roller is stopped temporarily to align the leading edge of the paper sheet, after which the registration roller is rotated forward to convey the paper sheet. However, this method also requires the use of a complicated power coupling device and increase manufacturing costs of the image forming apparatus. 
   SUMMARY OF THE INVENTION 
   The present general inventive concept provides a registration device suitable to a high-speed printing operation and an image forming apparatus having the registration device. 
   The present general inventive concept also provides a registration device with a low cost and simple structure, and an image forming apparatus having the registration device. 
   Additional aspects and advantages of the present general inventive concept 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 general inventive concept. 
   The foregoing and/or other aspects of the present general inventive concept may be achieved by providing a registration device including a registration roller, a registration lever able to rotate between an alignment position to block and align a leading edge of a paper sheet supplied to the registration roller and an opening position to allow the paper sheet to be fed beyond the registration lever, and a resilient member to resiliently urge the registration lever to rotate into the alignment position, the resilient member having a center portion and first and second arms extending from the center portion, wherein an end of the first arm is coupled to the registration lever and the resilient member is pivotable about an end of the second arm. 
   The foregoing and/or other aspects of the present general inventive concept may also be achieved by providing an image forming apparatus including a printing element to form an image on a paper sheet, and a registration device to align a leading edge of the paper sheet supplied to the printing element, the registration device including a registration roller, a registration lever able to rotate between an alignment position to block and align a leading edge of a paper sheet supplied to the registration roller and an opening position to allow the paper sheet to be fed beyond the registration lever, and a resilient member to resiliently urge the registration lever to rotate into the alignment position, the resilient member having a center portion and first and second arms extending from the center portion, wherein an end of the first arm is coupled to the registration lever and the resilient member is pivotable about an end of the second arm. 
   The registration roller may be disposed on an inlet side of the printing element and feed the paper sheet at a predetermined printing speed. 
   The registration roller may be positioned between a pickup roller and a feed roller. 
   The registration lever may be rotatably attached to the registration roller. 
   When the registration lever is in the opening position, a line joining a center of the registration roller and the end of the first arm may not exceed a line joining the center of the registration roller and the end of the second in a clockwise direction of the center of the registration roller. An angle formed by the line joining the center of the registration roller and the end of the first arm and the line joining the center of the registration roller and the end of the second arm may be greater than 3 degrees. A restriction member may be provided to restrict the registration lever from rotating beyond a position where the opening angle is equal to or greater than 3 degrees when the registration lever rotates to the opening position. The registration lever may comprise a registration portion to block the leading edge of the paper sheet and a guide portion to guide a movement of the paper sheet when the registration lever is in the opening position. The guide portion may protrude from the center of the registration roller farther than the registration portion and may have an end of round shape. 
   The foregoing and/or other aspects of the present general inventive concept may also be achieved by providing a registration device usable in an image forming apparatus, including a registration roller rotable with a shaft to feed a printing paper along a path, a registration lever disposed around the shaft to move between an alignment position disposed in the path, and an open position disposed apart from the path, and a resilient member to apply a first force to the registration lever to be in the alignment position and to apply a second force to the registration lever to move from the open position to the alignment position. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and/or other aspects and advantages of the present general inventive concept will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
       FIG. 1  is a view illustrating a conventional paper sheet registration method; 
       FIG. 2  is a schematic view illustrating an image forming apparatus according to an embodiment of the present general inventive concept; 
       FIG. 3  is a perspective view illustrating a registration device employed in the image forming apparatus of  FIG. 2 , according to an embodiment of the present general inventive concept; 
       FIG. 4  is a side view illustrating the registration device of  FIG. 3 ; 
       FIGS. 5 and 6  are perspective views illustrating examples of a resilient member used in the registration device of  FIG. 3 , according to an embodiment of the present general inventive concept; 
       FIG. 7  is a view illustrating the registration lever of the registration device of  FIG. 3  placed in an alignment position; 
       FIG. 8  is a view illustrating the registration lever of the registration device of  FIG. 3  placed in an opening position; 
       FIGS. 9A ,  9 B and  9 C are views illustrating an acute angle formed in the registration device of  FIG. 3 ; and 
       FIG. 10  is a view illustrating a process of aligning a paper sheet in an image forming apparatus according to an embodiment of the present general inventive concept. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Reference will now be made in detail to the embodiments of the present general inventive concept, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present general inventive concept by referring to the figures. 
     FIG. 2  is a schematic view illustrating an image forming apparatus according to an embodiment of the present general inventive concept. 
   Referring to  FIG. 2 , the image forming apparatus includes a cassette  10  wherein printing media, such as paper sheets P are stacked, a pickup roller  20  to pick up the paper sheets P one by one, and a feed roller  40  and a driven roller  41  that are pressed against each other and rotated to feed the paper sheet P at a predetermined speed. The image forming apparatus may further include a drive roller  30  and an idle roller  31  provided between the pickup roller  20  and the feed roller  40  to assist a feeding process of the paper sheet P. A plurality of pairs of the drive roller  30  and the idle roller  31  may be used. A drive motor  60  is employed to rotate the pickup roller  20 , the drive roller  30 , and the feed roller  40 . Reference numeral  50  is an exemplary printing element that prints images on the paper sheet P. In the embodiment of  FIG. 2 , the printing element  50  is a shuttle-type inkjet head that reciprocates in a direction perpendicular to the feeding direction of the paper sheet P and ejects ink droplets on the paper sheet P through a nozzle portion  51  to thereby print an image. Alternatively, it is possible to employ an array-type ink jet head as the printing element  50 , which has a nozzle portion whose length corresponds to a width of the paper sheet P. An electrophotographic printing unit may also be used to print an image on the paper sheet P by an electrophotography method. A variety of other printing element may be used to print an image on the moving paper sheet P. 
   The paper sheet P should be aligned, i.e., registered, prior to reaching the ink jet head  50 . Thus, the image forming apparatus may include a registration device. For example, the drive roller  30  or the feed roller  40  may be used as a registration roller to align or register the paper sheet P. In the present embodiment, the drive roller  30  is used as the registration roller, and therefore, the drive roller  30  will be referred to as the registration roller  30  in the following description. 
     FIG. 3  is a perspective view illustrating the registration device used in the image forming apparatus of  FIG. 2 , according to an embodiment of the present general inventive concept, and  FIG. 4  is a side view illustrating the registration device shown in  FIG. 3 . Referring to  FIGS. 3 and 4 , the registration device includes the registration roller  30  disposed on a shaft  61 , a registration lever  70  to rotate between an alignment position (as illustrated in  FIGS. 4 and 7 ) to block and align a leading edge of the paper sheet P and an opening position (as illustrated in  FIG. 8 ) to allow the paper sheet P to be fed beyond the registration lever  70 , and a resilient member  90  to resiliently urge the registration lever  70  to rotate into the alignment position. 
   The registration lever  70  may be rotatably attached to the registration roller  30  and has a registration portion  71  and a guide portion  72 . The registration lever  70  may also be disposed around the shaft  61  and/or disposed between a pair of registration rollers  30 . The registration portion  71  is positioned on an inlet side of the registration roller  30  so as to contact the leading edge of the paper sheet P supplied to the registration roller  30 . As used herein, the inlet side of the registration roller  30  denotes an area before a contact nip formed between the registration roller  30  and the idle roller  31 . The guide portion  72  guides a movement of the paper sheet P when the registration lever  70  is in the opening position. The guide portion  72  protrudes from a center C of the registration roller  30  farther than the registration portion  71  and may have a leading end having a round shape. The resilient member  90  has a center portion  95  and first and second arms  91  and  92 , respectively extending from the center portion  95 . An end  93  of the first arm  91  is coupled to the registration lever  70 , whereas an end  94  of the second arm  92  serves as a center of rotation around which the resilient member  90  pivots. Thus, in the present embodiment, the end  94  of the second arm  92  is coupled to a mounting bracket (reference surface)  103  of the image forming apparatus. 
   Although a torsion spring is employed as an example of the resilient member  90  in the present embodiment, it should be appreciated that the resilient member  90  is not limited to a torsion spring but may be other types of resilient members that have a center part, a first arm and a second arm. For example, the resilient member  90  may be molded of plastics as illustrated in  FIG. 5  or may be a linear spring as illustrated in  FIG. 6 . The registration lever  70  may further include a projection arm  73 , such that, when the projection arm  73  contacts a stopper  101 , the registration lever  70  is placed in the alignment position. 
   The opening position of the registration lever  70  may be changed depending on a stiffness of the paper sheet P. When the registration lever  70  is in the opening position, it is desirable that a line L 1  linking the center C of the registration roller  30  with the end  93  of the first arm  91  do not coincide with a line L 2  joining the center C of the registration roller  30  with the end  94  of the second arm  92 , as illustrated in  FIG. 9A . Additionally, line L 1  should not be located over the line L 2 , I.e. L 1  should not lie on a clockwise side of L 2 , as illustrated in  FIG. 9B . The resilient force F of the first arm  91  has a radial component Fr and a tangential component Ft, the latter of which rotates the registration lever  70 . Accordingly, under the conditions illustrated in  FIG. 9B , the tangential component Ft acts clockwise with respect to the center C of the registration roller  30 , i.e., in a direction opposite to the alignment position, thus impeding the registration lever  70  from returning back into the alignment position. Furthermore, under the condition illustrated in  FIG. 9A  where the line L 1  coincides with the line L 2  and makes a right angle with the first arm  92 , the tangential component Ft of the resilient force F of the first arm  91  becomes zero, which increases the possibility that the registration lever  70  will fail to return back to the alignment position. 
   To allow the registration lever  70  to return back to the alignment position when the paper sheet P has moved past the guide portion  72 , the tangential component Ft of the resilient force F of the first arm  91  must be oriented counterclockwise with respect to the center C of the registration roller  30 , i.e., in a direction of the alignment position. This becomes possible by making the line L 1  lie on a counterclockwise side of the line L 2  as illustrated by  FIG. 9C . It has been experimentally confirmed that, in order to make the tangential component Ft of the resilient force F of the first arm  91  act in the direction in which the registration lever  70  is constantly urged to return back to the alignment position, the line L 1  should lie on a counterclockwise side of the line L 2  and should make an acute angle B of at least 3 degrees with respect to the line L 2 , as illustrated in  FIG. 9C . 
   A restriction member  102  that contacts the projection arm  73  may further used to restrict the registration lever  70  from rotating beyond a position where the acute angle B is equal to or greater than 3 degrees. As the paper sheet P moves past the guide portion  72 , the registration lever  70  is rotated toward the alignment position by the resilient force F of the resilient member  90  and stops in the alignment position when the projection arm  73  contacts the stopper  101  as illustrated in  FIG. 7 . 
   A process of aligning the paper sheet P using the registration device is as follows. 
   The drive motor  60  begins to rotate when a printing command is inputted to a control part  100  of  FIG. 2  by, e.g., a host computer not shown in the drawings. Accordingly, the pickup roller  20 , the registration roller  30 , and the feed roller  40  are rotated in a direction such that the paper sheet P is fed toward the inkjet head  50  as illustrated in  FIG. 2 . The paper sheet P is picked up from the cassette  10  by the pickup roller  20 . As illustrated in  FIG. 7 , the registration lever  70  is initially kept in the alignment position to block the leading edge of the paper sheet P. The paper sheet P may be skewed when is picked up from the cassette  10  by the pickup roller  20  and fed to the registration roller  30 . Thus, a side portion FE 1  of the leading edge FE of the paper sheet P contacts the registration roller  30  as indicated by a dotted line P 1  in  FIG. 10 . A paper jam may occur if the paper sheet P is further moved toward the inkjet head  50  by the feed roller  40  in this skewed state. Even if no paper jam occurs and image printing is performed, some amount W of ink ejected from the inkjet head  50  will land outside the paper sheet P, thereby decreasing printing quality. 
   To align or register the paper sheet P moving with a skew, the registration portion  71  blocks the paper sheet P before the leading edge FE thereof enters the contact nip formed between the registration roller  30  and the idle roller  31 . At this time, the tangential component Ft of the resilient force F applied to the registration lever  70  by the resilient member  90  may be in a range of 70˜120gf. If the tangential component Ft is smaller than a lower limit of the range, the registration lever  70  may be prematurely rotated into the opening position prior to finishing the alignment of the paper sheet P because a force from the paper sheet P can be greater than the tangential component Ft. In the event that the tangential component Ft is greater than an upper limit of the range, damage may be caused to the leading edge of the paper sheet P. The continued rotation of the pickup roller  20  causes the side portion FE 1  of the leading edge FE of the skewed paper sheet P to be pressed against the registration portion  71 . The registration lever  70  is not rotated in this state (non-flexing state) because the pressing force of the paper sheet P exerted on the registration lever  70  is insufficient to overcome the resilient force F. The side portion FE 1  of the leading edge FE of the paper sheet P that has reached a portion of the registration portion  71  is slightly flexed as indicated by reference character “A” (flexing state) in  FIGS. 2 and 7 , while the other side portion of the leading edge FE continues to move forward until it contacts another portion of the registration portion  71 . This makes sure that the paper sheet P turns around the side portion FE 1  of the leading edge FE as indicated by an arrow “R” in  FIG. 10 . Through this process, the paper sheet P is aligned with the registration portion  71  as illustrated by a solid line P 2  in  FIG. 10 . As the pickup roller  20  continues to rotate, the leading edge FE of the paper sheet P pushes the registration lever  70  into the opening position as shown in  FIG. 8 . The paper sheet P is then moved by the registration roller  30  and the idle roller  31 , and thus the paper sheet P is moved past the registration portion  71  and contacts the guide portion  72 . According to a width of the paper sheet P, a plurality of registration levers  70  and registration parts  71  may be used. At least two registration parts  71  are needed to align the paper sheet P. A relatively high contact noise is generated if the paper sheet P continuously contacts the registration portion  71  while moving. According to the registration device of the present embodiment, the contact noise of the paper sheet P can be reduced because, at the termination of the alignment process, the paper sheet P does not contact the registration portion  71  and is fed along the guide portion  72 . A smaller number of the guide portions  72  than that of the registration portions  71  may be used. The contact noise can be further reduced by making the distal end of the guide portion  72  into a round shape. The paper sheet P is guided by the guide portion  72  and enters between the feed roller  40  and the driven roller  41 . The feed roller  40  feeds the paper sheet P at a predetermined printing speed and the inkjet head  50  ejects ink on the paper sheet P. When the trailing edge of the paper sheet P has moved past the guide portion  72 , the registration lever  70  is returned back to the initial alignment position by the resilient force F of the resilient member  90 , as illustrated in  FIG. 7 . 
   As set forth in the foregoing, according to the registration device and the image forming apparatus using the same, the registration roller  30  is rotated only in a paper feeding or forward direction without having to rotate in forward and reverse directions to perform a conventional registration process. Thus, the structure of a power coupling mechanism (not shown) that delivers rotational power from the drive motor  60  to the registration roller  30  may be simplified. Furthermore, the possibility of damaging the leading edge FE of the paper sheet P is reduced unlike the case of a conventional device in which a registration roller has to be rotated in reverse. Thus, the image forming apparatus can be operated at an increased speed and can perform the paper registration process with ease even when the paper sheet P is fed at a higher rate of speed. 
   Although in the foregoing embodiment the drive roller  30  is employed as a registration roller, this should not limit the scope of the present general inventive concept. Alternatively, the feed roller  40  may be used as the registration roller, in which case the registration lever  70  has to be rotatably attached to the feed roller  40 . 
   As apparent from the foregoing, the registration device and the image forming apparatus having the same in accordance with the present general inventive concept have the following advantages. 
   First of all, the structure of a power coupling device to drive a registration roller is simplified because there is no need to rotate the registration roller in forward and reverse directions to perform the registration process. 
   Second, since no change in the direction of rotation of a registration roller occurs throughout the entire paper feeding processes, including an alignment process, it is possible to reduce the possibility of damaging the leading edge of a paper sheet and increase the operating speed of the image forming apparatus, thereby ensuring that a paper registration process is performed with ease even when the paper sheet is fed at a higher rate of speed. 
   Third, noise is reduced by using a paper guide part. 
   Although a few embodiments of the present general inventive concept have been shown and described, it will be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the general inventive concept, the scope of which is defined in the appended claims and their equivalents.