Patent Publication Number: US-2004046309-A1

Title: Paper pick-up device of image forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001] This application claims the benefit of Korean Application No. 2002-5225, filed Aug. 31, 2002 and Korean Application No. 2003-35170 filed May 31, 2003, in the Korean Intellectual Property Office, the disclosures of which are incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002] 1. Field of the Invention  
       [0003] The present invention relates to a device to pick up and transfer paper stacked on a paper feeding cassette of an image forming apparatus such as a printer, a photocopier, and the like, and more particularly, to a paper pick-up device to pick up paper, by changing a position of a pick-up roller according to type and characteristic of the paper.  
       [0004] 2. Description of the Related Art  
       [0005] Generally, an image forming apparatus such as a laser printer or a photocopier has a paper feeding cassette which is removably disposed in a body of the image forming apparatus, to stack therein a plurality of sheets of paper, and a paper pick-up device to consecutively pick up the sheets of paper from a paper stack of the paper feeding cassette and transferring the paper sheets to an image forming engine unit.  
       [0006] As shown in FIG. 1, a paper pick-up device of a conventional image forming apparatus includes a paper feeding cassette  3 , which stacks therein a plurality of sheets of paper  1  and has a friction resistance plate  2  inclined by a predetermined angle to a contact with leading ends of the paper sheets  1 , and a pick-up roller  5  rotatably supported by a free end of a pick-up bracket  4  so as to pick up and transfer the paper sheets  1 . Inside the pick-up bracket  4  is disposed a gear train  6  to transmit a driving force from a driving source (not shown) to the pick-up roller  5 .  
       [0007] In such a paper pick-up device for the general image forming apparatus, as the paper feeding cassette  3  is mounted in the body of the image forming apparatus with the paper sheets  1  stacked therein, the pick-up roller  5  disposed above the paper feeding cassette  3  comes into contact with a topmost one of the paper sheets  1  stacked in the paper feeding cassette  3  as shown in FIG. 1. When the driving source is driven by a controller (not shown) during a printing and the driving force of the driving source is transmitted to the pick-up roller  5  through the gear train  6 , the pick-up roller  5  is rotated and thus there occurs a friction between the pickup roller and the paper sheet, thereby picking up the topmost sheet. The paper sheets are picked up one by one due to the presence of the friction resistance plate  2 .  
       [0008] However, in the paper pick-up device for the general image forming apparatus with the above-described construction, the pick-up roller  5  comes into contact with the paper sheet  1  at a fixed distance X from the friction resistance plate  2  regardless of paper characteristics such as thickness, surface roughness, and strength. Therefore, in case of printing thin paper which is usually weak in strength, there occurs a multiple-transferring in which plural paper sheets are picked up at one time. Whereas, in a case of using thick paper which is usually great in strength, in a case of using thin paper a paper jam caused by picking up an incorrect number of sheets occurs.  
       [0009] Also, in order to pick up the thick paper without a paper jam, a torque of a driving motor has to continuously increase, thereby causing the problems of power consumption and increased noise.  
       SUMMARY OF THE INVENTION  
       [0010] The present invention has been developed in order to solve the above problems in the related art. Accordingly, an aspect of the present invention provides a paper pick-up device of an image forming apparatus, capable of picking up paper, by changing a picking-up position according to paper characteristics set by a printing command, such as thickness, strength, and the like, thereby providing stable paper pick up with respect to every type of paper.  
       [0011] Another aspect of the present invention provides a paper pick-up device of an image forming apparatus, capable of constantly controlling a pick-up force by properly changing a pickup position of a pick-up roller according to thickness and/or strength of paper, thereby reducing power consumption and noise.  
       [0012] The above and/or other aspects are achieved by providing a paper pick-up device of an image forming apparatus, comprising a paper feeding cassette of a plurality of sheets of paper, the paper feeding cassette having a friction resistance plate inclined by a predetermined angle to come into contact with a leading end of the paper sheet, the friction resistance plate to separate the paper sheets one by one, a pick-up roller to rotate in contact with a topmost paper of the paper feeding cassette, and to convey the topmost paper toward the friction resistance plate, a pick-up bracket to rotationally support the pick-up roller, and having a gear train to transmit a rotational driving force to the pick-up roller, and pick-up position varying unit to move the pick-up roller to one position among at least two positions which are pre-set in accordance with the paper characteristics.  
       [0013] The two pick-up positions comprise a first pick-up position where a distance between the friction resistance plate and the pick-up roller is set to L1 to allow the pick-up roller to pickup a paper of strength, and a second pick-up position where the distance is set to L2 shorter than L1 for allowing the pick-up roller to pick-up a paper of low strength.  
       [0014] The pick-up position varying unit comprises a rotary member connected to the pick-up bracket by a shaft to rotate about the shaft, the rotary member having a pair of the pick-up rollers rotatably disposed on an end thereof, a driving unit to rotationally drive the rotary member to move the pick-up roller between the first and the second pick-up positions, and a control unit to detect the paper characteristics and control the driving unit based on the detected paper characteristics.  
       [0015] The driving unit comprises a pair of first link members each having first ends linked with both sides of the rotary member, a pair of second link members each having first ends linked with the second ends of each first link member, which are opposite the first ends of the first link members, by a pin, a shaft fixed to second ends of the second link members, which are opposite the first ends of the second link members, a third link member having a first end fixed to the shaft between the second ends of the second link members, and a driving source connected to the second end of the third link member, which is opposite the first end of the third link member, to link movements of the first, the second and the third link members.  
       [0016] In an embodiment of the invention, the pairs of first link members and second link members may be replaced by a single first link member and a single second link member, respectively.  
       [0017] In an embodiment of the invention, the driving source is a solenoid.  
       [0018] According to another aspect of the present invention, a paper pick-up device of an image forming apparatus, comprises a paper feeding cassette of a plurality of sheets of paper, the paper feeding cassette having a friction resistance plate inclined by a predetermined angle to come into contact with a leading end of the paper sheet, the friction resistance plate to separate the paper sheets one by one, a pick-up roller to rotate in contact with a topmost paper of the paper feeding cassette, and conveying the topmost paper toward the friction resistance plate, a pick-up frame disposed in the paper feeding cassette, a pick-up bracket movably disposed in the pick-up frame, one end of which the pick-up roller is rotatably disposed, and inside of which a gear train is provided to transmit a rotational driving force to the pick-up roller, and a pick-up position varying unit to move the pick-up roller to one among at least two positions which are pre-set in accordance with paper characteristics.  
       [0019] The two pick-up positions comprise a first pick-up position where a distance between the friction resistance plate and the pick-up roller is set to L1 to allow the pick-up roller to pickup a paper of high strength, and a second pick-up position where the distance is set to L2 shorter than L1 to allow the pick-up roller to pick-up a paper of low strength.  
       [0020] The pick-up position varying unit comprises a conveyance frame reciprocally disposed in the pick-up frame, the conveyance frame supporting a fixed end of the pick-up bracket, a conveyance unit to linearly reciprocate the conveyance frame, and a control unit to detect the paper characteristics and control the conveyance unit based on the detected paper characteristics.  
       [0021] A pair of guide bars outwardly protrude from both sides of the conveyance frame, and a pair of guide grooves are defined in the pick-up frame to receive the pair of guide bars, thereby guiding a movement of the conveyance frame in the pick-up frame.  
       [0022] Also, the conveyance means comprises a rack member provided in the conveyance frame, a pinion engaged with the rack member; and a driving source disposed in the pick-up frame for rotationally driving the pinion.  
       [0023] Additional and/or other aspects and advantages 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.  
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0024] These and/or other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the preferred embodiments taken in conjunction with the accompanying drawings in which:  
     [0025]FIG. 1 is a schematic side section view showing a paper pick-up device of a conventional image forming apparatus;  
     [0026]FIGS. 2 and 3 are schematic perspective views showing a paper pick-up device of an image forming apparatus according to an embodiment of the present invention;  
     [0027]FIG. 4 is a block diagram showing the paper pick-up device according to the present invention;  
     [0028]FIG. 5 is a side section view showing the paper pick-up device to describe the operation thereof according to the preferred embodiment of the present invention;  
     [0029]FIG. 6 is a perspective view showing an image forming apparatus employing a paper pick-up device according to another embodiment of the present invention;  
     [0030]FIG. 7 is a perspective view showing the paper pick-up device of the image forming apparatus according to another embodiment of the present invention;  
     [0031]FIG. 8 is a side section view showing the paper pick-up device to describe the operation thereof according to another embodiment of the present invention; and  
     [0032]FIG. 9 is a perspective view showing the pick-up bracket of the paper pick-up device for the image forming apparatus according to another embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0033] Reference will now be made in detail to the present preferred embodiments of the present invention, 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 invention by referring to the figures.  
     [0034] As shown in FIGS.  2  to  5 , a paper pick-up device of an image forming apparatus according to an embodiment of the present invention includes a paper feeding cassette  10 , a pick-up roller  20 , a pick-up bracket  30 , and pick-up position varying unit  40 .  
     [0035] The paper feeding cassette  10  has a space defined therein in which a plurality of sheets of paper are stacked, and has a friction resistance plate  11  inclined by a predetermined angle to come into contact with leading ends of the paper sheets. The friction resistance plate  11  causes the paper sheets conveyed by the pick-up roller  20  to be separated sheet by sheet.  
     [0036] The pick-up roller  20  rotates in contact with the topmost paper of the paper feeding cassette  10 , thereby transferring the topmost sheet toward the friction resistance plate  11 .  
     [0037] The pick-up bracket  30  rotatably supports the pick-up roller  20  and includes a gear train  31  to transmit a rotational driving force from a pick-up driving source (not shown) to the pick-up roller  20 .  
     [0038] The pick-up position varying unit  40  moves the pick-up roller  20  to one position among at least two pick-up positions which are pre-set in correspondence with the characteristics of the paper sheets stacked in the paper feeding cassette  10 , such as thickness and strength, thereby changing a pick-up position of the pick-up roller  20  suitably to the characteristics of the paper.  
     [0039]FIG. 5 shows the two pick-up positions, i.e., a first pick-up position where a distance between the friction resistance plate  11  and the pick-up roller  20  is set to L1 to allow the pick-up roller  20  to pick up thick paper of high strength, and a second pick-up position where the distance is set to L2 shorter than L1 to allow the pick-up roller  20  to pick up thin paper of low strength. Although this embodiment shows only the first and the second pick-up positions between which the pick-up roller  20  moves variably according to the characteristics such as the thickness and the strength of the paper, there is no limitation, and more pick-up positions can be designated.  
     [0040] The pick-up position varying unit  40  according to the present invention includes a rotary member  50 , a driving unit  60 , and a control unit  70 .  
     [0041] The rotary member  50  is disposed at the pick-up bracket  30  to rotate about an axis  51  to a predetermined angle. A pickup roller shift  52  is included through the rotary member  50 . Two pick-up rollers  20  are mounted on both sides of the pick-up roller shaft  52 .  
     [0042] The driving unit  60  rotationally drives the rotary member  50  so the pick-up rollers  20  move between the first and the second pick-up positions. The driving unit  60  includes a pair of first link members  61 ,  61  A each having first ends linked with both sides of the rotary member  50  and extended backward from the rotary member  50 , a pair of second link members  63 ,  63 A each having first ends linked with second ends of each of the first link members  61 ,  61  A, which are opposite the first ends of the first link members, by a pin  62 ,  62 A, a third link member  65  having a first end fixed to a shaft  64  which is fixed to the second ends of the second link members  63 ,  63 A, which are opposite the first ends of the second link members, and a driving source  66  connected to the other end of the third link member  65 , to drive the link movements of the link members  61 ,  61  A,  63 ,  63 A, and  65 .  
     [0043] In another embodiment, a single first link member and a single second link member replace the pairs of first and second link members, respectively.  
     [0044] In the above noted embodiments, the driving source  66  is depicted as a solenoid (FIG. 2). However, this should not be considered a limiting structure. For example, the driving source  66  may be an electromagnet. A frame (not shown) supports the shaft  64 .  
     [0045] As shown in FIG. 4, the control unit  70  detects characteristics of the paper sheets stacked in the paper feeding cassette  10  and controls the driving source  66  based on the detected information. According to an embodiment of the present invention, the paper pick-up device of the image forming apparatus includes a sensor  80  to detect the characteristics, such as thickness and strength, of the paper sheets stacked in the paper feeding cassette  10 . The control unit  70  receives a signal from the sensor  80 , determines the characteristics of the paper sheets based on the received signal, and thereby controls the driving of the driving source  66  according to the determined paper characteristics.  
     [0046] Meanwhile, as shown in FIG. 5 the gear train  31  provided in the pick-up bracket  30  is comprised of a plurality of gears, which are interposed between a rotational driving shaft  33 , on the one hand, and the pick-up roller shaft  52  disposed through the rotary member  50  on the other hand. The rotational driving shaft  33  penetrates through the pick-up bracket  30  at an opposite side to the position of the rotary member  50 . Also, a pick-up gear  32  is mounted on the rotational driving shaft  33 . Accordingly, a driving force generated at a pick-up driving source (not shown) is transmitted to the rotational driving shaft  33  through the pick-up gear  32  and then to the pick-up roller shaft  52  through the gear train  31 , to thereby rotate the pick-up roller  20 .  
     [0047] Referring to FIG. 4, when a printing command is input by a user, the paper pick-up device of the image forming apparatus, according to an embodiment of the present invention, detects characteristics of the paper sheets stacked in the paper feeding cassette  10  by the sensor  80 , and transmits the detected paper characteristic information to the control unit  70 . The control unit  70  determines a pick-up position of the pick-up roller  20  based on the detected paper characteristic information by referring to pre-stored information and the detected paper characteristic information. Meanwhile, where no sensor  80  is provided in the image forming apparatus, the image forming apparatus may be designed such that a user himself/herself sets a paper type on a printer driver as he/she inputs a printing command. The paper characteristic information is transmitted to the control unit  70  and the control unit  70  accordingly, determines a pick-up position of the pick-up roller  20 .  
     [0048] Determining operation of the pick-up position of the pick-up roller  20  according to the paper characteristic will be described below in detail.  
     [0049] In case of general paper, which is usually weak in strength, as shown in FIGS. 2 and 5, the solenoid acting as the driving source  66  is driven in an arrowed direction as shown in FIG. 2 by the control of the control unit  70 . By the driving of the solenoid, the third link member  65  rotates about the shaft  64  in a counterclockwise direction, and the second link member  63 ,  63 A rotates about the shaft  64  in a counterclockwise direction in association with the third link member  65 . Accordingly, the first link member  61 ,  61  A connected to the second link member  63 ,  63 A advance in a direction opposite the arrow in FIG. 2. Due to the movement of the first link member  61 ,  61  A, the rotary member  50  rotates about the axis  51  in a counterclockwise direction so that the pick-up roller  20  supported by the rotary member  50  is positioned at the second pick-up position which is distanced from the friction resistance plate  11  as much as L2. As described above, when the pick-up roller  20  is positioned at the second pick-up position to thus narrow a gap between the friction resistance plate  11  and the pick-up roller  20 , strength of the paper per a length of the paper is increased. Thus, a resistance force at the friction resistance plate  11  becomes as much as is obtained when the thick paper is picked up. Accordingly, the paper sheets are picked up without multiple transferring.  
     [0050] Meanwhile, in case that the paper is of high strength, as shown in FIGS. 3 and 5, the solenoid acting as the driving source  66  is driven in an arrowed direction as shown in FIG. 3. Then, the third link member  65  rotates about the shaft  64  in a clockwise direction, and the second link member  63 ,  63 A rotates in association with the third link member  65  about the shaft  64  in a clockwise direction. Accordingly, the first link member  61 ,  61  A connected to the second link member  63 ,  63 A retreats. Due to the movements of the first link member  61 ,  61  A, the rotary member  50  rotates about the axis  51  in a clockwise direction so that the pick-up roller  20  supported by the rotary member  50  is positioned at the first pick-up position distanced from the friction resistance plate  11  as much as L1. As described above, when the pick-up roller  20  is positioned at the first pick-up position to thus broaden a gap between the friction resistance plate  11  and the pick-up roller  20 , the strength of the paper per a length of the paper is decreased. Thus, a resistance force at the friction resistance plate  11  becomes as much as is obtained when thin paper is picked-up. That is, with the same degree of the pick-up driving force, the thick paper can be picked up.  
     [0051] When the pick-up position of the pick-up roller  20  is properly determined according the thickness and the strength of the paper, a driving force is transmitted from the pickup driving source (not shown) to the pick-up roller  20  via the pick-up gear  32 , a rotational driving shaft  33 , and the gear train  31  to thus rotate the pick-up roller  20 . Then, due to the friction occurring between the rotating pick-up roller and the paper, the topmost sheet is picked up and is conveyed to the friction resistance plate  11  and the sheet is separated from the next paper by the friction resistance plate  11 .  
     [0052] In another embodiment of the invention, the second and third link members are combined to form a single feature (not shown) that pivots around a central point when the driving source  66  is driven.  
     [0053] FIGS.  6  to  9  are views showing a paper pick-up device of an image forming apparatus according to another preferred embodiment of the present invention. Referring to the drawings, a paper pick-up device of an image forming apparatus according to another embodiment of the present invention includes a paper feeding cassette  100 , a pick-up roller  200 , a pick-up frame  300 , a pick-up bracket  400 , and a pick-up position varying unit  500 .  
     [0054] The paper feeding cassette  100  has a space defined therein to stack a plurality of sheets of paper  1  and a friction resistance plate  110  inclined by a predetermined angle to contact with the leading ends of the paper sheets  1 . The friction resistance plate  110  separates the paper conveyed by the pick-up roller  200  sheet by sheet.  
     [0055] The paper feeding cassette  100  is removably mounted in a cassette mounting portion  610  provided in a body  600  of the image forming apparatus.  
     [0056] The pick-up roller  200  rotates in contact with a topmost sheet of the paper sheets  1  stacked on the paper feeding cassette  100  and conveys the topmost sheet toward the friction resistance plate  110 .  
     [0057] The pick-up roller  200  is rotatably disposed at an end of the pick-up bracket  400 . The pick-up bracket  400  is provided with a gear train  420 , as shown in FIG. 8, to transmit a driving force of a first driving motor  410  to the pick-up roller  200 .  
     [0058] The pick-up bracket  400  is movably disposed at the pick-up frame  300 .  
     [0059] The pick-up position varying unit  500  moves the pick-up bracket  400  in order for the pick-up roller  200  to be positioned at one position among at least two pick-up positions which are pre-set in correspondence with the characteristics of the paper.  
     [0060] The two pick-up positions include a first pick-up position where a distance between the friction resistance plate  110  and the pick-up roller  200  is set to L1 to allow the pick-up roller  200  to pick up the thick paper of high strength, and a second pick-up position where the distance is set to L2 shorter than the L1 to allow the pick-up roller  200  to pick up the thin paper of low strength.  
     [0061] The pick-up position varying unit  500  includes a conveyance frame  510 , conveyance unit  520 , and a control unit  70  (see FIG. 4).  
     [0062] The conveyance frame  510  supports a fixed end of the pick-up bracket  400  and is reciprocally disposed at the pick-up frame  300 .  
     [0063] A pair of guide bars  511 ,  512  outwardly protrude from both sides of the conveyance frame  510 , and a pair of guide grooves  311 ,  312  are defined in the pick-up frame  300  to receive the pair of guide bars  511 ,  512 , thereby guiding the movement of the conveyance frame  510  in the pick-up frame  300 . The first guide bar  511  is connected to both of the fixed ends of the pickup bracket  400  and the conveyance frame  510 . Accordingly, the pick-up bracket  400  reciprocates in response to the position of the first guide bar  511  to a predetermined angle and thus the pick-up roller  200  disposed at one end of the pick-up bracket  400  comes into contact with the topmost sheet stacked on the paper feeding cassette  100 .  
     [0064] The conveyance unit  520  allows the conveyance frame  510  to reciprocate in the pickup frame  300 . The conveyance unit includes a rack member  521  disposed on the conveyance frame  510 , a pinion  522  engaged with the rack member  521 , and a second driving motor  523  disposed in the pick-up frame  300  to rotationally drive the pinion  522 .  
     [0065] The control unit  70  performs the same operation as that of the above-described embodiment. That is, the control unit  70  detects characteristics of the paper and controls the driving of the second driving motor  523  of the conveyance unit  520  based on the detected paper characteristic information. As in the above-described embodiment, the paper pick-up device of the image forming apparatus includes a sensor  80  to detect characteristics of the paper such as thickness and strength according to a paper type, so that the control unit  70  receives a signal from the sensor  80 , determines the characteristic of the paper according to the paper type, and accordingly controls the second driving motor  523  based on the determined characteristics.  
     [0066] Hereinafter, operations of the paper pick-up device for the image forming apparatus according to another embodiment of the present invention will be described with reference to FIGS. 4, 8, and  9 .  
     [0067] The basic operations are performed in the same way as in the above-described embodiment.  
     [0068] That is, when a printing command is input, the sensor  80  detects the characteristic information of the paper stacked in the paper feeding cassette  100  and transmits the information to the control unit  70 . The control unit  70  determines a pick-up position of the pick-up roller  200  based on the detected paper characteristic information, and then controls the second driving motor  523  so the pick-up roller  200  is moved to the determined pick-up position.  
     [0069] That is, in case of thin paper of low strength, the second driving motor  523  is rotationally driven in a clockwise direction in order for the pick-up roller  200  to pick-up the paper at the second pick-up position L2. Then, the conveyance frame  510  is moved to the left-hand side of the drawings by the pinion  522  and the rack member  521  and the pick-up bracket  400  connected to the conveyance frame  510  is accordingly moved, so that the pick-up roller  200  is positioned at the second pick-up position. At this position, a driving force of the first driving motor  410  is transmitted to the pick-up roller  200  through the gear train  420  to rotate the pick-up roller  200 . Due to the rotation of the pick-up roller  200 , there occurs a friction between the pick-up roller  200  and the paper, and due to the friction, the topmost paper sheet alone is picked up and conveyed toward the friction resistance plate  110 . As described above, when the pick-up roller  200  is positioned at the second pick-up position to thus narrow a distance between the friction resistance plate  110  and the pick-up roller  200 , the strength per a length of the paper becomes high. Accordingly, since there occurs a resistance force at the friction resistance plate  110  as that occurring of the resistance force when thick paper is picked-up, the paper is picked-up without multiple transferring.  
     [0070] Meanwhile, in case of thick paper, the second driving motor  523  is rotationally driven in a counterclockwise direction so the pick-up roller  200  picks-up the paper at the first pick-up position L1. Then, the pick-up bracket  400  is moved to the right-hand side of the drawings, which is opposite to the thin paper case, so that the pick-up roller  200  is changed from the second pick-up position L2 to the first pick-up position L1. As described above, when the pickup roller  200  is positioned at the first pick-up position to thus broaden the distance between the friction resistance plate  110  and the pick-up roller, the strength per the length of the paper becomes low. Thus, since there occurs a resistance force at the friction resistance plate  110  as of the resistance force when thin paper is picked-up, the thick paper is picked up with the same level of the pick-up force that picks up the thin paper.  
     [0071] According to the present invention as described above, the pick-up device of the image forming apparatus picks up the paper sheets with a variably changing pick-up position in accordance with the characteristic, such as thickness and surface roughness, of the paper, thereby preventing paper slip, multiple transferring, and paper jam during the conveyance of the paper. Accordingly, there is an advantage of having precise paper picking-up and conveying operations.  
     [0072] Also, since a pick-up force is variable controlled by changing the pick-up position according to the characteristic of the paper, power consumption and noise can be reduced.  
     [0073] Although a few 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 spirit of the invention, the scope of which is defined in the claims and their equivalents.