Patent Publication Number: US-8126386-B2

Title: Sheet feeder, image forming apparatus and sheet feeder control method

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2006-205438 filed on Jul. 27, 2006, the entire contents of which are incorporated herein by reference 
     BACKGROUND 
     1. Field of the Invention 
     The present invention relates to a sheet feeder, an image forming apparatus, and a sheet feeder control method. 
     2. Description of the Related Art 
     Generally, an image forming apparatus such as a copying machine is equipped with roller pairs which are called as aligning rollers. These aligning rollers are provided at a position of the upstream side in the conveying direction of an image forming apparatus (an unit to transfer a toner image on sheets conveyed using a photosensitive drum, etc.) and functions to correct the oblique ends of sheets conveyed from the sheet feeder. 
     The aligning rollers are rotated to properly correct sheets conveyed obliquely by bending sheets fed from the sheet feeder at the nip position by putting them to the nip position of the aligning rollers which are kept stopped to rotate and to send out the sheets at an optimum timing to transfer a toner image on the sheets at the image forming unit as described above. 
     The sheet feeder is provided at the upper-stream side in the conveying direction of the aligning rollers; however, feed rollers may be provided at the upper-stream side of the aligning rollers in the relation of the length of the conveying path from the sheet feeder to the aligning rollers. These feed rollers are to convey sheets supplied from the sheet feeder to the aligning rollers; but the aligning rollers are first in the rotation stopped state as described above, and for the reason that a prescribed flexion is formed on sheets, the feed rollers are stopped to rotate at a timing when the flexion formed on sheets by the aligning rollers reaches a specified amount. 
     This feed roller have no exclusive driving source and use the driving source jointly with other rollers (for example, sheet feed rollers, aligning rollers, etc.) in many cases. Because of this, as disclosed in the Japanese Patent Application Publication No. 2003-155138, the driving power of this feed roller is transmitted from the commonly using driving source via gears, etc. and further, the feed rollers are rotated or stopped using a clutch, etc. In other words, the rotation and stopping of the feed rollers are controlled by the ON/OFF of this clutch. 
     However, as the rotation/stopping of the feed roller is made by this clutch, when the driving power is transmitted/cut off from the driving source by the clutch, a sudden torque is applied to the driving shaft and vibration is generated. This vibration adversely affects especially the optical unit, the transfer belt, the photosensitive drum, etc. in the image forming apparatus, and gives a jitter to an image. In other words, this vibration is transmitted to a mirror of the optical system and laser light pitch is changed and an electrostatic latent image formed on the photosensitive drum may become uneven. 
     SUMMARY 
     It is an object of the present invention to provide a sheet feeder generating less vibration when a clutch is engaged, an image forming apparatus and a sheet feeder control method. 
     According to the embodiment of the present invention, there is provided a sheet feeder comprising a sheet feed roller provided at a position of the upstream side of an aligning roller along the sheet conveying direction; a clutch to transmit and cut off the driving force from a driving source to rotate the feed roller; a rotary shaft connected to the clutch in the rotatable state; a torque limiter provided on the rotary shaft; and an inertial member provided to the rotary shaft via the torque limiter. 
     According to the embodiment of the present invention, there is provided an image forming apparatus, comprising an image carrying body; a developing unit to form a developer image on the image carrying body; a transferring unit to transfer the developer image onto a sheet from the image carrying body; and a sheet feeder to feed the sheet to the transferring unit, wherein the sheet feeder including: a sheet feed roller provided at a position of the upstream side of an aligning roller along the sheet conveying direction; a clutch to transmit and cut off the driving force from a driving source to rotate the feed roller; a rotary shaft connected to the clutch in the freely rotatable state; a torque limiter provided on the rotary shaft; and an inertial member provided to the rotary shaft via the torque limiter. 
     According to the embodiment of the present invention, there is provided a control method of a sheet feeder including a sheet feed roller provided at a position of the upstream side of an aligning roller along the sheet conveying direction, a driving source to rotate the sheet feed roller, a clutch to transmit and cut off the driving force from the diving source, a rotary shaft connected to the clutch and provided in the rotatable state, a torque limiter provided on the rotary shaft, and an inertial member provided to the rotary shaft via the torque limiter, comprising making the first clutch engagement; disengaging the clutch; and making the second clutch engagement. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic cross-sectional view of the image forming apparatus involved in the first embodiment of the present invention; 
         FIG. 2  is a cross-sectional prospective view of the surrounding part of the feed roller involved in the first embodiment of the present invention; 
         FIG. 3  is a cross-sectional view of the surrounding part of the feed roller involved in the first embodiment of the present invention; 
         FIG. 4  is a sectional view of the electromagnetic clutch involved in the first embodiment of the present invention; 
         FIG. 5  is a time chart relative to the vibration of the feed roller at the time when the electromagnetic clutch is engaged in the first embodiment; 
         FIG. 6  is a flowchart showing the sheet feeder control method involved in the second embodiment of the present invention; 
         FIG. 7  is a time chart relative to the vibration of the feed roller when the electromagnetic clutch is engaged in the second embodiment of the present invention; 
         FIG. 8  is a cross-sectional view of the surrounding part of the feed roller in a conventional example; and 
         FIG. 9  is a time chart relative to the vibration of the rotary shaft at the time when the magnetic clutch is engaged in a conventional example. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Hereinafter, the embodiments of the present invention will be described with reference to the attached drawings. 
       FIG. 1  is a schematic diagram of the image forming apparatus in a first embodiment of the present invention. The image forming apparatus comprises a sheet feeder  100  provided at the lower part of a main body  1 , a sheet conveying portion  200  provided at the side and the upper portion of sheet feeder  100 , an image forming unit  300  provided on the upper part of sheet conveying unit  200 , a fixing unit  400  provided at the discharging side from image forming unit  300 , and a image reading unit  500  which comprises optical system members arranged above these image forming unit  300  and fixing unit  400 . 
     Sheet feeder  100  sends out a sheet  115  to the exit side of a sheet cassette  111  (the right side in  FIG. 1 ) by the rotating action of a sheet feed roller  112  from sheet cassette  111  selected from  4  sheet cassettes  111  and separate sheets each other by a separation pad  117  provided at the upper portion of both ends in the width direction of sheet cassette  111 , and feeds sheet  115  at the top position one by one certainly. Further, these  4  sheet cassettes  111  is in the structure that sheet can be freely pulled out for main body  1 . 
     Sheet conveying portion  200  conveys sheet  115  supplied from sheet feeder  100  toward image forming unit  300  by a conveying roller  201 , a sheet feed roller  202  (a conveying roller at the lowest-stream side in conveying rollers and an aligning roller  203 , and further, discharges sheet  115  with the image forming made in fixing unit  400  on a sheet receiving tray  204  by an exit roller  205  from image forming unit. Conveying roller  201 , sheet feed roller  202 , aligning roller  203  and exit roller  205  are composed by a pair of rollers, respectively. In front of aligning roller  203 , an aligning roller sensor  203   a  is arranged so as to turn ON/OFF according to the conveyance of sheet  115 . The ON/OFF signal of aligning sensor  203   a  is sent to a control means that is not shown in  FIG. 1 . 
     Aligning roller  203  is provided at the upper-stream side in the conveying direction of image forming unit  300  and functions to correct the oblique end of sheet  115  conveyed from sheet feeder  100  and convey sheet  115  at an optimum timing to transfer a toner image on sheet  115 . Therefore, aligning roller  203  is driven by power transmitted from the driving source through the gear and the clutch and at the time when sheet  115  is conveyed, aligning roller  203  is stopped to rotate and the end of conveyed sheet  115  is brought to contact the nip portion of aligning roller  203 , forming a bend at the end of sheet and then, sheet  115  is conveyed to image forming unit  300  by rotating aligning roller  203 . 
     As described above, in order to form a proper flexion on sheet  115  by aligning roller  203 , the rotation and stopping of sheet feed roller  202  provided at a position of the upstream side of aligning roller  203  along the sheet conveying direction are important functions. The driving force is transmitted to sheet feed roller  202  from the driving source (not shown) by way of various gears and the clutch, and at the time when sheet  115  is conveyed. Sheet feed roller  202  is rotating (the driving force is transmitted from a driving source when the clutch is turned ON) and is rotating continuously until a specified flexion is formed on the end of the sheet  115 . When the specified flexion is formed on sheet  115  by aligning roller  203  (after a specified time passed from the turn ON of aligning roller  203 ), the sheet feed roller  202  stops to rotate (the driving force from the driving source is shut off when the clutch is turned OFF). The definite structure of sheet feed roller  202  and the clutch will be described later. 
     Image forming unit  300  forms a toner image on sheet  115  and is comprising photosensitive drum  301  as an image carrying body which has photo-conductivity and is rotatably supported, with a charging unit  302 , an exposure unit  303 , a developing unit  304 , a transferring unit  305 , a cleaner  306  and a neutralization unit  307  arranged around photosensitive drum  301  in its rotating direction. 
     Charging unit  302  is provided with a charging wire to which high voltage is applied and a specified potential is given to the surface of photosensitive drum  301  by the corona discharge from this charging wire. Exposure unit  303  irradiates the laser light output from a laser luminous organ based on an image data of a manuscript read by an image reading unit  500  which is described later to photosensitive drum  301  through a polygon mirror and a reflecting mirror. An electrostatic latent image is thus formed on the surface of photosensitive drum  301  by selectively attenuating the potential on its surface. Developing unit  304  develops the electrostatic latent image using a toner and forms a toner image or a developer image on the surface of photosensitive drum  301 . Transferring unit  305  transfers the toner image formed on the surface of photosensitive drum  301  on sheet  115 . In this image forming apparatus, transferring unit  305  is composed of transfer rollers which are separated by a specified distance from photosensitive drum  301 . Cleaner  306  removes toner remained on the surface of photosensitive drum  301  after transferring an image. Neutralization unit  307  removes residual charge on the surface of photosensitive drum  301 . 
     Fixing unit  400  is arranged at the down-stream side of image forming unit  300  in the sheet conveying direction and fixes a toner image transferred on the sheet in image forming unit  300  thereon by clamping and heating the sheet with heating roller  401  and a pressing roller  402  which is pressed against this heating roller  401 . 
     image reading unit  500  irradiates the light from an exposure lamp to a document placed on a contact glass  501  and reads image data of the document by leading the reflecting light to a photoelectric converter that is comprising a CCD line sensor, etc. Further, the exposure lamp and the reflecting mirror form a scanning movement unit and it is possible to read an image on the whole surface of a document by scanning the whole surface of a document placed on contact glass  501  when this scanning movement unit moves a moving area  508  in the left and right directions in  FIG. 1  at a specified speed. 
     Next, the definite construction of sheet feed roller  202  and its surrounding will be explained with reference to  FIG. 2  and  FIG. 3 .  FIG. 2  is a perspective cross-sectional view of the feed roller and its surrounding area in the first embodiment.  FIG. 3  is a cross-sectional view of the feed roller and its surrounding area in the first embodiment of the present invention. 
     Sheet feed roller  202  is driven to rotate by rotary shaft  221  which is extending in the longitudinal direction. Rotary shaft  221  is provided with an electromagnetic clutch  240  which transmits and shut off the driving force. Further, at the position opposite to a clutch gear  241  of electromagnetic clutch  240 , there is a drive gear  262  provided, to which the drive force from the drive source is transmitted. When a clutch gear  241  of electromagnetic clutch  240  meshes with drive gear  262  and the witch of electromagnetic clutch  240  is turned ON, electromagnetic clutch  240  is engaged and the drive force is transmitted to rotary shaft  221 . 
     Further, rotary shaft  221  is provided with a torque limiter  230  and a flywheel  289  is mounted in the freely rotatable state through this torque limiter  230 . Torque limiter  230  has an inner ring  231  and an outer ring  232 . Inner ring  231  is fixed to rotary shaft  221 , while outer ring  232  is fixed to flywheel  280 . These rings are fixed according to known methods such as screwing, press fitting, adhesion, etc. In this embodiment, the screwing is used. 
     Inner ring  231  and outer ring  232  of torque limiter  230  are always connected each other at a specified connecting force of the magnetic force or springs, and a torque limiter in such a structure that when rotary torque more than a certain level is given in the sheet conveying direction, the connecting force is weakened is used. 
     Accordingly, if the driving force is transmitted to rotary shaft  221  at a rotating torque more than a specified value from the driving source, the driving force higher than the upper limit value of torque limiter  230  is not transmitted o flywheel  280 . 
     Next, electromagnetic clutch  240  will be explained with reference to  FIG. 4 .  FIG. 4  is a cross-sectional view of the electromagnetic clutch involved in the first embodiment of the present invention. In electromagnetic clutch  240 , a cylinder portion  242  that is in one unit with clutch gear  241  is freely fitted to a hollow shaft  243  that is fixed to rotary shaft  221 , and an armature  245  is provided in cylinder portion  242  via a blade spring  244 . Further, a rotor  246  and electromagnetic coil  247  are fixed to hollow shaft  243  opposing to armature  245 . When current flows to this electromagnetic coil  247 , armature  245  is pulled to rotor  246  by the magnetic force and the driving force of clutch gear  241  is transmitted to rotary shaft  221 . 
     Thereafter, current flows to magnetic coil  247  and armature  245  is pulled to rotor  246  by the magnetic force and the driving force of clutch gear  241  is kept being transmitted to rotary shaft  247 . This is the state where electromagnetic clutch  24  is ON. Further, when the flow of current to electromagnetic coil  247  is stopped, and armature  245  and rotor  246  which are pulled to each other by the magnetic force is separated and the driving of clutch gear  241  with rotary shaft  221  is shut off. This is the state where electromagnetic clutch  24  is turned OFF. 
     In succession, the vibration produced on rotary shaft  221  when electromagnetic clutch  240  is engaged will be explained with reference to  FIG. 5 .  FIG. 5  is a time chart relative to the vibration of the feed roller when the electromagnetic clutch is engaged in the first embodiment. 
     When clutch  140  is engaged (ON) at a time T 1 , the driving force is transmitted to rotary shaft  221 . Because flywheel  280  that I an inertial member is connected to rotary shaft  221 , rotary shaft  221  does not rotate rapidly but begins to rotate slower than when flywheel  280  is not connected. Further, since this flywheel  280  is connected to rotary shaft  221  via torque limiter  230 , the rapid generation of torque when electromagnetic clutch  240  is engaged can be suppressed. As a result, the vibration generated on rotary shaft  221  at the time T 1  becomes small and the image formation is extremely less influenced. In succession, when electromagnetic clutch  240  is disengaged (OFF) at a time T 2 , no driving force is received and rotary shaft is rotated gently by the inertial force and stops at a time T 3 . 
     A second embodiment of the present invention will be explained with reference to  FIG. 6  and  FIG. 7 .  FIG. 6  is a flowchart showing the sheet feeder control method in the second embodiment of the present invention.  FIG. 7  is a time chart relative to the vibration of the feed roller when the electromagnetic clutch is engaged in the second embodiment of the present invention. In this embodiment, such a method is adopted that electromagnetic clutch  240  is once engaged for transmitting the driving force to rotary shaft  221  when driving sheet feed roller  202  (S 601 ) and then, this electromagnetic clutch  240  is disengaged (S 602 ) and thereafter, electromagnetic clutch  240  is again engaged (S 603 ). 
     At this time, electromagnetic clutch  240  becomes the ON state at Time  1  and Step S 601  that is the first clutch engagement is executed as shown in  FIG. 7 . In succession, electromagnetic clutch  240  becomes the OFF state at Time T 2  and the Step S 602  that is the disengagement of the clutch) is executed. Here, even after electromagnetic clutch  240  is disengaged and no driving force is received, rotary shaft  221  is rotating slowly by the inertial force. 
     Then, Step S 603  that is the second clutch engagement was executed successively at Time T 4 , the torque acts in the direction to support the rotation of rotary shaft  221  by the inertial force of flywheel continuously rotating gently when the clutch is engaged. Therefore, the shock given to rotary shaft at the time of engagement is made weak and becomes less than the shock given to stopped rotary shaft  221 . 
     Further, when the number of revolutions of rotary shaft  221  is adequate, it is also possible to provide a supplementary effect when applying the driving force to rotary shaft  221  when engaging electromagnetic clutch  240 . Therefore, in a sheet feeder in such structure as that in this embodiment, a good image forming hardly generating the vibration and less jitter is executed. 
     Regarding a value of rotary load to a feed roller by torque limiter  230 , it is possible to select a value appropriately by changing a size of torque limiter  230  by taking a rotary torque values from the driving source. Further, because a time of stopping the rotary shaft from disengaging the clutch by the inertial moment of flywheel  280  and drop in number of revolutions can be calculated, it is possible to provide a sheet feeder of less vibration at the time of engaging the clutch by properly designing torque limiter  230  and flywheel  280 . 
     In the embodiments described above, a copying machine is explained as an example of an image forming apparatus. However, the present invention is also applicable to facsimiles, printers, etc. 
     In succession, the vibration that is generated on rotary shaft when the electromagnetic clutch is engaged in a conventional example will be explained with reference to  FIG. 8  and  FIG. 9 .  FIG. 8  is a cross-sectional diagram of a feed roller and its surrounding parts in a conventional example.  FIG. 9  is a time chart relative to the vibration of the rotary shaft when the electromagnetic clutch is engaged in a conventional example. In a conventional example, there is no flywheel  280  provided via torque limiter  230 . When electromagnetic clutch  240  is engaged (ON) at Time T 1  for a feed roller in this structure, rotary shaft  221  begins to rotate rapidly by the driving force because flywheel  280  is not connected and the inertia moment is small. By this rapid revolution, the vibration is generated on rotary shaft  221 . When electromagnetic clutch  240  is disengaged (OFF) at Time T 2 , sheet feed roller  202  losses the driving force and stops to rotate at Time T 3 .