Patent Publication Number: US-7708266-B2

Title: Sheet feeder and image forming apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   The present application claims priority from Japanese Patent Application No. 2006-323918, which was filed on Nov. 30, 2006, the disclosure of which is herein incorporated by reference in its entirety. 
   TECHNICAL FIELD 
   The present invention relates to a sheet feeder for feeding sheets (including the concept of documents, etc.) and an image forming apparatus in various types of image processing apparatuses such as a printer, a copier, a document reading apparatus, etc. 
   BACKGROUND 
   Conventionally, as a so-called twin-roller type sheet feeder in which a feed roller and a separation roller are integrally composed, there is such a type as shown in, for example, Patent Document 1. As shown in  FIG. 15 , the type has a spring clutch unit  107  based on a twisted coil spring  113  which is twined on the input hub  111  and the output hub  112 , and the spring clutch unit  107  is fixed to the rotating shaft  104  of a feed roller  101  by setting the output hub  111  by means of a screw  114 . The type has a delivery roller  102  which is caused to go up and down by swinging the frame  106  with the delivery roller  102  retained by the output hub  112 . 
   [Patent Document 1] Japanese Published Unexamined Patent Application No. H6-72581 
   SUMMARY 
   It is necessary that the delivery roller  102  and the feed roller  101  be replaced since these rollers are worn through long period of use. However, in this case, since the spring clutch unit  107  is fixed to the rotating shaft  104  of the feed roller  101 , it is impossible that the delivery roller  102  and the feed roller  101  are smoothly replaced. 
   According to an aspect of the invention, there is provided a sheet feeder comprising: a feed roller which feeds sheet by rotating in contact with the sheet; a separation roller which is disposed at a downstream side of a sheet feeding direction; a supporting member which supports the feed roller and the separation roller, the supporting member is supported so as to be swingable around the rotation axis of the separation roller; a drive source which drives the supporting member so as to swing; an arm pivot which is disposed between the drive source and the supporting member; a first arm which is disposed at a side of the drive source; and a second arm which is disposed at a side of the supporting member, the second arm is able to be separated from the first arm; wherein the first arm and the second arm are integrally swung around the arm pivot by the drive source, thereby the supporting member swinging. 
   According to the first aspect of the invention, since the arm is composed so that it can be separated from the first arm and the second arm, it is possible to replace the feed roller and the separation roller without removing the first arm from the arm pivot. Therefore, replacement of the rollers can be easily carried out, and the time required for the replacement can be shortened. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Illustrative aspects of the invention will be described in detail with reference to the following figures wherein: 
       FIG. 1  is a side sectional view showing the major parts of a laser printer according to first illustrative aspect of the present invention; 
       FIG. 2  is a side sectional view showing the major parts of a laser printer with the MP tray opened; 
       FIG. 3  is a perspective view showing a vertical drive mechanism of a feed roller (in a state where the feed roller is located at its elevated position); 
       FIG. 4  is a perspective view showing a vertical drive mechanism of a feed roller (in a state where the feed roller is located at its descended position); 
       FIG. 5  is a left side view of the vertical drive mechanism in a state where the feed roller is located at its elevated position; 
       FIG. 6  a left side view of the vertical drive mechanism in a state where the feed roller is located at its descended position; 
       FIG. 7  is a perspective view of the major parts of an arm, etc., according to second illustrative aspect of the present invention; 
       FIG. 8  is a disassembled perspective view showing a state where the first arm and the second arm are made integral with each other; 
       FIG. 9  is a front elevational view of a laser printer according to second illustrative aspect of the present invention; 
       FIG. 10  is an enlarged sectional view taken along the line X-X in  FIG. 9 ; 
       FIG. 11  is a view showing the MP sheet feeding mechanism observed from upside with the sheet feeding cover removed; 
       FIG. 12  is a view showing the interior of a printer, which is observed from the upside with the front cover opened; 
       FIG. 13  is a view showing a state where the arm covering member is removed in  FIG. 12 ; 
       FIG. 14  is a perspective view of the major parts of an arm, etc., according to exemplary illustrative aspect of the present invention; and 
       FIG. 15  is a perspective view showing a vertical drive mechanism of a related art feed roller. 
   

   DETAILED DESCRIPTION OF THE PREFERRED ILLUSTRATIVE ASPECTS 
   First Illustrative Aspect 
   1. Entire Structure 
   A description is given of first illustrative aspect of the present invention with reference to  FIGS. 1 through 6 .  FIG. 1  is a side sectional view showing the major parts of a laser printer  1  as an image forming apparatus according to the present invention. The laser printer  1  comprises an image-forming portion  5  to form images on a sheet  3  being a fed recording sheet of paper in the main body casing  2 . 
   (1) Main Body Casing 
   The main body casing  2  comprises a front cover  7 . Also, in the following description, it is assumed that, in the laser printer  1  and a process cartridge  18  (including a development cartridge  27  described later), the side at which the front cover  7  is mounted is the “front side,” and the side opposite thereto is the “rear side.” In addition, it is assumed that the right side when being observed from the front side of the laser  1  (that is, the paper far side) is the “right side,” and the side opposite thereto (that is, the paper near side) is the “left side.” 
   (2) Image Forming Portion 
   The image-forming portion  5  comprises a scanner portion  19 , a process cartridge  18 , and a fixing portion  20 , etc. 
   (a) Scanner Portion 
   The scanner portion  19  is provided on the upper part in the main body casing  2 . A laser beam emitted from a laser light source and based on image data is irradiated on the surface of a photosensitive drum  28  described later, of the process cartridge  18  through high-speed scanning as shown by broken lines in  FIG. 1 . 
   (b) Process Cartridge 
   The process cartridge  18  is mounted downward of the scanner portion  19  detachably with respect to the main body casing  2 . The process cartridge  18  comprises a drum cartridge  26  and a development cartridge  27  detachably mounted with respect to the drum cartridge  26 . 
   The drum cartridge  26  has the development cartridge  27  at its front side and comprises the photosensitive drum  28 , a scorotron type electrifier  29 , and a transfer roller  30  at its rear side. 
   The development cartridge  27  comprises a toner accommodation chamber  32  in which toner is accommodated, a toner feed roller  33 , a development roller  34 , and a thickness restricting blade  35 . 
   Toner in the toner accommodation chamber  32  is discharged toward the toner feed roller  33 , and is fed to the development roller  34  by rotation of the toner feed roller  33 . The toner fed onto the development roller  34  invades between the thickness restricting blade  35  and the development roller  34  in accordance with rotation of the development roller  34 , and the toner is carried onto the development roller  34  as a thin film of a fixed thickness. 
   After the scorotron type electrifier  29  uniformly positively electrifies the surface of the photosensitive drum  28 , the surface of the photosensitive drum  28  is exposed by high-speed scanning of a laser beam emitted from the scanner portion  19 , and n electrostatic latent image corresponding to an image to be formed on a sheet  3  is formed on the surface of the photosensitive drum  28 . 
   Next, positively electrified toner carried on the development roller  34  is fed to the exposed portion, the potential of which is lowered by being exposed by a laser beam, of the surface of the uniformly positively electrified photosensitive drum  28 , whereby the electrostatic latent image on the photosensitive drum  28  is made into a visible image, and a toner image by reverse development is carried on the surface of the photosensitive drum  28 . 
   After that, the toner image carried on the surface of the photosensitive drum  28  is transferred onto a sheet  3  by transfer bias applied onto the transfer roller  30  while the sheet  3  conveyed by the registration roller  15  passes through the transfer position between the photosensitive drum  28  and the transfer roller  30 . The sheet  3  on which the toner image was transferred is conveyed to the fixing portion  20 . 
   (c) Fixing Portion 
   The fixing portion  20  is provided at the rear side of the process cartridge  18 , and the fixing portion  20  comprises a heating roller  37 , a compression roller  38  and a transfer roller  39 . 
   The toner transferred onto the sheet  3  is melted by heat while it passes through the heating roller  37  and the compression roller  38  and the toner is adhered to and fixed at the sheet  3 . The sheet  3  is conveyed toward the discharge roller  40  by the conveying roller  39 . After that, it is discharged onto a sheet discharging tray  42  by the discharge roller  40 . 
   2. Multi-Purpose Mechanism 
     FIG. 2  is a sectional view of the major parts, showing a state where the multi-purpose tray (hereinafter referred to as MP tray  41 ) is opened. The laser printer  1  comprises a multi-purpose mechanism (manual sheet feeding mechanism operating as a sheet feeder) for conveying sheets  3  from the front side of the laser printer  1  to the transfer position by manual feeding. The multi-purpose mechanism includes an MP tray  41  and a multi-purpose sheet feeding mechanism portion (hereinafter referred to as MP sheet feeding mechanism portion  42 ) for feeding sheets  3  onto the MP tray  41 . 
   (1) MP Tray 
   A rectangular opening  7   a  is penetrated and formed in the front side cover  7 , and the MP tray  41  is provided so as to cover the opening  7   a . In detail, the MP tray  41  comprises a cover portion  43 , which is made into the front side wall of the main body casing  2 , and a tray portion  44  on which sheets to be manually fed are placed. The cover portion  43  is provided, as shown in  FIG. 2 , so that the lower end portion side is axially supported by means of a cover turning shaft  43   a  with respect to the main body casing  2 , the cover portion  44  is made openable and closable centering around the cover turning shaft  43   a , and the cover portion  44  is locked in a state where an inner side portion  43   b  is turned upward. And, the tray  44  is provided on the inner side portion  43   b.    
   The tray portion  44  comprises a first tray plate  45  disposed on the inner side portion  43   b  of the cover portion  43  and an second tray plate  46  rotatably and axially supported at the front end part of the first tray  45 . The first tray plate  45  is located at the position where the first tray plate  45  can be accommodated in the inner side portion  43   b  of the cover portion  43  in a state where the MP tray  41  is closed (Refer to  FIG. 1 ). And the first tray plate  45  is provided so as to slide the position where the front end portion protrudes forward of the cover portion  43  along a guide groove  47  when the MP tray  41  is opened (Refer to  FIG. 2 ). 
   The second tray plate  46  is rotatably axially supported at the front end portion of the first tray  45 . The second tray plate  46  is rotatable between the position (refer to  FIG. 1 ) where it is stacked on the upper surface of the first tray plate  45 , and the position (Refer to  FIG. 2 ) where it is expanded forward of the first tray plate  45 . Also, in the tray portion  44 , the cover turning shaft  43   a  side (the leading edge side of insertion of the sheets  3 ) is tilted downward in a state where the MP tray  41  is opened, as shown in  FIG. 2 . 
   Also, the MP tray  41  comprises a guide mechanism  49  having a pair of guide ribs  48  and  48  (only the left side rib is illustrated in  FIG. 1  and  FIG. 2 ). When the MP tray  41  is opened, the pair of guide ribs  48  and  48  guides conveyance of sheets  3  loaded in the tray portion  44  with both ends thereof in their width direction nipped therebetween. The pair of guide ribs  48  and  48  is made slideable in the directions approaching each other and parting from each other, wherein the MP tray  41  is able to stack sheets  3  of optional sizes in layers. 
   The guide mechanism  49  is positioned rearward (in an upper space of the MP sheet feeding mechanism  42 ) of the upper end portion of the folded tray portion  44  in a state where the MP tray  41  is closed (Refer to  FIG. 1 ). The guide mechanism  49  is slideable along a guide groove  50  when the MP tray  41  is opened (Refer to  FIG. 2 ), and the guide mechanism  49  is positioned at the rear side of the first tray  45 . 
   (2) MP Sheet Feeding Mechanism Portion 
   As shown in  FIG. 2 , the MP sheet feeding mechanism portion  42  comprises a feed roller  51 , a separation roller  52  disposed at a further far side of the sheet feeding inlet side than the feed roller  51 , and a separation pad  53  pressed in a state opposed to the separation roller  52 . In a state where the separation roller  52  and the separation pad  53  are opposed to and are brought into contact with each other, the separation pad  53  is pressed toward the separation roller  53  by a pressing force of an pressing member (not illustrated). That is, the multi-purpose mechanism according to the first illustrative aspect is a twin-roller system consisting of the feed roller  51  and the separation roller  52 , the feed roller  51  is disposed at the MP tray  41  side and the separation roller  52  is disposed rearward thereof. 
   The uppermost sheet  3  stacked on the MP tray  41  is fed by rotation of the feed roller  51  and is nipped between the separation roller  52  and the separation pad  53 . After that, sheets  3  are fed one by one by cooperation thereof. Fed sheets  3  are conveyed to the registration roller  15  through a conveying path  54 . 
   In further detail, a roller unit, which axially supports the feed roller  51  and the separation roller  52  with both the rollers exposed downward, is provided. The feed roller  51  vertically moves in the downward inclination space as described below. 
   (3) Vertical Drive Mechanism of the Feed Roller 
     FIG. 3  and  FIG. 4  are perspective views showing the vertical drive mechanism  60  of the feed roller  51 . In these drawings, the paper left upper side is the front side of the laser printer  1 , the paper right lower side is the conveying direction of the sheets  3 , the paper right side is the left side of the laser printer  1 , and the paper left side is the right side of the laser printer  1 , respectively. 
   As shown in  FIG. 3  and  FIG. 4 , the roller unit  56  comprises the feed roller  51  and separation roller  52 . The feed roller  51  and separation roller  52  are provided on a bearing member  61  that is a common rotatably supporting member thereof. In detail, in the feed roller  51 , a gear  62  is integrally provided coaxially with the feed roller  51  at the sideward thereof (the left side, that is, the paper right side in the same drawings), and the feed roller  51  and the gear  62  are axially supported rotatably at the front end side of the bearing member  61 . On the other hand, a gear  63  is integrally provided coaxially with the separation roller  52  at the sideward thereof (the left side, that is, the paper right side in the same drawings), and the separation roller  52  and the gear  63  are axially supported rotatably at the rear end side of the bearing member  61 . And, the gears  62  and  63  are coupled to each other by means of an intermediate gear  64 . 
   At the further left side of the separation roller  52 , a rotation axial member  65  extending in the left and right direction is disposed coaxially with the separation roller  52 . The rotation shaft of the separation roller  52  is fixed at the right end portion of the rotation shaft body  65 , and a separation roller drive gear  66  being a part of the drive source is fixed at the left end portion. Therefore, by the separation roller drive gear  66  being given a drive force from a drive motor M, the separation roller  52  rotates. In line therewith, the feed roller  51  dependently rotates. In addition, the feed roller  51  side of the roller unit  56  is swingable centering around the separation roller  52 . A drive motor M gives a drive force not only the separation roller drive gear  66  but also other gears. 
   Also, an arm  67  consisting of the first arm  107  and the second arm  117  is disposed upward of the rotation axial member  65  so as to go along the left and right direction of the laser printer  1 . The first arm  107  has two arm bosses  103   a  and  103   b  in the axial direction of the separation roller  52 . And, a rotation center boss  140  in which the arm pivot  102  inserts is disposed between these two arm bosses  103   a  and  103   b . Further, an outward-opening resilient locking claw is provided at the distal end of the arm pivot  102 , the rotation center boss  140  in which the arm pivot  102  inserts is composed so as not to come off from the arm pivot  102  by the upper end surface thereof being locked with the resilient locking claw. 
   Two arm holes  104   a  and  104   b  are provided in the second arm  117 , and a rotation center hole  141  is provided between these two arm holes  104   a  and  104   b.    
   The arm bosses  103   a  and  103   b  of the first arm  107  are fitted into the arm holes  104   a  and  104   b  of the second arm  117  (since the rotation center boss  104  is smaller than the rotation center hole  141 , these bosses are inserted into the holes in an idle state), wherein these components can be positioned to each other. Therefore, the first arm  107  and the second arm  117  are made integral with each other, wherein they integrally swing centering around the arm pivot  102 . Also, the arm pivot  102  is a boss attached to the sheet feeder main body. 
   Although not being illustrated, a part of the cover of the sheet feeder, which covers the vertical drive mechanism  60  of the feed roller  51 , is detachably provided so as to be opposed to the upper surface of the arm  67 , whereby the second arm  117  is prevented from being floated upward so that it is not disengaged from the first arm  107 . 
   And, a through-hole  67   a  is formed at one end portion side (the right end portion side) of the second arm  117  and penetrates the second arm in the vertical direction. A protrusion portion  61   a  protruding from the rear end side of the upper surface of the bearing member  61  is inserted into the through hole  67   a.    
   And, rearward of the other end portion side (the left end portion side) of the first arm  107 , the pressing member  68  is provided so that the upper end portion thereof can tilt centering around the lower end portion thereof. And, as shown in  FIG. 3 , in a state where the upper end portion of the pressing member  68  tilts to the front side, the pressing member  68  is brought into contact with the left end portion of the arm  67  and locks the same by pressing it forward. At this time, since the right end portion of the arm  67  presses the protrusion portion  61   a  rearward, the feed roller  51  is located at an elevated position spaced from the upper surface of the sheet conveyance supporting member  55  for conveying and supporting the sheets  3 . 
   On the other hand, as shown in  FIG. 4 , as the upper end portion of the pressing member  68  is tilted rearward, the pressing member  68  is spaced from the left end portion of the first arm  117 , and the locking between them is released. Therefore, rearward pressing to the protrusion portion  61   a  by the right end portion of the second arm is released, wherein the feed roller  51  moves, by the self-weight of the feed roller  51 , to a descending position where it can be brought into contact with the upper surface of the sheet conveyance supporting member  55 , thus enabling feeding of sheets  3 . Herein, in the first illustrative aspect, as shown in  FIG. 2 , the height of the feed roller  51  is flush with the height of the separation roller  52  when it is located at its elevated position, wherein the height is made into the uppermost position, and takes a lower position than the separation roller  52  in a state where the feed roller  51  is at its descended position. 
   A solenoid switch  69 , a sector gear  70  and an input gear  71  that rotates upon receiving a drive force from a drive motor (not illustrated) are disposed in the vicinity of the pressing member  68 . 
   The solenoid switch  69  functions as switching means that is turned on whenever it receives a sheet feeding commencement signal. A solenoid lever  72  is devised so that its roughly central portion  72   a  is rotatably supported and its front end portion descends downward by turning-on motions of the solenoid switch  69 . Also, a locking claw  72   b  that is engaged with the locking protrusion  70   a  protruding from the outer circumferential surface of the sector gear  70  is provided at the rear end portion of the solenoid lever  72  integrally therewith. 
   The sector gear  70  comprises the first cam  74 , the first notched teeth gear  75 , the second notched teeth gear  76  and the second cam  77 , which turn integrally with the same gear turning shaft  73 . 
   (a) First Notched Teeth Gear 
   In further detail, as shown in  FIG. 5 , the first notched teeth gear  75  has partially consecutive notched teeth and is driven to turn by engagement with the input gear  71  when a drive force is inputted from the drive motor. Herein, when the locking claw  72   b  of the solenoid lever  72  is engaged with the locking protrusion  70   a  of the sector gear  70 , the first notched teeth gear  75  is adjusted so that the notched teeth thereof face the input gear  71 . At this time, the drive force from the input gear  71  is not transmitted to the sector gear  70  (Refer to  FIG. 3  and  FIG. 5 ). 
   (b) Second Notched Teeth Gear 
   The second notched teeth gear  76  is disposed at the left side (the paper right upper direction in  FIG. 3  and  FIG. 4 , and the deep direction of paper in  FIG. 5  and  FIG. 6 ) of the first notched teeth gear  75 . Also, roughly one-third the entire circumference of the second notched teeth gear  76  is consecutively notched. By the second notched teeth gear  76  being engaged with the feed roller drive gear  66 , the second notched teeth gear functions to drive and rotate the separation roller  52 . In addition, in the state shown in  FIG. 3  and  FIG. 5 , the second notched teeth gear  76  gear is not engaged with the separation roller drive gear  66 , wherein the separation roller idly rotates. 
   (c) Second Cam 
   The second cam  77  is disposed at the left side (the paper right upper direction in  FIG. 3  and  FIG. 4 , and the paper far side in  FIG. 5  and  FIG. 6 ) of the second notched teeth gear  76 . Also, the section, orthogonal to the gear rotation shaft  73 , of the second cam  77  is roughly D-shaped as the entirety, and one end portion of the flat portion  77   a  is made into a protruded large-diameter portion  77   b . In the state shown in  FIG. 5 , a sector spring  78  that is brought into contact with the large-diameter portion  77   b  of the second cam  77  in a pressed state is provided in the vicinity of the second cam  77 . The sector spring  78  forcibly rotates the second cam  77  in the clockwise direction of paper in  FIG. 6  when engagement by the solenoid lever  72  is released by turning-on of the solenoid switch  69 , and the sector spring functions to turn the sector gear  70  to the position where the first notched teeth gear  75  is engaged with the input gear  71 . 
   (d) First Cam 
   The first cam  74  is disposed at the right side (the left lower direction of  FIG. 3  and  FIG. 4 , and the paper near side in  FIG. 5  and  FIG. 6 ) of the first notched teeth gear  75 . Further, roughly one-third of the entire circumference of the first cam  74  is made into a consecutively large-diameter portion  74   a , and the upper end portion of the pressing member  68  is disposed at the near side of the first cam  74 . In the state shown in  FIG. 4  and  FIG. 6 , the large-diameter portion  74   a  of the first cam  74  is bumped against the upper end portion of the pressing member  68 , thereby locking the upper end portion at the front side position. 
   Next, a description is given of motions of the vertical drive mechanism  60  of the feed roller  51 . The vertical drive mechanism  60  is located at its home position as shown in  FIG. 3  and  FIG. 5  before a sheet feeding commencement signal is given to the solenoid switch  69 . The feed roller  51  is located at its elevated position spaced from the sheets  3 , wherein the separation roller  52  idly turns with no drive force given. 
   And, as a sheet feeding commencement signal is given to the solenoid switch  69 , engagement of the locking protrusion  70   a  with the locking claw  72   b  is released as shown in  FIG. 4  and  FIG. 6 , and the sector gear  78  turns to the position, at which the first notched teeth gear  75  and the input gear  71  are engaged with each other, by a pressing force of the sector spring  78 . Therefore, the sector gear  70  is driven to turn in the clockwise direction. In addition, at this time, the large-diameter portion  74   a  of the first cam  74  is set back to release the locking of the pressing member  68 , wherein due to the self-weight of the feed roller  51 , the feed roller  51  moves to the descended position where the feed roller  51  is brought into contact with the upper surface of sheets  3  located on the upper surface of the partitioning member  55  (Refer to  FIG. 4 ). However, since the second notched teeth gear  76  is not engaged with the separation roller drive gear  66  yet, the separation roller  52  can idly turn. 
   After that, since the sector gear  70  rotates, the second notched teeth gear  76  and the separation roller drive gear  66  are engaged with each other, wherein the separation roller  52  is driven to rotate. In line therewith, the feed roller  51  is driven. Accordingly, feeding of sheets  3  on the MP tray  41  is commenced, and the sheets  3  are separated one by one at the position where the separation roller  52  and the separation pad  53  are opposed to each other, and a separated sheet  3  passes through the conveying path  54 . 
   And, as the sector gear  70  turns to the position where the large-diameter portion  74   a  of the first cam  74  is brought into contact with the upper end portion of the pressing member  68  again, the left end portion of the arm  67  is gradually pressed to the front side along the tapered surface of the rear side of the pressing member  68 , and the feed roller  51  is reset to its elevated position. At this time, since the second notched teeth gear  76  is still engaged with the separation drive gear  66 , the separation roller  52  and the feed roller  51  are being driven and rotated. Herein, the length in the circumferential direction of the large-diameter portion  74   a  of the first cam  74  is adjusted so that the timing at which the feed roller  51  is reset to its elevated position comes before the rear end of the separated sheet  3  goes through the opposed position. In particular, in the first illustrative aspect, the length is adjusted on the basis of the length (for example, the short side length of a postcard) in the conveying direction of sheets of the minimum size, which can be used in the present laser printer  1 . 
   Second Illustrative Aspect 
   A description is given of second illustrative aspect of the present invention with reference to  FIG. 7  through  FIG. 13 . Since the vertical drive mechanism  60  of the feed roller  51  has almost the same configuration as that in first illustrative aspect, a detailed description thereof is omitted.  FIG. 7  and  FIG. 8  are perspective views of the major parts of the arm  267 , etc., in second illustrative aspect. The following description is based on these drawings. 
   The first arm  207  includes two arm bosses  203   a  and  203   b  in the axial direction of the separation roller  52 . A rotation center boss  240 , with which the arm pivot  102  disposed at the apparatus main body intervenes, is provided between the arm bosses  203   a  and  203   b.    
   The second arm  217  includes two arm holes  204   a  and  204   b . A rotation center hole  241  is provided between the two arm holes  204   a  and  204   b . By the two arm bosses  203   a  and  203   b  of the first arm  207  being fitted in the armholes  204   a  and  204   b  of the second arm (since the rotation center boss  240  is smaller than the rotation center hole  241 , idle fitting is brought about), these components can be positioned with respect to each other. Accordingly, the first arm  207  and the second arm  217  are made integral with each other, and the first arm  207  and the second arm  217  are able to swing integrally with each other centering around the arm pivot  102 . Further, the arm covering member  145  is provided so as to be opposed to the upper surfaces of the first arm  207  and the second arm  217 , which are positioned to each other. The arm covering member  145  comprises a pressing plate portion  145   a  opposed to the upper surface of the arm  67  and a resilient locking claw  145   b  engaged with a locking step portion  245  disposed at the sheet feeder main body. 
     FIG. 9  is a view showing the printer  1  observed from the front side.  FIG. 10  is an enlarged sectional view taken along the line X-X in  FIG. 9 . In  FIG. 9 , the front side cover  132  of the printer  1  which is an image forming apparatus comprises a sheet feeding cover  131  concurrently used as the MP tray  41 . The cover turning shaft axially supports the lower end portion of the sheet feeding cover  131 , and the sheet feeding cover  131  can be opened and closed to the near side direction in the drawing around the cover turning shaft. 
   As shown in  FIG. 10 , the second arm  217  is provided on the upper surface of the first arm  207 , and the pressing plate portion  145   a , which is a part of the arm covering member  145 , faces the upper surface of the second arm  217 . The arm covering member  145  is prevented from being floated upward by the resilient locking claw  145   b  being engaged with the locking step portion  245  of the sheet feeder main body, whereby the second arm  217  is also prevented from being floated upward so that it does not come off from the first arm  207 . 
     FIG. 11  shows a state where the MP sheet feeding mechanism  42  is observed from its front side with the sheet feeding cover  131  open (however, illustration of the sheet feeding cover  131  is omitted). If the sheet feeding cover  131  is turned to near side in the drawing, the MP sheet feeding mechanism  42  become a state in which the MP sheet feeding mechanism  42  may be used. The front cover  133  of the sheet feeder is located at the position opposed to the sheet feeding cover  131  and is a part of the front cover  132  to enclose the front side of the printer  1 . The arm covering member  145  is a part of the front cover  133 . The MP sheet feeding mechanism  42  comprises a feed roller  51 , a separation roller  52 , and a separation pad  53  pressed in a state where it is opposed to the separation roller  53 . Sheets  3  are fed by rotation of the feed roller  51 . After the sheets  3  are nipped between the separation roller  52  and the separation pad  53 , the sheets  3  are separated one by one by cooperation thereof and are fed. A fed sheet  3  is conveyed to the registration roller  15  through the conveying path  54 . 
   As shown in  FIG. 12 , the front side cover  132  of the printer  1  can be opened to near side of the drawing integrally with the front cover  133  of the sheet feeder together with the MP sheet feeding mechanism  42 . The arm covering member  145  has a pressing plate portion  145   a  at the drive source side (the left direction in the drawing), the drive source has a power for swinging the first arm  207  and the second arm  217 . By operating two resilient locking claws  145   b  provided in the arm covering member  145  and releasing the engagement of the sheet feeder main body with the locking step portion  245 , the entirety of the arm covering member  145  can be removed from the sheet feeder main body. 
     FIG. 13  shows a state where the arm covering member  145  is removed from the sheet feeder main body, which is a view showing the inside of the apparatus main body observed from the upside with the front cover  133  opened. 
   When the arm covering member  145  is removed, the first arm  207  and the second arm  217  are exposed and can be observed. The first arm  207  is mounted swingably centering around the arm pivot  102  in a state where the first arm  207  is prevented from coming off upwards by the arm pivot  102  being inserted into the hole provided at the center of the rotation centering boss  204  and an outwardly-opening resilient locking claw disposed at the distal end of the arm pivot  102  being engaged with the upper end surface of the rotation center boss  240 . 
   On the other hand, since the second arm  217  is fitted in only the upper side of the first arm  207 , it can be easily removed. Therefore, the supporting member  61  that supports the feed roller  51  and the separation roller  52  can be simply removed as the roller unit. 
   Since the arm covering member  145  is constructed as a part of the front cover  133 , an opening  146  is brought about at the position from which the arm covering member  145  is removed, when the arm covering member  145  is removed from the printer  1 . Through the opening  146 , it becomes easy to access from the outside of the printer  1  to the inside thereof, wherein it becomes possible to replace the rollers not only through the inside of the printer  1  but also from the outside thereof through the opening  146 . 
   In addition, in first illustrative aspect described above, although two pairs of the arm boss  103   a  and arm hole  104   a  and the arm boss  103   b  and arm hole  104   b  are employed as the positioning portions, it is not necessary that two positioning portions are provided, wherein three or more positioning portions may be employed. Furthermore, in first illustrative aspect, although the first arm  107  comprises the arm bosses  103   a  and  103   b , and the second arm  117  comprises the arm holes  104   a  and  104   b , the arms are not limited thereto. For example, the first arm  107  may be comprises the holes  104   a  and  104   b , and the second arm  117  may comprises the arm bosses  103   a  and  103   b.    
   Further, the first arm  107  may comprise the arm boss  103   a  and the arm hole  104   b , and the second arm may comprise the arm hole  104   a  and the arm boss  103   b . Further, the first arm  107  may comprise the arm hole  104   a  and the arm boss  103   b , and the second arm  117  may comprise the arm boss  103   a  and the arm hole  104   b.    
   Still further, with respect to the first arm  207  and the second arm  217  according to second illustrative aspect, they may be constructed as in the modified versions of first illustrative aspect. 
   In addition, as shown in  FIG. 14 , the first arm and the second arm may be constructed as follows. 
   The first arm  307  includes two arm bosses  303   a  and  303   b  in the axial direction of the separation roller  52 . A rotation center boss  340 , with which the arm pivot  102  disposed at the apparatus main body intervenes, is disposed on the first arm  307 . The arm bosses  303   b  are disposed between the arm boss  203   a  and the rotation center boss  340 . 
   The second arm  317  includes two arm holes  304   a  and  304   b . By the two arm bosses  303   a  and  303   b  of the first arm  207  being fitted in the arm holes  304   a  and  304   b  of the second arm, these components can be positioned with respect to each other. Accordingly, the first arm  307  and the second arm  317  are made integral with each other, and the first arm  307  and the second arm  317  are able to swing integrally with each other centering around the arm pivot  102 . Further, the arm covering member  145  is provided so as to be opposed to the upper surfaces of the first arm  307  and the second arm  317 , which are positioned to each other. 
   Also, the first arm may be connected to the second arm via an intermediate material, for example, a third arm that connects the first arm and the second arm. 
   As shown in  FIG. 7  and  FIG. 14 , since at least two positioning portions are provided for the first arm and the second arm with some spacing, it is possible to reduce play produced between the first arm and the second arm. As shown in  FIG. 7  and  FIG. 8 , since the arm pivot is provided between the respective positioning portions, operation of integral swinging of the first arm and the second arm can be stabilized. 
   According to the above illustrative aspects, since the boss provided at one arm can be fitted in the hole provided at the other arm, it is possible to easily and securely position both the arms. 
   According to the above illustrative aspects, since the first arm and the second arm are covered by a arm covering member, it is not necessary to fix the first arm and the second arm, wherein it is possible to securely prevent the second arm from coming off from the first arm when swinging. 
   According to the illustrative aspects, since the arm covering member is composed as a part of the cover to enclose the main frame of the image forming apparatus, it is possible to make access the interior through an opening from which the arm covering member is removed, in a state where the arm covering member is removed when replacing the rollers. 
   According to the above illustrative aspects, it is possible to compose an image forming apparatus capable of easily carrying out replacement of the feed roller and the separation roller.