Abstract:
The present invention provides an image forming apparatus including a sheet supply device having a detachable sheet supply roller for feeding stacked sheets, an image forming device having a process cartridge for forming an image on the sheet fed by the sheet supply device, a cartridge containing portion for detachably containing the process cartridge within a body of the image forming apparatus, and a sheet discharge device for discharging and stacking the sheets on which the images were formed by the image forming device. The sheet supply roller and the process cartridge are disposed adjacent to each other, and, after the process cartridge is disengaged from the cartridge containing portion, the sheet supply roller is mounted and dismounted through the cartridge containing portion.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an image forming apparatus such as a laser beam printer, a copying machine, a facsimile and the like and an improvement in a sheet supply portion of such an apparatus. 
     2. Related Background Art 
     Recently, laser beam printers have been made more compact and inexpensive, with the result that the laser beam printers which were used under limited conditions such as office equipment and/or business purposes have been used in private offices and/or homes since personal computers have progressed. To this end, the laser beam printers themselves have been improved so that the performance thereof is enhanced and so that they can easily be used by any person. For example, by only opening an open/close cover, the user himself can easily exchange consumed parts such as a process cartridge and easily effect jam treatment. 
     Further, in the past, a large number of sheets having certain characteristics recommended by electrophotographic makers were used. However, recently, various kinds of paper sheets (for example, no-brand low cost sheets, ink jet printing sheets and the like) available from stationery shops or discount stores have frequently been used. Further, for an individual, a user may use various sheets such as a post card, a letter-paper, an envelope and sheets having various thicknesses. 
     Since such sheets may have features different from features of sheets to be used in the apparatuses recommended by the makers, various problems may occur. For example, some kinds of paper sheets may reduce a friction force of a sheet supply roller for supplying a sheet to the laser beam printer, thereby causing poor sheet supply. More particularly, a coating on the sheet, a pigment coated on the sheet and/or additives to the sheet (talc, calcium carbonate or Kaolin) can adhere to and accumulate on a surface of the sheet supply roller, and, a rubber surface of the sheet supply roller is worn by a rough surface of the sheet or fibers of the sheet, thereby causing such problems. 
     Such sheet supply roller must be cleaned by using a solvent such as alcohol, or the sheet supply roller itself must be exchanged. However, since the solvent such as alcohol may not easily be available and the sheet supply roller cannot easily be exchanged by the user (even when the improvement is made so that anyone can handle the apparatus easily), generally, the user leaves repair of the apparatus to the maker. 
     To avoid this, it is requested to provide an arrangement in which any user can easily exchange the sheet supply roller. However, the conventional arrangements have the following disadvantages. 
     (1) Since the sheet supply roller is disposed within the body of the apparatus, a space available to exchange the sheet supply roller is small. 
     (2) As shown in FIG. 7A, in general, in a sheet supply roller unit  100 , a sheet supply roller  101 , a sheet supply sub-roller  102  and cams  106 ,  109  are fitted on a sheet supply shaft  104  and are secured to the sheet supply shaft by fixing members  103 ,  105 ,  108  and  110 . When parts are exchanged, the unit  100  integrally including the sheet supply shaft  104  is dismounted from a body of the apparatus, and, as shown in FIG. 7B, the sub-roller  102  and the fixing members (parallel pins)  103 ,  105  provided on the shaft are slid along a longitudinal direction of the shaft to be removed. Accordingly, it is difficult for the user to exchange the sheet supply roller. 
     (3) A sheet supply roller unit  122  shown in FIG. 8 includes a rubber portion  122   a  having a high coefficient of friction and a sheet supply roller metal core  122   b.  In this unit, the user can easily exchange the sheet supply roller only by disengaging a pawl  122   c  of a snap fit  122   d  provided on the metal core  122   b  from a recess  120   a  provided in a shaft  120  and sliding the roller laterally. However, as shown in FIG. 8, the exchange of the sheet supply roller can be effected only when the sheet supply roller is supported by a bearing portion  121  in a cantilever fashion and other parts are not provided on the shaft. Other arrangements cannot be used. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to permit easy exchanging by a user of a sheet supply roller in an image forming apparatus. 
     To achieve the above objects, according to the present invention, there is provided an image forming apparatus comprising a sheet supply means having a detachable sheet supply roller for feeding stacked sheets, an image forming means having a process cartridge for forming an image on the sheet fed out by the sheet supply means, a cartridge containing portion for detachably containing the process cartridge within a body of the image forming apparatus, and a sheet discharge means for discharging and stacking the sheets on which the images were formed by the image forming means. Wherein, the sheet supply roller and the process cartridge are disposed adjacent to each other, and, after the process cartridge is disengaged from the cartridge containing portion, the sheet supply roller is mounted and dismounted through the cartridge containing portion. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional view of an image forming apparatus to which the present invention is applied; 
     FIGS. 2A,  2 B and  2 C are partial enlarged explanatory views showing a mounting/dismounting arrangement of a sheet supply roller of the image forming apparatus of FIG. 1; 
     FIG. 3 is a front view showing the main part of FIGS. 2A,  2 B and  2 C; 
     FIGS. 4A,  4 B and  4 C are explanatory views showing a sheet supplying condition of the sheet supply roller of FIG. 1; 
     FIGS. 5A,  5 B and  5 C are partial enlarged explanatory views showing another mounting/dismounting arrangement of a sheet supply roller; 
     FIG. 6 is a view showing an embodiment in which a detachable sheet supply roller is provided at a cover side; 
     FIGS. 7A and 7B are front views showing a conventional sheet supplying apparatus using a shaft supported at both ends; and 
     FIG. 8 is a perspective view showing a conventional sheet supplying apparatus using a shaft supported in a cantilever fashion. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An embodiment of the present invention will now be fully explained with reference to FIGS. 1,  2 A,  2 B,  2 C,  3 ,  4 A,  4 B and  4 C. 
     FIG. 1 schematically shows a laser beam printer M (referred to merely as “printer M” hereinafter) using a detachable process cartridge, as an example of an image forming apparatus according to the present invention. A conveying direction of a recording sheet P has an upstream side (right side) and a downstream side (left side) in FIG.  1 . Although the recording sheet P may be a thick sheet, a special sheet such as an envelope, or film sheet such as OHP sheet, as well as a normal sheet, the normal sheet is used as the recording sheet in the illustrated embodiment. 
     In the printer M, a sheet supply tray  32  for supporting the recording sheets P (before image formation) longitudinally or vertically is provided at an upstream side of a printer body  50  (referred to merely as “body  50 ” hereinafter) in a recording sheet supplying direction (rear or remote side of the body  50 ), and a sheet discharge tray  33  for supporting the recording sheets P (after image formation) longitudinally is provided at a downstream side of the body  50  (front or near side of the body  50 ). 
     A lower end of the sheet supply tray and a lower end of the sheet discharge tray are interconnected within a convey path extending from the right to the left (from the rear side to the front side) of the body  50  in FIG. 1 so that a sheet supply portion  3 , a process cartridge  1  and a fixing portion  6  are arranged adjacent to each other as much as possible, thereby providing a compact U-shaped path (referred to as “vertical U-shaped path” hereinafter). The process cartridge  1  incorporates therein at least a photosensitive drum (image bearing member)  1 A on which an electrostatic latent image is formed in an electrophotographic manner and a developing means having a developing sleeve  1 B (if necessary, process means such as a charge means  1 C may be added) as a cartridge unit which can be detachably mounted to the body of the image forming apparatus. 
     A body frame includes left and right side plates (not shown), a central stay member  31 , a top plate  30  on which a laser scanner  2  for forming the latent image on the photosensitive drum  1 A is mounted, and a bottom plate on which an electric portion  7  is mounted. A transfer portion  4 , a convey guide portion  5  and the fixing portion  6  are mounted on the stay member  31 . 
     In a condition that an open/close cover  9  having the sheet discharge tray  33  is opened by shifting it from a position shown by the two dot and chain line to a position shown by the solid line, the process cartridge  1  is inserted into a cartridge containing portion S along guide portions  10  provided on both sides of the body  50  to be held at a predetermined position. The open/close cover  9  is provided with a switch (now shown) so that when the open/close cover is opened a main power source is turned OFF, and when the open/close cover is closed the main power source is turned ON. 
     The sheet supply portion  3  is provided at a rear side of the process cartridge  1  and a sheet supply roller  12  is disposed at the center of the sheet supply portion, so that, after the open/close cover  9  is opened, when the process cartridge  1  is dismounted, an operator can easily access the sheet supply roller  12  through the cartridge containing portion S. 
     A sheet supply roller unit for supplying a recording sheet according to the present invention is constituted by a sheet supply shaft  11  (described later), a sheet supply roller support member provided on the sheet supply shaft, and the sheet supply roller  12  supported by the support member. A sheet supply means is constituted by the sheet supply tray  32  and the sheet supply portion  3 , and a sheet discharge means is constituted by a pair of discharge rollers  34  and the sheet discharge tray  33 . 
     The recording sheets P stacked on the sheet supply tray  32  are separated and supplied one by one by the sheet supply portion  3 , and the separated recording sheet is conveyed by a convey roller  19  downstream inclined downwardly by about 20 degrees within the electrophotographic apparatus. The recording sheet P is sent to a nip between the photosensitive drum  1 A and the transfer portion  4 , where a toner image formed on the drum is transferred onto the recording sheet. Then, the recording sheet is sent to the fixing portion  6 , where the toner image is thermally fixed to the recording sheet. Thereafter, the recording sheet is discharged onto the sheet discharge tray  33  by the pair of discharge rollers  34 . 
     Explaining the sheet supply portion  3  in more detail, as shown in FIGS. 2A to  2 C,  3  and  4 A to  4 C, the sheet supply portion includes an intermediate plate  23  for urging the recording sheet P against the sheet supply roller  12  by a spring  22 , a frictional separation means  18  biased toward the sheet supply roller  12  by a spring  21  disposed between the separation means and the body frame  20  in order to separate the recording sheets one by one by a friction force, a semi-circular sheet supply roller  12  attached to a sheet supply shaft  11  and arranged at the center of the recording sheet, sheet supply sub-rollers  13  disposed on both sides of the sheet supply roller, cams  16 ,  17  provided on both ends of the shaft  11  and adapted to push the intermediate plate  23  downwardly, and a clutch (not shown) for controlling one revolution of the sheet supply roller and the cams. 
     A guide member  14  for guiding the recording sheet P separated by the sheet supply roller  12  and the frictional separation means  18  is rotatably supported on the sheet supply shaft  11 , and a driven sub-roller  15  opposed to the convey roller  19  provided on the body frame  20  is provided on the guide member  14 . The recording sheet P conveyed by the convey roller  19  is guided toward an image forming portion of the process cartridge  1  between the guide member  14  and a body frame portion  20  located below the guide member. 
     As shown in FIGS. 2A to  2 C, the sheet supply roller  12  has a rubber portion  12   b  formed from a member having a high coefficient of friction, and a metal core portion  12   c,  and the rubber portion has a cylindrical shape and the metal core portion has a solid or hollow cylindrical shape. First positioning projections  12   a  are provided on the metal core portion in the vicinity of a portion A (referred to as “sheet supply tip end portion” hereinafter) which is contacted with the recording sheet in the initial sheet supply condition when the sheet supply roller  12  is rotated in a direction shown by the arrow D in FIG. 2A, and the projections may be pins as shown, for example. 
     Further, second projections  12   d  and third slit-shaped recesses  12   e  are provided at both sides of the metal core portion in the vicinity of a portion B (referred to as “sheet supply trail end portion” hereinafter) which is contacted with the recording sheet in the last sheet supply condition when the sheet supply roller is rotated in the direction shown by the arrow D. Preferably, each projection  12   d  is a prismatic projection having a square cross-section. The projections  12   a,    12   d  and the recesses  12   e  act as a locking means for the roller support member and the sheet supply roller, which will be described later. 
     At a central portion of a shaft portion  11   a  of the sheet supply shaft  11 , outside of the sheet supply roller  12 , there are provided elastic sheet supply roller support plates  11   b  formed integrally or formed independently from the shaft portion  11   a.  The sheet supply roller support plates  11   b  are provided at their sheet supply tip end portion sides with first recesses  11   c  adapted to be engaged by the sheet supply roller positioning projections  12   a  and are provided at their sheet supply trail end portion sides with second recesses  11   d  adapted to be engaged by the second projections  12   d  of the sheet supply roller. For example, each second recess is a square hole. When the sheet supply roller is inserted between the roller support plates, the second projections are snap-fitted into the second recesses. The first projections and recesses, and second projections and recesses constitute first and second locking means, respectively. 
     At the sheet supply trail end portion side within the sheet supply roller support plates  11   b,  there are provided rib-shaped projections  11   e  adapted to be engaged by the slit-shaped recesses  12   e  of the sheet supply roller to effect the positioning of the sheet supply roller  12 , and these projections and recesses constitute a third locking means. 
     In this way, the positioning of the sheet supply roller  12  with respect to the sheet supply roller support plates  11   b  in a direction E is effected by the first projections  12   a  and recesses  11   c,  second snap-fit projections  12   d  and recesses  11   d,  and third recesses  12   e  and projections  11   e,  and, the positioning of the sheet supply roller in a direction G is effected by fitting the third projections  11   e  into the third recesses  12   e.    
     In the sheet supply roller  12  so attached, as shown in FIGS. 4A to  4 C, a force applied in the sheet supplying operation is dispersed to prevent occurrence of any play and flexion. That is to say, FIG. 4A shows a condition where the recording sheet P is supplied at the sheet supply tip end portion A immediately after the sheet supplying operation is started. In this condition, due to a reaction force, the sheet supply roller  12  tries to shift toward a direction shown by the arrow J to be separated from the support plates  11   b.  However, since the first projections  12   a  are positively fitted into the recesses  11   c  to receive the force, the snap-fit portion at the sheet supply trail end side is not subjected to any force, so that the attachment position of the sheet supply roller  12  is stabilized. 
     FIG. 4B shows a sheet supplying middle condition. Also in this condition, since the first projections  12   a  are positively fitted into the recesses  11   c  so that the force K acting on the sheet supply roller  12  is supported by the projections  12   a,  no problem occurs. FIG. 4C shows a condition that the recording sheet P is supplied at the sheet supply trail end portion B immediately before the sheet supplying operation is completed. In this condition, due to the reaction force, the sheet supply roller  12  is biased toward the support plates  11   b  (direction shown by the arrow L). However, since the third positioning projections  11   e  are positively fitted into the third recesses  12   e  and the support plates  11   b  are rigid, the snap-fit portion at the sheet supply trail end side is not subjected to any force, with the result that the attachment position of the sheet supply roller  12  is stabilized. 
     When the sheet supply roller  12  is replaced the open/close cover  9  is opened as shown in FIG.  1  and the process cartridge is removed, so that the sheet supply roller can be replaced through the cartridge containing portion S. In this case, by removing the process cartridge  1 , the great working space for exchanging the sheet supply roller can be ensured. 
     As shown in FIG. 2A, portions C of the sheet supply roller support plates  11   b  are widened or bent in opposite directions to release the snap-fit, and the sheet supply roller  12  is rotated around the first projections  12   a  in a direction shown by the arrow F. Then, as shown in FIG. 2C, the sheet supply roller  12  is slid in a direction shown by the arrow G to disengage the first projections  12   a  from the recesses  11   c.  In this way, the sheet supply roller can easily be dismounted. On the other hand, when the sheet supply roller is mounted on the sheet supply shaft, since the reverse operation may be effected, the user can easily exchange the sheet supply roller. 
     Since the detect means for detecting the open or close condition is provided on the open/close cover, when the open/close cover is opened to perform the exchanging operation, the high voltage power source for driving the apparatus is turned OFF on the basis of a signal from the detect means. With this arrangement, even in a construction in which the sheet supply roller can be mounted and dismounted in a direction perpendicular to the sheet supply roller, the metal core portion is not required to be supported in a cantilever fashion as shown in FIG. 8 but can be supported with sufficient strength. 
     Incidentally, in the present invention, other than the above-mentioned arrangement, an arrangement in which after the open/close cover is opened the process cartridge is removed and then by opening another cover or sheet guide the exchange of the sheet supply roller is permitted may be used. Further, in the illustrated embodiment, while an example that the sheet supply roller is mounted and dismounted along the direction perpendicular to the sheet supply shaft was explained, the sheet supply roller may be mounted and dismounted along a longitudinal direction of the shaft. Further, the projections and recesses (as locking means) provided on the sheet supply roller and the roller support members may have a reverse relation (i.e., provided on the roller support members and the sheet supply roller). 
     FIGS. 5A to  5 C show another embodiment for mounting and dismounting a sheet supply roller. Reference numerals that are the same as those in FIGS. 2A to  4 C represent like items. A sheet supply roller  52  is constituted by a semicircular rubber portion  52   b  and a metal core portion  52   c,  similar to the sheet supply roller shown in FIGS. 2A to  2 C, and these portions have a semi-circular cylindrical shape. When it is assumed that the sheet supply roller  52  is rotated in a direction shown by the arrow D, first and second projections (positioning pins)  52   a,    52   d  are provided on both sides of the metal core in the vicinity of a sheet supply tip end portion A and a sheet supply trail end portion B, respectively. 
     At a central portion of a shaft portion  51   a,  outside of the sheet supply roller  52 , there are provided sheet supply roller support plates  51   b  formed integrally or formed independently from the shaft portion  51   a,  and the sheet supply roller support plates  51   b  are provided at their sheet supply tip end portion sides with first recesses (straight grooves)  51   c  adapted to be engaged by the sheet supply tip end side positioning pins  52   a  and provided at their sheet supply trail end portion sides with second recesses (L-shaped grooves)  51   d  adapted to be engaged by the sheet supply trail end side positioning pins  52   d.  Each L-shaped groove is constituted by an inlet side groove, and a rear side groove extending perpendicular to the inlet side groove  51   c  and parallel with the straight groove. Projections  51   e  for snap-fitting the pins  52   d  are provided at the entrance of the sheet supply trail end side grooves  51   d  to make the grooves narrower. 
     Fig. 5A shows a sheet supply permitting condition in which the sheet supply roller  52  is mounted on the sheet supply shaft. When the sheet supply roller is dismounted, the sheet supply roller  52  is shifted along the rear side grooves of the L-shaped grooves  51   d  extending in parallel with a first diametrical direction (direction M) of the sheet supply shaft and the grooves  51   c,  thereby disengaging the first and second projections  52   a,    52   d  from these grooves. Then, by shifting the second projections  52   d  along the inlet side grooves of the L-shaped grooves  51   d  extending in parallel with a second diametrical direction (direction N) perpendicular to the first diametrical direction, the sheet supply roller  52  can be dismounted from the sheet supply shaft  51   a  or the roller support plates  51   b.  When the sheet supply roller is mounted on the sheet supply shaft, a reverse operation may be effected. 
     Incidentally, projections similar to the snap-fitting projections  51   e  may be provided in association with the first recesses  51   c.    
     Next, a further embodiment will be explained with reference to FIG.  6 . Incidentally, elements same as or similar to the elements of the apparatus shown in FIG. 1 are designated by the same reference numerals and detailed explanation thereof will be omitted. 
     A process cartridge  1  can be extracted out of the apparatus through guide means (not shown) after an open/close cover  9  provided on an upper surface of a body of the apparatus is opened. 
     A sheet supply roller  12  of a sheet supply portion  3  is the same as that in the above-mentioned embodiments and can easily be mounted and dismounted with respect to a sheet supply shaft  11 . A sheet supply cover  62  provided above the sheet supply roller  12  and adapted to cover the sheet supply roller  12  is supported by a body  60  of the image forming apparatus in such a manner that, after the process cartridge  1  is dismounted, the cover  62  can be rotated around pivot  64  within a cartridge containing portion S. In a closed condition shown by the two dot and chain line in FIG. 6, the sheet supply cover  62  also acts as a guide means for guiding a sheet fed out by the sheet supply roller  12  toward an image forming position. 
     With this arrangement, after the open/close cover  9  of the body  60  of the image forming apparatus is opened and the process cartridge  1  is removed, when the sheet supply cover  62  is opened within the cartridge containing portion S, the sheet supply roller  12  can be mounted/dismounted from the sheet supply shaft  11 .