Patent Publication Number: US-2011062649-A1

Title: Sheet feeding device and image forming apparatus having same

Description:
This application is based on an application No. 2009-213298 filed in Japan on Sep. 15, 2009, the entire content of which is hereby incorporated by reference. 
     TECHNICAL FIELD 
     The invention relates to a sheet feeding device, and more specifically relates to a sheet feeding device including two sheet feeding stockers placed side by side in left and right directions, in which sheets are taken out from one sheet feeding stocker and conveyed through a horizontal conveying path provided above the other sheet feeding stocker for paper feed operation. 
     The invention also relates to an image forming apparatus having such a paper feeding device. 
     BACKGROUND ART 
     One example of conventional image forming apparatuses having a sheet feeding device of this kind has been disclosed in JP H05-097262 A. The sheet feeding device includes two sheet feeding stockers (decks) placed side by side in right and left directions below an image forming apparatus main body, in which sheets (paper sheets) are taken from a left-side feed stocker by a pickup roller provided in the upper part thereof, conveyed to the right direction through a horizontal conveying path provided above a right-side sheet feeding stocker, and then fed upward through a longitudinal conveying path. The sheets stocked in the right-side sheet feeding stocker is taken out by the pickup roller provided above the sheet feeding stocker, and fed upward through the longitudinal conveying path. 
     These two sheet feeding stockers can be pulled from the main body in directions intersecting with the respective feeding directions. The member constituting the horizontal conveying path (referred to as “horizontal conveyance unit”) can also be pulled from the main body in a manner independent of the two sheet feeding stockers in a direction intersecting with the feeding direction. With this configuration, users can easily remove jammed sheets by respectively pulling the two sheet feeding stockers and the horizontal conveyance unit at the time of jamming relating to paper feeding operation. 
     SUMMARY OF THE INVENTION 
     Technical Problem 
     However, in the above configuration, the two sheet feeding stockers and the horizontal conveyance unit can be pulled out independently, and therefore when a sheet stops at a position lapping over both the left-side sheet feeding stocker and the horizontal conveyance unit at the time of jamming relating to paper feed operation, sheet tear (so-called “tearing separation”) may occur if users pull out only the horizontal conveyance unit, for example, from the main body. 
     Accordingly, an object of the present invention is to provide a sheet feeding device which enables users to easily remove jammed sheets while preventing sheet tear at the time of jamming relating to paper feed operation. 
     Another object of the present invention is to provide an image forming apparatus having such a sheet feeding device. 
     Solution to Problem 
     In order to accomplish the above object, a sheet feeding device in one aspect of the present invention, comprising: 
     first and second sheet feeding stockers provided in a main body and placed side by side in a horizontal direction, wherein 
     sheets are taken out from the first sheet feeding stocker and conveyed through a horizontal conveyance unit provided above the second sheet feeding stocker, wherein 
     the respective first and second sheet feeding stockers can independently be pulled out forward from the main body in a direction intersecting with a sheet conveying direction in the horizontal conveyance unit, and wherein 
     an engaging mechanism is provided for engaging the horizontal conveyance unit and the first sheet feeding stocker so that the first sheet feeding stocker is pulled out integrally with the horizontal conveyance unit when the horizontal conveyance unit is pulled out forward from the main body. 
     An image forming apparatus in one aspect of the present invention is an image forming apparatus having the sheet feeding device. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein: 
         FIG. 1  is a front view showing an entire image forming apparatus having a sheet feeding device in one embodiment of the invention; 
         FIG. 2  is a cross sectional view showing the schematic configuration of the image forming apparatus; 
         FIG. 3  is a front view showing the layout of left-side and right-side sheet feeding stockers and a horizontal conveyance unit of the sheet feeding device; 
         FIG. 4  is a perspective view showing a protrusion as an engaging mechanism provided in the horizontal conveyance unit of the sheet feeding device; 
         FIG. 5  is a front view showing a protrusion as a locking mechanism provided in a conveyance door of the sheet feeding device; 
         FIG. 6  is a perspective view showing the protrusion as a locking mechanism provided in the conveyance door of the sheet feeding device corresponding to  FIG. 5 ; 
         FIG. 7  is a front view showing the locking mechanism in an unlocked state; 
         FIG. 8  is a perspective view showing the locking mechanism in an unlocked state corresponding to  FIG. 7 ; 
         FIG. 9A  is a plan view showing the left-side and right-side sheet feeding stockers and the horizontal conveyance unit of the sheet feeding device in the state of being housed in the main body; 
         FIG. 9B  is a plan view showing the horizontal conveyance unit of the sheet feeding device in the state of being pulled out from the main body together with the left-side sheet feeding stocker; 
         FIG. 10  is a perspective view showing the left-side and right-side sheet feeding stockers and the horizontal conveyance unit of the sheet feeding device in the state of being housed in the main body; 
         FIG. 11  is a perspective view showing the left-side sheet feeding stocker of the sheet feeding device in the state of being pulled out from the main body; 
         FIG. 12  is a perspective view showing the right-side sheet feeding stocker of the sheet feeding device in the state of being pulled out from the main body; and 
         FIG. 13  is a perspective view showing the horizontal conveyance unit of the sheet feeding device in the state of being pulled out from the main body together with the left-side sheet feeding stocker. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
       FIG. 1  shows an entire image forming apparatus (designated by reference sign  100 ) of a color tandem system having a sheet feeding device in one embodiment of the invention seen from the front side.  FIG. 2  shows a schematic sectional configuration of the image forming apparatus  100 . As shown in  FIG. 2 , the image forming apparatus  100  includes an intermediate transfer belt  108  as an annular image carrier provided generally in the center inside a main body casing  101 , the intermediate transfer belt  108  being wound around two rollers  102  and  106  and moving in the circumferential direction. One roller  102  out of two rollers  102  and  106  is placed on the left-hand side in the drawing, while the other roller  106  is placed on the right-hand side in the drawing. The intermediate transfer belt  108  is supported on these rollers  102  and  106 , and is rotated in an arrow X direction. 
     Toner containers  128 Y,  128 M,  128 C and  128 K for storing respective color toners of yellow (Y), magenta (M), cyan (C) and black (K) are placed side by side in order from the left-hand side in the drawing above the intermediate transfer belt  108 . These toners are respectively fed from the toner containers  128 Y,  128 M,  128 C and  128 K to later-described developing devices  193  of imaging units of corresponding colors  110 Y,  110 M,  110 C and  110 K. 
     The imaging units  110 Y,  110 M,  110 C and  110 K as image forming sections corresponding to respective color toners of yellow (Y), magenta (M), cyan (C) and black (K) are placed side by side in order from the left-hand side in the drawing below the intermediate transfer belt  108 . These imaging units  110 Y,  110 M,  110 C and  110 K are detachably mounted on the main body of the image forming apparatus  100 . An unshown door used for attachment and detachment of these imaging units  110 Y,  110 M,  110 C and  110 K is provided on the main body casing  101 . 
     The respective imaging units  110 Y,  110 M,  110 C and  110 K have completely similar configuration except for a difference in toner color that the respective units handle. More specifically, the yellow imaging unit  110 Y for example is integrally composed of a photoconductor drum  190 , a charging device  191 , an exposure device  192 , a developing device  193  for development with use of toner, and a cleaning device  195 . A primary transfer roller  194  is provided in a position facing the photoconductor drum  190  across the intermediate transfer belt  108 . At the time of image formation, the surface of the photoconductor drum  190  is first uniformly charged by the charging device  191 , and then the surface of the photoconductor drum  190  is exposed by the exposure device  192  in response to an image signal inputted from, for example, an unshown external unit to form a latent image thereon. Next, the latent image on the surface of the photoconductor drum  190  is developed into a toner image by the developing device  193 . This toner image is transferred onto the intermediate transfer belt  108  upon voltage application to between the photoconductor drum  190  and the primary transfer roller  194 . The transfer residual toner on the surface of the photoconductor drum  190  is cleaned by a cleaning device  195 . 
     As the intermediate transfer belt  108  moves in the arrow X direction, overlapped toner images of four colors are formed on the intermediate transfer belt  108  by each of the imaging units  110 Y,  110 M,  110 C and  110 K. 
     Provided on the left-hand side of the intermediate transfer belt  108  are a cleaning device  125  for removing residual toner from the surface of the intermediate transfer belt  108  and a toner collecting box  126  for collecting the toner removed by the cleaning device  125 . A secondary transfer roller  112  is provided on the right-hand side of the intermediate transfer belt  108  across a conveying path  124  for paper sheets. Conveying rollers  120  and  119  are provided respectively at positions corresponding to upstream and downstream sides of the secondary transfer roller  112  on the conveying path  124 . It is to be noted that a photo sensor (toner concentration sensor)  115  for detecting a toner pattern on the intermediate transfer belt  108  is provided integrally with the conveying roller  120 . 
     A fixing device  130  for fixing toner onto paper sheets is provided on the upper right part inside the main body casing  101 . The fixing device  130  is composed of a paper feed sensor  116  as a paper sensor for detecting paper sheets as sheets conveyed into the fixing device  130 , a heating roller  131  extending vertically with respect to the page of  FIG. 2 , and a pressure roller  132  as a pressure applying member also extending vertically with respect to the page of  FIG. 2  and being in pressure contact with the heating roller  131 . In this example, the heating roller  131  incorporates an unshown heating source. The pressure roller  132  is biased toward the heating roller  131  with an unshown spring. Accordingly, the heating roller  131  and the pressure roller  132  form a nip area N for fixation. As a sheet (e.g., paper sheet  90 ) carrying a toner image transferred thereon passes through the nip area N, the toner image is fixed onto the paper sheet  90 . It is to be noted that the paper feed sensor  116  is provided upstream from the nip area N with respect to a sheet conveying direction. The fixing device  130  operates based on the timing of the paper feed sensor  116  detecting a sheet. 
     Paper cassettes  140  and  141  for respectively stocking paper sheets  90  and  91  as the sheets on which images are to be formed are provided in two levels below the imaging units  110 Y,  110 M,  110 C and  110 K within the main body casing  101 . Feed rollers  150  and  151  are respectively attached to upper right portions of the paper cassettes  140  and  141  in the drawing. Paper sheets  90  are sent out from the upper-side paper cassette  140  to the conveying path  124  extending upwards one by one by the feed roller  150 . Similarly, paper sheets  91  are sent out from the lower-side paper cassette  141  to the conveying path  124  extending upward one by one by the feed roller  151 . It is to be noted that a part of the conveying path  124  (a portion generally facing the right ends of the paper cassettes  140 ,  141  and a later-described horizontal conveyance unit  148 ) is constituted of a conveyance door  145  which can be opened and closed with respect to the main body casing  101 . 
     In a position corresponding to the lowermost part of the main body casing  101  below the paper cassette  141 , a first sheet feeding stocker  142  for stocking paper sheets (hereinafter referred to as “left-side sheet feeding stocker”) and a second sheet feeding stocker  143  for stocking paper sheets  93  (hereinafter referred to as “right-side sheet feeding stocker”) are placed side by side in right and left directions in the drawing. In a position corresponding to a section directly above the right-side sheet feeding stocker  143 , a horizontal conveyance unit  148  equipped with feed rollers  152   a  and  152   b  is provided separately from the left-side sheet feeding stocker  142  and the right-side sheet feeding stocker  143 . In a position corresponding to the right-hand side of the right-side sheet feeding stocker  143 , a sheet feeding unit  149  equipped with the feed rollers  153   a  and  153   b  is provided (the sheet feeding unit  149  is fixed to the main body casing  101 ). The paper sheets  92  are sent out from the left-side sheet feeding stocker  142  to the horizontal conveying path  117  formed by the horizontal conveyance unit  148  and then to the conveying path  124  extending upward one by one by the feed rollers  152   a  and  152   b . The paper sheets  93  are sent out from the right-side paper cassette  143  to the conveying path  124  extending upwards one by one by the feed rollers  153   a  and  153   b . It is to be noted that  FIG. 3  shows the left-side sheet feeding stocker  142 , the right-side sheet feeding stocker  143 , the horizontal conveyance unit  148 , and the sheet feeding unit  149  as the components of a sheet feeding device seen from the front side. 
     When the image forming apparatus  100  receives a print job from the outside for example, a control section  200  constituted of a CPU (Central Processing Unit) shown in  FIG. 2  controls the entire image forming apparatus  100  to execute image forming operation according to the print job. 
     At the time of image formation, the paper sheets  92  are sent out by the feed rollers  152   a  and  152   b  from, for example, the left-side sheet feeding stocker  142  to the conveying path  124  extending upward one by one through the horizontal conveying path  117 . The paper sheets  92  are then sent into a toner transfer position between the intermediate transfer belt  108  and the secondary transfer roller  112  by the conveying roller  120 . Meanwhile, an overlapped toner image of four colors is formed on the intermediate transfer belt  108  by each of the imaging units  110 Y,  110 M,  110 C and  110 K as mentioned before. The toner image of four colors on the intermediate transfer belt  108  is transferred onto a paper sheet  92 , which was sent into the above-mentioned toner transfer position, by the secondary transfer roller  112 . The paper sheet  92  with the toner image transferred thereon receives heat and pressure while being conveyed through the nip area N formed between the heating roller  131  and the pressure roller  132  of the fixing unit  130 . As a result, the toner image is fixed onto the paper sheet  92 . The paper sheet  92  with the toner image fixed thereto is then discharged by a paper ejecting roller  121  into a paper ejection tray section  122  provided on the upper surface of the main body casing  101 . It is to be noted that the same image forming operation applies when the paper sheets  90 ,  91 ,  93  are sent out to the conveying path  124  from the paper cassettes  140 ,  141  or the right-side sheet feeding stocker  143 . 
     As shown in  FIG. 1 , the left-side sheet feeding stocker  142 , the right-side sheet feeding stocker  143 , and the horizontal conveyance unit  148  respectively have front doors  42 ,  43 , and  48  integrally provided. The front doors  42 ,  43  and  48  have handles  42   a ,  43   a  and  48   a , respectively. These handles  42   a ,  43   a  and  48   a  are used by users to pull out the left-side sheet feeding stocker  142 , the right-side sheet feeding stocker  143  and the horizontal conveyance unit  148  from the main body casing  101  to the front side. 
     As shown in  FIG. 4 , a plate-like protrusion  48   p  protruding to the left side is integrally provided at the left edge of the front door  48  of the horizontal conveyance unit  148 . The protrusion  48   p  of the front door  48  is structured to engage with a back side portion  42   b  of the front door  42  of the left-side sheet feeding stocker  142  to function as an engaging mechanism (as described later). In  FIG. 4 , the left-side sheet feeding stocker  142  is in the state of being pulled out forward (in a direction shown with an arrow a) for the sake of graphic presentation. 
     As shown in  FIG. 5 , a protrusion  145   p  in a shape of a quarter of a circle protruding to the left side and curved downward is integrally provided in the lower part of the conveyance door  145 . The conveyance door  145  is attached to the main body casing  101  (see  FIG. 1 ) by a hinge  146  so that it can be opened and closed with respect to the main body casing  101 . When the conveyance door  145  is in the state of being closed with respect to the main body casing  101  (in the state where the conveyance door  145  stands perpendicularly as shown in  FIG. 5 ), the protrusion  145   p  of the conveyance door  145  engages with a front side portion  148   f  of the horizontal conveyance unit  148  and functions as a locking mechanism for prohibiting the horizontal conveyance unit  148  from being pulled out forward from the main body casing  101 .  FIG. 6  shows the state corresponding to  FIG. 5  as seen from a diagonally upward side. In the state where the conveyance door  145  is opened with respect to the main body casing  101  (in the state where the conveyance door  145  is inclined in a direction shown with an arrow c) as shown in  FIG. 7 , engagement between the protrusion  145   p  of the conveyance door  145  and the front side portion  148   f  of the horizontal conveyance unit  148  is canceled so that the horizontal conveyance unit  148  is permitted to be pulled out forward from the main body casing  101 . Therefore, as shown in  FIG. 8 , users can pull out the horizontal conveyance unit  148  from the main body casing  101  to the front side (direction shown with an arrow b). 
     As described before, a plate-like protrusion  48   p  protruding to the left side is integrally provided at the left edge of the front door  48  of the horizontal conveyance unit  148 . Therefore, as seen from the above for example, in the state where the left-side and right-side sheet feeding stockers  142  and  143  and the horizontal conveyance unit  148  are housed in the main body as shown in  FIG. 9A , the protrusion  48   p  of the front door  48  of the horizontal conveyance unit  148  is in contact with the back side portion  42   b  of the front door  42  of the left-side sheet feeding stocker  142 . When users try to pull out the horizontal conveyance unit  148  to the front side (in the direction shown with the arrow b) in this state, the protrusion  48   p  of the front door  48  of the horizontal conveyance unit  148  engages with the back side portion  42   b  of the front door  42  of the left-side sheet feeding stocker  142  as shown in  FIG. 9B , so that the left-side sheet feeding stocker  142  is pulled out integrally with the horizontal conveyance unit  148 . It is to be noted that in  FIG. 9B , stationary members are shaded for easy understanding. 
     In this image forming apparatus, the following operations are executed with respect to the sheet feeding device. 
     First, during operation of the image forming apparatus, the front doors  42 ,  43  and  48  are closed to the main body casing  101  so that the left-side sheet feeding stocker  142 , the right-side sheet feeding stocker  143  and the horizontal conveyance unit  148  are in the state of being housed in the main body casing  101  as shown in  FIG. 10 . It is to be noted that in  FIG. 10  and later-described  FIG. 11 ,  FIG. 12  and  FIG. 13 , a side panel of the main body casing  101  is omitted for easy understanding. 
     When users wish to restock the left-side sheet feeding stocker  142  with paper sheets, the users pull the handle  42   a  of the front door  42  to the front side (in the direction shown with the arrow a) as shown in  FIG. 11 , and pull out the left-side sheet feeding stocker  142  forward from the main body casing  101 . In this state, users can easily load paper sheets onto the left-side sheet feeding stocker  142 . 
     Similarly, when users wish to restock the right-side sheet feeding stocker  143  with paper sheets, the users pull the handle  43   a  of the front door  43  to the front side (in the direction shown with an arrow d) as shown in  FIG. 12  and pull out the right-side sheet feeding stocker  143  forward from the main body casing  101 . In this state, users can easily load paper sheets onto the right-side sheet feeding stocker  143 . 
     It is to be noted that for restocking both the left-side and right-side sheet feeding stockers  142  and  143  with paper sheets at the same time, users pull handles  42   a  and  43   a  of the front doors  42  and  43  to the front side and pull out both the left-side and right-side sheet feeding stockers  142  and  143  forward from the main body casing  101 . In this state, users can easily load paper sheets onto both the left-side and right-side sheet feeding stockers  142  and  143 . 
     At the time of jamming relating to paper feed operation, it is predetermined as procedures of jam processing that the conveyance door  145  is first opened as shown in  FIG. 7 , and a jammed paper, if visible, is removed, or the horizontal conveyance unit  148  is pulled out forward if a jammed paper is invisible. Such procedures may be prescribed in a manual or may be presented to users by a device structured so that the procedures are displayed at the time of jam occurrence. 
     It is assumed herein that users try to pull out the horizontal conveyance unit  148  to the front side (in the direction shown with the arrow b) as shown in  FIG. 13  according to the procedures of the jam processing prescribed by the manual. In this case, since the conveyance door  145  is opened with respect to the main body casing  101 , engagement between the protrusion  145   p  of the conveyance door  145  and the front side portion  148   f  of the horizontal conveyance unit  148  is canceled so that the horizontal conveyance unit  148  is permitted to be pulled out forward from the main body casing  101  (see  FIG. 7 ). Consequently, when users try to pull out the horizontal conveyance unit  148  to the front side (in the direction shown with the arrow b) in this state, the protrusion  48   p  of the front door  48  of the horizontal conveyance unit  148  engages with the back side portion  48   b  of the front door  42  of the left-side sheet feeding stocker  142  as shown in  FIG. 13 , so that the left-side sheet feeding stocker  142  is pulled out integrally with the horizontal conveyance unit  148 . This enables users to easily remove jammed paper sheets while preventing paper sheet tear even when the paper sheets stop at a position lapping over both the left-side sheet feeding stocker  142  and the horizontal conveyance unit  148  at the time of jamming relating to paper feed operation. 
     Next, it is assumed that users try to pull out the horizontal conveyance unit  148  to the front side (in the direction shown with the arrow b) at the time other than jamming relating to paper feed operation (at the time of normal operation for example). In this case, since the conveyance door  145  is closed with respect to the main body casing  101 , the protrusion  145   p  of the conveyance door  145  engages with the front side portion  148   f  of the horizontal conveyance unit  148  so that the horizontal conveyance unit  148  is prohibited from being pulled out forward from the main body casing  101 . As a result, the horizontal conveyance unit  148  is prevented from being unnecessarily pulled out from the main body casing  101 . 
     In the above-mentioned embodiment, the protrusion  145   p  of the conveyance door  145  engages with or disengages from the front side portion  148   f  of the horizontal conveyance unit  148  in response to opening and closing of the conveyance door  145  with respect to the main body casing  101 , as a result of which pulling out the horizontal conveyance unit  148  from the main body casing  101  is permitted or prohibited (locked). Therefore, at the time of jamming relating to paper feed operation, users can unconsciously cancel locking mechanism ( 145   p ,  148   f ) with respect to the horizontal conveyance unit  148 . 
     It should be understood that the sheet feeding device of the invention is widely applicable not only to image forming apparatuses but also to various equipment having a conveyance system similar to that in the image forming apparatus  100 . 
     As is described above, a sheet feeding device in one aspect of the present invention comprises: 
     first and second sheet feeding stockers provided in a main body and placed side by side in a horizontal direction, wherein 
     sheets are taken out from the first sheet feeding stocker and conveyed through a horizontal conveyance unit provided above the second sheet feeding stocker, wherein 
     the respective first and second sheet feeding stockers can independently be pulled out forward from the main body in a direction intersecting with a sheet conveying direction in the horizontal conveyance unit, and wherein 
     an engaging mechanism is provided for engaging the horizontal conveyance unit and the first sheet feeding stocker so that the first sheet feeding stocker is pulled out integrally with the horizontal conveyance unit when the horizontal conveyance unit is pulled out forward from the main body. 
     In this sheet feeding device, the respective first and second sheet feeding stockers can independently be pulled out forward from the main body in a direction intersecting with a sheet conveying direction in the horizontal conveyance unit. Therefore, for restocking paper sheets, users can easily load sheets onto the first and second sheet feeding stockers in the state where the respective first and second sheet feeding stockers are pulled out independently or both of them are pulled out forward from the main body. At the time of jamming relating to paper feed operation, users are assumed to pull out the horizontal conveyance unit forward from the main body. In that case, an engaging mechanism engages the horizontal conveyance unit and the first sheet feeding stocker so that the first sheet feeding stocker is pulled out integrally with the horizontal conveyance unit. This enables users to easily remove jammed paper sheets while preventing paper sheet tear even when the paper sheets stop at a position lapping over both the first sheet feeding stocker and the horizontal conveyance unit at the time of jamming relating to paper feed operation. 
     In the sheet feeding device of one embodiment, the engaging mechanism includes a protrusion protruding horizontally from an edge of a front door of the horizontal conveyance unit so as to overlap with a back side portion of a front door of the first sheet feeding stocker. 
     The sheet feeding device of one embodiment comprises a locking mechanism which permits the horizontal conveyance unit to be pulled out forward from the main body at a time of jamming relating to paper feed operation while prohibiting the horizontal conveyance unit from being pulled out forward from the main body at a time other than jamming relating to paper feed operation. 
     In the sheet feeding device of this one embodiment, the horizontal conveyance unit is permitted to be pulled out forward from the main body at the time of jamming relating to paper feed operation. Therefore, users can easily pull out the horizontal conveyance unit forward from the main body together with the first sheet feeding stocker. As a result, users can easily remove jammed sheets while preventing sheet tear as mentioned before. At the time other than jamming relating to paper feed operation, the horizontal conveyance unit is prohibited from being pulled out forward from the main body by the locking mechanism. As a consequence, the horizontal conveyance unit is prevented from being unnecessarily pulled out from the main body. 
     The sheet feeding device of one embodiment comprises: 
     a door which can be opened and closed with respect to the main body, the door being provided in a region of a lateral surface of the main body which faces an end portion of the horizontal conveyance unit, wherein 
     the locking mechanism executes permitting or prohibiting operation according to opening and closing of the door with respect to the main body. 
     At the time of jamming relating to paper feed operation, jammed sheets tend to exist in a region of the lateral surface of the main body which faces an end portion of the horizontal conveyance unit. Accordingly, a door which can be opened and closed with respect to the main body is generally provided in this region to facilitate jam processing. At the time of jam processing, users first open the door, find out a jammed sheet, and try to remove the sheet. In this regard, in the sheet feeding device of this one embodiment, the locking mechanism executes permitting or prohibiting operation according to opening and closing of the door with respect to the main body. Therefore, when the door is opened with respect to the main body for jam processing, the horizontal conveyance unit is permitted to be pulled out forward from the main body. As a result, users can easily remove a jammed sheet while preventing sheet tear as mentioned before. At the time other than jamming relating to paper feed operation, the door is closed with respect to the main body, so that the locking mechanism prohibits the horizontal conveyance unit from being pulled out forward from the main body. As a consequence, the horizontal conveyance unit is prevented from being unnecessarily pulled out from the main body as described before. With this configuration, users can unconsciously unlock the locking mechanism at the time of jamming relating to paper feed operation. 
     It is to be noted that the door should preferably constitute a part of the conveying path for conveying the sheets. 
     In the sheet feeding device of one embodiment, the locking mechanism includes a protrusion which can engage with a front side portion of the horizontal conveyance unit, the locking mechanism being provided in the region of the lateral surface of the main body which faces the end portion of the horizontal conveyance unit. 
     In the sheet feeding device of one embodiment, the protrusion has a circular arc shape horizontally protruding from the region and curved downward. 
     An image forming apparatus in one aspect of the present invention comprises the sheet feeding device. 
     The image forming apparatus has the sheet feeding device, which enables users to easily remove jammed sheets while preventing sheet tear at the time of jamming relating to paper feed operation. 
     As is clear from the above, according to the sheet feeding device or the image forming apparatus of the invention, users can easily remove jammed sheets while preventing sheet tear at the time of jamming relating to paper feed operation. 
     The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.