Abstract:
A double-sided image forming device comprises a double-side operation unit. The double-side operation unit includes a sheet reversing unit including a switchback conveying path for reversing a front side and a back side of a sheet conveyed from an image forming unit, and a reconveying path for reconveying the sheet to the image forming unit so as to form an image on the back side. The switchback conveying path has a length smaller than a length of a conveyable maximum-size sheet. The double-side operation unit can slide from/toward a body of the double-sided image forming device in a direction perpendicular to a direction of conveying the sheet. A rear end guide is further provided in the switchback conveying path so as to guide a rear end of a large-size sheet.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to a double-sided image forming device, and more particularly, to a double-sided image forming device, such as a copying machine, a printer, or a facsimile apparatus, having a double-side operation unit that forms an image on a sheet fed thereto, and reverses the sheet so as to cause an image to be formed on a reverse side. 
     2. Description of the Related Art 
     To begin with, a description will be given of a sheet conveying operation of a double-side operation unit included in a conventional double-sided image forming device. 
     FIG. 1 is an illustration outlining the double-side operation unit included in the conventional double-sided image forming device. As shown in FIG. 1, a sheet having an image formed on one side enters from a fixing unit of an image forming unit provided in a body of the image forming device into a sheet reversing unit of the double-side operation unit. The sheet is temporarily contained in a switchback conveying path  2  via a reversibly rotatable switchback roller  1 . Then, the switchback roller  1  rotates reversely so as to send the sheet to a reverse roller  3 . The reverse roller  3  turns the sheet by 180° toward a horizontal conveying path (a reconveying path)  5  provided underneath. The horizontal conveying path  5  comprises a plurality of horizontal conveying rollers  4  arranged at intervals corresponding to a length of a minimum-size sheet, and transfers the sheet to a relay roller  6  provided further downstream. Then, the sheet returns to the image forming unit provided in the body of the image forming device so that an image is formed on the other side of the sheet. 
     Next, a description will be given of an operation of conveying a maximum-size sheet. FIG.  2 A and FIG. 2B are illustrations explaining the operation of conveying a maximum-size sheet in a conventional double-side operation unit. 
     In the double-side operation unit shown in FIG. 2A, the switchback conveying path  2  has a length L smaller than a length L Pmax  of the maximum-size sheet so that the body of the image forming device occupies little space. Upon conveying the maximum-size sheet in the double-side operation unit, a rib  7  is provided as shown in FIG. 2B so as to bring a rear end of the sheet to a refuge space upward. 
     However, drawing out the double-side operation unit in a direction perpendicular to the direction in which the sheet is conveyed (i.e., toward the foreground of FIG.  2 B), requires a space  8  occupied by the double-side operation unit as indicated by a dashed line in FIG. 2B, which is a drawback for the body of the image forming device to occupy little space (to be thinned down). 
     SUMMARY OF THE INVENTION 
     It is a general object of the present invention to provide an improved and useful double-sided image forming device in which the above-mentioned problems are eliminated. 
     A more specific object of the present invention is to provide a double-sided image forming device which can minimize a space occupied by a double-side operation unit by adopting simple structures so that the double-sided image forming device occupies little space (is thinned down). 
     In order to achieve the above-mentioned objects, there is provided according to the present invention a double-sided image forming device comprising a double-side operation unit including a switchback conveying path having a length smaller than a length of a maximum-size sheet, and a movable rear end guide guiding a rear end of a large-size sheet. 
     According to the present invention, a space occupied by the double-side operation unit upon being drawn out from a body of the double-sided image forming device can be reduced. Consequently, the double-sided image forming device occupies little space. 
     Additionally, the rear end guide is turnable in accordance with a drawing and a setting of the double-side operation unit. A turning angle of the rear end guide is determined by a positioning member provided on a board of the body of the double-sided image forming device and a stopper provided on a side surface of the double-side operation unit. This simple arrangement enables the double-sided image forming device to occupy little space. 
     Further, the turning angle of the rear end guide can be varied continuously by indefinite steps by mounting a dial member on a turning axle of the rear end guide and providing a conical stopper on the side surface of the double-side operation unit. The present arrangement eliminates variations in dimensional tolerances of components composing the double-sided image forming device so as to realize an optimal sheet conveyance in the double-sided image forming device. 
     Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an illustration outlining a double-side operation unit included in a conventional double-sided image forming device; 
     FIG.  2 A and FIG. 2B are illustrations explaining an operation of conveying a maximum-size sheet in a conventional double-side operation unit; 
     FIG. 3 is an illustration outlining a double-side operation unit included in a double-sided image forming device according to the present invention; 
     FIG. 4A is an illustration of an operation of a rear end guide shown in FIG. 3 upon drawing out the double-side operation unit; 
     FIG. 4B is an illustration of an operation of the rear end guide upon setting the double-side operation unit; 
     FIG. 5 is a plan view of the double-side operation unit shown in FIG.  4 A and FIG. 4B; 
     FIG. 6A is a sectional view illustrating an operation of the rear end guide upon drawing out the double-side operation unit; 
     FIG. 6B is a sectional view illustrating an operation of the rear end guide upon setting the double-side operation unit; 
     FIG. 7A is a plan view of the double-side operation unit in which a turning angle θ of the rear end guide is varied to a turning angle θ1; 
     FIG. 7B is a plan view of the double-side operation unit in which the turning angle θ of the rear end guide is varied to a turning angle θ2; 
     FIG. 8A is a sectional view of the rear end guide upon drawing out the double-side operation unit; 
     FIG. 8B is a sectional view of the rear end guide upon setting the turning angle θ1; 
     FIG. 8C is a sectional view of the rear end guide upon setting the turning angle θ2; 
     FIG. 9 is an illustration showing details of a part where a stopping ring shown in FIG.  7 A and FIG. 7B is mounted; 
     FIG. 10 is a plan view of the double-side operation unit in which the turning angle θ of the rear end guide can be varied continuously by indefinite steps; and 
     FIG. 11 is an illustration showing details of a part where a dial member shown in FIG. 10 is mounted on a turning axle shown in FIG.  10 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A description will now be given, with reference to the drawings, of embodiments according to the present invention. 
     FIG. 3 is an illustration outlining a double-side operation unit included in a double-sided image forming device according to the present invention. As shown in FIG. 3, the double-side operation unit according to the present invention comprises the switchback roller  1 , the switchback conveying path  2 , the reverse roller  3 , the horizontal conveying rollers  4 , the horizontal conveying path  5 , and the relay roller  6 , as does the conventional double-side operation unit shown in FIG.  1 . Also, the double-side operation unit according to the present invention performs the same sheet conveying operation as does the conventional double-side operation unit. Also, the switchback conveying path  2  has the length L smaller than the length L Pmax  of the maximum-size sheet. 
     The double-side operation unit according to the present invention comprises a movable rear end guide  9  as means for bringing the maximum-size sheet to a refuge space beyond the switchback conveying path  2 , in place of the rib  7  provided in the conventional double-side operation unit shown in FIG.  2 B. The rear end guide  9  springs up to a position A upon setting the double-side operation unit, and withdraws to a position B upon drawing out the double-side operation unit in a direction perpendicular to the direction in which the sheet is conveyed (i.e., toward the foreground of FIG.  3 ). Accordingly, drawing out the double-side operation unit according to the present invention only requires a space  10  occupied by the double-side operation unit as indicated by a dashed line in FIG. 3, the space  10  being smaller than the space  8  occupied by the conventional double-side operation unit shown in FIG.  2 B. Consequently, this structure reduces a space occupied by a body of the image forming device. 
     The rear end guide  9  is turnable in accordance with the drawing and the setting of the double-side operation unit. Mechanisms for turning the rear end guide  9  include a mechanism using a solenoid to detect the setting of the double-side operation unit and turn the rear end guide  9  in accordance with the setting. 
     Next, a description will be given of other mechanisms for turning the rear end guide  9 . 
     FIG. 4A is an illustration of an operation of the rear end guide  9  upon drawing out the double-side operation unit. FIG. 4B is an illustration of an operation of the rear end guide  9  upon setting (inserting) the double-side operation unit. 
     The rear end guide  9  is provided on a double-side operation unit  13 , with a turning axle  9   a  functioning as a fulcrum. Additionally, a projection  9   b  is provided on the rear end guide  9 . The projection  9   b  comprises an elastic member  14 , such as a plate spring. 
     A positioning member  11  is provided on a board  12  of the body of the double-sided image forming device so as to position the double-side operation unit  13  in a vertical direction. The rear end guide  9  is turned by the positioning member  11  contacting the elastic member  14 . Upon setting the double-side operation unit  13 , the positioning member  11  is inserted into a long hole  15  formed in a side surface of the double-side operation unit  13 , and contacts the elastic member  14  so as to turn the rear end guide  9  in a direction indicated by an arrow C, as shown in FIG.  4 B. Upon drawing out the double-side operation unit  13 , the elastic member  14  returns to an original position thereof so that the rear end guide  9  falls down, as shown in FIG.  4 A. 
     A turning angle of the rear end guide  9  is set as follows. 
     FIG. 5 is a plan view of the double-side operation unit shown in FIG.  4 A and FIG.  4 B. FIG. 6A is a sectional view illustrating the operation of the rear end guide  9  upon drawing out the double-side operation unit. FIG. 6B is a sectional view illustrating the operation of the rear end guide  9  upon setting the double-side operation unit. 
     A turning angle θ of the rear end guide  9  in the direction indicated by the arrow C is set by a stopper  16 . As shown in FIG. 6B, the positioning member  11  and the elastic member  14  contact each other at a point D. The rear end guide  9  turns so that the projection  9   b  contacts the stopper  16  at a point E so as to position the rear end guide  9 . In this course, the elastic member  14  elastically shrinks by (δ1-δ2) so as to enable a sure contact of the projection  9   b  and the stopper  16  at the point E. Additionally, the elastic shrinkage of the elastic member  14  compensates variations in dimensional tolerances of the heretofore-mentioned components so as to secure an accuracy of the turning angle θ of the rear end guide  9 . 
     Additionally, the turning angle θ of the rear end guide  9  can be made variable by the following arrangement. 
     FIG.  7 A and FIG. 7B are plan views of the double-side operation unit in which the turning angle θ of the rear end guide  9  is variable. Specifically, FIG. 7A illustrates a position of the rear end guide  9  upon setting a turning angle θ1. FIG. 7B illustrates a position of the rear end guide  9  upon setting a turning angle θ2. FIG. 8A is a sectional view of the rear end guide  9  upon drawing out the double-side operation unit. FIG. 8B is a sectional view of the rear end guide  9  upon setting the turning angle θ1. FIG. 8C is a sectional view of the rear end guide  9  upon setting the turning angle θ2. 
     In the present arrangement, the rear end guide  9  can slide in directions indicated by a double-pointed arrow shown in FIG. 7 k . Additionally, two grooves are formed in the turning axle  9   a  at an end portion (right in FIG.  7 A and FIG. 7B) opposite to an end where the positioning member  11  contacts the elastic member  14 . Further, a stepped stopper  17  composed of two steps of cylindrical projections is provided on the side surface of the double-side operation unit  13  in place of the stopper  16 . In this arrangement, the number of the grooves formed in the turning axle  9   a  and the number of the steps composing the stepped stopper  17  are not limited to two, but may be more than two. 
     In FIG. 7A, the rear end guide  9  is arranged at such a position that the projection  9   b  contacts the larger-diameter cylindrical projection of the stepped stopper  17 . A positioning of the rear end guide  9  in the sliding directions thereof is performed by inserting a stopping ring  18  into the outer groove formed in the turning axle  9   a.    
     FIG. 9 is an illustration showing details of a part where the stopping ring  18  is mounted. An axle bearing  13   a  formed in the other side surface of the double-side operation unit  13  accepts the outer groove formed in the turning axle  9   a  passed through and supported on a hole  13   b  of a supporting board. The stopping ring  18  is fit into the axle bearing  13   a  so as to fix the turning axle  9   a . In this state, a turning of the rear end guide  9  is stopped at a point G such that the turning angle becomes θ1, as shown in FIG.  8 B. 
     In FIG. 7B, the rear end guide  9  is slid toward right (in the figure) to such a position that the projection  9   b  contacts the smaller-diameter cylindrical projection of the stepped stopper  17 . The axle bearing  13   a  accepts the inner groove formed in the turning axle  9   a , and the stopping ring  18  is fit into the axle bearing  13   a  so as to fix the turning axle  9   a . In this state, a turning of the rear end guide  9  is stopped at a point H such that the turning angle becomes θ2, as shown in FIG.  8 C. 
     The above-described arrangement enables the turning angle θ of the rear end guide  9  to be varied arbitrarily with ease. Accordingly, the present arrangement can secure a stacking space for a still larger-size sheet, and also can secure an allowance for a curling paper, according to requirements on each occasion. Consequently, the present arrangement increases a general-purpose property of the double-side operation unit  13  per se. 
     Further, the following arrangement enables the turning angle θ of the rear end guide  9  to be varied continuously by indefinite steps. 
     FIG. 10 is a plan view of the double-side operation unit in which the turning angle θ of the rear end guide  9  can be varied continuously by indefinite steps. The rear end guide  9  can slide in directions indicated by a double-pointed arrow shown in FIG. 10. A positioning of the rear end guide  9  in the sliding directions thereof is performed by a dial member  20  mounted on the turning axle  9   a  at an end (right in FIG.  7 A and FIG. 7B) opposite to an end where the positioning member  11  contacts the elastic member  14 . 
     FIG. 11 is an illustration showing details of a part where the dial member  20  is mounted on the turning axle  9   a . A male screw is formed on the turning axle  9   a , and a female screw is formed in a through hole of the dial member  20 , so as to together form a screw structure fixing the turning axle  9   a  borne by the axle bearing  13   a . Additionally, an outer peripheral surface  20   a  of the dial member  20  has a nonskid form such as grooves. Accordingly, the rear end guide  9  can slide continuously by indefinite steps in accordance with revolutions of the dial member  20  in directions indicated by a double-pointed arrow F. 
     A conical stopper  19  composed of a conical projection is provided on the side surface of the double-side operation unit  13  in place of the stepped stopper  17 . In the present arrangement, a contact point J between the projection  9   b  of the rear end guide  9  and the conical stopper  19  can be shifted continuously by indefinite steps in accordance with above-described indefinite-step slide of the rear end guide  9 . Accordingly, the turning angle θ of the rear end guide  9  can be adjusted finely by indefinite steps. Therefore, this arrangement enables an adjustment of varying angles resulting from variations in dimensional tolerances of the heretofore-mentioned components so as to realize an optimal sheet conveyance. 
     The present invention is not limited to the specifically disclosed embodiments, and variations and modifications may be made without departing from the scope of the present invention. 
     The present application is based on Japanese priority application No. 2001-122170 filed on Apr. 20, 2001, the entire contents of which are hereby incorporated by reference.