Abstract:
The sheet stacking-aligning apparatus or the sheet processing apparatus includes a substantially horizontal stacking tray, a rear end aligning unit for aligning a rear end of a sheet bundle on the stacking tray, and a control unit for controlling an operation of the rear end aligning unit for aligning the sheet bundle when it is in an upstream position of the stacking tray, and the stacking tray is provided substantially horizontally. It is thus made possible to increase the stacking space, thereby increasing the number of stackable sheets and to achieve the alignment of the rear end of the sheet bundle with a simple configuration, thereby improving the stacking-aligning property of the sheet bundle on the stacking tray.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a sheet stacking-aligning apparatus for aligning and stacking sheets, a sheet processing apparatus provided with such sheet stacking-aligning apparatus, and an image forming apparatus provided with such sheet processing apparatus. In particular, the present invention provides a sheet stacking-aligning apparatus with an improved stacking-aligning ability for a sheet bundle, one that is capable of achieving a space saving, a cost reduction and an increase in the capacity of the number of stacked sheets, a sheet processing apparatus provided with such sheet stacking-aligning apparatus, and an image forming apparatus provided with such sheet processing apparatus. 
   2. Related Background Art 
   In an image forming apparatus such as a printing press, a copying apparatus or a printer, sheets S subjected to image formation in a main body of the image forming apparatus are temporarily stacked on a process tray  140  in a sheet processing apparatus  100 , and there are executed sheet post-processes such as alignment and stapling of the sheet S. Thereafter a bundle is discharged by bundle discharge means  108  onto a stacking tray  400  having an inclined stacking surface as shown in  FIG. 10 . The discharged sheets S move by its own weight on the inclined stacking surface of the stacking tray  400 , and rear ends (trailing edges) of the sheets are aligned on a rear end (trailing edge) aligning wall. The number of stacking sheets S is dependent on a vertically movable stroke of the stacking tray  400 . 
   Also in a sheet processing apparatus as shown in  FIG. 12 , a bundle of sheets S is conveyed by a gripper  401  of bundle discharge means to a box-shaped stacking tray  400  having a horizontal stacking surface and stacked therein. 
   Also in a sheet processing apparatus in which a stacking tray  400  has a conventional horizontal stacking surface as shown in  FIG. 13 , a rotation of a sheet returning paddle  501  causes the sheets S to be stacked with the rear ends thereof aligned. 
   However, in case of stacking sheets of low rigidity or showing a downward curl on the stacking tray  400  having a conventional inclined stacking surface as shown in  FIG. 10 , there may result a buckling of the sheets caused by a weight thereof because of a steep inclination, thereby deteriorating the aligning property. 
   Also in case of stacking stapled sheet bundles S on the stacking tray  400  having the conventional inclined stacking surface as shown in  FIG. 11 , a rear end of a sheet bundle S may catch on a staple of an already stacked sheet bundle S so that it cannot slide to a rear end aligning wall  70 , whereby the stacking property is deteriorated. 
   Also in the sheet processing apparatus as shown in  FIG. 12 , the gripper  401  is indispensable as the bundle discharge means, and a combination thereof with the box-shaped stacking tray  400  having a horizontal stacking surface renders the entire apparatus bulky and expensive. 
   Also in the sheet processing apparatus in which the stacking tray  400  has a horizontal stacking surface as shown in  FIG. 13 , the alignment by the sheet returning paddle  501  is effective only for the uppermost sheet, whereby the discharge of sheets in a bundle is not possible. 
   SUMMARY OF THE INVENTION 
   An object of the present invention is to improve stacking-aligning property for stacked sheet bundle with a simple configuration, and to increase a capacity for the number of stacked sheets while achieving downsizing of the apparatus. 
   For attaining the above-mentioned objective, a representative configuration of the present invention is featured by including stacking means which stacks sheets or sheet bundles, sheet rear end aligning means which achieves alignment by pressing a rear end of sheets or sheet bundles conveyed onto the stacking means, sheet conveying means which conveys sheets or sheet bundles onto the stacking means, and control means which actuates the sheet rear end aligning means at a timing when the rear end of the sheet or the sheet bundle, conveyed by the sheet conveying means, is positioned at an upstream side of the stacking means, thereby aligning the rear end of the sheets or the sheet bundles. 
   Also the above-mentioned configuration includes a processing tray for temporarily stacking sheets for a sheet post-process, wherein the sheet or the sheet bundle subjected to the post-process in the processing tray is conveyed by the aforementioned sheet conveying means to the stacking means. 
   As explained in the foregoing, the present invention allows for improvement of the sheet aligning properties even in cases where the stacking tray is made substantially horizontal, whereby a space corresponding to the inclination of the ray can be utilized for a vertical stroke, thus increasing a capacity of the number of sheets stackable on the stacking tray. Also a space saving and a cost reduction can be achieved since a box-shaped stacking tray or a gripper for bundle movement is not employed. 
   Also, since the stacking on the stacking trays is achieved with an alignment in the sheet conveying direction by conveying a sheet bundle until a rear end thereof reaches an upper end of a rear end aligning wall thereby causing the rear end to impinge on an upper end of a rear end reference wall, and pressing the rear end of the sheet bundle by the rear end aligning wall, whereby it is rendered possible to avoid positional aberrations of the front end and the rear end of the sheet bundle in the conveying direction and to improve the stacking and aligning of the sheet bundles on the stacking tray. 
   Further, since the stacking tray can be positioned with a smaller inclination, it is rendered possible to prevent a buckling phenomenon resulting from a weight of a bundle of sheets. 
   Further, in the present invention, as the rear end of a discharged sheet bundle is aligned to the already stacked sheet bundles, at an upstream side in the discharge direction, it is possible to prevent a positional aberration resulting from trapping of the rear end of the discharged sheet bundle by a staple of the already stapled and stacked sheet bundles. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic cross-sectional view showing the entire configuration of a sheet processing apparatus constituting first and second embodiments; 
       FIG. 2  is a plan view of a sheet stacking-aligning apparatus; 
       FIG. 3  is a cross-sectional view showing moving mechanisms for a rocking roller and an alignment member provided in a processing tray; 
       FIGS. 4A ,  4 B and  4 C are cross-sectional views showing functions of the rocking roller; 
       FIGS. 5A and 5B  are cross-sectional views showing functions of a return belt; 
       FIGS. 6A ,  6 B and  6 C are cross-sectional views showing a discharge operation for a sheet bundle; 
       FIGS. 7A ,  7 B and  7 C are cross-sectional views showing an aligning operation for a rear end of a sheet bundle in the first embodiment; 
       FIGS. 8A ,  8 B and  8 C are cross-sectional views showing an aligning operation for a rear end of a sheet bundle in the second embodiment; 
       FIG. 9  is a magnified view showing a moving mechanism for a rear end aligning wall; 
       FIG. 10  is a cross-sectional view showing the entire configuration of a conventional sheet processing apparatus; 
       FIG. 11  is a plan view of a conventional sheet stacking-aligning apparatus; 
       FIG. 12  is a cross-sectional view showing a sheet processing apparatus employing a conventional box-shaped horizontal stacking tray; 
       FIG. 13  is a cross-sectional view showing a sheet processing apparatus employing a horizontal stacking tray provided with a conventional sheet returning paddle mechanism; and 
       FIG. 14  is a block diagram of a sheet processing apparatus of the first and second embodiments. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   In the following there will be given a detailed description of an embodiment of the sheet stacking-aligning apparatus, sheet processing apparatus and image forming apparatus embodying the present invention, with reference to accompanying drawings. 
   (First Embodiment) 
   In the following, there will be given a detailed explanation on an embodiment of the image forming apparatus of the present invention, with reference to the accompanying drawings.  FIG. 1  is a cross-sectional view of a main body  30  of an image forming apparatus equipped with a sheet processing apparatus  1  constituting a first embodiment of the present invention,  FIG. 2  is a plan view of the sheet processing apparatus  1 , and  FIG. 3  is a cross-sectional view of the sheet processing apparatus  1 . 
   The following description will be given of an example of the sheet processing apparatus  1 , which is provided in the main body  30  of the image forming apparatus and under an original reading apparatus as shown in  FIG. 1 , and which temporarily stacks sheets S, discharged after image formation, to a process tray  40 , and, after post processes such as alignment and stapling, stacks and aligns the processed sheets S on a substantially horizontal stacking tray. 
   However, the present invention is also effective in a configuration in which the sheet stacking-aligning apparatus for aligning and stacking the sheets S, discharged after image formation from the main body  30  of the image forming apparatus, on the stacking tray  4  is directly connected to the main body  30  of the image forming apparatus without the process tray  40 , or in a configuration in which the aforementioned sheet processing apparatus  1  is mounted outside the main body  30  of the image forming apparatus. 
   Referring to  FIG. 1 , a numeral  1  indicates a sheet processing apparatus of the present invention mounted in the main body  30  of the image forming apparatus, and an automatic original reading apparatus  35  is mounted in an upper part of the main body  30  of the image forming apparatus. The image forming apparatus of the present invention is comprises the main body  30  of the image forming apparatus, the sheet processing apparatus  1  and the automatic original reading apparatus  35 , but the process tray  40  may be dispensed with in the sheet processing apparatus  1 . 
   In the main body  30  of the image forming apparatus, as shown in  FIG. 1 , an original is automatically supplied by the automatic original reading apparatus  35  to a reading position and an image is read by an image reading unit  36 . Then, based on read image information, a controller (not shown) sends a signal to a laser scanner unit  2  whereby a laser light is emitted. 
   The laser light is reflected by a rotating polygon mirror, further reflected by a mirror and irradiates a photosensitive drum  3  constituting image forming means of which surface is uniformly charged, thereby forming an electrostatic latent image. The electrostatic latent image on the photosensitive drum  3  is developed by a developing device  5 , and is transferred as a toner image onto a sheet S which is constituted by paper or an OHP sheet. 
   The sheet S is selectively advanced from sheet cassettes  31 ,  32 ,  33 ,  34  by pickup rollers  38 , constituting sheet feeding means, separated and fed one by one by separating means  37 , and, after correction of skewing by a pre-registration roller pair, advanced to a transfer position in synchronization with the rotation of the photosensitive drum  3 , whereby the toner image formed on the photosensitive drum  3  is transferred via a transfer belt  11  to the sheet S. 
   Thereafter the sheet S is guided to a paired fixing rollers  6 , and given heat and pressure by the paired fixing rollers  6  whereby the toner image transferred to the sheet S is permanently fixed thereon. The paired fixing rollers  6  are in contact respectively with an upper separating claw and a lower separating claw, whereby the sheet S is separated from the paired fixing rollers  6 . 
   The separated sheet S is conveyed by paired discharge rollers  7  of the main body to the exterior of the main body  30  of the image forming apparatus, and is guided to a sheet processing apparatus  1  connected to the main body  30  of the image forming apparatus. 
   Referring to  FIG. 1 , the sheet processing apparatus  1  is constituted by a process tray  40  constituting sheet stacking means positioned at an upstream side, and a stacking tray  4  provided substantially horizontally at a downstream side, and the sheet S discharged from the paired discharge rollers  7  of the main body  30  of the image forming apparatus is subjected to a post-process in the process tray  40  and is then stacked on the stacking tray  4 . 
   As shown in  FIGS. 2 and 3 , the sheet S discharged from the image forming apparatus  30  is discharged toward the stacking tray  4  by a discharge unit  8  constituted by a discharge roller  8   a  of the sheet processing apparatus  1  and an idler discharge roller  8   b , but, at a time when a rear end of the sheet S passes through the discharge unit  8 , the rear end of the sheet S is lowered by a rocking roller  50  and is pinched between the rocking roller (oscillating roller)  50  and an idler roller  71 . 
   Thereafter, the rocking roller  50  reversely rotates whereby the rear end of the sheet S is guided, in a direction opposite to the prior conveying direction, along a lower guide  61  to the process tray  40 , and an alignment in the sheet conveying direction and in the sheet transversal direction is executed for each sheet. 
   The alignment in the sheet conveying direction is achieved, by the weight of the sheet S obtained from the inclination angle of the process tray  40  and by a return belt  60 , by causing the sheet S to impinge on a rear end stopper  62  which is positioned at an end of the process tray  40  and constitutes sheet receiving means for receiving the sheet S on the process tray  40 , while the alignment in the sheet transversal direction is achieved by aligning plates  41 ,  42  which are operated by unshown control means (for example a rack and a pinion gear drive source). 
   In case a stapling mode is selected, a stapler unit  10  executes a stapling on an aligned sheet bundle S. The sheet bundle S thus subjected to a post-process is discharged and stacked on the stacking tray  4  by a counterclockwise rotation of the rocking roller  50 . 
   In the following a detailed description will be given on the configuration of the sheet processing apparatus  1 . 
   &lt;Rocking Roller (Oscillating Roller)&gt; 
   The function of the rocking roller  50  will be explained with reference to  FIGS. 2 ,  4 A,  4 B and  14 . The rocking roller (oscillating roller)  50  functions to press the rear end of the discharged sheet  2  and to drop the rear end portion of the sheet S onto the process tray  40 . 
   As shown in  FIGS. 4A ,  4 B, and  4 C, the rocking roller  50  is mounted on a rocking arm (oscillating arm)  51  which is capable of a vertical rocking motion about a rocking roller shaft  52 . A driving force is transmitted from a rocking arm drive motor  82  to a rocking arm shaft  53  through a rocking cam  54 , and a drive signal from a finisher CPU  79  is transmitted to the rocking arm drive motor  82  through a rocking arm drive motor driver  83  ( FIG. 14 ). A rotation of the rocking arm drive motor  82  causes the rocking arm  51  to execute a vertical rocking motion about the rocking roller shaft  52 , integrally with the rocking cam  54  (oscillating cam). The rocking arm  51  is provided with a rocking arm tension spring  55  for assisting an upward rocking motion. 
   The rocking roller  50  is connected to the rocking roller shaft  52  and the rocking roller drive motor  84  via a rocking timing belt  56  and a rocking pulley  57 , and rotates counterclockwise when a drive signal is transmitted from the finisher CPU  79  to a rocking roller drive motor  84  through a rocking roller drive motor driver  85 . 
   The rocking roller  50  has a home position not in contact with the sheet S discharged by the discharge unit  8  onto the process tray  40  ( FIG. 4A ). When the sheet S is discharged from the discharge unit  8 , the rocking arm  51  rotates counterclockwise by the rocking arm drive motor  82  about the rocking roller shaft  52 , thereby lowering the rocking roller  50  to press down the rear end of the sheet S by the rocking roller  50  onto the process tray  40  ( FIG. 4B ). 
   Then the rocking roller  50  forms a nip with the idler roller (following roller)  71  and rotates counterclockwise by the rocking roller drive motor  84 , thereby drawing in the sheet S until the rear end of the sheet S on the process tray  40  comes into contact with the return belt  60 . Thereafter the rocking roller  50  is elevated again to the home position, thereby preparing for a next sheet discharge ( FIG. 4C ). 
   &lt;Return Belt&gt; 
   As shown in  FIGS. 2 ,  5 A and  5 B, the return belt  60  is supported in a vertical direction by the discharge roller shaft  9 , and is normally so positioned as to be in contact with the sheet S on the process tray  4 . The return belt  60 , constituting at least a sheet conveying rotary member positioned perpendicularly to an impinging direction of the sheet S onto the sheet rear end stopper  62 , is constituted by a belt member  65  positioned between the sheet discharge roller  8   a  and a return belt pulley  64  supported by a housing  63  ( FIG. 3 ), and the belt member  65  conveys the sheet S toward the sheet rear end stopper  62  by a counterclockwise rotation of the discharge roller shaft  9  ( FIG. 5A ). 
   Also the return belt  60  is constructed so as to deflect in a direction of the thickness of the sheets S, according to the number of the sheets S stacked on the process tray  40  ( FIG. 5B ). 
   &lt;Bundle Discharge Means&gt; 
   An explanation will now be given of the bundle discharge means, with reference to  FIGS. 6A ,  6 B and  6 C. The return belt  60  draws in a last sheet S until it comes into contact with the rear end stopper  62 , and the rocking roller  50  is lowered under the drive of the rocking arm drive motor  84  and about the rocking roller shaft  52  until it comes into contact with the sheet bundle S ( FIG. 6A ), and, after forming a nip with the idler roller  71 , rotates clockwise to convey the sheet bundle S, aligned or stapled on the process tray  40 , until a rear end thereof reaches a vicinity of an upper end of a rear end aligning wall  70  and stops the sheet bundle in such position ( FIG. 6B ). 
   Thereafter the rocking roller  50  is separated from the sheet bundle S and returns to the home position ( FIG. 6C ). At the same time the rear end aligning wall  70  moves, about the cam rocking rotation shaft  73 , in a direction opposite to the sheet conveying direction by a cam  72  positioned under the rear end aligning wall  70 . 
   &lt;Alignment of Sheet Rear End&gt; 
   In the following there will be explained, with reference to  FIGS. 7A ,  7 B and  7 C, means for discharging the sheet bundle S from the process tray  40  onto the stacking tray  4  and aligning and stacking the sheet bundle thereon. As shown in  FIGS. 7A ,  7 B and  7 C, the rear end aligning wall  70  serves as an aligning wall for aligning the rear end of the sheet bundle S at the discharge and stacking of the sheet bundle S from the process tray  40  onto the stacking tray  4 . The rear end aligning wall  70  is placed in an alignment reference position by a biasing with a spring  12  and a contact with the cam  72  in a home position ( FIG. 3 ). 
   When a drive signal is transmitted from the finisher CPU  79  through a rear end aligning wall drive motor driver  86  to a rear end aligning wall drive motor  76  to cause a rotation thereof, the rear end aligning wall  70  exerts a rocking motion in the sheet conveying direction by the cam  72 , about the rocking rotation shaft  73  ( FIGS. 7B and 14 ). 
   In a state where the rear end of the sheet bundle S discharged by the bundle discharge means impinges on the upper end of the rear end aligning wall  70  ( FIG. 6B ), the rear end aligning wall  70  is retracted to the upstream side in the sheet conveying direction ( FIG. 6C ), thereby causing the rear end of the sheet bundle S to impinge on an inclined face of the rear end aligning wall  70  ( FIG. 7A ). Then, in the course of returning thus retracted rear end aligning wall  70  to the home position about the rocking rotation shaft, the rear end of the sheet bundle S is aligned by pressing by the rear end aligning wall  70 , whereby the sheet bundle S is stacked on the stacking tray  4  ( FIGS. 7B and 7C ). 
   In the present embodiment, the stacking tray  4  has a substantially horizontal stacking surface, but the sheet rear end aligning means also functions effectively when the sheet stacking surface is inclined, although it functions most effectively when the sheet stacking surface is substantially horizontal. Also the sheet stacking surface  4   a  is given a downward inclination angle of 18° or less toward the aforementioned sheet rear end aligning wall, thereby realizing a compactization of the apparatus while avoiding an interference between the rear end of a sheet bundle already stacked on the stacking tray  4  and a succeeding sheet bundle discharged from the process tray  40 . Also, in order to maintain the uppermost surface of the stacked sheet bundles S at a constant height, the stacking tray  4  is rendered vertically movable by unrepresented drive means. 
   (Second Embodiment) 
   In the following there will be explained a second embodiment of the image forming apparatus  3  of the present invention, wherein components equivalent to those in the foregoing first embodiment are represented by same numbers and will not be explained further. 
   In the following there will be given an explanation, with reference to  FIGS. 8A ,  8 B and  8 C, of means for discharging the sheet bundle S by parallel displacement of the rear end aligning wall  70  in the sheet conveying direction. As shown in  FIGS. 8A ,  8 B and  8 C, the rear end aligning wall  70  is provided with a rack gear  78  formed in the sheet conveying direction integrally with the rear end aligning wall  70 , and exerts a parallel displacement in the sheet conveying direction by a driving force transmitted from the rear end aligning wall drive motor  76  through a pinion gear  74  to the rack gear  78  which is supported on the other side by a rack supporting roller  77 . Also as shown in  FIG. 9 , a home position sensor  75  is provided for detecting the home position of the rear end aligning wall  70 , and an amount of the movement of the rear end aligning wall  70  is controlled by counting a number of pulses for the rear end aligning wall drive motor. 
   In a state where the rear end of the sheet bundle S is stopped at the upper end of the rear end aligning wall  70  ( FIG. 8A ), the rear end aligning wall  70  is moved in a parallel displacement toward the upstream side in the sheet conveying direction thereby dropping sheet bundle S onto the stacking tray  4  ( FIG. 8B ). In this state, since the rear end of the sheet bundle S is placed in an upstream position, in the sheet conveying direction, of the home position of the rear end aligning wall  70 , the rear end aligning wall  70  is further moved once toward the upstream side in the sheet conveying direction, then moved to the downstream side until it comes in contact with the rear end of the sheet bundle S and further moved to the home position of the rear end aligning wall  70 , thereby aligning the rear end of the sheet bundle S and achieving the stacking of the sheet bundle S on the stacking tray  4 .