Paper stacker for use with image forming apparatus

1. Field of the Invention

The present invention relates to a paper stacker for stacking papers with an image recorded thereon in such a state that each set of a predetermined number of papers is displaced or shifted by a given distance on one another which is designed to use with an image forming apparatus such as a copying machine, a printer, a facsimile and a composite machine thereof.

2. Description of the Prior Arts

There is an image forming apparatus, provided with a paper stacker for stacking a predetermined number of papers each with an image recorded thereon as a set in such a manner that each set is displaced or shifted by a given distance on one another. The sets of papers are stored in a state sectioned per set so as to be supplied to a post processing stage such as stapling, folding for book-binding, or the like.

In a conventionally proposed paper stacker, conveyance of supplied papers is stopped by a shift roller, and the papers are shifted together with the shift roller in a direction orthogonal to the paper conveyance direction, that is, in the lateral direction per each paper so as to be stacked.

However, in the above-mentioned paper stacker designed to shift the papers in the lateral direction with respect to their conveyance direction, subsequent papers cannot be fed during movement for shift and therefore the conveyance of papers has to be stopped intermittently in the shifting operation. Moreover, since the shifting operation in the lateral direction should be carried out by a shift roller pair, the shifting mechanism is extremely complicated. In addition, a problem arises in that it can hardly be used for image forming apparatus with a high copying speed, because there is a problem of inertia derived from the mass of the shift rollers.

Accordingly, the present invention has been achieved in view of the above-mentioned problems, and an object thereof is to provide a paper stacker for use with an image forming apparatus, and particularly such apparatus with a high copying speed.

In order to achieve the above-mentioned object, a paper stacker of the present invention comprises a paper conveying means for conveying paper with an image recorded thereon to a stacking position; a top end stopper arranged on an extreme forward position of a conveyance path of the paper in said stacking position for defining a top end position of the paper to be stacked; a paper receiving plate arranged below the paper conveyance path in the stacking position for receiving papers thereon in a shifted state; a rear end stopper arranged on a backward position of the paper conveyance path in the stacking position for defining a rear end position of the paper to be stacked; and a lifting means for moving up and down said paper receiving plate, wherein said top end stopper and said rear end stopper are movable in association with each other in the direction of the paper conveyance or vice versa alternately for every given number of papers to be stacked.

The top end stopper and/or the rear end stopper may be provided movably in the conveyance direction according to the paper size in the conveyance direction, or either one of the top end stopper or the rear end stopper may be provided movably so as to have a paper on the paper placing base abutted on the other one.

FIG. 1 shows the configuration of a paper stacker of the present invention; and

FIG. 2 shows an essential part of the paper stacker of FIG. 1 in an enlarged scale.

The present invention will now be explained with reference to the accompanied drawings.

FIG. 1 shows the entirety of a paper stacker 100 of the present invention, and FIG. 2 shows an essential part of the inside of the paper stacker 100 in an enlarged scale. The stacker 100 shown in these drawings is designed to receive a paper S with an image formed thereon by an image forming apparatus not shown at an inlet 101 and selectively to stack the papers S as each set or to simply discharge the papers S onto a discharged paper tray 103 .

The paper S introduced through the inlet 101 into the stacker 100 is conveyed by conveyance rollers 105 and 107 and reaches to a conveyance path changeover means 109 . The paper S is discharged directly onto the discharged paper tray 103 or stacked in the stacker 100 by means of the conveyance path changeover means 109 .

In case it is selected that the paper S is discharged directly onto the discharged paper tray 103 , the conveyance path changeover means 109 is actuated to close the conveyance path toward an inlet roller 121 . As a result, the paper S is conveyed by conveyance rollers 111 , 113 , 115 and 117 and discharged onto the discharged paper tray 103 where the papers S are stacked on one another.

In contrast, in case it is selected that the paper S is stacked in the stacker 100 , the conveyance path changeover means 109 is actuated to close the conveyance path toward the conveyance roller 111 as shown in FIG. 2 . As a result, the paper S passes the inlet roller 121 to be introduced into the stacker 100 and reaches the end part of circulating means 123 composed of a belt which is rotatable in a direction shown by an arrow A. The circulating means 123 is provided on its opposite positions with a pair of paper gripping means 125 which are separate equidistant from each other. When the paper S reaches the end of the circulating means 123 , the paper S is gripped by the paper gripping means 125 by its top end and conveyed by the circulating means 123 leftward as shown by an arrow A in FIG. 2 . The paper gripping means 125 comprises a grasping member made of hard rubber which is partly pressed with a weak force against 123 by a wire spring.

On both lateral sides of the circulating means 123 are provided a set of reciprocating means 124 composed of a belt which is moved reciprocatively in a paper conveying direction by a driving mechanism such as servo motor and a pulley. A top end stopper 127 as hatched in FIG. 2 is provided at a position close to an forward extreme end (leftmost end in the drawing) on each reciprocating means 124 . The driving mechanism is controlled by a controller including a computer installed in the image forming apparatus to move the reciprocating means 124 in a direction indicated by an arrow B or vice versa so that the top end stopper 127 is moved to desired position. The position of the top end stopper 127 is determined in terms of a size in the feeding or conveyance direction of the paper S on use, and the size of the paper S in its conveyance direction is determined by the size of paper S and whether it is to be conveyed with its longer edge facing front or with its shorter edge facing front. Specifically, the size of the paper in its conveyance direction is determined in terms of selection of the tray or the like at the time of forming an image by the image forming apparatus. Upon determination of the paper size and the conveyance direction thereof, the position of the top end stopper 127 is determined as well. Two or more top end stoppers 127 may be provided widthwise of the paper S, because they are small and light in comparison with the conventional shift roller unit, and therefore force needed for movement of the top end stoppers is small and the inertial is smaller, and thus it hardly arises a problem.

When the rear end of the paper S passes the nip position of the inlet roller 121 , the rear end of the paper S is released so that the paper S may drop onto a paper receiving plate 131 which is arranged under the travelling path of the paper gripping means 125 . This position is called a stacking position.

The top end of the paper S proceeds together with the paper gripping means 125 , and when the top end of the paper S gripped by the paper gripping means 125 , or the paper gripping means 125 itself collides against the top end stopper 127 in the stacking position, the grip of the paper gripping means 125 is released so that the top end of the paper S drops onto the paper receiving plate 131 .

The paper receiving plate 131 which is arranged below the paper conveyance path in the stacking position is adapted to be elevated or lowered by an elevating device 133 . As the paper S is stacked on the paper receiving plate 131 successively, the uppermost surface of the papers S on the paper receiving plate 131 is raised gradually. Therefore, the paper receiving plate 131 is lowered gradually by the elevating device 133 by the thickness of the stacked papers S. More particularly a sensor (not shown) is provided to detect the height of the uppermost paper S on the paper receiving plate 131 so as to control the elevating device 133 such that a constant level of the stacked papers S is kept. However, in case it is difficult to control the height of the paper S per one sheet strictly due to the sensitivity of the sensor or the elevation accuracy of the elevating device 133 , the height may be adjusted per several sheets of paper.

A rear end stopper 129 for determining the rear end position of the paper S is provided close to the rear end (close to the rightmost end of the conveyance path in FIG. 2 ). The rear end stopper 129 is mounted on the frame or the like of the stacker 100 , and is driven to take two positions along the conveyance direction, one of which is shown by a solid line but the other 129 ′ of which is shown by a chain line is FIG. 2 . A driving mechanism for the rear end stopper 129 may comprise a servo motor and a pulley, a belt or the like, and can drive the servo motor to move the rear end stopper 129 to desired two positions. The rear end stopper 129 may be constituted by rod members that are actuated by a solenoid to raise at the position shown by the solid line or at the position shown by the chain line in FIG. 2 . A distance between these two positions that the rear end stopper 129 takes is equal to a shift distanced of the sets of papers stacked on the paper receiving plate 131 .

It is to be noted a distance between the top end stopper 127 and the rear end stopper 129 is selected to be larger by a given distance (for example 10 mm) than the actual length of the paper to be stacked in its conveyance direction for the below mentioned.

The elevating device 133 actuates the paper receiving plate 131 to lower slightly and gradually so that the paper S can fall onto the paper receiving plate 131 between the top end stopper 127 and the rear end stopper 129 .

While a paper S falls onto the paper receiving plate 131 , the top end stopper 127 is caused to move in the direction of the rear end stopper 129 so as to have the rear end of the paper S butt against the rear end stopper 129 . At this time, the widthwise position of the paper S is confined from its both sides by paper width aligning means 135 , whereby the paper S is placed in position on the paper receiving plate 131 as desired.

The size of the paper S in its conveyance direction is known in advance from the size of the paper size and its conveyance direction. Therefore, the top end stopper 127 is moved to such a position that the top end stopper 127 has a distance from the rear end stopper 129 that is equal to the size of the paper in its conveyance direction so that the top end stopper 127 can push the paper S on the paper receiving plate 131 against the rear end stopper 129 .

The above-mentioned operation is repeated until a given number of the papers S for given sets of papers are stacked on the paper receiving plate 131 . The given number of papers constitutes a set of recorded papers. The number of papers for one set can be known as for example, the number of documents to be counted by an automatic document feeding device provided in the image forming apparatus. Alternatively, the number of papers for one set can preliminarily be input manually in the image forming apparatus by an operator.

In the above-mentioned embodiment, the paper is stacked in place by shifting the top end stopper 127 toward the rear end stopper 129 , but the rear end stopper 129 may be shifted toward the top end stopper 127 for the same purpose.

When the papers for one set are stacked at the same position on the paper receiving plate 131 , both of the top end stopper 127 and the rear end stopper 129 are shifted in the same direction by the same distance in the conveyance direction of the paper S. For example, in FIG. 2 , the top end stopper 127 is shifted to the position 127 ′ shown by the chain line, and the rear end stopper 129 is shifted to the position 129 ′ shown by the chain line. Thereafter, in the same manner as mentioned above, another set of papers S is stacked on the paper receiving plate 131 . Repeating the same operation thereafter, the papers S are stacked on one another in the stacker 100 in such a state that each set of papers S is shifted in the paper conveyance direction.

In the embodiment as above described, two paper gripping means 125 are provided on the circulating means 123 , but more than two paper gripping means may be provided on the circulating means 123 according to designing of the paper stacker.

As heretofore explained, according to the present invention, a paper stacker comprises a paper conveying means for conveying paper with an image recorded thereon to a stacking position; a top end stopper arranged on an extreme forward position of a conveyance path of the paper in said stacking position for defining a top end position of the paper to be stacked; a paper receiving plate arranged below the paper conveyance path in the stacking position for receiving papers thereon in a shifted state; a rear end stopper arranged on a backward position of the paper conveyance path in the stacking position for defining a rear end position of the paper to be stacked; and a lifting means for moving up and down said paper receiving plate, wherein said top end stopper and said rear end stopper are movable in association with each other in the direction of the paper conveyance or vice versa alternately for every given number of papers to be stacked.

Therefore the papers each with an image recorded thereon can be stacked only by shifting the top end stopper and the rear end stopper in the conveyance direction so that the stacker configuration can be extremely simplified and the paper stacker can be applied to an image forming apparatus of a high speed.

Moreover, the surface for conveying the papers and the surface for allotting the papers on the stacker are different in the paper stacker according to the invention and therefore the paper conveyance need not be stopped during the paper allocation. This is advantageous for achieving a high speed stacking.

Since either one of the top end stopper or the rear end stopper is provided movably so as to have a paper on the paper placing plate abutted on the other one, the papers to be stacked can be positioned accurately as required.