EP0421173A2

EP0421173A2 - Paper stacking arrangement

Info

Publication number: EP0421173A2
Application number: EP90117792A
Authority: EP
Inventors: Fritz Dietiker
Original assignee: Printronix LLC
Current assignee: Printronix LLC
Priority date: 1989-10-06
Filing date: 1990-09-15
Publication date: 1991-04-10
Also published as: CA2026029A1; EP0421173A3

Abstract

In a paper stacking arrangement in which a length of prefolded printer paper (16) with series of spaced-apart apertures (26) adjacent the opposite edges (28; 30) thereof is driven through a printer (10) by opposite tractor drives (12; 14) and then pulled from the printer (10) by paper-pulling rollers (74; 84) and then dropped into a paper basket (52) where the paper (16) folds to form a stack (63), a paper ironing mechanism (82) presses the paper (16) flat at the opposite series of apertures (26) prior to stacking to avoid paper jams and to provide a flatter stack of the paper (16) within the paper basket (52). Portions of the edges (38) of the apertures (26) in the paper (16) which are often bent out of the plane of the paper (16) by the pins (36) of the tractor drive (12, 14) are ironed flat by the paper ironing mechanism (82) which includes an arrangement of rollers (74, 84) disposed on opposite sides of the paper (16) at the series of apertures (26) and biased toward one another.

In a preferred embodiment of a paper ironing mechanism (82), the paper pulling rollers (74) of an arrangement for pulling the length of paper (16) out of the printer (10) are disposed on one side of the paper (16) at the opposite series of apertures (26). Idler rollers (84, 90) disposed on the opposite side of the paper (16) are biased against the paper (16) and the opposite paper puller rollers (74) by leaf springs (86) on which the idler rollers (84, 90) are rotatably mounted.

Description

Background of the Invention

1. Field of the Invention

The present invention relates to arrangements in which paper is stacked upon being advanced through a printer, and more particularly to paper stacking arrangements in which a length of prefolded printer paper having series of spaced-apart apertures adjacent the opposite edges thereof is advanced through a printer by opposite tractor drives and then stacked by folding within a paper basket.

2. History of the prior art

It is well known in the case of dot matrix line printers as well as other types of printers used in computer systems to advance a length of printer paper through the printer using opposite tractor drives. Such tractor drives typically have moving belts with pins thereon which extend into series of spaced-apart apertures adjacent the opposite edges of the paper. The length of paper is typically fan-folded such that page-sized portions are folded in alternating directions and the paper forms a stack in this fashion. Paper from the stack is unfolded as it is fed upwardly through the printer by the opposite tractor drives. At the opposite side of the printer, a paper pulling mechanism may be employed to assist in pulling the paper out of the printer as the paper is lowered into and folded within a paper basket so as to reform the stack of paper.
As the stack of paper is formed within the paper basket, the opposite sides of the stack tend to build up at a greater rate than the center of the stack. This is due to the presence of the apertures adjacent the opposite edges of the paper as well as to the folds in the paper. Because of this the paper tends to stack less compactly at the sides of the stack than at the center of the stack.
Because the opposite sides of the paper stack tend to build up more rapidly than the center of the stack, stacking difficulties begin to occur as the stack builds up. The problem is accentuated in the case of light weight paper such as 15 pound paper which has a thickness of approximately 0.003 inch and which may have as many as 3,000 folded sheets within a single box of paper. As stacking of the paper continues, a point is reached at which the concave configuration at the top of the stack may make continued stacking of the paper extremely difficult or impossible. Paper jams may occur as a result. Paper jams are a particular problem in those instances in which paper stacking takes place without an operator being present. If a paper jam and the resulting improper stacking which follows continue unnoticed, the resulting task of then stacking the paper by hand can be enormous.
A further problem in stacking the paper within the paper basket lies in the occasional tendency of an edge of the paper to momentarily catch on one or more of the apertures in the paper as the stacking process takes place. This often results in the paper jamming or otherwise failing to continue to stack properly.
One measure commonly employed in an effort to facilitate orderly stacking of the paper is to provide a "tent" at the bottom of the paper basket. Such a tent consists of a raised portion at a central region of the bottom of the paper basket adjacent the center of the paper stack. The raised portion or tent has the effect of initially elevating the central portion of the paper stack relative to the opposite sides thereof, in order to retard the buildup of the opposite sides relative to the central portion. However, it has been found that even with a tent present at the bottom of the paper basket, the paper buildup may be such that jamming occurs. This is particularly so in the case of light weight paper which has a larger number of sheets in a stack of given size. There is also the continuing danger that an edge of the paper may catch on one or more of the apertures in the paper so as to create a jam condition.
Accordingly, it would be advantageous to provide an improved paper stacking arrangement. It would be particularly advantageous to provide an improved paper stacking arrangement in which the tendency of the paper stack to build up at the opposite sides relative to the central portion is minimized. It would still further be advantageous to provide an improved paper stacking arrangement in which the problem of a paper edge catching on one or more of the apertures in the paper is minimized or eliminated.

Brief Summary of the Invention

The foregoing and other objects and advantages are accomplished in accordance with the invention by a paper stacking arrangement having a paper ironing mechanism which irons and thereby flattens the opposite edges of the paper at the series of apertures. The nature of fan-folded printer paper is such that the edges of the apertures are usually serrated. As the paper passes through the opposite tractor drives in the printer, the pins of the tractor drives enter the apertures to assist in pulling the paper along. The pins are typically of slightly larger diameter at their base than the diameter of the apertures in the paper in order to provide a relatively snug fit of the pins within the apertures. Consequently the serrations at the aperture edges tend to be bent away from or out of the plane of the paper. This becomes particularly accentuated at the "upstream" portion of each aperture where the force of the pin on the paper is primarily exerted.
Bending of the serrated edges of the apertures out of the plane of the paper is a major cause of uneven buildup of the paper stack as it is formed. The bent serrated edges are also a major cause of an edge of the paper catching one or more of the apertures as the paper is stacked.
In accordance with the invention the opposite edges of the paper at the series of apertures are ironed or pressed flat so as to restore the serrated edges of the apertures to the plane of the paper. This results in improved stacking of the paper and less tendency for the paper to catch one of the edges thereof in an aperture as stacking takes place.
The opposite edges of the paper are ironed in accordance with the invention by biasing one or more members disposed on one side of the paper at the opposite edges of the paper against one or more members disposed on an opposite side of the paper. The members disposed on either side of the paper may comprise one or more rollers so as to permit advancement of the paper while at the same time squeezing or pressing the paper flat at the apertures.
In a preferred embodiment of a paper stacking arrangement according to the invention, a pair of paper pulling rollers which form part of a mechanism for pulling paper out of a printer and into a paper basket also form part of a paper ironing mechanism. The paper pulling rollers are disposed against one side of the paper at the series of apertures adjacent the opposite edges of the paper. Idler rollers disposed against the paper on the opposite side thereof are biased so as to press the opposite edges of the paper at the apertures against the paper pulling rollers. The idler rollers may be rotatably mounted on leaf springs coupled to a common mounting member and operative to bias the idler rollers against the paper and the paper pulling rollers on the opposite side of the paper.

Brief Description of the Drawings

A better understanding of the invention may be had by reference to the following description, taken in conjunction with the accompanying drawings, in which:

Fig. 1 is a perspective view of a printer having opposite tractor drives for advancing a length of print paper therethrough;
Fig. 2 is a detailed perspective view of one of the tractor drives of Fig. 1;
Fig. 3 is an enlarged plan view of an edge portion of the length of printer paper of Fig. 1 illustrating the serrated edge of one of the apertures in the paper;
Fig. 4 is an enlarged sectional view of a portion of the tractor drive of Fig. 2 showing the manner in which the pins thereof engage the apertures in the length of printer paper of Fig. 1;
Fig. 5 is a side view of several folds of paper within a stack of the length of printer paper of Fig. 1 illustrating the manner in which the serrated edges of the apertures may extend out of the plane of the paper to prevent a flat stack;
Fig. 6 is a plan view of a paper stack within a paper basket and illustrating the manner in which the non-planar configuration illustrated in Fig. 5 can result in uneven stacking of the paper;
Fig. 7 is a plan view of a paper stacking arrangement according to the invention in which a paper ironing mechanism forms part of an arrangement for pulling paper from a printer and in which a relatively flat paper stack is formed when compared with the paper stack of Fig. 6; and
Fig. 8 is a perspective view of a portion of the paper stacking arrangement of Fig. 7 illustrating the manner in which spring biased idler rollers are used in conjunction with paper pulling rollers to iron the opposite edges of the paper flat as the paper is pulled from the printer and lowered to form a paper stack within the paper basket.

Detailed Description of the Invention

Fig. 1 shows a dot matrix line printer 10 having opposite tractor drives 12 and 14 for advancing a length of printer paper 16 through the printer 10. The opposite tractor drives 12 and 14 advance the length of printer paper 16 incrementally in an upward direction through a print station 18 at which a shuttle assembly 20 is located. The shuttle assembly 20 undergoes reciprocating motion across the print station 18 so that a hammerbank within the shuttle assembly 20 impacts a length of ink ribbon 22 against the length of printer paper 16 to effect printing on the paper. The ink ribbon 22 is provided by a ribbon deck 24.
The length of printer paper 16 has series of spaced-apart apertures 26 therein adjacent opposite side edges 28 and 30 thereof. The length of printer paper 16 is prefolded and is of the so-called "fan-folded" type such that the length of printer paper 16 is folded in alternating directions to form a stack of page-sized sheets or portions. The opposite tractor drives 12 and 14 which advance the length of printer paper 16 through the printer 10 pull the paper upwardly from a stack thereof. The paper unfolds from the stack as it is pulled upwardly and into the printer 10 by the tractor drives 12 and 14. Following printing, the length of printer paper 16 is advanced over the top of and out of the back of the printer 10 where it is typically refolded into a stack.
Fig. 2 shows the tractor drive 12 with a cover 32 thereof in the open position. Only a portion of the length of printer paper 16 is shown in Fig. 2 so that the details of the tractor drive 12 are visible. The tractor drive 12 includes an endless belt 34 having a plurality of pins 36 disposed along the length thereof. The pins 36 are spaced apart from one another along the length of the belt 34 by a generally uniform distance approximately equal to the generally uniform distance by which the apertures 26 in the length of printer paper 16 are spaced apart. The belt 34 extends around opposite pulleys within the tractor drive 12 which advance the front portion of the belt 34 visible in Fig. 2 in an upward direction. The pins 36 along the belt 34 enter and engage the apertures 26 in the length of printer paper 16 to provide positive engagement of the edge of the printer paper as the printer paper is advanced through the tractor drive.
The opposite tractor drive 14 is of like configuration to the tractor drive 12 and engages the apertures 26 adjacent the opposite side edge 30 of the length of printer paper 16 in similar fashion. The configuration of the tractor drives 12 and 14 and the manner in which they operate to advance the length of printer paper 16 through the printer 10 are conventional and well-known in the art.
Fig. 3 depicts an enlarged portion of the length of printer paper 16 adjacent the side edge 28 of the paper. The paper portion shown in Fig. 3 includes one of the apertures 26 which, as shown, has a serrated edge 38. The serrated edge 38 provides the aperture 26 with an inner diameter slightly smaller than the diameter of each of the pins 36 at the base thereof. This insures a relatively snug fit of the pins 36 within the apertures 26.
Fig. 4 depicts a portion of the endless belt 34 of the tractor drive 12 of Fig. 2 together with one of the pins 36 shown inserted in one of the apertures 26 in the length of printer paper 16. The endless belt 34 is assumed to be moving in a direction toward the left as represented by an arrow 40 in Fig. 4. The resulting tension on the length of printer paper 16 distorts the "upstream" portion of the serrated edge 38 of the aperture 26, causing portions of the serrated edge 38 to bend away from the plane of the length of printer paper 16 as shown in Fig. 4 which shows such distorted portions 42.
As the length of printer paper 16 leaves the tractor drives 12 and 14 and is advanced out of the printer 10 and lowered into a stack thereof, the distorted portions 42 of the serrated edges 38 of the apertures 26 remain, as shown in Fig. 5 which illustrates several folds of the length of printer paper 16. The distorted portions 42 prevent the folded portions of the length of printer paper 16 from lying flat. The result is a greatly distorted paper stack of the type illustrated in Fig. 6.
Fig. 6 illustrates a paper stack 43 formed within a paper basket 44 as the length of printer paper 16 is advanced out of the printer 10 and lowered into the paper basket 44. Because of the phenomenon illustrated in Fig. 5, the opposite sides of the stack shown in Fig. 6 build up at a much greater rate than the central portion of the stack, despite the presence of a tent 46 at a central portion of a bottom 48 of the paper basket 44. The tent 46 which comprises an upwardly extending indentation in the bottom 48 elevates a central portion of the bottom of the stack relative to the opposite sides. Nevertheless, as the stack increases in height, the buildup of the opposite sides relative to the central portion is so great as to result in a severely concave configuration at the top of the stack. The severe concave configuration at the top of the stack greatly increases the possibility of a paper jam in which the length of printer paper 16 stops folding and stacking properly.
A further problem relates to the presence of the distorted portions 42 of the apertures 26, as shown in Fig. 5. The distorted portions 42 greatly increase the risk that one of the side edges 28 and 30 of the length of printer paper 16 will catch on the distorted portions 42 as the paper is folded and stacked, resulting in a paper jam condition.
Such problems are largely prevented by a paper stacking arrangement according to the invention, which arrangement 50 is illustrated in Fig. 7. The paper stacking arrangement 50 includes a paper basket 52 having a movable bottom 54 with a tent 56 therein and which is raised and lowered by a piston drive 58. The paper basket 52 includes a light source 60 mounted on one side thereof near the top and an opposite photodetector 62. The photodetector 62 which is coupled to the piston drive 58 responds to a light beam from the light source 60 by causing the piston drive 58 to raise or lower the bottom 54 as necessary to maintain the top of a paper stack 63 within the paper basket 52 at the level of the light source 60 and the photodetector 62. As the paper stack 63 on the bottom 54 begins to build up, the photodetector 62 responds by causing the piston drive 58 to lower the bottom 54 so as to maintain the top of the paper stack 63 at the level of the light source 60 and the photodetector 62.
As the length of printer paper 16 exits a printer such as the printer 10 of Fig. 1, the paper is directed between an opposite pair of guides 64 and 66 and then between a pair of guides 68 and 70. From the guides 68 and 70, the length of printer paper 16 is lowered onto the stack 63 in the paper basket 52. As the paper is lowered from the guides 68 and 70, the action of gravity causes the length of paper to fold along the prefolded creases so as to form the paper stack 63.
The paper stacking arrangement 50 includes a paper puller mechanism 72 which includes a plurality of paper puller rollers. One such paper puller roller 74 is shown in Fig. 7 adjacent the guide 64. The paper puller roller 74 is mounted on a shaft 76 which is rotatably driven in a direction shown by an arrow 78 to pull the length of printer paper 16 out of the printer and through the space between the guides 64 and 66. An antistatic brush assembly 80 mounted at the lower end of the guide 66 brushes the side of the length of printer paper 16 to prevent the buildup of a static charge within the paper which could interfere with the folding and stacking of the paper.
In accordance with the invention the paper puller roller 74 and its shaft 76 form part of a paper ironer mechanism 82 which irons the paper flat at the spaced-apart apertures 26 adjacent the opposite side edges 28 and 30 of the length of printer paper 16. The paper ironer mechanism 82 includes an idler roller 84 disposed on an opposite side of the length of printer paper 16 from the paper puller roller 74 and biased in a direction toward the paper puller roller 74. The idler roller 84 which is rotatably mounted at the lower end of a leaf spring 86 presses one of the apertured edges of the length of printer paper 16 against the paper puller roller 74 so as to iron or flatten the paper at the apertures. This has the effect of restoring the distorted portions 42 of the serrated edges 38 of the paper apertures 26 to the plane of the paper. As a result the buildup of the opposite sides of the paper stack relative to the central portion thereof is controlled so as to result in a much flatter stack which is far less prone to paper jams. In addition, flattening of the paper at the apertures 26 greatly reduces the possibility of one of the side edges 28 and 30 of the length of printer paper 16 catching on the serrated edges 38 of the apertures 26.
Fig. 8 is a perspective view of the paper ironer mechanism 82 which includes the paper puller roller 74 with its shaft 76, the idler roller 84 and the leaf spring 86 on which the idler roller 84 is rotatably mounted. As seen in Fig. 8 the idler roller 84 presses the length of printer paper 16 flat against the outer surface of the paper puller roller 74 at the series of apertures 26 adjacent the side edge 30 of the paper 16. A paper puller roller 88 mounted at an opposite end of the shaft 76 engages the length of printer paper 16 at the series of apertures 26 adjacent the opposite side edge 28. The paper is pressed flat or ironed at such series of apertures by an opposing idler roller 90 which is rotatably mounted on and biased toward the paper puller roller 88 by a leaf spring 92.
The idler rollers 84 and 90 have the associated leaf springs 86 and 92 thereof mounted on a common mounting member 94, together with the leaf spring 96 of a central idler roller 98. The central idler roller 98 under the biasing of the leaf spring 96 presses a central portion of the length of printer paper 16 against an opposing paper puller roller 100 mounted on a central portion of the shaft 76 between the paper puller roller 74 and the paper puller roller 88.
It will be seen that the paper puller rollers 74 and 88 combine with the biased idler rollers 84 and 90 to iron and thereby flatten the length of printer paper 16 at the series of apertures 26 adjacent the opposite side edges 28 and 30 of the length of printer paper 16. This enables the length of printer paper 16 to form a much flatter and therefore less jam-prone stack, while at the same time minimizing the chances of one of the side edges 28 and 30 of the length of printer paper catching within an aperture 26 so as to create a jam condition. In the case of the paper ironer mechanism 82 of Fig. 8, the paper puller rollers 74 and 88 and the idler rollers 84 and 90 must be positioned so that they face the apertures 26 adjacent the side edges 28 and 30 of the length of printer paper 16. To accommodate printer paper of different widths, it may be necessary to make the paper puller rollers 74 and 88 and the idler rollers 84 and 90 either wider or adjustable relative to the shaft 76 and the common mounting member 94. Alternatively, the paper puller rollers 74 and 88 can be combined with the paper puller roller 100 into a single roller extending across the entire width of the printer paper on one side thereof, with the idler rollers 84 and 90 being combined with the central idler roller 98 into a single roller extending along the opposite side of the printer paper. This allows different widths of printer paper to be accommodated without adjustment.
In the particular embodiment of Figs. 7 and 8, the paper ironer mechanism 82 is combined with and forms part of the paper puller mechanism 72. However, it will be understood that the paper ironer mechanism 82 can form a separate mechanism apart from and unrelated to the paper puller mechanism 72. It is only necessary that the paper ironer mechanism 82 include opposite rollers or other devices for ironing the paper flat at the apertures adjacent the opposite side edges of the paper. Such paper ironer mechanism 82 can be located anywhere "downstream" of the tractor drives 12 and 14 within the printer and can, for example, comprise opposing rollers located at the upper ends of and mounted on the tractor drives 12 and 14. Mounting the opposing, paper ironing rollers on the tractor drives has the advantage that the rollers need not be adjusted for different widths of printer paper since they are mounted on and therefore move with the tractor drives.
While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

Claims

1. An arrangement for stacking a length of prefolded, tractor driven paper having series of apertures therein adjacent opposite edges thereof comprising:
means for pressing against opposite sides of the length of paper at the apertures adjacent the opposite edges to flatten the paper at the apertures;
a container; and
means for advancing the length of paper downwardly toward the container so that the paper folds and forms a stack within the container.

2. The invention set forth in claim 1, wherein the means for pressing includes a first member disposed against the length of paper on one side thereof and a second member disposed against the length of paper on the other side thereof and biased toward the first member.

3. The invention set forth in claim 2, wherein the first member comprises a first roller and the second member comprises a second roller.

4. The invention set forth in claim 3, wherein the second roller is biased toward the first roller by a spring.

5. An arrangement for ironing the apertured opposite edges of a length of prefolded printer paper to be stacked, comprising the combination of:
a first arrangement disposed on one side of the length of paper at the apertured opposite edges thereof;
a second arrangement disposed on the opposite side of the length of paper at the apertured opposite edges thereof and opposite the first arrangement; and
means for biasing the first and second arrangements towards one another to flatten the apertured opposite edges of the length of paper therebetween.

6. The invention set forth in claim 5, wherein each of the first and second arrangements comprises at least one roller.

7. The invention set forth in claim 6, wherein the at least one roller of the first arrangement comprises a drive roller for advancing the length of paper and the at least one roller of the second arrangement comprises an idler roller.

8. The invention set forth in claim 5, wherein the first arrangement comprises a first pair of rollers disposed against one side of the length of paper at the apertured opposite edges thereof and the second arrangement comprises a second pair of rollers disposed against the opposite side of the length of paper at the apertured opposite edges thereof, each of the second pair of rollers being opposite a different one of the first pair of rollers.

9. The invention set forth in claim 8, wherein the first pair of rollers are mounted spaced apart on a common shaft and comprise drive rollers for advancing the length of paper, and the second pair of rollers comprise idler rollers biased toward the drive rollers by springs.

10. The invention set forth in claim 9, wherein the second pair of rollers are rotatably mounted on a common mounting member by resilient leaf springs.

11. An arrangement for stacking a length of prefolded tractor driven printer paper having apertured opposite edges, comprising:
a printer;
a container;
a paper puller mechanism disposed above the container and operative to pull the length of paper from the printer into the container to form a stack of paper within the container, the paper puller mechanism including cylindrical roller portions engaging one side of the length of printer paper at the apertured opposite edges thereof; and
means for pressing the length of printer paper against the cylindrical roller portions at the apertured opposite edges thereof to iron the opposite edges flat.

12. The invention set forth in claim 11, further including means for guiding the length of printer paper past the paper puller mechanism and into the container.

13. The invention set forth in claim 12, wherein the means for pressing the length of printer paper against the cylindrical roller portions includes cylindrical idler rollers engaging an opposite side of the length of printer paper at the apertured opposite edges opposite the cylindrical roller portions.

14. The invention set forth in claim 13, wherein the means for pressing the length of printer paper against the cylindrical roller portions includes a common mounting member and resilient springs extending from the common mounting member and having the cylindrical idler rollers rotatably mounted thereon.