The present invention pertains to an apparatus and method for stacking conveyed sheets of media without scratching the media. BACKGROUND OF THE INVENTION

Media, whether ordinary paper or sensitive material such as photographic, x-ray or imaging film, is stacked as it is produced. During manufacturing, sheets of media travel along a conveyer belt in a stream and are stacked at the end of the stream. As each sheet emerges from the conveyer, it is stacked atop the preceding sheet in the stack. As each sheet emerges from between rollers in the conveyer, there is a tendency for the sheet to droop because the free end is unsupported. As the drooping free end of an emerging sheet slides across the preceding sheet in the stack, the preceding sheet can be scratched thereby degrading the preceding sheet. With sensitive x-ray and imaging media, scratching can make the media unusable.

To reduce scratching, air jets have been used to lubricate and support the emerging sheets. Air injected between the emerging sheet and the top stacked sheet delays contact until the sheets are aligned whereby the emerging sheet simply drops onto the stack. With air jets there is a lack of lateral or transverse motion between the sheets; hence, no scratching. Adding air jets has the disadvantage of increasing machine complexity, cost and space requirements. In addition, air jets can disturb previously stacked sheets causing scratching, and can create airborne particles that can contaminate sensitive media. Also, the use of air jets destabilizes the stacking process causing stacker jams. Drooping is a major cause of scratching because the free end of the emerging sheet drags across the stack. While making sheets thicker would solve the tendency to droop, thicker media sheets require more material and are therefore more expensive, which is undesirable. Also, there are equipment and use restraints that limit material thickness. Imaging and x-ray sheets require smooth, homogenous surfaces; so, reinforcing ribs and the like cannot be used to stiffen the sheets. Thus, there is a need for a conveyer and stacking system that stacks sheets of sensitive media without scratching the media.

SUMMARY OF THE INVENTION

The present invention is directed to overcoming one or more of the problems set forth above. Briefly summarized, according to one aspect of the invention, an apparatus for stacking sheets of material traveling along a conveyor, comprises a plurality of entrance rollers; a plurality of exit rollers downstream of the plurality of entrance rollers arranged horizontally in a contoured pattern; a plurality of conveyor belts, one for each roller of the plurality of exit rollers, each conveyor belt twisting between an associated one of the plurality of entrance rollers and an associated one of the plurality of exit rollers; and means for pinching the belts and improving tracking of the belts on the entrance and exit rollers.

The means for pinching the belts and improving tracking includes a first plurality of twist rollers positioned between the plurality of entrance rollers and the plurality of exit rollers, and a second plurality of twist rollers positioned between the plurality of entrance rollers and the first plurality of twist rollers. AU belt twisting occurs between the first plurality of twist rollers and the second plurality of twist rollers so that there is no tracking problem at the entrance and exit rollers.

The exit rollers are arranged in a U-shaped contoured pattern. Each sheet adopts the U-shaped contoured pattern which increases the moment of inertia of the sheet and prevents the sheet from drooping as it emerges from the exit rollers. Without drooping, there is no scratching. The U-shape of each sheet has a top projected view wherein the width of the sheet is less than the width of the stacked sheets making sheet steering less critical. According to another aspect of the invention, a method for stacking sheets of material traveling along a conveyor, comprises the steps of: aligning a plurality of entrance rollers horizontally; arranging a plurality of exit rollers horizontally in a contoured pattern; providing a plurality of conveyor belts, one for each roller of the plurality of exit rollers; positioning a pair of twist rollers for each conveyor belt between the entrance and exit rollers; twisting each the conveyor belt during travel between associated twist rollers; and passing the sheet

along the contoured exit rollers whereby the sheet adopts the contoured pattern of the exit rollers.

The method includes arranging the exit rollers in a U-shaped contoured pattern. Each sheet adopts the U-shaped contoured pattern increasing its moment of inertia to prevent drooping and scratching of the preceding sheet. The method also includes pinching the belts and improving tracking of the belts using twist rollers positioned between the entrance and exit rollers. BRIEF DESCRIPTION OF THE DRAWINGS The above and other aspects, objects, features, and advantages of the present invention will become more apparent when taken in conjunction with the following description and drawings wherein identical reference numerals have been used, where possible, to designate identical features that are common to the figures, and wherein:

FIG. 1 is diagrammatic side view of the roller arrangement for a preferred embodiment of an apparatus for conveying and stacking according to the present invention;

FIG. 2 is a diagrammatic perspective view of a conveyed sheet of media entering the stacker;

FIGS. 3-5 are diagrams illustrating belt tracking error; FIG. 6 is a diagrammatic front view illustrating an exit roller configuration; and

FIG. 7 is a diagram illustrating other roller configurations for stiffening a media sheet.

DETAILED DESCRIPTION OF THE INVENTION Referring to FIGS 1-5, an apparatus 10 for stacking sheets 12 of material traveling along a conveyor 14 into a receiving bin 16 shapes each sheet 12 as the sheet 12 exits conveyor 14. Shaping sheet 12 increases its moment of inertia adding rigidity so that the sheet supports itself as it enters bin 16 without dragging across the top of the stack of sheets in the bin. Apparatus 10 includes a plurality of primary exit rollers arranged horizontally in a contoured pattern. As illustrated, the contoured pattern is a U-shaped pattern (FIG. 6) that increases the moment of inertia thereby adding

rigidity so that the sheet supports itself as it enters bin 16 without dragging across the top of the sheets stacked in the bin. There are a set of upper exit rollers 18 and a set of lower exit rollers 20. There are a set of upper entrance rollers 22 located upstream of upper exit rollers 18, and a set of lower entrance rollers 24 located upstream of lower exit rollers 20. An upper conveyor belt 26 is entrained about upper entrance and exit rollers 22, 18, and a lower conveyor belt 28 is entrained about lower entrance and exit rollers 24, 20. Belts are equal in number to the number of sets of entrance and exit rollers. For the arrangement illustrated in FIG. 6, there are four sets of upper rollers and four sets of lower rollers so that there are a total of eight belts.

FIG. 7 illustrates other patterns or configurations (FIG. 7) that could be used that would have the desired effect of increasing the moment of inertia thereby adding rigidity so that the sheet supports itself as it enters b>in without dragging across the top of the sheets stacked in the bin. Pattern A. is a general concave shape, pattern B is a general convex shape, pattern C shape is a W and pattern D is an M shape. Pattern E is a V shape while pattern F is an inverted V shape. Pattern G is channel configuration while pattern H is an inverted channel configuration. Pattern I is a partial circle with an open portion oriented upward and pattern J is a partial circle with an open portion oriented downward. Patterns K and L are multi-channel configurations.

Referring now to FIGS. 3-5, conveyor 14 has a plurality of conveyor belts arranged in pairs of upper and lower belts 26, 28, one pair for each pair of upper and lower exit rollers. To obtain the U-shape of the media, exit roller 18 is offset from entrance roller 22. Each of the conveyor belts 26, 28 twists between entrance rollers 22 and exit rollers 18. Twisting is required for th.e belts because the contoured exit rollers are set at an angle horizontally relative to the entrance rollers. As belt 26 travels in the direction of arrow A from entrance roller 22 to exit roller 18 and in the direction of arrow B between exit roller 18 and entrance roller 22, twisting causes the belt to want to slip or track in the direction of arrow C which would cause instability. As can be seen, paths along arrows A and B are not perfectly aligned producing a belt tracking error.

Again referring to FIG. 1 , to remove the belt twist and maintain desired belt tension at the entrance and exit rollers, there are upper and lower twist idler rollers positioned between the entrance and exit rollers. Upper twist rollers include upper entrance twist roller 30 and upper exit twist roller 32. Twist roller 30 has the same orientation as entrance roller 22 while twist roller 32 has the same orientation as exit roller 18 so that there is no belt twisting between upper entrance roller 22 and upper twist roller 30, and there is no belt twisting between upper twist roller 32 and upper exit roller 18. All belt twisting occurs between twist rollers 30 and 32. Locating the twist rollers close to the entrance and exit rollers minimizes tracking error because the belts are close together when they twist.

Similarly, lower twist rollers include lower entrance twist roller 34 adjacent lower exit roller 20 and lower exit twist roller 36 adjacent lower entrance roller 24. Twist roller 34 has the same orientation as exit roller 20 while twist roller 36 has the same orientation as entrance roller 24 so that there is no belt twisting between lower entrance roller 24 and lower twist roller 36, and there is no belt twisting between lower twist roller 34 and lower exit roller 20. All belt twisting occurs between twist rollers 34 and 36. Locating the twist rollers close to the entrance and exit rollers minimizes tracking errors because the belts are close together when they twist. The invention pertains to the stacking of sheet type product from a conveyance process. As the sheet enters the stack it is folded into a "U" shape. This allows the sheet to be suspended over the stack, fully supporting its own weight. The sheet can then be driven its full length into the stacker without sliding on any of its surfaces. Once the sheet has traveled the full length into the stacker it is released from the conveyance process and drops straight down into the stacker with little to no relative movement or pressure between the sheet and stack.

Folding the sheet into a "U" shape using a set of nipped belts presents belt tracking issues. This is apparent when the top projected view of a sheet folded into a "U" is compared to a sheet that is not folded into a "U". The folded sheet appears to be of a narrower width. When a "U" shape is made from a set of belts at the exit end and a flat shape at the entrance end, the U-shaped end

must be narrower to prevent relative motion between the belt and sheet. Also each belt must twist as it runs from the flat entrance to the "U" exit. Consider the top projected view of a belt around an entrance and exit idler as it twists. In the case of the entrance idler, the belt approaching the idler is aligned under the belt departing the idler. In the case of the exit idler, the belt approaching the idler is shifted to one side of the belt departing the idler. This action of entering one side of the exit idler and departing from the other causes the belt to aggressively track off. This problem is resolved by the present invention by placing the approaching and departing belt paths very close together, twisting the belt paths, then spreading them back apart to accommodate idlers.

It can now be appreciated that apparatus and method for stacking sheets of media without scratching the media has been presented. The apparatus includes upper and lower exit rollers arranged horizontally in a contoured pattern to fold the media sheets into a U-shape, or other pattern, that increases the rigidity due to increased moment of inertia. This allows a sheet to support itself as it enters the stacker without touching the top of the stack. The entering sheet is suspended above the stack until it reaches the stacker backstop where it drops into place without scratches. The U-shape of a sheet washes out product variation that would normally influence the stacking process, such as beam strength. Also, steering of a sheet is not critical because the U-shape of the entering top sheet has projected a top view less than that of the stacker.

The method for stacking sheets of material traveling along a conveyor comprises the steps of: aligning a plurality of entrance rollers horizontally; arranging a plurality of exit rollers horizontally in a contoured pattern; providing a plurality of conveyor belts, one for each roller of the plurality of exit rollers; positioning a pair of twist rollers for each conveyor belt between the entrance and exit rollers; twisting each conveyor belt during travel between associated twist rollers; and passing the sheet along the contoured exit rollers whereby the sheet adopts the contoured pattern of the exit rollers. The method includes arranging the exit rollers in a U-shaped contoured pattern. Each sheet adopts the U-shaped contoured pattern increasing its moment of inertia to prevent drooping and scratching of the preceding sheet.

The method also includes pinching the belts and improving tracking of the belts using twist rollers positioned between the entrance and exit rollers.

PARTS LIST

10 apparatus shaping and stacking sheets of material

12 media sheets

14 conveyor 16 receiving bin

18 upper exit rollers

20 lower exit rollers

22 upper entrance rollers

24 lower entrance rollers 26 upper conveyor belt

28 lower conveyor belt

30 upper entrance twist roller

32 upper exit twist roller

34 lower entrance twist roller 36 lower exit twist roller