SHEET STACKER WITH SHEET FLIPPING CONFIRMATION

Abstract

To ensure reliable and productive processing of printed sheets into stacks, a sheet stacker includes: a flipping device for flipping a sheet with respect to the sheet's orientation before being received by the flipping device onto a stack support or a stack of sheets on the stack support; a sensor assembly for detecting an out-of-plane deformation of a top sheet with respect to the underlying stack support or a stack of sheets on the stack support at least for each sheet added to the stack; and a controller configured to determine from data from the sensor assembly whether the top sheet was successfully flipped and stacked.

Claims

1. A sheet stacker comprising: a flipping device for flipping a sheet with respect to an orientation of the sheet before being received by the flipping device onto a stack support or a stack of sheets on said stack support; a sensor assembly arranged for detecting an out-of-plane deformation of a top sheet with respect to the stack support or the stack of sheets on said stack support at least for each sheet added to the stack; and a controller configured to determine from data from the sensor assembly whether the top sheet was successfully flipped and stacked.

2. The sheet stacker according to claim 1, wherein the sensor assembly is arranged to sense each sheet added to the stack individually after the respective sheet has been added to the stack.

3. The sheet stacker according to claim 2, wherein the sensor assembly and the stack support are movable with respect to one another.

4. The sheet stacker according to claim 3, wherein the sensor assembly defines a detection position and the sensor assembly is arranged such that the detection position is at the top of the stack during the entire stack forming process.

5. The sheet stacker according to claim 1, wherein the controller is configured to emit an error signal when the controller determines that the top sheet was flipped and/or stacked incorrectly.

6. The sheet stacker according to claim 5, wherein the error signal is configured to trigger one or more of the following: inform an operator via a user interface; stop stacking of sheets onto the stack support; and redirect to be stacked sheets to a further flipping device for stacking onto a further stack support.

7. The sheet stacker according to claim 1, wherein the sensor assembly is configured to detect an out-of-plane deformation of the top sheet with respect to a sheet below the top sheet.

8. The sheet stacker according to claim 1, wherein the sensor assembly comprises an optical detector.

9. The sheet stacker according to claim 8, wherein the sensor assembly further comprises an optical emitter configured for emitting a light beam towards the top sheet.

10. The sheet stacker according to claim 9, wherein the emitter and detector are positioned with respect to one another, such that an intensity of light received by the detector from the emitter is different when the top sheet is planar as compared to when the top sheet is non-planar.

11. The sheet stacker according to claim 10, wherein the emitter and the detector are positioned substantially diagonally on opposite sides of the top sheet with respect to one another.

12. The sheet stacker according to claim 3, wherein an actuator is provided for adjusting a spacing between the stack support and the flipping device during use, and wherein a detector of the sensor assembly is stationary with respect to the flipping device during use.

13. The sheet stacker according to claim 1, wherein the controller is configured for determining position information of an out-of-plane in the top sheet from data from a detector of the sensor assembly.

14. The sheet stacker according to claim 1, wherein the controller is configured to derive at least flipping fault parameter from data from a detector of the sensor assembly and to transmit information for the at least flipping fault parameter to a database with a look-up table for determining a root cause of a flipping fault.

15. The sheet stacker according to claim 14, wherein the transmitted information for the at least flipping fault parameter comprises at least one of the following: positional information of a deformation in the top sheet; sheet media information; and operational information of the flipping device.

16. The sheet stacker according to claim 15, wherein the controller is configured: to receive a flipping fault root cause identifier determined by comparing information for the at least flipping fault parameter to the look-up table; and to display information identifying the flipping fault root cause identifier on a user interface.

17. The sheet stacker according to claim 16, wherein the displayed information identifying the flipping fault root cause identifier includes technical specification data which includes instructions for resolving the root cause.

18. A method for stacking sheets comprising the steps of: flipping a sheet onto a stack support or a stack on said stack support; and sensing whether the flipped sheet comprised an out-of-plane deformation for each sheet in the stack individually, followed by either: flipping a further sheet onto the sheet in case no out-of-plane deformation was detected; or preventing further flipping of sheets and emitting an error signal.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The present invention will become more fully understood from the detailed description given herein below and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein:

[0043] FIG. 1 is a schematic side view of an embodiment of a sheet stacker according to the present invention;

[0044] FIG. 2 is a schematic top view of the sheet stacker in FIG. 1 with a correctly flipped sheet;

[0045] FIG. 3 is a schematic top view of the sheet stacker in FIG. 1 with an incorrectly flipped sheet;

[0046] FIG. 4 is a schematic side view of another embodiment of a sheet stacker according to the present invention; and

[0047] FIG. 5 is a block diagram illustrating the steps of the method according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0048] The present invention will now be described with reference to the accompanying drawings, wherein the same reference numerals have been used to identify the same or similar elements throughout the several views.

[0049] FIG. 1 illustrates schematically a side view of a sheet stacker 1. The sheet stacker 1 is positioned at the end of a sheet transport path formed by a transport pinch 8 downstream of one or more sheet guides 9. The transport pinch 8 is positioned to feed sheets into one of the slots 3 of the flipping device 2. The slots 3 are configured to releasably hold a leading edge of a sheet, as the flipping device 2 is rotated around its axis 4. This results in the sheet being flipped with respect to the orientation it in the transport pinch 8 and/or at the sheet guides 9. A stop element (not shown) is positioned underneath the flipping device 2, such that contact between the sheet and the stop element releases the sheet from the slot 3. Thereby, sheets can be stacked quickly onto the stack support 14. It will be appreciated that the flipping wheel 5 may be provided with one, two, or any suitable number of slots 3. Such a flipping device 2 is described in detail in U.S. Pat. No. 9,457,980 BB which description is hereby incorporated by reference.

[0050] While stacking, the stack 10 on the stack supports 14 grows. An actuator 15 is provided for raising and lowering the stack support 14 with respect to the flipping device 2, such that the top surface of the stack 10 is at the correct height position for receiving the sheet from the flipping device 2. The actuator comprises a drive 15 mounted on a spindle 16, though other suitable actuators and supports may be applied.

[0051] A sensor assembly formed of an emitter 20 and a detector 21 is provided at the level of the top sheet 11 of the stack 10. The sensor assembly is arranged to sense the top sheet 11 in order to determine whether the top sheet 11 was flipped successfully, i.e. whether the top sheet 11 has regained its flat or planar shape after flipping. The sensor assembly is configured to detect the presence of any out-of-plane deformations in the top sheet S, such as folds, or wrinkles. It will be appreciated that very small out-of-plane deformations in the top sheet 11 may be allowed and do not render the top sheet 121 as incorrectly flipped.

[0052] In the embodiment in FIG. 1, the sensor assembly comprises an optical emitter 20, such a laser or (focused) light source. The output of the emitter 20 is such that its emission will be disturbed by any out-of-plane deformations in the top sheet 11. An example is illustrated in FIG. 2, wherein the top sheet 11 has been successfully flipped onto the stack support 14 (or the stack already positioned thereon). The light beam 22 emitted by the emitter 20 is allowed to travel unobstructed over the top sheet 11 towards the detector 21. In FIG. 2, the emitter 20 and the detector are positioned, such that the light beam 22 travels over a substantial portion of the top sheet 11 at a non-zero angle with respect to the edges of the top sheet 11. It is preferred to have the light beam 22 travel substantially diagonally over the top sheet 11, though the degree of diagonality may vary dependent on the dimensions of the top sheet 11 and its position with respect to the emitter 20 and detector 21. The sensor assembly has been rigidly fixed with respect to the flipping device 2, for example by mounting it on the same frame.

[0053] The intensity of light received by the detector 21 is compared by the controller (25 in FIG. 1) to a predetermined threshold, which may be a value or setting stored on a memory of the controller 25. The threshold may e.g. be set before stacking by measuring the received light intensity before a sheet is flipped onto the stack support 14. A safety or correction value may be applied to this measurement. For example the threshold may be 90%, 80%, 70%, etc. of this measured intensity. After flipping a sheet, the controller 25 compares whether the detected light intensity with the threshold, and if said detected light intensity is above said threshold, the top sheet 11 is assumed to be free of out-of-plane deformations. The controller 25 based on that determines that the top sheet 11 has been successfully flipped and commences the flipping of a further sheet.

[0054] In FIG. 3, the top sheet 11 has been incorrectly flipped. The top sheet 11 has collapsed upon itself while in the flipping device 2, resulting in one or more folds protruding out of the plane of the top of the stack 10. The light beam 22 is at least partially prevented from reaching the detector 21. The detected light intensity in FIG. 3 is lower than that the threshold and the controller 25 determines that the top sheet 11 has been flipped incorrectly. The controller 25 then proceeds to emit an error signal, which prevents a further sheet from being flipped onto the stack 10. It will be appreciated that in case of high stacking speeds, the error signal from the controller 25 may be too late to prevent the subsequent one or more sheets to be stacked on the top sheet 11 before stopping the flipping device 2.

[0055] FIG. 4 illustrates another embodiment of the sheet stacker 100, wherein the sensor assembly is formed by a camera 120 arranged to image the top surface of the stack 10. Additional light sources may be provided to improve the workings of the camera 120. The controller in this embodiment is provided with image analysis software, which may detect out-of-plane deformations from e.g. dark and light contrasting areas in the sensed image of the top sheet 11. A successfully flipped top sheet 11 will yield a substantially homogenous image, while for examples wrinkles, folds, or dog-ears will show up as having dark lines. In another example, the sensor assembly may utilize a 3D scanner.

[0056] FIG. 5 illustrates the steps of the method according to an embodiment of the present invention. In step i a sheet is transported from the sheet transport path, where the sheet has a first orientation, into the sheet flipping device 2. The sheet flipping device 2 in step ii flips the sheet into a second orientation, wherein the surfaces of the sheet are reversed with respect to the first orientation. The sheet is thereby positioned onto the stack support 14 or a stack 10 on said stack support 14. Step iii comprises the sensor assembly sensing the sheet. Data from the sensor assembly is transmitted to the controller 25. In step iv, the controller 25 based on said data determines whether the sheet has been successfully flipped. The controller 25 preferably does this by comparing the data to a threshold, which threshold is a measure for out-of-plane deformation in the top sheet 11. The determination step iv can have one of two outcomes, illustrated by steps v and vi. Step v illustrates the case wherein the controller 25 determines that the top sheet 11 is substantially free of out-of-plane deformation and thus has been successfully stacked. The stack 10 in that case is then ready for receiving a further sheet and the controller 25 proceeds to repeat steps i to iv.

[0057] Step vi illustrate the situation wherein the controller 25 determines the top sheet 11 to have been incorrectly flipped, which has resulted in one or more out-of-plane deformations in the top sheet 11. This triggers the controller 25 to execute one or more of the steps vii to ix. Step vii comprises stopping the operation of the flipping device 2 to prevent further sheets from being stacked on the incorrectly flipped top sheet 11. Step viii may also be executed, in which the controller instructs further sheets to be directed to another flipping device for forming the remained of the stack there. This allows the stacking operation to be continued, but it requires multiple sheet stackers connected to a single source or printer. Step ix comprises the controller 25 emitting the error signal towards one or more user interfaces, where the received error signal prompts a warning or status indication to appear on the user interface. The operator is thereby informed that a stacker is offline and requires maintenance. Additionally, in case step viii has been performed the operator may informed that stack has been completed, but was divided over different output locations.

[0058] Although specific embodiments of the invention are illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations exist. It should be appreciated that the exemplary embodiment or exemplary embodiments are examples only and are not intended to limit the scope, applicability, or configuration in any way. Rather, the foregoing summary and detailed description will provide those skilled in the art with a convenient road map for implementing at least one exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope as set forth in the appended claims and their legal equivalents. Generally, this application is intended to cover any adaptations or variations of the specific embodiments discussed herein.

[0059] It will also be appreciated that in this document the terms “comprise”, “comprising”, “include”, “including”, “contain”, “containing”, “have”, “having”, and any variations thereof, are intended to be understood in an inclusive (i.e. non-exclusive) sense, such that the process, method, device, apparatus or system described herein is not limited to those features or parts or elements or steps recited but may include other elements, features, parts or steps not expressly listed or inherent to such process, method, article, or apparatus. Furthermore, the terms “a” and “an” used herein are intended to be understood as meaning one or more unless explicitly stated otherwise. Moreover, the terms “first”, “second”, “third”, etc. are used merely as labels, and are not intended to impose numerical requirements on or to establish a certain ranking of importance of their objects.

[0060] The present invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the present invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.