Patent Application
20230159298
The invention relates to a sheet stacker and a method for printing sheets.
Sheet stackers may be provided at the output side of a printer for forming stacks of printed sheets. Certain sheet stackers comprise a flipping device which flips the sheet over as it is being stacked. During flipping a sheet may collapse upon itself. One or more sheets in the stack may then become unsuited for use and require reprinting and re-inserting these sheets back into the stack at the proper positions. This is generally considered cumbersome and affects productivity.
It is known from US2009121424, US10011453, US2006208414, and US2014239578 to provide a sensor assembly to detect deformations in the shape of the entire stack formed by a non-flipping stacker. These sensor assemblies focus on the stack and can track deviations that build up in the stack over a longer period.
It is an object of the invention to provide a sheet stacker with improved productivity, specifically a sheet stacker which can appropriately address wrongly flipped sheets.
In accordance with the present invention, a sheet stacker according to claim 1 and a method according to claim 15 are provided. The sheet stacker comprises:
Using the sensor data the controller determines for each sheet flipped onto the stack whether said sheet has been correctly flipped. This check is performed for each sheet, from the first to the last sheet in the stack. Since all sheets in the stack have passed this check, it can be safely assumed that the stack has the desired stack integrity (no stacking faults). This is due to the fact that the check is performed for each sheet individually. When it is determined that a sheet has been incorrectly flipped, appropriate action can be taken and stacking can be easily resumed. Productivity is improved since the problem is limited to the last flipped sheet and can be quickly resolved. Stacking can be quickly resumed since the integrity of the underlying stack is ensured by checking that that each individual is correctly flipped or not. Thereby the object of the present invention has been achieved.
More specific optional features of the invention are indicated in the dependent claims.
In an embodiment, the sensor assembly is arranged to sense each sheet added to the stack individually after the respective sheet has been added to the stack. The sensor assembly is configured to check each sheet after it has been added to the stack, and preferably before a further sheet is stacked on top of it. Regardless of the number of sheets in the stack, the sensor assembly is arranged to sense or scan the top sheet, being the most recently added sheet. The sensor assembly preferably defines a detection position, which detection position is at the top of the stack during the entire stack forming process. This may be achieved by moving the stack support with respect to the sensor assembly, such that the top sheet of the stack is kept at the detection position.
In an embodiment, the controller is configured to emit an error signal when the controller determines that the top sheet was flipped and/or stacked incorrectly. A further sheet is stacked similar to the top sheet, when it was determined that flipping was successfully executed. In case the sensor data indicates that the top sheet was incorrectly flipped, the controller is configured to emit an error signal to one or more different devices. The error signal may be in any suited format.
In an embodiment, the error signal is configured to trigger one or more of the following:
The error signal may be transmitted to a user interface, such as a screen on a device handled by an operator (e.g. a computer or mobile device). The operator is thereby promptly informed, as the error signal triggers a visual feature to appear on the user interface. The visual feature may comprise information regarding identification of the problem, for example an indication of an incorrectly flipped sheet in a sheet stacker at an indicated location. The error signal may further be transmitted to the flipping device to prevent the flipping of further sheets. Additionally, the error signal may also stop or pause the printing operation of a printer connected to the sheet stacker. In case, the printer has been provided with multiple sheet stackers, the error signal may also control the printer to redirect sheets to another sheet stacker, such that the remainder of the stack may be formed there. The wrongly flipped sheet or sheets are therein preferably reprinted in the correct order, such that the different parts of the stack can be easily merged by the operator.
In an embodiment, the sensor assembly is configured to detect an out-of-plane deformation of the top sheet with respect to the sheet below it. The sensor assembly is arranged to distinguish between the top sheet being flat and/or planar or at least partially deformed, such that portions of the sheet protrude out of a plane parallel to the sheet underneath the top sheet. Since the previous sheets have been correctly stacked, these have a similar planar shape. If the top sheet is flipped incorrectly, its deformation will extend perpendicular to the plane of the underlying sheet. The sensor assembly is arranged to sense such deformations.
In an embodiment, the sensor assembly comprises an optical detector. An optical detector allows for contactless sensing the sheet, thus without the risk of altering its form or position. The detector may be a camera, light sensor, photodiode, etc.
In an embodiment, the sensor assembly further comprises an optical emitter configured for emitting a light beam towards the top sheet. A low costs embodiment of the sensor assembly may be formed by an optical emitter, such as a laser or focused light beam emitter, or even a sufficiently strong lamp. The emitted light can be applied to identify a presence of a deformation in the sheets by the different reflection of light as compared to the flat (non-deformed) areas of the top sheet (or the underlying sheet).
In an embodiment, 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. When the sheet has been correctly flipped and stacked, the top sheet of the stack is flat. The emitter may be positioned such that the light beam extends over the flat surface in that case. When the top sheet is deformed, deformations protrude out of the plane of the light beam and partially obstruct the light beam, reflecting the light beam. This results in a change in the intensity of light received by the detector. Incorrectly flipped sheets can thus be derived from a signal change from the detector. The detector may be positioned opposite to the emitter such that the highest intensity of light is received when the top sheet is planar and that the received intensity is reduced when the sheet comprises deformations reflecting part of the light beam. In an alternative embodiment, the detector is positioned to receive light only when the light beam at least partially reflects of one or more deformations in the sheet, for example in the form of a laser distance meter. The detector in another example may be relatively large and extend over a large portion of the support. Incorrect flipping of a sheet can then be determined from a rise in signal intensity from the detector.
In an embodiment, the emitter and the detector are positioned substantially diagonally on opposite sides of the top sheet with respect to one another. The light beam thereby covers a relatively large portion of the sheet, resulting in a more accurate determination of whether the flipping was executed correctly. It will be appreciated that diagonally is herein defined as roughly parallel to a diagonal direction of the support. Since different sheet dimensions may be applied, while the detector and emitter are stationary with respect to the support, diagonally may be defined as a direction which extends between two points adjacent opposite corners of the top sheet.
In an embodiment, an actuator is provided for adjusting a spacing between the stack support and the flipping device during use, and wherein the sensor is stationary with respect to the flipping device during use. The top of the stack is kept at a constant level with respect to the flipping device to ensure reliable flipping and stacking. As the stack increases, the support is lowered with respect to the flipping device. The sensor and preferably also the detector are however stationary with respect to the flipping wheel during use, for example by being mounted on a common frame.
In an embodiment, the controller is configured for determining position information of an out-of-plane in the top sheet from data from the detector. The controller is able to determine a relative position of a deformation in the top sheet, for example its distance from the emitter or detector or any other relevant point. The positional information can be applied to determine the underlying cause for the incorrect flipping. Simple linear distance sensors or more elaborate scanners or cameras may be applied to obtain the positional information.
In an embodiment, the controller is configured to derive at least one flipping fault parameter from data from the detector 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 the flipping fault. The flipping fault parameter may for example be above mentioned positional information. The transmitted information is compared to a look-up table in a database, which can be stored either locally or ‘in the cloud’. The look-up table comprises a list with root causes, each root cause being provided with one or more identifiers which allow a root cause to be matched to the at least flipping fault parameter. This allows the controller to identify the underlying problem and take appropriate action.
In an embodiment, the transmitted information for the at least flipping fault parameter comprises at least one of the following:
The positional information gives information regarding the manner in which the sheet collapsed during flipping. This may be combined with information regarding the sheet itself and the flipping operation to determine whether suitable settings for applied for flipping the sheet in the manner it was flipped. The look-up table is preferably based on test and/or operational data.
In an embodiment, he controller is configured:
After comparison to the look-up table a root cause has been determined and the operator is informed of said root cause. Preferably, the displayed information identifying the flipping fault root cause identifier includes technical specification data which includes instructions for resolving the root cause to help the operator resolve the problem. Alternatively, the operator may have configured the controller to automatically adjust operations based on said received information.
The present invention further relates to a method for stacking sheets comprising the steps of:
The method may be performed on a sheet stacker as described above. Therein a controller determines from a signal from a detector whether a sheet has been correctly flipped or not. In case of correct flipping, the stacking operation is continued and a new sheet is flipped and stacked on top of the previous sheet. In case of an incorrectly flipped sheet, the controller emits an error signal. The error signal may for example stop the flipping by pausing or stopping the flipping device, inform an operator via a user interface, and/or reroute the to be stacked sheets to an alternative sheet stacker.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the present invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the present invention will become apparent to those skilled in the art from this detailed description.
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:
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.
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.
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.
In the embodiment in
The intensity of light received by the detector 21 is compared by the controller (25 in
In
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.
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.
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.
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 21209928.7 | Nov 2021 | EP | regional |
