WASTE REDUCTION IN SHEET PRINTING SYSTEMS

Abstract

When a sheet ejector ejects an unsuitable sheet from a transport path in a printing system, additional sheets downstream of said unsuitable sheet are generally discharged to preserve the image order as prescribed by the print instructions. This results in large amounts of waste material (sheets and ink). The amount of waste may be reduced by providing a controller which, when receiving print instructions concerning a first and a second set of images, schedules the images of the first and second sets into an alternating image sequence defining the print order. Sheets printed with images from the first set are designated to a first output holder while sheets printed with images from the second set are transported to the second output holder. When a sheet for the second image set is rejected, the first image set need not be discharged, resulting in a reduced amount of waste material.

Claims

1. A printing system comprising: a print station disposed at a sheet transport path diverging to a first and a second output holder; a sheet feeder arranged to feed a stream of media sheets into the transport path so as to be fed sequentially to the print station; a sheet ejector for ejecting unsuitable sheets from the transport path to a discharge path ; and a controller arranged to receive print instructions concerning a first and a second set of images to be printed and to schedule a print order of images to be consecutively printed on the sheets, wherein: the controller is further arranged to: schedule images of the first and second sets into an alternating image sequence defining the print order, such that the print station alternatingly prints images of the first and second set on the sheets in the stream; direct sheets printed with images from the first set to the first output holder; and direct sheets printed with images from the second set to the second output holder.

2. The printing system according to claim 1, wherein the controller is further configured to: when at least one sheet in the second set is ejected to the discharge path: direct printed sheets of the first set following the rejected sheet to the first output holder; and direct sheets of the second set following the rejected sheet to the discharge path.

3. The printing system according to claim 2, wherein the transport path comprises an buffer transport path section upstream of the sheet ejector, wherein the controller is further configured to: when the controller designates a sheet in the second set to be ejected to the discharge path: direct sheets of the first set on the buffer transport path section to the first output holder; designate sheets of the second set on the buffer transport path section for ejection; direct the designated sheets of the second set to the discharge path; and reroute images assigned to the designated sheets of the second set on the buffer transport path section to unprinted sheets to be fed to the print station.

4. The printing system according to claim 2, wherein the controller is further arranged to: when at least one sheet in the second set is ejected to the discharge path: reroute the images for sheets of the second set which sheets are designated for ejection to sheets en route to the print station, such that the print station reprints the rejected images on the latter sheets; and direct the sheets with the rerouted images to the second output holder to complete a sheet stack for the second set.

5. The printing system according to claim 1, wherein, when the print instructions define a first image order for the first set of images and a second image order for the second set of images, the controller is arranged to: schedule images of the first and second sets into an alternating image sequence, such that in the print order images from the first set are alternating with images from the second set ; direct sheets printed with images from the first set to the first output holder to form a stack of sheets with images in the first image order; and direct sheets printed with images from the second set to the second holder to form a stack of sheets with images in the second image order; and when at least one sheet in the second set is ejected to the discharge path: direct printed sheets of the first set following the rejected sheet to the first output holder; designate sheets of the second set following the rejected sheet for ejection and direct the designated sheets of the second set to the discharge path; and reroute the images for the designated sheets of the second set in the print order, such that the relative image order in the second set is restored.

6. The printing system according to claim 1, further comprising: a sensor arranged at the transport path for detecting a quality condition of the sheets being fed to the print station, and the controller is adapted to receive a quality signal from the sensor and, when the quality of a sheet is found to be insufficient, wherein the controller is arranged to control the sheet ejector to transport the respective sheet to the discharge path upon receipt of the quality signal.

7. The printing system according to claim 6, wherein the sensor is arranged to scan a surface relief of a sheet that is moving past the sensor.

8. The printing system according to claims 6, wherein the sheet ejector further comprises a switch that is disposed in the sheet transport path in a position between the sensor and the print station and is arranged to divert sheets into the discharge path.

9. The printing system according to claim 6, comprising a duplex loop, wherein the sensor is disposed at a point of the sheet transport path between the print station and a junction where sheets returning from the duplex loop enter into the sheet transport path again.

10. The printing system according to claim 1, wherein the controller schedules images of the first and second sets into an alternating image sequence defining the print order, thereby forming a stream of images wherein at least one image of the first set is provided in between images of the second set.

11. A method for scheduling a print job for a printing system comprising a print station disposed at a sheet transport path diverging into a plurality of output holders and a sheet ejector for ejecting unsuitable sheets from the transport path to a discharge path, said method comprising the steps of: receiving print instructions comprising a plurality of image sets to be printed; scheduling the image sets into a print order by alternating images of the different image sets; printing the images in the scheduled print order; and directing each of the printed image sets to a different one of the plurality of output holders.

12. The method according to claim 11, further comprising the step of: assigning each one of the image set to one of the plurality of output holders.

13. The method according to claim 12, wherein the image sets are distributed over the different output holders.

14. The method according to claim 11, further comprising the steps of: discharging a number of sheets associated with one of the image sets from the transport path; directing the sheets associated with at least of one of the other image sets to its respective output holder; and rerouting the discharged images associated with the one of the image sets into the print order, such that the relative image order in the one of the image sets is restored.

15. The method according to claim 11, further comprising the steps of: detecting a quality condition of the sheets being fed to a print station; and transporting a sheet to a discharge path, when the quality of said sheet is found to be insufficient.

16. A software product comprising program code on a non-transitory computer-readable medium, wherein said program code, when loaded into a computer that is connected to a printing system having a print station disposed at a sheet transport path, a sheet feeder arranged to feed media sheets into the transport path so as to be fed sequentially to the print station, and a sheet ejector for ejecting unsuitable sheets from the transport path to a discharge path, causes the computer to act according to the method according to claim 11.

17. The printing system according to claim 2, further comprising: a sensor arranged at the transport path for detecting a quality condition of the sheets being fed to the print station, and the controller is adapted to receive a quality signal from the sensor and, when the quality of a sheet is found to be insufficient, wherein the controller is arranged to control the sheet ejector to transport the respective sheet to the discharge path upon receipt of the quality signal.

18. The printing system according to claim 3, further comprising: a sensor arranged at the transport path for detecting a quality condition of the sheets being fed to the print station, and the controller is adapted to receive a quality signal from the sensor and, when the quality of a sheet is found to be insufficient, wherein the controller is arranged to control the sheet ejector to transport the respective sheet to the discharge path upon receipt of the quality signal.

19. The printing system according to claim 4, further comprising: a sensor arranged at the transport path for detecting a quality condition of the sheets being fed to the print station, and the controller is adapted to receive a quality signal from the sensor and, when the quality of a sheet is found to be insufficient, wherein the controller is arranged to control the sheet ejector to transport the respective sheet to the discharge path upon receipt of the quality signal.

20. The printing system according to claim 5, further comprising: a sensor arranged at the transport path for detecting a quality condition of the sheets being fed to the print station, and the controller is adapted to receive a quality signal from the sensor and, when the quality of a sheet is found to be insufficient, wherein the controller is arranged to control the sheet ejector to transport the respective sheet to the discharge path upon receipt of the quality signal.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0070] 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:

[0071] FIG. 1 is a schematic view of a printing system according to the invention;

[0072] FIG. 2 is a diagram illustrating an example of scheduling images in a printing system according to the present invention;

[0073] FIG. 3 is a diagram illustrating another example of scheduling images in a printing system according to the prior art (top row) compared to the present invention (bottom row);

[0074] FIGS. 4A-D are schematic views of a printing system according to the prior art during the different steps of a method applied in the prior art;

[0075] FIGS. 5A-F are schematic views of a printing system according to the present invention during the different steps of a method according to the present invention; and

[0076] FIG. 6A-B are diagrams of the steps of the method according to the present invention; and

[0077] FIG. 7 is a diagram of an embodiment of the scheduling algorithm according to the present invention for printing multiple identical image sets.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0078] 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.

[0079] As is shown in FIG. 1, a printing system that is described here as a representative example comprises an input section or sheet feeder 10, a main body 12, and an output section or sheet receiver 14. The main body 12 comprises a print station 16 disposed at a sheet transport path 18, an electronic controller 20 and a user interface 22.

[0080] The controller 20 may be formed by a computer, a server or a workstation and is connected to all the functional components of the printing system for controlling the printing system and is further connected to the user interface 22 and to a network 24 via which the controller may communicate with a remote workstation 26 of a user or operator. In an alternative embodiment, the controller 22 may also be installed outside of the main body 12 for controlling the various system components via the network 24.

[0081] The hardware and/or the software of the controller 20 includes among others a print job receiving section 28, a scheduler 30, a feed control section 32, a print control section 34, an output control section 36, and a sheet manager 38. The print job receiving section 28 is arranged to receive, e.g., via the network 24, print jobs each of which includes image data for one or more pages to be printed as well as various job settings. Optionally, the image data may also be received from a local scanner whereas the job settings are input at the user interface 22. The job settings include among others instructions that specify for each image to be printed the properties or type of a recording medium on which the image shall be printed.

[0082] The sheet feeder 10 includes a plurality of holders 40 each of which accommodates a supply, e.g. a stack of media sheets of a certain media type. The media types in the different holders 40 may differ in sheet thickness, sheet material, surface properties of the sheets and the like. The input section 10 further includes a feed mechanism 42 arranged to separate individual sheets from a selected one of the holders 40 and to supply them one by one into the sheet transport path 18 under the control of the feed control section 32.

[0083] When the job receiving section 28 has received a print job, the scheduler 30 determines a sequence in which the images of this print job shall be printed. For the purposes of this description, the term image shall designate a page size image that is to be printed onto one side of a recording sheet. The scheduler 30 further has access to a data base that stores the media types and properties of the sheets accommodated in the various holders 40. Based on the job settings that concern the media properties, the scheduler 30 selects the holders 40 from which the sheets with the desired properties are to be taken and determines a sequence in which the sheets of the different media types are to be fed into the sheet transport path 18 such that the sequence of sheets matches the sequence of images to be printed.

[0084] When the print process has been started, the feed control section 32 controls the feed mechanism 42 to supply the sheets in the sequence as scheduled into the sheet transport path 18, and the print control section 34 controls the print station 16 so as to print a corresponding image on the top side of each sheet.

[0085] In the example shown, the output section 14 has a plurality of holders 44 on which the sheets may be stacked after they have left the print station 16. When a stack, which may for example comprise a set of sheets forming a complete copy of a multi page document, has been completed, the holder 44 will forward the stack onto an associated output tray 46. In an alternative embodiment the completed stacks may also be forwarded to a finisher (not shown) for performing finishing operation such as stapling, punching and the like.

[0086] The output section 14 further includes a switch 48 which is controlled by the output control section 36 for directing each sheet to a designated one of the holders 44.

[0087] In the example shown, the main body 12 of the printing section also includes a duplex loop 50 which branches off from the sheet transport path 18 downstream of the print station 16, reverses the orientation of the sheets in a sheet reversing mechanism 52 and then returns the sheets upside down to the entry side of the sheet transport path 18.

[0088] It shall further be assumed in this example that the print station 16 includes as print engine an ink jet print head 54 that is disposed above the sheet transport path 18 and is adjustable in height by means of a height adjustment mechanism 56. Dependent upon the thickness and other properties of the sheets, the height of the print head 54 is adjusted such that a nozzle face 58 at the bottom side of the print head forms only a very narrow gap with a top surface of a sheet 60 that is being conveyed past the print head. In this way, it will be assured that, for each individual sheet, the ink jet print process will be performed with an optimal nozzle-to-sheet distance.

[0089] As the gap between the nozzle face 58 and the sheet 60 may be very small, any wrinkles or a surface waviness or other surface irregularities of the sheet 60 may result in a poor image quality or even in a collision of the sheet with the print head. For this reason, a sensor 62 for monitoring the quality of the sheets is disposed at the sheet transport path 18 upstream of the print station 16. The sensor 62 may for example be a 3D laser scanner that scans the entire surface of the sheet in order to capture a surface relief. The relief data are transmitted to the sheet manager 38 in the controller 20, where they are processed further to decide whether the quality of the sheet is acceptable or not. The sensor 62 may also detect other quality criteria relating to, for example, alignment errors or skew errors of the sheets.

[0090] When a sheet is found to be inacceptable, the sheet manager 38 controls a switch 64 in the sheet transport path 18 in order to excise this sheet from the scheduled sequence and to divert it into a discharge path 66 via which the sheet is discharged into a discharge bin (not shown). In this way, the defective sheet will be skipped in the print process. However, the image that was designated for being printed onto the discarded sheet must nevertheless be printed. Normally, this situation would lead to an abortion of the print process, with the result that the entire print process, including the scheduling process, has to be started anew, and all the sheets that had been present already in the sheet transport path 18 and in the duplex loop 50 would have to be discarded.

[0091] It should be observed in this context that FIG. 1 is only a schematic sketch and that, in practice, the number of sheets that can be accommodated in the sheet transport path 18 and in the duplex loop 50 may be considerably large. For example, the duplex loop 50 may be arranged to accommodate as many as 32 sheets.

[0092] In order to reduce the amount of waste material when a sheet is found to be unacceptable, the sheet controller 20 forms a print order wherein the images of different image sets S1-S3 are alternated with respect to one another while assigning sheets 60 of each image set S1-S3 to be output to a different output holder 44. An example of such a scheduling algorithm will now be explained in conjunction with FIG. 2.

[0093] FIG. 2 illustrates print instructions comprising two image sets S1, S2 being received at the job receiving section 28. Each image set S1, S2 is provided a predefined image order PO which determines the sequence PO in which the images are to be output at the output holders 44. The scheduler 30 shuffles the images of the received image sets S1, S2 to form an alternating image order PO as shown in FIG. 2. Sheets of the first image set S1 are interchanged with images of the second image set S2. This scheduled print order PO or queue PO determines the sequence PO in which the images are to be printed by the print station 16. The scheduler 30 designates each image set S1, S2 to a different one of the output holders 44. Images of the first image set S1 are thus transported to a different output holder 44 than images of the second image set S2. The advantages of the scheduling algorithm will be now explained with respect to FIGS. 3, 4, and 5.

[0094] The top row in FIG. 3 as well as FIGS. 4A-D represent a scheduling algorithm as applied in the prior art. The print instructions comprise three image sets S1-S3. In the shown print order PO, the first set S1 is scheduled first with its images in a following order, namely S1-1, S1-2, . . . , S1-5. The second image set S2 follows the first image set S1 with its images S2-1-S2-5 ordered in ascending order. Similarly, the third image set S3 is scheduled behind or upstream of the second image set S2. All images S1-1 to S3-5 are designated to be output at the same output holder 44, thereby forming a single stack comprising sub-stacks of the respective sets S1-S3.

[0095] In the example shown in FIG. 4A, during operation, the sheets 60 assigned with the images S1-1 to S3-2 reside on the duplex pass 50. The duplex pass 50 forms a loop 50 returning the sheets 60 to the print station 16, thereby passing the feed path of the sheet feeder 10. This allows the sheet feeder 10 to insert blank sheets 60 into the sheet stream. As the sheets 60 on the duplex pass 50 have passed the print station 16, an image has been printed on one side of these sheets 60.

[0096] In FIG. 3 and FIG. 4B, the sheet with the fourth image S1-4 in the print order PO is rejected onto the discharge path 66. Sheets 60 trailing the rejected sheet 60 in the duplex pass 50 have already been printed on one side. In order to re-establish the original image order, those sheets 60 following the rejected sheet 60 are also discharged to the discharge path 66, as indicated in FIG. 4C. In the example of FIG. 3, this results in the loss of eight additional sheets 60, namely those designated with the images S1-5 to S3-2. The rejected images S1-4 to S3-2 are then re-assigned to blank sheets 60 upstream of the print station 16, as indicated by the sheets labelled with S1-4 to S2-3 in FIG. 4D.

[0097] The lower row in FIG. 3 as well as FIGS. 5A-F represent a scheduling algorithm according to the present invention. The scheduler 30 according to the present invention receives print instructions for three image sets S1-S3, as described above. The scheduler 30 assigns each of the three sets S1-S3 to a different one of the output holders 44. The scheduler 30 then, prior to printing, shuffles the images sets S1-S3 to form groups each comprising at least one image from each of the image sets S1-S3. Thereby, an alternating print order PO of the images is formed. In the example shown in FIG. 3, the scheduler 30 schedules the first image S1-1 of the first image set S1 at the start of the print order queue PO. Subsequently, the first image S2-1 of the second set S2 is scheduled, followed by the first image S3-1 of the third set S3. After that, the scheduler 30 schedules the second images S1-2, S2-2, and S3-2 of the three image sets S1-S3. After that a third group is formed comprising the third images S1-3, S2-3, S3-3 of the different image sets S1-S3. As such, the print order shown in FIG. 3 and FIG. 5A is defined.

[0098] After scheduling, the printing process is started, for example based on a readiness signal from the scheduler 30. Sheets 60 associated with the first image set S1 are transported to the first output holder 44, while sheets 60 with images of the second and third image sets S2, S3 are transported respectively to the second and third output holder 44.

[0099] During the print process as shown in FIG. 5B, the fourth sheet with image S1-2 belonging to the first image set S1 is rejected to the discharge path 66. The completed upstream sheets S1-1, S2-1, S3-1 are each transported to their respective output holder 44, as shown in FIG. 5C.

[0100] The scheduling algorithm according to the present invention has the advantage that then no sheets 60 for the second and third image sets S2, S3 need to be discharged, as these sheets 60 may be transported to their respective output holders 44 and deposited there in the desired order. To restore the image order for the first image set S1, the sheet ejector 64 need only discharge the sheets 60 on the duplex pass 50 that are associated with the first image set S1, namely the sheets 60 with images S1-3, S1-4, as indicated in FIG. 5D. While sheets 60 on the duplex pass 50 of the first set S1 are discharged, sheets 60 of the other sets S2, S3 are transported to their respective output holders 44, as shown in FIG. 5E. In contrast to the example given for the prior art, the number of additionally discharged sheets 60 is limited to only two. The amount of waste paper is thereby reduced by applying the algorithm according to the present invention.

[0101] The scheduler 30 then reroutes the discharged images S1-2, S1-3, S1-4 to blank sheets 60 upstream of the print station 16, as shown in FIG. 5F. The discharged images S1-2, S1-3, S1-4 are inserted into the printer order PO behind the last image S3-4 on the duplex pass 50. The inserted images S1-2, S1-3, S1-4 delay the scheduled images S1-5, S2-5 by the number of images S1-2, S1-3, S1-4 discharged to the discharge path 66. After inserting the discharged images S1-2, S1-3, S1-4, the print order PO may resume in its originally scheduled alternating manner. It will be appreciated that the FIGS. 5A-F are illustrated schematically to indicate the separate steps performed by the algorithm according to the present invention and that different orders of the steps or the simultaneous execution of multiple steps is within the scope of the present invention.

[0102] FIG. 6A illustrates the various steps of the method according to the present invention. After receiving the print instructions, the controller 20 determines the image sets S1-S3. Therein the controller 20 may define subsets as will be illustrated with regard to FIG. 7. The image (sub)sets are then designated to an output holder 44, wherein at least two (sub)sets S1-S3 are assigned to different output holders 44. In case the number of sets S1-S3 exceeds the number of output holders 44, multiple sets S1-S3 may be assigned to the same output holder 44. The controller 20 then forms the alternating image order PO where at least one image of a first set S1 is inserted in between images of a second set S2. The controller 20 then commences printing.

[0103] FIG. 6B illustrates the operation of the method according to the present invention in case of a sheet rejection. The controller 20 identifies the image set S1-S3 of the rejected sheet 60. Sheets 60 on the buffer transport path 50 section belonging to the identified image set S1-S3 are then also discharged. Sheets 60 associated with other image sets S1-S3 are passed to their assigned output holders 44. The controller 20 then inserts the discharged images into the print order PO, such that these images are reprinted on the desired medium type.

[0104] FIG. 7 illustrates an embodiment of the method according to the present invention particularly suited for printing multiple copies of a single image set. The print instructions in FIG. 7 comprise three identical image sets S1-S3. The scheduler 30 then divides at least one set S1 of the image sets S1-S3 into subsets comprising a portion of the images of the original image set S1, as indicated by the dotted line. The alternating print order PO is then formed

[0105] The scheduler 30 then assigns one of the subsets to a first output holder 44 on the left in FIG. 7. The subset is e.g. half of the original image set S1. The alternating printer order PO is then formed by inserting the second subset in between the second image set S2, which is thereby divided into two subsets. The first subset of set S1 is then designated to the first output holder 44 on the left in FIG. 7, while consecutive first subset of the second image set S2 is then assigned to the second output holder 44 in the middle of FIG. 7. The second subset of set S1 is then assigned to the middle output holder to complete an image set. Likewise, the second subset of set S2 completes the image set at the left output holder 44.

[0106] In case of a sheet rejection, the controller 20 discharges a number of sheets to continue stacking images at either of the output holders 44. During printing, one output holder 44 comprises a sheet stack provides a lower or first half of the image set S1-S3, while another output holder 44 comprises an upper or second half of the image set S1-S3. In case the rejected sheet 60 is part of the first half of the image set S1-S3, the controller 20 discharges sufficient sheets 60 to allow continued stacking at the stack with the second half of the image set S1-S3 and vice versa. Alternatively, the controller 20 may choose to start a new sheet stack at the third output holder 44 on the right side in FIG. 7. This stack can then also be completed up to half the image set to repeat the above mentioned method. Thereby, the number of wasted sheets 60 is reduced. It will be appreciated that any type of division into subsets may be made, e.g. thirds, halves, quarters, etc. for one or more image sets supplied by the print instructions. Within the present invention subsets in the alternating print order may be assigned to any output holder 44, as long as the image order of the sheet stack at the output holder 44 is preserved.

[0107] 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.

[0108] 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.

[0109] 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.