SHEET PROCESSING MACHINE

Abstract

A sheet processing machine (10) has a device (44) for monitoring sheets (12) and a transfer mechanism (26) for moving sheets (12) along a handling direction within the sheet processing machine (10). The device (44) comprises a light emitting element forming a light barrier in a sheet passage between the light emitting element and the light receiving element. A control unit (46) is connected to the light receiving element and is adapted to register each sheet (12) passing the sheet passage.

Claims

1. A sheet processing machine with a device for monitoring sheets and a transfer mechanism for moving the sheets along a handling direction within the sheet processing machine, the sheet processing machine comprising: the device comprising a light emitting element and a light receiving element assigned to the light emitting element forming a light barrier in a sheet passage between the light emitting element and the light receiving element, and a control unit connected to the light receiving element and adapted to register each sheet passing the sheet passage, wherein the control unit comprises a storage module for storing information about the sheets and/or the sheet processing machine, and wherein a target shape of the sheets is stored in the storage module of the control unit.

2. The sheet processing machine according to claim 1, wherein the light barrier formed in the sheet passage by the light emitting element and the light receiving element is a light curtain.

3. The sheet processing machine according to claim 2, wherein the light curtain extends over at least 80% of a width of the sheet passage, especially over at least 90% of the width of the sheet passage.

4. The sheet processing machine according to claim 1, wherein the light receiving element and the light emitting element are mounted on a first rail and a second rail, respectively.

5. The sheet processing machine according to claim 4, wherein the first rail and the second rail are parallel to each other.

6. The sheet processing machine according to claim 1, wherein an expected number of sheets is stored in the storage module of the control unit, the expected number being determined based on the number of sheets provided in a loading station of the sheet processing machine and/or the number of sheets taken from the loading station, and the control unit is adapted to compare a current number of sheets having passed the sheet passage with the expected number of sheets.

7. The sheet processing machine according to claim 1, wherein the target shape of the sheets is determined based on a reference sheet being passed through the sheet passage.

8. The sheet processing machine according to claim 1, wherein the target shape of the sheets is determined by the control unit based on a reference file transferred to the sheet processing machine from a remote computer.

9. The sheet processing machine according to claim 1, wherein the target shape comprises a target size of the sheet and/or a target contour of the sheet.

10. The sheet processing machine according to claim 6, wherein the sheet processing machine comprises a human-machine-interface connected to the control unit.

11. The sheet processing machine according to claim 10, wherein the control unit is adapted to transmit a warning message to the human-machine-interface of the sheet processing machine if the current number of sheets is lower than the expected number of sheets, especially if there are no more sheets in the loading station.

12. The sheet processing machine according to claim 10, wherein the control unit is adapted to transmit a warning message to the human-machine-interface if the target shape of at least one sheet is not matching the target shape.

13. The sheet processing machine according to claim 1, wherein the device for monitoring sheets is arranged between a waste removal station and a blank separation station of the sheet processing machine.

14. The sheet processing machine according to claim 1, wherein the sheets are made of paper, cardboard, foil or a composite material thereof.

Description

[0044] Further advantages and features will become apparent from the following description of the invention and from the appended figures which show a non-limiting exemplary embodiment of the invention and in which:

[0045] FIG. 1 schematically shows a sheet processing machine according to the invention;

[0046] FIG. 2 schematically shows top views of a sheet being processed by the sheet processing machine of FIG. 1; and

[0047] FIG. 3 shows a perspective view of a device for monitoring sheets of the sheet processing machine of FIG. 1.

[0048] FIG. 1 schematically shows a sheet processing machine 10 making it possible to cut blanks 11 (see FIG. 2) from a succession of sheets 12. These blanks are usually intended to be subsequently folded and bonded to form packaging boxes. However, the sheets 12 might generally be made of e.g. paper, cardboard, foil, a composite material thereof or any other material routinely used in the packaging industry.

[0049] The sheet processing machine 10 comprises a series of processing stations that are juxtaposed but interdependent one another in order to form a unitary assembly. The processing machine 10 includes a loading station 14 followed by a cutting station 16 (also usually named punching station) comprising for example a die or platen press 18 where the sheets 12 are transformed by cutting, a waste removal station 20 wherein most of the waste parts are stripped, a blank separation station 22 (also usually named reception station) for separation of the blanks 11 (or blanking operation) by means of a blanking tool 23 and an evacuation station 24 for removing the residual waste sheets 25 (see FIG. 2) of the punched sheets 12.

[0050] The number and nature of the processing stations may vary depending on the nature and the complexity of the converting operations to be carried out on the sheets 12.

[0051] The sheet processing machine 10 also has a transfer mechanism 26, which in the shown embodiment is a conveyor, to make it possible to individually move each sheet 12 from an outlet of the loading station 14 to the evacuation station 24.

[0052] The conveyor uses a series of gripper bars 28 that are mounted so as to be moveable by means of two loops of chains 30 one placed laterally on each side of the sheet processing machine 10. Each loop of chains 30 travels around a loop which allows the gripper bars 28 to follow a trajectory passing successively by the cutting station 16, the waste removal station 20, the blank separation station 22 and the evacuation station 24.

[0053] Each gripper bar 28 travels on an outward path in a substantially horizontal plane of passage between a driven wheel 32 and an idler wheel 34, and then a return path in the top portion of the sheet processing machine 10. Once returned to the driven wheel 32, each gripper bar 28 is then able to grip a new sheet 12 at a front edge of the sheet 12.

[0054] In FIG. 1, each processing station is illustrated in the form of two rectangles symbolizing respectively its top portion and its bottom portion that are positioned on each side of the plane of movement of the sheets 12.

[0055] In FIG. 1, a transverse (or lateral), longitudinal and vertical direction are indicated by the orthogonal spatial system (T, L, V).

[0056] The terms upstream and downstream are defined with reference to the direction of movement of sheets 12 in a handling direction as illustrated by the arrow D in FIG. 1.

[0057] In FIG. 2, the current state and shape of the sheet 12 being processed by the sheet processing machine 10 (see FIG. 1) is shown, wherein the top views of the sheets 12 are arranged according to the sequence of the stations of the sheet processing machine 10 of FIG. 1.

[0058] In the loading station 14, the sheet 12 is provided as flat sheet with a rectangular or quadratic surface.

[0059] In the cutting station 16, a contour of the blanks 11 is prepared by forming weakened edges 38 in the sheet 12, e.g. by a sequence of nicks and/or perforations.

[0060] In the waste removal station 20, selected parts of the sheet 12 are cut out and are ejected from the sheet 12, as indicated with shaded areas 40 in FIG. 2.

[0061] Finally, the blanks 11 are separated from the sheet 12 in the blank separation station 22 such that two cross-shaped blanks 11 with a central opening 42 are obtained from the sheet 12 in the shown embodiment.

[0062] The rest of the sheet 12, i.e. the residual waste sheet 25, is removed in the evacuation station 24.

[0063] Of course, the sequence shown in FIG. 2 is illustrative in nature, only. Different shapes and sizes of the sheet 12 and/or of the blank 11 can be used and formed by the sheet processing machine 10, respectively, depending on the used type of sheets 12 and on the processing stations provided by the sheet processing machine 10.

[0064] Coming back to FIG. 1, the sheet processing machine 10 further comprises a device 44 for monitoring sheets 12 being moved downstream from the waste removal station 20 to the blank separation station 22 by the transport mechanism 26.

[0065] In principle, the device 44 could be placed between any two of the processing stations of the sheet processing machine 10, depending on which current state of the sheet 12 is the most important and/or the most suited one for monitoring the correct operation of the sheet processing machine 10.

[0066] The device 44 is connected to a control unit 46, e.g. by an Ethernet connection.

[0067] However, the device 44 could also be connected to the control unit 46 by any means which provides a sufficiently fast exchange of signals between the device 44 and the control unit 46. E.g., the connection can also be established wireless, e.g. by Wi-Fi.

[0068] The control unit 46 comprises a storage module 48 in which the number of sheets 12 provided in the loading station 14 and the processing speed, i.e. the number of sheets 12 per second to be processed by the sheet processing machine 10, is stored.

[0069] The control unit 46 is further connected to a human-machine-interface 50 which in the shown embodiment is a touch-sensitive display. By the human-machine-interface 50, a (not shown) operator of the sheet processing machine 10 can be informed on the current status of the sheet processing machine 10 and can control the operation of the sheet processing machine 10, too.

[0070] In FIG. 3, the device 44 for monitoring sheets 12 is shown in a perspective view.

[0071] The device 44 comprises a first rail 52 and a second rail 54, wherein the first rail 52 comprises an integrated (i.e., not explicitly shown) light emitting element and the second rail 54 comprises an integrated (i.e., not explicitly shown) light receiving element. The light emitting element has a multitude of light emitting sources, especially a multitude of laser emitting spots, while the light receiving element has a multitude of light receiving sensors, wherein each of the light receiving sensors is associated to one light emitting source. This arrangement results in an essentially continuous light curtain 56 between the first rail 52 and the second rail 54.

[0072] The first rail 52 is attached to a frame 58 of the blank separation station 22 by means of several mounting points 60of which only one is shown in FIG. 3such that the light curtain 56 is located in a sheet passage 62.

[0073] As can be seen from FIG. 3, the light curtain 56 extends over most of the width of the sheet passage 62 along the transverse direction T. The light curtain 56 especially extends over at least 80% or at least 90% of the width of the sheet passage 62. In principle, the light curtain 56 could also extend over the full width of the sheet passage 62.

[0074] In the following, the mode of action of the sheet processing machine 10 in regard to the device 44 will be described in more detail.

[0075] As described before, the sheet processing machine 10 is used for converting a pile of sheets 12. More specifically, the sheet processing machine 10 is used to cut out blanks 11 from the sheets 12.

[0076] The device 44 for monitoring the sheets 12 is used to provide feedback for determining if the sheet processing machine 10 operates correctly, i.e. if all sheets 12 provided in the loading station 14 are processed and if all produced blanks 11 are of the correct shape.

[0077] For this purpose, the loading station 14 is connected to the control unit 46 such that the loading station 14 sends to the control unit 46 the total number of sheets 12 provided in the loading station 14. The total number of sheets 12 can also be provided by the operator of the sheet processing machine 10 via the human-machine-interface 50. The control unit 46 stores the total number of sheets 12 in the storage module 48.

[0078] Further, before processing the sheets 12, the operator provides a reference sheet which is passed through the sheet passage 62. The reference sheet corresponds to the desired form of the sheets 12 after leaving the waste removal station 20 and before entering the blank separation station 22 (see FIG. 3). For providing the reference sheet, the sheet processing machine 10 can have an additional (not shown) operator access in the processing station upstream of the device 44 for monitoring sheets, i.e. in the waste removal station 20 in the shown embodiment.

[0079] The control unit 46 records the signal sequence received from the light receiving element of the device 44 when the reference sheet is passed through the sheet passage 62 and stores said signal sequence in the storage module 48 for reference. Based on this signal sequence, the control unit 46 calculates a target size and/or a target contour of the sheets 12.

[0080] Additionally, the control unit 46 can store machine information about the sheet processing machine 10 in the storage module 48, e.g. a target processing speed of sheet processing machine 10 in sheets per second. The machine information can also be set by an operator via the human-machine-interface 50.

[0081] As soon as the processing job for converting the sheets 12 has started, the control unit 46 registers each sheet 12 passing the device 44, more specifically passing the sheet passage 62. Registering includes counting the sheets 12 passing the device 44 for obtaining a current number of sheets 12 as well as comparing the signal sequence provided by the light receiving element of each passing sheet 12, corresponding to the shape of each sheet 12, with the signal sequence stored in the storage module 48, i.e. the target shape.

[0082] As an alternative, the control unit 46 may use a reference file to compute a reference signal sequence received from the light receiving element of the device 44 when a sheet 12 is passed through the sheet passage 62. To do so, based on the target shape of the sheet 12, the control unit determines for each reading of the light receiving elements whether the light is totally blocked, partially blocked, or not blocked at all by a sheet 12 having the correct shape. The transparency level, i.e., the light intensity detected by the light receiving element when the light is totally blocked by the sheet, may be computed from the mean, median, or any suitable statistics of the set of totally blocked readings from the first sheet or from the first few sheets of a processing job.

[0083] Preferably, during the analysis using the reference file, the control unit may ignore the readings which may be partially blocked by the sheet and only use the ones that are either totally blocked or not blocked at all. As an alternative, the control unit my decide to assign target value for each individual light receiving element reading that depends on the proportion of the light blocked by the sheet at that location and time. Then, it may compare this target value to the real reading during the assessment. This last alternative may preferably be used when the field of view of the light receiving elements is larger than the waste (i.e., the parts of the sheet to be ejected by the machine), thereby allowing to control the quality despite a coarse array of light receiving elements.

[0084] The control unit 46 is adapted to calculate an expected number of sheets 12 based on the number of sheets 12 originally provided in the loading station 14 and the number of sheets 12 already being taken from the loading station 14. For this purpose, the loading station 14 sends the number of sheets 12 already taken from the loading station 14 to the control unit 46.

[0085] The control unit 46 essentially continuously compares the expected number of sheets 12 with the current number of sheets 12. If the current number of sheets 12 is lower than the expected number of sheets 12, the control unit 46 transmits a warning message to the human-machine-interface 50 to inform the operator of the sheet processing machine 10 that there might be a problem with the operation of the sheet processing machine 10. E.g., one of the sheets 12 could be trapped inside the waste removal station 20 instead of being delivered to the blank separation station 22.

[0086] If no more sheets 12 are present in the loading station 14 and the current number of sheets 12 is still lower than the expected number of sheets 12, the control unit 46 can send an error message to the human-machine-interface 50.

[0087] The error message can be visually more prominent than the warning message to ensure that the operator cannot ignore that there is a discrepancy in the number of sheets 12.

[0088] Further, if the control unit 46 asserts that the shape of at least one sheet 12 is not matching the target shape stored in the storage module 48, the control unit 46 transmits a warning message to the human-machine-interface 50 to inform the operator that the blanks 11 coming from this sheet 12 might not have the desired shape or have not being successfully pushed out of the sheet 12 at all.

[0089] Also, the control unit 46 can transmit the current number of sheets 12 in this case such that the operator can easily identify said blanks 11 in the resulting pile of blanks 11 produced by the sheet processing machine 10 and being collected in the blank separation station 22.

[0090] Therefore, the sheet processing machine 10 according to the invention provides a simple and reliable device for monitoring the correct processing of sheets 12 in the sheet processing machine 10. In this way, any unexpected situations during production of the blanks 11, e.g. damaged blanks 11 or missing sheets 12, can be identified to ensure high quality of the blanks 11 and minimize waste produced by and downtimes of the sheet processing machine 10.