Quality control station with camera calibration system for sheet element processing machine

Abstract

A quality control station (2) for a sheet element processing machine, the station having at least one camera (6) arranged for capturing images of sheet elements (4) transported through the quality control station (2), and further having a camera calibration system (10). The camera calibration system (10) having a target holder (12) for holding an optical target (14), and a drive (15) for the target holder (12). The drive (15) is adapted for displacing the target holder (12) between a rest position, in which it is outside of the viewing area (7) of the camera (6), and a calibration position in which it is arranged in the viewing area (7) of the camera (6).

Claims

1. A quality control station for a sheet element processing machine processing sheet elements along a path of transportation, the quality control station comprising: at least one camera arranged for capturing images of sheet elements transported through the quality control station, the camera having a viewing area; and a camera calibration system comprising: a target holder configured for holding an optical target and the target holder is positioned below the path of transportation; a drive for the target holder, the drive being positioned above the path of transportation and configured for displacing the target holder between a rest position, in which the target holder is outside of the viewing area of the camera, and a calibration position in which the target holder is arranged in the viewing area of the camera; and a carrier arm connecting the target holder to the drive and moving the target holder in accordance with movement of the drive.

2. The quality control station of claim 1, wherein the drive includes a guide element extending transversely to the direction of transportation of the sheet elements and across the entire width of a passage along which the sheet elements are being transported.

3. The quality control station of claim 2, wherein the guide element is a pneumatic or hydraulic rod on which a moveable driven element is arranged.

4. The quality control station of claim 2, wherein the guide element is a screw driven by a motor, on which a moveable driven element is arranged.

5. The quality control station of claim 2, further comprising a belt associated with the guide element and located and configured for advancing a driven element along the guide element.

6. The quality control station of claim 1, wherein the drive is arranged either upstream or downstream of the viewing area of the camera.

7. The quality control station of claim 1, wherein the target holder has a laterally arranged and located introduction opening for receiving an optical target, the introduction opening being arranged and located laterally outside a machine frame when the target holder is in the rest position.

8. The quality control station of claim 1, further comprising a fixation device defining a position of the target holder in the rest position.

9. The quality control station of claim 8, wherein the fixation device comprises a spring, or a fixation pin, or a spring and a fixation pin.

10. The quality control system of claim 1, further comprising a position control configured for providing information on the position of the target holder along the drive.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 schematically shows a quality control station employed in a sheet element processing machine;

(2) FIG. 2 schematically shows in a side view a quality control station according to the invention using a camera calibration system;

(3) FIG. 3 schematically shows a top view of the quality control station of FIG. 2; and

(4) FIG. 4 schematically shows in a perspective view the portion identified with IV in FIG. 3.

DESCRIPTION OF AN EMBODIMENT

(5) In FIG. 1, a quality control station 2 is schematically shown, which is employed in a sheet element processing machine of which conveyor tables 3 are shown. The sheet element processing machine can process sheet elements 4 which are being transported in the direction of arrow A. The sheet elements 4 can be sheets of paper, cardboard or a similar material, or they can be in the form of a longer web. The sheet element processing machine can be a printing machine, a stamping machine, a laminating machine, a folding machine, a gluing machine, etc.

(6) The quality control station 2 is used for controlling the quality of the sheet elements 4. Generally stated, a light source 5 is used which directs light onto a surface of a sheet element which is currently being inspected.

(7) A camera 6 is used in the quality control station 2 for capturing an image of the sheet element 4 currently being advanced through the quality control station. More precisely, camera 6 captures an image in a viewing area 7 which is a very narrow area extending over the entire width of the sheet elements in a direction perpendicular to the direction A along which the sheet elements are being advanced through the quality control station 2.

(8) It is also possible to use more than one light source 5, and it is also possible to use more than one camera 6 in the quality control station 2. In particular, it is possible to use two cameras which are arranged adjacent each other, with a first camera capturing an image of the left half of the sheet and the second camera capturing an image of the right half of the sheet.

(9) The image captured by camera 6 is supplied to a control 8 where it is being compared with stored reference images and/or analyzed in various respects. Control 8 then makes a determination whether or not the quality of the respective sheet element 4 satisfies predetermined criteria.

(10) In order to make sure that the images captured by camera 6 correspond to a certain reference, camera 6 is being calibrated from time to time. To this end, a calibration system 10 (see FIGS. 2 to 4) is provided within quality control station 2.

(11) Camera calibration system 10 comprises a target holder 12 in which an optical target 14 can be arranged, and a drive 15 with which target holder 12 can be displaced between a rest position (shown in FIGS. 3 and 4) and a calibration position 12′ shown in FIG. 3 with broken lines.

(12) Drive 15 is configured for displacing target holder 12 in a direction D perpendicular to the direction A across the width of the quality control station. Generally, the target holder 12 can be displaced back and forth between the two sides of a machine frame 16 of the quality control station.

(13) In the embodiment shown, drive 15 comprises a guide element 18 which is here in the form of a pneumatic or hydraulic rod on which a moveable driven element 20 is arranged. Such combination of driven element 20 and pneumatic or hydraulic rod is also known as “rodless pneumatic or hydraulic piston” as it does not use a rod which extends in conventional hydraulic or pneumatic actuators from the piston through one of the end plates of the hydraulic or pneumatic cylinder.

(14) Drive 15 further comprises hoses 22 and switching valves 24 for supplying hydraulic or pneumatic pressure at the desired level to guide element 18.

(15) Target holder 12 is connected to driven element 20 by means of a thin carrier arm 26. Carrier arm 26 allows arranging guide element 18 at a certain distance (viewed in a direction parallel to direction A along which the sheet elements 4 are being advanced) from target holder 12. In the embodiment shown in the drawings, guide element 18 is arranged downstream of viewing area 7. Depending on constructional constraints, it is also possible to arrange the entire drive 15 upstream of viewing area 7.

(16) Furthermore, it can be seen in particular in FIG. 2 that drive 15 is arranged above the surface along which sheet elements 4 are being advanced (here schematically indicated as the top surface 9 of conveyor table 3) while target holder 12 is arranged beneath surface 9. This makes it possible to arrange optical target 14 at the level of surface 9 while at the same time arranging drive 15 within quality control station 2 and above conveyor table 3.

(17) Target holder 12 can be considered as a flat tray in which an optical target can be arranged. Advantageously, it is possible to fix the optical target to target holder 12. This is exemplified in FIG. 4 with springs 28.

(18) As can be seen in FIGS. 3 and 4, target holder 12 partially extends outside machine frame 16 when being in the rest position. This allows an operator to place an optical target in the target holder very conveniently.

(19) For calibrating camera 6, an appropriate optical target 14 is placed in target holder 12, and drive 15 is being used for moving target holder 12 together with target 14 in the direction of arrow D into the viewing area 7 of camera 6. There, the appropriate calibration is being made, and after the calibration is completed, target holder 12 is transferred back into the rest position outside of the viewing area.

(20) A calibration of camera 6 can be made in different respect, and different types of optical targets are being used for making the calibration. The calibration of camera 6 can relate to color, focus, geometry, white balance and potentially other parameters, and the optical target 14 can either be a target which is dedicated to a single aspect only, or it can comprise marks, patterns and/or imprints which allow a simultaneous calibration with respect to two or more aspects.

(21) A position control can be associated with drive 15. The position control provides information on the position of driven element 20 and/or target holder 12 either continuously along the possible travel between the machine frames 16 or specifically at certain locations which are relevant. As an example, a position sensor 30 is shown in FIG. 3 in a position which corresponds to target holder 12 being arranged in the middle between the two sides of machine frame 16. Such central position can be helpful for calibrating a single camera 6. In case two cameras are being used, two position sensors 30 might be advantageous.

(22) As an alternative to the pneumatic or hydraulic rod used in the described embodiment, other structure can be used for moving the target holder 12 into the viewing area of the camera and out of it again.

(23) As an example, the driven element 20 can be arranged on a guide rod and connected to a belt drive. It is also possible to arrange the driven element on a spindle (an endless screw) which extends over the width of the machine and is driven by an electric motor. It is even possible to move the target holder manually into and out of the viewing area of the camera.