Method and device for inspecting images on print products using an image inspection robot

Abstract

A method for inspecting images on print products in a printing material processing machine includes recording and digitizing produced print products using at least one image sensor in an image inspection process of a print job using an image inspection system. The recorded digital prints that have been created are compared to a digital reference image by using a computer and, if deviations are found between the recorded digital prints and the digital reference image, print products found to be defective are removed. The image sensor records the produced print products from at least two different viewing angles and/or viewing distances and the computer evaluates the at least two recorded digital prints as a function of the at least two viewing angles and/or viewing distances and assesses them in terms of deviations. A device for inspecting images on print products is also provided.

Claims

1. A method for inspecting images on print products in a printing material processing machine, the method comprising the following steps: using at least one image sensor to record and digitize produced print products in an image inspection process of a print job carried out by an image inspection system, the image sensor recording the produced print products from at least one of different viewing angles or different viewing distances; using a computer to compare at least two created and recorded digital prints to a digital reference image, the computer evaluating the at least two recorded digital prints as a function of the at least one of different viewing angles or different viewing distances and the computer assessing the at least two recorded digital prints in terms of deviations; using the computer to control a robot arm having the image sensor by moving the robot arm back and forth during an image recording process to simulate a shaking motion of the printed product during the inspection process; and removing defective print products upon finding deviations between the recorded digital prints and the digital reference image.

2. The method according to claim 1, which further comprises taking the at least two different viewing angles into consideration from 0 to 180° both vertically in terms of elevation and horizontally in terms of azimuth.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

(1) FIG. 1 is a block diagram illustrating an example of an image inspection system in a lithographic offset printing machine;

(2) FIG. 2 is a diagrammatic, perspective view of configurations of an image sensor provided by the robot arm; and

(3) FIG. 3 is a flow chart of the method of the invention.

DETAILED DESCRIPTION OF THE INVENTION

(4) Referring now in detail to the figures of the drawings, in which mutually corresponding elements have the same reference symbols, and first, particularly, to FIG. 1 thereof, there is seen an example of an image recording system 2 implementing the method of the invention. The system is formed of at least one image sensor 5, usually a camera 5, which is integrated into a sheet-fed printing machine 4. The at least one camera 5 records the printed images generated by the printing machine 4 and transmits data to a computer 3, 6 for analysis. This computer 3, 6 may be a separate computer 6, e.g. one or more dedicated image processors 6, or it may be identical with the control unit 3 of the printing machine 4. At least the control unit 3 of the printing machine 4 has a display 7 for displaying the results of the image inspection process. In the preferred exemplary embodiment, a sheet-fed lithographic offset printing press 4 is used, although the method of the invention may just as well be used in an inkjet printing context.

(5) FIG. 2 diagrammatically shows a preferred embodiment of the device of the invention. One can clearly see how, due to a robot arm 17, which is controlled by the computer 3, the camera 5 is capable of assuming different positions above a print product 8 to be inspected, in the present case a printed sheet 8. The positions provide different viewing angles and viewing distances from which the sheet 8 to be inspected may be inspected. One can clearly see two viewing angles of elevation 10, i.e. a vertical angle, an and azimuth 9, i.e. a horizontal angle, as well as a distance d 16 between the camera 5 and the inspection sheet 8.

(6) A flow chart of the method of the invention, which is implemented by the device of the invention shown in FIG. 2, is shown in FIG. 3. The first step of the method is to record and digitize the inspection sheet 8 with the printed images created thereon from different viewing angles in terms of the azimuth 9, elevation 10 between 0° and 180°, and from different viewing distances 16 by using the camera 5 and the device of the invention. An algorithm implemented on the computer by software derives quality parameters 12 from individual image data 11 as a function of the viewing angles 9, 10 and the viewing distance d 16. The parameters are a function of the viewing angles 9, 10 and the viewing distance 16: K(φ, θ, d). It may additionally be dependent on the quality requirements of the print job and on the personal characteristics of a potential inspector 1 in terms of age, sex, etc. The result is a typical end customer's personalized requirement for the image to be printed. For a final assessment of the inspection sheet 8, the value with the worst quality parameter 12 or with the best quality parameter 12 is selected as an assessment criterion 13 and compared to a typical parameter 12 defined by the operator as a basis for evaluation 14. If the method of the invention is used in a continuous monitoring process in the course of the image inspection during the printing operation, a threshold needs to be defined. When the threshold is exceeded, the printed sheets to be inspected are waste depending on a result 15 of the assessment.

(7) In a further preferred embodiment, the camera 5 is moved back and forth or from side to side by the robot arm 17 to simulate what is practically a shaking motion, which is a common image inspection process among persons 1 skilled in the art.

(8) The device of the invention and the method of the invention thus scan sample prints from various viewing angles 9, 10 and viewing distances 16. The subsequent automated print quality assessment is reproducible, promotes standardization, and saves time because it does not require an assessment by a skilled operator. In addition, the method of the invention provides a way of factoring in an end consumer's assessment.

(9) The following is a summary list of reference numerals and the corresponding structure used in the above description of the invention: 1 operator 2 image recording system 3 control unit 4 printing machine 5 image sensor/camera 6 image processor 7 display 8 inspection sheet 9 azimuth 10 elevation 11 digitized prints recorded from different angles 12 established parameters 13 criterion for selection 14 selected parameters 15 assessment result 16 distance between camera and inspection sheet 17 robot arm