BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
FIG. 1 is a diagrammatic, partly perspective and partly elevational view of a motor-driven color measurement device provided on a measurement table and connected to a computer; and
FIG. 2 is a perspective view showing a detailed representation of a measuring head in the motor-driven positioning device of the color measurement device.
DETAILED DESCRIPTION OF THE INVENTION
Referring now to the figures of the drawings in detail and first, particularly, to FIG. 1 thereof, there is seen a color measurement device connected to a computer 4. The color measurement device is formed of a measurement table 2, on which print substrates 3 that have been produced may be placed. A measuring bar 1, in the from of a motor-driven positioning device, is provided for carrying out color measurements, for example, on the print substrates 3 placed on the measurement table 2. The measuring bar 1 shown in FIG. 1 is movable in the X direction in order to move across the entire length of a print substrate 3 resting on the table. The measuring bar 1 includes a measuring head 8, which is movable in the Y direction and can be moved to specific measurement locations on the print substrate 3 to carry out color measurements on the measurement locations. In addition, the measuring head 8 may be used, for example, to register, identify, and measure color control strips 13 on the print substrate 3. The data measured by the measuring head 8 are transmitted to the computer 4 and may be displayed on a display device such as a screen 5 connected to the computer 4. The computer 4 and the screen 5 are controllable by an operator through an input device such as a keyboard 6 and a mouse 11. The computer 4 may be a standard desktop or laptop PC equipped with appropriate control software for operating the color measuring device. A communication connection connects the computer 4 to a printing press 7 so that adjustment and control operations can be carried out on an inking unit of the printing press 7. For this purpose, the computer 4 has access to the digital data of the original image of the print substrate 3 that is currently being produced. In the computer 4, the data obtained by the measuring head 8 are compared to the corresponding data of the original image to recognize deviations. If the deviations exceed an acceptable tolerance, adjustments can be carried out in the inking units of the printing press 7 to reach the desired value.
The color measurement device in question preferably measures individual spots on the print substrate 3. These measurement locations may either be present in the original image stored in the computer 4, if they have been introduced as measurement locations in the file of the original image by a pre-press department. However, in many instances, the press operator wants to define his or her own individual measurement locations for a calorimetric inspection of the printed sheet 3. In the embodiment shown in FIG. 1, he or she can do so prior to the measurement operation by using the mouse 11 and the keyboard 6 to select individual measurement locations on the screen 5. For this purpose, the original image is displayed on the screen 5 in a way that is as detailed and as accurate as possible. The resolution of the displayed original image is limited by the resolution of the screen 5. Since even high-resolution screens 5 usually do not exceed a display capacity of more than 2 million pixels, the computer 4 gives the operator the option of enlarging specific areas on the screen 5. This magnifying function allows the operator to define and mark a certain area on the complete image of the original displayed on the screen 5 with the mouse, for example. The selected area is then displayed in an enlarged form on the screen 5 as desired. In order to be able to make an accurate selection of measurement locations on the screen 5, the selected section ought to be displayed in a resolution of at least 25 dpi. The operator can then use the mouse 11 to indicate the desired measurement locations on the screen 5. The selected measurement locations are then stored in the computer 4. It is thus possible to select any desired number of measurement locations by switching between full image and enlarged section. Once the operator has selected all desired measurement locations, the latter are forwarded to the measuring device. Then the measuring head 8 is sequentially moved to the selected measurement locations on the print substrate 3. For this purpose, the computer 4 may calculate the most favorable path of movement including all measurement locations, so that the inspection of the selected measurement locations on the print substrate 3 can be carried out as quickly as possible.
In order for the measurement locations selected on the screen 5 to correspond to the measurement locations 3 that are actually inspected on the print substrate 3, the coordinates of the measured print substrate 3 must be correlated with the image data displayed on the screen 5. This is important, in particular, for a case in which the print substrate 3 has been placed on the measurement table 2 in a skewed orientation. For this purpose, the measuring head 8 may initially measure one corner of the print substrate 3 and then further marks on the print substrate 3, such as color control strips 13. With the aid of these marks, the computer 4 may then determine the actual position of the printed image on the print substrate 3. Based on this actual position, the coordinates of the measurement locations selected by the operator are adjusted in an appropriate way so that the measuring head is moved to the desired measurement locations even if the print substrate 3 is skewed. The original image may be stored in the computer 4, or the computer 4 may directly access the computer of the pre-press department through an internal network or the web to display the original image data online on the screen 5.
The measuring head 8 of the measuring device shown in FIG. 1 is illustrated in more detail in FIG. 2. As can be seen, the measuring head 8 is equipped with a color sensor 10 for the spectral measurement of individual measurement locations on the print substrate 3. In addition, the measuring head 8 includes a preview sensor 9, which also scans the print substrate 3 optically. The preview sensor 9 is provided upstream of the color sensor 10, as viewed in the scanning direction of the measuring bar 1, so that the preview sensor 9 is the first to scan the surface of the print substrate 3, followed by the color sensor 10. It is the task of the preview sensor 9 to scan the surface of the print substrate 3 at a high geometric resolution of at least 50 dpi in order to target precisely the measurement location that the operator selected on the screen 5. Once the desired position has been reached, the color sensor 10 is positioned with the aid of the data registered by the preview sensor 9 in such a way that a calorimetric measurement can be taken at precisely the selected measurement location. A great advantage of this feature is that the color sensor 10 does not need a high geometric resolution. Moreover, the area scanned by the color sensor 10 may be considerably smaller than the area scanned by the preview sensor 9, because it is not the task of the color sensor 10 to position the measuring head 8. As a consequence, the color sensor 10 does not have to scan the environment of the measurement location. The preview sensor 9, which has a high geometric resolution, is perfectly suited to detect borders and color strips 13 on the print substrate 3 and thus to use the position of the color strip 13 as an indicator of the position of the print substrate 3 on the measurement table 2. Likewise, the preview sensor 9 can register the structure of the color control strip 13 and assign the color control strip 13 to a specific type of color control strips.
Furthermore, the measuring head 8 has two lighting devices 12, which illuminate the area that is registered by the measuring head 8 on the print substrate 3 for the purpose of a better detection of image dots. The lighting devices 12 may be constructed in such a way that one is associated with the preview sensor 9 and the other is associated with the color sensor 10. In addition, the measuring head 8 is provided with a light pointer 14. The light pointer 14 is formed of a bright, dot-shaped light source that optically marks the measurement location that has been reached on the print substrate 3. Thus, the measurement location is brightly lit on the print substrate 3 for the operator, so that the operator can see which measurement location is currently being targeted on the print substrate. This gives the operator the opportunity to optically control the targeted measurement location and to compare the latter with the one selected on the screen 5. The user interface on the screen 5 may be constructed in such a way that once the measuring position has been reached on the print substrate 3, the operator is asked whether or not he or she accepts the measurement location marked on the print substrate 3 by the light pointer 14. If the operator accepts the measurement location, the latter will be measured and the measuring continues. If the operator does not accept the indicated measurement location, he or she may be given a chance to correct the displayed measuring position. Thus, at all times the operator is able to compare the measurement location selected on the screen 5 to the measurement location actually targeted on the print substrate 3 and can thus visually monitor the measuring operation with his or her own eyes.
The measuring bar 1 and the measuring head 8 shown in FIG. 1 are provided with electric drives for moving the measuring bar 1 in the X direction as desired and for moving the measuring head 8 in the Y direction as desired. These drives may be linear drives. The computer 4 can automatically move the measuring devices to the measurement locations selected by the operator by controlling the drives for the measuring bar 1 and the measuring head 8. The screen 5 may also be a touch screen so that the operator can select the measurement locations on the screen 5 simply by touching the surface of the screen. This input method is especially intuitive, because the operator only has to point at the desired measurement locations on the screen 5. In addition or as an alternative to the screen 5, a large-format projection by a video projector is possible. In this case, individual measurement locations may be selected with the aid of a mouse 11, having a pointer which is also projected. It is likewise possible to register the gestures of the operator with a camera, so that in this case too, the operator only needs to point at the measurement locations.
Patent Application
20080087114
