CA1241865A - Method of determining the area coverage of a printing original or printing plate for printing presses - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A Measuring device which is equipped with a number of sensors determines the area coverage of a printing original or printing plate for printing presses. Each individual sensor of the measuring device is calibrated with the aid of calibration strips. By means of an additional sensor of the measuring device there is a printing-plate- and/or printing-original-specific correction calibration and an adjustment to identical values of all sensors. The correction calibration and adjustment are performed by way of a calibration field and a calibration area which are on the printing plate and/or printing original.

Description

`EIDELBERG / ~-359 ~ f~ March 1983 The invention relates to a method of determining the area coverage of a printing original or printing plate for printing presses by means of a measuring device equipped with a number of sensors in which each individual sensor is calibrated with the aid of at least one calibration strip with both minimum and maximum area coverage.

A syst~m for predetermining the settings for the ink zone adjusting screws on printing presses is known from US
patent speciEication 3,958,509. With the aid of an elec-tronic camera the area coverage of two calibration plates, one for the 0 ~ calibration and the other ~or the 100 ~
calibration, is measured and these va~ues are stored. In a further measuring operation the area coverage of the printing plate is measured, and these measured values are brought into agreement with the measured values of the two previously measured calibration plates. Thereupon the corrected measured values are stored. The ink zone adjusting screws are set in accordance with these corrected measured values.

In addition, DE-OS 29 50 606 describes a device for the zone-wise optoelectronic measurement of the area coverage of a printing original. The brightness distribution of a printing original is ~neasured by recording elements and supplied to a computer which then supplies appropriate signals for setting the ink zone screws.

A disadvantage of this system for predetermining the settings for the ink zone adjus-ting screws is that there is no automatic calibration of the measuring device in order to compensate for fluctuations of the illumination device and the receiver elements as well as of the entire analogue electronics and the different reflection con-ditions of the plates being measured. Furthermore, if illumination is by means of fluorescent tubes, the fluctua-tion in intensity which is dependent on the mains fre-quency has a very disadvantageous effect with regard to a

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scanning measuring run which should be as fast as pos-sible. Moreover, this system is most inconvenient for the operator since it is difIicult to take account of the different formats and types of plate. Furthermore, the designs are usua]ly very elaborate, expensive and complex with the result that the cost of their imple-mentation bears no sound economic relation to the desired savings in waste and set-up times by presetting the ink-ing control on the printing presses.

The object of the invention is to develop a method of determining the area coverage of printing plates, images of the printing plates, printed colour separations, films etc., and thus to be able to calculate the respec- ~"
tive ink requirement.

The technical object of the invention is achieved by the characterizing clauses of Claims ~ and 10.

The intention of the invention is to provide simpler operation and reproducibility when measuring area coverage pro~iles o~ printing originals. Furthermore, gr.eat flexi-bility is to be guaranteed with regard to types of printing original and formats of printing original, which leads to considerable savings in cost. Moreover, reliable preset-ting of the press i5 obtained through the high accuracy.

A particular advantage which becomes apparent is the cor-rection calibration by way of a special calibration field which is on the printing original in which several refer-ence points are scanned in the calibra-tion area.

An advantageous evaluation takes place via the automatic status recognition which is composed of several cornponents:
. Verification of the presence, exact position and cor-rect length of a calibration strip, 2. Detection of the calibration field on the printing plate and/or printing original, and

3. Scanning of the type and format of the printing plate and/or printing original.

To obtaln high measuring accuracy and thus to improve ~he quality of the prese-tting, if there is no calibration area on the printing plate and/or printing original, the minimum and the maximum values of the area coverage of the printing plate and/or printing original are advantageously measured by the sensors of the measuring device, and there is a subsequent normalization to these values.

It is practical to design the measuring device such that inside there is an illumination device consisting of fluorescent tubes whose fluctuations in intensity are smoothed, as a result of which high measuring speeds can be obtained.
The lenses in front of the ill~lmination device are for the improved, i.e. more homogeneous, illumination of the e.g. ink-zone-width areas of the printing plate. Disturb-ing shining effects can be suppressed by the use of polarization filters and dispersion films in the measuring head.

A preferred embodiment of the invention consists in that the receiving means are composed of sensors, and via a multiplexer the signals of the individual sensors are supplied to an amplifier for amplification and are digitized by an analogue/digital converter for storage. Control and calculation functions are performed by a computer which is integrated in the control panel.

The safety rollers fitted to the measuring device are a particular advantage since they prevent any damage to the printing original which may possibly rest uneven.

Calibration field masks are provided to facilitate the making of the measuring field on the different types of printing plate.

An embodiment of the invention is explained with refer-ence to the following drawings.

Fig. 1 shows an arrangement of the calibration strip and the printing plate on the printing plate support surface with measuring device.

Bii5 Fi~. 2 shows a vertical section through the measuring device.

Fig. 3 shows the operator keyboard for the printing plate reader.
r Fig, 4 shows the components of the rneasuring device.

Fig. 5 shows a film for making the calibration strip.

Fig. 6 shows a calibration field.mask with window slipped over a negative plate (negative copyl. r~r' Fig. 7 shows a calibration field mask without window slipped over a positive plate (positive copy).

Fig. 1 shows the printing plate support surface 1 with the measuring device 7 which is attached thereto and which runs in guide tracks 62. On the printing plate support sur~ace -1 there is a stop bar 10 whi.ch is at right angles to the scale strip 12. The horizontal stop bar 10 is, or example, divided into thirty-two measuring zones 11, corresponding to the ink duct zones of a certain press format, and the vertical scale strip 12 is, for example, divided into twenty-two measurinq zones 11, corresponding to the number of sensors. ~he printing plate 2 with the register and clamping rail stampings 63 is aligned at the stop bar 10 on the printing plate support surface 1 and is centralized with respect to the scales in the region of the printing plate 2. On the surface of the printing plate 2 are the ink-carrying surface 3 and the calibration ~ield 4 as well as the calibration area 20 with the meaSuring track 46. ~urthermore, disposed on the printing plate support surface 1 left of the vertical scale strip 12 is the calibration strip 6~ which is subdivided such that the left-hand field 6 is pro~ided for the minimum calibration and the right-hand field 5 or the maximum calibration of the ink control.

/ _ 5 ~ T~r3 Inside the measurin9 device 7, as shown in Fig. 2, there . are twenty~two sensors 9 and an additional sensor 8 which, in the course of a measuring run, determine the ink values of the calibration strip 64, the ink-carrying surface 3, the calibration field 9 and the calibration area 20 of the printing pla-te 2.

Inside the measuring device 7 there are illumination de-vices 14 with two fl.uorescent tubes 51 which are attached by holding devices 65. In the path of radiation of the fluorescent tubes 51 towards the printing plate support surface 1 there are lenses 15 which may also be in the form of polarization filters ~. The sensors 9 are dis- /.
posed above a focussing lens 18 directly over the measuring slit 19 and are coupled to a matching electronics 47.
Also in t.his path of rays are polari~ation filters 58 and dispersion films 39. The areas of the printing plate 2 and of the calibration strip 6~ which are to be measured by the sensors 8 and 9 are laid down by the measuring slit 19 and the partitions 29 of the light shafts. The measuring device 7 i5 driven by a motor (not shown) via a toothed belt and is guided in guide tracks 62. Disposed underneath on the measuring device 7 are safety rollers 16 which are attached to it by means of brackets 17.

Fig. 3 shows the individual controls (output possibilities and information on operator control) 21 to 55 which are situated on the desk panel 13 of the printing plate reader in order to perform.-the measuring operation. The s-teps of the method are performed, for example, in the fol~
lowing order:

The calibration strip 64, made preferably of the same material as the printing plate, is placed on the printing plate support surface 1 left of the printing plate 2.
Thereupon the unit is put into operation by means o the on/off switch-25. ~i.th the aid of the button 30 a vacuum is set up in the area of the format~dependent vacuum slits 38 which are in the printing plate support surface 1.

~his vacuum first of all draws i~ the calibration strip 64. The printing plate 2 is placed in position such that the register and clamping rail stampings 6~ are at the upper edge of the printing plate support surface 1 and are aligned with the stop bar 10 in such a way that the left-hand edge of the printing plate 2 is inside the first measuring zone 11 and is centered between the first and final measuring zones. Aligning is made easier by line markings 32 for the nominal width of Heidelberger Druckmaschinen standard plates.
Thereupon a preselection is made of the desired output, log and reset modes by the operator by pressing the buttons for output selection 52, log selection 53 and ,~
reset selection 54. The opera-tor can choose between a numeric, a graphic and a test log. sy means of the output button 24 the operator can have the log strip 23 printed out by the log printer 22.

The most important type of output of the printing plate reader is an automatically readable data carrier, e 7 g ~
a cartridge 55, The measured values of a complete plate set can be stored on this cartridge 55. This cartridge 55 is then preferably read by an input unit,in the control panel of the printing press. The data ~or the ink require-ment are then converted into press presetting values.

The format of the printing plate 2 i5 set at the encoding switches 26 which are identified by the symbols for format t width 27 and format length 28. Those figures are set which are covered by the printing plate 2 as it rests on the stop bar 10 and the scale strip 12. The format width which is input determines the travel of the measuring device 7.
The format which is set at -the encoding switches 26 is stored by pressing -the forrnat input bu-tton 45.

The colour separation of the printing plate 2 is selected with the aid of the colour separation selector b,utton 31, a~

_ 7 /
e.g. black, cyanl magenta, yellow or X and ~ ~or two additional colours. The suction air for the printing plate 2 is activated by means of the vacuum button 30 whereby the suction air is limited to the format-dependent vacuum slits 38. The measuring run is started by pressing the start button 33.

The measuring run begins with the measuring of the field 6 for minimum calibration and the field 5 ~or maximum calibration. This is followed by the measurement on the printing plate 2 beginning with the first measuring ~one 11 up to that measuring zone which corresponds to ~he set format width of the printing plate 2. '~

The measuring device 7 glides back at high speed over the printing plate support sur~ace 1 to its starting point.
After the output button 24 has been pressed, the selected output is initiated. It is a]so possible beforehand to measure further printing plates 2 with other colour separa tions. The paper feed button 21 is ~or the paper feed of the log strip 23 on the log printer 22. ~Irther func-tions which are useful for the operator are activated by the selective actuation of the emergency stop button 37, restart button 36 and cancelling button 35 (for colour separation selection and/or calibration field switch-of~). The special additional sensor 8 can be switched off via the calibration sensor switch-off button 34.

Fig. 4 shows in diagrammatic form the flo~ of signals within the rneasuring device 7. The individual components are the focussing ]enses 18, sensors 8 and 9, matching electronics 47, multiplexer 48 and amplifier 49. The measuring device 7 is driven by a motor (not shown) which is connected to a gear unit. By means, for example, of an inductive measuring pickup the basis is established for determining the position of the measuring device 7 on the printing plate support surface 1. The positions of the measuring device 7 are determined via a counter which accep-ts the pulses received by a pulse disc and via a comparator The measurementS take place during the continuous run of the measuring device 7 over the printing plate support surface 1. The measured values are supplied to the A/D converter 50 which is in the processing electronics of the unit.

The light reflected by the printing plate 2 is received via focussing lenses 18 by sensors 8 and 9, processed by the matching electronics ~7 and supplied via a multi-plexer 48 to an amplifier 49 and then to an A/D converter 50. To make optimum use of the resolution capability of the A/D converter 50, the amplification factor of the amplifier 49 is matched to the maximum signal of the sensors 9 of the field for minimum calibration 6 of the calibration strip 64. If a minimum number of steps o~ the usable converter range is fallen below, then the offset circuit of the amplifier ~9 is changed via the measured values o~ the fields for maximum calibration 5 of the calibration strip 64. In the event of a reaction between offset setting and amplifier setting, the ampli-fier circuit is r~-optimized. This may necessitate a new calibration run before the actual measuring run.
In general, the calibration run and the measuring run run into one another, at any rate within a printing plate set after the ~irst printing plate.

The individual sensors B and 9 are calibrated on the cali-bration strip 64. The additional sensor 8 determines the contrast conditions between calibration strip 64 and printing plate 2 via the calibration field 4 and the calibration area 20 on the printing pla-te 2. By means of special mathematical operations the previously established characteristics of the sensors ~ and 9 are matched to the conditions of the printing plate 2.

If an area coverage value less than 0~ is found in a measuring zone on the printing plate, then there is a calibration error as a result of defective calib~ation measuring areas. The minimum calibration is to be replaced by this value, i.e. the negative measured value is to be set equal to zero.

To have ~s low a difference as possible between the con-trast conditions of the prin-ting plate 2 and those of -the calibration strip 64` the calibration strip 64 should be made of the sarne material as the printing plate 2.
'The different calibra-tion strips 69 can be kept in a special calibration strip store which is, for example, in the measuring desk.

By means of a visual comparison between printing plate 2 and callbration strip 64 the printer should select the best possible calibratio~ strip 64 and place it in the measuring position on the measuring desk. This ensures that the receiving rneans is calibrated in the later work-ing range of -the printting plate 2. In con~unction with re-calibration this leads to OptiTTIUTII resolution and measuring accuracy. This is of particular importance if, owing to the possible absence of the calibration field 4 or a de-fective calibra-tion area 20 and/or calibration field 9, the additional sensor 8 has to be switched off by pressing the calibration sensor switch-off button 34.

Fig. 5 shows the film 56 for rnaking the calibra-tion strips 64. The two fields 41, 92 correspond to the minimum and maximum area c~verage. The marking lines 43 are for trimming to the different plate lengths. The identification corner 94 of the film 56 is, e.g. in the case of aluminium plates, cut off, and is retained in the case of multi- ¦
metal plates. When workin~ without automatic plate--type recognition, a microswitch in the printing plate support surface 1 in the region of the calibration strip 69 is actuated by the calibration strip 69 with the aid of which th~ type of plate is recognized.

The calibration Eield mask 60 showll in Fig. 6 has a window 59 for the copy of the calibration field 9 in t:he case of negative copies. I'he calibration field mask 57 shown in Fiy. 7 is used for making the calibration field 9 in the case of positive copies. The calibrattion field masks 57 and 60 are made of any material; calibration field masks made of sheet metal have proved particularly effective.

For the dimensionally correct copying of the calibration field ~ on the printing plate 2, the appropriate cali-bration field mask 57 or 60 is, in this special design, slipped over the right-hand top corner of the printing plate 2, i.e. at the end of printing since there are no stamped holes there.

The copying of the calibration strip 64 in the printing direction of the plate is particularly important in the case of printing plates 2 with a pronounced direction of shine (brushed, etc.). In principle, it would also be possible to integrate shine-reducing measures within the measuring device 7, e.g. dispersion films 39 or the use of polarization filters 40 in the measuring slit 19 and/
or in the path of the illumination and receiving rays.

-In contrast to aluminium printing plates, much light is reflected by the ink-carrying parts of the plate in the case of multi-metal printing plates. This makes it necessary for the measuring signal to be inverted. This is cornmunicated to the unit either by automatic actua-tion of a special microswitch when the calibration strip is placed in position, or automatically by the above-described plate type recognition.

The additional sensor ~i is preferably of the type which can be switched off by means of the calibration sensor ii switch-off button 34 in case the calibration field 4 is deEective or entirely missing.

In an embodiment which is different from the above-described input via encoding swi.ches 26, it is also possible to specify the forma-t automatically in that the jump in contrast from the printiny plate support surface 1 to the printing plate 2 is measured by the sensors 9 in the vertical (plate length~ direction and by the sensors 8 or 9 in the horizontal (plate width) direction.

The result of the measurement of the measuring device 7 are area coverages per zone. The area determined by zone width and number of sensors serves as a basis in this connection. In general, the format-dependent printing length is not identical with this basic area.
Therefore, there is an automatic correction of the measured value for normalization to 100%. This is done by multi- ;
plying the result with the format-dependent, fixed factors.

These area coverage values do not yet permit the direct presetting of the inking control in the printing unit of a printing press. Depending on the type of press and the ink, the area coverage values must now be used to calculate the presetting of the ink duct (zone opening) and the ductor (ink strip width~. This is done prefer-ably in the control desk of the printing press, but can, in principle~ also be performed with the computer of the printing plate reader.

The use of a special presetting computer is also possi~le.
By means of such a presetting computer with appropriate presetting programs it is possible to obtain the universal operation of all machines with presetting data insofar as they are in the format range. This presetting computer could also convert the zone intervals and ~one widths which are dependent on the ink duct and are fixed-programmed in the printing plate reader so that they can be used ~or other ink ducts.

From the area coverage data it is possible -to calculate also the ink requirement per sheet, or in the case of web-fed presses, per section length by including the ink film thickness on the sheet. Thus, it is possible to estimate the ink requirement for the production run in advance.

Claims (20)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. Method of determining the area of coverage of a printing plate means for printing presses by means of a measuring device equipped with a number of sensors in which each individual sensor is calibrated with the aid of at least one calibration strip with both maximum and minimum areas of coverage, said printing plate means including an area corresponding to a maximum area of coverage and an area corresponding to a minimum area of coverage, said method including scanning in the calibration strip maximum areas of coverage, and scanning in the calibration strip minimum areas of coverage with said sensors and effecting calibration thereof, measuring the maximum and minimum values of said printing plate means with one of said sensors and effecting a common calibration of all sensors as necessary by means of the measured plate means values, and measuring the printing plate means by means of said number of sensors.

2. A method as claimed in Claim 1, including;
determining the sequence of the areas of minimum and maximum area coverage from the measured calibration strip and using the determined sequence to verify the correct position of the calibration strip.

3. Method according to any one of the preceding Claims 1 or 2 wherein, the correct length of the calibration strip for the printing plate means is checked by assessing the measured values of one or more sensors taking account of the contrast between printing plate support surface and calibration strip.

4. Method according to Claims 1 or 2, wherein said printing plate means includes a separate calibration field and calibration area which define respectively said maximum and minimum areas of coverage, and wherein by means of said measuring device the presence of the calibration field is checked by scanning the minimum and maximum measured values in at least one of the calibration area and in the calibration field in the printing plate means.

5. Method according to Claims 1 to 2 wherein, said printing plate means includes a calibration field and a calibration area which define respectively said maximum and said minimum areas of coverage, and the type of printing plate means is detected by scanning the measured value magnitudes in the calibration field and in the calibration area preferably in relation to the calibration strip measured values.

6. Method according to Claims 1 or 2, wherein the correct length of the calibration strip for the printing plate means is checked by assessing the measured values of one or more sensors taking into account the contrast between the printing plate support surface and the calibration strip, and wherein the format of the printing plate means is automatically determined by assessing the change in contrast between printing plate support surface and printing plate means.

7. Method according to Claims 1 or 2 wherein, the minimum and the maximum measured values of the area coverage are determined by sensors of the measuring device on the printing original itself, whereby all measured values are normalized to said values, the area coverage thus likewise being determined in a manner specific to the printing plate means.

8. Method according to Claims 1 or 2, wherein, the measuring device includes an illumination device which emits light which is reflected by individual sections of the printing plate means, and wherein, the reflected light is converted by the sensors of the measuring device into an analogue signal corresponding to the area coverage, wherein the signal is supplied via a multiplexer and an amplifier to an analogue/digital converter and is subsequently stored for further processing.

9. In an apparatus apparatus for implementing the method of determining the area coverage of a printing plate or printing original for printing presses by means of a measuring device equipped with a number of sensors according to Claims 1 or 2 7 wherein, the measuring device is provided with an illumination device comprising fluorescent tubes whose fluctuations in intensity are smoothed, whereby lenses or polarization filters are disposed in front of the fluorescent tubes which homogeneously illuminate a defined ink-zone-width area of the printing plate 9 whereby the sensors measure the reflected light of individual sections of the zone width area of the measured object.

10. In an apparatus for determining the area coverage of a printing plate or printing original for printing presses by means of a measuring device equipped with a number of sensors, an illumination device comprising fluorescent tubes whose fluctuations in intensity are smoothed, whereby optical means selected from the group consisting of lenses and polarization filters are disposed in front of the fluorescent tubes which homogeneously illuminate a defined ink-zone-width area of the printing plate, whereby the sensors measure the reflected light of individual sections of the zone-width area of the measured object.

11. In an apparatus according to Claim 10, wherein, the sensors measure the reflected light of individual sections of the zone-width area of the measured object via a polarization filter.

12. In an apparatus according to Claim 10, wherein the sensors measure the reflected light of individual sections of the zone-width area of the measured object via a dispersion film.

13. In an apparatus according to Claim 10, 11 or 12, wherein safety rollers are provided on the measuring device in order to prevent possible damage to the printing original and/or printing plate.

14. Method of determining area coverage of an article selected from the group consisting of an original print and a printing plate by means of a measuring device equipped with a plurality of sensors with which each sensor, respectively, is calibrated with the aid of at least one calibration strip separate from the article and of the same material and surface condition as the article, said strip including minimum and maximum areas of coverage, said method comprising calibrating each sensor by means of said calibration strip, subsequently performing a further specific correction calibration of the article by scanning the article by one of said sensors, adjusting to identical values all of the plurality of sensors by means of one of the sensors used to scan the article, and thereafter determine the area of coverage by scanning the article with said measuring device.

15. Method according to Claim 14, which comprises performing the specific correction calibration and adjustment by means of a calibration field and a calibration region along a measuring track located on the article by sampling at least one reference measuring point in the calibration field having the maximum area coverage and, in the calibration region along the measuring track, having the minimum area coverage.

16. Method according to Claim 14, which comprises first performing an automatic status recognition by means of the measuring device, which verifies the presence and correct position of the calibration strip by checking the sequence of the areas with minimum and maximum area coverage.

17. In an apparatus for implementing a method of determining the area coverage of a printing plate or printing original for printing presses by means of a measuring device equipped with a number of sensors characterized by the features that for the measuring device (7) there is provided an illumination device (14) comprising fluorescent tubes (51) whose fluctuations in intensity are smoothed; that polarization filters (40) are disposed in front of the fluorescent tubes (51) which homogeneously illuminate a defined ink-zone-width area of the printing plate; and that the sensors (9) measure the reflected light of individual sections of the zone-width area of the measured object.

18. A method of determining area coverage of an original print, printing plate or the like by means of a measuring device equipped with a plurality of sensors, said method comprising calibrating each sensor with the aid of at least one calibrating strip having maximum and minimum areas of coverage, said calibration strip being separate from the printing plate or the like, yet formed of the same material as the printing plate or the like and having substantially similar surface conditions, conducting by means of at least one of the sensors a correction calibration specific to the printing plate or the like and adjusting all sensors by identical correction values determined by said correction calibration, and thereafter measure the original print, printing plate or the like by scanning the same with said mesuring device.

19. A method as claimed in claim 18, wherein said correction calibration is conducted whenever any of said sensors determines a lower measured value than said minimum area of coverage or determines a higher measured value than said maximum area of coverage.

20. A method as claimed in claim 18, wherein said printing plate or the like includes a separate calibration field and calibration area which define respectively said maximum and minimum areas of coverage and said correction calibration effects scanning of said areas.