EP0802047B1 - Half tone screen and method and means for its realisation - Google Patents

Abstract

The method involves engraving a template pattern hole structure in a template pattern region (2) of a template base body to form a template pattern (3). Several uniform reference hole structures (4) with different degrees of transmissivity are laser engraved into the template base body outside the template pattern region. The degree of transmissivity of each reference hole structure is compared with each of several desired degrees of transmissivity and the structures are newly engraved depending on the deviations so that deviations are reduced. The process is performed stepwise at least once.

Description

The invention relates to a method for producing a halftone template according to the preamble of claim 1, a device for performing of the method according to the preamble of claim 15 and a Halftone stencil produced by the process according to the preamble of Claim 22. Such devices and such a method are e.g. known from document EP-A-0 679 510.

Templates for textile printing, which, for example and due to the Apply different colors per unit area (Halftone printing) are generally known.

The problem with halftone printing is that there are many settings of operating parameters both on the used to manufacture the template Engraving device as well as on the printing press assessing and Skill left to the engraver or the printer, and thus straight unintentional, strong deviations from the desired in the area of halftone printing Intensity course of the halftone print arise. So z. B. by Halftone stencils that do not have the nominally correct opening ratios were engraved, or as a result of an inadvertently incorrectly set printing machine or one of the printing stations some of the colors with wrong intensity be applied. Especially with polychromatic prints, this leads immediately to a sensitive disturbance of color reproduction, which is nothing else means that those colors whose correct reproduction is more accurate on compliance The proportions of the individual components are based on the color reproduced incorrectly.

The invention has for its object to provide halftone templates or to specify a process for their manufacture, with which a halftone print can be carried out more accurately or true to color. It is the aim of the invention Furthermore, a device suitable for producing such halftone stencils to accomplish.

A method according to the invention is characterized in that in the template body several outside of the template pattern area uniform reference hole structures are engraved, each different Have permeability levels.

The reference hole structures can also be used as halftone marks or area marks be designated. These reference hole structures or surface marks can directly adjacent to each other, but can also be spaced apart or be separate.

According to the invention, in addition to one at the edge of the halftone template possibly existing print mark (Pico) the mentioned reference hole structures generated with which certain predetermined color intensities should be achieved when printing with the stencil. These reference hole structures consist of small areas, e.g. B. squares, rectangles or Circles with different but predetermined permeability be engraved and with the nominally correct permeability and at correct setting of all parameters on the printing press during later Print with such a halftone stencil a defined and therefore verifiable Sequence of color intensity values from the intensity range from 0 to 100% surrender.

By checking the intensity values using the reference hole structures obtained print images and, if necessary, by changing the print parameters depending on the result of the check, an improved result can be obtained Also achieve halftone printing in the stencil pattern area, since the existing one Template pattern hole structure in relation to the reference hole structure (both do not necessarily have to be identical).

According to an advantageous development of the invention, the degree of permeability of each reference hole structure with a respective target permeability compared to the uniform depending on the respective deviation To re-engrave reference hole structures in such a way that the mentioned Deviation is reduced, this sequence of steps being carried out at least once becomes.

The advantage of this measure can be seen in the fact that even before the actual Pressure of the parameters "permeability" can be brought to its setpoint can (or at least approximates this), so that later in the actual No longer print the remaining printing parameters to such a large extent need to be changed, which maybe not at all would be more possible to get to the desired color intensities for the given ones Permeability levels (target permeability levels) to come. As The target permeability should be the nominally correct opening ratio of the Halftone stencil can be understood. The actual permeability then refers to the actually achieved opening ratio of the halftone template.

According to another advantageous development of the invention, that in the template pattern area lying template pattern hole structure depending of the deviations mentioned. So it takes place when the actual deviates Permeability level from the target permeability level not just one New engraving of the respective reference hole structure, but there will also be a change the engraving parameters were made to result in an improved stencil pattern hole structure get. As already mentioned, the permeability levels in different areas of the template pattern hole structure not necessarily with the degrees of permeability of the reference hole structures be identical. The former are rather related to the latter, so that when changed the permeability of the reference hole structure due to a deviation from the corresponding target permeability, the relationship mentioned must also be changed accordingly.

According to one embodiment of the invention, the old reference hole structures, after its permeability with the target permeability was compared, eliminated. This can eliminate the old reference hole structures be done before new ones are engraved. The elimination is e.g. B. possible that the old reference hole structures simply from the template body be cut off. However, it is more advantageous to paint over them and new reference hole structures in the corresponding areas engrave.

According to a very advantageous further embodiment of the invention, the Degree of permeability of a respective reference hole structure is measured automatically. Basically, the comparison between permeability and target permeability can be made of a respective reference hole structure, that is by the engraver. However, an automated control is more useful because it can be done faster and more accurately. For visual comparison In addition, the reference hole structures must be relatively extensive, that is the rectangles, squares or circles already mentioned at the beginning, for example be relatively large. The respective reference hole structure then comprises a great many Stencil openings. However, if the permeability is measured automatically, this means that relatively fewer template openings can be used or smaller reference hole structures take up what time and space saves the template body.

As a template body z. B. a sieve can be used on which one Cover layer comes to rest, the screen openings to form a reference hole structure leaves free at least in some areas.

The covering layer can be a lacquer layer covering the sieve, with the help of a portion of a laser beam is burned away to expose the screen openings. It can also have polymerizable properties to pass through point exposure by means of z. B. to be cured by a laser beam. The unexposed are then exposed in a subsequent development process Areas of the varnish layer removed to expose the screen openings. The cover layer However, if it has polymerizable properties, be covered at points with the help of liquid that is opaque is. This is followed by a large-scale exposure and curing of the covered layer areas and then a development process for Removal of the uncured layer areas. Alternatively, the paint layer but also by spraying a liquid covering material onto it Sieve can be made using a nozzle. Wherever stencil openings are created the nozzle is switched off.

As a basic template body, one with a closed one can also be used Surface is used, on which there is a covering layer, which leaves the surface areas free to form the reference hole structure.

Here too, the cover layer can be burned off by means of a laser beam, by spot exposure and subsequent development (if they are polymerizable is) or be prepared by liquid using a Nozzle is sprayed onto the surface of the template body. As well here too, the covering layer can initially be covered with liquid at certain points that is opaque. After that, a large area can be used Exposure takes place around those not covered by the liquid Harden layer areas. Then there is a development process for detaching of the uncured layer areas.

After the cover layer with the corresponding several reference hole structures is completed, these are measured to determine the degree of permeability to determine the respective reference hole structures. Is that true Finally, the permeability corresponds to the target permeability or if it has been adequately approximated to this, then metallic will become on the cover layer Material applied to obtain a sieve, which is then from Template body is removed. Is this z. B. made of nickel, so nickel can be galvanically deposited on its surface to form sieves. The finished screen then contains not only the multiple reference hole structures, but also the finished template pattern.

In the case of a sieve that is present from the outset, the permeability becomes the reference hole structure by means of a light beam passing through the sieve openings measured, which is essentially perpendicular to the stencil surface runs and can enforce this in one direction or the other. The The light beam is focused, with the focus being on the stencil surface is coming.

Alternatively, the degree of permeability of the reference hole structure can be used in this case also by means of a gas flow passing through the sieve openings be measured.

In the case of a template body with a closed surface the permeability of the reference hole structure in the on this surface lying lacquer layer by means of a reflected on the exposed surface Beam of light measured. Depending on the size of the reference hole structure The amount of reflected intensity changes, which is a measure of the openings Size of these openings is. However, it must be taken into account here that the Sieve openings of the sieve that was later applied come to lie where at the Measurement still material of the cover layer is present. This must be done when determining the degree of permeability are taken into account.

It is determined after measuring the degree of permeability that this from Target permeability differs depending on the manufacturing variant preferably the pulse ratio of the laser beam or an on / off cycle the nozzle spraying the liquid changes to the degree of permeability to match the target permeability.

In a development of the invention, the template body can be a hollow cylinder be designed so that according to the inventive method also halftone rotary printing stencils are producible.

An inventive device for producing a halftone stencil contains a bearing device for the rotatable mounting of a hollow cylinder; a Means for machining the outer peripheral surface of the hollow cylinder; one Slidable parallel to the hollow cylinder axis, the at least one Carries part of the processing device; and a control device for Control of the machining device and for moving the carriage with rotating hollow cylinder. This device is characterized by that they have a measuring device for measuring the transmittance of in has reference hole structures lying in a predetermined template area.

The reference hole structures are preferably located on only one end face End of the hollow cylinder so that the location of the measuring device is chosen accordingly is. You can therefore z. B. attached to the storage facility.

Last but not least, a halftone stencil is drawn with an approximately central one Stencil pattern area by being outside the stencil pattern area several uniform reference hole structures, each with a different one Has degree of permeability. The halftone template can be used be hollow cylindrical to obtain a rotary printing stencil. The reference hole structures can lie directly on one another or separately be arranged from each other.

It should be pointed out again that under the term reference hole structure an area is understood in which there are several uniform or even open sieve openings or several uniform or uniform Structures used to form sieve openings. In the case of sieve openings the different degrees of permeability are achieved that these screen openings are more or less covered by the cover layer will. In the case of the structures mentioned to form the sieve openings different degrees of permeability in the sieve to be formed later achieved that the structures are more or less wide.

Fig. 1

eine Halbton-Rotationsdruckschablone mit mehreren Referenzlochstrukturen jeweils unterschiedlichen Durchlässigkeitsgrads;

Fig. 2

eine Rotationsdruckmaschine, bei der Halbton-Rotationsdruckschablonen nach Fig. 1 zum Einsatz kommen:

Fig. 3

eine Laser-Gravieranlage zur Herstellung der in Fig. 1 gezeigten Halbton-Rotationsdruckschablone;

Fig. 4

einen Axialschnitt durch den rechten Lagerbereich der Laser-Gravieranlage nach Fig. 3;

Fig. 5

eine optische Reflexions-Meßeinrichtung zur Ausmessung des Durchlässigkeitsgrads einer Referenzlochstruktur auf der Oberfläche eines Schablonenrohlings, auf den zur Bildung einer Siebdruckschablone metallisches Material galvanisch aufgebracht wird: und

Fig. 6

einen Axialschnitt im rechten Lagerbereich der Laser-Gravieranlage nach Fig. 3 mit einem strömungstechnisch arbeitenden Meßgerät zur Messung des Durchlässigkeitsgrads einer Referenzlochstruktur.

The drawing shows exemplary embodiments of the invention.

Fig. 1

a halftone rotary printing stencil with several reference hole structures, each with a different degree of permeability;

Fig. 2

a rotary printing press in which halftone rotary printing stencils according to FIG. 1 are used:

Fig. 3

a laser engraving system for producing the halftone rotary printing stencil shown in FIG. 1;

Fig. 4

an axial section through the right storage area of the laser engraving system of FIG. 3;

Fig. 5

an optical reflection measuring device for measuring the transmittance of a reference hole structure on the surface of a stencil blank, to which metallic material is galvanically applied to form a screen printing stencil: and

Fig. 6

an axial section in the right bearing area of the laser engraving system of FIG. 3 with a fluid dynamics measuring device for measuring the permeability of a reference hole structure.

1 shows a hollow cylindrical rotary printing stencil produced according to the invention 1 for halftone printing, which in its middle part or Template pattern area 2 with an engraving or template pattern hole structure is equipped to form a template pattern 3. The template pattern 3 has different permeability ratios in different Areas on. In the present case, the halftone template 1 exists from a hollow cylindrical sieve with a covering layer on which the Stencil pattern hole structure has been engraved around screen openings in the to expose cylindrical carrier sieve at least in regions.

Outside the template pattern area 2 are z. B. on an end Edge of the halftone template 1 area marks 4, each of which is uniform Have reference hole structure, but differ in terms of permeability differentiate. In Fig. 1 four surface marks 4 are shown, each Have permeabilities of 10, 50, 75 and 100% and separate from each other are arranged. The permeability doesn't just depend on it to what extent the respective screen openings of the one below the cover layer Cylinder screen have been exposed, but also on the type and viscosity the color that later passes through the stencil openings, from fluid pressure, etc. The permeability in the area of the area marks 4 must not be identical to those in the respective Areas of the template pattern 3 are present.

In addition, a print mark 5 (Pico) is provided, which here is a circular ring is realized. It has the task of adjusting several halftone templates to help each other in a rotary printing press.

At the surface marks 4 or uniform reference hole structures shown here can be used as a comparison standard for the purpose of visual assessment of the engraving be stopped, which z. B. also made of lacquer-coated, engraved Sieve pieces, e.g. B. nickel screen pieces. In such a visual comparison the engraving system must of course be shut down. However, the Measurement of the degree of permeability of a respective reference hole structure or Area mark 4 automatically, so the comparison can be made with the engraving system running be carried out, i.e. the comparison between the degree of permeability and Target permeability level for the respective area mark 4.

2 shows a rotary printing press 6 on which the invention is based Manufactured templates 1 are used. With such a machine 6 the stencils 1 are driven via gear wheels 7 and repeat gear 8, so that it is synchronized with that under the templates 1 through the machine 6 run web 9 run. The gears 7 are attached to template heads, which are glued into the end faces of the templates 1. The web 9 is glued to the printing blanket 10 with a very easily removable adhesive and held by the blanket 10 during printing. The printing blanket 10 is a very wide rubber fabric conveyor belt; it is driven by two deflecting rollers 11 driven, which are wrapped by the printing blanket 10. By this arrangement becomes the mentioned synchronous operation between templates 1 and 2 printing web 9 reached. The area marks 4 of each template 1 are printed together with the pattern on the web 9 and result area mark images there 12. A video camera 13 is at the end of the Printing machine 6 mounted on its side wall 14 and continuously measures the color intensities of the area mark images 12. If there is a deviation in the color tone or the color intensity, then either an acoustic or a emitted optical signal or it can be adjusted via the inking unit Servomechanics can be influenced, if there is one.

A laser engraving system is shown in FIG. 3. The template to be engraved 1 is centered and held between two clamping cones 15 and 16. Of the Clamping cone 15 is rotatably driven and mounted in a gear box 17, in which the drive motor is also located. The template is on this 1 pushed on with her left face. The clamping cone 16 is in a tailstock 18 rotatably mounted and is not driven in this embodiment. The tailstock 18 can on guides 19 in the direction of the connecting axis 20 adjusted between the two clamping cones 15 and 16 and so any Lengths of template 1 can be set. Torsionally rigid connected to the Clamping cone 15 is an encoder 21 which transmits the pulse or via a line 21a Provides rotational position signals for the engraving system computer 22. For engraving is a laser beam 23, which is emitted from the laser 24, via deflecting mirror 25 and an optic 26 focused on the surface of the template 1. The laser beam 23 is according to the requirements of pattern 3 via a line 22a clocked by the computer 22, d. H. on or off, and accordingly a lacquer layer 1a is removed from the cylinder screen 1b or cured. While the engraving rotates the template 1 at about 500 to 1200 rpm and at the same time, a carriage 28, which carries the optics 26, advanced in the direction of the connecting axis 20. The carriage is shifted under the control of the computer 22 via a Line 22b.

At the beginning of the engraving work, the area marks 4 are first engraved. This are immediately after their manufacture, even before the actual engraving Pattern 3 is started, subjected to inspection. A measuring or Inspection device 27 is attached to tailstock 18 in this embodiment. However, it may well be useful to have this device 27 on the gearbox 17 attach and then the area marks 4 on the opposite To provide the edge of the template 1. The inspection device 27 can of the designs described in the following figures. Its output signals are transmitted to the computer 22 via a line 22c.

4 shows an inspection device 27 which uses an optical measurement method used to determine the degree of permeability of the engraved area marks 4. The tailstock 18 contains not only that mounted on ball bearings 29 Clamping cone 16, but also a projection device 30 for the generation an aerial photograph 31. This lies approximately in the area of the jacket of the template 1. A Tube 33 carries a lamp house 32 from its right end. This tube 33 is by a conical clamping sleeve 34 in a matching conical Location hole in tailstock 18 held. A pressure plate 35 presses the Clamping sleeve 34 in this receiving bore. Inside the lamp house 32 a projection lamp 36 is provided, which is held by a holder 37 becomes. A concave mirror 38 serves to increase the luminous efficiency of the projection lamp 36. Part of the useless amount of light emitted is through this Concave mirror 38 reflected back into the condenser 39. A metallic bezel 40 contains a diaphragm opening in the form of a circle or in the form of a square. This Aperture 40 is illuminated as evenly as possible by the condenser 39. The aperture is opened by optics 41 (achromatic) via a deflecting mirror 42 projected as an aerial image 31 onto the jacket of the template 1. From this aerial photo 31 only those positions are perceptible from the outside that relate to the disclosed Make the template 1 fall. From a holder 43 on the tailstock 18 one Semiconductor camera 44 carried, which over the visible parts of the aerial image 31 a further optics 45 on a light-sensitive semiconductor (photodiode, phototransistor, Photoresistor) 46. That triggered by the incidence of light The output signal of this semiconductor 46 is through an integrated preamplifier 47 reinforces and serves as a measure of permeability in this way measured engraving.

5 shows a further inspection device 27 'working on an optical basis, which reflects the radiation reflected from the area of the area mark 4 Measurement of the engraving quality used. This device 27 'is then used if the engraving is in a layer 1c on a closed (i.e. not screen-like) Hollow cylinder 1d is to be introduced. Via an optic 48 of a lamp house 32, the lighting area of a lamp 49 on the surface of the area mark 4 shown. Of course, this lamp house 32 can do something again more complex - approximately as shown in Fig. 4 - are formed. In any In this case, the area mark 4 is illuminated in such a way that the whole of your occupied area is illuminated as evenly as possible. That from the Area mark 4 reflected light or rather the intensity of the same measured by the semiconductor camera 44 and for assessing the degree of permeability the area mark 4 used. An image of the area mark 4 is from the optics 45 projected onto the photosensitive semiconductor 46 and its output signal amplified by the integrated amplifier 47 and no longer shown evaluation unit 22 forwarded.

In Fig. 6 is a fluid working and designed as a measuring nozzle Inspection device 27 '' for determining the quality of the engraving or the degree of permeability the area marks 4 shown. The inside of the template 1 is shown this embodiment under a slightly excessive air pressure, approximately in the size of 0.1 to 0.3 bar overpressure. This pressure is created by the feed of compressed air through a hollow shaft 55, which carries the clamping cone 16. A source that is no longer shown and possibly serves as the source for this compressed air multi-stage radial fan. The pressure can only last as long as long as larger sample areas are not exposed, but this can Compressed air can be provided with little energy as long as long the area marks 4 are the only open areas of the template 1. The engraving of these surface marks 4 must be done anyway at the beginning of the engraving work, because the result from the measurement of these marks 4 for one at best necessary correction of the setting parameters of the engraving machine before the start the actual pattern engraving must be available. Therefore, the above mentioned Restriction is not an obstacle. Those from the areas disclosed The area mark 4 emerging air is from the mouth 49 of the pneumatically working Inspection device 27 '' collected. The distance of the mouth 49 from the outer jacket the template 1 is preferably less than 1/4 of the mouth diameter. The air caught by the mouth 49 then flows through a taper 51 of the flow channel 50. It is known from fluid mechanics that the speed increases in the taper and the static pressure drops if the flow channel 50 has no opening to the outside here. In this Tapering is a first temperature-dependent resistor 52 (NTC resistor), which is arranged as centrally as possible in the channel and which is attached in this way is that there are no leaks from the attachment. This resistance 52 is strongly cooled here by the high flow rate. The channel 50 is then widened again like a diffuser so that none high energy losses occur and as much air as possible through the measuring nozzle flows and as little air as possible over the gap in front of the mouth 49 into the outside atmosphere exit. In an edge position of the diffuser that is as flow protected as possible expanded flow channel 50 is then a second temperature-dependent Resistor 53 (NTC resistor) is provided. This is only through one weak flow washed around and cooled only a little. If you switch these two Resistors 52, 53 in a half-bridge and supplemented by the half-bridge two more resistors to the full bridge, then you can see their diagonal voltage as a measurement signal for the permeability of the engraving of the area mark Use 4. This device 27 ″ already responds to very small ones Flow speeds extremely sensitive. Of course you can also two temperature-dependent resistors in the tapered one and arrange the expanded flow channel position and this in the form of a Interconnect full bridge, which leads to an increase in the measurement signal receives.

Of course, one could pass through the area marks 4 Air quantity also via a measuring orifice arrangement known per se or determine via a known differential pressure load cell. In the latter Case, the static differential pressure between the digits is the highest and lowest flow rate of that shown in FIG. 6 Measure the measuring nozzle.

Claims (24)

1. Process for producing a half-tone stencil (1), in which, in a predetermined stencil pattern area (2) of a basic stencil element (1a, 1b; 1c, 1d), a stencil pattern hole structure is engraved to form a stencil pattern (3), characterized in that a plurality of uniform reference hole structures (4), which each have different degrees of permeability and lie outside the stencil pattern area (2), are engraved into the basic stencil element (1a, 1b; 1c, 1d).
2. Process according to Claim 1, characterized in that the degree of permeability of each reference hole structure (4) is compared with a respective desired degree of permeability, in order to engrave the uniform reference hole structures anew, as a function of the respective deviation, in such a way that the said deviation decreases, this sequence of steps being executed at least once.
3. Process according to Claim 2, characterized in that the stencil pattern hole structure lying in the stencil pattern area (2) is engraved as a function of the said deviations.
4. Process according to Claim 2 or 3, characterized in that the respective old reference hole structures (4) are removed after their degree of permeability has been compared with the desired degree of permeability.
5. Process according to Claim 4, characterized in that the removal of the old reference hole structures (4) is carried out before new engraving.
6. Process according to one of Claims 2 to 5, characterized in that the degree of permeability of a respective reference hole structure (4) is measured automatically.
7. Process according to one of Claims 1 to 6, characterized in that use is made, as basic stencil element, of a screen (1b) on which a covering layer (1a) is applied which leaves screen openings free, at least in some areas, to form a reference hole structure (4).
8. Process according to one of Claims 1 to 6, characterized in that use is made, as basic stencil element, of one (1d) having a closed surface, on which a covering layer (1c) is applied which leaves the surface free, in some areas, to form the reference hole structure (4).
9. Process according to Claim 6 and 7, characterized in that the degree of permeability of the reference hole structure (4) is measured by means of a beam of light passing through the screen openings.
10. Process according to Claim 6 and 7, characterized in that the degree of permeability of the reference hole structure (4) is measured by means of a stream of gas passing through the screen openings.
11. Process according to Claim 6 and 8, characterized in that the degree of permeability of the reference hole structure is measured by means of a beam of light reflected at the free surface.
12. Process according to one of Claims 2 to 11, characterized in that, in order to form the reference hole structure (4), a laser beam (23) is used whose pulse duty factor is varied in accordance with the deviation between degree of permeability and desired degree of permeability of the reference hole structure (4).
13. Process according to one of Claims 2 to 11, characterized in that, in order to form a reference hole structure (4), a nozzle for spraying out covering lacquer is used whose on/off switching cycle is varied in accordance with the deviation between degree of permeability and desired degree of permeability of the reference hole structure (4).
14. Process according to one of Claims 1 to 13, characterized in that the basic stencil element is designed as a hollow cylinder.
15. Device for producing a half-tone stencil, having

    a bearing device (15, 16) for the rotatable mounting of a hollow cylinder (1a, 1b; 1c, 1d);

    a device (24 to 26) for machining the outer peripheral surface of the hollow cylinder;

    a carriage (28) which can be displaced parallel to the hollow cylinder axis (20) and carries at least part of the machining device; and

    a control device (22) for controlling the machinining device and for displacing the carriage (28) when the hollow cylinder is rotating,
    characterized in that it has a measuring device (27, 27', 27'') for measuring the degree of permeability of reference hole structures (4) lying in a prescribed stencil area.
16. Device according to Claim 15, characterized in that the control device (22) has a comparison device for comparing the measured degree of permeability with a desired degree of permeability, and the machining device (24 to 26) can be controlled as a function of the comparison result.
17. Device according to Claim 16, characterized in that the measuring device (27) has a source of rays (36) for emitting a beam of rays, and a ray detector (47), which are positioned in a transmission arrangement in relation to the hollow cylinder wall.
18. Device according to Claim 15 or 16, characterized in that the measuring device (27') has a source of rays (49) for emitting a beam of rays, and a ray detector (49), which are positioned in a reflection arrangement in relation to the hollow cylinder wall.
19. Device according to Claim 18, characterized in that the source of rays (49) is designed to emit a monochromatic beam of rays.
20. Device according to Claim 15 or 16, characterized in that the measuring device has a measuring nozzle (27'') which is placed on the outside essentially radially in relation to the hollow cylinder (1a, 1b), and in that the bearing device (16) is provided with a gas supply channel (55) for the introduction of a gas under overpressure into the interior of the hollow cylinder (1a, 1b).
21. Device according to one of Claims 15 to 20, characterized in that the measuring device (27, 27', 27'') is fastened to the bearing device (16).
22. Half-tone stencil having a stencil pattern area (2) located approximately centrally, characterized in that it has, outside the stencil pattern area (2), a plurality of uniform reference hole structures (4) each having a different degree of permeability.
23. Half-tone stencil according to Claim 22, characterized in that it is of hollow cylindrical design.
24. Half-tone stencil according to Claim 22 or 23, characterized in that the respective reference hole structures are arranged separately from one another.

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