HK1050932B - Image-recording device for a printing form,having macrooptics of the offner type - Google Patents

Description

Printing plate imaging device with Offner type macro-lightset

Technical Field

The invention relates to an image-producing device for printing plates, comprising an array of light sources and a downstream micro-light fixture which generates a virtual image of the light sources.

Background

The use of an array of light sources in columns or in a matrix in a plate exposer or in a direct imaging printing unit for producing images on printing plates places high demands on the imaging light to be used. Typically, the light source array consists of a number of diode lasers, preferably single-mode lasers, which are arranged at a distance from one another on a semiconductor substrate, typically at substantially the same distance from one another, and which have a common, precisely defined exit plane at the crystal fracture plane. The emission cones of these light sources or diode lasers are flared in two mutually substantially orthogonal planes of symmetry by different widths. Therefore, it is necessary for the imaging optics to reduce, preferably minimize, this asymmetry with preferably a smaller number of components on the one hand and to be able to image the emitter array as globally as free as possible of imaging errors on the other hand.

From the prior art, a series of imaging lightings are known which are provided specifically for diode laser imaging in rows for producing images on an image carrier. A semiconductor laser array is known, for example from US 4,428,647, in which a lens is arranged in the vicinity of each laser between the laser array and the objective. The purpose of these lenses is to change the divergence angle of the light beams emerging from the surface of the laser array so that the light is collected and focused by the objective lens onto the image carrier as efficiently as possible. The refractive powers of the lenses are selected such that for each laser an intermediate virtual image is produced behind the emission surface with a spacing approximately corresponding to the spacing of the emission beam, wherein the emission intermediate image is enlarged.

EP 0694408B 1, for example, describes how a microoptical device can reduce the divergence of the emerging light by means of an axially symmetrical optical element.

Such arrays of light sources often have very different lateral line sizes, e.g. 10 x 0.001mm²Thus requiring special micromirror imaging devicesAnd a macro mirror imaging device. Spherical lightings of this size can only be solved by relatively large and complex lightings. A disadvantage of using a spherical macro-scope (Makrooptik) is that the imaging quality varies as a function of distance from the optical axis. Until now, even the use of cylindrical lenses and cylindrical lens arrays has not allowed the desired constant quality of the imaging of light source arrays, in particular in the form of diode lasers in rows.

From US 3,748,015 an optical system for shaping an image of an object with a single magnification and high resolution is known, which comprises an arrangement of a convex and a concave spherical mirror, the curvature centre points of which coincide at a point. The mirror arrangement produces at least three reflection points in the system and two conjugate regions of single magnification spaced from the optical axis in a plane containing the center point of curvature where the system optical axis is orthogonal to this plane. Such a combination of mirrors is free from spherical aberration, coma and distortion, and if the algebraic sum of the intensities or refractive powers of the mirror surfaces used is 0, the resulting image is free from third-order astigmatism and field curvature. Such an optical system is also known as an Offner type optical device.

In connection with this it is mentioned that a method and an apparatus for writing data on an optical storage medium in multiple tracks simultaneously are described, for example, in US 5,592,444. The imaging optics described in this document for a plurality of individually controllable diode lasers comprises a spherical mirror arrangement of the Offner type described above, that is to say a combination of a spherical concave mirror and a spherical convex mirror having a common center point of curvature, but whose low-divergence microoptics do not produce a virtual, in particular enlarged, intermediate image.

However, when using a plate imaging device in a plate exposer or a printing unit of a printing press, additional measures are required. Since, on the one hand, the installation space in such machines is limited and, on the other hand, the design or configuration of the plate exposer or of the printing couple is rarely modified slightly to implement the imaging system, the installation space required is reduced. Furthermore, the imaging optics on the printing press or on the plate exposer are subject to vibrations or vibrations, so that the imaging optics should have as few components as possible which must be aligned relative to one another, so that the optical devices known from the prior art cannot be used simply on the plate exposer or in the printing units of the printing press.

Disclosure of Invention

It is an object of the present invention to provide an imaging light fixture for a light source array, which makes it possible to simply reduce the divergence of the emitted light and to image with small aberrations. Furthermore, an imaging optics for use in a printing plate imaging device should be realized which has the smallest possible installation space requirement and the fewest possible components and thus the fewest possible degrees of freedom of alignment.

This object is achieved by an image forming apparatus having the following features.

The inventive printing plate imaging device has a light source array and a micro-lens arranged behind it, which produces a virtual image of the light source, and is characterized in that an optical arrangement is arranged behind the micro-lens, which optical arrangement comprises at least one convex mirror section and one concave mirror section having a common center point of curvature, wherein preferably the algebraic sum of the refractive power intensities is 0, in other words a combination of the micro-lens or Offner type is arranged, which produces a real image of the intermediate virtual image. In the following, reference is briefly made to an optical arrangement consisting of a convex mirror and a concave mirror, although at least one mirror may also have only a section in a certain partial spatial angular region of at most 4 pi, which section may define either a single coherent (einfach zusammenhaengende) surface or a non-coherent surface. In order to be able to apply the desired properties of an optical device of the Offner type with sufficient accuracy to the imaging device according to the invention in the realization of a specific embodiment, the curvature centers of the concave mirror and the convex mirror do not have to overlap one another exactly.

In the following description, advantageous embodiments and further developments of the image-forming device according to the invention are described.

In the imaging device according to the invention, each light source of the array is adapted to the requirements of the microscope, in particular the divergence, by an intermediate virtual image, by using a small number of light refracting surfaces. By making good use of the known properties of the combination of an optical device of the Offner type, that is to say at least one convex mirror section and one concave mirror section having a common center point of curvature, it is possible to advantageously image points along a line which runs substantially circularly. The optical device in the imaging device according to the invention, which is arranged as a macro-lens behind a micro-lens, is embodied in such a way that the central virtual image points of the light sources arranged substantially in a row have a small distance to the circular line. In other words: the image forming apparatus of the present invention can stabilize emission correction of a plurality of light sources, particularly diode lasers, with a small number of optical elements. By combining cylindrical lenses, the intermediate virtual images of each light source are magnified while being microoptically symmetrical, and the intermediate virtual images are imaged as aberration-free as possible into a real image by means of a downstream optical arrangement consisting of a convex mirror and a concave mirror, a printing plate image device having particularly advantageous imaging properties is created.

In order to adapt to the divergence of the light emitted by the light source, the low-light-level light is preferably aspherical. For example, a combination of cylindrical lenses or anamorphic prisms may be involved. The macro-optic, which is arranged behind and consists of a convex mirror and a concave mirror, has at least one circular segment of a rotationally symmetrical optic, the projections of the intermediate virtual image point rows, which run essentially straight, having a small distance to the circular line of the object arranged in correspondence with them, wherein the circular line of the object is located in one of the two conjugate regions of the optic consisting of a convex mirror and a concave mirror. Thus, a substantially linearly extending intermediate virtual image point row can be imaged in real-time at a single magnification in the second conjugate region by means of the optical device of the Offner type. It is particularly advantageous here if the optical arrangement consisting of a convex mirror and a concave mirror is free from aberrations.

In order to reduce the installation space requirement of the imaging device according to the invention, it is advantageous if at least one deflection of the beam path is carried out in the optical arrangement consisting of a convex mirror and a concave mirror. It is therefore advantageous if, in the optical arrangement arranged behind the microoptics, at least one light deflecting element is arranged in front of and/or behind the reflection surface of the optical arrangement consisting of a convex mirror and a concave mirror and/or a beam shaping element is arranged between the reflection surfaces of the optical arrangement consisting of a convex mirror and a concave mirror. Thus, the imaging optics in the imaging device according to the invention make the beam path compact, which reduces the installation space for installation in a plate exposer or in a printing unit. It is also advantageous if at least a part of the optical arrangement consisting of a convex mirror and a concave mirror is formed as a single component, i.e. as a single piece of a suitable material having a different refractive index than the surrounding object, for example made of glass or other transparent material. The individual component or the entire block can then have, in part, inwardly reflecting surfaces which realize, for example, concave and convex reflecting surfaces of the optical device consisting of a convex mirror and a concave mirror. These internal surfaces are also referred to as the activated internal faces of the monolith. Advantageously, the active inner face of the monolithic structure is made specular. At least one entrance window and one exit window are provided on the block for the light emitted by the at least one light source, which are preferably provided with an antireflection coating in the form of an interference filter. In an advantageous further development, the overall structure can be provided with further optical elements, such as prisms or light deflection surfaces for deflecting the radiation.

Advantageously, the monolithic structure has a piece of glass with a high refractive index compared to its surroundings.

The inventive imaging device can be used particularly advantageously in a plate exposer or in a printing unit. The printing machine of the invention comprises a feeder, at least one printing unit and a delivery unit, and is characterized in that the printing machine comprises at least one printing unit provided with the image-forming device of the invention.

Drawings

Further advantages and advantageous embodiments and further developments of the invention are described with the aid of the figures and their description. The figures show that:

FIG. 1 is a schematic view showing the arrangement of optical elements in one embodiment of the plate imaging apparatus of the present invention,

FIG. 2 is a schematic view showing the arrangement of optical elements in another embodiment of the plate making apparatus of the present invention with an additional beam profile filter,

figure 3 is a schematic diagram for explaining the position of the focal line of the mirror optics consisting of a convex mirror and a concave mirror with respect to the virtual image point columns of the light source array,

figure 4 is a schematic diagram of a monolithic optical device consisting of one convex mirror and one concave mirror,

FIG. 5 is a schematic view of an alternative integral optical device consisting of a convex mirror and a concave mirror, making full use of two beam deflections,

figure 6 shows a schematic view of an alternative symmetrical integral optical device consisting of one convex mirror and one concave mirror with additional beam-deflecting elements in the form of prisms,

fig. 7 is a schematic illustration of an alternative overall optical arrangement consisting of a convex mirror and a concave mirror, with a convex spherical mirror and a prism for coupling in the light to be imaged.

Detailed Description

Fig. 1 is a schematic view showing an arrangement of optical elements in one embodiment of the printing plate image forming apparatus of the present invention. The inventive imaging device has a light source 12 with a correspondingly configured micro-lens 14 and a rear optical device 10. The divergent light 16 emitted by the light source 12 is imaged by the micro-optics 14 onto a virtual image 18. By means of the optical arrangement 10 arranged downstream, the light beam 20 originating from the intermediate virtual image 18 is converted into a real image point 28 by means of different optical elements. In the present embodiment, the optical device 10 first has a deflection element 22 and a pair of mirror surfaces arranged along an optical axis 23 and rotationally symmetrically with respect to the optical axis 23, namely a concave mirror 24 and a convex mirror 26 having a common center point of curvature 25 along the optical axis 23. The pair of mirrors formed by concave mirror 24 and convex mirror 26 image a point in the object area onto a point in the image area. The two regions are conjugated to each other. Due to the additional deflection element 22, the symmetry of the light path through the optical device 10 is broken, so that the image point 28, which is the conjugate point, corresponds to the intermediate virtual image 18, rather than the conjugate point 27 in the printing plate plane 29 without the deflection element. However, the optical path length between virtual intermediate image 18 and concave mirror 24 is equal to the optical length between concave mirror 24 and image point 28 in plate plane 29.

For a better understanding of the imaging device according to the invention, fig. 1 shows diagrammatically the imaging process of a light source 12 with a micro-lens 14 and a rear-mounted optical device 10, i.e. a macro-lens, while, with a corresponding preferred embodiment of the invention, a plurality of light sources 12, which are typically arranged in a row, are imaged by a micro-lens 14, which is preferably pressed individually for each light source 12, and a macro-lens, which acts on the plurality of intermediate images 18 and corresponds to the optical device 10 consisting of a convex mirror and a concave mirror.

Fig. 2 shows a schematic view of the arrangement of optical elements in another alternative embodiment of the inventive plate-making image device with an additional beam profile filter. The inventive imaging device comprises a light source 12, a micro-optic 14, an entrance window 32 of a box 33 and an exit window 34 with a printing plate 29 arranged behind, the optical device 10 being located in the box 33. The optical device 10 comprises a deflection element 22, a concave mirror 24, a wavefront correction element or beam shaping element 30, a so-called beam profile filter, which is preferably used to transmit the fundamental mode of the light source 12, for example with a gaussian beam profile, and a concave mirror 26. The optical arrangement 10 therefore likewise consists of a convex mirror and a concave mirror with conjugated regions, wherein the intermediate virtual image 18, which is produced by the divergent light 16 of the light source 12 by means of the microoptics 14, is in the first conjugated region and the image point 28 in the printing plate plane 29 is in the second conjugated region. The light path is deflected by the use of a deflection element 22, as shown in fig. 2, in front of a convex mirror 26, intersecting the light path between the convex mirror 26 and a concave mirror 24, or otherwise passing behind the convex mirror. By folding in this way, a more compact structure can be achieved.

Fig. 3 schematically illustrates the position of focal lines, that is to say points selected in the first conjugate region of an optical arrangement consisting of one convex mirror and one concave mirror, relative to a virtual image point row of the light source array. Fig. 3 shows a projection along the optical axis 23 of the concave mirror 24 and the convex mirror 26 of the optical device 10. The essentially circular focal line 36 represents the projection of the conjugate area onto concave mirror 24 in the case of the symmetrical optical path illustrated here. In other words, the object point and the image point of the optical arrangement consisting of a convex mirror and a concave mirror lie substantially in anti-phase on a circular focal line 36, i.e. opposite each other by 180 degrees around the optical axis 23. The focal line 36 essentially describes those points which have a very favorable transformation behavior, that is to say have minimal aberrations. The aim at this time is to bring the column of virtual image points 38 as close as possible to the focal line 36. It is not essential to the invention here what exact rhythm or what unit of measure is selected for measuring the distance of the line 38 from the circular arc segment 36. For example, the average distance of the light sources in the projection 38 from the optical axis 23, that is to say the sum of the distances, divided by the number of light sources, can be used as a unit of measure. To achieve favorable imaging with minimal aberrations by the optical device 10, the projection of the column of virtual image points 38 is kept small or matched to the spacing of the radii of the focal lines 36.

It is furthermore clear that the optical arrangement 10, which consists of a convex mirror and a concave mirror, is designed such that the projection of the focal line 36 has a radius of curvature which is as large as possible. In other words, the focal line 36 should extend as far as possible, viewed locally, that is to say on the pitch scale of the image points of the light source which are furthest apart from one another in the projection of the light source 38, compared with the projection of the columns of the light source 38. The optical device 10 used therefore only needs to have at least one circular arc segment of a rotationally symmetrical luminaire consisting of one convex mirror and one concave mirror.

Fig. 4 is a schematic view showing an overall structural embodiment of the optical device in the image forming apparatus of the present invention. A further reduction of the optical arrangement consisting of a convex mirror and a concave mirror should be achieved by the overall construction. Also, to explain the overall structure, a symmetrical optical path is illustrated in fig. 4. The optical device 10 is symmetrical with respect to the axis 41. Starting from the central virtual image 18 of the light source, which is not shown here, including the micro-optics, the light beam 20 passes through an entrance window 32 into a block 40, which block 40 is made of, for example, a strongly refractive glass or a wavelength-transparent polymer used. The block has a concave surface 42 which reflects the beam 20 such that the beam 20 strikes a substantially flat mirror surface 46 opposite the concave surface 42. The light beam is projected from the mirror 46 onto a convex surface 44, from where it emerges symmetrically on the other side of the axis of symmetry 41, impinges again on the mirror 46 and subsequently on the concave surface 42, until it leaves the block through an exit window 34 and converges on an image point 28, which expediently lies in the printing plate plane not shown here. As shown in fig. 4, this overall structure takes full advantage of this: in an optical arrangement consisting of a convex mirror and a concave mirror, the areas of the concave mirror remote from the optical axis or axis of symmetry 41 are used primarily to reflect the first conjugated area onto the convex mirror and from the convex mirror into the second conjugated area. A specularly reflecting surface 46 can thus be introduced, so that the concave surface 42 in the vicinity of the optical axis or axis of symmetry 41 can be replaced by a convex surface 44. The position and curvature are, of course, determined by the conditions of the optical arrangement consisting of one convex mirror and one concave mirror. Convex surface 44 corresponds to a convex mirror at position 48 onto which beam 20 is directed along optical path 50 without mirror 46. The side of the block 40 that is to reflect the light beam 20 is made as reflective as possible by means of a suitable coating, by means of a metal layer or by means of an interference filter. An antireflection coating is provided for the entrance window 32 and/or the exit window 34, for example by means of an interference filter, so that the light can be coupled in and out of the bulk as strongly as possible.

Fig. 5 shows a further schematic view of an integrated optical arrangement consisting of a convex mirror and a concave mirror, which makes use of two beam deflections. A light source 12 is transformed into an intermediate virtual image 18 by means of a micro-light fixture 14. The light beam 20 emerging from the intermediate virtual image 18 enters the block 40 and is projected onto a concave surface 42 at a first deflection surface 51 and a second deflection surface 52. The light beam 20 then strikes a mirror 46, strikes a convex surface 44, re-strikes the mirror 46 and strikes the concave surface 42, so as to then leave the block 40 through an exit window 34 and converge on an image point 28.

Fig. 6 schematically shows another symmetrically implemented optical imaging process of one convex mirror and one concave mirror, wherein additionally a deflection element in the form of a prism is used. Starting from the central dashed line 18 of the light source 12, which is not shown here, the light beam 20 enters a prismatic deflection element 54, is reflected at its base and reaches the block 40. A symmetrical optical path is provided, the beam 20 first striking a concave surface 42, a mirror 46, a convex surface, re-striking the mirror 46 and striking the concave surface 42. Next, a prismatic deflection element 54 is likewise provided, on the base of which the light beam 20 is totally reflected. The light is focused on an image point 28.

Fig. 7 shows a schematic view of a further integral optical arrangement consisting of a convex mirror and a concave mirror, with an additional convex spherical surface and a prism for the coupling-in of the light to be imaged. Starting from an intermediate virtual image 18 of a light source, not shown here, comprising a micro-light fixture, the light 20 enters a prism 58 and from there enters a convex spherical surface 56. In the surface of the convex spherical surface, a region is provided through which the light beam 20 can enter the monolith 40 as reflectionlessly as possible. The light beam 20 is reflected on various interior surfaces of the block, including the prism face 60, a concave face 42, a mirror face 46, and a convex face 44. The light path of the light beam 20 up to the image point 28 is shown. The light may leave the block 40 through an exit window 34. Typically, the convex surface 44 is formed as a mirror surface so that light is reflected within the monolith 40.

Reference numerals

10 optical device 12 light source

14 micro-optical device 16

18 intermediate virtual image 20 beam

22 deflecting element 23 optical axis

24 concave mirror 25 center point of curvature

26 convex mirror 27 without conjugate points of deflecting elements

28 image point 29 printing plate plane

30 beam shaping element 32 entrance window

33 box 34 entrance window

36 focal line projection 38 source projection

40 monolithic block 41 symmetry axis

42 concave surface 44 convex surface

46 mirror surface 48 convex mirror position

50 first deflection surface of a light beam 51 without mirror surface

52 second deflection surface 54 prismatic deflection element

56 convex spherical surface 58 prism

60 facet

Claims (13)

1. Imaging device for printing plates (29), comprising an array of light sources (12) and a downstream micro-optic (14) having a number of light-refracting surfaces, and an optical arrangement (10) comprising at least one convex mirror (26) section and one concave mirror (24) section, which have a common center of curvature and have a first conjugate region and a second conjugate region, and the optical arrangement (10) generating a real image (28) of the first conjugate region in the second conjugate region, characterized in that the micro-optic (14) generates an intermediate virtual image (18) of the light sources (12), and the optical arrangement (10) is arranged downstream of the micro-optic (14) in such a way that the intermediate virtual image (18) is located in the first conjugate region.

2. An image-making apparatus for a printing plate (29) according to claim 1, characterized in that the intermediate virtual image (18) is an enlarged image of the light source (12).

3. An image-making device for printing plates (29) according to claim 1 or 2, characterized in that the microoptics (14) are aspherical in order to adapt to the divergence of the emitted light (16) of the light source.

4. An image-making device for printing formes (29) according to claim 1, characterized in that the optical device (10) consisting of a convex mirror (26) and a concave mirror (24) has at least one circular arc segment of a rotationally symmetrical light tool, the substantially linearly extending projection of the column of intermediate virtual image points (38) having a selected small distance from the circular line (36) of the object corresponding to the circular arc segment.

5. An image-forming device for printing formes (29) according to claim 1, characterized in that at least one light deflecting element (22) is arranged in front of and/or behind the reflecting surface of the optical device (10) consisting of a convex mirror (26) and a concave mirror (24) and/or that a beam shaping element (30) is arranged between the reflecting surfaces of the optical device (10) consisting of a convex mirror and a concave mirror.

6. An image-making device for printing forms (29) according to claim 1, characterized in that the optical means (10) are at least partly integrally formed.

7. An image-forming device for printing plates (29) according to claim 6, characterized in that the active inner face of the integral structure (40) is made as a mirror surface.

8. An image-making device for a printing plate (29) according to claim 6 or 7, characterized in that the optical device (10) has at least one entrance window (32) and one exit window (34), and that said at least one entrance window (32) and said exit window (34) are provided with an anti-reflection coating.

9. An image-making device for printing plates (29) according to claim 6, characterized in that the integral structure (40) is provided with further optical elements (54, 56, 58) for beam deflection and/or beam shaping and/or wavefront correction.

10. An imaging device for printing forms (29) according to claim 6, wherein the integral structure (40) comprises a piece of glass having a high refractive index compared to its surroundings.

11. Printing plate exposer, characterized in that it comprises at least one imaging device according to claim 1.

12. Printing device, characterized in that it comprises at least one image-forming device according to claim 1.

13. Printing machine with a feeder, at least one printing unit and a delivery, characterized in that it has at least one printing unit according to claim 12.