EP2513690A1

EP2513690A1 - Device for examining an object, preferably a document of value, by using optical radiation

Info

Publication number: EP2513690A1
Application number: EP10795242A
Authority: EP
Inventors: Bernd Wunderer
Original assignee: Giesecke and Devrient GmbH
Current assignee: Giesecke and Devrient Currency Technology GmbH
Priority date: 2009-12-14
Filing date: 2010-12-13
Publication date: 2012-10-24
Also published as: DE102009058244A1; US8952317B2; WO2011082766A1; US20120248299A1

Abstract

The invention relates to a device for examining an object, preferably a document of value, by using optical radiation, having an optical waveguide which has an anisotropic retro-reflector section, which is formed along a surface curved in a plane of curvature and which reflects radiation components specularly in a first plane of incidence parallel to the plane of curvature but retro-reflects radiation components orthogonally with respect to the first plane of incidence, so that at least a proportion of the optical radiation falling in a glancing manner on the retro-reflector section is at least partly guided on the convex side of the surface by means of reflection on the retro-reflector section.

Description

Device for the examination of an object, preferably a value document, using optical radiation

The present invention relates to a device for the examination of an object, preferably a value document, using optical radiation, in particular a device for illuminating an object and / or a device for detecting an image of a value document.

Under value documents are understood leaf-shaped objects that represent, for example, a monetary value or an authorization and therefore should not be arbitrarily produced by unauthorized persons. They therefore have features which are not easy to manufacture, in particular to be copied, whose presence is an indication of the authenticity, i. the manufacture by an authorized agency. Examples of such value documents are chip cards, coupons, vouchers, checks and in particular banknotes.

For the investigation of objects, in particular documents of value, optical sensors are frequently used which detect spatially resolved optical properties of an object to be examined and for this purpose illuminate strip-shaped areas on the object at least partially with optical radiation using a lighting device and onto a substantially cell-shaped field Imagine receiving elements of an image capture device of the sensor. The receiving elements form, as a function of the radiation incident on them, received signals which together form an image of the respective region of the object. By moving the article across the direction of the line or strip and sequentially detecting such images during movement past the sensor, a two-dimensional image of the object can be captured. Under optical radiation in the According to the invention, electromagnetic radiation in the infrared, visible and ultraviolet wavelength range is understood. The components described below need not be designed for use in the entire optical spectral range, but the training in one, for example, by the type of object or the desired investigation, predetermined spectral range within the optical spectral range is sufficient.

In many applications, it is desirable that the sensor can be constructed very compact and inexpensive. In contrast, the optical resolution does not always have to meet high requirements. Sensors with conventional imaging systems, which use only lenses or mirrors, do not always meet these requirements to the desired extent with line-shaped imaging. In the past, self-focusing optical fibers, so-called SELFOCs, have been used for this purpose, but their availability is decreasing. This applies in particular to those SELFOCs which have required cutting widths to achieve required depth of field. For good detection of holes in a document of value or of specularly reflecting areas, for example reflective security features or adhesive strips, it is desirable to illuminate the area to be imaged with a constant aperture defined over the largest possible area; SELFOCs have also been used in the past for this purpose. In order to achieve good images, simple but good illumination of the area to be imaged is also desirable.

The present invention is therefore based on the object, a device for the investigation of objects, preferably value documents, using optical radiation, in particular for an optimal see sensor for the investigation of objects, in particular value documents to create, which allows a simple and compact construction of an optical sensor at least low optical resolution, even without SELFOCs, and to provide an optical sensor with such a device.

The object is achieved by a device for the examination of an object, preferably a value document, using optical radiation with a light guide, the anisotropic retroreflector section formed along a curved surface in a plane of curvature, the radiation components in a first plane of incidence parallel to the plane of curvature specularly reflected orthogonally to the axis, however, radiation components orthogonal to the first plane of incidence are retroreflected so that incident on the retroreflector portion incident optical radiation at least partially on the convex side of the surface by reflection at the retroreflector portion is feasible and in particular at least one grazing on the retroreflector portion falling portion the optical radiation is guided at least partially on the convex side of the surface by reflection at the retroreflector section and preferably held together.

In this context, radiation incident on the retroreflector section is radiation that falls in a predetermined range from angles to the plane of curvature onto the retroreflector section, so that specular reflection, in particular with a large angle of incidence, can take place in the first plane of incidence; Due to the curvature, this specular reflection may, if appropriate, take place several times and thus bring about guidance in the first incidence plane along the retroreflector section. The surface curved in the plane of curvature is understood to mean a surface which has a curvature in the plane of curvature, ie whose orthogonal projection onto the curvature plane results in a curved curve in the curvature plane; however, in a direction orthogonal to the plane of curvature, it preferably has no curvature. This means that the curved in the plane of curvature surface is preferably a surface whose curvature lies only in the plane of curvature or planes parallel thereto or which is curved only along the plane of curvature. The fact that the retroreflector section runs along the curved surface in the plane of curvature, it is understood that the retroreflector section along the curved surface optically effective, preferably identically formed anisotropic reflective structures that cause the anisotropic reflection behavior. The guidance of the optical radiation takes place on the convex side of the curved surface. In the context of the invention, specular reflection in the first plane of incidence is understood to mean that a beam in the first plane of incidence, which includes a given angle of incidence with a normal to the plane of the retroreflector section, from the retroreflector section in a new direction, given by a reject angle is distracted from the normal to the level of the retroreflector section. Incidence and exit angles are then the same as usual.

By the terms "retroreflected" or "retroreflection" it is understood in the context of the invention that an incident beam in a second plane of incidence, which is orthogonal to the first plane of incidence and tangent to the curved surface, and that resulting from the retroreflection of the incident beam retroreflected beam parallel, with some offset of the beams from each other in a direction parallel to the second plane of incidence of the retroreflector section occur can. Since the retroreflector section extends along the curved surface in the crimping plane, for each point of impact of a beam on the retroreflector section, there is a second plane of incidence orthogonal to the first plane of incidence. That is, incident rays in a direction orthogonal to the first plane of incidence are retroreflected by the retroreflector portion.

However, depending on the type of retroreflector section, this behavior occurs only in a certain range of angles of incidence. Unless otherwise stated, it is assumed in the context of the invention that the incident rays are within an angular range in which the retroreflection is possible, at least to a good approximation.

An anisotropic retroreflector section in the sense of the invention can, for example, have a body with a surface curved in the plane of curvature, for example a curved or curved plate, of a transparent material, on or in the surface of which as a curved surface as anisotropically reflecting structures a field of parallel to a curve corresponding to the curvature of the surface curved in the first plane of incidence extending prisms, preferably roof prisms with a prism angle of 90 °, is formed. The prisms provide in the second plane of incidence for the retroreflection in a conventional manner, wherein the reflection at the interfaces of the prisms can be given by total reflection or reflection on a reflective layer on the surface of the prisms.

Compared with a simple mirror, an anisotropic retroreflector section in the sense of the invention thus exhibits an unusual behavior, for the description of which one can imagine the following: If a beam fails In a given direction to the anisotropic retroreflector section, the reflected beam results from the fact that the incident beam or the incident radiation is decomposable into first and second directional components lying in the first and second incident plane and their vectorial sum just the direction of incident beam or the incident radiation. The first directional component becomes specular, but the second directional component is retroreflected and the two reflected directional components are again vectorially summed. In the first level, a specular reflection takes place, at the same time a retroreflection takes place in the second level. It is assumed that the direction of the incident beam is predetermined so that a retroreflection can take place at all. In the case of said roof prisms as a retroreflective structure, the direction of the incident beam may be such that the angle of incidence of the component in the second plane of incidence is less than 45 °.

Rays incident on the retroreflector section on its convex side are thus reflected as follows. Directional or

Radiation components of such rays in the first plane of incidence, in particular grazing on the retroreflector portion or the curved surface covered direction components in the first plane of incidence are specularly reflected so that they are not deflected orthogonal to the first plane of incidence and guided by single or multiple specular reflection at the retroreflector section become. Any divergence of these directional components is prevented by the curvature of the surface, so that some focusing of these directional components occurs during the guidance on the retroreflector section, which, however, is not perfect. The direction or radiation components orthogonal to the first plane of incidence or in the second incidence planes on the other hand, retroreflective effects occur, so that due to retroreflection, some focusing or focusing occurs in a direction orthogonal to the first incidence plane. Overall, this results in a bundling of guided at the retroreflector section rays or optical radiation, resulting in a map with a limited resolution.

The light guide can be designed differently. It may be formed as a waveguide or as a light guide made of a transparent material. Further, the optical fiber can be guided on the concave side of the curved surface, so that the optical radiation is guided on the outside thereof. Preferably, however, the optical radiation is guided in the light guide. This then preferably has a strip-shaped entrance surface through which the optical radiation is coupled into the light guide, so that it is at least partially guided in the light guide on the convex side of the surface by reflection at the retroreflector section, and an exit surface through which through the entrance surface coupled into the light guide and guided in this guided optical radiation from the light guide, has. The optical waveguide may have, in addition to the retroreflector section located on the outer surface, in particular, an inner surface with a greater curvature that preferably runs parallel thereto.

This has the advantage that, depending on the design of the light guide and entry angle relative to the curved surface as well as the entry point in the entry surface optionally after reflection on a top or inner surface of the light guide, by a point or small area of the entrance surface into the light guide, which is located on the convex side of the curved surface, coming from the light guide can fall on the retroreflector section on the outside of the light guide, so that a collecting function can be achieved. Overall, this results bundling the optical radiation exiting through the exit surface, resulting in imaging with a limited resolution.

By using such devices, which can be made very small in structure and, due to the avoidance of lenses or imaging mirrors, very small, so a very compact and simple construction of an imaging system and an optical sensor is made possible with such a system. A device for the examination of an object with optical radiation is generally understood here to mean a device which can be used for the stated purpose, in particular for illuminating the object or for imaging an illuminated area. In principle, for example, the device only needs to be designed to illuminate or capture an image of at least one area of the object.

According to a first embodiment, the device can therefore have a source for emitting the optical radiation in a predetermined spectral range, the optical radiation of which at least partially strikes the retroreflector section or preferably is coupled into the optical waveguide through the entrance surface and is guided thereby , Such a device, which is also referred to below as a lighting device, can be used in particular as a lighting device of very simple design, which serves for illuminating the object to be examined, preferably a value document. A particular advantage may be provided by the use of the device if the radiation used is to illuminate the object at all locations with the same aperture. Particularly preferably, the source for emitting the optical radiation in a beam having a strip-shaped cross-section at the entrance surface may be formed, wherein the longitudinal direction of the cross section, ie the direction parallel to the strip, orthogonal to the first plane of incidence. This offers the advantage that a very large portion of the radiation emitted by the source can actually be coupled into the optical waveguide and used for illumination after being guided through the optical waveguide and exiting through the exit surface.

In a second embodiment, the device may preferably have a receiving device for detecting optical radiation guided, preferably as an image, out of the exit surface, preferably from the exit surface. The image may be particularly preferably cell-shaped. The corresponding radiation incident on the retroreflector section from the detection area represents the radiation used for the examination. This embodiment of the device, hereinafter also referred to as an image capture device, can advantageously be used as a receiving or detecting device of an imaging optical sensor. Whose detection range is given by the fact that at least a portion of the optical radiation coming from it can be detected by the device.

Particularly preferably, the receiving device for spatially resolved detection of the guided radiation, preferably of the emergent from the exit surface optical radiation along at least one line, preferably a straight line, particularly preferably be formed close behind the exit surface. Preferably, the line is parallel to the longitudinal direction of a cross section of the beam at the receiving device. tion, which has emerged from the exit surface. This is particularly advantageous when the entry and / or the exit surface are strip-shaped, so that their largest extension or longitudinal direction is orthogonal to the first plane of incidence. Thus, the device can be used, for example, as an optical part of a line scan camera which images optical radiation originating from a detection area or a value document in the detection area and entering through the strip-shaped entrance area, which corresponds to a line, through the exit area onto the receiving device.

The preferred embodiments described below are particularly advantageous in the case of the above-described first and second exemplary embodiments of the device, according to which the device can be embodied as a lighting device or as a sheet detection device.

The retroreflector section can be configured as desired except for the features described above. In particular, the curved surface and thus the retroreflector section need not have a constant radius of curvature. However, it is preferred that the curved surface has the shape of a sector of a circular cylinder, which preferably has a sector angle greater than 30 °, more preferably greater than 80 °. The sector angle is understood here to mean the angle enclosed by straight lines in the plane of curvature through the circular cylinder axis running orthogonally to the plane of curvature and in each case by one of the end point of the projection of the curved surface on the plane of curvature. Very particular preference is given to angles of 90 ° or 180 °. In principle, the curvature of the curved surface or the curvature of the projection of the surface on the first plane of incidence can be chosen as desired as long as at least one reflection occurs at the retroreflector section. However, in the first incidence plane, ie, an orthogonal projection of the curved surface onto the first incidence plane, the curved surface preferably has a radius of curvature between 10 mm and 100 mm. This results in a good bundling by the light guide, preferably in a circular cylindrical shape and sector angles greater than 80 °.

The optical waveguide can in principle be shaped as desired, as long as it has the retroreflector section. However, the light guide preferably has the shape of a curved plate in the plane of curvature, preferably of constant thickness. The thickness is the thickness of the plate in the first incidence plane. It is preferably in the range between 0.5 mm and 3 mm. The retroreflector section may then extend in particular along the curved outer surface of the plate. Under the outer surface is understood to mean the curved outer surface of the plate, on the convex side of the light guide lies or which has the lower curvature, in a circular cylinder so a larger radius of curvature. Particularly preferably, the height of the plate, d. H. the extent of the plate orthogonal to the first plane of incidence at least by a factor of two, preferably five greater than the thickness.

The optical waveguide can in principle be formed from any materials transparent to the optical radiation used. For example, it can be made of a suitable glass. Preferably, however, it is formed of a transparent plastic. Preferably, the material of the light guide is chosen so that the specular reflection as well as the retroreflection takes place by total reflection. However, it is alternative or additional also a silvering, for example by a suitable coating conceivable.

The retroreflector section can be formed in different ways. In particular, a corresponding structure can be produced by milling or embossing or injection molding.

A particularly simple production of the light guide results from the following method, which is also the subject of the invention. A plane plate of thermoplastic, transparent material, one surface of which already has the retroreflector section, is cut into strips which have two opposite edges or end faces, respectively orthogonal to the first plane of incidence and are preferably polished to form the entrance and exit surfaces. These strips are bent after heating so that the curved shape with a curvature in one

Curvature plane parallel to the first plane of incidence results. After cooling, the light guide can be used or further processed.

In principle, it suffices that the reflection takes place only at the retroreflector section, which extends along the curved surface, which in particular can form the outer surface of the optical waveguide.

However, it is also possible for the optical waveguide to be reflective along the inner surface opposite the curved surface, lying on the convex side of the curved surface, preferably parallel thereto, for the optical radiation, in particular in the predetermined spectral range. As a result, radiation from a particularly large angular range coupled into the light guide and in this be guided, which is an advantage both in training as a lighting device and as a receiving device.

However, the optical waveguide can also have an inner anisotropic retroreflector section along a curved surface lying on the convex side of the curved surface, preferably parallel thereto, the radiation components in a first plane of incidence parallel to the plane of curvature that is orthogonal to the plane of curvature However, the axis is specularly reflected, but radiation components orthogonal to the first plane of incidence are retroreflected, so that the optical radiation can be guided at least partially between the retroreflector sections. This design of the inner surface as a retroreflector section offers the advantage that an improved bundling is made possible in particular at large bends or highly divergent beams at the entrance surface. The guidance of the optical radiation is analogous to that by the first retroreflector section. Even comparatively strongly divergent bundles of rays can be guided and regrouped in this way. If the optical waveguide is not a waveguide and has an entrance surface and the exit surface, these can in principle be shaped and aligned as desired. According to a preferred embodiment, the entrance and / or exit surface may be formed as flat surfaces. In particular, these flat surfaces may be orthogonal to the plane of curvature and the second plane of incidence of the retroreflector section at the entry or exit side.

Be arranged exit surface. This avoids a deflection of rays running parallel to the plane of curvature. According to another preferred embodiment, the entrance and / or exit surface is orthogonal to the plane of curvature and at a predetermined angle inclined to the second incidence plane at the entrance or exit surface. As a result, a bending of the beam path at the Eintrittsbzw. Exit surface can be achieved.

According to a further preferred embodiment, however, the inlet and / or the exit surface may also be formed so curved that it acts as a lens. Thus, a reduction or enlargement effect can be achieved. The curvature can preferably be circular-cylindrical (with the cylinder axis orthogonal to the first plane of incidence or the curvature plane) or aspherical-cylindrical.

The optical waveguide can also have a further anisotropic retroreflector section which is formed along a further curved surface in the plane of curvature and reflects the radiation components specularly in a first plane of incidence parallel to the plane of curvature, but retroreflects radiation components orthogonal to the plane of curvature, so that the coupled optical waveguide is retroreflected Radiation along an S-shaped surface is performed. In this case, the further curved surface continues the inner surface, which lies opposite the first, closer to the inlet surface, preferably opposite to this, curved surface. In turn, it lies on the outside of the light guide, which lies on the convex side of the outer surface. This allows an offset in the beam path, which would otherwise be achievable only with an optical system that takes up considerable space.

The devices according to the invention are particularly suitable for the construction of optical sensors. The subject matter of the present invention is therefore also an optical sensor for detecting optical properties of an object, preferably a value document, in a predetermined detection area, which comprises an imaginary receiving device. In the device according to the invention, and in which optical radiation coming from the detection area, in particular an object, preferably value document, is guided on the retroreflector section in the detection area, preferably into the entrance surface of the light guide, depending on the design of the light guide is coupled. In principle, the sensor does not need to have any special illumination device if illumination of the object or value document with optical ambient radiation, in particular visible light, is sufficient. However, the optical sensor preferably has a lighting device which is designed to emit optical radiation in a predetermined spectral range onto the detection area or an object or a value document in the detection area.

In principle, the lighting device can be configured as desired. Preferably, however, the optical sensor has an illumination device according to the invention, as described above, wherein the guided by the reflector reflector portion of the device for lighting, depending on the design of the light guide, preferably from the exit surface of the light guide of the device for lighting or Illumination device emitting, optical radiation illuminates the detection area. This embodiment allows a particularly compact construction. Particularly preferably, the optical waveguide can be designed and arranged such that the optical radiation is emitted with more than two thirds of the detection area, preferably the entire detection area of constant aperture.

Another object of the invention is an optical sensor for detecting optical properties of an object, preferably a value document in a predetermined detection range with an inventive A device according to the invention for illumination, as described above, whose optical radiation guided by the retroreflector section of the device, depending on the design of the optical waveguide, preferably emerging from the exit surface of the optical waveguide illuminates the detection area, and with a receiving device for detecting of optical radiation coming from the detection area and forming signals which describe properties of the detected radiation. The receiving device in this case does not necessarily have to be designed like a device according to the invention for detection.

The described optical sensors, which have both a lighting and a receiving device, can be designed in particular for detecting luminescence, remission and / or transmission properties of value documents.

In the case of the luminescence and remission properties, the illumination and the detection device or their exit or entrance surfaces are arranged on the same side of the detection area, so that emitted from the illumination device optical radiation remitted from the value document and the remitted radiation is detected by the detection device can; In the second case, the illumination and detection device or their exit or entry surfaces are arranged on opposite sides of the detection area or a value document located therein.

When detecting luminescence properties, the illumination radiation may lie in a different spectral range than the luminescence radiation finally detected by the receiving device. The invention will be further explained by way of example with reference to the drawings. 1 shows a schematic view of an optical waveguide with an anisotropic retroreflector section extending along a curved surface from a direction orthogonal to a plane of curvature of the optical waveguide,

2 is a schematic view of a cross section of the light guide in Fig. 1,

Fig. 3 is a schematic perspective view of a short portion of the optical fiber in Fig. 1 illustrating the reflection at the retroreflector portion, Fig. 4 is a schematic representation of the specular reflection of a beam on an outer surface of the light guide, along which the retroreflector section is arranged in a Fig. 5 is a schematic representation for comparing the specular with the first plane of incidence of the retroreflector section parallel to the plane of curvature. Retroreflecting the marginal rays of a beam through the retroreflector section in which the beams are projected onto a plane passing through a axis of curvature about which the outside of the fiber is curved;

6 shows a schematic representation of a device for processing value documents, FIG. 7 shows a schematic illustration of an optical sensor of the processing device in FIG. 6 from the side which is designed to detect remission properties of a value document, FIG.

8 is a schematic representation of a receiving device of the sensor in Fig. 7,

9 is a schematic representation of a further optical sensor from the side, which is designed to detect transmission properties of a value document,

10 is a schematic table view of a device for the examination of a value document using optical radiation, in which an offset of the emitted radiation takes place with respect to the coupled-in radiation,

11 shows a schematic view of a further device for the examination of a value document using optical radiation, in which an offset of the radiation emerging from an optical waveguide of the device takes place with respect to the radiation coupled into the optical waveguide,

FIG. 12 shows a schematic view of a further apparatus for the examination of a value document using optical radiation, in which a curvature of the light guide is not circular, FIG.

13 is a schematic view of a light guide at an entrance surface, which is curved or arched, 14 shows a schematic view of a cross section of a further optical waveguide of a device for analyzing documents of value, and FIG

15 shows a schematic view of a light guide designed as a waveguide with an anisotropic retroreflector section extending along a curved surface and a reflective inner surface guiding optical radiation in a cavity, from a direction orthogonal to a plane of curvature of the light guide. An apparatus for the examination of an object, in the example of a value document, in the form of a lighting device in Fig. 1, has a source 10 for optical radiation, in the example visible light, and a light guide 12 with an entrance surface 14, by the optical radiation of the source 10 is coupled into the light guide, and an exit surface 16, by the optical radiation passing through the entrance surface 14 in the

Optical fiber 12 has been coupled, can be coupled out of the light guide 12 or can escape.

The light guide 12, the cross section of which is schematically shown in FIG. 2, is formed by an originally plane-parallel plate 20 which is curved in a curvature plane 18, the xy-plane, in the direction z orthogonal to the plane of curvature 18, however is curved. In the example, the plate 20 has a constant thickness and has the shape of a circular cylinder segment with a sector angle ß and a cylinder or Krüm- mungsachse 22. In the example, the sector angle is 180 °, the axis of curvature is orthogonal to the plane of curvature 18. The light guide 12 therefore has a curved in the plane of curvature 18 surface 24, the outer surface, on the convex side of the plate or the interior of the light guide 12 is located. This has accordingly the form of a sector of a Circular cylinder on which has a sector angle ß, which is greater than 30 °, more preferably greater than 80 °, in the example 180 °. Due to the circular cylindrical shape, the curved surface has a single axis of curvature, namely the cylinder or curvature axis 22.

Along the curved outer surface 24, an anisotropic retroreflector section 26 of the light guide 12 is formed, which specularly reflects radiation components in a first plane of incidence 28 parallel to the plane of curvature 18 and radiation components in a plane orthogonal to the plane of curvature 18 or the first plane of incidence 28 and tangential to the plane of curvature curved outer surface 24 extending second incidence plane 30 retroreflected. Because the second plane of incidence in each case runs tangentially to the curved outer surface 24, the direction of the second incidence planes changes along the optical waveguide 12. In FIG. 1, second incidence planes 30 'and 30 "at the entry and exit surfaces 14 and 14, respectively 16 shown.

At the anisotropic retroreflector section 26, radiation components 32 in the first incidence plane 28 are specularly reflected; Radiation components 34 in the second planes of incidence 30, however, are retroreflected on it, ie in the same direction from which they originate or parallel to the direction from which they originate (see FIGS. 3 to 5). If the propagation direction of the radiation is represented locally as a vector, this means that the radiation can be represented as a superposition of two vector components in the first and the second plane of incidence. The radiation reflected by the retroreflector portion 26 then propagates in a direction given by components in the two planes of incidence. The component in the first incidence plane corresponds to specular reflection, the component in the second incidence planes corresponds to retroreflection. The retroreflector section 26 includes in the present example as an anisotropically reflecting structure parallel to each other and extending to the first plane of incidence 28 extending straight, equally spaced, elongated symmetrical prisms 36, more precisely roof prisms with a prism angle of 90 °, in the curved outer surface 24 of the light guide 12, in the example of the plate 20 are formed. Since the retroreflector portion 26 is formed along the curved outer surface, corresponding edges of the prisms 36 are respectively in parallel to the outer surface 24 extending surfaces. Fig. 2 shows a schematic representation of a cross section of the light guide in the radial direction, but for the sake of clarity, the size ratios are not drawn to scale and in particular the number of prisms is substantially less than in the corresponding real light guide. The cross-sections of the prisms 36 orthogonal to their longitudinal extent, ie in the second plane of incidence 30, in the example have the shape of an isosceles triangle with a vertex angle α of 90 ° and a base width B of about 300 pm. The refractive index of the material of the prisms is chosen so that the retroreflection takes place by twice total reflection on the flanks of the prisms. The retroreflection preferably occurs over a whole range of angles of incidence onto the plane of the retroreflector section 26 or the prism arrangement. Due to the curvature of the outer surface 24, there is a second plane of incidence orthogonal to the first plane of incidence for each radial cross section through the light guide 12. The reflection of radiation components 32 and 34 in the first incidence plane 28 and the second incidence planes 30 along the light guide 12 is illustrated again in FIGS. 4 and 5. Radiation components 32 (see Fig. 4), which are coupled in through the entry surface 14 and lie in the first plane of incidence, strike the outer surface 24 or the surface Retroreflector Abschriitt 26 are generally reflected specular multiple times and guided due to the curvature of the light guide 12 along its outer surface 24 until they emerge from the exit surface 16 again.

On the other hand, in second incidence planes 30 orthogonal to the first incidence plane 28, radiation components 34 of rays coupled in by the entrance surface 14 are retro-reflected at the retroreflector portion 26 and thus focused to a certain degree. This is illustrated in FIG. 5, in which the radiation components 34 are represented by dotted lines in a projection onto a plane perpendicular to the first incidence plane and passing through the axis 22. Without such a retroreflection, a radiation component 35 in the second plane of incidence at the entrance surface 14 would not be deflected, a ray bundle would diverge in this direction. This is illustrated in FIG. 5 by the solid lines 35.

The entry and exit surfaces 14 and 16 are each in the form of flat surfaces which extend orthogonally to the plane of curvature 18 and the second incidence planes 30 'and 30 "of the retroreflector section 26 at the entry and exit surfaces 14 and 16, respectively ,

The surface opposite the outer surface 24, i. the inner surface is formed specular reflective.

The light guide 12 therefore forms an imaging optical system that provides 1: 1 imaging but does not have a very high resolution. Thus, with a radius of curvature of 10 mm, a plate thickness of 2 mm and a structure width of 300 μιη the resolution in the order of 1 mm.

The source 10 is designed as line-shaped or strip-shaped illumination which runs with its longitudinal direction parallel to the strip-shaped entry surface 14. The optical waveguide 12 thus deflects the optical radiation of the source 10 that has entered it and ensures bundling of the optical radiation, so that a predetermined area can be illuminated with the radiation. Because of the imaging properties, each point of the source is blurred into a spot on the object to be illuminated.

As will be explained in the following example, an image acquisition device operates with such a light guide and a downstream receiving device for emerging from the exit surface optical radiation in an analogous manner. The light guide forms an object or an object with a suitable arrangement of the receiving device on this, so that they can capture an image of the object or object. If the receiving device offers a spatially resolved detection of optical radiation in the z-direction, then a strip-shaped detection region can be imaged in a spatially resolved manner onto the receiving device, which emits signals representing a line image. Through the use of flat entrance and exit surfaces, an I: 1 mapping is achieved along the line, transversely at least approximately. A possible use of such devices for the examination of a value document using optical radiation, and in particular for an optical sensor operating in a device for processing value documents, is illustrated in FIGS. 6 to 8. A value-document processing device 38 in FIG. 6, in the example a bank-note processing device, has in a housing 40 an input pocket 42 for input of value documents 44 to be processed, in the example banknotes, a separator 46, which access value documents 44 in the input pocket 42 and these can singulate, a transport device 48 for transporting the isolated value documents with points 50 and in branches of a given by the transport device 48 transport path 52 in the direction of transport to the switches 50 each output pockets 54 for receiving processed by the Wertdokumentbearbeitungs- device 38 value documents. Stacker wheels 56 are arranged in front of the output compartments 54. Furthermore, the value document processing device 38 possesses, along the transport path 52 given by the transport device 48, a sensor arrangement 58 arranged in front of the switches 50 for detecting properties along the transport path 52 and a machine control 60 which is at least connected to the sensor arrangement 58 and the points 50 is connected via signal connections and is designed to evaluate at least one property of a sensor document 58 sensed value document 44 reproducing sensor signals of the sensor array 58 and driving at least one of the switches 50 in response to the result of evaluation of the sensor signals.

In this exemplary embodiment, the sensor arrangement 58 comprises a sensor 62 for detecting optical properties of the value documents, in the example of a color image of the value documents, for example for checking for contamination, and / or for determining the nominal value of the value documents and / or for determining the authenticity of the value documents predetermined criteria. The sensor arrangement may further include, for example, a sensor not shown in FIG. 6 for detecting the condition of Value documents, such as the presence of adhesive tape include.

The machine controller 60 detects the signals from the sensor assembly 58 and determines whether the value documents sensed by the sensor assembly 58 meet at least one predetermined criterion corresponding to fouling in a trafficable, i. is still suitable for further use as a means of payment, state, or which denomination it has or whether it is genuine. Depending on the result of the test, the machine controller 60 controls at least one of the switches 50 so that the document of value 44 from the transport device 48 in a test result assigned or a certain predetermined type, in particular face value of value documents corresponding output tray 54th promoted and stored there.

The sensor 62 used to determine the color image of the value document is shown roughly schematically in FIGS. 7 and 8. The sensor 62 is designed to detect a color image of the value document line by line on the sensor 62 during transport. The lines run transversely to the transport direction T. The sensor 62 has an illumination device 64 for illuminating a detection area 66 or a value document 44 in the detection area 66 with optical radiation, in the example with visible light, preferably additionally also infrared radiation, and an image acquisition device 68 for detecting a line-shaped image of at least a part of the illuminated area on the value document 44. For controlling the illumination device 64 and for processing and evaluating the signals of the image capture device 68, a sensor control and evaluation device 70 connected to the devices 64 and 68 via signal connections serves after the evaluation signals via the signal connection to the Maschinensteuerurig 60 outputs, which represent the result of the evaluation.

The illumination device 64, like the illumination device of the first embodiment, has an optical radiation source 10 'and a light guide 12' into which the optical radiation of the source 10 'is coupled. The source 10 'is adapted, depending on the control by the Sensorsteuer- and -auswertei direction 70 as optical radiation light of a predetermined color, in the example red, green or blue, leave. For this purpose, for example, corresponding light or laser diodes may be provided, whose light is formed via a homogenizing optical fiber to a beam with strip-shaped cross-section. Alternatively, a strip or line-shaped arrangement of the light or laser diodes is conceivable. The Sensorsteuer- and -auswerteinrichtung 70 controls the source 10 'so that it cyclically successively emits light each of a different one of the three colors.

The light guide 12 'is formed as the first light guide 12 except for two differences. On the one hand, the light guide 12 'does not extend beyond a sector angle β of 180 °, but only over a sector angle β of 90 °. On the other hand, although the exit surface 16 'is flat as the exit surface 16, it forms an acute angle, in the example of approximately 30 °, with the second plane of incidence 30 "at the intersection between the curved outer surface 24' of the light guide 12 'and the exit surface 16' This has the consequence that the light coupled out of the exit surface at the exit surface 16 'in

Direction of the outer surface 16 'is broken and therefore adjacent to the light guide 12' on the detection area 66 and a value document therein and illuminated this or this. As in the first embodiment, the source 10 'and the entrance surface 14' of the light guide 12 'are arranged so that the longitudinal direction, ie the direction parallel to the direction of the strip or the largest Erstrec- effect of the cross section of the output from the source 10' Beam, parallel to the longitudinal direction or the second incidence plane 30 extends; ie the longitudinal directions of source and entrance surface coincide.

The image acquisition device 68 has an optical waveguide 12 ", which is mirror-inverted to the optical waveguide 12 ', and a receiving device 72 for spatially resolved reception of optical radiation coupled out of the optical waveguide 12' and formation of signals which reproduce the intensity of the decoupled optical radiation A portion of the sensor control and evaluation device 70 is connected to the receiving device 72 via a signal connection and detects and processes the signals.

The receiving device 72 has a plurality of receiving elements arranged along a line, for example photodetection elements, as illustrated schematically in FIG. 8. The line is arranged perpendicular to the first incidence plane and parallel to the longitudinal direction of the strip-shaped exit surface 16 "of the light guide 12".

The light guides 12 'and 12 "are mirror images of each other so arranged that an illuminated by the illumination device 64 strip in the detection area 66 of the light guide 12" is displayed spatially resolved to the receiving device. The spatial resolution is made possible by the fact that the retroreflection has a beam-bundling effect in the light guide 12 ". The inclination of the exit surface 16 'in mirror-inverted fashion corresponding to the inclination of the entrance surface 14' enables imaging of the light Detection area between the two light guides 12 'and 12 ", which are aligned with their first planes of incidence and thus the longitudinal directions of the exit surfaces or entrance surfaces 16' and 14 'parallel to each other.The Sensorsteuer- and -auswerteinrichtung 70 detects the signals of the receiving elements 74 and the receiving device in time with the cyclic illumination, so that the sensor control and -auswerternrichtung 70 cyclically red, blue and green line images are detected, from which it forms a color image of the value document after the transport of the value document.

Another exemplary embodiment in FIG. 9 differs from the preceding exemplary embodiment in that, in contrast to the sensor 62, the optical sensor 62 'is designed as a transmission sensor. It has an illumination device 64 'and an image capture device 68', which are designed like the illumination device 64 and the image capture device 68. For identical components or parts, therefore, the same reference numerals are used and the explanations to these apply accordingly. In FIG. 9, the sensor control and evaluation device 70 is not shown for the sake of clarity. The only difference with the illumination or image capture device 64 or 68 is that the entry and exit surfaces are formed as in the first embodiment. The illumination device 64 'and the image capture device 68' are arranged relative to each other so that the exit surface 16 "of the light guide 12"'of the illumination device 64' and the entrance surface 14 "of the light guide 12""of the image capture device 68 'are opposite, wherein the transport path for Value documents passes between them. Accordingly, the sensor does not detect remission but transmission images.

Further exemplary embodiments differ from the two last-described exemplary embodiments in that the light guides of the illumination and the stop detection device have different radii of curvature.

Further embodiments of illumination and / or image capture devices differ from the illumination and / or image capture device in Fig. 8 by the use of differently shaped, in particular S-shaped bent light guide. In the examples in Figs. 10 and 11, only the optical fiber is shown for the sake of simplicity. In the example in Fig. 10, the optical fiber 76 comprises two adjoining segments 77 and 77 ', which are formed like the conductor 12 in the first embodiment and each have the shape of a circular cylinder sector with a sector angle of 180 °. Such optical fibers allow a 1: 1 imaging, where the object and image are four times the radius of the circular cylinder in the x-direction in the first plane of incidence and approximately no offset occurs in the y-direction.

In another example in Fig. 11, the light guide 78 comprises two adjoining segments 79 and 79 'which, like the light guide 12 in the first embodiment, have the shape of a circular cylinder sector with a sector angle of 90 °. Such optical fibers allow a 1: 1 imaging in which object and image are offset from each other by two times the radius of the circular cylinder in the x direction in the first plane of incidence and approximately also in the y plane. The image with S-shaped curved optical fibers has the further advantage that the image remains symmetrical in the x-direction, although it runs primarily on the curved outer surface.

In other embodiments, the curved surface of the optical fiber, in the example, does not need to have the shape of a sector of a circular cylinder, the curved outer surface of the optical fiber 80. Rather, curvatures as in FIG. 12, in particular elliptical, parabolic or other curve shapes in the plane of curvature are also conceivable. All other properties of the light guide may be, for example, like those in the first embodiment.

A further embodiment of an illumination or image capture device differs from the illumination or image capture device in FIGS. 8 and 9 by the formation of the entrance and / or exit surfaces. As shown schematically in Fig. 13, they may be curved so as to have an enlarging, reducing or imaging effect in the first plane of incidence. In Fig. 13, the entrance surface 82 has a circular cylindrical shape and may serve as a cylindrical lens to increase or decrease the size of the object or detector in the X direction and increase the focal distance. With respect to the other properties, the optical fiber is formed as in the first embodiment, so that the same reference numerals are used for the same parts.

A further variant of a device with a light guide differs from the preceding embodiments only in that the light guide on an outside curved surface 24 opposite the curved inner surface 84 anisotropic retroreflective Retro Reflector Abschrütt 36 ', which has the same first incidence plane and is preferably formed as the outer retroreflector section 36. It preferably has the same prism structure. As a result, even more divergent bundles of radiation can be combined with other components.

Other variants of the preceding embodiments distinguish them from them in that the optical radiation outside the light guide, i. is guided on the convex side 24 'of the inner surface of a curved plate, which itself may represent a light guide, to which the surface of the retroreflector section along the curved surface 24' may be mirrored. This is schematically illustrated in FIG. 15, wherein the dashed line as in FIG. 1 illustrates the retroreflector structure. In this way, by adding an inner surface 84 "applied on a further carrier, a hollow-fiber light guide can be formed or a solid optical fiber can be combined with a hollow-fiber light guide.

Claims

P a n t a n s p r e c h e

Apparatus for inspecting an object, preferably a document of value, using optical radiation having a light guide speculatively reflecting an anisotropic retroreflector portion formed along a curved surface in a plane of curvature specularly reflecting radiation components in a first plane of incidence parallel to the plane of curvature, radiation components orthogonal to the first one However, incidence plane is retroreflected so that at least a portion of the optical radiation incident on the retroreflector section is guided at least partially on the convex side of the surface by reflection at the retroreflector section.

Device according to one of the preceding claims, wherein the curved surface has the shape of a sector of a circular cylinder, which preferably has a sector angle greater than 30 °, particularly preferably greater than 80 °.

Device according to one of the preceding claims, wherein the curved surface has a radius of curvature in the first plane of incidence between 10 mm and 100 mm.

Device according to one of the preceding claims, in which the light guide has the shape of a plate, preferably of constant thickness, which is released in the plane of curvature.

Device according to one of the preceding claims, in which the light guide has a further anisotropic retroreflector section which extends along a curved surface in the plane of curvature is formed and the radiation components in a plane parallel to the plane of curvature first plane of incidence orthogonal to the axis specularly reflective, radiation components orthogonal to the first plane of incidence, however, retroreflected, so that the coupled optical radiation is guided along an S-shaped surface.

6. Device according to one of the preceding claims, wherein the optical waveguide an entrance surface, through which the optical radiation is coupled into the optical waveguide, so that it is at least partially guided in the optical waveguide on the convex side of the surface by reflection at the reflector reflector portion , And an exit surface, through which emerges through the entrance surface into the optical fiber coupled and guided therein optical radiation exiting from the optical fiber has. Apparatus according to claim 6, wherein the entrance and / or exit surfaces are planar surfaces and are inclined orthogonal to the plane of curvature and at a predetermined angle to the second plane of incidence at the entrance and exit surfaces, respectively.

Apparatus according to claim 6 or 7, wherein the entry and / or exit surface are formed curved so that they act as a lens.

9. Device according to one of the preceding claims, wherein the light guide along one of the curved surface opposite, lying on the convex side of the curved surface, preferably designed to be parallel to this inner surface for the optical radiation is reflective.

10. Device according to one of the preceding claims, wherein the optical waveguide along one of the curved surface, lying on the convex side of the curved surface, preferably parallel to this inner surface has an inner anisotropic reflector reflector portion of the radiation components in one to the plane of curvature however, retroreflects radiation components orthogonal to the first plane of incidence so that the optical radiation is at least partially feasible between the retroreflector sections.

11. Apparatus according to any one of the preceding claims, comprising a source for emitting the optical radiation in a predetermined spectral range, the optical radiation of which falls at least partially grazing on the retroreflector portion and is guided therethrough.

12. The apparatus of claim 11 and one of claims 7 to 10, wherein the source for emitting the optical radiation is formed in a beam having a strip-shaped cross section at the entrance surface, and wherein a longitudinal direction of the cross section is orthogonal to the first EinfaDsebene.

13. Device according to one of claims 1 to 10, which further comprises a receiving device for detecting the light guided by the optical fiber, preferably emerging from the exit surface, optical radiation, preferably as an image having.

14. The apparatus of claim 13, wherein the receiving device for spatially resolved detection of the guided optical radiation along at least one line, preferably a straight line is formed.

15. An optical sensor for detecting optical properties of an object, preferably a value document, in a predetermined detection area with a device according to claim 13 or claim 14, wherein optical radiation coming from the detection area is guided at the retroreflector section, wherein it is preferably located in the entrance surface of the light guide is coupled.

16. An optical sensor according to claim 15, which has a device according to claim 11 for illuminating the detection area, and in which the light directed by the retroreflector section of the device for illumination, preferably emerging from the exit surface of the light guide of the device for illumination , Optical radiation illuminates the detection area.

17 optical sensor for detecting optical properties of an object, preferably a value document, in a predetermined detection range with a device according to any one of claims 11 or 12, guided by the retroreflector guided, preferably emerging from the exit surface of the optical fiber, optical radiation illuminates the detection area , and with a receiving device, which is designed to detect optical radiation from the detection area and formation of the characteristics of the detected radiation descriptive signals.