EP2443490A1

EP2443490A1 - Optical system and sensor for checking value documents having such an optical system

Info

Publication number: EP2443490A1
Application number: EP10725694A
Authority: EP
Inventors: Bernd Wunderer
Original assignee: Giesecke and Devrient GmbH
Current assignee: Giesecke and Devrient GmbH
Priority date: 2009-06-18
Filing date: 2010-06-17
Publication date: 2012-04-25
Also published as: RU2012101487A; DE102009025368A1; WO2010146103A1; US20120092648A1; CN102460235A; RU2528036C2; US8721091B2; CN102460235B

Abstract

The invention relates to an optical system having a flat anisotropic retroreflector section, which specularly reflects radiation components in a first plane of incidence but retroreflects radiation components in a second plane of incidence, a first imaging section, which produces a linear intermediate image on the retroreflector section from an object point in an object plane at a specified relative position to the system, which intermediate image extends along a line in the second plane of incidence, and a second imaging section, by means of which the linear intermediate image is imaged into an image point.

Description

Optical system and sensor for testing value documents with such an optical system

The present invention relates to an optical system, in particular an imaging optical system, a sensor for checking value documents with such an optical system and a method for imaging an object point.

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. Important examples of such value documents are cards, coupons, vouchers, checks and in particular banknotes. Banknotes in the context of the invention are leaf-shaped.

In the following, optical systems generally are understood to be systems which influence optical radiation, in particular change its beam path. Optical radiation refers in a known manner electromagnetic radiation in the UV and / or IR and / or in particular in the visible wavelength range.

For the investigation of value documents, optical sensors are often used which detect spatially resolved optical properties of a value document to be examined and, to this end, map strip-shaped areas on the value document at least partially to a substantially row-shaped field of receiving elements. 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 value document. By moving the value document across the direction of the line or the Strip can be detected by sequentially capturing such images during movement past the sensor, a two-dimensional image of the value document.

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 parabolic mirrors, do not always meet these requirements with line-shaped imaging to the desired extent. In the past, partially self-focussing 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.

It is therefore the object of the present invention to provide an optical system for imaging areas of a document of value, a corresponding imaging method and a sensor for detecting optical properties of a document of value, which allow a compact construction even without the use of SELFOCs.

The object is achieved by an optical system having a planar anisotropic retroreflector section which specularly reflects radiation components in a first plane of incidence but retroreflects radiation components in a second plane of incidence, a first imaging section extending from an object point in an object plane in a predetermined relative position to the system generates a line-shaped intermediate image on the retroreflector section, which extends along a line in the second plane of incidence, and a second imaging section, by means of which the linear intermediate image is imaged into a pixel.

The object is further achieved by a method for imaging an object point, in which the object point is imaged onto a linear intermediate image on an anisotropic retroreflector section such that the intermediate image extends with its longitudinal direction in an incidence plane in which the retroreflector section is retroreflective and in which the intermediate image is displayed on a pixel. The longitudinal direction of the intermediate image is understood in particular to be the direction of the line formed by the intermediate image.

From the fact that the retroreflector section is flat, it is understood that beams which are incident from the same direction on the retroreflector section, but which meet at different locations, are reflected in the same directions, respectively. In particular, the retroreflector section can for this purpose have optically effective, preferably identically formed structures, which are arranged along a plane.

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. Upon incidence orthogonal to the plane of the retroreflector section, ie an angle of incidence of 0 °, the beam is reflected back in the first plane of incidence. The term "retroreflected" or retroreflection is used in the context of the invention By contrast, it is understood that an incident beam in the second plane of incidence and the retroreflected beam resulting from the retroreflection of the incident beam are parallel, with some offset of the beams from one another in a direction parallel to the plane of the retroreflective scan. 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 in an angular range in which the retroreflection is possible, at least in good approximation.

An anisotropic retroreflector section in the sense of the invention may, for example, comprise a body with a flat surface, for example a plate, of a transparent material, on or in the same surface of which a field of prisms running parallel to a straight line in the first plane of incidence, preferably Roof prisms with a prism angle of 90 °, is formed. In the second plane of incidence, the prisms provide retroreflection in a manner known per se, wherein the reflection at the boundary surfaces of the prisms can be given by total reflection or reflection at a reflecting 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: If a beam falls from a predetermined direction onto the anisotropic retroreflector section, then it can be imagined that the reflected beam results from the incident beam or beam. the incident radiation can be decomposed into first and second directional components whose vectorial sum is precisely the direction of the incident beam or of the incident beam Radiation reproduces and lie in the first and the second plane of incidence. 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 to the direction of the incident beam may be so that the angle of incidence of the component in the second plane of incidence is less than 45 °.

For imaging purposes, a point or object point from a given object plane is imaged onto the retroreflector section by means of the first imaging section, which is designed accordingly, the intermediate image formed there being, however, only linear, preferably straight-shaped. The first imaging system is formed and arranged relative to the anisotropic retroreflector section such that the linear intermediate image lies in or extends in the second plane of incidence. The line is formed by divergent beams emanating from the object point, which are directed by the first imaging section only to the retroreflector section in such a way that they have parallel or in particular diverging components in the second plane of incidence immediately before the retroreflector section, but converge in the first incidence plane to be focused. Since the intermediate image or the line extends in the second plane of incidence, the beam or radiation components lying in this plane of incidence are reflected in their direction of incidence, although depending on the type of retroreflector section, the position of the incident beam relative to the retroreflector section, when using roof prisms relative to the roof edge of one of the roof prisms, and the angle of incidence may be offset. On the other hand, the radiation components in the first plane of incidence are specularly reflected, which is why the incident radiation is not reflected on itself, but is deflected. The retroreflected radiation components formed by the radiation components in the second plane of incidence now converge again while the other components must be re-focused. This purpose is served by the second imaging section, by means of which the linear intermediate image is imaged into a pixel. This formation of the pixel thus takes place with the cooperation of both the anisotropic retroreflector section and the second imaging section.

The fact that the intermediate image is formed on the retroreflector section and has only a small extent in the first plane of incidence, geometric errors are greatly reduced. These may be, in particular, errors due to the finite extent of the retroreflective structures in the first plane of incidence and oblique incidence thereon in the second plane of incidence, and thereby differences in the length of the optical paths between the point of object and the retroreflector section can arise in the second incidence level. At the same time, it is possible to construct a compact optical system in which no SELFOCS need to be used. In addition, such systems can have very different cutting widths and can thus be easily adapted to given requirements, in particular also greater depth of field. Next, they can be easily manufactured with suitable training. In order for the pixel to be as sharp as possible, the optical system is preferably designed such that it effects a 1: 1 imaging. In a particularly simple manner, this can be obtained by the fact that the two imaging sections have the same imaging properties, for example the same focal lengths and / or cutting widths.

The generation of the intermediate image can in principle be done in any manner. However, in the optical system, at least one of the imaging sections preferably has at least one cylindrical optics, preferably a cylindrical lens and / or a cylindrical or parabolic mirror, which preferably generates the intermediate image. In this case, a cylinder optics is understood to mean optics which are representative of beams in a plane given by the cylinder optics, i. particular bundling, has properties for rays in an orthogonal plane but not. In this case, a cylindrical lens is understood to mean a transparent body or a section of a transparent body which has at least one surface section with the shape of a cylindrical section or forms an aspherical lens with corresponding imaging properties. Accordingly, a cylindrical mirror is understood to mean a section of a reflective surface or a reflective layer which is cylindrically shaped. This embodiment has the advantage that the image can be generated with very simple means.

Preferably, in the optical system in the beam path between at least one of the imaging sections and the retroreflector section, a reflective element is arranged. This embodiment makes it possible to bend or fold the total beam path of the optical system, in particular in the first incidence plane, at least once. In the simplest case, the reflective element can be replaced by a preferably reflective de, in particular be given totally reflecting surface of a transparent body. The system may be designed so that at least one of the imaging sections kinks or folds the beam path. This allows a particularly compact design of the system.

In particular, in the optical system of at least one of the imaging sections may comprise a cylindrical lens and an imaging reflective element, preferably a parabolic or cylindrical mirror, which preferably serve to form the intermediate image or the image of the intermediate image. The imaging system then fulfills two functions, namely the generation of the intermediate image or the image of the intermediate image and the folding or folding of the beam path. In a particularly favorable embodiment, preferably the beam path between the cylindrical lens and the imaging reflective element projected onto a plane orthogonal to the cylinder axis, preferably in the first plane of incidence, be parallel or run.

In this embodiment, it is particularly preferred that the imaging reflective element is formed by a reflective surface of a cylindrical lens-forming body. This makes it possible to form the respective imaging section in one piece, which not only allows a simple production, but also ensures a good alignment of the cylindrical lens and the imaging reflective element, in particular also on each other.

Furthermore, it is preferred that at least one of the imaging sections, preferably the two optical sections and the retroreflector section, are or are formed together in one piece. This also allows a particularly simple production. The imaging section can then be designed in particular as described in the preceding paragraph.

It is further preferred for a diaphragm, preferably a slit diaphragm, to be formed in the second plane of incidence, the edge of which is at least partially formed by the retroreflector section. An edge section of the diaphragm opposite the retroreflector section can then run at a predetermined distance from the plane of the retroreflector section. This training offers two advantages. On the one hand, the diaphragm can reduce scattered light, which arises as a result of multiple reflections depending on their design at the imaging sections. On the other hand, it can limit the intermediate image and thus act as a visual field diaphragm, which greatly simplifies the structure of the optical system. Preferably, the diaphragm is then arranged in the center plane of the beam path in the region of the retroreflector section.

A particularly simple construction results, in particular in a design for a 1: 1 imaging, in that the optical system is constructed mirror-symmetrically with respect to a plane or mirror plane parallel to the second plane of incidence. In particular, the plane can at least approximately intersect the intermediate image on the retroreflector section. If a diaphragm is provided in the second plane of incidence, it is preferably located in the aforementioned mirror plane.

In another development, the optical system has a further plane anisotropic retroreflector section parallel to the retroreflector section. The first imaging section can then be designed to produce a further linear intermediate image of the object point on the further retroreflector section. The second depicting Cut is then preferably formed so that it images the further linear intermediate image on the pixel. Preferably, the two retroreflector sections are arranged parallel to one another. Particularly preferably, the system is mirror-symmetrical to a plane parallel to the reflector reflector sections.

An inventive optical system can be used advantageously in sensors for documents of value. The invention therefore also relates to a sensor for detecting optical properties of a value document having an optical system according to the invention, which images in particular a region of the document of value under investigation.

The optical system proves to be particularly advantageous in the case of sensors which spectrally dissect the optical radiation emanating from the object point and detect the spectral components. The sensor referred to in the preceding paragraph may then in particular comprise a dispersing device arranged downstream of the optical system and a field of receiving elements for receiving various spectral components generated by the dispersing device. The array of receiving elements, in particular for the radiation from an object point, may comprise a row of receiving elements arranged relative to the dispersing device such that different receiving elements of the line receive different spectral components. As a result, in combination with the dispersing device, the optical system then forms in each case a spectral component or spectral components from a predetermined wavelength range onto a corresponding one of the receiving elements. In particular, the dispersing device may have, as a dispersing element, a diffractive element, for example a grating, or preferably a prism. Furthermore, the sensor may preferably have a radiation source, the optical radiation, preferably radiation in the visible and / or IR wavelength range, on the region of the object plane of the optical system in a detection range of the sensor, ie a region of the object plane that is imaged onto the receiving elements , gives up. Preferably, the radiation source generates a stripe-shaped illumination pattern.

The invention will be further explained by way of example with reference to the drawings. Show it:

1 is a schematic view of a very simple embodiment of an optical system,

2 shows a schematic view of a part of a retroreflector section in FIG. 1,

3 shows a schematic representation of a device for processing value documents,

4 shows a schematic partial representation of a sensor of the device in FIG. 3, which is designed to detect optical properties of value documents,

5 shows a perspective view of an optical system of the sensor in FIG. 4 in the form of a body serving as first and second imaging section and retroreflector section, FIG. Fig. 6 is a view of an optical path in the body in Fig. 5 from one side, and

7 shows a view of an optical path of a body of an optical system serving as first and second imaging section and retroreflector section according to a further preferred embodiment.

An optical system 10 in FIG. 1 is used to image a subject spot 12 onto a pixel 14. For this purpose, it has a planar anisotropic retroreflector section 16, a first imaging section 18, which extends from the object spot 12 in an object plane 20 in a predetermined Relative position to the system 10 is formed, a line-shaped intermediate image 22 on the retroreflector section 16 generates, and a second imaging section 24, by means of which the line-shaped intermediate image 22 is imaged in the pixel 14.

The term "imaging" in the context of the invention also includes the case that the image is not perfectly sharp, but has a limited by the components of the optical system resolution.

The planar anisotropic retroreflector section 16 specularly reflects radiation components 26 in a first plane of incidence 28; Radiation components 30 in a second plane of incidence 32, however, are retroreflected, that is, reflected in the same direction from which they come or parallel to the direction from which they come. 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 signals returned by the retroreflector section 16 Thrown radiation then propagates in a direction given by components in the two planes of incidence. The component in the first plane of incidence corresponds to specular reflection, the component in the second plane of incidence corresponds to retroreflection.

The position of the first and second planes of incidence relative to one another depends on the design of the retroreflector section. In the example, the first and second incidence planes 28 and 32 are orthogonal to each other.

The retroreflector section 16 is flat, i. the above reflection properties are independent of where the rays fall from the imaging section to the retroreflector section.

The retroreflector section 16 comprises in the present example as an anisotropically reflecting structure along mutually parallel straight lines extending, equally spaced, elongated symmetrical prisms 34, more precisely roof prisms with a prism angle of 90 °, which are formed in a flat surface of a base 36. Since the retroreflector section 16 is planar, corresponding edges of the prisms 34 are each at least approximately in one plane. The cross section of the prisms 34 orthogonal to the longitudinal extent, ie in the second plane of incidence, in the example has the shape of an isosceles triangle with a vertex angle α of 90 ° and a base width B of about 300 μm. 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 an entire range of angles of incidence on the plane of the retroreflector section 16 or the prism arrangement. The first and the second imaging section 18 and 24 are formed in the example to achieve a 1: 1 imaging in conjunction with the Retroreflektor- section 16 and have this same imaging properties. For this purpose, they are the same and each comprise cylindrical lenses 38 and 40 of the same focal lengths or cutting widths.

The first imaging section 18, in the example the cylindrical lens 38, is arranged so that it images the object point 12 in the object plane 20 into the linear intermediate image 22 on the retroreflector section 16, more precisely the area of the prisms 34. The first imaging section 18 and in particular its cylindrical lens 38 are arranged relative to the retroreflector section 16 such that the linear intermediate image extends at least to a good approximation along a line in the second plane of incidence. The object plane 20 is at least approximately orthogonal to an optical plane 42 of the cylindrical lens, i. a plane through the cylindrical lens axis, with respect to which the imaging properties of the cylindrical lens are mirror-symmetrical. In the example, this plane runs through the cylindrical lens axis and the apex line of the cylindrical lens.

In general, beams emanating from the point of object 12 directed at the retroreflector section 16 by the first imaging section 18 will fall obliquely to both the first and second incident planes 28 and 32 on the retroreflector section 16, respectively. Such a beam is reflected according to its components or direction components, ie projections of a unit vector along the incident beam onto the planes of incidence. The component in the first incidence plane 28, ie the projection of the unit vector onto the first incidence plane 28, becomes specular in the direction reflected on the pixel 14, the component in the second plane of incidence 32, that is, the projection of the vector to the second plane of incidence 32, retroreflected. The direction of the beam reflected from the retroreflector section 16 resulting from the specular and retroreflected components results from vector addition of the reflected components and is directed at the pixel 14. In particular, the retroreflection ensures that in a projection onto the second plane of incidence, the linear intermediate image can again be imaged onto a point, the pixel 14.

The sharpness of the image is influenced, among other things, by the aberrations in the retroreflection at the prisms and the diffraction at the prisms. Due to the principle of retroreflection, an offset between incident and retroreflected beam, which depends on the width B of the prism base, occurs in the second plane of incidence. Since the object point is imaged onto the linear intermediate image on a retroreflective structure of the retroreflector section 16, in the example the prisms 34, these aberrations are greatly reduced by the retroreflection.

An optical system which operates on the principle of the optical system described above can be used in particular in sensors for the optical examination of documents of value.

A value-document processing device 44 in FIG. 3, in the example a bank-note processing device, has in a housing 46 an input pocket 48 for input of value documents 50 to be processed, in the example banknotes, a separator 52, which access value documents 50 in the input pocket 48 and these can singulate a transport device 54 for transporting the isolated value documents with switches 56 and in branches of a given by the transport device 54 Transport path 58 in the transport direction after the switches 56 each output compartments 60 for receiving processed by means of Wertdokumentbearbeitungs- device 44 value documents. Stacker wheels 62 are arranged in front of the output compartments 60. Furthermore, the value document processing device 44 possesses, along the transport path 58 given by the transport device 54, a sensor arrangement 64 arranged in front of the points 56 for detecting properties along the transport path 58 of transported value documents 50 and a control and evaluation device 66 connected at least to the sensor arrangement 64 and connected to the switches 56 via signal connections and is designed to evaluate at least one property of a sensed by the sensor arrangement 64 value document 50 reproducing sensor signals of the sensor assembly 64 and control of at least one of the switches 56 in response to the result of evaluation of the sensor signals.

In this embodiment, the sensor arrangement 64 comprises a sensor 68 for detecting optical properties of the value documents, in the example of a spectrally resolved image of the value documents, for example for testing for contamination, and / or for determining the nominal value of the value documents and / or for determining the value Authenticity of value documents according to predetermined criteria. The sensor arrangement may further comprise, for example, an ultrasonic sensor (not shown in FIG. 3) for detecting the state of documents of value, for example the presence of adhesive strips, which detects transmission properties of the value documents for ultrasound.

The control and evaluation device 66 detects the signals of the sensor arrangement 64 and determines whether the value documents detected by the sensor arrangement 64 meet at least one predetermined criterion in accordance with FIG Pollution in a marketable, ie 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 control and evaluation device 66 controls at least one of the switches 56 in such a way that the value document 50 from the transport device 54 corresponds to value documents corresponding to the test result or to a specific predefined type, in particular nominal value Output tray 60 promoted and stored there.

The sensor 68 used to determine the spectrally resolved image of the value document is shown roughly schematically in FIG. 4 together with a part of the transport device 54. The sensor 68 is designed to detect a spectrally resolved image of the value document line by line on the sensor 68 during transport. The lines run transversely to the transport direction. The sensor 68 has an illumination device 70 for emitting optical radiation, in the example visible light, preferably additionally infrared radiation, to the value document, an optical system 72 for imaging at least a portion of the illuminated area on the document of value 50 on a receiver 74, the has a two-dimensional array of receiving elements 76 arranged in a matrix, and a dispersing device 78 arranged in the optical path between the optical system 72 and the receiver 74, which spatially splits incident radiation as a function of the wavelength, so that spectral components of the incident radiation depend on the degree of radiation Splitting on different receiving elements 76 fall. For processing and evaluation of the signals of the receiver 74 or the receiving elements 76 and preferably also for controlling the illumination device 70, a sensor output connected to the receiver 74 and preferably the illumination device via signal connections is used. teeinrichtung 80, which emits signals after the evaluation via the signal connection to the control and evaluation device 66, which represent the result of the evaluation.

The document of value 50, which is conveyed past the sensor 68 by the transport device 54, is illuminated during the transport with optical radiation from an illumination device 70 for emitting optical radiation, in the example of visible light. The illumination device 70 is embodied such that the optical radiation illuminates only one strip on the value document 50, which extends with its longitudinal direction transversely to the transport direction of the value document 50 over its entire width and lies at least partially in the detection range of the sensor, in particular the object plane. The detection range of the sensor is given by the area imaged by the optical system 72 on the receiver 74.

Optical radiation emanating from at least part of the illuminated area of the value document in the detection area is imaged by the optical system 72 onto the receiver 74, wherein the dispersing device 78 spectrally splits the optical radiation. For this purpose, the optical system 72 is arranged relative to the transport device 54 or the transport path 58 in such a way that a value document lies at least to a good approximation in the transport path section in the sensor in an object plane of the optical system 72. In this exemplary embodiment, the dispersing device comprises a prism made of a transparent material which disperses in the visible, preferably also in the infrared wavelength range. The illumination device 70, the optical system 72, the dispersing device 78 and the receiver 74 are aligned so that the spectral splitting is transverse to the plane in which the beam path for the line or the strip for a wavelength, and both spatially resolved detection in one of the direction of the strip or the line transversely to the direction of transport corresponding direction as well as a spectrally resolved detection in a transverse, in particular orthogonal thereto direction takes place.

The optical system 72 is shown in more detail in Fig. 5 in a perspective view and in Fig. 6 in a sectional view. In this case, the illustration without the dispersing device 78 is shown to simplify the illustration.

In this embodiment, the optical system 72 comprises an integral body including both a retroreflector portion 82, a first imaging portion 84 for imaging an object point 12 in the object plane 20, in the example the plane in which the value document 50 on the sensor 68 is transferred to a linear intermediate image 22 on the retroreflector section 82 and a second imaging section 86 which images the partially specular and partially retroreflected intermediate image of the retroreflector section onto a pixel 14 in an image plane when applied to the sensor 68 in the plane the receiving elements 76 is located.

The body may, for example, be made of a material transparent to optical radiation in the spectral range to be examined by the sensor, for example a suitable plastic or glass. The refractive index at least in the area of the retroreflector section 82 is present. zugweise chosen so that the retroreflection occurs by total reflection. Otherwise or in addition, the corresponding retroreflective surface of the retroreflector section 16 may be mirrored, for example by applying a suitable layer.

The retroreflector section 82 is constructed like the retroreflector section 16, but the base body 88 is designed differently on its side facing away from the retroreflective structure, since it also forms the first and second imaging sections 84 and 86 at the same time. Since the retroreflector portion 82 is constructed like the retroreflector portion 16 and the characteristics of the retroreflector portion 82 correspond to those of the retroreflector portion 16, the same reference numerals as above are used for the same elements, planes, and images, and the corresponding explanations apply here as well.

The imaging sections are mirror-symmetrical with respect to a plane orthogonal to the plane retroreflector section 82 and parallel to the second plane of incidence 32, respectively.

It is therefore sufficient to describe only the first imaging section 84 in more detail. The description then applies to the second section 86 accordingly.

Imaging section 84 acts as a cylinder optic which, as previously described, images a point in the object plane into a line-shaped intermediate image 22 on retroreflector section 82, and at the same time bends the beam path such that an almost orthogonal incidence of the radiation onto retroreflector section 82 he follows. This has the advantage that the occurrence of stray light is reduced. The imaging section 84 has for this purpose a first curved surface section 90 with the shape of a cylinder section, the radius of which is selected such that it images the point in the plane of the object to an infinite extent. This means that the components lying in a plane orthogonal to the cylinder axis or, in the example, in the first plane of incidence, of the rays emanating from the object point 12 run parallel after passing through the surface section 90. The surface portion 90 therefore acts like a cylindrical lens.

A second, the first surface portion 90 opposite surface portion 92 of the body 88 is formed, for example by a reflective layer, as a linear parabolic mirror. The cylinder axis 94 of the first curved surface portion 90 and the longitudinal axis 96 of the second curved surface portion 92 are aligned parallel to each other, so that they are parts of a Zy-cylinder optics. Specifically, in this example, the longitudinal axis 96 lies in the optical plane of the first surface portion 90. The parabolic axis 98 of the parabolic mirror is inclined with respect to the first surface portion 90 such that an angle between the plane through the cylinder axis of the first curved surface portion 90 and the longitudinal axis 96 of FIG second surface portion 92 and the parabolic axis 98 between 35 ° and 55 °, preferably 40 ° and 50 °, in the example at 42 °. As a result, the beam path is folded or bent in the direction of the retroreflector section 82. The curvature of the second surface portion 92 is selected so that the focal line of the parabolic mirror lies on or in the retroreflector section 82, so that an object point 12 in the object plane 20 is aligned or a line-shaped intermediate image on or in the retroreflector section 82 is shown. The curvature of the second surface portion 92 and the parabolic mirror is further selected so that the focal length is smaller than that of the first surface portion 90. As a result, the distance to the retroreflector 82 can be kept low. Furthermore, a smaller intermediate image is formed on this, which helps to reduce the aberrations caused by the optical system.

Between the regions of the base body 88 which form the first and second imaging sections 84 and 86, in this exemplary embodiment, an aperture 100 which extends orthogonally to the plane of the retroreflector section 82 or parallel to the second plane of incidence is formed Side is limited by the retroreflector section 82. On the opposite side, in the example, it is delimited by the end of a gap 102 in the base body 88, which extends orthogonal to the plane of the retroreflector section 82 between said regions of the base body 88 and at a small distance, in the example of about 0.1 mm, ends above the retroreflector section 82. The gap limiting surfaces of the body 88 are formed or designed, for example, by coating with a non-transparent material, that a diaphragm for the beam path of the optical system is formed. In other embodiments, the gap could also be replaced by another element which delimits the beam path, for example an opaque layer. The diaphragm 100 therefore runs with its longitudinal extent parallel to the second plane of incidence and in a mirror symmetry plane of the optical system.

On the one hand, this aperture 100 reduces scattered light, which can result from multiple reflection on unused surfaces of the base body 88 and on the optically active surfaces themselves. But since it ultimately also limits the intermediate image 22 on the retroreflector section 82, it also acts as visual field stop. Thus, the sensor 68 does not need to have any slit-shaped illumination of the value document 50 or a slit-shaped field diaphragm arranged directly above the value document in order to obtain a slit-shaped image necessary for the spectral decomposition by means of the dispersing device 78. The aperture 100 is in this context in particular aligned so that the image of its narrow side on the receiver 74 extends transversely to the spectral splitting.

In other exemplary embodiments, the imaging can take place solely through the first arched surface section, while the second surface section is flat and only serves to bend the beam path.

In still further embodiments, the optical axes or planes of the imaging section may be arranged parallel to each other inclined relative to each other instead of as in the previous examples, whereby the kink of the beam path of the sensor can be compensated by the dispersing device 78.

Another embodiment of a sensor differs from the embodiment in FIG. 4 in that another embodiment of an optical system replaces the optical system 72.

The optical system 104 differs from the optical system 72 in that it comprises two plane retroreflector sections 106 and 106 ', on each of which a line-shaped intermediate image of an object point 12 in the object plane 20 is generated. The retroreflector portions 106 and 106 'are formed the same and arranged parallel to each other so that their first and second incident planes are parallel to each other. The optical system 104 is again formed by a base 108 which includes both the retroreflector portions 106 and 106 'and first and second imaging portions 110 and 112.

The body 108 is symmetrical about a median plane 114 that is parallel to the planes of the retroreflector portions 106 and 106 'midway therebetween.

The areas of the body 108 on both sides of the median plane 114 are each shaped like the body 88, but the first domed surface portion 90 and its counterpart in the second imaging portion are replaced by common arched surface portions 116 and 118 which are also cylindrically shaped. however, their cylinder axes lie in the middle plane 114. As with the optical system 72, there are provided second reflective domed linear parabolic mirror forming surface portions 120 which form the incident plane 28 components of the parallel beam coming from the domed surface portion 116 from the object point 12 to the respective retroreflector portions 106 and 106 ', respectively focus on a linear intermediate image. Corresponding surfaces 120 parallelize the components of the beam emanating from the intermediate image parallel to the plane of incidence 32, which are then focused by the curved surface section 118 onto the pixel.

One half of a bundle of rays emanating from an object point in the plane of the object is therefore subtracted from the region of the main body 108 in FIG. 7 above the center plane 114, the other half of the bundle of rays from the lower region of the main body 108 in FIG. forms. This embodiment offers the advantage that the imaging characteristics are also more symmetrical in the direction orthogonal to the medial plane.

In other embodiments, the lighting can also be clocked.

In still other embodiments, the illumination device may also be designed for the emission of infrared radiation or of infrared radiation and visible light.

The base bodies 88 and 108 can be produced inexpensively by injection molding from a suitable plastic or by embossing suitable glass.

Another embodiment may differ from the embodiment in Fig. 5 in that the parabolic mirror 92 is mirrored by appropriate choice of the material by total reflection.

Claims

Patent claims

An optical system having a planar anisotropic retroreflector section that speculatively reflects radiation components in a first plane of incidence but retroreflects radiation components in a second plane of incidence, a first imaging section that is linear from an object point in an object plane in a predetermined relative position to the system Intermediate image on the retroreflector section generates, which extends along a line in the second plane of incidence, and a second imaging section, by means of which the linear intermediate image is imaged into a pixel

2. An optical system according to claim 1 adapted to effect a 1: 1 imaging.

3. An optical system according to claim 1, wherein the two imaging sections have the same imaging properties.

4. Optical system according to one of the preceding claims, wherein at least one of the imaging sections has a cylinder optics, preferably at least one cylindrical lens and / or a parabolic or cylindrical mirror.

5. Optical system according to one of the preceding claims, wherein in the beam path between at least one of the imaging sections and the retroreflector section, a reflective element is arranged.

6. Optical system according to one of the preceding claims, wherein at least one of the imaging sections kinks or folds the beam path.

7. An optical system according to any one of the preceding claims, wherein at least one of the imaging portions, preferably the two optical portions and the retroreflector portion, is integrally formed together or are.

8. Optical system according to one of the preceding claims, wherein in the second plane of incidence, a diaphragm, preferably a slit, is formed, the edge of which is partially formed by the retroreflector section.

9. An optical system according to one of the preceding claims, which is constructed mirror-symmetrically with respect to a plane parallel to the second plane of incidence.

10. An optical system according to any one of the preceding claims, comprising in parallel to the retroreflector portion a further planar anisotropic retroreflector portion, and wherein the first imaging portion is adapted to produce another intermediate linear image of the object point on the further retroreflector portion, and the second imaging section is adapted to image the further line-shaped intermediate image onto the pixel.

11. A sensor for detecting optical properties of a value document with an optical system according to one of the preceding claims.

12. A sensor according to claim comprising a dispersing means downstream of the optical system and a array of receiving elements for receiving various spectral components generated by the dispersing means.

13. A method for imaging an object point, in which the object point is imaged onto a linear intermediate image on an anisotropic retroreflector section so that the intermediate image extends with its longitudinal direction in an incidence plane in which Retroreflek- torabschnitt acts retroreflective, and in which the intermediate image on a pixel is displayed.