Device and system for inspecting at least one diffractive optical element of a document

Abstract

The invention relates to a device for inspecting at least one diffractive optical element DOE of a document, said device having: a document support means for supporting a document to be inspected; a radiation source for coherent electromagnetic radiation; a deflection unit, which is arranged on a first side of the document support means, for deflecting radiation emitted by the radiation source onto the document supported by the document support means; a screen, which is arranged on a side of the document support means opposite the first side, for displaying an image projected onto the screen by transmissive diffractive interaction of the deflected radiation with a DOE provided on or in the document; an image sensor for sensing the image projected on the screen and for providing image data representing the sensed image; and an evaluation means for evaluating the image data in respect of at least one inspection criterion. The deflection unit is configured to be movable in an adjustable manner relative to the document support means such that, during operation of the device, it deflects the radiation emitted by the radiation source onto a corresponding point on the document to be inspected, supported by the document support means, variably depending on the currently set position of the deflection unit.

Description

[0001] The present invention relates to a device for inspecting at least one diffractive optical element (DOE) of a document, in particular a security document, and to a document inspection system comprising such a device.

[0002] To increase the counterfeit protection of documents, especially so-called security documents such as passports, identity cards, and many other types of personalized chip cards, such as bank cards, credit cards, ID cards, membership cards, access cards, or banknotes and other valuables, it is known to equip such documents with one or more security features. These security features can be overtly visible or covert, meaning they are only visible or readable with special equipment, for example, under a UV lamp.In particular, optical security features can be used; these are security features that influence electromagnetic radiation, especially in the visible, infrared, or ultraviolet range of the electromagnetic spectrum, in a characteristic and detectable way suitable for distinguishing counterfeits. Examples of such optical security features are holograms or luminescent substances that exhibit characteristic optical reactions when exposed to suitable optical excitation.

[0003] Diffractive optical elements (DOEs) are optical elements used to shape, particularly beam shaping or beam splitting, an electromagnetic beam, often in the form of a laser beam, by means of optical diffraction at an optical grating. A well-known application of DOEs is the anti-counterfeiting of plastic banknotes. In this case, a so-called "hyalic" window is formed in such a banknote, which is visible as a transparent area on the plastic banknote. The hyalic windows used in a DOE have an optically milky film.This visible film is a microstructure that can only be deciphered with a laser, whose laser beam is projected through the microstructure onto a projection surface, on which a characteristic image generated by the diffracting interaction of the laser beam with the microstructure of the DOE then becomes visible and can be used for authenticity verification.

[0004] While the authentication of banknotes is often carried out as an individual check of a single banknote or a small quantity of banknotes, for example at a point of sale, the production of documents bearing one or more DOE usually involves producing a large quantity of such documents in a very short time and inspecting the quality of the DOE produced or applied or incorporated into the documents as part of quality assurance.

[0005] It may also be necessary in other cases to inspect a large number of such documents "in the field," particularly for authentication purposes. Furthermore, such mass inspection can be carried out for quality assurance purposes, for example, as part of a personalization process following the actual document production and possibly being carried out by another party, especially for identity documents, based on pre-printed document blanks with DOE (Detailed Electronic Signature).

[0006] Furthermore, the form factor of such documents to be inspected, as well as the position of one or more DOE on or in such documents to be inspected, can vary depending on the document type or even individually.

[0007] Document DE 100 05 835 A1 discloses a method for the rapid and automatic authentication of documents secured with optical features, where the positions of the features relative to the coordinate system of the document and / or a verification machine are unknown or only approximately known, wherein in a first step of the method the document in its entirety or in parts is illuminated with lighting means whose spectral and geometric distribution, degree of polarization and / or orientation, coherence and temporal activity are selected such that one or more images of the illuminated document surfaces, detectable by one or more imaging sensors, are produced in which the position of the security features differs relative to the rest of the document background and these positions are automatically determined by image recognition methods relative to the coordinate system of the document.

[0008] The present invention is based on the objective of providing devices or systems with which high efficiency, in particular high speed, can be achieved in the inspection of diffractive optical elements (DOE) of different documents.

[0009] The solution to this problem is achieved according to the teaching of the independent claims. Various embodiments and further developments of the invention are the subject of the dependent claims.

[0010] A first aspect of the invention relates to a device (hereinafter also referred to as a "DOE inspection device") according to claim 1 for inspecting at least one diffractive optical element, DOE, of a document, in particular a security document. The device comprises: (i) a document carrier for holding a document to be inspected that is provided with a DOE; (ii) a radiation source for coherent electromagnetic radiation, which may in particular be a laser light source (laser); (iii) a deflection unit, in particular a mirror, arranged on a first side of the document carrier for deflecting radiation emitted by the radiation source onto the document carried by the document carrier; (iv) a screen arranged on a side of the document carrier opposite the first side for displaying a signal transmitted by transmissive diffractive interaction (i.e.,(a) a document carrier device (DOE) that projects an image onto the screen using transmissive optical diffraction of the deflected radiation with a DOE provided on or in the document; (v) an image sensor for sensorially detecting the image projected onto the screen and for providing image data representing the detected image; and (vi) an evaluation device for evaluating the image data with regard to at least one inspection criterion. The deflection unit is configured to be movable relative to the document carrier device in such a way that, during operation of the device, it variably directs the radiation emitted by the radiation source, depending on the currently set position and / or orientation of the deflection unit, to a corresponding location, in particular to a transparent or opaque (especially milky) window area (e.g., a so-called "transmissive optical diffraction")."Clear Window"), in which the DOE is trained, deflects the view onto the document to be inspected, which is carried by the document carrier device.

[0011] The document carrier device includes a transport mechanism for moving the document to be inspected, in particular for the sequential transport of a large number of documents to be inspected, into the beam path of the deflected radiation. The use of a transport device allows for the automatic feeding and removal of documents to be inspected from an inspection area of ​​the device defined by the beam path.

[0012] A "document carrier device" within the meaning of the invention is in particular a device which is suitable and intended to carry a document to be inspected, to hold it in position relative to the beam path of the electromagnetic radiation, and thus to enable a transmissive fluoroscopy of a DOE of the document in the beam path.

[0013] A "projection screen" within the meaning of the invention is understood to be, in particular, a device or a part thereof that has a projection surface, which may be flat or curved, such that an image generated by a transmissive diffractive interaction of coherent radiation with the DOE can be projected onto the projection surface. "Transmissive" here means that the DOE is irradiated by the radiation, whereby, due to the diffractive interaction, the image projected onto the projection surface is formed "behind" the DOE in the direction of radiation.

[0014] An "inspection criterion" within the meaning of the invention is to be understood in particular as a predetermined test procedure according to which, when applied to the image projected onto the screen during operation of the DOE inspection device, it can be checked and determined whether the DOE generating the image (or the document provided therewith) is an original or a forgery in the sense of a counterfeit check, or whether it has a defect-free condition or at most defects within a predetermined tolerance range in the sense of a required minimum quality.

[0015] Any terms used herein, such as "comprises," "includes," "features," "has," "with," or any other variant thereof, are intended to cover non-exclusive inclusion. For example, a method or apparatus comprising or featuring a list of elements is not necessarily limited to those elements but may include other elements not expressly listed or inherent in such method or apparatus.

[0016] Furthermore, unless explicitly stated otherwise, "or" refers to an inclusive or and not an exclusive "or". For example, a condition A or B is satisfied by any of the following: A is true (or present) and B is false (or not present), A is false (or not present) and B is true (or present), and both A and B are true (or present).

[0017] The terms "ein" or "eine," as they may be used here, are defined as "one or more." The terms "ein anderer" and "ein Weitere," as well as any other variant thereof, are to be understood as "at least one more."

[0018] The term "plural", as it may be used here, is to be understood in the sense of "two or more".

[0019] The device's movable deflection unit allows for configuration of the specific location on a document being inspected, while maintaining the document's orientation, within the path of the electromagnetic radiation. This enables the device to be configured for inspecting a wide variety of documents, particularly those with differing DOE (Devices of Exclusion) positions, or documents that themselves contain multiple DOE at various locations. This configuration is even possible during a single inspection run, where such diverse documents or DOE are to be inspected sequentially in rapid succession.A sufficiently high configuration speed, which makes this possible, results in particular from the fact that only the position of the deflection unit needs to be adjusted accordingly for a given configuration, while the other components of the device, with the possible exception of a transport device for feeding and removing the documents to be inspected, can remain stationary. This also allows for a correspondingly low complexity of the device, since no moving or tilting devices or similar are required for the stationary components to enable the device to be configured for the aforementioned purpose.

[0020] Furthermore, apart from the deflection unit and the screen (and of course the DOE belonging to the document), the device does not require any other optical imaging elements in the beam path, so that on the one hand the complexity of the optical imaging can remain low and on the other hand loss of sharpness and other imaging errors can be kept low or even avoided.

[0021] Preferred embodiments of the device are described below, which, unless expressly excluded or technically impossible, can be combined with each other and with the other described aspects of the invention as desired.

[0022] In some embodiments, the deflection unit is configured to perform a translational, rotational, or combined translational-rotational movement relative to the document carrier and independently of the screen in one or more spatial dimensions. This allows the radiation emitted by the radiation source to be deflected onto the document carried by the document carrier in a spatially variable manner. In this way, only the deflection unit itself needs to be moved to perform a DOE inspection at different positions on the document being examined. Movement of other components, particularly the screen, radiation source, evaluation unit, or document carrier, is not strictly necessary, although it is optional.This allows the complexity of the device to be kept low, or, if desired, a high degree of configurability to be achieved. Furthermore, a high throughput of the device, i.e., a high inspection rate, is particularly attainable if the deflection unit is designed with low mass and is therefore subject to only low inertial forces even during highly accelerated movements, such as those that can occur at high throughput rates with different DOE positions.

[0023] In some embodiments, the device further comprises a signal-controlled drive unit, wherein the position of the deflection unit relative to the document carrier is automatically adjustable by means of the drive unit depending on a position signal representing the position of a document to be inspected, a window area (especially a clear window), or a DOE thereof. The position signal can, in particular, be supplied by a position detection device configured to sensorially detect the position of the document to be inspected or of its, or at least one, DOE and to generate the position signal accordingly. In this way, a correction of the deflection unit's position can be made for each document, depending on its position on the document carrier, to ensure the correct placement of a DOE of the document in the beam path of the deflected radiation.

[0024] In some embodiments, the projection screen is a partially transparent screen, particularly a ground glass screen, or incorporates such a screen. Furthermore, the image sensor is configured to detect the transmitted image projected onto the back of the screen when the image is projected onto the front surface. This allows for a simple arrangement of the image sensor, in which its optical axis can be perpendicular to the screen, thus preventing perspective distortions that would otherwise need to be compensated for or otherwise addressed during image processing.

[0025] In some alternative embodiments, the image screen is, or has one, a reflective image screen, and the image sensor is configured to detect the image created by reflection from the reflective image screen when the image is projected onto a front surface. This allows, in particular, the device to be designed with a small form factor, since no device components located beyond the image screen (i.e., "behind" it in the direction of the incident radiation) are required.

[0026] In some embodiments, the transport device includes a vacuum conveyor belt for moving the document to be inspected into the path of the deflected radiation. In particular, the conveyor belt solution also enables high throughput for the mass inspection of a large number of documents or DOEs.

[0027] In some embodiments, the device further includes a position detection unit for sensorially acquiring the instantaneous position of the document, a window area thereof, or its DOE itself, and for triggering the image sensor, the radiation source, or both depending on this detected position, in order to effect image sensor acquisition of the image projected onto the screen when the DOE(s) of the document is located in the path of the deflected radiation. This ensures that the image sensor acquires the projected image at the correct time and thus a reliable inspection result can be obtained even if the document or DOE is moving, particularly at high speed, or if it remains in the path of the deflected radiation for only a short period of time for inspection purposes before being moved out of the path.The position detection device can advantageously be the same as the one previously described in connection with generating a position signal. The device can be designed to be configurable for both slower throughput (e.g., 2,000 units (documents) per hour, UPH) and higher, particularly much higher, throughput (e.g., 30,000 UPH). It is also possible to achieve a much higher throughput. The triggering can affect the image sensor, the radiation source, or both. If it affects only the image sensor or only the radiation source, the other component, i.e., the radiation source or the image sensor, can be in continuous operation, so that no position-dependent triggering is required for it.

[0028] In embodiments with a position detection device, this device can be configured, in particular programmable, to allow adaptation to the type and position of a window area or a DOE or several DOEs on or in the document.

[0029] In some embodiments, the device further includes a speckle reduction unit for reducing speckles when imaging the coherent radiation from the radiation source onto the image screen. "Speckles" here, as is common in laser technology, refer to granular interference phenomena that can be observed when optically rough object surfaces (unevenness on the order of the wavelength) are illuminated with sufficient coherence. In these embodiments, the image quality, and consequently the accuracy and reliability of the DOE inspection, can be improved, since speckle-induced image disturbances, which could otherwise lead to image misinterpretations, can be reduced or even avoided.Speckler reduction devices are particularly suitable if they employ one or more of the following methods for speckler reduction, especially with regard to laser light: (i) illumination from different angles (angle diversity), (ii) use of different optical polarizations (polarization diversity); (ii) use of laser sources whose wavelengths differ only slightly (wavelength diversity). Speckler reduction devices can be integrated into the radiation source or arranged separately from it, particularly in the beam path of the radiation source.

[0030] In some embodiments, the evaluation unit is configured to identify, during the evaluation of the image data, at least one virtual object projected onto the screen, or to detect a dimension, line width, angle, or other characteristic in the image, and to compare each of these with at least one inspection criterion in order to determine an inspection result. The inspection criterion can therefore be defined, in particular, by an acceptable line width range, specific object criteria, especially dimensional or angular ranges for certain dimensions or angles, or other characteristics of a virtual object.This allows a variety of different inspection criteria to be defined and used as testing criteria, which on the one hand allows the use of a wide variety of DOE types and on the other hand increases the achievable security level of document protection using DOE, since not only can a wide variety of DOE types be used, but it also makes it more difficult for a potential attacker to find out which inspection criteria will be used during field inspections, which a forgery attempt would have to target.

[0031] In some embodiments, the projection screen comprises a laminate consisting of multiple stacked, diffracted-radiation resistant, and transparent laminating films, and a semi-transparent film that seals the stack on one side and is also diffracted-radiation resistant. This stacking concept allows for flexible configuration of the projection screen depending on the specific application and device design, particularly regarding the screen's thickness and optical imaging properties. Furthermore, it enables the use of readily available and easily manufactured raw materials, especially laminating films, when otherwise custom-made components would be required. The semi-transparent film plays a key role as at least the primary projection surface of the stack.

[0032] In some of these embodiments, the image screen is oriented such that the semi-transparent film, which closes off one side of the stack and is resistant to diffracted radiation, faces the image sensor. This ensures that the image captured by the image sensor is obtained with maximum clarity, since no further stack layers lie in the beam path between this film, on which the image is primarily formed, and the image sensor.

[0033] A second aspect of the invention relates to a method according to claim 13 for inspecting at least one diffractive optical element, DOE, of a document, wherein the method comprises: (i) Receiving a document (D) to be inspected, provided with a DOE, by a document carrier device for carrying the document; (ii) irradiating the document with coherent electromagnetic radiation from a coherent radiation source, in particular a laser, wherein the radiation is radiated onto a deflection unit arranged on a first side of the document carrier device, by which the radiation is deflected onto the document carried by the document carrier device and passes through the document as deflected radiation, and wherein an image is projected onto a screen arranged opposite the first side of the document carrier device, which results from transmissive diffractive interaction of the deflected radiation with a DOE provided on or in the document;(iii) image sensor-based acquisition of the image projected onto the screen and provision of image data representing the acquired image; and (iv) evaluation of the image data with regard to at least one inspection criterion; wherein (v) the position of the deflection unit, configured to be movable relative to the document carrier device, is adjusted such that it deflects the radiation emitted by the radiation source onto the DOE of the document to be inspected, which is carried by the document carrier device.

[0034] The method corresponds to the device according to the first aspect, so that what was said there, in particular also with regard to the different embodiments, also applies here accordingly and is therefore not listed again here in order to avoid repetition.

[0035] A third aspect concerns a document inspection system comprising multiple modules for the sequential inspection of at least one predetermined property of a document, wherein one of the modules includes a device according to one of the preceding aspects for inspecting at least one diffractive optical element (DOE) of the document. Thus, the document inspection system enables the combination of various document inspection methods within a single system, with the modular design allowing for a high degree of system configurability and individual maintenance or repair of the various modules. In addition to inspection modules, the document inspection system may also include one or more further modules, particularly for handling the documents, such as loading, turning, dispensing, and sorting them during processing by the system.The relative position of the various modules to one another, in particular the order in which the documents pass through the modules, can be configured. Depending on the type of documents to be inspected, the system may also include more or fewer modules, and in particular more or fewer different inspection modules, depending on the specific configuration.

[0036] According to some embodiments, the document inspection system is configured to inspect the document with respect to its front and back sides, the sequence of modules according to which the document passes through the various modules during its inspection being such that: (i) either first an inspection of the front side is carried out by appropriately assigned one or more of the modules, then the DOE inspection is carried out by means of the module with a device according to the first aspect of the invention, and then an inspection of the back side of the document is carried out by appropriately assigned one or more of the modules; or (ii) in reverse order, first the inspection of the back side of the document is carried out, then the DOE inspection, and finally the inspection of the front side of the document.

[0037] This represents an optimized solution insofar as the DOE inspection, which is based on scanning the DOE of a document and can therefore inherently affect both the front and back of the document, is performed at a point in the overall process flow where, conveniently, the document can be turned over before or after the DOE inspection from one of the two sides, in order to subsequently inspect the second side, which has not yet been inspected at that point in the process. If a DOE inspection is also to be performed in the opposite direction, so that the same or a different DOE of the document is now scanned in the opposite direction relative to the document than in the previous DOE inspection, this system design allows the two DOE inspections to be carried out immediately consecutively at the same point in the process flow, separated from each other only by turning the document over.Accordingly, a transport step between these two DOE inspections can be omitted.

[0038] According to some embodiments, the document inspection system further comprises: (i) a sensor device for detecting the position of a document to be inspected on a document carrier and for generating a position signal representing this detected position; and (ii) a device according to the first aspect, configured to receive the position signal and, depending on this, to control the drive unit of the device in order to automatically adjust the position of the deflection unit depending on the received position signal. In particular, this allows for a correction of the deflection unit's position for each document, depending on its position on the document carrier, to ensure correct placement of a DOE of the document in the beam path of the deflected radiation.The sensor device can be provided, in particular, by the aforementioned position detection device of the DOE inspection device itself, or it can be designed separately or provided instead. As a rule, it will suffice to provide such a sensor device or...

[0039] A position detection device should be provided in its entirety, although solutions with several such sensors are also possible.

[0040] According to some of these embodiments, the sensor device can be arranged, in particular, in a module of the document inspection system that is upstream of the device after the first aspect with respect to a sequential inspection process of the device that can be carried out by the document inspection system using several of the modules. In this way, the position of the document can be detected sensorially at an early stage within the sequential inspection process and also be used by other modules upstream of the DOE inspection device. Based on this, an adjustment or configuration of these modules as well as the DOE inspection device can be carried out depending on the position signal representing the position. This can be used to increase the efficiency and reliability of the system, especially because the position signal can be used for several modules, and thus individual position determinations for each module are or become obsolete.

[0041] Further advantages, features and applications of the present invention will become apparent from the following detailed description in conjunction with the figures.

[0042] This shows: Fig. 1 schematically a device for inspecting DOEs according to a first exemplary embodiment of the DOE inspection device with transmitted light screen; Fig. 2 schematically a device for inspecting DOEs according to a second exemplary embodiment of the DOE inspection device with a reflection screen; Fig. 3 schematically an exemplary drive device for moving the deflection unit of the DOE inspection device Fig. 1 oder 2 ; Fig. 4 an exemplary instance, during the inspection of a corresponding DOE using one of the devices from Fig. 1 oder Fig. 2 Image created on the respective screen, on the basis of which an evaluation for the purpose of inspection can be carried out; Fig. 5 a schematic representation of a stacked structure of a screen of the device according to an exemplary embodiment of the invention; and Fig. 6 A schematic representation of the structure of a multi-modular system for document inspection according to an exemplary embodiment of the invention.

[0043] The same reference numerals are used throughout the figures for the same or corresponding elements of the invention.

[0044] The in Fig. 1 The illustrated device 100 for inspecting DOEs according to a first exemplary embodiment has a document carrier device 110 in the form of a conveyor belt, which may in particular be designed as a vacuum conveyor belt. The document carrier device 110 serves to transport a document D to be inspected, in particular a security document, or sequentially a plurality of such documents, into an inspection area of ​​the device 100 and, after inspection, to transport it further from there, in particular to a potentially subsequent inspection module of a higher-level document inspection system, for example, a system according to Fig. 5 In device 100, the inspection area is defined by a spatial area in which the conveyor belt 110 is guided over deflection rollers in such a way that a support gap is created along the movement path of the document D at this point, which can be bridged by the document, so that the side of the document D facing the conveyor belt 110 is freely accessible in the area of ​​the gap and can thus be inspected through the gap.

[0045] The device 100 further comprises a radiation source 120 for coherent electromagnetic radiation L1. The radiation source 120 can, in particular, be a laser that emits coherent radiation L1 in the ultraviolet, visible, and / or infrared range of the electromagnetic spectrum and directs it onto a deflection unit 130 of the device 100. Preferably, the radiation source 120 itself, particularly in the case of a laser, comprises a speckle reduction device 120a, which is suitable and designed to reduce or even prevent any speckles that may occur in images produced by the radiation L1.

[0046] The deflection unit 130 can, in particular, be a mirror for deflecting the radiation L1. It is located in a cavity defined by the deflection of the conveyor belt 110 adjacent to the aforementioned gap, and it is configured to deflect the radiation L1 through the gap as deflected radiation L2 onto a document D that may bridge the gap. When the rejected radiation L2 strikes a diffractive optical element DOE of the document D, it is optically diffracted during the resulting transmission of the DOE and exits the DOE as diffracted radiation L3 towards the front face of a semi-transparent screen 140. The screen 140 serves as a projection surface for the diffracted radiation L3, so that a projected image B is formed there, the properties of which are defined, in particular, by the diffraction effect of the DOE.

[0047] Furthermore, the device 100 includes an image sensor 150, which can in particular be a camera, preferably a digital camera. The image sensor 150 is designed and configured to capture the image projected onto the semi-transparent screen 140 from the front by the radiation L3 from the front of the screen 140, from the rear side opposite the front side, and to generate corresponding image data characterizing the captured image. The device 100 also includes an evaluation unit 160, to which the image data is transmitted and where it can be evaluated for authenticity or counterfeiting testing or quality control of the illuminated DOE based on at least one defined inspection criterion, as will be described further below with reference to Fig. 4 will be explained.

[0048] The device 100 can also include a position detection device 170, which is configured to sensorially detect the instantaneous position of the document D, a window area (e.g., Clear Window) thereof, or its DOE itself. Depending on this detected position, it can also trigger or activate the image sensor 150, for example, directly or – as in Fig. 1 shown - indirectly via the evaluation unit 160, in order to effect an image sensor detection of the image B projected onto the screen 140, at the time when the respective DOE of the document D is in the beam path of the deflected radiation L2.

[0049] The in Fig. 2 The illustrated second embodiment 200 of a device for inspecting DOEs essentially corresponds to the device 100 from Fig. 1 However, with the exception that instead of the semi-transparent screen 140, a substantially reflective screen 190 is used, whereby the diffracted radiation L3 is reflected at the screen 190 and can be detected by the image sensor 150, which is suitably positioned to detect the reflected radiation. This design is particularly suitable when small form factors are required or desired, as no additional installation space beyond the position of the screen is needed.

[0050] Incidentally, according to one variant of this embodiment (not shown), it is also possible to direct the deflected radiation, without it first striking the document, onto the reflective screen 190, where it is reflected and then reflected onto the DOE in the document, so that the optical diffraction effect of the DOE occurs there. The resulting diffracted radiation can then be detected by image sensors and evaluated accordingly.

[0051] Fig. 3 Figure 1 schematically illustrates an exemplary drive unit 300 for moving the deflection unit 130. Both can, in particular, be components of the respective device made of Fig. 1 oder Fig. 2 The drive unit 300 has a rotary axis 310 to which the deflection unit 130, in particular a mirror, is attached. The rotary axis 310 is rotatably mounted in a frame 320 and can be rotated about its axis of symmetry by means of a rotary actuator 340, for example a stepper motor with or without a gearbox. Overall, this allows for orientation (angle). αThe deflection unit 130 can be variably adjusted by means of a rotary movement of the axis of rotation 310. The drive unit 300 further comprises a cross table 330 on which the frame 320 is mounted, so that the frame can be moved translationally along two, preferably horizontal, spatial dimensions X and Y by means of the cross table 330, which have corresponding drives 330a and 330b, respectively.

[0052] Furthermore, the drive unit 300 has a control unit 350 which is configured to control both the actuator 340 and the drives 330a and 330b of the cross table by means of corresponding control signals 360, 370 and 380 respectively, in order to control the position, i.e. the XY position and orientation (angle). α ) of the deflection unit 130. For the sake of simplicity, it is also possible to adjust up to two of these movement dimensions (X, Y, α) to forgo, which, however, may result in less configurability of the DOE inspection device with regard to the position of a window area or DOE on a document to be inspected.

[0053] To generate the control signals 360, 370, and 380, the control unit 350 is configured to evaluate a received position signal 180 (generated by the DOE inspection device itself) or 180a (generated outside the DOE inspection device) when adjusting the position of the deflection unit 130. This signal represents a sensor-detected position of a document D transported on the document carrier device 110, a window area thereof, or even a DOE within it that is to be inspected. Thus, the optimal adjustment of the position of the deflection unit 130 can be made depending on the detected position of the document, the window area, or, in particular, the DOE to be inspected on the document D. This also allows for the correction of any tolerances regarding the exact position of the document D, the window area, or, in particular, the DOE to be inspected.The position of the DOE, or of different arrangements of DOEs on documents D to be processed sequentially, or even of multiple window areas and / or DOEs per document D, can be taken into account. The position of the respective document, window area, or DOE represented by the position signal 180 or 180a can be specified, in particular, with respect to a reference point or coordinate system defined by the device 100 or 200, the drive unit 300, or, in the case of a window area or DOE, by the document D itself. If only the position of the document or window area is detected, the device can be configured to infer the position of the DOE from the position of the document based on a relative position of the DOE on or within the document known through corresponding information.

[0054] Fig. 4 Figure B illustrates an example of how a DOE can be generated on screen 140 using a corresponding DOE, and shows a perspective view of an object 410 in the form of a cube in line or framework representation. If the projected image B represents a defined virtual object, as shown here, then the inspection criterion can be defined, in particular with respect to one or more dimensions of the virtual object, for example, in the form of specific values ​​for these dimensions, including associated tolerance ranges. If, during an image evaluation of image B by the evaluation unit 160, the corresponding dimensions in image B are determined and fall within the tolerance ranges, then the DOE is classified as genuine or error-free; otherwise, it is classified as a forgery or defective.Instead of or in addition to dimensions, other inspection criteria can also be used, such as line widths, object types or shapes (for example, cubes or pyramids), or certain angles or other characteristics of the virtual object.

[0055] As part of the image analysis, in Fig. 4 Several rectangular image areas were defined and marked, each enclosing an edge or line of the cube's framework, so that the corresponding line width within these image areas could be determined and compared with the inspection criterion. Furthermore, an angle 430 was identified, corresponding to a tilt of the virtual cube relative to the vertical, so that this too could be compared with a corresponding inspection criterion during the evaluation. For example, the DOE that generates image B can be classified as genuine or error-free if a virtual object 410 in the form of a perspectively rendered cube is detected, the lines detected in the image areas 420 of which have a line width within a predetermined line width range, and the detected angle 430 also lies within a predetermined angle range.In summary, at least three inspection criteria can be used cumulatively in this example.

[0056] One in Fig. 5 The illustrated exemplary semi-transparent image screen 140 is constructed as a stack of several layers. This stack comprises, in particular, a plurality of at least largely transparent laminating films 505 to 545 (in the present example, these are nine laminating films, each 100 µm thick), which are resistant to material changes caused by the radiation from the radiation source 120. The stack is closed off on one side by an additional layer, which is a semi-transparent film 550, in particular a matte film. All layers of the stack are laminated to their respective adjacent layers, thus forming a laminate. The semi-transparent film 550 is preferably arranged such that it faces the image sensor 150. If, as in Fig. 1 As illustrated, when the diffracted radiation L3 hits the laminating film 505 of the screen 140 closest to the DOE, it first traverses the substack of transparent laminating films 505 to 545, until it hits the semi-transparent film 550 and there generates the image B as a representation (see, for example, Fig. 4 Since the foil 550 allows a portion of the incident radiation to pass through, this image B is also visible from the outside of the stack beyond the foil 550 and can therefore be detected by the image sensor 150.

[0057] This stacked structure makes it possible to configure the image screen 140 individually, particularly with regard to its thickness and optical properties, depending on the application. In particular, it is also possible for one or more of the films 505 to 550 to have an additional imaging function, especially a filtering function, for example to filter out interference radiation incident laterally that does not originate from the radiation source 120.

[0058] Optionally, on at least one layer within a stacked or laminated structure of the document D, in particular on one or both surfaces and / or one or more internal layers of the document D, further visible security elements, e.g., characters, text or images, may be present, congruent with or overlapping the DOE or a window area of ​​the document D containing the DOE, in particular in the form of a suitable imprint or laser engraving, which is sufficiently transparent to the deflected radiation so that the DOE remains "visible" to the radiation through these additional security features and the radiation is projected onto the screen as diffracted radiation L3 after its diffraction at the DOE.

[0059] Fig. 6 Figure 600 shows a schematic representation of the structure of an exemplary multi-modular document inspection system for inspecting documents D. The document inspection system comprises a plurality of modules 601 to 620 connected sequentially to carry out a sequential inspection process. These modules are designed to inspect a document D, or sequentially a large number of documents D to be processed consecutively, with regard to various aspects within the framework of an inspection process executable with the system. In particular, the document inspection system 600 is designed to inspect documents D, especially card-shaped documents, on both sides.

[0060] Accordingly, the document inspection system 600 has a first process line 630 for inspecting a respective front side of the documents D.The first process line 630 comprises one or more of the following modules, preferably in the following order: a document feeder module 601, a laser engraving inspection module 602, a document alignment and document front cleaning module 603, a document hinge inspection module (for book-like documents such as passports), a surface inspection module 605, a printed document front inspection module 606, a microtext inspection module 607, and a test module 608 for an electronic chip (especially RFID chips) that may be present in the document, a UV inspection module 608, and a hologram inspection module 609.

[0061] Following the first process line 630 is a module 610 for DOE inspection, which includes a DOE inspection device, in particular a device 100 according to Fig. 1 or a device 200 according to Fig. 2 , may exhibit. Since the DOE inspection involves an examination of the document, more precisely its DOE, this module is not necessarily assigned to a document-page-specific process line. In the Fig. 6 The depicted variant of system 600 is a module preceding module 610, for example, the immediately preceding module 609, equipped with a sensor device 609a (in particular, a position detection device) for detecting the position of a document D on the document carrier device 110 or of a window area or DOE of the document. A position signal 180a can be generated by means of this sensor device, which represents the position of the document D, the window area, or the DOE and is transmitted to the control unit 350 of the drive device 300 (see figure). Fig. 3 If only the position of the document or window area is detected, the device can be configured to infer the position of the DOE from the position of the document based on a relative position of the DOE on or in the document known through appropriate information.

[0062] Before a second process line 640 follows for the inspection of the document backs, a module 611 for turning the documents over is provided in the module sequence, so that the inspection of the document backs can be carried out from the same side of the system 600, for example from above.

[0063] The process line 640 comprises one or more of the following modules, preferably in the following order: a module 612 for document alignment and cleaning of the document reverse, a module 613 for surface inspection of the document reverse, a module 614 for inspection of printing on the document reverse, a module 615 for UV inspection of the document reverse, a module 616 for hologram inspection of the document reverse, a module 617 for inspection of microtext on the document reverse, a module 618 for marking reject documents, a module 619 for key rotation, i.e., for exchanging or changing a key or code for access restriction on an electronic chip that may be present in the document, and finally an output module 620, optionally with a sorting function for the inspected documents, in particular for sorting into, on the one hand, error-free or genuine documents and, on the other hand, defective or...forged documents.

[0064] While at least one exemplary embodiment has been described above, it should be noted that a large number of variations exist. It should also be noted that the described exemplary embodiments are merely non-limiting examples, and it is not intended to restrict the scope, applicability, or configuration of the devices and methods described herein. Rather, the preceding description will provide the person skilled in the art with guidance for implementing at least one exemplary embodiment. It is understood that various modifications to the function and arrangement of the elements described in an exemplary embodiment can be made without deviating from the subject matter defined in the appended claims. REFERENCE MARK LIST

[0065] 100 Device for DOE inspection, first embodiment 110 Document carrier device, in particular transport device 120 Radiation source for coherent electromagnetic radiation, in particular laser 120a Specular reduction device, here integrated in radiation source 130 Deflection unit, in particular mirror 140 Screen, in particular semi-transparent screen 150 Image sensor, in particular camera 160 Evaluation device 170 Position detection device 180 Position signal 190 Screen, in particular reflective screen 200 Device for DOE inspection, second embodiment 300 Drive device for deflection unit 310 Rotary axis 320 Frame, bearing for rotary axis 330 Cross table 330a First drive (X-direction) of the cross table 330b Second drive (Y-direction) of the cross table 340 Actuator orDrive for mirror rotation 350 Control unit 360 Control signal for first drive of the cross table 370 Control signal for second drive of the cross table 380 Control signal for actuator 340 400 Image on screen 410 Virtual object in the image 400 420 Lines of the object 430 Angle of position of the object 500 Image sensor arrangement relative to a screen constructed as a laminate 505-545 Transparent laminating films 550 Semi-transparent film, in particular matte film 600 Document inspection system for document inspection 601 Document feeder module 602 Module for laser engraving inspection 603 Module for document alignment and cleaning of the document front 604 Module for inspection of a document hinge, in particular a transparent one 605 Module for surface inspection of the document front 606 Module for inspection of printing on the document front 607 Module for inspection of Microtext regarding608 Module for UV inspection of the document front and for chip testing 609 Module for hologram inspection of the document front 609a Sensor device (in particular position detection device) 610 Module or device for DOE inspection 611 Module for turning the document 612 Module for document alignment and cleaning of the document back 613 Module for surface inspection of the document back 614 Module for inspection of printing on the document back 615 Module for UV inspection of the document back 616 Module for hologram inspection of the document back 617 Module for inspection of microtext on the document back 618 Module for marking reject documents 619 Module for key rotation 620 Output module with sorting function 630 Process line for document front inspection 640 Process line for document back inspection . Image projected onto the screen; Document, in particular a security document; Diffractive optical element; L1 incident radiation; L2 deflected radiation; L3 diffracted radiation

Claims

1. A device (100; 200) for inspecting at least one diffractive optical element, DOE, of a document (D), wherein the device (100; 200) has: a document carrier means (110) for carrying a document (D) to be inspected provided with a DOE; a radiation source (120) for coherent electromagnetic radiation; a deflection unit (130) arranged on a first side of the document carrier means (110) for deflecting radiation (L1) emitted by the radiation source (120) onto the document (D) carried by the document carrier means (110); a projection screen (140; 190) arranged on a side of the document carrier means (110) opposite the first side for representing an image (B) projected onto the projection screen (140; 190) by transmissive diffractive interaction of the deflected radiation (L2) with a DOE provided on or in the document (D); an image sensor (150) for sensory detection of the image (B) projected onto the projection screen (140; 190) and for providing image data representing the detected image (B); and an evaluation means (160) for evaluating the image data with regard to at least one inspection criterion; wherein the deflection unit (130) is configured to be movable relative to the document carrier means (110) in an adjustable manner in such a way that during operation of the device (100; 200) it variably deflects the radiation (L1) emitted by the radiation source (120) as a function of the currently adjusted location of the deflection unit (130) to a corresponding point on the document (D) to be inspected carried by the document carrier means (110), wherein the document carrier means (110) has a transport means for transporting the document (D) to be inspected into the beam path of the deflected radiation (L2).

2. The device (100; 200) according to claim 1, wherein the deflection unit (130) is configured to execute a translational movement, a rotational movement or a combined translational and rotational movement in one or more spatial dimensions (X, Y; α) relative to the document carrier means (110) and independently of the projection screen (140; 190) in order to deflect the radiation (L1) emitted by the radiation source (120) in a locally variable manner to the document (D) carried by the document carrier means (110).

3. The device (100; 200) according to any one of the preceding claims, further having a signal-controlled drive means, wherein the location of the deflection unit (130) relative to the document carrier means (110) can be adjusted automatically by means of the drive means (300) as a function of a location signal (180) which represents a location of a document (D) to be inspected or of a window area or DOE thereof.

4. The device (100; 200) according to any one of the preceding claims, wherein the projection screen is or has a transmitted light projection screen (140) which is partially transparent to the radiation and the image sensor (150) is configured such that when the image (B) is projected onto a front side of the transmitted light projection screen (140; 190), it can sensorily detect the transmitted light image (B) created on the back side thereof.

5. The device (100; 200) according to any one of claims 1 to 3, wherein the projection screen is or has a reflection projection screen (190) and the image sensor (150) is configured to be able to sensorily detect the image (B) created during the projection of the image (B) onto a front side of the reflection projection screen (190) by means of reflection on the reflection projection screen (190).

6. The device (100; 200) according to any one of the preceding claims, wherein the transport means (110) has a vacuum transport belt for transporting the document (D) to be inspected into the beam path of the deflected radiation (L2).

7. The device (100; 200) according to any one of the preceding claims, further having a position detection means (170) for sensory detection of a current position of the document (D), a window area thereof or its DOE itself and for triggering the image sensor (150), the radiation source or both as a function of this detected position in order to cause an image sensory detection of the image (B) projected onto the projection screen (140; 190) when the or a respective DOE of the document (D) is in the beam path of the deflected radiation (L2).

8. The device (100; 200) according to claim 7, wherein the position detection means (170) is designed to be configurable in order to enable an adaptation to the type and location of a window area or a DOE or several DOEs on or in the document (D).

9. The device (100; 200) according to any one of the preceding claims, further having a speckle reduction means (120a) for reducing speckles when imaging the coherent radiation from the radiation source (120) onto the projection screen (140; 190).

10. The device (100; 200) according to any one of the preceding claims, wherein the evaluation means (160) is configured, within the scope of the evaluation based on the image data, to identify at least one virtual object (410) imaged on the projection screen (140; 190) or to detect a dimension, a line width (410) or an angle (430) in the image (B) and to compare each one with the at least one inspection criterion in order to determine an inspection result as a function thereof.

11. The device (100; 200) according to any one of the preceding claims, wherein the projection screen (140) has a laminate of a plurality of stacked transparent laminating films (505 to 545) that are resistant to the diffracted radiation (L3) and a semi-transparent film (550) that closes off the stack on one side and is resistant to the diffracted radiation.

12. The device (100; 200) according to claim 11, wherein the projection screen (140; 190) is oriented in such a way that the semi-transparent film (550) which closes off the stack on one side and is resistant to the diffracted radiation (L3) faces the image sensor (150).

13. A method for inspecting at least one diffractive optical element, DOE, of a document (D), wherein the method has: receiving a document (D) to be inspected provided with a DOE by a document carrier means (110) for carrying the document; irradiating the document (D) with coherent electromagnetic radiation (L1) from a radiation source (120) for coherent radiation, wherein the radiation is radiated onto a deflection unit (130) arranged on a first side of the document carrier means (110), through which the radiation (L1 ) is deflected onto the document (D) carried by the document carrier means (110) and scans the document as deflected radiation (L2), and wherein an image (B) projected onto a projection screen (140; 190) arranged on a side of the document carrier means (110) opposite the first side is represented that results from transmissive diffractive interaction of the deflected radiation (L2) with a DOE provided on or in the document (D); image sensory detection of the image (B) projected onto the projection screen (140; 190) and providing image data representing the detected image (B); and evaluating the image data with regard to at least one inspection criterion; wherein the location of the deflection unit (130) configured to be movable relative to the document carrier means (110) is adjusted in such a way that it deflects the radiation (L1) emitted by the radiation source (120) to the DOE of the document (D) to be inspected carried by the document carrier means (110), wherein the document (D) to be inspected is transported into the beam path of the deflected radiation (L2) by means of a transport device of the document carrier device (110).

14. A document inspection system (600), having a plurality of modules (601 to 620) for the sequential inspection of at least one respective predetermined property of a document (D), wherein one of the modules (610) has a device (100; 200) according to any one of claims 1 to 12 for inspecting at least one diffractive optical element, DOE, of the document (D).

15. The document inspection system (600) according to claim 14, wherein the document inspection system (600) is set up to inspect the document (D) with respect to its front side and its back side, wherein the order of the modules (601 to 620) according to which the document (D) passes through the various modules during its inspection is determined in such a way that: either the front side is first inspected by correspondingly assigned one or more of the modules (601 to 609), then the DOE inspection is carried out by means of the module (610) with a device (100; 200) according to any one of claims 1 to 12, and then the back side of the document (D) is inspected by correspondingly assigned one or more of the modules (612 to 620); or in reverse order, first the inspection of the back side of the document (D), then the DOE inspection and finally the inspection of the front side of the document (D) is performed.

16. The document inspection system (600) according to claim 14 or 15, having: a sensor means (609a) for detecting a location of a document (D) to be inspected on a document carrier means (110) or a window area or a DOE of the document (D) and for generating a location signal (180a) representing this detected location; and a device (100; 200) according to claim 3, which is configured to receive the location signal (180a) and to control the drive means (300) as a function thereof in order to automatically adjust the location of the deflection unit (130) as a function of the received location signal (180a).

17. The document inspection system (600) according to claim 16, wherein the sensor means (609a) is arranged in a module (609) of the document inspection system (600) which is upstream with respect to a sequential inspection process of the device (100; 200) according to claim 3 which can be executed by the document inspection system (600) using several of the modules.

Images