Patent Publication Number: US-8115910-B2

Title: Apparatus and method for the optical examination of value documents

Description:
FIELD OF THE INVENTION 
     The present invention relates to an apparatus and method for optical analysis of value documents. 
     BACKGROUND 
     Value documents are understood here to be card- or in particular sheet-shaped objects that represent for example a monetary value or an authorization and/or are not to be producible at will by unauthorized persons. They therefore have features that are not easy to produce, in particular to copy, whose presence is an indication of authenticity, i.e. production by an authorized body. Important examples of such value documents are chip cards, coupons, vouchers, checks and in particular bank notes. 
     Value documents are often analyzed optically for recognition of their type and/or their state and/or for a check of authenticity. It is fundamentally possible to use ambient light for the analysis, but such analyses show excessive errors due to fluctuations in the properties of the ambient light. 
     Analysis is therefore done using apparatuses that possess an illumination device for illuminating with optical radiation of given properties at least a part of a value document portion determined by a recording area of the apparatus, and a detection device for detecting optical radiation coming from the recording area, in particular a value document illuminated by the illumination device. 
     Although it is possible to use light sources such as halogen lamps for illumination, they consume a lot of power compared with the radiated power emitted in a desired spectral range and therefore require adequate cooling. They further have the disadvantage of not having a very long life. Furthermore, such light sources have considerable space requirements. 
     SUMMARY 
     The present invention is therefore based on the problem of providing an apparatus for optical analysis of value documents that permits good illumination of a value document to be analyzed while having a compact structure, as well as of specifying a corresponding method. 
     This problem is solved by an apparatus for optical analysis of at least one value document in a recording area of the apparatus, having an illumination device for illuminating the value document in at least a part of the recording area and possessing at least one surface emitting laser diode, and a control device for driving the laser diode, and a detection device for recording optical radiation from at least a part of the recording area. 
     The problem is further solved by a method for optical analysis of a value document in a recording area wherein the value document is illuminated with at least one surface emitting laser diode. 
     In the method it is possible to preferably record optical radiation from at least a part of the recording area that occurs through the illumination of the value document. This can be in particular luminescence radiation excited in the value document, optical radiation reflected by the value document or transmitted therethrough. 
     The detection device can accordingly be disposed relative to the illumination device and the recording area in particular in such a way that its radiation entry is located on the same side of the value document where it is illuminated, or on the opposite side. This means that the detection device can be so disposed that analysis is possible with incident or transmitted light or in reflection or transmission. 
     The analysis can fundamentally be done when the value document is at rest relative to the analysis apparatus and in particular to the illumination device. However, in particular upon use in a value document processing apparatus in which value documents are analyzed automatically in succession, the value document can also be moving during illumination. The subject matter of the invention is therefore also an apparatus for processing value documents, hereinafter also referred to as a value document processing apparatus, having an inventive analysis apparatus and a transport device for moving a value document through the recording area at a given transport speed. The transport speed can be given in particular in dependence on properties of the analysis apparatus or of the transport device. Upon sequential detection it is thus possible to obtain an image of the value document portion moving through the recording area. 
     The invention departs completely from the conventional manners of illumination. Although it is possible to use conventional edge emitting laser diodes instead of halogen lamps for illumination, they radiate optical radiation with a very inhomogeneous and not simply symmetric intensity distribution. This can impair the analysis of the value document. 
     According to the invention, a surface emitting laser diode is used for illumination. A surface emitting laser diode is understood in the context of the present invention more precisely to be a vertical surface emitting laser diode or in particular a semiconductor device also referred to in English as a “vertical cavity surface emitting laser” (VCSEL), whose laser resonator is aligned with its output direction, in which radiation is to be coupled out of the laser resonator, at least approximately perpendicular to the surface of the device or chip. In particular, the laser resonator of such surface emitting laser diodes can have reflection devices, for example reflecting layers or reflecting layer systems, extending at least approximately parallel to the surface. 
     Surprisingly, the use of such surface emitting laser diodes offers not one but several advantages for use in an apparatus for analyzing value documents, also referred to hereinafter as an analysis apparatus. 
     Further, they can be produced with large exit windows compared with edge emitting laser diodes, so that the radiated beam is not, or hardly, influenced by diffraction on the edges. 
     Furthermore, surface emitting laser diodes have a beam profile that is rotationally symmetric in good approximation, which substantially facilitates a beam shaping with simple optical elements compared to edge emitting laser diodes. 
     Further, in surface emitting laser diodes the emission wavelength range is determined more strongly by the laser resonator than in edge emitting laser diodes. This allows narrower emission wavelength ranges and leads to higher thermal stability of the emission wavelength range. 
     The full width at half maximum (FWHM) of the emission spectrum is preferably less than 1 nm. 
     Also, the spatial coherence of the emitted radiation is lower than in edge emitting laser diodes, so that speckle patterns can be largely or completely avoided on a value document illuminated with the laser diode. 
     Due to the favorable beam shape of the surface emitting laser diodes, they can be advantageously combined with each other for illumination purposes, so that besides the laser diode at least one further surface emitting laser diode is used for illumination in the method. It is therefore preferred in the analysis apparatus that the illumination device possesses at least one further surface emitting laser diode for producing a given illumination pattern in the recording area, and the control device is configured to drive the further laser diode. 
     In this case it is particularly preferable that the laser diodes are configured in a component or chip. Such a configuration is readily possible only with surface emitting laser diodes and has the advantage that it is easy to produce a large array of laser diodes. A further advantage is that only one component needs to be handled as the radiation source upon assembly of the analysis apparatus, which substantially simplifies production. 
     Particularly preferably, more than 50 laser diodes are disposed on a component. 
     The drive of the laser diodes by means of the control device can be effected in different ways. In the simplest variant, all laser diodes of the illumination device are driven jointly, so that the illumination pattern obtained in the recording area is determined substantially by the number and arrangement of the laser diodes. 
     According to another embodiment, the illumination device has at least two groups of surface emitting laser diodes which comprise the above-mentioned surface emitting laser diodes, and the laser diodes of one group are drivable independently of those of the other group. The control device is configured to drive one group of laser diodes separately from the drive of the other groups of laser diodes. In the method the value document can then be illuminated with at least two groups of surface emitting laser diodes which contain the laser diode, the laser diodes of one group being driven separately from those of the other group. Thus, drive of the groups permits in particular a temporal and spatial variation of the illumination pattern, which offers the advantage of greater variability of the illumination. A separate or independent drive or drivability is understood here to mean that the laser diodes permit such a drive. Further, the control device must be able to drive the groups independently of each other, whereby the drive of the two groups of laser diodes can of course be coupled, for example through a programming of the control device. 
     According to a further embodiment, in the analysis apparatus the laser diodes are drivable singly and the control device is configured to drive the laser diodes singly. If further surface emitting laser diodes are used for illuminating the value document in the method, the laser diodes can then be driven singly. In particular, the drive can be effected independently or separately in the above-mentioned sense. The possibility of singly driving laser diodes on a chip is a further advantage of surface emitting laser diodes. 
     The arrangement of the laser diodes and their drive permit the illumination pattern to be largely determined in its form when only a simple illumination optic is used i.e. in particular an illumination optic with optical components, such as lenses, that are rotationally symmetric at least approximately around an optical axis, optionally folded by deflecting elements, in the area of the beam path. The use of only such an illumination optic simplifies and cheapens the production of the illumination device. 
     An illumination device having a plurality of surface emitting laser diodes preferably configured in a chip or component can be used advantageously for producing an areal illumination pattern due to the form of the beam profile of the laser diodes. For this purpose, the analysis apparatus is preferably configured to illuminate a given area with an illumination pattern whose location-dependent intensity variation over the area illuminated by the laser diodes is smaller than 20% of the maximum intensity of the illumination pattern. In the method the laser diodes can be driven in such a way that the laser diodes illuminate a given area of the value document with an illumination pattern whose location-dependent intensity variation over the area is smaller than 20% of the maximum intensity of the illumination pattern. Such an illumination is particularly homogeneous and thus facilitates a reliable detection of features. The given area preferably has an extent greater than 0.5 mm 2 . 
     This homogeneity can fundamentally be obtained by using suitable optical components or homogenization devices in the analysis apparatus. However, the surface emitting laser diodes are preferably disposed relative to each other for illuminating a given area with an illumination pattern so that the illumination pattern produced therewith has a location-dependent intensity variation over the area smaller than 20% of the maximum intensity of the illumination pattern. This makes it possible to avoid the use of special optical components and in particular that of homogenization devices, such as diffusing disks, diffractive optical elements or light guides, which reduce the intensity of the emitted optical radiation. The analysis apparatus therefore particularly preferably has no homogenization elements, such as diffusing disks, light guides or microlens arrays, for homogenization. 
     The center distance between next adjacent surface emitting laser diodes of the illumination device is for this purpose preferably smaller than 150 μm. 
     According to a first variant, the laser diodes can be disposed in the form of a matrix in the analysis apparatus. They can be disposed in particular on the grid points of a rectangular or square grid. This permits a particularly simple production of a laser diode array on a chip, in particular since in the case of a single drivability of the laser diodes the corresponding signal connections can be simply designed. Furthermore, a particularly simple drive can be effected with this arrangement. 
     In a second variant of the analysis apparatus, the laser diodes are disposed on the points of a hexagonal point grid. This arrangement has the advantage that a particularly dense arrangement of the laser diodes is obtained in a simple manner, thereby permitting a particularly homogeneous illumination pattern. 
     As stated above, the illumination pattern can be determined in the recording area or on the value document at least in its form substantially by the arrangement of the radiating laser diodes. In the analysis apparatus the control device is therefore preferably configured to drive only some of the laser diodes in each case to emit optical radiation to produce a given illumination pattern. Accordingly, in the method the laser diodes are preferably driven to emit optical radiation so that a given illumination pattern is produced. This embodiment has the advantage that, depending on the configuration, a change of the illumination pattern requires only a change of the control device. If the latter is programmable, as is preferred, it is even only necessary to change the program. 
     Higher flexibility is obtained when, in a preferred embodiment of the analysis apparatus, the control device is configured to drive the laser diodes in dependence on a signal or data stored in the control device in such a way that the same illumination pattern is producible at different given locations in the recording area in dependence on the signal or data. In the method the laser diodes can then be driven in such a way in dependence on a signal or data that the same illumination pattern is producible at one of at least two different locations in dependence on the signal or data. The signal can be for example read in from an external data entry terminal via an interface or transmitted by a device of the value document processing apparatus containing the analysis apparatus. The drive of the laser diodes can consist in particular in only some of the laser diodes being switched on or off. 
     Thus, in a preferred embodiment of the analysis apparatus, the control device can in particular drive the surface emitting laser diodes in such a way that an extension of a detection area of the detection device in the transport direction is smaller than the extension of the illumination pattern in the transport direction, and the illumination pattern extends further with respect to the detection area regarded in the trans-port direction than contrary to the transport direction. The detection area is understood here to be that portion of the recording area from which the detection device can receive optical radiation for detection, in particular except for scattered radiation alone. A signal or data on the transport direction can be made available to the control device in the above-mentioned ways, which effects the drive of the laser diodes in dependence on the signal or data. This permits two things to be obtained at the same time. Firstly, the greater extension of the illumination pattern in the transport direction permits a greater amount of optical radiation, i.e. more energy, to be radiated onto a given area of the value document, for example a track with feature substances, upon an analysis, in particular a luminescence analysis, so that the strength of the detection radiation can be increased. Secondly, the adjustment of the analysis apparatus, more precisely, of the position of the illumination pattern relative to the detection area, can be adjusted automatically in dependence on the transport device upon installation in the value document processing apparatus by corresponding signals being transmitted to the control device for example from a drive system of the transport device or another device of the value document processing apparatus or being entered manually via an interface. The analysis apparatus can therefore be designed and used as a simply configurable module. 
     In the embodiment just described, the drive can in particular be switchable between two or more illumination pattern positions. 
     Alternatively or in combination, in the analysis apparatus the control device can be configured to drive the laser diodes in such a way that an illumination pattern changing in time during illumination is produced in the recording area. In the method it is then preferred that the laser diodes are driven in such a way that an illumination pattern changing in time during illumination is produced. The temporal change can be in particular given, for example by a corresponding configuration and/or programming of the control device. 
     The illumination pattern can be changed here in any desired way; in particular the form of the illumination pattern can be changed. However, it is preferred for many applications that the laser diodes are driven in such a way that a given illumination pattern is moved in a given direction at a given speed. In the analysis apparatus the control device is then configured to drive the laser diodes in such a way that a given illumination pattern is moved in a given direction at a given speed. The motion needs only to be effected for a given period of time, for example until the recording area has been swept once by the illumination pattern. Further, it is assumed that the laser diodes are disposed suitably for producing the illumination pattern. This embodiment has a number of advantages since it is usable for different purposes. 
     This embodiment makes it possible in particular to record a one- or two-dimensional image sequentially. In particular, in this case in the analysis apparatus the detection device only needs to be configured to detect optical radiation from the recording area integrally or only one-dimensionally in a direction perpendicular to the moving direction of the illumination pattern. Integral detection is understood here to be a detection that is non-locally resolving at a given moment. Consecutive illumination of different locations during motion of the illumination pattern and corresponding sequential detection thus make it possible to produce an image by assembling the data or signals recorded at each single detection into the image. 
     To permit a complete illumination that is as simple as possible to produce, the analysis apparatus can be configured in particular to produce a rectangular, in particular linear, illumination pattern. 
     The analysis apparatus can be used in particular for recording one- or two-dimensional bar codes through motion of the illumination pattern. 
     The value document can fundamentally be at rest during recording. However, for faster analysis of a large number of value documents with only one analysis apparatus, it is preferred in the method that the value document is moved in a given transport direction and at a given transport speed during illumination. 
     The motion speed of the illumination pattern can fundamentally be different from the transport speed. 
     However, in the method the value document is preferably moved in a trans-port direction at a transport speed, the direction being the transport direction and the speed being the transport speed. In a particularly preferred embodiment of the processing apparatus for processing value documents, the transport device is then configured to move a value document through the recording area at a given transport speed, and the control device is configured to drive the laser diode in such a way that the illumination pattern is moved in the transport direction at the transport speed. This embodiment makes it possible in a particularly advantageous manner for an area of the analyzed value document, in particular an optical security feature, to be followed during detection, so that analysis is possible even at very high transport speeds. 
     In general, but in particular also in connection with the last described embodiment, it is possible in the analysis apparatus that the control device is configured to produce an illumination pattern in a given part of the recording area in dependence on position signals from a position detection device. In the method it is accordingly preferred that the laser diodes are driven in such a way that an illumination pattern is produced in a given part of the recording area in dependence on position signals from a position detection device. This embodiment has the advantage that a device for determining the position of a value document or the position of a feature to be analyzed optically can be used to produce the position signal representing the position, in particular relative to the analysis apparatus, and that precisely this feature can be illuminated and analyzed in dependence on said position signal. This permits the amount of data arising upon an analysis of the total value document to be strongly reduced, so that an analysis can be effected faster and an evaluation device for evaluating the detection results can be constructed more simply. In particular in the case that the detection device is configured for locally resolved recording of optical radiation in at least one given spectral range, a considerable data reduction and an increase in data processing speed can be obtained when following the feature. 
     Alternatively to, or in combination with, the previously described embodiments, in the analysis apparatus the detection device can be configured for locally resolved recording of optical radiation in at least one given spectral range, and the control device configured to drive the laser diodes in such a way that a variation of a sensitivity of the detection device to the optical radiation in the spectral range is at least partly compensated in dependence on the location. In the method it is accordingly preferred that the laser diodes are driven in such a way that a variation of a sensitivity of a detection device for locally resolved recording of optical radiation in at least one given spectral range is at least partly compensated in dependence on the location. In this way a local adaptation of the illuminance to the sensitivity of the detection device can be effected, even after a relatively long time, thereby permitting an exact optical analysis lastingly. 
     Within the scope of the invention the laser diodes can be operated as continuously luminous or pulsed radiation sources, for which the control device is then configured accordingly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will hereinafter be explained more closely by way of example with reference to the drawings. These show: 
         FIG. 1  a schematic representation of a value document processing apparatus according to a first preferred embodiment; 
         FIG. 2  a schematic representation of an analysis apparatus of the value document processing apparatus in  FIG. 1 , 
         FIG. 3  a schematic plan view of an edge emitting laser diode, 
         FIG. 4  a schematic representation of a beam profile of the edge emitting laser diode in  FIG. 3  in the form of a contour diagram, 
         FIG. 5  a schematic lateral sectional view of a surface emitting laser diode, 
         FIG. 6  a schematic representation of a beam profile of the surface emitting laser diode in  FIG. 5  in the form of a contour diagram, 
         FIG. 7  a schematic plan view of a chip of the analysis apparatus in  FIG. 2  with a matrix arrangement of surface emitting laser diodes, 
         FIG. 8  a lateral view and a plan view for two possible illuminations by drives of the laser diodes in  FIG. 7 , 
         FIG. 9  a schematic representation of a value document processing apparatus according to a second preferred embodiment 
         FIG. 10  a schematic representation of a temporal evolution of an illumination of a value document transported in the value document processing apparatus in  FIG. 9 , wherein the illumination pattern is guided after the value document, in a lateral view and a plan view, 
         FIG. 11  a schematic representation of a temporal evolution of an illumination of a value document at rest wherein the illumination pattern is guided over the value document, in a lateral view and a plan view, 
         FIG. 12  a schematic representation of a part of a detection device of an analysis apparatus according to a further embodiment of the invention, and 
         FIG. 13  a schematic plan view of a chip of the analysis apparatus in  FIG. 2  with an arrangement of surface emitting laser diodes on grid points of a hexagonal point grid. 
     
    
    
     DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS 
     A value document processing apparatus  10  in  FIG. 1  which comprises an apparatus for optical analysis of value documents  12 , in the example bank notes, has an input pocket  14  for the input of value documents  12  to be processed, a singler  16  which can access value documents  12  in the input pocket  14 , a transport device  18  with a gate  20 , and, along a transport path  22  given by the transport device  18 , an apparatus  24  for analyzing value documents which is disposed before the gate  20 , and after the gate  20  a first output pocket  26  for value documents recognized as authentic and a second output pocket  28  for value documents recognized as non-authentic. A central control and evaluation device  30  is connected at least to the analysis apparatus  24  and the gate  20  via signal connections and is used for driving the analysis apparatus  24 , evaluating check signals from the analysis apparatus  24  and for driving at least the gate  20  in dependence on the result of evaluation of the check signals. 
     The analysis apparatus  24  in connection with the control and evaluation device  30  is used for recording optical properties of the value documents  12  and forming check signals representing said properties. 
     While a value document  12  is transported past at a given transport speed in a transport direction T given by the transport path  22 , the analysis apparatus  24  records optical property values of the value document, whereby the corresponding check signals are formed. 
     From the check signals of the analysis apparatus  24  the central control and evaluation device  30  determines upon a check signal evaluation whether the value document is recognized as authentic or not according to a given authenticity criterion for the check signals. 
     The central control and evaluation device  30  has for this purpose in particular, besides corresponding interfaces for the sensors, a processor  32  and a memory  34  connected to the processor  32  and storing at least one computer program with program code upon the execution of which the processor  32  controls the apparatus or evaluates the check signals and drives the transport device  18  in accordance with the evaluation. 
     In particular, the central control and evaluation device  30 , more precisely the processor  32  therein, can check an authenticity criterion which includes for example reference data for a value document to be considered authentic which are given and stored in the memory  34 . In dependence on the determined authenticity or non-authenticity, the central control and evaluation device  30 , in particular the processor  32  therein, drives the transport device  18 , more precisely the gate  20 , in such a way that the value document  12  is transported, according to its determined authenticity, for storage into the first output pocket  26  for value documents recognized as authentic or into the second storage pocket  28  for value documents recognized as non-authentic. 
     The analysis apparatus  24  is shown more exactly in  FIG. 2 . It comprises an illumination device  36  for illuminating at least a part of a flat recording area  38  in the transport path  22  which is reached via the transport path  22  by value documents  12  to be analyzed, and a detection device  40 . A control device  42  for driving the illumination device  36 , and an evaluation device  44  for evaluating signals from the detection device  40  are combined in a programmed data processing device  46  which in this example comprises a processor (not shown) and a memory (not shown) which stores a program, executable by the processor, for controlling the illumination device  36  and for evaluating the signals from the detection device  40 . The control and evaluation devices  42 ,  44  are connected to the central control and evaluation device  30  via a signal connection. 
     The illumination device  36  has a semiconductor device or a semiconductor chip  48  in which a matrix arrangement of at least fifty surface emitting laser diodes  50  for emitting optical radiation in a given spectral range is configured (cf.  FIG. 7 ), and an illumination optic  52 . The latter possesses, along an illuminating beam path, a beam-concentrating optic  54 , a deflecting element  56  for deflecting the optical radiation leaving the beam-concentrating optic into the recording area  38 , and a focusing optic  58  for focusing the deflected illumination radiation as an illumination pattern  60  onto an illumination field  62  in the recording area  38 . 
     The spectral range is given by the type of value documents to be analyzed, more precisely of security features formed thereon. In this example, luminescence properties of the value documents are to be analyzed. For this purpose the spectral range is selected so that the excitation radiation for luminescence of an authentic value document is within the spectral range. The deflecting element  56  is deflective for the excitation radiation, but in good approximation transparent to the luminescence radiation, so that the latter can pass through the deflecting element  56  without deflection. 
     Optical radiation emanating from the recording area  38  or from a value document  12  therein, i.e. detection radiation, is imaged into infinity by the focusing optic  58  and passes through the deflecting element  56  without deflection into the detection device  40 , which in the example comprises a detection optic  64 , a spectrographic device  66 , for example an imaging optical grating, illuminated by means of the detection optic  64 , and detection elements  68  for recording the intensity of spatially separated spectral components of the detection radiation which are produced by the spectrographic device  66 . For transmission of detection signals representing the intensity of the impinging spectral components to the evaluation device  44  the detection elements  68  are connected thereto via signal connections. The detection device  40  therefore records the detection radiation in locally unresolved fashion, so that an integral recording of the detection radiation is given. 
     As illustrated in  FIG. 7 , the surface emitting laser diodes  50  are disposed in the semiconductor device  48  of the illumination device  36  in parallel rows and columns perpendicular to the rows, whereby the distance between next adjacent laser diodes is 110 μm immediately before the particular laser diode. 
     To distinguish clearly from conventional edge emitting laser diodes,  FIG. 3  shows a schematic plan view of a semiconductor device  70  with an edge emitting laser diode. The semiconductor device  70  has configured therein, parallel to the surface of the semiconductor device  70  or of the wafer for producing the semiconductor device, a resonator  72  which on its edges  74  and  74 ′ along a low indexed lattice plane is partly reflective to the laser radiation to be produced and in which the laser active zone, i.e. a p-n junction, of the laser diode is located. The output laser radiation is emitted, as indicated in  FIG. 3 , perpendicular to the edges  74  and  74 ′ and parallel to the surface. The beam profile, i.e. the intensity distribution over a plane perpendicular to the beam direction, is shown in  FIG. 4  schematically as a contour diagram in which x and y are Cartesian coordinates in the plane and the lines represent lines of equal intensity. One can clearly recognize a saddle shape of the distribution, which is therefore not rotationally symmetric. 
       FIG. 5  shows schematically, in contrast, a surface emitting laser diode  76  wherein a substrate  78  has disposed thereon a resonator  80  which is given by reflection structures or reflecting layer structures  84 ,  84 ′, for example in the form of interference layers, extending parallel to the substrate  78  and the wafer surface  82 . The laser radiation is now emitted perpendicular to the surface  82  of the wafer or the substrate  78 . For simplicity&#39;s sake the electrodes and the distribution of the current-carrying layers are not explicitly shown. 
       FIG. 6  shows, in a representation corresponding to  FIG. 4 , the beam profile of the laser beam emitted by the surface emitting laser diode. It is in good approximation rotationally symmetric around the beam direction and is therefore very well suited for further beam shaping with a simple illumination optic with spherical and planar optical elements as in this embodiment. 
     The surface emitting laser diodes  50  are configured and contacted in the semiconductor device  48  so as to be singly drivable independently of each other. 
     Number, arrangement and area of the surface emitting semiconductor diodes  50  and the illumination optic  52  are selected so that a contiguous areal illumination field with a superficial extent of at least 0.5 mm 2  can be illuminated in the recording area  38  homogeneously, i.e. with an intensity fluctuation based on the maximum intensity in the illumination area smaller than 20%. 
     The control device  42  is used for separately driving the laser diodes  50 . In this embodiment the analysis apparatus  24  is designed as a module to be installed in a value document processing apparatus, said module being so constructed that the value documents  12  are fundamentally feedable thereto from opposite directions. 
     To obtain as long an illumination as possible of luminescent substances in a value document to be analyzed, the control device  42  drives the laser diodes  50  in such a way that an illumination field  62  or an illumination pattern  60  extending further beyond a detection field  86  (cf.  FIG. 8 ) contrary to the transport direction T than in the transport direction T is produced in the recording area  38 . The detection field  86  is defined in that, except for scattered radiation, only optical radiation from the detection field  86  can reach the detection device  40 . This achieves that an area on the value document is exposed to the illumination or excitation radiation for a time that is longer than the time in which it is located in the detection field  86 . This permits an increased luminescence radiation to be obtained, which facilitates the detection of the luminescence. 
     The control device  42  is so adapted, here through corresponding programming, that upon a signal from the central control and evaluation device  30  which represents the transport direction T with respect to the position of the analysis apparatus  24 , it drives the laser diodes  50  in such a way that one of the two illumination patterns  60 ,  61  shown in  FIG. 8  is produced by the laser beams  88  in the recording area  38  in dependence on the transport direction T or the signal representing it. They are shifted relative to the chip  48  so that the above-described effect occurs. For this purpose, only some of the laser diodes  50  are switched on, namely the laser diodes on the left (a)) or right (b)) in  FIG. 8 , while the others remain switched off. The figure does not show the illumination optic  52  or its influence on the beam path for simplicity&#39;s sake. “Switched on” is understood here to mean that they are operated either continuously or also in pulsed fashion. 
     A second embodiment in  FIG. 9  differs from the first embodiment in that there is now disposed along the transport path  22  upstream of an analysis apparatus  24 ′ an image sensor  90  which is used for recording images of fed value documents and transfers the images to a central control and evaluation device  30 ′ via an image signal connection. All other components are unchanged, so that the same reference signs are used for them as in the first embodiment and the comments on the first embodiment also apply accordingly here. 
     The central control and evaluation device  30 ′ differs from the central control and evaluation device  30  in that it has an interface (not shown in  FIG. 9 ) for recording the image data of the image sensor  90  and is configured, in the example through a corresponding program module, to determine from the image data the position of an area of the value document, for example of a certain feature area, to be analyzed more exactly with the optical analysis apparatus  24 ′ and to output it to the analysis apparatus  24 ′. The image sensor  90  therefore constitutes, in conjunction with the central control and evaluation device  30 ′, a position detection device. 
     The analysis apparatus  24 ′ differs from the analysis apparatus  24  of the first embodiment solely in that the control device is now changed compared to the control device  42 . The control device is, more precisely, configured to drive the laser diodes  50  differently from the control device  42 . As shown schematically in  FIG. 10  in a time sequence a), b), c) in a manner corresponding to  FIG. 8 , the control device drives the laser diodes  50  in such a way that laser diodes  92  at the front in the transport direction are switched on and laser diodes  94  at the back in the transport direction are switched off progressing in the transport direction T in each case in time sequence. This is effected in such a way that the same illumination pattern  60 ′ or illumination field  62 ′ which is produced from laser beams  88  of the front laser diodes is carried along directed onto the selected area  98  in the transport direction T at the transport speed T. Thus, in effect only the selected area  98  is illuminated while it is transported through the detection field  86 . This makes it possible to effectively reduce the production of scattered radiation or interfering radiation from other areas of the value document  12 . 
     In other embodiments the image sensor  90  can also be replaced by other devices, compared to the last embodiment, that permit recognition of the position of certain features to be analyzed. For example, it is also possible, depending on the feature, to use a signal from an edge detector for recognizing an edge of the value document leading in the transport direction, for example a light barrier or an ultrasonic sensor, in connection with the known transport speed and the known position of the feature on the value document to produce a suitable position signal. 
     A further embodiment differs from the first embodiment in that for analysis of a value document the value document is stopped completely and after it is stopped in the recording area a start signal is outputted to an analysis apparatus  24 ″, for which purpose the central control and evaluation device  30  is modified accordingly. The analysis apparatus  24 ″ differs from the analysis apparatus  24  of the first embodiment solely by the configuration or programming of the control and the evaluation devices  42 ,  44 . For all other components the same reference signs are therefore used as in the first embodiment and the comments thereon also apply accordingly here. 
     The control device is configured to drive the laser diodes  50  in such a way that they produce an illumination pattern changing in time during illumination. More precisely, the laser diodes are driven in such a way that the same illumination pattern  60 ″ is moved over the value document  12  at a speed that is constant in the example, as illustrated in  FIG. 11  corresponding in representation to  FIG. 10  in a time sequence a), b), c). At the same time the reflected detection radiation is recorded at constant time intervals, in case of pulsed drive of the laser diodes in synchronism with the pulses, by the detection device  40  and the evaluation device  44  and stored in the evaluation device  44  according to the time sequence and thus the location on the value document, or transferred directly to the central control and evaluation device. Thus, an image of the value document is obtained. Optionally after intermediate storage in the evaluation device, the corresponding image data are transmitted to the central control and evaluation device  30  and evaluated further there. 
     The illumination pattern  60 ″ has a rectangular slot shape, as illustrated in  FIG. 11 . The illumination pattern  60 ″ is preferably so narrow that it can serve as a “virtual” entrance slit for the detection device or the spectrographic device, which then need no longer have an entrance slit. 
     Such an analysis apparatus can also be used advantageously for recognizing bar codes. In particular in this case the detection device need then only have a detection element but not a spectrographic device. 
     In another variant, it is possible to provide in the detection device, instead of only one detection element, a row of detection elements by means of which areas in the recording or detection area are recordable in locally resolved fashion along a row perpendicular to the moving direction of the illumination pattern. Such an analysis apparatus can in particular also be used for recording two-dimensional bar codes. 
     In a further embodiment, the analysis apparatus differs from the analysis apparatus of the first embodiment by a different detection device  40 ″′ as well as a different control and evaluation device. 
     The detection device  40 ″′ (cf.  FIG. 12 ) has a field  100  with a two-dimensional arrangement of detection elements  102  for locally resolved detection of optical radiation coming from the recording area  38  or the detection field  86 , as well as an imaging optic  104  for focusing the infinite beam path after the focusing optic  58  onto the arrangement of detection elements  102 . The detection elements  102  can have different sensitivities to optical radiation in the same spectral range, for example due to fluctuations during production or to different aging. 
     The control device  42 ″ is changed, i.e. configured, as opposed to the control device  42  in such a way as to drive the laser diodes  50  according to the sensitivity of the detection elements  102  in such a way that the differences in sensitivity are evened out. More precisely, this means that the laser diodes  50  are driven in such a way that all detection elements  102  output the same detection signals. 
     Errors in the imaging optic can also be compensated in this way. 
     The evaluation device  44 ″ is configured to record the detection signals of the detection elements  102 . 
     In a particularly preferred embodiment, the control device is configured to record the detection signals from the detection elements for a given drive of the laser diodes by means of the evaluation device, and to automatically change the drive of the laser diodes in such a way that all detection elements emit the same detection signal. 
     This corresponds in a sense to a calibration of the analysis apparatus. This process can, depending on the embodiment, be carried out automatically at given intervals in the service life of the analysis apparatus or upon each switch-on or switch-off of the analysis apparatus, for which purpose the control device can be configured accordingly, for example through corresponding programming. 
     Yet a further embodiment differs from the first embodiment only in that the surface emitting laser diodes  50  are configured in the semiconductor device and contacted so as to be drivable separately or independently of each other in at least two groups, in this embodiment row by row. The control device  42  is accordingly modified in such a way as to drive the groups, i.e. here the rows, singly separately from each other, whereby the same illumination pattern as in the first embodiment can be obtained. 
     Further embodiments differ from the previously described embodiments only by the arrangement of the laser diodes  50  in the semiconductor device  48 ′. All other parts are unchanged. The surface emitting laser diodes  50  are now disposed in the semiconductor device  48 ′ (cf.  FIG. 13 ) on the grid points of a hexagonal point grid at a distance of nearest neighbors smaller than 120 μm, in the example 100 μm, thereby making it possible to obtain a further increase in the homogeneity of the illumination pattern. 
     In yet further embodiments, the illumination device does not have the deflecting element  56 , so that a straight illuminating beam path is obtained. The detection device is configured and disposed for detecting optical radiation after transmission through the value document. It has its own optic, corresponding in its properties to the focusing optic, for imaging at least a portion of the value document on the side not illuminated by the illumination device. 
     In other embodiments, the illumination of the value document can also be effected at angles other than 90°, in which case the detection device might be configured and disposed accordingly.