News Column

Patent Issued for Sensor for Checking Value Documents

June 25, 2014



By a News Reporter-Staff News Editor at Electronics Newsweekly -- From Alexandria, Virginia, VerticalNews journalists report that a patent by the inventors Frankenberger, Jorg (Markt Schwaben, DE); Deckenbach, Wolfgang (Schechen, DE); Hennerkes, Urs (Furstenfeldbruck, DE); Rauscher, Wolfgang (Parkstetten, DE), filed on December 16, 2010, was published online on June 10, 2014.

The patent's assignee for patent number 8749768 is Giesecke & Devrient GmbH (Munich, DE).

News editors obtained the following quote from the background information supplied by the inventors: "A. Field of the Invention

"This invention relates to a sensor for checking value documents and to a method for manufacturing the sensor from a sensor platform, as well as to a sensor family having at least two sensors manufactured from the same sensor platform.

"B. Related Art

"For checking value documents there are usually employed sensors with which the type of the value documents is determined and/or with which the value documents are checked for authenticity and/or for their state. Such sensors are employed for checking value documents such as e.g. bank notes, checks, identity cards, credit cards, check cards, tickets, vouchers and the like. The check of the value documents is effected in an apparatus for value-document processing, in which one or several different sensors are contained, depending on the value-document properties to be checked. Upon checking, the value documents are usually scanned in one or several tracks, whereby the sensor and the value document are moved relative to each other.

"The value documents are frequently checked using optical sensors that capture the light reflected by the value documents. Previous optical sensors have been restricted to the spectral properties of the sensor that are defined upon the development of the sensor, such as e.g. the spectral resolution and the position and width of the spectral region capturable by the sensor. To adapt such an optical sensor to different requirements, e.g. a different spectral region or a different spectral resolution, basic changes of the optical components of the sensor are required. With optical sensors whose spectral selection is effected through different color filters which are respectively arranged in front of a detector, it would e.g. be necessary to replace the color filters to change the capturable spectral region. To increase the spectral resolution in such a sensor, additional detectors with different color filters would have to be installed in the sensor. This is usually hardly possible, however, on account of the limited space within the sensor housing.

"It is also known to illuminate a value document by employing several different-colored light sources whose light is directed onto the value document via a common light guide. On account of the relative motion between the sensor and the value document transported past it, however, a minimum distance is required between the light guide and the sensor. Because the light diverges after exiting from the light guide, this minimum distance results in the illuminated region on the value document being relatively large and the illumination intensity accordingly low. Hence, such an illumination is unfavorable when the optical properties of a value document are to be captured in a spatially limited region."

As a supplement to the background information on this patent, VerticalNews correspondents also obtained the inventors' summary information for this patent: "An object of the present invention is hence to provide a sensor platform for a sensor for checking value documents, from which platform there can be manufactured in a simple manner, for different spectral requirements, different sensors for capturing the optical properties of a value document in a spatially limited region.

"The sensor is constructed for checking value documents and contains an illumination device for illuminating a value document to be checked by the sensor, an imaging optic and a detection device. Through the imaging optic the light emitted by the illumination device can be imaged onto the value document to be checked by the sensor. The detection device is constructed for detecting detection light which, upon operating of the sensor, emanates from the value document to be checked when the value document is illuminated by the illumination device.

"The illumination device has a light source receiving means on which a multiplicity of light source positions are provided, each of which is constructed for receiving a light source, in particular for receiving a chip-shaped light source. At several of the light source positions of the light source receiving means there is respectively arranged exactly one light source. The light source positions are arranged side by side on the light source receiving means and are defined e.g. by a multiplicity of individual depressions by which exactly one light source can respectively be received. Preferably, the light sources are of chip-shaped construction and the depressions so constructed that one chip-shaped light source is respectively insertable therein. However, the light source positions can also be defined by elevations and/or by electrical contact areas, which the light source receiving means can have, and which are constructed for receiving a chip-shaped light source. To obtain a one-to-one association between the microlenses and the light sources to be arranged at the light source positions, the arrangement of the microlenses in the microlens array and the arrangement of the light source positions on the light source receiving means are identical.

"At least two of the light sources arranged on the light source receiving means have mutually different emission spectra. This means that at least one of the light sources has an emission spectrum whose maximum lies at a different wavelength compared to the maxima of the emission spectra of the other light sources which are arranged on the light source receiving means. For example, each light source is constructed for emitting an emission line at a certain wavelength. Preferably, the illumination device has a multiplicity of different light sources, i.e. a multiplicity of light sources with mutually different emission spectra whose intensity maxima lie at different wavelengths. In particular, there are arranged on the light source receiving means a multiplicity of light sources whose emission spectra lie in the visible spectral region, and/or a multiplicity of light sources whose emission spectra lie in the infrared spectral region and/or whose emission spectra lie in the ultraviolet spectral region. As light sources there are preferably used light-eradiating diodes, for example light-emitting diodes (LED), in particular semiconductor light-emitting diodes or organic light-emitting diodes (OLED), and/or laser diodes, in particular vertical-cavity surface-emitting lasers (VCSEL).

"Moreover, the illumination device of the sensor has a microlens array which contains a multiplicity of microlenses. The microlens array and the light source receiving means are arranged relative to each other such that each of the light sources arranged on the light source receiving means has exactly one of the microlenses associated therewith. Upon operating of the sensor the emission light of each of the light sources is thus collected by exactly one microlens of the microlens array. Each of these microlenses, in so doing, collects only the emission light of exactly one of the light sources. By the microlens associated with the respective light source the emission light of each of the light sources is collected with high efficiency.

"Preferably, the microlenses are arranged in the microlens array in the same one- or two-dimensional grid as the light source positions are arranged on the light source receiving means. In particular, the microlens array is constructed as a one-pieced body which preferably has fastening means which are an integral part of the microlens array, in particular of the one-pieced body. The light source receiving means has a counter-piece matching the fastening means of the microlens array. The fastening means of the microlens array are constructed e.g. as fastening pins or as holes for receiving fastening pins which are provided on the light source receiving means. In particular, all microlenses of the microlens array are arranged coplanarly with each other. Preferably, all microlenses of the microlens array are identically constructed to guarantee a greatest possible variability in the arrangement of the light sources on the light source receiving means. In particular, all microlenses have for this purpose the same form and/or the same focal length. Alternatively, some microlenses of the microlens array can also have a form and/or focal length deviating from the remaining microlenses. There could thus be obtained e.g. an individual adaptation of the microlenses to the optical properties of the light sources with which they are associated and for whose light collection they are provided.

"Employment of the microlens array results in great advantages in comparison to an illumination device wherein a single lens is employed for each light source. For in this case an individual mount would have to be provided for each of the single lenses, and the exact positioning relative to the respective light source ensured upon the fastening of the single lenses. In so doing, it may be necessary that the exact position and/or orientation of the single lenses must be subsequently adjusted. In contrast, upon employment of a microlens array having exactly one microlens for each light source, a single exact positioning is sufficient. This positioning can be effected through the fastening means of the microlens array which are connected to the corresponding counter-pieces of the light source receiving means. The manufacture of the sensor can hence be effected much more simply and without adjustment. In contrast to the realization of a corresponding illumination device with single lenses which must be individually mounted and whose arrangement always leaves interstices, the microlens array moreover involves no or only a minimal interstice between the individual microlenses. Because the microlens array is constructed as a one-pieced body, the microlenses can pass directly into each other. There can hence be obtained by the microlens array quasi an area-covering light collection. There can hence be formed by the microlens array an illumination device that has a high light collection efficiency and is very compact.

"The sensor moreover has an imaging optic which is constructed for imaging the emission light of each of the light sources, after it passes through the respective microlens, onto a value document to be checked by the sensor. The microlenses and the imaging optic are arranged relative to each other such that the emission light of each of the light sources can be imaged by the respectively associated microlens and the imaging optic onto a value document that is to be captured by the sensor. The imaging optic preferably has one or several refractive and/or diffractive optical elements which image the illumination light onto the value document. Preferably, the imaging optic is constructed as an imaging lens. To image the light emitted by the different light sources of the illumination device onto the same illuminated region of the value document to a great extent, the imaging optic is preferably so arranged that the illuminated region of the value document lies precisely or approximately at the focal point of the imaging optic. It can thereby be achieved that in spite of the illumination of the value document with different light sources, the same region of the value document to be checked can always be illuminated and detected by the detection device.

"The imaging optic is arranged on the side of the microlens array facing the value document. The imaging optic is constructed for imaging the emission light of each of the light sources, after it passes through the respective microlens, onto a value document to be checked by the sensor. The light emitted by the illumination device is imaged by the imaging optic via a defined ray path onto the illuminated region of the measuring plane or of the value document. Because an imaging of the illumination light onto the value document is effected, the illuminated region of the value document is clearly defined and spatially limited. This constitutes an advantage compared with a direct illumination of the value document by the light sources (without an optic therebetween) and compared with a simple light guide optic (without an imaging optic), through which the light is not imaged, but rather brought onto the value document by the light guide without a defined ray path.

"For the sensor there is provided a control device which is adapted to successively switch the light sources of the illumination device on and off again in order to successively illuminate the value document with different emission spectra. The control device can be constructed as part of the sensor, but it can also be constructed as an external control device, e.g. as part of an apparatus for value-document processing in which the sensor is installed. The control device is adapted to drive the illumination device of the sensor, in particular the light sources, and the detection device of the sensor. Upon operating of the sensor the control device successively switches the light sources on and off again, for example such that exactly one of the light sources is switched on at any time. At one or several of the times, however, several of the light sources can also be switched on simultaneously, e.g. several light sources with the same emission spectrum. The value document is in this way illuminated successively with the different emission spectra of the different light sources. Moreover, the control device causes the detection device to respectively capture, during the switched-on phase of the light sources, one measured value which corresponds to the light intensity emanating from the value document. Because the detection device respectively senses one measured value in synchronism with the illumination by the light sources, the light intensity emanating from the value document is thus detected for those wavelengths that are predetermined by the emission light of the light sources. Preferably, the sensor has a multiplicity of different light sources which, upon operating of the sensor, are successively switched on and off to capture the spectral intensity distribution of the light emanating from the value document.

"The detection device preferably has a spectral sensitivity which is so spectrally broad-band that the emission light of each of the light sources of the illumination device is detectable by the detection device. In particular, at least visible light and/or infrared and/or ultraviolet light is detectable by the detection device. The measured values sensed by the detection device are subsequently evaluated by an evaluation device which can be part of the sensor or is also formed by an external evaluation device. Preferably, there is already effected by the sensor, in particular by an internal evaluation device of the sensor, at least a pre-processing of the measured values. The further evaluation can likewise be effected through the internal evaluation device or alternatively through a central evaluation device of the apparatus in which the sensor is installed. For detecting the remission light the sensor can also contain several identical detection devices, e.g. in order to capture the remission light over a greater angular range. The sensor can also have several different detection devices, e.g. in order to extend the spectral region capturable by the sensor. Said different detection devices can be arranged side by side or one behind the other, e.g. in the form of a sandwich structure.

"The invention moreover shows a method for manufacturing a sensor for checking value documents by which the sensor to be manufactured can be tailored to different spectral requirements with little effort.

"The sensor is manufactured from a sensor platform. The sensor platform comprises at least the above-mentioned light source receiving means with the multiplicity of light source positions, the microlens array with the multiplicity of microlenses, the imaging optic and the detection device. To form the illumination device, the light source receiving means is equipped with light sources, whereby at several of the light source positions there is respectively arranged exactly one light source. At least two of the light sources, preferably a multiplicity of the light sources, have mutually different emission spectra. For forming the illumination device the microlens array and the light source receiving means are subsequently arranged relative to each other such that each of the light sources arranged on the light source receiving means has exactly one of the microlenses associated therewith and such that, upon operating of the sensor, the emission light of each of the light sources is collected by exactly one microlens of the microlens array. Preferably, the microlens array and the light source receiving means are, in so doing, fastened to each other. For manufacturing the sensor, the imaging optic is moreover arranged relative to the illumination device such that the emission light of each of the light sources received at the light source positions, after passing through the respective microlens, can be imaged by the imaging optic onto the value document to be checked. Moreover, for manufacturing the sensor, the illumination device, the imaging optic and the detection device are arranged relative to each other such that the detection device can detect detection light which, upon operating of the sensor, emanates from the value document illuminated by the illumination device.

"Upon configuring of the sensor, illumination sequences are defined, it being defined in particular which light sources are switched on and off for illuminating the value document. The control device is, in so doing, so configured that the light sources of the illumination device, upon operating of the sensor, are successively switched on and off, so that the value document can be successively illuminated with different emission spectra. The control device provided for the sensor can be already configured upon the manufacture of the sensor. It can be provided, however, that the configuration of the control device is only carried out after the completion of the sensor. Further, it can be provided that the configuration of the control device is also changeable after the sensor has been put into operation. Such a reconfiguring after putting into operation can be carried out e.g. by the manufacturer of the sensor or by an operator of the apparatus in which the sensor is installed. Upon reconfiguring it may also be necessary to adapt the driving of the detection device to the driving of the illumination, e.g. when the number of the light sources switched on and off for measurement is changed. Upon reconfiguring, the evaluation device employed for evaluating the sensed measured values must also be adapted to the changed configuration of the control device, e.g. when different light sources are employed for measurement.

"The sensor is not constructed for a full-area check of the value document, but rather for checking the value document in one or in several tracks on the value document. In the case of checking in several tracks, there are respectively arranged between the tracks value-document regions which are not checked by the sensor. The regions illuminated for checking the value document form tracks which extend parallel to each other and along the transport direction of the value document. The tracks are distributed discretely on the value document. For each of the tracks there are provided at least an illumination device, an imaging optic and a detection device according to the above description. The illumination sequences preferably succeed one another so fast that the value document is checked quasi continuously along each of the tracks.

"Optionally, there can be arranged in front of the detection device a detection optic by which the detection light emanating from the value document is collected and directed onto the photosensitive region. The detection optic can be realized e.g. by refractive or diffractive optical elements or by mirrors. Preferably, the sensor moreover has a housing in which there are arranged the illumination device, the imaging optic and the detection device, optionally also the control device and detection optic.

"The sensor is manufactured from a sensor platform which is formed by the light source receiving means, the microlens array, the imaging optic and the detection device. Optionally, the sensor platform also includes the control device, which can be arranged within or outside the housing. However, said device is not necessarily a part of the sensor. Optionally, the sensor platform can also include the housing and/or the detection optic. However, the sensor can also be realized without a housing and/or without a detection optic. Different sensors can be manufactured from the sensor platform, depending on the selection of the light sources with which the light source receiving means is equipped. Depending on the spectral requirements to be met by the sensor to be manufactured, there can be manufactured from the same sensor platform a first-type sensor which is constructed for checking value documents by illumination with several first emission spectra, or a second-type sensor which is constructed for checking value documents by illumination with several second emission spectra, at least one of which differs from the first emission spectra.

"The invention moreover relates to a sensor family which is formed by several sensors for checking value documents, which are different but manufacturable from the same sensor platform. The sensor family comprises at least one first-type sensor which is constructed for checking value documents by illumination with a multiplicity of first emission spectra, and at least one second-type sensor which is constructed for checking value documents by illumination with a multiplicity of second emission spectra, at least one of which differs from the first emission spectra. The at least one first-type sensor and the at least one second-type sensor have for example the same microlens array and/or the same light source receiving means and/or the same imaging optic and/or the same detection device. Preferably, the at least one first-type sensor and the at least one second-type sensor are manufacturable from the same sensor platform, whereby this sensor platform is formed by the light source receiving means, the microlens array, the imaging optic and the detection device. In this case, the first-type sensors and the second-type sensors have the same light source receiving means on which a multiplicity of light source positions are respectively provided, each of which is constructed for receiving a light source, and/or the same microlens array which respectively has a multiplicity of microlenses, whereby the microlens array and the light source receiving means can be arranged relative to each other such that each of the light source positions is associated with exactly one of the microlenses, and the same imaging optic and the same detection device.

"In one embodiment example, the selection of the light sources with which the first-type sensors and the second-type sensors are equipped is also the same. The first-type sensors and the second-type sensors are configured differently, however, so that, upon operating of the second-type sensors, one or several different light sources are switched on and off compared to the operating of the first-type sensors. The second-type sensors are so configured that they employ a different subset of the light sources for checking the value documents compared to the first-type sensors. For example, the second-type sensors check the value documents with light of one or several wavelengths which the first-type sensors do not employ for checking the value documents.

"In another embodiment example, the number and selection of the light sources with which the first-type sensors and the second-type sensors are equipped are different. The first-type sensors are e.g. equipped with a first selection of light sources and the second-type sensors with a second selection of light sources which differs from the first selection. In particular, one or several light sources of the second selection respectively have an emission spectrum whose spectral position is different in comparison to the spectral position of all emission spectra of the light sources of the first selection.

"Besides the first-type and second-type sensors, the sensor family can also have one or several sensors of one or several further types which are manufactured from the same sensor platform and are likewise constructed for checking value documents. Like the second-type sensors, the sensors of the further types belonging to the sensor family can also either be equipped with the same selection of light sources and be configured differently, or be equipped with a different selection of light sources."

For additional information on this patent, see: Frankenberger, Jorg; Deckenbach, Wolfgang; Hennerkes, Urs; Rauscher, Wolfgang. Sensor for Checking Value Documents. U.S. Patent Number 8749768, filed December 16, 2010, and published online on June 10, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=8749768.PN.&OS=PN/8749768RS=PN/8749768

Keywords for this news article include: Electronics, Light-emitting Diode, Giesecke & Devrient GmbH.

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Source: Electronics Newsweekly


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