Holographic display device for a contactless finger scanner

Abstract

Described are techniques for combining a contactless finger scanner (90) with a holographic display device (70). A floating hologram (71) can be used to provide a positioning aid for a user of the finger scanner (90) such that the user can position one or more fingers or a hand in a measurement area (81).

Description

[0001] DESCRIPTION

[0002] HOLOGRAPHIC DISPLAY DEVICE FOR CONTACTLESS FINGER SCANNER

[0003] TECHNICAL FIELD

[0004] Various aspects of the disclosure relate to techniques for supporting the positioning of a portion of a hand within a measurement area of ​​a contactless finger scanner using one or more holograms. Various aspects relate to corresponding control logic for controlling a holographic display device and the finger scanner. Various aspects of the disclosure relate to structural details of the holographic display device and the system integration of the holographic display device of the finger scanner.

[0005] BACKGROUND

[0006] Finger scanners are used to capture people's fingerprints, for example, for identity verification. Currently, finger scanners are primarily based on contact methods, in which the fingers are placed on a surface during scanning. While this method is proven and robust, it also has various disadvantages, e.g., in terms of cleanliness, hygiene, deformation of the print depending on contact pressure, etc.

[0007] Therefore, there is a growing desire to establish contactless methods in which images of fingers are captured when they are placed in a freely positioned measuring area. A corresponding contactless finger scanner is described, for example, in DE 10 2020 131 513 B3.

[0008] The measuring range typically refers to a measuring volume arranged freely in space which has a limited extent. This is because an optical image can only be captured in a limited depth of field of around 20 mm. See DE 10 2019 126 419 A1 . Due to the limited measuring range, precise positioning of the hand is necessary. This requires a positioning aid. In the prior art, a positioning aid is provided by a frame structure roughly specifying the target position of the hand and the actual position being determined via a sensor. Using instructions on a screen, the hand is then guided to the required target position until one or more fingers are positioned in the optically displayed measuring range. The guidance of the hand can be supported by an ultrasonic sensor which is arranged in such a way that it generates haptically perceptible pressure points. See e.g. DE 10 2020 131 513 B3.

[0009] Such technologies have certain disadvantages. In particular, a corresponding finger scanner, with its frame structure and screen, and possibly ultrasonic transducers, is comparatively large and complex. Furthermore, it has been observed that users can sometimes have difficulty translating graphical instructions displayed on the screen into appropriate hand movements; accordingly, the positioning process takes a relatively long time, which limits throughput.

[0010] SHORT SUMMARY

[0011] Therefore, there is a need for improved techniques to assist in positioning a user's hand within a measurement area of ​​a contactless finger scanner. There is a need for corresponding techniques to provide a positioning aid that addresses or at least mitigates the limitations and disadvantages mentioned above.

[0012] This problem is solved by the features of the independent patent claims. The features of the dependent patent claims define embodiments.

[0013] According to various examples of the invention, a positioning aid for arranging the hand of a user in the measuring range of a contactless finger scanner is achieved by means of at least one floating hologram.

[0014] A system comprises a contactless finger scanner. The contactless finger scanner is configured to capture an optical image of a measurement area. A portion of a user's hand can be positioned in the measurement area. A holographic display device of the system is configured to generate at least one floating hologram positioned in or near the measurement area. This assists in positioning the portion of the user's hand in the measurement area.

[0015] Depending on the size of the measuring area, different sized areas of the user's hand can be optically captured in a single measurement process (single shot). For example, it is conceivable for the measuring area to have relatively small dimensions, such as 3 cm x 2 cm x 5 mm. In such an example, only a single finger or fingertip would be captured per measurement process. Sometimes, however, the optical finger scanner could define a sufficiently large measurement area so that more than one single finger can be captured per measurement process. Typically, the contactless finger scanner is controlled according to a measurement protocol. This protocol can then define that several areas of the user's hand should be optically imaged sequentially.

[0016] The term "finger scanner," as used here, does not imply a conventional fingerprint scan. Rather, an optical image of the measurement area and one or more fingers within it can be captured using a camera, such as a CCD camera or a CMOS camera.

[0017] The holographic display device may comprise one or more holographic optical elements. These could, for example, be illuminated in edge-lit geometry (explained in detail later in connection with FIG. 5) or in waveguide geometry (explained in detail later in connection with FIG. 6). Reconstruction can generally also be performed using incoherent light, e.g., from a light-emitting diode.

[0018] In edge-illuminated geometry, light is coupled into a side edge of an optical block. Unlike waveguide geometry, where internal reflections guide the light through the block, in edge-illuminated geometry, the light typically hits the holographic optical element without further redirection after being coupled into the block. The light then illuminates the holographic optical element and is diffracted accordingly to create the desired hologram. In waveguide geometry, the light is coupled into an optical block, but instead of directly hitting the HOE, it undergoes multiple reflections within the block by total internal reflection. These multiple reflections guide the light through the block and ensure that it eventually hits the HOE from a specific location or region within the block.The result is that light falls on the HOE from different locations within the block, which can result in more uniform and broader illumination. This geometry can be particularly useful when systems with a shallow build depth are required.

[0019] These geometries are particularly suitable for the display of holograms with a high levitation height and for the control of unwanted stray light, e.g. from the 0th order of diffraction or Fresnel reflections.

[0020] The holographic display device can illuminate the holographic optical elements in transmission geometry or reflection geometry. A light guide, for example made of transparent glass or a PMMA substrate, can absorb light from one side and guide it to the upper surface of the light guide. Several layers can be located on this upper surface. First, there is a layer containing the holographic optical element. On top of this is a layer of triacetate (TAC), followed by a transparent adhesive layer or adhesive film, which in turn is covered by a polycarbonate (PC) layer. Ideally, there is only a small difference in the refractive index between the substrate and the applied layers, as well as between the layers themselves. This ensures that total internal reflection of the rays coupled into the light guide only occurs at the uppermost layer, which typically borders on air.The surface at which the light coupled into the light guide exits or is reflected is called the output surface. In one possible configuration, the holographic optical element can be designed as reflective (reflection geometry). Here, coupled-in light coming from the direction of the substrate is not diffracted by the reflective holographic optical element, but simply transmitted. However, light that was previously transmitted through the holographic optical element and reflected at the output surface is reflected by the reflective holographic optical element and diffracted according to the desired luminous function. The undiffracted light, often referred to as zeroth order, is transmitted back into the substrate of the light guide. In another configuration, the holographic optical element can be designed as transmissive.Here, the holographic optical element directly diffracts the light coming from the direction of the substrate, without this light having previously undergone total internal reflection at the output surface. Only the undiffracted light, also often referred to as zeroth order, is totally reflected at the output surface and is no longer diffracted by the transmissive holographic optical element, but rather transmitted back into the substrate of the light guide. In summary, with the reflective geometry, the light is first transmitted through the reflective holographic optical element and then reflected, whereas with the transmissive geometry, the light is directly diffracted by the transmissive holographic optical element.

[0021] The holographic display device can therefore provide a positioning aid by means of one or more floating holograms. The one or more floating holograms are arranged freely in space, for example in the measuring area or at an edge of the measuring area or adjacent to the measuring area. Because the floating holograms are arranged freely in space, the user can be intuitively shown where in space the measuring area is located. There is no need for a complex or large screen to display the corresponding information. The user does not have to translate information displayed two-dimensionally on a screen into a three-dimensional movement of the hand, but can intuitively place the desired area of ​​the hand in the measuring area by perceiving the at least one hologram.

[0022] In one example, the holographic display device could generate the at least one hologram statically, i.e., for example, in particular independently of a progress of a measurement protocol for detecting one or more areas of the user's hand using the contactless finger scanner. For example, the at least one hologram could be arranged at edges of the measurement area and thus highlight the dimensions of the measurement area. The at least one hologram can then be statically activated so that the user can perceive the measurement area using the at least one hologram. In some examples, however, it would also be conceivable for the at least one hologram to be dynamically activated or deactivated. The at least one hologram can be activated or deactivated in particular depending on a progress of the measurement protocol.

[0023] The system may include a data processing unit. This may, for example, be embodied as a processor with memory. For example, an application-specific integrated circuit (ASIC) could be used. A field-programmable array (FPGA) could also be used. The data processing unit may assume control functionality for the system. The data processing unit may, in particular, be configured to determine a relative positioning of the user's hand with respect to the measurement area based on a sensor signal and / or the optical image of the contactless finger scanner. The holographic display device can then be controlled based on the relative positioning.

[0024] In other words, the relative positioning can be detected using a separate sensor. For example, a radar sensor could be used. An optical time-of-flight sensor (TOF camera) could also be used. An ultrasonic sensor could be used. Alternatively or additionally, the relative positioning can also be determined based on image data from the finger scanner itself. For example, if the hand is partially visible, a model of the hand can be used to determine the relative positioning of the desired area of ​​the hand, for example, a specific finger or fingertip, in relation to the measurement area.

[0025] The relative positioning may indicate a translational offset or tilt of the respective area of ​​the hand with respect to the measuring area (or in particular with respect to a reference point in or near the measuring area).

[0026] There are different variants of how the information relating to the relative positioning can be used to provide a suitable positioning aid. In particular, the implementation of the positioning aid based on the relative positioning can depend on how the at least one hologram is designed, i.e., for example, what semantic content and / or spatial arrangement the at least one hologram has. It would be conceivable, for example, for the holographic display device to be set up to generate a plurality of floating holograms. It is then conceivable for the data processing unit to be set up to control the holographic display device in such a way that different holograms of the plurality of floating holograms are activated depending on the relative positioning - e.g., depending on the distance and / or rotation between the area of ​​the user's hand and the measuring area.For example, a "traffic light hologram" could be used, with the displayed traffic light changing from red to yellow to green depending on the distance. This can be achieved through a suitable color mix, whereby the color mix is ​​achieved by activating or deactivating corresponding monochromatic holograms. Alternatively or in addition to such selective switching on / off of different holograms, it would also be conceivable for one or more holograms to be generated with different brightness depending on their relative positioning, for example, in particular depending on the distance and / or rotation of the area of ​​the hand to be measured from the measuring area.

[0027] Alternatively or in addition to such consideration of relative positioning when controlling the holographic control device, it would also be conceivable for the holographic display device to be controlled depending on the progress of a measurement protocol for sequentially capturing different areas of the hand (typically different fingers). For example, the measurement images captured using the contactless finger scanner could be used to check whether a particular area of ​​the hand is depicted with sufficient quality in the corresponding measurement image, and then proceed to the next entry in the measurement protocol. The data processing unit can thus be configured to control the display device in such a way that different holograms are activated depending on the progress of the measurement protocol.Alternatively or additionally, one or more holograms could be varied in their brightness.

[0028] From the above, it is clear that it is possible to provide continuous user guidance in connection with finger scanning. For example, the positioning aid can respond interactively to the progress of the measurement protocol. The positioning aid can respond interactively to the current position of the user's hand in relation to the measurement area.

[0029] Typically, a higher level of interaction is achieved by using more than one hologram. Different holograms can then be activated sequentially and / or simultaneously, and / or their relative brightness can be adjusted.

[0030] There are different variants for how the multiple floating holograms are arranged relative to one another. For example, it would be possible for the multiple holograms to be offset from one another at different spatial positions. In this way, optical guidance to the measurement area can be achieved by sequentially activating different holograms at different spatial positions. The different holograms at different spatial positions can, for example, carry different semantic content, i.e., display different images, etc. In some examples, it would also be possible for the multiple holograms to be arranged superimposed on one another.

[0031] In some examples, the at least one hologram is monochromatic. This means that the holographic display device can, for example, have a single channel in the corresponding color. However, it would also be conceivable for multiple channels to be present that are associated with multiple colors, for example, green and red. For example, three or more colors could be used, for example, red, green, and blue. In this way, any desired color can be reproduced by mixing the corresponding color channels. To realize multiple colors, the holographic display device can comprise multiple corresponding channels. A red, green, and blue light source, for example, an RGB laser diode, can be used as the light source. Multiple channels can be used to implement different colors of a single icon (mixing the corresponding holograms by adjusting the appropriate brightness).Alternatively, different pictograms can be switched on or off, for example to convey further semantic content to the user, i.e. to indicate to the user that a certain action is necessary. If, for example, two or more superimposed holograms are used, these can be assigned different color channels. For example, a red hologram displaying a specific pictogram can be overlaid with a green hologram displaying the same pictogram, and with a blue hologram displaying the same pictogram. By adjusting the brightness of the holograms in the colors red, green, and blue relative to one another, the pictogram can be displayed with a variable color. The color mixing can be gradual or continuous.For example, depending on the distance of the area of ​​the user's hand to be measured from the measurement area, the color of the pictogram could be continuously varied in the color spectrum from red (great distance) to green (position of the area to be measured within the measurement area). In such examples, multiple color channels are used to illuminate corresponding holographic optical elements and generate corresponding holograms.

[0032] A description and definition of the term "channel" can be found, for example, in WO 2022 / 157082 A1, the corresponding disclosure of which is incorporated herein by cross-reference. Switchability of specific image content can be achieved alternatively or additionally through the use of liquid crystal cells in conjunction with polarizers placed on the holographic optical element. This is described, for example, in German patent application 10 2023 206 165.1, filed June 29, 2023.

[0033] A method for use in a data processing unit of a system as described above comprises controlling the contactless finger scanner to implement a measurement protocol for sequentially capturing different areas of the hand. The method further comprises controlling a holographic display device to selectively activate the at least one floating hologram and / or with variable brightness based on the measurement protocol.

[0034] The features set forth above and the features described below may be used not only in the corresponding explicitly set forth combinations, but also in further combinations or in isolation, without departing from the scope of the present invention. BRIEF DESCRIPTION OF THE FIGURES

[0035] FIG. 1 schematically illustrates a system according to various examples, which includes a contactless finger scanner and a holographic display device.

[0036] FIG. 2 schematically illustrates several holograms having different semantic content that can be displayed by the holographic display device to provide a positioning aid for a hand in a measuring range of the contactless finger scanner.

[0037] FIG. 3 is a flowchart of an exemplary method.

[0038] FIG. 4 is a flowchart of an exemplary method.

[0039] FIG. 5 schematically illustrates structural details of a holographic display device according to various examples.

[0040] FIG. 6 schematically illustrates details of a holographic display device according to various examples.

[0041] FIG. 7 schematically illustrates the use of multiple optical channels in a holographic display device according to various examples.

[0042] FIG. 8 schematically illustrates the use of multiple optical channels in a holographic display device according to various examples.

[0043] FIG. 9 schematically illustrates the use of multiple optical channels of a holographic display device according to various examples.

[0044] DETAILED DESCRIPTION

[0045] The present invention is explained in more detail below using preferred embodiments with reference to the drawings. In the figures, identical reference numerals designate identical or similar elements. The figures are schematic representations of various embodiments of the invention. Elements shown in the figures are not necessarily drawn to scale. Rather, the various elements shown in the figures are depicted in such a way that their function and general purpose will be understood by those skilled in the art. Connections and couplings between functional units and elements shown in the figures can also be implemented as an indirect connection or coupling. A connection or coupling can be implemented wired or wirelessly. Functional units can be implemented as hardware, software, or a combination of hardware and software.

[0046] The following describes techniques for using one or more holograms to provide a user with positioning assistance for positioning an area of ​​the hand within the measuring range of a contactless finger scanner. For example, the actual position of the hand can be determined using a sensor. The color of the content / pictogram displayed by the hologram can indicate whether the hand is in the target position or within the measuring range. If, for example, the hand is outside the measuring range covered by the one or more cameras of the finger scanner, the hologram can be displayed in red. If it is positioned in the target position, it is displayed in green. A soft or continuous color transition can also be used, depending on how far the hand is from the target position.a color transition from red (far from the target position) via yellow (close to the target position) to green (in the target position) can be covered (this can already be achieved by combining a red with a green channel).

[0047] FIG. 1 schematically illustrates a system 80. The system 80 includes a contactless finger scanner 90.

[0048] The finger scanner 90 is configured to capture an optical image of a measuring area 81—here, a three-dimensional measuring volume in space. A region of a user's hand, for example, one or more fingertips, can be arranged in the measuring area 81. For this purpose, the contactless finger scanner 90 comprises an illumination module 91 configured to emit light along a beam path 95 into the measuring area 81. Furthermore, the finger scanner 90 has one or more cameras 92 configured to detect light along a beam path 96. For example, a stereoscopic camera 92 could be used. The beam path 96 originates in the measuring area 81. If a region of a user's hand is arranged in the measuring area 81 from one side 31, this region of the hand is illuminated from the opposite side 32, typically from below.This illumination and associated image capture along the beam paths 95, 96 takes place through an optical plate 73, on one side of which a holographic optical element 74 is arranged.

[0049] Additional optical elements can also be arranged in the beam path of the light 79 between the light source 75 and the holographic optical element 74. Examples include deflection units or collimation optics. Such optical elements can also be diffractive.

[0050] When positioning the light source 75, care must be taken to ensure that the 0th order and the Fresnel reflection on the top side of the holographic optical element 74 do not point toward the viewer. Furthermore, it must be ensured that 0th order diffraction and the Fresnel reflection do not affect image capture by the finger scanner 90. This can be achieved, for example, by using different spectral ranges for the light from the light source 75 and the light from the illumination module 91 or the camera 92.

[0051] The system 80 also includes a data processing unit 85. The data processing unit 85 is configured to control the various components 91, 92, 75. The data processing unit 85 is thus configured to control the finger scanner 90 and the holographic display device 70.

[0052] In the example of FIG. 1, a distance sensor 86 is provided, for example, a radar sensor, a TOF camera, or an ultrasonic sensor. The data processing device 85 can also receive measurement signals from the sensor 86.

[0053] Generally speaking, one or more holograms, such as hologram 71 (shown only schematically as a circle in FIG. 1, can have any semantic content), can provide a positioning aid for arranging a portion of the hand to be measured in the measuring area 81. This is shown in FIG. 2.

[0054] FIG. 2 illustrates the measuring area 81 and several holograms 41, 42, 43, 44. In

[0055] FIG. 2 shows a scenario in which several holograms 41, 42, 43, 44 are used to provide the corresponding positioning aid. The hologram 41 indicates the measuring area 81 by extending along its circumference in a bracket-like or frame-like manner. For example, the hologram 41 could be statically activated during operation of the finger scanner 90, so that the user receives orientation regarding the positioning of the measuring area 81 - regardless of the progress of the measurement protocol, etc. The hologram 42 can be dynamically activated, e.g., triggered by an event. The hologram 42 provides, for example, positive feedback regarding the progress of a stage of a corresponding measurement protocol.For example, hologram 42 on the left could be activated when all required fingers of the left hand have been successfully imaged; hologram 42 on the right could be activated when all required fingers of the right hand have been successfully imaged. Holograms 43, 44 each indicate whether the left or right hand should be positioned in the measuring area 81. For example, a 4+4+2 principle could also be used, in which four fingers of the left hand are first detected, then four fingers of the right hand, and finally the thumbs. Thus, it would be conceivable for hologram 44 to be activated first to signal to the user that the four fingers of the left hand should be positioned in the measuring area 81; when the four fingers of the left hand have been successfully imaged, hologram 43 can be activated to signal to the user that the four fingers of the right hand should be positioned in the measuring area 81.Once the four fingers of the right hand have been successfully imaged, the hologram 42 can be activated to signal the user that both thumbs should be positioned in the measurement area 81. Generally speaking, holograms can be displayed dynamically and / or statically.

[0056] The example in FIG. 2 illustrates only one possible implementation for the semantic content of the holograms used for the positioning aid, and other variants are conceivable. For example, the relative positioning—for example, a tilt or a distance—of the area of ​​the user's hand to be measured in relation to the measurement area 81 could be indicated using a hologram. For example, color feedback or even spatial feedback—by activating a hologram that is suitably arranged in space in accordance with the relative positioning—could be provided.

[0057] FIG. 3 is a flowchart of an exemplary method. The method of

[0058] FIG. 3 is computer-implemented. The method of FIG. 3 can be executed by a processor when it executes program code loaded from memory. For example, the method of FIG. 3 can be executed by a data processing device configured to control a contactless finger scanner and a holographic display device. For example, the method of FIG. 3 can be executed by data processing device 85.

[0059] In box 3005, the contactless finger scanner is controlled (see finger scanner 90 in FIG. 1). The finger scanner can be controlled based on a predefined measurement protocol. The measurement protocol can comprise multiple stages. The different stages can be associated with different areas of the hand to be measured. This means that the user successively places, for example, different hands (left - right) or different fingers (e.g., index finger - middle finger - thumb) in the measurement area. Controlling the finger scanner can comprise switching a light on and off. Controlling the finger scanner can comprise checking the relative positioning of the respective area to the measurement area of ​​the finger scanner. Controlling the finger scanner can comprise capturing an image using a camera. Controlling the finger scanner can comprise activating ultrasonic actuators.

[0060] In box 3010, the holographic display device is controlled (see holographic display device 70 in FIG. 1). This may involve turning various one or more light sources on and off. One or more optical channels may be activated simultaneously or sequentially. The different channels may be associated with different light colors. The different optical channels may illuminate different holographic optical elements.

[0061] In particular, Box 3010 can be executed synchronously with Box 3005. This means that the holographic display device in Box 3010 is controlled in correlation with the control of the contactless finger scanner in Box 3005.

[0062] An exemplary implementation for such a synchronized and coupled control of the finger scanner on the one hand and the holographic display device on the other hand is illustrated in FIG. 4. FIG. 4 is a flow chart of an exemplary method. The method from FIG. 4 is computer-implemented. The method from FIG. 4 can be carried out by a processor when it executes program code that is loaded from a memory. For example, the method from FIG. 4 can be carried out by a data processing device that is set up to control a contactless finger scanner and a holographic display device. For example, the method from FIG. 4 can be carried out by the data processing device 85. The method from FIG. 4 can in particular implement the method from FIG. 3. The method from FIG.4 corresponds to the processing of a multi-stage measurement protocol for the sequential capture of images of several fingers of a user.

[0063] In box 3105, the system first checks whether another finger should be measured. This means that the measurement protocol checks whether it contains a further step for another finger.

[0064] If this is the case, a corresponding hologram for the current finger is activated in box 3110. For example, the respective hologram could be a pictogram highlighting the finger currently being measured.

[0065] Then, in box 3115, it is checked whether the finger to be measured is correctly positioned within the measurement range of the finger scanner. For this purpose, the relative positioning between the finger to be measured and the measurement range is determined. The relative positioning can comprise one or more of the following variables: distance between the finger to be measured and a reference point of the measurement range; tilt of the finger to be measured relative to a reference direction of the measurement range; etc. The technique used to determine the relative positioning is not essential for the techniques described herein. For example, a sensor measurement value (see FIG. 1: sensor 86) could be used. Alternatively or additionally, an optical image of the finger scanner could also be evaluated, for example, using an object recognition algorithm that operates on a corresponding measurement image.

[0066] If it is determined in box 3115 that the positioning is incorrect, box 3120 is then executed. In box 3120, a hologram-based positioning aid is activated. For example, a specific hologram could be activated that at least partially surrounds the measurement area (see FIG. 2: hologram 41). Alternatively or additionally, the brightness of one or more holograms could be adjusted so that, for example, a specific color impression provides optical feedback regarding the relative positioning.

[0067] For example, in connection with Box 3120, the distance between the finger to be measured and the measurement area could be taken into account. Alternatively or additionally, whether the finger is tilted or correctly oriented could also be considered.

[0068] If it is determined in box 3115 that the finger to be measured is correctly positioned within the measurement range of the finger scanner, an image of the measurement range in which the respective finger is located is captured in box 3125 (see FIG. 1: camera 92). A corresponding measurement image is obtained. From this, the fingerprint can be extracted.

[0069] In a next iteration 3130, the next stage of the measurement protocol can then be carried out if necessary.

[0070] Depending on iteration 3130, different holograms can be activated in box 3110. This means that, depending on the progress of the measurement protocol, different holograms can be activated and / or holograms with different brightness can be generated. This allows for continuous user guidance during the implementation of the measurement protocol.

[0071] Aspects related to the functionality of finger scanning and the corresponding positioning aid were discussed above. The positioning aid is enabled by a holographic display device. Aspects related to the holographic display device are described below.

[0072] FIG. 5 shows a possible embodiment of the holographic display device 70. In FIG. 5, the holographic display device 70 is designed in a so-called "edge-lit" geometry. For this purpose, an optical block 73 (e.g., made of glass or transparent plastic) is provided, on whose upper side 75 a holographic optical element 74 is arranged. There, the refractive index is modulated as a function of position. The holographic optical element 74 is illuminated from the side. For this purpose, a light source 111 is provided, which emits its light onto a deflection element 120. The deflection element 120 reflects the light towards a side surface 76 of the optical block 73 (the deflection element 120 can provide further optical functionality, e.g., collimation of the light; for this purpose, the deflection element 120 itself can be designed as a holographic optical element).The light is coupled into the optical block 73 at the side surface 76 and then illuminates the holographic optical element 74, so that the floating hologram 71 is generated in transmission geometry at a distance (double file) from the surface 75. Details of the edge illumination geometry are described in WO 2022 / 238109 A1, the corresponding disclosure of which is incorporated herein by reference. Such a geometry can also be used for a reflection hologram.

[0073] FIG. 5 is only one of several possible variants. Further variants are conceivable. For example, in FIG. 5, the holographic-optical element is illuminated in transmission geometry. However, illumination in reflection geometry (as indicated, for example, in FIG. 1) would also be conceivable.

[0074] Another variation concerns the edge illumination geometry. Alternatively, a so-called waveguide geometry would also be conceivable, in which the light beam is guided within the optical block by means of total resection. A corresponding variant is illustrated in FIG. 6.

[0075] In FIG. 6, the optical block 73 forms a waveguide, so that within the block 73, the light is reflected multiple times below the holographic-optical element 74 (this characterizes the "waveguide geometry"; see also DE 10 2021 207 574 A1: FIG. 12 and FIG. 13 - there, the waveguide is referred to as a "light guide" - the disclosure content of which is incorporated herein by cross-reference). Several light sources 211 and a collimation optic 220 are provided. Then, a coupling surface 221 of a side part of the optical block 73 is illuminated. A reflector 222 is provided on an inner surface of the side part, which deflects the incident light to the holographic-optical element 74. Such an implementation in waveguide geometry is described in detail in WO2022 / 229257 A2, the corresponding disclosure content of which is incorporated herein by reference. While in the examples of Figs. 5 and 6, the respective light source 111 orthe light sources 211 are arranged below the optical block 73, this represents only one possible arrangement. The light sources 211 can also be arranged offset from the optical block 73, so that the beam paths for illuminating and imaging the measuring area 81, as used by the contactless finger scanner (cf. FIG. 1: beam paths 95, 96), are not obstructed by the light source or light sources.

[0076] FIG. 5 and FIG. 6 each show how the beam paths 95 and 96 pass through the holographic optical element 74.

[0077] In particular, by using light in a first spectral range for the finger scanner and light in a different, particularly disjoint, second spectral range for the holographic display device, interaction between the light used for the finger scanner and the holographic optical element 74 can be avoided. For example, the finger scanner can use visible light in the blue spectral range, while the holographic display device uses visible light outside the blue spectral range. In this way, interactions between the holographic display device and the finger scanner can be reduced.

[0078] FIGS. 5 and 6 each show a single optical channel for generating the respective hologram 71. However, in some examples, the holographic display device 70 could have more than a single optical channel. For example, multiple holograms could be generated, each associated with a corresponding optical channel. The optical channels can be configured for light of different wavelengths.

[0079] An example of such an arrangement of optical channels is shown in FIG. 7. Two optical channels 301, 302 with corresponding light sources 311-1, 311-2 and corresponding deflection elements 320-1, 320-2 (which may also be diffractive) are shown there. A holographic optical element 74 in edge-illuminated geometry is illuminated from opposite sides to generate a hologram (not shown in FIG. 7) in transmission (although a reflection geometry would also be possible; the details of the transmission or reflection geometry are described in DE 10 2021 207 574 A1: FIG. 11, the disclosure content of which is incorporated herein by cross-reference). This means that the central axes 321, 322 (thick dashed lines) of the beam paths of the two optical channels 301, 302 lie in the same plane (the plane of the drawing) (ie are positioned at an azimuth angle offset of 180° to each other).However, it is also conceivable for the central axes of the beam paths of the two optical channels to lie in planes that enclose an angle with one another. For example, FIG. 8 shows a scenario for the two optical channels 401, 402 with associated light sources 411-1, 411-2, in which the central axes 431, 432 (thick dashed lines) of the respective beam paths lie in planes oriented orthogonally to one another (azimuth angle offset of 90°). In both FIG. 7 and FIG. 8, the beam paths of the optical channels 301, 302, 401, 402 only overlap in the area of ​​the holographic-optical element 74. In addition, the beam paths each enter the optical block 73 at different side surfaces. In FIG. 9 shows a variant in which the beam paths of the optical channels 501, 502 overlap or cross before the holographic-optical element 74.As a result, both beam paths of the optical channels 501, 502 can be coupled into the optical block 73 via the same side surface 76.

[0080] The use of multiple optical channels, as described above, enables the reconstruction of multiple superimposed holograms. This allows, for example, color mixtures to be created by adjusting the relative brightness of two superimposed holograms corresponding to optical channels of different colors.

[0081] In summary, techniques were described above for enabling positioning assistance for a contactless finger scanner using one or more holograms. When using three or more optical channels, in addition to a positioning pictogram (which at least partially delimits the measurement area; see hologram 41 in FIG. 2), additional pictograms can be selectively or optionally displayed using the holograms, provided individual fingers are not located within the measurement volume. These can represent individual instructions, such as "correcting incorrect finger spacing" or "correcting incorrect hand rotation." The various holograms can also have a different hovering height (particularly in-plane) to ensure good reconstruction quality. Furthermore, the switchable pictograms could be used to accompany the recording process. This means:The holograms can be adjusted depending on the progress of the measurement protocol. For example, a first symbol can be displayed to represent the action "recording the fingers of the left hand." A second symbol would represent the action "recording the fingers of the right hand." A third symbol would represent the action "recording the thumbs."

[0082] Of course, the features of the previously described embodiments and aspects of the invention can be combined with one another. In particular, the features can be used not only in the described combinations, but also in other combinations or on their own, without departing from the scope of the invention.

[0083] For example, techniques were described above in which a holographic optical element is illuminated to reconstruct a hologram using an optical block. In this way, the holographic optical element can be illuminated using edge-illumination geometry or waveguide geometry. However, free-beam geometries are also conceivable, in which no optical block is used to illuminate the holographic optical element. Here, illumination can be implemented using reflection geometry or transmission geometry, or even as a z-hologram. The light source can be arranged to the side of the measuring area so that there is no interference with the beam paths of the finger scanner (for illumination and image capture). For example, the light source could be integrated into a frame structure for rough positioning of the hand in the measuring area, or arranged below the camera of the finger scanner.

[0084] Furthermore, various aspects related to the structural implementation of the holographic display device, and in particular the arrangement of multiple optical channels in an edge-illuminated geometry, were illustrated above (see FIG. 7, FIG. 8, and FIG. 9). A corresponding arrangement of the optical channels can be used not only in edge-illuminated geometry, but also in waveguide geometry. Furthermore, corresponding techniques for arranging the various optical channels can be used not only for an application for displaying holograms as a positioning aid for a finger scanner, but also in other applications.

Claims

PATENT CLAIMS 1 . System (80) comprising: - a contactless finger scanner (90) configured to capture an optical image of a measurement area (81) in which an area of ​​a user's hand can be positioned, and - a holographic display device (70) configured to generate at least one floating hologram (41, 42, 43, 44, 71) positioned in or near the measuring area (81) so as to assist in positioning the area of ​​the user's hand in the measuring area (81).

2. System (80) according to claim 1, further comprising: - a data processing unit (85) configured to determine a relative positioning of the user's hand with respect to the measuring area (81) based on at least one sensor signal or the optical image of the contactless finger scanner (90), wherein the data processing unit (85) is further configured to control the holographic display device (70) based on the relative positioning.

3. System (80) according to claim 2, wherein the at least one floating hologram (41, 42, 43, 44, 71) comprises a plurality of floating holograms (41, 42, 43, 44, 71), wherein the data processing unit (85) is further configured to control the holographic display device (70) such that, depending on the relative positioning, different holograms (41, 42, 43, 44, 71) of the plurality of floating holograms (41, 42, 43, 44, 71) are activated.

4. System (80) according to claim 2 or 3, wherein the data processing unit (85) is further configured to control the holographic display device (70) such that Relative positioning that at least one hologram (41, 42, 43, 44, 71) with different brightness is generated.

5. System (80) according to one of the preceding claims, wherein the at least one floating hologram (41, 42, 43, 44, 71) comprises a plurality of floating holograms (41, 42, 43, 44, 71), the system (80) further comprising: - a data processing unit (85) configured to control the holographic display device (70) such that different ones of the plurality of floating holograms (41, 42, 43, 44, 71) are activated depending on the progress of a measurement protocol for sequentially capturing different areas of the hand.

6. System (80) according to one of the preceding claims, wherein the at least one floating hologram comprises a plurality of floating holograms arranged superimposed on one another.

7. System (80) according to one of the preceding claims, wherein the holographic display device (70) is arranged to generate a plurality of holograms (41, 42, 43, 44, 71) by means of a plurality of optical channels (301, 302, 401, 402, 501, 502).

8. System (80) according to claim 7, wherein the plurality of optical channels (301, 302, 401, 402, 501, 502) each comprise a beam path, wherein the beam paths of the plurality of optical channels (301, 302, 401, 402, 501, 502) are arranged at least partially overlapping or intersecting in front of a holographic-optical element (74) for reconstructing the plurality of holograms (41, 42, 43, 44, 71).

9. System according to claim 7, wherein central axes of beam paths of the plurality of optical channels (301, 302, 401, 402, 501, 502) lie in one plane or lie in two planes which enclose an angle of 90° with one another.

10. System (80) according to one of the preceding claims, wherein the holographic display device (70) comprises one or more holographic-optical elements (74) which are configured to reconstruct the at least one floating hologram (41, 42, 43, 44, 71), wherein the contactless finger scanner (90) comprises a light source (91) which is configured to emit light towards the measuring area (81) along an illumination beam path (95), wherein the illumination beam path (95) passes through at least one of the one or more holographic-optical elements (74).

11. System (80) according to one of the preceding claims, wherein the holographic display device (70) comprises one or more holographic-optical elements (74) configured to reconstruct the at least one floating hologram (41, 42, 43, 44, 71), wherein the contactless finger scanner (90) comprises a camera (92) configured to detect light emanating from the measuring area (81) along a measuring beam path (96), wherein the measuring beam path (96) passes through at least one of the one or more holographic-optical elements (74).

12. System (80) according to one of the preceding claims, wherein the holographic display device (70) is arranged to generate the at least one floating hologram (41, 42, 43, 44, 71) with light in a first wavelength range, wherein the contactless finger scanner (90) is configured to generate the optical image with light in a second wavelength range, wherein the first wavelength range and the second wavelength range are different from one another.

13. The system (80) of claim 12, wherein the first wavelength range comprises visible light except in the blue spectral range, wherein the second wavelength range comprises visible light in the blue spectral range.

14. System (80) according to one of the preceding claims, wherein the at least one hologram (41, 42, 43, 44, 71) has a semantic content selected from the following group: indication of a region of the hand to be positioned in the measuring region (81); indication of an offset of the region of the user's hand with respect to the measuring region (81); indication of a limitation of the measuring region (81).

15. System (80) according to one of the preceding claims, wherein the holographic display device (70) comprises at least one respective holographic optical element (74) for each of the at least one floating hologram (41, 42, 43, 44, 71), wherein the holographic optical elements (84) of the holographic display device (70) are illuminated in edge-illumination geometry or in waveguide geometry.

16. System (80) according to one of the preceding claims, wherein the holographic display device (70) comprises at least one respective holographic optical element (75) for each of the at least one floating hologram (41, 42, 43, 44, 71), wherein the holographic-optical elements (75) are illuminated in transmission geometry or in reflection geometry.

17. A method for use in a data processing unit (85) of a system (80) according to any one of the preceding claims, the method comprising: - controlling (3005) the contactless finger scanner (90) to implement a measurement protocol for sequentially detecting different areas of the hand, and - controlling (3010) a holographic display device (70) to activate the at least one floating hologram (41, 42, 43, 44, 71) selectively and / or with variable brightness based on the measurement protocol.

18. The method according to claim 17, wherein the holographic display device (70) is controlled such that continuous user guidance is provided to the user during the implementation of the predefined measurement protocol.

19. The method according to claim 17 or 18, wherein the holographic display device (70) is controlled based on a relative positioning of the area of ​​the user's hand with respect to the measuring area.

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