DEVICE FOR BIOMETRIC IDENTIFICATION WITH THE AID OF FINGERPRINTS AND/OR HAND CHARACTERISTICS, AND METHOD OF BIOMETRIC IDENTIFICATION WITH THE AID OF THESE CHARACTERISTICS

Abstract

The invention relates to a device for biometric identification with the aid of fingerprints and/or hand characteristics, the device comprising a sensor unit (1) directed at the region of an optical gate (2) in a scanning direction (S), wherein the optical gate (2) is adapted to initialize the sensor unit (1) for scanning an in-focus scan image or scan images of the fingers and/or hand of a person, wherein the device further comprises at least one light source (5), which is likewise directed at the region of the optical gate (2), wherein the sensor unit (1), the optical gate (2) and optionally also the light source (5) are coupled to a control and computing module (6) with software for controlling the device and its parts and for scanning a scan image or the scan images of fingers and/or a hand, and for evaluating the fingerprints and/or hand characteristics, wherein the sensor unit (1) is fixedly set to focus into a focal volume (3) which is assigned to the optical gate (2), and the sensor unit (1), the optical gate (2), the control and computing module (6) and optionally also the light source (5) are configured to scan a single in-focus scan image of the fingers and/or the hand at the time of the passage thereof through the focal volume (3).

Claims

1.-12. (canceled)

13. A device for biometric identification using at least one of fingerprints and hand characteristics, the device having a sensor unit which is directed in a scanning direction into the area of an optical gate, the optical gate adapted for initializing the sensor unit for scanning at least one sharp scan image of at least one of a person's fingers and hand, the device further comprising at least one light source also directed into the area of the optical gate, wherein the sensor unit and the optical gate are coupled with a control and computing module having software for controlling the device and its parts and for scanning at least one scanned image of the at least one of the fingers and the hand and for evaluating the at least one of the fingerprints and hand characteristics, wherein the sensor unit is focused fixedly on a focus space that is assigned to the optical gate; and the sensor unit, the optical gate, the control and computing module and optionally also the light source are configured for scanning a single sharp scan image of the one of the fingers and the hand at the time of their passage through the focus space.

14. The device according to claim 13, wherein the light source is also coupled with the control and computing module.

15. The device according to claim 13, wherein the optical gate has at least one of an IR, a near IR, a visible laser and a LED radiation source which is directed transverse to the scanning direction of the sensor unit onto a photodiode which is arranged on an opposite side of the optical gate.

16. The device according to claim 13, wherein the optical gate has a proximity sensor.

17. The device according to claim 13, wherein the optical gate has a 3D camera which is adapted to detect the speed of the hand movement in the area to be scanned relative to the focus space and is adapted to determine the hand position in the area to be scanned relative to the focus space by a method of active triangulation.

18. The device according to claims 13, wherein the light source is a light source in the green part of the spectrum.

19. The device according to claim 13, wherein in addition to the light source at least one NIR radiation source with a wavelength of 760 to 840 nm is directed into in the focus space, capable of penetrating melanin and at the same time being absorbed by hemoglobin for detection of hand liveness during biometric identification.

20. The device according to claim 19, wherein an auxiliary scanning camera is directed into the focus space, the auxiliary camera being sensitive in at least one of the NIR or IR radiation range and adapted for scanning one of a scanned image and a scanned image sequence for detecting the liveliness of the hand in the focus space.

21. The device according to claim 13, wherein at least one light source of a visible radiation, at least one UV radiation source and at least one of an IR Radiation source and a near IR radiation source are directed into the focus space for simultaneous biometric identification using the at least one of fingerprints and hand characteristics and for determination of the liveliness of the hand.

22. The device according to claim 13, wherein at least one heat-sensitive sensor for detecting the liveness of the hand during the biometric identification is directed into the focus space.

23. The device according to claim 13, wherein the sensor unit has a maximized aperture number in relation to the illumination of the focus space and the diffraction limit, a target focus space begins in a position of the optical gate in relation to the sensor unit, which position is shifted in the scanning direction towards the sensor unit by a value, wherein the target focus space ends in a position of the optical gate in relation to the sensor unit, which position is shifted in the scanning direction towards the sensor unit by another value.

24. The device according to claim 13, wherein the device is formed in a cranked manner, the device having a vertical stand which is open at its upper side and in which in the direction pointing upwards a sensor unit with its optics is arranged, wherein in the vertical stand a control and computing module, one of a supply source and a supply adapter, and other electronics are also arranged, wherein a reflection unit having an inclined reflection surface and an entry window for entry of the scanned image of the hand to be scanned into the reflection unit and further into the sensor unit via the inclined reflection surface is arranged in the open upper side of the vertical stand, wherein an additional camera for scanning at least one of a depth and a discontinuous movement, and an auxiliary scanning camera for detecting the liveness are arranged in the reflection unit, wherein a control and guidance display is further arranged on the reflection unit.

25. A method for biometric identification using at least one of fingerprints and hand characteristics using the device according to claim 13, wherein a sharp scan image of the hand is scanned with the sensor unit, the scan image being sent as scanned image data to the control and computing module, in which a scan image analysis is carried out, whereby hand contours are searched and the areas of occurrence of biometric data are detected, which are then analyzed and processed for the identification of at least one of the fingerprints and the hand characteristics and then compared with a database of at least one of existing fingerprints and existing hand characteristics, wherein only a single sharp scan image of the hand is scanned and processed for biometric identification using the at least one of the fingerprints and hand characteristics.

Description

[0031] Exemplary embodiments of the invention are explained in more detail below with reference to drawings.

[0032] FIG. 1 is a schematic view of a device for biometric identification (and/or verification) using fingerprints and/or hand characteristics with an optical barrier,

[0033] FIG. 2 is a schematic view of a device for biometric identification (and/or verification) using fingerprints and/or hand characteristics with a proximity sensor,

[0034] FIG. 3 is a schematic view of a cranked arrangement of a device for biometric identification (and/or verification) using fingerprints and/or hand characteristics,

[0035] FIG. 4 is a schematic view of another example of a cranked arrangement of a device for biometric identification (and/or verification) using fingerprints and/or hand characteristics,

[0036] FIG. 5 is a schematic view of a line arrangement of a device for biometric identification (and/or verification) using fingerprints and/or hand characteristics,

[0037] FIG. 6 a schematic view of a possible specific implementation of a device for biometric identification (and/or verification) using fingerprints and/or hand characteristics, and

[0038] FIG. 7 a schematic view of an exemplary embodiment of a device for biometric identification (and/or verification) using fingerprints and/or hand characteristics with compensation for delay of a camera system.

[0039] Corresponding parts are given the same reference numerals throughout the drawings.

[0040] Exemplary embodiments of the device for biometric identification using fingerprints and/or hand characteristics and of a method using the device are described below.

[0041] FIG. 1 is a schematic view of a device for biometric identification (and/or verification) using fingerprints and/or hand characteristics with an optical gate 2 forming a switching device in the form of an optical barrier.

[0042] The device for biometric identification (and/or verification) using fingerprints and/or hand characteristics has a sensor unit 1 which, for example, is a monochromatic camera with a resolution of a CCD or CMOS scan chip in the range of 10 MP to 25 MP, preferably with a resolution of the CCD or CMOS scan chip from 12 MP to 20 MP. The value of the resolution of the CCD or CMOS scan chip of the sensor unit 1 influences the size of the area to be scanned, so it influences the size of the area in space in which the hand to be scanned may be located, so that contactless scanning of the scan image of the hand with fingers reliably occurs. A surface resolution of the sensor unit 1 is, for example, in the range from 400 to 1000 DPI, preferably 500 DPI. In the specific case of the exemplary embodiment, a camera is used as sensor unit 1 (e.g. Basler ace acA4024-29um, Basler ace acA5472-17um, another camera without an IR filter or another camera without an IR filter and with a higher sensitivity of the scan image recording in the IR range). In another exemplary embodiment, which is not shown, the sensor unit 1 is designed as a color camera with suitable optical properties and light properties for scanning a scan image.

[0043] The sensor unit 1 may be directed with its CCD or CMOS scan chip in a scanning direction S toward an optical gate 2 and toward a focus space 3 of the sensor unit 1, the optical gate 2 being adapted to initialize the sensor unit 1 for scanning a sharp scan image, in particular a single sharp scan image, of the object, which is located in the focus space 3 of the sensor unit 1. The focus space 3 of the sensor unit 1 is a three-dimensional space in front of the sensor unit 1, on which the sensor unit 1 is fixedly focused, and in which the sensor unit 1 always scans a sharp scan image of the object that is located somewhere in the focus space 3. In particular, the sensor unit 1 may have suitable optics 10, which are adapted for focusing the sensor unit 1, in particular for fixedly focusing the sensor unit 1, into the focus space 3.

[0044] In the exemplary embodiment from FIG. 1, the optical gate 2 has a radiation source 20, in particular an IR or “near IR” radiation source or a laser or LED radiation source 20 radiating in a visible range of the spectrum, which, for example, transversely to the scanning direction S of the sensor unit 1, is directed to a photodiode 21, which is placed on an opposite side of the optical gate 2. The optical gate 2 may include operational amplifiers, not shown, which amplify and monitor the voltage across the photodiode 21 on which the laser and/or LED beam is incident, and by momentarily interrupting this laser and/or LED beam the hand to be scanned occludes the photodiode 21 of the optical gate 2 and the voltage drop across it changes, for example on the basis of a switching transistor (not shown), which then leads to the initialization of the sensor unit 1 and the scanning of one or more sharp scan images, in particular a single sharp scan image, of the focus area 3 with the hand to be scanned.

[0045] FIG. 2 is a schematic view of an embodiment of the device for biometric identification (and/or verification) using fingerprints and/or hand characteristics with a proximity sensor 22.

[0046] In the exemplary embodiment from FIG. 2, the optical gate 2 has a proximity sensor 22, in particular a so-called proximity sensor, which, in contrast to the IR or “near IR” or visible laser and/or LED beam from FIG. 1 does not require interruption of the IR laser beam by the hand passage between the laser and/or LED source 20 and the photodiode 21 and therefore does not require any special design of the body of the optical gate 2 either. The proximity sensor 22 has one to three sources of modulated light radiation, not shown here, which are directed into the area of an expected appearance of the hand in relation to the focus space 3 and which emit one to three modulated light beams, the proximity sensor 22 also having a detector for a reflection of the modulated light beams from a hand or palm that approaches or is in the focus space 3. Electronics (not shown) of the proximity sensor 22 are used to determine the appearance of the hand in the focus area 3, which, for example, uses a method of trilateration (time of flight) based on the modulated light beams from the named sources of the modulated radiation and based on the reflection of these modulated light beams by the hand in the space of the expected appearance of the hand, after which a point in time may be determined by extrapolation at which the hand is actually in the scanning position in the focus space 3. At this point in time, the sensor unit 1 is initialized and a sharp scan image, in particular a single sharp scan image, of the focus area 3 with the hand to be scanned is scanned.

[0047] In an exemplary embodiment that is not shown, the optical gate 2 may be replaced or supplemented by a 3D camera adapted to detect the speed of the hand movement in the area to be scanned and to determine the hand position in the area to be scanned using an active triangulation method. Alternatively or additionally, the scanned room data may be used for additional biometric identification (and/or verification) based on the 2D and/or 3D hand geometry.

[0048] In an exemplary embodiment that is not shown, the optical gate 2 has a combination of a light barrier as in FIG. 1 (with a radiation source 20, which is directed transversely to the scanning direction S of the sensor unit 1 toward the photodiode 21, which is mounted on an opposite side of the optical gate 2) and a proximity sensor 22 as in FIG. 2, whereby this combination is supplemented by a 3D camera according to the further embodiment not shown, which is adapted to detect the speed of the hand movement in the area to be scanned in relation to the focus space 3 and to determine the hand position in the area to be scanned relative to the focus space 3 with the method of active triangulation.

[0049] At least one light source 5 may also be directed into the focus space 3, which light source is adapted to illuminate the hand in the focus space 3 for scanning a high-quality, sharp scan image of the hand by the sensor unit 1. The light source 5 is designed, for example, to emit the light in the “green” range of the spectrum, preferably with a dominant wavelength of 520 to 530 nm.

[0050] In order to facilitate to also detect a liveliness of the hand during the detection of biometric and/or dactyloscopic data, in an exemplary embodiment that is not shown, at least one, but preferably more than one, NIR radiation source with a wavelength from 760 to 840 nm, capable of penetrating melanin and being absorbed by haemoglobin, may be directed into the focus space 3. Since the CMOS and CCD standard scan chips are also sensitive in the range of NIR and IR radiation, it is possible to use the same device, the same method and the same scan image of the hand to detect a bloodstream in a hand, i.e. for the liveliness detection, which was scanned with a simultaneously activated light source 5 and NIR radiation source, both for dactyloscopic analysis and for detection of the liveliness of the hand to be scanned and/or the fingers to be scanned. This may advantageously be used in the evaluation, on the one hand, for detecting counterfeits of the hand and/or the fingers and, on the other hand, for biometric identification based on the shape of the bloodstream of the hand to be scanned. To improve the detection of the liveliness of the hand, an auxiliary scanning camera may be directed into the focus space 3 in an embodiment that is not shown, which is sensitive in the NIR or IR radiation range and is able to scan not only individual scan images, but also sequences of scan images to scan for better detection of the liveliness of the hand.

[0051] In a further exemplary embodiment, which is not shown, at least one light source 5 of visible radiation, and at least one UV radiation source (UV) and at least one IR or “near IR” radiation source (IR) are directed into the focus space 3 at the same time, wherein a single scanned image of the hand scanned by the sensor unit 1 or a single scanned image of the hand scanned by the sensor unit 1 and a sequence of scanned images scanned with an auxiliary scanning camera are evaluated from the point of view of the absorption properties of the material to be scanned for all types of radiation used with different wavelengths, from which is then determined whether it is the skin of a living user or not.

[0052] In a further exemplary embodiment, which is not shown, at least one bolometric sensor (i.e. a heat-sensitive sensor which, e.g. having an array of bolometers) which enables the acquisition of a baseline thermal scan image of the hand with a thermal distribution of the palm surface is directed into the focus space 3 at the same time.

[0053] Due to the heat distribution, the liveness of the presented hand may be detected.

[0054] A reliable scanning of a high-quality sharp scan image, in particular a single high-quality sharp scan image, of the hand by the device disclosed here and the method disclosed here is given by the fact that a narrow band of the depth of focus of the sensor unit 1, i.e. small depth A of the focus space 3, in combination with precise determination of the position of the hand, is used to obtain a high-quality sharp scan image, which is intended for subsequent processing. The scanning position, i.e. the position of the focus space 3 in the scanning direction S in relation to the sensor unit 1, and the scanning time of the hand by the sensor unit 1 are given by a large number of parameters of the sensor unit 1 and the illumination system of the hand, i.e. at least one light source 5. The scanning time of the hand by the sensor unit 1 represents the smallest possible (minimum) time interval during which the forward movement of the hand through the focus space 3, even despite a non-negligible speed of this movement, does not cause any distortion of the scan image of the hand scanned by the sensor unit 1 from front, and during which the perpendicular (transverse) movement of the hand is at the same time negligible.

[0055] With regard to the changing position of the hand during its scanning when moving through the focus space 3, it is therefore necessary to maximize the depth A of the focus space 3 in which the sensor unit 1 operates (scans) with maximum focus. This maximization of the depth A of the focus space 3 is achieved by maximizing a aperture number of the sensor unit 1 in combination with the pixel size of the CCD or CMOS scan chip and in a combination with an increase in the scan width, i.e. a width between the sensor unit 1 and the focus space 3. A maximization of the aperture number of the sensor unit 1 is achieved for example by reducing the diameter of an entrance lens, not shown, of the sensor unit 1 using an aperture.

[0056] In view of the fact that the requirements for the pixel size of the CCD or CMOS scan chip and the increase in the scan width are usually limited by the requirements for the practical design and price of the resulting device, one of the most effective ways is precisely to maximize the aperture number of the sensor unit 1, which is essentially limited by the lighting requirements of the focus area 3 and the diffraction limit.

[0057] In an exemplary embodiment of the device, the scan width is 1 m, the sensor unit 1 has the pixel size of the CMOS scan chip 1.85 μm×1.85 um, aperture f/5.6, shutter speed 546 us, the light source 5 has a luminous flux of 9120 lm of diffuse light with a suitable wavelength and a depth of focus of −4 cm (i.e. dimension A of the focus space 3) is obtained.

[0058] The scanning position of the hand is therefore given by the focus space 3, which may be determined as follows: The target focus space 3 in relation to the sensor unit 1 begins in a position P.sub.m (distance of the optical gate 2 to the sensor unit 1) of the optical gate 2, which is shifted in the scanning direction S towards the sensor unit 1 by the value σ, i.e. P.sub.m+σ, where σ is an empirically determined (considered) delay between the hand presence and the start of scanning by the sensor unit 1 (or a displacement of the hand to be expected during this empirically determined delay). At the same time, it is true that the target focus space 3 ends in the position P.sub.m of the optical gate 2 relative to the sensor unit 1, which is shifted in the scanning direction S towards the sensor unit 1 by the value D.sub.of, i.e. P.sub.m+D.sub.of, where:

D.sub.of=D.sub.f−D.sub.n,

[0059] where

[00001]$D_n=\frac{s\left(H-f\right)}{H+s-2f}$$D_f=\frac{s\left(H-f\right)}{H-s}$$H=\frac{f^2}{Nc}+f$

[0060] with:

[0061] H—hyperfocal width [mm],

[0062] f—focal width of the lens [mm],

[0063] s—distance between the sensor unit 1 and the object to be scanned (hand),

[0064] D.sub.n—shortest distance to the focus area,

[0065] D.sub.f—largest width in the focus area,

[0066] N—aperture number (fl diameter of the entrance aperture),

[0067] c—diameter of the circle of confusion (CoC) which is proportional to the pixel size of the chosen CCD or CMOS scan chip.

[0068] Optimizing the arrangement of the device and the process based on said mathematical model makes it possible to choose a sensor unit 1 and arrangement of the device that is capable of collecting useful biometric and/or dactyloscopic data within the limits of the depth of field once, i.e. in the form of a single scan image without computationally expensive and time-consuming reconstructions of the scanned data after the end of the scanning, as is the case in the prior art.

[0069] The device also has a control and computing module 6 for scan image processing and control of individual peripherals, which is here, for example, a computer of the miniPC category, e.g. a computer UP Squared, thanks to which very low requirements or cooling and space are achieved, which allows to design the resulting device very small, with a low nominal electric power consumption and with a minimal acoustic impact on the environment.

[0070] FIG. 5 is a schematic view of an embodiment of the device for biometric identification (and/or verification) using fingerprints and/or hand characteristics in a linear arrangement.

[0071] From the point of view of the actual implementation of this presently disclosed device, a schematic of a line arrangement of the device is shown in FIG. 5, wherein the individual components oft he device are arranged consecutively in a line, which results in the formation of a device with a certain overall length but with a low height and small depth with regard to the required distance of the beginning and end D.sub.n, D.sub.f of the focus space 3 from the sensor unit 1.

[0072] FIGS. 3 and 4 are schematic views of embodiments of the device for biometric identification (and/or verification) using fingerprints and/or hand characteristics in a cranked configuration.

[0073] If the device cannot be used in the linear arrangement as in FIG. 5, e.g. for reasons of space at the installation site, there is the possibility of inserting a suitably tilted reflection surface 7 between the sensor unit 1 and the focusing space 3, which, while maintaining the target width of the beginning and end D.sub.n, D.sub.f of the focus space 3 results in the formation of a “cranked device” with the same total length of individual branches a, b of the distance of the beginning and end D.sub.n, D.sub.f of the focus space 3 from the sensor unit 1. Such a cranked device is for example shown in FIGS. 3 and 4, where the device has a substantially smaller overall length than in the embodiment according to FIG. 5 while maintaining the same distance of the beginning and end D.sub.n, D.sub.f of the focus space 3 from the sensor unit 1. In contrast to this, however, such a cranked device has a greater height and/or width, depending on the plane or planes in which the scanning direction S is cranked. In an exemplary embodiment that is not shown, the scanning direction S is cranked more than once other than in FIGS. 3 and 4, allowing fort he formation of an even more compact device, but increasing the requirements to the quality and precision of the of the reflection surfaces 7, due to the elimination of deformations of the reflected scan image of the hand and due to the elimination of the lowering of the light properties of the scan image to be scanned.

[0074] FIG. 6 is a schematic view of a possible specific implementation of a device for biometric identification (and/or verification) using fingerprints and/or hand characteristics.

[0075] In the embodiment of FIG. 6, the device is cranked as shown in FIG. 4. This device 8 has a vertical stand 80 which is open on its upper side and in which a sensor unit 1 with its optics 10 is arranged in the upward direction. Furthermore, a control and computing module 6, a power source or a power adapter and other electronics may be arranged in the vertical stand 80. In an open upper side of the vertical stand 80, a reflecting unit 81 having a slanted reflecting surface 7 and an entrance window 810 adapted for entry of the scan image of the hand to be scanned from the reflecting unit 81 and further via the slanted reflecting surface 7 into the sensor unit 1 is arranged. Optionally, an additional camera for scanning the depth and/or a discontinuous movement and possibly also an auxiliary scanning camera for detecting the liveliness based on the absorption properties of the material to be scanned for different types of radiation with different wavelengths (visible, UV and IR) and/or a bolometric sensor are arranged in the reflection unit 81. A display 82, for example a touch display, may be arranged on the reflection unit 81, which on the one hand may be adapted for primary user registration, and also for informing the user, e.g. about the course of personal identification, showing an animation visualizing the reason for a scanning failure (e.g. incorrect position of the hand), and also for operating personnel and a setting of the device, etc.

[0076] In the exemplary embodiment shown, a guide plate 83 is mounted on one side of the vertical stand 80 and/or the reflection unit 81, which is adapted to guide the person to be identified to move their hand in a respective plane, speed, etc. in relation to the entry window 810 of the reflection unit 81. In an embodiment that is not shown, the guide plate 83 is replaced by a display 82 with a guide animation that illustrates an operating manual for the device disclosed herein. The display 82 is placed at a suitable location on the device 8. The guide plate 83 may be placed either in the position shown, possibly in the upper part (lighting down) or in the lower part (lighting up).

[0077] The respective device may be operated with a method in which the sensor unit 1 is in a standby mode and expects a signal from the optical gate 2 about the appearance of a hand in the area of the optical gate 2. As soon as the hand appears in the area of the optical gate 2, this emits the said signal, which is the impulse for initiating the scanning of a sharp scan image, in particular a single sharp scan image, of the hand in the focus space 3 by the sensor unit 1. This scanned, sharp scan image is sent as scan image data to the control and computing module 6, e.g. formed by a miniPC The control and computing module 6 performs a scan image analysis of this, in particular single, scan image, searches for contours of the hand and fingers and detects the areas where biometric and/or dactyloscopic data occur for biometric identification (and/or also verification). The areas of occurrence of biometric and/or dactyloscopic data are then subsequently further analyzed and processed for identification and/or verification of fingerprints or hand characteristics, which are then compared to a database of stored fingerprints or hand characteristics. Thereafter, based on a match or non-match found, a decision is made on positive or negative biometric verification of the individual, or the identified identity of the individual is communicated.

[0078] FIG. 7 shows a schematic view of a further exemplary embodiment of a device 9 with a sensor unit 1 for biometric identification (and/or verification) using fingerprints and/or hand characteristics with compensation for a delay σ of a camera system.

[0079] The scanning position of the hand is given by the focus space 3 or detection space. The target focus space begins in a position P.sub.m−σ (distance of the optical gate 2 to the sensor unit 1, taking account of a delay σ of the sensor unit 1) and ends in a position P.sub.m+D.sub.of. The target field of focus is thus determined by a distance between the position P.sub.m−σ and the position P.sub.m+D.sub.of.

[0080] The position P.sub.m represents the distance from the sensor unit 1 to the optical gate 2.

[0081] Reference a represents an empirically observed delay σ of the sensor unit 1 or of a camera system when the hand is detected when it enters the focus space 3, which is or should be compensated (delay σ between the hand presence and the start of scanning by the sensor unit 1, in order to take account of a displacement of the hand to be expected during this empirically determined delay σ when determining the correct spacing or the correct distance).

[0082] When a hand enters focus area 3, a trigger occurs upon the first entry of the hand, specifically a finger or thumb of the hand.

[0083] Herein, in order to take account of the delay σ of the sensor unit 1, the position P.sub.m is shifted as the correct distance or as the correct spacing from the sensor unit 1 to the optical gate 2 by the delay σ of the sensor unit 1 according to the relation: P.sub.m−σ, and this value is considered as the correct distance or correct spacing.

REFERENCES

[0084] 1 sensor unit

[0085] 2 optical gate

[0086] 3 focus space

[0087] 5 light source

[0088] 7 reflection surface

[0089] 8 device

[0090] 9 device

[0091] 10 optics

[0092] 20 radiation source

[0093] 21 photodiode

[0094] 22 proximity sensor

[0095] 80 stand

[0096] 81 reflection unit

[0097] 82 display

[0098] 83 guiding plate

[0099] 810 entry window

[0100] a branch

[0101] b branch

[0102] A depth, dimension of the focus space

[0103] D.sub.n shortest width to the focus space

[0104] D.sub.of value

[0105] P.sub.m, P.sub.m+D.sub.of, P.sub.m−σ position

[0106] S scanning direction

[0107] σ delay of the sensor unit