JP2005010860A - Fingerprint authenticator, and method for detection of finger positioning on fingerprint sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect whether a finger is correctly positioned without using a special device. <P>SOLUTION: A fingerprint authenticator 10 comprises a fingerprint sensor 12 for detecting two-dimensional image signals indicating an irregular image of the surface of a target for detection positioned on a detection surface 14, a registered fingerprint storage part 21 for storing a registered fingerprint, and a matching part 22 for matching the two-dimensional image signals of the target for detection detected by the fingerprint sensor 12 with the registered fingerprint to authenticate the user having positioned the target for detection. The collating part 22 calculates absolute values of the two-dimensional image signals acquired from a given area in the detection surface 14, and integrates the absolute values in the given area. The collating part 22 generates a time-series signal of the integral value, and differentiates the time-series signal with respect to time to generate a differential signal. The fingerprint collation is executed when the waveform of the differential signal peaks at a plus crest. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention uses a fingerprint of a human finger, a fingerprint authentication device that authenticates a person if the person is a person and rejects if the person is a person (or substance) other than the person, The present invention relates to a finger placement detection method for a fingerprint sensor of a fingerprint authentication device.
[0002]
[Prior art]
2. Description of the Related Art There is a fingerprint authentication device that performs personal authentication by identifying a spiral pattern (fingerprint) formed on the surface of an inner portion on the tip side of a first joint of a human finger. The fingerprint authentication apparatus is provided with a fingerprint sensor, and the fingerprint is detected by the fingerprint sensor. As the fingerprint sensor, for example, a capacitance detection type fingerprint sensor that detects the fingerprint by sensing the capacitance of each point on the detection surface when the inner part of the tip of the finger is placed on the detection surface (for example, Patent Documents) 1), a pressure detection type fingerprint sensor that detects the fingerprint by sensing the pressure of each point on the detection surface when the inner portion of the finger tip is placed on the detection surface, or the inner portion of the finger tip There is a photodetection type fingerprint sensor that detects a fingerprint by sensing reflected light from each point on the detection surface when placed on the detection surface. The fingerprint authentication device authenticates the user by collating the fingerprint image detected by these sensors with a fingerprint image registered in advance.
[0003]
[Patent Document 1]
JP-A-11-197135
[0004]
[Problems to be solved by the invention]
By the way, the fingerprint authentication apparatus is always required to improve accuracy in order to bring the authenticity of the personal authentication closer to 100% because of the essential request of the function. That is, in the fingerprint authentication device, it is always required to improve the accuracy of authenticating the person's fingerprint and rejecting the person's fingerprint (or substance).
[0005]
Therefore, it is necessary for the fingerprint authentication apparatus to capture a fingerprint image in a stable state in which finger movement is not shaken as much as possible. In order to capture a fingerprint image in a stable state, for example, a separate sensor is provided to detect that a finger is placed on the fingerprint sensor (for example, Patent Document 1), or the subject himself / herself is pressed with a start button. It is necessary to control the capture timing.
[0006]
However, if the fingerprint authentication device is provided with a sensor or a start button for detecting that a finger is placed, the cost and the size are increased.
[0007]
The present invention has been proposed in view of such a situation, and a fingerprint authentication device and a fingerprint sensor capable of capturing a fingerprint image at an optimal timing without using a special member when performing fingerprint authentication. An object of the present invention is to provide a finger placement detection method for.
[0008]
[Means for Solving the Problems]
A fingerprint authentication apparatus according to the present invention includes a fingerprint sensor that detects a two-dimensional image signal that has a planar detection surface, and that shows a concavo-convex image of the surface of an object to be detected placed on the detection surface, and the fingerprint. Registered fingerprint storage means for storing fingerprint information for identifying each user, two-dimensional image signal of the detected object detected by the fingerprint sensor, and user fingerprint information stored in the registered fingerprint storage means Authentication means for authenticating the identity of the user who placed the object to be detected, and the authentication means calculates an absolute value of the two-dimensional image signal obtained from a predetermined area in the detection surface. The absolute value is integrated within the predetermined area, a time series signal of the integrated value is generated, the time series signal is differentiated in the time direction to generate a differential signal, and the fingerprint is based on the signal waveform of the differential signal. Sensor detection Detecting a timing at which the object to be detected is placed on a surface, performing the authentication of the user takes in the unevenness image of the surface of the object to be detected according to the above timing.
[0009]
In the fingerprint authentication device, the absolute value of the two-dimensional image signal obtained from the fingerprint sensor is integrated within a predetermined area, the time series signal of the integrated value is differentiated in the time direction, and a differential signal is generated. And detecting that the finger is placed on the fingerprint sensor. For example, in the above-described fingerprint authentication device, when the waveform of the differential signal changes from the state in which the finger is not placed on the fingerprint sensor to the peak shape on the positive side, it is determined that the finger is placed on the fingerprint sensor.
[0010]
A finger placement detection method for a fingerprint sensor according to the present invention includes a fingerprint sensor that detects a two-dimensional image signal that has a planar detection surface and indicates an uneven image of a surface of an object placed on the detection surface. The registered fingerprint storage means for storing the fingerprint information for specifying the fingerprint for each user, the two-dimensional image signal of the detected object detected by the fingerprint sensor, and the registered fingerprint storage means Detecting that a fingerprint of a finger is placed on a detection surface of the fingerprint sensor in a fingerprint authentication device comprising an authentication means for authenticating the identity of a user who placed the detected object by collating with the fingerprint information of the user A finger placement detection method for a fingerprint sensor, wherein an absolute value of the two-dimensional image signal obtained from a predetermined region in the detection surface is calculated, the absolute value is integrated in the predetermined region, and the integration is performed. The time series signal is generated, the time series signal is differentiated in the time direction to generate a differential signal, and the timing when the detected object is placed on the detection surface of the fingerprint sensor is detected based on the signal waveform of the differential signal. In accordance with the above timing, the surface of the object to be detected is captured to perform user authentication.
[0011]
In the finger placement detection method for the fingerprint sensor, the absolute value of the two-dimensional image signal obtained from the fingerprint sensor is integrated within a predetermined region, and the time series signal of the integrated value is differentiated in the time direction to generate a differential signal. Based on the differential signal, it is detected that the finger is placed on the fingerprint sensor. For example, in the finger placement detection method for the fingerprint sensor, the finger is placed on the fingerprint sensor when the waveform of the differential signal changes to a positive chevron from a state where the finger placement is not performed on the fingerprint sensor. Judge that
[0012]
DETAILED DESCRIPTION OF THE INVENTION
As an embodiment of the present invention, a fingerprint authentication device to which the present invention is applied will be described in detail with reference to the drawings.
(Appearance configuration)
FIG. 1 shows an external view of a fingerprint authentication device 10 according to an embodiment of the present invention.
[0013]
As shown in FIG. 1, the fingerprint authentication device 10 includes a fingerprint sensor 12 provided on a housing 11 so that a planar detection surface 14 is exposed, and a fingerprint authentication result (OK or NG) as an external device. And an interface terminal 13 for output.
[0014]
The fingerprint sensor 12 applied to the fingerprint authentication device 10 is a sensor that detects a concavo-convex pattern on the surface of a fingerprint of a finger placed on a detection surface 14 by a capacitance method. As shown in FIG. 2, the capacitive fingerprint sensor 12 includes a plurality of capacitors 15 arranged in a matrix in parallel to the detection surface 14 at a pitch sufficiently finer than the pitch of the fingerprint irregularities. Is provided. Each capacitor 15 serves as a sensing element of the fingerprint sensor 12. When each substance is close to the capacitor 15, the capacitance value changes according to the distance to the substance. Therefore, when the inner part on the tip side from the first joint of the finger is placed on the detection surface 14, the capacitance value of the capacitor 15 located in the opposite part changes according to the unevenness of the fingerprint of the finger.
[0015]
The fingerprint sensor 12 detects the capacitance values of the plurality of capacitors 15 arranged in a matrix by raster scanning on a plane in a zigzag manner, and detects a two-dimensional signal in which a two-dimensional position is associated with its level. Generate. This two-dimensional signal becomes a two-dimensional image signal indicating the uneven pattern of the fingerprint. The fingerprint sensor 12 outputs this two-dimensional image signal.
[0016]
Here, the capacitance detection type fingerprint sensor is described as an example, but if the fingerprint sensor 12 can detect a two-dimensional image corresponding to the pattern of the concave and convex portions of the fingerprint, the detection method is Any thing is acceptable. For example, a pressure detection type fingerprint sensor that detects the fingerprint by sensing the pressure at each point on the detection surface when the inner part of the finger tip is placed on the detection surface, or the inner part of the finger tip is placed on the detection surface A photodetection type fingerprint sensor that detects a fingerprint by sensing reflected light from each point on the detection surface at the time may be applied as the fingerprint sensor 12.
[0017]
(Internal structure)
Next, the internal configuration of the fingerprint authentication device 10 will be described. FIG. 3 shows an internal block diagram of the fingerprint authentication device 10.
[0018]
As shown in FIG. 3, the fingerprint authentication device 10 includes a fingerprint sensor 12, a registered fingerprint storage unit 21, a collation unit 22, and an output unit 23.
[0019]
The fingerprint sensor 12 detects a two-dimensional image signal indicating an uneven pattern of an object placed on the detection surface 14 and outputs it to the outside. The registered fingerprint storage unit 21 stores information (feature information) obtained by extracting only the two-dimensional image signal of the registered fingerprint of the user or the feature portion of the uneven image of the registered fingerprint. The collation unit 22 collates the two-dimensional image signal detected by the fingerprint sensor 12 with the registered two-dimensional image signal (or feature information), and authenticates the user who placed the finger on the detection surface 14. . The collation unit 13 outputs OK if the user is authenticated, and outputs NG if the user is not authenticated. The output unit 23 encrypts the OK / NG determination result output from the verification unit 22, converts the determination result into a format corresponding to the transmission interface, and is provided outside via the interface terminal 13. For example, the security device or the like is notified.
[0020]
When the fingerprint authentication device 10 having the above block configuration is specifically configured by hardware, the configuration shown in FIG. 4 is obtained.
[0021]
The fingerprint authentication device 10 includes a fingerprint sensor 12, a USB terminal 32 to which a USB interface cable is connected, a USB controller 33, a CPU 34, a program RAM or ROM 35, a flash memory 36, and a fingerprint verification LSI 37. ing. The USB controller 33, CPU 34, program RAM or ROM 35, flash memory 36, and fingerprint verification LSI 37 are connected to a data transfer bus 38, respectively.
[0022]
The USB controller 33 is a circuit that transfers data to and from an external device via the USB terminal 32 in accordance with the USB protocol. The USB controller 33 implements the function of the output unit 23 shown in FIG. The USB controller 33 is an interface circuit that transfers data to / from an external personal computer or security device according to the USB protocol, for example. Note that the fingerprint authentication apparatus 10 may transfer data with an external personal computer or the like using another interface such as RS232C instead of the USB interface.
[0023]
The CPU 34 is a circuit that controls the operation of the entire apparatus based on a program stored in the program RAM or ROM 35. For example, the CPU 34 controls the operation of the matching unit 22 shown in FIG.
[0024]
The flash memory 36 is a nonvolatile memory. The flash memory 36 realizes the function of the registered fingerprint storage unit 21 shown in FIG. 3, and stores a registered fingerprint image or its characteristic information.
[0025]
The fingerprint verification LSI 37 authenticates the fingerprint image detected by the fingerprint sensor 12 based on the registered fingerprint image (or feature information) stored in the flash memory 36. The fingerprint verification LSI 37 implements the function of the verification unit 22 shown in FIG.
[0026]
(Authentication operation)
Next, the operation of the fingerprint authentication device 10 will be described.
[0027]
The fingerprint authentication device 10 performs fingerprint registration as a precondition process for fingerprint authentication. The fingerprint authentication device 10 outputs an authentication result “OK” when the user who has registered the fingerprint performs the fingerprint authentication, and outputs an authentication result “NG” when the user (or object) who has not registered the fingerprint performs the fingerprint authentication. Output.
[0028]
When performing fingerprint registration, first, after setting that it is registration processing, the user places an inner portion (fingerprint) above the first joint of a predetermined finger (for example, index finger) on the detection surface 14. . The fingerprint authentication device 10 captures a two-dimensional image of the placed fingerprint with the fingerprint sensor 12. The fingerprint authentication device 10 stores the feature information obtained by extracting the captured two-dimensional image of the fingerprint or the feature portion of the two-dimensional image in the registered fingerprint storage unit 21 as registration data. By performing the above operation, the user's fingerprint registration is completed. When fingerprint registration is performed for a plurality of users, for example, an ID or the like may be provided for each user, and fingerprint registration may be performed in correspondence with the ID.
[0029]
The operation during fingerprint authentication is as follows.
[0030]
First, the fingerprint authentication device 10 detects that a finger is placed on the detection surface 14. The fingerprint authentication device 10 starts an authentication operation when detecting that a finger is placed on the detection surface 14. Details of the detection method of whether or not the finger is placed on the detection surface 14 and the start timing of the authentication operation will be described later.
[0031]
When the authentication operation is started, the fingerprint authentication device 10 detects a two-dimensional image of the object placed on the detection surface 14 by the fingerprint sensor 12 and supplies the detection signal to the verification unit 22.
[0032]
The collation unit 22 determines whether or not the two-dimensional image detected by the fingerprint sensor 13 and the registered two-dimensional image (or feature information) of the fingerprint match, for example, by performing pattern matching or the like. The collation part 22 will judge that it is a registered user's fingerprint if it corresponds. If they do not match, the collation unit 22 determines that the fingerprint (or substance) is other than the registered user.
[0033]
When the collation unit 22 obtains a collation result indicating that the user is a registered user, the collation unit 22 outputs a determination result (OK) of the personal authentication that the user is a registered user. In addition, when the collation unit 22 obtains a collation result indicating that the user is not a registered user, the collation unit 22 outputs a determination result (NG) of personal authentication that the user is not a registered user.
[0034]
The fingerprint authentication device 10 encrypts the determination result obtained by performing the above operation by the output unit 23 and supplies it to a computer and various security devices to realize access management, privacy protection, and the like.
[0035]
(Fingerprint image detection method)
Next, a method for detecting a fingerprint image by the fingerprint sensor 12 will be described.
[0036]
The fingerprint sensor 12 is a capacitance detection type sensor in which a capacitor is used as a sensing element. The fingerprint sensor 12 has a plurality of capacitors arranged in a matrix in parallel to the flat detection surface 14. As shown in FIG. 5, the fingerprint sensor 12 raster-scans each sensing element (capacitor) 15 arranged in a matrix in units of one line, and sequentially outputs the sensing level (RF level) of each capacitor. In the case of the capacitive fingerprint sensor 12, the sensing level (RF level) of the capacitor is a value inversely proportional to the capacitance of the capacitor. That is, when the capacitance of the capacitor is large, the sensing level (RF level) of the capacitor is small, and when the capacitance of the capacitor is small, the sensing level (RF level) of the capacitor is large.
[0037]
Here, typical examples of the output of the fingerprint sensor 12 are shown in FIGS.
[0038]
FIG. 6 shows an RF level obtained from a capacitor for one line when nothing is in contact with the detection surface 14 of the fingerprint sensor 12 (when only air is in contact). When nothing is in contact with the detection surface 14, the capacitance of each capacitor increases uniformly. Therefore, the RF level obtained from the capacitors arranged in a matrix form has very little variation in the spatial direction, has a small value, and is substantially the same.
[0039]
FIG. 7 shows an RF level obtained from a capacitor for one line when water droplets are attached on the detection surface 14 of the fingerprint sensor 12. When water droplets are attached to the detection surface 14, the water droplets serve as electrodes, and the capacitance of each capacitor is uniformly reduced. Therefore, the RF levels obtained from the capacitors arranged in a matrix form have very small fluctuations in the spatial direction, have large values and are substantially the same.
[0040]
FIG. 8 shows an RF level obtained from a capacitor for one line when dirt or the like of finger oil adheres to the detection surface 14 of the fingerprint sensor 12. When dirt is attached to the detection surface 14, the capacitance of the capacitor located in the dirt portion becomes low, but the capacitance does not decrease to the minimum value. Therefore, the RF level obtained from each capacitor arranged in a matrix is very small in the spatial direction, has a medium value, and is substantially the same.
[0041]
FIG. 9 is an RF level obtained from a capacitor for one line when a fingerprint (ideal fingerprint) with an ideal amount of moisture on the skin surface is placed on the detection surface 14 of the fingerprint sensor 12. . When an ideal fingerprint is in contact with the detection surface 14, the capacitance of the capacitor is increased in the recessed portion of the fingerprint, and the capacitance of the capacitor is decreased in the protruding portion of the fingerprint. That is, when an ideal fingerprint is in contact with the detection surface 14, the RF level is small at the concave portion of the fingerprint, and the RF level is high at the convex portion of the fingerprint. Therefore, when an ideal fingerprint is in contact with the detection surface 14, the RF level varies in amplitude with respect to the spatial direction according to the unevenness.
[0042]
FIG. 10 shows an RF level obtained from a capacitor for one line when a fingerprint (dry fingerprint) with a small amount of moisture or oil on the skin surface is placed on the detection surface 14 of the fingerprint sensor 12. When the dry fingerprint is in contact with the detection surface 14, the moisture acting as an electrode is reduced, so that the capacitance of each capacitor is offset in the direction of overall increase. The capacitance of the capacitor becomes relatively large, and the capacitance of the capacitor becomes relatively small at the convex portion of the fingerprint. That is, the RF level is offset in the lower direction as a whole, and is relatively low in the recessed portion of the fingerprint around the offset, and relatively high in the convex portion of the fingerprint. Therefore, even when a dry fingerprint is in contact with the detection surface 14, the RF level varies in amplitude with respect to the spatial direction according to the unevenness.
[0043]
FIG. 11 shows an RF level obtained from a capacitor for one line when a fingerprint having a high moisture content on the skin surface (moisture fingerprint) is placed on the detection surface 14 of the fingerprint sensor 12. When a moisture fingerprint is in contact with the detection surface 14, since there is a lot of moisture serving as an electrode, the capacitance of each capacitor is offset in the direction of decreasing overall, but in the recessed portion of the fingerprint, The capacitance becomes relatively large, and the capacitance of the capacitor becomes relatively small at the convex portion of the fingerprint. That is, the RF level is offset in the overall high direction, and is relatively low at the recessed portion of the fingerprint around the offset, and relatively high at the convex portion of the fingerprint. Therefore, even when a moisture fingerprint is in contact with the detection surface 14, the RF level varies in amplitude with respect to the spatial direction according to the unevenness.
[0044]
Looking at the representative examples of the sensor output of the capacitive fingerprint sensor 12 shown in FIGS. 6 to 11, in the case of the capacitive fingerprint sensor 12, the fingerprint irregularities are sensed in two dimensions. It can be seen that the RF level obtained from the element (capacitor) is represented by a two-dimensional high frequency component.
[0045]
Therefore, in the fingerprint sensor 12, as shown in FIG. 12, the RF level output from a plurality of sensing elements (capacitors) arranged in a matrix is low-pass filtered in a two-dimensional direction to reduce the RF level. A frequency component (AVE_Rf) is calculated. Subsequently, at each two-dimensional position, the difference between the RF level and the calculated low frequency component (AVE_Rf) is obtained. This difference value indicates the unevenness level of the crest and trough portions of the fingerprint. The fingerprint sensor 12 outputs the difference value calculated in this way as two-dimensional information corresponding to the position on the detection surface 14. This output signal is supplied to the collation unit 12 as a two-dimensional image signal indicating the uneven pattern on the surface of the object to be detected. Note that the cut-off frequency of the low-pass filtering is a frequency that is sufficiently smaller than the uneven pitch of the human fingerprint.
[0046]
(Finger placement timing detection method)
Next, a finger placement detection method and authentication operation start timing will be described.
[0047]
When the inner part (fingerprint) above the first joint of the finger is placed on the detection surface 14 of the fingerprint sensor 12, the RF level contains a large amount of high frequency components. On the other hand, when no fingerprint is placed on the detection surface 14 of the fingerprint sensor 12 or when something other than the fingerprint is placed, the RF level contains almost no high-frequency component. Therefore, if the energy of the high frequency component of the RF level becomes sufficiently large, it can be considered that the finger is placed on the detection surface 14. The fingerprint authentication apparatus 10 of the present embodiment uses this fact to determine finger placement as described below.
[0048]
In the fingerprint authentication device 10, as shown in FIG. 13, a detection area X for finger placement detection is set at a substantially central position of the detection surface 14. The size of the detection area X may be any size as long as it is smaller than the detection surface 14.
[0049]
The collation unit 22 of the fingerprint authentication device 10 always detects the two-dimensional image signal obtained from the detection area X. That is, as shown in FIG. 14, only the component obtained from the detection area X is always detected from the signal obtained by subtracting the low-frequency component (AVE_RF) in the two-dimensional direction of the RF level from the RF level (RF).
[0050]
The collation unit 22 calculates the absolute value of the two-dimensional image signal obtained from the detection area X, integrates the absolute value in the range of the detection area X, and calculates the integrated value (S). This integrated value (S) is the sum of absolute values of the RF signals in the detection area X. In other words, the integrated value (S) increases if a difference between the peaks and valleys of the fingerprint is detected in the detection area X, and the integrated value (S) decreases if the difference in the peaks and valleys of the fingerprint is detected in the detection area X. Become.
[0051]
The matching unit 22 generates time series data of the integrated value (S), differentiates the time series data of the integrated value (S) in the time direction, and places a finger on the detection surface 14 based on the differential signal (D). Detect whether or not For example, the collation unit 22 calculates an integrated value (S) at regular sampling intervals and stores it in a shift register or the like, and generates a differential signal (D) using the integrated value (S) in the shift register.
[0052]
And the collation part 22 always monitors the signal waveform of a differential signal (D), and judges whether the user put the finger | toe from the signal waveform. If the collation unit 22 determines that the finger is placed, it starts the fingerprint authentication operation.
[0053]
Specifically, FIG. 15 shows a time series signal of the integrated value (S) and a differential signal (D) corresponding to the integrated value (S). FIG. 15A is a timing chart when a finger is placed on the detection surface 14 and then released. FIG. 15B is time-series data of the integrated value (S) when the finger is placed at the timing of FIG. FIG. 15C and FIG. 15D are differential signals (D) with respect to the integrated value (S) in FIG.
[0054]
First, as shown in FIG. 15, in a state where the finger is far away from the detection surface 14 (separated state S1), the integrated value (S) is a value close to zero. Strictly speaking, it has a certain value as a noise component. Subsequently, when the finger is brought close to the detection surface 14 from the separation state S1, the detection surface 14 and the finger start to contact (start operation state S2), and the integrated value (S) increases from 0 to the plus side. Subsequently, when the finger is completely in contact with the detection surface 14 and the movement of the finger is reduced (finger placement stabilization process S3), the integrated value (S) decreases and the value starts to saturate. When the finger rests on the detection surface 14 and is completely placed (placed state S4), the integrated value (S) is constant at a predetermined value (H) on the plus side.
[0055]
When the finger begins to move away from the placement state S4 (end operation state S5), the integrated value (S) decreases from a predetermined value (H) on the plus side. Subsequently, when the finger is separated from the detection surface 14 (finger separation stabilization process S6), the decreasing rate of the integrated value (S) decreases and the value starts to approach zero. When a predetermined time elapses after the finger is completely separated from the detection surface 14 (separated state S1), the integrated value (S) is constant at 0.
[0056]
With respect to the time series signal of such integrated value (S), the signal waveform of the differential signal (D) transitions from the start operation (S2) to the finger placement stable process state S3 as shown in FIG. It can be seen that there is a plus-side peak waveform peak at the timing of the transition, and a minus-side peak waveform peak at the timing of transition from the end operation (S5) to the separated state 1.
[0057]
Here, the fingerprint authentication process can capture a fingerprint image if the finger is sufficiently in contact with the detection surface 14. That is, a stable authentication process is possible at any timing as long as it is in the finger placement stable process (S3) and the placement (S4) state.
[0058]
Therefore, in the fingerprint authentication device 10 according to the present embodiment, the signal waveform of the differential signal (D) is analyzed to detect the peak of the positive peak waveform, and the user's fingerprint image is captured at the peak position for authentication. Is going. As a result, the throughput of the apparatus can be maximized.
[0059]
When a differential coefficient having a large delay time is set, the peak portion of the differential signal (D) becomes flat as shown in FIG. In such a case, the fingerprint image is taken in and authentication is performed with the time point when the inclination becomes negative as the peak position.
[0060]
Alternatively, a plurality of differential signals (D) may be generated using a plurality of differential coefficients having different delay times, and finger placement timing may be detected based on the plurality of differential signals. For example, when the delay amount is large, the sensitivity of detecting the change amount is increased, but the response is delayed. On the other hand, when the delay amount is small, the change amount detection sensitivity is small, but the response is fast. Therefore, for example, when a person with good finger condition uses, a differential signal (D) is generated by using a coefficient with a small delay amount such as poor detection sensitivity but quick response, and used by a person with poor finger condition. In this case, the differential signal (D) is generated using a coefficient with a large delay amount such as good detection sensitivity but slow response.
[0061]
Furthermore, two differential signals (D) are generated simultaneously, and only one differential signal (D) whose peak value level of the mountain-shaped waveform is equal to or higher than a predetermined threshold value is automatically selected for finger placement determination. It may be used.
[0062]
(Finger placement timing detection method 2)
Incidentally, the time-series data of the integrated value (S) when an ideal fingerprint is placed on the detection surface 14 is as shown in FIG. 15B, but the fingerprint (oil When the fingerprint is placed on the detection surface 14, when the finger is released from the detection surface 14, the oil stains remain on the detection surface 14 and an afterimage is produced on the fingerprint image.
[0063]
As shown in FIG. 16B, the integrated value (S) of such an oil fingerprint decreases the RF level with perspiration even when a finger is placed. Therefore, the value may increase without decreasing in the end operation state S5.
[0064]
When the control of authentication timing is performed by detecting the peak on the plus side of the differential signal (D) waveform, the peak position at the start of finger placement must be detected effectively, and the peak position at the time of finger removal must be ignored. Don't be. Therefore, in the fingerprint authentication device 10 of this embodiment, state management is performed by the state machine 50 shown in FIG. 17, and control is performed so that the authentication operation is performed only when the finger is placed.
[0065]
Hereinafter, the state machine 50 will be described.
[0066]
The state machine 50 detects the change amount Z of the differential signal (D) and determines whether the sign of the change amount Z is plus (+), minus (−), or no change (0). Accordingly, transition control is performed.
[0067]
First, the transition is made to the separated state S1 by the reset operation. The separated state S <b> 1 is a state in which the user's finger is far away from the detection surface 14. When the change amount Z is “0” in the separation state S1, the separation state S1 is maintained. When the change amount Z changes to “+” in the separation state S1, the state transitions to the first start operation state S2.
[0068]
The first start operation state S2 is a state in which the finger gradually approaches the detection surface 14, the detection surface 14 and the finger are in contact with each other, and the pressure is increasing. When the change amount Z is “+” in the first start operation state S2, the first start operation state S2 is maintained. When the amount of change Z changes to “−” in the first start operation state S2, a transition is made to the finger placement stabilization process state S3. When the change amount Z changes to “0” in the first start operation state S2, the state transits to the second finger placement stabilization process state S2 ′.
[0069]
When a transition is made to the finger placement stability process state S3 or the second finger placement stability process state S2 ′, an authentication start command is given at the time of the transition, and authentication processing is performed. That is, the authentication process is performed when the change amount Z of the differential signal (D) becomes negative or zero. By performing the authentication process at such timing, the authentication process can be performed earlier.
[0070]
When the change amount Z is “−” in the finger placement stability process state S3, the finger placement stability process state S3 is maintained. When the amount of change Z becomes “−” in the finger placement stability process state S3, the state transitions to the finger placement stability process state S3. When the change amount Z becomes “0” in the finger placement stabilization process state S3, the state transits to the placement state S4.
[0071]
The second finger placement stabilization process state S2 ′ is a stable state. However, in the second finger placement stabilization process state S2 ′, for example, when a differential coefficient having a large delay time is set, a flat portion of the peak portion of the mountain shape is detected from the differential signal (D). It is in the middle. When the change amount Z is 0 in the second finger placement stabilization process state S2 ′, the second finger placement stabilization process state S2 ′ is maintained. When the change amount Z changes to “−” in the second finger placement stability process state S2 ′, the state transitions to the finger placement stability process state S3.
[0072]
The placement state S4 is a state in which the finger is stably placed on the detection surface 14. When the change amount Z is 0 in the mounting state S4, the mounting state S4 is maintained. When the change amount Z changes to “−” in the mounting state S4, it is determined that the finger release has started, and the state transitions to the first end operation state S5. When the change amount Z changes to “+” in the placement state S4, it is determined that the finger release of the oil fingerprint has started, and the state transitions to the second end operation state S5 ′.
[0073]
The first end operation state S5 is a state in which the finger gradually moves away from the detection surface 14. When the change amount Z is “−” in the first end operation state S5, the first end operation state S5 is maintained. When the change amount Z changes to “+” in the first end operation state S5, the state transits to the finger separation stabilization process state S6. When the change amount Z changes to “0” in the first end operation state S5, the state transits to the third end operation state S5 ″.
[0074]
Similar to the first end operation state S5, the second end operation state S5 ′ is a state in which the finger gradually moves away from the detection surface. However, in the case of the second end operation state S5 ′, this is a state in which the placed finger is a fingerprint to which dirt such as an oil fingerprint is attached. When the change amount Z is “+” in the second end operation state S5 ′, the second end operation state S5 ′ is maintained. When the change amount Z changes to “−” in the second end operation state S5 ′, the state transits to the finger separation stable state S6. When the change amount Z changes to “0” in the first end operation state S5, the state transits to the third end operation state S5 ″.
[0075]
The third end operation state S5 ″ maintains the third end operation state S5 ″ when the change amount Z is “0” in the third end operation state S5 ″. When the change amount Z changes to “+” or “−” in FIG.
[0076]
When the change amount Z is “+” or “−” in the finger separation stable process state S6, the finger separation stable process state S6 is maintained. When the change amount Z becomes “0” in the finger separation stable process state S6, the state transits to the loading / separation state S1.
[0077]
As described above, the state machine 50 manages the state of whether the finger is placed or the finger is separated, thereby ignoring the positive peak position generated when the finger is released. Thus, the correct authentication timing can be controlled.
[0078]
As described above, in the fingerprint authentication device 10 according to the present embodiment, the start timing of the authentication process is controlled by determining whether or not a finger is placed based on the sensor output of the fingerprint sensor 12. For this reason, the fingerprint authentication apparatus 10 can automatically start fingerprint authentication simply by placing a finger on the detection surface 14 of the fingerprint sensor 12 without providing an authentication start button or finger placement sensor.
[0079]
【The invention's effect】
In the fingerprint authentication device and the finger placement detection method for the fingerprint sensor according to the present invention, the absolute value of the two-dimensional image signal obtained from the fingerprint sensor is integrated within a predetermined region, and the time-series signal of the integrated value is differentiated and differentiated. A signal is generated, and it is detected that the finger is placed on the fingerprint sensor based on the differential signal. For example, in the present invention described above, when the waveform of the differential signal changes from the state in which the finger is not placed on the fingerprint sensor to the peak shape on the positive side, it is determined that the finger is placed on the fingerprint sensor.
[0080]
As a result, in the fingerprint authentication apparatus and the finger placement detection method for the fingerprint sensor according to the present invention, it is possible to capture a fingerprint image at an optimal timing without using a special member. Therefore, the accuracy of personal authentication can be improved.
[Brief description of the drawings]
FIG. 1 is a schematic perspective view of a fingerprint authentication device according to an embodiment of the present invention.
FIG. 2 is a diagram for explaining the arrangement of sensing elements provided in a fingerprint sensor.
FIG. 3 is a block configuration diagram of the fingerprint authentication device according to the embodiment of the present invention.
FIG. 4 is a block diagram when the fingerprint authentication device is configured by hardware.
FIG. 5 is a diagram illustrating a method for scanning a plurality of sensing elements in a fingerprint sensor.
FIG. 6 is a diagram showing an RF level obtained from a capacitor for one line when nothing is brought into contact with the detection surface of the fingerprint sensor.
FIG. 7 is a diagram showing an RF level obtained from a capacitor for one line when water droplets are attached on the detection surface of the fingerprint sensor.
FIG. 8 is a diagram illustrating an RF level obtained from a capacitor for one line when dirt or the like of finger oil adheres to the detection surface of the fingerprint sensor.
FIG. 9 is a diagram showing an RF level obtained from a capacitor for one line when a fingerprint having an ideal amount of moisture on the skin surface (ideal fingerprint) is placed on the detection surface of the fingerprint sensor; is there.
FIG. 10 is a diagram showing an RF level obtained from a capacitor for one line when a fingerprint (dry fingerprint) with a small amount of moisture or oil on the skin surface is placed on the detection surface of the fingerprint sensor.
FIG. 11 is a diagram showing an RF level obtained from a capacitor for one line when a fingerprint having a high moisture content on the skin surface (moisture fingerprint) is placed on the detection surface of the fingerprint sensor.
FIG. 12 is a diagram for explaining an Rf level and its low frequency component;
FIG. 13 is a diagram for explaining an example of arrangement of detection areas;
FIG. 14 is a diagram for explaining an RF level and the like detected from a detection area.
FIG. 15 is a diagram illustrating a time-series signal of integrated values (S) and a differential signal (D) corresponding to the integrated values (S) when an ideal fingerprint is placed.
FIG. 16 is a diagram illustrating a time-series signal of integrated values (S) and a differential signal (D) corresponding to the integrated values (S) when an oil fingerprint is placed.
FIG. 17 is a diagram illustrating a state machine that performs state management;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Fingerprint detection apparatus, 12 Fingerprint sensor, 14 Detection surface, 21 Registered fingerprint storage part, 22 Verification part

Claims (8)

A fingerprint sensor that has a planar detection surface and detects a two-dimensional image signal indicating a concavo-convex image of the surface of the detection object placed on the detection surface;
Registered fingerprint storage means for storing fingerprint information for identifying the fingerprint for each user;
Authentication means for verifying the identity of the user who placed the detected object by comparing the two-dimensional image signal of the detected object detected by the fingerprint sensor with the user's fingerprint information stored in the registered fingerprint storage means And
The authentication means is
Calculating an absolute value of the two-dimensional image signal obtained from a predetermined area in the detection surface, integrating the absolute value in the predetermined area;
Generate a time series signal of the above integrated value, differentiate the time series signal in the time direction to generate a differential signal,
Based on the signal waveform of the differential signal, detects the timing when the object to be detected is placed on the detection surface of the fingerprint sensor,
A fingerprint authentication device that authenticates a user by capturing a concavo-convex image of a surface of an object to be detected according to the timing. The fingerprint sensor is a capacitance detection type fingerprint sensor, and calculates a low-frequency component in a two-dimensional direction of a sensing signal obtained from a plurality of sensing elements arranged two-dimensionally in parallel with the detection surface, 2. The fingerprint authentication apparatus according to claim 1, wherein the two-dimensional image signal is generated based on a difference between a frequency component and the sensing signal. The authentication means is
2. The fingerprint authentication apparatus according to claim 1, wherein the authentication is performed by capturing a concavo-convex image of the surface of the detected object at a positive peak timing of the differential signal. The authentication means is
The state control is performed by distinguishing between the first state where the detection object is not placed on the detection surface and the second state where the detection object is placed on the detection surface,
At the first descending timing after the value of the differential signal rises from 0, the object to be detected is transited from the first state to the second state and from the first state to the second state. 4. The fingerprint authentication apparatus according to claim 3, wherein the authentication is performed by capturing an uneven image on the surface of the fingerprint. The authentication means is
Transition from the second state to the first state at the first fall timing after the value of the differential signal rises from 0 or at the first rise timing after the value of the differential signal falls from 0 The fingerprint authentication device according to claim 4, wherein: The authentication means is
2. The fingerprint authentication apparatus according to claim 1, wherein it is determined whether or not an object to be detected is placed on a detection surface of the fingerprint sensor based on a plurality of differential signals whose detection sensitivity in the time direction is changed. The authentication means is
2. The integrated value obtained from a predetermined region of the detection surface of the fingerprint sensor is detected at predetermined sampling intervals, and it is always determined whether or not an object to be detected is placed on the detection surface of the fingerprint sensor. The fingerprint authentication device described. A fingerprint sensor that has a planar detection surface and detects a two-dimensional image signal indicating a concavo-convex image of the surface of the object to be detected placed on the detection surface, and fingerprint information for identifying the fingerprint for each user The registered fingerprint storage means stored in the memory, the two-dimensional image signal of the detected object detected by the fingerprint sensor and the user's fingerprint information stored in the registered fingerprint storage means, and the detected object A finger placement detection method for a fingerprint sensor for detecting that a fingerprint of a finger is placed on a detection surface of the fingerprint sensor in a fingerprint authentication device comprising an authentication means for authenticating a user who has placed
Calculating an absolute value of the two-dimensional image signal obtained from a predetermined area in the detection surface, integrating the absolute value in the predetermined area;
Generate a time series signal of the above integrated value, differentiate the time series signal in the time direction to generate a differential signal,
Based on the signal waveform of the differential signal, detects the timing when the object to be detected is placed on the detection surface of the fingerprint sensor,
A finger placement detection method for a fingerprint sensor, wherein a user's identity authentication is performed by capturing an uneven image on the surface of an object to be detected according to the timing.

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