JP2004013654A - Fingerprint reader - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that an optical fingerprint reader may determine a forged fingerprint as a genuine if the forged fingerprint, which has the same pattern as a fingerprint, is attached to a finger and then the reader reads it, and to provide a means for certainly authenticating personal identification. <P>SOLUTION: A method to read out the projection and recess form of a fingerprint detects temperature characteristics in heating the body heat of a fingerprint part using a minute thermistor element that heats it and measures its temperature. In this method, a risk of incorrect recognition due to attaching a forged pattern to the finger is removed. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a device that stores confidential information, such as a computer system, a data communication system, and various types of dedicated terminals, when confirming that an operator is an authorized person, or in a building having confidential information. The present invention relates to a system technology for confirming that a person is authorized in advance when entering a room.
[0002]
[Prior art]
Conventionally, when confirming that the operator of a device storing confidential information is the authorized person or when entering a building room with confidential information, the operator is an authorized person in advance. As means for confirming this, techniques such as reading of a card issued in advance and issued to the user, voice recognition, recognition of the iris of the eye, and optical image recognition of a fingerprint have been used.
[0003]
[Problems to be solved by the invention]
As mentioned above, various methods have been considered in the past to confirm the identity of the person.However, impersonating the person in place of the person due to forgery or fraudulent acts could not be avoided by conventional means. . For example, even if the person who brought the magnetic card or the IC card is regarded as the person, or even if a password is used in combination, the person can be the person other than the person. In addition, voice recognition that recognizes voiceprints has uncertainty, and it cannot be said that all human voiceprints are different, and it is uncertain because the voice will be different from normal, such as when a cold is caught. You can say that.
[0004]
Discrimination based on the iris of the eye is not yet a completed technique, is not a simple method, and is not practical.
[0005]
Fingerprints are unique to each individual, and are relatively easy to detect and identify.
[0006]
However, if the fingerprint pattern of the person is obtained by some other means, the image is printed on the surface of a film or rubber film, and the image is attached to a finger, it is scanned by a conventional fingerprint reader that detects optically. It is thought that it will be relatively easy in the future to read the forged pattern as it is and to impersonate the person only by optical processing.
[0007]
Therefore, it has been desired to realize a detection means based on characteristics of a human finger on a living body. That is, it is desired to realize a new type of fingerprint reading means that focuses on the warmth of fingers and the thermal energy transfer characteristics of fingers.
[0008]
The present invention solves these problems of existing identity verification means, and provides means for reliably determining whether or not the identity is the identity.
[0009]
[Means for Solving the Problems]
As described above, conventional fingerprint recognition is an effective means for personal identification, but as long as the fingerprint image pattern is optically recognized, if the fingerprint of the person himself is obtained by some other means, the image can be obtained on a film or the like. When printed on the surface of the rubber film, attached to a finger, and scanned by a conventional fingerprint reader that optically detects, the forged image pattern is read as it is just by scanning with light and recognizing it, It is thought that spoofing can be relatively easy in the future. In order to avoid this situation, it has been found that a solution is to apply the reaction characteristics as a living body by being a human finger. That is, since a finger is a part of the human body, it has heat energy due to body temperature, and when heat energy is applied from the outside, its heat radiation characteristic is a fingerprint printed on paper or a rubber film. Due to the fact that it is different from the image and the actual fingerprint of the finger has a three-dimensional uneven shape due to its pattern, this shape has different thermal characteristics from the printed image on paper or rubber film . By detecting these characteristics with a new thermal head according to the present invention, it is possible to determine the authenticity.
[0010]
That is, the present invention provides an electric circuit unit as a thermal head composed of a small thermistor resistor group arranged in a line,
A mechanical part incorporating the electric circuit unit,
A circuit for heating and driving the micro thermistor resistors when scanning the fingerprint surface by the same mechanism;
The fingerprint reading device includes a voltage detection circuit for detecting a change in the resistance value of the micro thermistor resistor group as a result of the heating drive.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
First, a description will be given of a thermal head 600 in which a heat detecting element also serving as a heating element is incorporated in the fingerprint reader according to the present invention.
[0012]
FIG. 1 shows an example of the external shape of the thermal head 600.
[0013]
In the figure, micro heating elements (resistor elements) 101, 102,... 109 are about 100 μm square for reading the pattern of a fingerprint, and aluminum is formed on a copper body plate so as to have a thickness of about 1 to 2 μm. It is manufactured by a technique of depositing an alloy metal made of chromium or the like into a thin film and a photo etching technique.
[0014]
The manufacturing technique and production equipment used for this purpose are not different from those for the production of ordinary thermal heads, only the material deposited on the copper body is replaced by a thermistor element made of chrome or aluminum alloy. In addition, as a finish of the element, silicon nitride having the hardness next to diamond is also overcoated by a thin film deposition technique to form a protective film layer.
[0015]
Note that even if the present elements 101, 102,... 109 are produced by the thick film technique, the object of the present invention can be achieved without departing from the gist of the present patent.
[0016]
Each of the micro heating elements 101, 102,... 109 is an independent resistance element, and when current is applied to each of them, generates heat energy in the same manner as general resistance. However, the characteristics of the thermistor element are shown in FIG. As shown, the resistance value gradually changes as the temperature rises. Therefore, by detecting the resistance value r1 with additional circuit means as described later, it is possible to know the heat generation temperature t1 of the resistance element at that time from FIG.
[0017]
In FIG. 1, circuit patterns 201, 202,..., 209 further branched off from the constant voltage power supply circuit pattern 299 are connected to one end of each of the resistance elements 101, 102,. 309 are outputted as circuit patterns 301, 302,... 309 and output to the control circuit of FIG.
Note that since the resistance elements are usually arranged in a line with a size of about 100 μm as described above, 300 resistance elements are arranged in a straight line with a margin to detect a fingerprint having a width of about 20 mm. Become.
[0018]
In fingerprint reading, these 300 resistance elements detect temperature independently of each other.
[0019]
In reading the fingerprint, the finger from which the fingerprint is read moves as shown in FIG. 8 or crosses the resistive elements arranged in a line as described later, or the finger stops as shown in FIG. Then, as the resistance element group moves under the same finger, reading described later is performed.
[0020]
Next, the operation of the finger for reading the fingerprint and the operation of the thermal head 600 during reading will be described.
[0021]
As shown in FIG. 8, when the finger 605 for reading a fingerprint is placed on the thermal head 600 and the reading start timing generation button 603 is pressed at the same time, reading is started at a constant period after the pressing timing. In addition, a finger for reading a fingerprint is placed in a direction perpendicular to the arrangement direction of the micro thermistor group of the mechanism portion that is fixed and does not move, and the finger surface is moved so as to sequentially scan the fingerprint surface. A preferred embodiment of the present invention is a form in which a rotary gear is provided, and the gear further rotates by the movement of the same finger to further generate a main scanning timing. That is, as a structure, a rotating gear is provided instead of the read start timing generation button 603, and as the finger moves the thermal head 600, the finger touches the gear and simultaneously rotates the same, thereby detecting the rotation operation optically or magnetically. , And obtaining a periodic reading timing can be regarded as a specific embodiment of the present invention.
[0022]
Further, a step motor for step-driving the mechanism portion, a switch component for generating a timing for starting driving of the step motor, and starting driving of the step motor by a drive start signal from the switch, A preferred embodiment of the present invention is a form further including a drive circuit for driving the step motor for a fixed time.
[0023]
Specifically, in the format shown in FIG. 9, in a state where the finger 704 is not moved and is placed on the thermal head 600, the step motor 703 connected to the timing belt 702 for indexing the thermal head 600 rotates. Thus, when the thermal head 600 moves, the fingerprint pattern is read at a reading timing synchronized with the rotation of the motor. Although not shown in FIG. 9, fingerprint reading is started by a sensor that detects that the finger 704 is placed on the thermal head 600 or by a push switch or the like.
[0024]
Next, referring to FIG. 3, a description will be given of how any one element of the thermal head 600 using the above-described micro thermistor resistor group is used for fingerprint detection.
[0025]
Since all elements are independently controlled as described above, it may be considered that only one element is described and other elements are similarly controlled.
[0026]
3, an arbitrary signal among the circuit patterns 301, 302,... 309 of FIG. 1 is input as the input signal 401 of FIG.
[0027]
In the example of FIG. 3, the left end element 101 in FIG. 1 is connected by circuit patterns 201 and 301, but the other elements 102, 103,... All connected. The bold line pattern 299 in FIG. 1 is a power supply pattern and is usually connected to a low voltage power supply set to a constant voltage of about 12 to 15 V. This terminal is designated by the terminal VCC in FIG.
[0028]
The other patterns among the circuit patterns 301, 302,... 309 in FIG. 1 are connected to the same circuit as in FIG.
[0029]
Next, how the fingerprint of the finger is read by the thermal head equipped with the micro thermistor group will be described below.
[0030]
Fingerprints are formed on the skin of a finger by lines of unevenness that are continuous in a curve.
[0031]
The temperature rise curve when the thermistor is overheated is different between the convex portion that contacts the micro thermistor and the concave portion that does not contact the thermistor. This will be described with reference to FIG. In FIG. 6, a curve t1-t2-t4-t5 shows a temperature change at the time of heating the micro thermistor in contact with the convex part of the fingerprint, and a curve t1-t3-t5 shows the temperature change of the concave part of the fingerprint. In this figure, a current flows through the micro thermistor from time t1 to time t2 or time t3, and the current drive stops after time t2 or t3. This causes the temperature to drop.
[0032]
Both are first-order lag response curves referred to in automatic control, but the time constants of the two curves are different. In other words, when the convex part of the fingerprint is in contact with the micro thermistor, if the temperature exceeds the body temperature of the human body, the heat generated in the micro thermistor is absorbed by the human body, so that the curve becomes as shown by a curve t1-t2-t4-t5. Does not greatly exceed body temperature.
[0033]
However, since the fingerprint portion does not contact the surface of the micro thermistor in the portion where the fingerprint concave portion is in contact with the micro thermistor, there is no heat energy absorber as compared with the convex portion, and the temperature is high as shown by the curve t1-t3-t5. The curve changes.
[0034]
Therefore, when the temperature of the minute heating element is measured at the timing of time t2 or time t3, the peak temperature is different, so that the minute thermistor is in contact with the concave portion of the fingerprint or is in contact with the convex portion of the fingerprint. Can be determined.
[0035]
The specific reading method will be described below.
[0036]
FIG. 3 shows a control circuit for reading a fingerprint.
[0037]
In FIG. 3 which is a circuit diagram, a circuit surrounded by a broken line on the upper left indicates a portion of the micro thermistor 101 on the left end and the patterns 201 and 301 in the thermal head composed of the micro thermistor of FIG. That is, the control circuit of FIG. 3 corresponds to one bit of the micro thermistor. Therefore, assuming that the number of micro thermistors is N dots on the thermal head, the circuit of FIG. 3 also exists N times. Therefore, in order to realize the present invention, it is considered necessary to integrate these circuits at a high density, for example, as an LSI. As a result, the fingerprint reader of the present invention can be integrated into a small unit.
[0038]
Before the fingerprint is read, the reading start signal 400 is input by pressing the reading start button of the apparatus, and the flip-flop 403 is set. The flip-flop 403 becomes "1" until the reset signal 402 at the end of reading is input, during which the reading operation is performed. The drive control signal 407 of the micro thermistor is initially “0”. Therefore, the driving signal inverted by the inverter 408 is ANDed with the output of the flip-flop 403 by the AND gate 405 to become “1”. As a result, the drive transistor 410 is turned on, and a current flows through the minute thermistor 101 from the constant voltage power supply terminal VCC. As a result, the micro thermistor 101 generates Joule heat and the temperature rises.
[0039]
At this time, the amount of heat energy generated by the human body differs depending on whether the minute heating element is in contact with the convex part or the concave part of the fingerprint, and when the small heating element is in contact with the concave part, as shown by waveforms t1-t3-t5 in FIG. It changes as shown in the waveform t1-t2-t4-t5 in FIG. 5, the signal 405 is “1” in FIG. 5 from time t1 to time t2 or t3, and during this time, the transistor 410 is in the ON state, so that the temperature is rising. Next, when the signal 407 changes from “0” to “1”, as shown in FIG. 5, the signal 405 becomes “0”, and thus the transistor 410 is turned off and the current stops, so that the temperature of the thermistor 101 starts to decrease. I do.
[0040]
When the signal 407 changes to “1”, the output of the logical product 409 becomes “1” because the flip-flop 403 is “1”. At this rising transition point, the one-shot pulse generator 411 generates a short-time pulse output of about 1 μsec. This pulse turns on transistor 412 for 1 μs.
[0041]
At this time, when the transistor 410 is turned off, it can be seen that all the current flowing through the thermistor 101 flows into the transistor 412. This current flows to the ground level after flowing to the fixed resistor 415. The voltage generated at the fixed resistor 415 is amplified by a DC operational amplifier 416 in the next stage, and is converted from analog to digital by an A / D converter in the next stage to be converted into an 8-bit value.
[0042]
At this time, if the fingerprint portion in contact with the thermistor 101 is a concave portion, since the heat absorption by the human body is lower than when the fingerprint portion is in contact with the convex portion as described above, the temperature becomes higher. The resistance value becomes low, and the flowing current value increases. Therefore, the voltage of the fixed resistor 415 becomes larger, and as a result, the output value of the A / D converter 418 becomes larger than when it is in contact with the projection. Conversely, if the output value of the A / D converter 418 is larger than a certain threshold, then the thermistor 101 is in contact with the concave part of the fingerprint, and the output value of the A / D converter 418 is at a certain threshold. If smaller, it can be said that the thermistor 101 is in contact with the convex portion of the fingerprint.
[0043]
Therefore, if this is repeated continuously as the fingerprint portion moves, information on the shape of the fingerprint can be obtained.
[0044]
Note that, for example, at room temperature, the thermistor 101 has a slight variation in resistance when compared with other thermistors, such as 102, 103,..., 109, and the transistor 412 is also different from other transistors. In the comparison, there is variation in the ON resistance value at the time of measurement, and the DC amplifier also has variation in its offset value. These can be comprehensively checked in advance, the compensation values can be stored, and the accuracy of reading can be increased by subtracting the compensation values from the measured values at the time of actual reading.
[0045]
These compensation values are, for example, numerical values indicated by numerical values a in FIG.
[0046]
The measurement for compensating the numerical value a does not have to be performed by heating. For example, the signal of the flip-flop 403 and the signal 407 are input for a very short time during the preliminary adjustment of the apparatus, and the one-shot generator 411 outputs a single shot. The current value flowing by driving the transistor 412 is changed to a voltage by the resistor 415, and the output value of the DC operational amplifier 416 and then the A / D converter 418 is stored in the compensation value register 420. Can be. At the time of actual fingerprint reading, the subtraction circuit 424 subtracts the value of the compensation register 420 from the output value of the A / D converter 418. As a result, a in FIG. 6 is subtracted, and the value at the time t2 or t3 when the numerical value a is removed as shown in FIG. 7 is the maximum value in each scan, and this value is a numerical value with an 8-bit configuration. This value and the 8-bit threshold input value 434 are compared in magnitude by the comparator 427. As a result, when the value of the subtraction circuit 424 is larger than the threshold input value 434, it is determined that the concave portion of the fingerprint is detected. 1 "is set in the shift register 428. Similarly, when the value of the subtraction circuit 424 is smaller than the threshold input value 434, "0" is set in the shift register 428 on the assumption that the convex portion of the fingerprint has been detected. That is, as shown in FIG. 5 which is a circuit diagram, the output value of the comparator 427 is determined based on the temperature rise of the thermistor 101 and stored in the shift register 428. At this time, a clock pulse used for storage is used by delaying an output pulse of the one-shot generator 411 by a delay circuit 426.
[0047]
This is because the A / D conversion in the A / D converter 418 takes some time, and is delayed until timing when the converted value is guaranteed.
[0048]
As the shift register 428 sequentially scans the fingerprint portion of the finger, the result of the sequential reading is input to the shift register 428 in a cycle in which the signal 407 is input.
[0049]
As described above, there are as many circuits as shown in FIG. 3 as the number of heating elements in FIG. 1, and therefore, there are as many shift registers 428 as the number of heating elements.
[0050]
As a result, as shown in FIG. 4, a shift register group having the number of stages equal to the number of the heating elements is formed, and the number of stages of the shift register matches the number of scans when the fingerprint is scanned. As a result, a two-dimensional matrix read result register is formed. FIG. 10 is a diagram showing the correspondence between the register in which the actual reading result is stored and the fingerprint image stored in the register.
[0051]
The read result is shifted from the output signal 435 every time the shift clock signal 429 of FIG. 3 is input, output to the outside, and sent to the fingerprint recognition circuit.
[0052]
The feature of this patent is that heating and temperature detection are performed on a fingerprint of a finger by a thermal head, but the actual heating time is about 1 ms for each scanning time, and continuous overheating is not performed at the same location. Furthermore, the temperature is at most about 50 ° C., and particularly, no damage such as burns is given to the human body.
[Brief description of the drawings]
FIG. 1 is a diagram showing an external shape of a group of minute detection resistors.
FIG. 2 is a diagram showing temperature-resistance characteristics of a detection resistance element.
FIG. 3 is a diagram showing a control circuit for reading a fingerprint.
FIG. 4 is a diagram of a two-dimensional register for storing a read result.
FIG. 5 is a timing chart illustrating an operation of the control circuit of FIG. 3;
FIG. 6 is a diagram showing a temperature change during heating of a micro thermistor in contact with a convex part and a concave part of a fingerprint.
FIG. 7 is a correction diagram showing a temperature change during heating, from which a in FIG. 6 has been subtracted.
FIG. 8 is a diagram showing one embodiment of the present invention.
FIG. 9 is a diagram showing another embodiment of the present invention.
FIG. 10 is a diagram illustrating a relationship between a two-dimensional register for storing a reading result and storing of a pattern of a fingerprint reading result.
[Explanation of symbols]
600 thermal heads 101 to 109 minute heating elements 201 to 209 circuit patterns 301 to 309 circuit patterns 299 constant voltage power supply circuit patterns

Claims (3)

An electric circuit unit as a thermal head composed of a small thermistor resistor group arranged in a line,
A mechanical part incorporating the electric circuit unit,
A circuit for heating and driving the micro thermistor resistors when scanning the fingerprint surface by the same mechanism;
A fingerprint reading device comprising a voltage detection circuit for detecting a change in the resistance value of the micro thermistor resistor group as a result of the heating drive. A step motor for step driving the mechanism part,
A switch component for generating a timing to start driving the step motor,
2. The fingerprint reading device according to claim 1, further comprising: a driving circuit that starts driving the step motor in response to a driving start signal from the switch and drives the step motor for a predetermined time. Place a finger that reads a fingerprint in a direction perpendicular to the arrangement direction of the micro thermistor group of the mechanism part that is fixed and does not move, and scans the fingerprint surface sequentially by moving the finger, so that it is adjacent to the mechanism part. 2. The fingerprint reading apparatus according to claim 1, further comprising means for installing a rotating gear, and generating a main scanning timing by rotating the gear by movement of the finger.

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