RU2686619C1 - Hand sensor - Google Patents

Abstract

FIELD: physics.SUBSTANCE: invention relates to security space violation signalling devices. Proposed device comprises electrodes arranged in one plane and connected to transformer winding. Transformer winding is connected to the output of the amplifier with positive feedback, at that the electrodes, the transformer and the amplifier form an LC-generator with loop amplification installed depending on the required sensitivity of the sensor. With simultaneous contact of palm and fingers of electrodes, capacitors are formed, which have high losses caused by properties of human body. As a result, the Q-factor of the LC-circuit is reduced so that loop amplification of the LC-generator becomes less than one and the generation is terminated. Absence of generation is a sign that the real hand has taken the correct position.EFFECT: technical result consists in failure of generation of LC-generator when touching fingers and palm only real hands of working surface of device with required area of contact.1 cl, 3 dwg

Description

Technical field

The invention relates to the field of means of signaling the violation of the protected space, which are actuated electrically and operate when the capacitance or inductance of the circuit caused by the approach or intrusion of an intruder changes.

More specifically, the invention can be used in access control systems, for example, in biometric human identification devices according to hand geometry, devices for detecting traces of explosives on a hand, etc., which require protection from attempts to trick the device using a hand layout .

Prior art

Today, biometric identification devices, for example, in the shape of fingers, are one of the priority areas for the development of security systems. In such devices, it is required that a person places his hand on the surface of the device to identify a person by the geometry of the hand. At the same time, it is necessary to check whether the hand or the layout is really presented - an object that has the silhouette of a person’s hand. This requires a sensor that works only on a real hand, and only when the palm and fingers touch the surface of the device, and with a certain minimum area of contact.

Known detector, described in Japanese patent JP 201141836 (A) "HUMAN BODY DETECTOR"("Detector of the human body"); IPC ⁷ : G01V 3/08; applicant SUMITOMO CHEMICAL CO + (SUMITOMO UNDER CO LTD); published on 25 May 2001; Priority JP 19990322826 19991112. The detector contains an electrostatic capacitive sensor in the form of two opposed electrodes, an inductive element connected in series with the sensor, a resistor, a frequency generator and output terminals connected to both terminals of the resistor. The sensor, the inductive element and the resistor form a series resonant circuit. When an object approaches even with such a small capacity as the human body, the output will be a significant change in the signal.

The disadvantage of the detector can be considered that such a detector will work on the metal layout of the hand. Such a device is not able to work only at the moment when the hand has taken a certain position (the palm and fingers are simultaneously attached to the surface of the device), therefore, it cannot be used in the identification device according to the geometry of the hand.

A device described in US patent US5,760,688 "Body detection device" is known; May 24, 1996; published 07/02/1998; IPC (20060101): G01D 5/12; G01R 27/02; G01D 5/20; by Kasai Eiji (Kyoto, JP). The device contains a generator equipped with a detection coil. In the absence of a person near the detection coil, the generator generates a high-frequency signal of large amplitude to detect it with a detector so that the controller transistor turns on. At the moment when the human body is near the detection coil, the generation stops due to a decrease in the quality factor of the LC circuit of the generator caused by the influence of the magnetic permeability of the human body. The signal from the detector to the transistor becomes extremely low and the transistor turns off.

The disadvantage of such a device can be considered the inability of it to work only at the moment when the hand has taken a certain position (the palm and fingers are simultaneously attached to the working surface of the device). Therefore, it cannot be used in the device identification on the geometry of the hand.

As a prototype for the proposed device, an alarm device with an oscillator was selected, which is switched off by the capacity introduced by the body of a potential intruder, described in US patent US 4173755; IPC (20060101): G08B 13/22, G08B 13/26, G08B 013/26; priority date 06.03.1978; published 11/06/1979, by Butler; George N. (Boca Raton, FL).

The burglar alarm device operates from a battery and contains a battery, an oscillator that receives energy from the above battery for normal oscillation generation, a sensor operatively coupled to the above oscillator to stop the above oscillations in response to the capacitance introduced by the human body touching the sensor him, and means operatively coupled with the above oscillator to give an audible alarm when the oscillator stops oscillation.

The disadvantages of this burglar alarm device can be considered its inability to operate only at the moment when the hand has taken a certain position (the palm and fingers are simultaneously attached to the working surface of the device) and the possibility of triggering a hand using a metal layout.

DISCLOSURE OF INVENTION

The problem to which the invention is directed is to create a sensor that generates a signal when the working surface of the device is touched by the fingers and the palm of a real hand, but does not work on a metal or dielectric layout.

The technical result achieved in solving this problem is to disrupt the generation of the LC generator when only the real hand of the device touches the fingers and palm with the required contact area due to the influence of the electrical properties of the hand on the quality factor of the LC circuit.

The technical result is achieved by the fact that in the sensor of a human hand, containing a power source, which gives energy to the generator for generating oscillations, is connected to means for detecting the fact of stopping generation and generating a corresponding signal, according to the invention, the sensor has two electrodes. Moreover, one electrode is located in the zone intended for placing the fingers of the hand, and the second - in the zone of the base of the palm. The sensor is equipped with a transformer. The electrodes are connected to the first winding of the transformer and form an oscillating LC circuit with it. The second winding of the transformer is connected to the output of the amplifier with positive feedback. The electrodes, the transformer and the amplifier form a loop-mounted LC generator, depending on the required sensitivity of the sensor, expressed in the contact area of the hand and the electrodes, at which the sensor triggers. At least one electrode must have a protective, special or decorative coating of a thin dielectric, the second electrode may have a coating of a thin dielectric or metal. A dielectric coating is necessary so that the metal layout of the hand cannot be short-circuited the electrodes, as this can lead to a breakdown of generation, i.e. triggering a sensor on a hand layout.

The set of essential features ensures obtaining a technical result - disrupting the generation of an LC generator - when the area of contact between the fingers and the palm of a real hand with the electrodes exceeds the desired value specified by adjusting the loop gain of the LC generator.

Brief description of drawing figures

FIG. 1 shows the location of the electrodes relative to the fingers and palm.

FIG. 2 shows a functional diagram of a hand sensor.

FIG. 3 shows capacitances formed between the hand and the electrodes of the hand sensor, as well as between the electrodes of the hand sensor.

An embodiment of the invention

Below, an embodiment of a hand sensor for a finger-shaped identification device is described. FIG. 1. shows the working surface of the device biometric identification in the form of a table 1, designed to accommodate the hand 2.

To implement the invention, the first electrode 3 is located in the zone of the table 1, designed to accommodate the fingers 4 of the hand 2. The device in which the hand sensor is installed does not use a thumb for identification, therefore it is placed outside the zone to accommodate the other fingers. The second electrode 5 is located in the area of the table 1, designed to accommodate the palm 6. The zones with electrodes 3 and 5 are isolated from each other.

Electrode 3 is covered with a retroreflective film (not shown in Fig. 1), providing improved image quality of hand 2, as well as isolation of hand 2 from electrode 3.

FIG. 2 shows a block diagram of a sensor. The electrodes 3 and 5 are connected to the winding 6 of the transformer 7 and form with it an LC circuit. Winding 8 is connected to the output of the amplifier 9 with positive feedback. The electrodes 3 and 5, the transformer 7 and the amplifier 9 form an LC generator. The loopback gain of the LC generator (without a hand) is set depending on the required sensitivity of the sensor. Under the sensitivity refers to the area of contact between the fingers 4 and the palm 6 with the electrodes 3 and 5, at which the sensor is triggered. The area of contact, in turn, depends on the pressing force of the palm 6 and fingers 4 on the table 1. The signal from the LC generator is fed to the signal processing circuit 10, which generates a signal for the identification device.

The transformer 7 is made on the core with low losses. The circuit of the LC-generator is designed so that the losses as low as possible are introduced into the LC-circuit. Small losses are required if it is necessary to ensure the operation of the sensor even with a weak pressing of fingers 4 and palms 6 against electrodes 3 and 5.

The sensor works as follows.

When a person places hand 2 on table 1, a capacitance 11 is created between fingers 4 and electrode 3, and a capacitance 12 (FIG. 3) is created between palm 6 and electrode 5, the values of which depend on the areas of contact between fingers 4 and palm 6 with electrodes 3 and 5. The contact areas depend on the pressing force of the fingers 4 and the palm 6 on the electrodes 3 and 5. The larger these capacitances, the greater the losses due to the flow of current through the arm 2, are introduced into the LC circuit. Electrodes 3 and 5 have a small thickness and are located with a gap (as shown in Fig. 1). Due to this, the capacitance between them is small and the quality factor of the LC circuit can decrease several times when fingers 4 and palm 6 are pressed to electrodes 3 and 5. With a certain pressing force of fingers 4 and palm 6, the quality factor of the LC circuit decreases so that the loop gain of LC- the generator becomes less than one and generation stops. The lack of generation is a sign that the real hand 2 is in the correct position. By adjusting the loop gain of the LC generator, you can adjust the sensitivity of the sensor from a light touch to a strong pressure with a large area of contact between fingers 4 and electrode 3 and palm 6 with electrode 5.

If you press hand 2 to only one electrode, for example, fingers 4 to electrode 3, then generation will not fail, because the capacitance between palm 6 and electrode 5 will be too small for hand 2 to affect the quality factor of the LC circuit. That is, the sensor provides a signal to the identification device only when hand 2 has taken the correct position on the table 1 of the device.

At the same time touching the metal layout of the hand electrodes 3 and 5 will not break the generation, but only decrease the oscillation frequency of the LC generator 8, since capacitors 11 and 12 formed by the metal layout of the hand with electrodes 3 and 5 will have small losses, and the metal has a very low resistance, therefore, the losses introduced into the LC circuit will be very small and will not degrade the quality factor of the LC circuit by an amount sufficient to disrupt the oscillations of the LC generator.

When electrodes 3 and 5 touch the dielectric layout simultaneously, the capacitance between electrodes 3 and 5 will slightly increase, since the dielectric constant of the dielectric is greater than that of air, but due to the extremely high resistivity of dielectrics, the quality of the oscillating circuit of the LC generator does not deteriorate by an amount sufficient to break the oscillations of the LC-generator. Therefore, the generation will continue, albeit with a slightly lower frequency.

Consequently, the sensor, built using all the distinctive features, allows us to solve the problem of forming a signal when the real surface of the device is touched by the fingers and the palm of the device, but fails to work on a metal or dielectric layout.

Industrial Applicability

The described embodiment of the invention is implemented in a finger-shaped identification device developed and used at VNIITF. The sensor has passed tests confirming actuation on a real hand, but failure on a metal or dielectric layout. The sensor is in operation. This confirms the performance of the invention and its industrial applicability.

Claims (1)

A sensor for detecting a person’s hand, which contains a power source that provides energy to the generator for generating oscillations, is connected to means for detecting the fact that generation has ceased and generating a corresponding signal, characterized in that the sensor is equipped with a transformer and two electrodes, one electrode located in the area of the surface intended for placing the fingers, and the second - in the area of the palm, the electrodes are connected to the first winding of the transformer, the second winding of which is connected to the output force With positive feedback, the electrodes, the transformer, and the amplifier form a loop-amplified LC generator, depending on the required sensitivity of the sensor.

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