WO2008023873A1

WO2008023873A1 - Module of infrared sensor

Info

Publication number: WO2008023873A1
Application number: PCT/KR2007/001786
Authority: WO
Inventors: Man-Sun Yun
Original assignee: Santoma Ltd.; Innova. Inc.
Priority date: 2006-08-22
Filing date: 2007-04-12
Publication date: 2008-02-28
Also published as: CN101632005A; KR100775015B1; CN101632005B

Abstract

There is provided an infrared sensor module. The present invention includes an infrared sensor configured to sense an object by radiating infrared rays; a piezoelectric actuator formed using dome-shaped piezoelectric elements, configured such that the polarization direction thereof is oriented toward the center of curvature thereof, and configured to repeat expansion and contraction in the direction of a normal line with respect to a dome vertex according to the waveform of an applied signal; a vibration shaft formed in a bar shape such that the one side thereof is fastened to the dome vertex of the piezoelectric actuator; a movable element coupled to the vibration shaft so as to be moved in an axial direction; a shading plate fastened to the movable element, located in front of the infrared sensor, and configured to alternately pass and block incident infrared rays; an oscillation unit configured to output square waves and apply the output square waves to the piezoelectric actuator; and a control unit configured to operate the piezoelectric actuator by controlling the oscillation unit in response to a signal read from the infrared sensor. In accordance with the present invention, the infrared sensor module has advantages in that it is constructed in a simple structure using a dome-shaped piezoelectric actuator, has a relatively large generated force, and can operate at low voltage.

Description

[DESCRIPTION]

[invention Title]

MODULE OF INFRARED SENSOR [Technical Field] The present invention relates to an infrared sensor module and, more particularly, to an infrared sensor module, which can continuously sense an immovable infrared radiator using a method of alternately passing or blocking infrared rays. [Background Art]

Generally, a pyroelectric type infrared sensor is a sensor that uses the pyroelectric characteristic of pyroelectric material, and also uses variation in temperature, which is caused by infrared radiation energy based on blackbody radiation. The pyroelectric type infrared sensor can sense infrared rays radiated from the human body, and thus it is most widely used for the purpose of sensing the human body and is used for an automatic illumination lamp, an automatically opening and closing entrance door, an automatic water supply device, and an intrusion alarm device. Furthermore, the pyroelectric type infrared sensor is also used for various devices using infrared absorption, for example, a gas detector, a toxic gas alarm device and a fire alarm device. Such a pyroelectric type infrared sensor detects variation in transient temperature, so that the output signal thereof is no longer detected when the temperature of pyroelectric material enters a stable state after it changed. That is, the output signal is generated only once when infrared rays are incident for the first time and, thereafter, the output signal is no longer generated in the case where a heat source remains motionless. For this reason, the pyroelectric type infrared sensor has a definite problem in that the applications thereof are limited. For example, an automatic lamp having the pyroelectric type infrared sensor is often installed in a bathroom, an apartment hall, a basement staircase, and so on. The automatic lamp is turned on once when a person appears, but is turned off after a predetermined time despite the continued presence of the person. In order to solve the problem with this kind of pyroelectric type infrared sensor, the temperature experienced by the pyroelectric material must be continuously varied through the periodical and alternately passing and blocking of the incident infrared rays.

FIG. 1 is a diagram showing the construction of a conventional pyroelectric type infrared sensor.

The pyroelectric type infrared sensor is generally made of a Pb(Zr,Ti)O3-based piezoelectric ceramic material, or a single crystal material such as LiTaO3 and, as shown in FIG. 1, has a structure in which a silicon window 2 for selectively passing only an infrared wavelength therethrough is installed at the upper center of a cap body 6, a pyroelectric material 4 for sensing the infrared wavelength passing through the silicon windows 2 is fastened to the top surface of a conductive support 5 using an adhesive, a high- impedance element 7 and a Field Effect Transistor (FET) 8 are connected with each other so as to amplify a signal generated in the pyroelectric material 4, and are installed on a lower support 3, and then a cap 1 is sealed after nitrogen is injected into the cap 1. Meanwhile, wires 9 for transmitting signals to the outside are installed on the lower support 3.

The operational principle of the pyroelectric material 4 is shown in FIG. 2. FIG. 2 is a diagram illustrating the operational principle of the pyroelectric material of the conventional pyroelectric type infrared sensor. When absorbing thermal energy, the pyroelectric material 4 varies spontaneous polarization 10, which induces surface charges. Furthermore, the surface charges 11 are proportional to variation in the spontaneous polarization. This phenomenon is called a pyroelectric effect. A pyroelectric sensor using ceramic material can sense minute amounts of infrared energy that radiates from the human body, which will be described in more detail below.

As shown in FIG. 2 (a) , when the spontaneous polarization is induced in the pyroelectric material 4 in a specific direction, the surface charges 11 are induced to a surface electrode at a temperature T [K] at which thermal equilibrium is achieved, so that the pyroelectric material 4 maintains electrical neutrality. However, in this state, when the infrared rays having thermal energy are incident on the pyroelectric material, the temperature of the pyroelectric material 4 is increased from T[K] to (T+ΔT) [K], and the amount of spontaneous polarization 10 is decreased in proportion to the increase in temperature, as shown in FIG. 2 (b) . The variation in the spontaneous polarization is rapidly performed, and free charges 12 are generated from some of the surface charges 11 bound to the surface of the pyroelectric material. The free charges 12, which are not coupled with the internal spontaneous polarization 10, as described above, flow through a conducting wire 13 connected with the surface electrode of the pyroelectric material, and then disappear through a high-impedance load 14 installed at the intermediate portion of the conducting wire 13. In this case, when a voltmeter is connected between the two ends of the high-impedance load 14, a voltage that is proportional to the amount of the flowing free charges is detected. When the free charges 12 are discharged along the conducting wire and then no variation in temperature occurs any longer, the free charges are not discharged from the pyroelectric material and no voltage from the high-impedance load 14 is detected, and thus a signal from the infrared sensor is no longer detected. Accordingly, in order to detect a continuously output signal, the temperature of the pyroelectric material must cause continuous reversible variation from T[K] to (T+ΔT) [K] through the alternate passing and blocking of the infrared rays that are incident on the pyroelectric material.

In this case, when the passing and blocking period is too short, the pyroelectric material is not heated by the infrared rays, so that the variation in temperature is decreased, and the magnitude of the output voltage is decreased. In contrast, when the passing and blocking period is too long, the spontaneous polarization of the pyroelectric material is gradually decreased, so that a small amount of free charges flows through the high-impedance load 14, therefore a large amount of free charges cannot be simultaneously generated. Accordingly, it is necessary to adjust the passing and blocking period in consideration of the heat capacity of the pyroelectric material. FIG. 3 is a graph showing the outputs of the conventional pyroelectric type infrared sensor with respect to frequencies. As shown in FIG. 3, it can be seen that the maximum output is obtained when the frequency is 1 [Hz] . That is, when the passing and blocking period of the infrared is set to 1 [Hz] , the maximum output of the pyroelectric type infrared sensor is acquired.

Recently, an infrared passing and blocking device using two piezoelectric bimorph vibrators and two slit plates has been developed. First, the operational principle of a piezoelectric bimorph element will be described below with reference to FIG. 4. Piezoelectric elements have a characteristic of generating displacement when electrical energy is applied thereto. In this case, the generated displacement is obtained using the following Equation 1. [Equation l] x=dE where x denotes the displacement amount, d denotes the piezoelectric constant, and E denotes the applied voltage. In the typical piezoelectric material, a displacement of about 10 μm occurs when 10 kV is applied to a piece of piezoelectric material having a length of 1 cm. In order to increase the above-described small displacement, when a metal elastic plate 22 is interposed between the piezoelectric elements 21 and is adhered thereto using an adhesive, and then one end of the adhered product is fastened to a fixture 23, as shown in FIG. 4, the displacement of the other end thereof is obtained using the following Equation 2. [Equation 2]

3 /²

Δ^χl o «31 2 ^

where Δxl denotes the generated displacement, d31 denotes the diametrical piezoelectric constant, 1 denotes the length of the free end, t denotes the thickness of each piezoelectric element, and E denotes the applied voltage. In this case, when the typical length is set to 10 mm and when a voltage of 1 kV is applied, a displacement of about 100 μm occurs. That is, if the infrared sensor is manufactured using piezoelectric bimorphs, the displacement can be amplified tens of times.

The entire construction of a pyroelectric type infrared sensor that has recently been developed using this basic principle is shown in FIG. 5. FIG. 5 is a perspective view of a conventional pyroelectric type infrared sensor including piezoelectric bimorphs and slits.

In FIG. 5, a silicon window 60 for selectively transmitting infrared rays is installed at the upper portion of a cap 61, and the infrared rays 62 are incident through the silicon window. The incident infrared rays are alternately passed and blocked by slit plates 64 and 64 ' installed on respective free ends of the piezoelectric bimorphs 63, pass through a circular hole 67, which is formed in the upper portion of a shield box 66 in which a pyroelectric element 65 is installed, and are incident on the pyroelectric element 65. In this manner, the pyroelectric type infrared sensor is constructed to detect a voltage that is proportional to the amount of infrared rays .

FIG. 6 is a diagram illustrating a principle of alternately passing and blocking infrared rays in the pyroelectric type infrared sensor of FIG. 5. In the case where a voltage of 0 [V] is initially applied to the piezoelectric bimorphs, an upper slit plate 82 and a lower slit plate 83 are open, as shown in FIG. 6 (a), and thus the infrared rays 81 pass through the slit plates. However, when a specific voltage is applied to the piezoelectric bimorphs, the slit plates move in opposite directions, and thus the infrared rays 81 are blocked, as shown in FIG. 6(b).

The infrared passing and blocking device, having the above-described structure, is advantageous in that the consumption power thereof can be reduced to 30 mW, which is a small consumption power corresponding to about 1/40 times that of a motor type, and the size thereof can also be reduced to 1/20. Furthermore, the infrared passing and blocking device can make use of an operating frequency lowered to 5 Hz. However, the incident infrared rays are reduced by 1/2 due to closed surfaces other than the slits of the slit plates, and thus the output voltage is reduced by 1/2 in proportion to this reduction. In the case where the slits are not processed with high precision, variation in sensitivity is great, and the cost of processing the slits is high. In practice, the ends of respective piezoelectric bimorphs follow arcs, rather than moving linearly, so that the processing of the slits is made more difficult. Furthermore, because the two piezoelectric bimorphs must accurately match each other in dimensions and in piezoelectric characteristics, there are difficulties in the aspect of production. Furthermore, a hole is formed in the upper portion of the shield box, in which the infrared sensor is provided, and the slit plates, which are installed on the ends of the respective piezoelectric bimorphs arranged over the shield box, generate airflow while moving in opposite directions. Accordingly, a problem occurs in that this causes noise. This problem occurs because the displacement of the piezoelectric bimorphs is not sufficiently large. For this reason, research into schemes for increasing the generated displacement has been conducted, but such schemes are not commercially useful due to the structural complexity thereof.

In order to solve such problems, an infrared passing and blocking device using a dome-shaped piezoelectric linear motor has been devised. A piezoelectric linear motor that has been developed in the past is not suitable for a small- sized motor because the circuits thereof are complicated in order to generate triangular waves applied to the device. Furthermore, in the case of using a multi-layer piezoelectric actuator in order to increase axial displacement, the infrared passing and blocking device is advantageous in that it can operate at low drive voltage and can increase generated force, but is disadvantageous in the aspect of price and durability. Furthermore, in the case of using the piezoelectric bimorphs, the infrared passing and blocking device is disadvantageous in that the drive voltage thereof is high and the generated force thereof is low. Furthermore, a problem occurs in that the reduction of the durability caused by separation between the metal plate and the piezoelectric elements during continuous driving cannot be avoided. [Disclosure] [Technical Problem] Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide an infrared sensor module, which is configured to have excellent production efficiency and high dimensional accuracy, is constructed in a simple structure using a dome-shaped piezoelectric actuator that is manufactured using a powder injection molding method of easily manufacturing a product having an arbitrary shape, is configured to have a relatively large generated force, and is provided with an infrared passing and blocking device that can operate at low voltage.

[Advantageous Effects]

As described above, in accordance with the present invention, the infrared sensor module has advantages in that it is constructed in a simple structure using a dome-shaped piezoelectric actuator, has a relatively large generated force, can operate at low voltage, and can detect a continuous signal even from an immovable infrared radiator.

[Description of Drawings] FIG. 1 is a diagram showing the construction of a conventional pyroelectric type infrared sensor;

FIG. 2 is a diagram illustrating the operational principle of the pyroelectric material of the conventional pyroelectric type infrared sensor; FIG. 3 is a graph showing the outputs of the conventional pyroelectric type infrared sensor, with respect to frequencies;

FIG. 4 is a diagram showing the construction and displacement of piezoelectric bimorphs;

FIG. 5 is a perspective view of a conventional pyroelectric type infrared sensor including piezoelectric bimorphs and slits;

FIG. 6 is a diagram illustrating a principle of alternately passing and blocking infrared rays in the pyroelectric type infrared sensor of FIG. 5;

FIG. 7 is a diagram showing the displacement of a piezoelectric actuator, which depends on an applied waveform, in an infrared sensor module, according to an embodiment of the present invention;

FIG. 8 is a diagram showing the displacement of the piezoelectric actuator, which is obtained using finite element method analysis, according to an embodiment of the present invention; FIGS. 9 and 10 are the states of a piezoelectric actuator and a movable element in the infrared sensor module, which depend on an applied waveform, according to an embodiment of the present invention; FIG. 11 is a diagram showing the appearances of a piezoelectric actuator, a vibration shaft and a movable element of the infrared sensor module, according to an embodiment of the present invention; FIG. 12 is a diagram showing the case where a shading plate is added to FIG. 11;

FIG. 13 is a diagram showing the case where a guide is added to FIG. 12;

FIG. 14 is a diagram showing the actual appearance of an infrared sensor module according to an embodiment of the present invention;

FIG. 15 is a graph showing the output waveform of an infrared sensor according to an embodiment of the present invention; and FIG. 16 is a block diagram showing the internal structure of an infrared sensor module according to an embodiment of the present invention. [Mode for Invention]

In order to accomplish the above object, the present invention provides an infrared sensor module, including an infrared sensor configured to sense an object by radiating infrared rays; a piezoelectric actuator formed using dome- shaped piezoelectric elements, configured such that the polarization direction thereof is oriented toward the center of curvature thereof, and configured to repeat expansion and contraction in the direction of a normal line with respect to a dome vertex according to the waveform of an applied signal; a vibration shaft formed in a bar shape such that the one side thereof is fastened to the dome vertex of the piezoelectric actuator; a movable element coupled to the vibration shaft so as to be moved in an axial direction; a shading plate fastened to the movable element, located in front of the infrared sensor, and configured to alternately pass and block incident infrared rays; an oscillation unit configured to output square waves and apply the output square waves to the piezoelectric actuator; and a control unit configured to operate the piezoelectric actuator by controlling the oscillation unit in response to a signal read from the infrared sensor.

The infrared sensor module may further include a guide installed on the vibration shaft to limit the moving distance of the movable element.

The infrared sensor module may further include a booster unit for boosting the square waves, which are output from the oscillation unit, to a voltage level suitable for the piezoelectric actuator. The infrared sensor module may further include an OP amplifier for amplifying signals output from the infrared sensor.

The infrared sensor module may further include an elastic body located between the vibration shaft and the movable element and configured to couple the movable element with the vibration shaft.

When a signal having a value equal to or greater than a reference value is received from the infrared sensor, the control unit may cause the piezoelectric actuator to contract or expand by controlling the oscillation unit, whereas, when a signal having a value less than the reference value is received from the infrared sensor, the control unit may stop the operation of the piezoelectric actuator after operating the piezoelectric actuator so that the shading plate does not shade the infrared sensor by controlling the oscillation unit. In this case, when no signal has been received from the infrared sensor for a predetermined period, the control unit may turn off the power of the oscillation unit. When square waves having a pulse width equal to or greater than a predetermined level are applied by the oscillation unit, the piezoelectric actuator may expand in the direction of the normal line with respect to the dome vertex. That is, when square waves having a pulse width equal to or greater than a predetermined level are applied by the oscillation unit, the piezoelectric actuator may expand in the direction of the normal line with respect to the dome vertex in intervals in which the respective square waves rise and maintain the maximum value thereof, and may be restored to the original shape thereof in intervals in which the respective square waves fall.

When square waves having a pulse width less than a predetermined level are applied by the oscillation unit, the piezoelectric actuator may contract in the direction of the normal line with respect to the dome vertex. That is, when square waves having a pulse width less than a predetermined level are applied by the oscillation unit, the piezoelectric actuator may contract in the direction of the normal line with respect to the dome vertex in intervals in which the respective square waves rise and maintain the maximum value thereof, and may be restored to the original shape thereof in intervals in which the respective square waves fall.

Embodiments of the present invention are described in detail with reference to the accompanying drawings below. First, it should be noted that, when assigning reference numerals to components in each drawing, the same components are represented by identical reference numerals even though they are shown in different drawings. Furthermore, when detailed descriptions of well-known functions or constructions are determined to make the gist of the present invention needlessly unclear in the description of the present invention, such detailed descriptions will be omitted.

FIG. 16 is a block diagram showing the internal structure of an infrared sensor module according to an embodiment of the present invention. The infrared sensor module includes a piezoelectric actuator 100, a vibration shaft 103, a movable element (not shown) , a shading plate 107, an infrared sensor 200, an oscillation unit 300, a control unit 400, a booster unit 500, an OP amplifier 600 and a power source unit 700.

The infrared sensor 200 functions to emit infrared rays and sense an object. In FIG. 16, the infrared sensor 200 includes an infrared window 203 for selectively passing only infrared rays therethrough. In an embodiment of the present invention, the infrared sensor may be a pyroelectric type infrared sensor. The piezoelectric actuator 100 is formed using dome- shaped piezoelectric elements, configured such that the polarization direction thereof is oriented toward the center of curvature thereof, and configured to repeat expansion and contraction in the direction of the normal line with respect to a dome vertex according to the waveform of an applied signal. In an embodiment of the present invention, the piezoelectric actuator 100 may have excellent production efficiency and high dimensional accuracy, may be manufactured using a powder injection molding method of easily manufacturing a product having an arbitrary shape, and may include a dome shape and a three-dimensional shape similar thereto.

The vibration shaft 103 is formed in a bar shape such that one end thereof is fastened to the dome vertex of the piezoelectric actuator 100.

The movable element (not shown) is coupled to the vibration shaft 103 so as to be moved in an axial direction.

The shading plate 107 is fastened to the movable element and is located at the front of the infrared sensor

200, and is responsible for alternately passing and blocking incident infrared rays. In the present invention, a detailed description of the parts for alternately passing and blocking infrared rays, such as the piezoelectric actuator 100, the vibration shaft 103, the movable element, and the shading plate 107, is given later.

Under the control of the control unit 400, the oscillation unit 300 outputs square waves and applies the output square waves to the piezoelectric actuator 100. The control unit 400 controls the oscillation unit 300 in response to a signal read from the infrared sensor 200 and thus operates the piezoelectric actuator 100.

The booster unit 500 functions to boost square waves, which are output from the oscillation unit 300, to a voltage level suitable for the piezoelectric actuator 100. The booster unit 500 may be omitted depending on the embodiment of the invention.

The OP amplifier 600 functions to amplify signals output from the infrared sensor 200. The OP amplifier 600 may be omitted depending on the embodiment of the invention.

The power source unit 700 functions to supply power to the oscillation unit 300 and the control unit 400.

FIG. 11 is a diagram showing the appearance of a piezoelectric actuator, a vibration shaft and a movable element of the infrared sensor module, according to an embodiment of the present invention.

A piezoelectric actuator 100 formed using dome-shaped piezoelectric elements, a vibration shaft 103 formed in a bar shape such that one end thereof is fastened to the dome vertex of the piezoelectric actuator 100, and a movable element 105 coupled to the vibration shaft 103 so as to be moved in an axial direction are shown in FIG. 11. In an embodiment of the present invention, an elastic body 109, which is located between the vibration shaft 103 and the movable element 105 and is configured to couple the movable element 105 with the vibration shaft 103, may be further included, as shown in FIG. 11. The case where a shading plate 107 is added to the device of FIG. 11 is shown in FIG. 12. The shading plate 107 is fastened to the outside of the elastic body 109 and is located in front of the infrared sensor 200, thus alternately passing and blocking incident infrared rays. In an embodiment of the present invention, the shading plate 107 may be implemented such that the one side thereof is wound in a spring form to thereby be fastened to the outside of the movable element 105 and the other side thereof shades the infrared sensor 200, through the processing of a stainless steel plate.

FIG. 13 is a diagram showing the case where a guide is added to FIG. 12. The guide 111 is installed on the vibration shaft 103 to limit the moving distance of the movable element 105. Now, the principle in which the piezoelectric actuator 100 is operated according to the applied voltage is described with reference to the accompanying drawing.

FIG. 7 is a diagram showing the displacement of a piezoelectric actuator, which depends on an applied waveform, in the infrared sensor module, according to an embodiment of the present invention. In FIG. 7 (b) and 7 (d) , portions indicated by arrows A are polarization directions, and a reference character E indicates the direction of the electric field.

In the present invention, the piezoelectric actuator 100 is configured such that the polarization direction thereof is oriented toward the center of curvature thereof, and there is a difference between the electrode area of the upper surface thereof and the electrode area of the lower surface thereof, and thus expansion and contraction are repeated according to the variation in pulse width at the same frequency.

That is, when square waves having a pulse width equal to or greater than a predetermined level are applied by the oscillation unit 300, as in FIG. 7 (a) , the piezoelectric actuator 100 expands in the direction of the normal line with respect to the dome vertex. The state in which the piezoelectric actuator 100 is expended is shown in FIG. 7 (b) . In FIG. 7 (b) , the piezoelectric actuator 100 expands like the portion 100a indicated by the dotted line.

In contrast, when square waves having a pulse width less than a predetermined level are applied by the oscillation unit 300, as in FIG. 7 (c) , the piezoelectric actuator 100 contracts in the direction of the normal line with respect to the dome vertex. The state in which the piezoelectric actuator 100 contracts is shown in FIG. 7 (d) . In FIG. 7 (d) , the piezoelectric actuator 100 contracts, like the portion 100b indicated by a dotted line.

FIG. 8 is a diagram showing the displacement of the piezoelectric actuator, which is obtained using Finite Element Method (FEM) analysis, according to an embodiment of the present invention. FIG. 8 (a) shows the case where the piezoelectric actuator 100 expands, and FIG. 8 (b) shows the case where the piezoelectric actuator 100 contracts.

FIGS. 9 and 10 are the states of a piezoelectric actuator and a movable element in the infrared sensor module, which depend on an applied waveform, according to an embodiment of the present invention.

FIG. 9 (a) is a waveform that is applied to expand the piezoelectric actuator 100. The displacement of the vibration shaft 103, which is generated when the waveform is applied, is shown in FIG. 9(b). FIG. 9 (a) is square waves having a maximum value of 30 [V] .

In FIG. 9(c), when the square waves shown in FIG. 9 (a) are applied, the piezoelectric actuator 100 expands in the direction of the normal line with respect to the dome vertex in an interval a-b-c in which a square wave rises and maintains the maximum value thereof, and is restored to the original shape thereof in an interval c-d, in which the square wave falls. In this case, the movement of the movable element 105 is as follows. In the interval a-b-c, in which the square wave rises and maintains the maximum value thereof, charging is slowly conducted due to the time constant effect caused by the resistance and capacitance of a piezoelectric body, so that the piezoelectric actuator 100 is relatively slowly expanded and the movable element 105 is moved from location 1 to location 2 by the frictional force between the movable element 105 and the vibration shaft 103. Furthermore, in the interval c-d, in which the applied square wave falls, charges transmitted into the dome-shaped piezoelectric actuator 100 are rapidly discharged to ground, so that the piezoelectric actuator 100 is relatively rapidly restored to the original shape, therefore the inertia becomes greater than the frictional force. As a result, the movable element 105 stays at location 2. As this process is repeated, the movable element 105 continuously moves in the direction indicated by the arrows.

In contrast, FIG. 10 (a) is a waveform that is applied to contract the piezoelectric actuator 100. The displacement of the vibration shaft 103, which is generated when the waveform is applied, is shown in FIG. 10 (b) . FIG. 10 (a) shows square waves having a maximum value of 30 [V] .

In FIG. 10 (c) , when the square waves shown in FIG. 10

(a) are applied, the piezoelectric actuator 100 contracts in the direction of the normal line with respect to the dome vertex in an interval a-b-c in which a square wave rises and maintains the maximum value thereof, and is restored to the original shape thereof in an interval c-d in which the square wave falls. In this case, the movement of the movable element 105 is as follows. In the interval a-b-c, in which the square wave rises and maintains the maximum value thereof, charging is slowly conducted due to the time constant effect caused by the resistance and capacitance of a piezoelectric body, so that the piezoelectric actuator 100 is relatively slowly contracted and the movable element 105 is moved from location 1 to location 2 by frictional force between the movable element 105 and the vibration shaft 103. Furthermore, in the interval c-d, in which the applied square wave falls, charges transmitted into the dome-shaped piezoelectric actuator 100 are rapidly discharged to ground, so that the piezoelectric actuator 100 is relatively rapidly restored to the original shape thereof, therefore the inertia becomes greater than the frictional force. As a result, the movable element 105 stays at location 2. As this process is repeated, the movable element 105 continuously moves in the direction indicated by the arrows.

As described above, in the present invention, only the pulse signal width is modulated, so that the movable element 105 can easily reciprocate from the right end of the vibration shaft 103 to the left end of the vibration shaft 103 in an arbitrary period. Furthermore, the shading plate 107 is installed on the movable element 105, and thus infrared rays incident on the infrared sensor 200 can be alternately passed and blocked.

That is, in the present invention, the control unit 400 can control the signal width of the square waves by controlling the oscillation unit 300 in response to a signal read from the infrared sensor 200. In an embodiment of the present invention, when a signal having a value equal to or greater than a reference value is received from the infrared sensor 200, the control unit 400 controls the oscillation unit 300, and thus causes the piezoelectric actuator 100 to contract or expand. In contrast, when a signal having a value less than the reference value is received from the infrared sensor 200, the control unit 400 controls the oscillation unit 300, and thus stops the operation of the piezoelectric actuator 100 after operating the piezoelectric actuator 100, so that the shading plate 107 does not shade the infrared sensor 200.

In this case, when no signal has been received from the infrared sensor 200 for a predetermined period, the control unit 400 may turn off the power of the oscillation unit 300.

FIG. 14 is a diagram showing the actual appearance of an infrared sensor module according to an embodiment of the present invention. FIG. 14 (a) shows the case where the shading plate 107 does not shade the infrared window 203 of the infrared sensor 200, and FIG. 14 (b) shows the case where the shading plate 107 shades the infrared window 203 of the infrared sensor 200.

The present invention, as shown in FIG. 14 (a) , maintains the initial state of the infrared sensor module, that is, the state in which the infrared window 203 is open, and thus prevents the incidence of infrared rays from being interrupted.

FIG. 15 is a graph showing the output waveform of an infrared sensor according to an embodiment of the present invention. FIG. 15 (a) is a waveform that is output when the infrared sensor 200 has sensed a radiation object. Conventionally, when no movement of the radiation object is sensed after the waveform shown in FIG. 15 (a) has been generated, the output waveform is no longer generated. However, the present invention causes the infrared sensor 200 to periodically and alternately pass and block infrared rays using the piezoelectric actuator 100 and the shading plate 107, so that it can continuously operate the infrared sensor 200, even in an immovable radiator. That is, the continuous output waveform shown in FIG. 15 (b) is output from the infrared sensor 200.

Meanwhile, when the radiator is gone, and thus there is no object that radiates infrared rays, the output signal shown in FIG. 15 (c) is not generated from the infrared sensor 200 even if the infrared sensor 200 operates to alternately pass and block infrared rays. In this case, the control unit 400 controls the oscillation unit 300 so that it is restored to a standby mode and, thus, causes the operation of the piezoelectric actuator 100 to be changed to a stopped state after operating the piezoelectric actuator 100, so that the shading plate 107 does not shade the infrared sensor 200.

As described above, although the present invention has been described with reference to several preferred embodiments, these embodiments are illustrative but not restrictive. Those having ordinary knowledge in the art to which the present invention pertains will appreciate that various variations and modifications are possible without departing from the spirit of the present invention or from the scope defined by the accompanying claims.

Claims

[CLAIMS]

[Claim l]

An infrared sensor module, comprising: an infrared sensor configured to sense an object by radiating infrared rays; a piezoelectric actuator formed using dome-shaped piezoelectric elements, configured such that a polarization direction thereof is oriented toward a center of curvature thereof, and configured to repeat expansion and contraction in a direction of a normal line with respect to a dome vertex according to a waveform of an applied signal; a vibration shaft formed in a bar shape such that one side thereof is fastened to the dome vertex of the piezoelectric actuator; a movable element coupled to the vibration shaft so as to be moved in an axial direction; a shading plate fastened to the movable element, located in front of the infrared sensor, and configured to alternately pass and block incident infrared rays; an oscillation unit configured to output square waves and apply the output square waves to the piezoelectric actuator; and a control unit configured to operate the piezoelectric actuator by controlling the oscillation unit in response to a signal read from the infrared sensor.

[Claim 2]

The infrared sensor module according to claim 1, further comprising a guide installed on the vibration shaft to limit a moving distance of the movable element.

[Claim 3]

The infrared sensor module according to claim 1, further comprising a booster unit for boosting the square waves, which are output from the oscillation unit, to a voltage level suitable for the piezoelectric actuator.

[Claim 4]

The infrared sensor module according to claim 1, further comprising an OP amplifier for amplifying signals output from the infrared sensor.

[Claim 5]

The infrared sensor module according to claim 1, further comprising an elastic body located between the vibration shaft and the movable element and configured to couple the movable element with the vibration shaft .

[Claim 6] The infrared sensor module according to any one of claims 1 to 5, wherein, when a signal having a value equal to or greater than a reference value is received from the infrared sensor, the control unit causes the piezoelectric actuator to contract or expand by controlling the oscillation unit, whereas, when a signal having a value less than the reference value is received from the infrared sensor, the control unit stops operation of the piezoelectric actuator after operating the piezoelectric actuator so that the shading plate does not shade the infrared sensor by controlling the oscillation unit.

[Claim 7]

The infrared sensor module according to claim 6, wherein, when no signal has been received from the infrared sensor for a predetermined period, the control unit turns off power of the oscillation unit.

[Claim 8] The infrared sensor module according to any one of claims 1 to 5, wherein, when square waves having a pulse width equal to or greater than a predetermined level are applied by the oscillation unit, the piezoelectric actuator expands in the direction of the normal line with respect to the dome vertex.

[Claim 9]

The infrared sensor module according to claim 8, wherein, when square waves having a pulse width equal to or greater than a predetermined level are applied by the oscillation unit, the piezoelectric actuator expands in the direction of the normal line with respect to the dome vertex in intervals in which the respective square waves rise and maintain a maximum value thereof, and is restored to an original shape thereof in intervals in which the respective square waves fall.

[Claim 10] The infrared sensor module according to any one of claims 1 to 5, wherein, when square waves having a pulse width less than a predetermined level are applied by the oscillation unit, the piezoelectric actuator contracts in the direction of the normal line with respect to the dome vertex. [Claim ll]

The infrared sensor module according to claim 10, wherein, when square waves having a pulse width less than a predetermined level are applied by the oscillation unit, the piezoelectric actuator contracts in the direction of the normal line with respect to the dome vertex in intervals in which the respective square waves rise and maintain a maximum value thereof, and is restored to an original shape thereof in intervals in which the respective square waves fall.