JP3414563B2 - Piezoelectric chopper and pyroelectric infrared sensor - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chopper for various sensors and a pyroelectric infrared sensor for detecting infrared rays emitted from an object in a non-contact manner.

[0002]

2. Description of the Related Art In recent years, pyroelectric infrared sensors have been used in a wide range of fields such as measuring the temperature of food in a microwave oven and detecting the position of a human body in an air conditioner. The pyroelectric infrared sensor utilizes the pyroelectric effect of a pyroelectric material such as a LiTaO ₃ single crystal.

[0003] Pyroelectric materials have spontaneous polarization and always generate surface charges, but in the steady state in the atmosphere, they are electrically neutral by being combined with the charges in the atmosphere. When infrared rays are incident on this pyroelectric body, the temperature of the pyroelectric body changes, and along with this, the charge state of the surface also changes, breaking the neutral state. The pyroelectric infrared sensor measures the incident amount of infrared rays by detecting the charges generated on the surface.

An object emits infrared rays according to its temperature, and the temperature and position of the object can be measured by using this sensor. The pyroelectric effect is caused by a change in the incident amount of infrared rays, and it is necessary to change the incident amount of infrared rays when detecting the temperature of an object as a pyroelectric infrared sensor. A chopper is used as this means and detects the temperature of the detection object by forcibly interrupting the incident infrared rays.

As a conventional chopper, a chopper utilizing an electromagnetic motor and a piezoelectric actuator has been mainly used. FIG. 15 shows a conventional example of a pyroelectric infrared sensor using an actuator in which a piezoelectric ceramic is adhered to an elastic thin plate as a chopper. Generally, an actuator that bonds a piezoelectric ceramic to an elastic thin plate such as a metal to form a bonded element, holds and fixes one end, and generates a bending motion due to strain when a voltage is applied to the piezoelectric ceramic,
A piezoelectric thin plate having piezoelectric ceramics bonded to both sides is called a bimorph type, and a plate having only one surface bonded to it is called a unimorph type. Also, elastic thin plate is called elastic shim material,
Hereinafter, each member will be referred to as such.

The pyroelectric infrared sensor shown in FIG. 15 is
A bimorph type element is used as a chopper of a pyroelectric infrared sensor, 10 is an elastic shim material, 11a, 11
b is a piezoelectric ceramic, 12 is a shielding plate, 13 is a pedestal, 14
Reference numeral a is a fixture, 15 is an infrared detector, and 16 is incident light.

Piezoelectric ceramics 11a and 11b are bonded to both surfaces of the elastic shim material 10 to form a bimorph type element. Electrodes are formed on the surfaces of the piezoelectric ceramics 11a and 11b, and polarization processing is performed in the thickness direction. The polarization directions of the piezoelectric ceramics 11a and 11b are the same as those of the elastic shim material 10 and the piezoelectric ceramics 11a and 11b.
The piezoelectric ceramics 11a and 11b are determined so as to always generate strains in directions opposite to each other, depending on the direction of the electric field applied between the respective 11b.

That is, the piezoelectric ceramics 11a and 11b
The direction of the applied electric field and the direction of polarization are determined so that when one of the two is distorted in the extending direction, the other is contracted. The bimorph element is held by the pedestal 13 and the fixture 14a by sandwiching a part of the elastic shim material 10 and a part of the piezoelectric ceramics 11a and 11b at the same time.

A shield plate 12 is attached to the free end of the bimorph element. An infrared detector 15 is arranged near the shield plate 12 so as not to contact the shield plate 12 and the bimorph type element.

The elastic shim material 10 and the piezoelectric ceramic 11a,
When an electric field is applied between 11b, the bimorph element generates a bending motion with one end fixed, and the shield plate 12 attached to the tip reciprocates according to the change in the direction of the electric field application. Due to the reciprocating movement of the shielding plate 12, the incident light 16 incident on the infrared detecting section 15 is interrupted.

[0011]

In the piezoelectric bimorph type chopper, it is necessary to make the distance between the infrared detecting section 15 and the shield plate 12 as small as possible in order to efficiently interrupt the incident light. However, in the conventional piezoelectric bimorph type chopper, since the shielding plate 12 performs the shielding movement and the movement in the same direction as the incident light at the same time, the distance between the infrared detecting unit 15 and the shielding plate 12 is extremely small. Can not do it.

As a result, there are major obstacles to miniaturization, high performance, and cost reduction of the sensor itself. Further, the conventional piezoelectric chopper ensures a large amount of displacement while adopting a configuration of directly supporting the piezoelectric body. For this reason, the strain of the piezoelectric body portion of the support portion is significantly increased, which is a great obstacle to achieving high reliability.

It is an object of the present invention to provide a high performance chopper mechanism by downsizing the piezoelectric chopper, increasing the amount of displacement, improving reliability and reducing manufacturing cost.

[0014]

DETAILED DESCRIPTION OF THE INVENTION The piezoelectric chopper according to claim 1 is
An arm portion made of a pair of elastic thin plates facing each other, and a connecting portion made of an elastic thin plate connected to the arm portion and having a direction of a normal vector aligned with the length direction of the arm portion,
A piezoelectric body provided on one surface or both surfaces of the connecting portion, and on the connecting portion or the piezoelectric body for fixing the central portion of the connecting portion in a direction perpendicular to a line connecting the arm portions on the connecting portion.
A fixing member provided on the body , and a shield plate for entering / blocking incident light having a normal vector at the tip of the arm portion in the direction of the mating surface and in the direction perpendicular to the length direction of the arm portion. Prepare,
The resonance frequency of the arm portion is set lower than the resonance frequency of the connecting portion, and the driving frequency of the piezoelectric body is set to be near the resonance frequency of the arm portion.

According to another aspect of the pyroelectric infrared sensor of the present invention, a pair of elastic thin plates facing each other, and an arm portion connected to the arm portion, and a direction of a normal vector thereof coincides with a length direction of the arm portion. a connecting portion made of a thin elastic plate which is provided by a piezoelectric body provided on one side or both sides of the connection portion, for fixing the line perpendicular direction connecting the arm portion in the connecting portion on the central portion of the connecting portion On the connection part or the piezoelectric body
A fixing member provided on the upper portion, a shield plate for entering / blocking incident light having a normal vector at the tip of the arm portion in the direction of the mating surface and in a direction perpendicular to the length direction of the arm portion, An infrared detector for detecting the incident light through a shielding plate, the resonance frequency of the arm is lower than the resonance frequency of the connecting portion, and the driving frequency of the piezoelectric body is near the resonance frequency of the arm. It is characterized by having done.

According to another aspect of the present invention, there is provided a pyroelectric infrared sensor having a pair of elastic thin plates facing each other, an arm portion connected to the arm portion, and a direction of a normal vector coinciding with a length direction of the arm portion. A connecting part made of an elastic thin plate, a piezoelectric body provided on one or both sides of the connecting part, and a protruding part
A pedestal but formed, mating surface on the fixed member, wherein comprising a low material than the elastic modulus of the piezoelectric member for the central portion of the connecting portion is fixed to the base seat, the tip of the front Kiude portion having a piezoelectric And a shield plate for entering / blocking incident light having a normal vector in a direction perpendicular to the arm length direction, and an infrared detector for detecting the incident light through the shield plate. , The fixture and the protrusion formed on the pedestal
The connecting portion having a piezoelectric body is clamped and fixed, the resonance frequency of the arm portion is lower than the resonance frequency of the connecting portion, and the driving frequency of the piezoelectric body is near the resonance frequency of the arm portion. Is characterized by.

In the pyroelectric infrared sensor according to a fourth aspect of the present invention, an arm portion made of a pair of elastic thin plates facing each other, and a direction of a normal vector which is connected to the arm portion and coincides with a length direction of the arm portion. a connecting portion made of a thin elastic plate which is provided by, a piezoelectric disc-shaped provided on one side or both sides of the connecting portion, to 0.5 times 0.95 times the position of the outer diameter of the piezoelectric those A fixture having a concentric annular first protrusion that contacts ,
The same type as the fixture that holds the connecting portion with the fixture
And a pedestal having an annular second protrusion , and makes / blocks incident light having a normal vector at the tip of the arm portion in the direction of the mating surface and in the direction perpendicular to the length direction of the arm portion. A shield plate; and an infrared detector that detects the incident light through the shield plate , the first projection body and the second projection body.
It is characterized in that the connecting portion having the piezoelectric body is sandwiched and fixed .

The pyroelectric infrared sensor of claim 5, wherein, in any one of claims 2 to 4, that it has at least twice the resonant frequency of the bending vibration resonance frequency of the torsional vibration of the arm portions Characterize.

According to a sixth aspect of the present invention, there is provided the pyroelectric infrared sensor according to the fifth aspect, wherein the arm portion is provided with a wavy curved portion.

[0020]

The pyroelectric infrared sensor of claim 7, wherein, in any one of claims 2 to 6, the distance between the shielding plate and the infrared detector, the free end side from the fixed end side of the shield plate It is characterized in that it is changed continuously so that it becomes longer as it goes to.

[0022]

[0023]

[0024]

[0025]

[First Embodiment]

FIG. 1 shows a pyroelectric infrared sensor according to the first embodiment.

The pyroelectric infrared sensor is composed of an infrared detecting section 15 and a piezoelectric chopper for controlling the incidence of light on the infrared detecting section 15. The piezoelectric chopper is composed of a bimorph type piezoelectric actuator.

The piezoelectric chopper is constructed as follows. The elastic shim material (elastic thin plate) 10 is bent into a U shape with the connecting surface 10c at the center, and the arm portions 10a, 1 are formed.
0b is formed. On the connecting surface 10c of the elastic shim material 10, the first and second piezoelectric ceramics 11a and 11b are attached to the front surface and the back surface with the elastic shim material 10 at the center.

The first and second piezoelectric ceramics 11a,
In the elastic shim member 10 to which 11b is attached, the center of the connecting surface 10c is fixed to the pedestal 13 connected to the fixed side by the fixing tool 14a.
It is attached and fixed in.

The shield plates 12a and 12b are used for the infrared detector 1
It is attached to the free ends of the arms 10a and 10b so as to cover the upper side of the arm 5. It should be noted that the first and second piezoelectric ceramics 11a and 11b have electrodes formed on their surfaces and are polarized in the thickness direction, and when they are attached to the elastic shim material 10, the polarization direction is the applied electric field. Considering the direction of
The first and second piezoelectric ceramics 11a and 11b are bonded so as to generate strains in directions opposite to each other.

Due to the above construction, the elastic shim member 10
When an electric field is applied between the elastic shim material 10 and the second piezoelectric ceramic 11b by applying an electric field between the first piezoelectric ceramic 11a and the first piezoelectric ceramic 11a, the connecting surface 10c excites bending vibration, and the vibration is generated by the arm portion 10a. , 10b, and the shield plate 12 at the tip
Drive a and 12b.

Incident light 16 directed to the infrared detector 15 is
It is shielded by the driven shield plates 12a and 12b, or passes through between the shield plates 12a and 12b and enters the infrared detection unit 15.

The connecting surface 10c of the arms 10a and 10b
The height of attachment to the shield plates 12a and 12b is 1
Height d so that they do not hit each other when 6 is cut off
It is attached with a shift.

With the above structure, the vibration excited at the end of the connecting surface 10c can be magnified by utilizing the resonance of the arms 10a and 10b, and the shield plates 12a and 12b can be largely driven.

Further, in this structure, since the vibration of the connecting surface 10c is magnified by the arm portions 10a and 10b, the strain generated in the piezoelectric ceramic portion is sufficiently larger than the brittle fracture strain of the ceramic even if the take-out displacement amount is increased. The size of the piezoelectric ceramic can be reduced and brittle fracture of the piezoelectric ceramic can be prevented.

Since the arm portions 10a and 10b are installed so that the lengthwise direction thereof is perpendicular to the direction of the incident light 16, the shield plates 12a and 12b are in the same direction as the incident direction of the incident light 16. The amount of movement can be reduced to 0.5 mm or less, and the shielding plates 12a and 12b and the infrared detection unit 15 are set to 1 mm.
It can be installed at the following distances.

Further, in the present invention, the arm portions 10a and 10b including the blocking plates 12a and 12b have the resonance frequency of the torsional vibration,
Designed to be more than twice the resonance frequency of flexural vibration. Here, the resonance frequency f _{rb of} flexural vibration and the resonance frequency f _rr of torsional vibration are approximately expressed as follows. Here, L is the total length E of the arm portion, the longitudinal elastic modulus of the arm portion Ip is the second moment of area ρ of the arm portion, the density A of the arm portion, the cross-sectional area G of the arm portion, the lateral elastic modulus of the arm portion m is the tip addition. Mass J is the rotational moment of the mass added to the tip.

[0037]

[Equation 1]

Further, n is a solution of the following equation.

[0039]

[Equation 2]

[0040]

[Equation 3]

Therefore, in the present invention, an arbitrary element shape can be realized by substituting the above two expressions into the conditional expression of f _rb <1 / 2f _rr .

With the above structure, the vibration excited at the end of the connecting surface can be enlarged by utilizing the resonance of the arm, and the shield plate can be largely driven. Further, in this configuration, since vibration of the connecting surface is magnified by the arm portion, even if the take-out displacement is increased, the strain generated in the piezoelectric ceramic portion can be made sufficiently smaller than the brittle fracture strain of the ceramic, and the piezoelectric ceramic becomes brittle. It is possible to prevent destruction.

Further, since the chopper is installed so that the length direction of the arm of the chopper is perpendicular to the infrared ray incident direction and the torsional vibration of the arm portion is hard to excite, the shield plate is in the same direction as the infrared ray incident direction. The amount of movement to can be made almost "0", and the shield plate and the pyroelectric sensor can be installed at a distance of 1 mm or less.

In this embodiment, the shielding plates 12a, 12
Although b is a separate component from the elastic shim member 10, the shield plate 1
2a and 12b and the elastic shim material 10 can be made into an integral member, and the number of parts and man-hours can be reduced.

Needless to say, the same effect can be obtained not only when the connecting surface is a bimorph type element but also when a unimorph type element is used. [Second Embodiment] FIG. 2 and FIG. 3 show [Second Embodiment].

Incidentally, the first embodiment shown in FIG.
Those having the same operation as will be described with the same reference numerals. This [second embodiment] is [first embodiment]
Is the shape of the first and second piezoelectric ceramics 11a and 11b, and the first and second piezoelectric ceramics 11a and 11b.
The attachment structure of the elastic shim material 10 to which b is attached to the pedestal 3 is different.

Specifically, the connecting surface 10 of the elastic shim member 10
Disk-shaped piezoelectric ceramics 11a, so as to sandwich c.
11b is attached to the elastic shim material 10, and the central hole of the connecting surface 10c and the piezoelectric ceramics 11a and 11b are bonded together.
Fixing screw 1 made of relatively soft metal or resin in the center hole
4b is inserted and fixed to the pedestal 13.

Electrodes are formed on the surfaces of the piezoelectric ceramics 11a and 11b, and polarization treatment is performed in the thickness direction. However, the direction of polarization of the piezoelectric ceramics 11a and 11b takes into consideration the direction of the applied electric field, and
a and 11b are determined so as to generate strains in directions opposite to each other.

As a result, between the elastic shim material 10 and the piezoelectric ceramic 11a, and between the elastic shim material 10 and the piezoelectric ceramic 11a.
When an electric field is applied between points b, the coupling surface 10c excites bending vibration, propagates the vibration to the arms 10a and 10b, drives the shield plates 12a and 12b at the tips, and enters the infrared detection unit 15. Light 16 is turned on and off.

As shown in FIG. 3, the pedestal 13 is formed with a hole into which a fixing screw is inserted and a protrusion 13a having a circular shape having a height of 0.1 mm or more for holding the connecting surface 10c or a similar shape. ing. Piezoelectric ceramic 11a,
The connecting surface 10c having 11b attached on both sides is installed on the pedestal 13 so as to ride on the protrusion, and the connecting surface 10c
It is fixed by a fixing screw 14b through a hole provided in the central portion of the.

With the above structure, the vibration excited at the end of the connecting surface can be magnified by utilizing the resonance of the arm and the shield plate can be largely driven. Further, in this configuration, since vibration of the connecting surface is magnified by the arm portion, even if the take-out displacement is increased, the strain generated in the piezoelectric ceramic portion can be made sufficiently smaller than the brittle fracture strain of the ceramic, and the piezoelectric ceramic becomes brittle. It is possible to prevent destruction.

Further, by supporting and fixing the center of the connecting surface, the primary mode vibration can be efficiently excited in the radial direction, and the amplitude of the vibration excited at the end of the connecting surface becomes large. As a result, the enlargement ratio due to the arms can be suppressed to be small, and a chopper having excellent characteristics such as temperature characteristics and variations can be obtained.

Since the chopper is installed so that the arm length direction of the chopper is perpendicular to the infrared ray incident direction, the amount of movement of the shielding plate in the same direction as the incident light incident direction is set to 0.5 mm or less. It is possible to install the shielding plate and the detection unit such as a sensor at a distance of 1 mm or less.

It goes without saying that the above-mentioned effects can be obtained not only when the connecting surface is a bimorph type element but also when a unimorph type element is used. [Third Embodiment] FIGS. 4 and 5 show [Third Embodiment].

The components having the same operations as those in the second embodiment will be described with the same reference numerals. This [third embodiment] is the same as [second embodiment]
The attachment structure of the elastic shim material 10 in which the second piezoelectric ceramics 11a and 11b are bonded to the pedestal 3 is different.

Specifically, the piezoelectric ceramics 11a and 11
The elastic shim material 10 with the b bonded together has a width at a position 0.5 to 0.95 times the radius of the piezoelectric ceramics 11a and 11b from the center on the connecting surface 10c.
Fixture 14c having a concentric annular protrusion 14d having a radius of 0.1 times or less of b, and protrusion 14ds having the same shape as protrusion 14ds.
It is supported and fixed by a pedestal 13b having.

Further, when the shielding plates 12a and 12b block infrared rays, the mounting positions of the arm portions 10a and 10b on the connecting surface 10c are shifted so as not to collide with each other.

With the above structure, the vibration excited at the end of the connecting surface can be expanded by utilizing the resonance of the arm, and the shield plate can be largely driven. Further, in this configuration, since vibration of the connecting surface is magnified by the arm portion, even if the take-out displacement is increased, the strain generated in the piezoelectric ceramic portion can be made sufficiently smaller than the brittle fracture strain of the ceramic, and the piezoelectric ceramic becomes brittle. It is possible to prevent destruction.

In addition, the outer diameter of the piezoelectric ceramic on the connecting surface
By supporting and fixing the position of 0.5 to 0.95 times,
It is possible to efficiently excite the secondary mode vibration in the radial direction with the supporting position as a node. Therefore, a stable support can be obtained while exciting a vibration of large amplitude at the end of the connecting surface.

As a result, it is possible to suppress the enlargement ratio due to the arm portion, obtain a good temperature characteristic and an excellent chopper with less variation, and stabilize the supporting portion to change the supporting condition with temperature. Is less likely to occur and excellent temperature characteristics can be obtained.

Since the chopper is installed so that the length direction of the arm of the chopper is perpendicular to the infrared incident direction, the amount of movement of the shield plate in the same direction as the incident direction of the incident light is 0.5 mm or less. It is possible to install the shielding plate and the detection unit such as a sensor at a distance of 1 mm or less.
In addition, the shielding plates 12a and 12b and the elastic shim member 10 can be made into an integral member, and the number of parts and the number of steps can be reduced.

Needless to say, the effects described above can be obtained not only when the connecting surface is a bimorph type element but also when a unimorph type element is used. [Fourth Embodiment] FIG. 6 shows a fourth embodiment.

The components having the same functions as those of the [first embodiment] shown in FIG. 1 will be described with the same reference numerals. Rigid embodiment is the [first embodiment] arm part 1.
The structures of 0a and 10b are different.

Specifically, the arm portions 10a and 10b are partially formed with a wavy curved portion 17. Arm 1
0a, 10b are installed so that the longitudinal direction thereof is perpendicular to the incident direction of the incident light 16, and the arm portions 10a, 10b are provided with the curved portions 17 to increase the torsional rigidity thereof. , 10b are less likely to excite torsional vibrations, and the amount by which the shield plates 12a, 12b move in the same direction as the incident direction of the incident light 16 can be made approximately “0”.
The shield plates 12a and 12b and the infrared detection unit 15 can be installed at a distance of 1 mm or less.

It is also possible to make the shielding plates 12a and 12b and the elastic shim member 10 into an integral member, and by doing so, the number of parts and man-hours can be reduced, and the connecting surface is a bimorph type element. Not only in the case but also in the case of the unimorph type element, the same effect can be obtained.

[Fifth Embodiment] FIG. 7 shows [Fifth Embodiment]. It should be noted that components having the same operations as those of the [first embodiment] shown in FIG.

This embodiment is different from the [first embodiment] in the structure of the arms 10a and 10b. Specifically, each of the arm portions 10a and 10b is provided with a slit group 18 in which a plurality of slits extending in the width direction are formed.

As described above, the arms 10a and 10b are installed so that the lengthwise direction thereof is perpendicular to the direction of incidence of the incident light 16, and the slits 18 are provided on the arms 10a and 10b.
By not significantly lowering the torsional rigidity and significantly reducing the flexural rigidity, it becomes difficult to excite the torsional vibration in the arm portion, and the amount by which the shield plate moves in the same direction as the infrared ray incident direction can be made almost "0", The shield plates 12a and 12b and the infrared detector 15 can be installed at a distance of 1 mm or less.

It is also possible to form the shielding plates 12a and 12b and the elastic shim member 10 as an integral member, and by doing so, the number of parts and man-hours can be reduced, and the connecting surface is a bimorph type element. Not only in the case but also in the case of the unimorph type element, the same effect can be obtained.

[Sixth Embodiment] FIGS. 8 and 9 show a sixth embodiment.
Of the present invention] and is different from each of the above-described embodiments in the following points.

As shown in FIG. 8, the shield plates 12a and 12b that control the incidence and shielding of the incident light 16 are normal to the surface of the other arm and in the direction perpendicular to the length of the arm. It is attached near the free ends of the elastic shim arm portions 10a and 10b so as to have a vector, forms an angle with the diagonal line of the shielding plate as a boundary, and is separated from the sensor from the fixed end side to the tip end.

As shown in FIG. 9, a point a is a shield plate portion which interrupts incident light on the most free end side incident on the sensor,
Point b is a shield plate portion that interrupts the incident light on the most fixed end side incident on the sensor.

By the way, in the chopper of this construction,
The point b has a slower opening / closing speed than the point a, and the opening / closing amount is small. In this case, it is difficult to make the opening / closing speed and the opening / closing amount at the points a and b the same.

Therefore, in order to make the opening / closing speed and the opening / closing amount the same, the shielding plate is constructed so that the point b is closer to the sensor than the point a. As a result, from the sensor field of view at point a, b
The sensor's field of view at the point becomes smaller, and the shield plate is optimally designed to optimize the difference in this sensor's field of view, so that the motion of the shield plate seen from the sensor is uniform in all parts with respect to the sensor. Can be set to. Next, the guidelines for the optimum design of this shielding plate will be shown.

The distance from the fixed end of the arm portion to the point a is La. The distance from the fixed end of the arm portion to the point b is Lb. The sensor lens diameter is r. The viewing angle of the sensor is 2θ. The distance from the point a to the sensor is hab. Assuming that the distance from the point to the sensor is hb, the optimum value of the difference (ha-hb) between the distance from the sensor to the point a and the distance to the point b (ha-hb) is

[0076]

[Equation 4]

It is represented by With this configuration, the movement of the shielding plate seen from the sensor is uniform in any part with respect to the sensor, and it is possible to obtain a highly accurate sensor, and the opening / closing time, opening / closing speed, and opening / closing amount are constant in any part of the sensor. High performance sensor characteristics can be obtained.

[Seventh Embodiment] FIGS. 10 and 11 show [Seventh Embodiment]. FIG. 10 shows an example of the admittance characteristic of the chopper for the pyroelectric infrared sensor of the first embodiment, where the vertical axis is the admittance and the horizontal axis is the frequency. f _r1 represents the resonance frequency of the arm, f _r2 represents the resonance frequency of the connecting surface, and the frequency deviation is 1 of the higher of the resonance frequency of the arm and the resonance frequency of the connecting surface.
It is kept below 0%. The shaded area shows an example of the area for driving a normal piezoelectric actuator, and by suppressing the frequency deviation within 10%, it can be used as a drive frequency up to the resonance frequency. The magnification of the vibration of the surface can be set to a significantly large value. As a result, the pyroelectric infrared sensor chopper can be driven with an extremely small applied voltage, which is particularly effective for a sensor that is easily affected by the voltage.

Further, with the same element structure as in the [first embodiment], the following effects also exist. With this configuration, the vibration of the connecting surface is magnified by the arm, so even if the take-out displacement is increased, the strain generated in the piezoelectric ceramic part can be made sufficiently smaller than the brittle fracture strain of the ceramic, and the piezoelectric ceramic undergoes brittle fracture. Can be prevented.

Further, since the chopper is installed so that the arm length direction of the chopper is perpendicular to the infrared ray incident direction, the movement amount of the shielding plate in the same direction as the incident light incident direction is 0.5 mm. The following can be set, and the shield plate and the detection unit such as a sensor can be installed at a distance of 1 mm or less. In addition, the shield plate and the elastic shim material can be integrated into one member, and the number of parts and the number of steps can be reduced.

Since the resonance frequency also varies depending on the same bimorph type element depending on the ambient temperature condition and the like, a circuit for tracking the resonance frequency is often used. FIG. 11 shows an example of a resonance frequency tracking circuit for a bimorph type element, where 201 is a bimorph type element, 202 is a resistor, and 203.
Is a bandpass filter, 204 is a phase shift circuit, 205 is a limiter, and 206 is an amplifier.

The current flowing in the bimorph type element 201 is converted into a voltage by the resistor 202, and the bandpass filter 203
After shaping the waveform with, the phase shift circuit 204 determines the resonance point, the amplifier 206 amplifies the signal, and the bimorph element 2
Return to 01. By tracking the resonance point, it is possible to always drive at the resonance frequency, and it is not necessary to adjust for the variation of the resonance frequency due to the processing variation of the bimorph type element or the fixed position variation.

Although the first embodiment has been described as an example here, the second embodiment to the sixth embodiment can be similarly implemented. [Eighth Embodiment] FIG. 12 shows [Eighth Embodiment].

FIG. 12 shows an example of the admittance characteristics of the chopper for the pyroelectric infrared sensor according to the first embodiment. The four vertical axes represent admittance and the horizontal axis represents frequency. f
_r1 represents the resonance frequency of the arm portion, f _r2 represents the resonance frequency of the connecting surface, and f _r1 is a frequency sufficiently lower than f _r2 . The shaded area shows an example of the area for driving a normal piezoelectric actuator, and the driving frequency is brought near f _r1 to increase the magnification for enlarging the vibration of the coupling surface. . Further, since the driving is performed at a frequency much lower than the resonance frequency f _r2 of the connecting surface, it is possible to cancel the influence of the temperature characteristic of the vibration of the connecting portion which hits the vibration source and the variation among the individuals due to the dimensional error of the element.

Moreover, the following effects also exist due to the same element structure as in the [first embodiment]. With this configuration, the vibration of the connecting surface is magnified by the arm, so even if the take-out displacement is increased, the strain generated in the piezoelectric ceramic part can be made sufficiently smaller than the brittle fracture strain of the ceramic, and the piezoelectric ceramic undergoes brittle fracture. Can be prevented.

Further, since the chopper is installed so that the lengthwise direction of the arm of the chopper is perpendicular to the infrared ray incident direction, the movement amount of the shielding plate in the same direction as the incident light incident direction is 0.5 mm. The following can be set, and the shield plate and the detection unit such as a sensor can be installed at a distance of 1 mm or less. In addition, the shield plate and the elastic shim material can be integrated into one member, and the number of parts and the number of steps can be reduced.

Although the first embodiment has been described as an example here, the same effect can be obtained with the second embodiment to the sixth embodiment. [Ninth Embodiment] FIG. 13 shows [Ninth Embodiment].

FIG. 13 shows a pyroelectric device according to the first embodiment.
Of admittance characteristics of chopper for infrared infrared sensor
For example, the vertical axis is admittance and the horizontal axis is frequency.
It f _r1Represents the resonance frequency of the arm, f_r2Is the joint surface
Represents the vibration frequency, f_r2Is f_r1Low frequency compared to
It has become a number. The shaded area is usually a piezoelectric actuator.
It shows an example of the area when driving the data.
Drive frequency f_r2By bringing it near,
The vibration of the joint surface is made large enough. This allows the arm
It is possible to eliminate variations in characteristics due to the dimensional accuracy of
It

Further, with the same element structure as in the [first embodiment], the following effects also exist. With this configuration, the vibration of the connecting surface is magnified by the arm, so even if the take-out displacement is increased, the strain generated in the piezoelectric ceramic part can be made sufficiently smaller than the brittle fracture strain of the ceramic, and the piezoelectric ceramic undergoes brittle fracture. Can be prevented.

Since the chopper is installed so that the arm length of the chopper is perpendicular to the infrared ray incident direction, the movement amount of the shielding plate in the same direction as the incident light incident direction is 0.5 mm. The following can be set, and the shield plate and the detection unit such as a sensor can be installed at a distance of 1 mm or less. In addition, the shield plate and the elastic shim material can be integrated into one member, and the number of parts and the number of steps can be reduced.

Although the first embodiment has been described as an example here, the same effect can be obtained with the second embodiment to the sixth embodiment.

[0092]

As described above, according to the present invention, by configuring a piezoelectric chopper with one element having two shield plates, the displacement amount of one element becomes about 1/2, so that the element is driven at a low voltage. It is possible to At the same time, since the amount of displacement is small, the strain is small and reliability can be secured.

Further, by installing the chopper so that the length direction of the arm of the piezoelectric chopper is perpendicular to the incident direction of the incident light, the amount by which the shield plate moves in the same direction as the incident direction of the incident light is increased. Since it becomes almost “0”, the shield plate and the infrared detecting section can be installed at an arbitrary distance. In addition, by determining the shape of the arm so that it is driven at a frequency sufficiently lower than the resonance frequency of the torsional vibration of the arm, the amount of movement of the shielding plate in the same direction as the incident direction of incident light is smaller. Become.

As a result, the amount of displacement required for shielding is reduced, and driving with a low driving voltage is possible. Further, since the displacement amount can be reduced at the same time, the strain amount can be reduced and high reliability can be secured.

Furthermore, by constructing a pyroelectric infrared sensor using this piezoelectric chopper, it is possible to provide a compact, highly reliable, and more versatile pyroelectric infrared sensor.

[Brief description of drawings]

FIG. 1 is a perspective view of a pyroelectric infrared sensor according to a first embodiment.

FIG. 2 is a perspective view of a pyroelectric infrared sensor according to a second embodiment.

FIG. 3 is an exploded perspective view of a main part of the same embodiment.

FIG. 4 is a perspective view of a pyroelectric infrared sensor according to a third embodiment.

FIG. 5 is an exploded perspective view of a main part of the same embodiment.

FIG. 6 is a perspective view of a pyroelectric infrared sensor according to a fourth embodiment.

FIG. 7 is a perspective view of a pyroelectric infrared sensor according to a fifth embodiment.

FIG. 8 is a perspective view of a pyroelectric infrared sensor according to a sixth embodiment.

FIG. 9 is a plan view of a main part of the same embodiment.

FIG. 10 is an admittance characteristic diagram of the piezoelectric chopper of the pyroelectric infrared sensor of the seventh embodiment.

FIG. 11 is a drive circuit diagram for driving the bimorph type element in the same embodiment to track resonance frequency.

FIG. 12 is an admittance characteristic diagram of the piezoelectric chopper according to the eighth embodiment.

FIG. 13 is an admittance characteristic diagram of the piezoelectric chopper according to the ninth embodiment.

FIG. 14 is a perspective view of a conventional pyroelectric infrared sensor.

[Explanation of symbols]

10 Elastic shim material 10a, 10b Elastic shim arm 10c Connection part of elastic shim material 11a, 11b Piezoelectric ceramic 12a, 12b shield plate 14a fixture 14b fixing screw 15 Infrared detector 16 incident light 17 Curved part 18 slits

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References Japanese Unexamined Patent Publication No. 7-294331 (JP, A) Actual exploitation Sho 59-78948 (JP, U) Japanese Patent Sho 39-12540 (JP, B1) (58) Field (Int.Cl. ⁷ , DB name) G01J 1/02-1/04 G01J 5/02 G01J 5/62 G01R 29/12 G02B 26/00-26/04 H03H 9/24

Claims (7)

(57) [Claims] 1. A pair of elastic thin plates facing each other, and a connecting part made of elastic thin plates connected to the arms and provided so that the direction of a normal vector matches the length direction of the arms. A piezoelectric body provided on one surface or both surfaces of the connecting portion, and on the connecting portion or the above in order to fix the central portion of the connecting portion in a direction perpendicular to a line connecting the arm portions on the connecting portion.
A fixing member provided on the piezoelectric body , and a shield plate for entering / blocking incident light having a normal vector at the tip of the arm portion in the direction of the mating surface and in a direction perpendicular to the length direction of the arm portion. A piezoelectric chopper in which the resonance frequency of the arm portion is lower than the resonance frequency of the connecting portion and the drive frequency of the piezoelectric body is close to the resonance frequency of the arm portion. 2. An arm portion made of a pair of elastic thin plates facing each other, and a connecting portion made of an elastic thin plate connected to the arm portion and having a direction of a normal vector aligned with the length direction of the arm portion. A piezoelectric body provided on one surface or both surfaces of the connecting portion, and on the connecting portion or the above in order to fix the central portion of the connecting portion in a direction perpendicular to a line connecting the arm portions on the connecting portion.
A fixing member provided on the piezoelectric body , and a shield plate for entering / blocking incident light having a normal vector at the tip of the arm portion in the direction of the mating surface and in a direction perpendicular to the length direction of the arm portion. An infrared detector that detects the incident light through the shield plate, the resonance frequency of the arm portion is lower than the resonance frequency of the connecting portion, and the drive frequency of the piezoelectric body is the resonance frequency of the arm portion. Pyroelectric infrared sensor near the frequency. 3. An arm portion made of a pair of elastic thin plates facing each other, and a connecting portion made of an elastic thin plate connected to the arm portion and having a direction of a normal vector aligned with the length direction of the arm portion. When a piezoelectric body provided on one side or both sides of the connecting portion, and the pedestal protruding portion is formed, the elastic modulus of the piezoelectric body and the center portion of the connecting portion for fixing to the base seat having a piezoelectric a fixture comprising a lower material, a shielding plate for tip incident / block the incident light having the normal vectors in the longitudinal direction and the direction vertical and the arm portion in the direction of the mating surfaces of the front Kiude portion, An infrared detector for detecting the incident light through the shield plate, and a piezoelectric element formed by the fixture and the protrusion formed on the pedestal.
A pyroelectric device in which the connecting portion having a body is sandwiched and fixed, the resonance frequency of the arm portion is lower than the resonance frequency of the connecting portion, and the driving frequency of the piezoelectric body is near the resonance frequency of the arm portion. Type infrared sensor. 4. An arm portion made of a pair of elastic thin plates facing each other, and a connecting portion made of an elastic thin plate connected to the arm portion and having a direction of a normal vector aligned with the length direction of the arm portion. When, a piezoelectric disc-shaped provided on one side or both sides of the connecting portion, to 0.5 times 0.95 times the position of the outer diameter of the piezoelectric those
A fixture having a concentric annular first protrusion that is in contact with the fixture, and the fixture has the same shape as the fixture that holds the connecting portion with the fixture.
And a pedestal having an annular second protrusion , and makes / blocks incident light having a normal vector at the end of the arm portion in the direction of the mating surface and in the direction perpendicular to the length direction of the arm portion. A shield plate and an infrared detector that detects the incident light through the shield plate are provided, and the first projection body and the second projection body have a piezoelectric body.
A pyroelectric infrared sensor in which the connecting portion is sandwiched and fixed . 5. The pyroelectric infrared sensor according to any one of claims 2 to 4, wherein the resonance frequency of the torsional vibration of the arm portion is twice or more the resonance frequency of the flexural vibration. 6. The corrugated curved portion is provided on the arm portion.
The pyroelectric infrared sensor described in. 7. The distance between the shield plate and the infrared detector is continuously changed so as to become longer from the fixed end side to the free end side of the shield plate. The pyroelectric infrared sensor described in.