JPH07294331A - Pyroelectric infrared sensor - Google Patents

Abstract

PURPOSE:To improve stability and reliability in driving a small chopper of a pyroelectric infrared sensor using a piezoelectric actuator. CONSTITUTION:Piezoelectric bodies 12a and 12b are bonded to shims 11a and 11b, respectively, and only a fixing part hole 21a at one end of the shin 11a is fixed with a sensor pedestal 14 and an unimorph element fixture 15a, thus a unimorph piezoelectric element is constituted. Since resonance frequency of a unimorph element is lowered so that a chopper drives at the frequency lower than resonance frequency by about 10%, displacement can be enlarged without using the resonance point whose displacement is unstable, so, the sensor is miniaturized, and adjustment of resonance frequency becomes easier, and rigidity in the direction other than the vibration direction is raised due to multiple supporting paints, thus, more stable driving is realized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to 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 temperature measurement of cooked foods in microwave ovens and position detection of human bodies in air conditioners, and it is expected that demand will increase further in the future. Pyroelectric infrared sensor
It utilizes the pyroelectric effect of a pyroelectric material such as a LiTaO ₃ single crystal. Pyroelectric materials have spontaneous polarization and always generate surface charges, but in the steady state in the atmosphere, they are electrically neutral because they are associated 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 with the neutral state collapsed. A pyroelectric infrared sensor measures the amount of incident infrared rays by detecting the charges generated on the surface. An object emits infrared rays according to its temperature, and the position and temperature of the object can be detected 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, an electromagnetic motor, a piezoelectric actuator, etc. have been used.

FIG. 3 shows a conventional example of a pyroelectric infrared sensor using an actuator in which a piezoelectric material is bonded to an elastic flat plate as a chopper. An actuator that bonds a piezoelectric body to an elastic flat plate such as metal to form a bonded element, fixes one end, and uses the strain of the piezoelectric body to generate a bending motion over the entire surface is generally an elastic flat plate. The one to which the piezoelectric material is adhered is called a bimorph type, the one to which only one surface is adhered is called a unimorph type, and the elastic flat plate is called a shim. Hereinafter, each member is called as such.

FIG. 3 shows a bimorph type element used as a chopper of a pyroelectric infrared sensor, 31 is a shim,
32a and 32b are piezoelectric bodies, 33 is a shielding plate, 34 is a pedestal,
Reference numeral 35 is a fixture, 36 is wiring for shims, 37a and 37b are wiring for piezoelectric bodies, 38 is an infrared detecting section, 39 is a slit, 4
0 is infrared. On both sides of the shim 31, a piezoelectric body 32a,
32b are adhered to each other to form a bimorph type element. Electrodes are printed on the surfaces of the piezoelectric bodies 32a and 32b, and polarization treatment is performed in the direction perpendicular to the bonding surface. The polarization directions of the piezoelectric bodies 32a and 32b are the wiring 36 extracted from the shim and the piezoelectric material. Wirings 37a and 37b taken out from the body allow the shim 31 and the piezoelectric bodies 32a and 3a.
It is determined that the piezoelectric bodies 32a and 32b always generate strains in directions opposite to each other, depending on the direction of the electric field applied between the two 2b. That is, the piezoelectric body 32a,
The direction of the applied electric field and the polarization direction are determined such that when one of 32b is distorted in the direction of extension, the other is contracted in the direction of polarization. The bimorph type element has a base 34 and a fixture 3.
The portion of the shim 31 and the portions of the piezoelectric bodies 32a and 32b are simultaneously sandwiched by 5 and held. The shim wiring 36 is attached to a portion of the shim 31 where the piezoelectric bodies 32a and 32b are not adhered.
Piezoelectric wires 37a and 37b are attached to the surfaces of a and 32b. A shield plate 33 is attached to the free end of the bimorph element, and a slit 39 is provided in the shield plate 33. An infrared detector 38 is arranged near the shield plate 33 so as not to contact the shield plate 33 and the bimorph type element. The shim 31 and the piezoelectric wires 32a, 3b are formed by the shim wire 36 and the piezoelectric wires 37a, 37b.
When an electric field is applied between 2b, the bimorph element generates a bending motion with one end fixed, and the shield plate 33 and the slit 39 attached to the tip end make a reciprocating motion according to the change in the direction of the electric field application. . The reciprocating movement of the slit 39 interrupts the infrared rays 40 incident on the infrared detecting section 38.

However, in the bimorph type chopper having the above construction, it is necessary to increase the size from the fixed portion to the moving portion at the tip end in order to obtain a sufficient moving distance for interrupting infrared rays, and it is very high. Requires a drive voltage.

Therefore, as a means for improving it, a load is applied to the tip moving portion of the bimorph type element or the unimorph type element to lower the resonance frequency, and fixing is performed only at the shim portion so that the piezoelectric body is brittlely broken. It is conceivable that a large displacement can be obtained by driving at a low voltage by preventing it and further lowering the resonance frequency by means such as providing a notch in a shim near the fixed portion if necessary.
A conventional example of the structure of a chopper having this characteristic is shown below.

FIG. 4 is a perspective view showing an example of a conventional example in which a unimorph type element as a chopper for a pyroelectric infrared sensor is molded so that the width of the fixing place of the shim portion becomes narrow. In FIG. 4, 41a and 41b are shims, 42a and 42b are piezoelectric bodies, 43a and 43b are weights,
44 is a sensor pedestal, 45a and 45b are unimorph type element fixtures, 46a and 46b are shim wirings, 47a and 47b.
Is a wiring for a piezoelectric body, 48 is an infrared detector, 49a, 49
b, 49c and 49d are unimorph type element fixing screws, 50
Is infrared.

FIG. 5 is a perspective view showing the details of the shim 41a. 51 is a shielding portion, 52 is a piezoelectric body bonding portion, 53 is a cutout portion, 54 is a positioning portion, and 55a and 55b are fixing holes. . The shielding portion 51 and the piezoelectric body bonding portion 52 form a right angle by bending, and the piezoelectric body bonding portion 52 to the positioning portion 54 are formed.
A notch portion 53 formed to have a width narrower than that of the piezoelectric bonding portion 52 is provided, and fixing holes 55a and 55b are provided at both ends of the positioning portion 54.

In FIG. 4, the shims 41a and 41b are provided with a notch 53 having a narrow width as described with reference to FIG. 5, and the notch 53 is sandwiched between the sensor pedestal 44 and the unimorph type element fixtures 45a and 45b. Further, the unimorph type element fixing screws 49a, 49b, 49c and 49d are inserted into the fixing holes 55a and 55b, respectively, positioned and fixed at one end, and arranged so as to face each other in parallel. In addition, the piezoelectric bodies 42a and 42b are provided on the surfaces of the shims 41a and 41b that face each other, that is, the piezoelectric body bonding portion 52.
However, the sensor pedestal 44 and the unimorph type element fixture 45a,
The unimorph type piezoelectric actuator is configured by being bonded at a position where it does not come into contact with the shielding portions at the tips of the shims 45a and the shims 41a and 41b as well as the notch portion 53. Infrared detector 4
8 is arranged on the sensor pedestal 44 in the vicinity of the free end of the unimorph type element and receives or blocks the infrared rays 50. The shields that connect and disconnect the infrared rays 50 are shims 41a and 41b.
It is configured by bending an end portion on the side opposite to the fixing side, and weights 43a and 43b are adhered to the plane portions of this portion, respectively. The shim wiring 46 is provided at a location other than the movable portions of the shims 41a and 41b, that is, at a location of the positioning portion 54.
a, 46b are attached to the piezoelectric bodies 42a, 42b at the positions close to the fixing portion of the unimorph type element, respectively, and the wirings for shim 46a, 4b are provided.
The shim 41a is formed by 6b and the piezoelectric wires 47a and 47b.
When an electric field is applied between the piezoelectric body 42a and the shim 41b and the piezoelectric body 42b, the unimorph type element bends and the shield portion at the tip moves. The two unimorph type elements are driven at the same frequency in the opposite directions, and the infrared rays 50 are interrupted.

By providing the notch in the shim portion between the piezoelectric member and the fixed portion of the unimorph type element, the resonance frequency can be further reduced as compared with the unimorph type element having the same size and not having the notch. Therefore, it is possible to reduce the size of the chopper and increase the amount of displacement during low frequency driving, as compared with the case where the notch is not provided.

[0011]

However, the conventional bimorph type or unimorph type chopper having a notch portion and a weight at the tip portion is very sensitive to external vibration, and in particular, the chopper of There is a problem that vibration in the direction of rotation with respect to the longitudinal axis is likely to occur, it is difficult to obtain an accurate displacement, and an additional stress is applied to the chopper due to the rotational vibration.

Further, when the resonance frequency is lowered by mounting a weight or installing a cutout portion and the displacement is increased by driving near the resonance frequency, if the resonance frequency is too close, the influence of temperature change of the outside air, etc. The displacement of the chopper changes remarkably due to the change of the resonance frequency due to, and it is necessary to more accurately match the resonance frequency between the solids of the chopper. Conversely, if the drive frequency is too far from the resonance frequency, the effect of displacement expansion due to resonance is reduced.

Further, since the driving is performed in the vicinity of the resonance frequency, it is necessary to match the structure of the chopper itself with the target driving frequency. However, the chopper opening / closing frequency that can sufficiently secure the sensitivity of the infrared detecting element by polishing conventional ceramics is In one example, the frequency is about 10 Hz. If the resonance frequency of the chopper is lowered to the vicinity, the rigidity of the chopper is remarkably reduced, and the unnecessary vibration is significantly generated.

It is an object of the present invention to provide a pyroelectric infrared sensor using a piezoelectric actuator which is more reliable and has stable driving characteristics.

[0015]

In order to achieve the above object, a hole is formed in an elastic member portion for fixing a chopper by a bonded type element of a piezoelectric body and an elastic member instead of a cutout portion, and a chopper is formed. The fixing is performed at two positions having a larger distance in the width direction of the above, and the weight of the tip is attached so as to be positioned inside the width between the fixing positions.

The frequency used for driving is 5 to 15% lower than the resonance frequency of the chopper itself.

An element for detecting infrared rays of the pyroelectric infrared sensor is formed of a thin film, and a chopper that drives near the resonance frequency is used for the pyroelectric infrared sensor.

[0018]

The hole is formed in the portion where the shim, which is a constituent member of the chopper, is fixed, and the chopper is fixed in this hole portion so that the chopper does not lose the effect of lowering the resonance frequency in the predetermined vibration direction. Since the fixing is performed at two places, it is possible to suppress the generation of unnecessary vibration due to the force applied from the outside and more accurately generate the vibration only in a predetermined direction. Also, by placing the weight attached to the tip of the chopper inside the width between the fixed points,
The generation of unnecessary vibration can be reduced.

By driving the chopper at a frequency 5 to 15% lower than the resonance frequency of the chopper itself, it is possible to drive the chopper away from the resonance point where the displacement is unstable while utilizing the effect of displacement expansion by resonance. As a result, the driving characteristics can be further stabilized.

Further, the infrared detecting element composed of a thin film has extremely high sensitivity as compared with an infrared detecting element processed by a mechanical method such as polishing such as a ceramic element, and especially when opening and closing the chopper in a short time. Since it has a high output, the open / close frequency of the chopper can be set high by combining a thin-film infrared detection element and a chopper driven near the resonance frequency, and unnecessary vibration due to insufficient rigidity of the chopper accompanying the reduction of the resonance frequency is reduced. it can.

[0021]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a perspective view showing an example of a chopper for a pyroelectric infrared sensor using a unimorph type piezoelectric actuator in an embodiment of the present invention.

In FIG. 1, 11a and 11b are shims and 1
2a and 12b are piezoelectric bodies, 13a and 13b are weights, 14 is a sensor pedestal, 15a and 15b are unimorph type element fixtures, 16a and 16b are shim wiring, 17a and 17b are piezoelectric body mounting wirings, and 18a and 18b are Piezoelectric wiring,
Reference numeral 19 is an infrared detecting portion, 20 is infrared rays, and 21a and 21b are fixing portion holes.

The shim 11a has a bent portion which is perpendicular to one end,
A fixing portion hole 21a and two fixing portions 23a and 24a are provided, and a wide portion is provided again at the tip of the fixing portion hole 21a, and the shim wiring 16a is provided at this portion.
Are soldered to the shim 11a. Shim 11a
A weight 13a is attached to the bent portion of the above, and contributes to the reduction of the resonance frequency of the fixing portion hole 21a and the matching chopper. The weight 13a is attached so as to be inside the width of the fixing portions 23a and 24a of the shim 11a. The shim 11a is sandwiched between the sensor pedestal 14 and the unimorph type element fixture 15a at the fixing points 23a and 24a, and further fixed by soldering or fixed at one end by screwing (not shown). These configurations are the same on the side of the shim 11b.
Two portions of the sensor pedestal 14 where the chopper is fixed have steps, and when the chopper is fixed, the chopper is arranged such that each movable end has a step. The shims 11a and 11b are arranged so that the surfaces on the bent sides face each other in parallel, and the piezoelectric bodies 12a and 12b have shims 11a and 12b on the respective facing surfaces.
A unimorph type element, which is a chopper, is configured by being bonded so as not to come into contact with the bent portion of 11b and the fixing portion holes 21a and 21b. On the surfaces of the piezoelectric bodies 12a and 12b, the wirings 17a and 17b for mounting the piezoelectric body have shims 1
The piezoelectric body mounting wiring 17 is soldered to the portions 1a and 11b close to the fixing portion holes 21a and 21b, and further via the relay substrate 22 mounted on the end surface of the sensor pedestal 14.
The wires a, 17b are electrically connected to the piezoelectric wires 18a, 18b. The piezoelectric bodies 12a and 12b are pre-polarized so that the surfaces not bonded to each other are positive. An infrared detector 19 is arranged on the sensor base 14 so as to be electrically insulated from the sensor base 14.
Wirings 16a and 16b for shims and wirings 18a and 18 for piezoelectric bodies
When an electric field is applied to the piezoelectric bodies 12a and 12b by b, the piezoelectric bodies 12a and 12b are deformed, the movable portion of the chopper is bent and deformed, and the tip portions to which the weights 13a and 13b are attached are displaced. When the same electric field is applied to each of the two choppers, the tip parts of the two choppers are always displaced in opposite directions, so that both tip parts enter or block the infrared rays 20 incident on the infrared detecting section 19, and the pyroelectric type. Functions as a chopper for infrared sensors.

2 (a) and 2 (b) are perspective views for explaining in detail the shape of the shim used in the chopper.

In FIG. 2A and FIG. 2B, 25
a and 30 are bent portions, 11a and 26 are piezoelectric bonded portions,
21a and 27 are fixing hole, 23a, 24a, 28 and 29
Is a fixed point.

Bending portions 25a and 30 and fixing portion holes 21a and 27 are integrally formed at both ends of the piezoelectric body bonding portions 11a and 26, respectively, and the bending portions 25a and 30 of the piezoelectric body bonding portions 11a and 26 are bent. Piezoelectric bodies are adhered to the surfaces in the indicated direction, and weights are attached to the upper surfaces of the bent portions 25a and 30 if necessary, and fixed portions 23a
And 24a or 28 and 29 are fixed at one end to form a chopper having a bent portion at the tip as a movable portion. Since only two members having a small width are fixed in this way, the resonance frequency of the chopper can be reduced as compared with the case where the members are fixed in a portion having no fixing hole as in the related art.

The shim shown in FIG. 2A has a constant width as a whole, but in some cases, the shim has a shape in which the width of the shim is tapered toward the longitudinal direction like the shim shown in FIG. 2B. Alternatively, a shape (not shown) having a change in a curved shape may be used. By tapering the width, the distance between the members for fixing the chopper can be increased, and the effect of lowering the resonance frequency can be obtained, and more stable fixing can be performed.

Further, if the outer shape of the weight attached to the tip portion is set within the interval of the portion for directly fixing the chopper, it is stable even when the attachment position of the weight deviates in either one of the width directions, and the predetermined weight is obtained. It is possible to suppress the occurrence of vibration of the chopper other than the direction.

If a method of driving in the vicinity of the resonance frequency is adopted in the chopper having the above-mentioned structure or the chopper of the conventional example, an extremely large displacement can be obtained due to the influence of resonance, but the displacement amount at the resonance point is unstable. , It is difficult to obtain constant drive characteristics. Therefore, a method of driving the chopper at a frequency lower by 5 to 15% than the resonance frequency is adopted. Specifically, the driving frequency at which the resonance frequency is reduced by 10% is 20 Hz with respect to a unimorph type chopper having a length of about 12 mm in which a piezoelectric body is bonded to a shim made of phosphor bronze and the resonance frequency is about 22 Hz. In this case, if a voltage of 80 V is applied as an alternating current only in the polarization direction of the piezoelectric body and an electric field that does not cause polarization breakdown in the direction opposite to the polarization is applied, it is possible to obtain a displacement of the chopper of 1.2 mm or more. . By using this drive frequency, the instability of resonance can be avoided and the effect of displacement expansion due to resonance can also be obtained, so that a large displacement amount can be obtained. On the contrary, the same effect can be obtained when the driving is performed by shifting the frequency to the side higher than the resonance frequency, but if the sensitivity of the infrared detection section of the sensor is to be increased, the lower drive frequency is better. .

If the frequency shift is less than 5%,
The effect of stabilizing the vibration is weak, and conversely, if the frequency shift exceeds 15%, the effect of displacement expansion due to resonance becomes small, so the frequency setting range is 5
~ 15% lower is good.

FIG. 6 is a perspective view of another embodiment of the present invention. The structure is almost the same as that in FIG. 1, and the portions having the same functions are denoted by the same numbers as in FIG. The difference from FIG. 1 is a unimorph-type element fixing tool 15c, which was attached so as to directly sandwich the fixing portion hole 21a in FIG. 1, but in the present embodiment, a shim is formed at a lower portion slightly apart from the hole processing portion 21c. 11a is sandwiched.

By pressing in the vicinity of the hole-processed portion 21c in this manner, the shim 11a can be fixed in a wider area as compared with the case where the hole-processed portion is directly sandwiched as shown in FIG.
The stable fixing allows the resonance frequency of the chopper itself to be stabilized, and even when a large number of choppers are manufactured, it is possible to suppress variations in the resonance frequency among the chopper solids, which results in uniform quality. Products can be provided.

Further, since the fixing is performed in a wider area than the case where it is fixed in a small area around the hole processing portion and the hole processing portion is not directly pressed, stress concentration in the vicinity of the hole processing portion in the shim 11a is prevented. Since it can be relaxed, the mechanical reliability is increased.

The effect of increasing the fixing area by shifting the position of the fixing tool in this way has the same effect in the chopper having the cutout portion as in the conventional example shown in FIG. Is.

Although the unimorph type element is used as the chopper in this embodiment, it goes without saying that the same effect can be obtained by using the bimorph type element.

[0036]

As described above, according to the present invention, in the chopper in which the resonance frequency is lowered by fixing only the shim portion of the unimorph type element or the bimorph type element, it is more stable by providing the fixing portion at a plurality of positions. The chopper can be fixed, and rotational vibration about the longitudinal axis,
It is possible to suppress the occurrence of vibration in directions other than the predetermined vibration, reduce the occurrence of unnecessary vibration due to external vibration, and improve the driving characteristics of the chopper. In addition, by attaching a weight attached to the tip of the chopper to reduce the resonance frequency inside the widthwise space of the chopper fixing point, the length of the chopper caused by the displacement of the center of gravity when attaching the weight and the movement of the center of gravity during driving. It is possible to prevent the occurrence of vibration in an unnecessary direction such as rotational vibration around the direction.

Further, by setting the drive frequency at a value 5 to 15% lower than the resonance frequency of the chopper, it is possible to use the displacement magnifying effect by resonance without using the unstable point of displacement at resonance. In addition, it is possible to reduce the displacement amount difference between solids and the variation of displacement of the same element over time, and the resonance frequency of the chopper can be adjusted with a certain width between solids, which facilitates assembly and adjustment of characteristics. It can be done and productivity is improved.

[Brief description of drawings]

FIG. 1 is a perspective view of a pyroelectric infrared sensor according to an embodiment of the present invention.

FIG. 2A is a perspective view showing an example of a shim shape in the embodiment of the present invention. FIG. 2B is a perspective view showing an example of the shim shape in the embodiment of the present invention.

FIG. 3 is a perspective view showing an example of a conventional pyroelectric infrared sensor.

FIG. 4 is a perspective view showing an example of a conventional pyroelectric infrared sensor.

FIG. 5 is a perspective view showing an example of a shim shape in a conventional example.

FIG. 6 is a perspective view of a pyroelectric infrared sensor according to another embodiment of the present invention.

[Explanation of symbols]

 11a, 11b Shim 12a, 12b Piezoelectric body 13a, 13b Weight 19 Infrared detector 21a, Fixing part hole 23a, 24a Fixing part

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsumi Imada 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (5)

[Claims] 1. A chopper that has an infrared shielding portion at its tip, and a flat piezoelectric member is attached to a flat elastic member, and vibrates when an AC voltage is applied to the piezoelectric member, and infrared rays are generated by a pyroelectric effect. A pyroelectric infrared sensor, comprising: an infrared detecting section for detecting; and the elastic member being fixed at a plurality of locations close to the hole processing section formed on the elastic member. 2. A weight is attached to the infrared shielding portion at the tip,
The pyroelectric infrared sensor according to claim 1, wherein the weight is located inside a width of a plurality of fixing points for fixing the flat plate. 3. A chopper that has an infrared ray shielding portion at its tip, a flat plate-shaped piezoelectric member is attached to a flat plate-shaped elastic member, and vibrates by applying an AC voltage to the piezoelectric member, and infrared rays are generated by a pyroelectric effect. A pyroelectric infrared sensor having an infrared detecting section for detecting, and vibrating the chopper at a frequency 5 to 15% lower than the inherent resonance frequency of the chopper. 4. The pyroelectric infrared sensor according to claim 1, wherein the chopper is vibrated at a frequency 5 to 15% lower than the intrinsic resonance frequency of the chopper. 5. The pyroelectric infrared sensor according to claim 1, 2 or 3 or 4, wherein the element of the detector having the pyroelectric effect is formed of a thin film.