JP3239628B2 - 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 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, and the demand is expected to increase in the future. Pyroelectric infrared sensors are
This utilizes the pyroelectric effect of a pyroelectric material such as a LiTaO ₃ single crystal. The pyroelectric body has spontaneous polarization and always generates a surface charge. However, in a steady state in the atmosphere, the pyroelectric body is electrically neutral with the charge in the atmosphere. When infrared light is incident on the pyroelectric body, the temperature of the pyroelectric body changes, and accordingly, the charge state of the surface changes due to the neutral state being broken. A pyroelectric infrared sensor detects charges generated on the surface and measures the amount of incident infrared light. An object emits infrared rays according to its temperature, and by using this sensor, the position and temperature of the object can be detected. The pyroelectric effect is caused by a change in the amount of incident infrared light. When a pyroelectric infrared sensor detects the temperature of an object, it is necessary to change the amount of incident infrared light. A chopper is used as this means, and forcibly interrupts the incident infrared rays to detect the temperature of the detection object. As a conventional chopper, an electromagnetic motor, a piezoelectric actuator, and the like have been used.

FIG. 4 shows a conventional example of a pyroelectric infrared sensor using an actuator in which a piezoelectric body is bonded to an elastic flat plate as a chopper. Generally, a piezoelectric element is bonded to an elastic flat plate made of metal or the like to form a bonding element and one end is fixed,
In general, actuators that generate a bending motion using the distortion caused by a piezoelectric body are generally called a bimorph type, in which a piezoelectric body is bonded to both sides of an elastic flat plate, and a unimorph type, in which only one side is bonded. The elastic flat plate is called a shim, and each member is hereinafter referred to as such.

FIG. 4 shows a bimorph-type element used as a chopper for a pyroelectric infrared sensor.
62a and 62b are piezoelectric bodies, 63 is a shielding plate, 64 is a pedestal,
65 is a fixture, 66 is shim wiring, 67a and 67b are piezoelectric wiring, 68 is an infrared detector, 69 is a slit, 7
0 is an infrared ray. A piezoelectric body 62a is provided on both sides of the shim 61,
62b are adhered to each other, and the three are integrated to form a bimorph-type element. Electrodes are printed on the surfaces of the piezoelectric bodies 62a and 62b, and a polarization process is performed in a direction perpendicular to the bonding surface. The direction of polarization of each of the piezoelectric bodies 62a and 62b is determined by the wiring 66 taken out from the shim and the piezoelectric body. Although it differs depending on the direction of the electric field applied between the shim 61 and the piezoelectric members 62a and 62b due to the wirings 67a and 67b taken out of the body, the piezoelectric members 62a and 62b are always determined to generate strain in directions opposite to each other. Can be That is, the direction of the applied electric field and the polarization direction are determined so that when one of the piezoelectric bodies 62a and 62b is distorted in the direction of extension in the polarization direction, the other contracts in the polarization direction. The bimorph-type element is held by the shim 61 and the piezoelectric members 62a and 62b being simultaneously sandwiched between the pedestal 64 and the fixture 65. A shim wiring 66 is attached to a portion of the shim 61 where the piezoelectric bodies 62a and 62b are not bonded, and a piezoelectric wiring 6 is provided on the surfaces of the piezoelectric bodies 62a and 62b.
7a and 67b are attached. A shielding plate 63 is attached to the free end of the bimorph-type element, and a slit 69 is provided in the shielding plate 63. Shield plate 6
In the vicinity of 3, the infrared detecting section 68 is arranged so as not to contact the shielding plate 63 and the bimorph type element. The shim 61 is formed by the shim wiring 66 and the piezoelectric wirings 67a and 67b.
When an electric field is applied between the piezoelectric element and the piezoelectric members 62a and 62b, the bimorph-type element generates a bending movement fixed at one end, and the shielding plate 63 and the slit 69 attached to the tip end.
Reciprocates in the movement direction indicated by the arrow in FIG. 4 according to the change in the direction of application of the electric field. The reciprocating motion of the slit 69 intermittently blocks the infrared ray 70 incident on the infrared ray detector 68.

However, the bimorph-type chopper having the above configuration needs to have a large dimension from the fixed portion to the tip moving portion in order to obtain a moving distance sufficient to intermittently block infrared rays. Very high drive voltages are required.

Therefore, as a conventional improvement method, a piezoelectric body is brittlely broken by applying a load to the tip moving portion of a bimorph-type element or a unimorph-type element to lower the resonance frequency and fixing only the shim. By further reducing the resonance frequency by, for example, providing a notch in the shim near the fixed portion as necessary, a large displacement can be obtained with low voltage driving. An example of the structure of the chopper having the above characteristics will be described below.

FIG. 5 is a perspective view showing an example of a conventional improved example in which a unimorph-type element as a chopper for a pyroelectric infrared sensor is formed so that a width of a fixing portion of a shim portion is reduced. In FIG. 5, 71a, 71b
Is a shim, 72a and 72b are piezoelectric bodies, 73a and 73b are weights, 74 is a sensor pedestal, 75a and 75b are unimorph-type element fixing tools, 76a and 76b are shim wirings, 77a and 7
7b is a wiring for a piezoelectric body, 78 is an infrared detector, 79a and 7
9b, 79c and 79d are unimorph type element fixing screws, 8
0 is an infrared ray.

FIG. 6 is a perspective view showing details of the shims 71a and 71b, where 81 is a shielding portion, 82 is a piezoelectric bonding portion,
83 is a notch, 84 is a positioning part, 85a and 85b
Is a fixing hole. The shielding portion 81 and the piezoelectric bonding portion 82 form a right angle by bending, and a cutout portion 83 formed so that the width becomes smaller than the piezoelectric bonding portion 82 from the piezoelectric bonding portion 82 to the positioning portion 84. And fixing holes 85a and 85b are provided at both ends of the positioning portion 84.

The shims 71a and 71b are provided with a notch 83 having a small width as shown in FIG. 6, and the notch 83 is sandwiched between the sensor pedestal 74 and the unimorph-type element fixtures 75a and 75b as shown in FIG. Further, the unimorph-type element fixing screws 79a and 79b are respectively inserted into fixing holes 8a.
5a and 85b, are positioned and fixed at one end, and are arranged so as to face each other in parallel. Piezoelectric bodies 72a and 72b are provided on the opposing surfaces of the shims 71a and 71b, that is, on the piezoelectric body bonding portion 82, respectively.
4 and unimorph-type element fixtures 75a, 75b and shim 7
The unimorph type piezoelectric actuator is formed by being bonded at a position where it does not come into contact with the shielding portion at the tip of 1a, 71b and the notch portion 83. The infrared detecting section 78 is provided for the sensor base 7.
4 is disposed near the free end of the unimorph-type element, and receives or blocks infrared rays 80. The shielding portion for intermitting the infrared light 80 is formed by bending the end of the shim 71a, 71b opposite to the side to which the shim 71a, 71b is fixed, and the weights 73a, 73b are bonded to the flat portion of this portion. The shim wirings 76a and 76b are provided at one position other than the movable portions of the shims 71a and 71b, that is, at one position of the positioning portion 84, and the piezoelectric wirings 77a and 77b are provided at the piezoelectric members 72a and 72b, respectively. When the electric field is applied between the shim 71a and the piezoelectric body 72a and between the shim 71b and the piezoelectric body 72b by the shim wirings 76a and 76b and the piezoelectric wirings 77a and 77b, the unimorph type element bends. Wakes up and the shield at the tip moves. 2
The two unimorph elements are driven in the opposite direction at the same frequency to intermittently block infrared light 80.

By providing a notch in the shim between the piezoelectric body and the fixed portion of the unimorph element, the resonance frequency can be further reduced as compared with a unimorph element having the same dimensions and no notch. Therefore, it is possible to reduce the size of the chopper and increase the amount of displacement at the time of low-frequency driving, as compared with the case where the notch is not provided.

The same effect can be obtained even when a hole is formed in place of the notch.

[0012]

However, according to the conventional improvement described above, the notch and the tip have weights, and the resonance frequency of the bimorph type or unimorph type chopper is controlled by driving near the resonance frequency. Because there is
When the resonance frequency varies between the solids, the difference between the individual displacement amounts increases, and fine adjustment is required to match the resonance frequency of the chopper between the solids.

Further, since the infrared detector and the plurality of choppers are fixed on the sensor pedestal, it is difficult to fix them at the time of assembly, and once assembled, one component is repaired or the resonance frequency of the chopper is adjusted. When performing the entire operation, it is difficult to fix the whole, and the movement and replacement of the target part is hindered by other parts, resulting in poor workability.If the whole is disassembled, the resonance frequency changes due to the movement of the fixed position of the chopper. As a result, the drive characteristics fluctuate and extra adjustment is required. Further, since the rigidity of the chopper is low, there is a problem that the chopper other than the work purpose is easily damaged during the work.

In view of the above, the present invention provides a pyroelectric infrared sensor that uses a chopper that is driven at a frequency near the resonance frequency with less variation in the resonance frequency and has improved workability during assembly. With the goal.

[0015]

In order to achieve this object, a pyroelectric infrared sensor according to the present invention comprises a pedestal for fixing a sensor, a chopper fixed to each of the pedestals, or a different rigidity. After fixing to the member,
The rigid member is fixed to the sensor base.

[0016]

The member for fixing the chopper is a pedestal for the infrared detecting unit, and the pedestal can be divided into a plurality of parts so that each chopper is fixed, so that each of the chopper and the infrared detecting unit can be assembled, Fixing, repair,
Adjustment of the resonance frequency of the chopper can be performed individually, which facilitates assembly and management of the entire sensor, and breaks parts other than the chopper for the purpose of repair and adjustment, especially for other choppers with low rigidity. Damage can be prevented, and replacement work of each part is simplified. Alternatively, the chopper is attached to another small member, and the structure in which the chopper is attached to the infrared detection unit pedestal by the small member has the same effect as described above, and the sensor unit and the chopper can be managed separately. Workability is improved.

[0017]

【Example】

(Embodiment 1) Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows an embodiment of the present invention.
FIG. 3 is a perspective view showing an example of a chopper for a pyroelectric infrared sensor using a unimorph type piezoelectric actuator.

In FIG. 1, 11a and 11b are shims, 1
2a and 12b are piezoelectric bodies, 13a and 13b are weights, 14
a and 14b are sensor pedestals, 15a and 15b are unimorph-type element fixtures, 16a and 16b are shim wirings, 17a and 17b.
17b is a wiring for attaching a piezoelectric body, 18a and 18b are wirings for a piezoelectric body, 19 is an infrared detector, 20 is an infrared ray, 21
a, 21b (not shown because they are on the back side in the perspective view), shim-hole processing parts, 22a, 22b are relay boards, 23a, 23
b, 23c and 23d are unimorph element fixing screws (23
c and 23d are not shown), and 24a and 24b are sensor base fixing screws (24b is not shown).

Each of the shims 11a and 11b is provided at one end with a bent portion perpendicular to the surface and with shim holes 21a and 21b, and a wide portion is provided again before the shim holes 21a and 21b. In this portion, the shim wirings 16a and 16b are soldered to the shims 11a and 11b. Weights 13a and 13b are attached to the bent portions of the shims 11a and 11b, respectively, and contribute to the reduction of the resonance frequency of the chopper together with the shim holes 21a and 21b. Weights 13a, 1
Reference numeral 3b is set to be substantially symmetric with respect to the center in the width direction of the shims 11a and 11b. The shims 11a and 11b are located near the shim holes 21a and 21b.
a, 14b and the unimorph-type element fixing tools 15a, 15b, and the unimorph-type element fixing screws 23a, 2b.
3b, 23c, and 23d are fixed at one end by screwing,
The sensor pedestal 14a is formed with a hole (not shown), and the sensor pedestal 14b is formed with a screw hole (not shown), and is fixed to one by sensor pedestal fixing screws 24a and 24b.
The two portions of the sensor pedestals 14a and 14b for fixing the chopper have a step, 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 such that the surfaces on the bent sides face each other in parallel, and the piezoelectric members 12a and 12b are provided with the bent portions of the shims 11a and 11b and the shim hole processing portions 21 on the facing surfaces.
A unimorph-type element as a chopper is formed by being adhered so as not to come into contact with a and 21b. The piezoelectric body 12a,
On the surface of 12b, the wiring 17a, 1
7b is a shim hole processing part 21a, 2 of the shim 11a, 11b.
1b is soldered at a portion close to the sensor base 1b.
4a, 14b, relay boards 22a,
The piezoelectric wirings 17a and 17b are electrically connected to the piezoelectric wirings 18a and 18b via the wiring 22b. The piezoelectric bodies 12a and 12b are preliminarily polarized so that the surfaces that are not bonded are positive. On the sensor pedestals 14a and 14b, an infrared detecting unit 19 is arranged so as to be electrically insulated from the sensor pedestals 14a and 14b. Shim wiring 16a, 16b and piezoelectric wiring 18
When an electric field is applied to the piezoelectric bodies 12a and 12b by the a and 18b, the piezoelectric bodies 12a and 12b are deformed and the movable parts of the chopper are bent and deformed.
Is displaced. When the same electric field is applied to each of the two choppers, the tips of the two choppers are always displaced in opposite directions, and the tips open and close in the opening and closing directions indicated by arrows in FIG. Inject or block the infrared ray 20 incident on the infrared ray detection unit 19,
It functions as a chopper for a pyroelectric infrared sensor.

FIG. 2 is a perspective view for explaining in detail the shape of the shim used in the chopper. In FIG. 2, 31 is a bent portion, 32 is a piezoelectric bonding portion, 33 is a shim hole processed portion, 34 is a fixed portion, 35a and 35b are fixing holes, and 36a and 36b are groove processed portions.

At both ends of the piezoelectric bonding portion 32, a bent portion 31 and a shim hole processing portion 33 are integrally formed, respectively, and a surface of the piezoelectric bonding portion 32 in a direction in which the bending portion 31 is bent is formed. By bonding a piezoelectric body, attaching a weight to the upper surface of the bent portion 31 if necessary, and fixing one end at or near the shim hole processing portion 33,
A chopper having the bent portion 31 at the tip as a movable portion is configured. When the fixing is performed below the shim hole forming portion 33, the members directly fixing the driving portion of the chopper are only two members having small widths on both sides in the width direction of the shim hole forming portion 33. Fixing hole 35 provided in fixing portion 34
a, 35b, chopper sensor pedestals 14a, 14b
Then, the sensor bases 14a and 14b are integrated in the grooved portions 36a and 36b.

The chopper of the type driven near the resonance frequency, such as the chopper having the above configuration, can obtain an extremely large displacement due to the influence of resonance, but the amount of displacement at the resonance point is unstable, and constant driving characteristics are obtained. It is difficult to obtain. Therefore, the chopper is driven at a frequency lower by 5 to 15% than the resonance frequency. Specifically, a piezoelectric body is bonded to a phosphor bronze shim with a length of about 12 mm and a resonance frequency of about 2 mm.
For the unimorph type chopper of 2 Hz, a drive frequency of 20 Hz, which is 10% lower than the resonance frequency, is selected. In this case, it is possible to obtain a displacement of the chopper of 1.2 mm or more by applying a voltage of 80 V as an alternating current only in the polarization direction of the piezoelectric body and applying an electric field that does not cause polarization breakdown in the direction opposite to the polarization. is there. The use of this drive frequency avoids the instability of resonance and also has the effect of increasing the displacement due to resonance, so that a large displacement can be obtained. Conversely, the same effect can be obtained when the frequency is shifted to a higher side than the resonance frequency, but if it is desired to increase the sensitivity of the infrared detector of the sensor, the lower the driving frequency, the better.

With the above configuration, when repairing the infrared detecting section from the sensor base, the chopper can be separated from the infrared detecting section without removing the chopper from the fixing section. And the risk of damaging the chopper during operation is reduced. In addition, when the chopper is detached from the pedestal, the resonance frequency of the chopper tends to change and the characteristics are hardly stable. However, if the chopper is detached from the pedestal, the fluctuation of the resonance frequency can be prevented.
In addition, when the resonance frequency of the chopper is adjusted for each individual object, the adjustment can be performed only with the chopper and the pedestal, and the work and management are facilitated.

Although a unimorph type element is used as the chopper in this embodiment, the same effect can be obtained by using a bimorph type element. In addition, when the resonance frequency of the chopper is near the driving frequency in a state where there is no hole of the weight or the shim, it is needless to say that the driving can be performed without using these.

(Embodiment 2) Another embodiment of the present invention will be described below with reference to the drawings. FIG. 3 shows a second embodiment of the present invention.
FIG. 5 is a perspective view showing an example of a chopper for a pyroelectric infrared sensor using a unimorph type piezoelectric actuator in the example of FIG.

In FIG. 3, reference numerals 41a and 41b denote shims,
2a and 42b are piezoelectric bodies, 43a and 43b are weights, 44 is a sensor pedestal, 45a and 45b are unimorph-type element fixtures A, 46a and 46b are shim wirings, and 47a and 47b are piezoelectric mounting wirings (47b is a figure). Not shown), 48a, 4
8b is a wiring for a piezoelectric body, 49 is an infrared detector, 50 is an infrared ray, 51a and 51b are notches (51b is not shown), 52a and 52b are relay boards (52b is not shown), 53a, 53b, 53c and 53d are fixing screws A
(53c, 53d are not shown), 54a, 54b, 54
c and 54d are fixing screws B (54c and 54b are not shown), and 55a and 55b are unimorph-type element fixing tools B.

Each of the shims 41a and 41b is provided at one end with a bent portion perpendicular to the surface and with notches 51a and 51b, and further with a wide portion provided at the end of the notches 51a and 51b. Part 4 for shim
6a and 46b are soldered to the shims 41a and 41b. Weights 43a and 43b are attached to the bent portions of the shims 41a and 41b, respectively.
The notches 51a and 51b and the matching chopper contribute to the reduction of the resonance frequency. The weights 43a and 43b are arranged so as to be substantially symmetric with respect to the center in the width direction of the shims 41a and 41b. Unimorph type element fixing device A45
a and 45b are provided with through holes (not shown), and the unimorph-type element fixing members B55a and 55b are provided with female screw holes (not shown) and through holes, and the shims 41a and 41b are provided with notches 5a and 4b.
In the vicinity of 1a and 51b, a unimorph-type element fixing device A4
5a, 45b and Unimorph-type element fixture B55a, 55
b, and are fixed by fixing screws A53a, 53b and 53c, 53d. Further, a female screw hole (not shown) is provided in the sensor pedestal 44,
The unimorph-type element fixing members B55a and 55b are fixed to the sensor base 44 with fixing screws B54a, 54b, and 54, respectively.
c, 54d, whereby the chopper is fixed to the sensor base 44. The two portions of the sensor pedestal 44 for fixing the chopper have a step, and when the chopper is fixed, the chopper is arranged such that each movable end has a step. The shims 41a and 41b are arranged so that the surfaces on the bent sides face each other in parallel, and the opposing surfaces are each provided with a piezoelectric body 42.
a, 42b are adhered so as not to contact the bent portions and the notched portions 51a, 51b of the shims 41a, 41b, thereby forming a unimorph type element as a chopper. On the surfaces of the piezoelectric bodies 42a and 42b, the wirings 47a and 47b for attaching the piezoelectric bodies are soldered at portions near the notches 51a and 51b of the shims 41a and 41b, and further, the relay board 52a mounted on the sensor base 44. , 52
The wirings 47a and 47b are electrically connected to the wirings 48a and 48b for the piezoelectric body through the wiring b.
The piezoelectric bodies 42a and 42b are preliminarily polarized so that the surfaces that are not bonded are positive. On the sensor pedestal 44, an infrared detecting unit 49 is arranged so as to be electrically insulated from the sensor pedestal 44. Shim wiring 46
When an electric field is applied to the piezoelectric bodies 42a and 42b by the piezoelectric bodies a and 46b and the piezoelectric wirings 48a and 48b, the piezoelectric bodies 42a and
Deformation occurs in the movable portion 2b, bending deformation occurs in the movable portion of the chopper, and the distal ends where the weights 43a and 43b are attached are displaced. When the same electric field is applied to each of the two choppers, the tips of the two choppers are always displaced in the opposite directions. Therefore, both the tips receive or block the infrared rays 50 incident on the infrared detector 49, and the pyroelectric type Acts as a chopper for infrared sensors.

With the above configuration, the infrared detector and the
Two choppers can be managed independently. The chopper changes its resonance frequency depending on the fixed position, which affects the drive characteristics, and it may be necessary to adjust the resonance frequency if it varies between solids. Work is easy because it is possible. In addition, the choppers can be managed in a fixed state, and the choppers having the same resonance frequency can always be stored, so that the management is easy and the replacement of the choppers can be smoothly performed.

Further, since the left and right choppers having exactly the same length and the same shape can be configured simply by shifting the positions, mass productivity of the chopper is good.

Although a plurality of choppers are used in this embodiment, this is not necessary when the area for opening and closing the infrared ray can be performed by a single chopper. In this case, the same effects as described above can be obtained for the management of the chopper and the stabilization of the resonance frequency. Needless to say, there is.

[0031]

As described above, the present invention relates to a chopper in which only the shim of a unimorph-type element or a bimorph-type element is fixed and a part of the shim is machined to reduce the resonance frequency to near the drive frequency. By making the pedestal for directly fixing the choppers individually divisible, it is easy to adjust, replace, and repair the resonance frequency of multiple choppers, and always use a chopper whose resonance frequency is stable between solids. As a result, the driving characteristics when the sensor is mounted are stabilized. In addition, assembly during mass production is facilitated, and productivity is improved.

[Brief description of the drawings]

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

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

FIG. 3 is a perspective view showing an example of a configuration of a pyroelectric infrared sensor according to the embodiment of the present invention.

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

FIG. 5 is a perspective view showing an example of an improved pyroelectric infrared sensor in a conventional example.

FIG. 6 is a perspective view showing an example of a conventional chopper shim shape.

[Explanation of symbols]

 11a, 11b Shim 12a, 12b Piezoelectric 13a, 13b Weight 14a, 14b Sensor base 19 Infrared detector

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01J 1/02-1/04 G01J 5/02 G01J 5/62 G02B 26/04

Claims (1)

(57) [Claims] 1. A flat elastic member as a means (hereinafter referred to as a chopper) for injecting / blocking infrared rays of a pyroelectric infrared sensor for detecting an object by causing infrared rays emitted from an object to enter a pyroelectric sensor unit. On the other hand, on one or both sides of the plane, a flat plate-shaped piezoelectric body polarized in a direction perpendicular to the elastic member surface is bonded to form a bonding element, and one end of the bonding element is fixed by a fixing member. The bonding element is bent by applying an electric field to the bonding element, so that the other end of the bonding element is used as a movable portion. A chopper in which only a part of the member is fixed, and a hole or a cutout is provided in the elastic member between a fixed portion of the elastic member and a bonded portion; A plurality of pedestals, wherein the pedestal portion on which the infrared detection unit is disposed has a structure capable of being separated into a plurality of pedestals.
One chopper can be fixed to each separated member
A pyroelectric infrared sensor characterized by being performed .