JPH0974234A - Piezo-electric actuator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stabilize the driving of laminated element type piezo-electric actuator mainly for the purpose of a chopper for an infrared ray sensor for driving close to a resonance. SOLUTION: A shim 11, a displacement enlarging part 13, a bending part 15 and a coupling part 16 are integrated in one body by bending an elastomer on a flat plate for bending the shim 11 onto a piezo-electric body 12 so as to compose an unimorph type laminated element. Since the series resistor Ra 18 is fitted to the unimorph laminated element in series in a circuit to be impressed with AC signals, the driving waveform can be easily got blunt thereby making the driving of actuator in such a constitution stable.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric actuator used for a pyroelectric infrared sensor or the like and converting an electric signal into a mechanical motion.

[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 food in microwave ovens and position detection of human body in air conditioners, and it is expected that demand will increase further in the future. This pyroelectric infrared sensor 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. The 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 pyroelectric infrared sensor. The pyroelectric effect is caused by a change in the incident amount of infrared rays, and when the temperature of an object is detected by a pyroelectric infrared sensor, it is necessary to intermittently open or close the infrared incident amount and forcibly change it. A mechanism used as this means is called a chopper, and forcibly interrupts the incident infrared rays to detect the temperature of the detection object. As a conventional chopper, an electromagnetic motor and a piezoelectric actuator have been used.

FIG. 5 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. Generally, an actuator is an elastic plate which is made by adhering and bonding a piezoelectric body to an elastic flat plate such as a metal to form an element, fixing one end, and utilizing the strain of the piezoelectric body to generate a bending motion in its entirety. The one in which the piezoelectric body is adhered to both surfaces 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, and hereinafter, each member is called as such.

FIG. 5 shows a bimorph type element used as a chopper for a pyroelectric infrared sensor, 51 is a shim,
52a and 52b are piezoelectric bodies, 53 is a shielding plate, 54 is a pedestal,
55 is a fixture, 56 is a wiring for shims, 57a and 57b are wirings for a piezoelectric material, 58 is an infrared detection part, 59 is a slit provided in the shielding plate 53, and 60 is infrared rays. Piezoelectric bodies 52a and 52b are adhered to both surfaces of the shim 51, and the three members are integrated to form a bimorph type element.

Electrodes are printed on the surfaces of the piezoelectric bodies 52a and 52b, and polarization treatment is applied in a direction perpendicular to the bonding surface. The polarization directions of the piezoelectric bodies 52a and 52b are as follows.
The wiring 56 and the piezoelectric bodies 52a, 5 taken out from the shim 51
The shim 5 is formed by the wirings 57a and 57b taken out from 2b.
Although it depends on the direction of the electric field applied between 1 and the piezoelectric bodies 52a and 52b, it is determined that the piezoelectric bodies 52a and 52b always generate strain in opposite directions. That is, the direction of the applied electric field and the polarization direction are determined such that when one of the piezoelectric bodies 52a and 52b is distorted in the direction of extension in the polarization direction, the other is contracted in the polarization direction.

The bimorph type element has a base 54 and a fixture 55.
The portion of the shim 51 and the portions of the piezoelectric bodies 52a and 52b are simultaneously sandwiched by and are held. The shim wiring 56 is attached to a portion of the shim 51 where the piezoelectric bodies 52a and 52b are not bonded, and the piezoelectric body 52a,
Piezoelectric wires 57a and 57b are attached to the surface of 52b. A shield plate 53 is attached to the free end of the bimorph element, and a slit 59 is provided in the shield plate 53. An infrared detector 58 is arranged near the shield plate 53 so as not to contact the shield plate 53 and the bimorph element.

Shim wiring 56 and piezoelectric wiring 57a,
When an electric field is applied between the shim 51 and the piezoelectric bodies 52a and 52b by 57b, the bimorph type element generates a bending motion with one end fixed, and the shield plate 5 attached to the tip.
3 and the slit 59 reciprocate according to the change in the direction of application of the electric field. The reciprocating movement of the slit 59 interrupts the infrared rays 60 incident on the infrared detecting section 58.

However, in the bimorph type chopper having the above-mentioned structure, in order to obtain a sufficient moving distance for interrupting infrared rays, it is necessary to increase the size from the fixed portion to the moving portion at the tip, and the driving force is very high. Voltage is needed.

Therefore, as a conventional improvement method, 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 the fixing is performed only at the shim portion, whereby the piezoelectric body is brittlely broken. It is possible to obtain a large displacement by driving at a low voltage by preventing the above phenomenon and further lowering the resonance frequency by means such as providing a notch in a shim near the fixed portion as necessary. An example of the structure of the chopper having the above characteristics is shown below.

FIG. 6 is a perspective view showing an example of a case where a unimorph type element as a chopper for a pyroelectric infrared sensor in a conventional improvement example is formed so that the width of the fixing place of the shim portion becomes narrow. In FIG. 6, 61a and 61b are shims, 62a and 62b are piezoelectric bodies, 63a and 63b are weights,
64 is a sensor pedestal, 65a and 65b are unimorph type element fixtures, 66a and 66b are shim wirings, 67a and 67b.
Is a piezoelectric wire, 68 is an infrared detector, 69a, 69
b, 69c and 69d are unimorph type element fixing screws, 70
Is infrared.

FIG. 7 is a perspective view showing the details of the shims 71a and 71b, where 71 is a shielding portion, 72 is a piezoelectric material bonding portion, 73 is a cutout portion, 74 is a positioning portion, and 75a, 7a.
5b is a fixing hole. Shielding portion 71 and piezoelectric bonding portion 72
Is bent to form a right angle, and a notch 73 having a width smaller than that of the piezoelectric bonding portion 72 is provided between the piezoelectric bonding portion 72 and the positioning portion 74. Has fixing holes 75a and 75b.

As shown in FIG. 7, the shims 71a and 71b are provided with a cutout portion 73 having a narrow width. The cutout portion 73 is sandwiched between the sensor pedestal 64 and the unimorph type element fixtures 65a and 65b as shown in FIG. Further, the unimorph type element fixing screws 69a, 69b, 69c and 69d are inserted into the fixing holes 75a and 75b, respectively, positioned and fixed at one end, and arranged so as to face each other in parallel.

Further, the piezoelectric bodies 62a, 6 are provided on the surfaces of the shims 61a, 61b which face each other, that is, on the piezoelectric body bonding portion 72.
2b is a sensor pedestal 64 and a unimorph type element fixture 65.
The a, 65b and the shims 61a, 61b are bonded at a position where they do not come into contact with the shielding portions at the tips and the cutout portions 73 to form a unimorph type piezoelectric actuator. The infrared detecting section 68 is arranged on the sensor pedestal 64 near the free end of the unimorph type element, and receives the infrared ray 70 or is blocked. The shields for connecting and disconnecting the infrared rays 70 are shims 61a, 61
It is configured by bending an end portion of the side opposite to the side where b is fixed, and weights 63a and 63b are adhered to the plane portions of this portion, respectively.

The shim wiring 66 is provided at one location other than the movable portions of the shims 61a and 61b, that is, at one location of the positioning section 74.
a and 66b are attached to the piezoelectric bodies 62a and 62b, respectively, and piezoelectric body wirings 67a and 67b are attached at positions close to the fixing portion of the unimorph type element.
6b and the wirings 67a and 67b for the piezoelectric body, the shim 61a
When an electric field is applied between the piezoelectric body 62a and the shim 61b and the piezoelectric body 62b, 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 opposite directions to intermittently block the infrared rays 70.

By providing the notch in the shim portion between the piezoelectric body and the fixed portion of the unimorph type element, the resonance frequency can be further lowered 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.

As described above, various advantages can be obtained by driving the bonded type element including the unimorph type element in the vicinity of resonance, but since it is driven in the vicinity of the resonance frequency,
When the resonance frequency of the chopper varies among the solids, a large difference in displacement occurs, and it is necessary to perform fine adjustment to maintain a constant displacement and to process and assemble parts that require high precision. Also, when the resonance frequency changed with time, the displacement changed significantly. Furthermore, when the drive frequency is moved away from the resonance in order to stabilize the displacement, the displacement amount decreases, and a high drive voltage is required to obtain the same displacement. In addition, when the shape is downsized and displacement is obtained, the load on the adhesive layer between the shim and the piezoelectric body increases, causing peeling. Such a problem is not limited to the chopper of the conventional example, and is the same problem when using resonance.

In order to improve the above problems of resonance driving, the following piezoelectric actuator has been proposed.

FIG. 8 is a perspective view showing an example of a chopper for a pyroelectric infrared sensor in which a displacement expanding portion is provided on a unimorph type piezoelectric actuator.

In FIG. 8, reference numeral 81 is a shim, 82 is a piezoelectric body, 83 is a displacement enlargement portion, 84 is a sensor pedestal, 85 is a fixture, 86a and 86b are fixing screws, and 87 is shim wiring.
Reference numeral 88 is a piezoelectric wire, 89 is an infrared detecting section, 90 is infrared, and 91 is a bent section.

By bending an elastic flat plate made of phosphor bronze, stainless steel alloy or the like into a U-shape, the shim 81 and the displacement enlarging portion 83 are integrated, and the shim 81 and the displacement enlarging portion 83 are parallel to each other from the joint portion. And has a longitudinal dimension in the same direction. Further, in the displacement enlarging portion 83, a bent portion 91 is formed at a right angle on the tip opposite to the joint portion and on the side opposite to the shim 81. The piezoelectric body 82 is adhered to the surface of the shim 81 to form a piezoelectric body adhesive portion (unimorph type element). The shim 81 is the displacement magnifying section 8
The sensor pedestal 8 is provided in the vicinity of the end portion on the side opposite to the coupling portion with
4 and the fixture 85, and the sensor base 84
A female thread is processed on the fixing tool 85 and a hole is processed on the fixing tool 85, and the fixing tool 86 is fixed by fixing screws 86a and 86b. An infrared detecting section 89 is arranged on the sensor pedestal 84, and is located in the vicinity of the bent section at the tip of the displacement enlarging section 83.

A shim wiring 87 is provided near the fixing portion of the shim 81, and a piezoelectric wiring 88 is provided at a position closer to the fixing portion of the shim 81 on the surface opposite to the bonding side of the piezoelectric body 82.
Are attached respectively. Wiring 87 for shim
When an AC signal is applied from the wiring 88 for the piezoelectric body, the shim 81
A potential difference is generated between the piezoelectric body 82 and the piezoelectric body 82, the joint portion of the piezoelectric body adhesive portion with the displacement magnifying portion 83 is displaced, and accordingly, the bent portion 91 at the tip of the displacement magnifying portion is also displaced. The infrared ray 90 entering the infrared ray detector 89 is interrupted to serve as a chopper.

Here, FIG. 9 shows the resonance characteristics of the piezoelectric actuator (chopper) having the above structure.

FIG. 9 shows an example of resonance characteristics of a piezoelectric actuator comprising a shim bent in a U-shape and a displacement magnifying portion. The vertical axis represents admittance and the horizontal axis represents drive frequency. It has been found that there is a resonance phenomenon at each frequency of f1 and f2, and these are caused mainly by the resonance of the piezoelectric actuator due to the vibration of the piezoelectric bonding portion and the resonance of the displacement magnifying portion. One of the resonances, which corresponds to either one depending on the configuration of the piezoelectric actuator, and the difference between f1 and f2 also changes depending on the configuration.

By configuring the shim and the displacement enlarging portion to have the longitudinal dimension in the same direction from the connecting portion as described above, the relative positions of f1 and f2 can be easily manipulated.
For example, when the longitudinal dimension of the displacement magnifying member is constant and only the length from the fixed portion of the piezoelectric body bonding portion to the piezoelectric body is changed,
That is, when only the longitudinal dimension of the piezoelectric body adhesive portion is changed, when the resonance frequency due to the piezoelectric body adhesive portion is initially equal to f2 with the longitudinal dimension of the piezoelectric body adhesive portion being short, that is, When the resulting resonance frequency is higher than the resonance frequency due to the displacement magnifying section, when the longitudinal dimension of the piezoelectric body bonding section is gradually lengthened, the resonance frequencies of both become relatively close to each other, and at a certain length When the piezoelectric bonded portions are overlapped as one resonance and the longitudinal dimension of the piezoelectric bonded portion is further lengthened, the relative positions of the two are reversed, and the resonance frequency caused by the displacement magnified portion is caused by the piezoelectric bonded portion. It has a value higher than the resonance frequency.

At this time, FIG. 10 shows the relationship between the displacement of the tip of the displacement magnifying portion and the drive frequency in the case where f1 and f2 are arranged close to each other.

In FIG. 10, the vertical axis represents the displacement of the displacement magnifying portion and the horizontal axis represents the drive frequency.

It can be seen that there is a frequency region in which the displacement is magnified by the influence of both resonances and the displacement amount is relatively stable at the driving frequency between f1 and f2. Therefore,
By bringing f1 and f2 close to each other and driving them at a frequency between both frequencies, a displacement expansion effect due to resonance and a stable displacement can be obtained.

Further, f1 is a resonance frequency mainly caused by the piezoelectric bonding portion, and f2 is a resonance frequency mainly caused by the displacement expanding portion, that is, the displacement expansion is larger than the resonance frequency mainly caused by the piezoelectric bonding portion. By having a configuration in which the resonance frequency mainly caused by the part is higher, the displacement is expanded and stable, and it is possible to further secure a wider frequency region in which the applied AC signal and the time difference between the tip of the displacement expanding part are constant.

The unimorph type actuator using ordinary resonance shows a large change in displacement depending on the driving frequency.
In order to stabilize this, when driven at a frequency about 5% away from the resonance frequency, a high voltage was required to obtain the same displacement. On the other hand, in the case of the piezoelectric actuator having the above configuration, the shim has a longitudinal dimension of about 16 mm, the resonance frequency f2 due to the displacement magnifying portion is about 100 Hz, and the resonance frequency due to the piezoelectric bonding portion is When f1 is set to about 85 Hz, it is possible to obtain a displacement of 1.1 ± 0.05 mm at the tip of the displacement magnifying section in a section of about 6 Hz by applying an alternating voltage of ± 30 V when driven between f1 and f2. .

The same effect is obtained when the longitudinal dimension of the piezoelectric bonding portion is 1.
In the case of a piezoelectric actuator having a configuration in which f2 is 120 Hz or less according to the longitudinal dimension of the displacement magnifying portion in a state of 8 mm or less, the difference between f2 and f1 is approximately 5 to 25% of f2.
Obtained in between. Even if it is within 5%, the same effect can be obtained, but in this case, the frequency range in which driving can be performed may be reduced, or one resonance may not be excited.

With the above-mentioned structure, the drive utilizing the resonance can be stably performed at a lower voltage, and the drive, the assembly, and the processing of the members can be facilitated. Further, since the amount of vibration of the portion bonded to the piezoelectric body can be reduced, peeling between the piezoelectric body and the shim is less likely to occur. Also, the bent configuration reduces the overall longitudinal size, and by using this configuration as a chopper for a pyroelectric infrared sensor, the overall size of the sensor can be reduced, and the infrared detector can be fixed to the same pedestal. By doing so, the infrared detector can be easily integrated, and the vicinity of the infrared detector can be opened and closed, so that the opening and closing area can be reduced and the load on the chopper can be reduced. Further, driving with a low voltage can reduce the influence of noise from the piezoelectric body on the infrared detecting section.

The chopper having the above characteristics is hereinafter referred to as a W resonance type chopper or actuator for simplicity.

[0034]

However, the conventional W
The resonance type chopper also excites unnecessary vibrations other than the vibration mode used for driving, which makes the chopper uncontrollable, and when used as a chopper of a pyroelectric infrared sensor, temperature measurement may not be possible at all. It was often seen in the case of square wave drive. On the other hand, when the sine wave drive is used, unnecessary vibration is reduced, but a phenomenon in which the displacement amount is reduced by 20% or more in the stable region as compared with the rectangular wave drive having the same voltage is observed.

An object of the present invention is to provide a piezoelectric actuator in which driving is stabilized and a displacement amount can be sufficiently secured.

[0036]

In order to achieve the above object, the piezoelectric actuator of the present invention has a waveform in which an alternating voltage waveform to be applied is blunted with a time constant τ, and particularly, a driving frequency is 55.
For piezoelectric actuators up to 120 Hz,
As one means for making the time constant τ 0.02 to 0.15 times the driving voltage cycle, a resistor is provided in series with the actuator.

[0037]

By making the drive voltage waveform blunt by the time constant τ rather than the rectangular wave, unnecessary vibration due to the instability of the displacement output of the piezoelectric actuator is less likely to be excited, and thus stable driving can be performed. Further, since the amount of displacement obtained by this driving method is larger than that in the case of driving with a sine wave, it is possible to prevent deterioration of the basic characteristics of the piezoelectric actuator. The level of unwanted vibration decreases as the time constant τ increases, especially when the drive frequency is W from 55Hz to 120Hz.
With respect to the resonance type actuator, the effect begins to appear remarkably when the time constant τ is approximately 0.02 times the driving voltage cycle, and when the time constant τ is greater than a certain time constant, almost no unnecessary vibration is confirmed. If the time constant τ is raised too much, the amount of displacement will decrease.
Good characteristics can be obtained by driving up to 15 times. By using such a small-sized, large-displacement, and stable-driving chopper, the pyroelectric infrared sensor can be made compact and highly accurate.

[0038]

An embodiment of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIGS. 1 (a) and 1 (b) are perspective views showing an example in which a W resonance type actuator and a series resistor are connected in a drive circuit according to a first embodiment of the present invention. It is an equivalent circuit diagram.

In FIG. 1A, 11 is a shim, 12 is a piezoelectric body, 13 is a displacement magnifying portion, 14a and 14b are fixtures,
Reference numeral 15 is a bent portion, 16 is a coupling portion, 17 is an AC signal source, 1
Reference numeral 8 is a series resistance Ra. Shim 11, displacement magnifying section 13,
The bending portion 15 and the connecting portion 16 are integrally configured by bending a single plate-shaped conductive metal body. A piezoelectric body 12, which is polarized in the thickness direction and has electrodes formed on both surfaces, is bonded to one surface of the shim 11. In the vicinity of the end of the shim 11 opposite to the connecting portion 16, the fixtures 14a, 1
A W resonance type actuator is formed by being sandwiched by 4b and fixing one end thereof. Fixture 14
Similarly to the shim 11, a and 14b are also made of a conductive material, and wirings for applying an electric field are attached to the electrode portions of the surfaces of the fixture 14a and the piezoelectric body 12 which are not adhered. The series resistor Ra18 is arranged adjacent to the piezoelectric body 12 through the electric field applying wiring, and further, the connection with the AC signal source 17 forms an electric circuit for applying an AC voltage between the shim 11 and the piezoelectric body 12.

FIG. 1B is an electric circuit diagram including an equivalent circuit of the W resonance type actuator in FIG. 1A, a series resistor Ra connected to the equivalent circuit, and an AC signal source. The series resistance Rb, the series capacitance Ca, the series inductance L, and the parallel capacitance Cb are general internal parameters showing an equivalent circuit of the piezoelectric vibrator, and the equivalent circuit is generally the series resistance Rb, the series capacitance Ca, and the series inductance as shown in the figure. It is composed of a series connection of L and a parallel capacitance Cb connected in parallel with the series connection.
As can be seen from the figure, the piezoelectric vibrator has a capacitance C composed of Ca and Cb. By connecting a series resistance Ra in series to the piezoelectric vibrator and applying a rectangular alternating waveform, As shown in FIG. 2 (b), a waveform having a round shape with a time constant τ = RaC is applied. Alternatively, to be exact, the series resistance Rb also influences.

FIG. 2 (a) is a rectangular AC voltage waveform, FIG.
(B) is an example of an AC voltage waveform having a rounded time constant τ. By adjusting the value of Ra, the time constant of the drive waveform can be adjusted.

The W resonance type actuator has various resonance frequencies and vibration modes depending on the size and mounting position of each constituent member. For example, the resonance caused by the flexural vibration of the displacement magnifying portion used for driving the W resonance type actuator is at least the shape dimension of the displacement magnifying portion itself, the shape of the bent portion, the shape and bonding position of the piezoelectric body, and the piezoelectric body bonding portion. It is affected by the shape, etc. For example, when the displacement magnifying portion has a large longitudinal dimension, the bent portion has a large shape, that is, has a large mass, and the piezoelectric bonding portion has a large length, the resonance frequency decreases.

One method for making the vibration of the displacement magnifying portion closer to the flexural vibration mode of fixing one end is to make the bonding position of the piezoelectric body closer to the coupling portion. In this embodiment, the conductive metal is used. It is separated from the joint to make it easier to bend the body. It is also effective to adjust the mass of the bent portion and the shape of the displacement magnifying portion.

The W-resonance type actuator has various resonances in addition to the resonances used for normal driving, and during driving, unnecessary resonances of other vibration modes are excited at the same time in addition to the desired resonances. Is also affected by the parameters of each component. If the vibration energy of the unnecessary resonance in the vicinity of the driving frequency is sufficiently small, the driving will not be hindered. On the contrary, if the vibration energy is large, it will hinder the normal displacement as shown in FIG. The vibration of the entire resonance type actuator may be completely different from the normal vibration, and it may not be possible to drive.

FIG. 3A shows a normal displacement waveform, and FIG. 3B.
Is an example of a displacement waveform distorted by unnecessary resonance. FIG.
FIG. 3A shows a substantially sine wave, and FIG. 3B shows that the driving is performed, but the waveform is distorted due to unnecessary resonance, and a normal displacement amount cannot be obtained. In addition, unstable behavior causes the W resonance type. It adversely affects the mechanical life of the actuator. If the energy of these unnecessary resonances is larger, the W resonance type actuator becomes unstable vibration of other modes,
In some cases, it may lead to sudden destruction.

Such unnecessary resonance is often a resonance having a higher frequency, and it is possible to reduce it by accurately grasping the vibration modes of these resonances and adjusting the shape of the W resonance type actuator. Although possible, it is difficult to accurately grasp a plurality of resonance modes and obtain a configuration that simultaneously reduces the resonance modes, and also causes fluctuations in the resonance inherent in the W resonance type actuator. On the contrary, the presence or absence of instability of vibration can be seen depending on the degree of assembly variation.

By blunting the waveform of the driving voltage as described above, the level of unnecessary resonance can be lowered, the driving can be stabilized, and the vibration can be prevented from shifting to another mode. To give an example, the overall length is about 16 mm, the width is 1.5 mm, and the thickness of the metal body is 0.05 m.
m super invar, piezoelectric size 11 × 1.5 × 0.
1. Displacement magnifying section length is about 13mm, drive frequency is 83H
In the W resonance type actuator having the shape of z shown in FIG. 1A, resonance of another mode vibrating at about 800 Hz was confirmed. In this vibration, the joint portion, the displacement magnifying portion, and the bent portion are simultaneously bent, and the bent portion vibrates at one end with the joint portion with the displacement magnifying portion as the fixed end.

As the series resistance value was gradually increased while measuring the displacement amount of the bent portion, the displacement of the bent portion decreased, and the displacement was not measured at a certain value or more. When a series resistance was inserted into the W resonance type actuator that had changed to the vibration of another mode during driving, it became a normal vibration mode and was not unstable thereafter.

In this case, the capacitance of the W resonance type actuator was about 5000 pF, and the displacement of the bent portion was remarkably reduced by the series resistance of about 30 kΩ, and became almost 0 at about 80 kΩ. The time constant at this time is about 0.3 ms to 0.
6 ms, which is 0.025 to 0.05 times the period of the driving frequency of 83 Hz. If the time constant is increased, the unnecessary resonance is further reduced and the sine wave becomes more stable, but on the other hand, the amount of displacement obtained decreases as the time constant increases. As an example, the displacement is reduced by about 20% in the sine wave drive with respect to the displacement amount in the rectangular wave drive, and a value which is blunted by the time constant τ takes a value between the displacement amounts of both drive methods.

A similar tendency is confirmed in the W resonance type actuator having a similar dimension, and from the viewpoint of both the stabilization of driving and the securing of the amount of displacement, the driving frequency is from 55 Hz to 120 Hz.
In the W resonance type actuator of Hz, it is almost optimal that the time constant is 0.02 to 0.15 times the driving cycle.
More specifically, the total length is from 13 mm to 1
8 mm, the width of the metal body and the piezoelectric body is 0.25 times or less of the whole length, the length of the piezoelectric body is 0.9 times or less of the whole length, and the capacitance is 4000 pF to 7000 pF, 55H
In the W resonance type actuator driven from z to 120 Hz, good drive can be obtained with a series resistance of 20 kΩ to 150 kΩ.

This driving method can be used as it is for the pyroelectric infrared sensor chopper having the structure described in the conventional example. The movement of the chopper largely affects the accuracy of temperature detection, and the chopper is required to have large displacement and accurate movement. When a non-resonant drive type piezoelectric bimorph or the like is used, the accuracy is improved, but the shape becomes extremely large and the versatility of the sensor unit itself is impaired. By using the W resonance type actuator as the chopper for the pyroelectric infrared sensor and using the above-mentioned driving method, it is possible to realize a compact chopper that can be opened and closed with high accuracy, which contributes to downsizing and high accuracy of the sensor unit. .

(Embodiment 2) In FIG. 4, a displacement member having a substantially flat surface is provided in a part in the vicinity of the tip of the displacement amplification portion, and the normal direction of the substantially flat surface is substantially perpendicular to the tangential direction of the displacement direction of the displacement amplification portion. FIG. 3 is a perspective view of a W resonance type actuator having a configuration that is substantially perpendicular to the direction from the joint between the shim and the displacement enlarging portion toward the tip of the displacement enlarging portion.

In FIG. 4, reference numeral 41 is a shim, 42 is a piezoelectric body, 43 is a displacement enlargement portion, 44 is a fixed portion, 45 is a wiring for piezoelectric body, 46 is an infrared detection portion, 47 is infrared rays, 48 is a displacement member, and 49 is a displacement member. Is the joint.

The shim 41, the displacement enlarging portion 43, and the displacement member 4
8 and the connecting portion 49 are made of an integral metal member, and are formed by bending each in a flat plate shape. The shim 41 and the displacement enlarging portion 43 are parallel to each other, and have a U-shape through the joint portion 49. A piezoelectric body 42 polarized in the direction perpendicular to the plane is attached to one side of the shim 41. The opposite side of the shim 41 from the side where the shim 41 is joined to the joint portion 49 is fixed to the fixing portion 44 by screwing, bonding, welding, or the like. The piezoelectric wire 45 is attached to the surface of the piezoelectric body 42, and the material of the fixing portion 44 is a conductive material such as copper. The substantially flat surface portion of the displacement member 48 is bent substantially at right angles to the plane of the displacement enlargement portion.

Other constitutions, driving methods, and characteristics are the same as those of the first embodiment. In addition, the W resonance type actuator of the first embodiment is smaller in size and larger in displacement, that is, the longitudinal displacement of the bent portion, that is, The displacement due to the turning movement becomes large,
Contact with other members such as a sensor may pose a problem. On the other hand, in the W resonance type actuator having the above-described configuration, the plane of the displacement member is substantially parallel to the displacement direction, and there is no fear that the displacement member approaches the sensor due to the rotational movement accompanied by the flexural vibration with one end fixed. The arrangement of the members is easy, and the unit can be efficiently downsized. Further, the closer the shielding portion of the chopper is to the sensor, the smaller the displacement, and the similar characteristics can be obtained. Therefore, the long-term reliability of the chopper can be secured and the accuracy can be improved.

In the present embodiment, the displacement member is integrally bent and bent, but it goes without saying that the above characteristics are not impaired even if the displacement member is constructed and joined.

[0058]

INDUSTRIAL APPLICABILITY As described above, the present invention is a method of driving a piezoelectric actuator that is small and can obtain large displacement. By blunting the driving voltage waveform from a rectangular wave by the time constant τ, unnecessary vibration of the W resonance type actuator can be reduced. The excitation can be suppressed, the uncontrollable state of the piezoelectric actuator can be prevented from appearing, and the unnecessary mechanical load on the constituent members due to unnecessary vibration can be reduced to improve the reliability. Further, by using the time constant τ within a certain range, it is possible to suppress unnecessary vibration, minimize the decrease in the displacement amount, and perform driving with almost no deterioration in the basic characteristics. Particularly, in the piezoelectric actuator driven at 55 Hz to 120 Hz, good driving and basic characteristics can be obtained at the same time by driving the time constant τ within the range of 0.02 to 0.15 times the driving voltage period. Since the W resonance type actuator is small and can obtain large displacement, it contributes to the miniaturization of the entire unit such as the sensor. Especially, the pyroelectric infrared sensor that requires a chewper for temperature detection is smaller and more accurate. And by combining with the same driving method,
A sensor with higher reliability and versatility can be realized.

[Brief description of drawings]

FIG. 1A is a perspective view showing a configuration of a first embodiment of the present invention. FIG. 1B is an electric circuit diagram showing a configuration of a first embodiment of the present invention.

FIG. 2A is a normal drive waveform diagram in the first embodiment of the present invention. FIG. 2B is a drive waveform diagram in the first embodiment of the present invention.

FIG. 3A is a normal displacement characteristic diagram in the first embodiment of the present invention. FIG. 3B is a displacement characteristic diagram with unnecessary resonance in the first embodiment of the present invention.

FIG. 4 is a perspective view showing the configuration of a second embodiment of the present invention.

FIG. 5 is a perspective view showing a configuration of a conventional piezoelectric bimorph type chopper.

FIG. 6 is a perspective view showing a configuration of a conventional resonance type chopper.

FIG. 7 is a perspective view showing details of the structure of a conventional resonance type chopper.

FIG. 8 is a perspective view showing a configuration of a conventional W resonance type actuator.

FIG. 9 is an admittance characteristic diagram of a conventional W resonance type actuator.

FIG. 10 is a displacement characteristic diagram of a conventional W resonance type actuator.

[Explanation of symbols]

 11, 41 Shim 12, 42 Piezoelectric body 13, 43 Displacement expanding part 15 Bending part 19, 49 Coupling part 48 Displacement member

Claims (6)

[Claims] 1. A flat plate-shaped piezoelectric body subjected to polarization treatment is bonded to one or both surfaces of a flat plate-shaped elastic member, and one end is fixed by a fixing member, and the piezoelectric body bonding section is coupled to the piezoelectric body bonding section. Then, the free end has a displacement magnifying portion located at a distance closer to the fixing portion of the piezoelectric body bonding portion than the coupling portion,
An electric field is applied to the piezoelectric body bonding section to cause the piezoelectric body bonding section to bend, whereby the free end of the piezoelectric body bonding section and the free end of the displacement enlarging section are displaced. The difference between the resonance frequency f1 generated due to the vibration and the resonance frequency f2 caused due to the vibration of the displacement magnifying portion is brought close to each other, and within 30% of the frequency on the side where the difference between f1 and f2 is high. A piezoelectric actuator having the structure described above, wherein an AC voltage is applied and driven at a frequency between f1 and f2, and the AC voltage waveform has a roundness of a time constant τ from a rectangular wave. 2. The piezoelectric actuator according to claim 1, wherein the drive frequency is between 55 and 120 Hz, and the time constant τ is between 0.02 and 0.15 times the drive voltage period. 3. The displacement magnifying portion and the elastic member for bonding the piezoelectric body are integrally configured by bending a plate-shaped metal body, and the displacement magnifying portion is not coupled to the piezoelectric body bonding elastic member. The piezoelectric actuator according to claim 1, wherein the piezoelectric actuator has a bent portion near the other tip. 4. At least 1 in the vicinity of the other end of the displacement magnifying portion, which is not connected to the piezoelectric body bonding elastic member.
Is provided with a displacement member having a substantially flat surface, the normal direction of the substantially flat surface is substantially perpendicular to the connection direction of the displacement direction of the displacement magnifying portion, and the piezoelectric body bonding elastic member and the displacement magnifying portion. The piezoelectric actuator according to claim 1, wherein the piezoelectric actuator is also substantially perpendicular to a direction from the coupling portion to the tip of the displacement enlarging portion. 5. The piezoelectric actuator according to claim 1, wherein the driving voltage waveform is rounded by connecting a predetermined resistor in series relationship with the piezoelectric actuator in an electrical circuit manner. 6. The distance from the fixed end to the connecting portion is 13 mm to 1
8 mm, the width of the metal body and the piezoelectric body is uniform, and is 0.25 times or less the length from the fixed portion to the coupling portion, and the length of the piezoelectric body is 0 with respect to the length from the fixed end to the coupling portion. Less than 9 times,
The piezoelectric actuator according to claim 5, wherein the drive frequency is 55 Hz to 120 Hz, the electrostatic capacity is 4000 pF to 7000 pF, and a resistance of 20 kΩ to 150 kΩ is used.