JP2019180174A - Piezoelectric actuator - Google Patents

Abstract

To provide a piezoelectric actuator capable of achieving both of a stable driving force and a suppression of an abnormal noise.SOLUTION: A piezoelectric actuator contacting an oscillator 11 formed by a laminate structured piezo electric element generating a composite vibration of a telescopic oscillation and a bend oscillation to a slide member with a pressure, and moving the slide member, includes: a pressure member pressing one end part of the oscillator while being contacted to the slide member; an elastic member 35 arranged so as to circumference at least two node parts of the oscillator; and a holding member 32 holding a posture of the oscillator while holding the elastic member.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a piezoelectric actuator in which a plurality of piezoelectric elements are stacked.

The piezoelectric actuator generates one specific ultrasonic vibration or two different specific ultrasonic vibrations at a predetermined frequency and timing in the vibration body, so that the vibration output unit of the vibration body can rotate or reciprocate such as an ellipse. A motion is generated, and this motion is transmitted to a driven body such as a rotor brought into contact with the vibration output unit to drive the driven body. This piezoelectric actuator can realize low speed and high torque, is excellent in quietness, and is suitable for reduction in size and weight. For this reason, it is widely used as a drive source for various movable mechanisms that require precise positioning, such as a camera autofocus function and a scanning electron microscope.
By the way, in such a piezoelectric actuator, a laminated piezoelectric element is mainly used as a vibrating body. According to this laminated piezoelectric element, it is known that, for example, when compared with a single plate-like piezoelectric body having the same thickness, a larger deformation strain and generating force can be obtained with a low applied voltage.

  For example, in Patent Document 1, the vicinity of a node where a piezoelectric element is generated is directly supported and fixed by a leaf spring to eliminate slipping or backlash of the vibrator, and without changing vibration energy loss and vibration characteristics. It is disclosed that an efficient and stable output can be obtained.

  In Patent Document 2, a vibrator is guided only in the pressurizing direction without moving the vibrator in a direction perpendicular to the pressurizing direction by supporting the vicinity of the node of the piezoelectric element with a support member integrated with the case. Therefore, it is disclosed that a large and stable driving force generation can be realized by stabilizing the bending vibration and expansion vibration generated in the vibrator.

  In Patent Document 3, an elastic member such as a conical spring material is disposed in a concave portion on one inner wall surface of a storage portion of a holding member that stores a vibrator, and a rolling element is disposed on the other inner wall surface, whereby a storage portion It is disclosed that the whole is held by a conical spring and a rolling element to suppress the vibration of the vibrating body from propagating to surrounding members via the holding member.

  Patent Document 4 discloses that by fixing the center of a piezoelectric vibrator with a screw, it is possible to realize support and fixing without displacement, and at the same time, it is possible to satisfactorily transmit vibration that affects driving force.

JP 2010-41777 A JP 11-346486 A JP 2013-179733 A JP-A-4-145879

  By the way, in the piezoelectric actuator, it is necessary not to reduce the driving force from the vibrator and to prevent the extra vibration from the vibrator that does not affect the driving force from propagating to surrounding members.

  However, in Patent Document 1, since the vicinity of the node where the piezoelectric element is generated is directly supported and fixed by a leaf spring, when the vibrator is assembled obliquely, the posture of the contact deteriorates and is accurate. In this case, the actuator cannot be driven efficiently because it does not hit the sliding member. Furthermore, the vibration unrelated to the driving force from the vibrator propagates to the surrounding members, and there is a drawback that the generation of abnormal noise cannot be suppressed.

  In Patent Document 2, since the piezoelectric element is supported by four support portions integrated with a case made of plastic, rubber, or the like, the piezoelectric element itself is assembled so that its posture is the same as the pressing direction. It is difficult, and since the support part made of rubber or the like is compressed and the vibrator side part is not fixed, it is difficult to transmit vibration stably, and because it supports only at four places, It is difficult to suppress propagation of extra vibrations that do not affect the driving force to other members, and there is a drawback that it is not possible to sufficiently prevent abnormal noise.

  Further, in Patent Document 3, it is difficult to suppress vibration propagation to surrounding members because the vibrator is structured to be sandwiched by point contact using a member made of a metal material such as a spring material and a rolling sphere. It has a drawback that the generation of sound cannot be suppressed.

  In addition, in Patent Document 4, since only one central portion of the piezoelectric vibrator is screwed, the posture of the vibrator becomes unstable and stable due to the frictional force generated between the vibrator and the sliding member. High output cannot be obtained. Furthermore, since the piezoelectric vibrator is fixed with a metal material such as a screw, there is a drawback that extra vibration that does not affect the driving force cannot be absorbed and abnormal noise is generated.

  According to the present invention, by preventing the vibrator from being in an unstable posture, it is possible to realize a stable driving force and to transmit an extra vibration that does not directly affect the driving force without propagating to other members. An object of the present invention is to provide a piezoelectric actuator that can solve both of the suppression of sound generation.

The present invention includes the following.
[1] In a piezoelectric actuator that moves a sliding member by pressing a vibrator composed of a piezoelectric element having a laminated structure that generates combined vibration of stretching vibration and bending vibration to the sliding member, one end of the vibrator is A pressure member that presses against the sliding member, an elastic body disposed so as to surround at least two node portions of the vibrator, and holds the elastic body and has an attitude of the vibrator. And a holding member for holding the piezoelectric actuator.
[2] The piezoelectric actuator according to [1], wherein the node of the vibrator is a node of bending vibration.
[3] The piezoelectric actuator according to [1], wherein the elastic body has a heat resistant temperature of 150 ° C. or higher and a loss coefficient (tan δ) according to JIS K6394 of 0.15 or lower.
[4] The elastic body has a size that surrounds at least a node region of the bending vibration of the vibrator, and the holding member has a concave portion that supports the relative position of the elastic body in an immovable manner. ] To [3] The piezoelectric actuator according to any one of the above.
[5] The elastic body has a convex portion that contacts and supports one or both of the vibrator and the holding member, and only the convex portion surrounds the node portion of the vibrator [1] to [4]. ] The piezoelectric actuator as described in any one of the above.
[6] When the length of the vibrator is L and the width is W, the following expression (1) is satisfied 0.21 <W / L <0.26 (1)
The piezoelectric actuator according to any one of [1] to [5].
[7] The piezoelectric element having the laminated structure includes an internal electrode provided on a plurality of rectangular piezoelectric element surfaces, and the internal electrode includes a flexural vibration electrode, an expansion / contraction electrode, and a ground electrode. Formed on the surface of the piezoelectric element, the bending vibration electrode and the expansion / contraction electrode are respectively laminated in a pair with a ground electrode, and a voltage supply electrode is provided on a side surface of the laminated piezoelectric element. The piezoelectric actuator according to any one of [1] to [6].
[8] The sliding member is configured as a linear actuator so as to reciprocate linearly in the longitudinal direction by being formed to be long and supported so as to be movable in the longitudinal direction. ] The piezoelectric actuator as described in any one of the above.

  According to the present invention, by having an elastic body that surrounds the outer periphery of the vicinity of the bending vibration node of the vibrator and a holding member that holds the posture of the elastic body, an unstable posture of the vibrator is prevented, In addition, it is possible to provide a piezoelectric actuator that suppresses the generation of abnormal noise without propagating excessive vibration that does not directly affect the driving force to other members.

1 is an overall view of a piezoelectric actuator according to an embodiment of the present invention. The disassembled perspective view of the piezoelectric actuator shown in FIG. The exploded view of vibrator ASSY. The piezoelectric element electrode pattern figure. It is a vibration expansion / contraction vibration explanatory drawing, (a) Initial state, (b) At expansion, (c) At contraction. It is an oscillator bending vibration explanatory view, (a) initial state, (b) at the time of bending (at the time of forward rotation), (c) at the time of bending (at the time of inversion). An example of a vibrator holding structure. Another embodiment of the vibrator holding structure.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. 1-7 is a figure which shows an example of the piezoelectric actuator based on one Embodiment of this invention.

  In FIG. 1, the piezoelectric actuator 10 includes a vibrator 11 and a moving unit 21, and causes the moving unit 21 to reciprocate linearly by the vibration of the vibrator 11.

  As shown in FIGS. 2 and 3, the vibrator ASSY 31 includes the vibrator 11, a holding member 32 that holds the vibrator 11, a case 33 that fits the holding member 32 and covers the vibrator 11, and the pressure member 13. And a tension spring 14.

  Further, the vibrator ASSY 31 is supported in the housing 15 so as to be movable in the vertical direction. The pressurizing member 13 is formed in a rod shape, and tension springs 14 are attached to both end portions 13 a and 13 b, and a pressing force is applied to the vibrator 11 by the tension springs 14.

  Each of the side surface portions 32s of the holding member 32 includes a pair of protrusions 32p. By inserting the protrusions 32p into slide grooves 15d formed in the housing 15, the vibrator ASSY 31 can be moved in the vertical direction. Yes. Further, the housing 15 includes a ceiling surface portion for storing the pressing member 13 and a groove 15e. The housing 15 includes a base portion 15b, and the base portion 15b is fixed to a base 24 described later using screws or the like.

Further, the pressing member 13 has a spherical protrusion (not shown) formed at a portion facing the upper end surface 11 u (see FIG. 2) of the vibrator 11.
With this spherical protrusion, the vibrator 11 can properly apply the pressing force by the tension spring 14 by making the spherical protrusion of the pressure member 13 make point contact with the upper end face 11u (see FIG. 2) even in a slightly tilted posture. Therefore, a piezoelectric actuator with good driving efficiency can be realized. The contact 19 is integrated with the vibrator 11.

  Here, the moving unit 21 includes a sliding member 22 and a slider 23, and reciprocates linearly via a rolling member 25.

  Further, as shown in FIG. 2, the base 24 is provided with three holding grooves 24d and three holding grooves on the back of the slider 23 (not shown), and a guide portion formed by two holding grooves. By accommodating the rolling member 25 (not shown), the moving unit 21 having the slider 23 integrated with the sliding member 22 can reciprocate linearly.

  Meanwhile, as shown in FIG. 3, the vibrator 11 is formed in a laminated structure in which rectangular piezoelectric elements 12 are stacked in a prismatic shape, and is housed and held in a holding member 32. This vibrator 11 is a part of the elastic member 35 such that an elastic member (elastic body) 35 formed in a rectangular frame shape is positioned around the node 11e of the vibrator 11 as shown in FIG. The elastic member 35 is held by being compressed and deformed and fitted between the holding ribs 32r (concave portions) of the holding member 32.

The laminated vibrator 11 is formed by laminating a plurality of piezoelectric materials made of lead zirconate titanate (PZT, Vickers hardness 350 to 380) having a thickness of 50 to 200 μm. As the piezoelectric material, lead zirconate titanate having a mechanical quality factor of 1000 or more is preferable.
Here, the mechanical quality factor is a numerical value that represents a loss factor due to vibration, and is precisely the reciprocal of the elastic loss factor. Therefore, a material having a large mechanical quality factor has a small elastic loss factor, and the material itself has a small internal loss, so that a good vibration can be generated.

The elastic member 35 is made of a rubber material such as silicone rubber or ethylene / propylene rubber (EPT, EPDM). In particular, the rubber material used here is effective in suppressing the generation of abnormal noise so that unnecessary vibration other than the vibration of the vibrator 11 that directly contributes to the driving force is not transmitted to the holding member 32 and the case 33. For this purpose, it has been experimentally found that the loss coefficient (tan δ) must be a certain value or less as a rubber material.
Specifically, the silicone rubber or ethylene / propylene rubber described in Table 1 was excellent. Furthermore, in order to obtain a driving force, an externally applied voltage is continuously applied to the vibrator 11 to cause microvibration, and thus the temperature of the vibrator 11 itself is inevitably increased. Therefore, it was found that the rubber material also needs to have a certain level of heat resistance. The results are shown in <Table 1>. As can be seen from this table, from the viewpoint of heat resistance, the heat resistance temperature of ethylene propylene rubber or higher was necessary.

なお、損失係数の測定は、基本的には、ＪＩＳ Ｋ６３９４準拠しておこなった。具体的測定方法を以下に記載する。
＜損失係数（ｔａｎδ）測定方法＞
・測定器：上島製作所製 粘弾性アナライザＹＲ−７１３０
・測定温度：室温
・変形方法：引張
・周波数：１００Ｈｚ
・振幅：±１％
・プレロード：４８０ｍＮ
・試験片形状：２０ｍｍ（つかみ間隔）×４ｍｍ（幅）×２ｍｍ（厚さ））の短冊形状片
また、＜表１＞における総合評価とは損失係数、耐熱温度、耐オゾン性、電気絶縁性をすべて満足するものを「○（丸）」、一つでも満足しない項目がある場合には「×（バツ）」とした。以上の結果から、弾性部材３５として使用可能なゴム（熱硬化性エラストマ）は、損失係数（ｔａｎδ）が０．１５以上で、かつ耐熱温度が１５０℃以上の物性値を有することが必要であることが判明した。 <Table 1>

The loss factor was basically measured in accordance with JIS K6394. A specific measurement method is described below.
<Method of measuring loss factor (tan δ)>
-Measuring instrument: Viscoelastic analyzer YR-7130 manufactured by Ueshima Seisakusho
・ Measurement temperature: Room temperature ・ Deformation method: Tensile ・ Frequency: 100 Hz
・ Amplitude: ± 1%
・ Preload: 480mN
-Test piece shape: strip shape piece of 20 mm (grip interval) x 4 mm (width) x 2 mm (thickness)) Also, the comprehensive evaluation in <Table 1> is loss coefficient, heat resistance temperature, ozone resistance, electrical insulation “○ (circle)” indicates that all of the items are satisfied, and “× (x)” indicates that there is an item that does not satisfy even one item. From the above results, the rubber (thermosetting elastomer) that can be used as the elastic member 35 is required to have a physical property value such that the loss coefficient (tan δ) is 0.15 or more and the heat-resistant temperature is 150 ° C. or more. It has been found.

Hereinafter, the reason why the elastic member 35 is arranged so as to cover the outer periphery of the vibrator 11 including the node portion of the vibrator 11 will be described in detail. The same applies to elastic members 55 in other embodiments described later.
First, when the vibrator 11 undergoes bending vibration and expansion / contraction motion, a node having a small displacement is formed (11e and 11m in FIG. 6). And in the area | region except a node part, the abdominal part from which the vibrator | oscillator 11 is displaced largely by bending vibration and expansion-contraction movement is formed.

  For this reason, the vibrator 11 has an elastic member 35 attached to the outer periphery of the bending vibration node (11e) of the vibrator 11 for the purpose of holding down a portion where the displacement of the vibrator 11 is small, and a holding rib of the holding member 32. It is compression-supported between 32r (concave part). That is, the elastic member 35 has a uniform width (thickness) in the length (L) direction of the vibrator 11 with the bending vibration node (11e) of the vibrator 11 as the center. The length (= thickness) of the elastic member 35 in the length direction of the vibrator 11 is greater than 0.5 mm and less than 1.5 mm. The reason is that when the thickness of the elastic member 35 is 0.5 mm or less, the posture of the vibrator 11 cannot be kept good, and when the thickness is 1.5 mm or more, the bending vibration of the vibrator 11 is excessively suppressed. This is because sufficient driving force cannot be obtained. Further, the elastic member 35 having such a thickness has an inner peripheral surface that is smaller than the outer periphery of the vibrator 11, thereby compressing and holding the vibrator 11 and an outer surface larger than the inner peripheral surface of the holding member 32. By having the diameter, the holding member 32 is compression-fitted. Further, between the holding ribs 32r (recessed portions) of the holding member 32 is formed smaller than the thickness of the elastic member 35 so that the elastic member 35 can be compression-fitted. Note that an elastic member 55 of another embodiment described later is illustrated in FIG.

  In this way, the vibrator 11 can compress and hold the bending vibration node 11e (see FIG. 6) of the vibrator 11 while the elastic member 35 absorbs the size and assembly errors. Since it is compression-fitted between the members 32r (recesses) in the member 32, excess vibration of the vibrator 11 can be absorbed. Even if the vibrator 11 is assembled in a slightly tilted state, the posture of the contact 19 is not deteriorated and can be stably brought into contact with the sliding member 22. Therefore, efficient driving of the actuator can be obtained.

  As described above, the vibrator 11 compresses and holds the bending vibration node 11e by the elastic member 35. Therefore, even if the vibrator 11 is assembled in a slightly tilted state, the contactor posture is deteriorated. Without being able to make stable contact. For this reason, the actuator can be efficiently and stably driven. At the same time, it is possible to provide a piezoelectric actuator that can realize generation of abnormal noise without propagating excessive vibration that does not directly affect the driving force to other members.

  By the way, the vibrator 11 has a plurality of rectangular piezoelectric elements stacked and has an internal electrode on the surface of the piezoelectric element. The internal electrode is provided on the surface of the piezoelectric element as a bending vibration electrode, an expansion / contraction electrode, and a ground electrode. It is formed. Each of the bending vibration electrode and the expansion / contraction electrode is laminated in a pair with a ground electrode, and a voltage supply electrode is provided on a side surface of the laminated piezoelectric element. A desired driving operation is performed by appropriately applying a driving voltage between these electrodes.

  The electrode pattern formed on each piezoelectric element having a laminated structure constituting this vibrator will be described with reference to FIG. The electrode symbols (+, −) shown in FIG. 4 indicate the polarization state inside the piezoelectric element. FIG. 4A is formed on the surface of the piezoelectric element and is connected to the power supply side to function as an input pattern of a drive signal. FIG. 4B functions as a drive electrode for a telescopic operation described later. FIG. 4C functions as an input pattern of a driving signal for bending operation described later. FIG. 4D functions as a ground (G) pattern connected to the ground. 4 (e) and 4 (f) function as external extraction patterns for connecting the signals or ground patterns of FIGS. 4 (a) to 4 (d).

  The manner in which the vibrator 11 expands and contracts and bends and vibrates by inputting a signal from the outside to the laminated vibrator 11 described above will be described with reference to FIGS. 5A to 5C and FIGS. 6A to 6C. To do. When a drive signal for expansion / contraction operation is input to the vibrator 11, expansion / contraction vibration is performed in the longitudinal direction of the vibrator 11, as shown in FIGS. Further, when a driving signal for bending operation is input to the vibrator 11, bending vibration of the vibrator 11 is performed as shown in FIGS.

  As described above, the piezoelectric actuator 10 causes the elliptical motion and moves the sliding member 22 by shifting the phase of the driving power signal frequency for causing the vibrator 11 to expand and contract and the driving power signal frequency for bending vibration by approximately 90 °. . Note that the direction of movement of the sliding member 22 is reversed by inverting the phase of the input signal.

  Further, as shown in FIG. 3, the vibrator 11 has a ratio of the length L to the width W (W / L) such that 0.21 <W / L <0.26. It is preferable from the viewpoint of speed and power consumption, and more preferably 0.22 ≦ W / L ≦ 0.25.

  Hereinafter, the reason will be described with reference to Table 2. <Table 2> changes the ratio (W / L) of the length (L) to the width (W) of the piezoelectric element 12 to change the moving speed (mm / s) of the sliding member 22 and the power consumption (W) ) Was measured. Here, the moving speed of the sliding member 22 represents the driving efficiency of the piezoelectric actuator, and the power consumption means that the smaller the value, the more efficiently the driving force can be obtained.

＜測定条件＞
・負荷：５０ｇ
・駆動電圧：３．５〜４．５Ｖｒｍｓ
・駆動周波数 ：１５０〜１７０ＫＨｚ <Table 2>

<Measurement conditions>
・ Load: 50g
・ Drive voltage: 3.5-4.5Vrms
・ Drive frequency: 150-170KHz

The meanings of “◎ (double circle)”, “◯ (circle)”, “Δ (triangle)”, and “× (X)” described in the evaluation results in the table are described below.
(Moving body speed)
A: 75 mm / s or more,
○: 50 mm / s / more and 75 mm / s or less Δ: 30 mm / s or more and less than 50 mm / s ×: less than 30 mm / s (power consumption)
◎: Less than 1W
○: 1W or more and less than 1.5W
Δ: 1.5 W or more and less than 2 W
×: 2W or more
From the evaluation results of <Table 2>, in order to satisfy both the moving body speed (mm / s) and the power consumption (W), the ratio of the width (W) to the length (L) of the vibrator 11 (W It can be seen that / L) needs to be larger than 0.21 and smaller than 0.26. Further, it can be seen that the ratio is more preferably 0.22 or more and 0.25 or less. Thus, by optimizing the shape of the vibrator 11, a piezoelectric actuator capable of obtaining a highly efficient driving force can be realized.

  Hereinafter, another aspect of the present embodiment will be described with reference to FIG. As shown in FIG. 8, the elastic member 55 compressing and holding the vibrator 11 does not bring the entire inner peripheral surface of the elastic member 55 into contact with the vibrator 11, so that a constant space is formed. There are two support protrusions 55p. As described with reference to FIG. 7, the four support convex portions 55p surround the bending vibration node portion 11e of the vibrator 11 and are formed so as to be compressed and held.

  Accordingly, the vibrator 11 can compress and hold the outer periphery of the node portion 11e of the vibrator 11 with a smaller area than the elastic member 35 of the embodiment shown in FIG. 7, and directly affects the driving force of the sliding member 22. Thus, an efficient driving force can be applied to the sliding member 22 without hindering the bending vibration that gives the vibration. Further, since the vibrator 11 compresses and holds the vibrator 11 only by the support convex portion 55p of the elastic member 55, the vibrator 11 is driven using four spaces 55s formed on both sides of the support convex portion 55p. The heat generated sometimes can be effectively dissipated.

  The scope of the present invention is not limited to the illustrated and described exemplary embodiments, but includes all embodiments that provide the same effects as those intended by the present invention. For example, it is a matter of course that the same effect can be obtained even when applied to an actuator that rotates.

DESCRIPTION OF SYMBOLS 10 ... Piezoelectric actuator 11 ... Vibrator 11e ... Bending vibration node 11m ... Stretching vibration node 12 ... Piezoelectric element 13 ... Pressure member 14 ... Tension spring 15 ... Housing 19 ... Contact Child 21 …… Moving unit 22 …… Sliding member 23 …… Slider 24 …… Base 24d …… Holding groove 25 …… Rolling member 31 …… Oscillator ASSY
32: Holding member 32r: Holding rib (concave)
33 …… Case 35, 55 …… Elastic member 55p …… Supporting convex portion 55s …… Space

Claims (8)

In a piezoelectric actuator that moves a sliding member by pressing a vibrator made of a piezoelectric element having a laminated structure that generates a combined vibration of stretching vibration and bending vibration to the sliding member,
A pressurizing member for pressurizing one end portion of the vibrator in contact with the sliding member;
An elastic body arranged so as to surround at least two nodes of the vibrator;
A holding member for holding the elastic body and holding the posture of the vibrator;
A piezoelectric actuator. The piezoelectric actuator according to claim 1, wherein the node of the vibrator is a node of bending vibration. 2. The piezoelectric actuator according to claim 1, wherein the elastic body has a heat resistant temperature of 150 ° C. or more and a loss coefficient (tan δ) in accordance with JIS K6394 of 0.15 or less.   The said elastic body has a magnitude | size which surrounds the area | region of the at least node part of the bending vibration of the said vibrator | oscillator, The said holding member has a recessed part which supports the relative position of the said elastic body so that a movement is impossible. Item 4. The piezoelectric actuator according to any one of Items 3 to 3.   The elastic body has a convex portion that contacts and supports one or both of the vibrator and the holding member, and only the convex portion surrounds the node portion of the vibrator. The piezoelectric actuator according to one item. When the length of the vibrator is L and the width is W, the following expression (1) is satisfied. 0.21 <W / L <0.26 (1)
The piezoelectric actuator as described in any one of Claims 1 thru | or 5. The piezoelectric element having the laminated structure has internal electrodes provided on a plurality of rectangular piezoelectric element surfaces,
The internal electrode includes a flexural vibration electrode, an expansion / contraction electrode, and a ground electrode formed on the surface of each piezoelectric element, and the flexural vibration electrode and the expansion / contraction electrode are laminated in pairs with the ground electrode. ,
The piezoelectric actuator according to claim 1, wherein a voltage supply electrode is provided on a side surface of the stacked piezoelectric elements.   8. The linear actuator according to any one of claims 1 to 7, wherein the sliding member is formed in a long shape and is supported so as to be movable in the longitudinal direction so as to reciprocate linearly in the longitudinal direction. A piezoelectric actuator according to claim 1.

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