Vibration actuators, electronic equipment, optical instruments

Abstract

To provide a vibration-type actuator, an electronic device, and an optical device to solve problems in that a felt is hardened and power consumption is increased, resulting in a decrease in driving efficiency in a low-temperature region below -20°C, which is below glass transformation temperature, when the felt is used as a vibration damping member in the vibration actuator equipped with a piezoelectric element made of a non-lead piezoelectric material.SOLUTION: A vibration-type actuator according to the present invention includes: a vibration body having an electro-mechanical energy conversion element with a lead content of 1000 ppm or less and a protrusion portion protruding in a direction intersecting a main surface of a plate portion and the plate portion; and a contact body in contact with the protrusion portion. The vibration body and the contact body move relative to each other due to the vibration of the vibration body, and the vibration-type actuator further includes a pressure member that presses the vibration body against the contact body and a foam member provided between the pressure member and the vibration body. The foamed member has a main skeleton composed of siloxane bonds made of silicon and oxygen and the average equivalent circular diameter of the bubbles contained in the foamed member is larger than 120 μm.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a vibration actuator, an electronic device including the vibration actuator, and an optical device.

Background Art

[0002] A vibration actuator includes a vibrating body composed of an electro-mechanical energy conversion element such as a piezoelectric element and an elastic body, and a contact body that comes into pressure contact with the vibrating body. The vibration actuator is used as a vibration wave motor that relatively moves the contact body by utilizing the friction generated by the driving force of the vibration excited in the vibrating body.

[0003] Generally, a lead zirconate titanate (PZT)-based material is used as the piezoelectric material used for the piezoelectric element. However, in recent years, the impact on the environment of lead has been regarded as a problem, and a piezoelectric material using a perovskite-type metal oxide that does not contain lead (the lead content is less than 1000 ppm) has been proposed.

[0004] Further, Patent Document 1 discloses a vibration wave motor using a vibrator including a rectangular vibration plate and a piezoelectric element made of a non-lead-based piezoelectric material. The structure and driving principle of a vibration wave motor, which is a type of vibration actuator, are schematically shown. The vibration wave motor includes a vibrating body and a contact body that is brought into pressure contact with the vibrating body by a pressing member. At this time, in order for the pressing member to uniformly apply pressure to the vibrating body, it is desirable to increase the rigidity and contact the vibrating body. However, when a member with high rigidity contacts the vibrating body, the vibration of the vibrating body is inhibited, causing deterioration of the driving characteristics of the motor. Therefore, a structure in which a member that does not inhibit vibration is disposed between the pressing member and the vibrating body as a vibration damping member is known.

[0005] For example, Patent Document 2 lists sponge, styrofoam, and felt as supports for the vibrating body, and discloses that wool felt is particularly excellent among them. The support for the vibrating body in Patent Document 2 uses a member for not inhibiting vibration, and is considered to have the same function as the vibration damping member described in Patent Document 1.

[0006] However, according to the inventors' research, the following problems were found. In a vibratory actuator equipped with a piezoelectric element made of lead-free piezoelectric material, when felt was used as a vibration damping member, a decrease in driving efficiency was observed at low temperatures. In particular, in the low temperature region below -20°C, which is below the glass transition temperature of felt, the felt hardens, increasing the power consumption during low-temperature operation (input power at a constant speed, for example, 100 mm / s), and causing a significant decrease in driving efficiency. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2018-107437 [Patent Document 2] Japanese Patent Application Publication No. 3-289371 [Overview of the project] [Problems that the invention aims to solve]

[0008] This invention addresses the aforementioned problems and provides a vibration-type actuator that suppresses the increase in power consumption during low-temperature operation even when using lead-free piezoelectric materials. This makes it possible to achieve stable operation within the operating temperature range (e.g., -30°C to 60°C). Furthermore, this invention provides electronic and optical equipment using the vibration-type actuator. [Means for solving the problem]

[0009] The vibration actuator of the present invention, which solves the above problems, comprises an electromechanical energy conversion element with a lead content of 1000 ppm or less, and a vibrating body having a plate portion and an elastic body with a projection that protrudes in a direction intersecting the main surface of the plate portion. A contact body that comes into contact with the aforementioned projection, A vibratory actuator comprising the vibration of the vibrating body, wherein the vibrating body and the contact body move relative to each other due to the vibration of the vibrating body, The system further comprises a pressurizing member that pressurizes the vibrating body against the contact body, and a foaming member provided between the pressurizing member and the vibrating body. The foamed material is characterized by having a siloxane bond composed of silicon and oxygen as its main framework, and by the average equivalent diameter of the bubbles contained in the foamed material being greater than 120 μm. [Effects of the Invention]

[0010] According to the present invention, it is possible to maintain vibration isolation even in low-temperature environments, and in a vibration-type actuator using lead-free piezoelectric materials, it is possible to improve the driving efficiency in low-temperature environments while maintaining the driving efficiency at room temperature. This makes it possible to achieve stable operation within the operating temperature range (for example, -30°C to 60°C). [Brief explanation of the drawing]

[0011] [Figure 1] This figure illustrates the schematic structure of the vibration-type actuator of the present invention, which uses an annular piezoelectric material or a rectangular piezoelectric material. (a)(d) Side view, (b)(e) Perspective view, (c)(f) Rear view [Figure 2] This diagram illustrates the two vibration modes emitted by the oscillator of the present invention, which is equipped with a rectangular piezoelectric material. (a) Mode A, (b) Mode B [Figure 3] This is a schematic cross-sectional view of the foamed member in the present invention. [Figure 4] This is a schematic diagram of the foamed material in the present invention, viewed from the side. [Figure 5] This is a diagram illustrating the schematic structure of the optical instrument of the present invention. [Figure 6] This figure shows the temperature dependence of the relative permittivity of a piezoelectric material according to one embodiment of the present invention. [Figure 7] This figure shows the driving characteristics of a vibratory actuator according to one embodiment of the present invention. [Modes for carrying out the invention]

[0012] Hereinafter, embodiments for implementing the present invention will be described.

[0013] The vibration type actuator of the present invention includes an electro-mechanical energy conversion element having a lead content of 1000 ppm or less and a vibrating body having an elastic body provided with a protrusion protruding in a direction intersecting the main surface of the plate portion. Further, it includes a contact body in contact with the protrusion, and is a vibration type actuator in which the vibrating body and the contact body relatively move due to the vibration of the vibrating body. This vibration type actuator further has a pressing member that presses the vibrating body against the contact body, and a foaming member provided between the pressing member and the vibrating body. The foaming member has a siloxane bond composed of silicon and oxygen as a main skeleton, and is characterized in that the average circle equivalent diameter of the bubbles contained in the foaming member is larger than 120 μm.

[0014] The schematic structure of the vibration type actuator of the present invention is illustrated in FIGS. 1 and 2. In the vibration type actuators illustrated in FIGS. 1 and 2, a vibrating body having an annular plate portion and a vibrating body having a rectangular plate portion are used, respectively. The vibration type actuator 100 of the present invention includes an electro-mechanical energy conversion element 120 composed of an electrode 101 and a piezoelectric material 102. Further, an elastic body 103 provided with a protrusion 106 protruding out of the plane in a direction intersecting the main surface of the plate portion 108 is provided, and a vibrating body 110 in which these are arranged in order is configured. The vibration type actuator 100 further includes a contact body 104 in contact with the protrusion 106. In addition, it has a configuration in which a pressing member 121 for pressing the vibrating body 110 into pressure contact with the contact body 104 and a foaming member 122 are provided between the vibrating body 110 and the pressing member 121.

[0015] The contact body 104 only needs to be a member that can move relative to the vibrating body 110, and is not limited to a member that directly contacts the vibrator 110, and may be a member that indirectly contacts the vibrating body 110 through other members. The surface of the electro-mechanical energy conversion element 120 is pressed by the pressing member 121 via the foaming member 122. ​

[0016] (Piezoelectric material) The shape of the piezoelectric material 102 is not limited. However, when the shape of the plate portion is annular, the piezoelectric material is preferably annular, and when the shape of the plate portion is rectangular, the piezoelectric material is preferably rectangular.

[0017] The form of the piezoelectric material 102 is not limited. For example, it may be a piezoelectric material (sintered body) without crystal orientation, crystal orientation ceramics, piezoelectric single crystal, etc. The shape that the piezoelectric material can take is not limited. For example, in order to form a laminate of an electrode and a piezoelectric material, a layered piezoelectric material may be adopted, or a single plate of the piezoelectric material may be adopted. From the viewpoint of the cost of the piezoelectric material, a single plate is excellent. In order to drive the vibration type actuator, the piezoelectric material is subjected to poling treatment. When the frequency of the alternating electric field applied to the poled piezoelectric material approaches the resonance frequency of the piezoelectric material, the piezoelectric material vibrates greatly due to the resonance phenomenon.

[0018] (Electrode) When using an annular piezoelectric material, the piezoelectric material is provided with electrodes 101 divided in the circumferential direction, and an annular piezoelectric element is formed. The electrode 101 consists of a driving phase electrode 101e and a non-driving phase electrode 101f. The length of the driving phase electrode in the circumferential direction is 1 / 2 of the wavelength λ of the vibration wave generated in the circumferential direction of the annular piezoelectric element when an alternating voltage is applied to the driving phase electrode. The length of the non-driving phase electrode (ground electrode, monitoring electrode) in the circumferential direction is 1 / 4 of the wavelength λ. The number of driving phase electrodes and non-driving phase electrodes changes according to the number of traveling waves excited in the annular piezoelectric material. The piezoelectric material corresponding to each driving phase electrode is poled with voltages of different polarities from adjacent regions.

[0019] The driving phase electrodes are separated by an odd number of non-driving phase electrodes. After the poling treatment, the first electrode 101a and the second electrode 101b are provided so as to short-circuit two driving phase electrode groups separated by the non-driving phase electrodes respectively. The first electrode 101a and the second electrode 101b are used for driving a vibration type actuator using an annular piezoelectric material.

[0020] When a rectangular piezoelectric material is used, a rectangular electrode 101 is provided. The electrode 101 consists of a first electrode 101a and a second electrode 101b. The first electrode 101a and the second electrode 101b are used for polarization treatment of the rectangular piezoelectric material and for driving a vibratory actuator using the rectangular piezoelectric material.

[0021] The electrode consists of a metal film with a thickness of approximately 0.3 to 10 μm. The material is not particularly limited, but generally silver, gold, or platinum electrodes are used. The method of manufacturing the electrode is not limited and can be formed by screen printing, sputtering, vacuum deposition, etc. In order to fabricate an electromechanical energy conversion element with a lead content of 1000 ppm or less, it is necessary to use a paste or target with a lead content of less than 1000 ppm in the electrode formation process.

[0022] (Elastic body) The elastic body 103 is preferably made of metal from the viewpoint of its elastic properties and workability. Examples of metals that can be used for the elastic body 103 include aluminum, brass, and stainless steel. Among stainless steels, martensitic stainless steel is preferred, and SUS420J2 is the most preferred. The elastic body has protrusions 106 that come into contact with the contact body. To further improve the wear resistance of the protrusions, the elastic body may be subjected to quenching, plating, or nitriding.

[0023] (Foam material) As shown in Figure 1(a), the foam member 122 is provided on the surface of the electromechanical energy conversion element 120 opposite to the surface on which the elastic body 103 is located. The foam member 122 is required to uniformly pressurize the vibrating body 110 against the contact body 104 and also to function as a vibration damping member. Its function as a vibration damping member is to dampen vibrations from adjacent members by absorbing them, etc., and the foam member 122 may be provided separately as long as the driving characteristics do not deteriorate.

[0024] Figure 3 shows a horizontal (XY plane) cross-sectional view of the foamed member of the present invention. Figure 4 shows a vertical (Z direction) side view of the foamed member of the present invention. Figure 4(a) shows a side view of a foamed member without a skin layer on the surface, and Figure 4(b) shows a side view of a foamed member with a skin layer on the surface.

[0025] The foamed member 122 is characterized by having a siloxane bond consisting of silicon and oxygen as its main framework, and the average equivalent diameter of the bubbles contained in the foamed member is greater than 120 μm. By having a siloxane bond as its main framework, the mobility of the molecules constituting the foamed member is increased, making it possible to lower the glass transition temperature of the foamed member below the operating temperature range of -30°C, and thus maintaining the same physical properties of the foamed member as at room temperature even at low temperatures.

[0026] It is preferable that the average equivalent diameter of the bubbles in the foamed member 122 is greater than 120 μm. The presence of bubbles in the foamed member allows it to have spring properties, enabling it to uniformly pressurize the vibrating body 110 against the contact body 104 and function as a vibration damping member. Furthermore, having an average equivalent diameter of the bubbles greater than 120 μm makes it possible to maintain vibration isolation even at low temperatures in a vibration-type actuator using lead-free piezoelectric material, thereby improving the driving efficiency at low temperatures while maintaining the driving efficiency at room temperature.

[0027] The average equivalent diameter is preferably calculated from the cross-sectional shape of the foamed material. If the average equivalent diameter of the bubbles in the cross-section of the foamed material is greater than 120 μm, it is possible to uniformly pressurize the vibrating body while maintaining the motor's driving characteristics without hindering the vibration of the vibrating body.

[0028] The average equivalent diameter of the foamed member 122 can be determined by image processing or other methods using cross-sectional images obtained from cross-sectional observation. Methods for performing cross-sectional observation include exposing the cross-section by cutting the sample and observing it with an optical microscope or laser microscope. Alternatively, a non-destructive method of obtaining tomographic images using X-ray CT scanning is also possible. Furthermore, if the shape of the bubbles can be confirmed, the surface in contact with the electromechanical energy conversion element 120 may be treated as the cross-sectional shape. Image processing software can be either optimized for microscopes or commercially available software. Since bubbles of various sizes exist, it is preferable to observe many bubbles when calculating the average equivalent diameter. Specifically, it is preferable to calculate the average equivalent diameter from 50 or more bubbles.

[0029] The foamed member of the present invention may have columnar bubbles as shown in Figure 4(b), or it may have a skin layer on its surface. As shown in Figure 4(b), if a skin layer is present on the surface, it is not possible to accurately observe the bubbles from the surface, so it is preferable to expose the cross-section by cutting. The obtained cross-sectional photograph can be used to calculate the average equivalent diameter of the circle by image processing.

[0030] The foamed member preferably has a siloxane bond as its main backbone, with methyl groups bonded to the backbone as its main component. This structure makes it possible to maintain vibration insulation even at low temperatures. The same effect can be obtained by substituting some of the methyl groups with vinyl groups or phenyl groups. The foamed member may also be a sponge containing silicone rubber.

[0031] Preferably, the bubbles in the foamed material are mainly closed bubbles. Closed bubbles are bubbles that are not connected to the front and back surfaces of the foamed material. Closed bubbles are impermeable to gases and liquids. For this reason, closed bubbles are preferable for the foamed material to have spring properties. On the other hand, open bubbles are undesirable because the bubbles are connected, making it easy for air to enter and exit, and they tend to collapse when pressure is applied. This can lead to poor spring properties, potentially preventing uniform pressure distribution of the vibrating body and reducing vibration damping function. Preferably, the number of closed bubbles is greater than the number of open bubbles, that is, the number of closed bubbles accounts for 50% or more of the total number of bubbles in the foamed material. In this case, the number can be counted from a cross-sectional photograph containing 50 or more bubbles.

[0032] It is more preferable that the average equivalent diameter of the bubbles in the foamed material is 200 μm or more. By setting the average equivalent diameter of the bubbles to 200 μm or more, the driving efficiency in the low-temperature region can be improved in a vibratory actuator using a piezoelectric material whose phase transition temperature is -10°C or lower in order to achieve stable operation within the operating temperature range (e.g., -30°C to 60°C). More preferably, it is 300 μm or more.

[0033] The average equivalent diameter of the foam member is preferably less than half the thickness t of the foam member. This allows for uniform pressure distribution to the vibrating body and enables it to function as a vibration damping member. More preferably, a diameter less than one-third the thickness t of the foam member is used.

[0034] (contact body) From the viewpoint of rigidity, stainless steel is preferred for the contact body 104. Among stainless steels, martensitic stainless steel is preferred, and SUS420J2 is the most preferred. Since the contact body 104 is in frictional contact with the elastic body 103, it needs to have excellent wear resistance, and its surface is subjected to nitriding or anodizing treatment. A frictional force acts between the projection 106 and the contact body 104 due to pressurized contact. The tip of the projection 106 vibrates elliptically due to the vibrations emitted by the electromechanical energy conversion element 120, which can generate a driving force (thrust) to drive the contact body 104. The contact body is generally called a slider or rotor. Note that "contact body" refers to a member that is in contact with a vibrating body and moves relative to the vibrating body due to the vibrations generated in the vibrating body. Contact between the contact body and the vibrating body is not limited to direct contact without other members interposed between the contact body and the vibrating body. Contact between the contact body and the vibrating body may be indirect contact with other members interposed between the contact body and the vibrating body, as long as the contact body moves relative to the vibrating body due to the vibrations generated in the vibrating body. "Other components" are not limited to components independent of the contact body and the vibrating body (for example, high-friction materials made of sintered bodies). "Other components" may also be surface-treated parts formed on the contact body or vibrating body by plating, nitriding, or the like.

[0035] (Vibration-type actuator using annular piezoelectric material) In an annular piezoelectric element, the piezoelectric material in contact with adjacent driving phase electrodes is polarized with different polarities. Therefore, when an electric field of the same polarity is applied to the driving phase electrode 101e, the expansion and contraction polarity of the piezoelectric material in that region alternately reverses at a pitch of λ / 2. When an alternating voltage is applied to the first electrode 101a, a first standing wave with wavelength λ is generated around the entire circumference of the oscillator. Similarly, when an alternating voltage is applied to the second electrode 101b, a second standing wave is generated, but the position of the wave is rotated by λ / 4 in the circumferential direction relative to the first standing wave. On the other hand, when two types of alternating voltages with the same frequency and a temporal phase difference of π / 2 are applied to the first and second electrodes, the following traveling wave is generated. That is, as a result of the combination of the first and second standing waves, a traveling wave of bending vibration (vibration with amplitude perpendicular to the surface of the oscillator) (wavenumber n along the annulus, wavelength λ) is generated around the entire circumference of the oscillator.

[0036] When a bending vibration traveling wave (hereinafter sometimes simply referred to as a "bending vibration wave") is generated, each point on the surface of the diaphragm constituting the oscillator undergoes elliptical motion. As a result, a moving object in contact with this surface receives a circumferential frictional force (driving force) from the diaphragm and rotates. The direction of this rotation can be reversed by switching the positive or negative phase difference of the alternating voltage applied to the first and second electrodes. Furthermore, the rotation speed can be controlled by the frequency and amplitude of the alternating voltage applied to the first and second electrodes.

[0037] Figure 2 illustrates two vibration modes emitted by the oscillator of the present invention, which comprises a rectangular piezoelectric material. The rectangular piezoelectric material is provided with the first electrode 101a and the second electrode 101b, and their respective regions are designated as the first region and the second region.

[0038] Mode A When both the first and second regions are stretched or contracted, a first bending vibration mode (mode A) is generated. Mode A is most strongly excited when the phase difference between the alternating voltages VA and VB applied to the first electrode 101a and the second electrode 101b is 0° and the frequency is near the resonant frequency of mode A. Mode A is a first-order out-of-plane vibration mode in which two nodes (where the amplitude is minimum) appear approximately parallel to the long side of the oscillator 110. The two projections 106 protruding in the same direction in the elastic body are positioned near the antinodes (where the amplitude is maximum) of mode A. Therefore, the tip surfaces of the projections 106 reciprocate in the Z direction due to vibration mode A.

[0039] Mode B When the first region stretches and contracts, the second region also contracts and stretches, respectively, a second bending vibration mode (mode B) is generated. Mode B is most strongly excited when the phase difference between the alternating voltages VA and VB applied to the first electrode 101a and the second electrode 101b is 180° and the frequency is near the resonant frequency of mode B. Mode B is a second-order out-of-plane vibration mode in which three nodes appear approximately parallel to the short side of the oscillator 110. The elastic projection 106 is positioned near the location of the nodes of mode B. Therefore, the tip surface of the projection 106 reciprocates in the X direction due to mode B.

[0040] In the vibration actuator 100, when the phase difference between the alternating voltages VA and VB is 0 to ±180°, modes A and B are excited simultaneously, and elliptical vibration is excited in the projection 106 of the elastic body. A vibration actuator that uses a rectangular piezoelectric material and is driven by modes A and B is preferable because it is easy to miniaturize.

[0041] To prevent vibration inhibition due to deformation of the foamed material under pressurization, it is preferable that the area of ​​the contact portion between the foamed material and the electromechanical energy conversion element is smaller than the area of ​​the planar portion of the electromechanical energy conversion element including the aforementioned portion. This is expected to suppress problems such as deformation causing the foamed material to wrap around to the side of the piezoelectric element (which is the electromechanical energy conversion element), thereby inhibiting the vibration of the piezoelectric element, or deformation causing interference with surrounding materials, thereby inhibiting vibration. Furthermore, it is preferable that the foamed material is smaller than the elastic material.

[0042] (Composition of piezoelectric material) The composition of the piezoelectric material 102 is not particularly limited, as long as the lead content is less than 1000 ppm (i.e., lead-free). The lead content can be measured, for example, by ICP emission spectroscopy.

[0043] Preferably, the main component of the piezoelectric material is barium titanate-based.

[0044] From the viewpoint of having a high piezoelectric constant and being relatively easy to manufacture, piezoelectric materials are preferably made of barium titanate-based materials. Here, barium titanate-based materials include barium titanate (BaTiO3), calcium barium titanate ((Ba,Ca)TiO3), and barium zirconate titanate (Ba(Ti,Zr)O3). Calcium barium zirconate titanate ((Ba,Ca)(Ti,Zr)O3) is another example. Furthermore, compositions such as sodium niobate-barium titanate (NaNbO3-BaTiO3), sodium bismuth titanate-barium titanate, and potassium bismuth titanate-barium titanate are also examples. The term refers to materials whose main components are these compositions.

[0045] Furthermore, piezoelectric materials containing these compositions as main components or in combination can be used in the vibration-type actuator 100 of the present invention.

[0046] Among these lead-free piezoelectric materials, the piezoelectric material 102 of the electromechanical energy conversion element 120 in the present invention is preferably barium titanate-based. Barium zirconate titanate is even more preferred due to its excellent temperature dependence of piezoelectric properties within the operating temperature range.

[0047] In particular, the following materials are preferred from the viewpoint of achieving both the piezoelectric constant and the mechanical quality coefficient of the piezoelectric material. Specifically, it is preferable that the main components be barium calcium zirconate titanate ((Ba,Ca)(Ti,Zr)O3) and sodium niobate-barium titanate (NaNbO3-BaTiO3). In addition to the main components, it is preferable that manganese and bismuth are included. The main component refers to a material whose weight fraction is greater than 10%.

[0048] It is preferable that the main component of the piezoelectric material is barium calcium zirconate titanate (hereinafter referred to as BCTZ). When BCTZ is the main component, the piezoelectric properties of BCTZ can be adjusted according to the application by adjusting the amount of Ca and Zr. In addition, the amount of expensive niobium used can be reduced.

[0049] The piezoelectric material is a piezoelectric material containing an oxide with a perovskite-type structure containing Ba, Ca, Ti, and Zr, and Mn. The molar ratio x of Ca to the sum of Ba and Ca is 0.02 ≤ x ≤ 0.30, and the molar ratio y of Zr to the sum of Ti and Zr is 0.020 ≤ y ≤ 0.095, and y ≤ x. Preferably, α, which is the ratio of the molar amounts of Ba and Ca to the molar amounts of Ti and Zr, is 0.9955 ≤ α ≤ 1.01, and the content of Mn per 100 parts by weight of the oxide is 0.02 parts by weight or more and 1.0 part by weight or less in terms of metal.

[0050] Such piezoelectric materials can be represented by the following general formula (1). (Ba 1-x Ca x ) α (Ti 1-y Zr y )O3(1) however, 0.986≦α≦1.100, 0.02 ≤ x ≤ 0.30, 0.02 ≤ y ≤ 0.095 Preferably, the piezoelectric material has a perovskite-type metal oxide represented by as the main component, and the content of metal components other than the main component in the piezoelectric material is 1 part by weight or less in terms of metal per 100 parts by weight of the metal oxide.

[0051] In particular, it is preferable that the metal oxide contains Mn, and that the Mn content is between 0.02 parts by weight and 0.40 parts by weight in terms of metal per 100 parts by weight of the metal oxide. Containing Mn within this range improves insulation properties and the mechanical quality coefficient Qm. Here, the mechanical quality coefficient Qm is a coefficient that represents the elastic loss due to vibration when the piezoelectric material is evaluated as an oscillator, and the magnitude of the mechanical quality coefficient is observed as the sharpness of the resonance curve in impedance measurement. In other words, it is a constant that represents the sharpness of the oscillator's resonance. When the mechanical quality coefficient Qm is large, the amount of strain in the piezoelectric material becomes larger near the resonance frequency, and the piezoelectric material can be vibrated more effectively.

[0052] The metal oxide represented by the general formula (1) above means that the metal elements located at the A site of the perovskite structure are Ba and Ca, and the metal elements located at the B site are Ti and Zr. However, some Ba and Ca may be located at the B site. Similarly, some Ti and Zr may be located at the A site.

[0053] In general formula (1), the molar ratio of the element at the B site to the element O is 1:3, but even if the molar ratio deviates slightly, as long as the metal oxide has a perovskite structure as its main phase, it falls within the scope of the present invention.

[0054] The perovskite structure of a metal oxide can be determined, for example, from structural analysis using X-ray diffraction or electron diffraction.

[0055] In general formula (1), x, which represents the molar ratio of Ca at the A site, is in the range of 0.02 ≤ x ≤ 0.30. Substituting a portion of the Ba in perovskite-type barium titanate with Ca within this range shifts the phase transition temperature between orthorhombic and tetragonal phases to the lower temperature side, thus enabling stable piezoelectric vibration within the operating temperature range of the vibration actuator. However, if x is greater than 0.30, the piezoelectric constant of the piezoelectric material becomes insufficient, which may lead to inadequate performance of the vibration actuator. On the other hand, if x is less than 0.02, the dielectric loss (tanδ) may increase. Increased dielectric loss increases the heat generated when applying voltage to the piezoelectric material to drive the vibration actuator, which may reduce motor driving efficiency and increase power consumption.

[0056] In general formula (1), y, which represents the molar ratio of Zr at site B, is in the range of 0.02 ≤ y ≤ 0.1. If y is greater than 0.1, Td becomes low, below 80°C, which is undesirable as it limits the temperature range in which the vibration actuator can be used to below 80°C.

[0057] In this specification, Td refers to the lowest temperature at which the piezoelectric constant decreases by more than 10% compared to the piezoelectric constant before heating, after heating the piezoelectric material from room temperature to Td and then cooling it back to room temperature, one week after polarization treatment.

[0058] Furthermore, in general formula (1), α, which represents the ratio of the molar amounts of Ba and Ca at site A to the molar amounts of Ti and Zr at site B, is preferably in the range of 0.9955 ≤ α ≤ 1.010. If α is smaller than 0.9955, abnormal grain growth is more likely to occur in the crystal grains constituting the piezoelectric material, and the mechanical strength of the piezoelectric material decreases. On the other hand, if α is larger than 1.010, the piezoelectric material does not become dense enough and its insulating properties become extremely brittle.

[0059] The means for measuring the composition of piezoelectric materials are not particularly limited. Examples of such methods include X-ray fluorescence analysis, ICP emission spectrometry, and atomic absorption spectrometry. Regardless of the measurement method used, the weight ratio and composition ratio of each element contained in the piezoelectric material can be calculated.

[0060] The metal equivalent of Mn content is calculated by determining the content of each metal, Ba, Ca, Ti, Zr, and Mn, from piezoelectric materials using methods such as X-ray fluorescence analysis (XRF), ICP emission spectrometry, and atomic absorption spectrometry. From this content, the elements constituting the metal oxide represented by general formula (1) are converted to oxide equivalents, and the value is expressed as the ratio of the weight of Mn to the total weight of these elements, with the total weight set to 100.

[0061] If the Mn content is less than 0.02 parts by weight, the polarization treatment necessary for driving the vibratory actuator may not be sufficiently effective. On the other hand, if the Mn content is greater than 0.40 parts by weight, the piezoelectric properties of the piezoelectric material may not be sufficient, or hexagonal crystals without piezoelectric properties may appear. The Mn is not limited to metallic Mn; it is acceptable as long as it is included in the piezoelectric material as a Mn component, and the form of its inclusion is not important. For example, it may be solid-dissolved at the B site or contained within the grain boundaries. A more preferable form of inclusion is solid-dissolved at the B site from the viewpoint of insulation and ease of sintering.

[0062] (Composition of piezoelectric material 4) The piezoelectric material preferably contains 0.042 parts by weight or more and 0.850 parts by weight or less of Bi in terms of metal equivalent.

[0063] The piezoelectric material may contain 0.85 parts by weight or less of Bi (in terms of metal equivalent) per 100 parts by weight of the metal oxide shown in general formula (1). The Bi content relative to the metal oxide can be measured, for example, by ICP emission spectroscopy. Bi may be present at the grain boundaries of the ceramic piezoelectric material, or it may be in a solid solution within the perovskite-type structure of (Ba,Ca)(Ti,Zr)O3. When Bi is present at the grain boundaries, inter-particle friction is reduced and the mechanical quality coefficient increases. On the other hand, when Bi is incorporated into the solid solution forming the perovskite structure, the phase transition temperature is lowered, which reduces the temperature dependence of the piezoelectric constant and further improves the mechanical quality coefficient. It is preferable that the position of Bi when incorporated into the solid solution is at site A, as this improves the charge balance with Mn.

[0064] The piezoelectric material may contain elements other than those in the general formula (1) and Mn and Bi (hereinafter referred to as "sub-components"), as long as the properties do not change. Preferably, the total amount of sub-components is less than 1.2 parts by weight per 100 parts by weight of the metal oxide represented by the general formula (1). If the amount of sub-components exceeds 1.2 parts by weight, the piezoelectric properties and insulating properties of the piezoelectric material may deteriorate.

[0065] Since the piezoelectric properties of the vibrating actuator exhibit excellent temperature dependence within its operating temperature range (e.g., -30°C to 60°C), it is even more preferable if the phase transition temperature is -10°C or lower.

[0066] The piezoelectric material of the present invention undergoes a sequential phase transition from tetragonal to orthorhombic as the temperature decreases from room temperature. The phase transition temperature referred to herein refers to this phase transition. The phase transition temperature is calculated by measuring the dielectric constant while varying the temperature, and determining the temperature at which the derivative of the dielectric constant with respect to the sample temperature is maximized. The crystal system can be evaluated by X-ray diffraction, electron diffraction, or Raman scattering. Near the phase transition temperature, the dielectric constant and electromechanical coupling coefficient reach maximums, while Young's modulus reaches minimums. The piezoelectric constant is a function of these three parameters and exhibits a maximum value or inflection point near the phase transition temperature.

[0067] The electronic device of the present invention is characterized by comprising a vibratory actuator of the present invention, a member connected to the contact body of the vibratory actuator, and a means for detecting the position of the member (e.g., an encoder). The electronic device can precisely control the position of the member by detecting the position of the member and operating the vibratory actuator until the member reaches a target position.

[0068] The optical instrument of the present invention is characterized by comprising the electronic device of the present invention and an optical element and / or an image sensor. Figure 5 is a schematic diagram showing one embodiment of the optical instrument of the present invention (focus lens section of the lens barrel device). In Figure 5, the vibrating body 110, which is made of a rectangular piezoelectric material, is in pressurized contact with the contact body (slider) 104, similar to Figure 1(d). The power supply member 507 is connected to the side having first and second regions. When a desired voltage is applied to the vibrator 110 via the power supply member 507 by a voltage input means (not shown), elliptical motion occurs in the protrusion of the elastic body (not shown). The holding member 501 is joined to the vibrating body 110 and is configured to prevent the generation of unwanted vibrations. The movable housing 502 is fixed to the holding member 501 with screws 503 and is integral with the vibrator 110. These components form the electronic device of the present invention. By attaching the movable housing 502 to the guide member 504, the electronic device of the present invention can move linearly in both directions (forward and reverse directions) along the guide member 504.

[0069] Next, the lens 506 (optical component) that serves as the focusing lens for the lens barrel device will be described. The lens 506 is fixed to the lens holding member 505 and has an optical axis (not shown) parallel to the direction of movement of the vibration actuator. The lens holding member 505, like the vibration actuator, performs focus adjustment (focusing operation) by moving in a straight line on two guide members 504, which will be described later. The two guide members 504 are components that engage the moving housing 502 and the lens holding member 505, enabling the moving housing 502 and the lens holding member 505 to move in a straight line. With this configuration, the moving housing 502 and the lens holding member 505 can move in a straight line on the guide members 504.

[0070] Furthermore, the connecting member 510 is a member that transmits the driving force generated by the vibrating actuator to the lens holding member 505, and is fitted and attached to the lens holding member 505. As a result, the lens holding member 505 can move smoothly in both directions along the two guide members 504 together with the movable housing 502.

[0071] Furthermore, the sensor 508 is provided to detect the position of the lens holding member 505 on the guide member 504 by reading the position information of the scale 509 attached to the side surface of the lens holding member 505. As described above, the focus lens section of the lens barrel device is formed by assembling each of the above-mentioned components.

[0072] In the above, we described a lens barrel device for a single-lens reflex camera as an optical instrument, but it can be applied to a variety of optical instruments equipped with a vibration actuator, regardless of the type of camera, such as compact cameras with integrated lenses and camera bodies, and electronic still cameras.

[0073] Furthermore, as another configuration for a vibratory actuator, multiple vibrators may be in contact with a single common contact body, and the contact body may be arranged so that it moves relative to the multiple vibrators due to the vibration of the multiple vibrators.

[0074] Furthermore, the vibration actuator of the present invention can be applied to medical or engineering fields. Specifically, it is also possible to configure a wire-driven actuator comprising an elongated member, a wire inserted through the elongated member and fixed to a part of the elongated member, and the vibration actuator described above that drives the wire, wherein the elongated member bends when the wire is driven. [Examples]

[0075] The vibration-type actuator and vibrator of the present invention will now be described with reference to examples, but the present invention is not limited to the following examples.

[0076] (Example 1) The metal oxide powder was calcined at 1340°C to obtain the piezoelectric material described in Manufacturing Composition 1 of Table 2. Manufacturing composition 1 is the composition represented by general formula (1), and the values ​​of x, y, and a shown in Table 2 correspond to the values ​​of general formula (1) described above.

[0077] The obtained piezoelectric material was ground and polished to a thickness of 0.5 mm and then processed into an annular shape with an outer diameter of 62 mm and an inner diameter of 54 mm. On one side of the shaped piezoelectric material 102, the driving phase electrode 101e and non-driving phase electrode 101f shown in Figure 1(c) were formed. The electrodes were formed by applying silver paste to the piezoelectric material 102 by screen printing, drying, and baking.

[0078] Next, an adhesive was applied to an elastic body 103 made of SUS420J2, and it was pressed against a piezoelectric material 102 on which electrodes were formed. The annular piezoelectric material and the annular elastic body were positioned using a positioning jig so that the centers of their respective circles coincided. Next, a heat treatment was performed to cure the adhesive. The piezoelectric material with the elastic body pressed against it was heated to a temperature T1 = 160°C and held for 180 seconds, then cooled to room temperature, and the pressure was released to obtain the oscillator. Next, an FPC coated with ACP was thermocompressed onto the electrodes provided on the piezoelectric material. The thermocompression conditions were a temperature T2 = 140°C and a holding time of 20 seconds. After that, the SUS420J2 elastic body was grounded, and polarization treatment was performed by alternately applying voltages of different polarities to adjacent driving phase electrodes 101e. In the polarization treatment, multiple external electrodes connected to a power supply were brought into contact with the electrodes used as sensors among the driving phase electrodes 101e and driven phase electrodes 101f. After heating to T3 = 100°C, an electric field equivalent to 2 kV / mm was applied for 30 minutes. Then, while the electric field was still applied, the material was cooled to 40°C over 40 minutes before the voltage application was terminated. Subsequently, the first electrode 101a and the second electrode 101b were printed and dried to obtain the vibrator. In the drying process, the temperature of the piezoelectric material was kept below 80°C to prevent depolarization of the piezoelectric material. The obtained vibrator was then pressed into contact with a contact body (rotor) made of SUS420J2 to fabricate a vibrating actuator. The type of foamed material with siloxane bonds as its main framework, which was placed between the electromechanical energy conversion element and the pressurizing member, is shown in Example 1 of Table 1. The foamed material contained silicone rubber, and the number of closed cells accounted for more than 50% of the total number of bubbles in the foamed material.

[0079] Furthermore, piezoelectric elements were fabricated to evaluate the properties of the piezoelectric material using the following method. The piezoelectric material obtained by firing was polished to a thickness of 0.5 mm, and gold electrodes with a thickness of 400 nm were formed on both the front and back surfaces by DC sputtering. A 30 nm thick titanium film was deposited between the electrodes and the ceramic as an adhesion layer. The ceramic with electrodes was cut to fabricate strip-shaped piezoelectric elements measuring 10 mm × 2.5 mm × 0.5 mm. The obtained piezoelectric elements were subjected to polarization treatment by setting the surface temperature of a hot plate to 60°C to 100°C and applying an electric field of 1 kV / mm on the hot plate for 30 minutes. The capacitance of the polarization-treated piezoelectric element was measured using an impedance analyzer (Agilent Technologies 4194A) while changing the temperature of the sample, and the relative permittivity was calculated. The phase transition temperature is the temperature at which the crystal system changes from tetragonal to orthorhombic, and was defined as the temperature at which the derivative of the relative permittivity with respect to the sample temperature was maximum while the sample was cooled. Figure 6 shows the relative permittivity with respect to the sample temperature for the piezoelectric material described in Example 1. From the results in Figure 6, the phase transition temperature of the piezoelectric material described in Example 1 was -20°C.

[0080] (Example 2) A piezoelectric material described in Manufacturing Composition 1 was obtained in the same manner as in Example 1. The obtained piezoelectric material was ground and polished to a thickness of 0.35 mm and then processed into a rectangle of 8.9 × 5.7 mm. The first to third electrodes shown in Figure 3 were formed on both sides of the shaped piezoelectric material using the same method as in Example 1.

[0081] Next, an adhesive was applied to an elastic body made of SUS420J2, and it was pressed against a rectangular piezoelectric material on which electrodes had been formed. The elastic body used had a rectangular section measuring 9.1 × 5.8 mm, which was larger than the piezoelectric material, and the thickness of the elastic body was between 0.25 and 0.30 mm. The rectangular piezoelectric material and the elastic body were positioned using a positioning jig so that the centers of their respective rectangular sections coincided and the sides of the rectangular sections were parallel. While pressed together, the piezoelectric material was heated to a temperature T1 = 160°C and held for 180 seconds, then cooled to room temperature, and the pressure was released to obtain the oscillator.

[0082] Next, using a soldering iron with a temperature T2 = 140°C, the FPC coated with ACP and the piezoelectric material were pressed together for 20 seconds, thus thermocompressing the FPC to the electrodes provided on the piezoelectric material.

[0083] Next, the piezoelectric material was subjected to polarization treatment. In the polarization treatment, the elastic body was grounded, and external electrodes connected to the power supply were brought into contact with the first and second electrodes, respectively. Although the first and second electrodes already had FPCs connected to them, the entire structure was not covered by the FPCs, and the external electrodes for polarization treatment made contact with the exposed portions. After heating to T3 = 100°C, an electric field equivalent to 2 kV / mm was applied for 30 minutes, and then the material was cooled to 40°C over 40 minutes while the electric field was still applied, after which the voltage application was terminated. The vibrator obtained through the above process was brought into pressurized contact with a contact body (slider) made of SUS420J2 to fabricate a vibrating actuator. The type of foamed material with siloxane bonds as its main framework, which was placed between the electromechanical energy conversion element and the pressurizing member, is shown in Example 2 of Table 1.

[0084] [Table 1]

[0085] (Examples 3 to 6) Examples 3 to 6 of the vibration-type actuator were fabricated using the same method as in Example 2, except that the type of foamed member with a siloxane bond as its main framework, which was placed between the electromechanical energy conversion element and the pressurizing member, was one of those shown in Table 1.

[0086] (Comparative Example 1) A vibrating actuator was fabricated using the same method as in Example 1, except that felt was placed between the electromechanical energy conversion element and the pressurizing member.

[0087] (Comparative Example 2) A vibration-type actuator was fabricated using the same method as in Example 2, except that felt was placed between the electromechanical energy conversion element and the pressurizing member.

[0088] (Evaluation method for vibration-type actuators) For each embodiment and comparative example, a driving test was performed on the vibration-type actuator by applying an alternating voltage with an amplitude of 130 Vpp to the first and second electrodes. At that time, the phase difference between the voltages of the first and second electrodes was set to -90° and 90°.

[0089] When the frequency of the alternating voltage is swept from a frequency higher than the resonant frequencies of vibration modes A and B towards the resonant frequencies, the contact body is driven in a direction according to the phase difference of the alternating voltage and stops after reaching its maximum speed. For convenience, the directions of travel when the phase difference is -90° and 90° are called the reverse direction and the forward direction, respectively. The maximum speed of the oscillator and the frequency at which it reached its maximum speed were measured using a sensor. The power at a certain rated speed lower than the maximum speed (rated power) was calculated from the current flowing through the drive circuit. Figure 7 shows an example of the measurement results of speed and power against frequency.

[0090] Furthermore, to confirm temperature stability, the maximum speed and rated power were measured under ambient conditions of 20°C (room temperature) and under low-temperature conditions of -20°C and -30°C, and the average values ​​in the reverse and forward directions were calculated.

[0091] At each temperature, the change in the maximum speed of the vibration actuator fabricated in Comparative Example 1 and the change in rated power were calculated for Example 1. Similarly, the change in the maximum speed of the vibration actuator fabricated in Comparative Example 2 and the change in rated power for Example 3 to Example 6 were calculated. The results are shown in Table 1.

[0092] Compared to the vibration actuators of Comparative Examples 1 and 2, which used felt, Examples 1 and 2, which used foamed material A with siloxane bonds as the main framework, showed an increase in maximum speed and a decrease in rated power at each temperature.

[0093] Furthermore, as shown in Example 3, it was confirmed that in foam member B, the maximum speed increased and the rated power decreased at each temperature.

[0094] In Examples 4 to 6, foam members C, D, and E showed no change compared to Comparative Example 2 at a temperature of 20°C. On the other hand, a reduction in rated power was confirmed compared to Comparative Example 2 at low temperatures of -20°C and -30°C.

[0095] (Example 7) The vibrating actuator and optical element fabricated in Example 2 were mechanically connected to create the optical device shown in Figure 5. By controlling the alternating voltage applied to the piezoelectric material based on the position information provided to an encoder consisting of a sensor and a scale, the vibrating actuator and the optical element connected to it could be precisely driven to the target position. In this optical device, an optical lens was connected to the vibrating actuator, and it was confirmed that it has an autofocus function.

[0096] The above description uses manufacturing composition 1 as an example, but it was confirmed that the driving characteristics of the vibration-type actuator of the present invention are improved compared to felt, similar to Example 2, even with manufacturing compositions 2 to 86. The phase transition temperatures of the piezoelectric materials from manufacturing composition 2 to 4 are in the range of 5°C to -10°C, and the improvement in driving characteristics was smaller than that of manufacturing composition 1.

[0097] As described above, it was found that it is beneficial to provide a foamed member with a siloxane bond as its main structure and an average equivalent circle diameter greater than 120 μm between the pressurizing member and the vibrating body. By configuring it in this way, it is possible to provide a vibrating actuator that suppresses the increase in power consumption during low-temperature operation in a vibrating actuator using lead-free piezoelectric material.

[0098] [Table 2] [Industrial applicability]

[0099] The vibration actuator of the present invention can be used in a variety of applications, such as driving lenses and image sensors in imaging devices (optical instruments), rotating the photosensitive drum of a copier, and driving stages. Although this specification describes a single vibration actuator, multiple vibration actuators can be arranged in a ring shape to rotate a ring-shaped contact body. [Explanation of symbols]

[0100] 100 Vibration-type actuators 101 Electrode 101a 1st electrode 101b 2nd electrode 101c 3rd electrode 101d 4th electrode 101e drive phase electrode 101f Non-driving phase electrode 102 Piezoelectric materials 103 Elastic body 104 Contact body 106 Protrusion 107 Support part 108 Board part 110 Vibrating Body 120 Electromechanical Energy Conversion Elements 121 Pressurizing member 122 Foamed material 133 bubbles 134 skin layers 501 Retaining member 502 Mobile enclosure 503 Bis 504 Guide member 505 Lens holding member 506 Lens 507 Power supply component 508 Sensor 509 scale 510 Connecting member

Claims

1. An electromechanical energy conversion element with a lead content of 1000 ppm or less, and a vibrating body having an elastic body with a plate portion and a projection that protrudes in a direction intersecting the main surface of the plate portion, A contact body that comes into contact with the aforementioned projection, A vibratory actuator comprising the vibration of the vibrating body, wherein the vibrating body and the contact body move relative to each other due to the vibration of the vibrating body, The system further comprises a pressurizing member that pressurizes the vibrating body against the contact body, and a foaming member provided between the pressurizing member and the vibrating body. The aforementioned foamed material has a siloxane bond composed of silicon and oxygen as its main framework, and the average equivalent diameter of the bubbles contained in the foamed material is greater than 120 μm, characterized in that it is a vibrating actuator.

2. The vibrating actuator according to claim 1, characterized in that the foamed member mainly consists of a polymer in which a methyl group is bonded to the main skeleton.

3. The vibrating actuator according to claim 1, characterized in that the foamed member contains silicone rubber.

4. The vibration-type actuator according to claim 1, characterized in that the plate portion is rectangular in shape.

5. The vibration actuator according to claim 4, characterized in that the projection is two projections that protrude in the same direction.

6. The vibration-type actuator according to claim 1, characterized in that the plate portion is annular.

7. The vibration-type actuator according to claim 1, characterized in that the average circle equivalent diameter is 174 μm or more and 439 μm or less.

8. The vibrating actuator according to claim 1, characterized in that the average circular equivalent diameter of the bubbles is 200 μm or more.

9. The vibration actuator according to claim 1, characterized in that the area of ​​the foam member projected in the direction of pressurization by the pressurizing member is smaller than the area of ​​the electromechanical energy conversion element projected in the direction of pressurization by the pressurizing member.

10. The vibration actuator according to claim 9, characterized in that the area of ​​the contact portion between the foam member and the electromechanical energy conversion element is smaller than the area of ​​the planar portion of the electromechanical energy conversion element including the aforementioned portion.

11. The vibration actuator according to claim 1, characterized in that the area of ​​the foam member projected in the direction of pressurization by the pressurizing member is smaller than the area of ​​the elastic body projected in the direction of pressurization by the pressurizing member.

12. The vibration actuator according to claim 1, wherein the number of closed cells accounts for 50% or more of the total number of bubbles in the foamed material.

13. The vibration-type actuator according to claim 1, wherein the electromechanical energy conversion element comprises an electrode and a piezoelectric material, and the main component of the piezoelectric material is barium titanate.

14. The vibrating actuator according to claim 13, wherein the main component of the piezoelectric material is barium calcium zirconate titanate.

15. The vibration-type actuator according to claim 14, characterized in that the phase transition temperature of the piezoelectric material is -10°C or lower.

16. Components and An electronic device comprising a vibrating actuator according to claim 1 provided on the aforementioned member.

17. Components and At least one of the optical element and the image sensor provided on the member, An optical device comprising the vibration-type actuator described in claim 1, provided on the aforementioned member.

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