JP2006195137A - Lens drive device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a configuration in which thrust necessary for driving a lens holder holding a movable lens is sufficiently secured and which is suitable for reducing a lens drive device in size in the application to the lens drive device. <P>SOLUTION: A magnetic-mechanical conversion element providing extremely large magnetostriction by Joule effect is used as a drive means 19 (or 21) by which a lens holder 18 (or 20) holding a movable lens 10 (or 14) is moved along a guide shaft 16 (or 17). Drive force caused by a contractive or expansive change in the element, according to a magnetic field change, is transmitted to the lens holder, thereby moving the lens holder. Thus, drive force necessary to move the movable lens is obtained by producing large force without requiring a conversion mechanism to convert a rotating motion to a rectilinear motion. In addition, the moving speed of the lens is high when compared with that of a conventional electrostrictive element or magnetostrictive element under the application of the same voltage. The produced force is also large when compared with that of such a conventional one under the same volume. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention enables high-speed feed control of a lens holder holding a movable lens by using a magneto-mechanical conversion element capable of obtaining a giant magnetostriction due to the Joule effect in a lens driving device, improving response performance and downsizing. It is related with the technology for realizing.

  2. Description of the Related Art A lens barrel of an imaging apparatus is known that includes a mechanism and a drive source for driving a movable lens for focus control and zooming.

  As a mechanism for moving the lens holder that holds the movable lens along the guide shaft, for example, a configuration using a linear actuator as shown below can be given.

(1) Motor and mechanism for changing its rotation to linear motion (2) A microactuator using an electrostrictive element or a magnetostrictive element.

  In (1) above, in the form using a stepping motor or the like, the rotational force of the rotor is converted into a linear motion, and the driving force is transmitted to the lens holder (see, for example, Patent Document 1).

  Further, in the above (2), the driving force can be directly transmitted to the lens holder using an element utilizing a displacement effect by an electric field or a magnetic field.

JP 2002-112520 A

  However, the conventional driving mechanism has the following problems when applied to a lens driving device.

  First, in the form of (1), since a conversion mechanism from rotational motion to linear motion is required, the structure becomes complicated, causing a problem in miniaturization and compactness. Further, since the rotation angle of the motor is controlled in units of pitches related to the coil arrangement of the stator, high-precision positioning is difficult.

  In the above (2), for example, in the case of an impact drive type linear actuator using an inverse piezoelectric effect element, a driving force necessary for driving the lens cannot be obtained sufficiently, or an inverse piezoelectric effect element is used. In the case of the ultrasonic motor, there is a problem that it generates a large amount of heat and cannot withstand continuous use for a long time.

  Conventional actuators using electrostrictive elements or magnetostrictive elements generally require a high voltage, so a booster circuit using a transformer or the like is often required, making the configuration complicated and compact. Is difficult. Further, it is considered that the generated force is small, and it is difficult to produce a small actuator having a large thrust.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a configuration suitable for miniaturization and miniaturization while sufficiently securing a thrust necessary for driving a lens holder that holds a movable lens in application to a lens driving device.

  In order to solve the above-described problems, the present invention provides a magneto-mechanical transducer (or a magneto-mechanical transducer) that can provide a giant magnetostriction due to the Joule effect in a driving means for moving a lens holder that holds a movable lens along a guide axis. A magnetic-displacement conversion element) is used to transmit the driving force accompanying the expansion / contraction change of the element according to the change of the magnetic field to the lens holder to move the lens holder.

  Therefore, in the present invention, by using a magneto-mechanical conversion element (so-called “super magnetostrictive element”) capable of obtaining a giant magnetostriction by the Joule effect, a large force is generated without requiring a conversion mechanism from a rotational motion to a linear motion. Thus, a driving force necessary for moving the movable lens can be obtained. Further, when compared with conventional electrostrictive elements and magnetostrictive elements, the moving speed of the lens is large under the same applied voltage, and when compared with the same volume, the generated force of the giant magnetostrictive element is orders of magnitude (for example, (In other words, when the driving force is constant, the size can be reduced as compared with the conventional configuration).

  According to the present invention, it is possible to realize a lens driving device that is suitable for downsizing and downsizing and has a larger thrust. Further, in lens drive control, it is effective for improving performance such as high speed and responsiveness and highly accurate positioning, and it is possible to obtain effects such as unnecessary application of high voltage and low power consumption.

  Then, the drive shaft is formed using a material having a small surface roughness or friction coefficient as compared with the giant magnetostrictive material forming the magneto-mechanical transducer, and the drive shaft is fixed to the magneto-mechanical transducer, According to the configuration in which the drive shaft and the lens holder are brought into contact with each other with a frictional force, the power consumption at the time of driving the lens can be reduced as compared with a configuration in which the drive shaft is formed of a giant magnetostrictive material.

  Further, in the configuration including the control circuit for changing the expansion / contraction state so that the speed of the extension amount and the speed of the contraction amount of the magneto-mechanical conversion element are different, the magneto-mechanical conversion element or the element is fixed to the element. The process in which the lens holder moves without slipping with respect to the drive shaft and the process in which the lens holder slips with respect to the magneto-mechanical conversion element or the drive shaft fixed to the element are repeated to move the lens holder in a certain direction. Move to. That is, it is possible to obtain high-speed response characteristics by skillfully utilizing the friction between the drive shaft and the lens holder and the inertia of the lens holder trying to stop in place.

  In application to a lens driving mechanism, a driving means is provided around a vibration excitation coil wound around an axis extending in the vibration direction of the magneto-mechanical conversion element and a magneto-mechanical conversion element. Adoption of a configuration including a yoke and a fixing member made of a material having a large specific gravity for fixing one end of the magneto-mechanical transducer is advantageous for simplification and miniaturization.

  The present invention provides a lens driving device capable of high-speed driving using a giant magnetostrictive element, and a driving device having a larger generating force than a conventional driving device using a magnetostrictive element or an electrostrictive element. Can be realized. The present invention can be widely applied to, for example, small cameras and cameras for portable electronic devices.

  FIG. 1 is a diagram illustrating the principle when a moving body is moved linearly using a giant magnetostrictive element.

  (A) As shown in the figure, the actuator 1 includes a rod-like giant magnetostrictive element as the magneto-mechanical conversion element 3 in order to move the moving body 2 along a predetermined direction, one end of which is a fixed portion. 4 is fixed.

The giant magnetostrictive element is a magneto-mechanical conversion element that can obtain giant magnetostriction by the Joule effect, and is formed using a giant magnetostrictive material. A giant magnetostrictive material is a material that can obtain a giant magnetostriction that is two orders of magnitude larger than that of a conventional magnetostrictive material even at room temperature, and its practical application has been rapidly promoted in recent years. For example, it is composed of a lanthanoid element (referred to as “R”) having a large magnetic moment and an iron group element “T” (T = Fe, Ni, Co, etc.), and a Laves type cubic material (RT ₂ : R and T For example, in the case of iron, TbFe ₂ , DyFe ₂ , SmFe ₂ , HoFe ₂ , ErFe _2, etc.) may be mentioned. The magnetostriction of a conventional magnetostrictive material is 40 to 80 ppm (magnetostriction: ppm = ΔL / L × 10 ⁶ ), whereas in the case of a supermagnetostrictive material, a magnetostriction of about 2,000 ppm is obtained. Compared to other displacement materials, the amount of dimensional change (joule effect) generated according to the strength of the magnetic field is large, and the generated stress, which is the product of the displacement and the strength of the magnetic field, is large. On the other hand, the amount of change in magnetic susceptibility (bilari effect) caused by external stress is as large as about 40%, and the conversion speed of these changes can follow a frequency corresponding to microseconds.

Note that the magnetization direction inside the element changes due to an external magnetic field or an external stress. For example, in the case of the Joule effect, the balance point between magnetic energy and elastic energy changes. The correlation in the linear region is as follows: Strain: ΔI = s · T + dH
Driving force: F = Y · (ΔI / I)
However, each symbol is “s: elastic modulus”, “T: stress”, “Y: Young's modulus”, “H: strength of external magnetic field, dH: amount of change in strength of external magnetic field”, “(ΔI / I): magnetostriction value ".

  The super magnetostrictive material is superior to other materials in that the amount of magnetostriction and stress are large, and the change in permeability due to the stress T, that is, the variation range of inductance is large. This is due to the large magnetic moment of the lanthanoid elements. On the other hand, this increases the magnetic anisotropy energy, which means that there is hysteresis due to remanent magnetization between the external magnetic field stress and the magnetization change and dimensional change that occur inside the element (the magnetic anisotropy that causes it). Can be adjusted by the ratio of constituent elements.)

  As shown in FIG. 1 (B1), among the ends of the giant magnetostrictive element, the end opposite to the fixed portion 4 is formed using metal, carbon fiber (carbonized fiber) reinforced resin, or the like. A member (friction member) 5 is fixed, and the movable body 2 is held by frictional coupling while being movable with respect to the member 5. That is, the movable body 2 and the member 5 are configured to contact with each other with a frictional force. In the figure, the contact portion 6 (friction portion) between the moving body 2 and the member 5 is indicated by hatching.

  By changing the external magnetic field with respect to the giant magnetostrictive element, the giant magnetostrictive element slowly extends in the direction of arrow A as shown in FIG. (B2) (the amount of extension is exaggerated in the figure).

  The member 5 is displaced in the direction indicated by the arrow A according to the elongation of the giant magnetostrictive element. However, the member 5 moves without sliding between the two due to the friction between the moving body 2 and the member 5.

  Thereafter, as shown in FIG. (B3), when the giant magnetostrictive element is contracted in the direction of arrow B (the contraction amount is exaggerated in the figure), the moving body 2 is connected to the member 5 due to its inertia. A slip occurs between them and tries to stay in the current position.

  FIG. 2 exemplifies temporal changes in the displacement amount and speed. In the above figure, the horizontal axis represents time and the vertical axis represents the amount of displacement, and the relationship between the two is schematically illustrated. A graph curve g2 indicated by a broken line represents the amount of displacement of the moving body 2, and a solid line. A triangular wave-like graph curve g3 indicated by indicates the expansion / contraction change of the giant magnetostrictive element. In the figure below, time is taken on the horizontal axis, and speed is taken on the vertical axis. A graph curve G2 indicated by a broken line represents the speed of the moving body 2, and a wavy graph curve G3 indicated by a solid line represents the giant magnetostrictive element. Expresses expansion and contraction speed.

  In the graph curve g3, during a period in which the curve rises to the right with a gentle slope (see “Δt1”), the giant magnetostrictive element is in the extended state shown in FIG. 1 (B2), and from a certain point in time (at the time of zero speed). During a period of rapid downward descent (see “Δt2”), the giant magnetostrictive element is in the contracted state shown in FIG. 1 (B3). As described above, the displacement of the moving body 2 increases in a predetermined direction by repeatedly expanding and contracting the giant magnetostrictive element. That is, the moving body 2 can be moved in a desired direction by controlling the expansion / contraction state so that the speed of the extension amount and the speed of the contraction amount are different.

  The following is a summary of the structural points of the actuator 1 described above.

  The magnetic-mechanical transducer element 3 and the member 5 coupled to the element and displaced together are provided, and the moving body is frictionally coupled to the member.

  The state in which the moving body 2 moves substantially together with the member by frictional coupling with the member 5 by making the expansion and contraction speeds of the magneto-mechanical transducer 3 different, and the moving body 2 with respect to the member 5 It can take a state that does not move substantially (inertia).

  The moving body 2 moves in the displacement direction (stretching direction) of the magneto-mechanical transducer 3 and the direction of the movement is the speed of expansion and contraction of the magneto-mechanical transducer 3 (absolute value of velocity). ) In a displacement direction with a slow speed (a direction in which the displacement changes relatively slowly).

  The speed is proportional to the feed amount per 1 pulse and the driving frequency, and the thrust depends on the generated force of the element and the frictional force corresponding to the generated force.

  With the above configuration, a high-speed response is possible, and a small impact driving actuator or driving unit with a large thrust can be realized.

  For example, when a conventional magnetostrictive element or electrostrictive element is used, it is only a minute extension of 20 to 30 nm (nanometer) at a driving voltage of 3 V, whereas in the case of a super magnetostrictive element, a magnetic circuit is used. However, it shows an elongation of 1 to 3 μm (microns) at a driving voltage of 3V. That is, the giant magnetostrictive element can move the moving body 2 at a higher speed at the same voltage. Alternatively, if a conventional magnetostrictive element or electrostrictive element is used to obtain the same elongation as that of a giant magnetostrictive element, a voltage of several tens to several hundreds V is required (a booster circuit using a drain or the like is necessary). become.).

  Further, when the generated force in the same volume is compared between the case where a conventional magnetostrictive element or electrostrictive element is used and the case where a giant magnetostrictive element is used, the latter can obtain a force about 200 times that of the former. For example, in the same circuit (with a driving voltage of about 3 V), the former has a generated force of 4 to 5 gf (gram force) at a diameter of φ1 × length of 5 mm, but a giant magnetostrictive element has a diameter of φ1 × length of about 3 mm. The generated force is about 900 gf (≈8.82 N).

  Thus, in comparison with conventional magnetostrictive elements and electrostrictive elements, it is shown that the configuration using the giant magnetostrictive element is suitable for use in moving a heavier moving body at high speed.

  In the linear drive (linear drive) mechanism using the actuator described above, the giant magnetostrictive element and the member 5 move synchronously, and the moving body moves along the expansion / contraction direction of the element with a driving speed corresponding to the expansion / contraction speed of the element. Then, the control that the moving body holds the current position is repeated, and it is possible to obtain a high-speed response characteristic by skillfully utilizing the friction and the inertia of the moving body. For example, as a use of the zoom lens or the focus lens moving mechanism in the camera device, a driving unit using a giant magnetostrictive element is used, so that the driving unit (lens holder) is small and has a large thrust. An actuator can be realized (that is, an actuator having the same configuration using a giant magnetostrictive element can be applied without using an actuator having a different configuration corresponding to a difference in movable lens, etc.).

  FIG. 3 shows a lens barrel used in a video camera recorder or the like and a main part of its control system in a configuration example of the imaging device 7 to which the lens driving device according to the present invention is applied.

  In the lens barrel including the lens driving device 8, an objective lens 9, a variable magnification lens 10, a lens 11, an iris device 12, a filter 13, a focus lens 14, and a solid-state image sensor 15 are arranged from the subject side.

  In this example, the variable power lens 10 and the focus lens 14 are movable lenses, and are held by the lens holder so as to be movable along the optical axis direction indicated by “OL” in the drawing.

  The guide shafts 16 and 17 are arranged and fixed in parallel to the optical axis OL in the lens barrel, and have a role of guiding a lens holder described later.

  The lens holder 18 of the variable magnification lens 10 is supported in a state where the guide shaft 16 is inserted into one end portion thereof, and the other end portion is supported in a state in which the lens holder 18 is movable to the driving shaft 19a of the driving means 19 by frictional coupling. . That is, in the zoom adjustment mechanism, the lens holder 18 corresponds to the moving body 2, the drive shaft 19 a corresponds to the member 5, and the lens holder 18 is positioned in the optical axis direction by the drive means 19.

  Further, the lens holder 20 of the focus lens 14 is supported in a state where the guide shaft 17 is inserted into one end thereof, and the other end is supported in a state in which the lens holder 20 is movable to the drive shaft 21a of the drive means 21 by frictional coupling. Yes. That is, in the focus adjustment mechanism, the lens holder 20 corresponds to the movable body 2, the drive shaft 21 a corresponds to the member 5, and the lens holder 20 is positioned in the optical axis direction by the drive means 21.

  These driving means 19 and 21 have the same configuration, and use giant magnetostrictive elements that can obtain giant magnetostriction by the Joule effect. That is, one end of each drive shaft is fixed to the giant magnetostrictive element, and the other end of the drive shaft is held in a state of being received in the support holes 8a and 8a formed in the lens barrel (the giant magnetostrictive element is The configuration of the actuator used will be described in detail later.)

  The iris device 12 has, for example, a pair of blades, and by driving them, it also functions as an incident light amount adjustment function and a shutter function.

  The image output obtained by the solid-state imaging device 15 is sent to the image processing unit 22 and subjected to predetermined processing. The image processing unit 22 sends information necessary for control or the like to the arithmetic processing unit 23, sends the captured image to a viewfinder, a monitor, or the like, or displays the image information or the like on a recording medium in accordance with a user operation instruction. Let The arithmetic processing unit 23 using a microcomputer or the like sends a control command to the control unit 24 to control the iris device 12 and the driving means 19 and 21.

  The control unit 24 includes an iris control circuit 24a, a control circuit 24b for zoom control, and a control circuit 24c for focus control.

  Aperture control and shutter operation control for light amount adjustment are performed by a signal sent from the iris control circuit 24a to the iris device 12.

  Further, as described above, the control circuits 24b and 24c perform control for changing the expansion / contraction state so that the speed of the expansion amount and the speed of the contraction amount of the magneto-mechanical transducer (super magnetostrictive element) are different. That is, a process in which the lens holder 18 (or 20) moves without slipping with respect to the drive shaft 19a (or 21a) and a process in which the lens holder slips with respect to the drive shaft are repeated (for example, driving) The lens holder moves in a certain direction.

  FIG. 4 shows a structural example 25 of the actuator using the giant magnetostrictive element, and shows a cross-sectional configuration with a part cut away.

  In this example, a drive shaft 27 is fixed to the giant magnetostrictive element 26, and a vibration excitation coil 28 and a yoke 29 are arranged around the drive shaft 27 as a central axis.

  The giant magnetostrictive element 26 is formed in a columnar shape, and one end thereof is fixed to the fixing member 30. The arrow “α” in the figure indicates the vibration direction of an element formed as an axis (vibration axis) using the giant magnetostrictive material. The fixing member 30 is formed using a material having a large specific gravity (for example, tungsten) in consideration of resonance prevention and the like.

  One end of the drive shaft 27 is fixed to the giant magnetostrictive element 26. As for the material of the drive shaft 27, it is desirable that the surface roughness or the friction coefficient is small, the vibration waveform of the giant magnetostrictive element 26 (see the triangular waveform in FIG. 2) is easily transmitted, and the rigidity is large. . For example, it is formed using the same metal (stainless steel, iron, etc.) as that of the guide shaft, carbon coating or the like, or carbon fiber reinforced plastic.

  The yoke 29 is provided around the giant magnetostrictive element 26. For example, the yoke 29 has a shape such that disk portions 29a and 29a having a center hole are connected by a cylindrical portion 29b, and is formed using a magnetic material such as iron. ing. The yoke 29 has one disk portion 29 a fixed to the fixing member 30.

  The vibration exciting coil 28 is wound around an axis extending in the vibration direction of the giant magnetostrictive element 26 as a central axis. In this example, it is wound around the outer peripheral surface of the cylindrical portion 29b of the yoke 29. When current flows in the direction indicated by the arrow “θ”, it follows the vibration direction of the giant magnetostrictive element 26 in accordance with the right-handed screw law. A magnetic field is generated (the direction of the magnetic field changes depending on the direction of the coil current). In response to this magnetic field change, the giant magnetostrictive element 26 expands and contracts, and the driving force associated with the change is transmitted from the drive shaft 27 to the lens holder.

  In the above-described position control of the movable lenses (10, 14), there is a configuration in which the portion of the giant magnetostrictive element, that is, the shaft (vibration shaft) formed of the giant magnetostrictive material and the drive shaft of the lens holder are combined. However, a configuration in which the functions of both shafts are distinguished, the drive shaft is formed of a metal or carbon fiber reinforced material, and is fixed to the giant magnetostrictive element is preferable. For example, when a drive shaft is also formed using a giant magnetostrictive material, the problem is that the surface roughness is large (power consumption during driving increases due to friction).

  Therefore, such a problem can be solved by forming the drive shaft using a material having a surface roughness or a friction coefficient smaller than that of the giant magnetostrictive material, and the drive shaft is fixed to the giant magnetostrictive element. Thus, it is preferable that the drive shaft and the lens holder are brought into contact with each other with an appropriate frictional force.

  FIG. 5 schematically shows the main part of such a configuration example.

  For example, as shown in (A), one end of the drive shaft 27 is fixed to the vibration shaft 31 formed of a giant magnetostrictive material by bonding or the like, and as shown in (B), one end of the vibration shaft 31 is fixed. The bottomed hole 32 is formed in the end, and the end of the drive shaft 27 is press-fitted into the hole or fixed by bonding or the like. In addition, when the adhesive strength, mechanical strength, etc. are considered, the latter form is preferable.

  According to the configuration described above, for example, the following advantages can be obtained.

-To improve zooming and autofocus response performance when applied to camera zoom and autofocus mechanisms-Effective for miniaturization of camera zoom and autofocus mechanisms (for example, PM-type rotary motors) Compared to the configuration using, the conversion mechanism from rotational motion to linear motion is not required, and the drive unit can be saved in space.)
・ When constructing a camera device zooming and focus adjustment drive mechanism using a mechanism using an electric motor such as a stepping motor, it is necessary to use multiple types of motors, but a configuration using giant magnetostrictive elements In the configuration, drive units and devices with the same configuration can be used. ・ Silent noise and low vibration are possible (no influence on sound collection by the microphone, etc., and the lens holder is controlled against the drive shaft during lens drive control). (They only slip and are not accompanied by vibration like a stepping motor.)
・ A thrust of about 200 to 250 times can be obtained with the same volume compared to conventional magnetostrictive elements and electrostrictive elements. ・ Linear drive because the amount of elongation in the same volume is larger than conventional magnetostrictive elements and electrostrictive elements. The speed of the.

  -Compared to conventional magnetostrictive elements and electrostrictive elements, the number of drive pulses (total number) for the same movement amount is small, and power consumption is low.

・ The use of giant magnetostrictive elements is not limited to lens driving, but can also be used as a sensing element by measuring its inductance (the amount of compressive stress applied to the element can be detected from the amount of change in inductance. (It can also be used as a sensor to prevent unit destruction.)
・ Responsiveness of conventional electrostrictive element is on the order of millisecond, but using super magnetostrictive element, the response is on the order of microsecond and the displacement response is faster. ・ Compared with multilayer electrostrictive element. In that case, it is possible to drive at a lower voltage (for example, 10 V or less). ・ The magnetic hysteresis loss is small as compared with a conventional magnetostrictive element.

It is principle explanatory drawing of the linear movement mechanism using a giant magnetostrictive element. It is the figure which illustrated the temporal change of the displacement and speed of a moving body and a giant magnetostrictive element. FIG. 4 shows a configuration example to which the present invention is applied together with FIG. 4, and this diagram is a diagram showing a cross-sectional configuration example of the imaging apparatus. It is the figure which showed the structural example of the actuator using a giant magnetostrictive element. It is explanatory drawing which illustrated the fixed form of the drive shaft.

Explanation of symbols

DESCRIPTION OF SYMBOLS 3 ... Magneto-mechanical conversion element, 8 ... Lens drive device, 10, 14 ... Movable lens, 18, 20 ... Lens holder, 16, 17 ... Guide shaft, 19, 21 ... Drive means, 19a, 21a ... Drive shaft, 24b 24c ... control circuit, 27 ... drive shaft, 28 ... vibration excitation coil, 29 ... yoke, 30 ... fixing member

Claims (4)

A movable lens supported in a movable state along the optical axis direction, a lens holder that holds the movable lens, a guide shaft that guides the lens holder, and the lens holder that moves along the guide axis In a lens driving device provided with a driving means for
Using a magneto-mechanical conversion element capable of obtaining giant magnetostriction by the Joule effect for the driving means, and transmitting the driving force accompanying the expansion / contraction change of the element in accordance with a change in the magnetic field to the lens holder to move the lens holder. A lens driving device. The lens driving device according to claim 1,
A drive shaft is formed using a material having a smaller surface roughness or friction coefficient than the giant magnetostrictive material forming the magneto-mechanical transducer, and the drive shaft is fixed to the magneto-mechanical transducer, and the drive A lens driving device characterized in that the shaft and the lens holder are in contact with each other with frictional force. The lens driving device according to claim 1,
A control circuit is provided for changing the expansion / contraction state so that the speed of the extension amount and the speed of the contraction amount of the magneto-mechanical transducer are different from each other.
The lens holder moves without slipping with respect to the magneto-mechanical transducer or the drive shaft fixed to the element, and the lens holder slips with respect to the element or the drive shaft fixed to the element. The lens driving device is characterized in that the above-mentioned process is repeated and the lens holder moves in a certain direction. The lens driving device according to claim 1,
The drive means includes a vibration excitation coil wound around an axis extending in the vibration direction of the magneto-mechanical conversion element as a central axis, a yoke provided around the magneto-mechanical conversion element, A lens driving device comprising: a fixing member made of a material having a large specific gravity in order to fix one end of the magneto-mechanical conversion element.

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