JP2523027B2 - Magnetostrictive actuator - Google Patents

Description

TECHNICAL FIELD The present invention relates to a magnetostrictive actuator.

[Prior Art] Recently, a magnetostrictive element is being used instead of a piezoelectric element as a movable element in a vibrator, an audio equipment, and a displacement actuator. This is because the magnetostrictive element, which is superior to the energy density, electromechanical conversion coefficient, usable temperature, etc. of the piezoelectric element, has begun to appear. Among such magnetostrictive elements (hereinafter referred to as magnetostrictive materials), particularly rare earth-based magnetostrictive materials, which have remarkable magnetostrictive characteristics, have recently been in the spotlight. A conventional magnetostrictive actuator using such a magnetostrictive material will be described with reference to the drawings. FIG. 2 shows an example thereof. The magnetostrictive actuator 1 shown in FIG. 1 is roughly composed mainly of a cylinder-shaped magnetostrictive material 3 in a cylinder 2 and a ram 4 for outputting the magnetostrictive displacement x of the magnetostrictive material 3 to the outside. Specifically, a coil 6 wound around a bobbin 5 is provided on the outer circumference of the magnetostrictive material 3, and the coil 6 is further provided.
A bias magnet (usually a permanent magnet) 7 is provided on the outer circumference of the. A coil 6, a bias magnet 7, and yokes 81 and 82 for easily forming a magnetic circuit formed by the magnetostrictive material 3 are provided at both ends of the magnetostrictive material 3 in the longitudinal direction.
The yoke 81 at the left end in the figure is in contact with the cylinder 2 and constitutes the fixed side of the magnetostrictive actuator 1. The yoke 81 on the other side, the left end in the drawing, has the left end in the drawing contacting the magnetostrictive material 3 and the right side in the drawing via the retainer 9 made of a non-magnetic material.
Is in contact with The ram 4 slidably projects to the outside from an opening at the right end of the cylinder 2 in the figure. An elastic body 10 is housed between the retainer 9 and the cylinder 2,
A compressive force is constantly applied to the magnetostrictive material 3 via the retainer 9 and the yoke 82. This compressive force is a prestress on the magnetostrictive material 3. As is well known, the pre-stress and the bias magnetic field generated by the bias magnet 7 bring about an effect of improving the magnetostrictive characteristic of the magnetostrictive material 3. The magnetostrictive actuator 1 becomes a vibrator when an alternating current or a pulsating current is passed through the coil 6. On the contrary, when a direct current is applied to the coil 6, the magnetostrictive actuator 1 becomes a displacement actuator. In the magnetostrictive actuator 1 shown in the figure, the length of the magnetostrictive material 3 in the longitudinal direction is shorter than the length of the coil 6 in the longitudinal direction. The reason for this is that the coil 6 and the bias magnet 7 are
This is because, in the magnetic circuit formed by the magnetic fluxes from and through the yokes 81 and 82 and the magnetostrictive material, the magnetic flux in the magnetostrictive material 3 is made parallel.

[Problems to be Solved by the Invention] The magnetostrictive material has the advantages described above as compared with the piezoelectric element (or piezoelectric material). However, even such a magnetostrictive material cannot be said to have no problem. One of the biggest problems is that magnetostrictive materials are sensitive to gap fluctuations. In particular, in rare earth type magnetostrictive materials having good magnetostrictive characteristics, since the magnetic permeability is low, there is a disadvantage that the leakage magnetic flux increases if there is a gap and the high magnetostrictive characteristics inherent in the magnetostrictive material are offset. .
Therefore, the gaps and fluctuations in the gaps in magnetostrictive actuators are roughly classified into the following three.

(1) Gap on the longitudinal side of the magnetostrictive material and its variation Usually, as described above, the magnetostrictive material is pre-stressed to improve the magnetostrictive property and is contracted in the longitudinal direction in advance (thus, in the radial direction of the magnetostrictive material). Is applied with tensile stress, and in extreme terms, the side surface of the magnetostrictive material has a barrel-shaped bulge. When the magnetic flux from the coil flows through this magnetostrictive material, the magnetostrictive material expands in the longitudinal direction and contracts in the circumferential direction, so that a gap is created between the magnetostrictive material and the bobbin. This gap causes leakage flux. In particular, when an alternating or pulsating current is applied to the coil, the skin effect occurs when the magnetic field generated by the coil is an alternating magnetic field, and the penetration depth of the magnetic flux flowing in the magnetostrictive material is affected by the frequency of this alternating magnetic field. It That is, the higher the alternating frequency of the alternating magnetic field,
The penetration depth of the magnetic flux in the magnetostrictive material becomes shallow. Therefore, in the case of the alternating magnetic field, the gap on the side surface in the longitudinal direction of the magnetostrictive material and its fluctuation (that is, leakage magnetic flux) are larger than those in the DC magnetic field.

(2) Gap in the longitudinal direction of the magnetostrictive material and its variation Similar to (1) above, in the case of an alternating magnetic field, a skin effect occurs. The skin effect is closer to the center of the magnetostrictive material,
This is a phenomenon in which a large amount of eddy current is generated due to the magnetic flux, and therefore the magnetic flux decreases toward the center. In other words, on the end face of the magnetostrictive material,
The strain is small in the center of the magnetostrictive material (does not extend), but there is a large amount in the periphery (extends). Therefore, when an alternating magnetic field is applied, both end surfaces of the magnetostrictive material become concave, and the center of this concave becomes a gap.

(3) Other gaps and their variations Magnetostrictive actuators basically require a gap in their configuration. For example, referring to FIG. 2, in the magnetostrictive actuator 1, the fixed members are the cylinder 2, the yoke 81, the bobbin 5, the coil 6 and the bias 7, and the movable members are the yoke 82, the retainer 9 and the ram 4. Further, the one end fixed member and the other end movable member are the magnetostrictive material 3 and the elastic body 10. That is, when the magnetostrictive material 3 is fully shrunk, if the yoke 82 is not arranged with a certain gap with respect to the bobbin 5 and the bias 7, they will collide and self-destruct. Therefore, this gap must be installed in advance as a fixed gap. However, when the magnetostrictive material receives a magnetic field and extends in the longitudinal direction, this gap increases by the amount of extension of the magnetostrictive material. That is, the amount of elongation of this length changes in this gap.

In response to the above-mentioned typical gap and its variation, the conventional magnetostrictive actuator does not take any countermeasures against it. Therefore, in the conventional magnetostrictive actuator, no consideration is given to the generation of leakage magnetic flux due to the gap variation and the deterioration of the magnetostrictive characteristic based on the result.

The present invention has been made in view of the above problems of the conventional technique, and an object of the present invention is to provide a magnetostrictive actuator that is resistant to gap fluctuation and therefore can exhibit high magnetostrictive characteristics.

[Means for Solving the Problems] In order to achieve the above object, a magnetostrictive actuator according to the present invention includes a hermetically sealed body such as a casing or a cylindrical body, a magnetostrictive material, an exciting coil, a bias magnet, and the like which are built in the hermetically sealed body. In a magnetostrictive actuator including a yoke and a ram that outputs the movement of the magnetostrictive material to the outside from the sealed body, in a gap of a magnetic circuit formed by the magnetostrictive material, the exciting coil, the bias magnet, and the yoke. A high-permeability material is interposed in a compressible manner.

[Operation] With the above-described configuration, since the high-permeability material is compressively inserted in the gap of the magnetic circuit formed by the strained magnetic material, the exciting coil, the bias, and the yoke, The leakage flux can be reduced significantly. The term “compressible” means that the high-permeability material should not be solid or liquid that fills the gap. With such a structure, since these high magnetic permeability materials are incompressible, the magnetostrictive actuator will self-destruct when it is movable. Some magnetostrictive actuators do not have a bias magnet, and the magnetic circuit in this case is composed of a magnetostrictive material, a bias, and a yoke. In consideration of this, the configuration of the present invention (claim) includes this configuration.

[Embodiment] An embodiment of the present invention will be described below with reference to FIG. This figure is based on the example diagram (FIG. 2) of the magnetostrictive actuator described in the section of the prior art. Therefore, the magnetostrictive actuators in FIGS. 1 and 2 have the same names and reference numerals of their constituent parts. Therefore, in the following embodiments, the configurations described in the section of the prior art will not be duplicated, and only the additional configurations according to this embodiment will be described.

In the embodiment, as shown in FIG. 1, a hermetically sealed body (cylinder 2) such as a housing or a cylinder, a magnetostrictive material 3, an exciting coil 6, a bias magnet 7 and a yoke 8 built in the hermetically sealed body (cylinder 2).
1, 82, and a ram 4 that outputs the movement (expansion / contraction movement x) of the magnetostrictive material 3 from the sealed body (cylinder 2) to the outside, a magnetostrictive material 3, an exciting coil 6, and a bias. In the gaps 31, 32, 33, 51, 71 of the magnetic circuit formed by the magnet 7 and the yokes 81, 82, a high-permeability material (ferrite in this embodiment) is formed into a compressible state (powder in this embodiment). (Powder) was interposed. Gap 31,3 above
2, 33, 51, 71, reference numerals 32, 33 indicate gaps at both ends in the longitudinal direction of the magnetostrictive material 3, reference numeral 31 indicates gaps around the entire longitudinal side surface of the magnetostrictive material 3, and reference numerals 51, 71 indicate other gaps. Refers to the gap. The other gaps 61 and 71 at the end refer to the bobbin 6, the yoke 82 and the gap, and the reference numeral 71 to the bias magnet 7, the yoke 82 and the gap. Next, to describe another embodiment, the high magnetic permeability material to be interposed in these gaps 31, 32, 33, 51, 71 is, for example, a magnetic fluid whose volume ratio is not 100%, magnetic powder or this magnetic powder is added. It may be an elastic body such as rubber. The point is that any material having a high magnetic susceptibility, which is interposed in a compressible state, may be used. In addition, in order to reduce the eddy current loss, that is, to facilitate the flow of the magnetic flux and reduce the leakage flux, this high magnetic permeability material should be selected and used with high electric resistance. Further, as another embodiment, as described in the section of the operation, the magnetostrictive actuator not including the bias magnet may have a configuration in which the gap 71 of the above embodiment is removed.

Experimental Examples Some experimental results of the above examples will be described. The experiment was conducted on the magnetostrictive actuator shown in FIG.
A configuration in which nothing is inserted in 1,32,33,51,71 (that is,
A magnetostrictive actuator according to the prior art) A, based on the embodiment, B having ferrite powder interposed in the gaps 31, 32, 33, 51, 71 and permalloy C in the gaps 31, 32, 33, 51, 71. Improvement of operating efficiency (relative value) of magnetostrictive actuator (more precisely, magnetostrictive material 3) in the case of interposing C
Is the one that was investigated. The test results are shown in the following table.

In the experiment, as shown in the above table, the operation efficiency of the magnetostrictive actuators B and C according to the embodiment is greatly improved over the conventional magnetostrictive actuator A.

[Effects of the Invention] As described above, the magnetostrictive actuator according to the present invention has a structure in which a high-permeability material is interposed in a compressible manner in the gap of the magnetic circuit of the magnetostrictive actuator.
In its operation, the leakage flux in the gap can be reduced. That is, it is possible to provide a magnetostrictive actuator that is not affected by gap fluctuation. Furthermore, it is possible to provide a magnetostrictive actuator with significantly improved operating efficiency.

[Brief description of drawings]

FIG. 1 is a sectional view of an embodiment of a magnetostrictive actuator according to the present invention, and FIG. 2 is a sectional view of an example of a conventional magnetostrictive actuator. 1 ... Magnetostrictive actuator 2 ... Cylinder 3 ... Magnetostrictive material 31,32,33,51,71 ... Gap (high magnetic permeability material) 4 ... Ram 5 ... Bobbin 6 ... Coil 7 ... Bias magnet 81 , 82 …… Yoke 9 …… Retainer 10 …… Elastic body x …… Magnetic strain displacement

Claims (1)

(57) [Claims] 1. A hermetically sealed body such as a casing or a cylinder, a magnetostrictive material, an exciting coil, a bias magnet and a yoke built in the hermetically sealed body, and a ram for outputting the movement of the magnetostrictive material from the hermetically sealed body to the outside. A magnetostrictive actuator comprising a magnetostrictive material, the exciting coil, the bias magnet and the yoke, and a compressible high-permeability material interposed in a gap of a magnetic circuit formed by the magnetostrictive material, the exciting coil, the bias magnet and the yoke. .