Voice coil actuator

Abstract

A voice coil actuator includes a first magnetic body, a second magnetic body facing the first magnetic body via a gap, and a coil disposed in the gap between the first magnetic body and the second magnetic body. At least one of the first magnetic body and the second magnetic body has a multilayer structure including a transition metal layer and a rare earth magnet layer.

Description

Technical Field

[0001] The present disclosure relates to a voice coil actuator. Background Art

[0002] A voice coil actuator (also known as a voice coil motor or linear actuator) is driven by the electromagnetic force generated by current flowing through a coil within the magnetic field (magnetic circuit) of a permanent magnet. For example, Patent Document 1 discloses a voice coil actuator with a coil disposed between a center yoke and an outer yoke, each containing a permanent magnet. Conventional voice coil actuators such as those described in Patent Document 1 typically use adhesives or other methods to attach bonded or sintered magnets to the yoke wall.

[0003] The electromagnetic force that drives a voice coil actuator is proportional to the magnitude of the magnetic field. Therefore, using permanent magnets with high magnetic energy allows for overall device miniaturization. However, conventional voice coil actuators using bonded or sintered magnets tend to reduce the magnetic flux density in the gap where the coil is located when miniaturization is attempted, making miniaturization difficult. Furthermore, conventional voice coil actuators using sintered magnets also face the challenge of making the sintered magnets thinner.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2006-81342 Summary of the Invention

[0007] Technical problem to be solved by the invention

[0008] An object of exemplary embodiments of the present disclosure is to provide a voice coil actuator that can obtain a large driving force even when miniaturized.

[0009] Technical solutions to technical problems

[0010] To achieve the above object, the voice coil actuator of the present disclosure includes: a first magnetic body, a second magnetic body facing the first magnetic body via a gap, and a coil arranged in the gap between the first magnetic body and the second magnetic body.

[0011] At least one of the first magnetic body and the second magnetic body has a multilayer structure including a transition metal layer and a rare earth magnet layer.

[0012] The voice coil actuator having the above-mentioned features can increase the magnetic flux density in the gap where the coil is located compared to conventional voice coil actuators using bonded magnets or sintered magnets. As a result, the voice coil actuator disclosed herein can achieve a greater driving force than conventional ones even when miniaturized.

[0013] An intermediate layer may be interposed between the transition metal layer and the rare earth magnet layer.

[0014] It is preferable that no intervening layer exists between the transition metal layer and the rare earth magnet layer, and between the intermediate layer and the rare earth magnet layer.

[0015] It is preferable that the intermediate layer contains the transition metal element contained in the transition metal layer and the rare earth element contained in the rare earth magnet layer.

[0016] The intermediate layer is not particularly limited, but preferably has a layer containing Sm2Co 17 composition.

[0017] The transition metal layer is not particularly limited, but preferably has a composition containing Co. The rare earth magnet layer is not particularly limited, but preferably has a composition containing SmCo 5 .

[0018] It is preferable that both the first magnetic body and the second magnetic body have the multilayer structure.

[0019] Preferably, the first magnetic body has a columnar shape,

[0020] In the multilayer structure of the first magnetic body, the rare earth magnet layer is preferably located outside the first magnetic body relative to the transition metal layer. For example, in the multilayer structure of the first magnetic body, the transition metal layer, (intermediate layer), and rare earth magnet layer are preferably arranged in the order listed from the interior toward the outer peripheral surface of the first magnetic body.

[0021] In the first columnar magnetic body,

[0022] Preferably, the intermediate layer covers the entire circumference of the outer peripheral surface of the transition metal layer.

[0023] It is preferable that the rare earth magnet layer covers the entire circumferential direction of the outer peripheral surface of the intermediate layer.

[0024] Preferably, the second magnetic body has a cylindrical shape.

[0025] In the multilayer structure of the second magnetic body, the rare earth magnet layer is preferably located outside the first magnetic body relative to the transition metal layer. For example, the transition metal layer, (intermediate layer), and rare earth magnet layer are preferably arranged in the order described, from the outer circumference side toward the inner circumference side of the second magnetic body.

[0026] In the second cylindrical magnetic body,

[0027] Preferably, the intermediate layer covers the entire circumference of the inner circumferential surface of the transition metal layer.

[0028] It is preferable that the rare earth magnet layer covers the entire circumferential direction of the inner peripheral surface of the intermediate layer.

[0029] It is preferable that the average thickness of the rare earth magnet layer is not less than 10 μm and not more than 300 μm.

[0030] It is preferable that the easy magnetization axis of the rare earth magnet layer is oriented in a direction perpendicular to the surface of the Co layer, and the orientation degree of the easy magnetization axis in the perpendicular direction is 90% or more.

[0031] It is preferable that the easy magnetization axis of the rare earth magnet layer is oriented in a radial direction, and the orientation degree of the easy magnetization axis with respect to the radial direction is 90% or more.

[0032] Preferably, when the thickness of the rare earth magnet layer in the second magnetic body is represented by t23, the length is represented by L2, and the outer diameter of the second magnetic body is represented by d2a, t23 ≥ 0.10 mm and L2 / d2a ≤ 0.70. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is an exploded perspective view showing a voice coil actuator according to one embodiment of the present disclosure.

[0034] Figure 2A Yes Figure 1 Schematic diagram of a cross section of a voice coil actuator is shown.

[0035] Figure 2B Yes Figure 2A Schematic diagram of a modified example of the cross section shown.

[0036] Figure 2C Yes Figure 2A A schematic diagram of another modified example of the cross section shown.

[0037] Figure 3 It is a schematic diagram showing a cross section of the first magnetic body and the second magnetic body.

[0038] Figure 4 This is a schematic cross-sectional view showing a modified example of the voice coil actuator. DETAILED DESCRIPTION

[0039] An embodiment of the present disclosure is described below with reference to the accompanying drawings. The embodiments of the present disclosure described below are examples for illustrating the present disclosure. The various components of the embodiments, such as numerical values, shapes, materials, and manufacturing processes, may be modified or altered within the scope that does not cause technical problems. Furthermore, the shapes and other aspects shown in the drawings of the present disclosure may not necessarily correspond to actual shapes and other aspects. This is because the shapes and other aspects may be altered in the drawings for illustrative purposes.

[0040] like Figure 1 As shown, the voice coil actuator 100 of this embodiment includes a first magnetic body 10, a second magnetic body 20, and a coil portion 30. The first magnetic body 10 and the second magnetic body 20 constitute the magnetic circuit in the voice coil actuator 100. In addition to the first magnetic body 10 and the second magnetic body 20, the voice coil actuator 100 may also include a bottom yoke 40 as a component of the magnetic circuit. However, the bottom yoke 40 is not essential, and the magnetic circuit can be formed using only the first magnetic body 10 and the second magnetic body 20.

[0041] In addition, the voice coil actuator 100 Figure 1 In addition to the magnetic circuit ( 10 , 20 , 40 ) and coil portion 30 shown, the device may further include a package (container), various sensors such as a displacement sensor, and a driven object (eg, a magnetic head, a lens, a vibration plate, etc.).

[0042] In the voice coil actuator 100, the magnetic circuit side can also be fixed to drive the coil unit 30. Alternatively, the coil unit 30 can be fixed to drive the first magnetic body 10 and / or the second magnetic body 20 that constitute the magnetic circuit. In other words, the voice coil actuator 100 can adopt a moving coil type or a moving magnet type. In addition, the method of fixing the magnetic circuit or the coil unit 30 is not particularly limited. For example, the voice coil actuator 100 can have a package (container) not shown in the figure, and the magnetic circuit or the coil unit 30 can be assembled and fixed to the package.

[0043] Figure 2A 4 is a cross-sectional view of the voice coil actuator 100 taken along the central axis AX of the coil portion 30 . Figure 2A The central axis AX shown is an imaginary line extending along the inner circumferential surface of the coil portion 30 and passing through the center of the area (coil inner area) surrounded by the inner circumferential surface of the coil portion 30. In addition, the Z axis in each drawing is parallel to the central axis AX, and the X axis, Y axis, and Z axis are perpendicular to each other.

[0044] like Figure 2A As shown, the first magnetic body 10 is located at the center of the voice coil actuator 100. In other words, the first magnetic body 10 is arranged in the inner area of ​​the coil through which the central axis AX of the coil portion 30 passes. The first magnetic body 10 preferably has a cylindrical shape (see Figure 1 However, the shape of the first magnetic body 10 is not necessarily limited. For example, the first magnetic body 10 may have a prismatic shape, a cylindrical shape, or a square cylindrical shape.

[0045] The dimensions of the first magnetic body 10 are not particularly limited and can be appropriately determined depending on the intended use of the voice coil actuator 100. To minimize the size of the voice coil actuator 100, the diameter d1 (outer diameter) of the first magnetic body 10 is preferably between 0.5 mm and 4 mm, and the length L1 of the first magnetic body 10 in the Z-axis direction is preferably between 1 mm and 20 mm. Furthermore, if the first magnetic body 10 is cylindrical, the inner diameter of the first magnetic body 10 is preferably, for example, between 0.2 mm and 3 mm, and the thickness of the first magnetic body 10 is preferably between 0.1 mm and 1.9 mm.

[0046] like Figure 2A As shown, the second magnetic body 20 is located outside the first magnetic body 10 and the coil portion 30 in a direction parallel to the XY plane, and faces the first magnetic body 10 via the gap 50. The second magnetic body 20 preferably has a cylindrical shape (see Figure 1 ),like Figure 2A As shown, the inner circumferential surface 20b of the cylindrical second magnetic body 20 faces the outer circumferential surface 10a of the first magnetic body 10 via a gap 50. However, the shape of the second magnetic body 20 is not necessarily limited; for example, the second magnetic body 20 may also have a rectangular cylindrical shape. Alternatively, the second magnetic body 20 may have a pair of plates that sandwich the first magnetic body 10 via the gap 50.

[0047] The dimensions of the second magnetic body 20 are not particularly limited and can be appropriately determined based on the intended use of the voice coil actuator 100. If the second magnetic body 20 is cylindrical, to minimize the size of the voice coil actuator 100, the outer diameter d2a of the second magnetic body 20 is preferably between 1 mm and 6 mm, and the inner diameter d2b of the second magnetic body 20 is preferably between 0.8 mm and 5 mm. The thickness of the second magnetic body 20 is represented by (d2a - d2b) / 2 and is, for example, preferably between 0.1 mm and 2 mm. Furthermore, the length L2 of the second magnetic body 20 in the Z-axis direction can be, for example, between 1 mm and 20 mm.

[0048] The width t5 of the gap 50 between the first magnetic body 10 and the second magnetic body 20 (see Figure 3 ) is represented by (d2b - d1) / 2 and is preferably, for example, not less than 0.1 mm and not more than 1 mm. Furthermore, the ratio of the inner diameter d2b of the second magnetic body 20 to the diameter d1 of the first magnetic body 10 (d2b / d1) is preferably, for example, not less than 1.2 times but not more than 3 times. The ratio of the length L2 of the second magnetic body to the length L1 of the first magnetic body 10 (L2 / L1) is not particularly limited and can be, for example, not less than 0.5 times but not more than 3 times.

[0049] As mentioned above, the bottom yoke 40 is an optional component of the magnetic circuit in the voice coil actuator 100, for example, Figure 1As shown, the bottom yoke 40 may have a circular plate shape. Alternatively, the bottom yoke 40 may be a plate having a substantially rectangular or polygonal shape when viewed from above, or may have a ring shape. The thickness of the bottom yoke 40 in the Z-axis direction is not particularly limited, and may be, for example, 0.5 mm to 2 mm. The bottom yoke 40 may be made of any soft magnetic material such as Co, and the material of the bottom yoke 40 is not particularly limited.

[0050] The first magnetic body 10 and / or the second magnetic body 20 may be bonded to the upper surface of the bottom yoke 40 in the Z-axis direction using an adhesive or the like. Alternatively, a gap may be provided between the bottom yoke 40 and the other magnetic body (the first magnetic body 10 and / or the second magnetic body 20). Furthermore, the bottom yoke 40 may be integrated with the base of the first magnetic body 10 or the base of the second magnetic body 20.

[0051] Figure 1 and Figure 2A The coil portion 30 illustrated in the figure has a coil 31 and a winding frame 32 made of a non-magnetic material. The winding frame 32 integrally includes a disc-shaped upper cover portion 32a and a cylindrical body portion 32b, and the coil 31 is formed by winding a conductive wire around the outer circumference of the body portion 32b. There is no particular limitation on the winding method and number of turns of the conductive wire in the coil 31. In addition, there is no particular limitation on the shape and size of the winding frame 32. For example, the winding frame 32 may have only a cylindrical body portion 32b without the upper cover portion 32a. In addition, the body portion 32b of the winding frame 32 may also have a square cylindrical shape.

[0052] The area surrounded by the inner peripheral surface of the body portion 32b formed with the coil 31 is the coil inner area. Figure 2A As shown, the first magnetic body 10 is inserted into the inner region of the coil. In other words, the coil 31 is arranged in the gap 50 between the first magnetic body 10 and the second magnetic body 20.

[0053] As described above, the coil portion 30 in the voice coil actuator 100 includes a coil 31 and a bobbin 32. However, the configuration of the coil 31 is not limited to a structure in which a conductive wire is wound around the bobbin 32. For example, a flexible printed circuit board with coil wiring printed thereon may be used as the coil portion 30 of the voice coil actuator 100. Alternatively, a molded coil in which the windings are sealed with a resin such as epoxy resin or polyester resin may be used as the coil portion 30 of the voice coil actuator 100. Alternatively, the coil portion 30 may be formed using a self-welding conductive wire. Even when using a coil formed from a flexible printed circuit board, a molded coil, or a self-welding conductive wire as the coil portion 30, it is sufficient to place the coil portion in the gap 50 between the first magnetic body 10 and the second magnetic body 20.

[0054] In the voice coil actuator 100 of this embodiment, as Figure 2AAs shown, the first magnetic body 10 and the second magnetic body 20 each have a multilayer structure. The multilayer structure of the first magnetic body 10 and the second magnetic body 20 includes a transition metal layer 1, an intermediate layer 2, and a rare earth magnet layer 3.

[0055] The following is based on Figure 2A and Figure 3 The multilayer structure of the first magnetic body 10 and the second magnetic body 20 will be described in detail. Figure 3 The cross-sections of the first magnetic body 10 and the second magnetic body 20 are perpendicular to the central axis AX. In the following description of the multilayer structure, when describing features common to both the first magnetic body 10 and the second magnetic body 20, the reference numerals "1, 2, and 3" are used to designate the layers. Furthermore, when describing the multilayer structure of the first magnetic body 10, the layers are referred to as "transition metal layer 11, intermediate layer 12, and rare earth magnet layer 13." Similarly, when describing the multilayer structure of the second magnetic body 20, the layers are referred to as "transition metal layer 21, intermediate layer 22, and rare earth magnet layer 23."

[0056] In the multilayer structure of the first magnetic body 10 and the second magnetic body 20, the transition metal layer 1 is preferably in direct contact with the intermediate layer 2, and the intermediate layer 2 is preferably in direct contact with the rare-earth magnet layer 3. That is, a layer thinner than the 0.5-4 nm resolution observable by a scanning electron microscope (SEM) may exist between the transition metal layer 1 and the intermediate layer 2, and between the intermediate layer 2 and the rare-earth magnet layer 3 (between layers in the multilayer structure). However, it is preferred that no intervening layer composed of a non-magnetic material such as an oxide layer, resin layer, or adhesive layer be present that is thicker than the 0.5-4 nm resolution observable by an SEM. In this embodiment, as described above, "no intervening layer" between the layers of the multilayer structure means that the intervening layer cannot be identified at a resolution observable by an SEM.

[0057] In this embodiment, transition metal layer 1 is a soft magnetic layer primarily containing Co and serves as the base material of each magnetic body (10, 20). "Primarily containing Co" means that the Co content in this layer is the highest. Transition metal layer 1 may also contain other metal elements such as Cr, Mn, Fe, Ni, Cu, Pb, and Mo. The Co content in transition metal layer 1 is preferably 95 wt% or greater, and more preferably 99 wt% or greater, for example.

[0058] In this embodiment, the intermediate layer 2 comprises Sm2Co 17 As the main phase layer. The main phase of Sm2Co 17 Is Th2Zn 17 The alloy of Sm and Co with a crystal structure of the type is a soft magnetic material with a saturation magnetization higher than that of SmCo5 described later.17 With Th2Zn 17 Type crystal structure, Sm2Co 17 The ratio of Sm atoms to Co atoms in the intermediate layer 2 may deviate slightly from the stoichiometric ratio. For example, in order to improve the magnetic properties, other elements such as Ti, Zr, Nb, Ta, Cu, Ce, and Fe may be added to the intermediate layer 2. When other elements are added, the ratio of Sm atoms to Co atoms may deviate slightly from the stoichiometric ratio.

[0059] In addition, in this embodiment, the "main phase" refers to the phase with the highest content in the specified layer. The intermediate layer 2 may also contain a composition and / or a crystal structure different from that of Sm2Co. 17 Different phases (heterophases), grain boundary phases, etc. The content of the intermediate in the intermediate layer 2 may be, for example, 70 wt% or more, preferably 80 wt% or more, more preferably 90 wt% or more, and even more preferably 95 wt% or more.

[0060] In this embodiment, the rare-earth magnet layer 3 is a hard magnetic layer containing SmCo5 as its main phase. The SmCo5 main phase is an alloy of Sm and Co having a CaCu5-type crystal structure. As long as the SmCo5 main phase has a CaCu5-type crystal structure, the ratio of Sm atoms to Co atoms in the SmCo5 may deviate slightly from the stoichiometric ratio. For example, to improve magnetic properties, other elements such as Ti, Zr, Nb, Ta, Cu, Ce, and Fe may be added to the rare-earth magnet layer 3. When these other elements are added, the ratio of Sm atoms to Co atoms may deviate slightly from the stoichiometric ratio.

[0061] The rare earth magnet layer 3 may also contain a phase (heterophase) having a different composition and / or crystal structure from that of SmCo5, as well as a grain boundary phase. The SmCo5 content in the rare earth magnet layer 3 may be, for example, 70 wt% or greater, preferably 80 wt% or greater, more preferably 90 wt% or greater, and even more preferably 95 wt% or greater. Examples of heterophases in the rare earth magnet layer 3 include an Sm-rich phase having a higher Sm ratio than SmCo5.

[0062] In the first magnetic body 10 and the second magnetic body 20, the rare earth magnet layer 3, which serves as a hard magnetic layer, is a magnet, while the transition metal layer 1 and the intermediate layer 2, which serve as soft magnetic layers, function as a yoke that collects magnetic flux. More specifically, the transition metal layer 11 and the intermediate layer 12 of the first magnetic body 10 serve as the center yoke, while the transition metal layer 21 and the intermediate layer 22 of the second magnetic body 20 serve as the outer yoke.

[0063] In the multilayer structure of the first magnetic body 10, a transition metal layer 11, an intermediate layer 12, and a rare earth magnet layer 13 are arranged in the order described from the inside of the first magnetic body 10 toward the outer peripheral surface 10a. In the first magnetic body 10 having a multilayer structure, the transition metal layer 11 serves as a base, and the intermediate layer 12 and the rare earth magnet layer 13 are stacked on the outer peripheral surface of the transition metal layer 11 in the order described. Figure 3 As shown, each layer ( 11 to 13 ) of the first magnetic body 10 is a continuous layer without any joints or gaps in the circumferential direction.

[0064] The first magnetic body 10 may also have a region where a portion of the outer peripheral surface of the transition metal layer 11 as the base is not covered by the intermediate layer 12 and the rare earth magnet layer 13. For example, one or both ends of the first magnetic body 10 in the Z-axis direction may have a non-laminated region where the intermediate layer 12 and the rare earth magnet layer 13 are not formed. However, the portion of the outer peripheral surface 10a of the first magnetic body 10 that faces the inner peripheral surface 20b of the second magnetic body 20 preferably has a multilayer structure in which the non-laminated region does not exist and the intermediate layer 12 and the rare earth magnet layer 13 are laminated. Figure 2A More preferably, the first magnetic body 10 has a multilayer structure along its entire length. That is, the intermediate layer 12 preferably covers the entire outer peripheral surface of the transition metal layer 11 , and the rare earth magnet layer 13 more preferably covers the entire outer peripheral surface of the intermediate layer 12 .

[0065] When the first magnetic body 10 has a cylindrical shape, the average diameter (outer diameter) d11 of the transition metal layer 11 is not particularly limited, but is preferably not less than 0.5 mm and not more than 4 mm from the perspective of miniaturizing the voice coil actuator 100. Furthermore, when the first magnetic body 10 has a cylindrical shape, the average thickness of the transition metal layer 11 is preferably not less than 0.1 mm and not more than 1.8 mm.

[0066] like Figure 3 As shown, the average thickness t12 of the intermediate layer 12 in the first magnetic body 10 is not particularly limited, but is preferably, for example, not less than 1 μm and not more than 100 μm. The coefficient of variation of the thickness of the intermediate layer 12 is preferably, for example, not more than 50%. The "coefficient of variation" is a coefficient indicating thickness variation and is expressed as the ratio of the standard deviation of the thickness to the average thickness (standard deviation / average thickness).

[0067] The average thickness t13 of the rare earth magnet layer 13 in the first magnetic body 10 is preferably 10 μm to 300 μm. The percentage of the coefficient of variation (standard deviation / average thickness) of the thickness of the rare earth magnet layer 13 is preferably 50% or less, for example.

[0068] In addition, the ratio (t13 / t12) of the average thickness t13 of the rare earth magnet layer 13 to the average thickness t12 of the intermediate layer 12 is preferably 1 or more and 100 or less, and more preferably 5 or more and 100 or less. When the first magnetic body 10 has a cylindrical shape, the ratio of t13 of the first magnetic body 10 to the diameter (outer diameter) d1 (refer to Figure 1 ) ratio (t13 / d1) is preferably 0.01 or more and 0.6 or less. On the other hand, when the first magnetic body 10 has a cylindrical shape, when the sum of t12, t13, and the average thickness of the transition metal layer 11 is defined as T10 (not shown), the ratio of t13 to T10 (t13 / T10) can be 0.01 or more and less than 1. By controlling t13 / t12, t13 / d1, or t13 / T10 within the above ranges, the magnetic properties of the first magnetic body 10 can be further improved.

[0069] The Rz (maximum height difference) of the roughness curve of the outer peripheral surface of the rare earth magnet layer 13 is preferably 20 μm or less. When calculating the Rz, it is preferable to obtain a roughness curve based on the contour line of the outer peripheral surface of the rare earth magnet layer 13 in both a cross section perpendicular to the Z axis and a cross section along the Z axis.

[0070] In the first magnetic body 10, another layer may be present outside the rare-earth magnet layer 13. For example, a layer containing a rare-earth oxide such as Sm2O3 may be formed to cover part or all of the inner circumference of the rare-earth magnet layer 13. Furthermore, the outer circumference of the rare-earth magnet layer 13 may be covered with a protective layer containing Ni, Cu, Sn, or the like. The average thickness of this protective layer is preferably 5 μm to 25 μm, for example.

[0071] Furthermore, when the first magnetic body 10 has a cylindrical shape, such as a cylindrical shape, the transition metal layer 11 can be located on the inner circumference of the first magnetic body 10, and the intermediate layer 12 and the rare earth magnet layer 13 can be stacked on the outer circumference of the transition metal layer 11 in the order described. In this case, the inner circumference of the transition metal layer 11 can also be covered with a protective layer containing Ni, Cu, or Sn. Alternatively, a layer containing a high-melting-point non-magnetic material such as W, Ta, Nb, or Mo can be formed on the inner circumference of the transition metal layer 11. The thickness of the protective layer or the high-melting-point non-magnetic material layer is not particularly limited, but is preferably not less than 5 μm and not more than 25 μm, for example.

[0072] In the multilayer structure of the second magnetic body 20, the transition metal layer 21, the intermediate layer 22, and the rare earth magnet layer 23 are arranged in the order described from the inner peripheral surface 20b side toward the outer peripheral surface 20a side of the second magnetic body 20. In the second magnetic body 20 having a multilayer structure, the transition metal layer 21 serves as a base, and the intermediate layer 22 and the rare earth magnet layer 23 are stacked in the order described on the inner peripheral surface side of the transition metal layer 21. Figure 3 As shown, each layer ( 21 to 23 ) of the second magnetic body 20 is a continuous layer without any joints or gaps in the circumferential direction.

[0073] The second magnetic body 20 may also have a region where a portion of the inner peripheral surface of the transition metal layer 21 as the base is not covered by the intermediate layer 22 and the rare earth magnet layer 23. For example, one or both ends of the second magnetic body 20 in the Z-axis direction may have a non-laminated region where the intermediate layer 22 and the rare earth magnet layer 23 are not formed. However, the portion of the inner peripheral surface 20b of the second magnetic body 20 that faces the outer peripheral surface 10a of the first magnetic body 10 preferably has a multilayer structure in which the non-laminated region does not exist and the intermediate layer 22 and the rare earth magnet layer 23 are laminated. Figure 2A More preferably, the second magnetic body 20 has a multilayer structure along its entire length. That is, the intermediate layer 22 preferably covers the entire outer peripheral surface of the transition metal layer 21 , and the rare earth magnet layer 23 preferably covers the entire outer peripheral surface of the intermediate layer 22 .

[0074] like Figure 3 As shown, the average thickness t21 of the transition metal layer 21 in the second magnetic body 20 is not particularly limited, but is preferably 0.1 mm to 1.8 mm from the viewpoint of miniaturization of the voice coil actuator 100 .

[0075] The average thickness t22 of the intermediate layer 22 in the second magnetic body 20 is not particularly limited, but is preferably, for example, 1 μm to 100 μm. The coefficient of variation of the thickness of the intermediate layer 22 is preferably, for example, 50% or less.

[0076] The average thickness t23 of the rare earth magnet layer 23 in the second magnetic body 20 is preferably 10 μm to 300 μm. The percentage of the coefficient of variation (standard deviation / average thickness) of the thickness of the rare earth magnet layer 23 is preferably 50% or less, for example.

[0077] Furthermore, the ratio of the average thickness t23 of the rare-earth magnet layer 23 to the average thickness t22 of the intermediate layer 22 (t23 / t22) is preferably 1 or more and 100 or less, and more preferably 5 or more and 100 or less. When the sum of the average thicknesses t21, t22, and t23 of the second magnetic body 20 is defined as T20, the ratio of t23 to T20 (t23 / T20) can be 0.01 or more and less than 1. By controlling t23 / t22 or t23 / T20 within the above range, the magnetic properties of the first magnetic body 10 can be further improved.

[0078] The average thickness of each layer in the second magnetic body 20 may be approximately the same as or different from the thickness of each layer in the first magnetic body 10. For example, the ratio of t23 in the second magnetic layer 20 to t13 in the first magnetic layer 10 (t23 / t13) may be set to 0.5 or more and 2 or less.

[0079] The Rz (maximum height difference) of the roughness curve of the inner circumferential surface of the rare-earth magnet layer 23 is preferably 20 μm or less, and more preferably 10 μm or less. Similar to the case of the first magnetic body 10, when calculating the Rz, it is preferable to obtain a roughness curve based on the contour line of the inner circumferential surface of the rare-earth magnet layer 23 in both a cross section perpendicular to the Z axis and a cross section along the Z axis.

[0080] In the second magnetic body 20, other layers may be present outside the transition metal layer 21 and / or inside the rare-earth magnet layer 23. For example, a portion or the entire inner surface of the rare-earth magnet layer 23 may be covered with a layer containing Sm2O3. Alternatively, the inner surface of the rare-earth magnet layer 23 may be covered with a protective layer containing Ni, Cu, Sn, or the like. The average thickness of this protective layer is preferably, for example, not less than 5 μm and not more than 25 μm.

[0081] Similar to the inner surface of the rare-earth magnet layer 23, the outer surface of the transition metal layer 21 may be covered with a protective layer containing Ni, Cu, or Sn, for example. The average thickness of this protective layer is preferably, for example, 5 μm to 25 μm. Alternatively, a layer containing a high-melting-point non-magnetic material such as W, Ta, Nb, or Mo may be formed on the outer surface of the transition metal layer 21. The average thickness of this high-melting-point non-magnetic material layer is preferably, for example, 5 μm to 25 μm.

[0082] The composition of each layer constituting the first magnetic body 10 and the second magnetic body 20 can be analyzed by component analysis using, for example, inductively coupled plasma atomic emission spectrometry (ICP-AES), fluorescent X-ray analysis (XRF), energy dispersive X-ray analysis (EDS), or wavelength dispersive X-ray analysis (WDS). The crystal structure of each layer can be analyzed using, for example, X-ray diffraction (XRD), electron beam diffraction, or electron backscatter diffraction (EBSD). Furthermore, when measuring the thickness of each layer in a multilayer structure, it is preferred that the magnetic body (10, 20) be equally divided and analyzed at least three cross sections approximately perpendicular to the Z axis. In each cross section, the thickness is preferably measured at at least four points at equal intervals along the circumference. Specifically, the thickness of each layer is preferably measured at at least 12 points uniformly distributed in three-dimensional space, and the average thickness and the standard deviation of the thickness are calculated.

[0083] When the first magnetic body 10 and the second magnetic body 20 have a cylindrical or columnar shape, the easy magnetization axis of the rare earth magnet layer 3 is preferably oriented radially in both the first magnetic body 10 and the second magnetic body 20. Figure 3 As indicated by the two arrows, "radial" refers to a direction perpendicular to the central axis AX (Z-axis) of the coil portion 30. Specifically, "radially oriented" means that the easy magnetization axes, when viewed from the Z-axis, are arranged radially about the central axis AX. Furthermore, the easy magnetization axes of the rare earth magnet layer 3 are preferably aligned with the crystal orientation [00L] of SmCo5, which is radially oriented. "L" in the crystal orientation is an arbitrary natural number, and even when L is an arbitrary natural number, "00L" refers to the same direction. For example, L is 2.

[0084] In the first magnetic body 10 and the second magnetic body 20, the radial orientation of the easy magnetization axis of the rare-earth magnet layer 3 enables a high surface magnetic flux density. Furthermore, because the magnetic circuit in the voice coil actuator 100 has a multilayer structure comprising a transition metal layer 1, an intermediate layer 2, and a rare-earth magnet layer 3, the orientation of the rare-earth magnet layer 3 can be improved compared to conventional magnetic circuits using a yoke with a sintered magnet or bonded magnet attached to the wall surface.

[0085] When using a conventional yoke to which sintered magnets or bonded magnets are attached, the radial orientation of the easy magnetization axis of the sintered or bonded magnets is, at best, approximately 80%, making it difficult to achieve an orientation of 90% or greater. On the other hand, the magnetic circuit of the voice coil actuator 100 of this embodiment, by having a multilayer structure comprising a transition metal layer 1, an intermediate layer 2, and a rare earth magnet layer 3, can achieve a radial orientation of the easy magnetization axis of the rare earth magnet layer 3 of 90% or greater. While the reason is unclear, it is speculated that the inclusion of the intermediate layer 12 between the transition metal layer 11 and the rare earth magnet layer 13 achieves radial anisotropy with an orientation of 90% or greater. In other words, the radial orientation of the easy magnetization axis of the rare earth magnet layer 3 is preferably 90% or greater, more preferably exceeding 90%, and even more preferably 95% or greater.

[0086] Furthermore, when the first magnetic body 10 and the second magnetic body 20 have a prismatic or rectangular cylindrical shape, the easy magnetization axis of the rare earth magnet layer 3 in both the first magnetic body 10 and the second magnetic body 20 is preferably oriented perpendicularly to the surface of the transition metal layer 1 (i.e., in the thickness direction of the rare earth magnet layer). In the case of a prismatic or rectangular cylindrical shape, similar to the case of a cylindrical or circular column shape, a high surface magnetic flux density can be achieved by aligning the easy magnetization axis of the rare earth magnet layer 3 perpendicularly to the surface (outer or inner surface) of the transition metal layer 1. Furthermore, since the magnetic circuit in the voice coil actuator 100 has a multilayer structure comprising the transition metal layer 1, the intermediate layer 2, and the rare earth magnet layer 3, the orientation of the rare earth magnet layer 3 can be improved compared to conventional magnetic circuits using a yoke with a sintered magnet or bonded magnet attached to the wall surface.

[0087] In the case of a prismatic or square cylindrical shape, similar to the cylindrical or columnar shape, the degree of orientation of the easy magnetization axis in the rare earth magnet layer 3 in the vertical direction can be improved compared to conventional yokes to which sintered magnets or bonded magnets are attached. The degree of orientation of the easy magnetization axis in the rare earth magnet layer 3 in the vertical direction relative to the surface of the transition metal layer 1 is preferably 90% or greater, more preferably exceeding 90%, and even more preferably 95% or greater.

[0088] By setting the orientation of the rare-earth magnet layer 3 to 90% or greater in the radial or vertical direction, the magnetic flux density in the gap 50 where the coil 31 is located can be increased compared to conventional methods. This allows for a sufficiently high driving force to be achieved even when the voice coil actuator 100 is miniaturized (e.g., with an outer diameter d2a of 6 mm or less). Furthermore, the rare-earth magnet layer 13, serving as the magnet, is preferably magnetized along its easy axis.

[0089] The orientation direction of the easy magnetization axis and the degree of orientation of the easy magnetization axis in the radial direction can be calculated by crystal orientation analysis using EBSD. The orientation degree can be calculated by calculating the orientation degree at each location in the rare earth magnet layer 13 using EBSD and then averaging these orientation degrees over the entire rare earth magnet layer 13.

[0090] In addition, Figure 2A In the voice coil actuator 100 shown, both the first magnetic body 10 and the second magnetic body 20 have a multilayer structure, but it is sufficient that at least one of the first magnetic body 10 and the second magnetic body 20 has a multilayer structure. Figure 2B In the embodiment, the second magnetic body 20 has the multilayer structure described above, and the first magnetic body 10 is composed of a transition metal layer 11 without forming an intermediate layer 2 and a rare earth magnet layer 3. Figure 2C In the embodiment, the first magnetic body 10 has the above-mentioned multilayer structure, and the second magnetic body 20 is composed of a transition metal layer 21 on a matrix without forming the intermediate layer 2 and the rare earth magnet layer 3 .

[0091] like Figure 2B and Figure 2C As shown, only one of the first magnetic body 10 and the second magnetic body 20 may have a multilayer structure. Figure 2B and Figure 2C In the case of , the magnetic flux density of the gap 50 can be increased compared to the past, and a large driving force can be obtained even if the size is reduced. Figures 2A to 2C When the structure is preferably Figure 2A Thus, both the first magnetic body 10 and the second magnetic body 20 have a multilayer structure. When both the first magnetic body 10 and the second magnetic body 20 have a multilayer structure, the magnetic flux density in the gap 50 can be further increased compared to a case where only one of them has a multilayer structure.

[0092] Hereinafter, an example of a method for manufacturing the first magnetic body 10 and the second magnetic body 20 used in the voice coil actuator 100 will be described.

[0093] The multilayered first magnetic body 10 and second magnetic body 20 are preferably both manufactured using a molten salt impregnation method or a method that utilizes the molten salt impregnation method. First, a Co substrate serving as a transition metal matrix and a reaction solution containing an Sm source serving as a rare earth source and a molten salt are prepared. For example, a cylindrical Co substrate can be used to manufacture the first magnetic body 10, and a cylindrical Co substrate can be used to manufacture the second magnetic body 20.

[0094] When preparing the reaction solution, first, a predetermined inorganic salt is dried to dehydrate it. Examples of the inorganic salt include KCl (potassium chloride), LiCl (lithium chloride), and NaCl (sodium chloride). One inorganic salt may be used, or two or more inorganic salts may be used in combination. The dehydrated inorganic salt is heated to a predetermined temperature to melt the inorganic salt (molten salt). The temperature for melting the inorganic salt can be appropriately determined according to the type of inorganic salt used, for example, preferably 400° C. or higher, more preferably 500° C. or higher, and even more preferably 600° C. or higher.

[0095] An Sm source is added to the above-mentioned molten salt (melted inorganic salt) to obtain a reaction solution. As the Sm source, for example, metallic Sm and Sm alloys can be cited. One Sm source can be used, or two or more Sm sources can be used. When the total number of moles of the Sm source and the number of moles of the inorganic salt in the reaction solution is set to 100 mol%, the proportion of the Sm source in the reaction solution is preferably, for example, not less than 0.2 mol% and not more than 6 mol%. In addition, when adding an additive element to the intermediate layer 2 and / or the rare earth magnet layer 3, it is sufficient to add a raw material containing the desired additive element together with the Sm source to the molten salt. In addition, a common reaction solution can also be used in both the manufacture of the first magnetic body 10 and the manufacture of the second magnetic body 20.

[0096] Next, the reaction solution is brought into contact with the surface of the Co substrate, causing the Sm source in the molten salt to react and diffuse toward the surface of the Co substrate, thereby forming a magnetic coating containing Sm on the inner circumference of the Co substrate. This step is called a reaction and diffusion step.

[0097] In the reaction-diffusion step when manufacturing the first magnetic body 10, a cylindrical Co substrate is simply immersed in a reaction solution at a predetermined temperature for a predetermined time to form a magnetic coating containing Sm on the outer circumference of the Co substrate. On the other hand, in the reaction-diffusion step when manufacturing the second magnetic body 20, if the cylindrical Co substrate is directly immersed in the reaction solution, a magnetic coating containing Sm will form not only on the inner circumference of the Co substrate, but also on the outer circumference and end surfaces (surfaces perpendicular to the Z axis), resulting in a reduced yield. Therefore, when manufacturing the second magnetic body 20, it is necessary to ensure that the Sm source reacts and diffuses only on the inner circumference of the Co substrate, while suppressing reaction and diffusion on the outer circumference and end surfaces.

[0098] For example, it is preferable to form a mask of a high-melting-point material on the outer circumference and end faces of a cylindrical Co substrate. Examples of the high-melting-point material include W, Ta, Nb, Mo, or alloys containing at least one of these elements. The mask of the high-melting-point material can be formed by, for example, vapor deposition. After forming the mask of the high-melting-point material on the outer circumference and end faces, the Co substrate is immersed in a reaction solution. This allows the Sm source to react and diffuse only on the inner circumference of the Co substrate, forming a magnetic coating containing Sm on the inner circumference.

[0099] Alternatively, a method for forming a mask of a high melting point material may be employed in which the reaction solution is caused to flow into an area (inner peripheral area) surrounded by an inner peripheral surface in a cylindrical Co substrate. For example, an inlet pipe is connected to both ends of the Co substrate, and a pump or a mass flow controller is used to cause the reaction solution to flow into the inner peripheral area of ​​the Co substrate at a certain flow rate. At this point, it is preferred that the reaction solution be circulated so that the reaction solution flowing out from one end of the Co substrate flows into the inner peripheral area again. In the method in which the reaction solution is caused to flow into the inner peripheral area, the uniformity of the thickness of the magnetic coating can be improved compared to the case in which the Co substrate is immersed in the reaction solution.

[0100] During the reaction-diffusion step, the reaction solution is maintained at a temperature at which the inorganic salt remains molten. To effectively form a magnetic coating, the reaction solution temperature is preferably between 500°C and 900°C, and more preferably between 650°C and 800°C. The reaction time can be appropriately set based on the reaction temperature and the proportion of the Sm source in the reaction solution to form a magnetic coating of the desired thickness. For example, the reaction time can be set between 1 hour and 48 hours.

[0101] The magnetic coating formed on the surface of the Co substrate during the reaction-diffusion process is a precursor to the intermediate layer 2 and the rare-earth magnet layer 3. Specifically, the magnetic coating after the reaction-diffusion process preferably contains SmCo2 as the main phase. SmCo2 is an alloy of Sm and Co with a MgCu2-type crystal structure. If the main phase of SmCo2 has a MgCu2-type crystal structure, the ratio of Sm atoms to Co atoms in SmCo2 may deviate slightly from the stoichiometric ratio. For example, when additive elements are added to improve magnetic properties, the ratio of Sm atoms to Co atoms may deviate slightly from the stoichiometric ratio.

[0102] In addition to the main phase, the magnetic coating may also contain a different phase such as an Sm-rich phase having a higher Sm ratio than SmCo2, and a grain boundary phase. The SmCo2 content in the magnetic coating may be 50 wt% or more, preferably 70 wt% or more, and more preferably 90 wt% or more.

[0103] Furthermore, after the reaction diffusion step, the Co substrate on which the magnetic coating is formed may be washed with an organic solvent such as ethanol or pure water.

[0104] Next, the Co substrate on which the magnetic coating containing SmCo2 is formed is heated at a predetermined temperature for a predetermined time (heating step). In this heating step, the reaction between SmCo2 and the Co of the substrate is further carried out, and a magnetic film containing SmCo2 is generated on the surface of the Co substrate and the magnetic coating. 17 The intermediate layer 2 is composed of and the rare earth magnet layer 3 is composed of SmCo5.

[0105] The heating rate in the heating process is not particularly limited, and for example, it is preferably 1°C / min or more and 20°C / min or less. The holding temperature (reaching temperature) is preferably 800°C or more and 1200°C or less, more preferably 850°C or more and 1150°C or less, and further preferably 900°C or more and 1100°C or less. The holding time at the above-mentioned holding temperature is, for example, preferably 2 hours or more and 48 hours or less. In addition, the cooling rate during cooling after heating is preferably 5°C / min or more, more preferably 10°C / min or more, and further preferably 20°C / min or more.

[0106] The atmosphere in the heating step is not particularly limited, but an inert gas atmosphere is preferred from the viewpoint of suppressing oxidation of the rare earth magnet layer 3. As the inert gas, for example, Ar gas and N2 gas may be used.

[0107] Both the multilayered first magnetic body 10 and the second magnetic body 20 can be manufactured through the aforementioned steps (reaction diffusion step and heating step). In the first magnetic body 10, an intermediate layer 12 and a rare earth magnet layer 13 are formed on the outer circumference of a cylindrical Co substrate in the order described, resulting in a multilayered structure. In the second magnetic body 20, an intermediate layer 22 and a rare earth magnet layer 23 are formed on the inner circumference of a cylindrical Co substrate in the order described, resulting in a multilayered structure. Furthermore, when manufacturing the second magnetic body 20, if a mask of a high-melting-point material is formed on the outer circumference and end faces of the transition metal substrate, the mask of the high-melting-point material may be removed after the heating step, or the mask of the high-melting-point material may remain.

[0108] The rare earth magnet layer 3 (13, 23) formed by the above-described method is a molten salt magnet, unlike sintered magnets and bonded magnets. Furthermore, the above-described method provides a multilayer structure in which no non-magnetic layer, such as an adhesive layer, is interposed between the transition metal layer 1 (Co matrix) and the intermediate layer 2, or between the intermediate layer 2 and the rare earth magnet layer 3.

[0109] The voice coil actuator 100 is Figure 2A The first magnetic body 10 , the second magnetic body 20 , the coil portion 30 , and the bottom yoke 40 may be combined and manufactured in the manner shown.

[0110] The voice coil actuator 100 of this embodiment is suitable for various applications, including magnetic heads, lens drive devices for mobile phone camera modules, speakers, and headphones. For example, when the voice coil actuator 100 is used in a lens drive device, a lens holder having a lens can be placed above the Z axis of the coil 31, instead of the upper cover 32a of the coil unit 30. When the voice coil actuator 100 is used in a speaker or headphone, a vibration plate such as drum paper can be placed above the Z axis of the coil 31, instead of the upper cover 32a.

[0111] (Summary of Implementation Methods)

[0112] The voice coil actuator 100 of this embodiment includes a first magnetic body 10, a second magnetic body 20 facing the first magnetic body 10 via a gap 50, and a coil 32 disposed in the gap 50. Furthermore, at least one of the first magnetic body 10 and the second magnetic body 20 has a multilayer structure including a transition metal layer 1, an intermediate layer 2, and a rare earth magnet layer 3. It is particularly preferable that both the first magnetic body 10 and the second magnetic body 20 have such a multilayer structure.

[0113] By having the multilayer structure described above for the first magnetic body 10 and / or the second magnetic body 20, the easy magnetization axis of the rare-earth magnet layer 3 can be oriented radially or perpendicular to the layer surface (i.e., in the thickness direction of the rare-earth magnet layer 3). Furthermore, the degree of orientation of the easy magnetization axis in the rare-earth magnet layer 3 can be improved compared to the case of using a conventional yoke to which a sintered magnet or a bonded magnet is attached. Therefore, in the voice coil actuator 100 of this embodiment, the magnetic flux density in the gap 50 can be increased compared to conventional methods. As a result, even when the voice coil actuator 100 is miniaturized, a sufficiently large driving force for practical use can be obtained. In particular, by having both the first magnetic body 10 and the second magnetic body 20 have the multilayer structure described above, the magnetic flux density in the gap 50 can be further increased, resulting in a greater driving force.

[0114] Furthermore, when the shape of the magnetic body is a column or cylinder, the orientation degree of the easy magnetization axis in the rare earth magnet layer 3 relative to the radial direction is preferably 90% or greater. Furthermore, when the shape of the magnetic body is a prism or a square cylinder, the orientation degree of the easy magnetization axis of the rare earth magnet layer 3 relative to the vertical direction of the surface (inner or outer surface) of the transition metal layer 1 is preferably 90% or greater.

[0115] In the first magnetic body 10 and / or the second magnetic body 20, the average thickness (t13, t23) of the rare earth magnet layer 3 is preferably 10 μm to 300 μm. By controlling the average thickness of the rare earth magnet layer 3 within the above range, the magnetic characteristics of the magnetic circuit can be further improved.

[0116] In the above embodiment, the thickness of the rare earth magnet layer 23 (3) in the second magnetic body 20 is represented as t23 (see Figure 3 ), the length is expressed as L2 (refer to Figure 1 ), the outer diameter of the second magnetic body 20 is represented as d2a (refer to Figure 1 ) in the case of t23≥0.10mm and L2 / d2a≤0.70. By setting it within this range, the magnetic flux density is further improved.

[0117] It is preferable that no intervening layers, such as adhesive layers, exist between the layers of the multilayer structure (i.e., between the transition metal layer 1 and the intermediate layer 2, and between the intermediate layer 2 and the rare-earth magnet layer 3). By eliminating intervening protective or adhesive layers, the proportion of nonmagnetic layers in the magnetic circuit is reduced, increasing the proportion of magnets. Consequently, the driving force of the voice coil actuator 100 can be further enhanced.

[0118] As mentioned above, although embodiment of this disclosure was described, this disclosure is not limited to the said embodiment, Various changes can be made within the range which does not deviate from the meaning of this disclosure.

[0119] For example, Figure 4 As shown in the voice coil actuator 101, a magnetic circuit can be formed using a U-shaped Co substrate 60. The U-shaped Co substrate 60 has a first wall 61 inserted into the inner side of the coil portion 30 and a second wall 62 facing the first wall 61 via a gap in which a portion of the coil portion 30 is arranged.

[0120] exist Figure 4 In the voice coil actuator 101, the intermediate layer 11 and the rare earth magnet layer 12 are stacked on the inner surface of the first wall 61, and the intermediate layer 21 and the rare earth magnet layer 22 are stacked on the inner surface of the second wall 62. That is, the first wall 61 having the intermediate layer 11 and the rare earth magnet layer 12 corresponds to the first magnetic body 10, and the second wall 62 having the intermediate layer 21 and the rare earth magnet layer 22 corresponds to the second magnetic body 20. The first wall 61 and the second wall 62 are connected as a whole via the connecting portion 63, forming a structure in which the first magnetic body 10 and the second magnetic body 20 are integrated. In addition, Figure 4 In addition to the above-mentioned embodiment, an E-shaped transition metal matrix can also be used to form a magnetic circuit.

[0121] The compositions of the transition metal layer 1 (or 11 or 21, and the same below), the intermediate layer 2 (or 12 or 22, and the same below), and the rare earth magnet layer 3 (or 13 or 23, and the same below) that constitute the first magnetic body 10 or the second magnetic body 20 are not limited to the above-described combinations. For example, in the above-described embodiment, the intermediate layer 2 and the rare earth magnet layer 3 both contain Co as a transition metal element and Sm as a rare earth element. In addition to Co, the intermediate layer 12 and the rare earth magnet layer 13 may also contain at least one or more transition metals such as Fe and Ni. Furthermore, in addition to Sm, they may also contain at least one or more rare earth elements such as Nd, Pr, Dy, and Tb. However, the intermediate layer 2 preferably contains the transition metal element contained in the transition metal layer 1 and the rare earth element contained in the rare earth magnet layer 3.

[0122] Specifically, the intermediate layer 2 can be Sm2Fe 17 、Nd2Fe 17 、Pr2Fe 17 , especially preferably Sm2Co 17 In addition, the rare earth magnet layer 3 can be SmCo5, Sm2Fe 17 N3、SmFe 12 、NdFe 12 、PrFe 12 The transition metal layer 1 preferably contains at least one transition metal element that is repeated in the intermediate layer 2 , and more preferably contains the same transition metal element as that contained in the intermediate layer 2 .

[0123] In addition, depending on the composition of the transition metal layer 1 and the rare earth magnet layer 3, the intermediate layer 2 may not be formed. For example, when the transition metal layer 1 is Fe and the rare earth magnet layer 3 is Sm2Fe 17 In the case of , even if the same production method as in the above embodiment is used, the intermediate layer 2 may not actually be formed.

[0124] Example

[0125] Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples.

[0126] Example 1

[0127] A cylindrical Co substrate (diameter d1: 2.4 mm, height L1: 3.0 mm) was prepared as the raw material for the first magnetic body. A cylindrical Co substrate (outer diameter d2a: 5.0 mm, thickness: 0.4 mm, height L2: 3.0 mm) was prepared as the raw material for the second magnetic body. A Mo mask was formed on the outer circumference of the cylindrical Co substrate using a known method. Next, the surface of the cylindrical Co substrate and the inner circumference of the cylindrical Co substrate were polished and cleaned with acetone.

[0128] Prepare LiCl and dehydrate it by drying. The dehydrated LiCl is heated to 600°C in a metal Mo container using an external heater to melt it. Sm metal powder is added to the molten LiCl as a Sm source. The addition of the Sm source is carried out in a manner such that LiCl and Sm have a molar ratio of LiCl:Sm=100:3. Next, a cylindrical Co substrate and a cylindrical Co substrate are immersed in molten LiCl. The reaction diffusion temperature is set to 700 degrees and the reaction diffusion time is set to 30 hours. By the reaction diffusion process, a laminate having a SmCo2 film formed on the Co substrate is obtained.

[0129] The resulting laminate was heated to 1050°C. Next, the laminate was heated at 1050°C for 100 hours without applying a magnetic field. The laminate was then cooled without applying a magnetic field, yielding a cylindrical first magnetic body and a cylindrical second magnetic body. The heating rate was set at 0.15°C / second, and the cooling rate at 50°C / second. The atmosphere during the heating step was Ar. Finally, the Mo mask on the second magnetic body was removed.

[0130] The structure of the first magnetic body obtained was confirmed by using an X-ray diffraction measuring device and an energy dispersive X-ray analyzing device. The Sm2Co 17 In addition, it was confirmed that the structure of the second magnetic body is that Sm2Co 17 Furthermore, crystal orientation analysis using EBSD revealed that the first and second magnetic bodies were radially oriented, the orientation degree of the rare earth magnet layer was 98%, and the thickness of the rare earth magnet layer was 0.2 mm.

[0131] The magnetic flux density and driving force in the gap 50 of the voice coil actuator using the obtained first and second magnetic bodies were calculated by simulation (JMAG). Specifically, the outer peripheral surface of the cylindrical first magnetic body has a transition metal layer composed of a Co base material with a thickness of d1: 2.8 mm and L1: 3.0 mm, and is in contact with a Sm2Co layer with a thickness of t12 of 0.02 mm.17 The outer peripheral surface of the intermediate layer of the first magnetic body is in contact with a SmCo5 layer with a thickness of t13 of 0.2mm as a rare earth magnet layer. The cylindrical second magnetic body has a transition metal layer composed of a Co base material with d2a: 5.0mm and L2: 3.0mm. The inner peripheral surface of the second magnetic body is in contact with a Sm2Co layer with a thickness of t22 of 0.02mm as an intermediate layer. 17 A SmCo5 layer with a thickness t23 of 0.2 mm is attached to the inner circumference of the second magnetic intermediate layer. The rare earth magnet layers of the first and second magnetic bodies are radially magnetized, with an orientation degree of 98%. Furthermore, the width t5 of the gap between the first and second magnetic bodies is set to 0.5 mm. The coil portion is configured to pass a 10 mA current through a 0.5 mm diameter enameled wire wound 20 times. The yoke portion is a 5.0 mm diameter Co disc.

[0132] Example 2

[0133] A cylindrical second magnetic body was produced in the same manner as in Example 1 except that the mask made of Mo was not formed. The structure of the obtained second magnetic body was confirmed by an X-ray diffraction measuring device and an energy dispersive X-ray analyzing device to be a structure in which Sm2Co 17 In addition, Sm2Co2O3 and SmCo5 films are sequentially formed on the outer peripheral surface of the cylindrical Co substrate. 17 The structures of the film and SmCo5 film were also analyzed. Furthermore, crystal orientation analysis using EBSD revealed that the second magnetic body was radially oriented, with the rare earth magnet layer having an orientation degree of 98% on both the inner and outer surfaces, and a thickness of 0.2 mm. Furthermore, a simulation (JMAG) was performed on the voice coil actuator under the same conditions as in Example 1, except that the resulting second magnetic body was used, to determine the magnetic flux density and driving force in the gap.

[0134] Example 3

[0135] Compared to Example 1, there is no intermediate layer on the inner circumferential surface of the second magnetic body, and a 0.2 mm thick SmCo5 layer is connected to it as a rare earth magnet layer. Otherwise, under the same conditions as Example 1, the magnetic flux density and driving force in the gap of the voice coil actuator were calculated through simulation.

[0136] Example 4

[0137] Compared to Example 1, in order to adjust L2 / d2a, L1 of the first magnetic body was set to 2.0 mm, L2 of the second magnetic body was set to 2.0 mm, and d2a was set to 6.0 mm. Otherwise, under the same conditions as Example 1, the magnetic flux density in the gap of the voice coil actuator was calculated through simulation.

[0138] Example 5

[0139] Compared to Example 1, in order to adjust L2 / d2a, L1 of the first magnetic body was set to 4.0 mm, L2 of the second magnetic body was set to 4.0 mm, and d2a was set to 6.0 mm. Otherwise, under the same conditions as Example 1, the magnetic flux density in the gap of the voice coil actuator was calculated through simulation.

[0140] Example 6

[0141] Compared to Example 1, in order to adjust L2 / d2a, L1 of the first magnetic body was set to 5.0 mm, L2 of the second magnetic body was set to 5.0 mm, and d2a was set to 6.0 mm. Otherwise, under the same conditions as Example 1, the magnetic flux density in the gap of the voice coil actuator was calculated through simulation.

[0142] Comparative Example 1

[0143] Compared to Example 3, except that the SmCo5 film on the first magnetic body was isotropically oriented, a simulation was conducted under the same conditions as Example 1 to determine the magnetic flux density and driving force in the gap of the voice coil actuator. Specifically, the simulation replicated a conventional configuration in which an SmCo5 bonded magnet was attached to the inner circumference of the second magnetic body.

[0144] The results of the simulations of Examples 1 to 3 and Comparative Example 1 are shown in Table 1. The results of the simulations of Examples 4 to 6 are shown in Table 2.

[0145] [Table 1]

[0146]

[0147] [Table 2]

[0148]

[0149] The results shown in Tables 1 and 2 demonstrate that, in the voice coil actuator of the present disclosure, increasing the magnetic flux density in the gap leads to improved driving force, compared to Comparative Example 1, which utilizes isotropic bonded magnets. Furthermore, it is shown that further increasing the magnetic flux density in the gap yields even greater driving force when t23 ≥ 0.10 mm and L2 / d2a ≤ 0.70 are satisfied.

[0150] Explanation of symbols:

[0151] 100, 101…voice coil actuator, 10…first magnetic body, 10a…outer circumferential surface (of the first magnetic body), 20…second magnetic body, 20a…outer circumferential surface (of the second magnetic body), 20b…inner circumferential surface (of the second magnetic body), 1, 11, 21…transition metal layer, 2, 12, 22…intermediate layer, 3, 13, 23…rare earth magnet layer, 30…coil portion, 32…winding frame, 31…coil, 40…bottom yoke, 50…gap.

Claims

1. A voice coil actuator, characterized in that: The invention comprises a first magnetic body, a second magnetic body facing the first magnetic body via a gap, and a coil arranged in the gap between the first magnetic body and the second magnetic body. At least one of the first magnetic body and the second magnetic body has a multilayer structure including a transition metal layer and a rare earth magnet layer.

2. The voice coil actuator according to claim 1, wherein: An intermediate layer is interposed between the transition metal layer and the rare earth magnet layer.

3. The voice coil actuator according to claim 2, wherein: There is no intervening layer between the transition metal layer and the rare earth magnet layer, and between the intermediate layer and the rare earth magnet layer.

4. The voice coil actuator according to claim 2, wherein: The intermediate layer includes the transition metal element contained in the transition metal layer and the rare earth element contained in the rare earth magnet layer.

5. The voice coil actuator according to claim 2, wherein: The intermediate layer has a Sm2Co 17 composition.

6. The voice coil actuator according to any one of claims 1 to 5, wherein: The transition metal layer has a composition containing Co, and the rare earth magnet layer has a composition containing SmCo5.

7. The voice coil actuator according to any one of claims 1 to 5, wherein: Both the first magnetic body and the second magnetic body have the multilayer structure.

8. The voice coil actuator according to any one of claims 1 to 5, wherein: The first magnetic body has a columnar shape, In the multilayer structure of the first magnetic body, the rare earth magnet layer is located outside the first magnetic body relative to the transition metal layer.

9. The voice coil actuator according to any one of claims 1 to 5, wherein: The second magnetic body has a cylindrical shape, In the multilayer structure of the second magnetic body, the rare earth magnet layer is located on the inner side of the first magnetic body with respect to the transition metal layer.

10. The voice coil actuator according to any one of claims 1 to 5, wherein: The average thickness of the rare earth magnet layer is not less than 10 μm and not more than 300 μm.

11. The voice coil actuator according to any one of claims 1 to 5, wherein: The easy magnetization axis of the rare earth magnet layer is oriented perpendicularly to the surface of the transition metal layer, and the orientation degree of the easy magnetization axis relative to the perpendicular direction is 90% or more.

12. The voice coil actuator according to any one of claims 1 to 5, wherein: The easy magnetization axis of the rare earth magnet layer is radially oriented, and the orientation degree of the easy magnetization axis with respect to the radial direction is 90% or more.

13. The voice coil actuator according to any one of claims 1 to 5, wherein: When the thickness of the rare earth magnet layer in the second magnetic body is represented by t23, the length is represented by L2, and the outer diameter of the second magnetic body is represented by d2a, t23≥0.10mm and L2 / d2a≤0.70.

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