Linear vibration motor

Abstract

To provide a linear vibration motor which achieves miniaturization and long life.SOLUTION: A linear vibration motor 1A includes: a fixing body 10; and a movable body 20 which reciprocates in a center axis direction with respect to the fixing body. The movable body has an upper side back yoke 21 and a lower side back yoke 22, which face in the center axis direction, a pole piece 23 which is provided between the upper side back yoke and the lower side back yoke, an upper side magnet 31, and a lower side magnet 32. The fixing body has a case 11 which is formed of a magnetic material and surrounds the movable body. When a distance along the center axis direction from an external surface 21b of the upper side back yoke up to an external surface 22b of the lower side back yoke is a yoke facing interval L1 and a distance along the center axis direction from an upper end face 11a of the case 11 up to a lower end face 11b is a case whole length L2, the yoke facing interval L1 is the same as the case whole length L2. The movable body is held to be reciprocable in the fixing body by magnetic suction force.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a linear vibration motor.

Background Art

[0002] Currently, vibration generating devices such as vibration motors and vibration actuators are installed in various devices. For example, communication devices such as smartphones are equipped with a vibration generating device that generates vibration to notify incoming calls and received emails. In addition, vibration generating devices are also installed in input devices such as stylus pens (touch pens) and VR devices such as smart glasses.

[0003] Patent Document 1 describes a vibration actuator, which is an example of the vibration generating device as described above. The vibration actuator described in Patent Document 1 includes a fixed body and a movable body that is vibratably accommodated within the fixed body. The movable body is supported by an upper leaf spring and a lower leaf spring provided above and below the fixed body so as to be movable in the vibration direction.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In a vibration generating device in which a movable body is supported by an elastic member such as a leaf spring, it is necessary to secure a space for arranging the elastic member between the fixed body and the movable body, and there is a risk that the device will become larger. In addition, there is a risk that the elastic member will fatigue, plastically deform, or break due to excessive movement of the movable body or repeated movement over a long period of time.

[0006] An object of the present invention is to achieve miniaturization and long life of a linear vibration motor. [Means for solving the problem]

[0007] A linear vibration motor according to one embodiment comprises a stationary body and a movable body that reciprocates in the direction of the central axis relative to the stationary body. The movable body includes a first outer yoke and a second outer yoke facing each other in the direction of the central axis, an inner yoke provided between the first outer yoke and the second outer yoke, a first magnet provided between the inner yoke and the first outer yoke, and a second magnet provided between the inner yoke and the second outer yoke. The stationary body includes a case formed of a magnetic material surrounding the movable body and a coil portion provided between the case and the movable body. The first outer yoke is a plate-shaped member having an inner surface facing the first magnet and an outer surface opposite to the inner surface, and the second outer yoke is a plate-shaped member having an inner surface facing the second magnet and an outer surface opposite to the inner surface. The case is a cylindrical member having a first end surface located on one side in the direction of the central axis and a second end surface located on the other side in the direction of the central axis. Furthermore, when the distance along the central axis from the outer surface of the first outer yoke to the outer surface of the second outer yoke is defined as the yoke-facing distance, and the distance along the central axis from the first end face of the case to the second end face of the case is defined as the total case length, the yoke-facing distance is either the same as the total case length or shorter than the total case length. In addition, the movable body is held reciprocally within the fixed body by magnetic attraction. [Effects of the Invention]

[0008] According to the present invention, miniaturization and extended lifespan of linear vibration motors can be achieved. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is an external perspective view of a linear vibration motor according to the first embodiment. [Figure 2] Figure 2 is a longitudinal cross-sectional view of the linear vibration motor shown in Figure 1. [Figure 3]Figure 3 is a cross-sectional view showing the movement of the movable body when current is applied in the forward direction to the coil shown in Figure 2. [Figure 4] Figure 4 is a cross-sectional view showing the movement of the movable body when current is applied in the reverse direction to the coil shown in Figure 2. [Figure 5] Figure 5 is a cross-sectional view showing a modified example of a linear vibration motor according to the first embodiment. [Figure 6] Figure 6 is a cross-sectional view showing another modified example of the linear vibration motor according to the first embodiment. [Figure 7] Figure 7 is a longitudinal cross-sectional view of a linear vibration motor according to the second embodiment. [Figure 8] Figure 8 is a longitudinal cross-sectional view of a linear vibration motor according to the third embodiment. [Figure 9] Figure 9 is a longitudinal cross-sectional view of a linear vibration motor according to the fourth embodiment. [Figure 10] Figure 10 is a cross-sectional view showing the movement of the movable body when current is applied to the coil shown in Figure 9. [Modes for carrying out the invention]

[0010] Hereinafter, several embodiments of the present invention will be described in detail with reference to the drawings. In all drawings used to describe the embodiments, the same or substantially the same components and elements will be denoted by the same reference numerals. Furthermore, components and elements that have already been described will not be described again in principle.

[0011] (First Embodiment) Figure 1 is an external perspective view of the linear vibration motor 1A according to this embodiment. Figure 2 is a cross-sectional view of the linear vibration motor 1A. Note that the cross-section shown in Figure 2 is a longitudinal cross-section of the linear vibration motor 1A along the central axis C shown in Figure 1.

[0012] <Overview of Linear Vibration Motors> The application of the linear vibration motor 1A according to this embodiment is not particularly limited. The linear vibration motor 1A is mounted on, for example, communication devices, input devices, and VR devices. The linear vibration motor 1A mounted on these devices functions as a vibration generating device that generates vibrations for providing, for example, a sense of use or a sense of presence.

[0013] As shown in FIGS. 1 and 2, the linear vibration motor 1A includes a fixed body 10 and a movable body 20. The movable body 20 reciprocates in the direction of the central axis C inside the fixed body 10. When the movable body 20 reciprocates inside the fixed body 10, the entire linear vibration motor 1A including the fixed body 10 and the movable body 20 vibrates. In the following description, the direction of the central axis C may be referred to as the "central axis direction", the "vertical direction", or the "vibration direction". However, such a designation is for convenience of explanation and does not limit the direction of the central axis C to the vertical direction or the perpendicular direction. For example, when the linear vibration motor 1A is mounted on some device, the central axis C may be horizontal.

[0014] <Movable body> As shown in FIG. 2, the movable body 20 includes a first outer yoke 21, a second outer yoke 22, an inner yoke 23, a first magnet 31, a second magnet 32, and a shaft 40. The first outer yoke 21, the first magnet 31, the inner yoke 23, the second magnet 32, and the second outer yoke 22 are arranged in a row in the central axis direction (vertical direction) in this order, and the shaft 40 passes through the centers of these.

[0015] Viewed in another way, the first outer yoke 21 and the second outer yoke 22 face each other in the central axis direction (vertical direction). The inner yoke 23 is provided between the opposing first outer yoke 21 and second outer yoke 22. As a result, the first magnet 31 is provided between the inner yoke 23 and the first outer yoke 21, and the second magnet 32 is provided between the inner yoke 23 and the second outer yoke 22. These yokes and magnets are penetrated by the shaft 40 and are integrated.

[0016] The integrated first outer yoke 21, second outer yoke 22, inner yoke 23, first magnet 31, and second magnet 32 are located at the center of the shaft 40 in the vertical direction. In another view, the center of the assembly of the first outer yoke 21, second outer yoke 22, inner yoke 23, first magnet 31, and second magnet 32 coincides with the center of the shaft 40.

[0017] In the following description, the first outer yoke 21 may be referred to as the "upper back yoke 21", the second outer yoke 22 may be referred to as the "lower back yoke 22", and the inner yoke 23 may be referred to as the "pole piece 23". Also, the first magnet 31 may be referred to as the "upper magnet 31", and the second magnet 32 may be referred to as the "lower magnet 32".

[0018] <Back yoke, pole piece> The upper back yoke 21, lower back yoke 22, and pole piece 23 are plate-like members formed of a magnetic material. More specifically, the upper back yoke 21, lower back yoke 22, and pole piece 23 are annular plate-like members formed of a magnetic material.

[0019] The upper back yoke 21 includes an inner surface 21a facing the upper magnet 31 and an outer surface 21b opposite to the inner surface 21a. Similarly, the lower back yoke 22 includes an inner surface 22a facing the lower magnet 32 and an outer surface 22b opposite to the inner surface 22a.

[0020] <Upper magnet, lower magnet> The upper magnet 31 and the lower magnet 32 are ring-shaped permanent magnets magnetized in the vertical direction. The upper magnet 31 and the lower magnet 32 are arranged with their like poles facing each other. More specifically, the upper magnet 31 and the lower magnet 32 are arranged with their S poles facing each other.

[0021] In other words, the north pole of the upper magnet 31 faces the upper back yoke 21, and the south pole of the upper magnet 31 faces the pole piece 23. Also, the north pole of the lower magnet 32 ​​faces the lower back yoke 22, and the south pole of the lower magnet 32 ​​faces the pole piece 23.

[0022] <Fixed body> As shown in Figure 2, the fixed body 10 comprises a case 11, a coil section 12, an upper cover 13, and a lower cover 14, and houses the movable body 20.

[0023] <Case> Case 11 is a cylindrical member formed of a magnetic material and surrounds the movable body 20. More specifically, case 11 is a cylindrical member formed of a magnetic material.

[0024] Case 11 comprises a first end face 11a located on one side (upper side) in the direction of the central axis, and a second end face 11b located on the other side (lower side) in the direction of the central axis. In the following description, the first end face 11a may be referred to as the "upper end face 11a," and the second end face 11b may be referred to as the "lower end face 11b."

[0025] The case 11 having the above shape can be formed, for example, by rolling up a strip of steel or silicon steel sheet and connecting the ends together.

[0026] <Coil section> The coil section 12 comprises a bobbin 15 and a coil 16, and is located between the case 11 and the movable body 20. In other words, the case 11 surrounds the movable body 20 via the coil section 12. Alternatively, the movable body 20, coil section 12, and case 11 are arranged in this order from the radially inner to the radially outer.

[0027] The bobbin 15 is formed in a cylindrical shape from a non-magnetic material, and the movable body 20 is positioned inside the bobbin 15. Alternatively, the bobbin 15 is a cylindrical body with an inner diameter through which the movable body 20 can be inserted. An air gap exists between the inner surface of the bobbin 15 and the outer surface of the movable body 20.

[0028] The bobbin 15 is provided with an annular coil holding portion 15a. The coil holding portion 15a is a groove formed around the entire circumference of the bobbin 15, and the coil 16 is wound around the coil holding portion 15a.

[0029] <Upper cover, lower cover> The upper cover 13 and the lower cover 14 are made of a non-magnetic material. For example, the upper cover 13 and the lower cover 14 are made of the same material as the bobbin 15. The upper cover 13 is attached to the upper end of the case 11, and the lower cover 14 is attached to the lower end of the case 11.

[0030] The upper cover 13, attached to the upper end of case 11, closes one opening of case 11 and covers the upper side of the movable body 20 and coil section 12. The lower cover 14, attached to the lower end of case 11, closes the other opening of case 11 and covers the lower side of the movable body 20 and coil section 12.

[0031] <Yoke spacing, case length> The arrow L1 shown in Figure 2 indicates the distance between opposing yokes. The arrow L2 shown in Figure 2 indicates the total length of the case. From Figure 2, it can be understood that the distance between opposing yokes L1 is the distance along the central axis from the outer surface 21b of the upper back yoke 21 to the outer surface 22b of the lower back yoke 22. It can also be understood that the total length of the case L2 is the distance along the central axis from the upper end surface 11a of the case 11 to the lower end surface 11b of the case 11.

[0032] The yoke-to-yoke distance L1 is the same as the total case length L2 (L1=L2). As a result, the outer circumferential surface 21c of the upper back yoke 21 faces the upper end portion 11c of the inner circumferential surface of the case 11. Also, the outer circumferential surface 22c of the lower back yoke 22 faces the lower end portion 11d of the inner circumferential surface of the case 11.

[0033] <Magnetic attraction> The above-described positional relationship between the upper back yoke 21, the lower back yoke 22, and the case 11 provides a magnetic attractive force that holds the movable body 20 in a reciprocating motion. More specifically, the magnetic attractive force F1 is obtained by the magnetic flux passing through the magnetic circuit including the upper magnet 31, the upper back yoke 21, the case 11, and the pole piece 23. In addition, the magnetic attractive force F2 is obtained by the magnetic flux passing through the magnetic circuit including the lower magnet 32, the lower back yoke 22, the case 11, and the pole piece 23.

[0034] The movable body 20 is held within the fixed body 10 so that it can reciprocate (move up and down) due to magnetic attractive forces F1 and F2. Alternatively, when the coil 16 is not energized, the movable body 20 floats at a position where its center coincides with the center of the fixed body 10. In the following explanation, the position of the movable body 20 when the coil 16 is not energized may be referred to as the "neutral position".

[0035] <Movement of movable parts> As described above, the movable body 20 is held in the position shown in Figure 2 (neutral position) by magnetic force (magnetic attraction), rather than by the elastic force of an elastic member such as a leaf spring. Alternatively, the movable body 20 is held to reciprocate within the fixed body 10 by a magnetic spring. Therefore, there is no need to secure space inside the fixed body 10 for arranging an elastic member such as a leaf spring. Furthermore, there is no risk of the elastic member such as a leaf spring deforming or breaking.

[0036] Figure 3 is a cross-sectional view showing the movement of the movable body 20 when current is applied to the coil 16 shown in Figure 2 in the first direction (forward direction). Figure 4 is a cross-sectional view showing the movement of the movable body 20 when current is applied to the coil 16 shown in Figure 2 in the second direction (reverse direction), which is opposite to the first direction.

[0037] When current is applied in the forward direction to the coil 16 shown in Figure 2, the movable body 20 receives an upward thrust (Lorentz force). As a result, the movable body 20 shown in Figure 2 moves from the position shown in the same figure (neutral position) to the position shown in Figure 3 (upper position). In other words, the movable body 20 rises.

[0038] When current is applied in the reverse direction to the coil 16 shown in Figure 2, the movable body 20 receives a downward thrust (Lorentz force). As a result, the movable body 20 shown in Figure 2 moves from the position shown in the same figure (neutral position) to the position shown in Figure 4 (lower position). In other words, the movable body 20 descends.

[0039] Therefore, if the direction of current flow to the coil 16 is reversed at a constant period, the movable body 20 reciprocates vertically inside the fixed body 10, generating vibration.

[0040] Here, the magnetic attractive forces F1 and F2 act on the movable body 20 that has moved to the upper position (Figure 3) to return it to the neutral position (Figure 2). Also, the magnetic attractive forces F1 and F2 act on the movable body 20 that has moved to the lower position (Figure 4) to return it to the neutral position (Figure 2).

[0041] Therefore, when the direction of current supply to the coil 16 shown in Figure 3 is switched from the forward direction to the reverse direction, the movable body 20 is subjected to downward magnetic attractive forces F1 and F2 in addition to the downward Lorentz force. In other words, a larger downward thrust acts on the movable body 20. On the other hand, when the direction of current supply to the coil 16 shown in Figure 4 is switched from the reverse direction to the forward direction, the movable body 20 is subjected to upward magnetic attractive forces F1 and F2 in addition to the upward Lorentz force. In other words, a larger upward thrust acts on the movable body 20. As a result, the vibration characteristics of the linear vibration motor 1A (e.g., vibration intensity and responsiveness) are improved.

[0042] (Variation 1) Figure 5 is a cross-sectional view showing a modified example of the linear vibration motor 1A according to the first embodiment. The upper back yoke 21 shown in Figure 5 has a larger diameter than the upper magnet 31. As a result, the peripheral edge of the upper back yoke 21 extends beyond the edge of the upper magnet 31 and around the upper magnet 31. Similarly, the lower back yoke 22 shown in Figure 5 has a larger diameter than the lower magnet 32. As a result, the peripheral edge of the lower back yoke 22 extends beyond the edge of the lower magnet 32 ​​and around the lower magnet 32.

[0043] From another perspective, the outer circumferential surface 21c of the upper back yoke 21 shown in Figure 5 is closer to the upper end 11c of the inner circumferential surface of the case 11 than the outer circumferential surface 21c of the upper back yoke 21 shown in Figure 2. Similarly, the outer circumferential surface 22c of the lower back yoke 22 shown in Figure 5 is closer to the lower end 11d of the inner circumferential surface of the case 11 than the outer circumferential surface 22c of the lower back yoke 22 shown in Figure 2.

[0044] In other words, in the linear vibration motor 1A shown in Figure 5, the gap between the back yokes 21, 22 and the case 11 is reduced compared to the linear vibration motor 1A shown in Figure 2. Therefore, a larger (stronger) magnetic attractive force acts on the movable body 20.

[0045] (Modification 2) Figure 6 is a cross-sectional view showing another modified example of the linear vibration motor 1A according to the first embodiment. A first weight 51 is attached to the upper back yoke 21 shown in Figure 6, and a second weight 52 is attached to the lower back yoke 22.

[0046] The first weight 51 has the same or substantially the same shape as the upper back yoke 21 and is superimposed on the outer surface 21b of the upper back yoke 21. The second weight 52 has the same or substantially the same shape as the lower back yoke 22 and is superimposed on the outer surface 22b of the lower back yoke 22.

[0047] The upper end of the shaft 40 is inserted into the first weight 51, and the lower end of the shaft 40 is inserted into the second weight 52. In other words, the shaft 40 penetrates the first weight 51 and the second weight 52, in addition to the upper back yoke 21, upper magnet 31, pole piece 23, lower magnet 32 ​​and lower back yoke 22.

[0048] In the linear vibration motor 1A shown in Figure 6, the weight of the movable body 20 is increased compared to the linear vibration motor 1A shown in Figure 2. Therefore, larger and stronger vibrations can be obtained.

[0049] The first weight 51 can also be attached to the upper back yoke 21 shown in Figure 5. The second weight 52 can also be attached to the lower back yoke 22 shown in Figure 5.

[0050] The weights of the first weight 51 and the second weight 52 can be increased or decreased as needed. The weights of the first weight 51 and the second weight 52 can be increased or decreased by changing their outer diameter, thickness, or material.

[0051] (Second Embodiment) Next, another embodiment of the present invention will be described. Figure 7 is a cross-sectional view of the linear vibration motor 1B according to this embodiment. More specifically, Figure 7 is a longitudinal cross-sectional view of the linear vibration motor 1B according to this embodiment along the central axis C.

[0052] The linear vibration motor 1B according to this embodiment has the same basic structure as the linear vibration motor 1A according to the first embodiment (Figure 2). Therefore, the explanation of the structure that is the same as or substantially the same as that of the linear vibration motor 1A will be omitted, and only the structure that differs from that of the linear vibration motor 1A will be explained.

[0053] As shown in Figure 7, the case 11 of the linear vibration motor 1B is provided with a first rib 61 and a second rib 62. The first rib 61 is provided at one end of the case 11 in the direction of the central axis, and the second rib 62 is provided at the other end of the case 11 in the direction of the central axis.

[0054] The first rib 61 protrudes radially inward from the case 11 and is sandwiched between the upper cover 13 and the bobbin 15. Similarly, the second rib 62 protrudes radially inward from the case 11 and is sandwiched between the lower cover 14 and the bobbin 15.

[0055] From another perspective, the first rib 61 and the second rib 62 protrude toward the movable body 20. More specifically, the first rib 61 protrudes toward the upper back yoke 21, and the second rib 62 protrudes toward the lower back yoke 22.

[0056] In the linear vibration motor 1B, the upper end surface 11a of the case 11 is formed by the outer surface of the first rib 61 that protrudes toward the upper back yoke 21. The lower end surface 11b of the case 11 is formed by the outer surface of the second rib 62 that protrudes toward the lower back yoke 22. At the same time, the upper end portion 11c of the inner circumferential surface of the case 11, which faces the outer circumferential surface 21c of the upper back yoke 21, is formed by the inner circumferential surface of the first rib 61. The lower end portion 11d of the inner circumferential surface of the case 11, which faces the outer circumferential surface 22c of the lower back yoke 22, is formed by the inner circumferential surface of the second rib 62.

[0057] In other words, in the linear vibration motor 1B, similar to the linear vibration motor 1A shown in Figure 5, the gap between the back yokes 21 and 22 and the case 11 is reduced. As a result, a larger (stronger) magnetic attractive force acts on the movable body 20.

[0058] The first rib 61 and the second rib 62 are formed by press working. More specifically, the first rib 61 and the second rib 62 are parts of the case 11 that are bent radially inward.

[0059] However, there are embodiments in which the first rib 61 and the second rib 62 are formed by separate parts. For example, in another embodiment, the first rib 61 and the second rib 62 are formed by annular plate members that are welded or bonded to both ends of the case 11.

[0060] (Third embodiment) Next, another embodiment of the present invention will be described. Figure 8 is a cross-sectional view of the linear vibration motor 1C according to this embodiment. More specifically, Figure 8 is a longitudinal cross-sectional view of the linear vibration motor 1C according to this embodiment along the central axis C.

[0061] The linear vibration motor 1C according to this embodiment has the same basic structure as the linear vibration motor 1B according to the second embodiment (Figure 7). Therefore, the explanation of the structure that is the same as or substantially the same as that of the linear vibration motor 1B will be omitted, and only the structure that differs from that of the linear vibration motor 1B will be explained.

[0062] As shown in Figure 8, the case 11 of the linear vibration motor 1C is composed of a first case member 71 and a second case member 72. The first case member 71 and the second case member 72 are cylindrical members formed of a magnetic material and are arranged coaxially in the central axis direction (vertical direction).

[0063] Furthermore, an annular gap 73 surrounding the movable body 20 is provided between the first case member 71 and the second case member 72. Alternatively, the first case member 71 and the second case member 72 are aligned vertically with the gap 73 in between. In other words, an annular slit is provided in the vertical center of the case 11.

[0064] When the movable body 20 is in the neutral position, the vertical center of the movable body 20, where the pole piece 23 is located, is at the same height as the vertical center of the case 11. On the other hand, the width (vertical dimension) of the gap 73 is equal to or narrower than the movement stroke of the movable body 20. In other words, the gap 73 always surrounds the pole piece 23, and the pole piece 23 always faces the gap 73.

[0065] In this case, when the pole piece 23 and the case 11 are facing each other, a magnetic attractive force F3 is generated between them acting perpendicular to the direction of movement of the movable body 20. As a result, there is a risk that the reciprocating motion (up and down movement) of the movable body 20 will be hindered by the magnetic attractive force F3.

[0066] In contrast, in the linear vibration motor 1C of this embodiment, where a gap 73 surrounding the pole piece 23 is provided in the case 11, the magnetic attractive force F3 is reduced, thus improving the vibration characteristics. Furthermore, a magnetic attractive force including a component parallel to the direction of movement of the movable body 20 is generated between the pole piece 23 and the first case member 71, and between the pole piece 23 and the second case member 72, and it is expected that the reciprocating motion (vertical motion) of the movable body 20 will be stabilized. Note that this effect can be obtained even if the gap 73 is not provided around the entire circumference of the case 11. However, in this embodiment, where the gap 73 is provided around the entire circumference of the case 11, the above effect is more pronounced.

[0067] (Fourth Embodiment) Next, another embodiment of the present invention will be described. Figure 9 is a cross-sectional view of the linear vibration motor 1D according to this embodiment. More specifically, Figure 9 is a longitudinal cross-sectional view of the linear vibration motor 1D according to this embodiment along the central axis C.

[0068] The linear vibration motor 1D according to this embodiment has the same basic structure as the linear vibration motor 1B according to the second embodiment (Figure 7). Therefore, the explanation of the structure that is the same as or substantially the same as that of the linear vibration motor 1B will be omitted, and only the structure that differs from that of the linear vibration motor 1B will be explained.

[0069] As shown in Figure 9, in the linear vibration motor 1D, the yoke-to-yoke distance L1 is shorter than the total case length L2. Alternatively, when the movable body 20 is in the neutral position, the outer circumferential surface 21c of the upper back yoke 21 does not face the upper end 11c of the inner circumferential surface of the case 11, and the outer circumferential surface 22c of the lower back yoke 22 does not face the lower end 11d of the inner circumferential surface of the case 11.

[0070] As shown in Figure 10, when the movable body 20 rises due to energization of the coil 16, the outer circumferential surface 21c of the upper back yoke 21 approaches the upper end 11c of the inner circumferential surface of the case 11, while the outer circumferential surface 22c of the lower back yoke 22 moves further away from the lower end 11d of the inner circumferential surface of the case 11. Although not shown in the figure, when the movable body 20 descends due to energization of the coil 16, the outer circumferential surface 22c of the lower back yoke 22 approaches the lower end 11d of the inner circumferential surface of the case 11, while the outer circumferential surface 21c of the upper back yoke 21 moves further away from the upper end 11c of the inner circumferential surface of the case 11.

[0071] From another perspective, when the movable body 20 rises, the magnetic attractive force F1 acting on the upper back yoke 21 increases, while the magnetic attractive force F2 acting on the lower back yoke 22 decreases. Conversely, when the movable body 20 descends, the magnetic attractive force F2 acting on the lower back yoke 22 increases, while the magnetic attractive force F1 acting on the upper back yoke 21 decreases.

[0072] In other words, within a certain range of movement stroke, the increase or decrease in the magnetic attractive force F1 acting on the upper back yoke 21 and the increase or decrease in the magnetic attractive force F2 acting on the lower back yoke 22 cancel each other out. As a result, the change in the spring constant of the magnetic spring holding the movable body 20 becomes small, and vibration detection becomes stable.

[0073] The present invention is not limited to the embodiments described above, and can be modified in various ways without departing from its essence. Furthermore, the structures of the linear vibration motors according to each embodiment can be combined as appropriate. For example, the gap 73 (Figure 8) provided in the case 11 of the linear vibration motor 1C may be provided in the case 11 of the other linear vibration motors 1A, 1B, and 1D. The first weight 51 and second weight 52 (Figure 6) provided in the linear vibration motor 1A may be provided in the other linear vibration motors 1B, 1C, and 1D. The upper back yoke 21 and lower back yoke 22 provided in the linear vibration motors 1B, 1C, and 1D may be replaced with the upper back yoke 21 and lower back yoke 22 (Figure 5) provided in the linear vibration motor 1A.

[0074] The shaft 40 can be omitted. The upper magnet 31 and the lower magnet 32 ​​may be arranged so that their north poles face each other.

[0075] This technology can be configured as follows:

[0076] (1) A linear vibration motor comprising a fixed body and a movable body that reciprocates in the direction of the central axis relative to the fixed body, The movable body includes a first outer yoke and a second outer yoke facing each other in the central axis direction, an inner yoke provided between the first outer yoke and the second outer yoke, a first magnet provided between the inner yoke and the first outer yoke, and a second magnet provided between the inner yoke and the second outer yoke. The fixed body includes a case formed of a magnetic material surrounding the movable body, and a coil portion provided between the case and the movable body. The first outer yoke is a plate-shaped member having an inner surface facing the first magnet and an outer surface opposite to the inner surface. The second outer yoke is a plate-shaped member having an inner surface facing the second magnet and an outer surface opposite to the inner surface. The case is a cylindrical member comprising a first end face located on one side in the direction of the central axis and a second end face located on the other side in the direction of the central axis. When the distance along the central axis from the outer surface of the first outer yoke to the outer surface of the second outer yoke is defined as the yoke-opposing distance, and the distance along the central axis from the first end face of the case to the second end face of the case is defined as the total case length, the yoke-opposing distance is either the same as the total case length or shorter than the total case length. The movable body is a linear vibration motor, which is held in a reciprocating position within the fixed body by magnetic attraction.

[0077] (2) The first outer yoke has a larger diameter than the first magnet, and the peripheral edge of the first outer yoke protrudes around the first magnet. The linear vibration motor according to (1), wherein the second outer yoke has a larger diameter than the second magnet, and the peripheral edge of the second outer yoke protrudes around the second magnet.

[0078] (3) The linear vibration motor according to (1) or (2), wherein the movable body includes a first weight superimposed on the outer surface of the first outer yoke and a second weight superimposed on the outer surface of the second outer yoke.

[0079] (4) The case comprises a first rib provided at one end in the direction of the central axis and a second rib provided at the other end in the direction of the central axis. The first rib protrudes toward the inside of the case, forming a first end face. The linear vibration motor according to any one of (1) to (3), wherein the second rib protrudes toward the inside of the case and forms a second end face.

[0080] (5) The case is composed of a first case member and a second case member that are arranged coaxially in the direction of the central axis, A linear vibration motor according to any one of (1) to (4), wherein an annular gap surrounding the inner yoke is provided between the first case member and the second case member.

[0081] (6) The movable body includes the first outer yoke, the second outer yoke, the inner yoke, the first magnet, and a shaft passing through the second magnet, as described in any of (1) to (5).

[0082] (7) The coil portion includes a bobbin made of a non-magnetic material and a coil wound around the bobbin. The movable body is a linear vibration motor according to any one of (1) to (6), which is located inside the bobbin. [Explanation of Symbols]

[0083] 1A, 1B, 1C, 1D... Linear vibration motor, 10... Fixed body, 11... Case, 11a... First end face (upper end face), 11b... Second end face (lower end face), 11c... Upper end of inner circumference, 11d... Lower end of inner circumference, 12... Coil section, 13... Upper cover, 14... Lower cover, 15... Bobbin, 15a... Coil holder, 16... Coil, 20... Movable body, 21... First outer yoke (upper back yoke), 21a... Inner surface, 21b... Outer surface, 21c... Outer circumference, 22... Second outer yoke ( Lower back yoke), 22a...inner surface, 22b...outer surface, 22c...outer surface, 23...inner yoke (pole piece), 31...first magnet (upper magnet), 32...second magnet (lower magnet), 40...shaft, 51...first weight, 52...second weight, 61...first rib, 62...second rib, 71...first case member, 72...second case member, 73...gap, C...central axis, F1, F2, F3...magnetic attraction force, L1...yoke distance, L2...total case length

Claims

1. A linear vibration motor comprising a fixed body and a movable body that reciprocates in the direction of the central axis relative to the fixed body, The movable body includes a first outer yoke and a second outer yoke facing each other in the central axis direction, an inner yoke provided between the first outer yoke and the second outer yoke, a first magnet provided between the inner yoke and the first outer yoke, and a second magnet provided between the inner yoke and the second outer yoke. The fixed body includes a case formed of a magnetic material surrounding the movable body, and a coil portion provided between the case and the movable body. The first outer yoke is a plate-shaped member having an inner surface facing the first magnet and an outer surface opposite to the inner surface. The second outer yoke is a plate-shaped member having an inner surface facing the second magnet and an outer surface opposite to the inner surface. The case is a cylindrical member having a first end face located on one side in the direction of the central axis and a second end face located on the other side in the direction of the central axis. When the distance along the central axis from the outer surface of the first outer yoke to the outer surface of the second outer yoke is defined as the yoke-opposing distance, and the distance along the central axis from the first end face of the case to the second end face of the case is defined as the total case length, the yoke-opposing distance is either the same as the total case length or shorter than the total case length. The movable body is held within the fixed body in the direction of the central axis and in a direction perpendicular to the central axis by the magnetic attractive force generated between the first outer yoke and the second outer yoke and the case, and reciprocates in the direction of the central axis. Linear vibration motor.

2. The first outer yoke has a larger diameter than the first magnet, and the peripheral edge of the first outer yoke protrudes around the first magnet. The second outer yoke has a larger diameter than the second magnet, and the peripheral edge of the second outer yoke protrudes around the second magnet. The linear vibration motor according to claim 1.

3. The movable body includes a first weight superimposed on the outer surface of the first outer yoke and a second weight superimposed on the outer surface of the second outer yoke. The linear vibration motor according to claim 1.

4. The case comprises a first rib provided at one end in the central axis direction and a second rib provided at the other end in the central axis direction. The first rib protrudes toward the inside of the case, forming a first end face. The second rib protrudes toward the inside of the case, forming the second end face. The linear vibration motor according to claim 1.

5. The case is composed of a first case member and a second case member that are arranged coaxially in the direction of the central axis, An annular gap surrounding the inner yoke is provided between the first case member and the second case member. The linear vibration motor according to claim 1.

6. The movable body includes the first outer yoke, the second outer yoke, the inner yoke, the first magnet, and a shaft passing through the second magnet. The linear vibration motor according to claim 1.

7. The coil portion includes a bobbin made of a non-magnetic material and a coil wound around the bobbin. The movable body is located inside the bobbin. The linear vibration motor according to claim 1.

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