Vibration motor

Abstract

A vibration motor having a tubular case, a shaft protruding from a front end of the case, a weight eccentrically fixed to an end of the shaft, and a metallic holder surrounding the case, the holder being surface-mounted on a wiring board by reflow-soldering, wherein the holder has a planate bottom placed on the wiring board, a pair of forward tilting prevention portions that extends up to a position facing the weight is formed at the bottom, a notch is provided on a center line extending along the bottom between the forward tilting prevention portions, and the notch extends from the front end of the forward tilting prevention portions beyond the position facing the weight.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view showing an embodiment of a vibration motor according to the present invention.

FIG. 2 is a bottom view showing the embodiment of the vibration motor according to the present invention.

FIG. 3 is a front view showing the embodiment of the vibration motor according to the present invention.

FIG. 4 is a rear view showing the embodiment of the vibration motor according to the present invention.

FIG. 5 is a perspective view showing a holder adopted for the vibration motor according to the present invention.

FIG. 6 is a side view showing the holder adopted for the vibration motor according to the present invention.

FIG. 7 is a front view showing the holder adopted for the vibration motor according to the present invention.

FIG. 8 is a rear view showing the holder adopted for the vibration motor according to the present invention.

FIG. 9 is a sectional view along an IX-IX line in FIG. 6.

FIG. 10 is an exploded perspective view showing a mobile phone equipped with a wiring board on which a vibration motor is mounted.

FIG. 11 is an exploded perspective view showing a game controller equipped with the wiring board on which the vibration motor is mounted.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A suitable embodiment of a vibration motor according to the present invention will be described in detail below with reference to drawings.

As shown in FIG. 1 to FIG. 4, a vibration motor 1 is a small vibration motor surface-mounted on a printed wiring board PWB by reflow-soldering, and includes a motor part A having a tubular case 2 of about 4 mm in diameter and about 10 mm in length and a holder 3 in a tubular and rectangular cross-sectional shape into which the tubular case 2 is press-fitted.

The tubular case 2 is comprised of a metallic cylindrical housing 4 and a resin bracket 6 press-fitted into an open rear end of the housing 4. A protruding neck 4a is formed by contraction on the front end side of the housing 4 and a portion of a shaft 7 protrudes from the front end of the neck 4a. A weight 8 whose cross section is fan-shaped is eccentrically fixed to the end of the shaft 7 by crimping or press fitting. A dent 8a into which a portion of the neck 4a is fitted is formed on the rear end side of the weight 8. The shaft 7 is pivotally supported by the tubular case 2 via a bearing fixed inside the neck 4a and a bearing fixed to the bracket 6.

In the motor part A, a stator 9 consisting of permanent magnets bonded to the inner wall surface and a rotor 10 surrounded by the stator 9 and fixed to the shaft 7 are accommodated inside the tubular case 2. A coil is wound around a core of the rotor 10 and the coil is connected to a commutator fixed to the shaft 7 on the rear end side of the tubular case 2. A pair of brushes fixed to the bracket 6 is slidingly contact with the commutator.

The bracket 6 has a cylindrical front portion press-fitted into the tubular case 2 and a rectangular rear portion insertable into the holder 3. Connection terminals 12a and 12b provided at brush ends are embedded in the bracket 6. The pair of connection terminals 12a and 12b is exposed from the rear end of the bracket 6, and external terminals 13 and 14 are soldered to the connection terminals 12a and 12b of brush respectively. Each of the pair of the external terminals 13 and 14 is a copper sheet bent in L-shape. Ends 13a and 14a on one side of the external terminals 13 and 14 are in contact with the rear end of the bracket 6 and soldered to the connection terminals 12a and 12b, and ends 13b and 14b on the other side are directed toward the weight 8 side and extend in parallel with an axis of rotation C1 of the shaft 7 (See FIG. 1). The ends 13b and 14b of the external terminals 13 and 14 are reflow-soldered on the printed wiring board PWB.

As shown in FIG. 5, the holder 3 with board thickness of 0.2 mm into which the tubular case 2 is press-fitted is formed by stamping out a stainless flat plate to a predetermined shape and then bending the flat plate to a rectangular cross-sectional shape and joining ends together. The holder 3 is comprised of a planate bottom 17 in which a joint 16 is formed, a pair of flanks 18 and 19 erected from the right and left sides of the bottom 17, and a planate top 21 bridging both the flanks 18 and 19.

As shown in FIG. 2 and FIG. 5, a trapezoidal convex portion 16a whose tip is broadened and a concave portion 16b into which the trapezoidal convex portion 16a is fitted are formed in the joint 16 formed at the bottom 17 of the holder 3. The convex portion 16a and concave portion 16b are alternately lined up along a center line C2 extending in parallel with the axis of rotation C1 (See FIG. 1) of the shaft 7 and through the center of the bottom 17, and the convex portion 16a and concave portion 16b are fitted in with each other with a narrow slit 16c. The slit 16c runs from the front end to the rear end of the bottom 17. An outer wall surface 17a of the bottom 17 of the holder 3 is in contact with and reflow-soldered to the printed wiring board PWB.

A pair of right and left forward tilting prevention portions 17b and 17c extending up to a point facing the weight 8 is formed at the bottom 17, and each of the forward tilting prevention portions 17b and 17c extends in the center line C2 direction up to a position beyond the center of the weight 8. As shown in FIG. 5, each of the forward tilting prevention portions 17b and 17c has a part arranged in the same plane as the bottom 17 and that arranged in the same plane as the flanks 18 and 19 respectively. In this case, material strength such as flexural strength and impact strength can be increased when compared with a case in which the forward tilting prevention portions are formed solely of flat plates. The pair of the forward tilting prevention portions 17b and 17c is symmetrical with respect to the center line C2 of the bottom 17 and a rectangular notch 17d is formed between the pair of the forward tilting prevention portions 17b and 17c. The notch 17d reaches, from the front end of the forward tilting prevention portions 17b and 17c beyond the rear end of the weight 8, a root of the neck 4a of the tubular case 2. As a result, a clearance between the weight 8 and forward tilting prevention portions 17b and 17c can be secured even if the shaft 7 is temporarily bent by receiving an external shock caused by, for example, a fall of the vibration motor 1.

As shown in FIG. 5 to FIG. 9, the holder 3 has front-and-rear pairs of claws 18a, 18b, 19a, and 19b in contact with an outer surface of the tubular case 2 formed on the right and left flanks 18 and 19 respectively, and each of the claws 18a, 18b, 19a, and 19b biases the tubular case 2 toward an inner wall surface 21a of the top 21. The front claws 18a and 19a are provided facing each other on the front side of the flanks 18 and 19, and the rear claws 18b and 19b are provided facing each other on the rear side of the flanks 18 and 19. The front claws 18a and 19a, each consisting of a rectangular piece, are bent from a fixed end on the top 21 side to a free end on the bottom 17 side so as to come closer to each other having a curved shape corresponding to the outer surface of the tubular case 2. Similarly, the rear claws 18b and 19b are bent so as to come closer to each other having the curved shape corresponding to the outer surface of the tubular case 2.

As shown in FIG. 1 to FIG. 4, the tubular case 2 is inserted from the rear end side of the holder 3, and the housing 4 is press-fitted between the four claws 18a, 18b, 19a, and 19b and the inner wall surface 21a of the top 21. Then, the bracket 6 is press-fitted into the rear end of the holder 3 and also the tubular case 2 is press-fitted into the holder 3 until the neck 4a protrudes from the front end of the holder 3. As a result, the tubular case 2 is firmly fixed inside the holder 3. Then, the weight 8 is fixed to the shaft 7. The housing 4 of the tubular case 2 is a metallic cylinder and the holder 3 has a rectangular cross-sectional shape, and thus contact places of the housing 4 and holder 3 will be the claws 18a, 18b, 19a, and 19b and portions of the top 21. Therefore, a contact area will be much smaller when compared with a case in which the whole inner wall surface of the holder 3 is in contact with the tubular case 2. The tubular case 2 is supported by the claws 18a, 18b, 19a, and 19b while being biased toward the inner wall surface 21a of the top 21, resulting in a state in which the tubular case 2 is lifted from the bottom 17. As a result, the radius of rotation of the weight 8 can be made larger than the tubular case 2 as long as not in contact with the bottom 17.

By adopting the aforementioned holder 3, it becomes harder to conduct heat to the tubular case 2 via the holder 3 during reflow-soldering, reducing an influence of heat on the vibration motor 1. Further, the tubular case 2 is lifted from the bottom 17 by the claws 18a, 18b, 19a, and 19b and, as a result, the bottom 17 and tubular case 2 are separated. Therefore, an influence of heat on the vibration motor 1 when reflow-soldering the bottom 17 to the printed wiring board PWB is further reduced.

Further, the vibration motor 1 to which the weight 8 is fixed is placed at a predetermined position on the printed wiring board PWB by a mounting machine. The mounting machine holds the vibration motor 1 by pressing an adsorption nozzle to suck against an outer wall surface 21b of the top 21 of the holder 3 and transports the vibration motor 1 to the predetermined position on the printed wiring board PWB. Since the outer wall surface 21b of the top 21 of the holder 3 is plane, suction by the adsorption nozzle is maintained in an excellent state.

The overall center of gravity of the conventional vibration motor (See Patent Document 1) deviates forward because of a heavy weight and thus the weight side is likely to tilt forward when the vibration motor is placed on a printed wiring board. However, since the pair of the forward tilting prevention portions 17b and 17c is provided on the weight 8 side at the bottom 17 of the holder 3, it is made more difficult for the weight 8 to tilt forward, with the forward tilting prevention portions 17b and 17c acting as a support. As a result, the vibration motor 1 is stabilized on the printed wiring board PWB and can be reliably soldered by reflow-soldering. As a result, solder can be made more unlikely to separate even if the vibration motor 1, incorporated in a portable communication apparatus such as a mobile phone or game machine such as a game controller, receives a dropping impact.

It is also made easier for the holder 3 to broaden outwardly by the slit 16c generated when the holder 3 is formed. However, the slit 16c is provided at the bottom 17 and thus the slit 16c can be arranged on the printed wiring board PWB when mounting the vibration motor 1 on the printed wiring board PWB. Therefore, broadening of the slit 16c can be stopped using solder by soldering the bottom 17 and printed wiring board PWB. Consequently, even when the vibration motor 1 receives a dropping impact, it becomes possible to prevent broadening of the holder 3 and to appropriately avoid the motor part A from protruding from the holder 3.

Further miniaturization of a small motor such as the vibration motor 1 is demanded, while on the other hand, upsizing of the weight 8 is demanded as well. Thus, by providing the notch 17d between the pair of the forward tilting prevention portions 17b and 17c on the center line C1 extending along the bottom 17, the radius of rotation of the weight 8 can be increased by board thickness of the bottom 17. This enables upsizing of the weight 8 in the centrifugal direction. If the radius of rotation of the weight 8 can be increased by board thickness even though the board thickness of the bottom 17 is, for example, less than 0.5 mm, the weight 8 can have extremely large influence on overall vibration by increasing the radius of rotation of the weight 8 only slightly due to smallness of the vibration motor 1. Therefore, the vibration motor 1 is very effective in promoting miniaturization.

Though the above embodiment has been described by assuming that the tubular case 2 is cylindrical, the vibration motor may have a tubular case whose cross section is oval-shaped.

Vibration motors according to the present invention are versatile and can be applied to various kinds of vibration annunciators. As shown in FIG. 10, for example, a wiring board 23 on which the vibration motor 1 is mounted is provided inside a mobile phone 22. Also, as shown in FIG. 11, a wiring board 25 on which the vibration motor 1 is mounted is provided inside a game controller 24, which is an example of game machine.

Claims

1. A vibration motor comprising: a tubular case accommodating a rotor and stator; a shaft protruding from a front end of the case; a weight eccentrically fixed to an end of the shaft; and a metallic holder surrounding the case, the holder being surface-mounted on a wiring board by reflow-soldering, wherein the holder includes a planate bottom placed on the wiring board, and a pair of forward tilting prevention portions that extends up to a position facing the weight is formed on the weight side of the bottom, and whereina notch is provided on a center line extending in parallel with an axis of rotation of the shaft and along the bottom between the forward tilting prevention portions, and the notch extends from the front end of the forward tilting prevention portions beyond the position facing the weight.

2. The vibration motor according to claim 1, wherein a slit extending from an end of the notch in the direction of the center line to a rear end of the bottom is formed at the bottom of the holder.

3. The vibration motor according to claim 1, wherein the holder is formed in a rectangular cross-sectional shape from the bottom, a pair of flanks erected from both sides of the bottom, and a top bridging the flanks, and claws that are in contact with an outer surface of the case and bias the case toward an inner wall surface of the top are provided on the pair of flanks.

4. The vibration motor according to claim 3, wherein the forward tilting prevention portions have the flanks erected continuously from the holder.

5. A communication apparatus comprising a wiring board on which the vibration motor according to claim 1 is mounted.

6. A game machine comprising a wiring board on which the vibration motor according to claim 1 is mounted.

7. A vibration motor comprising: a tubular case accommodating a rotor and stator; a terminal protruding from the case; a shaft protruding from a front end of the case; a weight eccentrically fixed to an end of the shaft; and a metallic holder surrounding the case, the terminal and the holder being surface-mounted on a wiring board by reflow-soldering, wherein, the holder includes a planate bottom placed on the wiring board, and a pair of forward tilting prevention portions that extends up to a position facing the weight is formed on the weight side of the bottom, and whereina notch is provided on a center line extending in parallel with an axis of rotation of the shaft and along the bottom between the forward tilting prevention portions, and the notch extends from the front end of the forward tilting prevention portions beyond the position facing the weight.