Vibration motor and mobile communication apparatus

A vibration motor includes a base portion arranged to extend perpendicularly to a central axis extending in a vertical direction; a magnet portion fixed above the base portion, and arranged to point in the vertical direction; a vibrating portion including a coil portion arranged radially opposite to the magnet portion, and arranged around the magnet portion to vibrate in the vertical direction; a cover portion arranged to cover upper and lateral sides of the magnet portion and the vibrating portion, and fixed to the base portion; an elastic member arranged around the magnet portion between an inner surface of an upper portion of the cover portion and an upper portion of the vibrating portion, and arranged to extend radially inward in a downward direction from the inner surface of the upper portion of the cover portion; at least one adhesive layer fixed to an upper surface of the vibrating portion, and arranged in a circumferential direction below the elastic member; and at least one viscous body in a paste, arranged in the circumferential direction on an upper surface of the at least one adhesive layer, arranged vertically opposite to the elastic member, and including an upper end portion arranged at a level higher than the level of the upper surface of the vibrating portion.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a vibration motor and a mobile communication apparatus.

2. Description of the Related Art

In recent years, vibration motors that cause a vibrating portion to vibrate in a vertical direction through interaction between a coil and a magnet arranged in a radial direction have often been used as silent notification devices in mobile communication apparatuses or the like or for other purposes. In a vibration motor disclosed in US 2012/0169149, a damper 124 is arranged on an upper surface of a weight 122 arranged opposite to an elastic member 125. The damper 124 prevents the weight 122 from making direct contact with the elastic member 125. A reduction in noise caused by a direct contact between the weight 122 and the elastic member 125 is thus achieved.

The vibration motor disclosed in US 2012/0169149 includes the damper 124 as an additional component. Accordingly, the number of components of the vibration motor and the number of steps for assembling the vibration motor increase, and this may result in an increased production cost of the vibration motor. In a common vibration motor, the vibration frequency of a weight is set close to the natural vibration frequency of an elastic member to increase the amount of vibration of the vibration motor. The addition of the damper 124 as mentioned above may cause the vibration frequency of the elastic member 125 to deviate from the natural vibration frequency thereof due to a contact between the elastic member 125 and the damper 124, which may result in a reduction in the amount of vibration. In other words, the contact of the elastic member 125 with the damper 124 may increase unwanted frequency components other than the natural vibration frequency in the vibration of the elastic member 125, which may result in a reduction in the amount of vibration.

SUMMARY OF THE INVENTION

A vibration motor according to a preferred embodiment of the present invention includes a base portion arranged to extend perpendicularly to a central axis extending in a vertical direction; a magnet portion fixed above the base portion, and arranged to point in the vertical direction; a vibrating portion including a coil portion arranged radially opposite to the magnet portion, the vibrating portion being arranged around the magnet portion to vibrate in the vertical direction; a cover portion arranged to cover upper and lateral sides of the magnet portion and the vibrating portion, and fixed to the base portion; an elastic member arranged around the magnet portion between an inner surface of an upper portion of the cover portion and an upper portion of the vibrating portion, and arranged to extend radially inward in a downward direction from the inner surface of the upper portion of the cover portion; at least one adhesive layer fixed to an upper surface of the vibrating portion, and arranged in a circumferential direction below the elastic member; and at least one viscous body in a paste, the at least one viscous body being arranged in the circumferential direction on an upper surface of the at least one adhesive layer, arranged vertically opposite to the elastic member, and including an upper end portion arranged at a level higher than a level of the upper surface of the vibrating portion.

According to the above preferred embodiment of the present invention, the vibration frequency of the elastic member is stabilized to increase the amount of vibration of the vibration motor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

It is assumed herein that a vertical direction is defined as a direction in which a central axis J1of a vibration motor1extends, and that an upper side and a lower side along the central axis J1inFIG. 3are referred to simply as an upper side and a lower side, respectively. It should be noted, however, that the above definitions of the vertical direction and the upper and lower sides are not meant to indicate relative positions or directions of different members or portions when those members or portions are actually installed in a device. Also note that a direction parallel to the central axis J1is referred to by the term “vertical direction”, “vertical”, or “vertically”, that radial directions centered on the central axis J1are simply referred to by the term “radial direction”, “radial”, or “radially”, and that a circumferential direction about the central axis J1is simply referred to by the term “circumferential direction”, “circumferential”, or “circumferentially”.

FIG. 1is a plan view of the vibration motor1according to a first preferred embodiment of the present invention.FIG. 2is a side view of the vibration motor1.FIG. 3is a vertical sectional view of the vibration motor1.FIG. 4is an exploded side view of the vibration motor1.FIG. 5is an exploded perspective view of the vibration motor1. Parallel oblique lines are omitted for sections of details inFIG. 3. InFIG. 3, a state in which a vibrating portion14described below is stationary, without vibrating in a vertical direction, is illustrated. The position of the vibrating portion14inFIG. 3will be hereinafter referred to as a “stationary position”. Also in each ofFIGS. 8,9,10, and11, which are described below, the vibrating portion14is located at the stationary position.

The vibration motor1is a linear resonant actuator (LRA). The vibration motor1is used as, for example, a silent notification device in a mobile communication apparatus, such as a cellular phone. In other words, the vibration motor1is included in the mobile communication apparatus, for example.

The vibration motor1includes a cover portion11and a base portion12. The cover portion11is substantially in the shape of a covered cylinder. The base portion12is arranged to extend perpendicularly to the central axis J1extending in the vertical direction. The cover portion11is fixed to the base portion12. The base portion12is arranged to close a lower opening of the cover portion11. Each of the cover portion11and the base portion12is made of, for example, a metal. The cover portion11and the base portion12are joined to each other through, for example, welding. The base portion12may not necessarily be exactly perpendicular to the central axis J1, but may extend substantially perpendicularly to the central axis J1. In other words, the base portion12is arranged to extend perpendicularly or substantially perpendicularly to the central axis J1.

The base portion12includes a base projecting portion121arranged to extend substantially perpendicularly to the central axis J1. The base projecting portion121is arranged to project radially outward from the cover portion11. A plurality of cuts111each of which extends in a circumferential direction are defined at a lower edge of the cover portion11. The base projecting portion121is arranged to project radially outward from one of the cuts111. In other words, a radially inner end portion of the base projecting portion121is arranged in one of the cuts111. The plurality of cuts111defined in the cover portion11make it easy to align the base projecting portion121with one of the cuts111when fixing the base portion12to the cover portion11.

The vibration motor1includes a magnet portion13, the vibrating portion14, an elastic member15, a circuit board16, an adhesive layer71, and a viscous body72. The magnet portion13is a substantially columnar member centered on the central axis J1. The magnet portion13is defined by a single monolithic member. The magnet portion13is fixed above the base portion12, and is arranged to point in the vertical direction. For example, a lower end portion of the magnet portion13is fixed to an upper surface, i.e., an inner surface, of the base portion12through an adhesive or the like. Alternatively, an upper end portion of the magnet portion13may be fixed to a lower surface of a top cover portion of the cover portion11, i.e., an inner surface of an upper portion of the cover portion11, through an adhesive or the like.

The vibrating portion14is a substantially cylindrical member centered on the central axis J1. The vibrating portion14is arranged to extend all the way around the magnet portion13. The vibrating portion14is arranged to have an inside diameter greater than the outside diameter of the magnet portion13. The vibrating portion14is arranged to vibrate in the vertical direction along the magnet portion13without making contact with the magnet portion13. Upper and lateral sides of the magnet portion13and the vibrating portion14are covered with the cover portion11.

The vibrating portion14includes a coil portion41, a mass portion42, and a yoke43. The coil portion41is a substantially cylindrical member centered on the central axis J1. The coil portion41is arranged radially opposite to the magnet portion13. An inner circumferential surface of the coil portion41is arranged radially opposite to an outer circumferential surface of the magnet portion13with a predetermined gap therebetween.

The yoke43includes a cylindrical portion431and a flange portion432. The cylindrical portion431is substantially cylindrical, and is centered on the central axis J1. The flange portion432is substantially in the shape of a circular ring, and is centered on the central axis J1. The flange portion432is arranged to extend radially outward from a lower end portion of the cylindrical portion431. The cylindrical portion431and the flange portion432are defined by a single continuous monolithic member. The yoke43is arranged radially outside of the coil portion41. An inner circumferential surface of the cylindrical portion431is fixed to an outer circumferential surface of the coil portion41. The cylindrical portion431is fixed to the coil portion41through an adhesive, for example. The flange portion432may alternatively be arranged to extend radially outward from an upper end portion of the cylindrical portion431, for example, or may not be provided.

The mass portion42is a substantially cylindrical member centered on the central axis J1. The mass portion42is a so-called weight. The mass portion42is arranged radially outside of the cylindrical portion431of the yoke43and the coil portion41. An inner circumferential surface of the mass portion42is fixed to an outer circumferential surface of the cylindrical portion431of the yoke43. An upper surface of the flange portion432of the yoke43is arranged to be in contact with a lower surface of the mass portion42. The mass portion42is fixed to the yoke43through, for example, an adhesive or a double-sided tape, or through press fitting. The mass portion42is indirectly fixed to the coil portion41with the yoke43therebetween.

The elastic member15is arranged around the magnet portion13between the inner surface of the upper portion of the cover portion11and an upper portion of the vibrating portion14. The elastic member15is a member capable of elastically deforming in the vertical direction through application of a vertical force. The elastic member15is, for example, defined by a plate-shaped spring material wound in a spiral shape. The elastic member15is, for example, defined by a volute spring the external shape of which is substantially a truncated cone. The elastic member15is arranged to extend radially inward in a downward direction from the inner surface of the upper portion of the cover portion11. In other words, the elastic member15has an external shape projecting downward with decreasing distance from the central axis J1. An upper end portion of the elastic member15is fixed to the lower surface of the top cover portion of the cover portion11, i.e., the inner surface of the upper portion of the cover portion11. The upper end portion of the elastic member15is fixed to the cover portion11through welding, for example. A lower end portion of the elastic member15is fixed to an upper surface44of the vibrating portion14. The lower end portion of the elastic member15is fixed to an upper surface of the mass portion42through welding, for example.

The adhesive layer71is fixed to the upper surface44of the vibrating portion14. The adhesive layer71is arranged to extend in the circumferential direction below the elastic member15. In other words, the adhesive layer71is arranged vertically opposite to the elastic member15. In the preferred embodiment illustrated inFIGS. 3 to 5, the adhesive layer71is annular. The adhesive layer71is arranged on an annular recessed portion441defined in the upper surface44of the vibrating portion14. Each of the adhesive layer71and the recessed portion441is, for example, substantially in the shape of a circular ring, and is centered on the central axis J1. The recessed portion441is defined in, for example, the upper surface of the mass portion42.

In the preferred embodiment illustrated inFIGS. 3 to 5, an upper portion of the adhesive layer71is arranged at a level higher than the level of a portion of the upper surface44of the vibrating portion14which surrounds the recessed portion441. An upper surface711of the adhesive layer71is entirely arranged at a level higher than the level of a portion of the upper surface44of the vibrating portion14which surrounds the adhesive layer71, for example. The upper surface711of the adhesive layer71is arranged to be convex upward over the entire radial extent thereof. In addition, the upper surface711of the adhesive layer71is arranged to have a substantially identical shape over 360 degrees in the circumferential direction. The upper surface711of the adhesive layer71may be convex upward practically over the entire radial extent thereof. In other words, the upper surface711of the adhesive layer71is arranged to be convex upward over substantially the entire radial extent thereof. The upper surface711of the adhesive layer71is arranged to have a curvature continuously varying in a radial direction. For example, the curvature of the upper surface711of the adhesive layer71gradually decreases radially outward from a radially inner end of the upper surface711to an upper end of the upper surface711, and gradually increases radially outward from the upper end of the upper surface711to a radially outer end of the upper surface711.

The adhesive layer71is defined by, for example, applying an adhesive in an uncured state to the recessed portion441in such a manner that the adhesive will rise above the upper surface44of the vibrating portion14inside the recessed portion441, and curing the adhesive. The adhesive layer71is defined by, for example, applying the adhesive to the vibrating portion14only once.

The viscous body72is in a paste, having viscosity. The viscous body72is, for example, grease. Note that the viscous body72may be a material other than grease as long as the material is in a paste having viscosity. The viscous body72is arranged to extend in the circumferential direction on the upper surface711of the adhesive layer71. The viscous body72has a relatively high viscosity, so high as to maintain the shape of the viscous body72on the adhesive layer71when no external force is applied to the viscous body72. In the preferred embodiment illustrated inFIGS. 3 to 5, the viscous body72is annular. The viscous body72is, for example, substantially in the shape of a circular ring, and is centered on the central axis J1.

The viscous body72is arranged below the elastic member15. In other words, the viscous body72is arranged vertically opposite to the elastic member15. An upper end portion of the viscous body72is arranged at a level higher than the level of the upper surface44of the vibrating portion14. In the preferred embodiment illustrated inFIGS. 3 to 5, the viscous body72is arranged on an upper end portion of the upper surface711of the adhesive layer71.

The circuit board16is arranged to supply an electric current from a power source to the coil portion41. The circuit board16is a flexible substrate including a flexible printed circuit (FPC). The circuit board16is relatively thin and soft. The circuit board16is arranged between the base portion12and the vibrating portion14, and is fixed to the upper surface of the base portion12and a lower surface of the vibrating portion14. The circuit board16is fixed to each of the base portion12and the vibrating portion14through, for example, an adhesive.

In the vibration motor1, once the electric current is passed in the coil portion41through the circuit board16, a magnetic field is generated around the coil portion41and the yoke43. This magnetic field and a magnetic field around the magnet portion13together generate forces that cause the vibrating portion14to move in the vertical direction. The forces that cause the vibrating portion14to move in the vertical direction will be hereinafter referred to as “vibrating forces”. The vibrating portion14is supported by the elastic member15in the vertical direction, and accordingly vibrates in the vertical direction through forces received from the magnetic fields and resilience of the elastic member15.

When the vibrating portion14vibrates in the vertical direction, the elastic member15expands and contracts in the vertical direction. When the vibrating portion14moves upward above the stationary position to compress the elastic member15, the vertical distance between the upper surface44of the vibrating portion14and a lower surface of the elastic member15is reduced at a radial position where the adhesive layer71is provided as illustrated inFIG. 6. This causes the elastic member15to make contact with the viscous body72on the adhesive layer71. The viscous body72on the adhesive layer71is deformed as a result of a contact with the elastic member15. In addition, the elastic member15makes contact with the upper surface711of the adhesive layer71as well.

Specifically, the elastic member15includes a “viscous body opposed portion”51arranged vertically opposite to the viscous body72, and a radially inner portion of the viscous body opposed portion51makes contact with the upper surface711of the adhesive layer71. As a result, a gap is maintained between the elastic member15and the upper surface711of the adhesive layer71over a region radially outside of an area of contact between the viscous body opposed portion51and the adhesive layer71. This allows the viscous body72to be held in the gap without being scattered radially outward by being compressed by the elastic member15.

As illustrated inFIG. 7, when the vibrating portion14moves downward thereafter, a portion of the viscous body72on the adhesive layer71sticks to the elastic member15, and separates upward from the viscous body72on the adhesive layer71together with the elastic member15. In the vibration motor1, as the vertical movement of the vibrating portion14is repeated, portions of the viscous body72on the adhesive layer71move to the elastic member15one after another. In other words, as the vibrating portion14vibrates, portions of the viscous body72are intermittently supplied from the vibrating portion14to the elastic member15.

As described above, the vibration motor1includes the cover portion11, the base portion12, the magnet portion13, the vibrating portion14, the elastic member15, the adhesive layer71, and the viscous body72. The base portion12is arranged to extend perpendicularly to the central axis J1extending in the vertical direction. The magnet portion13is fixed above the base portion12, and is arranged to point in the vertical direction. The vibrating portion14includes the coil portion41arranged radially opposite to the magnet portion13. The vibrating portion14is arranged around the magnet portion13, and vibrates in the vertical direction. The cover portion11covers the upper and lateral sides of the magnet portion13and the vibrating portion14, and is fixed to the base portion12. The elastic member15is arranged around the magnet portion13between the inner surface of the upper portion of the cover portion11and the upper portion of the vibrating portion14. The elastic member15is arranged to extend radially inward in the downward direction from the inner surface of the upper portion of the cover portion11. The adhesive layer71is fixed to the upper surface of the vibrating portion14, and is arranged to extend in the circumferential direction below the elastic member15. The viscous body72is arranged to extend in the circumferential direction on the upper surface of the adhesive layer71, and is arranged vertically opposite to the elastic member15. The viscous body72is in a paste. The upper end portion of the viscous body72is arranged at a level higher than the level of the upper surface44of the vibrating portion14.

In the vibration motor1, a portion of the viscous body72sticks to the elastic member15when the elastic member15approaches and makes indirect contact with the vibrating portion14. Accordingly, vibration at an unwanted frequency component that is caused in the elastic member15by the indirect contact of the elastic member15with the vibrating portion14, e.g., vibration at a frequency component other than a natural vibration frequency, is absorbed by elastic action of the viscous body72. In other words, the sticking of a portion of the viscous body72to the elastic member15reduces variations in vibration frequency components of the elastic member15caused by the indirect contact of the elastic member15with the vibrating portion14, leading to stabilizing the vibration frequency of the elastic member15. This allows the vibrating portion14to vibrate at a desired vibration frequency to increase the amount of vibration of the vibration motor1. The desired vibration frequency is, for example, a natural vibration frequency of the elastic member15. Note that, although the sticking of portions of the viscous body72to the elastic member15also reduces vibration at the above desired frequency component to some degree, the reduction of the vibration at the unwanted frequency component results in a greater proportion of the desired frequency component in all frequency components. This leads to an increased amount of vibration of the vibration motor1as mentioned above.

In addition, in the vibration motor1, when the elastic member15is compressed, the elastic member15makes contact with the adhesive layer71, and this prevents or reduces the likelihood of a direct contact between the elastic member15and the vibrating portion14. This contributes to preventing noise caused by a collision between the elastic member15and the vibrating portion14. Moreover, compared to the case where a damper separate from the vibrating portion14is fitted onto the vibrating portion14to prevent a direct contact between the elastic member15and the vibrating portion14, a reduction in the number of parts of the vibration motor1and a reduction in the number of steps for assembling the vibration motor1are achieved. This contributes to preventing or reducing an increase in the production cost of the vibration motor1.

In the vibration motor1, the upper surface711of the adhesive layer71is arranged to be convex upward over the entire radial extent thereof. In addition, the viscous body72is arranged on the upper end portion of the upper surface711of the adhesive layer71. This allows the gap to be maintained between the elastic member15and the upper surface711of the adhesive layer71over the region radially outside of the area of contact between the elastic member15and the adhesive layer71. In other words, an excessive contact between the elastic member15and the viscous body72is prevented. This contributes to preventing the viscous body72from being scattered radially outward by being compressed by the elastic member15, and maintaining appropriate holding of the viscous body72on the adhesive layer71.

As mentioned above, the adhesive layer71is annular, and the viscous body72is also annular. This allows the viscous body72on the adhesive layer71to easily stick to the elastic member15at at least one position in the circumferential direction. This contributes to more securely causing the viscous body72on the adhesive layer71to stick to the elastic member15.

In addition, the adhesive layer71is arranged on the annular recessed portion441defined in the upper surface44of the vibrating portion14. This allows the adhesive layer71to be easily defined on the vibrating portion14. Further, the adhesive layer71can be arranged on the vibrating portion14with high positional precision.

FIG. 8is a vertical sectional view illustrating a vibration motor1aaccording to a second preferred embodiment of the present invention. The vibration motor1ais similar in structure to the vibration motor1, and is different from the vibration motor1illustrated inFIG. 3only in the shape of an adhesive layer71and the arrangement of a viscous body72. In the following description, members or portions of the vibration motor1athat have their equivalents in the vibration motor1will be designated by the same reference numerals as those of their equivalents in the vibration motor1.

The adhesive layer71of the vibration motor1aincludes an adhesive lower portion73and a projecting portion74. The adhesive lower portion73is fixed to an upper surface44of a vibrating portion14. The adhesive lower portion73is arranged, for example, inside an annular recessed portion441defined in the upper surface44of the vibrating portion14. The adhesive lower portion73includes an upper surface extending perpendicularly to a central axis J1. The upper surface of the adhesive lower portion73may not necessarily be exactly perpendicular to the central axis J1, but may be substantially perpendicular to the central axis J1. In other words, the adhesive lower portion73includes an upper surface extending perpendicularly or substantially perpendicularly to the central axis J1. The upper surface of the adhesive lower portion73is arranged, for example, at a level the same or substantially the same as the level of a portion of the upper surface44of the vibrating portion14which surrounds the adhesive lower portion73. The projecting portion74is arranged to project upward from the adhesive lower portion73. The viscous body72is arranged on an upper end portion of the projecting portion74. Each of the adhesive lower portion73and the projecting portion74is arranged to extend in the circumferential direction below an elastic member15. In other words, each of the adhesive lower portion73and the projecting portion74is arranged vertically opposite to the elastic member15. In the preferred embodiment illustrated inFIG. 8, each of the adhesive lower portion73and the projecting portion74is annular.

In the vibration motor1a, the adhesive lower portion73is defined by applying an adhesive in an uncured state inside the recessed portion441and curing the adhesive, and the projecting portion74is defined by applying an adhesive in an uncured state onto the adhesive lower portion73and curing the adhesive, for example. The adhesive layer71of the vibration motor1ais defined by applying the adhesive to the vibrating portion14twice, for example.

When the vibrating portion14moves upward above the stationary position to compress the elastic member15, the elastic member15makes contact with the viscous body72on the adhesive layer71. In addition, the elastic member15makes contact with the projecting portion74of the adhesive layer71as well. This allows a gap to be maintained between the elastic member15and an upper surface711of the adhesive layer71over a region radially outside of an area of contact between the elastic member15and the projecting portion74. The viscous body72is thus held in the gap without being scattered radially outward by being compressed by the elastic member15.

In the vibration motor1a, as in the vibration motor1illustrated inFIG. 3, when the elastic member15makes indirect contact with the vibrating portion14, a portion of the viscous body72sticks to the elastic member15. This leads to stabilizing the vibration frequency of the elastic member15. This allows the vibrating portion14to vibrate at a desired vibration frequency to increase the amount of vibration of the vibration motor1a.

In the vibration motor1a, the adhesive layer71includes the adhesive lower portion73and the projecting portion74. The adhesive lower portion73includes the upper surface extending perpendicularly to the central axis J1. The projecting portion74is arranged to project upward from the adhesive lower portion73. The viscous body72is arranged on the upper end portion of the projecting portion74. In the vibration motor1a, the elastic member15makes contact with the projecting portion74over a region radially inside of the viscous body72, and this contributes to preventing the viscous body72from being scattered by an excessive contact between the elastic member15and the viscous body72. This in turn contributes to maintaining appropriate holding of the viscous body72on the adhesive layer71. In addition, the amount of the adhesive used to define the adhesive layer71can be reduced.

FIG. 9is a vertical sectional view illustrating a vibration motor1baccording to a third preferred embodiment of the present invention. The vibration motor1bis similar in structure to the vibration motor1a, and is different from the vibration motor1aillustrated inFIG. 8only in the shape of an adhesive layer71and the arrangement of a viscous body72. In the following description, members or portions of the vibration motor1bthat have their equivalents in the vibration motor1awill be designated by the same reference numerals as those of their equivalents in the vibration motor1a.

The adhesive layer71of the vibration motor1bincludes an adhesive lower portion73and an outer projecting portion75. The adhesive lower portion73is similar in structure to the adhesive lower portion73of the vibration motor1aillustrated inFIG. 8, and includes an upper surface extending perpendicularly to a central axis J1. The upper surface of the adhesive lower portion73may not necessarily be exactly perpendicular to the central axis J1, but may be substantially perpendicular to the central axis J1. In other words, the adhesive lower portion73includes an upper surface extending perpendicularly or substantially perpendicularly to the central axis J1. The outer projecting portion75is arranged to project upward from the adhesive lower portion73. The viscous body72is arranged radially inside of the outer projecting portion75and in contact with the outer projecting portion75. Each of the adhesive lower portion73and the outer projecting portion75is arranged to extend in the circumferential direction below an elastic member15. In other words, each of the adhesive lower portion73and the outer projecting portion75is arranged vertically opposite to the elastic member15. In the preferred embodiment illustrated inFIG. 9, each of the adhesive lower portion73and the outer projecting portion75is annular.

In the vibration motor1b, the adhesive lower portion73is defined by applying an adhesive in an uncured state inside a recessed portion441and curing the adhesive, and the outer projecting portion75is defined by applying an adhesive in an uncured state onto the adhesive lower portion73and curing the adhesive, for example. The adhesive layer71of the vibration motor1bis defined by applying the adhesive to a vibrating portion14twice, for example.

When the vibrating portion14moves upward above the stationary position to compress the elastic member15, the elastic member15makes contact with the viscous body72on the adhesive layer71. In addition, the elastic member15makes contact with the outer projecting portion75of the adhesive layer71as well. This allows a gap to be maintained between the elastic member15and an upper surface711of the adhesive layer71over a region radially inside of an area of contact between the elastic member15and the outer projecting portion75. The viscous body72is thus held in the gap without being compressed by the elastic member15. The viscous body72is arranged radially inside of and in contact with the outer projecting portion75, and this prevents or reduces the likelihood of a radially outward movement of the viscous body72caused by a contact with the elastic member15.

In the vibration motor1b, as in the vibration motor1illustrated inFIG. 3, when the elastic member15makes indirect contact with the vibrating portion14, a portion of the viscous body72sticks to the elastic member15. This leads to stabilizing the vibration frequency of the elastic member15. This allows the vibrating portion14to vibrate at a desired vibration frequency to increase the amount of vibration of the vibration motor1b.

The adhesive layer71of the vibration motor1bincludes the adhesive lower portion73and the outer projecting portion75. The adhesive lower portion73includes the upper surface extending perpendicularly to the central axis J1. The outer projecting portion75is arranged to project upward from the adhesive lower portion73. The viscous body72is arranged radially inside of the outer projecting portion75and in contact with the outer projecting portion75. In the vibration motor1b, the elastic member15makes contact with the outer projecting portion75, and this contributes to preventing the viscous body72from being scattered by an excessive contact between the elastic member15and the viscous body72. In addition, a radially outward movement of the viscous body72caused by a contact with the elastic member15can be prevented, or the likelihood thereof can be reduced. This in turn contributes to maintaining appropriate holding of the viscous body72on the adhesive layer71. Further, the amount of the adhesive used to define the adhesive layer71can be reduced.

FIG. 10is a vertical sectional view illustrating a vibration motor1caccording to a fourth preferred embodiment of the present invention. The vibration motor1cis similar in structure to the vibration motor1a, and is different from the vibration motor1aillustrated inFIG. 8only in the shape of an adhesive layer71and the arrangement of a viscous body72. In the following description, members or portions of the vibration motor1cthat have their equivalents in the vibration motor1awill be designated by the same reference numerals as those of their equivalents in the vibration motor1a.

The adhesive layer71of the vibration motor1cincludes an adhesive lower portion73and an inner projecting portion76. The adhesive lower portion73is similar in structure to the adhesive lower portion73of the vibration motor1aillustrated inFIG. 8, and includes an upper surface extending perpendicularly to a central axis J1. The upper surface of the adhesive lower portion73may not necessarily be exactly perpendicular to the central axis J1, but may be substantially perpendicular to the central axis J1. In other words, the adhesive lower portion73includes an upper surface extending perpendicularly or substantially perpendicularly to the central axis J1. The inner projecting portion76is arranged to project upward from the adhesive lower portion73. The viscous body72is arranged radially outside of the inner projecting portion76and in contact with the inner projecting portion76. Each of the adhesive lower portion73and the inner projecting portion76is arranged to extend in the circumferential direction below an elastic member15. In other words, each of the adhesive lower portion73and the inner projecting portion76is arranged vertically opposite to the elastic member15. In the preferred embodiment illustrated inFIG. 10, each of the adhesive lower portion73and the inner projecting portion76is annular.

In the vibration motor1c, the adhesive lower portion73is defined by applying an adhesive in an uncured state inside a recessed portion441and curing the adhesive, and the inner projecting portion76is defined by applying an adhesive in an uncured state onto the adhesive lower portion73and curing the adhesive, for example. The adhesive layer71of the vibration motor1cis defined by applying the adhesive to a vibrating portion14twice, for example.

When the vibrating portion14moves upward above the stationary position to compress the elastic member15, the elastic member15makes contact with the viscous body72on the adhesive layer71. In addition, the elastic member15makes contact with the inner projecting portion76of the adhesive layer71as well. This allows a gap to be maintained between the elastic member15and an upper surface711of the adhesive layer71over a region radially outside of an area of contact between the elastic member15and the inner projecting portion76. The viscous body72is thus held in the gap without being compressed by the elastic member15.

In the vibration motor1c, as in the vibration motor1illustrated inFIG. 3, when the elastic member15makes indirect contact with the vibrating portion14, a portion of the viscous body72sticks to the elastic member15. This leads to stabilizing the vibration frequency of the elastic member15. This allows the vibrating portion14to vibrate at a desired vibration frequency to increase the amount of vibration of the vibration motor1c.

The adhesive layer71of the vibration motor1cincludes the adhesive lower portion73and the inner projecting portion76. The adhesive lower portion73includes the upper surface extending perpendicularly to the central axis J1. The inner projecting portion76is arranged to project upward from the adhesive lower portion73. The viscous body72is arranged radially outside of the inner projecting portion76and in contact with the inner projecting portion76. In the vibration motor1c, the elastic member15makes contact with the inner projecting portion76, and this contributes to preventing the viscous body72from being scattered by an excessive contact between the elastic member15and the viscous body72. This in turn contributes to maintaining appropriate holding of the viscous body72on the adhesive layer71. In addition, the amount of the adhesive used to define the adhesive layer71can be reduced.

FIG. 11is a vertical sectional view illustrating a vibration motor1daccording to a fifth preferred embodiment of the present invention. The vibration motor1dis similar in structure to the vibration motor1billustrated inFIG. 9except that an adhesive layer71further includes an inner projecting portion76. In the following description, members or portions of the vibration motor1dthat have their equivalents in the vibration motor1bwill be designated by the same reference numerals as those of their equivalents in the vibration motor1b.

The adhesive layer71of the vibration motor1dincludes an adhesive lower portion73, an outer projecting portion75, and the inner projecting portion76. The inner projecting portion76is similar in structure to the inner projecting portion76of the vibration motor1cillustrated inFIG. 10, and is arranged to project upward from the adhesive lower portion73. An upper end portion of the inner projecting portion76is arranged at a level lower than the level of an upper end portion of the outer projecting portion75, for example. The outer projecting portion and the inner projecting portion76are arranged to be concentric, with a central axis J1as a center. A viscous body72is arranged radially inside of the outer projecting portion75and radially outside of the inner projecting portion76. In other words, the viscous body72is arranged between the outer projecting portion75and the inner projecting portion76. The viscous body72is arranged to be in contact with both the outer projecting portion75and the inner projecting portion76.

In the vibration motor1d, the adhesive lower portion73is defined by applying an adhesive in an uncured state inside a recessed portion441and curing the adhesive, and the outer projecting portion75is defined by applying an adhesive in an uncured state onto the adhesive lower portion73and curing the adhesive, for example. In addition, the inner projecting portion76is defined by applying an adhesive in an uncured state onto the adhesive lower portion73and curing the adhesive. The adhesive layer71of the vibration motor1dis defined by applying the adhesive to a vibrating portion14three times, for example.

When the vibrating portion14moves upward above the stationary position to compress an elastic member15, the elastic member15makes contact with the viscous body72on the adhesive layer71. In addition, the elastic member15makes contact with the inner projecting portion76of the adhesive layer71as well. This allows a gap to be maintained between the elastic member15and an upper surface711of the adhesive layer71over a region radially outside of an area of contact between the elastic member15and the inner projecting portion76. The viscous body72is thus held in the gap without being compressed by the elastic member15. In addition, the viscous body72is arranged radially inside of and in contact with the outer projecting portion75, and this prevents or reduces the likelihood of a radially outward movement of the viscous body72caused by a contact with the elastic member15. The elastic member15may make contact with the outer projecting portion75, or may make contact with both the inner projecting portion76and the outer projecting portion75.

In the vibration motor1d, as in the vibration motor1illustrated inFIG. 3, when the elastic member15makes indirect contact with the vibrating portion14, a portion of the viscous body72sticks to the elastic member15. This leads to stabilizing the vibration frequency of the elastic member15. This allows the vibrating portion14to vibrate at a desired vibration frequency to increase the amount of vibration of the vibration motor1d. In the vibration motor1d, the elastic member15makes contact with at least one of the outer projecting portion75and the inner projecting portion76, and this contributes to preventing the viscous body72from being scattered by an excessive contact between the elastic member15and the viscous body72. In addition, the outer projecting portion75prevents or reduces the likelihood of a radially outward movement of the viscous body72caused by a contact with the elastic member15. This contributes to maintaining appropriate holding of the viscous body72on the adhesive layer71. Further, the amount of the adhesive used to define the adhesive layer71can be reduced.

In the vibration motor1, each of the adhesive layer71and the viscous body72may not necessarily be annular as long as at least one adhesive layer71is arranged in the circumferential direction and at least one viscous body72is arranged in the circumferential direction. The recessed portion441defined in the upper surface44of the vibrating portion14may not necessarily be annular, either. The same is true of each of the vibration motors1ato1d.

FIG. 12is a plan view illustrating a vibrating portion14, adhesive layers71, and viscous bodies72of a vibration motor according to another preferred embodiment of the present invention. As illustrated inFIG. 12, a plurality of recessed portions441discontinuous in the circumferential direction are defined in an upper surface44of the vibrating portion14, and the adhesive layer71is arranged on each of the plurality of recessed portions441. In the preferred embodiment illustrated inFIG. 12, the adhesive layers71are arranged discontinuously in the circumferential direction, and the viscous bodies72are arranged discontinuously in the circumferential direction on the adhesive layers71. This contributes to reducing the amount of the adhesive used to define the adhesive layer(s)71, and the amount of the viscous bod(ies)72used.

InFIG. 12, each of the recessed portions441, the adhesive layers71, and the viscous bodies72is circular or substantially circular in a plan view. Note, however, that the shape of each of the recessed portions441, the adhesive layers71, and the viscous bodies72may be modified in various manners. Also note that the number of recessed portions441, the number of adhesive layers71, and the number of viscous bodies72are not limited to four, but may be modified in various manners. In the vibration motor1, the viscous bodies72may be arranged discontinuously in the circumferential direction on the annular adhesive layer71on the annular recessed portion441defined in the upper surface44of the vibrating portion14. The same is true of each of the vibration motors1ato1d.

Note that each of the vibration motors1and1ato1ddescribed above may be modified in various manners.

In the vibration motor1illustrated inFIGS. 1 to 5, the elastic member15may be in contact with the viscous body72on the adhesive layer71in a situation in which the vibrating portion14is located at the stationary position illustrated inFIG. 3. In this case, the area of contact between the elastic member15and the viscous body on the adhesive layer71increases as the vibrating portion14moves upward above the stationary position. When the vibrating portion14moves downward thereafter, a portion of the viscous body72on the adhesive layer71sticks to the elastic member15, and separates upward from the viscous body72on the adhesive layer71together with the elastic member15. The same is true of each of the vibration motors1ato1dillustrated inFIGS. 8 to 11, respectively.

The magnet portion13may not necessarily be defined by a single monolithic member. The magnet portion13may alternatively include, for example, two substantially columnar magnets each of which points in the vertical direction, and a pole piece arranged between the two magnets.

The structure and shape of each of the vibrating portion14and the elastic member15may be modified appropriately. For example, the yoke43may be omitted from the vibrating portion14with the coil portion41directly fixed to the inner circumferential surface of the mass portion42. Also note that the recessed portion441may not necessarily be defined in the upper surface44of the vibrating portion14. For example, the upper surface44may be flat, and the adhesive layer71may be fixed on the flat upper surface44.

Fitting and fixing of the members of each of the vibration motors1and1ato1dmay be achieved indirectly. For example, the elastic member15may be fixed to the cover portion11with another member intervening therebetween, and the cover portion11and the base portion12may be fixed to each other with another member intervening therebetween.

Vibration motors according to preferred embodiments of the present invention may be used for various purposes. Vibration motors according to preferred embodiments of the present invention are preferably used as silent notification devices in mobile communication apparatuses, such as, for example, cellular phones.