Production method of vibrating motor and rotor for vibrating motor

A vibrating motor has a shaft, a stator including a yoke having pole teeth extending toward an axis of the shaft from an inner circumference and coils wound around the pole teeth, a rotor including an eccentric weight formed on a radially outer surface of the shaft, and a permanent magnet integrally formed with the eccentric weight, and a bearing device rotatably supporting the rotor maintaining clearance between the inner circumference of the pole teeth and the rotor. The rotor has a structure in which the shaft, the eccentric weight, and the permanent magnet are integrally formed with each other by a thermoplastic magnetic material composing the permanent magnet.

RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119 to Japanese Patent Application Nos. 2010-012945 filed on Jan. 25, 2010 and 2010-167930 filed on Jul. 27, 2010, the entire contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a production method for a vibrating motor and a rotor for a vibrating motor having a specific structure for fixing an eccentric weight.

2. Related Art

Some kinds of inner rotor type vibrating motors having a permanent magnet are used in products such as portable telephones. For example, Japanese patent application, First Publication No. 2008-271719 discloses a structure of a vibrating motor having a rotor composed of an axially eccentric weight and a permanent magnet. The vibrating motor includes a stator radially outwardly separated from the rotor for generating power for rotation and having a driving coil and a yoke.

Japanese patent application, First Publication No. 11-299148 discloses a production method for the rotor, including inserting an annular nonmagnetic material and a permanent magnetic material into a mold, injecting a resin such as a thermoplastic into the mold and integrally forming the resin, the annular nonmagnetic material, and the permanent magnet. A method in which a shaft is fixed to an eccentric weight by an adhesive is provided.

SUMMARY OF THE INVENTION

In the production method in which the rotor, including inserting an annular diamagnetic material and a permanent magnetic material into a mold, injecting resins such as thermoplastics into the mold and integrally forming the resins, the annular diamagnetic material and a permanent magnet, the number of parts is not easily reduced. In the method in which a shaft is fixed to an eccentric weight by adhesives, since a clearance for adhesives is necessary, accuracy such as coaxial accuracy of a rotor is limited. According to conventional production methods, a rotor for a vibrating motor requires many steps for production, and production costs for the rotor are not reduced. Therefore, an object of a present invention is to provide a rotor having high coaxial accuracy for a vibrating motor, which can be obtained by simplified processes.

The present invention provides a vibrating motor, including a yoke having pole teeth extending toward an axis thereof on an inner circumference, a stator having coils wound around the pole teeth, a shaft, an eccentric weight axially arranged, a rotor having a permanent magnet integrally formed with the eccentric weight, a bearing rotatably supporting the rotor with predetermined clearance in an axial inner surface of the pole teeth of the stator. In a vibrating motor the rotor has a structure in which the shaft, the eccentric weight and the permanent magnet are integrally formed by a thermoplastic magnetic material composing the permanent magnet.

According to a first aspect of the present invention, since the rotor of the vibrating motor is integrally formed of thermoplastic materials composing a permanent magnet, the rotor can be produced in fewer steps. The rotor has a structure in which the shaft, the eccentric weight and the permanent magnet are integrally formed, and therefore a rotor that can have high coaxial accuracy is provided for a vibrating motor.

According to a second aspect of the present invention, the rotor is formed by insertion molding of a thermoplastic material composing the permanent magnet in such a way that the shaft and the eccentric weight are disposed as insertion materials.

According to the second aspect of the present invention, the rotor has a structure in which the thermoplastic magnetic material is inserted into a mold (a die), in such a way the shaft and the eccentric weight are disposed as insertion materials therein, and therefore the rotor can have high coaxial accuracy and fewer steps for production.

According to a third aspect of the present invention, an outermost axial length excluding that of the shaft of the rotor is smaller than an outermost radial length of the rotor.

According to a fourth another aspect of the present invention, the eccentric weight is extended up to an outer surface of the permanent magnet.

According to a fifth aspect of the present invention, the concavity is formed in a peripheral portion of the shaft in the eccentric weight, and a part of the bearing is disposed in the concavity.

According to a sixth aspect of the present invention, a portion in which the shaft is connected to the eccentric weight is composed of the thermoplastic magnetic material composing the permanent magnet. According to this aspect, the shaft and the eccentric weight are not directly connected but are connected with the thermoplastic material as an insertion material.

According to a seventh aspect of the present invention, a connecting portion has a cylindrical shape and is connected to the shaft on an inner surface thereof, and a gap between the eccentric weight and the shaft is filled by the thermoplastic magnetic material composing the permanent magnet. According to this feature, error in positioning of the shaft and the eccentric weight and error in accuracy of dimensions of the eccentric weight are compensated by the thermoplastic magnetic material.

According to an eighth aspect of the present invention, a shape of the connecting portion when viewed from an axial direction is polygonal.

According to a ninth aspect of the present invention, the eccentric weight overlaps with the pole teeth when viewed from the axial direction.

According to a tenth aspect of the present invention, the eccentric weight overlaps with the coil when viewed from the axial direction.

According to an eleventh aspect of the present invention, a portion at which the eccentric weight overlaps the pole teeth when viewed from the axial direction is formed on both surfaces of the eccentric weight.

According to a twelfth aspect of the present invention, a portion at which the eccentric weight overlaps the coil when viewed from the axial direction, is formed on both surfaces of the eccentric weight

The present invention provides a production method for a rotor for a vibrating motor in which a shaft, an eccentric weight, and a permanent magnet are integrally formed, the method including: disposing the shaft and the eccentric weight in a mold; and injecting the thermoplastic magnetic material composing a permanent magnet into the mold.

According to the first aspect of the present invention, the rotor is integrally formed by the thermoplastic magnetic material composing the permanent magnet, whereby the vibrating motor having high coaxial accuracy is obtained and the number of steps for production is reduced.

According to the second aspect of the present invention, the motor having a high accuracy in positioning between the shaft and the eccentric weight is provided.

According to the third aspect of the present invention, the vibrating motor that is axially thin and easily installed into a portable electronic device is provided.

According to the fourth aspect of the present invention, in the vibrating motor, radial mass unbalance of the rotor can be increased by increased radial mass of the outer portion, whereby high performance for vibration can be obtained.

According to the fifth aspect of the present invention, since the bearing of the shaft can be disposed in an axially inner portion of the eccentric weight, the vibrating motor can be thin

According to the sixth aspect of the present invention, since an error in positioning between the shaft and the eccentric weight and an error in accuracy of size of the eccentric weight are compensated by the material composing the permanent magnet, the rotor can obtain high coaxial accuracy.

According to the seventh aspect of the present invention, since the error in positioning between the shaft and the eccentric weight and the error in accuracy of size of the eccentric weight are compensated by thickness of a cylindrical structure composing the permanent magnet, the shaft is accurately located.

According to the eighth aspect of the present invention, the shaft is strongly connected to the rotor since the shaft and the rotor are engaged each other.

According to the ninth aspect of the present invention, when viewed from an axial direction, since a radially outer portion of the eccentric weight is extended up to the position at which the radially outer portion of the eccentric weight overlaps with the pole teeth of the stator, radial mass unbalance of the eccentric weight is increased and a high performance for vibration can be obtained in a limited size.

According to the tenth aspect of the present invention, when viewed from the axial direction, since the radially outer portion of the eccentric weight is extended up to the position in which the radially outer portion of the eccentric weight overlaps with the coil of the stator, radial mass unbalance of the eccentric weight is increased and the high performance for vibration can be obtained in the limited size.

According to the eleventh and twelfth aspects of the present invention, when viewed from the axial direction, since both sides of the outer portion of the eccentric weight are extended up to the position at which both sides of the outer portion overlap with members of the stator, radial mass unbalance of the eccentric weight is effectively increased in the limited size.

According to a thirteenth aspect of the present invention, a vibrating motor is provided.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1Ais a plane view showing a first embodiment of the invention andFIG. 1Bis a cross sectional view taken along line A-A inFIG. 1A. A vibrating motor1is shown inFIG. 1. The rotor15has a structure in which a stator10is provided on an inner surface of a case11as a package, and a rotor15is rotatably arranged with respect to the stator10. Both axial sides of the vibrating motor1are closed by an upper cover12and a bottom cover16. The upper cover12is fixed to the case11by an adhesive, and the bottom cover16is integrally formed with the case11.FIG. 1Ashows the vibrating motor1when viewed from an axial direction, in which the upper cover12and a bearing13are removed.

The stator10is explained as follows. The stator10is provided with a yoke7, a coil8, and pole teeth9. The yoke7has the pole teeth9extending toward the axis thereof on an inner circumference and six coils8wound around the pole teeth9. That is, the yoke7is a cylindrical member formed by a magnetic material. On the inner circumference of the yoke7, six pole teeth9extending toward the axis are integrally formed with the yoke7. Each of the pole teeth is wound around with the coil8acting as a driving coil. In this embodiment, each of the pole teeth9is arranged in an equal angle. Since the structure of wire bonding and a means for driving of the coil8are the same as in ordinary DC brushless motors, further explanation is omitted.

The rotor15is explained as follows. The rotor15is shown inFIGS. 2 and 3. The rotor15is arranged in a position that is separated from heads of the pole teeth9of the stator10with a clearance14as a magnetic gap (seeFIG. 1). The rotor15is provided with a shaft2, a permanent magnet3, a sleeve4, and an eccentric weight6. The shaft2is an axis for rotation of the vibrating motor1and is rotatably supported by the bearing13and a bearing17with respect to the upper cover12and the bottom cover16. The shaft2, for example, may be composed of stainless steel. The permanent magnet3functions as a magnet for the rotor15and is magnetized in multiple poles. Since the structure of magnetizing is the same as in ordinary DC brushless motors, further explanation of the structure is omitted. The material of the permanent magnet may be composed of a thermoplastic magnetic material such as neodymium type materials.

The eccentric weight6is used to generate vibration in rotating, and the eccentric weight6has a shape to obtain eccentric mass balance with respect to the axis for the shaft2. In this embodiment, the shape of the eccentric weight6viewed from the axial direction is substantially a semicircle. The eccentric weight6is not only radially larger (longer) than the inner diameter of the permanent magnet3, but also axially larger (longer) than the permanent magnet3. As the material of the eccentric weight6, for example, tungsten having heavy specific gravity is used. The shape of the eccentric weight6when viewed from an axial direction is not restricted to the shape shown inFIG. 3if eccentric mass balance is ensured.

The sleeve4is a cylindrical member made from the same material as the permanent magnet3and is simultaneously formed in molding the permanent magnet3. The shaft2is connected to the eccentric weight6via the sleeve4. The sleeve4functions as a member to locate the position of the shaft2, (in other words, a member for centering), as described later. In this embodiment, the outer shape of the sleeve4is square when viewed from an axial direction. Therefore, the structures of the sleeve4and the eccentric weight6are engaged with each other, and the sleeve4and the eccentric weight6are strongly connected. The outer shape of sleeve4when viewed from the axial direction is not restricted to a square, and it may be a polygon such as a hexagon, a star shape, or it may be an ellipse.

The outermost axial length of the rotor15(excluding the axial length of the shaft2) is smaller than the outermost radial length of the rotor15. That is, the rotor15has a flat structure in which the axial length is shorter than the radial length, whereby the structure has an advantage when installed in flat electronic devices such as portable telephones.

As shown inFIG. 3, a step portion6ais radially formed, and a concavity6bthat is partially thinned is formed in a peripheral portion of the shaft2of the eccentric weight6. As shown inFIG. 1B, a part of the bearing13is disposed in a portion of the step portion6a. For this structure, the axial length of the vibrating motor1is reduced, and the vibrating motor1can be thin.

A production process for the rotor15is explained as follows. First, the shaft2, the eccentric weight6, and a mold (a die), not shown, are prepared. The mold is used to form the permanent magnet3and the sleeve4from the thermoplastic magnetic material, in such a way the shaft2and the eccentric weight6are disposed as insertion materials therein.

The eccentric weight6and the mold are prepared in advance, and the shaft2and the eccentric weight6are disposed at predetermined locations. Then, the thermoplastic magnetic material is injected into the mold and an insertion molding is performed by injection. In this process, the sleeve4and the permanent magnet3are synchronously formed as a molded magnet5, and the shaft2is integrally formed with the eccentric weight6by the thermoplastic magnetic material composing the molded magnet5as a bonding material. That is, a molding in which the shaft2, the sleeve4, the permanent magnet3and the eccentric weight4are integrally formed is obtained. Then, the molding is removed from the mold, thereby obtaining an original form of the rotor15. Then the permanent magnet3is subjected to magnetizing. Thus, the rotor15is completed.

In the rotor15produced in the above process, the shaft2, the eccentric weight6, and the permanent magnet3are integrally formed by the thermoplastic magnetic material composing the permanent magnet3. That is, the rotor15is formed in the insertion molding by the thermoplastic magnetic material composing the permanent magnet3in such a way that the shaft2and the eccentric weight6are disposed as insertion materials.

According to the embodiment, the rotor15in which the shaft2, the eccentric weight6, and the permanent magnet3are integrally formed by the thermoplastic magnetic material composing the permanent magnet3is provided. The sleeve4is formed by the thermoplastic magnetic material composing the permanent magnet3, and the shaft2is integrally formed with the eccentric weight6. Therefore, the vibrating motor can have high coaxial accuracy and be produced in fewer steps.

That is, the rotor15is integrally formed with the permanent magnet3by the thermoplastic magnetic material as a bonding material, in such a way that the shaft2and the eccentric weight6are disposed as insertion materials in the mold (not shown). In this embodiment, the shaft2is integrally formed with the eccentric weight6by the thermoplastic magnetic material as the bonding material, and the permanent magnet3is integrally formed. Therefore, the rotor15can be integrally formed without another molding material (such as resins or adhesives for integral molding).

Moreover, in the embodiment, the shaft2is located in the rotor15according to the position of the shaft2in the mold in spite of an error in positioning between the shaft2and the eccentric weight6and an error in accuracy of dimensions of the eccentric weight6. That is, the sleeve4is integrally formed with the permanent magnet3by the thermoplastic magnetic material injected into the mold and a gap between the eccentric weight6and the shaft2is filled up therewith. Therefore, the error in positioning between the shaft2and the eccentric weight6and the error in accuracy of dimensions of the eccentric weight6are compensated by the thickness of the sleeve4.

In other words, even if the position of the eccentric weight6in the mold is not accurate and dimensions of the eccentric weight6is not accurate, the position of the shaft2can be accurately located (that is, centering of the shaft2is performed), since the errors are compensated by the thickness of the sleeve4and the radial thickness of the permanent magnet3as long as the sleeve4is not prevented from being formed by the errors and the positioning of the shaft2is not affected thereby. This means that the sleeve4functions as a member to locate the position of the shaft2(a member for centering). According to the embodiment, the position of the shaft2is accurately located and high coaxial accuracy can be obtained even in the simplified process. The error in positioning between the shaft2and the eccentric weight6described in this embodiment means unevenness of mutual relationship in positioning between the shaft2and the eccentric weight6, and the error in accuracy of dimensions of the eccentric weight6means unevenness in dimensions of the eccentric weight6. The errors in dimensional accuracy are caused by working precision and a nonuniformity in materials of the eccentric weight6.

Moreover, according to this embodiment, resins and adhesives are unnecessary in this process compared to conventional processes in which resins or adhesives are used, and surplus clearances for intervention of reins or adhesives are unnecessary. Therefore material cost and labor in the producing process can be reduced. This is because surplus clearance is not required, degradation in dimensional accuracy caused by the clearance is avoidable, and high coaxial accuracy can be obtained.

Second to fifth embodiments according to the invention will be explained as follows.

FIG. 4A is a plane view andFIG. 4Bis a cross sectional view of a vibrating motor20in accordance with a second embodiment, each ofFIGS. 4A and 4Bis viewed from the same direction asFIGS. 1A and 1B. The shape of an eccentric weight21of a rotor22is different from that of the vibrating motor1inFIGS. 1A and 1B. In the vibrating motor20, an extensional portion21ais provided, in which the outer surface of the eccentric weight21is extended up to the outer surface of the permanent magnet3for more effective vibration. The shape of the extensional portion21apartially overlaps with the permanent magnet3when viewed from an axial direction. According to the structure of the embodiment, a mass of the extensional portion21ais added to an outer surface of the rotor22, whereby mass unbalance to the shaft2is increased and more effective vibration is obtained.

FIG. 5Ais a plane view of the rotor22andFIG. 5Bis a cross sectional view of the rotor22taken along line B-B inFIG. 4A. As shown inFIGS. 5A and 5B, the eccentric weight21is extended up to a radially peripheral portion of the permanent magnet3, whereby mass of an outer portion of the rotor22is increased and more effective vibration is obtained.

According to a second embodiment, since the permanent magnet3is formed by molding with the thermoplastic magnetic material which is injected into the mold, the eccentric weight21having a shape such one as shown inFIGS. 4A and 4Bcan be used with less labor and difficulty in the production process. That is, the shape of the eccentric weight21may be more freely chosen. Therefore the eccentric weight21can be reduced in size and easily yield necessary performance of vibration. Complicated shapes may be applied in assembling parts. These advantages are obtained in structures of the following embodiments.

According to a third embodiment,FIG. 6Ais a plane view andFIG. 6Bis a cross sectional view of a vibrating motor30, each ofFIGS. 6A and 6Bis viewed from the same direction asFIGS. 1A and 1B.FIG. 7Ais a plane view of a rotor32inFIG. 6A, andFIG. 7Bis a cross sectional view of the rotor32taken along line B-B inFIG. 7A. The vibrating motor30is shown inFIGS. 6A and 6B. In the vibrating motor30, an extensional portion31ais provided, and in order to obtain effective vibration, one side of an outer surface of the eccentric weight31is radially extended up to the position overlapping with the pole teeth9when viewed from an axial direction. The extensional portion31adoes not contact the members in the stator10. Portions other than the eccentric weight31in the vibrating motor30are the same as the portions of the vibrating motor1shown inFIG. 1A. According to the structure, the mass of the extensional portion31ais added at an outer side of the rotor32, whereby mass unbalance to the shaft2is increased and more effective vibration is obtained.

According to a fourth embodiment,FIG. 8Ais a plane view andFIG. 8Bis a cross sectional view of a vibrating motor40, eachFIGS. 8A and 8Bis viewed from the same direction asFIGS. 1A and 1B.FIG. 9Ais a plane view of a rotor42inFIG. 8A, andFIG. 9Bis a cross sectional view of the rotor42taken along line B-B inFIG. 9A. The vibrating motor40is shown inFIG. 8A. In vibrating motor40, an eccentric weight41is more extended in an outer direction than the eccentric weight31inFIGS. 6A and 6Bof the third embodiment. That is, in the vibrating motor40, in order to obtain more effective vibration than the vibrating motor30, one side of an outer surface of the eccentric weight41is radially extended beyond the pole teeth9to the position overlapping with the coil8in the stator10. In this embodiment, an extensional portion41ais provided in a portion in which the eccentric weight41overlaps with the pole teeth9and an external portion41bradially extending from the extensional portion41ais provided in a portion in which the eccentric weight41overlaps with the coil8. The external portion41acorresponds to the external portion31ainFIGS. 6A,6B,FIGS. 7A and 7B. In this embodiment, the external portions41aand41bdo not contact the members in the stator10. The structure of other portions of the vibrating motor40are the same as that of the vibrating motor1shown inFIG. 1Aand the rotor30inFIGS. 6A and 6B. According to the structure, the mass of the extensional portion42aand41bis added at an outer side of the rotor42, whereby mass imbalance at a shaft2is increased.

According to a fifth embodiment,FIG. 10Ais a plane view andFIG. 10Bis a cross sectional view of a vibrating motor40, and each ofFIGS. 10A and 10Bis viewed from the same direction asFIGS. 1A and 1B.FIG. 11Ais a plane view of a rotor52inFIG. 10A, andFIG. 11Bis a cross sectional view of the rotor42taken along line B-B inFIG. 11A. A vibrating motor50is shown inFIGS. 10A and 10B. In the vibrating motor50, both axial sides of the outer surface of an eccentric weight51are radially extended up to the same position in the vibrating motor40shown inFIGS. 8A and 8B. That is, in the vibrating motor50, an eccentric weight51is provided such that both upper and lower axial sides thereof are radially extended as shown inFIG. 10B. An external portion51aand an external portion51bare provided at an upper side of the extended portion of the eccentric weight51, an external portion51cand an external portion51dare provided at a lower side of the extended portion. The external portions51aand51cradially overlap with the pole teeth9when viewed from an axial direction, and the external portions51band51dradially overlap with the coil8. According to the embodiment, mass imbalance to the shaft2can be further increased and more effective vibration can be obtained in a limited size compared to the vibrating motor40inFIGS. 8A and 8B.

It should be noted that, in the rotor50, the external portions51band51dmay be omitted in the structure, but the external portions51aand51care provided. This structure corresponds to a structure in which the external portions31radially overlapping with the pole teeth9when viewed from an axial direction, is provided not only on the upper side of the surface, but on the lower side of the surface of the eccentric weight3of the vibrating motor30inFIGS. 6A,6B,7A and7B.

The present invention is not limited to the above embodiments and includes variations obvious to those skilled in art, and effects of the invention are not restricted by the above embodiments. That is, various additions, modifications, and partial omissions are possible within the scope of the concept and the objects of the invention, as claimed and equivalents thereof.

The present invention can be used for vibrating motors.