Abstract:
A weight for a vibration motor, the weight including: a resin part including: a semi-cylindrical portion having a shaft hole in which a rotary shaft is fitted and expanding radially from the shaft hole at a given center angle so as to be eccentrically weighted with respect to the shaft hole; and a pair of locking projections respectively disposed at both axial end areas of an outer circumferential surface of the semi-cylindrical portion so as to extend radially outwardly threfrom; and a metal part attached to the resin part so as to sit on the outer circumferential surface of the semi-cylindrical portion, the metal part including: a pair of locking recesses positioned and configured to correspond respectively to the locking projections of the resin portion, wherein an elevated portion formed between the pair of locking recesses makes contact with the pair of locking projections of the resin portion.

Description:
CROSS-REFERENCE TO THE RELATED APPLICATION(S) 
       [0001]    The present application is based upon and claims priority from prior Japanese Patent Application No. 2008-113955, filed on Apr. 24, 2008, the entire content of which are incorporated herein by reference. 
       TECHNICAL FIELD 
       [0002]    The present invention relates to a weight for a vibration motor for generating vibration in electronic equipments such as a mobile phone. 
       BACKGROUND 
       [0003]    A weight for vibration motors has conventionally been formed of tungsten which has a large specific gravity so as to increase a vibration amount. 
         [0004]    When a weight made only of tungsten is attached to a shaft (a rotating shaft) of a motor, the shaft needs to be press-fitted in a through-hole of the weight as disclosed in JP-A-2006-345599 (counterpart U.S. publication is: US 2006/0284501 A1), or alternatively, an opening provided in the weight needs to be crimped so that the weight is secured to the shaft as disclosed in JP-A-10-336949. 
         [0005]    In the case when the shaft is press-fitted in the through-hole, a powerful and massive press fitting apparatus is used thus requiring a large-scale manufacturing system, and the number of manufacturing steps increases. 
         [0006]    On the other hand, in the case when the opening is crimped to the shaft, the shaft is secured by the deformation of the crimped portion, wherein the fastening force at the crimped portion may decrease over time due to deterioration with age while the crimped portion receives stress and vibration during the motor rotation. 
         [0007]    Furthermore, since the conventional vibration motor weight is made of a uniform material having a high specific gravity, the rotational moment is inevitably large which is unfavorable to the start-up characteristics. Additionally, since the conventional weight has a large mass, the starting current of the motor is increased to such an extent as to cause a problem. Further, since the weight is wholly made of tungsten, which is expensive, the production cost is increased. 
         [0008]    In order to solve these problems, the weight of a vibration motor weight is reduced, the rotation performance of a vibration motor is enhanced. In addition, to reduce the production costs, the vibration motor weight is secured to a shaft of the vibration motor with a resin. An example of such configuration is disclosed in JP-A-9-182363. 
         [0009]      FIGS. 8A-8E  are diagrams showing some configurations of vibration eccentric weights disclosed in the publication JP-A-9-182363. 
         [0010]    As viewed in cross section, an eccentric weight  100  shown in  FIG. 8A  is made of a substantially trapezoidal weight part  101  and a resin part  102  in which a shaft holding portion  102   b  is provided on a semi-circular portion  102   a  which grips the weight part  101  in such a manner as to project therefrom. 
         [0011]    As viewed in cross section, in the substantially trapezoidal weight part  101 , a top side  101   a  of the trapezoid configures a continuous arc together with an outer circumferential side  102   c  of the resin part. A horizontal distance or width A between lateral sides  101   b  of the weight part  101  is moderately narrowed or decreased as they extend towards the top side  101   a.    
         [0012]    As viewed in cross section, while the resin part  102  is configured to grip the lateral sides  101   b  the horizontal width between which is moderately decreased as they extend towards the top side  101   a  of the weight part  101 , since the horizontal width A is made to be decreased moderately, the holding force of the resin part  102  with which the weight part  101  is held thereby is weak and is more or less a force which can resist a centrifugal force generated when the weight part  101  rotates. 
         [0013]    Accordingly, a structural problem resides in the resin part  102  that in the event that an excessive impact which exceeds an anticipated centrifugal force is applied to the resin part  102 , the resin part  102  is forcibly expanded to such an extent that it fails by the weight part  101 . 
         [0014]    As viewed in cross section, an eccentric weight  110  shown in  FIG. 8B  is made of a substantially arc-shaped weight part  111  having a constant width B and a resin part  112  in which a shaft holding portion  112   b  is provided on a semi-circular portion  112   a  which grips the weight part  111  in such a manner as to project therefrom. 
         [0015]    As viewed in cross section, in the weight part  111 , an outer arc-shaped side  111   a  of the weight part  111  configures a continuous arc together with a circumferential side  112   c  of the resin part  112 . A horizontal width C between lateral sides  111   b  of the weight part  111  is gradually increased as they extend towards the outer arc-shaped side  111   a.    
         [0016]    As viewed in cross section, while the resin part  112  is configured in such a manner as to grip the lateral sides the horizontal width C between which is made to be increased gradually as they extend towards the outer arc-shaped side  111   a  of the weight part  111 , since the horizontal width C is made to be increased gradually towards the outer arc-shaped side  111   a,  the holding force of the resin part  112  with which the weight part  111  is held thereby is extremely weak. Because of this, the weight part  111  is held on to the resin part  112  by virtue of the adhesion of an adhesive, and the holding force of the resin part  112  with which the weight part  111  is held thereby is more or less a force which can resist a centrifugal force generated when the weight part  111  rotates. 
         [0017]    Accordingly, a structural problem resides in the resin part  112  that in the event that an excessive impact which exceeds an anticipated centrifugal force is applied to the resin part  112 , the resin part  112  becomes unable to hold the weight part  111 . 
         [0018]    As viewed in cross section, an eccentric weight  120  shown in  FIG. 8C  is made of a semi-circular arc-shaped weight part  121  having a constant width D and a resin part  122  in which a shaft holding portion  122   b  is provided on a semi-circular portion  122   a  which holds the weight part  121  on an outer side thereof with an adhesive in such a manner as to project therefrom. As viewed in cross section, the resin part  122  is configured to hold the weight part  121  on the outer side thereof with the adhesive. Because of this, the weight part  121  is held on to the resin part  122  by virtue of the adhesion of the adhesive, and the holding force of the resin main body  122  with which the weight part is held thereby is more or less a force which can resist a centrifugal force generated when the weight part  121  rotates. 
         [0019]    Accordingly, a structural problem resides in the resin part  122  that in the event that an excessive impact which exceeds an anticipated centrifugal force is applied to the resin part  122 , it is anticipated that the resin part  122  becomes unable to hold the weight part  121 . 
         [0020]    An eccentric weight  130  shown in  FIG. 8D  illustrates an example in which the weight part of the eccentric weight shown in  FIG. 8A  is divided into two weight parts  131   a,    131   b  of a smaller size, and this involves the same structural problem as that of the eccentric weight of  FIG. 8A . 
         [0021]    An eccentric weight  140  shown in  FIG. 8E  illustrates an example of a resin part  142  in which a side confronting a semi-circular arc-shaped side is made of straight lines E which are connected to each other in such a manner that a shaft holding portion  141  does not project therefrom, and this involves the same structural problem as that of the eccentric weight of  FIG. 8A . 
         [0022]    Thus, it is said that in the related-art eccentric weights shown in  FIGS. 8A-8E , the resin part has the holding force which is more or less the force which can resist the centrifugal force which is applied to the weight part in the radial direction when the eccentric weight rotates in cooperation with the adhesive. 
         [0023]    In particular, when viewing only the configurations of the eccentric weights themselves without considering the adhesion of the adhesive, in the examples shown in  FIG. 8A , the configuration in which the resin part holds the weight part relies only on the wedge configuration which tapers with a slight inclination, and hence, the resin part cannot hold the weight part strongly and rigidly. When looking at the examples shown in  FIGS. 8B and 8C  from the same viewpoint, no configuration for holding the weight part is adopted. 
         [0024]    The related art examples have the problem that they adopt the configurations having the extremely weak holding force or no holding force in consideration of the centrifugal force applied to the weight part. 
         [0025]    Further, in recent years, there is emerging a demand to resist an unexpected strong impact such as impact resulting from the fall of a vibration motor. However, it can be said when looking at their configurations that the related art examples have a problem that they cannot resist such an impact. 
       SUMMARY 
       [0026]    One of objects of the present invention is to provide a weight for a vibration motor which can maintain a good impact resistance without reducing the amount of vibration while reducing the utilization amount of a material having a high specific gravity. 
         [0027]    A vibration motor weight according to an aspect of the invention includes a resin part in which a predetermined center angle portion (semi-cylindrical portion) extends radially from an axis center of a shaft hole and locking projections are provided integrally at axial ends thereof (axial end areas) and a metal part having locking recesses which closely contact and cover the predetermined center angle portion of the resin part and which are locked, respectively, on the locking projections. 
         [0028]    In detail, the vibration motor weight includes the resin part in which a semi-tubular portion is formed integrally on a longitudinal flat surface side of a semi-cylindrical portion in such a manner as to form the shaft hole together with the semi-cylindrical portion and the locking projections are formed integrally at the ends of the semi-cylindrical portion in the longitudinal direction of the shaft hole and the metal part which sits on a radially outer side (outer circumferential surface) of the resin part including the locking projections in such a manner that an outer surface of the metal part configures a semi-tubular surface. 
         [0029]    Radial and axial impacts applied to the metal part are suppressed by locking the metal part on the locking projections of the resin part. 
         [0030]    The locking projection may be formed into an edged T-shaped projecting portion which projects radially outwards from an outer surface of the semi-cylindrical portion. 
         [0031]    The locking projection may be formed into an edged locking projection. Since corners of a top surface of the edged locking projections form edges (right angles), as a result, an angle formed by the outer surface of the semi-cylindrical portion and a lateral side of the edged locking projection is formed as a right angle. 
         [0032]    The locking projection may be formed into a tapered arc-shaped projecting portion (triangular shape in an axial cross section). When used herein, taper means basically that a rising angle of the locking projection from the outer surface of the semi-cylindrical portion in the axial direction becomes an arbitrary angle ranging from 0 degree to 90 degrees. The rising angle is preferably in the range of 26 degrees±4 degrees. 
         [0033]    Since a top surface of the tapered arc-shaped projecting portion is formed into a tapered face (axially inner face) having no angle at an opposite side to the axial end face of the semi-cylindrical portion, as a result, an angle formed by the outer surface of the semi-cylindrical portion and the tapered arc-shaped projecting portion, that is, the rising angle in the axial direction is formed as an arbitrary angle ranging from 0 degree to 90 degrees, and an angle in a circumferential direction is formed as a right angle. 
         [0034]    The following configurations may be adopted. 
         [0035]    (1) A weight for a vibration motor includes: a resin part including: a semi-cylindrical portion having a shaft hole in which a rotary shaft is fitted and expanding radially from the shaft hole at a given center angle so as to be eccentrically weighted with respect to the shaft hole; and a pair of locking projections respectively disposed at both axial end areas of an outer circumferential surface of the semi-cylindrical portion so as to extend radially outwardly therefrom; and a metal part attached to the resin part so as to sit on the outer circumferential surface of the semi-cylindrical portion, the metal part comprising: a pair of locking recesses positioned and configured to correspond respectively to the pair of locking projections of the resin portion, wherein an elevated portion formed between the pair of locking recesses makes contact with the pair of locking projections of the resin portion. 
         [0036]    (2) The locking projections of the resin part may have a triangular shape in an axial cross section. 
         [0037]    (3) The locking projections may each include an axially inner face inclined with respect to a longitudinal direction of the shaft hole; and a pair of circumferential end faces may be engaged respectively with a pair of circumferential end faces of each of the locking recesses of the metal part. 
         [0038]    (4) The locking projections of the resin part may have a substantially rectangular shape in an axial cross section. 
         [0039]    (5) The locking projections may each include: a top face; an axially inner face connecting between the top face and the outer circumferential surface of the semi-cylindrical portion and oriented substantially perpendicular to the top face and the outer circumferential surface; and a pair of circumferential end faces engaged respectively with a pair of circumferential end faces of each of the locking recesses of the metal part. 
         [0040]    (6) The locking projections of the resin part may have a substantially T-shape in a radial cross section wherein a base portion extends radially outwardly from the outer circumferential surface of the semi-cylindrical portion and a pair of arm portions extend circumferentially from a distal end of the base portion in respective opposite directions. 
         [0041]    (7) The elevated portion of the metal part may be configured to make contact with axially inner faces of the locking projections of the resin part. 
         [0042]    (8) The center angle of the semi-cylindrical portion of the resin part may be set to an angle obtained as a required amount of vibration from center angle variation characteristics of a vibration amount in the weight for a vibration motor when the metal part has a constant radial dimension. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0043]    A general configuration that implements the various feature of the invention will be described with reference to the drawings. The drawings and the associated descriptions are provided to illustrate embodiments of the invention and not to limit the scope of the invention. 
           [0044]      FIGS. 1A-1H  are explanatory diagrams showing configurations of a vibration motor weight which employs tapered locking projections. 
           [0045]      FIGS. 2A-2H  are explanatory diagrams showing configurations of a vibration motor weight which employs edged locking projections. 
           [0046]      FIGS. 3A-3E  are explanatory diagrams showing configurations of a vibration motor weight which employs T-shaped locking projections. 
           [0047]      FIGS. 4A-4D  are explanatory diagrams showing a wide arc-shaped model. 
           [0048]      FIGS. 5A-5C  are graphs showing characteristics shown in Tables 5 to 7. 
           [0049]      FIG. 6  is a graph representing characteristics shown in Table 8. 
           [0050]      FIGS. 7A-F  are diagrams showing configurations of modified examples to first to third embodiments of the invention, in which locking configurations between a metal part and a resin part are inversed. 
           [0051]      FIGS. 8A-8E  are drawings showing configurations of vibration eccentric weights disclosed in JP-A-9-182363. 
       
    
    
     DETAILED DESCRIPTION 
       [0052]    Embodiments according to the present invention will be described in detail with reference to the accompanying drawings. The scope of the claimed invention should not be limited to the examples illustrated in the drawings and those described in below. 
         [0053]    A vibration motor weight of the invention includes a resin main body portion which has a shaft hole into which a shaft of a vibration motor is fitted (inserted in a fitted state) and in which a predetermined angle portion extends from a center axis of the shaft hole in a radial direction (a direction extending radially from the center axis orthogonal to the center axis) and locking projections are provided integrally at axial ends thereof and a metal part having locking recesses which closely contact and cover the predetermined angle portion of the resin part and which are locked on the locking projections, respectively. 
         [0054]    The locking projection and the locking recess can be configured arbitrarily, provided that configurations adopted function as required or designed or to prevent or suppress the dislocation of the metal part from the resin main body or the damage to the resin part when not only a expected centrifugal force generated when the weight rotates but also impact generated otherwise such as when the motor happens to fall are applied to the weight. 
         [0055]    Hereinafter, three representative combinations of locking projections and locking recesses will be described which employ tapered arc-shaped locking projections, edged arc-shaped locking projections and T-shaped locking projections, respectively. 
       First Embodiment 
       [0056]      FIGS. 1A-1H  show explanatory diagrams showing configurations of a weight for a vibration motor according to a first embodiment, which employs tapered arc-shaped locking projections. 
         [0057]      FIG. 1A  is a side view of the vibration motor weight employing the tapered arc-shaped locking projections when viewed in an axial direction,  FIG. 1B  is a perspective view of the same vibration motor weight as viewed from therebelow, and  FIGS. 1C-1H  are explanatory diagrams explaining impact suppressing functions. 
         [0058]      FIG. 1C  is an explanatory diagram explaining a case where an axial impact force is being applied to the weight or mainly to a metal part, in which the metal part is shown by solid lines as being transparent.  FIG. 1D  is an explanatory diagram explaining how a resin part functions to suppress the impact force in  FIG. 1C . 
         [0059]      FIG. 1E  is an explanatory diagram explaining a case where a radial impact force is being applied similarly to the metal part, in which the metal part is shown by solid lines as being transparent.  FIG. 1F  is an explanatory diagram explaining how the resin part functions to suppress the impact force in  FIG. 1E . 
         [0060]      FIG. 1G  is an explanatory diagram explaining a case-where an impact force is being applied similarly to the metal part in a direction which is orthogonal to the axial direction and the radial direction, in which the metal part is shown by solid lines as being transparent.  FIG. 1H  is an explanatory diagram explaining how the resin part functions to suppress the impact force in  FIG. 1G . 
         [0061]    A vibration motor weight  1  is basically an eccentric weight and is made of a metal part  2  and a resin part  3 . The vibration motor weight  1  is configured in such a manner that the metal part  2  is securely attached to a shaft (whose illustration is omitted) of a vibration motor by the resin part  3 . 
         [0062]    In addition, the vibration motor weight is basically made of the resin part  3  in which, for example, as is shown in the side view in  FIG. 1A  and in the perspective view in  FIG. 1B , a semi-tubular portion  3   d  is formed integrally on a flat surface side  3   b  of a semi-cylindrical portion  3   a  in a longitudinal direction in such a manner as to form a shaft hole  3   c  together with the semi-cylindrical portion  3   a  and as is shown in  FIGS. 1C and 1D , locking projections  3   e  are formed integrally at axial ends of the semi-cylindrical portion  3   a  in a longitudinal direction of the shaft hole  3   c  and the metal part  2  which covers a radially outer side of the resin part  3  including the locking projections  3   e  in such a manner that an outer side of the metal part  2  configures a tubular surface  2   a.  The shaft (the rotating shaft whose illustration is omitted) of the vibration motor is fittingly disposed in the shaft hole  3   c.    
         [0063]    Specifically, the resin part  3 , which is basically configured in the way described above and which has the locking projections which are formed into tapered arc-shaped locking projections, is formed from a resin having a necessary impact strength and a necessary heat resistance, for example, Genestar® G2330 (made by Kuraray Co., Ltd., Japan). The semi-tubular portion  3   d  is formed integrally on the flat surface side of the semi-cylindrical portion  3   a  in the longitudinal direction in such a manner that the shaft hole  3   c  is formed together with the semi-cylindrical portion  3   a,  and the locking projections  3   e  are formed integrally at the ends of the semi-cylindrical portion  3   a  in the longitudinal direction (the axial direction) of the shaft hole  3   c.  The locking projections  3   e  denote radial projecting portions (portions where tapered faces  3   g  are formed) from a central outer surface (an outer surface of an area where no tapered face  3   g  is formed) of the semi-cylindrical portion  3   a  and extensions thereof. 
         [0064]    The locking projections  3   e  are each formed into the tapered arc-shaped locking projection, and as is shown in  FIG. 1C  which is an axial sectional view of the vibration motor weight taken along the axial direction of the shaft hole  3   c  and in  FIGS. 1D ,  1 F and  1 H which shows the resin part  3 , the tapered faces  3   g  are provided on the locking projections  3   e  in such a manner that their radii from the axis center decrease as they extend from the axial ends  3   h  towards the center of the resin main part  3 . 
         [0065]    As is shown in  FIG. 1D , the tapered faces  3   g  so provided are each formed into a strip-like shape having a predetermined width E measured from each axial end  3   h  and extending in a rotational direction over a predetermined center angle range from the center axis. As is shown in  FIG. 1A , a center angle θ 1  of the resin part  3  is 180 degrees, and a center angle of the tapered face  3   g  is referred to as an angle which results after an angle twice an angle θ 2  which corresponds to a length from the flat surface side  3   b  to a cut-off  3   i  on which a locking recess  2   b  of the metal part  2  is locked is deducted from 180 degrees. As is shown in  FIGS. 1F and 1H , a cut-off face  3   j  of the cut-off  3   i  which is oriented in the rotational direction configures a triangle due to the tapered face  3   g  which tapers from the axial end towards the center of the resin part  3 . 
         [0066]    The angle of the cut-off  3   i  is set to an angle at which the metal part  2  is prevented from being displaced from the resin part  3  even when an impact force is applied to the weight in directions indicated by arrows in  FIGS. 1E and 1G , that is, for example, an angle of 90 degrees ±5 degrees. 
         [0067]    Axial surfaces shown in  FIG. 1F  which are formed at the ends of the locking projections  3   e  in the rotational direction as the cut-off  3   i  reaching the outer surface  3   f  of the resin part  3  are each referred to as the cut-off face  3   j  of the locking projection  3   e  which is oriented in the rotational direction or the side face  3   j.  These side faces  3   j  are provided in four locations in total on the resin part  3 , two at each axial end  3   h  of the resin part  3 . 
         [0068]    The resin part  3  is formed by a resin injection molding technique such as an injection molding technique. Since structurally, end portions  2   c  of the metal part  2  are exposed from the resin part  3 , for example, when injection molding a resin part main body  3 , the metal part  2  is disposed to be erected within the dies in such a manner that one end portion  2   c  of the metal part contacts a bottom surface within the dies, and a resin is injected into the dies in such a state. The resin so injected comes to stay on an inside of the metal part  2  and is then allowed to set there. Because of this, in the weight according to the embodiment, since the end portions  2   c  of the metal part  2  are level with the corresponding end faces of the resin part  3 , the manufacturing system and manufacturing process can be made easy and simple. 
         [0069]    The metal part  2  is made of a material having a high specific gravity such as, particularly, tungsten (W) or lead (Pb). The metal part  2  is formed in such a manner as to cover the resin part  3  in the radial direction and its radial outer surface is formed into the tubular surface  2   a.  The locking recesses  2   b  of the metal part  2  are configured in such a way as to be combined with the corresponding locking projections  3   e  of the resin part  3 . The locking recess  2   b  has recessed lateral faces  2   d  which are brought into engagement with the side faces  3   j  of the corresponding locking projection  3   e.    
         [0070]    An elevated portion  2 A is provided between the locking recesses  2   b  at the axial ends of the metal part  2 . This elevated portion  2 A is brought into locking abutment with the tapered faces  3   g  of the locking projections  3   e  at the axial ends  3   h  of the resin part  3 . 
         [0071]    The position of center of gravity of the conventional weight, which is made of only tungsten, lies in a position in the vicinity of the center axis of the shaft hole, whereas the position of center of gravity of the weight in which the metal part is locked on the resin part is shifted improvably to a position, which lies apart from the axis center of the shaft hole to be in the vicinity of where the resin part is in abutment with the metal part. 
         [0072]    By this improvement in position with respect to the center of gravity of the weight, the position of center of gravity can be shifted to the position which is spaced apart from the axis center of the shaft hole  3   c  by such a length as to obtain a necessary rotational moment. 
         [0073]    Since a suppressing function to suppress a radial load resulting when vibration is generated during normal rotation of the vibration motor weight employing the tapered arc-shaped locking projections becomes the same as a suppressing function to suppress a radial impact which is imparted to the tapered arc-shaped locking projections as is shown in  FIGS. 1E and 1F , a description which will be made hereinbelow with respect to a radial impact force should be understood as describing the suppression of the aforesaid radial load. 
         [0074]    An axial impact force will be described. 
         [0075]    As is shown in  FIG. 1C , when an impact force F 1  is applied in the axial direction, as is shown in  FIG. 1D , the impact force transmitted to the elevated portion  2 A is dispersed over a wide range on the whole surface of the tapered face  3   g  and hence is received as small impact forces  2 F. Because of this, the value of an impact force per unit area of the tapered face  3   g  becomes small, thereby making it possible to suppress quite a large magnitude of impact force. 
         [0076]    Next, a radial impact force will be described. 
         [0077]    As is shown in  FIG. 1E , when a radial impact force F 3  is applied to the weight, mainly to the metal part  2 , as is shown in  FIG. 1F , the impact force is received as small impact forces  4 F at the two side faces  3   j  of each of the pair of locking projections  3   e  of the resin part  3  via the recessed lateral faces  2   d  of the corresponding locking recesses  2   b  of the metal part  2 . Since the engagement between the recessed lateral faces  2   d  of the locking recesses  2   b  and the side faces  3   j  of the corresponding locking projections  3   e  is strong and rigid, the radial impact force  3 F is made to be suppressed by the cut-off faces  3   j  of the resin part  3 . 
         [0078]    Next, an impact force will be described which is applied in a direction which is orthogonal to the axial direction and the radial direction (hereinafter, as a matter of conveniences, referred to as an orthogonal direction). 
         [0079]    As is shown in  FIG. 1G , when an impact force F 5  is applied to the weight, mainly to the metal part  2  in the orthogonal direction, as is shown in  FIG. 1H , the impact force F 5  is received as small impact forces F 6  at the two side faces  3   j  of each of the pair of locking projections  3   e  of the resin part  3  via the recessed lateral faces  2   d  of the corresponding locking recesses  2   b  of the metal part  2 . Since the engagement between the recessed lateral faces  2   d  of the locking recesses  2   b  and the side faces  3   j  of the corresponding locking projections  3   e  is strong and rigid, the radial impact force F 5  is made to be suppressed by the cut-off faces  3   j  of the resin part  3 . 
       Second Embodiment 
       [0080]      FIGS. 2A-2H  show explanatory diagrams showing configurations of a weight for a vibration motor according to a second embodiment, which employs edged arc-shaped locking projections. 
         [0081]      FIG. 2A  is a side view of the vibration motor weight employing the edged arc-shaped locking projections when viewed in an axial direction,  FIG. 2B  is a perspective view of the same vibration motor weight as viewed from therebelow, and  FIGS. 2C-2H  are explanatory diagrams explaining impact suppressing functions. 
         [0082]      FIG. 2C  is an explanatory diagram explaining a case where an axial impact force is being applied to the weight or mainly to a metal part, in which the metal part is shown by solid lines as being transparent.  FIG. 2D  is an explanatory diagram explaining how a resin part functions to suppress the impact force in  FIG. 2C . 
         [0083]      FIG. 2E  is an explanatory diagram explaining a case where a radial impact force is being applied similarly to the metal part, in which the metal part is shown by-solid lines as being transparent.  FIG. 2F  is an explanatory diagram explaining how the resin part functions to suppress the impact force in  FIG. 2E . 
         [0084]      FIG. 2G  is an explanatory diagram explaining a case where an impact force is being applied similarly to the metal part in a direction which is orthogonal to the axial direction and the radial direction, in which the metal part is shown by solid lines as being transparent.  FIG. 2H  is an explanatory diagram explaining how the resin part functions to suppress the impact force in  FIG. 2G . 
         [0085]    A resin part  3  is formed from a resin having a necessary impact strength and a necessary heat resistance, for example, Genestar® G2330 (made by Kuraray Co., Ltd., Japan) and is configured in such a manner that a semi-tubular portion  3   d  is formed integrally on a flat surface side  3   b  of a semi-cylindrical portion  3   n  in a longitudinal direction in such a manner as to form a shaft hole  3   c  together with the semi-cylindrical portion  3   n  and that locking projections  3   m  are formed integrally at ends of the semi-cylindrical portion  3   n  in an axial direction of the shaft hole  3   c.    
         [0086]    The locking projections  3   m  are each formed into an edged arc-shaped locking projection, and as is shown in  FIGS. 2C ,  2 E,  2 G which are perspective views of the vibration motor weight with a metal part  2  indicated by solid lines as being transparent and in  FIGS. 2D ,  2 F,  2 H which show the resin part  3 , the resin part  3  has edged (angled) arc-shaped projecting shapes at ends thereof in the axial direction of the weight. The locking projections  3   m  each include a top surface  3   p  which has a constant radius from an axis center of the shaft hole  3   c,  and angles formed by the top surface  3   p  and lateral faces in the axial direction each become a right angle. 
         [0087]    The locking projection  3   m  according to the second embodiment has a rectangular cross section as viewed in the axial direction and exhibits the edged arc-shaped projecting shape which extends along an outer circumferential surface of the semi-cylindrical portion  3   n  in a rotational direction centered at the center axis of the shaft hole  3   c  in the semi-cylindrical portion  3   n.  Edge means a right-angled corner. Since axial edges  3   q  of the top surface (a radially outermost surface)  3   p  of the edged arc-shaped locking projection ( 3   m ) are each made into an edge, as a result, angles formed by the outer surface  3   f  of the semi-cylindrical portion  3   n  and lateral faces  3   s  of the edged arc-shaped locking projections ( 3   m ) (lateral faces which continuously follow the aforesaid “corners”) each become a right angle. 
         [0088]    Ends in the rotational direction or rotational direction ends of the edged arc-shaped locking projection are made into cut-off faces in the rotational direction or side faces  3   t  which are angled so that locking recesses of the metal part  2  can be locked thereon. 
         [0089]    In the embodiment, the lateral faces  3   s  serve as an edged side face connecting the top face  3   p  of each of the locking projections  3   m  and the circumferential face  3   f  of the semi-cylindrical portion  3   n  and formed to be perpendicular to the top face  3   p  and the circumferential face  3   f.    
         [0090]    As is shown, for example, in  FIG. 2D , the top surface  3   p  which is defined by the edges is provided in the form of a strip-like shape having a predetermined width F measured from each axial end and extending over a predetermined center angle range θ 3  from the center axis. As is shown in  FIG. 2A , a center angle θ 1  of the resin part  3  is 180 degrees, and a center angle of the locking projection  3   m  is referred to as an angle which results after an angle twice an angle which corresponds to a length from the flat surface side  3   b.  to the cut-off  3   t  on which the locking recess  2   e  of the metal part  2  is locked is deducted from 180 degrees. As is shown in  FIGS. 2F and 2H , an axial cross section of the cut-off  3   t  configures a rectangular shape having edges as a result of the configuration of the top surface  3   p.    
         [0091]    The angle of the cut-off  3   t  is set to an angle at which the metal part  2  is prevented from being displaced from the resin part  3  even when an impact force is applied to the weight in directions indicated by arrows in  FIGS. 2E and 2G , that is, for example, an angle 90 degrees ±5 degrees. 
         [0092]    Axial surfaces shown in  FIG. 2F  which are formed at the ends of the locking projections  3   m  in the rotational direction as a cut-off reaching the outer surface  3   f  of the resin part  3  are each referred to as a cut-off face  3   t  of the locking projection  3   m  which is oriented in the rotational direction or the side face  3   t.  These side faces  3   t  are provided in four locations in total on the resin part  3 , two at each axial end  3   h  of the resin part  3 . 
         [0093]    The resin part  3  is formed by a resin injection molding technique such as an injection molding technique. Since structurally, end portions  2   c  of the metal part  2  are exposed from the resin part  3 , for example, when injection molding a resin part main body  3 , the metal part  2  is disposed to be erected within the dies in such a manner that one end portion  2   c  of the metal part contacts a bottom surface within the dies, and a resin is injected into the dies in such a state. The resin thus injected comes to stay on an inside of the metal part  2  and is then allowed to set there. Because of this, in the weight according to the embodiment, since the end portions  2   c  of the metal part  2  are level with the corresponding end faces of the resin part  3 , the manufacturing system and manufacturing process can be made easy and simple. 
         [0094]    The metal part  2  is made of a material having a high specific gravity such as, particularly, tungsten (W) or lead (Pb). The metal part  2  is formed in such a manner as to cover the resin part  3  in the radial direction and its radial outer surface is formed into the tubular surface  2   a.  The locking recesses  2   b  of the metal part  2  are configured in such a way as to be combined with the corresponding locking projections  3   e  of the resin part  3 . The locking recess  2   e  has recessed lateral faces  2   d  which are brought into engagement with the side faces  3   t  of the corresponding locking projection  3   m.    
         [0095]    An elevated portion  2 B is provided between the locking recesses  2   e  at the axial ends of the metal part  2 . This elevated portion  2 B is brought into locking abutment-with lateral faces  3   s  of the locking projections  3   m  at the axial ends  3   h  of the resin part  3 . 
         [0096]    The position of center of gravity of the conventional weight which is made of only tungsten lies in a position in the vicinity of the center axis of the shaft hole, whereas the position of center of gravity of the weight of the invention in which the metal part is locked on the resin part is shifted improvably to a position which lies apart from the axis center of the shaft hole to be in the vicinity of where the resin part  3  is in abutment with the metal part  2 . 
         [0097]    By this improvement in position with respect to the center of gravity of the weight, the position of center of gravity can be shifted to the position which is spaced apart from the axis center of the shaft hole  3   c  by such a length as to obtain a necessary rotational moment. 
         [0098]    Since a suppressing function to suppress a radial load resulting when vibration is generated during normal rotation of the vibration motor weight employing the edged arc-shaped locking projections becomes the same as a suppressing function to suppress a radial impact which is imparted to the edged arc-shaped locking projections as is shown in  FIGS. 2E and 2F , a description which will be made hereinbelow with respect to a radial impact force should be understood as describing the suppression of the aforesaid radial load. 
         [0099]    An axial impact force will be described. 
         [0100]    As is shown in  FIG. 2C , when an impact force is applied in the axial direction, as is shown in  FIG. 2D , the impact force is received as small impact forces  8 F which are dispersed over a wide range on the whole lateral face  3   s  of the locking projection  3   m  via the elevated portion  2 B of the metal part  2 . Because of this, the value of an impact force per unit area of the lateral face  3   s  of the locking projection  3   m  becomes small, thereby making it possible to suppress quite a large magnitude of impact force. 
         [0101]    Next, a radial impact force will be described. 
         [0102]    As is shown in  FIG. 2E , when a radial impact force F 9  is applied to the weight, mainly to the metal part  2 , as is shown in  FIG. 2F , the impact force  9 F is received as small impact forces  10 F at the two side faces  3   t  of each of the pair of locking projections  3   m  of the resin part  3  via the recessed lateral faces  2   d  of the corresponding locking recesses  2   e  of the metal part  2 . Since the engagement between the recessed lateral faces  2   d  of the locking recesses  2   e  and the side faces  3   t  of the corresponding locking projections  3   e  is strong and rigid, the radial impact force  9 F is made to be suppressed by the cut-off faces  3   t  of the resin part  3 . 
         [0103]    Next, an impact force will be described which is applied in a direction which is orthogonal to the axial direction and the radial direction (hereinafter, as a matter of conveniences, referred to as an orthogonal direction). 
         [0104]    As is shown in  FIG. 2G , when an impact force F 11  is applied to the weight, mainly to the metal part  2  in the orthogonal direction, as is shown in  FIG. 2H , the impact force F 11  is received as small impact forces F 12  at the two side faces  3   t  of each of the pair of locking projections  3   m  of the resin part  3  via the recessed lateral faces  2   d  of the corresponding locking recesses  2   e  of the metal part  2 . Since the engagement between the recessed lateral faces  2   d  of the locking recesses  2   e  and the side faces  3   t  of the corresponding locking projections  3   m  is strong and rigid, the radial impact force F 11  is made to be suppressed by the cut-off faces  3   t  of the resin part  3 . 
       Third Embodiment 
       [0105]      FIGS. 3A-3E  show explanatory diagrams showing configurations of a weight for a vibration motor according to a third embodiment, which employs T-shaped locking projections. 
         [0106]      FIG. 3A  is a side view of the vibration motor weight when viewed in an axial direction,  FIG. 3B  is a perspective view of the same vibration motor weight, and  FIGS. 3C-3E  are explanatory diagrams explaining impact suppressing functions. 
         [0107]      FIG. 3C  is an explanatory diagram explaining a function to suppress an axial impact force by a resin part when such an axial impact force is applied to the weight or mainly to a metal part, with the metal part shown by solid lines as being transparent. 
         [0108]      FIG. 3D  is an explanatory diagram explaining a function to suppress a radial impact force by the resin part when such a radial impact force is applied to the metal part, with the metal part shown by solid lines as being transparent. 
         [0109]      FIG. 3E  is an explanatory diagram explaining a function to suppress an impact which is applied in a direction which is orthogonal to the radial direction and the axial direction by the resin part when such an impact force is applied to the metal part, with the metal part shown by solid lines as being transparent. 
         [0110]    Each of locking projections  3   v  according to the third embodiment exhibit a T-shaped projecting shape which has a rectangular cross section as viewed in an axial direction and projects radially from an axial end  3   h  of a semi-cylindrical portion  3   a.  A horizontal bar portion of the T-shape is formed into an arc-like shape. Angles formed by a top surface (a radially outermost surface)  3   w  of the T-shaped locking projections ( 3   v ) and axial lateral faces  3 A each become a right angle. As a result, angles formed in the axial direction by an outer surface  3   f  of the semi-cylindrical portion  3   a  and the lateral faces  3 A of the T-shaped locking projections ( 3   v ), that is, axially formed angles become a right angle. 
         [0111]    In the embodiment, each of the locking projections  3   v  is formed to have a T-shape having a base portion extending from the circumferential face  3   f  of the semi-cylindrical portion  3   a  and a pair of lateral portions extending outward from the base portion along the circumferential face  3   f.    
         [0112]    The resin part  3  is formed from a resin having a necessary impact strength and a necessary heat resistance, for example, Genestar® G2330 (made by Kuraray Co., Ltd., Japan) and is configured in such a manner that a semi-tubular portion  3   d  is formed integrally on a flat surface side  3   b  of the semi-cylindrical portion  3   a  in a longitudinal direction in such a manner as to form a shaft hole  3   c  together with the semi-cylindrical portion  3   a  and that locking projections  3   v  are formed integrally at axial ends of the semi-cylindrical portion  3   a.    
         [0113]    The locking projections  3   v  are each formed into the T-shaped locking projection, and as is shown in  FIGS. 3B and 3C  which are perspective views of the vibration motor weight with the metal part  2  indicated by solid lines as being transparent and in  FIGS. 3D and 3E  which shows the resin part  3 , the resin part  3  has edged (angled) arc-shaped projecting shapes at ends thereof in the axial direction of the weight. The locking projections  3   v  each include a top surface which has a constant radius from an axis center of the shaft hole  3   c,  and angles formed by the top surface and lateral faces in the axial direction each become a right angle. 
         [0114]    As is shown, for example, in  FIG. 3C , the top surface  3   w  which is defined by the edges is provided in the form of a strip-like shape having a predetermined width measured from each axial end  3   h  and extending in a rotational direction. As is shown in  FIG. 3A , a center angle of the resin part  3  is 180 degrees, and a center angle of a portion thereof which is occupied by a vertical bar of the T-shape is referred to as an angle which can somehow resist an impact force imparted to the metal part. As is shown in  FIG. 3D ,  3 E, the T-shaped portion has a rectangular axial cross section corresponding to a location thereon in the rotational direction. 
         [0115]    As is shown in  FIGS. 3D and 3E , the horizontal bar of the T-shape is formed in such a manner that a radius from the center axis becomes constant as viewed in the side views. 
         [0116]    In the T-shaped locking projections  3   v,  dimensions and angles of respective portions are set to values with which the metal part  2  is prevented from being displaced from the resin part  3  even when impact forces F 13 , F 15 , F 17  are imparted to the weight in directions indicated by arrows in  FIGS. 3C ,  3 D and  3 E. 
         [0117]    The resin part  3  is formed by a resin injection molding technique such as an injection molding technique. Since structurally, end portions  2   c  of the metal part  2  are exposed from the resin part  3 , for example, when injection molding a resin part main body  3 , the metal part  2  is disposed to be erected within the dies in such a manner that one end portion  2   c  of the metal part  2  contacts a bottom surface within the dies, and a resin is injected into the dies in such a state. The resin so injected comes to stay on an inside of the metal part  2  and is then allowed to set there. Because of this, in the weight according to the embodiment, since the end portions  2   c  of the metal part  2  are level with the corresponding end faces of the resin part  3 , the manufacturing system and manufacturing process can be made easy and simple. 
         [0118]    The metal part  2  is made of a material having a high specific gravity such as, particularly, tungsten (W) or lead (Pb). The metal part  2  is formed in such a manner as to cover the resin part  3  in the radial direction and its radial outer surface is formed into the tubular surface  2   a.  Locking recesses  2   f  of the metal part  2  are configured in such a way as to be combined with the corresponding locking projections  3   v  of the resin part  3 . 
         [0119]    An elevated portion  2 C is provided between the locking recesses  2   f  at the axial ends of the metal part  2 . This elevated portion  2 C is brought into locking abutment with lateral faces  3 A of the T-shaped locking projections  3   v  at the axial ends  3   h  of the resin part  3 . 
         [0120]    The locking recess  2   f  has a T-shaped opening  2   g  which is brought into engagement with the T-shaped portion of the corresponding locking projection  3   v.    
         [0121]    The position of center of gravity of the conventional weight which is made of only tungsten lies in a position in the vicinity of the center axis of the shaft hole, whereas the position of center of gravity of the weight of the invention in which the metal part  2  having the T-shaped openings  2   g  is locked on the resin part  3  having the T-shaped locking projections  3   v  is shifted improvably to a position which lies apart from the axis center of the shaft hole  3   c  to be in the vicinity of where the resin part  3  is in abutment with the metal part  2 . 
         [0122]    By this improvement in position with respect to the center of gravity of the weight, the position of center of gravity can be shifted to the position which is spaced apart from the axis center of the shaft hole  3   c  by such a length as to obtain a necessary rotational moment. 
         [0123]    Since a suppressing function to suppress a radial load resulting when vibration is generated during normal rotation of the vibration motor weight employing the T-shaped locking projections becomes the same as a suppressing function to suppress a radial impact which is imparted in a direction shown in  FIG. 3D , a description which will be made hereinbelow with respect to a radial impact force should be understood as describing the suppression of the aforesaid radial load. 
         [0124]    An axial impact force will be described. 
         [0125]    As is shown in  FIG. 3C , when an impact force F 13  is applied in the axial direction, the impact force is received as small impact forces  14 F which are dispersed over a wide range on the whole lateral face  3 A of the locking projection  3   v  via the elevated portion  2 B of the metal part  2 . Because of this, the value of an impact force per unit area of the lateral face  3 A of the T-shaped locking projection ( 3   v ) becomes small, thereby making it possible to suppress quite a large magnitude of impact force. 
         [0126]    Next, a radial impact force will be described. 
         [0127]    As is shown in  FIG. 3D , when a radial impact force F 15  is applied to the weight, mainly to the metal part  2 , the impact force is received by the T-shaped locking projection ( 3   v ) of the resin main body  3  via a lower surface of the T-shaped opening  2   g.  Since the engagement between the lower surface of the T-shaped opening  2   g  and a radial surface of the T-shaped locking projection ( 3   v ) is strong and rigid, the radial impact force so applied is suppressed by the T-shaped locking projection portion ( 3   v ) of the resin part  3 . 
         [0128]    Next, an impact force will be described which is applied in a direction which is orthogonal to the axial direction and the radial direction (hereinafter, as a matter of conveniences, referred to as an orthogonal direction). 
         [0129]    As is shown in  FIG. 3E , when an impact force F 17  is applied to the weight, mainly to the metal part  2  in the orthogonal direction, the impact force is received by the T-shaped locking projection ( 3   v ) of the resin main body  3  via a lateral face of the T-shaped opening  2   g  of the metal part  2 . Since the engagement between the lateral face of the T-shaped opening  2   g  and an orthogonal surface of the T-shaped locking projection ( 3   v ) is strong and rigid, the orthogonal impact force thus applied is suppressed by the T-shaped locking projection portion of the resin part  3 . 
         [0130]    Next, impact force resistant characteristics of the weight for a vibration motor according to the embodiments will be described. 
         [0131]    In the following description, it is assumed that the weights according to the first to the third embodiments are prepared having the following particulars of (a)-(c). 
         [0132]    (a) Weights according to the first embodiment, in which the tapered arc-shaped locking projections are employed, are prepared. The weights according to this group has the following dimensions (refer to  FIG. 1A ). L 1  is 2.30 mm, L 2  is 1.75 mm, and L 3  is 1.50 mm. The taper angle is 26 degrees, and the width of the taper portion is 0.5 mm. As is shown in  FIG. 1C , the taper angle is referred to as the rising angle θ of the taper portion when the shaft direction of the outer surface of the metal part  2  is regarded as a base. 
         [0133]    (b) Weights according to the second embodiment, in which the edged arc-shaped locking projections are employed, are prepared. The weights according to this group has the following dimensions (refer to  FIG. 2A ). L 1  is 2.30 mm, L 2  is 1.75 mm, and L 3  is 1.50 mm. The axial width of the projecting portion is 0.43 mm. The length measured radially from the center axis of the shaft hole to the outer surface of the metal part is referred to as L 1 , the length measured similarly to the top surface of the locking projection as L 2 , and the length measured similarly to the outer surface of the axially central portion of the resin part as L 3 . 
         [0134]    (c) Weights according to the third embodiment, in which the T-shaped locking projections being employed, are prepared. The weight according to this group has the following dimensions (refer to  FIG. 3A ). L 1  is 2.30 mm, L 2  is 1.75 mm, and L 3  is 1.50 mm. The axial width of the projecting portion is 0.43 mm. The length measured radially from the center axis of the shaft hole to the outer surface of the metal part is referred to as L 1 , the length measured similarly to an inner surface of the horizontal bar of the T-shape of the T-shaped locking projection as L 2 , and the length measured similarly to the outer surface of the axially central portion of the resin part as L 3 . 
         [0135]    The impact force resistant characteristics of the weight employing the tapered arc-shaped locking projections, which is considered as having a lowest impact force resistant characteristic in the weights of three types, are be simulated. 
         [0136]    Conditions for measuring an impact force to be applied are the following (1)-(3). 
         [0137]    (1) A vibration motor equipped with the vibration motor weight of the invention is fitted in a mobile telephone, and an impact is to be measured which results when the mobile phone is caused to fall in a natural fashion from a height of 1 m. 
         [0138]    (2) A vibration motor of rubber type is used as the vibration motor placed in the mobile phone, and an impact applied to the weight is set to 5000 G. 
         [0139]    An impact that is actually applied to the weight under these conditions becomes as will be described later. 
         [0140]    (3) Genestar® G2330 (made by Kuraray Co., Ltd., Japan) is used as the material of the resin part, and tungsten is used as the material of the metal part. 
         [0141]    A measurement made under these conditions will result as shown in Table 1 below. 
         [0000]    
       
         
               
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                   
                 Impact 
               
               
                   
                   
                 applied to 
               
               
                   
                 Weight of 
                 the weight 
               
               
                   
                 the weight 
                 (N) 
               
               
                   
                 (g) 
                 5000 G 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Sample 1 
                 0.385 
                 18.9 
               
               
                   
                   
               
             
          
         
       
     
         [0142]    It is concluded from the result of the measurement that when the impact of 5000 g is applied to the weight of 0.385 g, an impact of 18.9 N is applied to the metal part. Herein, the impact (N: newton) applied to the weight is defined as below. 
         [0000]      Impact=weight of the weight (kg)×impact ( G )×9.8 (m/s 2 ) 
         [0143]    Analyzing conditions for analyzing the impact data above will be as below. 
         [0144]    (1) ANSYS Workbench Products 8.1 (made by CYBERNET SYSTEM Co., Ltd., Japan) is used as analyzing software. 
         [0145]    (2) Genestar® G2330 (made by Kuraray Co., Ltd., Japan) is used as the resin which is used in the weight. 
         [0146]    (3) Physical properties of the resin described under the item (2) are as follows: Young&#39;s modulus: 10280 MPa; Poisson&#39;s ratio: 0.37; Density: 1680 kg/m 3    
         [0147]    (4) Directions of load are as follows: 
         [0148]    (4a) Direction in which the metal part is displaced (axial direction); and 
         [0149]    (4b) Radial direction. 
         [0150]    A stress will be such as shown in Table 2 below which is applied to the rein main body part of the weight when an impact of 5000 g is imparted to the weight. 
         [0000]    
       
         
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
             
             
               
                   
                   
               
               
                   
                 Stress (MPa) 
               
             
          
           
               
                 (Resin main 
                   
                 Load to the 
                 axial 
                 radial 
               
               
                 body part) 
                 Impact (G) 
                 weight (N) 
                 direction 
                 direction 
               
               
                   
               
               
                 Sample 1 
                 5000 G 
                 18.9 N 
                 43.4 
                 355.8 
               
               
                   
               
             
          
         
       
     
         [0151]    According to the results of the analysis, assuming that the impact applied to the weight is 5000 G and the impact is applied to the weight in (4a) in the direction in which the metal part is displaced (the longitudinal direction of the shaft) and in (4b) the radial direction, stresses applied to the resin part then becomes 43.4 MPa in the axial direction and 355.8 MPa in the radial direction. 
         [0152]    The result is that since the strength of the resin of Sample 1, which is Genestar® G2330 (made by Kuraray Co., Ltd., Japan), is 222 MPa, although the resin of Sample 1 can resist the impact force in the axial direction, the resin cannot resist the impact force in the radial direction. However, since the cut-off portions of the resin part which act as the locking portions are provided in the four locations, the impact force per location becomes one fourth of the radial impact force. 
         [0153]    A resulting stress when the radial load applied to each of the cut-off portions of the resin of Sample 1 is one fourth becomes as shown in Table 3 below. 
         [0000]    
       
         
               
               
               
               
               
             
           
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                   
                 Impact 
                 Load Applied to 
                 Stress (MPa) 
               
               
                   
                   
                 Applied 
                 each Cut-off 
                 radial 
               
               
                   
                 (Cut-off) 
                 (G) 
                 (N) 
                 direction 
               
               
                   
                   
               
             
             
               
                   
                 Sample 1 
                 5000 G 
                 4.7 N 
                 89.0 
               
               
                   
                   
               
             
          
         
       
     
         [0154]    From the result shown in Table 3, when the four cut-off portions acting as the locking portions, since the radial stress applied to each cut-off portion becomes 89.0 MPa, the stress per cut-off portion becomes far smaller than the 222 MPa, which is the value of strength of the resin of Sample 1, Genestar® G2330 (made by Kuraray Co., Ltd., Japan). Therefore, the impact force can be suppressed sufficiently. 
         [0155]    It can be said from the results of the simulations that as long as the conditions described above are maintained, the vibration motor weight of the invention which employs the tapered arc-shaped locking projections has the sufficient impact force resistant characteristics against an anticipated large impact force. 
         [0156]    Next, the impact force resistant characteristics of the weight employing the edged arc-shaped locking projections are be simulated. 
         [0157]    As is shown in  FIGS. 2A-2H , when the edged portions (the angled stepped portions) being used as the support portions for the metal part in place of the tapered portions, since the axial cross section is changed from the triangular shape of the tapered portion to the rectangular shape of the edged portion, the cross sectional area of the edged portion can be increased to twice the cross sectional area of the tapered portion. Namely, the rectangular cross section is cut diagonally along the diagonal line connecting two diagonally confronting corners, the rectangular cross section or shape is divided into two triangles. Because of this, a stress resulting when the impact force is applied becomes one half the stress applied to the tapered locking projection as is shown in Table 4 below. 
         [0000]    
       
         
               
               
               
               
               
             
           
               
                   
                 TABLE 4 
               
               
                   
                   
               
               
                   
                   
                 Impact 
                 Load Applied 
                 Stress (MPa) 
               
               
                   
                 (Stepped 
                 Applied 
                 to weight 
                 radial 
               
               
                   
                 portion) 
                 (G) 
                 (N) 
                 direction 
               
               
                   
                   
               
             
             
               
                   
                 Sample 2 
                 5000 G 
                 18.9 N 
                 177.9 
               
               
                   
                   
               
             
          
         
       
     
         [0158]    As a result, when the load applied to the weight of Sample 2 is 18.9 N, a stress applied to the weight in the radial direction becomes 177.9 MPa, which is smaller than the value of strength of the resin (222 MPa) in the Sample 1, the resin of Genestar® G2330 (made by Kuraray Co., Ltd., Japan). Because of this, since the stress applied to the edged arc-shaped locking projection by the impact force becomes far smaller than 222 MPa which is the value of strength of Genestar® G2330 (made by Kuraray Co., Ltd., Japan), the impact force can be suppressed sufficiently. 
         [0159]    In this way, by changing the configuration of the locking projection from the tapered configuration to the edged configuration, the resin locking projection can be made to resist sufficiently the impact force generated when the mobile phone falls. 
         [0160]    A relationship between vibration amount and metal utilization amount is studied on the weight of the invention in which the resin part and the metal part are combined so as to be integrated into the single weight and the conventional weight which is made of only tungsten. 
         [0161]    As to the weight of the invention, from the viewpoint of standardizing the various parameters in relation to the metal parts which are formed into the different shapes, samples are specified to the weight which employs the tapered arc-shaped locking projections and the weight which employs the edged arc-shaped locking projections, and their configurations are standardized into a wide arc-shaped model shown in  FIGS. 4A-4D . 
         [0162]      FIGS. 4A-4D  shows explanatory diagrams of the wide arc-shaped model.  FIG. 4A  shows an example in which the center angle θ is fixed to 180 degrees and the width L of the arc is changed.  FIG. 4B  shows an example in which the center angle θ is fixed to 180 degrees and the width L of the arc is 1.2 mm,  FIG. 4C  shows an example in which the center angle θ is fixed to 150 degrees and the width L of the arc is 1.2 mm, and  FIG. 4D  shows an example in which the center angle θ is fixed to 110 degrees and the width L of the arc is 1.2 mm. 
         [0163]    In the following description, it is assumed that the vibration amount and respective parameters used to calculate a vibration amount are as below. 
         [0000]      Vibration amount  F=mrω   2 ( N ) 
         [0164]    where, 
         [0165]    m: mass (g); 
         [0166]    r: radius of center of gravity (mm); 
         [0167]    a: angular velocity (2πr)(rad/s); and 
         [0168]    f: rotational speed/60 (s). 
         [0169]    Values of the parameters of the conventional weight are assumed to be as below. 
         [0170]    m: 0.684; 
         [0171]    r: 0.805; 
         [0172]    rotational speed: 9000; 
         [0173]    F: 0.49; and 
         [0174]    specific gravity of the weight: 19.2 
       MEASUREMENT EXAMPLE 1  
       [0175]    An arc-shaped model shown in  FIG. 4A  is used. The arc-shaped model configures the example in which the center angle θ is 180 degrees and the width L of the arc is a variable L. In order to maintain the integrally molded shape constant, the radial thickness of a resin part changes as the width of the arc of a metal part changes. 
         [0176]    Characteristics with respect to vibration amount when the metal part is made of tungsten and the width L of the arc of the metal part is made to change become as shown in Table 5. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 5 
               
               
                   
               
               
                 Center Angle: 180 degrees, Rotational Speed: 9000 rpm 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Tungsten 
                 L (variable) (mm) 
                 0.4 
                 0.6 
                 0.8 
                 1.0 
                 1.2 
               
               
                   
                 m1 (g) 
                 0.20 
                 0.29 
                 0.36 
                 0.45 
                 0.49 
               
               
                   
                 r1 (mm) 
                 1.35 
                 1.29 
                 1.23 
                 1.18 
                 1.13 
               
               
                   
                 ω (rad/s) 
                 942 
                 942 
                 942 
                 942 
                 942 
               
               
                   
                 F1 (N) 
                 0.24 
                 0.33 
                 0.39 
                 0.47 
                 0.49 
               
               
                 Resin 
                 m2 (g) 
                 0.037 
                 0.031 
                 0.025 
                 0.020 
                 0.016 
               
               
                   
                 r2(mm) 
                 0.60 
                 0.48 
                 0.37 
                 0.24 
                 0.11 
               
               
                   
                 ω (rad/s) 
                 942 
                 942 
                 942 
                 942 
                 942 
               
               
                   
                 F2 (N) 
                 0.0197 
                 0.0132 
                 0.0082 
                 0.0043 
                 0.0016 
               
               
                 Integrally molded 
                 F total (N) 
                 0.259 
                 0.345 
                 0.401 
                 0.475 
                 0.493 
               
               
                 weight 
               
               
                   
               
             
          
         
       
     
         [0177]    A relationship between the width L (variable) of tungsten and F total of the integrally molded weight shown in Table 5 is shown in  FIG. 5A .  FIGS. 5A-5C  show graphs representing characteristics of Table 5 to Table 7. 
         [0178]    It can be said from  FIG. 5A  that the width L (variable) of tungsten and the vibration amount F total of the integrally molded weight are substantially in a proportional relationship. 
       MEASUREMENT EXAMPLE 2  
       [0179]    The arc-shaped model shown in  FIG. 4A  is used. The arc-shaped model configures an example in which the width of an arc is 0.8 mm and the center angle θ is a variable. In order to maintain the integrally molded shape constant, the center angle of the resin part changes as the center angle of the metal part changes. 
         [0180]    Characteristics with respect to vibration amount when the metal part is made of tungsten and the center angle θ of the metal part is made to change are becomes as shown in Table 6. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 6 
               
               
                   
               
               
                 Width of Arc of Metal Part: 1.2 mm, Rotational Speed: 9000 rpm 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Tungsten 
                 Center angle 
                 100 
                 120 
                 140 
                 160 
                 180 
               
               
                   
                 (variable) 
               
               
                   
                 (degrees) 
               
               
                   
                 m1 (g) 
                 0.20 
                 0.24 
                 0.28 
                 0.32 
                 0.36 
               
               
                   
                 r1 (mm) 
                 1.69 
                 1.59 
                 1.48 
                 1.36 
                 1.23 
               
               
                   
                 ω (rad/s) 
                 942 
                 942 
                 942 
                 942 
                 942 
               
               
                   
                 F1 (N) 
                 0.30 
                 034 
                 0.37 
                 0.39 
                 0.39 
               
               
                 Resin 
                 m2 (g) 
                 0.014 
                 0.017 
                 0.019 
                 0.022 
                 0.025 
               
               
                   
                 r2(mm) 
                 0.045 
                 0.40 
                 0.36 
                 0.35 
                 0.37 
               
               
                   
                 ω (rad/s) 
                 942 
                 942 
                 942 
                 942 
                 942 
               
               
                   
                 F2 (N) 
                 0.0056 
                 0.006 
                 0.0061 
                 0.0068 
                 0.0082 
               
               
                 Integrally molded 
                 F total (N) 
                 0.306 
                 0.345 
                 0.374 
                 0.393 
                 0.401 
               
               
                 weight 
               
               
                   
               
             
          
         
       
     
         [0181]    A relationship between the center angle θ of the metal part and vibration amount F total of the integrally molded weight shown in Table 6 is shown in  FIG. 5B . 
         [0182]    It can be said from  FIG. 5B  that the center angle θ (variable) and the vibration amount F total of the integrally molded weight are substantially in a proportional relationship. 
       MEASUREMENT EXAMPLE 3  
       [0183]    The arc-shaped models shown in  FIGS. 4B ,  4 C and  4 D are used. These arc-shaped models configure an example in which the width of the arc is 1.2 mm and the center angle is a variable. In order to maintain constant the shape of the integrally molded weight, the center angle of the resin main body is made to change as the center angle of the metal part changes. 
         [0184]    Characteristics with respect to variation amount when the metal part is made of tungsten and the center angle θ of the metal part is made to change become as shown in Table 7. 
         [0000]    
       
         
               
             
               
               
             
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 7 
               
             
             
               
                   
               
               
                 Width of Arc of Metal Part: 1.2 mm, Rotational Speed: 9000 rpm 
               
             
          
           
               
                   
                 Center angle (variable) 
               
               
                   
                 (degrees) 
               
             
          
           
               
                   
                 110 
                 150 
                 180 
               
               
                   
                   
               
             
          
           
               
                 Tungsten 
                 m1 (g) 
                 0.30 
                 0.41 
                 0.49 
               
               
                   
                 r1 (mm) 
                 1.51 
                 1.31 
                 1.13 
               
               
                   
                 ω (rad/s) 
                 942 
                 942 
                 942 
               
               
                   
                 F1 (N) 
                 0.40 
                 0.48 
                 0.49 
               
               
                 Resin 
                 m2 (g) 
                 0.0098 
                 0.0133 
                 0.0160 
               
               
                   
                 r2(mm) 
                 0.43 
                 0.36 
                 0.11 
               
               
                   
                 ω (rad/s) 
                 942 
                 942 
                 942 
               
               
                   
                 F2 (N) 
                 0.0037 
                 0.0042 
                 0.0061 
               
               
                 Integrally molded weight 
                 F total (N) 
                 0.406 
                 0.481 
                 0.493 
               
               
                   
               
             
          
         
       
     
         [0185]    A relationship between the center angle θ (variable) of the metal part and vibration amount F total of the integrally molded weight shown in Table 7 is shown in  FIG. 5C . 
         [0186]    It can be said from  FIG. 5C  that the center angle θ (variable) of the metal part and vibration amount F total of the integrally molded weight are substantially in a proportional relationship. 
         [0187]    Summary of Results of Measurements 
         [0188]    Lastly, in the measured data in the measurement examples 1 to 3 described above, vibration amount F and mass ml of the metal part (tungsten) are compared with those of the conventional examples and the results of the comparison are shown in Table 8 below. 
         [0189]    The tungsten amount (g) in Table 8 is a tungsten amount (g)=(the amount of tungsten in the metal part of the integrally molded weight of the invention)/(the amount of tungsten in the conventional weight which is made of only tungsten), which is represented in percent. When the tungsten amount of the integrally molded weight is reduced based on the tungsten amount of the conventional example, a minus sign, “−”, is put before numbers in percent. 
         [0190]    Similarly, the vibration amount in Table 8 is a vibration amount (N)=(the vibration amount of the integrally molded weight of the invention)/(the vibration amount of the conventional weight the whole of which is made of tungsten), which is represented in percent. When the vibration amount of the integrally molded weight is reduced based on the vibration amount of the conventional example, a minus sign, “−”, is put before numbers in percent. 
         [0000]    
       
         
               
               
             
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 8 
               
             
             
               
                   
                   
               
               
                   
                 Center angle θ 
               
               
                   
                 (variable) (degrees) 
               
             
          
           
               
                   
                 110 
                 150 
                 180 
               
               
                   
                   
               
             
          
           
               
                   
                 Tungsten amount (g) 
                 −56% 
                 −40% 
                 −28% 
               
               
                   
                 Vibration amount (N) 
                 −18% 
                 −2% 
                 0% 
               
               
                   
                   
               
             
          
         
       
     
         [0191]      FIG. 6  shows a graph which represents the characteristics shown in Table 8. 
         [0192]    It can be said from  FIG. 6  that the results of the comparison of the tungsten amounts in the metal arts are substantially in a proportional relationship as is shown as characteristic a in is  FIG. 6 . The results of the comparison of the vibration amounts are shown as characteristic b in  FIG. 6 . 
         [0193]    When the center angle θ is 180 degrees, the vibration amount of the weight of the invention remains the same as that of the conventional example while the utilization amount of tungsten is reduced by 28%. In addition, when the center angle θ is 150 degrees, the vibration amount of the weight of the invention is reduced only by 2% from that of the conventional example, while the utilization amount of tungsten is reduced by as much as 40%. Consequently, it is seen from these facts that with the center angle θ ranging from 150 degrees or more to 180 degrees or less, the weight of the invention is largely advantageous over the conventional example. 
       Other Embodiments 
       [0194]      FIGS. 7A-7F  show diagrams illustrating configurations of modified examples of the first to third embodiments, in which the locking configuration between a metal part and a resin part is inversed. 
         [0195]      FIGS. 7A and 7D  show a modified example to the weight which employs the tapered arc-shaped locking projections, of which  FIG. 7A  is an axial sectional view of the weight and  FIG. 7D  is a perspective view of a resin part. 
         [0196]      FIGS. 7B and 7E  show a modified example to the weight which employs the edged arc-shaped locking projections, of which  FIG. 7B  is a side view of the weight and  FIG. 7E  is a perspective view of a weight with a metal part indicated by solid lines as being transparent. 
         [0197]      FIGS. 7C and 7F  show a modified example to the weight which employs the T-shaped locking projections, of which  FIG. 7A  is an axial sectional view of the weight and  FIG. 7D  is a perspective view of a weight with a metal part indicated by solid lines as being transparent. 
         [0198]    In the modified example to the weight which employs the tapered arc-shaped locking projections, tapered faces are formed in such a manner as to be inclined in a reverse direction to that shown in  FIG. 1C  and an elevated portion is also formed in such a manner as to project in a reverse direction to the direction in the same figure, and a metal part  2  and a resin part  3  are configured in such a manner as to be locked together by axial recessed grooves  2   k  on the metal part  2  and elongated projections  3 D on the resin part  3 . 
         [0199]    The modified example will be described specifically below. Firstly, tapered faces  3 B are provided at axial ends of the resin main body  3  in such a manner that a radius from an axis center is increased as they extend from the respective axial ends towards the center of the resin part  3 . The tapered faces  3 B are represented as reverse tapered faces, and as is shown in  FIG. 7D , are provided in the form of a strip-like shape which has a predetermined width as measured from the respective axial ends and extend over a predetermined center angle range from the axis center in a rotational direction. In addition, the elongated projections  3 D are provided at ends of the resin part  3  in the rotational direction in such a manner as to extend in an axial direction. The elongated projection  3 D is preferably formed into a rectangular shape as viewed from the side. 
         [0200]    Reverse tapered faces  2   m,  which are combined with the reverse tapered faces and which has the same inclination as that thereof, are formed at axial ends of the metal part  2 . In addition, the axial recessed grooves  2   k  are provided in the vicinity of ends of the metal part  2  in the rotational direction. 
         [0201]    The reverse tapered faces  2   m  and  3 B of the metal part  2  and the resin part  3  are brought into abutment with each other in the axial direction, so as to suppress an impact force in the axial direction in which the reverse tapered faces  3 B of the resin part  3  are added to the reverse tapered faces  2   m  of the metal part  2 . 
         [0202]    The elongated projections  3 D of the resin part  3  are brought into linear engagement with the recessed grooves  2   k  of the metal part  2 , so as to suppress impact forces which are applied to the metal part in a radial direction and in an orthogonal direction. 
         [0203]    In the modified example to the weight which employs the edged arc-shaped locking projections, edges and an elevated portion are formed in reverse directions to the directions shown in  FIG. 2C , and an engagement configuration is adopted in which locking recesses which are provided at axial ends of a metal part in such a manner as to extend in a rotational direction and locking projections which are provided at axial ends of a resin part  3  in such a manner as to extend in the rotational direction are brought into engagement with each other. 
         [0204]    The modified example to the weight which employs the edged arc-shaped locking projections will be described specifically. While in the configuration shown in  FIG. 2C , the locking projections  3   m  are provided at the axial ends of the resin part  3  while extending in the rotational direction in such a manner as to project from the outer surface of the main body part  3 , in the modified example, as is shown in  FIG. 7E , locking projections  3 F are provided as stepped portion which are stepped one step downwards from an outer surface of the resin part  3 . As a result, side surfaces  3 E are produced between the locking projections  3 F and the outer surface of the resin part  3 . 
         [0205]    Since the locking projections  3 F of the resin part  3  are brought into engagement with the locking recesses  2   q  of the metal part  2 , impact forces acting on the metal part in a radial direction and an orthogonal direction can be suppressed. 
         [0206]    The side surfaces  3 E which drop perpendicularly from the outer surface of the resin part  3  in the vicinity of the axial ends thereof and connect to the locking projections function to suppress strongly an impact force acting on the metal part in the axial direction. 
         [0207]    In the modified example to the weight which employs the T-shaped locking projections, as is shown in  FIGS. 7C and 7F , T-shaped projecting portions  2 r are provided at axial ends of a metal part  2 , and T-shaped openings  3 G are formed in a resin part  3  in such a manner that the T-shaped projecting portions  2   r  are embedded therein. 
         [0208]    The T-shaped openings  3 G in the resin part suppress impact forces acting on the metal part in an axial direction, a radial direction and an orthogonal direction via the T-shaped projecting portions  2   r  which are brought into engagement with the openings. 
         [0209]    It is seen from the results of the measurements and analyses made on the representative examples that the configuration of the weight of the invention can be modified as long as the designed operations and functions are not altered. 
         [0210]    As described with reference to the embodiments, the weight for a vibration motor according to the invention adopts the configuration in which the metal part is placed to cover the outer side of the resin part which is securely attached to the shaft of the vibration motor and is locked thereon strongly and rigidly. Since the metal part is configured in such a manner as to be only placed to cover the outer side of the resin part in place of the metal part configuring the whole weight as in the conventional manner, compared with the conventional manner in which the whole weight is made of a metallic material only, the utilization amount of an expensive metallic material can be reduced. 
         [0211]    Since the resin metal part made of a resin and having a smaller specific gravity than the metal part is formed in such a manner as to extend from the rotational center and the metal part is disposed radially outwards of the resin part, the position of center of gravity of the weight can be shifted largely radially outwards compared with the position of center of gravity of the conventional weight which is made of metal only. By this configuration, although the weight of the metal part can be reduced much compared with the weight of the conventional weight, a value of rotational moment that is more or less the same as that obtained by the conventional weight can be obtained by extending the length from the axis center to the center of gravity. 
         [0212]    By adopting the configuration in which the locking projections at the axial ends of the resin part being locked, respectively, on the locking recesses at the axial ends of the metal part and the elevated portion lying between the locking recesses at the axial ends of the metal part being brought into abutment with the locking projections at the axial ends of the resin part, impacts acting on the weight, in particular, the metal part in three directions, the radial direction, the axial direction and the direction which is orthogonal to these directions, can be suppressed. 
         [0213]    In particular, by the locking projection being formed into any of the tapered arc-shaped locking projection which extends along the outer circumference of the semi-cylindrical portion, the edged arc-shaped locking projection and the T-shaped locking projection, impact acting on the locking projection in all the directions, that is, the radial direction, the axial direction and the direction which is orthogonal to these directions can be suppressed. 
         [0214]    The radial width and center angle of the metal part are appropriately set to determine a radial width and a center angle which can obtain a required vibration amount from the width/vibration amount characteristics and the center angle/vibration amount characteristics of the vibration motor weight of the invention which is made of the metal part and the resin part, and the radial width and the center angle so obtained are then reflected to the configuration of the vibration motor weight, thereby making it possible to provide a vibration motor weight having an appropriate configuration. 
         [0215]    In addition, a metal reduction ratio according to a center angle is obtained by comparing the conventional weight which is made of metal only with the metal/resin integrated weight of the invention, and then, a center angle according to a necessary reduction ratio is obtained from the center angle/reduction ratio characteristics, the center angle so obtained being reflected to an appropriate configuration. 
         [0216]    It is to be understood that the present invention is not limited to the specific embodiments described above and that the invention can be embodied with the components modified without departing from the spirit and scope of the invention. The invention can be embodied in various forms according to appropriate combinations of the components disclosed in the embodiments described above. For example, some components may be deleted from all components shown in the embodiments. Further, the components in different embodiments may be used appropriately in combination.