Abstract:
In a vibration actuator having a magnetic circuit component ( 10 ) and a coil ( 17 ) arranged in a gap ( 14 ) which is made at one side of the magnetic circuit in a predetermined direction, a space defining member ( 31, 32, 19 ) defines an accommodation space ( 34 ) to accommodate the magnetic circuit component and the coil. A supporting unit ( 16,18 ) supports the magnetic circuit component and the coil so that they are separately movable in the predetermined direction. The space defining member has a sound release hole ( 33 ) faced to the other side of the magnetic circuit component in the predetermined direction.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    This invention relates to a vibration actuator of a multi-functional type mounted in a mobile communication apparatus, such as a mobile telephone, to generate a ringing tone, a speech sound, and a vibration.  
           [0002]    A vibration actuator of the type comprises a magnetic circuit component having a gap on one side in a predetermined direction, a coil arranged in the gap of the magnetic circuit component, a supporting unit supporting the magnetic circuit component and the coil so that the magnetic circuit component and the coil are separately movable in the predetermined direction, and a vibration transmitting portion made of an elastic material such as rubber and fixing the supporting unit. The magnetic circuit component comprises a permanent magnet and a yoke coupled thereto. The supporting unit comprises a leaf spring through which the magnetic circuit component is supported on the vibration transmitting portion, and a vibration member through which the coil is supported on the vibration transmitting portion.  
           [0003]    When the coil is supplied with a driving current, the magnetic circuit component or the coil performs a reciprocal movement in the predetermined direction. When the driving current has a low frequency, the vibration transmitting portion serves as a fixed portion. On the other hand, when the driving current has a high frequency, the vibration transmitting portion serves as an elastic body which vibrates as a part of the vibration member. Thus, in each of a vibration mode and a sound mode, the magnetic circuit component and the vibration member are operated under mutual interference to transmit a sound or a vibration to the outside.  
           [0004]    However, since the magnetic circuit component is supported simply by the leaf spring, the operation will become unstable around a resonance frequency. This results in generation of a large harmonic distortion component.  
         SUMMARY OF THE INVENTION  
         [0005]    It is therefore an object of this invention to provide a multi-functional vibration actuator which is capable of suppressing an unstable operation around a resonance frequency to reduce a harmonic distortion component.  
           [0006]    It is another object of this invention to provide a multi-functional vibration actuator which is capable of preventing a coil from being released from a vibration member.  
           [0007]    Other objects of the present invention will become clear as the description proceeds.  
           [0008]    According to an aspect of the present invention, there is provided a vibration actuator comprising a magnetic circuit component having a gap on one side in a predetermined direction, a coil arranged in the gap, a supporting unit supporting the magnetic circuit component and the coil so that the magnetic circuit component and the coil are separately movable in the predetermined direction, and a space defining member defining an accommodation space accommodating the magnetic circuit component and the coil, the space defining member having a sound release hole faced to the other side of the magnetic circuit component in the predetermined direction.  
           [0009]    According to another aspect of the present invention, there is provided a vibration actuator comprising a magnetic circuit component having a gap on one side in a predetermined direction, a coil arranged in the gap a supporting unit supporting the magnetic circuit component and the coil so that the magnetic circuit component and the coil are separately movable in the predetermined direction, and a space defining member defining an accommodation space accommodating the magnetic circuit component and the coil, the space defining member having a sound release hole faced to the other side of the magnetic circuit component in the predetermined direction, the magnetic circuit component cooperating with the space defining member to define a damper space arranged between the magnetic circuit component and the cover and communicating with the sound release hole.  
           [0010]    According to still another aspect of the present invention, there is provided a vibration actuator comprising a magnetic circuit component having a gap on one side in a predetermined direction, a coil arranged in the gap, a supporting unit supporting the magnetic circuit component and the coil so that the magnetic circuit component and the coil are separately movable in the predetermined direction, and a space defining member defining an accommodation space accommodating the magnetic circuit component and the coil, the space defining member having a sound release hole faced to the other side of the magnetic circuit component in the predetermined direction, the magnetic circuit component cooperating with the space defining member to define a damper space arranged between the magnetic circuit component and the cover and communicating with the sound release hole, the sound release hole having an area corresponding to about 1.3 to 3.5% of an area of the cover. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0011]    [0011]FIG. 1A is a vertical sectional view of a vibration actuator according to a first embodiment of this invention;  
         [0012]    [0012]FIG. 1B is a partially-cutaway bottom view of the vibration actuator illustrated in FIG. 1A;  
         [0013]    [0013]FIG. 2 is a bottom view of a cover used in the vibration actuator illustrated in FIGS. 1A and 1B;  
         [0014]    [0014]FIG. 3 is a graph showing the relationship between a sound pressure level and a frequency characteristic of the vibration actuator;  
         [0015]    [0015]FIG. 4 is a vertical sectional view of a vibration actuator according to a second embodiment of this invention;  
         [0016]    [0016]FIG. 5 is a vertical sectional view of a vibration actuator according to a third embodiment of this invention;  
         [0017]    [0017]FIG. 6A is a vertical sectional view of a vibration actuator according to a fourth embodiment of this invention; and  
         [0018]    [0018]FIG. 6B is a partially-cutaway bottom view of the vibration actuator illustrated in FIG. 6A. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0019]    Referring to FIGS. 1A and 1B, description will be made of a vibration actuator according to a first embodiment of this invention.  
         [0020]    The vibration actuator has an internal magnet structure and comprises a magnetic circuit component  10  including a yoke  11 , a plate  12 , and a disk-shaped permanent magnet  13  interposed between the yoke  11  and the plate  12 . The vibration actuator further comprises a center shaft  15 , a suspension  16  of a plate shape, a coil  17  of a ring shape, a vibration member  18  of a plate shape, a vibration transmitting portion  19  of a ring shape. The center shaft  15  has a bolt-like shape or a pin-like shape and is inserted into a center hole of the magnetic circuit component  10  to coaxially position the yoke  11 , the plate  12 , and the permanent magnet  13 , and is fixed to the yoke  11 , the plate  12 , and the permanent magnet  13  by caulking or staking. Each of the yoke  11  and the plate  12  is fixed to the permanent magnet  13  under attraction force of the permanent magnet  13 , by a combination of the attraction force and an adhesive, or by caulking or staking. The center shaft  15  may be removed after the yoke  11 , the plate  12 , and the permanent magnet  13  are coaxially positioned. The magnetic circuit component  10  is provided with a gap  14  on one side in a predetermined direction, i.e., on an upper side.  
         [0021]    The suspension  16  comprises a ring-shaped plate provided with a plurality of helical leaf springs formed between an inner periphery and an outer periphery thereof. The suspension  16  has an inner peripheral portion fixed to an outer peripheral portion of the yoke  11  by the use of an elastic material  21 , such as a tackiness agent, an adhesive, or a resin or by means of caulking or staking. By fixing the suspension  16  to the outer peripheral portion of the yoke  11 , the magnetic circuit component  10  is prevented from being shaken. The suspension  16  has an outer peripheral portion fixed to the vibration transmitting portion  19 . Thus, the suspension  16  flexibly supports the magnetic circuit component  10  to the vibration transmitting portion  19 .  
         [0022]    In order to prevent the magnetic circuit component  10  from being brought into contact with the vibration member  18  due to an excessive amplitude of vibration, the vibration transmitting portion  19  is provided with at least stopper  22  formed on its inner peripheral portion. The number of stopper(s)  22  may be any desired number. The stopper  22  may be formed throughout the inner peripheral portion of the vibration transmitting portion  19 .  
         [0023]    The vibration member  18  has at the lower surface thereof an L-shaped portion  23  shaped in an L shape in section to make two particular surfaces perpendicular to each other. One of the particular surfaces is directed outward in a radial direction of the vibration actuator. An adhesive or the like fixedly attaches the coil  17  to the particular surfaces of the L-shaped portion  23  of the vibration member  18 . The coil  17  is disposed in the gap  14  of the magnetic circuit component  10 . Since the vibration member  18  with the coil  17  fixedly attached thereto has an L shape, the coil  17  is kept in contact with the vibration member  18  at two surfaces. Thus, the coil  17  is hardly released, as compared with the case where the coil  17  is attached to the vibration member  18  at a single surface.  
         [0024]    A coil wire  24  is extracted from the coil  17 . The coil wire  24  is adhered to the surface of the vibration member  18  by an adhesive or a tackiness agent so as not to cause an adverse influence upon the vibration of the vibration member  18 . Furthermore, the coil wire  24  is connected by a solder  27  to a terminal  26  of a terminal support  25  disposed at an outer peripheral portion of the vibration transmitting portion  19 . The coil wire  24  and a connecting portion thereof are covered with a protector  28 .  
         [0025]    The vibration transmitting portion  19  is formed by an elastic material such as a resin and has a cylindrical shape with an upper opening and a lower opening. The vibration transmitting portion  19  has an upper part and a lower part to which an upper cover  31  and a lower cover  32  are fixed, respectively. The upper cover  31  completely covers the upper opening of the vibration transmitting portion  19 . On the other hand, the lower cover  32  covers the lower opening of the vibration transmitting portion  19  but has a plurality of through holes  33  having a relatively small diameter. The through holes  33  collectively serve as a sound release hole or a sound emission hole for releasing or emitting a sound which will be generated by the vibration actuator. Each of the through holes  33  has a circular shape in the illustrated example but may have a shape of an ellipse, an elongated circle, a polygon, or a combination thereof. Alternatively, only a single through hole  33  may be formed. During the operation, the through holes  33  exhibit vibration attenuating function utilizing air viscosity. The upper and the lower covers  31  and  32  cooperate with the vibration transmitting portion  19  to serve as a space defining member defining an accommodation space  34  accommodating the magnetic circuit component  10  and the coil  17  and as a protector for a functional body providing the vibration.  
         [0026]    The yoke  11  has a lower part protruding outward to approach an inner peripheral surface of the vibration transmitting portion  19 . As a consequence, the yoke  11  cooperates with the lower cover  32  to define a damper space  35  located between the yoke  11  and the lower cover  32  and communicating with the through holes  33 . As will later be described in conjunction with a specific example, the total area of the sound release holes is selected to fall within a range between about 1.3% and about 3.5% of the bottom area of the lower cover  32 .  
         [0027]    The vibration member  18  has a flat shape, a saucer shape, a curved shape, a corrugated shape, or a combination thereof. If the vibration member  18  has a curved shape, a single radius of curvature or a combination of different radii of curvature is appropriately selected to achieve a predetermined sound characteristic. By increasing the rigidity of the vibration member  18  within the coil  17 , a harmonic distortion in a high-frequency region can be reduced.  
         [0028]    The vibration member  18  is made of polyether imide (PEI). Alternatively, the vibration member  5  may be made of another plastic film material such as polyethylene terephthalate (PET), polycarbonate (PC), polyphenylenesulfide (PPS), polyarylate (PAR), polyimide (PI), and aramide (PPTA, poly-(paraphenylene terephthalamide)).  
         [0029]    In order to assure a wider amplitude of the vibration member  18 , an outer peripheral portion of the vibration member  18  is fixed to the vibration transmitting portion  19  through an elastic material such as a tackiness agent, an adhesive, or a resin.  
         [0030]    When the coil  17  is supplied with a driving current, the magnetic circuit component  10  flexibly supported by the vibration member  18  and the suspension  16  vibrates. At this time, the vibration transmitting portion  19  serves as a fixed portion at a low frequency and, on the other hand, serves as an elastic body at a high frequency to vibrate as a part of the vibration member  18 . Thus, in each of a vibration mode and a sound mode, the magnetic circuit member  10  and the vibration member are operated under mutual interference. Herein, the through holes  33  exhibit a vibration attenuation function utilizing air viscosity.  
         [0031]    Referring to FIG. 2, description will be made of the lower cover  32 .  
         [0032]    The lower cover  32  has an outer diameter of 17 mm and a plurality of through holes  33 , five in number, formed at desired positions of the bottom surface to serve as sound release holes. The total area of the sound release holes falls within a range between about 3 and about 8 mm 2 . The number of the through holes  32  may be four or less or six or more. The vibration actuator as a whole has an outer dimension including the outer diameter of 17 mm substantially equal to that of the lower cover  32  and the thickness (the length in the vertical direction) of 4 mm.  
         [0033]    Referring to FIG. 3, description will be made of the relationship between a sound pressure level and a frequency characteristic, i.e., a sound characteristic of the vibration actuator.  
         [0034]    In the FIG. 3, a dash-and-dot line (a) and a dotted line (b) represent a fundamental wave and a harmonic distortion in case where the lower cover  32  is not used. In case where the lower cover  32  is not used, a desired sound pressure level is satisfied. However, the harmonic distortion of a large magnitude is produced due to an unstable nonlinear operation of the vibration member  18  around a resonance frequency (f 0 ).  
         [0035]    A thick solid line (c) and a thick dotted line (d) represent a fundamental wave and a harmonic distortion in case where the lower cover  32  in FIG. 2 is used. In case where the lower cover  32  is used, it is possible to suppress the unstable nonlinear operation of the vibration member  18  around the resonance frequency (f 0 ) so as to reduce the harmonic distortion component. In addition, it is possible to flatten the characteristic in a low frequency region.  
         [0036]    Referring to FIG. 4, description will be made of a vibration actuator according to a second embodiment of this invention. Similar parts are designated by like reference numerals and will not be described any longer.  
         [0037]    The vibration actuator of FIG. 4 is different from that of FIGS. 1A and 1B in that the L-shaped portion  23  of the vibration member  18  in FIG. 1A is replaced by an L-shaped portion  35 . The L-shaped portion  23  is shaped in an L shape in section to make two particular surfaces perpendicular to each other. The particular surfaces are directed inward in the radial direction of the vibration actuator. An adhesive or the like fixedly attaches the coil  17  to the particular surfaces of the L-shaped portion  23  of the vibration member  18 .  
         [0038]    Referring to FIG. 5, description will be made of a vibration actuator according to a third embodiment of this invention. Similar parts are designated by like reference numerals and will not be described any longer.  
         [0039]    The vibration actuator of FIG. 5 is different from that of FIGS. 1A and 1B in that the L-shaped portion  23  of the vibration member  5  in FIG. 1A is replaced by a U-shaped portion  36 . With this structure, the coil  17  is fitted in the U-shaped portion  36  and kept in contact with the vibration member  18  at three surfaces. Therefore, the coil  17  is hardly released from the vibration member  18  as compared with the L shape illustrated in FIGS. 1A or  4  and providing two surfaces as contact surfaces. Thus, this structure is highly reliable.  
         [0040]    Referring to FIGS. 6A and 6B, description will be made of a vibration actuator according to a third embodiment of this invention. Similar parts are designated by like reference numerals and will not be described any longer.  
         [0041]    In the vibration actuator of FIGS. 6A and 6B, the lower cover  32  is provided with a single through hole  37  having a relatively large diameter. The through hole  37  is faced to the magnetic circuit component  10  and serves as a sound release hole.  
         [0042]    While the present invention has thus far been described in connection with a few embodiments thereof, it will readily be possible for those skilled in the art to put this invention into practice in various other manners. For example, instead of the inner magnet structure mentioned above, the magnetic circuit component  10  may have an external magnet structure well known in the art. In the magnetic circuit component  10 , an end portion of the yoke may have an uneven or non-flat shape having a protrusion or a recess in order to facilitate generation of a high magnetic flux density. A magnetic pole of the permanent magnet  13  may be oriented in any direction. The suspension  16  may be integrally formed with the vibration transmitting portion by insert molding, welding, adhesion, or the like.