Abstract:
A vibrator includes a voice coil and a vibrating member that vibrates along the axial direction of the voice coil when it is excited by application of an alternating current thereto. A suspension supports the vibrating member vibratably in the axial direction. A casing houses the voice coil, the vibrating member, and the suspension. A buffering member is provided so that the vibrating member strikes the buffering member when the vibration amplitude of the vibrating member has exceeded a predetermined value in a resonance region around the resonance point of the vibrating member.

Description:
[0001]    This application claims priority under 35 U.S.C. §119 to Japanese Patent Application Nos. JP2006-047317 filed Feb. 23, 2006, and JP2006-101559 filed Apr. 3, 2006, the entire content of which is hereby incorporated by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a vibrator that may be incorporated in a small-sized device such as a mobile cellular phone, a watch and other portable devices. More particularly, the present invention relates to a vibrator for use in a cellular phone to indicate an incoming call to a user. 
         [0004]    2. Description of the Related Arts 
         [0005]    Conventionally, a portable terminal device such as a cellular phone has a vibrator incorporated therein as a device that indicate an incoming call to the user by vibrations of the cellular phone body, and there has been a demand for miniaturization of the vibrator. Under these circumstances, the present applicant proposed a compact vibrator as shown in  FIG. 10  (see Japanese Patent Application No. 2006-026447). 
         [0006]    The proposed vibrator includes a voice coil  10  and a vibrating member  20  that vibrates in the axial direction of the voice coil  10  in response to the application of an alternating current to the voice coil  10 . First and second suspensions  3  and  5  are disposed facing each other across the vibrating member  20  to support it vibratably in the axial direction. The vibrator further has a casing that houses the voice coil  10 , the vibrating member  20 , and the suspensions  3  and  5 . When the voice coil  10  is supplied with an alternating current, the vibrating member  20  is reciprocated in the vicinity of a resonance frequency determined by the weight of the vibrating member  20  and the spring constant of the pair of suspensions  3  and  5 , thereby generating vibrations. 
         [0007]      FIG. 11  is a graph showing the relationship between the frequency and acceleration of the above-described vibrator. In the conventional vibrator, an input signal of a predetermined frequency in a narrow resonance frequency region t is applied to the voice coil  10 , thereby obtaining vibrations with a desired amplitude. The resonance frequency region is, however, determined by the weight of the vibrating member  20  and the spring constant of the suspensions  3  and  5 , as stated above. Therefore, if there are variations in the weight of the vibrator constituent elements and the spring constant of the suspensions for each vibrator, the resonance frequency region shifts in accordance with the variations. Consequently, even if an input signal of a predetermined frequency is supplied to the voice coil, the frequency of the input signal may fail to fall within the resonance frequency region t of the vibrator. In such a case, the amplitude of vibrations reduces to a considerable extent. If such a vibrator is installed in a cellular phone, it may be impossible to obtain a sufficient vibration amplitude to surely indicate an incoming call to the user. 
       SUMMARY OF THE INVENTION 
       [0008]    Accordingly, an object of the present invention is to provide a vibrator capable of surely transmitting vibrations of the vibrating member to the casing even if the frequency of the input signal deviates from the resonance point (resonance frequency) of the vibrating member. 
         [0009]    The present invention provides a vibrator including a voice coil and a vibrating member that vibrates along the axial direction of the voice coil when it is excited by application of an alternating current thereto. A suspension supports the vibrating member vibratably in the axial direction. A casing houses the voice coil, the vibrating member, and the suspension. A buffering member is provided so that the vibrating member strikes the buffering member when the vibration amplitude of the vibrating member has exceeded a predetermined value in a resonance region around the resonance point of the vibrating member. 
         [0010]    The term “resonance region” as used herein means a frequency region including the resonance point and the rising to and the falling from the resonance point. In this vibrator, even if the frequency of the alternating current applied to the voice coil deviates from the resonance point, or resonance frequency, of the vibrating member, variations of vibrators can be reduced by appropriately setting the buffering member. 
         [0011]    The buffering member may be made from a foam material such as a microcellular polymer. 
         [0012]    The arrangement may be as follows. The vibrating member and the buffering member have respective surfaces that strike each other when the vibration amplitude of the vibrating member has exceeded the above-described predetermined value, and at least one of the surfaces has a plurality of projections extending toward the other surfaces. 
         [0013]    In this case, the buffering member is preferably made from silicone rubber. 
         [0014]    The suspension may have a first and a second suspensions that support the vibrating member from both sides thereof in the axial direction. 
         [0015]    Further, the vibrator may be arranged as follows. The casing includes a cup-shaped member having a tubular portion coaxial with respect to the voice coil, a bottom wall portion that closes one end of the tubular portion, and an opening at the other end of the tubular portion. The casing further includes a circular base plate that closes the opening of the cup-shaped member and that supports the voice coil. The base plate has wiring for supplying an input signal to the voice coil. The buffering member is mounted on the base plate so as to face the vibrating member inside the voice coil. The spacing a between the buffering member and the vibrating member in the axial direction and the spacing b in the axial direction between the vibrating member and the bottom wall of the casing satisfy the relationship of b≧1.2×a. 
         [0016]    The above and other objects, features and advantages of the present invention will become more apparent from the following description of the preferred embodiments thereof, taken in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1A  is a perspective view of a vibrator according to a first embodiment of the present invention. 
           [0018]      FIG. 1B  is a sectional view taken along the line  1 B- 1 B in  FIG. 1A . 
           [0019]      FIG. 2  is a graph showing the relationship between the frequency and acceleration of the vibrator according to the first embodiment of the present invention. 
           [0020]      FIG. 3  is a sectional view of a vibrator according to a second embodiment of the present invention. 
           [0021]      FIG. 4  is a sectional view of a vibrator according to a third embodiment of the present invention. 
           [0022]      FIG. 5  is a sectional view of a vibrator according to a fourth embodiment of the present invention. 
           [0023]      FIG. 6  is a sectional view of a vibrator according to a fifth embodiment of the present invention. 
           [0024]      FIG. 7A  is a plan view of a first suspension in an embodiment of the present invention. 
           [0025]      FIG. 7B  is a sectional view taken along the line  7 B- 7 B in  FIG. 7A . 
           [0026]      FIG. 8A  is a plan view of a second suspension in an embodiment of the present invention. 
           [0027]      FIG. 8B  is a sectional view taken along the line  8 B- 8 B in  FIG. 8A . 
           [0028]      FIG. 9  is a sectional view of a vibrator according to a sixth embodiment of the present invention. 
           [0029]      FIG. 10  is a sectional view of a vibrator according to a related art. 
           [0030]      FIG. 11  is a graph showing the relationship between the frequency and acceleration of the vibrator according to the related art. 
           [0031]      FIG. 12  is a sectional view of a vibrator according to a seventh embodiment of the present invention. 
           [0032]      FIG. 13  is a perspective view of a buffering member used in the vibrator according to the seventh embodiment. 
           [0033]      FIG. 14  is a graph showing the results of a simulation analysis to examine the cushioning properties of the buffering member used in the vibrator according to the seventh embodiment and buffering members used in other embodiments. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0034]    Embodiments of the vibrator according to the present invention will be described below with reference to the accompanying drawings. 
         [0035]    A vibrator according to a first embodiment of the present invention has, as shown in  FIG. 1B , a cylindrical voice coil  10 , a vibrating member  20 , and a first and a second suspensions  3  and  5  that resiliently support the vibrating member  20 . When the voice coil  10  is supplied with an alternating current, the vibrating member  20  is reciprocated in the axial direction of the voice coil  10 , thereby generating vibrations. The voice coil  10 , the vibrating member  20 , and the first and the second suspensions  3  and  5  are housed in a casing  15 . The casing  15  is formed from a cup-shaped member  6  that is coaxial with respect to the voice coil  10 . The casing  15  further has a circular base plate  1  that closes the opening of the cup-shaped member  6  and that supports the voice coil  10 . The base plate  1  has wiring for supplying an input signal to the voice coil  10 . The vibrating member  20  has a cup-shaped yoke  9  placed coaxially with respect to the voice coil  10 . A magnet  8  and a top plate  2  are successively stacked in the yoke  9  in coaxial relation thereto. The magnet  8  is secured to the bottom inner surface of the yoke  9 . Further, an annular weight  7  is secured to the outer periphery of the yoke  9 . The voice coil  10  is inserted into a magnetic gap g formed between the outer peripheral surface of the top plate  2  and the inner peripheral surface at the upper end of the yoke  9 . 
         [0036]    The first suspension  3  has, as shown in  FIGS. 7A and 7B , a ring-shaped inner peripheral portion  21 , a ring-shaped outer peripheral portion  22 , and a pair of arcuate arm portions  23  provided in an annular space between the inner and outer peripheral portions  21  and  22 . Each arm portion  23  is connected at one end thereof to the inner peripheral portion  21  and at the other end thereof to the outer peripheral portion  22 . The inner peripheral portion  21  of the first suspension  3  is fixed to the upper end surface of the yoke  9 . The outer peripheral portion  22  of the first suspension  3  is secured to a frame member  4  fixed to the inner peripheral surface of the casing  15 . The second suspension  5  has, as shown in  FIGS. 8A and 8B , a ring-shaped inner peripheral portion  25 , a ring-shaped outer peripheral portion  26 , and a pair of arcuate arm portions  27  provided in an annular space between the inner and outer peripheral portions  25  and  26 . The inner peripheral portion  25  has a stepped portion  25   a  that is joined to the lower end surface of the yoke  9 . The outer peripheral portion  26  is integrally formed with a tubular member that is engaged with the bottom wall of the cup-shaped member  6  and that is fitted in engagement with the inner peripheral surface of the cup-shaped member  6 . 
         [0037]    The base plate  1  has a buffering member  11  secured to the lower surface thereof (i.e. the surface facing the vibrating member  20 ) with an adhesive or pressure-sensitive adhesive tape, for example. The buffering member  11  is made from a microcellular polymer foam. The buffering member  11  is provided so that the vibrating member  20  strikes it when the vibration amplitude of the vibrating member  20  has increased to a predetermined amplitude on its way to the amplitude at the resonance point thereof. “Poron” (trade name), which is commercially available, is usable as a microcellular polymer foam for the buffering member  11 . It is also possible to use foam materials such as polyurethane foam and polyethylene foam for the buffering member  11 . Experimental results revealed, however, that the most favorable effects were obtained when “Poron” (trade name), which is commercially available, was used as a microcellular polymer foam. 
         [0038]      FIG. 2  is a graph showing the relationship between the frequency and acceleration of the vibrator according to this embodiment. It will be understood from  FIG. 2  that in this vibrator the vibrating member  20  strikes the buffering member  11  in a frequency region (band) s, with the vibration amplitude of the vibrating member  20  being suppressed. 
         [0039]    Conventionally, to obtain a desired vibration amplitude (acceleration) from a vibrator, the frequency of the input signal is set substantially the same as the natural frequency of the vibrating member of the vibrator thereby obtaining an amplitude in the vicinity of the resonance point of the vibrating member. In this case, however, if the resonance point of the vibrating member varies for each vibrator owing to variations in weight of the vibrator constituent elements, large variations occur in the obtained vibration amplitude (acceleration) of the vibrating member. To solve this problem, the buffering member is provided so that the vibrating member strikes it as stated above, whereby the amplitude (acceleration) to be obtained is made smaller than that obtained at the resonance point [like an amplitude (acceleration) obtained with an input frequency in a predetermined range s around the resonance point, as shown in  FIG. 2 ]. If the desired vibration amplitude (acceleration) of the vibrating member of the vibrator is set small as described above, the casing can be surely vibrated as long as the frequency of the input signal falls within a range in which the desired amplitude is obtained. Consequently, it is possible to solve the above-described problem with the conventional vibrator. 
         [0040]    Generation of noise can be prevented by setting the space b in  FIG. 1B  larger than the space a (e.g. b≧1.2a) so that the vibrating member  20  cannot strike the bottom wall of the casing  15  even if the vibrating member  20  oscillates to a considerable extent due to an excessive input. 
         [0041]      FIG. 3  shows a vibrator according to a second embodiment of the present invention. In this vibrator, as shown in the figure, a buffering member  12  formed from “Poron”, which is a microcellular polymer foam, is provided on the upper surface (surface facing the vibrating member  20 )  6   a  of the bottom wall of the cup-shaped member  6  of the casing  15 . 
         [0042]      FIG. 4  shows a vibrator according to a third embodiment of the present invention. In this vibrator, as shown in the figure, a buffering member  11  made from “Poron”, which is a microcellular polymer foam, is provided on the lower surface  1   a  of the base plate  1 . In addition, a buffering member  12  made from “Poron”, which is a microcellular polymer foam, is provided on the upper surface  6   a  of the bottom wall of the cup-shaped member  6 . The vibrator of this embodiment offers the same advantageous effects as those obtained from the vibrator of the first embodiment. It should be noted, however, that the vibrator of the first embodiment is preferable because it needs to install a buffering member at only one place. 
         [0043]      FIG. 5  shows a vibrator according to a fourth embodiment of the present invention. In this vibrator, as shown in the figure, a buffering member  13  made from “Poron”, which is a microcellular polymer foam, is provided on the upper surface (surface facing the base plate  1 ) of the top plate  2 , and a buffering member  12  made from “Poron” is provided on the bottom wall  6   a  of the cup-shaped member  6 . In addition, ring-shaped buffering members  16  and  17  are provided on the weight  7 , which is secured to the yoke  9 . The upper surface of the buffering member  16  provided on the weight  7  is substantially flush with the upper surface  7   a  of the weight  7 . The buffering member  17  is positioned on the lower surface  7   b  of the weight  7  so as to face the bottom wall of the casing  15 . The buffering member  17  has an inner diameter with which it will not interfere with the second suspension  5 . 
         [0044]      FIG. 6  shows a vibrator according to a fifth embodiment of the present invention. In this vibrator, as shown in the figure, a buffering member  14  made from a microcellular polymer foam is provided on the second suspension  5 , and a buffering member  11  is provided on the lower surface  1   a  of the base plate  1 . In addition, buffering members  16  and  17  are provided on the weight  7 , which is secured to the yoke  9 . The buffering members  14 ,  11 ,  16  and  17  may be made from “Poron”. 
         [0045]    The buffering member  14  provided on the second suspension  5  is secured to the lower surface of the inner peripheral portion  25  of the second suspension  5 . The buffering member  14  extends downward beyond the stepped portion  25   a  of the second suspension  5 . 
         [0046]      FIG. 9  shows a vibrator according to a sixth embodiment of the present invention. In this vibrator, as shown in the figure, a buffering member  13  is provided on the top plate  2 , and a buffering member  14  is provided on the lower end surface of the yoke  9 . In addition, buffering members  16  and  17  are provided on the weight  7 . 
         [0047]    In the vibrators according to the foregoing embodiments, the vibrating member is arranged to strike the casing through the buffering member at frequencies in a wide frequency region including the resonance point of the vibrating member. Therefore, even if the resonance point (i.e. natural frequency) of the vibrating member varies for each vibrator due to variations in weight of the vibrator constituent elements, the casing can be surely vibrated as long as the frequency of the input signal to the coil falls within the above-described wide frequency region. 
         [0048]    The vibrators according to the foregoing embodiments use a microcellular polymer as a material of the buffering members  11  to  14 , by way of example. This material is, however, unsuitable for surface mount processing carried out at high temperature because of its relatively low heat resistance.  FIG. 12  shows a vibrator according to a seventh embodiment of the present invention, which has a buffering member improved in heat resistance in the view mentioned above. 
         [0049]    The vibrator of the seventh embodiment has the same basic structure as that of the first embodiment shown in  FIGS. 1A and 1B . The seventh embodiment differs from the first embodiment as follows. The buffering member  11  provided on the base plate  1  is made from silicone rubber, which is more heat-resistant than microcellular polymer. Further, as shown in  FIG. 13 , the buffering member  33  is formed into an annular shape as a whole, and a plurality of circular columnar projections  33   a , each having a hemispherical distal end, are formed on one side of the annular buffering member  33 . The number of the projections  33   a  and the size of the outer diameter thereof are determined according to the required buffering capacity.  FIG. 14  shows the results of a simulation analysis (FEM analysis) to examine flexibility of two different types of buffering members when the top plate  2  of the vibrating member  20  strikes these buffering members by vibration. One of the two types of buffering members was formed into a merely annular member from a microcellular polymer as in the case of the vibrator shown in  FIG. 1 . The other type of buffering member was made from silicone rubber as shown in  FIG. 13  (the number of projections  33   a:  8; the size of the outer diameter: 0.3 mm). It will be understood from  FIG. 14  that the buffering member having a configuration as in the seventh embodiment (i.e. the configuration as shown in  FIG. 13 ) exhibits fairly high flexibility, or cushioning properties, as compared with the buffering member having a merely annular shape as in the other embodiments. 
         [0050]    It should be noted that the present invention is not necessarily limited to the foregoing embodiments but can be modified in a variety of ways without departing from the gist of the present invention.