Abstract:
A vibrating device has an axially elongated frame, and a vibrating assembly including a hollow yoke. A magnetic driving device is provided for axially vibrating the vibrating assembly. A supporting shaft is provided for axially slidably supporting the vibrating assembly in the frame.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to a vibrating device having an axially driven movable member, and more particularly to a vibrating device mounted in a portable telephone for signaling a user by vibration of the movable member.  
           [0002]    In recent years, there is popularized various portable instruments such as portable telephone, PDA (Personal Digital Assistant), wearable computing instruments and so forth. In these instruments, vibrating devices are mounted for informing signals, by vibration without producing sounds.  
           [0003]    [0003]FIG. 7 is a perspective view showing a conventional vibration device disclosed in Japanese Patent Laid Open 7-107699. A direct current motor  131  has a rotating shaft  136  supported by a bearing  133 . There is formed an annular groove  135  on which an eccentric weight  134  is secured by a fixer  140 .  
           [0004]    In such a motor, since a commutator and a brush assembly are provided, manufacturing cost increases. It takes a time before the rotating speed approaches 7000˜8000 rpm. Therefore, the device is improper to a device which vibrates in accordance with a music signal. Furthermore, arcs generated between the commutator and brushes cause the quality and the life of the motor to reduce.  
           [0005]    The applicant of this patent application has proposed a vibrating device which may remove disadvantages of the prior art.  
           [0006]    [0006]FIG. 5 is a sectional side view of the vibrating device, FIG. 6 is a sectional view taken along a line VI-VI of FIG. 5.  
           [0007]    The vibrating device  210  comprises a cylindrical frame  211  made of a resin, a vibrating assembly  220  axially movably mounted in the frame  211 , and a magnetic driving device  219  mounted in the frame  211  at an end thereof.  
           [0008]    The vibrating assembly  220  comprises a cup-shaped yoke  221  having a bottom  221   b,  a cylindrical permanent magnet  222  secured to the yoke  221  at the axis thereof, and a pair of weights  223   a  and  223   b  secured to the outside and inside of the bottom  221   b  of the yoke  221 . The yoke  221  is slidably supported by three projections  214  formed on the inside wall of the frame  211 , so that the vibrating assembly  220  can be smoothly vibrated.  
           [0009]    The vibrating assembly  220  is resiliently held at a neutral position by a pair of coil springs  224  and  225  provided between both axial ends and the frame  211 .  
           [0010]    The magnetic driving device  219  comprises a coil bobbin  213  cantilevered in the end of the frame  211  and a driving coil  212  provided on the coil bobbin  213 . The coil bobbin  213  is made of a metal pipe, on the peripheral surface of which is formed an insulation layer. The coil bobbin  213  is inserted in a space  226  between the yoke  221  and the permanent magnet  222 .  
           [0011]    The primary resonance frequency of the vibrating assembly  220  is 100-160 Hz, the vibration at which is properly transmitted to the user&#39;s body. An alternating signal having a basic frequency of the primary resonance frequency is applied to the driving coil  212  from terminals  235  and  236 , so that the vibrating assembly  220  is axially vibrated.  
           [0012]    However, large friction generates between the outside wall of the vibrating assembly  220  and the inside wall of the frame  211 , because of a large sliding area there-between. The large friction causes the efficiency of the device to reduce.  
         SUMMARY OF THE INVENTION  
         [0013]    An object of the present invention is to provide a vibrating device in which the friction is reduced, thereby improving the efficiency of the device.  
           [0014]    According to the present invention, there is provided a vibrating device comprising an axially elongated frame, a vibrating assembly including a hollow yoke having an opening at an end thereof, and a permanent magnet secured to the yoke, a magnetic driving device including a coil bobbin cantilevered in the frame and having an end portion inserted in the yoke from the opening, a driving coil mounted on the coil bobbin, at least one spring provided for resiliently holding the vibrating assembly in the frame, characterized in that at least one supporting shaft is provided for axially slidably supporting the vibrating assembly in the frame.  
           [0015]    In an aspect of the present invention, the supporting shaft is axially slidably mounted in the frame, and the vibrating assembly is secured to the supporting shaft.  
           [0016]    In another aspect, the supporting shaft is secured to the frame, and the vibrating assembly is slidably mounted on the supporting shaft.  
           [0017]    In further aspect, the supporting shaft comprises a pair of shafts, the shafts are secured to axial both ends of the vibrating assembly, and slidably mounted in the frame.  
           [0018]    The fixed supporting shaft has a small diameter portion at a central portion of the shaft.  
           [0019]    These and other objects and features of the present invention will become more apparent from the following detailed description with reference to the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0020]    [0020]FIG. 1 is a sectional side view showing a first embodiment of the present invention;  
         [0021]    [0021]FIG. 2 is a sectional side view of a second embodiment of the present invention;  
         [0022]    [0022]FIG. 3 is a sectional side view showing a third embodiment of the present invention;  
         [0023]    [0023]FIG. 4 is a driving circuit for driving the vibrating device;  
         [0024]    [0024]FIG. 5 is a sectional side view of the vibrating device;  
         [0025]    [0025]FIG. 6 is a sectional view taken along a line VI-VI of FIG. 5; and  
         [0026]    [0026]FIG. 7 is a perspective view showing a conventional vibration device. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0027]    [0027]FIG. 1 is a sectional side view showing a first embodiment of the present invention.  
         [0028]    A vibrating device  10  of the present invention comprises a cylindrical frame  11  made of a resin, a supporting shaft  29  axially movably mounted in the frame  11 , a vibrating assembly  20  secured to the shaft  29 , and a magnetic driving device  19  mounted in the frame  11 .  
         [0029]    The vibrating assembly  20  comprises a cup-shaped yoke  21  secured to the shaft  29 , a cylindrical permanent magnet  22  and a cylindrical pole piece  23  secured to the shaft  29 , and a weight  28  secured to the outside of the bottom of the yoke  21 .  
         [0030]    The vibrating assembly  20  is resiliently held at a neutral position by a pair of coil springs  24  and  25  provided between both axial ends and the frame  11 .  
         [0031]    The magnetic driving device  19  comprises a coil bobbin  13  cantilevered in the end of the frame  11  and a driving coil  12  provided on the coil bobbin  13 . The coil bobbin  13  is made of a metal pipe, on the peripheral surface of which is formed an insulation layer. There is formed spaces  30  and  31  between the yoke  21  and the permanent magnet  22 . The shaft  29  is slidably supported by a supporting member  11   a  secured to the coil bobbin  13  and a supporting member  32  secured to the frame  11 .  
         [0032]    The primary resonance frequency of the vibrating assembly  20  is 100-160 Hz, the vibration at which is properly transmitted to the user&#39;s body. An alternating signal having a basic frequency of the primary resonance frequency is applied to the driving coil  12  from terminals  35  and  36 , so that the vibrating assembly  20  is axially vibrated.  
         [0033]    [0033]FIG. 4 is a driving circuit for driving the vibrating device.  
         [0034]    In operation, when a low frequency signal of about 100-300 Hz is applied to an input terminal  48  of the driving circuit  50 , the transistors  51  and  54  are turned on at a high level of the input signal. Consequently, a current passes the driving coil  12  through the transistors  51  and  54  from the Vcc to GND. And the current passes through the transistor  53 , coil  12  and transistor  52  at a low level of the input signal. Thus, an alternating current of the low frequency corresponding to the input low frequency signal flows in the coil  12 . Consequently, the vibrating assembly  20  is axially vibrated together with the shaft  29 .  
         [0035]    The sliding area between the shaft  29  and the supporting members  11   a  and  32  is small. Therefore, the friction there-between is very small compared with that of the conventional device of FIG. 5.  
         [0036]    [0036]FIG. 2 is a sectional side view of a second embodiment of the present invention.  
         [0037]    In the device, a shaft  40  is secured to the supporting members  11   a  and  32 . The yoke  21 , permanent magnet  22 , pole piece  23  and weight  28  are fixed with each other and slidably mounted on the shaft  40 . There is formed a small diameter portion  41  at a central portion of the shaft  40  so that the sliding area between the vibrating assembly  20  and the shaft  40  is reduced. Other parts are the same as the device of FIG. 1 and identified by the same reference numerals.  
         [0038]    The vibrating assembly  20  is vibrated along the shaft  40 .  
         [0039]    [0039]FIG. 3 is a sectional side view showing a third embodiment of the present invention.  
         [0040]    A vibrating device  50  of the third embodiment comprises, a vibrating assembly  55 , and a magnetic driving device  51  mounted in the frame  11 .  
         [0041]    The vibrating assembly  55  comprises a cup-shaped yoke  52 , a cylindrical solid permanent magnet  53  secured to the bottom of yoke  52 , a cylindrical solid pole piece  54  secured to the permanent magnet  53 , and a weight  55  secured to the outside of the bottom of the yoke  52 . There is a provided a pair of supporting shafts  56  and  57 . The supporting shaft  56  is secured to the pole piece  54  and slidably supported by the supporting member  11   a.  The supporting shaft  57  is secured to the yoke  52  and slidably supported by the supporting member  32 .  
         [0042]    Other parts are the same as the first embodiment.  
         [0043]    The vibrating assembly  55  vibrates together with the supporting shafts  56  and  57 .  
         [0044]    While the invention has been described in conjunction with preferred specific embodiment thereof, it will be understood that this description is intended to illustrate and not limit the scope of the invention, which is defined by the following claims.