Patent Publication Number: US-7583812-B2

Title: Electro-acoustic converter and electronic device using the same

Description:
This application is a U.S. NATIONAL PHASE APPLICATION OF PCT INTERNATIONAL APPLICATION PCT/JP2005/011414. 
     TECHNICAL FIELD 
     The present invention relates to an electro-acoustic converter used in an audio apparatus or a data communications apparatus of various kinds, and also an electronic device such as a mobile telephone and an electronic game machine. 
     BACKGROUND ART 
       FIG. 6  is a cross-sectional view of a conventional electro-acoustic converter used as a loud speaker or a receiver incorporated in an electronic device such as a mobile telephone. Magnet  1  is sandwiched between upper plate  2  and yoke  3  to configure magnetic circuit  4  of an inner-magnet type. Yoke  3  is press-fitted into frame  6  made of a resin material and bonded with adhesive. Diaphragm  7  is fixed to a circumferential edge of frame  6 . Voice coil  8  for vibrating diaphragm  7  is attached to diaphragm  7  in a manner that it is located in magnetic gap  5  of magnetic circuit  4 . 
     A lead wire of voice coil  8  is connected to one end of terminal  10  by soldering. Frame  6  retains a part of terminal  10  in its molded structure. Terminal  10  is bent over at bent portion  10 A so as not to protrude outward from a boundary of an outer dimension of frame  6 . Terminal  10  is formed by a process of bending a piece of sheet metal, and movable end  10 B is used to make contact with an power supply section of a system by taking advantage of a spring tension of the sheet metal. Frame  6  is provided with stopper  9  protruding from the lower end thereof, which is formed unitary with frame  6  during a process of injection-molding the resin material. 
     Stopper  9  restricts a bending range of terminal  10  so as to prevent it from being bent beyond a threshold value of reversibility of a material of the sheet metal constituting terminal  10 . This prevents terminal  10  from being bent to any such degree that exceeds the threshold value of reversibility even when loud speaker  11  is forcibly pressed while being mounted to an apparatus. It thus clears such drawbacks as terminal  10  getting damaged when loud speaker  11  is mounted to an apparatus, and terminal  10  becoming unstable to maintain contact with the apparatus due to a deficiency of spring tension of terminal  10 . Loud speaker  11  illustrated above is disclosed in, for example, Japanese Patent Unexamined Publication, No. 2003-37890. 
     When an apparatus incorporating loud speaker  11  is accidentally dropped, however, there may be a possibility that stopper  9  becomes broken due to an excessive force of impact. If stopper  9  is broken in this way, it may cause metal terminal  10  to exceed the threshold value of reversibility of the spring tension, thereby resulting in an unstable contact with the power supply section of the apparatus. As a consequence, there can be a failure of contact, which interrupts signals whenever the apparatus is subjected to an impact or a vibration. 
     SUMMARY OF THE INVENTION 
     An electro-acoustic converter of the present invention has a magnetic circuit, a diaphragm, a voice coil, a terminal, and a stopper. A frame is bonded to the magnetic circuit, and the diaphragm is bonded to a circumferential edge of the frame. The voice coil is attached to the diaphragm in a manner that a part of it is located in a magnetic gap of the magnetic circuit. The terminal is made of a sheet metal having both spring property and electrical conductivity, and a part of it is fixed to the frame. The terminal has a bent portion and a contact portion, and it is electrically connected to the voice coil. The stopper is provided around a portion of the sheet metal constituting the terminal at one side nearer to the frame than the bent portion, and it protrudes from a surface of the frame where the contact portion of the terminal protrudes. The stopper restricts bending of the sheet metal constituting the terminal to an extent within a threshold value of reversibility of a material of the sheet metal. The stopper of this reinforced structure limits deformation of the stopper itself to a smallest possible extent. This prevents the stopper from being deformed or damaged even if a thrusting dimension of the electro-acoustic converter is set to an increased value when mounting it to the apparatus, or if an excessively large impact is applied to the electro-acoustic converter and the terminal when the electronic device such as a mobile telephone is accidentally dropped. The present invention also includes an electronic device provided with an electro-acoustic converter of the type discussed above and an electronic circuit for supplying power to the electro-acoustic converter. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a cross-sectional view of a loud speaker according to an exemplary embodiment of the present invention; 
         FIG. 2  is a cross-sectional view of the loud speaker shown in  FIG. 1  with a terminal in a state of being bent; 
         FIG. 3A  is a perspective view of the loud speaker shown in  FIG. 1 ; 
         FIG. 3B  is an enlarged perspective view depicting a main portion around a stopper of another configuration according to the exemplary embodiment of the present invention; 
         FIG. 4  is a cross-sectional view depicting a main portion of an electronic device according to the exemplary embodiment of the present invention; 
         FIG. 5  is a cross-sectional view depicting the main portion of the electronic device shown in  FIG. 4  with the terminal in a state of being bent; and 
         FIG. 6  is a cross-sectional view of a conventional loud speaker. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  and  FIG. 2  are cross-sectional views depicting a loud speaker as an electro-acoustic converter according to an exemplary embodiment of the present invention, in which  FIG. 1  shows the loud speaker with a terminal in a relaxed state without a stressing force on it, and  FIG. 2  shows the terminal in a state of being bent to its bottom dead point.  FIG. 3A  is a perspective view of the same loud speaker. Although a typical example shown in this exemplary embodiment is the loud speaker of a slim type having an exterior shape of rectangle, this invention is not limited only to this example. 
     Magnet  21  is sandwiched between upper plate  22  and yoke  23  to configure magnetic circuit  24  of an inner-magnet type. Yoke  23  constituting a part of magnetic circuit  24  is press-fitted into frame  26  made of a resin and bonded to it with adhesive. Diaphragm  27  is bonded (glued) to a circumferential edge of frame  26 . Voice coil  28  configured to drive diaphragm  27  is attached to diaphragm  27  and a part of it is located in magnetic gap  25  of magnetic circuit  24 . Although  FIGS. 1 and 2  show the magnetic circuit formed into the inner-magnet type, it can also be an outer-magnet type. 
     A lead wire of voice coil  28  is electrically connected to terminal  30  by soldering. A part of terminal  30  is embedded in frame  26  and secured to it. Terminal  30  is bent over at bent portion  30 A so as not to protrude outward from a boundary of an outer dimension of frame  26 . Terminal  30  is formed by a process of bending a piece of sheet metal having spring property and electrical conductivity, and makes contact with a power supply section of an apparatus by taking advantage of a spring tension of the sheet metal at contact portion  30 B. Terminal  30  is constructed of a sheet metal of such a material as phosphor bronze and copper-titanium alloy, which has both properties of electrical conductivity and spring property. Besides any one of the above unitary materials, terminal  30  may be made of a clad material using a good conductive material such as copper or gold plating on one side serving contact portion  30 B, and another material such as spring steel or titanium having superior spring property on the other side thereof. 
     Stopper  29  is formed by a process of bending at least a part of the periphery of the sheet metal constituting terminal  30  into an angle substantially perpendicularly at one side nearer to frame  26  than bent portion  30 A. This structure makes stopper  29  of terminal  30  abut upon and restricts further movement of loud speaker  35  even when loud speaker  35  is pushed forcibly for mounting. Stopper  29  thus restricts bending of the sheet metal constituting terminal  30  to an extent not exceeding a threshold value of reversibility of the metal material. 
     This structure also prevents stopper  29  from being deformed or damaged even when the electronic device such as a mobile telephone is accidentally dropped, which produces an excessively large impact upon terminal  30 . As a result, stopper  29  keeps terminal  30  from being bent beyond the threshold value of reversibility of the spring tension of metal terminal  30 , thereby avoiding terminal  30  from loosing its spring tension. 
     Stopper  29  is formed in a manner to protrude from surface  26 A of frame  26  where terminal  30  protrudes. It is preferable that stopper  29  protrudes in a direction substantially perpendicular with respect to surface  26 A, as described above. In this configuration, stopper  29  supports loud speaker  35  substantially perpendicularly against a pressure impressed upon it by the power supply section of the electronic device such as a mobile telephone. This structure not only protects terminal  30 , but also reduces deformation of stopper  29  itself to a minimum extent. It is also desirable that edge face  29 C opposite to surface  26 A is substantially parallel to surface  26 A. Stopper  29  can thus carry a weight of loud speaker  35  with the entire surface of edge face  29 C. Any of the above structures helps avoid stopper  29  from being deformed when loud speaker  35  is mounted while being depressed with an excessively large force. 
     In  FIG. 1 , the embodiment shown is provided with stopper  29  at one location for each terminal  30 . However, stoppers may be provided at two or more locations, for instance as shown in  FIG. 3B , wherein stoppers  29 ′ are formed at two confronting sides of the metal that constitutes terminal  30 . This structure further reduces the possibility of the stoppers to get deformed. 
     In addition, stopper  29  may be so constructed as to form a reinforcing portion referred to as surface  29 A by further bending at least a part of stopper  29  into an angle substantially orthogonal, as shown in  FIG. 3A . In other words, it is desirable that stopper  29  has two surfaces  29 A and  29 D which are orthogonal with respect to each other when viewed from the front side of surface  26 A. The provision of reinforcing portion  29 A further improves strength of stopper  29 . However, surfaces  29 A and  29 D need not be orthogonal to each other, but any angle greater than 0° but less than 180° formed between them provides a similar effect. 
     Moreover, any of stopper  29  and reinforcing portion  29 A may be provided with reinforcing rib  29 B, as shown in  FIG. 3A . Reinforcing rib  29 B is to be formed substantially in parallel with a direction, to which stopper  29  protrudes from frame  26 . This structure further improves strength of stopper  29 . 
     Description is provided next of a structure wherein loud speaker  35  having stopper  29  is built into an electronic device.  FIGS. 4 and 5  are cross-sectional views depicting a main portion of a mobile telephone according to the exemplary embodiment of this invention. Mobile telephone  80  representing the electronic device has loud speaker  35  mounted thereto. 
     Mobile telephone  80  has loud speaker  35 , electronic circuit  40 , and display module  60  such as a liquid crystal panel. These parts, module, and the like components are mounted inside of outer enclosure  70  to compose the main portion of mobile telephone  80 . Terminal  30  of loud speaker  35  is in contact with electronic circuit  40  via contact portion  30 B under the spring tension, and it completes an electrical connection between them. Electronic circuit  40  supplies an electric power for driving loud speaker  35  to generate sound. 
     According to this structure, stopper  29  prevents terminal  30  from being deformed excessively even if a depressing dimension of loud speaker  35  is set to an increased value when mounting loud speaker  35  to mobile telephone  80 . The structure also prevents stopper  29  from being deformed or damaged even if an excessively large impact is applied to terminal  30  when mobile telephone  80  is accidentally dropped. In other words, terminal  30  is prevented from being bended to an extent exceeding the threshold value of reversibility of the spring tension of its sheet metal, so as not to weaken the spring tension of terminal  30 . This threshold value is determined according to a bending angle of the sheet metal, a shape of bent portion  30 A, strength of impressed load, i.e., stress, and a cycle of the impressed load. 
     Accordingly, terminal  30  can maintain its strong spring tension at all the time to ensure the stable contact continuity with the power supply section of electronic circuit  40  in mobile telephone  80 . Since there is not likely any contact failure even when mobile telephone  80  receives impacts and vibrations, it operates steadily without any interruption of signals. As a result, the invention improves reliability and quality of the electronic device such as mobile telephone. 
     INDUSTRIAL APPLICABILITY 
     An electro-acoustic converter according to the present invention is suitable for use in an electronic device such as an audio video apparatus, data communications equipment, game machine, and the like device that require improvement of reliability and quality.