Abstract:
A jack device which does not malfunction because of overcurrent in an apparatus or a device that is connected to the jack device by preventing short-circuit between contacts in inserting a plug. The jack device, into which a single-head plug ( 50 ) having plug poles in the direction of insertion is inserted for connection, has a contact piece ( 11 ) that is arranged at the end of plug ( 50 ) and brought into contact with a first plug pole (plug pole  54 ) and contact piece ( 10 ) that is arranged neighboring the first plug pole and brought into contact with a second plug pole (plug pole  52 ). To widen the spacing between the two plug contact pieces ( 11 ), ( 10 ) in the direction of plug insertion, the spacing D between the plug connecting parts ( 11   p ), ( 10   p ) of both contact pieces ( 11 ), ( 10 ) is almost equal to or greater that the length L of the first plug pole (plug pole  54 ), so that when the first plug pole (plug pole  54 ) contact with the inside contact piece ( 11 ), the contact piece ( 10 ) on the inlet side contacts with the second plug pole (plug pole  52 ).

Description:
TECHNICAL FIELD OF THE INVENTION 
     The present invention relates to a jack device for connecting a headphone to be used on a passenger seat of an airplane, for example, in particular to the structure of contacting parts with a plug. 
     BACKGROUND OF THE TECHNOLOGY 
     In recent aircrafts, an entertainment system is installed to provide music and movie entertainment to passengers. In such a system, individual passengers can listen to selected music or movie audio through a headphone installed on each passenger seat. 
     In order to improve the sound quality of such an entertainment system, noise-reduction type headphones are increasingly used. A noise reduction type headphone is one in which a noise is cancelled with a sound having a phase opposite to that of the noise. Left and right sound signals as well as DC power are supplied to this type of headphones. 
     In this type of headphones, three single-head plugs each having plural (mainly two) plug poles are normally used. These plugs are inserted into a jack device provided on a passenger seat for connection. A passenger can listen to desired audio through this connection. 
     FIG. 10 is an external appearance of a jack device for a conventional headphone. As is illustrated in FIG. 11, the jack device comprises case  200  and cable  26  having a connecting member for connection with a central apparatus of an entertainment system. Case  200  comprises upper case  21  and lower case  22  and is provided with three jack sections ( 23 ,  24 ,  25 ). Of the three jack sections ( 23 ,  24 ,  25 ), jack section  23  is for supplying DC power, and the other two jack sections ( 24 ,  25 ) are used for left and right sounds. A single-head plug having plural plug poles is inserted into the inlet port of a jack section to a predetermined position. With this, connection of the single-head plug with the jack section is performed. Cable  26  extends out from case  200  for connection with a central apparatus of an entertainment system. 
     Inside cases  21 ,  22  of the jack device, substrates  27 ,  28 ,  29  are provided for each respective jack sections  23 ,  24 , and  25  as illustrated in FIG.  11 . Each of substrates  27 ,  28 ,  29  is soldered to corresponding jack sections  23 ,  24 ,  25 . Lead wires contained in cable  26  are connected to each of the substrates  27 ,  28 ,  29 . 
     A single-head plug is inserted into each of the jack sections  23 ,  24 ,  25  as described earlier. Each of these plugs has plural plug poles in the direction of insertion. 
     Referring to FIG.  12  and FIG.  13  and taking jack section  23  as an example, a description will now be given below on the structure of jack section  23  and the plug to be inserted into it. FIG. 12 shows the cross section of jack section  23 . 
     Jack section  23  for supplying DC power comprises: 
     a. base  34  having opening  34   a  for insertion of a plug; 
     b. movable contact piece  31  as a first contact piece with the plug; 
     c. grounding spring  30  as a second contact piece with the plug; 
     d. fixed piece  32 ; and 
     e. hollow holder  33  for affixing movable contact piece  31 , grounding spring  30 , and fixed piece  32 . 
     The structure of the other jack sections  24 ,  25  is approximately the same as the structure of jack section  23  for supplying DC power. 
     For example, FIG. 13 is an illustration of a state in which single-head plug  50  has been inserted halfway into jack section  23 . Plug  50  has plural plug poles (two plug poles in FIG. 13) in the direction of insertion. As illustrated in FIG. 13, plug  50  comprises plug pole  54  as a first plug pole disposed at the front end of the plug, plug  52  as a second plug pole disposed adjacently to plug pole  54 , and insulating collar  56  between plug pole  54  and plug pole  52 . 
     When plug  50  is inserted into jack section  23 , plug pole  54  is first brought into contact with grounding spring  30 . As plug  50  is further inserted, plug pole  54  is brought into contact with movable contact piece  31 . 
     In conventional jack devices of this type, the spacing (DB in FIG. 12) between movable contact piece  31  and grounding spring  30  on the inlet side is relatively small. As a result, as illustrated in FIG. 13, there occurs a case where plug pole  54  on the front end of the plug is simultaneously brought into contact with movable contact piece  31  and grounding spring  30  in the middle of insertion of plug  50 , namely, a state in which plug  50  has been inserted halfway. In the event such simultaneous contact occurs, movable contact piece  31  and grounding spring  30  are short-circuited through plug pole  54 . 
     In such a case, if the jack section is one for supplying a relatively small current such as an audio current, no serious trouble is caused. However, if the jack section is for supplying DC power, the following difficulty will be caused. 
     Short circuit of contact pieces for DC power inside a jack device will cause an overcurrent in a DC power supply unit of a central apparatus of an entertainment system. The overcurrent may trigger a protection circuit in the central apparatus thus causing suspension of system operation, malfunction or a failure. 
     DISCLOSURE OF THE INVENTION 
     The present invention addresses the above-described problems and provides a structure in which plural con tact pieces will not short-circuit in the middle of insertion of a plug. It is an object of the present invention to prevent suspension of operation, malfunction, or failure of an apparatus that is directly or indirectly connected to a jack device. 
     The present invention provides a jack device into which a single-head plug having plural plug poles in the direction of insertion is inserted for connection, and which comprises: 
     a base having an opening for insertion of a plug; 
     a first contact piece that is brought into contact with a first plug pole disposed at the front end of the plug; 
     a second contact piece that is brought into contact with a second plug pole disposed adjacently to the first plug pole; where 
     the first and the second contact pieces are provided in the direction of plug insertion; and 
     the spacing between the plug-contacting portion of the first contact piece and the plug-contacting portion of the second contact piece is made approximately equal to or greater than the length in the direction of plug insertion of the first plug pole of the plug. 
     Also, a hollow holder to which the first and the second contact pieces are affixed has a notch. When a plug is inserted, the second contact piece is pushed down toward the notch. The notch makes it possible to make the outer dimensions of a jack device with the above structure equal to the outer dimensions of a conventional jack device. 
     According to the above-described structure, the spacing between the two contact pieces is greater than the length of the above first plug pole. Accordingly, there will not occur any case in which the two contact pieces are simultaneously brought into contact with the first plug pole provided at the front end of the plug. Consequently, the two contact pieces will not make a short circuit through the first plug pole in the middle of plug insertion. Also, the outer dimensions of a jack device with the above structure can be made equal to the outer dimensions of a conventional jack device while preventing short circuit of the two contact pieces. That is, the jack device of the present invention can be used for a conventional plug without changing its length. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a perspective view of a jack device of the present invention. 
     FIG. 2 is a plan view of an entire jack device in a first preferred embodiment of the present invention with the upper part of the case removed to show the inside. 
     FIG. 3 is an enlarged cross-sectional view of a jack section for supplying DC power, being a part of the jack device, indicating a state before insertion of a plug. 
     FIG. 4 is a cross-sectional view of the jack device in FIG. 3 taken along the plane  4 — 4 . 
     FIG. 5 is an enlarged cross-sectional view of the jack device for supplying DC power indicating a state in the middle of inserting a plug. 
     FIG. 6 illustrates a state of a jack device before insertion of a plug in a second preferred embodiment of the present invention. 
     FIG. 7 is a cross-sectional view of the jack device in FIG. 6 taken along the plane  7 — 7 . 
     FIG. 8 illustrates a state of a jack device before insertion of a plug in another example of the second preferred embodiment. 
     FIG. 9 is a cross-sectional view of the jack device in FIG. 8 taken along the plane  9 — 9 . 
     FIG. 10 is an external perspective view of a conventional jack device. 
     FIG. 11 is a plan view of the above conventional jack device with the upper case removed to show the inside. 
     FIG. 12 is an enlarged cross-sectional view of a jack section, being a part of the above conventional jack device, for supplying DC power showing a state before insertion of a plug. 
     FIG. 13 is an enlarged cross-sectional view of the above conventional jack section for supplying DC power showing a state in which a plug is inserted halfway. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred Embodiment—1 
     Referring to drawings, a description will now be given below on a jack device in the first preferred embodiment of the present invention. 
     A jack device in the first preferred embodiment of the present invention will be described below with reference to FIGS. 1 through 5. FIG. 1 is an external view of the jack device in the first embodiment of the present invention. 
     The jack device of the first preferred embodiment has three jack sections for inserting single-head plugs. The single-head plugs to be inserted are provided with plural plug poles in the direction of insertion. As illustrated in FIG. 2, substrates ( 7 ,  8 ,  9 ) are provided inside case  100  for each respective jack sections ( 3 ,  4 ,  5 ). Each of the substrates ( 7 ,  8 ,  9 ) is soldered to the corresponding jack sections ( 3 ,  4 ,  5 ). Lead wires contained in connecting cable  6  are connected to each of the substrates ( 7 ,  8 ,  9 ). This structure is not particularly different from the conventional jack devices of this type shown in FIG.  10  and FIG.  11 . Also, out of the three jack sections ( 3 ,  4 ,  5 ), jack section  3  is for supplying DC power. The other two jack sections ( 4 ,  5 ) are used for left and right audio signals. 
     Taking jack section  3  for supplying DC power as an example, a description of the jack device of the present invention will be given below. FIG. 3 shows a state before insertion of a plug. FIG. 4 is a cross-sectional view of the jack device in FIG. 3 taken along the plane  4 — 4 . 
     As illustrated in FIG. 3, jack section  3  for supplying DC power has three contact pieces, namely, movable contact piece  11  as a first contact piece with a plug, grounding spring  10  as a second contact piece with a plug, and a fixed piece  12 . These three contact pieces are affixed to hollow holder  13 . Also, base  14  having opening  14   a  for reinforcing the entrance of jack section  3  is provided at the entrance of jack section  3 . Notch  13   a  having a width WA (ref. FIG. 4) is formed near opening  14   a  of hollow holder  13 . 
     Single-head plug  50  to be inserted has plug poles  52  and  54  in the direction of insertion. Also, insulating collar  56  is provided between plug pole  52  and plug pole  54  for insulating them. 
     When plug  50  is inserted to a predetermined position from base  14  of jack section  3 , grounding spring  10  is brought into contact with plug pole  52  (second plug pole) of plug  50 , and movable contact piece  11  is brought into contact with plug pole  54  (first plug pole) at the front end of plug  50 . 
     This state is not different from a jack section for supplying DC power of conventional jack devices of this type. 
     In jack device  3  of this preferred embodiment, the spacing between the contacting portion of grounding spring  10  (plug contacting portion  10   a ) and the contacting portion of movable contact piece  11  (plug contacting portion  11   a ) is defined as D (shown in FIG.  3 ). Also, the length of plug pole  54  (first plug pole) at the front end of plug  50  is defined as L (shown in FIG.  5 ). 
     In jack device  3  in the present preferred embodiment, the relationship between the spacing D and length L is set as 
     
       
         
           D≧L. 
         
       
     
     A point of difference from conventional jack devices lies in that notch  13   a  is formed close to opening  14   a  of hollow holder  13 . Notch  13   a  allows grounding spring  10  to extend to a position close to the entrance of jack section  3 . 
     With this structure, the spacing (for example, D in FIG. 3) between contacting portion  10   a  of grounding spring  10  and contacting portion  11   a  of movable contact piece  11  in the direction of insertion of a plug can be made greater than conventional spacing (for example, DB in FIG.  12 ). Moreover, the outer dimensions of the jack device (LA in FIG. 1) can be made equal to the outer dimensions of a conventional jack device (LB in FIG.  10 ). Consequently, by employing this structure, conventional plugs can be used as is without changing their length. 
     In this case, grounding spring  10  and movable contact piece  11  are elastically deformed due to inserted plug  50 . The spacing D between contacting portion  10   a  and contacting portion  11   a  is determined taking the deformation into account. 
     As exemplified in this preferred embodiment, grounding spring  10 , being one of the contact pieces, is deformed by insertion of plug  50  in a manner such that it departs from movable contact piece  11 . Accordingly, the spacing D between contacting portions  10   a  and  11   a  when plug  50  is not inserted may be slightly smaller than the length L of plug pole  54  of plug  50 . 
     Referring to FIG. 5, a description will be given on the motion of insertion of single-head plug  50  into jack section  3  to a predetermined depth. 
     When single-head plug  50  having plural (two, for example) plug poles is pushed in, the following motion will occur. 
     1. First, plug pole  54 , namely, first plug pole disposed at the front end of plug  50 , is brought into contact with grounding spring  10 . 
     2. Upon further pushing, grounding spring  10  is pushed down by plug pole  54  toward notch  13   a.    
     3. Upon further pushing, contact between plug pole  54  and grounding spring  10  is released, and grounding spring  10  is brought into contact with insulating collar  56 . 
     4. Upon further pushing, the contact between grounding spring  10  and insulating collar  56  of plug  50  is released, and grounding spring  10  is brought into contact with plug pole  52 , namely, second plug pole. 
     5. Upon further pushing, movable contact piece  11  is brought into contact with plug pole  54 . 
     In the above motion of inserting single-head plug  50  into jack section  3  to a predetermined depth, the sequence of motion  4  and motion  5  may be reversed. 
     As has been described above, by the time plug pole  54  is brought into contact with movable contact piece  11 , plug pole  54  has already passed contacting portion  10   p  of grounding spring  10 . Accordingly, plug pole  54  will never be simultaneously brought into contact with grounding spring  10  and movable contact piece  11 . In other words, grounding spring  10  and movable contact piece  11  will never make a short circuit through plug pole  54 . Consequently, no overcurrent will flow to a DC power supply unit of an apparatus or device connected through cable  6 . Therefore, no malfunction due to an overcurrent will be caused in an apparatus or device that is connected to a jack device of the present invention. 
     As has been described above, by the time plug pole  54  is brought into contact with movable contact piece  11 , plug pole  54  has already passed contacting portion  10   a  of grounding spring  10 . Accordingly, plug pole  54  will never be simultaneously brought into contact with grounding spring  10  and movable contact piece  11 . In other words, grounding spring  10  and movable contact piece  11  will never make a short circuit through plug pole  54 . Consequently, no overcurrent will flow to a DC power supply unit of an apparatus or device connected through cable  6 . Therefore, no malfunction due to an overcurrent will be caused in an apparatus or device that is connected to a jack device of the present invention. 
     Furthermore, in this preferred embodiment, grounding spring  10 , being one of the contact pieces, is deformed due to inserted plug  50  in a manner such that its contacting portion  10   a  departs from the other movable contact piece  11 . As a result, the spacing D between contacting portion  10   a  of grounding spring  10  and contacting portion  11   a  of movable contact piece  11  is further widened from that before insertion. Consequently, the jack device in accordance with the present invention further assures prevention of a short circuit. 
     In a conventional jack device as shown in FIG. 12, when the spacing DB between contacting portions  30   a  and  31   a  is widened, normally the dimension LB (ref. FIG. 10) increases though not illustrated. Therefore, the length of the plug has to be made greater in accordance with the increase in the dimension LB. 
     However, according to the structure of the present invention, the spacing D between the two contact pieces is greater compared with the first plug pole. Accordingly, there will not occur any case in which these two contact pieces are simultaneously brought into contact with the first plug pole provided at the front end of a plug. Therefore, the two contact pieces will never make a short circuit through the first plug pole in the middle of insertion of a plug. Also, the outer dimensions LA of a jack device with the above structure can be made equal to the outer dimensions LB of a conventional jack device while preventing a short circuit of, the two contact pieces. As a result, a jack device in the present preferred embodiment can be used as is without making the length of a conventional plug greater. 
     For the above preferred embodiment, description of only jack section  3  for supplying DC power out of the, three jack sections ( 3 ,  4 ,  5 ) was given and its internal structure was shown. However, the other jack sections ( 4 ,  5 ) may be of the same structure. By employing this structure, a short circuit between grounding spring  10  and movable contact piece  11  through plug pole  54  at the front end of a plug can also be prevented in the other jack sections ( 4 ,  5 ). 
     In the above-described preferred embodiment, a description was made on a single-head plug having two plug poles in the direction of insertion as an example. Needless to say, however, the present invention may be embodied in a jack device in which a single-head plug having three or more (three, for example) plug poles in the direction of insertion is inserted for connection. 
     Preferred Embodiment—2 
     Referring to FIG.  6  and FIG. 7, a description of a jack device in a second preferred embodiment of the present invention will be given below taking a jack section for supplying DC power as an example. FIG. 6 shows a state before insertion of a plug of a jack device in a second preferred embodiment of the present invention. FIG. 7 is a cross-sectional view of a jack device of FIG. 6 taken along the plane  7 — 7 . The jack device in the second preferred embodiment is basically of the same structure as the jack device in the first preferred embodiment as shown in FIGS. 1 to  5 . 
     The point of difference from the jack device in the first preferred embodiment lies in that the position of the front end lob of grounding spring  10  as shown in FIG. 6 is at notch  13   a . Namely, assuming that the height of both sides of notch  13   a  as shown in FIGS. 6 and 7 to be HA, and the height of the position of the front end  10   b  of grounding spring  10  to be HB, this jack device satisfies a positional relationship of 
     
       
         
           HA≧HB. 
         
       
     
     Both sides of notch  13   a  work as guides for grounding spring  10  while it is being bent downward due to insertion of a plug. This structure allows smooth downward bending of grounding spring  10  due to insertion of a plug. 
     FIG. 8 is an illustration of another example of a jack device in the second preferred embodiment. FIG. 9 is a cross-sectional view of the jack device of FIG. 8 taken along the plane  9 — 9 . The jack devices illustrated in FIG.  8  and FIG. 9 are basically of the same structure as the jack devices illustrated in FIG.  6  and FIG.  7 . The point of difference from the jack devices of FIG.  6  and FIG. 7 is that, while grounding springs  10  shown in FIG.  6  and FIG. 7 are a flat plate, the grounding springs of the jack devices of FIG.  8  and FIG. 9 are a wire spring, which allows the width WB of a notch shown in FIG. 9 to be made smaller than the notch width WA of the jack devices illustrated in FIG.  6  and FIG.  7 . This structure allows smooth downward bending of grounding spring  10  due to insertion of a plug. Furthermore, as the notch width of the jack devices illustrated in FIG.  8  and FIG. 9 is smaller, there is less play between a plug and the jack devices. 
     INDUSTRIAL APPLICABILITY 
     In a jack device in accordance with the present invention, the spacing between two contact pieces of the jack device is greater than the length of the first plug pole. Accordingly, these two contact pieces will not be simultaneously brought into contact with the first plug pole provided at the front end of a plug. Consequently, there will not occur any case in which the two contact pieces will make a short circuit through the first plug pole in the middle of insertion of a plug. Also, the outer dimensions of a jack device having this structure can be made equal to the outer dimensions of a conventional jack device while being able to prevent a short circuit of the two contact pieces. As a result, the jack devices of the present preferred embodiments can be used for a conventional plug as is without making its length longer. 
     Therefore, the present invention enables prevention of suspension of operation and malfunction of an apparatus or a device connected to the jack device due to an overcurrent.