Abstract:
An electric shaver comprises an inner case which retains an electronic part board  5  and an outer casing which retains a plug pin board which secures a plurality of plug pins. The inner case is fabricated of a plastic integral with a bottom wall. The electronic part board is disposed above the lower separating wall while the plug pin board is disposed under the lower separating wall. Metal pins penetrating the lower separating wall connects the electronic part board and the plug pin board. The bottom opening of the outer casing is closed with a bottom cover. The bottom cover has a pair of through holes through which extend outwardly a pair of plug pins.  
     An electric shaver comprises an inner case which retains an electronic part board 5 and an outer casing which retains a plug pin board which secures a plurality of plug pins. The inner case is fabricated of a plastic integral with a bottom wall. The electronic part board is disposed above the lower separating wall while the plug pin board is disposed under the lower separating wall. Metal pins penetrating the lower separating wall connects the electronic part board and the plug pin board. The bottom opening of the outer casing is closed with a bottom cover. The bottom cover has a pair of through holes through which extend outwardly a pair of plug pins.

Description:
[0001]    This application is based on applications No. 053346/2000 filed in Japan on Feb. 29, 2000, No. 046537/2000 filed in Japan on Feb. 23, 2000 and No. 054822/2000 filed in Japan on Feb. 29, 2000, the contents of which incorporated hereinto by references.  
         BACKGROUND OF THE INVENTION  
         [0002]    The present invention relates to an electric shaver having a circuit board with electronic parts thereon, and a pair of plug pins projecting from the body casing.  
           [0003]    There are two types of electric shaver, i.e. the one having built-in wire, and the other having detachable electrical wire.  
           [0004]    The latter must be provided with a plug pins protruding from the body casing in order to detachably connect a power source electric wire.  
           [0005]    Shavers of prior art have a pair of plug pins secured on a plug board and the plug board is firmly retained in the casing so as to secure the plug pins to the body casing.  
           [0006]    The plug board needs a set of lead wires connected to the plug pins. Related art shavers have a circuit board provided with electronic parts as well as a plug board, electrically connected to each other but separately secured in the body casing.  
           [0007]    The structure of the related art shavers has the drawbacks that assembling work takes a lot of time because the electronic parts board and the plug board together with electrical wires connecting these boards must be placed into the casing.  
           [0008]    The structure has also incurs a higher manufacturing cost because of a rather complicated configuration of the casing due to the fact that the casing must be so configured as to receive the part board and the plug board separately.  
           [0009]    Further there are washable electric shavers. This type of electric shaver is convenient because the use can wash it. Waterproof electric shaver requires a watertight casing. Watertight structure is easily produced by employing a cylindrical body casing. With a cylindrical casing, watertight structure is readily achieved by employing watertight sealing means on the upper and lower end of the casing. However, a cylindrical casing makes it difficult to insert a part board and a plug board, electrically connected to each other by means of electrical wires. Mounting these boards in a cylindrical casing can be facilitated by employing an outer casing and an inner case to be inserted in the outer casing, on which inner case part board and plug board are mounted.  
           [0010]    The electric shaver with the structure has the part board secured to the inner case, the part board being electrically connected by means of lead wires of the plug board.  
           [0011]    The electric shaver of the structure requires the assembling work in which the part board and plug board are inserted together with electrical wires connecting the boards, which electrical wires cause troubles.  
           [0012]    In the case where the part board and the plug board are separately secured to the inner case, the configuration of the inner case becomes so complicate that it requires a higher production cost.  
         SUMMARY OF INVENTION  
         [0013]    The present invention is proposed to overcome these drawbacks. The most important object of the present invention is to propose an electric shaver having a simple structure and yet easy to assemble with a part board and plug board secured on the inner case.  
           [0014]    Another important object of the present invention is to provide an electric shaver with a plug board firmly secured to the inner case on which plug board are fixed plug pins.  
           [0015]    The above and further objects and features of the invention will be more fully be apparent from the following detailed description and accompanying drawings.  
           [0016]    The electric shaver of the present invention includes an electric motor for reciprocating inner blade assembly, batteries for supplying power to the motor, an electronic part board connected to the batteries, an inner case securing the electronic part board, the electric motor and the batteries and inserted into an outer casing, and a plug pin board securing the plug pins protruding from the outer surface of the outer casing.  
           [0017]    Furthermore, the electric shaver of the present invention has the construction described below.  
           [0018]    The inner case has a lower separating wall integral therewith and made of a plastic, the periphery of which sealingly abuts on the inner surface of the outer casing. The inner case secures an electronic part board above the lower separating wall. Furthermore, the inner case secures a plug board parallel to the case under the lower separating wall. The electronic part board and the plug board are connected by metal pins. One end of each of the metal pins is fixed to the electronic part board and the other is fixed to the electronic part board. Each of the metal pins pierces through a hole and is retained in the inner case. The outer casing has an open end which is closed by a bottom cover. The bottom cover has a plurality of through holes for plug pins which extend outwardly from the outer casing.  
           [0019]    The construction of the electric shaver is characterized by the simplicity of construction and easiness of assembling work wherein the electronic part board and the plug board are fixed on the inner case and the inner case is then inserted into the outer casing. The advantage of the electric shaver according to the present invention is obtained by the construction wherein the inner case is formed integral with the lower separating wall abutting on the internal surface of the outer casing, and the electronic part board and the plug board are connected by metal pins penetrating the lower separating wall. With its simple construction, the electric shaver according to the present invention enables to secure the electronic part board on the plug pins in a position. Using the metal pins instead of lead wires connecting the electronic part board and the plug board, the shaver according to the present invention enables to eliminate lead wires connecting the electronic part board and the plug board whereby facilitating the assembly work.  
           [0020]    The outer casing of the shaver according to the present invention is preferably fabricated of a plastic with tubular configuration. The lower separating wall is provided with an O-ring at its periphery for a watertight connection with the outer casing, while the plug pins are provided with an O-ring abutting on the inner surface of the bottom cover for a watertight connection with the through holes. The construction of the electric shaver of the present invention can be used for a watertight electric shaver.  
           [0021]    The electric shaver with a watertight lower separating wall and the bottom cover with a watertight plug pins is preferably provided with a safety valve on the bottom cover which functions as a relief valve at a predetermined pressure level in a space enclosed by the lower separating wall, bottom cover and the outer casing. The safety valve thus prevent gas from entering the upper block whereby avoiding damages to electronic parts.  
           [0022]    Furthermore, the inner case made of a plastic has latch means integral with the case to retain the electronic part board. Thus the electric shaver of the present invention enables to retains the electronic part board in the inner case.  
           [0023]    The ends of the metal pins of the electric shaver of the present invention are fixed by soldering to the electronic part board or to the plug board. By this method, the metal pins are secured to the electronic part board and to the plug board.  
           [0024]    The inner case according to the present invention is formed integral with a tubular case to retain two batteries disposed side by side and parallel to the electronic part board. The inner case is preferably formed integral with hub portions for retaining the bottom cover. The hub portions are disposed at hollow spaces between the two cylindrical batteries.  
           [0025]    The electric shaver having the construction that the inner case with an integral tubular case, in which batteries are retained, is preferably provided with the retainer having a closed upper end and an open bottom end. The lower ends of the batteries retained in the tubular retainer are connected to lead plates which are in turn connected to the plug pins. The electric shaver is capable of retaining the batteries by means of lead plates and plug pins. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0026]    [0026]FIG. 1 is an exploded oblique view of an embodiment according to the present invention.  
         [0027]    [0027]FIG. 2 is an exploded rear view of the electric shaver shown in FIG. 1.  
         [0028]    [0028]FIG. 3 is a side elevational view of the inner case shown in FIG. 2.  
         [0029]    [0029]FIG. 4 is a circuit diagram showing the electrical circuit of an embodiment according to the present invention.  
         [0030]    [0030]FIG. 5 is a cross-sectional view of the inner case shown in FIG. 2.  
         [0031]    [0031]FIG. 6 is a vertical cross-sectional view of the inner case shown in FIG. 2.  
         [0032]    [0032]FIG. 7 is an exploded oblique view of an outer casing and an inner case as partly inserted in the outer casing.  
         [0033]    [0033]FIG. 8 is an exploded cross-sectional view of lower portion of the electric shaver shown in FIG. 1.  
         [0034]    [0034]FIG. 9 is a cross-sectional view of lower portion of an electric shaver.  
         [0035]    [0035]FIG. 10 is an enlarged oblique view of a bottom cover.  
         [0036]    [0036]FIG. 11 is an oblique view of another embodiment of the electric shaver according to the present invention.  
         [0037]    [0037]FIG. 12 is an oblique view of the chamber shown in FIG. 11.  
         [0038]    [0038]FIG. 13 is a cross-sectional view of the chamber shown in FIG. 12.  
         [0039]    [0039]FIG. 14 is a vertical cross-sectional view of the chamber shown in FIG. 12.  
         [0040]    [0040]FIG. 15 is a schematic view of a power source connector.  
         [0041]    [0041]FIG. 16 is an oblique view of an adapter connected to the plug shown in FIG. 15.  
         [0042]    [0042]FIG. 17 is a front view of the plug shown in FIG. 15. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0043]    The electric shaver as shown in an exploded oblique view in FIG. 1, in a rear view in FIG. 2, and in FIG. 3 comprises a motor  4  which drives an inner blades  6 , a battery  3  for energizing the motor  4  an electronic part board  5  connected to the battery  3 , an inner case  2  to which the part board  5 , the battery and the motor  4  are secured, and a plug board  33  having a pair of plug pins  32  the extremities of which project beyond the outer casing  1 . FIG. 3 shows an inner case  2  partly drawn out of the outer casing.  
         [0044]    The motor  4  drives the inner blades in a reciprocating motion by means of a transforming mechanism which transforms the rotational motion into a reciprocating motion. The transforming mechanism may be of the type presently in use or in the future. For example, a mechanism comprising a cam shaft  12  secured to a motor spindle  11 , and a reciprocating member  14  to which the cam shaft  12  as well as the inner blades  6  is secured. The inner blades  6  reciprocate in slidable engagement with the inner surface of the outer blade  7  to cut off hairs projecting through beard cutting ports of the outer blade  7 .  
         [0045]    The battery  3  may be a Ni-MHD,Ni-CD, or Ni-Lithium type. One or several batteries are retained in the inner case  2 . FIG. 2 shows a pair of batteries  3  retained in a retainer  8  of the inner case  3 .  
         [0046]    [0046]FIG. 4 shows a circuit diagram which includes electronic parts mounted on the part board  5 . The circuit on the part board  5  includes a charge-control circuit for the battery  3  and a motor  4 -controlling circuit. The battery-charging circuit includes a switching device connected to the battery  3  and the charging terminals  15 , a microprocessor  16  for controlling ON/OFF states of the device Q 1 , and a charging resistor R connected in series between the switching device Q 1  and the battery  3 . The part board may include a power supply circuit capable of transforming the 100 V commercial power to a charge voltage of the battery.  
         [0047]    The charge-control circuit supply a charging current to the battery  3  through the switching device Q 1  and the charging resistor R. The switching device Q 1  generates heat by the energy proportional to the multiplication of current and voltage drop. The charging resistor R generates heat due to the energy proportional to the multiplication of the square of current and resistance. The switching device Q 1  and the charging resistor R are heat-generating parts  10  because these parts conduct large currents. The power supply circuit also generates heat because the circuit includes a transformer for lowering 100 V commercial voltage into a charging voltage, a switching device and a rectifying diode which conduct a large current.  
         [0048]    The charge-control circuit shown in the figures for the battery  3  is capable of calculating by means of a microprocessor the residual power of the battery based on the discharge time. The residual power is displayed by means of LEDs (not shown). The microprocessor  16  calculates ON time of switching device Q 1  based on the residual power and controls the switching device. The battery  3  is charged when the switching device is turned on as the electric shaver is placed on the charger or the power cable is connected to a commercial power outlet. The microprocessor calculates the time needed to fully charge the battery  3  and turns off the switching device Q 1  when the battery 3  is fully charged, thus terminating the charging operation.  
         [0049]    The motor-controlling circuit includes a switching device Q 2  such as FET, a switching circuit  18  for turning on and off the switching device Q 2 , and a push switch  19  for inputting switching signals into the switching circuit 18 . The switching circuit  18  switches on and off the switching device Q 2  as the push switch  19  is pushed to send “H” or “L” signals. The circuit is characterized in that a push switch of simple structure is capable of turning on and off the motor. As the circuit supplies large currents to the motor, the switching device Q 2  in the circuit generates greater amount of heat. Therefore, the switching device Q 2  is preferably placed in a section of the inner case. Instead of placing the switching device Q 2  in a section, the device may be mounted on the rear side of the part board because the switching device Q 2  conducts smaller currents compared with the switching device Q 1  generating less heat.  
         [0050]    The device board  5  shown in FIG. 3 has electronic parts on both sides. Heat generating device  10  is mounted protruding into the section  9  on the front side of the electronic part board  5 . The electronic part board  5  has electronic parts  20  on the rear side at the position corresponding to the battery  3  and the motor  4 . The electronic part board  5  is secured close to the battery  3  and the motor  4  in the inner case  2 .  
         [0051]    The inner case  2  is formed of plastics as an integral part. The inner case  2  shown in FIG. 3 is provided with a mounting surface at the rear for the part board  5 . Holding latches are provided integral with the inner case, at both sides of the mounting surface, resiliently holding the board  5  at both sides. Each of the holding latches has a hook-like end as shown in FIG. 5, which holds the part board at its sides. The inner case  2  shown in the figure is provided with a pair of holding latches  21  at each side, totaling four holding latches, securing the electronic part board  5  at two location on each side.  
         [0052]    As shown in FIG. 2, the inner case  2  is further provided with a section  9  between the motor  4  and the battery  3 . The section  9  is provided to admit heat-generating part  10  mounted on the part board. The room  9  has a separating wall separating the room  9  from the battery  3 . The inner case  2  has another wall  23  which is lower than the wall  22  separating the room from the motor  4 . As shown in FIG. 2, the wall  23  has a groove  24  on the side facing the motor  4  which receives a bearing housing  4 A projecting from the casing. The groove  24  receives the motor housing projection  4 A whereby securing the motor  4 .  
         [0053]    The wall  22  facing the battery  3  serves as a cover to close the bottom opening of the tubular retainer  8 .  
         [0054]    The inner case  2  shown in FIG. 2, FIG. 3 and FIG. 6 is provided with a tubular retainer  8  as an integral part for receiving the battery  3 . The tubular retainer ends in a wall  23  at its bottom which separates the room  9  from the battery and prevents the battery  3  from slipping into the room  9 . The opposite end of the retainer  8  is open for loading the battery  3 . The inner case shown in the figures has a tubular retainer  8  capable of retaining a pair of juxtaposed cylindrical batteries.  
         [0055]    Furthermore, the inner case  2  has side walls  25  integral with the inner case, which hold the motor  4  on both sides. The side walls  25  join with the tubular retainer  8  for the battery  3  at their lower end.  
         [0056]    Thus, the inner case  2  shown in the figures is provided with the square room  9  enclosed by the side walls  25 , separating wall  22  facing the motor  4 . The room  9  receives the heat-generating parts  10  mounted on the electronic part board. The room  9  is open  29  toward the electronic parts board so as to admit the heat-generating parts  10  into the room.  
         [0057]    Furthermore, the heat-generating part  10  in the FIG. 5 admitted in the right-side room is covered with a heat-resistant tube  31 . The heat-resistant tube  31  prevent the heat-generating part  10  from contacting the inner case  2 , whereby protecting the batteries from heat.  
         [0058]    As shown in FIG. 5 and FIG. 6 (lateral cross-section), the inner case is open at both upper and lower end of the room  9 . Furthermore, each of the side walls  25  has an opening at the bottom as shown in FIG. 5 and  6  so as to let the air out. The height of the side walls is lower than the battery case  8  so that air can pass through the gap between them.  
         [0059]    The rooms  9  which are open at top and bottom allow leading wires connecting the electronic part board  5  and the motor  4  to go through the open end. In the electric shaver shown in the figures, the leading wires  30  are connected e.g., by soldering at their one end to the upper surface of the part board  5 . The leading wires  30  go upward through the room to terminals of the motor  4 . The structure of the room allows an optimum wiring of the leading wires  30  because leading wires no more require a clearance between the inner case and outer casing for the wires to pass through.  
         [0060]    The inner case  2  shown in FIG. 3, FIG. 7 and FIG. 8 has a lower separating wall  26  as its integral part which closes the bottom end of the outer casing  1 , and to which is connected, at its upper surface, the electronic part board  5 , and at its lower surface a plug board  3  parallel with the separation wall. The lower separating wall  26  has a groove  26 A at its periphery for receiving an O-ring  34 . The O-ring  34  in the groove  26 A establishes a watertight contact with the inner surface of the outer casing, as the inner case  2  is retained in the outer casing to give the outer casing watertight structure.  
         [0061]    The lower separating wall has through holes  26 B through which a metal pin  35  is inserted connecting the electronic part board  5  and the plug board  23 . The lower separating wall  28  of the inner case shown in FIG. 7 and FIG. 8 is provided with three though holes  26 B. Each of the through holes  26 B is a circular hole having the diameter equal to that of the metal pin. Thus, the holes  26 B are able to keep the metal pin in a fixed position.  
         [0062]    The lower separating wall  26  shown in FIG. 8 has an enlarged recess at the lower surface, in which an O-ring is received so that the pin  35  is secured watertight to the tower separating wall  26 . The through holes in the lower separating wall  26  receive a flanged portion  35 A of the metal pin  35 . Each of the through holes  26 B admits the metal pin  35  inserted from the plug board  33  until the pin reaches the electronic part board  5  whereby holding the metal pin  35  and the electronic part board in position. The O-ring-flange structure gives the through holes  26 B water tightness.  
         [0063]    The lower separating wall  26  shown in FIG. 7 and FIG. 8 has, as integral parts thereof, support members  37  for supporting the plug board, projecting toward the bottom of the case, and support members  38  for supporting the bottom cover  39 . The plug board support members  37  and bottom cover support members  38  support the plug board  33  at four points. With these support members, the inner case is capable of supporting the lower separating wall  26  and the plug board  33  parallel to each other. The support members  37 ,  37  support the plug board  33  on the bottom sides, whereas the support members  38 , 38  support the board on both sides as shown in FIG. 9. Each of the support members  37 ,  37  has a L-shaped recess for receiving the plug board  33 . As shown in FIG. 8 and FIG. 8, the support members  38 ,  38  have an enlarged portion  3 A at their root to form a shoulder to support the plug board  33 .  
         [0064]    The support member  38  has a threaded hole which provides an anchor for a screw  40  which secures the bottom cover  39 . The inner case  2  shown in FIG. 7 has bottom cover supports  38 ,  38  aligned with the gorge between two juxtaposed batteries. The support arrangement enables to make the inner case  2  and lower separating wall  26  smaller because the space between the batteries is used to put the support members  38 ,  38 .  
         [0065]    The metal pin  35  inserted into the through hole  26 B is fastened at one end to electronic part board  5  and at the other end to the plug board  33 , whereby holding these boards in place. The metal pin  35  is fastened, e.g., by means of soldering to the electronic part board and plug board 33 . As the other way, the metal pin  35  can be detachably fastened to the electronic part board and plug board 33 . The inner case  2  shown in figures has three metal pins connecting the electronic part board  5  and plug board  33 . Each of the two metal pins  35 ,  35  is connected to either of the plug pins  32 ,  32 . Either of the two plug pins  32 ,  32  is connected to either of the electrodes of the battery  3  by means of a leading plate  41 . The other plug pin  32  is also connected to the electrode of the battery by means of a leading plate  41 .  
         [0066]    The electronic part board  5  and the plug board  33  are made of a printed circuit board of epoxide resin with a thin conductive metal layer on its surface. The part board  5  and plug board  33  have an enlarged metal layer to which the metal pin is connected. The plug board  33  has a recess  33 A intended to insert the metal pin  35  in order to firmly secure the board in the inner case  2 . The recess  33 A may be a through hole or a groove capable of holding the metal pin  35 . The plug board  33  is provided with a thin layer of metal connecting a pair of plug pins  32  and a pair of metal pins  35 .  
         [0067]    The outer casing  1 , which is made of plastics, as shown in FIG. 1 and FIG. 2, exposes an oscillating rod  13  secured on a reciprocating member  14  through a watertight sealing member at its upper end while the bottom end is closed by means of a bottom cover  39  with watertight sealing means. In order to ensure a watertight contact of the reciprocating mechanism, the upper opening  1 A of the outer casing  1  has a rubber membrane  42  through which extends the oscillating rod  13 . The rubber membrane  42  is fixed watertight at its periphery to the opening  1 A of the outer casing  1  which penetrates the oscillating rod  13 . The through hole of the rubber membrane  42  is secured watertight to the oscillating rod  13 .  
         [0068]    As shown in FIG. 8 and FIG. 9, the bottom cover  39  has a pair of through holes  39 A,  39 A for the plug pins  32 . The plug pins penetrate the through holes  39 A, 39 A with watertightness so that the ends of the plug pins protrude out of the outer casing  1 . In order for the plug pins  32  to penetrate with water tightness, the pins  32  are provided with an O-ring  43  which is tightly pressed on the inner surface of the bottom cover  39 . Furthermore, the bottom cover  39  is provided with another O-ring  44  at its periphery to ensure watertight coupling.  
         [0069]    The bottom cover  39  has a chamber  45  aligned with the plug pins  32  to admit the pins  32 . The chamber  45  is deep enough to prevent the pins from protruding out of the contour of the outer casing. The chamber is so configured as to receive a power source plug. The plug pins  32  are connected by means of the power source plug to the power outlet.  
         [0070]    The bottom cover  39  is provided with a safety valve to discharge the gas emitted by the battery  3  when the internal pressure becomes critical. The safety valve  46  consists of a membrane fixed in the inner surface of a relief hole  39 B which penetrates the bottom cover  39 . The membrane sealing the relief hole  39 B breaks and let out air when the internal pressure rises high enough. As shown in FIG. 10 schematically, the relief hole  39 B is made inside the chamber  45  and communicates with a groove  47  on the wall of the chamber  45 . The relief hole  39 B is protected from damage by piercing with e.g., a needle by the user. The other material of the sheet of a membrane is one through which the air can communicate and water cannot communicate.  
         [0071]    The above-mentioned electric shaver has an air-tight chamber between the lower separating wall  26  and bottom cover  39 , both of which are sealed by resilient O-ring  34  and  44  at their periphery. The battery case which retains the battery  3  is sealed at the upper end whereas communicates with the air tight chamber at the bottom end. The structure of the battery case enables air-tight retention. Once gas is emitted from the battery  3 , the chamber pressure rises. When the pressure rises over the preselected level, the membrane is broken by the pressure to let air out. In the electric shaver with the structure above, the gas emitted from the battery  3  is not allowed to go into the chamber for the electronic parts including the motor  4 , whereby protecting electronic part board from the gas. Even if the membrane is broken and water comes into the chamber, the electronic part board or the motor  4  is protected from water.  
         [0072]    Furthermore, the inner case  22  is provided with a cross rib  27  at the top of the side walls  25  for retaining the motor  4 . The motor  4  is retained by the cross rib  27 , side walls  25  and separating wall  23 . Furthermore, the inner case  22  has a connecting mechanism  28  at the top of the side walls  25  for securing resilient arms of reciprocating member  14 .  
         [0073]    [0073]FIG. 11 shows another embodiment having a bottom cover with a chamber of another configuration for receiving power source plug. FIG. 12 shows schematic view of the chamber  145  on an enlarged scale, FIG. 13 and FIG. 14 show a cross-sectional and vertical cross-sectional view respectively. The chamber  145  shown in these figures has a horizontally elongated square configuration. The chamber  145  has an axially elongated configuration as shown in FIG. 15 and FIG. 16 so that it enables smooth and guided insertion of the power source plug. The power source plug  53  is inserted perpendicularly to the surface of the bottom cover  139 . Therefore, the chamber  145  has an axially elongated column-like configuration. “column-like” means an chamber having the same cross-section along the direction of insertion.  
         [0074]    The chamber  145  shown in FIG. 12 through  14  has an elongated guide projection  148  to prevent a wrong insertion of the plug  53 . The guide projection  148  formed integral with the bottom cover extends in the direction of insertion of the plug  53 . The guide projection  148  has a triangular cross-section and is formed at the middle of the side walls. Furthermore, the chamber  145  shown in the figures has rounded corners at both sides, the corner of each side having different diameter so that wrong insertion of the plug is avoided. The chamber  145  shown in the figures has a kind of rounded corners with a smaller diameter on the side where the guide projection is formed as well as another kind of rounded corners with different diameter on the other side.  46  Furthermore, the chamber  145  shown in the figures is provided with a groove  147  opposite to the guide projection  148 , which communicate with a through hole  139 B in the bottom cover  139 . The through hole  139 B is closed with a membrane  149  at the inner face of the outer casing  101 . The membrane  149  seals the through hole  139 B in normal use, but it breaks under pressure to discharge the air inside the outer casing when the pressure inside the outer casing  101  rises to a certain level. The through hole  139 B communicating with the groove inside the chamber together with sealing membrane  149  function as a safety valve  146 . The safety valve is protected from piercing with e.g. a needle by the user.  
         [0075]    The chamber  145  is provided with a leak prevention wall  150  at the bottom to prevent leakage of current due to conductive water and corrosion of the plug pins by current due to conductive water. The chamber  145  shown in the figures is divided into two blocks by leak prevention wall  150 . The leak prevention wall is formed at the bottom of the chamber as a projection integral with the bottom cover made of plastics. The leak prevention wall  150  prevents currents from flowing between the plug pins  132 , 132 . The leak prevention wall is made of insulating materials. The outer casing of electric home appliances is made of plastics without exception. Therefore, the leak prevention wall  150  is made integral with the outer casing of plastics.  
         [0076]    The leak prevention wall is not capable of preventing leakage if it is too low. Therefore, the height of the wall is preferably 1-5 mm or more preferably 2-4 mm. The leak prevention wall  150  is formed as a continuing part of the guide projection  148 . The leak prevention wall  150  functions as a guiding member for the power source plug  53  when the plug is inserted into the chamber  145 . The leak prevention wall  150  avoids improper insertion of the plug into the chamber  145  by virtue of the recess  54  of the plug  53  shown in FIG. 17. To avoid faulty insertion of the plug  53 , the leak prevention wall  150  must be strong enough. Therefore it is 0.5-2 mm in thickness or more preferably 1 mm in thickness.  
         [0077]    The chamber shown in FIG. 13 is provided with a leak prevention wall  150  which is joined at one end to the inner face of the chamber  145 , but is separated at the other end from the chamber wall leaving a narrow gap  151  for the through hole  139 B of the safety valve.  
         [0078]    A pair of plug pins  132 ,  132  are fixed, one on each side of the leak prevention wall, spaced apart and parallel to each other. In the figure, Two plug pins are fixed in the chamber spaced apart along the longer side of the chamber. To supply power, at least two plug pins are needed. If needed, three or more plug pins may be used, in which case two of them are used for supplying power, one for sending signals.  
         [0079]    In order to realize water-proof structure of the outer casing  101  of the shaver shown in the figures, the plug pins  132 , 132  are sealed and fixed to the bottom cover  139 . As shown in FIG. 14, the plug pins have a flange  152  which presses an O-ring  143  to the inner surface of the bottom cover whereby realizing water-proof plug pins. The plug pin  132  is fixed to the plug board  133  secured in the outer casing  101 . The flanged plug pin  132  exerts pressure on the O-ring  143  to obtain water-proof bottom cover 139 .  
         [0080]    As shown in FIG. 15, the power source plug  53  has an insert portion  53 A at its end which is to be inserted in a right position or pulled out of the chamber  145 . The insert portion  53 A of the plug is configured corresponding to the inner configuration of the chamber  145 , whereby ensuring smooth and sufficient insertion.  
         [0081]    The power source plug  53  is connected by way of the power cord  55  to the adaptor  56 .  
         [0082]    Next to the insert portion  53 A, the power source plug  53  shown in the figures has a gripping part  53 B, and a resilient bushing part  53 C integral therewith of plastics. The gripping part  53 B is sized large so that the user can grip easily. The bushing part  53 C is flexible to prevent the cord from severing from wear.  
         [0083]    As shown in FIG. 17, the power source plug  53  has an recess  54  at the end of the insert portion  53 B to admit the leak prevention wall  150  in the chamber  145 . The depth of the recess  54  is equal or little greater than the height of the leak prevention wall  150 . The width of the recess  54  is equal to that of the wall  150 . As the power source plug  53  is inserted into the chamber  145 , the recess  54  in the insert portion  53 A receives the leak prevention wall  150 .  
         [0084]    The insert portion  53 A is provided with connecting terminals (not shown) to be connected to the plug  132 ,  132 . The connecting terminals are made with metal plate which is formed in a resilient cylinder. The internal diameter of the cylinder is slightly less than the external diameter of the plug pin  132 . When the plug pins  132 , 132  are inserted into the cylindrical connecting terminals, the resilient cylinders expand slightly and exert pressure on the plug pins  132 , 132  to establish a firm connection. The insert portion  53 A is provided with a pair of guide holes to receive the plug pins  132 .  
         [0085]    Furthermore, each of the connecting terminals is connected to a lead wire within the gripping part  53 B, which lead wire is connected to the adaptor  56 . When the power source plug  53  is inserted in the chamber 145 , the adaptor  56  is connected via lead wire and connecting terminals to the plug pin  132  to supply power to the electric apparatus.  
         [0086]    The electric shaver of the type described above has the advantages that current leakage flowing through the water trapped in the chamber as well as faulty connection of the plug and plug pin is avoided. The advantage is attained by implementing leak prevention wall in the chamber separates the water trapped around the plug pins and makes a longer leakage channel whereby avoiding current leakage. The leak prevention wall reduces current leakage even if water is trapped in the chamber thus reducing electro-erosion of plug pins or connector terminals. The advantage is especially important for a washable electric household appliance e.g., an electric shaver, because electro-erosion shortens service time of electric appliances even if the sealing of the casing is perfect.  
         [0087]    Furthermore, the electric shaver with the leak prevention wall has the advantage that the wall functions as a guide member when the power source plug is inserted ensuring a smooth and sufficient insertion of the power source terminals into the plug pins.  
         [0088]    Furthermore, the electric shaver described above is capable of preventing inclined insertion of the power source plug into the chamber by virtue of the guiding recess of the plug. In other words, the power source plug is perfectly inserted into the chamber avoiding faulty connection between the plug pins and the connector terminals. Undesirable forces can be eliminated when the plug is pulled out of the chamber.  
         [0089]    As this invention may be embodied in several forms without departing from the spirit of essential characteristics thereof, the present embodiment is therefore illustrative and not restrictive, since the scope of the invention is defined by the appended claims rather than by the description preceding them, and all changes that fall within meets and bounds of the claims, or equivalence of such meets and bounds thereof are therefore intended to be embraced by the claims.