Abstract:
The electronic flash unit disclosed comprises: a transformer ( 14 ) to vary voltages of a power supply; an accumulator ( 16 ) composed of a main capacitor ( 17 ) to charge an electric energy supplied from the transformer ( 14 ); a lamp unit ( 4 ) provided with a flashlamp ( 20 ), set inside of a reflector ( 19 ), that flashes by discharging of energy storages in the main capacitor ( 17 ) upon applying a voltage on a trigger terminal ( 21 ); and a trigger circuit ( 10 ) to generate the voltage to apply on the trigger terminal ( 21 ), wherein at least the lamp unit ( 4 ) is coated with an insulation material.

Description:
RELATED APPLICATIONS 
     This application is a divisional of application Ser. No. 10/497,025, filed on May 28, 2004, now U.S. Pat. No. 7,652,434, which in turn claims the benefit of PCT/JP02/12430, filed on Nov. 28, 2002, which in turn claims benefit of Japanese Patent Application No. 2001-365882, filed on Nov. 30, 2001, the disclosures of which Applications are incorporated by reference herein. 
    
    
     TECHNICAL FIELD 
     The present invention relates to an electronic flash unit employing a flashlamp, a valuable artificial light source, to take photographs using camera (an imaging apparatus) equipped with a silver film or an electronic imaging element such as charge-coupled device (CCD) or complementary metal-oxide semiconductor (CMOS) sensor as a photographic sensitive material, and a manufacturing method thereof. 
     BACKGROUND ART 
       FIG. 7  shows a typical electronic flash unit basically comprising: flashlamp  20  for instance a xenon lamp (set inside of a reflector, but not shown); lamp unit  4  provided with trigger terminal  21 ; trigger circuit  10  provided with trigger coil  11  and trigger capacitor  13 ; transformer  14  composed of transformer coil  15 ; accumulator  16  composed of main capacitor  17 ; and power source  22  composed of DC source  23 . Main capacitor  17 , on a charged condition of for instance 300 V by DC source  23 , allows trigger circuit  10  to apply a several kV of trigger voltage on trigger terminal  21  of flashlamp  20 , thereby causing flashlamp  20  to ignite for flashing by discharging the power storage in main capacitor  17 . 
     Other types of electronic flash units would have dimming circuits  25  provided with Insulated Gate Bipolar Transistor (IGBT)  26 , optical sensor  27  or the like added to the aforesaid configuration to control the amount of flashing light by dimming circuits  25 . 
     A lot of conventional electronic flash units like described above are used in various kinds of cameras such as silver film cameras, well known digital cameras employing CCD or CMOS sensor as an imaging element, and single-use-cameras having a simplified structure of a film incorporated with a lens unit and the electronic flash unit built-in the camera body. 
     As portable telecommunication terminals or cell-phones capable of transmitting stored images using built-in digital camera have become popular in the market, electronic flash units detachable to the cell-phones have also begun to be provided. Along with recent trends of downsizing in cameras and cell-phones, or built-in design in cell-phones, a more compact sized electronic flash units are required to meet the market needs. 
     Downsizing of the electronic flash unit, however, cannot be achieved without solving the problem of so-called “trigger leak”. The trigger leak means a poor flashing due to occurring a creeping discharge that results in an ineffective ionization in flashlamp  20  caused by a decrease in clearance between trigger terminal  21  provided on the glass bulb of flashlamp  20  and main electrode  20   a  of flashlamp  20 . 
     SUMMARY OF THE INVENTION 
     The electronic flash unit comprises: a transformer to vary voltages of a power supply; an accumulator composed of a main capacitor to charge an electric energy supplied from the transformer; a lamp unit provided with a flashlamp, set in a reflector, that flashes by discharging the electric energy storage in the main capacitor upon applying a voltage on a trigger terminal; and a trigger circuit to generate the voltage to apply on the trigger terminal, wherein at least the lamp unit is coated with an insulation material. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows an exploded perspective view from the front side of the electronic flash unit used in preferred embodiment 1 of the present invention. 
         FIG. 2  shows an exploded perspective view from the front side of the lamp unit used in preferred embodiment 1 of the present invention. 
         FIG. 3  shows a perspective view from the backside of the lamp unit used in preferred embodiment 1 of the present invention. 
         FIG. 4  shows a partial perspective view of a different embodiment of the lamp unit used in preferred embodiment 1 of the present invention. 
         FIG. 5  shows a cross-sectional side view of the electronic flash unit used in preferred embodiment 1 of the present invention. 
         FIG. 6A  shows a perspective view from the backside of the electronic flash unit used in preferred embodiment 2 of the present invention. 
         FIG. 6B  shows a perspective view from the front side of the electronic flash unit used in preferred embodiment 3 of the present invention. 
         FIG. 6C  shows a perspective view from the front side of the electronic flash unit used in preferred embodiment 4 of the present invention. 
         FIG. 6D  shows a perspective view from the front side of the electronic flash unit used in preferred embodiment 5 of the present invention. 
         FIG. 7  shows an electric block diagram of a typical electronic flash unit. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Now, the preferred embodiments of the present invention are described with reference to the drawings. 
     (Preferred Embodiment 1) 
       FIG. 1  shows an example of electronic flash units in which lamp unit  4 , trigger circuit  10 , transformer  14 , dimming circuit  25  and accumulator  16  are shown coated with an insulation material individually. 
     The electronic flash unit explained in preferred embodiment 1, capable of connecting to an earphone jack of a cell-phone having built-in digital camera using CCD or CMOS sensor detachable freely, flashes upon receiving power supply and signals to start photographing from the cell-phone. As shown in  FIG. 1 , the electronic flash unit includes elements of: circuit board  3 ; lamp unit  4  except optical surface  5   a , exposed critically through opening  2   a  formed in the front half of housing  2 , of optical panel  5 ; and base  6   a  of plug (external terminal)  6  in a hermetically sealed generally box shaped resin molded housing  2  capable of separating into halves. 
     Circuit board  3  has patterned circuits to drive the electronic flash unit. The pattern in circuit board  3  comprises circuit elements connected electrically: various kinds of lead wires such as lead wire  7  to the plug, lead wire  8  to flashlamp  20 , and lead wire  9  to trigger terminal  21 ; trigger circuit  10  including trigger coil  11 , trigger capacitor  13  (not shown) or the like; dimming circuit  25  including IGBT (not shown), optical sensor (not shown) or the like; transformer  14  composed of transformer coil  15 ; and accumulator  16  composed of main capacitor  17 . 
     Lamp unit  4 , other than aforesaid optical panel  5 , comprises: resin molded frame  18  fixed to circuit board  3 ; reflector  19 ; flashlamp  20  provided with a conductive layer, for instance a transparent conductive layer, formed on the outer surface of glass bulb; and trigger terminal  21  connected electrically to the conductive layer formed on the glass bulb of flashlamp  20  through reflector  19  as shown in  FIGS. 2 and 3 . 
     Reflector  19  is fitted to opening  18   a  of frame  18  from the front. Flashlamp  20  is inserted inside of reflector  19  from side openings  19   a  of reflector  19  projecting to the back of opening  18   a  of frame  18 . A pair of lead wires  8  to flashlamp  20  is soldered to each of main electrodes  20   a  of flashlamp  20  respectively. A lead wire  9  to trigger terminal  21  is soldered to trigger terminal  21  appressed to the back of reflector  19 . Optical panel  5  is fitted to the front surface of frame  18 , or optical panel  5 , in a condition of being fitted to opening  2   a  of housing  2 , is included in housing  2  eventually. 
     Reflector  19  is made of a bright aluminum sheet cut into a predetermined shape, formed into generally U-shaped and bent inward in edges, comprising a U-shaped cross-sectional or concavely curved inner surface to reflect a flash light and a pair of side panels,  19   b  and  19   b , in both right and left ends. 
     A pair of side panels  19   b  are designed to provide side opening  19   a  with a slightly larger dimension than the outer diameter of flashlamp  20 , causing both ends (including main electrodes  20   a ) of flashlamp inserted from a side opening  19   a  to project out of side openings  19   a  externally. 
     Flashlamp  20  has a structure of a straight glass tube with metal rod main electrodes  20   a  sealed in both ends, partially extending externally along axial direction, and with a filling gas in the tube of for instance xenon. 
     One of main electrodes  20   a  of flashlamp  20  is connected to lead wire  8  connected to main capacitor  17  and another main electrode  20   a  is connected for instance to lead wire  8  grounded directly. 
     Trigger terminal  21  is made of a copper sheet bent arc shaped corresponding to reflector  19 . Practically, the copper sheet, reflector  19  and the conductive layer provided on the glass bulb of flashlamp  20  all together make up trigger terminal  21 . The copper sheet, however, is not necessary if lead wire  9  to trigger terminal  21  can be soldered directly to reflector  19  or to the surface of glass bulb of flashlamp  20 . 
     Extending reflector  19  partially to act as a terminal, portion  19   c  can be coupled directly with high voltage terminal  11   a  of trigger coil  11  as shown in  FIG. 4 . The configuration can not only make lead wire  9  to trigger terminal and the copper sheet unnecessary but also can save works of pasting the copper sheet or soldering lead wire  9  to trigger terminal  21 . 
     As aforementioned and shown in  FIG. 1 , housing  2  contains; circuit board  3  including various circuit elements, lamp unit  4  and base  6   a  of plug (external terminal)  6  in a hermetically sealed condition. 
     Though the relevant positions are sealed hermetically in fitting optical surface  5   a  of optical panel  5  to opening  2   a  of housing  2  and in fitting plug base  6   a  of plug  6  to opening  2   b  provided at separate surfaces of the housing halves, housing  2  is not sealed in a complete air-tight condition. 
     The reason is that housing  2  is provided with a pair of fine through holes  2   c  and  2   d . Through holes  2   c  and  2   d  are formed halved at the separate surfaces of housing  2  to form circular holes by combining halves of housing  2 . The positions to provide through holes  2   c  and  2   d  are not restricted particularly. Among these two, through hole  2   c  is to work for filling housing  2  with an insulation resin (insulation material), and the other through hole  2   d  is to let air in housing  2  out at the resin filling. Specifically, housing  2  is filled with the insulation resin using a filling nozzle fitted in through hole  2   c  formed at the bottom surface of housing  2 , allowing air in housing  2  to leave via through hole  2   d  formed at the top surface of housing  2 . 
     Number of hole is not restricted within one pair if the resin filling and air releasing will be performed well, and hole other than circular shaped may be acceptable. Polyurethane, silicone, epoxy, polyimide or the like can be adopted for the insulation resin, and glasses may be used as insulation materials. 
     A feasible configuration has a reflector filled with an insulation material internally if a glass or resin, transparent or translucent, with insulation property is adopted as the insulation material. In this case, the internal of reflector as well as lamp unit is filled with the glass or resin for insulation at the same time. The glass or resin, transparent or translucent, can effectively prevent a loss in incident light intensity of flashlamp through the air atmosphere inside of the reflector to optical panel that occurs when the glass or resin is not applied, enabling to increase in performance characteristics of the electronic flash unit. 
     Additionally, the resins can be mixed with glass beads to improve light diffusion effects. 
     As described above, the electronic flash unit elements consisting of circuit board  3  (including trigger circuit  10 , transformer  10 , accumulator  16 , dimming circuit  25  or the like) and lamp unit  4  are all allowed completely coated with the resin, since the sealed inside space of housing  2  is filled with a resin entirely as shown in  FIG. 5  (housing  2  under a condition filled with a resin is not shown). Above all, positions required highly insulated such as the clearance between main electrodes  20   a  and  20   a  of flashlamp  20  and trigger terminal  21  (reflector  19 ), terminals  11   a  of trigger coil  11 , transformer coil  15  (especially, secondary coil) and terminals of main capacitor  17  (especially, high voltage terminal) are electrically insulated completely, enabling to prevent the trigger leak or possible electric shocks at breakage of housing  2  from occurring. Additionally, the configuration can improve their own insulation characteristics of trigger coil  11  and transformer coil  15  and can strengthen resistances to dropping impacts or the like. 
     (Preferred Embodiment 2) 
       FIG. 6A  shows an example of lamp unit  4  in  FIG. 7  coated with an insulation material. 
     The electronic flash unit used in preferred embodiment 2 includes lamp unit  4  alone in housing  2  independently as shown in  FIG. 6A . The configuration is suitable for a detachable lamp unit to an electronic flash unit (or a camera body or cell-phone body, in case of a camera or cell-phone with a built-in electronic flash unit). 
     Box-shaped housing  2 , provided with optical panel  5  in one surface and open in the opposite surface, includes reflector  19 , flashlamp  20  and trigger terminal  21 . 
     Housing  2  includes a pair of lead wires  8  and  8  to flashlamp  20 , and lead wire  9  to trigger terminal including soldered ends. 
     Housing  2  is filled with an insulation resin under this condition. 
     Consequently, the clearances between main electrodes  20   a  and  20   a  of flashlamp  20  and trigger terminal  21  (reflector  19 ) are electrically insulated completely, enabling to prevent the trigger leak or possible electric shocks at breakage of housing  2  from occurring and to strengthen resistances to dropping impacts or the like. 
     (Preferred Embodiment 3) 
       FIG. 6B  shows an example of lamp unit  4 , trigger circuit  10 , transformer  14  and dimming circuit  25  in  FIG. 7  coated with an insulation material. The electronic flash unit used in preferred embodiment 3 includes lamp unit  4  and circuit board  3  in an independent housing  2 , exposing main capacitor  17  out of housing  2  as shown in  FIG. 6A . 
     Box-shaped housing  2  provided with optical panel  5  in one surface, includes reflector  19 , flashlamp  20 , trigger terminal  21  and circuit board  3  carrying circuit elements (trigger circuit  10 , transformer  14 , dimming circuit  25  or the like) except main capacitor  17 . 
     Lead wires connected to terminals of main capacitor  17  and lead wires to receive electric power or signals externally are connected to internal circuit board  3  through housing  2 . 
     Housing  2  is filled with an insulation material under this condition. Consequently, the clearances between main electrodes  20   a  and  20   a  of flashlamp  20  and trigger terminal  21  (reflector  19 ), terminals  11   a  of trigger coil  11  and transformer coil  15  are electrically insulated completely, enabling to prevent the trigger leak or possible electric shocks at breakage of housing  2  from occurring and to strengthen resistances to dropping impacts or the like. 
     (Preferred Embodiment 4) 
       FIG. 6C  shows an example of lamp unit  4 , trigger circuit  10 , transformer  14 , dimming circuit  25  and a terminal of main capacitor  17  in  FIG. 7  coated with an insulation material. 
     The electronic flash unit used in preferred embodiment 4 includes lamp unit  4 , circuit board  3  and a portion of main capacitor  17  in an independent housing  2 , exposing the other portion of main capacitor  17  (except terminal) out of housing  2  as shown in  FIG. 6C . 
     Box-shaped housing  2  provided with optical panel  5  in one surface, includes reflector  19 , flashlamp  20 , trigger terminal  21  and circuit board  3  carrying circuit elements (trigger circuit  10 , transformer  14 , dimming circuit  25 , accumulator  16  or the like). 
     Housing  2  includes terminal side half of main capacitor  17  while the other half of explosion-protection valve side is exposed out of housing  2  critically. Lead wires to receive electric power or signals externally are connected to internal circuit board  3  through housing  2 . 
     Housing  2  is filled with an insulation material under this condition. Consequently, the clearances between main electrodes  20   a  and  20   a  of flashlamp  20  and trigger terminal  21  (reflector  19 ), terminals  11   a  of trigger coil  11 , transformer coil  15  and terminal of main capacitor  17  are electrically insulated completely, enabling to prevent the trigger leak or possible electric shocks at breakage of housing  2  from occurring and to strengthen resistances to dropping impacts or the like. 
     Explosion-protection valve  17   a  provided in main capacitor  17  is to protect whole of the capacitor from breakage by blowing out itself at an abnormal increase in inner pressure of main capacitor  17 . The valve is introduced on the assumption of possible failures. Though, typically, it seems unlikely for explosion-protection valve  17   a  to blow out, it would be a wise measure to expose a relevant portion out of housing  2  beforehand to protect housing  2  from damaging influences if possible failures are assumed. 
     Therefore, housing  2  is not influenced even in an abnormal condition (over current) of main capacitor  17 , as explosion-protection valve  17   a  is positioned exposed outside of housing  2 . 
     (Preferred Embodiment 5) 
       FIG. 6D  is an example showing lamp unit  4 , trigger circuit  10 , transformer  14 , dimming circuit  25  and a terminal of main capacitor  17  in  FIG. 7  are coated with an insulation material. 
     The electronic flash unit used in preferred embodiment 5 includes lamp unit  4 , circuit board  3  and a portion of main capacitor  17  in an independent housing  2 , exposing the other portion of main capacitor  17  (except terminal) and projection terminal  24  to receive electric power and signals externally from housing  2  as shown in  FIG. 6D . 
     A feasible configuration further comprises a projection terminal to connect to the power supply electrically that protrudes out of the housing. Namely, the electronic flash unit can be a detachable device if camera or cell-phone has a terminal capable of connecting to the projection terminal 
     Box-shaped housing  2  provided with optical panel  5  in one surface, includes reflector  19 , flashlamp  20 , trigger terminal  21  and circuit board  3  carrying circuit elements (trigger circuit  10 , transformer  14 , dimming circuit  25 , accumulator  16  or the like). Housing  2  includes most of terminal side of main capacitor  17  while the remaining side with explosion-protection valve  17   a  is exposed out of housing  2 . Projection terminal  24  exposing out of housing  2  critically is connected to circuit board  3  through inside of housing  2  or an end of circuit board exposed out of housing  2  critically acts as a projection terminal. 
     Housing  2  is filled with an insulation material under this condition. Consequently, the clearances between main electrodes  20   a  and  20   a  of flashlamp  20  and trigger terminal  21  (reflector  19 ), terminals  11   a  of trigger coil  11 , transformer coil  15  and terminal of main capacitor  17  are electrically insulated completely, enabling to prevent the trigger leak or possible electric shocks at breakage of housing  2  from occurring and to strengthen resistances to dropping impacts or the like. 
     Other Preferred Embodiments 
     The present invention is not so limited to the aforesaid preferred embodiments but is susceptible to various changes without departing from the scope of the invention. 
     For instance, if the housing is used as a package of the electronic flash unit (including a case when the housing is used for an element of the electronic flash unit for instance lamp unit  4  alone), the housing can be applied a conductivity to perform protective shield effects against electric or magnetic noises. The housing should, preferably, be filled with an insulation resin after inner (or outer) surface of the housing is provided with a shield layer by conductive resin coating or metal plating. 
     The configuration of housing with the shield layer can shut off electric noises properly. 
     Additionally, the description, “internal elements are hermetically sealed in the housing”, does not mean to shut off in-and-out air flowing completely but means not to leak out the filled resin. Therefore, in all of the aforementioned descriptions, housing  2  does not require a high accuracy as to secure a perfect airtight condition. However, to reduce inward and outward air flowing paths, optical panel  5  should preferably be made integrally with housing  2  using a same material. Consequently, optical panel  5  is not required to form an attachable periphery to housing  2  or housing  2  does not need to have an opening provided with a frame mountable to optical panel  5 , resulting in a contribution to the downsizing of electronic flash unit due to thin thickness optical panel  5  and compact sized housing  2 . 
     Additionally, if the configuration of optical panel  5  molded integrally with housing  2  is adopted instead of disposed in front of the opening of reflector  19  as a separate parts, low profile optical panel  5  and down sized housing  2  can be achieved, resulting in a downsizing of the electronic flash unit. Moreover, the configuration can provide a high quality electronic flash unit, with no danger of leaking the filled insulation materials out of the electronic flash unit as no joint surfaces exist between optical panel  5  and housing  2 . 
     Additionally, the applying way of insulation resins are not so limited to the insulation resins poured into the housing through holes or the like externally. A feasible method for instance would be to provide respective halves of a housing with the insulation resin beforehand and to complete a housing by combining the respective halves. 
     Additionally, the filling insulation resin should preferably have a certain degree of elasticity. This is to prevent the housing or parts included in the housing from being damaged due to an expansion of insulation materials caused by heats generated in elements of the electronic flash unit. 
     Moreover, to prevent air bubbles from generating in the insulation materials, the housing is allowed pumped to a vacuum pressure during or after the resin filling and then the insulation resins should preferably be hardened under a pressure higher than the vacuum pressure. 
     Additionally, the aforesaid resin filling process pumps air in the reflector also, causing to fill inside of the reflector with the resin. However, the resin can be prevented from pouring inside of the reflector, if gaps between side openings of the reflector and the flashlamp, and between both side plates are sealed by some sealing means (for instance, a silicone bond or a rubber bushing). (No insulation resin pours into from the front opening, as the optical panel closes the opening). 
     Additionally, the reflector filled with the insulation resin has an advantage to prevent a loss in incident light through the air atmosphere inside of the reflector to optical panel resulting in no decrease in light intensity (in case of a transparent insulation resin), but has a disadvantage to reduce light diffusion effects of a light diffusion surface formed on the back surface of the optical panel due to the approximate refraction factors of the optical panel and the insulation resin. 
     The configuration of the reflector filled with the insulation resin, therefore, should preferably adopt an insulation resin mixed with a diffusion agent as an additive, and glass beads for instance used as a diffusion agent will improve the light diffusion effects. 
     Moreover, instead of the housing used as a mold to fill with the insulation resin as described in the aforesaid preferred embodiments, a possibility would be the electronic flash unit regardless of the housing (covered by a housing if needed), wherein elements of the electronic flash unit (all of or a part of) are set in another mold and released from the mold after the mold is filled with the insulation resin. 
     Additionally, to produce the electronic flash unit contained in the housing filled with the insulation resin, internal elements of the electronic flash unit are disposed after selected into two groups: high voltage group to be insulated (for instance, the lamp unit, the trigger circuit, at least secondary terminal of the transformer, at least high voltage terminal of the main capacitor or the like); and the remaining low voltage group. 
     If filled-in insulation resins are hardened disposing elements in high voltage group on lower positions and elements in low voltage group on upper positions in the housing, the elements in high voltage group can be insulated properly as the elements in high voltage group is securely covered in the insulation resin even in up and down flowing movements in upper portions of the insulation resin caused by bubbling under a vacuum condition in case of the housing filled with the insulation resin incompletely. 
     Moreover, members such as lamp unit  4  or the like to be filled with insulation materials should preferably be filled with the insulation materials once coating the surface with the insulation resin by dipping or the like. This is to achieve an effective insulation coating as gaps in each parts are filled with the insulation resin reliably. 
     As described above, among elements of the electronic flash unit disclosed in the present invention at least lamp unit is coated with the insulation resin to insulate the clearance between the trigger terminal (or reflector itself, or the reflector attached to the trigger terminal), enabling to prevent the trigger leak from occurring properly. Consequently, a further downsizing of the electronic flash unit can be achieved by solving the trigger leak problem. 
     Industrial Applicability 
     The present invention relates to an electronic flash unit using a flashlamp as a light source and a manufacturing method thereof. The electronic flash unit can prevent the occurrence of the trigger leaks accompanied by downsizing significantly, while achieving a compact design. 
     REFERENCE MARKS IN THE DRAWINGS 
     
         
           1  electronic flash unit 
           2  housing 
           2   c  through hole (resin filling) 
           2   d  through hole (venting) 
           3  circuit board 
           4  lamp unit 
           5  optical panel 
           6  plug (external terminal) 
           10  trigger circuit 
           11  trigger coil 
           13  trigger capacitor 
           14  transformer 
           15  transformer coil 
           16  accumulator 
           17  main capacitor 
           17   a  explosion-protection valve 
           19  reflector 
           20  flashlamp 
           20   a  main electrode 
           21  trigger terminal 
           22  power source 
           23  DC source 
           24  projection terminal 
           25  dimming circuit 
           26  Insulated Gate Bipolar Transistor (IGBT) 
           27  optical sensor