Abstract:
To test the integrity of waterproof cases for cameras and like apparatus to be used underwater, a casing with a detector is provided. The air inside the casing is pressurized and the detector indicates leakage based on the difference between the pressurized air and atmospheric pressure. A decrease in pressure of the initial level of pressurized air implies leakage.

Description:
[0001]    This application is a continuation-in-part of international application number PCT CA99/00122, filed Feb. 9, 1999 which is a continuation-in-part of U.S. patent application Ser. No. 08/819,339 (issued as U.S. Pat. No. 5,870,632). 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention relates to the detection of leakage in a casing based on sensing changes in the air pressure.  
         BACKGROUND OF INVENTION  
         [0003]    Airtight or waterproof cases are used to enclose cameras and other sensitive apparatus to protect them from their operating environment external to the case (herein “environment”), which may have moisture, dust, gases and other harmful elements. Cases may suffer from manufacturing defects and may consequently leak.  
           [0004]    Detection of leaks in supposedly waterproof cases has been conventionally attempted by detecting the presence of moisture. Schwomma (U.S. Pat. No. 4,312,580) is a representative example. Not only are moisture detectors difficult and expensive to build and maintain, the detection of moisture comes often too late (e.g. moisture has already entered the casing).  
           [0005]    As well, detection of leaks has been conventionally attempted by observing changes in the air pressure inside the casing after artificially increasing it. Hayakawa (U.S. Pat. No. 5,305,031) is a representative example. One defect of such attempts is that the means for increasing the air pressure and detecting changes, is itself a potential source of leakage in addition to possible leakage in the casing. For example, after using the Hayakawa device to test the integrity of the casing, it is neither clear that the “self-closing” seal will maintain its integrity nor how to test for that post-testing integrity. Takamura (U.S. Pat. No. 4,763,145) and Prager (DE 38 37 624) are further examples wherein differential pressure of sub-chambers is used to detect leaks, however not all of such sub-chambers are in communication with the environment.  
         SUMMARY OF THE INVENTION  
         [0006]    To address the above defects with the conventional approaches, this invention provides a case comprising: (a) sealed housing with an outer wall; and (b) a leakage detector firmly located in said wall having: (i) a chamber with first and secondsub-chambers; (ii) first port means by which said first sub-chamber communicates with the environment; (iii) second port means by which said second sub-chamber communicates with the environment; (iv) a partition separating said first sub-chamber from said second sub-chamber which moves in response to the difference in the respective air pressures of said first and second sub-chamber; and (v) indicator means, located proximate said partition and responsive to movement of said partition, for indicating leakage.  
           [0007]    To address the above defects with the conventional approaches, this invention provides a leakage detector for a sealed housing with an outer wall, comprising: (i) a chamber with first and second sub-chambers; (ii) first port means by which said first sub-chamber communicates with the environment; (iii) second port means by which said second sub-chamber communicates with the environment; (iv) a partition separating said first sub-chamber from said second sub-chamber which moves in response to the difference in the respective air pressures of said first and second sub-chamber; and (v) indicator means, located proximate said partition and responsive to movement of said partition, for indicating leakage.  
           [0008]    To address the above defects with the conventional approaches, this invention provides a method of detecting leakage in a case, comprising the steps of: (a) creating a first sub-chamber of pressurized air in communication with the interior of the case; (b) creating a second sub-chamber of air; (c) abutting a portion of said first sub-chamber with a portion of said second sub-chamber where the abutment is in the form of a membrane whose profile changes in response to the relative differences in air pressures of said first and second sub-chambers. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    Advantages of the present invention will become apparent from the following detailed description taken in conjunction with preferred embodiments shown in the accompanying drawings, in which:  
         [0010]    [0010]FIG. 1 is a rear perspective view of an underwater camera housing employing a leakage detector according to the present invention;  
         [0011]    [0011]FIG. 2 is a perspective view of the leakage detector according to the present invention;  
         [0012]    [0012]FIG. 3( a ) is a top view of the detector of FIG. 2;  
         [0013]    [0013]FIG. 3( b ) is a side view of the detector of FIG. 3( a ) taken along line II-II therein;  
         [0014]    [0014]FIG. 4( a ) is a top view of the injector head of the present invention;  
         [0015]    [0015]FIG. 4( b ) is a side view of the injector head of FIG. 4( a ) taken along line II-II therein;  
         [0016]    [0016]FIG. 5( a ) is a top view of the plug of the present invention;  
         [0017]    [0017]FIG. 5( b ) is a side view of the plug of FIG. 5( a ) taken along line II-II therein;  
         [0018]    [0018]FIG. 6 is a side view of the injector head inserted into the detector according to another embodiment;  
         [0019]    [0019]FIG. 7 is a side view of the plug inserted into the detector;  
         [0020]    [0020]FIG. 8 is a perspective view of the leakage detector according to the present invention;  
         [0021]    [0021]FIG. 9( a ) is a top view of the detector of FIG. 8;  
         [0022]    [0022]FIG. 9( b ) is a side view of the detector of FIG. 9( a ) taken along line II-II therein;  
         [0023]    [0023]FIG. 10( a ) is a top view of the injector head of the present invention;  
         [0024]    [0024]FIG. 10( b ) is a side view of the injector head of FIG. 10( a ) taken along line II-II therein;  
         [0025]    [0025]FIG. 11( a ) is a top view of the plug of the present invention;  
         [0026]    [0026]FIG. 11 ( b ) is a side view of the plug of FIG. 11( a ) taken along line II-II therein;  
         [0027]    [0027]FIG. 12 is a side view of the injector head inserted into the detector;  
         [0028]    [0028]FIG. 13 is a side view of the plug inserted into the detector;  
         [0029]    [0029]FIGS. 14 a  to  14   f  are side and top views of an alternative embodiment of the invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0030]    [0030]FIG. 1 shows underwater camera housing  10 , which has front part  10   a  and rear part  10   b  held together by several spring-loaded latches (one,  10   c , is shown in FIG. 1). Silicon or rubber O-ring  10   d  provides a waterproof seal between front and rear parts  10   a  and  10   b  when latched together. Leakage detector  20  is connected to housing  10  at hole  15  in rear part  10   b  (explained below). Leakage detector  20  has several purposes, in addition to detecting leakage. To pressurize the air in housing  10 , plastic hand or finger pump  99 , is employable with leakage detector  20  through injector head  40 . Leakage detector  20  is plugged with plug  50 .  
         [0031]    As shown in FIGS. 2 and 3, detector  20  has a convex, annular upper body  21  with a central port  23  to receive injector head  40  or plug  50  (explained below), and a hollow stem  22  depending downwardly. Stem  22  and hole  15  are respectively profiled to create a tight friction fit when stem  22  is inserted in hole  15  and the connection is conventionally sealed with glue, O-rings and ultrasonically bonded. The base of body  21  is profiled to hug rear part  10   b  in a flush manner. Body  21  has three sockets  27  which interact with corresponding wings  28  of injector head  40  or plug  50  (explained below) to create a tight interlock therewith. Within body  21  is elastic membrane  25  (explained below) and the portion of body  21  proximate membrane  25  is transparent and has a visible scale of graduations  26  to permit viewing of the profile of membrane  25  relative thereto (as shown in FIG. 2).  
         [0032]    Body  21  has atmospheric sub-chamber  30 , in the shape of a partial torus, in communication with the environment by sub-chamber port  31  and detector central port  23 . Body  21  has pressurized sub-chamber  32 , in the shape of a partial torus, in communication with the interior of housing  10  through stem  22 . Detector central port  23  communicates with sub-chamber  32  by a one-way valve  24 . Atmospheric sub-chamber  30  is separated from pressurized sub-chamber  32  by flexible membrane  25 . As the air pressure in sub-chamber  32  increases above atmospheric pressure, the profile of membrane  25  will change. From an initial flat profile, membrane  25  will curve or bulge inwardly into atmospheric sub-chamber  30 . The profile of membrane  25 , and in particular the crown of a bulged profile, is visible to the user through the transparent portion of body  21  relative to graduations  26  thereon. One particular graduation may signify the appropriate pressure for testing particular housing  10 . Generally, the graduations are usable as visual markers and the exact significance of any particular graduation can be determined by the user based on the particular housing being tested.  
         [0033]    Injector head  40 , as shown in FIG. 4, has O-ring  41  and three equi-spaced wings  28  which interact with corresponding sockets  27  of detector  20  for a bayonet or similar type secured interlock with detector central port  23 .  
         [0034]    Plug  50 , as shown in FIG. 5, has a bottom protuberance  51 , upper O-ring  42  and lower O-ring  43 , and three equi-spaced wings  28  which interact with corresponding sockets  27  of detector  20  for a bayonet or similar type interlock with detector central port  23 . Upper O-ring  42  and lower O-ring  43  are disposed on plug  50  such that when plug  50  is inserted and secured in detector central port  23 , upper O-ring  42  and lower O-ring  43  bracket sub-chamber port  31 . Protuberance  51  is located on plug  50  so that when plug  50  is inserted and secured in detector central  23 , protuberance  51  pushes down and thereby opens valve  24  to permit air from pressurized sub-chamber  32  to enter detector central port  23 .  
         [0035]    Plug  50  also has a gripping means  55 , which may be a coin slot or plastic handle which the user may easily manipulate to insert and secure the wing-socket interlock mentioned above.  
         [0036]    As shown in FIG. 6, the user drills a hole in housing  10  rear part  10   b  with a suitable profile to accept stem  22  of detector  20  in a tight friction fit (and sealed as described above); inserts detector  20  and then inserts injector head  40  into detector central port  23 . O-ring  41  is disposed below sub-chamber port  31  so that atmospheric sub-chamber  30  is in direct communication with the environment. By user manipulation of pump  99 , air is forced through valve  24 , into sub-chamber  32  and then into the interior of housing  10 . The resulting increased air pressure will tend to create a curved profile of membrane  25  and the extent of curve will be visible to the user relative to graduations  26 . The user will stop pressurizing at a suitable pressure level (after considering the movement of membrane  25  relative to graduations  26 , membrane  25  will have its initial profile), withdraw injector head  40 , and insert and insert and secure plug  50  in detector central port  23 , as shown in FIG. 7. The user will observe if membrane  25  changes its initial curved profile. If there is leakage in housing  10 , the air pressure in pressurized sub-chamber  32  will decrease and the curved profile will flatten. A suitable period to observe for changes depends on factors like the confidence level sought by the user.  
         [0037]    The opening of valve  24  by protuberance  51  (as explained above) allows pressurized air from pressurized sub-chamber  32  to move into the tiny cracks between plug  50  and proximate portions of detector central port  23  which are circumscribed from above by lower O-ring  43 . If the seal created by lower O-ring  43  leaks, air will escape through sub-chamber port  31  into atmospheric sub-chamber  30 . The result will be a decrease in pressure in sub-chamber  32  and a corresponding change in profile of membrane  25  can be detected by the user. In such a condition, even if the seal of upper O-ring  42  was sufficient to prevent leakage, a change in the profile of membrane  25  would be interpreted as a warning to the user to consider replacing plug  50  because lower O-ring  43  had failed. Also, although atmospheric sub-chamber  30  is typically in communication with the atmosphere during testing for leakage, the operating environment of detector  20  in housing  10  typically has hostile elements and therefore, atmospheric sub-chamber  30  is advantageously sealed therefrom by upper O-ring  42 .  
         [0038]    Thus it is seen that beyond naturally doubling the integrity of the seal of plug  50 , having a pair of O-rings  42  and  43  configured as described above, provides additional benefits.  
         [0039]    The profile of membrane  25  that indicates the absence of leakage (i.e. the constancy of the profile from the initial curve of membrane  25 ) will be present only if there is no leakage in housing  10  and no leakage in detector  20 . Upon detection of leakage, suitable corrective action can be taken. For example, during the quality checking process as the last step in the manufacture of housings, a particular housing  10  which leaked can be rejected or returned for correction. After successful manufacture and testing (e.g. while it is stored in inventory or being transported), housing  10  equipped with detector  20  provides continuous detection of leakage, whether of housing  10  or plug  50 .  
         [0040]    For example, housing  10  for a camera may be dimensioned 6″×4″×2″ and made of polycarbonate. Detector  20  may be dimensioned 1″ in diameter and body may be 2″ in height and made mainly of polycarbonate.  
         [0041]    Sub-chamber  30  may be a part toroidal-shaped cylinder with one end closed and the other end open. Sub-chamber  32  may be similarly constructed. Sub-chambers  30  and  32  are joined at their open ends and separated by membrane  25 , which may a sheet of elastic material covering one open end and sealed conventionally. Membrane  25  may be made of such elastic material and dimensions, and secured in place, as are appropriate for the particular application but in any case, membrane  25  must be sufficiently strong to provide an air tight separation between sub-chambers  30  and  32  even while being sufficiently flexible to bulge without undue air pressure. For example, membrane  25  may be latex rubber or silicon sheet which is bracketed conventionally over the open end of pressurized sub-chamber  32 . Membrane  25  and its connection should be able to withstand pressure up to 8 psi for testing housing  10  for a typical camera.  
         [0042]    Valve  24  may be a conventional silicon or rubber one-way valve but biasing on springs or other conventional means are possible as long as the self-closing sealing action is quick.  
         [0043]    A second embodiment of the invention, as shown in FIGS.  8 - 13 , is very similar to the first embodiment shown in FIGS.  1 - 7 . In FIGS.  8 - 13 , reference numerals which are identical to those in FIGS.  1 - 7  represent similar or identical elements.  
         [0044]    In contrast to the first embodiment, in the second embodiment, atmospheric sub-chamber  30  is separated from pressurized sub-chamber  32  by oil drop  125 . In effect, the indication of leakage created by the movement of flexible membrane  25  in the first embodiment is replaced with the indication of leakage created by the movement of oil drop  125  within transparent tube  126  which is itself disposed within a proximate, transparent portion of body  21  to permit viewing of the location of oil drop  125 . Tube  1   26  is conventional and is at most 1 millimeter in diameter. Oil drop  125  is conventional industrial oil (as can be obtained from suppliers like Texaco) having attributes of low viscosity, non-vaporizing, and surface cohesion appropriate for the detection of a pressure leak according to this invention.  
         [0045]    Injector head  140  is the same as injector head  40  but has an additional cross bars  28   a  at the bottom thereof, as shown in FIG. 10.  
         [0046]    Plug  150  (unlike plug  50  as shown in FIG. 5) has no bottom protuberance.  
         [0047]    Valve  124  (unlike valve  24  as shown in FIGS.  3 , 6 , 7 ), is a conventional one-way valve, spring biased into the closed postion. Valve abutment  124   a  protrudes above the floor of central port  23  in closed position. Valve  124  is opened by the downward pressing against valve abutment  124   a  by cross-bars  28   a  of injector head  140  (as shown in FIG. 12) or by plug  150  (as shown in FIG. 13).  
         [0048]    Valve  124  may be a conventional silicon or rubber one-way valve biased in the closed position by quickly acting springs. Other conventional means are possible as long as the self-closing sealing action is quick.  
         [0049]    In a third embodiment, as shown in FIGS. 14 a  to  14   f , instead of using pump  99  to force air into sub-chamber  32 , pump  99  is used to withdraw air from sub-chamber  32 . In this embodiment membrane  25  will change its curved profile in the opposite direction as in the case where air is forced into sub-chamber  32 . As shown in the FIGS. 14 a  to  14   f , a spring loaded valve  61  is used that is biased in the closed position. Such a valve  61  is useful for either when air is pumped into sub-chamber  32  or when air is withdrawn from sub-chamber  32 .  
         [0050]    Alternative means of displaying pressure differences between sub-chambers  30 ,  32  include an LED display coupled with a pressure sensor or a spring loaded bellows.  
         [0051]    It will be appreciated that the dimensions given are merely for purposes of illustration and are not limiting in any way. The specific dimensions given may be varied in practising this invention, depending on the specific application.