Abstract:
A water resistant actuating mechanism for a plunger type limit switch using a bowed spring to activate the plunger of a plunger type switch mounted within an actuating mechanism housing includes a flexible seal for covering the hole or opening in through which the bowed spring extends. The seal may be dome shaped and cover a circular opening. A glide or shoe is positioned on or connected to each end of the spring and are held in place between an upper wall of the housing and a backing sheet connected to the housing. The glide reduces the amount of deflection of the bowed spring required to activate the plunger type switch such that the additional thickness added by the flexible seal does not increase the overall required thickness of the actuating mechanism.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to improvements in actuating mechanisms for plunger type switches, and more specifically improvements which make the mechanism water resistant. 
   U.S. Pat. No. 5,446,252, issued Aug. 29, 1995, discloses an actuating mechanism for a plunger type switch which is particularly well adapted for use as a limit switch or proximity sensor and which may be positioned in relatively narrow spaces. The length of a plunger-type switch (the dimension of the switch extending along the axis of the plunger) is generally considerably greater than the thickness of the plunger-type switch. Therefore, to ensure minimum thickness of the limit switch, the actuating mechanism should translate a force applied perpendicular to the axis of the plunger to a force directed coaxially with the plunger. 
   In the actuating mechanism disclosed in U.S. Pat. No. 5,446,252, a bowed length of spring steel is used to translate a force directed perpendicular to the axis of the switch plunger to a force directed coaxially with the plunger. The bowed spring is secured within a housing along with the plunger-type switch such that a first end of the spring is spaced in close proximity to or in engagement with the plunger in the extended position. A middle or bowed portion of the spring extends above an upper surface of the housing through an opening or slot. The second end of the spring abuts against the housing (or a set screw) at an end of the opening or slot opposite the first spring end. Ends of the spring are turned upward to form feet for engaging the plunger or the housing or a set screw extending through the housing. 
   Application of an external force to the middle or bowed portion of the spring directed towards the upper surface of the housing changes the position of the plunger and more specifically advances the first spring end toward the switch a distance sufficient to move the plunger to the retracted position. Upon removal of the external force, the spring returns to its original bowed state such that the first end of the spring advances away from the switch and the plunger is allowed to move to the extended position. 
   Although the actuating mechanism works well for its intended purpose of providing a limit switch positionable in relatively narrow spaces, there remain needs for improvements to the actuating mechanism to increase its life. For example, there remains a need for such a switch actuator which resists migration of water or other liquids through the housing and into the plunger type switch and electrical connections, without unnecessarily increasing the thickness of the actuating mechanism. 
   SUMMARY OF THE INVENTION 
   The present invention comprises an improved version of the actuating mechanism for a plunger-type switch as disclosed in U.S. Pat. No. 5,446,252. The actuating mechanism is particularly well adapted for actuating plunger-type switches having relatively small dimensions such as the B3-32131 sub miniature basic switch manufactured by Otto Engineering, Inc. The actuating mechanism disclosed in U.S. Pat. No. 5,446,252 comprises a bowed flat-type spring mounted in a housing for the plunger-type switch with one leg of the spring engaging and depressing the plunger when the bowed spring is compressed upon the application of a force perpendicular to the axis of the switch plunger. The bowed portion of the spring extends through an opening or slot in the housing and a backing sheet holds the spring and the switch in the housing. 
   In the improved actuating mechanism a flexible seal is connected to an upper surface of the housing and encloses and forms a seal around the spring and the spring opening in the housing. In a preferred embodiment the opening for the spring is circular and the seal is semi-spherical. A glide or shoe is positioned on or connected to each end of the spring and are held in place between the upper wall of the housing and the backing sheet connected to the housing. As with the upturned feet of the previously disclosed flat spring actuating mechanism, one of the glides is positioned proximate the outer end of the plunger of the plunger-type switch and the other glide is positioned proximate an opposite inner wall of the housing or proximate a set screw extending through the inner wall. The set screw (which is not shown in U.S. Pat. No. 5,446,252) is used to adjust the overall amount of compression of the bowed spring to cause the opposite end of the spring to fully depress the plunger and change the switch condition. 
   The glides are designed to result in a more efficient translation of the distance which the bowed spring is compressed to the distance traveled by the outer surface of the glide thereby reducing the overall height required for the bowed portion of the spring to extend above the upper surface of the housing. 
   Reducing the height that the bowed portion must extend above the housing upper surface to result in the necessary travel of the spring ends to actuate or change the condition of the switch is particularly helpful in accommodating for any added height resulting from the addition of the seal. 
   Water-proof or water resistant potting compound may be applied around the wiring of the switch in channels or cavities formed in the housing for receiving the switch and associated wiring to further seal the wiring from water infiltration. Similarly a sealing compound may be applied to the threads of the set screw in the housing to prevent migration of water between the screw and the housing. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of a limit switch actuating mechanism for a plunger-type switch. 
       FIG. 2  is a bottom plan view of the limit switch actuating mechanism with a backing sheet removed to show detail thereof. 
       FIG. 3  is a cross-sectional view generally taken generally along line  3 — 3  of  FIG. 1  and showing the limit switch actuating mechanism secured within an ejector plate assembly of an injection mold with the ejector plate in an extended position. 
       FIG. 4  is a view similar to  FIG. 3  showing the ejector plate advanced into engaging relation with the actuating mechanism showing compression of a bowed spring of the actuating mechanism with glides on ends thereof to actuate the limit switch. 
       FIG. 5  is an enlarged perspective view of a glide of the actuating mechanism. 
       FIG. 6  is a left side elevational view of the glide as shown in  FIG. 5 . 
       FIG. 7  is a top plan view of the glide as shown in  FIG. 5 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure. 
   Referring to the drawings in more detail, the reference numeral  1  refers to an actuating mechanism for a plunger-type switch  2 . The actuating mechanism  1 , including switch  2  may also be referred to as a switch or limit switch. The plunger-type switch  2 , as best seen in  FIG. 2 , is a plunger actuated type switch having a plunger  3  projecting from a switch casing  4 , such as the B3-32131 switch discussed above. The switch  2  operates with a snap action upon axial movement of the plunger  3  through a given distance between an extended position to a retracted position. The plunger  3  is normally biased to the extended position. Securement holes  5  extend through the switch casing  4  to facilitate securement of the switch to a selected structure. Three terminals  7  extend rearward from an end  10  of the switch opposite the plunger  3 . 
   The actuating mechanism  1  includes housing means such as housing  20  for securing the switch  2  therein. The housing  20  is preferably formed from a relatively hard, rigid material such as a hard plastic. The housing  20  includes an upper surface  21  and a lower surface  22 . As is best seen in  FIGS. 3 and 4 , the distance between the upper surface  21  and the lower surface  22  of the housing  20  is preferably only slightly greater than the thickness of the switch  2 . A switch receiving cavity  23  is formed in the housing  20  and extends from the lower surface  22  toward the upper surface  21  thereof. The switch  2  is securable within the switch receiving cavity  23  on posts  24  formed in the housing  20  and extending into the securement holes  5  of the switch  2 . The switch  2  is secured in the cavity  23  such that the axis of the plunger  3  extends in parallel relation with the upper and lower surfaces  21  and  22  of the switch  2 . 
   A spring receiving opening or hole  25  extends through the housing  20  from the upper surface  21  to the lower surface  22  with a diameter of the hole  25  aligned with the axis of the plunger  3 . A spring receiving channel or slot  27  is formed in and extends into the housing  20  from the lower surface  22  toward the upper surface  21 . The spring receiving slot  30  is preferably rectangular and extends across the spring receiving hole  25  coaxially with the axis of the plunger  3 . A first end  31  of the slot  30  connects to and opens into the switch receiving cavity  23  such that the plunger  3  extends into the slot  30 . In addition, the slot  30 , near its first end  31  does not extend completely through the housing  20  such that a portion of the housing  20  extends over the slot  30  at the slot first end  31  to form a first overhang  32 . Similarly, the slot  30 , near a second end  33  thereof, does not extend completely through the housing  20  such that a portion of the housing  20  extends over the slot  30  at the slot second end  33  to form a second overhang  34 . 
   A wiring channel  40  is also formed in the housing  20  so as to extend from the lower surface  22  and toward but not completely to the upper surface  21  of the housing  20 . A first end of the channel  40  opens into the switch receiving cavity  23  at an end of the cavity  23  at which the terminals  7  are positioned. The channel  40 , at a second end thereof, extends out a side  43  of the housing  20 . Electrical wiring  45  is securable to the terminals  7  and extendable through the channel  40 . The side of the housing  20  to which the electrical wiring  45  needs to be routed may vary depending on the particular application sought and therefore the routing of the channel  40  may vary. 
   A sealant injection hole  47  extends through the housing  20  from the upper surface  21  to the lower surface  22  and is flow connected to the wiring channel  40  by a distribution channel  48 . The distribution channel  48  extends into the housing  20  from the bottom surface  22  toward the upper surface  21 . A waterproof or water resistant sealing compound or potting compound  49  may be injected into the wiring channel  40  through the injection hole  47  and distribution channel  48  to form a water-tight seal around the wiring  45 . It is foreseen that the sealant injection hole  47  could be routed through the side or edge of the housing  20 , or that the potting compound could be injected directly into the channel  40  through the open end on the side  43  of the housing  20 . 
   A spring  50  preferably formed from a bowed length of spring steel (sometimes referred to as a flat-spring or leaf spring) is secured within the spring receiving hole  25  and slot  30 . The spring  50  includes a first spring end  51 , a second spring end  52  and a middle portion  53 . In its resting state, the spring  50  is bowed. A first glide or shoe  59  is positioned on the first spring end  51  and a second glide or shoe  60  is positioned on the second spring end  52 . 
   Each glide  59  and  60  includes a front face  61 , a rear  62 , an upper surface  63 , sidewalls  64  and  65  and a bottom surface  66 . A notch or groove  68  extends into each glide  59  and  60  from the rear  62  thereof from sidewall  64  to sidewall  65  and is sized and shaped for receiving the first or second spring end  51  or  52  of spring  50 . A rearward projecting overhang or upper flange  70  is formed in the glides  59  and  60  above the notch  68  and a rearward projecting tail or lower flange  71  is formed in the glides  59  and  60  below the notch  68 . The upper flange  70  is preferably shorter than the lower flange  71  and includes a beveled face  72  on its lower, outer corner to accommodate the bow of the spring  50 . The glides  59  and  60  are preferably formed from material exhibiting a relatively low coefficient of friction, such as plastic resin sold under the trademark Delrin. 
   The switch  2 , spring  50 , glides  59  and  60  and wiring  45  are held within the housing  20  by a backing or backing sheet  75 . The backing  75  is formed from a layer of relatively thin material, such as a relatively rigid polyester plastic sheet. The relative thickness of the backing sheet  75  shown in the drawings is exaggerated to make the backing sheet  75  readily discernable. The backing  75  is secured to the lower surface  22  of the housing  20  by securement means such as an adhesive. The backing  75  extends across the switch receiving cavity  23 , the spring receiving opening  25  and slot  30  and the wiring channel  40  and secures the switch  2 , the spring  50 , the glides  59  and  60  and the electrical wiring  45  respectively therein. The glides  59  and  60  slide across the backing sheet  75  upon compression and subsequent release of the spring  50  as discussed in more detail below. Adhesive is selectively omitted from the backing  75  in the area in which the glides  59  and  60  will slide across the backing  75  to ensure proper functioning of the actuating mechanism  1 . The potting compound  49  is typically injected into the wiring channel  40  through the injection hole  47  and distribution channel  48  after the backing sheet  75  is secured to the housing  20 . 
   The spring  50  is positioned within the hole  25  and slot  30  of the housing  20  in the resting state, such that the middle portion  53  of the spring  50  extends through the hole  25  and bows above the upper surface  21  of the housing  20 . The spring  50  is sized such that when it is positioned in the slot  30  the front face  61  of glide  59  on the first spring end  51  is positioned in closely spaced relation to the end of the plunger  3  positioned in the extended position and the front face  61  of glide  60  on the second spring end  52  is positioned in closely spaced relation to an inner wall  78  of the housing  20  at the slot second end  33 . The phrase “in closely spaced relation” is intended to mean in actual engagement or positioned slightly apart. In addition, when the spring  50  is positioned within the slot  30 , the first glide  59  is generally positioned beneath the first overhang  32  and the second glide  60  is generally positioned beneath the second overhang  34 . The distance between the inner surface of the backing  75  and the inner surface of the first and second overhangs  32  and  34  is just slightly greater than the thickness of the glides  59  and  60  such that the glides  59  and  60  are allowed to slide therebetween without binding. 
   A set screw  80  is threaded into a threaded bore  81  formed in the housing  20  and extending from an end  83  of the housing  20  to the second end  33  of spring receiving slot  30 , through inner wall  78 . The inner end of the set screw  80  may be advanced past the inner wall  78  and into the spring receiving slot  30  a selected distance to reduce the effective length of the spring receiving slot  30 , thereby reducing the required distance to be traveled by the first glide  59  to depress the plunger  3 . When the inner end of the set screw  80  is extended through inner wall  78  and into spring receiving slot  30 , the front face  61  of second glide  60  engages the set screw  80 , at least when the spring  50  is depressed. Prior to depression of the spring  50  the front face  61  of second glide  60  is positioned in closely spaced relation with the inner end of the set screw  80 . A thread sealing compound is preferably applied to the set screw  80  prior to threading the set screw  80  into the threaded bore  81  to form a water tight seal between the set screw  80  and threaded bore  81 . 
   As is best seen in  FIG. 4 , application of a force to the middle portion  53  of the spring  50  and toward the upper surface  21  of the housing  20  compresses the spring  50  such that the first glide  59  on first spring end  51  advances further away from the second glide  60  on second spring end  52  and toward the switch  2  a distance sufficient to drive or move the plunger  3  to the retracted position. The spring  50  thereby translates a force applied perpendicularly to the axis of the plunger  3 , to a force applied coaxially with the plunger. As the spring  50  is compressed, the first and second spring ends  51  and  52  are driven into a front lower corner in the groove or notch  68  in the respective glide  59  and  60 . 
   Removal of the force applied to the middle portion  53  of the spring  50  allows the spring  50  to return to the resting state such that the first spring end  51  and attached glide advance away from the switch a distance sufficient to allow the plunger  3  to advance back to the extended position. Although the glides  59  and  60  are generally only loosely connected to the first and second spring ends  51  and  52 , the downwardly and inwardly directed force exerted by the spring ends  51  and  52  on the rearwardly projecting lower flange  71  of the respective glide  59  and  60  may be sufficient to pull the glides  59  and  60  away from the switch plunger  3  and set screw  80  respectively. It is also foreseen that the first glide  59  may only retract the distance that it is pushed rearward by the plunger  3  once the force is removed from the middle portion  53  of spring  50  and the spring ends  51  and  52  will then slide rearward along the upper surface of the associated lower flange  71  of each glide  59  and  60 . The lower flange  71  of each glide  59  and  60  is sufficiently long and the distance between the opposed lower flanges  71  when the glides  59  and  60  are separated their furthest distance apart is sufficiently small to prevent either spring end  51  or  52  from sliding off of either of the associated lower flanges  71  when the spring advances to the resting, uncompressed position. It is also to be understood that the glides  59  and  60  could be fixedly secured to the spring ends  51  and  52  by a wide variety of means including adhesives or mechanical connections. 
   A flexible seal or sealing member  85  is mounted on the upper surface  21  of the housing  20  over the spring  50  and the spring receiving hole  25 . The flexible seal  85  preferably is dome shaped or hemispherical with a peripheral flange  87  for securing the seal  85  to the housing  20  in a seal receiving recess  89  formed in the upper surface  21  of the housing. The seal receiving recess is formed around the periphery of the spring receiving hole  25  and the depth of the recess  89  generally corresponds to the thickness of the peripheral flange  87  so that the upper surface of the flange  87  extends flush with the upper surface  21  of the housing  20 . The flexible seal may be formed from a polyurethane, thermoset film approximately 5 to 10 mils thick. The flange  87  of seal  85  may be secured to the housing by a urethane pressure sensitive adhesive. A circular, flattened area  91  may be formed in the seal  85  around its apex. 
   The limit switch actuating mechanism  1  is securable to various structures by securement means such as adhesives or bolting. The housing  20  includes bores  92  through which screws or bolts may be driven for securing the housing  20  to a structure. 
     FIGS. 3 and 4  is representative of one use of the actuating mechanism  1  of the present invention in an injection molding application, which is described in more detail in U.S. Pat. No. 5,446,252. Referring to  FIGS. 3 and 4  of the present application, the reference numeral  93  is representative of an ejector plate advanceable between an ejecting position and a retracted position by means not shown. In the retracted position, a lower surface  94  of the ejector plate  93  engages rest buttons  95  (one of which is shown in  FIGS. 3 and 4 ) positioned on and extending slightly above an inner surface  96  of an ejector housing  97 . 
   In the representative application of the actuating mechanism  1  as shown in  FIGS. 3 and 4 , the actuating mechanism  1 , is used to verify that the ejector plate  93  has returned to the retracted position. Due to its relatively narrow profile, the limit switch actuating mechanism  1  of the present invention may be secured within the ejector housing  97  by bolting the actuating mechanism  1  to the inner surface  96  thereof. The actuating mechanism  1  is sized such that the upper surface  21  of the actuator mechanism housing  20  is generally flush with the upper surfaces of the rest buttons  95  and the middle portion  53  of the spring  50 , when not engaged, extends above the upper surface  21  of the housing  20  and the upper surfaces of the rest buttons  95 . As the ejector plate  93  is advanced to a retracted position, the lower surface  94  of the ejector plate  93  engages the seal  85  and compresses the spring  50 , advancing the first spring end  51  and first glide  59  toward the switch  50 , moving the plunger  3  to the retracted position so as to change the condition of the switch  50  from an open condition to a closed condition or vice versa and send a signal indicating that the ejector plate  93  has returned to the retracted position. 
   As the seal  85  and spring  50  are compressed by advancement of the ejector plate  93  to the retracted position, the excess material of the seal  85  is forced into the spring receiving hole  25 . The spherical shape of the seal  85  and the round shape of the spring receiving hole  25  generally provide a relatively large area for receiving or taking up the excess material of the seal  85  as it is forced downward or inward by the retracting ejector plate  93 . The flattened area  91  on seal  85  is also believed to reduce the amount of excess material created when the seal  85  is generally flattened by retraction of the ejector plate  93 . The spherical shape of the seal  85  is also believed to result in less stress to the polyurethane material, increasing the life of the seal. 
   The flexible seal  85 , the potting compound  49  injected around the wiring  45  and the sealing compound applied to the set screw  80  function to form a water tight or liquid resistant seal around the plunger type switch  2  and the electrical connections between the switch  2  and wiring  45  including around the terminals  7 . The water resistant actuating mechanism  1  is particularly adapted for use in applications in which the actuating mechanism may be routinely exposed to water or other liquids. 
   It is foreseen that the actuating mechanism  1  of the present invention has numerous applications beyond the injection molding application discussed above and its use is not intended to be limited to such applications. 
   It is also foreseen that the spring  50  could be sized and positioned in the slot  30  such that in the resting state the first spring end  51  holds the plunger  3  in the retracted position and the application of a force to the middle portion  53  of the spring  50  to cause the spring to bow advances the first spring end  51  away from the switch  2  a distance sufficient to allow the plunger  3  to move to the extended position. Release of the force, then allows the spring  50  to advance back to the resting position so as to allow the first spring end  51  to advance toward the switch  2  thereby moving the plunger  3  to the retracted position. 
   It is to be understood that while certain forms of the present invention have been illustrated and described herein, it is not to be limited to the specific forms or arrangement of parts described and shown.