Abstract:
A multi-directional shock sensor including two masses arranged to move in directions, which are mutually perpendicular to one another. A moveable locking member prevents movement of a slider, which is used in the arming arrangement of a submunition. In response to an acceleration in a plane, one or both masses will move. The masses are operably coupled to the locking member to effect its movement out of its locking engagement with the slider, due to such acceleration.

Description:
STATEMENT OF GOVERNMENT INTEREST 
   The invention described herein may be manufactured and used by or for the Government of the United States of America for government purposes without the payment of any royalties therefor. 
   BACKGROUND OF THE INVENTION 
   Various scenarios exist where it is desirable to delay the initiation of an event until some time after an initial shock or acceleration. By way of example, in order to prevent premature detonation, many munition rounds, such as artillery shells, go through a multi-stage arming sequence after being fired. It is required that the sequence commence only after the shell has been fired, and for this purpose a delay after firing is imposed in the procedure. 
   The same delay procedure also applies to submunition arrangements where an artillery shell contains a plurality of smaller rounds, or a bomb contains a plurality of bomblets, by way of example. That is, after separation from the carrier shell or bomb, a time delay is imposed on these submunitions to prevent premature detonation. 
   This delay may be accomplished by an electronic sensor connected to the munition fuze. This sensor would sense the acceleration upon separation of the submunition from the carrier and convert this to an electronic signal which could be used to activate an actuator to remove a lock in the arming arrangement. Such sensor however, requires a power supply, signal processing circuitry and occupies an objectionably large space. 
   The present invention obviates these drawbacks. It is an object of the present invention to provide a multi-directional shock sensor having a mechanical design, which requires no power supply and can be fabricated by MEMS (micro electromechanical systems) techniques resulting in a relatively small shock, or acceleration sensor. 
   It is another object of the present invention to provide a multi-directional shock sensor that is responsive to a shock from any direction in a plane of the sensor. 
   It is a further object of the present invention to provide a multi-directional shock sensor that is responsive and serves rough handling during shipping, for example, if a package is dropped. 
   SUMMARY OF THE INVENTION 
   A multi-directional shock sensor is described and includes an elongated moveable member normally situated at a first location. A first mass is operable to move the moveable member out of the first location to a second location, in response to an acceleration having an acceleration component in a first positive or negative direction. A second mass is operable to move the moveable member out of the first location to the second location, in response to an acceleration having an acceleration component in a second positive or negative direction. A plurality of supports is provided and a plurality of springs connect the first and second masses and the elongated moveable member to respective ones of the supports. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be better understood, and further objects, features and advantages thereof will become more apparent from the following description of the exemplary embodiments, taken in conjunction with the accompanying drawings, in which: 
       FIG. 1  is a view of an SOI (silicon on insulator) wafer prior to fabrication of the multi-directional shock sensor. 
       FIG. 2  illustrates one embodiment of the present invention. 
       FIGS. 3A to 3D  illustrate the operation of the device of  FIG. 2 . 
       FIG. 4  illustrates another embodiment of the invention. 
   

   DETAILED DESCRIPTION OF THE EMBODIMENTS 
   In the drawings, which are not necessarily to scale, like or corresponding parts are denoted by like or corresponding reference numerals. 
     FIG. 1  illustrates a portion of an SOI wafer  10  from which the sensor of the present invention will be fabricated. The structure of  FIG. 1  includes a silicon substrate  12  (also known as a handle layer) covered by an insulating layer  14 , such as silicon dioxide, over which is deposited another silicon layer  16  (also known as the device layer), which is the layer from which the sensor will be produced. 
     FIG. 2  is a view of one embodiment of a sensor  20  formed from the wafer  10  of  FIG. 1 . The sensor is formed by a DRIE (deep reactive ion etching) process which removes unwanted portions of layer  16 . The DRIE process is a well developed micromachining process used extensively with silicon based MEMS devices. For this reason, silicon is a material for the sensor of the present invention, although other materials are possible. Sensor  20  is one of a multitude of similar sensors fabricated on the same wafer  10 , with all of the sensors being separated after fabrication for use as individual multi-directional shock sensors. Sensor  20  is responsive to a shock from any direction in a plane of the sensor  20 . 
   Sensor  20  has many uses; however it will be described, by way of example, with respect to use in a submunition which is expelled from a carrier. Sensor  20  includes a first mass  22  operable to move in a first direction, as indicated by arrow  24 , or opposite direction, as indicated by arrow  25 . Sensor  20  further includes a second mass  26  operable to move in a second direction, as indicated by arrow  27 , or opposite direction, as indicated by arrow  28 . Movement of the masses  22  and  26  is perpendicular to one another and is effected by an acceleration having an acceleration component lying in any of the four indicated directions, with mass movement being opposite to that of the acceleration component. Accordingly, first direction  24  and related opposite direction  25  are substantially perpendicular to second direction  27  and related opposite direction  28 . Sensor  20  is mounted in the submunition in a manner that it will experience acceleration in the plane of the sensor when expelled. Masses  22  and  26 , as well as other moveable components to be described, are connected to a plurality of supports  30  by means of respective springs  32 . 
   An elongated moveable member  36  is provided intermediate the masses  22  and  26  so that the elongated moveable member  36  is substantially adjacent the masses  22  and  26 . Further, in an exemplary embodiment, the elongated moveable member  36  is in contact with second mass  26 . The elongated moveable member  36  is oriented substantially perpendicular to a slider  38 . The elongated moveable member  36  (sometimes referred to herein as “locking member”  36 ) acts as a locking member to prevent movement of the slider  38 , which is part of the arming arrangement of the submunition. Locking member  36 , which is normally at a first position as illustrated in  FIG. 2 , engages a notch  40  of slider  38  to prevent its movement. When locking member  36  is withdrawn from the notch  40 , as will be described, slider  38  will be free to move, under the direction of an arm command  42 . 
   Mass  22 , or  26 , is operable to move locking member  36  to a second position where it will be latched to prevent movement back to its initial position. The latching is accomplished by latch  44 , which includes projecting arms  45  and  46  having respective arrowheads  47  and  48 . When locking member  36  travels far enough it will be captured by the latch  44  in view of the arrowhead configuration  47 / 48 , which latches with arrowhead  50  at the end of locking member  36 . 
   Mass  22  and locking member  36  include a first projection arrangement where projection members of the mass  22  and locking member  36  engage one another to effect movement of the locking member  36  to its latched position in response to movement of mass  22  due to an acceleration. In particular, the movement of the mass  22  causes a substantially perpendicular movement of locking member  36 , that is, the elongated moveable member  36 , relative to the movement of the mass  22 . The first projection arrangement includes a projection  60  connected to locking member  36  and a cam  61  at an end of the projection  60 . Mass  22  includes a projection portion  62 . The projection portion  62  includes a camming surface at its end. The camming surface is comprised of camming surfaces  63  and  64 , which form a V-shaped depression. It is to be noted that the arrangement can be reversed with projection  62 , which includes the cam  61 , and projection  60 , which includes the camming surfaces  63  and  64 . 
   Mass  26  and locking member  36  include a second projection arrangement where projection members of mass  26  and locking member  36  engage one another to effect movement of the locking member  36  to its latched position in response to movement of mass  26  due to an acceleration. The second projection arrangement includes first and second projections  70  and  71  connected to locking member  36  and first and second projection portions  72  and  73  connected to mass  26 . Projection portions  72  and  73  may be individual projections as illustrated, or they may form portions of a unitary piece  76 , shown dotted, forming part of mass  26 . 
   Projection portion  73  of mass  26  is positioned just above a beam  80  at a first end  81  thereof. The second end  82  of the beam  80  is positioned adjacent to projection  71  of the locking member  36 . Beam  80  is operable to pivot about a fulcrum  84  so as to move either the first end  81  or the second end  82  in a direction, which will cause movement of the locking member  36  to its latched condition. In an exemplary embodiment, the fulcrum  84  is situated intermediate the first end  81  and the second end  82 . Further, the fulcrum  84  is situated intermediate the beam  80  and the supports  30  so as to contact, simultaneously, the beam  80  and the supports  30 . 
   In order to operate as a shock sensor, masses  22  and  26 , as well as springs  32 , locking member  36  and attached projections, projecting arms  45  and  46  and beam  80  must be free to move and therefore must be free of any underlying silicon dioxide insulating layer  14  ( FIG. 1 ). One way to accomplish the removal of the underlying insulating layer is by applying an etchant such as hydrofluoric acid, which will dissolve the silicon dioxide. 
   The etchant will, in a relatively short period of time, dissolve the insulation beneath the springs  32 , since they are of small width, thus freeing them for movement. In order to shorten the time for dissolving the silicon dioxide under the remaining moveable components, they are provided with a series of apertures  86  which extend from the top surface down to the insulating layer  14 , thereby allowing the etchant direct access to the undersurface of these members. Although some of the etchant dissolves the insulation under the supports  30 , and fulcrum  84 , the process of freeing the remaining moveable components is completed before the supports and fulcrum are completely freed so that they remain immovable. 
   Operation of the sensor  20  will be described with reference to  FIGS. 3A to 3D , where, for simplicity and clarity, the supports  30 , springs  32  and apertures  86  have not been illustrated. Further, directional references such as right, left, up, down, vertical and horizontal, are given with respect to the sensor  20  as illustrated in the figures and not necessarily to movement in actual use. In  FIG. 3A , in response to an initial shock or acceleration of sufficient magnitude to the left, mass  22  will move to the right causing cam  61  to ride along camming surface  63  resulting in an upward movement of locking member  36  in the direction of arrow  68 , to its latched condition. 
   Similarly, acceleration of sufficient magnitude to the right will cause movement of mass  22  to the left, as illustrated in  FIG. 3B , such that cam  61  will ride along camming surface  64  likewise resulting in an upward movement of locking member  36  to its latched condition. 
   As illustrated in  FIG. 3C , an upward acceleration of sufficient magnitude will cause mass  26  to move downward allowing projection portion  73  to engage first end  81  of beam  80 . This action pivots beam  80  about fulcrum  84  whereby second end  82  of beam  80  engages and pushes on projection  71 , connected to locking member  36 , to move locking member  36  to its latched condition. 
   In  FIG. 3D , a downward acceleration has caused mass  26  to move upward whereby projection portion  72  engages projection  70 , resulting in an upward movement of locking member  36  to its latched condition. As indicated in  FIGS. 3C and 3D , the movement of the mass  26  causes a substantially parallel movement of locking member  36 , that is, the elongated moveable member  36 , relative to the movement of the mass  26 . In  FIG. 3C , as compared to  FIG. 3D , the substantially parallel movements of the mass  26  and locking member  36  are in opposite but substantially parallel directions. 
   If an acceleration is in a direction at an angle relatively near horizontal or vertical, the acceleration component may be enough to move a single mass to effect a full movement of locking member  36  to its latched position. At some intermediate angle however, the acceleration component may not be sufficiently large to enable a single mass to completely move the locking member  36 . In such a situation, though, there would exist an acceleration component in both the horizontal as well as vertical directions such that both masses  22  and  26  would move and contribute to the moving of the locking member  36  to its latched position. In an exemplary embodiment, masses  22  and  26  concurrently move to contribute to the moving of the locking member  36 . 
   In  FIG. 4 , sensor  88  illustrates an embodiment of the invention, which may be used for other than in a submunition. Components previously described have been given the same reference numeral. Numeral  36 , previously defining a locking member, in  FIG. 4  now represents an elongated moveable member, without the locking function. Projecting arms  45  and  46  are each connected to a respective electrically conducting section  90  and  91 , which are electrically isolated from one another. 
   When moveable member  36  is latched, by an action such as described in  FIGS. 3A to 3D , an electric circuit is completed by the path including section  90 , projecting arm  45 , moveable member  36 , projecting arm  46  and section  91 . Contacts  92  and  93  on sections  90  and  91  may then be used to detect the completed circuit. By way of example, sensor  88  may be hermetically enclosed (as would be sensor  20 ) in a housing  94 , shown dotted. Electrical leads  96  and  97  connect contacts  92  and  93  with external contacts  98  and  99  on the housing  94 . The completed circuit may be detected at external contacts  98  and  99  and may be utilized to initiate an event or may be used simply to provide an indication that an acceleration of sufficient magnitude has taken place in the plane of the sensor  20 . 
   Having thus shown and described what is at present considered to be the preferred embodiments of the present invention, it should be noted that the same has been made by way of illustration and not limitation. Accordingly, all modifications, alterations and changes coming within the spirit and scope of the present invention are herein meant to be included. 
   Finally, any numerical parameters set forth in the specification and attached claims are approximations (for example, by using the term “about”) that may vary depending upon the desired properties sought to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of significant digits and by applying ordinary rounding.