Abstract:
An apparatus for sensing relative positions of mechanically coupled devices. The apparatus includes a magnetically actuated switch connected to a set of flux conductors to form a switch assembly. A permanent magnet is affixed to a set of flux conductors to form a magnet assembly. The flux conductors are positioned adjacently to conduct flux from the permanent magnet to the magnetically actuated switch. Movement of either assembly results in the reduction of flux conduction between the magnet and the magnetically actuated switch. The apparatus can be integrated into a helmet mount for night vision goggles to sense the relative position of the helmet mount for controlling the operation of the night vision goggle.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims priority to and the benefit of Provisional Application No. 60/693,554, filed in the United States Patent Office on Jun. 23, 2005, and Provisional Application No. 60/711,876, filed in the United States Patent Office on Aug. 26, 2005, the entire disclosure of each of which is incorporated herein by reference. 
     
    
     TECHNICAL FIELD  
       [0002]     This invention relates generally to magnetically activated (or actuated) switches that use flux conveyed by flux conductors from a magnet to actuate a magnet sensor when certain physical alignments occur, and more particularly to a magnetically activated switch for a night vision goggle mount that is activated in an in-use position and deactivated in either a quick stowage or a flip-up stowage position.  
       BACKGROUND  
       [0003]     Permanent magnets have been widely used in proximity switch applications. Sensing actions have generally been accomplished by bringing the magnet sufficiently close to a sensor, for example, a reed switch, to cause it to actuate. The accuracy of position sensing is generally poor as position sensing is strongly dependent on the sensitivity of the reed switch and on the field strength of the magnet, which varies over temperature and initial magnetization. Furthermore, certain applications require careful balancing of the flux fields of multiple magnets to achieve their results.  
         [0004]     Night vision goggles (NVG) are commonly used by military personnel for conducting operations in low light or night conditions. The NVG used by the military typically include image intensifier tubes and associated viewable images. Assemblies for mounting NVG to a helmet are well-known in the art. These mounting assemblies allow a user&#39;s hands to remain free while viewing a scene through the NVG. Prior mounting assemblies typically include one or more of the following features: positional adjustment of the NVG between an in-use and a flip-up stowage position, tilt angle adjustment of the NVG relative to a user&#39;s eyes, focal adjustment of the location of the NVG relative to the user&#39;s eyes, and an automatic shutdown of the NVG when the NVG are not in the in-use position.  
         [0005]     There is a need to have a reliable and effective automatic shutdown of the NVG when the NVG are not in use. An automatic shutdown allows the user to simply move the NVG out of the user&#39;s line of site and allow the user to rely on the NVG to turn off automatically, eliminating the need for a user to activate a switch to turn off the NVG. Many options have been considered to achieve automatic shutdown. Sliding contacts have not been practical because of the severe environmental requirements. Previous proximity switch techniques have also not been satisfactory due to limited space and lack of well defined switch points. Furthermore, standard proximity detector approaches require multiple switches and magnets to logically combine the results of different sensor positions.  
         [0006]     The use of a system capable of being environmentally sealed, such as reed switches, provides excellent environmental immunity. There are known methods for automatic shutdown using a magnet module in a cavity, such as allowing a magnet to rotate within a cavity as the user moves the NVG from an in-use position to a flip-up position. However, automatic shutdown may be mistakenly triggered while the user is performing certain combat maneuvers such as rolling over. Since a user&#39;s “night vision” and safety may be affected during a critical moment of combat by the mistaken shutdown of the NVG, there is a need for a switch to be coupled to NVG that would reduce or eliminate the possibility of the NVG being accidentally turned off.  
         [0007]     Moreover, when the NVG are flipped up, the user has a tendency to forget about their presence. The NVG may protrude beyond the user&#39;s helmet and be damaged if the user inadvertently bumps into the surrounding environment, such as the roof inside a vehicle. It is desired for the helmet mount to have a quick stowage feature that allows the night vision goggles to move out of the line of sight, but still within the peripheral vision range to serve as a constant reminder of the presence and location of the NVG. Therefore, it is desired that the switch be able to turn off in both the quick stowage and flip-up stowage positions.  
         [0008]     Prior NVG designs are adapted to allow a user to use both eyes for viewing. The NVG is placed directly in front of both eyes and displays an image to both eyes. When a user operates the NVG during low light conditions, a bright light may essentially blind the user through over-exposure of light, disorienting the user for a period of time until the eyes readjust. To limit this problem, it is desired to use a monocular night vision goggle that will provide information to only one eye. The user simultaneously sees an unobstructed view through one eye and an enhanced image in the other. It is desired that the user can locate the night vision goggle in front of either eye, based upon preference or need. Therefore, it is desired that a single helmet mount be used for either eye, eliminating the need for a right eye helmet mount and a left eye helmet mount. Furthermore, it is desired that one switch be used for the helmet mount for both the right eye and left eye.  
         [0009]     Thus, there is a need for an improved switch that operates reliably during movement of the NVG from an in-use position to a quick stowage or flip-up stowage position. Furthermore, there is a need for an improved switch to operate when the NVG is in either the right eye position or the left eye position.  
       SUMMARY  
       [0010]     To overcome limitations in the prior art, and to overcome other limitations that will become apparent upon reading and understanding the present specification, in one embodiment the present invention relates to an apparatus for sensing relative positions of mechanically coupled devices. For example, based on relative positions of one or more devices such as a magnet, flux conductors and a magnetically activated switch, the apparatus may control the flow of magnetic flux through one or more flux conductors and a magnetically activated switch.  
         [0011]     An apparatus constructed in accordance with one embodiment of the present invention has a magnetically actuated switch with a first switch end and second switch end. The first switch end has affixed an incoming electrical lead. The second switch end has affixed an outgoing electrical lead. This allows the flow of electrical current through the magnetically activated switch to be controlled depending on whether the switch is magnetically activated. A first switch end flux conductor is affixed to the first switch end. A second switch end flux conductor is affixed to the second switch end. A magnet, e.g., a permanent magnet, is mounted at a non-actuating position. For example, the magnet may be located a given distance away from the magnetically actuated switch or the magnet may be positioned near a flux shunt. The magnet has a first magnetic end and a second magnetic end. A first magnetic end flux conductor is affixed to or positioned adjacent to the first magnetic end. A second magnetic end flux conductor is affixed to or positioned adjacent to the second magnetic end. The first magnetic end flux conductor is proximate to the first switch end flux conductor and separated by a first gap. The second magnetic end flux conductor is proximate to the second switch end flux conductor separated by a second gap. When the first and second gap is small, magnetic flux will flow activating the magnetically activated switch to, depending on the particular application, open or close contacts in the switch.  
         [0012]     In one embodiment, the permanent magnet, first magnetic end flux conductor and second magnetic end flux conductor can be affixed together into a magnet assembly for movement to increase and decrease the first and second gap. In another embodiment, a flux shunt can be placed adjacent to the first and second switch end flux conductor, so that the magnet assembly may move closer to the flux shunt and away from the first and second switch end flux conductor. This stops or reduces flux flow to the magnetically actuated switch. In various embodiments, the apparatus can be integrated into a helmet mount for a night vision goggle so that it may sense the relative position of the helmet mount to control operation of the night vision goggle. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]      FIG. 1  shows a conventional magnet and reed switch.  
         [0014]      FIG. 2  shows a top view of one embodiment of the present invention.  
         [0015]      FIG. 3A  shows a side view of the embodiment of  FIG. 2 .  
         [0016]      FIG. 3B  shows a side view of the embodiment of  FIG. 2  after a reed switch has released.  
         [0017]      FIG. 4  shows a side view of another embodiment of the present invention.  
         [0018]      FIG. 5  shows a side view of yet another embodiment of the present invention.  
         [0019]      FIG. 6  shows an isometric view of still another embodiment of the present invention.  
         [0020]      FIG. 7  shows an isometric view of another embodiment of the present invention.  
         [0021]      FIG. 8  shows a side view of yet another embodiment of the present invention.  
         [0022]      FIG. 9 , including  FIGS. 9A-9E , shows several simplified views of one embodiment of the present invention.  
         [0023]      FIG. 10  shows an exploded view of yet another embodiment of the present invention integrated into a helmet mount for a night vision goggle.  
         [0024]      FIG. 11  shows a partial isometric view of the embodiment of  FIG. 10 .  
         [0025]      FIG. 12  shows a partial isometric view of the embodiment of  FIG. 10 .  
         [0026]      FIG. 13  shows a partial isometric view of the embodiment of  FIG. 10 .  
         [0027]      FIG. 14  shows an exploded view of another embodiment of the present invention integrated into a helmet mount for a night vision goggle.  
         [0028]      FIG. 15  shows an exploded view of one embodiment of the present invention integrated into a helmet mount for a night vision goggle. 
     
    
     DETAILED DESCRIPTION  
       [0029]     A magnetically activated switch is controlled according to relative positions of associated magnetic flux-affecting components. For example, a magnetically activated switch may be activated based on the position of one or more devices such as one or more magnets, one or more flux conductors, and a switch. In some embodiments the magnetically activated switch uses flux from a permanent magnet to actuate a magnet sensor when a certain proximity between the magnet and the magnet sensor is achieved. In some embodiments a magnet sensor may be actuated by moving one or more flux conductors that alter the path of the flux.  
         [0030]     In conventional magnetic switches, the accuracy of position sensing has been generally poor as position sensing is strongly dependent on the field strength of the magnet which varies over temperature, initial magnetization, and the sensitivity of the switch. Furthermore, certain magnetic switch applications require careful balancing of the flux fields of multiple magnets to achieve their desired results.  
         [0031]     Through the addition of flux conductors, performance and reliability of the magnetically activated switch may be improved. One such use for a magnetically activated switch is to activate/deactivate night vision goggles (NVG) mounted on a helmet mount. The helmet mount may incorporate a magnetically activated switch to activate the NVG when the NVG are in an in-use position and to deactivate the NVG when they are in a stowage position. Of course, a magnetically activated switch may also be useful in other interfaces where the components of the interface move with respect to one another and where the position of the switch is determined by the relative location of the components of the interface with respect to one another.  
         [0032]     The magnetically activated switch is designed to conduct enough flux from the magnet to a switch such as a reed switch to activate the switch. Additionally, the magnetically activated switch provides alternate flux paths to control the reluctance in the path such as through air gaps, lower permeability magnetic materials, or non-magnetic materials such as aluminum to control the reed switch. In one embodiment, by providing pairs of flux conductors, one for the flux to the reed switch and the other as a return path to the magnet, and arranging the pairs of conductors to be moved in and out of alignment, a rapid and high ratio of ON to OFF flux values is achieved. The rapid and high ratio of ON to OFF flux values allow the magnet field created to be much stronger than the minimum magnet field strength required for actuation while ensuring that the switch will not actuate in the OFF position. Furthermore, providing a pair of flux conductors allows the magnetically activated switch to work over a wide temperature range despite permanent magnet strength variations over temperature and varying switch sensitivity. The use of a pair of flux conductors requires only one magnet and one reed switch activated by simple flux conductors between them, even in the presence of movement and varying position.  
         [0033]     In addition to the use of flux conductors, another exemplary embodiment of the present invention includes a flux shunt. By moving the flux conductors into alignment with an adjacent flux shunt, or vice versa, at least a potion of the flux may be shorted through an alternate path, thus removing the flux from the reed switch. Consequently, the reed switch may be turned off with an even shorter physical displacement of the flux conductors and/or flux shunt.  
         [0034]     The use of the flux conductors allows the switch to be controlled in accordance with Boolean logic operations. That is, the switch may be controlled in accordance with a logical AND function, a logical OR function, a logical NOT function and combinations of these functions (e.g., NAND, NOR, etc.). As an example, if a helmet mount has more than one stowage position, the magnetically activated switch may, in effect, sense movement in more than one direction. Here, the flux conductors can be arranged in an AND function equivalent so that two sets of flux conductors must be aligned to activate the switch. In other applications it may be desirable to form the physical equivalent of the OR function by providing an additional set of flux conductors in parallel from the magnet to the reed switch. In this case, the switch may be activated by proper physical alignment of any one of the parallel sets of flux conductors. A switch may be controlled in accordance with a logical NOT function, for example, through the use of a single pole, double throw (“SPDT”) reed switch. Such a switch may have a pair of contacts where one contact is a normally closed switch contact and the other is a normally open switch contact. Here, in some embodiments a signal may be coupled to the normally closed switch contact and no signal coupled to the normally open switch contact. Consequently, a signal may be coupled from the normally closed switch contact through the switch in a non-activated state, and no signal coupled from the normally opened contact through the switch in an activated state. Thus, an output signal from the switch may be deactivated when the switch is activated (one form of a NOT function). These and other aspects of logical operations that may be used in the context of a magnetically activated switch are discussed in more detail below in conjunction with  FIGS. 4, 7 ,  8  and  10 .  
         [0035]     Various embodiments for a magnetic switch are described below.  FIGS. 1-8  describe a magnetic switch in a general conceptual manner.  FIGS. 9-15  describe particular embodiments of a magnetic switch that may be incorporated into a helmet mount for NVG.  
         [0036]      FIG. 1  shows a conceptual embodiment of the prior art where a permanent magnet  2  is moved in different directions indicated by arrows  3  to activate and de-activate a reed switch  4 . As is known, moving a permanent magnet  2  closer to and farther away from the reed switch  4  causes switching of electrical current flow through the reed switch  4  as a result of the magnetic flux (not shown in  FIG. 1 ) that flows from a pole face  5 A on one end of the magnet  4  to a pole face  5 B (not visible in the perspective of  FIG. 1 ) on another end of the magnet  4 . The precise switching point is difficult to define due to variations in magnet strength, reed switch sensitivity and hysteresis of the reed switch  4 .  
         [0037]      FIG. 2  shows a top view of one embodiment of a magnetically activated switch according to the present invention using a flux conductor&#39;s relative alignment to control the activation of the reed switch  4 . Flux (represented in a simplified form by dashed line  7 ) from pole face  5 A of the axially magnetized magnet  2  is conducted through flux conductor  6 , across small air gap  8 , through flux conductor  10 , through the magnetic lead  12  of reed switch  4 , through the magnetic lead  14 , through flux conductor  16 , across small air gap  18 , and lastly back through flux conductor  20  to pole face  5 B of the magnet  2 . The low reluctance of this path with flux conductors  6 ,  10 ,  16 , and  20  and with relatively small air gaps  8 ,  18  allows magnet  2  to activate the reed switch  4  even though the magnet is spaced from the reed switch such that in air alone, the magnet would not activate or hold the reed switch  4 . The flux conductors  10 ,  16  are shaped to maximize flux coupling to the reed switch  4  through magnetic leads  12 ,  14 . Although a specific shape of the flux conductors  10 ,  16  is shown in  FIG. 2 , the flux conductors may be any shape that allows flux coupling to the reed switch  4 .  
         [0038]      FIGS. 3A and 3B  show a side view of the magnetically activated switch of  FIG. 2 . More specifically,  FIG. 3A  shows where movement of the magnet  2  and flux conductors  6 ,  20  indicated by arrows  9  may result in misalignment relative to the flux conductors  10 ,  16 . As represented by the respective arrowed reference number lines, flux conductors  20  and  16  are behind flux conductors  6  and  10 , respectively, and are thus not visible in the perspective of  FIGS. 3A and 3B .  FIG. 3B  shows the rapid increase in reluctance due to the increase of the air gaps  8 ,  18  from the misalignment movement shown in  FIG. 3A , causing the reed switch  4  to deactivate the NVG.  
         [0039]      FIG. 4  shows another embodiment of a magnetically activated switch with the addition of a second set of series flux conductors  21 ,  22  to form a physical version of the AND function equivalent. As represented by the arrowed line, flux conductor  22  is behind flux conductor  21  and, hence, is not visible in the perspective of  FIG. 4 . The magnet  2  and flux conductors  6 ,  20  must be aligned with the second group of flux conductors  21 ,  22 , and the third group of the flux conductors  10 ,  16  and reed switch  4  for activation. If any of the components are out of alignment (e.g., moved in a direction as indicated by arrows  9  or  13 ), then reed switch  4  will not activate.  
         [0040]      FIG. 5  shows another embodiment of the magnetically activated switch of  FIG. 2  including a flux shunt  24  that may be used, for example, to reduce the distance of displacement necessary to cause switching of a reed switch  4 . The flux shunt  24  is positioned adjacent to and across flux conductors  10 ,  16 . For example, in the view of  FIG. 2  the flux shunt  24  (not shown in  FIG. 2 ) could be positioned above the flux conductors  10 ,  16  and extending across the gap between the flux conductors  10 ,  16 . With the displacement of the magnet  2  and flux conductors  6 ,  20  toward the flux shunt  24 , the flow of flux switches to the lower reluctance path provided by the flux shunt  24 , thereby releasing reed switch  4  with relatively little displacement of the magnet and the flux conductors. That is, once the magnet  4  and flux conductors  6 ,  20  have been moved up as represented by the arrow  11 , the entire or predominant flux flow will now be from pole face  5 A, through flux conductor  6 , through flux shunt  24 , through flux conductor  20 , to pole face  5 B.  
         [0041]     In an alternative embodiment, the flux shunt  24  may be configured to conduct most or all of the flux from the magnet  2  when the flux shunt  24  is in the position shown in  FIG. 5 . Thus, the switch  4  is deactivated when the flux shunt  24  is in this position. The flux shunt  24  may then be moved away (e.g., in an upward direction in  FIG. 5 ) from the flux conductors  10 ,  16  to activate the switch  4 . Such a configuration also may be implemented using a flux shunt and flux conductors (not shown) coupled in any other way to (e.g., installed on the left hand side of) the magnet  2  in  FIG. 5 .  
         [0042]      FIG. 6  shows another embodiment of the magnetically activated switch of  FIG. 2  with the addition of rotational platforms  26 ,  30  to make the reed switch  4  sensitive to rotational movement. The magnet  2  and flux conductors  6 ,  20  are attached to platform  26  that rotates about axis  28 . The reed switch  4  and flux conductors  10 ,  16  are attached to platform  30  that rotates about axis  32 . The addition of the rotational platforms  26 ,  30  makes the sensor sensitive to the rotation angle of the two orthogonal axes.  
         [0043]      FIG. 7  shows a conceptual drawing of another embodiment of the magnetically activated switch of  FIG. 4  with the addition of rotational elements to make the switch sensitive to rotational movements. This embodiment incorporates elements that are useful for a helmet mounted scope application. The magnet  2  and flux conductors  6 ,  20  are mounted to platform  26  revolving about axis  28  that is attached to another platform  34 . Platform  34  supports flux conductors  21 ,  22  and rotates about axis  36 . Sensor reed switch  4  and flux conductors  10 ,  16  are shown in the activated position. Rotation of platform  26  or platform  34  (e.g., as represented by arrow  29  and arrow  15 , respectively) will deactivate the reed switch, resulting in deactivation of the NVG (not shown).  
         [0044]     As mentioned above, logical operations may be performed in conjunction with the reed switch by controlling the position of one or more components associated with the magnetically activated switch. For example, one or more of the magnet, the flux conductors, the reed switch or other components may be moved to control the output of the magnetically activated switch.  FIG. 4  illustrates an example where the assembly of the magnet  4  and flux conductors  6 ,  20  AND the assembly of the flux conductors  21 ,  22  must be at proper positions to activate the switch  4  (an AND function). In other words, if either assembly is not in the proper position, the switch  4  will not be activated.  FIG. 6  illustrates an example where the assembly  26  AND the assembly  30  must be rotated to proper positions to activate the switch  4  (an AND function).  FIG. 7  illustrates an example where the assembly  26  AND the assembly  34  must be rotated to proper positions to activate the switch  4  (an AND function).  
         [0045]      FIG. 8  show another embodiment of a magnetically activated switch that adds a second flux path to implement a logical OR sensor. Additional flux conductors  38 ,  40 ,  42  provide an additional path to the reed switch  4 . Not shown are the return path elements. In this configuration, when either flux conductor  6 ,  21  and  10  (and associated flux conductors  20 ,  22  and  16 , not visible in this perspective) are in alignment, OR when flux conductors  38 ,  40  and  42  (and associated flux conductors not visible in this perspective) are in alignment, the reed switch  4  will activate.  
         [0046]     It should be appreciated that actuation of the switch may result in different types of output signals depending on the configuration of the switch. For example, a switch may be a single pole, single throw switch; a single pole, double throw switch; or some other type of switch. For a reed switch, actuation of the switch generally refers to causing the switch contact or contacts to move from a normal position (e.g., open or closed) in the absence of magnetic flux to another position (e.g., closed or open) upon application of a sufficient amount of magnetic flux. Accordingly, activation of a switch may result in contact moving from a closed position to an open position and/or from an open position to a closed position. Accordingly, the output of the switch may be configured to, in effect, provide a normal output signal or an inverted output signal (e.g., a NOT function).  
         [0047]     It also should be appreciated that a given logic function may be provided by an equivalent inverse function. For example, in relation to  FIG. 4  the output of the switch  4  may be defined as an OR function whereby placing either the assembly of the magnet  2  and flux conductors  6 ,  20  OR the assembly of the flux conductors  21 ,  22  in a non-active position causes the switch to deactivate. The output of the switch may in this case, for example, turn off a device (e.g. NVG) when either assembly is in a non-active position. Referring to  FIG. 8 , the output of the switch may be defined as an AND function whereby placing both flux conductors  20 ,  21  and  10  out of alignment AND placing flux conductors  38 ,  40  and  42  out of alignment causes the switch to deactivate. The output of the switch may in this case, for example, turn off a device (e.g. NVG) when both sets of flux conductors are in a non-aligned position.  
         [0048]      FIGS. 9A-9E  illustrates in a simplified form one embodiment of a magnetically activated switch that may be incorporated into a helmet mount for NVG.  FIG. 9A  illustrates a pair of flux conductors  62 ,  60  and a magnet  56  (e.g., corresponding to flux conductors  6 ,  20  and magnet  2  discussed above) that are provided in a first assembly  58  upon which NVG (not shown) may be mounted (See  FIG. 9C ). Each flux conductor  60 ,  62  includes an enlarged end portion  61 ,  63  that has a flat portion  65 ,  67  for more effectively coupling with pole faces  69 ,  71 , respectively, of the magnet  56 . As represented by the dashed lines  73  and as shown in  FIG. 9C , when the components of  FIG. 9A  are assembled the flat portions  65 ,  67  will contact the pole faces  69 ,  71 .  
         [0049]      FIG. 9B  illustrates a pair of flux conductors  68 ,  66  (e.g., corresponding to flux conductors  21 ,  22  discussed above) that are provided in a second assembly  64  (See  FIG. 9C ). The assembly includes another flux conductor  75  that serves to redirect at least a portion of the flux flowing through the flux conductors  66 ,  68 . The flux conductor  75  may be used, for example, to reduce the amount of flux that may otherwise be imparted on a switch  44  (e.g., corresponding to switch  4  discussed above) when the second assembly  64  is in a non-actuating position (See  FIG. 9E ). The flux conductor  75  may be designed with a given shape and attributes depending on how and how much flux is to be diverted through the flux conductor  75 . For example, the flux conductor  75  may include a notch  77  to alter the direction of and/or reduce the amount of stray flux emanated from the flux conductor  75 . As represented by the dashed lines  79  and as shown in  FIG. 9C , when the components of  FIG. 9B  are assembled one end of each flux conductor  66 ,  68  will contact a face of the flux conductor  75 .  
         [0050]      FIG. 9C  illustrates in a simplified cut-away, top view how the assemblies  58  and  64  may interface with one another and with an assembly  46  including a switch  44 . The assembly  58  attaches to the assembly  64  via a rotating mount  85 . Thus, the assembly  58  may rotate relative to the assembly  64  along an axis  87 . The assembly  64  attaches to the assembly  46  via arms  89 A,  89 B that attach to rotating mounts  91 A,  91 B. Here, the assembly  64  (and, hence, assembly  58 ) may rotate relative to the assembly  46  along an axis  93 .  
         [0051]     In this example, the switch  44  is a SPDT switch that provides a ground signal via a normally closed (“NC”) contact to an ON/OFF control input  81  of a NVG control unit  83  when the switch  44  is not activated. In response to this signal, the control unit  83  may turn the NVG off. When the switch  44  is activated, the switch  44  switches to the normally open (“NO”) contact position. This, in turn, results in the input  81  being forced to a high level (e.g., VCC) by a pull-up resistor on the corresponding lead or by a signal (not shown) that drives the NO contact to a high level. The control unit  83  may thus turn the NVG on.  
         [0052]     The configuration of  FIG. 9C  is similar to the configuration described above in conjunction with  FIG. 7 . Thus, the NVG may be turned off when either the assembly  64  is rotated about the axis  93  (e.g., rotated up) or when the assembly  58  is rotated about the axis  87 . These aspects of the embodiment of  FIG. 9C  are further illustrated in  FIGS. 9D and 9E .  
         [0053]      FIG. 9D  illustrates a simplified cut-away, side view of the orientation of  FIG. 9C . Note that flux conductors  60  and  64  and the magnet  56  are not visible in the side view of  FIG. 9D . Here, the flux conductors are aligned to activate the switch  44 . That is, the assembly  58  is rotated to a position where the flux conductors  62 ,  60  are aligned with the flux conductors  68 ,  66 , respectively. In addition, the assembly  64  is rotated to a position where ends of the flux conductors  68 ,  66  are close to the switch  44 . In this orientation, the NVG is turned on.  
         [0054]      FIG. 9E  illustrates a simplified cut-away, side view of an orientation where the flux conductors are not aligned such that the switch  44  is not activated. For example, the assembly  58  is rotated so that the flux conductors  62 ,  60  are not aligned with the flux conductors  68 ,  66 , respectively. In addition, the assembly  64  is rotated so that the ends of the flux conductors  68 ,  66  are not close to the switch  44 . As discussed above, either of these conditions would be sufficient to deactivate the switch and, hence, turn off the NVG. The flux conductor  66  is not visible in the side view of  FIG. 9E .  
         [0055]     The conceptual embodiments shown should not be limited to the described configurations, but rather as examples of the flexibility of using flux conductors to construct physical position sensing mechanisms. For instance, instead of a reed switch, the magnetic sensor described herein could be a Hall Effect device, flux gate, GMR, or other magnetically sensitive detector. The flux conductors are generally shown as straight devices, but could also be formed in complex paths while presenting low reluctance to the magnetic flux. The flux paths are generally shown as equal in length, but this is not necessary. Additional paths or additional series elements could be added to form more complex logical structures. In addition, other methods may be used to interrupt or redirect the flow of flux between a magnet and a switch. For example, one or more flux shunts may be configurable to selectively redirect flux flow. Here, the flux shunt may be selectively positioned across flux conductors coupled with the pole faces of the magnet. Alternatively, a device that interrupts flux flow (e.g., made of or including a material with relatively high reluctance, e.g., aluminum, air, etc.) may be selectively positioned in the normal flux path between the magnet and the switch. Furthermore, a variety of materials may be used to construct the flux conductors or other components. For example, a flux conductor may comprise a material having relatively high magnetic permeability (e.g., a magnetic metal such as iron, ferrite, soft steel, etc.) and may include other material such as plating made of nickel or some other material. Also, all of the structural members described herein that may affect the flow of flux (flux conductors, flux shunts, high reluctance members, etc) may be mounted in a variety of ways to accomplish the desired positioning of the members. In addition, other structural members (e.g., as illustrated in  FIGS. 10-15 ) may be incorporated for the purpose of supporting and/or repositioning other members.  
         [0056]      FIGS. 10 through 15  depict specific embodiments of the magnetic switch concept described above as applied to a specific helmet mount for a NVG. The following descriptions of specific embodiments are not meant to limit the invention as disclosed herein, but are used merely to provide examples.  
         [0057]      FIG. 10  shows one embodiment of a simple configuration for a switch assembly. The magnetically operated switch  44 , such as a reed switch, in the circuit that controls the activation of the NVG carried on the mount is positioned in a vertical block  46  of the mount.  FIGS. 11 through 13  show additional aspects of the circuit containing the switch  44 . Receptacles  48 ,  50  adapted to be connected to a power source on the helmet are mounted in the back of housing  52  (see  FIG. 12 ). The back of housing  52  faces toward the helmet when placed on a helmet. An electrical conduit  54  travels from the receptacles in the housing  52  into the vertical block  46  containing the switch  44  ( FIG. 10 ). The conduit has some slack along its length as it moves down the housing to accommodate vertical adjustment of the vertical block  46  relative to the housing  52 .  
         [0058]     Referring again to  FIG. 10 , a magnet  56  is mounted in a tri monorail  58  from which the NVG (not shown) is suspended. A pair of flux conductors  60 ,  62  are also mounted in the tri monorail  58 . One end of each flux conductor  60 ,  62  is positioned at opposite poles of the magnet  56 . The other end of the flux conductors  60 ,  62  are positioned at an end of the tri monorail  58  where the tri monorail is rotatably attached to a chassis  64 . The chassis  64  in turn is pivotally connected to the vertical block  46 . A pair of flux conductors  66 ,  68  are mounted extending through the chassis  64 . In the in-use position, as shown in  FIG. 10 , one end of the flux conductors  66 ,  68  are adjacent and aligned with an end of the flux conductors  60 ,  62 . The other end of the flux conductors  66 ,  68  are adjacent and aligned with the opposite ends of the switch  44 . Thus, in the use position, the flux conductors are arranged so that the magnetic flux is conducted to the switch  44 , allowing the switch  44  to be activated, turning the NVG on.  
         [0059]     If the tri monorail  58  is rotated 90° about its longitudinal axis to move the NVG to a quick stowage position, flux conductors  60 ,  62  will no longer be aligned with flux conductors  66 ,  68 , causing the switch to open and turning the NVG off. Also, if the chassis  64  is flipped up relative to the vertical block  46  to move the NVG to a flip-up stowage position, flux conductors  66 ,  68  will pivot up and away from the switch  44 , causing the switch  44  to open and the NVG to be turned off.  
         [0060]      FIG. 14  shows an assembly similar to the assembly of  FIG. 10 . For conciseness, only the differences will be described in detail and like parts have been assigned the same reference numerals as the embodiment of  FIG. 10 . In the embodiment of  FIG. 14 , two flux conductors  70 ,  72  are mounted in the vertical block  46 . The flux conductors  70 ,  72  are positioned in front of and aligned in the same direction as the switch  44 . Thus, these additional conductors strengthen the connection between flux conductors  66 ,  68  in the chassis  64  and the switch  44  in the vertical block  46 , when flux conductors  66 ,  68  are positioned in the use position.  
         [0061]     The embodiment of  FIG. 14  also includes a shunt  74  mounted in the vertical block  46  and positioned above and away from the switch  44 . The shunt  74  provides a quicker disconnection of the magnetic flux from the switch  44  when the chassis  64  is pivoted upward. That is, as chassis  64  is pivoted upward, flux conductors  66 ,  68  also pivot upward along the outer front surface of the vertical block  46 . When the ends of the flux conductors  66 ,  68  are aligned with the shunt  74 , the switch  44  opens and the NVG turns off.  
         [0062]      FIG. 15  shows an embodiment for a switch assembly where a switch  44  is positioned at the top of the housing  52 . Positioning the switch  44  at the top of the housing  52  avoids the need for a conduit running down the housing  52 . The magnet  56  and the flux conductors  60 ,  62 ,  66 ,  68  are positioned and operate in much the same manner as in the previous embodiments. These components have been assigned the same reference numbers as the previous embodiments. However, due to the position of the switch  44 , additional flux conductors are needed. A pair of flux conductors  76 ,  78  extend upward along the back surface of the chassis. Another pair of flux conductors  80 ,  82  extend through the top of the vertical block  46 . Finally, an inverted U-shaped flux conductor  84  has legs extending up the front surface of the housing  52  and a cross bar extending across the top of the housing  52  near the switch  44 .  
         [0063]     The configuration of the flux conductors in the embodiment of  FIG. 15  provides an unbroken conductive path when the NVG are in an in-use position. However, as with the other embodiments, movement of the mount to a stowage position for the NVG breaks the path and opens the switch to turn off the NVG.  
         [0064]     The foregoing description of the preferred embodiments of the invention have been presented for the purposes of illustration and description. The description is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. The scope of the invention is not limited by this description, but by the claims and the equivalents to the claims appended hereto.