Abstract:
A generator including: a housing having an opening; a rotatable member having a slot formed for an angular length less than 360 degrees; a cable disposed in the slot and having a free end protruding from the opening in the housing; a cable stop disposed in a predetermined position in the slot; a spring for storing energy as the cable is unwound from the slot by pulling on the free end until the rotatable member rotates relative to the housing and the cable stop aligns with the opening; and an electromagnetic generator operatively connected to the spring such that the stored energy of the spring is transferred to an input side of the electromagnetic generator.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims benefit to U.S. Provisional Application No. 61/762,938 filed on Feb. 10, 2013, the entire contents of which is incorporated herein by reference. This application is related to U.S. patent application Ser. Nos. 13/297,234 filed on Nov. 15, 2011 and 13/797,938 filed on Mar. 13, 2013, the entire contents of each of which are incorporated herein by reference. 
    
    
     GOVERNMENT RIGHTS 
     This invention was made with Government support under contract FA8651-10-C-0145 awarded by the United States Air Force. The Government has certain rights in the invention. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to small weapon systems, and more particularly, to methods for enabling safe/arm functionality within small weapons. 
     2. Prior Art 
     All weapon systems require fuzing systems for their safe and effective operation. A fuze or fuzing system is designed to provide, as a primary role, safety and arming functions to preclude munitions arming before the desired position or time, and to sense a target or respond to one or more prescribed conditions, such as elapsed time, pressure, or command, and initiate a train of fire or detonation in a munition. 
     Fuze safety systems consist of an aggregate of devices (e.g., environment sensors, timing components, command functioned devices, logic functions, plus the initiation or explosive train interrupter, if applicable) included in the fuze to prevent arming or functioning of the fuze until a valid launch environment has been sensed and the arming delay has been achieved. 
     Safety and arming devices are intended to function to prevent the fuzing system from arming until an acceptable set of conditions (generally at least two independent conditions) have been achieved. 
     A significant amount of effort has been expended to miniaturize military weapons to maximize their payload and their effectiveness and to support unmanned missions. The physical tasking of miniaturization efforts have been addressed to a great extent. However, the same cannot be said regarding ordnance technologies that support system functional capabilities, for example for the case for fuzing. 
     It is important to note that simple miniaturization of subsystems alone will not achieve the desired goal of effective fuzing for smaller weapons. This is particularly the case in regards to environmental sensing and the use of available stimuli in support of “safe” and “arm” functionality in fuzing of miniature weapon technologies. 
     A need therefore exists for the development of methods and devices that utilize available external stimuli and relevant detectable events for the design of innovative miniature “safe” and “arm” (S&amp;A) mechanisms for fuzing of gravity dropped small weapons. 
     SUMMARY OF THE INVENTION 
     Accordingly, a generator is provided. The generator comprising: a housing having an opening; a rotatable member having a slot formed for an angular length less than 360 degrees; a cable disposed in the slot and having a free end protruding from the opening in the housing; a cable stop disposed in a predetermined position in the slot; a spring for storing energy as the cable is unwound from the slot by pulling on the free end until the rotatable member rotates relative to the housing and the cable stop aligns with the opening; and an electromagnetic generator operatively connected to the spring such that the stored energy of the spring is transferred to an input side of the electromagnetic generator. 
     The generator can further comprise an input gear connected to an end of the spring, such that the input gear rotates from the stored energy of the spring; and a generator gear operatively engaged with the electromagnetic generator and the input gear. 
     The generator can further comprise a flywheel operatively connected between the generator gear and the electromagnetic generator. 
     The generator can further comprise an idler gear engaged with the generator gear and partially engaged with the input gear such that the input gear loses engagement with the generator gear after a predetermined amount of revolution of the idler gear. 
     Also provided is a generator comprising: a housing having an opening; a rotatable member disposed in the housing; a release member having an end exposed through the opening and an other end selectively engaging the rotatable member; a spring having a pre-stored energy which is released to rotate the rotatable member upon disengagement of the other end with the rotatable member; and an electromagnetic generator operatively connected to the rotatable member such that the rotation of the rotatable member is transferred to an input side of the electromagnetic generator. 
     The generator can further comprise a shaft rotatable with the rotatable member. 
     The generator can further comprise a clutch having an input side connected to the shaft and an output side connected to the electromagnetic generator. 
     The generator can further comprise a flywheel connected between the clutch and the electromagnetic generator. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features, aspects, and advantages of the apparatus and methods of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings where: 
         FIG. 1  illustrates a dynamo-type event-detection and power generator. 
         FIG. 2  illustrates internal components of the dynamo-type event-detection and power generator of  FIG. 1 . 
         FIG. 3  illustrates a close-up view of three main sub-assemblies of the dynamo-type event-detection and power generator of  FIG. 1 . 
         FIG. 4  illustrates a cut-away view showing the developed dynamo-type event-detection and power generator attachment to the inside surface of the weapon shell. 
         FIG. 5 : The view of the developed dynamo-type event-detection and power generator from the weapon outside. 
         FIG. 6 : Cut-away view showing the dynamo-type event-detection and power generator of  FIG. 1  with a multi-directional pitot probe and a lanyard tethered cover. 
         FIG. 7  illustrates an optional mounting configuration of the dynamo-type event detection and power generator of  FIG. 1  on an outer surface of a weapon shell. 
         FIG. 8  illustrates a Bernoulli-effect detector opening that is exposed by the pulling of the lanyard (before the lanyard pull). 
         FIGS. 9   a  and  9   b  illustrate a Bernoulli-effect detector opening that is exposed by the pulling of the lanyard (after the lanyard pull). 
         FIGS. 10   a  and  10   b  illustrate an “omni-directional” airstream velocity detector that is exposed by the pulling of a split lanyard. 
         FIGS. 11   a - 11   c  illustrate an approximate size and position of a miniaturized dynamo-type event detection and power generator for a specific application. 
         FIGS. 12   a  and  12   b  illustrate a cable-pull power spring wounding and release gear train with and without an outer housing, respectively. 
         FIG. 13  illustrates internal components of the cable-pull power spring wounding and release gear train mechanism of  FIG. 12 . 
         FIG. 14  illustrates the gear train mechanism of the cable-pull power spring wounding and release mechanism. 
         FIG. 15  illustrates internal components of another miniaturized dynamo-type event detection and power generator design for hybrid integration. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Dynamo-Type Event Detection and Power Generator Prototype 
     An event-detection and power generator (alternatively referred to herein simply as “a generator”) is shown in  FIGS. 1-3  and is generally referred to by reference numeral  100 . The event-detection and power generator  100  are assumed to fit within a predetermined volume. For example, as shown in  FIG. 1 , the event-detection and power generator  100  can fit within a space with a rectangular face area (to be attached to the weapon shell) of at most 2.5 inch wide and 6 inches long, and a thickness of between 0.75 to 1 inches. The overall dimensions of the device can be 2.5″×6″×1.0″ and is expected to generate about 10 J of electrical energy with off-the-shelf components by the pulling of the lanyard  102 , reaching an efficiency of over 40%. However, the event-detection and power generator can be optimized to either reduce its size or increase its power output, particularly by using slightly customized components, such as for its gearings and generator. The elongated member is referred to herein as “a lanyard” for that portion extending from a housing  104  of the generator  100  and as “a cable” for that portion disposed within the housing  104 . 
     The generator  100  operates by extending the cable  102  from an interior of the housing and upward (e.g., in the direction opposite to gravity) by pulling of the lanyard  102  in the weapon assembly out of the top of the housing  104 . The cable  102  is routed inside the generator housing  104  to rotate a cable drum  106  about its axis  108 . Inside the cable drum  106 , a generator spring (not shown) is fixed to the housing  104  at its inner diameter, and to the cable drum  104  at its outer diameter. There is no energy stored in the generator spring before the cable  102  is pulled. When the cable  102  is pulled (i.e., unwound from the drum), the generator spring is wound, storing mechanical potential energy. As the generator spring reaches its maximum energy storage, the cable&#39;s  102  anchor to the drum  106  is in a position of imminent release from the drum  106  such that continuing to pull on the cable  102  will release the cable  102  from the cable drum  106 , allowing the generator spring to convert its mechanical potential energy into kinetic energy by rotating the cable drum  106 , which in turn rotates an electrical generator  110  through a clutch assembly  112 . 
     Once the cable  102  is released from the cable drum  106 , the cable  102  is prevented from pulling out of the housing  104 , such as by the cable termination end used to anchor the cable  102  to the cable drum  106  being larger than the cable diameter and smaller than at least one opening through which the cable  102  is routed through the housing such that the cable termination end will not pass through such routing passages in the housing  104 . Additionally, the cable  102  is prevented from traveling back towards the cable drum  106 , which would cause possible interference, by the presence of a friction shoe (not shown) near the opening  104   a  where the cable  102  exits the housing  104 . This friction shoe also ensures that the cable  102  will remain properly wound on the cable drum  106  prior to the cable being pulled and operation of the generator  110  commences. 
     As can be seen in  FIG. 3 , a drum assembly gear  114  is engaged with a clutch assembly gear  116 , while another gear  118  attached to an opposite side of the clutch  112  engages a generator gear  120  (directly or through intermediate gearing  122 ). Because of the constant engagement of the gears, rotation of the cable drum  106  turns the upper (input) gear  116  of the clutch assembly, during both loading and unloading of the generator spring. The clutch  112  is designed to only transmit torque to the lower (output) gear  118  of the clutch  112 , and therefore to the electrical generator  110 , when the generator spring is unwinding. While the generator spring is being wound (cable pulling), the clutch  112  transmits no torque to the electrical generator  110 . After the cable  102  has been released from the cable drum  106 , the torque generated by the unwinding of the generator spring is transmitted to the electrical generator  110 , which, because of the clutch  112 , is free to spin after the generator spring has unwound to its zero energy state, giving the electrical generator  110  increased time to convert the kinetic energy of the rotating clutch  112 , generator gear  120 , and generator rotor (not shown), into electrical energy. 
     The dynamo-type event-detection and power generator  100  can be attached to the interior surface  200  of a weapon shell  202  as shown in the cutaway view of  FIG. 4 . The attachment can be with any type of fasteners, such as four screws through the mounting holes  124  provided in the generator body  104 . The generator  100  would only require a very small hole in the weapon shell  202  to allow the cable/lanyard  102  to pass through. The view of the weapon of  FIG. 4  from outside the weapon shell  202  is shown in  FIG. 5 . 
       FIGS. 4 and 5  are illustrated with an optional multi-directional pitot tube (described below) to provide a means of differentiating accidental drop of the weapon  204  on the ground or weapon detachment without detaching the lanyard from air drop of the weapon. 
     Methods to Differentiate Air-Drops from Accidental Ground-Drops 
     Currently used deployable turbine generators have the capability of differentiating air-drops from accidental drops on the ground since when air-dropped, the air turbine begins to generate electrical energy while following an accidental ground dropping, the turbine generator is deployed but would not be generating any electrical energy. However, the lanyard operated event detection and power generation device  100  of  FIG. 1 , by itself, is incapable of differentiating accidental weapon release on land from an actual air drop. 
     Two methods are described for potential use for measuring air speed that can be used in event detection and power generation devices as well as for the purpose of differentiating weapon release from accidental drop. These two methods also have the advantage of potentially providing air speed information without being very sensitive to the direction of weapon descent. 
     In the first method, as shown in  FIGS. 4-7 , a second short cable  102   a  is attached to the lanyard  102  such that as it is pulled and activates the generator  100 , the lanyard  102  would also pull on the second short cable  102   a,  thereby activating a relatively small Pitot-tube  206  (or a cluster of more than one relatively short Pitot-tubes that are oriented at different angles—e.g., at 120 degrees). The activation of the Pitot tube  206  can be by attaching an end  102   b  of the second short cable  102   a  to a cap  206   a  that covers the Pitot tube  206 . Once pulled, the cap  206   a  would be removed from the Pitot tube, as shown in  FIG. 6  and the Pitot-tube(s)  206  would then serve to measure air speed, thereby allowing the weapon safety circuitry to differentiate air-drops from accidental drops on the ground. The Pitot-tube(s)  206  can be relatively small (externally mounted) since it is not used for very accurate air-flow measurement. 
     When provided, a multi-directional Pitot tube may be routed from the generator unit to an outer surface of the weapon shell. Such a feature could augment the safe/arm characteristics by using physical aerodynamic effects in the logic of the safe/arm system. For example, a requirement that the Pitot tube sense a high air-speed before arming would prevent arming if the aircraft were not actually in-flight. As discussed above, the ports of the Pitot tube  206  may be fitted with a protective cap  206   a,  as shown in  FIG. 6 , which is attached to the end  102   b  of the second short cable  102   a.  Upon pulling the cable  102 , the protective cap  206   a  of the Pitot tube  206  would be pulled off, exposing the ports of the Pitot tube  206  to the atmosphere. Such a cap  206   a  would serve two purposes: first, the cap  206   a  would guard against debris obscuring the Pitot tube  206 ; second, the cap  206   a  would act as a mechanical “turn-on” switch for the Pitot tube  206 , only when uncovered by pulling the generator cable  102 / 102   a  would the Pitot tube  206  sense any velocity. 
     For weapon systems which cannot accommodate the generator  100  on the interior of the weapon shell  202 , the generator  100  may be fixed to an exterior of the shell, as shown in  FIG. 7 . Naturally, the contour and dimensions of such a generator  100  would be altered to minimize the drag and avoid interference with adjacent hardware. Such a mounting of the generator  100  will only require a small hole in the weapon shell to pass any generator wires (providing electrical power) to inside the weapon  204 . Alternatively, the generator power wires may be routed from the outside of the shell  202  to, e.g., the weapon fuzing. The deployed Pitot-tube  206  may also be utilized as an auxiliary descent velocity measurement device in such configuration. 
     In the second method, referring now to  FIGS. 8 ,  9   a  and  9   b , the aforementioned short second cable  102   a  is similarly attached to the lanyard  102  such that as it is pulled and activates the generator  100 , it would also pull the second short cable  102   a,  as shown in  FIG. 8  (prior to lanyard pull). When pulled, the lanyard  102  actuates the generator  100  and the short second cable  102   a  removes a small plug  208  attached to the end  102   b  of the second short cable  102   a,  exposing a port  210  which can use a Bernoulli Effect to sense velocity, as shown in  FIGS. 9   a  and  9   b.    
     In an alternative version, the above two concepts can be “combined” to provide an effectively “omni-directional” airstream velocity detector  212  shown in  FIGS. 10   a  and  10   b . In this concept, similar to the Bernoulli-type detector  210  of  FIGS. 9   a  and  9   b , the airstream detector  212  is covered by a cover  212   a  fixed to the end  102   b  of the short second cable  102   a  prior to release and the cover  212   a  is removed by the lanyard/second short cable  102 / 102   a  upon weapon  204  release from an airframe (not shown). 
     The “omni-directional” airstream velocity detector  212  has multi-sided inlets  212   b  that would allow it to operate in airstream with any flow direction. The detector  212  would in fact operate similar to a Pitot-tube (but obviously not as accurately as a Pitot-tube with a long neck), but can serve well enough for differentiating air drops from accidental ground drops. The detector  212  may also have a central through hole (not shown) to sense pressure drop due to Bernoulli effects. 
     Hybrid Dynamo-Turbine Type Event Detection and Power Generators 
     Referring now to  FIGS. 11-15 , there is described a device achieved by integrating a highly miniaturized version of the lanyard operated dynamo-type event detection device  300  with a turbine type release event detection and power generator (FZU)  302 . 
     Such an integrated “hybrid” device has the advantages of both systems. The dynamo-type component of the device would provide the means to reliably detect release and provide fuzing power irrespective of the weapon drop altitude, i.e., even when the weapon is dropped from very high or very low altitude. The turbine component of the device would then serve as a power generation device and speed sensor during the flight when more power is required to be generated. 
     In one design, upon weapon deployment, the cable immediately provides an initial spin to the turbine dynamo before the turbine is capable of appreciable output. The system may be designed such that as the turbine begins spinning at the same time when the initial impetus provided by the cable is subsiding. The inclusion of a transmission/clutch in the device allows for the turbine to power the dynamo without the burden of continuing spinning the spool pulley and vice-versa. Such hybrid system has particular utility to provide reliable electrical power to the weapon throughout the duration of the weapon&#39;s flight. 
     A size of the miniaturized dynamo-type event detection and power generator  300  can be such that it can be integrated into a FZU-63B (shown as reference numeral  302 ), as shown in the three views of  FIGS. 11   a - 11   c . In such configuration, the miniaturized dynamo-type event detection and power generators  300  are 22 mm in diameter and 12 mm in height. 
     Hybrid Dynamo-FZU Event Detection and Power Generator—No Stored Mechanical Energy 
     A first embodiment of the dynamo-type event detection and power generator  304  is shown in  FIGS. 12   a  and  12   b . In this generator  304 , a power spring (see  FIG. 13 ) is not preloaded, i.e., there is no mechanical energy stored in the generator  304  prior to activation of the generator  304  resulting from release of the weapon having such generator  304  from an aircraft frame. 
       FIG. 12   a  illustrates an assembled dynamo-type event detection and power generator  304 , while  FIG. 12   b  illustrates the same with its housing  306  removed. An activating cable  308  and cable stop  310  are contained within a channel  312  in an input disc  314  which is attached to an input ring gear  316 , and both are free to rotate. As the cable  308  is pulled (such as by being attached to an air frame and the weapon having such generator  304  being released from the air frame), the input disc  314  and input ring gear  316  will rotate until the system rotates through 180 degrees (the length of the channel  312 ) at which point the cable stop  310  moves beneath a cable exit hole  318  in the housing  306 . At this point, the cable stop  310  is pulled out of its channel  312 , thereby freeing the power spring (see  FIG. 13 ) to begin to rotate a flywheel and generator, as described below. 
     Referring now to  FIG. 13 , therein is illustrated internal components of the generator  304  shown in  FIGS. 12 and 12   b . The generator  304 , as illustrated in  FIG. 13 , shows what transpires during the input pull of the cable  308 . An inner end or tang of the power spring  320  is fixed to the generator housing  306 , and an outer end or tang of the power spring  320  is connected to the input ring gear  316 . When the cable  308  is pulled, mechanical potential energy is stored in the spiral power spring  320 . When the cable stop  310  is pulled out of its channel  312  and up through the hole  318  in the housing ( FIG. 12   a ), the power spring  320  unwinds, rotating the input disc  314  and input ring gear  316 . As shown in  FIGS. 13 and 14 , the input ring gear  316  has a freewheel gap  322 , namely a gap in the internal teeth  324  of the input ring gear  316  such that at a particular angular position, idler  326  and generator input  328  gears are free to rotate separately from the rest of the system. This gap  322  is positioned at the unwound orientation of the power spring  320  such that after the power spring  320  has unwound, passing all of its potential energy to a flywheel  330  and generator  332 , the “generator side” of the system is free to rotate allowing many revolutions of the flywheel  330  and generator  332  beyond the half-turn input of the power spring  320 . An idler and input ring support  334  is provided for rotatably mounting the idler and generator input gears  326 ,  328  on corresponding shafts  326   a ,  328   a,  respectively. 
     Hybrid Dynamo-FZU Event Detection and Power Generator—With Preloaded Power Spring 
     A second embodiment of a dynamo-type event detection and power generator  400  is shown in the cut-away view of  FIG. 15 . The generator  400  differs from the generator of  FIGS. 12   a - 14  in that in  FIG. 15 , the power spring  402  is initially preloaded with stored mechanical energy. In the generator  400  of  FIG. 15 , an outer end or tang of the power spring  402  is anchored to a housing  404  with an inner end or tang being fixed within a rotatable arbor  406 . During manufacture/assembly, the power spring  402  is wound, storing mechanical potential energy, and the arbor  406  is immobilized through a release arm  408  and release pin  410  protruding from a top cap  412  of the housing  404 . When the release pin  410  is removed/disengaged, the release arm  408  and arbor  406  are no longer constrained against rotation and the power spring  402  begins to unwind, rotating the release arm  408  and arbor  406 . The rotating arbor  406  drives an inner race of an over-run clutch  414 , which in turn drives a flywheel  416  and generator  418 . Once the power spring  402  has completely unwound (mechanical potential energy of power spring passed into kinetic energy of rotating flywheel and generator), the over-run clutch  414  will allow the flywheel  416  and generator  418  to continue rotating, allowing the generator  418  to extract more energy from the system beyond the initial rotation given by the power spring  402 . 
     EXAMPLE 1 
     The first embodiment generator,  FIGS. 12   a - 14 , constructed with a power spring that is not pre-wound with an available (not optimized) power spring that is wound 130 degrees with the pulling of the indicated cable as the FZU is deployed following weapon release, around 300 mJ of mechanical energy is stored in the power spring. Considering a mechanical to electrical energy conversion efficiency of around 40% that was obtained from testing should result in a net available electrical energy of around 120 mJ becoming available to power fuzing electronics and for capacitor storage. Optimizing the power spring of the generator should result in an increase in the available electrical energy to over 150 mJ. This optimization would mostly be accomplished by varying the thickness of the spring to enable the torsion spring to be wound close to 180 degrees. 
     EXAMPLE 2 
     The second embodiment generator,  FIG. 15 , constructed with a power spring that is pre-wound which allows the use of thinner spring material and its winding of more than a full turn, thereby storing a significantly larger amount of mechanical energy in the power spring. As a result, the amount of available energy becomes significantly larger and is expected to nearly double due to more than doubling of its winding turn. Thereby, with the same mechanical to electrical efficiency of 40%, the available energy is expected to become around 240 mJ. Another advantage of this design option is that it is significantly simpler in design, has fewer parts, and is expected to be less costly. 
     While there has been shown and described what is considered to be preferred embodiments of the invention, it will, of course, be understood that various modifications and changes in form or detail could readily be made without departing from the spirit of the invention. It is therefore intended that the invention be not limited to the exact forms described and illustrated, but should be constructed to cover all modifications that may fall within the scope of the appended claims.