The present disclosure relates to on-board power sources and more particularly to a mechanical thermal battery initiator used to initiate power on-board a guided munition or round.
Current electronic initiator designs are expensive and have reliability issues. Electronic initiator designs require an internal power source, typically a chemical battery, with a limited lifespan. This lifespan requires periodic replacement of the battery, through disassembly and replacement of the electronic battery initiator. Batteries are prone to failure over time, when current leakage draws down the available power below that which can actuate the system. Electronic components used in these assemblies are also subject to obsolescence, making recurring design changes a necessity in order to keep technology up to date, and enable modern software implementations. All of these characteristics of conventional systems drives cost through engineering development and product qualification. Typically, the required energetic force to activate the battery is produced by a pyrotechnical assembly, which must fit inside a very small form factor. This creates reliability issues due to the very small amounts of energetic materials utilized, and the manufacturing of a reliable ignition system, due to volume and electrical power constraints. Wherefore it is an object of the present disclosure to overcome the above-mentioned shortcomings and drawbacks associated with the conventional on-board power sources.
One aspect of the present disclosure is a system comprising, a mechanical thermal battery initiator for a round, comprising: a body, comprising: an inner central bore configured to slidably retain a firing pin and a firing pin spring; a concentric outer bore spaced away from the central bore being configured to retain a setback ring and at least two ball bearings; and at least two spring-loaded centripetal pins each located in a cross bore and configured to engage with the setback ring at rest and disengage from the setback ring when under centripetal force; wherein once the initiator is exposed to centripetal force and acceleration due to a launch of the round the setback ring releases the at least two ball bearings and a spring force from the firing pin spring pushes the firing pin into contact with a primer on the thermal battery to initiate power on the round.
One embodiment of the initiator further comprises a mechanical interlock or Safety Switch configured to prevent inadvertent activation during shipping or handling. In some cases, the initiator further comprises a housing for containing the mechanical thermal battery initiator having an opening that exposes the firing pin.
Another embodiment of the initiator is wherein a shelf life of the initiator is longer than a shelf life of the thermal battery.
In some cases, a primer impact force for the thermal battery is less than or equal to 50 lbs. In certain embodiments, a minimum of 6 Hz rotation is needed to release the setback ring on the initiator.
Yet another embodiment of the initiator is wherein the initiator comprises four centripetal pins, evenly spaced about a central axis, thus preventing a single shock event from freeing all of the centripetal pins from the setback ring. In some cases, the centripetal pins are pointed and are configured to mate with a V-notch in the setback ring to allow the pins to consistently reseat on the setback ring. In certain embodiments, a spring force for the centripetal locking pins is less than a pound.
Still yet another embodiment of the initiator is wherein an activation time of the initiator is less than 200 ms of flight time.
Another aspect of the present disclosure is a method for mechanically initiating a thermal battery on a round, comprising: providing a mechanical initiator, comprising: an inner central bore configured to slidably retain a firing pin and a firing pin spring; a concentric outer bore spaced away from the central bore being configured to retain a setback ring and at least two ball bearings; and at least two spring-loaded centripetal pins each located in a cross bore and configured to engage with the setback ring at rest and disengage from the setback ring when under centripetal force; exposing the initiator to centripetal force and acceleration due to a launch of the round; disengaging the setback ring and releasing the at least two ball bearings; pushing the firing pin into contact with a primer on the thermal battery via a spring force from the firing pin spring; and initiating power on the round.
One embodiment of the method further comprises providing a mechanical interlock or Safety Switch configured to prevent inadvertent activation during shipping or handling.
Another embodiment of the method further comprises providing a housing for containing the mechanical thermal battery initiator having an opening that exposes the firing pin. In some cases, a shelf life of the initiator is longer than a shelf life of the thermal battery.
In certain embodiments a primer impact force for the thermal battery is less than or equal to 50 lbs. In some cases, a minimum of 6 Hz rotation is needed to release the setback ring on the initiator.
Yet another embodiment of the method is wherein the initiator comprises four centripetal pins, evenly spaced about a central axis, thus preventing a single shock event from freeing all of the centripetal pins from the setback ring. In some cases, the centripetal pins are pointed and are configured to mate with a V-notch in the setback ring to allow the pins to consistently reseat on the setback ring.
Still yet another embodiment of the method is wherein a spring force for the centripetal locking pins is less than a pound.
Yet another aspect of the present disclosure is a method of manufacturing a mechanical initiator for a thermal battery on a round, comprising: fabricating a housing configured for secure attachment to a thermal battery, the housing having a central borehole to contain a firing pin, a firing pin spring, and a setback ring; and providing bore holes in a transvers axis for retaining two or more ball bearings that engage the firing pin when the setback ring is held in place by centripetal pins and centripetal pin springs at rest.
Still yet another aspect of the present disclosure is a munition, comprising: a guidance unit; a controller; at least one sensor coupled to the guidance unit for directing the munition to a target area; an explosive charge; a fuse assembly coupled to the explosive charge; a battery; a mechanical battery initiator, comprising: an inner central bore configured to slidably retain a firing pin and a firing pin spring; a concentric outer bore spaced away from the central bore being configured to retain a setback ring and at least two ball bearings; and at least two spring-loaded centripetal pins each located in a cross bore and configured to engage with the setback ring at rest and disengage from the setback ring when under centripetal force; wherein once the initiator is exposed to centripetal force and acceleration due to a launch of the munition the setback ring releases the at least two ball bearings and a spring force from the firing pin spring pushes the firing pin into contact with a primer on the battery to initiate power to the munition.
These aspects of the disclosure are not meant to be exclusive and other features, aspects, and advantages of the present disclosure will be readily apparent to those of ordinary skill in the art when read in conjunction with the following description, appended claims, and accompanying drawings.
The foregoing and other objects, features, and advantages of the disclosure will be apparent from the following description of particular embodiments of the disclosure, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the disclosure.
It is understood that munitions with guidance require a power source. As used herein, a round is a weapon, a projectile, a ballistic, a bullet, a munition, a guided weapon, or the like. In many cases, the onboard power source is typically a lithium thermal battery. This battery requires a striker to impact a primer to initiate power. By including a simple mechanical interlock, a positive system safety can easily be established for a mechanical design, which provides a robust safety feature for processing, shipping, and end users. Thermal batteries are inert until activation, and this provides very long storage life and very high power output when finally activated, and makes them ideal for applications where the product may sit for long periods, and have a short lifespan when used, such as rockets, missiles, artillery projectiles, or the like.
A mechanical thermal battery initiator is a device that upon detecting the correct physical conditions, activates a lithium thermal battery, to provide internal power for various munitions guidance systems during flight. The device is reliable and simple to manufacture and can fit into a small physical volume while providing adequate force to initiate a lithium thermal battery. A mechanical solution provides a low cost, highly reliable system that is robust to environmental issues, such as vibration, shock, ionizing radiation, and humidity, while having a nearly unlimited shelf life. A mechanical solution is inherently safer, as it contains no high explosives content, which are required for electronic versions to operate. Mechanical solutions avoid the sensitivity of electronic designs to environmental concerns and major redesign efforts due to electronic and software component life cycle issues, such as obsolescence. Additionally, a mechanical design may be fabricated by a machine shop with a short supply base, no specialty materials, which reduces lead times and overhead costs.
One embodiment of the mechanical thermal battery initiator of the present disclosure is a mechanical solution that utilizes two factors to verify the need to initiate a battery on-board a round. In certain embodiments, the mechanical thermal battery initiator provides a striker mechanism and controls all within a small form factor. By utilizing ballistic rotation of a rocket or artillery projectile, or the like, and the linear acceleration forces, a reliable and repeatable initiation can be achieved. Additionally, in certain embodiments the mechanical thermal battery initiator is reconfigured for a variety of applications for any product that utilizes a Lithium thermal battery. These products may include artillery or missile guidance, telemetry, or flight controls.
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The mechanical thermal battery initiator according to the principles of the present disclosure must not fire when no launch condition exists, and it must fire when a launch condition exits. In some cases, the imitator activates the thermal battery on-board the round in approximately 120 ms, which is near current design timing in order to minimize design impact. It is understood that the shelf life and reliability must be as good as or better than current design and it should be a mechanical fit to the existing battery and guidance section so that there is no change to other components. In certain embodiments, the primer impact force less than or equal to 50 lbs. In certain embodiments, a mechanical safety is required. The mechanical thermal battery initiator according to the principles of the present disclosure is expected to cost less than ½ the current solution, while having no shelf life limitation, electronic obsolescence issues, and superior reliability while being inherently safe.
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It is desired that the system activate the battery approximately 100 ms after launch. From the data it can be seen that at this time in flight, the system consistently achieves a 6 Hertz rotation rate, this rate increases until about 500 ms or so. Using a minimum rotation rate, set by a maximum spring force, with a fail-safe mode of activating a few milliseconds later provides for a robust design. In some cases, a spring force, of less than a pound, is required for the centripetal locking pins. Tungsten material is used in one embodiment to provide a higher force and larger margin in manufacturing setting the spring tension.
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In a worst case example, a rocket motor at −40° C. and 100 ms acceleration would be on the order of 35 g. A conservative approach was therefore to use a 27 g setback to provide margins for manufacturing and design tolerance. The previous electronic design used a 27 g trigger, which was required because the system only utilized linear acceleration force to start the electronic timer. There was no fail-safe mode in this design and a failure to detect acceleration meant a failure to fire. Here, the mechanical design uses a rotation rate to provide timing, and linear acceleration to confirm a launch. Therefore, a high degree of precision in linear acceleration is not required.
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In one embodiment, the firing pin was machined from mild steel. The firing pin spring was designed to provide >50 lbs force on the firing pin. An ultimate spring load value may be tested and chosen such that it includes sufficient force to accelerate the firing pin against launch forces. In one embodiment, the ball bearings were standard 0.125 diameter 316 bearings. High hardness was desirable for the bearings to prevent galling and stainless-stainless adhesion. The centripetal pins were either steel or tungsten dowels e.g., 0.250 L×0.125, depending on the available spring force and form factor to fit. In some cases, a bevel angle and length were tunable parameters for the centripetal pins. In one embodiment, standard 8-32 set screws were used to adjust the spring force, and retain the springs in the assembly. In one embodiment, the setback ring was made of mild steel, and the spring value was set to provide full setback at 27 g +/−.
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A round or munition comprises a controller that contains software and when powered on controls the functions of the munition. A guidance unit operates with one or more sensors to guide the munition to the target once the munition has power. A fuse assembly is coupled to the explosive charge that operates to detonate at the appropriate time and location proximate the target area. The fuse assembly in one embodiment also requires power to operate. In one example the munition further comprises a control actuation system that deploys wings to guide the munition, wherein the control actuation system requires power to operate.
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While various embodiments of the present invention have been described in detail, it is apparent that various modifications and alterations of those embodiments will occur to and be readily apparent to those skilled in the art. However, it is to be expressly understood that such modifications and alterations are within the scope and spirit of the present invention, as set forth in the appended claims. Further, the invention(s) described herein is capable of other embodiments and of being practiced or of being carried out in various other related ways. In addition, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having,” and variations thereof herein, is meant to encompass the items listed thereafter and equivalents thereof as well as additional items while only the terms “consisting of” and “consisting only of” are to be construed in a limitative sense.
The foregoing description of the embodiments of the present disclosure has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the present disclosure to the precise form disclosed. Many modifications and variations are possible in light of this disclosure. It is intended that the scope of the present disclosure be limited not by this detailed description, but rather by the claims appended hereto.
A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made without departing from the scope of the disclosure. Although operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results.
While the principles of the disclosure have been described herein, it is to be understood by those skilled in the art that this description is made only by way of example and not as a limitation as to the scope of the disclosure. Other embodiments are contemplated within the scope of the present disclosure in addition to the exemplary embodiments shown and described herein. Modifications and substitutions by one of ordinary skill in the art are considered to be within the scope of the present disclosure.
This disclosure was made with United States Government support under Contract No. N00019-17-D-5517 and N0001918F2505 awarded by the United States Navy. The United States Government has certain rights in this disclosure.