ACCELERATION/DECELERATION SENSING SWITCH FOR MUNITIONS

HELD OF THE INVENTION

The present invention relates generally to acceleration and deceleration sensitive electrical switches applicable for munitions.

BACKGROUND OF THE INVENTION

Launched munitions projectiles are generally referred to as "combat rounds." For the purposes of this application they are referred to herein as "projectiles." Designing combat round fuzing systems for munitions systems has become a rather sophisticated design challenge. This is due to several factors that must be considered in contemporary designs, including safety factors, increasing functional density requirements, and restrictions on volume. These and other factors have combined to complicate the design of combat round fuzing.

One of the many functions required of a combat round munitions fuze is the ability to reliably detonate the projectile on impact. As will be appreciated by those skilled in the art, a combat round that does not detonate upon impact remains a hazard to human life and property until it is removed, detonated or disarmed. It will also be appreciated that the proper disposition of undetonated combat rounds is extremely expensive and dangerous. Unfortunately, many of the fuzes currently employed in the art do not reliably detonate the combat round upon impact at slight grazing angles, thus, often creating such hazardous conditions.

In addressing the detonation requirements for detonating a combat round, there are at least two types of impact detonation that must be considered in the design of a combat round fuze. The first type of impact is a "head-on" impact which occurs when the projectile hits a target head-on. A "head-on" impact results in the projectile being subjected to a high deceleration force directed mainly along its longitudinal axis. Designing for a "head-on" impact customarily employs some type of "crush switch" mechanism. As known in the art, a crush switch provides electrical switch closure of a pair of contacts as the nose of the projectile collapses upon impact of the projectile upon the target. The closed pair of contacts, in turn, activate detonation control electronics that initiate the fuze detonation process.

The second type of impact considered is a "non-head-on" impact which occurs when the round does not hit head-on, but rather, grazes a target. For a "non-head-on" impact, a crush switch may not reliably provide the switch contact closure function needed to detonate the fuze. This is particularly a problem if the target impact graze angle is too slight to activate the crush switch. At such a slight target impact angle, a diminished or incomplete crushing of the combat round nose may result in a lack of detonation.

One example of a crush switch often used in combat round munitions applications is an impact switch commonly known as a Lucey Switch, in honor of its inventor. One such impact switch is specified in Army Research Lab Specification Control Drawing for Part. No. #11718418, entitled "IMPACT SWITCH." In the specified impact switch, a spring is employed for exerting a selected spring force substantially against a conically shaped electrical contact. Upon impact of the projectile against a target, the spring collapses, thereby allowing the conically shaped electrical contact to electrically connect with a receiving electrical contact to initiate activation of a fuze resulting in detonation of the projectile.

Other factors must also be considered in fuze designs, for example, in many combat round munitions applications, as well as other munitions applications, firing of the projectile must be detected before detonation of the fuze. Firing of the projectile is referred to as the "firing event." In essence, detection of the firing event enables firing event detection electronics to initiate time dependent functions. An apparatus including firing event detection electronics is sometimes referred to as a setback detector.

A firing event setback detector is generally constructed so as to only detect the occurrence of an acceleration along the firing axis. Generally, the firing axis coincides with the longitudinal axis of the projectile since the velocity component along the firing axis increases rapidly from zero velocity before the firing event to a very high velocity after the firing event. In an ideal setback detection mechanism, the setback detector would provide a setback detection signal when the setback force along the firing axis increases above a selected acceleration threshold so as to provide a safety margin against premature detonation of the combat round. At the other extreme, an ideal impact detection mechanism would provide an impact detection signal under any deceleration condition along the firing axis above a selected deceleration threshold, so as to also provide a safety margin to assure detonation upon impact.

By way of further background, U.S. Patent 3,158,705 to Bliss, entitled "Combination Graze and Impact Switch," discloses a combination graze and impact switch. Bliss is directed to a laminated direct impact sensor consisting of electrical conductors of varying thicknesses and materials which are separated by dielectric elements.

European Patent A-0 466 021 discloses an acceleration switch with a snap-action spring primarily directed to an air bag triggering mechanism, not a munitions projectile as is the instant invention.

US-A-3,158,705 relates to a combination graze and impact switch and, more particularly, to a laminated direct impact sensor consisting of electrical conductors of varying thicknesses and materials which are separated by dielectric elements, and inertially operated spring-mass graze sensor.

EP-A-0 466 021 relates to an acceleration switch for closing of at least a pair of electrical contacts by using an inert-mass which acted on a snap-action spring.

SUMMARY OF THE INVENTION

In accordance with the present invention, a discriminating acceleration/deceleration electrical switch assembly is enclosed within a munitions projectile for dosing an electrical circuit path between a pair of electrical contacts upon acceleration/deceleration of the projectile exceeding a selected acceleration/deceleration threshold value. The discriminating acceleration/deceleration electrical switch assembly comprises a switch support having a bore hole therein for holding a spherical mass or ball. A tactile dome switch or snap switch is juxtaposed between an electrical contact assembly and the spherical mass. The electrical contact assembly has a pair of electrically conductive surface regions. The aforesaid components are arranged along the munitions firing axis such that, upon sufficient deceleration along the firing axis, a deceleration force acting on the spherical mass causes the dome switch to deform and make contact with the conductive surface regions thereby providing switch closure. Electrical paths leading from the electrically conductive surface regions are intended to be electrically connected to a detonation control circuit so as to initiate detonation of the munitions upon switch closure.

The snap switch and electrical contact assembly are arranged so as to provide an acceleration switch or setback detection mechanism such that switch closure is made upon the acceleration of the munitions exceeding a selected acceleration threshold.

A pair of dome switches are employed in combination with a pair of electrical contact assemblies and a single spherical mass so as to provide a combined acceleration/deceleration munitions switch assembly.

A pair of dome switches are employed in combination with a pair of electrical contact assemblies so as to provide a combined acceleration/deceleration munitions switch assembly wherein the dome switches dose upon being subjected to a selected threshold level of acceleration or deceleration force, as the case may be.

Other objects and features and advantages of the present invention will become apparent to those skilled in the art through the description of the preferred embodiment, claims and drawings herein wherein like numerals refer to like elements.

BRIEF DESCRIPTION OF THE DRAWINGS

• Figure 1 is a partial cross sectional view of a projectile employing a deceleration switch in accordance with one aspect of the present invention.
• Figure 2 is plan view of one embodiment of a dome switch depicted in Figure 1.
• Figure 3 is side view of the dome switch depicted in Figure 2.
• Figure 4 is a plan view of an electrical surface contact assembly as depicted in Figure 1.
• Figure 5 is a partial cross sectional view of a projectile employing an embodiment of the invention illustrating a combination acceleration and deceleration munitions switch.
• Figure 6 is a plan view of one embodiment of a switch housing as depicted in Figure 1.

DETAILED DESCRIPTION OF THE INVENTION

Illustrated in Figure 1 is a partial cross sectional view of a projectile 10 employing a discriminating deceleration switch constructed in accordance with one aspect of the principles of the invention. The discriminating deceleration switch is generally indicated by numeral designation 20 and is particularly applicable for munitions systems where the projectile is intended to be detonated upon impact with a target.

For exposition purposes, a projectile reference or firing axis 15 is shown. The firing axis 15 is generally aligned with an intended traveling or filing direction of the projectile, commonly the longitudinal axis of the projectile. In one embodiment the firing axis 15 may advantageously extend centrally from nose 12 to tail (not shown). Discriminating deceleration sensing switch 20 is disposed to sense directional motion along the firing axis axis in a manner described below.

Discriminating deceleration sensing switch 20 includes switch housing or switch support means 30 rigidly secured to projectile 10 by mechanical means not shown, but which may induce, among others, threadable engagement, cement, or other techniques for securing switch support means 30 to projectile 10. Switch support means 30 may also be made as an integral part of the projectile. Switch support means 30 includes a central chamber or bore hole 32 having an open end extending from a surface 33 of switch support means 30. In one embodiment of the invention, bore hole 32 is generally a circular hole having a selected bore hole diameter with a central bore hole reference axis passing axially therethrough. The central bore hole reference axis is advantageously aligned with the firing axis 15.

The switch support means 30 also has counter sunk bore holes 37 and 39 concentric with bore hole 32. Counter sunk bore holes 37 and 39 have larger diameters than the diameter of bore hole 32. Counter sunk bore hole 37 has a larger diameter than counter sunk bore hole 39. Counter sunk bore hole 37 is sized to receive an electrical contact assembly 200, and counter sunk bore hole 39 is sized and shaped to receive and hold a tactile dome switch member 100.

Referring now to Figures 2 and 3, further details of tactile dome switch member 100 are illustrated therein. Tactile dome switch member 100 is effectively an electrically conductive disk member having a convex surface 110 and a concave surface 120, opposite convex surface 110. Dome switch member 100 has a central disk reference axis 115 passing centrally through the concave and convex surfaces. In the example shown, dome switch member 100 further includes an optional central dimple 130 extending away from the concave surface 120. It will be understood that the central dimple 130 is not required for operation, although it is desirable in some embodiments of the invention. Dome switch member 100 may advantageously comprise a scalloped disc that further includes a plurality of contact terminals 101, 102, 103 and 104. An example of dome switch member 100 as depicted in Figures 2 and 3 may be provided by Snaptron Inc., Loveland Colorado, identified as F series Tactile Domes. Such domes are constructed of a electrically conductive material and may incorporate anti-oxidizing coatings such as nickel, silver, gold, or the like.

Referring again to Figure 1, an electrical contact assembly 200 is shown affixed to the switch support means 30 within counter bore hole 37 by means, not shown, such as cementing or other means. By way of illustration, electrical contact assembly 200 may be mounted to a support member or substrate 250 which may also serve, in part, as an end cap for enclosing the assembly of dome switch member 100 juxtaposed between mass 40 and electrical contact assembly 200. In one useful embodiment, mass 40 may be a spherical mass such as a ball bearing or the like. However, the mass need not be spherical. Any appropriate mass may be used so long as it is of sufficient size and shape to snap over the dome switch at the selected threshold force. For some applications the use of a mass is not even necessary because the dome switch, if suitably selected, will snap over when subjected to the acceleration or deceleration force at the selected threshold.

Referring now to Figure 4, the electrical contact assembly 200 is illustrated in more detail. The electrical contact assembly 200 may advantageously be an electrical conductor arrangement including a centrally located first electrically conductive surface region 212. The first electrically conductive surface region 212 has a contact reference axis 205 passing perpendicularly through the center (as best shown in Figure 1). Electrically isolated from electrically conductive surface region 212 is a plurality of electrically conductive surface regions 213, 214, 215, and 216. The plurality of electrically conductive surface regions 213, 214, 215, and 216 are electrically connected in common by an electrical conductor 210.

Referring now to Figure 6, one example of switch housing 30 is shown. The switch housing 30 includes a plurality of recesses 301, 302, 303 and 304 that are suitably sized and shaped to loosely receive terminals 101-104 respectively so as not to restrict the axial movement of the dome switch. When assembled, dome switch member is seated within the plurality of recesses so as to prevent rotation of dome member 30 within the projectile, thereby assuring alignment of the dome switch terminals 101-104 with the plurality of electrically conductive surface regions 213, 214, 215, and 216.

As illustrated in Figure 4, electrical contact assembly 200 may be a flexible circuit board or equivalent apparatus. The electrical conductor 212 may be advantageously configured so as to include an isolated region 229 around a soldering pad 224 that is integral to electrical conductor 212. A non-conductive coating may be deposited over electrical conductor 210 in a manner so as to leave electrically conductive surface regions 212, 213, 214, 215, and 216 exposed. Electrically conductive pads 222 and 224 may also be provided for electrically connecting electrically conductive paths 43 and 45 to electrically conductive surface region 212 and electrically conductive surface region 216, respectively.

The exemplary arrangement of electrical contact assembly 200 depicted in Figure 4 may also be provided by a wide array of equivalent schemes and techniques well known in the art. Examples of such schemes may be the employment of standard printed wiring boards, flexible wiring harnesses, hybrid circuit substrates, and the like, all of which are intended to be with in the scope and spirit of the present invention, the details of which are well known to the artisan. It should be noted that the exposed electrically conductive surface regions of the electrical surface contact assembly 200 may incorporate particular anti-oxidizing coatings, for example plate tin-lead fuzed, palladium, platinum, gold, and the like.

The structural configuration of the components of the discriminating deceleration switch 20 in accordance with the present invention will now be described. It will be understood that the following description is solely for illustrative purposes and the invention is not so limited. Since bore hole 32 and counter sunk bore holes 37 and 39 are concentric, the projectile reference axis or firing axis 15 will be aligned with the central bore hole reference axis, central disk reference axis 115, and the contact reference axis 205. The depth of bore hole 32, and counter-bore holes 37 and 39 are such that, at rest, mass 40 may rest within bore hole 32, with dome switch member 100 resting in counter-bore hole 39, and the central portion of convex surface 110 of dome switch member 100 in close proximity to the extremity of mass 40. Furthermore, with electrical contact assembly 200 secured within bore hole 37, the concave extremities forming the plurality of terminal legs of the dome switch member 100 contact the plurality of electrical contact regions 213-216 of electrical contact assembly 200 with dimple 130, if present, being aligned with electrically conductive surface region 212.

The arrangement as described above operates such that, if a force acts on mass 40 from left to right, as illustrated in Figure 1, tactile dome switch member 100 is depressed so as to make electrical contact with electrically conductive surface region 212. The plurality of contact terminals 101-104 are each positioned to be in electrical contact with one of the electrically conductive surface regions 213-216. Accordingly an electrically conductive path is provided between electrically conductive paths 43 and 45 by the switch closure between the electrically conductive surface regions.

Electrically conductive paths 43 and 45 are intended to be electrically coupled to a munitions detonation control system that is responsive to a detection of the switch closure as aforesaid. In this manner, detection of the switch closure will produce detonation of the projectile 10.

In one exemplary embodiment of the invention, the dome switch member 100 has a diameter in the range of 5 mm to 20 mm. The size of mass 40 is, of course, dependent upon the trip or deformation force of the tactile dome switch. Useful trip forces are generally in the order of several hundred newtons.

In one exemplary embodiment, deceleration switch closure was made when the deceleration exceeded a threshold of about 300g's for a ball mass of about 0.5 grams and a deformation force of about 150 grams for the tactile dome switch. For the same dome switch, acceleration switch closure (setback detection) was made when the acceleration exceeded a threshold of about 19,000 g's. There are, of course, a wide variation of dome switch deformation forces, and ball diameters that will perform in a manner as intended, all of which are within the true spirit and scope of the present invention.

Figure 5 illustrates an alternate embodiment of the present invention that functions as a setback detection mechanism employing a tactile dome switch member 500, similar to tactile dome switch member 100. In Figure 5 like components as those in Figure 1 have the same reference numeral. A double sided electrical contact assembly 520 is substituted for the electrical contact assembly 200 of Figure 1. The double sided electrical contact assembly 520 provides substantially similar and separate electrical conductor arrangements as the one already described with reference to the electrical contact assembly 200 illustrated in Figure 4.

An end cap 550 is secured to switch housing 30. The end cap 550 includes an outer diameter that, in some examples, may have about the same size as the diameter of bore hole 37. Of course, the end cap diameter is not so limited and may be designed using alternative sizes and shapes to accommodate the end cap function. The end cap 550 also has an inner bore hole with the same diameter as counter bore hole 39. The end cap 550 is shaped for holding in place tactile dome switch member 500 in similar alignment as tactile dome switch 100. However, in contrast to the arrangement of Figure 1, dome switch member 500 is in mirror arrangement relative to dome switch member 100. Additional electrically conductive paths 543 and 545 are provided so as to provide electrical connection to electrical surface regions 512 and 513, respectively, similar to electrically conductive paths 43 and 45 that are electrically connected to electrically conductive surface regions 212 and 213, respectively.

The arrangement and combination of dome switch member 500 and double sided electrical contact assembly 520 operates to provide a setback detector for munitions projectile 10. In operation, upon an acceleration of projectile 10 of sufficient magnitude to the right and along projectile reference axis 15, tactile dome switch member 500 will deform to make electrical contact with electrically conductive surface region 512. As is the case described above with reference to Figure 1, the scalloped terminals of dome switch member 500 are positioned to be in electrical contact with one or more of electrically conductive surface regions generally indicated by numeral 513. Thus, switch closure occurs as soon as the switch member 500 comes into electrical contact with the electrically conductive surface region 512 and a short circuit is provided between electrically conductive paths 543 and 545.

It should be noted that the munitions setback mechanism, namely the acceleration sensing switch as just described, may be employed independently of the deceleration sensing switch mechanism. That is, only dome switch member 500 and a single sided electrical conductor arrangement of electrically conductive surface region 512 and regions 513 are required to be mounted to a support means 30 and coupled to the munitions projectile 10. The embodiment described in Figure 5 is compact and alternate arrangements may be used in other applications where compactness of design is not required. Such examples may include, for example, a design employing separate electrical contact assemblies associated with each dome switch. Further, it will be appreciated that, for some alternate applications, dome switch member 500 may also double as a crush switch mechanism upon impact as well as an acceleration switch. In such a dual use, an impact pin or other device may be positioned in the nose, for example, to crush dome switch member 500 upon impact.

The present invention provides, either separately or in combination, a reliable electro-mechanical method of setback and deceleration detection to closely approximate both an ideal impact detection mechanism and an ideal setback detection mechanism. The deceleration and setback detection mechanisms may incorporate inexpensive stainless steel snap domes as switches as described. Upon setback, for example, caused by acceleration in excess of a selected acceleration threshold, dome switch member 500 in figure 5 snaps over to short circuit the pair of contacts provided by one electrical conductor arrangement of electrical surface contact assembly 500. One example of such an electrical conductor arrangement is illustrated in figures 1, 4 and 5 as a conductive layer of a two sided printed wiring board. In operation, impacts, even grazing impacts, with deceleration forces in excess of the detection threshold causes dome switch member 100, in combination with the mass enhancing weight of mass 40, to snap over.

The sensing switch assembly of the present invention offers other advantages over the prior art due to the bifurcated or scalloped design of the dome switch. Because of the scalloped shape, all of the switch contacts of the electrical contact assembly 200 may be printed on the same surface, thus eliminating the need for troublesome vias (i.e. plated through holes for providing a conductive path from one layer to another in a printed circuit assembly). The sensing switch has operated to provide a sensing signal in about 25 microseconds. This performance represents an improvement in accuracy of an order of magnitude over the prior art.

It should be recognized by those skilled in the art that the acceleration. deceleration sensing switch assemblies described in accordance with the preset invention may be made very small as compared to current techniques. Deformation of the dome switch is only affected by forces generally perpendicular to the central surface thereof which are intended to be aligned perpendicular to the firing axis of the munitions. Therefore the acceleration/deceleration switch assembly in accordance with the present invention are not appreciably affected by spin or non-spin dependencies as may affect other switch techniques commonly know in the munitions art. Furthermore, because of elegant simplicity of design, the acceleration/deceleration sensing switch assembles of the present invention are relatively inexpensive to build, highly reliable, and so versatile so as to be employable over a wide range of combat rounds from very small to very large, from smooth bore to rifled.