Ammunition and explosives – Igniting devices and systems – Accidental fuse ignition prevention means
Reexamination Certificate
2000-08-30
2003-05-06
Tudor, Harold J. (Department: 3641)
Ammunition and explosives
Igniting devices and systems
Accidental fuse ignition prevention means
C102S202700, C102S202900, C102S202140, C361S247000
Reexamination Certificate
active
06557474
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to initiating devices for combustible materials and, more particularly, to initiator headers used to initiate the detonation of propellants, pyrotechnics, explosive materials and the like.
A wide variety of devices are used to detonate or ignite explosives and pyrotechnic materials.
One type of device commonly referred to as an initiator header, generally includes one or more conductive pins, surrounded by an insulating layer. The one or more conductive pins generally terminate at a thin bridge wire disposed along a top surface of the insulating layer. When an electric current is passed through one of the conductive pins, the current passes through the bridge wire which rapidly heats due to its electrical resistance. The heat generated by the bridge wire ignites a propellant which, in turn, ignites a gas-generating composition. Combustion of the gas-generating composition results in the production of a gas which may be used to perform a task such as inflating an automobile air bag or ejecting a pilot from a combat aircraft.
For many years, automobile manufacturers have used initiator headers as part of automobile air bag safety systems, such as those described in U.S. Pat. Nos. 3,723,205 and 4,981,534. As is well known to those skilled in the art, air bag systems are designed to rapidly inflate sealed bags with an inflatable gas when a sensor detects an automobile collision. Due to the nature of their use, air bag systems may never be used or may remain idle for many years. Despite these extended periods of inactivity, air bag systems must operate properly when they are needed. Of equal importance is the fact that air bag systems must not inadvertently deploy, a highly undesirable event that could result in death or severe injury.
There have been many efforts directed to producing low cost and easily assembled initiator headers. For example, U.S. Pat. Nos. 5,230,287 and 5,431,101 to Arrell, Jr. et al. disclose an electronically-activated initiator formed by welding a hollow cap containing an explosive material to an initiator header. The outer diameter of the initiator header slightly exceeds the inner diameter of the hollow cap so that, as the two are joined together, the header and cap form a reliable, weldable joint.
U.S. Pat. No. 5,243,492 to Marquit et al. discloses a process for making an initiator device having a centrally located conductive pin.. The pin can be electrically connected to an outer portion of the device via a bridge wire, thereby forming a device that is particularly useful for igniting a gas-generating composition in an air bag safety system.
U.S. Pat. No. 5,793,476 to Bailey discloses an electronically activated initiator header for an air bag inflator. The initiator header is ignitable by thermal energy from a resistive element formed on a semiconductor substrate. The semiconductor substrate is secured to the initiator header by a glass-to-metal seal.
In spite of the above-mentioned improvements in initiator devices, there remains a need for a reliable initiator header which is inexpensive, has fewer parts, and is easier to assemble.
SUMMARY OF THE INVENTION
In accordance with certain preferred embodiments of the present invention, an initiator header subassembly includes an electrically conductive grounding tab having an outer perimeter. The grounding tab is preferably made of a conductive material, such as metal. In highly preferred embodiments, the grounding tab is made of an alloyed metal, such as the alloyed metal commonly sold under the trademark KOVAR®. The grounding tab may comprise a substantially flat plate having a top surface, a bottom surface and two holes extending between the top and bottom surfaces. In certain preferred embodiments, the grounding tabs are produced by first punching or stamping a plurality of coin-like grounding tabs from a sheet of conductive material. The conductive material may include a metal such as KOVAR® alloyed metal. Each grounding tab is then further processed to form the two holes extending between the top and bottom surfaces thereof. In certain preferred embodiments, a first one of the two grounding tab holes has a first diameter and a second one of the two grounding tab holes has a second diameter that is greater than the diameter of the first grounding tab. The entire process of producing the grounding tabs and then producing the holes extending therethrough may be done using a machine tool which punches or stamps the structure.
The initiator header subassembly of the present invention also desirably includes a mass of an insulating material that is secured atop the top surface of the grounding tab. The mass of an insulating material preferably has a top surface, a bottom surface and a sidewall extending between the top and bottom surfaces. After the mass of an insulating material has been secured to the grounding tab, the sidewall of the insulating mass is preferably in substantial alignment with the outer perimeter of the grounding tab. In other embodiments, the sidewall of the insulating mass defines the outer perimeter of the initiator head subassembly.
The mass of an insulating material may be an insulating disc preform having two longitudinal openings extending from the top surface to the bottom surface of the insulating disc. The two longitudinal openings desirably have a substantially similar diameter. As used herein, the term “insulating disc preform” means that a plurality of insulating discs may be mass-produced and stored for later use during final assembly of initiator headers. As such, each of the insulating disc preforms may be substantially similar in shape, composition and appearance so that the insulating discs are interchangeable with one another. In certain preferred embodiments, the insulating disc is an all-glass insulating disc having a relatively high hardness rating capable of withstanding up to 20,000 psi or more. The insulating disc may be made of such glasses as borosilicate glass.
The initiator header subassembly may also include a pair of electrically conductive pins extending completely through the grounding tab and the insulating disc. The conductive pins preferably pass through the respective first and second holes of the grounding tab. In certain embodiments, a first one of the electrically conductive pins is attached to and electrically interconnected with the grounding tab and a second one of the electrically conductive pins is electrically isolated from grounding tab. The electrically conductive pins may be made by cutting sections of wire, having a predetermined length from a spool of metal wire, such as KOVAR® alloyed metal. After a plurality of such predetermined lengths have been cut from the spool, the pins are placed in a tumbler which rounds off the ends of the pins. The pins may also be machine tooled to round off the ends.
A fixture may be used for assembling one or more of the above-described initiator header subassemblies. On the other hand, the outer diameter of the electrically conductive pins closely matches the inner diameter of the two longitudinal openings extending through the insulating disc. The fixture preferably holds all of the components of the initiator assembly in proper orientation relative to one another during the assembly process. This may be accomplished by matching the diameter of the outer surface of the first pin with the diameter of the first hole through the grounding tab, while the second grounding tab hole has a greater diameter than the first hole. In certain preferred embodiments, the fixture includes a lower member having one or more cavities for receiving the various components of the initiator header subassembly and an upper member or cap that is securable atop the lower fixture member. In one particularly preferred assembly method, the electrically conductive pins are cut to predetermined lengths as described above. The pins are then exposed to a chemical etchant that roughens or pits the outer surface of the pins. Although the present invention is not limited by any pa
Ferraid Richard L.
Morte Caesar B.
Glasseal Products
Lerner David Littenberg Krumholz & Mentlik LLP
Tudor Harold J.
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