Ammunition and explosives – Igniting devices and systems – Ignition or detonation circuit
Reexamination Certificate
1998-12-18
2001-04-24
Carone, Michael J. (Department: 3641)
Ammunition and explosives
Igniting devices and systems
Ignition or detonation circuit
C102S202500, C102S202900, C102S218000, C102S200000
Reexamination Certificate
active
06220165
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to pyrotechnic squibs and, particularly, to a pyrotechnic squib having an improved bridgewire circuit that addresses both all-fire and no-fire requirements.
In an electrically controlled explosive system, including a pyrotechnic system, an electro-explosive device translates an electrical signal into a pyrotechnic signal for selectively beginning the detonation of an explosive material. Depending on the particular industry in which they are used, such devices are referred to by various names including squibs, initiators, ignitors and electric matches. Moreover, the pyrotechnic signals provided by the devices may take several forms (e.g., gas pressure, a flame front or a shock wave) depending on the particular use. As used herein, the term “squibs” refers to electro-explosive devices collectively.
A conventional squib includes a bridgewire that heats up in response to an electrical current. In turn, the heat generated by the bridgewire initiates detonation. The bridgewire is a resistive component, such as a wire or filament, coated or otherwise in contact with a flammable or explosive composition. This pyrotechnic composition is typically the first in a sequence of compositions of decreasing sensitivity, increasing mass and increasing energy (i.e., a pyrotechnic or explosive train). Typically, the bridgewire components are enclosed in a metal, plastic, or paper housing for maintaining the proper juxtaposition of the components. The housing also protects the pyrotechnic composition from humidity and other environmental effects. A squib operates when the current heats the bridgewire until it reaches a temperature high enough to start a chemical reaction (e.g., burning or exploding) in the first composition of the pyrotechnic train. It is to be understood that the bridgewire need not be in the actual form of a wire and may be a metal, an alloy (e.g., nichrome or tungsten) or another conducting material (e.g., semiconductor).
One shortcoming of presently available squibs is their inability to simultaneously meet fairly precise all-fire and no-fire specifications. All-fire requirements specify a minimum current and duration at which all squibs of a particular design are expected to fire (i.e., ignite to begin detonation). On the other hand, no-fire requirements specify a maximum current and duration that can be applied to the particular squibs without causing them to activate. A squib is needed that is sensitive enough to meet the former all-fire requirements but insensitive enough to meet the latter no-fire requirements. The problem is complicated by the fact that the response of a conventional squib varies with temperature, pressure, acceleration and other environmental factors. Presently available squibs can be, for example, sufficiently sensitive to meet all-fire specifications at a minimum required operating temperature but too sensitive to meet no-fire specifications at a maximum operating temperature.
Squibs are useful in ignitors, pin pullers, pin pushers, wire cutters, exploding nuts, explosive bolts, detonators, explosive bolts, rocket motors, gas generators, thermal batteries, signal flares, safe-and-arm apparatus, pressure cartridges, pyro switches, pyro valves, bellows actuators, piston actuators, perforators, air bag inflators, seat belt tensioners, and the like.
SUMMARY OF THE INVENTION
The invention meets the above needs and overcomes the deficiencies of the prior art by providing a bridgewire circuit that improves the all-fire
o-fire characteristics of a squib. Among the objects and features of the present invention may be noted the provision of an improved bridgewire circuit that limits the current through the bridgewire to a relatively small fraction of the squib input current when the input current is below a desired firing current level and passes substantially all of the input current through the bridgewire when it is above the desired firing current level; the provision of such a bridgewire circuit that determines whether the desired firing current level has been reached; the provision of such a bridgewire circuit that permits squibs to have more precise no-fire and all-fire characteristics over a wider temperature range than conventional squibs; the provision of such a bridgewire circuit that permits squibs to have improved speed and reliability; the provision of such a bridgewire circuit that permits squibs to have improved performance at low temperatures; the provision of such a bridgewire circuit that is compatible with conventional squib firing circuitry; the provision of such a bridgewire circuit that permits continuity testing of the bridgewire; and the provision of such a bridgewire circuit that is economically feasible and commercially practical.
Briefly described, an electrical system embodying aspects of the invention is for use with an electro-explosive device. The system includes a heating element and an input circuit supplied by a power supply for providing an electrical input to the system. The system also includes a load control circuit receiving and responsive to the electrical input for energizing the heating element. The heating element selectively causes ignition of the electro-explosive device when its level of energization reaches a firing level. The load control circuit substantially limits current in the heating element when the electrical input is less than a predetermined threshold. This maintains energization of the heating element at a level less than the firing level to prevent the ignition of the electro-explosive device. In contrast, the load control circuit applies substantially all of the electrical input to the heating element when the electrical input is greater than the predetermined threshold. This maintains energization of the heating element at a level greater than the firing level to cause the ignition of the electro-explosive device.
Another form of the invention is directed to a component of an electro-explosive system. The component includes an explosive material and a heating element for causing ignition of the explosive material. An input circuit supplied by a power supply provides an electrical input to the component. The component also includes a load control circuit receiving and responsive to the electrical input for energizing the heating element. The heating element selectively causes ignition of the explosive material when its level of energization reaches a firing level. The load control circuit substantially limits current in the heating element when the electrical input is less than a predetermined threshold. This maintains energization of the heating element at a level less than the firing level to prevent the ignition of the explosive material. In contrast, the load control circuit applies substantially all of the electrical input to the heating element when the electrical input is greater than the predetermined threshold. This maintains energization of the heating element at a level greater than the firing level to cause the ignition of the explosive material. Further, the component includes a housing for the explosive material, heating element, input circuit and load control circuit.
In yet another form of the invention, an electrical system is for use with an electro-explosive device. The system includes an input circuit for providing an electrical input to the system in response to a signal supplied by a power supply. A semiconductor device is connected to the input circuit for causing ignition of the electro-explosive device. The semiconductor device heats in response to the electrical input for selectively causing the ignition of the electro-explosive device when the electrical input applied to the device exceeds a firing level. The system also includes a load control circuit, which includes the semiconductor device, connected to the input circuit for controlling the electrical input.
Yet another form of the invention is directed to a method of testing continuity of a bridgewire in an electro-explosive device. The method includes the st
Carone Michael J.
Samunegus Lulit
Senniger Powers Leavitt & Roedel
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