Ammunition and explosives – Igniting devices and systems – Arming devices
Reexamination Certificate
1998-09-22
2001-03-06
Tudor, Harold J. (Department: 3641)
Ammunition and explosives
Igniting devices and systems
Arming devices
C102S200000, C102S206000, C102S211000, C102S247000, C089S006500
Reexamination Certificate
active
06196130
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to a fuze device for an explosive projectile, and more particularly to a second environment sensor apparatus for detecting the exit of the projectile from the muzzle subsequent to firing in order to maintain fuze system safety and for initiating the timing for subsequent fuze functions.
BACKGROUND OF THE INVENTION
A safety and arming device is a required element of a munition to ensure that the munition is not armed and detonated until the desired time. The safety and arming device (S & A) is part of a munition's fuze and prevents arming of the fuze until certain conditions are met.
Many safety and arming devices require two environments or occurrences for operation and initiation of the fuze. The environments are two independent physical events which must be sensed by the projectile or munition prior to allowing arming. The first environment utilized is usually setback, which is both easily sensed and well known in the art. For example, commonly assigned patent U.S. Pat. No. 5,693,906 describes a first environment sensing device which utilizes setback. The second environment can be based on a number of different parameters such as timing, barrel escape, turns counting, etc. In addition, various techniques for determining muzzle or bore exit are known. For example, commonly assigned patents U.S. Pat. No. 5,497,704 and U.S. Pat. No. 5,265,539 both utilize magnetic sensors to determine muzzle exit. Commonly assigned patent U.S. Pat. No. 5,275,107 determines muzzle exit based on setback acceleration going to zero. The entire contents of commonly owned patents U.S. Pat. Nos. 5,693,906, 5,497,704, 5,265,539 and 5,275,107 are hereby incorporated by reference.
All of these prior art techniques for determining the second environment of muzzle exit require additional circuitry, which adds to the complexity of the device. What is needed is a technique for determining the second environment of muzzle exit with the circuitry which is already included in the munition.
SUMMARY OF THE INVENTION
Applicant has discovered an inventive technique for determining the second environment of muzzle exit, which utilizes existing circuitry on a munition. In particular applicant has discovered a technique for utilizing an inventive proximity sensor to also sense muzzle exit.
The inventive environment sensor apparatus includes an electrostatic sensor carried by the projectile. The electrostatic sensor has first and second electrical conducting areas separated by a dielectric material to form two plates of a capacitor. The first electrical conducting area is conductively connected to a current-to-voltage converter and the second electrical conducting area is conductively connected to the outside projectile body surface. A time changing electric field surrounding the projectile causes a time changing current to flow within the electrostatic sensor, which is converted to a time changing voltage by the current-to-voltage converter. A threshold detector device is conductively connected to an output of the current-to-voltage converter and provides a voltage signal to the safe and arm mechanism when the time changing voltage signal from the current-to-voltage converter exceeds a predetermined level, to indicate that a change has occurred in the sensed environment.
Applicant is the owner of Ser. No. 08/668690 filed Jun. 24, 1996, now issued as U.S. Pat. No. 6,094,054 on Jul. 25, 2000, and entitled “Radome Nose Cone Probe Apparatus For Use With Electrostatic Sensor”, the entire contents of which are hereby incorporated by reference. In working with this invention, which utilizes an electrostatic sensor as a proximity detector, applicant discovered a sharp voltage spike associated with the projectile exit from the muzzle. At first this voltage spike was thought to be merely “noise”. However, after investigation, Applicant discovered that this voltage spike was caused by the ionized gas “blow-by” associated with the projectile exiting the muzzle. The ionized gas “blow-by” creates an electric field which results in a voltage which when it exceeds a predetermined threshold indicates muzzle exit.
The use of the electrostatic sensor to detect the second environment condition of muzzle exit provides some advantages in that the electrostatic sensor is already used for proximity sensing. Therefore, the use of the electrostatic sensor to perform another function saves in cost and weight and reduces complexity which provides for a more reliable device.
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Ceola Kenneth D.
Crist Scott D.
Alliant Techsystems Inc.
Tudor Harold J.
Vidas Arrett & Steinkraus P.A.
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