Arm and safety switch

Details Arm and safety switch Arm and safety switch

2003-08-08

2004-05-25

Friedhofer, Michael A. (Department: 2832)

Electricity: circuit makers and breakers

Fluid pressure

Diaphragm

C200S0830SA

Reexamination Certificate

active

06740828

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to pressure responsive, electrical switches; and more particularly to an arming and safety switch within an ammunition round that arms the projectile's explosive payload upon sensing a predetermined pressure from the projectile's propellant, but will not arm the projectile if a misfire occurs.
2. Description of the Prior Art
Safety devices and arming devices have been utilized on ammunition to prevent inadvertent detonations. For example, projectiles such as grenades, rockets, large caliber ordnance, and aircraft carried bombs have utilized various arming mechanisms. These arming mechanisms are adapted to arm the explosive device upon sensing appropriate accelerations and decelerations that are characteristic of launch and impact with an intended target.
Some safe and arm devices are purely mechanical in nature, relying upon centrifugal effects of the spinning projectile. Typical safe and arm mechanical devices are disclosed by U.S. Pat. Nos. 3,742,854; 4,796,532; and 4,869,172. Other safe and arm devices have been designed to electronically sense launch, velocity, and impact, and in so doing, arm and detonate the main explosive charge. U.S. Pat. No. 3,359,904 to Nerheim, discloses a fuze, which utilizes a piezoelectric crystal compressed by the set back forces on launch to produce a charge, which is stored in a capacitor. Upon impact, a second piezoelectric crystal is compressed. A charge is thereby generated to actuate an electronic switch, thereby discharging the capacitor, which had been previously charged upon launch.
Another electronic device, described in U.S. Pat. No. 3,653,324 to Ferlani et al, utilizes two transducers to sense a peculiar signature, which results from a projectile launch. The first transducer is a set back sensing piezoelectric crystal and the second is a barrel exit sensing transducer. Upon receipt of a signal proportional to the correct launch acceleration followed by a signal representative of barrel exit, a switch is closed to actuate a separate arming device.
U.S. Pat. No. 3,808,975, discloses a piezoelectric crystal powered fuze circuit using a pair of back to back piezoelectric crystal cells. The cells develop a potential upon acceleration of the projectile and then develop a reverse potential upon relaxation of the acceleration when the projectile emerges from the firing weapon. Thus, the piezoelectric cells sense projectile launch and muzzle exit to arm the device. A third piezoelectric cell or element is utilized to sense impact and detonate the device.
U.S. Pat. No. 3,850,102, to Mauro discloses a single piezoelectric crystal, which is adapted to perform three functions. First, the crystal is compressed in one direction by the set back force of launch to produce a first voltage signal. During flight it senses the air impinging upon the launched projectile, thus generating a second lower voltage signal. Finally, it is compressed in the opposite direction upon impact to trigger the projectile detonation.
U.S. Pat. No. 3,967,555 issued To Gollick et al discloses a battery operated piezoelectric fuze, which has a piezoelectric element to convert the mechanical shock of impact and into a detonator ignition signal. An arrangement of two diodes and a thyristor prevent detonator actuation if the shock wave produced upon impingement of the fuze is less than a threshold value. The arrangement operates to prevent unintended ignition. It also provides ignition without there having been a response by the piezoelectric element, such as upon impact. In this case, the piezoelectric element merely controls the switch between the battery power supply and the detonator.
In U.S. Pat. No. 4,723,087, a piezoelectric polymer ring is utilized to sense impact at virtually any angle and generate a voltage to ignite the detonating charge.
Another device, disclosed in U.S. Pat. No. 4,739,705 to Hudson et al, requires power from a missile battery. The accelerations of the missile due to an expulsion motor and a boost motor are sensed. In addition, Hall sensors are utilized in conjunction with an inertial wheel to provide a signal proportional to velocity and distance. After a predetermined distance, the signal causes the detonator to be armed and aligned with the warhead stem.
Another example in which a piezoelectric crystal is used is disclosed in U.S. Pat. No. 4,848,234 to Farace et al. In this patent, a piezoelectric crystal is utilized to sense the spin rate of a projectile.
Snap-action pressure and electrical switches are known in the literature.
U.S. Pat. No. 3,330,925 to Andrew et al. discloses a snap-acting pressure switch. When fluid pressure exceeds a particular threshold value, the electrical switch snaps from a first electrical condition to a second electrical condition. Closure is accomplished by the snap action movement of a double diaphragm snap-acting cartridge, supported by a spring. U.S. Pat. No. 3,436,502 to Egli discloses an electric pressure-control snap switch. A snap-action diaphragm switch for controlling pressure of liquids or gases has at least one contact spring, controlled by the pressure-activated diaphragm through an intermediate lever. The diaphragm is acted upon by an adjusting spring as well as by a compensating spring that acts in a different direction to produce superimposed torques.
U.S. Pat. No. 3,573,410 to Budzich discloses a snap action pressure sensitive switch with snap disc resiliently supported between legs of a terminal. One switch contact is supported by an elongated bi-stable snap element and the snap element is mounted on cantilever springs. The snap element bends in single mode urging ends of the snap element to come together. While U.S. Pat. No. 4,214,137 to Hartley discloses a pressure switch with snap element. A pressure switch has a housing and a first contact mounted in it. A pressure responsive member is mounted in the housing for moving a second contact into and out of engagement with the first contact. U.S. Pat. No. 4,330,695 to Poling discloses a control device. This control device has a snap-action member that operates a switch device switching from one conductive mode to the other. An actuator between the snap-action member and the switch device, and a spring are provided and methods of assembly are described.
While some of the foregoing references arm the projectile and others disclose snap-action switch members, they neither address nor solve a serious problem, namely, the event of a projectile misfire. A misfire may result in the projectile having insufficient velocity to exit a safe zone around the launcher and cause the projectile to inadvertently fall on friendly forces. There remains a need in the art for a reliable, inexpensive switch system that senses a successful projectile launch and discriminates between successful and unsuccessful launches in the arming of an ammunition round.
SUMMARY OF THE INVENTION
The invention provides an arm and safety switch for an ammunition round such as a 120 mm multipurpose tank round. The switch senses launch detonation pressure. Advantageously, the switch will not arm the projectile if the pressure detected is less than or equal to a first predetermined pressure characteristic of a misfire; but will arm the projectile if the detected pressure is greater than the first predetermined pressure and less than or equal to a second predetermined pressure characteristic of a successful launch. The invention further provides a method for arming ammunition rounds by detecting launch detonation pressure and using that information to arm or not arm the projectile.
Generally stated, the switch has a housing with an open first end and an open second end. A diaphragm covers the open first end of the housing. An actuator has a first and second end. The first end of the actuator is positioned perpendicular to the diaphragm and is located at a first predefined distance therefrom. An electrically conductive pad is fixed to the second end of the actuator. A first firing pin points at the elect

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