Programmable Fuze for Projectiles

In all prior art fuzes, each fuze is constructed to operate in a single mode, i.e., proximity, impact, etc. In almost all projectile fuzes, safing and arming mechanisms are utilized and, in some instances, short circuit connections, or links, are utilized to prevent premature firing. Such a short circuit connection is described in U.S. Pat. No. 4,062,290, entitled "Electrical Fuze For Projectiles" and issued Dec. 13, 1977. Also, direct contact fuze setters, inductive fuze setters and RF fuze setters are utilized. However, none of these features are utilized to provide a plural mode, remotely programmable fuze.

The present invention pertains to a programmable fuze for projectiles wherein the fuze includes electronic circuitry for providing first and second modes of operation and a fusible electrically conducting link is provided in conjunction with the electronic circuitry for placing the fuze in a first mode of operation when the link is ruptured prior to firing of the projectile and in a second mode of operation when the link is ruptured within a predetermined time period subsequent to firing of the projectile.

It is an object of the present invention to provide a new and improved programmable fuze for projectiles.

It is a further object of the present invention to provide a new and improved programmable fuze for projectiles which is remotely programmable.

It is a further object of the present invention to provide a programmable fuze for projectiles having a fusible link therein and electronic circuitry for sensing the rupture of the link to set the fuze to a first mode of operation when the link is ruptured prior to firing of the projectile and to a second mode of operation when the link is ruptured within a predetermined time period subsequent to the firing of the projectile.

These and other objects of this invention will become apparent to those skilled in the art upon consideration of the accompanying specification, claims and drawings.

Referring to the drawings, wherein like characters indicate like parts throughout the Figures:

FIG. 1 is a sectional view of a fuze and projectile incorporating the present invention and situated in a gun barrel in firing position, portions thereof broken away;

FIG. 2 is a schematic block diagram of electronic circuitry located in the fuze of FIG. 1 and embodying the present invention; and

FIG. 3 is a temperature versus time graph approximating the aeroheating of the fuze subsequent to firing of the projectile; and

FIG. 4 illustrates two approximate voltage waveforms present in the circuitry illustrated schematically in FIG. 2.

Referring specifically to FIG. 1, the numeral 10 indicates a barrel designed to fire a projectile, generally designated 11. The projectile 11 has a fuze 12 affixed to the forward end thereof, which fuze is programmable in accordance with the present invention. The fuze 12 includes a body portion 13 containing the electronics and other operating portions of the fuze, which do not form a portion of this invention and will not be explained herein, and a forwardly projecting antenna 15 encapsulated in a nonconducting material 16 which provides the fuze 12 with the proper contours without affecting the operation of the antenna 15. A fusible link 20 is affixed to the outer surface of the material 16 and connected between the antenna 15 and the body 13 to short the antenna 15 and alter the loading effect thereof while the link 20 is intact.

Referring to FIG. 2, the electronics associated with the antenna 15 and the fusible link 20 are illustrated schematically. In FIG. 2, the fusible link 20 is schematically shown as a normally closed single pole switch having one contact grounded, or attached to the body 13, and the other contact coupled to the antenna 15. The antenna 15 is coupled to an input/output of an RF power divider 25. A second input of the divider 25 is connected to an output of an RF oscillator 30. The RF oscillator 30 receives power from a source (not shown) on a terminal 33. It should be understood that the oscillator 30 and divider 25 are shown in greatly simplified block form since they do not actually form a part of this invention and are only included for purposes of this explanation. The purpose of the divider 25 is to convey most of the power from the oscillator 30 to the antenna 15 for transmission and to convey a portion of the power of the oscillator 30 to an output of the divider for use as a local oscillator signal. The output of the divider 25 is applied to a mixer 26, which may be for example a diode. While a variety of RF configurations might be utilized, the present embodiment is illustrated for its simplicity. The terminal 33 is adapted to receive a positive voltage from the source that supplies voltage to the remainder of the electronics for the fuze 12, which generally consists of a battery that is activated after set back and spin (or firing) of the projectile 11. Voltage sources of this type are well known in the art and will not be described in detail herein.

The output of the mixer 26 is connected through a coupling or DC blocking capacitor 35 to an amplifier 38. The output of the amplifier 38 is connected to the anode of diode means 39 (this may be one or more diodes connected in series, depending upon the amount of voltage drop or threshold required), the cathode of which is connected through a resistor 40 to ground. The cathode of diode 39 is also connected to the base of an N-P-N type transistor 41, the emitter of which is connected to ground and the collector of which is connected through a resistor 44 to the positive voltage terminal 33. The collector of the transistor 41 is also connected to the input of a binary element, such as flip-flop 43. The diode means 39, resistors 40 and 44 and transistor 41 form a threshold detector for sensing a change in the DC voltage at the output of the amplifier 38. A timer 45, which is activated by the application of a voltage (such as the battery described above) to a terminal 46, supplies a signal to the reset terminal of the flip-flop 43. The timer 45 also supplies a signal for a predetermined interval, subsequent to firing of the projectile 11, to a pair of coincidence gates 48 and 49. One output of the flip-flop 43 is connected to a second input of the coincidence gate 48 and a second output of the flip-flop 43 is connected to a second input of the coincidence gate 49.

In the operation of the circuit of FIG. 2, when the link 20 is intact (shorting antenna 15) the antenna 15 is mismatched and reflects most of the power applied thereto back through the divider 25 to the mixer 26. The mixer half-wave rectifies the RF signal and provides a high DC signal which is blocked by the capacitor 35. The link 20 can be fused or ruptured prior to firing of the projectile 11 by forced heating (such as from a prior fired projectile) or by use of a heating element, such as illustrated in FIG. 1. The heating element of FIG. 1 consists of a plurality of loops of wire 50 fixedly positioned in the barrel 10 and energized by means of a voltage source 51 connected through an external switch 52. The coils 50 are positioned so as to be adjacent the fusible link 20 when the projectile 11 is correctly positioned in the barrel 10. While this relatively simple method of rupturing the link 20 is illustrated, it should be understood that any other method of rupturing the link 20 prior to firing of the projectile might be utilized.

If the link 20 is ruptured prior to firing of the projectile 11, the oscillator 30, divider 25, mixer 26 and antenna 15 operate in a normal manner once set back and spin provide power to the positive terminal 33. The power will also activate the timer 45 and, even if a signal is inadvertently applied to the flip-flop 43, it will not be applied during the predetermined interval (produced by the timer 45) subsequent to firing. The timer 45 will reset the flip-flop 43 (to ensure that it is in the correct state) prior to the application of the predetermined time period signals to the coincidence gates 48 and 49. Thus, once the predetermined time period signals from the timer 45 are applied to the coincidence gates 48 and 49, the output from the flip-flop 43 to the gate 49 will cause an output therefrom, which will place the fuze 12 in a first mode of operation. This first mode of operation may be, for example, operation upon impact.

If the switch 52 of the heating element is not operated prior to firing of the projectile 11, the fuse 12 will undergo aeroheating during flight which corresponds approximately with the graph illustrated in FIG. 3. The link 20 is designed to fuse or rupture from the effects of the aeroheating of the fuze 12 within a predetermined time subsequent to the firing of the projectile 11, generally coinciding with the predetermined time signals provided by the timer 45. Once the projectile 11 is fired and the oscillator 30 and timer 45 have a positive voltage applied thereto, the voltages at the antenna 15 and at the input to the amplifier 38 appear as illustrated in the first portion, designated 60, of the waveforms of FIG. 4a and FIG. 4b, respectively. Upon the rupture of the link 20 by aeroheating, the antenna 15 becomes properly matched and the reflected power drops to near zero, dropping the DC voltage out of the mixer 26 sharply. This sharp drop in DC voltage will pass through the capacitor 35 and be inverted by the amplifier 38 to appear as a sharp positive pulse at the diode 39. Under these conditions the pulse should be high enough to overcome the bias produced by the diode means 39 and drive the transistor 41 into saturation. Other signals, such as noise, etc., which might get through the capacitor 35 will generally not be high enough to overcome the bias of the diode means 39 and, thus, will not turn on the transistor 41. When the transistor 41 saturates a negative pulse will be applied to the flip-flop 43. The flip-flop 43 will change states and, if the rupturing of the link 20 occurs during the predetermined time period set into the timer 45, the output of the flip-flop 43 and the output of the timer 45 will coincide to cause the gate 48 to produce an output which will place the fuze 12 in a second mode of operation, which may be for example proximity operation.

Thus, a programmable fuze 12 is illustrated which may be remotely operated to function in first or second modes. The actual circuitry for switching between modes in response to the rupture of the link 20 is simplified for convenience of explanation and circuitry actually causing the modes of operation, in response to signals from gates 48 or 49, is not illustrated because it does not form a portion of this invention. However, typical circuitry illustrating different modes of operation is described in a copending application entitled "Electronic Time Delay Safety and Arming Mechanism", Ser. No. 843,621, filed Oct. 19, 1977, now U.S. Pat. No. 4,145,971. While we have shown and described a specific embodiment of this invention, further modifications and improvements will occur to those skilled in the art. We desire it to be understood, therefore, that this invention is not limited to the particular form shown and we intend in the appended claims to cover all modifications which do not depart from the spirit and scope of this invention.