US3805703A

US3805703A - Fuze

Info

Publication number: US3805703A
Application number: US00663472A
Authority: US
Inventors: J Cummings
Original assignee: Rockwell International Corp
Current assignee: Boeing North American Inc
Priority date: 1967-08-21
Filing date: 1967-08-21
Publication date: 1974-04-23
Anticipated expiration: 1991-04-23

Abstract

An ordnance fuse is provided for distinguishing interposed material, such as a forest canopy, from a true target; providing a firing signal at the latter and refraining from firing at the former. An electronic integrating comparator compares the time interval of contact with a target or canopy with a selected time interval and provides a firing signal when the contact time exceeds a threshold that distinguishes a true target from intervening material.

Description

[451 Apr. 23, 1974 United States Patent [191 Cummings l02/70.2 l02/70.2 X

[54] FUZE 3,327,631 6/1967 Howard at al. [75] inventor: Jerry W. Cummi Palos Verdes ,211 l|/19 6 Wlnston.........................

Estates, Calif.

Primary ExaminerSamuel W. Engle [73] Assignee: Rockwell International Corporation, Assistant E i Th H, W bb El q Calif- Attorney, Agent, or FirmR. D. Seibel Aug. 21, 1967 Appl. No.: 663,472

[22] Filed:

[57] ABSTRACT An ordnance fuse is provided for distinguishing inter- [52] U s C! 102/70 2 R 320 posed material, such as a forest canopy, from a true 15/40 i 11/02 target; providing a firing signal at the latter and refraining from firing at the former. An electronic inte- [5l] Int. CL... [58] Field of Search......................... lO2/70.2; 320/1 grating comparator compares the time interval of contact with a target or canopy with a selected time interval and provides a firing signal when the contact [56] References Cited UNITED STATES PATENTS time exceeds a threshold that distinguishes a true target from intervening material.

l02/7O 2 X 307/885 102/70 2 X 8 Claims, 6 Drawing Figures PATENTEDAPR 2 3 m4 SHEET 1 BF 2 TIMER DETONATOR FIRING COMMAND FIG. I

SENSOR COMPARATOR H2 ARMING SWITCH INVENTOR.

JERRY W. CUMMINGS BY W (QM FIG. 2

ATTORNEY ATENTEDAPR 23 19m 8 5; 7 03 SHEET 2 UF 2 VII/Ill 46 DETONATOR INVENTOR. 6 JERRY w. CUMMINGS ATTORNEY FUZE BACKGROUND In the selection of fuses for ordnance devices such as aerial bombs, rockets and artillery shells it is significant that the fuse be operable in conditions that anticipate the characteristics of potential targets of the weapon. Thus, for example, a weapon employed against concrete would employ a fuse different from one intended to impact on water. Four broad classes of fuses are employed in ordnance devices, viz., (l) fuses which depend upon deceleration sensing upon impact to cause detonation, (2) fuses which depend on structural deformation or mechanical displacement of elements during impact for detonation, (3) fuses which depend on sensing of target proximity by electromagnetic radiation for detonation, and (4) detonation after a selected time interval following some event.

A difficulty in the practical application of fuses arises when materials are interposed between the first entry of the weapon into the target vicinity and a point some distance further along the trajectory at which detonation would be most effective. Such a condition exists, for example, in the penetration of buildings, in which case detonation of a bomb near the foundation causes greater destruction than detonation at the roof. A similar practical example of this type is in the use of antipersonnel weapons against targets located below a screening layer of branches and the like, referred to hereinafter as canopy.

The problem of canopy discrimination is of particular concern in jungle environments where a heavy growth occurs at various heights above the ground. This is the type of growth one observes by looking upward toward the sky from a forest floor. A canopy is made up of many canopy elements such as branches of various thicknesses and lengths, leaves, vines, and other material. In any given forest the density of canopy elements may be uniformly distributed above the ground or they may be confined to one or more layers of varying thicknesses which are separated by spaces in which there are no canopy elements. It is also found that clearings and the like occur wherein no canopy elements whatsoever are involved. The ground beneath such a canopy is often swampy terrain or comprises a deep layer of rotting vegetation, both of which are generally soft and penetrable in nature. Because of this, relatively sensitive fuses are required for sensing impact with soft ground.

In a situation where penetration of interposed materials, such as truck or building roofs or forest canopy, is involved, the previously available types of fuses have not been completely satisfactory. Fuses sensing deceleration or relying on structural deformation are not completely satisfactory since, if the elements are strong or insensitive, functioning of the fuse at ground level may not occur in soft earth, mud, or water such as is often found beneath forest canopy. Similarly, if the fuses are very sensitive, in order to function upon impact with mud or water, they are also sufficiently sensitive to be actuated by the interposed material.

Electromagnetic sensing devices have not been developed, fordiscriminating between inter-posed material and target areas.

Attempts to introduce discrimination against interposed material have been employed in which the fusing device provides a selected time delay between first activation and subsequent detonation of the weapon. Thus, for example, a sensitive fuse is activated on contact with canopy and detonation occurs a short time later to allow time to fall closer to the ground. Delayed discrimination is unsatisfactory where the target is completely clear of interposed material, or when the height of the interposed material and the desired detonation point is variable. When a time delay is employed and there is no interposed material the weapon may be destroyed by impact before functioning of the detonator; or the weapon may tunnel deep into the ground before detonation which may not be the desired mode of operation. Variations in the velocity of the weapon near impact which are a necessary consequence of tactical delivery situations also make simple time delay discriminations impractical in many situations.

Another significant safety consideration in many ordnance fuses is a provision for arming the weapon only after it has separated a substantial distance from the launching system such as a rocket tube, gun barrel, or airplane.

It is also often desirable from the standpoint of security of weapon technology from analysis of duds by the enemy to provide in the fuse, means to separately detonate the weapon in the circumstance where a committed round is for some reason not detonated by the regular fusing arrangement. Such provisions are conventionally known as sanitization and may include simple time delays or auxiliary mechanisms which respond to attempts of enemy personnel to dismantle the round for examination of its construction.

SUMMARY OF THE INVENTION Thus there is provided in the practice of this invention according to a preferred embodiment an ordnance fuse capable of discriminating between interposed material and a target area with detonation at the latter. In a preferred embodiment discrimination is obtained by comparing the elapsed time of presence of the interposed material and preventing detonation when the elapsed time is less than a threshold and providing detonation when the elapsed time exceeds a threshold.

Objects and many of the attendent advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description, when considered in connection with the accompanying drawings wherein:

FIG. I comprises a block diagram of a fuse incorporating the principles of this invention;

FIG. 2 is a circuit diagram of an embodiment of the fuse of FIG. 1;

FIG. 3 is a switch preferred for use in the fuse of FIG.

FIG. 4 comprises a detailed view of a portion of the switch of FIG. 3;

FIG. 5 comprises another embodiment of sensor useful in the fuse of FIG. 1; and

FIG. 6 comprises a circuit diagram of another embodiment of the fuse of FIG. 1.

Throughout the drawings like numerals refer to like parts.

The description hereinafter is particularly directed to discrimination against canopies as often found in forests. It will be apparent that the descriptions are equally applicable to other kinds of interposed material such as man-made barricades, building structures, fabrics,

camouflage structures. truck and van roofs, and a wide variety of similar structures. It will also be apparent upon review of the description that the principles are also applicable to bombs designed to tunnel into the ground and a fuse can readily be provided which will cause detonation when such a bomb enters a void space in the earth, such as a man-made tunnel, thereby greatly enhancing the destructive effects.

As discussed herein the fuse is regarded as an element of a falling aerial bomb delivered against a soft target in a swampy jungle. It will be apparent to one skilled in the art that many other applications of such a fuse are of utility in other weapons and practical situations.

Reference is also made throughout to detonation of the weapon, however, it will be apparent to one skilled in the art that detonation is not the only yield of a weapon in practical situations and conflagration or smoke marking and other types of weapon yield may be involved in certain situations.

The passage ofa bomb through a canopy can be considered in terms of a series of mechanical impulses to the bomb due to impact with various elements of the canopy and ultimately the ground. It is found that the time that a falling bomb is in contact with a limb or other canopy element is relatively short compared with the time between when the bomb strikes the ground and destruction thereof due to the effects of extreme deceleration. Thus, for example, it is found that for a limb about 6 inches in diameter and a bomb velocity of about 300 feet per second, a contact duration of only about 1.6 milliseconds results. Where the velocity of the falling bomb is about 1,000 feet per second, the contact duration is reduced to about 0.5 milliseconds. This order of magnitude of contact duration is increased in the event the limb deflects under impact and will obviously vary with other size, strength, and inertial characteristics of the canopy. It will also be apparent that the maximum time of contact will be realized only in the instance ofa square hit and that glancing directions of impact will result in shorter impact durations. It will also be apparent that when numerous canopy elements are involved that the sum of the time intervals of contact with successive elements may increase appreciably. Since the force involved in an impact with a canopy element is dependent on size and inertial characteristics of the element, a threshold is readily provided for disregarding small forces such as encountered with leaves or twigs alone.

Thus a preferred embodiment discrimination of canopy is made by comparing a time interval of contact with canopy elements with a selected reference time interval.

FIG. 1 illustrates in block diagram form a fuse incorporating the principles of this invention. As illustrated therein there is provided an arming switch 10 which may comprise any of many conventional switches, operated by springs, lanyards and the like for initiating the functional mode of the weapon so that it is armed and ready for detonation upon reaching a target. If desired, a time interval can be employed in the arming switch with the function of delaying the arming to provide safety for the launching system. The arming switch 10 activates a timer 11 and a comparator 12. The timer 11 may comprise a conventional electronic, mechanical, electromechanical or chemical timer for providing a detonation signal after an elapsed time interval after arming. This interval is longer than the delivery time of the weapon and provides sanitization in case the weapon is not detonated by the primary fusing system. A time interval of from 500 to 1,000 seconds is conveniently employed in many applications for destroying duds.

A sensor 13 is provided for detecting occurrence of impulse conditions characteristic of impact with elements of a forest canopy and also the ground beneath. Thus the sensor 13 detects entry of the fuse into a canopy and exit therefrom. The sensor may comprise means for detecting impact of the weapon with canopy elements or means for sensing the proximity of the elements to the weapon.

The sensor 13 provides a momentary signal during occurrence ofa condition to be sensed, such as, for example, contact between the weapon and a canopy element. The signal ends when the condition ends. This signal is applied to the comparator 12 where it is compared with a preselected time interval which provides a threshold for actuation of the fuse. If the time duration of the signal from the sensor is less than the threshold interval there is no actuation of the fuse. If, however, the time interval is longer than the selected threshold, a signal is applied from the comparator 12 through an OR gate 14 to a firing command element 15 which provides firing power to a conventional detonator 16 for detonation of the weapon. If, for some reason, the comparator does not apply a signal longer than the threshold to the OR gate, such a signal is eventually applied by the timer 11 at the end ofits cycle and detonation is thereby caused.

FIG. 2 comprises a circuit diagram of a specific embodiment of the fuse of FIG. 1. Superimposed on the circuit diagram by dashed lines and identified by the same reference numerals, are the block elements illustrated in FIG. 1. Thus, there is provided in a preferred embodiment as illustrated in FIG. 2 an arming switch 10 which preferably comprises a double pole switch for operably connecting two

batteries

18 and 19 to the electronic circuitry of the fuse. The battery 18 provides a voltage of proper level for operating the electronic elements of the fuse and the battery 19 provides additional energy as may be required for operating the detonator 16. It will be apparent to one skilled in the art that by proper selection of electronic circuit elements that a single battery can be employed if desired.

In order to provide energy for detonation the

batteries

18 and 19 are employed for charging a firing capacitor 21 to a sufficient energy level for operating the detonator 16. The firing capacitor 21 serves to store energy and provide a heavier current upon command across the detonator 16 than may be available from the batteries alone. A high value leakage resistor 22 is provided across the capacitor 21 for safety reasons. The leakage resistor 22 slowly drains the capacitor 21 so that if the circuit is for some reason accidentally activated and inactivated the charge drains off of the capacitor and renders the fuse safe again. The leakage resistor also serves to bias a silicon controlled rectifier 39, hereinafter described, that operates as a switch to discharge the capacitor 21 upon receipt of an appropriate signal.

A safety resistor 23 is also provided in the arming circuit between the battery 19 and the capacitor 21 so that a time delay occurs after closing the arming switch 10 and before a sufficient energy level has built up in the capacitor 21 to initiate the detonator 16. A very few seconds delay is sufficient for protection of launching aircraft. It will be apparent that the safety resistor 23 can be deleted from the circuit and delay means associated with the arming switch to provide closure thereof at a selected time interval after launching the bomb from an aircraft.

As mentioned hereinabove upon closure of the arming switch 10 a timer 11 and a comparator 12 are activated. The timer 11 preferably comprises a conventional linear charging circuit which permits accurate presetting of time intervals of fairly long duration, such as from 5 to 15 minutes. In a preferred embodiment the linear timing circuit comprises a capacitor which is charged by the battery 18 through a resistor 26 and an NPN transistor 27. In order to linearize the charging rate on the capacitor 25 the voltage thereon is applied as bias to the base of an NPN transistor 28 which conducts correspondingly through a resistor 29. The voltage across the resistor 29 is applied as bias to the base of the transistor 27 for controlling the current therethrough for charging the capacitor 25. In this manner a more linear charging rate of the capacitor 25 is obtained. It will be apparent to one skilled in the art that other types of charging circuits or timers can be provided. .The comparator 12 is also activated upon closure of the arming switch 10, however, nothing actually occurs in the comparator until such time as the sensor 13 is actuated or until the timer 1 1 effects operation. In a preferred embodiment the sensor comprises a momentary switch as hereinafter described, which is normally open and is closed only during contact with an object such as forest canopy or the ground. Upon closing of the switch 13 a detonating cycle is initiated wherein current flows through a resistor 31 for charging a capacitor 32. It will be apparent that the rate of charging of the capacitor32 is dependent on the value of the resistor 31 and capacitor 32, therefore it is desirable in certain instances to employ a variable resistor 31 as illustrated in FIG. 2 for controlling rate of charge of the capacitor and hence the time required to reach a selected voltage level. Variation of the charging time to give a detonating cycle in the range of from one to ten milliseconds is readily provided. If desired, fixed values can be employed or a variable capacitor can be used in lieu of a variable resistor. The voltage on the capacitor 25 on the timer and the voltage on the capacitor 32 in the comparator are both applied to the OR gate 14 which comprises a pair of diodes 33 arranged so that the higher of the two voltages is applied to a unijunction transistor 34.

,The unijunction transistor 34 is reverse biased by

resistors

36 and 37 so that no current flows from the OR gate until a sufficient voltage is applied to the unijunction transistor to forward bias it. As mentioned hereinabove the voltage from the capacitor 25 is applied to the unijunction transistor and the voltage on the capacitor 32 is also applied to the unijunction transistor. When either of these voltages exceeds the reverse biasing voltage the unijunction transistor fires, thereby producing a substantial current flow and a voltage spike in the

R-C network

36, 37 and 38 which can be considered a detonating signal. The voltage spike is also applied to a silicon controlled rectifier 39 which is thereby swung to a conducting state. The silicon controlled rectifier 39 is normally biased in a nonconductive state by resistors 22 and 23. When the silicon controlled rectifier 39 becomes conductive a circuit through detonator 16 is completed. A heavy current flows from the capacitor 21 which has been charged through resistor 23 from battery 19. This current flows through the detonator 16 and the conducting silicon controlled rectifier 39.

It will be apparent that if no firing signal occurs from the sensor capacitor 32 the voltage on the capacitor 25 in the timer 1 1 will, after a preselected time interval, be sufficient to fire the unijunction transistor 34 and thereby detonate the aerial bomb in the same manner. In the usual situation, however, signal from the capacitor 32 causes detonation of the bomb.

In the embodiment of FIG. 2 the unijunction transistor 34 of the comparator 12 is also used with the timer circuit 11 via the OR gate 14 for providing a firing signal. Thus a portion of the comparator is employed in conjunction with elements of the timer. From one point of view, the unijunction transistor 34, with its bias resistors, can be considered a comparator and the resistor 31 and capacitor 32 considered a sensor-timer for providing a voltage signal to the comparator which is a function of the time the sensor switch 13 is closed.

As hereinabove mentioned, closing of the contact switch 13 charges the capacitor 32 through the resistor 31 at a selected rate. If the switch 13 remains closed for a time longer than the selected threshold the detonating cycle is completed and capacitor 32 is charged to a sufficient voltage level to fire the unijunction transistor. Thus, for example, if an aerial bomb strikes an element of a canopy the switch 13 is momentarily closed but reopens immediately upon breaking contact with the canopy element. If the time of contact is less than the threshold value no detonation of the bomb occurs. If, however, the bomb strikes the ground the contact switch 13 is kept closed and when the threshold time is exceeded the charge on the capacitor 32 builds to a level for firing the unijunction transistor and detonating the bomb.

It will be apparent that if the contact switch 13 is closed several times in rapid succession for an integrated time greater than the threshold, the detonating cycle is effectively completed and the capacitor 32 is charged to a sufficient voltage for detonating the weapon. If desired, therefore, a high value resistor 41 can be provided across the capacitor 32 to discharge the capacitor and practically eliminate the low frequency integration inherent therein such as when time intervals are present between intermittant closures of the contact switch 13. If this resistor is employed the capacitor 32 charges to the firing voltage only if the switch is continuously closed for a period in excess of the reference time, as by ground contact or is intermittantly closed at a high frequency for an integrated time greater than the threshold, allowing for the leakage occurring in the integrated time interval. It will be apparent to one skilled in the art that the described circuitry and duals and analogs thereof are readily adaptable to advanced miniaturization techniques thereby permitting use in relatively small tactical weapons.

A typical switch useful in the practice of this invention for contact with canopy elements, ground, and the like, is illustrated in FIGS. 3 and 4. As illustrated therein, there is provided a base plate 42 or the like forming the nose or leading end of a fin stabilized aerial bomb, the end of which is shown in phantom in FIG. 3.

On the base plate 42 is mounted an inner saucer-like plastic member 44, and concentric therewith an outer saucer-like plastic member 45. Each of the

plastic members

44 and 45 comprises a dished sheet of glass fabric impregnated with an epoxy resin which for a four inch diameter switch member is preferably about onesixteenth inch thick and the members are preferably spaced apart about one-half inch. Each of the plastic members is metallized on one side to provide an electrically continuous layer. An enlarged section of the

dishlike members

44 and 45 is illustrated in FIG. 4. The outer member 45 comprises a plastic sheet 46 with a metal layer 47 on the concave side thereof, such as may be provided by vacuum deposition, electroless plating, or the like. The saucer-like member 44 is similar with the metal layer 69 on the concave side of a plastic sheet 68 so as to be adjacent the metal layer 47 on the saucer-like element 45.

Referring again to FIG. 3 an electrical contact 48 is made to the metal 69 layer on the outside of the saucerlike element 44. Similarly an electrical contact 49 is made to the metal layer 47 on the inside of the saucerlike member 45. Thus the saucer-

like members

44 and 45 have electrically conductive metal layers facing each other and form a contact sensor 13. The

electrical connections

48 and 49 are connected to the electronic circuit hereinabove described in relation to FIG. 2 as leads to the sensor 13.

Upon contact of the aerial bomb 43 with a canopy element or the ground, the outer saucer-like member 45 is mechanically deformed so as to bring its metal layer in electrical contact with the metal layer on the inner saucer-like member 44 which may also elastically deform. These contacting metal layers serve as a switch. If bomb contact is made with a canopy element and said contact is broken in a short time, the saucerlike

plastic elements

44 and 45 elastically spring back to their original position and electrical contact therebetween is broken, thereby opening the switch. Thus the saucer-

like elements

44 and 45 form a momentary switch which is closed only during mechanical deformation of the elements. Upon striking the ground, or the like, the saucer-like elements are deformed into contact and remain in contact, thereby maintaining the switch closed for a time longer than the threshold and permitting the detonating cycle to go to completion.

It is found in building such a switch that glass fabric reinforced epoxy resin about one-sixteenth inch thick is sufficient to provide resiliency for re-opening the switch and sufficient strength and impact resistance to avoid cracking and destruction of the plastic upon impact. The plastic members are also sufficiently strong to avoid switch closing upon contact with minor canopy elements such as leaves, twigs, and the like. The described switch is sufficiently sensitive to close and remain closed upon contact with water or soft soil. It is desirable in a practical weapon to provide reliability by having several parallel and redundant

electrical contacts

48 and 49 with the metal layers on the saucerlike elements so that inadvertent cracking or damage to the metal layer will not render the switch inoperable. If desired, the base plate 42 can be provided as concentric conductive and non-conductive rings so that electrical contact is made around the entire periphery of the saucer-

like elements

44 and 45.

It will be apparent that the thickness, material and spacing of the plastic members can be varied as desired to obtain a selected closing force for operating the switch. The physical characteristics are thus selected according to the impact velocity of the weapon and the nature of canopy material it is expected to encounter. A significant factor is that the switch operating sensitivity or sensory threshold is separately and independently variable from the time threshold in the detonating cycle. An easily operated switch may be employed with a long time threshold in some tactical situations and a relatively insensitive switch with a short time threshold may be desirable under other conditions. Thus two discrimination thresholds are present in the fuse, one dependent on the magnitude of a sensory input such as contact with an element, and the other a time discrimination dependent on the presence or absence of a condition greater in magnitude than the selected sensory input threshold.

If the sensory input is selected as contact with an element it will also be apparent that discrimination can readily be obtained with other contact switch arrangements. It is significant that the switch indicate the presence or absence of contact above the threshold and this can be provided with springs and inertial masses, gas filled chambers, and other types of elastically resilient switches well known to those skilled in the art.

Another type of sensor 13 useful in the practice of this invention is illustrated in FIG. 5. This sensor comprises a light source 50 which is focused by a lens 51 to a point immediately outside a window 52 at the leading edge of a bomb. Light passing through the window 52 striking a canopy element 53 or the like (or the ground) is reflected back through the window so as to be focused on a photodetector 54 by a lens 55. In the absence of any solid material immediately outside the window no light is reflected to the photodetector and this sensor remains open. When, however, an element of canopy material or the ground is outside the window in immediate proximity thereto, light is reflected to the photodetector and the sensor is momentarily closed so long as the material remains in front of the window. Such a sensor is more sensitive to minor canopy elements than the mechanical switch and may be desirable in some situations. A discrimination threshold can be provided based on the reflectivity of the material outside the window or the distance from the window to the object or some aspect of the spectral signature of an expected target.

It will be apparent that in lieu of or in addition to the mechanically operated switch and the light reflection switch hereinabove described that other types of switching arrangements such as an integrating accelerometer or the like can be employed with a canopy discriminating fuse of the type described herein. It should also be appreciated that various combinations of sensors functioning as switches of types sensitive to different conditions characteristic of canopy and ground can be employed in different logic arrangements such as AND, OR, or NOR so that the detonator is tired in the alternative or when more than one switch is closed in order to provide greater discrimination between a true target and canopy elements or other false indicators of a target.

An alternative embodiment of fuse incorporating the principles of this invention is illustrated in FIG. 6. As illustrated therein an arming switch 'activates a timer 11, a threshold comparator 112, and also a firing command circuit 115. The timer 111 may comprise a simple R-C circuit for charging a capacitor 57 after the arming switch 110 is closed. Although this is not a linear charging circuit as provided in the preferred embodiment a sufficiently accurate timing interval for some purposes can be achieved. When the timing circuit has charged the capacitor 57 to a sufficient voltage level, a glow discharge or gas filled tube 58 connected across the capacitor 57 is fired thereby providing a pulse of light. Such a simple circuit is often known as a relaxation oscillator and a wide range of time constants can readily be provided. It is preferred to have a time constant of several hundred seconds. If desired, instead of the light pulse, the current, and hence voltage, pulse when the tube fires can be employed in a detonation cycle.

The comparator circuit 112 also comprises a short time constant relaxation oscillator including a capacitor 59, however, this circuit also contains a sensor 113 which in a preferred embodiment comprises a normally open, momentarily closable switch. As in the preferred embodiment closing of the switch 113 for a time greater than a selected threshold permits the charge on the capacitor 59 to build to a voltage value that is sufficient for firing a glow discharge tube 60 connected thereacross, thereby providing a pulse of light. The threshold voltage of the glow discharge tube provides the voltage comparison for a sensor-timer RC circuit if one prefers to consider the circuit in that nomenclature.

Upon closing of the arming switch 110 a battery 64 charges a capacitor 65 in the firing command circuit 115 to an energy level sufficient for firing a detonator 116.

Either the pulse of light from the timer glow tube 58 or from the comparator glow tube 60 may impinge on a photo-transistor 61 in the firing command circuit 115. The photo-transistor 61 is biased by

resistors

62 and 63 so as to be turned off in the absence of light impinging thereon. When light from either the timer 111 or the comparator 112 impinges on the phototransistor 61 it becomes conductive and the charge on the capacitor 65 is discharged through the photo-transistor and the detonator 116 thereby detonating the bomb. The net operation of an embodiment as illustrated in FIG. 6 is the same as in the preferred embodiment and there is the additional advantage that the electrical circuits are interconnected only by an optical path and somewhat greater safety may be achieved. if desired, a single glow tube can be employed and the two relaxation oscillators can both be connected thereto by an electronic OR gate. It may also be desirable to provide an opaque shield in the optical path prior to arming of the fuse for safety purposes.

In a fuse constructed according to the principles of this invention, values for the comparator were selected so that a threshold time of 1.4 milliseconds was required for a firing command to be generated. It was found in repeated tests that a contact switch pulse duration of 1.2 milliseconds consistently gave no firing command and a duration of 1.4 milliseconds consistently generated a firing command. This time interval is sufficiently short that, upon contact with the ground, structural deformation occurs in the contact switch and not in the body of the bomb. A short time is required so that the bomb is not damaged by impact forces before detonation for maximum effectivity.

It is to be understood that the above described embodiments are merely illustrative of the application of the principles of this invention. Those skilled in the art may readily devise other variations that will embody the principles of the invention. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than is specifically described.

What is claimed is:

1. An improved fuze for an ordnance device comprismg:

a sensor for detecting contact between the ordnance device and a target, and between the ordnance device and a forest canopy, said sensor providing a first signal upon contact with a target and a second signal upon contact with a forest canopy, said first and second signals being identical except as to duration;

a sensing circuit responsive to said first and second signals for providing a firing signal to the ordnance device; and

a time integration circuit interposed between said sensor and said sensing circuit for preventing a firing signal unless the duration of said first signal or said second signal exceeds a selected time threshold, said time threshold being greater than the time required for the ordnance device to break contact with a forest canopy.

2. A fuze as defined in claim 1 wherein said sensor comprises a contact switch biased to an open state and closable with a force exceeding a threshold value characteristic of both a target and a forest canopy.

3. A fuze as defined in claim 2 wherein the switch comprises: an outer non-conductive, elastic saucer-like member;

a conductive layer on the concave surface of the outer member;

an inner non-conductive, elastic saucer-like member spaced apart from the concave side of the outer member; and

a conductive layer on the convex surface of the inner member.

4. A fuze as defined in claim 2 wherein said sensing circuit and said time integration circuit collectively comprise:

a power supply;

a timing capacitor;

a resistor in series with said timing capacitor, said power supply, and said sensor so that a signal from said sensor causes charging of said timing capacitor at a selected rate;

a unijunction transistor connected to said timing capacitor and reverse biased for providing a current pulse when voltage on said timing capacitor exceeds a threshold;

a storage capacitor;

means connected to said power supply for charging said storage capacitor at a selected rate;

a silicon controlled rectifier reverse biased to be non conducting;

a network for forward biasing said silicon controlled rectifier to be conductive in response to a current pulse from the unijunction transistor, said silicon controlled rectifier being connected to said storage capacitor for discharge thereof through an external circuit.

5. A fuze as defined in claim 1 wherein said sensor comprises:

a light source;

means for focusing light from the source a short distance from the ordnance device; and

means for sensing light reflected from an object upon which the light falls.

6. A fuze for an ordnance device for discriminating a true target and a spurious indication of a target, and causing detonation of the ordnance device at the true target and preventing detonation at the spurious target comprising:

a contact switch resiliently biased to actuate upon application of a force greater than a threshold value and to deactivate upon release of force to less than the threshold value;

a time integration circuit operable only in response to switch actuation, said circuit providing a firing signal when the elapsed time of switch actuation exceeds a threshold time.

7. A fuze as defined in claim 6 wherein said time integration circuit comprises:

a power supply;

a timing capacitor;

a storage capacitor;

a silicon controlled rectifier reverse biased to be nonconducting;

8. A method of distinguishing a true target such as the ground and a spurious target such as a forest canopy in an ordnance fuze comprising:

sensing a contact between the ordnance fuze and an object when the contact force exceeds a threshold value;

commencing a firing cycle when the contact is sensed;

interrupting the firing cycle when the contact is broken; and

providing a firing signal when the duration of contact

Claims

1. An improved fuze for an ordnance device comprising: a sensor for detecting contact between the ordnance device and a target, and between the ordnance device and a forest canopy, said sensor providing a first signal upon contact with a target and a second signal upon contact with a forest canopy, said first and second signals being identical except as to duration; a sensing circuit responsive to said first and second signals for providing a firing signal to the ordnance device; and a time integration circuit interposed between said sensor and said sensing circuit for preventing a firing signal unless the duration of said first signal or said second signal exceeds a selected time threshold, said time threshold being greater than the time required for the ordnance device to break contact with a forest canopy.

3. A fuze as defined in claim 2 wherein the switch comprises: an outer non-conductive, elastic saucer-like member; a conductive layer on the concave surface of the outer member; an inner non-conductive, elastic saucer-like member spaced apart from the concave side of the outer member; and a conductive layer on the convex surface of the inner member.

4. A fuze as defined in claim 2 wherein said sensing circuit and said time integration circuit collectively comprise: a power supply; a timing capacitor; a resistor in series with said timing capacitor, said power supply, and said sensor so that a signal from said sensor causes charging of said timing capacitor at a selected rate; a unijunction transistor connected to said timing capacitor and reverse biased for providing a current pulse when voltage on said timing capacitor exceeds a threshold; a storage capacitor; means connected to said power supply for charging said storage capacitor at a selected rate; a silicon controlled rectifier reverse biased to be nonconducting; a network for forward biasing said silicon controlled rectifier to be conductive in response to a current pulse from the unijunction transistor, said silicon controlled rectifier being connected to said storage capacitor for discharge thereof through an external circuit.

5. A fuze as defined in claim 1 wherein said sensor comprises: a light source; means for focusing light from the source a short distance from the ordnance device; and means for sensing light reflected from an object upon which the light falls.

6. A fuze for an ordnance device for discriminating a true target and a spurious indication of a target, and causing detonation of the ordnance device at the true target and preventing detonation at the spurious target comprising: a contact switch resiliently biased to actuate upon application of a force greater than a threshold value and to deactivate upon release of force to less than the threshold value; a time integration circuit operable only in response to switch actuation, said circuit providing a firing signal when the elapsed time of switch actuation exceeds a threshold time.

7. A fuze as dEfined in claim 6 wherein said time integration circuit comprises: a power supply; a timing capacitor; a resistor in series with said timing capacitor, said power supply, and said sensor so that a signal from said sensor causes charging of said timing capacitor at a selected rate; a unijunction transistor connected to said timing capacitor and reverse biased for providing a current pulse when voltage on said timing capacitor exceeds a threshold; a storage capacitor; means connected to said power supply for charging said storage capacitor at a selected rate; a silicon controlled rectifier reverse biased to be nonconducting; a network for forward biasing said silicon controlled rectifier to be conductive in response to a current pulse from the unijunction transistor, said silicon controlled rectifier being connected to said storage capacitor for discharge thereof through an external circuit.

8. A method of distinguishing a true target such as the ground and a spurious target such as a forest canopy in an ordnance fuze comprising: sensing a contact between the ordnance fuze and an object when the contact force exceeds a threshold value; commencing a firing cycle when the contact is sensed; interrupting the firing cycle when the contact is broken; and providing a firing signal when the duration of contact exceeds a time threshold.