US2898857A - Fuze - Google Patents

Description

Aug- 11 1959 L. R. HAFsTAD ErAL 2,898,857

FUZE

Filed Aug.-7, 1944 5 Sheets-Sheet 1 AFSTAD A ORNEY A118- lll, 1959 L. R. HAFs-rD Erm. 2,898,857

FUZE

5 Sheets-Sheet 2l Filed Aug. 7, 1944 LAwREA/cyEA/fsma BY RICHARD ROBERTS ATT EY lulg. 11, 1959 ,-R, HAFsxTAD ETAL 2,898,857

Filed Aug. 7, 1944 5 Shets-Sheet 5 W uvmkvb v INVN LAWRENCE TORS R. HFSTAD Bv RICHARD B. ROBERTS ATT L. R. HAFSTAD ETF AL Aug. 11, 1959 FUZE 5 Sheets-Sheet 4 Filed Aug. 7, 1944 o mwv Mm mum Y wRMrMm ME n C D MM MH c, um

FIG. I4.

Aug. 11, 1959 l.. R. HAFs-TAD ErAL Fuzz:

Filed Aug'. 7, 1944 5 sheets-sheet s United Staes arent Y FUZE Lawrence R. Hafstad and Richard B. Roberts, Washington, D C., assignors to the UnitedStates of America as represented by the Secretary of the Navy This invention relates lto photoelectric devices and has particular reference to a novel light-sensitive fuze for explosive projectiles.

In the use of Va projectile against a target, such as an airplane, it is desired to cause the projectile to explode at the target or in the immediate vicinity thereof in order to produce maximum damage'.

An object of the present invention, therefore, is to provide a fuze which may be readily attached to projectiles of various types andV which will cause the projectile charge to explode when the projectile is within damaging range of an airplane, or other target, and at the proper position so that the fragmentation cone will intercept the target.

Another object is to provide'a fuze having a light-sensitive element [connected in an electrical circuit so that a changein the quantity of light striking the element, due to the fuze approaching the target, will re a detonator, thereby causing the projectile to explode.

A further object of the invention resides in the provision of a light-sensitive fuze, the sensitivity of which is largely independent of the actual light intensity but which is sensitive to a given fractional change of th light intensity existing at the time of use. l Y

An additional object is to provide a light-sensitive fuze having a window or lens which admits maximum light in a predetermined direction and has a narrow angle of optical field.

A further object is to provide a light-sensitive device which is equally sensitive to light striking the photoelectrie cell from any angular position around the axis of the cell, at a predetermined inclination to the axis.

Another object of the invention is to provide an improved electrical circuit for use with a light-sensitive fuze.v

Still another object of the invention is to provide a fuze having a squib operable by rthe plate current of a thyratron which is triggered by an amplied impulse from a photoelectric cell.

A still further object is to provide mechanical improvements for making a reliable and satisfactory lightsensitive fuze.

An additional object is to provide a light-sensitive fuze which may be used with a bomb, shell, or other explosive device so that ground approach will cause the bomb, for instance, to explode and scatter fragments downward, for greater elfectiveness against personnel.

These and other objects of the invention may be better understood by reference to the accompanying drawings, in which Figure 1 is a longitudinal sectional view of one form of the new fuze adapted for use :on a bomb;

Figures 2-7, inclusive, are sectional views on the lines 2-2 to 7-7, inclusive, respectively, in Fig. 1;

Figure 8 is a detail sectional View on the line 8 8 in Figure 6, showing the arming and self-destruction switches;

Figure 9 is a side elevational view of a bomb, with parts broken away, showing the photoelectric proximity fuze mounted `thereon and connected to the arming wire;V

Figure 10 is a sectional view on the line 10-10 in Figure l;

Figure l1 is a sectional view on the line 11-11 in Figure 5;

Figure 12 is a sectional view on the line 12-12 in Figure l;

Figure 13 is a detail sectional view on the line 13-*13 in Figure 7 i, showing plug and socket connections for coupling parts of the fuze, and

Figure 14 is a diagrammatic view of the wiring circuits for the fuze. v

The new fuze is illustrated in a form suitable for use on Y the tail portion of a bomb, although it will be understood that the fuze may be used on the nose of the bomb and on other types of projectiles.

Referring to the drawings, the numeral 20 indicates the fuze casing which is of cylindrical shape and is formed` of metal of suitable thickness to insure ruggedness. The casing 20 is open at its rear end where it receives a pho toelectric cell unit 21 including rear and front sections sections 22 and 23 are secured to the lens Vby suitable bolts (not shown) ex-tending through the sections and the lens. Thus, the lens is held rrnly in a xed position relative to the sections 22 and 23.

The rear section 22 is provided with an axially disposed cup 25 which is open at its front end. The side wall of the cup extends forwardly a substantial distance from the section 22 and terminates in a straight, annular rim 26 which is disposed substantially medially of the ends lof the unit 21. The front section 23 is formed with a rearwardly extending axial sleeve 27 terminating in an annular rim 28, the rims 26 and 28 cooperating to define an annular light slit 29 within the central portion of the lens 24. The front section 23 is also provided near its periphery with a forwardly extending sleeve 23h which fits closely in the open rear end of the casing 20. The photoelectric unit 21 is held inthe casing by a plurality. of screws 20a extending through the casing and threaded into the sleeve 23b.

t Mounted in the sleeve 27 and extending into the cup 25 is a photoelectric tube or photo-voltaic cell 32 having v its cathode or light sensitive element 32a disposed slightly to the rear of the slit 29. A clamping ring 33 is secured to the front face of section 23, as by means of screws 33a, and serves to hold the tube in position against an annular inclined surface 23C on the section. The tube 32 is cushioned by means of annular rubber pads 34 and 35 disposed between the annulus of the tube and the surface 23c and the ring 33, respectively.- The'tube 32 may be of any suitable construction,'such as that shown in a copending application of I. E. Henderson et al., Serial Number 568,020, filed December 13, 1944, and now abandoned.

Connected to the front section 23 of the photoelectric cell unit 21 is a frame including opposed side rails 36, the rear ends of which are doubled over and secured to the sleeve 23b by means of screws 37. At theirfront ends, the rails 36 are bent inwardly and secured to the rear face of an insulating plate 38, as by means of bolts 39 and nuts 40. Mounted on the rear face of the plate l38 is a clockwork mechanism 42.which may b e of con,-

ventional design. The clock mechanism 42 is normally locked against operation by a transverse plunger 43 (Fig. which is urged outwardly toward a clock-releasing position by a compression spring 44. The plunger 43 is slidably mounted in a bracket 45 secured to the insulating plate 38, and the spring 44` is seated at its inner end on the bracket 45 and at its outer end against a button 46 on the plunger. At its outer end, the button 46 engages a stop 47 slidably mounted in a hollow boss 48 on the casing 20. The stop 47 is normally held against outward movement in the boss by means of an arming wire 49 extending transversely through the boss, whereby the plunger 43 is held in its retracted position for locking the `clock 42 against operation. The stop 47 is retained in the boss 48 by a pin 50 extending transversely through the boss and through a longitudinal slot in the stop. It will be apparent that when the arming Wire 49 is withdrawn from the boss 48, the stop 47 is released and allows the spring 44 to move plunger 43 outwardly so as to release the clock.

A bail 51 is pivotally mounted on a pin 51a on the bracket 45, and before the fuze is assembled in the casing 20, the plunger 43 is pressed inwardly against spring 44 to its clock-locking position where it is held temporarily by swinging the bail 51 on its pivot until the transverse portion of the bail overlies the plunger button 46. The plunger 43 is then released, and as the fuze parts including plate 38 and rails 36 are inserted in casing 20, the rear end of the casing engages the transverse portion of bail 51 and forces it rearwardly out of line with the plunger 43. The latter is then held in its retracted position by the inner wall of the casing 20 until the fuze assembly including plate 38 and rails 36 reaches its innermost position in case 20, where the plunger is held retracted by engagement with the stop 47.

The clock mechanism 42 includes a driven shaft 42a which extends through the plate 38 and is adapted to operate a switch assembly 53 including an arming switch 54 and a self-destruction switch 55 mounted on the front face of plate 38. An insulating segment 56 is mounted on the front end of clock shaft 42a and is normally positioned between contact springs forming the switches 54 and 55. That is, the arming switch 54 includes a pair ot switch springs 54a'and 54b (Figure 8) which are northe self-destruction switch 55 includes a pair of switch mally separated from each other by the segment 56, and springs 55a and 55b which also are normally separated by the segment 56, whereby the switches are held open. When plunger 43 releases the clock mechanism 42, the latter drives the insulating segment S6 which, after a predetermined period of time, disengages the arming switch springs 54a and 54h, thereby causing the arming switch to close. Further rotation of segment 56 causes the self-destruction switch 55 to close after an additional time interval, due to disengagement of the segment from the switch springs 55a and 551;.

An electrical plug 58 is mounted in an opening in i11- sulating plate 38 where it is held on a bracket 59. The plug 58 (Figure 6) is provided with a plurality of prongs, numbered serially from l-lO, inclusive, the prongs projecting forwardly into sockets 60 mounted on an insulating plate 61 in the casing 20. As shown in Figure 12, the sockets 69 are numbered serially from 1-10, inclusive, to correspond to the respective plugs which they receive. The plate 61 is disposed in front of plate 38 in spaced relation thereto, and the sockets 60 are secured to plate 61 by means of rivets 62 extending through the plate. At their front ends, the rivets 62 are connected to wiring 63, as by means of soldered joints.

The plate 61 forms the rear end of a battery casing 64 which includes a generally U-shaped frame 65. The ends of the leg portions of the frame 65 are bent inwardly, as shown at 65a, and are connected to the plate 61 by bolts 66 and nuts 66a. Thus the bight portion of the frame 65 forms the front end of the battery casing,

and the legs of the frame 65 are disposed in closely adjacent relation to the inner wall of casing 20. A retaining plate 67 is secured to each of the legs of the frame 65. Between the retaining plates 67 are the battery elements which comprise an A battery 68, a B battery 69 made up of a plurality of serially connected cells, a C mattery 70 (Figure 14), and a battery condenser 71. The condenser and the cells constituting the A, B and C batteries are encased in a potting compound 72 which provides suitable insulation and protection against the elements. It also serves to protect the parts against mechanical shock.

An amplifier and thyratron unit i4 is disposed in the casing between the cell unit 21 and the clock mechanism 42, the unit 74 being electrically connected by wiring 75 through the plug 58, sockets 60 and wiring 63 to the battery unit 64. The amplier and thyratron unit 74 is mounted on an insulating plate 76 secured to the rails 36 by brackets 77 and 77a, respectively, the brackets being connected to the rails by screws 78. A resilient pad 79 is folded around the insulating plate 76 adjacent each of the brackets 77 and 77a, the insulating plate and pads being connected to the brackets by bolts 80. Thus,

the plate 76 is resiliently connected to the side rails 36 through brackets 77 and 77a, whereby the amplifier and thyratron unit is better adapted to withstand mechanical shock.

The amplifier and thyratron unit 74 includes amplifier tubes 82, 83 and 84 and a thyratron 85. The tubes 82 to 85, inclusive, are held in position on the rear face of plate 76 by clips 86 of brass or other suitable material. As shown in Fig. l0, the clips 86 are secured to the rear face of plate 76 by rivets 87 which extend through the plate and also serve to connect a retaining strap 88 to the front face of plate 76. The end portions of strap 88 extend forwardly and are interconnected by a strip 89, the ends of which are turned over the ends of strap 88, as shown at 89a. Thus, the strap 88 and the interconnecting strip 89 form a retainer for the necessary resistors, condensers and other components 90, all of which may be encased as a unit in a suitable potting compound (not shown).

The tubes 82 to 85, inclusive, the resistors and condensers 90, and the batteries 68, 69, and 70 are electrically connected with the light-sensitive device 32 and switches 54 and 55 in a circuit which is shown diagrammatically in Fig. 14. As there shown, the cathode 32a of the tube 32 is connected through a resistor 92 and one of the prong and socket connections 58a, 60 to a tap 93 on the B battery 69, while the anode of the tube 32 is connected to the control grid 82a of the iirst amplifier tube 82. One terminal of each of the tube laments 82b, 83b, 8411 and 85b is connected by a wire 94 through another prong and socket connections 58a, 60 to the positive side of A battery 68, and the other terminal of each tube iilament is connected by a wire 95 to a terminal 95a which, in turn, is connected to the plunger 43. The plunger 43, which is grounded to the battery casing 20, forms one element of `a switch, the other element of which comprises a pair of switch arms 96 mounted on the insulating plate 38. When the plunger 43 is in its normal retracted position, it is out of engagement with the spring arms 96, so that the switch 43, 96 is open. However, when the plunger 43 is released by arming wire 49, it engages the spring arms 96 so as to complete the circuit from the tube filaments to the negative side of A battery 68.

The screen grids 82C, 83C, and 84C of the amplier tubes are connected through a Wire 97 to a second tap 93a on the B battery 69. Each of the tube plates 82d, 83d and 84d is connected through a load resistor 98 and shunt condenser 98a to a wire 99 which leads through another of the prong and socket connections 58a, 60 to the positive side of B battery 69, an additional load resistor 10i) being interposed between the wire 99 and bination to provide a heavy `iilter arrangementforltering out battery noises and transients, and to attenuate'the low frequency signals needed to subsequently fire the detonator unit. A wire 101 is connected between the resistors 98 and 100 and leads throughbattery condenser 71 to a common battery terminal102 connected to the negative side of the B battery 69, the positivey side of C battery 70 and the negativeside of A battery 68.

V`Grid bias resistors 90a are connected 'between the control grids of the amplifier tubes 82, 83 and 84 and the wire 95 to provide the proper bias von the grids.'` The amplier tubes are coupled'by coupling condensers 90b and resistors 90C, and the output' of the third amplifier tube 84 is coupled to the control grid 85a of the thyratron by another coupling condenser 90b. A by-pass condenser 90d is coupled between the wire 95 and each of the control grids 83a and 84a. The control grid 85a of the thyratron is connected through a grid bias resistor 103 and wire 104 to the negative side of C battery 70, so that the proper bias is imposed upon the thyratron grid. A by-pass condenser 105 is coupled between the thyratron plate 85d and -wire 95. Y

The output of thyratron 85 is conducted through wire 106 and arming switch 54a, 54b to one side of an electrically operable squib or detonator 107, the other side of which is connected to wire 99 and the positive side of B battery 69. The contact arm 55a `of the selfdestruction switch 55 is connected through a resistor 108 to a point between the squib 107 and the arming switch 54, the other contact 55h of the self-destruction switch being connected through a wire 109 to the terminal 95a. It will be apparent that when arming switch 54 is closed, as previously described, the squib 107 is connected at one side to the positive terminal of battery 69 and at the other side through switch 54 to the plate of thyratron 85, the filament of which is connected to the negative side of battery 69. Accordingly, when the thyratron is triggered, the detonator 107 is operated. Also, if the detonator 107 has not been operated prior tok closing of the self-destruction switch 55, as previously described, the latter switch upon closing will complete a detonating circuit from the positive side of battery 69 through the detonator 107, the ten ohm resistor 108, self-destruction switch 55, terminal 95a, and switch 43--96 to the negative side of battery 69.

In the use of the new fuze, as shown, the casing 20 is mounted on the tail portion of a bomb 110, the front end of the casing tting closely in an adaptor 111 on the bomb. The adaptor 111 is slit longitudinally, and the segments deiined by the slits are clamped together against casing 20 by a releasable clamping ring 111a. The fuze casing 20 is housed within and protected by a tail assembly 112 on the bomb, the photoelectric unit 21 projecting rearwardly from the rear end of the tail assembly. In the nose portion of the bomb 110 is the usual mechanical `fuze 113 which may be used in lieu of or in conjunction with the proximity fuze 20. The fuze 113 is armed by a propeller 114 .which is normally locked by the arming wire 49 extending along the bomb casing and through the hollow boss 48, the intermediate portion of the arming wire 49 being connected to a iixture 115 on the airplane or other vehicle carrying the bomb.

In operation, when the lbomb is released, the arming wire 49 is withdrawn from the propeller 114 and from the hollow boss 48, thus releasing the propeller 114 and -across A battery 68 and are heated so that the fuze is prepared for operation upon closing of the arming switch 54. Y It been found that for safety purposes the arming switch 54 should "remain open for approximately six seconds after releasing the bomb, at which time the bomb will be approximately 600 feet below the bombing plane. It will be understood that safetydevices other than and in addition tothe'switches 43--96 and 54ag-'54b may be used. i and the light-sensitive element of the tube 32, within a The operation of the fuze is dependent upon the percentage change in the quantity of light reaching the lens` 24 narrow angle which may be called the width of transmission zone and which maybe defined as Ytheyangular separation between two directions in a plane through the axis of the fuze, in each of which the transmission of the lens-slit system is half the maximum transmission.` The forward angle is delined as the angle betweena plane normal to the axis of the fuze and a line midway between the two directions deiining the transmission zone. It will be apparent that the forward angle is dependent upon the relative positions of the lens 24, the annular slit 29 and the light-sensitive element or cathode 32a of the tube 32. With the construction described, light striking the cathode 32a of the tube 32 in appreciable quantity will, due to the design of the lens and slit system, come from a narrow region bounded by two conical surfaces and inclined forward. It will be understood that the forward angle may be varied to suit particular conditions.

The percent light signal may be expressed as the fraction or percent peak signal relative to the background light level. The Sensitivity is defined as lthe voltage output at the thyratron grid a, divided by the peak percent light signal. The threshold is defined as the peak percent light signal required to trigger the thyratron 85. Sensitivity and threshold are dependent upon the form of signal, but for any given form of signal the threshold, T, and sensitivity, S, are related as follows:

where C is the thyratron bias Voltage, Vg(crit.) is the critical bias at which the thyratron fires, and V(crit.) is the critical signal required to re the thyratron.

When the bomb approaches a target, such as an airplane, a certain amount of sky light which would otherwise reach the photoelectric tube 32 through the lens 24 is obscured by the airplane, and a sudden reduction of electron output from the light-sensitive cathode of the tube 32 occurs, since the bomb is traveling at high speed. This sudden decrease of electron emission from the cathode of the tube 32 results in a current pulse or a change in the bias on grid 82a of the first amplifier tube 82. This current pulse is amplified by the tubes 82, 83 and 84, and the ampliiied pulse acts on the control grid 85a of the thyratron to cause the latter suddenly to become conducting and tire the detonator 107. Preferably, the electrical componentsv are so designed that the thyratron 85 will be triggered when the light reaching the photo electric tube 32 is reduced by even as little as one percent, due to interception of some of the light by the target.

For test purposes, we provide a conductor 117 connected between the control grid 85a of the thyratron and the adjacent coupling condenser'90b and leading to a contact 118 mounted in a receptacle 118a (Figure 5) accessible from outside the casing 20. An additional test wire 119 is connected between Contact 55a of the self-destruction switch and resistor 108 and leads to a contact 120 mounted in a plug 120a (Figure 5) accessible from outside the casing through a removable cap 121. It is the function of the ten (l0) ohm resistor 108 to assist in giving a ring indication of the detonator 107 at contact 120 for test purposes.

The new li-ght-sensitive fuze, in combination with an explosive projectile, provides an eifective weapon for attacking and destroying enemy aircraft. In addition, the fuze may be used in causing bombs to explode on ground In a photoelectric fuzel, Ha` casing, a ,photo-r electric cell u`nit mounted atonel end of the casing, a framefmounted in the casing `adjacentfthe cell unit and removable from the casing,janfamp1iergand',thyratro electrically coupled to said cell and mountedon the frame,`

`a detonator,y means for coupling'the Ithyratron tothe detonator for firing the detonator upon triggering of the vthyratron by an amplified current` pulse from the cell unit,

a safety device 01'1 `the frame' for rendering said coupling means and said amplifier andthyratron inoperative, said mnpliler,y thyratron and safety devcebeing removable t fromfthe casing ori the fraxile` as aunit, `a battery assembly in the casingadjacent lthe frame, and releasable means for 3electricallyl connecting the battery to said amplifier and fthyratron.y

Referucesl ACited in the le ofthis *patent` V* UNITED STATES PATENTS Schweitzer Aug. 21, 1934 yHammam New. 10, 193,6 Wallace Nov. 2, 1937r Vos 1-- 1 Nov. 22,y 1938 Logan July?, 1940 Ferrel .-..f Sept. 9, 1941

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