US2997232A - Fuze order computation - Google Patents

Description

OR $997 232 W3 p X guu 9 G. A. CROWTHER 2,997,232

FUZE ORDER COMPUTATION a Filed Dec. 17, 1956 3 $heets sheet l 77M OF FLIGHT EA 7'5 0F (HA A/GE OF TIME OF FL /GH 7 \SECONOS P52 YA 190 OF CHANG E OF BAA/GE INVENTOR GEO/e65 A. CHOU/THEE ATTORNEY 1961' G. A. CROWTHER 2,997,232

FUZE ORDER COMPUTATION Filed Dec. 17, 1956 3 Sheets-Sheet 2 j/lg hl 1 T 1 i "5 l l T a; I ix;

N i g -mmhwmwyawwvmwx flmmw Q United Smtes Patent 2,997,232 FUZE ORDER COMPUTATION George A. Crowther, Manhasset, N.Y., assignor to Sperry Rand Corporation, Ford Instrument Company Division, Long Island City, N.Y., a corporation of Delaware Filed Dec. 17, 1956, Ser. No. 628,839 6 Claims. (Cl. 235-615) The present invention relates to a gun fire control system, in which the gun is supported on a moving carrier, such as a warship when engaging the target, and more particularly to that part of the system which computes the fuze setting order F for mechanically fuzed projectiles.

In firing projectiles, it is customary to explode the projectile body in the vicinity of the target to enhance its destructive eflect. One method of accomplishing this is to activate the explosive charge when a preset timing mechanism runs down. The time set should theoretically correspond to the time of flight T! of the projectile from the instant of firing to the computed future position of the target at the expiration of this time of flight interval. Since present mechanisms are such, that the timing mechanism on the projectile must be preset before the projectile is loaded in the gun, a certain amount of time elapses between the setting of the fuze mechanism and the firing of the projectile. This time interval is known as dead time (Tg) and the time in seconds to be set on the timing mechanism of the projectile to assure explosion at or in the vicinity of the target is known as fuze setting order (F).

In one prior type of fuze setting order computer proposed, an approximate advance range to target at time of burst of the fuzed projectile is computed and a three dimensional cam is employed in combination with advance elevation to determine the fuze setting order. The three dimensional cam required for this computer makes the computer expensive, complicated and sometimes inaccurate.

In another type of computer proposed, the fuze setting order F is obtained by extrapolating the time of flight T of the projectile at the present instant to encompass the dead time Tg. This form of computer requires the determination of dIf and 11 T and has inherent dynamic lags.

One object of the present invention is to provide a simplified method and computer for setting time fuzes on projectiles, which does not have the drawbacks of the prior art referred to.

It is recognized in conformity with the present invention that in accordance with the known exterior ballistics of a type of projectile, there exists for any particular time of flight Tf, a rate of change of the time of flight at the present instant with respect to the range determinable by analysis of said ballistics. This rate of change of time of flight T1 is applied to the change in range due to relative ship and target movement during the dead time interval Tg to determine the increment to be added or subtracted from the time of flight T to obtain fuze setting order F.

Various other objects, features and advantages of the invention are apparent from the following particular description and from the accompanying drawings, in which:

FIG. 1 is a graph showing the relationship between the time of flight T and the rate of change of the time of flight;

FIG. 2 is a diagram showing the relationships involved for fire of own ship and target and derived by observation in the direction looking from the vicinity of the target towards the gun;

FIG. 3 is a triangle constituting part of the diagram of FIG. 2 and employed to derive certain geometric and 2,997,?32 Patented Aug. 22, 1961 "ice trigonometric relations involved in determining range correction due to dead time Tg;

FIG. 4 is a triangle constituting another part of the diagram of FIG. 2 and employed to derive other geometric and trigonometric relations involved in determining range correction due to dead time Tg;

FIG. 5 shows diagrammatically one form of apparatus embodying the present invention for obtaining the fuze setting order F; and

FIG. 6 shows diagrammatically another form of apparatus embodying the present invention for obtaining the fuze setting order F.

Symbols, names and definition of quantities employed herein B True target bearing: Angle between north-south vertical plane and vertical plane through line of sight, measured in the horizontal plane clockwise from north.

dB Angular bearing rate: The time rate of change of true target bearing.

D113 Horizontal deflection: The angle between vertical plane through line of sight and vertical plane through line R3 measured in the horizontal plane clockwise from plane containing line of sight.

E2 Advance elevation in connection with projectile in guns and to be instantly fired: Angle between the horizontal plane through the director and the line of advance range R2 measured upward from the horizontal plane in the vertical plane through said line of range.

E3 Advance elevation in connection with projectile outside of gun and being set: Angle between the horizontal plane through the director and the line of advance range R3 measured upward from the horizontal plane in the vertical plane through said line of range.

F Fuze setting order: Time in seconds to be set on the timing mechanism of the projectile prior to its being loaded in the gun to assure explosion at or in the vicinity of the target, equal to the sum of the time of flight T) and the correction for dead time Ftg; F=Tf+Ftg.

Ftg Correction for dead time: The correction in seconds which is added to time of flight T1 to allow for the relative motion of target and projectile during dead time Tg.

H Height: Vertical distance of target above the horizontal plane through the director sights.

dH Rate of climb: The time rate of change of height.

R2 Advance range in connection with projectile in gun and to be instantly fired: The distance from the director to the advance position of the projectile in the gun, measured in yards along the line of advance position, i.e. the range at the end of the time of flight T1 of projectile in gun fired instantly.

R3 Advance range in connection with projectile outside the gun and being set: The range at the end of the time of flight T) of the projectile being set outside of gun and fired after a dead time interval Tg.

Rh Horizontal range: The horizontal projection of the present range R or of the distance from the director to the target measured in yards along the line of sight.

R112 Advance horizontal range in connection with projectile in gun and to be instantly fired: The horizontal projection of the advance range R2.

Rh3 Advance horizontal range in connection with projectile outside the gun and being set: The horizontal projection of the range R3.

RdE Linear elevation rate: The vertical component of relative velocity of ship and target which is at right angles to the line of sight in the vertical plane containing the line of sight (positive when upward).

RhdB Linear bearing rate: The horizontal component of relative velocity of ship and target which is at right angles to the vertical plane containing the line of sight (position to the right).

Rtg Range change due to dead time Tg.

dRh Horizontal range rate: The time rate of change of horizontal range Rh.

dR Range rate: The time rate of change of range (positive for relative motion of target away from own shi i s Corrected range rate: Range rate corrected for linear deflection and elevation of the target causing linear changes in advance range.

T Time of flight: Time of flight of projectile from the gun to the point of burst.

Tg Dead time: Time in seconds between the setting of the fuze of the projectile outside of gun and the firing of the projectile.

As was previously pointed out, from the exterior known ballistics of a type of projectile, the time rate of change of the time of flight T of the projectile fired at the present instant with respect to range can be determined. A particular type of projectile, for example, may have the following ballistic characteristics from which the following rate of change of the time of flight Tf at the present time with respect to range may be determined.

Rate of change Range R, Range Correcof Time of Time of Fhght Tf, Secs. yards tion, yards] Flight, SGCSJDGI' 2 secs. yard of change of range FIG. 1 shows a curve A indicating rate of change of time of flight Tf at the present instant in respect to range for the particular type of projectile whose ballistic table is indicated above. Similarly, the rate of change of the time of flight T at the present instant in respect to range of any type of projectile, whose ballistic characteristics is known, can be determined. From this rate of change of time of flight Tf with respect to range, the fuze setting order F for the projectile, may be determined in the manner to be described.

When the rate of change of time of flight T of a projectile fired at the present instant with respect to the ballistic range of the projectile corresponding to this time of flight is multiplied by the change in ballistic range Rts which will occur during the next succeeding selected time interval, i.e. dead time Tg, due to relative movements of the firing vessel and the target during this interval, there is obtained the equivalent change in time of flight T or correction for dead time indicated as Ftg. This correction for dead time Fig added to time of flight Tf results in the desired fuze setting order F.

Determination of the change in range during dead time, represented by the symbol Rtg, may be accomplished in many ways. It may be computed in accordance with the present invention by the expression Rtg=R3-R2 where R3=[H+dH(F+Tg)] sin E3 +RhdB(F-|-Tg) sin Dh3 cos E3 +[Rh+dRh=(F-ITg)] Cos Dh3 cos E3 (1) R2 is computed elsewhere in the gunfire control in the well known manner.

Equation 1 is derived from the diagrams of FIGS. 2, 3 and 4 as follows:

Referring to FIG. 3,

R3=H3 sin E3 +R h3 cos E3 (2) From FIG. 2 it is seen that H3=H+dH(F+Tg) (3) Smbstituting (3) into (2) results in R3: [H|dH(F-|Tg)] sin E3 +Rh3 cos E3 (4) Referring to FIG. 4

Substituting (5) into (4) results in which corresponds to Equation 1.

Equation 1 can be mechanized and solved by the apparatus of FIG. 5 for the quantity R3. In this apparatus electrical quantities such as voltages are indicated by dotted lines and mechanical quantities, such as shaft rotations are indicated by the full lines. In this equation mechanizing apparatus of FIG. 5, the components, per se, are well known units in the art and are indicated merely diagrammatically.

In the operation of the apparatus of FIG. 5, the quantities R2, Rh, dRh, RhdB, DH, T3 and H are derived from the computer of a gun control system in the usual well-known manner. A multiplier 10 for processing certain of these quantities is shown for the purpose of simple illustration in the form of a potentiometer having three multiplying units 11, 12 and 13 and a common input shaft 14. The quantities dRh, RhdB and Dh are delivered as electrical inputs to the three units 11, 12 and 13 of the multiplier 10 respectively, while the quantity F-I-Tg is fed as a mechanical input into the multiplier through the shaft 14. The input multiplier shaft 14 carries a gear 15 which is preset by hand with the dead time Tg quantity before being meshed to a drive gear 16. This drive gear 16 is driven by a feedback line carrying the fuze setting order F quantity obtained in a manner to be described, so that the rotative position of the shaft 1.4 corresponds to the quantity F-j-T g. The electrical outputs from the three units 11, 12 and 1-3 of the multi plier 10 are dRh(F-IT g), RhdB(F+Tg) and ciH (F T g) The quantity Rh directly from the computer and the quantity dRh (F+T g) from the multiplier 10 are fed as electrical inputs into anadding and amplifying network 17 to obtain the output Rh+dRh(F-|-Tg). This adding network 17 may be controlled for stability and accuracy from the feedback quantity [Rh-|-dRh(F+Tg)] cos Dh3 obtained from a resolver 18. The quantity RhdB(Fl-Tg) controlled by the feedback quantity RhdB(F+Tg) sin Dh3 from the resolver 18 and amplifiied in a unit 19 is fed in conjunction with the quantity Rh-l-dRh(F+Tg) into said resolver.

The resolver 18 is of the well-known type for obtaining trigonometric functions and may, for example, be of the electromagnetic type comprising basically of a motorlike device resembling a two phase, two pole induction motor, consisting of a stator and a rotor, each containing two pairs of distributed windings separated 90 mechanically with respect to the axes of the other windings. The winding distribution is thereby such, that the mutual coupling of the rotor and stator would be exactly sinusoidal with rotation of the rotor. The rotation of the rotor corresponds to the angle whose trigonometric function is obtained from the resolver.

The electrical quantities impressed as voltages on the two windings of the stator of the resolver 18 and a mechanical rotation impressed upon the rotor of the resolver and corresponding to the angle quantity Dh3, results in the output electrical quantity RhdB(F+Tg) sin Dh3l[Rh+dRh(F+Tg)] cos D123, which according to Equation 5 is equal to Rh3.

The angle quantity Dh3 for the rotor rotation of the resolver 18 is obtained through a servo mechanism 20 operating as a null seeking device. This servo mechanism is of well-known construction and consists basically of an adding, controlling and amplifiying network 22 and a servo motor 23 operated from the output of this network. The inputs from the resolver 18 into the network 22 are the quantities Rh+dRh(F +T g) sin Dh3 and RhdB(F+Tg) cos Dh3 and the output from this network corresponds to the difference between these two quantities. From a study of FIG. 4, it is seen that so that the adding and control network 22 computes a voltage deviating from zero by an error amount, which after being converted into a frequency of 60 cycles (assuming that the fuze network is operating generally at a higher frequency) by the servo control in the network 22, is supplied to the servo motor 23 to run said motor. The motor 23 converts voltage into mechanical output which is proportional to the angle quantity D113, when said motor rotates an amount corresponding to the actual value of the angle quantity Dh3, Equation 6 is satisfied. This rotation of the servo motor 23 rotates the rotor of the resolver 18 by the amount corresponding to the angle Dh3.

The quantity Rh3 obtained as described and the feedback control quantity R113 cos E3 obtained from a resolver 26 are fed into an adding, controlling and amplifying network 27 to produce the amplified quantity Rh3 for delivery to said resolver as an input.

The quantity dH (F +T g) obtained from the unit 13 of the multiplier and the quantity H obtained from the usual computer of the gun fire control system are fed into an adding, controlling and amplifying network 28 in conjunction with the feedback control quantity derived from the resolver 26, to obtain the amplified quantity H +dH (F +T g) for delivery to said resolver.

The resolver 26 is similar to the resolver 18 and the two electrical inputs H-l-dH (F +Tg) and Rh3, and the mechanical input E3 derived from a servo mechanism 30 are processed in the resolver 26 to obtain the quantity H+dH(F+Tg) sin E3 +Rh3 cos E3 corresponding to the quantity R3 in accordance with Equation 4. The servo mechanism 30 is similar to the servo mechanism 20 and operates similarly as a null seeking device to obtain the mechanical angle quantity E3 for input into the rotor of the resolver 26.

The electrical quantity R2 obtained from the computer of the gun control system and the electn'cal quantity R3 obtained from the resolver 26 in the manner described, are delivered as inputs into an adding network 32 to obtain the quantity Rt --R3 R2, which corresponds to the range change due to dead time Tg. This quantity Rtg is fed as an electrical input into a potentiometer 33 having the mechanical input Tf, which is determined in the ordinary manner by a ballistic network (not shown) in the computer of the gun control system. The potentiometer 33 operates as a multiplier and is wound to modify in effect the T value into the corresponding rate of change of time of flight at the present instant with respect to range in accordance with the curve A shown in FIG. 1 and the ballistic table referred to above. The output of the potentiometer 33 is therefore the product of the range change due to dead time Tg represented by the quantity Rtg and the rate of change of time of flight T1 at the present instant with respect to range, this product being represented by the electrical quantity Fig corresponding to the correction for dead time in seconds. This quantity Ftg when added to time of flight Tf produces the desired fuze setting order F.

The electrical quantities Ftg and T1 are added in an adding, controlling and amplifying network 35 and the resulting electrical fuze setting order F is processed through a servo mechanism 36 to convert this quantity F into mechanical form for transmission to the input shaft 14 of the multiplier 10 through the gear 16 and for transmission to the fuze setters at the gun mounts. The servo mechanism 36 serves the function of converting the electrical quantity F into the corresponding mechanical quantity without placing a load on the input side of the servo mechanism and comprises the well-known basic components, such as a servo motor 37 and a generator 38. The quantities Fig, Ti and F are fed into the summing network 35 which computes a voltage proportional to the error between a function of the input and a function of the output. This error voltage is converted into a frequency of cycles (assuming that the fuze network is operating at a higher frequency) by a servo control forming part of the network 35, is amplified by an amplifier forming part of said network and is supplied to the servo motor 37 for its control. The servo motor 37 converts voltage into mechanical output which corresponds to the fuze setting order F and drives from said voltage the generator 38. From this generator 38, a voltage proportional to the output velocity is supplied to the servo control forming part of the network 35. After being modified by the computing elements in this servo control, the modified voltage is combined with the error voltage to improve the operation of the servo mechanism 36.

The mechanical output from the servo motor 37 corresponding to the fuze setting order F is delivered to the multiplier shaft 14, is made to drive a generator 40 to produce a voltage corresponding to this fuze setting order for input feed into the summing, controlling and amplifying network 35 and is transmitted to a synchro transmitter 4-1 of the well-known type, shown consisting basically of two synchro generators 42 at the transmitting end. The fuze setting order F converted into voltage by the synchro transmitter 41 is transmitted to the fuze setters at the gun mounts.

Another way in which the quantity Rtg representing the range change due to dead time Tg can be obtained is to mechanize the formula.

Rtg: (fuze setting order F-time of flight Tf +dead time Tg) corrected range rate where corrected range rate is approximately equal to present range rate along the line of sight plus a constant times the sum of the square of the vertical linear or elevation rate and the square of the horizontal linear or bearing rate of the target. These relationships may be indicated symbolically as follows:

The constant quantity K is introduced by gear ratio in the apparatus for mechanizing Equation 8.

FIG. 6 shows an apparatus for mechanizing Equations 7 and 8 to obtain the fuze setting order F. In this apparatus, the dotted lines indicate electrical lines for transmitting electrical quantities in the form of voltages, and the full lines indicate mechanical lines for transmitting mechanical quantities, such as shaft rotations. The three quantities dR, RdE and RhdB are supplied to the apparatus of FIG. 6 as inputs from the computer of the gun control system in the manner well-known in the art. The quantities RaE and RhdB are amplified, squared and multiplied by the constant K by respective amplifying and squaring units 45 and 46 respectively to obtain the quantities K(RdE) and K(RhdB) These amplifying and squaring units 45 and 46 may be of any well-known type and each may comprise a motor driven by the amplified electrical quantity to be processed to produce a shaft rotation corresponding to this quantity, and a mechanical device for squaring this shaft rotation and multiplying it by the constant K through a gear drive of the required ratio. The resulting mechanical quantity is converted back into the corresponding electrical quantity by a generator driven by said mechanical quantity before being fed to a summing and amplifying unit 47 to be described. The amplifying and squaring units 45 and 46 may have the usual feedbacks of the electrical quantities RdE and RhdB for stability and control.

The two electrical quantities K(RdE) and K(RhdB) obtained in the manner described and the quantity dR are fed as input into the summing and amplifying network 47 to obtain the corercted range rate following the Equation 8.

The electrical quantity, dRs is fed into a multiplier 50, shown for purposes of illustration as a potentiometer, in conjunction with the fuze setting order F in mechan ical form obtained from the output of the apparatus of FIG. 6, to obtain the electrical product FdRs. Similarly, the mechanical quantity -Tf corresponding to the time of flight derived from the computer of the gun control system, is fed into a multiplier 51 in conjunction with the electrical quntity dRs, to obtain the electrical product TfdRs. Also, the mechanical quantity dead time Tg set by a handcrank 52 in a dial indicator system is transmitted as an input into a multiplier 53 into which is also fed the electrical quantity dRs to obtain the electrical product TgdRs.

The three electrical quantities FdRs, -TfdRs and TgdRs, obtained in the manner described, are fed as inputs into a summing and amplifying network 54 to obtain the range change due to dead time following the Equation 7.

The electrical quantity Rtg represents range change due to dead time is delivered as an input into a potentiometer 56 in conjunction with the mechanical quantity T This potentiometer 56 is similar to the potentiometer 33 in the construction of FIG. and is similarly wound to modify in eflect the T7 value into the corresponding rate of change of time of flight at the present instant with respect to range in accordance with the curve A shown in FIG. 1 and the ballistic table referred to above. The electrical output of the potentiometer 56 is therefore the product of the range change due to dead time Tg represented by the quantity Rtg and the rate of change of time of flight T f at the present instant with respect to the range, this product being represented by the electrical quantity Ftg corresponding to the correction for dead time in seconds. This quantity Ftg when added to time of flight Tf produces the desired fuze setting order F.

The electrical quantities Ftg and T are added in an adding, controlling and amplifying network 57 and the resulting electrical fuze setting order F is processed through a. servo mechanism 58 similar to the servo mecha- 8 nism 36 in the apparatus of FIG. 5 to convert quan tity F into mechanical form for transmission to the fuze setters at the gun mounts through a synchro transmitter 60.

In the following claims, by physical quantity is intended either an electrical signal in terms of its voltage or a shaft rotary displacement.

While the invention has been described with particular reference to specific embodiments, it is to be understood that it is not to be limited thereto, but it is to be construed broadly and restricted solely by the scope of the appended claims.-

What is claimed is:

1. An apparatus for determining the fuze setting order F for a fuzed projectile in a gun fire control system and for obtaining said order as a physical quantity, comprising means responsive to a physical quantity Tf representing the time of flight for producing a physical quantity representing the rate of change of the time of flight Tf at the present instant with respect to the range corresponding to the known ballistics of the projectile, means for multiplying the quantity representing the rate of change of the time of flight by a physical quantity Rtg representing the change in ballistic range which will occur during the dead time Tg due to relative movement between the gun mount and the target during the dead time, to produce the physical quantity Ftg, representing the correction which when added to time of flight T1 allows for the relative motion of target and projectile during dead time Tg and means for adding the quantity Ftg and the quantity T to produce the physical quantity F representing the fuze setting order.

2. An apparatus for determining the fuze setting order F for a fuzed projectile in a gun fire control system and for obtaining said order as a physical quantity, as described in claim 1, wherein the means for producing a physical quantity representing the rate of change of the time of flight and the means for multiplying the latter quantity by the quantity Rtg is a potentiometer having as inputs the quantity T and the quantity Rtg, the potentiometer being calibrated to translate the .TJ quantity into the corresponding rate of change of the time of flight, whereby the output of said potentiometer is the product of the quantity representing the rate of change of the time of flight and the quantity Rtg.

3. An apparatus for determining the fuze setting order F for a fuzed projectile in a gun fire control system and for obtaining said order as a physical quantity, comprising means responsive to the physical inputs, H, dH, Tg, RhdB, 'Rh and (R for obtaining the physical quantity R3 by mechanizing the equation wherein R3=advance range in connection with projectile outside the gun and being set H =height of target dH=rate of climb of target F=fuze setting order Tg=dead time RhdB=linear bearing rate of target Rh=horizontal range of target dRh=horizontal range rate of target E3 =advance elevation of target in connection with projectile outside of gun and being set Dh3 =horizontal deflection of target means for subtracting the physical quantity R2 representing the advance range in connection with the projectile in the gun and to be instantly fired, from the quantity R3, to produce the physical quantity Rtg representing the change in ballistic range which will occur during the dead time Tg due to relative movement between the gun mount and the target, means for multiplying the quantity Rtg by a physical quantity representing the rate of change of the time of flight at the present instant with respect to the range determined from the ballistics of the projectile to produce the physical quantity Ftg, representing the correction which when added to time of flight Tf allows for the relative motion of target and projectile during dead time Tg and means for adding the quantity Ftg to the physical quantity T f representing the time of flight to produce the physical quantity F representing the fuze setting order.

4. An apparatus for determining the fuze setting order F for a fuzed projectile in a gun fire control system and for obtaining said order as a physical quantity, as described in claim 3, wherein the means for multiplying the quantity Rtg by a physical quantity representing the rate of change of the time of flight constitutes a potentiometer having as inputs the quantity Tf and the quantity Rtg, said potentiometer comprising means for translating the T input quantity into a physical quantity representing the corresponding rate of change of the time of flight predetermined from the known ballistics of the projectile, to produce the physical quantity Fzg at the output of said potentiometer.

5. An apparatus for determining the fuze setting order F for a fuzed projectile in a gun fire control system and for obtaining said order as a physical quantity, comprising means responsive to input physical quantities dR, RhdB and RdE for obtaining the physical quantity a Rs by mechanizing the equation wherein dRs== corrected range rate dR=range rate K constant RhdB=linear bearing rate of target RdE=linear elevation rate of target 10 means for producing the physical quantity (FTf+Tg) wherein F=fuze setting order Tf=time of flight Tg= dead time means for multiplying the quantities dRs and (FTf+Tg) together to produce the physical quantity Rtg representing the change in ballistic range which will occur during the dead time Tg due to relative movement between the gun mount and the target during this dead time, means for multiplying the quantity Rtg by a physical quantity representing the rate of change of the time of flight Tf at the present instant with respect to the range determined from the known ballistics of the projectile to produce the physical quantity Ftg, representing the correction which when added to time of flight Tf allows for the relative motion of target and projectile during dead time Tg and means for adding the physical quantity Ftg to the physical quantity T1 to produce the physical quantity F.

6. An apparatus for determining the fuze setting order F for a fuzed projectile in a gun fire control system and for obtaining said order as a physical quantity, as described in claim 5, wherein the means for multiplying the quantity Rtg by a physical quantity representing the rate of change of the time of flight constitutes a potentiometer having as inputs the quantity Ty and the quantity Rtg, said potentiometer comprising means for translating the T input quantity into a physical quantity representing the corresponding rate of change of the time of flight predetermined from the known ballistics of the projectile, to produce the physical quantity F tg at the output of said potentiometer.

References Cited in the file of this patent UNITED STATES PATENTS 2,408,081 Lovell Sept. 24, 1946 2,493,183 Boghosian Jan. 3, 1950 2,658,676 Lundstrom Nov. 10, 1953 2,663,496 Heydenburg Dec. 22, 1953 2,696,947 Hauser Dec. 14, 1954

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