US2873067A - Fuze setting order computer - Google Patents

Description

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ATTORNEY l I l I l I I l l l I l Il QRSQ# fllig United States Patent FUZE SETTING ORDER COMPUTER George A. Crowther, Manhasset, N. Y., assignor to Sperry Rand Corporation, a corporation of Delaware Application February 26, 1954, Serial No. 412,747 2 claims. (cil zas-61.5)

Thelpresent invention `relates toa gun fire control system of the automatic type, 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 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 effect. 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 (Tf) of the projectile from the instant of tiring 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 ICC Fuze Setting Order (F) may be computed in accordance with the present invention, and

Fig. 2 is a diagram of a rate network which may be employed in connection with the fuze network shown in Fig. l.

Fuze Setting Order (F) will vary as some function of time. If we call this function f(T), and expand this function in accordance with Maclaurins theorem, there is obtained At `z'ero time (T=0), F equals Tf. The problem is to time elapses between the setting of the fuze mechanism i 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 order to arrive at a true value of Fuze Setting Order, it is necessary to solve .the gun ballistic problem for a time plus Tg seconds in the future. Since this method would obviously double the mechanism in a fire control computer, an approximation of the true Fuze Setting Order is computed. Hitherto, a fictitious range was computed which positioned a three dimensional cam whose configuration represented the Time of Flight of the type projectile in use. This fictitious range theoretically took into account the probable change in distance between the present instant and the instant the gun would be tired Tg seconds later.

One object of the present invention is to provide a new and improved method and mechanism for computing Fuze Setting Orders (F) attaining optimum resultswith minimum of assumptions and minimum of mechanical and/or electrical complications.

In accordance with a feature of the present invention the range computing mechanism and the three dimensional cam hitherto employed are eliminated by modifying the existing Time of Flight by reference to the dynamic behavior of the projectile. In accordance with the present invention, a relationship having the following basic form is employed in solving for the Fuze Setting Order (F), a'v in this relationship `representing the differential operator d/dt. A

Various other objects, features and advantages of the invention are apparent from the following particular description and from inspection of the accompanying draw ings, in which Fig. 1 is a diagram of a fuze network by which the determine F whenl T equals Tg. Substituting Tf for f(0) and Tg for T in Equation l, there is obtained Fuze Setting Order (F) is computed by using the first three terms of the series expressed in Equation 2, since the inherent inaccuracy of the dead time input (being a function of many variables, particularly gun elevation) does not warrant a more exact solution. The second and third terms of this Equation 2 represent the change in the time of flight during Tg.

Because of the nature of the fuze network employed for obtaining Fuze Setting Order (F), the equation solved by this network is instead of Equation 2. The term (dl`f)' differs from dT f and the term (d2Tf) differs from d2Tf by the delay time K inherent in the integrator employed as a component of the fuze network to be described. Correction for this delay time may be made by employing the equation Since, in general, the acceleration term will be small, the error in its computation may be neglected. Therefore, it 'can be assumed that (d2Tf)' is practically equal to (d2Tf), thereby obtaining Knowing the characteristics of the integrator, the delay factor K inherent therein can be determined and this factor substituted into Equation 4 for mechanization. In the specific embodiment of the fuze network illustrated in Fig. 1, the delay constant K built into the integrator circuit is considered to be l second, so that the actual equation solved by this network is The drawings show the method employed to compute Fuze Setting Order (F), the full lines representing mechanical lines and the dotted lines electrical lines. In the network illustrated in Fig. 1, Time of Flight (Tf) determined by the ballistic network and time (T) represented by the output of a synchronous motor are combined in a rate computing loop shown in basic form in Fig. 2 to produce (dT f)'. This loop utilizes a mechanical integrator 10 of the well-known type arranged in a loop circuit, so that it operates as a ditferentiator. This mechanical integrator 10 is shown of the well-known mechanical disc type. In this description, the letter C" aars-,oer

will be used to distinguish computed quantities from inputs. A time motor (not shown) drives the integrator disc 11 at a constant speed, so that the revolution of this disc represents (T). A differential 12 compares the output ATfc of the integrator roller 13 with the Time of Flight (Tf) whose rate of change is to be computed. The difference )Tf between Tf and ATfc turns a gearing 14 of ratio Q. The output of this gearing connects with the integrator carriage 15 and moves the carriage so as to reduce the difference. It will be shown that the position dT fc of the carriage 15 closely represents the rate of change of Tf.

Since the integrator disc 11 of the integrator 10 is driven at constant speed, the speed of its roller 13 is proportional to the displacement of its carriage 15 from the center of the disc. Expressed mathematically where ATfc is the roller output and d is the differential operator d/dt. The constant'proportionality has been omitted for simplicity. Integrating this equation,

AT fc: f dTfc T his is the mathematical expression for the roller output. Difference )Tf computed at the differential output, is defined by the relation:

Equation 6 shows that if Q is very large, dT fc very nearly equals d1 f. Q is commonly called the sensitivity, since it is a measure of the sensitiveness of a'Tfc to l changes in aTf.

The error in dlfc, the computed Time of Flight rate of change, is shown by Equation 6 to be 1 Q The error is proportional to the rate of change of dT fc, that is the rate of movement of the integrator carriage 15. Compensation is made for this error, in the manner described in deriving the Formula 5, by considering the time delay factor K and employing the corresponding value of K (1 second for the specific embodiment illustrated) according to the characteristics of the rate computing loop. The output of the rate computing loop is therefore equal approximately to (dT f) of Equation 5.

Referring back to Fig. 1, the output of the rate network comprising the integrator 10 and the differential 12, with mechanical inputs T and Tf produce the mechanical output (dTf), the computed time rate of change of Time of Flight (Tf). A potentiometer 17 converts the mechanical quantity (dTf) to a corresponding voltage l. quantity.

Similary, the mechanical quantities (Jlfy and T are combined in a rate network comprising an integrator 18 and a differential 19 to form the mechanical quantity (d2Tf), the computed second derivative of Time of Flight (Tf). This mechanical quantity (d2Tf) is converted into a corresponding voltage by means of a potentiometer 20 and increased in power by a loop comprising a summing network 21 and an amplifier 22. The Dead Time (Tg), a mechanical hand input is modified to (Tg4-2 sec.) and this mechanical quantity is multiplied by the voltage (d2Tf) in a potentiometer 23 to form the voltage having the value l/2(T,1i2)(d2Tf). This latter voltage is superposed on the voltage (d'1`f)' through [(dTf)'l- (Tg-l-Z)(d2Tf)'31fg and Time of Flight Tf) in the form of voltage are brought to a null seeking mechanism comprising a summing network 30, and a servo mechanism of the known type comprising basically a servo control 31, a servo amplifier 32, a servo motor 33 and an induction or rate generator 34 connected in a double loop circuit with the summing network 30. Essentially, the summing network 30 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 60 cycles (assuming that the fuze network is operating at a higher `frequency) byl the servo control 31, amplified by the servo amplifier 32 and supplied to the servo motor 33 for its control. The servo motor 33 converts voltage into mechanical output and drives thereto improve the operation of the servo mechanism.

from the induction or rate generator 34. From this rate generator 34, va voltage proportional to the output velocity is supplied to the servo control 31. After being modified by computing elements in the servo control 31, the modified voltage is combined with the error voltage In other words, the inputs and Tf when added algebraically in the summing network 30, should produce the Fuze Setting Order (F) in accordance with Equation 5 and the servo mechanism 31, 32, 33 and 34 operates to minimize any errors in the solution of this equation, until the proper quantity for the Fuze Setting Order (F) is achieved. This Fuze Setting Order (F) is transmitted, as for example, via synchro transmission, to the fuze Setters at the gun mounts. l

The network of Fig. 1 solves an equation, which basically has the form of series (2) as follows Since Time of Flight (Tf) as furnished by the ballistic network is fairly continuous and accurate, it may be found sufcient under certain conditions and in accordance with certain phases of the present invention, to dispense with smoothing in the rate network determining the quantity (aTf)' and thereby to ignore the time delay constant K. For this reason, the sensitivity of the rate network may be considered to be'unity. Under these conditions, Equation 7 may be mechanized in its basic form without being modified by the time delay factor K. The mechanization of this time equation would be similar to that shown in Fig. 1, except that Dead Time (Tg) would not be modified to (Tg-l-ZK) before being fed into the potentiometer 27.

What is claimed is:

1. A device for determining fuze setting order in a gun fire control system comprising means for continuously mechanizing the equation wherein F represents the fuze setting order, Tf the time of ight, Tg the dead time and d the differential operator d/dt, to obtain continuously the quantity F, said mechanizing means comprising a rate network for combining time and Tf as mechanical inputs to form mechanical quantity (dT f)' the computed rate of change of Tf, a rate network for combining the mechanical quantity (Jl`f)' and mechanical time to form the mechanical quantity (d2Tf)' the computed rate of change of (dTf), means for converting the mechanical quantities (dTf) and (d2Tf) into corresponding voltage quantities, means for converting the mechanical quantity Tg into (Tg-l-Z sec.), potentiometer means for multiplying the voltage (d21`f) by the mechanical quantity (Tg4-2) to form the voltage 1/z(Tg-{2) (dZTfV, means for adding the latter voltage to voltage (dTf) to obtain voltage potentiometer means for multiplying the latter voltage by mechanical quantity Tg to obtain voltage [(dT)+1/2(Tgl2)(d2Tf)'lTg summing means for adding together the latter voltage and the quantity Tf in the form of voltage to obtain the and a servo mechanism at the output of the last mcntioned summing means for reducing the error therefrom and to obtain F as a mechanical quantity.

2. A `device for determining fuze setting order in a gunre control system comprising means for continuously receiving as inputs physical quantities Tf the time of flight and Tg the dead time, a rate determining device responsive to Tf to obtain the quantity (dTf) representing the computed rate of change of Tf, means responsive to the quantity (aTf) to obtain the quantity (d2Tf)' the computed rate of change of (dTf), means for obtaining CFI the quantity l/z(Tg-i2K) wherein K is the delay factor in said rate determining device, means for multiplying the physical quantity (d2'I`f)' by 1/z(Tgi-2K) to obtain the quantity 1/2(Tg+2K) (d2Tf), means for combining the latter quantity and the quantity (dT f)' to obtain the quantity (dTfV-l-Vz (Tg4-2K) (dZTD means for multiplying the latter quantity by the quantity Tg to obtain the quantity [(dTf)'+1/2(Tgi2K)(d2Tf ]Tg and means for adding the latter quantity to the quantity Tf to obtain the quantity corresponding to the fuze setting order according to the equation References Cited in the le of this patent UNITED STATES PATENTS

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