US2919849A - Parallax computation apparatus - Google Patents

Description

Jan. 5, 1960 c. w. MILLER 2,919,849

PARALLAX COMPUTATION APPARATUS Filed Feb. 3, 1949 4 Sheets-Sheet 2 Ph cos E'b fia -Ph CATHOD E SERVO FOLLOWER AMPLIFIER INVENTOR CARLTON W. MILLER ATTORNEY Jan. 5, 1960 c. w. MILLER PARALLAX COMPUTATION APPARATUS 4 Sheets-Sheet 4 Filed Feb. 3, 1949 I INVENTOR CARLTON m MILLER BY X9 (9m ATTORNEY United States Patent PARALLAX COMPUTATION APPARATUS Carlton W. Miller, Rochester, N.Y., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Application February 3, 1949, Serial No. 74,442-

'5 Claims. (Cl. 23561) This invention relates to a parallax computation apparatus, and more particularly an apparatus employing electrical servo systems for rapidly and simply computing a unit horizontal parallax correction suitable for making horizontal parallax corrections to the train orders of a gun or a number of guns located at different points on a vessel and firing at the same target.

In gun fire control, the director is usually located at a distance of at least several yards from the gun; such an arrangement necessitates a horizontal parallax correction to take account of the horizontal component of the angle between the line from target to director, and the line from target to gun.

An accurate solution of the parallax problem would have to be based on the future position of a moving target. In the instant invention, the present or instant position of the target is utilized for parallax computation, and the computed parallax correction multiplied by a constant 9/8, to take account of the fact that the most dangerous targets are those moving toward the vessel.

The solution of the parallax problem involves solving the following equation:

B sin Brp Ph. cos Eb T Ic1 4 in which the terms employed may be defined as follows:

B'rp-Director train corrected for horizontal parallax to the reference point of the ship which is assumed to be 100 yards aft from the gun.

B'r'-Director train (sight non-stabilized). The angle between the fore-and-aft axis of own ship and the line of sight to the target vertically projected into the deck plane, measured clockwise from the bow of own ship.

E'bDirector elevation. The elevation of the director line of sight to the target above the deck, measured in a plane perpendicular to the deck.

R-Range. The distance in yards from the director to. the target (measured along the line of sight).

R Projected range. The vertical projection of R into the deck plane.

Ph-Horizontal parallax. The angular correction to be applied to gun train order for a gun which is 100 yards fore of the reference point.

ePh--Error signal of the parallax angle.

Pbh-Horizontal parallax base length to reference point of ship. The projection into the deck plane of the distance measured in yards between the director and a selected reference point of the ship on the fore-andaft axis of the ship, positive when the director is aft of the reference point.

Pbh and hence Ph will vary as the parallax solution is obtained for different gun positions.

The parallax computation apparatus of the instant invention is particularly well adapted for use with the invention described and claimed in the application of Ivan A. Getting for Gun Fire Control Method and System, Serial No. 61,558, filed November 23, 1948.

2,919,849 Patented Jan. 5, 1960 An object of the instant invention is to provide new and improved horizontal parallax computation apparatus employing a minimum number of servo systems.

Another object is to provide new and improved horizontal parallax computation apparatus characterized by simplicity and a high degree of accuracy.

A further object is to provide new and improved apparatus for computing a unit horizontal parallax correction which may be applied simultaneously to a number of guns positioned at different distances from the director or reference point.

Still a further object is to provide horizontal parallax computation apparatus in which the speed of computation is regulated to be substantially uniform over a wide range of parallax values.

Other objects and many of the attendant 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:

Figs. 1A, 1B and 1C taken together comprise a schematic circuit diagram of a complete electrical system and apparatus suitable for practicing the method of the in vention;

Fig. 2 is a simplified schematic diagram of the apparatus of Figs. 1A, 1B and 1C; and

Fig. 3 is a diagram illustrating the geometry of the parallax computation problem vertically projected into the horizontal plane including the gun, that is, the deck plane.

In Figure 3 the symbols used have the following meanmgs:

B'rThe horizontal director train angle.

BThe displacement of the director from the gun.

D-The director position.

R The projection of target range, R, into the horizontal plane.

T The projection of the target in the horizontal plane.

LA line perpendicular to the line GT Ph-The horizontal parallax angle.

Referring now to the drawings in which like reference numerals are used throughout to designate like parts, and in particular to Figs. 1A, 1B and 1C thereof, an Eb servo motor 26 positions the shaft of a synchro generator 16, to which v., A.C., 60 cycles is applied from a suitable source, not shown. The resistance network comprising resistors 31, 32 and 33 is connected across the three terminals of generator 16 to provide proper loading and to insure that the voltage developed across leads 54 and 55 is substantially proportional to the quantity cos Eb, generator 16 being suitably constructed for this purpose. Resistors 31 and 32 may have a value of 2 kilohms each and resistor 33 a value of 3.3 kilohms.

The voltage developed across leads 54 and 55 is applied by way of alignment potentiometer 34 to the terminals of a tapped potentiometer 19, the arm of which is positioned by the quantity Ph by suitable mechanical connection 50 to a Ph servo motor 13. Potentiometer 19 may have a value of 5 kilohms. Lead 56 is connected to the tap on potentiometer 19, and lead 57 is connected to the arm of potentiometer 19. The voltage appearing across leads 56 and 57 is proportional to Ph cos E'b it being understood that the constant k14, which may have a value of 9/8, may be introduced by suitable proportioning of the circuit constants.

The constant kl4 is necessitated by the fact that whereas the parallax correction should preferably be made for the future position of the target, in the instant system the correction is made for present or instant position, this being a simpler method of computation. Since the most dangerous targets are those which are moving toward the director, a constant is introduced to make the parallax angle larger. By experimentation, the value 9/8 has been found suitable for this purpose.

A Brp servo motor 15, by suitable mechanical cou pling to a generator 18, positions the shaft thereof. Generator 18 is energized by 110 v., A.C., 60 cycles and has three output terminals across which is connected the resistance network comprising the resistors 41, 42 and 43 to provide correct loading for the generator. Generator 18 is constructed and arranged so that the voltage developed therefrom across leads 56 and 71 is proportional to the quantity sin B'r'p.

Lead 71 is connected to the arm of a potentiometer 17 which may have a value of 100 kilohms, and which has the arm thereof positioned by the quantity R by suitable mechanical coupling to an R servo motor 30. One end of potentiometer 17 is connected by way of resistor 27, which may have a value of 3360 ohms, to lead 56, while the other end of potentiometer 17 is connected by way of resistor 28, which may have a value of 1748 ohms, and resistor 29, which may have a value of 1611 ohms, to lead 56.

The junction between resistors 28 and 29 is connected to one terminal of a secant attenuator 14 which may have a total value of 20 kilohms, the other terminal of the attenuator 14 being connected to lead 57.

The arm of attenuator 14 is positioned by the quantity of E'b by suitable mechanical coupling to an E'b servo motor 26, and the arm is connected by way of lead 45 to one input terminal of a filter 23, the other input terminal of filter 23 being connected by way of lead 44 to the junction between resistors 28 and 29.

The output of filter 23, which may be of conventional design, is delivered by leads 21 and 22 to a cathode follower 24, the output of which is applied to a servo amplifier 25 which in turn drives the Ph servo motor 13.

Motor 13 is operatively connected by aforementioned coupling 50 to an A.-C. tachometer 39, the tachometer being connected by way of lead 44, and lead 46 and resistor 38, which may have a value of 62 kilohms, to the input of filter 23, for providing a stabilizing voltage therefor. The tachometer 39, may, if desired, be a D.-C. tachometer, and means, not shown, provided for converting its output to A.C. before mixing with the error signal at 23.

Dial 47 indicates the value of the quantity of Ph. Coupling 50 also has connected thereto a Ph generator 20 suitably energized from a source of 110 v., A.C., 60 cycles, not shown, and is provided for giving a Ph output signal for transmission to gun and fuze servos.

A B'r' drive or servo motor 35 is operatively connected to a pair of servo generators 36 and 37, which are both suitably energized from a source, not shown, of A.C. potential of 110 v., 60 cycles. Connected across these generators 36 and 37 are capacitance networks 74 and 73 respectively, for increasing the power factors of the circuits. The output of generator 36 is applied to a differential generator 11, and the output of generator 37 is applied to a differential generator 11'. The shafts of both these differential generators are positioned through change gears 12 and coupling 50 from the Ph servo 13, and their outputs are proportional to the quantity B'r'p.

The output of the differential generator 11 is applied by way of leads 51, 52 and 53 to control transformer 59, while the output of generator 11' is applied by way of leads 71, 72 and 73 to control transformer 60. Transformer elements 59 and 60 have the shafts thereof positioned by the quantity B'r'p by suitable coupling 49 to the aforementioned B'rp servo motor 15. The voltage outputs of transformers 59 and 60 represent the instantaneous error in B'r'p.

Relay 70 is provided for purposes to be hereafter apparent; when unenergized, a circuit, by way of lead 67 and by way of lead 75, from control transformer 60 to filter 64, is completed. The output of filter 64 is applied to cathode follower 65, and the output thereof is applied to servo amplifier 66 which in turn controls servo motor 15. Motor 15 is connected to a suitable source of A.C. potential, not shown, of the order of 110 v., 60 cycles.

Control transformer 59 has connected in series with the output thereof the secondary of a transformer 61 which has the primary thereof energized from a suitable source of A.C. potential, not shown, of the order of 110 v., 60 cycles. The secondary voltage which may be of the order of 3 volts is of a polarity to oppose the voltage output of transformer 59. When the voltage from 59 is sufiicient to override the voltage from the secondary of 61, it is rectified at 62, amplified at 63, and energizes the winding 68 of relay 70, thereby providing a circuit in which the voltage diiferential between 59 and 61 is applied to filter 64.

The operation of the above traced circuit will be readily apparent to those skilled in the art and, therefore, need not be described in detail.

Any change in the quantities Eb, B'rp, or R results in an unbalance between the sin B'r'p R signal applied to attenuator 14, and an ePh signal appears between leads 44 and 45. This ePh signal drives servo motor 13, and shaft 50 operatively connected to motor 13 moves the arm of potentiometer 19 in the proper direction selectively in accordance with the polarity of the ePh signal until the signals at attenuator 14 are balanced.

Fig. 2 is a simplified schematic of the circuit and system of Figs. 1A, 1B and 1C, and need not be traced in detail. The designations of the various elements of Fig. 2 are the same as the corresponding elements of Figs. lA-lC but are shown in somewhat more schematic form to facilitate a ready understanding of the circuit operation, which is substantially the same as the operation of the circuit and system of Figs. 1A-1C.

The parallax equation employed in the instant invention may be derived as follows from Fig. 3. Gun and director are located at points G and D respectively and separated by a distance B which may be assumed, for ease in explanation, to be yards. The vertical projection of the target T into the horizontal plane is T The target T may be thought of as being a point directly above T if the drawing is on a horizontal surface. The horizontal parallax angle Ph is measured between the line from T to the gun and the line from T to director. The train angle Br is measured at point D, the director, between the lines DG and D--T The line L is dropped from G perpendicular to the line GT and intersecting line DT at X.

Since the angle Ph is small and since the distance DX is also small, we can assume sin Ph Ph-- We can also assume with negligible error that angle DXG is a right angle and therefore that sin B r Then,

B sin Br Ph R the vertical projection of range into the horizontal plane=R cos E72, where E'b is the elevation angle of the target T above T as is viewed from D, and R is the actual measurable range to the target T from D.

Therefore,

B sin B r R cos Eb Multiplying both sides by cos Eb and introducing a constant kl4 to account for anticipated motion of the target gives:

(cos Eb) Ph B sin B r 7014 R Brp, as has been stated, is the director train corrected for horizontal parallax to a predetermined reference point of the ship and may be conveniently substituted for Br'. The last mentioned equation then becomes:

(cos Eb) Ph B sin Brp kl4 R Accordingly, as stated before BsinB'rp Ph cos Eb If B is taken as the unit of measure for R the equation becomes sin Brp cos E b Before the solution of the last named equation takes place in the aforedescribed circuit, that is, before the error signal is reduced to zero, a voltage proportional to the parallax error, ePh, times cos Eb exists in the circuit. This gives for an unbalanced condition of the circuit the equation For a given error in Ph, the amount of this voltage depends on the value of cos Eb. As a result of this condition of operation the servo loop gain varies with Eb, and speed of response and stability might become unsatisfactory at extreme values of cos Eb. For this reason, the voltage is multiplied by sec Eb. It is to be noted that this multiplication does not materially affect the equation solved, but regulates the gain of the servo loop. This can be seen from a consideration that the secant of an angle varies inversely as the cosine, therefore, the cos Eb multiplied by the sec Eb yields a constant.

If, therefore, the term ePh cos Eb is multiplied by the sec Eb the variable angle function cos Eb cancels.

It is obvious that, if desired, the parallax angle might also be computed from a center or reference point on the vessel.

Since the unit parallax correction for a 100 yard base length is designated Ph, for the quantities into which the parallax corrections enter,

cos Eb:

Pbh I I I I B r p-B 1' Ph where Pbh is the distance from the director to the center point of the ship (positive if the director is aft of the center point). It is again to be noted that the factor Pbh only corrects the director train angle for parallax to the reference point of the ship.

As will be readily understood by those skilled in the art, the ratio of change gears 12 of Figs. 2 and 1B depends upon the distance between the director and the reference point.

Whereas certain values have been stated as suitable for the resistor elements employed in the circuit, it is understood that other values could be employed if desired.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed as new and desired to be secured by Letters Patent of the United States of America is:

1. In a ship, parallax computation apparatus for a gun and a director movable in elevation and train having a common reference point, said gun, director and said point being located in the same substantially horizontal deck plane of the ship, and having a target, comprising in combination, a synchro generator having the shaft thereof positioned in accordance with the angle of elevation of the target above the plane viewed from the director, Eb, said synchro generator being constructed and arranged to provide an output signal corresponding to the quantity which is the cosine function of the elevation angle, cos Eb, when said shaft is positioned, first adjustable potentiometer means operatively connected to said generator and having the cos Eb signal applied thereacross, the arm of said first potentiometer means being adapted to be set to a position in accordance with the parallax angle, which is the projection in the horizontal plane of the angle subtended at the target by the gun and the director, Ph, said first potentiometer means being constructed and arranged to provide an output signal corresponding to the quantity which is the product of the parallax angle and the cosine function of the angle of elevation divided by an empirical constant Ph cos Eb when said arm is positioned, generator means having the shaft thereof positioned in accordance with the angle subtended at the director by the gun and the perpendicular projection of said target in the horizontal plane corrected for parallax to a reference point of the ship, Brp, and constructed and arranged to provide an output signal corresponding to the quantity which is the sine function of the parallax corrected angle of train, sin Brp, when the shaft thereof is positioned, second adjustable potentiometer means connected to said generator means, the arm of said second potentiometer means being positioned in accordance with the quantity R, which is the range to the target, said second potentiometer means being constructed and arranged to provide an output signal corresponding to the quantity sin B'r'p R which is the sine function of the corrected angle of train divided by the range, when the arm thereof is positioned, secant attenuator means having a movable contact element therefor and operatively connected to said first and second potentiometer means and having said Sin Br'p R and Ph cos Eb signals applied thereto in mutual opposition, means operatively connected to said secant attenuator means for positioning said movable contact in accordance with the angle of elevation, Eb, said secant attenuator means providing an output signal, ePh, servo motor means controlled by said last output signal for providing a setting of the shaft thereof corresponding to the quantity Ph, said last named shaft being operatively connected to the arm ofsaid first potentiometer means for setting the arm to said Ph position, whereby said Ph cos E'b signals are continually maintained in substantial equality.

2. A parallax computer having input terminals for receiving voltages proportional to the elevation angle of a target, a train angle of a director and the target range, said computer having an output element, said computer including means receiving said train angle voltage and connected to receive a signal proportional to the computer output from said output element to produce a modified train angle signal proportional to the sum of the inputs, means receiving said modified train angle signal producing a sine function signal proportional to the sine of said modified angle, means receiving said sine function signal and a function signal of said range to produce a quotient of said sine function and said range; means receiving said elevation angle voltage to produce a cosine signal proportional to the cosine function of said elevation angle, means receiving a portion of the computer output and said cosine function to produce a voltage proportional to a product of said output and said cosine function, means receiving said product voltage and said quotient voltage to compare them and to produce a voltage proportional to their difference, said output element receiving said difference voltage to produce a parallax angle output for computer, said output means being operative to drive said means for producing said product voltage to reduce said difference voltage to zero.

3. In a ships horizontal parallax computation apparatus for a gun and a director movable in elevation and train and having a common reference point, said gun, director and said point being located in the same substantially horizontal deck plane of the ship, and having a target, in combination, first means for obtaining a signal proportional to the quantity which is the cosine function of the angle of elevation of the target above the plane viewed from the director, cos Eb, second means operatively connected to said first named means for obtaining from said signal a second signal proportional to the quantity which is the product of the vertical projection in the horizontal plane of the angle subtended at the target by the gun and director and the cosine function of the angle of elevation divided by a constant Ph cos E1) where kl4 is a constant, third means for obtaining a third signal proportional to the quantity which is the sine function of the angle subtended at the director by the gun and the perpendicular projection of said target in the horizontal plane divided by the range to the target a secant signal voltage attenuator means having said and sin B'r'p R and Ph cos Eb signals applied thereto in mutual opposition so as to provide a voltage proportional to their difference, said attenuator means providing a fractional part of said difference as an output, fifth means for adjusting said fractional output according to the secant of the angle of elevation of the target, said angle being E'b, servo motor means responsive to the output of said attenuator for producing rotation corresponding to the projection in the horizontal plane of the angle subtended at the target by the gun and director, said servo motor means being operatively connected to said second means receiving the output of said servo means.

4. In a ships horizontal parallax computation apparatus for a gun and a director movable in elevation and train and having a common reference point, said gun, director and said point being located in the same substantially horizontal deck plane of the ship, and having a target, in combination, means for obtaining a signal proportional to the quantity which is the cosine function of the angle of elevation of the target above the plane viewed from the director, cos E'b, a potentiometer operatively connected to said means and adapted to have said cos E'b signal applied therea-cross, said potentiometer be ing adapted to have the arm thereof positioned by means corresponding to the parallax angle, Ph, which is the vertical projection in the horizontal plane of the angle subtended at the target by the gun and the director, said potentiometer being adapted to supply an output signal corresponding to the quantity which is the product of the parallax angle and the cosine function of the angle of elevation divided by an empirical constant,

Ph cos Eb when positioned by said last named means, means for obtaining a signal corresponding to the quantity which is the sine function of the angle of train, that is, the angle subtended at the director by the gun and the perpendicular projection of said target in the horizontal plane, cor rected for parallax, sin B'rp, an additional potentiometer adapted to have said sin B'r'p, signal applied thereto, means for positioning the arm of said last named potentiometer by a signal proportional to the range, R, of the target, to provide an output voltage corresponding to the quantity which is the sine function of the angle of train corrected by parallax divided by the range,

sin B'r'p a secant attenuator means including a resistance element and including an adjustable tap for taking otf a fractional portion of the voltage thereon and having said sin B'r'p and said Ph cos E'b signals applied respectively at each end of said resistance element, said attenuator means providing an output signal between the tap and one end of the resistance ele ment proportional to the quantity which is the error signal for the parallax angle, ePh, and means responsive to said ePh signal for positioning the arm of the first named potentiometer by the parallax angle, Ph.

5. A horizontal parallax angle computation device for determining the angle in the horizontal plane subtended by the displacement of a first and second point in the horizontal plane at a third point in the horizontal plane being the vertical projection of a target point not in the horizontal plane, comprising, a first means producing a voltage proportional to the vertical angle between a line joining said first and target point and said plane, a second means producing a voltage proportional to the horizontal angle between said line joining said first and third points, and a line joining said first and second points, a third means for modifying the output of said second means to produce a voltage proportional to the sum of the horizontal angle and the computed parallax angle, a fourth means producing a signal proportional to the sine function of the output of said third means, a fifth output producing means which divides the output of said {with means by the distance between said first and tar get points, a sixth means producing a voltage proportional to the cosine function of the output of said first means, a seventh means combining the output of said sixth means and the computed parallax angle to produce an output proportional to the product of said parallax angle and said output of the said sixth means, an eighth means receiving the outputs of said first, fifth and seventh means to produce an error voltage proportional to the product of the difference between the outputs of said fifth 1 2,575,956

and seventh means and the cosine of the vertical angle, and a ninth means receiving the output of said eighth means to produce an output connected to said third means and which represents said parallax angle.

References Cited in the file of this patent UNITED STATES PATENTS Agins Mar. 29, 1949 Hereford et al. Nov. 20, 1951

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