US2611537A

US2611537A - Parallax correction circuit

Info

Publication number: US2611537A
Application number: US541750A
Authority: US
Inventors: Gifford E White; Robert L Graef; Forge Charles J La
Original assignee: Sperry Corp
Current assignee: Sperry Corp
Priority date: 1944-06-23
Filing date: 1944-06-23
Publication date: 1952-09-23
Anticipated expiration: 1969-09-23
Also published as: GB604213A

Description

sail-F...

Sept. 23, 1952 3 Sheets-Sheet 1 Filed June 23, 1944 COARSE Dl FFERENTiAL Azmufn GUN TURRET REC.

ELEVATION DIFFERENTIAL :II I .2 RN mm mm m 7 u A W A m P 23, 1952 G. E. WHITE EI'AL PARALLAX CORRECTION cmcun 3 Sheets-Sheet 2 Filed June 25, 1944 INVENTORS'. GIFFORD E. WHITE L. GRAEF- L'AFOEZZP ROBERT Patented Sept. 23, 1952 UNITED STATES PATENT OFFICE PARALLAX CORRECTION CIRCUIT Gifiord E. White, Hempstead, Robert L. Graef, Brooklyn, and Charles J. La Forge, Hempstead, N. Y'., assignors to The Sperry Corporation, a

corporation of Delaware Application June 23, 1944, Serial No. 541,750

1 a relatively low cost, a compact light weight parallax correcting apparatus suitable for use on airplanes having guns controlled from computing mechanism at a central sighting station.

The desirability of parallax correction is recognized and various devices have been proposed for the purpose of computing parallax correction angles. A parallax correcting system is disclosed in the Italian patent to Zeiss No. 362,981, issued September 14, 1938, and in the abandoned Papello application Serial No. 212,349, filed June 7, 1933, and published May 25, 1943, by the Alien Property Custodian. A parallax correcting apparatus for inter-aircraft fire control is disclosed in the patent application of Knowles and Harris, filed March 1, 1943, Serial No. 477.666, now Patent No. 2,428,372, issued October 21, 1947.

In view of the known prior art of fire control and parallax correction, it is not thought necessary to give here a detailed discussion of the problems involved in determining parallax correction angles, as this subject is known to those skilled in the art.

In one embodiment, the invention contemplates a central station which may be provided with separate port and starboard computing mechanisms, each being controlled by any suitable target tracking device. Switching means are provided by which the respective computing mechanisms may be coupled, if the need therefor arises, to the guns on the opposite side of the craft.

In the embodiment of the invention about to be described, gun aiming data from a computer is transmitted to the gun turrets by suitable means for reproducing angular motion at a distance, a preferred data transmission device being a known type of self-synchronous motor. Differential transformer devices connected in the circuits interconnecting transmitter and receiver self-synchronous motors have their rotary members offset under control of the parallax correcting circuits to effect the required parallax correction of the gun turrets.

The invention will now be described with the aid of the accompanying drawings of which? Figs. 1 and 2, when placed side by side, show a wiring diagram of an embodiment of the invention;

' Fig. 3 is a block diagram showing another form of the invention; and

Figs. 4 and 5 show details of transformer windings.

The production of the present apparatus is simplified by the use of standard radio tubes. These tubes have well known characteristics which are fully described in various tube manuals.

In computing fire control data for controlling the directing of a gun mounted on an airplane toward a target, five variables are usually used for accurate determination of the ballistic and prediction corrections. These variables are azimuth, elevation and slant range, air speed and altitude. In addition, the rate of change of the target azimuth, elevation, and range are needed to permit computation of the future position of the target. Gun aiming angles are derived by the computing mechanism from these variables and transmitted to the gun turrets to effect a corresponding positioning of the guns. The parallax computer of the present invention modifies the data transmitted to the gun positions from the control station to compensate for parallax due to the spaced relationship of the cenl/li tral station and gun positions.

In a preferred embodiment of the invention, the computation of correction angles involves the use of electronic circuits and computing transformers. The computing transformers are high impedance transformers which receive their inputs from the data transmission lines of the control station without any noticeable load on them. The outputs from the secondary circuits of these transformers are proportional to the sines and cosines of the control station transmitters in gun azimuth (Ag) or gun elevation (Eg).

Two types of electronic circuits are required. The first is a phase sensitive multiplier circuit which takes two alternating current signals and gives out an alternating current signal whose amplitude is proportional to the product of the amplitudes of the input signals. The second is a reciprocal circuit which takes two alternating current signals and gives out an alternating current signal which is proportional to the ratio of the amplitudes of the input signals.

Uncorrected data comes from the transmitters of the control station to corresponding electrical differential transformers, each having a threephase rotor and a three-phase stator. The rotary members of the differentials are rotated under control of the parallax correcting circuits according to the proper correction angles, and the corrected data of their outputs are used to control the receiver motors which position the gun or turret. Another rotary transformer is geared to each set of the electric differentials and measures their position electrically. The output of the rotary transformer is fed back to the servo amplifier input where it bucks the computed correction signal. The difference in signals is fed to the amplifier which in turn operates the servo motor which drives the electric differentials until the differentials have reached their proper positions where the signal difference is zero.

The parallax correction arrangement herein described may be also applied to an automatic gun laying system, or the like, using a radar scanner or any other system where parallax correction is desirable.

One embodiment of the invention contemplates parallax correction as applied to the most practical arrangement of control station and gun turrets wherein the control station and turrets are substantially in alignment along the longitudinal axis of the airplane.

When the control station and turrets are so positioned along the longitudinal axis of the airplane, the azimuth correction angle is closely proportional to the sine of the gun azimuth angle (Ag) divided by the product of the cosine of the gun elevation angle (E and slant range (Do) and the elevation correction angle is closely proportional to the cosine of the gun azimuth angle multiplied by the sine of gun elevation angle and divided by slant range. The circuits by which these functions are computed electronically will now be described.

In the control station, shown in Fig. 1, coarse and fine azimuth transmitters and 2| have the respective phase windings of their threephase rotors connected to corresponding phase windings of the three-

phase stators

22 and 23 of coarse and fine azimuth

differential transformers

24 and 25 of the parallax correcting circuits. The three-phase rotors 26 and 21 of these differential transformers have their respective phase windings connected to corresponding phase windings of the three-

phase stators

28 and 29 of coarse and fine azimuth turret receivers 30 and 3|. The rotor windings of the turret receivers 30 and 3| are energized from a source of alternating current as are the stators of the computer transmitters 20 and 2|.

In the same manner, the

elevation transmitters

32 and 33 of the control station are interconnected with the stators of coarse and fine

differential transformers

34 and 35, whose rotors are similarly connected to the stators of

elevation turret receivers

36 and 31. The rotors of

elevation turret receivers

36 and 31 and also the stators of the corresponding elevation transmitters in the control station are energized from a source of alternating current.

Differential transformers

25, 24, 34 and are so constructed that when there is no difference in mechanical position between rotor and stator the transformer ratio thereof is 1:1. When there is no parallax correction, the rotors and stators are thus aligned and the turret receivers will be positioned as though they were connected directly to the transmitters of the control station.

If the differential transformer rotors are rotated through some fixed angle, the new voltages induced in the rotor windings thereof will be the same as the voltages would be in the control station transmitter stator windings if the rotors associated with the latter had been rotated through the same angle. Thus, if the rotors of the differential transformers are rotated through an angle corresponding to the necessary correction 4 for parallax, the turrets will move away from the position of the transmitter by the corresponding correction angle.

Motors 40 and 4| are controlled by the parallax correction amplifier, described further on. These motors are driven in one direction or the other, and through proper gearing, indicated by dot-dash lines, turn the rotors of the differential transformers through the necessary correction angle, thereby inserting the parallax correction.

The parallax correction circuit has its input connected to the self-synchronous motor circuits through four trig-function transformers of novel construction having output functions proportional to sines or cosines of the control station transmitters. The primary windings of the transformers are energized from the wires interconnecting the coarse transmitters of the control station and the differential transformers.

Each of the four trig-function transformers comprises three separate transformer units, the respective primary windings of the transformer units being delta connected and energized by the circuits interconnecting the coarse control station transmitters and the coarse differential transformers. The circuit details of the transformer units are shown in Figs. 4 and 5. The respective secondary windings of each transformer are connected in series, and the turn ratios are such that the magnitude of the output of alternating current is directly proportional to the desired trigonometric functions of the actual A2 and Eg angles and the phase of which (0 or degrees) reverses as the algebraic signs of the functions change.

Referring to Fig. 4, with the described primary connections, where e1. oz, and e; are amplitudes of the A. C. voltage, and 0 the angle of rotation of the Selsyn, then in the primary windings of the respective transformer units T1, T2 and T3 ei=E sin 0 e2=E sin (0+120) ea=E sin (0l20) and in the secondary windings,

and the total secondary voltage and T are functions of T1, T2, and T3 and can be made any desired values. The particular values of =0 and =90 give a sine and a cosine function respectively.

The transformer shown in Fig. 5 is the trigfunction transformer 45 for sin Eg. This transformer differs from the other trig-transformers in that each transformer unit is provided with two secondary windings, corresponding windings of each unit being connected in series and one terminal of each of the serially connected windings being joined to the corresponding terminal of the other windings to provide a center tap for a circuit to take care of positive and negative values of sin Eg.

Transformer 45 has the three terminals of its delta connected primary winding connected to elevation Selsyn leads 46, 41 and 48. Its secondary is center-tapped as shown in Fig. 5, and across each section of the output are connected serially connected

resistances

49 and 50. Resistance 49 has a resistance of approximately forty thousand ohms. while that of resistance 59 is ten thousand ohms. The center tap is connected to the secondary winding of transformer whose primary is energized from a source of alternating current. The output of transformer 45 is an AC. voltage proportional to sine Eg.

A vacuum tube 52 (Fig. 2) known commerically as a 6H6 tube, which is a double diode, has its cathodes 53 and 54 connected by

circuits

55 and 56 to the junction points between the

respective resistors

49 and 59.

The plate 51 of the diode is connected through a half megohm resistor 59 to the control grid of a vacuum tube 69 of the 68K? type. Plate 58 is similarly connected to the control grid of another tube 6|, also of the 68K? type. The cathodes of both tubes 69 and 6| are connected to ground. An output load network is provided for tube 52 composed of half megohm resistors 62 and 63 and condensers 64 bridged across plates 51 and 58 and connected at its midpoint to ground. Conventional screen grid and suppressor grid connections are employed for tubes 69 and 6 I. It will be understood that suitable filament circuits are used with the various tubes although none are shown.

The control grids of tubes 69 and 6| are also connected respectively through

condensers

65 and 66, and circuit 61 through resistances 68 and 69, of forty thousand and twenty thousand ohms respectively, to opposite terminals of secondary winding 19 of a trig-function transformer 1| having a turn ratio such that the magnitude of the secondary voltage is proportional to cos Ag, the primary being energized from the leads 12, 13 and 14 which interconnect the azimuth coarse differential transformer with the corresponding transmitter of the control station. With the arrangement just described, the grids of tubes 69 and 6| are energized by voltages proportional to sin Eg and cos Ag, the output of the tubes being arranged to produce and A. C. current proportional to sin Ea X cos Ag. The output circuit of tubes 69 and GI will be taken up again after the operation of the circuits of tubes 52, 69 and 6| has been described.

Assuming that Eg is zero degrees, then sin Eg, the voltage at the output of transformer 45 is also zero. In this condition, the two cathodes of double diode 52 are always at the same potential with respect to one another. The center tap of the voltage divider 49-49 in the cathode circuit receives an A. C. voltage from transformer 5| with respect to ground. When the cathodes swing negative in potential, the plates of the double diode which are connected to ground through resistances 62 and 63 are at a higher potential than their cathodes and both sections of the diode will conduct. This will cause a voltage drop across the two load resistors 62 and 63, and the condensers 64 associated therewith will charge. Both plates will become negative with respect to ground. The condensers will discharge slightly during the next half cycle when the cathodes swing positive and there is no plate current. In other words, the tube will act as a retifier and the plate voltages will be D. C. voltages. The magnitude of the negative plate voltages depends on the I. R. drops in

resistances

52 and 63, which in turn depend upon the plate currents. The plate current in a diode depends upon the difference in potential between the cathode and plate. Thus, the cathode volttage determines the D. C. plate voltage. Both plate voltages of the double diode 52 are approximately 8 V. when sin Eg=0.

Assuming now that sin E3 is not zero, and that the output of transformer 45 is such that during the negative swing of the cathode voltage, the upper terminal of the secondary winding is more negative than the lowermost terminal of the winding. With this condition cathode 53 will go more negative and cathode 54 less negative as the transformer causes an alteration in cathode voltages. As stated above, the cathode voltage determines the D. C. plate voltage, and hence plate 51 will become more negative and plate 58 less negative due to this particular sin E3. The change in the two plate voltages depends upon the change in cathode voltage, and since this change is proportional to sin Eg, the plate voltage is proportional to sin Eg. If sin Eg increases, the change in plate voltage increases. If the guns are moved by the transmitters of the control station to the other side of zero degrees, the algebraic sign of sin Eg changes. In this case, the lower terminal of the secondary winding of transformer 45 will be negative with respect to the upper terminal thereof during the negative swing of the cathode voltage, and now, plate 58 will become more negative, and plate 51 will become less negative. Thus, one plate voltage of the double diode becomes more negative than -8 V. (from transformer 5|) by an amount proportional to sin Eg, while the other plate voltage becomes less negative by an equal amount, and Which plate is more negative and which plate is less negative depends upon whether sin Eg is positive or negative.

Tubes 69 and 6| are well known super control amplifier tubes of a type used in many radio sets. The characteristic of this type tube is a remote cut-off with a variable amplification. factor. Curves showing the characteristics of this tube may be found in almost any radio tube manual.

The amplification factor can be defined as the ratio of the incremental change in plate voltage to the incremental change in grid voltage which causes it; that is, the change in plate voltage is equal to the change in grid voltage multiplied by the amplification factor. In this type, the amplification factor varies with changes in the grid bias.

Since tube 52 supplies the grid bias for tubes 69 and GI, the effect of sin Eg on these tubes is to change their bias, and since changing the grid bias changes their amplification factors, the amplification factor of one becomes larger while that of the other becomes smaller, depending upon whether sin E; is positive or negative.

The output of trig-function transformer II is a voltage proportional to cos Ag. This voltage is used as the A. C. signal voltage applied to the grids of tubes 69 and 6|. Since the change in amplification factor is directly proportional to sin Eg, and since the grid signal is cos Ag, the plate voltage of tubes 69 and 6| will vary as the product (cos Ag) (sin Eg). The bias on one tube will increase, while the bias on the other tube will decrease. In one case, the amplification factor will increase with an increase in sin Eg. and in the other case, the amplification factor will decrease with an increase of sin Es. Thus, the A. C. plate voltage will increase in one tube, for instance, tube 69, but will decrease in the other tube 6|. A difference in the A. C. component will appear on the plates and an A. C. current will flow in the primary winding 89 of transformer 8|.

The terminals of primary winding 89 of transformer 8| are connected through condenser 82 to the respective plates of tubes 60 and 6|. Two fifteen hundred ohm load resistances 83 and 84 are connected between the plates, and their junction point is connected to a source of D. C. potential. This is a conventional arrangement for eliminating the biasing effect of a. D. C. plate voltage on the primary winding of a transformer.

The secondary winding 85 of transformer 8| has one terminal connected to the control grid of a tube 81, which is of the 6SK7 type. The opposite terminal is connected through condenser 86 to the cathode of the tube and also through a resistance 88 and circuit 89 to a plate of tube 90 which is a 61-16 double diode. The corresponding cathode of the latter is connected via circuit 92 to the arm 93 of the potentiometer 94 of a range solution device at the control station. The potentiometer is connected through a dropping resistance 95 to a source of A. C. potential.

The cathode voltage of diode 90 is controlled by the operation of the potentiometer, the plate of the diode becoming more negative as the range increases. This plate voltage is used to apply grid bias to tube 81, and since the bias increases as the range (Do) increases, the amplification factor decreases as the range increases. The circuit is so balanced that the amplification factor varies inversely as the range. Thus, the A. C. plate voltage component of tube 81 (which equals the product of the A. C. grid signal and the amplification factor) is directly proportional to the product: (cos Ag) (sin Eg) o).

This is the expression for elevation parallax correction and it includes all of the variables.

A rotary transformer 96 having windings such that its output is a linear A. C. voltage of a magnitude proportional to the angular displacement of its rotor, has its stator energized from a source of A. C. current, and its rotor coupled by suitable gearing, indicated by dash-dot lines, to the differential transformer rotors. The rotor winding of rotary transformer 96 is connected via

circuits

98 and 99 to opposite terminals of a twenty thousand ohm potentiometer I00. An eight thousand ohm resistor ml is included in circuit 98. The arm I02 of the potentiometer is connected to one of the control grids I03 of a vacuum tube I05. The potentiometer can be adjusted to give a matching voltage, which takes into account the distance between the sighting station and the gun station. v

Tube I05 is a twin pentode amplifier of the 1644 type each section of which consists of a plate, suppressor, screen and control grids. A common cathode is used for both sections. The cathode is biased through a half megohm resistor. A control grid I08 of tube I05 is resistance coupled to tube 81, reference character I06 indicating the coupling condenser, and I01 a one hundred thousand ohm resistor for grid I08.

The plates N of tube I are connected to each other and are resistance coupled to the,

grid II I of one section of a twin triode amplifier II2 of the 1633 type. Condenser II3 is a coupling condenser which is connected through a one-tenth megohm resistor II4 to grid III. The grid is grounded through a one-tenth megohm resistor II5.

Tube I I 2 is a cathode follower stage. The purpose of this tube is to couple the high-impedance output of tube I05 to the low-impedance input transformer of the servo amplifier which will be described later on.

Resistance I20 is a twelve hundred ohm bias resistance for cathode I2| of the input section of tube H2. The plate I22 associated therewith is energized from a source of D. 0. through a fifty thousand ohm load resistor I23 and is resistance coupled to grid I24 of the output section through condenser I25, a fifty thousand ohm resistor I26 being the grid resistor. A two thousand ohm resistor I21 is provided in the circuit for cathode I28 which is connected at its ungrounded end through a condenser I29 of large capacity to one terminal of the primary winding I30 of transformer |3I, the other terminal of the primary being grounded. With the arrangement just described, the primary winding of the transformer is shunted across resistance I21 and will be energized in acordance with current variations in the resistance which correspond to those appearing at the tube input circuit.

The voltage applied to grid I03 of tube I05 from rotary transformer 96 is 180 out of phase with that of the other control grid I08. This voltage produces an A. C. component in the plate current which varies with the actual parallax correction.

Thus, the total A. C. plate current component through load resistor I I6 is the sum of the above two currents. These component currents are 180 out of phase with one another. If they are equal, they balance one another in effect, and there is no actual A. C. current through load resistor H6, and hence no actual A. C. plate current. This is the condition when the actual and computed corrections are equal. When the actual and computed corrections are not equal, the A. C. grid voltages of tube I05 are not equal, the two A. C. components of plate current are not equal, and hence do not cancel. Therefore, under these conditions, there is an A. C. plate voltage which is coupled through condenser II3 and tube I I2 to the servo amplifier where it will eventually produce a voltage to operate the elevation correction motor to change the actual correction, making it equal to the computed correction.

The elevation servo amplifier comprises two twin triode amplifier tubes I and MI, both of the 1638 type, for the purpose of controlling the operation of the elevation correction motor 4|, Fig. l, to insert the proper correction in the position of the turret. Motor 4| is of a known type and is connected by suitable gearing to the rotors of the elevation differential Selsyns as indicated by dash-dot lines.

Cathodes I and I5I of tube I40 are connected to ground through a two hundred ohm resistor I52. Grids I53 and I54 are connected to opposite terminals of secondary winding of transformer I3I for push pull operation. Plates I55 and I56 are bridged by condenser I51 and are connected respectively to grids I58 and I59 of tube I4.I.

Cathodes I60 and I6I are connected through a four hundred ohm resistor I62 to the ungrounded side of the A. C. supply, which is also connected to grids I58 and I59 through individual twenty-five thousand ohm resistors I63 and I64. Plates I65 and I66 are connected respectively to one terminal of the winding of a relay magnet I61 or I68, whose opposite terminals are grounded. The windings are bridged respectively by condensers I69 and I10.

Relay magnets I61 and I68 operate a balanced armature, shown for purposes of explanation as a double armature |1II12, pivoted at I13 and I14. The armature is spring loaded to assume the neutral position shown when the magnetic circuit is balanced. The armatures operate a current reversing circuit for controlling the operation and direction of motor 4I. When either magnet is energized more strongly than the other, the armature will turn on its pivots and an appropriate pair of contacts carried thereby will make with a pair of stationary contacts. Stationary contacts I and I16 disposed on opposite sides of the pivot are connected to a source of direct current and cooperate with armature contacts I11 and I18. Similarly, stationary contacts I19 and I80 are grounded and cooperate with armature contacts I8I and I82. The armature members HI and I12 are connected by circuits I90 and I9I to motor 4I. With the arrangement just described, motor 4I will be started in one direction or the other, depending on which magnet I61 or I68 is more strongly energized.

The elevation servo amplifier operates as follows: Both plates I55 and I56 of tube I40 receive a constant A. C.'voltage with respect to their cathodes which are connected to ground through resistor I52. The grids of this tube receive an A. C. voltage from transformer I3I when the actual parallax correction is incorrect. The size of the A. C. grid voltage depends upon the size of the error in actual correction. The phase of the A. C. grid voltage depends upon whether the actual correction is too large or too small. Using as a reference the time when the A. C. voltage causes the plates to swing positive with respect to the cathode, one grid, for example, grid I53 will swing positive with respect to the oathode, while the other grid I54 will swing negative with respect to the cathode. Therefore, one half of tube I 40 will conduct an appreciable current, while the other half will conduct a much smaller current. Thus, for the conditions assumed' the plate current of plate I55 will be large, and that for plate I56 small.

With no A. C. voltage from transformer I3I, both plate currents are equal. If the plate current for plate I55 has increased and that for plate I56 decreased, plate I56 becomes higher in potential than plate I55, because the voltage drop through resistor I64 has decreased and the drop through resistor I63 has increased. This happens during each half cycle when the A. C. voltage on plates I55 and I58 causes both plates to swing positive with respect to the cathode. During each half cycle when both plates are negative with respect to the cathode, there is no plate current, irrespective of the grid voltages, and both plates tend to become equal in potential. The condenser I51 connected between the plates charges quickly during the half cycle when there is plate current and it discharges slowly when there is no plate current. Hence, an average or D. C. plate voltage appears between the plates. For the conditions assumed, plate I56 will be at a higher D. C. potential than plate I55 with respect to the junction point of resistors I63 and I64. Therefore, grid I59 of tube I4I which is connected directly to plate I56 will be at a higher D. C. potential than gri-d I58 which is connected to plate I55, with respect to the cathodes of tube I4I.

Both cathodes of tube I4I' receive an A. C. voltage from the same source as the plates of tube I40. When the plates of tube I40 are both positive, the cathodes of tube I4 I are also positive, and therefore the plates of tube I4I, which are connected to the ground through the windings of magnets I61 and I68, are both negative with respect to their cathodes and no plate current flows in tube I4I. During the next half cycle, the plates of tube I are both positive with respect to the cathodes, and there is a flow of plate current through the windings of magnets I61 and I68. The size of each plate current is determined by the grid-to-cathode voltages in the tube. For the conditions previously assumed the grid-tocathode voltage of grid I59 is greater than that of grid I58. Therefore, the current flowing through the winding of magnet I68 to plate I66 will be greater than that flowing through the winding of magnet I61 to plate I65.

When equal currents flow through the windings of magnets I61 and I68, equal forces are applied to the balanced armature and a light spring loading, not shown, keeps the armature in neutral position which is the condition when there is no error in the actual correction.

When there is an error, there will be a current in the primary winding of transformer I3I and this will cause an unbalance in the circuits of relay magnets I61 and I68. With the conditions already assumed, the current in the winding of magnet I68 will be larger than in the winding of the other magnet and the armature will be attracted, closing contacts I15 and I11 and also I19 and I8I. If, for example, this operation of the relay was due to the actual correction being too large, then the elevation correction motor M will rotate in a direction to decrease the actual correction. When all error is removed, there is no A. C. signal from tube I05, the balancer stage, to the servo amplifier, and the armature I1 I'I 12 will assume its neutral position. If the error in the actual correction were in the opposite direction, then the winding of magnet I61 would be the more strongly energized and the opposite set of relay contacts I16-I18 and I-I82 would close reversing the polarity of the circuit for motor M which would turn in the opposite direction to correct the error.

In Fig. 1 a switching means is indicated by reference character I0 for the purpose of switching the parallax correcting circuit from one computer to another. The computer transmitters of the circuits shown in the drawings are indicated as being associated with a computer A, While the uncompleted bracketed circuits indicated by the legend are connected -to a corresponding circuit arrangement for a computer B, not shown. The switching device may be of any suitable kind, for example, a relay arrangement or a rotary switch.

The azimuth parallax correction circuit solves electronically the function sin A D 1: cos E for azimuth parallax correction in a similar manner. A trig-function transformer 200 has its primary windings connected to the coarse azimuth differential stator circuits 20I, 202, and 203. The

secondary winding 204 of the transformer is bridged by two serially connected forty thousand ohm resistors 205 and 206 whose junction point is connected by circuit 201 and condenser 208 to the control grid 209 of a super control tube 2I0 of the 6SK'1 type. The output of transformer 200 is an A. C. voltage proportional to sin Ag.

The primary winding of trig-function transformer 2 is connected to

circuits

46, 41 and 48 of the stator of coarse elevation differential Selsyn 34. The output of this transformer is an A. Cuvoltage proportional to cos Eg. This voltage is too small to be applied directly to tube 2I0 so therefore it must be amplified. To this end, one terminal of the secondary winding 2I2 of the tarnsformer is grounded and the other terminal is connected via circuit 2 I 3 to the grid of a triode voltage amplifier 2 I4 which is of the 6J5 type. The output of tube 2I4 is a voltage proportional to cos Eg, the A. C. component of which is fed through a condenser 2 I5 to a cathode of a double diode 2I6 of the 6H6 type. The corresponding plate 2II of the diode is connected to ground through a one half megohm resistor, and through another half megohm resistor 2I9 to the control grid 209 of tube 2I0. The output from tube 2I6 is a negative D. C. voltage proportional to cos Eg- The negattive D. C. voltage from tube 2 I 6 varies the amplification factor of tube 2 I inversely with cos Eg. The A. C. voltage sin Ag is the grid signal voltage. The A. C. plate voltage of tube 2 I0 varies as the product of the grid voltage and amplification factor and is equal therefore to sin A /cos Eg- Plate 220 of tube 2I0 is connected through a load resistor 22I to a source of D. C. potential and through condenser 222 to the control grid 223 of a tube 224 which is similar to tube 2). Control grid 223 is also connected through a half megohm resistor 225 to a plate of range double diode 90. The plate of tube 224 is resistance coupled through condenser 226 to a control grid 221 of double pentode 228, of a type similar to tube I05. From this point on, the elevation and azimuth parallax correction circuits and the apparatus controlled thereby are identical, so the remainder of the elevation correction circuits will be briefly described.

The amplification factor of tube 224 is varied by the negative D. C. voltage from the plate of the range diode 90. It will be recalled that this voltage is directly proportional to range. Since the A. C. voltage on the grid of tube H0 is proportional to sin Ag/COS Eg, the effect of these grid voltages is to give an A. C. plate voltage component proportional to sin Ag/COS EgXDO. This is the voltage proportional to the computed azimuth parallax correction.

A rotary transformer 230, similar to transformer 96 has its rotor winding 23I connected by

leads

232 and 233 to opposite terminal-s of potentiometer 234, the adjustable arm 235 of which is connected to a second control grid of tube 228. As in the similar circuits of tube I of the elevation correction circuit, the computed correction voltage is compared with the actual correction voltage from transformer 230 and the net output of tube 228 is an A. C. voltage, the magnitude of which depends upon that of the error in correction, and the phase of which depends upon whether the correction was too large or too small. This voltage is coupled through a cathode follower stage comprising a double triode 240 to the primary winding of transformer 24I which is the input for the azimuth servo amplifier. In this amplifier,

twin triodes

242 and 243, current reversing relay 244, and azimuth correction motor 40 which is controlled by the relay over leads 245 and 243, all function to effect azimuth parallax correction in the same manner as elevation parallax correction is accomplished by corresponding elements of the elevation circuits.

The circuits just described compute parallax correction where the control station and gun turrets are disposed along a common longitudinal axis of the ship. If the gun turrets were placed in the wings of the airplane or otherwise offset from the zero azimuth axis, the correction cir- 12 cuits must be such as to take into consideration the distance (S) that the turret is spaced from the computer and the azimuth angle (a) at which the turret is displaced from the control station.

Depending on the position of the target with respect to the computer and turret, the gun aiming angles of the computer in azimuth and elevation will differ from those of the turret due to parallax and this difference must be corrected so that the turret guns are aimed at the proper angles.

The azimuth parallax correction angle (EA) is equal to the diiference between the azimuth angle of the target relative to the gun turret and the azimuth angle of the target relative to the computer (Ag) Likewise the elevation parallax correction angle (2E) is equal to the difference between the elevation angle of the target relative to the gun turret and the elevation angle of the target relative to the computer (Eg) It has been determined empirically that the azimuth and elevation parallax corrections may be approximated as S sin (er-A ZA D cos E9 and These functions are computed electronically in a second embodiment of the invention illustrated by the block diagram of Fig. 3. A block diagram is thought best under the circumstances as the actual circuits of the second embodiment require a substantial duplication of those of Figs. 1 and 2 with similar functions plus two other like circuits for further functions. From what has gone before, it is thought that no difliculty will be experienced in understanding the present embodiment as described in connection with a block diagram.

The present embodiment contemplates selfsynchronous control circuits like those of Fig. 1 having correction introduced therein by servo amplifiers as described. Four similar trig-function transformers are used as well as a voltage proportional to range for controlling the inputs to the parallax correction circuits.

In the diagram of Fig. 3, two squares 300 and 30I represent electronic reciprocal circuits, both having an input connected to the voltage source sin A cos A D D The output of the reciprocal circuit of block 300 is connected to an input of an electronic multiplier circuit 302 and to an input of an electronic and - reciprocal circuit 303. The output of the sin Eg trig-transformer is connected to an input of multiplier circuit 302 and also to the input of another multiplier circuit 304. The output of multiplier 302 is the product of its two inputs or sin E g sin A D0 The output of the reciprocal circuit of block 30I is connected to an input of a multiplier circuit 304 and also to an input of reciprocal circuit 305. The output of the multiplier circuit is the product of both itsinputs or sin E, cos A, o

The actual circuit and its method of operation for determining the latter function is similar to that described in connection with the first embodiment of the invention.

The output of the cos Eg trig-transformer is connected to a second input of each

reciprocal circuit

305 and 303. The output of the former is cos A D cos E g and the latter which is the-same as that for azimuth parallax correction described in the earlier embodiment and obtained in the same manner.

The outputs of

multipliers

302 and 304 are connected to the primary windings of

functional transformers

306 and 301 whose turn ratios are proportional to S. sin a, and S. cos a, respectively, the output of the transformers being an A. C. voltage proportional to input voltage and the transformer function.

The

transformers

306 and 301 may have single secondary windings where a gun turret is controllable from a single control station. Where a turret is controllable from any of a plurality of spaced control stations, the functional transformers may be modified by providing a corresponding number of secondary windings each having an appropriate turn ratio proportional to S. sin a and S. cos a of the turret with respect to the different control stations in order that when the turret is switched from one station to another the circuits will be compensated for changed spacing and relative angular position of the turret and control station.

In the present case it is assumed that two spaced control stations A and B are employed, either of which may be selectively connected to the parallax correction circuit by the operation of switch l of Fig. 1.

The parallax corrections 2A and 2E are the same as referred to above except that the functions for respective control stations are identified by sub A or sub B and will have different values owing to the spacing of the control stations.

For the two control

station arrangement transformers

306 and 307 are shown with two sets of serially connected secondary windings either set being selectively connected in circuit by switch I0.

Secondary winding 3l5 has one terminal grounded and the other connected through secondary winding 3|! of transformer 301 to contact 323 of switch l0 which is closed when the parallax correction circuit is connected to computer B, contact 323 being connected to the azimuth servo amplifier by the switch. 7

As already stated, the turn ratio of

transformers

306 and 301 is such that their output is a voltage proportional to the product of their inputs and S. sin a and 8'. cos a respectively.

Since the input of transformer 306 is sin A, sin E o then the output is, with the described secondary winding connection,

sin E g D0 The input for transformer 30'! is sin A sin 04 cos A, sin E, 0

which when multiplied by the transformer, becomes at the output sin E o cos A cos a sin E S D0 which is the elevation parallax correction for computer B. This voltage is connected via contact 323 of switch [0 to the elevation servo amplifier input circuit, where it is utilized in the same manner as the voltage from the plate of tube 81 of Fig. 2 for making the required parallax correction.

When the A computer is in use, secondary windings 3l6 and 3! of

transformers

306 and 301 are connected in circuit with the elevation servo amplifier by switch l0, windings M5 and 3 being disconnected at this time by the switch. Since the A computer is assumed to have a spacing from the turret differing from that of computer B, the turn ratios of the transformers with secondary windings 3H3 and 3; in use is proportional to SA sin Q11 and SA cos M respectively.

The combined output voltages of the transformers is a voltage proportional to cos (a A or {IE3 sin E which is the elevation parallax correction for computer A. This voltage is connected via contact 3 I4 of switch l0 to the elevation servo amplifier for use in the same manner as the voltages from secondary windings M5 and 3H.

The circuits associated with transformers 308 and 309 are generally the same as those of

transformers

306 and 301.

Transformer 308 has two secondary windings 3H) and 320 and transformer 309 also has two secondary windings 32| and 322. Secondary windings 3| 9 and SH are connected in series, one terminal of winding 3|9 is connected to contact 325 of switch I 0 and a terminal of winding 32! is connected to ground. The secondary windings just mentioned are used in connection with the B computer, and the turn ratios are such that the input voltages are multiplied by SB sin (15 and SB cos as respectively. The primary windings of the transformers are respectively connected to the outputs of

reciprocal circuits

305 and 303 whose output voltages are proportional to SA cos -A or ZE cos A D cos E g sin A,, D cos E g and since the functional transformers multiply their input viltages in accordance with their turn ratios, the output of transformer 309, with the connections described, is a voltage proportional to S sin A, cos D0 cos E,

and that of transformer 308 is a voltage proportional to S cos A, sin Do cos E,

These, voltages are added together in proper phase and their sum is SB Sin B s) D0 cos E which is the azimuth parallax correction ZAB for computer B. This voltage is connected via contact 325 of switch It to the azimuth servo amplifier where it is used in circuit arrangement to control the amplifier in the same manner as the voltage from the plate of tube 224, Fig. 2, to effect azimuth parallax correction.

Secondary windings

320 and 322 operate in the manner just described when the A amplifier is in use. With the latter windings in circuit, the turn ratios of transformers 388 and 309 are S. sin cm, and SA cos an, respectively, and the sum of their output voltages is SA SlIl (IA-A51 D0 cos E,

which is the azimuth parallax correction 2AA for computer A. This voltage is connected to the servo amplifier control circuit via contact 328 of switch I0 when the A computer is in use.

As many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrativ and not in a limiting sense.

What is claimed is:

1. In an aiming system wherein a control device transmits aiming angle data over selfsynchronous transmission means to a gun positioning device, the improvement which comprises, in combination, means for deriving from signals transmitted over said transmission means a plurality of different voltages, said voltages being proportional to sines and cosines respectively of azimuth and elevation angle data transmitted over said transmission means, means providing a voltage proportional to range, a device controlled by the range voltage and those proportional to the sines and cosines for deriving voltages proportional to parallax correction angles, transformer means interconnected with the selfsynchronous transmission means, and means for controlling said transformer means by the derived voltages to correct the aiming angle data for parallax.

2. In an aiming system wherein a control device transmits aiming angle data over selfsynchronous transmission circuit means to a gun positioning device, the improvement which comprises a plurality of transformers energized by signals transmitted over the transmission means having turn ratios adapted to produce output voltages respectively proportional to sines and cosines of transmitted elevation and azimuth aiming angles, means providing a voltage proportional to range, means jointly controlled by 16 the latter voltage and the output voltages of the several transformers for deriving voltages proportional to parallax correction angles for the gun positioning device, rotary differential transformer means in the transmission circuit means adapted with changes in the angular position of the rotary member means thereof to effect a corresponding change in the transmitted aiming angle data, rotary inductive means coupled with the rotary member means of the differential transformer means having linear output voltages, the magnitude of which is controlled by the angular position of the rotary differential transformer means, means for comparing the last mentioned output voltages with those proportional to parallax correction, and means controlled by a difference in said voltages for effecting angular movement of the differential transformer means as Well as the rotary inductive means until a difference no longer exists, whereby the differential transformer means are positioned so that the aiming angle data received at the gun positioning device is corrected for parallax.

3. In an aiming system wherein a control device transmits aiming angle data over selfsynchronous transmission circuit means to a gun positioning device, the improvement which comprises a plurality of transformers energized by signals transmitted over the transmission means having turn ratios adapted to produce output voltages respectively proportional to sines and cosines of transmitted elevation and azimuth aiming angles, means providing a voltage proportional to range, means jointly controlled by the latter voltage and the output voltages of the several transformers for deriving voltages proportional to parallax correction angles for the gun positioning device, rotary differential transformer means in the transmission circuit means adapted with changes in the angular position of the rotary member means thereof to effect a corresponding change in the transmitted aiming angle data, rotary inductive means coupled with the rotary member means of the differential transformer means having linear output voltages, the magnitude of which is controlled by the angular position of the rotary differential transformer means, means for further adjusting said voltages to compensate for the spacing between said devices, means for comparing the adjusted last mentioned output voltages with those proportional to parallax correction, and means controlled by a difference in said voltages for effecting angular movement of the differential transformer means as well as the rotary inductive means until a difference no longer exists, whereby the differential transformer means are positioned so that the aiming angle data received at the gun positioning device is corrected for parallax.

4. In an aiming system wherein a control device transmits aiming angle data over self-synchronous transmission circuit means to a gun positioning device, the improvement which comprises a plurality of transformers energized by signals transmitted over the transmission means having turn ratios adapted to produce output voltages respectively proportional to sines and cosines of transmitted elevation and azimuth aiming angles, means providing a voltage proportional to range, means jointly controlled by the latter voltage and the output voltages of the several transformers for deriving voltages proportional to parallax correction angles for the SRCH RGUM gun positioning device, rotary differential transformer means in the transmission circuit means adapted with changes in the angular position of the rotary member means thereof to eifect a corresponding change in the transmitted aiming angle data, rotary inductive means coupled with the rotary member means of the differential transformer means having linear output voltages, the magnitude of which is controlled by the angular position of the rotary differential transformer means, means comprising a potentiometer for further adjusting said voltages to compensate for the spacing between said devices, means for comparing the adjusted last mentioned output voltages with those proportional to parallax correction, and means controlled by a difference in said voltages for effecting angular movement of the difierential transformer means as well as the rotary inductive means until a difference no longer exists, whereby the differential transformer means are positioned so that the aiming angle data received at the gun positioning device is corrected for parallax.

5. In an aiming system wherein a control device transmits aiming angle data over transmission means to a gun positioning device, a parallax correction circuit comprising means controlled by signals transmitted over the transmission means for producing a voltage proportional to the product of the sine of the elevation angle and cosine of the azimuth angle of the transmitted data, a vacuum tube having its grid energized by said voltage, and a source of negative potential increasing with range for biasing said grid whereby the output voltage of the tube varies as the product of the sine of the elevation angle and cosine of the azimuth angle divided by range.

6. In an aiming system wherein a control device transmits gun azimuth, Ag and elevation, Eg, aiming angle data over transmission means to a gun positioning device, a parallax correction circuit comprising means controlled by signals transmitted over the transmission means for producing a voltage proportional to sin A,

cos E,

of the transmitted angle data, a vacuum tube having a rid circuit energized by said voltage, a source of negative potential increasing with range (Do) means for biasing said grid from said source whereby the output of the tube is proportionalto SsinE,

'sin A sin a D and S sin E, o

where S is the distance between the device and a. is the azimuth angle of the gun positioning device with respect to the control device, means for adding the product voltages whereby the sum of the voltages S sin E, cos (a-A,) 0

obtained is proportional to the elevation parallax correction voltage, and means comprising adjustable differential transmformer means interconnected with the transmission means and controlled by the last mentioned voltage for effecting elevation parallax correction in said angular data.

8. In an aiming system wherein a control device transmits gun azimuth, Ag and gun elevation, Eg, aiming angle data over transmission means to a gun positioning device offset therefrom by the distance S and b azimuth angle a, means providing a voltage proportional to range, Do, a parallax correcting system controlled by signals transmitted over said voltage and by said transinitting means for deriving voltages proportional -cos A, cos a sin E, o and sin E, cos A, o

a pair of transformers having turn ratios respectively proportional to S.sin a and 5.00s 0:. having their primary windings energized by the respective voltages and their secondary windings connected in series, the combined output voltages of the secondary windings being a voltage proportional to 8. sin E, cos (a-A,) 0

and means comprising adjustable differential transformer means interconnected with the transmission means and controlled by the last mentioned voltage for effecting elevation parallax correction of the aiming angle data.

9. In an aiming system wherein a control device transmits gun azimuth, Ag, and gun elevation, Eg, aiming angle data over transmission means to a gun positioning device offset therefrom by the distance S and by azimuth angle a, means providing a voltage proportional to range. Do. a parallax correcting system controlled by signals transmitted over said voltage and by said transmitting means for deriving voltages proportional to cos A, D cos E,

and

sin A, D cos E,

-cos A sin a D cos E,

and

---sin A 0 ea D cos E, 0

19 means adding said resultant voltages whereby a voltage S Sill (a-A D cos E,

is obtained which is proportional to azimuth parallax correction. and means comprising adjustable differential transformer means interconnected with the transmission means and controlled by the last mentioned voltage for effecting a corresponding correction of the aiming angle data.

10. In an aiming system wherein a control device transmits gun azimuth, Ag, and'gun'elevation, s, aiming angle data over transmission means to a gun positioning device offsettherefrom by the distance S and by azimuth'angle a, means providing a voltage proportional to'range, Do, a parallax correctingsystem'controlled by signals transmitted over said voltage and by said 20 transmitting means for deriving voltages proportionalto cos A a D cos E,

and

sin A 8 D cos E g a pair of transformers having turn ratios respectively proportional to S.sin a and S cos a energized by the respective derived voltages, the secondary windings of the transformers being connected in series, their combined output voltages being a voltage proportional to S.sin E cos (or-A o 20 and means comprising adjustable differential transformer means interconnected with the transmission means andicontrolled by the last mentioned voltage for effecting azimuth parallax correction of the aiming angle data.

GIFFORD E. WHITE. ROBERT L. GRAEF. CHARLES J. LA FORGE.

REFERENCES CITED The following references are of record in the file of this patent: V

UNITED STATES PATENTS Number Name Date 821,521 Moody May 22, 1906 1,173,094 Blume Feb. 22, 1916 1,200,233 Preston Oct. 30, 1916 1,242,649 Brand Oct. 9, 1917 ,612,117 Hewlett et a1. Dec. 23, 1926 1,637,039 Hewlett et a1 July 26, 1927 1,755,975 Willard Z. Apr. 22, 1930 2,129,880 Scherbatskoy Sept. 13, 1938 2,151,718 Riggs Mar. 28, 1939 2,244,369 Martin June 3, 19 1 2,359,768 Kiltie Oct. 10, 1944 2,405,028 Ford July 30, 1946 2,408,081 Lovell et a1 Sept. 24, 1946 2,421,230 Agins May 27, 1947 0,798 McCarthy Feb. 8, 1949 OTHER REFERENCES Ser. No. 212,349, Papello (A. P. (3.), published May 25, 1943.