US 2969018 A
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8. J. ERST ETAL QUADRANT HOMING SYSTEM Jan. 24, 1961 3 Sheets-Sheet 2 Filed May 1. 1957 W NF JOKFZOO 440m Y F- N R O T T A INVENTORS. STEPHEN J. ERST GEORGE E. BOWDEN BY self-propelled rocket.
United States Patent 2,969,018 Patented Jan. 24, 1961 QUADRANT HOMING SYSTEM Stephen 'J. Erst, New Haven, Ind-., and George E. Bowden, Plainview, N.Y., assignors to International Telcphone and Telegraph Corporation Filed May 1, 1957, Ser. No. 657,038
6 Claims. (Cl. 102-50) This invention relates to guided missiles and is particularly directed to homing systems for the missiles.
Photoelectric cells have now been developed which are quite sensitive to radiations in the visible and near visible portions of the spectrum. Further, such cells can now be made with relatively large planar sensitive areas, and the current through the cell, or voltage generated by the cell, is approximately proportional to the area illuminated. Accordingly, the terminal voltage of the cell can be made analogous to the shaded area of the cell in a field of given intensity.
The object of this invention is to provide a homing system for a missile which effectively utilizes the extended sensitive faces of photocells. Photocells, as used hereinafter, refer to radiation sensitive elements, such as lead sulphide or selenium layers deposited on a metal sheet.
The objects of this invention are attained in a missile having four extended planar photocells orthogonally arranged in a plane normal to the missile axis and optically shielded from each other by two flat opaque sheets on mutually perpendicular diameters of the missile barrel with the line of intersection of the sheets coincident with the missile axis. The sheets extend forwardly of the plane of the photocells so that the photocells are equally illuminated only when the target-source of illumination is in line with the missile'axis. The signals from the four cells are compared and appropriate forces applied to the aerodynamic control surfaces of the missile to turn the missile toward the target line of sight.
The above-mentioned and other features and objects of this invention and the manner of attaining them will become more apparent and the invention itself will be best understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein:
Fig. l is a three-dimensional vector diagram of the coordinates of the guidance system of this invention;
Fig. 2 is a perspective, partly sectioned, view of a missile embodying this invention;
Fig. 3 is a blockdiagram of the control circuits of this invention;
Fig. 4 is an alternative block diagram of the circuits embodying this invention;
Fig. 5 is an end view of a missile of this invention; and 1 Fig. 6 is a diagram of an energization circuit used in the system of Fig. 4.
Y The missile contemplated by this invention is an elongated tubular barrel 1, shown in Fig. 2, with orthogonal aerodynamic control fins 2. and 3. The fins may have aerodynamic-type control surfaces 4 and 5. The missile may be of the free-flight projectile type, or may be a At the forward end of the missile is the pointed dome 6 of a material which is transparent to the radiations of the target upon which the missile is to home. In a plane perpendicular to the missile axis are placed two pairs of extended planar radiation sensitive elements, or photocells, A, B, C and D. Opaque shields 7 and 8 are mutually at right angles, with their intersecting line coincident with the missile axis. The shields extend forwardly of the plane of the photocells so that the four photocells are equally illuminated only by a source on the extended missile centerline. The shields are in the plane of the control surfaces and the signals from the photocells are compared and appropriate forces applied to the control surface to bring or keep the missile on the target line of sight.
Referring more particularly to the embodiments shown in the drawing, the principles of this invention become apparent. In Fig. l is shown in three-dimension perspective view the coordinate system upon which the system of this invention operates. The missile is assumed to have a velocity component along the Y axis. The XY plane will be referred to as the horizontal plane, although it is not necessarily related to the earths horizon. The X--Z plane is vertical in that it is perpendicular to the XY plane. The position of target T, in space, and forwardly of the missile may be defined by projecting the line of sight 10 into said horizontal and vertical planes. The projected lines 311 and 12 will then, respectively, define the vertical or elevation angle B above or below the horizontal plane, and the angle of azimuth, B in the horizontal plane. The homing system of this invention reads quantitatively the two angles B and E and generates voltages analogous either to these angles or to the tangents of these angles. It will be assumed hereinafter that opaque shield 7 and control surfaces 3 -5 are in the XY plane, and the shield 8 and surfaces 24 are in the vertical plane. The shields are at right angles, intersecting on the missile axis and extend forwardly of the plane of the photocells A, B, C and D by distance a. Circumferentially around the missile is the skirt 15, also of opaque material and of a height b above the photocell plane. It follows that the shields will cast shadows on two or three of the photocells when the source of illumination is displaced from the extended missile centerline.
The planar photocells are assumed to be uniformly sensitive throughout their surfaces so that the voltage at the terminal of the cell is proportional to the area of the cell illuminated, or shaded, for any reference value at the source. 7
In Fig. 3 is shown a system for producing control surface defiection proportional to the tangent of B and B The signal from cells A and B are added by coupling the terminals of A and B together. Likewise, C and D, in the lower-hemisphere, are added together and subtracted from A-+B in the subtractor 20. The selector 21 receives both combined signals and produces at its output a voltage proportional to the maximum of either A+B or C+D. The's'electors may comprise, for example, a conventional dual cathode follower with a common cathode resistance. In divider 22 the ratio of the difference voltage at the output of the subtractor and the maximum voltage at the output of the selector is obtamed. This ratio is proportional to tan B Tan Bg, is then applied to a control system 23 of any desired design, such as a conventional synchro, the output of which isapplied to elevators 3. If desired, roll control 'may be superimposed upon the elevators 3-3 as by a gear system 24 for differential control of surfaces 3-3 by the output of a gyro in the roll control unit 25.
. Rudder control in the other plane is obtained in like manner. Signals from cells A and D are added, and signals from B and C are added. The difference between the two combined signals is obtained in subtractor 30, while the maximum of the two is obtained in selector 31. The ratio of the dilference signal to the maximum signal,- in the output of divider 32, is proportional to 3 tan B The output of the control system 33 is applied to rudders 22.
The rudder and elevator control signals are isolated from each other by means of suitable mixing, isolation and coupling circuits represented by the blocks A, B, C and D, respectively: typical such circuits are illustrated and described on page 10, section 19, of Electronic Designers Handbook by Landee, Davis, and Albrecht, published in 1957 by McGraw-Hill.
In the embodiment shown in Fig. 4, the radiation sensitive elements and shields are so shaped that the output controls will be proportional to B and E respectively. These outputs are differentiated and compared with the output of a rate gyro so that guidance corrections at the control surfaces are proportional to the angle of deviation of the target line of sight from the missile axis. Ln Fig. 4 the shields-are assumed to be rectangular and the outside edges of the planar photocell elements A,B, C and D are formed by two arcs whose equations are of the form:
where x=horizontal distance of boundary point from missile axis y=vertical distance of said point from missile axis a=height of shield above element plant K=arbitrary constant determined by maximum angle B or B for which system must operate The radius of the circle enclosing the photocells is taken as unity.
In the system of Fig. 4, the missile will home accurately when B or B are equal to or less than thirty degrees (30). For greater values of 13,, and B the missile will tend to react as if B and B were constant. In this embodiment, selector 21 selects the maximum signal from the individual photocells A, B, C and D and obtains the ratio of this maximum signal with the difference signals A minus B (AB) and D minus C (D-C). The two subtractors and 20a are connected to the two pairs of photocells, as shown. The double throw, multiple pole switch 27 is connected between the selector and subtractors, on the one hand, the dividers 22 and 22a on the other hand. The switch may be thrown in either of two directions, depending upon the quadrant from which the maximum signal is obtained. The direction of throw of the armatures of switch 27 may be made depending upon the energization of winding 28.
Fig. 6 shows one energization circuit for coil 28. Selectors for maximum A and B and maximum C and D could be connected, respectively, to the control grid 40 and cathode 41 of a thyratron-type amplifier. The coil 28 comprises the load impedance for the tube.
The three upper contacts u will be closed if A or B is a maximum among the signals A, B, C, and D. The down contacts d will close if either C or D is a maximum among the four signals A, B, C, and D. Hence, the'output of divider 22 is proportional to A minus B (AB)/ maximum, and the output of divider 22a is proportional to D minus C (DC) /maximum, either of which is proportional to B,,. The B signal is differentiated in the ditferentiator 29 and is added to the output of the gyro 29a. The output of the rate gyro is preferably a voltage proportional to the angle velocity of the missile about a vertical axis through the missile. The difierentiated B value is added to the rate gyro output in the control circuits 23 and applied to the horizontal control surfaces 22.
A similar channel is provided for developing the B signal for application to the vertical control surfaces 3--3. Here, the selector 31 is identical to selector 21. The functions of the two selectors may, in fact, be combined in one circuit. The subtractors 30 and 30a, however, derive the A minus D (AD) and B minus C (BC) signals, respectively. The signals thus obtained are compared in dividers 32 and 32a to develop A minus D (A -D)/maximum and B minus C (BC)/maximum, respectively, either of which is proportional to the line of sight angle B Contacts u of switch 270 are closed if either A or D is a maximum of the four signals A, B, C, and D. The down contacts d are closed if either B or C is a maximum among the signals A, B, C, and D. The B signals are differentiated in differentiator 29', are combined with the output of rate gyro 29a, converted to control forces in the control system 33, and applied to the vertical control surfaces 33.
The systems shown in Figs. 3 and 4 will require a roll rate limiter. Too much roll could produce interaction between the channels and eventually bring about instability of the system. Since all systems will have a finite response time, it is necessary for reliable operation that during this response time the missile does not roll too much.
In the embodiment shown in Fig. 5, the radiation sensitive elements are essentially point photocells. Where the same control is desired in each direction, the elements are placed on lines bisecting each quadrant as far from the missile axis as feasible. Here, also, the shields are rectangular in shape, their forward ends lying in a plane perpendicular to the missile axis. The outputs of the two adjacent elements are added and, together with the sum of the outputs of the other two elements, are fed into the computer, as described above. Such a system will have no output if both inputs have signal or if neither input has a signal. If one input has a signal and the other does not, the computer will produce a positive output; whereas, if the other input has a signal when the first does not, there will be a negative output. The output signals are fed through a control system which deflects one pair of the control surfaces through a presetangle in a direction such that the missile will turn toward the target. That is, this system has the characteristic of applying no control if B is less than a predetermined angle depending upon the design of the nose of the missile, and of developing a constant turning moment if B is greater than said angle. By placing shields around the elements as on the circumference of the missile barrel, the characteristic of the system can be changed so that no control will be applied when the'line of sight exceeds another angle design into the head. No roll control per se is required here.
It will be readily understood that Figs. 3 and 4 are one line, informational-flow type schematic diagrams, the conventional mixing, isolation and coupling devices and circuits being represented by the block diagrams A, B', C and D, respectively.
While the principles of the invention have been described in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of the invention.
What is claimed is:
1. In combination, in a homing missile having a barrel with adjustable aerodynamic control surfaces: four extended planar photocells A, B, C and D disposed in a plane perpendicular to the barrel axis; opaque planar shields disposed between and forwardly of the photocells so that the cells of each adjacent pair are uniformly illuminated only when a radiation source is located along a line coincident with the axis of said barrel and are differentially illuminated by said source of radiation when the same is displaced from said coincident line; means coupled to said cells for generating a voltage proportional to the difference between the signals provided by pairs of cells; means coupled to said generating means for comparing the difference voltage with the maximum voltage of either pair to provide the ratio thereof; and means coupled to said comparing means for applying forces to the control surfaces proportional to said ratios.
2. In combination in a homing missile: an elongated barrel with a nose and tail structure; orthogonal control surfaces on said tail structure for guiding the missile in two dimensions in flight; two pairs of side-by-side planar radiation sensitive elements A, B, C, and D positioned in said nose structure; right-angle planar shields opaque to radiant energy positioned between said elements, means coupled to said elements for deriving voltages A, B, C, and D proportional, respectively, with the illumination of elements A, B, C, and D; first and second computer circuits coupled to said elements including means for deriving voltages (A+B) minus (C+D) and (A +D) minus (B+C) respectively; first means coupled to said deriving means for isolating the maximum of (A +3) and (C+D); second means coupled to said deriving means for isolating the maximum of (A+D) and (B+C); a first divider coupled to said first computer circuit and said first isolating means for generating a voltage proportional to the ratio of (A+B) minus (C+D) and the first mentioned maximum; a second divider coupled to said second computer circuit and said second isolating means for generating a voltage proportional to the ratio of (A+D) minus (B+C) and the second mentioned maximum; and means coupled respectively to said first and second dividers and responsive to the two ratio voltages, respectively, operatively coupled to said control surfaces for operating the same.
3. In combination, in a homing missile: two pairs of planar photocells A, B, C, and D orthogonally arranged in a plane perpendicular to the missile axis; opaque planar shields arranged between and forwardly of said cells; a selector circuit coupled to said photocells for selecting the maximum voltage of each pair; a subtractor circuit coupled to said photocells for deriving voltages proportional to the dilference between the two pairs of voltages, a divider circuit coupled to said selector and subtractor circuits for generating a voltage proportional to the ratio of the diiference voltage to said maximum voltage, and means coupled to said divider circuit for controlling one of said control surfaces in response to the ratio voltage.
4. The combination defined in claim 3 further comprising another selector circuit coupled to said photocells for selecting the maximum voltage among A+D and B-l-C, another subtractor circuit coupled to said photocells for deriving the difference between A+D and B-i-C, another divider circuit coupled to said other selector and subtractor circuits for dividing said maximum voltage into said difference voltage, and means coupled to said other divider circuit for applying the last mentioned voltage to the other control surface.
5. In combination, in a homing missile: four extended planar photocells, A, B, C, and D, symmetrically arranged in a plane perpendicular to the axis of the missile; opaque shields disposed so that said photocells are uniaformly illuminated from a target source of radiant ;energy located on a line coincident with the axis of the missile and said photocells are diiferentially shaded when said target source is displaced from said coincident line; selector circuit coupled to said photocells for selecting the maximum signal among signals, A, B, C, and D; first and second subtractor circuits coupled to said photocells for deriving A--B signals and D-C signals, respectively; a first means for deriving the ratio of A-B and said maximum signal; second means for deriving the ratio D-C and said maximum signal; means for selectively coupling said first and second deriving means "to said first and second subtractor circuits and to said selector circuit respectively; means coupled to said first and second deriving means for differentiating the ratio signals; and means coupled to said differentiating means for applying the differentiating signals to one control surface of a missile.
6. The missile defined in claim 5 further comprising: a second selector circuit coupled to said photocells for selecting the maximum signals among signals A, B, C and D; third and fourth subtractors coupled to said photocells for deriving, respectively, voltages A-D and B-C; third means for deriving the ratio of AD and said maximum; fourth means for deriving the ratio of B-C and said maximum; means for selectively coupling said third and fourth deriving means to said third and fourth subtractor circuits and to said second selector circuit respectively; means coupled to said third and fourth deriving circuits for differentiating the last mentioned voltages; and means coupled to said third and fourth deriving means for applying the differentiated voltages to the other control surfaces of the missile.
References Cited in the file of this patent UNITED STATES PATENTS 2,060,201 Hammond Nov. 10, 1936 2,415,348 Haigney Feb. 4, 1947 2,418,137 Noell Apr. 1, 1947 2,457,393 Mufliy Dec. 28, 1948 2,520,433 Robinson Aug. 29, 1950 2,741,181 Marks Apr. 10, 1956