US 2825021 A
Abstract available in
Claims available in
Description (OCR text may contain errors)
Feb. 25, 1958 A. W, FR|END CONTROL FOR HEAT-HOMING BOMB 2 Sheets-Sheet 1 Filed Nov. 2l, .1946
l|||.| Illlul lll II.I|I|II.|||III l Il I I Il lllllltllllllllll..
,m IMA-. i--- INVENTOR. a afer 14./ Fe/f/va Feb. 25, 1958 A. w. FRIEND 2,825,021
CONTROLFOR HEAT-HOMING BOMB 4 Filed Nov. 2l, 1946 2 Sheets-Sheet 2 EEE Blzffd mili IN VEN TOR.
Afrox/yay CoNTRoL Fon HEAT-HOMING BOMB Albert W, ldriend, Cambridge, Mass., assigner to the United States of America as represented by the Secr'etary of Wai' Appiicanon November 21, 1946, serial No. '711,456
4 Claims. (Cl.l B18-489) The invention described herein may be manufactured and used by or for the Government for governmental purposes without payment to me of any royalty thereon.
This invention relates to the control system for a heathoming bomb of the type designed to be dropped at a high angle with the aid of a bombsight in the same manner as a freely falling bomb, and capable of steering itself toward that part of the target area from which the greatest amount of long wave length infrared radiation is being emitted. The steering of the bomb is accomplished by small elevator and rudder surfaces which are located in the tail and serve to angularly displace the axis of the bomb with respect to its velocity vector, the resulting lift produced by the body of the bomb being sufiicient to change the course of its fall. The bomb is stabilized as to roll by gyroscopically controlled ailerons also located inthe tail.
The control system of the bomb comprises an infrared sensitive eye located inthe nose of the bomb, an electronic control circuit and a servo-mechanism for operating the control surfaces. The eye is capable of scanning an area toward which the bomb is moving of size commensurate with the manueverability of the bomb and of producing a signal from infrared radiations emanating from the area scanned. The electronic control circuit analyzes the signal from the eye and causes the servomechanism to operate the control surfaces in such a way as to steer the bomb toward the strongest source of infrared radiation in the scanned field.
It is the object of this invention therefore to provide a control system of the above described type that is simple and reliable, and that occupies a minimum amount of space.
In the drawings:
Fig. l is a schematic diagram of the electronic control circuit;
Fig. 2 is -a simplified diagram of Fig. l for explaining the operation of the electronic control circuit; and
Fig. 3 is an analysis of the operation of the circuit of Fig. 2 through one scanning cycle Vfor various target positions.
Referring to Fig. 1, the eye comprises a bolometer 1 located at the primary focus of parabolic reflector 2 which is "mounted on shaft 3 in such a way that its optical axis lmakes an angle of about 5 degrees with the axis of the'shaft-and Vso 'that its primary focus falls on the axis of the shaft. The sensitive area of the bolometer is made circular andof such size as to subtend an angle at -Vthe optical center of the `reector that is twice the Aangle between the optical axis and the axis of the shaft, -in this case about degrees. With this arrangement the 'area on a piane perpendicular to the axis of the shaft, vor'` axisof rotation, from which radiations are caused to fall on the sensitive area of the bolometer is defined by a circle centered on the optical axis and having a radius practically equal to the distance in theplane from the optical -axis to the axis of rotation. This circular scanning area is shown nited States Patent n FV' ICC at 4, the plane having been rotated degrees from its true position for illustrative purposes. The shaft 3 is rotated at a constant speed of about 32 revolutions per second by constant speed motor 5. This causes the scanning circle 4 to rotate and scan an area defined by the circle 6. When the scanning circle includes a sourceY of infrared radiation such, for example, as the ship target 7, the radiation from the target falls on the bolometer 1 and a signal is produced. Also mounted on shaft 3 is a commutator 8, the details of which are shown to the right of the eye." The function of the commutator is to distinguish between signals received from the upper, lower, left and right semicircles of the scanned area as will be explained later.
The bolometer 1 is an element whose electrical resistance changes with the amount of infrared radiation falling on it. This element may be made of a material having a high temperature coefiicientof resistance with the resistive material coated with a black substance to convert the long wave length radiations into heat. The bolometer forms one arm of a bridge circuit, the other three arms of which vare composed of balancing resistor 9 and the two halves of the primary winding of transformer 10. The resistor 9 should have a value as nearly equal as possible to the resistance of bolometer 1 at its normal operating tempera-- ture in the absence of a signal. Operating current for the bridge is obtained through grounded leadll which is con-V nected to point 12 of the bridge, and through lead 13 which is connected between opposite point 14 of the bridge and the -6 v. terminal through relay 15 when this relay is energized by application of voltage to the +24 v. terminal. The resistor 16 serves to limit the bridge cur-V rent to the proper operating value.
When the scanning area 4 includes the target, infrared radiation therefrom falls on the bolometer 1 and causes its resistance to increase. This increase is represented by the o-m portion of the wave shown in Fig. 1 at (a). During the time when the scanning area does not include the target, the bolometer cools and its resistancev decreases as represented by the m-21r portion of the wave. Thus a saw tooth wave of resistance change is produced at the scanning frequency of about 32 cycles per second. This change in resistance causes an unbalance between the currents in the two halves of the primary winding and the resultant iiux produced by the unbalance induces a voltage in the secondary winding. Due to the filtering action ofV the transformer and its inability to pass the direct component of a wave, an alternating voltage is produced inthe secondary which approaches a sine wave in shape as shown at (b). The frequency of this voltage is likewisev 32 cycles per second.
The secondary voltage is applied between the grid and triode V3. The necessary grid bias for V2 is supplied by" the voltage drop across resistor 19 which is connected in series with resistor 20 between the -6 v.'terminal and ground.
The dual triode V3 acts as an amplifier and also as a phase inverter for coupling the unbalanced output circuit' of tube V2 to the input circuit of V4, which is balanced with respect to ground. Considering the upper 'section of V3, the signal from the output circuit of V2 is applied bei" tween the control grid 21 and ground. The cathode's of the two sections are connected together and to'grolundi: through resistor 22. The grid 23 of Vthe'lower sectionisjconnected through resistor '24, 'th'e'lower end' of 'which"$' at ground potential asfar as the signal is concerned because of the lter condenser 25. Assume that the signal causes the potential of grid 21 to increase in a positive direction, then the current flowing in resistor, 22 due to the upper section increases and the cathodes of the two sections become more positive with respect to ground or, in other words, grid 23 becomes more negative with respect to its cathode. The signal potentials on grids 21 and 23 are therefore 180 degrees out of phase and likewise the anode currents in the two sections of V3 are 180 degrees out of phase. Since the anode currents ot both sections flow through resistor 22, the voltage drop across this resistor, which constitutes the signal applied to grid 23, is the voltage drop produced by the difference in these two currents. The circuit therefore must adjust itself to a slightly unbalanced condition in which the anode current of the lower section is less than that of the upper section by an amount just sufficient to provide the proper signal voltage ou grid 23. The degree of unbalance is an inverse function of the amplification of the lower section of V3.
' The output signal of V3 is applied to the grids of tube V1 through coupling condensers 26 and 27. The tube V4 is part of a conventional resistance coupled push-pull stage having a feedba-ck resistor 28 common to the anode and grid circuits of both sections of the tube. If the stage is perfectly balanced, the two anode currents tiowing through resistor 28 are of equal amplitudes and 180 degrees out of phase. The resultant current is therefore zero and no signal is developed across resistor 28. However, if the currents in the two sections tend to become unequal, a signal is developed across resistor 28 proportional to the diference in the two currents. This signal is fed back to the two grids in such phase as to increase the signal on the grid'of the section having the lesser current and to decrease the signal on the grid having the greater current. The effect of resistor 28 therefore is to maintain a balance between the anode signal currents of the two sections of tube V4.
A positive potential obtained from the drop across resistor 29 is applied to the grids of tubes V3 and V4 by means of conductor 31. Resistor 29 is connected in series with resistor 30 between a source of positive direct potential and ground. The potential across resistor 29 is adjusted to such a value that the difference between this potenti-al and that produced across resistors 22 and 28 by the steady direct component of the anode currents of tubes V3 and V4 gives the proper biasing potential for these tubes.
In order to convert the sine wave output of transformer to substantially a square wave, resistors 32, 33, 34 and 35 having values of from one to two megohms are inserted in series with the grids of tubes V2, V3 Iand V4. Sufficient amplification is provided so that the signals applied to the input circuits of these tubes are of considerably greater amplitude than that required to drive the grids positive. Since the grids can go only slightly positive due to the drop in resistors 32 through 35 when grid current begins to ow, the result is a squaring of the positive. half cycle of the signal. Due to the ph-ase reversals produced by the tubes, both half cycles of the signal are` subjected to this squaring action. Any inequality in the amplitudes of the two half cycles of the signal appearing across resistors 36 and 37 is removed by condensers 38 and 39 through their inability to pass the direct current component of the signal, so that there appears across resistors 40 and 41 a symmetrical alternating voltage E substantially square in forni as shown in Fig. 2.
The commutator 8 comprises four sets of contacts 42-43, 44-45, 46--47 and 48-49,V and a cam 50 mounted on shaft 3. Cam followers 51, 52, 53 and 54 are arranged to open and close the contacts and to contact the cam at points 90 degrees apart. The cam is cut so that each set of contacts .is closed for about 175 degrees of the cams rotation. Contacts 42 and 44 are connected together as are also contacts 46 and 48, and the voltage E is applied between these two pairs of common contacts. Contacts 45 and 49 are connected together and through resistor 55 to one side of condenser C1, the other side of which is connected to ground. Likewise contacts 43 and 47 are connected together and through resistor 56 to one side of condenser C2, the other side of which is connected to ground. When either contacts 44-45 or 48-49 are closed, the condenser C1 is subjected to a potential that acts to charge or discharge the condenser depending upon the charge already in the condenser when the contacts close and the polarity of points B or A during the time the contacts are closed. Similarly a potential is applied to condenser C2 through resistor 56 when contacts 42-43 or 46-47 are closed, the effect on the condenser being determined by the previous condition of charge and the polarity of point B or A during the time the contacts are closed. Therefore, when the cam 50 rotates, a series of voltage pulses is applied to condensers C1 and C2. These pulses will be all positive, all negative, or mixed positive and negative depending upon the phase relationship between the voltage wave E and some reference point on the cam 50 or the scanning cycle.
The condenser C1 is connected between the grid and cathode of the upper section of V6 and the condenser C2 is connected between the grid and cathode of the lower section of this tube. Hence, the potentials across these condensers determine the potentials between the grids and cathodes of the two sections of V6. Resistors 57 and 58 have equal values land are connected between the -6 v. terminal and ground. The resulting 3 volt drop across resistor 57 is applied through resistors 40 and 41, the contacts of commutator S and resistors 55 and 56 tothe condensers C1 and C2. Therefore, in the absence of a signal, these condensers are charged to a potential of 3 volts with the ungrounded sides negative, which potential supplies the operating bias for the two sections of tube V6. The cathode of the upper diode section of V5 is connected to the ungrounded side of condenser C1 and the cathode of Vthe lower diode section to the ungrounded side of condenser C2. The anodes of the two diodes are connected together and to ground through the -6 v. source of potential. The anodes of the two diodes are therefore biased 6 volts negative with respect to their cathodes. With this arrangement, the condensers C1 and C2 may charge to a potential of 6 volts with the ungrounded side negative but any further charging will be prevented by the shunting effect of the diodes which become conductive at this point; 4also the condensers C1 and C2 may discharge to zero potential but any recharging with reversed polarity is prevented by the shunting effect of the grid-cathode paths of the two sections of V6 which becomes conductive at this point. Hence potential variations across condensers C1 and C2 are limited to a maximum of 3 volts in either direction from the 3 volt potential normally existing thereacross in the absence of a signal, and as a result the potential variations of the grids of tube V6 are limited to a maximum of 3 volts either side of the bias potential of -3 volts.
Considering again the series of Voltage pulses applied to condensers C1 and C2, if all the pulses are positive or if the positive pulses predominate in number, the condensers discharge and the grid potentials are raised; if all pulses are negative or if negative pulses predominate in number, the condenser charges are increased and the grid potentials are lowered; if there are equal numbers of positive and negative pulses, Ytheir net effect on the condenser charges is zero and the condensers either remain at or return to their normal no-signal charge, depending upon whether the condensers were previously at their normal charge or had been charged or discharged to a voltage greater or less than 3l volts. The values of condensers C1 and C2 and resistors 55 Iand 56 are such that the time constants of the two condenser circuits are sufficiently long to require a signal to remain for about six cycles of the scanning system in order to appreciably change the charge on the condensers.
The coils of relays 59 and 60 are connected in the anode circuits of the upper and lower sections respectively of V6. These relays are adjusted so as to operate when the grid potentials reach a value slightly above 3 volts. For grid voltages below this value, the anode currents are insuicient to operate the relays. The contacts of these relays are in circuit with the servomotors operating the control surfaces of the bomb. Thus when relay S9 is operated the D contact is closed and a down correction is made in the bombs direction of travel; likewise, when relay 60 is operated, the R contact is closed and a right correction is applied. In the deenergized condition, the U contact of relay 59 and the L contact of relay 60 are `closed so that in the absence of a signal the bomb is made to follow an up and to the left course. Thus the bomb follows a sinuous path toward the target.
The operation of the commutator may be more clearly understood by reference to Fig. 2. In the simplified diagram of this gure the semicircular conductive strips 61, 62, 63 and 64 each extend for about 175 degrees and with contacts 65 and 66 which rotate together, form an arrangement that is the electrical equivalent of commutator 8 in Fig. 1. The scanning area 4 and arrow 67 also rotate with contacts 65 and 66. The arrow 67 represents the angular position of the point at which the scanning area begins to include the target, which is the point at which voltage wave E is initiated. As previously shown the period of voltage wave E is the same as that of a complete scanning cycle. The intersection of the Up-Down and the Right-Left axes represents the point toward which the bomb is travelling. Hence if the target is above the Left-Right axis, an up correction is needed and if to the right of the Up-Down axis, a right correction is needed, etc.
Fig. 3 gives a tabulation of the polarities of the voltage pulses applied to condensers C1 and C2 for eight points on the scanning cycle and for Various angles of lag between the arrow 67 and the voltage wave E. The angle of lag is the angle through which arrow 67 rotates from the zero position before voltage wave E is initiated and is determined by the position of the target. The first column of the table shows the pulse polarities for zero phase angle which is the condition in which the voltage wave E is initiated when the arrow 67 is in the zero position, and is the condition shown in Fig. 2. Therefore for 180 degrees of the scanning cycle the point A, Fig. 2, will be positive and the point B negative. Since strip 61 is connected to point B and since contact 65 is on this strip for approximately 180 degrees, the potential applied to C1 from 0 to 180 degrees is negative as shown under C1. Since contact 63 is also connected to point B, the potential applied to C2 from 0 to 90 degrees is also negative as shown under C2 However, from 90 to 180 degrees, contact 66 is on strip 64 which is connected to point A and therefore the potential applied to C2 during this interval is positive. From 180 to 360 degrees, the point A is negative and the point B positive due to the reversal in polarity of E at 180 degrees. Therefore the voltage applied to C1 through contact 65 during the 180-360 degree interval is also negative, whereas the voltage applied to C2 through Contact 66 is negative from 180 to 270 and positive from 270 to 360 since this contact changes from strip 64 to strip 63 at 270 degrees. Therefore it is seen that for this phase angle the charge of C1 is increased and the grid of the upper section of V5 becomes more negative so that relay 59 is not operated; and since the voltage applied to C2 alternates equally between positive and negative polarity with neither polarity persisting long Yenough to appreciably change the charge of this condenser, the grid voltage of the lower section remains at -3 volts and the relay V60 is likewise not operated. The correction produced for this target position is therefore up and left A similar analysis of the operation of the circuit for lag angles `from .'45 to 315 degrees is given'in'the remaining columns of the table in Fig. 3, with the' correction' produced in each case given at the bottom. It will be noted that whenever the target is on the Up-Down axis, a left correction is given and whenever it is on the Right-Left axis, an up correction is given. If the target is at the intersection of the two axes, an up and left correctin is given. This is due to the previously mentioned fact that in the deenergized condition the U and L contacts of relays 59 and 60 are closed and is the reason for the aforementioned sinuous path taken by the bomb in travelling toward the target.
What I claim is:
1. A control system for a target seeking bomb comprising a circular scanning device and a thermal infrared sensitive device the resistance of which changes with temperature changes due to changes in the amount of infrared radiation falling thereon, said scanning device and said infrared sensitive device cooperating to produce a cyclic variation in the resistance of the infrared sensitive device at the frequency of the scanning cycle whenever a source of infrared radiation appears in the scanned field, the phase relation between said cyclic resistance variation and said scanning cycle being determined by the position of the source of infrared radiation in the scanned field, means for changing said cyclic resistance variation into substantially a sine Wave of voltage having the same frequency as the resistance variation, said changing means having an output circuit that is unbalanced with respect to ground, means for amplifying said voltage wave and converting said unbalanced output circuit into a circuit that is balanced with respect to ground, said amplifying and converting means also containing means for clipping the sine wave of voltage so that a substantially square of voltage is produced in said balanced circuit, commutating means comprising a cam and four sets of contacts, cam follower means contacting said cam at points ninety degrees apart and arranged to open and close said contacts, said cam being shaped to close each set of contacts for slightly less than one hundred and eighty degrees of the cams rotation, two condensers with one side of each connected to ground, means connecting the electrical center of said balanced circuit to ground through a source of constant direct voltage, means connecting one side of said balanced circuit through two of said sets of contacts operated by adjacent cam followers to the ungrounded side of each of said condensers, means connecting the other side of said balanced circuit through the remaining two of said sets of contacts to the ungrounded side of each of said condensers, a plurality of control circuits associated with the steering mechanism of the bomb, relay means for opening and closing said control circuits, and means utilizing the voltage across said condensers to control the operation of said relay means.
2. Apparatus as claimed in claim 1 in which each of said condensers has a resistor connected in series therewith of such value as to require any change in signal to persist for several scanning cycles in order to appreciably change the voltage across said condensers.
3. Apparatus as claimed in claim 1 in which said utilizing means comprises two electron tubes each having the coil of one of said relay means in its anode circuit and each having one of said condensers connected between its grid and cathode, and in which each of said condensers is shunted by a diode biased by a voltage equal to twice the voltage of said source of contant direct voltage whereby voltage variations across said condensers References Cited in the le of this patent i UNITED STATES PATENTS Rost et al July 1.5, 1947