US2408068A

US2408068A - Automatic positional control of objects

Info

Publication number: US2408068A
Application number: US425146A
Authority: US
Inventors: Harvard L Hull; William S Gorrill; William F Frost
Original assignee: Sperry Gyroscope Co Inc
Current assignee: Sperry Gyroscope Co Inc
Priority date: 1941-12-31
Filing date: 1941-12-31
Publication date: 1946-09-24
Anticipated expiration: 1963-09-24

Description

Sept. 24, 1946. H. 1.. H ULL ET AL I 2,408,068

AUTOMATiC POSITIONAL CONTROL OF OBJECTS Filed Dec. 31, 1941 3 Sheets-Sheet 1 I g. l'l

lNVENTORS, HARVARD L. HULL DIRECTOR Se t. 24, 1946. H. L. HULL ET AL AUTOMATIC POSITIONAL CONTROL OF OBJECTS 3 Sheets-Sheet 2 Filed Dec. 51, 1941 INVENTORS, H.HUL L, W.GORRILL, qnd

Sept. 24, 1946. H. L. HULL ETAL 2,408,068

AUTOMATIC POSITIONAL CONTROL OF OBJECTS Filed Dec. 31, 1941 SSheets-Sheet 3 7 I08 MANUAL 'AUTOMATiC INVENTORS, H. HULdL, W. GORRILL,

W. FROST;

Patented Sept. 24,1946

orso STATES AUTOMATIC POSITIONAL CON TRGL OF OBJECTS ration of New York Application December 31, 1941, Serial No. 425,146

Claims.

This invention relates to systems for controlling the movement of bodies possessing substantial inertia, such as rotatably mounted guns and the like, and it refers more particularly to a system for automatically positioning a gun in accordance with angular data supplied from a remote source such as a fire-control director.

In the past, guns and particularly anti-aircraft guns, have been aimed manually in elevation and in train (azimuth) according to data exhibited by indicators at the gun, such as dials rotated by the receivers of self-synchronous transmission systems over which the data arrived from a remote director. The men aiming the gun in accordance with received data, in such systems, are situated alongside of the gun and hence are subjected to the shock of gun fire while trying to perform the difiicult feat of continuously reproducing the received data as closely as possible in aiming angles. Our present system of control overcomes this and other disadvantages of earlier methods of control by rendering the aiming of the gun entirely automatic under the control of the received data without any need for manually setting angles or performing other manual operations at the gun but it permits a quick change to manual operation under abnormal conditions.

In providing a remote control system for an object such as a gun, which has high moments of inertia about its rotational axes, we have invented features which are particularly adapted to prevent the hunting or oscillation about a position of rest to which such objects are subject.

One object of the invention is, therefore, to provide automatic control of the aiming of a gun from a source such as a fire-control director.

.Another object of the invention is to provide, for an object possessing substantial inertia, a remote control system which is free from hunting tendencies.

Another object is to employ, as anti-hunting control terms, functions of the data (representing the position of a controlling object) and gun position and particularly time derivatives of the variation of these quantities.

A further object is to provide an indication of the functioning of a system of the above character which is influenced by the degree of positional disagreement of the controller and gun and the rate of change ofrelative position of these bodies.

Another object is to provide a system of the above character which is fully self-synchronous and free from ambiguity.

A further object is to provide in a system of the above character protection against overloading of the driving means, including means for causing delayed or only partial response to suddenly changing data.

A further object is to provide limit stops which prevent overrunning without putting undue strain on the driving means.

Still another object is to provide in an automatic system of the above character suitable switching means for conversion to manual operation.

In the drawings,

Fig. 1 is a schematic diagram of a gun-posi tioning system embodying one form of the invention.

Fig. 2 is a diagrammatic perspective View of a power limiter adapted for use with the system of Fig. 1.

Fig. 3 is a simplified perspective view of a gun mounted for rotation in train (azimuth) and in elevation, showing certain of the elements of the control system of Fig. 1.

Fig. l is a diagrammatic showing of certain details of Fig. 1.

Referring now to Fig. l, the apparatus units shown at the upper left-hand corner are associated with a gun fire director which may be, for example, of the type described in United States Patent No. 2,065,303, issued to E. W. Chafee et al., December 22, 1936, or which may incorporate certain features disclosed in the co-pending application of one of the present inventors, H. Hull, joint with W. Hartman and R. Goertz, Serial No. 403,618, filed July 23, 1941. The units shown are those concerned with the transmission of the angle 01 elevation only, it being understood that similar apparatus may be employed for the transmission of angle of train (azimuth) data. Likewise, at the gun, only elevation control elements are illustrated in the figure, a similar arrangement for azimuth positioning being implicit in the disclosure.

Gun elevation is represented in the director by the angular position of shaft 10, connected by gearing to drive the rotors l3 and I l of Selsyn transmitters H and I2, respectively, each of said rotors being excited from a suitable A. C. source. The two rotors l3 and M are driven at relatively difierent speeds, corresponding to the'ratio of gears l5 and [6, to provide coarse and fine data transmission channels, as is common practice in fire control data transmission systems, a ratio of 16:1 between the data amplitude of the two channels being often employed. The position of rotor l3 determines the voltages induced in the three windings of associated stator H, which voltages are transmitted over three-wire line H to three-winding rotor it of Selsyn receiver i9, located at the gun. Similarly, the position of rotor M determines the voltages induced in the windings of stator 20, which are transmitted over three-wire line 29' to rotor 2| of Selsyn receiver 22, likewise located at the gun. Receivers I9 and 22 are operated as locked rotor devices, sometimes called signal generators since a signal voltage is generated proportional to the displacement of each rotor from the datum position. Rotor it, for example, is connected to generate a gun position signal by being driven through gearing in correspondence with gun 23, while rotor 21 is similarly driven but at a different rate. The term synchro transformers is also applied to devices such as 19 and 22. It is immaterial in the transmitter whether the single-winding element, as shown, or the three-winding element be made the rotor, since only the relative position of the two elements determines the transmitted voltages.

The voltages in the windings of rotor I8 induce an A. C. voltage in stator winding 24, while the voltages in the windings of rotor 2| induce an A. C. voltage in stator winding 25. These two stator voltages, which are both proportional to the positional disagreement of gun 23 and shaft l0, but in a different ratio, are combined in a cir- I cuit which supplies an input to amplifier-modulator G, to be later described, and a voltage limiter 26 is connected across the output circuit of stator for the purpose of shifting control from the fine to the coarse transmission channel when the disagreement of the transmitter and receiver exceeds the range of fine transmission.

When the gun and director are in synchronism, the voltage in stator winding 25 of the fine transmission channel is zero. -Displacement of the director elevation shaft (data) by a small angle in one direction results in an A. C. voltage being induced in winding 25 proportional to the displacement and having a phase dependent upon the sense of the displacement. A displacement in the opposite direction results in a reversal of phase of this voltage. A position of stable equilibrium is thus defined. Considering the coarse channel, when the gun and director (data) are in synchronism the voltage across winding Ed is i not zero due to an initial or biasing displacement which is given the stator mounting this winding but this initial voltage is balanced out by the voltage from transformer 30, supplied from the common A. C. source and having a resistance-capacity phase adjustment 3| in its input circuit, which voltage is made equal in magnitude but opposite in phase thereto. The coarse as well as the fine channel is therefore in stable equilibrium at this point.

When the gun is positioned 180 away from the synchronous position, i. e., from the angular value of the data, the voltage in winding 25 is zero, but the voltage in winding 24 is reversed in phase and so is of the same phase as the voltage supplied by transformer 30. These two voltages therefore do not annul one another and no equilibrium of the coarse transmission channel results at this point. The purpose of the voltage supplied from transformer 36 is thus seen to be to prevent the occurrence of two positions of stable equilibrium in which the controlled object could otherwise move in synchronism with the controlling object. It will be found upon analysis that any position,

other than the synchronous position, at which zero Voltage exists simultaneously in winding 24 and 25 is one of unstable equilibrium for both the fine and coarse channels. This mode of operation is more fully described in the pending U. S. applications of Eric J. Isbister and Francis L. Moseley, Serial No. 304,895, filed November 17, 1939, and of Francis L. Moseley, Eric J. Isbister and H. B. Steinhauser, Ser, No, 382,020, filed March 6, 1941, both assigned to the assignee of the present inventors.

Voltage limiter 26 comprises saturable reactor 21, across which the output of the fine transmission channel is applied, and attenuator 28, the latter being shown for illustration in the form of a T resistance network. The voltage induced by stator 25 across reactor 21 may be adjusted by suitable choice of the characteristics of attenuator 28.

The constants of attenuator 28 and the saturation characteristics of reactor 2'! are preferably so chosen that the maximum voltage appearing across reactor 2'? is limited to a value which will allow the voltage of stator 24 (of the coarse transmission channel) to take control when the disagreement between gun and data is greater than the range in which the fine transmission gives correct electrical indication. When a ratio of 16:1 between fine and coarse transmission channels is used the shifting of control from one to the other should occur before the diasgreement reaches approximately 12 /4 degrees.

Since the ratio of the fine transmission channel is 16 to 1, the amplitude of the fine alternating potential signal would go through sixteen complete cycles for every 360 degree change in the angle of disagreement between the gun 23 and the director shaft iii. Were the fine transmission channel to solely control the position of the gun, the direction of control exerted thereby would only be correct for one-half cycle to either side of the zero disagreement position. Accordingly, it is necessary to render ineffective the control exerted by the line transmission sir,- nal beyond such limits.

This limitation of the range of control of the fine transmission signal is accomplished in the voltage limiter 26 which operates to prevent the fine alternating potential signal from ever exceeding a predetermined amplitude. This amplitude is so chosen that the sum of both the coarse and fine alternating potential signals is always of the same sign as that of the coarse potential signal. In this manner when there is only slight disagreement between the positions of the gun and the director shaft, the fine transmission potential signal exerts the preponderant control, since the coarse transmission potential signal has not as yet built up to a substantial tial agreement, which latter condition is the normal operating condition.

The circuits so far described provide means I for obtaining a signal voltage indicating disagreement of the gun position and the transmitted data and closely proportional to such disagreement, at least over a limited range, the phase of the voltage indicating the sense of the error. This voltage is applied across resistances 32 and 33, which form a voltage divider.

Means for obtaining auxiliary signals proportional to other quantities, which we combine with the disagreement or error signal, will be described later.

The voltage drop across resistance 33 is applied to imput resistances 32 and 43 of balanced modulator 5B in a mixer circuit which may be traced from one terminal of resistance 33 by way of lead SE to the outer terminal of resistance 53 and from the other terminal of resistance 33 by way of

resistances

35, 36, 31, 38, 46 and lead 4! to the outer terminal of resistance 42.

Modulator 50 is two triode or other multi-electrode vacuum tube units in a push-pull circuit, in which a bias is supplied to both units by the drop, due to plate current, across resistance 5|. The input to this modulator is a combination of A. C. and D. C. signal voltages from the mixer circuit and the output is an A. C. voltage, having components which, in phase, and magnitude, represent the polarity or phase and magnitude of the input signals.

The preferred form of modulator shown in Fig. 3. uses A. C. on the plates for converting the D. C. signal voltages to an A. C. voltage, the magnitude of which is proportional to the magnitude of the D. C. input, and the phase of which is determined by the polarity of the D. C.

A modulator may alternatively be used which is supplied with D. C. on the plates and obtains the conversion to A. C. by the use of fixed A. C. bias between cathodes and grids, it being immaterial whether the constant A. C. is supplied in the grid or plate circuit of the tubes. The output of modulator 52 to balanced amplifier 53 which supplies an amplified A. C. signal through transformer 54 to one stator winding 56 of two-phase motor 55, the other winding E1 of which is supplied from the common A. C. supply of the system. Condenser 58 is for phase adjustment or phase splitting.

Motor 55, through bevel gears 59, crank 60, push-rod BI and power limiter 62, positions stroke rod 63 of a Vickers hydraulic variable speed gear 34 comprising a pump or A end 65, a hydraulic motor or B end 66, and. an electric driving motor 61. The Vickers gear is well known to persons skilled in the art and is described in detail in United States Patent No. 2,189,823, issued February 13, 1940, in the names of H. F. Vickers and N. B. Frost and entitled Apparatus for controlling the movement of heavy masses, The speed of the motor or B end of this gear, neglecting leakage, is proportional to the setting of the stroke rod 653 which determines the angle of tilt of the pump cylinder block and hence the stroke of the pistons. Since the motor or B end 66 directly actuates the gun 23, the setting of the stroke rod 63 is proportional to the angular rate of rotation of gun 23. A sump for the operating fluid used in this gear, which is generally oil, is shown at 68 and a replenishing pump driven by motor 61 is shown at 69. In operation, fluid circulated by pump 65 causes rotation .of motor 36 and of gun 23 driven therefrom through gears 8|.

Returning now to the means for generating the different voltages which control the setting of the stroke rod of the Vickers gear, the means for generating a signal proportional to disagreement A. C. operated and comprises.

50 is passed by transformer of the gun position and datum have been dcscribed. In addition to this primary signal, as noted, auxiliary signals are employed. One of these auxiliary signals is proportional to the rate of change of the transmitted elevation data, that is, to the rate of change of position or speed of turning of shaft l0 and rotors l3 and M. This signal is supplied as a D. C. voltage by generator 10, shown as having a field excited by a suitable D. C. source. It may be preferable in some instances to employ permanent. magnet excited generators for those described herein as D. C. excited. Generator It is driven by a chaser motor controlled by the elevation data shaft Hi, here illustrated as reversible two-phase induction motor H having stator windings 12a and lib, the former winding being constantly excited from a suitable A. C. source. Motor H is constrained to follow the motion of shaft I0 through gearing nd a follow-up device 13, comprising roller contact 14 and cooperative contact segments l5 and H5 separated by insulating dead spot ll. The phase of the current in winding 12b, which is shifted relative to that in windings 120, by con denser 18, has opposite values depending on which contact segment roller 14 rests on, thereby providing reversible operation of the motor.' The output voltage of generator 'lll, which is proportional to the speed at which the armature is rotated, is applied across resistor 31 and is filtered by the resistance-capacitynetwork comprising resistance 36 and condenser 19 to smooth out or eliminate peaks due to sudden changes of the rate of change of the data, corresponding to acceleration of shaft H).

The next signal, means for obtaining which will be described, is one proportional to the speed of rotation of the gun in elevation. This is ob" tained as a D. C. voltage from generator 830 hav ing a permanent magnet field or one excited from a suitable D. C. source. Generator 8G is driven by gearing, including gears 8|, from gun 33 and applies a voltage proportional to the speed of rotation of the gun across a potential

divider comprising resistances

39 and 39 connected in series. Resistance 39 has a variable contact 65 by means of which the magnitude of the gun velocity signal to be utilized can be adjusted.

Two other signals are employed, one, a D. C. signal proportional to the position of stroke rod 63 of the variable speed gear and the other, a D. C. signal proportional to the rate of change of position of this rod. If there were no leakage in the hydraulic transmission and no lost motion in the gun drive, the position of the stroke rod would be strictly proportional to the speed of r0- tation of the gun. In practice, however, there is a slight lag in the response of the gun to a change of position of the stroke rod, and while at constant velocity either the stroke rod position or the gun velocity signal obtained from generator 3i! would be sufficient, in order to care for all transient conditions which might encourage instability, we prefer to use both signals and, in addition, a signal derived from the stroke red signal which is substantially proportional to the angular acceleration of the gun.

A variable coupling transformer having a rotatable winding 9| excited from a suitable A, C. source through multi-winding transformer 92 and rotated by motor 55, through gearing 59, in positional correspondence with stroke rod 63, is provided with a pair of

stator windings

93 and 94 in each of which an A. C. voltage is induced corresponding to the position of rotor 9 l the voltages 7 in windin s 93 and 94 being of opposite phase. In series with each of these two windings there is connected one of secondary windings 95 and 96 of transformer 92 to supply voltages of constant phase.

Windings

93 and 94 feed phase sensitive rectifier circuits including bridge type rectifiers 91 and 98 respectively. The D. C. output voltage of each rectifier is proportional to the A. C. input, and the polarity of the output is determined by the phase relation of the input A- C. voltage from 93 and 94 to that of the voltage supplied by winding 95 or 96 as the case may be. The outputs of rectifiers 9'! and 98 are serially combined and applied to low pass filter H10 across center-tapped input resistor 99. V The D. C. output of filter I00,

from which A. C. ripple has been substantially removed, is applied across tapped resistance 40 serving as a potential divider.

Also driven from motor 55 through gearing 59 and I6! is stroke rate generator I02 having a field excited from a suitable D. C. source. The armature of generator Hi2 being moved in positional correspondence with stroke rod 63, the generated D. C. voltage is proportional to the rate of change of stroke and therefore is substantially proportional to the acceleration of the gun, since the stroke position is proportional to the velocity of the gun, as previously brought out. This voltage is applied to resistances 35 and 35' connected in series as .a potential divider.

To summarize, there are applied to the input of modulator i to contro1 the operation of gun driving means, an A. C. error signal, and D. C. signals representing director shaft velocity or rate of change of data, gun .velocity, stroke rod position and stroke rod velocity, the two last named signals representing substantially gun velocity and gun acceleration respectively. The purpose of the auxiliary D. C. signals is to overcome the eifect of the inertia and other characteristics of the controlling and controlled objects, and of the means connecting these objects, in tending to promote overshootin and hunting of the controlled object (gun) relative to the angular positions, this object should assume in response to the data. For a further discussion of the use of time derivatives of the error signal to provide anti-hunt characteristics in a remote control system, reference may be had to U. S. Patent No. 2,233,415, dated March 4, 1941, to H. L. Hull, one of the present inventors.

We have described arrangements for causing the gun driving means to be actuated in a preferred manner. The gun, however, being possessed of high inertia, cannot respond instantly to change of transmitted data and there will consequently be periods when the data will not be accurately reproduced in aiming angles. The seriousness of any such discrepancy depends to a certain extent upon whether the gun position is approaching or moving away from the datum position, that is, upon the relative rate of change of gun position and datum. Accordingly, we supply an indication, somewhat in the nature of a figure of merit of .the system, which combines the error of gun following with the difference of the rates of change of gun position and of datum, the latter term representing the relative rate of change of the two angles.

Transformer I83 (Fig. 1) is connected to receive the voltage across resistances 32 and 33 which is proportional to th error in following. This transformer has two secondary or output windings and the voltage induced in each is comerror.

bined with a voltage of constant phase derived from the Selsyn exciting source through transformer IE3 to obtain a phase-sensitive device as described in connection with the circuit including transformers 90 and 92. Rectification of these voltages is accomplished in bridge type rectifiers Hi l and H14 which may be of the dry disc variety connected in a push-pull circuit. A D. C. voltage is thus obtained across center-tapped resistance I05 which is combined in series with a selected portion of the voltage across

resistances

31 and 38 and applied to meter H16, preferably of the high resistance or voltmeter type. The adjustment of the voltage derived from the drop across resistance 31, which drop, as has been pointed out, is proportional to the rate of change of transmitted data, is made by means of variable contact 31' while the adjustment of the voltage proportional to rate of change of gun position is mad .by sliding contact 38', these resistance adjustments determining the degree to which the lag error indication is modified by the relative rate of change of gun position and data.

The purpose of this arrangement is to cause the meter to give an indication which is a combination of the error and the rate of change of the error. In addition to showing the fidelity of automatic operation it enables an operator to anticipate the approach of the gun to the correct position during manual operation and to govern his control accordingly.

It will be apparent from the above description that a combination of three signals are applied to the meter: a voltage proportional to the error in following, a voltage proportional to gun speed; and a voltage proportional to rate of change of the angle transmitted from the director. The resistances across which the signal voltage drops are taken are so adjusted that when the gun 23 and director shaft ID are rotating at the same speed the two speed voltages generated by enerators If! and are equal and opposite and therefore annul one another. When the gun or the director shaft changes speed, however, a difference in voltage is produced which represents the speed of approach or separation of the gun and datum angle. This resultant signal, when added to the error signal in the proper relationship, causes the meter to "anticipate future The degree of anticipation provided is adjustable by means of contacts 31' and 38' and by moving these contacts to adjacent ends of the resistances with which they cooperate, meter I06 may be caused to indicate lagonly.

We have found that it is highly desirable to provide certain safety devices in connection with the Vickers gear as used in our control system to prevent excessive hydraulic pressures being built up and to prevent excessive power demands on the pump driving means 67. The location of these devices in the driving system is shown in Fig.41 by the block I08, details being shown in Fig.

One safety device is a pair of spring loaded pressure relief valves. Normally, outlet pipes Ill! of pump 65 are in connection with corresponding pipes I07 leading to hydraulic motor 88, and the pressure built up by pump 65 must therefore be sufiicient to overcome the entire load on motor 58. Under certain conditions, excessive pressures might thus be built up. To prevent this, relief valves HI and III are provided. As seen in Fig. 4, valve l i I, for example, comprises a ball H2 normally pressed against a spherical or frustoconical seat by spring H3 thus closing pipe H4 leading to one of pipes IIlI. When the pressure of spring I I3 is overcome by pressure in pipe IM, ball I12 lifts and provides a lay-pass to the other of pipes Iill. Ball I I of valve III is actuated by oil pressure in the reverse direction and would similarly provide a passage between pipes It! should the direction of fluid flow be reversed from that indicated in Fig. 4 and the pressure built up in the reverse direction between pipes Ill! exceed the maximum allowable pressure. Actuation of the valves interconnects pipes IIl'I and allows circulation of oil at maximum allowable pressure by pump 65 without corresponding rotation of motor 5'5.

Several conditions may occur under which the by-passing of pipes lol by valves III and III is essential to the operation of the system as, for example, when a shift to manual operation is made by operating transfer valve I80, and when limit stop valves I40 and I40 are actuated, as will be later referred to.

Another safety feature is provided in power limiter 62, shown in detail more particularly in Fig. 2. This device operates to prevent excessive power demands on the gun driving means, including the hydraulic transmission, under abnormal conditions as, for example, when stroke rod 63 is suddenly given a large displacement. Such a sudden and large stroke rod displacement calls for a correspondingly sudden and large change of speed of motor 66 and, where a high inertia load such as gun 23 must be suddenly accelerated, tends to cause a severe strain on the driving means. To prevent this, we provide means for limiting the maximum stroke of the pistons of pump 65 responsive to output pressure of the pump, and. since the power delivered by th ump is proportional to the product of stroke and pressure, we are thus enabled to limit the maximum power which can be delivered at any stroke setting and can select a preferred law of variation of this maximum pressure with stroke setting signal. Such a law may be, of example, constant power pump output regardless of the input to motor 67.

If motor 6'! driving pump 65 should be loaded so as to develop pressures equal to the relief valve settings, as, for example, if pipes Ill'I should be completely blocked, the stroke of the pump may, by our power limiter, be reduced to a value such that the power dissipated by the pump is well be: low the normally available maximum power. It is thus possible even to block rotation of the gun, as is desirable under conditions to be described, and maintain maximum pressures in pipes IS! without excessive power consumption or excessive heating of the equipment.

Stroke rod 63 (Fig. 2) is shown as operated by rotation of a cruciform member I29 pivotally mounted on shaft I22, pivoted to datum at I2I. The angular position of member I20 in normal operation is determined by the setting of push rod GI, the motion of which is communicated to shaft I22 through crank arm I 23. A second crank arm I 2 is also rigidly mounted on shaft I22.

Arm I24 mounts a pin or stud I25which is normally oppositely engaged by jaws I26 and I 21 mounted for independent free rotation about shaft I22, the two jaws being oppositely pressed against stud I25 by spring I28. Also oppositely engaged by jaws I26 and I21 is upwardly extending stud I29 mounted on the arm of member I20 opposite to that with which rod 63' connects. This arrangement of a pair of studs engaged by spring pressed jaws forms a coupling for transmitting motion from arm L24 to cruciform member I (or in the opposite direction) when the resistance to such motion is insufficient to overcome the pressure 'of spring I28 and open jaws I and I21, which is the case during normal actuation of rod 63.

For modifying the setting of rod 63 (shown in Fig. 2 in the position for zero stroke) to care for abnormal conditions, we provide two like cylinders I39 and I connected by pipes III] and H0, respectively, to pump outlet pipes I 01. A piston I3! is movable in cylinder I30 under the influence of fluid pressure transmitted by way of pipe IIll against the resistance of a compound spring comp-rising a stiff spring I32 and a concentric weak spring I32. Small displacements of piston ISI are controlled by spring I32. whereas both springs I22 and I32 act in controlling larger displacements. Piston rod I33 extends from piston I M through the cylinder head and is normally positioned with clearance between its outer end and one of the two opposite lateral extensions of member I29. Cylinder I39 contains a piston and spring similar to those described in connection with cylinder Hill. From the piston in cylinder I39 extends piston rod I33 ending a slightdistance from the other lateral extension of member I28. Member I28 is not engaged by either of piston rods I33 or I33 until a relative displacement occurs which is greater than the displacement of member I28 during normal operation.

Should, however, excessive pressure be built up in cylinder I39, for example, piston I3I and rod I23 will be moved, at first against the relatively slight opposition of spring I32 and later against the greater opposition of springs I32 and I32 in combination. If this occurs at a time of large stroke rod. displacement (calling for high acceleration and velocity of the B-end) contact is made with member I20, stopping further stroke rod movement. Further motion of rod I 33 will also cause rotation of this member in a clockwise direction resulting in movement of stroke rod 63 in a direction to shorten the stroke of pump 65 and thus limit the developed power. In moving rod 63, piston I3I does not have to move rod BI and thereby operate against the high resistance of all the elements connected to that rod, since the resistance of spring I28 is made relatively low and therefore allows stud I29 to move jaws I26 and I 21 apart as member I28 is rotated against the sole resistance of the spring without displacing arm I 24 and rod 6 I.

In a manner similar to that described, increas ing pressure in pipe HQ causes piston rod I33 eventually to engage member I20 and rotate said member in a counter-clockwise direction, thereby to limit the stroke of pump when operating in the reverse direction. By adjustment of clearances and suitably proportioning the relative strength of springs I32 and I32 and of the corresponding springs in cylinder I36, a preferred law of variation of maximum power may be attained. Furthermore, a change from one law to another may be had corresponding to the effective change of spring strength brought into play. Control automatically reverts to stroke motor 55 when abnormal conditions are abated.

A further safety feature is provided in the form of limit stops preventing overrunning of the gun in elevation, only, no azimuth stops for gun operation being'normally necessary or desirable. .These stops cooperate with power limiter 62 and relief valves II I and I II to bring the gun to stand still without imposing undue strain on the driving means or mount.

A pin I35 (Fig. 3) on gun elevation gear sector I64 engages a lever I35, pivoted on the gun mount, when the gun reaches the lower limit of its travel about horizontal trunnion I50. Lever I36 operates rod I31 which in turn operates valve rod I38 (Fig. l) through a crank or other suitable connection. Rod I38 mounts valve piston I39, slidable in valve cylinder I44, of the valve I 40, which cooperates with a port I4I connecting with pipe I42 leading to transfer valve I80, thus normally providing a free. connection between corresponding pipes I 01 and I01 by way of valves I40 and I80. When stop pin I35 engages lever I35, piston I39 is moved to the left and gradually obstructs port I 4|, it being seen that piston I38 is provided with a chamfered edge for obtaining a gradual throttling action. Gradual obstruction of port I M causes an increasing pressure to be built up in one of pipes I01 which eventually brings power limiter 62 into play to prevent excessive demands on pump 65 and motor 51. With port I II completely blocked, flow of fluid from the hydraulic motor 65, through the lower of pipes I01, through pipe I42 and port MI and the lower one of pipes I01 back to the pump 65 is prevented and motion of the gun in elevation ceases. The setting of relief valve III is normally such that when port MI is completely closed, this valve operates to by-pass fluid between pipes I 81.

When the elevation data is such as to require the gun to reverse its direction, that is, to increase its elevation, the direction of fluid flow will tend also to reverse and it is then necessary to provide a. path for a reversed circulation of oil, otherwise clocked by piston I39. Spring loaded check valve I45, which is actuated in response to such re- Ierse flow, under this condition by-passes valve I40 until such time as lever I 35 is no longer enraged with pin I35 and piston I39 returns to its normal position in response to the pressure of :pring I43.

A second pin (not shown) or gear sector I64 Lctuates valve I48 to prevent overrunning of the run beyond the highest desired elevation angle. Ehe operation of valve I48 is in all respects simiar to that of valve I40 except that the lever oprated by rod I31 is reversed, and as primed refrence numerals in Fig. 4 relate members of this *alve to like members of valve I40, its operation rill be readily understood without further decription or explanation.

In Fig. 3 the manner of mounting certain of the ontrol and indicating units at the gun is illusrated, as well as the rotatable mounting of the un itself. Gun 23 is pivoted about horizontal runnion I50 for rotation in elevation while plat- Jrm II on which the assembly of gun and as- Jciated units is supported is pivoted about a ertical pin (not shown) for rotation in azimuth.

The azimuth drive is mounted on a hollow colmn I52 supported from platform I5I. The hyraulic motor or B end of the azimuth variable )eed gear is connected to drive a vertical shaft ithin this column mounting a pinion I54 meshlg with a stationary azimuth gear I55. The amps or A ends of both azimuth and elevaon drives are enclosed in a housing I56 which .ay also enclose the stroke setting motors, aux- .ary signal generators and associated equipent. Mounted at the top of column I52 is an :imuth indicator I51, seen in rear aspect.

The elevation driving motor 66 (Fig. 1) is ounted in a housing I 58 on column I59, supported from the gun mount, and. is connected to drive a worm or pinion (not seen in Fig. 3) meshing with elevation gear sector I64. Elevation indicator I63 is mounted at the top of column I59 and comprises a Selsyn receiver I8I' (Fig. 1) operated as a free rotor device having a stator winding I68 excited from the common A. C. supply and a rotor I 59 on the shaft of which is mounted indicator dial I18.

The windings of rotor IE3 are connected across transmission line II in parallel with the windings of signal generator rotor I8. The position of dial I10 therefore indicates the transmitted data and provides a check on the operation of the automatic positioning equipment. The indication of this dial also is used in connection with operating means such as handwheels I64 provided for manual aiming of the gun. Similar handwheels I52 are provided for manual aiming of the gun in azimuth accordance with data shown by indicator I51.

The shift from automatic to manual operation in elevation is made by means of transfer valve I (Fig. having operating knob I8I on valve stem I82 for displacing pistons I03, I84 and I in cylinder I86. Normally, for automatic operation, pipe I 42 communicates with the lower of pipes I81 by way of the space between pistons I84 and I85 and similarly, pipe I42 communicates with upper pipe I01 by way of the space between pistons I83 and I34. This is the condition shown in the figure. For manual operation, knob I8! is pulled out to a position (determined by a stop, not shown) such that piston I85 completely blocks the opening of pipe I42 and such that the space between pistons I84 and I85 permits unimpeded flow between the two pipes I01. Thus, fluid displaced by motor 36 during operation of handwheels I 54 can circulate freely without passing through pump 65.

The blocking of pipe I42 brings into play power limiter 82 as in the case of the operation of the limit stops which limits the load imposed on pump 85 and motor 31 but allows these units to continue to operate so that a switch back to automatic operation can be quickly made at any time. The pressure developed may be suflicient to cause the operation of one of relief valves II! or III but the power delivered by the pump will still be kept by limiter 6?. well below the permissible maximum. It is to be understood that in order to maintain the hydraulic transmission in operative condition at all times, accessory devices may be necessary such as drainage pipes, etc., as is understood by those skilled in the art.

Briefly reviewing the functions of the apparatus shown in Fig. 4, a pressure is built up between pipes I01 by pump 55 in one direction or the other, depending upon the phase of the composite potential output signal of balanced amplifier 53. Ihe direction of pressure and resulting fluid flow indicated in Fig. 4 is that which would be caused by a signal voltage requiring a decrease in the elevational position of the gun. Under theseassumed conditions the direction of flow will normally be from pump 65 through the upper of pipes I81, through limit stop valve I40, through pipe I42, through transfer valve- I 80, and through the upper of pipes I01 to the hydraulic motor 58. In its return path from the hydraulic motor the fluid will traverse the lower of pipes I01, transfer valve I80, pipe I42, limit stop valve I40, and the lower of pipes I 81 back to pump 65.

The transfer valve I80 is provided in order to completely out off the hydraulic motor 66 from the fluid pressure supplied by pump 65, in case manual control of the gun is desired. The transfer valve I88 accomplishes this simply by blocking the path of oil from pipes I62 and M2 to pipes lill', respectively, and simultaneously providing an inter-connecting channel between pipes Hi7.

Limit stops M and MD are provided to also interrupt the supply of fluid to motor 66 in case the gun 23 should reach predetermined limits of operation. Thus, when the gun has reached its lower limit of operation, piston I39 of limit stop valve M9 is automatically displaced by the motion of the gun to such a position that it blocks port i il, thus interrupting the supply of fluid to the motor. While the elevation data remains such as to require that the gun be lowered in elevation, the direction of fluid pressure will remain the same and will tend to cause current flow as indicated in Fig. 4. However, fluid flow from the hydraulic motor will be prevented by valve Hill and hence valve I I2 will open to by-pass the fluid from the pump. Under such conditions it is apparent that check valve I45 will remain closed.

However, should the elevation data reverse, causing a reversal of pressure, check valve M5 will open, allowing fluid. flow in the opposite direction corresponding to increase in the elevational position of the gun. As the gun is thus elevated, piston I39 is automatically removed from port MI by the action of spring :53, and the normal conditions of operation of the system are restored. Limit stop M0 operates in exactly the same manner as limit stop I49 but becomes effective upon the gun reaching its upper limit in elevation.

Should the gun become jammed for any reason or should the transfer switch i811 be set to its manual position, it is apparent that the fluid pressure between pipes it)? will increase, since fluid flow will be prevented. In order to prevent this pressure from exceeding a predetermined safe limit under such conditions, the relief valves Ill and iii are provided. These valves are set so that when the pressure between pipes it! exceeds a desired limit, one or the other of these valves, depending on the direction of the pressure, opens, thus providing a direct channel between pipes It'l, by-passing the rest of the system, and thus preventing the pressure from exceeding a predetermined limit.

Briefly reviewing the operation of the entire system, a synchronous transmission system is provided whereby an alternating potential signal is obtained across resistors 32 and 33 which corresponds to the angular disagreement between the gun 23 and the director shaft l9. Two direct current generators ill and 8!! are provided, one being driven in correspondence with the director shaft ii! and the other being driven in correspondence with the gun 23, whereby a direct current voltage signal proportional to the angular rate of rotation of director shaft ill is obtained across resistor 3'1, and a direct current voltage signal proportional to the angular rate of rotation of gun 23 is obtained across resistor 38. A similar direct current generator 162 is provided in order to obtain a voltage across resistor 35 which is proportional to the angular acceleration of the gun 23, as will be explained hereinafter.

All of the above signals, comprising one alternating potential signal, and three direct poten- .14 tial signals are introduced into a balanced modulator 5!! which combines them into one corresponding composite alternating potential signal which appears across output transformer 52. This output signal is then amplified in the balanced amplifier 53 and he output applied to one phase of a two-phase motor 55, the other phase of which is constantly energized from a suitable alternating current source. In this manner the motor 55 is caused to rotate at a speed and in a direction corresponding to the magnitude and phase of the. composite alternating potential signal. I

A Vickers hydraulic variable speed unit is provided consisting essentially of electric motor 81 driving a hydraulic pump 65, the fluid pressure generated by said pump driving the hydraulic motor 66 which directly actuates gun The speed and direction of rotation of the hydraulic motor 66 and of the gun 23 may be controll d by the setting of a stroke rod E3 which in turn is directly connected to motor 55 and controlled thereby. In this manner the composite alternating potential signal controls the direction and the speed of rotation of gun 23.

Since the gun is rotated by the Vickers unit at an angular rate proportional to the setting of stroke rod t3, the rate of displacement of the stroke rod may be taken as a measure of the angular acceleration of the gun. Accordingly, direct current generator N32 is actuated in accordance with stroke rod 63, as by being directly connected to the same motor 55 as is the stroke rod. Thus, the voltage generated by generator "52 is proportional to the angular acceleration of the gun, and this generated voltage is applied across resistor 35 to supply that previously referred to component of the composite signal which i proportional to the angular acceleration of the gun.

As many changes could be made in the above construction and many apparently widely diilerent embodiments of thi 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 illustrative and not in a limiting sense.

Having described our invention, what we claim and desire to secure by Letters Patent is:

1. In a positional control system, a controlling object, a controlled object, means having a oneto-one relationship between s9 two objects producing an A. C. signal proportional to the positional displacement of said two objects and reversible in phase with the direction of said displacement, a second means having a multiple relationship between said two objects for producing a similar signal responsive to a smaller displacement in position between said two objects, said signals normally exercising joint control of said controlled object with said second signal preponderant, and means including a saturable reactor connected across said second signal for limiting the same to a predetermined amount, whereby, When the relative positions or the controlling and controlled objects exceed a predetermined angle, the first signal prevails and pro vents loss of synchronism.

2. A positional control system as claimed in claim 1, having means for preventing ambiguity of the first-named signal control, whereby complete self-synchronism is obtained.

3. In a system for positioning a heavy object troller, means producing an alternating current signal proportional to positional displacement of the object and controller, servo means controlled by said signal for driving the object including a variable speed hydraulic gear having a variable displacement pim'ip and a hydraulic motor driven therefrom, said gear having a control member moved in response to the sense and amplitude of said signal and governing, by its position, the speed of said servo means, and a generator connected to said member producing a variable direct current signal proportional to the acceleration of said gear for opposing said first signal and a modulator for combining said signals, the output of which controls said servo means.

4. In a positional control system, a controlling object, a controlled object to be kept in positional agreement with said controlling object, means for obtaining an alternating electric potential proportional to positional disagreement of said two objects and reversing in phase in correspondence with change of sign of said disagreement, means for obtaining unidirectional electric potentials respectively proportional to the velocities of said two objects, thermionic tube means jointly re ceiving said several potentials as an input and supplying a reversible phase alternating output proportional to the combination thereof, an alternating current source, and reversible driving means for said controlled object including a twophase motor having one phase-constantly excited from said source and a second phase receiving the reversible phase output of said thermionic means.

5. In an automatic system for positioning a rotatably mounted gun in positional correspondance with a remote controller, means for obtaining an electric potential measuring the positional disagreement of said gun and controller, means for rotating said gun including a variable speed hydraulic transmission having a positionable member determining the output speed thereof, neans for obtaining an electrical potential proportional to the position of said member, means :or deriving an electrical potential proportional ;o a combination of said first two potentials, and neans actuated by said derived potential for po- ;itioning said member.

6. In a system for automatically positioning a rotatably mounted gun in positional agreement avith the position of a remote controller, means .or obtaining an electrical potential proportional ,o the positional disagreement of the gun and :ontroller, means for rotating the gun including it variable speed hydraulic transmission having 2. positionable member determining the speed hereof, means for obtaining an electrical poten- ;ial proportional to the position of said member, neans driven from the gun for obtaining an :lectrical potential proportional to the velocity .hereof, means for deriving from said three poentials a further potential proportional to a combinatio-n thereof, and means actuated by said derived potential for positioning said member.

7. In a system for (positioning an object in correspondence with the position of a remote controller, means producing a signal proportional to the positional disagreement of the object and controller, servo means controlled by said signal for driving the object including a variable speed hydraulic gear having a variable displacement pump and a hydraulic motor driven therefrom, said gear having a control member moved in response to the magnitude of said signal and governing, by its position, the speed of said motor,

and means responsive to the pressure of the driving fluid for limiting or reversing the motion of said member at high speed positions to limit the power consumption.

8. In a system for positioning a gun in correspondence with the position of a remote controller, means producing a signal proportional to the positional disagreement of the gun and controller, servo means controlled by said signal for driving the gun including a variable speed hydraulic gear having a variable displacement pump and a hydraulic motor driven therefrom and operatively connected to the gun, and means for further controlling said driving means in accordance with the output pressure of said pump, said last means including means inversely responsive to the speed of rotation of the gun for adjusting the displacement of said pump to the power developed thereby.

9. In a system for positioning a rotatably mounted gun, a hydraulic variable speed gear driving said gun including a variable displacement pump with operating means therefor actuating a hydraulic motor operatively connected to the gun, displacement adjusting means limiting the increase of power delivered by said pump with increasegof output pressure, said adjusting means having a plurality of degrees of response sequentially effective with increase of pressure, and a limit stop comprising means actuated by th gun at a predetermined position in the travel thereof for effectively blocking the circulation of operating fluid between said pump and motor, the output pressure of said pump being then modified by said limiting means.

10. In a gun positioning mechanism, a variable displacement hydraulic pump, driving means for said pump, a hydraulic motor connected for driving a gun and actuated in accordance with the displacement of said pump, means controllingthe output .power of said pump with increase of pressure according to a desired law of variation over a selected range, said controlling means being difierently responsive to increase of pressure over selected portions within said selected range, and pressure relief means limiting increase of power beyond said range.

HARVARD L. HULL. WILLIAM S. GORRILL. WILLIAM F. FROST.