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Transcript
‘May 7, 1946. » H. A. SATTERLEE 2,399,695 FOLLOW-UP SYSTEM Filéd‘ Déc. 23, 1940 37 40 394/ 24 / 27 INVENTOR Howard ,4 J0 r‘fer/ee BY - ATTORNEY Patented May 7, 1946 2,399,695 uurrsn STATES PATENT OFFICE 2,398,895 FOLLOW-UP SYSTEM ' Howard A. Satterlee, Dayton, Submarine Signal Company, corporation of Maine Application December as, 1946, Serial No. 371,331 7 10 Claims. (Cl. 172-239) The present invention relates to follow-up sys tems. Various arrangements have heretofore been proposed for the purpose of causing a remote ob 24. High frequency by-pass condensers 26 and 21 are also provided between the cathodes and grids of the tubes 4 and 5, respectively. The potentiometer 32 is connected across a ject to take up a predetermined position in re sponse to the setting of a control indicator to 5 source of alternating current of the same fre quency as that which supplies the anodes of the a corresponding position by an operator at a recti?ers 4 and 5 but of a phase angle lagging control station. Among the di?lculties which the potential of anode II by approximately 90“. arise in such systems arethe dimculties of re ducing to a minimum the time lag between the 10 Similarly, the potentiometer 33 is connected across a source of alternating potential of the setting of the control indicator and the corre same frequency as that supplying the anode cir sponding motion of the remote object, the elim cuits of the tubes but of a phase angle lagging ination of hunting and the obtaining of su?icient the potential of anode I! by approximately 90°. accuracy in the final position of the remote ob The magnitudes of the two alternating poten Ject. It is an object of the present invention to tials thus introduced into the grid circuits of provide a follow-up system which will provide the recti?ers are adjusted to be of a very small accurate and close coupling of the remote ob ject with the control device, without hunting - and which moreover will have the desirable characteristics of simplicity and reliability. This and other objects of my invention will best be understood from the following descrip tion, taken in connection with the accompany ing drawing which schematically illustrates the invention. As indicated in the drawing, the driving mo tor I which may be geared or otherwise con ‘nected to the remote object is preferably of the direct current type having a commutator type value, depending upon the characteristics oi.’ the gaseous discharge tubes 4 and 5. The maximum values of these alternating grid potentials may, 20 for example, be of the order of the magnitude of the maximum negative potential of the critical grid voltage curve for the tubes in question‘ at the anodev voltage used. The critical grid'I-volt age curve is to be understood as the graph'of the grid-to-cathode voltage which is Just su?lcient ‘to initiate conduction through the tube at each instant in the positive hali' cycle of the anode Potential. ‘It will be understood, of course, that the type armature 2 and a field winding 3 separately ex- 30 of tubes referred to is that in which when con cited from a source of direct current. Two grid duction has once been started, it will continue, controlled recti?ers of the gaseous electron dis until the anode potential reverses its polarity, charge type 4 and 5 provide the armature op the grid having, control only prior to the time erating current. Anode potential for the two tubes is provided by a transformer 6 having a 35 conduction commences in any particular posi tive half cycle 01' anode potential. primary winding 1 connected to a source of al The grid circuit of tube 4 may thus be traced ternating current and two secondary windings 8 from the grid 20 through the resistor 22 the po and 9. The secondary winding 8 is connected tentiometer 32, the upper half of re tor 24, ' by one end to the anode ll of tube 4 and by the other end through conductors l2 and I 6 to the 40 the biasing battery 25 and the upper half of resistor l3 to the cathode i4. Similarly, the armature 2 and from the latter by conductor II grid circuit of tube 5 may be traced from the to the cathode l4 of tube 4. The secondary wind grid 2| through the resistor 23, the potentiome _ ing 9 is connected by one end to the anode ii ter 33, the lower half of resistor 24, the biasing of the tube 5 and by the other end by conductors 25 and the lower half of resistor l3 to l8 and I‘! to the armature 2 and thence by con 45 battery cathode It. ductor it to the cathode i9 or tube 5. The grids A control potential for the grids of the tubes 20 and 2| of the two tubes are respectively con is impressed across resistor 24. The circuit for nected through current-limiting resistors 22 and producing the grid control voltage which is to '23 to the movable contacts 28 and 28 of poten be impressed across resistor 24 will be described tiometers 32 and 33 and through the potentiome subsequently. ters to the extremities 30 and 3| of a center It is' convenient at the present time to con tapped resistor 24. The motor armature 2 is shunted by a center-tapped resistor l3, the center tap of which is connected through a b - sider the operation of the grid controlled recti-, ~ “tier circuit which has so far been described. ing battery 25 to the center tap of the resistor 55 Considering, ?rst, the tube 4, it will be noted that the anode circuit of the tube contains a source 9,399,095 2 tinue'rotation. the tube opposite to the one which was driving the motor will be made active by the E. M. 1". generated by motor’s motion, tending to of alternating current and. the armature 2 of motor I.‘ It will also be noted that the grid cir cuit of the tube 4'contains four sources of po tential in series, namely, the alternating poten- - reverse the motor. This action amounts to a form of dynamic braking which rapidly brings the motor to'a stop. tial provided by potentiometer 32, the direct po tential drop across the upper half of resistor Let ‘us now consider the circuit for producing the necessary control voltage for the grids of the 24, the direct potential provided by the biasing battery 25, and the direct potential drop across recti?ers 4 and 5. This circuit is shown in the the upper half of resistor 12. The drop across the resistor 24, as will be de 10 upper portion of the drawing. It is arranged to impress a potential across the terminals 30 and ' scribed later, is arranged to vary in polarity with ii of the resistor 24 which has a polarity corre the desired direction of rotation of the armature sponding to the direction of the required displace 2. The magnitude or the potential across resistor ment of the driven object and a magnitude which 24 may be made proportional to the magnitude may be proportiona1 to the magnitude of the de of position change required in the driven object. sired displacement, or may reach a maximum The potential of the biasing battery 20 is ?xed at value even for small required displacement of the a value su?loient to inhibit conduction through driven object. To this end a handwheel [0 may either tube when maximum anode voltage is ap be arranged to drive a pointer 34 which is plied and the system is at rest. The potential drop across resistor i3 is occasioned by the cur 20 mounted adjacent to a scale 35 in such a man ner that by rotating the handwheel the pointer rent ?owing through it due to the back E. M. F. may be rotated into a position corresponding to generated in the motor armature 2 by its rotation. If, now, it be assumed that the motor I is at ' the desired position of the driven object. ‘ The handwheel shaft is also connected mechanically rest and that a potential is impressed across re sistor 24 of su?icient magnitude and of such a 25 to the rotor or polyphase winding 38 of a self synchronous motor 31. The motor 31 is also pro polarity that the point 30 is positive and the point vided with a single-phase winding 30 which is 3| is negative, the grid 20 will become positive with respect to its cathode, thereby permitting anode current to ?ow through the tube 4 and the armature 2 during the half cycles of anode po tential or portions thereof in which the anode I I - is positive with respect to its cathode. The arma ture 2 being immersed in the continuous mag connected to a source of alternating current of a so netic ?eld provided by the winding 2 will there fore commence to rotate under the in?uence of the recti?ed current impulses ?owing through it. As the armature increases its speed, it will'gen high frequency. By this I mean a frequency which is high compared to the 60 cycle frequency heretofore used, say approximately 1000 to 2000 cycles per second; but I prefer to use a frequency in the neighborhood of 1500 cycles per second. The rotor 35 is electrically connected in parallel with the rotor 39 of a similar self-synchronous motor 40 having a single-phase stator winding M. The rotor 39 is mechanically connected to the driven object. When the rotor 38 is in the erate a back E. M. F. which is exactly propor same angular position with respect to its stator tional to the armature speed and is available for control of the recti?er grid at all times when no 40 winding 38 as the rotor 38 is with respect to its stator winding 4|, there will be no voltage in current flows through the tube. This back E. M. F. duced in the winding 4|. On the other hand, being applied across the resistor It, causes a when the rotor 36 is displaced relative to the rotor current to ?ow through this resistor which there 32 there will be a voltage induced in the winding byintroduces a potential into the grid circuit of 4|. The polarity or relative phase of this voltage 45 tube 4 which opposes the potential due to the depends upon the direction of the displacement drop across the upper half of resistor 24. when and the magnitude of the voltage depends upon the back E. M. F. across the upper half of resistor i3 reaches a magnitude substantially equal to the ' the magnitude of the displacement. The winding 4| is connected across a center potential drop across the upper half or resistor 24, the potential of grid 20 will automatically be 50 tapped resistor 42 whose extremities are con varied to cause the discharge in each positive halt nected to the grids of two high vacuum three tial across resistance 24 be reversed so that the are connected to the point 41 through ?lters 4| 65 and 48 which are of suitable value to ?lter out electrode tubes 43 and 44. The cathodes of these cycle of anode potential to take place at the right tubes are connected together and to the movable instant in each cycle to prevent the motor from contact 45 of a potentiometer resistance 48 whose increasing or decreasing its speed beyond that which corresponds to the magnitude of the poten 55 extremities are connected across the same source of high frequency alternating potential men tial then existing across resistor 24. The motor tioned above. The phase of the potential across speed is thereby accurately controlled. It should resistance 48 is therefore the same as that across also be noted that when the polarity of the po the winding 48. One end of the potentiometer tential impressed across the resistance 24 is such resistance 46 is connected to the center tap of as to make the point 30 positive, the point Si is resistance 42 and the other‘end is connected to negative and the grid 2| of tube 5 becomes nega the common point 41 or the anode circuits of tive so that when the tube 4 is operating, the the tubes 43 and 44. The anodes of these tubes tube 5 remains inactive. Similarly, if the poten point 3| becomes positive and the point 30 nega tive, tube I will become active, causing the motor armature 2 to rotate in the reverse direction. The tube 4 then remains inactive. - the‘ recti?ed high frequency alternating com ponent introduced by the potential drop across resistance 40. Each ?lter may comprise, for ex ' ample, a resistance and a parallelly connected If, after the motor has been running in one direction, it should be desired to stop it, the con 70 condenser as shown. The anode circuit of tube 43 may thus be traced from the anode of the tube trolling potential across resistor 24 is reduced to through the ?lter 40 to the terminal 41 through zero, so that the bias battery 25 is effective to a portion of resistance 46 to movable contact 45 hold both grids to cut-oft potential. However, to the cathode of the tube. Similarly, the anode should the reduction of the potential on resistor / 24 be sudden and should the motor tend to con 75 circuit of tube 44 may be traced from the anode 9,889,695 of the tube through the ?lter 43 to the terminal 41 through the resistance 43 to the movable con tact 45 and to the cathode of the tube. Since the portion of resistance 43, which lies between the terminal 50 and contact 45, is in series with _ the grid of each of the tubes 43 and 44,v it pro vides an alternating bias potential for the grids of these tubes. This potential is adJusted to be 3 the driven object also rotates the rotor 33 to which it is connected. the rotation being in such a direction as to bring the rotor 33‘ into positional correspondence with the rotor 36 and thereby ag reducing the voltage in the winding 4| to . Thus when the driven object reaches the desired position, the motor 2 will stop. of such a value that anode current flows through By the use of the above arrangement a tight both of the tubes even though there is zero volt 10 coupling is obtained between motion of the hand age induced in the winding 4|. It will be ob wheel l3 and motion of the driven object so that served that the voltage induced in this winding there is substantially no time lag between them. The maximum voltage impressed across resistor 24 should preferably be substantially equal to the full-speed back E. M. F. of the motor impressed by relative displacement between the two rotors 35 and 39 appears across the resistance 42 and adds or subtracts to the grid voltage of the tubes 43 and 44, depending upon the direction of the displacement. If the displacement is in one di across resistor l3. While it is often convenient to have the motor operate at a speed proportional rection, the potential drop across resistance 42 to the required displacement of the driven ob will be out of phase with the bias voltage on one of the grids but in phase with the bias voltage on 20 ject, this need not always be the case. Where, for example, a high sensitivity is desired and conse the other grid. One tube will therefore pass more quent rapid follow-up action, it may be preferable current while the current of the other will be re to arrange the amplifying ‘circuit so that full control voltage is impressed across resistor 24 even for small displacements between pointer 34 and the driven object. I have found that the gaseous grid controlled recti?er circuit described above operates in this duced. If the relative displacement of the two rotors 35 and 33' be in the opposite direction, the effect on the anode currents of the two recti?ers will, of course, be reversed. The result of the anode current flow in the anode circuits of the two tubes 43 and 44 will be to produce a potential difference across the ter minals of a center-tapped resistor 5| which is follow-up vsystem most satisfactorily when the controlling potential impressed across resistor 24 a substantially pure direct potential without connected between the two anodes. The ends of 30 is alternating components. It is necessary, there the resistor 5| are also connected to the grids of fore, to provide a suitable ?lter, as above de two amplifying tubes 52 and 53 which may be scribed, to remove any alternating components operated as Class A ampli?ers. The cathodes of which may otherwise be present. However, when the tubes 52 and 53 are connected together and ?lters are introduced into a follow-up system to the movable contact 54 of a potentiometer re there is likewise inevitably introduced a time de sistance 55 which is connected across a source of lay between the motion of the driven object and direct potential. The negative terminal of the the motion of the controlling indicator. Where resistance 55 is connected to the center tap of sensitivity and rapidity of response of the con resistance 5|, and the positive terminal of the re sistance 55 is connected to the center tap of a 40 trolled object to motions of the controlling device are required, such time lag is, of course, objec center-tapped resistor 55 Whose extremities are tionable, for it causes the system to act as though connected to the anodes of the tubes 52 and 53, an elastic coupling member had been introduced respectively. Any potential appearing across re between the controlling and the controlled mech sistance 5| is thus ampli?ed and will appear across resistance 56 and also across terminals 30 45 anisms. According to my invention, however, such elasticity is substantially entirely eliminated and 3| which lie in the grid circuit of the grid because of the fact that I use a high frequency controlled gaseous rectifiers 4 and 5. in the self~synchronous motor circuit for the pro It will now be evident that when the position of the driven object corresponds to the position 50 duction of the controlling potentials. Filters for such high frequencies can readily be constructed of the pointer 34‘ so that the position of rotor 35 which substantially eliminate the high frequency with respect to its stator 38 corresponds to the components from the control voltage output cir position of rotor 33 with respect to its stator 4|, cuit and which at the same time have only a no voltage will be produced across the winding 4| negligible time constant. and equal currents will ?ow in the anode circuits Having now described my invention, I claim: of tubes 43 and 44. Since these currents are in 1. In a follow-up system for driving an object opposite directions, there will be no voltage across into positional agreement with a controlling ob the resistance 5| and therefore no voltage across ject, a power motor for said driven object, a grid the terminals 30 and 3 I. The motor 2 will there controlled recti?er circuit for supplying power to fore remain at rest. When, however, the hand said motor in one direction or the other in re wheel I0 is rotated to set the pointer 34 into a 60 sponse to a direct potential which varies in po~ position corresponding to a desired new position larity in accordance with the direction of posi of the driven object, a voltage, corresponding in tional disagreement between said objects and phase to the direction of the position change means for generating said potential comprising a which was made, will appear across winding 4| 65 self-synchronous transmitter motor having a sta and resistance 42, causing the anode currents of tor winding energized by alternating current of tubes 43 and 44 to change. A potential differ a high frequency above approximately 1000 cycles ence will therefore exist across resistance ‘5|, per second and a rotor winding adapted to be ro which will correspond in polarity to the direction tated by the operator into a position correspond of the displacement of the pointer 34. This po 70 ing to the desired position of the driven object, tential will be ampli?ed by the tubes 52 and 53 a self-synchronous receiver motor having rotor and will appear across the terminals 30 and 3|, electrically connected in parallel with that of the causing either the recti?er 4 or 5 to energize the transmitter and mechanically connected to the motor 2 and to rotate the driven object in the de driven object and a stator winding adapted to have sired direction as above described. Rotation of 75 a voltage induced in it upon positional disagree 4 9,899,690 ' ment between the two rotors and their respective stators, said voltage having an instantaneous po- ' the direction of said disagreement and containing an alternating component oi said hlghirequency, larity corresponding to the direction of said dis agreement. rectifying means, means impressing said induced voltage on said rectifying means, the latter being adapted to produce a direct potential having a polarity corresponding to the direction a ?lter for removing said high irequency compo nent and means for impressing the resulting recti ?ed and ?ltered voltage upon said grid-controlled ?ltered voltage upon said grid-controlled recti?er agreement between said objects comprising self recti?er circuit. > 4; In a follow-up system ior driving an object into positional agreement with a controlling ob , of said disagreement and containing an alternat ject, means for producing a direct potential vary , ing component of said high frequency, a ?lter for removing said high frequency component and 10 ing in polarity and magnitude in accordance with the direction and magnitude oi positional dis means for impressing the resulting recti?ed and synchronous transmitter and receiver system. circuit. means exciting the same with alternating current 2. In a iollow-up system for driving an object into potential agreement with a controlling ob 15 oi a high irequency above approximately 1000 cycles per second, means mechanically connecting ject, a power motor for said driven object, a grid said system with said controlling object and said controlled recti?er circuit for supplying power to driven object for producing an alternating po said motor in one direction or the other in re tential of said high irequency having a magni sponse to a direct potential which varies in po larity and magnitude in accordance with the di 20 tude and an instantaneous polarity correspond ing to the magnitude and direction of said posi~ rection and magnitude of positional disagreement tional disagreement, rectifying means for said between said objects and means for generating high frequency potential adapted to produce a di said potential comprising a self-synchronous rect potential having a polarity and a magnitude transmitter motor having a stator winding ener gized by alternating current oi a high frequency 25 corresponding to the direction and magnitude oi said positional disagreement, and having an al above approximately 1000 cycles per second and a ternating component of said high frequency, and rotor winding adapted. to be rotated by the op a ?lter for removing said high frequency compo erator into a position corresponding to the de nent. sired position of the driven object, a self-syn 5. In a follow-up system for driving an object chronous receiver motor having a rotor electrically 30 into positional agreement with a controlling ob connected in parallel with that of the transmitter ject, means for producing a direct potential vary and mechanically connected to the driven ob ing in polarity and magnitude in accordance with ject and a stator winding adapted to have a volt the direction and magnitude oi positional dis age induced in it upon positional disagreement agreement between said objects comprising self between the two rotors and their respective sta synchronous transmitter and receiver system, tors, said voltage having an instantaneous po means exciting the same with alternating current larity and a magnitude corresponding to the di oi a high frequency above approximately 1000 rection and magnitude of said disagreement, rec cycles per second, means mechanically connecting tifying means, means impressing said induced voltage on said rectifying means, the latter being 40 said system with said controlling object and said driven object for producing an alternating po adapted to produce a direct potential having a po tential oi said high frequency having a magni larity and magnitude corresponding to said direc tude and an instantaneous polarity correspond tion and magnitude of said disagreement and con taining an alternating component of said high ire ing to the magnitude and direction of said posi tional disagreement, rectifying means ior said quency, a ?lter for removing said high frequency high frequency potential comprising a pair of component and means for impressing the result ing recti?ed and ?ltered voltage upon said grid oppositely connected vacuum tube recti?ers hav ing cathode, anode and grid electrodes, a source controlled recti?er circuit. 3. In a follow-up system for driving an object of anode potential for said tubes, means connect— into positional agreement with a controlling ob ing said tubes in opposite relation to each other, ject, a. power motor for said driven object, a grid means impressing a derivative of said high fre quency potential upon the grids of said tubes in controlled recti?er circuit for supplying power to opposite instantaneous polarity, means biassing said motor in one direction or the other in re both of said grids with an alternating potential sponse to a direct potential which varies in po larity in accordance with the direction oi posi 55 of said high frequency of the same phase as the potential of said sen-synchronous system excit tional disagreement between said objects and means for generating said potential comprising a ing current and of a magnitude to cause both self-synchronous transmitter motor having a tubes normally to pass current, whereby for one stator winding energized by alternating current instantaneous polarity oi said produced potential of a high frequency or approximately 1500 cycles the currentpassed by one tube will increase and per second and a rotor winding adapted to be 60 the current passed by the other tube will diminish rotated by the operator into a position corre and vice versa for the opposite instantaneous po sponding to the desired position of the driven larity of said produced potential, means in the anode circuit of each tube for separately ?ltering object, a self-synchronous receiver motor having rotor electrically connected in parallel with that 05 out the high frequency alternating component, means opposing the .?ltered recti?ed outputs of of the transmitter and mechanically connected to the two tubes, means deriving a resultant poten the driven object and a stator winding adapted to tial corresponding to said outputs and means re have a voltage induced in it upon positional dis sponsive to said resultant potential ior altering agreement between the two rotors and their re the position of said driven object to remove said spective stators, said voltage having an instanta positional disagreement. neous polarity corresponding to the direction of 6. In a follow-up system for driving an object said disagreement. rectiiying means, means im into positional agreement with a controlling ob pressing said induced voltage on said rectifying ject, means for producing a direct potential vary means, the latter being adapted to produce a di rect potential having a polarity corresponding to 75 ing in polarity and magnitude in accordance 2,899,095 with'the direction and magnitude of positional disagreement between said obiects comprising self-synchronous transmitter ‘and receiver sys tem, means exciting the same with alternating current of a high frequency above approximately 1000 cycles per sec d, means mechanically con necting said syste with said controlling object and said driving object for producing an alter nating potential oi’v said high frequency having a 5 tube will diminish and vice versa for the opposite instantaneous polarity’oi' said produced potential, means in the anode circuit of each tube for separately ?ltering out the high frequency alter nating component, means opposing the ?ltered recti?ed outputs of the two tubes, means deriving a resultant potential corresponding to said out puts and means responsive to said resultant po tential for altering the position of said driven ob magnitude and an instantaneous polarity corre 10 .iect to remove said positional disagreement. sponding to the magnitude and direction of said 8. In a follow-up system for driving an object positional disagreement, rectifying means for said into positional agreement with a controlling ob high frequency potential comprising a pair of op iect, means for producing a direct potential vary positely connected vacuum tube recti?ers having ing in polarity and magnitude in accordance with cathode” anode and grid electrodes, a source of 15 the direction and magnitude of positional dis~ anode potential for said tubes, means connecting agreement between said objects comprising self synchronous transmitter and receiver system, means exciting the same with alternating current of a high frequency above approximately 1000 opposite instantaneous polarity, means biassing 20 cycles per second, means mechanically connect both of said grids with an alternating potential ing said system with said controlling object and of said high frequency of the same phase as the said driving object for producing an alternating potential of said self-synchronous system excit potential of said high frequency having a mag ing current and of a magnitude to cause both said tubes in opposite relation to each other, means impressing a derivative of said high fre quency potential upon the grids of said tubes in tubesv normally to pass current, whereby for one _ instantaneous polarity of said produced poten tial the current passed by one tube will increase and the current passed by the other will diminish and vice versa for the opposite instantaneous po larity of said produced potential, means in the 30 anode circuit of each tube for separately ?ltering out the high frequency alternating component, a resistor connected between the anodes of the two tubes so that a direct current will ?ow through said resistor which is the resultant of the opposed recti?ed and ?ltered outputs of the two tubes and means responsive to the polarity and magnitude of the resulting potential drop nitude and an instantaneous polarity corre spondlng to the magnitude and direction of said positional disagreement, rectifying means for said high frequency potential comprising a pair oi’ op positely connected vacuum tube recti?ers having cathode, anode and grid electrodes, means con necting said tubes in opposite relation to each other, means impressing a derivative of said high frequency potential of the same phase as the potential of said self-synchronous system excit ing current upon the anodes of said tubes in the same instantaneous polarity, means biassing both 01' said grids with an alternating potential of said high frequency and of instantaneous po larity and magnitude to cause both tubes nor across said resistor for altering the position of mally to pass current, and means impressing a said driven object to remove said positional dis 40 derivative of said high frequency potential upon agreement. the grids of said tubes in opposite instantaneous 7. In a follow-up system for driving an object polarity, whereby for one instantaneous polarity into positional agreement with a controlling ob 01’ said produced potential the current passed by ject, means for producing a direct potential vary one tube will increase and the current passed by ing in polarity and magnitude in accordance with the other will diminish‘ and vice versa for the op the direction and magnitude of positional dis posite instantaneous polarity of said produced po agreement between said objects comprising self tential, means in the anode circuit of each tube synchronou's transmitter and receiver system, for separately ?ltering out the high frequency means exciting the same with alternating current alternating component, a resistor connected be of a high frequency above approximately 1000 tween the anodes of the two tubes so that a di cycles per second, means mechanically connecting rect current will flow through said resistor which said system with said controlling object and said is the resultant of the opposed recti?ed and ?l driven object for producing an alternating po tered outputs of the two tubes and means respon tential of said high frequency having a magnitude sive to the polarity and magnitude of the re and an instantaneous polarity corresponding to sulting potential drop across said resistor for the magnitude and direction of said positional altering the position of said driven object to re disagreement, rectifying means for said high fre movesaid positional disagreement. quency potential comprising a pair of oppositely 9. In a follow-up system for driving an object connected vacuum tube recti?ers having cathode, into positional agreement with a controlling ob anode and grid electrodes, means connecting said 60 ject, a self-synchronous transmitter and receiver tubes in opposite relation to each other, means system, means energizing the same with alter impressing a derivative of said high frequency nating current of a high frequency above approxi potential of the same phase as the potential of mately 1000 cycles per second, recti?er and ?lter said self-synchronous system exciting current means operatively associated with said system for upon the anodes of said tubes in the same instan delivering a direct current, said ?lter being taneous polarity, means biassing both of said adapted to remove- alternating current compo grids with an alternating potential of said high nents having a frequency not substantially less frequency and of instantaneous polarity and mag than said high frequency, motor means for driv nitude to cause both tubes normally to pass cur ing said object and means-for energizing said rent, and means impressing a derivative of said 70 motor, said energizing means being adapted to produced high frequency potential upon the grids be activated by said direct current, whereby time of said tubes in opposite instantaneous polarity, whereby for one instantaneous polarity of said produced potential the current passed by one tube will increase and the current passed by the other lag between operation of said self-synchronous System and said motor is reduced. 10. In a follow-up system for driving an ob ject into positional agreement with a controlling 6 ' aaoaeos object, a sell-synchronous transmitter and re ceiver system, means energizing ‘the same with‘ alternating current of a high irequeney above not substantially less than said hiah frequency. approximately 1000 cycles per second. recti?er and filter means operatively associated with said system for delivering a controlling direct cur rent, said filter being adapted to remove alter nating current components having a frequency same, said source having grid control means to which said controlling direct current is applied, whereby time lag between operation 01' said self synchronous system and said motor is reduced. a motor and a source or rectified alternating cur rent of relatively low frequency for operatin: the , HOWARD A. SA'I'I'ERIEE.