COHTROL SYSTEM Filed July 25, > 1941 mg $ a’ /6 2/ FiGil.‘ o /4 14 /5 32a TORQUE ourpur OF POWER MOTOR l I . 1 I POSITION OF FOLLOV-UP RELATIVE TO copesspomozmcs Inven’mor: John L’. Emwer“, 2,467,866 Patented Sept. 17, 1946 UNlTED STATES PATENT OFFICE 2,407,866 CONTROL SYSTENI John L. Bower, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application July 23, 7 Claims. 194 1, Serial No. 403.5199 (Cl. 172-439) 2 1 This invention relates to control systems, more particularly to follow-up control systems for driv ing an object into positional agreement with a pilot device, and it has for an object'the provi sion of a simple, reliable and improved control system or" this character. In the operation of follow-up systems, it fre~= use quently and occurs is disconnected that when from thethe system poweri" system, not the pilot device is moved out of positional corre spondence with the driven object by a large amount. When the follow~up system is recon» nected with the power system for the purpose of resuming operation, a very large syrchronizing torque is developed in a direction to restore the system to synchronism, i. e., to return the driven object toward correspondence with the pilot de vice. The initial positional disagreement may be so large that the’ synchronizing torque will be of su?icient magnitude to cause the driven object to be driven toward positional agreement at such a high velocity as to result in overshooting and a subsequent condition of hunting or oscilla torque amplifying system in which the driven ob ject is driven by an electric motor under the con trol of suitable means for producing a signal Voltage dependent upon the positional disagree ment of the pilot device and. driven object. For better and more complete understanding of the invention, reference should. now be had to the following speci?cation and to the accom» panying drawing of which Fig. 1 is a simple, dia gra'mmatical representation of an embodiment of the invention, and Fig. 2 is a chart of character istic curves which serve to facilitate an under standing of the operation of the invention. Referring now to the drawing, a massive ob ject M which may be a Searchlight, a gun, a gun director or other object is to be driven in posi tional agreement with a pilot or control device‘ l i by suitable driving means such, for example, as represented by the direct current electric motor !2 to the drive shaft of which the driven object if} is connected by imeans of suitable reduction gearing (not shown). Direct current is supplied positional disagreement of the pilot device and to the armature of the motor 52 by means of a suitable power ampli?er i3 and is under the con trol of a pair of electric valves l4, 55. The power ampli?er I?» may be of any suit able type. For example, it may be an electric valve type ampli?er, or it may be a dynamoelec~ driven object in excess of a predetermined value tric machine ampli?er such as an armature reac for reducing the synchronizing torque substan~ tially below the Value that would otherwise be developed for such positional disagreement. Follow-up systems of the character described tion excited dynamoelectric machine. Since the speci?c structure of the power ampli?er per se does not constitute a part of this invention, it is tion about the position or" correspondence. Such a condition is of curse highly undesirable. In order to minimize this undesirable condi~ tion, means are provided which are responsive to represented conventionally in the drawing. If the power ampli?er it should be of the electric preventing hunting during normal operation of valve type, it would preferably have two separate the system. One form of such antihunting conducting paths each controlled by a separate means utilizes a capacitor for modifying the ccn~ grid and these control grids would be connected trol of the driving means during the normal oper by means of conductors it and H to the anodes of the electric Valves M and I5. On the other ation of the system. However, during the oper ation of synchronizing the system from a large 40 hand, if the ampli?er is of the dynamoelectric initial positional disagreement, the ability of the machine type, it would preferably be provided with a pair of control ?eld windings and these capacitor to prevent hunting leaves much to be ?eld windings would be connected by means of desired. For the purpose of providing an im proved control during such synchronizing opera conductors l6 and ii to the anodes of the elec tion, means are provided which are responsive 45 tric valves l4 and lb. The electric valves iii and 55 may be of any suitable type but they are pref~ to speeds of the driving means in excess of a predetermined value for by-passing the capacitor erably vacuum triodes of the “hard” tube type. and supplying a control voltage to the controlling The cathodes of the valves iii. and it have a common connection iii to an intermediate point means for the driving means for modifying the of an adjustable voltage. divider 59 which is con control of the driving means in accordance with nected across a suitable source of alternating the speed of the driving means during the period are provided with suitable antihunting means for that the speed of the driving means exceeds a voltage represented by the two supply lines ‘it. A. pair of resistors 2i and 22 is connected across the anodes of the valves ill and I5, and the junc In illustrating the invention in one form there of, it is shown as embodied in a follow-up or 55 tion point of these two resistors is connected by predetermined value. . 2,407,866 3 means of conductor 23 to one side of the source 4 clear that the rotation of the rotor of the trans of alternating voltage 20. The cathode grid cir mitter or of the receiver regulator will vary the magnitude of the component voltage supplied to cuit of the electric valve ill extends from the cathode through conductor 58 and the right-hand the grid circuit of the electric valves M i5 portion of voltage divider l9 through conductor Cl which, in turn, will result in a variation in the 24, stabilizing resistor 25, and the right-hand sec— relationship of the current flowing in the valves ondary winding of input transformer 25 to the 14 and 15. This will ultimately result in causing grid of the valve l4. Similarly, the cathode grid the ampli?er l3 to supply current in one direc circuit of the electric valve I5 extends from the tion or the other to the armature of the driving cathode to the conductor 24 by the circuit pre 10 motor l2. The grid connections to the electric viously traced and thence through stabilizing re valves M and 15 are so made, as explained in the sistor 21 and the left-hand secondary winding of foregoing, that when the signal voltage supplied the input transformer 26 to the grid of valve 15. to the primary winding of the input transformer The voltages of the grids Ma and ‘5a with respect is varied, the voltage applied to the grid of one to the cathodes Mb and I511, respectively, as a re 15 of the valves is increased, and the voltage ap sult of the inclusion of a portion of the volt plied to the grid of the other valve is simultane age divider IS in the anode-cathode circuit of the ously decreased. Consequently, when the cur valves are such that both valves normally conduct rent through one of the valves is increased, the equal amounts of current. This condition of current through the other valve is simultane equal conduction in both valves l4 and it occurs 20 ously decreased. As a result of the increase in when the follow-up system is in correspondence, current flowing through one of the valves and 1. e., when the driven object in is in positional the decrease in current flowing in the other valve, agreement with the- pilot device i I, and the veloce the ampli?er i3 is caused to supply direct cur ity of the driven object I!) is unchanging. rent to the armature of motor I2 in one direction In order to vary the bias voltages of the grids or the other depending upon whether the cur Ida and 15a of the valves I4 and I5, respectively, rent is increased in the valve M or the valve H5. a component voltage of variable magnitude is The rotor member of the receiver regulator 28 supplied to the grid circuit substantally in phase is connected through suitable gearing 33 to the with the anode voltages of these valves through shaft of the driving motor 12. the input transformer 26 whose secondary wind For the purpose of preventing hunting during ings 26a and 25s are connected in the cathode the normal follow-up operation of the system, grid circuits of the electric valves l4 and I5, as that is to say, during operation other than syn explained in the foregoing, and whose primary chronizing the system from a condition of large winding is connected to the single phase alter nating current source 20 through suitable rotary 35 angular disagreement between the pilot device and driven object, a suitable electrical energy induction apparatus illustrated as comprising the, storage device such, for example, as a capacitor pilot device H which is referred to as a trans 3| is connected in series relationship with the mitter and the rotary induction device 28 re stabilizing resistors 2'5 and 2'! across the terminals ferred to as the receiver regulator. The rotary induction device ll comprises a rotor member 40 of a tachometer generator 32 which is driven by the driving motor [2 and generates a voltage Ila provided with a single phase winding (not substantially linearly proportional to the speed shown) connected across the single phase source of the motor 12. As a practical alternative, the 20, and a stator member lib provided with a capacitor 3! might be connected in series with distributed three-element winding (not shown) the stabilizing resistors 25 and 21 across the ar that is physically similar to the polyphase wind mature terminals of the drive motor l2, since ing of a wound rotor induction motor. The stator the countervoltage of the drive motor i2 is ap and rotor windings are arranged in inductive proximately proportional to its speed under most relationship with each other so that the normal operating conditions. It is preferred, alternating magnetic ?eld owing to the cur rent ?owing in the primary winding induces 50 however, to utilize the tachometer generator 32. This generator may either be provided with a voltages in the winding element of the second ?eld winding 322, as shown, or it may be of the ary winding. The receiver regulator 28 is in all permanent magnet type. The charge on the respects identical with the transmitter II, and capacitor 3! varies as the voltage of the generator the terminals of its stator winding are con 32 varies, which is to say that the charge on the nected to the terminals of the stator winding of capacitor varies as the speed of the driving mo the transmitter by means of conductors 29 so tor I2 varies. When the speed of the driving that the voltages induced in the stator winding motor l2 and the voltage of the generator 32 are of the transmitter cause current to ?ow in the constant, the charge on the capacitor is constant stator winding of the receiver regulator, there and when the voltage of the tachometer gen by producing a magnetic ?eld similar to the mag erator is varying at a high rate, the charge on netic ?eld produced by the current ?owing in the the capacitor is likewise varying at a high rate. rotor winding of the transmitter. Rotation of When the charge on the capacitor is varying, a the rotor member of the transmitter causes a current is caused to ?ow through the resistors 2'5 voltage to be induced in the rotor winding of the receiver owing to the shift in the position and 27 which is proportional to the rate at which the charge on the capacitor is varying. In other of the axis of the magnetic ?eld of the receiver regulator relative to the axis of the coil of the words, the current caused to flow in the stabiliz rotor member, and the magnitude of this in ing resistors is proportional to the rate of change duced voltage depends upon the relationship of of the charge on the capacitor which, in turn, the axis of this winding to the axis of the mag 70 varies in accordance with the rate of change of netic ?eld, e. g., when the axes of the magnetic the voltage of the tachometer generator, and ?elds and of the rotor winding are parallel, the therefore, to the rate of change of speed of the induced voltage is maximum, whereas when these motor I 2. Thus, the capacitor 31 introduces a axes are at right angles with each other, the correcting influence or voltage in the grid cir induced voltage is zero. It will therefore be 75 Quit Of the electric valves it‘ and i5 which is 2,407,866 5 6 proportional to the rate of change of speed of the driving motor‘ l2. of the. capacitor 31 and the stabilizing resistors 25 and 21. The voltage drop device 34 may be of any suit able type. An ordinary incandescent lamp has been found to give very good results. With the foregoing understanding. of the ele ments and their organization in the completed system, the operation of the system itself will readily be understood from the following detailed The polarity of the. connections of the ca pacitor 3! is such that the variations in the current flowing through the stabilizing re sistors 25 and Z'l' are out of phase and leading with respect to any incipient hunting of the driven object about the position of corre spondence. The e?ect is of transiently varying the current supplied to the driving motor it '10 description; Assuming that the switch 39 is closed to con ally supplied to the motor 12 is di?erent from nect the follow-up system to the power source 20 the amount that would be supplied for any and that the driven object Ill is in correspondence positional disagreement of the pilot device and with the pilot device II, the system will be in the driven object in the absence of the capacitor 35. 15 synchronized condition in which it is illustrated. general, when the system is approaching cor~ As previously pointed out, when in this condi respondence, the effect produced by the capacitor tion, both valves M and i5 are conducting equal is to reduce the current supplied to the motor amounts of current so that the net output of the power ampli?er l3 to the driving motor [2 is below the value of current that would otherwise be supplied to the motor for any given error. 20 zero. Manual rotation of the pilot device II ef However, if the system is approaching corre fects a corresponding rotation of the magnetic spondence at a very high velocity, the current ?eld of the stator of the receiver regulator 28 supplied to the motor l2 may even be reversed so that a voltage is induced in the rotor winding and braking torque thereby produced to prevent of the receiver regulator approximately propor~ overshooting. 25 tional to the amount of rotation of the pilot de vice ll. This induced voltage is applied to the For the purpose of effectively controlling the grid circuit of the electric valves is and I5 and operation of the system when synchronizing from results in increasing the current ?owing in one condition of large initial error, additional syn of the valves, e. g. the valve I4 and in decreasing chronizing means is provided which comprises the current flowing in the valve It. This results electric valve apparatus 33 and a variable voltage in causing a current to be supplied to the motor drop device 35'. The electric valve apparatus 33 [2 in such a direction that the motor is caused comprises a pair of electric valves 85 and 35 of to rotate in a direction to drive the object IE! to the gas containing triode type. Electric valve 35 ward correspondence with the pilot device 5 I. As has a cathode 35a and a starting anode 35b con~ nected across one of the secondary windings of ‘v the object Iii approaches correspondence with the pilot device, the signal voltage supplied through the synchronizing transformer 31 whose primary the input transformer 2% to the grid circuit of winding 3'53 is connected across the primary wind the electric valves l4 and it decreases and be ing of the input transformer 26 so as to be re comes zero when the condition of correspondence sponsive to the signal voltage that is supplied is reached, thereby cutting off the supply of cur from the receiver regulator 23 to the input trans rent to the driving motor l2. The operation just former. The valve 35 also has a main anode 3% described may be considered to be the normal which together with the cathode 35a is connected follow-up operation of the system. across the capacitor 35. The electric valve 35 is If the switch 33 should be opened to disconnect in all respects identical with the electric valve 35 and, as shown, it has a cathode 35a and a start 45 the follow-up system from the power source 2d, the synchronizing force between the driven object ing anode 2555s which are connected across the terminals of the other secondary winding of the and pilot device H would disappear. While in this condition the rotor of the pilot device I I may transformer 31s. The main anode 35c and the cathode 3311 are also connected across the capaci coast or easily be moved to a new position such that a large positional disagreement exists be tor 3!. A potentiometer 38 is connected across the terminals of the tachometer generator 32. tween the driven object and pilot device. This condition may and frequently does arise during The electric valves 35 and 36 are so designed normal use of the system. that when the voltage between the cathodes and so that the amount of current that is actu the starting anodes reaches or exceeds a prede termined value, such for example as 90 volts, con duction takes place between the cathodes and If new the switch 39 should be reclosed to re sume normal operation, a large signal voltage would be induced in the secondary winding of the receiver regulator 28 and supplied through the the starting anodes. This conduction will con tinue until the voltage across the cathodes and transformer 26 to the grid circuit of the electric starting anodes is reduced to some considerably valves Ill and I5, and a large current would be lower predetermined value, such for example as (ill supplied to the driving motor 52. This current 60 volts. If at the same time there is a positive would produce an excessively large synchronizing torque which would not only restore the driven voltage on the main anodes 350 or 36c, conduction object Ill to a position of correspondence with the will also take place between the main anode and the cathode. The triode valves 35 and 35 are so pilot device I i but would actually cause the driven designed that conduction does not take place be object to overshoot the position of correspond tween the main anodes and the cathodes unless the voltage supplied from the tachometer gener ator 32 equals or exceeds a predetermined value corresponding to a predetermined speed of the ence and initiate a series of oscillations. If the synchronizing means 3d and 35 were omitted, the relationship between the torque of the driving motor and error of the system, i. e., driving motor E2. 70 position of the driven object ill away from cor The cathode of each of the valves 35 and 3c is respondence, would be as indicated on curve ill connected to the main anode of the other valve, in Fig. 2 in which ordinates represent torque out so that regardless of the direction of operation put of the driving motor and abscissae represent of the system, there will be a conducting path the error or amount out of correspondence. from the potentiometer 38 to the junction point 75 With the connections from the main anodes of 2,407,866 7 8 the gas triode valves 35 and 33 to the capacitor 3| removed, the voltage drop in the incandescent lamp 34 is su?icient to reduce the torque of the synchronizing circuit ceases to operate and the follow-up system then returns to normal oper ation. The remaining operation of the system as the driven object I0 approaches the position of correspondence with the pilot device is in ac cordance with the curve 43. During normal follow-up operation, the system is una?ected by the synchronizing circuit as long as the speed of the driving motor does not rise to a value such that the adjustment of the poten tiometer 33 causes conduction to take place be driving motor for each value of error as repre sented by the broken curve 4 I. In describing this operating condition it is assumed that the error is of such magnitude as to cause voltages to be in duced in the secondary windings of the synchro nizing transformer 31 of suf?cient magnitude to cause conduction to take place between the cath- . odes and the starting anodes of the valves 35 and 36. In Fig. 2 the amount of error existing at the time of closing the switch 39 is represented by the abscissa of vertical line 42. tween tho cathodes and main anodes of the gas triode valves 35 and 36, or as long as the error does not exceed the critical value at which con With the connections. between the main an odes 35c and 360 of the valves 35 and 33 to the capacitor 3! intact, which is the condition illus trated in the drawing, the torque of the driving duction is initiated between the starting anodes and cathodes of these valves. Although in accordance with the provisions of the patent statutes this invention is described as motor ii for each value of error is represented embodied in concrete form and the principle by the dotted curve 43. This further modi?ca 20 thereof has been explained together with the best tion of the torque results from the variation in mode in which it is now contemplated applying grid voltage oi‘ valves hi and i5 produced by that principle, it will be understood that the ele conduction between the main anodes and cath ments and apparatus shown are merely illustra odes of valves 35 and 36 in response to the volt~ tive and that the invention is not limited there age of tachometer generator 32. Since the volt 25 to, since alterations and modi?cations will read age of tachometer generator 32 is zero at the ily suggest themselves to persons skilled in the instant of the closing of switch 33, zero current art without departing from the true spirit of this is conducted between the main anodes and cath invention or from the scope of the annexed odes of valves 35 and 33 and therefore the curves claims. iii and 43 coincide at the point of intersection What I claim as new and desire to secure by with the vertical line 42. Consequently at the Letters Patent of the United States is: instant of closing the switch 39, the motor it 1. A follow-up control system comprising in develops a synchronizing torque proportional to combination a pilot device, a driven object, an the ordinate of the intersection of the curve Iii electric motor for driving said object, means re with the vertical line 42. In other words, at the 35 sponsive to positional disagreement of said pilot instant of closing the switch 39, only the volt device and driven object for producing a con age drop across the incandescent lamp 34 is in trol voltage proportional to said disagreement, strumental in reducing the torque of the driving means responsive to said control voltage for sup motor. plying a variable voltage to said motor thereby However, the motor I?! comes up to speed 40 to cause said motor to develop a torque propor quickly and the tachometer generator 32 gener tional to said voltage to drive said object toward ates a voltage which is suf?cient to cause con correspondence with said pilot device, and means duction between the main anode and cathode of responsive only to positional disagreement of said one of the valves 35 or 36, and the magnitude of the current so conducted increases as the speed of the motor l2 increases. As the voltage of the tachometer generator 32 increases, the increas~ ing current through the stabilizing resistors 25 and 2'! resulting from the conduction through one or oe other of the valves 35 and 33 causes ' pilot device and driven object in excess of a pre determined amount for reducing said control voltage thereby to reduce the synchronizing torque of said motor. 2. A follow-up control system for a pilot de_ vice and driven object comprising in combina~ tion driving means for said object, a control cir the torque of the driving motor 12 to be de cult operatively connected to said driving means, means responsive to positional disagreement of other words, during this operating condition, the said pilot device and driven object for supplying torque of the driving motor is reduced by two to said control circuit a signal voltage varying e?ects: (1) The reduction of the torque as a re 55 with said positional disagreement thereby to sult of the voltage drop in the incandescent lamp, cause said driving means to produce a torque and (2) the voltage from the tachometer gener corresponding in magnitude to the amount of ator applied through one or the other of the gas said disagreement to drive said object toward triode valves to the stabilizing resistors '25 and correspondence with said pilot device, a voltage 21. 60 drop device in said control circuit, an electric As the driven object 15 approaches correspond discharge device connected to said circuit and ence with the pilot device H, the signal voltage responsive only to a control voltage in excess of supplied from the receiver regulator 28 to the a predetermined value for completing a current input transformer 25 decreases until ?nally at an conducting path to produce a voltage drop across error E the signal voltage decreases below the 65 said voltage drop device thereby to decrease said critical value which is required to support con signal voltage and reduce the synchronizing duction between the starting anodes of the valves torque of said driving means. 35 and 36 and the cathodes. By this time the 3. A iollow~up control system for a pilot device speed of the driving motor has been so reduced and driven object comprising in combination that the voltage generated by the tachometer 70 driving means for said object, a control circuit generator 32 is insufiicient to support conduction operatively connected to said driving means, means responsive to positional disagreement of between the main anodes of the valves 35 and 38 said pilot device and driven object for supplying and the cathodes. creased in accordance with the curve 43. In When the valves 35 and 35 cease conduction a signal voltage to said circuit to cause said driv both through the starting and main anodes, the 75 ing means to drive said object toward corre 2,407,866 10 device connected in said control circuit, means driving means for said object, means for control ling the energization of said driving means com for reducing the synchronizing torque of said prising electric valve apparatus provided with a spondence with said pilot device, a voltage drop control grid, means responsive to positional dis driving means comprising an electric discharge agreement of said pilot device and driven object device connected to said circuit and responsive for supplying a signal voltage to said control to a predetermined value of said control voltage grid to control said motor to drive said object to for completing a current conducting path to pro ward correspondence with said pilot device, an duce a voltage drop across said voltage drop de tihunting means comprising a capacitor connect vice thereby to decrease said signal voltage and means responsive to the speed of said driving 10 ed to said grid and means for supplying to said capacitor a second voltage proportional to the means for further modifying the torque of said speed of said driving means thereby to modify driving means. the voltage applied to said grid in accordance 4. A follow-up control system for a pilot de with the rate of change or speed of said driving vice and driven object comprising in combination driving means for said object, means for control 15 means, means responsive to said signal voltage in excess of a predetermined value for substan ling the energization of said driving means com prising electric valve apparatus provided With a control grid, means responsive to positional dis agreement of said pilot device and driven object tially decreasing said signal voltage, and means responsive to said second voltage in excess of a predetermined value for by-passing said capaci for supplying to said grid a signal voltage vary 20 tor so that said grid voltage is modi?ed in ac cordance with the speed of said driving means ing with said positional disagreement to control when the speed of said driving means is greater said driving means to drive said object toward than a predetermined value. correspondence with said pilot device, means re 7. A follow-up control system for a pilot de sponsive to a speed of said driving means in ex cess of a predetermined value for modifying the 25 vice and driven object comprising in combina tion driving means for said object, means for voltage supplied to said grid in accordance with controlling the energization of said driving said speed, and means responsive to said signal means comprising electric valve apparatus pro voltage in excess of a predetermined value for vided with a control grid, means responsive to substantially decreasing the signal voltage there by to reduce the synchronizing torque of said 30 positional disagreement of said pilot device ‘and driven object for producing a signal voltage driving means. varying with said disagreement, electrical con 5. A follow-up control system for a pilot de nections from said disagreement responsive vice and driven object comprising in combination means to said grid for applying said voltage to driving means for said object, means for con trolling the energization of said driving means 35 said grid to control said driving means to drive said object toward correspondence with said pi comprising electric valve means provided with a lot device, antihunting means for said system control grid, means responsive to positional dis comprising a capacitor connected to said control agreement of said pilot device and driven object grid and means for supplying a second voltage to for supplying a signal voltage to said grid to con said capacitor proportional to the speed of said trol said driving means to drive said object to driving means, a variable voltage drop device in ward correspondence with said pilot device, an cluded in said connections, means for substan tihunting means comprising an energy storage tially reducing said signal voltage comprising an device connected to said grid and means for sup electric valve device having a cathode and an plying a voltage to said energy storage device proportional to the speed of said driving means 45 anode connected to said connections and respon thereby to modify the voltage supplied to said grid, means responsive to positional disagree sive to a voltage in excess of a predetermined ment of said pilot device and driven object in ex cess of a predetermined amount for substantial ly decreasing said signal voltage, and means re sponsive to a speed of said driving means in ex cess of a predetermined value for rendering said energy storage device ineffective. 6. A follow-up control system for a pilot device to produce an increased voltage drop across said and driven object comprising in combination 55 value for completing a conducting path thereby voltage drop device, said electric valve device having a, second anode coacting with said cath ode in response to a predetermined value of said second voltage to complete a by-pass circuit about said capacitor thereby to render said ca~ pacitor ineffective. JOHN L. BOWER.