US2543950A - Coarse-fine electric motor control system - Google Patents

Description

March 6, 1951 M. N. YARDENY ETAL 2,543,950

COARSE-FINE nugcmxc mdToR con'mor. svs'rsu Filed llay.29, 1948 2' ShBQtS-ShGOt 1 INVENTOR. MIL'HEL N. YARDENY By ADOLPH RAZDONITZ AGENT March 6, 1951 v M. N. YARDENY ETAL 2,543,950

- COARSE-FINE ELECTRIC MOTOR CONTROL sysm Filed May 29, 1948 2 Sheets-Shed 2 &

SELECTOR O\ x 1% IN VEN TOR.

I MICHEL N. YARDENY BY ADOLPH RAzoow/rz AGENT Patented Mar. 8, 1951 COARSE-FINE ELECTRIC MOTOR CONTROL SYSTEM Michel N. Yer-deny and Adolph Itazdowitz, New York, N. Y.; laid Budowitl winner to said Yardeny Application May 29. ms, Serial No. 30,006

15 Claims.

The present invention relates to remote control systems and, more particularly, to control systems of the coarse-fine type wherein a preliminary setting and a vernier setting are to be given to a load located at a remote station.

The invention is particularly, though not exclusively, applicable to remote control systems of the type described generally in the co-pending United States patent application of Michel N. Yardeny and Robert Bemas, Ser. No. 5,276, filed January 30, 1948, now abandoned, and more specifically in our co-pending United States patent application Ser. No. 22,863, filed April 23, 1948, now Patent No. 2,531,187, granted November 21, 1950.

While the invention may be utilized for the purpose of controlling any type of load located at a remote station, a now preferred field of application thereof is the remote actuation of the tuning control of a radio receiver.

An object of the present invention is to provide a control system of the character set forth wherein coarse as well as fine control are effected by the manipulation of a single operating member (e. g. tuning knob).

Another object of the invention is to provide a coarse-fine system wherein the switching from coarse to fine control will be automatically effected upon reversal of the sense of actuation of a control member, while the return to coarse control will be automatically effected whenever the range for fine control is exceeded.

A further object of the invention is to provide, in a remote control system of the character described utilizing a transmission channel which is also used for the transmission of other signals (such as set forth in the co-pencling applications referred to), means for preventing false operation of the system by rendering the same insensitive to such other signals.

Still another object of the invention is to provide, in a coarse-fine control system, means for preventing false operation by disabling the vernier control until the preliminary positioning of the load or controlled device has been completed.

According to one of the features of the invention, there is provided, in a control system of the,

character described, an actuating member at a local station, first control means positively connected with said actuating member, second control means frictionally entrainable by said actuating member, stop means for arresting the second control means when the displacement of the latter surpasses predetermined limits, and switch means arranged to render the first control means a gear l4 2 effective in the arrested condition of the second control means to cause the displacement of a load at a remote station and to render the second control means similarly effective during entrainment thereof by said actuating member.

According to another feature of the invention, there is provided, in a system of the character set forth above, a load-positioning member at a remote station actuatable under the control of either of two follower means arranged to respond to signals from a respective control means at the control station, said two follower means including coarse follower means positively connected to and fine follower means frictionally coupled with said load-positioning member. Preferably, the two control means and the two follower means comprise two pairs of correlated potentiometers operating in the manner described in our aforesaid Patent No. 2,531,187.

According to a further feature of the invention, the two stations may be interconnected by a transmission channel to which said control means may be alternately connected, signal generator means operable simultaneously with said switch means being provided at the control station to indicate at the remote station which one of said control means is connected to said channel.

The above and other features and objects will become apparent and the invention will be better understood from the following description of an embodiment thereof, reference being had to the accompanying drawing in which:

Fig. 1 is a circuit diagram of a control station according to the invention, and

Fig. 2 is a circuit diagram of a remote station according to the invention.

Referring to the drawing, there is shown a control station (Fig. 1) and a remote station (Fig. 2) interconnected by a transmission channel shown in this exemplification as a two-wire transmission line I, 2. Conductor l of this line is connected at the control station to the positive terminals of two potentiometers 3, l in parallel and at the remote station to the positive terminals of two similar potentiometers 5, 6 in parallel. Potentiometers 3, 4 are energized from a battery I and potentiometers 5, 6 are energized from a battery 8.

Turning now to the control station (Fig. 1). there is provided an actuating member in the form of a knob 9 which is fixed to a shaft ll carrying a pinion I I as well as the lower coupling half of a clutch l2. The upper coupling half of the clutch I2 is mounted on a shaft l3 carrying which meshes with another gear l5 fixed to a shaft 18. The rotation of the shaft II is transmitted by means of two bevel gears l1, II to a shaft 19 carrying the wiper 20 of "fine" potentiometer I. 3

The pinion ll meshes with a gear 2! which is mounted on a shaft 22. The rotation of the shaft 22 is transmitted by means of two bevel gears 23, 24 to a shaft 25 carrying the wiper 26 of coarse potentiometer I. Shaft 22 also carries a bevel gear 21 which meshes with a bevel gear 28 integral with a pointer 22, the latter cooperating with a scale 20. The gear 22 is rotatably mounted on a stationary pin or stud shaft 2| on which there is frictionally held a collar portion 32 of a frame 23 which brackets the pointer .29. It will be understood that the frame 33 will be entrained by the pointer 22, e. g. by being engaged by a projection 34 thereof, whenever the pointer tends to move beyond the area defined by the sides of the frame, yet will remain at rest as long as the movements of the pointer are confined to this area.

If the ratio of gears II and I5 is 2:1 and that of gears Hand 2| is 1:5, then each quarter turn of the knob I will displace the wipers 2| and 26 by 180 and 18 degrees, respectively, pointer 28 undergoing the same displacement as wiper 26. The movement of the wiper 2. and, with it, of the shaft I6 is limited to a range of approximately 180 degrees by means of stops 2!, l8, further rotation of the knob l causing the friction clutch l2 to slip while wiper 26 and point 29 continue to advance. By making the angle of the apertured sector of frame 33 equal to 18 degrees. this sector will always indicate the range within which operation of the fine potentiometer 20 will be possible.

Connected between the stops 2!, 26 in parallel, on the one hand, and the wiper 22, on the other hand, is a series circuit comprising the primary of a transformer 31, a resistance 28 and a battery 39, Wiper 2| is also connected to the front contact of the lower armature of a fine" relay II. the circuit being extended by said armature to the back contact of the lower armature of a coarse" relay 4| and thence, over the last-men tioned armature, to the left-hand terminal of a resistor 42 in series with line conductor 2. Wiper 26 is connectable to the same terminal of resistor 42 b way of the back contact and upper armature of "fine" relay 4| and the front contact and lower armature of "coarse" relay II. The energizing circuits for each of these two relays include a battery 43, the armature of a side-stable relay 44 and a respective contact of the lastmentioned relay engageable by said armature. The term side-stable relay" imports that this relay is of a type which has no unoperated or released position and whose armature does not comprise a restoring spring, thereby remaining in engagement with one or the other of its two contacts, depending on which one of its two-windings has been energized last.

Relay 4 has two windings energizable from a battery 45 over an armature and respective contacts of a polarized relay 46. The energizing circuits for these windings also lead over a signal generator 41 whose function it is to send a suitable impulse to the line I, 2 whenever one of these windings becomes energized. Signal generator 41 may be of any well known and suitable design, yet we prefer to use a pair of self-locking relays each adapted to break the holding circuit for the other, when actuated, and to send a signal pulse to line which is generated by the current surge in its own holding circuit. An arrangement of this description has been fully disclosed in connection with Fig. l of our aforementioned Patent No. 2,531,187. 5 Polarized relay I8 is connected across the secondary of transformer 31 in series with a triode I! which is shunted by a rectifier 49. The grid and the cathode of tube 48 are connected across a resistor 5| which in turn is connected in series with the secondary of a transformer ii and a rectifier 52 by way of a smoothing network comprising an audio frequency choke 52 and a condenser 54. The primary of transformer 5| is connected across an alternating-current gensaturable-core reactor I, an indicator lamp 6! and the front contact and upper armature of "coarse relay ll. The rectifier I2 is poled so that any alternations induced in the secondary of transformer Iii will app y a negative bias to the control grid of triode II.

The left-hand terminal of resistor 42 is connected to the grid of a vacuum tube by way of a grid resistor ll, its right-hand terminal being connected to the cathodes of this tube and of a companion tube 62 by way of respective cathode resistors 62, N. The common terminal of these resistors is connected to the grid of tube 62 by way of a resistor 65. A battery 86 supplies space current to the tubes I, 62 by way of respective plate resistors 61, I. The plates or these tubes are also connected across the central winding 69 of reactor 58. Tubes 80, i2 and their respectively associated resistors are preferably identical. so that substantially no current will fiow through winding 69 when the voltage drop across resister 42 is zero.

Turning now to Fig. 2, there is shown a radio receiver ll provided with a tuning control II which is mounted on a shaft 12, the latter carrying a gear 12 as well as the wiper ll of "coarse" potentiometer 5. Gear 18 meshes with a pinion 15 which is fixed to a shaft 12, the latter having mounted thereon a bevel gear TI as well as one 45 of the coupling halves of a clutch 12 which is similar to clutch l2 in Fig. l. Bevel gear 11 meshes with a similar gear I! fixed to the housing of a conventional differential gearing Ill whose two planet gears are mounted on respective stud shafts ll, I2 each carrying a worm wheel l3, .4 which is engaged by a worm Ii. 88, respectively. The worm-carrying shafts ll, 88 each have mounted thereon a respective pinion 29, 90 meshing, respectively, with pinions ll, 92. Pinion Si is mounted on the shaft 83 of a D.-C. motor 94. while pinion 82 is similarly mounted on the shaft of another D.-C. motor 98; shaft 85 is also connected to a small damping generator 51 having a load resistor 88 connected across its terminals. A

condenser 89 is bridged across the armature of motor at.

The other coupling half of clutch II is fixed to a shaft llln carrying a gear lbl which meshes as with a gear I02, the latter being mounted on a common shaft I03 with the wiper I04 of "fine" potentiometer 6. Two stops I05, I08 limit the displacement of wiper IM to an angle of substantially degrees, in the same manner as the 70 movement of wiper 20 (Fig. 1) is limited by stopsli and 26.

It will be understood that, in the embodiment illustrated, the ratio of gears Ill, I22 on the one hand and gears 12, 15 on the other should be 75 selected so that the angular velocity of wiper erator 55 in series with the windings 56, 51 of a I04 (when disengaged from the stops I00. I) will be ten times that of wiper It, in order to duplicate the conditions existing at the local station (Fig. l). Worm drive 04. I0 is driven over a high-speed gearing 80, 02 from "coarse motor 00, while worm drive 82. CI is driven over a reduction gearing 80, 0| from fine" motor 80. The two worm drives represent respective selflocking inputs to the differential 80, each being adapted to effect the rotation of shaft I0 when the other drive is unoperated.

The upper terminal of load resistor 00 is connected to the right-hand terminal of a control resistor I01 which is in series with line conductor 2. Connected across the line I, 2 ahead of this resistor is a selector I08 whose function it is to respond to the impulses transmitted over the line by the signal generator 01 (Fig. l) Selector I00 "may be of any well-known and suitable design, depending upon the nature of the impulses produced by the generator 41, but preferably comprises a pair of selectively biased thyratrons responsive to positive D.-C. pulses of different magnitudes; such an arrangement has been fully disclosed in connection with Fig. 2 of our Patent No. 2,531,187. The selector controls the operation of a pair of relays I00. M0, the energizing circuits for these relays including a battery III as well as an armature and respective contacts of a side-stable relay I I2 included in the selector.

The right-hand terminal of control resistor I0? is connected to the armature Ill of "coarse" relay IIO, the circuit being extended by way of the back contact of this armature and front contact and armature Ill of line relay I09 to the wiper I0 of fine" potentiometer 6. Wiper II of coarse potentiometer 5 is connectable over back contact and armature II 0 of fine relay I00 and front contact and armature II3 of coarse" relay IIO to the same terminal. Armature IIB of relay H0 and armatures H1, H8 of relay I09 serve to effect the selective energization of motors 94, 96, depending on which one of the two relays is operated. These motors are energized from a source of alternating current I I9 by way of a rectification network I20 which includes a first pair of parallel thyratrons I2I, I22 and a second pair of parallel thyratrons I23, I24, the

two pairs being connected with opposite polarity r across the source II9. A rectifier I20 is bridged across the thyratrons I2I, I22 while 9, rectifier 826 is similarly bridged across the thyratrons I23, I24. Connected to the plates of the first pair, in series with the source I iii, are respective windings Of a synchronizing transformer I21 and to the plates of the second pair, in similar manner, respective windings of a synchronizing transformer m.

Each pair of thyratrons are provided with a common cathode resistor I29, I30, respectively, the common terminal of the two resistors being connected to the midpoint of the secondary of an input transformer I3I by way of a biasing battery I32. The circuit of this secondary is completed by a condenser I33 in series with a resistance I34, a tap on this resistance being connected to the grids of all thyratrons in parallel by way of a current-limiting resistor I35.

Conductor 2 is connected to the common terminal of the cathode resistors I36, I31 of a pair of vacuum tubes I38, I30 whose plates are connected across the primary of a transformer I40, the midpoint of this primary being connected to said common terminal by way of a battery I in series with the secondary of a transformer I42; the primary of the latter transformer is connected directly across the source I It. The upper terminal of the secondary of transformer I40 is connected to the grid of an amplifier tube I by way of a coupling condenser I. its lower terminal being connected to the junction of two series resisters I40, I inserted as a grid leak between the grid and the cathode of tube I. The load circuit of tube 3 includes the primary of input transformer I ll in series with a battery I" and a load resistance Ill.

A two-stage amplifier comprising vacuum tubes I40, I00 has the grids of both of its stages connected in parallel to the conductor 2 over respective coupling condensers Isl, I52. The plate of tube I40 is also connected to the grid of tube I00 over a coupling condenser I52 in series with a rectifier I and a grid leak I". The plate resistors of tubes "9, I 00 are indicated at I08, I01 and are connected in parallel to a battery I50. The plate of tube I50 is connected over a coupling condenser I00 to a load resistance I60, the latter being in series with a rectifier IBI and with a portion of resistor I06 which is shunted by a condenser I02; this condenser and the said resistor portion form a time constant circuit connected across the series combination of rectifier IBI and load resistance I60.

The operation of the control system just described is as follows:

Let us assume that the pointer 29 at the indicator of the control station is positioned substantially midway within the open sector of frame l3, wiper 20 at the same time contactin the mid-portion of potentiometer t as shown. With the armature of side-stable relay is in the position illustrated, due to a previous energization oi the right-hand winding of that relay, fine relay 40 will be operated and the wiper 20 of fine potentiometer 4 will be connected to line conduc tor 2 over a front contact of relay 40, a back contact of relay H and resistor 42. At the remote station, the upper winding of side-stable relay H2 in selector I08 will have previously responded to a signal from enerator Ill. thereby placing its associated armature in the position illustrated in which an energizin circuit is closed for fine relay I00. Thus at the remote station, too, the wiper I04 of the fine potentiometer 6 is connected to conductor 2 over a front contact of "fine" relay I09, a back contact of "coarse" relay I I0 and resistor I01.

When the wipers 20, I00 are in corresponding positions, the system is in balance and nothing further will happen until the operator displaces the knob 8 to select a different position of the indicator 20, 30. Assuming that the knob 0 is actuated in the sense of the arrow, then the wipers 20, 26 as well as the pointer 29 will also be rotated in the directions indicated by the respective arrows. After a rotation of the knob 9 through approximately 45 degrees, the wip'er 20 will strike the stop 38 while projection 34 on pointer 20 will simultaneously abut the righthand side of frame 33. A circuit is closed from battery 39 through resistance 38, primary of transformer 31, wiper 20 and stop 36, sending a current pulse through the secondary of trans= former 21 which (for reasons subsequently to become apparent) should be of such polarity as to to the left so as to restore "fine" relay 40 and operate "coarse relay 4|. At the same time the generator 41 will send a "coarse tuning pulse to line, this pulse being preferably of the opposite polarity as the voltage applied to the line by potentiometer 3 or 4. Wiper 20 is now insulated from resistor 42 which is instead connected to wiper 25 over a back contact of relay 40 and a front contact of relay 4|.

At the remote station. the arrival of the coarse tuning" selection pulse causes the reversal of the position of the armature of relay 1 I2 and operates coarse relay I I0, releasing fine relay I09. Thi insulates wiper I04 from resistor I01 while connecting thereto the wiper 14 over a front contact of relay I09 and a back contact of relay I I0. Since the two potentiometers 3, 5 are now in unbalance, wiper 26 having been displaced toward the more negative end of the potentiometers, current will now flow from right to left throughresistors' I01 and 42 in series.

Tubes I38, I38 are designed so that no current will flow in the secondary or transformer I40 when zero signal is applied to the grid of tube i238. It will be seen that the grid of tube I39 is connected directly to the common terminal of cathode res-stors I36, while that of tube I38 is connected to the right-hand terminal of control resistor I01 over a portion of load resistor 08. The unbalance current flowing through resistor I01 will drive the grid of tube I38 positive with respect to that of tube 539, thereby unbalancing the primaries of transformer I40 and giving rise to an output current in the secondary of this transformer. The oscillations corresponding to this output current are applied to the secondary of input transformer I3I after amplification in tube I43.

It will be understood that the output of amplifier tube I43 will be in step (that is, either in phase or in phase opposition) with the output of generator H9 but that both the amplitude and the polarity of control oscillations set up in transformer I3I will depend upon the magnitude and the sense of the current flow through resistor I01. In a coarse-fine tuning drive as herein contemplated, however, it is desirable to use a D.-C. motor whose speed may be regulated according to the amount of unbalance, whereby a more accurate setting will be obtainable and hunting will be virtually eliminated as will more fully appear hereinafter. Accordingly, th output of generator I I9 is applied to the armature of arespective D.- C. motor 94, 93 after rectification in the network I under the control of the output of tube 43; network 20 operates as follows:

Since the control oscillations from transformer I3I are applied to the grids of all thyratrons I2I through I24 in parallel, and since the output of source H9 is applied to the plates of the two pairs of thyratrons in push-pull, the signal on the grids of one pair (disregarding for the moment the phase shift introduced by the circuit I33, I 34) will be in phase with the corresponding plate potential while that of the grids of the other pair will be in phase opposition with respect to the potential on the associated plates. Accordingly, only one pair of thyratrons (say, the tubes I2I and I22) will fire, during alternate half-cycles, when the current through resistor I01 flows in a given direction. We can now trace an operating circuit for the motor 96 (which 'is the coarse motor) from generator II9, thyratrons I2I and I22 in parallel, armature H6 and front contact of relay H0, armature II! and back contact of relay I09, armature of motor 0', through rectifier I'26 back to the generator Ill. Had the voltage drop across resistor I01 been of opposite polarity, then the operating circuit for the motor would hav included thezthyratrons I23, I24 and the rectifier I25 instead of the corresponding elements referred to.

The use of two thyratrons in parallel is dietated by the necessity to prevent overloading of the tubes where the motor is liable to draw a large starting current; if this is not the case, each of the two pairs of thyratrons may be replaced by a single tube, Note that the transformers I21, I28 insure the simultaneous firing of the tubes of each pair, their windings being of course arranged so that a current surge through either winding will increase the positive potential or the anode connected to the other winding.

,As the voltage drop across resistor I01 decreases, the amplitude of the control oscillations set up in transformer I3I will diminish and the firing point of the 'thyratrons I2I, I22 (in the case assumed) will be more and mor delayed, resulting in progressively shorter ionization periods during each half cycle of oscillation; hence the period of current flow per cycle and, thereby, the average current density will decrease. Actually, the provision of condenser I33 and resistor I34 causes the grid voltage to lag behind the associated plate voltage, so that the two voltage peaks will not coincide and the bias of battery i32 will not be overcome unless the control oscillations exceed a predetermined amplitude. The sensitivity of the thyratrons may, of course, be varied by displacing the tap on the resistor I34 to which the grids of the thyratrons are connected.

It will be noted that the energizing circuit for the motor, whether including one or the other pair of thyratrons, is always shunted by the two cathode resistors I29, I in series. If, as the amplitude of the control oscillations decreases and the average current through the motor is reduced, the latter should fail to decelerate sufficiently, then the counter-e. m. f. built up by its armature will appear as a voltage drop across the two cathode resistors which will tend to overcome the negative signal on the grids of the opposite pair of thyratrons (e. g. tubes I23 and I24), leading to their ionization and energetically plugging the motor. It will thus be seen that the network I20 represents an efiective anti-hunting device, capable of reducing to a minimum the time required to obtain a desired setting.

A further means for reducing hunting is represented by the generator 91 which is driven through the shaft 95 regardless of whether or not motor 96 is energized. The output of generator 91 produces a voltage drop across the tapped-off portion of resistor 98 which opposes the voltage drop across resistor I01. The magnitude of this opposing voltage drop is selected so as to be small enough to be without appreciable effect during high-speed operation but to become effective upon approach to balanced condition in order to prevent the motor from overshooting its mark.

It is desirable that the transmission of transient voltages over the line I, 2 (e. g. the arrival of selection pulses from signal generator 41) have no disturbing effect upon the setting of the tuning drive shaft 12. This is accomplished by the provision of a transient blanking network which comprises the two-stage amplifier I49, I"

and its associated circuits. This network will be nonresponsive to D.-C. voltages, due to the provision of blocking condensers IBI, I52. but will operate in response to transients by blocking the input to the network I20. If, for example, a positive pulse appears across the line (conductor 2 positive r lative to conductor I), then the grids of both tubes I49, I80 will be driven positive; due to the provision of rectifier I54, however, the negative anode swing of tube I40 will have no effect upon tube I" whose plate potential will drop in response to the positive pulse applied to its grid. This drop in plate potential produces a current surge through resistor I which will pass the rectifier III and build up a voltage drop across the tapped-oi! portion of resistor I48 which is shunted by condenser I02, this voltage drop being of such polarity as to bias the tube I40 beyond cutofl'. If; on the other hand, a negative tran ient had been applied to the grids of tubes I 49, I50, then the positive anode swing of tube I49 would have overcome the negative grid swing of tube I50, due to the transient, and again a drop in the plate potential of tube I50 would have been the result. It will be seen that the period during which tube I43 remains blocked will depend upon the time constant of the circuit I46, I62.

Let us now assume that, at the control station, the operator has moved the pointer 29 past the desired setting and reverses the rotation of knob 8. Immediately, the primary circuit of transformer 3'! is broken and a current surge opposite to that previously described is induced in its secondary, its polarity being such that the current will be blocked by the rectifier 49 but may pass through the tube 48. The armature of relay 4B is now moved downward for the duration of this surge, energizing the right-hand winding of relay 44 and actuating the signal genera-tor 41 to send a fine tuning selection pulse to line. Relay 40 operates and relay 4i releases, thus restoring the conditions initially described.

At the remote station, the arrival of the appropriate selection pulse energizes the lower winding of relay II2 which moves its armature upward, operating relay I09 and releasing relay H0. With the wiper I04 reconnected to the line in lieu of the wiper 14, motor 94 now operates over an energizing circuit which is similar to that previously described for motor 96 but includes armature IIS and a back contact of relay lifl as well as armature H8 and a front contact of relay I09. Note that the line motor 94 has its armature shunted by condenser 99 which acts to reduce the voltage input to this motor, thus allowing the latter to follow all voltage changes across the resistor I01 at a relatively slow rate and afl'ording very precise tuning.

It may occur that, at the time when the rotation of knob 9 is reversed, the wiper 14 of coarse potentiometer 5 has not had time to occupy a position corresponding to that of wiper 26 at the control station; hence any switch at this instant to fine control would result in a misadjustment. In order to prevent this from happening an interlocking circuit is provided at the control station which will maintain coarse potentiometer 3 eiiective until complete balance is obtained. Referring again to Fig. 1, the load circuit of A.-C. generator 55 includes the impedance of reactor 58 which normally is sufliciently high to limit the amplitude of the oscillations in transformer 5| to such an extent that the bias voltage for tube 48, developed across resistor I0, will be less than that necessary to bias this tube to cutofi. -If, however, a voltage drop exists across the line resistor 42, the tubes 60 and 62 will have unbalanced outputs and a volt age drop will exist across the series combination of plate resistors 81 and 80, giving rise to a biasing current through the center winding 89 of reactor 58. This biasing current, in turn, decreases the reactance of the two windings I6 and 51', tube 48 will become blocked, and the relay 46 will not be energized when the wiper 20 leaves stop 35 or 38. Consequently, the "coarse" relay 4| will remain operated and the fine tuning signal will not be given.

Indicator lamp 59 in series with windings 58, ll apprises the operator of the fact that an unbalance exists between the two coarse potentiometers, preventing the switch-over to "fine" control. This lamp will not function during "ilne control operations, its circuit being open at the upper armature of relay 4I.

.While the invention has been described with reference to a single, now preferred embodiment, it is to be understood that it is capable of numerous modifications without departing from its spirit or exceeding its scope.

What we claim as novel, and desire to secure by Letters Patent, is the following:

1. In a control system, in combination, an actuating member, first control means positively connected with said actuating member, second control means frictionally entrainable by said actuating member, stop means for arresting said second control means in either of two limiting positions between them defining a predetermined range, a load, load-actuating means operable to change the position of said load, switch means selectively operable to render either of said con trol means exclusively effective to operate said load-actuating means and reversing means for said switch means actuated by said second control means in either of said limiting positions to place said load-actuating means under the control of said first control means, said switch means being effective in all other positions of said second control means to place said load-actuating means under the control of said second control means.

2. In a remote control system, in combination, a control station, a remote station, transmission means interconnecting said two stations, an actuating member at the control station, first control means positively connected with said actuating member, second control means frictionally entrainable by said actuating member, stop means for arresting said second control means in either of two limiting positions between them defining a predetermined range, switch means selectively operable to connect either of said control means to said transmission means to the exclusion of the other control means, reversing means for said switch means actuated by said second control means in either of said limiting positions to efl'ect the connection of said first control means to said transmission means said switch means being eilective in all other positions of said sec-- ond control means to connect said second control means to said transmission means, a load at said remote station, load-actuating means operable to change the position of said load, and circuit means for connecting said load-actuating means to said transmission means to effect a displacement of the load in response to signals from either one of said control means.

3. In a remote control system, in combination,

a control station, a remote station, a transmission channel interconnecting said two stations, an actuating member at the control station, first control means positively connected with said actuating member, second control means frictionally entrainable by said actuating member, stop means for arresting said secondcontrol means in either oi two limiting positions between them defining a predetermined range, switch means selectively operable to connect either of said control means to said transmission channel to the exclusion of the other control means. reversing means for said switch means actuated by said second control means in either of said limiting positions to eilect the connection of said first control means to said channel, said switch means being effective in all other positions of said second control means to connect said second control means to said channel, signal generating means operable simultaneously with said switch means to signal to said remote station which one oi. said control means is connected to said channel at said control station, a load at said remote site-- tion, first and second load actuating means alter natively operable to change the position oi said load, first and second follower means at the remote station each ada ted to control the operation of a res ective one of said load-actuating means. and selector means at the remote station operable under the control of said signal generating means to connect a respective one of said follower means to said transmission channel depending on which one of said control means is thus connect d at the control station.

4. In a control system. in combination, preliminary control means disolaceable over a predetermined ran e. vernier control means displaceable over a fraction of said range, a load, loadactuating means operable to chan e the position said load. stop means for arrestin said vernier control means in an extreme position. switch means having a first condition for rendering said preliminary control means eilective to operate said load-actuating rneans and a second condition for rendering said vernier control means similarly efl'ective, and circuit means including said stop means and controlled by said vernier control means to .olace said switch means in said iirst condition u on enga ement of said stop means by said vernier control means and to place said switch means in said second condition upon disen a ement oi said vernier control means from said stop means.

5. In a remote control in combination, a control station, a remote station. transmission means interconnecting said two stations. an ac tuating member at the control station. first control means positively connected with said actuating member. second control means irictionally entrainah e by said actuating member, stop means for arresting said second control means when the displacement of the latter sur asses a predetermined range, circuit means for connecting said control means to said transmission means. first and second follower means at the remote station, a load positively connected with said first follower means and irictionally coupled with said second follower means, drive means arranged to displace said load until said first and second follower means occupy positions corresponding to thou oi said first and second control means, respectively, and stop means for limiting the displacement of said second follower means to a range corresponding to that of said se ond 00 trol means.

8. In a remote control system} in combination, a control station, a remote station, a transmission channel interconnecting said two stations, an actuating member at the control station, a first control potentiometer at the control station, said potentiometer having a first wiper positively connected with said actu ting member, a second control potentiometer at the control station, said second potentiometer having a second wiper frictionally coupled with said actuating member, relay means operable to connect either 01' said wipers to said transmission channel, circuit means connecting a terminal of each of said potentiometers to said transmission channel, stop means engageable by the wiper 0! said second potentiometer in either of two limiting positions, switch means operable upon engagement of said stop means by the second wiper to actuate said relay means so as to disconnect said second wiper from said transmission channel while connecting said channel to the first wiper. said switch means being further operable upon disengagement of said second wiper from said stop means to actuate said relay means so as to disconnect said first wiper from said channel while connecting said channel to said second wiper, impulse generator means operable upon connec tion of said first or second wiper to said channel to send a first or second signal, respectively, to said remote station, a first follower potentiometer at said remote station, a second follower potentiometer at said remote station, a load at said remote station, said first follower potentiometer having a. third wiper positively connected with said load, said second potentiometer having a fourth wiper frictionally coupled with said load, relay means at said remote station operable to connect either of the last-mentioned wipers to said transmission channel, circuit means connecting a terminal of each of said follower potentiometers to said channel, a control impedance connected to said channel so as to register a voltage drop unless the setting of a follower potentiometer connected across said channel bears a predetermined relationship to the setting of a control potentiometer simultaneously connected across said channel, drive means connected with said load and adapted to displace the latter in response to a voltage drop across said control impedance, stop means adapted to arrest said fourth wiper in either of two limiting positions bearing a predetermined relationship to the limiting positions of said second wiper, and selector means arranged to actuate said relay means so as to connect either said third or said fourth wiper to said transmission channel in response to said first and second signal, respectively.

7. The combination according to claim 6, further comprising a control resistance connected to said transmission channel at the control station, and an interlocking circuit connected across said control resistance, said interlocking circuit being arranged to inactivate said switch means in response to a voltage drop across said control resistance occurring while said first and third wipers are connected to said channel.

8. The combination according to claim 7 wherein said interlocking circuit comprises a balanced amplifier, input means connecting said amplifier across said control resistance so as to produce a 11-0. output in response to a voltage drop across said control resistance, a source of alternating current, a saturable-core reactor in series with said source, circuit means for apply- 13 ing said D.-C. output to said reactor so as to decrease the reactance of the latter, an electric discharge device, said device forming part of a circuit for operating said switch means upon engagement of said stop means by said second wiper, .and biasing means for said discharge device, said biasing means being energizable from said reactor so that a bias tending to block said device will be developed when said reactance is reduced.

9. In a control system. in combination, control means, follower means, a load coupled with said follower means, circuit means interconnecting said control means and said follower means, said circuit means including a control impedance connected so that a voltage drop is produced thereacross when the positions of said control means and said follower means bear any but a predetermined relationship, a D.-C. motor coupled to said load, and energizing means arranged to maintain said motor operated until the voltage drop across said control impedance i substantially zero, said energizing means including a source of alternating current, balanced amplifier means connected across said source so as normally to have substantially zero output, circuit means connecting said control impedance to said amplifier means so that a finite output in step with the output of said source will be produced in re sponse to a voltage drop across said impedance, and a rectification network connecting said source to said motor, said network including two thyratrons connected in series with opposite polarity, input means connecting the grids of said thyratrons in parallel to the output of said amplifier means, circuit means connecting said source differentially across the plates of said thyratrons, and a pair of rectifiers each in series with a respective one end shunted across the other of said thyratrons.

10. The combination according to claim 9 wherein said input means comprises a phase shifting network arranged to introduce a lagging phase shift between the output of said amplifier means and the grids of said thyratrons.

11. The combination according to claim 9, furva D.-C. potential to said line, follower means at said remote station arranged to apply a balancing potential to said line, drive means for said follower means adapted to displace the latter, in response to any difference between said two potentials, until said transmission line is in balance,

14 a load coupled with said follower means for simultaneous displacement by said drive means, transient blanking means, said blanking means being arranged temporarily to inactivate said drive means, and an operating circuit for said transient blanking means reactively coupled to said line, thereby responding to the appearance of a transient voltage across said line.

13. The combination according to claim- 12 wherein said transient blanking means comprise an amplifier, input means including D.-C. blocking means connecting said amplifier across said line, and a time constant circuit connected across the output of said amplifier, said drive means comprising a motor, an energizing circuit for said motor including an amplifier tube, and biasing means for said amplifier tube including at least part of said time constant circuit connected so as to bias said tube beyond cutofi in response to a momentary change in the output of said amplifier.

14. The combination according to claim 13 wherein said amplifier has a first and a second stage, said D.-C. blocking means comprising condenser means connecting said two stages in parallel across said line, and a coupling between said stages, said coupling including a rectifier connected in such manner that transients of either polarity will result in an output pulse of predetermined polarity from the second stage.

15. In a control system, in combination, control means, follower means, a load coupled with said follower means, a motor coupled with said load and said follower means, and energizing means arranged upon displacement of said control means to cause operation of said motor until said follower means occupies a position bearing a predetermined relationship to that of said control means, said energizing means comprising a source of alternating current and a rectification network,- said network including at least two thyratrons connected in parallel across said source and a synchronizing transformer having two inductively coupled windings each connected between said source and the plate of a respective thyratron so as to increase the potential of the associated plate in response to an increase in current through the other winding.

MICHEL N. YARDENY. ADOLPH RAZDOWI'IZ.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS

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