US2449797A - Electronic control circuit - Google Patents

Description

' Sept. 21, 1948. e. A. WALDIE I 2,449,797 I nnncmonrc comm cmcun:

Origiril Filed Oct. 20. 1943 FIG/l mn VOLTAGE agvg CURRENT AREAS Anon: vow:

EQUAL OUTPUT- CURRENT AREAS came UNEQUAL ouwur FIG. 4

INVENTOR alone: A. WALDII ATTORNEYS Patented Sept. 21; 1948 George A. Waldle, Worthington,

Ohio, assignor to H-P-M Development Corporation, Wilmington, Del., a corporation of Delaware Original application Oct Divided and this ber 20, 1947, Serial No.

ober 20, 1943, Serial No.

application Septem- 2 Claims. (Cl. 318-297) 1 I The present invention relates to the control of mechanical operation, particularly by the use of electronic devices as applied to direct current loads such as motors, relays, etc.

This is a divisional application of the original application Serial Number 506,983, filed October-'- 20, 1943, which became Patent Number 2,437,140

on March 2, 1948.

Various schemes have been advanced to control the speed of direct current motors from a remote position, and in general, most of them depend on the use of a variableresistor connected either in v the field or in the armature circuit. Rheostats of this general character entail considerable losses when dealing with large power since they operate on the energy dissipative principle and, in addition, their effectiveness of controlis affected by a number of variables such as changes in room temperature, humidity and the presence of dust, etc. There is also present the danger fromelectric shock when operating the rheostat because the adjustable arm on the resistor is directly associated with the line and electrical leakage due to poor insulation of the parts may be involved.

Many forms-of mechanical operation require a sudden reversal of rotation of the motoras well as changes in speed, in which case, a reversing device such as a switch is usually provided in addition to the variable resistor to efiect reversal and speed control in the opposite direction. The difllculty of arcing and resulting burned contacts may be Still another object is to provide a direction control for motors in which the control element or elements are not electrically connected to the high voltage lines so as to eliminate all danger of shock.

A still further object is to provide a highly Y sensitive but stable speed and direction control ofdirect current motors in which the exercised control is so sensitive that individual movements of the control element produce accurately proportional movements 01' the motor.

Another obiectis to provide an efficient and a sensitive 'controi for direct current motors which permits reversal of the 'motor at the control element without the breaking of current carrying circuits and offers the same degree of sensitivity of speed control in either direction of rotation.

A more general object is to provide a control for a direct current load such as a motor or relay which is so sensitive'that only an infinitesimally small movement of the control element is necessairy to find adequate response in the operation of the motor or relay and a correspondingly small movement of the control-element is necessary to reverse the operation of the motor or relay and to control the speed of operation in the reverse encountered at the switch, particularly when large currents are being carried.

There is, therefore, a specific need in the art of electrical control systems for an improved structure and/or system by which the current supplied to a direct current load may be accurately controlled as to magnitude and direction without.

the breaking of contacts and without the necessity for auxiliary switches or other devices which load.

Another object is to provide a combined control and supply system for a direct current load of the character set forth which would have the advantage of being self-rectifying so that the load may be energized from an alternatin current source.

direction.

These objects are attained in brief by employing a plurality of electron discharge devices of the gaseous type and controllin the sequence of firing of the devices with respect to one another by means of a magnetic element having a control member which: is completely disconnected from the electric system, but the movement of which is so related to the control element 01' the electric circuits as to change the electrical conditions within the electron discharge devices sufficient to control the currents passing therethrough. These devices are preferably connected in opposition in the case of a reversible motor but may be connected in the same direction in case separate loads are employed with the individual devices.

The invention will be better understood when reference is made to the following description and the accompanying drawings in which:

Figure 1 is an elementary diagram of an improved electrical circuit and structure incorporating the features of this invention.

Figure 2 is a diagram particularly showing the control apparatus for the electric control circuit.

Figures 3 and 4 are diagrams indicating the voltage and current conditions within the improved'circuit and associated structure.

Referring more particularly to Figure 1, a pair of gaseous discharge devices I and 2. either of the glow discharge or are discharge typ depending on the current requirements of the load, may be employed. The device I includes a cathode 3 which may be directly or indirectly heated. an electrostatic control element or grid 4 and an anode 5, while the device 2 includes a cathode 6. a grid element I and an anode I. The anode 5 may be connected through a conductor 9 to a field winding III of a direct current motor II, the circuit being completed through a pair of fixed resistors I2 and a conductor I! back to the cathode I.

The input circuit of the device I'includes a variable reactor it connected between the grid 4 and a position between the resistors I2. A variable resistor III may also be connected between the grid element and the conductor I9.

The device 2 has corresponding elements and functions as those described in connection with device I except that it is connected to the field winding load circuit II in the reverse manner from the other device. A variable resistor I1 is connected between the grid element I and the conductor I8 which passes to the cathode 6 and there is a variable reactor I9 connected to the lower connection of the lower resistor I2 through conductor 20. While I have shown the field coils I9 and I6 of the motor II as constituting separate elements. it will be understood that if desired a single field winding may be provided for the motor as long as the tap is taken from the midpoint of the winding through the upper bridge resistor I2 to the inner terminals of the reactors I4, I9.

A supply of alternating current is taken to the devices I. 2 through mains 2i, 22, one of which is connected to the mid-tap between the fields I0 and I6 and the other is connected to conductors I3 and 20. The armature circuit of the motor II may be energized with direct current through a supply circuit 23.

It will be noted in the drawing that the arrows drawn across the reactors I4 and I9 point in opposite directions and are connected together. This is to signify that the reactances of these reactors are adjustable in a differential manner. Thus, as one of the reactances is increased in value the other reactance is decreased proportionately or in the same degree.

Any suitable structure may be provided in order to obtain this differential change in the reactors I4, I9 and one such structure has been illustrated in connection with Figure 2. The coils of the reactors III, I9 are wound on a common magnetic core 24 having a C shape, 1. e., one of the legs includes an air gap 25. A magnetic armature 28 is pivoted at 21 to the other leg of the core, this armature terminating in a knob 28 adapted to be operated by a stylus or lever 28a.

A pair of oppositely disposed springs 29 maintain the armature in an approximate midway position between a pair of supports 39. the arrangement being such that when the knob is moved upwardly, the lower spring 29 is placed under tension and the upper spring is relieved partly of its tension so that when the hand is removed from the knob the armature will assume a midway position within the air gap 25. It will be understood that this air gap-would in practice be of considerably less length than that illustrated in Figure 2 in order that the permeability of the core as a whole will be sufficiently large to provide the proper reactance effects at the coils. It is apparent that as the armature 28 is moved upwardly the effective air gap in the upper portion of the core 24 is decreased, thus increasing the reactance of the coil II while the effective air gap of the lower portion of the core is increased to decrease the reactance oi the coil I9. By thus simply swinging the armature 26 upwardly, the reactance of coil ll is increased and the reactance 0i. coil I! is decreased in a corresponding manner.

Referring now to Figure 1. it is apparent that alternating voltage is applied both to the output circuit which comprises the cathode 2 and the anode 8 and also to the input circuit which includes the electrodes 2 and l. The'phase relationship between the grid voltage and the anode voltage can obviously be changed by varying the reactance I 4 and the same thing applies to the voltage relationships in the tube 2 when the reactance I9 is correspondingly varied. The net result is that by varying the reactance II in one direction and the. reactance I9 in the opposite direction, the phase relationships of the voltages applied to the electrostatic control elements 4 and I are shifted with regard to the anode voltages applied to the respective tubes I and 2. This can be readily seen by examination of the diagrams shown in Figure 3 if it is assumed that the tubes I and 2 are of the are or glow type and each have a critical negative grid voltage characteristic as shown in the figure which prevents the device from starting unless this critical voltage is exceeded. Assume that the adjustment made on the reactor I4 is such that the actual voltage applied to the grid 4 intercepts the critical grid voltage at point II (Figure 3), the tube will fire and the resulting glow or are discharge will pass through the tube throughout the remainder of the positive half cycle of the anode voltage. The firing period of the tube is indicated by the shaded area in each half cycle of the anode voltage.

Now let us assume that the reactance II is increased, for example by raising the armature 26 (Figure 2) upwardly. The effective voltage applied to the grid will shift phase-wise so that the actual grid voltage curve will cut the critical grid voltage curve at a later period and the aggregate amount of current passing through the tube I will decrease. It is apparent that by varying the reactance ll over a sufliciently wide range 1 the tube I can be triggered at any point in the positive half cycle of the anode voltage and there-,

by change the average amount of current fiowing over a predetermined period of time through the field winding load III.

The tube'2 operates in the same manner as tube I except that it is reversely connected and when the reactance I9 is decreased in an amount corresponding with the increase of reactance I4, the alternating voltage applied to the grid 1 is shifted phase-wise, but in the opposite direction to trigger the tube 2 earlier in each half cycle of the anode voltage as shown in the lower portion of Figure 3. Under these circumstances the current flowing through the field winding load It is increased. It will be understood that rectified current flowing through field winding I0 tends to move the armature II in one direction and rectified current of opposite direction and flowing through the field winding I6 tends to cause the motor to rotate in the reverse direction. Thus, by differentially altering the reactances I4, I9 by means of a swingable armature 26 (Figure 2) or in any other suitable manner the motor II can be caused to rotate in one or the other direction depending on the relative magnitudes of the vreactances I4, I9.

Should the armature 26 remain in a position midway of the ends of the air gaps 25 so in effect to provide two air gaps of equal length within the upper and lower portions of the core 24, the phase relationships between the grid and anode voltages of the two tubes may be such as to. permit as much current to fiow through field coil ary, it remains in a sensitive condition ready instantly to rotate in either direction upon the slightest change being made in the magnitudes of the reactances l4, 19. This highly sensitive but motionless condition of the motor is useful when an instantaneous response of the motor in either direction is required.

The resistances l5, l1 are provided to adjust the sensitivity of the circuit and it is apparent that due to the high state of balance that is possible in the bridge form of circuit shown in Figure 1 extreme orders of sensitivity can be obtained so that even the slightest change in the reactors l4, I9 is suificient to bring instant response in the operation of the motor H, either by way of change in speed or change in direction of rotation or both. Any speed of the motor may be obtained in this manner from the highest practical speed down to the slowest speed because any degree of voltage phase shift in the tubes I and 2 may be obtained and the instantaneous speed of the motor is directly proportional to the instantaneous changes in the voltage phase shifts.

In Figure 2 is shown a practical application of the control system ofl igure 1 for regulating a D. C. motor II connected to a mechanismto be actuated indicated at 32. The vacuum tubes I and 2 and associated resistors and circuit wiring may be containedin a suitable cabinet 33 from which issue leads to the direct current motor field windings Ii.

From the foregoing, it is evident that I have disclosed a highly sensitive and efiicient control system, making use of gaseous discharge devices, both of the controllable and uncontrollable type, and the differential or the cumulative current through the devices may be advantageously employed to operate a direct current load which in turn may constitute a control element of a mechanical, electrical, or hydraulic system. The

differential or cumulative currents passing through the system are sensitively and efllciently controlled by means of one or more reactors which may be operated simultaneously and either ditferentially or cumulatively to vary the reactances within the circuits and thus control the currents in the load.

While I have disclosed my invention in connectrolled in order to provide a phase shift between the grid and the anode voltages. It will also be apparent to those skilled in the art that instead of employing arc discharge devices for translating and controlling currents within the circuits I may if desired, and depending on the character of the load, utilize glow discharge devices.

It will be understood that I desire to comprehend within my invention such modifications as come within the scope of the claims and the invention.

Having thu fully described my invention, what I claim as new and desire to secure by Letters Patent is:

1. In combination in an electrical control circuit for varying the rate and direction of rotation of a direct current motor having an armature, a

direct current source for exciting said armature. and first and second field windings associated with said armature, the combination of a first and second triode each having a cathode, an anode, and a grid, an alternating current supply including first and second leads, means connecting said fi st lead to one end of each of said field windings, means connecting said second lead to the cathode of said first triode and to th anode of said second triode, means connecting the other end of said first field winding to the anode of said first triode, means connecting the other end of said second field winding'to the cathode of said second triode, a variable resistor connected between the cathode and grid of each of said triodes, a pair of fixed resistors connected in series across said first and second leads, a first variable reactor connected between an intermediate point between said fixed resistors and the grid of said first triode, and a second variable reactor connected between said intermediate point and the grid of said second triode, and mechanically operated means for simultaneously differentially adjusting said reactors.

2. In combination in an electrical control circuit for varying the rate and direction of rotation of a direct current motor having an armature, a direct current source for exciting said armature, and first and second field windings associated with said armature, the combination of a first and second triode each having a cathode, an anode, and a, grid, an alternating current supply including first and second leads, means connecting said first lead to one end of each of said field windlngs, means connecting said second lead to the cathode of said first triode and to the anode of said second triode, means connecting the other end of said first field winding to the anode of said first triode, means connecting the other end oi said second field winding to the cathode of said second triode,'a variable resistor connected between the cathode and grid of each of said triodes. a pair of fixed resistors connected in series across said first and second leads, a first variable reactor connected between an intermediate point between said fixed resistors and the grid of said first triode, and a second variable reactor connected between said intermediate point and the rid 0! said second triode, mechanically operated means for simultaneously differentially adjusting said reactors, and means for normally positioning said last mentioned means to maintain said reactors at equal balanced values of reactance.

GEORGE A. WALDIE.

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