US2502188A - Random reversing motor control system - Google Patents

Description

Mgfch 28, 1950 J. R. WALKER ETAL. 2,502,188

RANDOM REVERSINGMOTOR CONTROL SYSTEM Filed March 29, 1946 24 "In" nun 22a. 22b

INVENTORSY Jm/za 2 MIA/(2 BY P q/nzn fl Co'oK Patented Mar. 28, 1950 UNITED STATES PATENT OFFICE RANDOM REVERSING MOTOR CONTROL SYS TEM

Application March 29, 1946, Serial No. 657,987

16 Claims. 1

The present invention relates to means for controlling an electric vmotor drive to produce continuous reversals of random duration. The invention more particularly relates to the use of gaseous discharge devices for producing intermittently interrupted trains of electrical impulses for exciting an electric motor.

An example of the uses to which an electric motor drive of this type may be put is to be found in the art relating to the lapping of valves against their seats, particularly very minute and precise poppet or check valves of hardened steel such as are frequently used in Diesel fuel injection systems. In the process of lapping valves such as those used in hydraulic systems a lapping tool driven by a high speed electric motor and a lapping compound of extreme fineness are used to produce surfaces of the desired smoothness and accuracy. However, in spite of the use of line lapping compounds, a microscopic examination of the lapped surface even after extensive treat" ment shows the presence of minute grooves and striations. In an effort to improve upon the fineness of the lapped surface and to reduce the time required for such treatment, it has been found that reversing the direction of rotation of the driving motor at frequent and irregular intervals both reduces the time required and increases the quality of the result. Although the reason for the marked improvement has not been determined with certainty, it would appear that frequent continuous reversal prevents individual particles of the lapping compound from being drawn repeatedly about the same circular path. It is believed that a reversal of motion tends to free the particles from the too] allowing them to continuously engage different portions of the work surface thereby producing an averaging effeet which is not attained by ordinary types of lapping drives.

The drive is by no means limited to the above described lapping operation, but is equally applicable in other fields. Application of the drive to uses such as liquid agitation and the driving of display devices will readily occur to persons skilled in the several arts.

The present invention relates to means for simply and effectively producing continuous reversal of an electric driving motor particularly adapted to a lapping or similar machining operation.

It is an object of the invention to produce a drive suitable for use in such a device as a lapping machine and which, by reason of the frequent and irregular nature of the reversal, enables production of a highly finished surface in a minimum of time.

It is another object of our invention to produce an electric drive including a gaseous discharge tube in which the grid bias of said tube is varied in a manner to produce conduction of impulse trains of random duration by said tube.

It is another object of the invention to provide a reversible electric drive using standard low cost components of proven reliability and which provides readily variable adjustment of the average driving characteristics at the control of the operator.

It is a further object of our invention to provide an electric drive in which the control components are few in number and small in size, enabling compact unitary mounting.

It is still another object of the invention to provide a motor reversing control scheme which is purposely random or erratic in nature thereby reducing the necessity for using accurately cali-- brated circuit components.

Other objects and advantages of the invention will become apparent from the following detailed description taken in connection with the accompanying drawing in which:

Figure 1 shows the use of a single gaseous triode in a control circuit producing random trains of unidirectional impulses.

Fig. 2 shows a scheme similar to Fig. 1 except that two gaseous triodes are used in cooperative relation to produce the driving impulses.

Fig, 3 is another embodiment of the invention using two gaseous triodes in which the motor windings are included in the plate circuits of the tubes.

Fig. 4 is' a diagrammatic illustration of the type of motor to be used with the control circuits shown in the foregoing figures.

While the invention is susceptible of various modifications and alternative constructions, we have shown in the drawing and will herein describe in detail certain preferred embodiments, but it is to be understood that we do not thereby intend to limit the invention to the specific forms disclosed, but intend to cover all modifications and alternative constructions falling within the spirit and scope of the invention. as expressed in the appended claims.

Referring more particularly to Fig. 1 which illustrates one of the simpler embodiments of our invention, it is seen that the main control element is a triode H! containing a cathode l2, a plate l4, and a grid IS. The triode is preferably gas filled although modified characteristics,

t which may be desirable under certain conditions, are obtainable using a vacuum tube. The output circuit of the tube including the cathode l2 and the plate I 4 is connected in series with a power source supplying terminals It and it'll and with a motor winding 22 having an inner terminal 24 and outer terminal 26. The inner terminal 24 is preferably connected to the cathode l2 as shown. The input circuit of the tube including the grid H3 and the outer terminal 26 is bridged by a capacitor 28 which enables a negative charge to be built up on the grid It. In order to provide a path to enable the charge to leak from the grid terminal of the capacitor 28, such capacitor is shunted by means of a resistor 3B and, if desired, by a variable resistor 32 enabling the control of the rate of leakage.

Referring now to Fig. l, it will be seen that the winding 22 of a driving motor 23 is wound about a magnetic pole structure having poles 34 and 30. The latter poles produce a diametrically oscillating field which acts upon a rotatable armature 38. It is obvious from an inspection of Fig. 4 that the reluctance path coinposed of the poles 3t, 36, and the magnetic arm ature 38 varies widely as the armature is rotated, being of a maximum value every 180 of rotation. The motor as thus far described is of a type known in the art which may be operated either by applying alternating voltage or pulsating direct voltage across the terminals 2% and 28. Its operation will be made clear by assuming that a pulsating direct voltage is applied. With the armature 38 in the position shown, the initial impulse will cause the armature to move in a direction of alinement with the poles and 36. Because of the inertia of the armature. it will not come to rest in an alined position but will tend to overtravel or coast beyond such position. In addition, by the time that the rotating armature 38 reaches the position of alinement, the

magnitude of the current flowing through the coil 22 is either zero or greatly reduced from its initial value thereby facilitating the overtravel so that upon reenergization of the winding 22 the motor has covered approximately 180 of rotation. A subsequent electrical impulse causing a strong torque impulse results in a recurrence oi the foregoing and the completion of one revolution. An additional factor which promotes rotation in the same direction for one or more revolutions upon application of a series of impulses is the distortion of the magnetic field caused by the rotation of the magnetic armature therein. as practically that rotation of the armature distorts the field so that it has rotating as well as diametrically oscillating components.

Using a motor of a type thus far described, it is of course possible that the motor will come to rest in a position of alinement with the poles 34 and 35 whereupon reenergization of the winding 22 will have no rotative effect. The resultant failure of starting torque may be overcome by the addition of an auxiliary, preferably light duty, winding 40 supplied from the alternating voltage source through terminals 42 and 34. The latter winding is wound on poles 46 and M; which are arranged at an angle, for example somewhat greater or less than 90 with respect to the poles 34 and 35 previously referred to. Although the poles may for purposes of convenience be spaced at 90 intervals, the resultant field produced thereby may be greater or less than 90 because of unlike resistance and reactance in the circuits It can be shown theoretically as well ill of windings 22 and 40 or because of various differences in the magnetic characteristics of the poles. In the case of the motor structure illus trated, should the armature 38 come to rest at the point of minimum reluctance with respect to poles 34 and 36, poles 46 and 48 would produce sufiicient rotative efiect to move the armature from such dead-center position. In a motor of this type the armature rotates initially in a direction to decrease the magnetic reluctance of the flux path. The direction of rotation upon receipt of an initial impulse may be counterclockwise as illustrated in Fig. 4, but it is to be noted that if the armature 38 were initially oriented at 90 to the position shown, the motor would start in a clockwise direction.

It is not necessary in order to practice our invention that the driving motor make the specific form outlined immediately above. It is desirable merely that the motor used be susceptible to excitation by electrical impulses, that the direction of rotation upon receipt of an initial impulse be dependent upon the relative position of the armature and exciting coils upon receipt of an initial impulse, and that provision be made to prevent stalling.

Since the characteristics of gaseous triodes are well known in the art, it will suffice to say that conduction will be initiated between the cathode and plate when the plate is sufiiciently more positive than the cathode as to sustain the discharge, and when the instantaneous biasing potential of the grid with respect to the cathode does not exceed cut-off. It is further important to note that in a gaseous triode the grid loses control once conduction starts between cathode and plate, such conduction ceasing when the cathode plate potential becomes insufficient to support the discharge. The following types of commercially available grid controlled rectifiers have been used among others in the circuits described herein: 5C21, C6J, CE306, ELCSJ. It will appear obvious to one skilled in the art that many other types of tubes may be used with equal success, the particular tube best suited depending to a large extent on the current capacity of the motor being excited.

Operation of circuit of Fig. 1

In operation, an alternating voltage of convenient magnitude and of a frequency which may be 60 cycles is applied across the input terminals I8 and 20. The same alternating voltage source may be used to heat the cathode l2 although for purposes of simplicity n0 specific means for heating the cathode is included in the diagram. Upon the terminal l8 becoming positive with respect to the terminal 20, current flows through the output circuit of the discharge tube I0 and the motor winding 22. Under such conditions, a voltage drop occurs in the winding 22 causing the potential of terminal 26 of the winding 22 to swing in a negative direction with respect to the cathode l2. Since under conditions of conductivity the internal resistance of the tube between the cathode l2 and the grid I6 is negligible, a charge of electrons will pass from the cathode 12 to the grid 16 tending to charge the upper plate 28a of the capacitor 28 negatively with respect to the cathode. Since the build-up of the charge does not occur instantaneously, and since the charge does not remain fixed but is constantly being dissipated it has been found that a number of successive half cycles of current will flow through the tube before the condition is attained wherein the grid is negatively biased to cut-off simul taneously with the plate being charged positively causing conduction to cease. During the time that the tube is in a conductive state, a train or succession ofv impulses will be conducted. As the tube becomes non-conducting for a short period, the train will come to an end. Subsequent periods of conduction will cause subsequent trains of impulses to be passed by the tube. The duration of each impulse train is indeterminate because of the various factors to be discussed, althoughthe average duration may be controlled to large extent by adjustment of the circuit constants.

Various factors prevent the tube from remaining in the cut-oil condition. A major factor is the leakage of the charge from the capacitor 28 through the shunt resistor 39-42 which causes the grid to become less negative. In addition, the voltage drop across Winding 22 does not remain constant but varies both in accordance with the applied. voltage and with the counter E. M. F. generated by the rotation of the armature The magnitude of the latter varies instantaneously depending upon the instantaneous position of the armature and upon its instantaneous rate of motion. Thus, after a few cycles of nonconduction, the bias existing on the grid will again be such as to again allow conduction of unidirectional impulses of current between the cathode in the counterclockwise direction. The armature will thereupon continue to rotate for a short time depending upon the rotational inertia and the nature of the load applied to the shaft after which it will come to rest at some indeterminate position. Assuming that the armature comes to rest at approximately 90 to the position shown in Fig. 4 subsequent conduction of impulses in the control tube will cause the ensuing rotation to occur in the opposite or clockwise direction. Succeeding trains of impulses will cause the armature 38 to rotate in first one direction and. then in another, depending upon the position of the armature when a given impulse is received.

It has been found that the constantly varying potential existing between the cathode and the grid is dependent upon at least four factors, all of which are subject to constant substantially independent variation. As the result, the condition of conduction or nonconduction as a function of time is not susceptible to theoretical analysis. One of the factors which controls the instantaneous grid bias is the instantaneous potential of the alternating voltage supply terminals l8 and. A second determining factor is the state of charge on the capacitor 28, the latter being determined to a large extent by the time constant of the R.-C. circuit consisting of capacitor 28 and the shunting resistor 3t-32. A third factor determining the voltage on the cathode I2 is the counter E. M. F. shunted in the winding 22 by the rotation of the armature 38. Such E. is proportional to the rate of change of magnetic flux linking the winding 22 as the magnetic armature revolves. Still another factor effecting the bias of the tube IE! is the instantaneous condition of conductivity or nonconductivity.

Of the foregoing factors, only the first factor, namely that of line voltage variation, is predeterminable with respect to time. The remaining factors, being indeterminable either singly 6 or in combination, coact to cause the length of a train of rectified impulses and. the periodicity of the trains to be unpredictable. In order that the impulse trains may be sufficiently long to cause the motor to rotate through a series of complete revolutions, it has been found desirable to use values for capacitor 28 and resistor ss sz which produce an R.-C. circuit having a time constant which is appreciably longer than the periodicity of the alternating line voltage applied to terminals l8-2ll. It hasalso been found to be desirable to choose a value for resistors 38-42 which allows the tube to be fired upon the existence across suchresistance of a potential approximately halfofthe maximum potential attained at any time during the operation. Because of the relative simplicity of the circuit and the small number of components used, it has been found in practice that values of capacitance and' resistance may be readily determined, using atube of given characteristics, by the process of trial and'adjustment. If desired, the capacitance 28 as Well as the resistor 32 may be variable to accomplish such adjustment.

The use of the circuit of Fig. 1 with the motor of Fig. 4 connected in the manner shown will cause random reversal of the armature. However, if desired, a phase shifting impedance may be included in series with the motor winding 40. Such impedance may, for example, consist of a capacitor 5d shown dotted in Fig. 1. If such capacitor isof extremely low impedance as compared with the impedance of the winding 40, there will be a tendency for the armature to rotate predominantly in one direction which'may be-desirable under some circumstances. If, on the other hand, the impedance of the capacitor is relatively great, intermittent unidirectional operation of the motor will be produced. If desired, the capacitor may be shunted with a resistor to vary its effect. It'is to be understood, however, that normally such series impedance is dispensed with and the circuit is utilized to produce completely random reversals of motor If desired, two circuits of the type illustrated in Fig. 1 may be used cooperatively to produce a continuously reversing electric drive. One embodiment of such a scheme is shown in Fig. 2. Upon inspection of the latter figure, it will be seen that two gaseous triodes Eli and 62 are used having the motor winding 22 in the cathode circuit. In this modification a center tap 25 divides the winding 22 into sections 220. and 22b. Section 220. is preferably wound in such direction with respect to section 2212 that the motor will rotate oppositely depending upon which of the sections is energized when the auxiliary winding 40 is used.

The tube as includes a plate 64, a grid 66 and a cathode 63 while tube 62 contains a plate 70, a grid 12 and a cathode I4. Alternating line voltage is applied to the outer circuit of the tube through terminals 16 and 18. In the case of each of the tubes, such output circuit defining the path of ourrent flow includes a winding of the driving motor,

in the input circuit of the tube between the grid. 66 and the center tap 25 of the motor winding 22..

asoaies 4' In the case of tube t2, the same function is performed by an R.-C. circuit including capacitor 84 and shunting resistor 85.

In order to promote alternative operation of the two tubes, it is preferred to apply a capacitor 86 between the respective cathodes 68 and 14. The eiiect of such capacitor may be illustrated by assuming that the tube 60 is initially conductive while the tube 62 is not. Under such circumstances, because of the voltage drop through the section 22a of the winding 22, the cathode B8 of the tube 60 will be charged to a more positive potential than the cathode '14 of the tube 62. Let it be assumed, for example, that the resultant charge across the capacitor 86 is 100 volts with the polarity indicated in Fig. 2. Next, let it be assumed that the voltage on the grid 12 of the tube 62 becomes such that the tube 62 begins to conduct. Under such circumstances, because of the voltage drop through the section 221) of the winding 22, the voltage on the cathode 14 becomes highly positive, for example, to the extent of 100 volts. Since the right-hand side of the capacitor 86 being connected to the cathode M also suffers a positive swing in potential of 100 volts, the voltage on the left-hand side of the capacitor will instantaneously become 200 volts positive. This will cause the cathode it of the tube 68 to become more posi tive than the plate 64, and thus conduction from the cathode to the plate of the tube 60 will cease. Thus, it is seen. that the initiating or conduction in the tube 62 has the effect of cutting on conduction in the tube 60. Similarly, it may be shown that the reestablishing of conduction in tube to will serve to put the tube 62 into a nonconducting state.

The operation of the remainder of the circuit will not be discussed in detail since each of the two symmetrical portions operates in the same manner as discussed in connection with Fig. 1. Also, as in the case of Fig. i, the state of grid bias is a function of the instantaneous excitation potential, the state of charge on the capacitors 8i? and t l, the counter E. M. F.s generated I in the motor windings, and the condition of conductivity or nonconductivity of the associated tube. These factors combine to produce random alternative energization oi the sections 22a and 22b of the motor winding 22. Although the circuit of 2 may be used with the motor of Fig. 4i without addition of auxiliary series impedance, we prefer as shown in 2 to use a series capacitor H in with the auxiliary This has the effect of displacing of the flux produced by the winding Ml, producing a clockwise or counterclockwise rotating field, depending upon whether the section 22a or of the main winding is energized.

Operation of circuit of Fig. 2

The operation of the foregoing embodiment may be summarized follows: Upon application of alternating voltage to the terminals i6 and iii, one of the tubes or will begin to conduct, thereby energ either section 22a or 22'!) and causii rotation of the motor armature. The pass ility of both tubes initially conducting is slight because of the unavoidable differences in tube characteristics, resistance, capacitance and winding inductance of the right and left-hand portions of the circuit respectively. After a given one of the tubes has conducted for a short space of time producing a train of successive current impulses, the grid of such tube will become sufficiently negatively charged with respect to the cathode to cause conduction to cease. By this time the remaining tube will become conductive producing a train of impulses in the associated motor winding. Because of the effect of the capacitor 86 discussed above there will be little or no tendency for the tubes to conduct simultaneously.

It has been found in practice that the capacitance of the capacitor 86 must be adjustedwith respect to the inductance of the associated motor windings so that a condition of resonance is not set up. Such resonance has the effect of producing periodic and alternate energization of the motor windings rather than the random unpredictable energization normally desired.

Dual tube impulse generator with motor windings in the plate circuit The same type of motor operation outlined in connection with Fig. 2 may be achieved by placing the sections 22a and 22b of the main motor winding 22 in the plate circuits of gaseous discharge tubes at and 92 rather than in the cathode circuits. Referring to Fig. 3, a gaseous discharge tube as includes a plate 94, a grid 96, and a cathode 538, while a companion tube 92 includes a plate Hi9, a grid I02, and a cathode IM. Alternating line voltage is supplied to the output circuit through terminals I05 and H38, the path of current flow in each of the tubes being defined by the cathode, the plate and one of the sections 22a or 22b of the motor winding 22.

In the present embodiment, the grid of each tube is coupled directly to the associated cathode, the tube input circuit including a parallel ReC. circuit but not including the motor winding. In the case of tube 90 the R.-C. circuit includes a capacitor lit and a resistor H2, this function in the case of tube 92 being performed by the capacitor H4 and the resistor H6.

In the foregoing circuits (Figs. 1 and 2) a given grid is coupled to a point of intermittently negative-going potential with respect to the cathode by means of one of the capacitors 28, 80, or 84 included in the R.-C. circuit. Since, in the circuit of Fig. 3, the grid and associated cathode are directly coupled by the R.-C. circuit and the potential across the motor winding is not directly available to vary the grid-cathode potential, a diiferent source of negative going potential must be used. The varying plate potential is utilized for this function in the present embodiment, coupling to the grids being accomplished through capacitors H8 and I20. Thus, the grid 96 of the tube 9:) is coupled to the plate tilt of the tube 52 while coupling capacitor 12!) is connected between the grid I02 of the tube 91. and the plate 94 of the opposite tube.

Operation of the circuit of Fig. 3

Although the circuit of Fig. 3, as in the case of the foregoing embodiments, contains several factors making its operation at a particular instant rather indeterminate, such operation may be understood in general by considering the following sequence of events: Upon application of line voltage to terminals Hit and H18 there will be a tendency for current to flow in both of the tubes Site-92. However, because of the various unavoidable differences in circuit constants between the two symmetrical portions of the circuit, one of the tubes will begin to conduct slightly before, and to a slightly greater extent than the remaining tube. Let it be assumed that such conduction takes place first in tube 90. Because of the voltage drop in the section 2211 of the motor winding, the potential on the plate 94 will swing negatively. Since the voltage across capacitor lie cannot change instantaneously, a negative potential will be induced on the grid 102 of the tube 92 preventing conduction therein. The negative potential on the grid will not be maintained, however, because of the leakage of charge through the grid resistor lid and eventually the grid (62 will become suificiently positive to allow conduction to take place in tube 92. Such conduction will in turn cause the potential of the plate mo of tube 92 to swing in a negative direction. The latter will cause the grid 95 to swing negatively because of the coupling capacitor H8. Thus, the initiating of conduction in the tube 92 tends to halt conduction in the tube 90 in the opposed portion. of the circuit.

In order to further insure that the conduction in tubes 90 and 92 takes place alternatively and to generally improve the operation of the circuit, we prefer to include a capacitor 33 shunted across the motor winding 22 and interconnectin the plates 94 and I00 of the gaseous tubes. The eiiect of such capacitor in this circuit is completely analogous to its efiect in the circuit of Fig. 2. Sufiice it to say that the initiating of conduction in one of the tubes causes a drop of potential on the plate of the remaining tube to such an extent that the plate voltage on the remaining tube is reduced to a point where a discharge can no longer be sustained within the tube.

As in the case of Fig. 2, we prefer to use an impedance, for example capac tor 50, in series with the auxiliary winding 40. This has the effect of displacing the phase of the flux produced by the winding 40 thereby producing either a clockw se rotating field or a counterclockwise rotating field, depending upon which of the sections 2211 or 221) happens to be energized. It will be undenstoo-d, however, that the use of such capacitance is by no means essential and that random reversing armature rotation will be obtained whether or not such series impedance is used.

For the sake of ready understanding, the invention has been described as being primarily directed toward a continuously reversing drive for a lapping tool or similar rotating device. It will be apparent to those skilled in the art, however, that the circuits herein disclosed are also applicable to other types of loads requirin random successive trains of electric impulses.

We claim as our invention:

1. A reversible electric drive of random periodicity and direction comprising: a reversible motor having an exciting winding, a relatively movable magnetic armature responsive to a train of electrical impulses applied to said exciting winding, and means to prevent said armature from being stalled with respect to said exciting winding; a gaseous discharge tube having a grid, plate and cathode, said windin being in series with said cathode; a source of alternating potential applied to said plate and in series with said winding; acapacitor between. said grid and the cathode side of said source; and a resistor shunting said capacitor to produce a circuit having a large time constant with respect to the period of the alternating potential source, said elements being connected so that the grid bias on said tube is de pendent upon the instantaneous resultant of the voltage across said capacitor and the voltage across said winding so that trains of current impulses of indeterminate duration are supplied to said winding.

2. An impulse generatin circuit for a motor having a first control winding, a second control winding and a relatively rotatable armature, each of said windings being individually effective to cause rotation of the armature upon excitation by a train of electrical impulses, comprising: first and second gaseous discharge tubes each having grid, a plate and a cathode; terminals for application of an alternating voltage source, said voltage being effective to cause flow of current from the cathode to the plate of each of said tubes, said windings being in series with the plate-cathode circuits of said tubes respectively and subject to the flow of plate current therein; means including a capacitor for coupling said grids to a source of potential which is intermittently negative-going with respect to the potential of the associated cathode thereby applying a negative charge to said grids intermittently effective to cut off the fiow of current in the associated plate-cathode circuit; a resistor for allowing said charge to leak off said grid thereby temporarily to restore conduction; and a capacitor interconnecting l ke current-carrying elements of said tubes to promote alternative conduction therein.

3. A reversible electric drive producing rotation of random duration and direction comprising an electric motor having a displaced phase winding, a forward winding and a reverse winding; forward and reverse gaseous discharge tubes each having a grid, a plate and a, cathode; a source of alternating voltage having a first terminal and a second terminal; said cathodes being connected to said first terminal of said source and said windings be ng connected in series with said plates respectively and to said second terminal of said source, coupling capacitors interconnecting the grid of each of said tubes to the plate of the remaining tube, respectively, an R.-C. circuit in-- cluding a resistor and a capacitor joining the grid and cathode of each tube; and a capactior interconnecting said plates tending to stop conduction in one of said tubes upon the initiation of conduction in the remaining one of said tubes.

4. A reversible electric drive of random periodicity and direction comprising: an electric motor having a displaced phase Winding, a forward winding, and a reverse winding; forward and reverse gaseous discharge tubes each having a grid, a plate and a cathode; a source of alternating voltage, said plates being connected to one terminal of said voltage source and said forward and reverse windings being connected in series with said cathodes respectively and to the remaining terminal of said source; capacitors coupling said grids to said remaining terminal for charging said grids; resistors shunting said capacitors respectively and enabling electrical charge to be dissipated from said grids respectively at a predetermined ratc; and a capacitor interconnecting said cathodes for increasing the tendency toward alternative conduction in said tubes.

5. An' electric drive comprising an electric motor of the type havin an exciting winding and an armature reversible in direction of rotation upon excitation by successive trains of elec trical impulses, means including a rectifier having a control grid, cathode, and plate for supplying successive trains of current impulses to said motor winding, the latter being included in the plate-cathode circuit of the rectifier, a source 11 of electrical potential which is intermittently negative-going with respect to the potential of said cathode, a capacitor coupling said grid to said potential source, and resistor means for leakin charge from said grid to cause said rectifier to conduct intermittently.

6. A power supply circuit for use with an electric motor of the type having an exciting winding and a relatively rotatable magnetic armature, rotation of said armature occurring upon excitation of said winding by a train of current impulses, comprising: a discharge tube having an input circuit and an output circuit, said output circuit including said winding, a source of alternating potential applied to said output circuit, said input circuit including a resistor-capacitor network connected in series therewith for causing said output circuit to be intermittently conducting for intervals appreciably longer than the cyclical period of said source.

'7. The combination with an electric motor having an exciting coil and a relatively rotatable magnetic element, rotation of said element occurring upon excitation of said coil by a train of current impulses, of means including: a gaseous discharge tube having a grid, plate and cathode; a. source of alternating potential, said tube, potential source and coil in series relation; and means including an R.-C. circuit for causing the bias of said grid to swing negatively upon conduction in said tube, the time constant of said R.-C. circuit being greater than the cyclical period of said alternating source thereby causing successive chains of current impulses to be passed by said tube.

8. In combination with a reversible electric motor having an exciting coil, a relatively rotatable magnetic armature, and an angularly positive auxiliary coil to prevent stalling of the armature in a position of minimum reluctance, of means including: a gaseous discharge tube having a grid, plate and cathode; a source of alternating potential, said tube, potential source and excited coil being in series relation; and means including an R.-C. circuit for causing the bias of said grid to swing negatively upon con-- duction in said tube, the time constant of said R.-C. circuit being greater than the periodicity of said alternating source thereby causing successive trains of current impulses to be passed by said tube.

9. A. circuit for supplying current to a reversible motor of the type having an exciting winding and a relatively movable magnetic armature, the direction of relative motion de-- pending on the positioning of said winding and armature upon application of an initial current impulse to said winding comprising: a gaseous discharge tube having a grid, plate and cathode, said winding being in series with said cathode; a source of alternating potential applied to said plate and in series with said winding; a capacitor between said grid and the cathode side of said source; a resistor shunting said capacitor, the magnitude of the resistor and capacitor being so related that trains of current impulses of indeterminate duration are supplied to said winding.

10. A current impulse generator for use with an electric motor having a control winding and a relatively rotatable magnetic element, the direction of rotation upon excitation by a train of electrical impulses being dependent upon the relative orientation of the winding and magnetic element upon receipt of the first of said impulses, comprising: a gaseous discharge tube having a grid, plate and a cathode; said control winding in series with said cathode; first and second input terminals for application of an alternating potential source, the plate of the tube being connected to said first terminal and said winding being connected to said second terminal, a capacitor coupling said grid with said second terminal, a resistor connected across said capacitor, the time constant of the resistorcapacitcr circuit being appreciably greater than the cyclical period of the alternating current source to cause the bias of said grid to intermittently cut off conduction in said tube.

11. An impulse generating circuit for a motor having a first control winding, a second control winding and a relatively rotatable armature, each of said windings being efiective to cause rotation upon excitation by a train of electrical impulses comprising: first and second gaseous discharge tubes each having a grid, a plate and a cathode; an alternating voltage source, said plates being connected to one terminal of said source, said windings being connected in series with said cathodes respectively and supplied by the remaining terminal of said source; capacitors coupling said grids respectively to said remaining terminal of said source for causing said grids to assume an increasingly negative charge with respect to the associated cathode upon flow of current from said cathode thereby to stop such flow; and resistors shunting said capacitors respectively, for allowing the charge to leak off the associated grid thereby restoring current flow, the time constant of the grid circuit being appreciably greater than the period of the voltage source.

12. An impulse generating circuit for a motor having a first control winding, a second control winding and a relatively rotatable magnetic armature, each of said windings being effective to cause rotation upon excitation by a series of electrical impulses comprising: first and second gaseous discharge tubes each having a grid, a plate and a cathode; an alternating voltage source having a first terminal and a second terminal, said cathode connected to the first terminal of said source; said windings being connected in series with said plates respectively and connected to the second terminal of said source; coupling capacitors connecting the grid of each of said tubes to the plate of the remaining tube respectively; an R.-C. circuit having a resistor and a capacitor in shunt relation coupling the grid of each tube to the associated cathode, the magnitude of the resistance and capacitance being so related that the time constant of said R.-C. circuit is appreciab y greater than the period of the voltage source.

13. A reversible electric drive of random periodicity and direction comprising: an electric motor having a displaced phase winding, a forward winding, and a reverse winding; forward and reverse gaseous discharge tubes each having a grid, a plate and a cathode; a source of alternating voltage having first and second terminals, said plates being connected to said first terminal of said source and said forward and reverse windings being connected in series with said cathodes respectively and to said second terminal of said voltage source; capacitors cou pling said grids to said second terminal for charging said grids; resistors shunting said capacitors respectively, enabling electrical charge to be dissipated from said grids respectively at a 13 predetermined rate; and a capacitor interconnecting said cathodes for increasing the tendency toward alternative conduction in said tubes, the capacity of said interconnecting capacitor being sufficiently low with respect to the inductance of the motor windings so that the rate of motor reversal is not appreciably controlled thereby.

14. A reversible electric drive producing rota tion of random duration and direction com prising; an electric motor having a displaced phase winding, a forward winding and a reverse winding; forward and reverse gaseous discharge tubes each having a grid, a plate and a cathode; a source of alternating voltage, said cathodes being connected to one terminal of said source and said windings being connected in series with said plates respectively and to the remaining terminal of said voltage source; coupling capacitors interconnecting the grid of each of said tubes to the plate of the remaining tube respectively; an R-C. circuit including a resistor and a capacitor joining the grid and cathode in each of said tubes; and a capacitor interconmeeting said plates tending to stop current fiow in one of said tubes upon the initiation of current fiow in the remaining one of said tubes, the capacity of said interconnecting capacitor being sufiiciently low with respect to the inductance of the motor windings so that the rate of motor reversal is not appreciably controlled thereby.

15. An electric drive comprising, in combination, an electric motor having a control winding and capable of starting in one direction or the other depending upon the position of the rotor upon excitation of the winding by the initial one of a train of electrical impulses, an alternating current supply, means including a rectifier having a control grid, cathode, and plate energized by said supply for supplying current to said winding, the latter being connected in the plate-cathode circuit of the rectifier, a source of grid bias for said rectifier, said bias source including a capacitor connected to the grid for the buildup of a negative charge thereon as a result of a flow of electrons from said cathode, resistor means for leaking charge from the grid, said rectifier having a connection to said motor Winding responsive to the voltage and providing ad- Number ditional bias which is dependent on the resultant of the applied and induced voltages in said winding, conduction through said winding being in the form of trains of rectified impulses except when the net bias is such as to produce cutoff, the time constant of the capacitor leakage circuit being large as compared to the period of the alternating current supply so that the trains of electrical impulses passed by said tube are cut ofi only momentarily at random intervals.

16. An electric drive comprising, in combination, an electri motor having a control winding and capable of starting in one direction or the other depending upon the position of the rotor upon excitation of the winding by the initial one of a train of electrical impulses; an alternating current supply; means including a rectifier having a control grid, cathode, and plate energized by said supply for supplying current to said winding, the latter being connected in the plate-cathode circuit of the rectifier; a source of grid bias for said rectifier, said bias source including a capacitor and means for leaking charge from the same and a connection to said motor winding responsive to the voltage therein; whereby the flow of current in said rectifier at an instant is controlled by (a) the charge on said capacitor, (2)) the voltage induced in said motor winding as a result of motor rotation, and (c) the voltage of said supply; the time constant of said capacitor leakage circuit being large as compared to the period of the alternating current supply so that trains of electrical impulses are passed by said rectifier, conduction being L momentarily interrupted at intervals by the buildup of charge on the capacitor.

JAMES R. WALKER. RICHARD H. COOK.

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

Welch Jan. 18, 1938 Lamb Feb. 10, 1942

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