Патент USA US2411357код для вставки
Nov. 19, 1946. 5. BERTRAM 2,41 1,357 SPLIT-PHASE SERVOIOTOR CONTROL Filed Oct. 3} 1944 mgWMIPMWHI .mnw mg "1w“MmmuIn. Iy "M06 a“ 1H.) M?Y : .. NVENTOR BERT/M” ,n _. Tlll . A1" Patented Nov. 19,‘ '1946 _ 2,411,357 UNITED stares PATET ~Ft‘lCE 2,411,357 SPLIT-PHASE SERVOMOTOR CQNTRGL Sidney Bertram, San Diego, Callil, assignor to. the "United States G overnment, as represented by the Secretary of the Navy Application October 3, 1944, Serial No. 556,989 :11 Claims. (oi. 172—-278) This invention relates to a servo-slave mecha nlsm, and particularly to a circuit for regulating the rotating ?elds of polyphase or split-phase induction motors. There are many instances where it is most de sirable and convenient to provide a follower means, where it is, at the same time, impossible to load the means to be followed. It is one of the objects of the invention to provide a circuit, in cluding a two-phase or split-phase. induction mo tor, which will drive the following means in such manner that it follows the movement of the de vice whose movement is to be repeated or ampll-‘ 9 among which may be listed the following: (1) training devices which may be to follow a rotating member such as a compass card, (2) industrial applications such as the maintenance of constant tension on moving belts, (3) opera tion of doors, drinking fountains, safety devices, etc, where interruption of the light beam may he made to result in a shifting or sliding rather than avrotating held, and. (4) any photo-cell actuated servo~mechanism In the drawing: He. 1 is a schematic diagram of the invention. Fig. 2 is a series of curves laid out along a _ It is well known in the art that the rotating 15 common abscissa and showing voltages in various I portions of the circuit. field produced by the stator windings in a two In Fig. 1 is shown a conventional two-phase phase induction motor is the resultantoi two motor in which the four terminals represent those independent ?elds, which are produced by sepa connected to the windings of the two—phase rate windings. It is also familiar to those skilled ‘winding of the stator. Terminals l, l on the in the art that the torque produced in such a mo motor are fed through a phase-shifting capacitor tor is dependent upon the relative magnitudes of tied. fl and the other winding is normally led, through an inductance S, at terminals 2. Alternative 1y. a conventional split-phase motor might be constant magnitude, maximum torque is pro» duced when the two ?elds are as electrical de 25 used in place or the two~phase unit, in which case the phase-shifting capacitor would he elimi these ?elds and their electrical phase displace ment with respect to one another. Assuming grees out of phase with one another; and mini mum, or zero, torque is produced when the two ilelds are in phase. Phase differences interme~ nated. A gas tube which may he of the con ventional RCA 2056 “'I‘hyratron” type, is con- ‘ nected in series with the primary of transformer produce intermediate torques. The second "When one phasev of the stator winding leads the 30 ‘l across the supply terminals 3, cry of transformer ‘l is also connected across second phase, rotation in'a given direction results. the second phase of the stator at ter When the phase relationship is reversed, so that minals ‘3. _ a the ?rst phase lags the second phase, rotation in The gas tube is controlled a g'zhoto-cell 8, the other direction is produced. Generally, then, the invention comprises means for governing this ' which may he of the RCA Q2‘? trace, connected to its grid. Grid bias for the tube 6 is sup phase relationship in a novel manner such that plied through resistor potentiometer it, the motor drives the follower means in one direc while the shield grid is tied to the thesis. This tion or the other, or when no phase difference bias is supplied across potentloninh l 9 by means exists, not at all. of a transformer ii, whose gorlrmvy is connected in its simplest form, the invention comprises across the voltage supply 1 ilnals El, El. Al» a photohcell connected to fire a trigger-acting or though not necessary to the i tioning of the discharge tube of the “Thyratron” type when the means to he followed causes a change in the light connected in series invention, with-and a capacitor on the high l2 may side or” potentiometer intensity which governs the photo-cell. The cathode-anode path or the discharge tube is con is ill for a purpose to be desert7 . In operation, the voltage sup heel terminals nected in series with the primary or a transformer 9, i, being fed through capacitor: leads the ap whose secondary is placed across one phase of plied voltage by substantially Qt". The other the stator windings of the motor, so that when phase winding of the motor ‘at a ‘ ?red, the discharge tube takes control of the voltage supplied to that phase of the stator and 50 terminals 2, 2 through intluc succ tube 6, when is not , , ~ supplies such voltage in opposite phase to that circuits the primary oi’ transfo normally supplied through a separate inductance these conditions. the inducta .ce when the discharge tube is not firing. 0nd phase or" the motor with a voltage approxi The device as described has very broad appll~ In that supplied at cation and may he used for a variety of purposes, £55 mately 93° out of phase terminals 3, i. ‘This is true since when the tube ‘ diate 0° and 90° ~ agrees? 6 is not ?ring and the primary of transformer ‘i is effectively open circuited, the secondary oi’ the transformer, although connected across the second phase of the motor, has very little e?ect, nals 2, 2 (curve C). Curve F shows a large com ponent of phase reversed to that in curve C being applied to terminals 2, 2 of the motor. However, . the D. C. component ‘has been removed with the result that the zero axis has been effectively its impedance being arranged to be very high. shifted. The voltage actually applied to termi The motor then runs in'a direction determined nals 2, 2 when the tube is ?ring is the resultant by the (in effect) direct connection of the second ' of that induced ‘in the secondary of the trans~= phase of the motor across the supply ‘voltage. former l (curve E)’ and that supplied by re This is explained by the fact that the motor winding across terminals 2, 2 is, of itself, highly 10 actance 5, and is illustrated in curve F. It should, of course, be noted that this latter com inductive and the ,effect of inductance 6 is to ponent is of the same phase as that supplied by cause only a lowering of the applied voltage such reactance to terminals 2, 2 when the tube rather than shifting its phase. ' is not ?ring (curve C), but that its magnitude The photo-cell 8 is so arranged that when light falls upon it, the current flow causes a substan 15 has been considerably reduced because, under ?ring conditions, reactance 5 is a relatively high tial change in the grid bias on gas tube ti, so that impedance. In any event, the resultant line fre— when its plate becomes positive with respect to quency component applied to terminals 2, 2 when the cathode, the tube ?res and the primary of the tube is ?ring (curve F) is opposite (180°) in transformer l is e?ectively connected directly across the supply voltage during positive excur 20 phase to that applied when it is not ?ring (curve C)._ 0f even more importance is the fact that sions. of thevoltage. The resulting D. C. (rec the line frequency component of the voltage thus ti?ed) component voltage appears across the sec applied to terminals 2, 2 under these conditions ondary of transformer ‘l as a large line frequency is also 90° out of phase with that applied at ter component, plus harmonics which have no effect on the resulting motor torque. Transformer 1 25 minals I, l (curve B), and thus again maximum torque isproduced. However,- it is to be noted is so phased that when tube 6 is ?ring its output that the torque thus produced is in opposite di is in the opposite phase (180°) to that supplied rection to that produced when terminals 2, 2 through inductance 5. Since the impedance of are supplied through inductance 5 ‘(curve C). transformer l is very materially reduced while. tube 6 is ?ring, the motor is supplied witha volt '30» Somewhere between these limiting conditions, age of such reversed phase, and the inductance’ ' ' operation of the device produces no torque be 5 appears as a relatively high impedance. The application of this voltage, reversed in phase, to . cause the resultant voltage applied to terminals ' 2, 2 is equal to zero. In this case, the component supplied from inductance 5 exactly cancels that . terminals 2, 2_ of the motor, causes a reversal in 35 supplied from the-secondary ‘of transformer ‘I, the direction of its rotation; and the motor comes to rest. ' The actual operation may be better understood The curves in Fig. 2, although generally illus by studying the curves in Fig. 2. Curve A repre trating the respective voltages, are not intended sents thevoltage which is supplied to the termi to be as accurate as those which might be ob nals 3, 3 by the external supply. Curve B repre sents the voltage applied to terminals i, l regard— 40 tained from‘an oscillograph. However, they are intended to and do illustrate the operation of the less of operation of the photo-cell and gas tube, invention, for which purpose highly accurate and it will be noted that it is 90° out of phase plots, including the various harmonics, are un with'the supply voltage of curve A, due to the necessary. ‘ action of capacitor 6. Curve C represents the voltage which is ap 45 Although the above description includes the principal features of- the invention, its usefulness plied to terminals 2, 2 when tube ii is not firing. may be considerably increased by an auxiliary In this case, since inductance 5, as has been capacitor i2. This capacitor, included in the stated, has little effect upon the phase of the grid circuit of gas tube 6, adds an A. C. voltage applied voltage, the curve shows that the volt age supplied to terminals ‘2, 2 is of the same phase 50 component which leads the plate voltage by sub as the supply voltage of curve A, but reduced in stantially 90°. The use of such a capacitor results in the ?ring‘ of the gas tube 6 earlier in the pos magnitude. Under these conditions, the voltage itive portion of the cycle, as the photo-cell 8 be supplied to terminals 2, 2 (curve C) is 90° out of comes increasingly conductive. ‘ Hence, the phase with that supplied to terminals i, i (curve average length of time during which the tube is B) and maximum torque is thus produced with 55 ?ring is made to depend upon the action of the the appropriate sign. Curve D shows the volt photo-cell; and the voltage supplied to motor ageappearing across the primary of transformer terminals 2, 2 is caused to shift in phase grad 7 when tube 6 is not ?ring. This voltage is im ually rather than abruptly. Stated another way, duced therein by the action of the secondary con there is a gradual shift in phase from a condi 60 nected to terminals 2, 2. When tube 6 ?res, the tion where motor terminals 2, ,2 are supplied ' recti?ed voltage across the primary of trans solely from inductance 5 (as in curve C), to a former l is as illustrated in curve E and is seen condition where the gas tube takes over control to consist of a series of positive pulses. Speé due to its ?ring for substantially one-half of ci?cally, the pulses of greater amplitude repre sent the voltage across the primary of trans 65 each cycle. At one point between these limits, i. e., for some particular intensity of light falling former ‘l during those half-cycles when tube 6 on the photo-cell 8, the resulting voltage applied ?res. The pulses of smaller amplitude represent to terminals 2, 2 will be of greatly reduced mag the voltage during the alternate half-cycles and nitude and in phase with that supplied to tenni ' therefore are the same as the positive half-cycle nals l, i. At this point, the motor will have no 70 pulses shown in curve D. Under these condi torque andwwill remain stationary. By varying tions, the voltage induced in the secondary of the light falling on the photo-cell, the circuit is transformer l is shown by curve F and is‘ opposite in phase to the voltage in the primary (curve E), ‘ but with its line frequency component substan tially 90° out of phase with that supplied to termi thus enabled to drive the motor in either direc tion, or to bring it to a full stop, with the torque 75 roughly proportional to the change in intensity. a,411,ss7 . 5 _ I It should also be noted that for most e?lcient operation, the supply voltage should be con 6 3. In combination with mechanism as de scribed in claim 1, a capacitor connected in se ries with said ?rst mentioned means. 4. In combination with mechanism as de siderably larger than is normally required by the motor. This will allow” the choice of in ductance 5 with anim‘pedance large compared to that of the motor when the tube is ?red. This Cl provides an additional advantage in thatthe scribed in claim 1, means for supplying grid voltage to said tube with a phase substantially .diilerentfrom that supplied at saidsource. gas tube may be operated at higher voltages, and correspondingly lower currents are required for 5. ‘A servo mechanism comprising a source of operation. This practice is necessarily limited 10 ‘alternating voltage, a split-phase motor, one winding of said motor being connected across by ‘the con'dition‘wherean exceedingly high volt-' a said source, age might cause the‘ tube to ?ash over in a man ner not consistent with the determining grid w voltage. Obviously the voltage and current must be maintained within the limits of the 15 tube rating. There is thus provided an e?ective and simple - servo-slave mechanism which is capable of ac-v curately repeating] or amplifying any desired - ‘ motion. 20 an impedance connected in series with a second winding of said motor across said source, a grid-controlled gas tube, control means connected to the grid of said tube, a transformer, said tube and one winding of said transformer being connected in series across said source, the other winding 0! said trasformer being connected across said second winding of said motor to sup v ply a voltage e?ectively 130° out of phase with‘ the voltage from said' source when said tube ?res. 6. A mechanism described in claim 5 in which said control means comprises a photo-cell. 7. In a mechanism as described in claim 5, enables the motor to realign such forces and 25 means for supplying grid voltage to said tube with a phase substantially diil’erent from that again bring them into the desired relationship. supplied at said source. I The applications discussed herein are in no 8. A servo mechanism comprising a source of ~way intended to illustrate‘ all of the uses to alternating voltage, a two-phase motor. one which the device may be put._ They are repre sentative only and many more will immediately 30' phase of said motor being connected across said source, an impedance, said impedance being con occur to those skilled in the art. nected in series with the second phase of said I claim: ~ motor across saidv source, a grid-controlled gas ,1. A servo mechanism comprising a source of ‘ tube, control means connected to the grid of alternating voltage, an armature, means con \As was\brie?y mentioned above. any element which exhibits mechanical distortion due to ex terna1 forces can easily be arranged to control the light falling on the photo-cell, which in turn nected across said source for producing a ?rst 35 said tube, a transformer, said tube and one wind ing 01' said transformer being connected in seriesv magnetic ?eld, an impedance, second means con nected in series with said impedance across said source for producing. a second magnetic ?eld displaced with respect to said first magnetic ?eld, ' both oi! said ilelds acting on said armature, ~a. 40 .across said source, the other winding 01' said transformer being connected across said second phase oi’ said motor to supply a voltage e?ectively 180° out 01' phase with the voltage from said coupled to said tube, a transformer, said ‘tube and one winding of said transformer being con nected in series across said source, the other 9. A mechanism asdescribedin claim 8 in which said control means comprises a photo-cell. 10. In a mechanism as described in claim 8, a capacitor connected in series with said one phase vapor-electric discharge tube, control means winding of said transformer being connected across said second means to supply a voltage which is phase-displaced with respect to the voltage from said source when said ‘tube fires. 2. A mechanism as‘ described in claim 1 in source when said tube ?res. of said motor. . _ ' 11. In 'a mechanism as described in claim 8, means for supplying grid voltage to said tube with a‘ phase substantially diii'erent from that which said\control means comprises a photo 50 supplied at said source. cell. - 4 - ' SIDNEY BER’I'RAM.