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NOV. 26, 1946.
R, LEsNlcK
2,411,608
SPLIT-PHASE MOTOR FOLLOW-UP SYSTEM
Filed May '1, 1943
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Patented Nov. 26, 1946
2,411,608
UNITED ' STATES‘ PATENT OFFICE
2,411,608
SPLIT-PHASE MOTOR FOLLOW-UP
SYSTEM
Robert Lesnick, Camden, N. J ., assignor to Radio
Corporation of America, a corporation of Dela
ware
Application May 1, 1943, Serial No. 485,301
3 Claims. (Cl. 172—-239)
1
i
,
2
~
Electron discharge tubes 29 and 3| are pro
vided with their anode-to-cathode circuits con
motors and more particularly to systems for con
nected across the primaries of the transformers
trolling the speed and/or angular displacement
I5 and I1 respectively. Resistors 33 and 35 are
of the rotor of an alternating current motor in
response to variations in the position of a me- 5 provided in the cathode circuits of the tubes 29
chanical input device.
and. 3|. A voltage divider 31 is connected across
Accurate control of the speed or angular disthe A.—C. supply and is provided with a variable
placement of an electric motor is desirable in
tap 39 which is connected to the cathode circuit
many applications; for example, the control of
of the tube 29 and through a resistor 4| to the
guns, searchlights, directive radio antennas and 10 control grid of the tube 3|. A second voltage
the like. In displacement control systems it is
divider 43 is connected across the A.—C. supply
usually desirable to control the relatively large
and is provided with a ?xed tap 45 which is con
mechanical power output of a motor in response
nected to the cathode circuit of the tube 3| and
to a relatively small input such as may be 0011through a resistor 41 to the control grid of the
This invention relates to the control of electric
veniently produced by a manually operable crank 15 tube 29.
or an indicator. Direct current motors are particularly adapted to such applications as require
wide variation of.motor speed and motor torque.
However, alternating current motors are less ex- ..
pensive and alternating current energy is usually 20
more readily available than direct current. Thus,
for reasons of economy, it is frequently desirable
to employ an A.—C. motor, although the required
control circuits may be more complex than those
which would be required for aD.-C. motor.
25
It is the principal object of this invention to
provide an improved method of and means for
controlling the speed of a two phase induction
motor.
Another object is to provide an improved elec- 30
trical follow-up system.
The operation of the above described system
is as follows:
The A.—C. supply voltage causes currents to
flow through the motor windings 3 and 5, the
wi?iiirgs’l and 9 of the transformer I5, as indi
cated by the solid arrows, and the windings H
and I3 of the transformer H, as indicated by
the dash arrows. The impedances presented to
the ?ow of current by the windings ‘| and 9 and
II and I3 are functions of the conductivities of
the tubes 29 and 3| respectively. When the tube
29 is conductive and the tube 3| is cut off, current
flows through the paths indicated by the solid
arrows, causing the motor | to rotate in one
direction. When the tube 3| is conductive and
the tube 29 is cut off, current flows through the
These and other objects will become apparent
paths indicated by the dotted arrows, reversing
to those skilled in the art upon consideration of
the polarity of the winding 5 and causing the
the following description. with reference to the
motor to run in the opposite direction. The mag
accompanying drawing, of which:
35 nitude of the currents through the motor wind
Figure 1 is a schematic circuit diagram of a
ings depends upon the impedances presented by
system for controlling the energization of an
the secondary windings ‘l and 9 or H and I3.
alternating current motor, and
V
The variation in these impedances may be ef
Figure 2 is a schematic circuit-diagram of an
fected in either of two ways: If the transformers
electrical follow-up system embodying the in- 40 l5 and H are designed so as to saturate as a
stant invention.
Referring to Figure 1, a two phase induction‘
motor | is provided with phase windings 3 and
5. The phase windings are connected through
the secondary windings ‘I, 9, H and HI of a pair 45
result of the plate currents of the tubes 29 and
3|, the inductances of these secondary windings
are varied according to the conductivities of the
tubes. If the transformers l5 and H are de
signed so as not to saturate, the dynamic plate
of transformers l5 and IT to an A.—C. supply,
resistances of the tubes 29 and 3| are reflected
not shown. The secondary windings l, 9, H and
in the secondaries providing corresponding varia
|3 are connected in a Wheatstone bridge circuit
tions in secondary impedance.
It will be ap
having conjugate pairs of terminals I9, 2|, 23
parent that both of these effects may be employed
and 25. The motor winding 3 is connected to 50 together, if desired, by proper design of the
the A.—C. supply through the bridge by way of
transformers l5 and H. In any event, the mag
the terminals l9 and 2|. The motor winding 5 is
connected across the bridge at the points 23 and
25. A capacitor 21 is connected across the motor
winding 3.
nitude as well as the directions of the currents
through the windings of the motor I are con~
trolled by variations in the conductivities of the
55 tubes 29 and 3|, thus providing control of the
2,411,608
4
speed as well as the direction of rotation of the
as variable impedance elements coupled to one
of the motor windings through a Wheatstone
bridge circuit and to the other of the motor
windings as a series impedance element. A
motor. The conductivities of the tubes 29 and
3| are controlled by variations in theamplitude
oi’ A.-C. Voltages applied to the control grids
from the voltage divider 31. The resistors 33
and 35 provide automatic bias and may be ad-'
typical application of this circuit in a follow-up
‘ system is described employing conventional syn
justed so that both tubes are substantially non
conductive when the variable tap 39 is in its mid
chro devices for deriving the displacement con
trol signals.
position.
_
‘
I claim as my invention:
I
When the tap 39 is moved away from its mid 10
1. A control system including a motor includ
position, for example toward the upper end of
ing two ‘phase windings, a pair of electron dis
the voltage divider 37, the control grid of the‘
tube 3| is provided with an A.-C. voltage which - charge tubes, two transformers each provided
with a primary winding connected between the
is in phase with the A.-C. plate voltage induced
in the primary of the transformer 11. At the 15 anode and cathode of one of said electron dis
charge tubes and each provided with two sec
same time an equal voltage of opposite polarity
ondary windings, all of said secondary windings
is applied to the control grid of the tube 29.
being interconnected to ,form a Wheatstone
The impedances presented by the secondary
bridge circuit, means for applying A.-C. voltage
windings H and I3 are lower than those pre
sented by the secondaries 1 and 9, causing cur 20 to one of the phase windings of said motor
through one pair of conjugate terminals of said
rent to ?ow through the motor I, as indicated
bridge circuit and applying said voltage to the
by the dash arrows. The magnitude of this cur
other of the phase windings of said motor
rent depends upon the distance the tap 39 is
through another pair of conjugate terminals of
moved away from the center of the voltage di
vider 31. Similarly the motor may be energized 25 said bridge circuit whereby A.-C. voltages are
presented between the anode and cathode of
to rotate in the opposite direction by moving the
each of said electron discharge tubes, and means
tap 39 toward the lower end of the voltage di
for applying ‘oppositely variable A.-C. voltages
vider 31. Thus the relatively small ‘amount of
between the control grids and cathodes of said
energy required to operate the voltage divider
31 will control the‘ relatively large mechanical 30
energy supplied by the motor, both as to mag
nitude and direction.
'
-
Figure 2 shows a follow-up system incorporat
ing the motor control circuit of Figure 1. Simi
electron discharge tubes.
'
2. A control system including a motor provided
with two power input windings, a pair of elec
tron discharge tubes, two transformers each pro
vided with a primary winding connected be
lar parts of the circuits of Figures 1 and 2 are. 35 tween the anode and cathode of one of said
discharge tubes. and each provided with two sec
designated by corresponding reference numerals.
ondary windings, allot said secondary windings
A pair of synchro devices 49 and 5| are con
being connected together to form a Wheatstone
bridge circuit, means for applying A.-C. voltage
a transformer 53. The secondary. of the trans
former 53 is connected between the control grids 40 to one of the power input windings of said mo
tor through one pair of conjugate terminals of
and the cathodes of the tubes 29 and SI. The
said bridge circuit, means for applying said A.-C.
rotor of- the synchro transformer 49 is coupled to
voltage to the other power input winding of said
a source of mechanical input, such as a manually. I
nected in cascade between the A.-C. supply and
motor through another pair of conjugate ter
operable crank 55. The rotor of the synchro
device 5! is mechanically connected, as indi 45 minals of said bridge circuit, and means for
applying a variable A.-C. control voltage in op
cated by the line 51, to the rotor of the induc
posite polarities to the control grids of said elec
tion motor I.
'
tron discharge tubes.
Voltage from the A.-C. supply is transmitted
3. An electrical follow-up system including an
through the synchro devices 49 and El to the
transformer 53. The amplitude of the voltage 50 output shaft which is to be driven to a prede
termined angular position, means for producing
across the primary of the transformer 53 and
an A.-C. control voltage having magnitude and
its polarity with respect to the polarity of the
polarity related in a predetermined manner to
supply voltage depends upon the relative posi
the difference between said predetermined angu
tions of the rotors of the synchro devices 49 and
5|. The voltage induced in the secondary of 55 lar position and the actual position of said out
put shaft, a motor provided with two power input
the transformer 53 controls the tubes 29 and 3H,
windings and coupled to said output shaft, two
causing the motor to rotate in one direction or
electron discharge tubes connected respectively
the other depending upon the relative positions
to a pair of transformers, each of said trans~
of the rotors of the transformers £59 and 5!. R0
tation of the motor drives the rotor of the syn 60 .formers being provided with two secondary wind~
chro device 5! toward an angular ~position cor
ings, all of said secondary windings being
connected together to form a Wheatstone
responding to that of the synchro device 69.
bridge circuit, means for applying A.-C. volt
When the rotors of the synchro devices 49 and
age to one of the power input windings of
5! are in positional agreement, the tubes 29 and
3! ‘are equally conductive and the motor stops. 65 said motor through one pair of conjugate ter
minals of said bridge circuit and to the other '
If the crank 55 is rotated to a new position the
power input winding of said motor through an
motor I will follow, driving the rotor of the syn
other pair of conjugate terminals of said bridge
chro device '5! and any mechanical load which
circuit, and means for applying said A.-C. con
may be connected thereto.
trol voltage to the control grids of ‘said electron
Thus the invention has been described as an 70 discharge
tubes in opposite polarities.
improved control system for a two phase induc
tion motor employing electron discharge tubes
ROBERT LESNICK.
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