1. No category

Oct. 11, 1949.
s. WALD
2,484,134
_
ELECTRIC MOTOR FOLLOW-UP CONTROL SYSTEM
Filed July 1, 1947
17:‘.1.
J“
'II/IIIJ I VII/III - - - -
INVEN TOR.
Slam-y mm
2,434,134
Patented Oct. 11, 1949
UNITED STATES PATENT OFFICE.
Sidney Wald, Philadelphia, Pa" assignor to Radio
Corporation oi’ America, a corporation of Dela
fwarc
Application July 1, 1947, Serial No. 758,453
.6 Claims. (01. 318-28)
1
This invention relates to follow-up control
systems of the type in which a D. C. control volt
age, whose polarity and amplitude correspond,
respectively, to the sense and degree of a con
z
'
.
voltages tend to unbalance and distort the out
put voltage." Synchronous vibrators driven by
the line voltage are adversely affected by me
chanical vibration. and are thus unsuitable for
trolling condition, is used to control the direction 6 use on aircraft. _ A commutator driven by a syn
chronous motor would provide the preferred solu
of rotation of a two phase alternating current
tion to the switching‘ problem except for one fac
motor, and in particular to such a system which
tor which it is the primary purpose of this inven
employs a commutator driven by a synchronous
tion to' eliminate. This factor'is that when a
‘ motor to convert the D. C. control voltage into
an alternating voltage suitable for the control 10 synchronous motor is started it may “pull-in”
arbitrarily at one of two possible rotor positions.
of the motor.
‘
Consequently, the position of the rotor, and thus
A system of the general type considered is de
of the commutator, may lag or advance so as to
scribed in U. S. Patent 2,300,742, issued to T. R.
e?ectively reverse the phase of the square wave
Harrison, et al., on November 3, 1942.
In accordance with previously known systems, 15 voltage and cause the motor to rotate in a ‘di
rection opposite to that desired. In the past,
the variation of some conditions, such as the
it has been necessary to stop and start the com
quantity of heat, light, distance, or any other
mutator motor until it synchronized properly.
factor which is to control the operation of‘ some
In accordance with the present invention, an
responsive device, such as a recorder, indicator,
or the like, operates through a responsive device 20 auxiliary commutator is provided which ismnitors
to produce a small D. C. voltage representative‘ ‘the operation of the principal commutator
through a control circuit which automatically
of the condition and which becomes positive or
reverses the phase of the square wave voltage ii’
negative with respect to a reference voltage level
the commutator motor falls into synchrou-ism in
in accordance with the variation of the condition
above or below some predetermined reference 25 such a manner that the phase of the square wave
voltage would be incorrect.
value. Because the voltage produced is very small
It is therefore a further object of this inven
it is necessary to provide su?icient ampli?cation
tion to provide means for automatically correct
to drive the motor or other output device.
ing the phase of a voltage produced by a com
.A. C. ampli?ers are usually preferred over D. C.
ampli?ers, and two-phase A. C. reversing motors so, mutator which is driven by a synchronous motor.
A further object of this invention is to provide
having one phase winding energized by the com
an improved D. C. controlled-servo system.
mercial A. C. power line are likewise used in
A still further object of this invention is to
preference to D. C. motors. Consequently, it has
porvide means for controlling the operation of
been proposed to reverse or interrupt the connec
tions to the D. C. voltage source in synchronism 35 a two-phase motor in response to variations in
a D. C. potential of small amplitude.
with the A. C. line voltage to produce a square
The novel features that are considered charac
wave voltage. The latter voltage is then ampli
teristic of this invention are set forth with par
?ed and ?ltered to produce a sine wave alternat
ing current for exciting the other phase winding
ticularity in the appended claims.
The inven
of the motor. The two currents are made to have 40 tion both as to its organization and method of
operation, as well as additional objects and ad
a phase quadrature relationship and the motor
vantages thereof, will best be understood from
will then run in a given direction. As is well
the following description when read in connec
known, if the phase of one of the exciting cur
rents is reversed, the direction of rotation‘of the
motor will likewise reverse. , It will be appreciated 45
tion with the accompanying drawings, in which
Figure 1 is a circuit diagram of a device illus
trating the principle of this invention, and
that the phase of theampli?-ed current will have
Figure 2 is a detail of a portion of the device
one value with respect to the line current when
illustrated in Fig. 1.
‘
the D. C. control voltage is positive and the op
Referring to Fig. 1, reference numeral 3 in
posite phase when the control voltage is nega
tive. The direction of variation of the control 50 dicates any source of D. C. control voltage of the
type in which the D. C. potential of output lead
voltage thus controls the direction of rotation
1 varies in polarity and amplitude with respect
of the motor.
to lead 5 in accordance with the sense and de
Electronic. switching of very smallD. C. volt
gree of variation of a controlling condition with
ages is not desirable because di?erences in tube
respect to some predetermined reference value.
characteristics, circuit components and supply
2,484,134
3
By way of example, this device may be respon
position at the instant the reference line voltage
sive to changes in temperature, as illustrated in
Fig. 2, in which a thermocouple 9 is connected
between lead 5 and one end of a potentiometer
H. A battery l3 and adjusting resistor l5 are
passes through some reference value, say maxi
mum positive voltage, or in duplicate positions
displaced therefrom by multiples of 120°, the
phase of the square wave voltage will be reversed,
and motor 49 will rotate in the wrong direction.
movable contact I‘! of the potentiometer is con-7
Thus if motor 23 falls in 60° ahead of its proper
nected to lead ‘I through a suitable ?exible link
position, which it may do as it is a six pole motor,
19. Thus, if contact H is initially set at about
for example, commutator 2| will be advanced 60°
the center of the potentiometer, resistor l5 may 10 at the instant the line voltage reaches its refer
be adjusted so that at the temperature the volt
ence value, and it will be seen that this will re
age of the thermocouple is exactly balanced out
verse the polarity of the commutator output.
by the potentiometer voltage, and the potential
To correct this ambiguity automatically a
difference between leads 5 and ‘I will be zero. If
monitor circuit is ‘provided. A second commuta
the temperature decreases, lead 5 will become 15 tor 5| is provided which is identical to the ?rst
negative with respect to lead ‘I by a proportionate
commutator 2|v and driven at the same speed by
amount. If the temperature increases lead 5 will
the same motor 23. The input is a constant D. C.
become positive by a proportionate amount, since
voltage produced by a battery or by a recti?er
the two voltages are connected in series bucking.
and ?lter 63 connected to the power line. The
Leads 5 and l are connected to the input of 20 output of the second commutator is applied be
commutator 2| which constitutes switching
tween the cathode and grid of a gas-?lled tube 65
means for cyclically reversing the polarity of the
commonly known as a “Thyratron.” The cath
D. C. control voltage to produce a square wave
ode is also connected to one side of the power line
voltage. The commutator is driven by a syn
while the anode is connected to the other side
chronous motor 23 energized by the commercial 25 of the power line through coil 6'! which actuates
A. C. line applied. to terminals 25, 21. The num
reversing switch 41 when tube 65 is conducting.
ber of switching commutator segments is deter
The polarity of the output of recti?er 63 is such
mined by the motor speed, so that the frequency
that when commutator 2| is properly oriented
of the square wave voltage is equal to the line
the square wave monitor voltage applied to tube
frequency. Assuming, for the purpose of illus 30 65 will be out of phase with the A. C. plate
tration, that the “commercial" line frequency is
voltage, and the tube will remain non-conduct
400 C. P. S., as is standard on aircraft, and that
ing. If, however, in starting up, motor 23 syn
the motor 23 is a six pole motor rotating at a
chronizes in the incorrect position in which the
speed of 8000 R. P. M., or 133%; R. P. 8., three
rotor is advanced 60° with respect to the line
equal commutator segments 29, 3! and 33 will be 35 voltage, the phase of the square wave voltage ap
required. Each segment will be as nearly equal
plied to tube 65 will also reverse, and will then be
to 120° as the requirements of suitable insulation
in phase with the Thyratron plate voltage, caus
will permit. Input is applied to contacts 35 and
ing the tube to draw plate current and operate
31, spaced 120°_ apart. Output is taken from con
the polarity reversing switch 41. This switch will
tact 39 lying midway between the input contacts, 40 be held in its reversed position so long as the out
and contacts 4| and 43 spaced 60° from the input
put of the ?rst commutator 2| is reversed, and
contacts, respectively.
thus normal operation is restored automatically.
The commutator output is connected to the in
It will be understood that the polarity revers
put of an audio frequency amplifier 45 through a
ing switch 41 may be connected in any point of
reversing switch 41. The ampli?er is preferably
the circuit which will produce a reversal in the
tuned to the line frequency so as to ?lter out the
phases of the currents applied to ?eld coils 5|
square wave and produce substantially sine wave
and 53. Thus the reversing switch may be in
output current su?icient to actuate the follower
cluded in the leads 5 and 1 in the ampli?er output
motor 49. The ampli?er output is applied to one
circuit, or in the leads connecting the ?eld coil 53
?eld winding 5| of the two-phase motor 49. The 50 to the line.
other ?eld winding 53 is connected to the line.
What I claim is:
The requisite 90° phase relation between the cur
1. In a control system, the combination of a
rents applied to the two ?eld windings may be
source of D. C. control voltage whose polarity and
connected in series across potentiometer II. The
provided either by suitably designing the ampli
?er, or by inserting the necessary time delay cir
cuits in one or the other ?eld winding circuits.
Motor 49 drives any desired follow-up device
55. The movement of the rotor may, if desired,
be transmitted back to potentiometer H by a
amplitude correspond, respectively, to the sense
65 and degree of a controlling condition; a source of
alternating current, switching means for cycli
cally reversing the polarity of said control volt
age to produce a square wave voltage whose fre
quency is equal to the frequency of said alternat
ing current; and which may have a desired phase
suitable mechanical link so as to rebalance the
D. C. network. This may be accomplished, for
with respect thereto, or a phase displaced 180°
example, by mounting contact H on a carrier
from said desired phase; a two-phase motor
51 which, for example, may be in the form of an
energized by said alternating current and by a
internally threaded nut adapted to ride on a
current under the control of said square wave
screw threaded rod 59 which is rotated in one di 65 voltage, the direction of rotation of said motor
rection or the other under the control of
being determined by the phase of said square
motor 49.
wave voltage; and monitor means responsive to
It will be observed that the phase of the ampli
deviation of the phase of said square wave voltage
?er output current and thus the direction of ro
from said desired phase to reverse the phase of
tation of motor 49 is under the control of the 70 said square wave voltage, whereby the direction
phase of the square wave voltage output of com
of rotation of said motor is determined by said
mutator 2 I, and thus of the polarity of the D. C.
D. C. control voltage.
control voltage produced by device 3. If, how
2. A device of the character described in claim
ever, motor 23 does not always fall into step so
1 in which said monitor means includes an aux
that the commutator 2| is not always in a given 76 iliary commutator driven by said synchronous
2,484,184
motor for producing a monitor voltage, a tube
controlled by the phase relation of said monitor
voltage and said source of alternating current,
said tube.
3. In a control system the combination of a
source of D. C. control voltage whose polarity
3 in which said polarity reversing means includes
a switch, and means for controlling the operation
of said switch in accordance with the orientation
of the rotor of said synchronous motor.
5. A device of the characted described in claim
4 in which said means for controlling the opera
tion of said switch includes means for producing
and amplitude correspond, respectively, to the
an alternating reference voltage whose phase de
and a polarity reversing switch controlled by
pends upon the orientation of said rotor, a dis
sense and degree of a controlling condition; a
source of alternating current, a commutator 10 charge tube having its plate and cathode elec
driven by a synchronous motor for cylically re
trodes connected across said source of alternating
versing the polarity of said control voltage to
current, and means for applying said reference
produce a square wave voltage whose frequency
voltage to the grid and cathode of said tube in
such relative polarity that said tube is normally
is equal to the frequency of said alternating
current, said synchronous motor being energized’
non-conductive, said switch being in the plate
circuit of said tube.
by said alternating current; the phase of said
square wave voltage with respect to said alter
6. A device of the character described in claim
nating current being dependent upon the orien
5 in which said means for producing a reference
voltage includes a second commutator driven by
tation at synchronous speed of the rotor of said
motor, a two-phase motor energized by said alter- _ said synchronous motor.
SIDNEY WALD.
nating current and by a current under the con
trol of said square wave voltage, and polarity
REFERENCES CITED
reversing means responsive to the relationship
between the phase of said alternating current
The following references are of record in the
source and the position of said commutator to
?le of this patent:
maintain a predetermined phase between the
UNITED STATES ‘PA'I'ENTS
polarity of said control voltage and direction of
rotation of said two-phase motor independently
Number
Name
Date
of the orientation of said rotor.
2,150,006
4. A device of the character described in claim 30
Parker et al _______ __ Mar. 7, 1939