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Patented Nov. 5, i946
James W. Conklin, Indianapolis, Ind., assignor to '
Radio Corporation of America, a corporation of ~
Application February 24, 1943, Serial No. 476,902
4 Claims. ( c1. 172-239)
an angular position corresponding to that to
tems of the follow-up type and more particularly
which it is desired to operate the driven device 3.
to the prevention of operation of the control
Alternating current is transmitted through .the
member of such systems at a rate exceeding the
cascaded synchro transformers 5 and 9 to the
maximum speed capability of the driving motor.
input circuit of the amplifier l.V The amplitude
The usual servo system comprises a control input
of the input voltage to the amplifier 1 is directly
shaft, an -output shaft, means for producing con- proportional lto the difference in the angular po
trol voltage related in some predetermined man
sitions of the rotors of -the transformers 5 and 9.
ner to the difference in the angular positions of
This voltage is amplified and is applied to the
'saidshaits and a driving motor controlled by
motor I, driving the output shaft, and with it the
said voltage to reduce said difference to zero.
device 3 to Vsuch a position that .the rotor of `the
Upon rotation of the control shaft, the driving
transformer 5 corresponds in angular position
motor will operate the output shaft at the same
with the rotor of the transformer 9. When this
rate, with an angular lag depending on the con
condition is attained the voltage applied to the
stants of the system. In general, this lag in 15 input circuit oi the ampliiler "i is zero, and the
creases with increase in speed of operation ofthe
motor I is deenergized.
control member. As the maximum speed capa
Ordinarily, the driving motor is of the induc
bility of the driving motor is approached, the lag
tion or repulsion type, and hence cannot operate
increases more rapidly andthe driven shaft final
above a predetermined speed, corresponding to
_ ly falls out of synchronism with the control shaft. ~ the synchronous speed. This speed depends upon
The principal object of the present invention is
construction o1' the motor and upon the frequency
to provide an improved method of and means for
of the A.-C. supply. As mentioned above it is un
limiting the rate of operation of the control mem
desirable >to operate the control shaft at a speed
ber of a servo system to prevent operation of the
approaching the synchronous speed of the driving
control at a rate exceeding the capabilities of the 25 motor because of the resultant increase in lag, and
driven device.
the possibility that the driven shaft may fall out
Another object is to provide an improved
of step with the control member. Accordingly,
method of and means for limiting the angle of
an A.~C. motor I3 is mechanically coupled to the
lag of the output shaft with respec-t to the con
control shaft and electrically connected to Ithe
30 output of the synchro transformer 5. The cou
trol shaft.
- ~
_ A further object is to providelimproved means
pling between the motor I3 and the rotor of the
for controlling the speed of operation of the con
control transformer 9 includes gearing I5, so de
trol input shaft of a servo system in response to
signed that the synchronous speed of the motor
the angular displacement between the input and
I3 will occur at a speed of rotation of .the control
output shafts. These and other and incidental " member I I which is somewhat less than the syn
objects will become apparent to those skilled in
chronous speed of the driving motor I. In -the
the art upon consideration of the following de
normal operation of the system the output volt
scription with reference to the accompanying
age of the transformer 5 is of the order of1 per
drawing which ls a schematic circuit diagram of ' cent of the A.-C. supply voltage. This voltage,
a servo system embodying the present invention. 40 when applied to the motor I3, will produce sub-y
An A,-C. motor I is mechanically connected to
stantially no effect. However, when the angular
the load device 3, and to the rotor of asynchro
lag between the rotor of the transformer 5 and
transformer 5. The rotor o1' the transformer 5
. that of the transformer 9 4approaches 90°, the
is electricallir connected to an amplifier ‘I which
output of the transformer 5 increases to a value
is connected to the input circuit of the~ motor I. 45 of the same order of magnitude as the supply
~ "The stator winding of the transformer 5 is elec
voltage. If, at the same time, the speed of ro
trically connected to the stator windingof a sec
tation of the motor I3, due to »the operation of
ond synchro transformer S. The rotor winding
the control input device I I, is substantially equal
to the synchronous speed of said motor, a strong
of the transformer 9 is connected to an A.-C.
supply. not shown. The rotor of the transformer 50 synchronizing torque is developed which effec
â is mechanically coupled to a control device
tively resists any increase in speed. By the proper
such as a manually operable crank -I I.
selection of gear ratios, this condition can be
The system as thus far described constitutes
caused to occur at any preselected >speed oi' the
’I’his invention relates to electrical servo sys
a conventional servo system of the follow-up type. '
In operation, the control member II is moved to 55
driving motor I.
Thus the invention has been described-as an l
improved electrical servo system of the follow-up
type, including means for preventing the opera
tion of the control input member at a rate greater
than a predetermined fraction of the synchronous
speed of the driving motor. This is accomplished
by coupling an auxiliary A.-C. motor to the input
shaft, and connecting said motor to the electrical
control channel ofthe system. The arrangement
is such that the auxiliary motor reaches syn
chronism at a lower speed of operation of the
control shaft than the driving motor. At syn
chronous speed of the auxiliary motor, a strong
lock-in torque is developed, effectively preventing
any further increase in speed.
I claim as my invention:
predetermined manner to the difference in the
angular positions of said shafts, a motor coupled
to said control shaft and connected to respond to
said control signal so as to prevent operation of
said control shaft at a speed exceeding the maxi
mum speed of said driving motor.
3. A servo system comprising a driving motor,
an output shaft coupled to said motor, a synchro
transformer coupled to said output shaft, an am
pli?ier connected between the rotor winding of
said synchro transformer and said driving motor,
a second synchro transformer with its stator
vwinding connected to the stator winding of said
first synchro transformer and its rotor coupled to
15 a control shaft, a source of A.-C. energy con
i. A remoto control system including a driven
nected to -the rotor winding of said second syn
shaft, a control shaft, means for deriving an
chro transformer, and -an A.-C. motor coupled to
A.-C. control voltage proportional in amplitude
said control shaft and connected to the rotor of
to the difference in the angular positions of said
said first synchro transformer.
shafts, a control member ‘connected to said con 20
4. 'I'he invention as set forth in claim 3 where
-trol shaft and to an A.-C. motor. and means for
in said A.-C. motor is coupled to said control shaft
applying said A.-C. voltage to said motor so' as
in such a manner that .the rate of rotation of said
.to prevent operation of said control member above
A.-C. motor is a greater fraction of the synchro
a predetermined speed.
nous speed of said motor than the speed of said
2. In a remote control system of the follow-up
driving motor is of the synchronous speed of said
type. `comprising -a driving motor, a load shaft
driving motor.
`connected to said motor, a control shaft and
means for deriving a control signal related in a
ÀJaimes w. coNKmN.
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