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Патент USA US3021081

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Feb- 13, 1952
c. E. G. BAILEY
3,021,071
SERVO SYSTEMS
Filed Oct. 25, 1956
2 Sheets-Sheet 1
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Feb. 13, 1962
C. E‘ G. BAILEY
3,021,071
SERVO SYSTEMS
Filed Oct. 25, 1956
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2 Sheets-Sheet 2
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Christopher E. G. Bailey, London, England, assignor to
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tentiometer P1 and the voltage F1 is, therefore, dependent
' I
upon the product of the positions of the shafts D1 and
‘D2. A feedback voltage F2 applied to the input of the
ampli?er A; may -be derived from any suitable .point
The present invention relates to servo systems adapted
to solve simultaneous equations.
.,
A feedback loop is shown applying an electrical varia
tion. F1 from the potentiometer P2 tothe input of the
ampli?er A1. The voltage across the terminals of the
potentiometer P2 is derived from the wiper of the po
Filed Oct. 25, 1956, Ser. No. 618,291
Claims priority, application Great Britain Nov. 9, 195
4 Claims.
,
shaft D2‘ constituting the outputqofythe second servo.
The Solartron Electronic Group Limited, Thames Dit
.
,
Patented Feb. '13, 1962
A, and an electro-mechanical transducer in the form
of amotor M2 driving a potentiometer P2 and an output
SERVO SYSTEMS
ton, Surrey, England
,
.
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according to circumstances, as shown, for instance from
The invention makes use of what are known as closed
loop servo systems, that is to say systems in which an
The loop gain of the system A1M,P1P2 depends upon
input variation applied to the input of a servo gives rise
to an output variation at the outputofthe servo, and 15 the position of the shaft D2 and if this system is to be
stable over the whole range of operation, the correspond
in which a variation dependent upon the output varia
ence'between I1 and the movements of the shaft D1 must
tion is fed back to the input of the servo in such a
be less accurate than would be desirable.
.
manner as to reduce the difference between the input and
the potentiometer P1.
output variations.
2
.
'
I
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1
FIG. 2 differs from FIG. 1 ‘in that ,the ampli?er. A
Such systems therefore comprise a
servo and a feedback path between the output and input 20 of FIG. 1, assumed to be a multi-stage ampli?er, is shown
divided into two parts AA, and BA1. The voltage ap- ~
of the servo. The-servo may be ofpany kind, such as
electro-mechanical or hydraulic for example.
'
plied from the output ofAA, to the input of BA, is
'
controlled by a further potentiometer P3 on the shaft
In such a servo system it is normally desirable to ar
range that the loop gain around the system, that is the
gain around the loop including the servo and, the, feed
D2 and the potentiometer P3 is arranged to have an
operating law that is as nearly as is practically con.
venient the inverse of that of the potentiometer P2. It
25
back path, shall be a maximum consistent with stability.
is, of course, not essential thatfthe two laws should be
the exact‘inverse of one another andindeed‘it may. be
impossible to make them so. In one example the poten
~ It is known, for the purpose of solving simultaneous
equations, to provide two or. more closed-loop servo
systems interconnected in such a way that the feedback
variation of one system is a function of the output varia
tion of the other system. The loop gain‘ around the ?rst
tiometer P2 is the sine winding of a sine-cosine poten
tiometer and the ideal law for the potentiometer P3 is
named system is then, over at least part of the range
then a cosecant whichtends to in?nity at 0°. Any ap~
of variation, less or more than the safemaximum.‘ If
proximation to a cosecant law will give an improvement ,
the ?rst-named system be arranged to ‘be stable ‘through
out its range of operation, the maximum departure from
in. comparison with the arrangement of FIG. 1.
The potentiometers P1, P2 and P3 can be regarded as
voltage generators or electro-mechanical transducers each
correspondence between the output and input variations
generating a voltage dependent upon the movements of,
of that system is greater than is desirable. This disad
the mechanically driven member coupled thereto.
vantage has‘sometimes led to the abandonment of such
interconnected systems even when otherwise they might 40 ,Referring now to FIG. 3, the ampli?er within the
broken line rectangle AA1 comprises two amplifying
have been desirable.
stages 10 and 11 and is connected through a potenti
It is the object of the present invention to provide an
ometer P3 to two valves 12 and 13 connected as a phase
interconnected system in which the disadvantage referred
splitter. The output of 12, 13 is applied to two valves
to is substantially avoided or at least markedly reduced.
According to the present invention there is provided 45 14 and 15 in push-pull arranged to feed one phaseof a
a servo arrangement for the solution of simultaneous
two-phase motor M1, the other phase of the motor being
equations comprising at least two closed-loop servo sys
tems each having an input at which variations represen
connected to terminals 16 and 17.
fed with an alternating current at 400 c./s. from a source
~
The valves 14, 15 are provided with negative feedback
two outputs, and means for introducing into the loop 50 through a transformer 18 in order to provide the damp
ing requisite in view of the high inductance of the Wind'
of one system a control dependent upon variations in
ing of the motor M1_ to which the valves are connected.
one or more of the other systems and such as to render
The motor M1 is shown as driving the wiper of ‘a po
the loop gain around the ?rst-named system more nearly
tentiometer P1 through, a' gear train 19 which also has
constant than in the absence of the said control.
The invention will be described by way of example with 55 an output shaft D1. The potentiometer P1 is centre
tapped to earth and each of its end terminals 20, 20’ is
reference to the accompanying drawings in which:
tative of one of the equations can be applied, at least '
FIG. 1 is a block circuit diagram of a known arrange
ment embodying two closed-loop electro-mechanical servo
systems,
'
I '
connected to an alternating current source at 400 c./s.
The wiper of the potentiometer P1 is coupled through
a cathode follower valve 21 and a transformer 22 to
FIG. 2 is a modi?cation of the arrangement of FIG. 1 60 the terminals of a potentiometer P2 which is also centre
.tapped to earth. The valve 21 is provided in order to
in accordance with the present invention, and
FIG. 3 is a practical circuit diagram of the circuit of
FIG. 2.
t
.
In the drawings electrical couplings are indicated by
full lines and mechanical couplings by broken lines.
In the known arrangement of FIG. 1 one electrical
variation 1, is applied to the input of a ?rst servo com
prising an ampli?er A, and an electro-mechanical trans
ducer in the form of a motor M1 driving a potentiometer
P1 and an output shaft D1 constituting the output of
the ?rst servo. Another electrical variation I2 is applied
to the input of a second servo comprisingan ampli?er
prevent the current in P2 from loading P1 and thereby
in?uencing its law.
The ampli?er A2 may be identical with AA1 and BA,
65 withthe exception that the valve 11 is coupled to the
valve 12 without the intermediary of the potentiometer
P3. One phase of the two-phase motor M2 is connected
to the output of the ampli?er A2, the other phase of the
motor being fed with alternating current at 400 c./s.
from terminals 23, 24 connected to a suitable source.
The motor M2 drives a gear train 25 having one out
put shaft D2, another driving the wiper of the potenti
3,021,071
3
4
ometer P2 and a third driving the Wiper of the potenti
ometer P3.
trically connecting said ?fth transducer between the out
put of said ?rst ampli?er portion and the input of said
second ampli?er portion.
2. An arrangement according to claim 1, comprising
means electrically coupling said second transducer to the
input of said third ampli?er portion.
The wiper of the potentiometer P2 is connected to pro
Vide the input P1.
In the example shown in FIG. 3 the input variations
I1 and I2 are alternatingcurrents at 400 c./s. varying in
amplitude in accordance with some control parameter.
3. An electro-mechanical servo arrangement compris
ing a ?rst servo system including ?rst and second ampli
?er portions each having an input and an output, a ?rst
The ampli?er AA1, BA1 is therefore A.C.-coupled. The
variations I1 and I2 may, however, be varying direct
currents, in which case a D.C.-coupled ampli?er is used
and the motors M1 and M2 are replaced by DC. motors.
If desired, the ampli?er A2 may be divided into two
electro-mechanical transducer electrically coupled to the
output of said second ampli?er portion, a ?rst potenti
ometer, means mechanically coupling said transducer to
parts, corresponding to AA1 and BAI and the voltage
applied from the ?rst part AA1 to the second part BAl
may be controlled by a potentiometer corresponding to
P3 driven by the shaft D1 and having a law which is
an approximate inverse of that of the potentiometer P1.
said potentiometer, a second servo system including a
third ampli?er portion, a second electro-mechanical
transducer electrically coupled to the output of said
third ampli?er portion, second and third potentiometers,
means mechanically coupling said second transducer to
said second and third potentiometers, means electrically
It Will also be evident that the invention can be applied
when there are more than two interconnected servo sys
tems.
connecting said second potentiometerv to the input of .
20 said ampli?er portion, and means electrically connecting
The way in which the invention can be applied to
said third potentiometer between the output of said ?rst
closed-loop servo systems other than electro-mechanical
ampli?er portion and the input of said second ampli?er
systems, for example to hydraulic systems, will be under
portion.
stood by those skilled in the art.
4. An arrangement according to claim 3, comprising
I claim:
25 means electrically coupling said ?rst potentiometer to the
1. An electromechanical servo arrangement compris
input of said third ampli?er portion.
ing a ?rst servo system including ?rst and second ampli
References Cited in the ?le of this patent
?er portions each having an input and an output, a ?rst
electro-mechanical transducer electrically coupled to the
UNITED STATES PATENTS
output of said second ampli?er portion, a second electro 30
2,784,501
Stern et al ______ _-'- ____ __ Mar. 12, 1957
mechanical transducer mechanically coupled to said ?rst
transducer, a second servo system including a third ampli
?er portion, a third electro-mechanical transducer elec
trically coupled to the output of said third ampli?er
portion, a fourth and a ?fth electro-mechanical trans 35
ducer mechanically coupled to said third transducer,
means electrically connecting said fourth transducer to
the input of said ?rst ampli?er portion and means elec
‘OTHER REFERENCES
Electronic Computers (Shannon), Electronics, August
1946, PP. 110-113.
An Automatic Simultaneous Equation Computer and
its use in Solving Secular Equations (Adcock), The Re
view of Scienti?c Instruments, vol. 19, No. 3, March
1948, pp. 181-187.
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