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Патент USA US2411871

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Dec. 3, 1946.
Filed Nov. 2. 1942
l5 ~/
Patented Dec. 3, 1946
Gerard de Westfelt, New York, N. Y., assignor to
Sperry Gyroscope Company, Inc., Brooklyn,
N. Y., a corporation of New York
Application November 2, 1942, Serial No. 464,297
5 Claims. (Cl. 172-239)
;This invention relates to electrical servo sys
tems and refers more particularly to an im
proved type of control for the driving means of
such systems.
A servo system operates to apply a strong
driving force in response to a weak controlling
force or signal. The ampli?cation of the weak
signal may be‘ brought about by a variety of
driven object to an element controlling the out
put of the system, a servo system is adapted to
cause the driven object to repeat the position
of the controlling object, and the invention has
particular application to positional control
systems of this time because of the smooth
and reliable operation obtained. Anti-hunting
means may be included to overcome any tend
known means, such as thermionic ‘ampli?ers.
ency of the controlled object to overshoot the
.While the ampli?cation ratio of a thermionic 10 'position of rest or to hunt about that position.
ampli?er may be high such devices are not adapt
It is one object of the invention to provide
ed in their usual forms to supply a large power
A. C. ampli?er means adapted to supply a rela
tively large power output.
When higher outputs were required, certain
Another object is to provide a servo or posi
types of rotating electrical machines have, in 15 tional control system having improved driving
prior systems, been used as D. C. power ampli
means control.
?ers,~either alone or in conjunction with ther
A further object is to provide power ampli?
mionic means. The use of these machines has
cation means employing rotating machines
required that commutators and brushes be in
without introducing commutators into the
cluded in the amplifying circuit, thereby ren
amplifying circuit.
dering the ampli?er subject to the known dis
Other objects and advantages will become
advantages of commutators, including wear,
apparent from the speci?cation, taken in con
sparking and variable contact resistance.
nection-with the accompanying drawing where
These disadvantages of commutator machines
in the invention is embodied in concrete form.
are highly objectionable in amplifying appa 25 In the drawing,
ratus, which greatly magni?es any electrical
Fig. 1 is a wiring diagram of one form of con
trol system, according to the invention.
To overcome the disadvantages of prior sys
Fig. 2 is a wiring diagram of a complete po
tems, the present invention provides servo
sitional control system utilizing the improved
means comprising a power ampli?er stage which 30 means of the invention.
has no commutators in the. amplifying circuit
Referring particularly to Fig. 1, the control
and is adapted to furnish graduated and re
ling object is illustrated as hanclwheel In, al
versible control of rugged A. C. driving means
though obviously such handwheel may be re
in the form of a polyphase induction motor.
placed by any positionable memberI including
Such a motor, too, avoids the disadvantages of 35 the movable member of a sensitive instrument. I
Handwheel i0 is connected to position primary
It is known that to control polyphase motors,
l2 of transformer l4, angularly, with respect
for example, a two-phase motor, it is .only
to secondary winding l5 of said transformer.
necessary to vary or reverse one stator phase,
the other phase being
Winding i2 is connected to a source of alter
excited. 40 nating potential l6. Winding l5 therefore re
According to the invention, this control of one
ceives an induced alternating potential propor
motor phase is exercised by the output of a
tional to the angular position of winding II,
single phase alternator the strength of whose
this potential reversing in phase as the axis of
?eld current is governed by the weak signal or
winding l2 crosses a line perpendicular to the
a version thereof. To provide constant excita 45 axis of winding [5.
tion for another or other phases of the driving
The variable magnitude, reversible phase
motor, a second alternator is driven synchro
potential induced in winding I5 is applied to
nously with the control alternator (to secure
a phase-sensitive recti?er l8 which derives its
current'of the same frequency) and in order
phase discriminating properties from a connec
to provide the necessary time phase displace 50 tion to source I 6.1 Recti?er I8 supplies, as an
ment between the currents of the different mo
output. a continuous potential reversing in
tor phases the magnetic axes of the two alter
- polarity with reversal ‘of phase of the input to
nators may be angularly offset, thus obviating
the need tor phase shifting networks.
When provided with a repeat-back from the
the recti?er. Such phase-sensitive recti?ers
are well known in the art, one‘form which may
be adapted for use‘ with the arrangements or
Fig. 1 being shown in Fig. 2, to be described
hereinafter. The output of recti?er I8 is ap
plied to the stationary ?eld winding 26 of a
single phase A. C. generator 2| having a rotor
constantly driven by D. C. motor 24, connected 5
chm-transformers." _Winding 59 is ‘ center
tapped and has the central point thereof con
' nected to the cathode of balanced modulator tube
66 and the outer terminals thereof respectively
connected to the two control grids of tube 60.
Biasing means, illustrated as grid battery 62,
to D. C. source 25.
Likewise driven by motor 26, is a. second A. C.
single phase generator Z'l having a ?eld 28 con- '
‘tube 60 to bias the two sections or the tube to
stantly excited from source 25.
serve as modulators or recti?ers. The anodes or
The output
may be included in the grid-cathode circuit of
amplitude and phaserexcites ‘stator winding 3! 10 'plates of tube 60 are supplied with alternating
potential from source I6, by way of a center-tap
of generatorv 2'5, at a substantially constant
on ?eld winding 55 of A. C. generator 66. Con
amplitude and phase, excites stator winding 3i
dens‘ers 6i, 6'?’ are bridged across the two halves
of two-phase induction motor 39, having 'a
of the output circuit of tube 60. respectively, to
squirrel cage rotor 32. The second stator phase
33 of motor 3G is excited by the output of gen .15 \provide low impedance paths for the A. C. com--v
vponents of the tube outputs. The current in
erator 2i. This latter output varies in ampli
coil 65, because of the high inductance of the coil,
tude with variation of the excitation of ?eld
is substantially continuous.
winding Eli and reverses in phase with reversal
The output of generator 66 is conducted by way
of the direction of the current through wind
brushes and slip rings as to stator winding 33
ing 29.
A. C. generators 2i ‘and 2? maybe of the in
ductor type and have similar characteristics.
Either the output or the input connections are
made .by way of slip rings, depending upon
whether the armature or. ?eld is the rotating 25
member. As here illustrated the output connec
of motor 38 as in the arrangement of Fig. 1.
A. C. generator ‘38, corresponding to generator 21
of Fig. 1, may be of the same design as‘ generator
86, no connection being made to the center-tap
on its ?eld winding. The load driven by'motor
Bil-by way of gears ‘l2, "i3 is shown in Fig. 2, by
way of example, as a rotatable platform ‘85 which tion from generator 28 is by way of slip rings 23.
may mount an object having substantial iner
It is known that slip rings and brushes are much
tia, such as a gun or Searchlight. A repeat-back
more constant in operation than commutators.
Since a very small change of current in ?eld it 30 connection is shown for rotating “selsyn” wind
ing '59, including pinion ‘ll meshing with gear
may produce a large change of generated voltage
73, and shaft ‘58 connected by gearing and shaft
in a low impedance circuit, it will be seen that
ing to shaft 8h.
the device provides means for securing high am
Additional ampli?cation by thermionic means
pli?cation and relatively large power output with
out a commutator in the amplifying cincuit. 35 may be provided and it is desirable that suitable
rate taking and phase adjustment circuits be ‘in
Constantly excited generator 2? being driven by
cluded to insure that the system shall be stable
the same motor which drives generator 2i, the
and free from hunting tendencies. Such cir
frequency of the inputs to motor windings 3i and
cults are well known.
33 is the same regardless of the speed of the mo»
In operation, displacement of handwheel it
tor. The required phase displacement between an induces
voltages in the three-part winding 52 ‘of
the generator output voltages may be secured by
,“selsyn” transmitter 59 which are transmitted to
angularly displacing the magnetic axes of. the
synchro-transformer 57 to reproduce the direc
' generatorsas has been noted. For a two-phase
of the axis of transmitter winding 5i‘ as a
motor this‘displacément is 90° and with similar
generators this displacement may be obtained at; corresponding direction of vthe resultant ?eld of
three-part winding 58 of receiver 5?. Winding
by relatively positioning the two rotors at this
thereby receives an induced voltage propor
angle on the driving shaft.
tional to its angular displacement from the nor
In operation; angular displacement of hand»
mal to said ?eld direction, said induced voltage
wheel it or other controlling object rotates wind-=
ing l2 and thereby, through described interme 50 being of reversible phase, as described in con
diate means, varies the direct current in wind-'
ing it of alternator 28. This current is zero or
a minimum when the axis of winding'l? is per»
1lriectillm with the operation of transformer id of
placementoi the axes of windings l2 and it, and ‘
the direction of this torque is reversible with re
controlling the current, in winding 33 of motor 3t.
ing three part winding 52, connected by three
made responsive to a factor having a distinctive
value at stand-by, such as rotor speed or torque.
As many changes could be made in the above
Since the plate circuits of tube 3e are supplied
with alternating potentials of the same ireouency
pendicular to that oi‘ winding id, and a maximum ‘
when the two axes are parallel. The current in 55 as the input signal, the balanced modulator is
rendered phase sensitive, as is known to those
winding 36 of motor 39 being constant and the
skilled in the art, and a continuous current will be
current in winding 33 being proportional to the
supplied to one half or the other of the ?eld
current in winding 2d, (but of much greater am
winding $5 of A. C. generator as, dependent upon
plitude) motor so exerts a torque tending to dis“
place load dd in proportion to the relative dis 60 the phase of the input to tube ?t, thus reversibly
While the excitation of one phase of induction
motor 35’) has been described as being substan=
versal of the phase or“ the current in winding
tially constant, this excitation may, within the
Referring now to the arrangementoi' Fig. 2,
handwheel it is shown as angularly positioning 65 scope or the invention, be reduced or even elimi
nated under stand-by conditions to reduce the
the single winding‘ iii of a “selsyn” transmitter
power then consumed. Such reduction may be
ht having a relatively stationary member mount-1
conductor transmission lines
to “selsyn” reg
ceiver 57 having a relatively stationary three-part
winding 53 and a rotatable single winding es.
Selsy‘n El is operated as a locked or positioned ro
construction and many apparently widely differ
ent embodiments of this invention could be made
without departing from the scope thereof. it is
tor device by virtue of a mechanical repeat-back intended that all matter contained in the above
from the driven object. Such devices are some-'
times referred to as “signal generators” or “sync 75 description or ‘shown in the accompanying draw
ing shall be interpreted as illustrative and not in
a limiting sense.
Having described my invention, what I claim
and desire to secure by Letters Patent is:
1. In combination, a motor, a pair of alternat
positional disagreement of the controlling and
controlledobiect. and a repeat-back connection
from the controlled object to said last means.
4. In a positional control system controlling
and controlled objects, a two-phase induction
motor driving the controlled object, means for
ing current generators coupled thereto and driven
thereby to supply outputs of the same frequency
supplying current of the same frequency to the
in substantially 90° phase relationships, a two
?elds of said motor in diil‘erent time phase rela
phase motor having the ?elds thereof excited by
comprising a motor, a Pair of angularly
potentials respectively derived from the outputs 10 spaced generators
synchronously driven thereby
of said two generators, and thermionic means
to supply current to
adapted to receive a reversible phase input and
direct current, one
supply a. reversible polarity continuous output pro
of said generators being constantly excited from
portional thereto for reversibly exciting at least
said source to supply substantially constant am
one of said generators to control the magnitude 15 plitude current to one phase of said two-phase
and direction of the torque exerted by said .two
motor, means providing variable excitation for
the other of said generators in proportion to the
2. In a servo system, substantially constant
positional disagreement of said controlling and
speed driving means, a pair of alternating cur—
controlled objects, and repeat-back means from
rent generators driven thereby at the same speed, 20 the controlled object to said variable excitation
means constantly exciting one of said generators, > means.
means furnishing a reversible phase alternating
5. In a positional control system of the Ward
potential measuring the angular position of a dis
Leonard type, having controlling and controlled
placeable member, phase sensitive means for con
‘objects, a two-phase induction motor for driv
verting said alternating potential into a reversible
25 ing the latter, a pair of continuously driven A, C.
polarity continuous potential, circuit means uti
generators for supplying two alternating currents
lining a version of said last potential .to excite
to said motor at substantially 90° out of phase,
phase motor.
.the other of said generators and a two-phase mo
one of which is variable in magnitude and re
tor having the phases thereof excited by poten
versible in phase for driving said controlled ole
tials respectively derived from the outputs of said 30 ~ject
at variable speed in either direction, means
3. A positional control system comprising a
controlling object, a controlled object, a two
producing an A. 0. signal proportional in magni
tude and reversible in phase with the amount and
direction of relative displacement of said objects,
phase induction motor driving the controlled ob
a phase sensitive recti?er connected thereto
Ject, means constantly exciting one ?eld of said
for supplying D. C. to the ?eld or one of said
motor and variably exciting the other ?eld, both
generators which varies in magnitude and direc
at the same frequency, including a motor, a pair
with the magnitude and phase sense of the
of alternating current generators synchronously
signal, whereby the variable field of said motor
driven thereby in out of phase relationship, each
of said generators supplying current to one phase 40 varies from zero in either of two opposite phases
to drive said motor in a direction and speed to
of said motor and means for varying the relative
maintain synchronism. _
excitation of said generators in proportion to the
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