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Патент USA US2411357

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Nov. 19, 1946.
5. BERTRAM
2,41 1,357
SPLIT-PHASE SERVOIOTOR CONTROL
Filed Oct. 3} 1944
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Patented Nov. 19,‘ '1946
_ 2,411,357
UNITED stares PATET
~Ft‘lCE
2,411,357
SPLIT-PHASE SERVOMOTOR CQNTRGL
Sidney Bertram, San Diego, Callil, assignor to.
the "United States G overnment, as represented
by the Secretary of the Navy
Application October 3, 1944, Serial No. 556,989
:11 Claims. (oi. 172—-278)
This invention relates to a servo-slave mecha
nlsm, and particularly to a circuit for regulating
the rotating ?elds of polyphase or split-phase
induction motors.
There are many instances where it is most de
sirable and convenient to provide a follower
means, where it is, at the same time, impossible
to load the means to be followed. It is one of the
objects of the invention to provide a circuit, in
cluding a two-phase or split-phase. induction mo
tor, which will drive the following means in such
manner that it follows the movement of the de
vice whose movement is to be repeated or ampll-‘
9
among which may be listed the following: (1)
training devices which may be
to follow
a rotating member such as a compass card, (2)
industrial applications such as the maintenance
of constant tension on moving belts, (3) opera
tion of doors, drinking fountains, safety devices,
etc, where interruption of the light beam may
he made to result in a shifting or sliding rather
than avrotating held, and. (4) any photo-cell
actuated servo~mechanism
In the drawing:
He. 1 is a schematic diagram of the invention.
Fig. 2 is a series of curves laid out along a
_
It is well known in the art that the rotating 15 common abscissa and showing voltages in various
I portions of the circuit.
field produced by the stator windings in a two
In Fig. 1 is shown a conventional two-phase
phase induction motor is the resultantoi two
motor in which the four terminals represent those
independent ?elds, which are produced by sepa
connected to the windings of the two—phase
rate windings. It is also familiar to those skilled
‘winding of the stator. Terminals l, l on the
in the art that the torque produced in such a mo
motor are fed through a phase-shifting capacitor
tor is dependent upon the relative magnitudes of
tied.
fl and the other winding is normally led, through
an inductance S, at terminals 2. Alternative
1y. a conventional split-phase motor might be
constant magnitude, maximum torque is pro»
duced when the two ?elds are as electrical de 25 used in place or the two~phase unit, in which
case the phase-shifting capacitor would he elimi
these ?elds and their electrical phase displace
ment with respect to one another.
Assuming
grees out of phase with one another; and mini
mum, or zero, torque is produced when the two
ilelds are in phase. Phase differences interme~
nated. A gas tube
which may he of the con
ventional RCA 2056 “'I‘hyratron” type, is con- ‘
nected in series with the primary of transformer
produce intermediate torques.
The second
"When one phasev of the stator winding leads the 30 ‘l across the supply terminals 3,
cry of transformer ‘l is also connected across
second phase, rotation in'a given direction results.
the second phase of the stator
at ter
When the phase relationship is reversed, so that
minals
‘3.
_
a
the ?rst phase lags the second phase, rotation in
The gas tube is controlled
a g'zhoto-cell 8,
the other direction is produced. Generally, then,
the invention comprises means for governing this ' which may he of the RCA Q2‘? trace, connected
to its grid. Grid bias for the
tube 6 is sup
phase relationship in a novel manner such that
plied through resistor
potentiometer it,
the motor drives the follower means in one direc
while the shield grid is tied to the thesis. This
tion or the other, or when no phase difference
bias is supplied across potentloninh l 9 by means
exists, not at all.
of a transformer ii, whose gorlrmvy is connected
in its simplest form, the invention comprises
across the voltage supply 1 ilnals El, El. Al»
a photohcell connected to fire a trigger-acting or
though not necessary to the i
tioning of the
discharge tube of the “Thyratron” type when the
means to he followed causes a change in the light
connected in
series
invention,
with-and
a capacitor
on the high
l2 may
side or” potentiometer
intensity which governs the photo-cell. The
cathode-anode path or the discharge tube is con is ill for a purpose to be desert7 .
In operation, the voltage sup heel
terminals
nected in series with the primary or a transformer
9, i, being fed through capacitor: leads the ap
whose secondary is placed across one phase of
plied voltage by substantially Qt". The other
the stator windings of the motor, so that when
phase winding of the motor
‘at a
‘
?red, the discharge tube takes control of the
voltage supplied to that phase of the stator and 50 terminals 2, 2 through intluc succ
tube 6, when
is not
, , ~
supplies such voltage in opposite phase to that
circuits the primary oi’ transfo
normally supplied through a separate inductance
these conditions. the inducta .ce
when the discharge tube is not firing.
0nd phase or" the motor with a voltage approxi
The device as described has very broad appll~
In that supplied at
cation and may he used for a variety of purposes, £55 mately 93° out of phase
terminals 3, i. ‘This is true since when the tube
‘ diate 0° and 90°
~
agrees?
6 is not ?ring and the primary of transformer ‘i
is effectively open circuited, the secondary oi’
the transformer, although connected across the
second phase of the motor, has very little e?ect,
nals 2, 2 (curve C). Curve F shows a large com
ponent of phase reversed to that in curve C being
applied to terminals 2, 2 of the motor. However, .
the D. C. component ‘has been removed with the
result that the zero axis has been effectively
its impedance being arranged to be very high.
shifted. The voltage actually applied to termi
The motor then runs in'a direction determined
nals 2, 2 when the tube is ?ring is the resultant
by the (in effect) direct connection of the second
' of that induced ‘in the secondary of the trans~=
phase of the motor across the supply ‘voltage.
former l (curve E)’ and that supplied by re
This is explained by the fact that the motor
winding across terminals 2, 2 is, of itself, highly 10 actance 5, and is illustrated in curve F. It
should, of course, be noted that this latter com
inductive and the ,effect of inductance 6 is to
ponent is of the same phase as that supplied by
cause only a lowering of the applied voltage
such reactance to terminals 2, 2 when the tube
rather than shifting its phase.
'
is not ?ring (curve C), but that its magnitude
The photo-cell 8 is so arranged that when light
falls upon it, the current flow causes a substan 15 has been considerably reduced because, under
?ring conditions, reactance 5 is a relatively high
tial change in the grid bias on gas tube ti, so that
impedance. In any event, the resultant line fre—
when its plate becomes positive with respect to
quency component applied to terminals 2, 2 when
the cathode, the tube ?res and the primary of
the tube is ?ring (curve F) is opposite (180°) in
transformer l is e?ectively connected directly
across the supply voltage during positive excur 20 phase to that applied when it is not ?ring (curve
C)._ 0f even more importance is the fact that
sions. of thevoltage. The resulting D. C. (rec
the
line frequency component of the voltage thus
ti?ed) component voltage appears across the sec
applied to terminals 2, 2 under these conditions
ondary of transformer ‘l as a large line frequency
is also 90° out of phase with that applied at ter
component, plus harmonics which have no effect
on the resulting motor torque. Transformer 1 25 minals I, l (curve B), and thus again maximum
torque isproduced. However,- it is to be noted
is so phased that when tube 6 is ?ring its output
that the torque thus produced is in opposite di
is in the opposite phase (180°) to that supplied
rection to that produced when terminals 2, 2
through inductance 5. Since the impedance of
are supplied through inductance 5 ‘(curve C).
transformer l is very materially reduced while.
tube 6 is ?ring, the motor is supplied witha volt '30» Somewhere between these limiting conditions,
age of such reversed phase, and the inductance’ ' ' operation of the device produces no torque be
5 appears as a relatively high impedance. The
application of this voltage, reversed in phase, to
. cause the resultant voltage applied to terminals
' 2, 2 is equal to zero. In this case, the component
supplied from inductance 5 exactly cancels that .
terminals 2, 2_ of the motor, causes a reversal in
35 supplied from the-secondary ‘of transformer ‘I,
the direction of its rotation;
and the motor comes to rest.
'
The actual operation may be better understood
The curves in Fig. 2, although generally illus
by studying the curves in Fig. 2. Curve A repre
trating the respective voltages, are not intended
sents thevoltage which is supplied to the termi
to be as accurate as those which might be ob
nals 3, 3 by the external supply. Curve B repre
sents the voltage applied to terminals i, l regard— 40 tained from‘an oscillograph. However, they are
intended to and do illustrate the operation of the
less of operation of the photo-cell and gas tube,
invention, for which purpose highly accurate
and it will be noted that it is 90° out of phase
plots, including the various harmonics, are un
with'the supply voltage of curve A, due to the
necessary.
‘
action of capacitor 6.
Curve C represents the voltage which is ap 45 Although the above description includes the
principal features of- the invention, its usefulness
plied to terminals 2, 2 when tube ii is not firing.
may be considerably increased by an auxiliary
In this case, since inductance 5, as has been
capacitor i2. This capacitor, included in the
stated, has little effect upon the phase of the
grid circuit of gas tube 6, adds an A. C. voltage
applied voltage, the curve shows that the volt
age supplied to terminals ‘2, 2 is of the same phase 50 component which leads the plate voltage by sub
as the supply voltage of curve A, but reduced in
stantially 90°. The use of such a capacitor results
in the ?ring‘ of the gas tube 6 earlier in the pos
magnitude. Under these conditions, the voltage
itive portion of the cycle, as the photo-cell 8 be
supplied to terminals 2, 2 (curve C) is 90° out of
comes increasingly conductive. ‘ Hence, the
phase with that supplied to terminals i, i (curve
average length of time during which the tube is
B) and maximum torque is thus produced with 55 ?ring
is made to depend upon the action of the
the appropriate sign. Curve D shows the volt
photo-cell;
and the voltage supplied to motor
ageappearing across the primary of transformer
terminals 2, 2 is caused to shift in phase grad
7 when tube 6 is not ?ring. This voltage is im
ually rather than abruptly. Stated another way,
duced therein by the action of the secondary con
there is a gradual shift in phase from a condi
60
nected to terminals 2, 2. When tube 6 ?res, the
tion where motor terminals 2, ,2 are supplied
' recti?ed voltage across the primary of trans
solely from inductance 5 (as in curve C), to a
former l is as illustrated in curve E and is seen
condition where the gas tube takes over control
to consist of a series of positive pulses. Speé
due to its ?ring for substantially one-half of
ci?cally, the pulses of greater amplitude repre
sent the voltage across the primary of trans 65 each cycle. At one point between these limits,
i. e., for some particular intensity of light falling
former ‘l during those half-cycles when tube 6
on the photo-cell 8, the resulting voltage applied
?res. The pulses of smaller amplitude represent
to terminals 2, 2 will be of greatly reduced mag
the voltage during the alternate half-cycles and
nitude and in phase with that supplied to tenni
' therefore are the same as the positive half-cycle
nals l, i. At this point, the motor will have no
70
pulses shown in curve D. Under these condi
torque andwwill remain stationary. By varying
tions, the voltage induced in the secondary of
the light falling on the photo-cell, the circuit is
transformer l is shown by curve F and is‘ opposite
in phase to the voltage in the primary (curve E), ‘
but with its line frequency component substan
tially 90° out of phase with that supplied to termi
thus enabled to drive the motor in either direc
tion, or to bring it to a full stop, with the torque
75 roughly proportional to the change in intensity.
a,411,ss7
.
5
_
I
It should also be noted that for most e?lcient
operation, the supply voltage should be con
6
3. In combination with mechanism as de
scribed in claim 1, a capacitor connected in se
ries with said ?rst mentioned means.
4. In combination with mechanism as de
siderably larger than is normally required by
the motor. This will allow” the choice of in
ductance 5 with anim‘pedance large compared
to that of the motor when the tube is ?red. This
Cl
provides an additional advantage in thatthe
scribed in claim 1, means for supplying grid
voltage to said tube with a phase substantially
.diilerentfrom that supplied at saidsource.
gas tube may be operated at higher voltages, and
correspondingly lower currents are required for
5. ‘A servo mechanism comprising a source of
operation. This practice is necessarily limited 10 ‘alternating voltage, a split-phase motor, one
winding of said motor being connected across
by ‘the con'dition‘wherean exceedingly high volt-'
a said source,
age might cause the‘ tube to ?ash over in a man
ner not consistent with the determining grid w
voltage. Obviously the voltage and current
must be maintained within the limits of the 15
tube rating.
There is thus provided an e?ective and simple -
servo-slave mechanism which is capable of ac-v
curately repeating] or amplifying any desired
- ‘ motion.
20
an impedance connected in series
with a second winding of said motor across said
source, a grid-controlled gas tube, control means
connected to the grid of said tube, a transformer,
said tube and one winding of said transformer
being connected in series across said source, the
other winding 0! said trasformer being connected
across said second winding of said motor to sup
v ply a voltage e?ectively 130° out of phase with‘
the voltage from said' source when said tube ?res.
6. A mechanism described in claim 5 in which
said control means comprises a photo-cell.
7. In a mechanism as described in claim 5,
enables the motor to realign such forces and 25 means for supplying grid voltage to said tube
with a phase substantially diil’erent from that
again bring them into the desired relationship.
supplied at said source. I
The applications discussed herein are in no
8. A servo mechanism comprising a source of
~way intended to illustrate‘ all of the uses to
alternating voltage, a two-phase motor. one
which the device may be put._ They are repre
sentative only and many more will immediately 30' phase of said motor being connected across said
source, an impedance, said impedance being con
occur to those skilled in the art.
nected in series with the second phase of said
I claim:
~
motor
across saidv source, a grid-controlled gas
,1. A servo mechanism comprising a source of
‘ tube, control means connected to the grid of
alternating voltage, an armature, means con
\As was\brie?y mentioned above. any element
which exhibits mechanical distortion due to ex
terna1 forces can easily be arranged to control
the light falling on the photo-cell, which in turn
nected across said source for producing a ?rst 35 said tube, a transformer, said tube and one wind
ing 01' said transformer being connected in seriesv
magnetic ?eld, an impedance, second means con
nected in series with said impedance across said
source for producing. a second magnetic ?eld
displaced with respect to said first magnetic ?eld, '
both oi! said ilelds acting on said armature, ~a. 40
.across said source, the other winding 01' said
transformer being connected across said second
phase oi’ said motor to supply a voltage e?ectively
180° out 01' phase with the voltage from said
coupled to said tube, a transformer, said ‘tube
and one winding of said transformer being con
nected in series across said source, the other
9. A mechanism asdescribedin claim 8 in
which said control means comprises a photo-cell.
10. In a mechanism as described in claim 8, a
capacitor connected in series with said one phase
vapor-electric discharge tube, control means
winding of said transformer being connected
across said second means to supply a voltage
which is phase-displaced with respect to the
voltage from said source when said ‘tube fires.
2. A mechanism as‘ described in claim 1 in
source when said tube ?res.
of said motor.
.
_
'
11. In 'a mechanism as described in claim 8,
means for supplying grid voltage to said tube
with a‘ phase substantially diii'erent from that
which said\control means comprises a photo 50 supplied at said source.
cell.
-
4
-
'
SIDNEY BER’I'RAM.
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