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Патент USA US2405046

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July 30, 1946-
2,405,046
w. H. NEWELL
MOTION REPRODUCING MECHANISM
Filed Sept. 24, 1942
4 Sheets-Sheet 1
'
INVENTOR
WuJJAM H.NEWELL.
ATTORNEY
July 30, 1946.
2,405,046
W. H. NEWELL
MOTION REPRODUCING MECHANISM
4 'Sheet's-Sheet 2
Filed Sept. 24, 1942 _
-
.
INVENTOR
%ILLIAMdT/QW'
H.NEWELL
/‘ P.
ATTORNEY
2,405,046 .
MOTION REPRODUCING MECHANISM
Filed Sept. 24, 1942
4 Sheets-Sheet 3"
V///// /////////
A
INVENTOR
WlLLlAM HgNsweLL
z?
ATTORNEY
July 30, 1946.
w. H. NEWELL
2,405,046
MOTION REPRODUGING MECHANISM
Filed Sept. 24, 1942
56
-
-
4 Sheets-Sheet 4
-
519.?
INVENTOR
%ULL1AM H.NEWELL.
A TTORNE Y
Patented July 30, 1946
2,405,046
UNITED STATES PATENT OFFICE
2,405,046
MOTION REPRODUCING MECHANISM
William H. Newell, New York, N. Y., assignor to
Ford Instrument Company, Inc., Long Island
City, N. Y., a corporation of New York
Application September 24, 1942, Serial No. 459,581
8 Claims.
1
(Cl. 172—239)
2
The invention relates to motion reproducing or
following mechanism where the movement of a
primary element is to be reproduced in a sec
Since both the ?ne and coarse controls are thus
equipped the return to synchronism is controlled
irrespective of the degree of error.
Due to the fact that the two controls have
ondary or following element, and particularly to
such mechanisms in which the transmission sys~
different ratios of movement, the characteristics
of the resisting means to dampen the return
tem operates a control member for a power unit
termed a servomotor.
movement of the control contacts must be such
as to satisfy the individual requirements. In
other words resisting means must permit of more
rapid movement of the ?ne control contacts than
of the coarse control contacts, in order to get the
proper relative speed of the follower element.
For this purpose it is satisfactory to use a mag
netic drag for the ?ne control which requires
comparatively rapid rotation to generate a re
The invention is typically embodied and will be
explained in connection with electric self-syn
chronous transmission systems, and is designed to
meet the requirement of correct synchronization
in systems that employ a two speed transmission.
In such systems the motion of the member that
is to be reproduced at a distance is transmitted at
two di?erent ratios and is received by a high
speed and a low speed receiver known commonly
tarding force which is proportional to the rate
as the ?ne and coarse receivers. These receivers
of motion.
are arranged in joint control of the servomotor,
the ?ne receiver having control so long as the
damper is suitable, the escape ori?ce of which is
For the coarse control a pneumatic
properly adjusted.
error, that is, the positional discrepancy between
Other objects and advantages of the invention
will appear from the following description of the
embodiment of the invention illustrated in the
the elements, is within a certain limit, and the
coarse receiver takes control when the error ex
ceeds that limit.
accompanying drawings.
In the mechanism of this invention the energiz
Fig. 1 is a side elevation of a complete receiver
ing circuit of the servomotor includes two sets 25 assembly embodying the invention.
of contacts connected in parallel and one con
Fig. 2 is a sectional elevation of the same on
trolled by each receiver, and a circuit breaker op
the plane indicated by the line 2—2 in Figs. 1
erated by the coarse receiver opens the ?ne con
and 3.
trol circuit when the coarse receiver takes over
Fig. 3 is a plan of the same.
the control. A feed back from the servomotor
v
Figs. 4, 5, 6 and '7 are sectional plans of the
opens the contacts when the controls are satis?ed,
coarse control mechanism in the planes indicated
that is, it opens the coarse control contacts when
by the lines 4—4, 5—5, 6—5 and 'l-'l, respectively,
the error is less than the stated limit, and it opens
in Figs. 1 and 2.
the ?ne control contacts when the two elements
Fig. 8 is a diagram of the electrical circuits.
are in positional agreement.
01
Essentially the assembly consists of a coarse
In accordance with this invention the contacts
receiver motor I and a ?ne receiver motor 2 of an
of both the ?ne and coarse controls are of such
electrical synchronous transmission system, an
a character that they will absorb limited errors
electric servomotor 3 and coarse and ?ne controls
and will gradually erase the error at a controlled
for the servomotor. These elements are secured
rate when the condition which produced the error -’.~ upon a mounting plate 4.
ceases. For example an error will arise from ac
The‘ coarse receiver motor I and the ?ne
celeration of the primary element, the following
receiver motor 2 are connected to coarse and
element lagging until the servomotor is able to
?ne transmitters of the electrical synchronous
transmission system. The transmission system is
develop a speed to erase the error.
By allowing one of the contacts to yield against
,1, in
a biasing or centralizing spring, a new position
will be assumed at which the contacts will be
satis?ed, that is, at which the following element
will match the speed of the primary element, but
there will be a positional error until the biasing -.>
not shown as it may be of any suitable type, the
only requirement being that the coarse and ?ne
transmitters be driven at a de?nite ratio, for ex
ample, the coarse transmitter may make one rev
olution for thirty-six revolutions of the ?ne trans
mitter. A suitable two speed transmission system
is shown in Patent 1,122,942.
position.
The ?ne receiver 2 is of the ?ange mounted type
Braking or resisting means, however, control
and the coarse receiver l is of the ball bearing
the rate at which the error is erased so that the
mounted type. In other words the stator of the
follower is brought smoothly into synchronism. 55 former is ?xed while the stator of the latter is
means restores the yielding contact to its biased
2,405,046
3
rotatable. The shaft 5 of the ?ne receiver rotor
may be considered the ?ne primary element and
the shaft 6 of the coarse receiver rotor may be
considered the coarse primary element. These
rotors will rotate at different ratios to the move
at
spect to the inner contact 23 by the servomotor
3, the shaft 32 of which may be considered the
secondary or following element which is to re
produce the movement of the primary elements
5 and 3. In other words the incoming move
ment operates the primary contact of the servo
motor control to close the energizing circuit;
and the response of the servomotor moves the
having a 1 to 1 ratio and the fine receiver rotor a
secondary contacts to open the circuit.
36 to 1 ratio thereto, this ratio being the same as
Surrounding the bearing member [6 and bear
that between the coarse and ?ne transmitters. 10
ing thereon through anti-friction bearings, as
These receiver rotors operate controls for the
ment that is to be reproduced by the follower
element, for example, the coarse receiver rotor
servomotor.
The servomotor 3 is a single phase, condenser
shown, is a slip ring supporting drum 33 which
has a top ?ange on which the outside contacts 24
are carried by contact arms 34. A ?ange on the
type, induction motor having a squirrel-cage rotor
‘i. The two legs 8 and 9 of the stator winding 15 bottom of the drum 33 is provided with spur gear
have a common connection ill with one side of
a single phase line H, the other side being con
nected to the inner contact of each receiver con
trol, as will later be described. The opposite ends
of the legs 8 and 9 of the stator winding are con
nected to the outer contacts of the receiver con
trols by leads l2 and it, as will be described, and
teeth which mesh with a spur gear 35 on the
shaft 32 of the servomotor. Rotation of the shaft
therefore rotates the drum and hence the sec
ondary contacts 24 in the proper ratio of move
20 ment.
The drum 33 is provided with three slip rings
33a, 33b and 330 which are engaged by brushes
in a holder on an arm 36 supported from the
a condenser is is connected across the leads I2
mounting plate 4. The center contact 23 is con
and it. Therefore when the inner contact of
either control is against one of the outer con 25 nected to the ring 33a the brush of which is
connected to one side of the line through a cir
tacts, one leg of the stator winding is connected
cuit breaker under the control of the coarse con
directly to the line wire and the other leg is
trol, as will be described, and the outer contacts
connected to it through the condenser. This
23 are connected to the rings 33b and 330. The
completes an approximate two phase circuit and
the rotor turns clockwise or counterclockwise, de 30 brushes of rings 33b and 330 are connected with
pending upon which connection is made.
Telescoping partially over the upper end of the
fine receiver 2 is an inverted cup-shaped bearing
member l5 that is secured to the mounting plate
£5 and has secured on its top a similar bearing
member iii of smaller diameter. Within the hear
ing member it are housed the elements of a mag
netic drag. A squirrel-cage rotor i‘! has trun
nions i8 and it‘: on its opposite ends which are
vertically disposed in line with rotor shaft 5,
the trunnion it bearing in the top of bearing
member it and trunnion i9 bearing in the top
of bearing member I5. A collar 20 couples shaft
5 with trunnion i9. Therefore rotation of the
?ne receiver rotor produces rotation of the squir
rel-cage rotor l'i.
Rotatively mounted in the rotor ll of the mag
netic drag is a magnetized cylindrical member
25 the axis of which turns in the trunnion I8
as a bearing and has on its upper end a contact
leads 23 and i2, respectively. Through this ar
rangement when the receiver is energized, move
ment of the inner contact against an outer con
tact causes the servomotor to drive the slip ring
assembly in such manner that the inner contact
tends to be centered between the outer con
tacts.
The function of the magnetic drag is to in
crease stability of operation and reduce the syn
chronizing time by its action on the inner con
tact arm. If the movement of the outer con
tacts synchronizes- with that of the inner con
tact, the movement of the arm 22 with that of
the rotor I7 is unimpeded and the arm 22 re
mains centralized by the springs 30. If the move
ment of the secondary contacts lags for any rea
son, such as acceleration, the centralizing springs
will allow the arm 22 to rotate relative to the
rotor H to absorb the error or lack of agree
ment, and one of the centralizing springs is placed
arm 22 that carries the inner double contact 23
under a tension proportional to the error. When
contact arm 22.
holding spring 29 are such that the torque tend
ing to return the contact arm 22 from a posi
the servomotor gets up to speed and starts to
of the fine control, the outer contacts 24 being
erase the error, the magnetic drag develops an
mounted to be moved by the servomotor in re
opposing torque on the arm 22 proportional to
sponse to the incoming movement. The precise
the
speed of the member 2! in the rotor l1, and
construction for accomplishing this will be de
the return movement of the contact arm is there
scribed later.
It follows therefore that the
' fore controlled.
The rotor l‘?! of the drag device drives the
servomotor
must
attain
Synchronization with the
contact arm 22 through a yieldable connection.
?ne receiver at a gradually decreasing rate. Con
The hub of a heart cam 25 is secured to the trun
nion iii. A roller 23, urged in contact with the 60 sequently the servomotor has little tendency to
overrun or hunt.
heart cam, is carried by the follower arm 21 that
The freedom of movement of the contact arm
is pivoted at one end on a plate 28 the hub of
22 relative to the plate 28 is limited by stops 31
which bears on trunnion l8 on top of the hous
which are upstanding arms on the edge of the
ing it, and the free end of the arm is urged to
ward the heart cam by a holding spring 29 at 65 plate 28 disposed on opposite sides of the arm
22 in equally spaced relation thereto. There
tached to a lug on the opposite edge of the
,fore
the displacement of the arm 22 by pressure
plate ‘23.
'
of inner contact 23 against an outer contact 24
The contact arm 22 is connected to the plate
will be absorbed by a centering spring 33 until
28 by centering springs 3d. The contact arm is
spaced above the plate and the springs are there 70 a stop arm 31 engages the contact arm, under
which condition displacement of the plate 28 rel
fore attached at their outer ends to upstanding
ative to the rotor I1 is absorbed by the heart
arms 35 on opposite corners of the plate, their
cam. The characteristics of the heart cam and
inner ends being attached to the outer end of the
The outer contacts 24 are positioned with re
2,405,046
5
tion of displacement greater than that within
the limits of the stops 3'! is also proportional to
the extent of displacement.
The coarse receiver control takes over when a
predetermined error has accumulated. It is satis
factory, for example, to allow the ?ne receiver to
be one-third of a rotation out of agreement when
the coarse receiver contacts close. If the ratio is
36 to 1, then the accumulated error in the coarse
6
arms 43, the contacts ea suitably extending
through holes in the arms, as indicated in Fig. 8.
A predetermined movement of arm 4 will cause
contact 4! to engage one or the other of contacts
132 and move one of contacts til away from contact
59.
Slip ring 33a is connected to one of the con
tact strips 6! by lead 62, and the other contact
strip 6% is connected to one side of the line by
receiver will be 31/3 degrees. This means that the 10 lead 53. Therefore when the scissor arms are
follower element will be 31/3 degrees out of agree
closed the inner contact 23 of the ?ne control is
ment with the movement to be followed when the
connected with the line, but the movement of the
coarse receiver takes control.
rotor of the coarse receiver enough to move one
Since the coarse receiver motor I is of the ball
of the scissor arms breaks that connection.
bearing mounted type, the response of the servo 15
Lead $3 is also connected with post 58 and
motor turns the stator of the receiver, thus dif
therefore the contacts A2 are live contacts. The
ferentially neutralizing the rotation of the mag
outside contacts 55 of the control arm 4? are con
netic ?eld, wherefore the rotation of the shaft 5
nected to leads l2 and E3 in parallel with slip
represents the difference between the incoming
rings 33c and 33b and hence in parallel with the
impulse and the response. When there is no er
ror the receiver rotor and hence the shaft 5 has
no rotation, Angular movement at the proper
ratio is imparted to the stator of receiver ! by the
servomotor shaft 32 by bevel gears 38 and worm
and worm wheel ‘29. The proper ratio for the
gearing between the drum
and the worm wheel
20 outer contacts 24 of the ?ne control. The arm 49
acts as a connector to connect the outside ener
39 is the same as the ratio between the coarse and
gizing contacts 42 with the outside control con
tacts 45.
The outer ends of the centralizing springs G8
are attached to pins ‘M5 that depend from the top
plate 55, and they allow the arm $7 and hence
the outer control contacts
to yield under pres
?ne transmitters and the coarse and ?ne receiv
ers, that is, 35 to l.
sure of the arm Llf! as the error accumulates and
t‘
to absorb the error. This creates a return
The rotor of the coarse receiver drives an arm
toroue proportional to the error. This torque is
carrying the inner or primary contacts of the
"
ted by the pneumatic damper 54 which per
forms muchrthe same function as the magnetic
coarse control through a heart cam.
This arm
after a movement of a predetermined amount,
say 31/3 degrees, opens the ?ne control circuit and
at the same time or, preferably, slightly before,
drag.
The pneumatic damper consists of two moving
'- vanes
interleaved with two stationary vanes 6'3
touches one or the other of the outside or second
ary contacts of the coarse control and closesv the
coarse control circuit. In this case, as will be
seen. it is the carrier for the outside contacts that
is made to yield to absorb an error and that is re
tarded in its return from a displaced position so
that the error is erased at a rate proportional to
the error and the operation is uniform and sta
ble as it passes from the coarse to the ?ne control.
so as to form nearly air'tight compartments be
tween adiacent sides of the vanes. The whole is a
cylindrical unit, the stationary vanes being se
cured to the inner wall of the cylindrical casing.
The inner contact arm is an upstanding mem
plate 4:? and the movable vanes move together.
Air flow from one compartment of the damper
to another is permitted by vent holes ‘69 in the
ber 40, T-shape in cross-section and carrying two
double contacts at different levels, the lower con
tacts 4: being energizing contacts engageable
with outer energizing contacts 42 on scissor arms
43 urged toward each other by a spring 44. The
upper contacts 45 on the inner contact arm 49
are engageable with outer control contacts 4% on
a pivoted control arm 4'! centralized by springs 48.
The inner contact arm 43 is secured at its lower
end on a plate 49 secured on a hub rotatively
bearing on the rotor shaft 5. A heart cam 59 is
also secured on the hub above the plate 43, and
The moving vanes are integral with an axial hub
67 that turns on trunnions bearing in the plate 55
and in the top plate 68 of the damper housing.
The control plate 41 is fastened on a reduced ex
tension of the bottom trunnion.
Therefore the
stationary vanes. the rate of flow being regulated
by two screws ‘til diametrically opposite in the
cylindrical casing. By turning in the vent screws
the vent holes are constricted and the damping
torque is increased. The torque exerted by the
pneumatic damper is balanced by the pull of the
centering springs, and hence the error decreases
at a rate proportional to its magnitude.
From the above it is evident that coarse con
trol is obtained through movement of the inner
an arm 51 is secured on the end of the shaft 6
contact arm I39. When the servomotor output
and extends across the heart cam. A roller arm
differs sufliciently from the received movement,
52 which. carries the follower roller is urged to 60 for example, by more than 1/1 revolution of the
ward the cam by a spring 53 which connects the
rotor of the fine receiver motor, the inner contact
arms 5| and 52. This yieldable heart cam drive
causes the arm 49 to follow the' movement of the
arm 48 displaces one of the scissor arms.
This
action disconnects th'e ?ne control by opening
shaft 6 within the limits of movement of the arm
after which the spring 53 yields and allows the
of the contacts 65, and simultaneously energizes
roller to ride up on the cam.
At the top of the coarse control is a pneumatic
the coarse control through one of the contacts
45. The air gap between the inner and outside
the connection between the contact 58 and one
damper 54 supported on the mounting plate 4 and
energizing contacts and also between the inner
closed at its lower end by a plate 55. Depending
and outside control contacts will be properly ad
from. this plate 55 are two hexagonal posts 56 70 justed for the desired result. The circuit breaker
which support a plate 51 on their lower ends.
This plate has a bearing post 58 for the scissor
arms 63 and it supports a central ?xed contact
contacts 59, 60 act as a stop to the inward move
ment of contacts 42 under the tension of the
59 engageable with outer movable contacts 6i!
carried by insulated conductive strips 6| on the
The pneumatic damper allows but In of a. turn
of the rotor of the coarse receiver, and if the
spring 44.
aeoaoec
7
8
error exceeds that amount, the inner control
contact is held continuously against an outer
themselves to the relative positions of the pri
mary and following elements and thereby to ab
control contact by the action of the heart cam
sorb error in positional relation of the elements,
means biasing the yieldable contact members in
the direction to remove error, drag means in the
?ne control including a member attached to the
relief, and the servomotor drives at full speed
to reduce the error.
It is obvious that changes may be made in the
construction shown in the drawings and above
particularly described within the principle and
scope of the following claims.
I claim:
1. Following mechanism comprising in combi
nation with two primary elements, one ?ne and
one coarse, having a predetermined ratio of rela
tive movement and a following element, a servo
yieldable contact member and opposing its return
movement by a torque proportional to the rate
of that movement, and a pneumatic damper at
10 tached to the yieldable contact member of the
coarse control and retarding its return movement.
4. Following mechanism comprising in combi
nation with two primary elements, one ?ne and
one coarse, having a predetermined ratio of rela
motor for actuating the following element, an 15 tive movement and a following element, a servo
motor for actuating the following element, an en
energizing circuit for the servomotor having a
ergizing circuit for the servomotor having a ?ne
?ne control and a coarse control, each control
including a primary and a secondary contact
control and a coarse control, each control includ
ing a primary and a secondary contact member,
member, the respective contact members being
connected in parallel and the primary contact 20 the respective contact members being connected
members being movable by the respective primary
in parallel and the primary contact members be
ing movable by the respective primary elements
elements to close the contacts, means actuated
by the servomotor to open the contacts, one of the
to close the contacts, means actuated by the
contact members of each control being yieldable
servomotor to open the contacts, one of the con
under the pressure of its cooperative contact 25 tact members of each control being yieldable to
member to allow the contact members to- adjust
absorb error in positional relation of the ele
themselves to the relative positions of the pri
ments, means biasing the yieldable contacts in
mary and following elements and thereby to ab
the direction to remove error, magnetic drag
sorb error in positional relation‘ of the elements,
means connecting the ?ne primary element with
means biasing the yieldable contact members in 30 the yieldable contact member of the ?ne control
the direction to remove error, and means in each
and opposing its return movement by a torque
control for retarding the return movement of its
proportional to the rate of that movement, and
yieldable contact member.
a pneumatic damper attached to the yieldable
2. Following mechanism comprising in combi
contact member of the coarse control and retard
nation with two primary elements, one ?ne and 35 ing its return movement.
one coarse, having a predetermined ratio of rela
5. Following mechainsm comprising in combi
tive movement and a following element, a servo
nation with two primary elements, one ?ne and
motor for actuating the following element, an
one coarse, having a predetermined ratio of rela
energizing circuit for the servomotor having a
tive movement and a following element, a servo
?ne control and a coarse control, each control 40 motor for actuating the following element, an en
including a primary and a secondary contact
ergizing circuit for the servomotor having a ?ne
member, the respective contact members being
control and a coarse control, each control includ
connected in parallel and the primary contact
ing a primary and a secondary contact member,
members being movable by the respective primary
the respective contact members being connected
elements to close the contacts, a circuit breaker 45 in parallel and the primary contact members be
in series with the primary contact member of the
ing movable by the respective primary elements
?ne control arranged under the control of the
to close the contacts, a circuit breaker in series
primary contact member of the coarse control,
with the primary contact member of the ?ne con
means actuated by ‘the servomotor to open the
trol arranged under the control of the primary
contacts, one of the contact members of each 50 contact member of the coarse control, means ac
control being yieldable under the pressure of its
tuated by the servomotor to open the contacts,
cooperative contact member to allow the contact
one of the contact members of each control being
members to adjust themselves to the relative posi
yieldable to absorb error in positional relation of
tions of the primary and following elements and
the elements, means biasing the yieldable con
thereby to absorb error in positional relation of 55 tacts in the direction to remove error, magnetic
the elements, means biasing the yieldable contact
drag means connecting the ?ne primary element
members in the direction to remove error, and
with the yieldable contact member of the ?ne
means in each‘ control for retarding the return
control and opposing its return movement by a
movement of its yieldable contact member.
torque proportional to the rate of that movement,
3. Following mechanism comprising in combi
nation with two primary elements, one ?ne and
one coarse, having a predetermined ratio of rela
tive movement and a following element, a servo
60 and a pneumatic damper attached to the yield
able contact member of the coarse control and
retarding its return movement.
6. Following mechanism comprising in combi
nation with two primary elements, one ?ne and
motor for actuating ‘the following element, an
energizing circuit for the servomotor having a 65 one coarse, having a predetermined ratio of rela
?ne control and a coarse control, each control
tive movement and a following element, an elec
including a primary and a secondary contact
tric servomotor for actuating the following ele
member, the respective contact members being
ment, an energizing circuit for the servomotor
connected in parallel and the primary contact
having a ?ne control and a coarse control, each
members being movable by the respective primary 70 control including a pair of outside contacts and
elements to close the contacts, means actuated
an inner contact, the respective contacts being
by the servomotor to open the contacts, one of the
connected in parallel, a movable contact arm
contact members of each control being yieldable
carrying the inner contact of each control, a
under the pressure of its cooperative contact
yieldable drive connection between the ?ne pri
member to allow the contact members to adjust 75 mary element and the contact arm of the ?ne
2,405,046
control, means biasing the latter contact arm to
central position, means for retarding the return
movement of the latter contact arm to central '
position when displaced therefrom, a pair of
spring arms connected to one side of the ener
gizing circuit and having each an energizing con
tact, a circuit breaker in series with the inner con
tact of the ?ne control and arranged to be oper
ated by the spring arms, the contact arm of the
engageable with the spring arms and having an
energizing contact cooperative with those on the
spring arms, a drive connection between the
coarse primary element and the contact arm of
the coarse control, a yieldable control arm car
rying the outside contacts of the coarse control,
means biasing the control arm to central posi
tion, and means for retarding the return move
ment of the control arm to central position when
10 displaced therefrom.
8. Following mechanism comprising in combi
ergizing contact cooperative with those on the
nation with two primary elements, one ?ne and
spring arms, a drive connection between the
one coarse, having a predetermined ratio of rela
coarse primary element and the contact arm of
tive movement and a following element, an elec
the coarse control, a yieldable control arm car 15 ric servomotor for actuating the following ele
rying the outside contacts of the coarse control,
ment, an energizing circuit for the servomotor
means biasing the control arm to central posi
having a ?ne control and a coarse control, each
tion, and means for retarding the return move
control including a pair of outside contacts and
ment of the control arm to central position when
an inner contact, the respective contacts being
coarse control being disposed between and en
gageable with the spring arms and having an en
displaced therefrom.
20 connected in parallel, a movable contact arm
7. Following mechanism comprising in combi
carrying the inner contact of each control, a drive
nation with two primary elements, one ?ne and
connection ‘between the ?ne primary element
one coarse, having a predetermined ratio of rela
and the contact arm of the ?ne control including
tive movement and a following element, an elec
magnetic drag means opposing the return move
tric servomotor for actuating the following ele 25 ment of the contact arm to central position when
ment, an energizing circuit for the servomotor
displaced therefrom by a torque proportional to
having a ?ne control and a coarse control, each
the rate of movement, means biasing the ?ne
control including a pair of outside contacts and
control contact arm to central position, a pair
an inner contact, the respective contacts being
of spring arms connected to one side of the en
connected in parallel, a movable contact arm 30 ergizing circuit and having each an energizing
carrying the inner contact of each control, a drive
contact, a circuit breaker in series wtih the inner
connection between the fine primary element and
contact of the ?ne control and arranged to be
the contact arm of the ?ne control including
operated by the spring arms, the contact arm
magnetic drag means opposing the return move
of the coarse control being disposed between and
ment of the contact arm to central position when 35 engageable with the spring arms and having an
displaced therefrom by a torque proportional to
energizing contact cooperative with those on the
the rate of movement, means biasing the ?ne
spring arms, a drive connection between the coarse
control contact arm to central position, a pair of
primary element and the contact arm of the
spring arms connected to one side of the energiz
coarse control, a yieldable control arm carrying
ing circuit and having each an energizing con 40 the outside contacts of the coarse control, means
tact, a circuit breaker in series with the‘ inner con
tact of the ?ne control and arranged to be op
erated by the spring arms, the contact arm of
the coarse control being disposed between and
biasing the control arm to central position, and
a pneumatic damper attached to the control arm
and retarding its return movement.
_
WILLIAM H. NEWELL.
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