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Патент USA US3038989

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June 12, 1962
‘Filed Aug. 19. 1957
4 sheets-sheet 1
June‘ 12, 1962
Filed Aug. 19. 195?
4 Sheets-Sheet 4
‘781160 ©
United States Patent O?ice
Patented June 12, 1962
labor and material cost of a separate external terminal
Florian F. Yanikoski, Natick, Mass., assignor to Fenwal
Incorporated, Ashland, Mass, a corporation of Massa
Filed Aug. 19, 1957, Ser. No. 679,010
12 Claims. (Cl. 200—-140)
block and connecting wiring. Accordingly, the controller
housing is partitioned to provide a switch chamber 19
located beneath the top of the box 15, and a precision
snap switch 20 is supported in this chamber with its ter
minals 21 underlying and for easy access upon removal
of the top cover 17.
The switch chamber 19 is seen as
completely closed off from the remainder of the box ex
cept for a bottom wall opening 19a, FIG. 4, exposing the
This invention relates generally to control apparatus
and more particularly to devices for the automatic con 10 switch button 22 for engagement by the control mecha
nism. Thus a protective barrier is provided whereby the
trol of temperature, pressure, or other independent vari
opening into the ‘chamber 19 for wiring to the terminals
able. The apparatus of the invention senses and indicates
21 affords no risk of injury to the rest of the controller
the condition or position being controlled, and functions
responsive to variable change at the control or set point
The switch 20 is provided also and at its ends with
to control or operate the remote device by which the vari 15
mounting brackets 23 clamped, as at the bottom wall of
able is regulated. The invention aims to provide an in
the chamber 19, by nut and bolt or the like fastenings 24,
dicating controller which is of simple, uniform design and
one or more of which, as the spring clamping screw 24a,
compact, economical construction, while also ef?cient
may be vertically adjusting, as for desired positioning
and accurate in operation and versatile and ?exible in
relative to the switch control mechanism.
application. A further object of the invention is to pro
Referring now to FIG. 2, for temperature control the
vide an indicating controller which is designed for long
invention apparatus incorporates an hydraulic actuator
life and easy, certain manipulation and adjustment. The
comprising a closed, sealed ?uid system consisting of a
invention will be better understood from a consideration
probe or bulb 25 adapted to be mounted in or for exposure
of the following speci?cation taken in conjunction with
the accompanying drawings in which:
25 to the space or process to be controlled and connected by
FIG. 1 is an assembly view of the invention controller,
shown as ?tted for temperature control;
FIG. 2 is a larger scale, partly sectioned elevation of
a capillary tube 26 to the operating or motor bellows. For
strength and ‘corrosion resistance the bulb 25 is of stain
less steel, while for economy the tube 26 may be fashioned
of nickel plated copper. The motor bellows consists of
an annular block 27 apertured to receive the capillary 26
and also the ?lling tube 28, and having an upstanding
tubular stem 29. A bellows 30 is received over and sealed
at its lower end to an annular ?ange 29a at the base
of said stem 29. Telescoping within it is a pin or push
35 rod 31 having an upwardly projecting rounded head or
the hydraulic actuator;
FIG. 3 shows the housing from the front and with the
cover removed;
FIG. 4 is a left side view along the line 4-4 of FIG. 3;
FIG. 5 is a right side view taken along the line 5—5
of FIG. 3;
FIG. 6 is a top view of the controller as seen with the
cover and switch chamber removed;
FIG. 7 is a detailed View, on a larger scale, of the lever
contact 31a and beneath it an annular ?ange 31b over
lying the upper end of stem 29 and to which the upper end
of bellows 301 is sealed.
FIG. 8 is a perspective view with the housing ,broken
away to show the switch control mechanism;
FIGS. 9—11 are like views of modi?ed forms of the
switch control mechanism; and
Calibration rate adjustment, compensating for unavoid
able diiferences in bellows activity, is aiforded the inven
tion controller by mounting the hydraulic actuator for
shift entire to the right or left of the controller housing,
for varying the e?ective length of the lever arm of the
control mechanism which is engaged by the actuator push
FIG. 12 shows a modi?cation of the invention as
adapted for pressure control.
The controller of this invention may be characterized 45 rod. The actuator motor bellows is seen more particularly
as a control switch with indication of the condition or
position of the variable to be controlled, and with cali
brated indication also of the set point. It combines means
to be supported in an actuator housing or tube 32 ?xed or
welded at its upper end to a lateral mounting ?ange 33
such as adapting it for support as by bolts or the like
fastenings 34 at the base of the controller housing 15.
responsive to change of the variable being controlled; 50 An economical and accessible lateral adjustment of the
?ange 33 is provided by forming in the housing bottom
a switch for controlling a remote variable regulating de
generating a control or expansion-contraction movement
vice; and a control linkage or lever mechanism position
ally relating the variable sensing or actuator means and
the switch for desired set point operation of the remote
device. The controller indication of temperature, pres
sure, or position correlated with that of the set point, and
dial and pointer means are provided for adjusting the set
point to any position in the control range.
Referring now to FIG. 1, the clean, compact design
Wall an elongated slot 35 receiving the fastenings 34 and
also the actuator push rod. The slot is sealed at its outer
face by a rubber gasket 36 clamped under ?ange 33, and
it is interiorly covered by a smooth sliding nut plate 37
to which the fastenings 34 are secured and which in com
bination ‘with the ?ange and gasket 33, 36‘ afford the
desired sealing of the housing 15 and accuracy of the
calibration rate adjustment. The accurate rate adjustment
of the invention controller is seen in the enclosure and 60 is seen to ?ow from the ‘co-action of the nut plate 34 with
support of the entire apparatus in and from a single small
the housing bottom wall, which plate and wall may be
box or housing 15. The controller housing 15 may be of
smooth surfaced, and will have a smooth sliding engage
rigid metal construction and is integral except for the
ment assuring the desired shift of the actuator housing 32
in parallelism with said bottom wall.
sealed by gaskets or the like to make the housing splash 65
Economical and exterior calibration offset adjustment
and dust proof. Brackets 18 may be provided for attach
is also provided the invention controller, herein by olfset
ing the box 15 to a wall or like support, or the apparatus
adjustor nut 38 threaded in the end of housing 32 and
may be otherwise ?tted as for ?ush mounting.
having the desired swivelling and supporting ?t over the
removable front and top covers 16, 17 which latter are
The invention controller is designed also for mounting
block 27. The adjustor nut 38 is seen to be ?xed in any
the switch in a ?xed position, and so placed that its ter~
desired vertical or o?'set position by means of lock nut
minals may be directly connected to the remote tempera
38a threaded over the same and turned up to bind against
the end of tube 32.
ture regulating means, thereby saving the space and the
The actuator ?uid system 25, 26, 30 will be understood
to be ?lled through ‘the tube 28 with a suitable liquid, as
?nished to the usual manufacturing tolerance is that the
shaft tends to climb or roll around the bearing before
for example normal propyl alcohol, which expands pre
starting to slip in position. The lever shaft bearings of
dictably on heating. Expansion of the system is of course
expressed as the elongation of bellows 30 and the ad
this invention are made independent of manufacturing
vance or upward movement of push rod 31. The rod head
31a is seen to engage a bearing plate 319. A main spring
ability by forming in the bracket arms 52, 57 the up
wardly and downwardly inclined notches or slots 53, 58 of
a width slidably to receive the shafts 50, 55 and de?ned
40 is compressed between housing ?ange 33 and the
opposite face of the bearing plate and so as to stiffen or
bias the motor bellows for reliable return, and more gen
erally for sensitive and accurate two Way response.
Further in accordance with the invention, ambient com
tolerances and are assured desired centering and repeat
at their ends by formations 53a, 58a characterized by
10 straight sides intersecting at an angle to provide the
desired two-point contact with the same. The lever
shafts 5t), 55 are clamped against the non-round bearing
pensator means are provided which are arranged as an
formations 53a, 58a by a spring 59 stretched between the
integral part of the hydraulic actuator and for sealing
within actuator housing 32, and herein comprising a small
short or right hand lever arms and having the further
functions as hereinafter mentioned. The levers 49, 54
pivots will be understood by this spring clamping and
two-point bearing support to be accurately positioned
at its upper end from‘ a tube 42 supported on hearing
regardless of the wide tolerance which may be given the
plate 39. The lower end of bellows 41 is seen as con~
slots 53, 58, and to be positively held against shift of
nected to the actuator force transmitting assembly, which 20 the shafts 50, 55 in the bearing formations 53a, 58a.
comprises U strap 43 inter?tting, as through the slots 4211,
The second input of the differential switch control
or compensator bellows 41 ‘which is inverted, or mounted
for expansion oppositely to the motor bellows by support
with tube 42 and mounting a sleeve or tube 44 telescoping
device of the invention is seen as an adjusting shaft 60
with said tube 42 and closed at its upper end by a plug or‘
mounted intermediate the lower and upper levers 49, 54
pin 45. A smaller or ambient compensator spring 46 is
and for projection through front cover 16, there to mount
compressed between actuator pin 45 and the tube 42 for 25 externally accessible manipulating knob 61. The adjust
return movement of bellows 41, and a ?ll tube 47 may be
ing shaft 60 has rotary bearings which are free of unde
mounted through one of the bellows end supports.
sired backlash effects, and which comprise at the front
Compensating bellows 41 will be understood to act
bearing a lateral block 62 apertured to receive the shaft
to offset or cancel the expansion of the motor bellows 3t),
and ?xed to a block 63 extending rearwardly to the back
and so to prevent false output motion of the actuator pin
‘wall of housing 15 and supported there as by screw fas
45, under conditions of slow heating, or ambient tem
tenings 63a. Tolerances in the front bearing are taken
perature change. It will be appreciated also that varia
up by a nylon plug 64 and set screw 65 received in a
tion in the hydraulic actuator activity, such as ?owing
from modi?cation of the capillary tube 26 length and
volume, or from change of the ?lling liquid, requires a
block 62 bore passage intersecting the shaft 60 opening
therein. It will be appreciated that when set screw 65
is turned down on plug 64 su?iciently to hold shaft 60
corresponding variation in the activity of the compensator.
This may be accomplished by changing either the com
securely in position, it serves additionally to subject the
shaft to desired looking or braking action.
pensator length or the compensator liquid, or both. How
Desired dust proof sealing of housing 15 is preserved
ever, it is convenient to standardize on the same bellows
at front projecting shaft 60 by sealing the same with one
or more soft rubber doughnuts 66 snugly embracing the
shaft, and which are ordered for even closer ?t by their
compression between the front cover 16 and the lateral
block 62.
At the rear end of adjusting shaft 60 is a needle hear
41, and there is a limited choice of suitable liquids.
Accordingly, additional compensator activity adjusting
means are employed by the invention controller and com
prise one or more, herein three, steel or the like balls 48
having a low coe?icient of expansion and deposited in the
bellows 41. The balls 48 will be understood to desensitize
the compensator ?uid, so that by the use of a selected
number of the balls, and for the same compensator bellows
length and liquid ?ll, a certain desired adjustment of the
compensator activity may be had.
The switch controlling and actuating mechanism of
the invention comprises a unique differential device pro
viding a ?exible linkage which allows the switch to re
main in a ?xed position, and which is conditioned also
for prompt and accurate control movement. The dif
ing which is pretensioned automatically, requiring no
adjustment for the purpose, and which comprises a ?at
spring 67 clamped at its one end between the block 63
and the housing rear wall. The spring strap 67 is bent
outwardly at its free end, FIG. 6, and is there apertured
for reception over the adjusting shaft, and more par
ticularly for engagement against a tapered or conical seat
60a formed on said shaft 60. The rear bearing of the
adjusting shaft is thus positively held in and uniformly
centered to the desired operating position.
ferential has a ?rst input or lower lever or plate 49 55
Further in accordance with the invention, the differen
welded or otherwise ?xed near its one, herein right hand,
tial inputs, namely lever 49 and adjusting shaft 60, are
end by a lateral pivot rod or shaft 50 engaging a bracket
coupled to the output, namely lever 54 by a deformable
51 mounted at the base of the housing 15 and having
linkage capable of de?ecting or releasing on overtravel
upstanding arms 52 receiving the shaft ends. The plate
of the variable sensing or actuator means, and herein
49 is seen to extend laterally from said bracket 51 to 60 comprising a ?exible non-extensible metal band 68 which
is wound and welded at its one end around a stiff wire
overlie housing bottom opening 35 for engagement of its
longer, herein left hand, lever arm by actuator pin 45.
69 supported as by clamps 70 at the end of the lower lever
49. For engagement with the band 68 and also with
the switch 20, the upper lever 54 mounts a ?xed plastic
as shown. The bar 54 is pivoted on a rod or shaft 55 65 or other substantially frictionless pulley 71 to which is
Above and aligned with lever 49 is the output or upper
lever 54, which is conveniently formed as a vertical bar,
passed through its right hand end and supported by a
bracket 56 paralleling bracket 51. The bracket 56 is
mounted at the bottom wall of switch chamber 19 and
for receiving the shaft 55 ends through its downwardly
conveniently applied the upwardly projecting cam 72 by
which the movement of the upper lever is transmitted
to the switch 20, and which has an arm 72a hooked over
the pulley 71 and for engaging switch button 22, FIGS.
extending arms 57. The upper lever 54 is seen to extend 70 4, 5 and 8. The metal band 68 is seen to be passed over
beneath switch chamber 19 in the similar generally hori
the ?xed pulley 71 and arranged for winding on adjust
zontal attitude as lower lever 49 projects over the housing
bottom, and so as to underlie the opening through which
ing shaft 60 by reception at its other end on a stud 73a
projecting radially of a pulley 73 keyed to, said shaft 60.
For calibrated set point indication there is provided a
the switch button 22 is exposed.
One disadvantage of the usual annular shaft bearing 75 pointer 74 supported from a pulley 75 keyed to the adjust
ing shaft, which pointer extends to the rear of and has
coupled by a metal band 94 to a pulley 95 integral with
or secured to and for controlling the orientation of pulley
75. This described arrangement will be understood to
provide independent external setting as well as indica
tion of the process and overheat control temperatures.
a conical tip 74a turned down over the face of a tempera
ture scale 76 supported in box 15 and for viewing through
a transparent panel 16a in the front cover 16. For tem
perature, pressure, or position indication there is pro
vided a pointer 77 having a tip 77a extending upwardly
over the face of scale 76 in opposition to tip 74a. The
The operation of the invention apparatus will be readily
appreciated by those skilled in the art to be one in which
pointer 77 is supported on a pulley 78 loose on shaft 60
the actual temperature cycles about the set point tempera
and driven or made to follow the switch actuator move
ture. That is, upon temperature increase above the set
ment by a metal band 79 having its one end ?xed to wire 10 point the motor bellows 30v expands and drives the con
trol linkage 49, 68, 54 so as to engage by the cam 72 the
spring 80 stretched between the base of the box 15 and a
stud 78b at the opposite side of pulley 78 from said stud
78a tensions the pulley and said band 79 for desired ac
switch button 22. The shifting of the switch 20 between
the normally open or closed positions makes or breaks
the circuit by which the remote process control means,
69 and its other end received on a pulley stud 78a.
curate positioning of the indicating pointer 77.
15 which may be a heater or refrigerator, or more particu
larly a gas or steam valve, is governed. Lowering of the
process temperature to below the set point is reflected at
the controller by contraction of the bellows 30, with fol
lowing movement of the control linkage, and thereby re
lease of the switch 201 for return to its normal position.
It will be understood that the invention apparatus may
be adapted for the control of variables other than tem
perature merely by change or substitution of the variable
ting without subjecting the snap switch to excessive forces,
sensing or actuator means. In FIG. 12 the controller is
still maintains the linkage su?iciently taut to provide ac
curacy of control action and eliminate back-lash effects. 25 shown as ?tted for pressure control, and to have a hous
ing or chamber 96 supported beneath box 15 in the
It will be appreciated also that the ?oating support or loop
similar fashion as housing 32. Chamber 96 is ?tted with
closing arrangement of the spring 59 provides a tension—
a tube 97 for communication with the apparatus or sys
ing which is constant throughout the range of control
tem whose pressure is to be controlled and indicated.
Referring still to the differential switch control mech
anism, the same will be understood to incorporate also
the aforementioned lever setting spring 59, which is seen to
form a closed loop with the flexible linkage 67. In addi
tion to taking up slack in the lever pivot bearings the
spring 59 is thus seen to subject the band 68 to a tension
which, while it allows overtravel beyond the control set
The invention is characterized also by the mounting of 30 A bellows 98 is sealed in chamber 96, and more pa ticularly clamped at its outer end between the hous
ing and the bottom wall of control box 15 and for ver
tion, namely, biasing the control linkage downwardly
the same spring 59 for accomplishing still another func
tical shifting of its free lower end responsive to pres—
sure changes. The bellows movement is transmitted by
fastened to the lower lever 49 at a greater distance from 35 an actuator or push rod 99 having a stem 99a project
ing through the bottom wall opening to engage lever 49,
the lever pivot or fulcrum than on the upper lever 54.
and having a ?ange 99b to which the bellows lower end
This will be seen to unbalance the loop, and permit the
against and for following or return movement in contact
always with actuator pin 45. To this end the spring 59 is
spring 59 to drive the linkage to the position of shortest
spacing of the right hand lever arms. With the described
spring arrangement the right hand lever arms move up
wardly to close, so that the action of spring 59 is to drive
the left hand lever arms as deisred to their lowermost or
actuator pin engaging position.
The simplicity of design and versatility of application
is sealed.
For return movement of the bellows a calibrat
ed spring 100 is mounted between the control box 15
and said actuator ?ange 9912.
From the foregoing it will be appreciated that the
controller may without departing from the invention be
?tted for control of still other variables, as for example
position. For controlling position, as for example the
of the invention controller is further shown in the modi 45 position of a valve stem of an air, steam, or water-?ow
control apparatus there need be provided only a simple ac
?ed forms of FIGS. 9—1 1. It may be desired for example
to control a process at one temperature and also to actuate
a remote alarm or safety device when the process is heat
tuator linkage to the lower lever 49 from and for move~
ment of the lever directly by the valve stem.
From the foregoing it will be appreciated also that
the present invention provides a controller characterized
ed to a higher or overheat temperature. For this two
switch control with ?xed temperature differential it is nec
essary only to mount an overheat alarm switch 81 in the
by a unique combination of advantageous features, and
chamber 19 along side process control switch 20; to pivot
by a design which is as simple as the several functions
a lever 82 on shaft 55 beside lever 54‘; to tension the
of the apparatus will allow. More particularly, it is
distinguished by the arrangement of the switch in a ?xed
position and with its terminals accessible for connection
directly to the external control device, and without risk
of injury to the controller mechanism. The invention
controller is improved further by a ?exible linkage pro
lever by a spring 83 stretched between it and the lever
49; and to adapt said lever 82 for di?erential actuation
of said switch 81 by a bent strap 84 secured to the lever
end and having an arm 84a engaging the switch contact
button and an arm 84b engaging at its underface ?xed
pulley 71. A set screw 85 threaded through strap 84
and bearing against the pulley may also be provided for
?ne adjustment of the temperature differential.
viding overtravel release, and also coupled and tensioned
for positive positioning and repeatability, and freedom
from backlash effects,
Referring now to FIG. 10, if it is desired to provide vis
The invention apparatus has been shown still further
ual indication of the differential temperature at which
to be distinguished by convenient and economical calibra
the controller is set to actuate overheat switch 81, there
tion and offset rate adjusting means, by unique compensa
may be employed in lieu of lever 82 a lever 86 duplicat 65 tor activity adjusting means, and by single spring means
ing lever 54 and positioned similarly by a band 867, which
providing the control mechanism tensioning and center
ing and overtravel release.
band is fastened to Wire 69, passed over ?xed pulley 88,
and secured to adjusting shaft pulley 89 mounting over
The simplicity and versatility of the invention con
heat indicating pointer 90.
troller is shown ?nally by its modi?cation from one- to
Still another adaptation of the invention controller is 70 two~point control and indication with maximum use of
shown in FIG. 11 to comprise an adjusting shaft 91
standard and minimum number of added parts.
mounted at the opposite side of block 63 from pulley
It will he understood that my invention is not limited
89, and supported front and rear by a block 92 and spring
to the particular embodiments thereof illustrated and de—
93 duplicating, herein integrally, block 62 and spring 67.
scribed herein, and I set forth its scope in my following
The overheat setting or adjusting shaft 91 is seen to be 75 claims.
7. A controller according to claim-6 wherein said ?exi
I claim:
ble non-extensible means is a tape having reverse pass
1. In a controller of the class having an independent
ing engagement with one and being secured to the others
variable sensing actuator and a remote device regulating
of said input means and output member.
switch, a differential switch control comprising a ?rst
8. In a controller, a lever having an arm arranged as
input means engaged and shittable by said actuator, a 01
a pivoted input means, a shaft constituting a rotary input
second input means including a control point adjusting
means, a shiftable output member, a ?exible tape passed
element, an output member engaging and to shift said
reversely over the output member and secured to said
switch, ?exible non-extensible linkage interconnecting
lever arm and shaft input means, and resilient means
said ?rst and second input means and said output mem
ber such that the shift switching movement of said output 10 engaging said input means and output member to tension
said ?exible tape.
member is the sum of the input movements and resilient
9. The apparatus of claim 1 wherein said contrnl point
means engaged btwn two of said input and output means
adjusting element is manipulable to change the effective
and member and to tension said linkage whereby the
length of said ?exible non-extensible linkage.
movement of said input means is transmitted through
10. In a controller having an independent variable sens
said linkage to said output member.
ing actuator and a remote device regulating switch, a lever
2. In a controller of the class having an independent
engaged at an arm and driven by said actuator, a lever
variable sensing actuator and a remote device regulating
engaging at an arm and for controlling said switch, ?exi
switch, a di?erential switch control comprising a first input
ble non-extensible linkage connected between said arms
means engaged and shiftable by said actuator, an output
member engaging and to shift said switch, a second input 20 of said levers, and means engaged at arms of and bias
ing the levers so as to tension said linkage.
means intermediate said ?rst input means and said output
11. The apparatus of claim 10 ‘wherein said ?exible
member, said second input means including a control point
non-extensible linkage is a metal strap.
adjusting element, a strap fastened at its ends to said ?rst
12. The apparatus of claim 10 wherein said linkage
and second input means and passed intermediately
tensioning means is arranged to bias said levers also to
around said output member and resilient means engaged
follow return movement of said actuator.
between two of said input means and output member and
to tension said linkage whereby the movement of said
input means is transmitted through said linkage to said
output member.
References Cited in the ?le of this patent
3. In a temperature controller, an actuator, a switch, 30
a differential device engaged by said actuator and con—
trolling said switch and including a lever member engag
ing at an arm with one of said actuator and switch mem
bers, and means for pivotally mounting said lever mem
ber comprising a pivot pin on said member, rotary bearings
for said pin, and two-point contact recesses on said bear
4. In a temperature controller, an actuator, a switch,
a differential device engaged by said actuator and con
trolling said switch and including a lever member engag 40
ing at an arm with one of said actuator and switch mem
bers, and means for pivotally mounting said lever member
comprising a pivot pin on said member, rotary bearings
for said pin, two-point contact recesses on said bearings,
and spring means clamping said pin in said bearings and
biasing said lever for return movement with said actuator.
5. In a controller having an actuator and a switch, a
lever engaged at an arm and driven by said actuator, a
James ______________ __ Sept. 16,
Radigan _____________ __ Nov. 8,
Burlog ______________ __ Apr. 14,
McKissick ___________ __ Oct. 13,
Phelan _______________ ___ Dec. 6,
Stover _______________ __ Oct. 27,
Reichold _____________ __ Mar. 8,
Pettee _______________ .... Dec. 24,
Smith _______________ ..._ Sept. 8,
Woodworth __________ __ Dec. 15,
Hubbard _____________ _.. Dec. 29,
Spencer ______________ __ Feb. 2,
Hausler _____________ __ Mar. 16,.
Titcomb _____________ __ Jan. 29,
Hennessy ____________ __ Feb. 1,
Oberschmidt __________ __ Apr. 12,
Bender _______________ __ Nov. 8,
Ettinger _____________ __ Aug. 1, 1950
lever controlling said switch, parallel pivots for said levers,
a ?exible strap linking said levers at one side of said 50
Allan ________________ __ Jan. 2, 1.951
Barr ________________ __ May 15, 1951
pivots, and spring means stretched between said levers
at the other side of said pivots and biasing the levers for
Richardson et a1 _______ __ Sept. 16, 1952
Carter ______________ __ Apr. 21, 1953
Grotenhouse _________ __ May 5, 1953
Filliette _____________ __ Nov. 30, 1954
Laing _______________ __ Sept. 13,
Calliham _________ __>___ Oct. 23,
Mertler ______________ __ May 7,
Leupold‘ _____________ __ June 25,
return movement with said actuator.
6. In a controller, a pivotal lever providing by its arm
a ?rst shiftable input means, a rotary shaft arranged as a
second shiftable input means, a shiftable output mem
ber, ?exible non-extensible means differentially linking
said input means with said output member, and resilient
means engaging said input means and output member to
tension said ?exible non-extensible means.
Trautman ____________ __ Dec. 9, 1958
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