US2437846A

US2437846A - Follow-up control

Info

Publication number: US2437846A
Application number: US507556A
Authority: US
Inventors: John O Yeida
Original assignee: Missouri Automatic Control Corp
Current assignee: Missouri Automatic Control Corp
Priority date: 1943-10-25
Filing date: 1943-10-25
Publication date: 1948-03-16
Anticipated expiration: 1965-03-16

Description

Fatented Mar. 16, 1948 UNITED STATES PATENT OFFICE FOLLOW-UP CONTROL John 0. Yeida, Herculaneum, Mo., assignor, by

mesne assignments, to Missouri Automatic Control Corporation, a corporation of Missouri Application October 25, 1943, Serial No. 507,556

15 Claims. 1

This invention relates to a follow-up control.

An object of the invention is to provide a followup mechanism of a construction for permitting the use of snap-action switches. More particularly, an object is to provide a switch operated by some external control device, such as a thermostat, to operate a motive means which, after a predetermined movement, opens the switch, together with limiting mechanism, also operated by the motive means, to determine maximum movements of the motive means through limiting actuation of the switch.

A further object of the invention is to provide a follow-up mechanism in which limiting means act upon the main switch means to override positioning thereof by the external operating means.

In the drawings:

Fig. 1 is a right end view of the device;

Fig. 2 is a vertical lengthwise section taken on the line 2-2 of Fig. 1;

Fig. 3 is a horizontal section looking forwardly on the line 3--3 at the bottom of Fig. 2;

Fig. 4 is a vertical section through the screw shaft taken on the line 4-4 at the left end of Fig. 2;

Fig. 5 is a vertical section taken on the line 5-5 at the right end of Fig. 2;

Fig. 6 is a wiring diagram; and,

Fig. 7 is an end view of a modified construction. The references to vertical and horizontal in this description are not limiting, but are used for clarity with reference to the drawings. The device is not limited to any particular position- The follow-up mechanism comprises switch means adapted to control operation of a motor M (Fig. 6) having a forward winding F and a reverse winding R, the motor M driving a shaft S.

The switch mechanism is contained within a housin I!) which, at one end, receives a power device generally indicated at H, and here shown as a diaphragm type of thermostat. The thermostat comprises a cup I2, secured to the housing H3, and containing an inner flexible cup-like member Iii, welded thereto around its edge, so that its bottom member may move to the left or to the right (Fig. 2) in response to changes in volume of a liquid contained in the thermostatic system. A

tube H2 is connected intothe cup I2 and leads to a bulb (not shown) disposed at the point at which the temperature is to be controlled. This may, for example, beat a point where it will respond to engine temperature where the device is employed to operate air-controlled louvers that regulate the temperature of the engine.

A stud shaft I6 is urged against the cup element It by a spring This stud shaft I6 projects through the end wall of the casing Ill and has a head l8 thereon, the inner surface of which is shaped to receive a self-adjusting washer IS. The stud I6 will be reciprocated by the power means and the spring IT in response to changes in temperature. The stud acts upon a switch lever 20, which has a generally channel-shaped section, through the web of which is an opening to receive the stud l5., The portions of the web portion adjacent the'opening are displaced outwardly, as shown in Figs. 2, 3 and 5 at 2|, to engage the washer IS. The switch lever 20 is of bell crank shape and is pivoted at 22 to a follow-up lever 23. The switch lever is acted upon on its other arm by springs 24 secured between it and the housing to urge the longer arm of the lever upwardly and to urge the elements 2| on the shorter arm of the lever into contact with the washer Hi. The springs 24, therefore, cause the lever 2|) to follow leftward movements of the stud |6; and the washer l9, acted upon by the head It, acts upon the lever when the stud moves to the right.

The longer end of the switch lever 20 is the switch-operating end, and is disposed between two

switches

25 and 26 that are supported by bosses 27 and 28, respectively, upon the back wall of the casing 10. These switches are of the snapaction type and have actuating

buttons

29 and 32, respectively, on opposite sides of the lever 20. When the lever is midway between the two

buttons

29 and 30 both switches are open, as shown in Fig. 6. It may be seen that as the lever 26 moves up, it will close the switch 25, and when it moves down, it will close the switch 26.

The outer end of the long arm of the lever 26 has two spaced heads thereon 32 and 33, (Figs. 2 and 4) for a purpose to be described.

The follow-up lever is also in the form of a channel-shaped bell crank. It is pivoted at 35 to a U-shaped bracket 36 that is secured to the right end of the housing Ill. The shorter arm or the lever 23 supports the pivot 22. The longer arm is bifurcated at its end to provide cars 31 and 38, for a purpose to be described.

A spring 39 acts between the bottom of the easing l0 and the longer arm of the follow-up lever 23 to urge the same in a clockwise direction.

It will be seen that displacement of the followup lever 23 about its pivot 35 will change the position of the pivot 22 of the switch lever 20, thereby to change the relationship of the elements 2| on the lever 20 with respect to the stud I6, and with an ultimate change in the relationship of the outer end of the lever 22 with respect to the

switch buttons

29 and 39.

'A follow-up screw shaft 40 is rotatably mounted in the end of the casing I0 and is adapted to be connected to the motor shaft S so that its rotation corresponds to the rotation of the motor shaft.

The shaft .40 receives three nuts 4|, 42, and 43,

all of which have teeth on their outer surfaces for engagement by

spring locks

44, 45, and 46. These locks are identical, and their operation is apparent from Fig. '3, wherein the lockdGis-shown. It comprises a spring blade having an end to engage between adjacent teeth on the nut 43. The spring characteristic urges the blade 66 to the left. It is maintained in its engaging position by a screw 48, there being corresponding screws for the other blades. When the screw 48 is loosened, the blade lia frees itself from the nut 43 and the latter may be turned upon the shaft for, adjustment. When the screw 48 is tightened, it holds'the blade to in position by the adjacent teeth on the nut.

The nuts ill and {i2 are spaced :aparta selected distance which will determine the maximum range of the motor operation that is permitted. They are disposed upon opposite sides of the a previously mentioned cars .32 on the lever 2-0.

By contact between one or :the other o-f-thenuts H and 42 with the ears132, the movement of the lever .28 with respect to the

switch buttons

29 and 39 will be Controlled.

The nut es acts against the'bifurcation 38 on the follow-up lever 23. It will be seen that the left end of the lever 23 is positioned by thespri-ng 3?) and the nut the spring gnorma'll-y urging the ears ee'intoengagement with the-nut 43. 7

Referring to the wiring diagram in Fig. 6, it will be seen that power from the line so is brought into both of the switches 25 and 2.6. When the switch 25 is closed, power is, conducted through the forward winding of themotor, whence it may return to the power line 5!. When the switch 26 is closed," power is introduced into the reverse Winding R of the motor, whence it returns lto'the other power line 5 i.

In Fig. 7 there are shown two changes which in some cases are desirable. :In this, modification the shaft to is divided into an upper sect-ion 46a and a lower section 45b. The upper section is provided with threads of a steeper pitch than the lower section, .so. that the limiting nuts will be moved greater distances per rotation of the shaft than will be thefollow-uphl t.

In this modification also the end wall contain-- ing the locking springsis detachable, andga separate partition 65 is provided beneath the detachable part, which containsthe locking springs l,

, 45, and 48, and the screws 68. This partition is provided with two windows Stand 62. Two nuts Md and 52a correspond to the nuts 41 and 42. These two nuts appear projecting through "the window 5!. d3, appears through the window 62.

The nuts are the same in construction, being I threaded to operate upon the screw d5. -Gf-course,

the nut 43d has low .pit-chedt-hreads and the-other two have high pitched threads. Otherwise they are identical. Referring to, the nut 425a as typical, it will be seen that it has a milled flange 63 which receives its lockin spring, which, in this instance, would be the spring {it mounted on the detachable end plate of the housing to. The nut also has a graduated portion 55 on its edge which is adapted to register with a pointer '65 formed on the edge of the window .65. A similar pointer 66 cooperates with the nut .2a and :a pointer 6? on the edge of the window c2 cooperates with the graduations on the nut 43a.

Operation This mechanism, as heretofore suggested, may

Nut 53a, corresponding to the nut trolling devices, such as louvers on an aircraft engine. When so employed, the louver actuat ing mechanism will be driven by the motor shaft S, which also maybe connected directlyor indirectly to the screw shaft 40.

When the position of the louvers is proper, supplyin sufilcient air to maintain the motor at its desired temperature, the switch lever 2o wiil be midway-between the switch buttons 28 and 3.0 and both switches will be open.

If there he a demand for more air in the mo tQIf, manifesting itself by an increase in temperature at the bulb, the liquid in the thermostat system, which is of the solid charge type, will e.-- pand, moving the shaft .16 to the left. This will withdrawthe washer 19 to the left and thesprings 24 will cause the lever 29 to follow. The springs 24 are also sufiicient in strength to overcome the snap-action mechanism of the switch 25, so that it will be moved to the closed position. This will energize the forward winding of the motor M, which-will then rotate, and, in so doing, will open the louvers to .agreater extent. The motor will also rotate the shaft in a direction to move the .nutsdown. As the nut d3 moves down, it acts upon theforks .38 of the follow-up lever 23 to pivot that lever about its pivot 35, which dis laces the pivot .22 mounted upon the followup lever 23 to the left. This action causes the switch lever .20 .to be pivoted about the contact between .the elements Zland the washer is in a counterclockwise direction, withdrawing the lever 20 to release the button 29, so that the lever assumes again a midposition between the switch buttons. This action stops the motor.

In similar fashion, the reverse action takes place when the thermostat cools. In such case, the stud shaft 16. moves to the right, this time pivoting the switch lever 28 -.counterclockwise about its pivot 22 and causing closing of the switch 26. This energizes the reverse winding of the motor, which then rotates in the opposite direction to close the louvers and to move theshaft 40, so tha the nuts .41 4'2, and 43 move upwardly. The upward movement of the not as withdraws it relative to the forks 38 on the follow-up lever 23, but the spring 39 causes the lever 23 to follow the nut 43, so that the lever is pivoted clockwise about its pivot 35. This causes clockwise displacement of the pivot 22 supporting the switch lever 20, producing a tenden y of the elements 2| on the lever 20 to withdraw from the washer IS on the stud I6, The springs'fil pivot the lever 23 to maintain the elements 2! in contact with the washer l9 and, in so doing, pivot the lever 2% to its midposi-tion once again between the

switch buttons

29 and 30. It thus may be seen that the springs 24 are strong enough to overcome the snap-action resistance of the switches.

It will be seen that for any particular temperature there are particular resulting positions of themotor, its shaft 5, and theshaft All. Correspondingly, here are particular positions of the igllow-up lever 2:3 and, in turn, of the switch lever It is necessary to preventexcess movement in either direction of the shaft S, as the amount of displacement of the louvers is limited to a range between certain completely closed positions and other wide open positions. In .order to prevent the motor from operating beyond these positions, the nuts 4| and 42 are provided. These nuts are normally spaced apart, so as to be out of contact with the arms 32 on the switch lever as. However, as thescrew 45 turns in one or the other direction, it causes one or the other of the two nuts Al and 42 to approach the arms 32.

For example, if it be assumed that there have been repeated demands for opening of the louvers, the result will have obtained that the stud i6 will have been moved inwardly a substantial distance, and the switch 25 will have been closed so that the shaft S will have been moved to open the louvers completely. Correspondingly, the several nuts will have been moved downwardly a predetermined maximum distance. t will be observed that little change results in the position of the switch lever 20 between a completely closed position and a completely open position of the louvers. This is necessary with fixed switches. However, after the shaft til has been rotated at predetermined number of times, the nut 4| will have been moved down into contact with the ears 32 on the lever 25 to force the lever 20 away from the switch button 29 to open the switch 25, regardless of the demand by the thermostat. In so doing, the nut ii displaces the lever 20, so that the elements 2% are moved away from the washer l9. Thus, even if the thermostat, under such circumstances, demands heat, the switch cannot be closed, but the switch arm 2%! will remain in its neutral position. In the meanwhile, the nut 42 will have been withdrawn further away from the ears 32, so that the lever 28 is free to act to close the other switch 26. This it may do when the demand for heat decreases, the thermostat contracts, and the stud I6 is moved to the right,

In like manner, if the thermostat becomes so cool that the louvers are completely closed, further operation of the switches and the motor is prevented. In such case, the nuts will have been moved upwardly, so that the nut 42 Will act upon the ears 32 to displace the lever 25 upwardly, in

spite of demand by the thermostat. In this action, the overriding displacement of the lever 23 will normally pivot the lever about the contact between the elements 2| and the washer l9. In this action, the spring IT may yield to permit the lever 29 to open the switch 26.

The limits in either direction may be determined by the initial adjustments of the nuts 4| and 42. These adjustments are made by releasing the spring blades M and 45 and turning the nuts on the shaft lil until they have the desired relationship to the ears 32 to compe1 opening of the switches after a predetermined number of rotations of the shaft. As the adjustment is set, screws are again turned down to lock the nuts in position.

In like manner, the nut 43 is adjustable. Adjustment of this particular nut also determines calibration of the switch, so that it will operate at the proper temperatures for given positions of the thermostat, or given temperatures thereof.

In the modification of Fig. 7, the follow-up nut sea operates upon the bifurcations 31 and 38 in the same manner as does the nut 43 in the other type. The operation of the nuts Ma and 42a is also the same except that these nuts move a greater axial distance revolution of the shaft. This attains the advantage that when the limits are reached the switches will be actuated quickly within a small amount of rotation of the shaft. The same is true when either limit nut is to be withdrawn. This may accommodate for a differ ential in the two switches between their opening and closing points, and will reduce the amount of rotation required to back one of the limit nuts off of the ears 32. This is accomplished without reducing the sensitiveness of the follow-up mechanism.

The windows 6| and 62 are made amply large to permit the necessary axial displacement of the several nuts. In a solid charge device, such as that illustrated, the total movement or" the nuts Ma and 42a will be only a very small fraction of an inch,

The graduations on the nuts shown in Fig. 7 facilitate adjustments. When the end plate is removed, the locks are taken with it and the nuts are movable for rotation on their shafts and their positions ascertainable by reference to their respective pointers.

The foregoing control is capable of use in many connections other than that mentioned. As an illustration, it may be used in controlling of valve means, or the like, in a heating system, so as to modulate the flame of the burner in accordance with the temperatures of the room being heated. Further, it is not limited to a heat-responsive mechanism, as the actuating means, here shown as the thermostat, may comprise any reversible motive means.

The use of snap-action switches is made pos sible by the fact that the follow-up lever does not substantially displace the total range of movement of the switch lever. This is brought about in part by the fact that the displacement of the pivot 22 of the switch lever 29 by the follow-up lever 23 is substantially lengthwise of the switch lever 20, resulting from disposition of the shorter arm of the lever 23 at substantially a right angle to the switch actuating arm of the lever 2%. This construction is made more compact by the use of bell crank levers, which also enable the limiting nuts, acting upon the switch lever, to be on the same shaft with the follow-up nuts, acting upon the follow-up lever; and the design thus permitting the use of follow-up nuts, as described, permits elimination of separate limit switches and their actuating mechanisms.

What is claimed is:

1. In a control, a power means, a motive means operable to effect operation of the power means, and mechanism to control operation of the power means in response to movements of the motive means, comprising a control device adapted to be displaced from an initial position in one direc tion to eiiect operation of the power means, and in the other direction to stop operation thereof, a member interposed between the motive means and the control device to apply movement of the former to the latter, a driven element operated upon operation of the power means, and engaging means operated by the driven element displaced in accordance to the amount of movement thereof, and adapted to engage the interposed member to displace the same to maintain the control device in its initial position after predetermined movement of the power means, regardless of the position of the motive means.

2. In a control, a power means, a motive means operable to effect operation of the power means, and mechanism to control operation or the power means in response to movements of the motive means, comprising a control device adapted to be displaced from an initial position in one direc tion to effect operation of the power means, and in the other direction to stop operation thereof, a lever interposed between the motive means and the control device to apply movement of the former to the latter, said lever being moved by the motive means but movable relative thereto, a driven element operated upon operation of the to engage the interposed lever to displace the same to maintain the control device in its initial position after predetermined movement of the power means, regardless of the position of the motive means.

3. In-a control, a power means, a motive means operable to efiect operation of the power means, and mechanism to control operation or the power means in response to movements of the motive means, comprising a control device adapted to be displaced from an initial position in one direction to effect operation of the power means, and in the other direction to stop operation thereof, a first lever interposed between the motive means and the control device to apply movement of the former to the latter, said lever being moved the motive means but movable relative thereto, a second lever upon which the first is pivoted, a driven element operatedupon operation of the power means, means operated upon movement the driven element to engage the second lever and displace the same to shift the pivot pointof the first lever to eflect-displacement thereof rela tive to'the control device and to efiect return the latter, and. engaging means operated by the driven element displaced in accordance to the amount of movement thereof, and adapted to engage the first lever to displace the same to mair tain the control device in its initial position after predetermined movement of the power regardless of the position of the motive means.

4. In acontrol, a power means, a motivemeans operable to effect operation of the power means, and mechanism to control operation of the power means in response to movements of the motive means, comprising a control device adapted to be displaced from an initial position in one direction to effect operation of the power means, and in the other direction to stop operation thereof, first lever interposed between the motive means and the control device to apply movement of the formerto thelatter, said lever being moved by the motive means but movable rela ive thereto, a second lever upon Which the first is pivoted, driven element operated upon operation or" the power means, means operated upon movement of the driven element to engage the second lever and, displace the same to shift the pivot point of the first lever to efieot displacement thereof relative to the control device and to effect return of the latter, and engaging means operated by the driven element displaced in accordance to the amount or movement thereof, and adapted to engage the interposed lever to displace the same to maintain the control device in its initial position after pres determined movement of the power means, regardless of the position of the motive said driven element comprising a threaded shaft, the means operated upon movement thereof, and the engaging means comprising nuts on the shaft and movable. upon movement of the shaft into contact'with their respective levers.

5. In acontrol, a power means, a motive means oppositely movablev in response to changes in physical conditions, for eiiecting operation of the power means, oppositely acting control means, movable from .a neutral position in opposite directions, circuits controlled by the control means to energize the power means for forward and reverse operation, respectively, a lever oppositely movable to displace the control means, means connecting the .lever to the motive means for displacement of the lever in response to. movements of the motive means, said connection being yieldable to permit relative movement between the motive means and the lever, a driven means operated in opposite directions upo operation of the power means, engaging means operated by the driven means, said engaging means being adapted to engage the lever on opposite sides thereof, the driving means being adapted to effect engagement after predetermined operation thereof, to cause the lever to be shifted to return the control means to neutral position regardless of the position of the motive means.

6. In a control, a power means, a. motive means oppositely movable in response to changes in physical conditions, for effecting operation of the power means, oppositely acting control means, movable from a neutral position in opposite directions, circuits controlled by the control means to energize the power means for forward and reverse operation, respectively, a lever oppositely movable to displace the control means, means connecting the lever to the motive means for dis placement of the lever in response to movements of the motive means, said connection bein yieldable to permit relative movement between the motive means and the lever, a driven means operated in opposite directions upon operation of the power means, engaging means operated b the driven means, said engaging means being adapted to engage the lever on opposite sides thereof, the driving meansbeing adapted to effect engagement after predetermined operation thereof, to cause the lever to be shifted to return the control means to neutral position regardless of the position of the motive means, said engaging means including two elements, one engageable on each side of the lever, and means for adjustment of at least one of said elements relative to the lever.

7. In a control, a power means, a motive means oppositely movable in response to changes in physical conditions, for effecting operation of the power means, oppositely acting control means, movable from a neutral position in opposite directions, circuits controlled by the control means to energize the power means for forward and reverse operation, respectively, a lever oppositely movable to displace the control means, means connecting the lever to the motive means for displacement of the lever in response to movements of the motive means, said connection being yieldable to permit relative movement between themotive means and the lever, a driven means operated in opposite directions upon operation of the power means, a second lever upon which the first is pivoted, and means operated by the driven means to shift the second lever and to displace the pivot point of the first lever relative to the motive means, said means operated by the driven means being moved in a direction to effect movement of the levers to return the control means to neutral position, corresponding to a particular condition of the motive means, engaging means operated by the driven means, said engaging means being adapted to engage the first lever on opposite sides thereof, the driving means being adapted to .eiiect engagement after predetermined operation thereof, to cause the lever to be shifted to return the control means to neutral position regardless of the position of the motive means, said engaging means including two elements, one engageable on each side of the lever, and means for adjustment of at least one of said elements relative to the lever.

B. In a control, power means, a motive means oppositely movable in response to changes in physical conditions, a control device, a lever between the control device and the motive means,

for transmitting movements of the motive means to the control device, a pivot for the lever, a supporting means for the pivot, comprising a second lever and a second pivot, said pivot for the first lever and the pivot for the second bein in a line substantially at right angles to the arm of the first lever between its pivot and the control device, and means operated by the power means to shift the supporting means to move the pivot substantially lengthwise of the arm of the lever between the pivot and the control device.

9. In a control, a housing, a motive means oppositely movable in response to changes in physical conditions, a stud, a spring yieldably maintaining the stud against the motive means, a first bell crank lever engaged by the stud for move ment by the same when the spring moves the stud, second spring means urging the bell crank lever in the other direction, a pair of switches fixedly mounted on the housing on opposite sides of the bell Crank lever, for actuation thereby, a second bell crank lever upon one arm of which the first lever is pivoted, a pivot for the second lever, a line between the two pivots being substantially at right angles to the switch operating arm of the first lever, a screw shaft adapted to be rotated, and mounted in the housing to extend adjacent the switch arm of the first lever, a pair of nuts on the shaft on opposite sides of the said switch arm, and adapted to contact the arm to displace the same, the second arm of the second bell crank extending to adjacent the screw shaft, a third nut on the shaft for contact with the second bell crank arm, and spring means for urging the said arm against the nut.

10. In a control, a housing, a motive means oppositely movable in response to changes in physical conditions, a stud, a spring yieldably maintaining the stud against the motive means, a first bell crank lever engaged by the stud for movement by the same when the spring moves the stud, second spring means urging the bell crank lever in the other direction, a pair of switches fixedly mounted on the housing on opposite sides of the bell crank lever, for actuation thereby, a second bell crank lever upon one arm of which the first lever is pivoted, a pivot for the second lever, a line between the two pivots being substantially at right angles to the switch operating arm of the first lever, a screw shaft adapted to be rotated, and mounted in the housing to extend adjacent the switch arm of the first lever, a pair of nuts on the shaft on opposite sides of the said switch arm, and adapted to contact the arm to displace the same, the second arm of the second bell crank extending to adjacent the screw shaft, a third nut on the shaft for contact with the second bell crank arm, spring means for urging the said arm against the nut, each of said nuts having graduations on the edge thereof, index means on the housing cooperable with said graduations, and locking means for releasably maintaining said nuts in adjusted positions.

11. In a follow-up type of control for use with a power means for causing self-limiting operations thereof, a control device, a force-applying member to produce force in one direction, a control device operable from an initial to a second position in a direction substantially at right angles to the force of the force-applying member, the control device being connectable to cause operation of the power means, a bell crank lever between the force-applying member and the control device for causing movements of the former to operate the latter, a second lever adapted for movement by the power means, the second lever supporting the pivot of the bell crank lever, and the second lever being movable to displace the pivot in the direction transversely of the direction of movement of the control device.

12. In a follow-up type of control for use with a power means for causing self-limiting operations thereof, a control device, a base, a forceapplying member to produce force in one direction, a control device operable from an initial to a second position in a direction substantially at right angles to the force of the force-applying member, the control device being connectable to cause operation of the power means, a bell crank lever between the force-applying member and the control device for causing movements of the former to operate the latter, a second lever pivoted to the base, and adapted for movement by the power means, the second lever supporting the pivot of the bell crank lever, and the second lever being movable to displace the pivot in the direction transversely of the direction of movement of the control device.

13. In a follow-up type of control for use with a power means for causing self-limiting operations thereof, a control device, a force-applying member to produce force in one direction, a control device operable from an initial to a second position in a direction substantially at right angles to the force of the force-applying member, the control device being connectable to cause operation of the power means, a bell crank lever between the force-applying member and the control device for causing movements of the former to operate the latter, follow-up means adapted to be operated by operation of the power means, said follow-up means supporting the pivot of the first lever, and being movable to displace the pivot in the direction transversely of the direction of movement of the control device.

14. In a follow-up type of control for use with a power means for causing self-limiting operations thereof, a control device, a force-applying member to produce force in one direction, oppositely fixed control devices each having a movable element facing the movable element of the other, each element being movable from an initial position to a second position, in directions transverse to the movements of the force-applying member, the control devices being connectable respectively to effect opposite movements of the power means, a bell crank lever extending from the forceapplying member to between the movable control elements for causing opposite movements of the member to actuate the control devices, follow-up means adapted to be operated by operation of the power means, and supporting the pivot of the bell crank lever, the follow-up means bein displaceable upon operation of the power means to shift said pivot in a direction transversely of the direction of movement of the control device elements.

15. In a control, a power means, a motive means operable to effect operation of the power means, and mechanism to control operation of the power means in response to movements of the motive means, comprising a control device adapted to be displaced from an initial position in one direction to efiect operation of the power means, and in the other direction to stop operation thereof, a first lever interposed between the operation of the power means,

'linsi 11 ,t motive means and the control device to apply movement of the. former to the latter, said lever being moved by the motive means, but movable relative thereto, a, seoondlever upon which the first isjpivotedadrlven element operated'upon V w means operated upon movement of thedriven element to engage the second lever and ldisplaoe the same to shift the pivotpoint of the first lever to efiect displacement thereof relative to the control device and to effect return of the latter, and engaging means operated hythe driven element displaced in accordanee to the amollhtof movement thereof, and a'da'ptedrto engage the interposed lever to displaee the'sametojfnaintain the control device in its'initial po sition after predetermined movement of the power meanaiegardless of the positiOri of ,the motive 'lj'i alh s', Said driven element comprising a threaded shaft, and the means operated upofi inovez'nent thereof, and the engaging means COlTiDfiSiI lg nuts Oh. the Shaft and m'ovable up'hn movement of the shaft into contact with their respective levers, thethreaded shaft havin'g'steepe'r pitch at its portion upon which a the nuts of at its porti the engaging means are mounted than on receiving the other nut means.

JOHN O. YEIDA.

REFERENCES CITED Number 20 Number Name Date Mofiett Apr. 10, 1934 Manley out. 6, 1936 Persons July '7, 1942 Olken L Jan. 18, 1944 Pefine'camp July 4, 1944 FOREIGN PATENTS h 7 Country Date 7 GreatBritain 1908