US2347837A - Servomotor - Google Patents

Description

y 1944- .1. s. MORRISON I 2,347,837

SERVOMOTOR Filed Dec. 31, 1940 6 Sheets-Sheet l ATTO m May 2, 1944. J, 5. MORRISON SERVOMOTOR 6 Sheets-Sheet 2 Filed Dec. 31, 1940 JESS S. MORRISON.

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SERVOMOTOR Filed Dec. 31, 1940 6 Sheets- Sheet 3 JJVVEWTOR: JESS S. MORRISON.

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May 2, 1 4 J. s. MoRRLsoN SERVOMOTQR Filed Dec. 31, 1940 6 Sheets-Sheet 5 1 'ill.

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INVIZFJVTOR JESS S. MORRISON.

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SERVOMOTOR Filed Dec. 31, 1940 6 Sheets-Sheet 6 INVENTOR. JESS s. MORRISON.

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RECEIVER I &

A M L In ER PatentedMay 2, 1944 I "UNITED STATES PATENT OFFICE? sanvoMo'roa Jess S. Morrison, Southgatc, Calif assignor to e Leo M. Harvey, La Canada, Calif.

Application December 31, 1940, Serial No. 372,441

Claims. (Cl. 121-48) This invention relates to servo-motors, particularly servo-motors adapted for operating the directional controls of vessels, including specifically rudder, aileron, and elevator controls for aircraft.

Among the objects of this invention are: To provide a servo-motor which is positive in action and light in weight; to provide a servo-motor which cannot be jammed by distorting stresses, all of the parts being freely floating; to provide a servo-motor which is sufflciently powerful to actuate any 01 the controls of an airplane but will hold the controls of an airplane fixed in any position to which they are moved, regardless of 'loading conditions until deliberately displaced therefrom by a new actuation. of said servo-motor; to provide a servo-motor wherein ultimate force which it is capable of applying is independent of its speed of action; to provide a servomotor which requires a minimum amount of servicing and lubrication; to provide a servo-motor which can be constructed as a single compact unit which may be mounted or dismounted with minimum time and trouble; and to provide a servo-motor having adjustable means for operating a proportionating potentiometer.

Other objects of my invention will be apparcut or will be specifically pointed out in the description forming a part of this specification,

I but I do not limit myself to the embodiment of theinvention herein described, as various forms may be adopted within the scope of the claims.

Considered broadly, the servo-motor of my invention comprises a pair of oppositely disposed bellows each including a bellows plate. The bellows plates are provided with risers both of which are pivotally connected to an operating lever at of operation in the two directions may be individuaily adjusted to equality or inequality as may be desired, and the overall speed may be adjusted without interfering with the individual adjustment; and there are also preferably provided check valves opening into and out of each of the two. bellows, permitting the device to be moved manually to override the motor in .case ofnecessity.

Where the device is used with a proportioning control, as described in the patent to Ralph S. Thacker, No. 2,257,203, there is also preferably provided adjustable ratio means for actuatlng one or more potentlometers in proportion to the degree of operation of the motor.

' Referring to the drawings:

Fig. 1 is a plan view of the Servo-motor of my invention. r

Fig. 2 is an end elevation of the. servo-motor shown in Fig. 1, the valve chest being shown partly in section. V

Fig. 3 is a side elevation of the same servomotor, a portion of the valve chest again being shown in section.

Fig. 4 is a longitudinal sectional view of the .tor taken on the plane indicated by the line 5-5 of the first figure.

Fig. 6 is a purely schematic diagram of the 1 device.

" tion it is to A'preferred form of the invention illustrated in the drawings is mounted on a formed base I of sheet metal Since the devic is intended for aircraft use the choice of material here is one of the high tensile strength aluminum or magnesium alloys, and throughout the specificabe assumed, where metal is specifled, that such light weight alloys are used where applicable, although naturally this assumption does not apply to such parts as shafts. pipe fittings, or the like.

' Supported on the base or frame I are two frusto-conical bellows housings 2, 2"which form the outer side members of the apparatus and are mounted with their axes horizontal and their bases spaced from each other by a distance which is approximately double the axial dimensions of ing horizontally from one side-oi each is a valve box 4, 4', These valve boxes, except where they intersect the conical surfaces of the housings, are substantially rectangular in form, and to them is mounteda main valve chest b which also acts as a structural member, bracing the housings and holding them parallel.

A similar structural function'is performed at the other end of the device by a bracket 1, on which a bell crank 9 is journaledon a shaft or pin it. The outer end or the bell crank is provided with an ,eye or bearing II, which forms the power takeoil for the device.

An annular bellows l2, of leather, "rubberized fabric, or other flexible material is secured to the flange 3 by a mountingring It. This bellows is so formed that when collapsed it very nearly contacts the wall of the housing and leaves very little residual space therein. The inner edge of the bellows fabric is clamped between an inner and an outer circular bellows-plate l4 and I5 respectively, each of which is provided with 9. rolled edge II to prevent cutting of the bellows fabric. A hanger or bracket I9 is mounted upon the composite plate thus formed, and in it is journaled a bearing pin 20 which passes through and is Journaled in the inner end of the bell crank 9 and serves to drive the latter. The axis oi this pin should intersect a perpendicular erected from the center of pressure of the bell'ows plate, so that whenthe bellows is under vacuum this plate will tend-to position itself stably in a plane parallel to the plane of the flange 3.

A similar bellows arrangement is mounted on the bellows housing 2', and the corresponding parts are identified with. the same reference characters as those used to distinguish the ones just described, accents being used throughout to distinguish those parts associated with the righthand bellows as shown in Fig. 5. The hanger I9 is articulated with the hanger I9 on the pin- 20, and since the device is vacuum operated and the'hangers I 9, l9 are always in tension, the parts thus far described, constituting the driving mechanism of the device, are always in stable equilibrium and the bellows plates H, H maintain themselves parallel whatever their position,

- and to whatever position they may have moved arm .in that direction. The pressure tends to equalize on both sides of the bellows which isopein to atmospherabut because of the movev ,mentf "egr tending the bellowsthe pressure will be lsllghtlyless within it and the stable position of thebellpws plate will be maintained.

T onnection to the vacuum or to atmospheret is accomplished throughv the mechanism within the valve chest 5, and can best be seen in Figs. 2 and 4, or in the schematic diagram oI-Fig. 6. The chest is divided by a vertical partition 2i into. inner and outer chambers 22' and .23, 23 respectively. The inner chamber, 22 conmeets to a main vacuum line 24 leading to a pump or other source of negative pressure. The

two outer chambers 23, 23' are separated bya diagonal septum 25, the-chamber 23 connecting directly through a port 21 into the bellows b0115- ber 2. is actuated by a flexible diaphragm 2U clamped over an aperture 20 in the outer wall of chamber 22 by means of a fitting 20, into which connects arelay pipe 21. The valve is of the tulip type. having a rounded head 32 which is formed integrally with the mushroom skirt 23. This skirt engages a separate valve seat 34 scr'ewed to the inner partition 2|. and the valve is normally held closed by a spring which surrounds the stem "of the valve. The endoi the stem enters and is centered by a guide bushing 88 mounted on the outer wall of the chamber, and the motion oi the valve is limited by an ad lusting set-screw 40.

If the control pipe 3| is closed, air within the housing 30 will leak through a small vent ll which connects the interior of this housing with the main vacuum chamber 22, and the pressure on both sides of the, diaphragm 28 equalizing, the spring 85 closes the valve. If, however, the pipe 3| be opened to atmosphere, the external pressure will operatethe-diaphragm against the force 01' the spring 315 and lift the skirt 33 to open a connection between the chamber 22 and the chamber 23, thereby exhausting the bellows housing 2 through the, port 21, collapse the corresponding bellows. and move the bell crank lever to the left, as seen from the aspect shown in Fig. 1 or 5.

In order that any such motion may take place, however, it is necessary that the opposite bellows be open to atmosphere. This is accomplished simultaneously with the opening of thepipe 3i to operate the xhaust valve by means of an electro-pneumatic relay mechanism mounted in a housing or relay box 42 on the bell crank bracket 1. The pipe 3| is carried up and overthe housing 2' and enters the side 01' the relay box.

by a tension spring 53.. Closing the circuit indicated by the leads 54 excites a magnet 55 and attracts the armature' 52 to actuate the two valves simultaneously. The pipe 3| opens fully instantly, so that the action of the exhaust valve tending to collapse its associated bellows is very rapid. The speed of operation of the device can, however, be adjusted by means 01 the valve 41', controlling the speed of admission of air into the opposite bellows.

The needle valves 51, 41' named to regulate the relative rates of action of the bellows; to regulate the overall speed of operation there is used a needle valve 56 in the main vacuum line 24, preferably mounted on the control panel 58 of the plane within easy reach of the pilot.

In order to permit a pilot to override the motor when necessary, two check valves, indicated by the general reference characters 60 and GI chamber 22' connects through" respectively, are mounted in the valve box 4, and a similar pair of valves 60', BI in the valve box 4'. Valvetli' is an outwardly opening check valve which permits the bellows housing to exhaust to atmosphere through a filter 62', the valve opening when the pressure within the bellows exceeds a value determined by a spring 83. The valve BI is an oppositely disposed check valve which admits air through a filter 64' when the pressure differential within and without the bellows becomes sufficient to actuate the spring 60', since the pressure to actuate them may be sufficiently accurately determined by the choice of the spring, and as in normal operation no positive pressure ever exists within the bellows chambers, the springs may be very light. Because, however, the bellows ordinarily operate under' vacuum it is desirable to havethe inlet checks 6|, Bi adjustable in order that they may not operate under differential pressures normally existing, and an adjusting'screw 61' is provided in the valve 6| for this purpose and a similar screw 21 in the valve 6i.

In the service for which this motor was primarily developed there is employed a potentiometer whose setting is dependent upon the position of the controls operated by the servo-motor, and it is highly desirable, in order to obtain the results wanted, that the ratio between the potentiometer setting and the movement of the controls should be made adjustable. Means are accordingly incorporated within this device to the ends mentioned.

It is not ordinarilynecessary to provide means for adjusting the exhaust valves 60 and Mounted on the lower end of the bearing pin a A sprocket chain 11 engages each of these sprockets, extending from an anchor 18 on bellows housing 2' around sprockets 13, 1|; and 10 in succession, to a tension spring I9 whose other end is fixed to an anchor pin 80 which extends downward from theinner end of thebell crank 9 near its bearing.

A crank arm 8| carrying a crank pin 82 is fixed to the sprocket II and turns with it. The crank pin is gripped by a second arm 83, mounted on a common shaft 84 for the potentiometers 85, 86 which shaft is mounted coaxially with the shaft Iii in a housing or box 81 secured to and beneath the bracket 1.

It will be seen that the-distance from the anage 18 to the position 18', 18", the ratio of movement of potentiometer to the movement of the bell crank may be changed in approximately the proportion of 2:1.

Certain features of the device are shown in the schematic diagram of Fig. 6. The'vacuum source 91, designated as a pump, may be a venturi or aspirator, although I prefer a positively driven pump. A filter 92 is provided at the outlet of the pump in order to prevent the entry of dust into the system during periods of idleness. The pump preferably has capacity to supply a considerably greater vacuum than that ac-. tually employed, and a regulator comprising a flap valve .93, held closed by a spring 84 adjustable by means of a screw 95 regulates the actual pressure used, which may be read upon a vacuum gauge 91. A filter 89 is also preferably provided for use on the regulator.

When the device is in operation, the solenoids 55, 55 ar operated by actuating one or the other of contacts I00, I00, closing the circuit from a suitable source I02 through the respective magnets.

The contacts may be operated by any suitable control device, preferably, however, the directional radio receiver IM whose nul axis is varied by the setting of the rudder by means of the potentiometer 85, as disclosed in the patent to Ralph S. Thacker, No. 2,257,203. It will be seen that the operation of this device is such that it will function satisfactorily in either of two ways. If the contacts I00, I00 are normally open, closure of one of,them will open the corresponding pneumatic pipes and cause the motor to actuate the controls in one direction. If the contacts be then opened the electro-pneumatic valve will close, and the motors will hold the plane rudder or other control surface of the plane in the position that has then been attained, until it is released or further actuated by again closingone of the contacts I09, I00. If, however, the contacts I00, Hi0 be normally closed, air will normally be admitted'to both bellows and the motor will exert no force, so that the plane may be controlled manually with a minimum of effort. Under these circumstances opening either of the contacts I00, I00 will put the motor into operation,- but it will release and chor pin 80 around the three sprockets to the 2 center line of the two sprockets II and 12 does not change with the position of the bell crank,

' but that the distance from this point to the anchorage 78 does change very nearly in the ratio of the change of angular position of the bell crank. This change can only be accommodated by variation in the length of the tension spring I9, all of the sprockets moving to accommodate such change in length and the sprocket 1| thereby operating the potentiometer. By changing the position of the stub shaft HI as .between the various holes provided for the purpose, with corresponding change of the anchor- The servo-motor here described has a number of features which render it particularly desirable in use. One of; the chief of these is the fact that it is completely self-contained, has only one bearing, and because of this structure it is impossible to warp or strain it so as to cause binding. The frame is small and rigid, and can readily be so mounted as not to be subject to twisting stresses, but even if such stresses do occur the fact that the bellows float freely on the lever arm prevents any effect on the action of the motor.

Furthermore, the motor as specifically described herein weighs but 12 pounds, but. will, with a 12 inch vacuum, pull 146 pounds. Since there is only 'one bearing to be oiled it is not ordinarily necessary to remove it from the plane for service, except for periodical check and overhaul after approximately 500 hours duty, but when such removal is required the light weight and accessible mounting of the device make it a simple matter.

I claim: 7

1. In a servo-motor having a pair of opposed bellows, mechanical means interposed between said bellows and movable thereby, and a source of vacuum, a normally closed diaphragm actuated valve associated with each bellows and operative when said diaphragm is opened to atmosphere to connect said source to said bellows, a duct connected to each of said diaphragms, a second duct connected to each bellows, and a pair of electro-pneumatic relays for energizing said servo-motor, each relay comprising an electromagnet, an armature for said magnet, a pair of valves carried by said armature, and means for normally closing said valves to block the ducts connecting respectively to one of said diaphragms and the opposed bellows from the atmosphere, whereby when neither of said relays is excited both of said bellows are completely sealed to lock said mechanical means in whatever position it may have been moved to.

2. In a servo-motor having a pair of opposed bellows, mechanical means interposed between said bellows and movable thereby, and a source of vacuum; walls defining a main chamber connected to said source, a pair of diaphragms each forming a part of the wallof said chamber, means defining separate diaphragm chambers around the outer sides of each of said diaphragms, a pair of auxiliary chambers eachconnected to one of said bellows, and each having valve openings connecting with said main chamber, a valve normally closing each of said openings and positioned to be operated by one oif said diaphragms, a duct connected to each of said bellows, a duct connected to each of said separate chambers, each of said bellows ducts opening to the atmosphere adjacent an opening to the atmosphere of a separate chamber duct, and

separate control valves movable to simultaneously seal, or selectively open each pair of adjacent duct openings to the atmosphere.

3. In a servo-motor havinga pair of opposed bellows, mechanical means interposed between said bellows and movable thereby, and a source of vacuum; walls defining a main chamber connected to said source, a pair of diaphragms each separate control valves movable to seal or open each pair of adjacent openings, means for normally holding said separate control valves closed to seal both of said bellows from the atmosphere in whatever position they may have moved to,

' and means for selectively moving saidvalves to forming a part of the wall of said chamber,

means defining separate diaphragm chambers around the outer sides of each of said diaphragms, a pair of auxiliary chambers each connected to one of said bellows, and each having valve openings connecting with said main chamber, a valve normally closing each of said openings and positioned to be operated by one of said diaphragms, a duct connected to each of said bellows, a duct connected to each of said separate chambers, each of said bellows ducts opening to the atmosphere adjacent an opening to the atmosphere of a separate chamber duct, and

open the adjacent valve controlled openings to the atmosphere thereby changing the position oi said bellows.

4. In a servo-motor having a pair of opposed bellows, mechanical means interposed between said bellows, and movable thereby, and a source of vacuum; a normally closed diaphragm actuated valve associated with each bellows and operative when said diaphragm is opened to atmosphere to connect said source to said bellows, a duct connected to each of said diaphragms, a second duct connected to each bellows, and a pair of electro-pneumatic relays for energizing said servo-motor, each relay comprising an electromagnet, an armature for said magnet, a pair of valves carried by said armature, means for normally closing said valves to block the ducts connecting respectively to one of said diaphragms and the opposed bellows from the atmosphere, whereby when neither of said relays is excited both of said bellows are completely sealed from the atmosphere to lock said mechanical means in whatever position it may have been moved to, and means for selectively exciting said relays to open the ducts controlled by the connected valve and thereby permit said source to the atmosphere to move said mechanical means to a new position.

5. In a servo-motor having a pair of opposed bellows, mechanical means interposed between said bellows, and movable thereby, and a source of vacuum; a normally closed diaphragm actuated valve associated with each bellows and operative when said diaphragm is opened to atmosphere to connect said source to said bellows, a duct connected to each of said diaphragms, a second duct connected to each bellows, and a pair of electro-pneumatic relays for energizing said servo-motor, each relay comprising an electromagnet, an armature for said magnet, a pair of valves carried by said armature, means for normally closing said valves to block the ducts connecting respectively to oine of said diaphragms and the opposed bellows from the atmosphere, whereby when neither of said relays is excited both of said bellows are completely sealed from the atmosphere to lock said mechanical means in whatever position it may have been moved to, means for applying an exterior force to override said servo-motor, and a pair of spring actuated check valves respectively opening .into and out of each of said bellows for admitting atmospheric air or releasing air respectively into or from said bellows as required to permit said override upon application of a predetermined exterior force.

JESS S. MORRISON.

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