US2997025A

US2997025A - Externally triggered actuator

Info

Publication number: US2997025A
Application number: US690774A
Authority: US
Inventors: Jack B Ottestad; Samuel A Skeen
Original assignee: General Dynamics Corp
Current assignee: General Dynamics Corp
Priority date: 1957-10-17
Filing date: 1957-10-17
Publication date: 1961-08-22
Anticipated expiration: 1978-08-22

Description

Aug. 22,1961 .1. B. oTTEsTAD ET AL 2,997,025

EXTERNALLY TRIGGERED ACTUATOR Filed Oct. 17. 1957 JW/r6.1.

i lf3 .ma 22 I i 16 f2, 96 1 ,HZ/rf?.

fag.

i If I p; 56 ig;

. l K l I i 40 f2 '12 l 76 o o jrw ,ZM/Maas 42 @596% ,HEL/rou rrEsr/QD, f j A snm/sz. Apr/4u@ 5x55@ f4 rranvgg l Ni; la @www ,50, 132 g 2,997 ,025 EXTERNALLY TRIGGERED ACTUATUR Jael: B. Uttestad, Claremont, and Samuel A. Skeen, West Covina, Calif., assgnors to General Dynamics Corporation, San Diego, Calif., a corporation of Delaware Filed Oct. 17, 1957, Ser. No. 690,774 16 Claims. (Cl. 121-38) This invention relates generally to actuators; more particularly, it relates to an actuator utilizing actuating pressure released by an externally controlled triggering force.

The present invention represents improvements upon the actuators described and claimed in the copending application of Jack Benton Ottestad, Serial No. 617,014, filed October 19, 1956, and in the copending application of I ack Benton Ottestad and Samuel Arthur Skeen, Serial No. 683,855, led September 13, 1957. In the actuators of those applications, a setting pressure urges a piston toward a wall or plate. The piston causes a sealing element disposed about an orifice in the plate to effect a positive pressure seal between the plate and the piston. A predetermined actuating pressure acts upon the por tion of the piston within this seal. To activate the actuator, this pressure is increased to overbalance the force of the setting pressure. The piston is thus moved from the orifice plate to eliminate the pressure seal and release the actuating pressure to act upon the area of the piston outside the sealing element. An output thrust is thereby produced on the piston.

In certain embodiments of the inventions of the copending applications, a setting pressure produces the setting force. For a given actuator, there must be a definite ratio of actuating pressure to setting pressure. This ratio is determined by the area of the portion of the piston upon which the actuating pressure initially acts, because to activate the actuator, this pressure must be increased to overbalance the setting force. The ratio limits the versatility of the actuator. The actuating pressure must be increased by means of a control to overbalance the setting force, making it difficult accurately to control the exact time of activation.

The improved actuator of the present invention utilizes means for applying an externally controlled triggering force. This force coacts with the force exerted by the actuating pressure on the above-mentioned portion of the piston within the seal to move the piston and eliminate the pressure seal. The actuating pressure is thereby released upon the piston area outside the seal. IThe actuating pressure and the setting pressure need not bear a ratio determined by geometric considerations. Much wider selection of pressures is therefore possible. Better control of the time of activation is pro-vided, because the triggering pressure may be suddenly applied, in contrast with the more gradual increase of actuating pressure to trigger the actuators of the copending applications.

It is, therefore, an object of the present invention to alleviate the foregoing and other disadvantages by providing an actuator having improved activation control.

lIt is an object of this invention to provide new and improved triggering means for activating an actuator.

An object of the present invention is the provision of an actuator wherein increased output versatility is provided by novel features which permit wide selection of the pressures utilized in the actuator.

It is an object of the present invention to provide an actuator which is adapted for accurate control of the time of activation.

`Other objects and features of the present invention, as well as many advantages thereof, will become apparent to those skilled in the art from a consideration of the 2,997,025 Patented Aug. 22, 1961 following description, the appended claims, and the accompanying drawings, in which:

-FIGURE 1 is an elevational view, partially in section, showing a preferred embodiment of the improved actuator' of the present invention;

FIGURE 2 is a perspective View showing a modified form of actuator triggering apparatus according to the present invention; and

FIGURE 3 is an elevational view showing two actuators interconnected for combined operation.

Referring to the drawings, and particularly to FIGURE 1, there is shown a preferred embodiment of the present invention. This embodiment is a pneumatic actuator utilizing principles of this invention.

The actuator includes an elongated cylindrical housing formed by three cylindrical sections, 10, 12 and 14. An apertured wall member 16 has a flange portion 18 disposed between adjacent ends of sections 10 and 12. Pressure sealing between wall member 16 and these cylindrical sections is provided by resilient annular seals disposed in appropriate annular grooves in the wall member at each side of flange portion 18. An aperture 22 in Wall member 16 is provided for a purpose which is mentioned hereinafter. `Internally threaded

annular members

24 and 26 are provided for engagement with threaded end portions of sections 10 and 12, as shown. A plurality of bolts 32 extend through spaced openings in the annular members and engage appropriate nuts to sel cure sections 10 and 12 in alignment and to clamp ange portion 18.

`

Cylindrical sections

12 and 14 are secured in alignment by internally threaded annular members 23 and 30, and by bolts 32, in the same manner as sections 1t] and 12 are secured. An orifice plate or wall member 34 is secured by its flange portion 36 in the same manner as wall member 16 is secured. Appropriate grooves in the orifice plate accommodate resilient seals 38, which provide pressure sealing between the plate and

sections

12 and 14. A contoured orifice 40 is provided for a purpose which is explained hereinbelow.

The cylindrical housing formed by

sections

10, 12 and 14, may be considered as divided into

pressure chambers

42, 44 and 46 by the orice plate 34 and the wall member .16.

Passages

48 and 50 are defined in the orifice plate and communicate respectively with

chambers

44 and 42, as shown. These passages are interconnected through a solenoid valve 52 by coupling 54, appropriate connections 56, a tubular member 58 and a coupling 60. Solenoid `valve 52 is of a conventional type and is connected with switch means (not shown) by an electrical conductor 62. The solenoid valve is normally closed and is adapted to be opened by electrical actuation to provide communication between

passages

48 and 50.

A piston 66 is slidably positioned in chamber 44 and has a threaded opening for engagement with a reduced threaded end portion 68 of a metering member 70. The metering member has an enlarged cylindrical section 74 and a contoured portion 76.

An annular seal base 78 is secured in an appropriate recess in piston 66 by metering member '711. A circular resilient pressure seal 811 encircles .-the metering member and is sceured to the seal base, as by bonding in an appropriate groove. An annular resilient sealing element 86 is positioned in la peripheral groove in piston 66 to provide pressure sealing between the piston and cylindrical section 12 of the housing.

A bearing ring 88 is spaced axially from sealing element 86 and is disposed in an appropriate recess in the piston. The ring reduces sliding friction and maintains Ialignment between the piston `and cylindrical section 12. A ylock ring 90 is in threaded engagement with a reduced bearing ring and a deceleration metering pin 94 by means of mutually engaging ange portions, as shown at 96. The deceleration metering pin has a peripheral surface 93, which is contoured along its length, and has an internal bore 100 adapted to fit about a thrust column .102. A reduced threaded end portion 104 of the column is in engagement with a threaded opening in the piston. Column 102 extends through aperture 22, chamber 46 and the end of the actuator. The thrust column lhas a reduced threaded end portion 106 exterior of the housing for engagement with a `workpiece 108, for utilization of the thrust produced by the Iactuator.

Metering member 70 and deceleration metering pin 94 are preferably formed as separate parts and are not formed integrally with the piston. As discussed hereinbelow, diferent contours of the metering member and of the pin provide different acceleration and deceleration patterns. Separate construction permits interchangeability of parts to provide a variety of such patterns.

An end member "110 has an opening defined therein through which the thrust column 102 extends. The end member is attached to cylindrical section by an internally threaded annular ring 112, which is in threaded engagement with this cylindrical section and which is secured to the end member as by bolts 32. An annular wiper 114 is disposed in an appropriate groove within the opening of the end member and engages the thrust column. A resilient annular sealing element 116 in an appropriate groove within the opening provides pressure sealing between the end member and the thrust column. A bearing ring 118 is disposed in an adjacent groove. The bearing ring and the sealing device 116 are secured in position as by a retaining plate 120 and bolts 122. Pressure sealing is provided by an annular seal 124 disposed in an appropriate recess in the retaining plate. A passage 126 and a fluid connection 128 interconnect chamber 46 with a source of pressure (not shown).

A base member 130 is provided at the end of the housing opposite end member 110, and is secured to cylindrical section 14 by an annular ring 132 and by bolts 134, in the same manner as end member 110 is secured to section 10. A sealing element 136 is disposed between the end of section 14 and the base member to provide pressure sealing. A passage 138 in the base member and a fluid coupling 140 interconnect a source of pressure (not shown) `with chamber 42.

In the operation of the above-described embodiment of the present invention, a setting pressure is first introduced into chamber K44 from a source of pressure (not shown) through passage 126 and connection 12S. The setting pressure acts upon the area of the piston between thrust column 102 and the housing, this being the transverse effective area of lock ring 90 and deceleration metering pin 94. This pressure exerts a setting force on the piston to seat it against the orifice plate or wall 34. Circular resilient seal 80 is compressed by this action against the surface of the orifice plate to effect positive pressure sealing between the piston and the orifice plate.

A predetermined actuaitng pressure is introduced into chamber 42 from a source of pressure (not shown) through passage 138 and coupling 140. This pressure acts upon the area of the metering pin surface and the area of piston 66 encompassed by seal 80, and opposes the force exerted by the setting pressure on the opposite side of the piston.

At a selected time, the solenoid valve 52 is actuated to release pressure to act upon the piston area outside circular seal 80. Opening the valve premits communicaiton between chamber 42 and this piston area through passage 50,

couplings

54 and 60, connections 56, tubular member 58, the valve, and passage 4S. The pressure on this piston area increases rapidly to a triggering pressure which is sufiicient to move the piston and to disengage seal 80. The triggering pressure coacts with the force exerted by the actuating pressure on the area within seal to overbalance the setting force produced by the setting pressure. Disengagement of the seal releases the actuating pressure upon the area of the piston outside the' seal and confronting the orifice plate. As discussed hereinbelow, the release of this pressure is regulated by metering member 70.

Resilient seal 80 is disengaged substantially instantaneously from the orifice plate. 1t will be understood that the seal performs a very important function in the operation of the present invention. This seal and its operation are described in the copending applications hereinbefore identified.

From the foregoing description, it will be understood that the present invention provides means for activating or triggering the actuator at a precisely predetermined time. The triggering is accomplished through the rapid application of an externally controlled triggering force to the piston, as by the introduction of a triggering pressure between the piston and the oritice plate while pressure sealing exists between these elements. The provision of such means constitutes an important feature of 'the present invention.

As described in the copending applications mentioned above, the gross potential thrust, which is available to be controlled for the production of a desired actuator output, is a `function of several factors. These include the values of the actuating and setting pressures, the ratio between these pressures, the masses of the piston and the thrust column, the area of the piston confronting the oritice plate, the area within seal 80, and the piston area upon which the setting pressure acts. If an actuating pressure of 2,000 pounds per square inch and a setting pressure of 200 pounds per square inch are utilized in an actuator wherein the piston area acted on by the setting pressure is 10 square inches and wherein the total piston area confronting the orifice plate (including the area within seal 80) is ll square inches, a maximum thrust of 20,000 pounds would be developed. This force would be produced when the metering member 70 has moved to a position where it does not restrict the release of pressure through orifice 40. It would be produced substantially instantaneously if no metering member were used. The flow is the difference between 22,000 pounds and 2,000 pounds acting oppositely on the piston. Assuming the mass being accelerated to be 10 pounds, the acceleration imparted to the piston would be 2,000 gs, in accordance with the equation F :maI

where F=force, m=mass, and a=acceleration.

An important feature of the present invention is the Versatility which results from the relatively unlimited range of pressure ratios which may be utilized. The utility of the actuator is increased because the wide choice of actuating pressures and setting pressures makes possible a great variety of thrust-time output patterns. In the operation of the actuators of the copending applications, the actuating pressure must bear a definite ratio to the setting pressure. The ratio is determined by the respective areas upon which the two pressures act prior to disengagement of the pressure seal between the piston and the orifice plate. The actuating pressure must overbalance the setting pressure to effect this disengagement. In effect, a given actuator has a fixed amplification ratio. It will be understood that the output versatility of such actuators is therefore limited.

The present invention does not require any particular ratio between the actuating and setting pressures. The provision of an externally controlled triggering force makes possible a very wide selection of pressures and ratios. The actuating pressure does not have to act upon the area within the resilient seal 80 to overbalance the force exerted by the setting pressure. The setting and actuating pressures may be varied as desired to effect a predetermined output from a given actuator. The only limitation is that the actuating pressure be sufficient to impart the desired thrust or acceleration to the piston agains the force exerted by the setting pressure. Wide variation and improved control of output waveform patterns is therefore obtainable with a given actuator through utilization of the plinciples of the present invention.

Although the actuator described above is a pneumatic actuator utilizing pressurized gas, it will be understood that the present invention may be utilized with actuators using hydraulic fluids. Each type is shown and described in the copending applications, hereinbefore identified.

The contoured metering member '70 controls the thrusttime or acceleration-time output of the actuator. The manner of determining the contouring of metering members to effect predetermined outputs is set forth in the copending applications. As set forth therein, metering members for use with gas differ from those used with hydraulic fluid. It is to be understood that the metering member is not an essential feature of the present invention, and that this invention may be utilized with actuators having no such member.

After disengagement of seal 80, the actuating pressure is released upon the piston through `a net orifice area governed by metering member 70. The net pressure on the piston varies according to this net flow area between the orifice and the metering member. The cross-sectional `area of contoured portion 76 of the member varies according to axial position thereon. The net flow area therefore varies in accordance with the position of the piston as it moves from the orifice wall or plate.

`It will `be understood that a selected output accelerationtirne pattern may be produced by providing an `appropriately contoured metering member.

Upon completion of the `acceleration phase of the predetermined output cycle, the deceleration metering pin 94 coacts with aperture 22 of wall member 16 to effect a predetermined deceleration pattern. Piston 66 forces the gas or fluid in chamber 44 through the deceleration aperture. rIhe net aperture flow `area is varied according to piston position by the longitudinal contour of the deceleration pin to produce a predetermined variation in back pressure. It will be understood that by using an appropriately contoured pin, a desired deceleration-time pattern may be obtained. It will be further understood that variations in the pressures in

chambers

42, 44, and 46, caused by volumetric changes during piston movement, affect the output acceleration-time pattern.

In addition to their function of admitting triggering pressure to act upon the piston, solenoid valve 52 its associated connections and couplings, and the passages in the orifice plate, perform the auxiliary function of relieving pressure which may be trapped between the piston and the orifice plate upon reseating the piston preparatory to repeated activation of the actuator. On reseating the piston by reducing the pressure in chamber 42 to a value slightly below the pressure in chamber 44, a gas pressure approximating this reduced pressure is trapped by circular seal Sil and by seal S6 between the piston and the orifice plate. If this trapped pressure were not relieved, it would act upon the piston area outside seal 80 and would tend to balance the force exerted oppositely on the piston by the setting pressure. Upon introducing the firing pressure into chamber 42, the piston would be moved by a pressure in chamber 42 which need only be sufiicient, in acting upon the area within seal 80, to overcome any net force exerted on the piston by the set pressure in excess of the force exerted by the trapped pressure. The actuator would therefore be inoperative, because the firing pressure could not be suddenly released over the piston area outside seal 80.

After the piston is reseated by the setting pressure, solenoid valve 52 is actuated. Pressure trapped as hereinbefore described is then relieved by passage through passage 48, the valve, connections 56, tubular member d y58, and passage 50, into chamber 42. It will therefore be understood that means are provided for the convenient release of pressure trapped as hereinbefore described.

External triggering according to the present invention may be accomplished by means other than those hereinbefore described. The triggering may be accomplished by mechanical means such as by the exertion on workpiece 108 of a mechanical triggering force. After the setting pressure and the actuating pressure are established in the manner hereinbefore described, this force is exerted on the workpiece in the direction indicated by the arrows in FIGURE l, to move piston 66 and disengage seal 80 from orifice plate 34. The piston surface outside the seal is thus exposed to the actuating pressure -in chamber 42. Thereafter, the operation of the actuator to produce a desired acceleration-time output pattern is as hereinbefore described.

It is to be understood that the application of force to the workpiece is merely one means of effecting mechanical triggering according to the present invention, and that various other means for effecting mechanical triggering will become apparent to those versed in the arts to which the present invention pertains.

In FIGURE 2, there is shown another form of valve apparatus for use in external triggering according to the present invention. lA conventional valve 142 controls a triggering pressure supplied through a coupling 144, which interconnects the valve with a source of pressure (not shown). The valve is manually operable by means of a handle `146 to release the triggering pressure through a coupling 150, an appropriate elbow connection 148, the coupling E54, and passage 48, in order toy apply it to the piston. It is generally preferred that the valve to be located immediately adjacent to passage 48, in order to minimize activation time of the actuator by shortening distance between the valve and the piston. However, the valve 142 is shown disposed at a distance from orifice plate 34 and passage 48 so that the actuator may be triggered from a convenient remote location.

It will be understood that the value of the triggering pressure supplied through connection e144 is determined by the relative values of the setting pressure and the firing pressure. -It is preferred that a high triggering pressure be utilized, because of the relatively faster triggering which is effected by such higher pressure. This is because the more rapid exertion of force by higher pressure `effects more rapid disengagement of seal 80 from the orifice plate. However, the actuator may be activated by a relatively very low triggering pressure. For example, if a setting pressure of l pounds per square inch acts upon the area of the piston about the thrust column, and an actuating pressure of 1750 pounds per square inch acts upon `an area of l square inch encompassed within seal 80, a triggering pressure of only 5 pounds per square inch will be sufficient, in acting upon a 10squareinch piston area outside the seal S0, to disengage this seal from the orifice plate and effect activation of the actuator.

From the foregoing description, it will be understood that means are provided whereby a relatively low triggering pressure may be utilized to control the activation of high thrust forces.

It will be apparent that the accurate control of the time of activation of the actuator, provided by external triggering according to the present invention, renders the present invention useful in coordinating actuator activation with a sequence or program of independent events. For example, such a sequence might be the steps in the operation of an apparatus under test, which is subjected to an acceleration-time pattern at a particular point in its operation.

The precise control of the time of activation provides an effective means for controlling the simultaneous activation of a plurality of actuators. In FIGURE 3 of the drawing there are shown two actuators of the type described here interconnected for simultaneous operation or for operation in predetermined sequence. A setting pressure is supplied through a common fluid connection 152 and a firing pressure is similarly supplied through a common coupling 154. A solenoid valve 52 is positioned adjacent to each actuator and is provided with a tubular member 58 and appropriate couplings and connections, as shown in FIGURE 1. Each solenoid valve is connected by an electrical connection 62 to switch means (not shown), by means of which the solenoid valves may be actuated simultaneously or in predetermined sequence.

Although specific embodiments of the present invention have been described and illustrated in detail, it is to be clearly understood that the same are by way of illustration and example only; it is to be understood that the invention is not limited thereto, as many variations will be readily apparent to those versed in the art and the invention is to be given its broadest possible interpretation within the terms of the appended claims.

We claim:

1. In an actuator having a piston movable within a housing by an actuating pressure, a thrust-generating apparatus comprising a wall with an orifice in said housing, sealing means positioned between and separating confronting surfaces of said piston and said wall for effecting a positive pressure seal therebetween about said orifice, setting means for urging said piston toward said wall to effect said pressure seal, means for establishing said actuating pressure to act upon a portion of said piston covering the orifice, and means for exerting triggering force on said piston for coacting with said pressure to move the piston from said wall surface to suddenly disengage said sealing means, thereby suddenly exposing an increased area of the piston to the actuating pressure, whereby thrust is produced on the piston.

2. In an actuator wherein a housing contains a wall defining an orifice and wherein a piston is movable by an actuating pressure, a thrust-generating apparatus comprising sealing means positioned between and separating confronting surfaces of said piston and said wall, setting means for exerting a force urging the piston to cover said orifice and scat said Sealing means against said wall surface to establish a positive pressure seal between the piston and said wall about said orifice, means establishing said actuating pressure to act upon the portion of the piston surface within said pressure seal, and means for introducing a triggering pressure to act upon an area of the piston outside said pressure seal, thereby suddenly disengaging said sealing means and suddenly exposing said area of the piston to the actuating pressure to produce thrust upon said piston.

3. In an actuator wherein a housing contains a wall defining an orifice and wherein a piston is movable by an actuating pressure for transmitting output thrust to a member connected therewith, a thrust-generating apparatus comprising sealing means positioned between said piston and said wall, setting means for exerting a force urging said piston to cover said orifice and seat said sealing means to establish a pressure seal between said piston and said wall about said orifice, means establishing an actuating pressure to act upon the portion of the piston within said pressure seal, and valve means connected with a source of triggering pressure for introducing said triggering pressure upon an area of the piston outside said pressure seal, whereby said sealing means is disengaged to expose said area of the piston to the actuating pressure to produce thrust upon said piston.

4. In an actuator wherein a housing has a wall defining an orifice and wherein a piston is movable by an actuating pressure for transmitting output thrust to a member connected therewith, a thrust-generating apparatus comprising sealing means positioned between said piston and said wall, setting means for exerting a force urging said piston to cover said orifice and causing said sealing means to establish a pressure seal between said piston and said wall about the orifice, means establishing said actuating pressure to act upon a portion of the piston within said pressure seal, valve means interconnecting a source of triggering pressure with an area of this piston outside said pressure seal, and control means for operating said valve means at a selected time to apply said triggering pressure to said area, thereby disengaging said sealing means and exposing said area of the piston to the actuating pressure to produce thrust upon said piston.

5. In an actuator wherein a housing contains a wall defining an orifice and wherein a piston is movable by an actuating pressure for transmitting output thrust to a member connected therewith, a thrust-generating apparatus comprising sealing means positioned between said piston and said wall, means establishing a setting pressure for exerting a force to urge said piston to cover the orifice and engage said sealing means to establish a pressure seal between said piston and said wall about said orifice, means establishing said actuating pressure to act upon a portion of the piston within said pressure seal, pressure conduit means for communicating the actuating pressure to an area of said piston outside said seal, and valve means in said conduit means, said valve means being operable to release the actuating pressure through said conduit means, thereby overbalancing said force to remove said pressure seal to product thrust on said piston.

6. In an actuator wherein a housing contains a wall defining an orifice and wherein a piston is movable by an actuating pressure, a thrust-generating apparatus cornprising sealing means positioned between said piston and said wall, setting means for exerting a force to urge said piston to cover the orifice and to cause said sealing means to establish a pressure seal between said piston and said wall about said orifice, means establishing said actuating pressure to act upon a portion of the piston within said pressure seal, valve means connected with a source of triggering pressure for introducing said triggering pressure upon an area of the piston outside said pressure seal, thereby removing said pressure seal to expose said piston area to the actuating pressure, and a contoured regulating member on the piston for regulating release of the actuating pressure through said orifice to produce a predetermined thrust pattern on the piston.

7. An actuator comprising a cylindrical housing, a plate within said housing, said plate having an orifice and defining first and second pressure chambers, a piston positioned in said first chamber and confronting said plate, a resilient pressure seal encircling said orifice for effecting positive pressure sealing between and for spacing confronting spaces of said piston and the plate, means establishing a setting pressure in said rst chamber to exert a force urging said piston toward said plate to cover said orifice and effect said pressure sealing, means for establishing an actuating pressure in said second chamber to act upon a portion of the piston within said seal, and means for applying a triggering pressure to an area of said piston outside said seal to overbalance said force and suddenly disengage said seal, thereby suddenly exposing said area of the piston to the actuating pressure to produce thrust on said piston.

8. An actuator comprising a cylindrical housing, a plate within said housing, said plate having an orifice and defining first and second pressure chambers, a piston positioned in said first chamber and confronting said plate, a resilient pressure seal encircling said orifice for effecting pressure sealing between said piston and the plate, means establishing a setting pressure in said first chamber to exert a force urging said piston toward said plate to cover said orifice and effect said pressure sealing, means for establishing an actuating pressure in said second chamber to act upon a portion of the piston within said seal, valve means interconnecting a source of triggering pressure with an area of the piston outside said seal, and control means for opening said valve means to apply said triggering pressure to said area, thereby disengaging said seal and exposing said area of the piston to the actuating pressure to produce thrust on said piston.

9. An actuator comprising a cylinder having a wall with an orifice, said wall cooperating with said cylinder to define first and second pressure chambers, a piston member positioned in said first chamber and having a surface confronting said wall, means for exerting a force urging said piston toward the wall to cover said orifice, a resilient sealing element positioned between said piston and said wall for effecting a pressure seal therebetween about said orifice, means for establishing in said second chamber an actuating pressure acting on a portion of said surface covering the orifice to oppose said force, and valve means for introducing a triggering pressure between the piston and the wall to act on an area of said surface outside said seal to overbalance said force and expose all of said surface to said actuating pressure, whereby thrust is produced upon said piston.

10. An actuator comprising a cylinder having a wall with an orifice, said wall cooperating with said cylinder to define first and second pressure chambers, a piston member positioned in said first chamber and having a surface confronting said wall, means for exerting a setting force urging said piston toward said wall to cover said orifice, a resilient sealing element positioned between and spacing confronting surfaces of said piston and said Wall for effecting a pressure seal therebetween about said orifice, means for establishing in said second chamber an actuating pressure acting on a portion of said surface covering the orifice to oppose said force, a thrust column connected with said piston, and means associated with said column for receiving a triggering force, said triggering force being capable of overbalancing said force to suddenly remove said pressure seal and suddenly expose all of said piston surface to said actuating pressure, whereby thrust is produced upon said piston.

11. An actuator comprising a cylindrical housing, a Wall within said housing, said Wall having an orifice and defining first and second pressure chambers, a piston positioned in said first chamber and confronting said wall, a resilient pressure seal encircling said orifice for effecting pressure sealing between said piston and the wall, means establishing a setting pressure in said first chamber to exert a force urging said piston toward said wall to cover said orifice and effect said pressure sealing, means for establishing an actuating pressure in said second chamber to act upon a portion of the piston within said seal, a solenoid valve connected with a source of triggering .pressure, means interconnecting said valve means with an area of the piston outside said seal, and control means for actuating said valve to release said triggering pressure upon said piston area, thereby disengaging said seal and exposing said area of the piston to the actuating pressure to produce thrust on said piston.

l2. An actuator comprising a cylindrical housing, a wall within said housing, said lwail having an orifice and defining first and second pressure chambers, a piston positioned in said first chamber and confronting said wall, a resilient pressure seal encircling said orifice for effecting pressure sealing between said piston and the wall, means establishing a setting pressure in said first chamber to exert a force urging said piston toward the wall to cover said orifice and effect said pressure sealing, means for establishing an actuating pressure in said second chamber to act upon a portion of the piston within said seal, pressure conduit means interconnecting said second chamber with an area of the piston outside said seal, and valve means being operable to permit communication through said conduit means, thereby overbalancing said force to disengage the seal and expose said area lto the actuating pressure to produce thrust on said piston.

13. An actuator comprising a cylinder having a wall with an orifice, said wall cooperating with said cylinder to define first and second pressure chambers, a piston member positioned in said first chamber and lhaving a surface confronting said wall, means for exerting a setting force urging said piston toward said wall to cover said orifice, a resilient sealing element positioned between said piston and said wall for effecting a pressure seal therebetween about said orifice, means for establishing in said second chamber an actuating pressure acting on a portion of said surface covering the orifice to oppose said force, pressure conduit means interconnecting said second chamber with an area of the piston outside said seal, a solenoid valve in said conduit means, and control means for actuating said valve to release said actuating pressure through said conduit means, thereby disengaging said sealing element and exposing said area to said actuating pressure to produce thrust on said piston.

14. An actuator comprising a cylinder having a Wall with an orifice, said wall cooperating with said cylinder to define first and second pressure chambers, a piston member positioned in said first chamber and having a surface confronting said Wall, means for exerting a setting force urging. said piston toward said wall to cover said orifice, a resilient sealing element positioned between said piston and said wall for effecting a pressure seal therebetween about said orifice, means for establishing in said second chamber an actuating pressure acting on a portion of said surface covering the orifice to oppose said force, valve means for introducing a triggering pressure between the piston and the wall to act on an area of said surface outside said seal to overbalance said force and expose all of said surface to said actuating pressure, and a contouredy regulating member carried by the piston for regulating release of the actuating pressure into said first chamber, whereby a predetermined output thrust pattern is produced on the piston.

15. An actuator comprising a cylindrical housing, a wall within said housing, said wall having an orifice and defining first and second pressure chambers, a piston positioned in said first chamber and confronting said wall, a resilient pressure seal encircling said orifice for effecting pressure sealing between said piston and the wall, means establishing a setting pressure in said first chamber to exert a force urging said piston toward the waill to cover said orifice and effect said pressure sealing, means for establishing an actuating pressure in said second chamber to act upon a portion of the piston within said seal, means for applying a triggering pressure to an area of the piston outside sai-d seal to overbalance said force and disengage said seal, thereby exposing said area to the actuating pressure to produce thrust on said piston, means defining a restricted passage within said housing, and a contoured `deceleration pin carried by said piston for movement into said passage to regulate flow therethrough to 'develop predetermined variation in deceleration force on the piston.

16. An actuator according to claim 15, and further including a contoured regulating member carried by the piston for regulating release of actuating pressure into said first chamber, whereby a predetermined output thrust pattern is produced on the piston.

References Cited in the tile of this patent UNITED STATES PATENTS 1,799,366 Heinkel Apr. 7, 1931 1,971,048 Parsons Aug. 21, 1934 2,133,170 Johnson Oct. 11, 1938 2,719,510 Elder Oct. 4, 1955 FOREIGN PATENTS 705,438 France Mar. 9, 1931 631,332 Great Britain Nov. 1, 1949 UNITED STATES, PATENT. OFFICE CERTIFICATE OF CORRECTION Patent No. 2,997,025 August-22, 1961 Jack B'. Ottestad et al. I

It is hereby certified that error appears in the above numb-eredfpatent requiring correction and that the 'said Letters Patent should read as corrected below.

Column 2, 'line 63, for "sceured" read secured -e' I ,f column 3, line 60, for v'factuaitng" read -m actuating lines 69 andfTO, for "premts communicaiton read permits communication column 5, line 4, for "agains" read against column 8, line 28, for "product"` read produce line 52, for "spaces" read surfaces Signed and sealed this 23rd day of January 1962',

(SEAL) Attest:

ERNEST W. SWIDER y y DAVID L, LADD Attesting Officer Commssionerof Patents