US2996072A - Actuator - Google Patents

Description

Aug. 15, 1961 R. D. ATCHLEY ACTUATOR 2 Sheets-Sheet 2 Filed May 23, 1960 Y ,5 j f/v 7b4/w, w @i d 0 6 2% L6 6 67 n@ .y W IIIIVU'IIIHHII.: .1E f... L] 9 w 7 7 f I w w ,w w M a @w l f7 5 f3 1 d A# United States Patent G 2,996,072 ACTUATOR Raymond D. Atchley, Los Angeles, Calif., assigner, by mesne assignments, to American Brake Shoe Company, New York, N.Y., a corporation of Delaware Filed May 23, 1960, Ser. No. 39,914 19 Claims. (Cl. 137-83) This application is a continuation-impart of application Serial No. 755,534, filed August 18, 1958, and Serial No. 755,775, filed August 18, 1958, now Patent Number 2,962,611, each of which is in turn a continuation-in-part of Serial No. 681,310, filed August 30, 1957, now Patent No. 2,884,907.

This invention relates to improvements in actuators.

IIt is an object of the present invention to provide a novel actuator design whereby a small change in signal input produces 'a large change in the unit controlled by the actuator.

Another object is the provision of an actuator comprising a movable beam or an armature and a motion transmitting device connected thereto, such armature and device being designed to be responsive to a small change in signal input.

A further object of the invention is the provision of an actuator in Iwhich the signal is mechanically applied to an armature in terms of an applied force or pressure tending to produce rotation of the armature.

-A still further object is the provision of an actuator in which fluid pressure responsive devices are mechanically connected to the armature and wherein a small effective pressure causes actuation of the armature, or alternatively, a large displacement of the armature can be produced for any given effective pressure applied against the armature.

The actuator of my invention is designed to have a low stiffness coefficient yand thus have a low natural frequency and to contain a movable member which is responsive to signals of low force and to have a relatively large displacement for low values 'of applied signal force.

The signal applied is in the preferred embodiment a mechanical force as distinguished from one applied by means of an electromagnetic transducer.

-In my preferred embodiment the force is applied to the movable member either hydraulically or pneumatically.

The system for -application of force to the movable member creates a balance of moments, each of large value but resulting in net moments of low value to cause the displacement of the movable member.

The actuator of the invention comprises basically a yieldably suspended armature mounted ladjacent the pole pieces of permanent magnet means. ln preferred practice the armature is suspended on a flexural constraint or ilexure member. Means are provided for deflecting the armature by application of a force to said `armature corresponding to the magnitude of a signal received by the force applying means. Unlike the actuator of my copending applicatiom the force is a mechanical force and does not of itself modify the flux of the permanent magnets. A motion transmitting device, e.g. in the nature of a rod or jet pipe, as described mo-re fully below, is connected to the armature for movement in response to displacement of the armature on the yieldable constraint or ilexure. lSuch rod or jet pipe transmits the motion of said armature in response to said signal to a unit such as a hydraulic motor which is being controlled by the actuator.

The armature is constructed of a magnetically permeable material, and as the armature is displaced from its initial position toward a magnet pole piece, a greater attractive force exists between the armature and the RCC pole piece of the permanent magnet means toward which it is being displaced. This attractive force is in a direction opposite to the restoring force of the stressed yieldable constraint or flexure on which the armature is mounted. This effectively reduces the restoring force. The displacement obtained by the application of the signal force is thus greater than would be obtained in the absence of the magnets. The coefficient (spring constant) which relates force to displacement is thus reduced, that is the stiffness of the device is thus effectively less. The mechanical stiffness is considered a positive stiffness or spring constant and for like reason the effect of the magnetic force is considered to `introduce a negative stiffness or spring constant. lldeally if the negative magnetic stiffness balances the mechanical stiffness there is ideally no restoring force exerted by the yieldable constraint to oppose the signal force causing displacement of the armature, and a minute signal force applied against the armature will produce a relatively large displacement thereof, and at zero stiffness an infinitely large response from the actuator control, that is, the, rod, jet pipe 'or other linkage connected to the armatufe, o'r a relatively large displacement of the armature is obtained `for a given applied force. As la practical matter the stiffnesses are n'ot exactly in balance and the net stiffness may be either positive or negative depending on' the system into which the actuator is embodied. p v

The armature restoring force is large and ideally substantially produced by any means applying la force independent of the system stiffness and which opposes the signal force in magnitude and direction to restore and maintain the system in a null or balanced condition. 'Such restoring force can be produced, for example, by a feedback to the armature and may come either directly as a result of the motion of the armature or from some device actuated by the motion of the armature. This feedback connection introduces a degeneration of the signal force and acts as a restoring force to null out the motion of the armature. An example of such feedback is described in my above copending applications.

The attractive force between the armature and the pole piece towards which it moves varies as the square of the distance between the armature and such pole piece'. The negative force or the mechanical stiffness of the )deldable constraint is substantially constant. Thus, the ratio bctween the mechanical stiffness of the yieldable constraint and the magnetic stiffness is variable. However, for small displacement of the armature, e.g. less than about one third the distance between the armature in its centered position and the adjacent pole piece, the magnetic stiffness provided by the pole pieces of the permanent magnet may be considered substantially constant because of the nature of the square law effect on the magneticstiffness.

Because of the feedback provided, the system of the invention is designed to operate as a null balance unfit so that the displacement of the armature is very minute, and under such operating conditions the ratio of the mechanical stiffness of the flexible constraint to the magnetic stiffness is substantially constant. Due to' the great reduction in stiffness of the system, a greater response is obtained for a given frequency of movement of the armature as compared to prior art systems. In employing the actuator described here with Ithe servo mechanism described in my copending applications and previous patent, a large gain from the hydraulic amplier is obtained. By permitting displacement of the armature by a small force, a greater dynamic response is obtained. e .A

The means for applying a force to the armature responsive to a signal received by such means,- can be any mechanical force applying means, such as a rod, diaphragm, bellows or the like. As a feature of the inventiom a plurality of such force applying means are employed in' an arrangement such that forces of large magnitude applied to the armature are resolved into a net ditferential force of small magnitude. Means may also be provided for setting the armature in its null position corresponding to a predetermined reference force applied to the armature.

According to one embodiment of :the invention a plurality of tiuid pressure diaphragms or bellows are attached mechanically to the armature which is mounted for angular motion about a pivot or hinges. One or more of such bellows may be actuating bellows to which the iiuid pressure being sensed or measured is conducted, while one or more bellows may be subjected to a constant pressure. The various bellows are positioned with respect to the pivot point of the armature so that a minute differential pressure resulting from the signal applied to the actuating bellows produces a moment tending to displace the armature angularly.

Instead of employing a plurality of bellows a single bellows can be connected to the armature to function as the force applying means responsive to the input signal.

The invention will be more readily understood by reference to the description below of a predeferred embodiment, taken in connection with the accompanying drawing wherein:

FIG. 1 is a section in elevation, through the invention actuator;

FIG. 2 is a section taken on line 2-2 of FIG. 1;

FIG. 3 is a perspective view of the torsional flexure for the armature of FIG. 1; and

FIG. 4 is a section taken on line 4-4 of FIG. 1.

Referring to the drawing, the valve case 1 is provided with an axial bore 2' therein. Case 1 also has a hole 2 (see FIG. 4) which intersects axial bore 2'. Additional bores such as 3 and 4 are also provided in case 1. Bores 3 and 4 may be connected to a reversible hydraulic or pneumatic motor (not shown) being controlled by the actuator herein described. Positioned in bore 2 is a sleeve 5 which is retained in case 1 by retaining nuts 6. The case 1 and bore 7 of sleeve 5 are sealed by two end caps 8 held in place by suitable bolts 9. Sleeve 5 is grooved at a plurality of locations 10 to give a series of lands 11, which are sealed by O-rings 12, and the sleeve 5 is ported with bores 13.

'I'he sleeve 5 ca rries a spool 14 in the form of a piston which makes a sliding engagement with the interior of sleeve 5 by means of lands 15, forming bores such as 16 intermediate the lands. Positioned at each end of bore l'7 are stop members 17 sealed by O-rings 18. The sleeve is further formed with bores at 19 into which the cone tip receptor jets 20 and 21 each provided with an inclined bore, 20 and 21', are pressed. The bore of jet 20 communicates via cross bore 22 with a port 22, and the bore of jet 21 communicates via cross bore 23 with a port 24, ports 22 and 24 connecting with chambers 25 and 26 in sleeve 5, adjacent the opposite ends of spool 14.

Positioned in the spool piston is a feedback spring held in the spool by means of a set screw 28 inserted through the threaded bore 29.

The structure described above and its function are more fully described in my Patent No. 2,884,907, and such description in said patent is hereby incorporated into this specilication by reference.

Carried on the upper face of the case 1 is an assembly, indicated generally by numeral 49, which is mounted on a mounting base 50 and is composed of a frame 52 which carries the armature 56 mounted on torsion members 55 (see FIGS. 3 and 4) formed by milling the shaft member 54 to form a thin spring web member. One end of the shaft S4 is rigidly xed to frame 52 by brazing, and the other end is formed as a fork 54' into which the armature 56 is rigidly fixed by brazing. At each end of the frame 52 is positioned a pole and magnet assembly composed of a C-shaped magnet 57 and a C-shaped magnet 57 oriented with their north poles and south poles opposite each other, each such assembly carrying a pole piece 58 at the north pole and a pole piece 59 at the south pole spaced from each other to produce a gap 58'. The armature 56 is positioned symmetrically in each of said gaps to give four equal gaps, two at one end of the armature and two at the other end between the adjacent pole pieces. Interiorly of the frame 52 and abutting the pole pieces 58, one at the north pole and one at the south pole, are the magnetically conductive members or pieces 60.

The frame 52 is bored at 63 and the bars 60 are bored at 60 and the armature is bored at 65 to receive the jet pipe 64 which is positioned within the bores 63, 60' and 6'5, pipe 64 being rigidly affixed to the armature 56 in the bore 65. The iiexible pipe 66, axially aligned with the pipe 64, is rigidly connected to the armature 56 in a counterbore 66. The mounting 50 of the torque motor is bored at 50' to permit the passage of the tube 66 and the pipe 64. The tube 66 is rigidly connected at its end 66" to the fitting 50. The fitting 50 is connected to the top of the case 1 and sealed by means of O-rings 50a as shown.

The pipe 64 has an ejector jet 65 brazed to it and extends into 4the slot 42 and is connected at its lower end to the .feedback spring 27 at the slot 42. The pipe 64 is bored with an axial bore 68, which connects with a cross bore 7i and a sufficiently flexible pipe 72 (see FIG. 4). The pipe 72 registers and is in liuid communication with the bore 73 which communicates with the bore 1 via restricted orifice 74 and the fittings 74 and 74 between which is positioned the screen 74a, as described more fully in Patent No. 2,884,907.

The receptor jets 20 and 21 are pressed into the sleeve 5 so that the angularly disposed bores 20' and 21' of the jets are so positioned that the center line of the bore 68 bisects the acute angle between the axis of the bores 20 and 21. The ends of the nozzles 20 and 21 are symmetrically positioned with respect to the center line of bore 68.

A iirst fluid pressure bellows 75 is connected between upper bar 6l) on frame 52 and one side of the upper face of the armature 56, and a second fluid pressure bellows 76 is connected betwen such bar 60 and the other side of the upper face of the armature 56. The axis of each of `these bellows is positioned equidistant from the axis of rotation of the armature 56. A third fluid pressure bellows 77 is connected between the lower bar 60 on frame 52 and the lower face of one side of armature S6, and a fourth fluid pressure bellows 78 is connected between the lower bar 60 and the lower face of the other side of the armature. The axis of each of the bellows 77 and 78 is positioned equidistant from the axis of rotation of the armature 56. However, it will be noted that the axis of each of the lower bellows 77 and 78 are each displaced an equal distance from the axis of rotation of the armature, somewhat greater than the distance of the axis of each of the upper bellows 75 and 76 from such axis of rotation. Fluid pressure inlets 79 and 79 are provided for uid communication with the interior of bellows 75 and 76, respectively. Fluid communication between bellows 7S and 77 and between bellows 76 and 78 is provided by the respective channels 86. Thus, the pressure in bellows 77 is the same as that ap plied to 75, and the pressure in bellows 78 is the same as the pressure applied to belows 76.

One end of the armature 56 has mounted thereon by means of screws 81 a yoke 80. A spring 82 has its upper end connected to the upper cross member 83 of the yoke, the other terminus of the spring being connected to an adjusting screw 84 threadably engaged in the upper face of case 1. By adjusting screw 84 the initial position of the armature between the pole faces of magnets 57 and 57 can be set as desired. Thus, for example, if the initial pressures applied to the bellows, as described more fully below, cause a clockwise rotation of armature 56, viewing FIG. 1, screw 84 is turned down sufficiently to center the armature between the pole pieces, and if there is a tendency toward counterclockwise rotation ofthe armature -due `to the initial -forces applied by the bellows, the screwp84 is backed off suciently to raise the arma- `ture to a centered position. During adjustment of screw "84, the cover 90, which normally encloses theassembly y49,is removed and after adjustment of screw 84, the

cover is'replaced and attached to the case 1 by means of screws 91.

The interconnected bellows 76 and 78, and/or the ` interconnected bellows 75 and 77 may be subjected to a positive pressure, atmospheric pressure, or a vacuum. A

Vreference pressure, which may be a positive absolute `zero level of the signal which is to be employed may be applied to bellows 75 and 77. At this base pressure corresponding to zero signal level the hydraulic or pneumatic motor being controlled by the actuator through ow of liluid via bores 3 and 4, is in the desired operating position. As result of the oiset position of bellows 75 and 77, a clockwise moment will be exerted by bellows 77 `against armature 56, as result of the base level pressure applied in bellows 75 and 77. Since such clockwise moment will be of greater magnitude than the opposing counterclockwise moment produced by the lower reference pressure in bellows 76 and 78, there will be a resulting net clockwise moment exerted against the armature. l1`his will cause the jet pipe 64 to pivot to the left, viewing FIG. 1, causing a greater pressure in the receptor jet 20 than in the receptor jet 2d, thus producing a greater pressure in chamber 25 than in chamber 26, and resulting in a displacement of the spool 14 to the right. This will result in a valving of the iluid by the spool to cause a ow of Huid through the valve to the tluid motor controlled by the spool valve.

In order to center the armature 56 to return the spool 14 to the null position shown in FG. l, the adjusting nut 84 is turned down to rotate armature 56 counterclockwise against the net clockwise moment applied by bellows 77 until the armature and the jet pipe are centered. Since now the moment on the armature produced by the signal force is balanced by the spring 82, the tension in the Vfeedback spring moves the spool back to its central null position. This adjustment of screw 84 and counterclockwise rotation of armature 56 rotates the pipe 64 back to its centered position shown in FlG. l, with respect to receptor jets 2t) and 21. This equalizes the ilow of fluid in bores 26" and 2li `of the receptor jets and equalizes the pressure applied against the ends of spool` 14. The centering of pipe 64 and the armature S6 and the balancing Vof the signal force by the spring SZ returns the spool 14 to its central position, as shown in FIG. 1. This will be indicated by a cessation `of ow of fluid from ports 3 and 4 to the hydraulic motor. rl'he armature 56 is now in a centered position with the oppositely applied moments of bellows 77 and 78 balanced, and the hydraulic motor being actuated is in the correct operating position desired for a net signal force at the design level of zero signal pressure.

Assume that no signal is impressed on the bellows 75 and 77,so that the armature 56 is in the null position and centered in [the gaps between the pole pieces 58 and 59, as shown in FIG. 1. The jet pipe 64 is undeected and the tube 66 is unbent and aligned symmetricallyV over 21' symmetrically placed, each of such bores will receive au equal amount of fluid from the jet'65. The'lluid 6 through 20 and 21 being thus under equal pressure exerts equal Ypressure against the opposite ends of spool'i1'4, and the spool 14 is centered,`as'shown in FIG. '1. The 'sp'oo'l 14 is thus hydraulically balanced, notwithstanding `flow Vof iluid yin jet pipe 64V and through receptor ,jets Z0v and 21, and the hydraulic motor is not actuated.'

If, new, the signal `generated .from the hydraulic or other motor being controlled by the actuator produces a pressure in bellows 75 and 77 ygreater than the initially set pressure therein, a relatively small ydifferential clockwise moment is-Iintroduced against the armature '56 yby bellows '77, tending to produce clockwise rotation of armature 56. The pipe 64 will rotate clockwise to the left as viewed in RIG. 1, producing a greater flow of duid in bore Z0' than 21 of the receptor jets and a displacement of the spool 14 to the right. This displacement of spool 14 causes a flow of Huid from the actuator via ports 3 and `4 to the hydraulic motor being controlled, to displace the hydraulic motor or to actuate it.

It `will be observed that as the spool is displaced to the right, viewing FIG. l, a spring force is imposed upon the pipe 64 by means 'of thespring 27, which spring force is Yproportional to the displacement of the piston spool so that the spring introduces a restoring Yforce in an amount equal to balance Vthe force causing movement of the armature in response to the signal, and to restore the pipe 64 to its neutral position, shown in FIG. 1, -at

which place the pressure in nozzles Z0 and 241 and chambers 25 and 26 are again equal, and further displacement of the piston cannot occur. The spring 27 thus acts as a force feedback to null out and balance the force of the signal causing the initial displacement. It will be ob served that in so doing the initial displacement of the piston occurring upon the reception of the signal is not altered so lon-g as the signal force applied to the actuator is at the original strength and direction. In consequence thereof, upon the reception of a signal by the armature the ejector jet pipe 64 is disp-laced an amount proportional to the force of the signal in Ia Idirection determined by the direction of the signal, and the piston spool is displaced an amount proportional to the signal strength in a direction determined by the direction of the signal, and is maintained in such displaced condition so long as the signal remains unchanged in Imagnitude and direction. Should the signal fall in strength but not reverse in direction, the spring force at Z7 will move the jet pipe 64 to the right, viewing FIG. l, and now the bore 21 receives more uid than does the bore 20, and the pressure in chamber 2.6 is greater than in chamber 245, and the spool 14 moves to the left. However, in so moving, the tension in the spring Z7 will move the jet 65' to the left to relax the tensi-'on to a value proportional to the new spool position closer to the center position, and reducing the flow of fluid exiting through 3 to the hydraulic motor and returning through 4. This may continue until the signal strength falls to zero, in which case the spool is centered and no fluid flow occurs in the hydraulic motor.

The function of the force feedback spring is described in greater detail in my Patent 2,884,907, and such disclosure in incorporated herein by reference.

Substantially the same mode of operation except in reverse to that described above takes place when the signal from the hydraulic motor being controlled by the actuator is reversed in direction, producing a pressure in bellows 75 and 77 less than the pressure at the set zero signal level, but in this situation the small net moment produced as result of the longer moment arm of bellows 7S as compared to bellows 76 will produce a counterclockwise motion of armature 56 and jet pipe 464, and a displacement of spool 14 to the left. This will result in a reversal of ow of fluid to the hydraulic motor.

It will be noted particularly that very large pressures can be introduced into the bellows 75 'and 77, but due ,.7 to the slightly oiset relation of bellows 77 with respect to bellows 7S, and of bellows 78 with respect to bellows 76, the net moment produced against armature 56 by the pressure in bellows 77 is very small, and hence the actuator of the invention can be made very small, yet is able to handle large signal pressures. Further, due to the balancing out of the mechanical stiffness of the ilexure 55 by the magnetic attraction of the magnets 57 and 57' for the armature 56, so that there exists substantially no restoring force exerted by the flexure SS to oppose the pressure, e.g. in bellows 77, causing a displacement of the armature, Weak exures can be used. In such case the natural frequency may be made low, and by suitable selection of magnets and thus the magnitude of the magnetic stiffness, this frequency may be adjusted up to the natural frequency of the system.

It is further to be noted that by means of the instant device, while the operation of the actuator has been described in terms of an actual rotation of the armature by the forces imposed thereon, there is actually practically no displacement of the armature, but rather only a tendency toward displacement, as result of changes in pressure in bellows 75 and 77 produced by changes in the input signal. The actuator hereof has as an additional advantage improved response at a given frequency.

Instead of employing a bellows system, any other mechanical means can be employed for impressing the signal on the armature from the device being controlled.

Instead of applying the invention actuator in conjunction with a servo mechanism of the type described in my above Patent 2,884,907, I may eliminate the jet pipe and spool valve structure described herein and connect the armature by suitable linking mechanism for control of any desired device. Thus, for example, I may employ my actuator, substituting, for example, a rod in place of the jet pipe 64, and eliminating the spool valve structure described herein, for controlling any other desired mechanism, by displacement of such rod, such as the system described in my application Serial No. 755,775, or by connecting a rod in the place of a jet pipe, the device may be used as a transducer to cause a displacement of a force summing means responsive to a pressure, e.g. as a pressure gage.

Although I have shown a Iforce feedback connection between the spool and jet pipe, I can instead employ a position feedback in the nature of a rigid connection between the jet pipe and spool.

Also, it will be understood that I can substitute any other suitable permanent magnet device for the specific permanent magnet system described above.

While I have described particular embodiments of my invention for the purpose of illustration, it should be understood that various modifications and adaptations thereof may be made within the spirit of the invention as set 4forth in the appended claims.

I claim:

1. An actuator which comprises an armature composed of magnetically permeable material, a yieldable mounting for said armature, permanent magnet means positioned in operative relation adjacent said armature, means for mechanically applying a force to said armature in response to a signal, to move said armature from a null position, the force of magnetic attraction of said permanent magnet means substantially balancing the mechanical stiffness of said yieldable mounting, and a motion transmitting device connected to said armature and operative in response to motion of said armature, and means for applying to said armature a restoring force independent of said mechanical stiffness and opposed in magnitude and direction to said signal force, to restore said armature to its null position.

2. An actuator which comprises an armature composed of magnetically permeable material, a yieldable mounting -for said armature, permanent magnet means positioned in operative relation adjacent said armature, means for mechanically applying a force to said armature in response to a signal, to move said armature from a null position, -the force of magnetic attraction of said permanent magnet means substantially balancing the mechanical stiffness of said yieldable mounting, and a jet pipe connected to said armature and movable in response to displacement of said armature, and means for applying to said armature a restoring force independent of said mechanical stiffness and opposed in magnitude and direction to said signal force, to restore said armature to its null position.

3. An actuator which comprises an armature composed of magnetically permeable material, a yieldable mounting for said armature permanent magnet means positioned in operative relation adjacent said armature, means 'for mechanically applying a -force to said armature, to move said armature from a null position, the force of magnetic attraction of said permanent magnet means substantially balancing the mechanical stiffness of said yieldable mounting, a motion transmitting device connected to said armature and operative in response to motion of said armature, means movable responsive to the motion of said motion transmitting device, and a feedback means connected to said motion transmitting device and said last named movable means for restoring said armature to its null position.

4. An actuator which comprises an armature composed of magnetically permeable material, a yieldable mounting for said armature permanent magnet means positioned in operative relation adjacent said armature, means for mechanically applying a force to said armature, the force of magnetic attraction of said permanent magnetic means substantially balancing the mechanical stiffness of said yieldable mounting, a jet pipe connected to said armature and movable 4from a null position in response to displacement of said armature, means movable responsive to the motion of said jet pipe and a feedback means connected to said jet pipe and said last named movable means for restoring said pipe to its null position.

5. An actuator which comprises an armature composed of magnetically permeable material, a yieldable mounting for said armature permanent magnet means positioned in operative relation adjacent said armature, means for mechanically applying a force to said armature, the force of magnetic attraction of said permanent magnet means substantially balancing the mechanical stitfness of said yieldable mounting, a jet pipe connected to said armature and movable from a null position in response to displacement of said armature, means movable responsive to the deflection of a fluid stream from said jet pipe on motion thereof, and a feedback means connected to said jet pipe and said last named movable means for restoring said pipe to its null position.

6` An actuator which comprises an armature composed of magnetically permeable material, a yieldable mounting for said armature, permanent magnet means positioned in operative relation adjacent said armature, means for mechanically applying a force to said armature, the force of magnetic attraction of said permanent magnet means substantially balancing the mechanical stiffness of said yieldable mounting, a jet pipe connected to said armature and movable from a null position in response to displacement of said armature, means movable responsive to the deflection of a uid stream from said jet pipe on `motion thereof, and a force feedback connected to said jet pipe and said last named movable means for restoring said pipe to its null position.

7. A11 actuator as defined in claim l, including means for adjusting said armature in said null position corresponding to a base signal force applied to said armature.

8. An actuator which comprises an armature support frame, an armature in said frame, said armature composed of magnetically permeable material, a shaft tixedly con- 'assente nected to said armature and to said frame, a torsional flexure in said shaft, permitting said armature to move angularly with respect to said shaft, a magnet vassembly mounted one at each end of said armature frame, said assembly comprising a pair of permanent magnets and a pair of pole pieces, one of the pole pieces Vin each assembly being connected to a north magnetic pole of each of said magnets of said pair, and another of the pole pieces in each assembly being connected to a south magnetic `pole of each said magnet of said pair, said pole pieces in each assembly being spaced to form a gap, one end of said armature being positioned in one of said gaps, and the other end of said armature being positioned in the other of said gaps, means for mechanically applying a force to said armature in response to a signal, to move said armature from a null position, the force of magnetic attraction of the pole pieces of said permanent magnets for said armature substantially balancing the mechanical stiffness of said flexure, and a motion transmitting device associated with said armature and operative in response to motion of said armature, and means for applying to said armature a restoring force independent of said mechanical stiffness and opposed in magnitude and direction to said signal force, to restore said armature to its null position.

9. An actuator which comprises a pair of spaced polarizing assemblies, each assembly composed of apair of permanent magnets, said magnets being fastened at their north poles to a pole piece and at their south poles to a second pole piece, said pole pieces being spaced to for-m a gap completing a magnetic circuit through the pole pieces and each of said permanent magnets in each of said assemblies, an armature, said armature composed of magnetically permeable material and extending into the gap in each of said `magnet assemblies, a mounting for said- Y armature, said mounting comprising a support, a flexure fixedly connected to said armature and said support for angular motion of said armature in said gaps about an axis through said flexure, and mechanical means for applying a force to said armature in response to a signal, to

move said armature from a null positio-n, the force of magnetic attraction of the pole pieces of said permanent magnets for said armature substantially balancing the mechanical stiffness of said fleXure, and -a jet pipe connected to said armature substantially at said axis and extendingmagnet assembly, an armature, said armature composed f of magnetically permeable material and extending into the gaps between adjacent pole pieces of said magnetic assembly, a mounting for said armature, said mounting comprising a support, a iiexure fixedly connected to said armature and said support for angular motion of said armature in said gaps about an axis'tthrough said flexure, a first mechanical force transmitting means connected to said armature on one side of said fiexure, a second mechanical force transmitting means connected to said armature on 'said one side of said flexure and in opposing relation to said first force transmitting means, the distance-between said flexure and said first means being somewhat greater than the `distance between said flex-ure and said second means, at least oneof said-force transmitting means being operative in response lto a signal, the force of magnetic attracl i6 assembly, pole pieces connected to said assembly, :said pole pieces being spaced to form a gap completing a niagnetic circuit through the pole pieces and said permanent magnet assembly, an armature, said armature composed of magnetically permeable material and extending into the gaps between adjacent pole pieces of said magnet assembly, a mounting for said armature, said mounting comprising a support, a flexure xedly connected to said armature and said support for angular motion of said armature in said gaps about an axis through saidiiexure, a first pressure responsive force transmitting member connected to said armature on one side of said fiexure, a second pressure responsive force transmitting member connected to said armature on the other side of said fiexure, said first and second members being mounted equidistant from said llexure and in force opposing relation on one face of said armature, a third pressure responsive force transmitting member connected to said armature on said one side of said ilexure, and a fourth pressure responsive force transmitting member connected to said armature on said other side of said flexure, said third and fourth members being mounted equidistant from said flexure and in force opposing relation on the other face of said armature, the distance between said flexure and each of said first and second members being slightly greater than the distance between said flexure and each of said third and fourth members, means for applying equal pressures to said first and third members in response to a signal, means. for applying equal pressures 'to said second and fourth members, the force of magnetic attraction of the pole pieces of said permanent magnets for said armature substantially Vbalancing the mechanical stiffness of said dexure, and a motion transmitting device associated with said armature and operative in response to motion of said armature.

12. An actuator as defined in claim l1, wherein said motion transmitting device includes a jet pipe connected to saidV armature substantially at the axis of said flexu're and extending perpendicular to said axis, means for passing fluid through said jet, and means responsive tothe movement of fluid from said jet pipe.

13. An actuator which comprises a pair of spaced polarizing assemblies, each assembly composed of a pair of permanent magnets, said magnets being fastened `at their north poles to a pole piece and at their south poles to a second pole piece, said pole pieces being spaced Vto form a gap completing a magnetic circuit through the pole pieces and each of said permanent magnets in each of said assemblies, an armature, said armature composed of magnetically permeable material and extending into the gap in each-of said magnet assemblies, a mounting for said armature, said mounting comprising a support fastened t-o each of said assemblies, a flexure fixedly connected to said armature and said support for angular motion of said armature in said gaps about an `axis through said fiexure, a first pressure responsive force transmitting bellows connected to said armature on one side of said flexure, a second pressure responsive force transmitting bellows connected to said armature on said one side of said flexure in opposing relation tosaid first bellows, the distance between said flexure and said rst bellows being slightly greater than the distance between said flexure and said second bellows, means for app-lying pressure to said first and second bellows, in response to a signal, the force of magnetic attraction of the pole pieces of said permanent magnets for said armature substantially balancing the mechanical stiffness of said ilexure, and a motion transmitting Idevice associated with said armature and operative in response to motion of said armature.

14. An actuator as defined in claim 13, wherein said motion transmitting device includes ajet pipe connected to said Varmature substantially at said aXis of said exure,

- and means responsive to the movement of fluid from said rjet pipe for applying to said armature a restoring force independent of said mechanical stiffness and opposed in 1 1 magnitude and direction to said signal force, to restore said armature to its null position.

15. An actuator as defined in claim 13, including adjustable spring means connected to one end of said armature for adjusting the armature in a centered position between said pole pieces corresponding to a base signal force applied to said armature.

16. An actuator which comprises a permanent magnet assembly, pole pieces connected to said assembly, said pole pieces being spaced to form a gap completing a magnetic circuit through the pole pieces and said permanent magnet assembly, an armature, said armature composed of magnetically permeable material and extending into the gaps between adjacent pole pieces of said magnet assembly, a mounting for said armature, said mounting comprising a support, a exure fixedly connected to said armature and said support for angular motion of said armature in said gaps about an axis through said flexure, mechanical means for applying a force to said armature in response to a signal, the force of magnetic attraction of the pole pieces of said permanent magnets for said armature substantially balancing the mechanical stiffness of said ytiexure, a jet pipe connected to said armature substantially at said axis and extending perpendicular to said axis and rotatable with said armature, an ejector jet at the end of said jet pipe, a pair of stationary receptor jets positioned adjacent said ejector jet and in fluid communication with said ejector jet, said ejector jet discharging a greater amount of fluid in one of said receptor jets than in the other on displacement of said ejector jet away from a centered position between said receptor jets, movable means responsive to the displacement of said ejector jet, and means connected to said movable means and said ejector jet for applying to said armature a restoring force independent of said mechanical stiffness and opposed in magnitude and direction to said signal force, to restore said armature to its null position.

17. An actuator which comprises a pair of spaced polarizing assemblies, each assembly composed of a pair of permanent magnets, said magnets being fastened at their north poles to a pole piece and at their south poles to a second pole piece, said pole pieces being spaced to form a gap completing a magnetic circuit through the pole pieces and each of said permanent magnets in each of said assemblies, an armature, said armature composed of magnetically permeable material and extending into the gap in each of said magnet assemblies, a mounting for said armature, said mounting comprising a support, a iexure fixedly connected to said armature and said support for angular motion of said armature in said gaps about an axis through said tlexure, mechanical means for applying a force to said armature in response to a signal, the force of magnetic attraction of the pole pieces of said permanent magnets for said armature substantially balancing the mechanical stiffness of said exure, a jet pipe connected to said armature substantially at said axis and extending perpendicular to said axis and rotatable with said armature, an ejector jet at the end of said jet pipe, a pair of stationary receptor jets positioned adjacent said ejector jet and in fluid communication with said ejector jet, said ejector jet discharging a greater amount of fluid in one of said receptor jets than in the other on rotation of said ejector jet away from a centered position between said receptor jets, a sleeve, a movable spool in said sleeve, closed first and second chambers in said sleeve at opposite ends of said spool, a first port in said sleeve communicating with said first chamber, a second port in said sleeve communicating with said second chamber, a first channel between one of said receptor jets and said first port, and a second channel between said other receptor jet and said second port, and feedback means connected between said spool and said jet pipe for restoring said pipe to its centered position.

18. An actuator which comprises a pair of spaced polarizing assemblies, each assembly composed of a pair of permanent magnets, said magnets being fastened at their north poles to a pole piece and at their south poles to a second pole piece, said pole pieces being spaced to form a gap completing a magnetic circuit through the pole pieces and each of said permanent magnets in each of said assemblies, an armature, said armature composed of magnetically permeable material and extending into the gap in each of said magnet assemblies, a mounting for said armature, said mounting comprising a support fastened to each of said assemblies, a exure xedly connected to said armature and said support for angular motion of said armature in said gaps about an axis through said tlexure, a first pressure responsive force transmitting bellows connected to said armature on one side of said exure, a second pressure responsive force transmitting bellows connected to said armature on the other side of said exure, said first and second bellows being mounted equidistant from said iiexure and in force opposing relation on one `face of said armature, a third pressure responsive force transmitting bellows connected to said armature on said one side of said flexure, and a fourth pressure responsive force transmitting bellows connected to said armature on said other side of said tlexure, said third and fourth bellows being mounted equidistant from said flexure and in force opposing relation on the other face of said armature, the distance between said flexure and the axis of each of said first and second bellows being slightly greater than the distance between said flexure and the axis of each of said third and fourth bellows, means for applying equal pressures to said first and third bellows, means for applying equal pressures to said second and fourth bellows, the force of magnetic attraction of the pole pieces of said permanent magnets for said armature substantially balancing the mechanical stiffness of said flexure, a jet pipe connected to said armature substantially at the axis of said exure and extending perpendicular to said axis and rotatable with said armature, an ejector jet at the end of said jet pipe, a pair of stationary receptor jets positioned adjacent said ejector jet and in fluid communication with said ejector jet, said ejector jet discharging a greater amount of fluid in one of said receptor jets than in the other on rotation of said ejector jet away from a centered position between said receptor jets, a sleeve, a movable spool in said sleeve, closed first and second chambers in said sleeve at opposite ends of said spool, a first port in said sleeve communicating with said first chamber, a second port in said sleeve communicating with said second chamber, a first channel between one of said receptor jets and said first port, and a second channel between said other receptor jet and said second port, and a force feedback spring connected between said spool and said jet pipe.

19. An actuator which comprises a permanent magnet assembly having north and south poles located opposite each other, pole pieces mounted adjacent each other at said north and south poles, respectively, said pole pieces being spaced to form a gap completing a magnetic circuit through the pole pieces and said permanent magnet assembly, an armature, said armature composed of magnetically permeable material and extending into 4the gaps between said adjacent pole pieces of said magnet assembly, a mounting for said armature, said mounting comprising a support, a exure connected to said armature and said support for angular motion of said armature in said gaps about an axis, said magnetic force substantially balancing the stiffness of said exure, a mechanical force transmitting means connected to said armature operative in response to a signal, and a motion transmitting device associated with said armature and operative in response to motion of said armature.

No references cited.

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