EP0229833A1

EP0229833A1 - Rotary actuator

Info

Publication number: EP0229833A1
Application number: EP19860904688
Authority: EP
Inventors: Paul P. Weyer
Original assignee: Individual
Current assignee: Individual
Priority date: 1985-07-16
Filing date: 1986-07-15
Publication date: 1987-07-29
Also published as: AU6138086A; WO1987000590A1

Abstract

Actuateur (10) mû par un fluide et comprenant un carter (12) possédant une chambre (26) présentant une paroi latérale interne à alésage lisse (16), un arbre (28) positionné à l'intérieur de la chambre de manière à pouvoir tourner par rapport au carter (12) autour d'un axe longitudinal excentrique par rapport à la chambre (26) et un piston (42) et un manchon (52) montés ß l'intérieur de la chambre (26) de manière à pouvoir effectuer un mouvement réciproque d'une extrémité à l'autre. Le piston (42) et le manchon (52) présentent chacun une ouverture (44, 54) à travers laquelle l'arbre (28) s'étend, ainsi qu'une paroi latérale externe coulissante latéralement sur la paroi latérale interne de la chambre de manière à permettre la transmission du couple entre les deux parois. Les ouvertures du piston et du manchon (44, 54) sont suffisamment excentrées par rapport à la chambre (26) pour empêcher la rotation du piston (42) ou du manchon (52) à l'intérieur du carter (12). Le manchon (52) et le piston (52) peuvent tourner indépendamment au moins dans une plage limitée suffisante pour leur permettre de s'engager latéralement dans la paroi latérale de la chambre (16). Des chemins de roulements de billes ou des cannelures (58, 60, 61) transmettent le couple entre l'arbre (28) et le piston (42) et le manchon (52). Des vis réglables (70) sont prévues entre le manchon (52) et le piston (42) pour permettre de déplacer l'un par rapport à l'autre afin d'obtenir une précharge. Des vis d'arrêt réglables (76) sont prévues soit dans les parois extrêmes de la chambre ou dans le piston (42) et dans le manchon (52) pour limiter leur course linéaire. Dans une variante, le carter possède une paroi latérale interne non cylindrique et l'arbre est positionné de manière coaxiale dans la chambre. Le piston et le manchon présentent une forme et une taille externes empêchant leur mouvement rotatif dans la chambre au-delà d'une plage limitée.Actuator (10) driven by a fluid and comprising a casing (12) having a chamber (26) having an internal side wall with a smooth bore (16), a shaft (28) positioned inside the chamber so as to be able rotate relative to the casing (12) about an eccentric longitudinal axis relative to the chamber (26) and a piston (42) and a sleeve (52) mounted inside the chamber (26) so as to be able reciprocate from one end to the other. The piston (42) and the sleeve (52) each have an opening (44, 54) through which the shaft (28) extends, as well as an external side wall sliding laterally on the internal side wall of the chamber. so as to allow the transmission of torque between the two walls. The openings of the piston and the sleeve (44, 54) are sufficiently eccentric with respect to the chamber (26) to prevent rotation of the piston (42) or of the sleeve (52) inside the housing (12). The sleeve (52) and the piston (52) can rotate independently at least within a limited range sufficient to allow them to engage laterally in the side wall of the chamber (16). Ball bearing paths or grooves (58, 60, 61) transmit the torque between the shaft (28) and the piston (42) and the sleeve (52). Adjustable screws (70) are provided between the sleeve (52) and the piston (42) to allow movement relative to each other to obtain a preload. Adjustable stop screws (76) are provided either in the end walls of the chamber or in the piston (42) and in the sleeve (52) to limit their linear travel. Alternatively, the housing has a non-cylindrical internal side wall and the shaft is positioned coaxially in the chamber. The piston and sleeve have an external shape and size preventing their rotary movement in the chamber beyond a limited range.

Description

ROTARY ACTUATOR

Cross-Reference to Related Applications

This is a continuation-in-par t of U.S. Patent Application Serial No. 575,228, filed January 30, 1984, and U.S. Patent Application Serial No. 692,293, filed January ₅ 17, 1985.

Technical Field

The present invention relates generally to actuators, and more particularly, to luid-powered actu-

■4_Q ators of the type in which axial movement of a piston produces relative rotational movement between a body and an output member.

Background Art

-^5 Rotary helical splined actuators have been employ¬ ed in the past to achieve the advantages of high-torque output from a simple linear pi s ton-and-cylinder drive arrangement. The actuators typically employ a cylindrical body with an elongated rotary output shaft extending from

20 ^en(^ ^{to en<}^ coaxially within the body, with an end portion of the shaft providing the drive output. Disposed between the body and the shaft is a piston sleeve splined to cooper¬ ate with corresponding splines formed on the body interior wall and the output shaft exterior. As an alternative to

25 forming splines on the interior wall of the body, a separate ring gear attached to the body may be used. The piston is reciprocally mounted within the body and has a head for the application of fluid pressure to one or the other opposing sides thereof to produce axial movement of

30 the piston. The sleeve is elongated and coaxially receives the shaft therein. As the piston linearly reciprocates in an axial direction within the body, the outer splines of the piston sleeve engage. the splines the body or ring gear to cause rotation of the sleeve. The resulting linear and rotational movement of the sleeve is transmitted through the inner splines of the sleeve to the splines of the shaft ^• to cause the shaft to rotate. Bearings are typically supplied to rotatably support one or both ends of the shaft relative to the body. With such an arrangement, the exterior surface of the shaft and the interior of the piston sleeve must be machined to produce inter es ing splines, and similarly, the exterior of the piston sleeve and the interior wall of the body must be machined to produce intermeshing splines. All components of the actuator so splined must have sufficient strength and thickness to permit the cutting of splines. Moreover, the cutting of splines is both expensive and time consumming, requiring precision machining. This results in ah actuator which is expensive to produce, heavy and large. Of course, this also requires that all components be manufactured from a material which is able to be machined and has sufficient strength so the cut splines will withstand the forces involved during fluid-powered operation. To avoid cutting splines in the body interior wall, a ring gear can be used; however, this results in a large diameter actuator as a result of the extra space the ring gear requires.

In the past, it has been difficult to manufacture a fluid-powered rotary actuator with relatively small size and a thin-walled construction at an economical price. Such an actuator is desirable for use in robotics and other situations in which a light, small sized, and inexpensive actuator operating on air or hydraulic fluid at pressures up to about 1500 psi is required. Furthermore, the actuator should be manuf acturable in large quantities without requiring as much precision machining as do existing actuators. The actuator should also be provided with precisely adjustable stops for setting the rotational limits of the output shaft while reducing any binding these stops might cause on the piston. The stops should be adjustable without requiring complete disassembly of the actuator. While using thin-walled construction, the actuator body must be sufficiently strong and durable. Another problem encountered with conventional actuators is backlash. As the piston reciprocally moves from one axial direction to the other to produce relative rotational movement between the body and the shaft in response to application of fluid pressure to the piston head, backlash results from the slack existing between the intermeshing splines of the piston sleeve and the body and the intermeshing splines of the piston sleeve and the shaft. While extremely accurate machining of the splines will reduce the backlash problem, this procedure substantially increases the manufacturing costs. Even with accurate machining, conventional machining techniques are virtually incapable of totally eliminating slack which produces the backlash problem. Furthermore, to the extent more accurate tolerances produce actuator parts which fit tightly together and reduce slack, the assembly of the actuator becomes difficult. It is desirable that the actuator should not require exceptionally accurate machining of the torque-transmitting parts to eliminate slack that produces backlash, and the actuator should be easy to assemble. To facilitate assembly, the design of an actuator ^' must incorporate a certain amount of slack, but the slack results in undesirable backlash during operation. Means should be provided for substantially complete elimination of the slack causing the backlash problem. Moreover, even though accurate machining reduces slack initially, should the torque- transmi tti ng parts wear during usage or otherwise lose their original tolerances, means should be provided for elimination of the slack that develops.

Elimination of the slack should be accomplished in a simple manner and with an adjustment which simultaneously remove the slack existing between all the torque-transmitting parts within the body which translate linear movement of the piston into rotational movement of the output member. The actuator should be usable with torque-transmitting means other than splines to avoid the undesirably high frictional coefficient of splines.

While actuators have been constructed using balls and helical ball races, and provide a higher output efficiency due to the rolling friction of the balls being less than the sliding friction of the splines, conventional helical ball screw actuators require recirculation of the balls as the ball carrier reciprocally moves within the actuator cylinder. The recirculation allows the balls to roll relatively unrestricted within the ball races to avoid the balls scuffing along the races. While the use of recirculation eliminates most of the ball scuffing problem, it is difficult and expensive to manufacture an actuator with a recirculation path; and no recirculation path can provide a totally unrestricted flow of the Balls. Additionally, to accommodate the recirculation path, the actuator must be made wider than ordinarly necessary since recirculation requires that the recirculation path double back over the ball races carrying the balls.

It is desirable to provide an actuator that avoids these problems, and that provides the benefits noted above. The present invention fulfills these needs and further provides other related advantages. Disclosure of Invention

The present invention resides in a fluid-powered actuator, including a body having a chamber with a smooth bore interior sidewall, and first and second ends; and a piston mounted within the chamber for endwise reciprocal movement therein responsive to the application of fluid pressure to one or the other opposing sid^"es thereof. In one embodiment of the invention, the piston has an endwise extending aperture therethrough eccentric with the chamber The actuator further includes adjustment means for selectively moving one of the member or the piston relative to the other to endwiae preload the member and the piston. The adjustment means provides sufficient adjustment to place the member and piston into sliding lateral engagement withthe chamber interior sidewall to thereby substantially eliminate backlash in the piston and member torque-transmitting means.

The adjustment means includes means for adjustably rotating or endwise moving one of the member or piston relative to the other b a selected amount to endwise preload them. In a disclosed preferred embodiment of the invention, the adjustment means includes an adjustable element extending between and engaging each of the member and the piston. The adjustable element provides^' an adjustable and oppositely directed endwise force on the member and the piston to move one of the member or piston relative to the other for endwise directed preloading of the member and piston.

The actuator body includes endwalls defining the first and second ends of the chamber and limiting endwise movement of the member and piston therein. In one embodiment of the invention, the piston and member each have a projecting stop adjustably extendable generally endwise outward therefrom to engage the corresponding endwall of the body and limit travel of the member and piston toward the endwalls. As such, the extent of linear travel of the member and piston toward the first and second ends can be selectively controlled, thereby setting precise preselected rotational movements on the shaft. In another embodiment, each of the endwals has a projecting stop adjustably extendable generally endwise inward therefrom to engage a corresponding one of the member or piston and limit travel thereof toward the endwalls. In both embodiments, the adjustable stops are located toward the axial center of the member and piston. and an exterior sidewall in sliding laterial engagement ^ with the interior sidewall of the chamber for transmitting torque between the piston and the body. A shaft is eccentirally positioned within the chamber and extends 5 through the piston aperature for rotation of the shaft about a longitudinal axis eccentric with the chamber. The piston aperture is sufficiently out of concentricity with the chamber to prevent rotation of the piston within the body as the piston reciprocates.

10 The shaft is supported for rotation relative to the body and connnectable to an external device. Piston torque-transmitting means are provided for transmitting torque between the piston and the shaft, and for producing

15 relative rotational movement between the shaft and the body in response to endwise movement of the piston. As such, the application of fluid pressure to the piston applies rotation causing torque on the shaft as the piston moves in the endwise direction in the chamber- in response to

20 selective application of fluid pressure to the piston. Rotation of the piston within the chamber about the shaft is prohibited by the eccentric location of the shaft.

In the preferred embodiment, a member is also mounted within the chamber for endwise reciprocal movement

25 therein in response to endwise movement of the piston. An endwise extending eccentric aperture is provided in the member generally corresponding to the piston aperture. The member is independently rotatable from the piston within at least a limited range sufficient to place the member and

30 the piston into slidng lateral engagement with the interior sidewall of the chamber. The actuator further includes ._j. member torque-transmitting means for transmitting torque between the member and the shaft, and for producing relative rotational movement between the shaft and the body 35 in response to endwise movement of the piston corresponding to the rotational movement produced by the piston torque-transmitting means. The piston and member torque-transmitting means includes ball races and stops arranged to permit substantially unimpeded rolling travel of the balls within the channels defined thereby and to engage and limit travel of the balls along the ball races. In alternative embodiments, the torque-transmitting means are innermeshing splines.

An alternative embodiment of the actuator utilizes a chamber with a non-cylindrical interior sidewall. The piston and member are mounted generall coaxially within the chamber and have an exterior shape and size preventing rotational movement within the chamber beyond a limited range. The shaft may be concentrically positioned within the chamber.

Other features and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings. Brief Description of the Drawings

Figure 1 is an isometric view of a fluid-powered actuator embodying the present invention utilizing an eccentric shaft with a cylindrical body.

Figure 2 is an enlarged, side elevational, sectional view of the actuator of Figure 1.

Figure 3 is a sectional view taken substantially along the line 3-3 of Figure 2.

Figure 4 is a schematic end view of the sleeve member and piston sleeve of the actuator of Figure 1 shown rotated to place them in lateral sliding engagement with the interior sidewall of the body, with the extent of rotation exaggerated for the purposes of illustration.

Figure 5 is a fragmentary side elevational, sectional view of a first alternative embodiment of the invention utilizing a splined piston and shaft arrangement and adjustable stops mounted in the end wall. Figure 6 is a side elevational, partial sectional view of a second alternative embodiment of the invention utilizing a concentric shaft with an elliptical body.

Figure 7 is a sectional view taken substantially along the line 7-7 of Figure 6.

Figure 8 is a fragmentary, isometric view of a third alternative embodiment of the invention utilizing an eccentric shaft and thin wall construction.

Best Mode for Carrying Out the Invention

As shown in the drawings for purposes of illustration, the present invention is embodied in a fluid-powered rotary actuator, indicated generally by reference numeral 10. The preferred embodiment of the actuator 10 is shown in Figures 1 through 4. The actuator 10 includes an elongated housing or body 12 having a generally cylindrical sidewall 14 with a smooth bore interior sidewall surface 16. A first end cap 18 is attached to the body 12 at a first end 20, and a second end cap 22 is attached to the body at a second end 24. The end caps 20 and 22 are attached to the sidewall 14 by threaded

^■fasteners 25. The sidewall 14 and the end caps 20 and 22 define a generally cylindrical chamber 26 within the body 12.

A rotary output shaft 28 is positioned within the body 12 for rotation about a longitudinal axis eccentric with the chamber 26, and is supported for rotation relative to the body 12. The end portions of the shaft 28 extend through an eccentric aperture 30 in each of the end caps 18 and 22, and the shaft is supported by axial thrust bearings 32 positioned between the caps and the shaft to prevent axial movement of the shaft. A circumferential ball race 34 is formed on each end portion of the shaft 28, and the caps 18 and 22 each have inserts 36 with axially inward opening ball races 38 extending about the apertures 30 and confronting the corresponding ball race on the shaft. The invention may be practiced with the shaft 28 rotatably driving an external device (not shown), or with the shaft being held stationary and the rotatable drive being provided by rotation of the body 12. With the present embodiment, the shaft 28 is provided with keyways 40 formed on the end portions of the shaft for attachment to an external device. Other means may be used for attachment of the external device to the shaft or the body. A cylindrical piston sleeve 42 is mounted within the chamber 26 for endwise or axially directed reciprocal movement therein, and has an eccentric endwise extending aperture 44 t erethrough, located to generally corresponding to the eccentric aperture 30 in each of the end caps 18 and 22. The shaft 28 projects through the piston sleeve aperture 44 and the aperture is sufficiently out of concentricity with the chamber 26 to prevent rotation of the piston sleeve within the chamber beyond a limited range. The piston sleeve 42. has a head portion 46 positioned toward the first end 20 of the body 12 and a sleeve portion 48 extending generally axially inward therefrom toward the second end 22. The head portion 46 carries conventional inner and outer seals 50 disposed between the head portion and the cor espo ding smooth-walled portions of the body sidewall 14, and between the head portion and a smooth surface portion of the shaft 28 to define fluid-tight compartments to each side of the head portion. The smooth-walled portion of the body sidewall 14 and smooth surface portion of the shaft 28 have su ficient axial length to accommodate the full stroke of the piston sleeve 42 within the chamber 26. Conventional seals 51 are disposed between the shaft 28 and the end caps 18 and 22 to prevent fluid leakage from the body 12. Reciprocation of the piston sleeve 42 within the body 12 occurs when hydraulic fluid or air under pressure selectively enters through one or the other of a pair of ports 53, located to opposing sides of the head portion .10

46 of the piston sleeve 42, which communicate with the fluid-tight compartments.

A sleeve 52 is reciprocally mounted within the chamber 26, generally coaxial with the sleeve portion 48 of the piston sleeve 42, for endwise reciprocal movement therein. The sleeve 52 is positioned between the sleeve portion 48 and the second end 22 of the body 12. The sleeve 52 also has an eccentric endwise extending aperture 54, located to generally corresponding to the apertures 30 in each of the end caps 18 and 22, and the aperture 44 in the piston sleeve 42. The shaft 28 projects through the aperture 54, and the aperture is sufficiently out of concentricity with the chamber 26 to prevent rotation of the sleeve within the chamber beyond a limited range.

The piston sleeve 42 and the sleeve 52 are independently rotatable in opposite directions within at least a limited range, sufficient to place a portion of the exterior sidewalls thereof into sliding lateral engagement with the smooth bore ^'interior sidewall surface 16 of the body sidewall 14 for transmitting torque therebetween and for backlash elimination purposes. The piston sleeve 42 and the sleeve 52 have an exterior diameter sufficiently less than the interior diameter of the chamber 26 to provide for the limited rotation. The actuator 10 utilizes no torque-transmitting splines or balls/ball races between the body 12 and the piston sleeve 42 and the sleeve 52.

A split nylon bearing 55 is positioned about the piston sleeve 42 and sleeve 52, and between them and the sidewall 14 of the body 12, which expands and contracts in circumference as the piston sleeve and sleeve are rotated relative to each other to eliminte backlash, as will be described in more detail below. The bearing 55 reduces the sliding friction as the piston and sleeve 42 and sleeve 52 reciprocate within the chamber 26 in sliding engagement into the body sidewall surface 16, and further improves the operation of the actuator 10 by eliminating the large 11

sliding friction associated with splines while still accomplishing the torque-transmission.

Positioned between the axially inward facing end walls of the sleeve portion 48 of the piston sleeve 42 and 5 the axially inward facing end wall of the sleeve 52 is a circular plate 56 with an eccentric aperture for the shaft 28. The piston sleeve 42 and the sleeve 52 are in sliding engagement with each other through the plate 56.

A helical ball race 58 is formed on the

10 midportion of the shaft 28 confronting and corresponding to both a helical ball race 60 formed on the radially inward facing wall of the piston sleeve aperture 44 along the sleeve portion 48 of the piston sleeve 42, and a helical

15 ball race 61 formed on the radially inward facing wall of the sleeve aperture 54 of the sleeve 52. The ball races 58, 60 and 61 have substantially identical lead and pitch, and form a pair of laterally confined, variable length ball channels defined by the area of coincidence of the

20 corresponding ball races. . ^■

One or more balls 62 are disposed in each of the ball channels for transmission of torque between the sleeve portion 48 of the piston sleeve 42 and the shaft 28, and between the sleeve 52 and the shaft. The pressure plate

25 56 serves as a ball stop, as do certain of the blocked ends of the ball races 58, 60 and 61, to engage and limit travel of the balls 62 and to regroup the balls, as will be described in more detail below. While for ease of understanding the ball races 58, 60 and 61 are described

30 herein as if single-start ball races, as shown in Figure 3, the ball races may be multiple-start ball races each with a corresponding ball race to form a ball channel and with one or more balls disposed therein. Of course, the more balls and ball races utilized the greater will be

35 torque-transmitting ability of the actuator.

The dashed lines, such as shown on Figure 2, indicate the linear extent of the ball races and the manner of termination of the ball races. As shown by the dashed lines on the piston sleeve 42 and the sleeve 52, the ball races 60 and 61 each have an axially outward end which terminates in a blocked end. The ball races 60 and 61 extend in the axially inward direction to the end of the piston sleeve and the sleeve, and terminate in an open end running out into the interior chamber 26 of the body 12. Both ends of the ball race 58 formed on the shaft 28 terminate in a blocked end 66. The apertures 44 and 54 of the piston sleeve 42 and the sleeve 52 are diametrically sized to produce minimal inner spacing between the piston sleeve and sleeve and the shaft 28 to increase ball contact with the ball channels and promote improved torque transmission by the balls 62 carried therein. The blocked end 66 of ball race 58 on the shaft

28, located toward the second end 24 of the body 12, engages and limits the travel of the balls 62 through the portion of the ball channel formed by the ball race 5B and

61 in the direction toward the second end 24. The blocked end 66 of the ball race 58 on the shaft 28 located toward the first end 20 of the body 12, engages and limits the travel of the balls 62 through the portion of the ball channel formed by the ball race 58 and 60 in the direction toward the first end 20. The plate 56 projects radially inward toward the shaft 28 sufficient to engage and limit the travel of balls

62 through the ball channels to engage and collect the balls to regroup them toward one of the blocked ends 66 of the ball race 58 on the shaft 28 as the piston sleeve 42 amd sleeve 52 travel in the direction toward the first or second ends 20 or 24. The plate 56 also blocks the open ends of the ball races 60 and 61 to prevent the balls 62 from passing out of the open end of one of the ball races into the open end of the other ball race. It is noted that the plate 56 will only operate to regroup the balls 62 in the ball channels should they not roll fully against the stops formed by the blocked ends 66 of the ball race 58, which limit travel of the balls 13

toward the first and second ends 20 and 24, when the piston sleeve 42 and the sleeve 52 complete their travel toward that end.

As measured with the piston sleeve 42 and the sleeve 52 positioned with the sleeve engaging the second end wall 22, as shown in Figure 2, the ball race 61 on the sleeve extends over an axial length of the sleeve projecting beyond the blocked end 66 of the ball race 58 toward the second end 24, at least one-half of the distance of the end-to-end axial travel of the sleeve within the chamber 26. The balls 62 disposed in the ball channel travel along the channel as they roll approximately one-half the distance the sleeve travels with respect to the body 12. To accommodate the slower travel of the balls 62, the ball race 61 must extend over a sufficient length of the sleeve 52 beyond the stop provided by the blocked end 66 of the ball race 58 to allow free rolling of the balls within the inner channel during the entire sleeve travel between its end limit at the^* second end 24 to its end limit at the first end 20 to avoid scuffing of the balls. Similarly, as measured with the piston sleeve 42 and the sleeve 52 positioned with the head portion 46 engaging the first end wall 18, the ball race 60 on the piston sleeve extends over an axial length of the piston sleeve projecting beyond the blocked end 66 of the ball race 58 toward the first end 20, at least one-half of the distance of the end-to-end axial travel of the piston sleeve within the chamber 26. To permit free rolling of the balls 62 in the ball channels, the ball race 58 extends unblocked over a sufficient axial length of the shaft 28 to each side of the plate 56, as measured with the piston sleeve 42 and sleeve 52 positioned at either end limit of theiraxial travel within the chamber 26, by at least one-half of the distance of the end-to-end axial travel of the piston sleeve and sleeve within the chamber. 14

The actuator 10 provides relative rotational movement between the body 12 and the shaft 28 through the conversion of fluid-actuated reciprocal linear movement of the piston sleeve 42 and the sleeve 52 into rotational movement of the shaft. As the piston sleeve 42 and the sleeve 52 linearly reciprocate between one or the other endwi sedir,ections within the chamber 26, torque is transmitted by the balls 62 through the coaction of the ball race 58 on the shaft 28 with the ball race 60 on the piston sleeve 42 and the ball race 61 on the sleeve 52. The transmitted torque causes the shaft 28 to rotate relative to the body 12 since the axial movement of the shaft is restricted by the thrust bearings 32. The transitted torque also tends to apply a counter-directed torque on the piston sleeve 42 and the sleeve 52 which is transmitted to the sidewall 14 of the body 12. As a result of the eccentric postioning of the shaft 28 relative to the chamber 26 and to the piston sleeve and sleeve, the counter-directed torque is prevented from rotating the piston sleeve and sleeve within the chamber 26. Hence, the linear movement of the piston sleeve 42 and the sleeve 52 is converted into rotation of the shaft 28.

As previously noted, the piston sleeve 42 and the sleeve 52 are independently rotatable within at least a limited range for backlash adjustment purposes. To accomplish the adjustment to eliminate backlash, the actuator 10 is provided with a plurality of axially extendable, circumferentially spaced apart set screws 70 each threadably received in a threaded bore 72 extending endwise through the sleeve 52. The set screws 70 are axially inwardly adjustable to project from the sleeve 52 and engage the plate 56 positioned between the sleeve and the piston sleeve 42. The set screws 70 thereby apply an adjustable and oppositely directed, axially outward force on each of the piston sleeve 42 and the sleeve 52 to force movement of the piston sleeve relative to the sleeve for axially preloading them. It is noted that while the force 15

is described as being axial, the movement of the piston sleeve 42 and sleeve 52 thereby produced is in opposite rotational directions. This is a result of the rotary action of the helical ball channels as the.set screw pushes the piston sleeve and sleeve apart.

The adjustment described is continued until, as shown schematically in Figure 4, the piston sleeve 42 and sleeve 52 are brought into tight sliding lateral engagement with the interior sidewall surface 16 of the sidewall 14 and sufficient oppositely directed axial force is applied on the piston sleeve and the sleeve to eliminate the slack in the ball races 58, 60 and 61 forming the ball channels. The piston sleeve 42 and sleeve 52 tend to move in opposite directions through the adjustment of the set screws 70 because of their tendency to rotate about the eccentrically positioned shaft 28. Unless the slack is eliminated between the ball races 58, 60 and 61 and between the piston sleeve 42 and th'e sleeve 52, when the actuator 10 is operated the slack will produce undesirable backlash.

In the preferred embodiment, the piston sleeve and sleeve are in contact with the expandable split bearing 55, rather than in direct contact with the sidewall surface. It is noted that the piston sleeve 42 and the sleeve 52 may be manufactured with a slightly oblong cross-section by relieving the sides of each in the area where they contact the sidewall 14 through the bearing 55 to enlarge the contact area between the piston sleeve and sleeve, and the sidewall. The adjustment of set screws 70 may be accomplished before the assembly comprising the shaft 28, piston sleeve 42 and sleeve 52 is inserted into the body chamber 26, or afterward if appropriately placed access parts are provided in the end cap 22 to gain access to the set screws 70. While described herein as an axial force, the same adjusting movement may be achieved by providing means for direct rotation of the piston sleeve 42 and sleeve 52 relative to each other to eliminate backlash since the helical ball channels produce both axial and rotational movement regardless of same movement may be achieved by providing means for direct rotation of the piston sleeve 42 and sleeve 52 to eliminate backlash since the helical ball channels produce both axial and rotational movement regardless of whether an axial or rotational force is applied to the piston sleeve and sleeve. It is noted that the same movement to eliminate backlash may be accomplished whether the set screws 70 apply opposite axially outwardly directed force on the piston sleeve and sleeve, or the piston sleeve and sleeve are spaced apart and the set screws are arranged to provide axially inward directed forces on the piston sleeve and sleeve to pull them toward each other. In both situations, the resultant oppositely directed axial and rotational movement of the piston sleeve and sleeve operates to eliminate the slack between the ball races of the ball channels.

Upon application of fluid pressure to one or the other side of the head portion 46 of the piston sleeve 52 during fluid-powered operation of the actuator 10, the piston sleeve 42 and the sleeve 52 move in unison, with substantially all backlash eliminated as the piston sleeve and the sleeve reciprocate within the chamber 26. Should usage of the actuator 10 cause wear of the ball races 58, 60 and 61 or the balls 62 therein, or should slack occur for any other reason, the slack can be easily removed in the same manner described above by further adjustment of the set screws 70. With the present invention, the ball races may be machined using conventional machining techniques with standard tolerances and sufficient slack to facilitate assembly of the actuator 10. The slack, which otherwise would create backlash problems can be simply eliminated by adjustment of the set screws 70 prior to fluid-powered operation of the actuator.

Furthermore, by not utilizing splines, ball channels/balls, ring gears or other space consumming torque-transmitting means to transmit torque between the 17

piston sleeve 42 and sleeve 52, and the body sidewall 14, a smaller diameter, lighter and less expensive actuator may be manufactured. A molded or tubular body may be used and precision machining of the body is eliminated. This facilitates easy and quick manufacture and assembly and reduces cost.

A thin wall body design is also made possible since no machining of splines or ball races is required on the body sidewall. The body sidewall need only have sufficient strength to withstand the forces transmitted on the wall by the counter-directed torque of the piston sleeve 42 and the sleeve 52. As -with the sidewall, the piston sleeve and sleeve do not require machining of splines or ball races, also reducing the size of the actuator. For robotics and other applications, this allows the manufacture of extremely small sized actuators of relatively high torque-transmitting capacity using tubular stock for the body sidewall 14. It is expected that an actuator can be made using the present invention with a .875 inch outer diameter using a plastic tube as the body sidewall. When using such a plastic tube for the sidewall, the split bearing 55 can be eliminated.- While the invention is not limited to such small sized actuators, it does allow the construction of an actuator in a size which might otherwise be impossible to achieve if splines or ball races were required to be cut on the interior wall of the body sidewall. Moreover, the use of a smooth bore body against which the piston sleeve and sleeve slide substantially eliminates the large sliding friction encountered with helical splines.

The actuator 10 is further provided with a pair of axially extendable stops 76 which limit the endwise linear travel of the piston sleeve 42 and sleeve 52 for setting precise preselective rotational limits on the shaft 28. One of the stops 76 is threadably received in an endwise extending threaded bore 78 in each of the piston sleeve 42 and the sleeve 52, and is axially outwardly 18

adjustable to project therefrom and engage the corresponding end cap 18 and 22. A threaded access port 73 is provided in the second end cap 22 for access to one of the stops 76 for its adjustment without further disassembling the actuator 10. The access port 73 is closed with a sealed threaded plug 74 when not in use to prevent the leakage of fluid therefrom. Access to the other stop 76 is through another threaded access port 79 provided in the first end cap 18. A sealed threaded plug 80 closes the access port 79 when not in use to prevent the leakage of fluid. As such, the adjustment to set the rotational limits of the shaft 28 may be achieved simply and without any significant disassembly of the torque-transmitting components of the actuator 10.

The eccentric^' shaft design of ' the actuator 10 with the shaft 28 located off center permits location of the stops 76 toward the axial center of the piston sleeve 42 and the sleeve 52. As such, the force aplied on the piston sleeve 42 and the sleeve 52 is more concentric than otherwise possible with a concentric shaft and a single contact stop. The usual resulting off-center force realized when using a concentric shaft and a single off-center stop which tends to cock and bind the piston sleeve and sleeve within the chamber is reduced or avoided.

In an alternative embodiment of the invention shown in Figure 5, the actuator 10 utlilizes an eccentric shaft having splines 82 formed on the shaft 28 intermeshing with splines 83 formed on each of the piston sleeve 42 and the sleeve 52 to transmit torque therebetween. In this embodiment splines are- used instead of the ball races and balls described above. Furthermore, instead of utilizing stops carried by the piston sleeve 42 and the sleeve 52 for setting the rotational limits of the shaft 28, a pair of stops 84 are provided, each threadably received in an endwise extending threaded bores 86 in one of the end caps 18 and 22. The stops 84 are axially inwardly adjustable to project from the end caps 18 and 22, and engage the 19

corresponding end of the piston sleeve 42 or the sleeve 52. A lock nut 88 is provided, and a seal 90 is positioned on the shaft between the lock and the end cap to prevent the leakage of the fluid. As discussed above for the first 5 embodiment, the eccentric shaft design of the actuator permits location of the stops 84 toward the axial center of the piston sleeve 42 and the sleeve 52 to reduce or eliminate binding.

It is noted that in both of the previously

]_Q described embodiments, the actuator 10 utilizes a relatively thick body sidewall 14 and is usable for high-pressure operation. The thickness of the sidewall can be reduced for lower pressue operation. As will be 5 described for the next described embodiments of the actuator, if the sidewall is so thin that it cannot be used to anchor fasteners connecting the end caps 18 and 22 to the sidewall, an alternative design can be employed using tie rods. Such an eccentric shaft actuator is shown in

2_Q Figure 8. -

Another alternative embodiment of the actuator 10 is shown in Figures 6 and 7. In many respects the actuator has the same construction as the previously described actuators and the description will not be repeated here.

25 Generally corresponding components will be assigned the same reference numerals. The actuator of Figure 6 and 7 is shown having a thin-wall construction, with the body sidewall 14 having its end portions set in correspondingly shaped recesses 92 in each of the end caps 18 and 22.

30 The end caps 18 and 22 are square in shape and the corner portions extend radially outward beyond the body sidewall 14. An aperture 94 is provided through each of the four corner portions of each of the end caps 18 and 22 outward of the body sidewall 14. The end caps 18 and 22

35 are held together with the body sidewall 14 positioned therebetween in the recesses 92 by tie rods 96 extending between and attached to each of the end caps. 20

The body 12 of the actuator 10 shown in Figures-6 and 7 has a non-cylindrical sidewall 14 with a smooth bore interior sidewall surface 16. With this arrangement, the output shaft 28 is positioned within the body 12 for rotation about a longitudinal access concentric with the chamber 26. Similarly, the apertures 30 in the end caps 18 and 22, and the apertures 44 and 54 and the piston sleeve 42 and the sleeve 52, respectively, are concentric with respect to the chamber 26. While this embodiment does not utilize the eccentric shaft previously described, the use of splines, ball channels, ring gears and other space consu ming torque-transmitting means to transmit torque between the piston sleeve 42 and sleeve 52, and the body sidewall 14 is similarly eliminated. The piston sleeve 42 and the sleeve 52 are prevented from rotating within the chamber 26 by the use of the non-cylindrical interior sidewall 14 in conjunction with the piston sleeve 42 and sleeve 52 having a corresponding shape and size which permits their sliding lateral engagement with the smooth bore interior sidewall surface 16, but prevents their rotation under the counter directed torque produced during fluid-powered operation of the actuator.

The shaft 28 may be concentrically positioned within the body and the bending moments experienced on the eccentric shaft of the previously described embodiments, as a result of the eccentric positioning of the shaft are eliminated. This embodiment does, however, maintain many of the benefits of the eccentric shaft actuator described above, including the ability to utilize a thin-wall design and to eliminate backlash, among others.

In the embodiment- of Figures 6 and 7, the bearing plate 56 is in the form of a ring and the set screws 70 for the elimination of backlash bear directly on the face of the piston sleeve 42. While the cross-sectional shape of the body sidewall 14 is shown as oblong or elliptical, other non-cylindrical shapes may be used. 21

It will be appreciated that, although specific embodiments of the invention have been described herein for purposes of illustration, various modifications may be made without departing from the spirit and scope of the invention. Accordingly, the invention is not limited except by the appended claims .

Claims

22Claims

1. A fluid-powered actuator, comprising: a body having a chamber with an interior sidewall, and first and second ends; a shaft positioned within said chamber and supported for rotation relative to said body about a longitudinal axis eccentric with said chamber; a first member mounted within said chamber for end¬ wise reciprocal movement therein; a second member mounted within said chamber, general¬ ly coaxial with said first member for endwise reciprocal move¬ ment therein, said second member being positioned between said first member and said second end, said first and second members each having an endwise extending eccentric aperture generally corresponding to the eccentricity of said shaft with said shaft projecting therethrough, said first and second members being independently rotatable about said shaft within at least a limited range sufficient to place said- first and second members into sliding lateral engagement with said interior sidewall of said chamber for transmitting torque therebetween, said apertures being sufficiently out of concentricity with said chamber to prevent rotation of said first and second members beyond said limited range; at least one piston reciprocally mounted within said chamber for application of fluid pressure to one or the other opposing sides thereof to produce endwise reciprocal movement, said piston operatively engaging at least one or the other of said first and second members to endwise move said members in response to endwise movement of said piston; first torque-transmitting means for transmitting torque between said first member and said shaft; second torque-transmitting means for transmitting torque between said second member and said shaft, said first and second torque-transmitting means producing corresponding 23

relative rotational movement between said shaft and said body in response to endwise movement of said piston; and adjustment means for selectively moving one of said first or second members relative to the other to endwise preload said first and second members, said adjustment means providing sufficient adjustment to place said first and second members into sliding lateral engagement with said interior sidewall of said chamber to thereby substantially eliminate backlash in said first and second torque-transmitting means.

2. The actuator of claim 1 wherein said adjustment means includes means for adjustably rotating one of said first or second members relative to the other by a selected amount to endwise preload said first and second members.

3. The actuator of claim 1 wherein said adjustment means includes means for adjustably endwise moving one of said first or second members relative to £he other by a selected amount to endwise preload said first and second members.

4. The actuator of claim 1 wherein said adjustment means includes an adjustable member extending between and engaging each of said first and second members, said adjustable member providing an adjustable and oppositely directly endwise force on said first and second members to move one of said first or second members relative to the other for endwise directed preloading of said first and second members.

5. The actuator of claim 4 wherein said piston is positioned outward of and fixedly attached to one of said first or second members for endwise movement thereof.

6. The actuator of claim 4 wherein said adjustable member includes a plurality of set screws threadably attached to one of said first or second members and projecting toward and engaging the other, said set screws being turnable in one direction forcing said first and second members to move relative to each other for endwise directed preloading of said first and second members.

7. The actuator of. claim 6 wherein said set screws slidably engage the other of said first or second members and are turnable to exert an axially outward force on each of said first and second members tending to separate said first and second members.

8. The actuator of claim 4 wherein said adjustable member is positioned completely within said chamber during fluid powered operation and wherein said adjustable member extends through an aperture in one of said first or second members and is adjustably extendable therefrom toward the other of said first or second members.

9. The actuator of claim 4 wherein said adjustable member is adjustably attached to one of said first or second members and projects toward and slidably engages the other, said adjustable member being selectively extendable to exert an axially outward force on said first and second members.

10. The actuator of claim 1 wherein said first torque-transmitting means includes a first ball race on said shaft, a second ball race on said first member corresponding to and confronting a first portion of said first ball race to form a first channel defined by the area of coincidence of said first and second ball races, a third ball race on said second member corresponding to and confronting a second portion of said first ball race to form a second channel defined by the area of coincidence of said first and third ball races, said first and second channels being helical; and the actuator further including: f i r s t and second s tops axi ally s tati onary wi t h respect to said shaft for engaging and limiting travel of balls 25

along said first ball race toward said first and second end, respectively, said second ball race extending over a sufficient endwise length of said first member projecting beyond said first stop toward said first end as measured with said piston positioned at its end limit of travel toward said first end, to permit substantially unimpeded rolling travel of balls within said first channel toward said second end as said piston travels from an end limit of travel at said first end to an end limit of travel at said second end, and said third ball race extending over a sufficient endwise length of said second member projecting beyond said second stop toward said second end as measured with said piston positioned at its end limit of travel toward said second end, to permit substantially unimpeded rolling travel of balls within said second channel toward said first end as said piston travels from an end limit of travel at said second end to an end limit of travel at said first end; at least one first ball seated in said first channel to^' a side of said first stop toward said second end for transmitting torque between said shaft and said first member upon endwise movement of said piston by the application of fluid pressure thereto; and at least one second ball seated in said second channel to a side of said second stop toward said first end for transmitting torque between said shaft and said second member upon endwise movement of said piston by the application of fluid pressure thereto.

11. The actuator of claim 10 wherein said first ball race extends over a sufficient axial length of said shaft to permit unimpeded rolling travel of said first and second balls within said first and second channels as said piston travels between said end limits of travel at said first and second ends.

12. The actuator of claim 10, further including: a third stop endwise stationary with respect to said first and second members, said third stop positioned between said first and second stops and dividing said first and second balls for engaging and collecting balls in said first channel for regrouping toward said first stop as said piston travels toward said first end, and for engaging and collecting balls in said second channel for regrouping toward said second stop as said piston travels toward said second end.

13. The actuator of claim 12^'wherein said third stop is a annular member endwise positioned within said body between said first and second members with said shaft extending therethrough, said annular member having a circumferential interior edge portion projecting inwardly sufficient to block travel of said first and second balls in said first race.

14. The actuator of claim 10 wherein said first and second stops are portions of said shaft forming the ends of said first ball race.

15. The actuator of claim 1 wherein said first and second torque-transmitting means include at least one or more grooves formed on said shaft for coacting with at least one or more grooves formed on each of said first and second members.

16. The actuator of claim 15 wherein said grooves are intermeshing splines.

17. The actuator of claim 15 wherein said grooves are ball races positioned in confronting and corresponding relationship to form ball channels, and said first and second torque-transmitting means further include one or more balls seated in each of said ball channels.

18. A fluid-powered actuator, comprising: 27

a body having a generally cylindrical chamber with an interior sidewall, and first and second ends; a shaft longitudinally positioned within said chamber and supported for rotation relative to sid body about a longitudinl axis eccentric with said chamber, said shaft being connectable to an external device; a first cylindrical member coaxially mounted within said chamber for longitudinal reciprocal movement therein; a second cylindrical member coaxially mounted within said chamber for longitudinal reciprocal movement therein, said first and second members each having a longitudinally extending eccentric aperture generally corresponding to the eccentricity of said shaft with said shaft extending therethrough and being independently rotatable about said shaft within at least a limited range sufficient to place said first and second members into lateral sliding engagement with said interior sidewall of said chamber for transmitting torque therebetween, said apertures being sufficiently out of concentricity with said chamber to prevent rotation of said first and second members beyond said limited range; a cylindrical piston coaxially mounted within said chamber for longitudinal reciprocal movement therein responsive to the application of fluid pressure to ^"one or the other opposing sides thereof, said piston operatively engaging at least one or the other of said first or second members to longitudinally move said members in response to longitudinal movement of said piston; first torque-transmitting means for transmitting torque between said first member and said shaft; second torque-transmitting means for transmitting torques between said second member and said shaft, said first and second torque-transmitting means producing corresponding relative rotational movement between said shaft and said body in response to longitudinal movement of said piston; and an adjustable member extending between and engagaing each of said first and second members, said adjustable member 28

being adjustably extendable for providing a selectable and oppositely directed longitudinal force on said first and second members to move one of said first or second members relative to the other member, thereby longitudinally preloading said first and second members, said adjustable member providing sufficient adjustment to place said first and second members into sliding lateral engagement with said interior sidewall of said chamber to substantially eliminate backlash in said first and second torque-transmitting means as said piston moves from one longitudinal direction to the other to produce relative rotational movement between said body and said shaft in response to selective application of fluid pressure to said piston.

19. The actuator of claim 18 wherein said body includes endwalls defining said first and second ends of said chamber and limiting endwise movement of said first and second members and said piston, and wherein the actuator further includes a pair of adjustable projecting stops within said chamber positioned to limit endwise travel of said first and second members and said piston toward said endwalls for setting precise preselected rotational limits on said shaft.

20. The actuator of claim 19 wherein said adjustable stops are located toward the axial center of said chamber.

21. A fluid-powered actuator, comprising: a body having a chamber with an interior sidewall, and first and second ends; a piston mounted within said chamber for endwise reciprocal movement therein responsive to the application of fluid pressure to one or the other opposing sides thereof, said piston having an endwise extending aperture therethrough eccentric with said chamber and an exterior sidewall in sliding lateral engagement with said interior sidewall of said

29

chamber for transmitting torque between said piston and said body; a shaft eccentrically positioned within said chamber and extending through said piston aperture for rotation of said shaft about a longitudinal axis eccentric with said chamber, said shaft being supported for rotation relative to said body and connectable to an external device; piston torque-transmitting means for transmitting torque between said piston and said shaft, said piston torque-transmitting means producing relative rotational movement between said shaft and said body in response to endwise movement of said piston, said piston aperture being sufficiently out of concentricity with said chamber to prevent substantial rotation of said piston within said body as said piston reciprocates, whereby the application of fluid power to said piston applies rotation causing torque on said shaft as the piston moves in the endwise direction in said chamber in response to selective application of fluid pressure to said piston, with rotation of said piston within said chamber about said shaft inhibited by the eccentric location of said shaft.

22. The actuator of claim 21, further including: a member mounted within said chamber for endwise reciprocal movement therein in response to endwise movement of said piston, said member having an endwise extending eccentric aperture generally corresponding to said piston aperture, said member being independently rotatabe from said piston within at least a limited range sufficient to place said member and said piston into sliding lateral engagement with said interior sidewall of said chamber, said piston aperture being sufficiently out of concentricity with said chamber to prevent rotation of said member and piston beyond said limited range; member torque-transmitting means for transmitting torque between said member and said shaft, said member torque-transmitting means producing relative rotational movement between said shaft and said body in response to 30

endwise movement of said piston corresponding to the rotational movement produced by said piston torque-transmitting means; and adjustment means for selectively moving one of said member or said piston relative to the other to endwise preload said member and said piston, said adjustment means providing sufficient adjustment to place said member and piston into sliding lateral engagement with said chamber interior sidewall to thereby substantially eliminate backlash in said piston.and member torque-transmi ting means.

23. The actuator of claim 22 wherein said adjustment means includes means for adjustably rotating one of said member or piston relative to the other by a selected amount to endwise preload said member and piston.

24. The actuator of claim 22 wherein said adjustment means includes mea₍ns for adjustably endwise moving one of said member or .piston relative to the other by a selected amount to endwise preload said member and piston.

25. The actuator of claim 22 wherein said adjustment means includes an adjustable element extending between and engaging each of said member and said piston, said adjustable element providing an adjustable and oppositely directed endwise force on said member and said piston to move one of said member or piston relative to the other for endwise directed preloading of said member and piston.

26. The actuator of claim 22 wherein said body includes endwalls defining said first and second ends of said chamber and limiting endwise movement of said member and piston, and wherein each of said piston and member includes a projecting stop adjustably extendable generally endwise outward therefrom to engage the corresponding endwall of said body and limit endwise travel of said member and piston toward said endwalls, whereby the extent of linear travel of said member 31

and piston toward said first and second ends can be selectively controlled, thereby setting precise preselected rotational limits on said shaft.

27. The actuator of claim 26 wherein said adjustable stops are located toward the axial center of said member and piston.

28. The actuator of claim 22 wherein said body includes endwalls defining said first and second ends of said chamber and limiting endwise movement of said member and piston, and wherein each of said endwalls has a projecting stop adjustable extendable generally endwise inward therefrom to engage the corresponding one of said member or piston and limit endwise travel of said member and piston toward said endwalls, whereby the extent of linear travel of said member and piston toward said first 'and second ends can be selectively controlled, thereby setting precise preselected rotational limits on said shaft.

29. The actuator of claim 28 wherein said adjustable stops are located to engage said member and piston toward the axial center thereof.

30. The actuator of claim 21 wherein said body includes endwalls defining said first and second ends of said chamber and limiting endwise movement of said piston, and wherein the actuator further includes a pair of adjustable projecting stops positioned to limit endwise travel of said piston towards said endwalls, whereby the extent of linear travel of said piston toward said first and second ends can be selectively controlled, thereby setting precise preselected rotational limits on said shaft. 32

31. The actuator of claim 30 wherein said adjustable stops are further positioned to apply a stop force on said piston toward the axial center thereof.

32. A fluid-powered actuator comprising: a body having a chamber with a smooth bore interior sidewall portion, and first and second ends; a piston mounted within said chamber for endwise reciprocal movement therein through said smooth bore sidewall portion responsive to the application of fluid pressure to one or the other opposing sides thereof, said piston having an endwise extending aperture therethrough and an exterior sidewall in sliding lateral engagement with said interior sidewall of said chamber for transmitting torque between said piston and said body; a shaft positioned within said chamber and extending through said piston aperture, said shaft being supported for rotation relative to said body and connectable. to an external device; piston torque-transmitting means for transmitting torque between said piston and said shaft, said piston torque-transmitting means producing relative rotational movement between said shaft and said body in response to endwise movement of said piston; and means without grooves for preventing substantial rotation of said piston within said body as said piston reciprocates, whereby the application of fluid power to said piston applies rotation causing torque on said shaft as the piston moves in the endwise direction in said chamber in response to selective application of fluid pressure to said piston, with rotation of said piston within said chamber about said shaft inhibited.

33. The actuator of claim 32, further including: a member mounted within said chamber for endwise reciprocal movement therein through said smooth bore sidewall 33

portion in response to endwise movement of said piston, said member having an endwise extending aperture generally corresponding to the aperture of said piston, said member being independently rotatable from said piston about said shaft within at least a limited range sufficient to place said member and said piston into sliding lateral engegement with said smooth bore sidewall portion of said chamber; means without grooves for preventing rotation of said member within said body as said piston reciprocates; member torque-transmitting means for transmitting torque between said member and said shaft, said member, torque-transmitting means producing relative rotational movement between said shaft and said body in response to endwise movement of said piston corresponding to the rotational movement produced by said piston torque-transmitting means; and adjustment means for selectively moving one of said member or said piston relative to the other to endwise preload said member and¹ said piston, said adjustment means providing sufficient adjustment to place said member and piston into sliding lateral engagement with said chamber interior sidewall to thereby substantially eliminate backlash in said piston and member torque-transmitting means.

34. The actuator of claim 33 wherein said adjustment means includes means for adjustably rotating one of said member or piston relative to the other by a selected amount to endwise preload said memver and piston.

35. The actuator of claim 33 wherein said adjustment means includes means for adjustably endwise moving one of said member or piston relative to the other by a selected amount to endwise preload said member and piston.

36. The actuator of claim 33 wherein said adjustment means includes an adjustably extendable element extending between and engaging each of said member and said piston, said 34

extendable element providing an adjustable and oppositely directed endwise force on said member and said^' piston to more one of said member or piston relative to the other for endwise directed preloading of said member and piston.

37. The actuator of claim 33 wherein said body includes endwalls defining said first and second ends of said chamber and limiting endwise movement of said member and piston, and wherein each of said piston and member includes a projecting stop adjustably extendable generally endwise outward therefrom to engage the corresponding endwall of said body and limit endwise travel of said member and piston toward said endwalls, whereby the extent of linear travel of said member and piston toward said first and second ends -can be selectively controlled, thereby setting precise preselected rotational limits on said shaft. -

^'38. The actuator of claim 37 wherein said adjustable stops are located toward the axial center of said member and piston.

39. The actuator of claim 33 wherein said body includes endwalls defining said first and second ends of said chamber and limiting endwise movement of said member and piston, and wherein each of said endwalls has a projecting stop adjustable extendable generally endwise inward therefrom to engage the corresponding one of said member or piston and limit endwise travel of said member and piston toward said endwalls, whereby the extent of linear travel of said member and piston toward said first and second ends can be selectively controlled, thereby setting precise preselected rotational limits on said shaft.

40. The actuator of claim 39 wherein said adjustable stops are located to engage said member and piston toward the axial center thereof. 35

41. A fluid-powered actuator, comprising: a body having a chamber with a non-cylindrical interior sidewall, and first and second ends; an axially extending rotatable shaft generally coaxially positioned within said chamber and supported for rotation relative to said body; a first member mounted within said chamber for end¬ wise reciprocal movement therein, said first member having an exterior shape and size preventing rotational movement within said chamber beyond a limited range; a second member mounted within said chamber for end¬ wise reciprocal movement therein, said second member having an exterior shape and size preventing rotational movement within said chamber beyond a limited range, said first and second members each having an endwise extending aperture with said shaft projecting therethrough and being independently rotatable about said shaft relative to each other sufficient to place said first and second members into sliding lateral engagement with said interior sidewall of said chamber for transmitting torque therebetween; at least one piston reciprocally mounted within said chamber for application of fluid pressure to one or the other opposing sides thereof to produce reciprocal axial movement of said piston, said piston operatively engaging at least one or the other of said first and second members to axially move said members in response to axial movement of said piston; first torque-transmitting means for transmitting torque between said first member and said shaft; second torque transmitting means for transmitting torque between said second member and said shaft, said first and second torque transmitting means producing corresponding relative rotational movement between said shaft and said body in response to endwise movement of said piston; and adjustment means for selectively moving one of said first or second members relative to the other of said second

36

members to axial ly preload said first and second members , said adjustment means providing sufficient ad justment to place sai d f i rst and second members i nto s liding lateral engagement with said interior sidewall of said chamber to thereby substant ially el imi nate backlash in said f irst and second torque transmitting means .

42 . The actuator of claim 41 wherein said adjustment means includes means for adjustably rotating one of said f i rst or second members relative to the other of said members by a selected amount to axi ally preload said f i rst and second members .

43 . The actuator of claim 41 wherein said adjustment means includes means for adjustably axially moving one of said first or second members relative to the other of said member by a selected amount to axially preload said f i rst and second members .

44 . The actuator of claim 41 wherei n said body includes endwalls defining said first and second ends of said chamber and limiting endwise movement of said first and second members and said piston, and wherein the axially outward ones of said piston and said members each include a projecting stop adjustably extendable generally axially outward therefrom to engage the corresponding endwall of said body and limit endwise travel of said members and piston , whereby the extent of linear travel of said members and piston toward said first and second ends can be selectively controlled , thereby setting preci se preselected rotational limits on said shaft.

4 5 . The actuator of claim 41 wherei n said body includes endwalls defining said f irst and second ends of said chamber and limiting endwise movement of said first and second members and piston, and wherein each of said endwalls has a projecting stop adjustable extendable generally axially inward therefrom to engage the corresponding one of said members or piston and limit endwise travel of said members and piston toward said endwalls, whereby the extent of linear travel of said members and piston toward said first and second ends can be selectively controlled, thereby setting precise preselected rotational limits on said shaft.

46. A fluid-powered actutor, comprising: a body having a chamber with a non-cylindrical smooth bore interior sidewall, and first and second ends; an axially extending rotatable shaft positioned within said chamber and supported for rotation relative to said body ; a first member generally coaxially mounted within said chamber for endwise reciprocal movement therein, said first member having an exterior shape and size_, preventing rotational movement within said chamber beyond a limited range; a second member generally coaxially mounted within said chamber for endwise reciprocal movement therein, said second member having an exterior shape and size preventing rotational movement within said chamber beyond a limited range, said first and second members each having an endwise extending aperture with said shaft proojecting therethrough and being independently rotatable about said shaft relative to each other sufficient to place said first and second members into sliding lateral engagement with said interior sidewall of said chamber for transmitting torque therebetween; at least one piston coaxially and reciprocally mounted within said chamber for application of fluid pressure to one or the other opposing sides thereof to produce reciprocal axial movement of said piston, said piston operatively engaging at least one or the other of said first and second members to axially move said members in response to axial movement of said piston; first torque-transmitting means for- transmitting torque between said first member and said shaft; 38

second torque transmitting means for transmitting torque between said second member and said shaft, said first and second torque transmitting means producing corresponding relative rotational movement between said shaft and said body in response to endwise movement of said piston; and adjustment means for selectively moving one of said first or second members relative, to the other of said members to axially preload said first and second members, said adjustment means providing sufficient adjustment to place said first and second members into sliding lateral engagement with said sidewall of said chamber to thereby substantially eliminate backlash in said first and second torque transmitting means .

47. The actuator of claim 46 wherein said adjustment means includes means for adjustably rotating one of said first or second members relative to the other of said members by a selected amount to axially _ preload said first and second members.

48. The actuator of claim 46 wherein said adjustment means includes means for adjustably axially moving one of said first or second members relative to the other of said members by a selected amount to axially preload said first and second members.

49. The actuator of claim 46 wherein said body includes endwalls defining said first and second ends of said chamber and limiting endwise movement of said first and second members and said piston, and wherein the actuator further includes a pair of adjustable projecting stops within said chamber positioned to limit endwise travel of said members and piston toward said endwalls and to selectively control the extent of linear travel of said members and piston toward said first and second ends, thereby setting precise preselected rotational limits on said shaft.