Recirculating ball screw rotary actuator

Abstract

To provide a compact rotary actuator having high torque efficiency and low friction features.SOLUTION: A rotary actuator for a hinged panel assembly of a fixed-wing aircraft includes ball bearings, an outer cylinder, a piston and an inner shaft. The cylinder admits fluid pressure from a fluid pressure supply device. The piston is surrounded by the cylinder. The piston, the cylinder and the ball bearings integrally form an outer ball screw. The piston translates along a longitudinal center axis according to the fluid pressure. The shaft is surrounded by the piston, and the shaft, the piston and the ball bearings integrally form an inner ball screw that is concentric with the outer ball screw. The ball screws form an interlaced ball circuit with one or more shared ball paths. Piston translation rotates the piston and the shaft to recirculate the ball bearings between the outer and inner ball screws through the interlaced ball circuit.SELECTED DRAWING: Figure 3

Description

[Background technology]

[0001] Fluid-driven linear and rotary actuators are used in a variety of dynamic systems to transmit torque and linear force to a driven load. A ball screw assembly is a commonly encountered type of linear actuator. A typical ball screw assembly uses a relatively short thread pitch to achieve large linear force and translation in response to a relatively low input torque. Rotary actuators often include an electric motor that is mechanically coupled to the driven load and selectively energized via a multi-cell battery pack or another power source. The energized motor responds by generating an output torque that can be transmitted to the coupled driven load. Rotary actuators may also be fluidically actuated, as in the case of rotor and rack-and-pinion actuators. A thread-on-thread Acme screw assembly is yet another example of an actuator commonly used to transmit force to a driven load. However, due to the high friction along the intermeshing threads, Acme screws are widely used in applications where such friction and the resulting potential failure modes are relatively well tolerated. Summary of the Invention [Means for solving the problem]

[0002] In its various embodiments, a compact rotary actuator is disclosed herein that is configured to provide high torque efficiency and low friction as compared to conventional actuators generally described above. The rotary actuator can be used as an on-axis or off-axis solution to efficiently drive the rotary hinged joints of a hinged panel assembly. Exemplary hinged panel assemblies include, but are not limited to, aerodynamic flight control surfaces / panels such as flaps, ailerons, rudders, trim tabs, or struts located on the wings and tails of fixed-wing aircraft, e.g., thin-wing aircraft. Other aviation applications, including, but not limited to, landing gear doors, cargo doors, and the like, can benefit from the present teachings, and the described rotary actuators also have utility across other industries requiring compact, highly efficient rotary actuation.

[0003] As described in more detail below, the rotary actuator of the present disclosure forms or defines two concentric ball screws that share / recirculate ball bearings via interlaced ball circuits having one or more shared ball paths. For further clarity, the two ball screws are referred to herein as an outer ball screw and an inner ball screw, since one ball screw is radially disposed within the other ball screw relative to the central longitudinal axis of the rotary actuator.

[0004] In the disclosed embodiment, one or two pistons translate within the outer cylinder in response to permissible fluid pressure from an external pressure supply. As this occurs, the outer and inner ball screws translate in opposite axial directions, and the translational motion and resulting rotation of the pistons ultimately causes the ball bearings to recirculate between the inner and outer ball screws. Because this occurs entirely within the envelope of the outer cylinder, the rotary actuator is characterized by the absence of an outer ball return path. Instead, the ball bearings roll within and translate along one or more shared ball paths, which may be embodied as a single continuous ball path or multiple shared ball paths, which together form the interlaced ball circuit described above. The rotation of the pistons ultimately imparts rotation to the inner shaft, which is then coupled to a driven load, such as, but not limited to, the rotary hinged joint or hinged panel assembly described above.

[0005] The outer cylinder defines a set of helical or spiral grooves which form the female threads of the outer ball screw. The piston translates within the outer cylinder by a pressure differential across the piston face and has an outer diameter which includes the male threads of the outer ball screw. The inner diameter of the piston includes the female threads of the inner ball screw. The inner shaft, enclosed by the piston and outer cylinder, includes the male threads of the inner ball screw. Thus, action of the inner ball screw causes the inner shaft to rotate relative to the piston.

[0006] The rotary actuators of the present disclosure may optionally be located on-axis with the rotary hinge joints of such hinged panel assemblies, thereby eliminating the need for associated crank assemblies and mechanical linkages to be housed within large underwing canoe fairings in the example thin-wing aircraft. In other configurations, the rotary actuators are located off-axis from the rotary hinge joints and connected to the rotary hinge joints via one or more mechanical linkages.

[0007] In a disclosed non-limiting embodiment, the rotary actuator includes a plurality of ball bearings, an outer cylinder, a piston, and an inner shaft. The outer cylinder has a plurality of fluid ports each configured to receive fluid pressure from a fluid pressure source. The piston is surrounded by the outer cylinder. The piston, the outer cylinder, and the ball bearing together form an outer ball screw. Further, the piston is configured to translate along a central longitudinal axis of the rotary actuator in response to the fluid pressure. The inner shaft is surrounded by the piston, and the inner shaft, the piston, and the ball bearing together form an inner ball screw concentric with the outer ball screw about the central longitudinal axis.

[0008] In this embodiment, the outer and inner ball screws together form an interlaced ball circuit having one or more shared ball paths. Translation of the piston along the longitudinal central axis in response to fluid pressure has a rotational dynamic effect, i.e., is effective to rotate the piston and inner shaft, and this action causes the ball bearings between the outer and inner ball screws to recirculate through the interlaced ball circuit.

[0009] A hinged panel assembly is also disclosed herein. According to a disclosed exemplary embodiment, the hinged panel assembly includes a rotary actuator and a rotary hinged joint interconnecting a first panel and a second panel and having an axis of rotation. The rotary actuator is connected to the rotary hinged joint and includes a rotatable inner shaft, a piston, an outer cylinder, and a plurality of ball bearings. The inner shaft is connected to the axis of rotation of the rotary hinged joint. The piston surrounds the rotatable inner shaft and is configured to translate along a central longitudinal axis of the rotary actuator in response to a fluid pressure. The outer cylinder surrounds the piston and has a plurality of fluid ports, each configured to receive a fluid pressure.

[0010] A rotatable inner shaft, a piston, and an outer cylinder are arranged concentrically about the longitudinal central axis to form two concentric ball screws that together define the interlaced ball circuits, and a ball bearing is disposed in at least one shared ball path of the interlaced ball circuits. In response to receipt of fluid pressure to the outer cylinder, translation of the piston along the longitudinal central axis is effective to recirculate the ball bearing between the two concentric ball screws via the at least one shared ball path and rotate the piston and inner shaft, thereby actuating the rotationally hinged joint and varying the angular position of the first panel relative to the second panel.

[0011] A fixed-wing aircraft is also disclosed herein. An exemplary embodiment of the fixed-wing aircraft includes a pair of wings and a tail connected to a fuselage, an aerodynamic flight control panel connected to one of the wings and / or the tail through a rotational hinged joint having an axis of rotation, and a rotational actuator connected to the rotational hinged joint and configured as described herein.

[0012] The above summary is not intended to represent all embodiments or all aspects of the present disclosure. Rather, the foregoing summary merely provides an illustration of some novel concepts and features described herein. The above features and advantages, as well as other features and advantages, will become readily apparent from the following detailed description of the illustrated embodiments and representative methods for implementing the present disclosure, when taken in conjunction with the accompanying drawings and the appended claims. Furthermore, the present disclosure expressly includes any and all combinations and subcombinations of the elements and features presented above and below. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic diagram of an exemplary fixed-wing aircraft having aerodynamic flight control surfaces, each actuable via a corresponding compact rotary actuator of the type described herein. [Figure 2A]FIG. 1 is a schematic diagram of an exemplary hinged aerodynamic flight control panel having a hinge axis powered via a rotary actuator of the present disclosure. [Figure 2B] FIG. 1 is a schematic diagram of an exemplary hinged aerodynamic flight control panel having a hinge axis powered via a rotary actuator of the present disclosure. [Figure 2C] FIG. 1 is a schematic diagram of a typical hinged aerodynamic flight control panel having two hinge axes each powered via a respective rotary actuator. [Figure 2D] FIG. 1 is a schematic diagram of a typical hinged aerodynamic flight control panel having two hinge axes each powered via a respective rotary actuator. [Diagram 3] FIG. 13 is a partial cross-sectional perspective view of a rotary actuator according to a possible single piston embodiment. [Figure 4] FIG. 4 is a schematic cross-sectional view of the rotary actuator shown in FIG. [Diagram 5] FIG. 1 is a schematic perspective view of an exemplary interlaced ball circuit formed from multiple shared ball paths that may be incorporated into the structure of the rotary actuator disclosed herein. [Figure 6] FIG. 5 is a schematic cross-sectional view of an alternative dual piston embodiment of the rotary actuator shown in FIGS. 3 and 4. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The present disclosure may extend to modifications and alternative forms, representative embodiments of which are shown by way of example in the drawings and described in detail below. The inventive aspects of the present disclosure are not limited to the disclosed embodiments. Rather, the present disclosure is intended to cover modifications, equivalents, combinations, and alternatives that are within the scope of the present disclosure, as defined by the appended claims.

[0015] The present disclosure is susceptible to embodiments in many different forms. Representative embodiments of the present disclosure are shown in the drawings and will be described in detail herein, with the understanding that these embodiments are provided as illustrations of the disclosed principles, rather than limitations of the broad aspects of the disclosure. To that extent, elements and limitations that are described, for example, in the Abstract, Background, Overview, and Detailed Description sections, but are not expressly recited in the claims, should not be incorporated into the claims, either individually or collectively, by implication, inference, or otherwise. For purposes of this detailed description, unless otherwise noted, singular includes plural and vice versa, for example, "a" means "at least one" or "one or more," the words "and" and "or" are both conjunctions and disjunctions, the words "any" and "all" both mean "any and all," and words such as "include," "contain," "comprise," "have" and the like each mean "including but not limited to." Furthermore, approximation terms such as "about," "approximately," "substantially," "approximately," "generally," and the like may be used herein to mean "in, near, or approximately," "within 0-5% of," "within acceptable manufacturing tolerances," or logical combinations thereof.

[0016] Referring to the drawings, in which like reference numbers refer to like features throughout the several views, an exemplary aircraft 10 is shown in FIG. 1. The aircraft 10, e.g., a fixed-wing aircraft as shown, includes a pair of wings 12 and a tail 14 connected to a fuselage 16. As will be appreciated by those skilled in the art, the wings 12 and tail 14 include various aerodynamic flight control surfaces or panels, generally indicated at 18. For example, each of the wings 12 may have one or more controllable flaps 18F and ailerons 18A, while the tail 14 includes a rudder 18R and elevators 18E. Other aerodynamic flight control panels 18, such as, but not limited to, spoilers, trim tabs, slats, etc., not explicitly shown in FIG. 1 but well understood in the art, may be used at other locations on the aircraft 10, such that the configuration and use of the aerodynamic flight control panels 18 may vary depending on the application and configuration of the aircraft 10.

[0017] Each of the aerodynamic flight control panels 18 is independently actuable via a respective compact rotary actuator 20 (FIGS. 3 and 4) or 200 (FIG. 6) constructed in accordance with the present disclosure. Each rotary actuator 20 and / or 200 used onboard the aircraft 10 is in fluid communication with a fluid pressure supply 15. In the illustrated exemplary aviation application, the fluid pressure supply 15 may optionally be embodied as a hydraulic fluid circuit for the aircraft 10, including hydraulic actuation fluid pumps, valves, fittings, hoses, and fluid filters, none of which are shown but which are well understood in the art.

[0018] 1 are selectively altered by the pilot of the aircraft 10, or autonomously by an on-board flight control unit or avionics unit (not shown) by receiving fluid pressure from a fluid pressure supply 15 to a rotary actuator 20, as described below. While the exemplary embodiment used herein to illustrate the present teachings contemplates the use of hydraulic fluid pressure for this purpose, other embodiments may be envisioned in which actuation of the aerodynamic flight control panels 18 is accomplished in other ways, such as by using compressed air or gas / pneumatic actuation. For ease of illustration, and without limiting actuation to such forms of actuation, the aerodynamic flight control surfaces 18 of the present disclosure are described below as being hydraulically actuated.

[0019] 2A and 2B, there is shown a hinged panel assembly 19 in which a first panel, in this case one of the wings 12 of FIG. 1, is connected to a second panel, in this case flap 18F, via a rotational hinge joint 21, which is aligned about a rotation axis or hinge axis A. 212A and 2B respectively show a "flap up" and "flap down" configuration of a representative aerodynamic flight control panel 18, with the other panels 18 shown in FIG. 1 being similarly arranged in other embodiments. FIGs. 2C and 2D similarly show a "flap up" and "flap down" configuration of another hinged panel assembly 190, with the notable difference being that the representative flap 18F shown in FIGs. 2A and 2B is replaced in FIGs. 2C and 2D by a two-piece flap assembly, namely, a leading edge flap 18F-1 and a trailing edge flap 18F-2, with "leading edge" and "trailing edge" referring to their relative positions with respect to the airflow over the wing 12. The leading edge and trailing edge flaps 18F-1 and 18F-2, respectively, are rotatably interconnected via a rotational hinge joint 21B.

[0020] In the configuration of Figures 2A-2D, the flap 18F and the leading edge flap 18F-1 are rotatably connected to the wing 12 using a rotary hinged joint 21 or 21A, respectively. The advantage of the rotary actuator 20 is its compact size and high torque efficiency. This allows the rotary actuator 20 to be rotated around the hinge axis A of the hinged joint 21, 21A, or 21B. 21 In the illustrated embodiment of FIG. 2A, for example, the rotary actuator 20 can be arranged on / coaxially with respect to a central longitudinal axis A of the rotary actuator 20. 20 and hinge axis A 21 The hinge axis A is aligned coaxially. 21 Such a coaxial arrangement reduces the packaging envelope required for the rotary actuator 20 and various mechanical arms or mechanical linkages that would otherwise be required, such as large canoe fairings of this type under the wings 12. Thus, the aircraft 10 of FIG. 1 when constructed using the present rotary actuator 20 may be characterized by the absence of such underwing fairings, with beneficial reductions in weight and drag.

[0021] Although shown in phantom in FIG. 2B to represent an optional alternative off-axis configuration, the rotational actuator 20 may be rotated about hinge axis A. 21 2C and 2D , as well as the other flight control panels 18 of FIG. 1 . Thus, while an on-axis placement of the rotary actuator 20 provides the above-described and other possible advantages, the present rotary actuator 20 may also be used off-axis within the scope of the present disclosure, for example, as a retrofit or aftermarket replacement for larger, less efficient actuators of the type typically housed in underwing fairings, as described above.

[0022] 3 and 4, the rotary actuator 20 incorporates two concentric / outer and inner ball screws to convert linear motion of the reciprocating piston 24 into rotational motion of the inner shaft 25. The inner shaft 25 may include a plurality of radial teeth or splines 125 as shown to facilitate meshing engagement of the inner shaft 25 with a driven load, for example, the rotationally hinged joint 21, 21A, or 21B of FIGS.

[0023] The rotary actuator 20 according to the exemplary embodiment of FIG. 3 includes three main components, namely, a piston 24, an inner shaft 25, and an outer cylinder 26, which are aligned along a central longitudinal axis A of the rotary actuator 20. 20 Therefore, the longitudinal center axis A 20are the central longitudinal axes of the piston 24, the inner shaft 25, and the outer cylinder 26, respectively. As will be explained in more detail below, fluid pressure is alternately received at opposite ends of the outer cylinder 26, as indicated by arrows P1 and P2. Such fluid pressure is selectively received into the outer cylinder 26 via corresponding fluid ports 41, one fluid port 41 being visible from the perspective of FIG. 3. For ease of illustration only, several ball bearings 42 are shown in FIG. 3. However, as will be understood by one of ordinary skill in the art, in an actual embodiment, all of the depicted ball paths 40 would be filled with ball bearings 42.

[0024] The multiple fluid ports 41 of the outer cylinder 26 may be formed at accessible locations of the outer cylinder 26, i.e., as bores or holes through the outer peripheral wall 26W of the outer cylinder 26. The inner diameter of the outer cylinder 26 defines / includes the female threads 28 of the outer ball screw 29-O. The outer diameter of the piston 24 defines or includes the male threads 32 of the outer ball screw 29-O, and the inner diameter of the piston 24 defines or includes the female threads 34 of the inner ball screw 29-I. Similarly, the outer diameter of the inner shaft 25 defines or includes the male threads 36 of the inner ball screw 29-I. The thread direction of the outer ball screw 29-O is opposite to the thread direction of the inner ball screw 29-I, thereby ensuring the desired movement and opposite translation.

[0025] As shown, for example, the female threads 28 and male threads 32 of the outer ballscrew 29-O are left-handed threads, and the female threads 34 and male threads 36 of the inner ballscrew 29-I are right-handed threads. However, in other embodiments, the opposite may be true, i.e., the female threads 28 and male threads 32 of the outer ballscrew 29-O may be right-handed threads, while the female threads 34 and male threads 36 of the inner ballscrew 29-I may be left-handed threads.

[0026] The piston 24 is configured to separate the outer cylinder 26 into multiple pressure cavities, e.g., pressure cavities 30A and 30B, as shown in FIG. 4. A plurality of fluid ports 41 in the outer cylinder 26 are configured to fluidly connect a fluid pressure supply 15 (see FIG. 1) to the multiple pressure cavities 30A and 30B. The position and configuration of the piston 24 forms a barrier between the oppositely disposed (nominally "right" and "left") fluid cavities 30A and 30B. A pressure differential across the piston 24 is defined by a pressure difference (pressure) between the oppositely disposed (nominally "right" and "left") fluid cavities 30A and 30B along a central longitudinal axis A. 20 3 and 4. The actuator 22 is used to drive the piston 24 in one of two possible axial directions along the axis of the actuator 22, i.e. to the right or to the left as viewed in FIGS.

[0027] Generally, the structure of the rotary actuator 20 ensures that the piston 24 is aligned along a central longitudinal axis A. 20 , allows the piston 24 to rotate radially relative to and within the outer cylinder 26. Such rotation is caused by operation of the outer ball screw 29-O. Similarly, translation of the inner ball screw 29-I and piston 24 causes the inner shaft 25 to rotate relative to the piston 24. In some configurations, the number of shared ball paths 40 of the inner ball screw 29-I also equals the number of shared ball paths 40 of the outer ball screw 29-O.

[0028] In the illustrated single piston representative embodiment of Figures 3 and 4, the piston 24 surrounds the inner shaft 25, whose axial ends E1 and E2 are supported by a pair of thrust bearings 35 (Figure 4), and sliding seals 37 are disposed at the sliding interfaces between the outer cylinder 26, the piston 24, and / or the inner shaft 25. Similarly, static seals 39 are used at the static interfaces.

[0029] In some embodiments, an optional rotational position sensor 42, shown diagrammatically in Figure 4, may be connected to the inner shaft 25 proximate an end cap 44 of the rotary actuator 20, which end cap 44 is configured to close off the cavities 30A and 30B. The rotational position sensor 42 is configured to measure and report the angular position of the inner shaft 25, for example, to an external electronic control unit (not shown). Various types of sensors may be used for such purposes, including, but not limited to, a rotary variable differential transformer or a rotary encoder.

[0030] The outer cylinder 26 shown in Figures 3 and 4 surrounds / encloses the piston 24, and the inner shaft 25, the piston 24, and the outer cylinder 26 are aligned along a central longitudinal axis A, as described above. 20 29-I and the outer ball screw 29-O are disposed concentrically relative to the inner ball screw 29-I and the outer ball screw 29-O, forming a unitary, concentric inner and outer ball screw 29-I and 29-O. Together, the inner and outer ball screw 29-I and 29-O include one or more helical or spiral grooves that collectively define at least one shared ball path 40, e.g., a single continuous ball path 40 that passes through and forms an integral part of the inner and outer ball screw 29-I and 29-O, or multiple shared ball paths 40 as shown in FIG. 5. A number of ball bearings 42 are disposed within the shared ball path 40. While the ball bearings 42 are shown to be approximately the same diameter for ease of illustration, the ball bearings 42 may have different diameters, e.g., alternating larger and smaller ball diameters, and adjacent ball bearings 42 may rotate in different directions while translating in the same direction along the shared ball path 40. The material of construction of the ball bearings 42 may also vary depending on the intended application, with the exemplary steel or ceramic embodiments being useful in a wide range of applications.

[0031] As best seen in FIG. 3, a ball guide 46 is formed at the transition of the shared ball path 40 to allow smooth movement of the ball bearing 42 from the outer ball screw 29-O to the inner ball screw 29-I. 20 The translation of the piston 24 along axis A provides the motive force for recirculating the ball bearings 42 within the respective shared ball paths 40 between the inner and outer ball screws 29-I and 29-O. 20 When translated along the longitudinal central axis A 20 , whereby the central longitudinal axis A 20 becomes the axis of rotation of the piston 24 and the inner shaft 25.

[0032] With respect to the ball bearings 42 and the shared ball path 40, this particular aspect of the disclosure ensures that the rotary actuator 20 can recirculate the respective ball bearings 42 between the outer ball screw 29-O and the inner ball screw 29-I while operating with significantly reduced friction compared to conventional thread-on-thread actuators. The ball bearings 42 in contact with the inner shaft 25 and piston 24 recirculate radially within the outer cylinder 26 to contact the outer cylinder 26 with the ball bearings 42 still in rolling contact with the piston 24. The rotational or angular velocity of the piston 24 as this occurs is approximately half the rotational velocity of the inner shaft 25, and friction from the radial rotation and translation of the piston 24 within the outer cylinder 26 causes the ball bearings 42 to translate at a constant rate. That is, the translational velocity of the plurality of ball bearings 42 in the inner ball screw 29-I is equal to the translational velocity of the plurality of ball bearings 42 in the outer ball screw 29-O.

[0033] To further optimize the present design, the rotary actuator 20 may use a relatively high thread pitch to rotate the inner shaft 25 one full revolution for every 2 inches or more of translation of the piston 24. The purpose of the long thread pitch is to ensure that the output torque on the inner shaft 25 remains large enough, while the input linear force remains small enough. An advantage of the present rotary actuator 20 configuration is the ability to back drive the inner shaft 25 by applying manual or electrical torque as needed, for example, if the ball bearing 42 becomes stuck. The long thread pitch compared to a conventional ball screw also allows multiple screws / ball starts to be oriented around the piston 24, outer cylinder 26, and inner shaft 25.

[0034] Furthermore, a greater number of screw / ball starts allows for more ball bearings 42 to be used to support greater contact loads. As a non-limiting illustrative example, as many as 18 screw / ball starts may be used on each of the inner and outer ball screws 29-I, 29-O. Each screw / ball start may rotate 20 degrees from the previous screw / ball start. However, a different number of screw / ball starts may be used based on the required size of the rotary actuator 20 and the size of the ball bearings 42, and thus the illustrated embodiment is representative and non-limiting of the present teachings.

[0035] With brief reference to FIG. 5, an exemplary interlaced ball circuit 50 includes at least six shared ball paths 40 with a total of twelve different threads / ball starts, each nominally labeled S1-S12 for clarity. The illustrated structure is a simulated solid / 3D representation of the ball paths 40 defined within the outer ball screw 29-O and the inner ball screw 29-I, as will be understood by those skilled in the art. Also, the illustrated ball paths 40 would be completely filled with ball bearings 42 in an actual embodiment, as described above, such that the ball bearings 42 within the outer ball screw / outer ball circuit tend to press the ball bearings 42 against the inner ball screw / inner ball circuit. Similarly, the ball bearings 42 within the inner ball screw 29-I tend to press the ball bearings 42 against the outer ball screw 29-O, with the ball paths 40 extending between the inner ball screw 29-I and the outer ball screw 29-O, respectively, effectively forming an inner ball return path.

[0036] In the illustrated embodiment, ball paths 40 with ball starts S1 and S7 are interconnected, as are ball paths 40 with ball starts S2 and S8, and so on, i.e., S3 and S9, S4 and S10, S5 and S11, and S6 and S12. The use of multiple ball paths 40 as shown in FIG. 5 increases redundancy and reduces sliding friction within the rotary actuator 20. That is, if a ball bearing 42 of FIGS. 3 and 4 happens to jam or become stuck when translating through a given shared ball path 40 in the interlaced ball circuit 50 of FIG. 5, the remaining ball bearings 42 in the interlaced ball circuit 50 will not be affected. This is not the case when using a single continuous ball path 40.

[0037] The ball guides 46 shown in FIG. 3 form transitions between shared ball paths 40 within a ball circuit 50, i.e., as a bend or turn where a given ball bearing 42 moves from one shared ball path 40 to another, such as when moving from the outer ball screw 29-O to the inner ball screw 29-I. The turn must be designed to prevent collisions of the ball bearings 42. Given the complexity of the required surface features, additive manufacturing / 3D printing methods such as selective laser melting may be optimal for constructing the interlaced ball circuit 50 and its various ball guides 46. Other combinations or quantities of ball starts and ball paths 40 are possible within the scope of the present disclosure, e.g., nine screws / ball starts, and thus the embodiment of FIG. 5 is intended to be illustrative and non-limiting of the present teachings.

[0038] To facilitate jam resistance of the ball bearings 42 in the interlaced ball circuit 50 illustrated in FIG. 5, particularly in the faster operating embodiments of the rotary actuator 20 of FIGS. 3 and 4 or the dual piston rotary actuator 200 illustrated in FIG. 6, more and / or shorter shared ball paths 40 may be used and the curves and ball guides 46 may be configured with gradual bends, as will be understood by those skilled in the art. When the rotary actuator 20 operates at high speeds, the translational speed of the constrained ball bearings 42 tends to be greater, thus increasing the effects of inertia. For example, when the ball bearings 42 translate, if a given ball bearing 42 stops rotating in the interlaced ball circuit 50 due to inertia, friction increases, wear occurs, and thus the operating efficiency decreases.

[0039] 6, as an alternative to the single piston rotary actuator 20 of FIG. 4, a dual piston rotary actuator 200 may be constructed that includes a first piston 124 and a second piston 224, an outer cylinder 126, and an inner shaft 225. An end cap 144, similar to the end cap 44 of FIG. 3, is disposed at the distal end E1. The rotary actuator 200 includes a pair of outer fluid ports 41 (P O) between the inner fluid port 41 (P I ) and the inner fluid port 41 (P I ) is located at approximately or exactly the axial midpoint of the rotary actuator 200. Fluid pressure is applied to both outer fluid ports 41 (P O When a voltage is applied to the rotary actuator 200 via the inner fluid port 41 (P I ) serves as an outlet port for discharging trapped fluid from the outer cylinder 126. Similarly, the inner fluid port 41 (P I Introduction of fluid pressure into the outer fluid port 41 (P) drives the pistons 124 and 224 in an axially outward direction, as indicated by arrows OO, to the outer fluid port 41 (P O ) serves as the exit port.

[0040] The exemplary dual piston embodiment of Figure 6 can help balance the load of the rotary actuator 200 in an optimal manner compared to the single piston embodiments of Figures 3 and 4, albeit at the cost of increased internal complexity. The configuration of Figure 6 thus eliminates the need for thrust bearing 35 shown in Figure 4. To ensure proper fluid sealing and load support, sliding seals 37 are carried at the contacting surfaces of any sliding or translating components, static seals 39 are located at the static interfaces, and journal bearings 55 are used to provide rotational support.

[0041] The exemplary rotary actuators 20 and 200 shown in Figures 3-4 and 6, respectively, allow for a compact construction, which in turn is desirable in multiple applications, such as, but not limited to, actuation of the flight control panel 18 of Figure 1, and allows for upsizing for applications such as actuation of cargo doors or landing gear doors. By using highly efficient inner and outer ball screws 29-I and 29-O instead of high friction Acme screws, and the disclosed interlaced ball circuit 50 and shared ball path 40 illustrated in Figure 5, a long thread pitch solution is enabled such that the rotary actuators 20 or 200 can be selectively back-driven by torque applied to the inner shaft 25 (Figures 3 and 4) or 225 (Figure 6), as needed.

[0042] The thread pitch varies slightly between the inner shaft 25 or 125 and the outer cylinder 26 or 126 in FIGS. 3 and 6, respectively, and other possible embodiments may desirably have the same thread pitch. Examples of relatively long thread pitches within the scope of the present disclosure include one revolution of the inner shaft 25 or 125 for a stroke of 2 inches or more of the piston 24, 124 or 224, e.g., about 3-4 inches per revolution in some embodiments. Furthermore, the use of larger thread pitches made possible by the disclosed solutions allows for multiple thread starts, which allows for the use of more ball bearings 42 (see FIGS. 3 and 4) to support contact loads between the various components.

[0043] For example, nine screw / ball starts may be used for each of the inner and outer ball screws 29-I and 29-O, each rotated 40 degrees from the previous start, or any number of starts may be used in other embodiments based on the size of the rotary actuator 20 or 200 and the size of the ball bearings 42. Ideally, without limitation, at least 6-12 screw or ball starts may be considered optimal without overly complicating the structure. Such a configuration allows the inner shaft 25 or 225 to rotate approximately 60 degrees or more when the piston 24, 124 or 224 translates several inches, e.g., 2 inches or more, as described above.

[0044] Thus, the rotary actuators 20 and 200 described above contemplate the use of concentric inner and outer ball screws 29-I and 29-O, and recirculating ball bearings 42 to convert the linear motion of one or more pistons, i.e., piston 24 of FIGS. 3 and 4 or first piston 124 and second piston 224 of FIG. 6, into the rotational motion of the inner shaft 25 or 225. Among the many advantages disclosed herein, low friction and compactness provide the present teachings for a wide range of applications beyond the aircraft 10 used herein as an exemplary application example. Similarly, the disclosed exemplary dimensions, ranges, materials of construction, etc. may be modified within the scope of the disclosure to suit a particular application. For example, larger and / or more ball bearings 42 and appropriately enlarged outer cylinder 26 or 126, piston 24, 124 or 224, and inner shaft 25 or 225 may be used to support a rotary device application requiring the actuation of a driven load of increased mass compared to the flight control surface 18 of FIG. 1. These and other advantages will be readily appreciated by those of ordinary skill in the art in view of the foregoing disclosure.

[0045] Aspects of the present disclosure have been described in detail with reference to exemplified embodiments. However, those skilled in the art will recognize that certain modifications may be made to the disclosed structures and / or methods without departing from the scope of the present disclosure. The present disclosure is also not limited to the exact structures and configurations disclosed herein. Variations evident from the foregoing description are within the scope of the present disclosure as defined by the appended claims. Furthermore, the present concepts expressly include combinations and subcombinations of the elements and configurations described above. [Explanation of symbols]

[0046] 10 aircraft 12 Wing / Main Wing 14 tail fin 15 Fluid pressure supply device 16. Torso 18 Aerodynamic Flight Control Surfaces / Aerodynamic Flight Control Panels 18A Aileron 18E elevator 18F Flap 18F-1 Leading edge flap 18F-2 Trailing edge flap 18R rudder 19 Hinged Panel Assembly 20 Rotation Actuator 21 Rotating hinged joint 21A Rotating hinged joint 21B Rotating hinged joint 23 Mechanical connections 24 Piston 25 Inner Shaft 26 Outer Cylinder 26W outer wall 28 External ball screw female thread 29-I Inner Ball Screw 29-O Outer Ball Screw 30A Pressure Cavity 30B Pressure Cavity 32 External ball screw male thread 34 Internal ball screw female thread 35 Thrust bearing 36 Internal ball screw male thread 37 Sliding seal 39 Static Seal 40 Shared Ball Path 41 Fluid Port 41(PI) Inner fluid port 41(PO) Outer fluid port 42 Ball bearing / rotational position sensor 44 End Cap 46 Ball Guide 50 Interlaced ball circuit 55 Journal bearing 124 First Piston 125 Inner Shaft / Spline 126 Outer Cylinder 144 End Cap 190 Hinged Panel Assembly 200 Rotation Actuator 224 Second Piston 225 Inner Shaft A 20 Longitudinal central axis A 21 Hinge shaft E1 Axial end E2 Axial end P1 pressure P2 Pressure

Claims

1. 1. A rotary actuator comprising: A plurality of ball bearings; an outer cylinder having a plurality of fluid ports each for receiving fluid pressure from a fluid pressure supply; a piston surrounded by the outer cylinder, the piston, the outer cylinder, and the plurality of ball bearings together forming an outer ball screw, the piston configured to translate along a central longitudinal axis of the rotary actuator in response to the fluid pressure; an inner shaft surrounded by the piston, the inner shaft, the piston, and the plurality of ball bearings together forming an inner ball screw concentric with the outer ball screw about the central longitudinal axis; Equipped with the outer ball screw and the inner ball screw together form an interlaced ball circuit having one or more shared ball paths, and translation of the piston along the central longitudinal axis in response to the fluid pressure is effective to rotate the piston and the inner shaft, thereby recirculating the plurality of ball bearings between the outer ball screw and the inner ball screw through the interlaced ball circuit. Rotary actuator.

2. 2. The rotary actuator of claim 1, wherein an inner diameter of the outer cylinder includes a plurality of female threads of the outer ball screw, an outer diameter of the piston includes a plurality of male threads of the outer ball screw, an inner diameter of the piston includes a plurality of female threads of the inner ball screw, and an outer diameter of the inner shaft includes a plurality of male threads of the inner ball screw.

3. 3. The rotary actuator of claim 2, wherein the female threads and the male threads of the outer ball screw are left-handed threads and the female threads and the male threads of the inner ball screw are right-handed threads.

4. 4. The rotary actuator of claim 1, wherein the piston is configured to separate the outer cylinder into a plurality of pressure cavities, and wherein a plurality of the fluid ports of the outer cylinder are configured to fluidly connect the fluid pressure supply to the plurality of pressure cavities.

5. 5. The rotary actuator of claim 1, further comprising a pair of thrust bearings, the piston being a single piston, each of the pair of thrust bearings being disposed at opposite distal ends of the inner shaft.

6. 6. The rotary actuator of claim 1, wherein the piston comprises a pair of pistons, and the plurality of fluid ports comprises an inner fluid port located at approximately a midpoint of the rotary actuator between the pair of pistons, and a pair of outer fluid ports sandwiching the inner fluid port.

7. 7. A rotary actuator according to claim 1, wherein the one or more shared ball paths include at least six shared ball paths.

8. The rotary actuator of claim 7 , wherein the one or more shared ball paths include ten or fewer shared ball paths.

9. 9. A rotary actuator according to claim 1, wherein the number of shared ball paths of the inner ball screw is equal to the number of shared ball paths of the outer ball screw.

10. 10. The rotary actuator of claim 1, wherein the rotary actuator is configured to rotate the inner shaft approximately 60 degrees for every 2 inches or more of translation of the piston along the central longitudinal axis.

11. 11. A rotary actuator according to claim 1, wherein the interlaced ball circuit includes a single continuous ball path through the inner ball screw and the outer ball screw and includes at least nine ball starts for the ball bearings.

12. 12. A rotary actuator according to claim 1, wherein a translational speed of the plurality of ball bearings in the inner ball screw is equal to a translational speed of the plurality of ball bearings in the outer ball screw.

13. A first panel; A second panel; a rotational hinged joint interconnecting the first panel and the second panel, the rotational hinged joint having an axis of rotation; a rotational actuator connected to the rotational hinged joint, a rotatable inner shaft connected to the axis of rotation of the rotation hinged joint; a piston surrounding the rotatable inner shaft and adapted to translate along a central longitudinal axis of the rotary actuator in response to fluid pressure; an outer cylinder surrounding the piston and having a plurality of fluid ports for receiving the fluid pressure, the rotatable inner shaft, the piston, and the outer cylinder being concentrically disposed about the longitudinal central axis to form two concentric ball screws that together define an interlaced ball circuit having at least one shared ball path; a plurality of ball bearings disposed in the at least one shared ball path of the interlaced ball circuit, wherein translation of the piston along the central longitudinal axis in response to receipt of the fluid pressure into the outer cylinder is effective to recirculate the plurality of ball bearings between the two concentric ball screws through the at least one shared ball path and rotate the piston and the inner shaft, thereby actuating the rotary hinged joint and changing the angular position of the first panel relative to the second panel; and A hinged panel assembly comprising:

14. 14. The hinged panel assembly of claim 13, wherein the axis of rotation of the rotational hinge joint is coaxially aligned with the central longitudinal axis of the rotational actuator.

15. 15. The hinged panel assembly of claim 13 or 14, further comprising at least one mechanical coupling connecting the rotatable inner shaft to the rotation hinge joint.

16. 16. The hinged panel assembly of claim 13, wherein the piston is configured to separate the outer cylinder into a plurality of pressure cavities, each of the pressure cavities in fluid communication with a respective one of the fluid ports of the outer cylinder.

17. 17. The hinged panel assembly of claim 16, wherein the piston comprises a pair of pistons, and the plurality of fluid ports comprises an inner fluid port located at approximately a midpoint of the rotary actuator between the pair of pistons, and a pair of outer fluid ports sandwiching the inner fluid port.

18. The torso and A pair of wings connected to the fuselage; A tail connected to the fuselage; an aerodynamic flight control panel connected to one of the wings and / or the tail via a rotationally hinged joint having an axis of rotation; a rotational actuator connected to the rotational hinged joint, a rotatable inner shaft connected to the axle; a piston surrounding the rotatable inner shaft and adapted to translate along a central longitudinal axis of the rotary actuator in response to fluid pressure; an outer cylinder surrounding the piston and having a plurality of fluid ports for receiving the fluid pressure, the rotatable inner shaft, the piston, and the outer cylinder being concentrically arranged about the longitudinal central axis to form two concentric ball screws that together define an interlaced ball circuit having at least one shared ball path, the piston being configured to separate the outer cylinder into a plurality of pressure cavities, the plurality of fluid ports being configured to connect a fluid pressure supply to the plurality of pressure cavities; a plurality of ball bearings disposed in the at least one shared ball path of the interlaced ball circuit, wherein translation of the piston along the central longitudinal axis in response to receipt of the fluid pressure into the outer cylinder is effective to recirculate the plurality of ball bearings between the two concentric ball screws through the at least one shared ball path and rotate the piston and the inner shaft, thereby actuating the rotary hinged joint and changing the angular position of the aerodynamic flight control panel; and A fixed-wing aircraft comprising:

19. 19. The fixed-wing aircraft of claim 18, wherein an inner diameter of the outer cylinder includes a plurality of female threads of an outer ball screw, an outer diameter of the piston includes a plurality of male threads of the outer ball screw, an inner diameter of the piston includes a plurality of female threads of an inner ball screw, and an outer diameter of the inner shaft includes a plurality of male threads of the inner ball screw.

20. 20. The fixed-wing aircraft of claim 18 or 19, wherein the piston comprises a pair of pistons, the plurality of fluid ports includes an inner fluid port located at approximately a midpoint of the rotary actuator between the pair of pistons, and a pair of outer fluid ports sandwiching the inner fluid port.

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