Rotary actuator with ball cage

Abstract

To provide a rotary actuator using a ball screw for converting linear motion into rotary motion.SOLUTION: Outer bearing balls (122) travel in a helical groove (120) between an outer cylinder (110) and a piston (150) to rotate the piston (150) as it translates due to fluid pressure. An inner shaft (190) is situated radially inward of the piston (150), and straight grooves (140) are disposed between the piston (150) and the inner shaft (190). Inner ball bearings (142) travel in the straight grooves (140) and rotate the inner shaft (190) as the piston (150) rotates. The ball screw rotary actuator (100) also includes an outer ball cage (124), an outer indexing gear (160-1), an inner ball cage (144), and an inner indexing gear (160-2).SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to the field of actuators, and in particular to rotary actuators. [Background Art]

[0002] A rotary actuator is a mechanical device that generates rotational motion. A lead screw rotary actuator is a type of actuator that is commonly used in heavy machinery. A lead screw rotary actuator is a mechanical device that converts linear motion into rotational motion. Screw rotary actuators are considered reliable and robust for industrial use, but they are heavy, have high friction, and cannot be back-driven, making them unsuitable for aerospace applications.

[0003] Ball screws are generally implemented as a type of linear actuator that converts rotational motion into linear force with low friction. Ball screws achieve lower friction than lead screws because the friction caused by the rolling of bearing balls along the path is less than the friction caused by sliding between the male and female parts of a lead screw. Common designs for ball screw actuators employ a small screw pitch (e.g., 4 to 20 threads per inch), allowing the rod to rotate with a relatively low input torque to generate a relatively high linear force. However, although ball screws are common linear actuators, they generally cannot be used as rotary actuators that generate rotational motion using linear force. [Summary of Invention]

[0004] Embodiments described herein describe a ball screw rotary actuator having a ball cage. One or more ball cages arranged within the ball screw rotary actuator house bearing balls within a mesh to reduce friction. In addition, the movement of the ball cage itself is restricted by positioning gears. This prevents the ball cage and bearing balls from slipping out of their positions (e.g., due to vibration or gravity), improving the efficiency, robustness, and lifespan of the ball screw actuator. Furthermore, because the position of the ball cage and bearing balls is controlled within the actuator, an external ball return track can be eliminated, simplifying the actuator and reducing its overall size. Moreover, the combination of these components reduces internal friction and, in combination with a large screw pitch or lead, can prevent the actuator from seizing up in the event of a power failure. Thus, the rotary actuators of this disclosure are suitable for many applications where size, weight, efficiency, and back-drive functionality are concerns. As an example, the ball screw actuator of this disclosure can be used in ailerons, flaps, and spoilers in low-profile wing aircraft structures, and can be mounted, for example, directly to or near the hinge line so as not to protrude from the wing's outer shell.

[0005] One embodiment is a ball screw rotary actuator comprising an outer cylinder containing a predetermined number of fluid ports, a piston configured to move translationally within the outer cylinder by fluid pressure, a helical groove disposed between the outer cylinder and the piston, and outer bearing balls configured to travel within the helical groove and rotate the piston within the outer cylinder when the piston moves translationally. The ball screw rotary actuator further comprises an inner shaft located radially inward of the piston, a linear groove disposed between the piston and the inner shaft, and inner bearing balls configured to travel within the linear groove and rotate the inner shaft when the piston rotates. The ball screw rotary actuator also includes an outer ball cage configured to position the outer bearing balls spaced apart from each other, an outer positioning gear configured to control the position of the outer ball cage, an inner ball cage configured to position the inner bearing balls spaced apart from each other, and an inner positioning gear configured to control the position of the inner ball cage.

[0006] Another embodiment is a method for assembling a ball screw rotary actuator. This method provides a piston that moves translationally within an outer cylinder by fluid pressure, a helical groove formed between the piston and the outer cylinder, one or more outer positioning gears located in one or more of the helical grooves, an outer ball cage mechanically connected to the one or more outer positioning gears, the outer ball cage positioned between the piston and the outer cylinder and positioning the outer bearing balls spaced apart within the helical grooves. This method further provides an internal shaft radially inside the piston, a linear groove formed between the internal shaft and the piston, one or more internal positioning gears located in one or more of the linear grooves, an internal ball cage mechanically connected to the one or more internal positioning gears, the internal ball cage positioned between the piston and the internal shaft and positioning the internal bearing balls spaced apart within the linear grooves.

[0007] The features, functions, and advantages described above can be achieved individually in various embodiments and may also be combined with other embodiments, and further details will become apparent by referring to the following description and drawings. [Brief explanation of the drawing]

[0008] Next, several embodiments will be described as illustrative examples, with reference to the accompanying drawings. In all drawings, the same reference numerals indicate the same element or element of the same type.

[0009] [Figure 1] This is a notched perspective view of a ball screw rotary actuator in an exemplary embodiment. [Figure 2] This is a partial cross-sectional side view of a ball screw rotary actuator in an exemplary embodiment. [Figure 3] This is a perspective view of the outer ball cage in an exemplary embodiment. [Figure 4] This is a perspective view of the inner ball cage in an exemplary embodiment. [Figure 5] This is a perspective view of a piston in an exemplary embodiment. [Figure 6] This is a perspective view of a helical sleeve in an exemplary embodiment. [Figure 7] This is a perspective view of the internal shaft in an exemplary embodiment. [Figure 8] This is a perspective view of a rotating gear in an exemplary embodiment. [Figure 9] This is a notched perspective view of a ball screw rotary actuator in an exemplary embodiment. [Figure 10] This is a flowchart illustrating a method for assembling a ball screw rotary actuator in an exemplary embodiment. [Figure 11A] This is a side view of a wing including a control surface rotatable by a ball screw rotary actuator in an exemplary embodiment. [Figure 11B] This is a side view of a multi-element wing in another exemplary embodiment, including a first control surface and a second control surface rotatable by a ball screw rotary actuator. [Figure 12] This is a block diagram of an aircraft including a ball screw rotary actuator in an exemplary embodiment. [Modes for carrying out the invention]

[0010] The drawings and the following description illustrate specific exemplary embodiments. Those skilled in the art will be able to devise various modifications that embody the principles described herein and that fall within the claims described therein, even if not explicitly described or illustrated herein. Furthermore, any embodiments described herein should be interpreted as intended to aid in understanding the principles of this disclosure, and not as limiting them. Accordingly, this disclosure is not limited to the specific embodiments or examples described below, but is limited only to the claims and their equivalents.

[0011] Figure 1 is a cutaway perspective view of a ball screw rotary actuator 100 in an exemplary embodiment. The ball screw rotary actuator 100 includes an outer cylinder 110, a piston 150, and an internal shaft 190. The outer cylinder 110 includes one or more fluid ports 112 for introducing hydraulic fluid from a hydraulic fluid source. The differential pressure of the hydraulic fluid causes the piston 150 to move from side to side. For example, Figure 1 shows a leftward arrow representing a linear force acting on the piston 150. The piston 150 is thus configured to translate within the outer cylinder 110 due to fluid pressure. The internal shaft 190 is located radially inward of the piston 150, and one or both ends of the internal shaft 190 protrude, for example, from the outer cylinder 110. The outer cylinder 110, piston 150, and internal shaft 190 can thus be arranged coaxially around a common long axis.

[0012] The ball screw rotary actuator 100 also includes a helical groove 120 positioned between the outer cylinder 110 and the piston 150. As the piston 150 moves in translation, the outer bearing balls 122 travel within the helical groove 120, causing the piston 150 to rotate within the outer cylinder 110. Advantageously, the outer bearing balls 122 are held in an outer ball cage 124 that keeps them spaced apart, reducing friction as the outer bearing balls 122 roll within the helical groove 120. Furthermore, by positioning the outer bearing balls 122 spaced apart, they do not need to recirculate within the helical groove 120, thus eliminating the need for an external ball return track, simplifying the ball screw rotary actuator 100 and reducing its overall size.

[0013] The ball screw rotary actuator 100 further includes a straight groove 140 positioned between the piston 150 and the internal shaft 190. As the piston 150 rotates (as shown by the rotational arrows in Figure 1), the internal bearing balls 142 travel within the straight groove 140, causing the internal shaft 190 to rotate. In other words, the internal bearing balls 142 fix the piston 150 to the internal shaft 190 so that the piston 150 and the internal shaft 190 rotate together, minimizing friction in the axial or longitudinal direction. In this way, the ball screw rotary actuator 100 converts linear force into rotational motion.

[0014] An advantage is that the inner bearing balls 142 are held in an inner ball cage 144 that keeps them apart from each other, reducing friction when the inner bearing balls 142 roll within the straight groove 140. Similar to the outer ball cage 124 described above, the inner ball cage 144 positions the inner bearing balls 142 so that they do not need to recirculate within the straight groove 140, thus eliminating the need for a return track for the inner balls, simplifying the ball screw rotary actuator 100 and reducing its overall size. Furthermore, the presence of the ball cages 124 / 144 eliminates the need to place the bearing balls 122 / 142 into their respective grooves, further simplifying the ball screw rotary actuator 100.

[0015] In addition, the ball screw rotary actuator 100 is enhanced by one or more indexing gears 160 configured to position the ball cages 124 / 144. For ease of explanation, Figure 1 shows the indexing gear 160 controlling the position of the inner ball cage 144, but similarly, the outer ball cage 124 can be positioned by another indexing gear. The positioning gears 160 control the position of the ball cages 124 / 144 within the ball screw rotary actuator 100, and the ball cages control the position of the bearing balls 122 / 142 so that they are spaced apart from each other, which has the advantage of preventing "creep," that is, the phenomenon in which the bearing balls attempt to slide without rolling, causing friction and wear. Compared to conventional Acme screw rotary actuators that achieve an efficiency of about 40-60 percent, the ball screw rotary actuator 100 achieves an efficiency of over 95 percent by using bearing balls 122 / 142 that roll with minimal friction. The ball screw rotary actuator 100 is also lightweight and has a back-drive configuration, making it suitable for various aerospace applications such as control surfaces where a dual actuator is required for increased reliability.

[0016] Figure 2 is an enlarged cutaway cross-sectional side view of a ball screw rotary actuator 100 in an exemplary embodiment. Figure 2 shows that the inner wall of the outer cylinder 110 may be formed by a helical sleeve 210. Thus, the outer bearing balls 122 may be positioned, for example, between the piston 150 and the helical sleeve 210. In other words, the outer diameter surface of the piston faces the inner diameter surface or inner wall of the helical sleeve 210 to form a helical groove 120. In one embodiment, the outer diameter surface of the piston 150 includes the male part of the ball screw (i.e., the male part or male thread of the helical groove 120), and the inner wall of the helical sleeve 210 (or outer cylinder 110) includes the female part of the ball screw (i.e., the female part or female thread of the helical groove 120). The helical sleeve 210 may be placed inside the pressure vessel formed by the outer cylinder 110 so as not to react to pressure loads, which has the advantage that the helical ball screw track can avoid deformation due to pressure.

[0017] In addition, Figure 2 shows a positioning gear 160 and bearing balls 122 / 142 configured to control the position of each ball cage 124 / 144. Specifically, an outer positioning gear 160-1 is positioned between the helical sleeve 210 and the piston 150. The outer positioning gear 160-1 is configured to control the position of the outer ball cage 124. The outer positioning gear 160-1 includes an outer rotating gear 262 (or pinion gear) configured to engage with one or more outer track gears 264-266 (or rack gears) while rotating.

[0018] In this embodiment, the first outer track gear 264 and the second outer track gear 266 act as tracks, and the outer rotating gear 262 acts as a pinion gear. The first outer track gear 264 is disposed on the inner wall surface of the spiral sleeve 210, and the second outer track gear 266 is disposed on the outer diameter surface of the piston 150. The outer track gears 264 to 266 include a series of recesses arranged along the spiral groove 120 and configured to receive teeth of the outer rotating gear 262 / engage with the teeth. Since the outer rotating gear 262 is located in the cavity of the outer ball cage 124, the engagement between the outer rotating gear 262 and the outer track gears 264 to 266 controls the movement of the outer ball cage 124 and the outer bearing balls 122, prevents sliding, and reduces friction.

[0019] Similarly, the inner positioning gear 160-2 is disposed between the piston 150 and the inner shaft 190. The inner positioning gear 160-2 is configured to control the position of the inner ball cage 144. The inner positioning gear 160-2 includes an inner rotating gear 272 configured to engage with one or more inner track gears 274 to 276 while rotating. In this embodiment, the first inner track gear 274 is disposed on the inner diameter surface of the piston 150, and the second inner track gear 276 is disposed on the outer diameter surface of the inner shaft 190. The inner track gears 274 to 276 include a series of recesses arranged along the linear groove 140 and configured to receive teeth of the inner rotating gear 272 / engage with the teeth. Since the inner rotating gear 272 is located in the cavity of the inner ball cage 144, the engagement between the inner rotating gear 272 and the inner track gears 274 to 276 controls the movement of the inner ball cage 144 and the inner bearing balls 142, prevents sliding, and reduces friction.

[0020] The helical groove 120 is sized to have a diameter slightly smaller than the diameter of the outer bearing balls 122, for example, such that the outer bearing balls 122 contact the inner wall and actively transmit load with almost no movement loss or play. In another embodiment, the helical groove 120 may be sized to have a diameter slightly larger than the diameter of the outer bearing balls 122, such that the outer bearing balls 122 contact the inner wall and actively transmit load after a slight rotational movement. The outer bearing balls 122 thereby rotate the piston 150 relative to the outer cylinder 110 by means of the twisted path shape and the fitting of the outer bearing balls 122 into the helical groove 120. Similarly, the straight groove 140 may also be sized to have a diameter slightly smaller or larger than the diameter of the inner bearing balls 142, such that the inner bearing balls 142 contact the inner wall to transmit load and rotate the inner shaft 190.

[0021] In some embodiments, the ball screw rotary actuator 100 includes a plurality of outer positioning gears 160-1 and / or a plurality of inner positioning gears 160-2. For example, the ball screw rotary actuator 100 may include three positioning gears 160 arranged at equal intervals on their respective corresponding outer circumferences. In one embodiment, the ball screw rotary actuator 100 employs a large screw pitch (e.g., a stroke of 10 inches or more per revolution) to allow the ball screw rotary actuator 100 to be back-driven by applying torque to the internal shaft 190. This prevents the ball screw rotary actuator 100 from seizing in the event of a power outage. In addition, it is possible to achieve relatively high output torque with relatively little linear force input. On the other hand, conventional ball screw designs for linear drives employ a small screw pitch to generate large linear force with low input torque. Furthermore, by increasing the screw pitch, multiple threads can be oriented around the piston 150, outer cylinder 110, and internal shaft 190. The more threads there are, the more bearing balls can transmit the contact load between the parts. The illustrated example has 15 threads. However, other numbers of threads can be used depending on the desired application and the size of the actuator.

[0022] Figure 3 is a perspective view of an outer ball cage 124 in an exemplary embodiment. The outer ball cage 124 includes a hollow cylindrical body having a plurality of spaces 310 configured to position the outer bearing balls 122 within a spaced grid. Each space 310 is sized slightly larger than the outer bearing balls 122, for example, to control the position of the outer bearing balls 122 while ensuring sufficient clearance for the outer bearing balls 122 to roll. A row of spaces 310 corresponds to a single helical groove 120.

[0023] In addition, the outer ball cage 124 includes one or more gear cavities 330 configured to position the outer rotating gear 262. The gear cavities 330 are sized slightly larger than the outer rotating gear 262, for example, to ensure clearance for the outer rotating gear 262 to float / rotate while minimizing play to control the position of the outer ball cage 124. The gear cavities 330 may include notches 332 to ensure sufficient clearance for the teeth of the outer rotating gear 262. In embodiments with multiple gear cavities 330, the gear cavities 330 are arranged, for example, at equal intervals around the outer circumference of the outer ball cage 124.

[0024] Figure 4 is a perspective view of an inner ball cage 144 in an exemplary embodiment. The inner ball cage 144 includes a hollow cylindrical body having a plurality of cavities 410 configured to position inner bearing balls 142 within a mesh. Each cavity 410 is sized slightly larger than the inner bearing balls 142, for example, to control the position of the inner bearing balls 142 while ensuring a gap in which the inner bearing balls 142 can roll. A row of cavities 410 corresponds to a single straight groove 140.

[0025] In addition, the inner ball cage 144 includes one or more gear cavities 430 configured to position the inner rotary gear 272. The gear cavities 430 are sized slightly larger than the inner rotary gear 272, for example, to ensure clearance for the inner rotary gear 272 to float / rotate while minimizing play to control the position of the inner ball cage 144. The gear cavities 430 may include notches 432 to ensure sufficient clearance for the teeth of the inner rotary gear 272. In embodiments with multiple gear cavities 430, the gear cavities 430 are arranged, for example, at equal intervals around the outer circumference of the inner ball cage 144.

[0026] Figure 5 is a perspective view of a piston 150 in an exemplary embodiment. As is clearly shown in Figure 5, the piston 150 includes a hollow cylindrical body with a second outer track gear 266 positioned on its outer diameter surface and a first inner track gear 274 positioned on its inner diameter surface. Figure 6 is a perspective view of a helical sleeve 210 in an exemplary embodiment. As is clearly shown in Figure 6, the helical sleeve 210 includes a hollow cylindrical body with a first outer track gear 264 positioned on its inner wall surface. The second outer track gear 266 of the piston 150 and the first outer track gear 264 of the helical sleeve 210 are aligned in a helical groove 120 to control the outer ball cage 124 between them. The outer track gears 264 / 266 can be configured to a length that facilitates the assembly of the outer rotary gear 262, the outer ball cage 124, and the outer bearing balls 122.

[0027] Figure 7 is a perspective view of the internal shaft 190 in an exemplary embodiment. As is clearly shown in Figure 7, the internal shaft 190 includes a cylindrical body with a second internal track gear 276 positioned on its outer diameter surface. The second internal track gear 276 of the internal shaft 190 and the first internal track gear 274 of the piston 150 are aligned in a straight groove 140 to control the internal ball cage 144 between them. The internal track gears 274 / 276 can be configured to a length that facilitates the assembly of the internal rotary gear 272, the internal ball cage 144, and the internal bearing balls 142.

[0028] Figure 8 is a perspective view of a rotating gear 800 in an exemplary embodiment. In one embodiment, the rotating gear 800 includes a sphere 802 with ring-shaped teeth 810 arranged on its outer circumference. The teeth 810 are sized and spaced to engage, for example, one or more outer track gears 264 / 266 and / or one or more inner track gears 274 / 276. The rotating gear 800 is sized to float / rotate, for example, within the gear cavities 330 / 430 of each ball cage 124 / 144. However, other configurations or relationships of the positioning gear 160 are also possible, including, for example, a cylindrical rotating gear, a wheel rotating gear, a rack and pinion gear, etc.

[0029] Figure 9 is a cutaway perspective view of a ball screw rotary actuator 100 in an exemplary embodiment. Figure 9 more clearly shows various parts of the ball screw rotary actuator 100 that have not yet been described. For example, the internal shaft 190 may include a shaft sleeve 990 that is fitted to the outside and connected to rotate together. In this case, the innermost inner diameter surface of the piston 150 may include the female portion of the straight groove 140, and the outer diameter surface of the shaft sleeve 990 may include the male portion of the straight groove 140.

[0030] In addition, the internal shaft 190 may include splines (not shown) for transmitting torque to desired mechanical elements such as spoiler fittings 992. The internal shaft 190 may also include journals 994 for mounting to bearings of the external structure. Depending on whether single or dual output is desired, one or both distal ends of the internal shaft 190, including the splines and / or journals 994, can protrude from the outer cylinder 110. An example in Figure 9 shows a dual output configuration with a right fluid port 112-1 and a left fluid port 112-2 for fluid input. Furthermore, the internal shaft 190 can be supported within the outer cylinder 110 at one or both ends of the outer cylinder 110 via bushings 912. One or more seals 914 maintain the pressure load within the ball screw rotary actuator 100. For example, the seal 914 positioned between the outer cylinder 110 and the adjustable end gland 916 maintains the pressure inside the outer cylinder 110.

[0031] Figure 10 is a flowchart of method 1000 for assembling a ball screw rotary actuator in an exemplary embodiment. Each step of method 1000 will be described with reference to the ball screw rotary actuator 100 in Figures 1 and 2, but as those skilled in the art will see, method 1000 can also be carried out with other rotary actuators. The steps in the flowchart described herein are not exhaustive and may include other steps not shown. Furthermore, the steps described herein may be performed in a different order.

[0032] In step 1002, a piston 150 is provided that moves translationally within the outer cylinder 110 by fluid pressure. In step 1004, a helical groove 120 is formed on the outer diameter surface of the piston 150. In step 1006, one or more outer positioning gears 160-1 are provided, located in one or more of the helical grooves 120. In step 1008, an outer ball cage 124 is mechanically connected to one or more outer positioning gears 160-1, and the outer ball cage 124 is positioned between the piston 150 and the outer cylinder 110, and is configured to position the outer bearing balls 122 spaced apart from each other within the helical grooves 120.

[0033] In step 1010, an internal shaft 190 is provided radially inside the piston 150. In step 1012, a straight groove 140 is formed between the internal shaft 190 and the piston 150. In step 1014, one or more internal positioning gears 160-2 are provided, located in one or more of the straight grooves 140. Then, in step 1016, an internal ball cage 144 is mechanically connected to one or more internal positioning gears 160-2. The internal ball cage 144 is positioned between the piston 150 and the internal shaft 190, and the internal bearing balls 142 are positioned spaced apart from each other within the straight grooves 140. As a result, the external bearing balls 122 rotate the piston 150 relative to the outer cylinder 110 when the piston 150 moves translationally due to fluid pressure, and the internal bearing balls 142 rotate the internal shaft 190 when the piston 150 rotates. In addition, the outer positioning gear 160-1 controls the position of the outer ball cage 124, which controls the position of the outer bearing balls 122, and the inner positioning gear 160-2 controls the position of the inner ball cage 144, which controls the position of the inner bearing balls 142. Method 1000 is advantageous in that it forms a ball screw rotary actuator 100 that brings many technical advantages in terms of size, weight, efficiency, and back-drive function.

[0034] Figure 11A is a side view of a wing 1100 in an exemplary embodiment, including a control surface 1110 rotatable by a ball screw rotary actuator 100. The control surface 1110 may include, for example, flaps, ailerons, or spoilers. Figure 11B is a side view of a multi-element wing 1150 in another exemplary embodiment, including a first control surface 1160 and a second control surface 1170 rotatable by a ball screw rotary actuator 100. The low height of the ball screw rotary actuator 100 has the advantage of being able to be incorporated into low-profile wing designs and implemented in multi-element flap systems, eliminating the need for conventional canoe fairings.

[0035] Figure 12 is a block diagram of an aircraft 1200 including a ball screw rotary actuator 100 in an exemplary embodiment. The aircraft 1200 includes a fuselage 1202 and one or more wings 1210 projecting from the fuselage 1202. The wings 1210 are connected to a control surface 1214 via a joint 1212. The ball screw rotary actuator 100 is connected to the joint and is configured to rotate the control surface 1214 relative to the wings 1210. A hydraulic fluid source 1204 of the aircraft 1200 supplies fluid 1206 to the ball screw rotary actuator 100 to move the control surface 1214.

[0036] Although specific embodiments have been described herein, the scope of this disclosure is not limited to these specific embodiments. The scope is defined by the following claims and their equivalents.

Claims

1. An outer cylinder including a fluid port, A piston configured to move translationally within the outer cylinder by fluid pressure, A helical groove is positioned between the outer cylinder and the piston, The outer bearing ball is configured to travel within the helical groove and rotate the piston within the outer cylinder when the piston moves in translation, An internal shaft located radially inward of the piston, A straight groove is disposed between the piston and the internal shaft, An inner bearing ball is configured to travel within the straight groove and rotate the internal shaft as the piston rotates, An outer ball cage configured to position the outer bearing balls spaced apart from each other, An outer positioning gear configured to control the position of the outer ball cage, An inner ball cage configured such that the inner bearing balls are positioned spaced apart from each other, A ball screw rotary actuator including an internal positioning gear configured to control the position of the internal ball cage.

2. The ball screw rotary actuator according to claim 1, wherein the outer positioning gear is located within a gear cavity of the outer ball cage, and the outer positioning gear includes a rotating gear configured to engage with one or more track gears to control the position of the outer ball cage.

3. The ball screw rotary actuator according to claim 2, wherein the rotating gear includes a sphere having ring-shaped teeth that engage with one or more track gears when the rotating gear rotates.

4. The ball screw rotary actuator according to claim 3, wherein the one or more track gears include a series of recesses along a helical groove configured to receive the teeth of the rotating gear.

5. The ball screw rotary actuator according to claim 4, wherein the one or more track gears include a first track gear disposed on the inner wall of the outer cylinder and a second track gear disposed on the outer diameter surface of the piston.

6. The ball screw rotary actuator according to any one of claims 1 to 5, wherein the internal positioning gear is located within a gear cavity of the internal ball cage, and the internal positioning gear includes a rotary gear configured to engage with one or more track gears to control the position of the internal ball cage.

7. The ball screw rotary actuator according to claim 6, wherein the rotating gear includes a sphere having ring-shaped teeth that engage with one or more track gears when the rotating gear rotates.

8. The ball screw rotary actuator according to claim 7, wherein the one or more track gears include a series of recesses along a straight groove configured to receive the teeth of the rotating gear.

9. The ball screw rotary actuator according to claim 8, wherein the one or more track gears include a first track gear disposed on the inner diameter surface of the piston and a second track gear disposed on the outer diameter surface of the internal shaft.

10. A method for assembling a ball screw rotary actuator, A piston is provided that moves translationally within the outer cylinder due to fluid pressure. A helical groove is formed between the piston and the outer cylinder. One or more outer positioning gears are provided located in one or more of the aforementioned spiral grooves. The outer ball cage is mechanically connected to the one or more outer positioning gears, and the outer ball cage is positioned between the piston and the outer cylinder, and is configured to position the outer bearing balls spaced apart from each other within the helical groove. An internal shaft is provided radially inward of the piston, A straight groove is formed between the internal shaft and the piston. One or more inner positioning gears are provided located in one or more of the aforementioned straight grooves. A method comprising mechanically connecting an inner ball cage to one or more inner positioning gears, wherein the inner ball cage is positioned between the piston and the inner shaft, and the inner bearing balls are positioned spaced apart from each other within the straight groove.

11. The method according to claim 10, wherein the outer bearing balls rotate the piston relative to the outer cylinder when the piston is translated by the fluid pressure.

12. The method according to claim 10 or 11, wherein the internal bearing balls rotate the internal shaft when the piston rotates.

13. The method according to claim 10 or 11, wherein the one or more outer positioning gears control the position of the outer ball cage that controls the position of the outer bearing balls.

14. The method according to claim 10 or 11, wherein the one or more internal positioning gears control the position of the internal ball cage that controls the position of the internal bearing balls.

15. Torso and, The wings protruding from the fuselage, The control surface connected to the wing via a joint, An aircraft comprising a ball screw rotary actuator connected to the joint and configured to rotate the control surface relative to the wing, wherein the ball screw rotary actuator is An outer cylinder including a fluid port, A piston configured to move translationally within the outer cylinder by fluid pressure, A helical groove is positioned between the outer cylinder and the piston, The outer bearing ball is configured to travel within the helical groove and rotate the piston within the outer cylinder when the piston moves in translation, An internal shaft located radially inward of the piston, A straight groove is disposed between the piston and the internal shaft, An inner bearing ball is configured to travel within the straight groove and rotate the internal shaft as the piston rotates, An outer ball cage configured to position the outer bearing balls spaced apart from each other, An outer positioning gear configured to control the position of the outer ball cage, An inner ball cage configured such that the inner bearing balls are positioned spaced apart from each other, An aircraft including an internal positioning gear configured to control the position of the internal ball cage.

16. The aircraft according to claim 15, wherein the helical groove has a screw pitch that causes the internal shaft to rotate once for at least 10 inches of translational movement of the piston.

17. The aircraft according to claim 16, wherein the screw pitch of the helical groove allows the ball screw rotary actuator to be back-driven.

18. The aircraft according to any one of claims 15 to 17, wherein the outer positioning gear is located within a gear cavity of the outer ball cage, and the outer positioning gear includes a rotating gear configured to engage with one or more track gears to control the position of the outer ball cage.

19. The aircraft according to any one of claims 15 to 17, wherein the internal positioning gear is located within a gear cavity of the internal ball cage, and the internal positioning gear includes a rotating gear configured to engage with one or more track gears to control the position of the internal ball cage.

20. The outer ball cage is configured to prevent the outer bearing balls from sliding. The aircraft according to any one of claims 15 to 17, wherein the inner ball cage is configured to prevent sliding of the inner bearing balls.

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