Damping actuator end stop

Abstract

A linear actuator comprising: a shaft and a nut engaged with the shaft such that, in response to relative rotation between the nut and the shaft, the nut translates axially relative to the shaft on a central axis within a linear range of motion; a stop located at a travel limit position and having a rotational input portion and an axial output portion, the rotational input portion configured to rotate relative to the shaft about the central axis, the axial output portion inhibited from rotating relative to the shaft about the central axis and configured to translate axially relative to the rotational input portion on the central axis in response to relative rotation between the axial output portion and the rotational input portion; and, an axial compliant member configured to bias the axial output portion toward the travel limit position.

Description

Technical Field

[0001] This invention relates generally to the field of ball screw actuators, and more specifically to an actuator with an improved damping end stop. Background Technology

[0002] Ball screw actuators are well known in the art and typically comprise a screw that is threaded into a nut and driven by a motor. The relative rotation between the screw and the nut produces axial displacement between them. This axial displacement typically drives the linear stroke of the actuator. In such systems, one or more end stops may be used to limit the actuator's travel in the fully retracted and / or fully extended positions and to limit damage to the motor, ball screw, or mechanical connections.

[0003] U.S. Patent No. 8,109,165 relates to a compliant, non-jamming end stop for a ball screw actuator. The ball screw actuator includes a torsion spring operatively arranged to absorb energy when a first and second stop of the ball screw actuator engage in a travel-limited position. Summary of the Invention

[0004] The bracketed references to corresponding parts, portions, or surfaces in the disclosed embodiments are for illustrative purposes only and not for limitation. The present invention provides a linear actuator (15) comprising: a shaft (16) oriented about a central axis (30); a nut (18) engaged with the shaft (16) such that, in response to relative rotation between the nut (18) and the shaft (16) about the central axis (30), the nut (18) is axially translated relative to the shaft (16) within a linear range of motion along the central axis (30); and a stop (20) positioned at a travel-limiting position within the range of motion between the shaft (16) and the nut (18); the stop (20) having… It has a rotary input portion (23) and an axial output portion (21); the rotary input portion (23) is configured to rotate about a central axis (30) relative to a shaft (16); the axial output portion (21) is suppressed from rotating about a central axis (30) relative to a shaft (16) and is configured to translate axially (27) relative to the rotary input portion (23) and the shaft (16) about the central axis (30) in response to the relative rotation between the axial output portion (21) and the rotary input portion (23) about the central axis (30); and an axial compliance member (19) configured to axially bias the axial output portion (21) toward a travel-limiting position on the central axis (30).

[0005] The shaft (16) may include an external ball track (43), and the nut (18) may include an internal ball track (44), and a plurality of balls (45) may be disposed in the external ball track (43) and the internal ball track (44). The axial compliance member (19) may include a spring acting between the shaft (17) and the axial output portion (36). The stop member (20) may include a plurality of balls (22) axially disposed between the rotary input portion (23) and the axial output portion (21).

[0006] The rotary input portion (23) may include a first annular cam surface (35a, 35b), and the axial output portion (21) may include a second annular cam surface (34a, 34b) facing the first annular cam surface (35a, 35b). A plurality of balls (22) may be axially disposed between the first annular cam surface (35a, 35b) and the second annular cam surface (34a, 34b).

[0007] The nut (18) may include a torsion input stop (26), and the rotation input portion (23) of the stop (20) may include a torsion output stop (25), which is configured such that when the torsion output stop (25) and the torsion input stop (26) are axially overlapped and rotatably engaged, as the nut (18) rotates relative to the shaft (16) about the central axis (30) in a first direction (28a), the rotation input portion (23) of the stop (20) rotates relative to the shaft (16) about the central axis (30) in a first direction (28b). Figure 6 and Figure 7 ). Attached Figure Description

[0008] Figure 1 is a partial cutaway perspective view of a ball screw assembly known in the prior art.

[0009] Figure 2 This is a perspective view of a first embodiment of an improved ball screw end stop assembly.

[0010] Figure 3 yes Figure 2 The image shows a longitudinal vertical cross-sectional perspective view of the ball screw end stop assembly.

[0011] Figure 4 yes Figure 2 The diagram shows a longitudinal vertical cross-section of the ball screw end stop assembly.

[0012] Figure 5 yes Figure 2 The diagram shows the ball screw end stop assembly in an axially overlapping position.

[0013] Figure 6 yes Figure 2The diagram shows the ball screw end stop assembly in the axial overlap and rotational contact position.

[0014] Figure 7 yes Figure 2 The diagram shows the ball screw end stop assembly in the damping position.

[0015] Figure 8 yes Figure 5 A schematic diagram of the recessed surface of the ball bearing ramp assembly. Detailed Implementation

[0016] First, it should be clearly understood that the same reference numerals are intended to consistently identify the same structural elements, portions, or surfaces in several figures, as these elements, portions, or surfaces can be further described or explained throughout the written specification, which is an integral part of the specification. Unless otherwise stated, the figures are intended to be read in conjunction with the specification (e.g., crosshairs, arrangement of parts, scale, extent, etc.) and are considered part of the entire written description of the invention. As used in the following description, the terms “horizontal,” “vertical,” “left,” “right,” “up,” and “down,” and their adjective and adverbial derivatives (e.g., “horizontally,” “to the right,” “upward,” etc.), simply refer to the orientation of the illustrated structure when a particular figure is facing the reader. Similarly, the terms “inward” and “outward” generally refer to the orientation of a surface relative to its axis of elongation or axis of rotation, as appropriate.

[0017] Figure 1 illustrates a type of ball screw assembly known in the art. As shown, this ball screw assembly utilizes the rolling motion of balls 145 located between a shaft 116 and a nut 118 to generate relative motion between the shaft 116 and the nut 118. The ball bearing assembly 118 acts as the nut, while the threaded shaft 116 provides helical raceways 143 for the ball bearings 145. The ball screw assembly can therefore operate as a mechanical linear actuator that converts rotational motion into linear motion with reduced friction.

[0018] Reference Figures 2-3An improved ball screw end stop assembly is provided, the first embodiment of which is generally indicated by 15. As shown, assembly 15 typically includes a ball screw shaft 16 oriented about an axis 30, a ball screw nut 18 rotatably engaged with the ball screw shaft 16, a spring 19 oriented about one end of the ball screw shaft 16, a ball ramp assembly 20 axially oriented between the spring 19 and the ball screw nut 18, and a torsion stop 24 oriented between the ball ramp assembly 20 and the ball screw nut 18. As shown, ball ramp assembly 20 typically includes an input ramp 23, an output ramp 21, and a plurality of balls 22 between the input ramp 23 and the output ramp 21. The damping end stop 15 provides a rotational stop at the end of the nut 18 relative to the desired axial travel of the ball screw shaft 16, which reduces the axial load on the shaft 16 of the ball screw assembly 15 and the torsional load on the interface between the nut 18 and the shaft 16 of the ball screw assembly 15.

[0019] As shown in the figure, the ball screw 16 includes a helical track 43, and the nut 18 includes an opposing track 44, with a ball bearing 45 between the helical track 43 and the opposing track 44. As shown, the left side of the nut 18 includes a first face 26 of a torsion dog-shaped stop 24, and the right side of the input ramp 23 includes a second face 25 of the torsion dog-shaped stop 24, which is configured to mate with the first face 26 of the torsion dog-shaped stop 24 on the nut 18. Therefore, as... Figure 6 and 7 As shown, when the corresponding mating surfaces 25 and 26 of the torsion dog-tooth stop 24 are rotated such that they overlap axially and rotate opposite each other and come into contact, the torque and rotation 28a of the nut 18 about axis 16 are transmitted to the input ramp 23 of the ball ramp assembly 20. The input ramp 23 is rotatable about the end of shaft 16 and axis 30 such that when the mating is engaged, as the nut 18 rotates 28a about axis 30 on shaft 16, the input ramp 23 rotates 28b about axis 30.

[0020] As shown in the figure, the output ramp 21 of the ball bearing ramp assembly 20 includes a longitudinally extending internal spline 31, which forms an interface 33 with a similar extended spline 32 on the outer surface of the end of the shaft 16. As a result, the output ramp 21 of the ball bearing ramp assembly 20 is suppressed and cannot rotate freely about the shaft 16 and the axis 30, but can move axially to the left 27 on the shaft 16.

[0021] The ball bearing ramp assembly 20 includes annular rings of balls 22 located between opposing ramp surfaces 35a, 35b and 34a, 34b of the input ramp 23 and the output ramp 21, respectively. Figures 5-7As shown in the process, when the input ramp 23 rotates about the shaft 16 and axis 30 in the first direction 28a, the output ramp 23 is prevented from rotating by the spline interface 33 at its end with the shaft 16. Therefore, the movement of the input ramp 23 relative to the output ramp 21 by the ball 22 between the input ramp 23 and the output ramp 21 causes the output ramp 21 to move axially to the left by 27. This axial load 27 is then absorbed by the spring 19 acting between the annular retaining end flange 17 of the shaft 16 and the annular end surface 36 of the output ramp 21.

[0022] In this embodiment, spring 19 is a friction spring oriented about axis 30 on shaft 16, and has an outer and inner coil stacked together, the outer and inner coils having opposing tapered surfaces and lubricant, assembled to provide a cylindrical friction spring column oriented about axis 30. Spring 19 has a high damping potential and absorbs kinetic energy with minimal resonance. Spring 19 biases the output ramp 21 axially to the right against the input ramp 23 and the annular retaining ring 38 of shaft 16. With respect to axial load 27, spring 19 acts as an axial damper. Although a friction spring is used in this embodiment, other types of springs or other energy-absorbing alternatives may be used. For example, but not limited to, helical springs, Bavarian washers or stacks of disc springs, elastomeric springs, or hydraulic dampers may be used as alternatives.

[0023] Therefore, the ball screw end stop assembly 15 includes a ball ramp assembly 20 located between the torsional toothed stop 24 and the spring 19. This ball ramp assembly 20 converts the rotational motion and torsional loads 28a and 29b of the torsional toothed stop 24 into linear motion and an axial load 27, which is then applied to the spring 19 to absorb impact energy. The axial load 27 generated by the ball ramp assembly 20 is isolated from the ball bearing 45 in the nut 18 of the ball screw assembly by an annular retaining ring 38 extending from the shaft 16, preventing rightward axial movement of the input ball ramp 23. Therefore, fatigue damage is not introduced into the ball screw assembly.

[0024] Therefore, the stop 26 on the nut 18 of the ball screw end stop assembly 15 can rotate to move to the left until it engages the stop 25 on the input ramp 23. At this point, as the nut 18 rotates 28a about the axis 30 and the shaft 16, the input ramp 23 begins to rotate 28b. However, the output ramp 21 resists rotation relative to the shaft 16 via the spline interface 33, and therefore it cannot rotate. The relative rotation between the input ramp 23 and the output ramp 21 forces the ramps to separate axially based on the separation distance 48 of the angles 40, 41 of the opposing ball ramp recesses 34a, 34b and 35a, 35b. The annular retaining ring 38 prevents the input ramp 23 from moving axially to the right on the shaft 16, which forces the output ramp 21b to move axially to the left 27, thereby compressing the spring stack 19. The spring stack 19 absorbs the kinetic energy of the system 15 during compression, preventing excessive torque peaks in the actuator's gear train at the actuator's stroke limit position.

[0025] The ball screw end stop assembly 15 can be arranged, for example but not limited to, to act between the wing surface and the fuselage of an aircraft to adjust the orientation of the wing surface relative to the fuselage. A motor drives relative rotation between the ball screw 16 and the ball nut 18 to cause axially guided relative movement between the ball screw 16 and the ball nut 18. As a non-limiting example, the motor can be an electric motor or a hydraulic motor.

[0026] The ball screw end stop assembly 15 protects the ball screw from axial loads generated by contact end stop 17 and absorbs the torsional kinetic energy of the drive motor in the actuator. The ball screw end stop assembly 15 provides a rotary stop at the end of the ball screw's stroke, preventing the guide or shaft of the ball screw from generating additional axial loads via the torsional dog-tooth stop 24. The ball screw end stop assembly 15 is an improvement over systems that only include a torsional dog-tooth stop and a spring. The problem with using only a torsional dog-tooth stop and a spring is that if the main actuator is equipped with a high-speed hydraulic or electric motor, the kinetic energy of the drive motor may not be adequately absorbed by the stop and the gear train between the motor and the stop. Because the kinetic energy can be very high, and the load path between the motor and the ball screw stop can be very rigid, the torque peak resulting from a full-speed impact on the torsional dog-tooth stop could damage the gear train or require a heavier design to accommodate such loads. Furthermore, if the stop is frequently subjected to impacts, especially in telescopic ball screws where the intermediate ball screw stop is impacted with each operation, this can lead to fatigue issues for the ball screw and transmission components. This system addresses this issue.

[0027] Various additions and modifications can be made to the disclosed embodiments. For example, but not limited to, the opposing ball ramp recesses 34a, 34b and 35a, 35b of the input ramp 23 and the output ramp 21 can have alternative constructions, angles, and cam surfaces to provide the desired axial separation range and rate depending on the application. Furthermore, alternative shaft thread constructions or profiles, as well as helical raceways between the ball shaft and the nut, and different ball return systems can be employed. As another alternative, a lead screw and nut without ball bearings can be used.

[0028] Therefore, although the form of the ball screw end stop assembly has been shown and described, and several modifications have been discussed, those skilled in the art will readily understand that various additional changes can be made without departing from the scope of the invention.

Claims

1. A linear actuator, comprising: A shaft, oriented about a central axis; A nut that engages with the shaft such that, in response to relative rotation between the nut and the shaft about the central axis, the nut translates axially relative to the shaft within a linear range of motion along the central axis. A stop element, wherein the stop element is located at a travel limit position within the range of motion between the shaft and the nut; The stop has a rotary input portion and an axial output portion; The rotary input portion is configured to rotate relative to the shaft about the central axis and has a torsion output stop configured to rotatably engage with the torsion input stop of the nut at the travel limit position, such that when the torsion input stop of the nut rotatably engages with the torsion output stop of the rotary input portion of the stop at the travel limit position, the rotary input portion of the stop rotates about the central axis relative to the shaft as the nut rotates about the central axis relative to the shaft; The axial output portion is suppressed from rotating about the central axis relative to the shaft, and is configured to translate axially relative to the rotary input portion and the shaft on the central axis in response to the relative rotation between the axial output portion and the rotary input portion about the central axis; as well as An axially compliant member is configured to axially bias the axial output portion toward the travel limit position on the central axis.

2. The linear actuator according to claim 1, wherein, The shaft includes an outer ball track, and the nut includes an inner ball track, and includes a plurality of balls disposed in the outer ball track and the inner ball track.

3. The linear actuator according to claim 1, wherein, The axially compliant member includes a spring acting between the shaft and the axial output portion.

4. The linear actuator according to claim 1, wherein, The stop includes a plurality of balls axially disposed between the rotary input portion and the axial output portion.

5. The linear actuator according to claim 4, wherein, The rotary input portion includes a first annular cam surface, and the axial output portion includes a second annular cam surface facing the first annular cam surface.

6. The linear actuator according to claim 5, wherein, The plurality of balls are axially disposed between the surface of the first annular cam and the surface of the second annular cam.

7. The linear actuator according to claim 1, wherein, When the torsion input stop of the nut and the torsion output stop of the rotation input portion of the stop are rotatably engaged at the travel limit position, the torsion input stop of the nut and the torsion output stop of the rotation input portion of the stop are configured to overlap axially and rotate abut against each other, such that when the torsion output stop and the torsion input stop are axially overlapped and rotate abut against each other, as the nut rotates relative to the shaft about the central axis in a first direction, the rotation input portion of the stop rotates relative to the shaft about the central axis in the first direction.

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