WO2011096913A1

WO2011096913A1 - Structurally-redundant actuators

Info

Publication number: WO2011096913A1
Application number: PCT/US2010/000297
Authority: WO
Inventors: David J. Manzanares
Original assignee: Moog Inc.
Priority date: 2010-02-03
Filing date: 2010-02-03
Publication date: 2011-08-11

Abstract

The present invention broadly provides improved structurally-redundant actuators (20) which are particularly suited for, but not limited to, controlling the position of an aircraft flight control surface (21). The improved actuators are adapted to control the movement of a member (21) relative to a support (22), and broadly comprises: a primary driving screw (24) having a primary nut (25) in threaded engagement with a primary screw (26), the primary driving screw being operatively arranged to transmit forces between the member and the support along the axis of the primary driving screw; a motor (52 or 58) operatively arranged to selectively rotate the primary screw relative to the primary nut to cause the member to move relative to the support; a secondary driven screw (28) having a secondary nut (29) in threaded engagement with a secondary screw (30), the secondary driven screw acting between the member and the support; a brake (70) associated with the secondary driven screw and selectively operable to brake relative rotation between the secondary nut and the secondary screw to cause forces to be transmitted between the member and the support along the axis of the secondary driven screw; and a fault sensor (65, 74) for sensing a fault in the operation of the primary driving screw and for selectively operating the brake when a fault is sensed to impede movement of the member relative to the support.

Description

STRUCTURALLY-REDUNDANT ACTUATORS

Technical Field

[0001] The present invention relates generally to the field of actuators, and, more, particularly, to improved structurally-redundant actuators that are particularly adapted for, but not limited to, use in controlling the position of a movable airfoil surface relative to a support.

Background Art

[0002] The present invention relates to structurally-redundant actuators, such as those used on aircraft primary flight control systems. These devices should provide structural redundancy with minimal complexity and backlash in either load path. The requirement for redundancy stems from F.A.R. § 25.671 (c)(2), which provides:

"(c) The airplane must be shown by analysis, tests, or both, to be capable of continued safe flight and landing after any of the following failures or jamming in the flight control system and surfaces (including trim, lift, drag, and feel systems), within the normal flight envelope, without requiring exceptional piloting skill or strength. Probable malfunctions must have only minor effects on control system operation and must be capable of being readily counteracted by the pilot."

[0003] Some prior art actuation systems have used a common ball screw in the primary and secondary load paths. (See, e.g., US 4,637,272 A) Another prior art actuation system has used two independent actuators acting between a common support and a common flight control surface. (See, e.g., US 6,755,375 B2) Still another prior art actuation system has addressed the issue of jam tolerance by allowing an actuator to be freed following the jam of a ballscrew assembly. (See, e.g., US 4,179,944 A)

[0004] In the traditional configuration, the damage tolerance is verifiable by analysis and test of a few selected components. The current damage tolerance requirement is set forth in F.A.R. § 25.571 , which provides in pertinent part:

"(a) General. An evaluation of the strength, detail design, and fabrication must shown that catastrophic failure due to fatigue, corrosion, manufacturing defects, or accidental damage will be avoided throughout the operational life of the airplane. This evaluation must be conducted in accordance with the provisions of paragraphs (b) and (e) of this section, except as specified in paragraph (c) of this section for each part of the structure that could contribute to a catastrophic failure (such as wing empennage, control surfaces and their systems, the fuselage, engine mounting, landing gear, and their related primary attachments. For turbojet powered airplanes, those parts that could contribute to a catastrophic failure must also be evaluated under paragraph (d) of this section. In addition, the following apply:

* * *

(3) Based on the evaluations required by this section, inspections or other procedures must be established, as necessary, to prevent catastrophic failure, and must be included in the Airworthiness Limitations Section of the Instructions for Continued Airworthiness required by Sec.

25.1529. Inspection thresholds for the following types of structure must be established based on crack growth analyses and/or tests, assuming the structure contains an initial flaw of the maximum probable size that could exist as a result of manufacturing or service-induced damage:

(i) Single load path structure, and

(ii) Multiple load path 'fail-safe' structure and crack arrest 'fail-safe' structure, where in cannot be demonstrated that load path failure, partial failure, or crack arrest will be detected and repaired during normal maintenance, inspection, or operation of an airplane prior to failure of the remaining structure."

[0005] The main concerns with flutter are backlash and wear. The traditional approach to dealing with backlash is to add an additional latching mechanism following the movement to the lock trigger. Wear is traditionally detected by applying a load to the actuator during in-service inspection. Wear is also checked during qualification testing. One known method of checking for wear is disclosed in US 7,277,800 B2.

[0006] The aggregate disclosures of each of the above-cited prior art patent references are hereby incorporated by reference.

[0007] Hence, it would be generally desirable to provide improved actuators that provide structural redundancy with minimal complexity and backlash

Disclosure of the Invention

[0008] With parenthetical reference to the corresponding parts, portions or surfaces of one or more of the disclosed embodiments, merely for purposes of illustration and not by way of limitation, the present invention broadly provides an improved structurally-redundant actuator (20) which is particularly suited for, but not limited to, controlling the position of a member (21 ), such as an aircraft flight control surface, relative to a support (22).

[0009] The improved actuator is adapted to control the movement of a member (21 ) relative to a support, and broadly comprises: a primary driving screw (24) having a primary nut (25) in threaded engagement with a primary screw (26), the primary driving screw being operatively arranged to transmit forces between the member and the support along the axis of the primary driving screw; at least one motor (52 and/or 58) operatively arranged to selectively rotate the primary screw (26) relative to the primary nut (25) to cause the member to move relative to the support; a secondary driven screw (28) having a secondary nut (29) in threaded engagement with a secondary screw (30), the secondary driven screw acting between the member and the support; a brake (70) associated with the secondary driven screw and selectively operable to brake relative rotation between the secondary nut and the secondary screw to cause forces to be transmitted between the member and the support along the axis of the secondary driven screw; and a fault sensor (65, 74) for sensing a fault in the operation of the primary driving screw and for selectively operating the brake when a fault is sensed to impede movement of the member relative to the support.

[0010] Substantially all of the forces transmitted between the member and the support may be transmitted along the longitudinal axis of the primary driving screw when no fault is sensed in the primary driving screw.

[0011] The primary nut may be attached to the member. [0012] The motor may be an electric motor.

[0013] The improved actuator may further include a primary gear train (54, 55, 56, 60, 61 , 62, 63, 64) operatively arranged between the motor and the primary screw.

[0014] The improved actuator may further include a torque limiter operatively interposed between the motor and the primary screw.

[0015] The improved actuator may further include a no-back primary brake (33 or

35) operatively interposed between the support and the primary screw.

[0016] The improved actuator may further include a primary position sensor (65) operatively arranged to sense the position of the primary screw.

[0017] The secondary nut may be attached to the member.

[0018] The improved actuator may further include a secondary gear train (72, 73) operatively arranged between the secondary screw and the brake.

[0019] The improved actuator may further include a thrust bearing (82) operatively interposed between the support and the secondary screw.

[0020] The improved actuator may further include a tachometer (71 ) operatively arranged to sense the rotational speed of the secondary screw.

[0021] The brake may be an electro-mechanical brake.

[0022] The improved actuator may further include a secondary position sensor (74) operatively arranged to sense the position of the secondary screw.

[0023] The improved actuator may further include an extend stop (38) on the primary driving screw for providing an extension limit of the primary driving screw and/or a retract stop (39) on the primary driving screw for providing a retraction limit of the primary driving screw.

[0024] The fault may be sensed as a function of a difference in the positions of the primary and secondary screws, or as a function of the rotational speed of the secondary screw.

[0025] The improved actuator may further include a damper operatively associated with the secondary driven screw to prevent a run-away condition of the secondary driven screw in the event of a failure of the primary driving screw.

[0026] The secondary driven screw may not be arranged to move the member relative to the support against an opposing load.

[0027] The secondary driven screw may be arranged to selectively brake movement of the member relative to the support under an aiding load. [0028] The primary driving screw and/or the secondary driven screw may be a ball screw.

[0029] Accordingly, the general object of the invention is to provide an improved actuator.

[0030] Another object is to provide an improved structurally-redundant actuator.

[0031] Still another object is to provide an improved structurally-redundant actuator for use in controlling the position of an airfoil surface relative to a support.

[0032] These and other objects and advantages will be come apparent from the foregoing and ongoing written specification, the drawings and the appended claims.

Brief Description of the Drawings

[0033] Fig. 1 is a schematic view of a first form of an improved actuator.

[0034] Fig. 2 is a schematic view of a second form of an improved actuator.

[0035] Fig. 3 is a schematic view of a third form of an improved actuator.

Description of the Preferred Embodiments

[0036] At the outset, it should be clearly understood that like reference numerals are intended to identify the same structural elements, portions or surfaces consistently throughout the several drawing figures, as such elements, portions or surfaces may be further described or explained by the entire written specification, of which this detailed description is an integral part. Unless otherwise indicated, the drawings are intended to be read (e.g., cross-hatching, arrangement of parts, proportion, degree, etc.) together with the specification, and are to be considered a portion of the entire written description of this invention. As used in the following description, the terms "horizontal", "vertical", "left", "right", "up" and "down", as well as adjectival and adverbial derivatives thereof (e.g., "horizontally", "rightwardly", "upwardly", etc.), simply refer to the orientation of the illustrated structure as the particular drawing figure faces the reader. Similarly, the terms "inwardly" and "outwardly" generally refer to the orientation of a surface relative to its axis of elongation, or axis of rotation, as appropriate.

[0037] Referring now to the drawings, the present invention broadly provides an improved actuator that is adapted to control the movement of a member relative to a support. Three different forms of the invention are depicted in the accompanying drawings. The first form is depicted in Fig. 1 , the second in Fig. 2, and the third in Fig. 3.

First Form (Fig. 1 )

[0038] Referring now to Fig. 1 , a first form of the improved actuator is generally indicated at 20. In this form, the member is generally indicated at 21 , and fragmentary portions of the support are severally indicated at 22. The member 21 is shown as being the horizontal stabilizer of an aircraft, and the actuator 20 is a horizontal stabilizer trim actuator ("HSTA"). Stabilizer 21 is shown as being mounted for pivotal movement about horizontal axis 23. However, it should be clearly understood that this particular use and environment is merely exemplary, and is not limitative of the invention or the scope of the appended claims.

[0039] Actuator 20 is shown as having a primary driving screw, generally indicated at 24, having a primary nut 25 in threaded engagement with a primary screw 26. The actuator is further shown as having a secondary driven screw, generally indicated at 28, having a secondary nut 29 in threaded engagement with a secondary screw 30. The primary driving screw 24 and the secondary driven screw 28 are both preferably ball-screws. However, other types of threaded actuators, or threaded connections, such as an Acme thread, could be substituted therefor.

[0040] In Fig. , the upper marginal end portion of the primary driving screw 24 is connected to brake housing 31 , which, in turn, is connected to the support by a clevis-like connection for rotation about pivotal axis 27. This brake housing specifically includes a single load path gearbox 32, a compression no-back device 33 acting on one side of a flange 34 mounted on screw 26 and a tension no-back device 35 acting between the housing and the other side of flange 34. The primary driving screw is shown as having an extend stop 38 mounted on screw 26, and a retract stop 39 also mounted on screw 26. These stops are adjustably mounted on the primary driving screw to provide limits for motion of nut 25 relative to screw 26.

[0041] Primary nut 25 is mounted for pivotal movement relative to member 21 about pivotal axis 40. As previously noted, the nut has an internally-threaded collar portion 41 in mating engagement with screw 26. Thus, as the primary driving screw 26 rotates, collar portion 41 will move nut 25 upwardly or downwardly, as appropriate, relative to screw thread 26, while nut portion 42 will pivot relative to collar portion 41 to accommodate such motion. [0042] Similarly, the driven secondary nut 29 is shown as having an extend stop 43 and a retract stop 44 adjustably mounted on screw thread 30. Here again, the driven nut 29 includes an internally-threaded tubular portion 46 in mating engagement with screw thread 30, and another portion 48 which is mounted on collar portion 46 for pivotal movement about axis 49.

[0043] As shown in the upper portion of Fig. 1 , the actuator is provided with a redundant drive signal via a first hydraulic control module 50, and a second hydraulic control module 51. First module 50 is arranged to receive electrical and hydraulic power through suitable connections (not shown), and is arranged to provide controlled hydraulic outputs to hydraulic motor 52 and to hydraulic brake 53. Hydraulic motor 52 and hydraulic brake 53 have pinions 54, 55, respectively, that are engaged with a differential-like mechanism, generally indicated at 56.

[0044] Hydraulic control module 51 is similarly provided with suitable electrical and hydraulic connections (not shown), and is arranged to provide controlled hydraulic outputs to hydraulic motor 58 and hydraulic brake 59. Motor 58 and brake 59 have pinions 60, 61 , respectively, engaged with the differential-like mechanism 56. The output of the differential-like mechanism drives a pinion 63, which, in turn, meshes with an output gear 64 mounted fast to shaft 26. A resolver 65 has a pinion 66 engaging a gear 68, which is driven by another gear 69 in meshing engagement with output gear 64. The gear train may also contain a torque limiter, if desired.

[0045] Hydraulic output module 51 is also arranged to supply a suitable hydraulic signal to a hydraulic brake 70, the speed of which is monitored by means of a tachometer 71 . A velocity damper 36 is associated with the tachometer to limit the rotational speed of the driven screw. Hydraulic brake 70 has a pinion 72 engaging an output gear 73 mounted fast to secondary driven screw 30. Another resolver 74 has a pinion 75 engaging a gear 76 which is connected to a pinion 77 in meshing engagement with output gear 73. The driven screw is connected to the support via a housing 78 which contains a single load path gearbox 72, 73, 77, 75, 76. A flange 81 connected to driven screw 30 is captured between thrust bearings, severally indicated at 82.

[0046] In this arrangement, the primary driving screw and the secondary driven screw are shown as being arranged at different arm distances from pivotal axis 23. This is merely for purposes of illustration. In practice, the two screws could be ar- ranged at equal arm distances from the pivot point 23, although one would obstruct the view of the other.

[0047] When it is desired to operate the device, suitable signals are provided to control modules 50, 51. This causes release of hydraulic brakes 53, 59, 70 and controlled operation of hydraulic motors 52, 58. Such action then causes the operation of the differential, and produces a controlled rotation of differential output pinion 63. This, in turn, cause rotation of output gear 64, and corresponding rotation of primary driving screw 26. As this occurs, the primary nut moves either upwardly or downwardly, as appropriate, along the primary driving screw 26. Such motion is accommodated by pivotal movement of nut portion 42 relative to nut collar portion 41.

[0048] The secondary driven screw is not powered, but follows movement of the primary driving screw, either upwardly or downwardly, as appropriate. Here again, such motion is accommodated by pivotal movement of nut portion 48 relative to nut portion 46. The extend and retract stops are provided to limit the extent of axial movement of the nuts relative to their appropriate screws.

[0049] During normal operation, the secondary driven screw simply follows movement of the primary driving screw within the range of motion defined by the respective extend and retract nuts. The operation of the device may be tested by the positions determined by resolvers 65, 74. The output speed of the driven output gear 73 is monitored by tachometer 71.

[0050] In the event of a failure of the primary driving screw, such as by the threads of primary driving screw 26 being stripped, the hydraulic control module 51 may supply a suitable signal to hydraulic brake 70 to selectively brake secondary output gear 72, and thereby lock and hold the position of member 21 relative to support 22. In this regard, the fault sensor includes resolvers 65, 74.

[0051] In the arrangement shown in Fig. 1 , where the driving and driven screws are depicted as being at different arm distances from the pivotal axis 23 of member 21 , the threads of the two screws may be the same or different from one another. In other words, the driven screw need not necessarily rotate at the same angular velocity as the driving screw. In another embodiment where the driving and driven screws are arranged at the same arm distance from pivotal axis 23, the same situation obtains, namely that the pitch of the driving and driven threads may be the same, or different from one another. Second Form (Fig. 2)

[0052] Referring now to Fig. 2, a second form of the invention is indicated at 20'. Persons skilled in this art will readily appreciate that many of the portions and elements of the second form are the same as those previously described. Hence, the same reference numerals are used in Fig. 2 to refer to the same structure previously described with respect to Fig. 1 , except as disclosed below.

[0053] The salient difference between the embodiment 20 shown in Fig. 1 and the embodiment 20' shown in Fig. 2 is that electric motors 52', 58' have been substituted for hydraulic motors 52, 58 in Fig. 1. Similarly, electric brakes 53', 59', 70' in Fig. 2 have been substituted for hydraulic brakes 53, 59, 70, respectively, in Fig. 1. Also, the control modules 50', 51' are arranged to provide suitable electrical signals to motors 52', 58' and brakes 53', 59', 70'. Otherwise, the device shown in Fig. 2 operates substantially as the device shown in Fig. 1.

Third Form (Fig. 3)

[0054] Referring now to Fig. 3, a third form of the improved actuator is generally indicated at 83. This third form includes many of the same portions or elements that have been previously described with respect to the first and second forms. Hence, the same reference numerals are used in Fig. 3 to refer to the same structure previously described with respect to Figs. 1 and 2, except as set forth below.

[0055] The salient difference of this third form is that the differential-like mechanism 56 has been omitted. Thus, hydraulic module 50 is arranged to supply appropriate hydraulic signals to hydraulic motor 52 and hydraulic brake 53. The output pinions 54, 55 of these two elements engage a gear 84, which has a pinion 85 in meshing engagement with gear 64. Moreover, the compressive and tensile no-back devices have been omitted. Flange 34 is constrained by thrust bearings 82, 82, respectively.

[0056] In the lower portion of Fig. 3, secondary hydraulic module 51 is similarly arranged to provide appropriate hydraulic signals to hydraulic motor 58 and/or hydraulic brake 59. The pinions 60, 61 of these two members are engaged in meshing engagement with a gear 62 having a pinion 72 in meshing engagement with gear 73. Thus, in this third embodiment, the differential-type drive mechanism has been omitted, with some of its function working with the driving screw, and others of its func- tion working with the driven screw. Here again, the device operates substantially as described with respect to the first and second embodiments.

Modifications

[0057] The present invention contemplates that many changes and modifications may be made. Control modules 50, 51 may be hydraulic. Alternatively, electrical control modules 50', 51 ', may be substituted therefore. Motors 52, 58 and 70 may be hydraulic motors, or may be electrical motors, such as indicated at 52', 58', 70'. The hydraulic brakes 53 and 59 may be hydraulic, or they may be electrical, as indicated at 53', 59'.

[0058] In each of the three illustrated embodiments, the driving and driven screws are indicated as being at different radial distances from pivotal axis 53. As previously explained, this is only for purposes of illustration. In actual practice, the arm distances may be the same, although the view of one would obstruct the view of the other.

[0059] Therefore, while three different forms of the improved actuators have been shown and described, and various modifications thereof discussed, persons skilled in this art will readily appreciate that various additional changes and modifications may be made without departing from the spirit of the invention, as defined and differentiated by the following claims.

Claims

Claims What is claimed is:

1. An actuator adapted to control the movement of a member relative to a support, comprising:

a primary driving screw having a primary nut in threaded engagement with a primary screw, said primary driving screw being operatively arranged to transmit forces between said member and said support along the axis of said primary driving screw;

a motor operatively arranged to selectively rotate said primary screw relative to said primary nut to cause said member to move relative to said support;

a secondary driven screw having a secondary nut in threaded engagement with a secondary screw, said secondary driven screw acting between said member and said support;

a brake associated with said secondary driven screw and selectively operable to brake relative rotation between said secondary nut and said secondary screw to cause forces to be transmitted between said member and said support along the axis of said secondary driven screw; and

a fault sensor for sensing a fault in the operation of said primary driving screw and for selectively operating said brake when a fault is sensed to impede movement of said member relative to said support.

2. An actuator as set forth in claim 1 wherein substantially all of the forces transmitted between said member and said support are transmitted along the axis of said primary driving screw when no fault is sensed in said primary driving screw.

3. An actuator as set forth in claim 1 wherein said primary nut is attached to said member.

4. An actuator as set forth in claim 1 wherein said motor is an electric motor.

5. An actuator as set forth in claim 1 , and further comprising: a primary gear train operatively arranged between said motor and said primary screw.

6. An actuator as set forth in claim 1 , and further comprising:

a torque limiter operatively interposed between said motor and said primary screw.

7. An actuator as set forth in claim 1 , and further comprising:

a no-back primary brake operatively interposed between said support and said primary screw.

8. An actuator as set forth in claim 1 , and further comprising:

a primary position sensor operatively arranged to sense the position of said primary screw.

9. An actuator as set forth in claim 1 wherein said secondary nut is attached to said member.

10. An actuator as set forth in claim 1 , and further comprising:

a secondary gear train operatively arranged between said secondary screw and said brake.

11. An actuator as set forth in claim 1 , and further comprising:

a thrust bearing operatively interposed between said support and said secondary screw.

12. An actuator as set forth in claim 1 , and further comprising:

a tachometer operatively arranged to sense the rotational speed of said secondary screw.

13. An actuator as set forth in claim 1 wherein said brake is an electro-mechanical brake.

An actuator as set forth in claim 1 , and further comprising a secondary position sensor operatively arranged to sense the position of said secondary screw.

15. An actuator as set forth in claim 1 , and further comprising:

an extend stop on said primary driving screw for providing an extension limit of said primary driving screw.

16. An actuator as set forth in claim 1 , and further comprising:

a retract stop on said primary driving screw for providing a retraction limit of said primary driving screw.

17. An actuator as set forth in claim 1 wherein said fault is sensed as a function of a difference in the positions of said primary and secondary screws.

18. An actuator as set froth in claim 1 wherein said fault is sensed as a function of the rotational speed of said secondary screw.

19. An actuator as set forth in claim 1 , and further comprising:

a damper operatively associated with said secondary driven screw to prevent a run-away condition of said secondary driven screw in the event of a failure of said primary driving screw.

20. An actuator as set forth in claim 1 wherein said secondary driven screw is not arranged to move said member relative to said support against an opposing load.

21. An actuator as set forth in claim 1 wherein said secondary driven screw is arranged to selectively brake movement of said member relative to said support under an aiding load.

22. An actuator as set forth in claim 1 wherein said primary driving screw is a ball screw.

23. An actuator as set forth in claim 1 wherein said secondary driven screw is a ball screw.