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EP-3685050-B1 - ACTUATOR ROTATIONAL ALIGNMENT DEVICE

EP3685050B1EP 3685050 B1EP3685050 B1EP 3685050B1EP-3685050-B1

Inventors

  • LEWENDON, James

Dates

Publication Date
20260506
Application Date
20180917

Claims (16)

  1. A linear actuator (30) comprising: a first component (32) extendable and retractable relative to a second component (33) along an operating axis of the actuator (30) whereby at one end of the actuator's operating axis the first and second components (32, 33) are extended relative to one another providing an extended position of the linear actuator and at the other end of the actuator's operating axis the first and second components (32, 33) are retracted relative to one another providing a retracted position of the linear actuator, the first and second components (32, 33) being configured to be freely rotatable relative to each other about the actuator's operating axis; characterized in that a helical orientation surface (40) is disposed about the actuator's operating axis in a fixed angular position relative to the first component (32); and in that a follower (50) is disposed in a fixed angular position about the actuator's operating axis relative to the second component (33); whereby when the first and second components (32, 33) are moved relative to one another towards one of the ends of the actuator's operating axis, the follower (50) moves from a disengaged condition in which the follower (50) is disengaged from the helical orientation surface ( 40) to allow free relative rotation of the first and second components (32, 33), to a condition in which the follower (50) engages and moves along the helical orientation surface (40) to rotate the first and second components (32, 33) relative to one another about the actuator's operating axis, until the follower (50) reaches a predetermined position along the helical orientation surface (40), so that the first component and the second component (32, 33) are brought to a predetermined angular orientation relative to each other about the actuator's operating axis by the movement of the follower (50) along the helical orientation surface (40).
  2. A linear actuator (30) as defined in claim 1, in which the end of the actuator's operating axis towards which the first and second components (32, 33) are moved comprises the end at which the first and second components (32, 33) are retracted relative to one another.
  3. A linear actuator (30) as defined in claim 2, in which the first and second components (32, 33) are provided with a further helical orientation surface and a further follower respectively, positioned and arranged to operate similarly to the helical orientation surface (40) and follower (50), so that the first and second components (32, 33) are brought into a predetermined angular orientation relative to one another about the actuator's operating axis, in both the extended and in the retracted position relative to one another.
  4. A linear actuator (30) as defined in any preceding claim, in which the follower (50) comprises a helical surface (54) complementary to the helical orientation surface (40).
  5. A linear actuator (30) as defined in any preceding claim, in which the follower (50) and/or the helical orientation surface (40) are resiliently mounted for limited movement along the actuator's operating axis.
  6. A linear actuator (30) as defined in any preceding claim, in which the helical orientation surface (40) comprises a single peak (A) and a single trough (C).
  7. A linear actuator (30) as defined in any of claims 1-5, in which the helical orientation surface (40) comprises a plurality of peaks (A, E) and a plurality of troughs (C, G).
  8. A linear actuator (30) as defined in claim 6 or 7, in which the helical orientation surface (40) is generally annular in plan, when viewed along the actuator's operating axis.
  9. A linear actuator (30) as defined in claim 8, in which the helical orientation surface (40) slopes helically to either side of a given peak (A, E) towards the next trough or troughs (C, G).
  10. A linear actuator (30) as defined in claim 8, in which the helical orientation surface (40) only slopes from one side of the (A) or each (A, E) peak towards the next trough (C, G).
  11. A linear actuator (30) as defined in any preceding claim, in which the first or second component comprises an operating member (33, 36).
  12. A linear actuator (30) as defined in claim 11, in which the other one of the first and second component comprises an external housing, casing or frame (31) of the linear actuator (30); or a chassis or frame or ground component to which the linear actuator (30) is fixed.
  13. A linear actuator (30) as defined in any preceding claim, in which the first and second components (32, 33) comprise parts internal to the linear actuator (30).
  14. A linear actuator (30) as defined in claim 13, in which one of the first and second components (32, 33) comprises a gas entry sleeve (32) of a multi-stage actuator and the other of the first and second components (32, 33) comprises an intermediate telescopic component (33) of the multi-stage actuator.
  15. A linear actuator (30) as defined in any preceding claim, in which the helical orientation surface (40) is formed on an insert (38) received in one of the first or second component (32, 33).
  16. A linear actuator (30) as defined in claim 15, in which the follower (50) comprises an insert received in the other one of the first or second component (32, 33).

Description

This invention concerns rotational alignment devices for linear actuators of the type that include parts which, when the actuator is extended, are or would be free to twist relative to one another about the extension axis, unless additional measures are taken to prevent such twisting. Fluid operated linear actuators typically include a piston slideable in a cylinder, with a fluid-tight seal required between these components. To make sealing easier, the piston and cylinder usually have matched circular cross-sections. This leaves the piston free to twist in the cylinder, unless constrained by the components or mechanism between which the piston and cylinder operate. Such constraint is not always available unless specifically provided, and such twisting is not always desirable. For example, when the actuator is a high speed, high pressure gas operated actuator used for emergency release, or used to eject a payload from an aircraft, once the load has been released or ejected, the end of the piston used to push against the load is freely projecting and can adopt an essentially random orientation by rotating about the piston axis. The piston will typically be equipped with a shaped ejector shoe or yoke which is used to push against the load. Once the load has gone, the shoe will rotate randomly and unpredictably in the aircraft slipstream, causing unpredictable changes in drag, radar cross section, vibration and airframe stresses, and upon retraction representing a rotational misalignment. As another example, the actuator may retractably suspend a castor wheel of an aircraft undercarriage. Difficulties may arise when attempting to retract the undercarriage into the body of the aircraft, if the castor wheel remains free to rotate about the actuator piston axis. Similar problems can arise in other kinds of linear actuators, such as electrically powered linear motors with armatures free to rotate about their operating axis. It is known to prevent the twisting of a fluid-operated actuator piston in its cylinder using a specially provided constraint arm, pivotally joined at one end to the cylinder or to another suitable fixed point, and pivotally joined at the other end to the free end of the piston. The arm has a central hinge or elbow, allowing it to extend and retract along with the actuator. However, the arm adds to the overall weight of the actuator assembly, even if made from lightweight, high strength materials, such as titanium alloys. These materials tend to be expensive. When the piston is retracted, the elbow of the arm projects laterally a considerable distance, which can be difficult to accommodate within the limited space available on an aircraft, and can increase drag significantly. Documents EP 2 508 773 A1, EP 2 532 821 A2, US 3 799 036 A disclose linear actuators according to the preamble of claim 1. Documents WO 2005/095047 A1 and US 3 948 502 A disclose linear actuators in which the follower does not have a disengaged position. These problems are addressed according to the present invention, which provides a linear actuator as defined in claim 1. The end of the operating axis towards which the first and second components are moved may be the end at which the first and second components are extended relative to one another, or it may be the end at which the first and second components are retracted relative to one another. Indeed, where required, the first and second components may be provided with a further helical orientation surface and a further follower respectively, positioned and arranged to operate similarly to the helical orientation surface and follower previously described, so that the first and second components are brought into a predetermined angular orientation relative to one another about the operating axis, in both the extended and in the retracted positions relative to one another. The follower may comprise a helical surface complementary to the helical orientation surface. This may assist in reducing impact forces and wear on both the helical orientation surface and on the follower. The follower and/or the helical orientation surface may be resiliently mounted for limited movement along the operating axis, to assist in cushioning impact forces and in reducing wear. The helical orientation surface may comprise a single peak and a single trough, whereby the first and second components are turned from a random angular orientation relative to one another about the operating axis, to a single predetermined angular orientation relative to one another about the operating axis. Such an arrangement is appropriate where the actuator is connected to an operating member, such as an ejector shoe or a castor wheel (to use the examples mentioned above) which has no rotational symmetry (rotational symmetry of order 1). Alternatively, the helical orientation surface may comprise a plurality of peaks and troughs. More generally, for example, n peaks and n troughs will be appropriate for an operat