ACTUATOR

An actuator for driving a rotatable component includes a first member comprising a screw thread and rotatable about an axis (X), and a second member comprising a screw thread configured to cooperate with the screw thread on the first, rotating member. The second member is restrained against rotational movement about the axis (X) such that rotation of said first member causes movement of said second member along the axis (X), and the second member comprises one or more helical grooves. The actuator also includes a third member rotatable about the axis (X) and restrained against axial movement, wherein the third member comprises one or more helical rails, each configured to ride within a respective one of the helical grooves such that movement of the second member along the axis (X) causes rotational movement of the third member about the axis (X).

FIELD

The present disclosure relates generally to an actuator for driving a rotatable component.

BACKGROUND

FIG. 1shows a conventional actuator10that is configured to rotate a component (not shown). The actuator10may comprise an electric motor (not shown) that is configured to rotate a first member, in the form of ball screw12. A second member, comprising nut14is threaded to said ball screw and is moveable in the longitudinal direction. Rotation of the screw12causes nut14to move longitudinally along the length of the screw12.

The second member comprises one or more moveable rods16fixed to the nut14that extend in a longitudinal direction, through an intermediate housing18of the actuator10. The one or more rods16may be coupled with a third member in the form of a slider20that forms part of the second member as well. The slider20moves in the axial or longitudinal direction along one or more fixed rods19.

Upon rotation of the screw12, the nut14moves in the axial or longitudinal direction. This causes moveable rods16and slider20to also move in the axial or longitudinal direction.

A fourth, rotating member, in the form of a sleeve30may be coupled to the slider20via a bearing system50. The bearing system50comprises one or more roller bearings52that move with the slider20. The roller bearings52are configured to contact a helical track54. Upon axial movement of the slider20, the roller bearings52move along the helical track. Due to the helical nature of the track, this causes the roller bearings52to push against the track and rotate the sleeve30.

The sleeve30has actuator arms35connected to it, and rotation of the sleeve30causes actuator arms35to rotate as well. The actuator arms35may comprise part of, or be coupled to, a rotatable component, for example an aircraft flight control system element such as one or more ailerons and/or elevators and/or rudders. In this manner, the actuator drives the rotatable component.

Although the actuator10has various benefits, for example a high load carrying capacity and high efficiency, it is desired to provide a compact actuator that is able to achieve rotation of a rotatable component with a reduced axial length. Furthermore, it is desired to provide a rotatable actuator that is relatively inexpensive.

SUMMARY

In accordance with an aspect of the disclosure, there is provided an actuator for driving a rotatable component. The actuator comprises a first member comprising a screw thread and rotatable about an axis, and a second member comprising a screw thread configured to cooperate with the screw thread on the first member. The second member is restrained against rotational movement about the axis such that rotation of said first member causes movement of said second member along the axis, and the second member comprises one or more helical grooves. The actuator further comprises a third member rotatable about the axis and restrained against axial movement, wherein the third member comprises one or more helical rails, each configured to ride within a respective one of the helical grooves such that movement of the second member along the axis causes rotational movement of the third member about the axis.

This provides a relatively compact and inexpensive rotary actuator as compared to conventional arrangements.

The actuator may further comprise a motor, e.g., an electric motor configured to drive the first member.

A pitch of the helical rails may be at least 10, 20, 30, 40 or even 50 times greater than a pitch of the screw thread on the first member and/or the second member. This can provide an additional, or alternative mechanism for transmitting the relatively small torque of a driving motor or screw shaft to a relatively large torque for rotating the third member.

The second member may be located concentrically around the first member. The third member may be located concentrically around the first member and the second member. Providing the first, second and third members in a concentric arrangement in this manner leads to a particularly compact arrangement that makes efficient use of space.

The actuator may further comprise one or more rods that are fixed against rotational movement, wherein the second member may be threaded onto the one or more rods such that the rods restrain the second member against rotational movement about the axis. The one or more rods may comprise at least a pair of rods located on opposite sides of the axis. Each of the one or more rods may be arranged parallel to the axis.

The second member may comprise an outer cylindrical surface and the helical grooves may be located in the outer cylindrical surface of the second member.

The actuator may further comprise opposed first and second mounting elements, wherein the first member, second member and third member may be located between the first and second mounting elements.

A portion of the first member at a first axial end thereof may be held between one or more bearings of the first mounting apparatus, and a portion of the first member at a second, opposite axial end thereof may be held between one or more bearings of the second mounting apparatus, such that the first member is held rotatably by the first and second mounting apparatus.

The third member may comprise a substantially cylindrical tube extending between the first and second mounting elements.

The one or more helical rails may be located on an inner cylindrical surface of the third member.

The cooperating screw threads of the first member and the second member, the helical grooves of the second member and the helical rails of the third member may all located in a volume defined by the inner cylindrical surface of the third member.

In various embodiments a reduction gearbox may be configured to transmit drive to the first member and rotate the first member about the axis. This can provide a mechanism for transmitting the relatively small torque of a driving motor to a relatively large torque for rotating the third member.

DETAILED DESCRIPTION

Herewith will be described various embodiments of an actuator for driving a rotatable component. An example of such an actuator is shown inFIG. 2.

FIG. 2shows an actuator100for driving a rotatable component (not shown). The actuator100comprises a motor110, which may be a DC motor although any suitable type of motor may be used. In addition, although a motor110is shown in the example any suitable drive mechanism may be used.

The actuator100may further comprise a gearbox (not shown) configured to transmit drive from the motor110to a component of the actuator100(e.g., screw shaft130as described below). The gearbox may be a planetary gearbox, although any suitable type of gearbox may be used. The gearbox may be configured to provide a geared reduction of the drive from the motor110such that the rotational rate of the motor110is reduced when the drive is transmitted through the gearbox to the component of the actuator100.

The actuator100comprises a first member or screw shaft130operatively connected to the motor110(e.g., via the gearbox), and driven by the motor110, such that driving the motor110causes a rotational movement of the screw shaft130, for example in the direction of arrow132. The screw shaft130is optionally coincident with a central, longitudinal axis X of the actuator, and may be rotatable around this axis X as well. The screw shaft130comprises a screw thread around an outer cylindrical surface thereof and extends from a first axial end132to a second, opposite axial end134.

The actuator100may comprise a first mounting apparatus140that is mounted to the gearbox and configured to remain stationary during operation of the actuator100. The first mounting apparatus140may be located at a first axial end of the screw shaft130and configured to receive a portion of the screw shaft130as described in more detail below.

The actuator100may further comprise a second mounting apparatus150, such that the second mounting apparatus150is configured to remain stationary during operation of the actuator100. The second mounting apparatus150may be located at the second axial end of the screw shaft130and configured to receive a portion of the screw shaft130as described in more detail below.

The actuator100further comprises one or more rods170that extend between the first mounting apparatus140and the second mounting apparatus150, wherein the one or more rods170are secured to the mounting apparatus140,150such that they are fixed in position relative thereto and remain stationary during operation of the actuator100.

In the illustrated embodiment, four rods170are shown (seeFIG. 4) and are located parallel to each other and such that they form two diagonally opposite pairs located around the central, longitudinal axis X of the actuator100. Although this may be an optimum arrangement, in the broadest aspects of the present disclosure any number of rods170may be provided to achieve the technical effects described herein.

The actuator100further comprises a second member or nut180that cooperates with the screw shaft130and is operatively connected thereto such that rotation of the screw shaft130causes axial movement of the nut180in the direction of arrow182. The nut180is threaded onto each of the one or more rods170, such that the rods170restrict movement of the nut182axial movement in the direction of arrow182, and prevent rotational movement of the nut180.

The actuator100further comprises a third member or sleeve200, a portion of which is cut away inFIG. 2to show other components of the actuator100. The sleeve200is located concentrically around the longitudinal axis X of the actuator100, and comprises one or more helical rails220located on an inner cylindrical surface204of the sleeve200.

In various embodiments (and as shown inFIG. 2), a pitch of the helical rails220is much higher than a pitch of the screw thread on the screw shaft130. For example, the pitch of the helical rails220may be at least 50 times greater than the pitch of the screw thread on the screw shaft130.

The sleeve200is rotatably mounted between the first mounting apparatus140and the second mounting apparatus150such that it can rotate about the longitudinal axis X. In various embodiments, the sleeve200may be attached to a rotatable component, such that rotation of the sleeve200causes rotation of the components to which it is attached. In the illustrated embodiment the sleeve200comprises a splined connection comprising a plurality of splines230onto which a component may be attached, wherein the component may have a corresponding set of splines to mate with the splines230of the sleeve200. Alternatively, or additionally, the sleeve200may comprise a clevis for attachment to a component.

The nut180comprises one or more grooves190, each configured to receive a respective one of the rails220. The rails220are configured to ride in the grooves190as the nut180moves in the axial direction as indicated by arrow182, which causes the sleeve200to rotate about the longitudinal axis X. This, in turn, causes rotation of a component to which the sleeve200may be attached.

FIG. 3shows a cross-section of the actuator100, from which it can be seen how the screw shaft130may be mounted to the first mounting apparatus140and second mounting apparatus150.

The first mounting apparatus140comprises a first member147located concentrically around the screw shaft130, as well as a second member148that is also located concentrically around the screw shaft130and is fastened to the first member147using one or more fasteners163. The second member148comprises an internal bore149that permits the screw shaft130to pass therethrough for operable connection to the motor110. The motor110is fastened to the second member148using one or more fasteners111, and encloses the actuator100at the first end132of the screw shaft130.

The second mounting apparatus150comprises a first member157located concentrically around the screw shaft130, as well as a second member158that is fastened to the first member157using one or more fasteners162. The second member158is provided in the form of a cap that encloses the actuator100at the second end134of the screw shaft130.

A portion of the screw shaft130at the first axial end132thereof may be held between one or more bearings142of the first mounting apparatus140, such that the screw shaft130is rotatable relative to the first mounting apparatus140. These bearings142are located between the screw shaft130and the first member147of the first mounting apparatus140.

Similarly, a portion of the screw shaft130at a second, opposite axial end134thereof may be held between one or more bearings152of the second mounting apparatus150, such that the screw shaft130is rotatable relative to the second mounting apparatus150. These bearings152are located between the screw shaft130and the first member157of the second mounting apparatus150.

The nut180may comprise a first portion184comprising a screw thread configured to cooperate with the screw thread on the screw shaft130, such that rotation of the screw shaft130causes the screw threads to cooperate and translate the nut180in the axial direction182.

The nut180may further comprise a second portion188in the form of a sleeve that is connected to and axially movable with the first portion184. The second portion188may comprise the one or more grooves190on an outer cylindrical surface189thereof. The nut180may comprise a locking piece187configured to lock the first portion184axially and rotationally with respect to the second portion188.

The sleeve200of the actuator100may be rotatably mounted to the first and second mounting apparatus140,150as described above, and as shown inFIG. 3the sleeve200may be provided in the form of a substantially cylindrical tube having end portions202. The end portions202are substantially annular and are located around respective bearings143,153of the first and second mounting apparatus140,150respectively.

FIG. 4shows an exploded view of the actuator100(along axis X), which shows the various components referred to above. The sleeve200is offset from the remainder of the components for clarity purposes. FromFIG. 4it can be seen that the one or more rods170are fastened to the first and second mounting apparatus140,150using one or more fasteners172that secure the rods172respective first members147,157of the first and second mounting apparatus140,150respectively.

It will be appreciated that aspects of the present disclosure lead to a rotary actuator that is relatively inexpensive and more compact than conventional arrangements. In various refinements, the inclusion of a reduction gearbox between the motor110and the screw shaft130(in particular a planetary gearbox) can mean that the torque of the motor110is able to translate the nut180(via the gearbox and screw shaft130) easily and without use of further, additional components.