GB2348537A

GB2348537A - Split tube actuator device provides mechanical advantage

Info

Publication number: GB2348537A
Application number: GB9907673A
Authority: GB
Inventors: James Peter Jeffs; Seamus Dominic Garvey
Original assignee: Individual
Current assignee: Individual
Priority date: 1999-04-01
Filing date: 1999-04-01
Publication date: 2000-10-04
Also published as: GB9907673D0

Abstract

The device comprises a cylinder 1 lying between two end plates 3, and having an axial split 2. Piezoelectric actuators 5 cause the edges of the split to move past each other in the direction of the cylinder's axis. This causes one end of the cylinder to twist relative to the other. The device may be incorporated into an aerofoil in order to provide pitch control (figs 2 and 3).

Description

SPLIT TUBE DEVICE PROVIDES MECHANICAL ADVANTAGE.

Field of the Invention.

This invention comprises a device which converts small displacements of one or more primary actuators into relatively large twisting movements. It has relevance wherever limited-angle controlled angular motion is required.

The invention is particularly applicable to controllable-pitch aerofoil. It applies to any aerofoil dynamically active wing or wing-like members of any aircraft, the blades of helicopter rotors and auto-gyros, aircraft propellers, missile control vanes, rotor blades and guide vanes of turbines and compressors, blades of horizontal and vertical axis wind-turbines and many other applications in which there are aerofoil whose length is substantial compared to at least one dimension of the cross-section and in which there may be any advantage to be had from having control over the pitch of the aerofoil.

Background to the Invention.

It is well known by most mechanical engineers that a hollow tube can be quite stiff in torsion whereas the same tube with one"axial"split will be very flexible in torsion by comparison. This is true irrespective of the cross-section of the tube and regardless of whether the tube is perfectly prismatic or not.

If a split tube is twisted, one end relative to the other, it will be found that one side of the split slides relative to the other side in the direction of the axis of the tube. By applying the conservation of energy principe, it is clear that the tube can be made to twist by exerting a force which tends to slide one side of the split relative to the other.

Because a substantial twist corresponds to a relatively small amount of sliding across the split, the forces required at the split to cause the twist may be large and the displacements will be small.

There are many actuators available which have the capability to provide large amounts of force but very small deflections. Piezo-electric actuators are particularly notable for these characteristics. There are many applications where finite amounts of angular motion are required. These are normally addressed through the provision of some kind of bearing. The application, which most directly motivates this invention, is the requirement for pitch control on long aerofoil.

Pitch control of an aerofoil is normally effected by pivoting the aerofoil at its root so that it can be rotated about an axis which is coincident (or almost coincident) with the longitudinal axis of the aerofoil. This facility has very large associated cost since the entire aerofoil is normally cantilevered off a bearing, requiring that the bearing be capable of withstanding very substantial moments about axes normal to its principle axis. Moreover, a given pitch correction applied to the aerofoil using such a facility results in a net rigid-body rotation of the aerofoil relative to its mounting structure.

Generally, the optimal pitch adjustment for maximum aerofoil dynamic efficiency would vary along the length of the aerofoil.

The present design provides for pitch control of aerofoil which does not require the presence of a bearing at the base of the aerofoil but which uses elastic deformation of the aerofoil instead. With suitable design of the aerofoil cross-section, the rate of change in pitch of the aerofoil can be made to depend on the position along the aerofoil.

Specific Embodiment A.

Figure 1 shows a very simple limited-angle motor constructed using a single circularsection tube (1) containing a split (2) along its length. The tube is fixed at each end to a circular plate (3) which has some provision (4) for allowing one side of the split in the tube to move relative to the other side in a direction coincident with the tube axis.

Piezo-electric actuators (5) are attached to the tube spanning the split and when these are energised, their effect is to force one side of the split to move axially relative to the other side. Because the actuators are stiff, the torsional stiffness of the limited-angle motor is almost identical to the torsional stiffness which would be obtained if the tube was not split.

Specific Embodiment B.

Figure 2 shows an aerofoil comprised mainly of a tube (1) which contains a split (2) along its length (near the trailing edge) such when the tube is twisted, one side of the split tends to slide relative to the other side in a direction which is broadly aligned with the principal axis of the tube. There is a sliding-provision (6) in place which constrains the tube from opening at the split but which allows one side of the split to slide relative to the other side in a direction broadly aligned with the principal axis of the tube.

Actuators (5) are located along the split each of which acts to slide (along the principal axis) one side of the split relative to the other.

Specific Embodiment C.

Figure 3 shows an aerofoil comprised mainly of a tube (1) which contains a split (2) along its length such when the tube is twisted, one side of the split tends to slide relative to the other side in a direction which is broadly aligned with the principal axis of the tube. There is a sliding-provision (6) in place which in this case resembles a piano hinge except that it allows some motion of one side of the hinge relative to the other in the direction of the hinge axis. Discrete disc actuators (5) are located along the hinge such that at several places along the split, the actuators act to slide one side of the split relative to the other. Preload provisions (7) are located along the split which act to exert a preload force tending to cause the split to slide in the opposite direction to the direction of slide caused by energising the actuators.

Claims

CLAIMS 1 A device comprising a tube in which there is a split running parallel to the axis and some actuation means provided at or near that split which can act in such a way as to cause one side of the split to tend to move relative to the other side in a direction which is broadly aligned with the axis of the tube.
2 A device as in claim 1 in which there is more than one axial split running along the length of the tube.
3 An aerofoil having controllable-pitch which is achieved through deformation of the aerofoil wherein the aerofoil includes, as a major component, a tube which contains one or more splits as described in claims 1 and 2 and some actuation provision which can force the two sides of the (each) split to move relative to each other such that the aerofoil is caused to twist about its principal axis thereby providing the ability to control aerofoil pitch. The principal axis of the tube may be curved, the cross-section of this tube may vary along the length of the aerofoil, the wall thickness of the tube may be dependent on position along the length of the aerofoil and may also vary from point to point on any given cross-section. There may be some support structure inside the tube and there may be complete or partial skins outside of the tube.
4 An aerofoil as described in claim 3 in which the section of the aerofoil is designed such that for a given amount of slide between the two sides of the split the rate of twist is an appropriate function of distance along the aerofoil.
5 An aerofoil as described in claims 3 or 4 in which two sides of the split are held together by some sliding arrangement which prevents the tube from opening.
6 An aerofoil as described in claims 3, 4 or 5 in which the actuation is realised at least in part by the presence of one or more discrete or distributed actuators along the split whose direct effect is to cause one side of the split to slide relative to the other in a direction which is broadly aligned with the principal axis of the tube thereby tending to cause the tube to twist.