WO2009016361A2

WO2009016361A2 - Control device

Info

Publication number: WO2009016361A2
Application number: PCT/GB2008/002582
Authority: WO
Inventors: David Anthony Cowling
Original assignee: Wittenstein Aerospace & Simulation Limited
Priority date: 2007-07-31
Filing date: 2008-07-28
Publication date: 2009-02-05
Also published as: WO2009016361A3; GB201001509D0; GB2463625A; GB2463625B

Abstract

A control device comprising: a reference frame (6a, 6b); a stick (3, 4); a pivot (7, 11) mounting the stick to the reference frame and defining a pivot axis (x); and an actuator (1, 2) for rotating the stick about the pivot axis. Mass balance is achieved by offsetting the centres of mass of the actuator and the stick from the pivot axis. A sensor is provided for sensing a force applied to the stick. The sensor is arranged to detect the output of the actuator whereby the sensor is substantially insensitive to g induced moments about the pivot axis caused by acceleration of the device. Typically a line joining the centres of mass of the actuator and the stick substantially passes through the pivot axis. The actuator is a rotary actuator having a stator coupled to the stick and a rotor coupled to the reference frame.

Description

CONTROL DEVICE

FIELD OF THE INVENTION

The present invention relates to a control device comprising: a reference frame; a stick; a pivot mounting the stick to the reference frame, the pivot defining a pivot axis; and an actuator for rotating the stick about the pivot axis.

BACKGROUND OF THE INVENTION

A first known control device of this kind is described in US 2006/0254377. The stick is driven about two perpendicular pivot axes (A, B) by respective rotary actuators. A balance weight is provided on the A-axis in order to provide vertical mass balance about the B-axis. In other words, the balance weight ensures that there is no net induced moment about the B-axis when the device is subjected to a vertical acceleration perpendicular to the A and B axes.

A first problem with this arrangement is that the balance weight adds to the total weight of the device. A second problem is that the balance weight adds to the total volume of the device. A third problem is that the device is not horizontally mass balanced. Therefore, if the device is subjected to a horizontal acceleration, then there will be a net induced moment about the A or B axis. This mass imbalance must be compensated by one or both of the actuators, which adds complexity to the system.

A second known control device of this kind is described in US6708580. This device is also not horizontally mass balanced.

In both US 2006/0254377 and US6708580, each actuator has a stator (that is, the non- rotating part of the actuator) coupled to the reference frame and a rotor (that is, the rotating part of the actuator) coupled to the stick. The drive axis of each actuator is co-linear with its respective pivot axis.

US 2008/0079381 describes a flight control stick where the actuator is positioned so as to provide mass balance. A force sensor is coupled to the stick. The force sensor supplies a control signal to a motor control unit which supplies flight control surface position signals to a flight control unit.

A conventional bending moment force sensor at the base of a controller handle 20 is shown in Figures 22-24. Strain gauges are arranged in line with both X and Y axes around a force sensor element 21. The strain gauges A1-A4 measure bending moments about the X axis direction and are arranged as shown in the cross section illustrated in Figure 23.

When a force is applied to the controller handle 20 orthogonal and displaced from the X axis a bending moment results around the X axis. When applied in the associated direction this moment causes a compression of the force sensor element in the position of gauges Al and A2. A complimentary tension force occurs at the position of gauges A3 and A4.

The gauges can be arranged in a Wheatstone bridge circuit such as shown in Figure 24 where an electrical supply is provided as shown. The tension and compression of the gauges results in a change of their electrical resistance such that a signal representative of the bending moment applied to the controller handle by the force is produced.

A problem with the arrangement of Figures 22-24 is that the X-axis bending moment sensor (gauges A1-A4) is sensitive to g-induced moments about the X-axis caused by acceleration of the device in the Y direction. As a result, if the aircraft on which the control device is mounted accelerates in the Y direction then the handle will bend and a signal will be output by the X-axis bending moment sensor. This g-load sensitivity is undesirable because the purpose of the sensor is to detect loads applied to the stick by the operator independent of such g-loads.

SUMMARY OF THE INVENTION

A first aspect of the invention provides a control device comprising: a reference frame; a stick; a pivot mounting the stick to the reference frame and defining a pivot axis; and an actuator for rotating the stick about the pivot axis, wherein the centres of mass of the actuator and the stick are offset from the pivot axis such that if the control device is subjected to an acceleration orthogonal to the pivot axis, then the mass of the actuator and the mass of the stick generate moments about the pivot axis which act in opposite directions.

Preferably a sensor for sensing a force applied to the stick is provided, and the sensor is substantially insensitive to g induced moments about the pivot axis caused by acceleration of the device.

By offsetting the centres of mass of the actuator and the stick from the pivot axis, the mass of the stick can be at least partially balanced by the mass of the actuator without requiring an additional balance weight.

The sensor may be arranged to detect the output of the actuator. By detecting the output of the actuator, instead of measuring bending forces in the stick, the sensor is substantially insensitive to g induced moments about the pivot axis caused by acceleration of the device.

Typically a line passing through the pivot axis and the centre of mass of the stick also passes through the actuator. Preferably this line passes substantially through the centre of mass of the actuator. This enables the device to be mass balanced with respect to both vertical and horizontal acceleration of the device (in the case where the pivot axis is horizontal). In the more general case, if the line passes substantially through the centre of mass of the actuator, then the device is mass balanced with respect to two axes which are perpendicular to the pivot axis. However the centre of mass of the actuator may be slightly offset from this line and still provide an element of mass balance.

The actuator may be a linear actuator (such as a hydraulic piston or linear electric actuator) but more preferably the actuator is a rotary actuator having a stator coupled to the stick and a rotor coupled to the reference frame by a drive link and configured to rotate relative to the stator about a drive axis which is not co-linear with the pivot axis.

In the case of an electric linear or rotary actuator, the sensor may sense an output of the actuator by sensing a drive current in the actuator, hi the case of a linear hydraulic piston the sensor may sense the pressure in a chamber of the piston. However these sensing methods are less preferred because the current/pressure may not be accurately representative of the actual forces acting on the stick. Therefore more preferably the sensor is fixed to one of the components of the device and measures deformation of that component. For instance the sensor may be fixed to the drive link, to the rotor or stator of the rotary actuator, to a pivot shaft of the drive link; or to a bracket between the drive link and the reference frame, hi the case of the arrangement shown in Figure 8 of US 2008/0079381, the force sensor may measure torque in the planet carrier gear 610 or bending in the sector gear 612.

The sensor is typically either a force sensor arranged to sense tensile or compressive forces acting along a length of the drive link or along the length of a linear actuator, or a torque sensor arranged to sense torque in a component such as the rotor or stator of a rotary actuator.

A further aspect of the invention provides a control device comprising: a reference frame; a stick; a pivot mounting the stick to the reference frame and defining a pivot axis; and a rotary actuator having a stator coupled to the stick and a rotor coupled to the reference frame by a drive link and configured to rotate relative to the stator about a drive axis which is not co-linear with the pivot axis.

Preferably a sensor is provided for sensing a force applied to the stick, and the sensor is substantially insensitive to g induced moments about the pivot axis caused by acceleration of the device. The sensor may be arranged to detect the output of the actuator.

In contrast with the devices described in US 2006/0254377 and US6708580 the drive axis of the rotary actuator is not co-linear with the pivot axis, enabling a more mass balanced arrangement. Also, a rotary actuator is typically more compact and lighter than a linear actuator, and is also typically easier to backdrive.

Preferably the drive link is pivotally coupled to the rotor by a first drive pivot and to the reference frame by a second drive pivot. In certain embodiments of the invention the drive axis is not parallel with the pivot axis. For instance it may lie at a perpendicular or acute angle with the pivot axis, hi other embodiments of the invention the drive axis is substantially parallel with the pivot axis.

Preferably the device is substantially mass balanced about the pivot axis.

A further aspect of the invention provides an active user interface assembly, comprising: a housing; a user interface coupled to and extending from the housing, the user interface rotatable, from a null position, about an axis; and a feedback motor coupled to the user interface and adapted to be selectively energized, the feedback motor operable, upon being energized, to supply a feedback force to the user interface that opposes user interface movement about the axis, the feedback motor disposed such that its centre of gravity is located at a position relative to the user interface to mass balance the user interface when it is in the null position.

A further aspect of the invention provides an active user interface assembly, comprising: a housing; a user interface coupled to and extending from the housing, the user interface rotatable, from a null position, about a first axis and a second axis, the first and second axes being perpendicular; a first feedback motor coupled to the user interface and disposed such that its center of gravity is located at a first position relative to the user interface, the first feedback motor adapted to be selectively energized and operable, upon being energized, to supply a feedback force to the user interface that opposes user interface movement about the first axis; a second feedback motor coupled to the user interface and disposed such that its centre of gravity is located at a second position relative to the user interface, the second feedback motor adapted to be selectively energized and operable, upon being energized, to supply a feedback force to the user interface that opposes user interface movement about the second axis, wherein at least one of the first position and the second position are selected to mass balance the user interface when it is in the null position.

Further preferred aspects of the invention are set out in the appended claims.

BRIEF DESCRPTION OF THE DRAWINGS Embodiments of the invention will now be described with reference to the accompanying drawings, in which:

Figure 1 is a front upper view of a first one-axis device in a nominal position;

Figure 2 is a rear ³A view of the first one-axis device in the nominal position; Figure 3 is a rear ³A view of the first one-axis device in a deflected position;

Figure 4 shows a second one-axis device in a nominal position;

Figure 5 shows the second one-axis device in a deflected position;

Figure 6 is a side view of a first two-axis device in a nominal position;

Figure 7 is an upper ³A view of the first two-axis device in the nominal position; Figure 8 is a front ¹A view of the first two-axis device in a rolled position;

Figure 9 is a side ¹A view of the first two-axis device in the rolled position;

Figure 10 is a side view of the first two-axis device in a pitched position;

Figure 11 is an upper side view of the first two-axis device in the pitched position;

Figure 12 is a side view of a second two-axis device in a nominal position; Figure 13 is a side view of the second two-axis device in a rolled position;

Figure 14 is a side view of the second two-axis device in a pitched position;

Figure 15 is a rear ¹A view of a third two-axis device in a nominal position;

Figure 16 is a front ¹A view of the third two-axis device in the nominal position;

Figure 17 is a front ¹A view of a fourth two-axis device in a nominal position; Figure 18 shows a third one-axis control device; Figure 19 shows a strain gauge arrangement;

Figure 20 is a sectional view through a drive link showing the arrangement of strain gauges;

Figure 21 is a circuit diagram showing how the strain gauges are connected to sense tensile and compressive forces;

Figure 22 shows a bending moment sensor at the base of a controller handle;

Figure 23 is a sectional view through the base of the controller handle showing the arrangement of strain gauges;

Figure 24 is a circuit diagram showing how the strain gauges are connected to sense bending of the controller handle; and

Figure 25 is a simplified view of the device of Figure 1 showing the forces acting on the device.

DETAILED DESCRIPTION OF EMBODIMENT(S)

The control device shown in Figures 1-3 comprises a mounting plate 6a and a pair of pivot supports 6b fixed to the mounting plate 6a. The mounting plate 6a is fixed in turn to the structure of a vehicle or flight simulator.

A stick user interface is attached to a pivot block 11. The stick comprises a shaft 3 and a handle 4. A pivot shaft 7 extends from opposite sides of the pivot block 11 , and is journalled in the pair of pivot supports 6b so that the stick is free to rotate about the pivot axis X defined by the pivot shaft 7. The stick is rotatable, from a nominal or null position shown in Figure 1, about the X-axis.

A rotary actuator has an output shaft 2 which is fixed to the pivot block 1 1 and extends from an opposite side of the pivot axis X. The actuator has a casing 1 coupled to the mounting plate 6a by a drive link 5. The drive link 5 is pivotally coupled to the casing 1 by a first drive pivot and to the mounting plate 6a by a second drive pivot. In the arrangement of Figure 1, the output shaft 2 of the actuator remains fixed in relation to the stick (and thus acts as a stator) and the casing 1 of the actuator is configured to rotate about the drive axis of the actuator relative to the stator (and thus acts as a rotor). If the casing 1 rotates anticlockwise, then the drive link 5 drives the actuator down and the stick up as shown in Figure 3. If the casing 1 rotates clockwise, then the drive link 5 drives the actuator up and the stick down.

A torque sensor (not shown) is provided to sense the torque applied to the output shaft 2. The torque sensor may be implemented for example by a set of strain gauges or piezoelectric elements. The torque sensor measures the force applied to the stick by a pilot. An example of such a torque sensor is described in further detail below with reference to Figures 19-21.

When operating in an active mode, the actuator applies a force to the stick, for instance to provide force feedback to the pilot. Thus the actuator acts as a feedback motor coupled to the stick and is adapted to be selectively energized, the actuator operable, upon being energized, to supply a feedback force to the stick that opposes stick movement about the X- axis. When in passive mode the actuator has no power applied to it and the pilot is able to move the stick by driving the actuator backwards without a significant resistance. Alternatively a device to disconnect the actuator drive may be fitted to decouple the actuator.

Instead of (or in addition to) employing a torque sensor for measuring the torque applied to the output shaft 2 of the actuator, a compression force sensor may be fixed to the drive link 5. In both cases the force/torque sensor will sense the moment about the pivot axis X.

By positioning the torque/force sensors to directly sense the output of the actuator, the sensors are insensitive to g induced moments and therefore the active control of the stick is also unaffected by g loads as described in further detail below with reference to Figures 19- 21.

The centres of mass of the actuator and the stick are offset on opposite sides of the pivot axis X. As a result the device is vertically mass balanced about the pivot axis X - the vertical direction being perpendicular to the pivot axis X and to the axis Y labelled shown in Figure 3.

Therefore if the stick is subjected to a vertical acceleration of ng, then the moment about the pivot axis X in the vertical direction is given by:

M = -l_λm_λng + l₂m₂ng equation (1)

where:

/_/ is the distance between the pivot axis X and the centre of mass of the stick;

mi is the mass of the stick (including the shaft 3 and the handle 4);

h is the distance between the pivot axis X and the combined centre of mass of the actuator and force sensor; and

rri₂ is the combined mass of the actuator and force sensor.

For mass balance we want M = 0 or:

l^m^ng = l₂m₂ng equation (2)

which reduces to:

equation (3)

Thus by choosing values which satisfy equation (3), the device is vertically mass balanced about the pivot axis X. In other words, the feedback motor is disposed such that its centre of gravity is located at a position relative to the stick to mass balance the stick when it is in the null position.

Also, a line (labelled A in Figures 1-3) passing through the pivot axis X and the centre of mass of the stick also passes substantially through the centre of mass of the actuator. Therefore the device is horizontally mass balanced about the pivot axis X. Figures 4 and 5 show a second one-axis control device. The device is similar to the device of Figures 1-3, and equivalent features are given the same reference numeral. In the arrangement of Figures 1-3 the drive axis of the actuator is substantially co-linear with the line A and perpendicular to the pivot axis X. By contrast, in the arrangement of Figures 4 the drive axis is perpendicular to the line A and parallel with the pivot axis X.

The casing 1 of the actuator is fixed to the pivot block 11 by an arm 12, and the output shaft 2 is coupled to the mounting plate 6a by the drive link 5, and a crank shaft 13 extending at right angles to the drive axis. The drive link 5 is pivotally coupled to the crank shaft 13 by a first drive pivot and to the mounting plate 6a by a second drive pivot.

In the arrangement of Figure 4, the casing 1 remains fixed in relation to the stick (and thus acts as a stator) and the output shaft 2 rotates (and thus acts as a rotor). If the output shaft 2 rotates anticlockwise, then the drive link 5 drives the stick up and the actuator down as shown in Figure 5. If the output shaft 2 rotates clockwise, then the drive link 5 drives the stick down and the actuator up.

In common with the device of Figure 1, a torque sensor (not shown) is provided to sense the torque applied to the output shaft 2.

Figures 6-11 show a first two-axis control device. The device is similar to the device of Figures 1-3, and equivalent features are given the same reference numeral.

The mounting plate 6a is fixed to a casing 8 of a second (Y-axis) actuator. The Y-axis actuator acts as a second feedback motor coupled to the stick and is adapted to be selectively energized, the Y-axis actuator operable, upon being energized, to supply a feedback force to the stick that opposes stick movement about the Y-axis. Instead of being fixed to the mounting plate 6a, the pivot supports 6b are fixed to a mounting bracket 9, which is fixed in turn to an output shaft 10 of the Y-axis actuator. Thus in the two-axis device the pivot supports 6b and mounting bracket 9 provide a first (X-axis) reference frame and the mounting plate 6a provides a second (Y-axis) reference frame. The drive link 5 is pivotally coupled to the casing 1 by a first drive pivot and to the mounting bracket 9 by a second drive pivot. Figures 12-14 show a second two-axis control device. The device is similar to the device of Figures 6-11, and equivalent features are given the same reference numeral.

hi contrast to the arrangement of Figures 6-11 (and in common with the arrangement of Figure 4) the drive axis of the X-axis actuator is at right angles to the line A. The casing 1 of the actuator is fixed to the pivot block 11, and the output shaft 2 of the X-axis actuator is coupled to the mounting bracket 9 by the drive link 5.

The two-axis devices shown in Figures 6-15 are provided with an X-axis torque sensor (not shown) to sense the torque applied to the X-axis output shaft 2 and a Y-axis torque sensor (not shown) to sense the torque applied to the Y-axis output shaft 2.

Figures 15 and 16 show a third two-axis control device. The device is similar to the device of Figures 12-14, and equivalent features are given the same reference numeral. In contrast to the arrangement of Figures 12-14, the output shaft of the X-axis actuator is coupled to an L-shaped bracket 10 which is rigidly connected to the pivot block 11. The casing 1 of the X-axis actuator is coupled to the mounting bracket 9 by the drive link 5. Thus in this case the output shaft of the actuator acts as a stator, and the casing acts as a rotor. This arrangement has the potential to save some space when roll deflections occur. A similar variant of the device of Figures 4 and 5 may also be used.

Figure 17 show a fourth two-axis control device. The device is similar to the device of Figures 6-11, and equivalent features are given the same reference numeral. In contrast to the arrangement of Figures 6-11, the casing 1 of the X-axis actuator is rigidly connected to the pivot block 11 , and the output shaft is coupled to the mounting bracket 9 by the drive link 5. Thus in contrast to the arrangement of Figures 6-11, the output shaft of the actuator acts as a rotor and the casing 1 acts as a stator.

Figure 18 show a third one-axis control device. The device is similar to the device of Figures 1-3, and equivalent features are given the same reference numeral. In contrast to the device of Figures 1-3, the actuator is angled downwardly with respect to the line A passing through the pivot axis X and the centre of mass of the stick. Although the device is not mass balanced against horizontal acceleration orthogonal to the pivot axis X, since the centre of mass of the actuator lies in a vertical plane containing the line A the device is mass balanced against vertical acceleration.

The two-axis devices of Figures 6-17 are vertically and horizontally mass balanced about both the X and Y-axes.

Figures 19-21 give examples of strain gauge force sensor arrangement which may be employed in any of the control devices described above with reference to Figures 1-18.

Strain gauges Al, A2 are fixed to the drive link 5 (for instance by an adhesive) and sense tensile and compressive forces in the link 5. The strain gauges Al, A2 are connected to strain gauges A3, A4 in a Wheatstone bridge as shown in Figure 21. The gauges A3 and A4 are not attached to the link 5 so that they are insensitive to the force in the link 5. An alternative arrangement for sensing compression and tension forces acting on the drive link 5 could be a load cell attached in line with link 5 or fastened at its mounting.

Figure 19 also gives an example of a strain gauge sensor arrangement which may be employed to sense torque in the actuator output shaft 2 of any of the control devices described above with reference to Figures 1-17. The torque sensor comprises four strain gauges 2a connected to a Wheatstone bridge in a manner that optimises the sensitivity of the output to torque. The construction of such a torque sensor is well know to someone skilled in the art so will not be described in further detail.

An advantage of using sensors on or close to the drive link 5 is that the sensor wires are more easy to route via the mounting plate 6a, since the drive link 5 is pivotally coupled to the mounting plate 6a.

The forces acting on the device of Figure 1 will now be considered with reference to Figure 25 in order to demonstrate that the force sensor in the drive link is substantially insensitive to g induced moments about the pivot axis caused by acceleration of the device. Taking moments about the (frictionless) pivot gives:

I₁ItI^g = 1₂m₂g + l₃f₃ Equation (4) where:

// is the distance between the pivot axis X and the centre of mass of the stick;

mi is the mass of the stick (including the shaft 3 and the handle 4);

h is the distance between the pivot axis X and the combined centre of mass of the actuator and force sensor;

/n? is the combined mass of the actuator and force sensor; and

fi is the force in the drive link that is mounted by frictionless pivots at each end.

If the system is mass balanced then, if there are no external forces applied to mi or wz₂, l,m,g = l₂m₂g so that if all elements are rigid then/₃ = 0, regardless of the amplitude of the local acceleration g.

Now if the beam 3 is flexible, under accelerations g it will be loaded at both ends and will bend and deflect say δ_\ and ^₃ at distances l_\ and /₃ respectively from the pivot. Under these conditions we need to consider the loads on the drive link.

First of all it can be noted that with no link in place and perfect mass balance the arm can be rotated to any angle and will still be balanced.

Secondly if the device is mass balanced using l_λm_λg = l₂m₂g , then in the absence of the drive link, bending of the beam 3 due to a g acceleration could lead to a very small deflection of m_\ and m₂ towards the pivot due to the bending of the beam. This effect may lead to an extremely small out of balance moment. However, if we ignore this then analysis of the balance of forces applied to the beam will show that the drive link forced must be zero for all beam positions and orientations of acceleration.

If/₃ is zero then there can be no deflection at the link mounting point as the link itself will not be compressed or stretched. Therefore the force sensor is substantially insensitive to g induced moments about the pivot axis caused by acceleration of the device. The same analysis applies if a torque sensor is used to measure torque in the actuator output shaft. However, the deflection of the beam 3 between the pivot and the link must still be <5₃ since this the elastic forces generated by this bending is required to generate the bending moment in the beam at the pivot that counteracts the moment from m_\.

Therefore as a result beam 3 rotates freely around the pivot sufficient to counteract the bending at the link position. As a result the deflection of mi is increased to approximately

' 2

The devices shown in the figures may be used on a vehicle such as a helicopter. For instance the one-axis devices shown in Figures 1-5 and 18 may be used as the collective lever of a helicopter. Alternatively the devices may be used in a simulator.

In the case of a vehicle such as a helicopter, then the force sensor(s) may supply flight control signals to a helicopter rotor blade motor control unit, or similar. The output of the force sensor(s) may also be directed to the relevant actuator which provides a feedback force to the stick in accordance with the output of the force sensor. In the case of a simulator, then the force sensor(s) may supply control signals to a control unit of the simulator.

Although the invention has been described above with reference to one or more preferred embodiments, it will be appreciated that various changes or modifications may be made without departing from the scope of the invention as defined in the appended claims.

Claims

1. A control device comprising: a reference frame; a stick; a pivot mounting the stick to the reference frame and defining a pivot axis; an actuator for rotating the stick about the pivot axis, wherein the actuator and the stick are offset from the pivot axis such that if the control device is subjected to an acceleration orthogonal to the pivot axis, then the mass of the actuator and the mass of the stick generate moments about the pivot axis which act in opposite directions; and a sensor for sensing a force applied to the stick, wherein the sensor is arranged so as to be substantially insensitive to g induced moments about the pivot axis caused by acceleration of the device.

2. The device of claim 1 wherein the actuator is a rotary actuator having a stator coupled to the stick and a rotor coupled to the reference frame by a drive link and configured to rotate relative to the stator about a drive axis which is not co-linear with the pivot axis.

3. A control device comprising: a reference frame; a stick; a pivot mounting the stick to the reference frame and defining a pivot axis; a rotary actuator having a stator coupled to the stick and a rotor coupled to the reference frame by a drive link and configured to rotate relative to the stator about a drive axis which is not co-linear with the pivot axis; and a sensor for sensing a force applied to the stick, wherein the sensor is arranged so as to be substantially insensitive to g induced moments about the pivot axis caused by acceleration of the device.

4. The device of claim 2 or 3 wherein the sensor is fixed to the drive link.

5. The device of claim 2, 3 or 4 wherein the sensor is arranged to sense tensile or compressive forces acting along a length of the drive link.

6. The device of claim 2 or 3 wherein the sensor is fixed to the rotor or stator of the actuator.

7. The device of claim 2, 3 or 6 wherein the sensor is a torque sensor.

8. The device of any of claims 2 to 7 wherein the drive link is pivotally coupled to the rotor by a first drive pivot and to the reference frame by a second drive pivot.

9. The device of any of claims 2 to 8 wherein the drive axis is not parallel with the pivot axis.

10. The device of any of claims 2 to 9 wherein the drive axis substantially intersects with the pivot axis.

11. The device of any of claims 2 to 10 wherein the drive axis is substantially parallel with the pivot axis.

12. The device of any of claims 2 to 11 wherein the drive axis is substantially co-linear with a line passing through the pivot axis and the centre of mass of the stick.

13. The device of any preceding claim wherein the device is substantially mass balanced about the pivot axis such that if the control device is subjected to an acceleration orthogonal to the pivot axis, then the mass of the actuator and the mass of the stick generate moments about the pivot axis which act in opposite directions and are substantially equal.

14. The device of any preceding claim further comprising a second pivot mounting the reference frame to a second reference frame and defining a second pivot axis; and an actuator for rotating the reference frame about the second pivot axis.

15. The device of any preceding claim, wherein a line passing through the pivot axis and the centre of mass of the stick passes substantially through the centre of mass of the actuator.

16. The device of any preceding claim, wherein the sensor is arranged to detect the output of the actuator whereby the sensor is substantially insensitive to g induced moments about the pivot axis caused by acceleration of the device.

17. A control device comprising: a reference frame; a stick; a pivot mounting the stick to the reference frame and defining a pivot axis; and an actuator for rotating the stick about the pivot axis, wherein the actuator and the stick are offset from the pivot axis such that if the control device is subjected to an acceleration orthogonal to the pivot axis, then the mass of the actuator and the mass of the stick generate moments about the pivot axis which act in opposite directions.

18. The control device of claim 17, wherein a line passing through the pivot axis and the centre of mass of the stick passes substantially through the centre of mass of the actuator.

19. The device of claim 17 wherein the actuator is a rotary actuator having a stator coupled to the stick and a rotor coupled to the reference frame by a drive link and configured to rotate relative to the stator about a drive axis which is not co-linear with the pivot axis.

20. A control device comprising: a reference frame; a stick; a pivot mounting the stick to the reference frame and defining a pivot axis; and a rotary actuator having a stator coupled to the stick and a rotor coupled to the reference frame by a drive link and configured to rotate relative to the stator about a drive axis which is not co- linear with the pivot axis.

21. The device of claim 20 wherein the drive link is pivotally coupled to the rotor by a first drive pivot and to the reference frame by a second drive pivot.

22. The device of claim 20 wherein the drive axis is not parallel with the pivot axis.

23. The device of claim 20 wherein the drive axis substantially intersects with the pivot axis.

24. The device of claim 20 wherein the drive axis is substantially parallel with the pivot axis.

25. The device of claims 20 wherein the drive axis is substantially co-linear with a line passing through the pivot axis and the centre of mass of the stick

26. The device of claim 17 wherein the device is substantially mass balanced about the pivot axis such that if the control device is subjected to an acceleration orthogonal to the pivot axis, then the mass of the actuator and the mass of the stick generate moments about the pivot axis which act in opposite directions and are substantially equal.

27. The device of claim 17 further comprising a sensor for sensing a force applied to the stick, wherein the sensor is arranged to detect the output of the actuator whereby the sensor is substantially insensitive to g induced moments about the pivot axis caused by acceleration of the device.

28. The device of claim 17 further comprising a sensor for sensing a force applied to the stick.

29. The device of claim 20 wherein the sensor is arranged to detect the output of the actuator whereby the sensor is substantially insensitive to g induced moments about the pivot axis caused by acceleration of the device.

30. The device of claim 28 wherein the sensor is fixed to the drive link.

31. The device of claim 28 wherein the sensor is arranged to sense tensile or compressive forces acting along a length of the drive link.

32. The device of claim 28 wherein the sensor is fixed to the rotor or stator of the actuator.

33. The device of claim 28 wherein the sensor is a torque sensor.

34. The device of claim 17 further comprising a second pivot mounting the reference frame to a second reference frame and defining a second pivot axis; and an actuator for rotating the reference frame about the second pivot axis.

35. The device of claim 20 further comprising a second pivot mounting the reference frame to a second reference frame and defining a second pivot axis; and an actuator for rotating the reference frame about the second pivot axis.

36. An active user interface assembly, comprising: a housing; a user interface coupled to and extending from the housing, the user interface rotatable, from a null position, about an axis; and a feedback motor coupled to the user interface and adapted to be selectively energized, the feedback motor operable, upon being energized, to supply a feedback force to the user interface that opposes user interface movement about the axis, the feedback motor disposed such that its center of gravity is located at a position relative to the user interface to mass balance the user interface when it is in the null position.

37. An active user interface assembly, comprising: a housing; a user interface coupled to and extending from the housing, the user interface rotatable, from a null position, about a first axis and a second axis, the first and second axes being perpendicular; a first feedback motor coupled to the user interface and disposed such that its center of gravity is located at a first position relative to the user interface, the first feedback motor adapted to be selectively energized and operable, upon being energized, to supply a feedback force to the user interface that opposes user interface movement about the first axis; a second feedback motor coupled to the user interface and disposed such that its center of gravity is located at a second position relative to the user interface, the second feedback motor adapted to be selectively energized and operable, upon being energized, to supply a feedback force to the user interface that opposes user interface movement about the second axis, wherein at least one of the first position and the second position are selected to mass balance the user interface when it is in the null position.