GB2253722A - Stabilising arrangement - Google Patents

Abstract

In a stabilising arrangement for stabilising a load 1, a supporting structure 2 and 3 is connected to the load 1 via flexural pivots 4 and 5. The displacement undergone by the flexural pivots 4 and 5 gives an indication of applied torque. By monitoring the displacement, the amount of torque applied may be determined before its effects are apparent, and compensating forces applied to decouple the torque and provide stabilisation. <IMAGE>

Description

STABILISATION ARRANGEMENT This invention relates to stabilisation arrangements and is more particularly, but not exclusively, concerned with arrangements for stabilising loads having small inertia.

Stabilisation of a load, such as an antenna reflector for example, is required when a supporting structure of the load is liable to move relative to some reference plane and it is wished to ensure that the load remains substantially stationary in space, for example, so that the pointing direction of a reflector sightline is maintained.

One way in which stabilisation is presently achieved is to combine two techniques, the technique applied depending on the timescale over which supporting structure of the loads is subject to disturbing torques. For forces which are exerted for a relatively short time, the inertia of the load is relied on to keep it substantially fixed in space. This requires that bearings between relatively moving parts of the stabilising structure are of very low friction to permit free movement. For forces which are applied over a greater timescale, the load cannot be stabilised by relying on its inertia alone. Therefore gyros are employed to detect movement of the load, being attached to move with it. The output of the gyros is used to control motors which move the supporting structure to oppose the motion caused by the applied forces.This method of stabilisation is satisfactory in many applications but problems may arise when inertia of the load is minimised. Also, even though very low bearing friction may be achieved, performance tends to be degraded when a large number of cables and compressed air services, for example, need to be carried across joints.

The present invention arose in an attempt to provide an improved stabilisation arrangement.

According to the invention there is provided a stabilising arrangement for stabilising a load comprising means for monitoring torque applied to a supporting structure of the load as the torque is applied, and means for using the monitored torque in compensating for its effects. In an arrangement in accordance with the invention, the torque is detected before it has any effect on the load. This enables the supporting structure to be moved in opposition to motion caused by the torque as the effects of the torque occur. In a conventional arrangement, the use of a feedback method using the detected motion of the load inevitably introduces delays in correction. In contrast to this, by employing-the invention, compensation can be applied simultaneously with movement caused by the applied torque such that there is substantially no movement of the load in space.The invention is particularly suitable for use with loads having small inertia. The torque may be applied between relatively moveable parts of the support structure, or between the load and the support structure.

It is preferred that a spring connection is included between relatively moveable parts of the arrangement. The use of such a connection, rather than a conventional frictional bearing, is highly advantageous because displacement of the spring connection may be made substantially linear with respect to the force applied, unlike frictional bearings which generally exhibit complex behaviour. This greatly facilitates the monitoring of the magnitude of the applied torque and thus enables almost exact compensation to be made. It is preferred that the spring connection is a flexural pivot. A particularly convenient way in which the load may be connected to its support structure is via two flexural pivots, arranged one on each side of the load along an axis through it about which relative movement may occur.Where the supporting structure of the load is capable of movement about a plurality of axes, movement about each axis may be provided by a flexural pivot. It is also preferred that means are included for monitoring displacement between relatively moveable parts whereby the applied torque is determined. Advantageously also, a cable along which signals or power is transmitted from one part of the arrangement to another relatively moveable part is arranged to act as a spring connection between the two parts. If most connections such as, say, cooling pipes or electric cables, are designed to act as spring connections, it is possible that any applied torque may be decoupled before any of its effects become apparent.

It may be advantageous to include a gyro arranged for movement with the load and means for using the output of the gyro to provide stabilisation. This enables variation in spring torques from cables and pipes and also uncompensated torque to be removed by the gyro feedback loop in the conventional manner, except that in this case the remaining torque effects are smaller than those in a conventional arrangement. It may prove possible in some low accuracy systems to dispense with the use of a gyro altogether.

According to a feature of this invention, a thermal imager sensor system includes a telescope which is arranged to be supported by a stabilising arrangement in accordance with the invention. In such a system, it is desirable to have a high degree of stabilisation but the load is generally of low inertia and thus conventional compensating techniques tend not to be entirely satisfactory. Other systems to which a stabilising arrangement in accordance with the invention may advantageously be applied include pointing and acquisition systems in which laser communication apparatus is the load which must be stabilised to maintain a lasersatellite link, or for applications in which mirrors must be stabilised.

One way in which the invention may be performed is now described by way of example with reference to the accompanying drawings, in which: Figures 1 and 2 are schematic diagrams of a stabilising arrangement in accordance with the invention, Figure 1 being a side view of the Figure 2 arangement; and Figures 3 and 4 schematically show a flexural pivot used in the arrangement of Figure 1.

With reference to Figures 1 and 2, a stabilising arrangement in accordance with the invention includes a load 1, which may be, for example, a high magnification telescope of a thermal imager sensor system, which it is wished to maintain in a substantially fixed position in space. The load 1 is carried by a support structure, which in this case is a 2-axis stabilised platform comprising an inner frame 2 and an outer frame 3. The load 1 is supported by the inner frame 2 via two flexural pivots 4 which are arranoed along an axis X-X about which the inner frame 2 is movable relative to the load 1. The inner frame 2 is itself supported by the outer frame 3, also via two flexural pivots 5 arranged along the second axis of movement Y-Y. Motors 6 and 7 are arranged to cause movement of the support structure about the X-X and Y-Y axes respectively on receipt of suitable control signals from a control circuit 8. Angle transducers 9 and 10 are located adjacent a flexural pivot on axes X-X and Y-Y respectively to monitor displacement about that axis.

When the support structure is subject to forces which cause it to move about its axes X-X and Y-Y, torque is applied to the flexural pivots 4 and 5. The flexural pivots 4 and-5-are displaced through angles which are dependent on the magnitude and direction of the applied torque. Thus the angle transducer 9 effectively measures the torque applied about the X-X axis before its effects on the load 1 are apparent. The outputs of the angle transducers 9 and 10 are applied to the control circuit 8, where they are converted into a suitable form for controlling movement of the motors 6 and 7 to oppose movement imposed by applied torques. The load 1 also carries a gyro 11 which monitors any movement of the load 1 which may occur and provides feedback to the control circuit 8 to enable this movement also to be compensated for.

One of the flexural pivots 4 and 5 is shown in greater detail in Figures 3 and 4. The two relatively moveable parts 12 and 13 are generally cylindrical in shape with the part 12 having a region of reduced diameter which is located within the cylinder 13. It is connected to the cylinder 13 by spring connections 14 and 15 which are arranged substantially normal to one another. Such a flexural pivot undergoes an angular displacement which is linearly dependent on the magnitude of the applied torque.

In this embodiment of the invention it is necessary to provide cooling to the load 1 using cooling pipes 16 between the support structure and the load 1. Also power cables 17 connect the relatively moveable load 1 and outer frame 3. The pipes 16 and cables 17 are designed to act as springs so that torque coupled through them may be compensated for by monitoring their displacement.

Claims (8)

1. A stabilising arrangement for stabilising a load comprising means for monitoring torque applied to a supporting structure of the load as the torque is applied, and means for using the monitored torque in compensating for its effects.

2. A stabilising arrangement as claimed in claim 1 and including a spring connection between relatively moveable parts of the arrangement.

3. A stabilising arrangement as claimed in claim 2 wherein the connection is a flexural pivot.

4. A stabilising arrangement as claimed in claim 2 or 3 and including means for monitoring displacement between the relatively moveable parts to determine the applied torque.

5. A stabilising arrangement as claimed in any preceding claim wherein a cable along which signals or power is transmitted from one part of the arrangement to another relatively moveable part is arranged to act as a spring connection between the two parts.

6. A stabilising arrangement as claimed in any preceding claim and including a gyro arranged for movement with the load and means for using the output of the gyro to provide stabilisation.

7. A thermal image sensor system including a telescope supported by a stabilising arrangement as claimed in any preceding claim.

8. A stabilising arrangement substantially as illustrated in and described with reference to the accompanying drawings.

8. A stabilising arrangement substantially as illustrated in and described with reference to the accompanying drawings.

Amendments to the claims have been filed as follows

1. A Stabilising arrangement for stabilising a load comprising: a supporting structure on which the load is mounted such that it is moveable relative to the structure about at least one axis; means for monitoring torque about the axis applied to the load during its application; and means for using the monitored torque to control relative movement between the load and the supporting structure to oppose the effects of the applied torque during its application so as to substantially stabilise the load in space about the axis.

2. A stabilising arrangement as claimed in claim 1 and including a spring connection between relatively moveable parts of the arrangement.

3. A stabilising arrangement as claimed in claim 2 wherein tile connection is a flexural pivot.

4. A stabilising arrangement as claimed in claim 2 or i and including means for monitoring displ acemeri t betwce the relatively moveable parts to determine the applied torque.

5. A stabilising arrangement as claimed in any preceding claim wherein a cable along which signals or power is transmitted from one part of the arrangement to arlotller relatively moveable part is arranged to act as a spring connection between the two parts 6. A stabilising arrangement as claimed in any preceding claim and including a gyro arranged for movement with the load and means for using the output of the gyro to provide stabilisation.

7. A thermal image sensor system including a telescope supported by a stabilising arrangement as claimed in any preceding claim.