GB2056063A

GB2056063A - Stabilized platforms

Info

Publication number: GB2056063A
Application number: GB8021401A
Authority: GB
Original assignee: UK Secretary of State for Defence
Current assignee: UK Secretary of State for Defence
Priority date: 1979-07-03
Filing date: 1980-06-30
Publication date: 1981-03-11

Abstract

The invention comprises a stable platform mounted on an orthogonal gimbal system (12) having a roll gimbal (14) and a pitch gimbal, there being a counter weight (15) suspended from the gimbal system (12) to accurately balance the total load carried by the system about both the roll and pitch gimbals. The pitch gimbal is mounted on the roll gimbal (14) and carries both the load (11) and the counter weight (15). The platform and load (11) remain, ideally, in the horizontal plane eliminating the need to accelerate the inertia of the system. A servo system torque is provided by motors (16) and tachometer-synchro assemblies (17) to maintain a vertical reference by overcoming gimbal bearing friction. <IMAGE>

Description

SPECIFICATION Improvements in or relating to stable platforms This invention relates to stable platforms and in particular but not exclusively to stable platforms for use on or in vehicles subject to random and irregular motion.

More specifically the stable platform of the invention has particular advantage in shipborne applications. Such an application is the provision of a stable platform for the mounting of projector systems utilised in aircraft visual approach indicators.

One specific application is in the provision of a visual reference during the landing phase for shipborne V/STOL aircraft such as the Hawker Harrier. Three platforms each supporting a projector system are provided on each ship to provide a stabilised visual reference in space so that the landing pilot can at a glance determine his position with respect to the ship during his approach. Safe angles of approach are low and the pilot requires an accurate spacial reference calling for an accurate stable platform.

According to the present invention a stable platform for stabilising a load comprises an orthogonal gimbal system having a roll gimbal and a pitch gimbal arranged to support the load to be stabilised, and a counter balance weight suspended from the gimbal system to accurately balance the total load carried by the system about both the roll and pitch gimbals.

Preferably the stable platform is totally enclosed to eliminate wind and other external effects.

Each gimbal axis is advantageously actuated by direct drive components mounted on the axis and operative in response to a servo system to reset the gimbals to a vertical reference. The servo system includes a tachometer and synchro mounted on each gimbal axis to sense departures of the gimbals from the vertical refernnce.

In a preferred embodiment the roll gimbal of the gimballed system is mounted on an A-frame with the pitch gimbal mounted on the roll gimbal.

The load to be stabilised and the counterbalance weight is carried by the inner pitch gimbal.

Additional and adjustable balance weights for accurate trimming of the balance of the system might conveniently be provided in the plane of each gimbal, offset from its axis centre line.

An embodiment of the invention will now be described by way of example only with reference to the accompanying schematic drawing.

The drawing shows, very schematically, the stable platform of the invention as mounted on a ship and applied in a stabilised visual landing aid system for V/STOL aircraft such as the Hawker Harrier.

The stable platform is housed within an enclosing case 10 which is secured to the deck or structure of the ship (not shown). The load to be stabilised, in this instance the optical system 11, is mounted on an orthogonal gimbal system 12 such that the optical output is always visible through a window 1 3 in the case 10 irrespective of the motion of the ship.

The gimbal system 1 2 comprises an outer roll gimbal 1 4 in the conventional form of an open square frame with an inner pitch gimbal (not shown) conventionally mounted therein such that the gimbal axes are at right angles to each other.

The outer roll gimbal 14 is supported in A-frames (not shown) which are secured to the base of the case 10. A counterbalance weight 1 5 detends from the inner pitch gimbal, the magnitude of the counterbalance weight 1 5 being such as to accurately balance the mass carried by the gimbal system 12 about both the roll and pitch gimbals.

Each gimbal axis is provided with a direct drive motor 16 at one end and a tachometer and synchro assembly 1 7 at the other end. The drive motor 1 6 and the tachometer and synchro assembly 17 are part of a servo system operative to maintain the gimbal system 12 in a vertical reference position as will be described later. The circuitry for the servo system is housed at the base of the case 10 at 18.

The stable platform of the invention is completely self-contained other than for an external power source, requiring only to be secured in position on the ship structure.

The design of the stable platform of the invention is such that on the ship the balanced mass, i.e. the optical system 11 and associated structure being supported on the gimbal system 12, actually remains still and it is the ship which may pitch and roll below the platform. The inertia of the optical system 11 therefore never has to be accelerated, the system 11 ideally always remaining in the horizontal plane. The torque required from the drive motors 1 6 needs only to be sufficient to overcome the gimbal friction which is very small.Since the drive motors 1 6 are directly coupled to the gimbals the drive system is stiff and the servo system 17, 18 which resets the gimbals to a vertical reference can thus be of high gain, i.e. high torque with low misalignment. The torque requirement is proportional to the misalignment and as the torque requirement is very low the platform misalignment to the horizontal reference is also very low. In ship trials the stable platform described was used in assisting the landing of the Hawker Harrier and misalignments of only 30 arc seconds were achieved.

The success of the stable platform is made possible largely by the efficient balancing of the mass involved. It has been found useful to include additional trimming weights (not shown) which are located on or adjacent to the sides of the gimbal frames parallel to the gimbal axis, i.e. in the plane of the gimbal frame but offset from its axis.

Sensitivity of trimming can be enhanced by making the trimming weights movable relative to the gimbal axis such as for example by screw means.

The stable platform of the invention is not to be limited by the above described embodiment, the principle of the counterbalance weight being applicable to stable platforms for use in any vehicle generated motion mode.

Claims

1. A stable platform for stabilising a load comprising an orthogonal gimbal system having a roll gimbal and a pitch gimbal arranged to support the load to be stabilised, and a counterbalance weight suspended from the gimbal system to accurately balance the total load carried by the system about both the roll and pitch gimbals.

2. A stable platform as claimed in claim 1 in which each gimbal axis is actuated by direct drive components mounted on the axis and operative in response to a servo system to maintain the gimbals in a vertical reference condition.

3. A stable platform as claimed in claim 2 in which the servo system includes a tachometer and synchro mounted on each gimbal axis to sense departures of the gimbals from the vertical reference.

4. A stable platform as claimed in claim 1.2 or 3 in which the pitch gimbal is mounted on the roll gimbal and the load to be stabilised and the counterbalance weight is carried by the inner pitch gimbal.

5. A stable platform as claimed in any one of any of the preceding claims in which additional balance weights are provided in the plane of each gimbal offset from its axis centre line, the balance weights being adjustable for accurate trimming of the balance of the system.

6. A stable platform as claimed in any one of the preceding claims in which the roll gimbal of the gimballed system is mounted on an A-frame support.

7. A stable platform as claimed in any one of the preceding claims in which the platform is totally enclosed to eliminate wind and other external effects.

8. A stable platform for stabilising a load substantially as hereinbefore described with reference to the accompanying drawing.