GB2483443A

GB2483443A - An oscillation damping system

Info

Publication number: GB2483443A
Application number: GB1014810.4A
Authority: GB
Inventors: Vince Herbert
Original assignee: ROYAL SHAKESPEARE Co
Current assignee: ROYAL SHAKESPEARE Co
Priority date: 2010-09-07
Filing date: 2010-09-07
Publication date: 2012-03-14
Also published as: GB201014810D0; WO2012032321A1

Abstract

A damping system for damping oscillation of a moving structure comprises: a rotatable mass 12; a motor 16 arranged to drive the rotatable mass 12; a movable mass 38; and a motor 32 arranged to drive the movable mass so as to move its centre of gravity. A sensing means 22, 38 is arranged to detect movement of the structure and a control means 20 is arranged to control the motors in response to detected movement of the structure, thereby damping the oscillation of the structure.

Description

OSCILLATION DAMPER

The present invention relates to a device for damping movement, and in particular for damping oscillation of a suspended or mounted device such as stage lighting units, image projectors, cameras or scenery.

The entertainment industry has used moving lights for many years. These lights can be remotely focussed, panned or moved sideways, tilted or moved up or down and coloured without the need for operator access via ladders or other means. The design of some video projectors incorporates remote controlled panning, tilting and focusing capabilities giving them the means of projecting an image onto many different screens or surfaces.

Remotely controlled video and film cameras are also widely used. In theatres, television studios, arenas or other similar venues, lighting units are currently hung or supported on wall or ceiling mounted rigs, floor supported truss systems, hanging truss systems, counterweighted bars or substantial floor stands. Panning or tilting a moving light, projector or camera generates rotational torque in an unsecured frame or flying structure, which can cause oscillation and render a unit unusable for several minutes. In certain eases, scenery is suspended above a stage area out of sight of the audience and when required, is lowered into view. This action can sometimes generate a rotational movement in that piece of scenery. Current mountings therefore need to be of a sufficient mass or have a strong enough anchorage so as not to be affected by the rotational torque transmitted to the structure when panning or tilting a moving light, projector or camera or when moving scenery.

The present invention has useful applications in broadcast and film, performing arts, corporate events, night entertainment, concerts and touring venues, amusement attractions and sporting events, as well as stabilizing technology in boats, on loads carried by cranes, on loads suspended from a winch, on loads suspended from helicoplers in rescue or similar scenarios or on motor vehicles that experience unwanted sideways rocking motions.

W02009/01072? discloses an oscillation damping device arranged to damp oscillations using a rotating mass.

The present invention provides a damping system for damping oscillation of a moving structure, the system comprising a rotatable mass, a motor arranged to drive the rotatable mass, a movable mass, a motor arranged to drive the rotatable mass, sensing means arranged to detect movement of the structure and control means arranged to control the motors in response to detected movement of the structure thereby to damp oscillation of the structure.

The rotatable mass may comprise a flywheel, which may comprise balanced, connected weights able to rotate about a central point or the rotor section of a motor that is able to spin about a centre point.

The movable mass may be arranged to move linearly. The linear movement may be in an arc, for example if the movable mass is mounted on a rotatable support, or it may be in a straight line.

Each motor may be of any form suitable for producing the required movement. For example it may be an electric motor, or it may be a hydraulic motor.

The sensing means may be arranged to produce one output indicative of rotational movement of the structure and one output indicative of linear movement of the structure. The sensing means may comprise separate sensors, such as accelerometers, for sensing rotational movement and linear movement respectively. In some cases the sensing means can comprise a plurality of sensors and processing means, which may form part of the control means, arranged to determine the linear and rotational movements from the outputs from the sensors.

The control means may be arranged to receive the output from the sensing means and to measure rotational movement of the structure and linear movement of the structure from the output.

The control means may be arranged to detect linear oscillation of the structure and in response to control movement of the movable mass to reduce the linear oscillation until it reaches a threshold, and when it determines that the threshold has been reached, to control movement of the rotatable mass to reduce rotational oscillation of the structure. The control means may be arranged, when said threshold has been reached, to stop movement of the movable mass and to start movement of the

rotatable mass.

The damping system may further comprise a further movable mass, the two movable masses being movable in different directions from each other. The different directions may be orthogonal to each other. The control means may be arranged to move the two movable masses simultaneously thereby to damp components of oscillation in each of said different directions simultaneously.

The present invention further provides a lighting system including a light and a damping system according to the invention wherein the light is the moving structure.

The present invention further provides a method of damping movement of an oscillating structure comprising monitoring linear movement of the structure, monitoring rotational movement of the structure, using a first motor to drive a movable mass and controlling the direction and speed of the motor in response to the linear movement of the structure to reduce the linear movement, using a second motor to drive a rotatable mass, and controlling the direction and speed of the further motor in response to the rotational movement to reduce the rotational movement. The first motor may be controlled so that movement of the movable mass converts the linear movement into rotational movement. The linear movement may be reduced and then subsequently the rotational movement may be reduced.

Preferably, the sensing means is arranged to continuously monitor the position and orientation of the structure and to send a signal to the control means indicative of any change in position or orientation of the structure.

The sensing means may be arranged to detect rotational or linear oscillating motion of the structure. The control means may be arranged to accelerate and decelerate the flywheel or the movable mass in response to such motion. The linear motion may be motion in an arc or movement in a straight line.

The acceleration and deceleration of the flywheel or the movable mass may be timed with respect to the sensed oscillation. The control means may comprise a logic control system storing a control programme and a motor amplifier arranged to control the direction and speed of at least one of the motors. The control means may alternatively directly control the direction and speed of at least one of the motors in proportion to the output of the sensing device.

The rotatable mass may be arranged to be accelerated to move in the same direction as the moving structure when rotational movement of the structure is first detected. The rotatable mass may also be arranged to be decelerated on detection of a change in direction of movement of the structure. Preferably, the velocity of the rotatable mass is arranged to be at a minimum when the displacement of the structure is at or near minimum.

Preferably, the sensing means includes any one of an angular rate sensor, accelerometer, gyroscope, solid state gyroscope or any other suitable sensing means.

The device may further comprise a power supply arranged to power the device and arranged to convert a supplied voltage, for example mains voltage, to a usable DC voltage.

The motor may be mounted on one side of a chassis and may be on the central axis of the rotatable mass or at an angle to the rotatable mass. The motor may be connected to the rotatable mass by a drive shaft or drive-belt or gears or a rotating component of the motor may itself be of sufficient mass to constitute at least a part of the rotatable mass. The motor may be of such a design as to limit or eliminate any noise generated by its movement. The power supply, control means and sensing means may also be supported on the chassis.

Preferably, the device is contained within a housing, which is arranged to be attached to the hanging structure. For example, the housing may be clamped to a hanging bar, bolted to a structure or mounted in any other suitable way as to efficiently transmit the movement generated by the acceleration and deceleration of the rotatable mass to the hanging structure. The hanging structure may be a suspended frame or bar, a theatre truss, a television pantograph, or a platform arranged to support a moving light, projector or camera for example, or may be hanging scenery. The hanging structure may be suspended on a plurality of support lines and the housing, and therefore the flywheel, may be placed within a volume at least partially defined by the plurality of support lines.

The device may if necessary, be attached with the rotatable mass in vertical plane, rotating about a horizontal axis to the hanging structure to dampen forward and backward or nodding motion of the suspended structure.

The device may comprise a plurality of rotatable masses. Each rotatable mass may be driven by a respective motor, each able to rotate independently of each other. Alternatively, a single motor may drive a plurality of rotatable masses.

According to a second aspect of the invention, there is provided a method of damping an oscillating structure comprising monitoring movement of the structure, using a motor to drive a movable mass to convert linear movement of the structure to rotational movement, and using a motor to drive a rotatable mass to damp the rotational movement. The method may comprise controlling the direction and speed of the motor in response to the movement of the structure.

Preferably, the method comprises using control means to control an appropriate acceleration and deceleration of the movable mass in response to linear movement of the structure. The method may comprise using control means to control an appropriate acceleration and deceleration of the rotatable mass in response to rotational movement of the structure.

Preferred embodiments of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a schematic illustration of a moving light supported on a hanging structure; Figure 2 is a schematic representation of a rotary damping system forming part of an embodiment of the present invention; Figure 3 is a schematic illustration of a linear damping system forming part of an embodiment of the invention; Figure 4 is a schematic illustration of a damping system according to an embodiment of the invention including the damping systems of Figures 2 and 3; Figure 5 is a schematic illustration of the damping system of Figure 4 attached to a support bar; Figure 6 is a graph of a sine wave illustrating the simple harmonic motion of the hanging structure; Figure 7 is a schematic illustration of a damping system comprising a plurality of damping units attached to a support bar; Figure 8 is a schematic illustration of a damping system forming part of a further embodiment of the invention and comprising a plurality of flywheels; Figure 9 is a schematic illustration of a damping system of Figure 4 incorporated into the construction of a moving light unit; and Figure 10 is a schematic illustration of a damping system mounted in the vertical plane to eliminate nodding oscillation and sway.

Referring to Figure 1, a moving light 2 is mounted by support brackets 4 on a hanging support frame 6. The hanging frame 6 is suspended by four hanging lines 8, each attached to a respective corner of the hanging structure 6. In use, motors drive movement of the tight 2 and are controlled remotely by an operator. The light can be controlled to pan or tilt and as it moves, approximately linear horizontal forces and rotational torque are applied to the hanging frame 6. The acceleration and deceleration of the moving light 2 induces an unwanted rotational oscillating motion of the hanging frame 6 about the centre of the area defined by the four hanging lines 8, and unwanted sway in the horizontal direction. The swaying and rotational oscillating motions are harmonic motions and may each be approximated to simple harmonic motion. The amplitude of these oscillations gradually decreases over time. For example, a hanging structure weighing approximately 100kg supported on hanging lines of around iSm would swing with harmonic motion with a duty cycle time period of approximately is. Under these conditions the oscillations would typically continue for over 8 minutes before naturally coming to a stop, rendering the light unusable for this period.

Referring to Figures 2 and 3, a damping system 10 is arranged to be clamped or attached to the hanging structure 6 and comprises a rotary damping system and a linear damping system. The rotary damping system comprises a flywheel or rotatable mass 12 mounted onto a shaft 18. The shaft 18 extends through the centre of the flywheel 12 and is arranged to rotate about its central axis. A motor 16 controls rotation of the flywheel 12 by driving the shaft 18. The motor 16 is mounted on one side of a chassis 14 and the shaft 18 extends through the chassis 14 to the flywheel on the opposite side of the chassis. Also mounted to the chassis is a power supply 24 that converts mains voltage to a suitable DC voltage to power the system. The power supply 24 is connected to an electronic control system 20 arranged to control the speed and direction of the motor 16 by varying the voltage or current and polarity of the voltage supplied to the motor in magnitude, frequency or polarity. A motion sensor 22 is also mounted to the chassis 14 and is connected to the electronics unit 20.

The motion sensor 22 continuously monitors its own position and therefore detects any oscillatory movement of the hanging structure 6. In one embodiment of the invention the motion sensor 22 is an angular rate sensor, although it will be appreciated that an accelerometer, gyroscope, solid state gyroscope or any other suitable measuring means may be used.

When motion of the hanging frame 6 is detected, the motion sensor sends a signal to the logic control system and motor amplifier 20, which drives the motor 16 in response to this signal.

Referring to Figure 3, the linear damping system comprises a support beam 30 with two motors 32 mounted on it, each arranged to drive a coupling arm 34 so that it rotates about the rotary axis of the motor 32. A beam mass 36 has each of its ends coupled to one of the coupling arms 34 so that it extends parallel to the support beam and can be moved linearly by rotation of the coupling arm. Because the coupling arms 34 each rotate it will be appreciated that the beam mass 36 will move in an arc, so that its motion includes a component perpendicular to its length as well as the main component along its length. However, as will be appreciated from the following description, only the component of motion in the direction parallel to the length of the beam mass (or more exactly tangential to the arc along which the structure will swing) is effective in damping, and linear actuators acting in that direction can be used as an alternative.

A linear motion sensor 38 is mounted on the support beam 30 and arranged to detect acceleration in the direction parallel to the length of the support beam. In this embodiment the motion sensor 38 comprises two linear accelerometers spaced apart in the direction perpendicular to the direction in which they sense motion. This enables the motion sensor 38 to detect rotational movement as well as linear movement, and isolate the pure linear movement. It will be appreciated that the linear motion sensor could be used to measure both rotary and linear motion for controlling both the linear and rotary damping systems, rather than having a separate sensor for each system.

Referring to Figure 4, when the system is installed in a lighting system similar to that of Figure 1, the rotatable mass 12 is mounted on the support frame 6 SO that it can rotate about a vertical axis, and the beam mass 36 is mounted so that it can move horizontally. The motion sensor 22 is arranged to sense rotation of the support frame 6 in the horizontal plane, i.e. about a vertical axis, and the linear motion sensor 38 is arranged to sense movement in the horizontal direction parallel to the main direction of motion of the beam mass 36. The beam mass 36 is offset laterally from the centre of mass of the whole lighting system, including the damping system, so that when it moves it generates a torque about the centre of mass of the system. This enables it to be used to convert linear swinging of the lighting system into rotary oscillation, that can then be damped by the rotary damper as described in more detail below.

Referring to Figure 6, operation of the rotary damping system, as controlled by the control system 20, will first be described. The rotational simple harmonic oscillation of the hanging frame 6 can be described as a sine curve of rotational displacement d of the frame about a central reference point 62 against time t. As soon as motion of the hanging structure 6 is detected at point 62, the motor 16 drives the shaft 18 to rotate the flywheel 12. Initially, the flywheel is accelerated to move in the same direction as the movement of the hanging frame 6. The velocity of the moving frame decreases as the displacement of the frame approaches a maximum. This can be determined by the gradient of the plot of displacement against time. The acceleration of the moving frame as it moves towards its point of maximum displacement is a negative acceleration and the initial acceleration of the flywheel is therefore in an opposite direction to the acceleration of the moving frame 6 to cause the flywheel to rotate in the same direction as the moving frame. The acceleration of the flywheel is timed and controlled by the logic control system.

At the point 64 of maximum positive displacement of the hanging frame 6, shown by the amplitude of the sine wave, the velocity of the structure is zero and a change in direction is detected by the motion sensor 22 as the structure begins to rotate back towards its starting point of zero displacement 66. On detection of this change, as the hanging frame accelerates towards the point of zero displacement, the flywheel begins a timed deceleration until it reaches a velocity of zero close to the point 66 of maximum velocity and zero displacement of the hanging structure 6. At this point, the hanging frame begins to decelerate and the flywheel 12 reverses and is accelerated to move in the same direction as the hanging frame 6 until the hanging structure 6 reaches its point of maximum negative displacement shown at point 68. Again, the change in direction of the hanging structure at point 68 is detected by the motion sensor 22 and, as the hanging frame 6 accelerates, the flywheel 12 begins a timed deceleration until it reaches a velocity of zero close to the point 70 of maximum velocity and zero displacement of the hanging structure 6.

The controlled motion of the flywheel 12 dampens the rotational oscillation of the hanging structure 6, reducing the amplitude of oscillation, by removing energy from the structure during every period of oscillation until the structure comes to rest.

Control of the linear damping system is similar to, and a linear equivalent of, control of the rotary damping system, and also controlled by the electronics unit 20 in response to sensor signals that it is arranged to receive from the motion sensor 38. In this case linear oscillation, or sway, in the horizontal direction is sensed by the motion sensor 38, and the movement of the beam mass 36 in that direction (or, in this case the component of the movement of the beam mass 36 in that direction, with vertical movement being ignored) is controlled so that the beam mass 36 moves to either side of a central position. The beam mass 36 is controlled so that its acceleration in the horizontal direction is in the same direction as the direction of movement of the support frame 6, and so as to be moving at zero velocity, relative to the support frame 6, when the position of the support frame 6 is at the centre point of its oscillation, i.e. at its lowest, equilibrium point. This produces a damping force which opposes the linear movement of the frame, thereby damping that movement.

Because the beam mass 36 is offset laterally, i.e. in the direction perpendicular to its main direction of movement relative to the support frame 6, from the centre of mass of the whole lighting system, damping of the linear sway movement provided by the linear damping system will, at the same time as damping the linear movement, generate a torque around the centre of mass of the lighting system. Therefore the linear damping system will tend to convert linear oscillation into rotary oscillation, which can then be detected and damped by the rotary damping system.

In this embodiment a further linear damping system (not shown) is also mounted on the support frame 6 orientated and arranged to operate in the direction perpendicular to the linear damping system shown. This allows sway in any direction to be damped by the two linear damping systems.

The control system is arranged to treat components of the oscillation in the two linear damping system directions independently, with each beam mass being moved in response to the sensed component of movement in the direction in which it can move. The two components can therefore be damped out simultaneously, although they could equally be damped out in sequence one after the other.

In one mode of operation, the control unit 20 is arranged to monitor the outputs from the rotary motion sensor 22 and the linear motion sensor 38 of each linear damping system. If linear motion is detected in either or both of the linear directions then the appropriate linear damping system, or both simultaneously if necessary, is controlled to damp the linear oscillation, and in general this will convert the linear oscillation into rotary oscillation. The flywheel 12 is not rotated while the linear damping is being provided. It is possible that the linear damping might coincidentally damp rotary oscillation rather than increase it, but in either case it will modify it. Once the control unit 22 determines that linear damping has been reduced to zero, or below a predetermined amplitude stored in memory in the control unit, then it is arranged to stop movement of the beam mass 36 and to start control the rotary damping system to damp the rotary motion until it determines that that has also been reduced to zero.

In other modes of operation the damping of the rotary and linear movement can be performed in different order or sequence. For example the controller may be arranged to reduce linear motion to a first threshold level, such as a first predetermined amplitude stored in memory in the controller, then to reduce rotational motion to a first threshold, which may again be a predetermined amplitude, and then to reduce each type of motion to zero, or a further threshold, in separate steps. In still further modes the controller can be arranged to control both the rotatable mass and the linearly movable mass simultaneously to damp both types of motion simultaneously.

The timing of movement of the flywheel 12 and each beam mass 36 can be controlled by the logic control system of the electronics unit 20. A control programme can be stored in the logic control system using solid-state electronic storage and is arranged to receive signals from the motion sensors indicative of movement of the hanging structure 6. The logic control system and motor amplifier control the speed and direction of the motors 16, 32 of each of the damping systems in response to the motion sensor signals. Any control programme can be updated externally if necessary.

Controlling the acceleration of the flywheel and beam masses 36 controls the damping force, enabling the desired damping forces to be achieved using a flywheel and beam masses of known mass. It will be appreciated that the mass of the flywheel and beam masses 36 therefore have an affect on the damping force. A flywheel or beam mass with a greater mass driven with a particular acceleration will generate a greater damping force than a flywheel or beam mass with smaller mass driven with the same acceleration and the oscillating frame 6 will therefore come to a stop quicker. However, a flywheel or beam mass with greater mass would clearly need a more powerful motor to drive it with that acceleration. The damping efficiency is therefore also affected by the speed, power and reaction time of the motors. An hanging structure 6 undergoing rotary oscillation has been shown to come to rest after an average of a single cycle, enabling the moving light 2 to be used again almost immediately. It may even be possible to bring the oscillating structure to a stop after only half a cycle.

In a modification to this embodiment, the logic control system and amplifier 20 is replaced by, for each motor, a simple amplifier which is arranged to receive the signals directly from the appropriate motion sensor 22, 38 and output a drive signal directly to the motor 16, 32. In this case the speed of the mass (flywheel or beam mass) is arranged to be proportional to the acceleration of the hanging frame 6. The timing and control of the motor is in this case provided directly in response to the output from the motion sensor 22, 38. If the rotary motion sensor 22 outputs a signal proportional to rotational acceleration, then the drive signal to the motor 16, which controls the speed and direction of the motor, can be simply in proportion to the sensor signal. If the sensor signal were proportional to the velocity of the frame 6, then the acceleration and deceleration of the flywheel would be controlled so as to be proportional to the sensor signal. For the linear damping system, if a linear motor is used to control the linear motion of the movable mass, then the same method can be used. In the embodiment of Figure 3 the same control method will also work, and will have the same benefits of simplicity, but it may be less effective as the movement of the beam mass 36 in the horizontal direction is not directly proportional to the rotary position of the drive motors 32.

The chassis 14 is made from metal that is sufficiently thick to minimise any flex that may be transmitted to it and the flywheel 12 is made from lathe turned or appropriately cut high density metal. However, it will be appreciated that any suitable material may be used. A system of balanced, connected weights able to rotate about a central point may also be used as the flywheel or even the rotor section of a motor that is able to spin about a centre point with sufficient mass and speed to generate the required moment of inertia. The beam mass 36 is made from high density metal or other suitable material.

Referring to Figure 5, the damping device 10 operates independently without the need for external control signals and can therefore be conveniently housed in a container 26. The container 26 is metal and is clamped using clamps 50 to the frame 6 or to a lighting bar 28.

Alternatively, the contained device can be fitted or clamped to any other structure requiring damping such as a hanging structure, a theatre truss, a television pantograph, a camera platform, hanging scenery or light-weight theatre cluster unit. The lighting bar 28 is suspended on two hanging lines 8 and is moving with a rotational oscillation about a point along the length of the lighting bar 28 between the two hanging lines 8. For rotary damping it is not necessary for the rotary damping device 10 to be at the centre of gravity of the moving structure and so the damping device is clamped to the lighting bar at any point along its length between the two hanging lines 8. For linear sway' damping each of the beam masses 36 is offset from the centre of mass of the whole lighting system. The device is orientated such that rotation of the flywheel 12 is in the same plane as oscillation of the lighting bar.

The rotary or linear damping effect can be increased by placing a number of flywheels 12 or beam masses 36 on a moving structure. For example, a number of self-contained damping systems 10 can be placed side by side or stacked on top of each other, increasing the damping effect in direct proportion to the number of damping devices used. Each self-contained system is independently controlled and driven. However, it will be appreciated that it would be possible in some circumstances to drive a number of flywheels collectively with a single motor, or a number of beam masses collectively with a single motor.

Referring to Figure 7, two damping devices 26 are clamped using clamps 50 to a lighting bar 28. The lighting bar may be oscillating laterally, in a forwards and backwards swinging or swaying motion, but also may be 1? rotating in the horizontal plane. The lighting bar 28 and the hanging lines 8 effectively form a pendulum. The two flywheels are controlled and driven independently and their rotation is controlled to compensate for the horizontal rotation, and the beam masses are controlled so as to damp the lateral swing.

As shown in Figure 8, multiple damping devices 10 can be used to increase the damping effect on a rotationally oscillating structure 6. In this illustration, four damping devices 10 are attached to the hanging structure 6 and are driven such that each flywheel rotates in the same direction and in the manner described above with reference to Figure 4.

The damping devices are arranged in a symmetrical manner across the upper surface of the hanging structure 6. However, it is not essential for the flywheels 12 to be placed at or distributed evenly about the centre of gravity of the structure 6 and it will therefore be appreciated that the damping devices 10 may be placed in an off-set arrangement. The combined effect of the four damping devices results in an improved damping efficiency. In a similar manner, multiple masses can be used for each linear damping system in place of the single beam mass 36, and can be located at any appropriate locations on the oscillating structure.

Referring to Figure 9, in an alternative embodiment, the damping device is incorporated into the construction of the light as a self-contained unit.

The housing 26 containing the flywheel 12, two beam masses 36, and other components is mounted onto the top of the moving light 2. The whole unit is then mounted onto a lighting bar 28 using clamps 90 attached to the upper outside surface of the container 26. In an alternative arrangement, the damping device may be mounted underneath the moving light 2. Incorporating a damping device in the light, or alternatively in a camera, projector or other suspended device means that the entire unit can easily be moved as required without having to attach a damping device each time.

Referring to Figure 10, the rotary damping devices do not have to be arranged to rotate in a horizontat plane, but can be arranged in the vertical plane or at any other angle. Certain movements of a moving light 2 clamped to a lighting bar 28 can induce a rotational oscillatory movement of the bar 28 about its central longitudinal axis. This is known as a nodding motion. A damping device 10 is therefore attached vertically to the lighting bar 28, such that rotation of the flywheel 12 is about a horizontal axis in the same plane as rotation of the lighting bar to eliminate this effect. The rotational motion sensor 22 detects the oscillatory motion of the lighting bar 28 and controls the speed and direction of the flywheel 12 accordingly, in the same way as described above for oscillation in a horizontal plane. The linear damping systems can operate in two horizontal directions, for example parallel and perpendicular to the lighting bar 28, or there can be only a single linear damping system in each device.

It will be appreciated that one or more damping devices may be attached to hanging structures in many different arrangements, according to the type of unwanted oscillatory movement experienced by the hanging structure. It will also be appreciated that there will be many ways of incorporating a damping device in a moving light, camera, projector, piece of scenery or other suspended article as a single unit, all within the scope of the invention.

In suspended systems such as those described above linear motion of the structure is along an arc. For other structures supported in other ways the linear motion may be in straight lines, or along linear paths of other shapes.

As mentioned above, the linear damping system can comprise, in place of each of the beam masses described above, a mass mounted on sliding bearings such that it can move in a straight line along the support frame.

Then, in place of the rotary motors 32 a linear motor can be provided for each mass, for example in the form of a rack and pinion drive, a stepper motor, or linear hydraulic actuator.

Claims

CLAIMS1. A damping system for damping oscillation of a moving structure, the system comprising a rotatable mass, a motor arranged to drive the rotatable mass, a movable mass, a motor arranged to drive the movable mass so as to move its centre of gravity, sensing means arranged to detect movement of the structure and control means arranged to control the motors in response to detected movement of the structure thereby to damp oscillation of the structure.
2. A damping system according to claim 1 wherein the sensing means is arranged to produce one output indicative of rotational movement of the structure and one output indicative of linear movement of the structure.
3. A damping system according to claim 1 or claim 2 wherein the control means is arranged to receive the output from the sensing means and to measure rotational movement of the structure and linear movement of the structure from the output.
4. A damping system according to claim 1 wherein the control means is arranged to detect linear oscillation of the structure and in response to control movement of the movable mass to reduce the linear oscillation until it reaches a threshold, and when it determines that the threshold has been reached, to control movement of the rotatable mass to reduce rotational oscillation of the structure.
5. A damping system according to claim 4 wherein the control means is arranged, when said threshold has been reached, to stop movement of the movable mass and to start movement of the rotatable mass.
6. A damping system according to any foregoing claim further comprising a further movable mass, the two movable masses being movable in different directions from each other.
7. A damping system according to claim 6 wherein the different directions are orthogonal to each other.
8. A damping system according to claim 6 or claim 7 wherein the control means is arranged to move the two movable masses simultaneously thereby to damp components of oscillation in each of said different directions simultaneously.
9. A lighting system including a light and a damping system according to any foregoing claim wherein the light is the moving structure.
10. A method of damping movement of an oscillating structure comprising monitoring linear movement of the structure, monitoring rotational movement of the structure, using a first motor to drive a movable mass and controlling the direction and speed of the motor in response to the linear movement of the structure to reduce the linear movement, using a second motor to drive a rotatable mass, and controlling the direction and speed of the further motor in response to the rotational movement to reduce the rotational movement.
11. A method according to claim 10 wherein the first motor is controlled so that movement of the movable mass converts the linear movement into rotational movement.
12. A method according to claim 10 or claim 11 wherein the linear movement is reduced and then subsequently the rotational movement is reduced.
13. A damping system substantially as hereinbefore described with reference to any one or more of the accompanying drawings.
14. A method of damping movement of an oscillating structure substantially as described herein with reference to any one or more of the accompanying drawings.