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 cases, 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 helicopters in rescue or similar scenarios or on motor vehicles that experience unwanted sideways rocking motions.
The present invention provides a damping system for damping oscillation of a moving structure, the system comprising a flywheel, a motor arranged to drive the flywheel, sensing means arranged to detect movement of the structure and control means arranged to control the motor in response to detected movement of the structure.
The flywheel 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.
Preferably, the sensing means is arranged to continuously monitor the position of the structure and to send a signal to the control means indicative of any change in position of the structure. The sensing means may be arranged to detect oscillating motion of the structure and the control means may be arranged to accelerate and decelerate the flywheel in response to such motion.
The acceleration and deceleration of the flywheel 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 the motor. The control means may alternatively directly control the direction and speed of the motor in proportion to the output of the sensing device.
The flywheel may be arranged to be accelerated to move in the same direction as the moving structure when movement of the structure is first detected. The flywheel may also be arranged to be decelerated on detection of a change in direction of movement of the structure. Preferably, the velocity of the flywheel is arranged to be at a minimum when the displacement of the structure is at or near minimum.
Preferably, the sensing means is 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 flywheel or at an angle to the flywheel. The motor may be connected to the flywheel 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 flywheel. 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 flywheel 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 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 flywheels. Each flywheel may be driven by a respective motor, each able to rotate independently of each other. Alternatively, a single motor may drive a plurality of flywheels.
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 flywheel and 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 flywheel in response to movement of the structure.
Preferred embodiments of the invention will now be described with reference to the accompanying drawings, in which:
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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.
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At the point 34 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 swing back towards its starting point of zero displacement 36. 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 36 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 38. Again, the change in direction of the hanging structure at point 38 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 40 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.
The timing of movement of the flywheel 12 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 sensor indicative of movement of the hanging structure 6. The logic control system and motor amplifier control the speed and direction of the motor in response to the motion sensor signal. Any control programme can be updated externally if necessary.
Controlling the acceleration of the flywheel controls the damping force, enabling the desired damping forces to be achieved using a flywheel of known mass. It will be appreciated that the mass of the flywheel therefore has an affect on the damping force. A flywheel with a greater mass driven with a particular acceleration will generate a greater damping force than a flywheel with smaller mass driven with the same acceleration and the oscillating frame 6 will therefore come to a stop quicker. However, a flywheel 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 motor. An oscillating hanging structure 6 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 a simple amplifier which is arranged to receive the signals directly from the motion sensor 22 and output a drive signal directly to the motor 16. In this case the speed of the motor 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. If the motion sensor 22 outputs a signal proportional to rotational acceleration, then the drive signal to the motor, 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.
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.
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The damping effect can be increased by placing a number of flywheels 12 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.
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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.
As the device functions by introducing energy into a hanging structure in the opposite direction of the unwanted oscillation of a structure, it must be understood that if the anti-oscillation device is attached upside-down to any hanging structure, it would add to the oscillating with potentially dangerous consequences. As part of the construction of the device, fail-safe mechanisms should be incorporated to ensure that it would not be possible for this to happen. This could consist of a mercury switch mounted onto the unit in such a way so that the electrical supply would be cut off if the device were mounted in the wrong orientation. It may also be use the an angular rate sensor, accelerometer, gyroscope, solid state gyroscope or any other suitable sensing means to sense the orientation of the unit to either cut the power and thus rendering it safe or to reverse the polarity of the motor and thus ensuring that the device will always function safely.
Number | Date | Country | Kind |
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0713862.1 | Jul 2007 | GB | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/GB08/02392 | 7/15/2008 | WO | 00 | 5/25/2010 |