Active tuned vibration absorber

1. An active tuned vibration absorber for reducing vibrations in a structure, the vibration absorber comprising:

a mount for attachment to the structure;

a moveable mass;

a spring arrangement connected between the mass and the mount;

an actuator arrangement for applying a force between the mass and the mount;

a first sensor for providing a first measurement indicative of a force exerted between the structure and the mount;

a second sensor for providing a second measurement indicative of an acceleration of the structure at or proximate to the mount; and

a control system for generating an actuator driving signal for driving the actuator using the first and second measurement,

wherein only one of a spring arrangement and actuator arrangement is directly connected between the mass and the mount via the first sensor, and

wherein the control system is operable to generate the actuator driving signal to cause the first measurement and second measurement to conform to a target relationship such that the active tuned vibration absorber dissipates energy transferred from the structure, and

wherein, in isolation from the actuator arrangement and control system, the moveable mass and the spring arrangement form a first resonant system having a first Q factor and, when controlled by and combined with the actuator arrangement and control system, the moveable mass and the spring arrangement form a second resonant system with a second Q factor, and wherein the second Q factor is larger than the first Q factor.

2. A vibration absorber according to claim 1 , wherein the control system is operable to generate the actuator driving signal to cause a frequency domain representation of the first measurement and a frequency domain representation of the second measurement to converge to a target ratio.

3. A vibration absorber according to claim 1 , wherein the control system is operable to generate an actuator drive signal to cause the mechanical impedance of the vibration absorber to converge to a target mechanical impedance substantially equivalent to the mechanical impedance of a passive tuned device.

4. A vibration absorber according to claim 1 , wherein the control system includes a feedforward control system.

5. A vibration absorber according to claim 4 , wherein the feedforward control system is operable to process signals using a reference model that is defined in terms of characteristics of the vibration absorber, whereby the reference model does not need to take into account characteristics of the structure.

6. A vibration absorber according to claim 1 , wherein the control system includes a feedback control system.

7. A vibration absorber according to claim 1 , wherein the first sensor is a force sensor attached to or proximate the mount.

8. A vibration absorber according to claim 1 , wherein the first sensor is an accelerometer attached to the moveable mass.

9. A vibration absorber according to claim 1 , wherein the second sensor is an accelerometer attached to or proximate the mount.

10. A vibration absorber according to claim 1 , further comprising a communications unit for communicating with a remote controller.

11. A vibration absorber according to claim 10 , wherein the vibration absorber is operable to receive a command signal from the remote controller, and to alter the target relationship in dependence on the command signal.

12. A vibration absorber according to claim 10 , wherein the vibration absorber is operable to receive a command signal from the remote controller, and to drive the actuator using the command signal.

13. A vibration absorber according to claim 10 , wherein the vibration absorber is operable to determine a communications failure between the vibration absorber and the remote controller, and to adapt to a local control mode in response to the communications failure.

14. A vibration absorber according to claim 10 , wherein the vibration absorber is operable to transmit at least one of the first and second measurements to the remote controller.

15. A vibration absorber according to claim 1 , operable to receive a signal indicative of a characteristic frequency of vibration in the structure, and to alter the target relationship in dependence on the received signal.

16. A vibration absorber according to claim 1 , operable to determine a characteristic frequency of vibration in the structure, and to alter the target relationship in dependence on the determined frequency.

17. A vibration absorber according to claim 16 , wherein the vibration absorber is operable to process the first or second measurements to determine the frequency of a harmonic of a frequency of vibration, and to alter the target relationship in dependence on the determined harmonic frequency in order to counteract the vibration.

18. A vibration absorber according to claim 1 , for use with a vibration source that generates vibrations having a frequency varying over time within a set of characteristic frequencies, wherein the control system further comprises:

a plurality of control subsystems taking the first and second measurements as an input, each control subsystem being tuned to a respective one of the set of characteristic frequencies; and

a processing unit for combining the output of the subsystems to generate the actuator driving signal.

19. A vibration absorber according to claim 18 , wherein each control subsystem includes an adaptive filter for generating the output of the subsystem, and the control system is operable to control the adaptation of each of the adaptive filters in dependence on the degree of excitation or response of each of the subsystems.

20. A system for attenuating vibrations in a structure, comprising a plurality of active tuned vibration absorbers as defined in claim 1 .

21. A system according to claim 20 , further comprising a central controller, operable to receive at least one signal representative of a vibration in the structure, and to transmit a command signal to at least one of the plurality of vibration absorbers to control the or each vibration absorber to reduce the vibration.

22. A vibration absorber according to claim 1 , wherein the control system is operable to estimate a total of the force exerted between the structure and the mount using the first signal and the second signal and/or a signal indicative of a force generated by the actuator.

23. A vibration absorber according to claim 22 , wherein the force indicated by the first measurement is not equal to the total of the forced exerted.

24. An active tuned vibration absorber for reducing vibrations in a structure, the vibration absorber comprising:

a mount for attachment to the structure;

a moveable mass;

a spring arrangement connected between the mass and the mount;

an actuator arrangement for applying a force between the mass and the mount;

a force sensor attached to or proximate the mount for outputting a measurement indicative of a force exerted between the structure and the mount; and

a control system for generating a drive signal for the actuator arrangement using the measurement, the actuator drive signal being generated to cause the mechanical impedance of the vibration absorber to converge to a target mechanical impedance substantially equivalent to the mechanical impedance of a passive tuned device such that the active tuned vibration absorber dissipates energy transferred from the structure,

wherein only one of the spring arrangement and actuator arrangement is directly connected between the mass and the mount via the first sensor, and

wherein, in isolation from the actuator arrangement and control system, the moveable mass and the spring arrangement form a first resonant system having a first Q factor and, when controlled by and combined with the actuator arrangement and control system, the moveable mass and the spring arrangement form a second resonant system with a second Q factor, and wherein the second Q factor is larger than the first Q factor.

25. A method of reducing vibrations in a structure, comprising:

providing a mount for attachment to the structure;

providing a moveable mass;

providing a spring arrangement connected between the mass and the mount;

providing an actuator arrangement for applying a force between the mass and the mount;

providing a first sensor for providing a first measurement indicative of a force exerted between the structure and the mount;

providing a second sensor for providing a second measurement indicative of an acceleration of the structure at or proximate to the mount; and

providing a control system for generating an actuator driving signal for driving the actuator using the first and second measurement,

wherein only one of the spring arrangement and actuator arrangement is directly connected between the mass and the mount via the first sensor, and

wherein the control system is operable to generate the actuator driving signal to cause the first measurement and second measurement to conform to a target relationship such that the active tuned vibration absorber dissipates energy transferred from the structure, and

wherein, in isolation from the actuator arrangement and control system, the moveable mass and the spring arrangement form a first resonant system having a first Q factor and, when controlled by and combined with the actuator arrangement and control system, the moveable mass and the spring arrangement form a second resonant system with a second Q factor, and wherein the second factor is larger than the first Q factor.