Active vibration absorber and method

An active vibration absorber is provided for absorbing vibrations in a member. An inertial mass is mounted on the member with a stiffness between the member and the mass. A force actuator arrangement applies a force between the inertial mass and the member. A damping arrangement provides for damping of a resonance of the active vibration absorber. A first sensor arrangement provides at least one first signal indicative of at least one movement and/or stress related parameter for the member and a second sensor arrangement provides for at least one second signal indicative of a reaction of the inertial mass. A control arrangement is provided for controlling the force actuator arrangement using the at least one first signal and the at least one second signal.

TECHNICAL FIELD

The present invention generally relates to an active vibration absorber for absorbing vibrations in a member.

BACKGROUND OF THE INVENTION

It is well known in the prior art that it is desirable to provide a vibration absorber that can absorb vibrations in a vibrating member.

One prior art technique for absorbing vibrations comprises a tuned vibration absorber. Such a passive absorber is illustrated inFIG. 1. As illustrated in this diagram, a vibrating member in which the vibrations are to be reduced by absorption comprises a base1. An inertial mass2is stiffly mounted to the base1by a stiffness element which is illustrated as a spring member3. As is well known in the art, the mass and the stiffness of the spring can be selected or tuned to a particular frequency to provide absorption at the frequency. At the particular chosen frequency resonance occurs by movement of the inertial mass2thus causing an absorption of the vibrations in the base1.FIG. 2is a graph illustrating the amplitude of vibrations in the mass2when the mass is mounted to the base1in an undamped manner.

It can be seen inFIG. 2that although the undamped vibration absorber provides for good absorption at the resonance frequency, the frequency range is limited. Thus, it is known to provide a damper4to damp the vibrations between the mass2and the base1. The damping provides for a reduction in the peak height of the resonance and a broadening of the peak. This is illustrated inFIG. 2.

The well-known passive tuned vibration absorber is limited in that it has a narrow frequency response. If the absorption of more than one frequency is required, typically more than one tuned vibration absorber is required. Also, the resonance frequency of the tuned vibration absorber is fixed by the effective mass of the inertial mass2and the spring stiffness of the spring member3.

A known active vibration absorber is illustrated inFIG. 3. An inertial mass11is mounted to a base10via a spring arrangement12. An actuator13is provided to provide a force between the mass11and the base10. A sensor14senses vibrations in the base10and provides for an error signal which is input to a controller15having a gain G to generate a control signal for the actuator13. Controller15comprises an adaptive controller which controls the actuator13in order to reduce the vibrations sensed by the sensor14. As the controller15achieves control, i.e. vibrations are absorbed in the base10, the error signal14provided for feedback control to the controller15reduce in amplitude and will tend towards zero. It is thus necessary for the controller15to have a very high feedback gain in order to provide for control. This provides a problem with stability. Further, although some passive damping can be provided between the mass11and the base10, this is not actively controlled.

SUMMARY OF THE INVENTION

An active vibration absorber is provided for absorbing vibrations in a member. An inertial mass is mounted on the member with a stiffness between the member and the mass. A force actuator arrangement applies a force between the inertial mass and the member. A damping arrangement provides for damping of a resonance of the active vibration absorber. A first sensor arrangement provides at least one first signal indicative of at least one movement and/or stress related parameter for the member and a second sensor arrangement provides for at least one second signal indicative of a reaction of the inertial mass. A control arrangement is provided for controlling the force actuator arrangement using the at least one first signal and the at least one second signal.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

It is an object of the present invention to provide an improved vibration absorber in the form of an active vibration absorber.

A first aspect of the present invention provides an active vibration absorber for absorbing vibrations in a member in which an inertial mass is mounted on the member with a stiffness between the member and the mass. A force actuator arrangement applies a force between the inertial mass and the member. A damping arrangement is provided for damping a resonance of the active vibration absorber. A first sensor arrangement provides at least one first signal indicative of at least one of movement and/or stress related parameters for the member. A second sensor arrangement provides at least one second signal indicative of a reaction of the inertial mass. A control arrangement controls the force actuator arrangement using the at least one first signal and the at least one second signal.

Thus in this aspect of the present invention active control of the application of a force between the mass and the member is actively controlled in dependence upon a feedback signal indicative of vibrations in the member and a second signal which does not tend to zero when control of the vibrations is achieved, i.e. the second signal is indicative of a reaction of the inertial mass.

In one embodiment of the present invention, the inertial mass can be mounted to the member using a stiffness arrangement such as a spring arrangement. In an alternative embodiment of the present invention, the force actuator arrangement can provide the stiffness and the mass is thus mounted with a stiffness to the member by the force actuator arrangement.

In one embodiment of the present invention the control arrangement comprises a first filter arrangement for filtering each first signal, a second filter arrangement for filtering each second signal, and a combining arrangement such as a summer (a summation unit) for combining outputs of the first and second filter arrangements for output to control the force actuator arrangement. In this embodiment of the present invention the first and/or the second filter arrangements can be adaptive filters responsive to the at least one first signal.

In one embodiment of the present invention the damping arrangement includes a third sensor arrangement for providing at least one third signal indicative of a velocity of the inertial mass, and a damping control arrangement adapted to use the third signal to control the force actuator arrangement to provide damping of a resonance of the active vibration absorber. Thus in this embodiment of the present invention active damping is provided using a third sensor arrangement.

In an alternative embodiment of the present invention, the second sensor arrangement is adapted to provide each second signal as indicative of a velocity of the inertial mass. In this arrangement the damping arrangement comprises a damping control arrangement adapted to use the second signals to control the force actuator arrangement to provide damping of a resonance of the active vibration absorber. Thus in this embodiment of the present invention, active damping is provided using an output of the second sensor arrangement which is provided in common to the damping control arrangement and the control arrangement.

In an alternative embodiment of the present invention the damping arrangement comprises a mechanical or fluid damping arrangement for connection between the inertial mass and the member. Thus in this embodiment of the present invention a separate damping configuration is provided in parallel with the stiff mounting of the mass to the member and the application of the force between the mass and the member.

A second aspect of the present invention provides an active vibration absorber for absorbing vibrations in a member in which an inertial mass is mounted on the member with a stiffness between the mass and the member. A force actuator arrangement is provided for applying a force between the inertial mass and the member. A first sensor arrangement provides at least one first signal indicative of a velocity of the inertial mass. The damping control arrangement controls the damping of a resonance of the active vibration absorber by controlling the force actuator arrangement using the at least one first signal. A second sensor arrangement provides at least one second signal indicative of at least one of movement and/or stress related parameters for the member. A feedback control arrangement is provided for controlling the force actuator arrangement using the at least one second signal to reduce the movement and/or stress in the member.

This aspect of the present invention provides for active vibration absorption in a member by providing for active damping in conjunction with an active feedback control of the application of the force between the inertial mass and the member.

In one embodiment of this aspect of the present invention the inertial mass is mounted on the member using a stiffness arrangement such as a spring arrangement.

In an alternative embodiment of the present invention the force actuator arrangement is used to mount the inertial mass and provide for the stiff mounting of the inertial mass to the member.

In one embodiment of the present invention the feedback control arrangement comprises a filter arrangement for filtering each second signal to generate a control signal for the force control arrangement. In a specific embodiment the filter arrangement comprises an adaptive filter arrangement which is adapted in response to the at least one second signal.

The present invention also provides a method of absorbing vibrations in a member comprising mounting an inertial mass on the member with a stiffness therebetween, applying a force between the inertial mass and the member using a force actuator arrangement, damping a resonance of the inertial mass, providing at least one first signal indicative of at least one movement and/or stress related parameter for said member, providing at least one second signal indicative of a reaction of the inertial mass, and controlling the application of the force using the at least one first signal and the at least one second signal.

The present invention also provides a method of absorbing vibrations in a member comprising mounting an inertial mass on the member with a stiffness therebetween, applying a force between the inertial mass and the member using a force actuator arrangement, providing at least one first signal indicative of a velocity of the inertial mass, controlling a damping of a resonance of the inertial mass by controlling the force actuator arrangement using the at least one first signal, providing at least one second signal indicative of at least one movement and/or stress related parameter for the member, and controlling the force actuator arrangement using the at least one second signal to reduce the movement and/or stress in the member.

FIG. 4illustrates a first embodiment of the present invention in which an active vibration absorber is provided with feedback control of the application of force as well as the active control of damping.

A base21comprises a member experiencing vibration which is to be controlled. The base21can thus experience displacement, velocity, acceleration, bending, and strain. All of these parameters are indicative of vibrations in the base21.

A mass22has an inertial mass and is mounted on the base21via a stiffness arrangement which in this embodiment comprises a spring arrangement24. Although the spring arrangement24is illustrated as a helical spring, any stiff mounting arrangement for the mass22on the base21can be used.

A force actuator23is provided coupled between the mass22and the base21in order to apply a force between the mass22and the base21. A force sensor25is provided to measure the force in the spring arrangement24. The force detected is proportional to the displacement of the spring arrangement24. The output of the force sensor25is thus differentiated by the differentiator26in order to provide a signal proportional to the relative velocity of the mass22and the base21. The output of the differentiator26is input to an amplifier27which applies a negative gain to the signal in order to generate a control signal for the actuator23. The output control signal from the amplifier27is input through a combining arrangement which in this embodiment comprises a summer28. The output of the summer28is then input into the actuator23for control of the force actuator23. In this way the damping of the active vibration absorber is achieved through active control using the force actuator23which receives a signal indicative of the relative velocity of the mass22and the base21.

A sensor29is provided on the base21for detecting vibration related parameters such as displacement, velocity, acceleration, bending, or strain. The output of the sensor29is thus an error signal indicating the degree of vibration experienced in the base21. A controller30is provided to operate adaptively using the error signal from the sensor29to generate a control signal for the actuator23. The output control signal from the controller30is input into the summer28to be combined with the output of the amplifier27for the control of the actuator23.

Thus this embodiment of the present invention provides for the active control of the damping as well as the active control of the application of the force for feedback control. The controller30can be implemented in analogue or digital technology or a combination of both. The controller implements well known feedback control methodology. The controller30can for example be implemented as a digital feedback controller as for example described in “Adaptive Signal Processing” by B. Widrow and S. Stearns (Prentice-Hall Inc., 1985).

This embodiment of the present invention in which the adaptive damping is used makes it simpler to implement the controller30with the high gain necessary to provide for feedback control.

FIG. 5illustrates a second embodiment of the present invention in which feedback control is provided together with a feedforward control of the application of a force between the mass and the base.

In this embodiment, a base31experiences vibrations which are to be absorbed. A mass32is provided stiffly mounted on the base31using a stiffness arrangement, which in this example comprises a spring arrangement33.

A damper arrangement35is provided for damping oscillations between the mass32and the base31. The damper35comprises a conventional passive damper arrangement such as a mechanical or fluid damping arrangement. Examples of such dampers are well known in the art and they can for example include eddy current damping, friction damping, viscous damping, or gas damping. Ideally, the damping arrangement35should provide relatively temperature independent damping to facilitate easy and accurate adaptive control.

Actuator arrangement34is provided between the mass32and the base31to provide for the application of a force between the mass32and the base31. Feedback control of the actuator34is provided by the provision of a sensor39on the base31. The sensor is provided for sensing vibration related parameters in the base31such as displacement, velocity, acceleration, strain, and bending. The output of the sensor39is input to the feedback controller40. The feedback controller40is adaptive and generates an output control signal for the actuator34which is input into a summer38before being input to the actuator34to control the actuator34.

A sensor36is provided on the mass32in order to provide a signal indicative of the reaction of the mass32. The sensor can measure the displacement, velocity or acceleration of the mass32. The sensor36could also be placed at either end of the spring arrangement33in order to sense the force. The sensor36could also be placed either side of the actuator34or damper35in order to detect the force. Thus the sensor36provides parameters related to the reaction of the mass. The output of the sensor36is input to a feedforward controller37which is adapted in dependence upon the feedback signal from the sensor39. The feedforward controller37thus implements an adaptive feedforward control methodology as is well known in the prior art and examples of which are described in the book by B. Widrow and S. Stearns identified hereinabove. The output of the feedforward controller37is input to the summer38for summation with the feedback control signal from the feedback controller40and the combined feedforward and feedback control signals are applied to control the actuator34.

Thus in accordance with this embodiment of the present invention, the problem of control of the actuator34when the output of the sensor39is small (or tends to zero) is overcome by the provision of the feedforward control arrangement.

The feedforward control arrangement can suffer from the disadvantage of the reference signal being corrupted by the controlling force from the actuator34. The controller37can thus carry out a control algorithm such as that described in the commonly assigned and co-pending U.S. Patent Application filed Nov. 14, 2005, entitled “AN ADAPTIVE CONTROL UNIT WITH FEEDBACK COMPENSATION”, having application Ser. No. 11/273 628, and UK Patent Application No. GB 0311085.5, both of which are herein incorporated by reference in their entirety.

FIG. 6illustrates a third embodiment of the present invention which is similar to the second embodiment of the present invention but also incorporates the principles of the first embodiment of the present invention. In this embodiment the actuator applies the force under the control of feedback and feedforward controllers and also performs active damping control.

A base41experiences vibrations which are to be absorbed. A mass42is provided stiffly mounted on the base41by a stiffness arrangement comprising a spring arrangement43. A force actuator44is provided coupled between the mass42and the base41to provide for the application of a force between the mass42and the base41. In order to provide for the active control of damping, a force sensor45is provided to generate a signal indicative of the force between the mass42and the base41. A differentiator46is provided to differentiate the signal to provide a signal indicative of the relative velocity of the mass42and the base41. For damping control, the signal is input to an amplifier47which performs amplification using a negative gain to generate a feedback control signal which is input to a summer48. The output of the summer48is used to control the actuator44. Thus in this way, in a similar manner to the first embodiment of the present invention, active damping is provided for.

The output of the differentiator46in this embodiment is also input to a feedforward controller49. The feedforward controller generates a control signal which is input to the summer48and is summed with the damping control signal before being applied to the actuator44. The feedforward controller49is fed with an error signal from an error sensor50mounted on the base41to provide for the adaptive feedforward control by the controller49. Thus the feedforward controller49can provide for adaptive feedforward control either in an analogue or digital implementation. One such digital implementation is the filtered X least mean square algorithm as disclosed in the book by B. Widrow and S. Stearn acknowledged hereinabove.

The sensor50provided on the base41provides a measure of the vibrations in the base41by providing a signal indicative of displacement, velocity, acceleration, bending or stress in the base41. The error signal is input to a feedback or virtual earth controller51which performs adaptive feedback control to generate an output control signal which is input to the summer48. The summer48thus combines the adaptive damping control signal, the adaptive feedforward signal from the feedforward controller49and the adaptive feedback control signal from the adaptive feedback controller51to provide for the control of the force actuator44.

This embodiment of the present invention is similar to the second embodiment of the present invention and also provides the advantage of avoiding the stability problems of providing for a high gain in the feedback controller51by provision of the feedforward controller49. The provision of the active damping control arrangement provides for an improved active vibration absorber. Also in this embodiment, conveniently, the signal required for the adaptive damping is used for the adaptive feedforward controller input.

FIG. 7illustrates a fourth embodiment of the present invention similar to the third embodiment of the present invention except that a separate reference sensor72is provided for the feedforward controller69.

The base61experiences vibrations which are to be absorbed. A mass62is provided mounted to the base61by a stiffness arrangement comprising the spring arrangement63. A force actuator64is provided mounted between the mass62and the base61to provide for the application of a force between the mass62and the base61. A force sensor65is provided to measure the force experienced between the mass62and the base61and the spring arrangement63. The output of the force sensor is input into a differentiator66to provide an output indicative of the relative velocity of the mass62and the base61. The output of the differentiator66is input to an amplifier67which performs amplification on the signal using negative gain to generate a damping control signal which is input to the summer68. The output of the summer68is input to the actuator64for control of the actuator64. Thus in this embodiment of the present invention active damping is provided for.

The feedback control is provided by a sensor70mounted on the base61to provide a measure of the vibration in the base61. The sensor70provides a measure of parameters related to displacement, velocity, acceleration, strain, or bending in the base61. The output of the sensor70is input to the feedback controller71to perform adaptive feedback control. The output of the adaptive controller71is input to the summer68.

The summer68sums the adaptive damping control signal and the adaptive feedback signal for control of the actuator64.

The feedforward control is provided for by a sensor72mounted to measure the reaction of the mass62. The sensor72can provide a measure of parameters indicative of the displacement, velocity or acceleration of the mass62, or a force experienced between the mass62and the base61, i.e. at any point in the spring arrangement63, or either side of the actuator64. The output of the sensor72is input to a feedforward controller69which performs adaptive feedforward control to generate a control signal which is input to the summer68. The feedforward controller69receives an output of the sensor70for adaptive control of the parameters of the controller69. Thus the actuator64is controlled by the output of the summer68to receive a damping control signal, a feedforward control signal and a feedback control signal.

In all of the embodiments described hereinabove with reference toFIGS. 4 to 7, an active vibration absorber is provided which is capable of broadband vibration absorption.

Although in the embodiments of the present invention the active damping is illustrated as being performed using an analogue amplifier, the generation of the active damping control signal can be carried out digitally, for example using a digital filter.

The adaptive feedforward controllers in the embodiments of the present invention can be implemented using analogue or digital technology or a combination of both. Digital algorithms for performing the adaptive feedback and feedforward controls are well known in the art.

Although in the embodiments illustrated inFIGS. 4 to 7the mass32is illustrated as being stiffly mounted on the base31by a spring arrangement33, the actuator34can provide for the stiff mounting of the mass32on the base31, thus obviating the need for the spring arrangement33. The actuator34can comprise any suitable force actuator such as an electromagnetic actuator, a piezoelectric actuator, a hydraulic actuator, a magnetostrictive actuator, a pneumatic actuator, an electrostatic actuator, or a thermal expansive actuator. Where an electromagnetic actuator is provided, usually a stiffness arrangement will be required to provide for the stiff mounting of the mass32on the base31. Where for example the actuator34comprises a piezoelectric actuator, the piezoelectric actuator provides not only for the application of the force, but also for the stiff mounting of the mass32on the base31.

Although in the embodiment ofFIG. 5a separate damper35is illustrated, the damper and stiffness arrangement33can be combined. The damper35can comprise any suitable well known passive damping arrangement such as an eddy current damper, a friction damper, a viscous damper or a gas damper.

In the embodiments of the present invention the sensor provided on the base can comprise any suitable sensor arrangement, i.e. a single sensor or a number of sensors, in order to provide one or more signals indicative of vibration in the base. The signal or signals can therefore comprise an indication of displacement, velocity, or acceleration in the base, or other physical parameters indicative of vibrations such as strain, or bending.

The reference sensor provided to output a signal indicative of the reaction of the inertial mass to the vibration in the base31, can comprise not just a single sensor, but any suitable sensor arrangement comprising a single sensor or multiple sensors. The sensor can provide a measurement of movement of the mass, i.e. displacement, velocity or acceleration, or a measurement of the force between the mass and the base. The force can thus be measured within the spring arrangement, either in the middle or at either end, either side of a separate passive damper, or either side of the force actuator.