GB2229511A

GB2229511A - Active vibration control

Info

Publication number: GB2229511A
Application number: GB8906069A
Authority: GB
Inventors: Mark Francis Lucien Harper
Original assignee: Topexpress Ltd
Current assignee: Topexpress Ltd
Priority date: 1989-03-16
Filing date: 1989-03-16
Publication date: 1990-09-26
Anticipated expiration: 2009-03-16
Also published as: GB8906069D0; DE4007442A1; GB2229511B

Description

1 1 1 1 J_ 1; ' C34 1 /T Title Active Vibration Control

Field of the invention

This invention relates generally to the active control of vibration.

Background to the invention

There are many instances in which unwanted mechaniral vibrations propagate through an extended structure or assembly of structures or bodies in m,-p-cl"an-4cal communication. One example is the transmission of vibrations from a spacecraft or satellite to antennae or other sensitive equipment or apparatus mounted from it at the end of' a thin boom. Typically the boom will no"-. be mechanically damped and the vibrations will be communicated along it to the antenna equipment or apparatus and so interfere with its normal functions.

Another example is the transmission of unwanted vibration from heavy machinery such as ships' engines via pipes, mounts or other members connecting it to the supporting structure.

Various publications deal with the cancellation oil specific modes of vibrations by point-acting actuators. Examples are the article by Schaechter et al in the Journal "Guidance" 1(5), 1984, at pages 527 to 534 and the article by Mace in the Jo.urnal "Sound and Vibration" 114(2), 1987 at pages 253 to 270. In copending Patent Application No. a m6thod is disclosed whereby mechanical vibrations of any type may be prevented from propagating along a beam, pipe or other extended part of a mechanical structure.

It is an aim of this invention to provide a method whereby vibrational displacements at a chosen point or small region of an extended mechanical structure may be modified as desired, or caused to disappear altogether. This is to be accomplished by the application of control signals to an actuator constructed as described below.

The invention The actuator in accordance with the invention consists of a P1ura-LiLv nf uni-axial inertlai. actuators wk,i--h are disposed so as to exert forces on the said point or re7--ion.

BY the teran lluni-axial inertial actuator", as used herein, is weant an actuator which is both uni-axial and inertial.. By an actuator is meant a device which produces an action in response to a control signal. By the terir, lluni-axial actuator" is meant an actuator which is capable of producing an action in only a single direction. The action in this case will be a force applied in the direction of action. By the term "inertial actuatorll is meant an actuator which produces a force by virtue of the inertial reaction of a mass which is caused to accelerate in a direction opposite to the direction of the force produced. Reference will be made to the euclidian line passing through the point at which the action is produced and parallel to the direction of action, and this line 1 will be termed the "axis of action". Examples of suitable devices are electrodynamic or hydraulic actuators backed by an inertial mass.

1.

The desired effect may conveniently be produced by supporting the inertial actuators from an intermediate rigid body such as a flange or plate which may then be rigidly attached to the said point or small region. In order to effect control over many degrees of freedom of vibration, i.e. control over translation in up to three independent directions and also over rotation about up -',c three independent axes, of the point to be controlled, then mori than one uni-axial. inertial actuator. muSIL, oe caused to act upon a substantially riaid intprm.edint body. The axes of action of the actuators must. be so disposed as to allow them to exert upon the intermediate hody the an,' 14n.ear forces which it is exert at the point to be controlled in order to control two or more degrees of freedom of vibratory motion. The intermediiate body,ray then be rigidly attachel to that point. in order to apply the control. If a minimum of six uni-axial inertial actuators are caused to act on the intermediate body along suitably disposed axes of action then control may be applied to all six degrees of freedom of motion of the point to be controlled. Possibly, if a lesser number of degrees of freedom have to be controLled, then a lesser number of uni-axial inertial actuators may be sufficient.

In the special case that the said point or small region is contained within or is equivalent to a part of the structure which is substantially rigid and of suitable extent then the intermediate body may.be dispensed with and the uni-axial actuators may be attached directly to the said rigid part of the structure which then acts as the rigid intermediate body. An actuator constructed in accordance with the above description may be used in conjunction with sensors providing information relating directly or indirectly to the vibration at the said.po.int or small region at which control is desired. For example, the control signals to the actuator may be determined with regard to the signals obtained from vibration sensors placed at or in the said point or small region. As another example, information from sensors or sources of vibration elsewhere in the structure may be used together with or instead of the signals from the Li!.st mentioned ser.--^-rs, toge'k'-.her with a knowledge of' f-ie vibration-communicating properties of the structurp, Inpredict vibrations at the said point or small region and so to determine the control signals to be applied to the a--tua,,,-r in order to achieve the iesired control. Aautomatic controller may be used to produce the control using information from the aforesaid sensers or sources and the aforesaid knowledge of the properties of the structure, in which case active control of vibration at the aforesaid point or small region may be achieved.

Description of embodiment

The method in accordance with the invention is exer-.iDlified in the following description, making reference to the accompanyinp, drawings, in which:-

Figure 1 is a peispective view of one arrangement of actuator; and Figure 2 is a view looking along the axis of the arrangement.

z WS 4 i W 1 Figures 1 and 2 illustrate an arrangement which may be used to realise the actuator. Six uni-axial inertial actuators are attached to a substantially rigid flange 1 at their points of action 2 and 3. Figure 1 shows the flange in side view while Figure 2 shows a face-on view.

In this example the flange 1 is a flat disc-shaped plate, whilst the bodies of the actuators 4 and 5 are shown without additional inertial masses being attached.

The points of action 2 are distributed at equal angular s--acin,s of one hundred and twenty degrpes cif arithe centre of the disc. The same is true of the points of action 3 but, as shown in Figure 2, the pointi of action 3 are d4.--Dose,.' at different ano'e--, w-th respert the poInts 2 on their left and right hands to ailow f'c)r, the disposition of the actuators 5. However, rne points 2 and 3. may be coincident. The centre of the disc 6 is indicated' in Figures 1 and 2 and the flange axis 7 which passes through, 6 and is normal to the flangta 1 i. SYi(-)wr. Figure 1. All six points of action lie at the same radius from the centre 6.

The axes of action of three of the actuators 4 are parallel to the flange axis 7 and the actuators 4 acting in concert may thus provide either a force on the flange parallel to the axis 7 or a couple about any chosen axis which passes thr.ough 6 and is normal to 7 or any of these in combination. The axis of action of each of the remaining three actuators 5 is normal to 7 and is tangential to the arc of an imaginary circle centred at 6 and passing through the actuators' point of action 3. The actuators 5 acting in concert may thus provide either a 6 - translational force parallel to any chosen axis normal to 7 or a couple about 7 or any of these in combinaton. The forces or torques produced will be determined by the control signals supplied to the uni-axial actuators.

z ...

1 t_ 1 C341 /T

Claims

1. A method of active vibration control according to which a plurality of uni-axial inertial actuators (as hereinbefore defined) are disposed and controlled to exer t forces on a point or small region of an extended mechanical structure so as to modify or cancel vibrational displacements at said point or small region.

2. A method according to claim 1, according to which the actuators are supported to act on said point or small region through an intermediate rigid part fixed to said point or region.

3. A method according to claim 2, according to which the intermediate rigid part is a part of the extended mechanical structure.

4. A method according to claim 2, according to which the intermediate rigid part is a body such as a flange or plate rigidly attached to said point or region.

5. A method according to claim 2 or claim 3 or claim 4, wherein the actuators are supported by the intermediate rigid part.

6. A method according to any of claims 1 to 5, employing at least six actuators in order to exercise control to all six degrees oil freedom of motion of the point or region to be controlled.

7. A method according to any of claims 1 to 6, according to which sensors are employed directly or indirectly to sense unwanted vibrations at sai. point or small region and to provide control signals which are employed to control the actuators.

8. A method according to claim 7, according to which the sensors are located at the point or small region to be controlled.

9. A method according to claim 7, according to which the sensors are remotely disposed from said point or small region, and the outputs thereof are combined with data representative of the vibration- communication properties of the structure in order to develop the actuator control signals.

10. A system for active vibration control comprising, in combination with an extended mechanical structure having a point or small region at which unwanted vibrations are to be modified or suppressed, a plurality of uniaxial inertial actuators (as hereinbefore defined) disposed at said point or region to exert forces thereon, and control means for the actuators which includes sensors for producing control signals controlling the actuators.

11. A method of active vibration control as claimed in claim 1 and substantially as hereinbefore described.

12. A system for active vibration control substantially as hereinbefore described with reference to the accompanying drawings.

Published 1990 a, The Patent office. State House 66 71 High Holborn. London WC1R 4TP. Purther copies may be obtained from The Patent Wice Sales Branch. St Mazy Crky. Orpingoi... Kent BRS 3RD. Printed by Multiplex techniques ltd. St Mary Cray. Kent. Con- l!87 1