GB2229789A

GB2229789A - Active control of vibration

Info

Publication number: GB2229789A
Application number: GB8906070A
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: 1990-10-03
Anticipated expiration: 2009-03-16
Also published as: DE4008568A1; GB2229789B; DE4008568C2; GB8906070D0

Description

Title: Improved methods and apparatus for the active control of vibration

Field of invention

This invention concerns methods and apparatus for. the active control of vibration particularly in the isolation of beans and pipes from vibration by compliance.

Background to the invention

In many situations, unwanted mecian4Ica"L vibratit-,n can be t ra nsini tted f rom a source vi a pines, beams or r Clexilble One examiple i_s th.e of.' vihrations from a spacecraft or satellite to antennae or other sensitive eclt-iipm.(-nt mokintpd or, it at the end of a thin supporting beam. Typically such a beam wil-1 not. be damped and the disturbing vibrations will cause disturbances at the antenna or vibration in thf-, e,-luit-)mett and so interfere with its normal '-:uncl-i(..)n.

Another examole is tht. transmission of vibrati(Dn from 1 heavy machinery such as ships' engines via pipe-work connected to it.

various publications deal with the cancellation of transverse modes of vibration in beams usinq multiple actuators in particular reference is made to Schaechter, D B, Eldred, D B, "Experimental Demonstration of the Controú of Flexible Structures", J Guidance 7 (5), 1984, pp527-534 and Mace, B R, "Active Control of Flexural Vibrations", J Sound and Vib. 114 (2), 1987, pp253-270.

It is an object of the present invention to cancel all modes of vibration using a single actuator, albeit a compound actuator,-attached to the beam.

For the purposes of this application beams and pipes and the like flexible members will be referred to as elongate members.

Furthermore references herein t-o a source of vibration means any source whether translational, torsional or compression.

Summary of the invention

Accordina to one aspect of the present invention t-here is provided a method whereby a source of vibration acting directly or indirectly on one relgion of an elongate member can be prevented from producing vibrations in another region of the elongate member, by attaching the ends of at least one constrictive element to the elongate member, at separate points along its length, in such a manner that the constrictive element is capable of producing a small deformation of the section of the elongate member between the attachment points, and supplying control signals to the constrictive element so as substantially to prevent movement to one side of the constrictive element from being transmitted to the other side.

BY the term "constrictive element" as used herein is meant an actuator whose length can be changed in a controllable way.

i Examples of such actuators are electrodynamict piezoelectric, hydralic and magnetrostrictive actuators.

In each case the actuator acts to increase or decrease its length in response to a control signal.

The invention extends to the case in which the beam is of f i ni te le ngth and the attachme nt poi nts f or the constrictive element or elements lie at the ends of the beams.

Thus for example if a beam of finite lenQth is caused to vibrate at one end, the invention may be employed to substantially prevent consequent motion bei na pro,-lticpti atthe other end of the beam.

By attaching se,.,eral such elements to the same section of an ellon-ate element wi!-h the attachment:Doint-c appropriately placed, a compound actucttor cdri oe realised which makes it possible to produce any desired sjia'J'-'L displacement of the section of beam immediately to one side of the region of attachment of the actuators with respect to the beam on the other side of the elongate element. This is done by supplying appropriate control signals to the various elements of the coftiiDou!,,, dctuato,-. In particular, if- the first side undergoes displacements, (eg linear or rotational about any axis) due to a source of unwanted vibration which acts directly or indirectly upon it, the actuator can be driven so that no corresponding displacements occur on the other side.

In general, at least six constrictive elements will be required for the control of all possible vibrations of an elongate element which is capable of supporting longitudinal (compressional), transverse and torsional modes of vibration. If not all of these modes are to be controlled, it may be possible to use fewer constrictIve elements.

In the case of a beam it will usually-be convenient to attach the ends of the elements to two flanges attached' to the beam; the elements will then act to deform the section of beam between the flanaes.

The control signals to effect the vibration isolation will normally be derived from an active control system. Trlis may consist of vibration sensors 4hich sense jibraiiuri,-, of the beam on one or other or both of the two sL,-],cs of t-le actuator and supply signals to an electronic controller which responds tn these by supplying the appropr-Late 1 1 '1 C1 1 control sianals to the constrictive elements 11-1nc actuator. The section of beam to which the elements dre attached is thus made to behave in response to the unwanted vibration as if it were substantially more compliant than the surrounding parts of the beam.

The invention also lies in the combination of an elonaate element and at least one constrictive element and control signal generating means for driving the element, as aforesaid.

The invention will be described by way of example with reference to the accompanying drawings in which:

Figure 1 shows a compound actuator for a straiqht beam, and Figure 2 is an end view along the axis of the beam.

Figure 1 illustrates an arrangement which may be used to provide a compound actuator for a straight beam of constant cross-section. Two annular flanges 1 are rigidly attached to a beam 2 (in this example of circular cross-section) in planes normal to the axis of the beam at the respective points of attachment. Six constrictive elements 3 are positioned with an end attached to each flange. There are three attachment points on each flange, angularly spaced 1200 apart and at tChe same railinc, with respect to the axis of the beam. The a,--lac"i,-,,ent points on one flange are rotated tliroucili 600 about the axis of the beam with respect to the attachment,)oi.nts on the other. There are two constrictive elerren-.z a n c at each attachment point, their other ends beinj anchiored at the two angularly nearest attachment poinits on the other flange.

1 --iqure 2 is a view along the axis oE the beam re'lative positions of attachment points on the t,..jo shown. Those on the nearer flange are numbere.i A] those on the further flange are numbered B1 to R. constrictive elements are then attached as follows:

Between Al and B1 Between Al and B3 Between A2 and Bl Between A2 and B2 Between A3 and B2 Between A3 and B3 It will be seen that, if the beam were perfectly compliant, one flange could be displaced linearly in any direction, or rotated about any axis, with respect to the other, by supplying appropriate control signals to the constrictive elements. If the beam is stiff, the displacements will be limited in magnitude by the forces obtainable from the constrictive elements acting against the stiffness of the beam.

The flanges should preferably be designed to be sufficiently stiff that they will not distort under the forces applied to them by the constrictive elements and the beam, and their attachments to the beam must be sufficiently sound to prevent slippage between and flange.

The radius of the attachment points and the distance between the flanges will be governed iny the of the beam, the forces that the constrictive elements can provide, the magnitude of 11-1he vibraLions to be isolated, and the bulk of the constrictive elements. The Llange separation and radius should be sufficient to accoinino(iae.e these elements.

The flange separation should also be sufficient for the elements to be able to produce such relative translational displacements of the flanges parallel to the axis of the beam as are required to isolate compressive vibrations.

The radius of the attachment points from the beat,.-t axis should be sufficient to allow the elements to produce the other relative transitional and rotational displacements necessary to isolate other modes of vibration.

tr,

Claims

Claims

C339/T 1. A method of active vibration control whereby a source of vibration acting directly or indirectly on one region of an elongate member is prevented from producing vibrations in another region of the elongate member, by attaching the ends of at least one constrictive element (as hereinbefore defined) to the elongate member, at seDarate points along its length, in such a manner that the or each constrictive element is capable of producing small deformations of the section of the elongate ember between the attachnent points, and supplying control signals to the constrictive element or elements so as substantially to Drevent unwanted movements of the elongate me-ber to one side of the constrictive element Irom bpinR transmitted to the other side.
2. A T-ethod accerdi-n!,:., to claim 1. accorgling to which one or more electrodynamic, piezoelectric, hydraulic or mp-rptrc,strict-ive actuators are ennloyed as the cc.nstr-.ct i-ve element or eleTrents, the or each such actua-c,r actinp- to increase or decrease its lenoth in resronse to a control sjpnal,.
3. A accordin,o. to clai- 1 or claiT 2,applied to th- case in which the elonpate member is of length ar,- -he at-Rchment. points.or the constrictive- elerent or li- at ti- ends c.' the T-eriber.
A method accordire: tc cia---- 1 or, - r clain 3, POOR GUALITY are attached to the same section of an elongate member with the attachment points appropriately placed to produce a compound actuator which produces any desired small linear and/or rotational displacements of the section of elongate member immediately to one side of the region of attachment of the actuators with respect to the member on the other side of the elongate element in response to appropriate control signals applied to the various constrictive elements of the compound actuator, whereby if the firt side undergoes small displacenents due to a source of unwanted vibration which acts directly or indirectly upon it, the actuator is driven so that no corresponding displacements occur on the other side.
5. A method according to claim 4, accordin,g to which the compound actuator is formed by at least six constrictive elements in order to control all possible vibrations of an elongate member which is capable of supporting longitudinal (compressional), transverse and torsional modes of vibration.
6. A method according to any of claims 1 to 5, according to which, in the case of an elongate member constituted by a beam., the ends of the or each constrictive element are respectively attached to two flanges secured to the beam, whereby the or each constrictive element acts to deform the section of beam between the flanges.
7. - A method according to any of claims 1 to 6, according 1 LO which the control signals to effect v-ibra"-,i-on isolation are derived fron an active control system.
- - i 1.1 P. A nethod accord-i-p- to claim 7, acco-,,",;,: to which the active control syste--- i-cludes vibration sensors which 1 sense vibrations of the elongate member on one or other or both of the two sides of the actuator and supply signals to an electronic controller which responds to these by supplying the appropriate control signals to the or each constrictive element of the actuator.
g. An active vibration control system for preventing transmission of unwanted vibrations along a beam, comprising, in combination with the beam, an actuator comprising at least one constrictive element (as hereinbefore defined), means attaching the actuator between two attachment points spaced apart along the beam, means for sensing unwanted vibrations applied to the beam in order to generate control signals, and an electronic controller for the or each constrictive eler.ent to cause change of length of the or each constrictive element responsively to the control signals.
10. A system according to claim 9, wherein the actuator includes at least one constrictive element attached parallel to the axis of the beam and at least one constrictive element attached between attachment points which are both longitudinally spaced along- and an-,,ularly spaced around the beam.
11. A nethod nIP active vibration control as clairn.ed in claim 1 and substantially as hereinbefore described.
12. An active vibration control svstem stubstantially as hereinbefore described with reference t,,, the accorinanyin,rdrawings.

Published 1 WWO at The Patent Mce. State House-8671 Hig'Holborn, londonWC1R4TP h=ther copies maybe obtained from The Patent Office gales Branch, St Mary Cray. Orpingwn, Kent B; UZ. Printed by Multiplex techniques ltd. St Mary Cray. Kent. Con. 1,87