GB2140124A - A device for damping an oscillatory system - Google Patents

Abstract

A device for damping an oscillatory system (e.g. a spring) comprises a first connection member 2 connectable to part of a spring (3) and a second connection member 24 connectable to a surface (25) on which the spring is mounted. One end of a first "bearing member" 4 is rotatably mounted in the first connection member 2 and the other end 6 is fixed in a mounting block 8. One end 9a of a second "bearing member" 9 is rotatably mounted in the block 8 to extend perpendicularly of the first "bearing member" 4. The other end 9b of the second "bearing member" 9 is fixed in part 11 of a planar component 12 which is pivotally connected by a flexible joint 13 to a second planar component 15. The device is symmetrical about the pivot line so that a third "bearing member" 19 and a fourth "bearing member" 22 corresponding to the second and first "bearing member", respectively, are provided between the second planar component 15 and the second connection member 24. The so- called bearing members rotate against a fluid resistance in response to vibrations in a particular direction. The device is responsive to vibrations of the spring in three mutually perpendicular planes. <IMAGE>

Description

SPECIFICATION A device for damping an oscillatory system THIS INVENTION relates to a device for damping an oscillatory system.

Oscillatory systems are used, for example, in mechanical vibration isolation systems for audio reproducing equipment. Typically, such mechanical vibration isolation systems comprise a plurality of mounting springs which in conjunction with the mass of the equipment produce an oscillatory system having a natural frequency which is typically below 1 2Hz. In order to provide some stability in the mounting, it is usual to provide some means for damping oscillation, for example a piece of plastics foam.

There are, however, a number of disadvantages associated with such damping devices.

Thus, the damping device will normally reduce the degree of vibration isolation attained and will also reduce, to some extent, the effective frequency bandwidth of the isolation system. Also, there are increasing practical difficulties in designing the damping devices when the natural frequency of the oscillatory system is reduced in order to reduce coupling with other oscillatory parts of the equipment and to increase the low frequency isolation.

Moreover, it is difficult to control the degree of damping in three planes of oscillation.

According to the present invention, there is provided a device for damping vibrations of an oscillatory system, comprising a first connection member connectable to part of an oscillatory system, a second connection member connectable to a surface on which the oscillatory system is mounted, a plurality of bearing members connected between the first connection member and the second connection member, the bearing members being arranged to be responsive to vibrations in a plurality of planes which are not parallel to one another.

The phrase 'bearing member' is used herein to mean a member which is movable in response to a force, for example a vibration, against a resistance, for example, a fluid.

In a preferred embodiment, the plurality of bearing comprises a first set of bearing members having a first and a second bearing member responsive to vibrations in a plurality of planes not parallel to one another and a second set of bearing members having a third and a fourth bearing member responsive to vibrations in a plurality of planes not parallel to one another, the first set of bearing members being connected to the second set of bearing members by a joining member.

Generally, the first and second sets of bearing members are connected by a flexible member which may comprise first and second components connected by a flexible joint. Alternatively, the first and second sets of bearing members are connected by a fifth bearing member Generally, the or each bearing member is movable against the resistance of a fluid.

In a preferred arrangement, each bearing member is rotatable in a respective mounting against the resistance of a fluid and the viscosity of the mounting fluid may be varied between mountings so that, in use, the degree of damping in different directions is selectively varied.

Thus, the present invention enables the provision of a damping device capable of damping vibrations in three mutually perpendicular planes.

The present invention also provides an oscillatory system having a damping device in accordance with the first or second aspect of the invention and audio reproduction equipment having mechanical vibration isolation in the form of one or more oscillatory systems, the or each oscillatory system incorporating a damping device in accordance with the first or second aspect.

For a better understanding of the present invention, and to show how the same may be put into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 is a schematic perspective-view of a device embodying the invention for damping an oscillatory system; and Figure 2 is a schematic cross-sectional view of part of audio reproducing equipment showing the device of Fig. 1 in use to damp oscillations of a spring.

Referring now to the drawings, a device 1 for damping vibrations of an oscillatory system comprises as shown in Fig. 1, a first connection member 2 connectable, as shown in Fig. 2, to part of an oscillatory system, in the example shown, a spring 3. A first bearing member 4 has one end 5 rotatably mounted in a seat 7 formed in the first connection member 2 and a second end 6 fixed in a mounting block 8. The seat 7 contains a fluid having a given selected viscosity for resisting rotation of the first bearing member 4. One end 9a of a second bearing member 9 is rotatably mounted in a seat 10 in the mounting block 8 so as to extend in a direction perpendicular to the first bearing member. The seat 10 contains a fluid having a given selected viscosity for resisting rotation of the second bearing member.The first and second bearing members are thus rotatable about respective axis which are mutually perpendicular so that the first bearingmember is rotatable in response to vibrations in a first plane and the second bearing member is responsive to vibrations in a second plane perpendicular to the first plane. The other end 9b of the second bearing member extends through, and is fixed in, an axial bore formed in a cylindrical member 11. The cylindrical member 11 is fixed to, or formed integrally with, one edge 1 2a of a planar component 1 2 so that the axis of the cylindrical member 11 extends parallel to the one edge 1 2a of the planar component 12.

An edge of the planar component 12 parallel to the one edge 1 2a is connected by means of a flexible joint 1 3 to an edge of a second similar planar component 1 5. Of course, the first and second planar components 1 2 and 1 5 may be integrally formed, the flexible joint being provided by a weakened region in the integral planar component or third connection member. Alternatively, where the first and second planar components are separate, they may be connected by a fifth bearing, similar to the first and second bearings which allows the planar components 1 2 and 1 5 to pivot relative to one another about the bearing.

An edge 1 7 of the second planar component 1 5 parallel to the one edge thereof is connected, or formed integrally with, a second cylindrical member 18 similar to the cylindrical member 11 so that the axis of the cylindrical member 18 is parallel to the edge 1 7. A third bearing member 1 9 similar to the second bearing member 9 has a first end 1 9a which extends through, and is fixed in, an axial bore formed in the cylindrical member 18. A second end 1 9b of the third bearing member 1 9 is rotatably mounted in a seat 20 formed in a mounting block 21. Again, fluid having a selected viscosity is provided in the mounting block 21 to provide a resistance to rotation of the bearing member 1 9.

One end 22a of a fourth bearing member 22 is fixedly mounted in the mounting block 21. The other end 22b of the fourth bearing member 22 is rotatably mounted in a seat 23 formed in a second connection member 24 connectable, as shown in Fig. 2, to a support surface 25 on which the spring 3 is mounted.

A fluid selected viscosity is provided in the seat 23. The fourth bearing member is arranged to extend in a direction perpendicular to the third bearing member and to be rotatable about an axis extending perpendicularly of the rotation axis of the third bearing member.

As can be seen from Fig. 1, the device is symmetrical about an axis extending along the flexible joint so that the first and fourth bearing member extend parallel to one another and are both responsive to vibrations in the first plane while the second and third bearing members also extend parallel to one another and are responsive to vibrations in the second plane.

The device is thus capable of damping vibrations in three mutually perpendicular planes.

In use of the device, the first connection member 2 is connected to part of the oscillatory system while the second connection member 24 is connected to a surface on which the oscillatory system is supported. In the arrangement shown in Fig. 2, the oscillatory system comprises a spring 3 mounted between equipment 26 to be isolated, such as the turntable of a gramophone, and a support surface 25, such as an internal surface of a casing in which the turntable is disposed. The first connection member 2 is connected, as shown, to part of the spring 3 while the second connection mmber 24 is connected to the support surface 25. Preferably, the first connection member 2 is connected to the spring so that the device is connected across part, for example two-thirds, of the length of the spring to improve the frequency bandwidth.The damping and the frequency bandwidth may be varied by aitering the proportion of the spring spanned by the device.

The device is connected to the spring 3 and the support member 25 so that the first and second planar components 1 2 and 1 5 pivot about the flexible joint 1 3 or further bearing member (not shown) in response to vibrations in a direction parallel to the axis of the spring, that is in response to compression and expansion of the spring.

The first and fourth bearing members 4 and 22 are rotatable in response to vibrations in a first plane perpendicular to the spring axis that is to vibrations in and out and to the left and right in Fig. 2. The second and third bearing members 9 and 1 9 are responsive to vibrations in a second plane perendicular to the plane of the paper and containing the spring axis, that is to vibrations in and out of the paper and to compression expansion of the spring. The flexible joint 1 3 together with the second and third bearing members are responsive to vibrations in the plane of the paper, for example to compression and expansion of the spring 3.

The damping device which can be applied to almost any compliance (spring)/mass system has a wide natural frequency range and three degrees of freedom enabling the device to damp vibrations in three mutually perpendicular planes. Moreover, by adjusting the viscosity of the bearing fluids, the degree of damping can be controlled. Also, the viscosity of the bearing fluids can be varied from bearing to bearing so that the degree of damping in different directions can be varied.

Claims (14)

1. A device for damping vibrations of an oscillatory system, comprising a first connection member connectable to part of an oscillatory system, a second connection member connectable to a surface on which the oscillatory system is mounted, a plurality of bearing members connected between the first connection member and the second connection member, the bearing members being arranged to be responsive to vibrations in a plurality of planes which are not parallel to one another.

2. A device according to Claim 1, wherein the plurality of bearing members comprises a first set of bearing members having a first and a second bearing member responsive to vibrations in a plurality of planes not parallel to one another and a second set of bearing members having a third and a fourth bearing member responsive to vibrations in a plurality of planes not parallel to one another, the first set of bearing members being connected to the second set of bearing members by a joining member.

3. A device according to Claim 2, wherein the first and second sets of bearing members are connected by a flexible member.

4. A device according to Claim 3, wherein the flexible member comprises first and second components connected by a flexible joint.

5. A device according to Claim 2, wherein the first and the second sets of bearing members are connected by a fifth bearing member.

6. A device according to Claim 2, 3, 4 or 5, wherein the bearing members in each set of bearing members are mutually perpendicular and the joining member is parallel to one of the bearing members in each set, the arrangement being such that the device is responsive to vibrations in three mutually perpendicular planes.

7. A device according to any preceding claim, wherein each bearing member is movable against the resistance of a fluid.

8. A device according to any preceding Claim wherein, each bearing member is rotatable in a respective mounting against the resistance of a fluid.

9. A device according to Claim 8, wherein the viscosity of the mounting fluid is variable between the mountings so that, in use, the degree of damping in different directions can be varied.

10. A device according to any preceding Claim, wherein the device is connected across part of a compliant member in an ocillatory system so as to provide a desired damping and frequency bandwidth for the oscillatory system.

11. A device for damping vibrations of an oscillatory system substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.

12. An oscillatory system having a damping device in accordance with any one of the preceding claims.

1 3. Audio reproduction equipment having a mechical vibration isolation in the form of one or more oscillatory systems, the or each oscillatory system incorporating a damping device in accordance with any one of Claims 1 to 11

14. Any novel feature or combinations of features described herein.