GB2234319A

GB2234319A - Vibration dampers and vibration-damped centrifuge suspension

Info

Publication number: GB2234319A
Application number: GB9012653A
Authority: GB
Inventors: Karl Heinz Roemer
Original assignee: Sigma Laborzentrifugen GmbH
Current assignee: Sigma Laborzentrifugen GmbH
Priority date: 1989-07-11
Filing date: 1990-06-06
Publication date: 1991-01-30
Anticipated expiration: 2010-06-06
Also published as: GB2234319B; FR2649770B1; FR2649770A1; GB9012653D0; DE3922744C2; DE3922744A1

Abstract

A vibration damper includes a rod-like piston 2 and spaced fluid chambers 7, 13 in communication by means of the piston guideway 17 and a bore 15, thus determining the damping characteristics. The piston is provided with a disc 9 to seat a spring 10, which determines spring characteristics of the device. The damper may be used in a centrifuge mounting and such mounts using separate springs and dampers are envisaged. <IMAGE>

Description

1'1 1 VIBRATION DAMPERS AND VIBRATION -DAMPED CENTRIFUGE SUSPENSION The

invention relates to vibration dampers and is 5 also concerned with vibration-damped centrifuge suspensions.

The vibration-damped suspension of centrifuges is fundamentally known. The known systems however have a number of disadvantages which are in part of a constructional nature and in part are concerned with the life or endurance of the systems. Thus. vibration dampers are known which are based upon the use of rubber as damping material, in which springiness and damping are exerted by the same material, so that a variation of the springiness independently of the damping is hardly possible from a constructional point of view and is generally not possible at all. In addition to this, metal fibre dampers are known in which the damping depends upon friction between metallic fibres whose life however is limited, since they are subject to a continuous rubbing action. Also, with these metal fibre dampers, springing and damping properties are combined in one common unit, namely a metal fibre bellows, with the result that in the same way there is no possibility or only a completely insufficient possibility of separating the spring and damping properties from one another. On the other side. there is a strong need for a vibration damper whose frequency characteristics can be varied by independent variation of spring parameters and damping parameters.

It is an object of the invention to provide a vibration damper whose vibration characteristics and damping characteristics can be modified in a simple manner, particularly in a constructional way.

i 2 In accordance with the invention there is provided a vibration damper comprising two parts which are movable relative to each other against the action of spring forces and damping forces, in which functional elements are provided for the springing on the one hand and for the damping on the other hand which are separate from each other and which can be dimensioned independently of each other.

It is essential that the vibration damper according to the present invention should have functional elements for springiness on the one hand and for damping on the other hand which are separate from each other and in particular can be dimensioned independently of each other. Consequently, damping and spring properties of the vibration damper are associated with functional elements which are distinct from each other bothin terms of their spatial arrangement and their mode of action. These functional elements can be formulated constructionally independently of each other according to a predetermined characteristic, so that the vibration damper can easily be varied from its basic concept and consequently has wide applicability.

Preferably the said parts comprise a rod-like piston on the one hand and a system having two spaced receiving chambers for a damping fluid on the other hand, wherein one end of the piston projects into one of the receiving chambers, wherein the receiving chambers are in communication by means of a guideway f or the piston and also by means of a bore forming a passage for damping fluid which together constitute damping means, and wherein spring means are provided in at least one of the receiving chambers.

In a preferred embodiment the receiving chambers are connected to each other by means of a hollow 1 f 3 cylindrical member which is constructed for the guidance of the piston, and the said bore extends through the wall of said hollow member.

The design of this embodiment of vibration damper 5 means that this damper consists essentially of two relatively movable parts which serve to secure the damper to machine elements which are to be mounted on one another and relative to one anothei, and which is thus to damp vibration movements which occur. The damping function depends upon the displacement effect exerted by the piston in one of the receiving chambers, which has the consequence of a reverse flow into the other receiving chamber which depends upon a defined flow cross-section of the bore in the hollow member, although it also depends upon the continuous fluid shear in the gap between the piston and its guide in the case of a vibration. Both the dimensions of the aforesaid gap and also the dimensions of the aforesaid bore can be varied in a structurally simple manner, so that, depending upon the viscosity of the damping fluid which is used, the damping parameter of the vibration damper can be calculated within wide limits. Silicon oil is preferred for use as the damping fluid, because its viscosity is very little affected by temperature.

The spring parameters of the vibration damper on the other hand are defined by spring means arranged in at least one of the receiving chambers. The constructional properties of the spring means can have basically any form. A plurality of spring elements could be used in combination in order to vary the spring characteristic. Depending upon the predetermined spring path in combination with the deformation energy stored in the spring means and the spring parameters resulting therefrom, any type of spring can be used, but having regard to the volume given by the receiving chamber.

r 1 4 It is to be understood in particular that the spring properties of the vibration damper should be chosen to be completely independent of the parameters which determine the damping.

Preferably, said one of the two receiving chambers is formed by a cylindrical container to which one of the said parts is fixedly connected, and the other of the two receiving chambers is formed by a member which is connected to both said parts and is 'made of an elastic material which is deformable at least in dependence upon the relative movements of the said parts.

The member may comprise a bead-type rotationally symmetrical hollow member whose respective ends are sealingly connected with the said parts.

This design of the receiving chambers can be particularly easily realised from a constructional point of view. According to this, the one of the two receiving chambers is a component which is fixed integrally with one of the said parts, with the walls of the other receiving chamber being arranged between the two parts and consequently having to be able to be deformed to such an extent that the relative movements of the two parts can be absorbed. For this purpose the last- mentioned receiving chamber is preferably made of a plastics material having suitably high elasticity. A spring effect arising from this plastics material is solely a supporting function to the action of the actual spring means. For the damping, the f low and shear of the damping fluid on the one hand is given by the movement of the piston in the one receiving chamber and on the other hand by the def ormation of the other elastic receiving chamber.

The features of claims 7 and 8 define alternative embodiments of the vibration damper, and indeed are directed towards dampers for tensile and compressive stresses respectively.

The easily dismantlable construction of the vibration damper according to the features of claim 9 enables simple variation of the damping and spring characteristics, particularly by replacement of individual ones of the said functional elements.

It is a further object of the invention to provide a vibration-damped suspension for a centrifuge, particularly a laboratory centrifuge, wherein the system makes it possible easily to change the vibration and damping characteristics by structural changes to the system.

According to one aspect of the invention such a suspension comprises vibration dampers according to the invention arranged to act axially and radially or to act at least partially in directions extending at an inclined angle to the radial or axial directions.

According to another aspect of the invention there is provided a vi brat ion-damped suspension for a centrifuge particularly a laboratory centrifuge, in which separate spring elements and damping elements are provided, and in which said elements are arranged to act axially or radially or to act at least partially in directions extending at an inclined angle to the radial or axial directions.

While in the case of the vibration dampers according to the invention, for the reasons given above, -the damping and spring parameters can be independently set, this can alternatively be achieved by spatially and functionally distinguishable spring elements on the one hand and damping elements on the other hand, which can be individually replaced. Further possibilities for changing the spring characteristics and damping characteristics are 6 available, starting from a direction of action which is either radial or axial, by using an inclined setting for the vibration dampers and/or for spring or damping elements.

A number of embodiments in accordance with the invention will now be described in detail by way of example and with reference to the accompanying drawings. In the drawings:

Fig. 1 is a longitudinal sectional view through a first embodiment of vibration damper in accordance with the invention; Fig. 2 is a longitudinal sectional view through a second embodiment of vibration damper in accordance with the invention; Fig. 3 is a schematic side view of a centrifuge suspension; and, Fig. 4 is a side view of a further embodiment of centrifuge suspension.

The vibration damper according to the invention as shown in Fig. 1 and intended to take up forces exerted in the direction of its longitudinal axis 1 consists essentially of a rod-like cylindrical piston 2 which is inserted slidably in the bore 3 of a comparatively thick-walled hollow cylinder 4 so as to permit a predetermined amount of radial play.

The hollow cylinder 4 is inserted at its one end region 5 into a support member 6 which is provided internally with a receiving chamber 7 for a damping f luid, such as a suitable oil, and with the chamber 7 being in communication with the bore 3 of the hollow cylinder 4. The support member 6 is rotationally symmetrical with reference to the longitudinal axis 1, and is provided at its end remote from the hollow cylinder 4 with a threaded pin 8 by means of which the vibration damper can be connected to another component, 7 which is not shown in the drawing. The connection between the hollow cylinder 4 and the support member 6 can be of any suitable type. It is only necessary that there should be a sufficient sealing between the parts and sufficient resistance to pressure.

The end of the piston 2 which projects into the receiving chamber 7 is provided with a circular disc 9 which is carried by the piston and which is secured to the piston in any suitable manner. The circular disc 9, and in particular its annular surface which projects radially beyond the piston 2, serves as a seat for one end of a spring 10 whose other end is seated against the annular face of that end of the hollow cylinder 4 which projects into the receiving chamber 7.

The end of the piston 2 which is remote from the circular disc 9 projects out of the hollow cylinder 4 and is formed at its end portion as a threaded pin 11 by means of which this end of the vibration damper can be secured to a machine component which is to be damped.

The end of the hollow cylinder 4 remote from the support member 6 is encircled by a sealing cuff 12 of an elastic plastics material which defines a rotationally symmetrical receiving chamber 13 for the said damping fluid. The end of the sealing cuff remote from the hollow cylinder 4 is fitted to a cylindrical closure member 14 which is secured to the piston 2. The closure member 14, in the illustrated position of movement of the piston 2 in which the circular disc 9 is in contact with the bottom of the receiving chamber 7, is spaced from the adjacent end of the hollow cylinder 4 which faces the closure member. Both the hollow cylinder 4 and also the closure member 14 are a push fit in the respective ends of the sealing cuff 12. The securement of the sealing cuff to the closure 1 i 1 8 member 14 and to the hollow cylinder 4 can be of basically any type, so long as it gives a sufficient sealing action. The sealing cuff 12, in the illustrated position of the piston 2, projects in the radial direction beyond the contour of the hollow cylinder 4 as well as of the closure member 14.

At 15 is indicated a bore which runs within the wall of the hollow cylinder 4 and which extends parallel to the longitudinal axis 1. This bore provides a connection between the receiving chambers 7 and 1 3 for the passage of the damping f luid therebetween.

The vibration damper shown in Fig. 1 and illustrated there in its relaxed state is intended to accept tractive forces, so that, in the mounted state. the piston is displaced from the illustrated position in the direction of the arrow 16, parallel to the longitudinal axis 1. In this displaced state, the exact position of which is determined by the characteristics of the spring 10, the vibration damper can perform movements of the piston 2 relative to the combination of hollow cylinder 4 and support member 6, in the direction of the longitudinal axis 1. Between the outside of the piston 2 and the inside of the bore 3 there is an annular gap 17 which forms a connecting passage between the receiving chambers 7 and 13 for the movement of damping fluid so that the two chambers and the gap are continuously filled with damping fluid. In the case of an oscillation about the aforesaid displaced position of the piston, a continuous shearing of the damping fluid takes place within the said gap 17, since the walls defining the gap are moved relative to each other. By virtue of the shearing, depending upon the viscosity of the damping fluid which is used, frictional and damping forces occur which are 9 converted into heat. Simultaneously, there occurs, because of the displacement effect caused by the piston 2 in the receiving chamber 7, a reverse f low of fluid through the comparatively small diameter bore 15, in the direction towards the receiving chamber 13 which has the function of an equalising chamber, and also, by virtue of a deformation of the sealing cuff 12, a flow in the contrary direction. namely in the'direction back towards the receiving chamber 7. These flows of fluid through the bore 15 are associated with high frictional losses, because of its comparatively small diameter, in dependence upon the viscosity of the damping fluid used, so that a damping effect consequently also results from this.

It will be appreciated that the damping effect of the vibration damper according to the invention depends chiefly upon three parameters, namely the viscosity of the damping fluid which is used, and the geometrical dimensions of the gap 17 and of the bore 15. By varying these parameters one can consequently change the damping quantitatively in a simple manner. The example shown in Fig. 1 shows a helical spring by means of which the elastic properties of the vibration damper, particularly its equilibrium position, are determined.

Basically however, one could use any other spring element, particularly combinations of spring elements, by means of which again the spring characteristic and consequently the overall characteristic of the vibration damper, which results from the combination of spring properties and damping properties, can be modified constructionally within wide limits.

The embodiment of vibration damper shown in Fig. 2, in which the components which correspond with those of Fig. 1 are indicated by the respective same reference numbers, differs from the first embodiment only in the 1 r 1 - 49 fact that in the relaxed, i.e. no load, state, the circular disc 9 f itted at the one end of the piston 2 now is in contact with the end-f acing annular surf ace of the portion of the hollow cylinder 4 which projects into the support member 6. The spring positioned in the receiving chamber 7 is consequently, in this position of the piston 2, seated between that face of the circular disc 9 which is remote from the hollow cylinder 4 on the one hand and the bottom surface 18 of the receiving chamber 7 on the other hand. The vibration damper according to Fig. 2 is thus designed to be mounted where the vibration damper is subjected to compression, i.e. forces exerted in the direction of the arrow 19. The method of operation of this vibration damper corresponds substantially to that of the vibration damper described with reference to Fig. 1, so that it is unnecessary to repeat that description.

Fig. 3 shows one example of a centrifuge 20 suspension. The rotor of the centrifuge is indicated schematically at 20. The rotor is mounted for rotation about a vertical axis 23 and is driven from a motor 22 by means of an intermediate shaft 21. The motor 22 for its part is mounted on a base plate 24.

The vibration-damping mounting of the centrifuge system, which is susceptible to oscillations and which consists of the rotor 20, motor 22 and base plate 24, is effected by means of a series of springs or dampers whose directions of action extend radially and axially corresponding to the directions of the forces and moments arising from the operation of the centrifuge. Thus, at the end of the motor 22 adjacent to the rotor 20 there are provided spring elements 25 and damping elements 26 which are separate from each other and which each act in radial directions, whereas in 1 1 contrast the underside of the base plate 24 is supported by vibration dampers 27 whose direction of action extends axially. The spring elements 25, the damping elements 26 and the vibration dampers 27 are arranged at regular intervals around the periphery of the motor 22 and around a circle which is concentric in relation to the axis 23 on the underside of the base plate 24. Instead of the physically separate spring elements 25 and damping elements 26 one could alternatively use vibration dampers 27 which correspond in terms of their structure to the embodiments described above with reference to Figs. 1 and 2. It is essential to the invention however that whether one uses the vibration dampers 27 of the present invention or individual spring elements and damping elements, the spring parameters and damping parameters should be adaptable individually in a constructional way to particular demands of the operation of the centrifuge. These demands are essentially determined by the mass to be damped, the operational speed of rotation, and the critical speed of rotation which results from the interaction of the mass and elasticity of the suspension. In particular, in each case, damping and springiness are variable independently of each other, so that on this basis the vibratable system of the centrifuge can be calculated more simply.

Instead of respective axially or radially acting spring elements, damping elements and vibration dampers, one could alternatively position these at an angle to the axial or radial direction as the case may be. This is indicated by way of example in the region of the vibration damper 27 by the broken lines which indicate a radially inwardly pivoted vibration damper 27' and the a outwardly pivoted vibration damper 27''.

By means of this angular setting in relation to the 0 1 2 true axial or radial direction one can vary the spring characteristics and damping characteristics in a constructional manner with given data for the individual spring elements or damping elements and 5 vibration dampers.

Fig. 4 shows an embodiment of a centrifuge suspension in which the base plate 24 is supported by separate spring elements 28 and dampifig elements 29, 30. The spring elements 28 and the damping elements 29 act axially, and the damping elements 30 act radially. Here again, on the basis of the spatially separate arrangement of springs and dampers, one has the essential feature of simple constructional possibilities for adapting the suspension to desired spring properties and damping properties. Furthermore, in a similar manner to that described in the case of the preceding embodiment, the spring elements and damping elements need not only act radially or axially but can act at an angle to the radial and axial directions. The latter is indicated in Fig. 4 by the broken line illustration of spring elements 28' and 28''.

In a comparable manner, additional damping elements and spring elements can be provided positioned at an angle to the radial or axial directions, whereby one has a further possibility for adjustment of the damping characteristic and spring characteristic of the centrifuge system.

1 13

Claims

CLAIMS:

1. Vibration damper comprising two parts which are movable relative to each other against the action of spring forces and damping forces, in which functional elements are provided for the springing on the one hand and for the damping on the other hand which are separate from each other and which can be dimensioned independently of each other.

2. Vibration damper according to claim 1. in which the said parts comprise a rod-like piston on the one hand and a system having two spaced receiving chambers for a damping fluid on the other hand, wherein one end of the piston projects into one of the receiving chambers, wherein the receiving chambers are in communication by means of a guideway for the piston and also by means of a bore forming a passage for damping fluid which together constitute damping means, and wherein spring means are provided in at least one of the receiving chambers.

3. Vibration damper according to claim 2, in which the receiving chambers are connected to each other by means of a hollow cylindrical member which is constructed for the guidance of the piston, and the said bore extends through the wall of said hollow member.

4. Vibration damper according to claim 2 or 3, characterised in that said one of the two receiving chambers is formed by a cylindrical container to which one of the said parts is fixedly connected, ahd the other of the two receiving chambers is formed by a member which is connected to both said parts and is made of an elastic material which is deformable at least in dependence upon the relative movements of the said parts.

9 14

5. Vibration damper according to claim 4. in which said member comprises a bead-type rotationally symmetrical hollow member whose respective ends are sealingly connected with the said parts.

6. Vibration damper according to claim 4 or 5, in which both the Dart comprising the piston and also the other part comprising the container and the said hollow cylindrical member constitute a system which is rotationally symmetrical with reference to the longitudinal axis. and in which the said parts are provided at their respective axial outer ends with threaded connection means.

7. Vibration damper according to any of claims 4 to 6, characterised in that in the receiving chamber of the said container there is provided a spring which is seated between a disc arranged on the piston on the one hand and the axial end of the hollow cylindrical member which projects into the receiving chamber on the other hand.

8. Vibration damper according to any of claims 4 to 6, in which in the receiving chamber of the container there is provided a spring which is seated between a disc arranged on the piston on the one hand and the bottom surface of the container on the other hand.

9. Vibration damper according to claims 3, 4 and 5, in which the hollow cylindrical member releasably connects together the container which defines the receiving chamber and the bead-type hollow member.

10. Vibration-damped suspension for a centrifuge, particularly a laboratory centrifuge, comprising vibration dampers according to any of the preceding claims, in which the vibration dampers are arranged to act axially and radially or to act at least partially in directions extending at an inclined angle to the C is radial or axial directions.

11. Vibration-damped suspension for a centrifuge, particularly a laboratory centrifuge, in which separate spring elements and damping elements are provided, and in which said elements are arranged to act axially or radially or to act at least partially in directions extending at an inclined angle to the radial or axial directions.

12. Vibration-damped suspension according to claim 10, comprising vibration dampers in combination with separate spring elements and damping elements, in which these are arranged to act axially or radially or to act at least partially in directions extending at an inclined angle to the radial or axial directions.

1 3. A vibration damper substantially as hereinbefore described with reference to the accompanying drawings..

14. A vi brat i on-damped suspension substantially as hereinbefore described with reference to the accompanying drawings.

Published 1991 at 7be Patent Office. State House, 66/71 High Holborn, London WClR4TP. Further copies Tnay be obtained from Sales Branch. Unit 6. Nine Mile Point, Cwmfelinfach. Cross Keys, Newport, NPI 7HZ. Printed by Multiplex techniques ltd. St Mary Cray. Kent.