GB2205920A - Anti-vibration mounting - Google Patents

Abstract

An anti-vibration mounting linking a payload (1) to a support (2) includes an electro-rheological fluid (9). The viscosity of this fluid at a region between electrodes (14, 15) is varied between a first, relatively high, value when it is desired to limit the amplitude of movement of the payload (1) and a second, relatively low, value when it is necessary to prevent shocks being transmitted from the support to the payload. The charge required for the electrodes (14, 15) and for a vibration amplitude detector (18, 19) can be provided by a piezo-electric element (16) which is stressed by movement of the payload (1) relative to the support (2). <IMAGE>

Description

Anti Vibration Mounting This invention relates to anti vibration mountings Typically such mountings are used between å payload which is to be protected from vibration and a mounting which vibrates. Generally this vibration will vary unpredictably over a wide range of frequencies and amplitudes.

A problem with such mountings is that they must compromise between providing high damping in order to prevent oscillation of the payload at the resonant frequency of the system and low damping to prevent shocks being transmitted from the supporting structure to the payload.

This invention provides an antivibration mounting resiliently linking a payload to a supporting structure and capable of altering the degree of damping in this linkage and including an electro-rheological fluid the degree of damping of the linkage being switched between a first, high, state and a second, low, state by switching (as herein defined) of the viscosity of the electrorheological fluid between corresponding first, high, and second, low, states.

The switching of the viscosity of the electrorheological fluid should be taken, in this specification, as meaning the changing of its viscosity from one value to another by any means.

In another embodiment this invention provides apparatus comprising two members which are subject to relative movement which varies between relatively fast and relatively slow speeds a chamber having a volume which changes with such movement, an electreological fluid in the chamber, and means allowing restricted flow of the fluid to and from the chamber to create a damping effect characterised in that means are provided for applying a potential to the fluid of a value such that it is relatively viscous during the slow movement but not during the fast movement.

This gives the advantage that the system can normally be set to give a high level of damping between the two members, keeping the amplitude of their relative movements low but if one member is subject to a sudden shock the damping will drop to a low level, decoupling the two members and preventing the shock from being transmitted between them.

Yet another aspect of the invention provides apparatus for providing a damping effect between two members comprising a chamber which changes its volume with relative movement between the members, electro-reological fluid in the chamber, means allowing restricted flow of the fluid to and from the chamber to create the damping effect, means for supplying a potential to the fluid to make it adapt a relatively viscous state, sensing means for sensing a property of the movement, and means for indicating such switching in response to an output of the sensing means.

Such a system provides the advantage that no external power source is needed and that the damping between the two members can normally be kept low, preventing vibration being transmitted between them, while if the amplitude of their relative movement becomes too great the damping can be raised.

A preferred embodiment of the invention will now be described with reference to the accompanying drawings in which; Figure 1 shows a first embodiment of the invention in schematic form and; Figure 2 shows a second embodiment fo the invention in schematic form, identical reference numerals being used for identical parts throughout.

Refering to Figure 1, a payload 1 which is sensitive to vibration is linked to a support 2 by some mechanical arrangement represented by a spring 3.

The payload 1 is linked to a diaphragm 5, and as the payload 1, moves relative to the support 2 it changes the volume of a sealed chamber 4 defined in part by the diaphragm 5. As the volume of the chamber 4 changes oil 6 is forced in and out of it along a pipe 7, moving a piston 8 along the pipe 7.

This movement of the piston 8 causes an electrorheological fluid 9 to be pumped in and out of a resevoir 10. In order to do this the electro-rheological fluid 9 must pass through a section of the pipe 7 across which an electric field is applied by two electrodes 11 and 12 powered by a D.C. power source 13.

This electric field causes the viscosity of the electro-rheological fluid to become relatively high in the regions where the field is applied.

So as the support 2 vibrates the movement of the viscous electro-rheological fluid 9 between the electrodes 11 and 12 produces heavy damping and so prevents any large movements of the payload 1. If, however, a sudden shock affects the support 2 the shear force exerted on the electro-rheological fluid will be so great that the fluid will "break", its viscosity dropping immediately to a relatively low value, thus de-coupling the movements of the payload 1 from the movement of'the support 2, dropping the damping to a low level and preventing the shock from being transmitted to the payload 1. When the shock has passed the electro-rheological fluid 9 will recover back to its normal, relatively viscous, condition in the region to which an electric field is applied.

Figure 2 shows apparatus similar to that shown in Figure 1 except that normally no voltage is applied to the electro-rheological fluid 9 between the electrodes 14 and 15 and so the electro-rheological fluid 9 normally has a relatively low viscosity. As a result the payload 1 is normally decoupled from the support 7 so shocks and movement affecting the support 2 are not transmitted to the payload 1.

This low damping means that the vibrations of the base 2 could drive the payload 1 to very large amplitude movements if the vibrations were near the resonant frequency of the system.

The mechanical arrangement includes, in addition to the spring 3, a piezo-electric element 16. As the payload 1 moves relative to the support 2 the piezo-electric element 16 is deformed and so generates a differential voltage, this electrical charge generated by the piezoelectric element 16 is stored in a capacitor 17.

The electric charge stored in the capacitor 17 is used to power a light emitting diode (L.E.D.) 18 and a photodiode 19. The L.E.D. 18 produces a beam of light which falls on the photodiode 19, causing it to pass current, this current passes through a relay 20, preventing it from closing. If the payload 1 moves with a larger than acceptable amplitude at one end of its travel it will block the light from the L.E.D. 18. going to the photodiode 19, as a result current through the photodiode 19 will drop and the relay 20 will close.

When the relay 20 closes it allows the voltage and charge stored in the capacitor 17 to be applied between the electrodes 14 and 15 on either side of the electrorheological fluid 9 in the pipe 7, causing the viscosity of the electro-rheological fluid to go to a relatively high value, increasing the damping between the payload 1 and support 3 to the critical damping level and thus stopping the oscillations of the payload 1. After a short time interval determined by the construction of the relay 20 and sufficient to allow the payload to settle, the relay 20 changes back and the ER fluid returns to its low viscosity state. If a sudden shock affects the support 2 while the electro-rheological fluid 9 is held in its high viscosity state the electro-rheological fluid 9 will behave as described with reference to Figure 1 and drop to a low viscosity state, isolating the payload 1 from the support 2.

Claims (10)

1. An antivibration mounting resiliently linking a payload to a supporting structure and capable of altering the degree of damping in this linkage and including an electro-rheological fluid the degree of damping of the linkage being switched between a first, high, state and a second, low, state by switching (as herein defined) of the viscosity of the electro-rheological fluid between corresponding first, high, and second, low states.

2. An antivibration mounting as claimed in claim 1 in which in use the electro-rheological fluid has an electric field applied to it continuously, keeping the electrorheological fluid's viscosity and the damping of the linkage high and where, if a shock larger than some predetermined value is applied through the supporting structure, the viscosity of the electro-rheological fluid drops to a low level, making the damping lighter and so preventing the shock being transmitted to the payload.

3. An antivibration mounting as claimed in claim 1 in which, in use, the electro-rheological fluid normally has no electric field applied to it and so the electrorheological fluid's viscosity and the damping of the linkage are low, and where, if the amplitude of vibration of the payload becomes larger than some predetermined value an electric field will be applied to the electrorheological fluid raising the viscosity of the electrorheological fluid and the damping of the linkage to a high value and so reducing the amplitude of vibration of the payload.

4. An antivibration mounting as claimed in claim 3 in which the charge used to produce an electric field across the electro-rheological fluid is generated by the stress produced in a piezo-electric device forming a part of the linkage between the payload and the supporting structure by the movements of the payload.

5. An antivibration mounting as claimed in claim 3 and including a light emitting diode and a photodetector arranged so that when the amplitude of vibration of the payload becomes larger than said predetermined value a part of the payload or some object connected to the payload crosses the path of light travelling between the light emitting diode and the photoconductor.

6. An antivibration mounting as claimed in claim 5 in which the photodiode and photodetector are supplied with electricity generated by the stress produced in a piezoelectric device forming a part of the linkage between the payload and the supporting structure by the movements of the payload.

7. Apparatus comprising two members which are subject to relative movement which varies between relatively fast and relatively slow speeds, a chamber having a volume which changes with such movement, an electro-rheological fluid in the chamber, and means allowing restricted flow of the fluid to and from the chamber to create a damping effect charaterised in that means is provided for applying a potential to the fluid of a value such that it is relatively viscous during the slow movement but not during the fast movement.

8. Apparatus for providing a damping effect between two members comprising a chamber which changes its volume with relative movement between the members, electro-rheological fluid in the chamber, means allowing restricted flow of the fluid to and from the chamber to create the damping effect, mean for supplying a potential to the fluid to make it adapt a relatively viscous state, means for sensing a property of the movement, and means for indicating such switching in response to an output of the sensing means.

9. An antivibration mounting substantially as shown in Figure 1 of the accompanying drawings and substantially as described with reference thereto.

10. An antivibration mounting substantially as shown in Figure 2 of the accompanying drawings and substantially as described with reference thereto.