GB2189803A

GB2189803A - Electro-rheological fluids

Info

Publication number: GB2189803A
Application number: GB08702381A
Authority: GB
Inventors: Dennis William George Byatt
Original assignee: GEC Avionics Ltd
Current assignee: Allard Way Holdings Ltd
Priority date: 1986-03-26
Filing date: 1987-02-03
Publication date: 1987-11-04
Also published as: GB8702381D0; GB2189803B

Abstract

An electro-rheological fluid comprises a fluid carrier medium such as light transformer oil having suspended therein a quantity of dry microscopic hollow glass particles of which the majority have diameters between 20 and 120 microns and wall thicknesses of between 0.5 and 2 microns. The apparent viscosity of the fluid increases an application of an electrical field.

Description

SPECIFICATION Improvements in or relating to electro-rheological fluids This invention relates to electro-rheological fluids, that is to say fluids which exhibit an apparent change ofviscositywhen subject to the influence of an electric field, and arrangements utilising such fluids.

Electro-rheological fluids essentially comprise a fluid carrier medium in which are suspended particles of material. In operation the viscosity of the fluid may be quite low, so as to flow readily, until subjected to the influence of a relatively high voltage electric field whereupon the apparent viscosity increases considerably so as to increase the resistance of the liquid to shear stress.

Atypical electro-rheological fluid as at present know consists of a light oil (e.g. transformer oil) having suspended therein finely divided solid material (e.g. plastic) with a small quantity of water.

Whilst the underlying mechanism is not presently well understood, it is believed that the water effectively coats the particles of solid material and, with electro-rheological fluids as at present known, plays an important part in the operation.

With all electro-rheological fluids as at present known, there is a tendencyforthe suspended material to separate out. This may be overcome by providing means for ensuring that the fluid is kept in motion (e.g. by pumping or agitation). The necessity to include a quantity of waterwithin the compostion ofthefluid presents a more serious problem since not only does this provide a possible cause of deterioration ofthefluid itself, but also a possible source of corrosion and an increase in the electrical conductivity ofthe field. In certain control systems, the last-mentioned may represent a very serious problem indeed.

The present invention seeks to provide an improved electro-rheological fluid and arrangements utilising the same in which one or more of the above problems are avoided or mitigated.

According to this invention an electro-rheological fluid comprises a fluid carrier medium in which are suspended dry particles of an electrically insulating material capable of responding to an applied electrical field to effect a change in the apparant viscosity of said fluid.

By "dry" is understood a condition in which said particles are not wetted with water before being suspended in said fluid carrier medium nor by any significant quantity of water being introduced into said fluid carrier medium.

In one electro-rheological fluid in accordance with the present invention said electrically insulating material is non-conductive glass. Glass is of course a dielectric material and other dielectric material may be suitable.

Normally said fluid carrier medium is, as known perse, a light oil such astransformeroil.

According to a feature ofthis invention an electro-rheological fluid comprises a fluid carrier medium in which are suspended hollow particles of an electrically insulating material capable of responding to an applied electrical field to effect a change in the apparent viscosity of said fluid.

Preferably said hollow particles are microscopic glass bubbles. In one example said microscopic glass bubbles are provided for introduction into said fluid carrier medium in the form of an aggregate having a size range in which the majority of bubbles have diameters between 20 and 100 microns and wall thicknesses of between 0.5 and 2 microns.

Said insulating material may substantially alone be suspended in said fluid carrier medium. However, it may be that satisfactorily low electronical conductance with an improved response time may be achieved by including with said insulating material, semiconductor material, and more particularly organic semiconductor material, for example in substantially equal parts by volume.

The invention is illustrated in and further described with reference to the accompaning drawings of which Figure 1 illustrates in a highly schematic manner and by a section, part of a simple control system utilising an electro-rheological fluid in accordance with the present invention and Figure2 similarly illustrates part of a printed circuit board test apparatus utilising an electro-rheological fluid in accordance with the present invention.

Referring to Figure 1, the mechanical components of the arrangement comprise a piston 1 connected to drive rod 2 (which in turn may be connected to actuate a mechanism, not shown). The piston moves within a cylinder3 of which the wall is formed in part by two opposing electrodes 4 and 5. Apart from the electrodes 4 and 5, the cylinder 3 is of electrically insulating material.Theelectrodes4and5are connected to terminals 6 and 7 across which may be applied a high d.c. voltage, in this case ofthe order of 6KV.

Piston 1 is moved, as knownperse, by compressing a fluid 8 within the cylinder 3. The fluid 8 is an electro-rheological fluid in accordance with the present invention and consists of a light transformer oil into which is suspended a quantity of dry microscopic glass bubbles of which the majority have diameters between 20 and 120 microns and wall thicknesses of between 0.5 and 2 microns. The fluid contains no, or at least no significant, amount of water.

The distance separating the two electrodes 4 and 5 isoftheorderof2mm,inthisparticularexample.

When the piston 1 is moved to its disired position as illustrated, with the electrodes 4 and 5 unenergised and thus the viscosity of the fluid relatively low and relatively free flowing, the electrodes 4 and 5 are energised by applying a d.c.

voltage of the order of 6KV to the terminals 6 and 7.

This establishes an electric field between the electrodes 4 and 5 which causes the viscosity ofthe liquid 8 to increase markedly. The shear strength of the liquid between the electrodes 4 and 5 with the field established approaches that of a solid and the piston 1 is thus held in position until the field is removed.

The piston may be returned to its original position by gravity or by means such as a spring (not shown), as known perse.

Referring to Figure 2, the printed circuit board test apparatus illustrated comprises a metal block 9 which is connected to a mechanical drive (not shown). At desired points, the block 9 is bored through with 2mm diameter holes 1 Oto form a number of 2mm diameter cylinders. Individual push rods 11, of diameter 1 mm, are supported concentrically within each cylinder by bearing plates 4,5. Each push rod 11 is connected to actuate a different mechanism (not shown).

The bearing plates 12,13 are of electrically insulating material whilst the push rods 11 and cylinders 10 are ofelectrically conductive metal.

Thusthepush rods 11 and cylinders 10form opposing electrodes which are connected across a high d.c. voltage source, in this case of about 1 KV.

Every cylinder 10 is connected to one side ofthe d.c. supply source by a single connection 14, made to the metal block 9. The push rods 11 are individually connected to the other side of the d.c. supply via slip rings 15 and electrical switches 16.

The gap between each push rod and its associated cylinder wall is 0.5mm and is filled with an electrorheological fluid 17 in accordance with this present invention. In this case the electro-rheological fluid 17 consists of a light transformer oil into which is suspended a quantity of dry microscopic glass bubbles of which the majority have diameters of between 20 and 120 microns and wall thicknesses of between 0.5 and 2 microns.

Without any voltage being applied, that is to say with all of the electrical switches 16 open, the viscosity ofthe fluid is such thatthe forces acting upon the push rods 11 by the movement, represented bydouble-headedarrowl8,ofthe cylinder block 9 are insufficientto overcome the bearing friction. The application ofthe high potential across a push rod cylinder pair bythe closing of the appropriate electrical switch 16 increases the ability ofthefluid contained in the respective cylinder 1 Oto withstand shearing forces to such an extentthatthe respective push rod 11 becomes mechanically attached to the metal block and will follow its movements to actuate the aforementioned respective mechanism to which the push rod is connected.

Claims

1. An electro-rheological fluid comprising a fluid carrier medium in which are suspended dry particles of an electrically insulating material capable of responding to an applied electrical field to effect a change in the apparentviscosity of said fluid.

2. Afluid as claimed in claim 1 and wherein said electrically insulating material is non-conductive glass.

3. Afluidasclaimedinclaiml or2andwherein said fluid carrier medium is, as knownperse, a light oil such as transformer oil.

4. An electro-rheological fluid comprising a fliud carrier medium in which are suspended hollow particles of an electrically insulating material capable of responding to an applied electrical field to effect a change in the apparent viscosity of said fluid.

5. Afluid as claimed in claim 4 and wherein said hollow particles are microscopic glass bubbles.

6. Afluid as claimed in claim 5 and wherein said microscopic glass bubbles are provided for introduction into said fluid carrier medium in the form of an aggregate having a size range of which the majority of bubbles have diameters between 20 and 100 microns and wall thicknesses of between 0.5 and 2 microns.

7. A fluid as claimed in any ofthe above claims and wherein said insulating material is substantially alone suspended in said fluid carrier medium.

8. Afluidasclaimedinanyofclaims 1 to 6 and wherein semiconductor material is included with said insulating material in said suspension.

9. Afluid as claimed in claim 8 and wherein said semiconductor material is included with said insulating material in said suspension in substantially equal parts by volume.

10. A control or actuating apparatus including electro-rheological fluid as claimed in any ofthe above claims.

11. An apparatus as claimed in claim 10 and comprising a printed circuit board test apparatus.