This invention relates to an electrically controlled flow control valve, and to a matrix of such valves in a sheet of material .

Such valves may have a variety of uses, but one particular use for a matrix of such valves in a sheet, is in a printing process where the matrix of valves are selectively controlled, in a desired pattern, to allow the flow of printing ink through the sheet on to a receiving surface to print a legend on to that surface.

A number of materials have been known which have the property that when they are subjected to an electric field, they suffer a mechanical stress resulting in a mechanical strain or distortion. Such materials have been referred to as being piezo-electric.

Previously known piezo-electric materials have invariably been crystalline in structure and thus comparati ely rigid solid material. Typical applications have been in electrical and mechanical transducers such as microphones and ultrasonic transmitters and receivers.

It has more recently been found that some synthetic polymers can exhibit piezo-electric properties while remaining flexible and comparatively elastic. Such synthetic polymers may be formed into thin flexible films. It is. an object of the present invention to utilise the piezo-electric effect in such polymers in the operation of a fluid flow control valve.

Accordingly, the present invention provides an electrically operated flow control valve comprising a valve member formed of a piezo-electric material and means arranged to apply an electric field to the valve member to cause it to distort selectively to a valve open or to a valve closed position.

The electric field may cause the valve member to extend or contract on the application of said electric field, to such open or closed position.

In one arrangement the application of the field is arranged to cause the valve to move from a closed to an open position while in a second arrangement the application of the field causes the valve to move from an open to a closed position.

In one preferred arrangement, the valve member comprises a sheet of flexible piezo-electric material with a valve aperture in the form of a slit therein, and said means for applying an electric field is arranged so that the application of an electric field causes the sheet to distort, at least locally, to open the valve aperture slit to allow the passage of a fluid, while removal of the field allows the valve aperture slit to close preventing the passage of fluid.

In a variation of that arrangement, the valve aperture may be in the form of an aperture formed in the sheet which allows the passage of fluid in the absence of the field, while the application of the field causes the valve member to distort, at least locally, to close the aperture to prevent the passage of a fluid.

In one preferred arrangement of the means to apply an

electric field, the electric field is applied in the direction of the plane of the sheet of piezo-electric material .

In a further preferred arrangement of the means to apply an electric field, the electric field is applied in a direction transverse to the plane of the sheet of material.

A number of such valves may be arranged in a single sheet of flexible piezo-electric material, and such number of valves may be arranged in a regular matrix over an area of the sheet. In each case means may be provided to selectively open or close the valves in a desired pattern on the sheet.

With such an arrangement the sheet may form a printing sheet, where the desired pattern corresponds to a legend to be printed; and opening of the valves in that pattern, allows the flow of printing ink through the sheet on to a receiving surface to print that legend on it.

The means to apply the electric field to the piezo-electric material may comprise conductors placed on the surface or in the body of the material, to define regions- of the material across which the field is to be applied. Such conductors may be in the form of a programmable matrix of transverse conductors when a number of valves is to be controlled in a sheet of material.

While the above discussion has been related to valves for the control of the flow of fluid or liquid; it should be understood that the invention is not limited to such use, and extends to the control of the passage of light or other radiation, either as a single beam or as a pattern or matrix of beams of such radiation. Further the control of

the size of the valve aperture may be used to modulate a beam of radiation, such as a laser beam, with an electrical signal applied to the valve, either in a digital or an analoged fashion.

A preferred piezo-electric material for use in any of the above arrangements is polyvinylidene fluoride (-CH ₂ CF ₂ -), a thermoplastic fluorocarbon resin, in its form 1 (3eta) crystalline phase.

In order to promote a fuller understanding of the above, and other, aspects of the present invention, some embodiments will now be described, by way of example only, with reference to the accompanying drawings in which:

Figure 1 shows a schematic diagram of a valve embodying the invention;

Figure 2 shows how a number of valves of the embodiment of Figure 1 may be arranged on a sheet of material in a matrix;

Figure 3 shows a schematic arrangement for a printirrg block embodying a number of valves of Figure 1; and

Figures 4A, B and C show an alternative embodiment of a valve of the invention in various stages of its operation.

Figure 1 shows in schematic outline, a fluid flow control valve embodying the invention. The valve member, which is shown in an open position, comprises a sheet of piezo¬ electric flexible polymer material indicated at 10, having a valve aperture 11 formed therein. In the free state of the sheet, that is to say the closed position of the valve, the valve aperture 11 is in the form of a fine closed slit.

When the valve member is moved to its open position, the material of the sheet 10 is distorted on either side of the valve aperture 11, to open it out into the double convex shape shown in Figure 1.

The material of the valve member is so distorted, in operation, on either side of the valve aperture 11, in the regions indicated at A and B, disposed between respective pairs of electrical conductors 12 and 13. The conductors 12 are connected to a negative, or earth rail, 14 whereas the conductors 13 are connected to a positive, or supply, rail 15. Thus when a DC voltage is applied to rail 15, which is positive with respect to the ra l 14, a respective electrical field is established across each of the regions A and B, causing the material of the valve member 10 to contract and thus distort to open the valve aperture 11 to the position shown in Figure 1. On removal of the voltage from the rail 15, the electric fields are removed from the regions A and B, and the material of the valve member 10 returns to its free state allowing the valve aperture 11 to revert to a closed slit.

In an alternative arrangement, the valve aperture 1"r may be in an open condition in the free state of the valve member 10, preferably in the form of an elongated aperture with the two convex sides as shown in Figure 1; and application of a voltage to the rail 15 causes electrical fields in the regions A and B to expand the material of the valve member 10 to close the valve aperture 11 into a closed slit.

Figure 2 shows schematically how a number of valves such as that shown in Figure 1 may be disposed on a sheet of piezo- electric material in a matrix, with a number of common earth or negative rails for groups of valves, each of which has an individual positive or supply rail 15.

A preferred material for the valve member 10 is polyvinylidene fluoride (PVdF) which is a thermo-plastic fluorocarbon resin. This material, when mechanically stretched and then polarised in an electric field, is rendered both piezo-electric and pyro-electric.

Polyvinylidene fluoride is a se i-crystalline polymer which exists in two principle crystalline phases designated form 1 (βeta) and form 2 (alpha). A significant presence of the orientated polar form 1 crystalline material is required in a sample for a high degree of piezo-electric activity. Stretching the material converts the non-polar form 2 phase, which predominates in material extruded from a melt during manufacture of a sheet, to the form 1 crystal!ined stage. The mechanism of piezo-electricity is thought to be a ferro-electric like response based on a net alignment through polarization, of the highly polar carbon-fluorine bond in the form 1 crystalline structure of the material.

Figure 3 shows in schematic outline how a flexible sheet of piezo-electric material, embodying a matrix of fluid valves of the kind discussed with reference to Figures 1 and 2, may be utilised in a device which may be used in the" manner of a conventional rubber-stamp, for stamping a -written legend or a logo on documents. The sheet of material indicated at 20 is formed, as discussed above, with a matrix of fluid valves which are collectively programmed to open by the application of an appropriate voltage to selected conductors in the manner discussed above. An ink- reservoir 21 is provided immediately behind the sheet 20, so that when the sheet 20 is applied to a document or other surface, with the selective valves in the matrix open, ink may be squeezed, for instance by the pressure of application, from the reservoir 21 through the open valve apertures on to the document.

A back-up reservoir 22 for a bulk ink supply may be provided behind the reservoir 21, and connected thereto by a passage or tube 23. The arrangement may be such that the ink in the reservoir 21, and/or the reservoir 22 is constantly under pressure from suitable means, and the valves in the sheet 20 are arranged to open momentarily in the desired pattern, for instance by momentarily connecting the earth rail or negative rail to the appropriate DC supply, to allow ink through to print the legend. In the alternative, the valves may be maintained constantly open by the constant application of the appropriate voltage in the desired pattern; and the pressure to force the ink through the valve on to the document, may be provided by momentary pressure being applied to the reservoir 21, or the reservoir 22, by for instance pressing the device on to the document with a handle (not shown) in the manner of a conventional rubbet—stamp.

Figures 4A, 4B and 4C show an alternative arrangement of a valve element in the sheet of piezo-electric material. In this arrangement, the sheet shown at 30, is provided in a similar manner to the previous arrangement, with a valve aperture in the form of a closed slit 31. Tn this arrangement conductors are placed above and below the sheet 30 with a negative conductor as indicated at 32 below the sheet, and a positive conductor as indicated at 33 above the sheet. By this arrangement, an electric field transversed to the thickness or plane of the sheet 30 may be applied to cause it to contract in thickness as shown in Figure 4B. This will cause the slit aperture 31 to open up in transverse cross-section, as indicated in Figure 4B, to form a cavity, which will be filled with fluid under pressure from above, but which will not necessarily allow the fluid to pass through the aperture 31 to below the sheet 30.

When the electric field is released, as shown in Figure 4C, the slit 31 will revert to its initial closed state, and provided the fluid above the sheet 30 is maintained under pressure, the fluid will squirt out below on closing of the slit as indicated at 34 in Figure 4C. This arrangement can be used to permit the flow of a small measured dose of fluid.

An additional pair of conductors 32 and 33 may be provided on the left-hand side of the slit 31 as seen in Figures 4A, B and C, as well as on the right-hand side as shown, so that the valve member contracts on both sides.

The electrical conductors to operate the valves in a matrix, particularly of the type shown in Figures 4A, B and C, may be arranged in an addressable transverse matrix across the surfaces of the sheet for the selection of valves to be opened.

The arrangement of Figure 4 is particularly suitable for use in a matrix of valves to be used as an ink printing sheet.

Thus it can be seen that the embodiments provide an electrically operated fluid control valve element, which is particularly suitable for arrangement in a matrix of such valve elements in a sheet of material. Such a matrix of valves is particularly suitable for use as a printing sheet or element, but other uses for such a matrix may be envisaged. For instance, a matrix of such valves in a sheet may be used as a controllable filter element for fluids, and it can be envisaged that by the application of variable electric fields to different regions of the sheet, the size of the filter apertures can be varied across the sheet to produce a graduated filter arrangement. Such

filters could be used for filtering gases or liquids.

It is further envisaged that the principle of the invention may also be applied to the control of the passage of light through a sheet of material as opposed to a fluid flow. Thus, it can be seen that if a sheet of opaque material is provided with a matrix of such valves, and the sheet is illuminated from one side, control of the matrix will enable an illuminated pattern to be produced on the other side of the sheet either for direct display; or by transmission, with or without the use of lenses, to be displayed elsewhere. Such a device may find application in a variety of displays, including the display of alpha¬ numeric characters on a screen in computers and other related devices. Further a single valve element when used to control the passage of light, may, if a variable signal is applied to the conductors, be used to modulate a beam of light with that variable signal. In such applications, in some cases the amplitude of movement required of the valve member will be small and thus more rigid piezo-electric materials might be used.