PIEZO CERAMIC BENDER AND VALVE INCORPORATING SAME

Abstract: A fluid valve comprising a valve body having a chamber, means for introducing fluid into the chamber at least one outlet port and a valve member for controlling fluid flow through the outlet port, characterised in that the valve member is a piezo ceramic bender having an arcuate shape and the chamber is of a co-operating arcuate shape with the or each outlet port being located in an arcuate wall of the chamber (12) whereby fluid flow through the outlet port is controlled by changing the diameter of the piezo ceramic bender.

Description: PIEZO CERAMIC BENDER AND VALVE INCORPORATING SAME The present invention relates to a piezo ceramic bender and a valve using such a bender as a valve member. The use of piezo ceramic cantilevers and other forms of bender for the manufacture of low pressure pneumatic valves is known. In these systems cantilever beams of various descriptions are used to cover and uncover a port with either a nitrile rubber or high or low stiffness neoprene. The primary disadvantage of such devices is that thev are unable in general to work at the normal pressure of the mains pneumatic system, which is typically 10 Newtons per mm 2 or 10 Bar. In order to use such valves, pressure reduction and fine filtering is required, making them prohibitively expensive. Where valves of sufficient strength are available to provide the operation at mains pressure the type of cantilever bender used is itself inherently expensive costing several tens of pounds. It is clearly desirable to combine high operating forces with low cost means of actuation. Traditional piezo ceramic fabrication involves the forming of a net shape through a pilling or coining process thus creating a material which is friable. that is subject to fracture if flexed or deformed. Recent advances in the manufacture of piezo ceramics have made it possible to create an initial stage material that is flexible and mouldable in the manner of a resinous plastic. According to the present invention there is now described a means of using the benefits of this technology to form a simple valve that is low cost and capable of controlling high operating pressures. In order that the present invention be more readily understood, an embodiment thereof will now be described by way of example with reference to the accompanying drawings, in which:- Figure 1 shows an exploded view of a valve according to the present invention; Figure 2 shows a perspective view of part of the valve shown in Figure 1 : and Figure 3 shows a sectional side view taken along the line A-A shown in Figure 2. Before describing a valve in detail, it is thought necessary to describe one of forming the piezo ceramic bender used in the valve. According to the present invention there is formed an extruded arcuate section of piezo ceramic material. The section is an arc of a circle but not exclusively of a diameter of approximate!}' 15mm and this extrusion is cut into it to give it an axial length of between 3 and 7mm although not exclusively. Ideally, the arc of the section extends over more than 270° but an C-section could be used. The parts. as part of their manufacturing process, are fired upon a retaining former and have a typical thickness of approximately 150-400 microns (0.15-0.4mm). After the firing process the parts are allowed to cool and are then given electrodes on their large surfaces prior to being poled in the traditional manner associated with piezo ceramics which is well known and does not require any further description here. The C-shaped ceramic is now fragile. A substrate of a material having the same co-efficient of expansion as the ceramic, preferably but not exclusively an alloy known as A42 having an expansion co-efficient of 4.2 x 10 "!: metres per meter per C C is formed to cover the ceramic on either its inner or outer surface but not to overlap it at any point. The benefit of being an exact fit particularly in the width is the elimination of pinning strains that will reduce deflection of the finished actuator. Depending upon the nature of the actuator, a former is made and for the purposes of description it is assumed in this case that the substrate is placed on the outside of the ceramic as this is the preferred embodiment. The former is substantially annular but has an internal diameter marginally less than the external diameter of the ceramic C-section. The substrate is firstly placed into the annular former and the ceramic part is then coated with conductive adhesive before being dropped into the former. In order to fit the ceramic into the former it must be compressed slightly. This is done using a vacuum or similar assembly system to minimise localised stresses. When the compression is released the ceramic presses against the substrate and a suitable inflatable ring or similar is used to press the ceramic and form a smooth continuous line of adhesive. After curing the ceramics assembly can be removed and will be found to change its diameter upon the application of a voltage. Specifically as the ceramic shrinks in its length when excited the diameter will reduce when the part is subjected to an electrical field. The amount of shape change will depend upon the precise dimensions and chemical composition of the ceramic and metal parts but by way of example using specific material a change of diameter of approximately 0.05-0.075mm will be achieved with a 15mm ring. Further details of forming a suitable actuator are given in EP-A- 018345. EP-A-288208 and EP-A-441528. The bender formed as described above can be used as an actuator for an annular valve and this will now be described in relation to the attached drawings. A fluid valve 10 comprises a valve body 1 1 provided with an annular chamber 12 having an internal diameter of approximately 14.5mm (for the 15mm actuator) and concentric with this surface a solid core 14 having an outside diameter which is equivalent to the internal diameter of a ceramic actuator 16 when placed in the annulus minus approximately 0.15mm. To retain and orientate the piezo actuator, there is provided a septum portion 17 between the annulus outer and inner portions, such that the chamber is now in the form of a C. The chamber 12 preferably is an arc of a circle extending over the same portion of a circle, eg more than 270 °. as the actuator 16 but may be slightly larger. A radial bore 20 is provided through the septum portion that passes from the outer face of the valve body to the centre. At a suitable point for the construction, a second port is created which penetrates this radial bore 20 and allows fluid to flow to the surface of the construction and on the top surface is also provided to a port 21 or channel to bring that fluid into the annular chamber. Diametrically opposite the septum 17 is provided a further set of ports 22. 23 w hich penetrate both the inner core 14 and the outer portion of the valve body 1 1 and communicate with respective bores 24. 25 through the body 1 1. The ceramic actuator 16 is coated on both sides with a thin layer of low shore hardness elastomer such a silicon neoprene or nitrile rubber. It can be seen from the diagrams that when the piezo actuator 16 is in its unexcited state it exerts a radial force upon the outer portion of the annular chamber sealing the port 23 with respect to the air-flow entering via the port 21. Upon excitation the ceramic actuator 16 contracts to change its diameter and exposes the port 23 to the outside but covers the port 22. thus control of two ports can be achieved through the excitation of this actuator. The pressure and sealing force of the system can be improved by having a multiplicity of such actuators placed sided by side preferably connected in a single piece of metal. Further control can be achieved to create manifolds and similar by nesting together actuators having different diameters. Binary operations can be achieved by eliminating one of the ports 22, 23. The preferred fluid is air. Differential exposure of the orifices can be achieved by varying the voltage applied to the actuator. Force may also be increased by linking a quantity of actuators of changing diameter and the independent location of tw o actuators one for the outer annulus and one for the inner will permit isolation and opening of one or both ports under independent control to provide the maximum flexibility .

Claims: CLAIMS: 1. A fluid valve comprising a vah e body ( 11 ) having a chamber ( 12). means for introducing fluid into the chamber ( 12 ) at least one outlet port (22.23 ) and a valve member ( 16) for controlling fluid flow through the outlet port, characterised in that the valve member ( 16) is a piezo ceramic bender having an arcuate shape and the chamber is of a co-operating arcuate shape with the or each outlet port (22.23) being located in an arcuate wall of the chamber 12 whereby fluid flow through the outlet port is controlled by changing the diameter of the piezo ceramic bender. 2. A fluid valve according to claim 1. wherein the chamber ( 12) and valve member ( 16) are substantially annular, extending over more than 270 ° of arc. 3. A fluid valve according to claim 2, wherein the valve body is provided with a plurality of fluid passageways (20.24,25) which penetrate the body through a septum (17) formed by the substantially annular chamber. 4. A fluid valve according to claims 1. 2 or 3. where the valve member (16) is formed by a ceramic material on a substrate having the same co-efficient of expansion as the ceramic. 5. A fluid valve according to claim 4. wherein the valve member is coated in at least one arcuate surface with an elastomer for sealing the outlet port.

Inventors: POWELL SIMON, POWELL, SIMON
Applicants: PBT IP LTD, POWELL SIMON, PBT (IP) LIMITED, POWELL, SIMON
Application year: 2000
Main classification: F16K31
IPC codes: F16K31