GB2240083A - Actuator - Google Patents

Abstract

Actuator of the artificial muscle type has first and second tensile substrates (2, 4), each made of a relatively inelastic material such as carbon ribbon, arranged to extend spaced from and substantially parallel to each other. A compressive structure (6) is supported between the two substrates (2, 4) to define an individual cell of the actuator. This compressive structure (6) includes two substantially identical compressive blocks (8), arranged between, and carried by, the two substrates (2, 4) to define a passageway (10), which communicates at its ends with an articulation cavity (16). A plurality of the cells are embedded in an elastically deformable matrix (20) such that when pressure is applied thereto in sequence, digitally incremented shape changes can be made in the actuator. The actuator forms a composite structure. A number of such cells can be confined to form a flexible arm or tentacle e.g. for prosthesis. The tentacle has the cells connected to an articulated spine structure. <IMAGE>

Description

A COMPOSITE The present invention relates to a composite.

WO 88/08620, the disclosure in which is incorporated herein by reference, describes an elongate element which in its preferred embodiment is formed from two prestressed layers. The prestressing is arranged to be in opposition so that the element forms a tube which is structurally rigid, but yet which can be wound into a coil in which state it is stable.

WO 89/05892, the disclosure in which is incorporated herein by reference, extends the original concept and provides elements which exhibit structural rigidity in more than one configuration. In the preferred embodiments, a plurality of compressive blocks are stitched to a tensile layer which is relatively inelastic such that if the tensile layer is placed under tension and the compressive blocks are placed under compression, the element will exhibit considerable structural rigidity.

Copending application No. 8916494.1, the disclosure in which is incorporated herein by reference, describes a composite comprising a substrate which is arranged to be relatively inelastic along one or more lines extending within the substrate, and a compressive layer affixed to said substrate, wherein said compressive layer comprises a plurality of elements embedded, but movable, within an elastically deformable matrix.

If the substrate is bent to place the substrate under tension, and to compress the compressive layer, the plurality of embedded elements allow this bending by moving together until they contact, and subsequently compact, at which stage great structural rigidity is exhibited.

For example, the substrate may be a web of a relatively inelastic material, being formed of high tensile fibres such as fibres of carbon, glass or kevlar. The compressive layer may comprise a plurality of even round hard beads within the elastically deformable matrix. The beads may be formed of sintered metals, ceramics, high compression plastics, or graphite reinforced acetyl.

The present invention seeks to extend the original concept of a composite comprised of both compressive and tensile elements.

According to the present invention there is provided a composite comprising a first substrate arranged to be relatively inelastic along one or more lines extending within the substrate, one or more compressive structures arranged to change shape under pressure, and an elastically deformable matrix.

In a preferred embodiment, the or each said compressive structure is affixed to said first substrate, and the or each said compressive structure is embedded within said elastically deformable matrix.

Preferably, the or each said compressive structure is provided with one or more internal cavities or passageways for the application of internal pressure to the structure by hydraulic or pneumatic pressure. In a preferred embodiment, each compressive structure comprises a plurality of compressive elements contiguously arranged whereby said cavities or passageways are defined between adjacent ones of said elements.

In a preferred embodiment at least one further substrate is provided and is arranged spaced from said first substrate, and wherein a plurality of compressive elements are affixed to each said substrate and are arranged contiguous to one another to define said compressive structures.

In a preferred embodiment two spaced substrates are provided and are arranged to be inelastic along two substantially parallel lines, each composite structure comprising a first compressive block affixed to said first substrate and a second compressive block affixed to said second substrate whereby the two compressive blocks define a compressive structure having a passageway extending therethrough. Preferably, hinge means are provided which extend through each of said substrates and through each of said compressive blocks of each structure. In this embodiment a cavity for hydraulic or pneumatic pressure is defined by the two blocks and is arranged to extend substantially transversely to the lines of inelasticity of the two substrates.

The or each substrate may be a web of a relatively inelastic material. For example, the web may be formed of high tensile fibres. These fibres may be of carbon, glass or kevlar.

Alternatively, the or each substrate may comprise a plurality of bands of relatively inelastic material, such as bands formed from fibres of carbon, glass or kevlar. With most embodiments the bands of each substrate will be arranged to extend substantially parallel to one another.

It would also be possible for the or each said substrate to be formed of spring metal or mesh or of other inelastic ribbon material.

Each compressive structure may comprise one or more hard beads or blocks of appropriate size and shape. The beads or blocks, for example, may be formed of sintered metals, ceramics, high compression plastics, or graphite reinforced acetyl.

In one embodiment, the compressive elements comprise fibres extending substantially parallel to the longitudinal extent of said substrate. The cross-sectional shape of these fibres could be chosen as required, but would generally be circular. Again, the fibres could be of sintered metals, ceramics, high compression plastics, or graphite reinforced acetyl.

Preferably, beads, fibres or other compressive elements and the or each said substrate are embedded in an elastically deformable matrix. The elastically deformable material could be a plastics material or even relatively rigid matrix materials such as epoxy resins and the like.

The composite materials defined can be used to simulate muscular actions. Preferably, a large number of compressive structures are provided in a composite material whereby incremental shape changes can be made to that material. Preferably, valve means are constructed in the material to control the application of pneumatic or hydraulic pressure to individual compressive structures.

The present invention also extends to a tentacle structure comprising a tube of a composite as defined above and an articulated spine extending through said tube, the articulated spine and the tube being connected at discrete points.

Preferably, lines are provided for selectively feeding hydraulic or pneumatic pressure to the composite forming the tube. For example, the lines may extend within the tube and may be supported by said articulated spine.

The pressure to be applied to the composite may be any suitable hydraulic or pneumatic pressure.

Generally, compressed air, or other fluid pressure would be used. In one particular embodiment, the hydraulic fluid is electrorheological.

Embodiments of the present invention will hereinafter be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows a section through a composite of the invention in its unpressurised condition, Figure 2 shows a section through the material of Figure 1 after the application of hydraulic or pneumatic pressure thereto, Figure 3 shows schematically a tentacle structure formed from a composite of the invention, and Figure 4 shows a section through the tentacle.

The composite shown in Figure 1 shows a first tensile substrate 2 made of a relatively inelastic material such as of carbon fibre ribbon. A second tensile substrate 4, also made of a relatively inelastic material is arranged to extend spaced from and substantially parallel to the first substrate 2. A compressive structure, generally indicated at 6 is supported by, and between the two substrates 2 and 4.

In the embodiment illustrated this compressive structure 6 includes two substantially identical compressive blocks 8, each carried by a respective one of the substrates 2, 4, and arranged between the two substrates 2 and 4 such that a passageway 10 is defined therebetween.

In the illustrated embodiment, the compressive blocks 8 are each substantially planar, rectangular blocks whose facing surfaces each have a substantially V-shaped channel 12 extending therethrough transversely of the extent of the passageway 10 and of the longitudinal extent of the substrates 2 and 4. It will also be seen that each transversely extending edge face 14 of each block 8 is inclined relative to its major surfaces whereby an articulation cavity 16 is defined adjacent to the transversely extending edge faces 14 of the two blocks 8. Furthermore, a transversely extending hinge line 18 is provided at each transverse edge of each block 8 by stitching through each substrate 2, 4 and the block 8 which is affixed thereto.

The structure shown in Figure 1 and described so far forms an individual cell of the composite. In this respect, the substrates 2 and 4 are extended longitudinally whereby further cells which are longitudinally aligned can be provided. Additionally, further cells which are transversely aligned may also be provided. In this case, the transverse extent of the substrates 2 and 4 may be formed by the transverse extent of a single ribbon, or a plurality of substantially parallel, aligned ribbons may form each substrate 2, 4. However the individual cells are constructed and aligned, the entire composite is embedded within an elastically deformable matrix 20.

The compressive blocks forming the compressive structure 6 are made of a compressive material such as sintered metal, ceramics, high compression plastics, or graphite reinforced acetyl. The material of the compressive structure 6 and its compressibility, the shapes and sizes of the individual blocks and their spacing can all be selected such that the overall compressibility and the action of each compressive structure under pressure can be chosen as required.

Similarly, the nature of the matrix material 20 can be chosen to suit the required application. For example, a readily elastically deformable plastics material may be used for the matrix, or for higher compressive loads, more rigid matrix materials such as epoxy resins could be employed. Similarly, the number, relative positioning and spacing of the cells formed within the composite can be chosen as is required.

Figure 2 illustrates the manner in which the cell of Figure 1 reacts to the application thereto of internal pressure. In this respect, as the cell of Figure 1 is an individual structure separated from all other cells and completely surrounded by the matrix 20, it is gastight.

It will be appreciated that the transversely extending cavity 12 and the passageway 10 within the cell can be thought of as hydraulic or pneumatic lines to which fluid can be provided under pressure by way of appropriate control valves. If such fluid is applied to the lines of Figure 1, the cell is urged to take up the shape shown in Figure 2 in which the two blocks 8 have been forced apart to effectively increase the depth of the cell, but to decrease its longitudinal extent defined between the two articulation cavities 16. The articulation cavities 16 and the hinge lines 18 assist the cell to take up the particular, predetermined shape shown in Figure 2. If the internal pressure is subsequently removed, the cell will return to its original condition as shown in Figure 1.

It will be appreciated that if a plurality of the cells are provided in a single composite, and pressure is applied thereto in sequence, digitally incremented shape changes can be made in the composite material.

The application of pressure to the individual cells can be controlled by way of any valving system (not illustrated). For example, it would be possible to form control valves within the composite. The control valves could each comprise co-operating valve members having a remembered stable shape in which the valve is in one condition, and movable to a second condition. In said one condition the valve could be open, for example, and in the other condition the valve could be closed. In known manner, the valve members may be formed as sacks containing, for example, an electrorestrictive or electrorheological fluid such that the application of electrical power to the fluid causes the change of state.

After the cell has been pressurised to take up the position shown in Figure 2, it can be relaxed again by the application thereto of a vacuum or by the opposition of other cells. In an alternative embodiment, an elastomer fibre as indicated at A-A can be provided within the cell to tend to pull the cell back into its relaxed condition as shown in Figure 1.

A composite material made from a plurality of the cells shown in Figures 1 and 2 can be used to form the tentacle illustrated in Figures 3 and 4. In this respect, a layer of the composite material, preferably containing only a single layer of the cells in a regular array is formed into a tube indicated at 22. Extending through the tube 22 is an articulated spine 24. This spine 24 may comprise, for example, a plurality of connected compressive discs, and/or interconnected ball and socket joints. At discrete points along the length of the tube 22, the spine 24 is connected to the tube.

For example, this might be by way of power and fluid lines indicated at 26 for the application of electricity and pressure to the tube 22. The electrical power can be used to selectively open and close valves for example, controlled by electrorestrictive, electrorheological or electroviscous fluids, which are arranged within the material forming the tube 22, whereby fluids applied to the fluid lines can be fed to selected cells to pressurise them and thereby change their length. By this means, the tentacle can be shaped substantially as is desired.

Additionally and/or alternatively, local intelligence, for example in the form of chips, could be embedded within the tube 22 to provide extra speed for its response to the applied stimuli.

It will be appreciated that the cells of the tentacle can assume an almost infinite combination of states. Because of this, it may be required to provide an analogue control system comprising a model of the tentacle in which the muscle cells are replaced by pressure transducers. It is the data from the pressure transducers which is then used to initiate control of the real system. For example, a movement manually forced on the model can be used to produce data which can be arranged to cause the same movement in the real system. Additionally and/or alternatively, light pipes, strain sensors and the like can be provided in the tentacle to monitor its movements.

Because of the almost infinite number of shapes which the material can take up, and because it is relatively easy to provide sensors within the material, it will be appreciated that it will find a ready application in prosthetics.

It will be appreciated that modifications and variations to the invention as described above may be made within the scope of this application.

Claims (27)

1. A composite comprising a first substrate arranged to be relatively inelastic along one or more lines extending within the substrate, one or more compressive structures arranged to change shape under pressure, and an elastically deformable matrix.

2. A composite as claimed in Claim 1, wherein the or each said compressive structure is affixed to said first substrate, and the or each said compressive structure is embedded within said elastically deformable matrix.

3. A composite as claimed in Claim 1 or 2, wherein the or each said compressive structure is provided with one or more internal cavities or passageways for the application of internal pressure to the structure by hydraulic or pneumatic pressure.

4. A composite as claimed in Claim 3, wherein each compressive structure comprises a plurality of compressive elements contiguously arranged whereby said cavities or passageways are defined between adjacent ones of said elements.

5. A composite as claimed in Claim 4, wherein at least one further substrate is provided and is arranged spaced from said first substrate, and wherein a plurality of compressive elements are affixed to each said substrate and are arranged contiguous to one another to define said compressive structures.

6. A composite as claimed in any preceding claim, comprising two spaced substrates arranged to be inelastic along two substantially parallel lines, and wherein each composite structure comprises a first compressive block affixed to said first substrate and a second compressive block affixed to said second substrate whereby the two compressive blocks define a compressive structure having a passageway extending therethrough.

7. A composite as claimed in Claim 6, wherein hinge means are provided which extend through each of said substrates and through each of said compressive blocks of each structure.

8. A composite as claimed in Claim 6 or 7, wherein a cavity for hydraulic or pneumatic pressure is defined by the two blocks and is arranged to extend substantially transversely to the lines of inelasticity of the two substrates.

9. A composite as claimed in any preceding claim, wherein the or each substrate is a web of a relatively inelastic material.

10. A composite as claimed in Claim 9, wherein the web is formed of high tensile fibres, for example, of carbon, glass or kevlar.

11. A composite as claimed in any of Claims 1 to 8, wherein the or each substrate comprises a plurality of bands of relatively inelastic material.

12. A composite as claimed in Claim 11, wherein the bands of each substrate are arranged to extend substantially parallel to one another.

13. A composite as claimed in Claim 11 or Claim 12, wherein the bands of each substrate are formed from fibres of carbon, glass or kevlar.

14. A composite as claimed in any of Claims 1 to 8, wherein the or each said substrate is formed of spring metal or mesh or of other inelastic ribbon material.

15. A composite as claimed in any preceding claim, wherein each compressive structure comprises one or more hard beads or blocks of appropriate size and shape.

16. A composite as claimed in Claim 15, wherein said beads or blocks are formed of sintered metals, ceramics, high compression plastics, or graphite reinforced acetyl.

17. A composite as claimed in any of Claims 1 to 14, wherein said compressive elements comprise fibres extending substantially parallel to the longitudinal extent of said substrate.

18. A composite as claimed in Claim 17, wherein the crosssectional shape of the fibres is circular.

19. A composite as claimed in Claim 17 or 18, wherein said fibres are of sintered metals, ceramics, high compression plastics, or graphite reinforced acetyl.

20. A composite as claimed in any preceding claim, wherein said compressive structures and the or each said substrate are embedded in an elastically deformable matrix, and wherein said elastically deformable material is a plastics material or a relatively rigid matrix material such as epoxy resin.

21. A composite as claimed in any preceding claim, for use to simulate muscular actions, wherein a large number of compressive structures are provided in said composite such that incremental shape changes can be made.

22. A composite as claimed in any preceding claim, wherein valve means are constructed in the composite for controlling the application of pneumatic or hydraulic pressure to individual compressive structures.

23. A tentacle structure comprising a tube of a composite as claimed in any preceding claim, and an articulated spine extending through said tube, the articulated spine and the tube being connected at discrete points.

24. A tentacle structure as claimed in Claim 23, wherein lines are provided for selectively feeding hydraulic or pneumatic pressure to the composite forming the tube.

25. A tentacle structure as claimed in Claim 24, wherein the lines extend within the tube and are supported by said articulated spine.

26. A composite substantially as hereinbefore described with reference to the accompanying drawings.

27. A tentacle structure substantially as hereinbefore described with reference to the accompanying drawings.