GB2280957A - Surface device configurable by shape memory actuation - Google Patents

Abstract

A configurable surface device (1) comprises a first surface (2) and a second surface (3) having connected therebetween at least one shape memory member (4) which is triggerable from a first state in which it has a first shape to a second shape different to the first, such that, the distance between ends of the shape memory member connected to the surfaces varies to urge the surfaces (2, 3) together or apart to configure at least one of the surfaces (2, 3) from a first configuration to a second configuration. Applications include virtual reality systems, Braille, moulding by applying glued material, and cutting leather. <IMAGE>

Description

A CONFIGURABLE SURFACE DEVICE This invention relates to a device a surface of which may be selectively configured. Such a device may be used for pressing materials into shape, for forming surfaces in computer simulations, or for other purposes.

According to the invention there is provided a configurable surface device comprising a configurable surface, and at least one shape memory member which is triggerable from a first state, in which it has a first shape, to a second state, in which it has a second shape different to the first, the at least one shape memory member being so operatively associated with the configurable surface that triggering of said at least one shape memory member alters the configuration of said surface from a first configuration to a second configuration.

Specific embodiments of configurable surfaces in accordance with the invention will now be described, by way of example only, with reference to the drawings in which: Figure 1 shows a perspective view of a conSigurable surface; Figures 2, 3 and 4 show configurable surfaces of different constructions; Figure 5 shows the variation of length with resistance of a particular memory alloy; Figure 6 shows schematically a control circuit; Figures 7 and 8 schematically show elements of the circuit shown in Figure 6; and Figure 9 shows an alternative form of measurement circuit for use with the control circuit of Figure 6.

With reference to Figure 1, a configurable surface device 1 is formed as a generally rectangular box and comprises an upper surface 2 of compliant electrically conductive material such as a conductive polymer or fabric, a lower surface 3 of a relatively stiff non-conductive material, and a plurality of shape memory alloy wires 4. A shape memory alloy is an alloy which returns, when triggered by reaching a particular temperature, to a shape into which it was earlier formed. The wires 4 are connected between a corresponding number of regularly spaced points on the inner faces of the upper and lower surfaces. For clarity only some of the wires 4 are shown.

Where the wires 4 connect to the lower surface 3, individual electrical connections to each wire 4 are made by respective connecting wires 5. A single connecting wire 6 is connected to the upper surface which thus acts as a common ground for the other ends of the wires 4. The connecting wires 5 pass to a computer controlled driver circuit 7.

The two end faces of the configurable surface device 1 are provided respectively with an inlet 8 and outlet 9.

Connected between the inlet 8 and outlet 9 is a coolant supply circuit comprising a pump 11, a coolant supply pipe 10 connected between an outlet to the pump 11 and the inlet 8, and a return pipe 14 connected between the outlet 9 and an inlet to a heat exchanger 12 whose outlet is connected to an inlet to the pump 11. A header tank 21, connected to the return pipe 14, pressurises the fluid in the coolant supply circuit.

To give the upper surface 2 the desired configuration, the driver circuit 7 applies a voltage across selected wires 4. The current that then flows through the wires causes resistive heating. The consequent rise in temperature causes a transition point to be reached in which the wires 4 endeavour to revert to an initial shape. This results in the upper surface 2 being pulled downwards where the selected wires 4 are attached producing a depression.

The coolant supply circuit provides a through flow of a high thermal conductivity fluid such as antifreeze.

This removes heat from the wires 4 to the heat exchanger 12 where it leaves the system. The coolant is recirculated from the heat exchanger under the action of the pump 11. In the absence of an electric current flowing through one of the wires 4, by the driver circuit 7 ceasing to apply a voltage, its temperature will quickly pass below the transition temperature because of the coolant flow. The wire 4 will no longer endeavour to return to its original shape and the surface 2 will be forced outwards by the pressure of the coolant flow.

Where it is necessary for a greater force to be applied to each respective point of the upper surface 2, a number of shape memory wires 4 may be arranged to act on the point. Figure 2 shows an arrangement where five memory wires 4 are attached between the lower surface 3 and a point 15. Figure 3 shows a similar arrangement in which a number of wires 4 act via an intermediary "T" bar.

Figure 4 shows an alternative arrangement of controlling the wires. In this arrangement, in which the same reference numerals are used to denote similar parts to those in the earlier described arrangements and in which common parts will not be described in detail, both the upper and lower surfaces 2,3 are made of electrically non-conductive material. However, both surfaces 2,3 carry flexible, electrically conductive strips indicated generally by the references a,b. The strips of the upper surface bl,b2,b3 are parallel and co-planar and extend in respective directions which are orthogonal to the direction in which the parallel co-planar strips a1 to a6 of the lower surface extend. The wires 4 again connect the upper and lower surfaces 2,3 and each wire 4 is in electrical connection with a respective upper surface strip b and a lower surface strip a. Thus wire 4a is electrically connected between strip a6 and strip b3.

With the arrangement it is possible to energise one of the wires 4 at any particular time by the driver circuit 7 energising one of the strips b1,b2 or b3 and one of the strips al to a6. In the figure, strip a6 of the lower surface 3 and strip b2 of the upper surface 2 have been selected. This energises wire 4b.

As a further example, to energise wire 4c, strips b and a2 have to be selected. The wires are cooled in a similar manner to the earlier described embodiments.

A greater variation of surface can be achieved by using memory alloy wires the length of which can be varied to give a range of lengths. A suitable memory alloy is Flexinol (Trademark) from Dynalloy Inc. This material has a resistance length characteristic as shown in Figure 5.

From Figure 5 it can be seen that the relationship of resistance and length is a linear relationship and that a one ohm change in resistance results in a change in the length of about 0.002 m in a wire of length 10 cm.

The driver circuit 7 of the earlier described embodiments will include the control-loop shown in Figure 6 where the wires 4 are made from such memory alloy.

In the control-loop a converter 16 converts a value representing a desired length generated by another part of the driver circuit 7 into a value representing a corresponding value of desired resistance. The desired resistance value is input into a summation device 17.

An output of the summation device 17 is input into a controller circuit 18 which generates a control voltage to be input into a voltage amplifier 19. The amplified output is then applied across a series resistance arrangement of the wire 4 and a defined resistance. A current flows as before causing a change in length.

A measurement system 20 determines the resistance of the wire 4 and produces a positive value which is representative of the measured resistance. The value is input into the summation device 17 thus creating an error value as its output. It is this error value which is passed to the controller 18 which generates a control voltage to minimise the error.

The measurement system 20 is a resistor bridge as shown schematically in Figure 7, where Uo is the voltage applied to a series resistance arrangement of Rw the wire resistance, and R a defined resistance, and U is the voltage detected across the defined resistance.

Then since U = R Uo R + Rw and U = 1 Uo 1 + Rw/R the resistance of the wire is given by

Rw = 1) The amplifier unit 19 comprises a voltage amplifier as shown in Figure 8 which controls the voltage Uo across the series resistance arrangement of the wire resistance Rw and the defined resistance R in response to a voltage provided by controller 18.

Figure 9 shows an alternative measurement system. In this circuit each wire 390, 391, 392 39n is in series with a known resistance 40O, 401, 402' 40n Each bridge circuit 390 400' 391 401, 392 402' 39n 40n thus formed is connected between a ground line 41 and a supply line 42.

An amplifier 430, 431 432 43n and a sample hold device 440, 441, 442, 44n are connected in series between each resistance 400, 401, 4023 40n. Two lines 450, 451, 452, 45n, 460, 4613 462' 46n are connected to each bridge circuit - one line 450, 451, 452, 45n leading from the connection between each wire 390, 391, 392' 39n and the associated resistance 40O, 401, 4023 40n and the other line 460, 4613 462, 46n leading from the connection between each resistance 40O, 401, 4023 40n and the associated amplifier 430, 431, 432, 43n. Each line of each pair is connected to a pole of a double gang switch 47O' 471, 472' 47n whose outputs are connected to associated common detector wires 48,49.

A control line 500, 501, 50, 50n is connected to the sample hold device 440, 441, 442, 44n and to the switch 470, 471, 472, 47n of each wire 390, 391, 392, 39n.

In use, the voltage Uout to be applied to a selected wire 390, 391 392 39n is applied to the supply line. A control current is applied to the control line 500, 501, 502, 50n of the selected wire 391 392' 39n This activates the sample hold device 440, 441w 442 44n, which holds the voltage Uout and so the voltage is applied across the associated bridge 390 400, 391 401, 392 402, 39n 40n The control line current also closes the associated switch 470, 471, 472, 47n and so the voltages in the lines 450 460, 451 461, 452 462, 45n 46n, are passed to the lines 48,49, with the instantaneous resistance Rw of the selected wire being given by Rw = RUb/(Ua - Ub).

In yet further alternative embodiments, the wires may be cooled by air blown through the device by a fan. As an alternative to the use of a pressurized fluid to restore the upper surface 2 to its original configuration springs or other resilient elements may be used to tension the shape memory wires 4. Whilst in the described embodiments the shape memory members are wires 4, other forms of shape memory members may be used.

In alternative embodiments it may be possible to make both surfaces 2,3 flexible and to configure both surfaces. Both surfaces may be made as relatively narrow strips to produce a linear strip-like device.

In order to increase the speed of response of the device, the coolant used may be maintained at a temperature close to the transition temperature of the shape memory member. Thus, only a small degree of heating and a short heating interval would be required to reach the transition temperature again.

Although the described and illustrated embodiments use a plurality of wires 4, only one wire 4 may be used in alternative embodiments.

The shape memory members may be permanently fixed to the surfaces or provided with an adjustable fixing.

It is envisaged that configurable surfaces in accordance with the invention would have application in virtual reality systems for forming passive and active touch feedback to augment the known visual systems. For example, an instrument panel for an automobile or aircraft could be created so that a user could feel switches or the like. Similarly, the surface could be used to provide an output device to be read by a visually impaired user in the manner of Braille reading.

The surfaces may be used to mould articles by temporarily gluing with a tacky adhesive a sheet of material to the surface. A further sheet of material could be glued with a permanent adhesive onto the first. Once set the assembly could be removed from the surface, with the shape being held by the set adhesive.

A yet further use continued for configurable surfaces in accordance with the invention is a process called skiving. Skiving is the selective thinning of a material usually leather, to produce feather edges for lap joints. The material is held on a platen formed by a configurable surface and the surface configured prior to passing the platen under a knife. Portions raised by the surface would be cut by the knife. Alternatively, the configuration can be varied as the material is fed between the surface and the knife to vary the gap therebetween and to vary the depth of the cut into the material.

Claims (16)

1. CLAIM 1. A configurable surface device comprising a configurable surface, and at least one shape memory member which is triggerable from a first state, in which it has a first shape, to a second state, in which it has a second shape different to the first, the at least one shape memory member being so operatively associated with the configurable surface that triggering of said at least one shape memory member alters the configuration of said surface from a first configuration to a second configuration.
2. 2. A device as claimed in claim 1 wherein the or each shape memory member comprises an electrically conductive element to which an electric current is applied to heat the element by resistive heating to trigger the change in state.
3. 3. A device as claimed in any one of claims 1 or 2 wherein the or each shape memory member has associated therewith a resilient member to oppose movement of the surface by the associated shape memory member, when triggered.
4. 4. A device as claimed in claim 1 or 2 wherein the surface forms part of a boundary of a sealed volume pressurized by a fluid contained therein to oppose movement of the surfaces under the action of the or each shape memory member when triggered.
5. 5. A device as claimed in any one of claims 2,3, or 4 including cooling means for cooling the shape memory member or members to permit a return from the second state to the first state and thus return the surface from the second configuration to the first configuration under the action of the resilient members or pressurized fluid.
6. 6. A device as claimed in claim 5 when dependent on claim 4 wherein the sealed volume has an inlet and an outlet through which a liquid coolant is respectively introduced and exhausted by the cooling means to cool the shape memory member or members.
7. 7. A device as claimed in any preceding claim comprising a second surface spaced apart from the configurable surface and having connected therebetween the or each shape memory member.
8. 8. A device as claimed in claim 7 wherein the second surface is a configurable surface.
9. 9. A device as claimed in any preceding claim comprising a plurality of shape memory members wherein each shape memory member has a common electrical input with a first group of shape memory members and a common electrical output with a second group of shape memory members such that a respective shape memory member may be selectively energised by connecting an electrical power source to a respective common electrical input and a respective common electrical output.
10. 10. A device as claimed in any preceding claim wherein the shape memory members comprise a plurality of wires which are controllable to provide various configurations of the surface or surfaces.
11. 11. A device as claimed in claim 10 wherein a group of wires are arranged to act at one point on the surface.
12. 12. A device as claimed in claim 11 wherein wires within the group are fixed directly to the point on the surface.
13. 13. A device as claimed in claim 11 wherein the wires within the group are connected to a coupling means which is connected to the point on the surface.
14. 14. A device as claimed in claim 13 wherein the coupling means comprises an arrangement of two bars, a first bar connected between the surface and a second bar, the wires being connected to the second bar to act through the arrangement on the surface.
15. 15. A device as claimed in any preceding claim including control means for triggering the change of state of the or each shape memory member.
16. 16. A configurable surface device substantially as hereinbefore described with reference to, and as illustrated by, the accompanying drawings.