GB2265746A

GB2265746A - Tactile display array

Info

Publication number: GB2265746A
Application number: GB9210109A
Authority: GB
Inventors: Gareth John Monkman
Original assignee: Individual
Current assignee: Individual
Priority date: 1992-04-04
Filing date: 1992-05-11
Publication date: 1993-10-06
Anticipated expiration: 2012-05-11
Also published as: GB9210109D0; GB2265746B

Abstract

A tactile display array comprises a solid substrate 1 containing electrically selectable tactor elements 2 over which an electrically insulating separating mesh 4 soaked in electrorheological fluid 5 is laid. The whole upper surface is covered by an electrically conducting compliant film 8 held at earth potential. The tactile image is created by the connection of a high voltage supply to those tactor elements which correspond to the geometric description of the desired image to be displayed. The image may then be haptically detected by finger pressure applied to the compliant surface. <IMAGE>

Description

ELECTRORHEOLOGICAL TACTILE DISPLAY Description.

This invention relates to the use of the characteristics of electrorheological fluid under compressive stress. Newtonian fluids experience a deformation in the form of displacement or flow when subjected to compressive stress. An electrorheological fluid acts as Bingham plastic when under the influence of an applied electric field and as a Newtonian fluid when no such field is present. The amount of compressive force required to cause the displacement of an activated (subject to an electric field) electrorheological fluid is considerably larger than that needed to displace the same electrorheological fluid, by the same volume, when in an unactivated state.

Electrorheological fluid is fluid which comprises of solid, electrically polar particles, such as starch, suspended in an electrically non-conductive liquid such as silicone oil. In the absence of an electric field the suspension flows freely, but when activated by the application of an electric field the electrorheological fluid experiences a phase change from a liquid-like to a solid-like state, resulting in an increase in apparent viscosity.

When such a suspension exists between two parallel, planer electrical conducting surfaces, carrying electrical charges of opposite polarity, the electrorheological fluid undergoes an increase in solidification proportional to the applied electric field density. If the two conductors are positioned such that a mechanical force may be applied causing the; two conductors to experience movement towards one another, the hardness cf the electrorheological fluid between the conductors increases as the gap between the conductors is reduced. Consequently, the closer the conductors are moved together, the greater the apparent. elastic modulus of the electrorheological fluid and hence the greater the force required to cause the activated electrorheological fluid to flow.

The above described attribute of electrorheological fluid may be cmployed in the construction of tactile display devices such as teleoperator feedback pads for underwater/space robotic guidance, aids to the blind etc. The invention is now described by way of example with reference to the accompanying drawings in which: Figure 1 shows a set of typical characteristic curves of applied pressure versus gap width of an electrorheological fluid subjected to compressive stress, for a range of applied voltages.

Figure 2 illustrates the construction of a tactile display device using a two dimensional array of individually controllable tactor elements.

Figure 3 demonstrates the operation of such a tactile display array.

Figure 1 provides an example of the typical physical displacement range (in the direction of the applied stress) available from the electrorheological fluid when subjected to compressive stress. This curve is a typical example from tests conducted on a polymethacrylate suspension in chlorinated hydrocarbon, and exact characteristics will vary depending on the electrorheological fluid used.

With reference to figures 2 and 3, a tactile display array may be constructed by the use of an insulating substrate 1 through which electrically conducting pegs or wires 2 are passed: These form the tactor surface 3 which an electrically insulating mesh 4 soaked in electrorheological fluid 5 is laid. Over these, an electrically conducting compliant sheet 6 is laid. This may be a conducting polymer material, a simple metal foil or a laminate comprising a compliant polymer 1 and an electrically conducting foil 8.

The foil 8 on the underside of the compliant surface 6 is electically connected to earth potential 9. The tactor elements 2 are activated by means of the connecting wires 10 (or any other electrically conducting means). Selection of appropriate tactor elements 2 by means of electrical connections 10 will allow a haptically detectable image to appear under the compliant surface 6 corresponding to the position of the activated tactors.

The purpose of the electrically insulating mesh 4 is to prevent the conducting foil 8 from comming into direct electrical contact with the tactor elements 2.

During use, the top of the compliant surface 6 may be pressed by the fingers thereby expelling electrorheological fluid from those areas between the foil 8 and the unactivated (uncharged) tactors 2 on the surface 3. However, when the same finger pressure is applied to the surface 6 over activated tactors 2 then the electrorheological fluid will experience an increase in hardness due to the applied voltage on the selected wires 10. This increase in apparent viscosity retards the flow of the activated electrorheological fluid thereby yielding a relatively solid impression to the touch.

Selecting appropriate tactor elements 2 though the voltage applied via cables 10 will cause the electrorheological fluid S to solidify causing the compliant surface 6 to appear hard to the touch only over those areas where the tactor elements 2 are selected. Elsewhere, the compliant surface 6 will appear soft to the touch as the electrorheological fluid 5 may be displaced from over the unactivated tactors 2 by the applied finger pressure.

Claims

Claims.

1. A device using an electrically active fluid medium held between two electrically conducting surfaces, in which the apparent viscosity, solidification or partial solidification of the fluid may be controlled by means of an externally applied electric field for the purposes of portraying haptically detectable tactile information.

2. A two dimensional array of such elements described in claim 1 which may be used for the purposes of forming a haptically detectable tactile image, whether in binary form as a result of two discrete charged and uncharged tactor states, or as an analog given by varying degrees of hardness due to analog voltage levels or pulsed voltages supplied to the tactors.

3. Any three (or more) dimensional extension to the implementation described in claims 1 and 2.

4. The use of an electrically insulating mesh, or fabric sheet, through which fluid may pass, used to prevent electrical short circuit and breakdown between two or more conductors in the construction of devices described in claims 1, 2 and 3.