GB2198237A

GB2198237A - Tactile force sensor

Info

Publication number: GB2198237A
Application number: GB08627462A
Authority: GB
Inventors: John Wilfrid Finch; Charles Robert Allen
Original assignee: Individual
Current assignee: Individual
Priority date: 1986-11-17
Filing date: 1986-11-17
Publication date: 1988-06-08
Also published as: GB8627462D0

Abstract

A tactile force sensor comprises a tube or sleeve (1, Fig. 1a) of conductive rubber or similar material with a core (9) of a highly electrically conductive substance within the sleeve. The composite sleeve and core may be positioned across a similar element or sleeve (2) of highly conductive material, force applied at the crossing node being sensed by varying electrical resistance between the crossed conductors. A plurality of sleeves (1) and (2) can be arranged to form an orthogonal matrix. In an alternative embodiment the sensor element forms a short cylinder (10, Fig. 3) which is axially compressible by a plunger against an annular contact (13) to vary the resistance between that contact and the conductive core of the element. <IMAGE>

Description

TACTILE FORCE SENSOR This invention relates to a tactile force sensor.

A tactile sensor pad produces signals which give a measure of the force distribution exerted on the pad by an object pressed againstit. This tactile force information can be used for many purposes including, for example: determination of force distribution and magnitude; detection of contact between object and sensor; surface feature recognition; determination of object shape and orientation.

One form of tactile sensor uses a flexible material which is partially electrically conductive. The sensor is then constructed so that the application of a tactile force at a particular point causes the local electrical resistance of the material to vary. This variation in resistance can be detected and used as a measure of the tactile force.

The resistance variation may be directly due to the material properties ( piezo-resistive), or may be caused by the distortion of the material, or a variation in the contact resistance through area or other variations between pieces of the material and other pieces of similar material or electrical good conductors placed nearby. Individual force sensors can be so constructed, but in a tactile sensor the usual aim is to produce a regular grid of points or nodes over a surface, at which locally applied force can be detected. One form of construction uses a sheet of conductive rubber material into which a set of orthogonal thin wires are introduced, perhaps while the rubber is still in a fluid state.Each individual pair of wires from the orthogonal sets ( rows and columns ) is separated by a thin layer of rubber at the point or node of crossover of the wires. Electrical connections to the ends of the wires enable resistance variations local to the node caused by tactile forces to be measured.

Such tactile sensors are difficult to construct reliably since the nodes have widely varying properties. Part of the reason for these variations is due to the variations in the amount of rubber material between individual wires. Other problems include ill defined current paths because a complete sheet of rubber material is used. This allows large and variable cross-coupling between nodes so that a force applied only at one node causes an apparent spurious force signal to occur at other nodes.

According to the present invention there is provided a tactile sensor comprising conductive rubber or similar material in the form of a tube or sleeve. A core of an highly electrically conductive substance is placed within the sleeve to allow continuous electrical contact to be made to points down the sleeve.The composite sleeve is then used to form a tactile sensor.

A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawing in which: Figure 1(a) shows a detailed view of a single node of a tactile sensor constructed using the composite sleeve 1 placed across a similar sleeve or across electrically highly conductive material 2. The point of action of the tactile force is shown by the arrow head. Figure l(b) shows a number of such nodes forming a sensing array.

Figure 2 shows a tactile sensing pad in which the composite sleeve is used by placing a grid of such sleeves 1 across another grid of such sleeves or a grid of electrically highly conductive material 2 in a series of rows.

The crossover node points of the two grids are forced into closer proximity by the application of a tactile force local to the node. The grids are supported by a backing plate 3 over which the grids are laid. The backing plate may contain holes 4 or grooves 5 into which the sleeves are placed to maintain the relative proximity of the grids An additional front plate 6 may also be provided for a similar purpose, or for protection. The tactile force may be applied directly to the nodes, or via a series of plungers 7, or through a flexible protective layer 8 not shown on this drawing. The inner electrically good conducting part 9 of the composite sleeving is shown in both Figures l(a) and 2.

Another specific embodiment of the invention will now be described by way of example with reference to the accompanying drawing in which Figure 3 shows a single node of the sensor in which the flexible outer section of the sleeving is cut into a short cylinder 10 with the line of action of the tactile force along the cylinder axis. The tactile force is applied to one face 11, while the face 12 is in close proximity to an electrical contact 13 through which the inner electrically good conducting part 14 of the composite sleeving may be allowed to pass without touching the contact 13. Application of a tactile force to the face 11 either directly or via a plunger 14 causes the effective electrical resistance between the inner conductor 14 and the contact 13 to vary. The sleeving cylinder 10 and the plunger 14 can be guided within a hole in an electrically insulating plate. The contact 13 may be part of an electrical track 15.

In an alternative form of the specific embodiment shown in Figure 3, the plunger 14 and the inner conductor 13 can be one single part 16 with connection being made to the conductor beneath the plate 17. A side view of this arrangement is shown in Figure 4.

Claims

CLAIMS.

1. A tactile force sensor comprising a tube or sleeve of conductive rubber or similar material and a core of a highly electrically conductive substance positioned within the tube or sleeve.

2. A tactile force sensor according to claim 1, wherein said composite tube or sleeve and core is positioned across a similar sleeve of highly conductive material, a force applied at the crossing node being sensed by electrical contact between the sleeves.

3. A tactile force sensor according to claim 2, wherein a plurality of composite tubes or sleeves and cores are arranged in parallel across a plurality of parallel highly conductive sleeves, the two sets of sleeves being orthogonal to one another, a force applied at any one of the crossing nodes being sensed by electrical contact between the sleeves.

4. A tactile force sensor according to claim 3, wherein the sleeves of highly conductive material are located within parallel holes in a backing plate, the composite tubes or sleeves and cores being located in a plurality of grooves on the surface of the backing plate at right angles to the holes.

5. A tactile force sensor according to claim 4, wherein a series of plungers are provided in a front plate located over said backing plate, the plungers transmitting forces at the nodes.

6. A tactile force sensor according to claim 1, wherein said composite tube or sleeve and core is in the form of a short cylinder, one face of which is in close proximity to an electrical contact, a force applied to the other face of the cylinder being sensed by changing electrical resistance between the core and the electrical contact.

7. A tactile force sensor according to claim 6, wherein a plunger is provided to transmit the force to said other face of the cylinder.

8. A tactile force sensor according to claim 7, wherein said plunger and said core of highly electrically conductive substance are integrally formed as single part.

9. A tactile force sensor constructed substantially as herein described with reference to Figure 1, or Figure 2, or Figure 3 or Figure 4 of the accompanying drawings.