WO1999036757A1

WO1999036757A1 - Sensor elements

Info

Publication number: WO1999036757A1
Application number: PCT/GB1999/000115
Authority: WO
Inventors: Mark Paul Norman
Original assignee: Mark Paul Norman
Priority date: 1998-01-16
Filing date: 1999-01-14
Publication date: 1999-07-22
Also published as: AU2066699A

Abstract

A sensor element comprises a body of resiliently deformable electrically conductive material, the resistance of the material itself varying in proportion to deformation of the conductive material, and electrical connection means provided at least at one end of the body of conductive material.

Description

SENSOR ELEMENTS

The present invention relates to a sensor element and to sensor apparatus including such elements. In particular, the invention relates to sensor elements in which variations in length, or deformation, of the element provide an output which is indicative of the degree of variation or deformation.

One electronic transducer that has been proposed is described in United States Patent No. 4090248. However, the transducer described is a relatively complicated construction comprising a pair of adjacent conductors helically wound to form a bifilar coil which is subsequently embedded in a dielectric material.

The present invention provides a sensor element comprising a body of resiliently deformable electrically conductive material, the resistance of the material itself varying in proportion to deformation of the conductive material, and electrical connection means provided at least at one end of the body of conductive material.

In one embodiment, the sensor element is of a generally elongate construction, with electrical connectors provided at opposing ends of the body.

In an alternative arrangement, the body of material is provided in a loop-like element with a connector at the end of each leg of the loop. Preferably, the legs of the loop are closely adjacent one another and separated by a suitable insulating material.

Advantageously, the material is a non-metallic material. Preferably, the material is a silicon based conductive rubber material.

The body may comprise a deformable outer tubular element that contains an electrically conductive deformable compound, such as PLAYDOH, (a registered trade mark).

The electrical connectors may be in the form of conductive clamps or a suitably electrically conductive adhesive may be used to connect the sensor element with the electrical contacts. A sensor apparatus comprising such a sensor element further includes means for measuring changes in resistance across the sensor element. Processing means may be provided for relating changes in resistance to a particular parameter being sensed.

The sensor element is such that when deformed directly or indirectly by extension or compression forces, a related change in the resistance, that can be measured from adjoining electrical connections, is derived. It will be immediately appreciated that the measured changes in resistance can arise from extension or compression forces applied to the sensor element from or in any direction.

Depending upon the application for the sensor, it may be desirable to measure the rate of change of resistance during an extension or compression event or indeed the rate of change of that rate of change.

Possible measurements may relate resistance to a degree of stretch, forces, radial expansion and/or contraction, torsion and/or vibration that are applied to the sensor element.

A sensor apparatus may comprise two or more sensor elements, the resistance of each element being monitored independently. For example, two elements may be arranged in parallel to measure changes in the degree of curvature of an element.

In order that the invention may be more readily understood, and so that further features thereof may be appreciated, sensor elements in accordance with the invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 illustrates a sensor element in accordance with the invention;

Figure 2 illustrates the sensor element of Figure 1 with a force applied thereto;

Figure 3 is similar to Figure 2 but illustrates one possible modification;

Figure 4 illustrates an alternative configuration of a sensor element in accordance with the invention and

Figure 5 is a graph illustrating the relationship between length and resistance of one sensor element in accordance with the invention. Referring to Figure 1 , a sensor element generally indicated at 1 comprises a sensor body 2 in the form of an elongate element with electrical contacts 3, 4 provided at opposing ends of the sensor body. The sensor body 2 is formed from a flexible material and may be easily deformed by compression or extension forces. The body 2 can be made from a single material, being a flexible conductive material, either in a solid or hollow tubular form or may be formed from a flexible outer tubing that contains an electrically conductive compound that can itself be deformed.

For example, the sensor body 2 may be constructed from a silicone conductive rubber. Preferably, the rubber has a resistance in the range of 1-10 ohms. Alternatively, the sensor body may be in the form of a silicone rubber outer tubing with a conductive material, such as PLAYDOH (registered trade mark) comprising the conductive deformable inner compound. In either case, electrical connections must make a good contact with the deformable conductive material. The contacts 2, 4 may be mounted using conductive clamps, a conductive adhesive, or in any other suitable manner.

Although a cylindrical or tubular sensor body has been described and illustrated, it will be appreciated that the sensor body may be of any convenient shape and cross-section. The size and shape of the sensor body may be chosen to suit a particular application.

As will be explained further hereinbelow, a meter or other means for measuring resistance can be attached between the electrical contacts 3 and 4 so that a measure of the resistance of the sensor body can be determined. If, as illustrated in Figure 1, there are no forces acting upon the sensor body, then a static resistance reading can be established.

Figure 2 illustrates the sensor element of Figure 1 , the electrical contact 3 being connected with the sensor body 2 at a connection point 5 and the electrical contact 4 being connected at a connection point 6. A force F, acting on either connection point 5, connection point 6 or both will cause the body to deform and the length, illustrated by the arrow L, to increase. A measure of the electrical resistance, measured by the meter connected with contacts 3 and 4, will provide a measure of resistance that is proportional to the new length L. Figure 3 illustrates an alternative arrangement in which a supplementary biasing element, such as an extension spring 7, is provided to apply an initial stretch or lengthening to the sensor element 2.

By establishing the sensor body in a pre-stretched state, the sensor can be readily used to measure resistance changes resulting from compressive forces, as indicated by F₂, applied at either of connection points 5, 6 or both. Depending upon the degree of pre-stretching applied, an arrangement as shown in Figure 3 can readily measure both extension or compression forces applied to the sensor element.

The path between the connection points 5, 6 does not need to be a straight line for the sensor to operate. For example, the sensor body could be looped around a cylindrical surface that is subject to expansion and contraction with the sensor fixed to the surface; expansion and contraction of the cylindrical body will result in corresponding changes to the length of the sensor body and thus enable measurements to be taken via the contacts 3, 4.

Turning to Figure 4, an alternative configuration of the sensor body in accordance with the invention is illustrated. Referring to Figure 4, a sensor element is generally indicated at 8 comprising a sensor body 9 with electrical connections 10, 1 1 connected at connection points 12, 13 respectively. In this arrangement the sensor body 9 comprises two flexible conducting elements 14, 15 spaced by an insulating element 16. As can be seen from the drawing, one end of the element 14 is connected to the electrical contact 10 at connection point 12 and one end of the element 15 is connected to the electrical contact 1 1 at connection point 13. The other end of the elements 14, 15 are joined together by an electrical conductor 17.

Of course, the coupling, between the sensor body and the electrical connectors, irrespective of the configuration, must be strong enough to withstand reasonable deforming forces applied to the sensor body.

Considering further the function of the sensor body and the relationship between length and resistance, it can be shown that an extension force applied directly or indirectly to the sensor body causes the body to deform such that the area (A) is reduced and the body length (L) is increased proportionally to the extension force applied. A compression force applied directly or indirectly to the sensor body causes the body to deform such that the area (A) is increased and the body length is decreased proportion (L) to the compression force applied. These deformations cause a proportional change in the internal resistance of the sensor which can be measured from the adjoining electrical contacts.

Thus, if the resistance of the sensor body is indicated as R, the cross sectional area of the body as A and the length as L, the resistivity can be determined:

Resistivity σ = RA L The resistivity of the sensor body is determined by the material selected and the length L and area A are dependent upon the initial size of the sensor body and the deforming force applied. Thus, as illustrated in Figure 5, the resistance R of the sensor body is proportional to the length L and area A of the sensor body.

The length (L) and resistance (R) are determined by the resistivity of the sensor body. A sensor body with uniform resistivity would give a linear proportional relationship between R and L (Figure 5). The slope of the relationship is determined by the choice of material.

The sensor body returns to its original shape once external forces are removed.

By varying the resistivity along the length of the sensor body one could obtain a non-linear relationship. A non-linar relationship could be useful for increasing output signal to highlight specific length/resistance ranges. It will be appreciated that customised resistance/deformation relationships can readily be manufactured, determined by the intended application of the sensor and that the sensor can be used to take static or dynamic measurements.

It is envisaged that the sensor will have a number of possible applications. As the choice of materials allows the sensor to be made in a small and light configuration and to be constructed in a relatively and simple straight forward manner, it will be attractive in a variety of applications. The sensor can be used in any direction and in a wide range of o dimensions. For example, applications for the invention have already been considered in the following areas:

• Robotics/Cybernetics/Bio-robotics/Animatronics

• Measure the action and angulation of joints.

• Used internally or externally to measure length

• Build into air muscles to measure length

• Built into other artificial muscles to measure length

• By attaching multiple sensors across a joint its position can be measured in 3 dimensions.

• 3DOF sensor

• 2DOF sensor

• To determine proprioception

• Proximity sensor

• Inclinometer

• Accelerometer

• Pressure sensor

• Gait sensor

• Vibration sensor

• Olfactory sensor

• Auditory sensor • Tension sensor

• Force sensor

• Strain sensor

• Stress sensor

• Protective sensor

• Virtual reality

• As for Robotics/Cybernetics Bio-robotics/Animatronics above

• A skin tight virtual reality suit can have miniature stretch sensors attached, arranged such that body movements cause sensor extension and contraction.

• A similar principle applies to virtual reality gloves where attachments at finger joints cause sensor extension and contraction.

• Biomedical

• Measure joint action and angulation

• The position of artificial joints can be measured

• Measure ankle swelling over a period and plot it

• Engineering

• Could be used to measure the position of a door or a window as part of a security system

• Could be used to measure how open a vent or duct is that needs to be controlled

• Could measure valve position

• Can detect lever position o

Electronics

Could be used to replace a linear potentiometer, more reliable due to the non mechanical nature

Could be used to replace a rotary potentiometer

Vehicle

Measure seat position and inclination

Measure window position

Electronically detect gear shift position

Tyre pressure sensor

Aviation

Measure position of variable flying surfaces

Detect door and undercarriage position

Detect seat, tray and seat belt positions to provide safety data.

Education

Scientific demonstration of Ohm's law of resistance change

Automation

All automation processes eg. detect gate positions

Detect point positions

Railway Industry

Detect point positions Nautical

Military

Space

Used to measure to muscle activity without gravity

Pharmaceutical processes

Scales (pressure)

Electronic ruler

Haptics

Horticulture

Measure plant growth

General Sensing

Biological and artificial joint action and angulation

Weights and measures

Instrumentation

Measure seat inclination and contour

Measure door/flap/gate/valve position

Measure vibration

Measure pressure

Reliable linear latching potentiometer

Reliable rotary latching potentiometer Electronic tape measure

Used to monitor moving parts

Can be used in instrumentation devices

Barometer

Altimeter

Can be implemented in safety precautions to prevent damage to instrumentation or biological matter.

Seat contour/inclination

Vehicle seat contour/inclination

Wheelchair applications

Mechanical gate position

Door/window position sensor

Flap/Valve position sensor

Vibration/Earthquake/Earth movement/Seismometer

Hinge position sensor

Meteorological sensors

Plate tectonic sensors

Personal security

Building and property security

Ratio control applications Home automation

Claims

1. A sensor element comprising a body of resiliently deformable electrically conductive material, the resistance of the material itself varying in proportion to deformation of the conductive material, and electrical connection means provided at least at one end of the body of conductive material.

2. A sensor element according to claim 1, in which the sensor element is of a generally elongate construction, with electrical connectors provided at opposing ends of the body.

3. A sensor element according to claim 1, in which the body of material is provided in a loop-like element with a connector at the end of each leg of the loop, the legs of the loop preferably being closely adjacent one another and separated by a suitable insulating material.

4. A sensor element according to any preceding claim, in which the material is a non-metallic material.

5. A sensor element according to any preceding claim, in which the body comprises a deformable outer tubular element containing an electrically conductive deformable compound.

6. A sensor element according to any preceding claim, in which the electrical connectors comprise conductive clamps or an electrically conductive adhesive.

7. Sensor apparatus comprising a sensor element according to any preceding claim, the apparatus further including means for measuring changes in resistance across the sensor element.

8. Sensor apparatus according to claim 7, including processing means for relation changes in resistance to a particular parameter being sensed.

9. Sensor apparatus according to claim 7 or claim 8, the apparatus comprising two or more sensor elements, the resistance of each element being monitored independently.

10. Sensoring apparatus according to any of claim 7 to 9, in which a supplementary biasing element is provided to apply an initial stretch or lengthening to the sensor element.

1 1. Sensor apparatus according to any of claims 7 to 10, in which the sensor body is looped around a cylindrical surface that is subject to expansion and contraction with the sensor fixed to the surface.

12. Sensor apparatus according to any of claims 7 to 10, in which the sensor element comprises a sensor body having two flexible conducting elements spaced by an insulating element.