Force sensor

• US 20010008389A1
• Filed: 03/09/2001
• Published: 07/19/2001
• Est. Priority Date: 09/11/1998
• Status: Active Grant

• Current Assignee: IEE International Electronics & Engineering SA (Aerospace Hi-Tech Holding Group Company Limited)
• Original Assignee: IEE International Electronics & Engineering SA (Aerospace Hi-Tech Holding Group Company Limited)
• Inventors: Huegens, Emmanuel, Schoos, Aloyse, Serban, Bogdan
• Granted Patent: US 6,531,951 B2
• Time in Patent Office: Days
• US Class Current: 338/47
• CPC Class Codes: G01L 1/142 using capacitors
• CPC Class Codes: G01L 1/18 using properties of piezo-resistive materials, i.e. materials of which the ohmic resistance varies according to changes in magnitude or direction of force applied to the material
• CPC Class Codes: G01L 1/20 by measuring variations in ohmic resistance of solid materials or of electrically-conductive fluids of piezo-resistive materials G01L1/18; by making use of electrokinetic cells, i.e. liquid-containing cells wherein an electrical potential is produced or varied upon the application of stress
• CPC Class Codes: G01L 1/205 using distributed sensing elements
• CPC Class Codes: H01H 3/141 Cushion or mat switches

Abstract

The invention concerns a force sensor (10) comprising a first electrode (22) and a second electrode (24) made of conductive material, which are arranged spaced from each other on a first insulating support (12). The invention is characterised in that a contact element (26) is conductive material is placed opposite the two electrodes and some distance therefrom, said contact element t(26) being pressed against said electrodes (22, 24) when a force is exerted on the pressure sensor (10) and at least one of the electrodes (22, 24) is coated with a pressure sensitive material layer (28, 30).

Claims

1. Force sensor comprising

two electrodes made of a conducting material, said two electrodes being arranged on a first insulating support in such a way that they are separated from each other, each of said two electrodes being coated with a layer of pressure-sensitive material, the two layers of pressure-sensitive material being electrically insulated from each other, and

a contact element made of a conducting material, said contact element being arranged at a certain distance from said two electrodes, said contact element being pressed against said electrodes when a force is exerted on the force sensor, wherein

each electrode comprises a conductor arranged substantially at a periphery of an active zone of the sensor, and wherein said layer of pressure-sensitive material covering each electrode extends towards the interior of the active zone, the two pressure-sensitive layers being separated by an interstice that passes roughly through a center of the active zone.

2. Force sensor according to

claim 1

, wherein said pressure-sensitive layer comprises microprojections on a surface of said layer, so that a surface resistance between said layer and the contact element decreases with the pressure exerted on the junction between the layer and the contact element.

3. Force sensor according to

claim 1

, wherein said pressure-sensitive material comprises a material whose specific resistance varies inversely with a compression of said material.

4. Force sensor according to

claim 2

, wherein said pressure-sensitive material comprises a material whose specific resistance varies inversely with a compression of said material.

5. Force sensor according to

claim 1

, wherein the layer of pressure-sensitive material comprises inclusions of conducting material, said inclusions of conducting material being arranged so as to change the specific resistance of the layer of pressure-sensitive material.

6. Force sensor according to

claim 1

, wherein said contact element comprises a layer of conducting material applied to a second flexible support, said second support being arranged at a distance from said first support by means of a separator located outside of said active zone so that, in the interior of said active zone, the layer of conducting material is opposite said electrodes.

7. Force sensor according to

claim 6

, wherein said separator comprises a printable adhesive, said adhesive serving to stick said first substrate to said second substrate.

8. Force sensor according to

claim 7

, comprising separator particles arranged inside said printable adhesive, said particles having a diameter substantially equal to the desired spacing of the two substrates.

16. Seat-occupancy detector comprising at least one force sensor according to

claim 1

.

9. Force sensor comprising

two separate electrodes made of a conducting material, said electrodes being arranged on a first insulating support at a periphery of an active zone of said sensor, each of said two electrodes being coated with a layer of pressure-sensitive material, said layers of pressure-sensitive material extending towards the interior of the active zone and being separated by an interstice that passes roughly through a center of the active zone, and

a contact element made of a conducting material, said contact element being arranged at a certain distance from said two electrodes, said contact element being pressed against said electrodes when a force is exerted on the force sensor.

10. Force sensor according to

claim 9

, wherein said pressure-sensitive layer comprises microprojections on a surface of said layer, so that a surface resistance between said layer and the contact element decreases with the pressure exerted on the junction between the layer and the contact element.

11. Force sensor according to

claim 9

, wherein said pressure-sensitive material comprises a material whose specific resistance varies inversely with a compression of said material.

12. Force sensor according to

claim 9

, wherein the layer of pressure-sensitive material comprises inclusions of conducting material, said inclusions of conducting material being arranged so as to change the specific resistance of the layer of pressure-sensitive material.

13. Force sensor according to

claim 9

, wherein said contact element comprises a layer of conducting material applied to a second flexible support, said second support being arranged at a distance from said first support by means of a separator located outside of said active zone so that, in the interior of said active zone, the layer of conducting material is opposite said electrodes.

14. Force sensor according to

claim 13

, wherein said separator comprises a printable adhesive, said adhesive serving to stick said first substrate to said second substrate.

15. Force sensor according to

claim 14

, comprising separator particles arranged inside said printable adhesive, said particles having a diameter substantially equal to the desired spacing of the two substrates.

17. Seat-occupancy detector comprising at least one force sensor according to

claim 9

.