GB2368176A

GB2368176A - Proximity sensor employing a flexible capacitive sensing element

Info

Publication number: GB2368176A
Application number: GB0113168A
Authority: GB
Inventors: John Christopher Rees
Original assignee: SMARTA SYSTEMS Ltd
Current assignee: SMARTA SYSTEMS Ltd
Priority date: 2000-08-03
Filing date: 2001-05-30
Publication date: 2002-04-24
Also published as: GB0018914D0; GB0113168D0

Abstract

An electronic safety control system comprising an elongate, flexible electrically-conductive sensing element 18,20 and electronic control means. The electronic control means are responsive to a change in capacitance arising from the close proximity to the element 18,20 of an object, to provide an output signal for controlling a powered device 14. Thus, where the powered device 14 is used to displace one part 10 of a mechanism 8 towards another 12, the sensing element 18,20 may be fitted to one or other or both of the approaching surfaces of the two parts 10,12 to prevent a object from becoming trapped therebetween. This system may be used in conjunction with an adjustable seat.

Description

ELECTRONIC SAFETY CONTROL SYSTEM The present invention relates to an electronic safety control system and, more particularly to a safety control system for preventing an object from becoming trapped between the approaching surfaces of two opposed parts of a mechanism in motion.

It is known to reduce the risk of an object, e. g. a human body part, becoming trapped between the approaching edges of two opposed parts of a mechanism in motion, by providing a compressible strip along one or other of the edges, the strip containing opposed electrical contacts which are connected to form a circuit, to arrest the relative movement of the two parts, when the strip is compressed.

A similar arrangement instead uses a hollow compressible strip, which is connected to a pneumatic sensor for detecting the resulting increase in internal pressure when the strip is compressed.

However, both of the above arrangements require physical contact between at least one of the opposed edges and an obstruction therebetween, and thus do not fully obviate the risk of damage to the object causing the obstruction.

Furthermore, the effectiveness of each of the known strips in providing a satisfactory output is known to be dependent upon the radius of curvature of the edge that the strip is to follow, there being, in each case, a limit to the extent to which the strip may be bent.

I have now devised an arrangement which overcomes the above-mentioned limitations of existing electronic safety control systems.

In accordance with the present invention, there is provided an electronic safety control system comprising an elongate, flexible electrically-conductive sensing element and electronic control means responsive to a change in capacitance arising from the close proximity to the element of an object to provide an output signal for controlling a powered device.

Thus, where the powered device is used to displace one part of a mechanism towards another, the sensing element may be fitted to one or other or both of the approaching surfaces of the two parts to prevent an object from becoming trapped therebetween.

Preferably the electronic control means comprise capacitance sensing means in the form of a charge transfer sensor, for example the QT 110 sensor produced by Quantum Research Group Limited, wherein a fixed charge is transferred from the sensing element to a sampling capacitor of known capacitance. The capacitance of the sensing element, which is affected by the proximity of the object, may then be calculated by measuring the voltage (or, in a burst-mode sensor, the accumulated voltage) across the sampling capacitor, as it is known that Cx = Cs. Vs/Vr Where Cx is the unknown capacitance of the sensing element, Cs is the known capacitance of the sampling capacitor, Vs is the fixed voltage to which the sensing element is charged and Vr is the measured voltage transferred to the sampling capacitor.

Preferably the sensing element comprises at least one wire. Most preferably the sensing element comprises a pair of parallel, spaced apart wires, incorporated into an elongate flexible strip. Preferably the system comprises at least one fixing device into the strip may be fitted. Preferably the fixing device comprises a second elongate strip having a suitably profiled channel for receiving the sensing strip and into which the sensing strip may be clipped or pressed to form an interference fit.

Where the sensing element comprises a pair of wires, the distal ends of those wires are preferably connected across a capacitor, such that the sensing element has a substantial

residual capacitance. Thus, any discontinuity in the sensing element, due, for example, to a break or short in the element, will result in a substantial drop in the capacitance of the cable, which may be detected by the electronic control means, for example to generate an alarm.

The electronic control means may be arranged to respond when the capacitance exceeds a pre-determined threshold value or when the capacitance deviates by more than a pre-determined amount from a residual value.

In either case, the sensitivity of the electronic control means to changes in capacitance is preferably adjustable, either manually or automatically.

Preferably at least the electronic control means are mains powered and are provided with an auxiliary power supply, preferably in the form of one or more re-chargeable batteries, to protect against a failure of the mains supply.

Preferably the electronic control means are arranged to emit an audible or visual signal warning signal whilst the powered device is operating.

Also in accordance with the present invention, there is provided a closure arrangement comprising at least one displaceable closure member, a powered device for operating the closure member, and an electronic safety control system, the electronic safety system comprising an elongate, electricallyconductive element extending along at least part of the leading surface of the closure member and electronic control means responsive to a change in capacitance arising from the close proximity to the element of an object to provide an output signal for controlling the powered device.

Preferably the electronic control means are arranged to control the powered device to arrest an advancing movement of the closure member and/or to reverse the direction of movement of the closure member, in response to the change in capacitance.

Preferably the arrangement comprises means for sensing

the position of the closure member to activate or de-activate the electronic safety control means. For example, the electronic safety control means may be de-activated when the closure means are approaching full deployment, when there is no longer any danger of entrapment, to prevent any change in capacitance that might subsequently arise (for example due to the proximity of the surface against which the leading edge of the closure member is to abut) from preventing the closure member from being fully deployed.

Preferably the closure arrangement comprises an arrangement for closing the gap between two opposed parts of a chair assembly, to adjust the position, e. g. the height or inclination, of the chair, the powered device being an actuator, such as an electric, hydraulic or pneumatic actuator, for effecting said closure.

An embodiment of the present invention will now be described by way of an example only and with reference to the accompanying drawings, in which: Figure 1 shows a re-configurable chair in a lowered configuration; and Figure 2 shows the same chair in an inclined configuration.

Referring to Figure 1, a re-configurable chair 2 is shown comprising a back 4 and squab 6 mounted to an articulated support frame 8, an upper portion 10 of the frame being arranged to pivot forwards, away from a lower portion 12 of the frame, as shown in Figure 2, to assist in unseating a person from the chair.

The degree of inclination of the chair 2 is controlled by an extensible actuator 14, which is remotely operable via a handset 16.

As shown in detail in Figure 2, respective capacitive sensing elements 18,20 extend along the opposing edges of the upper and lower frame portions 10, 12, the sensing elements 18,20 being connected to electronic control means (not shown), which are tuned to respond to an increase in capacitance arising from the close proximity to either of the elements 18,20 of an obstruction, such as a person's hand, to prevent the gap between the two frame portions 10,12 from closing as the chair 2 is lowered.

The arrangement thus prevents an object, such as a person's hand, from becoming trapped between the two converging parts 10,12 of the support frame 8 as the chair 2 is lowered.

Claims

Claims

1) An electronic safety control system comprising an elongate, flexible electrically-conductive sensing element and electronic control means responsive to a change in capacitance arising from the close proximity to the element of an object to provide an output signal for controlling a powered device.

2) An electronic safety control system as claimed in Claim 1, wherein the electronic control means comprise capacitance sensing means in the form of a charge transfer sensor, wherein a fixed charge is transferred from the sensing element to a sampling capacitor of known capacitance.

3) An electronic safety control system as claimed in Claim 1 or Claim 2, wherein the sensing element comprises at least one wire.

4) An electronic safety control system as claimed in Claim 3, wherein the sensing element comprises a pair of parallel, spaced apart wires, incorporated into an elongate flexible strip.

5) An electronic safety control system as claimed in Claim 4, comprising at least one fixing device into the sensing strip may be fitted.

6) An electronic safety control system as claimed in Claim 5, wherein the fixing device comprises a second elongate strip having a suitably profiled channel for receiving the sensing strip and into which the sensing strip may be clipped or pressed to form an interference fit.

7) An electronic safety control system as claimed in any of Claims 4 to 6, wherein the distal ends of the two wires are

connected across a capacitor. 8) An electronic safety control system as claimed in Claim 7, wherein the electronic control means are arranged to detect any drop in the capacitance of the sensing strip due to a discontinuity in the strip.

9) An electronic safety control system as claimed in Claim 7, wherein the electronic control means are arranged to generate an alarm signal in response to said drop in capacitance.

10) An electronic safety control system as claimed in any preceding claim, wherein the electronic control means are arranged to respond when the capacitance exceeds a predetermined threshold value.

11) An electronic safety control system as claimed in any of Claims 1 to 9, wherein the electronic control means are arranged to respond when the capacitance deviates by more than a pre-determined amount from a residual value.

12) An electronic safety control system as claimed in any preceding claim, wherein the sensitivity of the electronic control means to changes in capacitance is manually adjustable.

13) An electronic safety control system as claimed in any of Claims 1 to 11, wherein the sensitivity of the electronic control means to changes in capacitance is automatically adjustable.

14) An electronic safety control system as claimed in any preceding claims, wherein at least the electronic control means are mains powered and are provided with an auxiliary power supply.

15) An electronic safety control system as claimed in Claim 14, wherein the auxiliary power supply is in the form of one or more re-chargeable batteries.

16) An electronic safety control system as claimed in any preceding claim, wherein the electronic control means are arranged to emit an audible or visual signal warning signal whilst the powered device is operating.

17) A closure arrangement comprising at least one displaceable closure member, a powered device for operating the closure member, and an electronic safety control system, the electronic safety system comprising an elongate, electricallyconductive element extending along at least part of the leading surface of the closure member and electronic control means responsive to a change in capacitance arising from the close proximity to the element of an object to provide an output signal for controlling the powered device.

18) A closure arrangement as claimed in Claim 17, wherein the electronic control means are arranged to control the powered device to arrest an advancing movement of the closure member, in response to the change in capacitance.

19) A closure arrangement as claimed in Claim 17 or Claim 18, wherein the electronic control means are arranged to control the powered device to reverse the direction of movement of the closure member, in response to the change in capacitance.

20) A closure arrangement as claimed in any of Claims 17 to 19, comprising means for sensing the position of the closure member to activate or de-activate the electronic safety control means.

21) A closure arrangement as claimed in Claim 20, wherein the electronic safety control means are de-activated when the closure means are approaching full deployment, when there is no longer any danger of entrapment.

22) A closure arrangement as claimed in any of Claims 17 to 21, comprising an arrangement for closing the gap between two opposed parts of a chair assembly, to adjust the position of the chair, the powered device being an actuator for effecting said closure.

23) An electronic safety control system substantially as herein described with reference to the accompanying drawings.

24) A closure arrangement substantially as herein described with reference to the accompanying drawings.