CAPACITIVE SAFETY CONTROL (STRIP, MOTOR DRIVEN FURNITURE)

Abstract: An electronic safety controls 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 a 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 an object from becoming trapped therebetween.

Description: CAPACmVE SAFETY CONTROL (STRIP, MOTOR DRIVEN FURNITURE) 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 a part of a mechanism towards an opposed surface, the sensing element may be fitted to one or other or both of the approaching surfaces 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. The strip is preferably sufficiently flexible to allow it be folded substantially flat, to form one or more angled bends in the strip. Preferably the system comprises at least one fixing device into which 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 parallel, spaced-apart wires, one of the two wires is preferably held at a substantially constant reference potential, and is most preferably grounded, with such an arrangement having been found to substantially increase the consistency of capacitance measurements made by the sensing means over a period of time and/or between different operating environments and the uniformity of sensitivity of the sensing element along its length. Where the sensing element comprises a pair of wires, the distal ends of the two 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 decrease 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, electrically- conductive element extending along at least part of the leading surface of the closure member or of a surface opposed to said leading surface 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 vary the level of responsiveness of the electronic safety control means to changes in capacitance. For example, the electronic safety control means may be arranged to become less responsive 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. Further in accordance with the present invention, there is provided a method for installing an electronic safety control system comprising a sensing element, in the form of an elongate flexible strip incorporating at least two parallel, spaced-apart wires, and electronic control means responsive to a change in capacitance arising from the close proximity to the strip of an object, wherein the strip is bent and/or folded to follow a path across the surface of a substrate. Preferably the electronic control means are arranged to respond when the capacitance deviates by more than a predetermined amount from a residual value, the residual capacitance value being measured when the strip is fitted to the substrate and preferably when the substrate is located in its normal operating environment. 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 is a first perspective view of a re- configurable chair in an inclined configuration, the chair incorporating an electronic safety control system in accordance with the present invention; Figure 2 is an enlarged view of the portion of the chair shown at A in Figure 1; Figure 3 is a second perspective view of the chair of Figure 1 ; Figure 4 is an enlarged view of the portion of the chair shown at B in Figure 3; Figure 5 is a perspective, cut-away view of an re- configurable bed, the chair incorporating an electronic safety control system in accordance with the present invention; Figure 6 is a perspective view of a sink unit, of adjustable height and incorporating an electronic safety control system in accordance with the present invention; Figure 7 is a perspective view of the underside of the sink unit of Figure 6; Figure 8 is an enlarged view of the portion of the sink unit shown at C in Figure 6; Figure 9 is a perspective view of a sink unit, of adjustable height and incorporating an electronic safety control system in accordance with the present invention; Figure 10 is a perspective view of the underside of the sink unit of Figure 9; and Figure 11 is an enlarged view of the portion of the sink unit shown at D in Figure 10. 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 electric motor (not shown) , which is remotely operable via a handset 14. As shown in detail in Figures 2 to 4, respective capacitive sensing elements 18,20 extend along the opposed 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. A cushioned panel 24 is also attached to the front of the chair 2 and is arranged to pivot upwards about its upper edge (as shown) to provide a footrest, a third sensing element 26 being fitted to the front of the chair 2 to prevent the panel 24 from lowering if an obstruction is present between the panel 24 and the front of the chair 2. Each of the sensing elements 18,20 and 26 comprises a flexible strip incorporating a pair of parallel, spaced-apart wires, e.g. 28,30, one wire being permanently grounded, so that a fixed potential applied periodically across the two wires may be used to determine the capacitance of the sensing element (which will vary according to the proximity of to the element of an obstruction) . In order for the strips 18,20 and 26 to follow the profiles of the respective parts of the chair to which they are attached, the strips may be folded (for example as shown in Figure 4) to form bends at appropriate points along their lengths . In a preferred embodiment, a single drive motor (e.g. a linear actuator) is used both to adjust the degree of inclination of the chair and of the panel 24, such that the with the squab of the chair fully lowered, continued operation of the drive motor will raise the panel 24 to provide a footrest. When the panel is subsequently retracted, continued operation of the drive motor will then tip the squab of the chair in a forwards direction. In such an arrangement, the electronic control means may be arranged to selectively respond to a change in capacitance associated with one or more of the sensing strips 18,20 and 26 according to the phase of operation of the chair, to arrest or reverse the direction of the motion of the drive motor. Thus, the control means may be responsive to a change in capacitance associated with strips 18 and 20 only whilst the chair is at least partly inclined, and to a change in capacitance associated with the strip 26 only whilst the panel 24 is at least partly extended. The sensitivity of the control means to changes in sensed capacitance and the respective angles though which the seat and panel must be displaced away from their normal positions before the control means will actively respond to a change in capacitance, are set to ensure that the increase in sensed capacitance as the gap closes between the panel and the front of the chair or between the parts 10 and 12 of the support frame 8, will not prevent the full closure of those gaps, but also such that the control means will only become unresponsive to a change in capacitance associated with a particular strip, when the gap adjacent that strip is sufficiently small that there is no longer any risk of entrapment (the phase of operation/prevailing configuration of the chair being determined, for example, from the outputs position sensors fitted to the moving parts of the chair) . Alternatively, the three strips 18,20 and 26 may comprise portions of the same sensing strip, in which case, the control means may be arranged to respond to increases in capacitance above different thresholds according to the phase of operation of the chair, and preferably only in certain configurations of the chair, for example whilst none of the gaps adjacent the strip is less than a predetermined size (the phase of operation/prevailing configuration of the chair being determined, for example, from the outputs of position sensors fitted to the moving parts of the chair) . The above-described chair arrangements will thus prevent 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, or between the cushioned panel 24 and the front of the chair. A safety control system in accordance with the present invention may also be incorporated into various other motorised mechanisms, such as the furniture arrangements that will be described hereinbelow with reference to Figures 5 to 11. Referring to Figure 5 a re-configurable bed 32 is shown comprising a base-frame 34 and a mattress 36 supported by a plurality of portions 38 whose height and orientation may be independently adjusted by respective drive motors (not shown) . To prevent an object from becoming trapped between any any of the supporting portions 38 and the base-frame 34 of the bed, as the configuration of the bed is adjusted by the drive motors, the bed is fitted with an electronic safety control system, the proximity sensing strip 40 of which extends around the upper perimeter of the frame 34. Referring to Figures 6 to 8, a sink unit 42 is shown whose height may be adjusted by a drive motor 44, the proximity sensing strip 46 of an electronic control system being fitted around the underside of the sink unit 42 to prevent the unit from colliding with an obstruction, such as the legs of a person seated at the sink, as the drive motor 44 closes the gap between the sink unit 42 and the ground. Referring to Figures 9 to 11 a table 48 is shown whose height may be adjusted by a drive motor incorporated into the trunk 50 of the table, the proximity sensing strip 52 of an electronic control system extending around the underside of the table-top 52 to prevent the top from lowering against an obstruction, such as the legs of a person seated at the table, as the drive motor closes the gap between the table-top 52 and the ground.

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 3, wherein the strip is sufficiently flexible to allow it be folded substantially flat, to form one or more angled bends in the strip. 6) An electronic safety control system as claimed in Claim 4 or Claim 5, comprising at least one fixing device into the sensing strip may be fitted. 7) An electronic safety control system as claimed in Claim 6, 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. 8) An electronic safety control system as claimed in any of Claims 4 to 7, wherein one of the two wires is held at a substantially constant reference potential. 9) An electronic safety control system as claimed in Claims 8, wherein said one wire is grounded. 10) An electronic safety control system as claimed in Claim 3, wherein the sensing element comprises two wires, whose distal ends are connected to one another across a capacitor. 11) An electronic safety control system as claimed in Claim 10, 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. 12) An electronic safety control system as claimed in Claim 11, wherein the electronic control means are arranged to generate an alarm signal in response to said drop in capacitance. 13) 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. 14) An electronic safety control system as claimed in any of Claims 1 to 12, wherein the electronic control means are arranged to respond when the capacitance deviates by more than a pre-determined amount from a residual value. 15) 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. 16) An electronic safety control system as claimed in any of Claims 1 to 14, wherein the sensitivity of the electronic control means to changes in capacitance is automatically adjustable. 17) 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. 18) An electronic safety control system as claimed in Claim 17, wherein the auxiliary power supply is in the form of one or more re-chargeable batteries. 19) 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. 20) 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, electrically- conductive element extending along at least part of the leading surface of the closure member or of a surface opposed to said leading surface 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. 21) A closure arrangement as claimed in Claim 20, 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. 22) A closure arrangement as claimed in Claim 20 or Claim 21, 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. 23) A closure arrangement as claimed in any of Claims 20 to 22, comprising means for sensing the position of the closure member to vary the level of responsiveness of the electronic safety control means to changes in capacitance. 24) A closure arrangement as claimed in Claim 23, wherein the electronic safety control means are arranged to become less responsive when the closure means are approaching full deployment, when there is no longer any danger of entrapment. 25) A closure arrangement as claimed in any of Claims 20 to 24, 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. 26) A method for installing an electronic safety control system comprising a sensing element in the form of an elongate flexible strip incorporating at least two parallel, spaced- apart wires and electronic control means responsive to a change in capacitance arising from the close proximity to the strip of an object, wherein the strip is bent and/or folded to follow a path across the surface of a substrate. 27) A method as claimed in Claim 26, wherein the electronic control means are arranged to respond when the capacitance deviates by more than a pre-determined amount from a residual value, the residual capacitance value being measured when the strip is fitted to the substrate. 28) A method as claimed in Claim 27, wherein the residual capacitance value is measured when the substrate is located in its normal operating environment .

Inventors: REES JOHN CHRISTOPHER
Applicants: REES JOHN CHRISTOPHER, SMARTA SYSTEMS LTD, SMARTA SYSTEMS LIMITED
Application year: 2001
Main classification: A47C20
IPC codes: A47C7, A47C17, A47C20, A47C21, A47D15