WO2005093397A1

WO2005093397A1 - Moisture sensing apparatus

Info

Publication number: WO2005093397A1
Application number: PCT/GB2005/001092
Authority: WO
Inventors: Stuart Mark Walkington
Original assignee: Eleksen Limited
Priority date: 2004-03-22
Filing date: 2005-03-22
Publication date: 2005-10-06
Also published as: GB0406350D0

Abstract

Sensing apparatus comprising a fabric applicable to a target region and a processing device, having a first terminal and a second terminal, arranged to detect a change in an electrical characteristic. The fabric comprises a plurality of electrically conducting threads arranged individually or in groups to provide a plurality of conductive elements, and a plurality of insulating threads assembled with the conducting threads and arranged so as to separate the conductive elements. A first group of conductive elements are electrically connected together, a second group of conductive elements are electrically connected together and the first group and the second group are connected to the first terminal and the second terminal respectively. The presence of moisture absorbed by the fabric in the target region allows conduction between one or more of the first group of conducting threads with one or more of the second group of conducting threads.

Description

Moisture Sensing Apparatus

Background of the Invention

1. Field of the Invention The present invention relates to. an apparatus for sensing the presence of moisture, comprising a fabric, applicable to a target region, and a processing device.

2. Description of the Related Art Moisture sensing devices using electrical conduction are known.

JP2001-139983 (Gunze Limited) shows a moisture sensor implemented as a textile fabric. However, the problem with known moisture sensors when implemented in fabric is that they tend to be relatively insensitive and may not provide good response characteristics across the majority of the surface.

Brief Summary of the Invention According to a first aspect of the present invention there is provided sensing apparatus for sensing the presence of moisture, comprising a fabric applicable to a target region and a processing device having a first terminal and a second terminal and arranged to detect a change in an electrical characteristic, wherein said fabric comprises a plurality of electrically conducting threads arranged individually or in groups to provide a plurality of conductive elements; and a plurality of insulating threads assembled with said conducting threads to establish a fabric, wherein said insulating threads are arranged so as to separate said conductive elements; a first group of said conductive elements are electrically connected together; a second group of said conductive elements are electrically connected together; said first group are connected to said first terminal and said second group are connected to said second terminal; and the presence of moisture absorbed by said fabric in the target region allows conduction between one or more of said first group of conducting threads with one or more of said second group of conducting threads. According to a second aspect of the present invention at least one conductive element of said first group is arranged between at least two conductive elements of said second group. According to a third aspect of the present invention the first group is connected together by a first connecting strip, the second group is connected together by a second connecting strip displaced on the fabric from the first connecting strip; the first group is insulated from said second connecting strip and the said second group is insulated from said first connecting strip. According to a fourth aspect of the present invention the second group is insulated from the first connecting strip by the presence of an insulating band; conduction between the first group and the first connecting strip is provided by a first set of holes in said insulating band; and conduction between the second group and the second connecting strip is provided by a second set of holes.

Brief Description of the Several Views of the Drawings Figure 1 shows sensing apparatus including a fabric sheet that includes electrically conducting threads; Figure 2 shows an arrangement of conducting bands relative to conducting threads of a first fabric; Figure 3 shows an arrangement of conducting bands relative to conducting threads of a second fabric; Figure 4 shows a cross-section of the configuration of Figure 3; Figure 5 illustrates a type of yarn; Figure 6 shows an arrangement of conducting bands relative to conducting threads of a third fabric.

Written Description of the Best Mode for Carrying Out the Invention

Figure 1 A sensing apparatus embodying the present invention is shown in

Figure 1. A sheet 101 produced from a fabric is applied over a target region where moisture detection is required. Thus, for example, the sheet could be applied over a bed to detect excessive moisture generated by a patient (possibly through incontinence) or liquid spillage etc. It should be appreciated that the detector may be applied in many other applications where it is desirable to identify the presence of moisture in a target region. The sensing apparatus includes a processing device 102 having a first terminal 103 and a second terminal 104. The processing device 102 is arranged to detect change in an electrical characteristic when moisture is applied to the sheet 101, such as a change in conductance. However, it should be appreciated that other electrical characteristics may be determined, such as capacitance. Fabric sheet 101 includes electrically conducting threads 105, 106, 107, 108, 109, 110, 111 and 112. Each of these electrically conducting threads 105, 106, 107, 108, 109, 110, 111, 112 individually provides a conductive element. In an alternative arrangement, however, a plurality of conducting threads may in combination provide a conductive element. The fabric of sheet 101 is produced by including a plurality of insulating threads 113 assembled with the conducting threads 105, 106, 107,

108, 109, 110, 111, 112 during a weaving or knitting process. The insulating threads 113 are arranged to separate the conducting threads 105, 106, 107,

108, 109, 110, 111, 112. In the present embodiment, sheet 101 is produced from a warp-knit fabric. Conductive elements 105, 107, 109 and 111 are electrically connected together into a first group by means of a conducting band 114 that is in turn connected to second terminal 104. Similarly, conductive elements 106, 108,

110 and 112 are electrically connected together into a second group by a second conducting band 115 that is in turn connected to first terminal 103. In this embodiment, the first conducting band 114 and the second conducting band 115 are produced from strips of conducting fabric and these are in turn adhered to the sheet .101 by means of a conductive adhesive. When moisture is present in the target region for which the sensing apparatus is provided, a proportion of the moisture will be absorbed by the fabric sheet 101. This in turn facilitates conduction between one or more of the first group of conducting threads (105, 107, 109, 111) with one or more of said second group of conducting threads (106, 108, 110, 112). In this example, moisture is received at a target region 116. As previously described, conducting thread 108 is electrically connected to terminal 104 and conducting thread 109 is electrically connected to terminal 103. Thus, a potential difference exists across conducting threads 108 and 109. The presence of moisture within region 116 renders the previously insulating portion of the sheet electrically conductive thereby allowing current to flow between conducting threads 108 and 109, across the region 116. This increased flow of current is detected by the processing device 102, which in turn provides an appropriate output. Upon detecting electrical conduction that exceeds a predetermined threshold (due to a reduction in resistivity of the sheet at the target region) the processing device 102 may generate one or more responses. For example, an output from the processing device 102 may illuminate a light 117, sound an audible alarm via a loud speaker 118 or produce an output signal to a computer network via an output interface 119. It will be appreciated that in the embodiment shown in Figure 1, the conducting threads are dispersed throughout the sheet 101 thereby providing a relatively large target region. It can be appreciated that at least one of the conductive elements of the first group is arranged between at least two conductive elements of the second group. The spacing between the conductive elements will determine the resolution of the sheet and hence its sensitivity to the application of moisture. Thus, when the spacing is relatively close, relatively small drops of moisture will be detected. In alternative embodiments it may be preferable to produce an alarm only when a relatively large region of the sheet has received moisture. However, for many applications it is desirable to identify relatively small regions therefore experimentation has shown that a spacing of between two millimetres (2mm) and ten millimetres (5mm) (with a spacing of three to five millimetres (3-5mm) being preferred) is considered appropriate. As previously described, a first group of conductive elements are connected together by a first connecting strip 114 and a second group of conductive elements are connected together by a second connecting strip 115, which is displaced on the fabric sheet 101 from the first connecting strip 114. The first group of conductive elements is insulated from the second connecting strip by the presence of holes 121, 122 and 123. Similarly, the second group of conductive elements is insulated from the first connecting strip 115 by the presence of holes 124, 125, 126 and 127. In this embodiment, conductive elements are provided by individual threads included within the fabric during the production process.

Figure 2 In an alternative embodiment, each conductive element is defined by a plurality of conducting threads. For example, in a woven fabric all of the warp threads could be conducting threads and a set of threads defining a conductive element may be defined by the positioning of holes, such as holes 201, 202, 203, 204, 205 and 206 in masking band 207. A first conducting band 211 provides conduction through holes 201 , 202 and 203. Hole 201 defines a set of threads 212, 213 and 214, which are exposed to the first conducting band 211. Adjacent threads are insulated from the first conducting band 211 but are available at holes 204 and 205 in the insulating band 207, making contact with a second conducting band 215. A single insulating masking band may be used, with holes exposing one or more conducting threads to a first conducting band offset or staggered from holes exposing one or more conducting threads to a second conducting band. Alternatively, a separate insulating masking band may be provided to each conducting band.

Figure 3 In an alternative embodiment, it is possible to achieve insulation by using a relatively coarse weave. Conducting warp threads 301, 302, 303 and 304 are separated by insulating weft threads 311 , 312 and 313. At the position of a first conducting band 321 , alternating conducting threads come into contact with the band such that the band only makes electrical contact with alternating threads. Thereafter, a similar conducting band 322 may be positioned at the next weft thread such that again, alternating warp threads make electrical contact; these being the alternatives to the ones making contact with band 321. As an alternative, a second conducting band could be placed on the opposing surface, as illustrated at 323.

Figure 4 A cross section of the configuration illustrated in Figure 3 is shown in Figure 4. An insulating thread is shown at 401 with threads 402, 403, 404, 405, 406 and 407 being conducting threads. A first conducting band 411 is placed on an upper surface so as to make electrical contact with conducting threads 405, 406 and 407. Similarly, a second conducting band 412 is placed on a lower surface so as to make electrical contact with conducting threads 402, 403 and 404.

Figure 5 In an alternative embodiment, insulating thread 401 is replaced by a staple yarn 501 taking the form of a short yarn thread having a relatively fluffy appearance. A staple yarn of this type has advantages in the moisture detection application given that it has greater absorbent properties.

Figure 6 An alternative embodiment is illustrated in Figure 6. A weaving operation is configured such that the conducting yarns are exposed at selected regions, such as region 601. The yarns exposed at region 601 provide a conductive element and are also exposed at position 602 and position 603. Adjacent conductive elements have yarns exposed at region

S04, at region 605 and at region 606. At region 602, a first conductive element comes into contact with a first conducting band 607. Similarly, at region 605 a second conductive element comes into contact with a second conducting band 608. Thus, in this way, a first set of conductive elements contact first band 607 and a second set of conductive elements contact band 608.

Claims

1. Sensing apparatus for sensing the presence of moisture, comprising a fabric applicable to a target region and a processing device having a first terminal and a second terminal and arranged to detect a change in an electrical characteristic, wherein said fabric comprises a plurality of electrically conducting threads arranged individually or in groups to provide a plurality of conductive elements; and a plurality of insulating threads assembled with said conducting threads to establish a fabric, wherein said insulating threads are arranged so as to separate said conductive elements; a first group of said conductive elements are electrically connected together; a second group of said conductive elements are electrically connected together; said first group are connected to said first terminal and said second group are connected to said second terminal; and the presence of moisture absorbed by said fabric in the target region allows conduction between one or more of said first group of conducting threads with one or more of said second group of conducting threads.

2. Sensing apparatus according to claim 1 , wherein at least one conductive element of said first group is arranged between at least two conductive elements of said second group.

3. Sensing apparatus according to claim 1 or claim 2, wherein said first group is connected together by a first connecting strip; said second group are connected together by a second connecting strip, displaced on said fabric from said first connecting strip; said first group is insulated from said second connecting strip; and said second group is insulated from said first connecting strip.

4. Sensing apparatus according to claim 3, wherein said first group is Insulated from said second connecting strip by the presence of insulating means.

5. Sensing apparatus according to claim 4, wherein said insulating means is a masking band.

6. Sensing apparatus according to claim 4 or claim 5, wherein said second group is insulated from said first connecting strip by the presence of said insulating band; conduction between said first group and said first connecting strip is provided by a first set of holes in said insulating band; and conduction between said second group and said second connecting strip is provided by a second set of holes.

7. Sensing apparatus according to claim 3, wherein said first group is exposed at the position of said first connecting strip and said second group is exposed at the position of said connecting second strip.

8. Sensing apparatus according to claim 6, wherein the exposure of said conductive elements is configured during the production of the fabric.

9. Sensing apparatus according to claim 3, wherein said insulating threads define a first surface and a second surface; said first group is arranged on said first surface; and said second group is arranged on said second surface.

10. Sensing apparatus according to claim 9, wherein said first connecting strip is attached to said first surface and said second connecting strip is attached to said second surface.

11. Sensing apparatus according to any of claims 1 to 10, wherein said insulating threads are provided by staple yarn taking the form of short yarn thread.

12. Sensing apparatus according to any of claims 1 to 11 , wherein upon detecting electrical conduction that exceeds a predetermined threshold said processing device generates at least one response from: illuminating a light, sounding an audible alarm and producing an output signal to a computer network.