2. Description of the Related Art A fabric sensor is shown in US 6,501, 465 in which, by the provision of two conducting layers separated by an insulating layer, it is possible to determine the level of pressure applied to the sensor by taking a measurement of current. An enhanced fabric sensor is shown in US 6,452, 479 in which additional conductive and insulating layers are provided so as to facilitate flexing and folding of the sensor while preventing false triggering.

In these known sensors, a substantially linear response is provided over an operational region such that an output varies with the degree of pressure applied. However, in some circumstances fabrications exist in which there is an initial bias pressure applied to the sensor before the sensor is required to become operational in response to an actual interaction.

Brief Summary of the Invention According to a first aspect of the present invention, there is provided a fabric sensor having a first fabric layer and a second fabric layer in physical contact with said first layer, wherein said first layer is knitted as a spacer fabric in which individual spacer threads extend between a first planar portion

and a second planar portion; said spacer threads are insulating threads; said first planar portion and said second planar portion include electrically conducting threads that run in a first direction; said second fabric layer includes conductive threads that run in a second direction; and a force applied to a region of interaction of said sensor greater than a threshold force causes spacer threads at said region of interaction to collapse and thereby allow electrical conduction to occur between said first planar portion and said second planar portion.

Brief Description of the Several Views of the Drawings Figure 1 shows an orthopaedic chair as presenting an environment in which the invention may be deployed ; Figure 2 shows an alternative environment for the invention to be deployed consisting of a soft furnishing; Figure 3 identifies a third environment in which the invention may be deployed in the form of an automobile panel ; Figures 4a and 4b illustrate a known sensor; Figure 5 illustrates output responses of the sensor shown in Figure4; Figure 6 shows a diagrammatic illustration of the environments of Figures 1, 2 and 3; Figure 7 shows a response curve for the sensor shown in Figure 6; Figure 8 shows an example of a spacer fabric as used in the present invention; Figure 9 illustrates a response curve for the spacer fabric shown in Figure 8;

Figure 10 illustrates different types of spacer threads ; Figure 11 illustrates further modifications to response characteristics; Figure 12 illustrates changes to rigidity of the spacer fabric; Figure 13 shows an electrically insulating thread and a conducting fibre of the type used in the preferred embodiment; Figure 14 shows constructions using threads of different sizes; Figure 15 illustrates the sensor with conductive planes ; Figure 16 shows an illustration of a preferred spacer fabric; Figure 17 shows an alternative embodiment of the sensor; Figure 18 shows a cross-section of a spacer fabric; Figure 19 shows an approach to reducing sensor fraying ; and Figure 20 shows a screen printing process.

Written Description of the Best Mode for Carrying Out the Invention Many systems and devices are known that include manually operable controls for controlling various attributes of devices and systems.

The aforesaid United States published patent specifications relate to fabric sensors that may be used to control devices. Fabric sensors of this type have many advantages, one of which being that they are readily incorporated within aspects of the apparatus or devices themselves, particularly when these devices include portions of or sections that are finished in fabric, or fabric-like materials.

By way of example only, a number of examples are given below, including an orthopaedic chair (Figure 1), soft furnishing (Figure 2) and an automotive door panel (Figure 3).

Figure 1 An orthopaedic chair is shown in Figure 1, consisting of a solid framework with soft upholstery applied thereto and finished with a fabric covering 101. The chair includes armrests 102 and 103 over which the fabric covering has been applied. At position 104, beneath the fabric covering, there is provided a fabric sensor responsive to physical interactions brought about by the application of the occupant's fingers. The fabric material is placed in a condition of tension and, as such, applies a compressive force to the fabric sensor. The sensor, as described below, is fabricated so as to require a force at an interaction to exceed a predetermined threshold before conduction and thereby control takes effect. Thus, in response to the activation of controls by an occupant's fingers, said controls control the movement of the chair, brought about by the provision of electrical motors, so as to raise a leg support 105 and, in addition, when selected, to cause the chair seat 106 to rise in an elevated orientation so as to assist an occupant in terms of reaching a standing position when leaving the chair itself.

Figure 2 An alternative application for soft furnishings is shown in Figure 2. In this example a fabric sensor is retained under an outer covering at location 201. In this way, it. is possible for regions of the sensor to be activated so as to control equipment in the home, such as audio visual equipment 202.

Figure 3 A third application for a fabric sensor embodying the present

invention is illustrated in Figure 3. In this example, the fabric sensor is used to control devices within an automobile and may be located, for example, within a door panel 301. The door panel has a fabric or fabric-like outer cover which again applies compressive pressure to the sensor at a location 302. Indications may be printed onto the outer cover so as to illustrate the operations of the sensor, and particular positions at which interaction should take place, along with directions for movement while in contact with the sensor. In this way, it is possible for the sensor to be used as a control for many different types of equipment within the vehicle. This equipment may include, for example, but not exclusively, control for automated seats, such as height control, recline control, rake control and headrest control.

Alternatively, or in addition, the sensor may be used to control the position of an opening window. Furthermore, an interaction may be dragged in an upward or downward orientation such that when the drag stops, this indicates the extent to which the window is to be opened or closed.

Similarly, the fabric sensor could be used to control the operation of a sun roof, external mirrors, such as mirror 303, audio visual systems or environmental conditions, via an appropriate climate control system.

Figures 4A and 4B A sensor is shown in Figures 4A and 4B. Figure 4A shows sensor 401 in a rest condition. Sensor 401 comprises a first pliable outer conductive layer 402, a second outer conductive layer 403 and a separator insulating layer 404 disposed between the first and second outer layers 402,403. The separator insulator layer 404 defines at least one aperture 405.

Figure 48 illustrates the response of sensor 401 to a force F applied to the first outer conductive layer 402 in the region of aperture 405. Under the applied pressure, the first conductive layer 402 is brought into electrical contact with the second conductive layer 403, through aperture 405. In this way, sensor 401 is arranged to detect a mechanical interaction.

Figure 5 Figure 5 shows a graph 501 illustrating output values Z (indicative of the strength of a mechanical interaction) of sensor 401 against applied force.

It can be seen from graph 501 that the Z output response of sensor 401 to pressure under a mechanical interaction is dependent on both the applied force and the size of the contact area. Graph 501 shows different response curves corresponding to different contact areas. For example, response curve 502 corresponds to a relatively large contact area and response curve 503 corresponds to a relatively small contact area. It can be seen that the output response to a similar applied force varies according to the size of the contact area of the mechanical interaction.

Figure 6 A diagrammatic illustration of the environments of Figures 1, 2 and 3 is shown in Figure 6; it should be appreciated that this also represents many other types of similar environments. A fabric sensor 601 is supported by a backing panel 602, which could be part of the automotive door or a chair arm etc. The sensor 601 is responsive to mechanical interactions, such that the location of an interaction that exceeds a predetermined

threshold may be identified by associated processing equipment. However, the operation of the sensor 601 is somewhat modified by the application of a cover sheet 603 which is in contact with the sensor 601 and is also placed in a condition of tension. As such, a degree of force is applied to the sensor even when no manual interaction is taking place.

Figure 7 A response curve for sensor 601 is illustrated in Figure 7. In this curve an output signal 701 is plotted against applied force 702. With no cover applied, the sensor has an operational range of 703. However, with a cover applied, there is effectively a bias force which reduces the operational range of from 703 to 704.

Figure 8 The present invention is preferably embodied by the provision of spacer fabric, a known type of fabric that has two planar portions with individual spacer threads extending between a first planar portion and a second planar portion as shown in Figure 8. However in accordance with the present invention, the spacer fabric is manufactured using electrically conducting an electrically insulating yarns. The fabric itself is produced by a knitting process and the yarns are applied such that non-conducting individual spacer threads 801 extend between a first conducting planar portion 802 and a second conducting planar portion 803. As a result of the knitting process, the conducting threads will tend to run in the same direction, such as in direction 804, for both the first conducting planar portion 802 and the second conducting planar portion 803. Position

detection is then provided by the provision of an additional layer with conducting fibres running in a substantially orthogonal direction as described with reference to Figure 17.

Figure 9 The response of the spacer fabric identified in Figure 8 to an applied force at the position of an interaction is illustrated in Figure 9. The construction illustrated in Figure 8 is shown schematically at 901 and shown again at 902 after a collapse has taken place. A force 903 is applied at a position of an interaction and until said force 903 exceeds a predetermined threshold, little deformation occurs; thus the spacer fabric retains its spaced apart condition. However, as the extent of the applied force 903 increases such that the threshold is reached, the individual spacer threads 904 at the position of the interaction will collapse, resulting in conductive planar portion 905 being brought into contact with conductive planar portion 906 at the position of the interaction 904. Thus, with this particular configuration, the applied force either results in the conducting planes being separated by the spacer fabric or, as the threshold is reached, collapse takes place catastrophically resulting in the conducting layers being brought into contact. The fabric sensor thereby provides substantially an on or off response but, as described below, it is possible to identify the position of the interaction and thereby allow a single fabric sensor to provide for many different attributes of a device or many different devices to be controlled by providing switches and controls at different positions over the area of the sensor.

Figure 10 The nature of the spacer threads may take different orientations as illustrated in Figure 10. The orientation shown at 1001 is substantially vertical and the application of a force 1002 will tend to result in thread buckling as illustrated by arrows 1003 and 1004. A response of this type may be to some extent somewhat unpredictable and this condition may be undesirable in some applications. Consequently, in order to provide a greater degree of control in the way in which buckling occurs, a curve may be introduced to the spacer threads as illustrated at 1011. In this way, when a force 1012 is applied buckling will occur in a more predictable way as illustrated by arrow 1013. Experiments have shown that this configuration also provides a more distinctive"snap"with the collapse condition being more defined and thereby providing a greater degree of tactile feedback.

An alternative approach is illustrated at 1021 in which the spacer fibres are located at an angle. In this way, the application of a force 1022 results in a substantially diagonal buckling effect in the direction of arrow 1023.

As previously described, an attribute of spacer fabrics is that they tend to provide a more digital response in that they are either conducting or non-conducting. However, by providing a crossed configuration for the spacer fibres, as illustrated at 1031, it is possible to achieve a more linear collapse response, which may be referred to as a"squashy"response.

Thus, by changing the nature of the spacer thread orientations, it is possible to manipulate the response characteristics of the sensor so as to make it more suitable for particular applications.

Figure 11 Further modifications to the response characteristics of the sensor may be achieved by changing the nature of the spacer threads themselves.

In a preferred embodiment, the threads have a substantially circular cross- section as illustrated at 1101. If the angle of an applied force is somewhat offset, a similar response should occur irrespective of the actual direction of the force. However, in some circumstances, it may be preferable to change the characteristic of the response depending upon the direction of the force applied. Thus, in order to achieve this effect, it is possible to use spacer threads with an elliptical cross-section, as illustrated at 1102.

Figure 12 The rigidity of the sensor may also be adjusted by making changes to the density of the spacer threads. A first preferred density is illustrated at 1201 with spacer threads having a particular linear density (as usually measured in dernier or tex) and a particular thread spacing.

As illustrated at 1202, rigidity may be increased by increasing the density of the individual threads themselves, that is, by providing threads of a greater thickness. Alternatively, instead of increasing the density of the individual threads, the actual spacing between threads may be reduced as illustrated at 1203. Furthermore, the provision of more threads (as distinct from the same number of threads with a greater thickness) provides a stronger physical connection between the outer planar portions thereby improving overall operational integrity.

Figure 13 As previously described, the spacer threads themselves are non- conducting threads whereas the planar portions 802 and 803 include electrically conducting threads.

An electrically insulating thread 1301 of the type suitable for a spacer thread is shown in Figure 13. These are preferably implemented as monofilaments and preferred materials include mylar (registered trademark), polyester and grilon. The density should be at least 50 denier (the mass in grams of nine thousand metres of yarn), although if the monofilaments are too large construction becomes difficult due to difficulties involved with respect to bending the filaments into connecting stitches.

Thus when constructed using a weft knitting machine the yarns have a thickness typically of between 50 denier and eighty dernier.

A conducting fibre of the type present in the conducting planar portions is illustrated at 1302. These fibres are constructed from an inner non-conducting yarn 1303 with a conducting yarn 1304 wrapped around the non-conducting yarn. The non-conducting yarn may be constructed from polyester and the conducting yarns 1304 may be also be constructed from . polyester (or kevlar in specialist applications) coated with an appropriate metal such as copper or silver. This results in a construction which consists typically of 40% metal. Having being constructed as shown at 1302, the yarn has a density of typically between 70 and 160 dernier when weft knitting. If larger fibres are required, these may be implemented by a process of warp knitting but a disadvantage of the warp knitting approach is that the amount of material used or each run becomes considerably larger.

Figure 14 A construction is illustrated at 1401 in which relatively short conductive fibres 1402 are provided which results in a disadvantage to the effect that upon stretching a variation may occur in terms of electrical contacts resulting in variations to the measured resistance. A preferred implementation is shown at 1403 in which the conducting fibres are relatively large resulting in a substantially continuous conductive region 1404 such that undesirable changes to resistivity do not occur when stretching forces are applied to the fabric.

Figure 15 A sensor is illustrated in Figure 15 consisting of conductive planes 1501 and 1502 separated by the spacer threads 1503. The sensor is applied to a backing panel 1504 and the overall assembly is then covered by a cover sheet 1505. The cover sheet 1505 is held tightly in position resulting in a bias force 1506 being applied to the sensor. This force is below the threshold force and therefore it does not result in the sensor being triggered. Additional forces are required in order for the triggering of the sensors to take place.

To some extent, spacer fabrics can absorb compression forces thereby providing a degree of padding and spacer fabrics as such are known for use in such applications. The approach of the present preferred embodiment is to adopt this characteristic of spacer fabrics in a sensor where the spacer threads provide insulation between conducting planes when insufficient pressure is applied in order to cause the spacer threads to

collapse.

In addition to being used as a control device for the orthopaedic chair shown in Figure 1, sensors of this type may also be used to confirm that the chair is occupied by placing a sensor at an appropriate location over the seat. In this way, non-occupancy is identified and motorised control mechanisms may be disabled as a consequence. Thus, it is not possible for the motorised components of the chair to be operated when the chair is not occupied, such as may occur were a child to interfere with the control panel.

Figure 16 An illustration of a preferred spacer fabric for the present application is shown in Figure 16. Spacer threads 1601 separate a first conductive plane 1602 from a second conductive plane 1603. Ideally, in the first conductive plane 1602 the conductive threads run in a direction indicated by arrow 1604. Conductive strips 1605 and 1606 connect respective ends of the conductive fibres allowing an electrical potential to be applied across said conducting strips. When a mechanical interaction takes place, the circuit effectively defines a potential divider and the resulting trapped voltage may be measured to locate a position on the sensor in one dimension.

Thus, in the preferred implementation, conducting fibres in the opposing plane run in a substantially orthogonal direction as indicated by arrow 1607. Conducting strips 1608 and 1609 are provided such that, again, it is possible to apply an electrical potential to these conducting strips

such that a potential may be measured on the opposing plane when interaction takes place. Thus, with threads running in the orthogonal direction, a position of interaction is identified in a different dimension allowing a two-dimensional co-ordinate of the interaction to be identified.

Thus, an electrical potential would be applied across 1605 and 1606 and then across 1608 and 1609 alternately such that by taking two measurements it is possible to identify the position of an interaction in the two-dimensional plane.

A problem with the approach shown in Figure 1 is that it is desirable to construct the spacer fabric in a single operation, preferably a weft knitting operation. However, the result of the weft knitting operation is that the direction of the fibres will be the same in both the upper plane 1602 and the lower plane 1603. Thus an arrangement of the type shown in Figure 16, although preferred, is extremely difficult to implement in practice.

Figure 17 A solution to the problem identified in Figure 16 is shown in Figure 17. In preference to implementing the sensor using a single spacer fabric exclusively, a layered structure is developed. In particular, in the preferred embodiment, the sensor has a first fabric layer 1701 and a second fabric layer 1702 in physical contact with the first layer 1701. The first layer 1701 is knitted as a spacer fabric in which individual spacer threads 1703 extend between a first planar portion 1704 and a second planar portion 1705. The spacer threads 1703 are insulating threads, while the first planar portion 1704 and the second planar portion 1705 include electrically conducting

threads that both run in a first direction. Thus, in this example, the conducting threads of planar portion 1704 run in the direction of arrow 1706 with the conducting threads of the second planar portion 1705 running in a substantially similar direction. Thus, in this way, it is relatively straightforward for the spacer fabric to be produced in a single knitting operation.

The two-dimensional measurement process is achieved by arranging conducting threads present in the second fabric layer 1702 to run in a second direction (preferably orthogonal to the first) which, in the example shown in Figure 17, results in the threads of the second layer running in a direction illustrated by arrow 1707. Thus, when a force is applied to a region of an interaction of the sensor that is greater than the threshold force, the spacer threads 1703 at the position of the interaction collapse and thereby allow electrical conduction to occur between the first planar portion 1704 and the second planar portion 1705. The second planar portion 1705 is in contact with the second layer 1702 resulting in conduction taking place between the first planar portion 1704 (with threads running in a first direction) and a second layer 1702 with threads running in the second direction.

Figure 18 A cross-section of a spacer fabric is illustrated in Figure 18. It is appreciated that in many environments such as those illustrated in Figures 1 to 3, the detector and fabric surface may experience trauma due to the incursion of sharp objects, such as knitting needles, pins and other objects

presenting sharp surfaces. An example of such a trauma is illustrated in Figure 18, in which a sharp object 1801 has been inserted into a spacer fabric 1802. The nature of the fabric is such that incursions of this type cause relatively little damage. The fibres will tend to be displaced in preference to being cut and will then tend to return to their original condition once the incursion is removed.

However, it is appreciated that when using fibres of this type problems may occur at material edges which may, in some circumstances be susceptible to fraying as shown at 1803.

Figure 19 An approach to reducing risks of sensor damage due to fraying is illustrated in Figure 19. At step 1901 the spacer fabric is impregnated with a liquid elastomer, such as silicone rubber or polyurethane etc.

Having been impregnated with the liquid elastomer, the assembly is allowed to set or cure at step 1902 thereby resulting in an assembly with fabrics surrounded by a solid elastomer edging.

At step 1903 the elastomer edging is cut thereby providing clean edges and an assembly of a predefined size.

Figure 20 A screen printing process is illustrated at Figure 20. Thus, it is possible for the liquid elastomer operations illustrated with respect to Figure 19 to be conducted while a screen printing operation is taking place so as to apply graphics to an outer surface. A fabric sensor 2001 is applied to a base support 2002. A screen 2003 is applied over the sensor 2001 which

contains masking material 2004. Ink is introduced and a transfer of ink occurs onto the fabric 2001 at positions such as position 2005 where a gap exists.