This invention relates to a textile form touch sensor and to a method of manufacturing a textile form touch sensor
It is known to provide a touch sensor, such as a button on a flexible keyboard, from a multi-layered textile construction. For example, United States Patent Application Publication US 2002/0180578 discloses a position sensor that is arranged to detect the position of a mechanical interaction such as the application of manual pressure. A first fabric layer has electrically conductive fibers machined therein to provide a first conductive outer layer allowing conduction in all directions along the layer. A second fabric layer has electrically conductive fibers machined therein to provide a second conductive outer layer allowing conduction in all directions along the layer. A central layer is disposed between the first outer layer and the second outer layer. The central layer includes conductive elements. A first insulating separating element is disposed between the first conductive outer layer and the conducting elements. A second insulating separating element is disposed between the second conductive outer layer and the conducting elements. The conducting elements provide a conductive path between the first conducting outer layer and the second conducting outer layer at the position of a mechanical interaction. This five-layered structure measures the position and surface area of the press on the sensor. No direct measurement of the extent of the pressure is possible. The pressure applied by a finger can be deducted from the measured surface area, only for small pressure values
In the same Patent Application Publication, an alternative position sensor is shown in cross-section in
A further alternative embodiment is shown in cross-section in
It is therefore an object of the invention to provide a three-layer touch sensor that is an improvement of the known devices.
According to a first aspect of the invention, there is provided a textile form touch sensor comprising first and second outer conductive layers, and a third layer, intermediate of the first and second layers, wherein the third layer comprises a non-conductive textile coated with a piezoresistive material. The electrical conductance of this piezoresistive material depends on the pressure applied to it.
Owing to this aspect of the invention, it is possible to provide a three-layered textile form touch sensor that can measure position and also the extent of the pressure applied to the touch sensor, while being of simple construction. The resulting sensor is easier to construct than the known sensors.
Advantageously, the piezoresistive material is non-continuous on the non-conductive third layer, and is coated on the non-conductive third layer so as to form an arrangement of defined blocks of the piezoresistive material. The presence of defined blocks of the piezoresistive material on the third layer provides a number of distinct advantages. Each block can be considered as a separate button (in the final construction of the sensor) isolated from each other. This allows the buttons to have different electronic profiles and also allows the layers to be joined together (for instance by stitching) without making an electrical connection at the join of the layers.
Preferably the first, second and third layers are joined together at a point where no piezoresistive material is present. The first, second and third layers are joined together in a series of straight lines, the lines running in between the defined blocks of piezoresistive material. This results in a touch sensor that is more robust than current sensors. The layers are joined together and this helps prevent lateral movement of layers relative to each other. If this occurs (and it is a known problem) then false readings can be given when a user presses the touch pad.
The touch sensor may further comprise a fourth layer, the fourth layer being provided with visible indications. This fourth layer provides a user with a visible indication of the logical function of the sensor at any particular point on the sensor's external surface.
Preferably the touch sensor further comprises two pairs of electrodes, a first pair connected to the first outer layer and a second pair connected to the second outer layer, the pairs of electrodes being perpendicular to each other, and also further comprises electronic circuitry connected to the pairs of electrodes.
According to a second aspect of the invention, there is provided a method of manufacturing a textile form touch sensor comprising the steps of receiving first and second conductive layers, receiving a third layer, the third layer comprising a non-conductive textile coated with a piezoresistive material, and forming the layers such that the third layer is intermediate of the first and second layers.
Owing to this aspect it is possible to manufacture a three-layer textile form touch sensor in a straightforward and simple way.
Advantageously, prior to the receiving of the non-conductive third layer, the method further comprises coating the third layer with the piezoresistive material. The coating of the third layer with the piezoresistive material can be used to create a coating of piezoresistive material on the non-conductive third layer that is non-continuous. Preferably, the coating of the third layer with the piezoresistive material creates a coating of piezoresistive material on the non-conductive third layer that forms an arrangement of defined blocks of piezoresistive material.
Preferably, the method further comprises, prior to the forming of the layers, receiving a fourth layer, the fourth layer being provided with visible indications. The forming of the layers can further comprise joining together the layers at a point where no piezoresistive material is present. Advantageously, the forming of the layers comprises joining together the layers in a series of straight lines, the lines running in between the defined blocks of piezoresistive material.
The method can further comprise affixing two pairs of electrodes to the layers, a first pair connected to the first outer layer and a second pair connected to the second outer layer, the pairs of electrodes being perpendicular to each other, and can also further comprise connecting electronic circuitry to the pairs of electrodes.
Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:—
The structure shown in
The sensor 10 further comprises two pairs of electrodes, a first pair 20 connected to the first outer layer 12 and a second pair 22 connected to the second outer layer 14, the pairs of electrodes 20 and 22 being perpendicular to each other. The touch sensor also comprises electronic circuitry 30 connected to the pairs of electrodes 20 and 22.
The circuitry 30 is shown in detail in
Rx and Ry are the resistances of the top and bottom conducting layers 12 and 14. Rp is the variable resistance of the third layer 16 printed with the Tekscan 18. Rref is used both to detect the presence of a touch action as well as the exerted touch pressure. In effect when the variable resistance of the press is measured, the layers 12 and 14 (the resistors Rx and Ry) are at constant potential across their whole surface area and the circuit created is a potential divide with Rp and Rref with the buffer 32 reading the voltage at the point between Rp and Rref, thereby measuring the resistance of Rp (since Rref is known). The resistance of Rp is a measure of the extent of the press by the user on the touch sensor 10.
During the x position detection, a linear potential drop across the conducting layer Rx is applied. A potential probe consists of the electrical series configuration of part of Ry and Rp. However, the probe's resistance becomes irrelevant in reading the x-coordinate as a high impedance readout buffer is used. The same holds when determining the y coordinate. In effect the Rp as it touches the resistor Rx (when measuring the x coordinate) measures the voltage at that point, effectively measuring the position of the press on the touch sensor in the x direction. This is reversed when measuring the y coordinate.
As the piezoresistive material 48 is arranged in a series of blocks on the third layer 16, this allows the first, second and third layers 12, 14 and 16 to be joined together at a point where no piezoresistive material 48 is present. The first, second and third layers 12, 14 and 16 are joined together in a series of straight lines, the lines running in between the defined blocks of piezoresistive material 48. By joining together the layers a more stable structure is present and it also greatly reduces the likelihood of a false reading caused by the folding of the sensor when in use.
In
In this basic version of the method of constructing the touch sensor 10, the third layer 16 is provided already coated with the piezoresistive material 18. However the method can further comprise, prior to the receiving 604 of the non-conductive third layer 16, the step 602 of coating the third layer 16 with the piezoresistive material 18. By including within the method of constructing the touch sensor the step 602 of coating the third layer 16, greater flexibility is achieved in choosing the possible arrangements of coatings of the piezoresistive material 18.
For example, the coating 602 of the third layer 16 with the piezoresistive material can be used to create a coating of piezoresistive material on the non-conductive third layer 16 that is non-continuous. Such an arrangement is shown in
The method also includes the optional step 612 which means that the method of manufacture further comprises, prior to the forming 606 of the layers, receiving 612 a fourth layer 42, the fourth layer 42 being provided with visible indications 44. The step 606, which is the forming of the layers together to produce the body of the touch sensor 10, can also comprise joining together the layers 12, 14 and 16 at a point where no piezoresistive material 18 is present. In a preferred embodiment, as shown in
Following the forming 606 of the layers the method further comprises affixing two pairs of electrodes 20 and 22 to the layers 12 and 14 respectively, a first pair 20 connected to the first outer layer 12 and a second pair 22 connected to the second outer layer 14, the pairs of electrodes being perpendicular to each other. The method also further comprises connecting electronic circuitry 30 to the pairs of electrodes 20 and 22.
Once the touch pad sensor 10 is formed, it can be integrated in a wide range of fabrics, such as used in clothing or furniture. The following applications are appropriate uses of the sensor, a light dimmer/switch in wallpaper; a weight sensor in chair, sofa, mattress or bath mat; an interactive gaming playmat or wall hanging; a guidance or security carpet detecting the location of people walking on it, a fabric piano with force sensitivity; a touch panel in a sofa or in a blanket (home, automotive) to control ambient electronics and/or chair position; a shoe insole that analyses walking/running pattern; and the touch screen of a fabric display (a fabric display put on top of a fabric touch pad).
One such application is illustrated in
In summary, in comparison with the known prior art, the following problems are solved. Load sensitive material is not applied as a sheet of load-sensitive non-woven or a sheet of load sensitive elastomer but can be locally printed in any desired shape or structure. The threshold load needed to obtain a conductance larger than zero can be determined by the fraction of conducting particles present in the ink. The slope of the conductance versus the load, i.e. the load sensitivity of the pad is also dependent on the filling fraction of conducting particles in the ink. Due to the freedom opened up by printing, the textiles can be sewn to each other, avoiding sliding of the layers (sliding leads to the need for re-calibration). No spacers are needed and the material can be folded without the occurrence of false signals. The composite is fully textile with an open structure so that the natural breathing character of textiles is maintained.
Number | Date | Country | Kind |
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0407366.4 | Mar 2004 | GB | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/IB05/51013 | 3/24/2005 | WO | 9/27/2006 |