GB2511356A

GB2511356A - Pressure mat

Info

Publication number: GB2511356A
Application number: GB201303663A
Authority: GB
Inventors: David Jones; Simon John Harrison
Original assignee: ISENSOL Ltd
Current assignee: ISENSOL LIMITED
Priority date: 2013-03-01
Filing date: 2013-03-01
Publication date: 2014-09-03
Anticipated expiration: 2033-03-01
Also published as: GB2511356B; WO2014132018A1; GB201303663D0

Abstract

A pressure mat 10 and a method of operating it. The mat 10 comprises a first conductive layer 12, a resistive layer 14 whose resistance changes in proportion to the pressure applied to the resistive layer and an electrical circuit connected to the first conductive layer and/or the resistive layer and arranged to detect the change in resistance in the resistive layer. The mat may further comprise a spacer 18 located in-between the first conductive layer and the resistive layer. The spacer may be in direct contact with the first conductive layer and the resistive layer. The pressure mat may comprise a second conductive layer on the outside of the resistive layer. The first conductive layer may comprise two independent conductors. The spacer may comprise a plurality of apertures. The apertures may be arranged in a regular pattern and the apertures may all be the same size or may differ in size.

Description

PRESSURE MAT

S This invention relates to a pressure mat.

The detection of pressure using a pressure mat is well known. A wide variety of different mechanical and electrical systems are known for the detection of pressure. However, pressure mats tend to be able to detect the io presence or otherwise of an object on the mat, without giving any further information about the object that is causing the pressure to be exerted onto the pressure mat. In general, pressure mats provide a binary on/off reading as to whether a pressure is detected on the pressure mat.

It is therefore an object of the invention to improve upon the known art.

According to a first aspect of the present invention, there is provided a pressure mat comprising a first conductive layer, a resistive layer whose resistance changes in proportion to the pressure applied to the resistive layer, and an electrical circuit connected to the first conductive layer and/or the resistive layer and arranged to detect the change in resistance in the resistive layer.

According to a second aspect of the present invention, there is provided a method of operating a pressure mat comprising a first conductive layer, a resistive layer whose resistance changes in proportion to the pressure applied to the resistive layer, and an electrical circuit connected to the first conductive layer and/or the resistive layer, the method comprising the steps of supplying an electric current from the electrical circuit to the connected first conductive layer and/or the resistive layer and detecting the change in resistance in the resistive layer.

Owing to the invention, it is possible to provide a pressure mat that captures more information than just the detection of a pressure on the mat. By using a resistive layer in the construction of the pressure mat and detecting the change in the resistance in the resistive layer, it is possible to detect further information about the type of pressure being applied to the pressure mat. This additional information could relate to the magnitude of the pressure being applied, the surface area of the object applying the pressure and its location S on the pressure mat, and/or the type of object that is applying the pressure to the pressure mat, for example.

The occupancy detection mat is a device used to detect the presence, non-presence, addition or removal of an object/weight on its surface. The mat is constructed of layers of conductive and non-conductive materials in multiple io configurations and formats as per the need of the application it is used for. The mat can detect objects of various weight and size with a ratiometric output level relative to the weight and applied surface area. The mat can be a stand-alone device or a peripheral sensor to a host system. The mat has the ability to detect the presence of an applied load. The output of the mat is a value of electrical resistance. The output of the mat is relative to the applied mass and surface area of the applied mass. This provides different outputs relative to different loads and surface areas, thereby giving a ratiometric output relative to applied mass and surface area.

An example of the pressure mat's behaviour may be considered if an object similar in shape, size and weight to a house brick (rectangular block, sides/faces of differing shape/surface area) is applied to the mat. Although the applied mass/weight of the object is the same, the resistance of the mat would be different for each side/face of the object of differing surface area. This gives the ability to detect the orientation of an applied mass, movement of the mass, addition to the mass and reduction of the mass.

Preferably, the pressure mat further comprises a spacer located in-between the first conductive layer and the resistive layer, and in a preferred embodiment, the spacer is in direct contact with the first conductive layer and the resistive layer. A spacer can be used to separate the first conductive layer from the resistive layer and this can be used to in order to support more complex constructions of the pressure mat that will provide more accurate and/or more varied outputs.

The spacer can comprise a plurality of apertures, which allow the first conductive layer to contact the resistive layer when pressure is applied to the pressure mat. When the pressure mat is in position without any pressure applied, then the spacer ensures that the first conductive layer and the S resistive layer are not in contact. When pressure is applied to the pressure mat then the first conductive layer and the resistive layer will come into direct contact through the apertures in the spacer. The size and shape and arrangement of the apertures in the spacer can be selected according to the specific application of the pressure mat.

Advantageously, the pressure mat further comprises a second conductive layer located on the outside of the resistive layer. In a preferred embodiment, the second conductive layer is in direct contact with the resistive layer. The use of a second conductive layer within the pressure mat will be preferable in certain applications of the pressure mat and will also make the pressure easier to manufacture, depending upon the materials used.

Ideally, the first conductive layer comprises two independent electrical conductors and the electrical circuit is connected to the two independent electrical conductors. A single conductive layer can have two independent conductors present, both of which are connected to the electrical circuit. This simplifies aspects of the construction and operation of the pressure mat, as only one layer needs to be connected to the electrical circuit and the resistive layer will make a connection between the two independent conductors, when pressure is applied to the pressure mat.

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:-Figure 1 is a schematic diagram of a pressure mat, in three different configurations, Figures 2 and 3 are diagrams of electrical circuits modelling the behaviour of the pressure mat, Figure 4 is a schematic diagram of two different embodiments of a conductive layer of the pressure mat, Figure 5 is a schematic diagram of two further different embodiments of a conductive layer of the pressure mat, Figure 6 is a schematic diagram of two different embodiments of a spacer layer of the pressure mat, S Figure 7 is a schematic diagram of two further different embodiments of a spacer layer of the pressure mat, Figure 8 is a schematic diagram of a yet further embodiment of a spacer layer of the pressure mat, Figure 9 is a schematic diagram of various embodiments of the io pressure mat, and Figure 10 is a schematic diagram showing electrical connections within three different pressure mats.

Figure 1 shows the pressure mat 10. The mat 10 is constructed of layers and/or segments of conductive, resistive and non-conductive materials.

The materials used may differ per configuration and design per application.

The configuration of the layers andlor segments may differ per configuration and design. The inner layers can be bonded together to retain position and form as a whole or selectively or simply held in place by the outer layers.

Figure la shows a simple construction of the pressure mat 10, with no mass applied. The mat 10 comprises upper and lower outer protective layers 26, an upper resistive layer 14, a non-conductive layer 18 and a lower conductive layer 12. An electrical circuit (not shown) is connected to the first conductive layer 12 and/or the resistive layer 14.

Figure lb shows the same construction, with some mass applied.

Figure Ic shows the same construction, with more mass applied. With no mass applied, the conductive layers make no contact and the output of the mat is open circuit. With some mass applied, an amount of the conductive material makes contact, creating some resistance across the mat connections.

With more mass applied, more of the conductive material makes contact, reducing the overall resistance across the mat connections. The non-conductive layer 18 is a spacer 18 with apertures therein. Each aperture or contact area may be equated electrically to the function of a variable a resistor and switch.

The diagrams of Figures 2 and 3 show the equivalent electrical circuit of various mat configurations, with and without the non-conductive spacer layer 18. These Figures show an electrical model of the mat 10. The relationship between surface area and received pressure is equivalent to a variable resistor. With a mat 10 including a non-conductive layer 18, this is equivalent to including a switch in a circuit, as the non-conductive layer 18 separates the conductive layers when no mass/pressure is applied and is the equivalent of io an open switch. Figure 2a shows the equivalent circuit of a mat 10 constructed using a non-conductive spacer layer 18 and no mass applied. The circuit is equivalent to having a non-contact of conductive layers. The variable resistor is set to high value as no mass is applied. Figure 2b shows the equivalent circuit of a mat 10 constructed without a non-conductive spacer layer 18 and no mass applied. The circuit is the equivalent of a variable resistor set to high value as no mass is applied. Figure 2c shows the equivalent circuit of a mat 10 constructed using a non-conductive spacer layer 18 and some mass applied.

The circuit is equivalent to having a closed switch due to contact of conductive layers. The variable resistor is set to a lower value due to some mass applied.

This is the equivalent of a single area of pressure applied. Figure 2d shows the equivalent circuit of a mat constructed without a non-conductive spacer layer 18 and some mass applied. The circuit is the equivalent of a variable resistor set to a lower value as some mass is applied. This is the equivalent of a single area of pressure applied.

Figure 3a shows the equivalent circuit of a mat 10 constructed using a non-conductive spacer 18 and more mass applied. The circuit is equivalent to having a closed switch due to contact of the conductive layers. The variable resistor is set to a lower value due to more mass applied. This is the equivalent of a single area of pressure applied. Figure 3b shows the equivalent circuit of a mat 10 constructed without a non-conductive spacer layer 18 and more mass applied. The circuit is the equivalent of a variable resistor set to a lower value as more mass is applied. This is the equivalent of a single area of pressure applied.

With pressure/mass applied to multiple apertures, multiple areas will make contact, creating the equivalent of a parallel circuit of resistances.

S Subject to electrical configuration, this may be the equivalent of many parallel resistances. If the resistive and conductive sheets are not segmented in construction, the whole mat will act as a single variable resistance.

Pressure/mass applied anywhere with reduce the total resistance of the mat in relation to pressure/mass and surface area applied. If segmented conductive io layers are used, complex resistive series and parallel configurations will be formed. This will allow areas of greater/lesser sensitivity to be formed and adjust the resolution of the resistance response to mass and area.

Figure 3c shows the equivalent circuit of a mat 10 constructed using a non-conductive spacer layer 10 and mass applied to multiple areas. The circuit is equivalent to having a closed switch due to contact of conductive layers.

The variable resistors are set to values relating to the mass applied. This is the equivalent of multiple areas of pressure applied. Figure 3d shows the equivalent circuit of a mat 10 without a non-conductive spacer layer 10 and mass applied to multiple areas. The circuit is equivalent to having multiple variable resistors set to values relating to the mass applied. This is the equivalent of multiple areas of pressure applied. For simplicity and clarity, Figures 3c and 3d only illustrate two areas of pressure/mass applied. The actual configuration and equivalent circuit may be much more complex in actual applications and usage.

The mat 10 is provided with outer covering, rigid and protective layers 26. The mat 10 will have outer covering layer(s) 26 that may be used to provide protection for the internal layers and segments from general liquid and/or did ingress. The outer covering 26 may also provide higher waterproof and ingress protection if needed. The outer covering may also have protective materials to prevent cutting, abrasion, piercing, handling and application specific needs. A rigid or semi-rigid layer may also be used to provide strength and retain shape/form.

The conductive layers and/or segments may be conductive or resistive and may include (but not limited to) metal foil, sheet, thread, wire or tape, metalized foil, thread, wire or tape, metalized plastic, fibre or fabric, printed or deposited conductive ink or material on a substrate or an etched conductive S layer. The conductive materials will be configured and formed to assist the application requirement of the mat 10. The configuration may require single or multiple conductive layers or segments. At least one layer and/or segment will be a resistive layer 14, in order to provide ratiometric behaviour. The resistive material will provide a resistive value per m or m2. A resistive layer 14 and io conductive foil layer 20 may be used together as per the requirements of the application or assembly constraints.

The resistive material will preferably be a plastic sheet with conductive properties, offering a resistance over its surface area, thereby providing surface resistivity. Such conductive/resistive materials are used as antistatic protection and storage. Examples of such material include, but are not limited to Carbon-filled PEEK (PolyEtherEtherKetone), Tempalux® (PolyEtherlmide), PES (PolyEtherSulfone), PVDF (PolyVinyliDene Fluoride), Pomalux® (Acetal Copolymer), Lennite® (UHMW Polyethylene) and Zelux® (Polycarbonate).

Segmented conductive layers may be one or more electrical circuits.

Figure 4a shows a configuration of a first conductive layer 12, shown from above. The shaded area in the Figure represents conductive material and shows a single electrical circuit on the conductive layer 12. Figure 4b shows a second configuration of a first conductive layer 12 seen from above, using multiple (two in this example) electrical circuits 22 on the conductive layer 24.

The two conductors 22 that make up the first conductive layer 12 are electrically independent of each other.

Segmented conductive layers may be constructed from one or more conductive or resistive elements. The segments can be of any shape, size or form. Figure 5a shows a conductive layer 12 constructed from multiple conductive segments. Figure 5b shows a different embodiment of the conductive layer 12, which is constructed from multiple segments arranged as zones or areas, creating multiple conductive or resistive elements in order to create different sensing arrangements.

The non-conductive layers 18 and/or segments are present to separate the conductive layers 12 and 20. The material used to construct the spacer s layer(s) 18 may be compressible or rigid. Non-conductive layers are optional, but typically used in order to give open circuit output conditions with no mass applied, since they will keep separate the conductive layers. The material used will be dependent upon the application of the mat 10. For example, a softer separation layer 18 may be needed for increased sensitivity of lighter load mass, whereas a harder material may be needed for less sensitivity or higher load mass. The non-conductive materials will be configured and formed to assist the application requirements of the mat 10. The configuration may require single or multiple non-conductive layers 18 or segments.

The non-conductive spacer layers 18 will be formed with a layer and/or segments of non-conductive material, preferably creating aperture(s) 24 that allow the conductive layers above and below the spacer 18 to meet when a mass is applied to the outer surfaces. Examples of two different spacers 18 are shown in Figures 6a and 6b, which show views from above of two different embodiments of the spacer layer 18. The apertures 24 of the spacers 18 may take any shape, size or form, as required for the application requirements of the pressure mat 10. The selection and combination of aperture size/style, layer material and segment design will vary as per the needs of the application.

Figure 6a shows an illustration of a simple sheet of non-conductive layer 18, all holes 24 being of the same size and of a small aperture size, providing a lower sensitivity to applied mass, since there is less open space in the spacer 18 for layers above and below the spacer 18 to make contact.

Figure 6b shows an illustration of a simple sheet of non-conductive layer 18, all holes 24 being of the same size and of a larger aperture size, providing a higher sensitivity to applied mass, since there is more open space in the spacer 18 for layers above and below the spacer 18 to make contact.

Two further embodiments of the spacer 18 are shown in Figures 7a and 7b. In these embodiments, the arrangement and size of the apertures 24 in the spacer 18 are irregular. Figure 7a shows an illustration of a sheet of non-conductive layer 18, the centre area having larger holes 24, providing a higher S sensitivity compared to the edge holes 24 of smaller size. Figure 7b shows an illustration of a non-conductive layer 18, the centre area having smaller holes 24, providing a lesser sensitivity compared to the edge holes 24 of larger size.

These two spacers 18 illustrate that non-regular arrangements of apertures 24 can be used in the spacer layer 18 ot the mat 10, according to the specific application in which the mat 10 is being used.

Figure 8 shows an illustration of a yet further embodiment of the non-conductive layer 18, which in this case is constructed of segments of material, with spaces in-between. The gaps formed between the segments provide apertures 22 that allow the conductive material of the layers above and below the spacer 18 to meet, when an external mass is applied. Non-conductive layers 18 may also be constructed of sheet and segments elements. The shaded area in Figures 6 to 8 represents the non-conductive material.

Figure 9 shows various examples of arrangement of layers within the mat 10. Views from above of each layer are shown, with left to right through the layers from top to bottom in the mat 10. The examples show arrangements and layer combinations, but the design of the pressure mat 10 is not limited in any way to these illustrations. The outer and rigidity layers of the pressure mat are not discussed or shown. Figure 9a shows a simple mat 10 comprised (from bottom to top) of first conductive foil layer 12, non-conductive layer 18 with apertures 24, conductive (resistive) layer 14 and second conductive foil layer 20. The upper and lower foil layers 12 and 20 connect to the output connections.

Figure 9b shows a simple mat 10 comprised of conductive foil layer 12, segmented non-conductive layer 18, conductive (resistive) layer 14 and conductive foil layer 20. Again, the upper and lower foil layers 12 and 20 connect to the output connections. Figure 9c shows a simple mat 10 comprised of printed conductive layer 12 having two electrical circuits 22, non-conductive layer 18 and conductive (resistive) layer 14. In this embodiment, only the printed layer 12 has connections to the output connections.

Figure 9d shows a simple mat 10 comprised of printed conductive layer 12 having two electrical circuits 22, non-conductive layer 18 and segmented conductive (resistive) layer 14. Only the printed layer 12 has connections to the output connections. Figure 9e shows a simple mat 10 comprised of conductive layers only, with no spacer 18. A resistive layer 14 is sandwiched between two conductive layers 12 and 20, which connect to the output connections. Note that the Figure 9 images are for illustration only and have io no relation to actual size or scale of layer aperture, segment or spacing.

The electrical construction of the pressure mat 10 uses external connections which will be made via a connector (connector style and type will vary per application design) or internally wired connection to external wires The number of external electrical connections to the mat 10 will take two forms. Firstly, single contact construction can be used. In this form, there will be only two connections to the mat 10. Secondly, multiple contact/feature construction can be used. In this form, there may be multiple connections to the mat.

Figure 10 shows three different connection options for the pressure mat 10. These three embodiment show top views of the pressure mat 10. In Figure ba, the first conductive layer is connected via one wire to an electrical circuit 16 and the resistive layer is connected via a second wire to the electrical circuit 16. In Figure lOb, two mat assemblies A and B are present that are isolated from each other within the pressure mat 10. A single wire connects the resistive layers in both assemblies to the electrical circuit 16 and individual wires connect the conductive layers in the individual assemblies to the electrical circuit 16.

In Figure bc, there are four mat assemblies A, B, C and D present in the pressure mat that are isolated from each other. There are four connection wires from the electrical circuit 16. One wire connects the resistive layers in assemblies A and C to the electrical circuit 16 and a second wire connects the resistive layers in assemblies B and D to the electrical circuit 16. A third wire connects the conductive layers in assemblies A and B to the electrical circuit and a further wire connects the conductive layers in assemblies C and D to the electrical circuit.

The internal connections between layers, segments and external S connections may be stitched, stapled, soldered, welded, crimped, bonded, compression, eyelet or other suitable method for the materials used. The internal electrical connections between layers, segments and external connections will differ as per the application requirements.

The mat 10 may be connected to an external device that monitors the io mat connections. This device may be a standalone device or have some connectivity to other systems or devices via cable or wireless communications This device can be portable or fixed by nature of installation This device may be powered from a mains supply or battery. This monitoring/control device may be built into the mat 10.

The pressure mat 10 has a wide variety of different uses and applications. For example, the mat 10 could be used for bed occupancy detection (elderly and/or patient care/monitoring). The mat 10 may be fitted under, over the mattress as an aftermarket product. The mat 10 may be fitted to the mattress at manufacture or the mat 10 may be fitted to the bed itself during manufacture. This will provide monitoring of the occupancy of the bed.

The detected value will also change subject to the occupier lying on the side, front/back or sitting.

Similarly, the pressure mat 10 could be used for child bed/cot occupancy detection. The mat 10 may be fitted under, over the mattress as an aftermarket product. The mat 10 may be fitted to the mattress at manufacture or the mat 10 may be fitted to the bed/cot itself during manufacture. This will provide monitoring of the occupancy of the bed/cot. The detected value will change subject to the occupier lying on the side, front/back, standing or sitting.

Removal of the child from the cot/bed (by a third party or child escape) can be detected. The mat 10 could also be used for monitoring sofa and chair occupancy. The mat 10 may be fitted under or over the cushion as an aftermarket product or the mat 10 may be fitted to the furniture at manufacture.

This can be used for elderly care monitoring, allowing daily activity and home/room occupancy monitoring of a non-intrusive nature.

The pressure mat 10 can also be used as a floor mat. This may be used for eldey care monitoring, allowing daily activity and home/room occupancy monitoring of a non-intrusive nature. This may be used for security monitoring, monitoring stairs, doorways or any floor area. Due to the ratiometric detection, lower masses, such as pet or child detection could be distinguished and detected. If the mat 10 is being used as a floor mat, then direction detection can be utilised. By using at least two mats 10, direction detection may be detected. This could allow detection and/or counting of people entering or leaving a room for example.

Multiple pressure mats 10 can be used to create a floor mat array. By using multiple mats 10, wider area monitoring and detection is possible. The mats 10 can be configured in any shape or form factor. The mats 10 can be connected to a monitoring device as individual mats or in an array or matrix configuration. Theft/removal detection such as electronic equipment theft can be prevented using the pressure mat 10. A mat 10 could be placed under a valuable item, monitoring its presence and alerting of its removal.

Theft/removal/tamper detection could be used in a museum or stately home to protect heritage furniture, for example. A mat 10 could be placed under a valuable item, for example a chair, monitoring its presence and alerting of its removal and also monitoring if someone sat on it for example.

Claims

CLAIMS1. A pressure mat (10) comprising a first conductive layer (12), a resistive layer (14) whose resistance changes in proportion to the pressure applied to the resistive layer (14), and an electrical circuit (16) connected to the first conductive layer (12) and/or the resistive layer (14) and arranged to detect the change in resistance in the resistive layer (14).
2. A pressure mat according to claim 1, and lUrther comprising a spacer (18) located in-between the first conductive layer (12) and the resistive layer (14).
3. A pressure mat according to claim 2, wherein the spacer (18) is in direct contact with the first conductive layer (12) and the resistive layer (14).
4. A pressure mat according to claim 1, 2 or 3, and further comprising a second conductive layer (20) located on the outside of the resistive layer (14).
5. A pressure mat according to claim 4, wherein the second conductive layer (20) is in direct contact with the resistive layer (14).
6. A pressure mat according to any preceding claim, wherein the first conductive layer comprises two independent electrical conductors (22) and the electrical circuit (16) is connected to the two independent electrical conductors (22).
7. A pressure mat according to claim 2, or any one of claims 3 to 6 as appended to claim 2, wherein the spacer (18) comprises a plurality of apertures (24).
8. A pressure mat according to claim 7, wherein the apertures (24) are of the same size and are arranged in a regular pattern.
9. A pressure mat according to claim 7, wherein the apertures (24) are of differing sizes and are arranged in a regular pattern.
10. A method of operating a pressure mat (10) comprising a first conductive layer (12), a resistive layer (14) whose resistance changes in proportion to the pressure applied to the resistive layer (14), and an electrical circuit (16) connected to the first conductive layer (12) and/or the resistive layer (14), the method comprising the steps of supplying an electric current from the electrical circuit to the connected first conductive layer (12) and/or the resistive layer (14) and detecting the change in resistance in the resistive layer (14).
11. A method according to claim 10, wherein the pressure mat (10) further comprises a spacer (18) located in-between the first conductive layer (12) and the resistive layer (14).
12. A method according to claim 11, wherein the spacer (18) is in direct contact with the first conductive layer (12) and the resistive layer (14).
13. A method according to claim 10, 11 or 12, wherein the pressure mat (10) further comprises a second conductive layer (20) located on the outside of the resistive layer (14).
14. A method according to claim 13, wherein the second conductive layer (20) is in direct contact with the resistive layer (14).
15. A method according to any one of claims 10 to 14, wherein the first conductive layer comprises two independent electrical conductors (22) and the electrical circuit (16) is connected to the two independent electrical conductors (22).
16. A method according to claim 11, or any one of claims 12 to 15 as appended to claim 11, wherein the spacer (18) comprises a plurality of apertures (24).
17. A method according to claim 16, wherein the apertures (24) are of the same size and are arranged in a regular pattern.
18. A method according to claim 16, wherein the apertures (24) are of differing sizes and are arranged in a regular pattern.