WO2019073104A1

WO2019073104A1 - A device, a method, a computer program product and an apparatus for measuring pressure distribution between a foot and a surface

Info

Publication number: WO2019073104A1
Application number: PCT/FI2017/000016
Authority: WO
Inventors: Vesa Kajanus
Original assignee: Movesole Oy
Current assignee: Movesole Oy
Priority date: 2017-10-13
Filing date: 2017-10-13
Publication date: 2019-04-18
Anticipated expiration: 2020-04-13

Abstract

In the invention a sensor (106) or sensors made at least partly of an electroactive material (109) having a conductive part (107) are shielded and grounded by layer structures. On the both sides of the sensor (106) are insulating layers (105, 111) that are covered by layers of a conductive material (104, 112), which are covered by protective layers (103, 113) whose conductivity is smaller than conductivites of the layers they cover. The conductive part (107) of the sensor (106) and one of the conductive layers (112) are first and second electrode and electric properties are measured between said electrodes. These electric properties correspond to the pressure a foot (601) is causing to a surface (602) below.

Description

A device, a method, a computer program product and an apparatus for measuring pressure distribution between a foot and a surface

The invention relates to a device for measuring pressure distribution between a foot and a surface, the device comprising an electrical connector arrangement, and the device is a layered flexible structure having a first surface area and a second surface area and a method and a computer program product for measuring pressure distribution between a foot and a surface. The invention also relates to an apparatus for displaying pressure distribution between a foot and a surface, the apparatus comprising at least one memory, at least one processor, a display and an arrangement for a wireless data connection.

BACKGROUND

It is quite beneficial to know for pressure distribution between a person and the surface the person is on. Especially the plantar pressure distribution between a foot and a ground or shoe or similar surface can be used for many purposes. Some of uses could be for example gait analysis, sports medicine, diabetes treatment, orthodics and other podiatric studies. For analysis it is needed a temporal distribution or spatial distribution or both. The object of the study defines what the resolution of pressure distribution measurement is.

There are many different devices and methods for achieving a pressure distribu- tion between a foot and a surface. If an intention is, for example to measure time- spans longer that a few seconds or effects of the movements or how a foot fits in a shoe, the measurement device should be flexible and thin compared its total surface area. Usually those kinds of devices are layer structured and contain pressure or force sensors. One example is disclosed in the patent publication WO201255029. However, force sensors are usually expensive, quite big and some are prone to failures i.e. they break easily. Other possibility is to use in a measuring device some thin material that gives an electrical response when experiencing pressure. These electroactive materials can change shape or size when stimulated by an electric field and/or produce electric field when their shape or size is changed. If the relation between the force that affects to the material and produced electric field are known, the pressure could be estimated. Some of these materials that could be used as electroactive materials are piezoelectrical and some are materials that are electrically charged and they are discharged when they experience pressure. However, outer electrical fields and inducted electrical field can easily cause interferences and discharges. This is especially evident when a device is placed in a shoe because there is quite lots of materials that move in relation to each other and they produce static electricity. Because electrical properties to be measured are quite small, these static electric fields can easily distort results. Also, drifting offset is apparent with these constructs and constant calibration is needed in many cases. Some problems also arise because many materials are pyroelectric i.e. temperature effects to the electrical output of them.

Some electroactive materials could be charged by corona discharge method. One example of these materials is electromechanical films. One embodiment of an electromechanical film is a permanently charged thin film that is covered from both sides with layers, which conduct electricity. Outside pressure being applied to the film can be detected as a voltage signal produced by the film. A change of thickness of already a few micrometers is enough to produce a detectable voltage signal. In addition to this, the magnitude of the voltage signal can be used to assess the force applied to the film. Of course, there is many materials could be that charged by corona discharge method. Many polymers are such.

BRIEF DESCRIPTION

The object of the invention is a solution that can significantly reduce the disadvan- tages and drawbacks of the prior art. In particular, the object of the invention is a solution that allows a device that provides a reliable pressure distribution between a foot and a surface.

The objects of the invention are attained with an arrangement that is characterised by what is stated in the independent patent claims. Some advantageous embodi- ments of the invention are disclosed in the dependent claims.

The inventors have studied thin electroactive materials for use in a planar pressure distribution sensors and especially electroactive polymers. These materials, especially when used in a device that is configured to move with the person to be studied, are quite prone to all kinds of electrical disturbances. When prior art has tried to avoid these, the results have been quite complicated, which have produced even more electrical problems. The inventors have found a solution that diminishes electrical interferences and possibility of discharges. In the invention a sensor or sensors made at least partly of an electroactive material having a conductive part are shielded and grounded by a layer structures. On the both sides of sensor are insulating layers that are covered by layers of a conductive materials and these are covered by protective layers whose conductivity is smaller than conductivities of the layers the protective layers covers. The conductive part of the sensor and one of the conductive layers are first and second electrode and electric properties are measured between said electrodes.

The invention is especially suitable for a measurement device that is to be placed in a shoe or similar. When reference is made in the text to the upper or the lower parts or respective directions, a situation is described in which the apparatus according to the invention is in its normal deployed configuration unless otherwise is stated.

In one embodiment of the invention a device for measuring pressure distribution between a foot and a surface comprise an electrical connector arrangement and the device is a layered flexible structure having a first surface area and a second surface area. In one advantageous embodiment of the invention the device further comprises at least following layers: a first layer, which is protective layer covering at least part of the first surface area, and the first layer is conductive, a second layer, which is conductive material and the conductivity of the second layer is big- ger than the conductivity of the first layer, a third layer, which is a first support layer and it is configured to support the second layer and it is insulating material. The device further comprises one or more sensor arrangements that comprise at least following layers: a fourth layer which is conductive material and a fifth layer which is electroactive material. Said electroactive material produces an electric response when a force is directed to it. The device further comprises a sixth layer which is a second support layer, and it is insulating material and the sensor arrangement or sensor arrangements are attached to the sixth layer, a seventh layer which is a conductive material and an eighth layer which is protective layer covering at least part of the second surface area, and the eighth layer is conductive, and the conductivity of the eighth layer is less than the conductivity of the seventh layer. The first layer is configured to cover at least the second layer, and the eighth layer is configured to cover at least the seventh layer. The second layer and the seventh layer are configured to form a Faraday cage between them i.e. they shield outer electromagnetic fields from inner parts of the device. The fourth layer or fourth layers are first electrodes and the seventh layer is a second electrode, and the electrical connector arrangement is connected to the first electrode or first electrodes and to the second electrode for measuring electrical properties between the first electrode or electrodes and the second electrode. The layers are attached to each other for example using adhesives or such or they could be printed or pressed. On the surface areas could be additional structures for exam- pie shaping or the device could be placed in some structure for example a sole or a shoe or such.

In one embodiment of the device according to the invention there is a filtering capacitor and a measurement resistor, and the filtering capacitor is between the first electrode and the second electrode, and the measurement resistor is parallel to the filtering capacitor. In one advantageous embodiment the filtering capacitor and the measurement resistor are placed in the electrical connector arrangement. In a second embodiment of the device according to the invention there is a sensor capacitance between the first electrode and the second electrode i.e. between the fourth layer and the seventh layer, and the capacitance of the filtering capacitor is bigger than the sensor capacitance.

In a third embodiment of the device according to the invention in the sensor arrangement at least the fifth layer is electroactive polymer.

In a fourth embodiment of the device according to the invention the fifth layer is plastic material that is charged by corona discharge method. In a fifth embodiment of the device according to the invention the sensor arrangement is or it contains electromechanical film.

In a sixth embodiment of the device according to the invention the first layer is configured to ground the second layer and the eighth layer is configured to ground the seventh layer for preventing electrostatic discharge phenomena inside the de- vice.

In a seventh embodiment of the device according to the invention the surface area of the sensor arrangement or sensor arrangements is smaller than the surface areas of the support layers i.e. the third layer and the sixth layer, and the sensor arrangement or the sensor arrangements are attached to the support layers by adhesive and the adhesive is configured to fill at least partially the volume between the support layers.

In an eighth embodiment of the device according to the invention the device has two or more sensor arrangements and there is no direct electrical connection between sensor arrangements. In a ninth embodiment of the device according to the invention the measured electrical properties between the first electrode or electrodes and the second electrode are voltages over the measurement resistor.

In a tenth embodiment of the device according to the invention the measured elec- trical properties are send to an external device for displaying or at least partial processing or both. Some or all signal processing could be done with the device or it could be done with said external device. The connection between the device and the external device is advantageously wireless in some embodiments. The arrangement for establishing a connection between the device and the external de- vice can be included to the device. In one embodiment said arrangement is configured in a way that at least some part of the arrangement can be situated outside of the shoe when the device is in use. There are embodiments where the data connection between the device and the external device is one way from the device to the external device i.e. the external device only reads data from the device. One embodiment of the invention is a method for measuring pressure distribution between a foot and a surface. In one advantageous embodiment of the method the device disclosed previously is used and the device is placed between the foot and the surface. The surface could be, for example, some inner part of a shoe. The measured electrical properties corresponds spatial pressure distribution or temporal pressure distribution or both.

One embodiment of the invention is a computer program product comprising program instructions which, when executed on an apparatus comprising at least one processor and at least one memory causes the apparatus to make a connection to the device disclosed previously and to read electrical properties from the electrical connector arrangement and store the electrical properties in the memory. In an embodiment the computer program product comprise program instructions to transform the measured electrical properties to correspond to pressure distribution. In the simplest case the transformation could be only marking the relative electrical property changes to relative pressure changes. Of course, there could be some calculations to get real pressure values or estimations of them. In a second embodiment the computer program product comprise program instructions to produce a visual presentation based on the measured electrical properties. In a third embodiment the visual presentation is configured to include temporal distribution data. The visual presentation including temporal distribution data could be for ex- ample an animation based on the measured electrical properties. In one embodiment of the invention an apparatus for displaying pressure distribution between a foot and a surface comprise at least one memory, at least one processor, a display and an arrangement for a wireless data connection. In one advantageous embodiment of the invention the apparatus apparatus is configured to establish a data connection to the device disclosed previously, to read electrical properties from the electrical connector arrangement, to store the electrical properties in the memory, to transform the electrical properties to correspond pressure distribution and to display a visual presentation of the pressure distribution on the display. It is an advantage of the invention that it provides a solution that is easy to use and it can sense small changes in pressure. It also makes possible to do detailed spatial and temporal pressure distribution studies for feet. The invention can also used when the subject of the study is walking or running.

It is a further advantage of the invention that it could be used to remove the offset drifting in data processing.

It is a further advantage of the invention that it diminishes significally electrical disturbances. Thus it makes possible to use materials that have previously been quite hard to utilize.

It is a further advantage of the invention that it allows to measure long data sets. This is due to lack of need of regular calibrations and because the device according to invention can be thin and light compared to dimensions of a shoe.

An advantage is also that the materials used in the device are quite cheap and thus manufacturing costs can be lowered compared to previous products.

DESCRIPTIONS OF THE FIGURES In the following, the invention is described in detail. The description refers to the accompanying drawings, in which

Figure 1 shows a cross section of an embodiment of a device,

Figure 2 shows an explosion view of the cross section of the embodiment of figure 1 , Figure 3 shows a second embodiment of a device seen above, Figure 4 shows a third embodiment of a device seen above,

Figure 5 shows a simplified example of electrical connection of a device, and

Figure 6 shows an example of use a device according invention.

DETAILED DESCRIPTIONS OF THE FIGURES

The embodiments in the following description are given as examples only and someone skilled in the art can carry out the basic idea of the invention also in some other way than what is described in the description. Though the description may refer to a certain embodiment or embodiments in several places, this does not mean that the reference would be directed towards only one described embodiment or that the described characteristic would be usable only in one described embodiment. The individual characteristics of two or more embodiments may be combined and new embodiments of the invention may thus be provided.

Figures 1 and 2 shows a cross section of an embodiment of a device 00. In the figure 2 is an explosion view of the layers for the sake of clarity. The features and their functions are same on the both figures.

The device 100 is a flexible thin layered structure having a first surface area 101 and a second surface area 102. The device comprise a first layer 103, a second layer 104, a third layer 105, a sensor arrangement 106 comprising a fourth layer 107 and a fifth layer 109, a sixth layer 111 , a seventh layer 112 and an eighth layer 1 13. The device also comprises a first adhesive layer 108 and a second adhesive layer 110. It must be noted that the structure is exaggerated in the vertical direction for the sake of the clarity.

The first layer 103 is a protective layer and it covers first surface area 101 at least partly. The material the first layer is conductive. One example for this is an epoxy paint. The first layer should be thick enough for protecting inner layers. The first layer covers the second layer 104 and it is configured to ground the second layer.

The second layer 104 is conductive and the conductivity of the second layer is bigger than the conductivity of the first layer 103. One example for the material for the second layer is a silver ink, but naturally many different materials are suitable. The third layer 105 is a first support layer. It is insulating material. In one advantageous embodiment it is plastic and for example PET-film. The second layer could be printed on the surface of the third layer but naturally other methods could be used. The properties and the size of the third layer are chosen in a way that it iso- lates the first layer 103 and the second layer 104 from the inner parts of the device 100 and it gives supporting structure for the device.

The sensor arrangement 106 comprises at least the fourth layer 108 and the fifth layer 109. The fourth layer is conductive material and it is a first electrode of an electrical pair that is used for measurement. The fifth layer is electroactive material that gives an electrical response when an outer force is applied to the sensor arrangement. In this example there is the first adhesive layer 107 for attaching the fourth layer to the third layer 105. This can be implemented in many different ways.

As the fifth layer 109 can be used many different materials. One advantageous example of family of materials is materials that are charged by corona discharge method. These materials are manufactured for example stretching the material to form thin material layers separated by air filled voids. In the corona discharge method an electric filed whose strength exceeds locally the dielectric strength is used. When the thickness of this kind of charged material is changed, the dipoles inside the material are modified and a corresponding charge is produced. Electromechanical films are usually materials that are charged by corona discharge method. Some electromechanical films contain a conductive layer and layer of material that is charged by corona discharge method so they can be used as a sensor arrangement or it could be part of it. Many plastic polymers, such as polypropylenes, can be used as an electroactive material.

In this example are several sensor arrangements. In the figure is presented three sensor arrangements: the sensor arrangement 106, a second sensor arrangement 114 and a third sensor arrangement 1 15. These sensor arrangements are electri- cally isolated each other. The purpose of the device defines the size and the placement of sensor arrangements. Different applications demands different pressure distribution maps. For example some gait analysis may need only one pressure point and some shoe testing may require much more detailed pressure distribution. In some embodiments the volume between the sensor elements is at least partly filled with adhesive. In some embodiments the sensor elements or the sen- sor element is so thin that when the layers of the device are in the manufacturing process pressed together, the layers surrounding the sensor elements come together. In this example these layers are the third layer 105 and the sixth layer 11 1 which are the support layers. The sixth layer 11 1 is a second support layer and it is insulating material. In one advantageous embodiment it is plastic and for example PET-film. The sensor arrangement 106 is attached to the sixth layer using the second adhesive layer 110. The sensor arrangements are between the third layer 105 and the sixth layer.

The seventh layer 112 is conductive material. One example for the material for the seventh layer is a silver ink, but naturally many different materials are suitable. The seventh layer could be printed on the surface of the sixth layer 1 11. The seventh layer is a second electrode of an electrical pair that is used for measurement. The second layer 104 and the seventh layer are configured to form a Faraday cage between them. This means that there is an electrical connection between them.

The eighth layer 113 is a protective layer forming at least part of the second surface area. The eighth layer is conductive, and the conductivity of the eighth layer is less than the conductivity of the seventh layer. One example for material for the eighth layer is epoxy paint. The eighth layer should be thick enough for protecting inner layers. The eighth layer covers the seventh layer 113 and it is configured to ground the seventh layer.

The protective layers, the first layer 103 and the eighth layer 113, are electrically connected to each other. The first and the second support layers, the third layer 105 and the sixth layer 111 , are configured to seal the sensor arrangements be- tween them allowing only first electrode connections.

It must be noted that in some embodiments some above described layers could include several layers. For example support layers, the third layer and the sixth layer, could be composed different parts, one part where the conductive layers are printed and one frame part for supporting the device. Also there could be addi- tional layers for example attaching layers to each other or adding support or modifying the shape or other physical properties of the device. For example surface areas could be covered by layers that follow the shapes of a foot or a shoe. It also must be noted that the device could be placed either way, i.e. for example the first surface area could be towards a foot and the second surface area could be to- wards a shoe or vice versa. Of course, the position the device is to be used should be taken into account when calibrating the device and measurements.

Figure 3 shows a second embodiment of a device 300 seen above. The device comprises a first surface 301 and five sensor arrangements 302. The shape of the device is such that it will fit in a shoe. The sensor arrangements are inside the device but they are marked in the figure to make clear how they can be used. The shapes and sizes of the sensor arrangements are different so that they cover the areas of interest.

Figure 4 shows a third embodiment of a device 400. The device comprises four sensor arrangements: a first sensor arrangement 401 , a second sensor arrangement 402, a third sensor arrangement 403 and a fourth sensor arrangement 404. The device further comprises an electrical connector arrangement 405, a first first electrode connection 406, a second first electrode connection 407, a third first electrode connection 408 and a fourth first electrode connection 409, and a sec- ond electrode connection 410.

The electrical connector arrangement 405 is for measuring or providing connections for measurement. The object of the measurements is electrical properties between the first electrodes and the second electrode. There are four first electrode connections, one for each sensor arrangement, and the second electrode connection. The first electrode connections are connected to the fourth layers and the second electrode connection is connected to the seventh layer. When measuring the electrical connector arrangement is configured to change what sensor arrangement is to be measured. Means for that are in the electrical connector arrangement. Also other electrical components needed for measuring process, for example amplifiers, can be included in the electrical connector arrangement. There can be some signal processing means, but the data could be send to the some external device for processing and/or display. In one advantageous embodiment sending said data is done wirelessly.

Figure 5 shows show a simplified example of electrical connection of a device. There is a measurement arrangement 501 and an electrical connector arrangement 502. The measurement arrangement comprises a first electrode 503 and a second electrode 504. The first electrode is a fourth layer that is in a sensor arrangement and the second electrode is a seventh layer. The measurement arrangement has a sensor capacitance C_s 505 i.e. there is a capacitance value be- tween the first electrode and the second electrode. The electrical connector ar- rangement comprises at least a filtering capacitor 506 and a measurement resistor 507. The filtering capacitor is between the first electrode and the second electrode and the measurement resistor is parallel to the filtering capacitor. The capacitance of the filtering capacitor is bigger than the sensor capacitance. For example, if the sensor capacitance is 70 pF, the capacitance of the filtering capacitor could be 1.6 nF. The measured electrical properties between the first electrode and the second electrode are voltages over the measurement resistor.

Figure 6 shows an example of use a device 603 according invention. A foot 601 is placed in a shoe 602. The device is placed between the foot and the inner bottom of the shoe. The device comprises a first surface 604 and a second surface 605. Inside the device are four sensor arrangements: a first sensor arrangement 606, a second sensor arrangement 607, a third sensor arrangement 608 and a fourth sensor arrangement 609. The first surface area is towards the foot and the second surface area is towards the bottom of the shoe. When the foot causes pressure to the sensor arrangements, they deform. The electrical output corresponds to the pressure and it could be estimated. When output from all sensor arrangements is measures, a pressure distribution is achieved.

Some advantageous embodiments of the method and device according to the invention have been described above. The invention is however not limited to the embodiments described above, but the inventive idea can be applied in numerous ways within the scope of the claims.

Claims

Patent claims

1. A device (100; 300; 400; 603) for measuring pressure distribution between a foot and a surface, the device comprising an electrical connector arrangement (405; 502), and the device is a layered flexible structure having a first surface area (101; 301; 604) and a second surface area (102; 605), characterised in that the device further comprises at least following layers,

- a first layer (103), which is a protective layer forming at least part of the first surface area, and the first layer is conductive

- a second layer (104) which is conductive material and the conductivity of the second layer is bigger than the conductivity of the first layer

- a third layer (105) which is a first support layer and it is configured to support the second layer and the third layer is insulating material

- one or more sensor arrangements (106; 302; 401 , 402, 403, 404; 606, 607, 608, 609) that comprise at least following layers

- a fourth layer (107) which is conductive material and

- a fifth layer (109) which is electroactive material

- a sixth layer (111 ) which is a second support layer, and it is insulating material and the sensor arrangement or sensor arrangements are attached to the sixth layer

- a seventh layer (112) which is a conductive material

- an eighth layer (113) which is a protective layer forming at least part of the second surface area, and the eighth layer is conductive, and the conductivity of the eighth layer is less than the conductivity of the seventh layer, and

the first layer is configured to cover at least the second layer, and the eighth layer is configured to cover at least the seventh layer, and the second layer and the seventh layer are configured to form a Faraday cage between them, and the fourth layer or fourth layers are first electrodes (503) and the seventh layer is a second electrode (504), and the electrical connector arrangement is connected to the first electrode or first electrodes and to the second electrode for measuring electrical properties between the first electrode or electrodes and the second electrode.

2. The device (100; 300; 400; 603) according to claim 1 , characterised in that there is a filtering capacitor (506) and a measurement resistor (507), and the filter- ing capacitor is between the first electrode (503) and the second electrode (504) and the measurement resistor is parallel to the filtering capacitor.

3. The device (100; 300; 400; 603) according to claim 2, characterised in that there is a sensor capacitance (505) between the fourth layer (107) and the seventh layer (112) and the capacitance of the filtering capacitor (506) is bigger than the sensor capacitance.

4. The device (100; 300; 400; 603) according to any of claims 1 to 3, character- ised in that in the sensor arrangement (106; 302; 401 , 402, 403, 404; 606, 607,

608, 609) at least the fifth layer (109) is electroactive polymer.

5. The device (100; 300; 400; 603) according to any of claims 1 to 4, characterised in that in the fifth layer ( 09) is plastic material that is charged by corona dis- charge method.

6. The device (100; 300; 400; 603) according to claim 5, characterised in that the sensor arrangement (106; 302; 401 , 402, 403, 404; 606, 607, 608, 609) is or it contains electromechanical film.

7. The device (100; 300; 400; 603) according to any of claims 1 to 6, characterised in that the first layer (103) is configured to ground the second layer (104) and the eight layer (113) is configured to ground the seventh layer (112) for preventing electrostatic discharge phenomena inside the device.

8. The device (100; 300; 400; 603) according to any of claims 1 to 7, characterised in that the surface area of the sensor arrangement or sensor arrangements (106; 302; 401 , 402, 403, 404; 606, 607, 608, 609) is smaller than the surface areas of the support layers i.e. the third layer (105) and the sixth layer (11 1 ), and the sensor arrangement or the sensor arrangements are attached to the support layers by adhesive and the adhesive is configured to fill at least partially the volume between the support layers.

9. The device (100; 300; 400; 603) according to any of claims 1 or 8, characterised in that the device has two or more sensor arrangements (106; 302; 401 , 402, 403, 404; 606, 607, 608, 609) and there is no direct electrical connection between sensor arrangements.

10. The device (100; 300; 400; 603) according to any of claims 2 to 9, characterised in that the measured electrical properties between the first electrode or electrodes (503) and the second electrode are voltages over the measurement resistor (504).

11. The device (100; 300; 400; 603) according to any of claims 1 to 10, characterised in that the measured electrical properties are send to an external device for displaying or at least partial processing or both.

12. A method for measuring pressure distribution between a foot and a surface, characterised in that the device disclosed in claim 1 is used and the device is placed between the foot (601 ) and the surface (602) and the measured electrical properties corresponds spatial pressure distribution or temporal pressure distribution or both.

13. A computer program product comprising program instructions which, when executed on an apparatus comprising at least one processor and at least one memory causes the apparatus to make a connection to the device disclosed in claim 1 and to read electrical properties from the electrical connector arrangement (405; 502) and store the electrical properties in the memory.

14. The computer program product according to claim 13, characterised in that the computer program product comprise program instructions to transform the measured electrical properties to correspond to pressure distribution.

15. The computer program product according any of claims 13 to 14, characterised in that the computer program product comprise program instructions to produce a visual presentation based on the measured electrical properties.

16. The computer program product according to claim 15, characterised in that the visual presentation is configured to include temporal distribution data.

17. An apparatus for displaying pressure distribution between a foot and a surface comprising:

- at least one memory;

- at least one processor;

- a display, and

- an arrangement for a wireless data connection, characterised in that the apparatus is configured to establish a data connection to the device disclosed in claim , to read electrical properties from the electrical connector arrangement (405; 502), to store the electrical properties in the memory, to transform the electrical properties to correspond pressure distribution and to display a visual presen- tation of the pressure distribution on the display.