Device for measuring mechanical stress in a material with a network of elongated sensors, interlaced in an elastic material and sole to detect blisters or ulcers.

Abstract

The present invention relates to a device for measuring mechanical stresses in a material using one or more networks of sensors of elongated and intersecting shapes in an elastic material. The elastic and preferably incompressible material is shaped directly on the sensors which are thin strips of piezoelectric material, in order to ensure good cohesion and increase the signal of said sensors during the deformation of the material. This arrangement thus makes it possible, in addition to measuring the stress, to generate sufficient energy to power electronics and wireless communication to a smartphone to avoid the need for a battery to be recharged. One of the applications is a sole for detecting pressure and temperature conditions leading to the risk of blisters appearing for athletes, construction workers, etc., or ulcers for diabetics. Figure to be published for the abstract: Figure n3

Description

Title of the invention: Device for measuring mechanical stresses in a material with a network of elongated sensors, interlaced in an elastic material and sole for detecting blisters or ulcers.

[0001] The feet are the parts of the body that are most stressed due to the conditions of pressure, temperature, confined space, etc.

[0002] This is why foot ulcers are one of the most frequent complications among the 500 million diabetics in the world, 15 to 25% of whom will have a partial amputation during their lifetime (Prevention of Diabetic Foot Ulcer, International Journal of Preventive Medicine, Vol 4, No 3, Tuesday, 2013).

[0003] The article “Temperature and Pressure Regulating Insoles for Prevention of Diabetic Foot Ulcers” (J Foot Ankle Surg. 2020; 59(4): 685-688)” describes well the interest of monitoring pressure and temperature conditions at the level of the feet to avoid ulcers.

[0004] By detecting conditions at risk of ulcers, patients could be warned of the risks of worsening existing ulcers and even before they occur.

[0005] Patients would then be more inclined to leave their homes because ulcers, but also and above all the fear of developing them, are a barrier to activities such as walking, which is nevertheless essential for maintaining one's fitness and morale.

[0006] In addition to the traumatic and disabling nature of ulcers, the cost of treatment and even amputations must also be taken into account, which range between €5,000 and €100,000 per operation.

[0007] A device for monitoring the conditions under which the risk of ulcers appears, such as a sole equipped with a multitude of pressure and temperature sensors, connected to a smartphone, would thus make it possible to slow down or even stabilize the state of health of patients' feet and thus have a significant impact on their quality of life.

[0008] A user-friendly interface on the smartphone would then continuously warn the patient with great precision. In addition, with a history of measurements of these risky conditions, on a secure cloud or to a health professional for analysis and advice on the type of sole, shoe, gait, etc. recommended: a dialogue could thus be established between the medical profession and the patient on their habits and activities, whether correct or not.

[0009] But for such devices to be widely used, it would be necessary that: • The device is incorporated into a thin, soft and comfortable sole that is easy to forget, • the number of measurement points is sufficient to detect ulcer risk conditions over very small areas and therefore with at least a hundred sensors per foot, • the price is low (for example less than €200), • that it does not use a battery (no need to be recharged) so that it is always operational.

[0010] If we look at what already exists, we see that the only devices on the market are very expensive, require batteries and that the number of sensors is often limited, as shown in the study “Concurrent Plantar Stress Sensing and Energy Harvesting Technique by Piezoelectric Insole Device and Rectifying Circuitry for Gait Monitoring in the Internet of Health Things” (https: / / www.researchgate.net / publication / 33999216 2)

[0011] Similarly, the article in Electronics Review "A Comparative Review of Footwear-Based Wearable Systems" describes the following systems that do not meet the prerequisites for an efficient device: • The device offered by “Orpyx LogR”® can certainly have up to 99 sensors but requires batteries and costs around $3,500 for the 8-sensor version. • The “Moticon”® device only has around ten sensors, which is insufficient to detect risks in small areas, costs almost €2,000 and requires batteries. • Certainly, the “Novel Pedar”® device offers up to 256 measurement points but it requires batteries and is prohibitively expensive (more than $3,500). • Finally, the “TekScan F-Scan”® device offers up to 960 measurement points but requires batteries and at an equally exorbitant cost ($50 to $100 per sensor!).

[0012] If we also look at the patent databases, we certainly find interesting patents but which still do not meet the requirements for such devices to be widely used: US2010037709A1

[0013] The invention relates to a network-type pressure detection apparatus suitable for detection and quantification, said network certainly comprising a plurality of first axes, a plurality of second axes ... which can be arranged in a cross and a plurality of piezoresistive units ..., but it is not the sensors which are arranged along the various axes. Indeed, the piezoresistive units are arranged on the cross between a first axis and a second axis and said sensors therefore do not intersect at all and for each sensor it is necessary to have a measurement input on a microprocessor.

[0014] It is thus claimed a network type pressure detection apparatus adapted to pressure detection with a plurality of first axes, a plurality of second axes, arranged in a cross with the first axes but it is not the sensors which are thus arranged in a cross. WO03087737A1

[0015] A sensor unit for detecting mechanical vibrations is described therein comprising at least one strip of piezoelectric foil (piezo strip) as a sensor element but in no case is a network of intersecting sensors mentioned or claimed, even if several sensor units can be mounted together in a plastic material, they are never intersecting and even less mounted in an elastic material essential to increase the stresses on a piezo.

[0016] It is thus claimed a sensor unit for capturing mechanical vibrations with at least one strip of piezoelectric sheet which is claimed but never an array of intersecting sensors. US2017146493A1

[0017] There is described an array of piezoelectric sensors embedded in a fabric which may comprise multiple laminar layers, such as sensor layers...

[0018] It is therefore a piezoelectric sensor network fabric comprising one or more laminar layers which is claimed and not a network of intersecting sensors.

[0019] The present invention relates to a device for measuring mechanical stresses in a material using one or more networks of sensors of elongated and intersecting shapes in an elastic material.

[0020] One of the applications is a sole for detecting pressure and temperature conditions leading to risks of blisters appearing for athletes, construction workers, etc. or ulcers for diabetics.

[0021] Other applications for monitoring constraints on metal structures, concrete, etc. are possible.

[0022] In the case of an application to a sole, this will be made directly with the elastic material and will therefore be flexible. A matrix of piezoelectric sensors is incorporated in the elastic material and intertwined, offering more than a hundred pressure and temperature measurement points.

[0023] By incorporation we mean that the sensors are embedded in the elastic material so that there is a strong cohesion between the material and the sensors. Thus, when the material deforms, the flexible sensors will follow this deformation and their signals will be amplified.

[0024] Said sensors are of elongated shapes (thin strips of metallized PVDF type piezoelectrics for example) and arranged for a first part in one direction and the other part with an angle between 1° and 90° relative to the first part and preferably 90°.

[0025] Ideally, said sensors are incorporated into an elastic and preferably incompressible material such as elastomers (silicone, rubber, TPU, etc.) so that when a stress is exerted, said material induces fine and induces greater stretching of said sensors.

[0026] Said sensors are either flexible piezoelectric or flexible piezoresistive.

[0027] Preferably, the sensors are connected to tracks or cables, connecting them to signal processing electronics, using magnets or pressure contact systems (with springs for example). This choice is fundamental because a sole being subjected to multiple deformations, the electrical contacts will be just as much and pressurizing them by magnet or spring will allow micro displacements without breakage.

[0028] Of course, the longitudinal sensors must be separated from the transverse sensors by an insulating layer so as not to short-circuit the signals because the piezo films must be metallized on each face to conduct the electrical charges generated when they are stressed.

[0029] For example, silicone can first be poured onto the longitudinal sensors and then the transverse sensors can be placed, which will then also be covered with silicone.

[0030] The energy generated by the sensors is stored in a battery or supercapacitor and can power the electronics connected wirelessly to the smartphone, without the need for recharging.

[0031] An AI on the smartphone then makes it possible to compare the signals from the sensors with each other and over time and to precisely calculate risk situations.

[0032] This sole is thus based on a sensor matrix, consisting of fine piezoelectric strips 5 to 200 µm and preferably 25 µm wide, which are crossed and which makes it possible to divide up the entire surface of the sole (and then of the whole sock) by managing only a few inputs at the microprocessor level.

[0033] For example, with only 10 sensors along the entire length of the sole and 15 sensors arranged orthogonally across the width, this will represent only 25 inputs at the microprocessor level but 150 measurement points.

[0034] In addition, the energy generated by the sensors is recovered in a supercapacitor or a battery to power the chosen low-consumption microprocessor and a low-consumption Bluetooth module for connection to the smartphone.

[0035] Artificial intelligence on the said smartphone then makes it possible to compare the signals from the various sensors over time and to calculate the pressure at each intersection.

[0036] To limit the electrical consumption in the sole and so that the energy of the sensors is sufficient to transmit the information to the smartphone, it is the application on the smartphone which analyses the signals transmitted by the soles to convert them into pressure at each intersection of transverse and longitudinal sensors by analysis of the time shifts of said signals.

[0037] Indeed, when a support or impact is exerted on the sole in a superposition / intersection of sensors, the signal measured on each of these impacted orthogonal bands will give a similar value but above all at the same time. The signals of the adjacent bands, before or after these impacted bands, will give weaker signals but above all out of phase in time (positive or negative) compared to the impacted bands which will make it possible to geolocate exactly the precise area of ​​the impact.

[0038] This will allow us to precisely map the pressure on each foot.

[0039] On the other hand, the incorporation of the sensors in an elastic and preferably incompressible material such as silicone is of great importance.

[0040] Indeed, a flexible piezoelectric sensor of the PVDF type (or other) generates a relatively weak signal when it is subjected to mechanical stress, such as compression, while it is on a hard (or flexible) surface.

[0041] Indeed, this type of sensor generates a larger signal when it is stretched rather than compressed.

[0042] On the other hand, by incorporating this type of piezo sensor into an elastic and preferably incompressible material, such as for example by pouring silicone (or rubber, TPU, etc.) around said sensors so that there is good adhesion between the sensor and the silicone, the compression of the silicone / sensor assembly will lead to significant stretching of the sensor leading to a much larger signal (by a factor of 10).

[0043] Thus, not only will it be possible to obtain more energy to power the supercapacitor and the microprocessor with its Bluetooth wireless communication module, but in addition the signal will be stronger and therefore more easily measurable with better precision.

[0044] More precisely, [Fig.l] shows a sole according to the invention, in cross-section where one can see the transverse piezoelectric sensor strips (1), longitudinal piezoelectric sensor strips, i.e. in the length of the sole (2), all incorporated in the elastic material (3) constituting the sole.

[0045] [Fig.2] shows the sole according to the invention in top view: the silicone being transparent in this case, it allows a glimpse of the transverse sensors (1), longitudinal sensors (2), the electronic card (4), all incorporated in the elastic material (3).

[0046] [Fig.3] shows the foot (5) pressing in the direction of the arrow (6) on the sole made of the elastic material (3) which induces a lateral displacement following the arrows (7) and (8) but also in the direction orthogonal to these arrows (not shown) and therefore creates an extension of the transverse and longitudinal sensors to give a stronger signal.

[0047] Determination of the pressures exerted on the sole by the foot:

[0048] Piezo sensors produce energy when they are mechanically stressed. This signal will be conditioned with the least possible loss to then be recovered by an energy harvesting circuit to charge a battery or supercapacitor. When the energy level is sufficient for a signal measurement, the piezo sensors are switched to analog conditioning for pressure measurement, the latter is then converted to digital by a converter and then this data is formatted and transmitted in Bluetooth to be analyzed subsequently by an external system (mobile application, software, etc.).

[0049] The energy required for Bluetooth measurement and transmission will discharge the energy source and the cycle then repeats to charge this energy reservoir again.

[0050] To optimize this system we can therefore play on 2 elements:

[0051] - optimize energy recovery by playing on the previous points

[0052] - minimize energy consumption during measurement and transfer by Bluetooth

[0053] Our solution can thus be implemented in soles or even socks to detect pressure and temperature conditions conducive to the formation of ulcers or blisters and will include: - Piezoelectric or flexible piezoelectric sensors of elongated shapes and arranged for a first part in the direction of the length of said soles and the other part with an angle between 1° and 90° relative to the first part, - An elastic material that incorporates the said sensors, - Electronics for processing sensor signals, to calculate the values ​​of the pressures exerted by the feet, and to communicate these values ​​wirelessly and with low consumption to a smartphone, - Contact pressure connections, by magnets or springs, between the said sensors and the cables or tracks connected to the said electronics, - A battery or supercapacitor to store the energy of said sensors, - A smartphone application that analyzes the signals transmitted by the soles to convert them into pressure at each intersection of transverse and longitudinal sensors by analyzing the time shifts of said signals - The application on the smartphone displays audible and / or visual alerts and stores a history of values ​​for future analyses.

[0054] Of the 460 million diabetics worldwide, about 50 million will need foot surgery and sometimes foot amputation due to ulcers.

[0055] By knowing the pressure and temperature of the feet all day long, while walking... our solution will help avoid many ulcers and therefore surgical intervention: • Practitioners (podiatrists, etc.) will be able to understand when ulcers appear and treat them more quickly. • Customers can adapt their activities or modify their footwear...

[0056] .

Claims

Claims

1. Device for measuring mechanical stresses in a material comprising one or more networks of sensors, characterized in that said sensors are of elongated shape and arranged for a first part in one direction and the other part with an angle of between 1° and 90° relative to the first part.

2. Device for measuring mechanical stresses in a material comprising one or more networks of sensors according to claim 1, characterized in that said sensors are incorporated in an elastic material.

3. Device for measuring mechanical stresses in a material comprising one or more networks of sensors according to claims 1 and 2, characterized in that said sensors are flexible piezoelectrics.

4. Device for measuring mechanical stresses in a material comprising one or more networks of sensors according to claims 1 to 3, characterized in that said sensors are incorporated in an incompressible elastic material so that when a stress is exerted, said material induces a stretching of said sensors.

5. Device for measuring mechanical stresses in a material comprising one or more networks of sensors according to claims 1 to 4, characterized in that said sensors are connected to tracks or cables, connecting them to signal processing electronics, using magnets.

6. Device for measuring mechanical stresses in a material comprising one or more networks of sensors according to claims 1 to 5, characterized in that the energy generated by said sensors is stored in a battery or a supercapacitor,

7. Insoles for detecting pressure and temperature conditions conducive to the formation of ulcers or blisters comprising a device for measuring mechanical stresses in a material according to any one of claims 1 to 6, characterized in that they comprise: • Flexible piezoelectric sensors of elongated shapes and arranged for a first part in the direction of the length of said insoles and the other part with an angle of between 1° and 90° relative to the first part, • An elastic material incorporating said sensors, • Signal processing electronics for the sensors to calculate the values of the pressures exerted by the feet, and to communicate said values wirelessly and with low power consumption to a smartphone, • Contact pressure connections, by magnets, between said sensors and the cables or tracks connected to said electronics, • A battery or a supercapacitor to store the energy of said sensors, • An application on the smartphone that analyzes the signals transmitted by the soles to convert them into pressure at each intersection of the transverse and longitudinal sensors by analyzing the temporal phase shifts of said signals, • The application on the smartphone that displays audible and / or visual alerts and stores a history of the values for future analyses.

8. Socks for detecting pressure and temperature conditions conducive to the formation of ulcers or blisters comprising a device for measuring mechanical stresses in a material according to any one of claims 1 to 6, characterized in that they comprise: • Flexible piezoelectric sensors of elongated shapes and arranged for a first part in the direction of the length of said soles and the other part with an angle of between 1° and 90° relative to the first part, • An elastic material which incorporates said sensors, • Electronics for processing the signals from the sensors, to calculate the values ​​of the pressures exerted by the feet, and for communicating said values, wirelessly and at low consumption to a smartphone, • Contact pressure connections, by magnets, between said sensors and the cables or tracks connected to said electronics,• A battery or supercapacitor to store the energy of said sensors, An application on the smartphone that analyzes the signals transmitted by the soles to convert them into pressure at each intersection of transverse and longitudinal sensors by analyzing the time shifts of said signals, The application on the smartphone that displays audible and / or visual alerts and stores a history of the values ​​for future analyses.

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