Strain sensing smart label

Abstract

The present application describes an integrated autonomous textile strain sensing smart label engineered to allow the continuous monitorization of the mechanical integrity of rubber-based products, in particular rubber-based power transmission belts, identifying and signalling potential malfunctions or constructive defects. The developed device (100) for monitoring the mechanical integrity of rubber-based products surface (10), is characterized by comprising a strain sensor; a control board; and a piezoelectric generator.

Description

[0001] STRAIN SENSING SMART LABEL

[0002] Technical Field

[0003] The present application describes an integrated autonomous textile strain sensing smart label engineered to allow the continuous monitori zation of the mechanical integrity of rubber-based products , in particular rubber-based power transmission belts , identi fying and signalling potential mal functions or constructive defects .

[0004] Background art

[0005] Known state-of-the-art automotive applications use strain sensors to monitor the operational state of tires or for weight and load monitoring, for example to detect the occupation of vehicle seats . However, these technical developments do not consider an overall smart label solution .

[0006] Wireless tags comprising strain sensors can already be found in some technological developments , however these are mostly associated to structural monitoring, and none is adapted to the transport field requirements , as for example the automotive industry applications . Some of these existing applications suggest the monitoring of conveyor pulleys and the use of piezoelectric devices for energy generation . Until present days , this combination o f devices have been only used in some particular transport industry applications as for example in tires .

[0007] To support the above , document US2008216567A1 describes a vehicular tire monitoring system comprising a sensing system and an energy providing system arranged on the tire . The energy system generates energy from the rotation of the tire and provides the required energy to the sensing system, which gathers information from at least one mechanical property ( e . g . pressure ) . A communication system is included for wireless communication of the data gathered by the sensing system . A reactive system responsive to the data obtained by the sensing system is proposed ( e . g . display to present the data about the tire or a communication system to transmit the data about the tire to a remote site ) .

[0008] Considering prior knowledge provided by the state-of-the- art , the herein disclosed invention provides a groundbreaking technical solution in the field of continuous monitoring of mechanical integrity of rubber-based products , namely power transmission belts , in an autonomous and wireless approach, taking advantage of the mechanical events to which, the belt is submitted . In addition, the developed device , a textile strain smart label , is composed by a combination of di f ferent and particular systems like sensors , energy harvesters , communication systems and controlling electronics , whose combination is not foreseen or suggested in the above-mentioned transport applications .

[0009] Summary

[0010] The present invention describes a device for monitoring the mechanical integrity of rubber-based products surface characteri zed by comprising a strain sensor ; a control board; and a piezoelectric generator .

[0011] In a proposed embodiment of present invention, the control board is configured to acquire data from the strain sensor . Yet in another proposed embodiment of present invention, the data acquired from the strain sensor comprises an electrical resistance variation resultant from the deformation of the surface of the rubber-based material where applied .

[0012] Yet in another proposed embodiment of present invention, the strain sensor comprises an arrangement of layers comprising at least one of a piezoresistive layer on top of a polymeric layer, supported by an interlock substrate .

[0013] Yet in another proposed embodiment of present invention, the control board comprises at least one of an energy harvesting module , energy storage module , sensor acquisition module and communication module .

[0014] Yet in another proposed embodiment of present invention, the piezoelectric generator comprises an arrangement of layers composed of at least two printed conductive electrode layers arranged on a top and a bottom surface of a piezoelectric film layer .

[0015] Yet in another proposed embodiment of present invention, the device further comprises a display device composed of an electronic control module and a set of at least three multisegment display .

[0016] Yet in another proposed embodiment of present invention, the display device is configured to provide visual information to a user, said visual information being provided by the control board .

[0017] Yet in another proposed embodiment of present invention, the device is characteri zed by being integrated on the surface of a power transmission belt through a compatible adhesive rubber-based material .

[0018] General Description

[0019] The present application describes an integrated autonomous textile strain sensing smart label configured to continuously monitor mechanical integrity of rubber-based products , like power transmission belts , determining and signalling potential constructive defects , mal functions , or operational wear .

[0020] The developed device is a textile , active , hybrid and modular smart label with sensing, energy harvesting and communication capabilities , which is able to be embedded in a power transmission belt , of a vehicle for example , through the application of textile processes and printed electronics .

[0021] The invention further considers the possibility of including an innovative approach for the displaying of the information gathered by the smart label , including the integration of a flexible informative display that will be coupled to the smart label and produced by printed electronic techniques .

[0022] The herein disclosed hybrid strain sensing smart label , combining textile substrates and functional inks , allows wireless sensing of rubber-based composites , namely power transmission belts . The smart label also includes integrated flexible piezoelectric harvesters , assuring the sel fsuf ficiency of the device . The textile strain sensing smart label can also comprise a displaying device in order to provide visual information to a user about the acquired data.

[0023] Brief description of the drawings

[0024] For better understanding of the present application, figures representing preferred embodiments are herein attached which, however, are not intended to limit the technique disclosed herein.

[0025] Fig. 1 - illustrates the proposed integration of the device, i.e., the strain sensing smart label (100) in a textile substrate, and further integrated in a rubber-based power transmission belt (10) . The reference numbers are related to :

[0026] 10 - Power transmission belt;

[0027] 100 - Textile Strain sensing smart label.

[0028] Fig. 2 - illustrates a proposed embodiment of the textile strain sensing smart label (100) . The numerical references are related to:

[0029] 101 - Printed piezoelectric generator;

[0030] 102 - Printed strain sensor;

[0031] 103 - Printed circuit board (PCB) .

[0032] Fig. 3 - illustrates a vertical cross-section arrangement of the multilayer electroluminescent structure comprised in the printed flexible informative display (200) . The numeric references are related to:

[0033] 201 - Flexible polymeric substrate;

[0034] 202 - Printed transparent conductive layer;

[0035] 203 - Printed electroluminescent layer; 204 - Printed dielectric layer;

[0036] 205 - Printed conductive layer.

[0037] Fig. 4 - illustrates the structure of the printed piezoelectric generator (101) . The reference numbers are related to:

[0038] 1- Piezoelectric film layer;

[0039] 2- Printed conductive electrode layer.

[0040] Description of Embodiments

[0041] With reference to the figures, some embodiments are now described in more detail, which are however not intended to limit the scope of the present application.

[0042] The present application describes a textile smart label (100) with strain sensing, energy harvesting and communication capabilities, which are processed by a hybrid approach based on printing techniques and textile processes and integrated on the surface of a rubber-based material, in a particular embodiment of the present invention, in the surface of a power transmission belt (10) of a vehicle.

[0043] The strain sensing smart label (100) comprises a printed strain sensor (102) , printed onto a thermoplastic polyurethane (TPU) membrane laminated on a textile substrate, specifically an Interlock-type structure. In one of the proposed embodiments of the current invention, the textile end-substrate features a total thickness of 550-650 pm, providing flexibility and conformability. The strain sensor (102) is printed resorting to a piezoresistive carbon ink with a sheet resistance that can be adjusted within a level of 50 to 5000 ohm / sq / 25pm. The strain sensor (102) is printed through a screen-printing process over a 140x31 mesh (140 yarns / cm and 31 pm yarn diameter) . This mesh is based on a polymeric screen that allows the passage of the silver ink in a predefined pattern. This printing procedure is not meant to be limiting, as it can also be achieved resorting to the use of other existing techniques as inkjet, Physical Vapor Deposition (PVD) or sputtering. After the deposition of the ink in the defined pattern of the sensor (102) onto the textile end-substrate, the films are cured in a thermal oven at a temperature of approximately 120°C, withing a time interval of 5 to 10 minutes. The geometry of the printed strain sensor (102) can be dimensioned and adjusted according to the demands of the final layout, strain sensing's resolution and / or sensitivity, and others. After the curing the ink in the thermal oven, and to stabilize the mechanical structure of the printed strain sensor (102) , improving therefore its electrical features, the strain sensor (102) is subjected to a set of 30 to 50 deformation cycles, each one ranging from 0% to 5% of strain, being this procedure performed before its end application.

[0044] To ensure the connection of the printed strain sensor (102) to the printed circuit board (103) , which integrates the acquisition and control electronics, electrical connection wires are attached to the sensor (102) through a mechanical approach based on snap fasteners. These fasteners provide the required electrical contact between the conductive wires and the contact pads of the printed sensor (102) . The wires are then furtherly soldered onto the respective pads of the flexible PCB (103) by a conventional process.

[0045] Concerning the overall functionality of the printed circuit board (103) , that composes the strain sensing smart label (100) , it can be divided in four modules, namely the energy harvesting module, the energy storage module, the sensor acquisition module, and the communication module. The energy storage module is responsible for storing the harvested electrical energy generated in the energy harvesting module by the printed piezoelectric generator (101) during the deformation of the rubber-based power transmission belt (10) . The harvested energy is stored in a miniaturized battery that is also responsible for backup powering of the remaining systems of the label (100) . One of said remaining systems is the sensor acquisition module which is constituted by the strain sensor (102) and the required electronic components. The data therein collected by the sensor (102) is recorded and processed by the electronic components, and then sent to a receiving unit, for example, a flexible informative display (200) by means of a communication system module, based on a wireless Bluetooth protocol.

[0046] The textile end-structure where the strain sensor (102) is laminated consists of a Polyester (PET) -based interlock structure, which corresponds to a weft knitted fabric using two sets of needles. This substrate is used to improve the mechanical properties of the strain sensor (102) , allowing its stable stretching. A TPU membrane is used as interface layer between the textile structure and the printed film, promoting a good printing quality of the strain sensor (102) . This TPU membrane exhibits an approximate thickness of 130 pm and is laminated onto the textile through a heat and pressure process, for conditions of 140°C and 4 bars for 30 seconds. The same TPU membrane can be used to provide protection to the printed sensor (102) , working as an encapsulation layer. In one of the preferred embodiments of the present invention, a Bluetooth antenna, that will ensure the wireless communication features , is also directly printed onto the printed circuit board ( 103 ) , which comprises a flexible polyimide-based substrate . This substrate features a thickness of 50-75 pm, providing flexibility and conformability to the overall solution, allowing it to be applicable to the proposed end product , i . e . , to a rubberbased power transmission belt , ensuring enough resistance to mechanical events derived from it . The Bluetooth antenna is printed by resorting to a conductive silver ink with a theoretical sheet resistance within a range between 10 mQ / sq / mil and 20 mQ / sq / mil . Moreover, the Bluetooth antenna is printed through a screen-printing process over a 140x31 mesh ( 140 yarns / cm and 31 pm yarn diameter ) . After depositing the ink with the defined antenna pattern onto the end substrate , a curing process in a thermal oven is performed at an approximate temperature of 110 ° C, within a time interval of 10 to 20 minutes . The final printed Bluetooth antenna is then encapsulated to ensure the necessary protection to external aggressions . The printed antenna possesses a geometry and ef fective length compatible with the respective Bluetooth frequency range . The overall structure of the antenna can be adj usted to suit other frequencies of operation .

[0047] The final polyimide-based printed circuit board ( 103 ) comprises the printed antenna on the same substrate where the circuitry for the electronics controlling is designed and assembled . A flexible battery is attached on the opposed surface of the circuitry . The electrical connections of the antenna are printed directly onto the respective conductive pads , ensuring the correct connection to the remaining controlling electronics. The electrical connection between the printed strain sensor (102) with this PCB (103) is performed by conventional soldering of its wires to the respective conductive pads.

[0048] The textile smart label (100) is therefore constituted by the flexible printed circuit board (103) with the printed the printed Bluetooth antenna, the printed strain sensor (102) , and a printed piezoelectric generator for energy harvesting (101) . This piezoelectric generator (101) is constructed in a sandwich structure, with a piezoelectric intermediate film layer (1) and top and bottom conductive electrodes (2) . The piezoelectric active layer (1) of the piezoelectric generator (101) is based on a polyvinylidene difluoride - trifluoroethylene (PVDF-TrFE) film with a thickness ranging from 30 to 120 pm. The conductive electrodes (2) are screen printed on each face of the film by resorting to a conductive silver ink. A 140x31 mesh (140 yarns / cm and 31 pm yarn diameter) or 90x40 mesh (90 yarns / cm and 40 pm yarn diameter) is considered to print the silver electrodes on the piezoelectric film. After printing, these are thermally cured at an approximate temperature of 100°C during approximately 10 minutes in a thermal oven.

[0049] The piezoelectric generator (101) , in one of the proposed embodiments of the present invention, exhibits a rectangular geometry, with an active area of approximate dimensions of 40 mm x 60 mm. To maximize the generated power of the piezoelectric generator (101) , said device comprises support layers of polymeric nature to provide enhanced mechanical properties. An encapsulation layer is also therein included to provide protection to external aggressions. Therefore, the final structure of the generator (101) exhibits a total thickness ranging from 200 pm to 350 pm. The geometry and structure of the piezoelectric generator (101) can be dimensioned and adjusted according to the demands of the final layout and required energy output.

[0050] After assembling the elements that compose the final smart label (100) , its integration on the surface of a power transmission belt (10) is obtained resorting to adhesive compatible with rubber-based materials. The adhesive does not require any singular thermal or mechanical treatment, which simplifies the integration process. Furthermore, the materials applied in this invention were specifically chosen in terms of mechanical, electrical, thermal, and chemical properties to ensure both the functionality of the solution but also its integrity in the final application environment.

[0051] With the integration of the smart label (100) in the transmission belt (10) , strain effects up to 5% on the power transmission belt (10) during its operation can be assessed, by wirelessly gathering the respective outputs of the sensing smart label (100) through a Bluetooth protocol. In one of the preferred embodiments of the present invention, the determined strain effects on the power transmission belt (10) can be ranged between 0% and 5% with regard to its standard operation. However, this ranged can comprise higher values beyond the mentioned 5%. This smart label (100) is also configured to record mechanical conditions at which the belt (10) is subjected during its operation and infer about its overall structural integrity. Simultaneously, the integrated energy harvesting system, composed by the piezoelectric harvester (101) enables the complete autonomy of the smart label (100) , generating energy during the mechanical deformation of the power transmission belt (10) .

[0052] In another proposed embodiment of the current invention, the smart label (100) can also integrate a printed flexible informative display (200) . The structure of the proposed flexible electroluminescent display (200) is based on a multi-layered structure composed of four distinct layers; produced by screen-printing technology, resourcing to the application of different functional inks. To provide the required flexibility and light transmission, a polymeric substrate as Polyethylene Terephthalate (PET) or Polyethylene naphthalate (PEN) can be considered. Each layer of the lighting device is deposited onto the end substrate by resorting to screen printing techniques. In this proposed embodiment, the transparent conductive material (202) , which comprises on of a Poly ( 3 , 4-ethylenedioxythiophene ) polystyrene sulfonate (PEDOT:PSS) , is directly printed onto the polymeric substrate (201) . The subsequent layer (203) provides the electroluminescent feature, which can be of different colours, as blue or orange. A dielectric layer (204) is then printed to ensure the necessary insulation of the multi-layered structure. The final layer refers to the top electrode, being based on a conductive silver ink (205) . Regarding the printing process, the first functional layers are printed through a screen-printing process either over a 90x40 mesh (90 yarns / cm and 40 pm yarn diameter) , or a 140x31 mesh (140 yarns / cm and 31 pm yarn diameter) . After the printing of each ink with the defined pattern onto the end substrate, the respective films are cured in a thermal oven at temperatures ranging from 100°C to 110°C for approximately 10 to 20 minutes. At the end, the final printed display (200) is covered with an encapsulating layer over the top electrode, ensuring the necessary protection to external aggressions .

[0053] The electroluminescent display (200) is designed as a multisegment structure, providing the capability of displaying

Claims

numbers and letters, both in lowercase and uppercase. Each character is comprised by fourteen segments, with individual width of 3 mm per segment and overall dimension of 50 mm x 38 mm. The end display (200) is constituted by at least three of the abovementioned characters. Therefore, in this display, information of several types can be presented, either as text (e. g. MAX) or numerical (e. g. 99.9) .The operation of the electroluminescent display (200) requires a dedicated control electronics. The connections of the display segments to the electronics are ensured through the extension traces of the printed silver layer (top electrode) , creating a printed flat cable. At the end point of this flat cable, a connector ensures the connection to the remaining controlling electronics.CLAIMS1. Device (100) for monitoring the mechanical integrity of rubber-based products surface (10) characterized by comprising a strain sensor (102) ; a control board (103) ; and a piezoelectric generator (101) .

2. Device (100) according to the previous claim, wherein the control board (103) is configured to acquire data from the strain sensor (102) .

3. Device (100) according to any of the previous claims, wherein the data acquired from the strain sensor (102) comprises an electrical resistance variation resultant from the deformation of the surface of the rubber-based material (10) where applied.

4. Device (100) according to any of the previous claims, wherein the strain sensor (102) comprises an arrangement of layers comprising at least one of a piezoresistive layer on top of a polymeric layer, supported by an interlock substrate .

5. Device (100) according to any of the previous claims, wherein the control board (103) comprises at least one of an energy harvesting module, energy storage module, sensor acquisition module and communication module.

6. Device (100) according to any of the previous claims, wherein the piezoelectric generator (101) comprises an arrangement of layers composed of at least two printedconductive electrode layers (2) arranged on a top and a bottom surface of a piezoelectric film layer (1) .

7. Device (100) according to any of the previous claims, further comprising a display device (200) composed of an electronic control module and a set of at least three multi- segment display.

8. Device (100) according to any of the previous claims, wherein the display device (200) is configured to provide visual information to a user, said visual information being provided by the control board (103) .

9. Device (100) according to any of the previous claims, characterized by being integrated on the surface of a power transmission belt (10) through a compatible adhesive rubberbased material.

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