System and Method for a Surface Strain Gauge

• US 20130035878A1
• Filed: 04/12/2011
• Published: 02/07/2013
• Est. Priority Date: 04/19/2010
• Status: Active Grant

• Current Assignee: Single Wing Energy OY
• Original Assignee: Philip Wesby
• Inventors: Wesby, Philip, Turner, Christopher
• Granted Patent: US 9,618,420 B2
• Time in Patent Office: Days
• US Class Current: 702/42
• CPC Class Codes: F03D 17/00 Monitoring or testing of wind motors, e.g. diagnostics testing during commissioning of wind motors F03D13/30
• CPC Class Codes: F03D 7/042 by means of an electrical or electronic controller
• CPC Class Codes: F05B 2270/331 Mechanical loads
• CPC Class Codes: F05B 2270/332 Maximum loads or fatigue criteria
• CPC Class Codes: F05B 2270/808 Strain gauges; Load cells
• CPC Class Codes: G01M 5/0016 of aircraft wings or blades
• CPC Class Codes: G01M 5/0033 by determining damage, crack or wear
• CPC Class Codes: G01M 5/0083 by measuring variation of impedance, e.g. resistance, capacitance, induction
• CPC Class Codes: Y02E 10/72 Wind turbines with rotation axis in wind direction
• CPC Class Codes: Y02P 70/50 Manufacturing or production processes characterised by the final manufactured product

Abstract

A system and method for a surface strain gauge is described which has direct application to wind turbine structures and wind turbine blades and wind turbine struts. The invention is equally applicable to other airfoil structures such as aircraft wings and aircraft fuselages. The strain gauge comprises an array of carbon fibre material integrated with one or more microcontroller modules wherein the entire array may be incorporated into the surface of the structure to be monitored during manufacture of the structure. The array comprises separate sheets of carbon fibre reinforced epoxy which are linked together and which each comprise a separately addressable element such as a microcontroller wherein the microcontrollers are connected to a power supply and to a central bus which itself links to a central system controller. Differential measurements of the resistance of separate carbon fibre reinforced epoxy sheets may be determined in real time as well as the resistance between two or more sheets. In this way real time dynamic load monitoring can be performed and compared with original values determined at time of manufacture to provide data on fatigue of the structure with time before damage and failure occurs.

Claims

1. A smart surface strain gauge integrated into the surface of a structure for sensing real time strain and or cumulative damage of said structure characterised by:

an array comprising one or more separately addressable sheets and or fibre elements of carbon fibre reinforced epoxy (CFRE) or of carbon fibre reinforced epoxy matrix composite linked together, and or a material having similar resistance changing properties wherein

each of said separate sheets and or fibre elements being connected to one or more other sheets and or to one or more other fibre elements and

the electrical resistance of said carbon fibre reinforced epoxy (CFRE) or of carbon fibre reinforced epoxy matrix composite, or said other material having similar resistance changing properties, changing reversibly with tension and or compression, and

each of said separate sheets and or fibre elements comprising a separately addressable microcontroller being connected to a power supply and to a central bus linking to a central system controller, and further acting as a smart strain gauge sensor of said structure, and

each of said separate sheets and or fibre elements comprising one or more control points controlled by said microcontroller, and

means for sensing real time strain and or cumulative damage of said structure, and

means for providing said measurement data to a central system controller for determining

changes in resistance in one or more of said separate sheets and or one or more of said separate fibre elements while said structure is under load, and or

a measure of the rate of development of fatigue of said structure with time.

2. A smart surface strain gauge as disclosed in claim 1 wherein

said separately addressable microcontroller monitoring the dynamic load of said structure, and

said communication bus and power line being integrated with or into the surface of said structure, and

said microcontroller further comprising

means for making differential measurements of the resistance of each of said separate carbon fibre reinforced epoxy (CFRE) sheets and or fibre elements in real time, or of a material having similar resistance changing properties and

means for making differential measurements of the changes in resistance of one or more of said sheets and or fibres, and

means for comparing said measurement data with original values determined at time of manufacture or at a time prior to use.

3. A smart surface strain gauge as disclosed in claim 2 wherein said surface strain gauge monitoring the integrity and or dynamic loading and or surface deformation and or onset of fatigue of structures such as:

buildings and bridges, aircraft wings, aircraft fuselages, aircraft propellers, helicopter rotors, wind turbine structures, wind turbine blades, wind turbine struts, motor vehicle bodies, fuel tanker vehicles, boat hulls, marine vessels, and ship hulls such as oil tankers, and musical instruments, and support and control structures such as tools, and prosthetic joints, and prosthetic limbs, and prosthetic hands, and

changes in pressurised structures by providing real time data on the said integrity and or dynamic loading and or surface deformation and or fatigue of the structures, or

the dynamic loading and or the onset of fatigue of a synthetic heart valve wherein a layer of carbon fibre reinforced epoxy (CFRE) or an arrangement of fibre elements of carbon fibre reinforced epoxy (CFRE) or a material having similar resistance changing properties being incorporated into the heart valve itself and the onset of fatigue of the said synthetic heart valve being determined by monitoring permanent changes of resistance.

4. A smart surface strain gauge as disclosed in claim 2 further comprising

a plurality of said separate carbon fibre reinforced epoxy (CFRE) sheets (202) and or fibre elements each comprising at least one measurement point (203), and

At least one separately addressable microcontroller (M1), wherein

each of said sheets and or fibre elements being associated with the at least one microcontroller (M1), for performing resistance measurements, wherein said at least one microcontroller further connected to a power and communications bus (207) for sending and receiving data from said central system controller (208), and

said central system controller (208) being remote from the structure and said central power and communications bus (207) sending and receiving communications from a wireless communications circuit, or

said central systems controller (208) being integrated with the said structure and being interfaced with the said power and communications bus (207).

5. A smart surface strain gauge as disclosed in claim 4 comprising an arrangement of said carbon fibre reinforced epoxy (CFRE) sheets and or fibre elements wherein a single sheet element further comprising;

two microcontrollers (Mn1, Mn2) connected to a sheet element (307) via a plurality of connections (302, 303) respectively wherein

each microcontroller (Mn1, Mn2) been connected to a plurality of measurement points for performing resistance measurements, and

each microcontroller (Mn1, Mn2) been connected to said central communications and power bus (304) via 2 separate communications and power bus connections (305, 306) respectively.

6. A smart surface strain gauge as disclosed in claim 2 comprising an arrangement of said carbon fibre reinforced epoxy (CFRE) sheets and or fibre elements wherein

an arrangement of said carbon fibre reinforced epoxy (CFRE) sheets and or fibre elements being integrated into the strut (103) and the blade (102) of a vertical axis wind turbine, and

said central controllers (A, B) controlling the separate sheets and or fibre elements in said blade (102) and strut (103) respectively, wherein

said blade sheets or fibre elements being organised into an arrangement of alternating arrays between the two surfaces of said blade (102) each controlled by one or more of said separately addressable microcontrollers (u,v), and

said strut sheets or fibre elements being organised into an arrangement of alternating arrays between the two surfaces of said strut (103) each controlled by one or more of said separately addressable microcontrollers (u,v).

7. A smart surface strain gauge as disclosed in claim 6 comprising an arrangement of said carbon fibre reinforced epoxy (CFRE) sheets and or fibre elements wherein

said microcontrollers, being linked by a communication and power bus (109) wherein

said communication and power bus (109) comprising communication of power and data signals, and

said microcontrollers being linked to a solar cell and to a radio communications circuit for communicating with an external (non-rotating) controller via a radio link wherein

said external controller measuring the surface strain gauge readings and dynamically controlling the power take-off from the wind turbine and or activating a brake to slow or stop the rotation of the wind turbine as a function of the measured readings.

8. A smart surface strain gauge as disclosed in claim 7 comprising an arrangement of said carbon fibre reinforced epoxy (CFRE) sheets and or fibre elements wherein

each of said arrangement of sheets and or fibre elements providing the means to monitor changes in resistance varying as a function of the dynamic loading on the structure of the said blade (102) or said strut (103), and

in said blade (102) or in said strut (103), the two alternating sheet arrays and or fibre element arrays providing data of the loading on said blade (102) or on said strut (103) at points where the strain changing from compression to tension, or

said arrangement of sheets and or fibre elements providing a surface strain sensor wherein,

the changes in resistance determined by one array will be opposite in sense to that determined by the other, and

said resistance of each of said sheet arrays and or fibre element arrays being determined differentially and absolutely with time by one or more of said microcontrollers (u,v), wherein

each of said microcontroller (u,v) computing the absolute resistance across different measurement points in said sheet or fibre element or across a plurality of said sheets or fibre elements in order to detect absolute increases indicating fibre breakage and cumulative damage, or

said arrangement of sheets or fibre elements forming a slight overlap between said different sheet or fibre element arrays in order that all points in said structure being covered for fibre breakage detection and

each of said microcontrollers (u,v) comparing by subtraction or ratio in a bridge circuit said resistance of each separate array of sheets and or fibre elements so that the strain induced resistance change can be separated from temperature or other causes of resistance change.

9. A smart surface strain gauge as disclosed in claim 8 comprising an arrangement of said carbon fibre reinforced epoxy (CFRE) sheets and or fibre elements wherein

said central controller further comprising a control algorithm using a fuzzy logic self-learning strategy as a function of wind speed rotational speed and tip speed ratio and temperature and variations on wind power and wind direction as determined by sensors on the turbine and other operational characteristics of said turbine, wherein

said self-learning algorithm directing its load monitoring strategy to investigate the parts of the structure most under load with higher frequency such as the wind tips as a function of the wind speed and power generated by the wind turbine, wherein

the reference resistance values of said sheet arrays and or fibre element arrays being determined when manufactured or at a time prior to use, and further providing a baseline to determine the rate of development of fatigue of said structure with time, and or

an external central system controller determining the prevailing environmental conditions and implementing the optimum dynamic real time load monitoring strategy in order to monitor the structure effectively.

10. A smart surface strain gauge as disclosed according to claim 3 wherein the structure is a musical instrument and the resistance measurements are linked to data related to the deformation of the instrument such as a stringed instrument wherein the vibration of the said instrument can be tuned correctly, wherein the vibration of the instrument structure caused when a string is vibrated or when a woodwind instrument is blown, causes a deformation of the instrument body and a corresponding change in resistance in the surface strain gauge which is measured and processed by the central system controller (208) and which may be linked to:

a visible means such as an arrangement of one or more LEDs of the same or changing colour and or varying in intensity and or

an audible means of varying pitch wherein,

the said LED arrangement or audible means indicating when the resistance measurements get close to or match the signature resistance corresponding to one or more musical note frequencies for that instrument thereby providing a means to tune the said musical instrument.

11. A smart surface strain gauge as disclosed according to claim 3 wherein the surface of the structure comprises a high surface density of resistance measurement points thereby providing a microphone capability to capture and transmit sounds wherein the dynamically changing resistance measurements are transmitted by a communications link to an amplifier and loudspeaker where the sounds can be generated.

12. A method for sensing real time strain and cumulative damage of a structure by a smart surface strain gauge in carbon fibre reinforced epoxy (CFRE) or carbon fibre epoxy matrix composite integrated with or into the surface of said structure, said method comprising the steps of:

forming an array comprising separately addressable sheets and or fibre elements of carbon fibre reinforced epoxy (CFRE) or of carbon fibre reinforced epoxy (CFRE) matrix composite linked together, or a material having similar resistance changing properties wherein

each of said separate sheets and or fibre elements being connected in series to one or more other sheets and or fibre elements and

the electrical resistance of said carbon fibre reinforced epoxy (CFRE) matrix composite changing reversibly upon tension and or compression, and

connecting each of said separate sheets and or fibre elements comprising a separately addressable microcontroller to a power supply and to a central bus linking to a central system controller, and

controlling one or more control points of each of said separate sheets and or fibre elements by said microcontroller, and

sensing real time strain and cumulative damage of said structure by said array acting as a smart sensor across said structure surface and or throughout said structure, and

providing said measurement data to a central system controller and

determining changes in resistance across different parts of said structure while said structure is under load, and or the onset of fatigue of said structure with time.

13. A method for sensing real time strain and cumulative damage covering large sections of a structure as disclosed in claim 12 further comprising the steps of:

integrating said communication bus and power line with the said structure, and

measuring the resistance of each of said separate carbon fibre reinforced epoxy (CFRE) sheets and or fibre elements in real time by said microcontroller, and

measuring the changes in resistance or at least one of said sheets and or fibre elements by said microcontroller, and

comparing said measurement data with original values measured and stored at time of manufacture or at a time prior to use by said microcontroller wherein

said microcontroller further comprising means for doing differential measurements and means for comparing said measurement data with said original measured and stored resistance values.

14. A method for sensing real time strain and cumulative damage of a structure as disclosed in claim 13 wherein said surface strain gauge monitoring:

the integrity and or dynamic loading and or surface deformation and or onset of fatigue of structures such as;

buildings and bridges, aircraft wings, aircraft fuselages, aircraft propellers, helicopter rotors, wind turbine structures, wind turbine blades, wind turbine struts, motor vehicle bodies, fuel tanker vehicles, boat hulls, marine vessels, and ship hulls such as oil tankers, and musical instruments, and support and control structures such as tools, and prosthetic joints, and prosthetic limbs, and prosthetic hands, and

changes in pressurised structures by providing real time data on the said integrity and or dynamic loading and or surface deformation and or fatigue of the structures, or

the dynamic loading and or the onset of fatigue of a synthetic heart valve wherein a layer of carbon fibre reinforced epoxy (CFRE) or an arrangement of fibre elements of carbon fibre reinforced epoxy (CFRE) or a material having similar resistance changing properties being incorporated into the heart valve itself and the onset of fatigue of the said synthetic heart valve being determined by monitoring permanent changes of resistance.