WO2008113972A1 - Capteur - Google Patents

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Publication number
WO2008113972A1
WO2008113972A1 PCT/GB2008/000821 GB2008000821W WO2008113972A1 WO 2008113972 A1 WO2008113972 A1 WO 2008113972A1 GB 2008000821 W GB2008000821 W GB 2008000821W WO 2008113972 A1 WO2008113972 A1 WO 2008113972A1
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WO
WIPO (PCT)
Prior art keywords
waveguide
holder
grating
sensor according
dependent
Prior art date
Application number
PCT/GB2008/000821
Other languages
English (en)
Inventor
Thomas David Paul Allsop
John Arthur Robert Williams
Barbara Mary Cowie
Original Assignee
Aston University
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Filing date
Publication date
Application filed by Aston University filed Critical Aston University
Publication of WO2008113972A1 publication Critical patent/WO2008113972A1/fr

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B11/00—Measuring arrangements characterised by the use of optical techniques
    • G01B11/16—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge
    • G01B11/18—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge using photoelastic elements
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B11/00—Measuring arrangements characterised by the use of optical techniques
    • G01B11/30—Measuring arrangements characterised by the use of optical techniques for measuring roughness or irregularity of surfaces
    • G01B11/303—Measuring arrangements characterised by the use of optical techniques for measuring roughness or irregularity of surfaces using photoelectric detection means
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B90/00—Instruments, implements or accessories specially adapted for surgery or diagnosis and not covered by any of the groups A61B1/00 - A61B50/00, e.g. for luxation treatment or for protecting wound edges
    • A61B90/06—Measuring instruments not otherwise provided for
    • A61B2090/064—Measuring instruments not otherwise provided for for measuring force, pressure or mechanical tension
    • A61B2090/065—Measuring instruments not otherwise provided for for measuring force, pressure or mechanical tension for measuring contact or contact pressure

Definitions

  • the present invention relates to apparatus and methods for sensing properties of surfaces, and particularly, though not exclusively, for sensing properties of surface profiles or shapes .
  • Tactile sensing finds application in varied fields of science, technology and industry from keyhole surgery to robot control in unstructured environments .
  • the artificial sensing of surface texture, or surface profile is also of interest to industries such as road surfacing, textiles and abrasives, and in the area of machined finishes.
  • Fine surface finish information for machined surfaces typically in respect of dimensions of the scale of about 0.2-5 ⁇ m, is commonly measured using optical methods such as interferometry . Larger surface details, of dimensions typically of the scale of 0.1-5mm, are not easily characterisable using interferometric methods .
  • Known tactile sensors capable of sensing small-scale surface profile details typically consist of arrays of many sensors. Such systems are inherently complicated, expensive and prone to malfunction. The task of interconnecting and retrieving information from large arrays of such sensors requires intensive computational signal processing.
  • the present invention aims to provide a method and apparatus which may be used in sensing the properties of surface profiles, and which may overcome deficiencies in the prior art.
  • the invention proposed is to sense a property of a surface, such as a profile or shape, by sensing forces of deformation present within a body (e.g. an elastic or resiliently deformable body) caused to be urged against the surface in question.
  • a body e.g. an elastic or resiliently deformable body
  • the spatial distribution of reactive forces imparted by a surface against which a deformable body is urged is sensitively depended upon properties of the profile of that surface.
  • Those reactive forces contribute in deforming the deformable body such that the resultant forces of deformation within the deformed body result, at least in part, from characteristics of the surface profile in question.
  • the present invention proposes employing e.g.
  • optical means to monitor forces of deformation within such a deformable body, the optical means being coupled to the deformable body such that forces of deformation within the deformable body may also act upon the optical means.
  • Optical properties of the optical means may thereby vary in accordance with variations in the forces of deformation.
  • the optical means may be an optical waveguide coupled to the deformable body and arranged such that changes in the shape or position of the waveguide, or changes in (or the presence of) axial forces therealong and/or transverse forces thereacross, result in changes in the optical transmission/reflection characteristics of the waveguide.
  • the waveguide may include a waveguide grating having a reflectivity/transmissivity spectrum of a known form when in a quiescent state, aspects of which may change in response to the presence of forces of deformation within the deformable body to which the waveguide is coupled.
  • the extent and/or nature of changes in optical properties of such optical means have been found to correlate with aspects of the profile of a surface to which such a deformable body is urged. In this way, a characteristic of the optical properties of the optical means may be used to determine a characteristic of a profile of the surface in question.
  • references herein to "optical” includes a reference to microwave, visible or ultraviolet wavelengths of e/m radiation.
  • the present invention may provide a sensor (e.g. a surface profile sensor) having a waveguide, a deformable (e.g. resiliently deformable) waveguide holder arranged to hold the optical waveguide and arranged to be urged against a surface such that a deformation of the waveguide holder by action of said urging imparts a force to the waveguide (e.g. along and/or across the waveguide) , an analyser arranged to receive electromagnetic radiation via the waveguide while the waveguide holder is urged against a surface, for determining a spectral characteristic of the waveguide using received electromagnetic (e/m) radiation and for determining a characteristic of a shape or profile of the surface using the spectral characteristic.
  • a sensor e.g. a surface profile sensor
  • a deformable (e.g. resiliently deformable) waveguide holder arranged to hold the optical waveguide and arranged to be urged against a surface such that a deformation of the waveguide holder by action of said urging impart
  • the waveguide may include a waveguide grating at least a part of which is located between parts of the waveguide held by the waveguide holder such that a deformation of the waveguide holder by action of the urging imparts a force to (e.g. along and/or across) the waveguide grating.
  • the received e/m radiation may be received via the waveguide grating.
  • the waveguide grating may be a reflective waveguide grating (such as Bragg grating) , in which case the spectral characteristic of received electromagnetic radiation may be characteristic of the reflection or reflectivity spectrum.
  • the waveguide grating may be a transmissive grating, such as a long-period grating, in which case the spectral characteristic of received electromagnetic radiation may be associated with the transmission or transmissivity spectrum.
  • the analyser may include a sensor arranged to generate sensor signals according to the intensity of received electromagnetic radiation. The sensor may be responsive across a spectral range encompassing some or all of the relevant spectrum of the waveguide (e.g. the whole reflection/reflectivity or transmission/transmissivity spectrum of the waveguide grating) .
  • the analyser may include computer means responsive to sensor signals from the sensor.
  • the sensor signals may represent the spectrum of electromagnetic radiation received by the sensor.
  • the computer means may be arranged to perform a spectral analysis thereupon thereby to determine a spectral characteristic of the received electromagnetic radiation.
  • the computer means may be arranged to determine the width of a characteristic peak in the spectrum of received electromagnetic radiation, or the transmissivity/reflectivity spectrum of the waveguide, such as a width of a spectral reflectivity peak or of a spectral transmissivity peak. Additionally, or alternatively, the computer means may be arranged to determine the value of the wavelength of electromagnetic radiation at which a spectral peak occurs, or about which a spectral peak is substantially symmetrical, or is effectively "centered".
  • the computer means may be arranged to determine a spectral characteristic in the form of the first moment of the spectrum (Mi) , and/or the second moment of the spectrum of received electromagnetic radiation (M2) , or of the reflectivity/transmissivity spectrum of the waveguide.
  • the first moment, (Mi) , and second moment (M 2 ) , of a spectrum, S ( ⁇ ) may be defined in terms of the wavelength, ⁇ , of received electromagnetic radiation as:
  • spectral characteristics may be determined and used, such as : higher-order moments of the spectrum of the waveguide; a derivative of the spectrum with respect to signal wavelength at one or more selected wavelengths within the spectrum (e.g. 1 st , 2 nd , etc derivatives); any quantifiable characteristic or property of the spectrum, or a change therein (e.g. peak height, position, integral of the spectrum or a selected part of it, with respect to signal wavelength etc) .
  • the analyser may be arranged to determine a plurality of said spectral characteristics each associated with one of a respective plurality of different regions of a surface, and may be arranged for determining said characteristic of a shape or profile of the surface using some or each of said spectral characteristics.
  • the sensor may include translation means for moving the waveguide holder across a surface while urged thereagainst .
  • the translation means may be arranged to place the waveguide holder at a plurality of different stationary positions on a surface, and the analyser may be arranged to determine a said spectral characteristic at one, some or each said stationary position.
  • the translation means may be arranged to move the waveguide holder continuously across a surface, and the analyser may be arranged to determine one or more said spectral characteristics during said continuous movement.
  • the translating means may be arranged to move the waveguide holder in a direction substantially parallel to the transmission axis of the waveguide grating, and/or parallel to the surface to be sensed. Though translation transverse (at least in part) to axis of the waveguide grating is possible, increasing the component of translation parallel to that axis may assist in providing higher sensitivity/resolution in sensing the profile/shape of the surface being sensed.
  • the waveguide holder may have a substantially flat, or convex, and resiliently deformable outer surface region defining a contact region arranged to be urged against a surface.
  • the plane of the contact region, or a tangent of it, may be substantially parallel to the transmission axis of the waveguide grating.
  • the surface profile sensor may include urging means arranged to urge the waveguide holder with a force having a component generally transverse to the contact region.
  • the urging means may be operable to apply a variable urging force such that higher forces are applicable when sensing a relatively smooth surface, and lower urging forces are applicable when sensing a rougher or more uneven surface, or vice versa.
  • the waveguide grating may be positioned between the urging means and the contact region.
  • the waveguide grating may be embedded within the material of the grating holder.
  • the waveguide grating may be wholly encapsulated within the material of the grating holder.
  • the spectral characteristic may be any one or more of: the value of a measure of the width of a peak in the transmissivity or reflectivity spectrum of the waveguide or waveguide grating; the value of a measure of the position of a peak in the transmissivity or reflectivity spectrum of the waveguide or waveguide grating; higher- order moments of the spectrum of the waveguide; a derivative of the spectrum with respect to signal wavelength at one or more selected wavelengths within the spectrum (e.g. 1 st , 2 nd , etc derivatives); any quantifiable characteristic or property of the spectrum, or a change therein (e.g. peak height, position, integral of the spectrum or a selected part of it, with respect to signal wavelength etc) .
  • the waveguide may be an optical fibre, and the waveguide grating may be an optical fibre Bragg grating.
  • the optical fibre may terminate at an end within the waveguide holder, or at or immediately adjacent a surface of the waveguide holder.
  • the terminal end of the waveguide may be immersed in an index-matching fluid or material arranged to suppress reflection of optical signals from the terminal end.
  • a transmissive waveguide grating may me employed, such as a Long Period Grating (LPG) .
  • the LPG may include one or more phase discontinuities within the refractive index variations (e.g. periodic variations) in the material of the waveguide defining the waveguide grating. It has been found that inclusion of such phase discontinuities assist in reducing the length of the LPG required to achieve a suitable transmissivity spectrum for use in determining a characteristic of a sensed surface.
  • the length of the grating may be greater than about 5mm and less than about 50mm, or may be between about 5mm and about 30mm, or may be between about 15mm and about 30mm.
  • the waveguide holder may be formed from any elastic or resiliently deformable material such as: a Silicone rubber material; a synthetic rubber material; a natural rubber material .
  • the present invention may provide an endoscope including a surface profile sensor according the invention in its first aspect.
  • the present invention ay provide a surface finish evaluator for evaluating the surface finish of textiles or fabrics including a surface profile sensor according to the invention in its first aspect .
  • the present invention may provide a method for sensing (e.g. a shape or a profile of) a surface including: providing a waveguide; holding the waveguide using a deformable (e.g. resiliently deformable) waveguide holder; causing the waveguide holder to be urged against a surface to deform the waveguide holder thereby to impart a force to the waveguide (e.g. along and/or across it); receiving electromagnetic radiation via the waveguide while the waveguide holder is urged against the surface; determining a spectral characteristic of the waveguide using the received electromagnetic radiation, and determining a characteristic of a shape or profile of the surface using the spectral characteristic.
  • a deformable e.g. resiliently deformable
  • the waveguide may include a waveguide grating at least a part of which is between parts of the waveguide held by the waveguide grating, and the method may include causing the waveguide holder to be urged against a surface to deform the waveguide holder thereby to impart a force to (e.g. along and/or across) the waveguide grating.
  • the received e/r ⁇ radiation may be received via the waveguide grating.
  • the method may include determining a plurality of such spectral characteristics each associated with one of a respective plurality of different regions of a surface, and determining said characteristic of a shape or profile of the surface using some or each of said spectral characteristics .
  • the method may include moving the waveguide holder across a surface while urged thereagainst .
  • the method may include placing the waveguide holder at a plurality of different stationary positions on a surface, and determining a spectral characteristic at one, some or each stationary position.
  • the method may include moving the waveguide holder continuously across a surface, and determining one or more spectral characteristics during the continuous movement .
  • the method may include moving the waveguide holder in a direction substantially parallel to the transmission axis of the waveguide grating.
  • the method may include providing the waveguide holder with a substantially flat, or convex, and resiliently deformable outer surface region defining a contact region, and may include causing the contact region to be urged against a surface with the plane of (or a tangent of) said contact region being substantially parallel to the transmission axis of the waveguide grating.
  • the method may include urging the waveguide holder with a force having a component generally transverse to the contact region.
  • the method may include positioning the waveguide grating between the contact region and a point of application to the waveguide holder of an urging force causing said urging.
  • the method may include providing the waveguide grating embedded, or wholly encapsulated, within the material of the grating holder.
  • the spectral characteristic may be any one or more of: the value of a measure of the width of a peak in the transmissivity or reflectivity spectrum of the waveguide grating; the value of a measure of the position of a peak in the transmissivity or reflectivity spectrum of the waveguide grating.
  • the waveguide may be an optical fibre, and the waveguide grating may be an optical fibre Bragg grating.
  • the method may include providing the waveguide holder formed from a Silicone rubber material.
  • the present invention may provide a method of evaluating the surface finish of textiles or fabrics including the method in its further aspect or as generally described above.
  • Figure 2 schematically illustrates a waveguide holder in plan view and in side view
  • Figure 3 graphically illustrates a variation in the value of the wavelength at which the reflectivity spectrum of a fibre Bragg grating of the sensor of Figure 1 is centered, according to a variety of urging forces applied to the waveguide holder on the sensor;
  • Figure 4 graphically illustrates a variation in the value of the wavelength at which the reflectivity spectrum of a fibre Bragg grating of the sensor of Figure 1 is centered when a constant force is applied to the waveguide holder at the centre at each of a variety of directions;
  • Figures 5 (a) , (b) and (c) each schematically illustrate a respective one of a triangular, semicircular and a saw-tooth surface profile;
  • Figures 6 (a) and (b) graphically illustrate a change in a respective spectral characteristic (e.g. (a) central wavelength or (b) spectral width) of the waveguide of the sensor of Figure 1;
  • a respective spectral characteristic e.g. (a) central wavelength or (b) spectral width
  • Figures 7 (a) and (b) graphically illustrate changes in a measured value of a respective spectral characteristic (e.g. (a) central wavelength, or (b) spectral width) of the sensor of Figure 1 when translated with a surface with a triangular profile as illustrated in Figure 5 (a) ;
  • a respective spectral characteristic e.g. (a) central wavelength, or (b) spectral width
  • Figures 8(a) and (fc>) graphically illustrate changes in a measured value in a respective spectral characteristic (e.g. (a) central wavelength, or (b) spectral width) of the sensor of Figure 1 when translated across a surface with a semi-circular profile as illustrated in Figure 5 (b) ;
  • Figures 9 (a) and (b) graphically illustrate changes in a measured value of a respective spectral characteristic (e.g. (a) central wavelength, or (b) spectral width) of the sensor of Figure 1 when translated across a surface with a saw-tooth profile as illustrated in Figure 5 (c) .
  • Figure 1 illustrates a surface profile sensor 1, including a length optical fibre 3 containing a fibre
  • Bragg grating 4 adjacent a first terminal end of the optical fibre.
  • a section of the optical fibre containing the Bragg grating is encapsulated within a solid but resiliently deformable waveguide holder 2 formed from Poly siloxane (Methyl Vinyl Silicone Rubber) .
  • the whole length of the Bragg grating is so encapsulated, in addition to parts of the optical fibre adjacent the Bragg grating ends so as to be gripped by the material of the waveguide holder along the entire length of the encapsulated section of the optical fibre.
  • the encapsulated section of the optical fibre is straight, with substantially no bend therein.
  • the waveguide holder has an outwardly presented convex outer surface region (e.g. of a constant radius of curvature) defining a contact region arranged to be placed, in use, in contact with a surface t be sensed.
  • the contact region is contiguous with a substantially flat mounting surface region via the whole of which the waveguide grating holder is securely mounted to a translation stage 5.
  • the translation stage is a flat platform moveable in a direction parallel to the optical transmission axis of the encapsulated Bragg Grating at a velocity V, thereby to accordingly move with it the waveguide holder mounted upon it.
  • the translation stage is arranged to urge with a predetermined urging force F, the waveguide holder in a direction transverse to the direction in which the translation stage is moveable. This enables the contact region of the waveguide holder to be controllably urged into contact with a surface 6 to be sensed thereby.
  • the optical fibre has a second terminal end 13 free of the waveguide holder and connected to an optical input/output port of an optical analyser unit 8.
  • the analyser unit includes a three-port optical circulator 10, one port of which serves as the optical input/output port of the analyser unit, and is operatively coupled to the second terminal end 13 of the optical fibre 3 thereby to enable optical communication between the analyser unit and the embedded Bragg grating.
  • the analyser unit further includes a broadband optical radiation source 9, an optical output of which is coupled to a port of the optical circulator 10 proceeding (in the circulation direction) the optical circulator port at which the second end 13 of the optical fibre 3 is connected.
  • the broadband optical radiation source is arranged to generate optical radiation over a spectral range encompassing and exceeding the reflectivity bandwidth of the Bragg grating 4, and to direct such radiation into the optical port of the optical circulator to which it is coupled thereby to be directed out of the subsequent optical port of the optical circulator and along the optical fibre 3 towards the encapsulated Bragg grating 4.
  • the analyser unit includes an optical sensor unit 11 having an optical input port which is coupled to a port of the optical circulator 10 succeeding (in the circulation direction) the optical circulator port to which the second end 13 of the optical fibre 3 is connected.
  • the optical sensor unit is arranged to receive optical radiation via the optical circulator and to provide an optical sensor signal 14 indicative of the intensity of the received radiation and its wavelength, at any and all wavelengths within the bandwidth of the broadband optical radiation source 9.
  • an optical coupler may be used, such as a 2X2 optical coupler, with ports appropriately connected to the second terminal end 13 of the optical fibre, the broadband optical radiation source 9 and the optical sensor unit 11.
  • the analyser unit further includes a spectrum analyser unit 12 arranged to receive the optical sensor signals 14 generated by the optical sensor unit 11, being responsive thereto to determine a spectral characteristic of the reflectivity spectrum of the Bragg grating, and to use that spectral characteristic to determine a characteristic of a profile of the surface 6 being sensed.
  • a spectrum analyser unit 12 arranged to receive the optical sensor signals 14 generated by the optical sensor unit 11, being responsive thereto to determine a spectral characteristic of the reflectivity spectrum of the Bragg grating, and to use that spectral characteristic to determine a characteristic of a profile of the surface 6 being sensed.
  • the spectrum analyser unit is arranged to receive from the broadband optical radiation source data 15 defining the broadband output intensity spectrum of radiation output to the Bragg grating by the broadband optical radiation source. This enables the reflectivity spectrum of the Bragg grating to be accurately determined using the optical sensor signals received by the spectrum analyser unit.
  • the broadband optical radiation source may be assumed to be unchanging in terms of the spectrum of its output, and data defining that spectrum may be stored within the spectrum analyser unit 12 for use thereby as described above.
  • the spectrum analyser may include any suitable computer means designed, programmed or programmable to determine, from signals representative of the intensity of optical radiation received by the analyser unit, the aforesaid reflectivity spectrum of the Bragg grating, a suitable spectral characteristic of that reflectivity spectrum, and a characteristic of a profile of the surface 6 being sensed by the profile sensor.
  • the suitable spectral characteristics may be one or more of: the value of the first moment (Mi) of the spectrum; the value of a wavelength at which the reflectivity spectrum reaches a peak (e.g. maximum); the value of a wavelength about which the reflectivity spectrum is symmetric or is effectively centered; the value of the second moment (M 2 ) of the spectrum; a value of the width of the reflectivity spectrum or of the width of a peak (e.g. the largest peak, or an underlying peak/trend) in the reflectivity spectrum.
  • the first and second moment of a spectrum may be determined by the spectrum analyser according to the following equations :
  • ⁇ is the wavelength of optical signals defining the spectrum.
  • the spectrum analyser is arranged to permit a determination of a characteristic of a profile of the surface 6 being sensed, by comparing one or more measured values of a given spectral characteristic, associated with the sensing of a given surface, with one or more predetermined value (s) of the given spectral characteristic associated with the sensing of a surface of known profile. This enables determination of a measure of the degree of similarity of the sensed surface profile as compared to the known surface profile.
  • the spectrum analyser may be arranged to perform the aforesaid comparison, and to determine the measure of similarity, using objective analytical methods. These include, but are not limited to, convolution or correlation (e.g. cross correlation, auto-correlation) of the measured and the predetermined spectral characteristic values, and/or Fourier analysis of measured spectral characteristic values to determine the number, properties and/or distribution of Fourier components of the measured characteristic values, and comparing to the corresponding such properties and/or distribution of Fourier components of predetermined spectral characteristic values.
  • convolution or correlation e.g. cross correlation, auto-correlation
  • the spectrum analyser may present the measured value (s) of the given spectral characteristic to a user, along with one or more of the aforesaid predetermined spectral characteristics associated with a known surface profile. The user may then make a comparison and determine a characteristic of the profile of the surface being sensed.
  • the contact region of the waveguide holder 2 is urged into contact with a surface 6 of an object 7, a profile of which is to be sensed.
  • the urging is performed by action of an urging force F, of between about IN and 5N, imposed by the translation stage 5 to which the waveguide holder is mounted. This urging ensures sufficient contact is made between the contact region of the waveguide holder and the surface 6 being sensed.
  • the object 7 is held in fixed position relative to the translation stage with the surface 6 parallel to the direction of translation (V) of the translation stage.
  • the broadband optical radiation source 9 outputs radiation across its broadband spectrum. This radiation is directed to the optical circulator 10, and thence to the optical fibre 3, and to the encapsulated Bragg grating 4. Optical radiation falling within the reflectivity bandwidth of the Bragg grating is reflected thereby, back along the optical fibre 3 to the input/output port of the analyser unit 8 and to the sensor unit therein 11 via the optical circulator 10 of the analyser unit.
  • Sensor signals 14 representative of the intensity and spectrum of reflected signals are generated by the sensor unit and input thereby to the spectrum analyser 12 (optionally together with data 15 defining the broadband signal spectrum) of the analyser unit.
  • Characteristics of the reflectivity spectrum of the Bragg grating are determined by the spectrum analyser, and using those characteristics a corresponding characteristic of a profile of the sensed surface 6 is determined by the computing means (or by a user) as described above.
  • a tactile sensor may be provided consisting of a fibre Bragg grating embedded within a polymer "finger".
  • the tactile sensor When the tactile sensor is placed in contact with a surface and translated (e.g. tangentially) across it, measurements of the changes in the reflectivity spectrum of the Bragg grating provide a measurement of the spatial distribution of forces perpendicular to the surface and, thus, through the elasticity of polymer material of the "finger", a measure of the surface profile or roughness.
  • a sensor included a Poly Siloxane polymer (Methyl vinyl Silicone rubber) waveguide holder 2 as illustrated in Figure 2, in the form of a hemispherical "cap” with a flat mounting surface of 15 mm diameter (D) and a convex height (h) of 6 mm.
  • the polymer ⁇ cap is pressed into contact with a surface to be measured.
  • the “cap” resiliently deformed as a result of protruding surface features .
  • the elastic properties of the "cap” converted the deformation forces into internal strain, resulting in a variation in the distribution of strain along the fibre Bragg grating and, hence, a variation in the reflectivity spectrum of the fibre Bragg grating.
  • the reflected optical power spectrum from the fibre Bragg grating was measured and, using the broadband radiation source 9 and the spectrum analyser 12, the reflectivity spectrum of the Bragg grating was determined.
  • the reflectivity spectrum was characterised by its central wavelength (the first moment of the power spectrum) and its r.m.s. spectral width (the second moment of the power spectrum) .
  • the characterisation of the first and second moment of the reflectivity spectrum of the Bragg grating was determined when the "cap” was separately scanned across three different periodic surface profiles, namely: triangular; semicircular; and, saw-toothed periodic structures formed in a flat surface of a profile block 7, each with a modulation depth of between 0.5mm and 1 mm and a period of 2 mm.
  • Figures 5 (a) to 5(c) schematically illustrates these three differing surface profiles 6, and provides dimensions of aspects of each profile.
  • the resiliently deformable waveguide holder 2 was mounted upon the translation stage 5 with one of each of the three profile blocks 7 mounted, in turn, above the contact region of the waveguide holder such that the contact region made contact with the surface to be sensed while still being able to move freely beneath that surface as illustrated in Figure 1.
  • An urging force (F, typically a few Newtons) was applied such that the contact region of the waveguide holder was urged against the surface to be sensed (or vice versa) , the urging force being of a magnitude selected such that the spectral position of the peak in the reflectivity spectrum of the Bragg grating was shifted by about 300 picometers. This was done to ensure a suitably good contact between the sensor and the surface to be sensed.
  • the generally flat, but profiled, surface to be sensed was adjusted such that the plane of the surface was generally parallel to the direction of motion subsequently applied to the translation stage and to the waveguide holder mounted upon it.
  • the grating reflectivity spectrum was recorded at intervals during continuous and uniform translation of the contact region across the profiled surface in question.
  • an initial spectrum S (1) associated with the Bragg grating, and having a width W (1) may be changed when the Bragg grating is acted upon by forces to a new spectrum S (2) associated with the modified Bragg grating, and having a new width W ⁇ 2) .
  • Multiple of these changes in width and/or wavelength position are plotted in figures 7, 8 and 9.
  • a clear periodicity in both the first and second moments of the recorded spectrum can be observed.
  • the spectral width is modulated by 25 picometers.
  • the distortion may result in a periodically varying spacing of the bands of silica within the modulated refractive index of the optical fibre defining the fibre Bragg grating. This may cause a broadening of the spectral reflectivity peak of the grating, as well as a shift in the wavelength at which it is centred.
  • the spectrum analyser 12 may store spectral predetermined characteristics data sets such as the three data sets graphically illustrated in figures 7, 8 and 9, each associated with - and characteristic of - a predetermined surface profile structure. These predetermined data sets may be used for the purposes of the aforementioned comparison (either by the spectrum analyser, or by the user) in determining a characteristic of a surface profile being measured of characterised.
  • the sensor has been found to be responsive to the applied urging force (F), and the angle of applied urging force.
  • Figure 3 graphically illustrates the sensitivity of the central wavelength of the reflectivity spectrum of the fibre Bragg grating 4 in response to changes in the magnitude of the urging force F at the apex of the sensor "cap” (this being a reactive force in response to the urging force applied via the waveguide holder using the translation stage 5), and perpendicular to the contact region of the "cap". This illustrates that the response of the grating is not a linear function of the magnitude of applied urging force.
  • Figure 4 graphically illustrates changes in the spectral position of the central wavelength of the reflectivity spectrum of the fibre Bragg grating as a function of variation in the direction of the applied urging force (3.37 N in this example).
  • the urging force F was, in this example, applied in a direction tilted by between -5 degrees and +5 degrees relative to the perpendicular to the contact region of the waveguide holder .
  • the sensitivity and characteristics of the sensor 1 of the present invention may thus be tuned by varying the magnitude and/or direction of the urging force applied to the surface being sensed via the resiliently deformable waveguide holder. This may prove beneficial when sensing surfaces which have e.g. a saw-tooth type surface profile or shape wherein a suitably obliquely directed urging force may produce a larger change on measured spectral characteristics - and therefore greater sensitivity of sensing - than would other directions of urging force.
  • the present invention may find use in medical applications such as minimally invasive surgery, where a single connection to the sensor (i.e. a single optical fibre) is an attractive feature in any endoscopic equipment, where space is at a premium.
  • the invention may also find application in magnetic resonance imaging and equipment therefore, where immunity to electromagnetic interference is an asset.
  • the invention may find further application in the industry of textiles manufacture and surface finish evaluation.

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  • General Physics & Mathematics (AREA)
  • Investigating Or Analysing Materials By Optical Means (AREA)

Abstract

L'invention concerne un appareil de détection et un procédé pour détecter une propriété d'une surface, telle qu'un profil ou forme de surface (6), par la détection de forces de déformation présentes à l'intérieur du corps (par exemple, un corps élastique ou déformable de façon élastique (2)) amené à être poussé contre la surface en question. Des moyens optiques (3, 4) sont employés pour surveiller des forces de déformation à l'intérieur du corps déformable (2), les moyens optiques (3, 4) étant couplés au corps déformable (2) de telle sorte que les forces de déformation à l'intérieur du corps déformable (2) agissent également sur les moyens optiques (3, 4). Des propriétés optiques des moyens optiques (3, 4) peuvent ainsi varier selon des variations des forces de déformation. La mesure et/ou la nature des changements des propriétés optiques des moyens optiques (3, 4) sont corrélées avec des aspects du profil (6) de la surface contre laquelle le corps déformable (2) est poussé.
PCT/GB2008/000821 2007-03-16 2008-03-10 Capteur WO2008113972A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GBGB0705147.7A GB0705147D0 (en) 2007-03-16 2007-03-16 Sensor
GB0705147.7 2007-03-16

Publications (1)

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WO2008113972A1 true WO2008113972A1 (fr) 2008-09-25

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GB (1) GB0705147D0 (fr)
WO (1) WO2008113972A1 (fr)

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1384437A1 (fr) * 2002-07-23 2004-01-28 Aston Photonic Technologies Ltd. Appareil basé sur un guide d'ondes optiques pour le profilage superficiel
WO2005085766A2 (fr) * 2004-03-01 2005-09-15 University Of Washington Techtransfer Invention Licensing Capteur de guide d'onde de distribution a base de polymere de mesure de pression et de cisaillement

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1384437A1 (fr) * 2002-07-23 2004-01-28 Aston Photonic Technologies Ltd. Appareil basé sur un guide d'ondes optiques pour le profilage superficiel
WO2005085766A2 (fr) * 2004-03-01 2005-09-15 University Of Washington Techtransfer Invention Licensing Capteur de guide d'onde de distribution a base de polymere de mesure de pression et de cisaillement

Non-Patent Citations (5)

* Cited by examiner, † Cited by third party
Title
COWIE, BARBARA M.; WEBB, DAVID J.; TAM, BETTY; SLACK, PAUL; BRETT, PETER N., MEASUREMENT SCIENCE AND TECHNOLOGY, vol. 18, no. 1, January 2007 (2007-01-01), pages 138 - 146, XP002490764 *
DATABASE COMPENDEX [online] ENGINEERING INFORMATION, INC., NEW YORK, NY, US; 2007, COWIE BARBARA ET AL: "An optical fiber Bragg grating tactile sensor", XP002490766, Database accession no. E20074710926685 *
JIN-SEOK HEO, JONG-HA CHUNG, JUNG-JU LEE: "Tactile sensor arrays using fiber Bragg grating sensors", SENSORS AND ACTUATORS A: PHYSICAL, vol. 126, no. 2, 14 February 2006 (2006-02-14), pages 312 - 327, XP002490763 *
PROC SPIE INT SOC OPT ENG; PROCEEDINGS OF SPIE - THE INTERNATIONAL SOCIETY FOR OPTICAL ENGINEERING; OPTICAL SENSING TECHNOLOGY AND APPLICATIONS 2007, vol. 6585, 2007 *
S. C. TJIN, R. SURESH, N. Q. NGO: "Fiber Bragg Grating Based Shear-Force Sensor: Modeling and Testing", JOURNAL OF LIGHTWAVE TECHNOLOGY, vol. 22, no. 7, 7 July 2004 (2004-07-07), pages 1728 - 1733, XP002490765 *

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