WO2002095475A1 - Method and device for measurement by extended chromatism confocal imaging - Google Patents

Method and device for measurement by extended chromatism confocal imaging Download PDF

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Publication number
WO2002095475A1
WO2002095475A1 PCT/FR2002/001699 FR0201699W WO02095475A1 WO 2002095475 A1 WO2002095475 A1 WO 2002095475A1 FR 0201699 W FR0201699 W FR 0201699W WO 02095475 A1 WO02095475 A1 WO 02095475A1
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Prior art keywords
echo
pulse
light
probe
chromatic
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PCT/FR2002/001699
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French (fr)
Inventor
Joseph Cohen-Sabban
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Sciences Et Techniques Industrielles De La Lumiere
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Publication of WO2002095475A1 publication Critical patent/WO2002095475A1/en

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    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B21/00—Microscopes
    • G02B21/0004—Microscopes specially adapted for specific applications
    • G02B21/002—Scanning microscopes
    • G02B21/0024—Confocal scanning microscopes (CSOMs) or confocal "macroscopes"; Accessories which are not restricted to use with CSOMs, e.g. sample holders
    • G02B21/0052—Optical details of the image generation
    • G02B21/0064—Optical details of the image generation multi-spectral or wavelength-selective arrangements, e.g. wavelength fan-out, chromatic profiling
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
    • G01S17/02—Systems using the reflection of electromagnetic waves other than radio waves
    • G01S17/06—Systems determining position data of a target
    • G01S17/08—Systems determining position data of a target for measuring distance only
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
    • G01S17/88—Lidar systems specially adapted for specific applications
    • G01S17/89—Lidar systems specially adapted for specific applications for mapping or imaging
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B21/00—Microscopes
    • G02B21/0004—Microscopes specially adapted for specific applications
    • G02B21/002—Scanning microscopes
    • G02B21/0024—Confocal scanning microscopes (CSOMs) or confocal "macroscopes"; Accessories which are not restricted to use with CSOMs, e.g. sample holders
    • G02B21/0028—Confocal scanning microscopes (CSOMs) or confocal "macroscopes"; Accessories which are not restricted to use with CSOMs, e.g. sample holders specially adapted for specific applications, e.g. for endoscopes, ophthalmoscopes, attachments to conventional microscopes

Definitions

  • the present invention relates to improvements made to optical measurement systems by confocal imaging using an objective whose axial chromatism is adapted to the desired measurement range.
  • the technical field of the invention is that of the manufacture of dimensional measuring devices without contact with the object to be measured.
  • Patent application FR-A-2,738,343 (COH EN SABBAN et al) describes an opto-electronic device for microstratigraphy of an object at least partially transparent or translucent in the wavelength domain of the axial chromatism considered, which comprises: 15 - a light source which delivers a polychromatic beam with a continuous spectrum;
  • a measurement probe comprising a target whose known axial chromatism is adapted to the working distance and to the desired axial measurement range (depth) as a function of the object to be analyzed;
  • a 0 probe is for example offered by the company STIL, AIX EN PROVENCE, FRANCE, under the reference CHR 1 50, which has the following characteristics: measurement range: from 0 to 80 ⁇ , or else from 0 to 300 ⁇ , or from 0 to 3 mm; working distance: 1 mm, 4.5 mm and 38 mm respectively; respective axial resolution: 31 0 "9 m, 1 0 ⁇ 8 m, and 5 1 0 " 7 m;
  • spectrophotometer comprising a chromatic disperser (prism or grating) as well as a multiple linear photoelectric detector (for example a CCD or CMOS strip);
  • the length of the fiber sections which is of the order of one or more meters is adjusted as a function the distance between the object and the source (and / or the spectrophotometer).
  • Such a device allows simultaneous detection and / or simultaneous distance measurement of several interfaces separating superimposed layers or regions of the object which differ from one another by their refractive index, for each interface located in the measurement range of the probe, by analyzing the shape, the central wavelength and the amplitude of the peak (s) detected by the detector of the spectrophotometer.
  • An object of the invention is therefore to propose a method and a device - or system - for measurement by chromatic confocal imaging which are improved and / or which remedy, at least in part, the drawbacks of known measurement systems.
  • An object of the invention is to propose such systems which are simple and rapid.
  • the invention applies to a process in which a polychromatic light source, a chromatic confocal probe, a light guide connecting the source to the probe, and a return beam splitter (reflected and / or backscattered by the object) transported by the light guide, which is capable of directing the return beam towards a detector; in accordance with one aspect of the invention, there is available on the optical path of the incident beam (go) and / or the return beam, a chromatic retarder capable of modifying the duration of propagation of light, between the source and the probe on the one hand, and / or between the probe and the detector on the other hand, in a variable manner as a function of the wavelength; in addition, the emission, by the light source, of a polychromatic light pulse is provoked; the back and forth propagation time is measured, for one (or more) light pulse (s) received by a photoelectric detector, each pulse received corresponding to an echo of the pulse emitted due to a layer or portion of the object to be analyzed, and the position
  • the invention uses the temporal dispersion of the different monochromatic components of the polychromatic pulse emitted, and / or of the echo - which is mono or polychromatic -, due to the propagation of light in the chromatic retarder , instead of using the spatial dispersion resulting from the propagation of light in a disperser (prism or equivalent) of a spectrophotometer.
  • a single (and / or point-type) photoelectric detector can be used which delivers a continuous (analog) output signal which can be sampled and digitized at very high frequency; the resulting digital data are analyzed by an electronic data processing unit in order to calculate the time between the emission of a pulse and the reception of an echo, and to deduce therefrom by calculation the position in the chromatic field of the probe used, from the point of the object that caused this echo.
  • said chromatic retarder comprises - and / or is essentially constituted by - a section of optical fiber; the length of this section is chosen to be large enough so that the delay between two echoes - at two different wavelengths - corresponding to a single pulse emitted by the source is sufficient to allow the (temporal) separation of these two echoes: to use chromatic dispersion optical fiber, generally choose a section of optical fiber whose length is of the order of at least one or several hundred meters, in particular of the order of one or more kilometers.
  • a light source emitting in the visible and / or infrared range is preferably used, in particular in a wavelength range from 600 to 1500 nm approximately, in particular ranging from 600 to 1000 nm.
  • the curve representing the spectral distribution of the energy of the light pulse emitted by the source can be continuous or discontinuous: it can be a spectrum of “discrete” lines (reference 25, FIG. 4), a spectrum of bands (reference 24, FIG. 3), of a "flat” spectrum (reference 23, FIG. 2), or else of a spectrum having at the same time lines, bands and / or a "continuous component" .
  • the optical fiber section of the chromatic retarder is shaped compactly; in particular, this section can be wound to form one (or more) coil (s).
  • the duration (temporal width) of the pulse reflected by the object to be analyzed is small, so that one can distinguish, at inside a measurement time window, two echoes corresponding to two very similar measurement distances; in particular, it is advantageous to be able to distinguish (discriminate) several tens, hundreds or thousands of echoes in said measurement window; taking into account the fact that the duration of the echo pulse is greater than that of the pulse emitted by the source, it is desirable that the duration of the latter is short, in particular of the order of 1 0 to 1 000 pico seconds, for example of the order of 1 00 pico seconds.
  • a measuring device comprises a source of polychromatic light pulses, a chromatic confocal probe, a photoelectric detector, a light guide connecting the source to the probe on the one hand, and the detector probe on the other hand, as well as a chromatic retarder, in particular a section of optical fiber of adequate length inserted between the source and the probe and / or between the probe and the detector.
  • the device further comprises:
  • a subtractor for determining, for an emitted pulse and for an associated echo, a propagation duration (go and return) of the pulse, by difference between said time value (return time) and said time reference (start time) ; means for determining, from said propagation time, and as a function of calibration data specific to the retarder and to the chromatic probe, the target point position of the object having produced the echo, in the measurement field of the chromatic confocal probe.
  • the invention consists in proposing a hardware and / or software system for measuring dimensions by confocal imaging, with extended chromatism, which comprises means for determining a dimensional measurement result from the propagation time d 'a light pulse in said chromatic retarder.
  • the invention consists in using a coiled or compacted optical fiber in a dimensional measurement system by chromatic confocal imaging.
  • FIG. 1 schematically illustrates the main components of a device according to the invention.
  • Figures 2 to 4 are spectrograms of three alternative embodiments of a light pulse emitted by the source.
  • Figure 5 schematically illustrates the effect produced by the optoelectric system of Figure 1 and its use for non-contact distance measurement according to the invention; in this figure is illustrated a timing diagram of a light pulse emitted by the source, as well as a timing diagram of an output signal from a detector illustrating three echoes corresponding to three distinct positions of the target point in the chromatic measurement field.
  • the device comprises a light source 1 such as a light-emitting diode, which emits a polychromatic pulse light beam 12;
  • the device comprises a separator 2 constituted by two prisms 2a and 2b assembled by their interface 2c treated semi-reflecting to form a cube; alternatively, cube 2 could be replaced by a fiber optic coupler;
  • the beam 1 2 crosses the cube 2 to form at the output a bundle 1 3 penetrating at one end 3a of a section of optical fiber 3 of great length;
  • the beam 1 4 transmitted by the core of the fiber 3 is integrated at the input of the probe 4 comprising an objective 4a with accentuated chromatism along its optical axis 5; due to the chromaticism of the objective 4a, the incident light pulse 1 4 is spatially dispersed at the exit of the objective 4a, the radius 1 5 schematically indicating the path of a spectral component such as ⁇ l FIG.
  • the radius 1 6 schematically indicates the path of a spectral component such as ⁇ 3 in figure 4.
  • the object 27 to be analyzed is placed in the measurement field of the probe 4, so that a point 28 of its external contour 29 is located on the axis 5, between the points 17 and 1 8 of this axis which respectively correspond to the focus of the objective 4a for the wavelengths ⁇ l and ⁇ 3 of optical path 1 5, 1 6 respectively; according to the design of the objective 4a, the distance separating the points 17 and 18 may for example vary from a few microns to several tens of millimeters; this distance is the depth of the measurement color field.
  • the probe 4 operating according to the principle of confocal imagery, causes a "spatial" filtering: only the echo reflected or backscattered by the point 28, which propagates along an intermediate path between the extreme paths 1 5 and 1 6, is retransmitted by objective 4a to its object focus; moreover, due to the chromaticism of the objective 4a, this echo essentially consists of a spectral line of wavelength (such as ⁇ 2 in FIG.
  • the echo pulse 1 9 retransmitted by the probe 4 at the “downstream” end 3b of the fiber 3 therefore essentially consists of said intermediate spectral line ( ⁇ 2), as in the case of the device described in the patent FR-A -2,738,343 mentioned above.
  • the echo 1 9 is transported by the fiber 3, from 3b to 3a, with a propagation time characteristic of its wavelength ( ⁇ 2); this echo is reflected by the interface 2c and forms the directed echo pulse 21 to the single detector 6 which delivers an output signal 1 0, to a signal and data processing unit 7, consisting for example of a personal computer equipped with sampling and digitization cards for the signal 1 0.
  • the unit 7 is connected for this purpose to the detector 6 by a link 8; it is also connected to the source 1 by a link 9 to send to the source control signals for generating light pulses 12.
  • Part of the pulse 1 2 emitted by the source 1 is reflected by the interface 2c and directed by a light guide 22 towards the detector 6; this allows the unit 7 to receive from the detector 6 a signal corresponding to the emission of a pulse, which serves as a time reference for the calculation, by difference with the time value corresponding to the return of the echo on the detector, propagation time - go - of the incident pulse and propagation - return - of the echo.
  • the detector 6 or the unit 7 includes a time sampler allowing sufficient resolution along the measurement axis: typically 1000 samples must be available over the overall duration of a measurement (of the order of 1 00 ns) corresponding to the depth of field of observation, and also a few tens of samples (around 30) for an echo.
  • the main steps in processing the signal delivered by the detector 6 are:
  • a very short polychromatic pulse 12 (the duration of which is generally situated in a range going from 1 0 ps to 1 ns, typically 1 00 ps) corresponding to a pulse emission frequency of the order of 1 to 1 00 GHz, typically 10 GHz, is injected into the system at a referenced instant; part of the source pulse is directed to the detection system;
  • the pulse crosses the long optical fiber 3 (typically one or more km): the pulse is "spread out” in time but remains polychromatic;
  • the pulse 1 4 crosses the optical rod 4 and is focused on a segment of its optical axis 5 (chromatic coding);
  • each object point 28 reinjects into the optical pencil 4 part of the light (narrow spectrum) that it has received; only the object points efficiently inject flux back into the optical pencil (which works according to the principle of confocal imaging);
  • the optical pencil focuses each echo pulse always at the same point: the initial source point at the output of the optical fiber, whatever the axial position of the corresponding object point;
  • each echo 1 9 is injected into the optical fiber: it is once again widened in time; more and more importantly, it is delayed next its spectral composition characteristic of the altitude of the corresponding object point;
  • the delay Tj, T 2 , T 3 (FIG. 5) is variable as a function of the wavelength ⁇ l, ⁇ 2, ⁇ 3 of the echo 21 returned by point 28 of the surface 29 of the object 27, depending on whether this point 28 is located at one end 1 7 or 1 8 of the measurement field on the axis 5 ( Figure 1), or else in an intermediate position between points 1 7 and 1 8;
  • each echo 20 is directed by the separating cube on the photoelectric detector 6; on the detector, each echo 21 is sampled temporally;
  • the barycenter is determined all the more precisely the greater the number of samples useful for the calculation.
  • This number of samples is limited mainly on the one hand by the temporal width induced by the system (widening due to the guidance of the fiber, influence of the optical pencil on the duration of the echo due to the residual spectral width due to the assembly confocal realized, duration of the source pulse), on the other hand by the minimum flux necessary for the measurement; the width 30 of the echo 21 is greater than that 31 of the pulse 1 2 emitted by the source;
  • the "temporal" position of the barycenter represents the wavelength selected by the optical pencil, which is itself characteristic of the axial position of the object point.
  • the accuracy of the measurement of the position of the object depends on the accuracy of the determination of the time barycenter of the echo 21;
  • the object and the sensor can be moved laterally (along two XY axes forming with axis 5 a three-dimensional frame of reference) relatively to each other, to measure the altitudes of all the points of the measured object field. This gives the topography of the surface of the object.

Abstract

The invention concerns improvements to optical measurement systems by confocal imaging using an objective whereof the axial chromatism is adapted to the desired measurement range. The technical field of the invention is that of the production of dimensional measuring appliances without contact with the measured object. The invention is characterised in that it consists in: emitting a polychromatic light pulse (12), in transporting the pulse up to the input of a measuring probe (4) comprising a chromatic objective (4a), placing a spot (28) on the object in the measuring field (17, 18) of the objective, on the optical axis (5) thereof, transporting the echo (19, 20, 21) produced by the spot (28) of the object up to a photoelectric detector (6), causing a temporal dispersion of the chromatic components of the emitted pulse and/or of the echo, and determining the result of the measurement by computation based on said temporal dispersion.

Description

PROCEDE ET DISPOSITIF DE MESURE PAR IMAGERIE CONFOCALE A CHROMATISME ETENDUMETHOD AND DEVICE FOR MEASUREMENT BY CONFOCAL IMAGING WITH EXTENDED CHROMATISM
La présente invention est relative à des améliorations apportées 5 aux systèmes de mesure optique par imagerie confocale utilisant un objectif dont le chromatisme axial est adapté à la plage de mesure désirée.The present invention relates to improvements made to optical measurement systems by confocal imaging using an objective whose axial chromatism is adapted to the desired measurement range.
Le domaine technique de l'invention est celui de la fabrication d'appareils de mesure dimensionnelle sans contact avec l'objet à 10 mesurer.The technical field of the invention is that of the manufacture of dimensional measuring devices without contact with the object to be measured.
La demande de brevet FR-A-2,738,343 (COH EN SABBAN et al) décrit un dispositif opto-électronique de microstratigraphie d'un objet au moins partiellement transparent ou translucide au domaine de longueurs d'ondes du chromatisme axial considéré, qui comporte : 15 - une source lumineuse qui délivre un faisceau polychromatique à spectre continu ;Patent application FR-A-2,738,343 (COH EN SABBAN et al) describes an opto-electronic device for microstratigraphy of an object at least partially transparent or translucent in the wavelength domain of the axial chromatism considered, which comprises: 15 - a light source which delivers a polychromatic beam with a continuous spectrum;
- une sonde de mesure comportant un objectif dont le chromatisme axial connu est adapté à la distance de travail et à la plage de mesure (profondeur) axiale souhaitée en fonction de l'objet à analyser ; une telle 0 sonde est par exemple proposée par la société STIL, AIX EN PROVENCE, FRANCE, sous la référence CHR 1 50, qui présente les caractéristiques suivantes : plage de mesure : de 0 à 80 μ , ou bien de 0 à 300 μ , ou bien de 0 à 3 mm ; distance de travail : respectivement 1 mm , 4,5 mm et 38 mm ; résolution axiale respective : 31 0"9 m, 1 0~8 m, et 5 1 0"7 m ;- a measurement probe comprising a target whose known axial chromatism is adapted to the working distance and to the desired axial measurement range (depth) as a function of the object to be analyzed; such a 0 probe is for example offered by the company STIL, AIX EN PROVENCE, FRANCE, under the reference CHR 1 50, which has the following characteristics: measurement range: from 0 to 80 μ, or else from 0 to 300 μ, or from 0 to 3 mm; working distance: 1 mm, 4.5 mm and 38 mm respectively; respective axial resolution: 31 0 "9 m, 1 0 ~ 8 m, and 5 1 0 " 7 m;
- un spectrophotomètre comportant un disperseur chromatique (à prisme ou à réseau) ainsi qu'un détecteur photoélectrique linéaire multiple (par exemple une barrette CCD ou CMOS) ;- a spectrophotometer comprising a chromatic disperser (prism or grating) as well as a multiple linear photoelectric detector (for example a CCD or CMOS strip);
- des moyens électroniques de traitement des signaux délivrés par 0 le détecteur du spectrophotomètre ;- electronic means for processing the signals delivered by the detector of the spectrophotometer;
- trois tronçons de fibre optique connectés à un coupleur optique pour d'une part acheminer un faisceau incident de la source lumineuse jusqu'à la sonde de mesure fonctionnant sur le principe de l'imagerie confocale, et d'autre part acheminer un faisceau réfléchi ou rétrodiffusé par l'objet, de la sonde de mesure jusqu'au spectrophotomètre : la longueur des tronçons de fibre, qui est de l'ordre de un ou plusieurs mètres est ajustée en fonction de la distance séparant l'objet de la source (et/ou du spectrophotomètre) .- three sections of optical fiber connected to an optical coupler on the one hand to route an incident beam from the light source to the measurement probe operating on the principle of imaging confocal, and on the other hand to convey a beam reflected or backscattered by the object, from the measurement probe to the spectrophotometer: the length of the fiber sections, which is of the order of one or more meters is adjusted as a function the distance between the object and the source (and / or the spectrophotometer).
Un tel dispositif permet la détection simultanée et/ou la mesure de distance simultanée de plusieurs interfaces séparant des couches ou régions superposées de l'objet qui se différencient les unes des autres par leur indice de réfraction, pour chaque interface située dans la plage de mesure de la sonde, par l'analyse de la forme, de la longueur d'onde centrale et de l'amplitude de pic(s) détectés(s) par le détecteur du spectrophotomètre.Such a device allows simultaneous detection and / or simultaneous distance measurement of several interfaces separating superimposed layers or regions of the object which differ from one another by their refractive index, for each interface located in the measurement range of the probe, by analyzing the shape, the central wavelength and the amplitude of the peak (s) detected by the detector of the spectrophotometer.
Bien que de tels appareils présentent de nombreux avantages, leurs caractéristiques ne permettent pas de répondre à tous les besoins ; en particulier, certaines applications nécessitent des mesures plus rapides que celles permises par ces appareils ; la vitesse de mesure de ce genre d'appareil est en effet limitée notamment par la vitesse de rafraîchissement du détecteur photoélectrique du spectrophotomètre. Un objectif de l'invention est donc de proposer un procédé et un dispositif - ou système - de mesure par imagerie confocale chromatique qui soient améliorés et/ou qui remédient, en partie au moins, aux inconvénients des systèmes de mesure connus.Although such devices have many advantages, their characteristics do not meet all needs; in particular, some applications require faster measurements than those allowed by these devices; the measurement speed of this kind of device is in fact limited in particular by the refresh rate of the photoelectric detector of the spectrophotometer. An object of the invention is therefore to propose a method and a device - or system - for measurement by chromatic confocal imaging which are improved and / or which remedy, at least in part, the drawbacks of known measurement systems.
Un objectif de l'invention est de proposer de tels systèmes qui soient simples et rapides.An object of the invention is to propose such systems which are simple and rapid.
L'invention s'applique à un procédé dans lequel on utilise, comme dans le brevet mentionné, une source lumineuse polychromatique, une sonde confocale chromatique, un guide de lumière reliant la source à la sonde, et un séparateur du faisceau retour (réfléchi et/ou rétrodiffusé par l'objet) transporté par le guide de lumière, qui est apte à diriger le faisceau retour vers un détecteur ; conformément à un aspect de l'invention, on dispose sur le trajet optique du faisceau incident (aller) et/ou du faisceau retour, un retardateur chromatique apte à modifier la durée de propagation de la lumière, entre la source et la sonde d'une part, et/ou bien entre la sonde et le détecteur d'autre part, de façon variable en fonction de la longueur d'onde ; en outre, on provoque l'émission, par la source lumineuse, d'une impulsion lumineuse polychromatique ; on mesure le temps de propagation aller et retour, pour une (ou plusieurs) impulsion(s) lumineuse(s) reçue(s) par un détecteur photoélectrique, chaque impulsion reçue correspondant à un écho de l'impulsion émise due à une couche ou portion de l'objet à analyser, et on déduit de ce temps de propagation la position de ladite couche ou portion de l'objet, mesurée le long de l'axe optique de l'optique chromatique de la sonde.The invention applies to a process in which a polychromatic light source, a chromatic confocal probe, a light guide connecting the source to the probe, and a return beam splitter (reflected and / or backscattered by the object) transported by the light guide, which is capable of directing the return beam towards a detector; in accordance with one aspect of the invention, there is available on the optical path of the incident beam (go) and / or the return beam, a chromatic retarder capable of modifying the duration of propagation of light, between the source and the probe on the one hand, and / or between the probe and the detector on the other hand, in a variable manner as a function of the wavelength; in addition, the emission, by the light source, of a polychromatic light pulse is provoked; the back and forth propagation time is measured, for one (or more) light pulse (s) received by a photoelectric detector, each pulse received corresponding to an echo of the pulse emitted due to a layer or portion of the object to be analyzed, and the position of said layer or portion of the object, measured along the optical axis of the chromatic optics of the probe, is deduced from this propagation time.
En d'autres termes, l'invention utilise la dispersion temporelle des différentes composantes monochromatiques de l'impulsion polychromatique émise, et/ou de l'écho - qui est mono ou polychromatique -, due à la propagation de la lumière dans le retardateur chromatique, au lieu d'utiliser la dispersion spatiale résultant de la propagation de la lumière dans un disperseur (prisme ou équivalent) d'un spectrophotomètre.In other words, the invention uses the temporal dispersion of the different monochromatic components of the polychromatic pulse emitted, and / or of the echo - which is mono or polychromatic -, due to the propagation of light in the chromatic retarder , instead of using the spatial dispersion resulting from the propagation of light in a disperser (prism or equivalent) of a spectrophotometer.
En conséquence, on peut utiliser un détecteur photoélectrique unique (et/ou ponctuel) qui délivre un signal de sortie (analogique) continu qui peut être échantillonné et numérisé à très haute f réquence ; les données numériques résultantes sont analysées par une unité électronique de traitement de données afin de calculer le temps séparant l'émission d'une impulsion et la réception d'un écho, et d'en déduire par calcul la position dans le champ chromatique de la sonde utilisée, du point de l'objet ayant provoqué cet écho.Consequently, a single (and / or point-type) photoelectric detector can be used which delivers a continuous (analog) output signal which can be sampled and digitized at very high frequency; the resulting digital data are analyzed by an electronic data processing unit in order to calculate the time between the emission of a pulse and the reception of an echo, and to deduce therefrom by calculation the position in the chromatic field of the probe used, from the point of the object that caused this echo.
Selon un mode préféré de réalisation , ledit retardateur chromatique comporte - et/ou est essentiellement constitué par - un tronçon de fibre optique ; la longueur de ce tronçon est choisie suffisamment grande pour que le retard entre deux échos - à deux longueurs d'onde différentes - correspondant à une seule impulsion émise par la source soit suffisant pour permettre la séparation (temporelle) de ces deux échos : pour utiliser la dispersion chromatique de la fibre optique, on choisira généralement un tronçon de fibre optique dont la longueur est de l'ordre d'une ou plusieurs centaines de mètres au moins, en particulier de l'ordre d'un ou plusieurs kilomètres.According to a preferred embodiment, said chromatic retarder comprises - and / or is essentially constituted by - a section of optical fiber; the length of this section is chosen to be large enough so that the delay between two echoes - at two different wavelengths - corresponding to a single pulse emitted by the source is sufficient to allow the (temporal) separation of these two echoes: to use chromatic dispersion optical fiber, generally choose a section of optical fiber whose length is of the order of at least one or several hundred meters, in particular of the order of one or more kilometers.
Il est en revanche nécessaire de limiter la dispersion temporelle des impulsions transmises par la fibre optique qui résulte de la diversité des modes de propagation dans la fibre ; à cet effet, on utilisera de préférence une fibre dont le gradient d'indice est adapté à cette condition.It is however necessary to limit the temporal dispersion of the pulses transmitted by the optical fiber which results from the diversity of the propagation modes in the fiber; for this purpose, it is preferable to use a fiber whose index gradient is adapted to this condition.
Afin d'éviter qu'une ambiguïté (« double solution ») n'apparaisse lors de la détermination de la longueur d'onde centrale d'un écho à partir du temps de propagation dans le retardateur de l'impulsion lumineuse correspondante, en vue de la déduction de la distance du point de l'objet ayant généré l'écho, compte tenu du chromatisme précaractérisé de l'objectif de la sonde, il est préférable de choisir une fibre dont la variation de l'indice en fonction de la longueur d'onde, dans la plage de la longueur d'onde utile, soit monotone (et non nulle) , qu'elle soit croissante ou décroissante.In order to avoid an ambiguity ("double solution") appearing when determining the central wavelength of an echo from the propagation time in the retarder of the corresponding light pulse, in view from the deduction of the distance from the point of the object that generated the echo, taking into account the precharacterized chromaticism of the probe objective, it is preferable to choose a fiber whose variation of the index as a function of the length wavelength, in the useful wavelength range, either monotonous (and not zero), whether increasing or decreasing.
En outre, afin de bénéficier au mieux du chromatisme de la sonde, il est souhaitable que l'énergie de l'impulsion lumineuse soit distribuée dans une large bande de longueur d'onde ; on utilise de préférence une source lumineuse émettant dans le domaine visible et/ou infrarouge, en particulier dans une plage de longueur d'onde allant de 600 à 1 500 nm environ, en particulier allant de 600 à 1 000 nm.In addition, in order to make the most of the chromatism of the probe, it is desirable that the energy of the light pulse is distributed in a wide band of wavelength; a light source emitting in the visible and / or infrared range is preferably used, in particular in a wavelength range from 600 to 1500 nm approximately, in particular ranging from 600 to 1000 nm.
La courbe représentative de la distribution spectrale de l'énergie de l'impulsion lumineuse émise par la source peut être continue ou discontinue : il peut s'agir d'un spectre de raies « discrètes » (repère 25, figure 4), d'un spectre de bandes (repère 24, figure 3), d'un spectre « plat » (repère 23, figure 2) , ou bien d'un spectre présentant à la fois des raies, des bandes et/ou une « composante continue » . Selon un mode préféré de réalisation , le tronçon de fibre optique du retardateur chromatique est conformé de façon compacte ; en particulier, ce tronçon peut être enroulé pour former une (ou plusieurs) bobine(s) . Afin d'obtenir une résolution satisfaisante du système de mesure, il faut faire en sorte que la durée (largeur temporelle) de l'impulsion réfléchie par l'objet à analyser soit faible, de sorte que l'on puisse distinguer, à l'intérieur d'une fenêtre temporelle de mesure, deux échos correspondant à deux distances de mesure très voisines ; en particulier, il est intéressant de pouvoir distinguer (discriminer) plusieurs dizaines, centaines ou milliers d'échos dans ladite fenêtre de mesure ; compte tenu du fait que la durée de l'impulsion d'écho est supérieure à celle de l'impulsion émise par la source, il est souhaitable que la durée de cette dernière soit faible, en particulier de l'ordre de 1 0 à 1 000 pico secondes, par exemple de l'ordre de 1 00 pico secondes.The curve representing the spectral distribution of the energy of the light pulse emitted by the source can be continuous or discontinuous: it can be a spectrum of “discrete” lines (reference 25, FIG. 4), a spectrum of bands (reference 24, FIG. 3), of a "flat" spectrum (reference 23, FIG. 2), or else of a spectrum having at the same time lines, bands and / or a "continuous component" . According to a preferred embodiment, the optical fiber section of the chromatic retarder is shaped compactly; in particular, this section can be wound to form one (or more) coil (s). In order to obtain a satisfactory resolution of the measurement system, it is necessary to ensure that the duration (temporal width) of the pulse reflected by the object to be analyzed is small, so that one can distinguish, at inside a measurement time window, two echoes corresponding to two very similar measurement distances; in particular, it is advantageous to be able to distinguish (discriminate) several tens, hundreds or thousands of echoes in said measurement window; taking into account the fact that the duration of the echo pulse is greater than that of the pulse emitted by the source, it is desirable that the duration of the latter is short, in particular of the order of 1 0 to 1 000 pico seconds, for example of the order of 1 00 pico seconds.
Ainsi, selon un autre aspect, un dispositif de mesure selon l'invention comporte une source d'impulsions lumineuses polychromatiques, une sonde confocale chromatique, un détecteur photoélectrique, un guide de lumière reliant la source à la sonde d'une part, et la sonde au détecteur d'autre part, ainsi qu'un retardateur chromatique, en particulier un tronçon de fibre optique de longueur adéquate inséré entre la source et la sonde et/ou entre la sonde et le détecteur. De préférence, le dispositif comporte en outre :Thus, according to another aspect, a measuring device according to the invention comprises a source of polychromatic light pulses, a chromatic confocal probe, a photoelectric detector, a light guide connecting the source to the probe on the one hand, and the detector probe on the other hand, as well as a chromatic retarder, in particular a section of optical fiber of adequate length inserted between the source and the probe and / or between the probe and the detector. Preferably, the device further comprises:
- des moyens pour déterminer, pour chaque impulsion lumineuse émise par la source, une référence temporelle (instant de départ) ;- Means for determining, for each light pulse emitted by the source, a time reference (start time);
- des moyens pour déterminer, pour chaque impulsion lumineuse reçue par le détecteur (c'est à dire pour chaque écho) une valeur temporelle (instant de retour) ;- Means for determining, for each light pulse received by the detector (that is to say for each echo) a time value (instant of return);
- un soustracteur pour déterminer, pour une impulsion émise et pour un écho associé, une durée de propagation (aller et retour) de l'impulsion, par différence entre ladite valeur temporelle (instant de retour) et ladite référence temporelle (instant de départ) ; - des moyens pour déterminer, à partir de ladite durée de propagation, et en fonction de données d'étalonnage propres au retardateur et à la sonde chromatique, la position de point cible de l'objet ayant produit l'écho, dans le champ de mesure de la sonde confocale chromatique.a subtractor for determining, for an emitted pulse and for an associated echo, a propagation duration (go and return) of the pulse, by difference between said time value (return time) and said time reference (start time) ; means for determining, from said propagation time, and as a function of calibration data specific to the retarder and to the chromatic probe, the target point position of the object having produced the echo, in the measurement field of the chromatic confocal probe.
Selon un autre aspect, l'invention consiste à proposer un système matériel et/ou logiciel pour la mesure de dimensions par imagerie confocale, à chromatisme étendu, qui comporte des moyens pour déterminer un résultat de mesure dimensionnelle à partir de la durée de propagation d'une impulsion lumineuse dans ledit retardateur chromatique.According to another aspect, the invention consists in proposing a hardware and / or software system for measuring dimensions by confocal imaging, with extended chromatism, which comprises means for determining a dimensional measurement result from the propagation time d 'a light pulse in said chromatic retarder.
Selon un autre aspect, l'invention consiste à utiliser une fibre optique bobinée ou compactée dans un système de mesure dimensionnelle par imagerie confocale chromatique.According to another aspect, the invention consists in using a coiled or compacted optical fiber in a dimensional measurement system by chromatic confocal imaging.
D'autres caractéristiques et avantages de l'invention apparaissent dans la description suivante qui se réfère aux dessins annexés, qui illustrent sans aucun caractère limitatif des modes préférentiels de réalisation de l'invention.Other characteristics and advantages of the invention appear in the following description which refers to the appended drawings, which illustrate without any limiting character the preferred embodiments of the invention.
La figure 1 illustre de façon schématique les principaux composants d'un dispositif selon l'invention.FIG. 1 schematically illustrates the main components of a device according to the invention.
Les figures 2 à 4 sont des spectrogrammes de trois variantes de réalisation d'une impulsion lumineuse émise par la source. La figure 5 illustre schématiquement l'effet produit par le système opto électrique de la figure 1 et son utilisation pour la mesure de distance sans contact conformément à l'invention ; sur cette figure est illustré un chronogramme d'une impulsion lumineuse émise par la source, ainsi qu'un chronogramme d'un signal de sortie d'un détecteur illustrant trois échos correspondant à trois positions distinctes du point cible dans le champ de mesure chromatique.Figures 2 to 4 are spectrograms of three alternative embodiments of a light pulse emitted by the source. Figure 5 schematically illustrates the effect produced by the optoelectric system of Figure 1 and its use for non-contact distance measurement according to the invention; in this figure is illustrated a timing diagram of a light pulse emitted by the source, as well as a timing diagram of an output signal from a detector illustrating three echoes corresponding to three distinct positions of the target point in the chromatic measurement field.
Par référence à la figure 1 , le dispositif comporte une source lumineuse 1 telle qu'une diode électroluminescente, qui émet un faisceau lumineux impulsionnel 12 polychromatique ; le dispositif comporte un séparateur 2 constitué par deux prismes 2a et 2b assemblés par leur interface 2c traitée semi-réfléchissante pour former un cube ; alternativement, le cube 2 pourrait être remplacé par un coupleur à fibre optique ; le faisceau 1 2 traverse le cube 2 pour former en sortie un faisceau 1 3 pénétrant à une extrémité 3a d'un tronçon de fibre optique 3 de grande longueur ; le faisceau 1 4 transmis par le cœur de la fibre 3 est intégré à l'entrée de la sonde 4 comportant un objectif 4a à chromatisme accentué le long de son axe optique 5 ; du fait du chromatisme de l'objectif 4a, l'impulsion lumineuse incidente 1 4 est dispersée spatialement à la sortie de l'objectif 4a, le rayon 1 5 indiquant schématiquement le trajet d'une composante spectrale telle que λl figure 4, tandis que le rayon 1 6 indique schématiquement le trajet d'une composante spectrale telle que λ3 figure 4. L'objet 27 à analyser est placé dans le champ de mesure de la sonde 4, de telle sorte qu'un point 28 de son contour externe 29 soit situé sur l'axe 5, entre les points 17 et 1 8 de cet axe qui correspondent respectivement au foyer de l'objectif 4a pour les longueurs d'onde λl et λ3 de trajet optique 1 5, 1 6 respectivement ; selon la conception de l'objectif 4a, la distance séparant les points 17 et 1 8 pourra par exemple varier de quelques microns à plusieurs dizaines de millimètres ; cette distance est la profondeur du champ chromatique de mesure.With reference to FIG. 1, the device comprises a light source 1 such as a light-emitting diode, which emits a polychromatic pulse light beam 12; the device comprises a separator 2 constituted by two prisms 2a and 2b assembled by their interface 2c treated semi-reflecting to form a cube; alternatively, cube 2 could be replaced by a fiber optic coupler; the beam 1 2 crosses the cube 2 to form at the output a bundle 1 3 penetrating at one end 3a of a section of optical fiber 3 of great length; the beam 1 4 transmitted by the core of the fiber 3 is integrated at the input of the probe 4 comprising an objective 4a with accentuated chromatism along its optical axis 5; due to the chromaticism of the objective 4a, the incident light pulse 1 4 is spatially dispersed at the exit of the objective 4a, the radius 1 5 schematically indicating the path of a spectral component such as λl FIG. 4, while the radius 1 6 schematically indicates the path of a spectral component such as λ3 in figure 4. The object 27 to be analyzed is placed in the measurement field of the probe 4, so that a point 28 of its external contour 29 is located on the axis 5, between the points 17 and 1 8 of this axis which respectively correspond to the focus of the objective 4a for the wavelengths λl and λ3 of optical path 1 5, 1 6 respectively; according to the design of the objective 4a, the distance separating the points 17 and 18 may for example vary from a few microns to several tens of millimeters; this distance is the depth of the measurement color field.
La sonde 4 fonctionnant selon le principe de l'imagerie confocale, provoque un filtrage « spatial » : seul l'écho réfléchi ou rétrodiffusé par le point 28, qui se propage selon un trajet intermédiaire entre les trajets extrêmes 1 5 et 1 6, est retransmis par l'objectif 4a jusqu'à son foyer objet ; en outre, du fait du chromatisme de l'objectif 4a, cet écho consiste essentiellement en une raie spectrale de longueur d'onde (telle que λ2 figure 3 ou 4) intermédiaire entre les longueurs d'onde extrêmes λl et λ3, et une relation (bijection) relie cette longueur d'onde intermédiaire à la position du point 28 mesurée sur l'axe 5 ; l'impulsion d'écho 1 9 retransmise par la sonde 4 à l'extrémité « aval » 3b de la fibre 3 consiste donc essentiellement en ladite raie spectrale intermédiaire (λ2) , comme dans le cas du dispositif décrit dans le brevet FR-A-2,738,343 susmentionné.The probe 4 operating according to the principle of confocal imagery, causes a "spatial" filtering: only the echo reflected or backscattered by the point 28, which propagates along an intermediate path between the extreme paths 1 5 and 1 6, is retransmitted by objective 4a to its object focus; moreover, due to the chromaticism of the objective 4a, this echo essentially consists of a spectral line of wavelength (such as λ2 in FIG. 3 or 4) intermediate between the extreme wavelengths λl and λ3, and a relation (bijection) connects this intermediate wavelength to the position of point 28 measured on axis 5; the echo pulse 1 9 retransmitted by the probe 4 at the “downstream” end 3b of the fiber 3 therefore essentially consists of said intermediate spectral line (λ2), as in the case of the device described in the patent FR-A -2,738,343 mentioned above.
L'écho 1 9 est transporté par la fibre 3, de 3b en 3a, avec un temps de propagation caractéristique de sa longueur d'onde (λ2) ; cet écho est réfléchi par l'interface 2c et forme l'impulsion d'écho 21 dirigée vers le détecteur 6 unique qui délivre un signal 1 0 de sortie, à une unité 7 de traitement de signaux et de données, constituée par exemple d'un ordinateur personnel équipé de cartes d'échantillonnage et de numérisation du signal 1 0. L'unité 7 est reliée à cet effet au détecteur 6 par une liaison 8 ; elle est en outre reliée à la source 1 par une liaison 9 pour envoyer à la source des signaux de commande de génération d'impulsions lumineuses 1 2.The echo 1 9 is transported by the fiber 3, from 3b to 3a, with a propagation time characteristic of its wavelength (λ2); this echo is reflected by the interface 2c and forms the directed echo pulse 21 to the single detector 6 which delivers an output signal 1 0, to a signal and data processing unit 7, consisting for example of a personal computer equipped with sampling and digitization cards for the signal 1 0. The unit 7 is connected for this purpose to the detector 6 by a link 8; it is also connected to the source 1 by a link 9 to send to the source control signals for generating light pulses 12.
Une partie de l'impulsion 1 2 émise par la source 1 est réfléchie par l'interface 2c et dirigée par un guide 22 de lumière vers le détecteur 6 ; ceci permet à l'unité 7 de recevoir du détecteur 6 un signal correspondant à l'émission d'une impulsion, qui sert de référence temporelle pour le calcul, par différence avec la valeur temporelle correspondant au retour de l'écho sur le détecteur, du temps de propagation - aller - de l'impulsion incidente et de propagation -retour - de l'écho.Part of the pulse 1 2 emitted by the source 1 is reflected by the interface 2c and directed by a light guide 22 towards the detector 6; this allows the unit 7 to receive from the detector 6 a signal corresponding to the emission of a pulse, which serves as a time reference for the calculation, by difference with the time value corresponding to the return of the echo on the detector, propagation time - go - of the incident pulse and propagation - return - of the echo.
Aucune cohérence (ni spatiale, ni temporelle) n'est requise concernant l'impulsion 1 2 émise par la source 1 .No coherence (neither spatial nor temporal) is required concerning the pulse 1 2 emitted by the source 1.
Le détecteur 6 ou l'unité 7 comporte un échantillonneur temporel permettant une résolution suffisante le long de l'axe de mesure : on doit disposer de typiquement 1000 échantillons sur la durée globale d'une mesure (de l'ordre de 1 00 ns) correspondant à la profondeur de champ d'observation, et aussi de quelques dizaines d'échantillons (environ 30) pour un écho. Les principales étapes de traitement du signal délivré par le détecteur 6 sont :The detector 6 or the unit 7 includes a time sampler allowing sufficient resolution along the measurement axis: typically 1000 samples must be available over the overall duration of a measurement (of the order of 1 00 ns) corresponding to the depth of field of observation, and also a few tens of samples (around 30) for an echo. The main steps in processing the signal delivered by the detector 6 are:
- calcul de la référence temporelle provenant de la source (par exemple calcul de barycentre) et mise en mémoire ; l'instant d'émission de l'impulsion et l'instant d'arrivée sur le détecteur de l'écho signal sont séparés de quelques microsecondes,- calculation of the time reference from the source (for example calculation of barycenter) and storage; the moment of transmission of the pulse and the time of arrival on the echo signal detector are separated by a few microseconds,
- numérisation de l'écho signal,- digitization of the echo signal,
- calcul du barycentre (temporel) de l'écho (-gaussienne) , - calcul de l'écart temporel entre la référence provenant de la source et le barycentre de l'écho,- calculation of the (temporal) barycenter of the (-gaussian) echo, - calculation of the time difference between the reference coming from the source and the barycenter of the echo,
- détermination, à partir de cet écart temporel, de la position du point 28 le long de l'axe optique 5 du crayon optique (à partir des données d'étalonnage du capteur) . Exemple de mesure :- determination, from this time difference, of the position of point 28 along the optical axis 5 of the optical pencil (from the sensor calibration data). Example of measurement:
- une impulsion 12 polychromatique très brève (dont la durée est généralement située dans une plage allant de 1 0 ps à 1 ns, typiquement 1 00 ps) correspondant à une fréquence d'émission d'impulsion de l'ordre de 1 à 1 00 GHz, typiquement de 1 0 GHz, est injectée dans le système à un instant référencé ; une partie de l'impulsion-source est dirigée vers le système de détection ;a very short polychromatic pulse 12 (the duration of which is generally situated in a range going from 1 0 ps to 1 ns, typically 1 00 ps) corresponding to a pulse emission frequency of the order of 1 to 1 00 GHz, typically 10 GHz, is injected into the system at a referenced instant; part of the source pulse is directed to the detection system;
- l'impulsion traverse la fibre optique 3 de grande longueur (typiquement un ou plusieurs km) : l'impulsion est "étalée" temporellement mais reste polychromatique ;the pulse crosses the long optical fiber 3 (typically one or more km): the pulse is "spread out" in time but remains polychromatic;
- l'impulsion 1 4 traverse le crayon optique 4 et est focalisée sur un segment de son axe optique 5 (codage chromatique) ;- the pulse 1 4 crosses the optical rod 4 and is focused on a segment of its optical axis 5 (chromatic coding);
- compte-tenu de la dispersion chromatique axiale étendue du crayon optique, seule une partie spectrale étroite de la source est parfaitement focalisée sur le(s) point(s) objet(s) visé(s) 28 ; on peut le cas échéant viser simultanément plusieurs points objets, par exemple les deux points sur l'axe des faces d'une lame transparente ;- taking into account the extended axial chromatic dispersion of the optical pencil, only a narrow spectral part of the source is perfectly focused on the point (s) object (s) targeted (s) 28; if necessary, it is possible to simultaneously target several object points, for example the two points on the axis of the faces of a transparent blade;
- par rétrodiffusion et/ou réflexion spéculaire, chaque point objet 28 réinjecte dans le crayon optique 4 une partie de la lumière (spectre étroit) qu'il a reçue ; seuls les points objets réinjectent efficacement du flux dans le crayon optique (qui fonctionne selon le principe de l'imagerie confocale) ;- By backscattering and / or specular reflection, each object point 28 reinjects into the optical pencil 4 part of the light (narrow spectrum) that it has received; only the object points efficiently inject flux back into the optical pencil (which works according to the principle of confocal imaging);
- par retour inverse de la lumière, le crayon optique focalise chaque impulsion écho toujours au même point : le point source initial en sortie de la fibre optique, quelle que soit la position axiale du point objet correspondant ;- by reverse light return, the optical pencil focuses each echo pulse always at the same point: the initial source point at the output of the optical fiber, whatever the axial position of the corresponding object point;
- chaque écho 1 9 est injecté dans la fibre optique : il est une fois de plus élargi temporellement ; de plus et surtout, il est retardé suivant sa composition spectrale caractéristique de l'altitude du point objet correspondant ; le retard Tj , T2, T3 (figure 5) est variable en fonction de la longueur d'onde λl , λ2 , λ3 de l'écho 21 renvoyé par le point 28 de la surface 29 de l'objet 27, suivant que ce point 28 est situé à une extrémité 1 7 ou 1 8 du champ de mesure sur l'axe 5 (figure 1 ) , ou bien en une position intermédiaire entre les points 1 7 et 1 8 ;- each echo 1 9 is injected into the optical fiber: it is once again widened in time; more and more importantly, it is delayed next its spectral composition characteristic of the altitude of the corresponding object point; the delay Tj, T 2 , T 3 (FIG. 5) is variable as a function of the wavelength λl, λ2, λ3 of the echo 21 returned by point 28 of the surface 29 of the object 27, depending on whether this point 28 is located at one end 1 7 or 1 8 of the measurement field on the axis 5 (Figure 1), or else in an intermediate position between points 1 7 and 1 8;
- chaque écho 20 est dirigé par le cube séparateur sur le détecteur 6 photoélectrique ; sur le détecteur, chaque écho 21 est échantillonné temporellement ;each echo 20 is directed by the separating cube on the photoelectric detector 6; on the detector, each echo 21 is sampled temporally;
- un calcul est effectué sur les signaux successivement enregistrés afin de déterminer le(s) barycentre(s) de ces mesures, barycentre(s) temporel(s) de chaque écho ;- a calculation is carried out on the successively recorded signals in order to determine the barycenter (s) of these measurements, temporal barycenter (s) of each echo;
- le barycentre est déterminé d'autant plus précisément que le nombre d'échantillons utiles au calcul est grand. Ce nombre d'échantillons est limité principalement d'une part par la largeur temporelle induite par le système (élargissement dû au guidage de la fibre, influence du crayon optique sur la durée de l'écho du fait de la largeur spectrale résiduelle due au montage confocal réalisé, durée de l'impulsion source) , d'autre part par le flux minimal nécessaire à la mesure ; la largeur 30 de l'écho 21 est supérieure à celle 31 de l'impulsion 1 2 émise par la source ;- the barycenter is determined all the more precisely the greater the number of samples useful for the calculation. This number of samples is limited mainly on the one hand by the temporal width induced by the system (widening due to the guidance of the fiber, influence of the optical pencil on the duration of the echo due to the residual spectral width due to the assembly confocal realized, duration of the source pulse), on the other hand by the minimum flux necessary for the measurement; the width 30 of the echo 21 is greater than that 31 of the pulse 1 2 emitted by the source;
- la position "temporelle" du barycentre représente la longueur d'onde sélectionnée par le crayon optique, qui est elle-même caractéristique de la position axiale du point objet. Un étalonnage préalable de l'instrument permet de calibrer la position temporelle des différentes longueurs d'onde correspondant aux altitudes objet mesurées selon l'axe 5 ;- the "temporal" position of the barycenter represents the wavelength selected by the optical pencil, which is itself characteristic of the axial position of the object point. A prior calibration of the instrument makes it possible to calibrate the time position of the different wavelengths corresponding to the object altitudes measured along axis 5;
- la précision de la mesure de position de l'objet dépend de la précision de la détermination du barycentre temporel de l'écho 21 ;the accuracy of the measurement of the position of the object depends on the accuracy of the determination of the time barycenter of the echo 21;
- l'objet et le capteur peuvent être déplacés latéralement (selon deux axes XY formant avec l'axe 5 un référentiel à trois dimensions) relativement l'un par rapport à l'autre, pour mesurer les altitudes de l'ensemble des points du champ objet mesuré. On obtient ainsi la topographie de la surface de l'objet. - the object and the sensor can be moved laterally (along two XY axes forming with axis 5 a three-dimensional frame of reference) relatively to each other, to measure the altitudes of all the points of the measured object field. This gives the topography of the surface of the object.

Claims

REVENDICATIONS 1 . Procédé de mesure dimensionnelle sans contact avec l'objet (27) à mesurer, dans lequel :CLAIMS 1. Method of dimensional measurement without contact with the object (27) to be measured, in which:
- on provoque l'émission par la source lumineuse d'une impulsion ( 1 2) lumineuse brève et polychromatique,- the emission by the light source of a short and polychromatic light pulse (1 2) is caused,
- on transporte l'impulsion jusqu'à l'entrée d'une sonde (4) de mesure comportant un objectif (4a) chromatique et fonctionnant selon le principe de l'imagerie confocale,- the pulse is transported to the input of a measurement probe (4) comprising a chromatic objective (4a) and operating according to the principle of confocal imaging,
- on place un point (28) de l'objet dans le champ (1 7, 1 8) de mesure de l'objectif , sur l'axe (5) optique de celui-ci,- a point (28) of the object is placed in the field (1 7, 1 8) for measuring the objective, on the optical axis (5) thereof,
- on transporte l'écho (1 9, 20, 21 ) produit par le point (28) de l'objet jusqu'à un détecteur (6) photoélectrique unique qui délivre un signal de sortie analogique qui est échantillonné et numérisé à très haute fréquence, - on provoque une dispersion temporelle des composantes chromatiques de l'impulsion émise ainsi que de l'écho en disposant sur le trajet optique commun des faisceaux lumineux d'éclairage et de mesure, un retardateur chromatique (3) modifiant la durée de propagation de la lumière en fonction de la longueur d'onde, lequel retardateur chromatique présente une variation monotone de son indice de réfraction avec la longueur d'onde dans le domaine spectral utile,- the echo (19, 20, 21) produced by the point (28) of the object is transported to a single photoelectric detector (6) which delivers an analog output signal which is sampled and digitized at very high frequency, - one causes a temporal dispersion of the chromatic components of the emitted pulse as well as of the echo by placing on the common optical path of the light and measurement light beams, a chromatic retarder (3) modifying the propagation time light as a function of the wavelength, which chromatic retarder exhibits a monotonic variation of its refractive index with the wavelength in the useful spectral range,
- on analyse les données résultantes de la numérisation du signal de sortie par une unité électronique de traitement des données afin de calculer le temps de propagation global séparant l'émission de l'impulsion et de la réception d'un écho et d'en déduire par calcul, la distance par rapport à la sonde, du point de l'objet ayant provoqué cet écho.- the data resulting from the digitization of the output signal by an electronic data processing unit are analyzed in order to calculate the global propagation time between the emission of the pulse and the reception of an echo and to deduce therefrom by calculation, the distance from the probe, from the point of the object that caused this echo.
2 - Procédé selon la revendication 1 , dans lequel on mesure le(s) temps de propagation global (globaux) séparant l'émission d'une impulsion et le(s) écho(s) lumineux successif(s) reçu(s) par le détecteur (6) photoélectrique unique, chaque écho étant dû à une couche ou portion de l'objet à analyser et dans lequel on déduit de ce(s) temps de propagation la (les) position(s) de ladite (desdites) couche(s) ou portion(s) de l'objet, mesurée(s) le long de l'axe optique de la sonde confocale (4) .2 - Method according to claim 1, in which the global propagation time (s) between the emission of a pulse and the successive light echo (s) received by the single photoelectric detector (6), each echo being due to a layer or portion of the object to be analyzed and in which we deduce from this (these) propagation times the position (s) of said layer (s) (s) or portion (s) of the object, measured along the optical axis of the confocal probe (4).
3. Procédé selon l'une quelconque des revendications 1 ou 2, dans lequel on émet lesdites impulsions lumineuses dans le domaine visible et/ou inf rarouge, en particulier dans une plage de longueurs d'ondes allant de 600 à 1 500 nanomètres.3. Method according to any one of claims 1 or 2, wherein said light pulses are emitted in the visible and / or infra-red range, in particular in a wavelength range from 600 to 1,500 nanometers.
4. Procédé selon l'une quelconque des revendications 1 à 3, dans lequel la durée des impulsions émises par la source est de Tordre de 1 0 à 1 000 picosecondes. 4. Method according to any one of claims 1 to 3, wherein the duration of the pulses emitted by the source is of the order of 10 to 1000 picoseconds.
5. Dispositif de mesure dimensionnelle sans contact avec un objet (27) à mesurer, caractérisé en ce que qu'il comporte :5. Dimensional measuring device without contact with an object (27) to be measured, characterized in that it comprises:
- une source lumineuse ( 1 ) impulsionnelle, polychromatique,- a pulsed, polychromatic light source (1),
- une sonde (4) confocale chromatique,- a chromatic confocal probe (4),
- un détecteur (6) photoélectrique unique, - des moyens de transport et de guidage de la lumière reliant la source à la sonde et la sonde au détecteur, caractérisé en ce que les moyens de transport et de guidage ont une partie commune agissant en qualité de retardateur chromatique (3) constitué principalement d'un tronçon de fibre optique de grande longueur et dont l'indice de réf raction varie de façon monotone avec la longueur d'onde,- a single photoelectric detector (6), - means of transport and guidance of the light connecting the source to the probe and the probe to the detector, characterized in that the means of transport and guidance have a common part acting in quality chromatic retarder (3) mainly consisting of a long length of optical fiber, the refractive index of which varies monotonically with the wavelength,
- des moyens de traitement pour déterminer un résultat de mesure dimensionnelle à partir du temps de propagation global séparant l'émission de l'impulsion lumineuse et la réception de l'écho correspondant provenant du point de l'objet examiné.processing means for determining a dimensional measurement result from the overall propagation time separating the emission of the light pulse and the reception of the corresponding echo coming from the point of the object examined.
6. Dispositif selon la revendication 5, dans lequel ledit retardateur comporte un tronçon de fibre optique à gradient d'indice.6. Device according to claim 5, wherein said retarder comprises a section of optical fiber with index gradient.
7. Dispositif selon Tune quelconque des revendications 5 ou 6, dans lequel les moyens pour déterminer le résultat de mesure à partir de la durée de propagation dans le retardateur à fibre optique comportent :7. Device according to any one of claims 5 or 6, in which the means for determining the measurement result from the duration of propagation in the optical fiber retarder comprise:
- des moyens pour déterminer, pour chaque impulsion lumineuse émise par la source, une référence temporelle de départ ; - des moyens pour déterminer, pour chaque impulsion lumineuse reçue par le détecteur, c'est à dire pour chaque écho, une valeur temporelle de retour ;- Means for determining, for each light pulse emitted by the source, a starting time reference; means for determining, for each light pulse received by the detector, that is to say for each echo, a return time value;
- un soustracteur ou moyen équivalent pour déterminer, pour une impulsion émise et pour l'écho associé, une durée de propagation (aller et retour) de l'impulsion , par différence entre ladite valeur temporelle de retour et ladite référence temporelle de départ ;a subtractor or equivalent means for determining, for a transmitted pulse and for the associated echo, a propagation duration (outward and return) of the pulse, by difference between said return time value and said start time reference;
- des moyens pour déterminer, à partir de ladite durée de propagation, et en fonction de données d'étalonnage propres au retardateur et à la sonde confocale chromatique, une distance séparant un point cible de l'objet ayant produit l'écho et la sonde ou un référentiel lié à celle-ci,means for determining, from said propagation time, and as a function of calibration data specific to the retarder and to the chromatic confocal probe, a distance separating a target point from the object having produced the echo and the probe or a repository linked to it,
- des moyens de calcul de barycentre temporel de chaque écho détecté, et des moyens de calcul d'une valeur moyenne de ces barycentres et/ou de la durée pour une série d'une ou plusieurs dizaines d'impulsions émises successivement. means for calculating the temporal barycenter of each detected echo, and means for calculating an average value of these barycenters and / or the duration for a series of one or more tens of pulses emitted successively.
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