Ellipsoidal mirror of revolution measuring device
The measurement device with coaxial mirrors forming a revolution ellipsoid addresses the challenges of low light collection and dependency on angle and distance in existing interferometers and profileometers, achieving improved measurement accuracy and reliability.
Patent Information
- Application Number
- FR2023005177
- Authority / Receiving Office
- FR · FR
- Patent Type
- Patents
- Current Assignee / Owner
- Filing Date
- 2023-05-25
- Publication Date
- 2025-05-16
- Estimated Expiration
- 2043-05-25
AI Technical Summary
Existing interferometers and profileometers face challenges in efficiently collecting light due to Gaussian laser beam propagation in free space, leading to low light collection ratios and dependency on the angle and distance between the object and the light guide.
A measurement device utilizing two coaxial mirrors forming a revolution ellipsoid, allowing for light emission and collection at a distance from the object, thereby maximizing light collection and reducing dependency on the angle and distance between the object and the light guide.
The measurement device effectively collects more light and reduces dependency on the angle and distance between the object and the light guide, enabling more accurate and reliable measurements in various applications.
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Abstract
Description
Title of the invention: Measuring device with ellipsoidal mirror of revolution Technical field
[0001] The present invention relates to applications of interferometry, profilometry and real-time displacement control.
[0002] In particular, the present invention relates to the implementation of an optical path for one of the preceding applications, for example in interferometry the measurement of a path difference between said optical path and a reference optical path.
[0003] In general, the invention relates to a measuring device implementing an optical path comprising a reflection on the surface of an object studied. Prior techniques
[0004] Interferometry consists in a simplified manner of comparing the optical paths of a reference optical arm on the one hand, and a measuring optical arm on the other hand. An optical path is generally defined by the optical distance between a light source and a detector of said light or a screen, the refractive index of the medium in which the light propagates being taken into account.
[0005] The optical path difference between the reference optical arm and the measuring optical arm is generally called "path difference" and makes it possible to give indications on the quality or shape of an object to be measured, for example lenses or surfaces positioned on the optical path of the measuring optical arm.
[0006] Many current interferometers integrate optical fibers in each of the reference or measurement optical arms. These optical fibers make it possible to simplify the design and, above all, the integration of such interferometers in a space-constrained environment. Optical fibers allow a light source, for example a laser, and / or a detector or a screen to be moved outside a space-constrained environment, in other words one that cannot contain the light source and / or the detector or the screen, or that does not allow easy maintenance.
[0007] In such a configuration, the light following the optical path of the optical measuring arm passes into an optical fiber then propagates in free space in order to interact with the object to be measured, in refraction or in reflection, then returns in a second optical fiber towards the detector or the screen. Free space is understood to mean a space opposing a guided optical space, a free space being for example a gas such as air or a dielectric medium such as optical glass. second optical fiber can also be a second use of the first optical fiber in the opposite direction of light propagation.
[0008] However, the recollection of the luminous flux after the interaction of the light with the object to be measured is complex.
[0009] Indeed, due to the Gaussian propagation of the laser beam in free space, the ratio of the flux collected by the detector or by the screen to the flux emitted by the light source is very low, little light being collected by the second optical fiber.
[0010] [Fig.l] schematically shows an embodiment of an end 1 of an optical fiber 3 connected at its other end (not shown) to a laser. The end 1 of the optical fiber 3 shown comprises a ferrule 5 surrounding the optical fiber 3, a ferrule sleeve 7 surrounding the ferrule 5, a gradient index lens 9 (called "GRIN lens" in English terms) positioned at the end of the optical fiber 3, as well as an outer sleeve 11 surrounding the gradient index lens 9 as well as the ferrule sleeve 7. The output laser beam 13 is called Gaussian. It comprises a narrow portion 15 called "waist" then a widening 17 of the laser beam 13 responsible for the low flux collected.Furthermore, focusing the beam at the waist 15 involves constraints of positioning the object to be measured at a short distance from this waist and therefore short from the end 1 of the optical fiber 3, which is sometimes not possible or desirable, for example when the object to be measured reaches high temperatures, or is in motion, such as turbomachine blades.
[0011] The same problems arise with the use of a profilometer, the latter then comprising only an optical measuring arm and no optical reference arm. A profilometer can be used to determine an optical path, for example in order to determine the relief of a surface, or to control a movement, for example the rotation of a blade of a turbomachine by detecting or not detecting said blades opposite said profilometer.
[0012] Furthermore, when the object to be measured is a surface, and this surface is inclined relative to the axis of the light beam, existing interferometers and profilometers do not allow measurements to continue to be taken unless the light source and / or the detector or the screen and / or the optical fibers leading to the latter are oriented orthogonally to the surface. This orientation can be done manually or motorized but is often mechanically limited.
[0013] Existing profilometers and interferometers therefore collect little light flux at their detector or screen, and are both dependent on the angle between the observed surface and the axis of the light beam, and dependent on the distance between the object and the end of the optical fiber guiding the light from the light source or towards the detector or screen. Statement of the invention
[0014] The present invention therefore aims to overcome the aforementioned drawbacks and to provide a measuring device less dependent on the angle between the surface of the object to be measured and the measuring axis, and less dependent on the distance between the light guide and the object to be measured, and capable of collecting more light.
[0015] The present invention relates to a measuring device comprising two coaxial mirrors each comprising a reflecting surface, the reflecting surfaces of the two mirrors being positioned opposite each other, the reflecting surfaces of the two mirrors each forming a portion of the same ellipsoid of revolution, the ellipsoid of revolution being defined by a major axis and two equal minor axes and comprising a first and a second focus, the two mirrors extending longitudinally between the first focus and the second focus, the measuring device further comprising a light emission module along a main emission axis passing through the first focus, and a light collection module along a main collection axis passing through the first focus, the measuring device being configured to be positioned so that the second focus of the ellipsoid of revolution is positioned on the surface of an object to be measured.
[0016] Thus, the presence of two foci formed by the ellipsoidal shape of revolution of the mirrors makes it possible to move the measuring device away from the object to be measured, and makes it possible to be less dependent on the angle between the surface of the object to be measured and the major axis because any light ray passing through the second focus will return to the level of the first focus and therefore potentially into the light collection module. This second effect also makes it possible to maximize the quantity of light collected.
[0017] Advantageously, the light emitting module comprises a laser light source.
[0018] Advantageously, the two mirrors extend longitudinally over a distance greater than half the distance separating the two foci.
[0019] In one embodiment, the measuring device further comprises a planar glass slide with parallel faces configured to be positioned on the surface of the object to be measured.
[0020] In a particular embodiment, the light collection module comprises a collection lens and an optical fiber, the collection lens being configured to focus a light flux into the optical fiber.
[0021] Advantageously, the light emission module and the collection module are positioned at a distance from the first focus less than a quarter of the minor axis of the ellipsoid of revolution.
[0022] Advantageously, the angle between the main light emission axis of the light emission module and the major axis of the ellipsoid of revolution is equal to the angle between the main collection axis of the collection module and the major axis of the ellipsoid of revolution, the main emission axis, the main collection axis and the major axis being included in the same plane.
[0023] In a particular embodiment, the measuring device further comprises two plane mirrors parallel to the major axis and orthogonal to the plane comprising the main emission axis, the main collection axis and the major axis, the plane mirrors being respectively positioned at equal distance between the first focus and the light emission module on the one hand, and the first focus and the light collection module on the other hand.
[0024] The present invention also relates to an interferometer comprising a reference optical arm and a measuring optical arm comprising the measuring device as defined above.
[0025] The present invention also relates to a profilometer comprising a measuring device as defined previously and a detector connected to the light collection module. Brief description of the drawings
[0026] Other aims, characteristics and advantages of the invention will appear on reading the following description, given solely by way of non-limiting example, and made with reference to the appended drawings in which:
[0027] [Fig.l] which has already been mentioned is a sectional view of a fiber end according to the state of the art;
[0028] [Fig.2] is a sectional view of a first embodiment of a measuring device according to the invention;
[0029] [Fig.3] is a sectional view of a light ray passing through and reflected by a glass slide of a measuring device according to the invention;
[0030] [Fig.4] is a sectional view of a second embodiment of a measuring device according to the invention; and
[0031] [Fig.5] is a sectional view of a third embodiment of a measuring device according to the invention. Detailed description of at least one embodiment
[0033] [Fig. 2] schematically shows a first embodiment of a measuring device 19 for an object to be measured 21, and in particular for the surface 23 of said object to be measured 21. The measurements carried out are, for example, distance measurements of the surface relative to a reference point, or angle measurements of the surface relative to a predefined axis, these measurements being able to be used to trace the profile of the surface 23 of the object to be measured 21.
[0034] The measuring device 19 comprises two coaxial mirrors 25 each comprising a reflecting surface 27 positioned opposite each other.
[0035] The reflecting surfaces 27 of the two mirrors 25 each form a portion of the same ellipsoid of revolution 29, the ellipsoid of revolution 29 being defined by a major axis, said major axis being an axis of revolution of the ellipsoid and being defined by a semi-major axis a, and two equal minor axes, defined by the semi-minor axes b and c such that b=c, and comprising a first and a second focus F1 and F2.
[0036] The equation of the ellipsoid 29 can thus be established in the following manner:
[0037] x2 V^Z2 _ . + b2 -1
[0038] The two mirrors 25 extend longitudinally between the first focus F1 and the second focus F2. Optionally, the two mirrors 25 are two portions of the same ellipsoidal mirror of revolution.
[0039] In a particular embodiment, the two mirrors 25 extend longitudinally over a distance greater than half the distance separating the two foci F1 and F2. By longitudinal direction is meant a direction parallel to the direction followed by the major axis of the ellipsoid of revolution 29.
[0040] The measuring device 19 further comprises a light emission module 31 along a main emission axis 33 passing through the first focus F1, and a light collection module 35 along a main collection axis 37 passing through the first focus F1.
[0041] In a particular embodiment, the light emitting module 31 and the light collecting module 35 are positioned at a distance from the first focus F1 less than a quarter of the minor axis of the ellipsoid of revolution 29 so as to maximize the quantity of light collected in the light collecting module 35.
[0042] Advantageously, the angle A between the main light emission axis 33 of the light emission module 31 and the major axis of the ellipsoid of revolution 29 is equal to the angle B between the main collection axis 37 of the collection module 35 and the major axis of the ellipsoid of revolution 29, the main emission axis 33, the main collection axis 37 and the major axis being included in the same plane.
[0043] The measuring device 19 is configured to be positioned so that the second focus F2 of the ellipsoid of revolution 29 is positioned at the surface 23 of the object to be measured 21. In particular, the measuring device 19 comprises a free space 39 allowing the approach of an object to be measured 21 at the level of the second focus F2.
[0044] In one embodiment, the measuring device 19 comprises a structure 41 configured to support the two mirrors 25, as well as the light emission module 31 and the light collection module 35 in a manner integral with each other.
[0045] Optionally, the measuring device 19 comprises a motor and a rotation axis (not shown) connected to the structure and configured to tilt the major axis and thus follow the curvature of the object to be measured 21.
[0046] The light emitting module 31 comprises a light source 43, for example a light emitting diode or preferably a coherent light source such as a laser.
[0047] This configuration with two foci F1 and F2 makes it possible, due to the mathematical properties of an ellipsoid of revolution 29, to guarantee that all the light rays passing through the first focus F1 will pass through the second focus F2, and vice versa. Thus, depending on the dimensions of the ellipsoid of revolution 29, the focusing is no longer limited to the position of the waist 15 but is available at the second focus F2, making it possible to overcome a small distance between the light-emitting module 31 and the object to be measured 21. In other words, a first waist is available at the first focus F1, said first waist being imaged in a second waist at the second focus F2, in turn imaged in a third waist at the first focus F1. Hot or moving objects are then more easily measurable. The ellipsoid of revolution 29 also makes it possible to partially overcome the angle between the major axis and the surface of the object to be measured.Indeed, even if the surface is inclined, a light ray from the second focus will pass through the first focus and can be collected by the light collection module 35.
[0048] In one mode of use of the measuring device 19, light is emitted by the light emitting module 31, this light being mainly directed towards the first focus FL. This light is then reflected on a mirror 25 towards the second focus F2. The light interacts with the object to be measured 21 at the second focus F2 and is then reflected or diffused towards a mirror 25, then reflected again towards the first focus FL. The collection module 35 then makes it possible to collect a large part of the light passing through the first focus FL.
[0049] The measuring device 19 is for example integrated into an interferometer or a profilometer.
[0050] Thus, in a particular embodiment, an interferometer comprises a reference optical arm and a measuring optical arm comprising the measuring device 19. A path difference between the reference optical arm and the measuring optical arm can thus be measured in order to measure a distance at which the object to be measured 21 is located, or an angle of its surface, or even in order to control a movement. In particular, the collection module 35 sends, for example, light towards a screen 45, just like the reference optical arm, thus forming interferences which can then be studied to finalize the measurement.
[0051] In another embodiment, a profilometer comprises a single measuring arm comprising the measuring device 19 and a detector 47 connected to the light collection module 35. The time taken by the light between its emission and its detection by the detector 47 can then be studied to determine the distance at which the surface 23 is located, and therefore to determine a profile of the surface 23.
[0052] In one embodiment, the light emission module 31 comprises an optical fiber 48 guiding the light emitted by the light source 43, for example a laser, towards an end of the optical fiber 48 emerging close to the first focus F1. The end of the optical fiber is for example similar to the end 1 shown in [Fig.l], the waist 15 of which is preferentially positioned at the level of the first focus F1.
[0053] The optical fiber 48 of the emission module 31 is for example a polarization-maintaining optical fiber, which allows birefringence in the optical fiber and the manipulation of two orthogonal light emission modes.
[0054] The optical fiber 48 of the transmission module 31 is for example single-mode, making it particularly suitable for the formation of interference, in particular in an interferometer, and comprises a core with a diameter of between 5 and 100 microns.
[0055] In one embodiment, the light collection module 35 comprises an optical fiber 49 guiding the collected light, for example towards a detector 47 or a screen 45.
[0056] The optical fiber 49 of the collection module 35 is for example a polarization-maintaining optical fiber.
[0057] The optical fiber 49 of the collection module 35 is for example single-mode or multi-mode, and comprises a core with a diameter of between 100 and 1000 microns in order to be able to collect a maximum of light. Optionally, the optical fiber 49 of the collection module 35 comprises a thermally expanded core so as to optimize the coupling between the optical fiber and the free space in which the light evolves between the emission module 31 and the collection module 35, the free space comprising air.
[0058] The end of the optical fiber 49 of the collection module 35 is for example similar to the end 1 shown in [Fig.l], except that it is used to collect light rather than to emit it.
[0059] In a particular embodiment, the measuring device 19 comprises a flat glass slide 51 with parallel faces configured to be positioned on the surface 23 of the object to be measured 21.
[0060] [Fig. 3] schematically shows a flat glass slide 51 configured to be positioned on the surface 23 of the object to be measured 21. The slide 51 comprises a first surface 53 comprising an anti-reflective coating and a second surface 55 intended to be in contact with the object to be measured 21, the second surface 55 comprising a mirror treatment. The glass slide 51 makes it possible to measure the angle C between the surface 23 of the object to be measured 21 and the direction of the major axis. For this, the measurement of a path difference induced by the light passing through the glass slide 51 is necessary, this measurement of angle C only working within the framework of an interferometer. In this configuration, the object to be measured 21 is positioned so that the second focus F2 is positioned in the glass slide 51.
[0061] [Fig. 4] schematically shows a second embodiment of the measuring device 19 identical to the first embodiment, and in which the light collection module 35 further comprises an optical fiber 49 and a collection lens 57 configured to focus a light flux received from the object to be measured 21 into the optical fiber 49. This collection lens 57 makes it possible to increase the quantity of light collected.
[0062] [Fig. 5] schematically shows a third embodiment similar to the first and second embodiments, the measuring device 19 further comprising two plane mirrors 59 parallel to the major axis and orthogonal to the plane comprising the main emission axis 33, the main collection axis 37 and the major axis.
[0063] The plane mirrors 59 are respectively positioned at equal distance between the first focus F1 and the light emission module 31 on the one hand, and the first focus F1 and the light collection module 35 on the other hand.
[0064] The plane mirrors 59 make it possible to create an image of the focus F1 as close as possible to the emission 31 and collection 35 modules, and thus to maximize the light collected in the light collection module 35.
[0065] Generally speaking, the dimensions of the semi-major axis a and the semi-minor axes b and c influence the performance and robustness of the measuring device in the face of a change in distance between the measuring device and the object to be measured, or in the face of a change in angle between the surface 23 and the major axis. For example, an ellipsoid of revolution with a semi-major axis a = 15 mm and a semi-minor axis b = c = 7 mm is more sensitive to a change in distance than an ellipsoid of revolution with a semi-major axis a = 15 mm and a semi-minor axis b = c = 5 mm, which is more sensitive to a change in angle.
Claims
Claims
1. Measuring device (19) characterized in that it comprises two coaxial mirrors (25) each comprising a reflecting surface (27), the reflecting surfaces of the two mirrors being positioned opposite each other and each forming a portion of the same ellipsoid of revolution (29), the ellipsoid of revolution (29) being defined by a major axis and two equal minor axes and comprising a first and a second focus (F1, F2), the two mirrors (25) extending longitudinally between the first focus (F1) and the second focus (F2), the measuring device (19) further comprising a light emission module (31) along a main emission axis (33) passing through the first focus (F1), and a light collection module (35) along a main collection axis (37) passing through the first focus (F1),the measuring device (19) being configured to be positioned so that the second focus (F2) of the ellipsoid of revolution (29) is positioned on the surface of an object to be measured (21), the light emission module (31) comprising a laser light source (43).,
2. Device according to claim 1, in which the two mirrors (25) extend longitudinally over a distance greater than half the distance separating the two foci (F1, F2).
3. Device according to one of claims 1 and 2, further comprising a flat glass slide (51) with parallel faces configured to be positioned on the surface (23) of the object to be measured (21).
4. A device according to any one of claims 1 to 3, wherein the light collection module (35) comprises a collection lens (57) and an optical fiber (49), the collection lens (57) being configured to focus a light flux into the optical fiber (49).
5. Device according to any one of claims 1 to 4, in which the light emitting module (31) and the collecting module (35) are positioned at a distance from the first focus (Fl) less than a quarter of the minor axis of the ellipsoid of revolution.
6. A device according to any one of claims 1 to 5, wherein the angle (A) between the main light emission axis (33) of the light emission module (31) and the major axis of the ellipsoid of revolution (29) is equal to the angle (B) between the main collection axis (37) of the collection module (35) and the major axis of the ellipsoid of revolution (29). revolution (29), the main emission axis (33), the main collection axis (37) and the major axis being included in the same plane.
7. A measuring device according to claim 6, further comprising two plane mirrors (59) parallel to the major axis and orthogonal to the plane comprising the main emission axis (33), the main collection axis (37) and the major axis, the plane mirrors (59) being respectively positioned at equal distance between the first focus (F1) and the light emission module (31) on the one hand, and the first focus (F1) and the light collection module (35) on the other hand.
8. Interferometer comprising a reference optical arm and a measuring optical arm comprising the measuring device (19) according to any one of claims 1 to 7.
9. Profilometer comprising a measuring device (19) according to any one of claims 1 to 7 and a detector (47) connected to the light collection module (35).