Method for measuring the surface of an optical lens

Abstract

In a method for measuring an optical lens surface, a measuring beam (26, 27, 28) is generated using a light source (21) having a certain size, collimated via an optical arrangement (23) and detected by an optical detector (25) after reflection at the lens surface to be measured. Between the light source (21) and the optical detector (25), an aperture (24) is used to limit the measuring beam (26, 27, 28), which acts as a field stop causing vignetting. The field stop is blurred and imaged as a first light spot (26a) on the optical detector (25) by the measurement (beam 26, 27, 28) after reflection at a first lens surface. At least one second light spot (27a) obtained by reflection of the measuring beam (26, 27, 28) at a second lens surface of the optical lens arrangement (10) is also detected simultaneously by the optical detector (25). From the intensity distribution of both light spots (26a, 27a), the angle of each lens surface relative to the optical axis of the measurement beam (26, 27, 28) can be determined simultaneously for both lens surfaces, thereby providing a method for measuring lens surfaces of an optical lens system that allows for rapid measurement of the lens surfaces without the need for complex optical setups.

Description

Technical Field

[0001] The present invention relates to a method for measuring the surface of an optical lens, particularly a method for performing centering measurement of an aspherical lens. In this method, the reflection of the lens surface is measured using an optical measurement device. In the optical measurement device, an aperture for restricting optical measurement radiation is used, and the radiation is imaged as a blurred light spot on the optical detector of the measurement device.

[0002] During the manufacture of an aspherical lens, deviations from the desired aspherical shape may occur due to manufacturing errors or manufacturing tolerances, and these must be identified for quality assurance reasons. This can be done by non-contact centering measurement capable of detecting the vertex offset and axis tilt of the aspherical lens. In the centering measurement, first, the position of the curvature center (vertex) of the spherical portion of the aspherical lens surface is determined, and subsequently, measurement is performed in the aspherical portion, i.e., the edge region outside the vertex.

Background Art

[0003] Patent Document 1 describes a method for determining the position of the symmetry axis of an aspherical lens surface with respect to a reference axis. In this method, first, the position of the curvature center of the spherical portion of the lens surface is determined, and subsequently, to obtain the position of the symmetry axis of the aspherical lens surface with respect to the rotation axis, the wobbling motion of the aspherical portion is measured by rotating the lens around the rotation axis. This measurement is performed through reflection on the lens surface to be measured using an autocollimator.

[0004] Patent Document 2 provides a method and apparatus for non-contact measurement of angles or changes in angles in an object, which can be used in particular for measuring aspherical lens or mirror surfaces. In this method, an optical measurement beam is generated using a finite-sized light source (extended light source), the optical measurement beam illuminates through an aperture that functions as a field aperture, and after reflection from the surface of the object to be measured, it is detected using an optical detector. Here, the illuminated aperture is blurred and imaged as a point of light on the optical detector via the optical system. By determining the position of the aperture image relative to a reference position, the angle between the measurement surface and the optical axis at the intersection of the measurement surface and the optical axis of the measurement beam can be determined.

[0005] Patent Document 3 provides a known method for measuring an optical lens device based on back reflections from different lens surfaces. This method uses a relatively complex imaging optical system to generate different image planes at the estimated positions of the center of curvature of the lens surface.

[0006] Patent Document 4 describes a method for measuring optical lenses using an autocollimation telescope, in which each lens surface is measured sequentially by focusing on the corresponding lens surface. Patent Document 5 provides a further known method for measuring optical lens surfaces, in which a separate imaging optical system is used for each lens surface. In this method, each lens surface is measured only from the side to which the lens is pointed. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] European Patent No. 1918687 [Patent Document 2] European Patent No. 1636542 [Patent Document 3] European Patent No. 3037800 [Patent Document 4] International Publication No. 2014 / 114444 [Patent Document 5] U.S. Patent No. 7,286,212 [Overview of the project] [Problems that the invention aims to solve]

[0008] The object of the present invention is to provide a method for measuring the optical lens surfaces of an optical lens device that enables rapid measurement of at least two lens surfaces of the optical lens device without using a complex imaging optical system. [Means for solving the problem]

[0009] The above problem is solved by the method described in claim 1. Advantageous forms of this method are the subject matter of the dependent claims or may become apparent from the following description and examples of embodiments.

[0010] In the proposed method, an optical measurement beam is generated using a finite-sized light source, collimated through an optical device, directed onto a first lens surface of the object to be measured using an optical lens device, reflected off the first lens surface of the object to be measured, and then detected using at least one spatially resolved optical detector. In this method, an aperture is used between the light source and the optical detector to limit the measurement beam. The aperture acts as a field stopper that causes vignetting, and the measurement beam is blurred and imaged on the optical detector as a point of light (hereinafter referred to as the first point of light because it is reflected off the first lens surface of the object to be measured), which is then detected using the optical detector.

[0011] Here, the light source with size is configured to produce uniform surface brightness by using one or more LEDs, for example, with a diffuser plate placed in front, or a capacitor placed in front, or a combination of a diffuser plate and a capacitor placed in front. The spatially resolved optical detector can be formed, for example, by a CCD or CMOS area sensor. Of course, other spatially resolved optical detectors may also be used. It is also possible to arrange multiple spatially resolved detectors side by side.

[0012] The aperture that restricts the optical measurement beam is preferably formed by a diaphragm having a fixed or adjustable aperture. This aperture can also be formed by a suitable lens mount of the lens of the optical device. The aperture is positioned in a suitable location in the beam path of the measurement beam, preferably between or within an optical device for collimation, preferably an autocollimation optical system, and an optical lens device having a measurement lens surface, in order to obtain a vinetting effect that produces a blurred light spot on the detector. An optical lens device may refer to a single lens, for example, an aspherical lens having one aspherical surface and one spherical surface, i.e., an aspherical lens having one aspherical surface and one spherical surface, or an aspherical lens having two aspherical lens surfaces, or a configuration of multiple lenses spaced apart from each other.

[0013] In the proposed method, an optical detector is used to detect at least one second light point simultaneously with the detection of the first light point, which is obtained by the reflection of the measurement beam off a further lens surface of the optical lens device (hereinafter referred to as the second lens surface). This second light point is also produced when the aperture that limits the measurement beam acts as a field stopper causing vignetting, and this aperture (after reflection off the second lens surface) is imaged on the optical detector. Subsequently, the intensity distribution of both light points detected simultaneously using the optical detector is evaluated in order to determine the angle between the first lens surface and the optical axis of the measurement beam at the intersection of the first lens surface and the optical axis of the measurement beam, and the angle between the second lens surface and the optical axis of the measurement beam at the intersection of the second lens surface and the optical axis of the measurement beam. This angle can be determined, for example, by the same method as described in Patent Document 2 above. Furthermore, by displacing each light point relative to a known reference position (zero position) on the optical detector, the respective angles at the measurement position (the intersection of the optical axis of the measurement beam and the lens surface) can be determined. The vinetting effect of the aperture, which limits the measurement beam, allows for very precise determination of the position of the light point through the intensity distribution generated by the light point, which has a V-shape along a line passing through the center of the light point.

[0014] In the proposed method, when using a measuring device equipped with a field diaphragm that causes vignetting, it has been found that the light spot generated by a further second lens surface, which the measurement beam strikes after passing through the first lens surface, can also be detected and evaluated in conjunction with the first light spot on the detector. The second lens surface may refer to, for example, the rear lens surface of the lens or (in the case of a cemented lens) the inner lens surface. Both light spots on the detector must be sufficiently distinguishable or separable from each other in order to determine the angle. If this is not the case during measurement, the lens device or lens is displaced perpendicular to the optical axis of the measurement beam until both light spots are sufficiently distinguishable or separable. Here, the distance of the displacement is preferably determined and taken into consideration during evaluation. Thus, the proposed method allows for the simultaneous measurement of at least two lens surfaces with respect to the angle of the measurement beam with respect to the optical axis at each measurement position, without the use of additional or complex optical devices. Therefore, when measuring an aspherical surface, the precise location of the aspherical surface, particularly its inclination and lateral offset, can be determined by measuring the aspherical portion with at least one rotational measurement of 180 degrees (or correspondingly, multiple measurements at different positions on half of the aspherical surface).

[0015] The proposed method will be described in more detail below, based on examples of embodiments with reference to the drawings. [Brief explanation of the drawing]

[0016] [Figure 1] This is a schematic diagram of an exemplary optical configuration that can be used when implementing the proposed method. [Figure 2] This figure shows an example of the use of the above optical configuration when measuring an aspherical surface by the proposed method. [Figure 3] This is a diagram illustrating a further example of implementing the proposed method using such a configuration. [Figure 4] This is a diagram illustrating an example of measuring an aspherical surface using the proposed method. [Figure 5] This figure shows a further example of measuring an aspherical surface using the proposed method. [Figure 6a] FIG. is an example of measuring both-sided aspherical surfaces by the proposed method. [Figure 6b] FIG. is an example of measuring both-sided aspherical surfaces by the proposed method. DETAILED DESCRIPTION OF THE INVENTION

[0017] In the proposed method, by at least two lens surfaces that are at least partially reflective and can be configured as spherical or aspherical surfaces, a blurred exit aperture is imaged on the detector as an image of the restricted aperture or aperture stop of the optically effective system used in the method. To ensure this kind of effect of the aperture stop as the field stop, the aperture stop is positioned at a suitable position within the beam path of the measurement beam. Here, the emitted measurement beam bundle or object beam bundle is not stationary, for example, as in the case of a conventional autocollimator with a sight line. Rather, a light source (object illumination surface) having a size functions as an object preferably having at least the same dimensions or the same size as the detection surface of the detector, so that each object illumination point corresponds to a corresponding conjugate image point position, which corresponds to the inclination α of the corresponding principal beam passing through the center of the aperture stop. This angle of the principal beam is determined and evaluated during detection. It is particularly preferable that the object illumination surface is selected to be larger than the detection surface. Due to the principle of blurred imaging of the exit pupil of the entire system on the detector, it becomes possible to longitudinally evaluate the various blurred exit apertures on the detector from different lens surfaces (usually having different radii). Here, it is only important that the beams on the lens surfaces have different (separable) surface inclination angles. Therefore, it is also possible to detect three or more surfaces. To optimize the measurement, it is advantageous to adjust the beam divergence so that the light spots on the detector are sufficiently separated from each other by means of appropriate auxiliary lenses or by appropriate adjustment of an optical device such as a lens. Therefore, here, the light spots are adjusted so that they can be separated from each other without overlapping through an optical element and, in some cases, further through adjustment of the aperture size.

[0018] First, FIG. 1 schematically shows an exemplary configuration of a measurement system that can be used in the proposed method. This figure shows a (finite-sized) light source (diffuse light source) 21 having a size also called a planar radiator in this patent application. In this example, this is formed by irradiating a diffuser disk 21b from a radiation source 21a, such as an LED. The measurement beam bundle 28 emitted from the light source 21 having this size is irradiated onto an optical system via a beam splitter 22, deflected by 90 degrees, and illuminates through an aperture stop 24. In the lens 10 of the measurement object, the beam bundle is reflected, passes through the beam splitter 22 again via an objective lens 23, and is imaged on a photosensitive detector 25. Here, the reflection occurs not only on the lens surface facing the measurement system of the lens 10 but also on the lens surface not facing the measurement system. If the lens surface is not exactly at a 90-degree angle to this axis at the intersection with the optical axis 29 of this measurement system, light spots deviated from the intersection of the detector 25 and the optical axis 29 are imaged on the detector 25 for each of the lens surfaces. Here, as described in more detail by, for example, Patent Document 2, the light spots are caused by the vignetting effect of the aperture stop 24 and enable accurate measurement of the angular deviation from a 90-degree angle.

[0019] Furthermore, FIG. 2 shows a schematic diagram of the measurement of a spherical lens 10 in this case using the measuring device of FIG. 1, also referred to as sensor 20 in this example and the following examples. In front of this sensor 20, auxiliary lenses 50 for beam formation are arranged in these examples. The lens 10 to be measured is preferably installed on a lens receiver 30, such as a ring edge or a three-point support, on a turntable 40 for measurement, and the turntable 40 is rotatable around a rotation axis 41 (rotation C). Here, the lens receiver 30, for example, installs a polished sphere with known accuracy on the lens receiver 30 and uses this sphere to adjust the device, which also enables accurate reference of the sensor 20 to the lens to be measured. Therefore, a reference axis can be determined using the sensor 20 or a similar suitable instrument, and the lens support can be referenced as the reference plane of the lens to be measured.

[0020] Figure 3 shows a detailed diagram of the measurement of a spherical lens 10 using a sensor 20 according to the proposed method. In this figure, the sensor 20 is schematically shown to include a light source 21 with size, a detector 25, a beam splitter 22, and an objective lens 23 and an aperture diaphragm 24. An auxiliary lens 50 can also be seen in this figure. The spherical lens 10 to be measured is placed on a lens support 30 on a rotating table. The spherical lens 10 comprises a vertex 11, a peripheral region 12, a rear vertex 13, a rear peripheral region 14, and a cylindrical edge 15. In this example, the center of curvature 16 of the front lens surface and the center of curvature 17 of the rear lens surface are on the optical axis 18 of the lens, but it is shown that the optical axis 18 of the lens does not coincide with the rotation axis 41 of the rotating table. Figure 3 shows two main beams 26 and 27. These main beams 26 and 27, after being reflected from both lens surfaces, appear as blurred light spots on the detector 25 through the aperture diaphragm 24 due to vinening. In this case, the main beam 26 that causes vinening due to reflection from the front lens surface becomes light spot 26a on the detector, and the main beam 27 that causes vinening due to reflection from the rear lens surface becomes a blurred light spot 27a on the detector. The upper left portion of Figure 3 exemplifies the field of view or detection surface of the detector 25, which has both light spots 26a and 27b that are clearly separated laterally, allowing both to be detected and evaluated simultaneously. This method allows the inclination of the lens surface at the intersection of each lens surface and the optical axis of the measurement beam to be determined. As the turntable rotates, both light spots trace a circular or elliptical shape with corresponding diameters, which correspond to the actual (front surface 1) or virtual (rear surface 2) surface inclination angle. This circle is shown in the upper left portion of Figure 3, within the field of view of detector 25. Here, the meridional and sagittal beam paths can be evaluated separately. The actual surface inclination angle of the rear surface can be calculated through the optical design program using the measured optical effects (radius, refractive index, thickness) of the first (front) surface. The angular deviation can also be interpreted as the lateral offset of the meridional and sagittal curvature centers relative to the axis of rotation, respectively.

[0021] In non-paraxial measurements where the measurement beam strikes the first lens surface at an incident angle ε (vertical = angle relative to the incident normal), the nonlinear deviation caused by the refraction of the beam at the first lens surface becomes significant, and in some cases, this must be taken into account when calculating the surface inclination angle of the second lens surface. In the case of centering measurements of individual actual surface inclinations, the calculation of the inclination angle of the rear surface is always affected by the inclination of the lens surface in front of it and is accurately calculated by working backward from the beam path. In the nonlinear changes when the beam path is applied non-paraxially, even an incident angle of 15 degrees can result in an error that leads to a 5% deviation. At larger incident angles of 35 to 45 degrees, this error can range from 200 to 300 percent.

[0022] Here, we will idealize this application and roughly examine and establish the relationship. 1. Lens axis or aspherical axis = rotation axis 2. The reflective (second) surface immediately behind the first surface. 3. Reflected beam at the same position as the incident beam. The change in the angle ε' of the refracted beam is obtained by the refractive index n and the incident angle ε itself.

number

[0023] This yields a correction factor K = n × cosε / cosε', which is used to determine the actual surface inclination angle of the second surface. This correction factor can be provided, for example, by a LUT (lookup table) depending on the angle of incidence.

[0024] As shown in the example of measuring a one-sided aspherical surface in Figure 4, this method is similarly used for measuring aspherical surfaces. An aspherical surface has not one but multiple centers of curvature, all of which lie on an axis passing through a vertex (point of rotational symmetry). An aspherical surface has an aspherical axis. This axis can be tilted with respect to a reference axis, and the vertex or point of rotational symmetry of this surface can be offset laterally from the reference axis. Furthermore, Figure 4 shows an example of a one-sided aspherical surface 10 (one side is aspherical, the other side is spherical) having a vertex 11 or central region on the front of the aspherical surface and a peripheral region 12 on the front of the aspherical surface. The sensor 20 is simply shown in this figure with only the detector 25 and auxiliary lens 50. Both measurement beams reflected on the front and rear sides of the aspherical surface 10, i.e., the vinetated main beam 26 and the vinetated main beam 27, are similarly shown illustratively. The aspherical surface 10 has an apparent center of curvature 19 at its periphery and a center of curvature 16 at its apex. The aspherical axis 18 is also shown in the figure. Here again, the reflection of the measurement beam from both lens surfaces of the aspherical surface creates two light points on the detector 25, thereby allowing measurement of both lens surfaces not only in the central region but also at the periphery. This is again shown in Figure 5 using the same reference numerals, based on an example in which two sensors 20a and 20b are used so that measurements can be performed simultaneously in the center and periphery region of the aspherical surface 10.

[0025] In the case of bilateral aspheric surfaces (where the rear surface also has an aspheric surface), measuring only the center is insufficient to determine the aspheric axis with sufficient accuracy. Here, measurements at different positions are necessary, as schematically shown in Figures 6a and 6b, which involve additional measurements of the rear surface at the periphery using a third sensor 20c. Furthermore, according to the proposed method, it is also preferable to simultaneously measure both the front and rear surfaces at the periphery using only one sensor, for example, sensor 20b.

[0026] The internal centering error of an aspherical lens can be determined, for example, by the following steps: a) For example, using a sensor 20 or a similar suitable instrument that can measure the center of curvature of the lens surface without changing the auxiliary lens, without displacing the instrument along the optical axis, or without changing the focal point, the support portion (or lens receiving portion 30) is referenced as the reference plane of the lens using a sphere with a preferred approximate average radius of both lens surfaces. b) Measure the position of the center of curvature of the spherical portion of the aspherical lens surface to be measured. c) Measure the aspherical portion outside the vertex (simultaneously for both lens surfaces). d) Determine the inherent internal centering error by calculating together the measured values ​​of both using known design data (radius, thickness, refractive index, etc.).

[0027] The configuration of the optical device for measuring the lens surface may differ from the example in Figure 1, for example, by replacing the detector and light source, using a different beam splitter, positioning the vignetting diaphragm in a different location, or other modifications, as long as the vinetting effect of the field diaphragm or aperture diaphragm that produces blurred light spots on the detector is ensured. [Explanation of Symbols]

[0028] 10 lenses 11. The vertex or central region of the front of the lens 12. Edge region of the front of the lens 13. The vertex or central region of the rear surface of the lens 14. Rear edge region of the lens 15. The cylindrical edge of the lens 16. Center of curvature of the first surface 17. Center of curvature of the second surface 18. Optical axis of the lens 19. Apparent curvature center of an aspherical surface at its periphery. 20 sensors 20a First sensor 20b Second sensor 20c Third Sensor 21 Light sources of different sizes 21a Radiation source 21b Diffuse optical disc 22 Beam Splitter 23 Objective lens 24 Aperture diaphragm 25 Photosensitive detectors 26 Main beam causing post-reflection vignetting on the front lens surface 26a Light spot on the detector 27 Main beam subjected to post-reflection vignetting at the rear lens surface 27a Light spot on the detector 28 Measurement beam flux 29 Optical axis 30 Lens receiving section 40 Turntables 41 Rotation axis 50 auxiliary lenses

Claims

1. A method for measuring the surface of an optical lens, An optical measurement beam (26, 27, 28) is generated using a light source (21) as a planar emitter, collimated via an optical device (23), directed towards the first lens surface of the object to be measured in the optical lens device (10), reflected off the first lens surface of the object to be measured, and then detected using at least one spatially resolved optical detector (25). An aperture (24) is used between the light source (21) and the spatially resolved optical detector (25) to limit the optical measurement beams (26, 27, 28). The aperture (24) acts as a field stopper that causes vignetting, and through the aperture (24), the optical measurement beams (26, 27, 28) are blurred and imaged as a first light point (26a) on the spatially resolved optical detector (25), which is then detected by the spatially resolved optical detector (25). From the intensity distribution of the first light point (26a) on the spatially resolved optical detector (25) and the displacement of the first light point (26a) with respect to the reference position (zero position), the angle between the first lens surface of the object to be measured and the optical axis of the optical measurement beam at the intersection of the first lens surface of the object to be measured and the optical axis of the optical measurement beam is determined. Using the spatially resolved optical detector (25), at the same time as the detection of the first light point (26a), at least one second light point (27a) obtained by the reflection of the optical measurement beam (26, 27, 28) on the second lens surface of the optical lens device (10) to be measured is also detected. A method characterized in that the angle between the second lens surface of the object to be measured and the optical axis of the optical measurement beam (26, 27, 28) at the intersection of the second lens surface of the object to be measured and the optical axis of the optical measurement beam (26, 27, 28) is determined from the intensity distribution of the second light point (27a) on the spatially resolved optical detector (25) and the displacement of the second light point (27a) with respect to a reference position (zero position).

2. The method according to claim 1, characterized in that, if the first light point (26a) and the second light point (27a) on the spatially resolved optical detector (25) are not sufficiently distinguishable to determine the angle, the optical lens device (10) is displaced perpendicular to the optical axis until the light points (26a, 27a) become sufficiently distinguishable.

3. The method according to claim 1 or 2, characterized in that a diaphragm having a fixed or adjustable aperture is used as the aperture (24) that limits the optical measurement beams (26, 27, 28).

4. The method according to any one of claims 1 to 3, characterized in that an autocollimation optical system is used as the optical device (23).

5. The method according to any one of claims 1 to 4, characterized in that the light source (21) is provided by an illumination surface having at least the size of the detection surface of the spatially resolved optical detector (25).

6. A method for performing centering measurement in an aspherical lens as an optical lens device (10), wherein the aspherical lens comprises a first aspherical lens surface having a central spherical portion and an aspherical portion connected thereto, The method according to any one of claims 1 to 5, wherein first, the position of the center of curvature of the spherical portion of the first lens surface of the aspherical lens is determined, and then, at one or more positions of the aspherical portion, the angle between the first lens surface and the optical axis of the optical measurement beam (26, 27, 28) and the angle between the second lens surface of the aspherical lens and the optical axis of the optical measurement beam (26, 27, 28) are measured simultaneously.

7. The method according to any one of claims 1 to 6, characterized in that the optical lens device (10) is placed on a rotating table (40) for measurement and rotated around a rotation axis (41), and the angle between the lens surface to be measured and the optical axis of the optical measurement beam (26, 27, 28) is determined at a plurality of positions on a circular line or a portion of a circular line around the rotation axis (41).

8. The method according to claim 7, characterized in that the optical lens device (10) is rotated at least 180 degrees around the rotation axis (41) for measurement.

9. Multiple sensors (20a, 20b, 20c) are used for measurement, and for each of the sensors (20a, 20b, 20c), an optical measurement beam is generated using a light source as a planar radiator, collimated through an optical device, directed onto the lens surface of the object to be measured in an optical lens device, reflected off the lens surface of the object to be measured, and then detected using at least one spatially resolved optical detector, and an aperture is used between the light source and the spatially resolved optical detector to limit the optical measurement beam, and the aperture acts as a field stopper that causes vignetting, so that the optical measurement beam is blurred and imaged as a point of light on the spatially resolved optical detector through the aperture. The method according to any one of claims 1 to 6, characterized in that, using each of the sensors (20a, 20b, 20c), the angle between the lens surface to be measured and the optical axis of each of the optical measurement beams at another position on the lens surface to be measured is determined using the method according to claim 1.

10. The method according to claim 9, characterized in that one of the sensors (20a, 20b, 20c) is used to determine an angle at a position within the vertex region of the lens surface to be measured, and one or more other sensors (20a, 20b, 20c) are used to determine an angle at one or more positions within the peripheral region of the lens surface to be measured.

11. The method according to any one of claims 1 to 10, characterized in that when the optical measurement beam (26, 27, 28) is incident non-perpendicularly on the first lens surface of the object to be measured, the angle between the second lens surface of the object to be measured and the optical axis of the optical measurement beam (26, 27, 28) at the intersection of the second lens surface of the object to be measured and the optical axis of the optical measurement beam is determined using a correction coefficient K that takes into account the refraction of the optical measurement beam (26, 27, 28) on the first lens surface of the object to be measured.

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