Method for assembling or positioning optical semi-finished optical semi-finished optical semi-finished

Abstract

The invention relates to a method for assembling or positioning an optical semi-finished product (3) on a production mandrel (2) during the production of a spherical or aspherical lens, in which method the position of the semi-finished product (3) on the production mandrel (2) is determined by means of an optical method and / or the calibration of the semi-finished product (3) on the production mandrel (2) is carried out by means of an optical method, in the method, a transparent optical auxiliary element (5) having a polished upper surface and a lower surface adapted to the second surface of the semi-finished product (3) is applied to the second surface of the semi-finished product (3) with an intermediate medium (7) for adjusting the refractive index and is thus irradiated with at least one light beam (6), the auxiliary element (5) is arranged such that the light beam (6) is partially reflected on the upper surface of the auxiliary element (5) and on the first surface of the semi-finished product (3), and a beam component reflected at least by the first surface of the semi-finished product (3) is detected by means of at least one spatially resolved optical detector.

Description

Technical Field

[0001] The present invention relates to a method for assembling or fixing or determining the position or orientation of an optical semi-finished product on a manufacturing mandrel when manufacturing a spherical or aspherical lens. In this method, the semi-finished product has a first spherical or aspherical surface with one side being ground and polished and a second surface opposite to the first surface, which second surface also needs to be ground and polished to make a lens, and the semi-finished product is placed on the manufacturing mandrel with the first surface and glued (kitten). Background Art

[0002] The use of powerful, high-precision and at the same time lightweight optomechanical imaging systems is becoming increasingly important in industry. The use of aspherical surfaces is playing an increasingly important role, since the number of lenses can be reduced and the size and weight can be significantly minimized.

[0003] When manufacturing aspheres, there is a risk of eccentricity as vertex displacement and tilting (vertex offset and axis tilting), which are completely independent of each other. Therefore, the semi-finished product of the asphere must comply with certain centering rules during the grinding and polishing process and be adapted accordingly to the positioning of the manufacturing spindle (manufacturing spindle) in order to avoid scrap during production. Then, it is no longer possible to carry out the subsequent centering process as is customary when manufacturing spherical surfaces.

[0004] In addition to surface form errors, there is also a need in industrial production to characterize and correct internal and external centering errors quickly and easily in order to perfectly assemble multiple lenses. These requirements lead to increased demands on measuring technology equipment and on-site quality inspection of samples under production conditions. When manufacturing aspheres, high scrap rates sometimes occur due to centering errors > 0.5'. It is currently not possible to accurately measure the internal centering errors of aspheric lenses. Interferometry measurements are also not suitable for centering measurements. Sensors based on point sensors are not suitable because there are too many degrees of freedom and therefore many errors. Measurements with point sensors are only possible with the help of a well-centered system.

[0005] Fitting the semi-finished asphere as accurately as possible onto the manufacturing mandrel is a challenge that must be overcome in order to produce an accurate asphere with a centering error of less than 30 arc seconds and a lateral offset L of less than 5 μm. Haptic devices can be used for this purpose, but they require high investments, limited accuracy and long measurement times for high position resolution. In addition, the optical components can be scratched by the haptic device. The centering dimensions themselves cannot be measured on both sides in one clamping. For this purpose, the asphere must be fixed and replaced or rotated in a special bracket. In particular, there are clamping errors that can be greater than 1 μm and thus tilt angle errors greater than one arc minute at small radii of less than 10 mm.

[0006] The centering process of spherical lenses is usually carried out with the aid of a clamping centering machine. The clamping is achieved by a precisely manufactured bell on a precisely oriented spindle. If the tangential angle at the lens edge is large enough, the centering of the lens is carried out by a self-centering process. If the centering process is very effective, the optical axis generated by the two centers of curvature is parallel to the cylinder axis and coincides with the cylinder axis after the centering process. If this is not the case, for example in the case of meniscus lenses or concentric lenses with large radii, the spindle centering method is generally used. The lens is then calibrated on the spindle and glued using an optical measuring instrument, such as an autocollimator.

[0007] In general, the reference for the orientation of a spherical-aspherical lens is based on mechanical surfaces such as edge cylinders. In most cases (mainly in the case of short edge cylinders) a spherical surface (base A) and an edge cylinder (base B) are used, as in Figure 1 The aspheric axis then has a slope and a lateral displacement L from the reference axis at the vertex of the sphere. This is defined in ISO 10110-6 and is also called "external centering error" because it refers to external dimensions and / or external surface references.

[0008] If the spherical-aspherical lens is shifted and tilted in such a way that the aspherical axis coincides with the reference axis (reference axis = aspherical axis) (see Figure 2 ), the centering error is reduced to only one aspect in the same way as a spherical lens, namely the lateral offset of the center of curvature C1 relative to the aspheric axis or the equivalent tilt angle σ. This is also called "internal centering error". Therefore, the internal centering error of the aspheric surface is the inherent offset of the center of curvature of the spherical surface relative to the aspheric axis of the second surface. This internal centering error is an error inherent in the lens.

[0009] exist Figure 3 The schematic flow of the manufacturing process of the double aspheric surface is shown in FIG. Here, first, the glass blank 1 is applied to the manufacturing mandrel 2 ( Figure 3 a). The glass blank 1 is ground and polished on the first aspherical surface ( Figure 3 b). The polishing process in the polishing machine is not shown here. In the next step, the first edge processing ( Figure 3 c). The semi-finished product 3 having the ground and polished first aspherical surface is glued back onto the mandrel 2 ( Figure 3 d), followed by grinding and polishing on the second aspheric surface ( Figure 3 e). The polishing process is again not shown. Finally, a final edge processing is also performed ( Figure 3 f).

[0010] When manufacturing double aspheric surfaces, Figure 3Grinding the first asphere in step b is relatively problem-free, since it is measured on the mandrel 2 and can therefore be quality-controlled. The decisive step occurs during the re-clamping or re-gluing after grinding and polishing the first asphere and subsequent edge processing ( Figure 3 d). Before grinding the second aspheric surface, precise orientation must be carried out on the mandrel 2. This is currently performed using a measuring probe. After clamping once, the second aspheric surface is ground and polished, and finally the edges are removed. If the aspheric surface 4 is then removed from the mandrel 2 for the final measurement, the aspheric surface can no longer be clamped again. This means that the aspheric surface cannot be corrected and therefore ends up as waste if it does not meet the specifications. Automatic re-correction is also not possible after grinding the second aspheric surface. Typically, due to insufficient or missing intermediate results of the centering error measurement when re-gluing from one lens surface to the other, centering errors of about 3-10' are obtained in the final product using this manufacturing technology.

[0011] Therefore, in the current state of the art, when producing precision aspheres with indeterminate cuts using conventional grinding and polishing techniques, a cut or milled glass block or a pre-pressed blank (so-called blank) is fixed on a mandrel and first processed in a grinding machine. For this purpose, in the pre-processing process, a spherical surface or, in the case of aspheres, a best fit sphere (BFS) is first ground using a pot tool equipped with diamonds or a forming tool with diamond particles. After the first surface has been ground, the edge cylinder is usually edge-centered using another processing spindle in the same machine.

[0012] The mandrel with the test sample is removed from the machine, the lens is released and the ground first surface is then fixed back on the mandrel in order to carry out the grinding process on the second surface. If required, the lens edge can be centered during the fixing process (preferably with the aid of hot wax), for example using a mechanical or optical micrometer. The processing is then carried out as on the first side and the lens edge is centered again with an additional excess dimension (approximately 0.2 to 0.02 mm). The aspheric surface is thus extended precisely to the cylinder edge.

[0013] The subsequent polishing process is performed on a CNC polishing machine. The side of the aspheric surface that is now to be processed, because it extends perfectly to the main axis, obtains an optimal aspheric surface according to the invention during polishing, with a perfectly centered aspheric axis in all areas of the aspheric surface, namely the center, the zone and the edge. Since in this centered aspheric surface, the path of the aspheric surface is precisely moved by the CNC controller and there is no eccentricity and eccentricity, the exact same footprint is expected at any position on the surface and the polishing process is perfectly performed. Therefore, there are no polishing errors due to different footprints and different dwell times, and therefore there is also a precisely rotationally symmetrical surface at the vertex of the lens.

[0014] In a subsequent step, the lens is now re-fixed so that the aspheric surface faces downwards. In addition, a protective lacquer is provided to protect the lens from damage. The main task now consists in that the lower surface, which has already been produced and, if necessary, provided with a protective lacquer, is optimally located on the spindle axis so that the lower aspheric surface axis is parallel to and coincides with the spindle axis and thus coincides with the processing axis. In the simplest case, for this alignment, the heated lens is pressed onto the annular cutout by means of hot wax glue applied to the heated spindle (approximately 60 degrees Celsius) and the edge cylinder is mechanically centered. However, large deviations are currently to be expected here due to the influences listed below:

[0015] · 1 to 20 micron surface runout of the mandrel (from high quality to standard)

[0016] · Circular runout of the mandrel from 2 to 50 microns (from high quality to standard)

[0017] Variation of 10 to 20 microns in the paint layer (first order analysis)

[0018] · 1-5 micron roundness of the cylinder

[0019] · Roughness Rq of 1-10 microns of the cylinder

[0020] Temperature difference at fixed time (20°-65°C)

[0021] Micrometers are usually not accurate enough

[0022] Therefore, when the semi-finished product is fixed on the mandrel, different influences are evident, which significantly affect the centering process and the centering accuracy and thus lead to internal centering errors when producing aspheres. Summary of the invention

[0023] The object of the present invention is to avoid or at least reduce internal centering errors during the production process of a spherical-aspherical lens or a two-sided aspherical lens.

[0024] This object is achieved by means of a method according to claim 1. Advantageous embodiments of the method are the subject matter of the dependent patent claims or can be inferred from the following description or exemplary embodiments.

[0025] The proposed method is used to assemble or fix an optical semi-finished product on a manufacturing mandrel when manufacturing a spherical or aspherical lens. The method can also be used to determine the position or orientation of an optical semi-finished product on a manufacturing mandrel when manufacturing a spherical or aspherical lens. In the proposed method, the optical semi-finished product already has a first spherical or aspherical surface surface that is ground and polished on one side and a second surface opposite to the first surface, which second surface must also be ground and polished to produce a lens. In the method, the semi-finished product is placed on the manufacturing mandrel with the first surface, preferably calibrated there, and then glued or cured. The method therefore involves the above-described Figure 3 d's mandrel. The method is characterized in that the alignment or position or orientation of the semi-finished product is checked or determined by means of a special optical method and / or the alignment (especially the above-mentioned centering process) is performed with the help of a special optical method. In the optical method, a transparent optical auxiliary element having a polished upper surface and a lower surface adapted to the second surface of the semi-finished product is applied to the second surface of the semi-finished product via a medium for adjusting the refractive index, especially immersion oil, as an intermediate layer. Therefore, the optical auxiliary element is irradiated with a light beam (or multiple light beams) so that the light beams are partially reflected on the upper surface of the auxiliary element and the first surface of the semi-finished product, respectively. At least the light beam component reflected by the first surface of the semi-finished product, preferably the two reflected light beam components, are detected here with the help of at least one position-resolved optical detector.

[0026] By this process, despite the unpolished second surface of the semi-finished product, it is possible to obtain the reflection of the measuring beam or light beam from the first surface of the semi-finished product and thus to perform calibration of the semi-finished product on the production mandrel before gluing based on the detected reflection. The production mandrel is preferably rotated during the measurement. Only by the placed auxiliary elements and the medium used here for adjusting the refractive index can the reflection of the first surface of the already manufactured spherical or aspherical surface be utilized. Alternatively, the measurement is also not used for calibration, but only for detecting the position or orientation of the semi-finished product, in particular the lower surface of the semi-finished product, so as to then correctly perform the processing of the second surface based on this information.

[0027] When the second surface of the semi-finished product is flat, it is preferred to use an auxiliary element that is configured as a plane-parallel plate or a concave or convex lens with a flat lower surface. When the second surface of the semi-finished product is convex or concave, it is preferred to use an auxiliary element with a concave or convex lower surface and a flat, concave or convex upper surface.

[0028] In the proposed method, the auxiliary element is preferably designed such that it completely or almost completely covers the second surface of the semifinished product. The measurement is preferably performed with the light beam or two light beams, in order to detect reflected light beam components both in the center of the semifinished product and at the edge in the method. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The proposed method is described in more detail below with reference to the accompanying drawings according to an embodiment. It is shown here:

[0030] Figure 1 : An exemplary illustration of the external centering error of a spherical-aspherical lens having a tilted aspherical axis and a lateral offset L at the vertex (i.e., apex) of the aspherical surface;

[0031] Figure 2 : An exemplary illustration of the internal centering error of a spherical-aspherical lens with the aspherical axis as a reference axis and the offset of the spherical curvature center;

[0032] Figure 3 : Schematic flow of the manufacturing process when manufacturing a double aspheric surface;

[0033] Figure 4 : A diagram of the determination of the orientation of an optical semi-finished product on a production mandrel by means of a plane-parallel plate as an optical auxiliary element according to an exemplary embodiment of the proposed method;

[0034] Figure 5 : Two exemplary illustrations of the use of auxiliary elements of different configurations in the proposed method depending on the shape of the semi-finished product; and

[0035] Figure 6 :exist Figure 5 Two exemplary illustrations of measuring a semi-finished product at two different positions in a configuration of . DETAILED DESCRIPTION

[0036] The proposed method is used in the manufacturing process of spherical or aspherical lenses, as already in combination with Figure 3 As exemplarily described in the description introduction.

[0037] Figure 4 An exemplary diagram shows the determination of the orientation of an optical semi-finished product 3 on a production mandrel 2 according to the configuration of the proposed method. In this example, the semi-finished product has a flat second surface. A plane-parallel plate is used as an optical auxiliary element 5 here. Figure 4 For this purpose, a semi-finished product 3 is shown in the present embodiment with a spherical first surface, to which a corresponding lacquer is applied. In the figure, only the production mandrel 2 is shown visually, on which the semi-finished product 3 is placed and to which it is to be glued (verkitten). Then, a plane-parallel plate is placed as an auxiliary element 5 in the present example on the unprocessed, in this case flat second surface, which plane-parallel plate has a polished upper side accordingly. Immersion oil (not shown in the figure) is present between the underside of the auxiliary element 5 and the second surface of the semi-finished product 3 for adjusting the refractive index.

[0038] For the illumination with the light beam, in this and other possible configurations of the method, preferably the so-called vignetted field stop technique (VFS or V-SPOT) is used, with which two reflections can be detected on the detector, namely the reflection from the upper surface of the auxiliary element 5 and the reflection from the first upper surface of the semi-finished product, without any change in the focus. With this technique, local, meridian slope errors in the region or at the edge of the aspheric surface can be detected precisely and together with the centering deviation of the vertex the aspheric surface axis and thus the internal centering error can be determined.

[0039] By combining this VFS technology with Figure 4 Together with the corresponding measuring device EP shown in FIG. 1 , the two reflections shown in the upper right of the figure are obtained, in which the beam course of the correspondingly extended measuring beam 6 is shown. The current position or orientation of the semi-finished product 3 is then determined from the position of these reflections.

[0040] An exemplary embodiment of fastening the semi-finished product 3 to the production mandrel 2 is briefly explained in the following example.

[0041] Example:

[0042] 1. The test sample is a semi-finished product, including:

[0043] -Spherical or aspherical surface with polished surface on one side

[0044] - Grind the back side flat;

[0045] 2. Apply immersion oil corresponding to the refractive index of the semi-finished product (1.4-1.6) to the back side of the semi-finished product;

[0046] 3. Placement of high-quality plane-parallel plates made of glass as auxiliary elements of corresponding dimensions;

[0047] 4. According to the DoE, the measuring device EP (ELWIMAT brand) is adjusted by the angle α so that one reflection each on the front side and the back side of the detector can be evaluated simultaneously;

[0048] 5. Calibrate the semi-finished product by properly positioning it on the mandrel (minimum centering circle);

[0049] 6. Fix the semi-finished product; fill the gap with adhesive if necessary;

[0050] 7. Allow the semi-finished product to harden or cool and check the result at room temperature;

[0051] 8. Remove the flat panel and clean all sides;

[0052] 9. Grinding and subsequent polishing of the semi-finished product on the second side (according to known manufacturing processes).

[0053] In case the second surface which has not yet been machined is curved, for example has a convex or concave shape, an auxiliary element 5 is used which has a corresponding complementary shape on the underside.

[0054] In order to allow the measuring beam emitted by the measuring device to also illuminate the already machined first surface of the semi-finished product 3 as close to the edge as possible, the auxiliary element 5 can be configured with a correspondingly concave or convex upper surface, such as in Figure 5 and Figure 6 As schematically shown in . In these figures, a semi-finished product 3 with a concave and convex (polished) aspherical first surface is shown as an example. The second surface is only ground flat. In these figures, immersion oil 7 is shown between the auxiliary element 5 and the semi-finished product 3. The two auxiliary elements 5 are plano-concave or plano-convex elements polished on both sides, which also have the function of auxiliary lenses. Instead of plane-parallel plates, the use of such plano-convex or plano-concave lenses as auxiliary elements 5 is recommended for curved or negative (hollow) surfaces or for measurements completely at the edge (in the case of poor center axis) in order to obtain a better adaptation of the position of the two reflections with good angular resolution.

[0055] Preferably, in the proposed method for calibration or measurement, two measuring devices EP are used to measure at two different positions, both in the center and at the edge of the semi-finished product 3, or one measuring device EP is used to measure at two different positions one after the other. Figure 6 It is schematically shown in FIG.

[0056] The vignetting field stop method preferably used in the proposed method, as also known from EP 1636542 B1, is a measuring principle that uses vignetting as a physical effect to measure the tilt or inclination on a surface by reflected light. The measuring beam is a quasi-parallel beam set from an infinite light source on a widely diffused illumination field close to the focus of the collimating lens. The beam splitter guides the reflected light to a camera or a correspondingly position-resolved detector. In addition to the plane mirror or lens in front of the system, the exit pupil of the collimator system is also projected into the field of view behind the focus of the collimator. This is called the output window, and since the camera is located in the focal plane, there is a blurred image of the output window on the camera. Due to the unfocused output window, there is never a problem of leaving the focus as in a conventional AC (autocollimator). Due to the physical effect of the vignetting, the field of view is no longer limited. Therefore, only the camera or detector size (which preferably corresponds to the size of the illumination field) limits the field of view, which is only related to the focal length of the collimator and the size of the unfocused exit pupil (V-SPOT) on the camera. The size of the V-SPOT is then related to the distance from the exit pupil to the plane mirror or in the case of curved surfaces to the radius of curvature of the backup lens and the DUT.

[0057] By using this method instead of conventional AC, vignetting is no longer an issue but a simple solution to measure surface profile and centering deviation on aspheric surfaces with high resolution.

[0058] Reference numerals list

[0059] 1 Glass blank

[0060] 2. Manufacturing the mandrel

[0061] 3 Semi-finished products

[0062] 4Aspherical

[0063] 5. Optical auxiliary components

[0064] 6 Measurement beam

[0065] 7. Immersion oil

[0066] EP measurement device

[0067] C Center of curvature

[0068] R Radius

Claims

1. A method for mounting or fixing or determining the position or orientation of an optical semi-finished product (3) on a manufacturing mandrel (2) when manufacturing a spherical or aspherical lens, In the method, the semi-finished product (3) has a first surface which is a spherical or aspherical surface which has been ground and polished on one side and a second surface opposite to the first surface, which second surface must also be ground and polished to make a lens, and the semi-finished product is placed on the manufacturing mandrel (2) with the first surface and glued, in, The position or orientation of the semi-finished product (3) on the manufacturing mandrel (2) is determined by means of an optical method and / or the calibration of the semi-finished product (3) on the manufacturing mandrel (2) is performed by means of an optical method, in which a transparent optical auxiliary element (5) having a polished upper surface and a lower surface adapted to the second surface of the semi-finished product (3) is applied to the second surface of the semi-finished product (3) with a medium (7) located in between for adjusting the refractive index and is thereby irradiated with at least one light beam (6), so that the light beam (6) is partially reflected on the upper surface of the auxiliary element (5) and on the first surface of the semi-finished product (3), respectively, and at least one beam component reflected by the first surface of the semi-finished product (3), preferably two reflected beam components, is detected by means of at least one position-resolved optical detector.

2. The method according to claim 1, It is characterized in that When the second surface of the semi-finished product (3) is flat, the auxiliary element (5) is configured as a plane-parallel plate or as a concave lens or a convex lens having a flat lower surface.

3. The method according to claim 1, It is characterized in that When the second surface of the semi-finished product (3) is convex or concave, the auxiliary element (5) has a correspondingly concave or convex lower surface and a flat, concave or concave upper surface.

4. The method according to any one of claims 1 to 3, It is characterized in that The auxiliary element (5) is designed so that it completely or almost completely covers the second surface of the semi-finished product (3) and performs measurement with the aid of the light beam (6) or with the aid of two of the light beams (6) for detecting reflected beam components both in the center of the semi-finished product (3) and at the edge of the semi-finished product (3).

5. The method according to any one of claims 1 to 4, It is characterized in that In order to carry out the optical method, a measuring device (EP) is used, in which the light beam (6) is generated by means of an extended light source and is collimated by an optical component before it encounters the semi-finished product (3), wherein an aperture that limits the light beam (6) is used between the light source and the optical detector, the aperture serving as a vignetted field stop, and the light beam (6) is imaged blurrily as one or more light spots on the optical detector through the aperture after reflection on the upper surface of the auxiliary element (5) and on the first surface of the semi-finished product (3) and is detected by means of the optical detector.

6. The method according to claim 5, It is characterized in that An iris with a fixed or adjustable iris opening is used as an aperture which delimits the beam (6).

7. The method according to any one of claims 5 or 6, It is characterized in that The extended light source is provided with a light-emitting surface which has at least the size of a detection surface of the optical detector.

8. The method according to any one of claims 1 to 7, It is characterized in that During the measurement or during the execution of the optical method, the semi-finished product (3) is rotated with the production spindle (2) about the axis of rotation of the production spindle (2).

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