JPH04340406A - Aspheric surface measurement method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to an aspherical surface measurement method, and in particular uses a data processing method for evaluating aspherical surface shape errors with parallel eccentricity and rotational eccentricity caused by mechanical installation errors removed. This paper relates to a method for measuring aspheric surfaces.

0002

[Prior Art] As optical systems become more precise and more compact, the fields of application of aspherical surfaces are increasingly expanding. Conventionally, when measuring the shape of an aspheric surface, eccentric components of the surface, that is, axis deviations due to parallel eccentricity and rotational eccentricity, are corrected by humans making fine adjustments to the mechanical axis of the object to be measured relative to the measuring device before measurement. was going on. Furthermore, regarding the axis deviation as a surface, conventionally only each cross section was evaluated, and the evaluation of the entire surface was not particularly considered.

0003

However, in the conventional example described above, manual and mechanical removal of the axis misalignment of the aspherical object to be measured requires skilled work and is time consuming. The resulting measurement results also had poor reproducibility. Furthermore, it is virtually impossible to three-dimensionally evaluate the entire surface using the conventional method of measuring the cross section.

In order to solve the above-mentioned problems, the present invention makes it possible to automatically calculate the parallel eccentricity and rotational eccentricity by a computer from the measurement results of the aspherical surface shape, thereby eliminating the need for manual labor. The purpose is to provide a measurement method.

Furthermore, the present invention is characterized in that the axis deviation of the entire surface is determined by calculation from the amount of eccentricity of a plurality of cross sections, thereby making it possible to evaluate the shape of the entire surface. For the purpose of providing.

[0006]

[Means for Solving the Problems] The aspherical surface measurement method of the present invention compares rotational and parallel eccentricity errors contained in measured data with design data when measuring and inspecting an aspherical surface, and corrects the measured value. The method for measuring an aspheric surface is characterized in that parallel eccentricity is corrected at a point where the inclination, or differential value, of each of the aspheric shape design values and the reference spherical surface becomes equal.

[0007]

[Example] Figures 1 and 2 are flowcharts of calculation processing according to the present invention for processing data collected by an aspherical lens shape measuring device, and Figure 3 is a schematic diagram of the aspherical lens shape measuring device according to the present invention. be.

In the figure, an aspherical lens 30, which is an object to be measured, is mounted on a holder 8 of the object, and is moved to a non-contact type probe for aspherical surface measurement by an indexing axis motor 9 and rotation axis motors 2, 3. It is now possible to move around. Conventionally, what required skill was setting the aspherical lens, which is the object to be tested, in this area.

On the other hand, the sensor section for measuring the aspherical shape is
This is the part indicated by 0 to 20. The non-contact probe 20 measures the shape by focusing on the surface of the aspherical lens 30. The movement of the probe at that time is caused by the fine slide movement mechanisms 18 and 19 and the coarse slide movement mechanisms 13 and 14.
detected by. Reference numeral 12 represents a movement motor for a coarse slide, and reference numeral 11 represents a surface plate on which a sensor head is mounted.

Processing of data obtained from the hardware of the measurement system as described above will be explained using FIGS. 1 and 2. When the measurement is started, first in step S1, various data regarding the aspherical shape, that is, the focusing state detector 50, the tilt angle detector 51, the fine slide movement amount detector 53, the coarse slide movement amount detector 55, and the object to be inspected are collected. Data from the turning angle detector 57 indicating the position is input as processing data to the data processing computer 61 via the control computer 60.

FIG. 4 shows the relationship between the measured values and the designed values in this state. The design value is indicated by a solid line 302 in the figure.
The measured value is indicated by a broken line 304. Since the actual measured values include both parallel eccentricity and rotational eccentricity, the relationship is generally complicated as shown in FIG. 4. If a circle passing through the apex 311 of the design value 302 of the aspherical surface shape and the effective diameters 309 and 310 of the object to be measured is the reference spherical surface 303, the axis misalignment between the axis 301 of the aspherical surface design value and the axis 306 of the measured aspherical surface 304 The amount is rotational eccentricity αb 307 and parallel eccentricity α
a decomposed into 308. As shown in Fig. 4, the decomposition into two components is the amount of rotation αb when the axis of the design value is rotated to a position parallel to the axis of the measured value around the center 305 of the reference spherical surface 303, and the amount of rotation αb after rotation. is defined as the parallel eccentricity αa remaining as the component in the direction perpendicular to the axis of the design value of .

[0012] In order to accurately evaluate the aspherical shape, the above two eccentricities must be removed. Incidentally, in an aspherical shape, in addition to the apex 311, there are always points on the left and right sides where the inclination, that is, the differential value, is equal to that of the reference spherical surface. In this embodiment, attention is paid to the fact that the difference between the design value and the measured value at the point where the differential values become equal does not include an error due to rotational eccentricity, but only an error due to parallel eccentricity.

In step S2 of FIGS. 1 and 2, first, the point where the above-mentioned differential values are equal is used as an initial point for calculation of parallel eccentricity, and the amount of parallel eccentricity is calculated. Next, in step S3, a point different from step S2, for example, a point where the difference between the design value and the measured value appears largest due to rotational eccentricity, is selected as a calculation point, and the amount of rotational eccentricity is calculated. The parallel eccentricity and rotational eccentricity calculated from these two initial points are slightly different from the true values. As initial values, parallel eccentricity αsa(1)=0, rotational eccentricity αsb
(1) Rotation and parallel eccentricity αa calculated as = 0,
Add each αb. Furthermore, the next calculation point is corrected by αa and αb.

[0014] In steps S4 and S5, it is determined whether the obtained error amounts αa and αb are within predetermined tolerances A and B, and if no, steps S2 to S5 are performed.
Repeat the loop. αa, αb calculated one after another
are the starting values αsa(1) and αsb of the eccentricity in the previous loop
Correction is performed in addition to (1). Steps S2-S
αsa(1) and αsb(1) when exiting the loop of No. 5 are the calculation results of the amount of eccentricity in the first cross section. Step S2~
The loop up to S5 is a calculation method called a so-called convergence method.

Step S6 is a part for checking the number of cross sections to be calculated. The arguments in αsa and αsb are parameters representing the number of measurement cross sections, and it is determined whether the number of calculated cross sections has reached the predetermined number Na of measurement cross sections. If No, one argument of the section number is added in step S7, and steps S2 to S6 are repeated to calculate the eccentricity of the next section.

[0016] Step S8, which is proceeded to when step S6 is Yes, is a part for determining whether the measurement is of only one cross-section or of multiple cross-sections. In the case of only one cross section, the eccentricity αsa obtained from the measurement data of the cross section is determined in step S9.
(1), the measurement data is corrected using αsb(1), and the calculation is completed. Further, in the case of multi-section measurement, the process proceeds to steps S10 to S14 in order to obtain the shape of the entire surface from the correlation between the eccentricity values obtained for each step section.

At the stage when steps S10 and S11 have been reached, the parallel eccentricity αsa(1) to αsa(Na) and the rotational eccentricity αsb(1) to αsb(Na) of each cross section have been independently determined. . From these data, the parallel eccentricity Sd as a surface, its direction Sr, and the rotational eccentricity Rd
and its direction Rr are calculated by the method of calculating the first term of FFT. This is the axis of parallel eccentricity and rotational eccentricity when considering the shape of the entire aspherical surface.

The next steps S12 and S13 are step S
10. Decompose the axial deviation of the entire surface obtained in S11 into components of each cross section, and calculate the true parallel eccentricity {αsan(1) to αsan(Na)} and the true rotational eccentricity {αsan(1) to αsan(Na)} in each crosssection. This is the part that calculates αsbn(1) to αsbn(Na)}. Next, in step S14, the measurement data of each cross section is corrected based on the eccentricity error obtained in steps S12 and S13, and the process ends. The corrected measurement data and the amount of eccentricity are printed on the plotter 63 and printer 64 shown in FIG.
A cross-sectional shape or surface is displayed using an output device such as .

In this embodiment, since it is possible to measure multiple cross sections while the object to be measured is held on the mount, it is possible to comprehensively determine the parallel eccentricity of the entire surface from the mutual relationship between the measured cross sections. Rotational eccentricity can be calculated and determined. As a result, it has become possible to evaluate the shape of the aspheric surface with accurate eccentricity data removed.

In the first embodiment of the present invention shown in FIGS. 1 and 2, in steps S2 and S3, the parallel and rotational eccentricities were considered in a polar coordinate system with the center of the reference sphere as the origin. However, there are various other methods of determining the amount of eccentricity. For example, in the second embodiment of the present invention, the amount of eccentricity is detected using an xy orthogonal coordinate system. A conceptual diagram showing the concept of eccentricity in the orthogonal coordinate system is shown in FIG.

In FIG. 5, 401 is the design value of the aspherical surface, and 402 is input data obtained by measurement. In this case, the axis deviation due to rotation is αb 406, but the parallel eccentric component is not a simple axis deviation, but the measurement range 405 deviates by αa 407 from the design range 404 on the test object that reflects the design range 403. It appears as a result. Therefore, in Example 2, δ=Σ(f
n - Fn)2, and find the parallel eccentricity αa that satisfies the condition that δ is the minimum.
It is characterized by determining the amount of rotational eccentricity αb. This condition is expressed as αa by Lagrange's undetermined constant method.
It can be calculated by the so-called damped least squares method from simultaneous equations in which δ is partially differentiated by αb and αb.

The stage at which the parallel and rotational eccentricity of each cross section has been calculated is step S in the calculation flowchart of FIGS. 1 and 2.
6, but the rest is the same as in the first embodiment.

In the aspheric surface measurement method of the present invention, (a) Is the measurement performed using polar coordinates or rectangular coordinates?

(b) Is the calculation method a convergence method or a damped least squares method? In addition, although the measurement system in Figure 3 shows a measurement sensor with a non-contact probe, this can of course be a contact type, so the third parameter is (c) whether the probe is a contact method or a non-contact method. mosquito. There are such options. The invention can be practiced with any combination of these.

[0025]

[Effects of the Invention] As explained above, in the present invention, aspherical surface shape measurement, which conventionally relied on skilled hands, can be automatically measured, and the axis deviation of the measured object can be corrected statistically and automatically by a computer. It is characterized by being carried out. As a result of automation, it has become possible to significantly shorten the long inspection time. Further, in the present invention, since the work of correcting axis deviation, which requires a long time and skill, can basically be omitted, the handling of the apparatus becomes easier and the reproducibility of measurement can be improved.

Further, according to the present invention, by automatically and continuously performing measurements, it has become possible to measure a plurality of surfaces and perform data processing while correlating them with each other. As a result, it has become possible to comprehensively evaluate aspherical shapes, which could only be processed as individual cross sections, from a three-dimensional perspective of the entire surface.

[Brief explanation of drawings]

[Figure 1] Flowchart of Embodiment 1 of the present invention

[Figure 2
] Flowchart of Embodiment 1 of the present invention

[Figure 3]
Block diagram of an aspheric surface measuring device to which the present invention is applied

[Figure 4] Conceptual diagram showing the eccentricity relationship between measured values and design values using a polar coordinate system

[Figure 5] Conceptual diagram showing the eccentricity relationship between measured values and design values using an orthogonal coordinate system

[Explanation of symbols]

2, 3 Swivel axis motor 8 Test object holder 9 Index axis motor 11 Surface plate 12 Coarse motor 13,14 Coarse slide mechanism 18, 19 Fine movement slide mechanism 20 Measurement probe 30 Test object 50 Focus state detector 51 Tilt angle detector 52 Servo driver 53 Fine slide movement amount detector 54 Coarse motor driver 55 Coarse slide movement amount detector 56 Rotation axis motor driver 57 Turning angle detector 58 Index axis motor driver 59 Scanning board 60 Control computer 61 Data processing computer 62 Disc 63 Plotter 64 Printer 301 Axis of aspheric design value 302,401 Design value 303 Reference sphere 304,402 Measured value 305 Center of reference sphere of design value 306 Axis of measurement aspheric surface 307,406 Rotational eccentricity 308,407 Parallel eccentricity 311 Vertex of design value 403,404 Design range 405 Measurement range

Claims (2)

[Claims] Claim 1. An aspherical surface measurement method in which rotational and parallel eccentricity errors contained in measurement data are compared with design data and correction of the measured values is performed when measuring and inspecting an aspherical surface.
An aspherical surface measurement method characterized in that parallel eccentricity is corrected at a point where the inclination, that is, the differential value of each of the aspherical surface shape design values and the reference spherical surface becomes equal. 2. The aspheric surface is measured simultaneously on a plurality of cross sections, and the amount of rotation and parallel eccentricity of the aspheric surface as a whole is determined from the amounts of rotation and parallel eccentricity obtained independently from the plurality of cross sections. . An aspheric surface measuring method, comprising: correcting measurement data of the plurality of cross sections based on the obtained eccentricity of the entire surface.