Apparatus and method for measuring eccentricity of aspherical surface

• US 20050174566A1
• Filed: 11/03/2004
• Published: 08/11/2005
• Est. Priority Date: 11/07/2003
• Status: Active Grant

• Current Assignee: Olympus Corporation
• Original Assignee: Olympus Corporation
• Inventors: Namiki, Mitsuru
• Granted Patent: US 7,286,212 B2
• Time in Patent Office: Days
• US Class Current: 356/124
• CPC Class Codes: G01B 11/2408 for measuring roundness
• CPC Class Codes: G01M 11/025 by determining the shape of the object to be tested measuring contours or curvatures by optical means G01B11/24

Abstract

An apparatus for measuring the eccentricity of the aspherical surface has a light source unit; a condenser lens condensing light rays in the proximity of the center of paraxial curvature of a surface to be examined, of an aspherical lens; an angle changing means for entering the rays on the surface to be examined, at angles θ1i (i=1, 2, . . . , N) with an optical axis; a holding tool of the aspherical lens; a light-splitting element; an imaging lens; a light-detecting element detecting the situation of light collected by the imaging lens; and an arithmetical unit. The arithmetical unit is such as to calculate the amount of eccentricity of the surface to be examined, from amounts of shift ΔP1i (i=1, 2, . . . , N) between spot positions P1i (i=1, 2, . . . , N) based on the design data of the surface to be examined and spot positions P1mi (i=1, 2, . . . , N) derived from the light-detecting element, with respect to light rays Q1i (i=1, 2, . . . , N) produced by the angle changing means.

Claims

1. An apparatus for measuring eccentricity of an aspherical surface in which an amount of eccentricity of an aspherical lens is measured, the apparatus comprising:

a light source unit;

a condenser lens condensing light rays emitted from the light source unit in the proximity of a center of paraxial curvature of a surface to be examined, of the aspherical lens;

an angle changing means for entering the rays on the surface to be examined, at angles θ

1i (i=1, 2, . . . , N) with an optical axis;

a holding tool holding the aspherical lens;

a light-splitting element interposed between the angle changing means and the holding tool;

an imaging lens collecting light reflected by the light-splitting element;

a light-detecting element detecting a situation of light collected by the imaging lens; and

an arithmetical unit,

the arithmetical unit including the processes of;

storing spot positions P1mi (i=1, 2, . . . , N) derived from the light-detecting element with respect to light rays Q1i (i=1, 2, . . . , N) produced by the angle changing means;

calculating spot positions P1i (i=1, 2, . . . , N) relative to the rays Q1i (i=1, 2, . . . , N) on the basis of design data of the surface to be examined; and

calculating the amount of eccentricity of the surface to be examined, from amounts of shift Δ

P1i (i=1, 2, . . . , N) between the spot positions P1i (i=1, 2, . . . , N) and the spot positions P1mi (i=1, 2, . . . , N).

2. An apparatus for measuring eccentricity of an aspherical surface according to claim 1, further comprising a second light source unit placed on an opposite side of the light source unit, with the holding tool between the light source unit and the second light source unit;

a second condenser lens placed on the optical axis, condensing light rays emitted from the second light source unit in the proximity of a center of paraxial curvature of a second surface to be examined, situated on an opposite side of the surface to be examined;

a second angle changing means for entering the rays emitted from the second light source unit on the second surface to be examined, at angles θ

2i (i=1, 2, . . . , N) with the optical axis;

a second light-splitting element interposed between the second angle changing means and the holding tool;

a second imaging lens collecting light reflected by the second light-splitting element; and

a second light-detecting element detecting the situation of light collected by the second imaging lens, wherein the arithmetical unit includes the processes of storing spot positions P2mi (i=1, 2, . . . , N) derived from the second light-detecting element with respect to light rays Q2i (i=1, 2, . . . , N) produced by the second angle changing means;

calculating spot positions P2i (i=1, 2, . . . , N) relative to the rays Q2i (i=1, 2, . . . , N) on the basis of design data of the second surface;

calculating an amount of eccentricity of the second surface from amounts of shift Δ

P2i (i=1, 2, . . . , N) between the spot positions P2i (i=1, 2, . . . , N) and the spot positions P2mi (i=1, 2, . . . , N); and

calculating face-to-face eccentricity of the aspherical lens by using amounts of eccentricity of the surface be examined and the second surface to be examined.

5. An apparatus for measuring eccentricity of an aspherical surface according to claim 1, wherein the arithmetical unit previously has, from the design data of the surface to be examines, an inclination angle shift change function g_{A shift} (y) of the surface to be examined, found from differences between the spot positions P1i (i=1, 2, . . . , N) of rays Q1i′

(i=1, 2, . . . , N) where the surface to be examined is free of eccentricity and spot positions P1_{A si} (i=1, 2, . . . , N) of the rays Q1i′

(i=1, 2, . . . , N) where the surface to be examined is moved parallel with a direction perpendicular to the optical axis of the condenser lens by an amount of unit shift δ

_A0 and an inclination angle tilt change function g_{A tilt}(y) of the surface to be examined, found from differences between the spot positions P1i (i=1, 2, . . . , N) of the rays Q1i′

(i=1, 2, . . . , N) where the surface to be examined is free of eccentricity and spot positions P1_{A ti} (i=1, 2, . . . , N) of the rays Q1i′

(i=1, 2, . . . , N) where the surface to be examined is rotated and moved by an amount of unit tilt ε

_A0 in a plane containing the optical axis of the condenser lens so that an inclination angle distribution of the surface to be examined, calculated from the amounts of shift Δ

P1i (i=1, 2, . . . , N) of the spot positions of the rays Q1i′

(i=1, 2, . . . , N) actually obtained by the light-detecting element is expressed as a function g2(δ

_A, ε

_A, y)=α

g_{A shift} (y)+β

g_{A tilt} (y) in which the inclination angle shift change function g_{A shift}(y) and the inclination angle tilt change function g_{A tilt}(y), each of which is multiplied by a coefficient, are added and linearly combined to calculate amounts of shift and tilt (δ

_A, ε

_A)=(α

δ

_A0, β

ε

_A0) of the surface to be examined, from coefficients α and

β

.

6. An apparatus for measuring eccentricity of an aspherical surface according to claim 2, wherein the arithmetical unit previously has, from the design data of the surface to be examines and the second surface to be examined, an inclination angle shift change function g_{A shift}(y) of the surface to be examined, found from differences between the spot positions P1i (i=1, 2, . . . , N) of rays Q1i′

(i=1, 2, . . . , N) where the surface to be examined is free of eccentricity and spot positions P1_{A si}(i=1, 2, . . . , N) of the rays Q1i′

(i=1, 2, . . . , N) where the surface to be examined is moved parallel with a direction perpendicular to the optical axis of the condenser lens by an amount of unit shift δ

_A0;

an inclination angle tilt change function g_{A tilt}(y) of the surface to be examined, found from differences between the spot positions P1i (i=1, 2, . . . , N) of the rays Q1i′

(i=1, 2, . . . , N) where the surface to be examined is free of eccentricity and spot positions P1_{A ti} (i=1, 2, . . . , N) of the rays Q1i′

(i=1, 2, . . . , N) where the surface to be examined is rotated and moved by an amount of unit tilt ε

_A0 in a plane containing the optical axis of the condenser lens;

an inclination angle shift change function g_{B shift}(y) of the second surface to be examined, found from differences between the spot positions P2i (i=1, 2, . . . , N) of rays Q1i′

(i=1, 2, . . . , N) where the second surface to be examined is free of eccentricity and spot positions P2_{B si} (i=1, 2, . . . , N) of the rays Q1i′

(i=1, 2, . . . , N) where the second surface to be examined is moved parallel with a direction perpendicular to the optical axis of the second condenser lens by an amount of unit shift δ

_B0; and

an inclination angle tilt change function g_{B tilt}(y) of the second surface to be examined, found from differences between the spot positions P2i (i=1, 2, . . . , N) of the rays Q1i′

(i=1, 2, . . . , N) where the second surface to be examined is free of eccentricity and spot positions P2_{B ti} (i=1, 2, . . . , N) of the rays Q2i′

(i=1, 2, . . . , N) where the second surface to be examined is rotated and moved by an amount of unit tilt ε

_B0 in a plane containing the optical axis of the second condenser lens so that an inclination angle distribution of the surface to be examined, calculated from the amounts of shift Δ

P1i (i=1, 2, . . . , N) of the spot positions of the rays Q1i′

(i=1, 2, . . . , N) actually obtained by the light-detecting element is expressed as a function g2(δ

_A, ε

_A, y)=α

g_{A shift} (y)+β

g_tilt (y) in which the inclination angle shift change function g_{A shift}(y) and the inclination angle tilt change function g_{A tilt}(y), each of which is multiplied by a coefficient, are added and linearly combined to calculate amounts of shift and tilt (δ

_A, ε

_A)=(α

δ

_A0, β

ε

_A0) of the surface to be examined, from coefficients α and

β

, and an inclination angle distribution of the second surface to be examined, calculated from the amounts of shift Δ

P2i (i=1, 2, . . . , N) of the spot positions of the rays Q1i′

(i=1, 2, . . . , N) actually obtained by the second light-detecting element is expressed as a function g2(δ

_B, ε

_B, y)=α

g_Bshift (y)+β

g_Btilt (y) in which the inclination angle shift change function g_{B shift}(y) and the inclination angle tilt change function g_{B tilt}(y), each of which is multiplied by a coefficient, are added and linearly combined to calculate amounts of shift and tilt (δ

_B, ε

_B)=(α

δ

_B0, β

ε

_B0) of the second surface to be examined, from coefficients α and

β

B, and to calculate a relative face-to-face eccentricity (δ

_A-δ

_B, ε

_A-ε

_B) between the surface to be examined and the second surface to be examined, of the aspherical lens.

7. An apparatus for measuring eccentricity of an aspherical surface according to claim 1, wherein the angle changing means includes a condenser lens condensing rays emitted from the light source unit, a variable reflecting angle element in which reflecting angles of the rays can be changed by rotation, and a collimator lens making the rays reflected by the variable reflecting angle element parallel to the optical axis, and the variable reflecting angle element is placed so that a center of rotation is located in the proximity of a back focal plane of the condenser lens and a front focal plane of the collimator lens that coincide with each other and the rays Q1i (i=1, 2, . . . , N) are produced by the rotation of the variable reflecting angle element.

8. An apparatus for measuring eccentricity of an aspherical surface according to claim 2, wherein the angle changing means includes a first condenser lens condensing rays emitted from the light source unit, a first variable reflecting angle element in which reflecting angles of the rays can be changed by rotation, and a first collimator lens making the rays reflected by the first variable reflecting angle element parallel to the optical axis, and the variable reflecting angle element is placed so that a center of rotation is located in the proximity of a back focal plane of the condenser lens and a front focal plane of the collimator lens that coincide with each other and the rays Q1i (i=1, 2, . . . , N) are produced by the rotation of the variable reflecting angle element, while the second angle changing means includes a second condenser lens condensing rays emitted from the second light source unit, a second variable reflecting angle element in which reflecting angles of the rays emitted from the second light source unit can be changed by rotation, and a second collimator lens making the rays reflected by the second variable reflecting angle element parallel to the optical axis, and the second variable reflecting angle element is placed so that a center of rotation is located in the proximity of a back focal plane of the condenser lens and a front focal plane of the second collimator lens that coincide with each other and the rays Q2i (i=1, 2, . . . , N) are produced by the rotation of the second variable reflecting angle element.

9. An apparatus for measuring eccentricity of an aspherical surface according to claim 7, wherein the angle changing means has two variable reflecting angle elements arranged so that directions that the reflection angle is changed make right angles with each other, and the rays emitted from the light source unit are scanned in a two-dimensional direction through the two variable reflecting angle elements.

10. An apparatus for measuring eccentricity of an aspherical surface according to claim 8, wherein each of the angle changing means and the second angle changing means has two variable reflecting angle elements arranged so that directions that the reflection angle is changed make right angles with each other, and wherein the rays emitted from the light source unit are scanned in a two-dimensional direction through the two variable reflecting angle elements in the angle changing means and the rays emitted from the second light source unit are scanned in a two-dimensional direction through the two variable reflecting angle elements in the second angle changing means.

11. An apparatus for measuring eccentricity of an aspherical surface according to claim 7, wherein the variable reflecting angle element is constructed so that the reflecting angle can be set in a two-dimensional direction.

12. An apparatus for measuring eccentricity of an aspherical surface according to claim 8, wherein each of the variable reflecting angle element and the second variable reflecting angle element is constructed so that the reflecting angle can be set in a two-dimensional direction.

13. An apparatus for measuring eccentricity of an aspherical surface according to claim 1, wherein the angle changing means includes a beam expander expanding the beam section of collimating light produced by the light source unit and an aperture element in which an aperture position can be changed, so that the aperture element is moved in a plane perpendicular to the optical axis of the beam expander and thereby the rays Q1 (i=1, 2, . . . , N) are produced.

14. An apparatus for measuring eccentricity of an aspherical surface according to claim 2, wherein the angle changing means includes a first beam expander expanding the beam section of collimating light produced by the first light source unit and a first aperture element in which an aperture position can be changed, so that the first aperture element is moved in a plane perpendicular to the optical axis of the first beam expander and thereby the rays Q1i (i=1, 2, . . . , N) are produced, and the second angle changing means includes a second beam expander expanding the beam section of collimating light produced by the second light source unit and a second aperture element in which an aperture position can be changed, so that the second aperture element is moved in a plane perpendicular to the optical axis of the second beam expander and thereby the rays Q2i (i=1, 2, . . . , N) are produced.

15. An apparatus for measuring eccentricity of an aspherical surface according to claim 7, wherein afocal lenses increasing an angle magnification with respect to rays Q1i′

(i=1, 2, . . . , N) are interposed between the collimator lens and the imaging lens.

16. An apparatus for measuring eccentricity of an aspherical surface according to claim 8, wherein first afocal lenses increasing an angle magnification with respect to rays Q1i′

(i=1, 2, . . . , N) are interposed between the collimator lens and the imaging lens, and second afocal lenses increasing an angle magnification with respect to rays Q1i′

(i=1, 2, . . . , N) are interposed between the second collimator lens and the second imaging lens.

3. A method for measuring eccentricity of an aspherical surface in which an amount of eccentricity of an aspherical lens is measured, the method comprising the steps of:

finding an inclination angle shift change function g_{A shift}(y) on the basis of design data of a surface to be examined, of the aspherical lens;

finding an inclination angle tilt change function g_{A tilt}(y) on the basis of the design data of the surface to be examined, of the aspherical lens;

actually measuring an inclination angle distribution of a tangent of the surface to be examined, of the aspherical lens;

finding an inclination angle change function g2 (δ

_A, β

_A, y) that is a difference between the inclination angle distribution of the surface to be examined and the inclination angle distribution of the surface to be examined in a noneccentric state that is a design value, on the basis of a result obtained in the actually measuring step;

performing fitting of the inclination angle change function g2 (δ

_A, β

_A, y) to a function expressed by α

g_{A shift}(y)+β

g_{A tilt}(y); and

finding amounts of shift and tilt (δ

_A, ε

_A)=(α

δ

_A0, β

ε

_A0) of eccentricity of the surface to be examined, from α and

β

found by the fitting,

where the inclination angle shift change function g_{A shift}(y) is a function found by a difference between the inclination angle distribution where the surface to be examined is moved in parallel by an amount of unit shift δ

_A0 and the inclination angle distribution in the noneccentric state, the inclination angle tilt change function g_{A tilt}(y) is a function found by a difference between the inclination angle distribution where the surface to be examined is rotated and moved by an amount of unit tilt ε

_A0 and the inclination angle distribution in the noneccentric state, and the inclination angle change function g2 (δ

_A, β

_A, y) is a difference between the inclination angle distribution of the surface to be examined, based on an actual measurement and the inclination angle distribution in the noneccentric state that is the design value.

4. A method for measuring eccentricity of an aspherical surface according to claim 3, further comprising the steps of finding an inclination angle shift change function g_{B shift}(y) on the basis of design data of a second surface to be examined, situated on an opposite side of the surface to be examined, of the aspherical lens;

finding an inclination angle tilt change function g_{B tilt}(y) on the basis of the design data of the second surface to be examined, of the aspherical lens;

actually measuring an inclination angle distribution of a tangent of the second surface to be examined, of the aspherical lens;

finding an inclination angle change function g2 (δ

_B, β

_B, y) that is a difference between the inclination angle distribution of the second surface to be examined and the inclination angle distribution of the second surface to be examined in a noneccentric state that is a design value, on the basis of a result obtained in the actually measuring step;

performing fitting of the inclination angle change function g2 (δ

_B, β

_B, y) to a function expressed by α

g_{B shift}(y)+β

g_{B tilt}(y);

finding amounts of shift and tilt (δ

_B, ε

_B)=(α

δ

_B0, β

ε

_B0) of eccentricity of the second surface to be examined, from α and

β

found by the fitting; and

finding a face-to-face eccentricity (δ

_A-δ

_B, ε

_A-ε

_B) of the aspherical lens from amounts of eccentricity of the surface to be examine and the second surface to be examined,

where the inclination angle shift change function g_{B shift}(y) is a function found by a difference between the inclination angle distribution where the second surface to be examined is moved in parallel by an amount of unit shift δ

_B0 and the inclination angle distribution in the noneccentric state, the inclination angle tilt change function g_{B tilt}(y) is a function found by a difference between the inclination angle distribution where the second surface to be examined is rotated and moved by an amount of unit tilt ε

_B0 and the inclination angle distribution in the noneccentric state, and the inclination angle change function g2 (δ

_B, β

_B, y) is a difference between the inclination angle distribution of the second surface to be examined, based on an actual measurement and the inclination angle distribution in the noneccentric state that is the design value.