Device and method for measuring a surface topography, and calibration method

Patent metadata

Field	Value
Publication number	US-12372347-B2
Application number	US-202117158454-A
Country	US
Kind code	B2
Filing date	Jan 26, 2021
Priority date	Apr 8, 2016
Publication date	Jul 29, 2025
Grant date	Jul 29, 2025

Abstract

A method and a device for measuring the topography and/or the gradients and/or the curvature of an optically active surface of an object are disclosed. The device allows the object to be arranged in a receiving region with a contact surface for contact with the object. Inside the device, there is a plurality of point light sources that provide light that is reflected at the surface to be measured of an object arranged in the receiving region. The device includes at least one camera with an objective assembly and an image sensor for detecting a brightness distribution which is produced on a light sensor by the light of the point light sources reflected at the surface to be measured.

First claim

The invention claimed is:

1. A method for measuring at least one of a topography, a gradient, or a curvature of an optically effective surface of an article, the method comprising:
arranging the article on an abutment of a holding device resting against the article in a recording region;
reflecting light emitted by one or more light spots at the optically effective surface of the article to be measured;
capturing a brightness distribution of the reflected one or more light spots;
assigning the brightness distribution to the light spots caus ing the brightness distribution;
predetermining a first topography;
iteratively performing:
determining reflection locations on the article for the light emitted by the light spots;
calculating surface normals n at the reflection locations for the light emitted by the light spots; and
calculating a further topography of the article;

up to a convergence criterion;
ensuring that the convergence criterion is met by selecting a distance between principal planes of the article and an imaging system configured to capture the brightness distribution so that a Banach fixed point theorem applies;
establishing at least one of an absolute position or a relative position of at least one point on the optically effective surface of the article to be measured in a coordinate system that is fixed relative to an apparatus; and
determining a scaling point of a three-point bearing of the holding device holding the article in abutment,
wherein the scaling point is in a form of a vertex or a circumcenter of the three-point bearing,
wherein the scaling point is defined by scaling a brightness distribution about the one or more light spots in a radially symmetric manner, and
wherein the article to be measured is a spectacle lens.

2. The method as claimed in claim 1 , further comprising:
determining the reflection locations for the light emitted by the light spots on the article from intersections of light rays calculated from centroids of luminous spots of the brightness distribution with the further topography.

3. The method as claimed in claim 1 , further comprising:
determining the at least one of the absolute position or the relative position of the light spots with an optimization method.

4. A computer program stored on a non-transitory memory with program code for implementing a method as claimed in claim 1 when the computer program is executed on a computer unit.

5. The method according to claim 1 , wherein the iterative calculation up to the convergence criterion takes into account at least one of the following:
a size of a light-sensitive area of an image sensor of a camera and a spacing of pixels of the image sensor;
an optical imaging scale of the camera;
an absolute position, a relative position, or the absolute position and the relative position of the image sensor of the camera in relation to an optical axis of an optical imaging system of the camera;
a distortion of the optical imaging system of the camera;
a lateral displacement of the camera;
coordinates of each light spot in a coordinate system that is fixed in relation to the apparatus and referenced to the image sensor of the camera; and
coordinates of a center and radius of a spherical abutment in the coordinate system that is fixed in relation to the apparatus and referenced to the image sensor of the camera.

6. The method according to claim 1 , wherein determining reflection locations on the article for the light emitted by the light spots includes propagating an (x, y) position of a light spot based on a gradient increase or a mean shift.

7. An apparatus for measuring at least one of a topography, a gradient, or a curvature of an optically effective surface of an article, the apparatus comprising:
a holding device configured to arrange the article on an abutment resting against the article in a recording region;
a plurality of point light sources configured to illuminate the optically effective surface of the article and a recording device configured to capture a brightness distribution composed of luminous spots, the brightness distribution being caused by light of the point light sources, reflected at the surface of the article to be measured, to illuminate the optically effective surface of the article;
a position determination device configured to establish at least one of an absolute position or a relative position of the luminous spots;
a position determination device configured to establish the at least one of the absolute position or the relative position of at least one point on the optically effective surface of the article in a coordinate system that is fixed relative to the apparatus, the apparatus being configured to iteratively:
assign the brightness distribution to the point light sources causing the brightness distribution and predetermine a first topography;
determine reflection locations on the article for the light emitted by the point light sources;
surface normals n at the reflection locations for the light emitted by the point light sources;
calculate a further topography of the article by fitting local basis functions of the optically effective surface being modelled as a linear combination of the local basis functions;

up to a convergence criterion;
ensure that the convergence criterion is met by selecting a distance between principal planes of the article and an imaging system configured to capture the brightness distribution so that a Banach fixed point theorem applies; and
determine a scaling point of a three-point bearing of the holding device holding the article in abutment,
wherein the scaling point is in a form of a vertex or a circumcenter of the three-point bearing,
wherein the scaling point is defined by scaling a brightness distribution about the one or more light spots in a radially symmetric manner, and
wherein the article to be measured is a spectacle lens.

8. The apparatus as claimed in claim 7 , wherein the reflection locations for the light emitted by the point light sources on the article are determined from intersections of light rays calculated from centroids of the luminous spots of the brightness distribution with the further topography.

9. The apparatus as claimed in claim 7 , wherein the device for capturing the brightness distribution composed of luminous spots comprises at least one camera having a lens assembly and an image sensor, on which the brightness distribution of light that is reflected at the optically effective surface is caused.

10. The apparatus as claimed in claim 9 , wherein the lens assembly has an optical axis that lies flush with an adjustment axis.

11. The apparatus as claimed in claim 10 ,
wherein the abutment resting against the article in a recording region is a spherical abutment.

12. The apparatus as claimed in claim 11 , further comprising:
a multiplicity of point light sources that provide light, the light being reflected at the optically effective surface of an article to be measured that is arranged in the recording region.

13. The apparatus as claimed claim 10 , further comprising:
a computer unit having a computer program and a non-transitory memory, in which the computer program is stored, wherein the computer program calculates the at least one of the topography, the gradient, or the curvature of the optically effective surface of the article with an algorithm from a brightness distribution captured by the image sensor, the brightness distribution being caused on an image sensor by the light of the point light sources that is reflected at the optically effective surface to be measured.

14. The apparatus as c

Assignees

• Zeiss Carl Ag

Inventors

• Omlor Lars
• Glasenapp Carsten

Classifications

• G06T7/521

  from laser ranging, e.g. using interferometry; from the projection of structured light · CPC title

• G06T2207/30108

  Industrial image inspection · CPC title

• G06T7/0004

  Industrial image inspection · CPC title

• G06T7/514

  from specularities · CPC title

• G03B3/04

  adjusting position of image plane without moving lens · CPC title