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

Patent metadata

Field	Value
Publication number	US-10935372-B2
Application number	US-201816154670-A
Country	US
Kind code	B2
Filing date	Oct 8, 2018
Priority date	Apr 8, 2016
Publication date	Mar 2, 2021
Grant date	Mar 2, 2021

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:
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 luminous spots;
assigning the brightness distribution to the light spots causing 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 {right arrow over (n)} at the reflection locations for the light emitted from the light points, determining directional derivatives at the surface normal {right arrow over (n)} and interpolating the directional derivatives onto a regular polar grid; and
calculating a further topography of the article by integrating the directional derivatives, determined by the surface normals {right arrow over (n)}, on the regular polar grid by way of solving the linear system of equations (I) reproduced below:

(

A
T

⁢
A

C
T

C

1

)

⁢
z

=

(

∂
r
2

⁢
z

+

∂
φ
2

⁢
z

z
⁡

(

r
=
0

)

z
⁡

(
bearing
)

)

,

(
I
)

wherein A is a Jacobian matrix describing the numerical, polar derivatives on the polar grid and C a constraint matrix C describing the height of the article, measured at bearing points, and the polar condition z(0,φ)=z(0);
up to a convergence criterion; and
establishing at least one of an absolute position or a relative position of at least one point on the surface of the article to be measured in a coordinate system that is fixed relative to an apparatus.

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

3. 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 the light of the plurality of point light sources, reflected at the surface of the article to be measured, to illuminate the optically effective surface of the article;
a device configured to establish at least one of an absolute position or a relative position of the luminous spots;
a 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 an apparatus, the apparatus being configured to iteratively:
assign the brightness distribution to the point light sources causing the brightness distribution and predetermining a first topography;
determine reflection locations on the article for the light emitted by the point light sources;
calculate surface normals {right arrow over (n)} at the reflection locations for the light emitted from the point light sources, determine directional derivatives at the surface normals {right arrow over (n)}, and interpolate the directional derivatives onto a regular polar grid; and
calculate a further topography of the article by integrating the interpolated directional derivatives of the optically effective surface, the directional derivatives being determined by the surface normals {right arrow over (n)}, on the regular polar grid by solving the linear system of equations (I) reproduced below:

(

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