Method and apparatus for edge determination of a measurement object in optical metrology

• US 10,360,684 B2
• Filed: 04/25/2017
• Issued: 07/23/2019
• Est. Priority Date: 04/28/2016
• Status: Active Grant

• Current Assignee: Carl Zeiss Industrielle Messtechnik GmbH (Carl-Zeiss-Stiftung)
• Original Assignee: Carl Zeiss Industrielle Messtechnik GmbH (Carl-Zeiss-Stiftung)
• Inventors: Seitz, Dominik, Haverkamp, Nils
• Primary Examiner(s): Thirugnanam, Gandhi
• Application Number:
  US15/496,321
• Publication Number:
  US 20170316568A1
• Time in Patent Office: 819 Days
• Field of Search: None
• CPC Class Codes: G06T 2207/10004 Still image; Photographic image
• CPC Class Codes: G06T 2207/10152 Varying illumination
• CPC Class Codes: G06T 2207/20216 Image averaging
• CPC Class Codes: G06T 2207/30164 Workpiece; Machine component
• CPC Class Codes: G06T 7/0004 Industrial image inspection
• CPC Class Codes: G06T 7/13 Edge detection

Abstract

A method for edge determination of a measurement object in optical metrology, such as performed by an optical coordinate measuring machine. The method includes the steps of capturing first image data of the measurement object under reflected-light illumination, capturing second image data of the measurement object under transmitted-light illumination, and determining a position of an edge of the measurement object based on an evaluation in which both the first and the second image data are used.

Claims

1. Method for edge determination of a measurement object in optical metrology, comprising the steps of:

capturing first image data of the measurement object under reflected-light illumination;

capturing second image data of the measurement object under transmitted-light illumination;

determining a first preliminary edge position of an edge of the measurement object by evaluating the first image data;

determining a second preliminary edge position of the edge of the measurement object by evaluating the second image data; and

determining an edge position of the measurement object based on the first and second preliminary edge positions;

rotating the measurement object about a horizontal axis;

capturing third image data of the rotated measurement object under reflected-light illumination;

capturing fourth image data of the rotated measurement object under transmitted-light illumination;

determining a third preliminary edge position of the edge of the measurement object by evaluating the third image data;

determining a fourth preliminary edge position of the edge of the measurement object by evaluating the fourth image data;

determining a further edge position of the measurement object based on the third and fourth preliminary edge positions; and

comparing the edge position of the measurement object with the further edge position of the measurement object;

wherein determining the edge position of the measurement object comprises forming an arithmetic average between the first and second preliminary edge positions, and wherein determining the further edge position of the measurement object comprises;

forming an arithmetic average between the third and fourth preliminary edge positions.

2. Method according to claim 1, wherein the first image data of the measurement object is captured under bright-field reflected-light illumination, and wherein the second image data of the measurement object is captured under bright-field transmitted-light illumination.

3. Method for edge determination of a measurement object in optical metrology, comprising the steps of:

capturing first image data of the measurement object under reflected-light illumination;

capturing second image data of the measurement object under transmitted-light illumination;

forming synthesized image data by synthesizing the first and second image data, wherein each of the first and the second image data is normalized before the synthesized image data is formed; and

determining a position of an edge of the measurement object based on the synthesized image data, wherein determining the position of the edge of the measurement object based on the synthesized image data comprises determining positions at which grey levels in the normalized first image data correspond to grey levels in the normalized second image data and positions at which a difference between the grey levels of the normalized first image data and the grey levels of the normalized second image data is zero.

4. Method according to claim 3, wherein normalizing the first and second image data comprises:

normalizing a dynamic range of the first image data to a predefined value and normalizing a dynamic range of the second image data to said predefined value.

5. Method according to claim 3, wherein the first image data of the measurement object is captured under bright-field reflected-light illumination, and wherein the second image data of the measurement object is captured under bright-field transmitted-light illumination.

6. Method for edge determination of a measurement object in optical metrology, comprising the steps of:

capturing first image data of the measurement object under reflected-light illumination;

capturing second image data of the measurement object under transmitted-light illumination;

forming synthesized image data by synthesizing the first and second image data, wherein each of the first and the second image data is normalized before the synthesized image data is formed; and

determining a position of an edge of the measurement object based on the synthesized image data;

rotating the measurement object about a horizontal axis;

capturing third image data of the rotated measurement object under reflected-light illumination;

capturing fourth image data of the rotated measurement object under transmitted-light illumination;

determining a further position of the edge of the measurement object based on an evaluation in which both the third and the fourth image data is used; and

comparing the edge position of the measurement object that was determined based on the first and second image data to the further edge position of the measurement object that was determined based on the third and fourth image data.

7. Method according to claim 6, wherein determining the further edge position of the measurement object comprises:

forming second synthesized image data by synthesizing the third and fourth image data; and

determining the further edge position of the measurement object based on the second synthesized image data.

8. Coordinate-measuring machine, comprising:

an optical sensor for capturing image data of a measurement object;

a first illumination device for producing a reflected-light illumination of the measurement object;

a second illumination device for producing a transmitted-light illumination of the measurement object; and

a control device which is configured to;

illuminate the measurement object by means of the first illumination device and capture first image data by means of the optical sensor,

illuminate the measurement object by means of the second illumination device and capture second image data by means of the optical sensor,

normalize each of the first and the second image data,

form synthesized image data by synthesizing the normalized first and second image data, and

determine a position of an edge of the measurement object based on the synthesized image data, wherein determining the position of the edge of the measurement object based on the synthesized image data comprises determining positions at which grey levels in the normalized first image data correspond to grey levels in the normalized second image data and positions at which a difference between the grey levels of the normalized first image data and the grey levels of the normalized second image data is zero.