Machine vision inspection system and method for performing high-speed focus height measurement operations

Patent metadata

Field	Value
Publication number	US-9143674-B2
Application number	US-201313917581-A
Country	US
Kind code	B2
Filing date	Jun 13, 2013
Priority date	Jun 13, 2013
Publication date	Sep 22, 2015
Grant date	Sep 22, 2015

Abstract

A machine vision inspection system comprising an illumination source and an imaging system and a method for performing high-speed focus height measurement operations. The method comprises: placing a workpiece in a field of view of the machine vision inspection system; determining a region of interest for focus height measurement operations; operating the illumination source to illuminate the workpiece with strobed illumination; periodically modulating a focus position of the imaging system along a Z-height direction proximate to the workpiece; collecting an image stack, wherein each image of the image stack corresponds to an instance of strobed illumination matched with a phase of the modulated focus position corresponding to an appropriate Z height within the image stack; and determining a Z-height measurement for at least one portion of the region of interest.

First claim

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method for performing high-speed focus height measurement operations in a machine vision inspection system comprising an illumination source and an imaging system that comprises a camera system, the method comprising:
placing a workpiece in a field of view of the machine vision inspection system;
determining a region of interest for focus height measurement operations;
operating the illumination source to illuminate the workpiece with strobed illumination;
periodically modulating a focus position of the imaging system over a plurality of positions along a Z-height direction proximate to the workpiece;
collecting an image stack comprising respective images focused at respective Z heights, wherein each image of the image stack is exposed using an instance of strobed illumination timed to correspond with a phase of the periodically modulated focus position corresponding to a Z height within the image stack; and
determining a Z-height measurement for at least one portion of the region of interest based on analyzing the image stack to determine a Z height corresponding to a best focus position for the at least one portion of the region of interest.

2. The method of claim 1 , wherein the imaging system comprises a variable focal length lens and periodically modulating a focus position of the imaging system comprises modulating a focus position of a variable focal length lens.

3. The method of claim 2 , wherein the variable focal length lens is a tunable acoustic gradient index of refraction lens.

4. The method of claim 2 , wherein periodically modulating a focus position of the imaging system comprises modulating a focus position at a rate of at least 10 kHz.

5. The method of claim 1 , wherein modulating a focus position of a variable focal length lens comprises sinusoidally modulating the focus position.

6. The method of claim 1 , wherein illuminating the workpiece with strobed illumination comprises driving the strobed illumination at a frequency that matches the periodically modulated focus position of the imaging system and adding a phase shift timed to correspond to a Z height.

7. The method of claim 1 , further comprising moving a field of view relative to a workpiece along a direction of motion parallel to a pixel orientation of the camera system and collecting images of the image stack as the field of view moves, wherein the imaging system comprises a camera system with an electronic rolling shutter and each image of the image stack is a stripe of the pixel array with a width along the direction of motion equal to the at least one portion of the region of interest.

8. The method of claim 7 , wherein the imaging system comprises a plurality of camera systems comprising imaging arrays which receive image light offset relative to each other in a staggered manner by a distance at least equal to a width of the at least one portion of the region of interest used for determining a best focus height.

9. The method of claim 1 , wherein the at least one portion of the region of interest is a sub-region of the region of interest.

10. The method of claim 1 , wherein the at least one portion of the region of interest is the entire region of interest.

11. The method of claim 1 , wherein determining a Z-height measurement for at least one portion of the region of interest comprises determining a Z-height measurement for a plurality of sub-regions of the region of interest.

12. A machine vision inspection system configurable to collect a stack of images of a workpiece at a plurality of Z heights in order to measure Z heights based on a best focus height for a plurality of sub-regions of a region of interest, the machine vision inspection system comprising:
an imaging system comprising a variable focal length lens electronically controllable to vary the focus position of the imaging system; and
an illumination source configurable to illuminate a workpiece with strobed illumination in a field of view of the imaging system, wherein:
the machine vision inspection system comprises a control portion configured to:
periodically modulate a focus position of the variable focal length lens over a plurality of positions along a Z-height direction proximate to the workpiece; and
collect an image stack comprising respective images focused at respective Z heights, wherein each image of the image stack corresponds to an instance of strobed illumination timed to correspond with a phase of the periodically modulated focus position corresponding to a Z height within the image stack, and

the machine vision inspection system is configurable to:
determine a region of interest within a field of view for focus height measurement operations; and
determine a Z-height measurement for at least one portion of the region of interest based on analyzing the image stack to determine a Z height corresponding to a best focus position for the at least one portion of the region of interest.

13. The machine vision inspection system of claim 12 , wherein the imaging system comprises a tunable acoustic gradient index of refraction lens configurable to modulate the focus position of the imaging system.

14. The machine vision inspection system of claim 12 , wherein the imaging system comprises a camera system that comprises a global shutter system.

15. The machine vision inspection system of claim 14 , further comprising a focus height video tool, wherein the operations of periodically modulating a focus position of the imaging system over a plurality of positions proximate to the workpiece and collecting an image stack are selectable as an optional high-speed mode of the focus height video tool.

16. The machine vision inspection system of claim 12 , wherein the imaging system comprises at least one camera system that comprises an imaging array with an electronic rolling shutter system.

17. The machine vision inspection system of claim 16 , wherein:
the imaging system comprises a plurality of camera systems, each of which comprises an imaging array with an electronic rolling shutter system; and
each of the imaging arrays is configured in a staggered manner to receive image light offset relative to each other by a distance equal to a width of the at least one portion of the region of interest used for determining a best focus position.

18. The machine vision inspection system of claim 12 , wherein the camera system comprises an imaging array that is a one-dimensional line sensor.

Assignees

• Mitutoyo Corp

Inventors

• Gladnick Paul Gerard

Classifications

• G01B11/0608

  Height gauges · CPC title

• G06T7/571

  from focus · CPC title

• G06T2207/30164

  Workpiece; Machine component · CPC title

• G06T2207/10152

  Varying illumination · CPC title

• G06T2207/10016

  Video; Image sequence · CPC title