Balanced focus system and method for achieving optimal focus of different areas of an object that are concurrently imaged

• US 5,768,401 A
• Filed: 08/02/1995
• Issued: 06/16/1998
• Est. Priority Date: 08/02/1995
• Status: Expired due to Term

• Current Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Original Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Inventors: Csipkes, Andrei, Palmquist, John Mark
• Primary Examiner(s): Johns, Andrew W.
• Application Number:
  US08/510,219
• Time in Patent Office: 1,049 Days
• Field of Search: 382/108, 382/141, 382/148, 382/255, 382/284, 348/95, 348/218, 348/345, 348/349, 356/4.03, 356/4.04, 356/4.05, 356/125, 356/127
• US Class Current: 382/255
• CPC Class Codes: G02B 6/3843 with auxiliary facilities for movably aligning or adjusting the fibre within its ferrule, e.g. measuring position or eccentricity testing the alignment of axes, including eccentricity, G01B11/27
• CPC Class Codes: G02B 6/4221 involving a visual detection of the position of the elements, e.g. by using a microscope or a camera
• CPC Class Codes: G02B 6/4227 Active alignment methods, e.g. procedures and algorithms
• CPC Class Codes: G02B 7/28 Systems for automatic generation of focusing signals

Abstract

A balanced focus system and method achieve optimal focus of different areas of an object that are concurrently imaged and then combined to form a combined image. The balanced focus method is particularly suited for, but not limited to, use with an automatic inspection system for contactlessly measuring at an endface of an optical fiber termination the eccentricity of an optical fiber core relative to a theoretical ideal center of an alignment surface of the termination. The inspection system has an imaging system with a feature imager and one or more boundary segment imagers but preferably four in number, a focus adjustment mechanism (FAM) for adjusting the position of the imagers relative to the imaged object along an optical axis, and a machine vision system for receiving image data from the foregoing imagers and configured to control the FAM. The feature imager is positioned to capture an image of the feature (e.g., fiber core endface), and the one or more boundary segment imagers are positioned to capture an image of a corresponding boundary segment of the object (e.g., termination endface). The machine vision system determines the eccentricity based upon the feature image and the one or more boundary segment images. Significantly, the machine vision system employs the balanced focus system and method to achieve an optimal focus position for the imaging system based upon a series of combined images and a statistic S that is computed for each of the sampling locations.

Claims

1. A balanced focus system for achieving optimal focus of different areas of an object that are concurrently imaged and then combined to form a combined image, comprising:

an optical system for concurrently capturing respective area images of said different areas of said object;

a focus adjustment mechanism adapted to change a focus of said optical system relative to said object;

a camera adapted to receive said area images and combine said area images to form said combined image so that said area images appear as portions of said combined image;

a machine vision system configured to control said focus adjustment mechanism and to receive from said camera and store a series of combined images, each of said combined images of said series being captured during a different focus of said optical system; and

a balance focus means associated with said machine vision system for performing a gradient analysis on each of said respective area images and for determining an optimal focus for said optical system based upon said series of said combined images.

2. A balanced focus system for achieving optimal focus of different areas of an object that are concurrently imaged and then combined to form a combined image, comprising:

and optical system for concurrently capturing respective area images of said different areas of said object;

a focus adjustment mechanism adapted to change a focus of said optical system relative to said object;

a camera adapted to receive said area images and combine said area images to form said combined image so that said area images appear as portions of said combined image;

a machine vision system configured to control said focus adjustment mechanism and to receive from said camera and store a series of combined images, each of said combined images of said series being captured during a different focus of said optical system;

a balanced focus means associated with said machine vision system for determining an optimal focus for said optical system based upon said series of said combined images;

means for defining search areas in each of said combined images that encompass and correspond with said area images;

means for identifying pixel locations in each of said search areas that exhibit a maximum gradient and that exceed a predetermined threshold;

means for determining a number of pixel locations that are identified for each of said search areas to produce pixel sums corresponding to said search areas respectively;

means for computing a statistic for each of said sampling locations by mathematically combining said pixel sums; and

means for determining an optimal sampling location for said optical system based upon a local minimum of said statistic.

3. The system of claim 2, wherein said means for computing said statistic is configured to add together absolute values of differences between each pairing of said sums.

4. The system of claim 2, wherein said different areas are four in number and wherein said statistic is determined by said means for computing by the following equation:

S=|a-b|+|a-c|+|a-d|+|b-c|+|b-d|+|c-d|, where said statistic is denoted by S and said pixel sums are denoted by a, b, c, and d.

5. A balanced focus system for achieving optimal focus of different area of an object that are concurrently imaged and then combined to form a combined image, the object being imaged by an optical system having an objective, comprising:

(a) means for generating a series of combined images by the following steps;

(1) means for moving said objective incrementally along an axis relative to said object;

(2) means for concurrently capturing respective images of said different areas of said object with said optical system when said objective resides at various sampling locations along said axis; and

(3) means for combining said respective images corresponding with particular sampling locations of said objective so that said respective images appear as portions of each of said combined images; and

(b) means for determining an optimal focus position for said optical system along said axis based upon said series of said combined images; and

wherein said determining means further includes a means for performing a gradient analysis on each of said respective images.

6. A balanced focus system for achieving optimal focus of different areas of an object that are concurrently imaged and then combined to form a combined image, the object being imaged by an optical system having an objective, comprising:

(a) means for generating a series of combined images by the following steps;

(1) means for moving said objective incrementally along an axis relative to said object;

(2) means for concurrently capturing respective images of said different areas of said object with said optical system when said objective resides at various sampling locations along said axis;

(3) means for combining said respective images corresponding with particular sampling locations of said objective so that said respective images appear as portions of each of said combined images;

(b) means for determining an optimal focus position for said optical system along said axis based upon said series of said combined images according to the following steps;

(1) means for defining search areas in each of said combined images that encompass and correspond with said image areas;

(2) means for identifying pixel locations in each of said search areas that exhibit a maximum gradient and that exceed a predetermined threshold;

(3) means for determining a number of pixel locations that are identified for each of said search areas to produce pixel sums corresponding to said search areas respectively;

(4) means for computing a statistic for each of said sampling locations by mathematically combining said pixel sums; and

(5) means for determining said optimal focus position based upon a local minimum of said statistic.

7. The system of claim 6, wherein said means for computing said statistic includes a means for adding together absolute values of differences between each pairing of said sums.

8. The system of claim 6, wherein said different areas are four in number and wherein said means for computing said statistic includes a means for calculating the following equation:

S=|a-b|+|a-c|+|a-d|+|b-c|+|b-d|+|c-d|, where said statistic is denoted by S and said pixel sums are denoted by a, b, c, and d.

9. A balanced focus method for achieving optimal focus of different areas of an object that are concurrently imaged and then combined to form a combined images the object being imaged by an optical system having an objective, comprising the steps of:

(a) generating a series of combined images by the following steps;

(1) moving said objective incrementally along an axis relative to said object;

(2) capturing concurrently respective images of said different areas of said object with said optical system when said objective resides at various sampling locations along said axis; and

(3) combining said respective images corresponding with particular sampling locations of said objective so that said respective images appear as portions of each of said combined images;

(b) determining an optimal focus position for said optical system along said axis based upon said series combined images; and

wherein said determining step includes the step of performing a gradient analysis on each of said respective images.

10. A balanced focus method for achieving optimal focus of different areas of an object that are concurrently imaged and then combined to form a combined image, the object being imaged by an optical system having an objective, comprising the steps of:

(a) generating a series of combined images by the following steps;

(1) moving said objective incrementally along an axis relative to said object;

(2) capturing concurrently respective images of said different areas of said object with said optical system when said objective resides at various sampling locations along said axis;

(3) combing said respective images corresponding with particular sampling locations of said objective so that said respective images appear as portions of each of said combined images;

(b) determining an optimal focus position for said optical system along said axis based upon said series of said combined images according to the following steps;

(1) defining search areas in each of said combined images that encompass and correspond with said image areas;

(2) identifying pixel locations in each of said search areas that exhibit a maximum gradient and that exceed a predetermined threshold;

(3) determining a number of pixel locations that are identified for each of said search areas to produce pixel sums corresponding to said search areas respectively;

(4) computing a statistic for each of said sampling locations by mathematically combining said pixel sums; and

(5) determining an optimal sampling location for said objective based upon a local minimum of said statistic.

11. The method of claim 10, wherein said statistic is determined in step (b)(4) by adding together absolute values of differences between each pairing of said sums.

12. The method of claim 10, wherein said different areas are four in number and wherein said statistic is determined in step (e) by the following equation:

S=|a-b|+|a-c|+|a-d|+|b-c|+|b-d|+|c-d|, where said statistic is denoted by S and said pixel sums are denoted by a, b, c, and d.