Method and apparatus for focusing an optical inspection system
AssigneeCognex Technology and Investment Corporation
InventorsIvan Bachelder, Yusuf Akgul, Prabhav Morje, Juha Koljonen
Life of this patent
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Abstract
A method is provided for obtaining a focused image of an object in an application of machine vision in an optical inspection system. A coarse focus setting is first obtained by maximizing a coarse feature sharpness measurement performed on an image of the object of inspection. Then, a fine focus setting is obtained by maximizing a fine feature sharpness measurement performed on a portion of an image of the object of inspection. Finally, the fine focused image can be further analyzed, inspected, or otherwise processed.
Claims25
A method for determining an optimal focus setting of an optical imaging system, the method comprising:
- in a range of coarse focus settings;
- providing a first image of an object at a coarse focus setting;
- measuring a coarse feature sharpness response of the first image;
- setting a coarse focus to provide a maximum coarse feature sharpness response of the first image;
- in a range of fine focus settings from the coarse focus;
- providing a second image of the object at a fine focus setting, the second image having a fine focus area;
- measuring the fine feature sharpness response of the fine focus area;
- and
- setting the optimal focus to provide a maximum fine feature sharpness response.
An apparatus for focusing an optical inspection system, the apparatus comprising:
- an object having a structure and a surface;
- a camera for acquiring an image of the object;
- focusing means for adjusting a focal distance between the camera and the object;
- machine vision processor coupled to the camera, comprising;
- a) coarse feature sharpness measuring means, in cooperation with the focusing means, adapted to measure a coarse feature sharpness of at least a portion of the structure in the image;
- and
- b) fine feature sharpness measuring means, in cooperation with the focusing means and the coarse feature sharpness measuring means, adapted to measure a fine feature sharpness of at least a portion of the surface in the image.
A method for determining an optimal focus setting of an optical imaging system, the method comprising:
- in a range of coarse focus settings;
- providing at least one first image of an object at a coarse focus setting;
- measuring a coarse feature sharpness response of the at least one first image;
- setting a coarse focus to provide a maximum coarse feature sharpness response of the at least one first image;
- in a range of fine focus settings from the coarse focus;
- providing at least one second image of the object at a fine focus setting, the at least one second image having a fine focus area;
- measuring the fine feature sharpness response of the fine focus area;
- and
- setting the optimal focus to provide a maximum fine feature sharpness response.
A method for obtaining an optimally focused image of the surface of an object, the method comprising:
- acquiring an image of the surface of the object;
- localizing a coarse feature of the surface of the object;
- performing a coarse feature sharpness measurement on the coarse feature;
- using the coarse feature sharpness measurement, determining a maximum coarse feature sharpness measurement;
- using the maximum coarse feature sharpness measurement, acquiring an image of a region of the surface of the object;
- performing a fine feature sharpness measurement within the region;
- using the fine feature sharpness measurement, determining a maximum fine feature sharpness measurement;
- and
- using the maximum fine feature sharpness measurement to determine an optimal focus setting for obtaining an optimally focused image of the surface of the object.
Dependencies are inferred from the claim text.