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	Machine Vision Systems

Lighting Techniques

	Major Illumination Types
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Information About Lenses

	Lens Basics
	Lens Selection
	Lens Characteristics

Image Processing Techniques

	Major Image Processing Methods
	Grayscale Edge Detection
	Normalized Correlation Search
	Binarization Stabilization Technique
	Binarization Application Examples
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Examples of Technique Application

	Coated Glossy Surface, Engraved Mark Inspection
	Detection of Scratches and Chips on a Low Contrast Surface
	Detection of the Dimensions and Shape of Transparent Objects
	Detection of Concave and Convex, Print on Curved Surface, and Contamination

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	Machine Vision Systems

Lens Selection

Relation between the WD, Visual Field, and Focal Distance

The focal distance of lenses for the image processing sensor normally ranges between 3.5 and 75 mm; excluding special purpose lenses. As a rough guideline, a lens with a focal distance of 3.5 mm is suitable for short distance, wide-field objects. While a lens with a 75 mm focal distance is suitable for long distance targets.

The working distance (WD) and the size of the visual field is determined by the focal distance of the lens and the size of the CCD as expressed below:

WD: view angle = focal distance: CCD size

The CCD size is fixed according to the type of camera used.
For normal image processing, 1/3 type with a vertical length of about 3.6 mm is used.

For example, in order to view a 45 mm target 200 mm away, the focal distance is calculated as 200 mm x 3.6 mm/45 mm = 16 mm. Therefore, a lens with a focal distance of 16 mm is suitable in this case.

Select a Lens Using a Visual Field Graph

The graph on the left (visual field graph) shows the relationship between the focal distance, the working distance (WD), and the visual field. A suitable lens can be determined based on the intersection of WD and visual field. If an object is placed at a distance shorter than the minimum focal distance of the lens, attach a close up ring or spacer for a close shot. The dotted lines in the visual field graph indicate the size of the close up ring.

For example, by attaching a 50 mm photograph ring to a 50 mm lens, an image with visual field of 3 mm can be obtained at a working distance of 90 mm.

Macro Lens for High Magnification Images

Detecting a mark on a liquid crystal substrate

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Lens Selection

Lens Selection

Relation between the WD, Visual Field, and Focal Distance

The working distance (WD) and the size of the visual field is determined by the focal distance of the lens and the size of the CCD as expressed below:

WD: view angle = focal distance: CCD size

The CCD size is fixed according to the type of camera used. For normal image processing, 1/3 type with a vertical length of about 3.6 mm is used.

Select a Lens Using a Visual Field Graph

For example, by attaching a 50 mm photograph ring to a 50 mm lens, an image with visual field of 3 mm can be obtained at a working distance of 90 mm.

Macro Lens for High Magnification Images

The CCD size is fixed according to the type of camera used.
For normal image processing, 1/3 type with a vertical length of about 3.6 mm is used.