Concept of Shutter Speed

Warning on using high-speed shutters

As the shutter speed is increased, the required exposure time shortens and in many cases the aperture needs to be opened more to let in more light. Unfortunately, a wider aperture leads to a smaller depth of fi eld (range in focus). In the worst case, a sheet that is moved up and down, a limited depth of fi eld can lead to a blurry image and adversely affect the inspection results.

Image with aperture open (Range in focus is narrow.) Image with aperture closed to adjust exposure (Range in focus is wide.) Shutter speed is increased Aperture is opened to compensate for darkness Depth of fi eld becomes smaller Sheet moves up and down, going out of focus Flaws are skipped

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Ensuring successful inspections on a high-speed line.

It is important to determine the optimum settings.

Determine the shutter speed.
Determine the aperture.
Determine the necessary amount of light.

These steps aid in maintaining the highest level of stability.

Stable detection! Shutter speed [higher is better] Illumination[brighter is better] Aperture [narrower is better]

Summary

When determining the best method for in-line flaw inspection, keep the following points in mind.

First determine the minimum detectable size of the object; 2 or more pixels within the field of view.
Determine the speed that can be supported relative to the minimum detectable size obtained for:
a line with intermittent feed; determine the processing speed of the machine vision system.
a line with continuous feed; determine the shutter speed and then the processing speed of the machine vision system.
When capturing images on a high-speed line, pay close attention to the shutter speed, level of illumination, and lens aperture.