What is Machine Vision - How does it work?

A simple Three Word Definition: Computerized Light Measurement!
In order to get a good image- Create Contrast!
Sponsored by Nerlite

How does Machine Vision work with the camera?

We are actually re-mapping the image on our camera. With the right optics and lens we are putting the image directly on the CCD sensor. We are actually charging up each one of the pixels for the amount of light that we have mapped at the part. This will provide contrast.

To get a good image one must remember that cameras do not see objects

Cameras only see the light reflected from the objects toward them. Keep in mind that machine vision is all optically based.

The Three Machine Vision Elements that relate to Lighting:

There are three elements affecting proper lighting in a machine vision application

  1. The Light Collector
  2. The Light Source
  3. The Part and its Environment

The Light Collector Accomplishes the following:

  1. Vision System which processes signals
  2. CCD: Converting Photons to electrical charge (Spectral Response Curve)
  3. Lens: Acceptance of Light

How does the Lens affect the Acceptance of Light?

The lens is one of the areas that many people overlook when evaluating lighting applications. For example: If you are using real small field-of-views (high magnification) with extension tubes with a high F# we are losing light.

Do I want a higher F# on the lens to collect more Light?

No! The lower the physical F# on the lens, the better its ability to collect light.

How does the light source affect light?

We have two sources of light available:

  • Broadband – Which is white light composing of a variety of different wavelengths
  • Monochromatic Light – LED’s – with a very specific wavelength

How can monochromatic light benefit you in machine vision?

Think about a gauging application in which light passes through a lens or prism in trying to make a measurement of 2 lines. If I am using white light to do that, as the white light passes through the lens and tries focusing on an element, there is a certain dispersion angle because the lights different wavelengths are going to slow down at different speeds and will not converge at the exact same point. If we use one wavelength of light (Monochromatic -LED) products it will always focus at the same point.

The third area of importance is to control the Part and Environment

Many times ambient light in the environment will affect the machine vision results.

What are the best ways to control ambient lighting issues?

  1. If possible - Shield the application using a black box or make it matte
  2. Use Filters - We can choose a specific wavelength of light for our application. Can be used to combat ambient light by blocking out un desired light wavelengths.

What are long pass filters?

Long pass filters allows only wavelengths from a certain point up to pass through the lens. You can easily mount it with the filter thread of your lens. It screws right on the front of your lens and allows only certain wavelengths to pass through.

What is a good source for light filters?

http://www.machinevisionfilters.com

What is a common way to test for the amount of ambient light?

If you completely shut off your light source and you still see your part, you are getting a large amount of ambient light which must be controlled.

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