2. Vision Lightning Design

Machine vision requires good image quality to make accurate and repeatable measurements. A good image shows the features of interest with sufficient contrast and signal-to-noise to differentiate them from other surrounding features and background. There are fundamental lighting principles that influence the overall image quality:

Geometry

The geometry relates to the spatial relationship between the workpiece, light, and camera. The image produced depends on the direction and angle of illumination to the workpiece and the camera.

Workpiece Characteristics

The workpiece's unique characteristics influence how light interacts with it. These characteristics include color, surface texture, shape, and reflectivity. The inspected features and the rest of the workpiece often have different qualities, and both are important considerations when designing a lighting solution.

Form Factor

Machine vision lights are available in various form factors differentiated by lighting configuration, shape, and output intensity. These determine how the light projects onto the sample. Different levels of uniformity, degree of collimation, and structured light patterns can affect an image. The light intensity must also be sufficient to overcome any unwanted contributions from ambient light.

Wavelength

The wavelength of light used is another important consideration as ultraviolet (UV), visible, and infrared (IR, NIR, SWIR) wavelengths can produce different images.

Imaging

The resolution, spectral response, and sarating.of the

the final image. In addition, the lenses and apertures can affect both the amount and the spectral and spatial distribution of the light reaching the image sensor. The sensor must receive sufficient light from the inspected obiect to minimize the noise in an image.

There are many factors to evaluate for in lighting applications to optimize image quality, including:

• The shape, size, material, color, texture/finish, etc. of the part to be inspected

• What features must be detected?

• Does the part appearance vary?

• Is the workpiece moving during image acquisition, and if so, at what speed?

• What is the desired camera exposure time (if known)?

• How is the workpiece presented to the camera? (orientation, tolerance, etc.)?

• What is the working distance and the size of the field of view?

• Are there any environmental constraints (such as dust/dirt, heat, washdown, size, etc.)?

This evaluation process provides the framework to choose the best lighting solution for the particular application from the extensive range of commercially available machine vision lighting configurations.