In the selection and configuration of lighting you can never deduce a single appropriate way of doing things, there are always several options, each of which has its own advantages and disadvantages.
This is due to the geometric properties (edge shapes and machining marks), optical properties (colour, reflection, gloss level, dispersion) and even chemical properties (condensation, oxidation, oil, coolant) of the material to be inspected. All these properties have a considerable influence on the lighting and selection setting options.
The brightness can be influenced by the directional properties of the light that emerges from the lighting:
● Diffuse lighting is suitable for incident light and backlight illumination where smaller surface failures in the structure of the material to be inspected must be repaired.
● Directional lighting due to its strong directionality can ensure that the pronounced directional properties of the material to be inspected are particularly well highlighted. Directed lighting is often used in incident light.
● Telecentric lighting finds its essential use in combinations with telecentric objects for contrast in representation of test materials.
● Structured lighting is used due to light structures; for example, for 2D image processing tasks in incident light.
In general, the adjustment of the illumination to the optical geometric properties of the object to be inspected should be carried out during the selection and configuration of the illumination.
Transparent materials can be inspected particularly well. If the materials are partially or completely transparent, the top and bottom cannot be separated because the components will be illuminated from the inside.
Difficulties with incident lighting usually occur at the edges of the material to be inspected, as edge properties influence the interaction between light and material considerably. For this reason, incident lighting is not suitable for metric measurements.
Many image processing applications have to resort to incident lighting due to the industrial environment:
● Pick & Place robots.
● Inspection of the components on the conveyors.
● Automatic assembly machines.
Backlighting allows for a better representation of the contrast, a sharper definition of the silhouette and the contours of the non-transparent components.
Many of the transparent or partially transparent components can also be inspected with telecentric backlighting. The same is true for applications that rely on precision, such as the metric system.
Backlighting is generally independent of the lighting distance for the material to be inspected and is therefore particularly suitable for high-speed image processing applications.
Despite their advantages, the possibility of applying lighting is usually limited by the fact that they are largely based on the design of the machine and therefore cannot always be implemented.
This type of lighting, the incidence of light from the direction of the camera illuminates the surface of the material to be inspected. The incident lighting scatters in all directions and only a small amount returns to the camera, so it looks dark.
Without the object to be inspected, the lighting appears dark because the light is out of the camera's field of view. Only when the material is within the field of view, the edges of the element and the work surface are illuminated so that the data is recognized.
● Application in color or black and white.
(It affects the choice of wavelength / light colours).
● Speed of the material to be inspected.
(Affects light output and flash).
● Size of the field to be illuminated.
(Effect on the size of the illumination and the type of light source).
● Maintenance costs.
(Affecting the selection / omission of certain light sources).
● Environmental conditions.
(It affects the size of the illumination, wavelength, color of the light, etc.).
On the other hand, there are numerous factors that influence the choice of lighting. Therefore, having experts to select the right lighting is a service that makes sense in terms of cost and time.
