Solving daylight problems
During commissioning and in the following weeks it becomes clear whether the application works in an unimpeded manner in harsh every-day operation or if there are problems. Due to professional knowledge of such issues, the challenge can be met already in advance when planning and designing the machine vision inspection station.
A typical phenomenon is disturbance caused by variations in daylight. Glaring sunlight inciding through the skylight of a hall or just the regular room light can massively hamper the image processing.
Strategies to solve lighting problems
All strategies have the same approach of minimising the proportion of extraneous light. This can be accomplished by increasing the intended quantity of light or by reducing the extraneous light proportion.
- Increasing the proportion of intended light of light by using stronger illumination: It often becomes apparent that the problem can be solved by installing further, larger or stronger lighting. In particular, new LED lighting products often generate more light than products that have been available on the market for a longer time: If you use halogen or fluorescent illumination in incident light mode, you can simply increase the number of light spots or light tubes.
- Disturbing effects of light can also come from conventional fluorescent lamps, which have no electronic ballast and the lighting frequency of which is not synchronised with the camera frequency. Use electronic ballasts!
Video: 50-Hz flickering of fluorescent lamps in slow motion:
- The increase in LED power with the aid of a flash controller: The light output of an LED is proportional to the amount of electricity. Beyond certain values, however, damage is caused to the LED. However, since the LED lights are only required for few inspections per second, they can be clocked. In this case it is often possible to overflash the LED fourfold to fivefold, which then emit approximately 4x more light without being damaged.
- If these problems occur only after a longer operating time, dirt on optics or lighting can be a possible cause. In most cases, however, these problems come from aging effects. The timely replacement of the illuminants should be scheduled in the service plan of the plant.
- In the simplest case, the elimination of the extraneous light proportion can be achieved by housing the inspection area. A smoke-black dyed glass often helps, too. Please also keep the cover of reflective back and side walls in mind, if the camera station was not enclosed.
- By using certain light wavelengths in combination with colour filters or interference filters in front of the lens, extraneous light can also be eliminated. Typical is the use of an infrared camera lighting and a daylight elimination filter or red LED illumination and a filter that only passes the red wavelength range. Thus, larger proportions of sunlight or indoor lighting can partially or completely be eliminated.