Our experience over many years is, that this most critical element of a vision system is often underestimated. To select the appropriate illumination for a demanding task with the understanding of why different types of illumination are best suited for specific applications, requires experience and extensive knowledge. Often, even with this experience the only way to to gain confidence in the reliability of an approach is to undertake evaluation trials. At STEMMER IMAGING we have an evaluation laboratory with a wide range of illumination equipment allowing customers to either visit and experiment or send samples for us to undertake a free feasibility study.
A decisive factor when designing the illumination for an application is ensuring that changes in the environmental lighting do not affect the inspection results. If an application requires several stages of software preprocessing before the image can be analysed, the illumination should be re-evaluated, as optimising the illumination can often eliminate the need for costly and time consuming image manipulation and give a far better and more stable overall result.
Because cameras are much less versatile and flexible than the human eye, the illumination needs to be optimised, so that a camera can detect errors that the human eye can see even under poor conditions. Cameras do not see objects; instead, they only see the light reflected from them. By controlling the illumination, one can control how objects appear to the camera. For example, light is reflected differently from a ball bearing than from a flat white label or a printed circuit board and therefore different illumination techniques are required for each.
In the early days of vision, illumination systems were often hand-made for each application. Nowadays, rather than trying to design and develop custom illumination systems, there are many benefits to using off-the-shelf illumination solutions:
saves time, money and R&D resources, easy access to advice and support
Proven and reliable
lots of units are already in use, long service life, minimal maintenance
high quality units are available in scalable quantities
many different devices and techniques are available