Advanced illumination showcases its solution in solving the lighting for keg production inspection.
Concave, convex and cylindrical objects present a challenge for machine vision inspections, especially when constructed of a highly reflective or specular material such as aluminium or steel. When faced with inspections involving complex geometrical shapes, engineers have the difficult task of creating an appropriate and robust illumination solution that does not cause blooming or shadows, both of which result in inaccurate readings by the vision system.
Inspection of an aluminium beer keg is a challenge for machine vision. Advanced illumination was tasked by a regional camera distributor to provide the solution for a two-part inspection of beer kegs – before and after refilling.
In the first inspection, the vision system needed to check the top of the keg for roundness, rejecting any dents or damage that might indicate a potential weakness or leak in the keg. Although the concept behind the inspection is simple, the geometry creates difficulties when lighting is applied. The tubular-shaped uppermost rim reflects the most light with considerable intensity fall off as the surface
curves away from the camera. Increasing light intensity, to adequately illuminate the portions further from the vision system, results in excessive glare.
The AI solution
After testing several direct light sources, which resulted in significant blooming or uneven lighting, a diffuse dome light was tested. Unlike spotlights, linear arrays or ring lights, diffuse light is created by aiming light away from the object of the inspection into the reflective surface of a dome. Once it strikes the dome surface, light is scattered, losing its directional nature, thereby decreasing the potential for creating glare or harsh shadows. Initial diffuse light tests appeared promising, but the lights were too small to image the entire diameter of the keg in a single inspection.
To compensate for the keg’s size, AI designed and built a customised 18-inch square diffuse light. Populated with the new generation of high current LEDs, the diffuse light provided sufficient illumination to allow the vision system tools to determine the roundness of the rim. For this inspection routine, a 4mm focal length lens was used.
The second part of the inspection, performed after refilling, required the vision system to inspect the keg’s ball valve for signs of leakage. The recessed valve comprises a black rubber seal and a stainless steel ball that, when functioning properly, creates a tight seal that is broken only when the tap is inserted.
Once again applying the diffuse dome, the vision system – with a 25mm focal length lens – was able to detect the presence of liquid. The result was in part due to the foaming that occurs when the beer escapes, but also because the presence of liquid alters the reflectivity of the stainless steel, changing the average intensity response in the area of the valve.
This application resulted in a still-popular dome, being produced in a revised form. The success of the diffuse dome encouraged Ai to expand on other Full Bright Field Diffuse Lights, such as the FD Series and FX Series Flat Diffuse Lights, which provide space-saving illumination solutions for objects with high reflectivity.
Other Diffuse Lights available from Advanced illumination include larger hemispherical domes, such as the DL080 Large Dome Light and DL180 Extra Large Dome Light, along with cylinder-shaped specialty diffuse lights for use with area scan cameras (DL067 Wide Linear Diffuse Lights) and line scan cameras (DL151 Narrow Linear Diffuse Lights).