Human operators would find defects on a part by holding up the object and varying the angle to best reveal the defects. The reflection of a light in the background across the part is varied and the edge of the light is where the scratches are viewable. Spawning from how human operators would find defects on a clear material, the solution for this application was determined by engineers at Cyth Systems using a similar concept.

Various applications require a product to be defect- and scratch-proof when the product is released, which means inspections need to be performed on all products. Products with scratches are non-desirable. The scratched products often need to be discarded or repaired. A system needs to be developed to effectively view all the scratches on an entire surface, whether the surface is highly reflective or transparent because scratches to the surface could potentially cause unwanted oxygen/chemicals to penetrate the barrier. The challenge is even greater when scratches are in the coating of the part to be inspected, and both the part and the coating are clear.

To inspect the parts correctly, we would inspect the area at the edge of the reflection of a bright light. We only need to produce a line of light so we can use an off-the-shelf LED line light from Advanced Illumination, and only one horizontal line of the part would be ideal for inspection. Therefore, instead of using a standard 2-D camera to capture the image of the component, we can use a an off-the-shelf line scan camera from Basler. The part can be moved down a conveyor line and the line scan camera takes 2,000 to 3,000 images as the part moves through the scanning area. High resolution 2-D images of the parts can be made while the entire image was in the perfect zone of reflection for the light. The scratches and debris show up brighter than the rest of the part because they are deflecting light from the line scan camera to be on-axis with the camera, thus increasing the illumination to the camera at the location of the defects. The standard surface with no defects would be returning the non-illuminated levels of light.

The image acquisition and processing of the part revealing all the defects are viewable using off-the-shelf hardware and software from National Instruments. We used the Vision Acquisition software with an on-board GigE technology in the vision system to view the images. National Instrument’s Vision Builder for Automated Inspection (AI) is what we used to set our threshold levels for both brightness and size. The defects will show up brighter than the standard surface and some small defects may be acceptable in particular applications. Vision Builder for Automated Inspection also gave us the ability to control the part after inspection using measuring steps and sequences with standard outputs from an NI-DAQ board. If the component is defective, meaning a scratch on the surface is detected, the part will be rejected. If the component passes the inspection, then it can be used in further processing. The end result was a rapid application that allowed 100% inspection in a matter of seconds. This eliminated the need for a human operator, who would take a much longer time to only find defects visible to the human eye. This system also gives the user the capability to decide the threshold for the defects.
 
The use of a defect inspection system is useful in common applications from electronics and software to medical and life science devices. Especially for any product to be sold brand new, the absence of macroscopic defects is important since the product represents the company and their strive to perfection and high quality.