DMC’s customer was dispensing small drops of chemical reagent into a well on a clear plastic medical device. The precise location and volume of the drop is critical for the performance of the microfluidics medical device. To ensure each drop was dispensed properly, the customer asked DMC to implement an automated vision inspection that confirms the location and size of each droplet. 

The droplets are clear and dispensed onto a clear plastic background. To provide contrast, the customer added fluorescein dye to the droplets. Fluorescein is an organic compound that fluoresces green when exposed to blue light. DMC exploited this fluorescent property by illuminating the droplets with a blue LED light and using a green filter in front of the camera. This caused the background to be dark with only the drops showing up brightly. The area of each droplet was determined using simple blob analysis tools. 

To ensure accurate positioning of the droplets relative to the device, a fiducial measurement was needed. DMC added a white light inside the vision system. The white light was controlled by a digital output on the Basler camera. For each device under test, DMC’s software acquired two images: a fiducial image illuminated using the white light, and an inspection image illuminated only by the blue light. Using the fiducial image, DMC’s software found the position and rotation of the current device under test and then calculated the expected positions of the droplets. The inspection image was analyzed to confirm that the drops were actually contained by the acceptable position boundary.  

Result data was logged to NI’s TDMS format for later analysis and traceability purposes. The software also provided the option to save each acquired image.