Inspection system prints and verifies drug tablets

Engineers at Ackley Machine Corp. (Moorestown, NJ, USA) have developed a tablet printing machine based around Cognex (Natick, MA, USA) In-Sight vision systems that not only prints identification marks on tablets but also inspects them to ensure their integrity.

After printing the tablets, the machine drops them into the pockets of a carrier bar that holds up to 24 tablets. This then moves under an array of four Cognex In-Sight vision systems where each camera inspects six tablets. A histogram tool confirms the presence of the light-colored tablet against the dark background of the carrier bar. If a tablet is present, then the vision system performs a print quality check.

A PatMax pattern-recognition algorithm looks for a printed image, identifies and isolates key individual features, and correlates the spatial relationships between the key features of a trained image to the run-time image. The algorithm compares a good image to the most recently acquired image and rates the quality of the recently acquired image based on this match. The PatMax algorithm also returns the location of the printing's center to determine how well the logo is centered on the tablet.

Next, the tablet is checked to see if it is broken. A blob tool looks for light-colored blobs against a dark background that are smaller than the tablet. The final step is to look for a coating defect, which can be identified as a smaller white spot.

The inspection results for each tablet are sent to a PLC that controls a vacuum system, which picks up the tablets that have passed inspection and places them in a discharge chute; failed tablets remain in the carrier bar and are dumped into a reject bin. The integrated vision system enables inspection of more than 400,000 tablets per hour.