Philip A. Gulotta

March 11, 2015

5 Min Read
Vision System Upgrades Pharma Printing

Since 1975, the Food and Drug Administration (FDA) hasrequired that all prescription tablets or capsules have a unique identificationin terms of size, shape, color and imprint. Drug makers use the imprints toidentify the chemical substance and dosage as well as for promotional purposes.

Acceptable identification has traditionally been achieved bydebossing - pushing the image below the level of the product, embossing -pushing the image above the level of the paper, or printing. The problem withthese two approaches is that coating systems have a tendency to fill indebossed or embossed areas, sometimes rendering them unidentifiable, especiallyby those with less than perfect eyesight.

Tablet and capsule printing is normally accomplished byusing a hard roll engraved with the image to be printed. The hard roll contactsthe ink, then a wiper removes all of the ink except for that in the engravedarea. The ink is then transferred to a soft roll that contacts the tablet orcapsule. Vision System Upgrades Pharma Printing

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Inspection is critical because, if the wrong ink formulationis used, the ink might not adhere to the tablet, or the coating might flake offand contaminate the ink to the point that the printing becomes indistinct. Manualinspection has been used before, but with hundreds of thousands of tablets orcapsules being printed per hour, it's impossible to inspect more than a smallsample of product. This makes it impossible for the manufacturer to meet theFDA product identification regulations.

Ackley Machine originallyincorporated a vision system consisting of a camera, an image processing cardand image processing software running on a PC into its systems. The company wasabout to ship such a system to a customer when a computer failed and had to bereplaced. The computer ran on an older version of Windows that was no longeravailable so it had to be replaced with a computer that ran a newer version. Asa result, the new software, hardware and operating system each needed to bevalidated to meet FDA requirements.

To avoid encountering this problem again with next Windowsupgrade, Mark Ford, engineering manager for Ackley Machine, sought out a self-containedvision system that could easily be validated based on functionality alone.

Validation andTraining

Ford ended up selecting the Cognex In-Sight vision systembecause it provides a camera and image processing hardware and software withina protective enclosure. This small package approach makes it possible to writea short validation procedure, which also means that upgrading to a new model ofvision system is a relatively simple procedure. An added benefit is that higherperformance is achievable when multiple vision systems are used, because eachvision system processes its own images.

 Vision System Upgrades Pharma Printing

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The Ackley Machine Corp. adjustable angle ramp printer with vision inspection. Source: Cognex


After printing the tablets, Ackley Machine's latest tabletprinting machines drop them into the pockets of a carrier bar that holds up to24 tablets. The carrier bar moves under an array of four In-Sight visionsystems where each camera inspects six tablets. The vision system program firstuses a histogram tool to check for the presence of the light-colored tabletagainst the dark background of the carrier bar. If a tablet is present, thenthe vision system performs a print quality check.

The vision system's pattern recognition algorithm looks forthe printed image regardless of its location in the image acquired by thecamera. This eliminates the need for precision positioning of the camera ortablet. The system identifies and isolates the key individual features withinan object image and measures characteristics such as shape, dimensions, angle,arcs and shading. It then correlates the spatial relationships between the keyfeatures of the trained image to the run-time image, encompassing both distanceand relative angle. By analyzing the geometric information from both thefeatures and spatial relationships, the object's position can be determined withoutregard to the object's angle, size or appearance.

After being initially trained with an image of a goodquality printed table, the system then compares the good image to the mostrecently acquired image and rates the quality of the recently acquired imagebased on the match. The location of the center of the printing on the productthat was inspected is also determined to ensure the logo is centered on thetablet.

Damage Inspection

The next step for the system is to see if the tablet isbroken. A broken tablet shows up as several light-colored sections against adark background. It is identified by using the vision system's "blob" tool tolook for light-colored blobs smaller than the tablet. The final step is to lookfor a coating defect which can be identified as a smaller white spot, becausethe core of the tablet is white. The blob tool is used to search for whitespots.

The camera acquires the image and performs each of theseinspections and builds a binary word that contains the inspection results foreach of the six tablets in its field of view. The vision system sends theresults to the PLC that runs the machine. The vision system also sends eachinspection image to the corporate network where it can be called up by themachine operators or engineers.

The PLC then operates a vacuum system that picks up thetablets from the carrier bar and moves them to a discharge chute. Based on thesignal from the PLC, specific positions on the vacuum shoe are operatedindividually to either pick up or leave behind individual tablets. The tabletsthat have passed the inspection are picked up and placed in the dischargechute, while those that have failed remain in the carrier bar. In the next step,the tablets remaining in the carrier bar are dumped into a reject bin. Thisapproach makes it possible to eliminate in a positive manner individual tabletsthat fail inspection and ensure that only good tablets are passed along forpackaging.

The vision systems enable Ackley's machines to print andinspect more than 400,000 tablets per hour, which is "substantially faster thanany other tablet printing and inspection machine," Ford says. "The machine alsooffers a higher level of quality because it is able to reject individualtablets while other machines on the market can only reject batches of tabletswhich is wasteful when there is only one bad tablet in a batch."

PhilipA. Gulotta is salesengineer for Ackley Machine Corp.

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