A larg blue chip Pharmaceutical company was purchasing a new custom machine to produce transdermal patches. These patches were being mass produced by the company at the rate of 900 patches per minute. Obviously the rate of manufacture was too high for human inspection so an automated solution was required.

 

The Pharmaceutical client engaged a Machine Vision company to undertake the integration of multiple automated Inspection stations to guarantee the quality of the product being produced. Part of the brief was that the system conform with CFIR Part 11.

 

 The vision system was a standalone system using the most up-to-date and tested machine vision components. The camera elements are a combination of 2Mpixel 1394 digital fire-wire cameras and Camera Link Line Scan cameras. These cameras were triggered to catch the product at the required location during the cam cycle sensor trigger from the Pouching machine.

  

High Level Description of System

The system consisted of a number of cameras with suitable lighting at a number of Stations which were integrated with the Poucher machine.  The machine Vision system consisted of:

A Main Control panel.

Station 1 which to check visual defects on the topside & underside of the patch, verify the print on the patch and check the presence and position of the slit release.

Station 2 which to check miscuts, missing or multiple patches and the position of the patch.

Station 3  to verify text detail and text position.

Station 4  which to inspect the upper side of the Pouch.

The poucher is a standalone piece of equipment operating in continuous motion designed to pouch individual Nicotine patches with the capability of rejecting out-of-specification patches / pouches using automatic inspection stations. It will process up to and including 300 patches per lane per minute.

As the reels are fed through the first two stations  to detect patch defects, reject patches are identified by the vision system which sends signals to the Poucher Control System shift register for downstream rejection.

Following inspection the reels are cross-wise cut into individual patches. These are fed through Station 3 which will detect mis-cuts, missing and multiple patches and the position of the patch. These defect patches are identified by the vision system which sends signals to the Poucher Control System shift register for downstream rejection.

The patches are placed into the pouch stock material and heat sealed. Station 4 checks the text details of the pouch. The sealed pouch is then fed through lane slitting and crosswise cutting stations to produce individual pouches. Station 27 will check for visual defects on the upper side of the pouch. Pouches marked for rejection in the shift register system are rejected into two reject containers (one for empty pouches, one for full pouches) using an air pulse.

The first station of the vision machine inspected the product for the following:

1.Bubbles, streaks and visible contamination

2.Print Analysis/Text Check

3.Wrinkles and Ripples

4.Dog Ears

5.Pen marks

6.Splice Tape

7.Missing Systems

8.Overlapped systems

 

In relation to the Print Analysis/Text check it was done in a format that required user input to effectively calibrate the system when the reels are changed. The setup phase helped ensure that the checks maintain consistency and accuracy in spite of an extremely variable print process.

The Machine Vision company spent numerous hours revisiting the issue of text check for another client's patches. Standard OCR/OCV approaches will not work because of the variability of the stamping/printing process. In effect this means variations in the width on characters and intensity of the print is probable. Therefore the pre defined models that might work for one reel would be incompatible with another reel. The text on both might be perfectly acceptable but if it is not within certain boundaries of the base model then it will fail. Therefore the software solution needed to have adaptability built-in.

This meant the use of an edge based character recognition tool rather than just a standard off the shelf OCR package. These tools have the advantage of being more adaptable but are slower and can cause cycle time issues in Hi speed applications. However it this instance where the font did not conform to a standard but was rather a 'stamp' it was ideal.

 

Another of the stations needed to measure the position of the actual patch on the backing material prior to being cut. The distance between the edge of the patch and the edge of the liner was critical in this instance. Also the material was moving quite fast, so it was necessary to strobe the lighting to avoid motion blur.

Also at high speeds which can be the norm in Pharmaceutial machine vision systems, digital cameras exhibit motion blur due to a latency in the CCD array. Therefore it was critical that the strobing was synchronised with the cameras. In most electronic cameras there is a trigger output for this purpose.

The CCD doesn't switch off immediately and will allow small amounts of light in even after the shutter is supposedly closed. So it's important that the light switches off as the shutter closes. Remember ambient light is not really an issue at these high speeds as the required light level at fast speeds is quite high.

 

Earlier in the site you will have seen my comments about the illumination required. Well, from the image you can see that the transition from one shade of grey to the next is easy to see with the naked eye. If this is the case then it makes it simple for the software to cope.

 

The Interface

All the individual stations send their key signals eg Pass/Fail, system healthy, etc directly to the poucher via digital I/O. Each PC is also connected to a single Master Host system via an ethernet switch. The User interfaces with the individual stations via a KVM switch, but all settings, system parameters etc are downloaded to the individual stations through the Master PC. This PC is also on the client's LAN, so that data on parameter changes, Pass/Fail data. alarms etc can be downloaded for use offline.

There is no direct communication between the User LAN and the individual stations.

The individual PCs are connected directly to the cameras and the Main Power Distribution Panel

The Primary Interface Panel contains an array of opto-isolators and connectors, which interface the Vision system to the Poucher.

A Profibus PLC  on the poucher generates timing signals for the Line Scan cameras. A PLC on the Vision system adjusts the frequency to the cameras as the machine speeds up and slows down. The frequency output from the PLC varies with the speed of the conveyor. This is used as a more robust alternative to an encoder.

 Master PC