Pharma Packaging Systems (PPS) based in Pershore, UK, specialise in packaging systems for the pharmaceutical industry. Primary business is design and manufacture of electronic counting systems for tablets and capsules, either standalone, or as part of an integrated packaging line. With over 50 years of experience in this sector and references worldwide PPS are considered a leading supplier of this technology.
Multipix Imaging, a distributor specialising in machine vision, has been working with Machine Vision Technology Ltd (MVT), Leamington Spa, since 2003. Multipix offering advice, supply and support of machine vision components which include assisting with application evaluation and loaning equipment to MVT when necessary. MVT are independent vision systems integrators which means they are totally free to choose the right vision system for each application. Their staff, individually, have up to 30 year’s experience in the Machine Vision business.
Vision provides competitive advantage
MVT were approached by PPS after they identified an opportunity to offer their customers the benefits of Machine Vision by creating an inspection solution for their existing range of counting and packaging machines.
The purpose of the inspection is to check for broken, partially formed or cross contamination (rogue tablets from another batch). In the pharmaceutical industry, cross contamination, if left undetected before it leaves the manufacturer can cause the whole factory to be shut down for a period in addition to crippling fines.
Key advantages of the PPS online inspection system:
- Verify it is the correct tablet so avoiding cross-contamination
- Measure length, width, area, completeness
- Verify colour
- Ensure quality
- Avoid product returns and the possibility of substantial fines/losses
- 80 images per second across 24 lanes of continuous tablet flow
PPS ideally wanted to work with a local company that also had the experience and capability of developing such a specialised system, MVT had previously developed a system for Schwartz Pharmaceutical, USA to inspect tablets and so the cooperation was formed.
Challenges to overcome
In general terms the bulk product (tablets or capsules) feed from a hopper onto vibrating trays that feed and separate the product and guide them along the stainless steel trays. As the tablets leave the end of the feed trays they pass through high speed infrared optical sensors that count the products in free fall. The products are counted with high accuracy, at high speed, into bottles that are indexed on a conveyor by a scroll drive system.
This innovation has been to place cameras above the final feed tray to inspect the tablets just before they are counted and bottled. As the tablets are vibrating they are often touching and moving irregularly and therefore the trays can present the tablets to the camera in any possible orientation.
Another challenge to overcome is the bright and reflective finish of the stainless steel tablet feed trays which cause the tablets to reflect in the channels of the tray. Therefore the challenge for the Vision system when measuring the tablet length, width, area and colour is to differentiate between actual product and its reflection.
Innovative tablet tracking and multiple inspections ensure robust results
Each camera positioned above the tray images 6 lanes of tablets. Each tablet is typically inspected ten or more times as it passes from top to bottom through the camera’s Field Of View (FOV). The main problem to overcome was the product appearing to be either good or bad at any one instant in time depending on which face it was presenting to the camera as it feeds. MVT spent over one year developing some very sophisticated tablet tracking software that tracks each individual tablet.
As the tablets leave the tray and get counted into a bottle the vision system outputs the tablet inspection result. Once the inspection returns a ‘good’ result for a tablet it is ‘locked-in’ as good, even if it then bounces onto an edge and so appears to be ‘bad’ in subsequent inspections. The tablet must be deemed ‘good’ in at least one image, otherwise it is ‘bad’, and when a bad tablet is detected the bottle will be rejected.
The vibratory feeders start and stop several times a minute and feed at varying rates to maximise the throughput into each bottle as the bottles index past. This continuous tracking of numerous tablets, with their associated inspection results, is therefore a real accomplishment.
The Vision System has to find every tablet in each image, predict where it will be in the next image and match its new position and orientation in the new image to be able to identify it as the same tablet and so individually track it, building up its good / bad history.
Looking ahead
The machines described above are based on standard PPS machines with modifications that allow integration of machine vision and are basically still tablet counting machines.
The latest MVT/PPS evolution is designed as a machine vision inspection system and has a flat belt tablet feeder between the last vibrating tray and the output of the machine. This means the tablets are lying flat and are evenly separated and this system is designed to reject individual tablets as they leave the belt based on the good/bad status of the tablet. This system will inspect the tablets for width, length, area and colour in addition to thickness and will ensure only good product is discharged for further processing. This system can inspect up to 10,000 tablets per minute but is scalable to suit any application.
Technologies used in this solution
For lighting MVT chose to use multiple LED arrays and selected GigeVision colour camera’s for the image acquisition into one industrial PC. MVTec’s Halcon image processing software forms the basis of Machine Vision Technolgy’s customised C# application code.
A typical feed rate is up to 2500 tablets per minute per 6 track feed tray.
