Position inspection of stoppers in vials – with new laser measurement sensors

Laser sensor ZX-GT (Picture: Omron)

Maintaining the integrity of pharmaceutical products filled into vials is very important. The stoppers closing the vials are secured in place using a crimping cap. To prevent microbial contamination, the Annex 1 of the GMP (Good Manufacturing Practice) requires the inspection of the stopper position prior to the crimping with a measurement system. State of the art measurement solutions are systems using several cameras usually involving higher cost. The laser measurement system from Omron provides a reliable solution for best value for money.

Since March 1st, 2010 the following changes were made to Annex 1, GMP:
Paragraph 121. “Vials with missing or displaced stoppers should be rejected prior to capping. Where human intervention is required at the capping station, appropriate technology should be used to prevent direct contact with the vials to minimise microbial contamination”

The vials filled with powder or lyocake are fed to the capping and crimping machine on two asynchronous lines. Between the application of the rubber stopper and the crimping machine a system to inspect the correct position of the stopper had to be installed. Although there is a high probability that the mechanical layout of the crimping machine would push a not correctly positioned stopper in place, the Annex 1 now required the inspection of the stopper position prior to the crimping and the removal of vials with wrongly placed stoppers.

Initially a solution with vision systems with at least two cameras and background illumination per line was evaluated to ensure a 360° inspection. The installation of the 2nd camera between the lines was not possible due to space limitations. Alternatively a solution with a measuring laser system was evaluated.

The OMRON ZX-GT is a measuring laser light curtain and the sender and receiver could be mounted covering both lines. The configuration software configured the sender and receiver to achieve an accuracy of 5-10µm. The edge detection function allowed a detection of a horizontal edge vertically. The measurement was carried out vertically from the top end of the measurement system and the highest position of the stopper was measured. The decision threshold was then set appropriately. With a sampling rate of 0.5ms, every 0.5ms a new measurement of the position of the stopper is made. The measure profile of the stopper should be horizontal and if the stopper position is incorrect and e.g. slightly at an angle, then a measurement value higher than the decision threshold is acquired. Then automatically the line is turned off and the vial can be removed manually.

The calculated accuracy of the system is 5-10µm but due to vibrations of the conveyor belt, a minimum accuracy of the system of +/- 0.3mm was specified by the machine user. This proved to be no problem for the system using the ZX-GT. It is even possible to extend the system over more than 2 lines up to 500mm distance between sender and receiver.

Source: OMRON

Mail to Mr Gunnar Bischoff for more information

or find them online:
www.industrial.omron.eu