May 2020

38 n PHARMACEUTICAL AND MEDICAL May 2020 www.drivesncontrols.com Automated leak detection boosts quality on asthma inhaler line P ressurised metered-dose inhaler (pMDI) cannisters are used by asthma sufferers to deliver vital respiratory drugs. During production of these cannisters, they are filled with an optimum level of liquefied gas under pressure, then tested for gas leaks. Traditionally, the cannisters, manufactured in vast volumes, have been batch-tested. Manual off-line leak inspections are conducted as an end-of-line test on one or a few samples from each batch. If a single canister is defective, the entire batch may need to be scrapped. Conversely, if the sample examined passes the quality control test, there could still be defective items in the batch. A manufacturer of these asthma cannisters wanted to achieve 100% testing, so that it could scrap only defective containers. It has implemented an automated system based on a carousel conveyor that runs at constant speed and handles 180 cans per minute. There are 86 cavity holders, known as “pucks” that hold the individual cannisters and transport them through a tunnel, which concentrates any gas leakage by sealing the tops and bottoms of the pucks. Two Mitsubishi Electric four-axis Scara pick-and- place robots, controlled by a Q Series PLC, position the cannisters correctly into the moving pucks and remove them at the end of the process. The cannisters are taken from an upstream conveyor and moved onto an infeed conveyor with upstream machine monitoring and queue control to ensure synchronisation. The pMDIs are placed into the individual pucks, six at a time, and transported on the carousel conveyor, with queue control maintaining back-pressure to prevent misfeeds. The carousel conveyor moves the pucks through a tunnel containing a PLC- controlled Cascade CT300 gas leak detector. Before entering the tunnel, the air around the pMDI cannister is purged, and the pucks are then sealed individually. The location of the individual canisters is identified before the gas analyser removes a sample from the puck to measure for any leakage of propellant gas. The results are communicated to an industrial PC running Mitsubishi’s Maps Scada software, which analyses the data. A PLC logs the status of the individual pMDI tests. A high-speed data-logger module synchronises the sampling function with the sequence scan. The PLC interacts directly with the gas analyser, and logs the results of each individual pMDI test, as well as offering exportable reports of canister analytical data for each batch. The second robot moves the pMDIs from the pucks to a constant-speed outfeed conveyor, and their location is tracked. Defective pMDIs are removed at a reject station on the outfeed conveyor and collected in a reject bin with level detection. The number of cannisters which pass is monitored, as well as the number of rejects, with an alarm raised in the event of excessive numbers of rejects. Downstream machine monitoring enables smooth flow of returning MDIs, with optional downstream queue switch to prevent build- back onto the production conveyor. The Maps software produces an exportable report of analytical data for each batch, stored in an SQL database and accessed via the IPC’s touchscreen display. The system was implemented by Optimal Industrial Automation, which specialises in process control and system integration for pharmaceutical and life-science applications. The robots in the pMDI application are synchronised by the iQ PLC. By executing command processes in nanoseconds, it allows the robots to handle moving canisters without the need to stop the conveyor, thus avoiding any interruptions. “Synchronisation on this line is critical because the canisters are unstable and may topple unless the motion of the robots and conveyors matches perfectly,” explains Optimal director, Martin Gadsby. The articulated Scara robots are rigid in the Z-axis allow slight variations of position in the X-Y plane. The Scara robots are generally faster than comparable Cartesian robot systems and the controlling software requires inverse kinematics for linear interpolated moves. n A pharmaceutical manufacturer has improved leak detection 30-fold on a line that produces asthma inhalers by introducing an automated quality control system that includes two Scara robot arms. One of the two four-axis Scara robots that position the inhaler cannisters into the moving pucks and place items that pass through a leak-testing tunnel onto an outfeed conveyor. A carousel conveyor transports the pucks through a tunnel containing a gas leak detector. Any pMDIs found to be leaking are removed at a reject station on the outfeed conveyor.