Work Experience
Medical
ITL / Anaxsys Breath Monitor
This is a breath monitor for measuring the breathing rate of patients when they receive oxygen. It is designed for use in hospital and externally environments such as ambulances.
A coated ceramic sensor is mounted in the sensor assembly which is then attached to the oxygen mask. A custom connector reads the signal from the sensor. For hygiene reasons the sensor housing is clip on and disposable with rubber seals around the connector.
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A particular challenge was the multi-hinge clip mechanism. For convenience, the clip arm is fully integrated into the housing on both sides. This means for the clip to function three hinges are required on each side. Polypropylene was chosen as a material for its excellent ductile properties. The hinge design had to be tuned carefully by gradually taking metal off the mould tool over a number of sample runs.
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Another problem with the hinge was creep. If there was over-travel in the hinge it would deform permanently and the clip would fail. Careful detailing was required to reduce travel to safe limits.
To avoid cross contamination between patients, the sensor housing is single use (ie one per single patient) but it is not practical to replace the electrical connector. Great care was taken was make the connector safe, Seals made of thermoplastic elastomer were fitted around the sensor housing and around the sensor itself. The connector was over moulded with low pressure PVC, eliminating potential points of ingress. When it is not used the connector is cover with a rubber bung.
The housing was made in two parts which were also assembled with clips.
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The top half comprised all the hinges and the bayonet attachment into a single low cost, open-and-shut mould tool. There is a deep shut-off behind the bayonet which had to be engineered so it was just strong enough to survive high-pressure moulding without compromising the overall design