Voice Coil Controlled Inspiration and Expiration Valves

Abstract: This master thesis was performed at Maquet Critical Care located in Solna, Stockholm. Maquet Critical Care is a market leader in high performance medical ventilators. A ventilator is a medical device that helps patients to breathe. Two of the most vital components of a ventilator are the valves that are closest to the patient. These are the inspiration valve and the expiration valve. The main purpose with this thesis is to get, theoretical as well as practical insights into the inspiration and expiration valves to be developed. On top of this a ventilator using the developed valves was to be developed. On the base of theoretical knowledge, the aim of the thesis is to achieve a set of valve and ventilator requirements on developed prototypes. On top of this the thesis should be able to deliver advice and guidelines for possible future research on these valves. In order to use valves in a ventilator there were many requirement posed on the valves. These requirements included flow characteristics, power consumption, dynamic performance and cost. The methodology used included a pre study of fluid dynamics, valves and ventilators. Initial valve designs were developed with the use of flow simulations. The valve models were manufactured and tested as well as being compared to the flow simulations. The actuators used for the valves were voice coils. In this thesis a standard actuator was used to control the valves but in order to get the maximum performance an investigation into optimized voice coils were performed. In order to get insight into the control of the valves, a dynamic model of the voice coil were developed. This model was verified to have the same bandwidth as the measured voice coils and valve assembly. In order to realize a pressure controlled ventilation mode the inspiration valve and expiration valve were synchronized. The control algorithms were implemented in Matlab/Simulink with dSPACE. The tested requirements were fulfilled, resulting in valves that have a maximum power consumption of 2 Watts. The pressure controlled ventilation was executed on the developed demonstration ventilator. The performances of this ventilator were desirable and fulfilled the ventilator requirements. Two specializations topics have also been investigated, in the areas of flexure based voice coil suspension and gas modeling.