Air is life

A typical example of the performance capability of modern medical technology is provided by the Zeus Infinity Empowered (IE) anaesthesia machine from Dräger which makes the entire spectrum – from sophisticated ventilation therapy to the monitoring, integration of infusion technology and automation of sub-functions – possible with a single system.

Interchangeable and sterilisable turbine unit

With a turbine ventilator, the device can also be operated as a closed anaesthesia system with full rebreathing. The precise metering of the anaesthetic gas in the closed system reduces the uptake of the gas and anaesthetic. In addition, the turbine-based ventilation allows the patient to breath freely (spontaneous breathing) at all times. Both adults as well as children and newborns can therefore be adequately ventilated through the entire anaesthesia. The turbine unit, often identified as a blower unit, can be exchanged with ease when necessary and is autoclavable, i.e. it is sterilised after intensive treatment with hot steam at 134 °C.
However, high demands are put on the used components as the turbine, drive and co. must withstand the hot steam. The choice of material is in no way trivial. All components installed in the turbine unit may only be made from biocompatible materials as they come into direct contact with the breathing air of the patient. Furthermore, compact dimensions are required so that the unit can be well integrated into the anaesthesia machine and is easy to handle when replacing and cleaning. A high power density for the motor used is also necessary – in addition to bio compatibility and reliability.

Challenging requirement profile

These requirements cannot be realised with “off the shelf” components. “We have finally found a competent partner for the development of the turbine unit for our Zeus IE in FAULHABER who have won us over not only with their technical knowledge of drives but also their system expertise,” rejoices Torsten Theede, Global Commodity Manager Electronics at Dräger. “During development, we worked together very closely from the beginning and now the specialists from Schönaich provide us with the entire ready-to-install unit which consists 100 % of components that have been specially tailored to our application.”
The bldc motor for blower unit is the basis for the drive. The brushless motors from the FAULHABER program are designed for extreme operating conditions and are therefore happily used anywhere where high reliability, precise function and a long service life are demanded. Typical features also include very smooth-running operation, low audible noise, high performance and dynamics in a compact size. Nevertheless, the bldc motor for blower unit that was needed still posed a major challenge to the developers: after all, a little powerhouse was needed that accelerates in milliseconds and slows down again just as quick. “This is important so that the patient is not forced to breath against the machine,” explains Theede. “The blower unit and with it the drive must therefore react extremely quickly and precisely.”

The little powerhouse with special features

The challenges have been met and the result is impressive. The tailor-made bldc motor for blower unit is housed in a robust stainless steel housing and is only 24 mm in diameter and 46 mm long. Still, to come to the desired performance data, the magnets and sheets used had to be optimised. That only biocompatible lubricants and adhesives could be used and the entire unit must be autoclavable, made the selection of material a challenging task. For example, when selecting the ball bearings, the developer worked together with external specialists in order to find the optimal material pairing with biocompatible lubricants for extremely high speeds.
The system is also impressive from a mechanical point of view: the impeller pump, which generates the air current, is mounted directly onto the motor. The electrical connections are embedded into the external casting compound. Furthermore, an EPROM has been integrated into the casting compound from which the drive history and even the number of operating hours performed can be read, if necessary, in addition to the series number. The signals from the Hall sensors integrated into the motor are processed by the primary system controller which actuates the motor according to the anaesthesia and ventilation requirements.
The entire blower unit has a diameter of 120 mm and only is 220 mm long. “It has since performed very well in practical use,” rejoices Theede. “Collaboration has continued and the turbine unit for our Perseus A500 anaesthesia work station also originated from working together with the drive specialists from Schönaich. This system also offers sophisticated ventilation strategies which support the spontaneous breathing of the patients at all times and has also been employed successfully in many clinics for several years. “Of course, the tailor-made drive solution of using a bldc motor for blower unit also contributed to this”, concludes Theede.