Drive solutions for anaesthesia
4th Quarter 2017, This Week's Editor's Pick, Electrical switching & drive systems & components
There are many experiences we would happily do without. Operations under general anaesthetic are definitely one of them. Anaesthesia and ventilation systems are a critical part, and perfectly tuned drive solutions play a key role in these demanding systems. A typical example is provided by the Zeus Infinity Empowered (IE) anaesthesia machine from Dräger, which in a single system makes possible the entire spectrum – from sophisticated ventilation therapy to monitoring, integration of infusion technology and automation of sub-functions.
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 spontaneously at all times. The turbine unit, or blower unit, can be exchanged with ease when necessary and is autoclavable.
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 easily integrated into the anaesthesia machine. A high power density for the motor used is also necessary – in addition to biocompatibility and reliability.
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. The company has won us over, not only with its technical knowledge of drives but also its 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 totally of components that have been specially tailored to our application.”
The blower unit offers a brushless DC motor as a basis for the drive. The motors are designed for extreme operating conditions and are 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 drive that was needed for the blower unit still posed a major challenge to the developers. A little powerhouse was needed that accelerated in milliseconds and slowed down again just as quickly. “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 tailor-made brushless DC motor for the blower unit is housed in a robust stainless steel housing and is only 24 mm in diameter and 46 mm long. To meet the desired performance data, the magnets and sheets used had to be optimised. Only biocompatible lubricants and adhesives could be used and the entire unit had to be autoclavable, making 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 is only 220 mm long. “It has since performed very well in practical use,” says 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 the blower unit also contributed to this”, he concludes.
For more information contact David Horne, Horne Technologies, 076 563 2084, firstname.lastname@example.org, www.hornet.cc