Miniaturization in drive technology continues to throw up new advances in medical technology. Miniature microdrives have already proved their worth in countless medical applications. Typical examples are mini blood pumps, inhalers, volumetric infusion pumps and blood sugar meters.
The dwarves among the electrical drives are becoming smaller and smaller, yet ever more powerful and reliable. The compact drive system specialists at Faulhaber in Schönaich near Stuttgart are certainly playing their part in this trend. For instance, the worlds smallest brushless DC motor, with a diameter of just 1.9 mm, is a Faulhaber innovation. Dr. Fritz Faulhaber laid the foundation stone for this technical advance when he developed the self-contained coil for DC micromotors over 50 years ago. Today the company offers a comprehensive range of miniature drives for all kinds of different application areas.
One example of the performance capability and versatility of these miniature drives is an intracardiac blood pump used in heart surgery. The Helmholtz Institute for Biomedical Systems at the Technical University of Aachen developed the Impella system as an alternative to conventional cardio-thoracic machines. This effectively reduces heart-bypass operations to minimally invasive surgery. One pump each is inserted into the right and left chambers of the heart via the arteries and veins and positioned directly within the heart. The pump drive, a brushless, electronically commutated DC motor, then achieves remarkable feats:
with an external diameter of just 6 mm and a stator length of 18 mm, it takes over the role of pumping the heart at a speed of 33,000 U/min.
The drive is based on a self-contained coil and essentially consists of a three-phase winding and bi-polar permanent magnet. The retroactive generator voltage is measured and evaluated to determine the position of the rotor. This eliminates the need for any reverberation sensors. The motors achieve a very high level of effectiveness as they have been specifically modified to meet the delicate demands of the Impella project. The pressure sensors required for use in the chambers of the heart are merely 300 µm thick and installed in an external recess of the motor housing. In the case of the Impella system, the outstanding reliability, compact dimensions and favourable price-benefit ratio of the drive system are particularly beneficial in such a single-use medical device.
