Bearingless Twin Drive as Axial-Flow Pump Application

This paper presents the concept, design, and prototyping of a novel axial-flow pump system based on a bearingless twin drive configuration. Bearingless motors eliminate the need for mechanical bearings by utilizing magnetic forces for rotor suspension and torque generation, making them highly suitable for compact, high-reliability applications. The proposed system employs two bearingless motors on a shared hollow-shaft rotor to achieve five degrees of freedom actively controlled, with the axial direction passively stabilized by magnetic reluctance forces. The system targets low-power applications, operating at 5,000-10,000 rpm with a torque of 15-40 mNm and constrained to a compact geometry with an outer diameter below 50 mm. The study investigates optimal winding topologies and motor configurations using analytical and numerical methods. A comprehensive analysis of five- and six-phase systems with varying stator slot/rotor pole combinations was performed to evaluate torque and suspension force capability, considering non-overlapping concentric winding schemes to minimize axial length. Geometry optimization was carried out using finite element simulations, focusing on maximizing torque and suspension force while reducing losses and destabilizing forces. Ultimately, a six-phase, twelve-slot stator design with seven rotor pole pairs was chosen due to its superior electromagnetic performance and manufacturability. A prototype was built and is currently undergoing testing. This work demonstrates the feasibility of miniaturized axial-flow pumps using bearingless twin drives, offering significant potential in medical and precision engineering applications where compactness, efficiency, and minimal maintenance are critical.