Development of Lorentz Force‐Type Self‐bearing Motor for an Alternative Axial Flow Blood Pump Design

Abstract

A Lorentz force-type self-bearing motor was developed to provide delivery of both motoring torque and levitation force for an alternative axial flow blood pump design with an enclosed impeller. The axial flow pumps currently available introduce electromagnetic coupling from the motor's stator to the impeller by means of permanent magnets (PMs) embedded in the tips of the pump's blades. This design has distinct disadvantages, for example, pumping efficiency and electromagnetic coupling transmission are compromised by the constrained or poor geometry of the blades and limited pole width of the PMs, respectively. In this research, a Lorentz force-type self-bearing motor was developed. It is composed of (i) an eight-pole PM hollow-cylindrical rotor assembly supposedly to house and enclose the impeller of an axial flow blood pump, and (ii) a six-pole stator with two sets of copper wire and different winding configurations to provide the motoring torque and levitating force for the rotor assembly. MATLAB's xPC Target interface hardware was used as the rapid prototyping tool for the development of the controller for the self-bearing motor. Experimental results on a free/simply supported rotor assembly validated the design feasibility and control algorithm effectiveness in providing both the motoring torque and levitation force for the rotor. When levitated, a maximum orbital displacement of 0.3 mm corresponding to 1050 rpm of the rotor was measured by two eddy current probes placed in the orthogonal direction. This design has the advantage of eliminating the trade-off between motoring torques, levitating force, and pumping efficiency of previous studies. It also indicated the benefits of enclosed-impeller design as having good dynamic response, linearity, and better reliability. The nonmechanical contact feature between rotating and stationary parts will further reduce hemolysis and thromboembolitic tendencies in a typical blood pump application.

Validation of an Axial Flow Blood Pump: Computational Fluid Dynamics Results Using Particle Image Velocimetry

“…The impeller was the only rotating component enclosed inside a cylinder, which was driven by the Lorentz force. As a result, the impeller and the cylinder rotated simultaneously as a single component (27). As the magnet was installed in the rotor cylinder, there was a clearance gap between the rotor cylinder and the pump casing.…”

Parameter estimation and statistical analysis on frequency-dependent active control forces

“…This may be due to the effective stiffness coefficients calculations based on ideal conditions of Eq. (5). It is also noted in Fig.…”

“…Active magnetic bearings (AMB) have been receiving widespread applications in industry [1][2][3][4][5][6]. This is because they can support the rotor without contact, thus no friction and heat are generated and the need for lubrication is also eliminated.…”

Parameter Estimation and Actuator Characteristics of Hybrid Magnetic Bearings for Axial Flow Blood Pump Applications

“…The motoring coils wound around the stator are driven by three‐phase currents to provide higher average motoring torque on the rotor. The outstanding feature of the structure of the proposed blood pump is that it includes an enclosed impeller to enhance the motoring electromagnetic coupling (8).…”

“…Driven by the deficiency of hemodynamic reliability of the second‐generation VADs, the third‐generation VADs which utilize magnetic suspension techniques are an emerging therapy (7–15), as there is no mechanical contact between the bearings and the flowing blood. This attractive feature eliminates the problem of material wear, and therefore, red blood cells may flow freely in the blood pumps without being damaged by the bearings.…”