Design and analysis of a tubular linear oscillating motor for directly-driven EHA pump

This paper investigates a novel tubular DC linear oscillating motor (DLOM) for the application of directly-driven hydraulic servo pump in electro-hydrostatic actuator (EHA). A hollow mover structure is used to mount Halbach PM arrays, which not only reduces the mover mass for improvement of system dynamics, but also leaves space for installment of resonance springs. It helps to shorten the motor length, simplify the structure and improve the power density. Closed slot stator structure is used to reduce the cogging force. The performance is compared with that of semi-closed slot with finite element method (FEM). Employment of multiple windings helps to reduce the flux leakage, and increases the flux density. Air-gap flux density and thrust force are formulated with lumped magnetic circuit method analytically. The influence of design parameters on output performance is investigated with analytical model and FEM. Design optimization is conducted to improve the thrust and its stability with respect to displacement. A research prototype is developed for experimental purpose. Both FEM and experimental results validate the analytical models of air-gap flux density and thrust output. The working principle is also verified with resonance experiment without external load.