ETD

• Electromagnetic analysis
• multi DoF
• spherical actuator
• variable compliance

This thesis investigates the Finite Element (FE) analysis and equivalent circuit modeling of a 3 Degrees of Freedom (DoF) spherical actuator capable of generating both active and passive torque.
The device, available in the Applied Electromagnetics Lab (EMLab) at the University of Pisa, consists of a spherical stator equipped with coils and a concentric double-layer hollow-rotor composed of ferromagnetic solid core on which a spherical conductive shell is placed. A handle installed on the rotor transmits the rotating and tilting movements through a spherical joint, enabling the 3 DoF.
The joint cavity is filled with a magnetorheological fluid (MRF), capable of presenting a rapid and reversible transition from a liquid state to a near-solid state when a magnetic field is applied. Dedicated DC coils produce the magnetic field that excites the fluid, thus modulating the passive torque produced with the MRF.
The main contributions of this thesis are:
-investigation of the actuator's performances through a full-3D FE model, used to study both rotational and tilting movements;
-development of an electrical equivalent circuit that describes the behavior of the actuator considering the rotation around the vertical axis, resulting from FE analysis and experimental tests;
-preliminary validation of the equivalent circuit evaluating the active torque;
-parametric analysis of the device in different operating conditions, focusing on how variations in voltage amplitude and frequency affect the torque-speed curve, using the equivalent model.