The paper describes a new version of spherical actuator, which is capable of three degrees-of-freedom and a high specific torque. The three-dimensional magnetic field distribution is established using an analytical technique formulated in spherical co-ordinates, and enables the torque vector and back-emf to be derived in closed forms. This facilitates the characterisation of the actuator, and provides the foundation for design optimisation, actuator dynamic modelling and servo control development
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