3-DOF outer rotor electromagnetic spherical actuator

Conventionally, many single-degree-of-freedom actuators were used to realize devices with multi degrees of freedom. However, this makes the structure larger, heavier and more complicated due to the large number of actuators. To remove these drawbacks, the development of a spherical actuator with multi degrees of freedom is necessary, and various spherical actuators have been developed, including our own. However some problems such as low torque, large size and narrow rotation range remain. To solve these problems, the employment of an outer rotor structure is one of the solutions. In this paper, we propose a new 3-DOF outer rotor spherical actuator and its control methods. The basic construction and operating principle are described. The static torque characteristics and dynamic characteristics are computed employing 3-D FEM, in which two types of control methods are taken into account and finally verify it by the measurement on a prototype.