Dynamic modelling and parameter identification of a three-degree-of-freedom spherical actuator

This paper addresses both dynamic modelling and dynamic parameter identification of a permanent magnet spherical actuator, which is capable of performing three-degree-of-freedom (DOF) motion in one single joint. The dynamic model of the spherical actuator is derived from Lagrange's equations, but the parameters, called dynamic parameters, in the model are usually uncertain. Then the dynamic model is represented in a form that is linear in these parameters. A new identification method based on the output error (OE) method and recursive least square (LS) estimation is proposed to identify the parameters. This method only requires the current measurement of the stator coils in the identification procedure, which greatly simplifies the experimental process and improves the identification accuracy. Lastly, simulation and experimental results illustrate the effectiveness of the proposed method and its robustness to external disturbances. The proposed method can be also applied to other electromagnetic driving spherical actuators.