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Multi‐degree‐of‐freedom permanent magnet spherical actuators (PMSAs) are highly nonlinear, coupled, and multivariable systems that are subject to different types of disturbances including unknown payloads, unmodelled dynamics, frictions, and other external disturbances, which adversely affect the trajectory tracking performance of a system. In this paper, a disturbance‐observer‐based continuous non‐singular terminal sliding‐mode control (NDOB‐CNTSMC) strategy is developed for a PMSA to enhance its trajectory tracking performance. Firstly, a nonlinear disturbance observer (NDOB) with a parameter design method is proposed to suppress uncertainty and reject disturbance in a PMSA trajectory tracking control system. Secondly, a continuous non‐singular terminal sliding‐mode controller (CNTSMC) is presented to compensate for the effect of the disturbance observation error and unobservable disturbances. The stability of the proposed control strategy is proved by the Lyapunov theorem. Both simulation and experimental results have shown that the control strategy proposed in this research can effectively address the issues of the inaccuracy of modelling and various disturbances and improve the trajectory tracking precision of the PMSA. [ABSTRACT FROM AUTHOR]

Non‐linear friction between the rotor and the rotor support mandrels would occur during the movement of the permanent‐magnet spherical motor (PMSpM). The friction which varies with the position causes PMSpM jitter or even stop it when running at low speeds, and the system operation accuracy is reduced. To solve these problems, this work proposes a parameter identification method of the Coulomb friction model. First, a dynamics model with the Coulomb friction of PMSpM is established by using generalised Euler angles and the Lagrangian energy method. Then, a parameter identification method of the Coulomb friction model based on COMSOL Multi physics coupled simulation and MEMS experiment is proposed to obtain the friction torque data of the PMSpM. Finally, the friction torque compensation in a closed‐loop control experiment is completed by using the friction data. The results show that the accuracy of trajectory tracking control is significant, and the error is reduced by 49.32%. Hence, the distribution of the friction torque field is accurate and effective. [ABSTRACT FROM AUTHOR]

A spherical motor has multiple degrees of freedom. Its motion control requires an accurate attitude detection system. This study proposes a low‐cost microelectromechanical system (MEMS) inertial measurement sensor to detect the attitude of the spherical motor. The proposed sensor combines a three‐axis gyroscope and a three‐axis accelerometer to obtain raw position data of spherical motors to estimate rotor's attitude. To improve the accuracy of the estimated attitude from the raw position data, the authors reduce the inclination angle error between the motor's rotor and MEMS sensor's coordinate systems by compensating axial angle error. A high‐speed camera that generally provides high accuracy of the attitude is used as a calibration device for comparison and validation. Experimental results show that the MEMS inertial measurement sensor can achieve accurate attitude estimation that is suitable for motion control of a spherical motor. [ABSTRACT FROM AUTHOR]