Precise External Force Estimation of Helical Motors using Magnetic-attractive-force Error Compensation

Abstract

This paper presents the external force estimation for helical motors contain the magnetic levitation system. The helical shape of helical motors induces a wide inductive gap; thus, their thrust density is 1.5 times higher than that of general cylindrical linear motors. Furthermore, by magnetically levitating the mover, the motor can be directly driven. However, owing to the variations in the magnetic attractive force acting on the mover, the accuracy of external force estimation is lower than that of cylindrical motors. To solve this problem, this study proposed the combination of the thrust and torque disturbance observers of this motor for external force estimation irrespective of the magnetic attractive force. Numerical simulations and experimental results demonstrated that the proposed method can achieve the highest precision.