Low force ripples from permanent magnet linear motors (PMLMs) are typically essential requirements in a wide range of demanding control applications with high motion quality. Apart from the sources present in rotary PM machines, phase unbalance due to the end effect is another major contributor of the thrust force ripples in the PMLMs. In this paper, the phase unbalance and induced force ripples are investigated in the case of a planar PMLM typically equipped with single-layer concentrated windings and quasi-Halbach magnets. It demonstrates that although the PMLM is quite carefully deigned to minimize the end effect, the phase unbalance still exists, including both the amplitude and phase position unbalances. And the phase unbalances give rise to even order force ripple harmonics, in which the 2 nd -order force ripple is particularly significant. In order to compensate the end effect and the unbalance between the three phases, a novel PMLM topology is presented, in which the width of the two end teeth (instead of the edge teeth) is adjusted to reduce the force ripple. And the impact of the end teeth width on the ripple force magnitude is further revealed. It is shown that by proper design of the end teeth width, the 2 nd -order force ripple of the PMLM can be minimized to quite a low extent. In comparison with the original design, the 2 nd -order force ripple factor of the novel topology has been suppressed from 0.4% to less than 0.03% in the case study. Such a technique has provided a new way of force ripple minimization, and is applicable to other types of linear motors or actuators with appropriate changes.
A modified model of a limited-angle torque motor (LATM) with irregular slot numbers is proposed for developing an operational range extension method for LATMs. The modified model is derived by considering the effects of the asymmetrical winding structure and magnetic flux leakage, which are validated by finite element analysis and experimental measurements. Based on the modified model, accuracy and time consumption of the simulation can be improved. For the operational range extension method, extended angle range selection theory and constraint conditions are proposed, and the relationship between the sinusoidal tracking characteristic and leading parameters is established by theoretical analysis. A simulation and a prototype machine experiment on an LATM using the new method are carried out. The results show that the proposed operational range extension method can reduce the weight and volume of the LATM without changing sinusoidal tracking characteristics, which proves the feasibility of applying the new method in the oscillating scan system to realize lightness and miniaturisation of the system.This is an open access article under the terms of the Creative Commons Attribution-NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.
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