This paper explores the combination of a Hybrid Reluctance Actuator (HRA) with a Hybrid Tunable Magnet Actuator (HTMA) to realize a high bandwidth actuator that can generate low-frequency forces with greater efficiently. The HTMA allows desired forces to be sustained without continuous coil heating by manipulating the remnant magnetisation of an AlNiCo magnet. This enables the actuator to exert force through two modes of operation: by magnetisation of the Tunable AlNiCo Magnet (TM) or by inducing a proportionally force-dependent field. The second mode may furthermore be used to compensate for unwanted variations in forces during magnetisation. Although FEM analyses provide an understanding of the actuator behaviour in steady states, it is inefficient to integrate transient FEM models with accurate hysteresis models. Hence, firstly, an analytical framework is presented to determine the transient behaviour and the comparative energy efficiency of the two actuator modes. Then, a control strategy is presented for the operation of the combined actuator to track a reluctance force step reference. An experimental setup is designed and tested to validate the concept and control method.

Recent studies have shown that tunable magnets (soft permanent magnets) can significantly reduce Joule heating in electromagnetic actuators. To achieve high motion accuracy and repeatability, this article proposes a novel actuator design with a linearized force-flux relation. In prior designs of variable reluctance tunable magnet actuators, the force and flux are related quadratically via a C-shaped actuator. Hybrid tunable magnet actuators based on biased fluxes are developed using lumped parameter models. Using finite element analysis, it is shown that the force-flux relation is symmetric linear around the mid position depending on the magnetic flux direction in the magnet. Within a position range of ±500 μm and a force range of ±20 N, the linear fit produces a negligible error of 0.08 N. Finally, this linear relationship is validated with a 0.03-N error in an experimental setup.

The recent development of a hybrid tunable magnet actuator proposes to eliminate Joule heating when maintaining a force or position offset. By controlling the remnant magnetic flux in an AlNiCo magnet within the actuator, the actuation force can be linearly varied and maintained. While a method for tuning the magnetisation state of the magnet with minimal magnetic field changes has been demonstrated previously, the method is inefficient due to its slow tuning rate, which hinders its use in controlling the actuator’s position. This paper presents a novel method of magnetisation state tuning with a fast tuning rate and validates its effectiveness for controlling the position of a short-stroke linear actuator. This tuning method is implemented and verified for changing the flux density of an AlNiCo magnet in the range of ±1.2 T, with a root-mean-square error (RMSE) of 7.2 mT. An accurate estimation of the magnetisation state is furthermore achieved during positioning, guided by the design and experimental validation of a lumped parameter model, allowing the position to be controlled with an RMSE of 4.0 µm in a range of −157 to 320 µm.