A New Low-Profile Electromagnetic-Pneumatic Actuator for High-Bandwidth Applications

Abstract

This paper proposes a new electromagnetic-pneumatic actuator with high force density for wide bandwidth applications. The actuator includes an active electromagnetic actuator and a pneumatic spring, fused together into a hybrid design. The electromagnetic component acts as an active element, generating wide bandwidth high-density forces. It further provides a baseline stiffness, for the device, using its magnetic spring. The active electromagnetic actuator consists of a number of stacks positioned in a vertical arrangement. The modular design of the actuator, allows for reconfiguring the device with different number of stacks to adjust the strokes, depending on the target application. The pneumatic spring is then responsible for adding extra stiffness and support for heavy load masses. The added stiffness by the pneumatic spring can be easily adjusted by regulating the gas pressure. Based on the proposed active electromagnetic actuator, analytical and FEM models are developed, which are used for optimizing the design. The proposed actuator has a low-profile design, making it suitable for many applications with space limitations. The final design is prototyped, and experimentally tested. To evaluate the performance of the electromagnetic component, its force density (force to volume ratio) is compared with a voice coil actuator (that is widely used in both academic and industrial sectors). The FEM and experimental results confirmed the high force density of the electromagnetic component, comparing to a voice coil of similar size. The proposed design, with a diameter of $\sim {\text{125 mm}}$ and a height of $\sim {\text{60 mm}}$ , generates a force variation of $\sim {\text{318 N}}$ for the currents of $I=\pm {\text{2 A}}$ . Furthermore, it has small electromagnetic and electromechanical time constants of 5.2 and 10.5 $\text{ms}$ , respectively, with negligible eddy current effect. These findings make the actuator suitable for wide bandwidth applications.