Sub-Micrometer Resolution Self-Displacement Sensing for Electromagnetic Actuators

Recently, soft electromagnetic actuators (SEMAs) have emerged with promising features for haptic feedback, human-machine interfaces and soft robotics. It is challenging to integrate sensors into an SEMA-based system due to the incompatibility of conventional sensors and space restrictions. Here, we present a self-displacement sensing solution for SEMAs, which exploits the eddy-current effect coupling between the driving coil and the metal surface of the permanent magnets for displacement sensing. A self-displacement sensing and driving circuit (SDSDC) was developed and evaluated, in which low-frequency driving and high-frequency sensing signals can function simultaneously without interfering with each other. Experimental results reveal that an SEMA prototype with the SDSDC can produce a motion over 200 μm with a sensing resolution of 0.038 μm (0.02% motion range). It has a response time of 17 ms and can operate from 0.1 to 100 Hz. Moreover, the SDSDC can operate with the same characteristics when the driving current varies in amplitude and in the presence of external stimuli. Finally, the SDSDC was demonstrated on a conventional voice coil motor. The SDSDC represents a promising solution for designing interactive and responsive soft machines and interfaces, and it can also be implemented in various electromagnetic actuators.