A Miniature Direct-Drive Hydraulic Actuator for Wearable Haptic Devices based on Ferrofluid Magnetohydrodynamic Levitation

Hydraulic and pneumatic actuators in haptics offer the advantage of soft and compliant interfaces, with the drawback of cumbersome driving devices and limited modulation capabilities. We propose a miniature hydraulic actuator based on a linear electromagnetic motor with an embedded ferrofluid sealing. The solution has two main advantages: it shows no static friction due to the magnetohydrodynamic levitation effect of the ferrofluid, and the output force can be scaled (by varying the radius of the actuator) without introducing noise and friction of mechanical reduction mechanisms. Moreover, soft and compliant interfaces in the form of actuated pouches can be obtained on wearable devices with embedded actuators. As a concept prototype, we present here a compact and soft haptic thimble integrating the proposed actuator: experimental characterization at the bench, and perception experiments with the final prototype, evaluate the low-noise rendering capability of the method.