HAPSEA: Hydraulically Amplified Soft Electromagnetic Actuator for Haptics

Novel actuators that can provide squeeze, vibration, and localized forces while remaining soft and comfortable are essential for next-generation augmented reality applications. Despite this need, there are currently few soft actuator topologies that can provide high forces and high bandwidths at low voltages and temperatures. In this work, we present a new type of soft electromagnetic actuator architecture for haptics. These low-cost, easy-to-manufacture, and conformal actuators are composed of a coil, magnet, thin-film material, and water. Adding a thin ferromagnetic sheet further enables the creation of a latching actuator variant, which can improve force output while reducing power consumption. Each actuator combines low voltage (up to 2 V), high-bandwidth electromagnetics with hydraulics to amplify force output. In addition to force amplification, the hydraulics provide cooling and thermal mass, which enable the actuator to be used safely in wearables for longer durations. In this work, we characterize the output forces, frequency response, efficiency, and thermal profiles of the prototype actuators. Results from tabletop experiments show that with hydraulic amplification, a nonlatching actuator is able to exert 1.3 N of force at 4 A, and a latching actuator is able to exert up to 5.2 N when preloaded with 3.7 N of compression. Furthermore, the prototype actuator has a bandwidth of 30 Hz when operating in air. After 120 s of continuous operation (1.3 W) in ambient air (26
$^{\circ }$
C), the maximum actuator temperature reaches 36
$^{\circ }$
C, making it safe for haptic applications. Using these designs, we develop a prototype wearable wristband device that can render body-grounded squeeze and vibration. By expanding on the operating principles described in this work, novel augmented reality applications can potentially become possible.