Multimode Hydraulically Amplified Electrostatic Actuators for Wearable Haptics

The sense of touch is underused in today's virtual reality systems due to lack of wearable, soft, mm-scale transducers to generate dynamic mechanical stimulus on the skin. Extremely thin actuators combining both high force and large displacement are a long-standing challenge in soft actuators. Sub-mm thick flexible hydraulically amplified electrostatic actuators are reported here, capable of both out-of-plane and in-plane motion, providing normal and shear forces to the user's fingertip, hand, or arm. Each actuator consists of a fluid-filled cavity whose shell is made of a metalized polyester boundary and a central elastomer region. When a voltage is applied to the annular electrodes, the fluid is rapidly forced into the stretchable region, forming a raised bump. A 6 mm × 6 mm × 0.8 mm actuator weighs 90 mg, and generates forces of over 300 mN, out-of-plane displacements of 500 µm (over 60% strain), and lateral motion of 760 µm. Response time is below 5 ms, for a specific power of 100 W kg^-1 . In user tests, human subjects distinguished normal and different 2-axis shear forces with over 80% accuracy. A flexible 5 × 5 array is demonstrated, integrated in a haptic sleeve.