High energy-density electrostatic actuators for soft robotics

This thesis reports high energy-density electrostatic actuators for use in soft robotics. This thesis has two main parts: a) a detailed study of electro-adhesion using microfabricated electrodes, and b) a flexi-ble fiber-shaped linear motor. Electro-adhesion (EA) is widely used as a reversible and low-power adhesion mechanism of robots. High release pressure has been demonstrated but contact tackiness and slow-release time limits prac-tical applications. In first part of this thesis, I report the characterization of both pre- and post-contact forces for electro-adhesion. I built a setup that systematically measures EA forces as the EA patch is brought into proximity, during contact and upon removal from a surface. I fabricated interdigitated electrodes with gaps and spacings from 5 µm to 500 µm, exploring the effect of electrode geometry and film thickness on EA forces. The comparison of pre- and post-contact forces reveals the interplay be-tween surface forces, charge injection, and polarization inertia. Release pressures for conductive ob-jects ranged from 1 to 100 kPa at 400 V, exceeding pre-contact (ie "pure EA") adhesion forces by 1 to 10 times. My unique methodology contributes to advancing the understanding of the impact of contact on the release pressure and speed. This analysis can assist in the characterization process of electro-adhesive pads and allow optimized designs for future applications. In a second part, I developed a fiber-shaped linear electrostatic motor (LEMF), allowing for large dis-placement and bi-directional actuation. Unlike previously developed linear electrostatic motor, that have the form factor of a flat ribbon, our LEMF consists of two coaxial fibers, each made of three heli-cally wound electrodes encapsulated in a dielectric. A high voltage waveform is applied between the electrodes of the internal and external fibers, moving the external fiber relative to the internal one: the system acts as a synchronous motor. The helicoidal electrodes of the LEMF significantly simplifies the fabrication process and their connections. The modular nature of the coaxial fiber design allows for easy connection with other fibers, enabling scalability. The motor lifts loads up to 10 times its weight (3.3 g payload for 350 mg weight), with a maximum displacement limited only by its length. The fiber motor exhibits precise and repeatable movements at a speed of 44 mm/s without payload, achieving a maximum peak force of 53 mN/cm of fiber and an energy density of 195 J/m3. The LEMF form-factor enables integration into textile and sewed architecture. A future step will involve characterizing multi-ple fibers bundled together and explore applications for soft robotics.