A Two-Layer Electrostatic Film Actuator with High Actuation Stress and Integrated Brake

TL;DR

This work tackles the need for lightweight, compact actuators with high force output in air and integrated braking. It introduces a two-layer EFA with alternating top/bottom electrodes to reduce the effective electrode pitch, achieving approximately 241 N/m^2 actuation stress—about a 90.5% improvement over prior air-operating three-phase EFAs—and an integrated electrostatic adhesion brake for load retention. Finite element analysis guides design choices, while experiments demonstrate high speed (up to ~167 mm/s at 240 Hz), precise positioning (0.048 mm bidirectional error), and substantial payload capacity (≈68× the actuator’s own weight), validated through demonstrations including tug-of-war, payload handling, a one-DOF robotic arm, and a dual-mode gripper. The results highlight the potential of combining actuation and braking in a thin, flexible device for lightweight robotics, while acknowledging brake reliability under beads and proposing dielectric encapsulation and thickness optimization as future improvements.

Abstract

Robotic systems driven by conventional motors often suffer from challenges such as large mass, complex control algorithms, and the need for additional braking mechanisms, which limit their applications in lightweight and compact robotic platforms. Electrostatic film actuators offer several advantages, including thinness, flexibility, lightweight construction, and high open-loop positioning accuracy. However, the actuation stress exhibited by conventional actuators in air still needs improvement, particularly for the widely used three-phase electrode design. To enhance the output performance of actuators, this paper presents a two-layer electrostatic film actuator with an integrated brake. By alternately distributing electrodes on both the top and bottom layers, a smaller effective electrode pitch is achieved under the same fabrication constraints, resulting in an actuation stress of approximately 241~N/m$^2$, representing a 90.5\% improvement over previous three-phase actuators operating in air. Furthermore, its integrated electrostatic adhesion mechanism enables load retention under braking mode. Several demonstrations, including a tug-of-war between a conventional single-layer actuator and the proposed two-layer actuator, a payload operation, a one-degree-of-freedom robotic arm, and a dual-mode gripper, were conducted to validate the actuator's advantageous capabilities in both actuation and braking modes.

Figures (12)

• Figure 1: The two-layer electrostatic film actuator. (a) Demonstration of the flexible and thin structure of the actuator. (b) Comparison of the actuation stress of the proposed two-layer three-phase actuator with previously reported actuators operating in air.
• Figure 2: The principle and design of (a) conventional single-layer EFA and (b) the two-layer EFA.
• Figure 3: Analysis of the two-layer EFA. (a) The normalized electric potential distribution of Actuator 1. (b) Relationship between normalized actuation force and excitation phase in different electric angles. (c) Relationship between normalized peak actuation force and electric angle.
• Figure 4: The influence of design and fabrication parameters on the actuation force. (a) Relationship between actuation stress per volt squared and spacing. (b) Relation between normalized actuation force and misalignment.
• Figure 5: Fabrication of the two-layer actuator. (a) The illustration of the fabrication process. (b) The top and sectional views of the electrodes.