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

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.

Monitoring Electrostatic Adhesion Forces via Acoustic Pressure

Electrostatic adhesion is widely used in mobile robotics, haptics, and robotic end effectors for its adaptability to diverse substrates and low energy consumption. Force sensing is important for feedback control, interaction, and monitoring in the EA system. However, EA force monitoring often relies on bulky and expensive sensors, increasing the complexity and weight of the entire system. This paper presents an acoustic-pressure-based method to monitor EA forces without contacting the adhesion pad. When the EA pad is driven by a bipolar square-wave voltage to adhere a conductive object, periodic acoustic pulses arise from the EA system. We employed a microphone to capture these acoustic pressure signals and investigate the influence of peak pressure values. Results show that the peak value of acoustic pressure increased with the mass and contact area of the adhered object, as well as with the amplitude and frequency of the driving voltage. We applied this technique to mass estimation of various objects and simultaneous monitoring of two EA systems. Then, we integrated this technique into an EA end effector that enables monitoring the change of adhered object mass during transport. The proposed technique offers a low-cost, non-contact, and multi-object monitoring solution for EA end effectors in handling tasks.