Flying Hydraulically Amplified Electrostatic Gripper System for Aerial Object Manipulation

TL;DR

The study tackles the challenge of energy-efficient, versatile aerial object manipulation by integrating a soft, hydraulically amplified electrostatic gripper (HASEL) with a quadcopter (RAPTOR). It systematically compares actuator architectures, develops a Scorpion-inspired two-pouch and Hybrid finger designs, and validates performance through ground and in-flight experiments, including untethered operation up to 10 kV. Key findings show that combining actuator concepts yields higher force at small deflections, while the Scorpion-influenced design maintains large deflections, enabling safe, robust grasping of objects (e.g., 76 g) in air. The work demonstrates the feasibility of soft, hydraulic-electrostatic actuators for mobile aerial manipulation and outlines future avenues for weight and power efficiency improvements to broaden industrial applicability.

Abstract

Rapid and versatile object manipulation in air is an open challenge. An energy-efficient and adaptive soft gripper combined with an agile aerial vehicle could revolutionize aerial robotic manipulation in areas such as warehousing. This paper presents a bio-inspired gripper powered by hydraulically amplified electrostatic actuators mounted to a quadcopter that can interact safely and naturally with its environment. Our gripping concept is motivated by an eagle's foot. Our custom multi-actuator concept is inspired by a scorpion tail design (consisting of a base electrode with pouches stacked adjacently) and spider-inspired joints (classic pouch motors with a flexible hinge layer). A hybrid of these two designs realizes a higher force output under moderate deflections of up to 25° compared to single-hinge concepts. In addition, sandwiching the hinge layer improves the robustness of the gripper. For the first time, we show that soft manipulation in air is possible using electrostatic actuation. This study demonstrates the potential of untethered hydraulically amplified actuators in aerial robotic manipulation. Our proof of concept opens up the use of hydraulic electrostatic actuators in mobile aerial systems.

Figures (12)

• Figure 1: Picture of an eagle's foot on the left as taken from Eagle_Foot_Pic. Early visual of a potential implementation based on a bio-inspired design on the right. The main area for actuating the talon is highlighted in green and can be found close to the talon. The idea for the actuator was to narrow the area of rotation and place it as far to the front as possible.
• Figure 2: The quadcopter uses a motion capture system for position feedback control. A Raspberry Pi 4 is used as an onboard computer. The trajectory generation runs on a ground station computer which sends both position and gripper commands to the onboard computer. There, the commands are forwarded to the flight controller and the gripper over a serial connection.
• Figure 3: Manufacturing process of a HASEL actuator. A) Sealing two Mylar sheets to obtain the desired actuator geometry using a Prusa 3D printer. B) Sealed polymer film with reinforced mounting holes. The holes primarily served the fixation during the airbrushing process. C) Actuator clamped for airbrushing.
• Figure 4: Side-by-side comparison of a traditional and inverse gripper. A) Reverse gripper with a pouch length of 40 mm and width of 6 mm. In contrast to a classic gripper, the actuator is mounted on the outside of the toe. On the inside, a 1 mm thick cord was used for prestressing the system in the order of 0.2 N. B) & C) Visual comparison of the reverse gripper with a traditional model. The black tape is used to insulate the gripper and to avoid arching at high voltages.
• Figure 5: Performance comparison of PWT actuators. A) Illustration of a PWT actuator. B) Exceeded torque from the individual actuator types at different deflection angles. Second-order curve fits approximate the measurement response.