Shockingly Soft Artificial Muscles

Soft actuators are an active area of research in the field of robotics due to their unique advantages over traditional rigid actuators. One key advantage is their inherent flexibility, which allows for safer and more adaptable interactions with the environment. Soft actuators are made from compliant materials that can deform and conform to irregular shapes, making them well-suited for applications where rigid counterparts may struggle or pose safety concerns. This flexibility is particularly advantageous in scenarios involving human-robot collaboration, as the soft actuators can reduce the risk of injury during physical interactions.

Energy efficiency is another notable advantage of soft actuators. The compliance of these actuators allows for efficient energy storage and transmission during deformations, minimizing energy losses. This characteristic is particularly beneficial in robotics applications where energy conservation is critical, such as in untethered and battery-powered robotic systems. Soft actuators can contribute to longer operational durations and reduced power consumption, enhancing the overall sustainability and performance of robotic platforms.

Artificial muscles have been proposed as a lightweight and powerful type of soft actuator. In the most common scenario, these devices are composed of liquid-filled pouches that are covered with electrodes on the exterior. When an electrical current is applied to the electrodes, they are drawn together, simulating a muscular contraction in biological organisms. When a series of these pouches are connected in sequence, they can be leveraged to perform work, much like a real muscle.

Unfortunately, existing artificial muscles of this type, called electrostatic actuators, require very high voltage levels — often in the range of 6,000 to 10,000 volts. A voltage this high, on the surface of the actuator no less, is unsafe around humans, and also poses a serious safety concern around water or other conductive materials. Roboticists at ETH Zurich have recently unveiled a new soft actuator technology that could circumvent these issues. Called HALVE (Hydraulically Amplified Low-​Voltage Electrostatic) actuators, these artificial muscles are powerful, operate on lower voltage levels, and keep the electrodes inside of a protective, waterproof shell.

To build the actuators, a ferroelectric material that can store large amounts of electrical energy was combined with an electrode layer. Finally, the entire actuator was coated with a polymer shell that encases the electrodes. This shell does not impede the mechanical function of the device, but does protect it from coming into contact with humans or conductive materials that could result in safety issues or device failure.

Calling HALVE a low-voltage device is a bit of a stretch — it requires about 900 volts for operation — however, it is a reduction of several thousand volts when compared with present technologies. The polymer shell does at least keep the electrodes insulated from the outside world. And it does quite a good job of it. Certain common types of manufacturing issues can lead to electrical issues that punch a hole in the actuator’s shell, but the outer shell is self-sealing, keeping the system operational and safe even after such events.

To demonstrate the effectiveness of HALVE, the researchers built the actuators into a pair of soft robotic systems. In one case, a gripper was constructed. It was shown that the gripper could hold on to a cord tightly enough that the entire device could be lifted up into the air. In another demonstration, a robotic fish was developed, using a pair of actuators that gave it the ability to swim. This showcased both the flexibility of the system, as well as its ability to operate in water.

At present, the team is preparing for larger-​scale production of their artificial muscles. They are also in talks with some companies that would like to commercialize the technology for use in novel types of robots and wearables.