"Some of the advantages of soft robotic systems are that they can easily adapt to unstructured environments, or to irregular or soft surfaces, such as the human body," says Professor Yon Visell of UC Santa Barbara (UCSB).
Despite their promise – to date – most soft robots move slowly and clumsily when compared with many conventional robots. However, the gap is narrowing thanks to developments with actuators. Responsible for the mechanical movement of a mechanism or a machine, actuators do their work in various ways, relying on electromagnetic, piezoelectric, pneumatic or other forces.
Prof. Visell and his UCSB collaborators have married the electromagnetic drives used in most conventional robotic systems with soft materials, in order to achieve both speed and softness. "An interesting biological analog to the actuator described in our new work might be a fast twitch muscle," says Prof. Visell.
Prof. Visell explains that the main challenge was to build an actuator that could achieve speeds greater than what has typically been possible with soft robotic actuators, many of which depend on slow processes, such as air flow or thermal effects.
"In this project, we wanted to see how far we could push the idea of having very fast, low-voltage actuation within a fully soft robotic paradigm," he says. They based their work on the electromagnetic motor, a common type of fast and low-voltage actuator that is used in everything from electric cars to appliances, but has seen little effective application in soft robotic systems.
The team claim their work has resulted in an actuator that is fast, low voltage and soft - and also small, just a few millimetres in size. Using liquid-metal alloy conductors encased in hollow polymer fibres and magnetised polymer composites, the researchers created patterned, 3D components that form the basis of soft analogs of standard electrical motors. The fibres themselves are polymer composites that the team engineered to have high thermal conductivity, greatly improving their performance.
"We realised components that are each soft and stretchable, and combined them to create these motor-like structures that can move things," Prof. Visell adds. To demonstrate, they created a tiny, millimetres-wide gripper that can close in just milliseconds, and a soft tactile stimulator that can operate at frequencies of hundreds of cycles per second.
According to the team, the devices could find use in emerging areas such as haptics. "These soft electromagnetic actuators can be used to create tactile displays that conform to human skin, or miniature robotic tools for surgical endoscopy or other medical applications," says Postdoc Thanh Nho Do, who worked on the study alongside Prof. Visell.
"We look forward to applying these new soft robotic technologies in areas ranging from virtual reality, augmented reality, wearable technologies, healthcare and medicine," Prof. Visell concludes. "The horizon is wide open."