A new synthetic soft actuator makes it possible to create robots that mimic the movements of people and others very realistically. The 'soft muscle' can be printed with a 3D printer and consists of an artificial material that can expand without requiring an external compressor or high voltage.
The actuator was developed by researchers at Columbia University's Creative Machine Labs. The researchers describe their development in an article in the scientific journal Nature. The new artificial material has a load density - the ratio of load to recovery - that is 15 times higher than that of a natural muscle. In practice, this means that the actuator can lift 1,000 times its own weight.
Soft robots
Soft artificial actuators enable so-called 'soft robots', robots built from materials that closely resemble living organisms. Such robots, compared to traditional robots - produced from rigid materials - offer more flexibility and can adapt more easily to perform delicate tasks. In addition, as the name suggests, soft robots are usually produced from a softer material than traditional robots. This helps reduce possible injuries if a soft robot and a human collide unexpectedly.
Soft robots can be used for a variety of applications, including in the manufacturing and healthcare sectors. Compared to traditional rigid robots, the robots are better able to perform natural movements, such as grasping and manipulating objects. This enables it to perform delicate tasks that are impossible with traditional rigid robots.
Previous soft actuators
Work on soft actuators has been going on for some time, but until now they were not suitable for use in soft robots. Previous soft actuators were made of two materials: metal alloys with shape memory or liquid elastomer. However, both offer considerable limitations. For instance, a voltage of more than 1 kilovolt is required to move electro-active polymers made of metal alloys with shape memory, and these alloys cannot withstand high loads. Liquid elastomer can expand under the influence of air or liquid, but this requires an external compressor and pressure control equipment. These are too large to create soft actuators on a small scale, which hampered the development of soft robots.
The researchers claim to have found a solution with their new 'artificial muscle'. The new material consists of a silicone rubber matrix into which ethanol has been incorporated. As a result, the material consists of 80% silicone rubber and 20% ethanol. This ethanol is stored in tiny microbubbles embedded in the silicone rubber. The material can be printed into the desired shape using a 3D printer.
Material can expand 900%
The material can be heated using a thin wire put under a voltage of 8V, 1A. This causes the ethanol in the silicone rubber to reach a temperature where the liquid is converted to gas, causing the material to expand substantially. By heating the material to 80% in this way, the researchers managed to expand the material by 900%. The material can withstand a pressure of 1.3 MPa (megapascal).
It is possible to control this process using a computer system, which allows the actuator to make certain movements. By accurately programming this process, it is possible to use the soft actuator to make a soft robot make lifelike movements. A key advantage is that the material is available for as little as 3 US cents per gram, making it possible to produce soft actuators relatively cheaply.
Pushing, pulling, bending and twisting
"Our soft functional material can serve as a robust soft actuator, potentially revolutionising the way soft robot solutions are developed," explains Aslan Miriyev, a researcher at Creative Machine Labs. "It can push, pull, bend, twist and lift weight. It is the most like a natural muscle artificial material we have so far."
"We have made great strides in terms of robot brains, but robot bodies are still primitive," said Hod Lipson, who heads Columbia University's Creative Machine Labs. "This is a big piece of the puzzle. As in biology, the new actuator can be shaped and reshaped in thousands of ways. We have overcome one of the last barriers to creating lifelike robots."
Further development
The researchers want to further develop their development and hope to replace the thin wire they use in their current version with conductive material. This should both speed up the response time of the soft actuator and extend the life of the component. In the long term, the researchers hope to use artificial intelligence to control the actuator, with which the researchers hope to take another important step in replicating natural movements in robots.
Author: Wouter Hoeffnagel
Source: Columbia University
Source: Nature
Photo by: Aslan Miriyev/Columbia Engineering
