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Vacuum-powered actuators mimic muscle behaviour

09 June, 2016

Researchers in the US have developed an actuator that generates movements similar to those of muscles by using vacuum to shrink rubber beams. Like real muscles, the actuators are soft, shock-absorbing, and pose no danger to their environment or humans working alongside them. They could pave the way to soft-bodied robots that are safer than conventional rigid designs, the developers suggest.

“Functionally, our actuator models the human bicep muscle,” explains Dr George Whitesides, who led the development team at Harvard University’s Wyss Institute for Biologically Inspired Engineering. “There are other soft actuators that have been developed, but this one is most similar to muscle in terms of response time and efficiency.”

The team took the unconventional approach of relying on vacuum to decrease the actuator’s volume, causing it to buckle. Engineers would usually consider buckling to be a mechanical instability and a point of failure, but the team exploited this instability to develop the actuators, which it calls Vamps (vacuum-actuated muscle-inspired pneumatic structures).

Previous soft actuators – such as Festo’s fluidic muscle technology ­– have relied on pressurised systems that expand in volume. The American researchers say that their actuators mimic real muscle because they contract, making them an attractive candidate for use in confined spaces and for a wide range of applications.

The actuators — consisting of elastomeric, soft-rubber beams — are filled with small, hollow chambers like a honeycomb. When a vacuum is applied, the chambers collapse and the entire actuator contracts, generating movement. The honeycomb structure can be tailored to produce linear, twisting, bending or combined motions.

The team suggests that soft robots could make industrial production lines safer and faster, as well as making quality control easier to manage by allowing human operators to work in the same space.

“Having Vamps built of soft elastomers would make it much easier to automate a robot that could be used to help humans in the service industry,” says Dr Dian Yang, who was the lead author on a recently published paper describing the development. The researchers envisage robots containing Vamps being used to help the disabled or elderly, to serve food, to deliver goods, and to perform other service-related tasks.

An actuated Vamp (top) and a cross-section (below) showing the inner chambers that collapse when a vacuum is applied.
Photo: Wyss Institute at Harvard University

“These self-healing, bio-inspired actuators bring us another step closer to being able to build entirely soft-bodied robots, which may help to bridge the gap between humans and robots and open entirely new application areas in medicine and beyond,” suggests Dr Donald Ingber, founding director of the Wyss institute.

Although a sophisticated control system has yet to be developed for Vamps, the actuators should be easy to control because of their simplicity – when a vacuum is applied, they contract. They could be used as part of tethered or untethered systems, depending on environmental or performance needs.

The Vamps are designed to avoid failure. The team has demonstrated that, even when damaged with a 2mm hole, the actuators will still function, and if the system suffers major damage, it will fail safely. Loss of vacuum pressure simply renders the actuator motionless. “It can’t explode, so it’s intrinsically safe,” says Whitesides.

Harvard’s Office of Technology Development has filed patents for the actuators and related inventions, and the technology has been licensed to Soft Robotics, a start-up co-founded by Whitesides in 2013. The company is developing robotic grasping systems for applications such as picking and packing in unstructured environments — for example, handling fruit and vegetables in warehouses.




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