An EPFL team is developing soft, flexible and reconfigurable robots. Air-actuated, they behave like human muscles and may be used in physical rehabilitation. They are made of low-cost materials and could easily be produced on a large scale.
Robots are usually expected to be rigid, fast and efficient. But researchers at EPFL’s Reconfigurable Robotics Lab (RRL) have turned that notion on its head with their soft robots.
Soft robots, powered by muscle-like actuators, are designed to be used on the human body in order to help people move. They are made of elastomers, including silicon and rubber, and so they are inherently safe. They are controlled by changing the air pressure in specially designed ‘soft balloons’, which also serve as the robot’s body. A predictive model that can be used to carefully control the mechanical behavior of the robots’ various modules has just been published in Nature – Scientific Reports.
Potential applications for these robots include patient rehabilitation, handling fragile objects, biomimetic systems and home care. “Our robot designs focus largely on safety,” said Jamie Paik, the director of the RRL. “There’s very little risk of getting hurt if you’re wearing an exoskeleton made up of soft materials, for example” she added.
A model for controlling the actuators
In their article, the researchers showed that their model could accurately predict how a series of modules – composed of compartments and sandwiched chambers – moves. The cucumber-shaped actuators can stretch up to around five or six times their normal length and bend in two directions, depending on the model.
“We conducted numerous simulations and developed a model for predicting how the actuators deform as a function of their shape, thickness and the materials they’re made of,” said Gunjan Agarwal, the article’s lead author.
One of the variants consists of covering the actuator in a thick paper shell made by origami. This test showed that different materials could be used. “Elastomer structures are highly resilient but difficult to control. We need to be able to predict how, and in which direction, they deform. And because these soft robots are easy to produce but difficult to model, our step-by-step design tools are now available online for roboticists and students.”
A rehabilitation belt
In addition to these simulations, other RRL researchers have developed soft robots for medical purposes. This work is described in Soft Robotics. One of their designs is a belt made of several inflatable components, which holds patients upright during rehabilitation exercises and guides their movements.
“We are working with physical therapists from the University Hospital of Lausanne (CHUV) who are treating stroke victims,” said Matthew Robertson, the researcher in charge of the project. “The belt is designed to support the patient’s torso and restore some of the person’s motor sensitivity.”
The belt’s soft actuators are made of pink rubber and transparent fishing line. The placement of the fishing line guides the modules’ deformation very precisely when air is injected. “For now, the belt is hooked up to a system of external pumps. The next step will be to miniaturize this system and put it directly on the belt,” said Robertson.
Adaptable and reconfigurable robots
Potential applications for soft actuators don’t stop there. The researchers are also using them to develop adaptable robots that are capable of navigating around in cramped, hostile environments. And because they are completely soft, they should also be able to withstand squeezing and crushing.
“Using soft actuators, we can come up with robots of various shapes that can move around in diverse environments,” said Paik. “They are made of inexpensive materials, and so they could easily be produced on a large scale. This will open new doors in the field of robotics.”
Learn more: Soft robots that mimic human muscles
A soft actuator using electrically controllable membranes could pave the way for machines that are no danger to humans
In interacting with humans, robots must first and foremost be safe. If a household robot, for example, encounters a human, it should not continue its movements regardless, but rather give way in case of doubt. Researchers at the Max Planck Institute for Intelligent Systems in Stuttgart are now presenting a motion system – a so-called elastic actuator – that is compliant and can be integrated in robots thanks to its space-saving design.
The actuator works with hyperelastic membranes that surround air-filled chambers. The volume of the chambers can be controlled by means of an electric field at the membrane. To date, elastic actuators that exert a force by stretching air-filled chambers have always required connection to pumps and compressors to work. A soft actuator such as the one developed by the Stuttgart-based team means that such bulky payloads or tethers may now be superfluous.
Many robots have become indispensable, and it is accepted that they may be dangerous to humans in their workspace. In the automotive industry, for example, they assemble cars with speed and reliability, but are well shielded from direct contact with humans. These robots go through their motions precisely and relentlessly, and anyone who gets in the way could be seriously injured.
Robots with soft actuators that cannot harm humans, on the other hand, are tethered by pneumatic hoses and so their radius of motion is restricted. This may be about to change. “We have developed an actuator that makes large changes in form possible without an external supply of compressed air”, says Metin Sitti, Director at the Max Planck Institute for Intelligent Systems.