One of the impediments to developing miniaturized, “squishy” robots is the need for an internal power source that overcomes the power-to-weight ratio for efficient movement. An international group involving Inha University, University of Pittsburgh and the Air Force Research Laboratory has built upon their previous research and identified new materials that directly convert ultraviolet light into motion without the need for electronics or other traditional methods.
The group includes M. Ravi Shankar, co-author and professor of industrial engineering at Pitt’s Swanson School of Engineering. Lead author is Jeong Jae Wie, assistant professor of polymer science and engineering at Inha University, South Korea. The experiments were conducted at the Air Force Research Laboratory’s (AFRL) Materials & Manufacturing Directorate at Wright-Patterson Air Force Base, Ohio, under the direction of Timothy J. White.
Other investigations have proposed the use of ambient energy resources such as magnetic fields, acoustics, heat and other temperature variations to avoid adding structures to induce locomotion. However, Dr. Shankar explains that light is more appealing because of its speed, temporal control and the ability to effectively target the mechanical response. For the material, the group zeroed in on monolithic polymer films prepared from a form of liquid crystalline polymer.
“Our initial research indicated that these flexible polymers could be triggered to move by different forms of light,” Dr. Shankar explained. “However, a robot or similar device isn’t effective unless you can tightly control its motions. Thanks to the work of Dr. White and his team at AFRL, we were able to demonstrate directional control, as well as climbing motions.”
According to Dr. Wie, the “photomotility” of these specific polymers is the result of their spontaneous formation into spirals when exposed to UV light. Controlling the exposure enables a corresponding motion without the use of external power sources attached directly to the polymer itself.
“Complex robotic designs result in additional weight in the form of batteries, limb-like structures or wheels, which are incompatible with the notion of a soft or squishy robot,” Dr. Wie said. “In our design, the material itself is the machine, without the need for any additional moving parts or mechanisms that would increase the weight and thereby limit motility and effectiveness.”
In addition to simple forward movement, Dr. White and the collaborative team were able to make the polymers climb a glass slide at a 15-degree angle. While the flat polymer strips are small – approximately 15mm long and 1.25mm wide – they can move at several millimeters per second propelled by light. The movement can be perpetual, as long as the material remains illuminated.
“The ability for these flexible polymers to move when exposed to light opens up a new ground game in the quest for soft robots,” Dr. Shankar said. “By eliminating the additional mass of batteries, moving parts and other cumbersome devices, we can potentially create a robot that would be beneficial where excess weight and size is a negative, such as in space exploration or other extreme environments.”
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
The potential to develop “materials that compute” has taken another leap at the University of Pittsburgh’s Swanson School of Engineering, where researchers for the first time have demonstrated that the material can be designed to recognize simple patterns. This responsive, hybrid material, powered by its own chemical reactions, could one day be integrated into clothing and used to monitor the human body, or developed as a skin for “squishy” robots.
“Pattern recognition for materials that compute,” published today in the AAAS journal Science Advances (DOI: 10.1126/sciadv.1601114), continues the research of Anna C. Balazs, Distinguished Professor of Chemical and Petroleum Engineering, and Steven P. Levitan, the John A. Jurenko Professor of Electrical and Computer Engineering. Co-investigators are Yan Fang, lead author and graduate student researcher in the Department of Electrical and Computer Engineering; and Victor V. Yashin, Research Assistant Professor of Chemical and Petroleum Engineering.
The computations were modeled utilizing Belousov-Zhabotinsky (BZ) gels, a substance that oscillates in the absence of external stimuli, with an overlaying piezoelectric (PZ) cantilever. These so-called BZ-PZ units combine Dr. Balazs’ research in BZ gels and Dr. Levitan’s expertise in computational modeling and oscillator-based computing systems.
“BZ-PZ computations are not digital, like most people are familiar with, and so to recognize something like a blurred pattern within an image requires nonconventional computing,” Dr. Balazs explained. “For the first time, we have been able to show how these materials would perform the computations for pattern recognition.”
Dr. Levitan and Mr. Fang first stored a pattern of numbers as a set of polarities in the BZ-PZ units, and the input patterns are coded through the initial phase of the oscillations imposed on these units. The computational modeling revealed that the input pattern closest to the stored pattern exhibits the fastest convergence time to the stable synchronization behavior, and is the most effective at recognizing patterns. In this study, the materials were programmed to recognize black-and-white pixels in the shape of numbers that had been distorted.
Compared to a traditional computer, these computations are slow and take minutes. However, Dr. Yashin notes that the results are similar to nature, which moves at a “snail’s pace.”
“Individual events are slow because the period of the BZ oscillations is slow,” Dr. Yashin said. “However, there are some tasks that need a longer analysis, and are more natural in function. That’s why this type of system is perfect to monitor environments like the human body.”
For example, Dr. Yashin said that patients recovering from a hand injury could wear a glove that monitors movement, and can inform doctors whether the hand is healing properly or if the patient has improved mobility. Another use would be to monitor individuals at risk for early onset Alzheimer’s, by wearing footwear that would analyze gait and compare results against normal movements, or a garment that monitors cardiovascular activity for people at risk of heart disease or stroke.
Since the devices convert chemical reactions to electrical energy, there would be no need for external electrical power. This would also be ideal for a robot or other device that could utilize the material as a sensory skin.
“Our next goal is to expand from analyzing black-and-white pixels to grayscale and more complicated images and shapes, as well as to enhance the devices storage capability,” Mr. Fang said. “This was an exciting step for us and reveals that the concept of “materials that compute” is viable.”
Soft materials are great at damping energy — that’s why rubber tires are so good at absorbing the shock of bumps and potholes. But if researchers are going to build autonomous soft systems, like soft robots, they’ll need a way to transmit energy through soft materials.
Now, researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS), in collaboration with colleagues at the California Institute of Technology, have developed a way to send mechanical signals through soft materials.
The research is described in the Proceedings of the National Academy of Sciences.
“Soft autonomous systems have received a lot of attention because, just like the human body or other biological systems, they can be adaptive and perform delicate movements. However, the highly dissipative nature of soft materials limits or altogether prevents certain functions,” said Jordan Raney, postdoctoral fellow at SEAS and first author of the paper. “By storing energy in the architecture itself we can make up for the energy losses due to dissipation, allowing the propagation of mechanical signals across long distances.”
The system uses the centuries-old concept of bistable beams — structures stable in two distinct state — to store and release elastic energy along the path of a wave. The system consists of a chain of bistable elastomeric beams connected by elastomeric linear springs. When those beams are deformed, they snap and store energy in the form of elastic deformation. As the signal moves down the elastomer, it snaps the beams back into place, releasing the stored energy and sending the signal downstream like a line of dominos. The bistable system prevents the signal from dissipating downstream.
“This design solves two fundamental problems in transmitting information through materials,” said Katia Bertoldi, the John L. Loeb Associate Professor of the Natural Sciences at SEAS and senior author of the paper. “It not only overcomes dissipation, but it also eliminates dispersive effects, so that the signal propagates without distortion. As such, we maintain signal strength and clarity from start to end.”
The beam geometry requires precise fabrication techniques. If the angle or thickness of one beam is off by one degree or millimeter, the whole system fails.
The team used advanced 3D printing techniques to fabricate the system.
“We’re developing new materials and printing methods that enable the fabrication of soft materials with programmable bistable elements,” said Jennifer A. Lewis, the Hansjorg Wyss Professor of Biologically Inspired Engineering and coauthor of the paper.
The team designed and printed a soft logic gate using this system. The gate, which looks like a tuning fork, can be controlled to act as either as an AND or as an OR gate.
“It’s amazing what you can do using simple beams — a building block that’s been around hundreds of years,” said Bertoldi. “You can do new stuff with a very old, well studied and very simple component.”
Learn more: Transmitting energy in soft materials
Lightweight suit to increase the wearer’s strength and endurance
For decades engineers have built exoskeletons that use rigid links in parallel with the biological anatomy to increase the wearer’s strength and endurance, and to protect them from injury and physical stress. In recent years, a number of systems have been developed that show strong commercial potential for helping spinal-cord injury patients walk, or helping soldiers carry heavy loads. In these systems, there is an exoskeleton structure in parallel with the wearer’s skeletal structure that is typically connected at a few locations on the body using straps or belts. These devices use motors or elastic materials to assist with joint movements, thereby enhancing human power. However, exoskeletons often fail to allow the wearer to perform his or her natural joint movements, are generally heavy, and can hence cause fatigue.
The Wyss Solution
Targeting a specific set of applications where a wearer needs some partial assistance from a robot, Wyss Institute researchers are pursuing a new paradigm: the use of soft clothing-like “exosuits.” An exosuit does not contain any rigid elements, so the wearer’s bone structure must sustain all the compressive forces normally encountered by the body — plus the forces generated by the exosuit. The suit, which is composed primarily of specially designed fabrics, can be significantly lighter than an exoskeleton since it does not contain a rigid structure. It also provides minimal restrictions to the wearer’s motions, avoiding problems relating to joint misalignment.
Exosuits exemplify a new class of applications for soft robotics, an emerging field that combines classical robotic design and control principles with active soft materials.
Soft robots can bend, walk and grip. And, unlike their rigid counterparts, some can get flattened and bounce back into shape.
Now scientists report a new advance in the journal ACS Applied Materials & Interfaces: a way to make elastic material for soft robots that changes color when it stretches. They say this process opens the door to robot camouflage, new ways to deliver medicines and other applications.