Oct 31 2019
Salamanders, chameleons, and many different species of toads make use of stored elastic energy to put out their sticky tongues and catch unwary insects within a tenth of a second. These insects are usually located at a distance of about one-and-a-half body lengths of the reptiles.
Ramses V. Martinez, an assistant professor at Purdue University, and his students created this cover image. Chameleon tongue strikes inspired the team to create soft robots that catch live insects in the blink of an eye. (Image credit: Purdue University)
Ramses Martinez, an assistant professor in the School of Industrial Engineering at Purdue University, and also in the Weldon School of Biomedical Engineering at Purdue University’s College of Engineering, has now created a new class of fully soft robots and actuators. Other Purdue scientists at the FlexiLab have also contributed to this development.
The soft robots and actuators use stored elastic energy to re-produce bio-inspired, high-speed, and high-powered motions. They are developed using stretchable polymers that are analogous to rubber bands. These polymers have internal pneumatic channels that expand on pressurization.
The body of these robots is stretched in one or numerous directions to store their elastic energy; this is done during the fabrication process that follows bio-inspired principles.
Just like how the chameleon’s tongue strikes, a pre-stressed pneumatic soft robot can stretch five times its original length, trap a live fly beetle, and retrieve it in just 120 ms.
We believed that if we could fabricate robots capable of performing such large-amplitude motions at high speed like chameleons, then many automated tasks could be completed more accurately and in a much faster way. Conventional robots are usually built using hard and heavy components that slow down their motion due to inertia. We wanted to overcome that challenge.
Ramses Martinez, Assistant Professor, School of Industrial Engineering, Purdue University
The novel technology has been reported in the October 25th, 2019, edition of Advanced Functional Materials.
Several birds, such as the three-toed woodpecker, use the elastic energy to achieve zero-power perching. This energy, which is preserved in the stressed tendons at the back of the birds’ legs, helps them to remain in a perch when asleep.
The birds’ anatomy has served as an example to facilitate the development of robotic grippers that have a zero power holding capacity of up to 100 times their weight and can perch upside down from up to 116° angles.
The soft arms of these grippers conform to the gripped object, thus increasing the contact area. This, in turn, enhances grasping and facilitates zero-power holding and high-speed catching.
Moreover, certain plants know how to leverage elastic energy to realize high-speed movement using “trap mechanisms.” For example, the Venus flytrap utilizes the elastic energy preserved in its curved and bistable leaves to quickly trap prey that explores its internal surface.
Taking a cue from the trap mechanism of the Venus flytrap and exploring how lizards are able to capture insects, the Purdue researchers ultimately developed a soft robotic Venus flytrap. When this flytrap receives a short pressurized stimulus, it closes in just 50 ms.
According to Martinez, the novel pre-stressed soft robots offer several major benefits when compared to today’s soft robotic systems. First, the pre-stressed soft robots excel at holding, gripping, and controlling a wide range of objects at high speed. By using the elastic energy preserved in their pre-stressed elastomeric layer, the robots can hold objects that are up to 100 times their weight without using up any external power.
The soft skin of these robots can be effortlessly patterned with anti-slip microspikes, which considerably boost their traction. This allows them to perch upside down over extended periods of time and trap live prey.
We envision that the design and fabrication strategies proposed here will pave the way toward a new generation of entirely soft robots capable of harnessing elastic energy to achieve speeds and motions currently inaccessible for existing robots.
Ramses Martinez, Assistant Professor, School of Industrial Engineering, Purdue University
Martinez and his research group have also worked with the Purdue Research Foundation Office of Technology Commercialization to patent a few of his technologies associated with robots and other design breakthroughs.
Chameleon's elastic tongue inspires fast-acting robots
(Video credit: Purdue University)