Researchers at Ajou University in South Korea have built a miniature five-fingered robotic hand that uses electrified wires as sensors. This tiny robot is capable of handling snail eggs just 3 mm wide. It may one day be able to grasp objects as small as human eggs.
Engineers have long sought to model nature in interactions with our environment. The soft robotic gripper developed at Ajou University uses mechanical sensors to detect vibrations and pressure. Silver nanowires embedded in each finger enable it to apply heat and measure temperature.
Modeling Nature's Tools
The survival of the human species has depended on its ability to interact with its environment. Mammals, birds and other species have developed natural tools to build, hunt and feed. These tools allow them to interact with their environment in the most efficient manner.
For example, octopi have long, soft tentacles which are well adapted to their environment. The octopus' ability to elongate, compress and bend its tentacles is a good example of soft manipulators in nature.
The human hand itself is a model of excellent design. Four fingers and an opposable thumb made of rigid bones and soft ligaments have given humans a sophisticated sense of touch and grip. These natural tools have helped us craft complex structures, from the tiniest object to the tallest building.
Early robotic arms were designed for industrial applications. They were designed to apply mechanical force with a high degree of precision but with limited flexibility. Initial designs of human-inspired robotic hands utilized rigid body links, with limited degrees of freedom and low flexibility.3
However, there have been efforts to shift from this purely mechanical approach to an approach that mimics the processes observed in nature. Thus, continuous body configurations and soft materials are being used.
These robotic manipulators exhibit high degrees of freedom in movement. They're able to handle deformities and conform to the structure they handle.
Consequently, soft robotics uses materials and actuation methods that are soft and pliable. This is a significant change in direction promising many exciting applications in industry and medicine.
The Rise of Soft Robotic Grippers
With an increase in industrial automation, there's a growing demand for robots to perform in unstructured environments. Thus, soft robotics is a growing area of research that focuses on using soft materials and structures for highly adaptive robotics.
Soft grippers are an important development in the progress towards mechanically compliant - and multi-functional - surfaces adapted to sensing and stimulating soft objects and organisms.
The team at Ajou University developed a millimeter-scale soft robotic gripper based on a shape memory polymer. It can lift and manipulate a load 1,200 times its own weight. Further tests showed that it could carry a load of up to 6,400 times its weight. This represents the highest payload capacity achieved in soft grippers to date.
Sensing has always been a challenge in soft robotics. In Ajou University's robotic gripper, silver nanowires and crack-based strain sensors embedded in the fingers enable simultaneous measurement of temperature and pressure of the objects it grasps. They can also apply mechanical and thermal stimuli to these objects.
The fingers in this tiny robotic hand are a little over a quarter-inch long and about 8 times as wide as a piece of human hair. The "muscles" in each finger are made of a shape memory polymer. When electric currents are applied to the nanowires, they heat causing the polymer to bend and curl the fingers.2
Mechanical sensors within the hand detect pressure and vibration. They were even able to measure the blood pressure of a pig. Remarkably, the hand is also powerful enough to open lids on bottles, yet sufficiently gentle to handle salmon eggs without cracking them.2
"If the gripper can be used in such platforms that can mechanically and strongly fix cells without injury, we believe that it can make a great contribution to human health," - Seungyong Han, Mechanical Engineer - Ajou University
With potentially infinite degrees of freedom, soft sensors have the potential to significantly improve control systems. This will have important applications in areas that require soft interactions, heralding significant advances in industry and medicine.
References and Further Reading
Yeonwook R. et al. (2021). Vital signal sensing and manipulation of a microscale organ with a multifunctional soft gripper. DOI: 10.1126/scirobotics.abi6774
Hughes J. et al. (2016) Soft Manipulators and Grippers: A Review. Available at: https://doi.org/10.3389/frobt.2016.00069