By adding sensing mechanisms into 3D printable fingers, scientists have advanced robotic gripper by making them more "human-like."
Making more human-like robotic grippers are made possible by adding sensory capabilities to the "fingers," providing feedback to the gripper and allowing it to adjust appropriately. However, conventional sensors tend to compromise the mechanical properties of these soft robots.
Researchers' latest effort at Ritsumeikan University in Japan resulted in the design and fabrication of a 3D printable soft robotic finger fitted with a built-in sensor of adjustable stiffness. Details of their study are reported in the journal Nano Energy, included in its January 2021 issue.
Flexible 3D Printed Fingers
One of the challenges for soft grippers is a sense called proprioception - a sense of spatial awareness with respect to its own position - to empower them to safely execute a wide variety of tasks. In humans, proprioception allows us to close our eyes and touch our nose with our index finger because we know where our body parts in relation to each other. However, modern soft grippers are only usually limited to a single type of proprioceptive sensing: either gripping pressure or finger curvature.
To overcome these limitations, the Ritsumeikan researchers have developed a novel gripper design under the guidance of Associate Professor Mengying Xie. The team used a technique called multi-material 3D printing tech to fabricate their soft robotic fingers that have their own sensor.
With this new design, future robotic grippers can now enjoy numerous advantages and can be designed with more safety and flexibility. Additionally, the soft finger is fitted with a reinforced inflation chamber, allowing it to bend controllably depending on the input air pressure. The finger's stiffness is also tunable by creating a vacuum through a mechanism called vacuum jamming. In this process, multiple layers of bendable material can become rigid by reducing the air between these layers. They came up with a three-finger robot gripper with these two techniques that can grip and hold any object by applying only the force needed.
An Ingenious Approach to Gripper Sensitivity
Another innovation included in the study is using a single piezoelectric layer, embedded as a layer in the vacuum jamming materials. As the air is sucked out and the layers compress, the piezoelectric material generates electricity, which in turn is used to provide feedback for the finger. This offers a simple mechanism for sensing the finger's curvature and stiffness. The soft finger's sensitivity was further improved by adding a microstructured layer in the jamming layers to improve the pressure applied on the piezoelectric material.
"Our work suggests a way of designing sensors that contribute not only as sensing elements for robotic applications but also as active functional materials to provide better control of the whole system without compromising its dynamic behavior," shared Xie in a statement. Aside from providing feedback, the piezoelectric layer also powers the sensor. Since it has no external energy supply, it makes the design perfect for low-power applications.
"Self-powered built-in sensors will not only allow robots to safely interact with humans and their environment, but also eliminate the barriers to robotic applications that currently rely on powered sensors to monitor conditions," Xie added.
