Building a safe and dextrous robotic gripper with human-like capabilities is currently one of the most important goals in robotics, said the developers of the gripper, a team of scientists at Ritsumeikan University in Japan.
Existing robotic fingers are held back by rigid sensors that compromise the mechanical characteristics of soft parts, the team said. Previous soft grippers normally either sense just pressure or curvature, they added.
The team, led by associate professor Mengying Xie, used multi-material 3D printing to fabricate soft robotic fingers with built-in proprioception sensors.
The soft finger has a reinforced inflation chamber that makes it bend in a highly controllable way, the researchers said. The stiffness of the finger is also tuneable by creating a vacuum in a separate chamber. This was achieved through a mechanism called vacuum jamming, by which multiple stacked layers of a bendable material can be made rigid by sucking out the air between them.
The combined properties allowed a three-finger robotic gripper to grasp and maintain hold of many different objects, the team said.
The gripper also includes a single piezoelectric layer, included between the vacuum jamming layers as a sensor. The piezoelectric effect produces a voltage difference when the material is under pressure. The scientists leveraged this phenomenon as a sensing mechanism for the robotic finger, providing a simple way to sense both its curvature and initial stiffness. They further enhanced the finger's sensitivity by including a micro-structured layer among the jamming layers, to improve the distribution of pressure on the piezoelectric material.
The sensor is self-powered by the piezoelectric effect, meaning it requires no energy supply. Prof Xie said: “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.”
The work was published in Nano Energy.
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