Soft and Sensitive Robotic Finger Design That Provides Accurate Grip

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3D printable fingers integrated with sensing mechanisms make robots capable of executing tasks related to health and elderly care.

Even though robotics has reshaped and even redefined many industrial sectors to a large extent, gaps still exist between humans and machines in fields such as health and elderly care. For robots to safely manipulate or interact with fragile objects and living organisms, it is required that new strategies be developed to enhance their perception of the external world. In fact, building a safe and dexterous robotic gripper with human-like capabilities is currently one of the most important goals in robotics.

One of the main challenges in the design of soft robotic grippers is the integration of traditional sensors onto a robot’s fingers. Ideally, a soft gripper should have what’s known as proprioception—a sense of its own movements and position for safely executing varied tasks. However, traditional sensors are rigid and compromise the mechanical characteristics of the soft parts. Moreover, existing soft grippers are usually designed with a single type of proprioceptive sensation; either pressure or finger curvature.

To overcome these limitations, scientists at Ritsumeikan University, Japan have successfully used multi-material 3D printing technology to fabricate soft robotic fingers with a built-in proprioception sensor. This design strategy offers numerous advantages and represents a large step towards developing safer and more capable soft robots.

The soft finger has a reinforced inflation chamber that makes it bend in a highly controllable way according to the input air pressure. Additionally, the stiffness of the finger is also tunable by creating a vacuum in a separate chamber through a mechanism called vacuum jamming. In this, multiple stacked layers of a bendable material can be made rigid by sucking out the air between them. Both functions together enable a three-finger robotic gripper to properly grasp and maintain hold of any object by maintaining the required force.

Enhanced pressure effect

Most notable, however, is that a single piezoelectric layer was included among the vacuum jamming layers as a sensor. Since piezoelectric effect produces a voltage difference when the material is under pressure, this phenomenon served as a sensing mechanism for the robotic finger, providing a simple way to sense both its curvature and initial stiffness (before vacuum adjustment). The finger’s sensitivity was further enhanced by including a microstructured layer among the jamming layers to improve the distribution of pressure on the piezoelectric material.

The use of multi-material 3D printing, a simple and fast prototyping process, allowed for easy integration of the sensing and stiffness-tuning mechanisms into the robotic finger design.

“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 behaviour,” says Prof Mengying Xie.

Another remarkable feature of the design is that the sensor is self-powered by the piezoelectric effect, meaning that it requires no energy supply—essential 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, ” says Prof Mengying Xie.

Overall, this exciting new study will help future researchers find new ways of improving how soft grippers interact with and sense the objects being manipulated.

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