Skin-like sensor allows gripper to do challenging tasks

Researchers have developed a soft tactile sensor with skin-comparable characteristics.

The team, co-led by City University of Hong Kong (CityU), mounted the sensor to a robotic gripper at the fingertip and found it could accomplish challenging tasks such as stably grasping fragile objects and threading a needle.

The research provides new insight into tactile sensor design and could contribute to various applications in the robotics field. The study has been recently published in the scientific journal Science Robotics, titled ‘Soft magnetic skin for super-resolution tactile sensing with force self-decoupling’.

Mimicking human skin characteristics

A main characteristic of human skin is its ability to sense shear force, meaning the force that makes two objects slip or slide over each other when coming into contact. By sensing the magnitude, direction and subtle change of shear force, our skin can act as feedback and allow us to adjust how we should hold an object stably with our hands and fingers or how tight we should grasp it.

Researchers Dr Shen Yajing and Dr Pan Jia designed the soft tactile sensor to mimic this function.

The sensor is in a multilayered structure similar to human skin and includes a flexible and specially magnetised film, about 0.5 mm thin, as the top layer. When an external force is exerted on it, it can detect the change of the magnetic field due to the film’s deformation.

Decoupling

The researchers said one of the most important features of the sensor is that it can ‘decouple’.

Decoupling is when external force is automatically decomposed into two components — normal force (the force applied perpendicularly to the object) and shear force, providing the accurate measurement of these two forces respectively.

“It is important to decouple the external force because each force component has its own influence on the object. And it is necessary to know the accurate value of each force component to analyse or control the stationary or moving state of the object,” said Yan Youcan, PhD student at CityU’s Department of Biomedical Engineering (BME) and the first author of the paper.

Robotic gripper with the new sensor completes challenging tasks

By mounting the sensor at the fingertip of a robotic gripper, the team showed that robots can accomplish challenging tasks. For example, the robotic gripper stably grasped fragile objects like an egg while an external force tried to drag it away, and also threaded a needle by remote control.

“The super-resolution of our sensor helps the robotic hand to adjust the contact position when it grasps an object. And the robotic arm can adjust force magnitude based on the force decoupling ability of the tactile sensor,” Dr Shen said.

Applications

Designing a nimble, responsive gripper has been one of the challenges that have stopped the use of robotics for various applications in the food processing industry.

The variety in shape, weight and firmness of natural food products has made them difficult to handle for robotic grippers.

Currently, CityU’s soft tactile sensor is still in its infancy and its potential remains unrealised.

But breaking down the barriers of what makes a robotic gripper different from a human hand will likely increase the chance that the technology can be utilised in various applications. 

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