Aresearch team developed a soft tactile sensor with skin-comparable characteristics. A robotic gripper with the sensor mounted at the fingertip could accomplish challenging tasks such as stably grasping fragile objects and threading a needle.

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

To mimic this feature of human skin, the soft tactile sensor is integrated into a multi-layered structure like human skin and includes a flexible and specially magnetized film of 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. More importantly, it can decouple or decompose the external force automatically into two components: normal force (the force applied perpendicularly to the object) and shear force, providing the accurate measurement of these two forces, respectively.

Moreover, the sensor possesses another human skin-like characteristic: the tactile “super-resolution” that allows it to locate the stimuli’s position as accurately as possible. An efficient tactile super-resolution algorithm uses deep learning to achieve a 60-fold improvement of the localization accuracy for contact position. Such a tactile super-resolution algorithm can help improve the physical resolution of a tactile sensor array with the least number of sensing units, thus reducing the number of wirings and the time required for signal transmitting.

By mounting the sensor at the fingertip of a robotic gripper, the team showed that robots can accomplish challenging tasks. The robotic gripper stably grasped fragile objects like an egg while an external force tried to drag it away, and threaded a needle via teleoperation. The sensor can be easily extended to the form of sensor arrays or even continuous electronic skin that covers the whole body of the robot.

The sensitivity and measurement range of the sensor can be adjusted by changing the magnetization direction of the top layer (magnetic film) of the sensor without changing the sensor’s thickness. This enables the e-skin to have different sensitivity and measurement range in different parts, just like human skin. Also, the sensor has a much shorter fabrication and calibration process compared with other tactile sensors.

The sensor could be beneficial to applications in the robotics field such as adaptive grasping, dexterous manipulation, texture recognition, smart prosthetics, and human-robot interaction.

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Motion Design Magazine

This article first appeared in the June, 2021 issue of Motion Design Magazine.

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