A New Method to Measure the Motion of Soft Robots

University of Southern California, CA

A demonstration of using the strain sensors for sensing soft robot motion. (Image: USC)

USC researchers have developed an innovative solution to measure the motion of soft components in robotics.

In the field of soft robotics, a comparable method has been used to track the deformation — or changes in shape — of soft components such as the muscles of a robotic arm. Cameras can gather the data that enables researchers to measure stretchability and recovery, crucial information for predicting and therefore controlling the motion of the robot.

Here’s the catch: This process rarely works outside the lab. If a robot is navigating the ocean, operating up in space, or enclosed within the human body, a set-up of multiple cameras isn’t always practical.

That’s why Hangbo Zhao, who holds dual appointments as Assistant Professor in the Department of Aerospace and Mechanical Engineering and the Alfred E. Mann Department of Biomedical Engineering, decided to test an alternative approach.

Prompted by conversations with his colleagues in soft robotics, Zhao and his research group have developed a design for a new sensor using 3D electrodes inspired by the folding patterns used in origami, able to measure a strain range of up to three times higher than a typical sensor.

The sensors can be attached to soft bodies in motion — anything from the mechanical tendons of prosthetic leg, to the pulsating matter of human internal organs — for the purpose of tracking shape-change and proper functioning, no cameras required. “To develop the new sensor, we leveraged our previous work in the design and manufacture of small-scale 3D structures that apply principles of origami,” Zhao explained. “This allows the sensors to be used repeatedly, and to give precise readings even when measuring large and dynamic deformations of soft bodies.”

Existing stretchable strain sensors typically use soft materials like rubber — but this type of material can undergo irreversible changes in the material properties through repeated use, producing unreliable metrics when it comes to deformation detection. But what if the material of the sensor wasn’t inherently soft or stretchy? Instead, the 3D structure of the electrodes would convert stretch and release to a process of unfolding and folding.

“We integrate the 3D origami-inspired electrodes with a soft, stretchable substrate through covalent bonding,” Zhao explained. “This unique combination allows us to measure a very large deformation, as much as 200 percent strain, with an ultra-low hysteresis of around 1.2 percent. There’s also a very fast response, within 22 milliseconds.”

Because the sensors can accurately measure large, complex, and fast-moving deformations, there are countless opportunities for practical application in wearable electronics, prosthetics, and robotics.

For more information, contact Amy Blumenthal at This email address is being protected from spambots. You need JavaScript enabled to view it.; 213-821-1887.