Soft Robot Motion Measurement: Hybrid Soft Sensor with Embedded IMU’s

Soft Robots for Safety and Efficiency

Over the past 50 years, robotics have changed the face of our economy. From building cars to exploring space, humanity could not innovate at our current pace without the help of these machines. When you think of robots, you probably think of something like C-3PO from Star Wars: metal, rigid, shiny and jerky. But our common perception of a robot’s form may soon become outdated, as some tasks require a more delicate touch.

You may recognize this soft robot concept, Baymax, from the Pixar animated movie Big Hero 6.

Soft robots are made of flexible and adaptable material. Their elastic design is safer and more efficient in tasks like biomimicry, cooperative robotics, medicine, exploration, and wearable electronics. Soft robots are also more safe around humans in a manufacturing setting, as a fast-paced factory with traditional robots leaves room for serious collision injuries. Soft robots can even perform surgery because of their ability to change shape and minimize damage on impact.

Soft robots are improving, as new manufacturing techniques for their creation continue to grow. But to be able to reliably perform in these areas, soft robots need more development in their control systems and sensors.

Hybrid Sensors to Measure Soft Robot Movements

Osman Dogan Yirmibesoglu is a PhD candidate studying Robotics at Oregon State University. Yirmibesoglu has been building robots since his childhood in Turkey, and he “wants to enhance the future of soft robotics by measuring their motion. These things [his products] are going to make us see their motion instead of being blind to the pressure we are using with a soft robot.”

IMUs are a traditional way to measure robotic movement.

As robots have evolved in form, some of the technology supporting this innovation has not kept up. Robotic movement is traditionally measured with Inertial Measurement Units (IMUs), which are a combination of gyroscopes and accelerometers – accurate yet rigid tools. It is important to measure robotic movement because it gives robots the information they need to make precise and informed movements. Because the technology behind IMUs are rigid, they are not conducive to soft robot measurement. So, for soft robots, developers have used soft sensors using only soft strain gauges to measure motion. These soft sensors have lower accuracy those of traditional robots.

“There needs to be more proper measurement of the joints, angles, and motion,” Yirmibesoglu says. “So, I put the two types of sensors together.” He put rigid sensors into the soft strain sensors to build a platform to bring them together, thus creating more reliable measurements through a hybrid soft-and-rigid design for the sensor.

Creation of the Hybrid Sensor

“This hybrid structure acts as a platform for combining rigid and soft sensors to improve the accuracy of angle measurements.”

Like the soft strain sensor, the hybrid sensor is a hyperelastic silicone elastomer with conductive liquid metal inside. However, its ends have two rigid IMUs within a highly elastic material. This design incorporates the benefits of both types of sensors while maintaining the flexibility of a soft sensor.

The most challenging part of this project, Yirmibesoglu shared, was to stabilize rigid IMU circuits inside. He wanted to make sure the rigid circuits would not move and puncture the cushiony material. So, he created a buffer zone to put the rigid circuits inside. Read more in his published research dissertation, “Hybrid soft sensor with embedded IMUs to measure motion.”

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