Robotics and Biology Laboratory

Sensorization of Soft Hands and Actuators

Sensing is a necessity for robotics, and even more so for soft robots. Due to their high compliance, any interaction with the environment leads to complex deformations. To be able to react accordingly and to best leverage the beneficial compliance, we need to observe, i.e. measure, such interactions using sensors.

Most existing sensor technologies are not compatible with our highly-flexible soft robotic actuators. They often rely on joints and rigid links and are not compliant enough to work with silicone rubber based actuators.

Instead, we develop novel "soft" sensor technologies for soft hands and actuators. We create sensors that can stretch, bend, twist, and minimize their effect on the actuator's beneficial compliance. Additionally, we strive to use as much prior knowledge as possible, to extract the relevant measurements from the complex, high-dimensional sensor data. As a result, we can sense a wide variety of actuator properties, including deformation, contact forces, contact locations, and even object materials.

Acoustic Sensing

© RBO

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Contact Persons

Vincent Wall

Our most recent, surprisingly effective, approach to sensorization of soft actuators is to put "ears" inside them. By adding a microphone and a speaker into the air chamber of the PneuFlex actuator, we can hear contact anywhere on the finger.

For this, we record sound using the embedded microphone and because the specific modulation of sound depends on the current physical state of the actuator, e.g. its geometry, actuation, and also interaction, we can infer this state from only the sound. Impressively, the sound is so distinctive that we can even identify the location of contact, but also contact forces and even object material, all from sound alone.

Related publications:
Vincent Wall and Oliver Brock. A Virtual 2D Tactile Array for Soft Actuators Using Acoustic Sensing. IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), 2022

Gabriel Zöller and Vincent Wall and Oliver Brock. Active Acoustic Contact Sensing for Soft Pneumatic Actuators. Proceedings of the IEEE International Conference on Robotics and Automation (ICRA), 2020.

Gabriel Zöller and Vincent Wall and Oliver Brock. Acoustic Sensing for Soft Pneumatic Actuators. IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), pp. 6986–6991, 2018.

Liquid Metal Strain Sensors

Contact Persons

Vincent Wall

To measure the deformation of the soft actuators during interaction with objects and the environment, we use highly stretchable, liquid metal strain sensors. These sensors consist of a metal alloy that is liquid at room temperature, which is injected into thin silicone tubes. When stretched, they change their electrical resistance, which we can measure.

We found that even though the space of possible deformations of the soft actuator is extremely big, the deformations that actually occur are much more limited. Using a recursive feature elimination approach, we can identify a small set of strain sensors to measure the task-relevant actuator deformations.

Related publications:

Vincent Wall and Gabriel Zöller and Oliver Brock. A Method for Sensorizing Soft Actuators and Its Application to the RBO Hand 2. Proceedings of the IEEE International Conference on Robotics and Automation (ICRA), pp. 4965–4970, 2017.

Vincent Wall and Oliver Brock. Multi-Task Sensorization of Soft Actuators Using Prior Knowledge. Proceedings of the IEEE International Conference on Robotics and Automation (ICRA), pp. 9416–9421, 2019.

Sensorized RBO Hand 2

© RBO

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Contact Persons

Vincent Wall

The sensor feedback of the RBO Hand 2 is limited to the channel pressures. But the space of potential deformations of the PneuFlex actuators is very large. While it will not be possible to detect all those different deformations, we proposed a method to sensorize the fingers of the RBO Hand 2 to detect task relevant deformations. The result is the Sensorized RBO Hand 2. 

Related Publication:
Vincent Wall and Gabriel Zöller and Oliver Brock. A Method for Sensorizing Soft Actuators and Its Application to the RBO Hand 2. Proceedings of the IEEE International Conference on Robotics and Automation (ICRA), pp. 4965–4970, 2017.

Funding

Publications

2023

Wall, Vincent; Zöller, Gabriel; Brock, Oliver
Passive and Active Acoustic Sensing for Soft Pneumatic Actuators
The International Journal of Robotics Research, 42 :108-122
2023

2022

Wall, Vincent; Brock, Oliver
A Virtual 2D Tactile Array for Soft Actuators Using Acoustic Sensing
Proceedings of IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS)
Oktober 2022

2020

Zöller, Gabriel; Wall, Vincent; Brock, Oliver
Active Acoustic Contact Sensing for Soft Pneumatic Actuators
Proceedings of the IEEE International Conference on Robotics and Automation (ICRA), Seite 7966-7972
Mai 2020

2019

Wall, Vincent; Brock, Oliver
Multi-Task Sensorization of Soft Actuators Using Prior Knowledge
Proceedings of the IEEE International Conference on Robotics and Automation (ICRA), Seite 9416–9421
Mai 2019

2018

Zöller, Gabriel; Wall, Vincent; Brock, Oliver
Acoustic Sensing for Soft Pneumatic Actuators
IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), Seite 6986–6991
Oktober 2018
ISBN
978-1-5386-8093-3

2017

Wall, Vincent; Zöller, Gabriel; Brock, Oliver
A Method for Sensorizing Soft Actuators and Its Application to the RBO Hand 2
Proceedings of the IEEE International Conference on Robotics and Automation (ICRA), Seite 4965–4970
Mai 2017