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Sensorization of Soft Hands and Actuators

Due to the high deformability of soft actuators, most existing sensor technologies are not compatible. They often rely on joints and rigid links and are not flexible enough to work with silicone rubber based actuators.

This is why one branch of our research tackles this problem and investigates how to add rich tactile and proprioceptive feedback to highly flexible actuators like the PneuFlex.

Liquid Metal Strain Sensors

PneuFlex actuators with liquid metal strain sensors
Lupe

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.

Contact: Vincent Wall

Acoustic Sensing

Cross section of the PneuFlex actuator with embedded microphone for acoustic sensing
Lupe

Another, slightly surprising, approach to sensorization of soft actuators is to put "ears" inside them. By adding a microphone into the air chamber of the PneuFlex actuator, we can hear contact anywhere on the finger. This is possible, because any time the finger comes in contact with an object or the environment, this contact event creates a sound that travels through the air chamber -- similar to when something knocks on your headphones while you wear them.

Impressively, the contact 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.

In the next steps, we will investigate the addition of a miniature speaker into the air chamber to actively measure the contact state.

Related publications:

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.

Contact: Vincent Wall

Sensorized RBO Hand 2

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:
Wall, Vincent, Gabriel Zöller, and Oliver Brock. "A method for sensorizing soft actuators and its application to the RBO hand 2." Robotics and Automation (ICRA), 2017 IEEE International Conference on. IEEE, 2017. [Link]



You can find more videos of the soft hands on our YouTube channel!

 

Contact: Vincent Wall 

Funding

Lupe

Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany's Excellence Strategy - EXC 2002/1 "Science of Intelligence" - project number 390523135. SoMa - Soft Manipulation, Horizon 2020 project funded by the European Commission. May 2015 - April 2019. Alexander von Humboldt professorship - awarded by the Alexander von Humboldt foundation and funded through the Ministry of Education and Research, BMBF,
July 2009 - June 2015

Publications

Raphael Deimel and Oliver Brock. A Compliant Hand Based on a Novel Pneumatic Actuator. Proceedings of the IEEE International Conference on Robotics and Automation (ICRA), pp. 2047–2053, 2013.

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Raphael Deimel and Oliver Brock. A Novel Type of Compliant, Underactuated Robotic Hand for Dexterous Grasping. Robotics:Science and Systems (RSS), 2014.

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Vincent Wall and Raphael Deimel and Oliver Brock. Selective Stiffening of Soft Actuators Based on Jamming. Proceedings of the IEEE International Conference on Robotics and Automation (ICRA), pp. 252-257, 2015.

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Raphael Deimel and Oliver Brock. A Novel Type of Compliant and Underactuated Robotic Hand for Dexterous Grasping. The International Journal of Robotics Research 35(1-3):161-185, 2016.

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Raphael Deimel and Marcel Radke and Oliver Brock. Mass Control of Pneumatic Soft Continuum Actuators with Commodity Components. IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), pp. 774–779, 2016.

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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.

Download Bibtex entry

Raphael Deimel and Patrick Irmisch and Vincent Wall and Oliver Brock. Automated Co-Design of Soft Hand Morphology and Control Strategy for Grasping. IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), pp. 1213-1218, 2017.

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Espen Knoop and Moritz Bächer and Vincent Wall and Raphael Deimel and Oliver Brock and Paul Beardsley. Handshakiness: Benchmarking for Human-Robot Hand Interactions. IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), pp. 4982-4989, 2017.

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Keyan Ghazi-Zahedi and Raphael Deimel and Guido Montúfar and Vincent Wall and Oliver Brock. Morphological Computation: The Good, the Bad, and the Ugly. IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), pp. 464-469, 2017.

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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.

Download Bibtex entry

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.

Download Bibtex entry

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