'Soft' actuator could remove need for robotic tethers

Because of their ability to manipulate delicate objects and cope well with unexpected environments so-called soft robots are becoming increasingly widely used. However the fluidic actuators that they relay on to move around are often bulky and require large amounts of air or water, which are typically delivered via a tether.

The Harvard device harnesses a phenomenon in which an innovative arrangement of balloons can be used to trigger rapid changes in shape and size with only small changes in volume.

A paper in the Proceedings of the National Academy of Sciences explains that the actuator was inspired by a physics experiment in which two balloons are inflated to different sizes and connected via a tube and valve.

When the valve is opened, air flows between the balloons. But instead of equalising in size, as one might expect, the larger balloon inflates more while the smaller balloon deflates. This unexpected behaviour comes from the balloons’ non-linear relationship between pressure and volume, meaning that an increase in volume doesn’t necessarily increase the pressure.