Soft Actuators

A soft actuator is made of rubber with air chambers molded inside. One side has a stiff, unstretchable layer. When the chambers inflate, the soft side stretches and the finger curls toward the stiff side. Soft grippers can pick up delicate or oddly shaped objects without careful planning.

Air pressure Object Pump in and out automatically

Bending from pressure

A common simple model treats the finger as a constant-curvature arc. Its curvature $\kappa$ grows with pressure $p$, so the total bend angle over finger length $L$ is

$$\kappa \approx c\,p \qquad \theta_{\text{bend}} = \kappa\,L$$

where $c$ depends on the rubber's stiffness and the chamber shape.

What to notice

Each chamber bulges as pressure rises, and the finger curls into an arc. When it touches an object, the finger stops bending where it touches and wraps around the shape. That is called passive compliance: the gripper adapts to the object's shape by itself, with no sensing or planning. The contact force stays low, which is how soft grippers hold eggs and fruit.

The trade-off is precision and strength. Soft actuators are hard to model exactly, they are slower than motors, and they carry less load.