A bellows soft actuator is a flexible robotic part that moves when air pressure inflates a series of pleated chambers. Instead of using rigid motors and joints, it changes shape because its soft walls stretch, unfold, and push against each other. This makes it useful for handling fragile objects such as fruit, lab samples, or small electronics.
In a soft gripper, several bellows fingers can curl around an object and spread the contact force over a large area.
Key Facts
- Pressure is force per area: P = F/A.
- For a sealed chamber with fixed temperature, Boyle's law gives P1V1 = P2V2.
- A bellows actuator bends when one side expands more than the other side.
- Pleated chambers increase motion because the folds can unfold as air pressure rises.
- A stiffer bottom layer or strain-limiting layer helps turn inflation into curling motion.
- Grip force increases with pressure and contact area, but too much pressure can damage the actuator or object.
Vocabulary
- Soft actuator
- A soft actuator is a flexible device that converts energy, such as air pressure, into motion.
- Bellows
- A bellows is a pleated structure that expands or contracts as fluid pressure changes inside it.
- PneuNet
- A PneuNet is a pneumatic network of connected air chambers that produces motion when inflated.
- Strain-limiting layer
- A strain-limiting layer is a less stretchy layer that prevents one side of an actuator from lengthening much.
- Pneumatic pressure
- Pneumatic pressure is the pressure of compressed air used to create force and motion.
Common Mistakes to Avoid
- Treating the actuator like a rigid piston is wrong because a soft actuator moves through deformation of its walls and chambers, not just straight-line sliding.
- Ignoring the strain-limiting layer is wrong because bending depends on one side expanding more than the other side.
- Assuming higher pressure is always better is wrong because excessive pressure can burst the chambers, reduce control, or crush the object being gripped.
- Forgetting to convert units is wrong because pressure, area, and force calculations require consistent units such as pascals, square meters, and newtons.
Practice Questions
- 1 A bellows chamber has an effective area of 0.0008 m^2 and is inflated to a gauge pressure of 50,000 Pa. What force does the air exert on that area using F = PA?
- 2 A soft gripper finger has 8 identical chambers. Each chamber increases its volume from 2.5 cm^3 to 4.0 cm^3 when inflated. What is the total volume increase for the finger?
- 3 A bellows actuator has a stretchy top layer and a nearly inextensible bottom layer. Explain why it curls toward the bottom layer when pressurized.