Variation: Morphology

Even without changing the material, the actuator’s behavior can be modified by adjusting its shape (morphology). For example, simply making a wall thicker will make it stiffer than a thin wall of the same material.

As with material selection, predicting the behavior of a particular shape is difficult. FEM analysis and empirical testing can provide some insight, and the Modeling and Testing sections contain information on how researchers have modeled and tested these PneuNets actuators.

For example, the FEM analysis and empirical tests carried out by Polygerinos et al. (2013) yielded the following guidelines for morphology design:

• Thinner walls lead to an increased force output, and require less pressure for the actuator to reach maximum bending.

• Increased chamber height increases force output, but doesn’t seem to affect the trajectory of the actuator tip.

Empirical tests carried out by Mosadegh et al. (2013) found that (for a fixed overall actuator length):

• Up to a certain plateau, increasing chamber height lowered the required pressure.
• Increasing the number of chambers also decreased the required pressure.
• Increasing chamber wall thickness increased the required pressure.