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Material stiffness affects how much pressure is required to make the actuator bend. High strain/low durometer (stretchy) materials will deform more for a given pressure than low strain/high durometer (rigid) materials. There is a wide variety of both types of material available. Some examples are given below. High Strain/Low Durometer:
Low Strain/High Durometer:
Changing these materials and using them in different combinations leads to varied actuator behavior. In the graphs shown (taken from Mosadegh et al. 2013), compare the pressure-volume loop of PneuNets actuators made from Ecoflex 30 & PDMS (A) with those made from Elastosil & Paper (B). Ecoflex 30 has a lower durometer than Elastosil, and as a result the Ecoflex actuator has a greater increase in volume for a lower applied pressure. |
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Accurately predicting the effects of material selection is difficult due to the nonlinear elastic behavior of the materials and the complex shape of the actuator. The Modeling section of this documentation set contains a tutorial on using Finite Element Method (FEM) analysis to predict the behavior of the actuator. Performing this type of analysis with different materials, and performing empirical tests like those described in the Testing section, can help to guide design decisions.
When selecting a material for your actuator, the main tradeoff to consider is that lower-durometer actuators can’t apply as much force and move more slowly, but they can be operated at much lower pressures.
In the Fabrication section we describe the process for making an Elastosil & Paper PneuNets actuator; however the process will be almost identical for other materials such as Ecoflex or Dragon Skin.