19 Layered Jamming Multifunctional Actuators 175 Fig. 19.8 A schematic of the layer jamming concept for variable elongation stiffness Fig. 19.9 A schematic of a multi-mode soft actuator that can be programmed to bend up, linearly extend, or bend down 19.4.3 Layered Jamming for Multi-mode Control of Extension and Bending for Soft Actuators Previous work has shown that layered jamming is a promising solution for variable stiffness to normal loads [56]. We expanded this research to use layer jamming for variable elongation stiffness. Figure 19.8 is a schematic of the layer jamming concept for variable elongation stiffness. By interweaving the jamming layers and sealing them in an elastic pouch, when a stretching force is applied to the composite, the paper layers are free to slide against each other to allow for extension. However, when a vacuum is applied to the composite, the friction between the layers resists the layers from sliding against each other to extend thus increasing its elongation stiffness. With this variable stiffening elongation composite, we can combined it with a soft linear extending actuator to create a multi-mode soft actuator that can bend up, linearly extend, or bend down all while variably controlling the actuators stiffness at the same time. This gives layer jamming a multifunctional purpose of not only variably stiffening a soft actuator but also making is deformation more controllable. Figure 19.9 shows a schematic of the multi-mode soft actuator. Pressure applied to the silicone actuator controls the extension, while the vacuum applied to the top and/or bottom layer controls the bending direction. Due to this structure, there are three modes of actuation. First, applying a vacuum to the top layer increases its elongation stiffness, which results in an upward deflection under an applied pressure (Fig. 19.9 –mode 1). Second, in the absence of vacuum, an applied pressure will result in the whole actuator extending linearly (Fig. 19.9 –mode 2). Lastly, applying a vacuum to the bottom layer produces a downward deflection (Fig. 19.9 –mode3). In combination, this approach allows for not only the direction of bending to be controlled, but also the degree of bending (i.e., by regulating the magnitude of the vacuum). Figure 19.10 shows a prototype proof of concept where all there modes were achieved. A∼30 kPa pressure was applied to the linear actuator and ∼−80 kPa was applied to the jamming layers. The total length of the actuator was 100 mm with the silicone linear actuator having a height and width of 20 mm. The jamming layer were composed of 20 paper layers each with a total thickness of 2 mm. For mode 1, there was a vertical displacement of about ∼50 mm. For mode 2, the actuator extended by 50%. For mode 3, there was also vertical displacement of about ∼50mm.
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