Design
Laminar Jamming Structures are composed of stacked layers of flexible sheets, which are very compliant in their natural state. This feature enables the components to conform to complex shapes, allowing them to be used in biomedical applications and in a number of wearables. In addition, the choice of material and number of layers of these structures can be used to tune the desired stiffness and damping ability for specific applications.
The morphology of the LJS - meaning the structure, size and shape - can be easily changed during the fabrication process, allowing fast prototyping and a number of iterations in order to enhance the structure's performance. In addition, jamming structures have the ability to shape-lock, i.e., if they are deformed to a specific shape when they are in their natural, unjammed state and then vacuum is turned on, they can retain the deformed shape and resist static loading.
Furthemore, a number of other variables can affect the stiffness of the LJS, such as the choice of material, the thickness of layers as well as the total number of layers. For more information, refer to the Design Tool section.
Variation: Material
The properties of the material which will be enclosed in the airtight bag can greatly affect the behavior of the final jamming structure. Below, we present a number of reference values gathered from online databases and experiments of some materials that can be used in jamming structures. Please be aware that these values may need to be validated for your specific sample.
The overall performance will also depend on the number of layers used and the thickness of each layer, so a number of empirical tests may be necessary to ensure that the optimal mechanical properties for a specific application are achieved. The Design Tool section of this document can also provide useful inputs to guide design decisions according to specific requirements.
| Material | Young's Modulus (GPa) | Density (kg/m3) | Coefficient of friction |
| Paper | 5.5 | 800 | 0.5-0.7 |
| Polyester | 2 | 1052 | 0.2-0.4 |
| Steel | 200 | 7850 | 0.7 |
| Nylon | 3 | 1150 | 0.2 |
| LDPE | 0.4 | 928 | 0.25 |
| Polyurethane Foam | 0.003 | 480 | 0.38 |
Variation: Morphology
The simplest shape used for laminar jamming is that of rectangular sheets, Nevertheless, even the simplest shapes can achieve a number of conformations due to the shape-locking ability of Laminar Jamming Structures. Shape-locking enables LJS to achieve an arbitrary configuration when they are in their flexible state, lock in place after being jammed and resist static loading. When these jamming structures are used with soft actuators, they can save power by requiring no control effort to preserve the apparatus's shape, even if the actuation input is turned off. Furthermore, soft machines with high material strain (e.g. Pneumatic Artificial Muscles) can be deflated after locking, mitigating the risk of catastrophic rupture.
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On the left, you see a demonstration of the shape-locking ability of Laminar Jamming Structures by coupling one of them with Pneumatic Bending Actuators (PneuNets). PneuNets are soft actuators which bend when pressurized, but they return to their original shape when the pressure is relieved. In the experiment, a PneuNet is attached to an LJS and pressurized to obtain a desired bending angle. The jamming structure is activated by turning on vacuum, thus applying a pressure gradient that causes the LJS to lock in its stiff conformation. As a result, even when the PneuNet is depressurized, the system preserves its shape with high fidelity.
In addition, departures from the traditional rectangular shape can increase the range of shapes that Laminar Jamming Structures can achieve. Below you see videos of interesting geometries obtained after a woven mesh and a plus-shaped jamming structure were actively pressurized and depressurized by turning vacuum on or off.
