Fabric Jamming as an Enabler for Gentle Yet Effective Robotic Grasping

Layer jamming is a technology that adjusts the stiffness of layered materials, such as plastic or paper sheets, within a flexible elastic bag by adjusting the internal pressure. Among other applications, this stiffness tuning is valuable for soft grippers and manipulators to stabilize grasping and enhance the output force. However, despite its impressive stiffness capabilities, this technique struggles in scenarios requiring high conformability like ultra-gentle grasping. The system's compliance in its soft state is relatively low, especially at the layer level, resulting in poor shape-conforming behavior, in contrast, using fabric sheets as filler offers a more promising solution. This allows for greater flexibility and adaptability, enhancing the system's ability to conform to various shapes while maintaining the desired level of stiffness when jamming is induced. At atmospheric pressure, the fabric layers can slide on top of each other while keeping a two-dimensional flexibility. However, when the internal air is removed, the pressure difference causes the layers to adhere firmly, significantly increasing friction and preventing movement. The use of both knitted and non-knitted fabrics is investigated as layers of the variable stiffness assembly. Their variable stiffness capabilities are evaluated, and their double-curvature capabilities are demonstrated through their integration into a soft gripper. The gripper utilizes an origami-based pneumatic chamber that inflates to form a double-curvature shape, enveloping the target object with a larger contact area compared to finger-based grippers. This innovative design, combining fabric jamming and origami structures, enables the gripper to transition between soft and stiff states. This allows for effective shape-locking when necessary, without compromising its kinematic capabilities. The result is a lightweight, compact, and squeezable soft gripper, capable of handling highly delicate objects with precision and care. In particular, this research paves the way for a new generation of ultra-gentle soft grippers for confined spaces, such as food handling or manipulating small organs and soft tissues in minimally invasive surgery. Moreover, these advanced soft grippers may offer enhanced versatility, squeezability, and stiffness tuning, which are essential for dealing with the high unpredictability of unstructured environments.