Stiffness control in under-actuated robotic origamis with shape memory polymer

Under-actuated systems offer compact designs with easy actuation and control but at the cost of limited stable configurations and reduced dexterity compared to the directly driven and fully actuated systems. Here, we propose a compact origami-based design to control the stable configurations and the overall stiffness of an under-actuated robotic finger by modulating the material stiffness of the joint. The design of the robotic finger is based on the robotic origami design principle in which multiple functional layers are integrated to make a nominally 2D robot with a desired functionality. To control the stiffness of the structure, we controlled the elastic modulus of a shape memory polymer (SMP) via embedded customized stretchable heater. We monitor the configuration of the finger using the feedback from the customized curvature sensors embedded in each joint. We studied the stable configurations and the contact forces of a finger with 3 joints at different stiffness settings. A scaled down version of the design was used in a gripper with two fingers and different grasp modes were demonstrated through activating different set of joints.

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