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Empirical characterization of modular variable stiffness inflatable structures for supernumerary grasp-assist devices

This paper presents the design, fabrication, and experimental characterization of modular, variable stiffness inflatable components for pneumatically actuated supernumerary robotic (SR) grasp-assist devices. The proposed SR grasp-assist devices are comprised of soft rigidizable finger phalanges and variable stiffness pneumatic bending actuators that are manufactured using soft lithography fabrication methods. The mechanical and kinematic properties of these modular, inflatable components are characterized experimentally under various loading conditions and over a range of geometric design parameters. The resulting data-driven properties are then used to predict the grasp strengths and motion patterns of SR grasp-assist device configurations designed to accommodate the manipulation of daily living objects. Experimental results demonstrate the ability to program grasp synergies into SR fingers by strategic inflation of the bending actuator antagonist chambers (varying mechanical stiffness), without the need for complicated, high-power mechanisms or precise, low-level motion control. The results also demonstrate the underactuated grasp adaptations enabled by modular inflatable components and the ability to predict mechanical grasping capabilities of wearable pneumatic SR grasp-assist devices using insights from empirical data.