The tactile and proprioceptive sensation increases human manipulability, and soft tissue compliance stabilizes the grasping function. However, it is challenging to transpose this system to the small confined space of soft robotic fingers due to the material properties and complex wiring entailed. Furthermore, soft robotic fingers also incorporate actuating components, making such a system more difficult to bring to fruition. Therefore, optimizing soft robotic finger structure for greater functionality and manufacturability would be a desirable innovation. In this study, we developed a soft somesthetic robotic finger based on the conductive working liquid and an origami structure. The proposed design comprises an origami structure, porous scaffolds, and a silicone-coated fabric outer layer. The robotic finger was filled with conductive liquid used for both somesthetic sensing and bending actuation simultaneously. The origami structure was fabricated by connecting printed circuit boards (PCBs) and a polyimide film, with electrodes embedded on each PCB to enable somesthetic sensing. The electrodes were used to inject currents and measure voltage, with the measured data then used to reconstruct the deformation map and hinge angle by means of electrical resistance tomography (ERT). The experimental results confirm that the robotic finger could acquire tactile and proprioceptive information in real-time.

Hydrostatic transmission has shown promising results for enabling the manipulator to achieve low effective inertia, high stiffness, and high torque density. However, the incompressibility of fluid causes the lack of compliance, so that it could not provide intrinsic safety. Thus, it would be advantageous to introduce series compliance on the hydrostatic manipulator for adjusting stiffness depending on the situation. Here, we developed a safe and high-performance hydrostatic actuator based on the switchable stiffness mechanism implemented with an air spring and solenoid valve. The hydrostatic transmission is implemented with rolling diaphragms to attain zero fluid leakage and low seal friction. Air spring is serially connected to hydraulic lines for achieving compliance. Its modes (i.e., stiff and compliant modes) can be rapidly switched by modulating water flow via the solenoid valve. Block stiffness experiment shows that the stiffness of stiff mode is 9.63 times stiffer than one of compliant mode at 100 kPa. We experimentally demonstrated that compliant mode could mitigate the impact force to the level that a tangerine would not be crushed. The stiffness was switched within 12 ms; hence it is fast enough to be used for feedback application with vision or tactile sensors. As a result, the developed actuator can ensure safety without sacrificing the dynamic performance, owing to the simple and rapidly switchable stiffness mechanism.

An echinoderm can actively modulate the structural stiffness of its body wall by as much as 10 times, using the material and structural features that make up its body, including calcite ossicles, connective tissue and interossicular muscle. This capacity for variable stiffness makes it possible to adapt to the kinematics and dynamics required to perform a given task and the surrounding environment. This characteristic can improve the ability of soft material robots, which currently have limited application because of their low load-bearing capability. This paper presents a stiffness modulation method inspired by the connected ossicle structures of echinoderms. We introduce the mechanism, structure, and stiffness variation of the proposed design with respect to different ossicle shape, interval, and elastomer. Then we built a finger-shaped stiffening structure using the proposed design, measured its stiffness according to vacuum level, and showed its load-bearing capacity under control. The proposed design was then applied to a robotic gripper, a typical device that interacts with unpredictable environments and needs variable stiffening ability.