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This paper proposes a novel pneumatic valve adapter that decreases the size and quantity of pneumatic tubes and valves necessary for soft robotics by mimicking cardiovascular systems. Some cardiovascular systems, evolved to be powered by a single reservoir, the heart, which in turn powers the rest of the body by systematically opening and closing valves as needed. The presented valve adapter consists of a set of concentric tube, where both tubes have strategically patterned holes. The inner tube can be moved translationally and rotationally to align with designated hole positions in the outer tube, thus opening and closing pathways to chambers for pressure flow. The two-tube system can be used to either pressurize a chamber or depressurize a chamber or multiple chambers simultaneously.

 

Variable stiffness structures lie at the nexus of soft robots and traditional robots as they enable the execution of both high-force tasks and delicate manipulations. Laminar jamming structures, which consist of thin flexible sheets encased in a sealed chamber, can alternate between a rigid state when a vacuum is applied and a flexible state when the layers are allowed to slide in the absence of a pressure gradient. In this work, an additional mode of controllability is added by clamping and unclamping the ends of a simple laminar jamming beam structure. Previous works have focused on the translational degree of freedom that may be controlled via vacuum pressure; here we introduce a rotational degree of freedom that may be independently controlled with a clamping mechanism. Preliminary results demonstrate the ability to switch between three states: high stiffness (under vacuum), translational freedom (with clamped ends, no vacuum), and rotational freedom (with ends free to slide, no vacuum).

 

This paper proposes a novel flexible pneumatic valve adapter that seeks inspiration from vascular systems found in nature. Evolved vascular systems, such as the human cardiovascular system, pump fluid through a complex system composed of a single reservoir/pump. These systems regulate flow by systematically closing and opening valves appropriately through soft biological material constriction. The proposed pneumatic valve emulates this with two concentric flexible tubes with a single hole on the inner tube and patterned holes on the outer tube. This allows it to decrease the quantity of tubes and valves required for pneumatically actuated soft robots, with the trade-off being increased motion of the valve spool (the inner tube). Previous versions of this adapter used rigid members which decreased the number of tubes tethering the robot to a pressure source, but also hindered the soft robotic nature and movement. This adapter utilizes flexible materials to minimize the valve’s effect on the robot’s range of motion. The tubes have holes that are patterned by custom design determined by the needs of the soft robot with which it is to be used. The inner tube can be moved rotationally or translationally within the outer tube to align with designated holes to pressurize and depressurize chambers in a soft robot with only a single lightweight valve. 

This paper presents the design of a new soft pneumatic actuator whose direction and magnitude of bending may be precisely controlled via activation of different shape memory alloy (SMA) springs within the actuator, in conjunction with pneumatic actuation. This design is inspired by examples seen in nature such as the human tongue, where the combination of hydrostatic pressure and contraction of intrinsic muscle groups enables precise maneuverability and morphing capabilities. Here, SMA springs are embedded in the walls of the actuator, serving as intrinsic muscles that may be selectively activated to constrain the device. The pneumatic SMA (PneuSMA) actuator demonstrates remarkable spatial controllability evidenced by testing under different pressures and SMA activation combinations. A baseline finite element model is also developed to predict the actuator deformation under different pressure and activation conditions. 

This paper presents an approach for modeling new soft robotic materials which possess the ability to control directional stiffness. These materials are inspired by biological systems where movements are enabled by variable stiffness tissue and contraction of localized muscle groups. Here a low-melting-point (LMP) material lattice embedded in an elastomer serves as a rigid skeleton that may be locally melted to allow bending at selectable joint locations. The forward kinematics of the lattice has been modeled using the product of exponentials method with the incorporation of bending axis selectivity. In this paper, we develop this model to account for torques imposed by tendons, and we model the elastomer's resistance to bending as a torsional spring at the selected joints. Thus we obtain a two-way relationship between tendon forces and joint angles/axes. The concept of applying traditional robot modeling strategies to selectively compliant robotic structures could enable precise control of dexterous soft robots that satisfy stringent safety criteria. 

This paper presents a layering approach for the manufacturing of pneumatic soft actuators as a coalesced solution to the diverse array of existing fabrication methods. While most research groups have developed their own (often tedious) fabrication strategies for soft actuators, these methods are usually based on available equipment and project-specific design requirements, making them impractical for use in other laboratories. In contrast, the layered substrate approach enables repeatable production of highly-capable pneumatic actuators that can be easily customized to suit a variety of applications. Here we propose layering fiber-reinforced silicone on both sides of a thin pneumatic chamber to directionally constrain expansion. Similar in concept to the Venus flytrap, pressurization of the chamber causes the module to deform and expand where unrestrained. Strategic orientation and patterning of the fiber reinforcement layers results in multiple unique shear and bending capabilities upon pressurization. Combinations of multiple reinforced pneumatic units in series or parallel could match the capabilities of most soft pneumatic actuators, while requiring only simple, universal fabrication methods that may be replicated by other research groups. 

This research explores a new realm of soft robotic materials where the stiffness magnitude, directionality, and spatial resolution may be precisely controlled. These materials mimic biological systems where localized muscle contractions and adjustment of tissue stiffness enables meticulous, intelligent movement. Here we propose the use of a low-melting-point (LMP) metal lattice structure as a rigid frame using localized heating to allow compliance about selectable axes along the lattice. The resulting shape of the lattice is modeled using product of exponentials kinematics to describe the serial chain of tunably compliant axes; this model is found to match the behavior of the physical test piece consisting of a Field’s metal (FM) lattice encased in silicone rubber. This concept could enable highly maneuverable robotic structures with significantly improved dexterity. 

This paper presents an initial step towards a new class of soft robotics materials, where localized, geometric patterning of smart materials can exhibit discrete levels of stiffness through the combinations of smart materials used. This work is inspired by a variety of biological systems where actuation is accomplished by modulating the local stiffness in conjunction with muscle contractions. Whereas most biological systems use hydrostatic mechanisms to achieve stiffness variability, and many robotic systems have mimicked this mechanism, this work aims to use smart materials to achieve this stiffness variability. Here we present the compositing of the low melting point Field's metal, shape memory alloy Nitinol, and a low melting point thermoplastic Polycaprolactone (PCL), composited in simple beam structure within silicone rubber. The comparison in bending stiffnesses at different temperatures, which reside between the activation temperatures of the composited smart materials demonstrates the ability to achieve discrete levels of stiffnesses within the soft robotic tissue.