Though they are compliant, nimble and morpho-logically intelligent, fluidic soft robots often rely on bulky components for power and actuation. This work contributes a design methodology which enables development of soft fluidic robots that move in a sequenced fashion, enabling lightweight devices with embodied intelligence. Bezier-curved beams were introduced as a design building block whose antagonistic placement results in Representative Auxetic Element (RAE) that can be patterned on inflatable shells. Kinematics and loading behaviour of these design building blocks were studied through Finite Element Analysis (FEA). We give a methodology for patterning RAEs on cylindrical and conic shells to create soft fluidic components that move (motion components) and those that delay fluid flow (pinch components). We verify the physical concepts governing the design methodology through two prototype devices that produce sequenced motion under a single fluidic input. Devices using this framework have the potential to perform complicated sequenced motions with lightweight control components.

This paper presents a soft-robotic platform for exploring the ecological relevance of non-locomotory movements via animal-robot interactions. Coral snakes (genus Micrurus) and their mimics use vigorous, non-locomotory, and arrhythmic thrashing to deter predation. There is variation across snake species in the duration and curvature of anti-predator thrashes, and it is unclear how these aspects of motion interact to contribute to snake survival. In this work, soft robots composed of fiber-reinforced elastomeric enclosures (FREEs) are developed to emulate the anti-predator behaviors of three genera of snake. Curvature and duration of motion are estimated for both live snakes and robots, providing a quantitative assessment of the robots' ability to emulate snake poses. The curvature values of the fabricated soft-robotic head, midsection, and tail segments are found to overlap with those exhibited by live snakes. Soft robot motion durations were less than or equal to those of snakes for all three genera. Additionally, combinations of segments were selected to emulate three specific snake genera with distinct anti-predatory behavior, producing curvature values that aligned well with live snake observations.

Soft actuators with auxetic, or negative Poisson's ratio (NPR), behavior offer a way to create soft robots with novel kinematic behavior. This paper presents an original framework for reinforcement of a soft actuator using a generalized NPR element, called a Representative Auxetic Element (RAE), and an experimental validation of the kinematic behavior that it enables. We build a generalized kinematic model that enables the design of RAE-patterned actuators and reveal the distinct auxetic behavior of RAE actuators with comparable model accuracy to the legacy McKibben actuators. A simple, reproducible way of designing and fabricating RAE actuators is described and varied prototypes are shown. This RAE-based design scheme can be used to create actuators with specified kinematics like bending, extension, and radial expansion, which can also vary across the actuator's surface both circumferentially and axially in a tractable, scalable manner.

Fiber-Reinforced Elastofluidic Enclosures (FREEs), are a subset of pneumatic soft robots with an asymmetric continuously deformable skin that are able to generate a wide range of deformations and forces, including rotation and screw motions. Though these soft robots are able to generate a variety of motions, simultaneously controlling their end effector rotation and position has remained challenging due to the lack of a simple model. This paper presents a model that establishes a relationship between the pressure, torque due to axial loading, and axial rotation to enable a model-driven open-loop control for FREEs. The modeling technique relies on describing force equilibrium between the fiber, fluid, and an elastomer model which is computed via system identification. The model is experimentally tested as these variables are changed, illustrating that it provides good agreement with the real system. To further illustrate the potential of the model, a precision open-loop control experiment of opening a rotational combination lock is presented2.

Soft actuators comprised of fluidic structures with fiber-reinforced elastomeric enclosures are seen throughout nature, exhibiting strength, power density, resilience, and diverse motions and forces. However, these structures are rarely used by engineers, in part due to the absence of a generalized understanding of their kinematics and forces. A small subset of soft actuators generating only extension or compression, popularly known as McKibben actuators, has been thoroughly investigated. This paper introduces the entire design space of actuators built with two families of fibers, of which McKibben actuators occupy a subset. The helix angle of the actuator's translation and rotation deformation is determined from the kinematics of the fiber deformation for all fiber angles as the actuator is pressurized. The volumetric transduction of the actuators, relating the output motion to change in contained volume, is analytically determined. The results are discretized to provide a designer with an easy to use design selection chart. The kinematics, force, and moment of the actuators are experimentally validated for all fiber angles.

Tendril helical motions and snake robots have a multitude of potential applications from climbing to anchoring to complex manipulation in fields such as medical, gas/oil energy, and manufacturing. Constructing a snake robot from a fluid driven, fiber reinforced elastomeric enclosure (FREE), complex helical motions are created in a lightweight, low cost, simple structure. The snake-like manipulators are created by forming a hollow cylindrical elastomer that is reinforced with two families of fibers and one additional fiber. The manipulator is then driven by changing the volume of fluid contained within, thus forming the desired helical patterns. The design of this continuum structure is analyzed for all possible fiber angles and the FREE radius. The parameters of the resulting helix including pitch and radius are determined analytically, without the need for finite element methods. Three prototypes at different points in the design space are fabricated and tested to verify the analytical model.

Soft actuators are found throughout nature from elephant trunks to round worms, demonstrating large specific forces without the need for sliding components. These actuators offer impact resilience, human-safe interaction, versatility of motion, and scalability in size. Biological structures often use a fiber-reinforcement around a fluid filled elastomeric enclosure, in which the elastomeric material will capture the distributed pressure and transfer it to the fibers, which will in turn direct the forces to the ends. We previously discovered an entire domain of fiber-reinforced elastomeric enclosures (FREEs), of which McKibben actuators are a small subset. The range of forces and moments possible with FREEs has not been previously investigated. 45 FREE actuators across the span of fiber angle configurations were fabricated and tested. The reaction force and moment of each actuator was determined across a gamut of pressures. Analytical models were generated using a variety of simplifying assumptions. These models were created to provide a closed form expression that models the force and moment data. The models were compared to the experimental values to determine their fit; this provides an understanding of which simplifying kinematic assumptions best represent the experimental results. Interpolated experimental results and the analytical models are all graphically represented for use as an intuitive design tool.

Complex controlled motions, soft human interaction, and minimal moving mass all drive the need for soft robots using fluid filled fiber reinforced elastomer enclosures (FREEs). While a narrow class of FREEs known as McKibben's actuators have been extensively studied, there is a wide unexplored class with complex sets of motion patterns. Combining these actuators in parallel can yield versatile motion patterns resulting in a large overall workspace. Mobility of individual actuators is enforced by inextensibility of fibers and incompressibility of fluids, which in turn drives the net attainable motions. In this paper, we map the mobility of individual FREE actuators to all possible resultant motions that a combination of three sets of actuators arranged in a triangular configuration would undergo. This understanding has resulted in a preliminary design tool that determines individual FREE topologies for a required set of motion patterns. Five case studies that result from this methodology are prototyped and tested for comparison of the predicted and obtained motion directions.