Magnetohydrodynamic levitation for high-performance flexible pumps.

We use magnetohydrodynamic levitation as a means to create a soft, elastomeric, solenoid-driven pump (ESP). We present a theoretical framework and fabrication of a pump designed to address the unique challenges of soft robotics, maintaining pumping performance under deformation. Using a permanent magnet as a piston and ferrofluid as a liquid seal, we model and construct a deformable displacement pump. The magnet is driven back and forth along the length of a flexible core tube by a series of solenoids made of thin conductive wire. The magnet piston is kept concentric within the tube by Maxwell stresses within the ferrofluid and magnetohydrodynamic levitation, as viscous lift pressure is created due to its forward velocity. The centering of the magnet reduces shear stresses during pumping and improves efficiency. We provide a predictive model and capture the transient nonlinear dynamics of the magnet during operation, leading to a parametric performance curve characterizing the ESP, enabling goal-driven design. In our experimental validation, we report a shut-off pressure of 2 to 8 kPa and run-out flow rate of 50 to 320 mL⋅min-1, while subject to deformation of its own length scale, drawing a total of 0.17 W. This performance leads to the highest reported duty point (i.e., pressure and flow rate provided under load) for a pump that operates under deformation of its own length scale. We then integrate the pump into an elastomeric chassis and squeeze it through a tortuous pathway while providing continuous fluid pressure and flow rate; the vehicle then emerges at the other end and propels itself swimming.

Acoustophoretic Liquefaction for 3D Printing Ultrahigh-Viscosity Nanoparticle Suspensions.

An acoustic liquefaction approach to enhance the flow of yield stress fluids during Digital Light Processing (DLP)-based 3D printing is reported. This enhanced flow enables processing of ultrahigh-viscosity resins (µapp  > 3700 Pa s at shear rates γ ˙  = 0.01 s-1 ) based on silica particles in a silicone photopolymer. Numerical simulations of the acousto-mechanical coupling in the DLP resin feed system at different agitation frequencies predict local resin flow velocities exceeding 100 mm s-1 at acoustic transduction frequencies of 110 s-1 . Under these conditions, highly loaded particle suspensions (weight fractions, ϕ = 0.23) can be printed successfully in complex geometries. Such mechanically reinforced composites possess a tensile toughness 2000% greater than the neat photopolymer. Beyond an increase in processible viscosities, acoustophoretic liquefaction DLP (AL-DLP) creates a transient reduction in apparent viscosity that promotes resin recirculation and decreases viscous adhesion. As a result, acoustophoretic liquefaction Digital Light Processing (AL-DLP) improves the printed feature resolution by more than 25%, increases printable object sizes by over 50 times, and can build parts >3 × faster when compared to conventional methodologies.

Fluid Mechanics of Pneumatic Soft Robots.

Pressurization of gas within embedded channels and cavities is a popular method for actuating soft robots. Various previous works examined the effects of internal fluid mechanics on this actuation approach, as well as on leveraging viscous effects to extend the capabilities of soft robots. However, no existing works studied the combined effects of fluid viscosity and compressibility, relevant to miniaturized configurations, which is the aim of the current work. We derive a general model for compressible viscous flow in an elastic media representing a simplified miniaturized soft robot. We illustrate applying this model to periodic configurations, simplifying it via a long-wave approximation. Steady, and time-dependent solutions are obtained, allowing to model the flow and to provide insight into the actuation dynamics of miniaturized pneumatic soft robots.

Leveraging Internal Viscous Flow to Extend the Capabilities of Beam-Shaped Soft Robotic Actuators.

Elastic deformation of beam-shaped structures due to embedded fluidic networks (EFNs) is mainly studied in the context of soft actuators and soft robotic applications. Currently, the effects of viscosity are not examined in such configurations. In this work, we introduce an internal viscous flow and present the extended range of actuation modes enabled by viscosity. We analyze the interaction between elastic deflection of a slender beam and viscous flow in a long serpentine channel embedded within the beam. The embedded network is positioned asymmetrically with regard to the neutral plane and thus pressure within the channel creates a local moment deforming the beam. Under assumptions of creeping flow and small deflections, we obtain a fourth-order integro-differential equation governing the time-dependent deflection field. This relation enables the design of complex time-varying deformation patterns of beams with EFNs. Leveraging viscosity allows to extend the capabilities of beam-shaped actuators such as creation of inertia-like standing and moving wave solutions in configurations with negligible inertia and limiting deformation to a small section of the actuator. The results are illustrated experimentally.

Dynamics of Elastic Beams with Embedded Fluid-Filled Parallel-Channel Networks.

A pressurized fluid-filled parallel-channel network embedded in an elastic beam, asymmetrically to the neutral plane, will create a deformation field within the beam. Deformation due to embedded fluidic networks is currently studied in the context of soft actuators and soft-robotic applications. Expanding on this concept, configurations can be designed so that the pressure in the channel network is created directly from external forces acting on the beam, and thus can be viewed as passive solid-fluid composite structures. We approximate the deformation of such structures and relate the fluid pressure and geometry of the network to a continuous deformation-field function. This enables the design of networks creating steady arbitrary deformation fields as well as to eliminate deformation created by external time-varying forces, thus increasing the effective rigidity of the beam. In addition, by including the effects of the deformation created by the channel network on the beam inertia, we can modify the response of the beam to external time-varying forces. We present a scheme to design channel networks that create predefined oscillating deformation patterns in response to external oscillating forces. The ability to include inertial effects is relevant to the design of dynamic soft robots and soft actuators. Our results are illustrated and validated by numerical computations.