Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session R59: Actuation in Soft Matter IFocus
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Sponsoring Units: GSOFT Room: BCEC 257B |
Thursday, March 7, 2019 8:00AM - 8:36AM |
R59.00001: Actuation in soft matter Invited Speaker: Robert Shepard It has recently been shown that elastic materials may be architected to display remarkable functionality when harnessing mechanical instabilities. These so called mechanical-metamaterials are however often passive elastic structures, which undergo deformations when prompted by external loading. Different modes of actuation have been proposed, such as pressure controlled grabbing fingers in soft-robotics, swelling in shape-morphing gels, electrostatics in dielectric elastomers or temperature in liquid cristal polymers or shape memory alloys. How can these different solution be integrated in future manufactured devices? We are seeking contributions studying the fundamental and practical aspects of the integration of actuation in the design of soft materials. Particularly, we are interested in the (1) the mechanisms of amplification of an input via the architecture of the materials and (2) the programability of a complex response using a simple mode of actuation. This session would be in the core of recent GSOFT topics as illustrated in the previous editions of the March meeting, eg Soft Interfaces Mechanics, Robophysics, Extreme Mechanical Instabilities, Origami and kirigami of metamaterials. |
Thursday, March 7, 2019 8:36AM - 8:48AM |
R59.00002: Transition Wave-driven Sequential Actuation Provides Functionality to Soft Robotic Systems Nick Vasios, Benjamin Gorissen, David Melancon, Katia Bertoldi Soft robotic systems that rely on fluidic actuation are great candidates for producing sophisticated motions harnessing their inherent structural and material compliance. In most applications, soft robots are able to attain complex motions through the individual actuation of their constituent fluidic actuators. However, this results in multiple input lines connected to separate pressure supplies and a complex actuation process. In this study, we harness transition waves in bistable structures to dramatically simplify the actuation of soft robotic systems. Through a combination of experiments and numerical simulations we demonstrate that the transition waves propagating in a system comprising several bistable dome-shaped membranes that enclose fluid filled cavities can be exploited to trigger the sequential actuation of deformable actuators, producing a complex preprogrammed response with just a single and simple input. |
Thursday, March 7, 2019 8:48AM - 9:00AM |
R59.00003: Mechanically programmable sequential actuation of fluid-driven soft actuators Luuk Van Laake, Johannes Overvelde Fluid-driven actuators show great promise for robotics operating alongside human beings, for handling delicate and irregularly shaped objects, and for medical implants such as artificial muscles and even potentially heart prostheses. While soft actuators can be produced from materials that exhibit mechanical compliance close to that of human tissue, control of these actuators typically requires rigid elements such as electronic sensors, valves, and wires that may cause stress concentrations limiting the lifetime of the system. To circumvent this issue, we aim to replace the electronics by other modes of control using only soft elements that are embedded in the fluid that drives the soft actuators. Specifically, we focus on elastic hysteretic valves that allow us to program complex actuation patterns. We analyze the dynamic behavior using the electronic-hydraulic analogy and show that these circuits can deliver complex flows (e.g. pulsatile) to individual actuators, while fluidic power to the system is provided by a continuous fixed flow. We furthermore show that we can change the behavior of the soft system by varying the initial conditions, such that we can produce a soft robot that can be mechanically programmed to move using multiple gaits, without the need for electronics. |
Thursday, March 7, 2019 9:00AM - 9:12AM |
R59.00004: Walking Sheets: Locomotion in chemo-mechanically driven, non-Euclidean elastic plates Pearson Miller, Jörn Dunkel Spatio-temporally varying chemical patterns are an essential mechanism for coordinating force generation in biological systems. Inspired by this, the use of active materials driven by self-oscillating reaction-diffusion equations is increasingly being explored for engineering applications. This talk describes recent investigations into the locomotion of chemically-driven, deformable surfaces from the perspective of non-Euclidean elastic plate theory. Through a combination of numerical and analytical results, we examine the geometric and mechanical characteristics which optimize gait velocity in an elastic sheet driven along a frictional surface. Further, locomotion on non-uniform terrain is considered, in particular the conditions in which external geometry can inhibit or promote robust motion. Overall, we develop insights into how best to utilize incompatible geometry in the design of soft robotics and other applications. |
Thursday, March 7, 2019 9:12AM - 9:24AM |
R59.00005: Untethered Soft Machines and Robots by Printing Ferromagnetic Domains in Soft Materials Yoonho Kim, Hyunwoo Yuk, Ruike Zhao, Shawn A. Chester, Xuanhe Zhao Soft active materials capable of transforming into programmed shapes in a remotely controllable manner can bring promising applications in diverse fields such as soft robotics and biomedicine. Several types of shape-programmable soft matter have been proposed but often limited to simple geometries and thus with limited functionalities. We introduce a method of printing ferromagnetic domains in soft materials to realize highly responsive and fully programmable soft active materials that quickly transform into multiple desired shapes in applied magnetic fields. We also discuss the mechanics of our printed magnetic soft materials and the model-based simulation, which enable us to design complex structures with multiple modes of programmed actuation while guiding the material design for optimal actuation performance. Combined with the flexibility in design and fabrication, the fast and dynamic response of our printed soft machines and robots provides a range of potential applications, especially in biomedical areas where remote actuation of such untethered devices can be useful. To open this new avenue, we present a set of demonstrations that exemplify the concept of untethered soft machines and robots in biomedical applications such as magnetically steered catheters and guidewires. |
Thursday, March 7, 2019 9:24AM - 9:36AM |
R59.00006: Energy Release Through Volume Snapping in Soft Inflatable Actuators Benjamin Gorissen, David Melancon, Nick Vasios, Mehdi Torbati, Katia Bertoldi Traditionally, the actuation speed of soft inflatable actuators is limited by the influx of fluid, resulting in slow moving soft robots. To overcome this limitation, we have developed a bistable elastic actuator with an isochoric snap-through. As no external fluid input is needed to pass through this instability, the resulting actuator deformation happens quasi-instantaneous and is characterized by energy release. Besides optimizing the actuator’s design for energy release, we also demonstrate its ability to be reset to the initial, undeformed state, enabling cyclic energy release. |
Thursday, March 7, 2019 9:36AM - 9:48AM |
R59.00007: Soft Robot Actuated by Electrostatic Force Congran Jin, Jinhua Zhang, Ian Trase, Shicheng Huang, Zhe Xu, Lin Dong, John X.J. Zhang, Zi Chen Conventional robots are rigid, powerful and robust, and hence they have been serving as trustworthy tools to assist human in a variety of activities. However, due to their rigid body, they lack flexibility to cope with situations where space is confined, terrain is complex, or the environment is constantly changing. To solve these problems, researchers have focused on developing soft robots that can adapt to different environments. Nevertheless, most of the current locomotive actuation methods and materials have limited applications due to either large size, heavy weight, low speed, or complicated fabrication. We have designed, prototyped, and tested a thin-film-based electrostatic soft actuator that overcomes many of these drawbacks. A robotic bug based on this electrostatic actuator was designed and showed its (1) climbing ability through ascending inclines up to 30°, (2) flexibility through shape-recovery after crushing, (3) adaptability through walking on both rough and smooth surfaces and (4) maneuverability by precisely steering into a designated space. The development of such light weight flexible soft robotics will enable tasks such as surveillance, search-and-rescue, and detection that are challenging if not impossible for traditional robots in a cost-effective manner. |
Thursday, March 7, 2019 9:48AM - 10:00AM |
R59.00008: Artificial Muscle by Tailoring Compliance in Magneto-kirigami Lattice Yi Yang, Douglas Peter Holmes The emerging research in soft robotics and micro-robotics has sparked new opportunities for developing artificial muscles of variable length scales and in various working environments. The essential challenge lies in controlling the deformability and compliance of its structural component. In this presentation, we demonstrate a novel approach to precisely control the compliance and deformability via perturbing the elastic energy state of metastable kirigami lattices. Each metastable kirigami lattice has two stable configurations corresponding to two distinct local energy minima. Switching between these two minima leads to either stiffening or softening in lattice structures, which when cycled between these states produces an artificial muscle. Through a combination of experiments and mechanical modeling, we interpreted the stiffening or softening mechanism and characterized the performance of the designed artificial muscle. Since the underlying physics of the metastable kirigami lattice is scale invariant, this kirigami architecture may path a new way to design and fabricate low cost, lightweight artificial muscle at multiple scales. |
Thursday, March 7, 2019 10:00AM - 10:12AM |
R59.00009: Elastomeric focusing enables portable microvalves Nate Cira A continuing challenge in material science is creating active materials in which shape changes or displacements can be generated electrically or thermally. Here we borrow principles from hydraulics, in particular that confined geometries can be used to focus expansion into large displacements, to create solid materials with amplified shape changes. Specifically, we confined an elastomeric poly(dimethylsiloxane) sheet between two more rigid layers and caused focused expansion into embossed channels by local resistive heating, resulting in a 10x greater relative displacement than the unconfined geometry. We used this effect to create electrically controlled microfluidic valves that open and close in less than 100 ms, can cycle >10,000 times, and operate with as little as 20 mW of power. We investigate this mechanism and establish design rules by varying dimensions, configurations, and materials. We show the generality of elastomeric focusing by creating additional devices where local heating and expansion are generated either wirelessly through inductive coupling or optically with a laser, allowing arbitrary and dynamic positioning of a microfluidic valve along the channels. |
Thursday, March 7, 2019 10:12AM - 10:24AM |
R59.00010: Amplified Actuation in Symmetric Origami Mechanisms Andrew Gillman, Gregory Wilson, Kazuko Fuchi, Darren Hartl, Alexander Pankonien, Philip Buskohl The integration of soft actuating materials within origami-based mechanisms is a novel method to amplify the actuated motion and tune the compliance of the system for low stiffness applications. Origami structures provide natural flexibility given the extreme geometric difference between thickness and length, and the energetically preferred bending deformation mode can naturally be used as a form of actuation. However, origami fold patterns with specific actuation motions and mechanical loading scenarios are needed to expand the library of fold-based actuation strategies. In this study, an optimization framework is utilized to predict actuator topologies with different symmetry groups of input and output conditions with respect to the boundary conditions. Utilizing the patterns discovered through the optimization, the multistability of the actuator is further characterized through computational tracking of the bifurcating equilibrium branches and through empirical demonstration with actuator prototypes. This survey of origami mechanisms, comparison of actuation efficiency, and characterization of multistability provides a new set of origami actuators for future integration with soft actuating materials. |
Thursday, March 7, 2019 10:24AM - 10:36AM |
R59.00011: Improving the Robustness of Self-folding Gel Origami Ji-Hwan Kang, Christian Santangelo, Ryan Hayward Self-folding of responsive polymer networks represents a powerful tool to form arbitrary 3D shapes from an initially flat 2D sheet. For example, our groups have previously developed trilayer polymer films that reversibly fold into complex origami designs due to swelling of a temperature-responsive hydrogel mid-layer. However, the configuration space of even very simple origami designs features multiple branches bifurcating from the flat state, meaning that self-folding structures can easily become trapped in an undesired state. Here, we evaluate two methods to avoid such misfolding. First, as suggested by Tachi and Hull (J. Mech. Robot. 2017), we design a set of driving forces that renders the flat state a local minimum along undesired geometrically allowed branches. While we find the approach to be effective for a single degree-6 vertex, this approach is inherently limited to a highly restricted set of crease patterns. Second, we seek to locally program the buckling direction of each vertex by incorporating an orthogonally-addressable (pH-sensitive) element that pre-biases the structure along the desired branch. As this approach should be applicable for generic crease patterns of high complexity, it represents an important step in the design of robustly self-folding structures. |
Thursday, March 7, 2019 10:36AM - 10:48AM |
R59.00012: Diabolical configuration spaces in simple origami Mary Elizabeth Lee, Christian Santangelo Self-folding origami, flat sheets that use mechanical instabilities to fold into three-dimensional structures, have been actuated using swelling polymer gels, surface tension, and more. A universal problem with these structures is that there can be multiple fold configurations for one origami pattern, resulting in the possibility that the structure folds into a configuration other than the one desired. Using an energy model for the structures, we show that the configuration space of a generic origami structure takes the form of nested cones, and that the number of conical branches increases with the number of internal vertices. We will use this geometry to investigate misfolding, with a focus on origami with 5 external vertices. |
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