James J. Joo

Design Optimization Challenges of Origami-Based Mechanisms With Sequenced Folding

Reconfigurable structures based on origami design are useful for multifunctional applications, such as deployable shelters, solar array packaging, and tunable antennas. Origami provides a framework to decompose a complex 2D to 3D transformation into a series of folding operations about predetermined foldlines. Recent optimization toolsets have begun to enable a systematic search of the design space to optimize not only geometry but also mechanical performance criteria as well. However, selecting optimal fold patterns for large folding operations is challenging as geometric nonlinearity influences fold choice throughout the evolution. The present work investigates strategies for design optimization to incorporate the current and future configurations of the structure in the performance evaluation. An optimization method, combined with finite-element analysis, is used to distribute mechanical properties within an initially flat structure to determine optimal crease patterns to achieve desired motions. Out-of-plane and twist displacement objectives are used in three examples. The influence of load increment and geometric nonlinearity on the choice of crease patterns is studied, and appropriate optimization strategies are discussed.

Inverse Design of LCN Films for Origami Applications Using Topology Optimization

Liquid crystal polymer networks (LCNs) have unique advantages as potential constituents of origami-based smart materials due to their reversible actuations and availability of fabrication techniques to create complex strain fields. Although identifying functional designs is crucial in making use of this technology, conventional approaches have largely consisted of trial-and-error experimentation. We introduce an inverse design procedure based on a topology optimization method to map out an LCN pattern with a desired spontaneous strain field to achieve prescribed shapes. In this study, we focus on a target deformation of a film to create an improved hinge to be integrated into an origami structure. Our preliminary results indicate the potential of using computational tools to determine what designs yield desired functionalities and how to best pattern LCN films to achieve them.Copyright

Nonlinear Analysis and Optimization of Diamond Cell Morphing Wings

In this work, a design optimization procedure is developed to maximize the energy efficiency of a scissor mechanism for the NextGens Batwing application. The unit cells are modeled using a finite element approach. The model considers elastic skin, modeled as linear springs, as well as actuator and aerodynamic loads. A nonlinear large displacement analysis is conducted, and the position of the actuator is optimized using Matlabs gradient based optimization algorithm FMINCON. This optimization procedure is used to investigate the effect of different constraints and load cases. The model is expanded to include multiple unit cells and actuators. A two stage optimization process using a Genetic Algorithm and traditional gradient based optimization (FMINCON) is also developed. The two stage optimization is used to optimize actuator position and placement for different constraints and load cases. Results show that placement and position optimization produce small gains in maximizing energy efficiency; morphing using a soft isotropic skin is more efficient than stiff isotropic and anisotropic skin. In addition, the GA did not use the all of the available actuators to maximize energy efficiency.© 2006 ASME

Thermal Properties of Magnetite Nanoparticle and Carbon Fiber Doped Epoxy Shape Memory Polymer

Presented are the results of an experimental investigation into the effects of particle and carbon fiber (CF) doping in epoxy shape memory polymer (SMP). Motivation for the work originates from the need to increase the thermal performance, and thus decrease the time required to transition the polymer given a finite amount of thermal energy, of a SMP link in a bi-stable linkage. Such a multi-functional link is responsible for structural support, mechanism reconfigurability, as well as system damping. Thus any improvement in thermal properties must be weighed against increases in brittleness and weight as well as altered mechanical properties as a result of the chosen method. Two part epoxy SMP by CRG Industries is doped with Fe3 O4 (magnetite) nanoparticles (20–30nm spheres) at a weight fraction of 10% as well as 3mm and 10mm carbon fibers at a weight fraction of 5.4%; resulting in all dopants having a volume fraction of approximately 2.5%. The thermal conductivity, specific heat, and diffusivity are experimentally measured by a Hot Disk Thermal Constants Analyser from ambient through transition and the results compared with several thermal composite models. Changes in the thermal properties of the composites and neat polymers with respect to temperature are presented and the effects these changes have on the predictions of thermal models discussed, specifically the effect of changes in thermal properties near the transition temperature and the resulting change in predicted energy required for transition. The effects of adhesion between the particles and the matrix and particle dispersion on conductive paths and material thermal properties are also discussed.Copyright

Spatial tuning of a RF frequency selective surface through origami

Origami devices have the ability to spatially reconfigure between 2D and 3D states through folding motions. The precise mapping of origami presents a novel method to spatially tune radio frequency (RF) devices, including adaptive antennas, sensors, reflectors, and frequency selective surfaces (FSSs). While conventional RF FSSs are designed based upon a planar distribution of conductive elements, this leaves the large design space of the out of plane dimension underutilized. We investigated this design regime through the computational study of four FSS origami tessellations with conductive dipoles. The dipole patterns showed increased resonance shift with decreased separation distances, with the separation in the direction orthogonal to the dipole orientations having a more significant effect. The coupling mechanisms between dipole neighbours were evaluated by comparing surface charge densities, which revealed the gain and loss of coupling as the dipoles moved in and out of alignment via folding. Collectively, these results provide a basis of origami FSS designs for experimental study and motivates the development of computational tools to systematically predict optimal fold patterns for targeted frequency response and directionality.

Characterization of Creases in Polymers for Adaptive Origami Structures

Abstract : Techniques employed in origami are of interest for the design of actuating structures with multiple defined geometric states. Most research in this area has focused on manipulating material chemistry or geometry to achieve folding, but crease development through full material thickness has not been studied in detail. Understanding creasing is crucial for establishing material selection guidelines in origami engineering applications. Identification of the precise failure mechanisms is critical for understanding the residual fold angle and selecting optimal materials for specific origami applications. To characterize crease formation and development, polymer films were folded using a modified parallel plate bending technique which was successfully modeled with Euler beam theory in the elastic regime. Fold angles measured after creasing provided a means to quantitatively describe a materials ability to retain a fold, and degree of plastic deformation incurred during folding. SEM micrographs of creased regions revealed tensile deformations on exterior crease surfaces while compressive deformations such as wrinkling occurred inside. Profilometry was performed on crease interiors to identify and measure wrinkle topology. It was found that increased dissipative plastic deformation led to retention of smaller fold angles. These characterization techniques can be used as a means of classifying and organizing polymers by potential usefulness in structural origami applications.

Topology Optimization for Design of Origami-Based Active Mechanisms

Origami structures morph between 2D and 3D conformations along predetermined fold lines that efficiently program the form of the structure and show potential for many engineering applications. However, the enormity of the design space and the complex relationship between origami-based geometries and engineering metrics place a severe limitation on design strategies based on intuition. The presented work proposes a systematic design method using topology optimization to distribute foldline properties within a reference crease pattern, adding or removing folds through optimization, for a mechanism design. Following the work of Schenk and Guest, foldable structures are modeled as pin-joint truss structures with additional constraints on fold, or dihedral, angles. The performance of a designed origami mechanism is evaluated in 3D by applying prescribed forces and finding displacements at set locations. The integration of the concept of origami in mechanism design thus allows for the description of designs in 2D and performance in 3D. Numerical examples indicate that origami mechanisms with desired deformations can be obtained using the proposed method. A constraint on the number of foldlines is used to simplify a design.Copyright

Design, modeling, and optimization of a thermally activated reconfigurable wing system

Reconfigurable structures such as morphing aircraft generally require an on-board energy source to function. At high speeds, however, frictional heating generated at the nose of a morphing aircraft can provide a large amount of thermal energy during a short period of time. This thermal energy can be collected, transferred, and utilized to reconfigure the aircraft. Direct utilization of thermal energy has the ability to significantly decrease or eliminate the losses associated with converting thermal energy to other forms, such as electric. The following work describes possible system designs and components that can be utilized to transfer the thermal energy harvested at the nose of the aircraft to internal components for direct thermal actuation of a reconfigurable wing structure. Previously reported topology optimized heat collectors, vehicle trajectories, and the deployment mechanism are combined with the presented analytical model of a heat pipe for a system level model used to optimize the system based on weight and the desired wing deployment time.

Design tools for adaptive origami devices

Origami structures morph between 2D and 3D conformations along predetermined fold lines that efficiently program the form, function and mobility of the structure. The transfer of origami concepts to engineering design shows potential for many applications including solar array packaging, tunable antennae, and deployable sensing platforms. However, the enormity of the design space and the complex relationship between origami-based geometries and engineering metrics places a severe limitation on design strategies based on intuition. This motivates the development of design tools based on optimization to identify optimal fold patterns for geometric and functional objectives. The present work proposes a topology optimization method using mechanical analysis to distribute fold line properties within a reference crease pattern to achieve a target actuation. By increasing the fold stiffness, unnecessary folds are effectively removed from the design solution, which allows fundamental topologies for actuation to be identified. A series of increasingly refined reference grids were analyzed and several actuating mechanisms were predicted. The fold stiffness optimization was then followed by a node position optimization, which determined that only two of the predicted topologies were fundamental and the solutions from higher density grids were variants or networks of these building blocks. This two-step optimization approach provides a valuable check of the grid dependency of the design and offers an important step toward systematic incorporation of origami design concepts into new, novel and reconfigurable engineering devices.

Design Optimization and Challenges of Large Folding Origami Structures

Reconfigurable structures based on origami design are useful for multi-functional applications, such as deployable shelters, solar array packaging, and tunable antennas. Origami provides a framework to decompose a complex 2D to 3D transformation into a series of folding operations about predetermined fold lines. Recent optimization toolsets have begun to enable a systematic search of the design space to not only optimize geometry, but mechanical performance criteria as well. However, selecting optimum fold patterns for large folding operations is challenging as geometric nonlinearity influences fold choice throughout the evolution. The present work investigates strategies for design optimization to incorporate the current and future configurations of the structure in the performance evaluation. An optimization method, combined with finite element analysis, is used to distribute mechanical properties within an initially flat structure to determine optimal crease patterns to achieve desired motions. Out-of-plane and twist displacement objectives are used in three examples. The influence of load increment and geometric nonlinearity on the choice of crease patterns is studied and appropriate optimization strategies are discussed.Copyright