Effects of geometry and mass distribution in 3D printed metastructures for vibration mitigation

In this paper, we present the redesign and analysis of a century old walking toy. Historically, the toy is made up of two wooden pieces including a rear leg and a front leg and body (as a single piece) that are attached to each other by means of a pin joint. When the toy is placed on a ramp and given a slight perturbation, it ambles downhill powered only by gravity. Before the toy can walk successfully, it needs careful tuning of its geometry and mass distribution. The traditional technique of manual wood carving offers very limited flexibility to tune the mass distribution and geometry. We have re-engineered the toy to be three-dimensional (3D) printed as a single integrated assembly that includes a pin joint and the two legs. After 3D printing, we have to manually break-off the weakly held support material to allow movement of the pin joint. It took us 6 iterations to progressively tune the leg geometry, mass distribution, and hinge joint tolerances to create our most successful working prototype. The final 3D printed toy needs minimal postprocessing and walks reliably on a 7.87 deg downhill ramp. Next, we created a computer model of the toy to explain its motion and stability. Parameter studies reveal that the toy exhibits stable walking motion for a fairly wide range of mass distributions. Although 3D printing has been used to create nonassembly articulated kinematic mechanisms, this is the first study that shows that it is possible to create dynamics-based nonassembly mechanisms such as walking toys.

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Predicting precision grip grasp locations on three-dimensional objects

10.1101/476176 ◽

2018 ◽

Cited By ~ 5

Author(s):

Lina K. Klein ◽

Guido Maiello ◽

Vivian C. Paulun ◽

Roland W. Fleming

Keyword(s):

Mass Distribution ◽

Precision Grip ◽

Three Dimensional ◽

Behavioral Data ◽

Three Dimensional Objects ◽

3D Objects ◽

Contact Points ◽

Potential Contact ◽

3D Printed ◽

Precision Grasping

AbstractWe rarely experience difficulty picking up objects, yet of all potential contact points on the surface, only a small proportion yield effective grasps. Here, we present extensive behavioral data alongside a normative model that correctly predicts human precision grasping of unfamiliar 3D objects. We tracked participants’ forefinger and thumb as they picked up objects of 10 wood and brass cubes configured to tease apart effects of shape, weight, orientation, and mass distribution. Grasps were highly systematic and consistent across repetitions and participants. We employed these data to construct a model which combines five cost functions related to force closure, torque, natural grasp axis, grasp aperture, and visibility. Even without free parameters, the model predicts individual grasps almost as well as different individuals predict one another’s, but fitting weights reveals the relative importance of the different constraints. The model also accurately predicts human grasps on novel 3D-printed objects with more naturalistic geometries and is robust to perturbations in its key parameters. Together, the findings provide a unified account of how we successfully grasp objects of different 3D shape, orientation, mass, and mass distribution.Author SummaryA model based on extensive behavioral data unifies the varied and fragmented literature on human grasp selection by correctly predicting human grasps across a wide variety of conditions.

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Experimental Testing of Vibration Mitigation in 3D-Printed Architected Metastructures

Journal of Applied Mechanics ◽

10.1115/1.4044135 ◽

2019 ◽

Vol 86 (11) ◽

Cited By ~ 1

Author(s):

Ignacio Arretche ◽

Kathryn H. Matlack

Keyword(s):

Finite Element ◽

Band Gap ◽

Experimental Testing ◽

Loss Modulus ◽

Coherence Function ◽

Finite Element Simulations ◽

Experimental Results ◽

Band Gaps ◽

Vibration Mitigation ◽

3D Printed

Abstract Band gaps in metamaterials and phononic crystals provide a way to engineer vibration mitigation into a material’s geometry. Here, we present a comprehensive experimental characterization of band gaps in lattice-resonator metastructures, which have been previously analyzed with finite element simulations, to better understand this phenomenon in 3D-printed materials. We fabricate the metastructures with a new approach to obtain multimaterial structures using stereolithography. We experimentally characterize the material’s frequency-dependent storage and loss modulus over the band gap frequencies to confirm that the measured band gaps are due to geometry and not due to material properties. Experimental results using both frequency sweep and impulse excitations show that band gaps and attenuation efficiencies strongly depend on the lattice geometry as well as loading direction, and a comparison between axial and bending excitation responses reveals frequency ranges of “fluid-like” and “optical-like” behaviors. Comparison between finite element simulations and experimental results demonstrate the robustness of the metastructure design. While the experiments used here are well established, their combination allows us to gain additional insights into band gaps measurements. Specifically, we show that the coherence function, a common concept in signal processing, is a strong predictor of band gaps in linear materials and that the attenuation efficiency inside the measured band gap can be physically limited by fluid–structure interactions.

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Analysis of STEM micrographs of thick objects

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100081395 ◽

1978 ◽

Vol 36 (2) ◽

pp. 106-107

Author(s):

S. Golladay

Keyword(s):

Inelastic Scattering ◽

Multiple Scattering ◽

Mass Distribution ◽

Cross Sections ◽

Phase Contrast ◽

Image Point ◽

Contrast Effects ◽

Total Cross Sections ◽

Elastic And Inelastic Scattering

The theory of multiple scattering has been worked out by Groves and comparisons have been made between predicted and observed signals for thick specimens observed in a STEM under conditions where phase contrast effects are unimportant. Independent measurements of the collection efficiencies of the two STEM detectors, calculations of the ratio σe/σi = R, where σe, σi are the total cross sections for elastic and inelastic scattering respectively, and a model of the unknown mass distribution are needed for these comparisons. In this paper an extension of this work will be described which allows the determination of the required efficiencies, R, and the unknown mass distribution from the data without additional measurements or models. Essential to the analysis is the fact that in a STEM two or more signal measurements can be made simultaneously at each image point.

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