Intelligent Grasping with the Robotic Opposable Thumb

Recent advances in the field of grasp planning have used heuristics, dimensionality reduction, machine learning, and haptic feedback, with a high degree of success, to plan grasps for simple grippers and/or simple object geometry. We look at applying some of these techniques to the anthropomorphic Meka gripper. First, dimensionality reduction is attempted. We show that dimensionality reduction does not accurately predict the thumb position. A new algorithm is proposed in which measurements from 2D images are used to classify the thumb opposition angle to one of three positions. The remaining joints employ a reactive torque-control strategy to complete the grasp. The algorithm achieves force closure for 82% of 39 household objects. It is simple, computationally fast, and achieves a success rate that is similar to other contemporary grasp planning algorithms.     

An assumed‐gradient finite element method for the level set equation

The level set equation is a non‐linear advection equation, and standard finite‐element and finite‐difference strategies typically employ spatial stabilization techniques to suppress spurious oscillations in the numerical solution. We recast the level set equation in a simpler form by assuming that the level set function remains a signed distance to the front/interface being captured. As with the original level set equation, the use of an extensional velocity helps maintain this signed‐distance function. For some interface‐evolution problems, this approach reduces the original level set equation to an ordinary differential equation that is almost trivial to solve. Further, we find that sufficient accuracy is available through a standard Galerkin formulation without any stabilization or discontinuity‐capturing terms. Several numerical experiments are conducted to assess the ability of the proposed assumed‐gradient level set method to capture the correct solution, particularly in the presence of discontinuities in the extensional velocity or level‐set gradient. We examine the convergence properties of the method and its performance in problems where the simplified level set equation takes the form of a Hamilton–Jacobi equation with convex/non‐convex Hamiltonian. Importantly, discretizations based on structured and unstructured finite‐element meshes of bilinear quadrilateral and linear triangular elements are shown to perform equally well. Copyright © 2005 John Wiley & Sons, Ltd.     

Effects of composition and exposure on the solar reflectance of portland cement concrete

Increasing the solar reflectance (albedo) of a paved surface keeps it cooler in the sun, reducing convection of heat from pavement to air and thereby decreasing the ambient air temperature. Lower air temperatures decrease demand for cooling energy and slow the formation of urban smog. Variations with composition and environmental exposure of the albedos of portland cement concrete pavements were investigated through laboratory fabrication and exposure of 32 mixes of concrete. Concrete albedo generally correlated with cement albedo and sand albedo and, after abrasion, with rock albedo. Cement albedo had a disproportionately strong influence on the reflectance of concrete. Simulated weathering, soiling, and abrasion each reduced average concrete albedo, though some samples became slightly more reflective through weathering or soiling. Concrete albedo grew as the cement hydration reaction progressed, but stabilized within six weeks of casting.     

Solid phase extraction and determination of sub-ppb levels of hazardous Hg2+ ions

A simple, rapid and reliable method has been developed to selectively separate and concentrate ultra trace amounts of mercury(II) ions from aqueous samples for its highly sensitive measurement by cold vapor atomic absorption spectrometry (CV-AAS). The Hg(2+) ions were adsorbed selectively and quantitatively during the passage of aqueous samples through octadecyl silica membrane disks modified by isopropyl 2-[(isopropoxycarbothiolyl)disulfanyl]ethane thioate (IIDE). The retained Hg(2+) ions were then stripped from the disk with minimal amounts of 0.5 M hydrobromic acid (two 8 ml portions) as eluent, and determined by CV-AAS. The break-through volume of the method is greater than 3000 ml, which results in enrichment factors >150. Maximum capacity of the membrane disks modified with 10mg of the ligand was found to be 350+/-30 microg of mercury(II), and the limit of detection is 0.005 ng ml(-1). The effect of various cationic interferences on the recovery of mercury in binary mixtures was studied. The method was applied to the recovery of Hg(2+) ions from different synthetic and tap water samples, as well as the determination of mercury in human hair samples.     

Cationized Starch Derived From Pre‐Oxidized Starch For Textile Sizing and Printing

Maize starch was subjected first to oxidation using H₂O₂ in presence and absence of ferrous sulfate as catalyst and then to cationization using 3‐chloro‐2‐hydroxypropyl trimethyl ammonium chloride. A thorough investigation of the chemical and rheological characteristics of the oxidized starch and oxidized‐cationized starch samples was made. It was found that these modified starches display characteristics, which qualify them to function as excellent sizing agent and to less extent as thickeners for printing polyester fabric with disperse dyes. The differences among the oxidized samples prepared in acidic and alkaline media in presence and absence of ferrous sulfate with respect to carboxyl and carbonyl group content were explained on the basis of the different mechanisms involved in the oxidation reaction of starch. The amenability of the different oxidized starch samples to cationization and variation in the apparent viscosity after cationization of the oxidized starches were also reported.     

Fabrication of a New Polyimide/Titania (TiO2) Nanocomposite Thin Film by the Sol-Gel Route

Polyimide/titania nanocomposite (PI/TiO₂ NC) was successfully fabricated through the in situ formation of TiO₂ within a PI matrix by the sol-gel process. FT-IR and XRD results confirmed the formations of the TiO₂ in the PI matrix. Transmission electron microscopy of the NC10% showed that the TiO₂ phase was well dispersed in the polymer matrix. The mechanical properties of the NC films were increased and elongation at break decreased with increasing TiO₂ content. Thermogravimetric analysis results revealed that the decomposition temperature of hybrid materials was increased with an increase in the content of TiO₂ nanoparticles within the NC films.     

A thermal creep model for the contact of nominally flat surfaces: Jeffreys' linear visco-elastic model

This work considers the mechanics of contact of thermo-visco-elastic materials. In particular the creep behavior of a nominally flat rough surface in contact with a rigid half space is studied. The rough surface is modeled using fractal geometry. A synthesized profile, a Cantor structure, is utilized to model the surface. Such a profile has two scaling parameters and different heights for each generation of asperities. The effect of temperature will be included through the concept of activation energy using the Arrhenius equation.The objective of this model is to study the normal creep approach of the surface (punch) as a function of the applied creep load, time, and temperature. The material of the punch is assumed to behave according to Jeffreys' model. Such a model is an arrangement of springs and dashpots in parallel and/or in series.The creep approach of linearly visco-elastic materials is explored using elastic-visco-elastic correspondence analysis. An asymptotic power law is obtained, which relates the force and the bulk temperature acting on the punch to its approach. This model is valid only when the approach between the punch and the half space is in the range of the roughness size. The proposed model admits an analytical solution for the case when the deformation is linear thermo-visco-elastic. The obtained model shows a good agreement when compared with experimental results from literature.