Nam N Huynh

Performance Quantification of Conducting Polymer Actuators for Real Applications: A Microgripping System

In this paper, we report on modeling, characterization, and performance quantification of a conducting polymer actuator, driving a rigid link to form each finger of a two-finger gripping system, which is what we call a microgripping system. The actuator, which consists of five layers of three different materials, operates in a nonaquatic medium, i.e., air, as opposed to its predecessors. After the bending displacement and force outputs of a single finger are modeled and characterized including the effect of the magnitude and frequency of input voltages, the nonlinear behavior of the finger including hysteresis and creep effects is experimentally quantified, and then a viscoelastic model is employed to predict the creep behavior. The experimental and theoretical results presented demonstrate that while the hysteresis is negligibly small, the creep is significant enough so as not to be ignored. The response of the actuator and the finger under step input voltages is evaluated, and found that the actuator does not have any time delay, but only a large time constant. Two of the fingers are assembled to form a microgripping system, whose payload handling and positioning ability has been experimentally evaluated. It can lift up to 50 times its weight under 1.5 V. The payload handled was a spherical object covered with industrial type tissue paper. The friction coefficient between the object and the carbon fiber rigid link has been determined experimentally and used to estimate the contact force. All the theoretical and experimental performance quantification results presented demonstrate that conducting polymer actuators can be employed to make functional microsized robotic devices

Establishment of a biomimetic device based on tri-layer polymer actuators—propulsion fins

We propose to use bending type tri-layer polymer actuators as propulsion fins for a biomimetic device consisting of a rigid body, like a box fish having a carapace, and paired fins running through the rigid body, like a fish having pectoral fins. The fins or polymer bending actuators can be considered as individually controlled flexible membranes. Each fin is activated with sinusoidal inputs such that there is a phase lag between the movements of successive fins to create enough thrust force for propulsion. Eight fins with 0.125 aspect ratio have been used along both sides of the rigid body to move the device in the direction perpendicular to the longitudinal axis of the body. The designed device with the paired fins was successfully tested, moving in an organic solution consisting of solvent, propylene carbonate (PC), and electrolyte. The design procedure outlined in this study is offered as a guide to making functional devices based on polymer actuators and sensors.

Atomistic simulation of nanoindentation of iron with different indenter shapes

Abstract In this article molecular dynamics (MD) simulations have been conducted to investigate the effect of the indenter shape on the nanoindentation behaviours of iron with body centred cubic structure. Two types of indenters (hemispherical indenter and pyramidal indenter) with dimensions of several nanometres have been modelled. The simulation results have shown that the indenter shape significantly influences the nanoindentation behaviours at such small scale. The indentation force increases with indentation depth during loading for the hemispheri-cal indenter, while the indentation force is low in values for the pyramidal indenter. To validate the MD model nanoindentation experiments have been carried out. The calculated indentation hardness of the hemispherical indenter is in reasonable agreement with the experimental value.

A study of microstructural evolution around crack tip using crystal plasticity finite-element method

The microstructure plays a significant role in crack initiation and crack propagation in metals. In this paper, a crystal plasticity finite-element method has been developed to simulate the tensile tests on rectangle-notched, triangle-notched, and circle-notched aluminium samples. Polycrystalline aggregates are approximated by a Voronoi structure. Two sets of initial orientations are randomly assigned to the aggregate. Notch geometries after deformation, the maximum shear stresses, and crystal orientation rotations are presented and discussed. Simulation results reveal that deformation of polycrystalline aggregate is greatly influenced by both notch geometry and initial crystal orientation. The crystal orientation profoundly rotates around the thickness direction of the samples for all the notch geometries and the initial orientations.

Simulating Transport and Land Use Interdependencies for Strategic Urban Planning—An Agent Based Modelling Approach

Agent based modelling has been widely accepted as a promising tool for urban planning purposes thanks to its capability to provide sophisticated insights into the social behaviours and the interdependencies that characterise urban systems. In this paper, we report on an agent based model, called TransMob, which explicitly simulates the mutual dynamics between demographic evolution, transport demands, housing needs and the eventual change in the average satisfaction of the residents of an urban area. The ability to reproduce such dynamics is a unique feature that has not been found in many of the like agent based models in the literature. TransMob, is constituted by six major modules: synthetic population, perceived liveability, travel diary assignment, traffic micro-simulator, residential location choice, and travel mode choice. TransMob is used to simulate the dynamics of a metropolitan area in South East of Sydney, Australia, in 2006 and 2011, with demographic evolution. The results are favourably compared against survey data for the area in 2011, therefore validating the capability of TransMob to reproduce the observed complexity of an urban area. We also report on the application of TransMob to simulate various hypothetical scenarios of urban planning policies. We conclude with discussions on current limitations of TransMob, which serve as suggestions for future developments.

Force Analysis and Characterization of Polymer Actuators

There has been an increasing interest in conducting polymers, especially polypyrrole (PPy), as potential actuators for many cutting edge applications including micromanipulation and biomedical devices. Their performance needs to be assessed in terms of force and displacement outputs before they can be employed in practical devices. As part of an ongoing project to develop a robotic gripper for micromanipulation/fabrication applications, this study focuses on (i) deriving a mathematical model to predict the force produced at the tip of a trilayer bending type PPy-based actuator under input voltages, and (ii) experimentally verifying the model. The model has been used to estimate the force produced by a robotic finger consisting of a PPy actuator and a rigid link. The results presented show a good agreement between the experimental and predicted forces for two actuators with the dimensions of (10 mm times 1 mm times 0.17 mm) and (5 mm times 1 mm times 0.17 mm) with driving voltages up to 0.8 V

A Heuristic Combinatorial Optimisation Approach to Synthesising a Population for Agent-Based Modelling Purposes

This paper presents an algorithm that follows the sample-free approach to synthesise a population for agent based modelling purposes. This algorithm is among the very few in the literature that do not rely on a sample survey data to construct a synthetic population, and thus enjoy a potentially wider applications where such survey data is not available or inaccessible. Different to existing sample-free algorithms, the population synthesis presented in this paper applies the heuristics to part of the allocation of synthetic individuals into synthetic households. As a result the iterative process allocating individuals into households, which normally is the most computationally demanding and time consuming process, is required only for a subset of synthetic individuals. The population synthesiser in this work is therefore computational efficient enough for practical application to build a large synthetic population (many millions) for many thousands target areas at the smallest possible geographical level. This capability ensures that the geographical heterogeneity of the resulting synthetic population is best preserved. The paper also presents the application of the new method to synthesise the population for New South Wales in Australia in 2006. The resulting total synthetic population has approximately 6 million people living in over 2.3 million households residing in private dwellings across over 11000 Census Collection Districts. Analyses show evidence that the synthetic population matches very well with the census data across seven demographics attributes that characterise the population at both household level and individual level.

Synthetic Population Initialization and Evolution-Agent-Based Modelling of Population Aging and Household Transitions

A synthetic population (SP) aims at faithfully reproducing actual social entities, individuals and households, and their characteristics as described in a population census. Depending on the quality and completeness of the input data sets, as well as the number of variables of interest and hierarchical levels (usually, individual and household), a reliable SP should be able to reflect the actual physical social entities, with their characteristics and specific behavioural patterns. This paper presents a methodology to construct a reliable dynamic synthetic population for the Illawarra Region-Australia. The two main components in the population synthesizer presented in this paper are initialization and evolution. Iterative proportional fitting procedure (IPFP) is presented to help with the initialization of the population using 2011 Australian census. Then, population aging and evolution is projected using an agent-based modeling (ABM) technique over ten years.

A robotic gripper based on conducting polymer actuators

Conducting polymer actuators or as widely known as artificial muscles have many promising features such as being biocompatible and suitable to open loop control, and having high force to weight ratio. If properly engineered, they can be employed as actuators plus joints like active flexure joints articulating monolithic structures. Such structures or systems not containing any sliding and/or rolling components potentially have high positioning accuracy, which is crucial for micro/nano manipulation applications. In this paper, we employ a bending type polymer actuator to articulate two separate rigid links made up of carbon fibre such that a two-finger gripper is formed. We report on the force modeling and characterisation of the actuator and the finger, the fabrication of the fingers, and preliminary performance outcomes of the gripper. The size of each finger is (5 mm + 5 mm) times 1 mm times 0.17 mm. The results demonstrate that conducting polymer actuators can be employed as actuators to make functional robotic devices with reasonably high force output

An Orientation-Dependent Failure Criterion for FCC Crystals

The crystalline orientation significantly affects the fracture behavior of crystals. However, the orientation-dependent failure criterion is still lacking up to now. In this paper the failure criteria for different crystalline planes of aluminum have been developed. The critical normal stresses to separate two parallel crystallographic planes have been calculated based on Morse potential. The critical stresses on four different planes ({100}, {111}, {110} and {120}) were obtained. It has been found that plane {120} had the minimum critical normal stress. The developed failure criteria have been applied in the crystal plasticity finite element method (CPFEM) model to simulate the uniaxial tensile deformation of single crystal aluminum with a notch. The lattice orientation evolution during deformation has been predicted by the CPFEM model. Elements at notch tip reaching predefined orientation-dependent failure criterion were removed from the mesh so that the crack growing could be determined explicitly without any path assumption.