Performance Evaluation Methods for Microgrippers

In precise manipulation and assembly of components with sub-millimetric dimensions, the role of the gripping tools is fundamental. In the literature, many different types of the so-called microgrippers have been presented, based on different working principles, to cope with the issues related to the gripping, the handling and the release of different micro-components. Depending on the component properties, the task requirements and the system constraints, a microgripper could be more suitable than another and allow the achievement of higher performance. However, the performance assessment of the microgrippers lacks of a standardized and quantitative methodology. Many authors declare the good capabilities of their tools in a qualitative way or according to the results obtained executing specific and different tasks. For this reason, it is often difficult to compare different microgrippers and estimate the actual results that can be obtained e.g. in the gripping or the release of a component. In this context, after a preliminary survey of the adopted approaches in literature and of their meaning, this paper investigates the conception and formalization of methods and procedures to evaluate the performance of a generic microgripper and the definition of standard performance indices to support the presentation of the microgripper characteristics.

Simple and Accurate Analytical Solutions of the Electrostatically Actuated Curled Beam Problem

We present analytical solutions of the electrostatically actuated initially deformed cantilever beam problem. We use a continuous Euler-Bernoulli beam model combined with a single-mode Galerkin approximation. We derive simple analytical expressions for two commonly observed deformed beams configurations: the curled and tilted configurations. The derived analytical formulas are validated by comparing their results to experimental data in the literature and numerical results of a multi-mode reduced order model. The derived expressions do not involve any complicated integrals or complex terms and can be conveniently used by designers for quick, yet accurate, estimations. The formulas are found to yield accurate results for most commonly encountered microbeams of initial tip deflections of few microns. For largely deformed beams, we found that these formulas yield less accurate results due to the limitations of the single-mode approximations they are based on. In such cases, multi-mode reduced order models need to be utilized.

Nanocomposites Based on Multiwalled Carbon Nanotubes With Effective Young’s Modulus Dependent on Number of Layers

The excellent combination of high strength, stiffness, low density and aspect ratio makes carbon nanotubes ideal reinforcement for nanocomposites. The load transfer between the outer and inner layers of multiwalled carbon nanotubes (MWCNT) is one of the important factor in the reinforcement of nanocomposites. In this work, the effect of variation in number of layers of multiwalled carbon nanotubes on effective tensile, compressive and transverse modulus of composite is evaluated. A 3-D finite element model based on representative volume element, consisting of multiwalled carbon nanotube made of shell elements surrounded by solid matrix material is built. With the increase in number of layers in multiwalled carbon nanotubes, the compressive modulus of composite increases, while the tensile modulus decreases. The transverse modulus of composite is found to increase, with the increase in number of layers in MWCNT. The finite element results for composite are compared with the rule of mixtures results using formulae.

Energy Conservation Using Cost Minimization for Household Space Heating

Building insulation is considered as a solution to reduce the energy cost for both residential and commercial buildings. However, determining the best combination of insulation materials that result into the lowest total ownership cost is now becoming a bigger challenge. Various factors influence the efficiency of heat transfer within a room including geometry and size of the room, ambient temperature, heat and sink sources presented inside the building, type of insulation materials, etc. The aim of this paper is to develop an optimization-based decision making tool to help house owners select the best combination of given insulation materials considering all these factors. The purpose of design approach adopted in this paper is to minimize total ownership cost while providing the required heating in the building. The SQP, Quasi-Newton, line-search algorithm was used to obtain the optimized thermal conductivity values for the combination of insulation material to be used in the walls, floor, ceiling, window and the door of a room, along with the width of the air gap to be kept. The results help in deciding what combination of insulation material will achieve the required heating for the house owner while keep the total cost incurred to be minimum.

On the Applicability of Analytical Supply Chain Disruption Models for Selecting the Optimum Contingency Strategies for Electronic Supply Chain Disruption Management: A Comparison With Simulation

Due to the nature of the manufacturing and support activities associated with long life cycle products, the parts that products required need to be dependably and consistently available. However, the parts that comprise long lifetime products are susceptible to a variety of supply chain disruptions. In order to minimize the impact of these unavoidable disruptions to production, manufacturers can implement proactive mitigation strategies. Two mitigation strategies in particular have been proven to decrease the penalty costs associated with disruptions: second sourcing and buffering. Second sourcing involves selecting two distinct suppliers from which to purchase parts over the life of the part’s use within a product or organization. Second sourcing reduces the probability of part unavailability (and its associated penalties), but at the expense of qualification and support costs for multiple suppliers. An alternative disruption mitigation strategy is buffering (also referred to as hoarding). Buffering involves stocking enough parts in inventory to satisfy the forecasted part demand (for both manufacturing and maintenance requirements) for a fixed future time period so as to offset the impact of disruptions. Careful selection of the mitigation strategy (second sourcing, buffering, or a combination of the two) is key, as it can dramatically impact a part’s total cost of ownership. This paper studies the effectiveness of traditional analytical models compared to a simulation-based approach for the selection of an optimal disruption mitigation strategy. A verification case study was performed to check the accuracy and applicability of the simulation-based model. The case study results show that the simulation model is capable of replicating results from operations research models, and overcomes significant scenario restrictions that limit the usefulness of analytical models as decision-making tools. Four assumptions, in particular, severely limit the realism of most analytical models but do not constrain the simulation-based model. These limiting assumptions are: 1) no fixed costs associated with part orders, 2) infinite-horizon, 3) perfectly reliable backup supplier, and 4) disruptions lasting full ordering periods (as opposed to fractional periods).

Analysis of Design for X Methodologies for Complex Assembly Processes: A Literature Review

Historically, products have been developed following the “we design it, you build it” approach. Design and production belonged to two independent entities, with no feedback from downstream activities to upstream activities. In order to avoid redesign costs caused by the lack of feedback, pioneer organisations began to apply methodologies such as ‘Design for Assembly’ or ‘Design for Manufacture’ on a daily basis. Over the years, further research has been carried out to refine these generic methodologies adding previously unconsidered perspectives, such as quality, reliability, environmental, etc. which evolved into a concept called ‘Design-for-X’ (DfX). However, existing methodologies have largely focused on simply reducing product’s structural costs, without taking into consideration other important aspects of more complex assembly processes common in the aerospace industry. The complex assembly process that this paper focuses on is the systems’ installation process within the aerospace business. The installation of fuel, electrical and other systems must follow strict aerospace regulations, intra-organisational design rules, safety policies and many more restrictions, which are not considered as key factors in current methodologies. In this paper, we endeavour to provide an extensive analysis of existing DfX methodologies and support our conclusion that there is an opportunity to develop a new methodology which will ease the aerospace systems’ installation process for the shop-floor operator.

A Multi-Level Approach to Concept Selection in Sustainable Design

The motivation behind this work is to integrate economic and environmental sustainability into decision making at the early phases of design through the development of a hierarchical concept selection method. Life Cycle Assessment (LCA) is a frequently implemented technique used to assess the environmental impacts of products, but it does not provide a simple means for including preference at different levels that can be used for comparison across design alternatives. A method is proposed to accommodate this issue expanding the Hypothetical Equivalents and Inequivalents Method (HEIM) to handle multi-level and multi-attribute trade-offs. The selection of a coffee maker design is used as an example to illustrate the implementation of the method with actual LCA results. The example provides valuable insights into how preferences may be elicited at different hierarchical levels and then combined to create a single utility score that represents to what extent each design alternative is preferred by the decision maker.

An Application of Behavioral Game Theory in Equilibrium Analysis of Concurrent Product-Development Projects

This paper analyzes design equilibrium in a concurrent product-development project using the results from behavioral game theory. In this study, a project consists of a team of three engineers who represent three product-development stages: product design, material selection, and process selection. Product-development tasks are globally distributed, and engineers are allowed to independently make product-development decisions (i.e., non-cooperative design). In addition, the engineers are evaluated according to the outcomes of both individual and team product-development tasks. When multiple design equilibria exist, but a dominant design equilibrium does not, the past behavioral-game-theory studies indicate that design equilibrium may be reached under two conditions. In the first condition, one engineer is allowed to announce his/her intended alternative even though he/she does not need to actually choose the announced alternative. In the second condition, one engineer is selected to make his/her choice first but the other engineers do not know what that choice is. Sensitivity analysis indicates that a wide variety of design equilibria will emerge depending on how engineers are evaluated.

Dynamic Trapping in Bi-Stable Electrostatically Actuated Curved Micro Beams

Micro and nano devices incorporating bi-stable structural elements such as micro beams are designed to exploit the fact that the latter possess two stable configurations at the same actuation force. Generally, the transition of a micro beam from one table state to another, namely the snap-through which is essentially dynamic phenomenon, can be initiated by either static or dynamic activations. In this work, results of theoretical and numerical investigations of the transient dynamics of a pre-stressed initially curved double clamped micro beams actuated by a time dependent electrostatic load are presented. We show by means of a reduced order model of a shallow beam, derived using the Galerkin procedure, that the beam may exhibit various types of responses. For certain beam characteristics, the second stable state is inaccessible under a static loading but is attainable only by means of a specially tailored dynamic actuation. This gives way to the possibility of trapping the dynamically bi-stable beam at a stable configuration which is close to the electrode by applying special loading sequences.

Assessing the Greenhouse Gas Emissions and Cost of Thermoelectric Generators for Passenger Automobiles: A Life Cycle Perspective

Toward realizing a low-carbon society, a thermoelectric generator (TEG) is promising for energy harvesting by generating electricity from thermal energy, especially waste heat. While there are various technologies available for energy recovery, one of the strengths of TEGs is to retrieve usable energy from waste heat whose temperature is as low as 200∼300 degrees Celsius. Yet, the conversion efficiency of the current thermoelectric materials remains low at 5∼10%, which makes it difficult to diffuse TEGs in our society. In order to clarify required performances of TEGs to diffuse them in the future, this paper aims to assess the life cycle CO2 emissions (LCCO2) and life cycle cost (LCC) of TEGs based on several product lifecycle scenarios, each of which assumes different future situations in, e.g., conversion efficiency of TEGs. In this paper, we focus on TEGs for passenger automobiles since a range of the temperatures of their exhaust gas is suitable for TEGs. Additionally, we focus on bismuth telluride (Bi-Te) materials to develop TEGs since they have already been available for commercial use. A case study of installing Bi-Te TEGs in passenger automobiles is carried out. The region of interest is Suita City, Osaka, Japan. By describing two scenarios that assume different conversion efficiency of thermoelectric materials, we compare assessment results from the viewpoints of LCCO2 and LCC. The results reveal that using TEGs has the potential to reduce CO2 emissions of the city by 0.07∼0.30%. It is also shown that the TEG cost needs to be drastically reduced to make the usage of TEGs profitable.