In Memoriam

J. Mech. Des. 2018;140(10):100101-100101-2. doi:10.1115/1.4040905.

Faydor L. Litvin, world-renowned scientist, scholar, and educator, passed away on Apr. 26, 2017, at the age of 103. The Distinguished Professor Emeritus in the Department of Mechanical Engineering and Director of the Gear Research Center of the University of Illinois at Chicago (UIC) was widely regarded as the founder of the modern field of gearing and made significant contributions to the development of the theory of mechanisms.

Commentary by Dr. Valentin Fuster

Research Papers: Design Theory and Methodology

J. Mech. Des. 2018;140(10):101101-101101-11. doi:10.1115/1.4040625.

Personal context-specific experience can affect how a designer evaluates a design problem and proposes solutions. However, this effect was seldom discovered in a quantitative manner in problem-solving design tasks. This paper uses empirical evidence and quantitative methods to show the effects of novice designers' contextual experience on design tasks, particularly as it relates to the design process and design outcomes. Thirty-three people performed two design tasks while their cognitive states were assessed using electroencephalography (EEG). Moreover, the objective ratings (i.e., quantity, novelty and quality) from prospective users were analyzed to gauge the effect of contextual experience on design outcomes. Results suggest that during ideation, contextual experience has a negative effect on mental states associated with creativity and also on the novelty evaluations of the proposed solutions in the tested design tasks. This research advances the development of design methods for novice designers.

Commentary by Dr. Valentin Fuster
J. Mech. Des. 2018;140(10):101102-101102-16. doi:10.1115/1.4040627.

This study aimed to investigate the generation mechanism of pairwise associated sketches and different associated types through the experimental analysis of the cognitive processes of the designers in conceptual design process. The verbal protocol analysis (VPA) was carried out on three groups of participants (designers). The first group consisted of eight university students majoring in industrial design, the second consisted of eight university students majoring in mechanical design, and the third consisted of six product designers with degrees in industrial design and over 5 years of work experience. Their cognitive processes revealed by the think-aloud protocol and outcome sketches during a specific design task were recorded. Following a content-oriented encoding scheme, the verbal data were encoded into cognitive actions, and according to the generation sequence of the sketches, the encoding results were postprocessed for the further analysis of associated sketches. First, we identified which cognitive actions played important roles in the generation of associated sketches. Next, based on the encoding results and the analyses of all associated sketches, we found that all associations can be categorized into three types (in order from low to high association levels): shape association, behavior association, and function association. Finally, we found that the differences in major background had no significant effect on the number of associated sketches but did have some influence on the diversity of association types, the differences in experience background mainly influenced the number of associated sketches in each type of association. Meanwhile, by analyzing the key cognitive actions, we also found the advantages and disadvantages of each group in the generation of different types of associations. The findings of this study can help designers with different backgrounds to choose suitable strategies to stimulate the important actions at the right time, conceive appropriate association types, and ultimately generate diverse concept sketches with high quality.

Commentary by Dr. Valentin Fuster

Research Papers: Design Automation

J. Mech. Des. 2018;140(10):101401-101401-13. doi:10.1115/1.4040626.

Testing of components at higher-than-nominal stress level provides an effective way of reducing the required testing effort for system reliability assessment. Due to various reasons, not all components are directly testable in practice. The missing information of untestable components poses significant challenges to the accurate evaluation of system reliability. This paper proposes a sequential accelerated life testing (SALT) design framework for system reliability assessment of systems with untestable components. In the proposed framework, system-level tests are employed in conjunction with component-level tests to effectively reduce the uncertainty in the system reliability evaluation. To minimize the number of system-level tests, which are much more expensive than the component-level tests, the accelerated life testing (ALT) design is performed sequentially. In each design cycle, testing resources are allocated to component-level or system-level tests according to the uncertainty analysis from system reliability evaluation. The component-level or system-level testing information obtained from the optimized testing plans is then aggregated to obtain the overall system reliability estimate using Bayesian methods. The aggregation of component-level and system-level testing information allows for an effective uncertainty reduction in the system reliability evaluation. Results of two numerical examples demonstrate the effectiveness of the proposed method.

Commentary by Dr. Valentin Fuster
J. Mech. Des. 2018;140(10):101402-101402-13. doi:10.1115/1.4040548.

Many decisions within engineering systems design are typically made by humans. These decisions significantly affect the design outcomes and the resources used within design processes. While decision theory is increasingly being used from a normative standpoint to develop computational methods for engineering design, there is still a significant gap in our understanding of how humans make decisions within the design process. Particularly, there is lack of knowledge about how an individual's domain knowledge and framing of the design problem affect information acquisition decisions. To address this gap, the objective of this paper is to quantify the impact of a designer's domain knowledge and problem framing on their information acquisition decisions and the corresponding design outcomes. The objective is achieved by (i) developing a descriptive model of information acquisition decisions, based on an optimal one-step look ahead sequential strategy, utilizing expected improvement maximization, and (ii) using the model in conjunction with a controlled behavioral experiment. The domain knowledge of an individual is measured in the experiment using a concept inventory, whereas the problem framing is controlled as a treatment variable in the experiment. A design optimization problem is framed in two different ways: a domain-specific track design problem and a domain-independent function optimization problem (FOP). The results indicate that when the problem is framed as a domain-specific design task, the design solutions are better and individuals have a better state of knowledge about the problem, as compared to the domain-independent task. The design solutions are found to be better when individuals have a higher knowledge of the domain and they follow the modeled strategy closely.

Commentary by Dr. Valentin Fuster
J. Mech. Des. 2018;140(10):101403-101403-13. doi:10.1115/1.4040787.

In this paper, we present the results of a study of citation and co-authorship networks for articles published at the ASME Design Automation Conference (DAC) during the years 2002–2015. Two topic-modeling methods are presented for studying the DAC literature: A frequency-based model was developed to explore DAC topic distribution and evolution, as well as citation analysis for each core topic. Correlation analysis and association-rule mining were used to discover relationships between topics. A new unsupervised learning algorithm, propagation mergence (PM), was created to address identified shortcomings of existing methods and applied to study the existing DAC citation network. Influential articles and important article clusters were identified and effective visualizations created. We also investigated the DAC co-authorship network by identifying key authors and showing that the network structure exhibits small-world-network properties. The resulting insights, obtained by the both the proposed and existing methods, may be beneficial to the engineering design research community, especially with respect to determining future research directions and possible actions for improvement. The data set used here is limited; expanding to include additional relevant conference proceedings and journal articles in the future would offer a more complete understanding of the engineering design research literature.

Commentary by Dr. Valentin Fuster
J. Mech. Des. 2018;140(10):101404-101404-11. doi:10.1115/1.4040629.

Manufacturers must decide when to invest and launch a new vehicle segment or how to redesign vehicles existing segment under market uncertainties. We present an optimization framework for redesigning or investing in future vehicles using real options to address uncertainty in gas price and regulatory standards like the U.S. Corporate Average Fuel Economy (CAFE) standard. In a specific study involving a product of gasoline, hybrid electric, and electric vehicles (EV), we examine the relationship between gas price and CAFE uncertainties to support decisions by manufacturers on product mix and by policy makers on proposing standards. A real options model is used for the time delay on investment, redesign, and pricing, integrated with a robust design formulation to optimize expected net present value (ENPV) and net present value (NPV) robustness. Results for nine different scenarios suggest that policy makers should consider gas price when setting CAFE standards; and manufacturers should consider the trade-off between ENPV and robust NPVs. Results also suggest that change of product mix rather than vehicle redesign better addresses CAFE standards inflation.

Commentary by Dr. Valentin Fuster

Research Papers: Design of Mechanisms and Robotic Systems

J. Mech. Des. 2018;140(10):102301-102301-9. doi:10.1115/1.4040879.

An optimization approach is presented for generating linkage mechanisms consisting of frame members with arbitrarily inclined hinges. A second-order cone programming (SOCP) problem is solved to obtain the locations and directions of hinges of an infinitesimal mechanism. It is shown that the primal and dual SOCP problems correspond to the plastic limit analysis problems based on the lower-bound and upper-bound theorems, respectively, with quadratic yield functions. Constraints on displacement components are added to the dual problem, if a desirable deformation is not obtained. A finite mechanism is generated by carrying out geometrically nonlinear analysis and, if necessary, adding hinges and removing members. Effectiveness of the proposed method is demonstrated through examples of two- and three-dimensional mechanisms.

Commentary by Dr. Valentin Fuster
J. Mech. Des. 2018;140(10):102302-102302-11. doi:10.1115/1.4040779.

A method is presented to optimize the shape and size of a passive, energy-storing prosthetic foot using the lower leg trajectory error (LLTE) as the design objective. The LLTE is defined as the root-mean-square error between the lower leg trajectory calculated for a given prosthetic foot's deformed shape under typical ground reaction forces (GRFs), and a target physiological lower leg trajectory obtained from published gait data for able-bodied walking. Using the LLTE as a design objective creates a quantitative connection between the mechanical design of a prosthetic foot (stiffness and geometry) and its anticipated biomechanical performance. The authors' prior work has shown that feet with optimized, low LLTE values can accurately replicate physiological kinematics and kinetics. The size and shape of a single-part compliant prosthetic foot made out of nylon 6/6 were optimized for minimum LLTE using a wide Bezier curve to describe its geometry, with constraints to produce only shapes that could fit within a physiological foot's geometric envelope. Given its single part architecture, the foot could be cost effectively manufactured with injection molding, extrusion, or three-dimensional printing. Load testing of the foot showed that its maximum deflection was within 0.3 cm (9%) of finite element analysis (FEA) predictions, ensuring the constitutive behavior was accurately characterized. Prototypes were tested on six below-knee amputees in India—the target users for this technology—to obtain qualitative feedback, which was overall positive and confirmed the foot is ready for extended field trials.

Commentary by Dr. Valentin Fuster
J. Mech. Des. 2018;140(10):102303-102303-7. doi:10.1115/1.4040882.

The paper initially reports about the properties of an expression of dual generalized inverse matrix currently available in the literature. It is demonstrated that such a matrix does not fulfill all the Penrose conditions. Hence, novel and computationally efficient algorithms/formulas for the computation of the Moore–Penrose dual generalized inverse (MPDGI) are herein proposed. The paper also contains a new algorithm for the singular value decomposition (SVD) of a dual matrix. The availability of these formulas allows the simultaneous solution of overdetermined systems of dual linear equations without requiring the traditional separation in primal and dual parts. This should prove useful for the solution of many kinematic problems. The algorithms/formulas herein deduced have been also tested on the kinematic synthesis of the constant transmission ratio RCCC spatial linkage.

Commentary by Dr. Valentin Fuster

Technical Brief

J. Mech. Des. 2018;140(10):104501-104501-5. doi:10.1115/1.4040425.

Automotive differential gears are usually operating at very low speed and high load conditions and hence are usually designed to be protected against the root bending fatigue failure. Depending on application requirements and lubrication regime, surface failures may occasionally be encountered as well. Mainstream existing design procedures published by AGMA are based on analyzing one single gear pair engagement while up to four potential engagements, between two side gears and two differential pinions, exist. There are also differential designs with three or four differential pinions that increase potential number of engagements to, respectively, six and eight. Usually, the hypoid gear loading is divided by number of side gears, two, also differential pinion loads are usually assumed to be equal; this is a good estimate when no misalignments are present. When misalignments are present, load sharing between the differential pinions becomes greatly imbalanced. This study tries to come up with a simplified analytical approach to evaluate overload factor between the differential pinions as a result of misalignments realized by differential gears inside a differential case. The total indexing run-out quality of gears is also studied through treating it as a source of misalignment. This study will help designers to evaluate the effects of tolerance limits and differential case machining errors on differential gear bending lives.

Commentary by Dr. Valentin Fuster

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