Reinforcing ribs can significantly increase the stiffness of panels. In this study, we formulate a computational design method to determine the optimal position, dimensions and orientation of ribs made of stock plates and welded to a panel to maximize its stiffness. Typical applications of welded rib reinforcements are large metallic structures with low production volumes, for which other processes such as machining or stamping are either infeasible or too costly. These applications include, for example, ship hulls, fuel tanks, aircraft wing structures and linkage components in heavy machinery. To determine the optimal ribs layout, we formulate a topology optimization technique whereby a feature-based geometric representation of the rib is smoothly mapped onto a finite element mesh for analysis. This mesh remains fixed throughout the optimization, thus circumventing re-meshing upon changes in the ribs layout. Importantly, our method enforces geometric constraints to ensure manufacturability, namely that: a) ribs must remain vertical at all times to ensure a good quality weld; b) the ribs dimensions must not exceed those of available stock plates; c) ribs should not encroach the space above holes on the panel used for routing other components or for access; and d) there must be a minimum spacing between ribs to ensure adequate access for the welding gun. Ours is the first method to determine the optimal layout of welded ribs made of flat plates within a 3-dimensional design envelope that satisfies the foregoing geometric constraints.
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Hairong Wang; Shaowei Fan; Hong Liu
J. Mech. Des. 2016; 139(1):012304-012304-12
The force and/or motion transmissibility and the analyticity of inverse kinematics for a thumb mechanism depend on thumb configuration. This paper presents a general framework for the thumb configuration and performance evaluation in the design of dexterous robotic hand. The thumb configuration is described by the functional analysis of human thumb, and the thumb of robotic hand is generalized into fifteen configurations. A performance evaluation method is proposed based on kinetostatic and dynamic dexterity as well as workspace. The kinetostatic dexterity is based on a Jacobian matrix condition number. A dynamic dexterity measure is presented via acceleration analysis, which keeps a clear geometric meaning. The proposed method is applied to evaluate the performance of three examples, which cover thumb configurations of most existing dexterous hands. Performance evaluation results demonstrate the effectiveness of the proposed method. Using these results and the proposed performance evaluation method, meaningful design principles are presented to guide the design of the thumb configuration.
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Inspiration and Fixation: The Influences of Example Designs and System Properties in Idea Generation
Luis A. Vasconcelos; Carlos C. Cardoso; Maria Sääksjärvi; Chih-Chun Chen; Nathan Crilly
J. Mech. Des. 2017; 139(3):031101-031101-13
External inspiration stimuli can be very effective to help designers arrive at new ideas that they would be otherwise unlikely to generate. However, exposure to external stimuli can also hinder creativity and fixate designers on particular features of such stimuli. We conducted an experiment with novice designers to compare the inspiration effects from two stimuli types: a concrete example solution (a bike) and an abstract property that a solution might incorporate (modularity). Working alone in a short design session, participants were asked to generate ideas to eliminate the need for people to have multiple bikes as they grow up. We found that exposure to either the concrete example or the abstract property reduced the total number of ideas generated and how diverse those ideas were, and that exposure to both stimuli (together) reduced these measures even further. We also found that each stimulus affected participants differently, encouraging ideas like one type of stimulus, while discouraging ideas like the other type. These findings reinforce the idea that external stimuli can hinder creativity and should be accessed carefully. They also show how concrete and abstract stimuli can produce similar inspiration effects, challenging our intuitions about how to encourage wide-ranging ideas. This has the potential to shape how design is taught and how inspiration tools are developed.
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Development and Evaluation of a Mechanical Stance-Controlled Orthotic Knee Joint With Stance Flexion
Jan Andrysek; Matthew J. Leineweber; Hankyu Lee
J. Mech. Des. 2017; 139(3):035001-035001-7
People with severe impairment of the lower body caused by conditions such as polio or stroke often rely on assistive devices for mobility. Knee orthosis plays an important role in restoring mobility by stabilizing the weakened lower limb and providing support for standing and walking. Concurrently, the orthosis should allow for natural and efficient movement of the limb as required for walking. The focus of this work is to develop a new method for controlling orthotic knee joints. The new control method uses a mechanical system to monitor loading and timing events and patterns, and apply knee-locking function when the limb is loaded. A prototype was built and tested on a polio patient and demonstrated the feasibility of this approach for providing reliable orthotic function. Further work aims to test the knee joint on a larger group of individuals within the community.
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Design and Characterization of a Continuous Rotary Minimotor Based on Shape Memory Wires and Overrunning Clutches
An attractive but little explored field of application of the shape memory technology is the area of rotary actuators, in particular for generating endless motion. This paper presents a miniature rotary motor based on shape memory alloy (SMA) wires and overrunning clutches which produces high output torque and unlimited rotation. The concept features a SMA wire tightly wound around a low-friction cylindrical drum to convert wire strains into large rotations within a compact package. The seesaw motion of the drum ensuing from repeated contraction-elongation cycles of the wire is converted into unidirectional motion of the output shaft by an overrunning clutch fitted between drum and shaft. Following a design process formerly developed by the authors, a six-stage prototype with size envelope of 48´22´30 mm is built and tested. Diverse supply strategies are implemented to optimize either the output torque or the speed regularity of the motor with the following results: maximum torque = 20 Nmm; specific torque = 6.31´10-4 Nmm/mm3; rotation per module = 15 deg/cycle; free continuous speed = 4.4 rpm.
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Christine A. Toh, Andrew A. Strohmetz and Scarlett R. Miller
J. Mech. Des 138(10), 101105; doi: 10.1115/1.4034107
Concept selection is a critical stage of the engineering design process because of its potential to influence the direction of the final design. While formalized selection methods have been developed to increase its effectiveness and reduce human decision-making biases, research that understands these biases in more detail can provide a foundation for improving the selection process. One important bias that occurs during this process is ownership bias, or an unintentional preference for an individuals’ own ideas over the ideas of others. However, few studies have explored ownership bias in a design setting and the influence of other factors such as the gender of the designer or the “goodness” of an idea. In order to understand the impact of these factors in engineering design education, a study was conducted with 110 engineering students. The results from this study show that male students tend to show ownership bias during concept selection by selecting more of their own ideas while female students tend to show the opposite bias, the Halo Effect, by selecting more of their team members’ concepts. In addition, participants exhibited ownership bias for ideas that were considered good or high quality, but the opposite bias for ideas that were not considered good or high quality. These results add to our understanding of the factors that impact team concept selection and provide empirical evidence of the occurrence of ownership bias and the effects of gender and idea goodness in engineering design education.
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Cityplot is a new visualization technique for engineering design that uses a dimensionally-reduced representation of the design decisions to represent the mapping from the decisions to the criteria upon which a design is judged. The shown Cityplot depicts possible CubeSat constellations to support the 2007 Earth Science Decadal Survey. Each constellation is comprised of up to 4 CubeSats and each CubeSat can select from a list of 7 instruments. Possible CubeSat constellations are “cities” and are placed in a 2d space to be visualized. An individual constellation can also be seen as a table of instruments (rows) being present (black) on a given CubeSat (columns). The benefits, costs and risks of each possible constellation are represented as color-coded “buildings” in each “city”. The criteria in this example are: a tiered count of satisfied Decadal objectives (blue), the average CubeSat Technology Readiness Level (red), lifecycle cost (green), maximum number of lost instruments upon loss of a single satellite (black). A taller building indicates the possible constellation performs better in that criteria. Dark purple “roads” between two designs indicate that only one instrument is either added to or removed from one CubeSat to make one constellation identical to the other. Cityplot simultaneously shows sensitivity of criteria to decisions, criteria tradeoffs and design families via a quick intuitive view of the design space.
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Seda Yilmaz, Colleen Seifert, Shanna R. Daly and Richard Gonzalez
J. Mech. Des 138(7), 071102; doi: 10.1115/1.4032219
Current design theory lacks a systematic method to identify what designers know that helps them to create innovative products. In the early stages of idea generation, designers may find novel ideas come readily to mind, or may become fixated on their own or existing products. This may limit the ability to consider more, and more varied candidate concepts that may potentially lead to innovation. To aid in idea generation, we sought to identify “design heuristics,” or “rules of thumb,” evident in award-winning designs. In this paper, we demonstrate a content analysis method for discovering heuristics in the designs of innovative products. Our method depends on comparison to a baseline of existing products so that the innovative change can be readily identified. Through an analysis of key features and functional elements in the designs of over 400 award-winning products, forty heuristic principles were extracted. These Design Heuristics are outlined according to their perceived role in changing an existing product concept into a novel design, and examples of other products using the heuristics are provided. To demonstrate the ease of use of these Design Heuristics, we examined outcomes from a classroom study, and found that concepts created using Design Heuristics were rated as more creative and varied. The analysis of changes from existing to innovative products can provide evidence of useful heuristic principles to apply in creating new designs.
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The synthesis of functional molecular mechanisms is constrained by the notorious difficulties in fabricating nano-links of prescribed shapes and sizes. Thus, the classical mechanism synthesis methods, which assume the ability to manufacture any designed links, cannot provide a systematic process for designing molecular mechanisms. We propose a new approach to build functional mechanisms with prescribed mobility by only using elements from a predefined "link soup". The resulting synthesis procedure is the first of its kind that is capable of systematically synthesizing functional linkages with prescribed mobility constructed from a soup of primitive entities. Furthermore, the proposed systematic approach outputs the ATLAS of candidate mechanisms, which can be further processed for downstream applications. Although the scope of this technique is rather general, its immediate application is the design of molecular machines assembled from nano-links that either exist in nature or can be fabricated.
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Gwang Kim, Yunjung Kwon, Eun Suk Suh and Jaemyung Ahn
J. Mech. Des 138(7), 07140; doi: 10.1115/1.4033504
This paper proposes a framework to analyze the architectural complexity of systems developed with a product family. A product family is a set of products that are derived from common sets of parts, interfaces, and processes, known as the product platform. Through the use of product platforms, several variations of products can be developed in a short period of time with relatively low-engineering costs to capture market share in niche market segments as the demand arises. This work can be used in a variety of ways to guide product platform and variant architecture development during the initial concept generation stage. The effectiveness of the proposed framework is demonstrated through a case study of a train bogie platform.
The process starts with building the design structure matrix (DSM) model, which captures the structural architecture as well as mass, energy, and information flow, for the product platform and its variants. Using the DSMs created and the selected complexity metric, the architectural complexity, which includes the structural complexity and flow complexity values, is assessed. Based on the quantitative results obtained, the overall complexity for the product platform and the product family could be compared with other competing product platform architecture and product family concepts. Furthermore, this process also allows system architects and decision makers to manage overall complexity of an entire product family, either through complexity minimization or by designing the entire platform and product architecture to be less sensitive to engineering changes in terms of complexity fluctuation.
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This section includes brief descriptions of articles soon to be or recently published by the Journal of Mechanical Design. These featured articles highlight recent research developments and emerging trends in mechanical design. For Abstracts and Full Articles please see ASME's Digital Collection.