Showing papers in "Journal of Mechanical Design in 2008"

Microrobot Design Using Fiber Reinforced Composites

Abstract: Mobile microrobots with characteristic dimensions on the order of 1 cm are difficult to design using either microelectromechanical systems technology or precision machining. This is due to the challenges associated with constructing the high strength links and high-speed, low-loss joints with micron scale features required for such systems. Here, we present an entirely new framework for creating microrobots, which makes novel use of composite materials. This framework includes a new fabrication process termed smart composite microstructures (SCM) for integrating rigid links and large angle flexure joints through a laser micromachining and lamination process. We also present solutions to actuation and integrated wiring issues at this scale using SCM. Along with simple design rules that are customized for this process, our new complete microrobotic framework is a cheaper, quicker, and altogether superior method for creating microrobots that we hope will become the paradigm for robots at this scale.

Blind Kriging: A New Method for Developing Metamodels

Abstract: Kriging is a useful method for developing metamodels for product design optimization. The most popular kriging method, known as ordinary kriging, uses a constant mean in the model. In this article, a modified kriging method is proposed, which has an unknown mean model. Therefore, it is called blind kriging. The unknown mean model is identified from experimental data using a Bayesian variable selection technique. Many examples are presented, which show remarkable improvement in prediction using blind kriging over ordinary kriging. Moreover, a blind kriging predictor is easier to interpret and seems to be more robust against mis-specification in the correlation parameters.

Unified Uncertainty Analysis by the First Order Reliability Method

Abstract: Two types of uncertainty exist in engineering. Aleatory uncertainty comes from inherent variations while epistemic uncertainty derives from ignorance or incomplete information. The former is usually modeled by the probability theory and has been widely researched. The latter can be modeled by the probability theory or nonprobability theories and is much more difficult to deal with. In this work, the effects of both types of uncertainty are quantified with belief and plausibility measures (lower and upper probabilities) in the context of the evidence theory. Input parameters with aleatory uncertainty are modeled with probability distributions by the probability theory. Input parameters with epistemic uncertainty are modeled with basic probability assignments by the evidence theory. A computational method is developed to compute belief and plausibility measures for black-box performance functions. The proposed method involves the nested probabilistic analysis and interval analysis. To handle black-box functions, we employ the first order reliability method for probabilistic analysis and nonlinear optimization for interval analysis. Two example problems are presented to demonstrate the proposed method.

A Graph-Based Fault Identification and Propagation Framework for Functional Design of Complex Systems

Abstract: In this paper, the functional-failure identification and propagation (FFIP) framework is introduced as a novel approach for evaluating and assessing functional-failure risk of physical systems during conceptual design. The task of FFIP is to estimate potential faults and their propagation paths under critical event scenarios. The framework is based on combining hierarchical system models of functionality and configuration, with behavioral simulation and qualitative reasoning. The main advantage of the method is that it allows the analysis of functional failures and fault propagation at a highly abstract system concept level before any potentially high-cost design commitments are made. As a result, it provides the designers and system engineers with a means of designing out functional failures where possible and designing in the capability to detect and mitigate failures early on in the design process. Application of the presented method to a fluidic system example demonstrates these capabilities.

An Experimental Study of the Influence of Manufacturing Errors on the Planetary Gear Stresses and Planet Load Sharing

Abstract: In this paper, results of an experimental study are presented to describe the impact of certain types of manufacturing errors on gear stresses and the individual planet loads of an n-planet planetary gear set (n=3-6) The experimental setup includes a specialized test apparatus to operate a planetary gear set under typical speed and load conditions and gear sets having tightly controlled intentional manufacturing errors The instrumentation system consists of multiple strain gauges mounted on the ring gear and a multichannel data collection and analysis system A method for computing the planet load-sharing factors from root strain-time histories is proposed Influence of carrier pinhole position errors on gear root stresses is quantified for various error and torque values applied to gear sets having three to six planets The results clearly indicate that manufacturing errors influence gear stresses and planet load sharing significantly Gear sets having larger number of planets are more sensitive to manufacturing errors in terms of planet load-sharing behavior

Dynamic Modeling and Analysis of Tooth Profile Modification for Multimesh Gear Vibration

Abstract: This work studies the effects of tooth profile modification on multimesh gearset vibration. The nonlinear analytical model considers the dynamic load distribution between the individual gear teeth and the influence of variable mesh stiffnesses, profile modifications, and contact loss. The proposed model yields better agreement than two existing models when compared against nonlinear gear dynamics from a finite element/contact mechanics benchmark. These comparisons are made for different loads, profile modifications, and bearing stiffness conditions. This model captures the total and partial contact losses demonstrated by finite element. Perturbation analysis based on the proposed model finds approximate frequency response solutions for the case of no total contact loss due to the optimized system parameters. The closed-form solution is compared with numerical integration and provides guidance for optimizing mesh phasing, contact ratios, and profile modification magnitude and length. DOI: 10.1115/1.2976803

Quantifying Aesthetic Form Preference in a Utility Function

Abstract: One of the greatest challenges in product development is creating a form that is aesthetically attractive to an intended market audience. Market research tools, such as consumer surveys, are well established for functional product features, but aesthetic preferences are as varied as the people that respond to them. Additionally, and possibly even more challenging, user feedback requires objective measurement and quantification of aesthetics and aesthetic preference. The common methods for quantifying aesthetics present respondents with metric scales over dimensions with abstract semantic labels like "strong" and "sexy. " Even if researchers choose the correct semantics to test, and even if respondents accurately record their responses on these semantic scales, the results on the semantic scales must be translated back into a product shape, where the designer must take the consumers' numerical scores for a set of semantics and translate that into a form which consumers will find desirable. This translation presents a potential gap in understanding between the supply and demand sides of the marketplace. This gap between designer and user can be closed through objective methods to understand and quantify aesthetic preferences because the designer would have concrete directions to use as a foundation for development of the product form. Additionally, the quantification of aesthetic preference could be used by the designer as evidence to support certain product forms when engineering and manufacturing decisions are made that might adversely affect the aesthetics of the product form. This paper demonstrates how the qualitative attribute, form, cannot only be represented quantitatively, but also how customer preferences can be estimated as utility functions over the aesthetic space, so that new higher utility product forms can be proposed and explored. To do so, the form is summarized with underlying latent form characteristics, and these underlying characteristics are specified to be attributes in a utility function. Consumer surveys, created using design of experiments, are then used to capture an individual's preference for the indicated attributes and thus the form. Once preference is summarized in the utility function, the utility function can be used as the basis for form generation and modification or design verification.

3D Simplified Finite Elements Analysis of Load and Contact Angle in a Slewing Ball Bearing

Abstract: Bolted bearing connections are one of the most important connections in some industrial structures, and manufacturers are always looking for a quick calculation model for a safe design. In this context, all the analytical and numerical models reduce the global study to the study of the most critical sector. Therefore, the main inputs for these models are the maximal equivalent contact load and the corresponding contact angle. Thus, a load distribution calculation model that takes all the important parameters, such as the stiffness of the supporting structure and the variation in the contact angle, into consideration is needed. This paper presents a 3D finite element (FE) simplified analysis of load distribution and contact angle variation in a slewing ball bearing. The key element of this methodology, which is based on the Hertz theory, is modeling the rolling elements under compression by nonlinear traction springs between the centers of curvature of the raceways. The contact zones are modeled by rigid shells to avoid numerical singularities. Each raceway curvature center is coupled to the corresponding contact zone by rigid shells. The main contribution of this method is not only the evaluation of the contact loads with a relatively reduced calculation time but also the variation in the contact angle from the deformed coordinates of the curvature centers. Results are presented for several loading cases: axial loading, turnover moment, and a combined loading of axial force and turnover moment. The influence of the most important parameters such as the contact angle, the stiffness of the bearings, and the supporting structure is discussed. Finally, a preliminary experimental validation is conducted on a standard ball bearing. The results presented in this paper seem encouraging. The FE study shows an important influence of several parameters and a good correlation with experimental results. Consequently, this model can be extended to other types of slewing bearings such as roller bearings. Moreover, it can be implemented in complex industrial structures such as cranes and lifting devices to determine the corresponding load distributions and contact angles and, consequently, the most critical sector.

Reliability-Based Design Optimization Using Response Surface Method With Prediction Interval Estimation

Abstract: Since variances in the input variables of the engineering system cause subsequent variances in the product output performance, reliability-based design optimization (RBDO) is getting much attention recently. However, RBDO requires expensive computational time. Therefore, the response surface method is often used for computational efficiency in solving RBDO problems. A method to estimate the effect of the response surface error on the RBDO result is developed in this paper. The effect of the error is expressed in terms of the prediction interval, which is utilized as the error metric for the response surface used for RBDO. The prediction interval provides upper and lower bounds for the confidence level that the design engineer specified. Using the prediction interval of the response surface, the upper and lower limits of the reliability are computed. The lower limit of reliability is compared with the target reliability to obtain a conservative optimum design and thus safeguard against the inaccuracy of the response surface. On the other hand, in order to avoid obtaining a design that is too conservative, the developed method also constrains the upper limit of the reliability in the design optimization process. The proposed procedure is combined with an adaptive sampling strategy to refine the response surface. Numerical examples show the usefulness and the efficiency of the proposed method.

A Design-Driven Validation Approach Using Bayesian Prediction Models

Abstract: In most of the existing work, model validation is viewed as verifying the model accuracy, measured by the agreement between computational and experimental results. Due to the lack of resource, accuracy can only be assessed at very limited test points. However, from the design perspective, a good model should be considered the one that can provide the discrimination (with good resolution) between competing design candidates under uncertainty. In this work, a design-driven validation approach is presented. By combining data from both physical experiments and the computer model, a Bayesian approach is employed to develop a prediction model as the replacement of the original computer model for the purpose of design. Based on the uncertainty quantification with the Bayesian prediction and, subsequently, that of a design objective, some decision validation metrics are further developed to assess the confidence of using the Bayesian prediction model in making a specific design choice. We demonstrate that the Bayesian approach provides a flexible framework for drawing inferences for predictions in the intended, but maybe untested, design domain. The applicability of the proposed decision validation metrics is examined for designs with either a discrete or continuous set of design alternatives. The approach is demonstrated through an illustrative example of a robust engine piston design.

Geometry and Kinematic Analysis of a Redundantly Actuated Parallel Mechanism That Eliminates Singularities and Improves Dexterity

Abstract: This paper investigates the behavior of a type of parallel mechanisms with a central strut. The mechanism is of lower mobility, redundantly actuated, and used for sprained ankle rehabilitation. Singularity and dexterity are investigated for this type of parallel mechanisms based on the Jacobian matrix in terms of rank deficiency and condition number, throughout the workspace. The non-redundant cases with three and two limbs are compared with the redundantly actuated case with three limbs. The analysis demonstrates the advantage of introducing the actuation redundancy to eliminate singularities and to improve dexterity and justifies the choice of the presented mechanism for ankle rehabilitation.

Modeling Methods and Conceptual Design Principles for Reconfigurable Systems

Abstract: Reconfigurable systems can attain different configurations at different times thereby altering their functional abilities. Such systems are particularly suitable for specific classes of applications in which their ability to undergo changes easily can be exploited to fulfill new demands, allow for evolution, and improve survivability. This paper identifies the main factors that drive the need for reconfigurability and proposes methods for modeling reconfigurable systems. A survey of 33 different reconfigurable systems is also presented to provide broader insights and general design guidelines for reconfigurable systems.

Position and Orientation Characteristic Equation for Topological Design of Robot Mechanisms

Abstract: This paper presents the explicit mapping relations between topological structure of parallel mechanism and position and orientation characteristic (in short, POC) of its motion output link. It deals with: (1) The symbolic representation and the invariant of topological structure of mechanism; (2) The matrix representation of POC of motion output link; (3) The POC equations of parallel mechanism and its symbolic operation rules. The symbolic operation involves simple mathematic tools and fewer operation rules, and has clear geometrical meaning. So, it is easy to use. The forward operation of the POC equations can be used for structural analysis; its inverse operation can be used for structural synthesis. The method proposed in this paper is totally different from the methods based on screw theory and based on displacement subgroup.Copyright © 2008 by ASME

A Building Block Approach to the Conceptual Synthesis of Compliant Mechanisms Utilizing Compliance and Stiffness Ellipsoids

Abstract: Ellipsoids this paper, we investigate a methodology for the conceptual synthesis of compliant mechanisms based on a building block approach. The building block approach is intuitive and provides key insight into how individual building blocks contribute to the overall function. We investigate the basic kinematic behavior of individual building blocks and relate this to the behavior of a design composed of building blocks. This serves to not only generate viable solutions but also to augment the understanding of the designer. Once a feasible concept is thus generated, known methods for size and geometry optimization may be employed to fine-tune performance. The key enabler of the building block synthesis is the method of capturing kinematic behavior using compliance ellipsoids. The mathematical model of the compliance ellipsoids facilitates the characterization of the building blocks, transformation of problem specifications, decomposition into subproblems, and the ability to search for alternate solutions. The compliance ellipsoids also give insight into how individual building blocks contribute to the overall kinematic function. The effectiveness and generality of the methodology are demonstrated through two synthesis examples. Using only a limited set of building blocks, the methodology is capable of addressing generic kinematic problem specifications for compliance at a single point and for a single-input, single-output compliant mechanism. A rapid prototype of the latter demonstrates the validity of the conceptual solution. DOI: 10.1115/1.2821387

Biological Modeling and Evolution Based Synthesis of Metamorphic Mechanisms

Abstract: A methodology for synthesis and configuration design of metamorphic mechanisms is developed in this paper based on biological modeling and genetic evolution with biological building blocks The goal is to conceive an appropriate source-metamorphic-mechanism configuration when the multiple phases of kinematic functions are given The key enabler is the way of developing genetic evolution in modeling and design by capturing the metamorphic configuration characteristics With the unique characteristic of achieving multiple working-phase functions in a mechanism, the metamorphic mechanism possesses two features: one, the ametabolic feature referring to the specified working phases that can be accomplished by a number of traditional mechanisms; two, the metamorphic feature occurring in transition between different working phases, resulting in change of topology of the mechanism Based on this transition between phases, the concept of mechanism evolution is for the first time introduced in this paper based on biological building blocks in the form of metamorphic cells and associated intrinsic elements as the metamorphic gene This leads to development of cell evolution and genetic aggregation with mechanism decomposition and evolutionary operation based on mapping from the source-metamorphic mechanism to multiphase working configurations Examples are given to demonstrate the concept and principles

Nonlinear identification of machine settings for flank form modifications in hypoid gears

Abstract: This paper presents a new systematic method for identifying the values of the machine-tool settings required to obtain flank form modifications in hypoid gears. The problem is given a nonlinear least-squares formulation, and it is solved by the Levenberg-Marquardt method with a trust-region strategy. To test the method, the same ease-off topography was obtained by means of very different sets of machine-tool settings, including a set of only kinematic parameters and a highly redundant set of 17 parameters. In all cases, the goal was achieved in a few iterations, with residual errors well below machining tolerances and, even more importantly, with realistic values of all parameters. Therefore, significant improvements in practical gear design can be achieved by employing the overall proposed procedure.

Design of Nonlinear Springs for Prescribed Load-Displacement Functions

Abstract: A nonlinear spring has a defined nonlinear load-displacement function, which is also equivalent to its strain energy absorption rate. Various applications benefit from nonlinear springs, including prosthetics and microelectromechanical system devices. Since each nonlinear spring application requires a unique load-displacement function, spring configurations must be custom designed, and no generalized design methodology exists. In this paper, we present a generalized nonlinear spring synthesis methodology that (i) synthesizes a spring for any prescribed nonlinear load-displacement function and (ii) generates designs having distributed compliance. We introduce a design parametrization that is conducive to geometric nonlinearities, enabling individual beam segments to vary their effective stiffness as the spring deforms. Key features of our method include (i) a branching network of compliant beams used for topology synthesis rather than a ground structure or a continuum model based design parametrization, (ii) curved beams without sudden changes in cross section, offering a more even stress distribution, and (iii) boundary conditions that impose both axial and bending loads on the compliant members and enable large rotations while minimizing bending stresses. To generate nonlinear spring designs, the design parametrization is implemented into a genetic algorithm, and the objective function evaluates spring designs based on the prescribed load-displacement function. The designs are analyzed using nonlinear finite element analysis. Three nonlinear spring examples are presented. Each has a unique prescribed load-displacement function, including a (i) “J-shaped,” (ii) “S-shaped,” and (iii) constant-force function. A fourth example reveals the methodology’s versatility by generating a large displacement linear spring. The results demonstrate the effectiveness of this generalized synthesis methodology for designing nonlinear springs for any given load-displacement function.

A Functional Classification Framework for the Conceptual Design of Additive Manufacturing Technologies

Abstract: There exist many different layered manufacturing technologies for the realization of prototypes and fully-functional artifacts. Although extremely different in solution principle and embodiment, there exists functional commonality between each technology. This commonality affords the authors an opportunity to propose a new classification framework for layered manufacturing technologies. In addition to using it as a means of classifying existing processes, the authors present the framework as a tool to aid a designer in the conceptual design of new layered manufacturing technologies. The authors close the paper with an example of such an implementation; specifically, the conceptual design of a novel means of obtaining metal artifacts from three-dimensional printing.Copyright © 2008 by ASME

An Inductive Design Exploration Method for Robust Multiscale Materials Design

Abstract: Synthesis of hierarchical materials and products is an emerging systems design paradigm, which includes multiscale (quantum to continuum level) material simulation and product analysis models, uncertainty in the models, and the propagation of this uncertainty through the model chain. In order to support integrated multiscale materials and product design under uncertainty, we propose an inductive design exploration method (IDEM) in this paper. In IDEM, feasible ranged sets of specifications are found in a step-by-step, top-down (inductive) manner. In this method, a designer identifies feasible ranges for the interconnecting variables between the final two models in a model chain. Once feasible ranges of interconnecting variables between these two models are found, then, using this information, feasible ranges of interconnecting variables between the next to the last model and the model immediately preceding it are found. This process is continued until feasible ranged values for the input variables for the first model in the model chain are found. In IDEM, ranged sets of design specifications, instead of an optimal point solution, are identified for each segment of a multilevel design process. Hence, computer intensive calculations can be easily parallelized since the process of uncertainty analysis is decoupled from the design exploration process in IDEM. The method is demonstrated with the example of designing multifunctional energetic structural materials based on a chain of microscale and continuum level simulation models.

Exploring the Use of Functional Models in Biomimetic Conceptual Design

Abstract: The biological world provides numerous cases for analogy and inspiration. From simple cases such as hook and latch attachments to articulated-wing flying vehicles, nature provides many sources for ideas. Though biological systems provide a wealth of elegant and ingenious approaches to problem solving, there are challenges that prevent designers from leveraging the full insight of the biological world into the designed world. This paper describes how those challenges can be overcome through functional analogy. Through the creation of a function-based repository, designers can find biomimetic solutions by searching the function for which a solution is needed. A biomimetic functionbased repository enables learning, practicing, and researching designers to fully leverage the elegance and insight of the biological world. In this paper, we present the initial efforts of functional modeling biological systems and then transferring the principles of the biological system to an engineered system. Four case studies are presented in this paper. These case studies include a biological solution to a problem found in nature and engineered solutions corresponding to the high-level functionality of the biological solution, i.e., a housefly’s winged flight and a flapping wing aircraft. The case studies show that unique creative engineered solutions can be generated through functional analogy with nature. DOI: 10.1115/1.2992062 The designs of the biological world allow organisms to survive in nearly all of earth’s challenging environments filling niches from under-sea volcanic vents, tundras both frozen and desolate, poisonous salt flats, and deserts rarely seeing rain. Nature’s designs are the most elegant, innovative, and robust solution principles and strategies allowing for life to survive many of the earth’s challenges. Biomimetic design aims to leverage the insight of the biological world into the engineered world, but because of numerous challenges, biomimetic design is still undeveloped as a method for formal concept generation. Allowing design engineers’ formal and full access to the solution principles and strategies of the biological world remains beyond current methods and knowledge. Many challenges prevent immediate adoption of designing via biological inspiration including 1 a lack of equivalent engineering technologies, 2 a knowledge gap between designers and biologists, and 3 unawareness of analogous biological systems. Significant effort and time are required to become a competent engineering designer, which creates an equally significant obstacle to becoming sufficiently knowledgeable about biological systems to effectively execute biomimetic design. Formal design based on functional modeling and concept generation methods 1–9 provides a unique opportunity to extend biomimetic design to meet the challenges thwarting the adoption into formal engineering design practices. The generation of functional models based on what a product must do instead of how it will be accomplished provides designers with many benefits such as explicit correlation with customer needs, comprehensive understanding of the design problem, enhanced creativity through abstraction, and innovative concept generation focused on answering what must be done 7,8. Design based on functional modeling provides designers with the freedom to consider the functionality of analogous biological systems without the burden of technological feasibility, and when applied with automated concept generation techniques based on predefined and expandable knowledge bases such as a design repository, biological systems may be explored without the need for advanced training in biological sciences. The representation of products by function has enabled the creation of design repositories allowing designers to access solution principles that are outside their personal knowledge or expertise 10–13. The ability of functional representation to allow designers to access such design information is a key impetus toward the extension of biomimetic design through the method of functional modeling. If biological inspiration requires designers to have extensive knowledge of biological systems, then the insight of the biological world will never be fully accessible to engineering design. The objectives of the research presented in this paper are to functionally explore biological systems to discover the knowledge needed to enable a function-based biomimetic design repository. First, a brief summary of previous work in biomimetic design is provided. Next, the research methodology that was followed to generate the case studies found in Sec. 4 of this paper is discussed. Finally, conclusions reached thus far in this research are discussed as well as a summary of the direction for future work to be completed.

Design and Prototyping of a New Balancing Mechanism for Spatial Parallel Manipulators

Abstract: This paper proposes a new solution to the problem of torque minimization of spatial parallel manipulators. The suggested approach involves connecting a secondary mechanical system to the initial structure, which generates a vertical force applied to the manipulator platform. Two versions of the added force are considered: constant and variable. The conditions for optimization are formulated by the minimization of the root-mean-square values of the input torques. The positioning errors of the unbalanced and balanced parallel manipulators are provided. It is shown that the elastic deformations of the manipulator structure, which are due to the payload, change the altitude and the inclination of the platform. A significant reduction of these errors is achieved by using the balancing mechanism. The efficiency of the suggested solution is illustrated by numerical simulations and experimental verifications. The prototype of the suggested balancing mechanism for the Delta robot is also presented.

Flank Correction for Spiral Bevel and Hypoid Gears on a Six-Axis CNC Hypoid Generator

Abstract: Because the contact patterns of spiral bevel and hypoid gears are highly sensitive to tooth flank geometry, it is desirable to reduce the flank deviations caused by machine errors and heat treatment deformation. Several methods already proposed for flank correction are based on the cutter parameters, machine settings, and kinematical flank motion parameters of a cradle-type universal generator, which are modulated according to the measured flank topographic deviations. However, because of the recently developed six-axis Cartesian-type computer numerical control (CNC) hypoid generator, both face-milling and face-hobbing cutting methods can be implemented on the same machine using a corresponding cutter head and NC code. Nevertheless, the machine settings and flank corrections of most commercial Cartesian-type machines are still translated from the virtual cradle-type universal hypoid generator. In contrast, this paper proposes a flank-correction methodology derived directly from the six-axis Cartesian-type CNC hypoid generator in which high-order correction is easily achieved through direct control of the CNC axis motion. The validity of this flank-correction method is demonstrated using a numerical example of Oerlikon Spirac face-hobbing hypoid gears made by the proposed Cartesian-type CNC machine.

A Compliant Bistable Mechanism Design Incorporating Elastica Buckling Beam Theory and Pseudo-Rigid-Body Model

Abstract: In this work, a new compliant bistable mechanism design is introduced. The combined use of pseudo-rigid-body model (PRBM) and the Elastica buckling theory is presented for the first time to analyze the new design. This mechanism consists of the large deflecting straight beams, buckling beams, and a slider. The kinematic analysis of this new mechanism is studied, using nonlinear Elastica buckling beam theory, the PRBM of a large deflecting cantilever beam, the vector loop closure equations, and numerically solving nonlinear algebraic equations. A design method of the bistable mechanism in microdimensions is investigated by changing the relative stiffness of the flexible beams. The actuation force versus displacement characteristics of several cases is explored and the full simulation results of one of the cases are presented. This paper demonstrates the united application of the PRBM and the buckling Elastica solution for an original compliant mechanism kinematic analysis. New compliant mechanism designs are presented to highlight where such combined kinematic analysis is required.

Design Optimization With System-Level Reliability Constraints

Abstract: Reliability-based design optimization (RBDO) of mechanical systems is computationally intensive due to the presence of two types of iterative procedures-design optimization and reliability estimation. Single-loop RBDO algorithms offer tremendous savings in computational effort, but they have so far only been able to consider individual component reliability constraints. This paper presents a single-loop RBDO formulation and an equivalent formulation that can also include system-level reliability constraints. The formulations allow the allocation of optimal reliability levels to individual component limit states in order to satisfy both system-level and component-level reliability requirements. Four solution algorithms to implement the second, more efficient formulation are developed. A key feature of these algorithms is to remove the most probable points from the decision space, thus avoiding the need to calculate Hessians or gradients of limit state gradients. It is shown that with the proposed methods, system-level RBDO can be accomplished with computational expense equivalent to several cycles of computationally inexpensive single-loop RBDO based on second-moment methods. Examples of this new approach applied to series, parallel, and combined systems are provided.

An Extended Myard Linkage and its Derived 6R Linkage

Abstract: In this paper, a 6R linkage suitable as a building block for the construction of large deployable structures is presented. First, we report the possibility of construct an extended 5R Myard linkage by combining two complimentary Bennett linkages. Unlike the original 5R Myard linkage (also called Myard's "number 1" linkage), the angle of twists in the Bennett linkages is not necessary to be π/2. Then we show that a 6R linkage can be produced by merging two extended Myard linkages together and removing the common links. The closure equations for the 6R linkage are derived and its motion characteristics are discussed. Moreover, we demonstrate that a number of such 6R linkages can be assembled together to form a large-scale deployable structure, which opens to a flat profile.

A New Compliant Mechanical Amplifier Based on a Symmetric Five-Bar Topology

Abstract: A mechanical amplifier is an important device, which together with a piezoelectric actuator can achieve motion with high resolution and long range. In this paper, a new topology based on a symmetric five-bar structure for displacement amplification is proposed, and a compliant mechanism is implemented for the amplifier. In short, the new mechanical amplifier is called a compliant mechanical amplifier (CMA). The proposed CMA can achieve large amplification ratio and high natural frequency, as opposed to the existing CMAs, in terms of topology. Detailed analysis with finite element method has further shown that a double symmetric beam five-bar structure using corner-filleted hinges can provide good performances compared with its counterpart, which is based on four-bar topology. Finally, experiments are conducted to give some validation of the theoretical analysis.

Design and Analysis of a Hybrid Mobile Robot Mechanism With Compounded Locomotion and Manipulation Capability

Abstract: This paper presents a novel design paradigm as well as the related detailed mechanical design embodiment of a mechanically hybrid mobile robot. The robot is composed of a combination of parallel and serially connected links resulting in a hybrid mechanism that consists of a mobile robot platform for locomotion and a manipulator arm for manipulation. Unlike most other mobile robot designs that have a separate manipulator arm module attached on top of the mobile platform, this design has the ability to simultaneously and interchangeably provide locomotion and manipulation capability. This robot enhanced functionality is complemented by an interchangeable track tension and suspension mechanism that is embedded in some of the mobile robot links to form the locomotion subsystem of the robot. The mechanical design was analyzed with a virtual prototype that was developed with MSC ADAMS software. The simulation was used to study the robot's enhanced mobility characteristics through animations of different possible tasks that require various locomotion and manipulation capabilities. The design was optimized by defining suitable and optimal operating parameters including weight optimization and proper component selection. Moreover, the simulation enabled us to define motor torque requirements and maximize end-effector payload capacity for different robot configurations. Visualization of the mobile robot on different types of virtual terrains such as flat roads, obstacles, stairs, ditches, and ramps has helped in determining the mobile robot's performance, and final generation of specifications for manufacturing a full scale prototype.

Stiffness Characteristics of Carton Folds for Packaging

Abstract: Recent studies for packaging using cartons have modeled carton folds as equivalent mechanisms by considering creases as revolute joints and panels as links. This raises the interest in the study of stiffness characteristics of creases, which have a variable stiffness in contrast to a constant stiffness of a revolute joint and subsequently that of a whole carton fold. This paper investigates the stiffness characteristics of creases and reveals for the first time the folding motion and moment diagram in carton manipulation. Three characteristic stages were provided to characterize the crease stiffness, which has a variable value during carton manipulation. The paper further investigates the integrated stiffness of a combination joint and develops the integrated stiffness of a complete carton fold. The study is then extended to the integrated stiffness of a type of carton folds.