Research Papers

J. Mech. Des. 2014;136(7):071001-071001-9. doi:10.1115/1.4025021.

The scientific and industrial communities have begun investigating the possibility of making product recovery economically viable. Disassembly sequence planning may be used to make end-of-life product take-back processes more cost effective. Much of the research involving disassembly sequence planning relies on mathematical optimization models. These models often require input data that is unavailable or can only be approximated with high uncertainty. In addition, there are few mathematical models that include consideration of the potential of product damage during disassembly operations. The emergence of Immersive Computing Technologies (ICT) enables designers to evaluate products without the need for physical prototypes. Utilizing unique 3D user interfaces, designers can investigate a multitude of potential disassembly operations without resorting to disassembly of actual products. The information obtained through immersive simulation can be used to determine the optimum disassembly sequence. The aim of this work is to apply a decision analytical approach in combination with immersive computing technology to optimize the disassembly sequence while considering trade-offs between two conflicting attributes: disassembly cost and damage estimation during disassembly operations. A wooden Burr puzzle is used as an example product test case. Immersive human computer interaction is used to determine input values for key variables in the mathematical model. The results demonstrate that the use of dynamic programming algorithms coupled with virtual disassembly simulation is an effective method for evaluating multiple attributes in disassembly sequence planning. This paper presents a decision analytical approach, combined with immersive computing techniques, to optimize the disassembly sequence. Future work will concentrate on creating better methods of estimating damage in virtual disassembly environments and using the immersive technology to further explore the feasible design space.

Commentary by Dr. Valentin Fuster
J. Mech. Des. 2014;136(7):071002-071002-10. doi:10.1115/1.4025701.

This paper describes a framework for applying design for environment (DfE) within an industry setting. Our aim is to couple implicit design knowledge such as redesign/process constraints with quantitative measures of environmental performance to enable informed decision making. We do so by integrating life cycle assessment (LCA) and multicriteria decision analysis (MCDA). Specifically, the analytic hierarchy process (AHP) is used for prioritizing various levels of DfE strategies. The AHP network is formulated so as to improve the environmental performance of a product while considering business-related performance. Moreover, in a realistic industry setting, the onus of decision making often rests with a group, rather than an individual decision maker (DM). While conducting independent evaluations, experts often do not perfectly agree and no individual expert can be considered representative of the ground truth. Hence, we integrate a stochastic simulation module within the MCDA for assessing the variability in preferences among DMs. This variability in judgments is used as a metric for quantifying judgment reliability. A sensitivity analysis is also incorporated to explore the dependence of decisions on specific input preferences. Finally, the paper discusses the results of applying the proposed framework in a real-world case.

Commentary by Dr. Valentin Fuster
J. Mech. Des. 2014;136(7):071003-071003-11. doi:10.1115/1.4025960.

Prior research suggests that set-based design representations can be useful for facilitating collaboration among engineers in a design project. However, existing set-based methods are limited in terms of how the sets are constructed and in their representational capability. The focus of this article is on the problem of modeling the capabilities of a component technology in a way that can be communicated and used in support of system-level decision making. The context is the system definition phases of a systems engineering project, when engineers still are considering various technical concepts. The approach under investigation requires engineers familiar with the component- or subsystem-level technologies to generate a set-based model of their achievable technical attributes, called a technology characterization model (TCM). Systems engineers then use these models to explore system-level alternatives and choose the combination of technologies that are best suited to the design problem. Previously, this approach was shown to be theoretically sound from a decision making perspective under idealized circumstances. This article is an investigation into the practical effectiveness of different TCM representational methods under realistic conditions such as having limited data. A power plant systems engineering problem is used as an example, with TCMs generated for different technical concepts for the condenser component. Samples of valid condenser realizations are used as inputs to the TCM representation methods. Two TCM representation methods are compared based on their solution accuracy and computational effort required: a Kriging-based interpolation and a machine learning technique called support vector domain description (SVDD). The results from this example hold that the SVDD-based method provides the better combination of accuracy and efficiency.

Commentary by Dr. Valentin Fuster
J. Mech. Des. 2014;136(7):071004-071004-7. doi:10.1115/1.4025702.

Mechanical and aerospace applications often require that mechanisms deploy in a quick stable and reliable way. The objective of this study is to implement a general optimization procedure to perform a first stage conceptual design of HSD mechanisms, focusing on both kinematics and dynamics. In particular, the authors will focus on the development of design charts. In the very first part of the work, a parametric lumped-mass system will be modeled in order to reduce the number of parameters for the synthesis phase. A correlation will be established between geometry, inertia and initial position to guarantee the maximum value of acceleration during deployment of the deployable arm by means of the principle of virtual work. In the second part of this work, the influence of important factors such as friction and joint clearance on the overall dynamics of the system will be investigated. Finally, a coupled dynamic and structural analysis of the helical spring, that actuates the mechanism, will be carried out in order to achieve optimal performance. The developed charts will also take into account the space limitation requirement, that are often needed for both aerospace and mechanical applications. A final example will summarize all the points covered by this research effort. Results will be validated using the commercial software ABAQUS.

Commentary by Dr. Valentin Fuster
J. Mech. Des. 2014;136(7):071005-071005-6. doi:10.1115/1.4025295.

This paper introduces a novel methodology to embed desired reference trajectories into the modal dynamics of an underactuated system through eigenstructure assignment. A unique characteristic of the method is that it decomposes the control input into two parts: an open loop, periodic excitation signal, and a closed loop feedback signal. The periodic excitation causes the system’s natural modes to resonate in a fashion that matches the desired trajectory; modal dynamics, determined by the system’s eigenstates (eigenvectors and their corresponding eigenvalues), are shaped by tuning physical and control parameters concurrently. The method requires the solution of a dual-domain eigenstate factorization problem, in which it is necessary to compute certain unknown elements of a matrix and of its eigenvectors at the same time.

Commentary by Dr. Valentin Fuster
J. Mech. Des. 2014;136(7):071006-071006-9. doi:10.1115/1.4027284.

This paper outlines an experimentally based design method for a compatible 3-DOF shoulder exoskeleton with an adaptive center of rotation (CoR) by matching the mechanical CoR with the anatomical CoR to reduce human–machine interaction forces and improve comfort during dynamic humeral motion. The spatial–temporal description for anatomical CoR motion is obtained via a specific experimental task conducted on six healthy subjects. The task is comprised of a static section and a dynamic section, both of which are recorded with an infrared motion capture system using body-attached markers. To reduce the influence of human soft tissues, a custom-made four-marker group block was placed on the upper arm instead of using discrete markers. In the static section, the position of anatomical CoR is kept stationary and calculated using a well-known functional method. Based on the static results, the dynamic section determines the statistical relationship between the dynamic CoR position and the humeral orientation using an optimization method when subjects move their upper arm freely in the sagittal and coronal planes. Based on the resolved anatomical CoR motion, a new mechanical CoR model derived from a traditional ball-and-socket joint is applied to match the experimental results as closely as possible. In this mechanical model, the CoR motion in three-dimensional space is adjusted by translating two of the three intersecting joint axes, including the shoulder abduction/adduction and flexion/extension. A set of optimal translation parameters is obtained through proper matching criterion for the two CoRs. Based on the translation parameters, a compatible shoulder exoskeleton was manufactured and compared with a traditional shoulder exoskeleton with a fixed CoR. An experimental test was conducted to validate the CoR motion adaptation ability by measuring the human–machine interaction force during passive shoulder joint motion. The results provide a promising direction for future anthropomorphic shoulder exoskeleton design.

Commentary by Dr. Valentin Fuster
J. Mech. Des. 2014;136(7):071007-071007-9. doi:10.1115/1.4026264.

In this study, an optimization methodology is proposed to systematically define the optimal tooth modifications introduced by head-cutter geometry and machine-tool settings to minimize the influence of misalignments on the elastohydrodynamic (EHD) lubrication characteristics in face-hobbed spiral bevel gears. The goal is to simultaneously maximize the EHD load-carrying capacity of the oil film and to minimize power losses in the oil film when different misalignments are inherent in the gear pair. The proposed optimization procedure relies heavily on the EHD lubrication analysis developed in this paper. The core algorithm of the proposed nonlinear programming procedure is based on a direct search method. Effectiveness of this optimization was demonstrated on a face-hobbed spiral bevel gear example. A drastic increase in the EHD load-carrying capacity of the oil film and a reduction in the power losses in the oil film were obtained.

Commentary by Dr. Valentin Fuster
J. Mech. Des. 2014;136(7):071008-071008-10. doi:10.1115/1.4027285.

This paper presents the design, simulation, and testing of a compliant gripper that can provide a constant gripping force to handle objects of various sizes. Maintaining a proper gripping force is challenging when manipulating delicate objects with uncertain sizes and stiffnesses. To avoid damage and provide a stable grip of an object, force feedback is often required so that the gripping force can be directly or indirectly regulated. Without using additional sensors and control, the proposed gripper passively maintains a constant prespecified contact force between fingertip and object. The gripper is designed to have a constant input force generated by a constant-force mechanism (CFM). Transmitted through a statically balanced (SB) mechanism, a constant gripping force is obtained at the fingertip. After a formulation to find the optimal gripper configuration, the design is verified through comparison with simulation results. Finally, a prototype of the constant-force gripper is demonstrated. The novel gripper is expected to serve as a reliable alternative for object manipulation.

Commentary by Dr. Valentin Fuster
J. Mech. Des. 2014;136(7):071009-071009-10. doi:10.1115/1.4027161.

Surrogate models are widely used in simulation-based engineering design and optimization to save the computing cost. The choice of sampling approach has a great impact on the metamodel accuracy. This article presents a robust error-pursuing sequential sampling approach called cross-validation (CV)-Voronoi for global metamodeling. During the sampling process, CV-Voronoi uses Voronoi diagram to partition the design space into a set of Voronoi cells according to existing points. The error behavior of each cell is estimated by leave-one-out (LOO) cross-validation approach. Large prediction error indicates that the constructed metamodel in this Voronoi cell has not been fitted well and, thus, new points should be sampled in this cell. In order to rapidly improve the metamodel accuracy, the proposed approach samples a Voronoi cell with the largest error value, which is marked as a sensitive region. The sampling approach exploits locally by the identification of sensitive region and explores globally with the shift of sensitive region. Comparative results with several sequential sampling approaches have demonstrated that the proposed approach is simple, robust, and achieves the desired metamodel accuracy with fewer samples, that is needed in simulation-based engineering design problems.

Topics: Design , Errors , Simulation
Commentary by Dr. Valentin Fuster
J. Mech. Des. 2014;136(7):071010-071010-11. doi:10.1115/1.4027336.

This paper explores a two state rover concept called the Transforming Roving-Rolling Explorer (TRREx). The first state allows the rover to travel like a conventional 6-wheeled rover. The second state is a sphere to permit faster descent of steep inclines. Performance of this concept is compared to a traditional rocker-bogie (RB) architecture using hi-fidelity simulations in Webots. Results show that for missions involving very rugged terrain, or a considerable amount of downhill travel, the TRREx outperforms the rocker-bogie. Locomotion of the TRREx system using a continuous shifting of the center of mass through “actuated rolling” is also explored. A dynamics model for a cylindrical representation of the rover is simulated to identify feasible configurations capable of generating and maintaining continuous rolling motion even on sandy terrain. Results show that in sufficiently benign terrain gradual inclines can be traversed with actuated rolling. This model allows for increased exploration of the problem's design space and assists in establishing parameters for an Earth prototype.

Commentary by Dr. Valentin Fuster
J. Mech. Des. 2014;136(7):071011-071011-9. doi:10.1115/1.4026950.

An infinitely variable transmission (IVT) to provide a continuous output-to-input speed ratio from zero to a certain value is designed, and its working principle is illustrated. It is a geared IVT (GIVT), since its function to achieve the continuously varied speed ratio is implemented by gears. Crank-slider systems are used in the GIVT; the output-to-input speed ratio is changed with the crank length. Racks and pinions, whose motion is controlled by planetary gear sets, are used to change the crank length when the cranks rotate. One-way bearings are used to rectify output speeds from different crank-slider systems to obtain the output speed of the GIVT. Since the crank-slider systems can introduce variations of the instantaneous speed ratio, a pair of noncircular gears is designed to minimize the variations. A direction control system is also designed for the GIVT using planetary gear sets. Finally, a vehicle start-up simulation and a wind turbine simulation to maintain a constant generator speed are developed based on a GIVT module in the Matlab Simulink environment.

Commentary by Dr. Valentin Fuster
J. Mech. Des. 2014;136(7):071012-071012-9. doi:10.1115/1.4026825.

Bioinspired design, the practice of looking to nature to find inspiration for solutions to engineering problems, is increasingly a desired approach to design. It allows designers to tap a wealth of time-tested solutions to difficult problems in a domain less considered by designers. Only recently have researchers developed organized, systematic methods for bioinspired design. Traditionally, bioinspired design has been conducted without the benefit of any organized method. Designers relied on the informal “directed intuitive approach” of bioinspired design, which simply directs designers to consider how nature might solve a problem. This paper presents an experiment to explore the impact of the directed approach on idea generation. This experiment is foundationally important to bioinspired engineering design method research. The results of this experiment serve as a fundamental baseline and benchmark for the comparison of more systematic, and often more involved, bioinspired design methods. A group of 121 novice designers are given one of two design problems and instructed to either generate solutions using the directed approach or to generate solutions without being prompted in any additional fashion. Based on the findings presented here, the directed approach offers designers no advantage in the average number of nonredundant ideas, quality, novelty, or variety of the solutions produced. In conclusion, systematic and organized methods for bioinspired design should be sought to effectively leverage nature's design knowledge.

Commentary by Dr. Valentin Fuster

Technical Brief

J. Mech. Des. 2014;136(7):074501-074501-4. doi:10.1115/1.4027318.

Currently, there is intense competition in the industry for the development of new portable handsets. Maximizing the screen size and enhancing the performance are of utmost importance for the design of contemporary cellular phones. In particular, a sliding phone has a greater number of functions than other types of cellular phones, and the screen size of a sliding phone is relatively larger. However, because the existing spring units have limitations in terms of their mechanical performance, it is impossible for the display size to be maximized by transferring shortcut buttons, called navi-keys, which are located on the same plane of the display unit. The life cycle of a sliding phone is inversely proportional to the degree of spring deformation, which in turn depends on the sliding stroke. Therefore, a long-stroke sliding mechanism was investigated, and the manufacturing process for a novel sliding spring unit was proposed without increasing the thickness of the existing cellular phone. The possibility of performing semi-auto sliding strokes (>60 mm) was verified by flatness tests, life cycle tests, and sliding-force measurements. The performance of the designed spring unit was verified by carrying out reliability tests such as life cycle tests under the condition that the number of strokes was more than 100,000 and measurement tests to check whether the sliding force exceeded 250 gf.

Topics: Springs
Commentary by Dr. Valentin Fuster
J. Mech. Des. 2014;136(7):074502-074502-5. doi:10.1115/1.4027511.

An improved cumulative damage criterion is proposed for preloaded threaded fasteners. The proposed criterion takes into account the effect of bolt mean stress, damage history, and the loading sequence. Baseline mean stress-adjusted fatigue curves are first established for two sizes of A286 steel bolts with round socket heads. Fatigue curves are subsequently lowered due to calculable partial damage that each step of a loading spectrum. Theoretical results are experimentally validated using a three-stage loading spectrum that is applied in a low-to-high (L–H) or high-to-low (H–L) loading sequence.

Topics: Stress , Damage , Fasteners , Fatigue
Commentary by Dr. Valentin Fuster

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