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Editorial

J. Mech. Des. 2010;132(6):060201-060201-1. doi:10.1115/1.4001724.
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If there is one image that epitomizes mechanical engineering, indeed engineering itself among the non-engineers, it is the gear. I will pass up the term “gearhead” in the urban dictionary (look it up if you care) and settle just for Meriam-Webster's definition: a person who pursues mechanical or technological interests. These days, looking at the new hybrid automotive vehicle transmissions, one can only marvel at the elegance, efficiency, and reliability of this electromechanical embrace. JMD has long served as a host of the Power Transmission and Gearing (PTG) Technical Committee and has benefited from the continuing stream of high quality publications of its members. Among all Design Division technical committees, PTG has probably the best participation from practicing engineers.

Commentary by Dr. Valentin Fuster

Guest Editorial

J. Mech. Des. 2010;132(6):060301-060301-2. doi:10.1115/1.4001723.
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The Journal of Mechanical Design has long been established as one of the favorite venues for designers and researchers in gearing keen to disseminate their findings to a large international audience. Considering the various sections or research areas covered by JMD as defined in the scope of the Journal, “Power Transmission and Gearing” explicitly refers to a technological component which, beyond the words themselves, certainly illustrates the historical significance and symbolic weight of gearing and gears in Mechanical Engineering. Gear is indeed “old” since, according to etymological dictionaries, this word was already in use in the XIVth century in England after being very likely imported from Scandinavia (Old Norse). The sense at that time was that of generic equipment with no reference to power transmission between rotating parts. Its present multiplicity of meanings is indicative of widespread usage; of very solid roots in everyday life. Search engines on the Internet, for instance, produce a surprisingly varied list of results when it comes to the term “gear.” In 2009, the ASME Mechanical Engineering Magazine conducted a survey to determine the icon that was perceived as being most representative of Mechanical Engineering. Interestingly, the winner by a substantial margin was the humble gear followed by engines, robots, etc.! Gears constantly show up in newspapers, television, logos, etc., in a more or less symbolic form with, at times, no obvious link to actual gears (and rather strange tooth shapes). One obvious drawback of this long standing presence and iconic quality is a definite sense of déjà vu and the temptation to construe that, from a research perspective, gear behavior is perfectly understood and no longer worthy of research work and funding.

Topics: Gears
Commentary by Dr. Valentin Fuster

Research Papers

J. Mech. Des. 2010;132(6):061001-061001-8. doi:10.1115/1.4001529.

Rapid electrical heating cycle injection molding (ERHCM) technology is a promising green manufacturing technology for plastic parts. By using this technology, the defects that usually appear on the surface of conventionally injected parts, such as weld and flow marks, can be avoided effectively. This paper studies rapid electrical heating cycle injection molding technology and its mold structure design techniques. Temperature distribution uniformity and heating efficiency on the mold cavity surface are considered as the major influencing factors on product quality and production efficiency. A multi-objective optimization model for the heating rods layout in the mold cavity plate is formulated to optimize temperature distribution uniformity and heating efficiency with respect to the heating rods layout. An application to a liquid crystal display TV panel is implemented successfully using a genetic algorithm.

Commentary by Dr. Valentin Fuster
J. Mech. Des. 2010;132(6):061002-061002-11. doi:10.1115/1.4001532.

Design optimization problems under random uncertainties are commonly formulated with constraints in probabilistic forms. This formulation, also referred to as reliability-based design optimization (RBDO), has gained extensive attention in recent years. Most researchers assume that reliability levels are given based on past experiences or other design considerations without exploring the constrained space. Therefore, inappropriate target reliability levels might be assigned, which either result in a null probabilistic feasible space or performance underestimations. In this research, we investigate the maximal reliability within a probabilistic constrained space using modified efficient global optimization (EGO) algorithm. By constructing and improving Kriging models iteratively, EGO can obtain a global optimum of a possibly disconnected feasible space at high reliability levels. An infill sampling criterion (ISC) is proposed to enforce added samples on the constraint boundaries to improve the accuracy of probabilistic constraint evaluations via Monte Carlo simulations. This limit state ISC is combined with the existing ISC to form a heuristic approach that efficiently improves the Kriging models. For optimization problems with expensive functions and disconnected feasible space, such as the maximal reliability problems in RBDO, the efficiency of the proposed approach in finding the optimum is higher than those of existing gradient-based and direct search methods. Several examples are used to demonstrate the proposed methodology.

Commentary by Dr. Valentin Fuster
J. Mech. Des. 2010;132(6):061003-061003-11. doi:10.1115/1.4001534.

The two-phase method is a matrix-based approach for system decomposition, in which a system is represented by a rectangular matrix to capture dependency relationships of two sets of system elements. While the two-phase method has its own advantages in problem decomposition, this paper focuses on two methodical extensions to improve the method’s capability. The first extension is termed nonbinary dependency analysis, which can handle nonbinary dependency information, in addition to just binary information, of the model. This extension is based on the formal analysis of a resemblance coefficient to quantify the couplings among the model’s elements. The second extension is termed heuristic partitioning analysis, which allows the method to search for a reasonably good decomposition solution with less computing effort. This extension can be viewed as an alternative to the original partitioning approach that uses an enumerative approach to search for an optimal solution. At the end, the relief valve redesign example is applied to illustrate and justify the newly developed method components.

Commentary by Dr. Valentin Fuster
J. Mech. Des. 2010;132(6):061004-061004-11. doi:10.1115/1.4001596.

This paper presents a methodology toward designing, analyzing, and optimizing piezoelectric interdigitated microactuators using multiphysics finite element analysis. The models used in this paper were based on a circularly interdigitated design that takes advantage of primarily the d33 electromechanical piezoelectric constant coefficient. Because of the symmetric nature of the devices, a small number of 2D axisymmetric parametric models were developed to characterize the behavior of the diaphragms. The parametric models offered a large range of possible results from a very small number of models. The variations in the design parameters and their effects on deflection were captured using these models. The models also showed that several of the design parameters were naturally coupled. Discrete models were then used to capture the variations in the key design parameters during fabrication. The numerical models correlate well to the maximum deflection of the experimental devices.

Commentary by Dr. Valentin Fuster
J. Mech. Des. 2010;132(6):061005-061005-8. doi:10.1115/1.4001666.

Service robots used in human environments must be designed to avoid collisions with humans. A safe robot arm can be designed using active or passive compliance methods. A passive compliance system composed of purely mechanical elements often provides faster and more reliable responses for dynamic collision than an active one involving sensors and actuators. Because positioning accuracy and collision safety are equally important, a robot arm should have very low stiffness when subjected to a collision force that could cause human injury but should otherwise maintain very high stiffness. A novel safe joint mechanism (SJM) consisting of linear springs and a double-slider mechanism is proposed to address these requirements. The SJM has variable stiffness that can be achieved with only passive mechanical elements. Analyses and experiments on static and dynamic collisions show high stiffness against an external torque less than a predetermined threshold value and an abrupt drop in stiffness when the external torque exceeds this threshold. The SJM enables the robotic manipulator to guarantee positioning accuracy and collision safety and it is simple to install between an actuator and a robot link without a significant change in the robot’s design.

Commentary by Dr. Valentin Fuster
J. Mech. Des. 2010;132(6):061006-061006-10. doi:10.1115/1.4001530.

The honeycomb-based domain representation directly yields checkerboard and point flexure free optimal solutions to various topology design problems without requiring any supplementary suppression method. This is because the root cause behind the appearance of these pathologies, namely, the permitted single-point connectivity between contiguous subregions in rectangular-cell-based representation, is eliminated. The mesh-free material-mask overlay method further promises unadulterated “black and white” solutions in contrast to density interpolation schemes where the material is modeled between the “void” and “filled” states. Here, we propose improvements to the material-mask overlay method by judiciously increasing the number of material masks during a sequence of subsearches for the best solution. We used an alternative, mutation-based zero-order stochastic search, which, through a small population of solution vectors, can yield multiple solutions from a single search for nonconvex topology optimization formulations. Wachspress hexagonal cells are used as finite elements since they offer rich displacement interpolation functions. Singular solutions are penalized and filtered. With the improved material-mask overlay method, we showcase the synthesis using two classical small displacement problems each on optimal stiff structures and compliant mechanisms to illustrate the extraction of pathology-free, “black and white,” and multiple solutions.

Commentary by Dr. Valentin Fuster
J. Mech. Des. 2010;132(6):061007-061007-14. doi:10.1115/1.4001393.

Latches are essential machine elements utilized by all sectors (military, automotive, consumer, manufacturing, etc.) with a growing need for active capabilities such as automatic release and reset, which require actuation. Shape memory alloy (SMA) actuation is an attractive alternative technology to conventional actuation (electrical, hydraulic, etc.) because SMA, particularly in the wire form, is simple, inexpensive, lightweight, and compact. This paper introduces a fundamental latch technology, referred to as the T-latch, which is driven by an ultrafast SMA wire actuator that employs a novel spool-packaged architecture to produce the necessary rotary release motion within a compact footprint. The T-latch technology can engage passively, maintain a strong structural connection in multiple degrees of freedom with zero power consumption, actively release within a very short timeframe (<20ms, utilizing the SMA spooled actuator), and then repeat operation with automatic reset. The generic architecture of the T-latch and governing operational behavioral models discussed within this paper provide the background for synthesizing basic active latches across a broad range of applications. To illustrate the utility and general operation of the T-latch, a proof-of-concept prototype was designed, built, and experimentally characterized regarding the basic functions of engagement, retention, release, and reset for a common case study of automotive panel lockdown. Based on the successful demonstration and model validation presented in this study, the T-latch demonstrates its promise as an attractive alternative technology to conventional technologies with the potential to enable simple, low-cost, lightweight, and compact active latches across a broad range of industrial applications.

Commentary by Dr. Valentin Fuster
J. Mech. Des. 2010;132(6):061008-061008-9. doi:10.1115/1.4001601.

Shape memory alloys (SMAs) are used in many applications as actuators. The main drawbacks that limit the use of the SMAs in the field of mechanical actuation are the low mechanical bandwidth (up to a few Hertzs) and the unsatisfactory stroke (several millimeters). This paper contributes to enhancing the performances of SMA actuators by proposing a new SMA helical spring with a hollow section. The hollow spring is modeled, then it is constructed, and finally it is tested in compression to compare its performances with those of a spring with a solid cross section of equal stiffness and strength. Emptied of the inefficient material from its center, the hollow spring features a lower mass (37% less) and an extremely lower cooling time (four times less) than its solid counterpart. These results demonstrate that helical springs with a hollow construction can be successfully exploited to build SMA actuators for higher operating frequencies and improved strokes.

Topics: Springs
Commentary by Dr. Valentin Fuster

Technical Briefs

J. Mech. Des. 2010;132(6):064501-064501-6. doi:10.1115/1.4001600.

This paper presents a calculation of the general static load-carrying capacity of four-contact-point slewing bearings under axial, radial, and tilting-moment loads. This calculation is based on a generalization of Sjoväll and Rumbarger’s equations and provides an acceptance surface in the load space. This acceptance surface provides a solid basis to compute acceptance curves for the design and selection of bearings of this kind.

Commentary by Dr. Valentin Fuster
J. Mech. Des. 2010;132(6):064502-064502-7. doi:10.1115/1.4001669.

In this paper, a novel robust design approach is proposed to design the robustness of the nonlinear system under large uncontrollable variation. First, a variable sensitivity approach is proposed to formulate the nonlinear effect into the variable sensitivity matrix. Then, a variable sensitivity-based robust design is developed to minimize the variable sensitivity matrix so that the influence of the uncontrollable variation to the performance will be minimized. Since the proposed robust design considers the influence of the nonlinear term in a large design region, it can effectively improve the robustness of the nonlinear system despite large uncontrollable variation. Simulation examples have demonstrated the effectiveness of the proposed design method.

Commentary by Dr. Valentin Fuster
J. Mech. Des. 2010;132(6):064503-064503-5. doi:10.1115/1.4001595.

This paper derives formulas for evaluating the flowrate of gerotor pumps. The flowrate formulas are based on a deviation function, and the pitch and generating curves can be circular or noncircular. Two dimensionless parameters, the lobe noncircularity and the pitch noncircularity, are introduced so that gerotor performance can be analyzed systematically.

Commentary by Dr. Valentin Fuster

Design Innovation

J. Mech. Des. 2010;132(6):065001-065001-10. doi:10.1115/1.4001598.

This paper employs control techniques to analyze kinematic relationships via block diagrams for planetary gear systems. The revealed tangent-velocity equations at each contact point of the mechanical gearsets are utilized to plot the block diagrams. Then, the concepts of feedback and feedforward strategies are adopted to illustrate speed-reduction and increasing functions in kinematics with sensitivity analysis. The structural difference between unusual planetary gears and common ones is also explained based on the characteristic equation of feedback strategies for structural constraints in terms of stability conditions. A cam-controlled planetary gear is further illustrated for the constraint and kinematic analysis by using the block diagram technique and characteristic equation, and the computational simulations for the sensitivity and the motion output of this planetary gear are obtained. Through the correspondence between control and kinematics, this paper provides a guide for engineers in various fields to easily understand the function of mechanical design.

Commentary by Dr. Valentin Fuster

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