Research Papers: Design Theory and Methodology

J. Mech. Des. 2018;140(8):081101-081101-13. doi:10.1115/1.4040163.

Modeling and simulation for additive manufacturing (AM) is commonly used in industry. Nevertheless, a central issue remaining is the integration of different models focusing on different objectives and targeting different levels of details. The objective of this work is to increase the prediction capability of characteristics and performances of additively manufactured parts and to co-design parts and processes. The paper contributes to this field of research by integrating part's performance model and additive technology process model into a single early integrated model. The paper uses the dimensional analysis conceptual modeling (DACM) framework in an AM perspective to generate causal graphs integrating the AM equipment and the part to be printed. DACM offers the possibility of integrating existing knowledge in the model. The framework supported by a computer tool produces a set of governing equations representing the relationships among the influencing variables of the integrated model. The systematic identification of the weaknesses and contradictions in the system and qualitative simulation of the system are some of the potential uses of the model. Ultimately, it is a way to create better designs of machines and parts, to control and qualify the manufacturing process, and to control three-dimensional (3D) printing processes. The DACM framework is tested on two cases of a 3D printer using the fused filament fabrication (FFF) powder bed fusion. The analysis, applied to the global system formed of the 3D printer and the part, illustrates the existence of contradictions. The analysis supports the early redesign of both parts and AM process (equipment) and later optimization of the control parameters.

Commentary by Dr. Valentin Fuster

Research Papers: Design Automation

J. Mech. Des. 2018;140(8):081401-081401-12. doi:10.1115/1.4040176.

Understanding how humans decompose design problems will yield insights that can be applied to develop better support for human designers. However, there are few established methods for identifying the decompositions that human designers use. This paper discusses a method for identifying subproblems by analyzing when design variables were discussed concurrently by human designers. Four clustering techniques for grouping design variables were tested on a range of synthetic datasets designed to resemble data collected from design teams, and the accuracy of the clusters created by each algorithm was evaluated. A spectral clustering method was accurate for most problems and generally performed better than hierarchical (with Euclidean distance metric), Markov, or association rule clustering methods. The method's success should enable researchers to gain new insights into how human designers decompose complex design problems.

Commentary by Dr. Valentin Fuster
J. Mech. Des. 2018;140(8):081402-081402-12. doi:10.1115/1.4040170.

Reliability assessment is an important procedure in engineering design in which the probability of failure or equivalently the probability of survival is computed based on appropriate design criteria and model behavior. In this paper, a new approximate and efficient reliability assessment method is proposed: the conditional probability method (CPM). Focus is set on computational efficiency and the proposed method is applied to classical load-strength structural reliability problems. The core of the approach is in the computation of the probability of failure starting from the conditional probability of failure given the load. The number of function evaluations to compute the probability of failure is a priori known to be 3n + 2 in CPM, where n is the number of stochastic design variables excluding the strength. The necessary number of function evaluations for the reliability assessment, which may correspond to expensive computations, is therefore substantially lower in CPM than in the existing structural reliability methods such as the widely used first-order reliability method (FORM).

Commentary by Dr. Valentin Fuster
J. Mech. Des. 2018;140(8):081403-081403-10. doi:10.1115/1.4040547.

The moving morphable component (MMC)-based method is a newly developed approach for topology optimization. In the MMC-based method, the design problem is formulated using a set of morphable components, and the optimized structural topologies are obtained by optimizing shapes, sizes, and locations of these components. However, the optimization process often tends to break the connection between the load area and the supported boundary. This disconnection has a strong influence on the convergence, especially when the large deformation effects are considered. In this paper, a method is developed for topology optimization of geometrically nonlinear structures by using the MMC-based method. A scheme is developed to address the disconnection issue in the optimization process. Several numerical examples are used to demonstrate the validity of the proposed method.

Commentary by Dr. Valentin Fuster

Research Papers: Design of Mechanisms and Robotic Systems

J. Mech. Des. 2018;140(8):082301-082301-11. doi:10.1115/1.4040178.

Flasher, which has been used in space engineering, is a class of origami patterns. After modifying and introducing cuts for the flasher pattern, we add nonzero thickness to the flasher and taper its panels. We find that, if appropriately driven, the modified flasher can be used as the deployable mechanism, and even envelop the curved surface in its unfolded configuration. We establish a geometric model and a kinematic model for the mechanism. Then we propose a designing approach including folding design and driving method. The folding design, which ensures that the mechanism can be folded in the folded configuration, is based on geometric constraints. The driving method, which enables the multi-degree-of-freedom (DOF) mechanism to deploy in sequence with only one actuator, is based on underactuation. A prototype is built to validate this approach.

Commentary by Dr. Valentin Fuster
J. Mech. Des. 2018;140(8):082302-082302-14. doi:10.1115/1.4040174.

Constant-force mechanisms are designed to keep a constant or nearly constant input force along a prescribed stroke of the mechanism. The implementation of this kind of mechanisms has been approached in literature using compliant mechanisms or through a certain combination of springs and nonlinear transmissions. In this work, three new constant-force mechanisms based on the use of springs, rollers, and cams are presented and analyzed. The rolling friction forces between the rollers and the cam are included in the force equilibrium equations and considered in the integration of the cam profile. The influence of the friction force on the input force as well as the design parameters involved is studied based on numerical techniques and simulations. In fact, the results evidence that to obtain a precise constant-force mechanism, rolling friction forces must be considered in the cam profile definition. The main design guidelines for the three constant-force mechanisms proposed are described.

Commentary by Dr. Valentin Fuster
J. Mech. Des. 2018;140(8):082303-082303-11. doi:10.1115/1.4040171.

This paper presents a geometric method as a unified synthesis process of function generation for spatial linkages. The synthesis method utilizes the mapping relationship between spatial kinematic geometric model and two-plane projection system to transform the problem from spatial geometry to plane geometry. In this way, the synthesis process of mechanisms can be simplified through the corresponding transformation. Afterward, the line-guidance model is built up. Combining the kinematic inversion in two-plane projection system, this model can be used to realize the spatial linkages synthesis for function generation with three finite positions. Finally, revolute–sphere–sphere–revolute (RSSR) and revolute–sphere–sphere–prism (RSSP) mechanisms are offered to illustrate the application of this method.

Commentary by Dr. Valentin Fuster
J. Mech. Des. 2018;140(8):082304-082304-15. doi:10.1115/1.4040269.

In our previous work, we designed a three-degrees-of-freedom (3DOF) translational parallel mechanism based on a proposed design strategy. In this paper, the design strategy is further improved, and a novel spatial translation mechanism (STM) is found. The novel STM consists of a platform, a base, and six modules between the platform and the base. Each module is a passive planar 6R single-loop closed chain, and it is connected with two other modules. Meanwhile, three modules are connected to the base, and the other three modules are connected to the platform. All the connections among the modules, platform, and base are realized by revolute joints. There are no obvious limbs in the mechanism due to the complex connections. The mobility of the STM is analyzed, and the forward kinematics is investigated. To validate the effectiveness and feasibility of the design, one prototype is fabricated. At the end of the paper, we draw some conclusions and discuss the future works.

Commentary by Dr. Valentin Fuster

Technical Brief

J. Mech. Des. 2018;140(8):084501-084501-8. doi:10.1115/1.4039851.

Ten years prior to this paper, innovative mechanical products were analyzed and found to embody multiple innovation characteristics—an average of two more than competing products in the marketplace. At the time, it was not known whether these products would be successful over time and whether the number or type of innovation characteristics would be related with success. In this work, products from the previous study were categorized into well- and under-adopted products. Also, each product was categorized according to the type of firm that launched it: a new venture or an established firm. The innovative products enjoyed a success rate of 77% on average. The success was not dependent on the number or type of innovation characteristics embodied by the product. However, products developed in new ventures embody, on average, one more innovation characteristic and enjoy a slightly higher success rate than those launched by established firms.

Commentary by Dr. Valentin Fuster
J. Mech. Des. 2018;140(8):084502-084502-9. doi:10.1115/1.4040268.

As a prospective machining method for cylindrical gear, gear skiving has been promoted by many commercial companies, such as Gleason, Mitsubishi, and Prawema recently. Although the principle and mathematical model for gear skiving has been discussed by many works, the tooth modification was left behind in the literature. In fact, machine kinematics correction and tooth contact analysis (TCA) are widely used for tooth modification in gear processing, such as hobbing, grinding, and milling. Focusing on this, the paper generalizes machine kinematics correction and TCA to gear skiving. The influence of the modification parameters on tooth deviation, contact path, and transmission error are all investigated, showing that localized contact pattern and polynomial transmission error can be realized through cutter offset correction for one gear and cutter tilted (or crossed angle) correction for the other gear.

Topics: Gears , Errors
Commentary by Dr. Valentin Fuster

Design Innovation Paper: Design Innovation Papers

J. Mech. Des. 2018;140(8):085001-085001-8. doi:10.1115/1.4040172.

The energy harvesting backpack that converts the kinetic energy produced by the vertical oscillatory motion of suspended loads to electricity during normal walking is a promising solution to fulfill the ever-rising need of electrical power for the use of electronic devices in civilians and military. An energy harvesting backpack that is based on mechanical motion rectification (MMR) is developed in this paper. Unlike the conventional rack-pinion mechanism used in the conventional energy harvesting backpacks, the rack-pinion mechanism used in the MMR backpack has two pinions that are mounted on a generator shaft via two one-way bearings in a way that the bidirectional oscillatory motion of the suspended load is converted into unidirectional rotation of the generator. Due to engagement and disengagement between the pinions and the generator shaft, the MMR backpack has broader bandwidths than the conventional energy harvesting backpacks; thus, the electrical power generated is less sensitive to change in walking speed. Two male subjects were recruited to test the MMR backpack and its non-MMR counterpart at three different walking speeds. For both subjects, the MMR backpack for most of the time generated more power than the non-MMR counterpart. When compared with literature, the MMR backpack had nearly sixfold improvement in bandwidth. Finally, the MMR backpack generated nearly 3.3 W of electrical power with a 13.6 kg load and showed nearly two- to tenfold increases in specific power when compared with a conventional energy harvesting backpack.

Commentary by Dr. Valentin Fuster

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