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Research Papers: Design Theory and Methodology

J. Mech. Des. 2019;141(8):081101-081101-17. doi:10.1115/1.4042614.

Design project management is witnessing an increasing need for practitioners to rely on tools that reflect the integrated nature of the social and technical characteristics of design processes, as opposed to considering the two as separate concepts. For practitioners, this integration has the potential value of predicting the future behavior of design processes by allowing them to understand what task to do next, whom to assign a task given the availability of resource, and the levels of knowledge and expertise required. In response to these challenges, this paper contributes to the development of a new process modeling method, called actor-based signposting (ABS), that looks at the early stages of the product development processes from the perspective of integrated sociotechnical systems. The objective is to support managers and decision-makers on both typical planning issues, such as scheduling and resource allocation, and less conventional issues relating to the organizational planning of a design project, such as identification of criticalities, matching required skills and expertise, and factors of influence. Ultimately, the aim is to support organizations to be more adaptive in responding to change and uncertainty. Two case studies in the automotive and aerospace industries with different properties and modeling objectives were selected to demonstrate the utility of the proposed method. Experimental analysis of these cases led to a range of insights regarding the future of modeling for academia as well as the decision-making capabilities for managers and practitioners.

Commentary by Dr. Valentin Fuster
J. Mech. Des. 2019;141(8):081102-081102-10. doi:10.1115/1.4042615.

A multitude of studies in economics, psychology, political and social sciences have demonstrated the wisdom of crowds (WoC) phenomenon, where the collective estimate of a group can be more accurate than estimates of individuals. While WoC is observable in such domains where the participating individuals have experience or familiarity with the question at hand, it remains unclear how effective WoC is for domains that traditionally require deep expertise or sophisticated computational models to estimate objective answers. This work explores how effective WoC is for engineering design problems that are esoteric in nature, that is, problems (1) whose solutions traditionally require expertise and specialized knowledge, (2) where access to experts can be costly or infeasible, and (3) in which previous WoC studies with the general population have been shown to be highly ineffective. The main hypothesis in this work is that in the absence of experts, WoC can be observed in groups that consist of practitioners who are defined to have a base familiarity with the problems in question but not necessarily domain experts. As a way to emulate commonly encountered engineering problem-solving scenarios, this work studies WoC with practitioners that form microcrowds consisting of 5–15 individuals, thereby giving rise to the term the wisdom of microcrowds (WoMC). Our studies on design evaluations show that WoMC produces results whose mean is in the 80th percentile or better across varying crowd sizes, even for problems that are highly nonintuitive in nature.

Commentary by Dr. Valentin Fuster

Research Papers: Design for Manufacture and the Life Cycle

J. Mech. Des. 2019;141(8):081701-081701-12. doi:10.1115/1.4042624.

We present a system for 3D printing large-scale objects using natural biocomposite materials, which comprises a precision extruder mounted on an industrial six-axis robot. This paper highlights work on controlling process settings to print filaments of desired dimensions while constraining the operating point to a region of maximum tensile strength and minimum shrinkage. Response surface models relating the process settings to the geometric and physical properties of extruded filaments are obtained through face-centered central composite designed experiments. Unlike traditional applications of this technique that identify a fixed operating point, the models are used to uncover dimensions of filaments obtainable within the operating boundaries of our system. Process-setting predictions are then made through multi-objective optimization of the models. An interesting outcome of this study is the ability to produce filaments of different shrinkage and tensile strength properties by solely changing process settings. As a follow-up, we identify optimal lateral overlap and interlayer spacing parameters to define toolpaths to print structures. If unoptimized, the material’s anisotropic shrinkage and nonlinear compression characteristics cause severe delamination, cross-sectional tapering, and warpage. Finally, we show the linear scalability of the shrinkage model in 3D space, which allows for suitable toolpath compensation to improve the dimensional accuracy of printed artifacts. We believe this first-ever study on the parametrization of the large-scale additive manufacture technique with biocomposites will serve as reference for future sustainable developments in manufacturing.

Commentary by Dr. Valentin Fuster

Research Papers: Design of Mechanisms and Robotic Systems

J. Mech. Des. 2019;141(8):082301-082301-10. doi:10.1115/1.4043368.

A new one-stage type cycloid drive reducer named China Bearing Reducer (CBR) is designed and its tooth contact analysis is investigated. First, the CAD model is built in SolidWorks and the structure of CBR reducer is introduced. Its advantages and disadvantages are compared with rotor vector (RV) reducer and harmonic drive reducer. Second, the mathematic model of cycloid profile and modified cycloid profile are established based on gear meshing and differential geometry, and the tooth shapes of three different modifications are compared with CBR25 reducer. Third, the conventional TCA method is described and a new TCA method by using discretized points is proposed to calculate transmission error and contact force of cycloid drive. Both the methods are used to compute the unloaded transmission error of CBR25 reducer to compare the computational efficiency. Finally, three different modified methods of tooth profile are investigated by using the new TCA method to calculate transmission error and contact force of CBR25 reducer, and the results show that the negative isometric and negative offset modified method is best for CBR25 reducer to reduce transmission error and contact force. The prototype of CBR25 reducer is manufactured and the transmission error and hysteresis curve are measured by using a testing bench. The results show that the new TCA method can be used to calculate transmission error and help better design the CBR reducer.

Commentary by Dr. Valentin Fuster
J. Mech. Des. 2019;141(8):082302-082302-13. doi:10.1115/1.4042618.

This paper presents a novel design of soft arm with triplet spiral balloons weaving and a shape memory polymer (SMP) backbone mechanism, which enables dexterous actuation and an additional variable stiffness function. The soft arm is aimed for assisting minimally invasive surgery (MIS). The triplet spiral balloons, which are actuated by pressure air, are woven helically around the SMP backbone, covered by a rubber sheath. This structure gives the soft arm a wide range of actuation, which allows it to reach the target without damaging surrounding tissues blocking its way. The SMP backbone, whose stiffness changes with the temperature, gives the arm the ability of shape holding. Temperature control of the SMP backbone is realized by the electric wire and cooling channels. A prototype is manufactured and a set of experiments is conducted with the aim of assessing the performance of variable stiffness and actuation. The effects of different loads and pressures on trajectory of the arm are evaluated together with the force-deflection curves. The prototype has also been validated with abdominal phantom, demonstrating the potential clinical value of the system.

Commentary by Dr. Valentin Fuster

Research Papers: Design of Direct Contact Systems

J. Mech. Des. 2019;141(8):083301-083301-11. doi:10.1115/1.4043367.

Gear transmissions are widely used in industrial applications and are considered to be critical components. To date, the capabilities of gear condition indicators are controversial as some condition indicators can diagnose one type of fault at the early stages, yet cannot diagnose other types of faults. This study focused on fault detection and characterization based on vibrations in a spur gear transmission. Three different common local faults were examined: tooth face fault, broken tooth, and cracks at the tooth root. The faults were thoroughly analyzed to understand the fault manifestation in the vibration signature and to find condition indicators that are robust and sensitive to the existence and severity of the fault. The analysis was based on both experimental data and simulated signals from a well-established dynamic model of the gear system. The fault detection capability of common condition indicators, as well as newly defined condition indicators, was examined and measured using statistical distances. For each fault type, the investigated condition indicators were categorized according to their discrimination power between faulted and healthy states and the ability to rank the fault severity. It was concluded that faults that affect the involute profile throughout the tooth are easily detectable. Faults such as root cracks or chipped tooth, in which mainly the tooth stiffness is affected, are much more challenging to detect. It has been shown that while using a realistic model, the capabilities of different condition indicators can be tested, and the experiments can be replaced by simulations.

Commentary by Dr. Valentin Fuster

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