bluuebunny/crossref_metadata_2025 huggingface dataset:
Period-3 Motions in a Parametrically Exited Inverted Pendulum
Authors: Luo Albert C. J. , Guo Chuan
Published: November 2020

In this paper, period-3 motions in a parametrically exited inverted pendulum are analytically investigated through a discrete implicit mapping method. The corresponding stability and bifurcation conditions of the period-3 motions are predicted through eigenvalue analysis. The symmetric and asymmetric period-3 motions are obtained on the bifurcation tree, and the period-doubling bifurcations of the asymmetric period-3 motions are observed. The saddle-node and Neimark bifurcations for symmetric period-3 motions are obtained. The saddle-bifurcations of the symmetric period-3 motions are for symmetric motion appearance (or vanishing) and onsets of asymmetric period-3 motion. Numerical simulations of the period-3 motions in the inverted pendulum are completed from analytical predictions for illustration of motion complexity and characteristics.
Sensor Based Target Tracking With Application to Autonomous Docking and Self-Reconfigurability
Authors: Sohal Shubhdildeep S. , Ben-Tzvi Pinhas
Published: November 2020

This paper presents a target detection technique, which combines a supervised learning model with sensor data to eliminate false positives for a given input image frame. Such a technique aids with selective docking procedures where multiple robots are present in the environment. Hence the sensor data provides additional information for this decision making process. Senor accuracy plays a crucial role when the motion of the robot is defined by the use of data recorded by its sensors. The uncertainties in the sensory data can cause misalignments due to poor calibration of the sensor, which can result in poor positioning of the robot relative to its target. Such misalignments can play a significant role where certain accuracy is desired. Therefore, it is necessary to minimize such misalignments to achieve certainty for the robot interaction with its target. The work proposed in this paper allows achieving such accuracy using a vision-based approach by eliminating all false occurrences leading to selective interactions with the target. The proposed methodology is validated using a self-reconfigurable mobile robot capable of hybrid Wheeled-Tracked mobility, as an application towards autonomous docking of mobile robotic modules.
A Machine Learning-Based Design Recommender System for Additive Manufacturing
Authors: Ghiasian Seyedeh Elaheh , Lewis Kemper
Published: November 2020

To appropriately leverage the benefits of Additive Manufacturing (AM), it would be advantageous if a printing could be guaranteed before allocating the necessary resources. Further, when considering AM for an inventory of existing components traditionally fabricated through traditional means, such a guarantee could result in significant technical and economic advantages. To realize such advantages, this paper presents a platform that allows for a successful and efficient transition of part-inventories to AM. This is accomplished using a novel design recommender system supported by machine learning, capable of making suggestions towards effective design modifications. This system uses an automatic AM-feasibility analysis of existing parts and a clustering of the parts based on similarities in their AM-feasibilities to develop a set of recommendations for those part clusters whose current designs are deemed as infeasible and/or inefficient for AM. The design modifications leverage a re-design algorithm to address not only problematic geometric issues but also potential infeasibilities associated with resource consumption. The utility of the presented modification algorithm is demonstrated using a number of case studies.
Criticality of Hopf Bifurcation in Precision Motion Stage With PID and Time-Delayed Feedback Controls
Authors: Gupta Sunit K. , Wang Jiamin , Barry Oumar R.
Published: November 2020

The use of precision motion stages is very popular among advanced manufacturing and machining industries. However, the performance of these motion stages is usually undermined by friction-induced vibration. In this paper, we propose the use of time-delayed feedback control to minimize the undesirable effects of friction-induced vibrations. The use of time-delayed feedback control is well established in the literature; however, the use of time-delayed feedback control in PID controlled motion-stages has not been explored yet. Here, we consider a lumped parameter model of the PID controlled precision motion stage with a linear time-delayed state feedback control. The dynamical friction in the systemis modeled using the LuGre model. Stability and nonlinear analysis of the system are carried out using analytical methods. The stability analysis reveals the existence of multiple stability lobes and codimension-2 Hopf points for a given choice of system parameters. Also, the nature of Hopf bifurcation is determined by using the method of multiple scales. We observe the existence of both subcritical and supercritical Hopf bifurcations in the system, depending on the choice of control parameters. This observation implies that the nonlinearity in the system could both be stabilizing or destabilizing in nature.
Autonomous Cricothyroid Membrane Detection Using Neural Networks for First-Aid Surgical Airway Management
Authors: Han Xiaoxue , Ren Hailin , Ben-Tzvi Pinhas
Published: November 2020

Airway management is one of the most important priorities when dealing with patients with severe injuries, but knowledge of the important anatomy and physiology is needed for providers to perform a successful surgery. This paper provides a solution for the precise cricothyroid membrane detection problem for real-time surgical airway management applications. With a commercial compact and portable cricothyrotomy kit, the proposed method will enable providers with general knowledge to perform successful first-aid airway management. In this paper, we propose a Hybrid Neural Network (HNNet), consisting of two parallel computing ensembles. The first ensemble takes as an input a low-resolution global image and outputs the Region-of-Interest (ROI) from the predefined grids. The high-resolution image is then cropped according to the ROI, and fed into the second ensemble to achieve precise keypoint detection. Global features and their spatial information from the first ensemble are also fed into the second ensemble to improve the precision. A dataset that consists of over 16,000 images from 13 subjects is built, and the location of the cricothyroid membrane in each image is precisely labeled by medical experts. The training results are presented to show both the efficiency and improved performance of our proposed method compared to existing ones.
Multiscale Off-Road Mobility Simulation With Computational Load Balancing for Lower-Scale Discrete-Element Models
Authors: Chen Guanchu , Yamashita Hiroki , Ruan Yeefeng , Jayakumar Paramsothy , Sugiyama Hiroyuki
Published: November 2020

Scalable parallel computing schemes play an important role in physics-based off-road mobility simulations due to complexities in modeling soil behavior for vehicle-terrain interaction. With the hierarchical multiscale off-road mobility simulation capability, limitations of existing computational deformable terrain models can be eliminated, including the use of phenomenological constitutive assumptions in finite element (FE) approaches as well as high computational intensity of discrete element (DE) models. However, parallel computing algorithms for multiscale simulations need to be carefully developed due to possible unbalanced computational loads occurring in lower-scale RVE simulations, which prevents desirable computational speedup. Therefore, this study aims to develop a scalable hybrid MPI-OpenMP parallel computing framework for hierarchical FE-DE multiscale off-road mobility simulations with a special focus on computational load balancing for the lower-scale DE models.
Structure Synthesis of Multi-DOF Planar Metamorphic Mechanisms With a Single Driver
Authors: Yang Qiang , Murray Andrew P. , Myszka David H. , Li Shujun
Published: November 2020

This paper approaches the type synthesis of multi-degree of freedom planar metamorphic mechanisms with a single driver in a systematic process. The process is facilitated by implementing a constraint status matrix and a equivalent resistance matrix as a method for identifying an appropriate structure of planar metamorphic mechanisms with a single driver. Multi-structures can be obtained from the same source metamorphic mechanism by designing different constraint architectures of metamorphic joints. To determine the constraint architectures of metamorphic joints and their different assembly combinations, the constraint status matrix is built based on the task-based metamorphic cyclogram of a source mechanism. According to the equivalent resistance gradient model and the constraint status matrix, an equivalent resistance matrix for the metamorphic joints is proposed. A structural synthesis matrix of the metamorphic mechanism is then obtained from the equivalent resistance matrix by deducing the constraint-form vectors of the metamorphic joints. Furthermore, an effective kinematic diagram synthesis of the source mechanism of the planar metamorphic mechanism is proposed which is based only on the 14 one or zero degree-of-freedom (DOF) linkage groups. The entire structural design method of a metamorphic mechanism is based on the structural synthesis matrix and given in steps. Finally, a proposed structural design approach is illustrated by two examples.
Semi-Supervised Deep Learning for High-Dimensional Uncertainty Quantification
Authors: Wang Zequn , Li Mingyang
Published: November 2020

Conventional uncertainty quantification methods usually lacks the capability of dealing with high-dimensional problems due to the curse of dimensionality. This paper presents a semi-supervised learning framework for dimension reduction and reliability analysis. An autoencoder is first adopted for mapping the high-dimensional space into a low-dimensional latent space, which contains a distinguishable failure surface. Then a deep feedforward neural network (DFN) is utilized to learn the mapping relationship and reconstruct the latent space, while the Gaussian process (GP) modeling technique is used to build the surrogate model of the transformed limit state function. During the training process of the DFN, the discrepancy between the actual and reconstructed latent space is minimized through semi-supervised learning for ensuring the accuracy. Both labeled and unlabeled samples are utilized for defining the loss function of the DFN. Evolutionary algorithm is adopted to train the DFN, then the Monte Carlo simulation method is used for uncertainty quantification and reliability analysis based on the proposed framework. The effectiveness is demonstrated through a mathematical example.
Linearization of Characteristic Response of a Capacitive MEMS Pressure Sensor by Patterning the Dielectric Layer
Authors: Ebrahimpour Tolouei Nadia , Shavezipur Mohammad
Published: November 2020

The present work introduces a novel design that linearizes the characteristic capacitance-pressure (C-P) response of the pressure sensor in contact mode. The design relies on patterning the insulating (dielectric) layer that separates the two electrodes of the device when the device is in contact mode. Since the capacitance is inversely proportional to the gap between the electrodes and the dielectric constant of the insulating layer is several times more than that of air (or vacuum), the contact region of the two electrodes makes more significant contribution to the overall capacitance of the system. Therefore, if the dielectric layer is properly patterned, the shape of C-P response can be controlled. In this work, we focus on linearity of the sensor response, and design and optimize dielectric pattern to achieve the highest linearity. Finite element simulations are used to demonstrate the applicability of the design concept. Different sensor designs are modeled and simulated using ANSYS® Multiphysics solver and their responses are compared to that of a conventional capacitive pressure sensor. Coefficient of linear correlation between pressure and capacitance is used as a quantitative measure for improvement of linearity. The simulation results show that the linearity of the C-P response improves from 0.930 in a 600 μm-diameter conventional design to 0.978 for a sensor with patterned dielectric layer. Moreover, a smaller sensor with 300 μm diameter display linearity of 0.999 over a 1.25 MPa – 5.0 MPa pressure range.
Dynamic Modeling and Transient Analysis of a Deployable Miura-Origami Tube
Authors: Wu Haiping , Xu Jian , Chen Lifen , Fang Hongbin
Published: November 2020

Origami provides a rich library and unique benefits for developing deployable structures. Comparing with the vast amount of progress in pattern design, static configuration analysis, and folding kinematics, research on the dynamics of origami deployable structures remains at the early stage. This paper presents our effects in developing an effective and addressable dynamic model for studying the transient dynamics of a Miura-origami tube consisting of stacked Miura-ori (SMO) cells. The Miura-ori tube, in an ideal scenario, is rigid-foldable and flat-foldable, and its folding can be described via a single-degree-of-freedom (DOF) mechanism. However, practically, these features cannot be fully satisfied in a real prototype. In this research, five assumptions are proposed for dynamic modeling purposes, which, on one hand, retain the key characteristics of folding, and on the other hand, significantly simplify the problem. With the five assumptions and based on the Lagrange Equation for the general case, the governing equation of the Miura-ori tube can be derived. Taking a six-cell Miura-ori tube under free deployment as an example, numerical analyses reveal that in addition to the decayed vibrations in the deploying direction, the tube would also exhibit significant transverse vibrations. The transient dynamics in both the deploying and the transverse directions can be quantified by the overshoot values and the settling times. Moreover, by increasing the additionally-introduced crease torsional stiffness, which is used to constrain the deviation between the folding of adjacent half SMO cells, the multiple-DOF dynamic model would degenerate into the single-DOF dynamic model. In such a scenario, only vibrations in the deploying direction are possible. The constructed model and the preliminary understanding of the transient dynamics could provide useful guidelines for designing and optimizing origami-based tubular deployable structures.
Bioinspired Origami: Case Studies Using a Keyword Search Algorithm
Authors: Morris Elissa , McAdams Daniel A.
Published: November 2020

Numerous folding patterns, structures, and behaviors exist in nature that may provide design solutions to engineering problems. While applying biological solutions to engineering design is evidently valuable, the retrieval of useful design inspiration remains a primary challenge preventing the transfer of knowledge from biology to the engineering domain. In prior research, information retrieval techniques are employed to retrieve useful biological design solutions and a text-based search algorithm is developed to return passages where folding in nature is observed. The search algorithm, called FoldSearch, integrates tailored biological keywords and filtering methods to retrieve passages from an extensive biological corpus. The objective of this paper is two-fold — 1) to demonstrate the functionality of FoldSearch, and 2) to create abstract models of the retrieved biological systems from FoldSearch which can be used for the development of novel origami crease patterns and foldable structures. In this paper, the utility of FoldSearch is demonstrated through two case studies where the retrieved biological examples undergo a design abstraction process that leads to the development of bioinspired origami crease patterns and novel foldable structures. The abstraction process is presented as a systematic design methodology for bioinspired origami for the growing research field of origami engineering.
Bio-MEMS Circular Plate Sensors Under Electrostatic Hard Excitations: Frequency Response of Superharmonic Resonance of Fourth Order
Authors: Beatriz Julio , Caruntu Dumitru I.
Published: November 2020

This paper investigates the frequency-amplitude response of electrostatically actuated Bio-MEMS clamped circular plates under superharmonic resonance of fourth order. The system consists of an elastic circular plate parallel to a ground plate. An AC voltage between the two plates will lead to vibrations of the elastic plate. Method of Multiple Scales, and Reduced Order Model with two modes of vibration are the two methods used in this work. The two methods show similar amplitude-frequency response, with an agreement in the low amplitudes. The difference between the two methods can be seen for larger amplitudes. The effects of voltage and damping on the amplitude-frequency response are reported. The steady-state amplitudes in the resonant zone increase with the increase of voltage and with the decrease of damping.
On the Dynamics of a Quadratic-Oscillator-Based, Infinite-Equilibrium System
Authors: Xing Siyuan , Luo Albert C. J. , Huang Jianzhe
Published: November 2020

In this paper, the local and global dynamics of a periodically forced, quadratic-oscillator-based, infinite-equilibrium system is discussed. The local analysis of regular equilibriums and infinite-equilibriums is completed, and the global responses of the periodically forced infinite-equilibrium system are presented through numerical simulations. Near the infinite-equilibrium surface, the periodically forced infinite-equilibrium system can be reduced to a one-dimensional system and new contraction regions can be formed. The infinite-equilibrium surface can be artificially designed to control the motions of the original quadratic nonlinear oscillator. Such a property is like a discontinuous dynamical system, which can be used for controller design in nonlinear systems.
Basic Performance of Natural Fiber Bevel Gears Made From Only Bamboo Fibers Extracted With a Machining Center
Authors: Kawabata Tetsuya , Hirogaki Toshiki , Aoyama Eiichi , Nakagawa Masao , Nobe Hiromichi
Published: November 2020

Metal gears can transmit large torque. The disadvantages associated with metal gears are the noise produced and necessity of lubricants. Plastic gears are advantageous because they are lightweight and can be used without lubricants. However, plastic gears have relatively low strengths and damaging environmental effects. We propose the development of a new type of gear that overcomes the disadvantages associated with metal and plastic gears whilst maintaining their advantages. To address environmental issues within manufacturing, it is particularly important to utilize sustainable and reproducible natural materials. Therefore, we devised a method for extracting high-quality and high-precision bamboo fibers using a machining center. Bamboo bevel gears, which are complex-shaped mechanical elements, were manufactured using the hot-pressing method. This paper outlines the performance and characteristics of the molded bamboo bevel gears. We investigated the degree of burning and strength of the bamboo fiber gears at various cutting and forming conditions. The results demonstrated that the degree of burning (black color) did not affect the gear strength, and the gear strength was at a maximum when the fiber length was 50% of the module size.
Invariant Manifolds in Human Joint Angle Analysis During Walking Gait
Authors: Bhat Sandesh G. , Sugar Thomas G. , Redkar Sangram
Published: November 2020

The complex dynamics of human gait is yet to be completely understood. Researchers have quantified stability of walking gait using Floquet multipliers as well as Lyapunov exponents. In this article, we utilize the techniques and tools from dynamical system theory and invariant manifolds to map the gait data onto a time invariant representation of a dynamical system. As an example, the complex behavior of the joint angle during walking was studied using a conformal mapping approach that transformed the time periodic system into a time invariant linear system. Time-delay embedding was used to reconstruct the dynamics of the original gait system with time series kinematic data. This minimal realization of the system was used to construct a Single Degree of Freedom (SDOF) oscillator. The time evolution of the linear oscillatory system was mapped back using the conformal mapping derived using Lyapunov-Floquet Theory. This algorithm was verified for walking gait kinematics data for two healthy human subjects. A comparison was drawn between the phase space behavior of the original time periodic system and the remapped time invariant system. The two systems showed good correlation. The algorithm resulted in a well correlated phase space representation.
Explicit Time Integration of Multibody Systems Modelled With Three Rotation Parameters
Authors: Holzinger Stefan , Gerstmayr Johannes
Published: November 2020

Rigid bodies are an essential part of multibody systems. As there are six degrees of freedom in rigid bodies, it is natural but also precarious to use three parameters for the displacement and three parameters for the rotation parameters — since there is no singularity-free description of spatial rotations based on three rotation parameters. Standard formulations based on three rotation parameters avoid singularities, e.g. by applying reparameterization strategies during the time integration of the rotational kinematic equations. Alternatively, Euler parameters are commonly used to avoid singularities. State of the art approaches use Lie group methods, specifically integrators, to model rigid body motion without the need for the above mentioned solutions. However, the methods so far have been based on additional information, e.g., the rotation matrix, which has to been computed in each step. The latter procedure is thus difficult to be implemented in existing codes that are based on three rotation parameters. In this paper, we use the rotation vector to model large rotations. Whereby Lie group integration methods are used to compute consistent updates for the rotation vector in every time step. The resulting rotation vector update is finite, while the derivative of the rotation vector in the singularity becomes unbounded. The advantages of this method are shown in an example of a gyro. Additionally, the method is applied to a multibody system and the effects of crossing singularities are presented.
Damage Identification Using Static and Dynamic Responses Based on Topology Optimization and Lasso Regularization
Authors: Sugai Ryo , Saito Akira , Saomoto Hidetaka
Published: November 2020

This paper presents a damage identification method based on topology optimization and Lasso regularization. The method uses static displacements or dynamic responses to identify damages of structures. The method has the potential to identify damages with high fidelity, in comparison with ordinary damage identification method based on optimization with parameterized geometry of the damages. However, it is difficult to precisely detect damage using topology optimization due mostly to the large number of design variables. Therefore, supposing that the damage is sufficiently small, we propose a method adding Lasso regularization to the objective functions to suppress active design variables during topology optimization process. To verify the effectiveness of the proposed method, we conducted a set of numerical experiments for static and dynamic problems. We have succeeded in suppressing active design variables and delete artificially generated damages and the location and shape of damage have been precisely identified.
Complete, Minimal and Continuous Kinematic Error Models of Perfect Multi-DOF Joints for Parallel Manipulators
Authors: Kong Lingyu , Chen Genliang , Zhang Zhuang , Xie Anhuan , Wang Hao , Zhang Dan
Published: November 2020

Kinematic error model plays an important role in improving the positioning accuracy of robot manipulators by kinematic calibration. In order to get a better calibration result, the error model should satisfy complete, minimal and continuous criteria. In order to meet the complete requirement, the multi degree-of-freedom (DOF) joints, such as universal or spherical joint in parallel robots, have to be regarded as serial chains formed by multiple independent single DOF joints, such that the manufacturing errors of these joints can be considered. However, several previous work found that these manufacturing errors for some parallel manipulators have little effect on the accuracy improvement. Besides, considering these kind of errors will cause the kinematics to be much more complicated. Therefore, under the assumptions of perfectly manufactured universal, spherical and cylinder joints, a complete, minimal and continuous (CMC) error model is presented in this paper. The identifiability of the kinematic errors of these multi-DOF joints are analytically analyzed. In order to verify the correctness and effectiveness of the proposed method, a numerical simulation of kinematic calibration is conducted on a 6-UPS parallel manipulator. The calibration result is also compared to the one derived from the error model with 138 error parameters. Since the error model and calibration methods are described uniformly, it can be applied to most parallel manipulators.
DynManto: A Matlab Toolbox for the Simulation and Analysis of Multibody Systems
Authors: Held Alexander , Moghadasi Ali , Seifried Robert
Published: November 2020

The Dynamic Modeling and Analysis Toolbox DynManto is an acedemic Matlab code which allows the modeling, simulation and sensitivity analysis of spatial multibody systems. The kinematics of rigid and flexible bodies is described by the floating frame of reference formulation and the body properties are provided by standard input data files. In this way the evaluation of the equations of motion is computationally efficient and an arbitrary parameterization of the system can be achieved. The latter is important in the automated adjoint sensitivity analysis of multibody systems, which yields gradient information for system analyses, parameter identifications or gradient-based optimizations. The capabilities of DynManto are demonstrated by the application examples of a flexible two-arm manipulator and Chebyshev’s Lambda Mechanism.
Collocated Position Control of Oscillatory System in Presence of Delay
Authors: Szaksz Bence , Stepan Gabor
Published: November 2020

The stability of the collocated position control of a mass is studied when a pendulum is attached to it. The simplest proportional-derivative (PD) controller is applied, but the relevant constant time delay is taken into account. The linearized governing equations of the system are investigated. Stability charts are constructed for different pendulum parameters. Closed form expression is derived for the critical time delay; for delay values larger than the critical one, the PD controller cannot stabilize the desired position of the mass. The frequencies of the self-excited vibrations at the stability boundaries have essential role in identifying the types of loss of stability.
Assessment of Conceptual Design Problems Comprising Design Rationale and Sketches
Authors: Khan Sumbul , Maheshwary Khushbu , Arlitt Ryan , Blessing Lucienne
Published: November 2020

Conventional forms of design assessment are time consuming for instructors. Crowdsourced assessment of students’ design concepts raises the need of efficient rubrics that facilitate novices to score similar to experts, in reduced time. We investigate rubrics in the context of conceptual design problems, that comprise open-ended questions, requiring students to express their design concepts and supporting rationale using text and sketches. We conducted exploratory post-hoc analysis on assessment data collected by instructors of a Design program at a Singaporean secondary school. Our results suggest that integrated rubrics — that consider both text and sketch component together — are better suited for the assessment of conceptual design problems, than task-specific rubrics, that consider textual and sketch components separately. Evidence from both novice assessors as well as experts suggests that the articulation of design rationale using text is crucial for the assessment of conceptual design problems as it provides assessors input into why design decisions were taken, thus aiding in the evaluation process. Our insights are relevant for developing frameworks that employ crowdsourcing for the assessment of conceptual design problems.
A Two-Stage Extension of the Generalized-α Method for Constrained Systems in Mechanics
Authors: Jay Laurent O. , Merwine Brice Ch. , Sugiyama Hiroyuki , Yamashita Hiroki
Published: November 2020

We present a new two-stage second order extension of the generalized-α method of Chung and Hulbert for systems in mechanics having nonconstant mass matrix and holonomic constraints. Both the position and velocity level constraints are preserved. The extension lends itself to efficient implementation.
Multi-Objective Optimization of the Impeller Geometry for an Automotive Torque Converter Using RBF and NSGA-II Methods
Authors: Chen Jie , Wu Guangqiang
Published: November 2020

Since impeller shape has great influence on hydraulic performance of a torque converter, a multi-objective optimization method based on non-dominated sorting genetic algorithm II (NSGA-II) has been used to redesign the impeller geometry. Radial basis function (RBF) is attempted to establish the surrogate models for performance responses in impeller design. A sophisticated automotive torque converter case is exemplified, which demonstrates that RBF provides a better surrogate accuracy and NSGA-II is more effective than the other methods studied. To verify the optimization results, the complete numerical characteristic curves of the torque converter with the optimized impeller are compared to the validated numerical characteristic curves of the initial torque converter. The numerical results show that the stall torque ratio and peak efficiency are increased by 3.18% and 1.4%, respectively. The results indicate a reasonable improvement in the optimal design of torque converter impeller and a higher performance using the NSGA-II method.
A Heterogeneous Model for Gait Analysis of the Lower-Limb and the Prosthesis Coupled System
Authors: Lv Yang , Fang Hongbin , Xu Jian , Wang Qining , Zhang Xiaoxu
Published: November 2020

By considering the coupling effect between the healthy lower-limb and the passive prosthesis, this paper builds a heterogeneous dynamic model for gait analysis, where the motions of the healthy limb and the prosthesis are driven by the central pattern generator (CPG) and the hip joint swing, respectively. The foot-ground contact is modelled as the process of unilateral force reaction rather than the constraint to get a refined representation of the gait motion. The response of the heterogeneous model, solved by numerical calculation, is then analyzed by comparison with a real gait test. Preliminary results show that the heterogeneous model not only describes the amputee’s gait well but also reveals a new gait feature of period-doubling. Parameter analysis further indicates that the period-doubling gait will return to the single-period pattern by amplifying the vertical motion of the hip joint at the amputated side. This dynamic bifurcation, which mimics the process of hip swing adaption, provides new insight into the compensatory mechanism for lamely walking.
A Topology Optimization Method for the Design of Orthotropic Plate Structures
Authors: Smith Hollis , Norato Julian
Published: November 2020

This work introduces a topology optimization method for the design of structures composed of rectangular plates each of which is made of a predetermined anisotropic material. This work builds upon the geometry projection method with two notable additions. First, a novel geometric parameterization of plates represented by offset surfaces is formulated that is simpler than the one used in previous works. Second, the formulation presented herein adds support to the geometry projection method for geometric components with general anisotropic material properties. A design-generation framework is formulated that produces optimal designs composed exclusively of rectangular plates that may be made of a predetermined, generally anisotropic material. The efficacy of the proposed method is demonstrated with a numerical example comparing optimal cantilever beam designs obtained using isotropic- and orthotropic-material plates. For this example, we maximize the stiffness of the structure for a fixed amount of material. The example reveals the importance of considering material anisotropy in the design of plate structures. Moreover, it is demonstrated that an optimally stiff design for plates made of an isotropic material can exhibit detrimental performance if the plates are naively replaced with an anisotropic material. Although the example given in this work is in the context of orthotropic plates, since the formulation presented in this work supports arbitrary anisotropic materials, it may be readily extended to support the design of each component’s material anisotropy as a part of the optimization routine.
Estimation of Reaction Time During Human Balancing on Rolling Balance Board Based on Mechanical Models
Authors: Molnar Csenge A. , Insperger Tamas
Published: November 2020

Human balancing on rolling balance board in the sagittal plane is analyzed such that the geometry of the balance board can be adjusted: the radius R of the wheels and the elevation h between the top of the wheels and the board can be changed. These two parameters have a significant influence on the stability of standing on the board as shown by preliminary experiments. The human body was modeled by a single inverted pendulum, while the balance board was considered by the geometry of the mechanical model. Based on literature, it was assumed that the central nervous system (CNS) controls by signals proportional to the angle and angular velocity of the human body and the balance board and is able to tune the feedback gains with 40% accuracy during the balancing process. To take the reaction time into consideration, operation of the CNS was modeled as a delayed proportional-derivative feedback. The critical time delay for the stabilization process is defined such that if the delay is larger than the critical one then no control gains could stabilize the system. Four balance board configurations were chosen with different wheel radius and the corresponding critical time delays were computed based on the mechanical model. Eight young healthy individuals participated in the experiments. Their task was to perform 60 s long balancing trials on each balance board. The reaction time of the participants was estimated by comparing the numerical results obtained for the critical time delay and their successful and unsuccessful balancing trials. The reaction times were found to be in the range of 0.10–0.15 s which are in good agreement with the literature.
Generative Design of Origami-Inspired Mechanisms With a Variational Level Set Approach
Authors: Ye Qian , Gu Xianfeng David , Chen Shikui
Published: November 2020

Origami has inspired the engineering design of self-assemble and re-configurable devices. Under particular crease patterns, a 2D flatten object can be transformed into a complex 3D structure. This work intends to find out a systematic solution for topology optimization of origami structures. The origami mechanism is simulated using shell models where the in-plane membrane, out of plane bending, and shear deformation can be well captured. Moreover, the pattern of the folds is represented implicitly by the boundaries of the level set function. The topology of the folds is optimized by minimizing a new multiobjective function, aiming to balance the kinematic performance with the structural stiffness as well as the geometric requirements. Besides regular straight folds, our proposed model can mimic crease patterns with curved folds. With the folding curves implicitly represented, the curvature flow are utilized to control the complexity of the generated folds. The effectiveness of the proposed method is demonstrated through the computational generation and physical validation of a thin-shell origami gripper.
Virtual Reality to Improve the User Experience of Traditional Museums
Authors: Spadoni Elena , Carulli Marina , Bordegoni Monica
Published: November 2020

Museums have been subjected to important changes in the approach they use to involve visitors. Among the other trends, storytelling and interactive exhibitions are two of the most used approaches used to make exhibitions more interesting for users. Virtual Reality and Augmented Reality methods can be effectively used in the context of a museum exhibition to support both storytelling and interaction. The primary objective of the use of these technologies is to make the visit of museums much more engaging, and suitable for different types of visitors.

Among the several museums that are moving in this direction, there is the Museo Astronomico di Brera. The museum mainly consists of a corridor, hosting instruments used by astronomers, and the Cupola Schiaparelli, which is an observatory dome.

The aim of the research presented in this paper is to develop an interactive Virtual Reality application to be used for improving the users’ experience of visits to the Museo Astronomico di Brera. Specifically, the paper presents a VR application to virtually visit the Dome. Preliminary tests have been carried out for evaluating the users’ sense of presence in the VR environment. An analysis of the collected data is presented in the paper.
On the Design of an Innovative Eight-Bar Linkage Walking Machine
Authors: Lin Bo-Hong , Chen Yu-Hsun
Published: November 2020

A walking machine is equipped with leg mechanisms so that it can move across uneven ground. In this study, feasible leg mechanisms for walking machines are generated through the Creative Mechanism Design Methodology, including the steps of existing designs analysis, generalization, specialization, and particularization. One design of a linkage mechanism with eight links and ten joints is selected at the first step. Then, according to the concepts of generalization and specialization, one of the kinematic generalized chains with the same number of links and joints is chosen, and five feasible specialized chains are generated by assigning the frame, thigh link, calf link, and the crank, sequentially. Moreover, by applying feature encoding, two of the feasible designs are obtained by removing the results that cannot fit the motion characteristics, and the corresponding mechanism sketches are presented through particularization. One of the innovation designs is selected, and the dimensional synthesis is made through the techniques in geometric constraint programming. Finally, the motion characteristics are determined to verify its feasibility through theorical determination and computer simulation. The analysis results can be used to explore kinetics and mechanism advantage.
Development of a Multi-DOF Tuned Dynamic Absorber for Reducing Hand Vibrations on an Off-Highway Vehicle
Authors: Xu Hongan , Clark David , Zeis Marlin , Hill Mike , Zambito Tony
Published: November 2020

A variety of off-highway vehicles are subject to significant steering wheel vibrations during operation. Typical examples of such machines are vibratory asphalt and soil compactors. Large compacting forces, while essential for the proper compacting operation, will inevitably cause undesired effects such as severe vibrations of steering wheels. Traditional vibration control measures are often found either impractical or less effective in reducing the level of hand vibrations which is considered an important quality and safety issue in compacter design and sales. In this paper, an advanced concept of reducing hand vibrations is presented in the context of Multi-degree-of-freedom Tuned Dynamic Absorbers (MTDA). The MTDA essentially represents an assembly of simple dynamic absorbers individually tuned to different targeted vibration modes in different degree of freedoms. While the design concept and associated parameters are numerically determined by FEA, the prototype is fine tuned to the desired vibration modes through a bench test. The effectiveness of the MTDA is experimentally verified in-situ through a sequence of tests which are carefully designed to adequately reflect its performance under field conditions.
Inverse Identification of Non-Linear ODEs for the Dynamic Control of Material Testing Systems
Authors: Lunasin Evelyn M. , Iliopoulos Athanasios P. , Michopoulos John G. , Steuben John C.
Published: November 2020

The development of advanced robotic systems for material testing by the U.S. Naval Research laboratory has expanded the set of requirements for mechatronic system control. This expansion lies beyond the limits of readily available control system capabilities because of the high control rate requirements. To establish this capability, a control mechanism based on the online identification of the ordinary differential equation governing the coupled equations of motion and deformation is proposed in the present work. The part of the proposed approach involving the inverse identification of the ODEs at hand is described in its general form first. Subsequently, the numerical verification is demonstrated via synthetic tests for a compliant actuation system with varying levels of noise injected in the system.
Excimer Laser Treatment of Nylon Fibers for Improved Adhesion to Vulcanized Natural Rubber
Authors: Sancaktar Erol , Basan Satilmis
Published: November 2020

Cords made of steel, nylon or polyester are important reinforcement components used in tire industry. The bond strength between the cords and the rubber matrix is closely related to the surface properties of the cord fibers. Previous research revealed Ultraviolet (UV) laser-induced characteristic topography on synthetic fibers after irradiation, which is considered by us as an advantageous factor in developing bonding strength between fiber-rubber composites. We applied various UV laser treatments on the surfaces of nylon fibers in order to obtain similar topographic features. Adhesion is affected by the valleys and peaks that form on the surface of the fibers by laser radiation. In this study, nylon cords were irradiated with different number of UV pulses using an excimer laser to understand the effect of the laser beam on nylon fiber-rubber adhesion. A fiber pull-out test method developed by our research group for bonding strength of nylon cord fibers to carbon black filled and vulcanized natural rubber was utilized in pull-out configuration. The results showed that the maximum pull-out load was reached at 300 laser pulses and then decreased.
Favoring Complexity: A Mixed Methods Exploration of Factors That Influence Concept Selection in Design for Additive Manufacturing
Authors: Prabhu Rohan , Leguarda Rainmar L. , Miller Scarlett R. , Simpson Timothy W. , Meisel Nicholas A.
Published: November 2020

The capabilities of additive manufacturing (AM) open up designers’ solution space and enable them to build designs previously impossible through traditional manufacturing. To leverage AM, designers must not only generate creative ideas, but also propagate these ideas without discarding them in the early design stages. This emphasis on selecting creative ideas is particularly important in design for AM (DfAM), as ideas perceived as infeasible through the traditional design for manufacturing lens could now be feasible with AM. Several studies have discussed the role of DfAM in encouraging creative idea generation; however, there is a need to understand concept selection in DfAM. In this paper, we investigated the effect of two variations in DfAM education: 1) restrictive DfAM and 2) dual DfAM (opportunistic and restrictive) on students’ concept selection process. Specifically, we compared the creativity of the concepts generated by the students to the creativity of the concepts selected by them. Further, we performed qualitative analyses to explore the rationale provided by the students in making these design decisions. From the results, we see that teams from both educational groups select ideas of greater usefulness; however, only teams from the restrictive DfAM group select ideas of higher uniqueness and overall creativity. Further, we see that introducing students to opportunistic DfAM increases their emphasis on the complexity of designs when evaluating and selecting them. These results highlight the need for DfAM education to encourage AM designers to not just generate but also select creative ideas.
Morphological Analysis of 316L Laser Powder Bed Fusion Melt-Pool via the Enriched Analytical Solution Method
Authors: Michopoulos J. G. , Steuben J. C. , Birnbaum A. J. , Iliopoulos A. P. , Aroh J. , Rollett A. D. , Gould B.
Published: November 2020

The recent development of the Enriched Analytical Solution Method (EASM) for evaluating the spatio-temporal distribution of the temperature fields generated during the Laser Powder Bed Fusion (LPBF) Additive Manufacturing (AM) processes is provides an opportunity to study the sensitivity of the morphological parameters characterizing the associated melt-pools as a function of process parameters. The present work exercises the EASM for the case of a single-path trace over a 316L base plate under LPBF heat deposition conditions. To assist in the evaluation of solidification parameters, the spatial derivatives of the EASM are also derived. A process parameter subspace spanned by the scan velocity and the laser power is considered and the EASM is utilized for deriving a number of geometrical morphological characteristics of the melt pool as well as the quantities controlling the evolution of the solidification front. Finally, comparisons with initial experimental results obtained by in-situ high speed synchrotron X-ray imaging, capturing the spatio-temporal evolution of the melt pool profile are also presented.
Theoretical Framework for Design for Dynamic User Preferences
Authors: Arezoomand Mojtaba , Rouse Elliott , Austin-Breneman Jesse
Published: November 2020

A key assumption of new product development is that user requirements and related preferences do not vary on time scales of the process length. However, prior work has identified cases in which user preferences for product attributes can vary with time. This study proposes a method, Design for Dynamic User Preferences, which adapts reinforcement learning (RL) algorithms for designing physical systems whose functionality changes with user feedback. An illustrative case comprised of the design of a variable stiffness prosthetic ankle is presented to evaluate the potential usefulness of the framework. Lifetime user satisfaction for static and dynamic design strategies are compared over simulated user preferences under a number of conditions. Results suggest RL-based strategies outperform static strategies for cases with dynamic user preferences despite significantly less initial information. Within RL methods, upper-confidence bound policies led to higher user satisfaction on average. This study suggests that further investigation into RL-based design strategies is warranted for situations with possibly dynamic preferences.