bluuebunny/crossref_metadata_2025 huggingface dataset:
3D Spatial Layouts Using A-Teams
Authors: Sachdev Sanjay , Paredis Christiaan J. J. , Gupta Satyandra K. , Talukdar Sarosh N.
Published: February 2021

Spatial layout is the problem of arranging a set of components in an enclosure such that a set of objectives and constraints is satisfied. The constraints may include non-interference of objects, accessibility requirements and connection cost limits. Spatial layout problems are found primarily in the domains of electrical engineering and mechanical engineering in the design of integrated circuits and mechanical or electromechanical artifacts. Traditional approaches include ad-hoc (or specialized) heuristics, Genetic Algorithms and Simulated Annealing. The A-Teams approach provides a way of synergistically combining these approaches in a modular agent based fashion. A-Teams are also open to the addition of new agents. Modifications in the task requirements translate to modifications in the agent mix. In this paper we describe how modular A-Team based optimization can be used to solve 3 dimensional spatial layout problems.
Modelling and Simulation of a Multiloop Flexible High-Speed Mechanism Bending Out of the Plane of Motion
Authors: Fanghella Pietro , Galletti Carlo , Fiorini Valerio
Published: February 2021

A case study of dynamic simulation of a high-speed mechanism driven by three cams is presented. Starting from a planar inverse dynamic model, the following types of 3-D elastic and non-linear effects are taken into account to obtain an accurate model: a) deformations of the revolutes connecting the bodies; b) deformations and clearances in the couplings between cams and rollers; c) deformations of the bodies. Various types of models with up to six simultaneous flexible bodies have been developed by using a commercial multibody code (DADS) and the corresponding results are reported. The choice of the modal forms of the flexible bodies is discussed and the contributions of various effects to the dynamic behaviour of the system are analyzed. The paper shows that classical design techniques based on planar modelling yield unacceptable performances of the actual system.
Optimal Layout and Sizing of Ejector Pins for Injection Mold Design
Authors: Kwak Seongjoon , Lee Kunwoo
Published: February 2021

Injection molding is the most prevalent technology used for processing thermoplastic polymers. At the end of the injection molding cycle, the plastic molded part should be ejected when the injection mold opens. Complex moldings with bosses, ribs, or other features are generally ejected by ejector pins because they are economical and easy to be installed. However, the ejector pins can cause high local stresses and strains in the molding at the stage of ejection leading to the part deformation and damage. This paper proposes a method to determine the layout and size of the ejector pins required to eject thermoplastic moldings with minimizing the part deformation and damage. The proposed method calculates the distribution of the necessary ejecting forces to overcome the friction between the part and its mold. Then, it transforms the ejecting forces into a certain number of representative forces by the wavelet transform. Finally, we can get the location and size of the ejector pins corresponding to the discrete ejecting forces with the help of a rule-based system. The proposed method helps an injection mold designer to systematically obtain an optimum ejector design.
Optimization of Functional Distribution of Materials to Minimize Weight and Cost of Machine Elements Using Genetic Algorithm
Authors: Ohtani Yukio , Shoji Tetsuo
Published: February 2021

This paper proposes an optimizing design method which uses Genetic Algorithm (GA) to reduce both weight and cost of machine elements based on a methodology to optimize “functional distribution of materials”. According to this methodology, machine elements are fabricated of combined plural common materials, and selection and distribution of each material are optimized to satisfy the function to a minimum degree required for each part of the given machine element.

A piston pin for an air compressor and a spur gear for an industrial robot were chosen as examples of this study. Optimal structures of both elements were the multi-layered ones composed of two kinds of materials. The elements fabricated by the proposed optimization procedure showed remarkable reduction both in weight and cost as well as sufficient operational performance.
Effective Octree Generation of Parts for Virtual Prototyping
Authors: Chou T. C. , Liou F. W. , Reeves L. , McMillin B. , Suess Patricia
Published: February 2021

Virtual environment has become a future trend in design and development of new products, due to the current advances in simulation, computer graphics, robotics, and other related technologies. In order for the simulation engine to be efficient in performing tasks such as collision detection, the representation of the parts and components is very important. This paper presents an efficient algorithm to convert boundary representation (B-rep) to octree representation for efficient collision and interference detection. Traditionally, octree generation can be achieved through its original definition: build from the top level. This paper presents an innovative approach to build octree from the bottom level. This algorithm first transforms the boundary representation model into a triangle facet model and then a ray tracing technique is applied to scan all facets to create and record octants to a bit representation at the bottom level resolution. To save memory space, only the octants on the surface level are stored as black (solid) nodes. Finally a pointer representation of octree is built via the bit representation. The generation of a nine-level octree takes less then 60 seconds on a SunSparc 10. With this process, an octree can be quickly built for applications of collision and interference detection, such as robotic path planning, assembly planning, flight simulation, etc.
Building Block Design for Layered Shape Manufacturing
Authors: Binnard Mike , Cutkosky Mark R.
Published: February 2021

We are interested in designing complex mechatronic systems which closely integrate electronics, actuators, and sensors with mechanical structures. Rapid prototyping techniques open new design possibilities for these systems, such as the ability to fabricate pre-assembled mechanisms. This paper presents a design approach that should encourage exploration of these new possibilities and thereby facilitate robot design.

In the described approach, engineers build designs using a library of three dimensional primitives and aggregations of primitives. Associated with each primitive is enough manufacturing process information to enable immediate manufacturability analysis. An algorithm is presented which automatically combines the process information from multiple primitives. A prototype system using this algorithm has been implemented with AutoCAD and the ObjectARX programming interface.
An Incremental Part Manufacturing Cost Estimation Algorithm Using Petri Nets
Authors: Kiritsis Dimitris , Xirouchakis Paul
Published: February 2021

The problem under consideration is the cost estimation of part manufacturing while taking into account processing alternatives. In order to determine overall costs for feasible process plans we take into account, in our Petri net model, costs caused by machine, setup and tool changing in addition to the single operation cost. We introduce a new Petri net model that allows the application of incremental cost analysis algorithms. This is a CPP-net (Compact Process Planning net) which represents manufacturing knowledge in the form of precedence constraints and incorporates machining cost, machine, setup and tool information in each transition. We show that the CPP-net allows the calculation of the optimum process plan without the need to first develop all possible solutions. We apply the developed methods and calculate the optimum process plan to an industrial case study of a mechanical workpiece of moderate complexity.
Multi-Axis Roughing and Finishing of Ruled Surface Pockets for CAD/CAM Systems
Authors: Koc Bahattin , Lee Yuan-Shin
Published: February 2021

This paper presents a new methodology for 5-axis rough cutting of free-form ruled surface pockets. An Inclined Zig-zag method is proposed to rough cut the core region and an Ellipse-offset method is developed for semi-roughing and finishing the ruled surface pockets. The Ellipse-offset method is developed to calculate the non-constant offset curves for 5-axis tool path planning of rough cutting. Different from the traditional 2 1/2D machining method, the developed Ellipse-offset method allows the cutter to change its tool orientation and to get as close to the part surface as possible in roughing. The proposed method allows the manufacturing engineers to use 5-axis machining to rough cut the parts to near-finish shape for finishing. Computer implementation and illustrative examples are also presented in this paper.
A Geometric Theory for Formulation of Form, Profile and Orientation Tolerances: Problem Formulation
Authors: Gou J. B. , Chu Y. X. , Wu H. , Li Z. X.
Published: February 2021

This paper develops a geometric theory which unifies the formulation and evaluation of form (straightness, flatness, cylindricity and circularity), profile and orientation tolerances stipulated in ANSI Y14.5M standard. In the paper, based on an an important observation that a toleranced feature exhibits a symmetry subgroup G0 under the action of the Euclidean group, SE(3), we identify the configuration space of a toleranced (or a symmetric) feature with the homogeneous space SE(3)/G0 of the Euclidean group. Geometric properties of SE(3)/G0, especially its exponential coordinates carried over from that of SE(3), are analyzed. We show that all cases of form, profile and orientation tolerances can be formulated as a minimization or constrained minimization problem on the space SE(3)/G0, with G0 being the symmetry subgroup of the underlying feature. We transform the non-differentiable minimization problem into a differentiable minimization problem over an extended configuration space. Using geometric properties of SE(3)/G0, we derive a sequence of linear programming problems whose solutions can be used to approximate the minimum zone solutions.
A Single Function Agent Framework for Task Decomposition and Conflict Negotiation
Authors: Sreeram R. T. , Chawdhry P. K.
Published: February 2021

Researchers in agent-based concurrent engineering have identified a variety of techniques for product development with the use of multi-agents. Significant but less common are the techniques based on more task-specific single function agents. This paper proposes a single function agent framework for task-solving in a product development environment. This framework is based on Habermas’s theory of communicative action which is particularly suited for collaborative work. The inter-agent communication is based on Knowledge Query Manipulation Language (KQML). The task decomposition of the design process is based on the cluster identification algorithm. The conflicts which arise during the design process are resolved by using very specialized single function agents that detect conflicts based on violation of the design constraints. The case study on the design of a mechanical shaft demonstrates the appropriateness of the proposed framework.
Developing ‘Text Learning Capture’ to Examine How Students Learn From Texts and How Texts Learn From Students
Authors: Sheppard Sheri , Jones Kim , Jeremijenko Natalie
Published: February 2021

This paper describes an innovative assessment method that provides formative feedback on the effectiveness of an engineering textbook. We describe the development of the Text Learning Capture Method and the prior art that it is drawn from. We then go on to interpret and analyze the protocols captured with the method and describe the preliminary results generated with its application. Concrete examples of how the feedback enables us to identify the text’s readability, comprehensibility, and usability are given. From the analysis a list of questions was generated about how students learn from engineering textbooks.

The textbook assessment work presented here was motivated by a desire on the part of the author of the textbook (hereafter the text-author in contrast to the authors of this paper) to understand more fully the role of this textbook in supporting student learning. We began with questions such as: “Do students relate to the real-world examples given?”; “How do students work through the equations?”; “How are figures utilized?”; “Are students excited by a textbook that uses a familiar multi-faceted artifact to demonstrate engineering principles?”. In our attempts to carefully answer these questions we generated questions such as: “Can learning from a text book be thought of as passive?”; “What constitutes effective learning from texts?”; “What are best reading practices?”; and “How much control does an author have over this?”.
Identification of Limiting Factors for Improving Design Modularity
Authors: Coulter Stewart L. , McIntosh Mark W. , Bras Bert , Rosen David W.
Published: February 2021

In previous work, the idea of designing for the life cycle (DFLC) was investigated through the improvement of product architectures with an emphasis on increasing modularity. In this paper, that work is extended by developing a method for suggesting changes to the product to improve the correspondence between modules from different life-cycle viewpoints. Based on an analogy to the determination of critical paths in network analysis, the identification of limiting factors in a candidate design is intended to assist the designer in recognizing design changes that have the greatest impact on improving recyclability. The purpose of this paper is to illustrate how the identification of limiting factors can be used to improve product recyclability during configuration design. A general method for identifying and prioritizing the limiting factors is presented and applied in the context of improving recyclability. This method is shown to be capable of efficiently determining effective design changes to improve product modularity and recyclability. It is argued that the concept of limiting factors and the developed method are applicable to many different configuration design issues and not limited to recycling or even other DFLC issues. A validation of the limiting factor identification method is presented using a Genetic Algorithm and an exhaustive search.
A Design Process Modeling Approach Incorporating Nonlinear Elements
Authors: Andersson Johan , Pohl Jochen , Eppinger Steven D.
Published: February 2021

This paper extends the literature of engineering design process modeling. We focus on the modeling of design iterations using a task-based description of a development project. We present a method to compute process performance and to relate this outcome to critical activities within the process.

Design tasks are modeled as discrete-event activities with design information flowing between them. With every design task, we associate process characteristics such as the completion time and cost per time unit for the task. These characteristics can change with the advance of the design process. The method is especially suited for comparison of different design processes on the basis of overall process costs and lead time.

In order to illustrate the method a simple design process was modeled as an example. Based on this model the process lead time distribution and the process costs were simulated.
Design Information Retrieval: Improving Access to the Informal Side of Design
Authors: Wood William H. , Yang Maria C. , Cutkosky Mark R. , Agogino Alice M.
Published: February 2021

Capturing and reusing design experience holds great potential for improving designer effectiveness The first step toward leveraging lessons from the past for design decision making is gaining access to them Because decisions early in the design process largely determine its ultimate success, it is important to embrace the informal, unstructured information that is prevalent during conceptual design Information retrieval is proposed as the basis for access to this informal design information By creating hierarchical thesauri of life cycle design issues, design process terms, and component and system functional decompositions, we hope to establish an intermediate language in which design context can be captured Experiments in design information retrieval exploiting design context for determining document similarity within design case studies and design notebooks demonstrate the value of this approach.
A Workcell Based Robot Design Program
Authors: Derby Stephen
Published: February 2021

This paper discusses a computer graphics program that helps to design a robot based on an existing workcell that would be difficult or costly to modify. Standard robot bases, as well as tracked robots, are located to minimize the error of the desired taught robot gripper positions. Error levels are established based on the angle of the misalignment and the length of the required loading or unloading motion. Program implementation is detailed.
Incorporation of Vibration Control in Determination of Structural Parameters of Gear Systems
Authors: Wang Y. , Zhang W. J. , Kalker-Kalkman C. M. , Li Q.
Published: February 2021

A new design strategy of gear system is proposed in this paper. Traditionally, development of gear systems undergoes as such. First gear structural parameters are determined. Then control of dynamic behaviours such as control of vibration is dealt with, where gear structural parameters cannot be changed any more. The new strategy suggests that during the design process of determining gear structure parameters, vibration control is taken into account. In order to see the effects of such a design strategy, an optimal design model is developed which contains two conflicting objectives, system vibration and system volume. The design variables include both discrete ones and continuous ones. Genetic algorithm, together with Pareto sets, is employed to solve this complex optimal problem. Through the simulation studies on selected cases, improvement on the system vibration control is shown with this new design strategy.
Automated Motion Program Formulation for Cam Mechanism Design
Authors: Shooter Steven B.
Published: February 2021

The required motion for a cam mechanism is often an under-defined problem. Usually only part of the motion cycle is specified, giving the designer freedom to generate the remaining motion to best suit the dynamic constraints. Often, it is the motion program that has the greatest effect on the dynamic performance of the cam mechanism. Formulating the motion program often involves iteratively specifying motion types, selecting follower types and selecting cam characteristics. Many software programs have been developed to synthesize the cam profile when the desired motion program and the cam mechanism characteristics have been supplied, and the cam profile synthesis techniques have been well established. However, such programs do not assist the designer in formulating the motion program. This paper presents a software system which assists the designer through the process of formulating the motion program. The program provides information to aid decision making in this under-defined problem. It also includes an analytical technique for automating the curve-matching required to formulate the motion program. The automation of these procedures allows the designer to readily explore alternatives and produce a superior design.
Computation of Pressure Loads in the Three-Lobe Supercharger
Authors: Mimmi Giovanni C. , Pennacchi Paolo E.
Published: February 2021

The compression mechanism in this type of blower is produced by the action of two three-lobe rotors. In this paper the functioning of this kind of blower is analyzed in detail for both the helical and spur rotor types. The analysis allows us to point out specific problems regarding trapped volumes and to design special devices to avoid these problems.

The complete dynamics of the loads is determined on this basis, and the performances achieved by helical and spur rotors are compared.
The Torque Responses in Spur Gearing
Authors: Lin Ah-Der , Kuang Jao-Hwa
Published: February 2021

In this study, the frequency spectra of a meshing spur gear pair are derived. A two-step mesh stiffness model is assumed to account for the time varying stiffness during the teeth engagement. The analytic load of this simplified gear pair system is used to derive the corresponding Fourier expansion series of the transmitted torque in close form solutions. Numerical results have shown that the frequency spectra of the transmitted torque are dominated by the mesh stiffness alternation and the contact ratio of a gear pair. Furthermore, the amplitude modulation introduced by a harmonic input torque has also been investigated.
A New Inertia-Based Linear Stepper Motor for Micro-Surgical Procedures
Authors: Rizq Raed N. , Peichel David J. , Wulfman David R. , Erdman Arthur G. , Polla Dennis L.
Published: February 2021

A new hand held surgical device intended to aid physicians in microsurgery is reported. This device provides a means for delivering small implants through the use of a precision motion linear stepper motor fabricated from silicon and piezoelectric components. The stepper motor described here utilizes the inertial properties of a moving mass as part of the actuation process. Micro Electromechanical Systems-based (MEMS) technology is used in building the device. Test instruments have delivered over fifty implants with consistent performance. Typically the test instruments have attained 1.2 mm/s advancement speeds against 3 Newton resistance loads, a maximum output force of 4.6 Newtons, and maximum total displacement of 38 mm.
Optimal Design Using Chaotic Descent Method
Authors: Jovanovic Vojin , Kazerounian Kazem
Published: February 2021

This paper presents a novel method for locating global minima in design optimization problems. The method is applicable to any general nonlinear function. It is based on utilizing sensitive fractal areas to locate all of the solutions along one direction in variable space. The search begins from an arbitrary chosen point in the space and descends towards a better design along a randomly chosen direction. Descent depends on finding points that belong to Julia set from which all of the solutions along that direction can be located. The process is repeated until optimal design is obtained. To examine the behavior of the algorithm appropriate examples were selected and results discussed.
Numerical Solution for Manipulator Forward Dynamics BVPs
Authors: Pasic Hajrudin , Williams Robert L. , Hui Chunwu
Published: February 2021

A new algorithm is presented for iterative solution of systems of nonlinear ordinary differential equations (ODEs) with any order for multibody dynamics and control problems. The collocation technique (based on the explicit fixed-point iteration scheme) may be used for solving both initial value problems (IVPs) and boundary value problems (BVPs). The BVP is solved by first transforming it into the IVP. If the Lipschitz constant is large and the algorithm diverges in a single (‘long’) domain, the domain is partitioned into a number of subdomains and the local solutions of the corresponding BVPs are matched either locally (in parallel) or globally. The technique is general and may be applied to general systems of ODEs in any field. As an illustration, the forward dynamics problem of a manipulator is solved as an IVP and then as a BVP.
Geometric Criteria for Gouge-Free Three-Axis Milling of Sculptured Surfaces
Authors: Pottmann Helmut , Wallner Johannes , Glaeser Georg , Ravani Bahram
Published: February 2021

The paper presents a geometric investigation of collision-free 3-axis milling of surfaces. We consider surfaces with a global shape condition: they shall be interpretable as graphs of bivariate functions or shall be star-shaped with respect to a point. If those surfaces satisfy a local millability criterion involving curvature information, it is proved that this implies globally gouge-free milling. The proofs are based on general offset surfaces. The results can be applied to tool-motion planning and the computation of optimal cutter shapes.
An Assessment of Geometric Methods in Trajectory Synthesis for Shape Creating Operations
Authors: Sarma Radha
Published: February 2021

This paper presents an assessment of the steps involved in trajectory synthesis (e.g., trajectory layout, trajectory generation, trajectory spacing, trajectory postprocessing, and trajectory physics) for shape creating manufacturing operations, e.g., rapid prototyping, milling, electrical discharge machining. The rationale for this paper is that the trajectory plays an important role in determining the productivity as explained below.

Shape creating manufacturing operations are those that make use of a “tool” which operates on a “workpiece” to create the desired shape. The tool operates on the workpiece as dictated by the trajectory of the tool, resulting in the manufactured shape. Often, the geometric and functional properties of the end product are dependent on the trajectory of the tool. Moreover, the trajectory dictates the accuracy of the end product and the time taken to manufacture the product. Recognizing the important contribution of the trajectory in shape creating operations, this paper focuses on trajectory synthesis.
Classification and Interpretation of the Singularities of Redundant Mechanisms
Authors: Zlatanov Dimiter S. , Fenton Robert G. , Benhabib Beno
Published: February 2021

This paper introduces a unified approach to the singularity analysis of mechanisms with arbitrary kinematic chains and any number of inputs or outputs. The presented framework for the interpretation and classification of singularities is obtained by generalizing previous results (Zlatanov et al, 1995) valid only for non-redundant mechanisms. A velocity-space model is used to describe the instantaneous kinematics and interpret mechanism singularity. The definition of six singularity types and the study of their interdependence in the case of redundant mechanisms yield a comprehensive singularity classification.
Polynomial Solutions to the Displacement Analysis of 10-Link 1-DOF Mechanisms
Authors: Dhingra A. K. , Almadi A. N. , Kohli D.
Published: February 2021

This paper presents closed-form polynomial solutions to the displacement analysis problem of planar 10-link mechanisms with 1 degree-of-freedom (DOF). Using the successive elimination procedure presented herein, the input-output (I/O) polynomials as well as the number of assembly configurations for five mechanisms resulting from two 10-link kinematic chains are presented. It is shown that the displacement analysis problems for all five mechanisms can be reduced to a univariate polynomial devoid of any extraneous roots. This univariate polynomial corresponds to the I/O polynomial of the mechanism. In addition, one of the examples also illustrates how trigonometric manipulations in conjunction with tangent half-angle substitutions can lead to non-trivial extraneous roots in the solution process. Theoretical conditions for identifying and eliminating these extraneous roots are also presented.
A New Efficient Algorithm of Finding Optimum Code Based on Incident Degree
Authors: Deng Zhao-Hui , Luo Yu-Feng , Xu Zheng
Published: February 2021

A new efficient and robust algorithm based on incident degree, called recurrently dividing of matrix (RDM), has been developed for finding optimum code in detecting isomorphism among planar or spatial kinematic chains which can be represented by weighted graphs, adjacent matrices or matrix codes. The developed algorithm uses the recurring methods to order and divide adjacent matrix into various areas with different connection property so that the optimum code is found. Salient feature of this algorithm is removing computational inefficiency and remaining unique value of code approach in generating the codes, and able to detect symmetry in kinematic chains in the light of it.
Evolutionary Design of Planar Kinematic Chains
Authors: Nielsen David R. , Kazerounian Kazem
Published: February 2021

A procedure is developed to optimize planar mechanism type. A Genetic Algorithm is used to cycle populations of kinematic chain link adjacency matrices, through selection, crossover, and mutation. During this optimization, fit kinematic chains survive while unfit kinematic chains do not. Upon convergence, synthesized kinematic chains of high fitness remain. This technique was lead to be called the Genetic Algorithm for Type Synthesis (GATS). GATS introduces four new ideas for the type synthesis of mechanisms. First, it does not permute all possible kinematic chains. It searches for the best kinematic chains depending on a designer’s specifications. Second, larger size mechanisms can be generated because of the genetic algorithm’s evolutionary naturalness. Third, a novel approach was applied to genetic algorithms to allow the encodings to mutate in size. This allowed for addition or elimination of links in kinematic chains during evolution. Forth, a new property was deduced from mechanism topography that describes the mechanism design flexibility.
A Simple Finite Element Based Model for a Constrained-Layer of Viscoelastic Material: Part II — Application to Flexible Mechanism Systems
Authors: Sisemore Carl , Smaili Ahmad
Published: February 2021

This article investigates the effectiveness of constrained layer viscoelastic damping treatments in reducing the steady-state elastodynamic vibrations in flexible linkage mechanisms. The simple model that was proposed and verified in Part-I of this dual article is used to model the constrained layer of viscoelastic material applied to the coupler link of a flexible 4R mechanism. Full layer and patched layers of damping treatment are applied to the mechanism with three drive train conditions. The results indicate that with proper modeling of the mechanism as a system constrained layer passive damping can be very effective in reducing vibration magnitudes in flexible mechanisms.
Trajectory Synthesis for Selective Elimination of High Frequency Actuating Torque Harmonics
Authors: Ge Q. J. , Rastegar J. , Mattice M.
Published: February 2021

This paper deals with the problem of synthesizing joint trajectories of computer controlled machinery with tailored harmonic content for the actuating torques required to track the trajectories. For point-to-point motions with zero initial and final velocities and accelerations, a method is presented for shaping the harmonic content of the joint trajectories for the purpose of eliminating a specified high-frequency harmonic from the actuating torques. With such trajectories, the machine can perform the synthesized tasks with less residual vibration and increased settling time.
Singularity Analysis of a Class of the 6-6 Stewart Platforms
Authors: Wang Guozhen
Published: February 2021

In this paper, a method is presented for singularity analysis for a special form of the Stewart Platform in which the top and base platforms are similar in shape and the corresponding joints are connected by six prismatic joints. Analytical singularity conditions of this class of Stewart platform are derived by using the method. Examples are given to illustrate the theoretical results. It is shown that at the singular case, two or more pairs of branches of direct kinematic problems meet at the singular point.
Kinematics, Dynamics, and Control of Tendon-Driven Mechanisms Using Signal Flow Graphs
Authors: Chew Meng-Sang , Wongratanaphisan Theeraphong
Published: February 2021

This paper presents the analysis of the kinematics, dynamics and controls of tendon-driven mechanism under the framework of signal flow graphs. For decades, the signal flow graphs have been applied in many areas, particularly in controls, for determining the closed-loop transfer function of a control system. The tendon-driven mechanism considered here consists of several subsystems including actuator-controller dynamics, mechanism kinematics and mechanism dynamics. Each subsystem will be derived and represented by signal flow graphs. The representation of the whole system can be carried out by connecting the graphs of subsystems at the corresponding nodes. Transfer functions can then be obtained by using Mason’s rules. A 3-DOF robot finger utilizing tendon-driven mechanism is used as an illustrative example.
Architecture Optmization of a 3-DOF Parallel Mechanism
Authors: Carretero J. A. , Podhorodeski R. P. , Nahon M.
Published: February 2021

This paper presents a study of the architecture optimization of a three-degree-of-freedom parallel mechanism intended for use as a telescope mirror focussing device. The construction of the mechanism is first described. Since the mechanism has only three degrees of freedom, constraint equations describing the inter-relationship between the six Cartesian coordinates are given. These constraints allow us to define the parasitic motions and, if incorporated into the kinematics model, a constrained Jacobian matrix can be obtained. This Jacobian matrix is then used to define a dexterity measure. The parasitic motions and dexterity are then used as objective functions for the optimizations routines and from which the optimal architectural design parameters are obtained.
A Comparative Study on Some Modular Approaches for Analysis and Synthesis of Planar Linkages: Part II — Modular Dynamic Analysis, Modular Structural Synthesis and Modular Kinematic Synthesis
Authors: Yang Ting-Li , Yao Fang-Hua , Zhang Ming
Published: February 2021

This paper presents a systematical comparative study of various modular methods based on the different module types: basic kinematic chains (BKCs), single opened chains (SOCs), loops (or a tree and co-tree), links-joints, etc. for analysis and synthesis of structure, kinematics and dynamics of planar linkages. The basic idea is that any linkage can be divided into (or built up by) some modular components in sequence, and based on the component constraints and network entirty constraints of the linkage, the unified modular approaches have been used for analysis and synthesis. In systematical comparative study, the main issues of a modular method have been discussed, such as: the topological characteristics revealed via different module types; the dimension of a set of kinematic equations; the automated generation and solution of kinematic equations; the dimension and automated generation of dynamical equations, and computation complexity for generating and solving dynamical equation; the automated generation of structural analysis and type synthesis; the generation of kinematic synthesis equations etc.. This paper gives a summary of the use of modular techniques for analyzing and synthesizing planar linkages in the recently thirty years. This comparative study includes two parts: Part I-modular structural analysis and modular kinematic analysis; Part II-modular dynamic analysis, modular structural synthesis and modular kinematic synthesis. This paper is the second part.
Computerized Design, Generation and Simulation of Meshing of a Spiroid Worm-Gear Drive With Double-Crowned Worm
Authors: De Donno Mauro , Litvin Faydor L.
Published: February 2021

The authors propose methods of computerized design and analysis of a spiroid worm-gear drive with ground worm based on the following considerations:

(1) The theoretical thread surface of the hob is generated by a cone surface.

(2) The worm surface is crowned in profile and longitudinal directions in comparison with the hob thread surface.

(3) The double crowning of the worm enables to localize the bearing contact and obtain a predesigned parabolic function of transmission errors of an assigned level.

Computerized design of the worm-gear drive enables to discover and avoid singularities of the generated worm face-gear surface and pointing of teeth.

The meshing and contact of the double-crowned worm and the worm face-gear is simulated to determine the influence of misalignment on the shift of bearing contact and transmission errors. Computer program for numerical solution is developed and applied.

A numerical example that illustrates the developed theory is provided.
Using Dynamic Analysis for Compact Gear Design
Authors: Lin Ping-Hsun , Lin Hsiang Hsi , Oswald Fred B. , Townsend Dennis P.
Published: February 2021

This paper presents procedures for designing compact spur gear sets with the objective of minimizing the gear size. The allowable tooth stress and dynamic response are incorporated in the process to obtain a feasible design region. Various dynamic rating factors were investigated and evaluated. The constraints of contact stress limits and involute interference combined with the tooth bending strength provide the main criteria for this investigation. A three-dimensional design space involving the gear size, diametral pitch, and operating speed was developed to illustrate the optimal design of spur gear pairs.

The study performed here indicates that as gears operate over a range of speeds, variations in the dynamic response change the required gear size in a trend that parallels the dynamic factor. The dynamic factors are strongly affected by the system natural frequencies. The peak values of the dynamic factor within the operating speed range significantly influence the optimal gear designs. The refined dynamic factor introduced in this study yields more compact designs than AGMA dynamic factors.
Vibrations of Aircraft Gear Systems and Their Isolation
Authors: Buyukataman K. , Kazerounian K.
Published: February 2021

One of the most destructive factors in gear components with thin cylindrical rims, is the excessive stresses caused by the radial resonance modes. Dry friction dampers are an effective means of reducing structural vibratory response of gear components. This paper is the continuation of a previous report on vibration damping of aircraft gears [Buyukataman, AIAA-91-2550]. Similar notation and examples are used in this work. However, unlike the previous work which had stressed the damping mechanics and the design of the dampers, this report concentrates on computer implementation and design optimization of dampers.
Counting on Majorana modes
Authors: Sau Jay
Published: February 2021

Quantized conductance is a prerequisite of a topologically robust Majorana qubit
SARS-CoV-2 transmission during rugby league matches: do players become infected after participating with SARS-CoV-2 positive players?
Authors: Jones Ben , Phillips Gemma , Kemp Simon , Payne Brendan , Hart Brian , Cross Matthew , Stokes Keith A
Published: February 2021

Objectives

To examine the interactions between SARS-CoV-2 positive players and other players during rugby league matches and determine within-match SARS-CoV-2 transmission risk.

Methods

Four Super League matches in which SARS-CoV-2 positive players were subsequently found to have participated were analysed. Players were identified as increased-risk contacts, and player interactions and proximities were analysed by video footage and global positioning system (GPS) data. The primary outcome was new positive cases of SARS-CoV-2 within 14 days of the match in increased-risk contacts and other players participating in the matches.

Results

Out of 136 total players, there were 8 SARS-CoV-2 positive players, 28 players identified as increased-risk contacts and 100 other players in the matches. Increased-risk contacts and other players were involved in 11.4±9.0 (maximum 32) and 4.0±5.2 (maximum 23) tackles, respectively. From GPS data, increased-risk contacts and other players were within 2 m of SARS-CoV-2 positive players on 10.4±18.0 (maximum 88) and 12.5±20.7 (maximum 121) occasions, totalling 65.7±137.7 (maximum 689) and 89.5±169.4 (maximum 1003) s, respectively. Within 14 days of the match, one increased-risk contact and five players returned positive SARS-CoV-2 reverse transcriptase PCR (RT-PCR) tests, and 27 increased-risk contacts and 95 other participants returned negative SARS-CoV-2 RT-PCR tests. Positive cases were most likely traced to social interactions, car sharing and wider community transmission and not linked to in-match transmission.

Conclusion

Despite tackle involvements and close proximity interactions with SARS-CoV-2 positive players, in-match SARS-CoV-2 transmission was not confirmed. While larger datasets are needed, these findings suggest rugby presents a lower risk of viral transmission than previously predicted.
Evaluating the association of preoperative parecoxib with acute pain trajectories after video-assisted thoracoscopic surgery: a single-centre cohort study in Taiwan
Authors: Ling Yu-Hsiang , Tai Ying-Hsuan , Wu Hsiang-Ling , Fu Wei-Lun , Tsou Mei-Yung , Chang Kuang-Yi
Published: February 2021

Objective

The efficacy of parecoxib as pre-emptive analgesia still remains controversial. This study aimed to investigate how pre-emptive analgesia with parecoxib affected postoperative pain trajectories over time in patients undergoing thoracic surgery.

Design

Retrospective cohort study.

Setting

A single medical centre in Taiwan.

Participants

We collected 515 patients undergoing video-assisted thoracoscopic surgery at a tertiary medical centre between September 2016 and August 2017.

Interventions

Pre-emptive parecoxib before surgery.

Primary and secondary outcome measures

Daily numeric rating pain scores in the first postoperative week.

Results

A total of 196 (38.1%) of the recruited patients received parecoxib preoperatively. The latent curve analysis revealed that woman, higher body weight and postoperative use of parecoxib were associated with increased baseline level of pain scores over time (p=0.035, 0.005 and 0.048, respectively) but epidural analgesia and preoperative use of parecoxib were inclined to decrease it (both p<0.001). Regarding the decreasing trends of changes in daily pain scores, older age and epidural analgesia tended to steepen the slope (p=0.014 and <0.001, respectively). Preoperative use of parecoxib were also related to decreased frequency of rescue morphine medication (HR=0.4; 95% CI 0.25 to 0.65).

Conclusions

Pre-emptive analgesia with parecoxib was associated with decreased baseline pain scores but had no connection with pain decreasing trends over time. Latent curve analysis provided insights into the dynamic relationships among the analgesic modalities, patient characteristics and postoperative pain trajectories.
Seroprevalence of antibodies to SARS-CoV-2 in healthcare workers: a cross-sectional study
Authors: Ebinger Joseph E , Botwin Gregory J , Albert Christine M , Alotaibi Mona , Arditi Moshe , Berg Anders H , Binek Aleksandra , Botting Patrick , Fert-Bober Justyna , Figueiredo Jane C , Grein Jonathan D , Hasan Wohaib , Henglin Mir , Hussain Shehnaz K , Jain Mohit , Joung Sandy , Karin Michael , Kim Elizabeth H , Li Dalin , Liu Yunxian , Luong Eric , McGovern Dermot P B , Merchant Akil , Merin Noah , Miles Peggy B , Minissian Margo , Nguyen Trevor Trung , Raedschelders Koen , Rashid Mohamad A , Riera Celine E , Riggs Richard V , Sharma Sonia , Sternbach Sarah , Sun Nancy , Tourtellotte Warren G , Van Eyk Jennifer E , Sobhani Kimia , Braun Jonathan G , Cheng Susan
Published: February 2021

Objective

We sought to determine the extent of SARS-CoV-2 seroprevalence and the factors associated with seroprevalence across a diverse cohort of healthcare workers.

Design

Observational cohort study of healthcare workers, including SARS-CoV-2 serology testing and participant questionnaires.

Settings

A multisite healthcare delivery system located in Los Angeles County.

Participants

A diverse and unselected population of adults (n=6062) employed in a multisite healthcare delivery system located in Los Angeles County, including individuals with direct patient contact and others with non-patient-oriented work functions.

Main outcomes

Using Bayesian and multivariate analyses, we estimated seroprevalence and factors associated with seropositivity and antibody levels, including pre-existing demographic and clinical characteristics; potential COVID-19 illness-related exposures; and symptoms consistent with COVID-19 infection.

Results

We observed a seroprevalence rate of 4.1%, with anosmia as the most prominently associated self-reported symptom (OR 11.04, p<0.001) in addition to fever (OR 2.02, p=0.002) and myalgias (OR 1.65, p=0.035). After adjusting for potential confounders, seroprevalence was also associated with Hispanic ethnicity (OR 1.98, p=0.001) and African-American race (OR 2.02, p=0.027) as well as contact with a COVID-19-diagnosed individual in the household (OR 5.73, p<0.001) or clinical work setting (OR 1.76, p=0.002). Importantly, African-American race and Hispanic ethnicity were associated with antibody positivity even after adjusting for personal COVID-19 diagnosis status, suggesting the contribution of unmeasured structural or societal factors.

Conclusion and relevance

The demographic factors associated with SARS-CoV-2 seroprevalence among our healthcare workers underscore the importance of exposure sources beyond the workplace. The size and diversity of our study population, combined with robust survey and modelling techniques, provide a vibrant picture of the demographic factors, exposures and symptoms that can identify individuals with susceptibility as well as potential to mount an immune response to COVID-19.
Can routine blood tests be modelled to detect advanced liver disease in the community: model derivation and validation using UK primary and secondary care data
Authors: Hydes Theresa , Moore Michael , Stuart Beth , Kim Miranda , Su Fangzhong , Newell Colin , Cable David , Hales Alan , Sheron Nick
Published: February 2021

Objectives

Most patients are unaware they have liver cirrhosis until they present with a decompensating event. We therefore aimed to develop and validate an algorithm to predict advanced liver disease (AdvLD) using data widely available in primary care.

Design, setting and participants

Logistic regression was performed on routinely collected blood result data from the University Hospital Southampton (UHS) information systems for 16 967 individuals who underwent an upper gastrointestinal endoscopy (2005–2016). Data were used to create a model aimed at detecting AdvLD: ‘CIRRhosis Using Standard tests’ (CIRRUS). Prediction of a first serious liver event (SLE) was then validated in two cohorts of 394 253 (UHS: primary and secondary care) and 183 045 individuals (Care and Health Information Exchange (CHIE): primary care).

Primary outcome measures

Model creation dataset: cirrhosis or portal hypertension. Validation datasets: SLE (gastro-oesophageal varices, liver-related ascites or cirrhosis).

Results

In the model creation dataset, 931 SLEs were recorded (5.5%). CIRRUS detected cirrhosis or portal hypertension with an area under the curve (AUC) of 0.90 (95% CI 0.88 to 0.92). Overall, 3044 (0.8%) and 1170 (0.6%) SLEs were recorded in the UHS and CHIE validation cohorts, respectively. In the UHS cohort, CIRRUS predicted a first SLE within 5 years with an AUC of 0.90 (0.89 to 0.91) continuous, 0.88 (0.87 to 0.89) categorised (crimson, red, amber, green grades); and AUC 0.84 (0.82 to 0.86) and 0.83 (0.81 to 0.85) for the CHIE cohort. In patients with a specified liver risk factor (alcohol, diabetes, viral hepatitis), a crimson/red cut-off predicted a first SLE with a sensitivity of 72%/59%, specificity 87%/93%, positive predictive value 26%/18% and negative predictive value 98%/99% for the UHS/CHIE validation cohorts, respectively.

Conclusion

Identification of individuals at risk of AdvLD within primary care using routinely available data may provide an opportunity for earlier intervention and prevention of liver-related morbidity and mortality.