单搭接接头温度场与热应力分布的研究

为了对胶接接头承受热载荷时的温度场和热应力分布进行数值模拟,利用有限元法对单搭接接头的被粘物外表而承受不同温度、速度气流时的温度分布情况进行了分析.在考虑接头变形为几何非线性的前提下,研究了约束方式、胶层厚度及搭接长度对接头热应力分布的不同影响.结果表明,峰值热应力出现在搭接区边缘;当约束方式使胶层发生较大转动时,胶层处于高应力水平;随胶层厚度的增加,热应力降低且在胶层中分布更趋于均匀;搭接长度对热应力的影响因接头所受约束方式的不同,呈现不同的规律.     

HiL simulation in biomechanics: a new approach for testing total joint replacements

Instability of artificial joints is still one of the most prevalent reasons for revision surgery caused by various influencing factors. In order to investigate instability mechanisms such as dislocation under reproducible, physiologically realistic boundary conditions, a novel test approach is introduced by means of a hardware-in-the-loop (HiL) simulation involving a highly flexible mechatronic test system. In this work, the underlying concept and implementation of all required units is presented enabling comparable investigations of different total hip and knee replacements, respectively. The HiL joint simulator consists of two units: a physical setup composed of a six-axes industrial robot and a numerical multibody model running in real-time. Within the multibody model, the anatomical environment of the considered joint is represented such that the soft tissue response is accounted for during an instability event. Hence, the robot loads and moves the real implant components according to the information provided by the multibody model while transferring back the position and resisting moment recorded. Functionality of the simulator is proved by testing the underlying control principles, and verified by reproducing the dislocation process of a standard total hip replacement. HiL simulations provide a new biomechanical testing tool for analyzing different joint replacement systems with respect to their instability behavior under realistic movements and physiological load conditions.     

Automated sizing of automotive steering ball joints in parametric CAD environment using expert knowledge and feature-based computer-assisted 3D modelling

Ball joints used in the steering systems of vehicles are exposed to fluctuating loads, which can cause fatal accidents in case of failure. The design of ball joints is an iterative and time-consuming process. Even though the automotive industry is preparing for the era of autonomous self-steering vehicles, parts such as ball joints were not designed using a fully automated parametric design methodology. Recently, parametric design of automotive ball joints based on variable design methodology using knowledge and feature-based computer-assisted-3D modelling methods was studied. However, these studies do not give details of the interactive sizing process within the part and assembly module to determine the final dimensions for avoidance of fatigue failure.This work provides methods and discusses details of the configurable sizing of a ball joint assembly under the boundaries of the developed “parametric design platform”. The platform closes the software gap for the automated reconfiguration and sizing of the ball joint assembly using a three-dimensional (3D) modelling technique. The platform can parametrically change part, material, feature, geometry, assembly and dimension features in a programmable environment. It can also reconfigure the ball joint assembly model considering various structured data conforming to technical standards and reasoning mechanisms with “engineering and geometrical relations” provided in this work, and data gathering along the life cycle of a product. Parameterised 3D solid models and a knowledge base of ball joints are stored in a database, and then an evaluation process within the platform that is capable of sizing ball joints for infinite fatigue-life has been established to verify sizing. It demonstrates the practicability and validity of the automated sizing of a steering ball joint within a configurable design environment and with minimum human expert knowledge and interaction.     

Static Force-Based Modeling and Parameter Estimation for a Deformable Link Composed of Passive Spherical Joints With Preload Forces

To balance the contradiction between higher flexibility and heavier load bearing capacity, we present a novel deformable manipulator which is composed of active rigid joints and deformable links. The deformable link is composed of passive spherical joints with preload forces between socket-ball surfaces. To estimate the load bearing capacity of a deformable link, we present a static force-based model of spherical joint with preload force and analyze the static force propagation in the deformable link. This yields an important result that the load bearing capacity of a spherical joint only depends on its radius, preload force, and static friction coefficient. We further develop a parameter estimation method to estimate the product of preload force and static friction coefficient. The experimental results validate our model. 80.4% of percentage errors on the maximum payload mass prediction are below 15%.      

Sliding Mode Rest-to-Rest Stabilization and Trajectory Tracking for a Discretized Flexible Joint Manipulator

In this article, a difference flatness approach is used for trajectory tracking tasks of an approximately (Euler) discretized model of a nonlinear, single link, flexible joint manipulator. The system's flat output is commanded to follow a prescribed trajectory achieving a desired angular position maneuver. A new robust discrete time feedback controller design technique, of the sliding mode type, is then proposed for the closed loop regulation of the link position around the prescribed trajectory. The effectiveness of the approach is illustrated by means of digital computer simulations in a rest-to-rest stabilization maneuver and in a sinusoidal reference trajectory tracking task.     

复合材料π接头渐进失效分析

针对复合材料π接头复杂的失效形式,采用材料刚度退化的方法模拟结构的渐进失效过程,用Abaqus建立某复合材料π接头的三维有限元模型;采用三维Hashin失效准则和Ye分层准则判别复合材料层合板的5种失效形式,将理想弹塑性材料模型应用于胶层材料来模拟胶层材料的失效,在Abaqus中建立考虑复合材料层合板和胶层失效的分析子...     

基于道路载荷谱的车身焊点疲劳寿命分析

针对目前汽车焊点疲劳分析方法精度低、建模复杂等问题,以某自主SUV车身焊点为研究对象,采集道路载荷谱,通过载荷虚拟迭代得到底盘与车身连接点的载荷.研究结果表明,对车身焊点分别使用基于力(载荷)和应力的疲劳分析,可以准确预测试验样车焊点开裂位置,缩短焊点疲劳分析周期.改进后的样车顺利通过耐久试验场验证.     

An assessment of the realism of digital human manikins used for simulation in ergonomics

In this study, the accuracy of the joint centres of the manikins generated by RAMSIS and Human Builder (HB), two digital human modelling (DHM) systems widely used in industry for virtual ergonomics simulation, was investigated. Eighteen variously sized females and males were generated from external anthropometric dimensions and six joint centres (knee, hip and four spine joints) were compared with their anatomic locations obtained from the three-dimensional reconstructed bones from a low-dose X-ray system. Both RAMSIS and HB could correctly reproduce external anthropometric dimensions, while the estimation of internal joint centres location presented an average error of 27.6 mm for HB and 38.3 mm for RAMSIS. Differences between both manikins showed that a more realistic kinematic linkage led to better accuracy in joint location. This study opens the way to further research on the relationship between the external body geometry and internal skeleton in order to improve the realism of the internal skeleton of DHMs, especially for a biomechanical analysis requiring information of joint load and muscle force estimation.

Practitioner summary: This study assessed two digital human modelling (DHM) systems widely used in industry for virtual ergonomics. Results support the need of a more realistic human modelling, especially for a biomechanical analysis and a standardisation of DHMs.     

空间钢框架全焊接节点抗火设计的有限元分析

为考察钢框架梁-柱连接的抗火性能,建立平面钢框架全焊接节点有限元模型,用ANSYS分析其在火载荷作用下的行为,得到的温度-转角曲线与试验数据基本吻合;通过数值模拟得到不同载荷比值下的4种空间钢框架全焊接节点的温度-转角曲线.结果表明:载荷比值不同,空间钢框架全焊接节点在火灾作用下的临界温度不同;在相同的载荷比值下,不同空间钢框架全焊接节点的临界温度也不相同.在空间钢框架全焊接节点的抗火设计中,应加强对H型柱翼缘与梁连接方向的边节点和角节点的防火保护.     

机器人俯仰关节能耗特性分析

以降低架空线移动机器人能耗为目标,从结构设计角度出发提出一种基于平行四边形机构的机器人俯仰关节,由单电机配合柔索驱动。首先,在考虑摩擦因素的情况下进行了关节受力及能耗分析,分别给出本文关节与传统俯仰关节的能耗计算方法。再分别就多单元串联式机器人俯仰运动、以及架空线移动机器人越障运动的能耗特性,进行了本文关节和传统俯仰关...     

Dynamic modelling, simulation and control of a manipulator with flexible links and joints

The paper presents a dynamic modelling technique for a manipulator with multiple flexible links and flexible joints, based on a combined Euler–Lagrange formulation and assumed modes method. The resulting generalised model is validated through computer simulations by considering a simplified case study of a two-link flexible manipulator with joint elasticity. Controlling such a manipulator is more complex than controlling one with rigid joints because only a single actuation signal can be applied at each joint and this has to control the flexure of both the joint itself and the link attached to it. To resolve the control complexities associated with such an under-actuated flexible link/flexible joint manipulator, a singularly perturbed model has been formulated and used to design a reduced-order controller. This is shown to stabilise the link and joint vibrations effectively while maintaining good tracking performance.     

Topology optimization of frame structures—joint penalty and material selection

This paper deals with joint penalization and material selection in frame topology optimization. The models used in this study are frame structures with flexible joints. The problem considered is to find the frame design which fulfills a stiffness requirement at the lowest structural weight. To support topological change of joints, each joint is modelled as a set of subelements. A set of design variables are applied to each beam and joint subelement. Two kinds of design variables are used. One of these variables is an area-type design variable used to control the global element size and support a topology change. The other variables are length ratio variables controlling the cross section of beams and internal stiffness properties of the joints. This paper presents two extensions to classical frame topology optimization. Firstly, penalization of structural joints is presented. This introduces the possibility of finding a topology with less complexity in terms of the number of beam connections. Secondly, a material interpolation scheme is introduced to support mixed material design.     

联合优化深度神经网络和约束维纳滤波的单通道语音增强方法

深度神经网络（Deep neural networks,DNNs）依靠其良好的特征提取能力,在语音增强任务中得到了广泛应用。为进一步提高深度神经网络的语音增强效果,提出一种将深度神经网络和约束维纳滤波联合训练优化的新型网络结构。该网络首先对带噪语音幅度谱进行训练并分别得到纯净语音和噪声的幅度谱估计,然后利用语音和噪声的幅度谱估计计算得到一个约束维纳增益函数,最后利用约束维纳增益函数从带噪语音幅度谱中估计出增强语音幅度谱作为网络的训练输出。对不同信噪比下的20种噪声进行的仿真实验表明,无论噪声类型是否在网络的训练集中出现,本文方法都能够在有效去除噪声的同时保持较小的语音失真,增强效果明显优于DNN及NMF增强方法。     

A biomechanical analysis of hip compression loading during lifting

The aims of the present study were (i) to calculate the magnitude and direction of the hip joint compressive force, (ii) to determine the influence of hip flexion angle on the compressive force and (iii) to design a diagram for easy predictions of hip extensor muscular forces.

A biomechanical analysis was performed using data from dissection, combined with data from our previous investigations into hip load moments during lifting, and into length of hip extensor muscular moment arms. Waters' load-sharing data were also included in the biomechanical model.

The compressive force during lifting a 126 N ( 12.8 kg) box in the sagittal plane with flexed and with straight knees was calculated to be between 2.6 and 3.2 times body weight and the force was found to be directed medially and slightly dorsally. At a constant hip joint loading moment, the degree of hip flexion greatly influenced the compressive force, the least force being obtained at 35° hip flexion. The use of the force prediction diagram developed is described. This diagram is proposed for practical use when assessing different work postures.     

Evaluation of thermo-mechanical damage and fatigue life of solar cell solder interconnections

The soldering process of interconnecting crystalline silicon solar cells to form photovoltaic (PV) module is a key manufacturing process. However, during the soldering process, stress is induced in the solar cell solder joints and remains in the joint as residual stress after soldering. Furthermore, during the module service life time, thermo-mechanical degradation of the solder joints occurs due to thermal cycling of the joints which induce stress, creep strain and strain energy. The resultant effect of damage on the solder joint is premature failure, hence shortened fatigue life. This study seeks to determine accumulated thermo-mechanical damage and fatigue life of solder interconnection in solar cell assembly under thermo-mechanical cycling conditions. In this investigation, finite element modelling (FEM) and simulations are carried out in order to determine nonlinear degradation of SnAgCu solder joints. The degradation of the solder material is simulated using Garofalo-Arrhenius creep model. A three dimensional (3D) geometric model is subjected to six accelerated thermal cycles (ATCs) utilising IEC 61215 standard for photovoltaic panels. The results demonstrate that induced stress, strain and strain energy impacts the solder joints during operations. Furthermore, the larger the accumulated creep strain and creep strain energy in the joints, the shorter the fatigue life. This indicates that creep strain and creep strain energy in the solder joints significantly impacts the thermo-mechanical reliability of the assembly joints. Regions of solder joint with critical stress, strain and strain energy values including their distribution are determined. Analysis of results demonstrates that creep energy density is a better parameter than creep strain in predicting interconnection fatigue life. The use of six ATCs yields significant data which enable better understanding of the response of the solder joints to the induced loads. Moreover, information obtained from this study can be used for improved design and better-quality fabrication of solder interconnections in solar cell assembly for enhanced thermo-mechanical reliability.     

基于外观模型的人体下肢关节点定位方法

近年来,人体下肢关节点定位成为了人体运动跟踪与分析中一个重要研究课题。提出了一种下肢关节点自动定位方法,从无关节标记的人体运动图像序列中定位下肢关节点。该方法首先采用背景剪除技术从图像序列中分割人体目标对象,并建立人体下肢骨架模型。然后,利用关节角度预测方法估计膝踝关节点的位置,在基于下肢外观模型的匹配计算基础上获得下肢关节点的真实位置。实验结果表明,该方法简单有效,下肢关节点定位结果令人满意。     

Load moments and myoelectric activity when the cervical spine is held in full flexion and extension

Abstract

Sustained joint load in extreme positions (namely maximally flexed or extended positions) has been described as causing pain. The aim of the present study is to analyse eight different sitting work postures with respect to extreme positions, and to assess the mechanical load and the levels of muscular activity arising in defined extreme positions of the cervical spine. Ten healthy female workers from an electronics plant took part in laboratory experiments. For seven of these, levels of neck and shoulder muscular activity in sitting postures with the cervical spine in different manually-adjusted extreme positions were recorded using surface electrodes. Loading moments of force about the bilateral motion axis of the atlanto-occipital joint (Occ-C1) and the spinal cervico-thoractc motion segments (C7-T1) were calculated. Extreme or almost extreme positions occurred in sitting postures with the thoracolumbar back inclined slightly backwards or with the whole spine flexed. Electromyographic (EMG) activity levels were very low in the manually-adjusted extreme positions. The load moment for the Occ-Cl joint when the whole neck was flexed was only 1·2 times the value for the neutral position of the head, but for C7-T1 it increased to 3·6 times. It is concluded that extreme positions of the cervical spine do occur in sitting work postures, and that the levels of muscular activity in such positions are low. Thus, recordings of muscle activity and calculations of load moment alone are not a sufficient basis for evaluating work postures: thorough recordings of spine positions should be included.     

基于DNN与规则学习的机器翻译算法研究

通过以目标信息为指导的卷积体系总结相关源信息,提出了一种系统的处理语言方法;利用在解码过程中使用不同的引导信号,经过特殊设计的卷积+门控体系结构可以查明与预测目标单词相关的源句子部分,并将其与整个源句子的上下文融合在一起形成统一表示形式;研究结果表明,模型将表示形式与目标语言单词一起馈入深度神经网络(DNN),形成更强大的神经网络联合模型(NNJM);通过两个NIST汉英翻译任务的实验验证,在相同设置下,tagCNN和inCNN在Dep2Str基线上的改善幅度分别为+1.28,+1.75 BLEU,所提出的模型分别优于NIST MT04和MT05的平均值+0.36,+0.83 BLEU,比传统DNN机器翻译平均提高了+1.08 BLEU点;模型为统计机器翻译研究提供了新思路。     

基于FPGA的BGA焊点健康管理原理与实现

针对BGA封装的FPGA焊点故障频发的问题,提出了一种基于FPGA的BGA焊点失效监测模型及实现方法;对FPGA的BGA焊点失效原理进行了分析;基于IPC7095B确定了焊点易失效区域,并依据欧姆定律构建了检测模型;基于Xilinx的FPGA实现了对焊点健康信息的管理,并根据不同的检测标准对检测情况进行了比较     

Topology optimization of frame structures with flexible joints

A method for structural topology optimization of frame structures with flexible joints is presented. A typical frame structure is a set of beams and joints assembled to carry an applied load. The problem considered in this paper is to find the stiffest frame for a given mass. By introducing design variables for beams and joints, a mass distribution for optimal structural stiffness can be found. Each beam can have several design variables connected to its cross section. One of these is an area-type design variable which is used to represent the global size of the beam. The other design variables are of length ratio type, controlling the cross section of the beam. Joints are flexible elements connecting the beams in the structure. Each joint has stiffness properties and a mass. A framework for modelling these stiffnesses is presented and design variables for joints are introduced. We prove a theorem which can be interpreted as the fact that the removal of structural elements, e.g. joints or beams, can be modelled by a small strictly positive material amount assigned to the element. This is needed for the computations of sensitivities used in the applied gradient based iterative method. Both two and three dimensional problems, as well as multiple load cases and multiple mass constraints, are treated.