ANALYSIS OF ADHESIVE LAP JOINT

This paper is to solve the interlaminar stresses of adhesive lap joint by the energymethod without considering the adhesive layer. The joint is made of two identical narrowplates.Two cases are discussed:one is for the isotropic material and the other is fororthotropic material.Because of the different materials forming the joint,the length ofdistribution and the magnitude of the interlaminar stresses for the two cases will be verydifferent.     

THE EVOLUTION EQUATION OF JOINT PDF OF TURBULENT VELOCITY AND DISSIPATION

According to the hypothesis that the dissipation of turbulent kinetic energy satisfieslog-normal distribution,a stochostic model of dissipation is provided and the Langevinmodel of velocity is modified Then a joint Pdf equation of turbulent vilocity anddissipation is derived.we solve numerically the joint Pdf equation using Monte Carlomethod and obtain satisfactory results for decaying turbulence and homogeneous turbulentshear flow.The preliminary results show that the model is well working.     

The effect of waist twisting on walking speed of an amphibious salamander like robot

Amphibious salamanders often swing their waist to coordinate quadruped walking in order to improve their crawling speed. A robot with a swing waist joint, like an amphibious salamander, is used to mimic this locomotion. A control method is designed to allow the robot to maintain the rotational speed of its legs continuous and avoid impact between its legs and the ground. An analytical expression is established between the amplitude of the waist joint and the step length. Further, an optimization amplitude is obtained corresponding to the maximum stride. The simulation results based on automatic dynamic analysis of mechanical systems (ADAMS) and physical experiments verify the rationality and validity of this expression.     

THE DRAG EXERTED BY AN OBLATE ROTATING ATMOSPHERE ON AN ARTIFICIAL SATELLITE

A theory is formulated for the motion of an artificial satellite under the joint effects of Earth oblateness and atmospheric drag. The Hamilton ' s equations of motion are derived including the zonal harmonics of the geopotential up to J4 and the drag accelerations. The atmospheric model is an oblate rotating model in which the atmospheric rotation lags behind that of the Earth as the increasing distance from the Earth. The drag free problem is first solved via two canonical transformations to eliminate in succession the short and long period terms. An operator D is then defined and used to formulate the drag acceleration in terms of the double primed variables expressing the solution of the drag-free problem.     

Stability and oscillations in a slow-fast flexible joint system with transformation delay

Flexible joints are usually used to transfer velocities in robot systems and may lead to delays in motion transformation due to joint flexibility. In this paper, a linkrotor structure connected by a flexible joint or shaft is firstly modeled to be a slow-fast delayed system when moment of inertia of the lightweight link is far less than that of the heavy rotor. To analyze the stability and oscillations of the slowfast system, the geometric singular perturbation method is extended, with both slow and fast manifolds expressed analytically. The stability of the slow manifold is investigated and critical boundaries are obtained to divide the stable and the unstable regions. To study effects of the transformation delay on the stability and oscillations of the link, two quantitatively different driving forces derived from the negative feedback of the link are considered. The results show that one of these two typical driving forces may drive the link to exhibit a stable state and the other kind of driving force may induce a relaxation oscillation for a very small delay. However, the link loses stability and undergoes regular periodic and bursting oscillation when the transformation delay is large. Basically, a very small delay does not affect the stability of the slow manifold but a large delay affects substantially.     

DISTRIBUTION OF RANDOM ELEMENTS SUBJECTED TO A FLEXIBLE BOUNDARY CONDITION

The probability distribution function of n random elements subjected to the flexible boundary condition is derived. The probability density is a descending curve and converges to a delta function as n tends to infinity. The distribution of the minimum value is discussed in context of ordered statistics.     

THREE-DIMENSIONAL FINITE ELEMENT SIMULATION OF TOTAL KNEE JOINT IN GAIT CYCLE

Based on CT scanning pictures from a volunteer＇s knee joint, a three-dimensional finite element model of the healthy human knee joint is constructed including complete femur, tibia, fibular, patellar and the main cartilage and ligaments. This model was validated using experimental and numerical results obtained from other authors. The pressure distribution of contact surfaces of knee joint are calculated and analyzed under the load action of ‘heel strike＇, ‘single limb stance＇ and ‘toe-off＇. The results of the gait cycle are that the contact areas of medial cartilage are larger than that of lateral cartilage; the contact force and contact areas would grow larger with the load increasing; the pressure of lateral meniscus is steady, relative to the significant variation of peak pressure in medial meniscus; and the peak value of contact pressure on all components are usually found at about 4570 of the gait cycle.     

Dynamics and adaptive control of a dual-arm space robot with closed-loop constraints and uncertain inertial parameters简

A dynamics-based adaptive control approach is proposed for a planar dual-arm space robot in the presence of closed-loop constraints and uncertain inertial parameters of the payload. The controller is capable of controlling the po- sition and attitude of both the satellite base and the payload grasped by the manipulator end effectors. The equations of motion in reduced-order form for the constrained system are derived by incorporating the constraint equations in terms of accelerations into Kane＇s equations of the unconstrained system. Model analysis shows that the resulting equations perfectly meet the requirement of adaptive controller design. Consequently, by using an indirect approach, an adaptive control scheme is proposed to accomplish position/attitude trajectory tracking control with the uncertain parameters be- ing estimated on-line. The actuator redundancy due to the closed-loop constraints is utilized to minimize a weighted norm of the joint torques. Global asymptotic stability is proven by using Lyapunov＇s method, and simulation results are also presented to demonstrate the effectiveness of the proposed approach.     

Particle flow study on strength and meso-mechanism of Brazilian splitting test for jointed rock mass

A discrete element method （DEM） called particle flow code （PFC2D） was used to construct a model for Brazilian disc splitting test in the present study. Based on the experimental results of intact Brazilian disc of rock-like material, a set of micro-parameters in PFC2D that reflected the macro-mechanical behavior of rock-like materials were obtained. And then PFC2D was used to simulate Brazilian splitting test for jointed rock mass specimens and specimen containing a central straight notch. The effect of joint angle and notch angle on the tensile strength and failure mode of jointed rock specimens was detailed analyzed. In order to reveal the meso-mechanical mechanism of crack coalescence, displacement trend lines were applied to analyze the displacement evolution during the crack initiation and propagation. The investigated conclusions can be described as follows. （1） The tensile strength of jointed rock mass disc specimen is dependent to the joint angle. As the joint angle increases, the tensile strength of jointed rock specimen takes on a nonlinear variance. （2） The tensile strength of jointed rock mass disc specimen containing a central straight notch distributes as a function of both joint angle and notch angle. （3） Three major failure modes, i.e., pure tensile failure, shear failure and mixed tension and shear failure mode are observed in jointed rock mass disc specimens under Brazilian test. （4） The notch angle roles on crack initiation and and joint angle play important propagation characteristics of jointed rock mass disc specimen containing a central straight notch under Brazilian test.     

THEORY OF DIELECTRIC ELASTOMERS

In response to a stimulus, a soft material deforms, and the deformation provides a function. We call such a material a soft active material （SAM）. This review focuses on one class of soft active materials： dielectric elastomers. When a membrane of a dielectric elastomer is subject to a voltage through its thickness, the membrane reduces thickness and expands area, possibly straining over 100%. The dielectric elastomers are being developed as transducers for broad applications, including soft robots, adaptive optics, Braille displays, and electric generators. This paper reviews the theory of dielectric elastomers, developed within continuum mechanics and thermodynamics, and motivated by molecular pictures and empirical observations. The theory couples large deformation and electric potential, and describes nonlinear and nonequilibrium behavior, such as electromechanical instability and viscoelasticity. The theory enables the finite element method to simulate transducers of realistic configurations, predicts the efficiency of electromechanical energy conversion, and suggests alternative routes to achieve giant voltage-induced deformation. It is hoped that the theory will aid in the creation of materials and devices.     

自由漂浮空间机器人路径优化的Legendre伪谱法

基于Legendre伪谱法研究自由漂浮空间机器人非完整路径规划的最优控制问题.自由漂浮是空间机器人执行任务常用的工作模式,其路径优化是空间机器人完成复杂空间任务的基础.由于空间机器人不具有固定基座,机械臂和载体之间存在非完整约束,使得自由漂浮空间机器人路径规划完全不同于地面机器人而变得具有挑战性.本文提出自由漂浮空间机器人路径规划的最优控制伪谱方法.首先,利用多体动力学理论建立自由漂浮空间机器人动力学模型,给定系统的初始和目标位形,选取机械臂关节耗散能最小为性能指标,并考虑实际控制输入受限,建立其路径规划的Bolza问题.然后,应用Legendre伪谱法,将状态和控制变量在Legendre--Gauss--Lobatto(LGL)点上离散,并构造Lagrange插值多项式逼近系统状态和控制变量,将连续路径优化问题离散化为非线性规划问题求解.最后通过数值仿真表明,应用Legendre伪谱法求解自由漂浮空间机器人非完整路径规划问题,得到的机械臂和载体最优运动轨迹,较好地满足各种约束条件,且计算精度高、速度快,并具有良好的实时性.     

3-PRS并联机器人惯量耦合特性研究

惯量是影响机器人动态性能的主要因素,并联机器人因其多支链耦合的结构特点,关节空间各驱动轴出现惯量耦合的动力学特性,在高速、高加速度运动时易引起控制超调、振动等现象,破坏机器人的动态性能,因此研究并联机器人惯量耦合特性具有重要意义.以3-PRS并联机器人为例,通过虚功原理求得惯量矩阵,提出惯量耦合指标,该耦合指标表征了并联机器人在工作空间不同位姿时各驱动轴的耦合惯量大小,并给出了该耦合指标在机器人工作空间内的分布规律.进一步在一台3-PRS并联机器人样机上进行了实验验证,结果表明耦合惯量会改变驱动轴负载,负载的改变将最终影响动态性能.同时各驱动轴的负载变化量随着惯量耦合指标的变大而变大,与理论分析有较好的一致性.研究成果可帮助评价并联机器人的动力学耦合特性,并可用于并联机器人的结构参数优化及伺服参数调试以提高机器人的动态性能.     

A new approach of joint trajectories for cartesian path approximation of mechanical manipulators

Summary The path planning of the industrial robots is usually done in joint space to reduce the on-line computational amount. To do this, a sequence of Cartesian knots chosen carefully must be transformed into joint space. The joint trajectories are often interpolated by polynomial functions, usually by cubic splines. This paper presents a new method for joint trajectories approximation. The method requires to transform the positions, velocities and accelerations of the knots. It can reduce the number of needed points and consequently the total computational amount, and can realize the joint trajectories in real-time. A comparison to the usual cubic spline approach is shown by an illustrative example.

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Sommario La programmazione delle traiettorie Cartesiane dei robots industriali è fatta spesso nello spazio dei giunti per ridurre la quantità di calcolo on-line. Per fare questo, una sequenza di punti Cartesiani scelti attentamente deve essere trasformata nello spazio dei giunti. Le traiettorie dei giunti vengono interpolate dalle funzioni polinomiali, quasi sempre da splines cubici. Questo lavoro presenta un nuovo metodo per approssimare le traiettorie dei giunti; il metodo richiede di trasformare le posizioni, le velocità e le accelerazioni dei punti Cartesiani. Il metodo può ridurre il numero dei punti scelti e di conseguenza la quantità di calcolo totale, e può realizzare le traiettorie dei giunti in tempo reale. Un confronto con l'approccio di splines cubici è illustrato da un'esempio semplice.

     

L'espace articulaire de la Robotique Industrielle est un espace vectorielIndustrial Robotics joint space is a vector space

The mathematical modelling of industrial robots is based on the vectorial nature of the n-dimensional joint space of the robot, defined as a kinematic chain with n degrees of freedom. However, in our opinion, the vectorial nature of the joint space has been insufficiently discussed in the literature. We establish the vectorial nature of the joint space of an industrial robot from the fundamental studies of B. Roth on screws. To cite this article: B. Tondu, C. R. Mecanique 331 (2003).     

基于真实工况下的工业机器人关节转角辨识与分析

本文基于多目视觉测量系统，对真实工况下连续运动的工业机器人进行关节转角的实时重构．该方法通过机器人运动前后的坐标集，在对刚体运动进行最优拟合的条件下，采用最小二乘法获得了各关节的旋转矩阵与平移向量．在此基础上，在考虑相邻关节牵连运动的前提下，获得了各关节的相对旋转矩阵．结合罗德里格斯变换理论通过相对旋转矩阵，确定了各关节转角．仿真与实验分析，验证了该方法的有效性与正确性．在该测量与辨识体系下，初步确定了各关节转角随机器人运动的真实状态．2与3杆臂由于物理尺寸呈细长形状，连杆挠度较大，这时变形误差与振动建立了关系，角振动幅度很大，曲线随机性较强．其余杆臂由于刚度较大，关节转角曲线呈光滑状态．     

The Kinematics and the Full Minimal Dynamic Model of a 6-DOF Parallel Robot Manipulator

In this paper we present a particular architecture of parallel robots which has six-degrees-of-freedom (6-DOF) with only three limbs. The particular properties of the geometric and kinematic models with respect to that of a classical parallel robot are presented. We show that inverse problems have an analytical solution. However, to solve the direct problems, an efficient numerical procedure which needs to inverse only a 3 × 3 passive Jacobian matrix is proposed. In a second step, dynamic equations are derived using the Lagrangian formalism where the joint variables are passive and active joint coordinates. Based on the geometrical properties of the robot, the equations of motion are derived in terms of only nine coordinates related by three kinematic constraints instead of 18 joint coordinates. The computational cost of the dynamic model obtained is reduced by using a minimum set of base inertial parameters.     

Disturbance compensation of a dual-arm underwater robot via redundant parallel mechanism theory

Disturbance compensation is one of the major issues for underwater robots to hover as a mobile platform and to manipulate an object in an underwater environment. This paper presents a new strategy of disturbance compensation for a mobile dual-arm underwater robot using internal torques derived from redundant parallel mechanism theory. A model of the robot was analyzed by redundant serial and parallel mechanisms at the same time. The joint torque to operate the robot is obtained from a redundant serial mechanism model with null-space projection due to redundancy. The joint torque derived from the redundant parallel kinematic model is calculated to perfectly compensate for disturbances to the mobile platform and is included in the solution of the joint torque based on the serial redundant model. The resultant joint torque can generate force on the end-effector for required tasks and forces for disturbance compensation simultaneously . A simulation shows the performance of this disturbance compensation strategy. The joint torque based on the algorithm generates the desired task force and the disturbance compensation force together, and a little additional joint torque can generate a large internal force effectively due to the characteristics of a redundant parallel mechanism. The proposed method is more effective than compensation methods using thrusting force on the mobile platform.     

An evolutionary approach for the motion planning of redundant and hyper-redundant manipulators

The trajectory planning of redundant robots is an important area of research and efficient optimization algorithms are needed. The pseudoinverse control is not repeatable, causing drift in joint space which is undesirable for physical control. This paper presents a new technique that combines the closed-loop pseudoinverse method with genetic algorithms, leading to an optimization criterion for repeatable control of redundant manipulators, and avoiding the joint angle drift problem. Computer simulations performed based on redundant and hyper-redundant planar manipulators show that, when the end-effector traces a closed path in the workspace, the robot returns to its initial configuration. The solution is repeatable for a workspace with and without obstacles in the sense that, after executing several cycles, the initial and final states of the manipulator are very close.     

A unified solution to swing-up control for n-link planar robot with single passive joint based on virtual composite links and passivity

This paper concerns the swing-up control of an n-link revolute planar robot with any one of the joints being passive. The goal is to design and analyze a swing-up controller that can bring the robot into any arbitrarily small neighborhood of the upright equilibrium point, at which all the links are in the upright position. We present a unified solution based on the notion of virtual composite link (VCL), which is a virtual link made up of one or more active links. By using the angles of two series of VCLs separated by the passive joint and using the total mechanical energy of the robot, we design a swing-up controller and analyze the global motion of the robot under the controller. The main new results of this paper are: (1) we obtain a lower bound for each control gain related to the angle of each VCL such that the closed-loop system has only one undesired equilibrium point in addition to the upright equilibrium point, and we present an original proof of the conditions on the control gains for a class of n-link underactuation-degree-one planar robots with an active first joint; (2) we provide a bigger control gain region for achieving the control objective than those of previous results on three- and n-link robots with a passive first joint; (3) we validate the theoretical results via numerical simulations on a 4-link robot with the passive joint in each of the four positions. This paper gains an insight into the passivity-based control of underactuated multiple-DOF systems.     

一类新型仿生起竖结构设计及其动力学分析

由于生物能够通过丰富的运动形式完成特定的任务, 仿生设计方法受到了学者们的广泛关注. 蚯蚓在各种环境中具有出色的移动能力和适应性, 受此启发, 仿蠕虫机器人被提出并应用在搜救、医疗等领域. 然而现有的仿蠕虫机器人一般通过体节的轴向变形实现直线运动, 无法实现类似蛇类生物的起竖功能. 为了解决现有的仿蠕虫机器人无法起竖的问题, 本文提出了一种具有非线性多稳态性质的仿生柔性关节, 并在此基础上构建了多节仿生起竖结构以实现类似尺蠖、蛇等生物的起竖功能. 首先, 本文提出了一种仿生起竖关节模型, 推导了多节仿生起竖结构的总势能表达式, 从而建立了多节仿生起竖结构的动力学模型; 随后, 基于多节仿生起竖结构总势能的表达式和多元函数极值原理, 提出了实现需求起竖构型的结构参数设计准则, 利用动力学模型验证了结构参数设计准则的有效性, 并研究了需求构型的触发条件; 最后, 针对不同起竖节数的设计需求, 设计了相应节数的仿生起竖结构. 研究结果表明, 结构参数设计准则能够使得多节仿生起竖结构达到需求的仿生起竖构型, 并在需求构型处保持稳定平衡; 此外, 定义了初始激励与起竖构型的比例系数单调性变量, 并基于仿生起竖结构不同稳态的吸引盆揭示了上述变量构成的构型触发准则, 这为仿生起竖结构的构型切换提供了理论依据. 本文提出的仿生起竖结构对仿蠕虫机器人的功能拓展具有参考价值和指导意义, 也是对仿生设计理论的进一步完善.