Exploiting passive dynamics for robot throwing task

Throwing is a complex and highly dynamic task. Humans usually exploit passive dynamics of their limbs to optimize their movement and muscle activation. In order to approach human throwing, we developed a double pendulum robotic platform. To introduce passivity into the actuated joints, clutches were included in the drive train. In this paper, we demonstrate the advantage of exploiting passive dynamics in reducing the mechanical work. However, engaging and disengaging the clutches are done in discrete fashions. Therefore, we propose an optimization approach which can deal with such discontinuities. It is shown that properly engaging/disengaging the clutches can reduce the mechanical work of a throwing task. The result is compared to the solution of fully actuated double pendulum, both in simulation and experiment. © 2012 IEEE.

Learning legged locomotion

Legged locomotion of biological systems can be viewed as a self-organizing process of highly complex system-environment interactions. Walking behavior is, for example, generated from the interactions between many mechanical components (e.g., physical interactions between feet and ground, skeletons and muscle-tendon systems), and distributed informational processes (e.g., sensory information processing, sensory-motor control in central nervous system, and reflexes) [21]. An interesting aspect of legged locomotion study lies in the fact that there are multiple levels of self-organization processes (at the levels of mechanical dynamics, sensory-motor control, and learning). Previously, the self-organization of mechanical dynamics was nicely demonstrated by the so-called Passive Dynamic Walkers (PDWs; [18]). The PDW is a purely mechanical structure consisting of body, thigh, and shank limbs that are connected by passive joints. When placed on a shallow slope, it exhibits natural bipedal walking dynamics by converting potential to kinetic energy without any actuation. An important contribution of these case studies is that, if designed properly, mechanical dynamics can generate a relatively complex locomotion dynamics, on the one hand, and the mechanical dynamics induces self-stability against small disturbances without any explicit control of motors, on the other. The basic principle of the mechanical self-stability appears to be fairly general that there are several different physics models that exhibit similar characteristics in different kinds of behaviors (e.g., hopping, running, and swimming; [2, 4, 9, 16, 19]), and a number of robotic platforms have been developed based on them [1, 8, 13, 22]. © 2009 Springer London.

Bipedal walking and running with compliant legs

Passive dynamics plays an important role in legged locomotion of the biological systems. The use of passive dynamics provides a number of advantages in legged locomotion such as energy efficiency, self-stabilization against disturbances, and generating gait patterns and behavioral diversity. Inspired from the theoretical and experimental studies in biomechanics, this paper presents a novel bipedal locomotion model for walking and running behavior which uses compliant legs. This model consists of three-segment legs, two servomotors, and four passive joints that are constrained by eight tension springs. The self-organization of two gait patterns (walking and running) is demonstrated in simulation and in a real-world robot. The analysis of joint kinematics and ground reaction force explains how a minimalistic control architecture can exploit the particular leg design for generating different gait patterns. Moreover, it is shown how the proposed model can be extended for controlling locomotion velocity and gait patterns with the simplest control architecture. © 2007 IEEE.

Toward a human-like biped robot with compliant legs

Conventional models of bipedal walking generally assume rigid body structures, while elastic material properties seem to play an essential role in nature. On the basis of a novel theoretical model of bipedal walking, this paper investigates a model of biped robot which makes use of minimum control and elastic passive joints inspired from the structures of biological systems. The model is evaluated in simulation and a physical robotic platform with respect to the kinematics and the ground reaction force. The experimental results show that the behavior of this simple locomotion model shows a considerable similarity to that of human walking. © 2006 The authors.

不锈钢激光搭接焊接头温度场数值模拟及分析

温度场是影响激光焊接焊缝成形质量的关键因素. 针对非熔透型激光搭接焊接头焊缝成"钉头"状的特点,通过分析焊接时材料吸收激光能量的分布情况,提出了高斯面热源加线性递增式柱热源的复合体热源模型. 模型考虑板间接触热阻的影响,并将计算结果和试验结果进行了对比,发现模拟出的焊缝形状和试验吻合较好;此外基于本模型对焊缝各处的热循环与焊缝组织形貌及显微硬度的关系进行了分析. 结果表明,焊缝组织形貌及显微硬度除与加热和冷却速率有关外,峰值温度对其也有重要影响;在热循环基本一致的情况下焊缝的性能相似. 该模型较准确地模拟了薄板激光深熔焊接熔池温度场,对研究激光深熔焊接温度场问题和激光工艺参数的优化选择具有参考价值

Magnets for HIRFL-CSR rings

The magnet design, fabrication, and measurement of HIRFL-CSR (Heavy Ion Research Facility in Lanzhou Cooling Storage Ring) are presented. All magnets will be laminated And welded with an armor-coated surface between two big endplates made of sticking glue 0.5 mm-thick sheets. The dipole of CSRm was chosen an H type with an air circle on the pole to improve the field uniformity. The dipole of CSRe was chosen the C type with an air circle and two air slots on the pole to improve the field homogeneity. Its reproducibility of magnet to magnet was adjusted with inserting small laminating pieces before demountable pole ends to reach less than +/- 2 x 10(-4) at optimized field level. CSRm quadrupoles diameter is 170 mm and has two different lengths, and its endplates were made with punching pieces after coating with epoxy glue, there is chamfered directly on the pole ends to reduce 12th-order contribution of field and without the demountable pole ends. CSRe main quadrupoles diameter is 240 mm and has two different lengths, and its endplates were also made with punching pieces coated with epoxy glue, there is also chamfered directly on the pole ends to reduce 12th-order contribution of field like CSRm.

含环路布局和运动副轴线方位特征的运动链拓扑结构描述

构造一种含环路布局、构件类型、运动副类型和运动副轴线方位信息的运动链的拓扑特征矩阵。构件的类型构成特定的环路布局,运动副的类型及其轴线的方位配置决定运动的状态特征,多副构件是联系环路间的桥梁。以运动链构成的独立环路为基础构建特征矩阵的行数,运动链的构件数目构建特征矩阵的列数;以独立环路的旋向确定构件及其排序;以代表运动副类型的符号或数字表达构件及环路间的连接关系;以同一构件上两个运动副的相对轴线方位描述运动副的方位特征。构造的运动链特征矩阵为(2l+2)×n,而单环运动链为3×n矩阵。实例表明,该特征矩阵可以描述各类运动链,与传统n×n拓扑矩阵相比,结构大大简化,而且拓扑信息量多。该矩阵特别便于由特征矩阵构造对应的机构简图,同时也为计算机辅助运动学和动力学建模提供了一种便捷途径。

仿人机器人腰部机构的动力学建模、控制与仿真

本文介绍的仿人机器人具有差动腰部机构,它除了受自身的动力学影响以外,还受到手臂和车体运动以及外力、外力矩等对腰部机构关节力矩的影响。笔者利用高效牛顿-欧拉算法完成了仿人机器人的整体建模;在不考虑各关节间耦合运动的情况下,对整体动力学模型进行适当简化,得到了腰部机构的动力学模型。简化后的动力学模型既反映了机器人车体、腰部及双臂的动力学关系,又大大地减小了计算量,易于实现基于动力学的控制算法。基于动力学模型,给出了腰部机构PD伺服轨迹跟踪控制算法,并结合计算力矩方法用于补偿腰部机构两关节受到的力矩扰动。仿真分析表明,该控制方法可以明显提高腰部机构的位置跟踪精度,并提高仿人机器人的整体作业精度。

全地形轮式移动机器人运动学建模与分析

提出全地形轮式移动机器人的正逆运动学问题。将机器人看成一个混合串-并联多刚体系统,从每个轮-地接触点到机器人车体分别构成一个串联子系统,抛弃车轮纯滚动假设,在轮-地接触点处建立瞬时坐标系,考虑车轮的平面滑移,从而对每个串联子系统形成一个封闭的速度链。对于每个速度闭链,可直接在驱动轮轮心处写出从机器人各驱动轮到机器人本体之间的运动方程,将每个速度闭链的运动方程合并即可得到机器人的整体运动学模型。以一个具有被动柔顺机构的六轮全地形移动机器人为对象进行推导,该方法既考虑了地形不平的影响,又考虑了车轮的前向、侧向及转向滑移,已知机构参数后就可以直接写出机器人的速度方程,且便于运动学求解。该方法对于轮式移动机器人的运动学建模具有一般性,且具有物理意义明确、推导过程简洁等特点。

轮式移动仿人机器人的动力学建模与分析

利用高效迭代牛顿-欧拉方法对一个21自由度的轮式移动仿人机器人进行了整体动力学建模,该模型虽然维数较高,但消除了分块建模中需要对模块之间相互作用力进行建模的难点问题,并且由于机器人双臂的对称结构,当合理规划双臂运动时,动力学模型将得到部分简化。本文还对某关节运动时在各个关节所产生的力或力矩进行了仿真分析。解析及仿真结果表明,合理规划上臂各关节的协调运动,将极大地削弱车体及腰部各关节所受的力或力矩扰动,为基于动力学的机器人运动控制以及稳定性分析提供理论依据。

大型铰接并联六维测力平台摩擦建模

在已有制造工艺及标定技术基础上,为进一步改善大型铰接并联六维测力平台的测量精度,本文基于螺旋理论和影响系数原理,引入符号函数建立了Stewart结构大型铰接六维测力平台的摩擦模型。文中提出了关节摩擦对铰接并联六维测力平台测量精度的影响矩阵及I、H类误差表达式,绘制了在不同外载和关节摩擦系数条件下,六维测力平台的I、II类误差曲线,并总结丁关节摩擦和平台自重对测力平台测量精度的影响规律。为具有普通球形铰链人型Stewart平台六维测力下台精度的提高和改善提供了理论基础。

小型爬壁机器人系统设计与应用

针对一种小型的双足爬壁机器人,设计开发了基于DSP2812处理芯片的控制系统.该机器人系统采用双足真空吸盘式结构和用3个电机驱动5个关节的欠驱动结构.双足真空吸盘式结构使其可以在光滑的墙面和天棚行走,又能够在交接面之间完成跨步行走.而欠驱动结构减少了电机的数目,从而减小了机器人的尺寸和降低了机器人的质量和能量消耗,但它也给机器人的控制和运动规划带来了新的挑战.已完成的系统设计包括运动模式设计、关节控制、通信模块设计和吸盘足控制等.实验结果证明了所提出方案的可行性.

基于循环抑制CPG模型控制的蛇形机器人三维运动

具有三维运动能力和独特的节律运动方式,使生物蛇能在复杂的地形环境中生存.大多数动物节律运动是由中央模式发生器(Centralpatterngenerator,CPG)控制的.以此为理论依据,首次以循环抑制建模机理构建蛇形机器人组合关节运动控制的CPG模型.证明该模型是节律输出型CPG中微分方程维数最少的.采用单向激励方式连接该类CPG构建蛇形机器人三维运动神经网络控制体系,给出该CPG网络产生振荡输出的必要条件.应用蛇形机器人动力学模型仿真得到控制三维运动的CPG神经网络参数,利用该CPG网络的输出使“勘查者”成功实现三维运动.该结果为建立未探明的生物蛇神经网络模型提供了一种全新的方法.

塑料压力管道热板焊接接头瞬时应力有限元分析

基于热粘弹性积分型本构关系,考虑材料性能依赖于温度变化及相变潜热的影响,利用有限元软件ANSYS热-力耦合及载荷步功能模拟结晶型高密度聚乙烯塑料压力管道热板焊接过程。并对焊接接头的应力分布进行有限元分析,得到了环向、轴向及径向瞬态应力分布规律。采用盲孔法和锯切法测量焊后残余应力,实测结果与数值分析基本吻合。

模块化变形机器人非同构构形表达与计数

提出一种新型链式可重构模块机器人平台,该机器人平台具有手动可重构和自动变形的特点,介绍一种三模块变形机器人样机。组成机器人的单个模块可以简化为由模块本体、连接臂和偏置关节组成。模块的数量可以根据实际工作的需要进行选择,模块间的连接具有规则连接和非规则连接两种方式;同时,由连接模块的偏置关节的运动,模块间的相对位置可以改变。由于模块连接方式的不同和模块间相对位置的变化,变形机器人具有多种非同构构形;为此,根据模块的物理结构和邻接关系提出了用构形矩阵来表达机器人结构的拓扑信息,并在仿真环境下进行等效描述;提出基于组合计数原理的递归算法,用于多模块变形机器人的非同构构形的计数,并根据构形矩阵的拓扑信息对构形进行评价。最后根据仿真结果给出了一种三模块变形机器人样机对称构形的设计示例,验证了算法的可行性。