基于Canfield型关节的蛇形机器人运动仿真研究

应用虚拟机器人实验平台(V-REP)构建了一种基于Canfield关节型的运动机构,通过动力学仿真添加关节角度约束对其运动空间轨迹进行了观察与分析。利用该Canfield型机构作为关节模块组建成了蛇形机器人,并对该类蛇形机器人关节运动生成的蜿蜒、转弯和伸缩步态进行了实验研究和分析,为该类蛇形机器人设计提供了可行性。     

基于幅值调整法的蛇形机器人避障研究

设计了蛇形机器人及其双向被动轮地面接触机构,给出了相应模块单元工程实现的技术路线,测试了该机器人系统在具体环境中应用蛇形曲线公式参数α完成蜿蜒运动的性能及结合幅值调整法实现转弯的功能.应用红外传感器来感知障碍物的几何特性.针对不同尺寸障碍物采用绕障蜿蜒运动行进策略或顺障蜿蜒运动行进策略实现避障功能.该工作为蛇形机器人实用化提供技术储备.     

蛇形机器人伸缩运动性能研究

为研究蛇形机器人常用的典型步态——伸缩运动的性能与不同摩擦系数环境的关系,分别用单向被动轮和双向被动轮设计正交串联蛇形机器人地面接触机构。通过蛇形曲线公式控制蛇形机器人垂直关节节律实现伸缩运动。通过实验得出了摩擦系数对单向被动轮和双向被动轮接触面型蛇形机器人伸缩运动步态的影响及对应的蛇形曲线参数的调节策略。     

多关节蛇形机器人的结构设计和运动实现

针对蛇形机器人整体研制的关键问题，包括材料选取、结构设计和运动实现等，研制了一种新型的多关节蛇形机器人。该蛇形机器人由11个二自由度正交关节构成，可在保证灵活性的同时实现三维高仿生运动。采用蛇形曲线设计了蛇形机器人的蜿蜒、蠕动和翻滚等基本步态，并进一步提出了改进的越障步态。同时，在V-REP软件中对蛇形机器人的步态进行运动仿真，比较了不同步态的运动轨迹和运动效率。最后，通过蛇形机器人样机步态实验，对步态模型中各个控制参数对蛇形机器人运动波形和运动速度的影响进行了分析，验证了蛇形机器人本体结构与控制系统的可靠性。研究结果对实现蛇形机器人的步态规划与运动控制具有重要的理论意义与实际指导价值。     

单向被动轮接触机构蛇形机器人的设计

为了使蛇形机器人能有效地爬坡执行任务,为一个蛇形机器人样机设计了一种新型的单向被动轮(UPW)接触机构。通过大量试验证明,该单向被动轮接触机构可以实现蛇形机器人坡面静止及坡面摆头探测任务,避免采用双向被动轮作为地面接触机构的蛇形机器人在坡面上因下滑而无法完成探测任务的缺陷。本研究为蛇形机器人实用化提供了技术储备。     

蛇形机器人抬头运动分析

蛇形机器人需要抬头运动来获得环境信息。本文将蛇形曲线的蜿蜒运动步伐函数作适当改进后应用到蛇形机器人的抬头运动中,实现了蛇形机器人的动态抬头规划,并建立了动力学方程,对抬头运动的动力学作了分析。对抬头过程中ZMP的分析证明了运动规划的有效性。最后用仿真和实验验证了所提出的理论。     

水下蛇形机器人的滑翔运动性能研究

结合水下滑翔机在海洋中的较强续航能力,以及蛇形机器人在水中的良好机动性能,研制了一种具有两者特性的新型水下滑翔蛇形机器人,它具有水下滑翔机续航时间长、航行距离远,以及水下蛇形机器人机动性强、运动灵活的运动特性。对该水下滑翔蛇形机器人的滑翔运动性能进行了试验研究。首先对水下滑翔蛇形机器人的运动原理及关节结构进行了设计分析,其次对机器人的硬件及控制系统进行了结构分析,而且根据动量定理和动量矩定理,对机器人的滑翔运动方程进行了推导,并化简到垂直平面。最后对平衡状态进行了仿真分析,对机器人的运动能力进行了试验验证。试验结果验证了水下滑翔蛇形机器人机构的有效性。     

蛇形机器人的设计及摩擦力对其运动性能影响的分析

为使蛇形机器人的结构和运动形式能够适应各种复杂环境,研究了蛇形机器人运动性能与环境的关系及其运动控制,设计了一种单被动轮为接触面的正交串联蛇形机器人,分析了蛇形曲线参数对其运动的影响,通过实验研究了摩擦系数对其运动步态的影响,得出了蛇形机器人的前行速率随蛇形曲线参数α的增大而增大,随摩擦系数μ的增大而减小的结论,以及蛇形曲线步态参数的调节策略。     

一种装箱作业并联机器人机构的运动性能

目的针对目前食品、药品等装箱作业要求,将一种新型二自由度平面并联机器人用于装箱生产线的作业机构,并对其进行运动性能研究,确定其能否满足生产要求。方法对并联机构进行运动学分析,建立并联机器人的雅可比矩阵,利用几何法求解位置正、逆解;引入稳定性、运动分辨率和刚度性能指标,对机构进行运动性能分析,绘制稳定性和运动分辨率在工作空间内的性能分布图谱,研究机构在竖直方向上的刚度性能。结果该并联机构在实际装箱作业中的运动性能较为稳定,抓取或者放置物体阶段具有较高精度,且竖直方向的刚度较高。结论该新型二自由度平面并联机器人能够满足产品的装箱作业,在实际装箱作业中取得了广泛应用。     

基于相位调整法实现蛇形机器人避障功能的研究

为了提高蛇形机器人在实际环境中的实用性,研究了蛇形机器人的避障功能,并提出了一种基于相位调整的蛇形机器人避障方法。该方法用安装在蛇形机器人头部的红外避障传感器模块检测前方是否有障碍物,若有障碍物,则用相位调整法改变蛇形机器人每个关节的步态相位来控制蛇形机器人的蜿蜒运动以实现转弯,从而避开障碍物。而且应用红外传感器来感知障碍物的几何特性,若感知到大型障碍物,机器人蜿蜒运动行进采用顺障策略实现避障功能,若感知到小型障碍物,采用绕障策略。该研究可为推进蛇形机器人的实用化提供技术储备。     

Mechanics of peristaltic locomotion and role of anchoring

Limbless crawling is a fundamental form of biological locomotion adopted by a wide variety of species, including the amoeba, earthworm and snake. An interesting question from a biomechanics perspective is how limbless crawlers control their flexible bodies in order to realize directional migration. In this paper, we discuss the simple but instructive problem of peristalsis-like locomotion driven by elongation–contraction waves that propagate along the body axis, a process frequently observed in slender species such as the earthworm. We show that the basic equation describing this type of locomotion is a linear, one-dimensional diffusion equation with a time–space-dependent diffusion coefficient and a source term, both of which express the biological action that drives the locomotion. A perturbation analysis of the equation reveals that adequate control of friction with the substrate on which locomotion occurs is indispensable in order to translate the internal motion (propagation of the elongation–contraction wave) into directional migration. Both the locomotion speed and its direction (relative to the wave propagation) can be changed by the control of friction. The biological relevance of this mechanism is discussed.     

Aquatic manoeuvering with counter-propagating waves: a novel locomotive strategy

Many aquatic organisms swim by means of an undulating fin. These undulations often form a single wave travelling from one end of the fin to the other. However, when these aquatic animals are holding station or hovering, there is often a travelling wave from the head to the tail, and another moving from the tail to the head, meeting in the middle of the fin. Our study uses a biomimetic fish robot and computational fluid dynamics on a model of a real fish to uncover the mechanics of these inward counter-propagating waves. In addition, we compare the flow structure and upward force generated by inward counter-propagating waves to standing waves, unidirectional waves, and outward counter-propagating waves (i.e. one wave travelling from the middle of the fin to the head, and another wave travelling from the middle of the fin to the tail). Using digital particle image velocimetry to capture the flow structure around the fish robot, and computational fluid dynamics, we show that inward counter-propagating waves generate a clear mushroom-cloud-like flow structure with an inverted jet. The two streams of fluid set up by the two travelling waves ‘collide’ together (forming the mushroom cap) and collect into a narrow jet away from the cap (the mushroom stem). The reaction force from this jet acts to push the body in the opposite direction to the jet, perpendicular to the direction of movement provided by a single travelling wave. This downward jet provides a substantial increase in the perpendicular force when compared with the other types of fin actuation. Animals can thereby move upward if the fin is along the bottom midline of the body (or downward if on top); or left–right if the fins are along the lateral margins. In addition to illuminating how a large number of undulatory swimmers can use elongated fins to move in unexpected directions, the phenomenon of counter-propagating waves provides novel motion capabilities for systems using robotic undulators, an emerging technology for propelling underwater vehicles.     

Biomimetic Locomotion of Electrically Powered “Janus” Soft Robots Using a Liquid Crystal Polymer

Oriented liquid crystal networks (LCNs) can undergo reversible shape change at the macroscopic scale upon an order–disorder phase transition of the mesogens. This property is explored for developing soft robots that can move under external stimuli, such as light in most studies. Herein, electrically driven soft robots capable of executing various types of biomimetic locomotion are reported. The soft robots are composed of a uniaxially oriented LCN strip, a laminated Kapton layer, and thin resistive wires embedded in between. Taking advantage of the combined attributes of the actuator, namely, easy processing, reprogrammability, and reversible shape shift between two 3D shapes at electric power on and off state, the concept of a “Janus” soft robot is demonstrated, which is built from a single piece of the material and has two parts undergoing opposite deformations simultaneously under a uniform stimulation. In addition to complex shape morphing such as the movement of oarfish and sophisticated devices like self‐locking grippers, electrically powered “Janus” soft robots can accomplish versatile locomotion modes, including crawling on flat surfaces through body arching up and straightening down, crawling inside tubes through body stretching and contraction, walking like four‐leg animals, and human‐like two‐leg walking while pushing a load forward.     

A Light‐Powered Ultralight Tensegrity Robot with High Deformability and Load Capacity

Traditional hard robots often require complex motion‐control systems to accomplish various tasks, while applications of soft‐bodied robots are limited by their low load‐carrying capability. Herein, a hybrid tensegrity robot composed of both hard and soft materials is constructed, mimicking the musculoskeletal system of animals. Employing liquid crystal elastomer–carbon nanotube composites as artificial muscles in the tensegrity robot, it is demonstrated that the robot is extremely deformable, and its multidirectional locomotion can be entirely powered by light. The tensegrity robot is ultralight, highly scalable, has high load capacity, and can be precisely controlled to move along different paths on multiterrains. In addition, the robot also shows excellent resilience, deployability, and impact‐mitigation capability, making it an ideal platform for robotics for a wide range of applications.     

基于GPS的蛇形机器人导航方法

将GPS技术应用于蛇形机器人自主运动控制。根据蛇形机器人的基本运动方式,针对其现有的前进、后退、近似角度转弯等运动特点,提出了一种适用于该种蛇形机器人的自主移动算法,即用蛇头运动的方向近似看作蛇体运动方向。通过仿真验证了该算法的有效性,能够使蛇形机器人自主地到达目标点。     

Autonomous Motility of Polymer Films

Adaptive soft materials exhibit a diverse set of behaviors including reconfiguration, actuation, and locomotion. These responses however, are typically optimized in isolation. Here, the interrelation between these behaviors is established through a state space framework, using Nylon 6 thin films in a humidity gradient as an experimental testbed. It is determined that the dynamic behaviors are a result of not only a response to but also an interaction with the applied stimulus, which can be tuned via control of the environment and film characteristics, including size, permeability, and coefficient of hygroscopic expansion to target a desired behavior such as multimodal locomotion. Using these insights, it is demonstrated that films simultaneously harvest energy and information from the environment to autonomously move down a stimulus gradient. Improved understanding of the coupling between an adaptive material and its environment aids the development of materials that integrate closed loop autonomous sensing, actuation, and locomotion.     

Existence of longitudinal waves in anisotropic poroelastic solids

In anisotropic fluid-saturated porous solids, four waves can propagate along a general phase direction. However, solid particles in different waves may not vibrate in mutually orthogonal directions. In the propagation of each of these waves, the displacement of pore–fluid particles may not be parallel to that of solid particles. The polarization for a wave is the direction of aggregate displacement of the particles of the two constituents of a porous aggregate. These polarizations, for different waves, are not mutually orthogonal. Out of the four waves in anisotropic poroelastic medium, two are termed as quasi-longitudinal waves. The prefix ‘quasi’ refers to their polarization being nearly, but not exactly, parallel to the direction of propagation. The existence of purely longitudinal waves in an anisotropic poroelastic medium is ensured by the stationary characters of two expressions. These expressions involve the elastic (stiffness and coupling) coefficients of a porous aggregate and the components of phase direction. Necessary and sufficient conditions for the existence of longitudinal waves are discussed for different anisotropic symmetries. Conditions are also discussed for the existence of the apparent longitudinal waves, i.e., the propagation of wave motion with the particle displacement parallel to the ray direction instead of the phase direction. A graphical solution of a numerical example is shown to check the existence of these apparent longitudinal waves for general directions of phase propagation.     

Forming and fracture limits of aluminium alloy

Abstract

Forming and fracture limits of an AA 3104-H19 aluminium alloy sheet were studied by hydraulic bulging and Marciniak type deep drawing and tensile tests. The alloy appeared to be highly anisotropic, exhibiting distinctly different fracture patterns in the rolling and transverse directions. The preferred fracture direction was transverse to the rolling direction. In the tensile test, samples loaded in the rolling direction failed transverse to the rolling direction, but in the transverse direction, the fracture was inclined at ～55° to the tensile axis. In some cases, two such competing fractures in the characteristic directions could be observed. Scanning electron microscopy studies revealed a typical ductile fracture pattern. The fracture occurred by shearing in the through thickness direction, and typical alternating shear lips in a direction inclined at ～45° to the through thickness direction could be observed. Forming limit diagrams for both rolling and transverse directions were determined from the experiments. The measured limit strains in uniaxial tension were predicted well by the modified Rice–Tracey theory, but in equibiaxial tension, the theory overestimated the fracture limit strains.     

一种改进的强约束拓扑自适应snake模型

针对灰度图像的二维提取以及运动图像的跟踪问题,本文提出一种强约束拓扑自适应snake模型.该方法采用正交网格对图像和snake曲线进行离散化,约束snake节点只能沿网格线从一个网格点运动到下一个网格点,从而简化了计算过程.通过节点拆分获得拓扑变换能力,自动检测和处理拓扑冲突.通过对模拟图像和临床医学图像进行目标边缘提取的实验,结果表明模型具有较强的目标捕捉能力、拓扑结构变换能力和较快的运算速度.     

Epidermis architecture and material properties of the skin of four snake species

On the basis of structural and experimental data, it was previously demonstrated that the snake integument consists of a hard, robust, inflexible outer surface (Oberhäutchen and β-layer) and softer, flexible inner layers (α-layers). It is not clear whether this phenomenon is a general adaptation of snakes to limbless locomotion or only to specific conditions, such as habitat and locomotion. The aim of the present study was to compare the structure and material properties of the outer scale layers (OSLs) and inner scale layers (ISLs) of the exuvium epidermis in four snake species specialized to live in different habitats: Lampropeltis getula californiae (terrestrial), Epicrates cenchria cenchria (generalist), Morelia viridis (arboreal) and Gongylophis colubrinus (sand-burrowing). Scanning electron microscopy (SEM) of skin cross sections revealed a strong variation in the epidermis structure between species. The nanoindentation experiments clearly demonstrated a gradient of material properties along the epidermis in the integument of all the species studied. The presence of such a gradient is a possible adaptation to locomotion and wear minimization on natural substrates. In general, the difference in both the effective elastic modulus and hardness of the OSL and ISL between species was not large compared with the difference in epidermis thickness and architecture.