A low-complexity tracker design for uncertain nonholonomic wheeled mobile robots with time-varying input delay at nonlinear dynamic level

A low-complexity design problem of tracking scheme for uncertain nonholonomic mobile robots is investigated in the presence of unknown time-varying input delay. It is assumed that nonlinearities and parameters of robots and their bounds are unknown. Based on a nonlinear error transformation, a tracking control scheme ensuring preassigned bounds of overshoot, convergence rate, and steady-state values of a tracking error is firstly presented in the absence of input delay, without using any adaptive and function approximation mechanism to estimate unknown nonlinearities and model parameters and computing repeated time derivatives of certain signals. Then, we develop a low-complexity tracking scheme to deal with unknown time-varying input delay of mobile robots where some auxiliary signals and design conditions are derived for the design and stability analysis of the proposed tracking scheme. The boundedness of all signals in the closed-loop system and the guarantee of tracking performance with preassigned bounds are established through Lyapunov stability analysis. The validity of the proposed theoretical result is shown by a simulation example.     

Leaderless maneuver guidance and event-triggered formation control for distributed multi-space-robot systems

In this paper, the distributed displacement-based formation and leaderless maneuver guidance control problems of multi-space-robot systems are investigated by introducing event-triggered control update mechanism. A distributed formation and leaderless maneuver guidance control framework is first constructed, which includes two parallel controllers, namely an improved linear quadratic regulator and a distributed consensus-based formation controller. By applying this control framework, the desired formation configuration of multi-space-robot systems can be achieved and the center of leaderless formation can converge to the target point globally. Second, a pull-based event triggering mechanism is introduced to the distributed formation controller, which makes the control update independent of the events of neighboring robots, avoids unnecessary control updates, and saves the extremely limited energy of space robots. Furthermore, the potential Zeno behaviors have been excluded by proving a positive lower bound for the inter-event times. Finally, numerical simulation verifies the effectiveness of the theoretical results.

     

A robust-adaptive fuzzy coverage control for robotic swarms

In this paper, a decentralized adaptive control scheme for multi-robot coverage is proposed. This control method is designed based on centroidal Voronoi configuration integrated with robust adaptive fuzzy control techniques. We consider simple single integrator mobile robots used for covering dynamical environments, where an adaptive fuzzy logic system is used to approximate the unknown parts of control law. A robust coverage criterion is used to attenuate the adaptive fuzzy approximation error and measurement noises to a prescribed level. Therefore, the robots motion is forced to obey solutions of a coverage optimization problem. The advantages of the proposed controller can be listed as robustness to external disturbances, computation uncertainties, and measurement noises, while applicability on dynamical environments. A Lyapunov-function based proof is given of robust stability, i.e. convergence to the optimal positions with bounded error. Finally, simulation results are demonstrated for a swarm coverage problem simultaneous with tracking mobile intruders.     

Mobile robots with two independent coaxial drive wheels: Dynamics and the schemes of control

A two-wheeled robot and a robot composed of a snakelike chain of two-wheeled objects are considered. The problem of trajectory synthesis and the problem of motion planning and control are studied for these mobile robots. The mobile robots with two independently controlled coaxial wheels and with one or several passive wheels are called robots with differential drive. These problems are formulated in such a way that the construction of dynamically correct and precise control becomes possible for such robots.     

Adaptive fuzzy formation control for a swarm of nonholonomic differentially driven vehicles

In this paper, an adaptive fuzzy robust H ^∞ controller is proposed for formation control of a swarm of differential driven vehicles with nonholonomic dynamic models. Artificial potential functions are used to design the formation control input for kinematic model of the robots and matrix manipulations are used to transform the nonholonomic model of each differentially driven vehicle into equivalent holonomic one. The main advantage of the proposed controller is the robustness to input nonlinearity, external disturbances, model uncertainties, and measurement noises, in a formation control of a nonholonomic robotic swarm. Moreover, robust stability proof is given using Lyapunov functions. Finally, simulation results are demonstrated for a swarm formation problem of a group of six unicycles, illustrating the effective attenuation of approximation error and external disturbances, even in the case of robot failure.     

Output-feedback formation control of wheeled mobile robots with actuators saturation compensation

Nonlinear Dynamics - This paper addresses output-feedback formation control of a group of wheeled mobile robots with saturating actuators. A virtual leader–follower strategy and a...     

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.      

基于变形场不同离散方法的柔性机器人动力学建模与仿真

研究了基于变形场不同离散方法的柔性机器人动力学建模和仿真问题. 针对多杆空间链式柔性机器人系统,采用假设模态法、有限元法、Bezier 插值方法和B 样条插值方法对柔性杆变形场进行描述,构造统一形式,运用Lagrange 方法,结合4×4 齐次变换矩阵,在计入柔性杆横向弯曲变形引起的纵向缩短的情况下,推导得到多杆空间柔性机器人动力学方程,并编制基于4 种变形场不同离散方法的多杆空间链式柔性机器人仿真软件.通过仿真算例对柔性机器人系统的动力学问题进行研究. 仿真结果表明:有限元法的计算效率较低;假设模态法在处理较大变形问题时其精度低于Bezier 插值方法和B 样条插值方法的精度;作为新的变形体离散方法,Bezier 插值方法和B 样条插值方法可以有效地描述柔性杆的变形场,并能运用到多杆空间柔性机器人动力学建模中.      

室内惯性/视觉组合导航地面图像分割算法

导航技术是机器人实现自主移动的关键技术之一。针对惯性导航创建全局导航地图困难等问题,提出一种新的惯性/视觉组合导航室内全局地图创建方法。规定机器人只能在地面区域中移动,并利用室内俯视图像建立全局地图,提出一种俯视图像地面区域的自动分割算法。首先,利用主元分析算法对图像的局部颜色特征进行降维;其次,利用聚类算法对地面区域进行自动分割;最后,建立了室内俯视图像数据库并对算法的性能进行了验证。由于第四组图像中包含反光区域,算法的分割结果较差,平均正确分辨率为75%。算法在其他各组的平均正确分割率为85%左右。为提高算法的性能,可在应用本算法前利用反光区域检测算法对图像进行预处理。     

Framework of modelling concentric tube robot and comparison on computational efficiency

The continuum concentric tube robots (CCTRs) are infinite degree-of-freedom robots with elastic structure. The CCTRs have no distinct links/dedicated backbones and joints as the rigid-link robots and conventional continuum robots do. Their simple and flexible structure, along with the capability to be navigated actively, can benefit minimally-invasive surgical applications. However, modelling of the CCTRs is challenging due to the compliance of structure, and a significant number of frames involved. A framework is developed in this work, linking two modelling approaches. Furthermore, two variations of modelling approaches are derived by treating the key equations in different ways. The computational efficiencies of four modelling approaches are compared, in terms of the overall iteration time, number of iterations and the time for single iteration. The effect of iteration accuracy and step size on computational efficiency are investigated as well.     

软体机器人结构机理与驱动材料研究综述

软体机器人是一类新型机器人,具有结构柔软度高,环境适应性好,亲和性强,功能多样等特点,有着十分广阔的研究和应用前景. 智能材料在软体机器人结构设计及实际应用中扮演了重要的角色,其特殊的驱动机制极大拓展了软体机器人的功能. 介绍了软体机器人的发展和研究现状,按其应用场合及功能总结了几种典型的软体机器人. 从仿生机理的角度,介绍了蠕虫、弯曲爬行虫、鱼类游动等几类仿生运动机理以及其相应的软体机器人. 还按不同驱动类型将软体机器人归纳为气动、形状记忆合金、离子交换聚合物金属复合材料、介电高弹体、响应水凝胶、化学燃烧驱动等类型. 介绍了软体机器人的制作方法与工艺,分析了目前软体机器人研究的主要挑战,提出对未来研究的展望.      

The addendum for the generalized d'Alembert equations of motion

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Orientation-error observer-based tracking control of nonholonomic mobile robots

In this paper, a novel trajectory tracking controller is proposed for mobile robots with unknown orientation angle by employing the orientation-error observer (OEO). In order to overcome the local stability resulted from linearization design methods, an asymptotically stable controller is designed using Lyapunov’s direct method. This method breaks down nonlinear systems into low-dimensional systems and simplifies the controller design using virtual auxiliary error function and partial Lyapunov functions. A state-feedback controller for the nonlinear error dynamics of the mobile robot is combined with an observer that estimates the orientation-error based on available trajectory information and measurement of the position coordinates. The stability of the system is easily proved via the Lyapunov theory. Abundant simulation and experiment results validate the effectiveness and superiority of the proposed control method.     

Design of lightweight robots for over-snow mobility

Snowfields are challenging terrain for lightweight (<50 kg) ground robots. Deep sinkage, high snow-compaction resistance, traction loss while turning and ingestion of snow into the drive train can cause immobility within a few meters of travel. However, for suitably designed vehicles, deep snow offers a smooth, uniform terrain that can obliterate obstacles. Key requirements for good over-snow mobility are low ground pressure, large clearance relative to vehicle size and a drive system that tolerates moist, compactable snow.A small robot will invariably encounter deep snow relative to its ground clearance and thus must travel over the snow rather than gain support from the underlying surface. This can be accomplished using low-pressure tracks (<1.5 kPa). Even still, snow-compaction resistance can exceed 20% of vehicle weight. Also, despite relatively high traction coefficients for low track pressures, differential or skid steering is difficult because the outboard track can easily break traction as the vehicle attempts to turn against the snow. Short track lengths (relative to track separation) or coupled articulated robots offer steering solutions for deep snow.This paper presents guidance to design lightweight robots for good mobility over snow based on tests of two custom-designed over-snow robots, SnoBot and SnoBot-2, and driving experience with two commercially available robots, PackBot and Talon. Moreover, we used the present guidance to design SnoBot-2, and it displays excellent over-snow mobility. Because many other considerations constrain robot designs, this guidance can also help with development of winterization kits to improve the over-snow performance of existing robots.     

高自由度双足机器人数学模型及步行控制研究

基于ZMP理论及位姿矩阵,采用了相对重心以及相对坐标系的数学描述方法,对17自由度双足机器人步行稳定性控制进行数学建模研究．所建立的数学模型能够描述机器人稳定性控制．并经过Matlab数学计算和仿真研究,验证了所建立的模型可以描述双足机器人的步行规律,在理论上达到了双足机器人步行稳定性的控制目的．最后通过VC 把整个模型封装成一个可视化系统,便于将所研究的模型应用到实际的控制中,为未来机器人的实时控制的研究提供了技术支持．     

Connectivity-preserving adaptive synchronized tracking of heterogeneous spherical robots with limited communication ranges

A distributed connectivity-preserving problem is addressed for adaptive synchronized tracking of networked heterogeneous nonlinear spherical robots with a dynamic leader. We assume uncertain rolling resistances, limited communication ranges of robots, and that only a small fraction of follower robots have access to the time-varying leader information. Compared with the previous synchronized tracking scheme based on distributed hierarchical sliding surfaces (DHSSs) for multiple underactuated spherical robots, the main contribution of this paper is to present a new error transformation approach of DHSS for preserving the initial connectivity while achieving the synchronized tracking of longitudinal positions of all followers to the dynamic leader and the balance tracking of the swing-up angle of each follower to its swing-up balance angle under the limited communication ranges of robots. A local connectivity-preserving adaptive synchronized tracker is designed using the proposed DHSS with the estimate of the leader velocity and the swing-up balance angular velocity. In addition, we derive a technical lemma to analyze the asymptotic stability and the initial connectivity preservation of the overall closed-loop system in the Lyapunov sense.     

Distributed finite-time control for coordinated circumnavigation with multiple non-holonomic robots

Nonlinear Dynamics - The finite-time coordinated circumnavigation problem for multiple non-holonomic robots is investigated in this paper. All robots are required to be evenly circled a target, and...     

Control of manipulators and wheeled transport robots as systems of rigid bodies

Problems of control of robots (manipulators and wheeled transport robots) that are considered as controllable systems of rigid bodies with holonomic and nonholonomic constraints are reviewed. The basic problems that arise in designing systems of control of such facilities are considered. Namely, the equations of model motion are derived, a specified trajectory is parametrized, and a stabilization algorithm is synthesized (including linear, nonlinear, adaptive, and robust controllers). Some model examples are given to illustrate the efficiency of the algorithms considered. S.P. Timoshenko Institute of Mechanics, National Academy of Sciences of Ukraine, Kiev. Translated from Prikladnaya Mekhanika, Vol. 36, No. 4, pp. 35–67, April, 2000.     

软体智能机器人的系统设计与力学建模

机器人或机电装备通常由电机模组、液压元件、齿轮和铰链等硬质部件构成,具有动力足、精度高等优点,但在实现低噪声、高安全系数与亲和性等方面存在挑战.受自然界生物体的柔软特性与高环境适应性的启发,设计制造软体机器人是近年来机器人领域的研究热点.作为软体机器人的核心构成部分,智能软材料可在外界不同刺激下产生不同响应,具有材料柔韧、生物相容性好、易于制备、价格低廉等优点,可广泛应用于机器人的设计与制造.几类典型的具备驱动功能的智能软材料与结构获得广泛的研究,包括气动软体肌肉、形状记忆合金/聚合物、离子交换聚合物、介电高弹体、响应水凝胶等.本文介绍了多种驱动类型的软体智能机器人研究成果,并从软体智能机器人的系统设计与力学建模两个方面进行了归纳分析与讨论.      

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.