基于动力学约束的机械臂最优关节轨迹规划

本文提出了基于机械臂关节驱动力矩约束方程规划其关节最优运动轨迹的一种有效方法.该方法运用矩阵范数理论简化机械臂的动力学约束方程;在机械臂的关节空间内采用归一化的无因次量运用非线性规划法优化其运动轨迹.将所规划的无因次量轨迹方程作为机械臂产生实际运动轨迹的发生器,通过给定机械臂各运动段的起始和终止关节坐标,由系统的动力学约束方程计算出整个运动段所允许的最短运行时间,即生成所期望的运动轨迹.本文的轨迹规划方法计算效率高,可用于在线轨迹规划,文中通过算例证实了该方法的实用性.     

基于轨迹规划的平面三连杆欠驱动机械臂位置控制

针对中间关节为欠驱动的二阶非完整平面三连杆机械臂,提出一种基于轨迹规划的末端点位置控制策略.首先,建立系统的动力学模型,并根据几何关系利用差分进化算法求取所有连杆与目标位置相对应的目标角度;然后,根据驱动关节与欠驱动关节的耦合关系,采用时间缩放法和双向法分别规划两根驱动连杆的两条轨迹,并利用遗传算法优化合适的第1连杆中间位置,将两条轨迹拼接成一条完整可达轨迹;最后,设计滑模变结构控制器以跟踪完整可达轨迹,实现系统从初始位置到目标位置的控制目标.数值仿真结果表明了所提出控制策略的有效性.     

针对串联弹性驱动器抖动抑制的轨迹规划和跟踪控制

针对串联弹性驱动器（Series elastic actuator,SEA）的位置控制问题,本文提出了一种"规划+控制"的策略.首先根据连杆端运动学约束方程,基于数字滤波器对电机位置进行轨迹规划;为了使电机能够准确跟踪期望轨迹,根据电机端的动力学模型设计位置跟踪控制器.理论分析证明了规划的抖动抑制作用和跟踪控制系统的稳定性,随后的实验结果也表明了这种"规划+控制"方法在使连杆到达期望位置的前提下,能够有效地抑制残余抖动.     

基于改进动态运动基元的6D轨迹规划

动态运动基元(DMPs)轨迹规划方法可以简化机械臂控制中参数调整的复杂过程,快速生成运动轨迹,但是面对姿态的流形特性以及跨零点情况,现有的DMPs很难达到预期的效果.本文提出了一种基于改进DMPs的笛卡尔空间6D轨迹规划方法.该方法采用四元数描述姿态,实现了位置轨迹与姿态轨迹的无奇异表示.通过解耦强迫函数与起–终点状态差值项之间的关联,消除了跨零点引起的轨迹抖动、无法生成与翻转等问题.此外,基于机械臂和障碍物间的距离与偏角建立了虚拟阻抗关系,并将其耦合到动力学模型中,实现了机械臂末端的避障控制,避免了避障行为过早问题,有利于减少消耗.机械臂6D轨迹规划仿真和实验表明,本文提出的改进DMPs方法有效.     

基于三步法的机械臂轨迹跟踪控制

考虑机械臂末端轨迹跟踪控制问题,以跟踪逆运动学求解出的末端期望轨迹对应的各关节期望角度为控制目标.设计了一种基于三步法的控制器,该控制器由类稳态控制、可变参考前馈控制和误差反馈控制3部分组成.证明了该控制器可以通过控制机械臂的各关节力矩实现各关节实际角度对期望角度的状态跟踪,进而使得末端轨迹渐近跟踪期望轨迹,并且跟踪误差是输入到状态稳定的.仿真表明基于三步法控制器的空间机械臂末端可以渐近跟踪期望轨迹,并且该算法可以克服系统的末端负载质量变化等不确定性的影响.     

一种直接基于摆角约束的欠驱动桥式吊车轨迹规划方法

针对非线性桥式吊车系统,本文提出了一种新颖的基于摆角约束的轨迹规划方法.为了提高运送过程的效率和安全性,论文设计了期望轨迹以实现如下优点: 1)使台车很快到达目标位置; 2)将负载摆角抑制到可接受的范围之内; 3)当负载在目标位置停止时无残余摆动.具体而言,所设计的轨迹由三个阶段构成,每一阶段均根据抗摆和零残余摆角的要求来构造摆角曲线,在此基础上,利用桥式吊车的非线性运动学方程分析得到台车轨迹.论文引入了一种优化机制对运送时间,最大摆角等指标进行折衷考虑.文中通过仿真和实验结果表明了所设计的直接基于摆角约束的轨迹规划方法的性能.     

接触作业型飞行机械臂系统的力/位置混合控制

针对飞行机械臂系统移动接触作业问题,使用了一个力/位置混合控制框架,用以控制飞行器系统持续可靠地接触外部环境同时保持一定大小的接触力,并实现在接触过程中的期望轨迹跟踪.首先将作业空间分成2个子空间--约束空间和自由空间,并分别进行力控制和位置控制.对于力控制问题,证明闭环无人机系统是一个类弹簧-质量-阻尼系统,然后在约束子空间中设计逆动力学控制器来实现接触力控制.自由飞行空间中的运动控制依靠轨迹规划和位置控制器来实现.最后,开发了基于六旋翼飞行机器人的单自由度飞行机械臂系统,在飞行状态下进行接触墙面并跟踪倾斜直线轨迹的实验.结果显示本文所使用方法能够保证在平稳移动的同时控制期望的接触力.     

垂直三连杆欠驱动机械臂通用控制策略设计

本文针对一类含单一欠驱动关节的垂直三连杆欠驱动机械臂提出一种基于振荡衰减轨迹的通用控制策略. 与传统的分区控制策略相比, 本文控制策略无需采用分区方式就能快速地实现将机械臂末端点由垂直向下初始位 置开始移动, 并最终稳定在垂直向上目标位置的控制目标. 首先, 根据驱动连杆的初始和目标状态, 为驱动连杆规划 含可调参数的振荡衰减轨迹. 该轨迹能够在一定调节时间内将驱动连杆直接由初始状态移动至目标状态. 基于连 杆状态间的耦合关系, 利用粒子群优化算法优化轨迹参数使欠驱动连杆在相同调节时间内也运动至目标状态. 接 着, 利用滑模方法设计跟踪控制器使驱动连杆跟踪优化后的振荡衰减轨迹, 这样, 系统末端点将由初始位置移动至 目标位置. 进一步利用极点配置方法设计镇定控制器克服重力的作用将末端点稳定在目标位置. 最后, 通过仿真实 验验证所提控制策略的有效性.     

结合IMask R-CNN的绳驱机械臂视觉抓取方法研究

绳驱超冗余机械臂具有灵活性强、工作空间大等特点,在航天活动中可替代宇航员进行各种航空作业.以空间飞行器在轨维修为研究背景,模拟其实验环境,设计了一套基于RGB-D的可移动绳驱超冗余机械臂定位抓取系统.首先改进了Mask R-CNN算法,在保证检测精度的同时降低模型尺寸,通过Intel RealSense D435 i采集图像输入到目标检测模型得到目标的类别和位置信息,进一步利用自适应末端位置更新算法递推机械臂的正逆运动学模型,并结合轨迹规划完成目标的三维空间定位和抓取.实验结果表明,改进后的Mask R-CNN算法能在保证精度的情况下有效地降低模型尺寸,抓取系统的逆运动学求解速度快,具有较好的定位精度,能够有效地完成飞行器抓取的任务.     

基于干扰观测器的机械臂广义模型预测轨迹跟踪控制

为实现对多自由度机械臂关节运动精确轨迹跟踪,提出一种基于非线性干扰观测器的广义模型预测轨迹跟踪控制方法。针对机械臂轨迹跟踪运动学子系统,采用广义预测控制（Generalized Predictive Control,GPC）方法设计期望的虚拟关节角速度。对于机械臂轨迹跟踪动力学子系统,考虑机械臂的参数不确定性和未知外界扰动,利用GPC方法设计关节力矩控制输入,基于非线性干扰观测器方法实时估计和补偿系统模型中的不确定性。在李雅普诺夫稳定性理论框架下证明了机械臂关节角位置和角速度的跟踪误差最终收敛于零的小邻域。数值仿真验证了所提出控制方法的有效性和优越性。     

空间机器人抓捕目标后基于任务相容性的消旋策略

针对双臂空间机器人抓捕自旋目标后的镇定操作,在考虑机器人系统输入约束的条件下,提出了一种基于任务相容性的消旋规划与控制方法。首先,给出空间机器人抓捕目标后的组合系统的动力学模型,作为规划与控制的基础。然后,根据动力学可操作度和任务相容性设计了目标的快速消旋策略,其期望加速度的方向和大小分别取作速度的反方向和机器人系统输入约束允许的最大值。最后,基于所推导的运动学和动力学模型,通过对目标和机械臂末端分别建立柔顺度等式,提出了一种跟踪期望运动轨迹同时对末端接触力进行调节的柔顺控制方法。通过双臂7自由度空间机器人消除目标自旋运动的仿真结果,验证了所提方法的有效性。     

Boundary feedback stabilisation of a flexible robotic manipulator with constraint

In this paper, the flexible robotic manipulator is modelled as a distributed parameter system, represented by a group of partial differential equations and ordinary differential equations. Control is designed at the boundary of the robotic manipulator based on integral-barrier Lyapunov function to suppress the vibration of the elastic deflection and track the desired angular position. With the proposed boundary control, the manipulator can be driven to the desired set-point with angular position and elastic deflection stay under the former setting constraint. Uniformed boundedness of the closed-loop system under the unknown time-varying disturbance is achieved. Stability analysis of the closed-loop system is given by employing the Lyapunov stability theory. Simulation results illustrate the effectiveness of the proposed boundary controller for ensuring output constraint and suppressing vibrations.     

多移动机械臂系统动力学建模以及稳定性分析

随着社会生产力的发展和发展需求的提高,移动机械臂凭借着自身优势,受到学术界和工业界的广泛关注.但在许多工作场景下,单个移动机械臂有着自由度数以及载荷的限制,无法顺利完成任务.为了更好地满足任务需求,多移动机械臂系统应运而生.在上述工业背景下,本文建立了多移动机械臂系统的动力学模型,并针对该动力学方程进行了稳定性分析.首先通过拉格朗日方程建立单个移动机械臂的动力学方程,将多体动力学软件仿真结果同动力学模型数值计算结果进行对比,验证了模型的正确性.随后联立多个移动机械臂的动力学方程和操作对象的动力学方程,得到封闭形式的多移动机械臂系统的动力学方程.再利用关节位置误差和速度误差设计李雅普诺夫函数,通过反步法获得了关节力矩的控制律.最后在多体动力学软件仿真中,察看轨迹是否能跟踪上期望信号来检验控制律的有效性.     

Stability and control aspects of flexible link robot manipulators during constrained motion tasks

The effect of robotic manipulator structural compliance on system stability and trajectory tracking performance and the compensation of this structural compliance has been the subject of a number of publications for the case of robotic manipulator noncontact task execution. The subject of this article is the examination of dynamics and stability issues of a robotic manipulator modeled with link structural flexibility during execution of a task that requires the robot tip to contact fixed rigid objects in the work environment. The dynamic behavior of a general n degree of freedom flexible link manipulator is investigated with a previously proposed nonlinear computed torque constrained motion control applied, computed based on the rigid link equations of motion. Through the use of techniques from the theory of singular perturbations, the analysis of the system stability is investigated by examining the stability of the “slow” and “fast” subsystem dynamics. The conditions under which the fast subsystem dynamics exhibit a stable response are examined. It is shown that if certain conditions are satisfied a control based on only the rigid link equations of motion will lead to asymptotic trajectory tracking of the desired generalized position and force trajectories during constrained motion. Experiments reported here have been carried out to investigate the performance of the nonlinear computed torque control law during constrained motion of the manipulator. While based only on the rigid link equations of motion, experimental results confirm that high-frequency structural link modes, exhibited in the response of the robot, are asymptotically stable and do not destabilize the slow subsystem dynamics, leading to asymptotic trajectory tracking of the overall system. © 1992 John Wiley & Sons, Inc.     

Adaptive control of free-floating space manipulators using dynamically equivalent manipulator model

In this paper, adaptive control of free-floating space manipulators is considered. The dynamics based on the momentum conservation law for the free-floating space manipulator has non-linear parameterization properties. Therefore, the adaptive control based on a linear parameterization model cannot be used in this dynamics. In this paper, the dynamics of the free-floating space manipulator system are derived using the Dynamically Equivalent Model (DEM) approach. The DEM is a fixed-base manipulator system and allows us to linearly parameterize the dynamic equations. Using this linearly parameterized dynamic equation, an adaptive control method is developed to control the system in joint space. Parameter identification and torque calculations are done using the DEM dynamics. Simulations show that the tracking errors of the manipulator joints to a given desired trajectory become zero when the calculated torques act on the joints of the space manipulator system.     

快速连续反应-避障作业环境下的七自由度灵巧臂轨迹规划

人类经长期学习训练后能对高速物体 (如棒球、乒乓球等)具有快速连续反应作业的运动技能, 从深层次上揭示是由于人体在其训练过程中不断学习优选了相应手臂的动作轨迹, 并储存了丰富的经验和知识. 受人体手臂动作此行为机制启发, 本文提出一种 7-DOF灵巧臂快速连续反应-避障作业的轨迹规划方法. 该方法将灵巧臂对高速物体目标作业的轨迹规划问题转化为动作轨迹参数化优选问题, 考虑作业过程中灵巧臂的机构物理约束和障碍约束条件, 以灵巧臂目标可作业度指标构建适应度函数, 采用粒子群优化 (Particle swarm optimization, PSO)方法优选作业轨迹中的冗余参数; 在此基础上 利用灵巧臂动作轨迹参数化优选方法构建相应作业环境下的知识数据库, 实现灵巧臂对高速物体目标的快速连续反应作业. 以仿人机器人乒乓球对弈作业为例, 将该方法应用于 7-DOF灵巧臂乒乓球作业的轨迹规划中. 数值实验及实际对弈试验结果表明, 该方法不仅能使灵巧臂所规划的轨迹 满足灵巧臂机构物理约束与障碍约束条件, 同时能实现灵巧臂对乒乓球体的快速连续反应作业, 验证了该方法的有效性.     

Inverse cartesian trajectory control and stabilization of a three-axis flexible manipulator

This article treats the question of end point trajectory control of a flexible manipulator based on the nonlinear inversion technique. The manipulator has two rigid links and the third link is elastic. A parameterization of the Cartesian coordinates of a point close to the end effector position is suggested. Using these coordinates as output variables, an inverse feedback control law is derived for tracking reference Cartesian trajectories. The stability of the zero dynamics associated with the end point motion control is examined. It is shown that inverse control of the end point causes divergent oscillatory flexible modes. In addition, for regulating the end point to a fixed position, a linear stabilizer is designed to damp the elastic vibration. Simulation results are presented to show that in the closed-loop system, reference end point trajectories can be accurately followed in spite of the parameter uncertainty in the arm dynamic model. © 1994 John Wiley & Sons, Inc.     

Sliding mode force,motion control,and stabilization of elastic manipulator in the presence of uncertainties

This article considers the question of position and force control of three-link elastic robotic systems on a constraint surface in the presence of robot parameter and environmental constraint geometry uncertainties. The approach of this article is applicable to any multi-link elastic robot. A sliding mode control law is derived for the position and force trajectory control of manipulator. Unlike the rigid robots, sliding mode control of an end point gives rise to unstable zero dynamics. Instability of the zero dynamics is avoided by Controlling a point that lies in the neighborhood of the actual end point position. The sliding mode controller accomplishes tracking of the end-effector and force trajectories on the constrained surface; however, the maneuver of the arm causes elastic mode excitation. For point-to-point control on the constraint surface, a stabilizer is designed for the final capture of the terminal state and vibration suppression. Numerical results are presented to show that in the closed-loop system position and force control is accomplished in spite of payload and constraint surface geometry uncertainty. © 1995 John Wiley & Sons, Inc.