Human-robot collaboration while sharing production activities in dynamic environment: SPADER system

Interactive robot doing collaborative work in hybrid work cell need adaptive trajectory planning strategy. Indeed, systems must be able to generate their own trajectories without colliding with dynamic obstacles like humans and assembly components moving inside the robot workspace. The aim of this paper is to improve collision-free motion planning in dynamic environment in order to insure human safety during collaborative tasks such as sharing production activities between human and robot. Our system proposes a trajectory generating method for an industrial manipulator in a shared workspace. A neural network using a supervised learning is applied to create the waypoints required for dynamic obstacles avoidance. These points are linked with a quintic polynomial function for smooth motion which is optimized using least-square to compute an optimal trajectory. Moreover, the evaluation of human motion forms has been taken into consideration in the proposed strategy. According to the results, the proposed approach is an effective solution for trajectories generation in a dynamic environment like a hybrid workspace.     

基于机器视觉的喷涂机器人轨迹规划与涂装质量检测研究综述

随着智能喷涂技术的快速发展,机器视觉在喷涂机器人系统中的研究和应用引起广泛关注,合理的喷涂轨迹能保障油漆厚度均匀、减少漆膜缺陷产生,并且融合涂装质量检测技术形成闭环的喷涂系统.鉴于此,针对机器视觉在喷涂机器人轨迹规划与涂装质量检测中的研究进行综述.首先,对喷涂系统在现代产品制造中的快速发展所面临的机遇、挑战和机器视觉技术进行介绍;然后,综述基于机器视觉技术的喷涂机器人轨迹规划和涂装质量检测的研究成果,对基于机器视觉的喷涂机器人轨迹规划方法,包括待喷涂工件的三维重建、基于点云数据的喷涂轨迹自动规划和基于视觉伺服的喷涂轨迹补偿进行分析和讨论,并重点介绍机器视觉在涂装质量检测中的应用与研究现状,从数据增强和模型选择两个方面,对不同任务中基于深度学习的涂装质量检测算法性能的改善提供潜在解决方案;最后,总结与展望机器视觉技术在喷涂机器人轨迹规划与涂装质量检测中的研究方法和思路,为喷涂系统朝着智能化、柔性化的方向发展提供参考.     

Profile error-oriented optimization of the feed direction and posture of the end-effector in robotic free-form milling

In robotic milling of free-form surfaces, most existing studies tried to reduce the profile errors by optimizing the robot stiffness. However, the stiffness could not directly and rigorously reflect the milling performance to some content, especially, when the significant influence of feed direction on the profile error was ignored for robotic milling of free-form surfaces with large curvatures. In order to solve these problems, direct optimization of the feed directions and end-effector postures is theoretically formulated to seek the solution of a new profile error-oriented optimization model. This model characterizes the profile error in relation to the robot deformation caused by cutting forces, called force-induced profile error. The force-induced profile error is calculated and reduced at each cutter contact point on the free-form surface by comprehensively considering robot stiffness, free-form surface features, feed directions and cutting forces for generating feed direction and posture of the end-effector. The surface is partitioned into multiple sub-regions, in each of which the principle for determining the initial feed direction is proposed to ensure the smooth milling without abrupt change of feed direction. Robotic milling process of the workpiece with saddle contour is experimented. Feed direction and posture of the end-effector are generated by the proposed method and the existing method for comparative studies. Measured profile errors and photographs of machined surface indicate that the developed method can greatly improve the milling performance.     

B-splines joint trajectory planning

This paper describes how B-splines can be used to construct joint trajectories for robot manipulators. The motion is specified by a sequence of Cartesian knots, i.e., positions and orientations of the end effector of a robot manipulator. For a six joint robot manipulator, these Cartesian knots are transformed into six sets of joint variables, with each set corresponding to a joint. Splines, represented as linear combinations of B-splines, are used to fit the sequence of joint variables for each of the six joints. A computationally very simple recurrence formula is used to generate the B-splines. This approach is used for the first time to establish the mathematical model of trajectory generation for robot manipulators, and offers flexibility, computational efficiency, and a compact representation.     

Image‐guided robotic navigation system for neurosurgery

This paper presents an image‐guided robotic navigation system for neurosurgery, which can be applied to the electro‐stimulation treatment of Parkinson's leisure, the biopsy of deep tumors, and haematoma evacuation. The system integrates a computer containing CT images for surgical planning, a magnetic tracking device for measuring the coordinates of the markers and surgical instruments, and a robot manipulator for guiding surgical instruments to the preplanned position and orientation. The computer display of brain anatomy offers a convenient tool for surgeons to diagnose brain diseases and to plan safe surgical paths, while the tracking device guides the robot manipulator to automatically move surgical instruments to the preplanned position and orientation. An experiment of using a skull model for simulating a robotic biopsy of brain tumor has been done to verify the performance of the robotic navigation system. The results show that the positioning accuracy of the robot relative to the tracker frame is only related to the positioning resolution of the robot manipulator and the positioning accuracy of the tracking device. In other words, the positioning accuracy of the robot manipulator does not affect the final positioning accuracy of the surgical instruments. Therefore, using a robot manipulator for precise surgical navigation is feasible and reliable. © 2000 John Wiley & Sons, Inc.     

考虑柔性关节的机械臂自适应运动控制策略研究

具有柔性关节的轻型机械臂因其自重轻、响应迅速、操作灵活等优点,取得了广泛应用;针对具有柔性关节的机械臂系统的关节空间轨迹跟踪控制系统动力学参数不精确的问题,提出一种结合滑模变结构设计的自适应控制器算法;通过自适应控制的思想对系统动力学参数进行在线辨识,并采用Lyapunov方法证明了闭环系统的稳定性;仿真结果表明,该控制策略保证了机械臂系统对期望轨迹的快速跟踪,具有良好的跟踪精度,系统具有稳定性。     

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.     

State Space Constrained Iterative Learning Control for Robotic Manipulators

Real‐life work operations of industrial robotic manipulators are performed within a constrained state space. Such operations most often require accurate planning and tracking a desired trajectory, where all the characteristics of the dynamic model are taken into consideration. This paper presents a general method and an efficient computational procedure for path planning with respect to state space constraints. Given a dynamic model of a robotic manipulator, the proposed solution takes into consideration the influence of all imprecisely measured model parameters, making use of iterative learning control (ILC). A major advantage of this solution is that it resolves the well‐known problem of interrupting the learning procedure due to a high transient tracking error or when the desired trajectory is planned closely to the state space boundaries. The numerical procedure elaborated here computes the robot arm motion to accurately track a desired trajectory in a constrained state space taking into consideration all the dynamic characteristics that influence the motion. Simulation results with a typical industrial robot arm demonstrate the robustness of the numerical procedure. In particular, the results extend the applicability of ILC in robot motion control and provide a means for improving the overall trajectory tracking performance of most robotic systems.     

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.     

机器人操作臂跟踪动态目标的轨迹规划方法

针对机器人操作臂跟踪运动目标问题,提出一种基于遗传算法的轨迹规划方法。通过对关节加速度的增量进行编码,实现在操作臂的关节空间进行轨迹优化,得到操作臂在跟踪运动目标过程中所需要的轨迹。仿真计算的结果表明,所提出的方法是有效的。     

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.     

基于学习方法的机器人轨迹控制的实现

本文针对机器人周期性重复劳动的运动轨迹控制,提出了一种基于 PID 调节器型的学习控制方法.本文首先给出了线性时变系统学习控制方法的稳定性条件,并导出了非线性机器人系统的迭代学习方法.此方法结构简单,计算量小,便于实时控制.最后就 PUMA-560的前三关节机械手的轨迹控制作了仿真研究.结果表明,随着学习次数的增加,机械手的实际运动轨迹将收敛于期望轨迹.     

Sensor-based force decouple controller design of macro–mini manipulator

A robotic polishing system includes a force-controlled end-effector (mini manipulator) and a position-controlled industrial robot (macro manipulator). This combination mode has a fast response and a large workspace. However, the force-controlled axis component of the macro motions and the geometric of the workpiece surfaces will affect the contact force response rate and tracking accuracy due to the coupling dynamics between the macro and mini, limiting system performance. A new dynamic decoupling method employing dual force sensors (DFSs) is proposed to address these problems. One of the force sensors installed between the endpoint of the macro and the fixed platform of the mini realizes the dynamic decoupling of the macro and mini. The other one is added at the endpoint of the mini to obtain the interaction force in contact with the environment and feed it back to the control loop. When the disturbances produced by the macro trajectories and the uncertainties coming from the workpiece are introduced into the system, the proposed method can improve force response rate and tracking accuracy without knowing the dynamic models and parameters of the macro and the geometric of the workpiece surface. Several experiments are carried out under various conditions. Experimental results indicate that the contact force response rate and tracking error of DFSs are better than those of the conventional force-controlled and impedance matching methods, proving the proposed method’s effectiveness. In addition, the last comparison experiment verifies that the DFSs method applies to different kinds of end-effectors with various dynamics.     

Clock-turning gait synthesis for humanoid robots

Turning gait is a basic motion for humanoid robots. This paper presents a method for humanoid tuming, i.e. clock-turning. The objective of clock-turning is to change robot direction at a stationary spot. The clock-turning planning consists of four steps： ankle trajectory generation, hip trajectory generation, knee trajectory generation, and inverse kinematics calculation. Our proposed method is based on a typical humanoid structure with 12 DOFs （degrees of freedom）. The final output of clock-turning planning is 12 reference trajectories, which are used to control a humanoid robot with 12 DOFs. ZMP （zero moment point） is used as stability criterion for the planning. Simulation experiments are conducted to verify the effectiveness of our proposed clock-turuing method.     

三维可视化的喷涂机器人离线轨迹规划系统

传统的喷涂机器人采用人工示教的方式生成喷涂轨迹,该方法依赖工人经验,规划时间长,且不能产生最佳轨迹。为克服这些缺陷,提高喷涂机器人的喷涂质量与喷涂效率,文中通过对喷涂机器人喷涂过程建模、喷涂路径规划、喷涂过程仿真进行深入的研究与分析,建立了喷涂机器人离线轨迹规划与仿真系统整体框架。在此基础上,采用MFC和OpenGL开发了完整的离线轨迹规划与仿真系统,该系统能够针对不同的工件生成正确的轨迹,并能够进行三维可视化的仿真及效果显示。     

Task-oriented programming of large redundant robot motion

Large robots are a new domain of advanced robotics. Examples of their application fields are tasks like operations on large free-form surfaces, especially aircraft cleaning and removing paint from hulls. They are equipped with a programmable robot control comparable to a control system used for industrial robots. However, conventional teach-in methods are not able to manage the complexity of programming large redundant robot operation on free-form geometries. The Fraunhofer IPA has developed an innovative off-line programming system that allows the creation of robot motion programs which satisfy time and energy optimization criteria. This system helps to avoid collisions within the workspace and to fulfill conditions that arise from the robot kinematics and dynamics. This advanced programming system has been successfully used to generate motion programs for the world's largest mobile robot, the aircraft cleaning manipulator SKYWASH. In this context offline programs for eleven different types of aircraft have been developed.     

Optimal robot placement with consideration of redundancy problem for wrist-partitioned 6R articulated robots

Rapid set-up of robotic system is critical for realising the high-mix low-volume applications. This paper presents an efficient method to determine the optimal robot base placement for executing required end-effector trajectories while dealing with redundancy problem for wrist-partitioned 6 R articulated robots. The main feature of the method includes the integration of two multi-objectives optimization loops that involve parameterized inverse kinematics of the robot to find the proper robot configurations. Firstly, an optimization scheme is introduced in consideration of all the robot and operational constraints including reachability, singularity avoidance, and collision avoidance. Then, a redundancy resolution scheme is proposed based on a modified particle swarm optimization (MPSO) for the considered target point. Consequently, the optimal robot base placement is obtained via another optimization loop which includes all robot trajectories for the application. The method was applied in a complex robotic welding application. For a set of desired welding torch trajectories on the workpiece, the optimal robot base placement is computed within a few minutes.     

Time-varying isobaric surface reconstruction and path planning for robotic grinding of weak-stiffness workpieces

Severe deformations and vibration usually occur when grinding the weak-stiffness workpieces, then fluctuate the grinding force and damage the surface. In this paper, the time-varying isobaric surface (TVIS) is defined as a virtual surface to generate constant force during robotic grinding. Based on it, a novel robotic grinding method, including contact trial and surface reconstruction, is proposed. In the contact trial process, the robot actively samples the deformation and stiffness of contact point with a force sensor. Then, a TVIS mesh is constructed to replace the original geometry of the workpiece, which is utilized for grinding path planning. Experiments have been conducted to verify the feasibility of this method. The result shows that the proposed method can achieve constant grinding force and is robust to the types of workpieces and the processing techniques. Furthermore, it is considered as an intelligent method for customized robotic machining of the weak-stiffness workpieces.     

面向机械臂轨迹规划的强化学习奖励函数设计

针对基于深度强化学习的机械臂轨迹规划方法学习效率较低,规划策略鲁棒性差的问题,提出了一种基于语音奖励函数的机械臂轨迹规划方法,利用语音定义规划任务的不同状态,并采用马尔科夫链对状态进行建模,为轨迹规划提供全局指导,降低深度强化学习优化的盲目性。提出的方法结合了基于语音的全局信息和基于相对距离的局部信息来设计奖励函数,在每个状态根据相对距离与语音指导的契合程度对机械臂进行奖励或惩罚。实验证明,设计的奖励函数能够有效地提升基于深度强化学习的机械臂轨迹规划的鲁棒性和收敛速度。     

双连杆刚柔机械臂无残余振动位置控制

针对双连杆刚柔机械臂,提出一种基于轨迹规划的无残余振动位置控制方法,在将机械臂的末端执行器从任意初始位置移动到目标位置的同时,确保系统没有残余振动产生.首先,建立系统的动力学模型,并通过分析该模型得到系统的状态约束方程.其次,基于状态约束方程,运用双向轨迹规划方法规划一条系统前向轨迹和一条系统反向轨迹.然后,利用时间倒转方法及基于遗传算法的轨迹优化方法对两条轨迹进行拼合,得到一条从系统初始状态到目标状态的期望轨迹.最后,设计轨迹跟踪控制器使系统沿期望轨迹到达目标状态,实现系统的无残余振动位置控制目标.仿真结果验证了本文所提方法的有效性.