基于PH曲线的Delta机器人轨迹规划方法

针对Delta并联机器人高速作业时笛卡儿空间轨迹不平滑的问题,提出一种基于毕达哥拉斯速端曲线（PH曲线）的轨迹规划方法．首先,利用PH曲线平滑竖直运动与水平运动间的直角过渡部分,确定拾放操作轨迹;然后,利用多项式运动规律对轨迹的1维曲线位移进行规划,确定运动轨迹插补点的位置;最后,以最小化拾放操作周期为目标优化PH曲线参数,得到平滑的运动轨迹．仿真分析表明,基于该方法的拾放操作具有较短的运动周期,轨迹平滑且有较平稳的运动特性;实验结果表明,Delta机器人能够以90次/分钟的速度进行抓取操作,实现了并联机器人的高速作业．     

运行时间周期化工业机器人模型迭代寻优NURBS轨迹插补

为满足工业机器人高精度复杂曲线运动的需求,本文提出运行时间周期化工业机器人模型迭代寻优NURBS轨迹插补算法.首先,根据轨迹最大轮廓误差和机器人动力学特性对曲线分段.随后,提出优化回溯算法,使各子曲线段均可用S曲线加减速规划.之后,为保证机器人在进给速度极小值处不超速,将各加减速阶段运行时间调整为插补周期的整数倍,并对子曲线段衔接处速度平滑处理.最后,提出模型迭代寻优曲线插补,大大降低了速度波动率.仿真试验表明,该方法插补轨迹的各项指标均满足要求且最大速度波动率仅为0.000099%.真机试验也验证了该方法可有效减小轨迹误差.     

A novel cartesian trajectory planning method by using triple NURBS curves for industrial robots

This article presents a novel method of robot pose trajectory synchronization planning. First of all, based on triple NURBS curves, a method of describing the position and orientation synchronization of the robot is proposed. Then, through considering geometric and kinematic constraints, especially angular velocity constraint, and employing bidirectional interpolation algorithm, a robot pose trajectory planning approach is developed, which has limited linear jerk, continuous bounded angular velocity and approximate optimal time, and does not need an optimization program. Ultimately, two robot pose paths, blade-shaped curve and fan-shaped curve, are utilized for simulations, and the results indicate that the proposed trajectory planning method can satisfy the given constraint conditions, i.e. the linear jerk is limited and the angular velocity is continuous bounded. The trajectory tracking experiments are further carried out on a 6-DOF industrial robot, and the results show that the proposed planning method can generate smooth trajectories to ensure the stability of the robot motion without impact in practical situations.     

基于ROS的六自由度机械臂运动规划

针对传统机器人在复杂环境下的安全问题以及运动规划问题,采用开源机器人操作系统ROS搭建了机器人仿真平台,并进行运动规划。在ROS平台下,利用URDF文件完成机械臂3D建模;利用Movelt配置助手(setup assistant)配置机械臂模型并且生成启动文件。在Rviz中显示三维模型;利用Movelt完成对六自由度机械臂的运动规划,以及避障轨迹规划。结果表明,通过Rqt_plot导出机械臂运动过程中六个关节的位置关系信息,可为进一步改善和研究机械臂轨迹规划提供更加直观的方法。     

Vibration error-based trajectory planning of a 5-dof hybrid machine tool

This paper presents an approach for the trajectory planning of a hybrid machine tool based on vibration error, which aims at determining the optimal location and machining time of a given machining path. Firstly, an elastodynamic model of the hybrid robot is proposed by taking compliance of joints and limbs into account. Then, in order to evaluate vibration error in a typical machining path, two indices, i.e., the mean value and fluctuation of vibration error throughout the whole trajectory are proposed. Based on the Isight platform, sensitivity analysis is conducted. In addition, optimal trajectories are derived when adopting 3–4–5 polynomial and B-splines, respectively. Results show that the machining time and machining angle have important impacts on the mean value and fluctuation of vibration error. Especially, effects of the machining angle on the vibration error cannot be neglected. Comparison shows that adopting B-splines is conductive to decreasing the required torque and power. This paper provides a method on determining optimal machining location quickly for a given path throughout the whole workspace. The proposed method can be applied to trajectory planning of other hybrid robots or parallel kinematic machines.     

Smooth trajectory planning for a parallel manipulator with joint friction and jerk constraints

In order to achieve better tracking accuracy effectively, a new smooth and near time-optimal trajectory planning approach is proposed for a parallel manipulator subject to kinematic and dynamic constraints. The complete dynamic model is constructed with consideration of all joint frictions. The presented planning problem can be solved efficiently by formulating a new limitation curve for dynamic constraints and a reduced form for jerk constraints. The motion trajectory is planned with quartic and quintic polynomial splines in Cartesian space and septuple polynomial splines in joint space. Experimental results show that smaller tracking error can be obtained. The developed method can be applied to any robots with analytical inverse kinematic and dynamic solutions.     

Trajectory time scaling of a mobile robot to avoid dynamic obstacles on the basis of the INLVO

To ensure the collision safety of mobile robots, the velocity of dynamic obstacles should be considered while planning the robot’s trajectory for high-speed navigation tasks. A planning scheme that computes the collision avoidance trajectory by assuming static obstacles may result in obstacle collisions owing to the relative velocities of dynamic obstacles. This article proposes a trajectory time-scaling scheme that considers the velocities of dynamic obstacles. The proposed inverse nonlinear velocity obstacle (INLVO) is used to compute the nonlinear velocity obstacle based on the known trajectory of the mobile robot. The INLVO can be used to obtain the boundary conditions required to avoid a dynamic obstacle. The simulation results showed that the proposed scheme can deal with typical collision states within a short period of time. The proposed scheme is advantageous because it can be applied to conventional trajectory planning schemes without high computational costs. In addition, the proposed scheme for avoiding dynamic obstacles can be used without an accurate prediction of the obstacle trajectories owing to the fast generation of the time-scaling trajectory.     

提高柔性冗余度机器人动态特性的最小变形能法

冗余度柔性机器人的运动规划是机器人领域的重要前沿课题之一 .利用此机器人的冗余特性 ,可以改善其运动学和动力学性能 .柔性机器人的变形能能够很好地反映出其整体弹性变形程度 .本文提出了在最小变形能意义下的柔性冗余度机器人运动学规划的新方法 .以平面三柔性臂机器人为例进行了仿真 ,通过与最小末端误差意义下的规划策略进行比较 ,充分显示了最小变形能法在提高柔性机器人动态性能的有效性和优越性     

Toward a user-guided manipulation framework for high-DOF robots with limited communication

This paper presents our progress toward a user-guided manipulation framework for high degree-of-freedom robots operating in environments with limited communication. The system we propose consists of three components: (1) a user-guided perception interface that assists the user in providing task-level commands to the robot, (2) planning algorithms that autonomously generate robot motion while obeying relevant constraints, and (3) a trajectory execution and monitoring system which detects errors in execution. We report quantitative experiments performed on these three components and qualitative experiments of the entire pipeline with the PR2 robot turning a valve for the DARPA robotics challenge. We also describe how the framework was ported to the Hubo2+ robot with minimal changes which demonstrates its applicability to different types of robots.     

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.     

Joint stiffness identification of six-revolute industrial serial robots

Although robots tend to be as competitive as CNC machines for some operations, they are not yet widely used for machining operations. This may be due to the lack of certain technical information that is required for satisfactory machining operation. For instance, it is very difficult to get information about the stiffness of industrial robots from robot manufacturers. As a consequence, this paper introduces a robust and fast procedure that can be used to identify the joint stiffness values of any six-revolute serial robot. This procedure aims to evaluate joint stiffness values considering both translational and rotational displacements of the robot end-effector for a given applied wrench (force and torque). In this paper, the links of the robot are assumed to be much stiffer than its actuated joints. The robustness of the identification method and the sensitivity of the results to measurement errors and the number of experimental tests are also analyzed. Finally, the actual Cartesian stiffness matrix of the robot is obtained from the joint stiffness values and can be used for motion planning and to optimize machining operations.     

Feedrate planning for machining with industrial six-axis robots

Nowadays, the adaptation of industrial robots to carry out high-speed machining operations is strongly required by the manufacturing industry. This new technology machining process demands the improvement of the overall performances of robots to achieve an accuracy level close to that realized by machine-tools. This paper presents a method of trajectory planning adapted for continuous machining by robot. The methodology used is based on a parametric interpolation of the geometry in the operational space. FIR filters properties are exploited to generate the tool feedrate with limited jerk. This planning method is validated experimentally on an industrial robot.     

A parallel approach of the inverse kinematics solutions for robots using a transputer network

This article presents a parallel method for computing inverse kinematics solutions for robots with closed-form solutions moving along a straight line trajectory specified in Cartesian space. Zhang and Paul's approach¹ is improved for accuracy and speed. Instead of using previous joint positions as proposed by Zhang and Paul, a first order prediction strategy is used to decouple the dependency between joint positions, and a zero order approximation solution is computed. A compensation scheme using Taylor series expansion is applied to obtain the trajectory gradient in joint space to replace the correction scheme proposed by Zhang and Paul. The configuration of a Mitsubishi RV-M1 robot is used for the simulation of a closed-form inverse kinematics solutions. An Alta SuperLink/XL with four transputer nodes is used for parallel implementation. The simulation results show a significant improvement in displacement tracking errors and joint configuration errors along the straight line trajectory. The computational latency is reduced as well. The modified approach proposed in this work is more accurate and faster than Zhang and Paul's approach for robots with closed-form inverse kinematics solutions. © 1996 John Wiley & Sons, Inc.     

安全平滑的改进时间弹性带轨迹规划算法

传统TEB(time elastic band)算法在杂乱场景下规划易出现倒退、大转向等异常行为,造成加速度跳变,控制指令不平滑,机器人受到大冲击,不利于移动机器人轨迹跟踪.鉴于此,提出一种改进TEB算法,通过增加危险惩罚因子约束规划更安全的运动轨迹,增加加速度跳变以抑制约束减小运动中的最大冲击,增加末端平滑约束以减小末端冲击,实现目标点平滑、准确到达.构建图优化问题,以机器人的位姿和时间间隔为节点、目标函数和约束函数为边,利用问题的稀疏性快速获得相应时刻点的控制量.最后,通过基于机器人操作系统的大量对比仿真测试以及真实差速机器人上的物理实验对提出的改进TEB算法进行性能验证.结果表明,改进TEB算法在复杂环境中能够规划出更安全、平滑的轨迹,减小机器人所受冲击,实现移动机器人更合理地运动.     

多机器人协调操作大型物体的运动学分析及应用

本文研究多机器人协调系统在大型圆筒型工件加工中的应用，提出了基于多个3自 由度移动机器人协调操作工件进行空间6自由度位姿调整系统的结构和协调方法．在刚体小 位移运动模型基础上，建立了系统的运动模型以及逆运动学算法，并给出了满足实时运动规 划的简化算法．最后，通过实例对该算法进行了说明．     

Routing-based navigation of dense mobile robots

In the future, many teams of robots will navigate in home or office environments, similar to dense crowds operating currently in different scenarios. The paper aims to route a large number of robots so as to avoid build-up of congestions, similar to the problem of route planning of traffic systems. In this paper, first probabilistic roadmap approach is used to get a roadmap for online motion planning of robots. A graph search-based technique is used for motion planning. In the literature, typically the search algorithms consider only the static obstacles during this stage, which results in too many robots being scheduled on popular/shorter routes. The algorithm used here therefore penalizes roadmap edges that lie in regions with large robot densities so as to judiciously route the robots. This planning is done continuously to adapt the path to changing robotic densities. The search returns a deliberative trajectory to act as a guide for the navigation of the robot. A point at a distant of the deliberative path becomes the immediate goal of the reactive system. A ‘centre of area’-based reactive navigation technique is used to reactively avoid robots and other dynamic obstacles. In order to avoid two robots blocking each other and causing a deadlock, a deadlock avoidance scheme is designed that detects deadlocks, makes the robots wait for a random time and then allows them to make a few random steps. Experimental results show efficient navigation of a large number of robots. Further, routing results in effectively managing the robot densities so as to enable an efficient navigation.     

A Fast Approach for Robot Motion Planning

This paper describes a new approach to robot motion planning that combines the end-point motion planning with joint trajectory planning for collision avoidance of the links. Local and global methods are proposed for end-point motion planning. The joint trajectory planning is achieved through a pseudoinverse kinematic formulation of the problem. This approach enables collision avoidance of the links by a fast null-space vector computation. The power of the proposed planner derives from: its speed; the good properties of the potential function for end-point motion planning; and from the simultaneous avoidance of the links collision, kinematic singularities, and local minima of the potential function. The planner is not defined over computationally expensive configuration space and can be applied for real-time applications. The planner shows to be faster than many previous planners and can be applied to robots with many degrees of freedom. The effectiveness of the proposed local and global planning methods as well as the general robot motion planning approach have been experimented using the computer-simulated robots. Some of the simulation results are included in this paper.     

被动冗余度空间机器人运动学综合

分析了“被动冗余度”空间机器人主,被动关节之间的运动学耦合,得到了可用于运动 学规划的耦合指标;分析了“被动冗余度”空间机器人的运动学奇异问题,以及与对应全主 动关节冗余度空间机器人的运动学奇异的区别,得到的新的可操作性指标同样可用于机器人 的运动规划;推导出了“被动冗余度”空间机器人的最佳最小二乘运动学优化方程,通过“ 准自运动”实现被动冗余度空间机器人优化控制;通过对平面3DOF空间站机器人的仿真证实 了分析得到的结论．     

Motion planning and contact control for a tele-assisted hydraulic underwater robot

Implementing tele-assistance or supervisory control for autonomous subsea robots requires atomic actions that can be called from high level task planners or mission managers. This paper reports on the design and implementation of a particular atomic action for the case of a subsea robot carrying out tasks in contact with the surrounding environment.Subsea vehicles equipped with manipulators can have upward of 11 degrees of freedom (DOF), with degenerate and redundant inverse kinematics. Distributed local motion planning is presented as a means to specify the motion of each robot DOF given a goal point or trajectory. Results are presented to show the effectiveness of the distributed versus non-distributed approach, a means to deal with local minima difficulties, and the performance for trajectory following with and without saturated joint angles on a robot arm.Consideration is also given to the modelling of hydraulic underwater robots and to the resulting design of hybrid position/force control strategies. A model for a hydraulically actuated robot is developed, taking into account the electrohydraulic servovalve, the bulk modulus of oil, piston area, friction, hose compliance and other arm parameters. Open and closed-loop control results are reported for simulated and real systems.Finally, the use of distributed motion planning and sequential position/force control of a Slingsby TA-9 hydraulic underwater manipulator is described, to implement an atomic action for tele-assistance. The specific task of automatically positioning and inserting a Tronic subsea mateable connector is illustrated, with results showing the contact conditions during insertion.     

A decentralized approach for the conflict-free motion of multiple mobile robots

This article presents a novel approach to decentralized motion planning and conflict-resolution for multiple mobile robots. The proposed multi-robot motion planning is an on-line operation, based on cost wave propagation within a discretized configuration space-time. By use of the planning method, a framework for negotiation is developed, which permits quick decentralized and parallel decision making. The key objective of the negotiation procedure is dynamic assignment of robot motion priorities. Thus, robots involved in a local conflict situation cooperate in planning and execution of the lowest cost motion paths without application of any centralized components. The features required for individual and cooperative motion are embedded in a hybrid control architecture. Results obtained from realistic simulation of a multi-robot environment and also from experiments performed with two mobile robots demonstrate the flexibility and the efficiency of the proposed method.