基于模糊滑模的六足蛇形臂机器人的末端位姿控制

针对六足蛇形臂机器人的超关节极限和位形偏移量大、末端位姿的控制稳定性不好的问题,提出一种基于模糊滑模的六足蛇形臂机器人的末端位姿控制算法。在超冗余运动学逆解空间中建立蛇形臂机器人的运动学模型,采用修正的DH参数法进行六足蛇形臂机器人的末端位姿参数调节和融合处理,建立蛇形臂机器人的末端位姿力学控制模型,在末端跟随运动中采用外环滑模导纳控制方法进行末端位姿的自适应参数调节,采用滑模误差反馈调节方法确定六足蛇形臂机器人的末端位姿,实现六足蛇形臂机器人准确的姿态定位和参量解算,提高控制稳定性。仿真结果表明:采用该算法进行六足蛇形臂机器人的末端位姿控制的姿态校正性能较好,蛇形臂关节的空间位姿自适应调整能力较强,跟随运动准确,具有很好的位姿控制稳定性。     

机械臂的位姿分离求逆和改进RRT-connect算法研究北大核心CSCD

针对机械臂逆解求取过程中存在大量矩阵变换、计算成本高的问题,采用位姿分离法对逆运动学求解过程进行改进,并提出基于自适应步长的RRT-connect路径规划算法。首先建立六自由度机械臂连杆坐标系模型,采用Standard Denavit-Hartenberg(D-H)方法对机械臂进行正运动学分析,得到机械臂末端执行器位姿相对于基座的齐次变换矩阵。然后引入位姿分离法改进了机械臂的逆运动学求解方法,将机械臂运动学逆解分为位置逆解和姿态逆解两部分,分别用几何法和解析法进行求解,减少了整体计算量。再者提出基于自适应步长的改进RRT-connect路径规划算法,解决了扩展速度慢的问题。最后通过仿真验证所提出方法的正确性和有效性。     

物理受限冗余机械臂逆运动学凸优化求解

针对冗余机械臂逆运动学求解结果极有可能超过机械臂物理限制的问题,提出一种基于凸优化的逆运动学求解方法使得逆解结果满足物理约束.首先分析了关节速度与力矩关系,采用机械臂动能及重复运动为优化指标,以关节速度、关节力矩为优化变量.然后将逆运动学求解问题转化为凸优化问题,进一步转化为二次规划问题,充分利用冗余特性,实现逆运动学求解时避免关节位置、关节速度、关节力矩极限.最后利用7自由度冗余机械臂KUKA LBR iiwa进行仿真,求解关节量结果符合物理极限及优化准则.结果表明本文提出的方法适用于物理受限冗余机械臂的逆运动学求解.     

基于ELM-IWO机械臂运动学逆解算法研究

为了提高机械臂控制中运动学逆解的速度和准确度,提出了一种基于入侵性杂草优化的机械臂运动学逆解方法.通过D-H法建立了工业六自由度机械臂的正向运动学模型,并利用训练速度较快的ELM(极限学习机)计算机械臂关节角度向量,即输出其逆运动学初解.利用IWO(入侵性杂草优化)算法对得到的初始逆解进行优化,取最小适应度下的杂草位置作为输出,以便得到最佳的逆运动学求解.实验结果表明,相比基于PSO-BP神经网络的求解方法,基于ELM-IWO算法的机械臂末端执行器的精度更高,实时性更好.     

六自由度机械臂逆运动学算法

根据D-H参数法确定六自由度机械臂的运动学方程,结合平面几何法和欧拉角变换法将机械臂的逆运动学求解问题分为两部分,一通过平面几何法确定机械臂腕部点的坐标与前三个关节角的关系,二通过欧拉角变换法确定机械臂末端姿态与后三个关节角的关系,根据逆运动解的选取原则从八组解中选取最优解;利用MATLAB中的Robotics Toolbox建立机械臂的正运动学模型,通过多组位姿下的正逆运动解对比验证逆运动学求解算法的准确性;利用VC++中的QueryPerformanceCounter函数和MATLAB中tic-toc语句得到不同算法所消耗的平均时间,通过消耗时间的对比说明该算法的快速性;利用VC++编程实现机械臂写字的过程,通过对比输入字的形状与机械臂末端的实际运动轨迹,进一步验证该算法是一种快速而准确的逆运动学求解算法。     

冗余机器人逆运动学解流形的多目标优化

针对冗余机器人逆运动学插值优化算法运算量大、实时性差的缺点,提出一种基于流形的多目标优化算法.将冗余机器人逆运动学解空间看作一个光滑流形,对位置工作空间流形和姿态工作空间流形分别进行降维分析,然后结合提出的优化目标函数得到冗余机器人相应的优化逆解.在冗余机器人多目标优化中各个优化性能指标很可能是相互对立矛盾的,这就需要根据优先权的高低进行加权设置,以达到冗余机器人解空间的整体优化,得到的优化逆解往往不是单个的解,而是一个优化的解流形.最后利用飞机S形进气道进行逆运动学仿真验证了所用方法的合理性.     

面向三自由度平面关节机器人的“S”形轨迹规划算法研究

针对传统“S”形轨迹规划工业机器人稳定性差的缺点,提出了一种基于双变量反正切函数的改进“S”形轨迹规划算法。引入双变量反正切函数结合运动学逆解的方法求出关节转角的解。依据机器人运动准则得到关节转角的最优解。结合关节转角最优解和改进“S”形轨迹约束机器人运动过程中最大速度、加速度、加加速度的限制值,实现从位移到加加速度均为时间的连续有界轨迹。实验结果表明,改进“S”形轨迹规划算法相较于传统轨迹算法,有效提升了机器人的稳定性。     

基于软体机器人冗余自由度的实时避障位置控制

研究了如何利用软体机器人空间运动的冗余性,解决控制末端位置时环境中存在障碍物的问题.首先建立了软体机器人的运动学分段常曲率模型,设计了实现实时避障和末端位置控制双重任务的控制算法.算法中在障碍区周围划分警戒区,基于机械臂上标记点的位置反馈,分别给出末端无碰撞风险时的运动策略,以及当末端和中间点进入警戒区时的运动策略,并利用雅可比矩阵的广义逆求出应施加的控制变量.利用李亚普诺夫定理证明了逆雅可比法控制的稳定性.最后,在2维空间进行了实验,结果显示末端可以到达目标点,并且末端与机械臂体能够避开障碍物,验证了避障算法的有效性和位置控制的稳定性.     

排爆机械臂逆运动学的模拟退火神经网络算法

采用传统方法计算没有封闭解的机械臂的逆运动学运算量大、精度无法保证,对于复杂结构很难满足实时精确控制的要求;6个并行三层双隐层前馈神经网络被设计用来解决排爆机器臂的逆运动学问题,神经网络的应用受到输出误差的限制,需要减小网络输出误差;针对机械臂结构,以神经网络输出为初始值,对网络输出关节变量进行实值编码,采用分离位姿模拟退火算法对的机械臂末端位置、姿态分别进行优化;仿真结果显示,该方法有效地减小了网络输出误差,在运算结果精确性和运算速度方面满足排爆机械臂求逆运动学解的要求.     

冗余驱动仿壁虎机器人运动学分析与仿真

研究仿壁虎机器人处于多足吸附支撑状态时,出现冗余驱动问题,机器人驱动难度较大,为协调机器人各关节运动和姿态控制,讨论了一种冗余驱动的仿壁虎四足机器人的自然约束条件,推导了机器人三足吸附状态时冗余驱动变量与独立驱动变量的位置和速度关系,建立了机器人机体正运动学方程,同时建立了机器人的逆运动学方程,用来验证正运动学方程的正确性.机器人正运动学方程是一个高次方程,有16组解,数字仿真结果表明只有一组解满足实际模型要求.逆运动学分析结果及仿真结果验证了正运动学的正确性.     

Optimization and Control of Cable Tensions for Hyper-redundant Snake-arm Robots

International Journal of Control, Automation and Systems - Based on the feedback linearization of joints motion and the tension optimization of cables, a hyper-redundant snake-arm robot control...     

Comparison of RBF and MLP neural networks to solve inverse kinematic problem for 6R serial robot by a fusion approach

In this paper, a fusion approach to determine inverse kinematics solutions of a six degree of freedom serial robot is proposed. The proposed approach makes use of radial basis function neural network for prediction of incremental joint angles which in turn are transformed into absolute joint angles with the assistance of forward kinematics relations. In this approach, forward kinematics relations of robot are used to obtain the data for training of neural network as well to estimate the deviation of predicted inverse kinematics solution from the desired solution. The effectiveness of the fusion process is shown by comparing the inverse kinematics solutions obtained for an end-effector of industrial robot moving along a specified path with the solutions obtained from conventional neural network approaches as well as iterative technique. The prominent features of the fusion process include the accurate prediction of inverse kinematics solutions with less computational time apart from the generation of training data for neural network with forward kinematics relations of the robot.     

Real-time method for tip following navigation of continuum snake arm robots

This paper presents a novel technique for the navigation of a snake arm robot, for real-time inspections in complex and constrained environments. These kinds of manipulators rely on redundancy, making the inverse kinematics very difficult. Therefore, a tip following method is proposed using the sequential quadratic programming optimization approach to navigate the robot. This optimization is used to minimize a set of changes to the arrangement of the snake arm that lets the algorithm follow the desired trajectory with minimal error. The information of the Snake Arm pose is used to limit deviations from the path taken. Therefore, the main objective is to find an efficient objective function that allows uninterrupted movements in real-time. The method proposed is validated through an extensive set of simulations of common arrangements and poses for the snake arm robot. For a 24 DoF robot, the average computation time is 0.4 s, achieving a speed of 4.5 mm/s, with deviation of no more than 25 mm from the ideal path.     

A New Geometric Subproblem to Extend Solvability of Inverse Kinematics Based on Screw Theory for 6R Robot Manipulators

Geometric inverse kinematics procedures that divide the whole problem into several subproblems with known solutions, and make use of screw motion operators have been developed in the past for 6R robot manipulators. These geometric procedures are widely used because the solutions of the subproblems are geometrically meaningful and numerically stable. Nonetheless, the existing subproblems limit the types of 6R robot structural configurations for which the inverse kinematics can be solved. This work presents the solution of a novel geometric subproblem that solves the joint angles of a general anthropomorphic arm. Using this new subproblem, an inverse kinematics procedure is derived which is applicable to a wider range of 6R robot manipulators. The inverse kinematics of a closed curve were carried out, in both simulations and experiments, to validate computational cost and realizability of the proposed approach. Multiple 6R robot manipulators with different structural configurations were used to validate the generality of the method. The results are compared with those of other methods in the screw theory framework. The obtained results show that our approach is the most general and the most efficient.

     

Redundancy problem in writing: from human to anthropomorphic robotarm

This paper presents the analysis of motion of a redundant anthropomorphic arm during the writing. The modeling is based on the separation of the prescribed movement into two motions: smooth global, and fast local motion, called distributed positioning (DP). The distribution of these motions to arm joints is discussed. It is based on the inertial properties and actuation capabilities of joints. The approach suggested allows unique solution of the inverse kinematics of redundant mechanisms such as human arm and anthropomorphic robot arm. Distributed positioning is an inherent property of biological systems. Humans, when writing, as shown in literature and in our earlier work control their proximal joints, while the movement of distal joints follow them (synergy). To enhance capabilities of robots, new control schema are necessary. We show that robot control can be improved if it is biological analog. The major aim of this study is to promote such a hypothesis by using anthropomorphic robot arm in writing as an example.     

Closed‐loop inverse kinematics algorithm for constrained flexible manipulators under gravity

This work deals with the inverse kinematics problem for a flexible robot manipulator under gravity in contact with a stiff surface. This problem consists of finding the joint and deflection variables for a given tip position and constraint force. The solution algorithm is based on the well‐known closed‐loop inverse kinematics (CLIK) scheme, using the Jacobian transpose, developed for rigid manipulators. The Jacobian employed in the algorithm is obtained by correcting the equivalent rigid manipulator Jacobian with two terms that account for the static deflections due to gravity and contact force, respectively. The algorithm is tested in a number of case studies on a planar two‐link arm. ©1999 John Wiley & Sons, Inc.     

A biomimetic approach to inverse kinematics for a redundant robot arm

Redundant robots have received increased attention during the last decades, since they provide solutions to problems investigated for years in the robotic community, e.g. task-space tracking, obstacle avoidance etc. However, robot redundancy may arise problems of kinematic control, since robot joint motion is not uniquely determined. In this paper, a biomimetic approach is proposed for solving the problem of redundancy resolution. First, the kinematics of the human upper limb while performing random arm motion are investigated and modeled. The dependencies among the human joint angles are described using a Bayesian network. Then, an objective function, built using this model, is used in a closed-loop inverse kinematic algorithm for a redundant robot arm. Using this algorithm, the robot arm end-effector can be positioned in the three dimensional (3D) space using human-like joint configurations. Through real experiments using an anthropomorphic robot arm, it is proved that the proposed algorithm is computationally fast, while it results to human-like configurations compared to previously proposed inverse kinematics algorithms. The latter makes the proposed algorithm a strong candidate for applications where anthropomorphism is required, e.g. in humanoids or generally in cases where robotic arms interact with humans.     

Inverse kinematics of spherical wrist robot arms: Analysis and simulation

The spherical wrist robot arm is the most common type of industrial robot. This paper presents an efficient analytical computation procedure of its inverse kinematics. It is based on the decomposition of the inverse kinematic problem to two less complex problems; one concerns the robot arm basic structure and the other concerns its hand. The proposed computation procedure is used to obtain the inverse kinematic position models of two robot arms: one contains only revolute joints and the other contains both revolute and prismatic joints. The 1st and 2nd time derivatives of the obtained models give more accurate inverse kinematic velocity and acceleration models than numerical differentiation. These models are verified by simulation for two different trajectories. The obtained results demonstrate the effect of the proposed procedure on reducing the necessary computation time compared to other computation techniques.     

Analytical Inverse Kinematics Solver for Anthropomorphic 7-DOF Redundant Manipulators with Human-Like Configuration Constraints

It is a common belief that service robots shall move in a human-like manner to enable natural and convenient interaction with a human user or collaborator. In particular, this applies to anthropomorphic 7-DOF redundant robot manipulators that have a shoulder-elbow-wrist configuration. On the kinematic level, human-like movement then can be realized by means of selecting a redundancy resolution for the inverse kinematics (IK), which realizes human-like movement through respective nullspace preferences. In this paper, key positions are introduced and defined as Cartesian positions of the manipulator’s elbow and wrist joints. The key positions are used as constraints on the inverse kinematics in addition to orientation constraints at the end-effector, such that the inverse kinematics can be calculated through an efficient analytical scheme and realizes human-like configurations. To obtain suitable key positions, a correspondence method named wrist-elbow-in-line is derived to map key positions of human demonstrations to the real robot for obtaining a valid analytical inverse kinematics solution. A human demonstration tracking experiment is conducted to evaluate the end-effector accuracy and human-likeness of the generated motion for a 7-DOF Kuka-LWR arm. The results are compared to a similar correspondance method that emphasizes only the wrist postion and show that the subtle differences between the two different correspondence methods may lead to significant performance differences. Furthermore, the wrist-elbow-in-line method is validated as more stable in practical application and extended for obstacle avoidance.     

基于MATLAB的模块化机器人手臂运动学算法验证及运动仿真

针对由模块化关节构成的六自由度串联机器人手臂, 采用DH法对手臂的操作空间进行了描述, 得到了正运动学模型; 采用欧拉角表示手臂姿态, 得到了包含六个参数的用于表示手臂位姿的完备广义坐标, 并对欧拉角的几何关系进行了分析。针对SolidWorks虽然实体建模简洁方便但计算并非其强项的缺点, 编写相应接口程序, 将建立的手臂三维实体模型保留几何约束关系简化后导入MATLAB软件。基于MATLAB编写正逆运动学算法验证程序以及连杆驱动程序, 实现了手臂的仿真运动。通过仿真, 不仅更进一步验证了手臂正逆运动学解算的正确性, 而且非常直观地看出手臂末端在空间中运行的路径以及各关节的动作情况。机器人手臂正逆运动学算法正确性的验证及运动仿真为手臂的精确定位及其路径规划提供了必要的保证。