Singularity-robust decoupled control of dual-elbow manipulators

The ability of a robot manipulator to move inside its workspace is inhibited by the presence of joint limits and obstacles and by the existence of singular positions in the configuration space of the manipulator. Several kinematic control strategies have been proposed to ameliorate these problems and to control the motion of the manipulator inside its workspace. The common base of these strategies is the manipulability measure which has been used to: (i) avoid singularities at the task-planning level; and (ii) to develop a singularity-robust inverse Jacobian matrix for continuous kinematic control. In this paper, a singularity-robust resolved-rate control strategy is presented for decoupled robot geometries and implemented for the dual-elbow manipulator. The proposed approach exploits the decoupled geometry of the dual-elbow manipulator to control independently the shoulder and the arm subsystems, for any desired end-effector motion, thus incurring a significantly lower computational cost compared to existing schemes.     

On inverting singular kinematics and geodesic trajectory generation for robot manipulators

In this paper, a new method is proposed of solving the inverse kinematic problem for robot manipulators whose kinematics are allowed to possess singularities. The method is based upon the so-called generalized Newton algorithm, introduced by S. Smale, and can be adopted to both nonredundant and redundant kinematics. Moreover, given a pair of points in the external space of a manipulator, the method is capable of generating a minimum-length trajectory joining the points (a geodesic), in particular a straight-line trajectory. Results of representative computer experiments, including those with the PUMA 560 kinematics, are reported in order to illustrate the performance of the method.     

On generating the motion of industrial robot manipulators

In this study, an intelligent search algorithm is proposed to define the path that leads to the desired position and orientation of an industrial robot׳s manipulator end effector. The search algorithm gradually approaches the desired configuration by selecting and evaluating a number of alternative robot׳s configurations. A grid of the robot׳s alternative configurations is constructed using a set of parameters which are reducing the search space to minimize the computational time. In the evaluation of the alternatives, multiple criteria are used in order for the different requirements to be fulfilled. The alternative configurations are generated with emphasis being given to the robot׳s joints that mainly affect the position of the end effector. Grid resolution and size parameters are set on the basis of the desired output. High resolution is used for a smooth path and lower for a rough estimation, by providing only a number of the intermediate points to the goal position. The path derived is a series of robot configurations. This method provides an inexperienced robot programmer with flexibility to generate automatically a robotic path that would fulfill the desired criteria without having to record intermediate points to the goal position.     

Kinematic control of redundant robot manipulators: A tutorial

In this paper, we present a tentatively comprehensive tutorial report of the most recent literature on kinematic control of redundant robot manipulators. Our goal is to lend some perspective to the most widely adopted on-line instantaneous control solutions, namely those based on the simple manipulator's Jacobian, those based on the local optimization of objective functions in the null space of the Jacobian, those based on the task space augmentation by additional constraint tasks (with task priority), and those based on the construction of inverse kinematic functions.     

基于PVR技术的机器人动态仿真控制

详细分析了基于投射式虚拟现实技术的机器人动态仿真控制,提出了仿真控制系统的总体框架,实现了仿真任务,并对投射式虚拟现实技术进行了改进,就投射式虚拟现实技术在一般工程仿真中的应用进行了有益的探讨.     

Cartesian path generation of robot manipulators using continuous genetic algorithms

In this paper, the authors describe a novel technique based on continuous genetic algorithms (CGAs) to solve the path generation problem for robot manipulators. We consider the following scenario: given the desired Cartesian path of the end-effector of the manipulator in a free-of-obstacles workspace, off-line smooth geometric paths in the joint space of the manipulator are obtained. The inverse kinematics problem is formulated as an optimization problem based on the concept of the minimization of the accumulative path deviation and is then solved using CGAs where smooth curves are used for representing the required geometric paths in the joint space through out the evolution process. In general, CGA uses smooth operators and avoids sharp jumps in the parameter values. This novel approach possesses several distinct advantages: first, it can be applied to any general serial manipulator with positional degrees of freedom that might not have any derived closed-form solution for its inverse kinematics. Second, to the authors’ knowledge, it is the first singularity-free path generation algorithm that can be applied at the path update rate of the manipulator. Third, extremely high accuracy can be achieved along the generated path almost similar to analytical solutions, if available. Fourth, the proposed approach can be adopted to any general serial manipulator including both nonredundant and redundant systems. Fifth, when applied on parallel computers, the real time implementation is possible due to the implicit parallel nature of genetic algorithms. The generality and efficiency of the proposed algorithm are demonstrated through simulations that include 2R and 3R planar manipulators, PUMA manipulator, and a general 6R serial manipulator.     

Analytic generation of workspace using the robot kinematics

When designing workplaces, controls should be placed within the reach of an operator's arm or foot for guaranteeing effective performance. In designing a workplace which must cater to a wide range of operator size, it might be sufficient to plan only for the ‘average person’. Static arm reach measurements which are taken in conventional, standardized positions provide necessary information, but they cannot be applied to dynamic situations directly. To obtain reach envelope or workspace of the human body not by direct measurement but by analytic generation, data on range of joint motion(ROM) are required as an input. The purposes of this research are to measure the range of motion of two degrees of freedom for Korean young males, and to propose an approximate algorithm to generate the workspace of the human body including foot and trunk motion, in which joint mobility of two degrees of freedom motion are considered. The robot kinematics was employed to represent the human body as a multi-link system.     

Trajectory tracking control for robot manipulators using only position measurements

In the paper, the trajectory tracking control problem is investigated for robotic manipulators which are not equipped with the tachometers. Our contribution consists in establishing uniform asymptotic stability in closed-loop system by using the dynamic position-feedback controller with feedforward. Using Lyapunov vector function and comparison principle, we construct the non-linear controller with variable gain matrices and first-order linear dynamic compensator such that the origin of the closed-loop system is uniformly asymptotically stable. The controller is shown to be robust with respect to parameters incertainties. We illustrate the utility of our result by simulation tests with reference to a two-link planar elbow robot manipulator.     

动力学解析的四轮全向移动机器人电机解耦控制

四轮全向移动机器人是一个复杂的非线性、强耦合的机械系统,各轮驱动电机间存在强耦合现象,很难取得理想的控制效果。针对这一问题,提出一种基于动力学解析的多电机控制系统解耦方法。通过对四轮机器人的动力学解析推导出四轮转速与其驱动力矩间的状态方程,获得各电机输入输出量之间的耦合关系,在此基础上依据控制量一致思想设计解耦控制器,解决了传统参考模型解耦方法不能兼顾控制性能和解耦性能的问题,实现了四路电机的独立控制。仿真结果显示,该方法能够有效地减小控制系统各变量间的相互耦合作用,每路电机均很好地跟踪了各自的输入,解耦效果好。     

直线伺服6 位置环虚拟轴机床的运动学解耦

使用直线电机驱动虚拟轴机床 ,可满足高速时动态响应和提高精度的要求。如何解决 6位置环虚拟轴机床的强耦合 ,一直是虚拟轴机床伺服控制中的一个难题。为此 ,将局部结构化方法与解耦理论相结合 ,提出一种新的解耦算法 ,从理论上实现了对 6位置环虚拟轴机床的平动和转动之间的解耦     

三轮全向移动机器人的研究与设计

为了提高机器人运动控制的精度和机器人智能化的程度,基于传统机器人和移动机器人的优缺点的比较,通过对三轮全向机器人的硬件结构和运动学分析,得出了三轮全向移动机器人的运动控制模型,并结合移动机器人分布式结构的特点设计了一种三轮全向机器人的软件模型.通过对三轮全向移动机器人进行实际运动控制测试,校正了三轮移动机器人的运动学方程,有效的验证了软件模型的正确合理性,提高了移动机器人的运动效果.     

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。     

Design and experimental validation of a second-order sliding-mode motion controller for robot manipulators

This article presents an original motion control strategy for robot manipulators based on the coupling of the inverse dynamics method with the so-called second-order sliding mode control approach. Using this method, in principle, all the coupling non-linearities in the dynamical model of the manipulator are compensated, transforming the multi-input non-linear system into a linear and decoupled one. Actually, since the inverse dynamics relies on an identified model, some residual uncertain terms remain and perturb the linear and decoupled system. This motivates the use of a robust control design approach to complete the control scheme. In this article the sliding mode control methodology is adopted. Sliding mode control has many appreciable features, such as design simplicity and robustness versus a wide class of uncertainties and disturbances. Yet conventional sliding mode control seems inappropriate to be applied in robotics since it can generate the so-called chattering effect, which can be destructive for the controlled robot. In this article, this problem is suitably circumvented by designing a second-order sliding mode controller capable of generating a continuous control law making the proposed sliding mode controller actually applicable to industrial robots. To build the inverse dynamics part of the proposed controller, a suitable dynamical model of the system has been formulated, and its parameters have been accurately identified relying on a practical MIMO identification procedure recently devised. The proposed inverse dynamics-based second-order sliding mode controller has been experimentally tested on a COMAU SMART3-S2 industrial manipulator, demonstrating the tracking properties and the good performances of the controlled system.     

基于弹簧负载倒立摆模型的仿袋鼠机器人稳定跳跃控制

仿生跳跃机器人具备很强的越障和环境适应能力,但是由于机器人运动过程中较短的可控时间以及腾空阶段运动的不确定性,运动的稳定性对于仿生跳跃机器人至关重要.本文对仿袋鼠机器人跳跃运动过程中的稳定跳跃控制问题进行了研究.首先采用双质量弹簧负载倒立摆模型(spring-loaded inverted pendulum,SLIP)模型对袋鼠机器人的结构进行简化,建立了机器人系统的动力学模型,并对机器人的运动过程以及着地相与腾空相的切换条件进行了分析.然后采用解耦控制的思想,将SLIP模型的运动控制分解为水平速度控制和跳跃高度控制两个方面,分别通过控制着地角度实现对水平运动速度的控制,通过能量补偿实现对跳跃高度的控制.最后在ADAMS仿真环境中建立机器人模型并进行了机器人运动仿真实验.实验结果表明,本文提出的方法可以实现仿袋鼠机器人稳定的周期性跳跃运动.     

Repetitive control of electrically driven robot manipulators

This article presents a novel robust discrete repetitive control of electrically driven robot manipulators for tracking of a periodic trajectory. We propose a novel model, which presents the highly non-linear dynamics of robot manipulator in the form of linear discrete-time time-varying system. Based on the proposed model, we develop a two-term control law. The first term is an ordinary time-optimal and minimum-norm (TOMN) control by employing parametric controllers to guarantee stability. The second term is a novel robust control to improve the control performance in the face of uncertainties. The robust control estimates and compensates uncertainties including the parametric uncertainty, unmodelled dynamics and external disturbances. Performance of the proposed method is compared with two discrete methods, namely the TOMN control and an adaptive iterative learning (AIL) control. Simulation results confirm superiority of the proposed method in terms of the convergence speed and precision.     

Classification of kinematic singularities in planar robot manipulators

In [13, 14] we have proclaimed a singularity theory based programme of investigations of kinematic singularities in robot manipulators. The main achievement of the programme consists in providing local candidate models of kinematic singularities. However, due to the specific form of the manipulator kinematics, fitting the candidate models into the prescribed robot kinematics is a fairly open problem. The problem is easily solvable only around non-singular configurations of manipulators, where locally the kinematics can be modelled by linear injections or projections. In this paper we are concerned with planar manipulator kinematics, and prove that, under a mild geometric condition, such kinematics can be transformed around singular configurations to simple quadratic models of the Morse type. The models provide a complete local classification of generic planar kinematics of robot manipulators.     

Human-like behavior of robot arms: general considerations and the handwriting task—Part II: the robot arm in handwriting

This paper (Part II) investigates the motion of a redundant anthropomorphic arm during the writing task. Two approaches are applied. The first is based on the concept of distributed positioning which is suitable to model the “writing” task before the occurrence of fatigue symptoms. The second approach uses the concept of “virtual fatigue” (VF) which is a variable that dynamically behaves in a way analogous to the biological fatigue. VF enables the arm to reconfigure itself and take postures appropriate for the current level of fatigue. The study includes the analysis of legibility and inclination of handwriting, and a set of simulation results that show most practical aspects of robot human-like performance.     

Adaptive control of robot contact tasks with on-line learning of planar surfaces

In robot constrained motion problems on planar surfaces with frictional contacts, uncertainties on the contacted surface not only affect the control system performance but also distort control targets. The surface normal direction cosines are in this case uncertain parameters that are involved in both the control law and the control targets. This work proposes an adaptive learning controller that uses force and joint position/velocity measurements to simultaneously learn the surface orientation and achieve the desired goal. Simulation examples for a 6 dof robot are used to illustrate the theoretical results and the performance of the proposed controller in practical cases.     

关节联动的单孔手术机器人运动解耦方法

针对单孔腔镜手术机器人的执行器械从驱动空间至操作空间的强运动耦合问题,研究关节联动构型,实现运动解耦,简化运动学模型．首先分析联动构型的运动特性并设计滚轮约束式铰接关节．继而研发了7自由度的联动构型器械,它可实现2自由度的“联动展开”．建立了D-H（Denavit-Hartenberg）模型,分析联动构型器械的位姿分离,并通过解析法直接求解逆运动学．然后基于立体角度量手术器械末端在给定点的灵活度,优化联动构型器械的远端段关节布置．实验表明,联动构型器械末端的姿态只取决于远端段关节,“联动展开”只改变器械末端的位置．驱动空间至关节空间的最大误差小于3°,近端段与远端段的驱动之间互不干扰．     

考虑动力学模型的非完整移动机器人运动规划

针对非完整移动机器人,在运动学和动力学约束条件下提出了一种运动规划方法.在工作环境已知情况下,根据移动机器人的动力学模型和无打滑非完整运动约束条件,采用立方螺线对规划的路径光滑化,从而使得移动机器人易于跟踪所规划的路径,同时考虑了移动机器人速度的限制.最后采用Matlab对该算法进行了数值仿真,结果表明该方法是有效的.