6-DOF并联机器人并行控制算法与优化

为了实现对6-DOF并联机器人实时在线控制,并能取得良好的控制效果,对其运动控制算法的结构进行了深入剖析与研究,尤其对上平台中心的运动速度和角速度的计算及液压缸各杆的伸长速度计算矩阵进行了细致的研究,提出了并行算法及CPU的优化分配策略,大大提高了并联机器人的实时控制质量.     

Kinematics, dynamics and construction of a planarly actuated parallel robot

Kinematic and dynamic analysis of a parallel robot consisting of three planarly actuated links, is presented in this paper. Coordinated motion of three planar motors, connected to three fixed-length links, produces a six-degrees-of-freedom motion of an output link. Its extremely simple design along with much larger work volume than the commonly used parallel robots make this high performance-to-simplicity ratio robot very attractive. Experimental model verifies the unique combination of large work volume and high accuracy of this robot.     

Experiments on a floating underwater robot with a two-link manipulator

This article concerns experiments with a free-floating underwater robot with a two-dimensional, horizontal planar, two-link manipulator. Some dynamic models of underwater manipulators have been proposed, but only a few experiments have been carried out. Here, we derive a dynamic model for a free-floating underwater robot with a two-link manipulator, including the hydrodynamic forces, and validate the effectiveness of the model by simulation and experiment. We also show an experimental result using a resolved acceleration control method. These experimental results show the effectiveness the model and the control method. This work was presented in part at the 5th International Symposium on Artificial Life and Robotics, Oita, Japan, January 26–28, 2000     

6-DOF并联机器人控制算法结构化分析与设计

为了实现对六自由度并联机器人位置速度算法的控制,针时控制算法采用了软件工程的原理和方法进行了分析,并对机器人运动特性进行了研究.根据运动特性对位置与速度的控制算法进行了解析,提出位置反解的控制策略,给出了功能分析的DFD模型和软件结构化设计模型SC图.描述了算法的详细设计及实现,采用结构化语言表达工具,并对实现中重要的部分细节进行了细致的研究,其结果达到了位置速度控制的目的及机器人控制算法的软件结构化设计.     

6-DOF并联机器人位置正解的实用解法

对6-DOF并联机器人的位置正解进行了研究和分析,通过位置反解的求解思路来解位置正解的问题。将上下平台统一在一个坐标系下。按照空间两点间距离计算公式,以6个杆的伸长值为已知量,位姿参数为未知量,建立关于6个杆的参数方程。通过迭代法求得位姿参数。特点之一是未知量个数少,计算精度高;另一特点是从实现的角度来阐述,实用性强。通过实验验证该思路满足即时控制的要求。     

Structural design and kinematics of a new parallel reconfigurable robot

Reconfigurable robots can be defined as a group of robots that can have different geometries, thus obtaining different structures derived from the basic one, having different degrees of freedom and workspaces. Thanks to the optimum dexterity they offer, the user can accomplish a large variety of industrial tasks, using a structurally optimized robot leading towards better energy control and efficiency especially in case of batch size production lines where the task (for the robot) may vary periodically. Reconfigurable systems are a challenge for numerous scientists, due to the advantage of dealing with changes and uncertainties on the ever-changing manufacturing market. One of the main problems of reconfigurable robots is the proper structural geometry determination, so that the resulting structure is able to perform a variety of tasks. This paper presents the structural design of an innovative parallel robot with six degrees of freedom and its proposed configurations with five, four, three and two degrees of freedom. The kinematic analysis and the workspace representations of all the presented configurations of the parallel robot, called Recrob, are also presented.     

Digital type disturbance compensation control of a floating underwater robot with 2 link manipulator

We have proposed continuous and discrete time resolved acceleration control methods for underwater vehicle-manipulator systems and the effectiveness of the control methods have been shown by experiments. In this paper, we propose a digital type disturbance compensation control method based on the RAC method considering singular configuration of manipulator. Experimental results show the effectiveness of the proposed method. This work was presented in part at the 12th International Symposium on Artificial Life and Robotics, Oita, Japan, January 25–27, 2007     

高精度轨迹跟踪的6-PRRS并联机器人自抗扰控制研究

针对6-PRRS并联机器人控制系统的非线性、耦合等特性,采用分散控制策略。在关节空间设计强鲁棒性的自抗扰控制器对其进行控制．该自抗扰控制器由非线性跟踪微分器、扩张状态观测器、非线性PD和扰动补偿4部分组成．具有模型补偿功能的扩张状态观测器可以获得系统的状态估计和未知外扰的实时作用量,使系统性能得到有效补偿．该控制器以离散的形式进行设计,易于工程实现．仿真结果证明了所提出的控制策略具有强鲁棒性,跟踪性能良好．     

Dynamics modelling of a Stewart-based hybrid parallel robot

Matrix relations for kinematics and dynamics analysis of a spatial two-module Stewart-based hybrid parallel robot are established in this paper. Knowing the relative motions of two moving platforms, the inverse dynamics problem is solved based on a set of recursive explicit equations. Finally, compact results and graphs of simulation for the input forces and powers of all actuators are obtained.     

Dynamics of a six degrees-of-freedom parallel robot actuated by three two-wheel carts

This paper deals with a new, six degrees-of-freedom parallel manipulator comprising a platform, three links and three two-wheel carts supporting the links. The wheels are independently driven, allowing the manipulator a workspace which is limited only by the lengths of the links and the size of the plane on which the carts move. The direct and inverse dynamic problems of the manipulator are solved. It is shown that the Jacobian associated with the direct problem becomes identically singular when used to solve the inverse problem, and hence must be redefined; and that once redefined, it losses its standard structure and cannot be used to solve the direct problem. Three solution methods to the inverse problem are presented and are shown to lead to indistinguishable results.     

A 6-DOF reconfigurable hybrid parallel manipulator

This paper presents a case study on a reconfigurable hybrid parallel robot dubbed ReSl-Bot. It addresses the realm of reconfigurable 6-DOF parallel mechanisms, for sustainable manufacturing. It also features a self-reconfigurable architecture. A systematic analysis involving kinematics, constant orientation workspace, singularity and stiffness is developed in detail. Interesting features are discussed, revealing some unique characteristics of the studied architecture. A multi-objective optimization procedure is also carried out with weighted stiffness, dexterity and workspace volume as the performance indices.     

Trajectory tracking control of a 6-DOF hydraulic parallel robot manipulator with uncertain load disturbances

This study addresses the trajectory tracking control of a 6-DOF (degrees of freedom) hydraulic parallel robot manipulator with uncertain load disturbances. As load disturbances are the main external disturbances of the parallel robot manipulators and have a significant impact on system tracking performance, many researchers have been devoted to synthesize advanced control methods for improving the system robustness under the assumption that load disturbances are bounded. However, load disturbances are uncertain and vary in a large range in real situation happening in most hydraulic parallel robot manipulators, which is opposed to the assumption. In this paper, the load disturbances are directly measured by force sensors. Then a sliding mode control with discontinuous projection-based adaptation laws is proposed to improve the tracking performance of the parallel robot manipulator. Simulations and experiments with typical desired trajectory are presented, and the results show that good tracking performance is achieved in the presence of uncertain load disturbances.     

Kinematic analysis and error modeling of TAU parallel robot

The TAU robot presents a new configuration of parallel robots with three degrees of freedom. This robotic configuration is well adapted to perform with a high precision and high stiffness within a large working range compared with a serial robot. It has the advantages of both parallel robots and serial robots. In this paper, the kinematic modeling and error modeling are established with all errors considered using Jacobian matrix method for the robot. Meanwhile, a very effective Jacobian approximation method is introduced to calculate the forward kinematic problem instead of Newton–Raphson method. It denotes that a closed form solution can be obtained instead of a numerical solution. A full size Jacobian matrix is used in carrying out error analysis, error budget, and model parameter estimation and identification. Simulation results indicate that both Jacobian matrix and Jacobian approximation method are correct and with a level of accuracy of micron meters. ADAMS's simulation results are used in verifying the established models.     

Kinematic calibration of a five-bar planar parallel robot using all working modes

We present a simple low-cost calibration procedure that improves the planar positioning accuracy of a double-arm SCARA robot to levels difficult or impossible to achieve using an equivalent serial robot. Measurements are based on the use of five custom designed magnetic tooling balls fixed to the periphery of a detachable working plate. Three of these tooling balls define the world reference frame of the robot, and the positions of the centers of all balls are measured on a CMM. A special magnetic cup end-effector is used. Measurements are taken by manually positioning the end-effector over each of the tooling balls, with each of the maximum of four possible robot configurations. Each of these measurements is repeatable to within±0.015 mm. The robot calibration model includes all 12 kinematic parameters, and the calibration method used is based on the linearization of the direct kinematics model in each calibration configuration. The optimal number and location of the tooling balls is obtained by studying the observability index. Finally, an experimental validation at 14 additional tooling balls shows that the maximum position error with respect to the world frame is reduced to 0.080 mm within the entire robot's workspace of 600 mm×600 mm.     

Vision-based self-calibration and control of parallel kinematic mechanisms without proprioceptive sensing

This work is a synthesis of our experience over parallel kinematic machine control, which aims at changing the standard conceptual approach to this problem. Indeed, since the task space, the state space and the measurement space can coincide in this class of mechanisms, we came to redefine the complete modelling, identification and control methodology. Thus, it is shown in this paper that, generically and with the help of sensor-based control, this methodology does not require any joint measurement, thus opening a path to simplified mechanical design and reducing the number of kinematic parameters to identify. This novel approach is illustrated on the reference parallel kinematic mechanism (the Gough–Stewart platform) with vision as the exteroceptive sensor. This work was supported by European Community through the Integrated Project NEXT number 0011815. It was initially published in the Proceedings of the 13th International Conference on Advanced Robotics (ICAR’07), Jeju, Korea, 21–24 August 2007 [3]. During this work, Philippe Martinet was holding a visiting professor position at the Intelligent Service Robotics Center at Sungkyunkwan University, Suwon, South Korea.     

A robust adaptive control of a parallel robot

The work presented in this article deals with the robust adaptive control tracking of a 6 degree of freedom parallel robot, called C5 parallel robot. The proposed approach is based on the coupling of sliding modes and multi-layers perceptron neural networks (MLP-NNs). It does not require the inverse dynamic model for deriving the control law. The MLP-NN is added in the control scheme to estimate the gravitational and frictional forces along with the non-modelled dynamic effects. The nonlinearity problem, present in neural networks, is resolved using Taylor series expansion. The proposed approach allows to adjust the parameters of neural network and sliding mode control terms by taking into account a reference model and the closed-loop stability in the Lyapunov sense. We implemented our approach on the C5 parallel robot of LISSI laboratory and performed experiments to observe its effectiveness and the robust behaviour of the controller against external disturbances.     

Kinematic analysis of a new 5-DOF modular parallel robot for brachytherapy

Cancer represents one of the main causes of the death. Huge efforts have been made by the scientific community to provide better cancer treatment solutions. An innovative option is the brachytherapy (BT), a local radiation technique for cancer treatment, which enables the delivery of high doses of radiation inside the tumors. BT usage is limited by the insufficient accuracy of the radioactive seeds placement. In order to eliminate these limitations, the authors propose an innovative modular structure which would enable the precise positioning of the BT needles in any part of the patient body. The paper presents the kinematic modeling of the new 5-DOF robotic structure. The workspace analysis and the singularities are studied and the dexterous workspace for a given insertion point inside the patient is also shown. Finally, some numerical simulations of different BT needle trajectories are included.     

A parallel distributed control architecture for multiple robot systems using a network of microcomputers

This paper presents the design and implementation of a parallel distributed control architecture for industrial multiple robot systems. The design methodology is based on a concept of discrete states and actions, and a robotic task is represented as a sequence of primitive actions. For cooperative or exclusive tasks at the synchronous level of multiple robot systems, Petri net representation is applied, and discrete event-driven control is implemented as a data flow network of concurrent processes communicating with each other. Implementation of multiprocessing control on a microcomputer and a network of microcomputers is discussed.     

Optimal robot positioning using task-dependent and direction-selective performance indexes: General definitions and application to a parallel robot

Performance evaluation is an important issue for optimal robot positioning within workcells. Performance indexes can provide essential contributions to such an evaluation, in particular if they can account for the specific task with respect to which the optimization is carried out.