Determination of the orientation workspace of parallel manipulators

An important step during the design of a parallel manipulators is the determination of its workspace. For a 6-d.o.f. parallel manipulator workspace limitations are due to the bounded range of their linear actuators, mechanical limits on their passive joints and links interference. The computation of the workspace of a parallel manipulator is far more complex than for a serial link manipulator as its translation ability is dependent upon the orientation of the end-effector.We present in this paper an algorithm enabling to compute the possible rotation of the end-effector around a fixed point. This algorithm enables to take into account all the constraints limiting the workspace. Various examples are presented.     

一种柔索并联机器人的可达工作空间分析与刚度评价

大射电望远镜（LT）馈源柔索支撑系统可视为一种柔索并联机器人（WDPR）,基于馈源柔索支撑系统的非线性力学模型，引入张力、球铰和索长约束条件，确定了WDPR的可达工作空间．进而，借助于有限元分析方法,利用静刚度阵的最小奇异值来评价该机器人的刚度性能．通过对LT50m WDPR缩尺模型的空间运动数值仿真，绘制了三维可达工作空间图形及刚度曲面，分析结果表明．张力约束条件对LT可达工作空间影响最大，WDPR机器人与Stewart平台的刚度有明显差异．     

基于工作空间包络法的六杆并联机床结构尺寸设计

以6-SPS并联机床为例,对给定工作空间的并联六杆机床结构尺寸设计进行了分析与研究.以简化的球锥体工作空间为例,研究了六杆并联机床固定平台半径、运动平台半径、驱动杆杆长三者之间的关系,得出并联六杆机床结构尺寸设计的一些结论.     

Collaborative eScience libraries

In the context of collaborative eScience, digital libraries are one of many distributed, interoperable resources available to scientists that facilitate both human and machine collaboration: machine collaboration in the form of standards such as the Open Archives Initiative Protocol for Metadata Harvesting and human collaboration in the form of collaborative workspaces. This paper describes a set of collaborative workspaces created at the Los Alamos National Laboratory Research Library, initial patterns of use, and additional user requirements determined based on these initial patterns of use.     

Base position planning of mobile manipulators for assembly tasks in construction environments

With good mobility and flexibility, mobile manipulators have shown broad applications in construction scenarios. Base position (BP) planning, which refers to the robot autonomously determining its working station in the environment, is an important technique for mobile manipulators when performing the construction assembly task, especially in a large-scale construction environment. However, the BP planning process is tedious and time-consuming for a human worker to carry out. Thus, to improve the efficiency of construction assembly tasks, a novel BP planning method is proposed in this paper, which can lead to appropriate BPs and minimize the number of BPs at the same time. Firstly, the feasible BP regions are generated based on the grid division and the variable workspace of the mobile manipulator. Then, the positioning uncertainties of the mobile manipulator are considered in calculating the preferred BP areas using clustering. Lastly, a set coverage optimization model is established to obtain the minimum number of BPs using an optimization algorithm according to the greedy principle. The simulated experiment based on a 9-degree of free (DoF) mobile manipulator has been performed. The results illustrated that the time for BP planning was significantly reduced and the number of BPs was reduced by 63.41% compared to existing manual planning, which demonstrated the effectiveness of the proposed method. The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-022-00411-3     

Supporting collaborative software development over GitHub

GitHub is a web‐based, distributed Software Configuration Management (SCM) system build over Git, which enables developers to host shared repositories over the Internet and access them from any location, at any time. It helps developers to effectively orchestrate their activities over shared codebases by capturing direct conflicts arising because of concurrent editing on the same shared artifact. However, SCM systems have limited support for capturing inconsistencies arising because of indirect conflicts which arise because of software dependency relationships that exist between related artifacts, and lead to the introduction of syntactic and semantic inconsistencies in codebases. In this paper, we propose a novel collaborative software development (CSD) tool named, Collaboration Over GitHub (COG), that provides real‐time information about arising direct and indirect conflicts among collaborative developers, working over GitHub, through a collection of workspace awareness widgets. These widgets provide people‐centric information about direct and indirect collaborators over GitHub. Resource‐centric information about current and conflicting activities of real‐time collaborators is captured and propagated to others, based on the dependency relationships between software artifacts being manipulated by them. COG uses dependency graphs to store and process dependency relationship information which is required to ascertain information about indirect conflicts. Notably, the most important novel contribution of COG is that it not only captures indirect conflicts that lead to the introduction of syntactic inconsistencies but also changes that lead to semantic inconsistencies in the codebase. It also does so at finer levels of granularity, with changes to individual method's body being traced, thereby capturing statement‐level conflicts as well. Copyright © 2016 John Wiley & Sons, Ltd.     

基于一种新的姿态描述的并行结构机器人工作空间解析解

本文针对并行结构机器人的结构特点建立一种新的姿态描述,给出了相应的定义;并基于这 种描述及Grassmann线几何对6-3并行结构机器人工作空间的奇异问题进行分析,得到 一个简单而有效的非奇异边界,及该区域内的杆长约束条件下保守的工作空间解析解．且与 模型结构无关,具有普适性．因此只要并行结构机器人的模型描述采用了新的方法,那 么它的运动学研究就可以通过这种方法来进行．     

Analysis and Application of the Singularity Locus of the Stewart Platform

The direct use of the determinant of Jacobian matrix being equal to zero for the singularity analysis is generally difficult which is due to complexity of the Jacobian matrix of 6-DOF parallel manipulators,especially for Stewart platform.Recently,several scholars make their great contribution to the effective solution of this problem,but neither of them find the right answer.This paper gives a brief analysis of the kinematics of the Stewart platform and derives the Jacobian matrices of the system through the velocity equation.On the basis of the traditional classification of singularities,the second type of singularity is investigated.An assumption of any three of the six variables of the Stewart platform as constant is made,then the analytical expression of singularity locus equation of the second type singularity which contains another three pose variables is obtained.The singularity locus is represented in the three-dimensional space through the derived equation.The correctness and validity of the proposed method are verified through examples.Finally,the singularity analysis of an electric Stewart platform in its desired workspace and reachable workspace is implemented.Thus,one can easily identify whether singularity exists in a given workspace of a Stewart platform and determine whether the existed singularity can be avoided through the proposed method.The proposed method also provides theoretical principle for the design and application of the Stewart platform and has great significance for the trajectory planning and control.     

基于任务空间的 2P3RR 并联机构尺度综合

结合一种五坐标混联工作台的开发,对其少自由度并联机构部分进行了深入的研究。给出了该并联机构的运动学位置正、逆解,求解了雅可比矩阵,分析了工作空间,基于任务空间探讨了该并联机构主要结构参数之间的相互关系,采用雅可比矩阵条件数的倒数的全域均值作为该并联机构灵巧度评价指标,对其进行灵巧性分析,给出了混联工作台开发实例并进行了设计计算,为混联运动平台的设计开发奠定了理论基础。     

Geometric approach for kinematic analysis of a class of 2-DOF rotational parallel manipulators

Euler angles are commonly used as the orientation representation of most two degrees of freedom (2-DOF) rotational parallel mechanisms (RPMs),as a result,the coupling of two angle parameters leads to c...