Variable Stiffness Identification and Configuration Optimization of Industrial Robots for Machining Tasks

Industrial robots are increasingly being used in machining tasks because of their high flexibility and intelligence.However,the low structural stiffness of a robot significantly affects its positional accuracy and the machining quality of its operation equipment.Studying robot stiffness characteristics and optimization methods is an effective method of improving the stiffness performance of a robot.Accordingly,aiming at the poor accuracy of stiffness modeling caused by approximating the stiffness of each joint as a constant,a variable stiffness identification method is proposed based on space gridding.Subsequently,a task-oriented axial stiffness evaluation index is proposed to quantitatively assess the stiffness performance in the machining direction.In addition,by analyzing the redundant kinematic characteristics of the robot machining system,a configuration optimization method is further developed to maximize the index.For numerous points or trajectory-processing tasks,a configuration smoothing strategy is proposed to rapidly acquire optimized configurations.Finally,experiments on a KR500 robot were conducted to verify the feasibility and validity of the proposed stiffness identification and configuration optimization methods.

Configuration information acquisition and matching in self-reconfiguring process of modular self-reconfigurable robots

Configuration information acquisition and matching are two important steps in the self-reconfiguring process of self-reconfigurable robots. The process of configuration information acquisition was introduced, and a self-reconfiguring configuration matching strategy based on graded optimization mechanism was proposed. The first-grade optimization was to search common connection between matching scheme and goal configuration. The second-grade optimization, whose object function was constructed in terms of configuration connectivity, was to search connnon topology according to the results of the first-grade optimization. The entire process of configuration information acquisition and matching was verified by an experiment and genetic algorithm （GA）. The result shows the accuracy of the configuration information acquisition and the effectiveness of the configuration matching method.

The Configuration Optimization for Multilimbed Robots with the Viewpoint of Maximum Loading Capacity

This paper presents a method for optimizing the configuration of a multilimbed robot (the robot with both arms and legs) which works with a big load. A least-effort criterion is proposed as the base of optimization. When the applying Cartesian force and the task point are given, the best configuration of the robot will be easily found through a series of imaginary motions of the robot and some simple computations. The imaginary motion varies with the working environment related to the construction of the robot, the task point and the force direction. The working environment could be predicted by the proposed inequalities, so that the way of motion could be decided in advance.

Biped Robot with Triangle Configuration

A new biped robot with a triangle configuration is presented and it is a planar closed chain mechanism. The scalability of three sides of the triangle is realized by three actuated prismatic joints. The three vertexes of the triangle are centers of three passive revolute joints coincidently. The biped mechanism for straight walking is proposed and its walking principle and mobility are explained. The static stability and the height and span of one step are analyzed. Kinematic analysis is performed to plan the gaits of walking on an even floor and going upstairs. A prototype is developed and experiments are carried out to validate the straight walking gait. Two additional revolute joints are added to form a modified biped robot which can follow the instruction of turning around. The turning ability is verified by experiments. As a new member of biped robots, its triangle configuration is used to impart geometry knowledge. Because of its high stiffness, some potential applications are on the way.

Composite Configuration Interventional Therapy Robot for the Microwave Ablation of Liver Tumors

The existing interventional therapy robots for the microwave ablation of liver tumors have a poor clinical applicability with a large volume, low positioning speed and complex automatic navigation control. To solve above problems, a composite configuration interventional therapy robot with passive and active joints is developed. The design of composite configuration reduces the size of the robot under the premise of a wide range of movement, and the robot with composite configuration can realizes rapid positioning with operation safety. The cumulative error of positioning is eliminated and the control complexity is reduced by decoupling active parts. The navigation algo- rithms for the robot are proposed based on solution of the inverse kinematics and geometric analysis. A simulation clinical test method is designed for the robot, and the functions of the robot and the navigation algorithms are verified by the test method. The mean error of navigation is 1.488 mm and the maximum error is 2.056 mm, and thepositioning time for the ablation needle is in 10 s. The experimental results show that the designed robot can meet the clinical requirements for the microwave ablation of liver tumors. The composite configuration is proposed in development of the interventional therapy robot for the microwave ablation of liver tumors, which provides a new idea for the structural design of medical robots.

STUDY ON SINGULAR CONFIGURATIONS AND COMPUTER SIMULATION OF 6R ROBOT

When robot is at singular configuration, the limited hand velocity wouldrequire some joints with infeasible speeds so as to lead unsafely of the system. A method of solvingthe approximate velocity of joint near singular configuration point by adding damped vector isproposed and a modified algorithm is provided. With the analysis of J^(-1) the singularconfigurations of 6R robot are divided into structure boundary singularity , boundary singularity ,inner singularity and wrist singularity. The conditions of singularities of the robot have beenascertained. The computer simulations of the singularities of the robot are developed, which havemany advantages over previous description methods of the singular configurations of robot. With thehelp of boundary singularity analysis, a application in welding trajectory planning checking of therobot has been carried out and the simulation result proved visualized and useful.

Configuration Design of an Under-Actuated Robotic Hand Based on Maximum Grasping Space

Capture is a key component for on?orbit service and space debris clean. The current research of capture on?orbit focuses on using special capture devices or full?actuated space arms to capture cooperative targets. However, the structures of current capture devices are complex, and both space debris and abandoned spacecraft are non?cooperative targets. To capture non?cooperative targets in space, a lightweight, less driven under?actuated robotic hand is proposed in this paper, which composed by tendon?pulley transmission and double?stage mechanisms, and always driven by only one motor in process of closing finger. Because of the expandability, general grasping model is constructed. The equivalent joint driving forces and general grasping force are analyzed based on the model and the principle of virtual work. Which reveal the relationship among tendon driving force, joint driving forces and grasping force. In order to configure the number of knuckles of finger, a new analysis method which takes the maximum grasping space into account, is proposed. Supposing the maximum grasped object is an envelope circle with diameter of 2.5m. In the condition, a finger grasping maximum envelope circle with different knuckles is modeled. And the finger lengths with corresponding knuckles are calculated out. The finger length which consists of three knuckles is the shortest among under?actuated fingers consists of not more than five knuckles. Finally, the principle prototype and prototype robotic hand which consists of two dingers are designed and assembled. Experiments indicate that the under?actuated robotic hand can satisfy the grasp requirements.

Modeling and Configuration Design of Electromagnetic Actuation Coil for a Magnetically Controlled Microrobot

Non-contact actuated microbeads have attracted a lot of attention in recent years because of its enormous potential in medical, biological, and industrial applications. Researchers have proposed a multitude of electromagnetic actuation(EMA) systems consisting of a variety of coil pairs. However, a unified method to design and optimize a coil pair according to technical specifications still does not exist. Initially, this paper presented the modeling of an untethered ferromagnetic particle actuated by externally applied magnetic field. Based on the models, a simple method of designing and optimizing the EMA coil pair according to technical specifications, was proposed. A loop-shaped coil pair generating uniform magnetic and gradient fields was chosen to demonstrate this method clearly and practically. The results of the optimization showed that the best distance to radius ratio of a loop-shaped coil pair is 1.02 for a uniform magnetic field and 1.75 for a uniform gradient field. The applicability of the method to other shapes of coil configuration was also illustrated. The best width to distance ratio for a square-shaped coil pair is 0.558 and 0.958 for uniform magnetic and gradient fields, respectively. The best height to width ratio and distance to width ratio for a rectangle-shaped coil pair is h/w =[0.9,1.1], d/w =[0.5,0.6] for uniform magnetic field and h/w =[1.0,1.2], d/w =[0.9,1.1] for uniform gradient field. Furthermore, simulations of a microparticle tracking the targeted trajectory were conducted to analyze the performance of the newly designed coils. The simulations suggested the ability of manipulating microparticles via the coils designed by our proposed method. The research mainly proposed a unified design and optimization method for a coil pair, which can support researchers while designing a specific coil pair according to the technical requirements. This study is aimed at researchers who are interested in EMA system and microrobots.

Integration of a Didactic Manufacturing Cell with Different Robot Configurations

The present work makes the exhibition of a manfacturing cell for didactic pulposes, implemented as part of evaluation in the last cycle of mechatronics engineering formation within Technological University of North Aguascalientes. It includes the motivation that led to plnning and subsequent implementation of manufacturing system described, the characteristics of particular processing operations that it was decided to include, methodology to achieve joint work and synchronization of each operation performed, the results of operation obtained and their comparison with initial expectations, as well as the conclusions derived from process, which lead to considering such a project as an ideal model to verify the formation of the future mechatroonics engineers, when faced with applications of their area of exercise, reviewing operating principle of mechanical, electronic, control and computing systems to achieve their synergy in a mechatronic system.

Simple Path Planning for Mobile Robots in the Present of Obstacles

To obtain the near optimal path for the mobile robots in the present of the obstacles, where the robots are subject to both the nonholonomic constraints and the bound to the curvature of the path, a simple planning is applied by the heuristic searching method in which Reeds and Shepp’s shortest paths are chosen as heuristic functions. It has performed well in simulation of mobile robots moving in a cluttered environment.

Dynamic Analysis and Dimensional Synthesis of Easy-to-Protect Large-Load Robot for Extracting Fermented Grains

To improve the operation situation of difficulty and low efficiency in the extraction of fermented grains(FG),a high-load and large-workspace reclaiming robot for ceramic cylinder fermentation is designed,and a reclaiming effector is designed according to the operating characteristics.Firstly,the kinematics and singularity of the mechanism are analyzed.A multi-domain polar coordinate search method is proposed to obtain the workspace and the volume of the mechanism.Secondly,the dynamic modeling is completed and the example simulation is carried out.Thirdly,the motion-force transmission index of the mechanism is established.And based on the global transmissibility and the good-transmission workspace,the dimensional synthesis of the driving mechanism is completed by using the performance atlas-based method.Finally,aiming at the regular workspace size,stiffness and loading capacity,the Pareto optimal solution set of the executive mechanism dimension is obtained by using the multi-objective particle swarm optimization(MOPSO)algorithm.This paper can provide a theoretical basis for the optimal design and control of FG reclaiming robot.

柔性关节机械手模态分析的数值解析方法研究

针对六自由度柔性关节机械手的模态参数,建立了计入刚性连杆和柔性关节的机械臂的数值解析模态分析方法。首先拉格朗日公式建立了柔性关节机器人的动力学模型,然后利用泰勒级数展开法,推导了考虑重力、外力和控制参数的线性化模态分析方程,在此基础上可以通过状态空间矩阵来计算任意机器人构型的模态参数。采用解析法计算了六自由度柔性关节机器人的模态参数,为了验证该方法的有效性,利用基于矢量自回归模型的工作模态技术对模态参数进行了估计,结果表明两种方法的结果具有较好的吻合性。在给定的机器人构型基础上,通过该方法可以快速提取机器人的模态信息。

一种基于根管预备的绳驱机器人设计与分析

该文设计一种应用于根管预备手术中绳驱机器人构型。电机转动输出连接软轴,软轴与绳索滚筒采用锥度插孔相连,可以实现输出轴方便快捷的拆卸,便于末端机构的高温消毒程序。采用绳索驱动实现驱动元件与执行元件的相对远距离布置,保证末端执行部件的较小尺寸,便于在口腔狭小空间中进行动作。对末端执行机构根管锉软轴进行变形分析,并利用相邻关节间绳索的反向拉缩进行运动的补偿,保证关节间运动的解耦。最后进行样机的制作并验证其基本运动与运动补偿具备可行性。

可重构解耦并联移动机器人构型综合及性能分析

为提高机器人承载能力,减少驱动电动机能量消耗且使轮腿模式切换平稳高效,提出了一种可重构解耦并联移动机器人构型,并对其进行了构型综合研究及解耦性和奇异性分析。根据机器人机械腿期望自由度,综合出4种主运动支链;基于螺旋理论的去约束法,综合出58种约束支链;基于螺旋理论的虚拟链法,综合出3R球面并联机构作为机械腿承载支链。随后,给出两个机器人实例。以其中一个机器人为例,建立输入-输出方程,分析了机械腿解耦性;通过反证法,验证了可重构单元的奇异位形,并基于Grassmann线几何判断出奇异类型。最后,分析了承载支链的奇异性对于机械腿运动输出的影响。结果说明,机器人机械腿采用并联支链构型,具有较强的承载能力;机器人基于约束奇异方式实现轮腿切换,可使得切换动作更加平稳;机械腿的可重构性可使得驱动电动机能量消耗减少;机械腿各驱动相互解耦,降低了控制难度,使得机械腿轮腿模式切换更加高效。

张拉整体机器人构型与运动控制研究现状及进展

研究发现张拉整体结构存在于细胞骨架、肌肉-骨骼系统等生物体,并将其原理广泛应用于建筑、雕塑、空间探测等工程结构中。张拉整体结构具有形态可调性、受力可控性、绳索抗拉性和结构轻质、结构自稳定等优势,因此在机器人领域极具应用前景。而软体机器人作为一种新型、仿生、能与人安全交互的机器人,近年来成为力学、材料学、医学、生物学等多学科交叉领域的研究热点之一。但是,要想实现灵活准确的运动、高效地承受外载、迅速地适应环境等复杂特性和功能,张拉整体机器人在其构型、运动步态及控制研究等方面依旧面临着巨大挑战。本研究选取张拉整体机器人的三大典型类别(棱柱形张拉整体机器人、球形张拉整体机器人及构型较复杂的张拉整体机器人),对其构型、运动步态及控制的国内外相关研究现状和发展趋势进行综述,旨在为机器人的仿生学研究提供科学依据。

基于病态参数分离的机器人运动学标定测量构型优化

针对一种高灵巧性机器人及其连杆参数高敏感性与高定位精度需求,为解决机器人运动学标定随机测量构型存在绝对定位精度低、参数辨识效果及标定结果鲁棒性较差的问题,提出一种病态参数分离与DETMAX-改进差分进化(DETMAX-IDE)算法的机器人运动学标定测量构型分步优化方法。首先,建立机器人位置误差模型。其次,建立一种可观性综合指标,评价不同机器人标定测量构型的总体可观测性和灵敏度。最后,分离机器人运动学位置误差模型的病态参数,建立测量构型优化目标函数和约束条件,提出一种基于DETMAX算法与改进差分进化算法结合的分步迭代优化算法(简称为DETMAX-改进差分进化算法,简写为DETMAX-IDE算法),开展机器人运动学标定测量构型分步迭代优化。通过机器人运动学标定仿真与实验,验证了所提方法的有效性。实验结果表明,与随机测量构型相比,所提方法对应的机器人绝对定位精度的平均值和均方差分别降低了62.09%和62.45%。

METHODS OF IMPROVING COMPUTATIONAL ACCURACY OF ROBOT DYNAMICS

In this paper the geometric meaning of robot systems is expounded based on the theory of multibody system. The error accumulation for the known algorithm is analyzed and the cause of ‘Energy consumption’ is revealed, the relationship between the coefficients of dynamic equation is derived so as to establish the canonical equations. The error accumulation of dynamics can be eliminated by using canonical equations and the symplectic integral method so that the computational accuracy can be ensured effectively. As an example, a planar robotics system is considered.

MODELING OF ROBOT MANIPULATOR AND OBSTACLE AVOIDANCE

A robot intelligent path planning system RIPPS is developed, which can be utilized for a robot off line programming tool. The system consists of three parts: geometric modeler, kinematic modeler and path planer. The geometric modeler is used to construct the robot working environment cluttered with obstacles and the robot kinematic modeler to define robot manipulators by the input parameters. Giving robot start and the goal configurations, the path planer can produce a quasi optimal path. By transforming obstacles into the C space to form C obstacles, the path searching is performed in C space. The planning simulations are performed on a SGI workstation, the future research is to implement the planer on a commercial robot manipulators.

Stewart型并联机器人的奇异对其运动精度的影响

以9-3 Stewart型并联机器人为研究对象,分析其在机构接近奇异位形时动平台运动精度的情况。通过计算并联机器人速度Jacobian矩阵的行列式得到奇异点的坐标。通过虚拟样机实验,得到动平台参考点位置反解和正解计算的相对误差。用转动Jacobian矩阵条件数的倒数来度量机构接近奇异的程度,并分析该程度与上述相对误差之间的映射关系。研究结果表明:当指标值大于7.027×10^(-5)时,正、反解的相对误差可忽略不计,这为奇异规避、路径规划等后续工作提供了理论参考。

冗余漂浮空间机器人多任务轨迹规划

针对冗余漂浮空间机器人在单次行程中连续执行多项轨道任务的能耗最优轨迹规划问题,本文提出一种改进遗传算法,将同时优化3种类型基因引入,使得每条染色体包含3部分,即任务序列、与任务序列对应的关节构型序列和描述机器人关节轨迹的正弦多项式系数,对染色体的3部分进行独立编码,并在迭代寻优过程中对3个组成部分独立执行交叉和变异操作。仿真结果表明:与传统遗传算法相比,本文算法具有精度高、计算量少和CPU时间短的优点。