Kinematic chains for robot hands—II. Kinematic constraints, classification, connectivity, and actuation

The work in this paper follows on from Part 1. We now consider the specific example of robot hands and identify several kinematic constraints of these devices. The method for number synthesis of kinematic chains in Part 1 is applied in several different ways in order to synthesise chains suitable for application as robot hands; several examples of the structures so found are presented. So as to identify those kinematic chains that are more promising than others, the new concept of minimal sets of kinematic chains is defined. Another new concept, the variety of a kinematic chain, is defined and used to make generalisations about relative connectivity within kinematic chains, which has application in the selection of actuated pairs. Fractionation of kinematic chains is reviewed in light of the concept of variety. The work presented here has application far beyond the number synthesis of alternative structures for robot hands.     

Indenting with pyramids—I. Theory

Using an approximate method, expressions are obtained for the load necessary to indent a rigid-plastic non-hardening solid to a given depth with square-based and triangular-based pyramids. Experimental results will be presented in Part II.     

机器人运动支链构型设计新方法

机器人构型设计中的关键问题就是设计具有确定末端运动特征的支链。提出机器人运动单元、基本运动单元和复合运动单元的概念,给出了各种运动单元的合成原理与部分算法。最后以一类具有平面副运动特征的支链为例,表明该方法简便易行。     

Kinematic parameter calibration method for industrial robot manipulator using the relative position

A new calibration method for industrial robot system calibration on a manufacturing floor is presented in this paper. To calibrate the robot system, a laser sensor to measure the distance between robot tool and measurement surface is attached to the robot end-effector and a grid is established in the floor. Given two position command pulses for a robot manipulator and using the position difference between two command pulses, the relative position measurement calibration method will find the real robot kinematic parameters. The procedures developed have been applied to an industrial robot. Finally, the effects of the models used to calibrate the robot are discussed. This calibration method represents an effective, low cost and feasible technique for the industrial robot calibration in lab. projects and industrial environments.     

洁净精密装校机器人的运动学分析及轨迹规划

针对某大型激光器装置的装校过程模块化、阵列化及超洁净工作环境等特点,分析了洁净精密装校机器人的轨迹规划和智能化无人装校的实际需求,提出了“轨迹取点→单关节变化PTP口规划→初步轨迹拟合→基于时间和防料动轨迹优化”的轨迹规划思路和方法.根据该机器人结构特征,应用D-H法建立坐标系,完成了运动学正逆解分析.基于运动学位姿方程,按照机器人作业规划流程,完成了洁净精密装校机器人安装一个模块的轨迹规划和优化,并运用MATLAB 2008绘制了具体轨迹曲线.最后运用Pro/E 4.0进行了机构运动学仿真验证,验证表明洁净精密装校机器人在无人工干预及超洁净环境下可实现高洁净、高精密装校.     

高机动性越障机器人运动学分析与轨迹控制研究

高机动性越障机器人运动控制要求能适应野外复杂、多变的地形环境,灵活、准确地绕过不可攀越障碍,按照路径规划给定的路径行进.本文通过对越障机器人的结构及车轮排布,对越障机器人的轨迹控制进行运动学分析,在运动学分析的基础上提出一种比较好的速度匹配控制方法,进而实现越障机器人的轨迹控制,实验结果表明越障机器人运动学分析和控制方法符合设计要求.     

On plane Prager-structures—I

Prager-structures differ from classical least-weight trusses (or Michell continua) in two respects: the sign of all member forces must be the same and the vertical location of all external loads is to be optimized. A systematic method for constructing plane Prager-structures for any system of vertical loads is outlined and illustrated with examples. It is established that plane Prager-structures (a) always consist of a single funicular and (b) the optimal elevation of the loads also provides an influence line for the minimum weight.     

Kinematic analysis of the wire parallel mechanism for full coordinate measuring of industrial robot

This paper presents a wire parallel mechanism for full coordinate measuring of industrial robot. The mechanism is constructed with six parallel wires that act as links. The position and orientation of a robot end-effector are obtained from the wire lengths. The equations of the forward kinematics are solved by a Newton-Raphson method, and the unique solution is determined from the geometric configuration of the mechanism. A method to estimate the workspace is presented. Through simulations, it is verified that the proposed mechanism can measure a robot pose over a large workspace, and can be used effectively for full coordinate measuring of a robot with little cost and effort.     

Michell layouts for various combinations of line supports—I

The optimal layout of least-weight grillages or beam systems of given depth has been determined in a closed analytical form for almost all conceivable boundary and load conditions. In spite of its early introduction at the turn of the century, the theory of least-weight trusses or “Michell-frameworks” has yielded, on the other hand, only few solutions for relatively restricted supports and loadings. The aim of this paper is to explore Michell layouts, when supports are provided anywhere along given lines. It is shown that for this less restricted case the solutions correspond to fields of constant strain, which give layouts consisting of a finite number of straight members. More complex classes of solutions will be discussed in a separate paper.     

A computerized methodology for structural synthesis of kinematic chains: Part 1— Formulation

In an effort to develop a fully computerized approach for structural synthesis of kinematic chains the steps involved in the method of structural synthesis based on transformation of binary chains [38] have been recast in a format suitable for implementation on a digital computer. The methodology thus evolved has been combined with the algebraic procedures for structural analysis [44] to develop a unified computer program for structural synthesis and analysis of simple jointed kinematic chains with a degree of freedom 0. Applications of this program are presented in the succeeding parts of the paper.     

Flywheel energy storage—I: Basic concepts

The basic concepts of flywheel energy storage systems are described in the first part of a two part paper. General equations for the charging and discharging characteristics of flywheel systems are developed and energy density formulas for flywheel rotors are discussed. It is shown that a suspended pierced disk flywheel is competitive with the super-flywheel designs currently being suggested in the literature.In Part II the details of a magnetically levitated spokeless ring flywheel design are provided.     

Resistance distance method for determination of isomorphism,stiffness and best input link among planar Kinematic chains

The detection of isomorphism among kinematic chains and their derived mechanisms has been a hot area of research for the last several years. In this paper, a quantitative method (Resistance distance method) is proposed in order to compare all the distinct chains with specified number of links and degree of freedom, for rigidity of the chain and to select the best input link to introduce motion and to test isomorphism thoroughly and uniquely. In this method, the kinematic chains are represented in the form of resistance graph and from that graph a Laplacian matrix is generated which is further transformed into a resistance distance matrix.     

A computerized methodology for structural synthesis of kinematic chains: Part 3— application to the new case of 10-link, three- freedom chains

The unified computer program for structural synthesis and analysis developed in Part 1 has been employed to derive the new and complete collection of 97 10-link, three-freedom simple-jointed kinematic chains. The program shows that of these chains, 3 have total freedom, 70 have partial freedom and the remaining 24 have fractionated freedom and that the 97 chains yield a total of 676 distinct mechanisms.     

Interaction yield hypersurfaces for the plastic behaviour of beams—I. Combining bending, tension and shear

A variational method has been used to construct envelopes of the interaction yield surfaces for elastic, perfectly plastic beams subjected to combined bending moment, axial tension and transverse shear force. A lower bound of the envelope for the interaction yield curves relating bending moment and transverse shear force is obtained using a numerical scheme for beams having rectangular-shaped cross-sections. The result is recast into a simple equation with the aid of the least-squares method. A good upper bound of the envelope for the interaction yield curves which combine transverse shear force and axial tension is also derived. A formula for the interaction yield surfaces for combined bending moment, axial tension and transverse shear force is suggested.     

Long rod penetration models—Part I. A flow field model for high speed long rod penetration

A semi-infinite solenoid in a uniform velocity flow field is used as a model for the quasi-steady primary phase of long rod penetration. Assuming the materials are perfectly plastic and that the Lévy-Mises equations hold leads to a modified Bernoulli equation. Relationships between the strength factors R_t and Y_p and the dynamic yield strengths of the materials are indicated. The effects of unsteady motion are briefly examined.     

The thermal behaviour of thin cylindrical shells—I. Heat transfer and harmonic analysis

The combined heat transfer and thermal stress analysis of thin cylindrical shells is considered in this and a subsequent paper. This paper presents two typical heat transfer models and the harmonic analysis which is used to represent the temperature distributions as double Fourier coefficients. These models are (i) a circular hot spot caused by a postulated loss of part of the internal refractory lining in a high temperature cylindrical reactor vessel and (ii) a heated “band” caused by solar heating on a horizontal storage vessel. In the case of the hot spot the inside and outside surface temperature distributions vary independently in the axial and circumferential directions, with linear transition through the thickness. In the simpler case of solar heating, the through-thickness temperature gradient is negligible and the temperature only varies around the circumference. The use of the double Fourier coeficients to obtain the displacements and stresses is described in Part II     

Thick rectangular plates—I: The generalized Navier solution

Navier's classical solution for the problem of a statically loaded, rectangular plate which is simply-supported on all edges is generalized so as to provide a solution for the problem when transverse shear deformations are taken into account. Such solutions are provided for both Mindlin's plate theory and a new plate theory, recently published, which allows for warping of transverse sections of the plate. The results of the analyses are simple expressions for the Fourier coefficients in the expansions representing the transverse deflection and rotations of normals to the plate midsurface. Although both theories predict the same transverse deflection, the rotations and inplane stresses are different for the two theories. Some observations and comments concerning the effects of transverse shears on the deflections of plates and inplane stresses are made.     

Flexural-torsional buckling tests on beamcolumns with sheeting-rail type restraints—I. Elastic torsion tests

In preparation for a programme of tests as beam columns 50 specimens of a 305 × 101·6 mm × 25 kg/m U.B. were tested elastically to determine the St. Venant torsion constant of each, in order to isolate the effects of its known wide variation among nominally identical specimens.

The results showed a scatter from −20 to +18 per cent of the mean, which was itself about 50 per cent higher than that given in current design recommendations.

Details of the specimen dimensions and of the method of testing are given for comparison with similar tests elsewhere.