Synthesis of the forward kinematics problem algebraic modeling for the general parallel manipulator: displacement-based equations

This paper closes a triptic to address the issue of the forward kinematics problem (FKP) aimed at certified solving with an exact algebraic method. This solving method was described in the first article published in Advanced Robotics. The second one investigated the formulation specifically applied to the planar parallel manipulators. This third paper is the logical one in the footsteps of the formersones, since it continues the formulation analyses and brings them to the general spatial parallel manipulator. Hence, this paper focuses on the displacement-based equation systems. This paper is the first one to present a synthesis on forward kinematics modeling focusing on finding an optimal mathematical formulation based on the displacement-based equation systems. The majority of parallel manipulators in applications can be modeled by the 6-6 hexapod or so-called Gough platform which is constituted by a fixed base and a mobile platform attached to six kinematics chains with linear (prismatic) actuators located between two revolute or Cardan joints. Again, in order to implement algebraic methods, the parallel manipulator kinematics shall be formulated as polynomial equations systems where the equation number is at least equal to the unknown numbers. Six geometric formulations were derived. The selected algebraic proven method is implementing Gröbner bases from which it constructs an equivalent univariate polynomial system. The resolution of this last system exactly determines the real solutions which correspond to the manipulator postures. The FKP resolution of the general 6-6 parallel manipulator outputs 40 complex solutions. Several instantiations shall be computed in order to select the model which leads to the FKP resolution with the lowest response times and smaller file sizes. It was possible to reject three modelings leading to bad performances or resolution failure. It was possible to determine one formulation where the solving computations were definitely better than the others.     

Influence of clamping support distance on distortion of welded T joints

Abstract

A study is presented on the influence of the clamping support distance on welding distortion of 6 mm thick gas metal arc welded structural steel T joints. Experiments were performed for two clamping conditions and are compared to simulations based on a previously presented model. It was found that clamping closer to the weld seam reduces angular as well as bending distortion. In order to assess the accuracy of the results, sensitivity analyses were performed on the influence of predeformation and material parameters. It is shown that an initial predeformation has an influence on the final welding distortion. Additionally, it has been found that selection of material properties within the range of variations permitted by the material norms has a strong influence on the predicted distortion. Results were improved using material specific data rather than generic data for the relevant material class. Also the assumed phase volume change plays an important role.     

41—THE RETRACTION AND STRETCH OF WRAPPED ELASTOMERIC-FIBRE CORE YARNS

Equations are given that relate the structure of spirally wrapped elastomeric-fibre core yams to their stretch properties. The model employed improves upon previous ones by considering the effect of covering-yarn diameter. Graphs are given that facilitate the use of the theory for manufacturing purposes.

A comparison with available experimental data indicates an improved agreement between actual and predicted values of retraction in the most important case, where the input and output yarn lengths are measured. It is expected that the improved theory given here will show to much greater advantage with the present commercial fine-core wrapped structures.

In the special case where the wrapping or covering yarns have very low twist, the basic theory is inadequate. Modifications to account for compression of the cover yarn are accordingly included to enable an approximate relationship between yarn structure and stretch to be obtained in this case.     

基于MODELS的工频弧光接地过电压的仿真

弧光接地过电压是中性点不接地系统中危害最大的过电压之一.目前,关于弧光接地过电压的研究大都采用系统仿真,基于工频熄弧理论,通过控制开关的闭合来模拟电弧的熄灭和重燃,观察弧光接地过电压情况.由于电弧的熄灭和重燃具有强烈的统计特性,电弧不一定是在工频过零时熄灭,也不一定是在电压达到最大值时重燃.因此,按一个工频周期来设定开关的开闭时间模拟弧光接地过电压时,模型不够准确.鉴于这种情况,在对弧光接地过电压产生机理深入研究的基础上,提出了一种新的开关控制方法,采用EMTP中的控制系统暂态分析TACS模块和MODELS模块对开关的控制部分进行处理.运用MODELS模块中特定的MODELS语言编写控制程序,输出一个信号作为TACS开关的输入控制信号,当满足给定电压和电流门槛值时,开关便会相应地闭合及断开.不必按一个工频周期来设定开关的开闭时间,提高了仿真模型的精确性.将其应用于10 kV中性点不接地系统及小电阻接地系统的弧光接地过电压的研究,取得了预期效果,具有很好的应用前景.     

太阳能电池的仿真模型设计和输出特性研究

在考虑了光照强度和电池温度2种因素对太阳能电池技术参数和输出特性影响的基础上,采用了太阳能电池的实用化数学模型,在电力系统电磁暂态软件平台EMTP/ATP上利用MODELS语言和TACS功能搭建了太阳能电池的通用仿真模型.该模型的功能主要是通过改变短路电流,开路电压,最大功率点电流、电压等太阳能电池板的技术参数,研究不同型号太阳能电池板的伏安特性和功率特性.并针对3组不同光照强度和电池温度,对太阳能电池板的伏安特性和功率特性进行了仿真研究.研究结果表明:随着光照强度的减小,太阳能电池板的最大输出功率也减小;随着电池温度的减小,太阳能电池板的最大输出功率呈上升态势.     

Design of single element flow control device in twin strand billet tundish for continuous casting of steel using flow simulation model

Abstract

An optimal single element flow control device (SEFCD) is proposed in the present study for a small capacity twin strand tundish, to produce steel billet with the desired cleanliness, designed by means of numerical experimentation. To achieve this goal, a mathematical model based on the SOLA-SURF technique and the k-? (where k is the kinetic energy of the fluid and ? is its dissipation) two equation turbulence model has been developed to simulate the fluid flow phenomena of molten steel, as well as the mass transfer phenomena of tracer during steady state operation in the tundish. The accuracy of the mathematical model has also been verified by water model experiments, which indicate that the mathematical model is sufficiently accurate and suitable as a tool to develop an optimal SEFCD as required in the present study. Several SEFCD designs have then been evaluated using the mathematical model. The simulated results show that a billet tundish with a high, long, trough shaped pouring pad arrangement has the highest residence time, which promotes inclusion removal, and is thus considered the optimal SEFCD design for the billet tundish.     

Combined direct and indirect adaptive control of robot manipulators using multiple models

A novel methodology is proposed for the adaptive control of rigid robotic manipulators. The proposed method utilizes multiple adaptive models for the identification and control of the manipulator. The present study is an extension of our previous work which utilized an indirect adaptive control approach with multiple models for better transient performance. The proposed scheme uses a composite approach where both prediction and tracking errors are used in a combined direct and indirect adaptive control framework. Simulation results are given to demonstrate the efficient use of the methodology.     

Action recognition and understanding through motor primitives

In robotics, recognition of human activity has been used extensively for robot task learning through imitation and demonstration. However, there has not been much work performed on modeling and recognition of activities that involve object manipulation and grasping. In this work, we deal with single arm/hand actions which are very similar to each other in terms of arm/hand motions. The approach is based on the hypothesis that actions can be represented as sequences of motion primitives. Given this, a set of five different manipulation actions of different levels of complexity are investigated. To model the process, we use a combination of discriminative support vector machines and generative hidden Markov models. The experimental evaluation, performed with 10 people, investigates both the definition and structure of primitive motions, as well as the validity of the modeling approach taken.     

配电线路感应雷过电压计算

为研究雷电感应过电压特性,提出了一种基于MODELS语言并应用ATP-EMTP软件计算多导体传输线感应过电压的新方法.计算时考虑了大地损耗对垂直电场的影响,并且在计算过程中将线路本身等效为无损传输线.将实际计算的结果与火箭引雷实测数值以及其他模型计算结果进行了对比,验证了该方法的有效性。     

The Effect of Detection and Restoration Times for Error Recovery in Communication Networks

Detection and restoration times are oftenignored when modeling network reliability. In thispaper, we develop Markov Regenerative Reward Models(MRRM) to capture the effects of detection andrestoration phases of network recovery. States of the MRRMrepresent conditions of network resources, while statetransitions represent occurrences of failure, repair,detection, and restoration. Reward rates, assigned to states of the MRRM are computed based on aperformance model that accounts for contention. Wecompare our model with ones that ignore these parametersand show significant differences, in particular for transient measures.