Path-following steering control for articulated vehicles

Passive steering systems have been used for some years to control the steering of trailer axles on articulated vehicles. These normally use a 'command steer' control strategy, which is designed to work well in steady-state circles at low speeds, but which generates inappropriate steer angles during transient low-speed maneuvers and at high speeds. In this paper, 'active' steering control strategies are developed for articulated heavy goods vehicles. These aim to achieve accurate path following for tractor and trailer, for all paths and all normal vehicle speeds, in the presence of external disturbances. Controllers are designed to implement the path-following strategies at low and high speeds, whilst taking into account the complexities and practicalities of articulated vehicles. At low speeds, the articulation and steer angles on articulated heavy goods vehicles are large and small-angle approximations are not appropriate. Hence, nonlinear controllers based on kinematics are required. But at high-speeds, the dynamic stability of control system is compromised if the kinematics-based controllers remain active. This is because a key state of the system, the side-slip characteristics of the trailer, exhibits a sign-change with increasing speeds. The low and high speed controllers are blended together using a speed-dependent gain, in the intermediate speed range. Simulations are conducted to compare the performance of the new steering controllers with conventional vehicles (with unsteered drive and trailer axles) and with vehicles with command steer controllers on their trailer axles. The simulations show that active steering has the potential to improve significantly the directional performance of articulated vehicles for a wide range of conditions, throughout the speed range. © VC 2013 by ASME.

轮式仿人机器人的ZMP建模及动态稳定判据

介绍了ZMP的概念,比较常见的几种ZMP建模方法,提出将高效牛顿-欧拉算法(RENA)与ZMP的概念相结合的迭代ZMP建模方法,并利用该方法完成轮式仿人机器人的ZMP建模.通过模型分析,得出该轮式仿人机器人的ZMP简化计算公式.最后得出此类轮式仿人机器人的稳定性判据及稳定度的定义.

一种基于反作用力的仿人机器人ZMP建模与测量

“零力矩点”是判定仿人机器人动态稳定运动的重要指标。本文根据零力矩点的概念,利用机器人车体的几何及动力学关系,建立基于反作用力的正交轮式移动仿人机器人的零力矩点模型;提出了基于电流传感器、电机编码器等传感器的零力矩点的实时测量方法,并给出了该方法的结构框图。由于轮式移动仿人机器人与地面呈点式接触,难于安装力传感器,所以这种方法尤其适用于轮式移动仿人机器人。

可重构模块机器人倾翻稳定性研究

介绍了一种可重构模块机器人,它可以通过构形的变化来提高系统的稳定性和抗倾翻能力.该机器人由3个模块组成,采用履带驱动,具有直线、三角、并排3种对称构形.在对移动机器人的倾翻因素和倾翻对策等问题进行分析的基础上,提出稳定锥方法,用倾翻性能指数对移动机器人的静、动态稳定性进行综合判定.讨论了变形机器人3种对称构形在仰俯、偏转、倾斜等干扰组合作用下的倾翻性能指数和综合稳定性,并进行了仿真实验和非结构环境实验.

轮式仿人机器人动态稳定性分析及腰部控制研究

仿人机器人研究从仿生学角度具有拟人功能的智能机器人，它需要结合机构、控制、传感和材料等技术。随着社会经济与科技水平的发展，使仿人机器人引入人类环境，与人类一同工作、合作和交互成为可能，仿人机器人的研究也成为当今机器人研究中的热点内容之一。本论文以中科院沈阳自动化研究所机器人学重点实验室承担的国家863计划“十五”项目——“宜人化双臂操作型服务机器人”为依托，以本项目中的轮式仿人机器人为研究对象。本论文的主要内容包括：对项目样机中的差动腰部机构的运动学、动力学建模，腰部机构基于运动学的控制算法及实验研究；仿人机器人的整体动力学建模，基于动力学模型的腰部机构控制算法与仿真研究；依据零力矩点(ZMP)理论完成轮式仿人机器人的ZMP建模及其动态稳定性的深入分析。人类的腰部具有高度的灵活性、柔韧性，是人体系统运动的调节中枢。仿人机器人的腰部机构同样应具有调节系统平衡、协调系统运动的作用。本文中仿人机器人的腰部采用新颖的差动并联驱动的腰部机构。本文建立了该机构的运动学和动力学模型，采用分解运动速度控制实现了差动腰部机构的运动学控制，并进行了实验研究。仿人机器人是一个多自由度、非线性、具有复杂运动学、动力学特性的多刚体系统。本文在合理简化的基础上，利用高效牛顿－欧拉动力学建模方法完成了本轮式仿人机器人的整体动力学建模，分析了各关节间的动力学影响，并在此基础上给出了仿人机器人腰部机构动力学模型，该模型考虑了车体、手臂运动及手部外负载的动力学影响。本文还对基于动力学模型的腰部机构带计算力矩补偿的PD伺服控制与腰部机构基于运动学的PD伺服控制进行了仿真比较研究，仿真结果表明，基于动力学模型的腰部机构计算力矩控制算法能有效地提高腰部机构的位姿跟踪精度。本轮式仿人机器人移动性好，但支撑点少，上身重量偏大，它的动态稳定性成为不容忽视的问题。零力矩点理论是用于判定机械系统动态平衡的经典理论，至今仍被广泛应用。本文基于零力矩点概念，结合机器人的高效牛顿－欧拉动力学模型，建立了仿人机器人的基于车体坐标系的迭代ZMP计算模型，该模型考虑了机器人关节的质量、惯量等参数，包含了惯性力、离心力、重力等对ZMP的影响。经分析可知，腰部机构的运动模式和车体运动加速度是影响ZMP的主要因素，进而给出了ZMP的简化计算模型，依据该简化模型，本文深入讨论了腰部机构与车体的协调运动和轮式仿人机器人的动态稳定性之间的关系，为考虑机器人动态稳定性的腰部机构运动规划及仿人机器人的动态稳定性控制奠定了基础。

边坡动力响应分析及应用研究

As a marginal subject, dynamic responses of slopes is not only an important problem of engineering geology (Geotechnical problem), but also of other subjects such as seismology, geophysics, seismic engineering and engineering seismic and so on. Owning to the gulf between different subjects, it is arduous to study dynamic responses of slopes and the study is far from ripeness. Studying on the dynamic responses of slopes is very important in theories as well as practices. Supported by hundreds of bibliographies, this paper systemically details the development process of this subject, introduces main means to analyze this subject, and then gives brief remarks to each means respectively. Engineering geology qualitative analysis is the base of slopes dynamic responses study. Because of complexity of geological conditions, engineering geology qualitative analysis is very important in slopes stability study, especially to rock slopes with complex engineering geology conditions. Based on research fruits of forerunners, this paper summarizes factors influencing slopes dynamic stability into five aspects as geology background, stratums, rock mass structure, and topography as well as hydrogeology condition. Based on rock mass structure controlling theory, engineering geology model of the slope is grouped into two typical classes, one is model with obvious controlling discontinuities, which includes horizontal bedded slope, bedding slope, anti-dip slope, slide as well as slope with base rock and weathered crust; the other is model without obvious controlling discontinuities, which includes homogeneous soil slope, joint rock mass slope. Study on slope failure mechanism under dynamic force, the paper concludes that there are two effects will appear in slope during strong earthquake, one is earthquake inertia force, the other is ultra pore pressure buildup. The two effects lead to failure of the slope. To different types of slope failure, the intensity of two effects acting on the slope is different too. To plastic flow failure, pore pressure buildup is dominant; to falling rock failure and toppling failure, earthquake inertia force is dominant in general. This paper briefly introduces the principle of Lagrangian element method. Through a lot of numerical simulations with FLAC3D, the paper comprehensively studies dynamic responses of slopes, and finds that: if the slope is low, displacement, velocity and acceleration are linear enlarging with elevation increasing in vertical direction; if the slope is high enough, displacement, velocity and acceleration are not linear with elevation any more, on the other hand, they fluctuate with certain rhythm. At the same time, the rhythm appears in the horizontal direction in the certain area near surface of the slope. The distribution form of isoline of displacement, velocity and acceleration in the section of the slope is remarkably affected by the slope angle. In the certain area near the slope surface, isoline of displacement, velocity and acceleration is parallel to the surface of the slope, in the mean time, the strike direction of the extreraum area is parallel to the surface of the slope too. Beyond this area, the isoline direction and the strike direction of the extremum area turn to horizontal with invariable distance. But the rhythm appearing or not has nothing to with the slope angle. The paper defines the high slope effect and the low slope effect of slopes dynamic responses, discusses the threshold height H^t of the dynamic high slope effect, and finds that AW is proportional to square root of the dynamic elastic moduli El P , at the same time, it is proportional to period Tof the dynamic input. Thus, the discriminant of H^t is achieved. The discriminant can tell us that to a slope, if its height is larger than one fifth of the wavelength, its response regular will be the dynamic high slope effect; on the other hand, its response regular will be the dynamic low slope effect. Based on these, the discriminant of different slopes taking on same response under the same dynamic input is put forward in this paper. At the same time, the paper studies distribution law of the rhythm extremum point of displacement, velocity and acceleration, and finds that there exists relationship of N = int among the slope height H, the number of the rhythm extremum VHlhro) point N and ffthre- Furthermore, the paper points out that if N^l, the response of the slope will be dynamic high slope effect; \fNdynamic low slope effect, and the distance of the two adjacent extremum points equals to //,/,",. At the same time, the paper finds that the distance of two adjacent extremum districts near the slope surface is H,hn too. In chaptet 5, based on residual pushing force model as well as pore pressure model of Martin-Finn-Seed, a method for estimating the permanent displacement of the slide is put forward in this paper, and then put it into dynamic analysis of the left abutment slope of Jinping hydropower station. The forecasting result is almost coincided with numerical simulation result. The Jinping hydropower station, located at the middle stream of Yalongjiang River and the west side of Jinpingdahewan, is the highest double-curvature arch dam planned in building in the world. However, deep fractures are well developed at the left abutment slope, so stability of the slope is a key engineering geological problem. The paper studies the dynamic stability of the slope. In the analysis, considering regional geology and regional seismology of the slope, combining with characteristics of the slope as well as the scale of the project, PGA(peak ground acceleration) of the site is decided (about 197.1cm/s2) by engineering seismology, and then the seismic input used in the slope dynamic analysis is determined. Comprehensive studies are carried out on the slope, especially to its deep fractures, and then the paper concludes that the deep fractures of slope are the result of the combination unloading effect of gravity and tectonic stress. At the same time, the failure model of the slope under dynamic input is attained. Based on these, the stability is comprehensively studied for section IV-IV with numerical simulation method as well as method putting forward in chapter 5. At last, the paper concludes that under dynamic input, the section will slide along fault f9, some deep fractures and fault/5 with certain permanent displacement, and this must be taken into consideration in the engineering.

Dynamically Stable Legged Locomotion (September 1985-Septembers1989)

This report documents our work in exploring active balance for dynamic legged systems for the period from September 1985 through September 1989. The purpose of this research is to build a foundation of knowledge that can lead both to the construction of useful legged vehicles and to a better understanding of animal locomotion. In this report we focus on the control of biped locomotion, the use of terrain footholds, running at high speed, biped gymnastics, symmetry in running, and the mechanical design of articulated legs.

Measurement-based Method for Wind Farm Power System Oscillations Monitoring

The global increase in the penetration of renewable energy is pushing electrical power systems into uncharted territory, especially in terms of transient and dynamic stability. In particular, the greater penetration of wind generation in European power networks is, at times, displacing a significant capacity of conventional synchronous generation with fixed-speed induction generation and now more commonly, doubly fed induction generators. The impact of such changes in the generation mix requires careful monitoring to assess the impact on transient and dynamic stability. This study presents a measurement-based method for the early detection of power system oscillations, with consideration of mode damping, in order to raise alarms and develop strategies to actively improve power system dynamic stability and security. A method is developed based on wavelet-based support vector data description (SVDD) to detect oscillation modes in wind farm output power, which may excite dynamic instabilities in the wider system. The wavelet transform is used as a filter to identify oscillations in frequency bands, whereas the SVDD method is used to extract dominant features from different scales and generate an assessment boundary according to the extracted features. Poorly damped oscillations of a large magnitude, or that are resonant, can be alarmed to the system operator, to reduce the risk of system instability. The proposed method is exemplified using measured data from a chosen wind farm site.

A Wavelet-Prony Method for Modeling of Fixed-Speed Wind Farm Low-Frequency Power Pulsations

The increasing penetration of wind generation on the Island of Ireland has been accompanied by close investigation of low-frequency pulsations contained within active power flow. A primary concern is excitation of low-frequency oscillation modes already present on the system, particularly the 0.75 Hz mode as a consequence of interconnection between the Northern and Southern power system networks. In order to determine whether the prevalence of wind generation has a negative effect (excites modes) or positive impact (damping of modes) on the power system, oscillations must be measured and characterised. Using time – frequency methods, this paper presents work that has been conducted to extract features from low-frequency active power pulsations to determine the composition of oscillatory modes which may impact on dynamic stability. The paper proposes a combined wavelet-Prony method to extract modal components and determine damping factors. The method is exemplified using real data obtained from wind farm measurements.

A Tower-Shadow Model for Wind Turbines Using a Wavelet-Prony Method

The increasing penetration of wind generation on the Island of Ireland has been accompanied by close investigation of low-frequency pulsations contained within active power flow. A primary concern is excitation of low-frequency oscillation modes already present on the system, particularly the 0.75 Hz mode as a consequence of interconnection between the Northern and Southern power system networks. In order to determine whether the prevalence of wind generation has a negative effect (excites modes) or positive impact (damping of modes) on the power system, oscillations must be measured and characterised. Using time – frequency methods, this paper presents work that has been conducted to extract features from low-frequency active power pulsations to determine the composition of oscillatory modes which may impact on dynamic stability. The paper proposes a combined wavelet-Prony method to extract modal components and determine damping factors. The method is exemplified using real data obtained from wind farm measurements.

Analysis of Fixed-Speed Wind Farm Low-Frequency Power Pulsations using a Wavelet-Prony Method

The increasing penetration of wind generation on the Island of Ireland has been accompanied by close investigation of low-frequency periodic pulsations contained within the active power flow from different wind farms. A primary concern is excitation of existing low-frequency oscillation modes already present on the system, particularly the 0.75 Hz mode as a consequence of the interconnected Northern and Southern power system networks. Recently grid code requirements on the Northern Ireland power system have been updated stipulating that wind farms connected after 2005 must be able to control the magnitude of oscillations in the range of 0.25 - 1.75 Hz to within 1% of the wind farm's registered output. In order to determine whether wind farm low-frequency oscillations have a negative effect (excite other modes) or possibly a positive impact (damping of existing modes) on the power system, the oscillations at the point of connection must be measured and characterised. Using time - frequency methods, research presented in this paper has been conducted to extract signal features from measured low-frequency active power pulsations produced by wind farms to determine the effective composition of possible oscillatory modes which may have a detrimental effect on system dynamic stability. The paper proposes a combined wavelet-Prony method to extract modal components and determine damping factors. The method is exemplified using real data obtained from wind farm measurements.

Measurement-based Method for Wind Farm Power System Oscillation Monitoring

The global increase in the penetration of renewable energy is pushing electrical power systems into uncharted territory, especially in terms of transient and dynamic stability. In particular, the greater penetration of wind generation in European power networks is, at times, displacing a significant capacity of conventional synchronous generation with fixed-speed induction generation and now more commonly, doubly-fed induction generators. The impact of such changes in the generation mix requires careful monitoring to assess the impact on transient and dynamic stability. This paper presents a measurement based method for the early detection of power system oscillations, with attention to mode damping, in order to raise alarms and develop strategies to actively improve power system dynamic stability and security. A method is developed based on wavelet transform and support vector data description (SVDD) to detect oscillation modes in wind farm output power, which may excite dynamic instabilities in the wider system. The wavelet transform is used as a filter to identify oscillations in different frequency bands, while SVDD is used to extract dominant features from different scales and generate an assessment boundary according to the extracted features. Poorly damped oscillations of a large magnitude or that are resonant can be alarmed to the system operator, to reduce the risk of system instability. Method evaluation is exemplified used real data from a chosen wind farm.

Calculation of Critical Clearing Time of Embedded Generation for Relay Setting Based on Optimisation Method

his paper proposes an optimisation-based method to calculate the critical slip (speed) of dynamic stability and critical clearing time (CCT) of a self-excited induction generator (SEIG). A simple case study using the Matlab/Simulink environment has been included to exemplify the optimisation method. Relationships between terminal voltage, critical slip and reactance of transmission line, CCT and inertial constant have been determined, based on which analysis of impact on relaying setting has been further conducted for another simulation case.

Transient analysis of variable-speed wind turbines at wind speed disturbances and a pitch control malfunction

As wind power generation undergoes rapid growth, new technical challenges emerge: dynamic stability and power quality. The influence of wind speed disturbances and a pitch control malfunction on the quality of the energy injected into the electric grid is studied for variable-speed wind turbines with different power-electronic converter topologies. Additionally, a new control strategy is proposed for the variable-speed operation of wind turbines with permanent magnet synchronous generators. The performance of disturbance attenuation and system robustness is ascertained. Simulation results are presented and conclusions are duly drawn. (C) 2010 Elsevier Ltd. All rights reserved.

A physical packing sequence algorithm for the container loading problem with static mechanical equilibrium conditions

The container loading problem (CLP) is a combinatorial optimization problem for the spatial arrangement of cargo inside containers so as to maximize the usage of space. The algorithms for this problem are of limited practical applicability if real-world constraints are not considered, one of the most important of which is deemed to be stability. This paper addresses static stability, as opposed to dynamic stability, looking at the stability of the cargo during container loading. This paper proposes two algorithms. The first is a static stability algorithm based on static mechanical equilibrium conditions that can be used as a stability evaluation function embedded in CLP algorithms (e.g. constructive heuristics, metaheuristics). The second proposed algorithm is a physical packing sequence algorithm that, given a container loading arrangement, generates the actual sequence by which each box is placed inside the container, considering static stability and loading operation efficiency constraints.