Modeling and control of hydraulic excavator''''s arm

1 INTRODUCTIONA hydraulic excavator is a multi-functionalconstruction machine ,and is used for excavating,dumping,finishing,lifting work, etc . However ,operators who control hydraulic excavators mustbe trainedfor several years to do such work quicklyand skillfully . A hydraulic excavator has threelinks :boom,dipper and bucket . An operator hasonly two arms . Thus ,it is not easy for beginnersto execute elaborate work that manipulates threelinks at the same ti me . Moreover ,the operator…     

Dynamic modeling and analysis of 3-■RS parallel manipulator with flexible links

The dynamic modeling and solution of the 3-■RS spatial parallel manipulators with flexible links were investigated.Firstly,a new model of spatial flexible beam element was proposed,and the dynamic equations of elements and branches of the parallel manipulator were derived.Secondly,according to the kinematic coupling relationship between the moving platform and flexible links,the kinematic constraints of the flexible parallel manipulator were proposed.Thirdly,using the kinematic constraint equations and dyna...     

Modeling and parameter estimation for hydraulic system of excavator＇s arm

A retrofitted electro-hydraulic proportional system for hydraulic excavator was introduced firstly. According to the principle and characteristic of load independent flow distribution（LUDV） system,taking boom hydraulic system as an example and ignoring the leakage of hydraulic cylinder and the mass of oil in it,a force equilibrium equation and a continuous equation of hydraulic cylinder were set up. Based on the flow equation of electro-hydraulic proportional valve,the pressure passing through the valve and the difference of pressure were tested and analyzed. The results show that the difference of pressure does not change with load,and it approximates to 2.0 MPa. And then,assume the flow across the valve is directly proportional to spool displacement and is not influenced by load,a simplified model of electro-hydraulic system was put forward. At the same time,by analyzing the structure and load-bearing of boom instrument,and combining moment equivalent equation of manipulator with rotating law,the estimation methods and equations for such parameters as equivalent mass and bearing force of hydraulic cylinder were set up. Finally,the step response of flow of boom cylinder was tested when the electro-hydraulic proportional valve was controlled by the step current. Based on the experiment curve,the flow gain coefficient of valve is identified as 2.825×10^-4 m^3/（s·A） and the model is verified.     

Design of a New Type of Distribution Valve for Hydraulic Breaker and Analysis of Energy Consumption

Energy consumed by distribution valves causes an energy loss for the output energy of hydraulic breakers, which has a significant influence on its efficiency. A new type of distribution valve used for hydraulic breakers, designed to reduce energy consumption, is analyzed on the basis of the operating principle and energy loss of the current distribution valve. The new distribution valve adopts a cone valve and the optimization technique of unequal open degree for the valve port. Theoretical calculations and analyses have proven that the new distribution valve can reduce energy loss by 9.0127J, or energy consumption by 31%, during an impact cycle and the efficiency of the hydraulic breaker can be raised by 4.5%. It has the following characteristics： little leakage, little pressure loss and low energy consumption.     

Modeling and optimization of rotary kiln treating EAF dust

Electric arc furnace （EAF） dust from steel industries is listed by the United Sates EPA as a hazardous waste under the regulations of the Resource Conservation and Recovery Act due to the presence of lead, cadmium and chlorine. The disposal of the approximately 650000 t of EAF dust per year in the U.S. and Canada is an expensive and unresolved problem for the majority of steel companies. The Waelz process has been considered as the best process for treating the EAF dust. A process model, combined thermodynamic modeling with heat transfer calculations, has been developed to simulate the chemical reactions, mass and heat trans- fer and heat balance in the kiln. The injection of air into the slag and the temperature profile along the kiln have been modeled. The effect of （CaO＋MgO）/SiO2 on the solidus temperature of slag has also been predicted and discussed. Some optimized results have been presented.     

Modeling effects of constituents and dispersoids on tensile ductility of aluminum alloy

The modeling effects of constituents and dispersoids on the tensile ductility of aluminum alloy were studied.The results show that the tensile ductility decreases with the increase of the volume fraction and size of constituents.Thus,purification can improve the tensile ductility by decreasing the volume fraction of constituents(normally compositions of Fe and Si)and the first-class microcracks.The model also indicates that the tensile ductility decreases with the increase in the volume fraction of dispersoids.Decreasing the volume fraction of dispersoids along the grain boundaries by proper heat-treatment and improving the cohesion strength between dispersoids and matrix can also improve the tensile ductility by decreasing the volume fraction of the second-class microcracks.     

Failure analysis of corrosion cracking and simulated testing for a fluid catalytic cracking unit

The failure of a fluid catalysis and cracking unit (FCCU) in a Chinese refinery was investigated by using nondestructive detection methods, fracture surface examination, hardness measurement, chemical composition and corrosion products analysis. The results showed that the failure was caused by the dew point nitrate stress corrosion cracking. For a long operation period, the wall temperature of the regenerator in the FCCU was below the fume dew point. As a result, an acid fume NOx-SOx-H2O medium presented on the surface, resulting in stress corrosion cracking of the component with high residual stress. In order to confirm the relative conclusion, simulated testing was conducted in laboratory, and the results showed similar cracking characteristics. Finally, some suggestions have been made to prevent the stress corrosion cracking of an FCCU from re-occurring in the future.     

Kinetics of hydrogen absorption and desorption of a mechanically milled MgH2＋5at%V nanocomposite

The experimental data in the MgH2-5at%V composite was summarized and used to investigate the kinetic mechanism of hydrogen absorption and desorption using a new model. The research results indicate that a coincidence of the theoretical calculation values with the experimental data has been reached and the rate-limiting step is hydrogen diffusion through the hydride phase （β phase） with the activation energy of 47.2 kJ per mole H2 for absorption and the diffusion of hydrogen in the a solid solution （α phase） with that of 59.1 kJ per mole H2 for desorption. In addition, the hydriding rate of the MgH2-V composite is 2.9 times faster than that of MgH2 powders when compared with their characteristic absorption time directly.     

Analysis and Numerical Modeling of a 20W Microwave Electrothermal Thruster

The microwave electrothermal thruster (MET) is an electric propulsion device that uses an electromagnetic resonant cavity within which free-floating plasma is ignited and sustained in a propellant gas. The thrust is generated when the heated propellant gas is exhausted out of a gas-dynamic nozzle. For an empty cavity without any perturbing regions—e.g., dielectric regions or antenna regions—it is fairly straightforward to accurately calculate the cavitys resonant frequency and describe the electric field intensity distribution within the cavity. However, actual METs do contain perturbing regions, which means that analytical solutions are no longer possible to fully characterize the device. Hence, the numerical methods to simulate the electric field intensity and distribution within the resonant cavity were employed. The simulation results are that with the cap height increasing, the resonant frequency and electric field strength decrease, also increasing the permittivity of dielectric material causes decreasing the resonant frequency and electric field strength. A decrease in resonant frequency and maximum electric field strength, and an increase in resonant bandwidth, were observed with increasing antenna depth. Rounding an antenna of a given depth equals decreasing the depth.     

Analysis and Numerical Modeling of a 20W Microwave Electrothermal Thruster

The microwave electrothermal thruster (MET) is an electric propulsion device that uses an electromagnetic resonant cavity within which free-floating plasma is ignited and sustained in a propellant gas.The thrust is generated when the heated propellant gas is exhausted out of a gas-dynamic nozzle.For an empty cavity without any perturbing regions—e.g.,dielectric regions or antenna regions—it is fairly straightforward to accurately calculate the cavity's resonant frequency and describe the electric field inte...     

Singular perturbation approach for control of hydraulically driven flexible manipulator

The hydraulic flexible manipulator system is divided into two parts: flexible arm dynamics and hydraulic servomechanism, a driving Jacobian is derived to connect these two parts. Taking hydraulic actuator force as virtual input, a singular perturbed composite model is formulated and used to design composite controllers for the flexible link, in which the slow subsystem controller dominates the trajectory tracking, and then a fast controller is designed to damp out the vibration of the flexible structure. Moreover, the backstepping technique is applied to regulate the spool position of a hydraulic valve to provide the required force. Simulation results are provided to show the effectiveness of the presented approach. Foundation item: Project (2001AA4422200) supported by the Teaching and Research Award Program for Outstanding Young Teachers in Higher Education Institutions of the Ministry of Education of China; project supported by the Hi-Tech Research and Development Program of China     

液压机械臂基于反演的自适应二阶滑模控制

利用驱动Jacobian矩阵构建机械臂系统与液压伺服系统的耦合关系,进而建立整个系统的动力学模型。考虑系统未建模动态和外界干扰,通过定义虚拟控制量并选取合适的Lyapunov函数,设计此系统的自适应二阶滑模控制律,使系统在有限时间内精确跟踪期望轨迹且保持强鲁棒性,同时有效削弱了传统滑模控制对系统硬件不利的抖振。仿真结果验证了本文方法的有效性。     

基于期望关节角补偿的车载液压刚柔机械臂建模及轨迹跟踪控制

采用拉格朗日原理和假设模态法,通过引入驱动Jacobian矩阵,推导出液压刚柔机械臂动力学方程。针对柔性臂的特点,提出了关节角补偿方法。为了克服参数扰动和外界干扰,利用自适应律估计不确定性项提出了同时控制刚体运动和振动抑制的自适应滑模控制方法。最后,通过数值仿真验证了所提方法的有效性。     

机器人柔性臂的扭转振动主动控制研究

针对具有两连杆结构的空间机器人，设计了一种压电驱动器来抑制空间机器人柔性臂的扭转振动。采用拉格朗日方程和假设模态法对此机器人系统进行了理论建模，并建立了考虑随机干扰的状态空间表达式，基于随机最优控制理论设计了线性二次型高斯（LQG）状态反馈控制器。仿真结果表明，该主动控制策略能够有效衰减机器人柔性臂的扭转振动，从而提高了末端执行器的定位精度。     

基于铰链结构的机械臂操作柔性负载系统建模与控制

基于铰链结构研究了机械臂协调操作柔性负载系统的动力学建模与控制问题。提出了虚拟连杆的概念,以虚拟连杆为基准运用有限元法与拉格朗日方程建立了柔性负载的运动方程和振动方程,在负载坐标空间建立了系统的动力学模型。针对振动状态的不可测量性,应用刚性控制规律设计了控制器,给出了一种补偿系统动力学对位置控制影响的方法。仿真结果验证了该方法的有效性。     

基于铰链结构的机械臂操作柔性负载系统建模与控制

基于铰链结构研究了机械臂协调操作柔性负载系统的动力学建模与控制问题。提出了虚拟连杆的概念,以虚拟连杆为基准运用有限元法与拉格朗日方程建立了柔性负载的运动方程和振动方程,在负载坐标空间建立了系统的动力学模型。针对振动状态的不可测量性,应用刚性控制规律设计了控制器,给出了一种补偿系统动力学对位置控制影响的方法。仿真结果验证了该方法的有效性。     

采用积分流形与观测器的并联机器人轨迹控制

针对含柔性杆件并联机器人在高速运行时其末端存在弹性位移问题,以3RRR并联机器人为研究对象,提出一种基于积分流形与高增益观测器的柔性并联机器人轨迹跟踪复合控制算法.基于刚度矩阵引入小参数,将刚柔耦合动力学模型转为慢速与快速两个子系统.针对慢速子系统,采用反演控制,实现对末端刚体运动的跟踪控制,同时为避免杆件弹性变形与振动组成的弹性位移对机器人末端轨迹的影响,推导校正力矩,实现对弹性位移的补偿.针对快速子系统,采用滑模变结构控制,保证流形成立.为避免对曲率变化率的直接测量,引入高增益观测器对其进行估计.采用Lyapunov稳定性原理证明系统整体稳定性,并给出小参数上界.对提出的复合控制算法与奇异摄动及基于刚体动力学的反演控制算法进行仿真,从机器人末端振动抑制与轨迹跟踪性能两方面进行对比,验证了本文所提算法的控制效果.     

变负载条件下柔性臂自适应预整形振动控制

针对单连杆柔性臂负载发生变化的情况,提出克服柔性臂末端振动的在线自适应输入预整形（OAPCA）方法.该方法将柔性臂连杆角速度的变化看作2阶振动模态的组合,在线设计前馈脉冲预整形输入,脉冲的时间和幅值由模态频率和阻尼值计算得到.当系统振动频率随负载变化后,预整形器失去振动抑制作用,将前馈输入整形控制、比例积分（PD）控制及快速傅里叶变换（FFT）算法相结合,设计自适应整形器抑制柔性臂末端振动.理论上证明OAPCA方法的可行性,并对频率失配的情况进行鲁棒性能分析,进行仿真研究.结果表明,柔性臂OAPCA方法具有良好的末端振动抑制能力和关节角跟踪能力,能够有效解决变负载单模态振动控制问题.     

一种柔性机械臂末端轨迹跟踪的预测控制算法

针对柔性机械臂末端轨迹跟踪的内动态不稳定和模型不精确问题,提出一种用于柔性臂末端轨迹跟踪的预测控制算法.利用输入-输出线性化的方法使得柔性臂末端变量和弹性变量解耦,并根据状态反馈设计出一个非线性预测控制系统,将轨迹跟踪问题转换为状态跟踪问题.该控制系统通过平衡末端跟踪误差、弹性变量和控制力矩3个最优指标来克服内动态不稳定性,并采用最优控制律求解和力矩求解相分离的策略来提高运算速度,同时引入了实际输出数据进行误差补偿以减少模型误差对末端轨迹跟踪精度的影响.仿真结果表明,所提出的预测控制算法在保证柔性臂内动态稳定的同时,能有效解决模型失配引起的控制精度下降问题,并具有较快的运算速度.     

基于遗传算法的柔性机械手高阶终端滑模控制

针对双臂柔性机械手控制系统,提出了一种基于遗传算法的高阶终端滑模控制方法,以解决其非最小相位控制问题,实现末端位移控制。基于输出重定义方法,通过输入输出线性化,将系统分解为输入输出子系统和内部子系统,在此基础上,结合高阶滑模和终端滑模的控制思想设计输入输出子系统控制器,利用遗传算法优化内部子系统参数,以保证两个子系统稳定,同时削弱抖振对柔性模态的影响,提高末端位移控制精度。仿真结果证明了所提方法的有效性。