LED照明亮度控制新技术特征与应用

随着LED应用的不断增加,大功率LED的驱动控制日显重要。本文分析介绍了LED照明亮度控制的新技术特征与应用。     

Development of Sensor and Control Systems of a Wearable Robot to Walk on a Step

The goal of our study is to develop a system for walking on a step using a wearable robot. Our system consists of (1) sensing of a step from the movement of the walker, (2) detection of the foot placement state related to the step, and (3) generation of gait patterns of climbing and stepping down for the step. In the generation of gait patterns for the step, toe trajectories are generated according to the height of the step to avoid collision of the swinging leg with the step. The hip trajectory is generated by an optimization technique that minimizes the sum of the joint angular jerk of the robot subject to constraints on the hip position and the velocity at toe liftoff. Each joint angle trajectory is calculated from the generated trajectories by means of inverse kinematic equations. We investigated the feasibility of the proposed sensor and control systems for two steps with different heights.     

Finite element analysis of the plastic deformation in tandem process of simple shear extrusion and twist extrusion

Recently, simple shear extrusion (SSE) and twist extrusion (TE) are introduced to fabricate ultrafine grained bulk rod metallic materials. The SSE and TE processes generate significant deformation inhomogeneity, with higher and lower strains in the center, respectively, which easily causes mechanical instability of the materials. In this study, to overcome this deformation inhomogeneity problem in SSE and TE, a tandem process of SSE and TE (TST) is suggested. The finite element method is applied for plastic deformation behavior during the TST process. The results demonstrate that the TST process can produce relatively homogeneously deformed materials. In particular, the effects of back pressure and processing order on the plastic deformation behaviors in the TST process are systematically analyzed.     

双时间步时域有限体积方法计算时变电磁场

双时间步被引入到时域有限体积解算器这一直接求解麦克斯韦方程组的高精度数值方法中.双时间步方法作为非定常时间推进技巧,时间精度由物理时间步长决定,稳定性要求由定常子迭代时间步长所满足,从而放松了通常显式时间格式和网格对物理时间步长的限制,达到节约计算量的目的.典型目标电磁散射计算表明:通过对物理时间步长、最大子迭代步数、子迭代收敛判据的合理选取,双时间步方法在保证计算精度的同时,能提高计算效率.     

A neural network based system for predicting earthmoving production

An artificial neural network based system (NN earth) is developed for construction practitioners as a simple tool for predicting earthmoving operations, which are modelled by back propagation neural networks with four expected parameters and seven affecting factors. These networks are then trained using the data patterns obtained from simulation because there are insufficient data available from industrial sources. The trained network is then incorporated as the computation engine of NN earth. To engender confidence in the results of neural computation, a validation function is implemented in NN earth to allow the user to apply the engine to historic cases prior to applying it to a new project. An equipment database is also implemented in NN earth to provide default information, such as internal cost rate, fuel cost, and operator's cost. User interfaces are developed to facilitate inputting project information and manipulating the system. The major functions and use of NN earth are illustrated in a sample application. In practice, NN earth can assist the user either in selecting a crew to minimize the unit cost of a project or in predicting the performance of a given crew.     

焊缝跟踪RBF整定PID控制算法

针对电弧焊接系统,研究一种基于径向基神经网络与比例积分微分控制相结合的焊缝跟踪控制新方法。在建立基于视觉传感的电弧焊焊缝跟踪系统的基础上,分析系统运动机构原理并研究两相混合式步进电机驱动焊炬运动数学模型,结合研究对象进行计算机仿真研究。试验结果表明,基于径向基整定比例积分微分的控制方法能够有效提高焊缝跟踪性能。     

Slope reliability and back analysis of failure with geotechnical parameters estimated using Bayesian inference

A Bayesian approach is proposed for the inference of the geotechnical parameters used in slope design. The methodology involves the construction of posterior probability distributions that combine prior information on the parameter values with typical data from laboratory tests and site investigations used in design. The posterior distributions are often complex, multidimensional functions whose analysis requires the use of Markov chain Monte Carlo (MCMC) methods. These procedures are used to draw representative samples of the parameters investigated, providing information on their best estimate values, variability and correlations. The paper describes the methodology to define the posterior distributions of the input parameters for slope design and the use of these results for evaluation of the reliability of a slope with the first order reliability method (FORM). The reliability analysis corresponds to a forward stability analysis of the slope where the factor of safety (FS) is calculated with a surrogate model from the more likely values of the input parameters. The Bayesian model is also used to update the estimation of the input parameters based on the back analysis of slope failure. In this case, the condition FS = 1 is treated as a data point that is compared with the model prediction of FS. The analysis requires a sufficient number of observations of failure to outbalance the effect of the initial input parameters. The parameters are updated according to their uncertainty, which is determined by the amount of data supporting them. The methodology is illustrated with an example of a rock slope characterised with a Hoek-Brown rock mass strength. The example is used to highlight the advantages of using Bayesian methods for the slope reliability analysis and to show the effects of data support on the results of the updating process from back analysis of failure.     

煤矿开采岩层移动参数反演理论与方法

对地下开采引起的沉陷问题进行了三维模拟计算，根据优化理论和方法，在选定模型基础上完成了参数的选取及优化工作，并结合工程实际给出了应用实例。     

一种混合步进电机优化波形控制器设计

设计了一种基于人工神经网络的步进电机驱动电压波形控制器,对步进电机原有的驱动控制电压脉冲进行修正,提高步进电机的运行速度稳定度,该方案使用人工神经网络模拟输入输出样本即角位移与电压脉冲的映射关系,使经过训练后的网络对非样本输入有好的泛化能力;该方案只使用步进电机测量角位移不需要精确获取电机内部参数,实验证明,该驱动电压波形控制器方案是一种快速、简便、有效的设计,对电机低速空载和负载效应下的速度稳定度都有好的提高。     

M7650双端面磨床的数控改进

分析了M7650双端面磨床存在的不足,运用数控原理对进给补偿机构等进行了改进。满足了高精产品的质量要求,为应用数控技术改造旧设备开辟一条新路。