Design and implementation of an omnidirectional vision system for robot perception

To meet the demand of surrounding detection of a humanoid robot, we developed an omnidirectional vision system for robot perception (OVROP) with 5 Degrees of Freedom (DOFs). OVROP has a modular design and mainly consists of three parts: hardware, control architecture and visual processing part (omnidirectional vision and stereovision). As OVROP is equipped with universal hardware and software interfaces it can be applied to various types of robots. Our performance evaluation proves that OVROP can accurately detect and track an object with 360° field of view (FOV). Besides, undistorted omnidirectional perception of surroundings can be achieved through calibrations of both monocular and stereo cameras. Furthermore, our preliminary experimental results show that OVROP can perceive a desired object within 160 ms in most cases. As a result, OVROP can provide detailed information on surrounding environment for full-scope and real-time robot perception.     

Performance measurement of decision-making units under uncertainty conditions: An approach based on double frontier analysis

Data envelopment analysis (DEA) is an approach to measure the relative efficiency of a set of decision-making units (DMUs) which uses multiple inputs to produce multiple outputs. In real world situations, due to uncertainty, DEA is sometimes faced with imprecise inputs and/or outputs. Therefore, performance measurement must often be performed under uncertainty conditions. Generally, the performance of DMUs can be evaluated from two perspectives—optimistic and pessimistic. As a result, two different evaluations are obtained for each DMU. In this article, we first obtain the efficiencies of the DMUs under evaluation from both optimistic and pessimistic views. The optimistic view evaluates each DMU with a set of the most desirable weights; the efficiencies measured by the optimistic approach are called optimistic efficiencies. The pessimistic view evaluates each DMU with a set of the most undesirable weights; the efficiencies measured by the pessimistic approach are called pessimistic efficiencies. Then it is shown that the outcomes of these two evaluations are conflicting with each other, being undoubtedly biased, unrealistic, and unconvincing. To overcome this problem, we propose a new measure of overall performance which is used for integrating the measures obtained from optimistic and pessimistic views and we will use it to identify the DMU with the best performance under uncertainty conditions. Also, we propose new fuzzy DEA models that evaluate a DMU from the pessimistic perspective in a fuzzy context. The proposed measure will be shown with two numerical examples, including the selection of a flexible manufacturing system.     

Investigations on rheological strains of compressed concrete elements strengthened with external composite reinforcement CFRP

The results of experimental studies on rheological strains of compressed concrete elements strengthened with surface CFRP materials are presented in this paper. The objective of the investigations was to estimate the influence of long-term load on strains and load-bearing capacity of compressed elements strengthened with CFRP materials. The studies were performed on specimens with various types of reinforcement. The specimens were strengthened with external composite reinforcement – longitudinal segments of CFRP strips and transverse confinement executed with CFRP sheets. The experimental studies were divided into two stages, in which specimens were subjected to long-term axial compression. The objects of the investigations were cylindrical specimens with a diameter of 113 mm and height of 350 mm. The plain concrete specimens were loaded with the level of about 1/3f_cm,cyl (mean cylinder compressive strength of the concrete). After the period of initial loading the specimens were strengthened and the level of effort was increased to about 2/3f_cm,cyl. The tests were conducted in constant thermal and moisture conditions. In the paper, the dependences of long-term strains increase in time are presented for the experimental elements. Additionally, theoretical studies connected with rheological model identification were performed.     

Experimental behaviour of steel fiber high strength reinforced concrete and composite columns

This paper presents experimental behaviour of eccentrically loaded plain and steel fiber high strength reinforced concrete and concrete-encased composite columns. In the experimental study, a total of 32 square section both reinforced concrete and composite column specimens were fabricated at 0, 0.5, 0.75 and 1.0% volume fractions of steel fiber contents to examine the effects of steel fibers on column behaviour. Besides this, the composite columns were constructed and tested using almost the same conditions with reinforced concrete columns to investigate the column experimental behaviour. The complete load−deflection behaviour and strength of column specimens were obtained and the results were discussed in the study. In addition, the column specimens were analysed based on a theoretical method considering the nonlinear behaviour of the materials. The presented experimental study indicates that the inclusion of steel fibers in the range 0.75 to 1.0% volume fraction improves confinement and ductility features of high strength reinforced concrete and composite columns significantly.     

A Novel Fault Location Algorithm for Double-Circuit Transmission Lines based on Distributed Parameter

1 IntroductionWith the development of the power system,thedouble circuit transmission lines have been widely used.The increased complexities of power transmission systemmake the transmission line fault location studies morecomplicated and important.The fault location for thesemore complex lines has raised great attentions.Differentfault location algorithms can be developed depending onthe extracted data from one or both ends of thetransmission lines.The method using one end data isaffected by…     

基于改进YOLOv4-Tiny的矿井电机车多目标实时检测

为解决煤矿巷道环境恶劣以及人工疲劳驾驶电机车导致煤矿井下有轨电机车事故频发的问题,提出一种基于改进YOLOv4-Tiny算法的YOLOv4-Tiny-4S矿井电机车多目标实时检测方法。首先,为了提高网络模型对于小目标的检测能力,将传统YOLOv4-Tiny的两尺度预测增加至四尺度预测,并且在网络模型的颈部引入空间金字塔池化（SPP）模块,以丰富特征融合信息,增大网络模型的感受野;其次,以煤矿巷道中的行人、电机车、信号灯以及碎石作为检测目标,创建矿井电机车多目标检测数据集,并分别采用K-means和K-means++聚类分析算法对数据集重新聚类,通过对比分析验证了K-means++算法具有更好的聚类效果;最后,通过对传统YOLOv4-Tiny算法的消融实验,进一步直观了不同改进措施对网络模型检测性能的影响,并在电机车运行的煤矿巷道场景中,对比分析了YOLOv4-Tiny-4S算法与其他几种算法的检测性能。实验结果表明：YOLOv4-Tiny-4S算法能够准确检测并识别出图像中的各类目标,其平均检测精度（mAP）为95.35%,对小目标“碎石”的平均检测精度（AP）为86.69%,相比传统YOLOv4-Tiny算法分别提高了12.38和41.66个百分点;改进后算法的平均检测速度达58.7帧/秒（FPS）,模型内存仅为26.3Mb,YOLOv4-Tiny-4S算法的检测性能优于其他算法。本文提出的基于YOLOv4-Tiny-4S矿井电机车多目标实时检测方法可为实现矿井电机车的无人驾驶提供技术支撑。     

三通球阀式高速开关阀稳态液动力分析与结构改进

对于微小型高速开关阀,大流量和高频响都会增大阀芯所受的液动力进而影响其运动状态,因此,对液动力进行分析与补偿是提升高速开关阀性能的关键因素之一。为了解决球阀式高速开关阀在高频启闭状态下流场结构复杂导致传统的稳态液动力理论计算公式已不适用的问题,基于CFD数值计算方法对液动力进行研究。首先,利用COMSOL软件建立阀内流场流体域的几何模型;随后,选用弱可压缩流体、标准k-ε湍流模型并运用动网格技术,得到流体域的压力和流线分布图、流量曲线以及不同阀口开度下阀球和阀芯的稳态液动力变化曲线;最后,为了补偿阀口启闭过程中所减小的稳态液动力,根据不同的阀口结构参数与阀芯受力及阀口启闭时间之间的变化关系,对阀口结构进行优化并确定最优参数。结果表明：进油孔阀球所受的稳态液动力会随着阀口的开启产生先减小后增大的现象,但由于进油孔阀球的稳态液动力相比于回油孔阀球较小,故阀芯上的稳态液动力变化与回油孔阀球上的稳态液动力变化近似;适当减小阀球推杆直径及将靠近阀口的流道改成渐扩型流道能够有效地补偿启闭过程中所减小的稳态液动力,改进后的最优结构相较于原结构的一个周期启闭时间从1.047 ms下降到0.714 ms,稳态液动力补偿效果明显。     

两种新型双脊波导传输特性的研究

为了寻找最佳传输特性的对称双脊波导结构,提出了三角形和倒梯形两种新型对称双脊波导．应用有限元分析方法计算了这两种新型对称双脊波导TE模式的传输特性,即截止波长和单模带宽．分析传输特性随对称脊波导结构尺寸的变化关系曲线,得到脊间距越小,单模带宽越高,且单模带宽最大达8.0173;倒梯形对称双脊波导的截止波长较同尺寸矩形、三角形和梯形大,最大达9.5．这些结果将为脊波导器件的小型化提供指导．绘出的主模与第一个高次模的场结构图表明,在三角形对称双脊波导的顶点处场强变化最大,能量损失大．     

无差拍控制的PWM变换器电压矢量序列优化

为了降低PWM变换器有功功率和无功功率的稳态误差,减小其交流侧输出正弦电流的谐波含量,建立了PWM变换器的无差拍预测直接功率控制系统的功率变化模型,分析了传统直接功率控制中以电网电压角度位置为基准划分扇区时,选取的电压矢量序列存在辅矢量作用时间不合理的现象,给出了基于变换器交流侧电压角度位置划分扇区的电压矢量序列方法,由于扇区的分法与传统方法错开了一定的角度,避免了偶数扇区中出现所选的三个电压矢量对有功功率变化率或无功功率变化率的影响趋势相同的情况,避免了辅矢量作用时间不合理的现象。快速调节功率的同时,减小功率稳态误差,降低电流谐波含量,使开关频率固定,且无需坐标变换和空间电压矢量调制。     

The Triangular Pyramid Scheduling Model and algorithm for PDES in Grid

Grid is a perfect environment for the large scale Parallel Discrete Event Simulation (PDES), because its distribution and collaboration features match the PDES applications well. The PDES tasks or applications are modeled as a Directed Acyclic Graph (DAG), in which the simulation resources consist of three critical factors, simulation hosting machine (SHM), simulation service (SS) and simulation data (SD) in Grid environment. By solving the model we attempt to obtain an optimized triangular matching of the simulation resources on Grid, so that it can support the PDES activities better. We name the algorithm of solving the model Triangular Pyramid Scheduling (TPS). The PDES DAG is divided into three basic graph structures: Sequential structure, Fork structure, and Join structure. The TPS algorithm is developed based on these graph structures. The simulation results show that TPS algorithm can reduce the makespan and congestion, improve the simulation efficiency, and increase the resource utilization efficiency, compared to the existing algorithms.