永磁交流伺服系统PID最优化参数整定

为了构成高性能的永磁交流伺服系统速度环,实现高速变化下的速度跟随,引入微分环节,应用相位裕度的PID最优化参数整定方法整定控制器参数,建立了永磁交流伺服电机速度环数学模型,与工程常用PI控制器系统性能进行比较分析。仿真结果表明,系统的动态特性与稳态误差均可取得更好效果,并能达到速度高速跟随。另外,与传统几何推导PM法相比,根据相位裕度概念推导出参数整定公式,并为约束应用两次寻优的方法整定PID系统参数。     

虚拟训练动作获取系统软件设计

针对目前虚拟训练软件常用的输入设备逼真度不足的问题,为虚拟训练软件设计了一种新的人性化接口设备（Human Interface Device,HID）一基于MEMS器件的虚拟训练动作获取系统。系统将微惯性测量原理应用于人体姿态检测,选用微机电系统（Micro Electro Mechanical Systems,MEMS）惯性器件构建微惯性测量单元（Micro Inertial Measurement Unit,MIMU）作为人体训练动作的硬件采集设备;采用VC＋＋设计上位机系统软件,完成人体动作获取与识别算法,系统软件通过软件接口驱动虚拟训练软件。通过对原理样机测试,测试结果表明系统运行稳定可靠,解算精度在3°以内,满足虚拟训练的要求,且其操作体验较鼠标键盘操作更为逼真,沉浸感更强。该研究首次将微惯性测量单元应用于人体动作检测,拓展了MEMS器件的应用领域,极大增强了虚拟训练的真实感和训练效果,具有广阔的市场前景。     

随机分组抽样下子群体的流大小分布估计

随机分组抽样是网络管理和测量中最常见的抽样方法。已有的研究大都集中在此抽样方法下基于总体的流大小分布估计算法,但一些网络应用更关心总体流量中某个子群体的流大小分布。本文将总体的网络流划分成子群体S和子群体的补集-S,提出了一种在随机分组抽样下运用TCP协议信息的由S与S-共同组成流大小的联合分布的估计算法。实验证明,该算法能够较好地还原子群体及其在总体下的流大小分布的特征;另一方面,通过运用样本流中TCP协议信息,提高了子群体流大小分布估计算法的准确性。     

WCDMA空中接口的物理层测量

本文对空中接口的技术进行了简单的介绍,着重描述了WCDMA空中接口的结构与功能。并从测量可实现的角度出发,给出了对物理层性能指标和过程进行测量的方案,开发设计了测量分析软件。通过测量的结果,对网络的性能进行了分析。     

基于载波表的GPS载波跟踪环路研究

实时GPS软件接收机可以使用查找表的方法得到本地复现载波以减少运算量。载波表是由一组具有一定频率间隔和固定初始相位的正弦和余弦信号组成。传统的载波跟踪环路无法使用具有离散频率和不连续相位的复现载波完成GPS载波跟踪。针对这一问题,使用相位补偿算法对载波进行相位补偿,设计了基于载波表的载波跟踪环路。仿真结果表明该载波跟踪环路能有效实现GPS信号的载波跟踪,且与传统的载波跟踪环路相比仅有微小的信噪比损失和频率跟踪精度衰减,可用于实时GPS软件接收机设计。     

无人机空速测量系统仿真与设计

在无人机空速测量系统设计中,要经过系统功能划分,软硬件设计,电路制版,整体联调等步骤,结果是否符合设计要求通常需要软硬件设计完成调试通过后才能得知。而整个设计牵涉环节较多,很少一次达到目的。Proteus软件是一个完全脱离硬件平台进行系统虚拟开发的工具,结合Keil C51软件可以方便的完成整个系统的设计,仿真中可以随时修改设计、调整软硬件分工以提高系统性能降低系统误差。使用仿真软件对设计方案的各个环节进行验证和优化,测试系统性能,可及时发现系统瓶颈,优化软硬件设计,提高效率,缩短开发周期。     

相位可控双路同频信号源的FPGA部分设计与实现

介绍了直接数字频率合成(DDS)技术的基本原理,给出了基于Altera公司FPGA器件的相位可调双路同频正弦信号发生器的设计方案,同时给出了其软件程序和试验结果。试验结果表明:该方法生成的双路同频正弦信号具有波形失真小、频率和相位精度高,且输出频率与相位可调等优点。     

Vegetation water content during SMEX04 from ground data and Landsat 5 Thematic Mapper imagery

Vegetation water content is an important parameter for retrieval of soil moisture from microwave data and for other remote sensing applications. Because liquid water absorbs in the shortwave infrared, the normalized difference infrared index (NDII), calculated from Landsat 5 Thematic Mapper band 4 (0.76-0.90 μm wavelength) and band 5 (1.55-1.65 μm wavelength), can be used to determine canopy equivalent water thickness (EWT), which is defined as the water volume per leaf area times the leaf area index (LAI). Alternatively, average canopy EWT can be determined using a landcover classification, because different vegetation types have different average LAI at the peak of the growing season. The primary contribution of this study for the Soil Moisture Experiment 2004 was to sample vegetation for the Arizona and Sonora study areas. Vegetation was sampled to achieve a range of canopy EWT; LAI was measured using a plant canopy analyzer and digital hemispherical (fisheye) photographs. NDII was linearly related to measured canopy EWT with an R² of 0.601. Landcover of the Arizona, USA, and Sonora, Mexico, study areas were classified with an overall accuracy of 70% using a rule-based decision tree using three dates of Landsat 5 Thematic Mapper imagery and digital elevation data. There was a large range of NDII per landcover class at the peak of the growing season, indicating that canopy EWT should be estimated directly using NDII or other shortwave-infrared vegetation indices. However, landcover classifications will still be necessary to obtain total vegetation water content from canopy EWT and other data, because considerable liquid water is contained in the non-foliar components of vegetation.     

The impact of misregistration on SRTM and DEM image differences

Image differences between Shuttle Radar Topography Mission (SRTM) data and other Digital Elevation Models (DEMs) are often performed for either accuracy assessment or for estimating vegetation height across the landscape. It has been widely assumed that the effect of sub-pixel misregistration between the two models on resultant image differences is negligible, yet this has not previously been tested in detail. The aim of this study was to determine the impact that various levels of misregistration have on image differences between SRTM and DEMs. First, very accurate image co-registration was performed at two study sites between higher resolution DEMs and SRTM data, and then image differences (SRTM–DEM) were performed after various levels of misregistration were systematically introduced into the SRTM data. It was found that: (1) misregistration caused an erroneous and dominant correlation between elevation difference and aspect across the landscape; (2) the direction of the misregistration defined the direction of this erroneous and systematic elevation difference; (3) for sub-pixel misregistration the error due solely to misregistration was greater than, or equal to the true difference between the two models for substantial proportions of the landscape (e.g., greater than 33% of the area for a half-pixel misregistration); and (4) the strength of the erroneous relationship with aspect was enhanced by steeper terrain. Spatial comparisons of DEMs were found to be sensitive to even sub-pixel misregistration between the two models, which resulted in a strong erroneous correlation with aspect. This misregistration induced correlation with aspect is not likely specific to SRTM data only; we expect it to be a generic relationship present in any DEM image difference analysis.     

分布式测量系统服务窗口动态调度方法研究

在网络制造环境下, 动态时间性能是测量系统的重要指标. 针对基于 CORBA (Common object request broker architecture) 和尺寸测量接口标准 (Dimensional measurement interface standard, DMIS) 的分布式测量系统 (Distributed measurement system, DMS), 根据多用户非抢占优先排队网络静态性能模型, 提出基于无穷小摄动分析的样本轨道划分方法, 建立测量系统服务窗口的动态调度算法, 实现测量系统的时间性能调优. 通过在一个制造工厂中进行的应用实验, 证明了此方法的有效性.