Robust adaptive control of robotic manipulators without the regressor matrix

A new adaptive controller is presented here for rigid-body robotic manipulators. It is stable and robust with respect to a class of external disturbances. The robustness of the adaptive controller is established without the ‘slow-varying’ assumption and the computationally demanding regressor matrix. The control law consists of a non-adaptive PD control part and an adaptive control part. It uses two adaptive matrices to compensate two uniformly bounded coefficient matrices derived from the original dynamics. A α σ|q?|-modified adaptive law is designed to adjust the adaptive matrices. A Lyapunov-type stability analysis indicates that the closed-loop system is uniformly ultimately bounded. The tracking error and compensation error will eventually converge into a closed region, which can be made arbitrarily small by adjusting the controller parameters. Simulation results are included to demonstrate the performance of the proposed controller.     

NURBS曲线C~1连续参数优化算法

曲线的参数特性直接决定基于自由曲线的路径规划、运动控制等算法的质量.为了生成满足C1连续的近似弧长参数化,提出一种基于分段三次重新参数化的参数优化算法.首先利用Simpson方法离散积分能量,然后使用极值求解法求得初始解,最后通过LM(Levenberg-Marquardt)优化算法计算出曲线的最优参数表示.与C1连续的分段有理重新参数化方法相比,该算法能够在分段数量很少的情况下达到局部最优.最后通过实例说明了文中算法的有效性.     

湿法炼锌沉铁过程氧化速率优化控制

湿法炼锌沉铁过程针铁矿沉淀形成的条件要求苛刻, 亚铁离子的氧化速率必须控制在合理的范围内才能保证溶液中的铁离子以针铁矿形式除去. 本文在沉铁过程动态模型的基础上, 根据针铁矿沉淀形成的条件和结合流程工艺要求, 优化设定每个反应器出口的亚铁离子浓度, 进而建立针铁矿法沉铁过程氧化速率优化控制模型. 采用控制参数化方法将最优控制求解问题转化为非线性规划, 通过状态转移优化算法求取最优的氧气和氧化锌控制率, 以合理控制沉铁过程亚铁离子的氧化速率. 仿真结果表明, 优化控制模型计算所得的控制量不仅可以保证反应过程的氧化速率符合生成针铁矿沉淀的条件, 而且可以稳定生产流程.     

翼伞系统最优归航轨迹设计的敏感度分析方法

本文对三自由度翼伞系统归航轨迹优化问题进行了研究,采用控制变量参数化与时间尺度变换相结合的优化算法对翼伞系统的最优控制问题进行数值求解.该方法是基于灵敏度分析的优化算法,将控制量以及控制量转换时间转化为一系列参数优化问题同时进行求解.仿真结果表明,相对于基于两端边值优化算法而言,灵敏度分析法只需要正向积分进行求解,因而具有计算简单、耗时短等优点,其控制效果良好,距离偏差和方向偏差均满足实际需求,有效地提高了翼伞系统的着陆精度,验证了该优化算法的可行性.     

Stretch-Minimizing Volumetric Parameterization

Not many methods for parameterization guarantee bijectivity or local injectivity, which is essential for foldover-free mappings. Stretch-minimizing parameterization which is widely used for surface par...     

面向等几何分析的几何计算

等几何分析方法是一种直接基于CAD模型的精确几何表示进行物理性能仿真分析的新方法.文中从几何计算的视角出发,对等几何分析方法的基本框架,以及面向等几何分析的几何设计与计算的相关工作进行了介绍,重点介绍适合分析的计算域参数化、适合分析的新型样条理论、等几何配点法、面向等几何分析的并行计算等4个方向的研究进展.最后对需要进一步深入研究的关键问题进行了探讨.     

Ricci flow-based spherical parameterization and surface registration

This paper presents an improved Euclidean Ricci flow method for spherical parameterization. We subsequently invent a scale space processing built upon Ricci energy to extract robust surface features for accurate surface registration. Since our method is based on the proposed Euclidean Ricci flow, it inherits the properties of Ricci flow such as conformality, robustness and intrinsicalness, facilitating efficient and effective surface mapping. Compared with other surface registration methods using curvature or sulci pattern, our method demonstrates a significant improvement for surface registration. In addition, Ricci energy can capture local differences for surface analysis as shown in the experiments and applications.     

基于球面参数化的点模型渐变

为了获得光滑自然的点模型渐变效果,基于球面参数化,提出了一种鲁棒的渐变算法。该算法首先对源和目标模型进行球面参数化,使得参数化后的模型嵌入到单位球面上;然后在球面上自适应地对齐模型间的相应特征点,并将球面映射到矩形参数域上,基于该域建立模型间各采样点的对应关系;接着在渐变过程中,采用拉普拉斯算子计算出中间点模型的几何位置,以保持模型的细节;最后利用移动最小二乘曲面进行动态上采样,以消除中间模型的裂缝。实验结果表明,该算法具有良好匹配的采样点对应和光滑的渐变过程。     

均匀准保角球面参数化

针对闭的或者单边界亏格为0的三角网格,提出一种球面参数化方法．通过立体投影将现有的平面参数化方法推广到球面上,得到一个初始的球面参数化;为了减小变形,引入质心坐标进行全局优化;最后用Moebius变换均匀化最终的球面网格．该方法能够避免立体投影出现三角形折叠的情况,保证最后的映射是双射．通过大量典型的三维模型实验和比较可以看出：文中的参数化方法变形小,在复杂网格的纹理映射中的均匀化效果较现有的保角、保面积变换有明显的改善．     

First-order indicators for the estimation of discrete fractures in porous media

Faults and geological barriers can drastically affect the flow patterns in porous media. Such fractures can be modelled as interfaces that interact with the surrounding matrix. We propose a new technique for the estimation of the location and hydrogeological properties of a small number of large fractures in a porous medium from given distributed pressure or flow data. At each iteration, the algorithm builds a short list of candidates by comparing fracture indicators. These indicators quantify at the first order the decrease of a data misfit function; they are cheap to compute. Then, the best candidate is picked up by minimization of the objective function for each candidate. Optimally driven by the fit to the data, the approach has the great advantage of not requiring remeshing, nor shape derivation. The stability of the algorithm is shown on a series of numerical examples representative of typical situations.