The existing research on dynamics and slip ratio of wheeled mobile robot (WMR) are derived without considering the effect of height, and the existing models can not be used to analyze the dynamics performance of the robot with variable height while moving such as NOROS-Ⅱ. The existing method of dynamics modeling is improved by adding the constraint equation between perpendicular displacement of body and horizontal displacement of wheel into the constraint conditions. The dynamic model of NOROS-Ⅱ in wheel motion is built by the Lagrange method under nonholonomic constraints. The inverse dynamics is calculated in three different paths based on this model, and the results demonstrate that torques of hip pitching joints are inversely proportional to the height of robot. The relative error of calculated torques is less than 2% compared with that of ADAMS simulation, by which the validity of dynamic model is verified. Moreover, the relative horizontal motion between fore?hind wheels and body is produced when the height is changed, and thus the accurate slip ratio can not be obtained by the traditional equation. The improved slip ratio equations with the parameter of the vertical velocity of body are introduced for fore wheels and hind wheels respectively. Numerical simulations of slip ratios are conducted to reveal the effect of varied height on slip ratios of different wheels. The result shows that the slip ratios of fore?hind wheels become larger?smaller respectively as the height increases, and as the height is reduced, the reverse applies. The proposed research of dynamic model and slip ratio based on the robot height provides the effective method to analyze the dynamics of WMRs with varying height.
Ad hoc网络作为一种不依赖于任何固定设施的临时性多跳自治系统,是解决月球探测过程中多机器人通信问题的可行选择。由于月球探测多机器人通信系统对节能和实时性等方面的特殊要求,现有的Ad hoc网络路由协议还难以满足工程设计和实际应用的需求。因而,结合月球探测环境下的实际工程需要,对现有的Ad hoc网络路由协议进行优化设计就成为关键。在分析月球探测多机器人通信系统拓扑结构的基础上,给出了系统中各节点的能量消耗模型;进而,建立了路径寻优的数学模型,在动态源路由协议DSR的基础上设计了一种基于能量约束的Ad hoc网络路由协议。该协议综合考虑了通信系统对于节能和实时性两方面的需求,将路由跳数、路由传送功率、节点剩余电池能量作为路由度量,采用改进的离散Bellman-Ford算法进行最优路径的求解。仿真实验结果表明,该协议在保证通信系统实时性的前提下,可延长网络生存时间,能为月球探测多机器人系统提供更可靠的通信保障。
针对当前图像质量评价的研究现状,对各种评价方法进行了比较分析和归纳总结。利用U-Texas at Austin的LIVE图片库中的样本对几种常用的客观评价方法进行了测试,利用该数据库中得到广泛认可的主观评价分数,能够衡量客观评价指标与主观评价的符合程度,从而对这些评价指标的单调性、准确性和一致性进行了辨析和阐释,指出了其适用性和局限性。并利用VQEG推荐的方法对论断给出了实例印证。进而根据发展趋势和应用需求,对图像质量评价方法在应用中所必须面对的一些问题和解决途径提出了初步的见解。
