Machine fault diagnosis based on Gaussian mixture model and its application

This paper presents a simple and efficient machine fault diagnosis approach based on Gaussian mixture model (GMM). After feature vectors that represent different machine conditions are extracted, a GMM for each of the machine conditions is built based on the corresponding extracted feature vectors, machine fault diagnosis can be accomplished through finding out the GMM whose posteriori probability for a given testing feature vector is the maximum of all. Experimental results based on the application on bearing fault diagnosis have shown that GMM can reliably diagnose not only the type of bearing faults, but also the degree of fault severity that are associated with incipient faults, moderate faults, and severe faults. Meanwhile, GMM has better diagnostic performance as compared to the multilayer perceptron neural networks.     

Lubrication Performance of Connecting-Rod and Main Bearing in Di erent Engine Operating Conditions

Only the lubrication performance at rated engine operating condition was generally analyzed in current design and research of engine connecting-rod and main bearing. However, the actual engine(especially vehicle engine) does not always operate in rated operating condition and its operating condition changes constantly. In this paper, a fourstroke four-cylinder engine is taken as the studying object, the load and lubrication of connecting-rod and main bearing in di erent operating conditions are analyzed. The load of connecting-rod bearing is calculated by the dynamic calculation method, the loads of all main bearings are calculated by the whole crankshaft beam-element finite element method, and the lubrication performance of connecting-rod and main bearings are analyzed by the dynamic method. The results show that there are major di erences in the changes and numerical value at corresponding moment of the loads and lubrication performance of connecting-rod and main bearings in an engine operating cycle in di erent engine operating conditions; the most unfavorable case of the lubrication performance of connectingrod and main bearings may not take place in the rated engine operating condition. There are also major di erences between the lubrication performance of connecting-rod bearing and that of main bearing and between the lubrication performances of main bearings one another. Therefore, it will not be reasonable that the lubrication performance of a certain connecting-rod bearing or main bearing is analyzed in the design of the engine bearing. It is necessary to analyze simultaneously the lubrication performances of all bearings in di erent engine operating conditions.     

基于改进精英克隆选择算法的B样条曲线逼近方法

时间同步是多智能体网络协同工作的基础,具有重要意义。低成本无线传感器网络节点时钟易受到环境因素的影响,导致节点时间同步误差增大,网络信道负载增加。针对上述问题,提出了一种低时钟再同步周期、自适应温度补偿的无线传感器网络时间同步方法。首先,基于双向通信时间同步模型,提出了温度补偿的节点频移量动态估计模型;然后,采用Almon函数加权求和的方式对温度和频移量数据进行融合,解决数据采样率不匹配和模型维度高的问题;其次,为进一步提高时间同步精度,采用Kalman滤波器对频移量和相移量估计值进行滤波,并采用系统状态后验估计值对节点本地时间进行补偿;最后,参照IEEE 802.15.4标准对时间同步精度的要求,设计了一种失效风险最小化的再同步决策函数,最大限度提高节点再同步周期,减少信道负载。在高低温箱、室内和室外3种环境下进行实验以验证所提的方法。试验结果表明,与洪泛时钟同步协议(FTSP)时间同步协议相比,自适应温度补偿的时间同步(ATCTS)算法平均时间同步误差降低了97.4%,室外环境下平均时间同步周期为324 min。     

基于改进蚁群算法的移动机器人路径规划研究

针对蚁群算法在复杂环境下收敛速度慢且易陷入局部最优值的问题,提出一种改进的蚁群优化算法。该方法依据起始点和目标点位置信息选择全局有利区域增加初始信息素浓度,提高前期蚂蚁搜索效率;增加避障策略,避免蚂蚁盲目搜索产生大量交叉路径并有效减少蚂蚁死锁数量;采用动态参数控制的伪随机转移策略,提出优质蚂蚁信息素更新原则,自适应调整挥发系数,提高算法全局性;进行二次路径规划,优化路径并降低移动机器人能耗的损失。实验结果表明,该算法有较高的全局搜索能力,收敛速度明显加快,并且可以有效提高移动机器人工作效率,验证了该算法的有效性和优越性。     

可变磁路式永磁悬浮系统的防跌落防吸附控制

永磁悬浮系统是一种典型的非线性系统,随着导磁体与悬浮物之间的气隙变化,控制特性发生变化,影响系统的稳定性。为防止外界干扰引起系统偏离平衡点时,悬浮物跌落或吸附到导磁体上,提出一种基于气隙变化的防跌落防吸附控制方法。在整个悬浮气隙内选取多点预设悬浮力,基于各设计点预设的悬浮力计算控制参数,并依据插值原理得到完整的防跌落防吸附控制律,有效补偿悬浮物运动时不均匀变化的悬浮力,提高系统的可控性,稳定性和鲁棒性。仿真和实验表明,防跌落防吸附控制方法能缓和冲击,提高防跌落性能,当外扰使气隙变大时悬浮力迅速变大,防止悬浮物跌落,当外扰使气隙变小时悬浮力迅速变小,防止悬浮物吸附于导磁体上。     

一种高精度大行程2R1T并联定位平台

为了解决传统压电陶瓷驱动器所固有的高精度与大行程的矛盾,提出了一种新型可直接外力驱动的三自由度并联精密定位平台,利用压电直线电机直接驱动即可实现大行程与高精度定位。首先,分析了柔性铰链结构参数对其作动行程的影响机理,在此基础上设计了大行程圆柱柔性铰链,并对大行程圆柱柔性铰链的结构参数进行了模糊优化设计;接着,采用两个平移副和一个一体化、大行程圆柱形柔性铰链构建了并联分支链路,采用3条并联支路设计了2R1T并联精密定位平台,并通过坐标齐次变换方法构建了并联平台的运动学模型,推导出了并联平台位姿正反解;最后,对2R1T并联定位平台开展了实验研究。实验结果表明所设计的2R1T并联定位平台具有良好的运动同步性和重复性,利用压电直线电机的步进运动模式可实现精密定位,其平动定位分辨率为0. 09μm,转动定位分辨率分别为0. 8μrad、0. 9μrad和1. 0μrad;利用压电直线电机的连续运动模式可实现大行程空间定位,其平动工作行程为120 mm,转动工作行程分别为6. 18°、6. 74°和6. 58°。借助于压电直线电机的不同工作模式实现了并联平台的精密定位和大行程工作空间两个关键指标,为进一步研究2R1T并联机构的动态性能、精密定位及控制规律的实现等提供了重要的理论价值和实践基础。     

Multiple-motion mode switching robot platform

Developing an intelligent robot platform that has multiple motion modes and can actively adjust the motion mode according to an operation situation is necessary in resolving the inability of single-mode robots to adapt completely to complex environments. In this study, we designed a robot that has multiple motion modes and can switch freely in these existing modes. The robot has the following modes: Four-legged walking, two-legged walking, pulse scrolling, and crawler movement. In the robot’s design, these modes are not just simple mechanisms involving superposition and motion switching. These modes involve a degree of freedom in reuse, thereby reducing the number of drives and obtaining a compact structure while achieving a coherent transition of each action mode. For higher load ratios, motion continuity are increased. The robot platform can balance itself during movement by adjusting its own mechanism or providing additional force and change its shape and posture over some obstacles by adjusting its own mechanism.

     

Reliability assessment for multi-source data of mechanical parts of civil aircraft based on the model

Journal of Mechanical Science and Technology - In view of the abnormal, missing and multi-source reliability data, a complete reliability data processing method for civil machinery parts are...     

基于影像测量法的渐开线圆柱直齿轮齿形误差评定新方法

针对现行齿形误差测量方法误差来源多、存在评定原理误差等缺点,提出一种利用JT12A-A型数字式投影仪采集测量数据,实现渐开线圆柱直齿轮齿形误差评定的新方法。理论分析和实验结果表明,该方法具有数据采集精度高、测量过程人工干预少、评定方法不存在原理误差、评定精度高等优点。     

高速切削刀具磨损的有限元分析

采用DEFORM-3D软件,通过在不同速度下切削45钢的有限元模拟,得到了切削速度对刀具磨损的影响规律以及与切削温度之间的关系,为研究刀具磨损机理、合理选用切削加工速度提供了参考依据。