Dynamic analysis and simulation of four-axis forced synchronizing banana vibrating screen of variable linear trajectory

A new concept of banana vibrating screen which has the same effect as traditional banana vibrating screen in a new way was put forward.The dynamic model of vibrating screen was established and its working principle was analyzed when the action line of the exciting force did not act through the centroid of screen box.Moreover,the dynamic differential equations of centroid and screen surface were obtained.The motions of centroid and screen surface were simulated with actual parameters of the design example in Matlab/Simulink.The results show that not only the amplitude has a significant decrease from 9.38 to 4.10 mm,but also the throwing index and vibrating direction angle have a significant decrease from 10.49 to 4.59,and from 58.10° to 33.29°,respectively,along the screen surface,which indicates that motion characteristics of vibrating screen are consistent with those of traditional banana vibrating screen only by means of a single angle of screen surface.What's more,such banana vibrating screen of variable linear trajectory with greater processing capacity could be obtained by adjusting the relative position of force center and the centroid of screen box properly.

Algebraic Method‑Based Point‑to‑Point Trajectory Planning of an Under‑Constrained Cable‑Suspended Parallel Robot with Variable Angle and Height Cable Mast

To avoid impacts and vibrations during the processes of acceleration and deceleration while possessing flexible working ways for cable-suspended parallel robots(CSPRs),point-to-point trajectory planning demands an under-constrained cable-suspended parallel robot(UCPR)with variable angle and height cable mast as described in this paper.The end-effector of the UCPR with three cables can achieve three translational degrees of freedom(DOFs).The inverse kinematic and dynamic modeling of the UCPR considering the angle and height of cable mast are completed.The motion trajectory of the end-effector comprising six segments is given.The connection points of the trajectory segments(except for point P3 in the X direction)are devised to have zero instantaneous velocities,which ensure that the acceleration has continuity and the planned acceleration curve achieves smooth transition.The trajectory is respectively planned using three algebraic methods,including fifth degree polynomial,cycloid trajectory,and double-S velocity curve.The results indicate that the trajectory planned by fifth degree polynomial method is much closer to the given trajectory of the end-effector.Numerical simulation and experiments are accomplished for the given trajectory based on fifth degree polynomial planning.At the points where the velocity suddenly changes,the length and tension variation curves of the planned and unplanned three cables are compared and analyzed.The OptiTrack motion capture system is adopted to track the end-effector of the UCPR during the experiment.The effectiveness and feasibility of fifth degree polynomial planning are validated.

Optimal Trajectory of Underwater Manipulator Using Adjoint Variable Method for Reducing Drag

In order to decrease the fluid drag on an underwater robot manipulator, an optimal trajectory method based on the variational method is presented. By introducing the adjoint variables, which are Lagrange multipliers, we formulate a Lagrange function under certain constraints related to the target angle, target angular velocity, and dynamic equation of the robot manipulator. The state equation (the partial differentiation of the Lagrange function with respect to the state variables), adjoint equation (the partial differentiation of the Lagrange function with respect to the adjoint variables), and sensitivity equation (the partial differentiation of the Lagrange function with respect to torques) can be derived from the stationary conditions of the Lagrange function. Using the state equation, we can calculate the state variables (angles, angular velocities, and angular acceleration) at every time step in the forward time direction. These state variables are stored as data at every time step. Next, by using the adjoint equation, we can calculate the adjoint variables by using these state variables at every time step in the backward time direction. These adjoint variables are stored as data at every time step. Third, the sensitivity equation is calculated by using both the state variables and the adjoint variables. Finally, the optimal trajectory of the manipulator is obtained using the sensitivities. The proposed method is applied to the problem of two-link manipulators. It can obtain the optimal drag reduction trajectory of the manipulator under the constraints mentioned above.

融合反步法的无人驾驶汽车轨迹跟踪控制方法

为了解决无人驾驶汽车轨迹跟踪控制的准确性、稳定性和快速性问题,将反步法分别融合滑模变结构控制和模糊自适应控制.建立车辆三自由度运动学位姿误差微分方程,推导了基于反步法的车速和横摆角速度控制律,结合Lyapunov稳定性判据验证了系统稳定性.分别建立融合反步法的滑模变结构和模糊自适应轨迹跟踪控制方法,结合轨迹跟踪稳态误差、超调量和调整时间,验证、比较了控制方法准确性、稳定性和快速性3种性能的优劣.结果表明:融合反步法的滑模变结构轨迹跟踪控制的稳定性最好,轨迹跟踪超调量接近于0;融合反步法的模糊自适应轨迹跟踪控制快速性最好,轨迹跟踪调整时间相对于反步法缩短了18.2%.

一种变速度条件下控制攻击角度和时间的制导律

对攻击角度和时间进行控制,可以使得多枚导弹按照特定的角度和时间对目标进行打击,在军事上有广泛的应用前景.目前已有控制攻击角度和时间的制导律极少考虑速度变化的情况,在实际运用中具有较大的局限性.本文基于贝塞尔曲线加直线的二段式轨迹,首先分析并证明了该轨迹长度和最大曲率的变化规律,在此基础上,通过二分法确定初始轨迹,针对飞行过程中的诱导阻力和其它扰动,设计了Bezier-PI控制算法,通过动态调整轨迹长度来实现攻击时间的高精度控制.该制导算法计算量小,鲁棒性强,适用于弹载计算机实时计算.通过仿真实验,验证了该算法可以高精度的控制攻击时间以及攻击角度.

基于用户相关性的差分隐私轨迹隐私保护方案

在使用位置查询服务时需要提供用户真实位置信息,导致用户信息泄露。大部分研究只针对单个用户的隐私保护,而忽略了多用户之间的相关性。针对轨迹隐私保护中多用户相关性的问题,提出了一种基于用户相关性的差分隐私轨迹隐私保护方案。首先,构建历史轨迹树,利用变阶马尔可夫模型预测用户轨迹,从轨迹集合中生成一组高可用性的轨迹数据集;其次,根据用户轨迹之间的相关性获取一组关联性较低的预测轨迹集;最后,通过自定义隐私预算的方法,根据用户不同的隐私需求动态调整每个位置点的隐私预算并为发布轨迹添加拉普拉斯噪声。实验结果表明:与LPADP算法相比,该算法的执行效率提升了10%~15.9%;与PTPP和LPADP算法相比,该算法的数据可用性提升了11%~16.1%,同时提升了隐私保护程度。

Optimization design and experiment of the variable differential gear train planting mechanism

In order to improve the adaptability of the planting mechanism for different plant spacings,a variable differential gear train planting mechanism based on precise pose and trajectory control was proposed by combining the open chain 2R rod group and the variable differential gear train.According to the pose requirements of receiving seedling point,transporting seedling point and planting point,three precise pose points of constrained planting trajectory were determined.Through the three-position motion generation structural synthesis method,combined with computer-aided optimization design software,a set of mechanism parameters that meet the planting requirements were optimized.Based on the optimized mechanism parameters,by only changing the coordinates of two trajectory shape control points,three planting trajectories with key point position information adapted to 300 mm,400 mm and 500 mm plant spacing were obtained by interpolation,and three pairs of total transmission ratio of three groups of variable differential gear trains were calculated.When distributing the total transmission ratio of the mechanism,the fixed axis gear train and the differential gear train are combined.The fixed axis gear train included a pair of non-circular gear pairs and a pair of positive gear pairs,which were convenient for disassembly and assembly.The former drives the sun gear at variable speed,and the latter drives the planet carrier at uniform speed.Based on this structure,the transmission ratio of the positive gear pair is-1,and the transmission ratio of the differential gear train is 0.5.The sub-transmission ratio of the single-stage non-circular gear pair was calculated and the pitch curves of three pairs of noncircular gears were solved.Three pairs of non-circular gear pairs with different transmission ratios were replaced in turn and three sets of planting mechanisms were modeled in three dimensions.The virtual prototype motion simulation was completed by ADAMS software,and the physical prototype was built for vegetable pot seedling planting test.The theoretical solution was consistent with the attitude and trajectory of the actual test.When the test sample size was 100 plants,the actual average plant spacing was measured to be 303 mm,402 mm,and 503 mm,with errors of 1.3%,1.25%,and 1.88%.The width of the moving hole was 72 mm,70 mm,and 71 mm,and the planting success rate were 94%,96%,and 95%.The test results verified the correctness of the optimization design results of the mechanism,indicating that the variable differential gear train planting mechanism can adapt to a variety of plant spacing and has good planting effect.

基于往复式磁流变抛光磨粒轨迹分析

在往复式磁流变抛光过程中为获得光滑均匀的工件,文章采用加工磨粒轨迹分析法,通过对不同参数下磨粒运动轨迹的仿真分析,研究等速和变速两种往复运动工况下磨粒运动轨迹对工件加工质量的影响。结果表明,在变速往复运动条件下,加工磨粒运动轨迹更为复杂,更容易获得光滑均匀的工件。

毁伤高超声速目标的顺轨定角引战配合研究

为降低拦截器导引头的气动加热影响以及高相对速度对成像质量的影响,文中提出顺轨毁伤临近空间高超声速变轨飞行器的后向定角探测体制,通过约束弹目交会参数,结合高爆大飞散破片战斗部,构建后向定角的引战配合模型,实现低速拦截器有效毁伤高超声速临近空间飞行器HTV-2的目的,为防空反临系统提供一种新的前沿毁伤策略。

膜计算下自主机器人轨迹智能跟踪算法

为有效帮助自主机器人更好地规划和控制其运动轨迹,使其能够高效地导航到目标位置,并避免障碍物和碰撞等问题,采用膜计算的方法,给出一种新的跟踪算法。首先,利用膜计算构建具有多个步长的细胞膜型结构,来增加自主机器人找到可行路径的机会。其次,基于上述膜的运行规则,对快速连通阶段工作流程进行设计,寻找得到可行的自主机器人轨迹路径,从而使自主机器人可避免障碍物和碰撞等问题,为后续跟踪提供支持。最后,基于多步长并行膜结构寻找获得可行的自主机器人轨迹路径,使用滑模变结构函数来设计控制率,通过控制率对位置误差进行调整,实现自主机器人轨迹跟踪。实验结果表明:机器人跟踪几乎与实际运动轨迹相同,误差较小,在X轴与Y轴上的误差均小于3 mm,且具有较强的鲁棒性,收敛速度在1.1 s以下,可适应不确定性情况;跟踪轨迹平滑度可维持在96%以上,具有较高的稳定性,跟踪性能较佳,并且追踪响应时间最低为5 s,具有实用性。

船用水下航行器移动轨迹自动跟踪研究

针对复杂运行环境扰动导致水下航行器轨迹跟踪结果产生偏差的问题,研究船用水下航行器移动轨迹自动跟踪方法。构建船用水下航行器空间运动模型(包含运动学模型与动力学模型),设计船用水下航行器移动轨迹自动跟踪控制器,其中主要包含自适应可变参滑模控制器与扰动观测器两部分,利用扰动观测器在复杂运行环境下未知扰动的准确观测;在扰动观测器的基础上,设计自适应可变参滑模控制器,滑模控制器构建误差滑模面的同时,在当前水下环境未知扰动估计结果的影响下获取预期的虚拟控制,并针对指数项趋近系数造成的周期振动问题,将指数项趋近系数转换为自适应可变参。实验结果显示,该方法能够有效实现船用水下航行器移动轨迹自动跟踪过程中位置与速度的准确跟踪。

基于加权变时域MPC的无人车辆轨迹跟踪控制

为提高无人车辆轨迹跟踪的准确性和稳定性,提出一种基于加权变时域模型预测控制(MPC)的车辆运动控制方法。通过灰色关联分析法确定不同速度工况下的最优时域,使用傅里叶逼近法对时域参数进行拟合,将控制器计算时间作为权重系数,得到时域参数随车速变化的加权变时域MPC半经验模型。该模型可根据车辆轨迹跟踪速度的变化选择相对最优时域,提升控制器在不同车速下跟踪的精度和稳定性。选取50和100 km/h为代表车速,对传统定时域MPC控制器和加权变时域MPC控制器的控制效果仿真对比。结果表明:加权变时域控制器有效提升了控制器跟踪性能,最大横向偏差降低1.98%,最大横摆角偏差降低60%,控制器求解时间减少7.2%,同时对不同的目标车速工况也有较强的适应性。

基于前馈型变论域模糊PID控制的智能小车轨迹跟踪方法

为提高智能小车轨迹跟踪的精度及抗干扰能力,提出1种基于前馈型变论域模糊控制方法。以自动导向小车(automated guided vehicle,AGV)为研究对象,建立小车运动学模型对其进行动力学分析;在保持主控制参数不变的情况下,将前馈控制加入变论域模糊控制,搭建前馈型变论域模糊PID(proportional-integral-derivative)控制系统,通过变论域模糊PID控制调整参数使系统获得较好的稳定性,再通过调整前馈控制参数使系统的目标跟踪性能达到最佳;设定S形曲线跟踪路线,在Matlab/Simulink平台下搭建传统PID、模糊PID、变论域模糊PID及前馈型变论域模糊PID等4种控制模型进行仿真实验,比较验证本文方法的控制性能。结果表明:无干扰情况下,4种控制方法的车辆转弯最大横向偏差分别为0.2580,0.1988,0.1792和0.1125m,本文方法的偏差最小,轨迹跟踪精度最高;模拟真实路况下,4种控制方法的车辆转弯最大横向偏差分别为0.8917,0.8209,0.7917,0.6833 m,本文方法的偏差依然最小,抗干扰能力最强,验证了本文所提控制方法兼具跟踪高精度和良好稳定性的优点。

Lower-Elementary Level School Pupils' Developmental Trajectories of Chinese Verbal Vocabulary Knowledge and Influential Factors

149 elementary school pupils were selected as the subjects for this study, to whom five tracking assessments of their verbal vocabulary knowledge were given over a period of three years. In addition, a latent variable growth model was adopted to explore grades 1-3 elementary school pupil's developmental trajectory for verbal Chinese vocabulary knowledge. The phonological awareness, homomorphic morpheme awareness, compound morpheme awareness and family socioeconomic status(SES) on the students' verbal vocabulary knowledge were also investigated. The ndings are: 1, grades 1-3 elementary school pupils verbal Chinese vocabulary knowledge developmental trajectory shows a curvilinear form, of which linear development is trended in the first two years, and as of the third year the developmental rate doubles the previous two years, whereas individual di erences are remarkable in both the initial level and the growth rate; 2, awareness of phonetics, homomorphic morphemes and complex morphemes as well as the family socioeconomic status can be referred to for a positive forecast of the students' initial level of verbal vocabulary knowledge; 3, only the awareness of homomorphic morphemes and the family socioeconomic status can be applied to a positive prediction of the students' verbal vocabulary knowledge growth rate..

基于变论域模糊补偿的机械臂自适应控制

针对存在建模不确定性和外部干扰的机械臂系统,设计了一种结合标称计算力矩控制器和变论域模糊补偿器的复合控制方案,其中利用变论域自适应模糊控制器对建模不确定项进行估计和补偿,利用计算力矩控制器求解标称系统控制力矩。针对伸缩因子设计的自适应律使得变论域自适应模糊控制器在不同时刻适用于状态空间的不同区域,提高了系统的响应速度,大幅减小了系统的稳态跟踪误差,而且跟踪过程平稳柔顺、抖振极小,从而提升了系统的轨迹跟踪性能。仿真结果和实体试验结果均表明所提方法具有有效性。

直升机气动噪声抑制与飞行测试研究进展

直升机在军用和民用领域发挥着越来越重要的作用,新的旋翼技术和构型不断出现,对直升机噪声研究需不断深入和更新。本文首先概述了旋翼(尾桨)的噪声产生机理和传播规律,并扩展到存在复杂气动或噪声干扰的共轴刚性旋翼高速直升机和倾转旋翼机;接下来介绍了直升机飞行噪声测量进展,已发展成多种测量方式作为降噪设计的验证和评估手段;然后综述了降噪设计技术的发展现状:旋翼被动降噪技术已在直升机领域得到大量应用,直升机噪声水平稳步降低;变转速控制技术和低噪声轨迹优化技术逐渐走向成熟;旋翼主动降噪技术更多地停留在实验室阶段,尚需在驱动装置、控制规律等方面开展进一步研究。最后总结了直升机降噪设计现状,并展望了未来发展方向。

变后掠翼制导火箭弹气动特性分析与弹道优化

为提升制导火箭弹射程,对变后掠翼制导火箭弹气动特性进行分析,并加入了弹翼后掠角动态变化策略对火箭弹弹道进行优化。采用计算流体力学(CFD)仿真计算不同后掠角下火箭弹气动参数,并进行气动特性分析,总结了其变化规律。采用hp-自适应Radau伪谱法对火箭弹的弹道进行了优化。考虑到火箭弹的弹翼变形策略,将后掠角的变化纳入计算,对不同后掠角下的固定翼和可变掠翼火箭弹的滑翔段轨迹进行了对比分析。仿真计算结果表明,相对于固定翼火箭弹,采用变后掠翼制导火箭弹可以获得10.8%至34.6%的射程增益,这对提升火箭弹射程具有一定的理论指导意义。

多约束多输入拦截器姿轨一体化复合控制

针对临近空间动能拦截器,提出了一种高精度、低能耗的姿轨一体化复合控制方法。首先,基于拦截器运动学、动力学方程、执行机构特性及全捷联导引头结构,建立了全捷联姿轨复合控制拦截器制导控制系统模型;其次,利用反正切函数设计了包含体视线角约束的映射函数,并针对姿轨耦合问题,结合高阶滑模控制设计了姿轨一体化复合控制律,在满足体视线约束和交会角约束的同时,完成了多个控制任务;最后,基于李雅普诺夫稳定性理论证明了控制律控制下系统的稳定性,并通过仿真验证了一体化设计方法的优越性、映射函数约束的有效性,以及控制律的鲁棒性。

有限时间收敛的引信滚转角控制方法

针对目前二维弹道修正引信滚转角控制方法中存在的气动力矩难以精确计算,精度过于依赖建模准确度,抗干扰能力差的问题,提出一种有限时间收敛的引信滚转角控制方法。该方法基于滑模变结构的理论,利用系统有限时间收敛的概念,选取合适的切换平面以及有限时间收敛的趋近律,使滚转角速率在有限时间内快速收敛到零,并控制翼面滚转角收敛到期望的滚转角。通过对算法的有限时间稳定性分析与仿真验证表明,对于二维弹道修正引信的滚转角控制系统,设计的算法同时满足对滚转角的精确控制和滚转角速度的快速响应,系统的快速性和鲁棒性均有所提升。

图书自动盘点机器人变结构轨迹跟踪方法研究

图书自动盘点机器人是图书馆智能化、数字化的有效方案,其轨迹跟踪方法是保证图书自动盘点机器人稳定运行的关键技术。针对传统图书自动盘点机器人轨迹跟踪位置和姿态的双目标控制问题,提出了一种基于改进趋近律的图书自动盘点机器人轨迹跟踪变结构非线性控制方法,该方法可以有效解决传统变结构控制方法快速性和抖震之间矛盾的问题,最后在Matlab环境下搭建了图书自动盘点机器人的仿真模型。仿真结果表明,所提出的方法不仅具有较快的响应速度,还对抖震有较好的抑制作用。