Analysis of stress and natural frequencies of high-speed spatial parallel mechanism

In order to grasp the dynamic behaviors of 4-UPS-UPU high-speed spatial parallel mechanism, the stress of driving limbs and natural frequencies of parallel mechanism were investigated. Based on flexible multi-body dynamics theory, the dynamics model of 4-UPS-UPU high-speed spatial parallel mechanism without considering geometric nonlinearity was derived. The stress of driving limbs and natural frequencies of 4-UPS-UPU parallel mechanism with specific parameters were analyzed. The relationship between the basic parameters of parallel mechanism and its dynamic behaviors, such as stress of driving limbs and natural frequencies of parallel mechanism, were discussed. The numerical simulation results show that the stress and natural frequencies are relatively sensitive to the section parameters of driving limbs, the characteristic parameters of material on driving limbs, and the mass of moving platform. The researches can provide important theoretical base of the analysis of dynamic behaviors and optimal design for high-speed spatial parallel mechanism.

Dynamic Analysis of High-Speed Boat Motion Simulator by a Novel 3-DoF Parallel Mechanism with Prismatic Actuators Based on Seakeeping Trial

In this study,we focused on a novel parallel mechanism for utilizing the motion simulator of a high-speed boat(HSB).First,we expressed the real behavior of the HSB based on a seakeeping trial.For this purpose,we recorded the motion parameters of the HSB by gyroscope and accelerometer sensors,while using a special data acquisition technique.Additionally,a Chebychev highpass filter was applied as a noise filter to the accelerometer sensor.Then,a novel 3 degrees of freedom(DoF)parallel mechanism(1T2R)with prismatic actuators is proposed and analyses were performed on its inverse kinematics,velocity,and acceleration.Finally,the inverse dynamic analysis is presented by the principle of virtual work,and the validation of the analytical equations was compared by the ADAMS simulation software package.Additionally,according to the recorded experimental data of the HSB,the feasibility of the proposed novel parallel mechanism motion simulator of the HSB,as well as the necessity of using of the washout filters,was explored.

Dynamic Modeling and Analysis of 4UPS-UPU Spatial Parallel Mechanism with Spherical Clearance Joint

Clearance between the moving joints is unavoidable in real working process. At present, many researches are mainly focused on dynamics of plane revolute joint in plane mechanism, but few on dynamics of spatial spherical joint clearance in spatial parallel mechanism. In this paper, a general method is proposed for establishing dynamic equations of spatial parallel mechanism with spatial spherical clearance by Lagrange multiplier method. The kinematic model and contact force model of the spherical joint clearance were established successively. Lagrange multiplier method was used to deduce the dynamics equation of 4 UPS-UPU mechanism with spherical clearance joint systematically. The influence of friction coefficient on dynamics response of 4 UPS-UPU mechanism with spherical clearance joint was analyzed. Non-linear characteristics of clearance joint and moving platform were analyzed by Poincare map, phase diagram, and bifurcation diagram. The results show that variation of friction coefficient and clearance value had little effect on stability of the mechanism, but the chaotic phenomenon was found at spherical clearance joint. The research has theoretical guiding significance for improving the dynamic performance and avoiding of chaos of parallel mechanisms including spherical joint clearance.

Determination of the workspace of a new coordinate-measuring machine using parallel-link mechanism

Presents the detailed algorithm established for determination of workspace for a 3-DOF coordinate measuring machine using parallel link mechanism by constructing the inverse kinematic model first and then reviewing the physical and kinematical constraints from the structural characteristics of the parallel link mechanism, and discusses the actual geometries of workspace and the factors having effect on workspace through computer simulation thereby providing necessary theoretical basis for the research and development of coordinate measuring machines using parallel link mechanism.

Position, Singularity and Workspace Analysis of 3-PSR-O Spatial Parallel Manipulator

Although the parallel mechanisms have the advantages of high accuracy, velocity, stiffness, and payload capacity, the shortcomings of the space utilization and workspace limit the applications in the confined space. A novel 3 degrees of freedom spatial parallel manipulator 3-PSR-O（prismatic-spherical-revolute） is proposed, which possesses a compact architecture and extended workspace while maintaining the inherent advantages of the parallel mechanisms. The direct-inverse position, singularity and workspace are investigated. The mapping method is adopted in the position analysis, and the closed form solution is derived in the form of a six order equation. The singularity analysis of the mechanism is also carried out based on the geometrical constraints, including six singularity boundaries. A feature boundary, which is independent of the prismatic joints＇ stroke limit, is obtained by integrating the six singularity boundaries. According to the formation of the reachable workspace, a concept of basic workspace is also introduced and presented in the analytical way. By demarcating the basic workspace along the central height with the feature boundary, the reachable workspace can be derived and analyzed more efficiently. Finally, a comparative study on the space utilization between the 3-PSP parallel mechanism and the new mechanism is also presented. The area of feature boundary of the new mechanism is about 140% of the 3-PSP parallel mechanism, while its installation radius is only 1/2 of the 3-PSP parallel mechanism. The proposed parallel mechanism shows great space utilization, and is ideally suited for applications in confined space occasions such as immersion lithography, nano-imprint etc.

复杂战场环境下改进YOLOv5军事目标识别算法研究

复杂战场环境下军事目标识别技术是提升战场情报获取能力的基础和关键。针对当前军事目标识别技术在复杂战场环境下漏检误检率高、实时性差等问题,提出一种基于改进YOLOv5模型的PB-YOLO军事目标识别算法。将改进的目标识别算法对于陆战场军事单元的识别锚框进行重新聚类,以提升模型对于目标大小适应度,加速模型收敛;采用通道-空间并行注意力机制,增加模型对复杂战场环境下目标特征信息与位置信息关注度;在特征融合网络部分使用BiFPN以提升模型对于特征的融合能力与速度;采用Alpha_IoU损失函数加速模型收敛,解决当真实框与预测框重合时IoU计算退化问题。实验结果表明,在自建军事目标数据集下,改进算法与主流目标识别算法相比,在保证模型空间复杂度的同时,mAP值达到了90.17%。消融实验对比结果表明,改进后网络较原模型精度提升11.57%,具有较好的识别性能,能够为战场情报获取提供有效的技术支撑。

考虑润滑间隙效应的空间并联机构动力学优化

为了改善润滑间隙效应引起的空间并联机构动态性能的渐变劣化问题,以3-RRPaR冗余并联机构为研究对象,提出一种考虑润滑间隙效应的空间并联机构动力学优化方法。建立了考虑润滑转动副间隙的3-RRPaR冗余并联机构动力学模型;以优化末端执行器的动力学响应误差和优化间隙关节处的约束反力为目的设置目标函数,通过优化末端执行器质量以及转动惯量的方式来缓解运动副间隙导致的劣化效应,建立了考虑润滑间隙效应3-RRPaR冗余并联机构动力学优化模型;试验验证了所建动力学模型的有效性,对比分析两种目标函数对优化效果的影响以选择最佳优化方式,并分析优化前后考虑润滑间隙效应的空间并联机构动力学特性,结果表明动力学优化使润滑间隙转动副处约束反力峰值降低16.16%,为改善间隙效应提高空间并联机构动态性能提供了理论支撑。

考虑球面副润滑间隙的空间并联机构动力学建模与响应分析

为了分析含球面副润滑间隙的空间并联机构动力学响应特性,以2RPS-SPR(R转动副,P移动副,S球面副)空间并联机构为研究对象,结合Reynolds方程和Gümbel边界条件,建立了含多个球面副润滑间隙的空间并联机构动力学模型,对比分析了含润滑间隙、不考虑间隙的理想情况和含干摩擦间隙的机构动力响应特性,以及分析了不同动力粘度、不同间隙值对润滑状况下的机构动力学响应的影响。结果表明,润滑间隙相比于干摩擦间隙能有效改善并联机构的动力特性,且随着润滑油动力粘度的增大以及间隙值的减小,机构运行状况越好。该研究为含球面副润滑间隙并联机构动力学响应特性分析提供了理论方法,为指导实际生产提供了理论依据。

考虑混合间隙的空间并联机构非线性动力学特性分析

为了掌握同时考虑球面副间隙和三维转动副间隙的空间并联机构的非线性动力学特性,研究考虑混合间隙的空间并联机构多体系统动力学特性分析方法。首先以4-UPS/RPU空间并联机构为研究对象,建立三维转动副间隙和球面副间隙的模型,推导同时考虑球面副间隙和三维转动副间隙的4-UPS/RPU空间并联机构动力学方程;然后利用龙格库塔法对动力学方程进行数值求解,分析不同间隙类型、间隙、驱动速度和摩擦因数对并联机构动力学响应的影响,通过ADAMS虚拟样机仿真验证动力学模型和数值计算的正确性;最后利用相轨迹图、庞加莱映射图和分岔图等分析考虑混合间隙的4-UPS/RPU并联机构的非线性特性。该研究为考虑混合运动副间隙的空间并联机构动力学建模和非线性动力学特性分析提供了依据。

空间并联指向机构实验平台动力学建模与仿真分析

为了提高学生的动力学建模和分析能力,基于3自由度3-转动副-转动副-转动副-转动副-转动副(3-RRRRR)空间并联指向机构实验平台,开展动力学建模与仿真分析研究。首先,分析3-RRRRR空间并联指向机构实验平台的结构特征,建立并联指向机构平台的运动学模型;然后,利用拉格朗日乘子法推导并联指向机构平台的刚体动力学模型,基于四阶龙格库塔(Runge-Kutta)算法求解机构平台动力学模型,通过数值仿真分析不同驱动速度对并联指向机构平台动力学响应的影响;最后,采用ADAMS虚拟样机仿真验证动力学模型及模型求解的正确性。该研究为空间并联机构实验平台刚体动力学建模和仿真分析提供了有效方法,为机构动力学分析与控制奠定了理论基础。

新型4自由度并联机器人运动学分析

研究一种新型3-RRUR并联机器人,这类并联机器人结构简单对称,刚度大,可用于实现高精度装配,也可用来开发力传感器或构造并联机床以及微动机器人,且分支中不含移动副,便于使用维护。首先利用螺旋理论,建立分支运动螺旋系,然后求解各分支对运动平台的约束螺旋,分析约束螺旋系,在此基础上确定3-RRUR并联机器人的自由度数是4,自由度性质为三维移动和一维转动,转动轴线垂直于固定平台与3个分支相连接的运动副轴线所在的平面。再以反螺旋理论为基础,采用刚化驱动运动副后分析运动平台所受约束性质和约束相关性的方法,给出合理的输入方案。并结合自由度性质分析,建立约束方程,进行运动学正反解,给出相应的算例。研究结果将对推动此类机器人的应用起重要作用。

基于广义坐标形式牛顿-欧拉方法的空间并联机构动力学正问题分析

基于具有广义坐标形式的牛顿-欧拉方法建立一般空间并联机构动力学正问题建模与仿真的通用方法。在动力学建模时,选取空间并联机构动平台的工作空间变量作为系统广义坐标,从各构件的牛顿-欧拉方程出发,结合运动学逆解和虚功原理,得到与广义坐标相对应的系统动力学方程-运动微分方程和系统理想铰约束力方程。对6-UPS型空间并联机构进行动力学建模,计算外力作用下的动态响应,验证了该方法的有效性。理论分析和仿真案例表明,该方法可以简化并联机构动力学正问题的建模步骤,提高计算效率。

5自由度空间并联机构运动学优化设计

定义了一种能综合评价不同位形下并联机构灵巧度的指标——平方平均灵巧度系数,分别考察了4-UPSRPS空间并联机构的定平台和动平台上铰链点的分布角、定平台铰链点分布圆的半径以及动平台铰链点分布圆的半径对平方平均灵巧度系数的影响规律,并据此对这些参数进行优化设计,得到该并联机构定平台铰链点的均布角为π/2,动平台铰链点的均布角为2π/5,定平台上第1个铰链点到定坐标系原点的距离为650 mm,定平台上其余4个铰链点分布圆的半径为800 mm,动平台上铰链点分布圆的半径为160 mm。仿真结果表明,经过优化设计,4-UPS-RPS空间并联机构的平方平均灵巧度系数指标比优化前明显增大,运动学性能得到了较大改善。

空间并联机构连续刚度非线性映射

基于影响系数法并借助虚功原理建立包含主、被动关节弹性变形,杆件及其平台自重的空间并联机构连续刚度非线性映射通用模型。空间并联机构连续刚度非线性映射通用模型与以往刚度模型区别在于,它不仅考虑了机构主动驱动关节、被动关节弹性变形及各部件重力对机构刚度的影响,而且考虑了机构刚度变化的连续过程,没有忽略机构在广义外力下变形时雅可比矩阵的变化,通过引进机构的二阶影响系数,从而使空间并联机构刚度非线性映射还原。从机构简化约束方程出发,推导空间并联机构几类连续刚度简化映射矩阵。在此基础上,结合刚度矩阵瑞利商定义了空间并联机构连续刚度性能判定指标k′。最后给出一空间并联机构刚度分析实例,分别计算两种模型下的刚度矩阵,并对比两种模型下机构刚度性能。

6-5平台型并联机构的位置正解

研究了６－５平台型空间机构位置正解问题．导出了２０次输出输入方程，并由此得到动平台的４０个不同位姿．经数值验证所得结果正确．

一种三维移动并联平台机构的运动学分析

介绍了一种能实现空间三维移动的并联平台机构——空间 3-RRC机构。该机构结构简单对称 ,运动副少 ;可用于运动工作台 ,并联机床等。分析了该机构的运动学 ,推导了速度、加速度正反解方程。与 Stewart平台等并联机构比 ,该机构的运动学解相对简单 ,计算量小 ,便于实时控制。通过典型输入时工作平台的位置、速度及加速度的对应关系曲线 。

三自由度3-RPS并联机器人机构的运动分析

讨论了具有三自由度的３－ＲＰＳ并联机器人机构的运动分析。在这种机构操作器平台的六个运动位姿参数中，只有三个是独立的，而其它三个参数不是独立的。因此，这种机构的雅可比矩阵是一长方阵，这就是这种机构的运动分析的难点所在。本文根据这种机构的结构特点，给出了操作平台的输出运动参数的三个运动约束方程，并且建立了三个独立输出运动参数和三个独立运动输入参数之间的速度和加速度关系的显式数学模型。

5-5型并联机器人位置正解的简单算法

对一类5—5台体型并联机器人机构的结构特征进行了深入分析，提出了其位置正解分析与求解的简单方法。首先利用序单开链的思想对该机构进行拓扑特征分析和结构分解，将其运动学方程维数降至最小，然后利用一维搜索法得到全部实数解，最后将该方法应用于具体实例，结果不仅表明了该方法的有效性，而且首次给出了具有20组实数解的机构实例。

旋量键合图在并联机构动力学建模中的应用

旋量键合图将旋量理论与键合图相结合,兼具了旋量理论描述空间并联机构简洁、直观及键合图多能域建模统一、规范的特点。对空间并联机构基本组成单元——构件和运动副,利用旋量键合图,构建动力学模型,并进行模块化处理。在此基础上,调用单元模块,就可建立与可视化的机构一一对应的并联机构旋量键合图模型,按照规则化推导方法,得到适用于现代控制理论的空间并联机构状态方程。以曲柄滑块机构及空间3-UPS/S并联机构为研究对象,验证旋量键合图模块化建模的可行性,给出空间并联机构具有通用性的规则化动力学建模过程,并且进一步分析空间3-UPS/S并联机构匀速及加速运动状态下驱动力、支链约束反力变化规律。这种建模方法的应用为后续构建机器人系统全局动力学模型及控制研究奠定基础。

三自由度3－RPS并联机器人操作器的瞬时独立运动分析

讨论了具有三自由度的３－ＲＰＳ并联机器人机构的独立运动及其与机构结构设计的关系。根据这种机构的结构特点，给出了操作平台的输出运动参数的三个运动约束方程，并且建立了三个独立输出运动参数和三个独立运动输入参数之间的一阶速度影响系数矩阵的显式数学模型，分析了机构的独立运动与机构结构设计的关系，并给出了这种机构的操作平台的瞬时运动螺旋的确定方法。