Dynamic modelling and properties analysis of 3RSR parallel mechanism considering spherical joint clearance and wear

The collision and wear caused by inevitable clearance in kinematic pair have an effect on the dynamic characteristics of the mechanism.Therefore,we established the dynamic model of a 3RSR(R is the revolute joint and S is the spherical joint)parallel mechanism with spherical joint clearance based on the modified Flores contact force model and the modified Coulomb friction model using Newton-Euler method.The standard quaternion was introduced in the constraint equation,and the four-order Runge-Kutta method was adopted to solve the 3RSR dynamic model.The simulation results were compared and analyzed with the numerical results.The geometrical parameters of the worn ball socket were solved based on the Archard wear model,and the geometrical reconstruction of the worn surface was carried out.The geometric reconstruction parameters were substituted into the dynamic model,which was to analyze the dynamic response of the 3RSR parallel mechanism with wear and spherical joint clearance.The simulation results show that the irregular wear occurs in the spherical joint with clearance under the presence of the impact and friction force.The long-term wear will increase the fluctuation of the contact force,thereby decreasing the movement stability of the mechanism.

Theory of Degrees of Freedom for Parallel Mechanisms with Three Spherical Joints and Its Applications

The analysis of degrees of freedom（DOF） of a moving platform is the fundamental problem in kinematics of parallel mechanism. However, many problems should be considered to correctly perform the DOF calculation by using the traditional DOF criterion, and it is difficult to find a DOF criterion suitable for all kinds of mechanisms. A rule that can be used to determine the position and orientation of the moving platform is presented. Based on the proposed rule, a new form of DOF criterion is proposed, which is suitable for a class of parallel mechanisms with three spherical joints attached to the moving platform. The basic types of generalized limb structures are given based on the possible dimension of achieving the center of spherical joint attached to the moving platform, and the general steps of analyzing the DOF are presented. This proposed formula simplifies the DOF analysis of parallel mechanisms with spherical joints attached to the moving platform, and plays an important role in structural synthesis of such parallel mechanisms.

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.

Static Force-Based Modeling and Parameter Estimation for a Deformable Link Composed of Passive Spherical Joints With Preload Forces

To balance the contradiction between higher flexibility and heavier load bearing capacity,we present a novel deformable manipulator which is composed of active rigid joints and deformable links.The deformable link is composed of passive spherical joints with preload forces between socket-ball surfaces.To estimate the load bearing capacity of a deformable link,we present a static force-based model of spherical joint with preload force and analyze the static force propagation in the deformable link.This yields an important result that the load bearing capacity of a spherical joint only depends on its radius,preload force,and static friction coefficient.We further develop a parameter estimation method to estimate the product of preload force and static friction coefficient.The experimental results validate our model.80.4%of percentage errors on the maximum payload mass prediction are below 15%.

Ultimate Bearing Capacity of Hollow Spherical Joints Welded with Circular Pipes under Eccentric Loads

The hollow spherical joints welded with circular pipes applied to the National Swimming Center of China are subjected to large bending moments, but the influence of bending moments is not considered in the design equations in Technical Specification for Latticed Shells. Based on the von Mises yield criterion, multilinear isotropic hardening rule and associated flow rule, the elasto-plastic finite element model is put forward to analyze the behavior of the joints, and a calculation method for the joints under bending moments or eccentric loads is proposed. It is shown by the analytical results of joint that the stiffening rib can improve the ultimate bearing capacity by 10% for joints under axial tensile load, by 40% for joints under axial compressive load, and by 50% for joints under bending moment. The unified calculation equations for joints with or without stiffening rib are put forward, which can be applied to calculating the ultimate bearing capacity of the hollow spherical joints with circular pipes under eccentric loads.

Experiments on Large-Diameter Welded Hollow Spherical Joint

We experimented on welded hollow spherical joint of a stadium steel roof to investigate the stress and strain distributions on the surface of the joint and determine the ultimate bearing capacity. Then, finite element analysis was made to experimental results. When the test load was 140% of the design load, the stress at the bottom of the fourth wimble pipe reached the yield point. The experimental results agree with the analytical results well.

Design and Strength Analysis of A Spherical Connector for Lifting Subsystem in Deep Sea Mining System

A flexible connector of lifting pipes in a deep sea mining system is designed. The buttress thread （ based on API standard） is used and foreign experience in connector design is referred to. With this kind of connector, the lifting pipe wiU only bear the axial force, free of moment. The strength of the connector is analyzed in detail, including the connecting strength of the buttress thread, the dynamic load of the pipe system, pressures inside and outside of the pipe, the lateral stress of the pipe wall and so on. Especially, a geometric model is built for 3-D contact stress analysis. The distribution graph of contact stress is presented. It is indicated that the strength of the spherical connector meets the demand.

Structural Design and Performance Analysis of a Deep-Water Ball Joint Seal

To overcome the current difficulties of high-precision machining and the high manufacturing and maintenance costs of spherical seals for deep-water drilling ball joints,a new spherical seal technique is proposed in this paper.The spherical seal is mainly composed of silicone rubber and polytetrafluoroethylene(PTFE).Rational structural design makes the seal independent from the ball and other components,making it easy to replace if leakage occurs at its surface.PTFE can elastically deform over a certain deformation range,which guarantees that two sealing surfaces fit tightly together.O-Ring and PTFE elasticity makes up for any lack of accuracy during spherical machining and decreases the machining precision requirements for spherical surfaces.Using a finite element technique and nonlinear theory,the performance of the spherical seal under the influence of various factors is determined.The results show that the spherical seal designed in this paper exhibits excellent sealing performance under lowtemperature and high-pressure conditions.The spherical seal,a combination of an O-ring and PTFE,has the advantages of cheap manufacturing and maintenance costs and excellent sealing performance.

单板焊接空心球节点受拉承载性能研究

单板焊接空心球节点常用做弦支穹顶上部结构连接拉杆或拉索的节点,单板主要承受拉力并传递至焊接空心球,为了满足工程设计的要求,需对其受拉承载性能进行研究.通过试验,研究了不同参数的单板焊接空心球节点轴拉状态下的受力性能和破坏机理,建立有限元模型并进行验证,该模型能较好地反映单板焊接空心球节点轴拉性能,通过有限元模型参数化分析揭示了节点尺寸、加劲肋、单板尺寸等参数对其力学性能的影响规律,并提出单板焊接空心球轴拉承载力计算公式.研究结果表明:单板焊接空心球在轴拉作用下为应力集中导致的剪切强度破坏,破坏发生在单板端部与空心球连接处,表现为焊接空心球被撕裂;有限元应力云图得出破坏时沿着单板平面内拉力方向的剪应力起主要作用;单板焊接空心球节点的受拉承载力随单板宽度及空心球壁厚的增大而明显增大,空心球直径的增大会使承载力略有降低,单板的厚度增加使节点承载力略有提高,单板的高度对节点承载力的影响较小,空心球内设置加劲肋能使承载力提高至少20%;基于参数化提出的单板焊接空心球节点的受拉承载力计算公式能简便地计算出单板焊接空心球节点的承载力,相对误差在±15%以内,满足工程设计误差要求.研究工作可为今后外接单板的焊接空心球节点分析设计提供参考.

A Novel Engineering Spherical Bearing, with Potential Application for a Hip Implant

It is a research which could enter into contradiction with the current trend concerning the hip implants. It is known as sliding friction, which is characteristic of present artificial hip joints, is higher than in the case of rolling friction. The paper reports the studies of the functioning mode of a novel spherical bearing MoM （metal on metal） with rolling friction, with potential application for an artificial hip joint obtained by introducing a number of balls between the femoral head and the acetabular cup. After over 15 years of research upon the functional principle and constructive solution, a version that offered a coefficient of minimum friction in the hip joint came to light. This version was based on a constructive solution of motion with lower friction, ＂Omnitrack~ movement solutions＂, which has been modified and rebuilt to be used as a joint of a total hip prosthesis--MOMJ. The joint was built entirely in stainless steel, SS316L medical grade. Tests have been carried out on the experimental laboratory devices that showed very low values of the coefficient of friction （μ = 0.0225）. For validation, the prosthesis had to be put through tests for 500,000 cycles, in terms of physiological motion and dynamic loading, according to ISO 14242-3. Testing was conducted on a multiaxial dynamics machine, MTS Bionix, equipped with system for hip implant testing. The testing results of this total hip prosthesis with rolling friction have been successful in signing up for a friction moment of 0.525 kNmm which means a coefficient of friction la = 0.0143, for a joint with femoral head diameter 28 mm.

基于球面角点特征的鱼眼相机与激光雷达联合标定方法

针对鱼眼相机和激光雷达的联合标定问题,提出一种基于球面角点特征的鱼眼相机与激光雷达联合标定方法。首先利用静电斥力物理模型得到了均匀分布在球面上的点集,并以这些点集为生长点对球面进行Voronoi划分,得到了均匀的球面像素,实现了鱼眼相机图像在球面上的均匀重采样;之后在球面上提取了鱼眼相机图像的角点特征,有效地避免了图像畸变带来的角点提取困难的问题;最后利用17组标定数据在球面上实现了鱼眼相机和激光雷达联合标定,在鱼眼图像上的重投影误差小于2个像素,并通过数据融合实验复现了真实场景中的彩色三维效果。

钢板加固螺栓球节点力学性能试验研究

针对螺栓球节点高强螺栓漏拧、少拧的情况,实际工程中常采用焊接钢板加固螺栓球节点来保障螺栓球节点承载力。为探究钢板加固螺栓球节点的破坏形式及极限承载力规律,对三组高强螺栓拧入深度0.5d(d为螺栓直径)螺栓球节点采用钢板加固并进行受拉承载力试验。试验结果表明,钢板加固螺栓球节点虽能提高节点的承载力,但试件高强螺栓和钢板变形很难协调,共同受力不理想,易发生局部破坏。故对原有加固方法进行改进,并进行加固后螺栓球节点拉伸破坏试验。结果表明,改进后的钢板加固螺栓球节点力学性能得到很好的提升,可为螺栓节点加固提供保障。

双耳板焊接空心球节点轴拉力学性能研究

目的探究双耳板焊接空心球节点的受拉力学特性,揭示破坏机理并探讨影响其承载力的主要因素。方法针对8个双耳板焊接空心球节点进行轴心受拉极限承载力试验,并采用ABAQUS有限元分析软件对节点进行参数化数值分析,重点讨论节点几何尺寸对其承载力的影响。结果在轴向拉力作用下,双耳板焊接空心球节点破坏形式分为空心球开裂破坏,耳板与空心球连接处焊缝失效,且个别试件出现球面局部起皮;空心球与耳板连接端部处应力集中明显,随着荷载增大,在空心球与耳板连接处沿径向逐步进入屈服阶段。结论节点轴拉极限承载力,与空心球直径、耳板宽度与球外径比、耳板厚度与球壁厚度比呈正相关,与空心球径厚比呈负相关,且上述影响因素中空心球壁厚与耳板厚度比对承载力影响相对较小。

环口板加强带脱空缺陷的钢管混凝土T型节点滞回性能试验研究

为研究环口板加强带脱空缺陷的钢管混凝土T型节点的抗震性能,完成了12根节点试件在主管受恒定轴拉力与支管受轴向往复荷载作用下的滞回试验,基于试件破坏模式、荷载-位移滞回关系和应变发展考察了采用环口板加强带脱空缺陷T型节点试件的效果,并对比分析支主管直径比和主管径厚比对试件加强效果的影响。试验结果表明:采用环口板加强T型节点有效抑制了脱空缺陷导致的主管塑性变形,并实现带缺陷T型节点承载力、刚度、延性和耗能能力的完全恢复,甚至优于相应的无脱空试件,其中加强试件的承载力较带脱空缺陷试件提升12.6%以上,较无脱空试件提升6.5%以上,表明经合理设计的环口板加强措施能够弥补脱空缺陷对节点抗震性能的不利影响。

Si_(3)N_(4)陶瓷关节轴承内圈外球面磨削研究

为探究氮化硅陶瓷关节轴承内圈外球面精密范成磨削方法,以表面粗糙度为主要评价指标,用立式五轴加工中心进行正交试验,确定各磨削参数对其表面粗糙度的影响顺序;再通过单因素试验探究磨削参数对其表面质量的影响规律,并用粒子群算法对陶瓷关节轴承内圈磨削表面粗糙度进行回归预测,最终获得最佳加工工艺参数。结果表明:砂轮粒度与砂轮进给速度对氮化硅关节轴承内圈外球面磨削表面的粗糙度影响最显著,砂轮线速度次之,工件线速度影响最小;陶瓷轴承内圈外球面表面粗糙度随进给速度的提高而增大,随砂轮线速度、工件线速度的提高先减小后增大。模型的预测值与实际测量值相对误差小于5%,表明该模型的预测效果较好,为实际加工选取磨削参数提供了理论依据。

球形关节关键技术研究进展

球形关节是一种结构简单紧凑、响应快、精确度高的单一球转子多自由度电机,在航天航空、先进医疗设备、智能机器人等众多领域有着广阔的应用前景。针对球形关节的部分关键技术进行了分析总结,首先对当前一些主流球形关节的驱动原理和结构进行了分类整理,介绍了各类球形关节的驱动方法和技术特征;其次针对位姿检测研究主要技术路线进行了总结归纳。最后,基于上述讨论分析了球形关节研究的关键技术发展趋势,为后续球形关节研究提供了参考。

含间隙球面4R机构运动区间可靠性分析

为分析转动副间隙对球面4R机构运动精度的影响,提出一种球面机构输出角位移误差区间可靠性分析方法。分析转动副间隙对球面4R机构实际位姿的影响,基于D-H参数,将机构参数的1阶微分表示为运动副间隙造成的误差,使用环路增量法建立机构角位移输出精度分析模型。针对球面4R机构单周期运动,阐述了机构运动区间可靠性与机构角位移输出误差的数学关系;结合极值法建立球面4R机构区间可靠性分析模型,计算得到了球面4R机构运动区间可靠度;蒙特卡洛仿真结果作为评价可靠度计算的标准值,最后结合球面4R机构可靠性分析实例验证了所提分析方法的有效性。

双耳板焊接空心球节点轴拉承载力研究

为揭示双耳板焊接空心球节点受拉破坏机理,并建立其受拉承载力计算公式。针对8个双耳板焊接空心球节点进行轴心受拉极限承载力试验,并采用ABAQUS有限元分析软件对节点进行参数化数值分析,讨论节点几何尺寸对其承载力的影响。研究结果表明,在轴向拉力作用下,双耳板焊接空心球节点破坏形式为空心球开裂破坏,耳板与空心球连接处焊缝失效,且个别试件出现球面局部起皮。提出了适用于球外径在160~500mm的双耳板焊接空心球节点的受拉承载力计算参考公式,研究成果可为类似工程设计提供参考。

基于TRIZ理论的新型关节轴承节点的研究

传统的关节轴承节点,具备面内和面外转动性能,基本可解决大部分钢结构建筑的卸力要求。以TRIZ理论为指导,迅速揭示设计的主要矛盾,激发新的创意和解决方案,通过对传统关节轴承节点设计技术的改进与创新,创新研制出一种刚铰接可切换的新型关节轴承节点,满足某些大型钢结构建筑的特殊连接需求,并形成自主知识产权与标准规范,对助力各类高、大、长、斜等结构特异建筑结构设计方案的实现形成安全可靠的技术支撑。

某悬挂球幕结构设计分析

某场馆采用框架-剪力墙结构,于场馆中庭悬挂直径16 m的展馆球体。采用通用分析有限元软件SAP2000作为主要分析软件,重点考察球体拉杆在各设计工况下的位移与构件应力比、某一拉杆断裂后其余拉杆的设计内力及变形、球幕内楼板舒适度分析。对受拉节点进行有限元分析并加强支座环梁,各项测算均满足要求^([1-3]),从设计分析层面保证了悬挂球幕的可行性。