INVERSE KINEMATIC AND DYNAMIC ANALYSIS OF A 3-DOF PARALLEL MECHANISM

According to the structure character of the passive sub-chain of the 3TPS-TPparallel mechanism, the kinematic constraint equations of the movable platform are established,based on which the closed-form inverse kinematics formula of the parallel mechanism are presented.Through parting the spherical joints of the active sub-chains and using the force and momentequilibrium of both the active sub-chains and passive sub-chain, the constraint forces acting on theparted joints are determined. Subsequently, the analytic expressions of the actuator driving forcesare derived by means of the force equilibrium of the upper links of active sub-chains.

Rotation Control of a 3-DOF Parallel Mechanism Driven by Pneumatic Muscle Actuators

The pneumatic muscle actuator(PMA)has many advantages,such as good flexibility,high power/weight ratio,but its nonlinearity makes it difficult to build a static mathematical model with high precision.A new method is proposed to establish the model of PMA.The concept of hybrid elastic modulus which is related to the static characteristic of PMA is put forward,and the energy conservation law is used to achieve the expression of the hybrid elastic modulus,which can be fitted out based on experimental data,and the model of PMA can be derived from this expression.At the same time,a 3-DOF parallel mechanism(a new bionic shoulder joint)driven by five PMAs is designed.This bionic shoulder joint adopts the structure of two antagonistic PMAs actualizing a rotation control and three PMAs controlling another two rotations to get better rotation characteristics.The kinematic and dynamic characteristics of the mechanism are analyzed and a new static model of PMA is used to control it.Experimental results demonstrate the effectiveness of this new static model.

Topology Search of 3-DOF Translational Parallel Manipulators with Three Identical Limbs for Leg Mechanisms

Three-degree of freedom（3-DOF） translational parallel manipulators（TPMs） have been widely studied both in industry and academia in the past decades. However, most architectures of 3-DOF TPMs are created mainly on designers＇ intuition, empirical knowledge, or associative reasoning and the topology synthesis researches of 3-DOF TPMs are still limited. In order to find out the atlas of designs for 3-DOF TPMs, a topology search is presented for enumeration of 3-DOF TPMs whose limbs can be modeled as 5-DOF serial chains. The proposed topology search of 3-DOF TPMs is aimed to overcome the sensitivities of the design solution of a 3-DOF TPM for a LARM leg mechanism in a biped robot. The topology search, which is based on the concept of generation and specialization in graph theory, is reported as a step-by-step procedure with desired specifications, principle and rules of generalization, design requirements and constraints, and algorithm of number synthesis. In order to obtain new feasible designs for a chosen example and to limit the search domain under general considerations, one topological generalized kinematic chain is chosen to be specialized. An atlas of new feasible designs is obtained and analyzed for a specific solution as leg mechanisms. The proposed methodology provides a topology search for 3-DOF TPMs for leg mechanisms, but it can be also expanded for other applications and tasks.

Kinematics and dynamics analysis of a 3-7R parallel decoupling mechanism

One kind of movable-pair analysis method is adopted to analyze the configuration of a 3-7R （revolute-pair） parallel decoupling mechanism, and the mechanism＇s characteristics are summarized. The mechanism has three orthogonal distributional branch-chains, and all movable pairs are rotational joints. The movable platform of the mechanism has x, y, z translational decoupling directions. Furthermore, in order to verify the mechanism＇s decoupling characteristics, the mechanism＇s kinematics analysis is solved, and the mechanism＇s direct/inverse kinematics model, input/output velocities and accelerations are deduced, which confirm its decoupling movement characteristics. Finally, one kind of mechanism link decomposed-integrated approach is adopted, and the mechanism＇s dynamics model is completed with the Lagrange method, which also proves its decoupling force characteristics. All of these works provide significant theory for the further study of the mechanism＇s control strategy, design, path planning etc.

Architecture Singularity Analysis of 4-U■S/U■U 5-DOF Parallel Mechanism

Architecture singularity of a parallel mechanism with five degrees of freedom (DOF) is analyzed. Such mechanism consists of a movable platform connected to the base by five active limbs. Four of them are identical 6-DOF limbs and the last one has the same DOF as the specified DOF of the movable platform. Based on the kinematics analysis, two categories of architecture singularities for such mechanism are proposed. Then the sufficient condition for each singularity is researched. Results show that the mechanism is singular when it employs each category of the proposed architecture, provided that it satisfies the corresponding sufficient condition. It can be concluded that the proposed two categories of architecture singularities should be avoided with the following dimensional synthesis of such mechanism.

PERFORMANCE ANALYSIS AND KINEMATIC DESIGN OF PURE TRANSLATIONAL PARALLEL MECHANISM WITH VERTICAL GUIDE-WAYS

Performance analysis and kinematic design of the 3-PUU pure translational parallel mechanism with vertical guide-ways are investigated. Two novel performance indices, the critical slider stroke and the main section area of workspace, are defined; The expressions of two other indices, i.e. the global dexterity and global force transfer ratio are revised based on the main section of workspace. Using these indices, performance changes versus the varieties of dimensional parameters of mechanism are investigated in detail and the graphic descriptions of change tendencies of the performance indices are illustrated. By means of these obtained graphic descriptions, kinematic parameters for the 3-PUU pure translational parallel mechanism with better characteristics can be directly acquired.

Bridge Crack Segmentation Method Based on Parallel Attention Mechanism and Multi-Scale Features Fusion

Regular inspection of bridge cracks is crucial to bridge maintenance and repair.The traditional manual crack detection methods are timeconsuming,dangerous and subjective.At the same time,for the existing mainstream vision-based automatic crack detection algorithms,it is challenging to detect fine cracks and balance the detection accuracy and speed.Therefore,this paper proposes a new bridge crack segmentationmethod based on parallel attention mechanism and multi-scale features fusion on top of the DeeplabV3+network framework.First,the improved lightweight MobileNetv2 network and dilated separable convolution are integrated into the original DeeplabV3+network to improve the original backbone network Xception and atrous spatial pyramid pooling(ASPP)module,respectively,dramatically reducing the number of parameters in the network and accelerates the training and prediction speed of the model.Moreover,we introduce the parallel attention mechanism into the encoding and decoding stages.The attention to the crack regions can be enhanced from the aspects of both channel and spatial parts and significantly suppress the interference of various noises.Finally,we further improve the detection performance of the model for fine cracks by introducing a multi-scale features fusion module.Our research results are validated on the self-made dataset.The experiments show that our method is more accurate than other methods.Its intersection of union(IoU)and F1-score(F1)are increased to 77.96%and 87.57%,respectively.In addition,the number of parameters is only 4.10M,which is much smaller than the original network;also,the frames per second(FPS)is increased to 15 frames/s.The results prove that the proposed method fits well the requirements of rapid and accurate detection of bridge cracks and is superior to other methods.

3-PRS并联机构工作空间求解的SimMechanics实现

3-PRS空间并联机构是2R1T的3自由度机构,由于该空间机构运动的复杂性,故对其工作空间的研究意义重大。以3-PRS并联机构的逆运动学为基础,运用Matlab中的Sim Mechanics功能模块绘制其结构框图,建立该机构的三维实体模型;然后利用数值实例根据滑杆的行程限制条件以及球面副和转动副的转角约束条件采用运动仿真法编程得出了3-PRS并联机构的工作空间。结果表明,该机构的工作空间具有对称性,且内部无空洞,为3-PRS并联机构进一步研究优化设计、控制研究等奠定了一定的理论基础。

3-DOF转动柔索驱动风洞机构的力雅可比矩阵

简要概述了柔索牵引并联机器人在国内外的研究和发展现状,提出一种新颖的基于5根柔索牵引并联机器人的三自由度转动角度机构及测力一体化风洞试验装置。应用并联机构基本理论研究了机构的运动学逆解。依据空间解析几何理论,直接推导出在各柔索安装单分量力传感器时模型的感、测力变换雅可比矩阵。最后给出了数值算例,验证了该装置应用于风洞测力试验的有效性,为该测力装置应用于风洞试验奠定了基础。

3-DOF平面并联机器人的类型分析与运动学

根据3-DOF平面并联机器人过渡关节为转动关节或移动关节,推知其过渡(关节)变量为转动变量或移动变量,将其分为两种类型,即过渡变量为转动变量的第一类和过渡变量为移动变量的第二类平面并联机器人。并导出了各类型具有的标准运动学模型及其解的结构。类型一的运动学正解为一元六次方程,最多有六组解;类型二的为一元二次方程,最多有两组解。反解运动学模型为一元二次方程或有惟一解。

基于SimMechanics的高速3-RRR并联机构动力学分析与控制

为了满足3-RRR并联机构在工业应用中高速操作,研究其在高速运动中的动力学行为和控制。采用SimMechanics建立3-RRR并联机构的动力学模型,基于该模型对其进行动力学分析。分析结果表明,速度越大,驱动力矩也越大;机构高速运行过程中驱动力矩变化大,且在某些时刻产生突变致使机构产生较大冲击。为了实现高速运动跟踪控制,利用PID控制的鲁棒性,设计PID控制器。仿真结果表明,动平台能较好地实现期望的轨迹,但在初始阶段,存在一定的跟踪误差。

Global Dynamic Modeling of Electro-Hydraulic 3-UPS/S Parallel Stabilized Platform by Bond Graph

Dynamic modeling of a parallel manipulator（PM） is an important issue. A complete PM system is actually composed of multiple physical domains. As PMs are widely used in various fields, the importance of modeling the global dynamic model of the PM system becomes increasingly prominent. Currently there lacks further research in global dynamic modeling. A unified modeling approach for the multi-energy domains PM system is proposed based on bond graph and a global dynamic model of the 3-UPS/S parallel stabilized platform involving mechanical and electrical-hydraulic elements is built. Firstly, the screw bond graph theory is improved based on the screw theory, the modular joint model is modeled and the normalized dynamic model of the mechanism is established. Secondly, combined with the electro-hydraulic servo system model built by traditional bond graph, the global dynamic model of the system is obtained, and then the motion, force and power of any element can be obtained directly. Lastly, the experiments and simulations of the driving forces, pressure and flow are performed, and the results show that, the theoretical calculation results of the driving forces are in accord with the experimental ones, and the pressure and flow of the first limb and the third limb are symmetry with each other. The results are reasonable and verify the correctness and effectiveness of the model and the method. The proposed dynamic modeling method provides a reference for modeling of other multi-energy domains system which contains complex PM.

Research on the operating characteristics of parallel 4-DOF electric platform with 4TPS-PS structure

The 4TPS-PS parallel platform designed for a stabilization and automatic tracking system is a novel lower-mobility parallel mechanism. In the first part of this paper, the structure of the platform is described and the kinematics model is built. The workspace of the platform is defined as the full reachable rotation workspace when the Z coordinate dimension of the upper plate varies continuously. A fast searching method of the full reachable workspace is presented, after which the inverse kinematics of the platform is deduced. The forward and inverse solutions of the speed and force of the platform are deduced. According to the characteristic of the 4TPS-PS platform’s structure, a fast searching algorithm of the maximum generalized speed and maximum generalized force output by the upper plate is put forward based on the forward and inverse solutions of the platform’s speed and force. The 4TPS-PS platform prototype built by the State Key Laboratory of Fluid Power Transmission and Control of China is taken as the research subject. The full reachable rotation workspace of the prototype is computed out and analyzed. The curves of maximum generalized speed and maximum generalized force of the prototype are computed out and plotted. Finally, the com- puting and analyzing results of the operating characteristics are confirmed through the experiment.

工程车辆3-RPS座椅悬架半主动滑模控制

工程车辆处于恶劣的工作环境中,垂向单维度的被动减振无法满足实际需求。为解决该问题,依据可实现三维减振的3-RPS并联机构座椅悬架,提出一种新型三维控制策略。基于“座椅-人体”三维振动数学模型,设计一种新的三维天棚控制模型,作为滑模控制的参考对象。设计滑模控制器,并根据Lyapunov稳定判据,对控制系统的稳定性进行分析判断。利用Simulink软件建立座椅-人体受振模型,对处于E、F、G级3种路面环境中,分别采用滑模控制以及被动控制模式的座椅的减振效果进行仿真对比分析。结果表明,相较于被动控制的座椅悬架,采用三维滑模控制的座椅悬架在垂直方向上的加速度下降率在38.88%至57.06%之间;俯仰方向上的角加速度的下降率在36.00%至54.89%之间;侧倾方向上的角加速度的下降率在49.58%至59.97%之间。且可有效降低垂直方向上的加速度峰值,对于冲击载荷减振性能良好。研究成果可为半主动多维减振座椅悬架控制策略的研究提供一定参考。

Rail-Pillar Net:A 3D Detection Network for Railway Foreign Object Based on LiDAR

Aiming at the limitations of the existing railway foreign object detection methods based on two-dimensional(2D)images,such as short detection distance,strong influence of environment and lack of distance information,we propose Rail-PillarNet,a three-dimensional(3D)LIDAR(Light Detection and Ranging)railway foreign object detection method based on the improvement of PointPillars.Firstly,the parallel attention pillar encoder(PAPE)is designed to fully extract the features of the pillars and alleviate the problem of local fine-grained information loss in PointPillars pillars encoder.Secondly,a fine backbone network is designed to improve the feature extraction capability of the network by combining the coding characteristics of LIDAR point cloud feature and residual structure.Finally,the initial weight parameters of the model were optimised by the transfer learning training method to further improve accuracy.The experimental results on the OSDaR23 dataset show that the average accuracy of Rail-PillarNet reaches 58.51%,which is higher than most mainstream models,and the number of parameters is 5.49 M.Compared with PointPillars,the accuracy of each target is improved by 10.94%,3.53%,16.96%and 19.90%,respectively,and the number of parameters only increases by 0.64M,which achieves a balance between the number of parameters and accuracy.

大口径天线3-RPS驱动机构结构优化设计与分析

采用并联机构替换现有的方位-俯仰式串联机构作为反射面天线的驱动机构可以满足其位姿调整的功能,并有效改善反射面天线整体结构的轻量化效果。目前少有将并联机构应用于大口径天线的分析与实际工程应用案例,故需要对承受较大载荷的并联机构展开力学分析并对其结构进行优化,从而使其满足承载与运动精度的要求。针对3-RPS并联机构承受较大载荷时支链的结构方案展开优化设计并进行有限元仿真分析。首先,对3-RPS并联机构展开静力学分析,得到在动平台承受一定载荷的情况下机构各个支链的受力特性;其次,在给定机构基本尺寸参数及活动范围要求下,对3-RPS并联机构支链的结构方案进行设计,针对并联机构支链弯曲变形较为严重的情况提出了并联液压缸的结构方案;最后,对并联液压缸结构方案进行了优化以及稳定性分析。结果表明,优化后的并联液压缸方案各项性能指标均优于原有方案,且满足稳定性安全性要求,为实际的工程应用提供参考。

3-PUU并联机构运动副间隙耦合误差特性分析

并联机构运动副间隙直接影响机构的运动精度,导致末端输出特性产生差异。为了探究并联机构运动副耦合特性对末端输出精度的影响,以3-PUU并联机构为研究对象,设置运动副间隙误差为0.05、0.1、0.15、0.2 mm,利用单开链-局部指数积公式法对其进行耦合误差建模,从理论上推导运动副耦合特性与末端输出精度之间的关系,采用MATLAB对运动副耦合误差进行仿真分析,并制作样机进行试验。结果表明:当并联机构不同支链运动副存在误差时,机构末端沿x轴位置偏差随机构运动时间和关节间隙误差的增大呈现波动且伴随拐点和曲线分离;y轴位置偏差波动较大,在运动中轨迹拐点、折点和分离点相继出现,运动不平稳且超出运动空间,当并联机构双支链运动副误差为0.2 mm时,超工作空间达到-5.31 mm;机构末端沿z轴的位置偏差随着运动时间和关节间隙的增大呈现轨迹相互交错,与仿真分析一致。

3-PCR并联机构的振动响应特性分析

当车辆运行路况恶劣,驾驶员不仅要承受振动的影响,还要承受严重的瞬时冲击力。为避开人体水平、横向及垂直方向上的敏感频率带,以及降低振动强度。首先,因减振装置的动力学模型为多自由度、多参数耦合且非线性复杂系统,利用矩阵变换法解耦,对有阻尼系统进行模态分析;然后,对三维减振装置进行振动响应分析,在动平台X、Y、Z方向上分别施加瞬时冲击力对系统进行仿真分析。仿真结果表明:该减振平台具有良好的减振效果,由于3-PCR并联机构三条支链相互耦合的原因,低频振动会维持一段时间然后再趋于稳定。

基于牛顿欧拉法的3-RPS并联机构逆动力学分析

以3-RPS机构为例,研究了对称少自由度并联机构的逆动力学问题。因其自由度数目小于6,该类机构的支链不仅传递驱动力,同时还需为动平台提供约束。然而,现有文献大多未对广义约束力给予足够的重视。采用牛顿欧拉法建立了3-RPS机构的刚体动力学方程,给定动平台的运动规律及外载荷后,可一并求解机构所需的驱动力与约束力矩。算例仿真表明,与动平台自由速度方向不一致的外载荷主要需由约束力矩平衡。因此,在对称少自由度并联机构动力学设计中,必须计入广义约束力的影响。

3SPR并联机构运动学分析"

针对一种3-SPR并联平台机构,依据机构的数学模型建立了机构的位置逆解模型,在此基础上推导出各支链的速度映射模型,通过算例和运动学仿真软件CosmosMotion的仿真结果对比分析验证了该速度模型正确有效,并通过利用SolidWorks软件进行虚拟机构的建模,对其工作空间进行仿真,得到机构工作空间的几何形状。