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.

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.

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.

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.

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.

3-PUU并联机构的运动学分析与验证

为提升少自由度并联机构设计的效率和准确性,针对自主设计的3-PUU并联机构进行了理论分析和实验研究。首先,利用螺旋理论和修正的Kutzbach-Grubler公式分析了并联机构的自由度;同时,解算了并联机构的运动学正反解和雅可比矩阵,并基于雅可比矩阵分析了其约束奇异和运动奇异。然后,利用极限边界搜索法分析了并联机构的工作空间,并以雅可比矩阵条件数的倒数作为局部灵巧度来构造全局灵巧度,分析了并联机构的运动性能。接着,搭建了并联机构的ADAMS/Simulink联合仿真模型,基于给定的动平台运动方程,通过仿真得到了动平台位置的仿真曲线及误差曲线。最后,利用并联机构样机、PC(personal computer,个人计算机)、STM32单片机、伺服电机及激光跟踪仪搭建了实验平台,并测定了并联机构动平台的位置曲线。结果表明,该并联机构具有较大的可达工作空间且其运动性能较好;通过对比理论结果与仿真结果可知,所构建的并联机构运动学模型正确;动平台位置的实测值与理论值之间存在一定误差,主要原因是并联机构存在机械误差以及控制系统精度不足,但实测曲线与理论曲线的变化趋势基本一致,进一步验证了并联机构运动学模型的正确性。研究结果可为少自由度并联机构的设计提供参考。

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.

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-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。

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。

新型3-PUU并联机构的运动学和动力学分析及建模仿真

介绍了一种新型3-PUU并联机构,对其运动学方程进行分析,根据机构特征推导出转动支链和动平台的速度公式;采用Lagrange方程建立机构的动力学模型;分别在机构的3个移动支链上施加运动,通过计算机模拟,得到动平台的运动轨迹、受力、速度和加速度随时间变化的关系。

3-PUU微动并联机构的尺寸型模型及性能图谱

为设计 3 PUU微动并联机构 ,使其获得良好的运动性能 ,提出用杆件无量纲参数建立机构尺寸型模型 ,该模型在有限区间内给出了 3 PUU微动机构所有可能的尺寸组合 ,模型空间中的任意一点代表具有相同或相似运动性能的同一族机构 ;定义反映微动机构运动性能的工作空间体积值、工作空间形状值及条件数 3种性能指标 ,在尺寸型模型中绘制一系列性能图谱 ,通过计算机仿真验证性能图谱的正确性 ,依据图谱提供优化设计机构的方法。

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。

3-PSS柔性并联微操作机器人柔度分析

柔度矩阵建模是进行全柔性机构分析的基础。针对3-PSS型柔性并联微操作机器人,首先基于坐标变换法计算机构单条支链柔度矩阵,并基于此建立机器人整体柔度矩阵模型。然后进行数值算例计算和Ansys有限元仿真分析,并将理论计算结果与有限元分析结果进行对比,验证了柔度矩阵建模的正确性。最后对柔性并联机器人进行了柔度性能分析,并得出了机构的结构参数对柔度的影响规律,分析结果对3-PSS型柔性并联机构的结构优化设计提供了依据。

基于Jacobian+RBF的3-PTT并联机构末端精确控制方法

为降低并联机构机械误差测量和补偿的难度,实现机构末端的精确控制,本文提出一种基于Jacobian和RBF神经网络相结合的末端误差补偿方法。以一种3-PTT并联机构为研究对象,分析机构正、逆运动学,验证数学模型的正确性。根据运动学模型解算Jacobian,分析机构约束奇异和运动奇异。为验证机构末端误差补偿方法的有效性,设置两种实验条件,分别为是否有丝杠的回程误差补偿和末端受不同负载,并通过激光跟踪仪测定末端位置。实验结果表明,使用本文的误差补偿方法后,机构末端轴向(x轴)、径向(y轴)位置误差均降低90%以上,竖直方向(z轴)位置误差均降低80%以上,证明了本文方法的有效性。

3-PUU并联机构的多目标可靠性优化设计

以提高并联机构多目标优化设计结果的可靠性为目的。首先根据性能评价指标构建3-PUU并联机构多目标优化设计模型,利用试验设计(DOE)和多目标优化算法(NSGA-Ⅱ)进行确定性多目标优化设计。然后分析量化3-PUU并联机构在设计制造中所涉及到的随机不确定性因素,利用6 Sigma设计(DFSS)方法进行6 Sigma可靠性分析以及考虑随机不确定性因素的6Sigma优化,建立一种有效的考虑不确定性的3-PUU并联机构多目标可靠性优化方法。研究结果表明,考虑不确定因素的多目标优化设计方法得到的优化结果可靠度更高,更加符合实际工程需求。

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.

基于3-PCR并联机构汽车座椅减振装置的构型设计与工作空间分析

针对汽车驾驶员长期处于低频高强度全身振动的难题,提出以3-PCR并联机构作为汽车座椅减振装置的主体机构,其结构简单、工作空间大。首先,利用机构拓扑结构学理论对3-PCR并联机构进行自由度分析;然后,建立3-PCR并联机构的运动学模型,推导上下平台位姿之间的数学关系;最后,在Matlab软件中采用极限边界搜索法求解工作空间。