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.

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。

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-PRRS并联机构动力学分析与控制策略

对应用于虚拟轴并联机床的新型少支链六自由度3-PRRS并联机构进行动力学分析,利用影响系数法推导出从任务空间到关节空间的速度和加速度的映射关系,并利用虚功原理法构建了3-PRRS并联机构完整的动力学模型,推导出驱动关节上驱动力的解析表达式。利用MATLAB软件对机构进行理论数值计算,运用ADAMS软件建立机构的动力学模型,进行并联机构的动力学仿真分析。结果表明:数值计算的结果与虚拟仿真分析结果是一致的,验证了机构的速度、加速度和驱动力的正确性。最后简述了所采用的控制策略,该策略能在有效载荷变化的情况下改变反馈增益,控制效果较好。

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。

3-PRRS六自由度并联机构奇异位形研究

研究一种应用于虚拟轴并联机床的新型少支链3-PRRS六自由度并联机构,通过建立3-PRRS并联机构的封闭矢量方程,构建运动学模型,求导得到机构的速度输入输出关系。利用MATLAB软件编程得到机构的速度曲线,并采用ADAMS软件对机构进行运动学仿真,仿真结果与理论分析一致,表明理论分析的正确性。利用机构的速度输入输出关系分析了边界奇异并利用变量代换化简推导位形奇异轨迹的解析表达式,并通过计算机仿真给出机构的位形奇异轨迹的三维可视化描述,为该并联机构在虚拟轴并联机床的轨迹规划和控制方面提供了重要的理论指导。

3-PRRS并联机构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。首先构建3-PRRS并联机构多目标优化设计模型,基于Isight集成Matlab软件,利用试验设计和多目标优化算法进行多目标确定性优化设计。然后分析3-PRRS并联机构在设计制造中所涉及到的随机不确定性因素,基于Isight进行6Sigma可靠性分析以及考虑随机不确定性因素的6Sigma优化,建立一种高效的考虑不确定性的3-PRRS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最佳设计解可靠度更高,更加符合设计要求。

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.

对称3-PRR并联机构的运动学分析与仿真

以对称3-PRR平面并联机构为研究对象,通过矢量分析建立了3-PRR并联机构的运动学模型。采用坐标变换法建立了机构的运动学方程,并对机构的位置正逆解进行了理论求解和Matlab求解,在理论求解机构位置正解时使用了半角公式法。运用Pro/E的Mechanism模块对机构进行了运动学仿真,并将动平台中心点的仿真轨迹与规划的路径进行了比较,验证了建模方法的正确性及机构的可行性。

空间3-PRR并联机构的奇异性及其在不规则曲面雕刻机中的应用

提出了一种空间3-PRR并联机构,该并联机构所有转动副的轴线均相互平行。基于螺旋理论计算得到1R2T机构具有3个自由度。用闭环矢量法求得并联机构的运动反解,基于运动反解求出了机构的Jacobian矩阵,并利用矩阵获得了该机构的两种奇异位形。由给定参数和约束条件,采用工作空间搜索法求得动平台的可达工作空间,给出了并联机构用于不规则曲面雕刻机的应用实例。实验研究表明,该机构可以满足雕刻的需求。

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。

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。