改进A*算法的AGV避障路径规划研究

针对传统A*算法在复杂栅格地图规划的路径不平滑存在多余转折点和多余共线节点，使用传统八叉树搜索策略时，AGV易发生碰撞障碍物现象，在复杂环境中随机出现在全局路径上的障碍物无法实现动态避障等问题，提出一种改进A*算法。由于传统A*算法的搜索效率主要取决于估价函数的设计，因此引入启发式函数的权重系数提高A*算法的搜索效率；设置障碍物安全距离，为判断障碍物区域内当前障碍物是否影响AGV通行提供参考，再次改进原有八叉树搜索策略提升避障性能，然后对得到的无碰撞路径进行路径优化处理，保留关键转折点；最后实现A*和DWA算法融合，进一步优化路径，并实现全局动态路径规划。实验结果表明：融合算法使得路径更加平滑，提高了算法的避障性能，表明了融合算法在机器人路径规划中的可行性。     

基于改进A~*算法在AGV路径规划中的应用

为了解决复杂环境下A~*寻路算法存在搜索节点多,搜索时间长,路径曲折的问题,提出了一种改进的A~*算法。首先,在具有障碍物的栅格地图中引入象限的概念,通过限制当前节点只朝目标节点所处的一个象限进行节点扩展,有效降低了寻路过程中搜索的节点数量。其次,在估价函数中考虑了AGV行驶和转向时间消耗成本,从而有效的搜索最短时间路径。通过仿真实验分析比较了文中算法与A~*算法以及另一种改进A~*算法的搜索性能。仿真结果表明,文中算法能有效减少寻路过程中的搜索节点数和转向次数,提高了路径搜索效率和平滑度。     

基于改进D^(*)算法的巡检机器人路径规划北大核心

路径规划技术是巡检机器人的热门研究,针对传统D^(*)算法存在的如拐点多、效率低、路径安全度不高等问题,对传统D^(*)算法进行了改进,优化了子节点的选取方式,将全局地图环境分解为多个局部环境,在选取局部环境中的目标点时,以局部环境关键节点为主,舍弃无用节点和危险节点;又改进了代价估计函数,并引入平滑度函数。最终用MATLAB建立栅格地图进行仿真,结果表明:改进后的算法得到的路径转弯次数有所优化,拐点数目减少了约30%;规划效率得到了提升,规划时间节约了约20%;并且所得路径与障碍物保持了适当距离,提升了机器人运行过程中的安全性。     

基于优化A*和DWA算法的移动机器人避障路径规划

针对移动机器人在路径规划过程中路径曲率不连续,避障能力差等问题,提出了一种将改进A*和动态窗口法（DWA）相结合的路径规划方法。首先,在传统的A*算法基础上,将传统的8个搜索方向改为5个,提高搜索效率;其次,将Floyd算法思想引入A*算法中,设计了一种新的启发式搜索函数,实现了无斜穿障碍物顶点,增加了路径的平滑度;最后,融合改进算法以及动态窗口法,构造了新的评价函数,在保证规划路径全局最优性的基础上达到避障效果。仿真结果表明：该研究对于移动机器人自主导航的应用具有一定的参考价值。     

复杂动态环境下自主机器人路径规划研究

为了提高复杂动态环境下的机器人路径规划性能,文章提出了全局路径规划和局部路径规划相融合的混合路径规划方法。分析了A*算法原理,提出了加权A*算法,使用权值调节启发信息在评价函数中的作用;改进了人工势场法,解决了传统方法目标不可达和局部极值问题;将加权A*算法的全局路径规划和改进人工势场法的局部路径规划相融合,以全局规划路径的拐点作为局部路径规划的子目标点,提出了混合路径规划方法。经仿真验证,对于固定静态障碍物、临时堆放障碍物、动态障碍物三种情况,混合规划方法都能得到平滑的无碰最优路径。     

基于扩展角度控制的改进RRT机械臂路径规划

针对传统的快速搜索随机树(RRT)算法在路径规划的过程中收敛速度慢、路径冗长且在复杂的环境下成功率低的问题,提出了一种改进的RRT路径规划算法。该算法引入基于障碍占空比的扩展角度控制策略,通过父节点附近障碍物分布情况控制新节点的扩展方向,增加算法规划速度的同时保证了算法的成功率。随后通过剪枝优化和二阶贝塞尔曲线对生成的路径进行平滑处理。通过多组仿真结果表明,改进RRT算法与原始RRT算法相比,改进RRT算法生成的路径长度更短,时间更快,扩展角度收敛性更高,规划成功率也有较大的提高。     

融合改进RRT和动态窗口法的路径规划算法北大核心

针对传统RRT算法在规划中随机性过大,搜索时间过长且不能够实现动态避障等问题,从3个方面进行改进。针对RRT算法搜索树扩展方向过于随机,根据以起始点与目标点为对角线的矩形中的障碍物占比向目标点方向扩展,分别在有障碍物与无障碍物的环境中与传统RRT算法对比,验证改进算法的高效性;对改进算法规划的路径进行关键节点提取,并按照关键节点进行优化;将优化后路径分段使用改进动态窗口法。将融合算法与传统动态窗口法以及RRT算法在路径拐点数量以及路径长度等方面进行比对,结果表明:融合算法具有高效性且在规划的路径中加入临时障碍物时,移动机器人也能很好地避开。     

基于交通约束及多元启发函数的改进A^*算法

针对多移动机器人的环境下容易出现碰撞的情况以及传统A^*算法规划的路径容易出现拐角数多的问题,基于栅格建模的方法,提出了交通约束法,并且在A^*算法原有启发函数的基础上,添加拐角数的评判指标,构成多元启发函数。在MATLAB仿真平台上对基于交通约束及多元启发函数A^*算法进行仿真实验,结果证明在多AGV系统下,基于交通约束及多元启发函数的A^*算法在规划出合理路径的前提下,减少了拐角数,降低了碰撞几率,提高了移动机器人完成路径的效率,具有较强的稳定性。     

基于PRM改进的路径规划算法

针对规划环境中障碍物较多,采样节点较少时,移动机器人使用传统PRM算法难以规划出路径的问题,提出一种改进的PRM算法,通过随机节点生成函数在自由空间生成随机节点,取代落在障碍物中的节点,在采样节点数目不变的情况下,提高自由空间中的节点数目,配合改进的节点增强法,优化路径,减少路径中的节点数目,完成路径规划。仿真结果验证了本算法的有效性,改进后的PRM算法能用较少的随机采样点找到一条可行路径,提高了节点的利用率,降低了路径中节点数目。     

基于改进Informed-RRT算法的路径规划研究

针对Informed-RRT~*算法在复杂环境重复规划稳定性差、收敛速度慢的问题,提出改进Informed-RRT~*的路径规划算法(Informed Bi-directional RRT~*)提升寻找可行路径的稳定性和效率。该算法引入基于状态子集直接采样的反向扩展策略,当路径规划遇到障碍时快速更新采样区间,在障碍物的边界区域获得接近最优路径成本的可行路径,同时结合基于多树搜索的双向搜索策略加快对状态子集的探索,提高算法的收敛速度。实验表明,与Informed-RRT~*算法相比,IBI-RRT~*算法稳定性更高,能够减少40%的迭代次数和20%～30%的搜索时间,并且规划路径接近最优路径,验证了IBI-RRT~*算法在复杂环境中路径规划的优势。     

Effects of Post-weld Heat Treatment on Microstructure,Mechanical Properties and the Role of Weld Reinforcement in 2219 Aluminum Alloy TIG-Welded Joints

In as-welded state, each region of 2219 aluminum alloy TIG-welded joint shows diff erent microstructure and microhardness due to the diff erent welding heat cycles and the resulting evolution of second phases. After the post-weld heat treatment, both the amount and the size of the eutectic structure or θ phases decreased. Correspondingly, both the Cu content in α-Al matrix and the microhardness increased to a similar level in each region of the joint, and the tensile strength of the entire joint was greatly improved. Post-weld heat treatment played the role of solid solution strengthening and aging strengthening. After the post-weld heat treatment, the weld performance became similar to other regions, but weld reinforcements lost their reinforcing eff ect on the weld and their existence was more of an adverse eff ect. The joint without weld reinforcements after the post-weld heat treatment had the optimal tensile properties, and the specimens randomly crack in the weld zone.     

The First Phase of the SRIF Industrialized Base in ＂West Area＂ Has Been Put into Operation

After nearly two years＇ tense construction, the first phase of industrialized base of Shenyang Research Institute of Foundry （SRIF）, located at the Tiexi Casting and Forging Industrial Park in the west of Tiexi District, has now been completed and formally put into operation.     

Thermodynamics Study on the Decomposition of Chromite with KOH

Institute of Process Engineering, Chinese Academy of Sciences, China, has proposed a method for oxidative leaching of chromite with potassium hydroxide. Understanding the mechanism of chromite decomposition, especially in the potassium hydroxide fusion, is important for the optimization of the operating parameters of the oxidative leaching process. A traditional thermodynamic method is proposed and the thermal decomposition and the reaction decomposition during the oxidative leaching of chromite with KOH and oxygen is discussed, which suggests that chromite is mainly destroyed by reactions with KOH and oxygen. Meanwhile, equilibrium of the main reactions of the above process was calculated at different temperatures and oxygen partial pressures. The stable zones of productions, namely, K2CrO4 and Fe2O3, increase with the decrease of temperature, which indicates that higher temperature is not beneficial to thermodynamic reactions. In addition, a comparison of the general alkali methods is carried out, and it is concluded that the KOH leaching process is thermodynamically superior to the conventional chromate production process.     

Influence of Heat Treatment on Damping Behaviour of the Magnesium Wrought Alloy AZ61

The effect of isochronal heat treatments for 1h on variation of damping, hardness and microstructural change of the magnesium wrought alloy AZ61 was investigated. Damping and hardness behaviour could be attributed to the evolution of precipitation process. The influence of precipitation on damping behaviour was explained in the framework of the dislocation string model of Granato and Lücke.     

Effect of Rare Earth Doping on Impedance,Modulus and Conductivity Properties of Multiferroic Composites:0.5(BiLa_xFe_(1-x)O_3)–0.5(PbTiO_3)

The Lanthanum-doped bismuth ferrite–lead titanate compositions of 0.5(Bi LaxFe1-xO3)–0.5(Pb Ti O3)(x = 0.05,0.10,0.15,0.20)(BLxF1-x-PT) were prepared by mixed oxide method.Structural characterization was performed by X-ray diffraction and shows a tetragonal structure at room temperature.The lattice parameter c/a ratio decreases with increasing of La(x = 0.05–0.20) concentration of the composites.The effect of charge carrier/ion hopping mechanism,conductivity,relaxation process and impedance parameters was studied using an impedance analyzer in a wide frequency range(102–106Hz) at different temperatures.The nature of Nyquist plot confirms the presence of bulk effects only,and non-Debye type of relaxation processes occurs in the composites.The electrical modulus exhibits an important role of the hopping mechanism in the electrical transport process of the materials.The ac conductivity and dc conductivity of the materials were studied,and the activation energy found to be 0.81,0.77,0.76 and 0.74 e V for all compositions of x = 0.05–0.20 at different temperatures(200–300 °C).     

Quantitative Analysis of the Crystallographic Orientation Relationship Between the Martensite and Austenite in Quenching–Partitioning–Tempering Steels

The orientation relationships(ORs)between the martensite and the retained austenite in low-and medium-carbon steels after quenching–partitioning–tempering process were studied in this work.The ORs in the studied steels are identified by selected-area electron diffraction(SAED)as either K–S or N–W ORs.Meanwhile,the ORs were also studied based on numerical fitting of electron backscatter diffraction data method suggested by Miyamoto.The simulated K–S and N–W ORs in the low-index directions generally do not well coincide with the experimental pole figure,which may be attributed to both the orientation spread from the ideal variant orientations and high symmetry of the low-index directions.However,the simulated results coincide well with experimental pole figures in the high-index directions{123}_(bcc).A modified method with simplicity based on Miyamoto’s work was proposed.The results indicate that the ORs determined by modified method are similar to those determined by Miyamoto’method,that is,the OR is near K–S OR for the low-carbon Q–P–T steel,and with the increase of carbon content,the OR is closer to N–W OR in medium-carbon Q–P–T steel.     

Growth Kinetics of Single Inclusion Particle in Molten Melts

On the basis of the single-particle framework, a new theory on inclusion growth in metallurgical melts is developed to study the kinetics of inclusion growth on account of reaction and collision. The studies show that the early growth of inclusion depends on reaction growth and Brawnian motion collision, and where the former is decisive, the late growth depends on turbulence collision and Stokes＇ collision, and where the former is dominant; collision growth is very quick during the smelting process, lessened in the refining process, but nearly negligible in the continuous casting process.     

Theoretical Analysis for the Motion and Temperature of Melt Droplets in Spray Degassing Process

The motion of melt droplets in spray degassing process was analyzed theoretically. The height of the treatment tank in spray degassing process could be determined by the results of theoretical calculation of motion of melt droplets. To know whether the melt droplets would solidify during spraying process, the balance temperature of melt droplets was also theoretically analyzed. Then proof experiments for theoretical results about temperature of melt droplets were carried. In comparison, the experimental results were nearly similar to the calculation results.     

Using Finite Element and Contour Method to Evaluate Residual Stress in Thick Ti-6Al-4V Alloy Welded by Electron Beam Welding

This work was to reveal the residual stress profile in electron beam welded Ti-6Al-4V alloy plates(50 mm thick) by using finite element and contour measurement methods.A three-dimensional finite element model of 50-mmthick titanium component was proposed,in which a column–cone combined heat source model was used to simulate the temperature field and a thermo-elastic–plastic model to analyze residual stress in a weld joint based on ABAQUS software.Considering the uncertainty of welding simulation,the computation was calibrated by experimental data of contour measurement method.Both test and simulated results show that residual stresses on the surface and inside the weld zone are significantly different and present a narrow and large gradient feature in the weld joint.The peak tensile stress exceeds the yield strength of base materials inside weld,which are distinctly different from residual stress of the thin Ti-6Al-4V alloy plates presented in references before.     

Microstructures and Tensile Properties of Ultrafine-Grained Ni–(1–3.5) wt% SiC_(NP) Composites Prepared by a Powder Metallurgy Route

Silicon carbide nanoparticle-reinforced nickel-based composites(Ni–Si CNP),with a Si CNPcontent ranged from1 to 3.5 wt%,were prepared using mechanical alloying and spark plasma sintering.In addition,unreinforced pure nickel samples were also prepared for comparative purposes.To characterize the microstructural properties of both the unreinforced pure nickel and the Ni–Si CNPcomposites transmission electron microscopy(TEM) was used,while their mechanical behavior was investigated using the Vickers pyramid method for hardness measurements and a universal tensile testing machine for tensile tests.TEM results showed an array of dislocation lines decorated in the sintered pure nickel sample,whereas,for the Ni–Si CNPcomposites,the presence of nano-dispersed Si CNPand twinning crystals was observed.These homogeneously distributed Si CNPwere found located either within the matrix,between twins or on grain boundaries.For the Ni–Si CNPcomposites,coerced coarsening of the Si CNPassembly occurred with increasing Si CNPcontent.Furthermore,the grain sizes of the Ni–Si CNPcomposites were much finer than that of the unreinforced pure nickel,which was considered to be due to the composite ball milling process.In all cases,the Ni–Si CNPcomposites showed higher strengths and hardness values than the unreinforced pure nickel,likely due to a combination of dispersion strengthening(Orowan effects) and particle strengthening(Hall–Petch effects).For the Ni–Si CNPcomposites,the strength increased initially and then decreased as a function of Si CNPcontent,whereas their elongation percentages decreased linearly.Compared to all materials tested,the Ni–Si CNPcomposite containing 1.5% Si C was found more superior considering both their strength and plastic properties.