Coating thickness optimization for a robotized thermal spray system

Thermal spraying techniques are used to protect or improve the surface performance of a workpiece by adding melted (or heated) powders onto the surface. Thickness and uniformity control are critical for obtaining an excellent thermal spraying coating. In the contemporary manufacturing industry, with the increasing demand for efficient and accurate processes, robot manipulators and handling systems have been developed to control the movement of the spray gun relative to the workpiece surface, where the robot manipulators and handling systems lead the spray gun to reciprocate along a predefined path. However, the research on optimizing the path for generating the desired coating thickness is very limited. In this paper, a parametric coating thickness prediction model is adapted from our previous research. Then, the Nelder-Mead method drives the model to find out the optimal kinematic parameters of a zigzag (meander) path for a uniform coating with the desired thickness. Based on the obtained kinematic parameters, the trajectory and program of a robot end effector (spray gun) are yielded. Finally, a prototype system with an intuitive user interface is developed to integrate these functions. From the input of a Gaussian coating growth model and a substrate, it can provide an optimal path directly. At the end of this work, one case was implemented by a homemade spray system and a robot system for verifying the effectiveness of the system.     

Paint deposition modeling for trajectory planning on automotive surfaces

This research is focused on developing trajectory planning tools for the automotive painting industry. The geometric complexity of automotive surfaces and the complexity of the spray patterns produced by modern paint atomizers combine to make this a challenging and interesting problem. This paper documents our efforts to develop computationally tractable analytic deposition models for electrostatic rotating bell (ESRB) atomizers, which have recently become widely used in the automotive painting industry. The models presented in this paper account for both the effects of surface curvature as well as the deposition pattern of ESRB atomizers in a computationally tractable form, enabling the development of automated trajectory generation tools. We present experimental results used to develop and validate the models, and verify the interaction between the deposition pattern, the atomizer trajectory, and the surface curvature. Limitations of the deposition model with respect to predictions of paint deposition on highly curved surfaces are discussed. Note to Practitioners-The empirical paint deposition models developed herein, which are fit to experimental data, offer a significant improvement over models that are typically used in industrial robot simulations. The improved simulation results come without the computational cost and complexity of finite element methods. The models could be incorporated, as is, into existing industrial simulation tools, provided the users are cognizant of the model limitations with respect to highly curved surfaces. Although the models are based on readily available information, incorporating the models into existing robot simulation software would likely require support from the software vendor.     

Path-following control of a mobile robot in the presence of actuator constraints

In this paper, we present a control law for a non-holonomic mobile robot that achieves path following. In the path-following problem, the objective is to control the angular velocity of the robot so that the robot tracks a given reference trajectory. In this paper, we propose a control law that achieves path following in the presence of a constraint on the angular velocity. By applying the proposed control law, the robot can track the reference trajectory even if the distance from the initial position of the robot and the reference trajectory is arbitrary large. Further, we extend the control law so that the linear velocity of the robot becomes small when the robot passes through corners. By using the control algorithm, we can prevent the angular velocity of the robot becoming extremely large when the robot passes through corners. Numerical examples are provided to illustrate the effectiveness of the proposed methods.     

非平坦地形下移动机器人安全路径规划

提出一种基于双分辨率2.5D分层栅格地图的Secure A*(SA*)路径规划方法,以解决移动机器人在非平坦地形下的安全路径规划问题.首先,设计一种双分辨率2.5D分层栅格地图,利用双分辨率栅格对环境中的障碍物信息与高程信息进行存储,以节约地图的存储空间;然后,结合移动机器人运动能力,将环境中的高程信息转化为约束因子,...     

Path planning for a tracked robot traversing uneven terrains based on tip-over stability

In the real-world environment, the path planning method of tracked robot is widely studied when driving on uneven terrain. How to solve the problem that the traditional path planning algorithm cannot adapt to uneven terrain because of the constraints of obstacle avoidance and path length is a challenge for tracked robots. In this paper, a stability-based path planning framework for tracked robot is proposed to reduce the risk of rollover when the tracked robot passes through uneven terrain. First, a virtual plane method is proposed to estimate the attitude of tracked robot. Second, on this basis, a dynamic high-stability path evaluation algorithm for tracked robot based on force angle stability margin (FASM) is proposed, which transforms the stability-based path planning problem into a hypergraph problem. Moreover, considering that the optimization problem is strongly nonlinear and nonconvex, a hybrid algorithm of covariance matrix adaptive evolution strategy (CMAES) and Levenberg–Marquardt (LM) is designed under the framework of generalized graph optimization (G2O) to improve the solution efficiency. Finally, simulation and experiments show that the stability-based path planning framework can effectively plan the high-quality path, and the maximum stability of the tracked robot is 0.9156 when the robot crosses uneven terrain using optimal path 2.     

Tool path planning for compound surfaces in spray forming processes

Spray forming is an emerging manufacturing process. The automated tool planning for this process is a nontrivial problem, especially for geometry-complicated parts consisting of multiple freeform surfaces. Existing tool planning approaches are not able to deal with this kind of compound surface. This paper proposes a tool-path planning approach which optimizes the tool motion performance and the thickness uniformity. There are two steps in this approach. The first step partitions the part surface into flat patches based on the topology and normal directions. The second step determines the tool movement patterns and the sweeping directions for each flat patch. Based on the above two steps, optimal tool paths can be calculated. Experimental tests are carried out on automotive body parts and the results validate the proposed approach. Note to Practitioners-This paper was motivated by the problem of automatically planning tool paths for spray forming using Programmable Powdered Preforming Process (P4) technology. However, the proposed approach can be applied to other surface manufacturing applications such as spray painting, spray cleaning, rapid tooling, etc. Existing tool planning approaches are not able to handle complicated, multi-patch surfaces. This paper proposes a methodology to partition complicated surfaces into easy-to-handle patches and generate tool paths with optimized thickness uniformity and tool motion performance. We tested the approach using simulation on sample automotive body parts and proved its feasibility. However, this approach requires that the parts to be sprayed belong to the sheet-metal type so that the part geometry can be analyzed on a plane. In our future research, we will run physical tests on actual parts and investigate the deposition effects on the thickness uniformity.     

Hierarchical Segmentation of Piecewise Pseudoextruded Surfaces for Uniform Coverage

Complete automation of trajectory planning tools for material deposition/removal applications has become increasingly necessary to reduce the ldquoconcept-to-consumerrdquo timeline for rapid product introduction in industries such as the automotive industry. The work in this paper is specifically motivated by automotive spray painting. Prior developments in automated trajectory planning tools promise to reduce the time required to program the robots; however, these approaches are limited to surfaces that are either approximately planar or topologically simple (i.e., with no holes). To extend the applicability of these planning tools to nonplanar and topologically complex surfaces, currently the user has to manually segment a complex surface into simpler subsets, i.e., subsets that are approximately extruded surfaces and contain no holes. However, the complex nature of the relationships between surface segmentation and resulting output characteristics such as material deposition uniformity, process cycle time, and material waste makes the task of manually segmenting the surface difficult. In this paper, we develop a hierarchical procedure that automatically segments a surface based on surface geometry, surface topology, and path geometry to obtain topologically simple subsets that are approximately extruded surfaces. Finally, we compare the effectiveness of our segmentation with the state of the art on a few automotive surfaces in simulation.     

双层优化A*算法与动态窗口法的动态路径规划

为满足动态环境中移动机器人既要动态避障抵到终点,又要尽可能地做到全局最优的路径规划需求,提出了一种双层优化A*算法与动态窗口法相结合的移动机器人路径规划算法。在传统A*算法求得的全局路径轨迹基础上,首先通过一层全局优化,计算路径节点间斜率,提取关键转折点,大幅度减少路径转折点数量;再通过二层全局优化,延长路径段求得路径交点,判断交点是否通过障碍物的方法,将路径转折点数降到最低;设计动态窗口法的轨迹评价函数,解决了机器人容易陷入“凹”“C”形障碍物的问题,同时保证了障碍物安全距离并选取全局最优的路径轨迹。最后分别在静态与动态的二维栅格地图中对传统A*算法、一层优化A*、二层优化A*以及融合算法进行仿真实验。实验结果表明一层优化A*算法大幅度降低了转折次数;二层优化A*算法将转折点数降到最低,但是路径长度小幅度增加;融合算法实现了机器人实时动态避障抵到终点,而且在保证安全距离的同时更加贴近全局最优规划。     

改进遗传算法与领航跟随法的机器人编队方法

针对传统遗传算法在求解机器人路径规划问题时存在的收敛速度慢、路径不平滑问题,对其进行了改进,在适应度函数中加入了路径平滑度因素,选择操作时平滑度较好的路径更容易被选中。在种群选择时将最优个体直接复制到下一代,有效地保留了父代优良基因。在领航机器人规划路径阶段,使用改进的遗传算法为领航机器人规划出一条安全无碰撞且平滑度较好的最优路径。在跟随机器人跟随阶段,使用领航跟随法控制每一个跟随机器人使其与领航者保持特定的距离与角度,从而形成设定的队形。最后通过MATLAB软件建立栅格地图进行仿真,验证了该算法的可行性,与传统遗传算法相比,改进遗传算法收敛速度更快,且路径更加平滑。     

A Note on Synthesis of Inductive Assertions

One of the principal impediments to widespread use of automated program verification methodology is due to the user burden of creating appropriate inductive assertions. In this paper, we investigate a class of programs for which such inductive assertions can be mechanically generated from Input-output specifications. This class of programs, called accumulating programs, are iterative realizations of problems in which the required output information is accumulated during successive passes over the input data structures. Obtaining invariant assertions for such programs is shown to be equivalent to the problem of generalizations of specifications to that over an extended closed data domain. For this purpose, a set of basis data elements are to be conceived of as generating the extended domain. An arbitary data element would thus be considered as uniquely decomposable into a sequence of basis elements. The structural relations between the components of a data element are used to extend program behavior and thus obtain the desired invariant.     

Robot sweep path planning with weak field constrains under large motion disturbance

The sweeping robot plans a path and moves along its prior path. In conventional studies, the target field is separated into square cells to enable the robot to sweep evenly. The prior sweep path is generated by passing all the target cells. However, an outdoor sweeping robot cannot move as expected, because the robot cannot go to the next target easily due to the uncertainty of the motion of the robot. The uncertain motion is caused by individual differences of motors, disturbances from the environment, and position error. As a result, the robot passes the same point many times and the actual path length becomes longer. In this study, we propose sweep path planning to solve this problem by decreasing the number of cells that the robot must pass. Numerical simulations are carried out to verify our method and to verify the relation among the sweeping rate and robot disturbances. Simulation results show that our method is effective enabling the robot to satisfy a sweep rate of 80% and more, even if the robot has uncertainty of movement.     

多地貌环境下的移动机器人路径规划研究

针对多地貌环境下的移动机器人路径规划问题,建立多目标优化模型,并采用微粒群算法解决该问题.首先,采用区域权值表示机器人在各种地形下的通行困难度;然后,结合局部优化准则计算机器人的通行时间,通过计算机器人与危险源之间覆盖的面积来衡量路径的危险程度,并将上述问题转化为两目标优化问题;最后,采用多目标微粒群优化算法优化上述问题.仿真结果表明了所提出方法的有效性.     

A sensor based technique for automated robot programming

This paper presents the concept of integrating a tactile sensor based, automated part measuring technique and a CAD programming scheme to perform off-line programming for a welding robot. The techniques used to achieve data flow throughout the production process include coordinate system referencing, interactive programming, tactile sensing seam tracing, and coordinate transformation. Together they form the backbone of the idea of integrating measurement and production operations where continuous path geometrical control is required. Techniques for referencing a workpiece with respect to different handling devices, and positioning the part on a suitable fixture, form an important portion of this work. Consequently, the positioning aspect and the data transfer capability between stages in the production process are highlighted. The welding of lap-joint type seams serves as an example. The integration of automated measurement and off-line robot programming actually constitutes a flexible manufacturing system operation that is capable of assuring the required process control. In this regard, linking a robot with an automated part measuring technique forms an important step towards upgrading a robot device from a difficult to program unit to a unit with a high degree of flexibility with rapid, convenient automatic contour programming.     

Parameter optimization for spray coating

The aim of planning path-oriented spray-coating processes is to find a time-dependent continuous sequence of spray gun configurations so that a coating of desired thickness is achieved when executing the sequence. A novel approach to solving the planning task, called “geometry-last”, is outlined which leads to a more general gun configuration cover problem. The gun configuration cover problem is to find a finite set of spray gun configurations, which minimizes the error between a target coating and the coating induced by simultaneously activating those configurations. A suitable objective function for gun configuration covers is defined, and algorithmic solutions for the optimization problem are presented, including speed-up by hierarchization and use of graphics hardware. An experimental evaluation shows that good approximations of the desired coatings can be achieved within reasonable computing times. In contrast to other approaches, geometry-last gains additional flexibility required to find complex paths for free-form workpieces.     

Process modeling,simulation, and paint thickness measurement for robotic spray painting

An algorithm and a computer program are developed for modeling of the spray painting process, simulation of robotic spray painting, and off‐line programming of industrial robots for painting of curved surfaces. The computer program enables the user to determine the painting strategies, parameters, and paths which will give the desired paint thickness. Surface models of the parts that are to be painted are obtained by using a computer‐assisted design (CAS) software. Models of relatively simple surfaces are formed by using the surface generation tools of the CAD software. For parts with more complex surfaces, point data related to the part is collected by using a laser scanner, and this data is used to form the CAD model of the part surface. The surface is then divided into small triangular elements and centroid coordinates, and unit normals of the elements are determined. Surface data together with the spray distance, painting velocity, and paint flow rate flux are used for simulation of the process and paint thickness analysis. Paint flow rate flux is determined experimentally by using different spray gun settings and painting parameters. During the experiments flat surfaces are painted by using a single painting stroke of the gun. Then, paint thickness measurements are made on the surfaces. It is observed that besides the technical specifications of the spray gun, air and paint nozzles, and paint needle, basic settings like paint tank pressure, spray air pressure, and gun needle‐valve position affect paint cone angle and paint flow rate, which finally characterize the spray painting process. For that reason, settings and parameters should be changed and the painting process should be simulated until an acceptable paint thickness distribution is obtained for the part that is going to be painted. The robot program is then generated in the robot's programming language. Paint thickness distribution on the painted surface is determined by measuring the thicknesses using the robot and the CAD model of the part surface. The thicknesses are measured at the centroids of the surface elements. A measurement probe of the coating thickness measurement gauge is attached to the wrist of the robot by using a feedback/safety adapter designed and manufactured for this purpose. © 2000 John Wiley & Sons, Inc.     

基于滚动优化和分散捕食者猎物模型的全覆盖路径规划算法

针对多机器人执行全覆盖任务效果差的问题,提出一种基于滚动优化和分散捕食者猎物模型的多机器人全覆盖路径规划算法.首先,利用栅格地图表示作业的环境空间,并基于栅格地图修正捕食者猎物算法中的避开捕食者奖励,添加移动代价奖励和死区回溯机制构建分散捕食者猎物模型;然后,引入滚动优化方法,避免机器人陷入局部最优,预测周期内机器人覆盖栅格的累计奖励值作为适应度函数,并使用鲸鱼优化算法(WOA)求解最优移动序列;最后,在不同环境下进行仿真实验,得到的平均路径长度与生物激励神经网络算法(BINN)和牛耕式A*算法(BA*)相比分别减少了16.69%sim17.33%、10.32%sim20.03%,验证了所提出算法在多机器人全覆盖路径规划中的可行性和有效性.     

Smoothing curvature of trajectories constructed by noisy measurements in path planning problems for wheeled robots

A path planning problem for a wheeled robot is considered. The problem consists in constructing a trajectory that approximates a given ordered sequence of points on the plane and satisfies certain smoothness requirements and curvature constraints. Such a problem arises, for example, when it is required to follow in an automated mode a path stored as a discrete set of points measured in the course of the first passage of this path in a manual mode. Due to errors inherent in the data points, the shape of the curve approximating the desired path may turn out inappropriate or even unacceptable from the control standpoint. The shape of the curve can be improved by applying the so-called fairing, which consists in moving the original data points with the aim to minimize some functional. Adequate small variations of the data points (within the measurement error) preserve the proximity of the resulting path to the original data points and, at the same time, may considerably improve its shape. In the paper, a new global fairing method for improving shape of curves consisting of elementary B-splines is proposed. The improvement is achieved through minimization of jumps of the spline third derivative. The problem of finding desired variations reduces to solving a quadratic programming problem with simple constraints. The discussion is illustrated by numerical examples.     

基于Netvlad神经网络的室内机器人全局重定位方法

针对已知地图的室内机器人全局重定位、绑架恢复问题,提出一种基于改进的Netvlad卷积神经网络的室内机器人全局重定位方法,通过激光雷达获取的障碍物信息引导机器人到达空旷区域,粗定位阶段,使用栅格地图最短连通域距离作为正样本判据,并对Netvlad引入残差网络,通过图像检索得到机器人的粗略位置及角度信息。使用粗定位阶段得到的位置和角度信息作为自适应蒙特卡罗定位的初始值来估计机器人的精确位姿。实验结果表明,与传统定位方法相比,该方法可以使机器人从绑架问题中快速恢复准确位姿。     

Kinematic modelling and emulation of robot for traversing over the pipeline in the refinery

Robotics always used to have an extraordinary contribution into multiple parts of operations in process industries, the one presently discussed in this research paper deals with the mathematical analysis and real-time replication model of out pipe crawler robot used for thickness measurement in refineries. The aim of this paper is to evaluate and emulate the movement of the robot in a 2-dimensional plane over a black track motif as a pipeline line which infers the effect of the real-time simulation prototype model. Robotic manipulators are more complex than its successors but there is a complete analysis of the kinematics of differential drive robot. The workspace of a wheel based mobile robot is not only limited to the position of end effector but it is a range of all possible positions that the robot makes while moving over or on the path. The analysis presented in this paper is very useful in developing a mathematical model and crafting a prototype of wheelbase mobile robot to traverse over an uneven surface of ferromagnetic pipelines with the help of an array of IR sensors used for estimation of the thickness of pipes.

     

穿越稠密障碍物的自适应动态窗口法

针对应用广泛的局部避障算法-----动态窗口法(DWA)穿越稠密障碍物时存在路径不合理、速度和安全性不能兼顾等问题,提出参数自适应的DWA算法,根据机器人与障碍物距离和障碍物的密集度自动调整目标函数中的权值,以自适应环境的动态变化,从而获得移动机器人的最佳运行速度和合理路径.该方法可明显改善机器人穿越稠密障碍物区域时的性能;同时,该方法还可避免机器人从密集障碍物区域外绕行以及轨迹不平滑现象.仿真实验表明:改进的DWA算法在复杂环境中通过逐步优化可使运行轨迹更加合理,能够同时兼顾路径平滑性和安全性;机器人在离稠密障碍物较远处保持高速,通过狭窄通道或者稠密障碍物区域时速度适当降低,安全性更高,实验中总迭代次数和运行时间可缩短20%以上.