An investigation on photopolymer solidification considering laser irradiation energy in micro-stereolithography

Micro-stereolithography technology has made it possible to fabricate freeform three-dimensional microstructures. This technology is based on conventional stereolithography, in which a UV laser beam irradiates the free surface of a UV-curable liquid photopolymer, causing it to solidify. In micro-stereolithography, a laser beam that is a few m in diameter is used to solidify a very small area of the photopolymer. Photopolymer solidification phenomena in response to variations in the scanning pitch of a focused laser beam were investigated experimentally in this study according to the irradiation energy. The effect of the layer thickness on the solidification width and depth was also examined. The study was conducted using both a relatively low laser power and high scanning speed (low irradiation energy method), and a relatively high laser power and low scanning speed (high irradiation energy method). The experimental results were compared with those obtained using a photopolymer solidification model. Based on these results, a new laser-scanning scheme is proposed according to the three-dimensional microstructure shape desired. Samples were successfully fabricated using both methods.This research was supported by the Center for Nanoscale Mechatronics and Manufacturing (CNMM; http://www.nanomecca.re.kr), which performs some of the 21st Centurys frontier R&D projects, and sponsored by the Korean Ministry of Science and Technology under the contract project code M102KN010001–02K1401–00211.     

Computing of the actual shape of removed material for five-axis flat-end milling

This paper describes an algorithm that predicts the shape of material removed by a flat-end milling tool, and this may be used to compute machining strip width and scallop height at different positions of the tool path track. The algorithm computes swept sections, profiles which are swept by a moving tool bottom by passing through given planes. The technique is applicable for finish and semi-finish multi-axis milling strategies that use flat-end tools. For these strategies, the algorithm complexity can be reduced from computation of the 3D envelope of swept volumes to computation of plane-circle intersections. A new adaptive derivative-free method to sample tool motion provides robust means to generate intermediate tool positions. The step length is constrained by and dependent on different geometrical measures. At each point of a tool path, in the plane perpendicular to the cutting direction, the bottom profile of the swept section is an estimate of the profile of material left. By calculating the distance between part geometry and the computed profile of removed material, machining strip width and a scallop profile can be derived. These results can be used by tool path generation and validation routines to accurately determine the step-over between tool path tracks and surface quality.     

Development of industrial SFF system using dual laser and optimal process

Selective laser sintering (SLS) is currently recognized as a leading process in the new field of solid freeform fabrication (SFF). SLS extends the applications to machinery and automobiles due to various employing materials. In order to develop more elaborate and speedy system for fabricating large objects compared to existing SLS, this study employs a new selective dual-laser sintering (SDLS) process. It contains three-axis dynamic focusing scanner system for scanning large area instead of the existing fθ lens used in commercial SLS. The optimal fabrication parameters such as sintering temperature, laser beam power and layer thickness should be determined when sintering polymer and metal powder. In this paper, we will address methods for the effective laser scanning path generation, the suitable temperature and the accurate z-axis control. Also, experiments have been performed to evaluate the effect of fabrication parameters on process and to fabricate the various 3D objects using polymer.     

Internal architecture design and freeform fabrication of tissue replacement structures

Modeling, design and fabrication of tissue scaffolds with intricate architecture, porosity and pore size for desired tissue properties presents a challenge in tissue engineering. This paper will present the details of our development in the design and fabrication of the interior architecture of scaffolds using a novel design approach. The interior architecture design (IAD) approach seeks to generate layered scaffold freeform fabrication tool path without forming complicated 3D CAD scaffold models. This involves: applying the principle of layered manufacturing to determine the scaffold individual layered process planes and layered contours; defining the 2D characteristic patterns of the scaffold building blocks (unit cells) to form the Interior Scaffold Pattern; and the generating the process tool path for freeform fabrication of these scaffolds with the specified interior architecture. Feasibility studies applying the IAD algorithm to example models with multi-interior architecture and the generation of fabrication planning instructions will also be presented.     

Automatic generation of basis test paths using variable length genetic algorithm

Path testing is the strongest coverage criterion in white box testing. Finding target paths is a key challenge in path testing. Genetic algorithms have been successfully used in many software testing activities such as generating test data, selecting test cases and test cases prioritization. In this paper, we introduce a new genetic algorithm for generating test paths. In this algorithm the length of the chromosome varies from iteration to another according to the change in the length of the path. Based on the proposed algorithm, we present a new technique for automatically generating a set of basis test paths which can be used as testing paths in any path testing method. The proposed technique uses a method to verify the independency of the generated paths to be included in the basis set of paths. In addition, this technique employs a method for checking the feasibility of the generated paths. We introduce new definitions for the key concepts of genetic algorithm such as chromosome representation, crossover, mutation, and fitness function to be compatible with path generation. In addition, we present a case study to show the efficiency of our technique. We conducted a set of experiments to evaluate the effectiveness of the proposed path generation technique. The results showed that the proposed technique causes substantial reduction in path generation effort, and that the proposed GA algorithm is effective in test path generation.     

激光快速成型中激光扫描路径的快速生成算法

在立体光固化（ＳＬ）快速成型中，零件是靠激光逐层扫描光敏树脂固化成型的，在由点到线、由线到面、由二维到三维的逐层累积过程中，扫描器要做大量的扫描，因而合理的扫描路径对提高成型效率无疑有重要意义；另外合理的扫描路径还能改善扫描器的工作状态，明显提高扫描器的使用寿命，本文提出了一种简捷有效的扫描路径生成算法，成功地于开发的快速成型机中。     

Mobile robot motion estimation by 2D scan matching with genetic and iterative closest point algorithms

The paper reports on mobile robot motion estimation based on matching points from successive two‐dimensional (2D) laser scans. This ego‐motion approach is well suited to unstructured and dynamic environments because it directly uses raw laser points rather than extracted features. We have analyzed the application of two methods that are very different in essence: (i) A 2D version of iterative closest point (ICP), which is widely used for surface registration; (ii) a genetic algorithm (GA), which is a novel approach for this kind of problem. Their performance in terms of real‐time applicability and accuracy has been compared in outdoor experiments with nonstop motion under diverse realistic navigation conditions. Based on this analysis, we propose a hybrid GA‐ICP algorithm that combines the best characteristics of these pure methods. The experiments have been carried out with the tracked mobile robot Auriga‐α and an on‐board 2D laser scanner. © 2006 Wiley Periodicals, Inc.     

A new seam-tracking algorithm through characteristic-point detection for a portable welding robot

The welding task in double-hulled structures in shipyards and in steel-frame structures is hazardous and difficult due to the toxic gas and limited workspace. Therefore, many efforts have been undertaken for automation. The main challenge for automation is the development of a simple and robust seam-tracking algorithm that can be applied to a portable welding robot that operates under irregular and diverse task conditions in the workspace. We developed a seam-tracking algorithm for weaving weld path planning using a laser displacement sensor. The goal of the proposed algorithm is to detect the seam of single-butt welding with manually tack-welded non-zero gaps. The focus is on keeping the algorithm simple and affordable so that it can be applied to portable robots that operate in hazardous fields. The algorithm consists of four steps: scanning, filtering, generation of the reference points, and path planning. In the scanning process, the depth data of a cross-section of the seam profile is obtained. Next, a Gaussian filter is used to remove noise from the raw data. A differential characteristic-point detection algorithm is applied to the filtered data to detect the reference points that represent the shape and location of the gap to be welded. Finally, path planning for single-V butt multi-pass welding is done based on the detected reference points. A portable four-axis welding robot is built using the developed algorithm. The algorithm is validated through welding experiments regarding a single-V butt welding task with a manually tack-welded non-zero gap.     

A real-time 3D motion planning and simulation scheme for nonholonomic systems

We propose a new motion planning and simulation scheme for nonholonomic systems in this paper to provide a practical solution for these application problems taking into account of real-time obstacle avoidance and the continuous curvature path generation simultaneously in 3D unknown environment. The proposed motion planning and simulation scheme generates the motion path using a new universal Euler spiral generation algorithm, which is locally optimal based on perceived points of view. The generated Euler spiral solution can be non-symmetrical and easily implemented while maintaining a C² continuous. It is therefore more flexible and powerful in dealing with dynamic situations in real-time, compared with current symmetrical Euler spirals solutions. Real-time solutions are particularly important in navigation in unknown environments. The universal Euler spiral algorithm proposed displays a smaller maximum curvature value and smaller mean square curvature value than the conventional symmetrical algorithm in tested cases. Another significant contribution of our work is the new motion planning scheme which extend current 2D based motion planning into three-dimensional (3D) space. In this paper, we have conducted experiments and describe simulation results including 3D motion trajectory modeling for a flight simulation.     

On the effective tool path planning algorithms for sculptured surface manufacture

This paper describes the cutter path planning and cutter interference (gouging) analysis algorithms developed to generate optimal tool path for manufacturing sculptured surfaces on three axes CNC machine tools. Cutter path planning algorithm approximates the parametric curves on three dimensional surfaces by a sequence of straight line segments and generates optimal tool paths by minimizing the number of interpolation points while keeping the path deviations within the specified tolerances. Cutter interference analysis algorithm checks for the self intersection of an offset surface and determines the self-intersection curve. The tool path is then planned over the cutter contact (CC) surface after removing the CC data that lies inside the self-intersection curve. Finally, the effectiveness of these algorithms is demonstrated by implementing them in CAD/CAM system.     

基于二叉树搜索空间缩减的测试数据生成

为了减小适应度函数计算量, 提高测试数据自动生成效率, 提出一种基于二叉树表示的搜索空间数据缩减方法。利用二叉树编码, 记录全空间中的覆盖路径和路径长度; 将目标路径和测试路径长度进行对比, 去除路径长度相差较大的路径; 利用遗传算法生成测试数据并同已有两种方法进行比较。实验结果表明, 在保证软件测试数据正确生成的情况下, 该方法在进化代数和运行时间上有明显优势, 生成测试数据效率高。     

基于IKGC-PSO算法的无人机三维路径规划系统

为了解决标准粒子群算法在无人机三维路径规划中存在的易陷入局部最优、动态化不足和路径平滑性差等问题,提出了一种基于粒子群算法和遗传算法的,融入K均值精英化和柯西变异的优化算法;采用K均值聚类算法进行精英初始化,优化粒子种群的分布;动态化学习因子,强化惯性权重的全局性,保留粒子群算法收敛速度快的优点;融入遗传思想,采用柯西变异的方法,提高寻解最优解的能力;在对比实验中,模拟了实际的复杂三维环境,选取了路径总长度、飞行高度差以及马尔科夫生存状态组成目标函数;结果表明改进算法的鲁棒性提高了98%,求解质量相较于IPSO算法和PSO算法分别提高了5.8%和10.6%,验证了优化后方法的有效性和鲁棒性。     

Adaptive restoration of complex geometry parts through reverse engineering application

After a certain number of hours of running, no two mechanical components are completely the same due to normal wear or foreign object damage. A nominal CAD model from a component designer is different from its corresponding worn one and therefore cannot be directly used for tool path generation for build up and machining repair processes. This is the main reason that most repair process used for complex geometry parts, such as gas turbine blades, is currently carried out manually and is called the “Black Art”.This paper proposes a defects-free model-based repair strategy to generate correct tool paths for build up process and machining process adaptive to each worn component through the reverse engineering application. Based on 3D scanning data, a polygonal modelling approach is introduced in this paper to rapidly restore worn parts for direct use of welding, machining and inspection processes. With this nominal model, this paper presents the procedure to accurately define and extract repair error, repair volume and repair patch geometry for the tool path generation, which is adaptive to each individual part. The tool paths are transferred to a CNC machine for the repairing trials. Further research work is performed on repair geometry extraction algorithm and repair module development within the reverse engineering environment.     

基于改进的生物激励神经网络机器人路径规划算法

针对传统生物激励神经网络（BINN）在点对点全局路径规划中存在的路径偏离和路径非最优问题,提出了基于路径修正和无障碍理想路径制导的生物激励神经网络算法。路径规划的初始阶段,通过判断起始单元外部激励输入和起始单元活性值大小决定是否触发路径生成策略,从而实现初始路径修正;在生成下一位置单元的算法中结合无障碍理想路径的导向,引入实际路径单元与无障碍理想路径单元间的理想路径接近率使路径神经元活性值增大,从而实现路径优化。在静态复杂环境下,分别以三种算法进行了对比实验。实验结果表明,改进后的路径规划算法相比传统生物激励神经网络算法和基于目标制导的生物激励算法,不仅解决了路径规划初始阶段的路径偏离问题,而且使路径长度和路径转折次数更低,效率更高。     

A corner-looping based tool path for pocket milling

In milling around corners, cutting resistance rises momentarily due to an increase of cutter contact length. NC tool path generation in dealing with sharp corners thus requires special consideration. This paper describes an improved NC tool path pattern for pocket milling. The basic pattern of the improved tool path is a conventional contour-parallel tool path. Bow-like tool path segments are appended to the basic tool path at the corner positions. When reaching a corner, the cutter loops around the appended tool path segments so that corner material is removed progressively in several passes. By using the corner-looping based tool path, cutter contact length can be controlled by adjusting the number of appended tool path loops. The procedures of creating the improved tool path for different corner shapes are explained. The proposed tool path generation was implemented as an add-on user function in a CAD/CAM system. Cutting tests were conducted to demonstrate and verify the significance of the proposed method.     

Control of 3D weld pool surface

The 3D weld pool surface in gas tungsten arc welding (GTAW) is characterized by its width, length, convexity and measured in real-time using an innovative machine vision system. The dynamic response of these characteristic parameters to welding current and speed as control variables is modeled. Based on the identified dynamic model, a predictive control algorithm is developed to control these characteristic parameters. The proposed algorithm is given in a closed form and no online optimization is required. Welding experiments confirm that the developed control system is effective in achieving the desired 3D weld pool surface geometry despite various disturbances.     

用计算机辅助几何技术对Stephenson六杆机构近似位姿的综合

机构尺寸综合的两个基本工具是几何法和解析法，适用于位置较少的机构尺寸综合，而且解析法求解复杂和不直观．提出计算机辅助几何技术的Stephenson六杆机构近似位姿综合法．先用CAD的几何约束和尺寸驱动技术，在多个复合精确和近似位姿情况下构造一个基本六杆模拟机构，再根据轨迹和运动综合的原则，由基本六杆模拟机构分别创造出轨迹和运动的近似位姿综合模拟机构．计算机模拟结果表明，该方法不仅具有简洁直观、求解精度高和重复性好的特点，而且可以增加机构综合的规定位置个数，为机构的尺寸综合提供更有效的工具．     

改进A*算法的机器人全局最优路径规划

针对传统A^*算法规划的路径存在很多冗余点和拐点的问题,提出了一种基于A^*算法改进的高效路径规划算法。首先,改进评价函数的具体计算方式,减小算法搜索每个区间的计算量,从而降低寻路时间,并改变生成路径;其次,在改进评价函数具体计算方式的基础上,改进评价函数的权重比例,减少生成路径中的冗余点和拐点;最后,改进路径生成策略,删除生成路径中的无用点,从而提高路径的平滑性;此外,考虑到机器人的实际宽度,改进后算法引入障碍物扩展策略保证规划路径的可行性。将改进A^*算法与三种算法进行仿真对比,实验结果表明,改进后的A^*算法规划的路径更加合理,寻路时间更短,平滑性更高。     

An efficient underwater coverage method for multi-AUV with sea current disturbances

This paper presents an online coverage method for the exploration of unknown oceanic terrains using multiple autonomous underwater vehicles (AUVs). Working from the concept of planar algorithm developed by Hert, this study attempts to develop an improved method. Instead of theoretical research, it focuses on the practical aspects of exploration by considering the equations of motion for AUVs that are actually used in oceanic exploration as well as on the characteristics of complex oceanic topography and other realistic variables, such as sea current. These elements are used to calculate cross track error (CTE) and path width for AUV movement. The validity of the improved algorithm for terrain coverage is first verified mathematically and then by a simulation of the real underwater environment that analyzes the path length and time taken for the coverage as well as the missed areas, which is the key element of efficiency. In order to apply the improved method to the multi-AUV operation, each AUV was assigned a covering or a scanning role by means of a dynamic role-changing mechanism. The results showed that the multi-AUV operation has an advantage over a single-AUV operation in many ways. The method proposed in this study will be useful not only for commercial applications but also for mine counter-measures (MCMs) and rapid environmental assessments (REAs) as part of naval military operations as well. We also believe that it will be ideal for use in variable oceanic environment, particularly in shallow water terrains. For the purposes of this study, we assume that the communication between AUVs is problem-free. Recommended by Editorial Board member Sooyong Lee under the direction of Editor Jae-Bok Song. This work was supported in part by MOCIE Industrial Technology Development Program, the ASRI, and BK21 Information Technology at Seoul National University. Yeun-Soo Jung received the Ph.D. degree in Electrical Engineering from Seoul National University in 2008. His research interests include autonomous underwater vehicles and multi-agent control. Kong-Woo Lee received the M.S. degree in Electrical Engineering from Seoul National University in 2007. His research interests include multi-agent control, autonomous mobile robot navigation and SLAM. Seong-Yong Lee received the M.S. degree in Electrical Engineering from Seoul National University in 2007. His research interests include intelligent robots, embedded systems, operating systems, and multi-agent control. Myoung Hwan Choi received the Ph.D. degree in Control and Instrumentation Engineering from Seoul National University in 1992. His research interests include ultrasonic Imaging, biomedical signal processing and biomedical imaging. Beom-Hee Lee received the Ph.D. degree in Computer, Information & Control Engineering from University of Michigan in 1985. His research interests include multi-agent system coordination, control, and application.     

Coverage path planning on three‐dimensional terrain for arable farming

Field operations should be done in a manner that minimizes time and travels over the field surface and is coordinated with topographic land features. Automated path planning can help to find the best coverage path so that the field operation costs can be minimized. Intelligent algorithms are desired for both two‐dimensional (2D) and three‐dimensional (3D) terrain field coverage path planning. The algorithm of generating an optimized full coverage pattern for a given 2D planar field by using boustrophedon paths has been investigated and reported before. However, a great proportion of farms have rolling terrains, which have a considerable influence on the design of coverage paths. Coverage path planning in 3D space has a great potential to further optimize field operations. This work addressed four critical tasks: terrain modeling and representation, coverage cost analysis, terrain decomposition, and the development of optimized path searching algorithm. The developed algorithms and methods have been successfully implemented and tested using 3D terrain maps of farm fields with various topographic features. Each field was decomposed into subregions based on its terrain features. A recommended “seed curve” based on a customized cost function was searched for each subregion, and parallel coverage paths were generated by offsetting the found “seed curve” toward its two sides until the whole region was completely covered. Compared with the 2D planning results, the experimental results of 3D coverage path planning showed its superiority in reducing both headland turning cost and soil erosion cost. On the tested fields, on average the 3D planning algorithm saved 10.3% on headland turning cost, 24.7% on soil erosion cost, 81.2% on skipped area cost, and 22.0% on the weighted sum of these costs, where their corresponding weights were 1, 1, and 0.5, respectively. © 2011 Wiley Periodicals, Inc.