机器人系统在NIF靶组件装校和测量中的应用

High Power Laser Science and Engineering 5, e 25 (2017)

二十世纪末,劳伦斯·利弗莫尔实验室在制备第一批供美国国家点火装置(NIF)使用的靶时,整个靶装校过程全由手工操作,并需要精心测量和仔细测试。最终的组件既是功能完全的高能密度物理靶,又是独一无二而且相当脆弱的一件艺术品——当真可谓是工程学的奇迹。原型靶的设计是基于前期NOVA装置的实验结果建立的。然而,早期的激光打靶实验获得的经验更新太快,使得靶设计需求几乎每发更新一次,将这次的经验立刻应用到下一次的实验中去。这类复杂的内爆靶的打靶频率约每周一次,靶的生产供应链很难满足这样的需求。

NIF的第一次内爆实验后不久,由于制靶的公差变得更严、靶型变得更复杂以及设计更迭速度更快,仅依靠少数精挑细选、技艺过人的工匠远远不够。靶的装校需要自动化的流程工艺。

过去的十年内,当NIF内爆实验型靶的设计显著趋于成熟,打靶的次数日益增加,以至靶的需求持续加大。然而靶生产的过程仍然相对缓慢,一天难以生产出十个以上完全相同的靶。将靶组件和界面标准化到可以简化固定装置、模具和测量算法的设计的程度,已经显著地提高了靶组装的效率。

研究人员、科学家和工程师们力图从已有行业中找到进一步简化生产流程的方法,如自动化系统或机器人辅助系统,来满足对靶日益增长的需求。相比汽车和半导体等其他行业,靶的生产数量仍然很低,从而限制了自动化系统的普及。

K.-J. Boehm等发表于High Power Laser Science and Engineering 2017年第4期的论文“Assembly and metrology of NIF target subassemblies using robotic systems”展示了机器人辅助平台能够在操作上简化NIF靶组件装校和定量测量步骤。这样能获得更快、重复性更好而且无需人工操作的结果,但是研发自动化系统的费用需要和它的使用频率相平衡。

当欧洲乃至全世界的新激光装置能开始以1-10 Hz重复频率运行时,对靶需求量的增长会把局势变得有利于机器人辅助或全自动化系统。为了备战这一新需求,通用原子能公司(GA)已经开始研发测试这类系统,证明了靶的高重频并不一定需要其复杂性和质量来妥协。

“随着世界上越来越多的惯性聚变研究装置上线,靶组件变得愈发精密和袖珍(微米到毫米),其装校和定量测量正变成高能密度物理实验中的关键性挑战。在大型装置领域,激光器已经变得功率更大、重复频率更高、体积更小、造价更低。这意味着在大型装置上开展实验的机会日渐增多,但是对于支撑该领域的材料学专家和工程师来说,提供各式物理配套设施(靶)的能力也要相应地跟上。机械化和自动化在这个关头大展身手。类似于汽车和电子行业,我们这个领域需要利用自动化手段来获得比人工手段可得到的更高的产量和更精密的装校。GA在过去的十年内已经集中设计建造灵活的机械和定量测量系统,可以处理多种材料与结构。

GA相信这些新激光装置和已有的装置为拓展高能密度物理领域的边界提供了极大的潜力,但这一切要以装置性能的进展与靶生产能力的相应提高相匹配为前提。”– Michael Farrell,GA惯性聚变技术部门主管

在过去十年中,GA已利用自动化手段将靶的生产率提高,从每周生产一两个到每天生产一个以上的NIF内爆靶,同时又能保持靶结构极高的精确度和质量。GA也为其他装置提供靶和靶组件,例如SLAC, Omega和桑迪亚国家实验室的Z箍缩装置。提高效率的工艺进步(如运用机器人辅助装校技术制备平面箔靶)能够从它被研发的平台传递到别处,因而造福了领域内整个团体。GA计划继续探索自动化能力,提升该领域内靶的生产率。

综上所述,靶生产的同行们在接下来数年面临的挑战包括靶的安装、靶碎片的处理、新材料和新工艺的研发等等,其中机器人能力的发展是一个需要解决的重要难题。

六轴机器人首先在偶配表面涂上胶水,抓取一个空腔,记录下空腔的旋转位置和精度,并放置在NIF内爆靶热机械配套设施的耦合面上。左图为机器人单元,右上图为放大的工作区域,右下角为完成的产品。点击此处观看装校过程的视频。

Assembly and Metrology of NIF target subassemblies using robotic systems

When the first targets for the National Ignition Campaign (NIC) at Lawrence Livermore National Laboratory (LLNL) were built to be fielded on the National Ignition Facility (NIF) in the late 2000’s, the assemblies were handcrafted, meticulously measured, and carefully tested. The resulting assemblies were literally one-of-a-kind and fairly fragile pieces of art, as well as fully functional high energy density physics targets. They were true engineering marvels. The baseline target design was built on results from previous experiments on the NOVA facility; however, a steep learning curve during the early shots caused the target design requirements to be updated almost from shot to shot as the lessons from one experiment were applied to the next. At a shot rate of one or so per week of these complex implosion-type targets, the demand for targets was barely met by the target production supply chain.

Soon after the first implosion experiments on NIF, the need for tighter tolerances, higher complexity, and faster turnaround demanded that processes other than those depending on a select few extremely skilled craftsmen needed to be deployed to assemble these targets.

While the design of NIF implosion-type targets has significantly matured over the past decade, the increasing number of shots has resulted in an increasing demand for targets, although the production process is still relatively deliberate, with rarely more than ten identical targets being produced at a rate of one-per-day. Significant improvements for more efficient target assembly have been achieved by standardizing components and interfaces to the extent possible to simplify the design of fixtures, tooling and measurement algorithms.

Researchers, scientists, and engineers have been looking at established industries to find ways to simplify the production process further, e.g. deployment of automated or robot-assisted systems, to meet the increasing demand. Compared with other industries such as automotive or semiconductor branches, the number of targets to be produced is still low, however, which limits widespread deployment of automated systems.

The paper published in High Power Laser Science and Engineering, Vol. 5, No. 4, e25, 2017 (K.-J. Boehm et al., Assembly and metrology of NIF target subassemblies using robotic systems) shows an example in which assembly and metrology steps for a NIF target subassembly could be operationally simplified by moving to a robot-assisted platform. This leads to faster, more repeatable, and operator-independent results, but in many cases the cost of the development of an automated system needs to be balanced with the frequency at which the operation will be performed.

When the new laser facilities in Europe and around the world start operating at the expected rates of 1-10 Hz, the increased target demand will tip the balance in favor of robot-assisted or fully automated systems. In preparation for this new demand, General Atomics (GA) has started developing and testing these systems, demonstrating that high-rep-rate targets do not necessarily mean that the complexity of the target or target quality need to be compromised.

“As more and more inertial fusion research facilities come online across the world, assembly and metrology of increasingly more precise and smaller (micron to millimeter) components is becoming a key challenge with respect to high energy density physics experiments. Once the domain of large facilities, lasers have become more powerful, rep rated, smaller, and cheaper. This means the opportunity to perform experimentation in this arena is increasing, but it must be matched by the capability to provide many physics packages (targets) of various constructions to the materials scientists and engineers who support this field. Enter robotics and automation. Much like the automotive and electronics industry, our field will need to use automation to achieve higher volume, more precise assembly than can be achieved by human power. GA has been focused over the past decade on designing and building flexible robotics and metrology systems that can work with many materials and configurations.

GA is convinced these new laser facilities—coupled with existing facilities—provide immense potential for exploring the boundaries of high energy density physics, but only if the advancement in facility capability is matched by corresponding improvements in the creation of targets.”

– Michael Farrell, Director, Inertial Fusion Technology Division at General Atomics.

In the past decade, GA has used automation to increase its productivity rate to match the demand to build one or two NIF implosion type targets per week to more than one per day, while still maintaining extreme precision and quality in the construction of the targets. GA has also produced targets and target components supporting campaigns on other machines such as SLAC, Omega and the Z-pinch machine at Sandia National Laboratory in the US. Process improvements towards higher efficiency such as applying machine-assisted assembly techniques for flat foils benefits the entire community as the technology can be transferred from the platform it was developed for to others. The company plans to continue to explore automation's ability to increase production rates in this field.

In conclusion, out of the many challenges the target fabrication community is facing for the coming years, such as target fielding, mitigation of debris, development of new materials and processes, the development of robotic capabilities is one important issue to be addressed.

A six-axis robot is being used to first apply glue onto the mating surface and second to pick up a hohlraum, register its clocking position and precision placing it into the mating interface on the thermo-mechanical package of a NIF implosion target. The robot cell is shown on the left, a close-up of the work area on the top right, the finished product on the bottom right. View the video that shows the assembly by CLICKING HERE.