Development of 5-axis polishing machine capable of simultaneous trajectory,posture, and force control

The buffing process for finishing an automobile's body is still done manually, and the final surface quality of the body depends on the skill and technique of the worker. To automate buffing, not only tool path control but also precise and fast force control is required. In this study, a novel methodology based on the sensor-less force control technique and the quarry matrix capable of the mode decoupling is proposed for a parallel mechanism polishing machine to control x–y trajectory, tool posture, and polishing force in z-direction, and its validity for automated buffing is verified.     

光纤传感技术及其在管道监测中的应用

管道安全关系到人类生命和财产安全,及时掌握管道结构健康状态是确保其安全运行的重要前提,近年来发展起来的光纤传感技术为管道结构的安全监测提供了技术保障。传感器的选择和使用是进行结构监测时首先考虑的问题,重点介绍了SOFO点式、FBG准分布式、BOTDR和BOTDA分布式光纤传感器等光纤传感技术的系统组成、基本原理及关键技术,对其性能和特点进行了对比分析;在此基础上,探讨了适用于管道变形监测的FBG和BOTDA光纤监测实用系统,及适用于管道泄漏监测的基于拉曼散射的OTDR分布式温度传感技术和基于模态分布调制干涉技术的油气管道检测系统。分析了其各自作为结构监测传感器的优缺点,为今后的管道监测选用提供了依据。     

光纤激光单道抛光模具钢的工艺参数研究北大核心

为提高效率、降低劳动强度,采用激光抛光技术进行表面抛光。使用激光辐射熔化材料层,通过材料自身的表面张力将熔化的材料均匀地分布在表面上。以9CrWMn模具钢为研究对象,使用波长为1 080 nm的光纤激光,以激光功率、扫描速度、离焦量作为影响抛光效果的变量,设计一组正交试验,对工件进行激光单道抛光试验,并分析试验后工件表面单道抛光痕迹。结果表明:在负离焦量的情况下,提高抛光速度、适当降低功率可提高抛光后的表面平整程度。     

The formation of pure aluminium corrosion sensing film on fiber and its electrochemical performance

Recently, more and more attention has been put on the research of taking advantages of a fiber sensor on corrosion monitoring, because of its small volume, low weight, quick response, and excellent electromagnetism disturbing resistance etc. But a report about the application of fiber optical sensor is hardly found. In this paper, with the technology of vacuum sputter, pure aluminum corrosion sensing film was directly deposited on the core of fiber corroded away clad. Metallographic Microscope and Scanning Electron Microscope (SEM) were used to analyze the structure of the film. It shows that the thickness of the pure aluminum corrosion sensing film is about 14.65 μm, and the film is distributed even and firm. Galvanostatic step were used to evaluate the corrosion resistance in NaCl solution with different concentrations (0.001–0.1 mol/L). The result shows that the corrosion resistance of the sensing film is similar to that of industrial pure aluminum in NaCl solution with the concentration less than 0.1 mol/L. The work in this paper contributes to the research of fiber optical corrosion sensor for monitoring corrosion of aluminum.     

光学精磨抛光机床性能参数的优化设计

在使用光学球面精磨抛光设备的过程中发现诸多问题。分析归纳出该设备整机结构存在的缺陷,针对设备性能的不足开展多参数优化设计,获得光学球面精磨抛光设备的优化设计方案,设计出性能更趋完善、各项功能协调性更好的新一代光学设备。基于优化的设备配置结构,验证新设备的使用性能。证实优化配置结构能有效提高设备的整机性能、使用寿命和生产效率,降低废品率和维修成本。     

Near-field 3D position sensing using optical fibers

Sensing position is of fundamental relevance to production systems, which deal with the adjustment and control of shape and placement. An arrangement of 2, 4, or 8 optical fibers can be used to track the 1D-, 2D- or 3D-position of a light spot or optical emitter. Non-complex signal processing as well as far reaching independence of the measurement function from emitter intensity add to the attractiveness of our sensor design. This work will expand on the design’s theoretical basis and will conclude with a simulation of the measurement error introduced by size and shape variations of the emitter. Such variations can occur when tracking curved surfaces or emitters of unknown shape such as the process radiation during laser machining.     

In situ monitoring of pH level with fiber optic evanescent field spectroscopy

Fiber optic evanescent field spectroscopy for in situ monitoring of pH levels is presented. Cladding of plastic clad silica fiber is replaced with polymethyl methacrylate doped with pH sensitive chromoionophores. The chromoionophores include methyl red, thymol blue, and thymolphtalein for pH in acidic, neutral and basic environments, respectively. The evanescent wave is used to selectively excite the indicator molecules within the fiber cladding for sampling aqueous media surrounding the fiber.     

Effects of pressure and shear stress on material removal rate in ultra-fine polishing of optical glass with magnetic compound fluid slurry

Optical glasses used in a range of industrially important optoelectronic devices must be polished to nano-level roughness for proper device operation. Polishing process with magnetic compound fluid slurry (MCF polishing) under a rotary magnetic field is an influential candidate for the method to precisely polish optical glass. MCF slurry has been successfully utilized to polish a variety of materials, ranging from soft optical polymers to hard optical glasses. MCF was developed by mixing a magnetic fluid and a magnetorheological fluid with the same base solvent, and hence includes not only μm-sized iron particles but also nm-sized magnetite particles. To elucidate the behaviour of material removal in MCF polishing, this study measured the normal and shear forces generated in the polishing zone during polishing. From these measurements, the distributions of pressure P and shear stress τ were obtained. The distribution of material removal rate (MRR) was investigated through spot polishing of borosilicate glass. The effects of three process parameters, namely magnet revolution speed, MCF carrier rotational speed and working gap, on pressure P, shear stress τ and the MRR were also investigated. The results revealed that P is higher near the centre of the interacting area (i.e. the polishing spot centre) and the point of maximum shear stress τ appears at about 5 mm from the polishing spot centre. All of P, τ and MRR are sensitive to MCF carrier rotational speed and working gap but insensitive to magnet revolution speed. Shear stress is more sensitive to these process parameters than the pressure. Cross-sectional profiles of the polishing spots exhibit a characteristic symmetric W-shape; material removals are minimal at the spot centre and maximal at approximately 8.2–10.2 mm from the spot centre depending on the process parameters. MRR is proportional to the MCF carrier rotational speed and is negatively correlated with working gap. An MRR model involving both the pressure and shear stress in MCF polishing is proposed. In the model, MRR is more dominated by shear stress than by pressure.     

Mechanistic force modeling for milling of carbon fiber reinforced polymers with double helix tools

Carbon fiber reinforced polymers (CFRP) have emerged as the material of choice to satisfy increasing demand for lighter aircrafts. Machinability characteristics of CFRPs are quite different than those of metals; therefore, special tool designs have been developed for CFRP machining. The double helix end mill design compresses the upper and lower sides of the laminate using opposite helix angles that eliminate delamination. A mechanistic force model for double helix tools is developed based on milling force data obtained on flat end mills. The proposed model can be used to improve double helix tool designs and to optimize milling process parameters.     

机器人遥控焊接力觉传感与控制进展

为了完成遥控焊接过程涉及的非结构化环境接触任务,机器人遥控焊接系统需要具有力觉传感与控制功能.通过对机器人力控制理论和工业机器人集成力控制策略研究的综述,结合遥控焊接非结构化环境接触任务中存在的主要问题,提出了适合遥控焊接任务特点的力控制策略,并从双向力反馈遥操作、接触力控制以及力觉精确建模三个方面分析了力觉传感与控制技术在机器人遥控焊接领域中的应用,最后探讨了机器人遥控焊接力觉传感与控制研究的发展趋势.     

光纤光栅在热力管道泄漏检测中的应用

采用光纤光栅温度传感技术实现热力管道泄漏在线检测。热力管道泄漏时,泄漏出的热水引起热力管道周围土壤温度场温度升高。利用光纤光栅温度传感器的温度特性,结合热力管道泄漏处的温度场变化规律,进行了埋地热力管道泄漏的理论分析和光纤光栅泄漏检测系统的工程应用,实现了热力管道关键点温度连续监测,能够及时准确地发现泄漏,为管道泄漏检测技术提供新方法。     

遥控焊接力觉遥示教点间变迁控制技术

在遥控焊接力觉遥示教过程中,为实现遥控焊接自主遥示教,需要对遥示教点间状态变迁技术进行基础研究.根据焊缝辨识模型,确定示教点位置,通过共享技术调整好示教点的姿态,辨识记忆好第一个焊缝示教点,向下一个示教点变迁控制,主要包括示教点z方向变迁控制和示教点在xSy平面内方向变迁控制.并对摩擦力对遥示教点间变迁影响进行分析,证明了摩擦力的存在会在xSy平面内减小机器人进给计算量,在z方向使Fz增加,但是在遥示教自适应控制准许范围内,不会影响焊缝辨识逻辑.通过遥示教变迁控制技术,实现了遥示教点间自动变迁,为自主遥示教创造条件.     

Surface modification of aramid fiber by air DBD plasma at atmospheric pressure with continuous on-line processing

Aramid fiber (AF) samples are modified by air dielectric barrier discharge (DBD) plasma at atmospheric pressure. Plasma discharge power density and sample treatment time are investigated as the major parameters. Modified AF is characterized by SEM, XPS and wettability tests. It is shown that the surface roughness is improved, the O/C atomic ratio is increased from 15.99% to 27.15%, and the surface wettability is also enhanced significantly. It is also found that the improvements of physical and chemical properties increased with increasing power density and treatment time. The experiment is operated in the case of continuous on-line processing with properly high speed of AF transmission. It is close to industrial production and application.     

四叶玫瑰线轨迹光纤连接器端面研磨机设计与仿真

为了获得高精度的光纤连接器端面,基于机构学中的四叶玫瑰线传动机构原理,设计出一台四叶玫瑰线轨迹的光纤连接器端面研磨机。并且利用MATLAB数学模型软件进行机构的运动仿真,获得了不同主轴转速对任意一点瞬时速度的影响规律。结果表明:选择合理的主轴转速可以获得稳定的工况。     

Realizing precision pulse TIG welding with arc length control and visual image sensing based weld detection

Methods of arc length control and risual image based weld detection for precision pulse TIG welding were investigated. With a particular all-hardware circuit, arc voltage during peak current stage is sampled and integrated to indicate arc length, deviation of are length and adjusting parameters are calculated and output to drive a step motor directly.According to the features of welding image grabbed with CCD camera, a special algorithm was developed to detect the central line of weld fast and accurately. Then an application system were established, whose static arc length error is 0. 1 mm with 20 A average current and 1 mm given arc length, static detection precision of weld is 0. 01 mm, processing time of each image is less than 120 ms. Precision pulse TIG welding of some given thin stainless steel components with complicated curved surface was successfully realized.