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Estimates of Identification Result Disturbances in Parallel Mechanism Calibration

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Tsinghua Science and Technology 2006年第1期11卷 80-87页

作者：高猛李铁民唐晓强段广洪 department of precision {2. and mechanology Tsinghua UniversityBeijing 100084 China

General QR decomposition of the observation matrix is used to solve identification functions to evaluate identification results of every parameter in parallel mechanism calibrations. A relationship between measured information and identification results is obtained by analyzing numerous matrix transforms and QR decompositions. When distributions of measurement error are determined, random distributions of identification result disturbances （IRDs） can be obtained from this relationship as a function of measurement errors. Then the ranges of the IRDs can be effectively estimated, even if true parameter values are unknown. An optimization index based on IRD estimate is presented to select measurement configurations to achieve smaller IRDs. Two simulation examples were carried out with different modes and calibration methods. The results show that the method is effective and that the optimization index is useful. Some regular parameter identification problems can be explained by the IRD estimates.

关键词： parallel mechanism calibration identification disturbance estimate

A Numerical Error Modeling Method for Parallel Kinematic Machines and Its Applications

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Tsinghua Science and Technology 2010年第5期15卷 489-497页

作者：刘大炜王立平李铁民黄鹏 Institute of Manufacturing Engineering Department of Precision Instruments and Mechanology Tsinghua University

Error model is the basis for accuracy-related computations and analyses for parallel kinematic machines（PKMs）.Traditional error modeling methods are usually based on differentiation of kinematic solutions,but the solving process is often complex and has limitations for certain specialized PKMs.A concise numerical error modeling method with the inverse kinematic solution as its only requirement is presented in this *** avoid complex Jacobian matrix computations,the difference matrix that can be quickly calculated by kinematic solutions was used to replace the differential *** quasi-Newton method,which has high speed and high precision,was introduced to solve the numerical forward kinematic *** verify the efficiency of this numerical error modeling method,three applications in error transformation matrix（ETM） modeling,error analysis,and kinematic calibration were simulated on a 4RRR PKM.A comparison with the results obtained by the traditional method shows that the numerical method is accurate,convenient,and has lower requirements and wider applicability,especially for certain specialized and manufactured PKMs.

关键词： error model difference matrix quasi-Newton method error transformation matrix(ETM) calibration

Accuracy Analysis and Calibration of Gantry Hybrid Machine Tool

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Tsinghua Science and Technology 2003年第6期8卷 702-707页

作者：唐晓强李铁民尹文生汪劲松 Manufacturing Engineering Institute Department of Precision Instruments and Mechanology Tsinghua University

The kinematic accuracy is a key factor in the design of parallel or hybrid machine tools. This analysis improved the accuracy of a 4-DOF (degree of freedom) gantry hybrid machine tool based on a 3-DOF planar parallel manipulator by compensating for various positioning errors. The machine tool architecture was described with the inverse kinematic solution. The control parameter error model was used to analyze the accuracy of the 3-DOF planar parallel manipulator and to develop a kinematic calibration method. The experimental results prove that the calibration method reduces the cutter nose errors from ±0.50 mm to ±0.03 mm for a horizontal movement of 600 mm by compensating for errors in the slider home position, the guide way distance and the extensible strut home position. The calibration method will be useful for similar types of parallel kinematic machines.

关键词： calibration accuracy hybrid machine tool

Micro-Friction and Adhesion Measurements for Si Wafer and TiB_2.Thin Film

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Tsinghua Science and Technology 2007年第3期12卷 261-268页

作者：卿涛邵天敏温诗铸 State Key Laboratory of Tribology Department of Precision Instruments and MechanologyTsinghua University

An apparatus was specifically developed for micro-friction and adhesion measurements. The force measurement range is 10-2.00 μN with a horizontal speed of 10-400 μm/s. The apparatus was tested using a 0.7-mm diameter steel ball as the upper specimen to measure the micro friction and adhesion behaviour of a Si （100） wafer and a TiB2.film. The effects of rest time, speed, and load were studied. The results show that the maximum static and sliding friction forces of both the Si （100） wafer and the TiB2.film increase with the load. At low speeds, the influence of speed on the friction force is significant. The adhesion forces of the Si （100） wafer and the TiB2.film increase with rest time, reaching stable values after about 3000 s. The TiB2.film has significantly less adhesion and micro friction forces than the Si （100） wafer.

关键词： micro friction adhesion apparatus Si wafer TiB2.film

Determination of Mean Thickness of an Oxide Layer on a Silicon Sphere by Spectroscopic Ellipsometry

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Chinese Physics Letters 2010年第5期27卷 40-43页

作者：张继涛李岩罗志勇吴学健 State Key Lab of precision Measurement Technology and instruments Department of Precision Instruments and Mechanology Tsinghua University Beijing 100084 National Institute of Metrology Beijing 100013

One of the biggest obstacles to reduce the uncertainty of the Avogadro constant NA is such that there will be an oxide layers on the surface of a silicon sphere. The thickness of this layer is measured by a modified spectroscopic ellipsometer, which can eliminate the influence of the curved surface, and the results are calibrated by x-ray reflectivity. Fifty positions distributed nearly uniformly on the surface of the silicon sphere are measured twice. The results show that the mean thickness of the overall oxide layer is 3.75 nm with the standard uncertainty of 0.2. nm, which means that the relative uncertainty component of NA owing to this layer can be reduced to 1.2.× 10^-8.

关键词： THICKNESS measurement OXIDES SILICON ELLIPSOMETRY AVOGADRO constant SURFACES (Technology) CALIBRATION

Electrothermal Driving Microcantilever Resonator as a Platform for Chemical Gas Sensing

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Tsinghua Science and Technology 2010年第5期15卷 481-488页

作者：董瑛高伟郑义尤政 department of precision {2. and mechanology Tsinghua University State Key Laboratory of precision Measurement Technology and instruments Tsinghua University

In the current research,the use of a micromachined cantilever resonator as a platform for chemical gas sensing was *** microcantilever resonator integrates an electrothermal driving unit and a piezoresistive detecting unit,and it is fabricated by direct bonding a silicon-on-insulator（SOI） *** a particular polymer layer coated on the surface of the microcantilever,a gas sensor for volatile organic components（VOCs） detection can be *** operation mechanism provides the microcantilever resonator with integrated circuit（IC） compatibility in terms of both the fabrication process and operating *** configuration of the microcantilever resonator can optimize the performance of the gas *** SOI wafer provides a solution for the integrated fabrication of the microstructure,transducers,electronics,and the precise control of the resonator *** this paper,the principles,design,analysis,process,and demonstration of the gas sensor based on the microcantilever resonator are *** experimental results provide confirmation that the polymer-coated microcantilever resonator has excellent performance with regard to VOC detection.

关键词： microcantilever resonator gas sensor electrothermal driving volatile organic component

Synthesis of Ultra-High-Molecular-Weight Polyethylene by Transition-Metal-Catalyzed Precipitation Polymerization

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precision Chemistry 2024年第2期2卷 63-69页

作者： Wenbing Wang Quan Wang Chen Zou Changle Chen Key Laboratory of precision and Intelligent Chemistry Department of Polymer Science and EngineeringUniversity of Science and Technology of ChinaHefei 230026China

Ultra-high-molecular-weight polyethylene(UHMWPE)plays an important role in many important fields as engineering *** this contribution,a precipitation polymerization strategy is developed by combination of highly active phosphino-phenolate nickel catalysts with polymer-insoluble solvent(heptane)to access UHMWPE(Mn up to 8.3×10^(6)g mol^(-1))with good product morphology,free-flowing characteristics,and great mechanical *** with the academically commonly used aromatic solvent(toluene),the utilization of heptane offers simultaneous enhancement in important parameters including activity,polymer molecular weight,and catalyst thermal *** system can also generate polar functionalized UHMWPE with molecular weight of up to 1.6×10^(6)g mol^(-1)in the copolymerization of ethylene with polar *** importantly,this precipitation polymerization strategy is generally applicable to several representative transition metal catalyst systems,leading to UHMWPE synthesis with good product morphology control.

关键词： transition metal catalysts polyolefin UHMWPE precipitation polymerization polar monomer

Single output LD end-pumped passively mode-locked Nd:YVO_4 laser with semiconductor saturable absorber mirror

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Chinese Physics B 2010年第4期19卷 278-280页

作者：夏帕克提于海娟闫平巩马理 Center for Photonics and Electronics State Key Laboratory of TribologyDepartment of Precision Instruments and MechanologyTsinghua University

A quarter-wave plate and the thin film polarizer （TFP） are used for the LD end-pumped passively mode-locked Nd：YVO4 laser with semiconductor saturable absorber mirror （SESAM） to obtain a single beam output with a total power of 4.8 W. An optical-optical efficiency is achieved to be 2.% for a stable CW mode-locking operation at 1064 nm, with a pulse repetition rate of 70 MHz and pulse width of 16 ps. The multipulse in the pulse sequence is eliminated for reaching a peak power as high as 4 kW.

关键词： single output passively mode-locked semiconductor saturable absorber mirror

Angular spectrum characters of high gain non-critical phase match optical parametric oscillators

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Chinese Physics B 2011年第5期20卷 261-265页

作者：刘建辉柳强巩马理 Center for Photonics and Electronics State Key Laboratory of Tribology and Department of Precision Instruments and MechanologyTsinghua University

The angular spectrum gain characters and the power magnification characters of high gain non-walk-off colinear optical parametric oscillators have been studied using the non-colinear phase match method for the first time. The experimental results of the KTiOAs04 and the KTiOP04 crystals are discussed in detail. At the high energy single resonant condition, low reflective ratio of the output mirror for the signal and long non-linear crystal are beneficial for small divergence angles. This method can also be used for other high gain non-walk-off phase match optical parametric orocesses.

关键词： optical parametric oscillator non-critical phase match angular spectrum divergenceangle