基于联邦滤波的室内多传感器融合导航定位方法研究

针对室内多传感器融合导航定位问题,提出一种基于联邦滤波的INS/3D LASER/单目视觉融合的室内导航定位方法.该方法是通过联邦滤波将INS分别同3D LASER与单目视觉构成子滤波器,主滤波器根据最小方差准则,利用最优系数加权法融合各子滤波器的最优估计,从而获得全局最优融合结果.实验证明,该方法能有效提高室内导航定位的精度和鲁棒性,比传统的视觉里程计法或激光雷达里程表法更准确.     

PET polymer ablation using excimer laser for nozzle plate application

Abstract

Polyethylene terephthalate (PET) film drilling using a 248 nm excimer laser through photomask projection is presented. The parameter effects of laser fluence, shot number and repetition rate on the processing results are examined. A high quality microhole array with 50 μm thick PET film is fabricated. When the projection process is carried out, the diameter differences in the microhole in the front and back side of PET are observed. This causes a conical shape in the kerf. The formation of this conical shape in terms of the laser process parameters is discussed. The process parameter effects are investigated and characterised to improve the PET microhole laser machining quality.     

Dynamic Young's modulus and glass transition temperature of selected tropical wood species

Abstract

Dynamic Young's modulus (E _d) of selected tropical wood species, namely Dyera polyphylla, Endospermum diadenum, Cratoxylum arborecens, Alstonia pneumatophora, Macaranga gigantea and Commersonia bartramia, used for the study was measured using the free–free flexural vibration method. Young's modulus from three point bending (E _3pb) and compression parallel to grain (E _cp) was also studied. The results show that the relationship between E _d and E _3pb for all wood species is very significant with the mean value of E _d consistently larger than or sometime equal to E _3pb. Surprisingly, the relationship between E _d and E _cp is not significant except for Alstonia pneumatophora. The dynamic mechanical thermal properties were also investigated using the dynamic mechanical thermal analyser (DMTA). The results showed that the storage modulus of the wood species at –90°C is in the range of 1·48–4·09 GPa with a glass transition temperature ranging from 50 to 70°C.     

Adhesion properties of functionally gradient diamond composite films on medical and tool alloys

We have investigated the adhesion properties of microcrystalline diamond thin films on Ti-Al-V alloy, Co-Cr-Mo alloy and steel. Microcrystalline diamond possesses high hardness, a low coefficient of friction, extreme chemical inertness and biocompatibility; these properties can enhance the performance of metal alloys used in medical implants and in machine tools. We have adopted three methods for improving the adhesion of microcrystalline diamond to commonly used metal alloys: (1) by alloying the substrate surface to minimize graphitization; (2) by employing appropriate buffer layers between the diamond film and the substrate; and (3) by creating functionally gradient diamond-(titanium carbide, tungsten carbide, titanium nitride and aluminum nitride) composites. We have demonstrated that functionally gradient discontinuous buffer layers of titanium carbide, titanium nitride, aluminum nitride and tungsten carbide are able to control stress and graphitization in microcrystalline diamond thin films. This work on buffer layers and functionally gradient coatings should allow the development of more adherent crystalline diamond films for medical and tribological applications.     

Research on Laser Direct Deposition Process of Ti-6Al-4V Alloy

Laser direct deposition （LDD） of metallic components is an advanced technology of combining CAD/CAM （computer aided design/computer aided manufacturing）, high power laser, and rapid prototyping. This technology uses laser beam to melt the powders fed coaxiaUy into the molten pool by the laser beam to fabricate fuUy dense metallic components. The present article mainly studies the LDD of Ti-6Al-4V alloy, which can be used to fabricate aircraft components. The mechanical properties of the Ti-6Al-4V alloy, fabricated by LDD, are obtained using the tension test, and the oxygen content of used powders and deposited specimens are measured. In the present article, it can be seen that the mechanical properties obtained using this method are higher than the ones obtained by casting, and equal to those got by wrought anneal. One aircraft part has been made using the LDD process. Because of this aircraft part, with sophisticated shape, the effect of the laser scanning track on the internal soundness of the deposited part was discussed.     

Method for welding highly crack susceptible magnesium alloy ZK60

Abstract

The highly crack susceptible magnesium alloy ZK60 plates of 2 mm thickness were successfully welded by laser beam welding (LBW) with filler strip, which has the advantages of low heat input and capability of adjusting the compositions of weld metal to a less susceptible level. The effects of the compositions of filler strips on the microstructures and mechanical properties of the joints were investigated. Compared with autogenous LBW, LBW with filler strip can produce a narrower joint and avoid the cracks and pits, which severely worsen mechanical properties of the joints. When the filler strip of ZK40 alloy is employed, the grains in fusion zone can be refined, and a high quality joint, with the ultimate tensile strength of 322 MPa up to 90·7% of the base metal, is obtained.     

Interfacial reaction mode and its influence on tensile strength in laser joining Al alloy to Ti alloy

Abstract

In order to obtain a robust dissimilar joint of Al/Ti alloys, a filler wire of Al–12 wt-%Si and 45° V shape groove on the base metal were used during CO₂ laser welding. Heat input had evident influence on the interfacial reaction mode. It was found that a dissolution mode for low heat input and a melting mode for high heat input exist at the joint interface, which was analysed from thermodynamic point of view. Tensile strength of the joints in the dissolution mode reached as high as 296 MPa, which was significantly higher than that in the melting mode.     

Hydrodynamical phenomena in the process of laser welding and cutting

Abstract

The main objective of the paper is to outline the 'bridges' existing between the outcomes of fundamental researches and the results of investigations in the field of industrial laser materials processing (LMP). An analysis is presented on the models based on non-stationary hydrodynamic phenomena caused by deeply penetrating high power CW laser beam into materials. This is typical of laser welding (LW) and laser cutting (LC). A physical analysis pertaining to melt removal and melt layer instability mechanisms of gas jet assisted CW–CO₂ laser fusion cutting is presented. The models deliberated here are melt squeezing out by gas pressure gradient, melt dragging by the friction force between melt surface and gas flow, formation of moving shelves at the cutting front. In case of high laser intensity, radiative flux interacts with material causing dynamical thermal transport onto the surface and phase transition at solid–liquid–gas interfaces. The solution is based on the non-stationary variables. Under these conditions the Mach number varies significantly due to laser intensity associated with laser flux energy instabilities. The connection among material surface temperature, laser intensity, laser flux and pressure in the plasma cloud is brought out. In addition, novel mechanisms based on hydrodynamics are proposed.