正时齿带轮粉末冶金模设计

根据正时齿带轮的结构特点,设计了粉末冶金工艺的压模结构,论述了其工作原理。由于该齿带轮具有中心孔、内外台阶的特点,故采用补偿法装粉、浮动式压制、顶出式脱坯并配以辅助气缸的模具设计。实践证明,该模具结构合理,产品质量可靠,效果良好。但由于阴模有内台阶,要求粉末有稳定的松装比重。

藏传时轮历的发展及其作用

文章着重论述了藏传时轮历的发展及其作用,藏传时轮历是藏族天文历算中的主要组成部分,至今仍然流传在藏区,对藏区的纪日、纪时的算法以及生活、生产、医药、文化等发展起着举足轻重的作用。

粉末冶金正时齿带轮

论述了汽车用粉末冶金正时齿带轮的结构及性能特点、模具设计要点、材料选择及生产工艺和使用效果。实践证明 :其模具结构合理 ,使用方便可靠 ,工艺简单。目前该产品已批量生产 ,质量稳定 ,替代了进口产品。

基于市场情绪强弱下的择时轮动策略

市场情绪指标(Market SentimentIndicators) 是投资者和机构研究关注的重点之一,于股票市场整体行情的预判能在很大程度上可以从投资情绪中反映出来。本研究通过对申万一级行业 28 个板块固定周期内动量变化测算A股市场的整体情绪指标,通过模型计算动量表现将股票市场分为弱、中性、较强、极强四个区间,基于四个区间采取不同的仓位及投资种类的选择进行择时轮动,最后测算该策略下的风险收益情况。

大型养路机械轮对及箱体实验台的改造设计

分析原试验台存在的问题 ,介绍为解决这些问题所进行的研究设计 ,以及改造后试验台的使用效果。

藏族传统天文历算中的二十八宿体系研究

文章以藏族天文历算对于恒星的认识程度为着眼点,以藏族天文历算中的物候历谚语、《虎耳譬喻经》(藏文版)、《白琉璃论》等文献为研究对象,从命名、观测与研究三个方面收集并整理了藏族天文历算中二十八宿体系的起源和演变过程。文章认为时轮历思想传入之前,藏族天文历算中已经有了对二十八宿的系统命名和对某些星宿的初步观测,但是对二十八宿的系统研究始于公元9世纪印度佛经《虎耳譬喻经》传入西藏地区后才兴起的。

微机控制标志板打号机

主要介绍了微机控制标志板打号机的工作原理及结构特点。该设备将自动化工控设备与 HMIS系统有机地结合起来应用于车辆配件的检修生产。

Kinematical system of breadth cam profile design

The design solutions for breadth cam mechanism was presented. The main topics of the shape design for breadth cam was to calculate the coordinate at each contact point to determine the cam profile. The proposed method according to velocity and geometric relationships of instant velocity centers can easily determine each contact point at any instant moment. The cam profile was defined by contouring of the contact points. And also a program was developed by using Microsoft Visual C++ program,which can quickly and easily draw a 2D cam profile through the displacement diagram. Finally,the program was used to confirm the accuracy on the breadth cam profile design by computer animation graphically.

A novel method to predict static transmission error for spur gear pair based on accuracy grade

This paper proposes a novel method to predict the spur gear pair’s static transmission error based on the accuracy grade,in which manufacturing errors(MEs),assembly errors(AEs),tooth deflections(TDs)and profile modifications(PMs)are considered.For the prediction,a discrete gear model for generating the error tooth profile based on the ISO accuracy grade is presented.Then,the gear model and a tooth deflection model for calculating the tooth compliance on gear meshing are coupled with the transmission error model to make the prediction by checking the interference status between gear and pinion.The prediction method is validated by comparison with the experimental results from the literature,and a set of cases are simulated to study the effects of MEs,AEs,TDs and PMs on the static transmission error.In addition,the time-varying backlash caused by both MEs and AEs,and the contact ratio under load conditions are also investigated.The results show that the novel method can effectively predict the range of the static transmission error under different accuracy grades.The prediction results can provide references for the selection of gear design parameters and the optimization of transmission performance in the design stage of gear systems.

Large Eddy Simulations of Mixing Time in a Stirred Tank

Large eddy simulations (LES) of mixing process in a stirred tank of 0.476m diameter with a 3-narrow blade hydrofoil CBY impeller were reported. The turbulent flow field and mixing time were calculated using LES with Sma-gorinsky-Lilly subgrid scale model. The impeller rotation was modeled using the sliding mesh technique. Better agree-ment of power demand and mixing time was obtained between the experimental and the LES prediction than that by the traditional Reynolds-averaged Navier-Stokes (RANS) approach. The curve of tracer response predicted by LES was in good agreement with the experimental. The results show that LES is a reliable tool to investigate the unsteady and quasi-periodic behavior of the turbulent flow in stirred tanks.

Study on pattern time delay shift coding scheme

Pattern Time Delay Shift Coding (PDS) scheme is robust for underwater acoustic communication. The digital information are encoded in the time delay shift values of the Pattern, so the PDS scheme belongs to the Pulse Position Modulation (PPM). Several Patterns are selected for code division that the communication system could have a high ability to mitigate the inter-symbol interference (ISI) caused by multipath channel. Four communication channels work on the same time divided by different frequency, which lead to 1000bits/s of the data rate of communication. The simulation experiments show that the PDS system could adapt to many underwater acoustic channels for high data rate and high reliability.

Electro-Discharge Fine Truing of Metal-Bonded Fine-Grain Diamond Wheel Based on Real-Time Monitoring

A data acquisition system based on LabVIEW is designed and implemented, and electro-discharge(ED) fine truing of metal-bonded fine-grain diamond wheel based on real-time monitoring is researched. Real-time monitoring not only makes efficient impulse specification of ED truing easily obtained, but also is good for timely identifying no-load, avoiding short circuit and arc discharge phenomena and then for obtaining normal machining state. ED fine truing of the fine-grain wheel includes two steps: rough truing for high efficiency and fine truing for high precision. Final ED truing precision and efficiency not only depend on electric process specification, but also is concerned with electrode shape, insulated performance of operating fluid and vertical feed quantity value and frequency. Experiments indicate that ED fine truing based on real-time monitoring can improve the truing precision and efficiency. Average machining efficiency of W10 wheel is about 0.95 μm/min; the final run-out by ED truing is less than 2 μm.

Dynamic load sharing behavior of transverse-torsional coupled planetary gear train with multiple clearances

A new nonlinear transverse-torsional coupled model with backlash and bearing clearance was proposed for planetary gear set. Meanwhile, sun gear and planet's eccentricity errors, static transmission error, and time-varying meshing stiffness were taken into consideration. The differential governing equations of motion were solved by employing variable step-size Rung-Kutta numerical integration method. The behavior of dynamic load sharing characteristics affected by the system parameters including input rate, sun gear's supporting stiffness and eccentricity error, planet's eccentricity error, sun gear's bearing clearance, backlashes of sun-planet and planet-ring meshes were investigated qualitatively and systematically. Some theoretical results are summarized at last which extend the current understanding of the dynamic load sharing behavior of planet gear train, enrich the related literature and provide references for the design of planetary gear train.

Timing Belts Dynamics Model Approach

Design of composites and usage of new polymer materials allows for improvement of constructional properties of belts. Different applications： transmission, conveying or controlling have different meshing in gear. The work presents meshing model between timing belt and pulley and constructional features of transmission timing belts depending on materials used for their production. While designing timing belt, much attention should be paid to selection of materials, which has significant influence on mechanical properties of belts. This paper attempts to identify the model material and the nature of cooperation of timing belt-pulley; this is basic knowledge for the development of timing belt gear.

Effect analysis of friction and damping on anti-backlash gear based on dynamics model with time-varying mesh stiffness

A nonlinear model of anti-backlash gear with time-varying friction and mesh stiffness was proposed for the further study on dynamic characteristics of anti-backlash gear. In order to improve the model precision, applied force analysis was completed in detail, and single or double tooth meshing states of two gear pairs at any timing were determined according to the meshing characteristic of anti-backlash gear. The influences of friction and variations of damping ratio on dynamic transmission error were analyzed finally by numerical calculation and the results show that anti-backlash gear can increase the composite mesh stiffness comparing with the mesh stiffness of the normal gear pair. At the pitch points where the frictions change their signs, additional impulsive effects are observed. The width of impulsive in the same value of center frequency is wider than that without friction, and the amplitude is lower. When gear pairs mesh in and out, damping can reduce the vibration and impact.

Design and implementation of space-time precoded systems with full diversity and lossless capacity

A new space-time(ST)code design is proposed based on the design criteria of space-time codes,which is applied to the MIMO systems with fewer receive antennas than transmit antennas.The space-time codes,referred to as full diversity lossless capacity(FDLLC)ST code,achieve full transmit diversity and lossless equivalent channel capacity for ST precoded systems.Combined FDLLC-ST codes with channel codes,ST bit interleaved coded modulation(ST-BICM)system is constructed and an iterative detector/decoder is employed at the receiver.Simulations are presented.It is proved that the proposed design has good performance compared with other ST precoded MIMO systems.

Nonlinear Dynamic Analysis of Planetary Gear Train System with Meshing Beyond Pitch Point

Nonlinear dynamic analysis was performed on a planetary gear transmission system with meshing beyond the pitch point.The parameters of the planetary gear system were optimized,and a two-dimensional nonlinear dynamic model was established using the lumped-mass method.Time-varying meshing stiffness was calculated by the energy method.The model consumes the backlash,bearing clearance,time-varying meshing stiffness,time-varying bearing stiffness,and time-varying friction coefficient.The time-varying bearing stiffness was calculated according to the Hertz contact theory.The load distribution among the gears was computed,and the time-varying friction coefficient was calculated according to elastohydrodynamic lubrication(EHL)theory.The dynamical equations were solved via numerical integration.The global bifurcation characteristics caused by the input speed,backlash,bearing clearance,and damping were analyzed.The system was in a chaotic state at natural frequencies or frequency multiplication.The system transitioned from a single-period state to a chaotic state with the increase of the backlash.The bearing clearance of the sun gear had little influence on the bifurcation characteristics.The amplitude was restrained in the chaotic state as the damping ratio increased.

APPLICATION OF TURBO CODES IN HIGH-SPEED REAL-TIME CHANNEL

The time delay of Turbo codes due to its iterative decoding is the main bottleneck of its application in real-time channel. However, the time delay can be greatly shortened through the adoption of parallel decod-ing algorithm, dividing the received bits into several sub-blocks and processing in parallel. This letter mainly discusses the applicability of turbo codes in high-speed real-time channel through the study of a parallel turbo decoding algorithm based on 3GPP-proposed turbo encoder and interleaver in various channel. Simulation re-sult shows that, by choosing an appropriate sub-block length, the time delay can be obviously shortened with-out degrading the performance and increasing hardware complexity, and furthermore indicates the applicability of Turbo codes in high-speed real-time channel.