基于PLC的龙门刨床直流调速系统改造

通过对龙门刨床工作台的工作原理和原调速系统的工作特性的分析,提出应用PLC和可逆直流调速器改造龙门刨床电气控制系统的实现方案,将发电机组及扩大机控制的龙门刨床改造成全数字智能化的直流PLC电气控制系统,适用于各种型号的老式刨床控制。     

带有负载观测器的直流调速系统

本文介绍采用线性最优调节器所设计的直流调速系统在龙门刨床控制系统中的应用。在控制系统中引入了负载观测器,使得龙门刨床在控制指标上得到了明显的改善。文中在理论设计的基础上,介绍了控制系统的工作原则。工业试验运行表明,该系统各项控制性能指标明显优于采用经典控制理论的设计指标。     

龙门刨床电气控制系统的改造设计

本文以4m龙门刨床电气系统为例叙述龙门刨电气控制系统的改造设计过程。     

交流伺服在龙门刨床的应用

本文简要介绍了交流伺服在龙门刨床的应用。     

交流伺服在龙门刨床的应用

本文简要介绍了交流伺服在龙门刨床的应用。     

B2025龙门刨床数字直流调速系统改造研究

某厂购置于20世纪70年代的B2025型龙门刨床,在生产中起到至关重要的作用,其机械部分仍然良好,但电气元件老化,实际生产中故障频发,维修难度较大。因此,对龙门刨床电气控制系统进行技术改造,保留原有机械设备,运用先进的控制技术,提高其加工精度和自动化程度具有重要意义。采用ETD790型直流调速器取代传统的交磁扩大机-发电机-电动机调速系统,实现对工作台主拖动直流电动机的控制和调速;用西门子S7-200型可编程控制器（PLC）逻辑控制取代传统的继电器-接触器控制系统,实现对龙门刨床的工作台直流电动机和右侧刀架,垂直刀架等三相交流电动机的起动、调速、正反向转换和制动的控制。改造后的系统结构简单,运行稳定,控制灵活,调速精度高,提高了龙门刨床的动态和静态性能。     

龙门刨床电气系统技术改造

龙门刨床电气控制系统比较复杂,经长时间的使用后,经常发生故障,为了充分挖掘设备的潜力,我们对该设备的电气控制系统进行了全面的技术改造,效果很好.     

龙门刨床全数字直流调速系统

根据龙门刨床的工艺特点及其对电力拖动自动控制系统的要求,研制出龙门刨床全数字直流调速系统。对该调速系统的构成、特点及主要性能指标进行了介绍。     

浅谈用PLC对B2012A系列龙门刨床的电气控制改造

通过分析龙门刨床传统控制改造的必要性提出课题,简要介绍了龙门刨床的基本结构及控制要求和改造前后的差别,阐述了用PLC等工控设备对传统电气控制技改的前景广阔。     

变频调速系统在龙门刨床上的应用

针对B2016A九米龙门刨床主传动存在的问题，采用变频调速系统对机床进行了主传动改造，充分发挥了大型龙门刨床的效率并降低了能耗。     

Markedness and its Interpretation in Language Use

Language markedness is a common phenomenon in languages, and is reflected from hearing, vision and sense, i.e. the variation in the three aspects such as phonology, morphology and semantics. This paper focuses on the interpretation of markedness in language use following the three perspectives, i.e. pragmatic interpretation, psychological interpretation and cognitive interpretation, with an aim to define the function of markedness.     

Features of Women's language

Language is a means of verbal communication. People use language to communicate with each other. In the society, no two speakers are exactly alike in the way of speaking. Some differences are due to age, gender, statue and personality. Above all, gender is one of the obvious reasons. The writer of this paper tries to describe the features of women＇s language from these perspectives： pronunciation, intonation, diction, subjects, grammar and discourse. From the discussion of the features of women＇s language, more attention should be paid to language use in social context. What＇s more, the linguistic phenomena in a speaking community can be understood more thoroughly.     

An Analysis of Catherine＇s Character——Wuthering Heights

Wuthering Heights, Emily Bronte＇s only novel, was published in December of 1847 under the pseudonym Ellis Bell. The book did not gain immediate success, but it is now thought one of the finest novels in the English language. Catherine is the key character of this masterpiece, because everybody and everything center on her though she had a short life. We can understand this masterpiece better if we know Catherine well.     

Lower Paleozoic oil relationships within Williston Basin, Canada

The Williston Basin is a significant petroleum province, containing oil production zones that include the Middle Cambrian to Lower Ordovician, Upper Ordovician, Middle Devonian, Upper Devonian and Mississippian and within the Jurassic and Cretaceous. The oils of the Williston Basin exhibit a wide range of geochemical characteristics defined as "oil families", although the geochemical signature of the Cambrian Deadwood Formation and Lower Ordovician Winnipeg reservoired oils does not match any "oil family". Despite their close stratigraphic proximity, it is evident that the oils of the Lower Palaeozoic within the Williston Basin are distinct. This suggests the presence of a new "oil family" within the Williston Basin. Diagnostic geochemical signatures occur in the gasoline range chromatograms, within saturate fraction gas chromatograms and biomarker fingerprints. However, some of the established criteria and cross-plots that are currently used to segregate oils into distinct genetic families within the basin do not always meet with success, particularly when applied to the Lower Palaeozoic oils of the Deadwood and Winnipeg Formation.     

低渗透非均质砂岩油藏启动压力梯度研究

理论推导与室内实验相结合,建立了低渗透非均质砂岩油藏启动压力梯度确定方法。首先借助油藏流场与电场相似的原理,推导了非均质砂岩油藏启动压力梯度计算公式。其次基于稳定流实验方法,建立了非均质砂岩油藏启动压力梯度测试方法。结果表明:低渗透非均质砂岩油藏的启动压力梯度确定遵循两个等效原则。平面非均质油藏的启动压力梯度等于各级渗透率段的启动压力梯度关于长度的加权平均;纵向非均质油藏的启动压力梯度等于各渗透率层的启动压力梯度关于渗透率与渗流面积乘积的加权平均。研究成果可用于有效指导低渗透非均质砂岩油藏的合理井距确定,促进该类油藏的高效开发。     

On Tragic Consciousness In The Works By Ernest Hemingway

As an American modern novelist who were famous in the literary world, Hemingway was not a person who always followed the trend but a sharp observer. At the same time, he was a tragedy maestro, he paid great attention on existence, fate and end-result. The dramatis personae's tragedy of his works was an extreme limit by all means tragedy on the meaning of fearless challenge that failed. The beauty of tragedy was not produced on the destruction of life, but now this kind of value was in the impact activity. They performed for the reader about the tragedy on challenging for the limit and the death.     

Design and analysis of generic LBS application developing platform

Location based services is promising due to its novel working style and contents.A software platform is proposed to provide application programs of typical location based services and support new applications developing efficiently. The analysis shows that this scheme is easy implemented, low cost and adapt to all kinds of mobile nework system.     

Achieving Unusual States of Matter Under High Pressure

正The periodicity of the elements and the non-reactivity of the inner-shell electrons are two related principles of chemistry,rooted in the atomic shell structure.Within compounds,Group I elements,for example,invariably assume the+1 oxidation state,and their chemical properties differ completely from those of the p-block elements.These general rules govern our understanding of chemical structures and reactions.Using first principles calcula-     

Exchange-Correlation and Electronic Excitation Energies from Pairing Matrix Fluctuations

We have developed an adiabatic connection to formulate the ground-state exchange-correlation energy in terms of pairing matrix linear fluctuations.This formulation of the exchange-correlation energy opens a new channel for density functional approximations based on the many-body perturbation theory.We illustrate the potential of such approaches with an approximation based on the particle-particle Random Phase Approximation(pp-RPA).This re-     

Density Functional Theory for the Response of Periodic Systems to Electric Fields Based on the Vector Potential Approach

正The electronic and nuclear(structural/vibrational)response of 1D-3D nanoscale systems to electric fields gives rise to a host of optical,mechanical,spectral,etc.properties that are of high theoretical and applied interest.Due to the computational difficulty of treating such large systems it is convenient to model them as infinite and periodic(at least,in first approximation).The fundamental theoretical/computational problem in doing so is that