英文简易文章（7篇）
1.英文简易文章 篇一
近来下载了很多英文书籍，分享一下自己的下载心得，希望对书友有好处。以前常常抱怨由于老外版权意识强，读英语原版书籍难。
后来有机会认识了rapidshare，很多新书都能够找到下载，才恍然大悟： 并不是找不到书籍阅读，而是没有找到方法。当然并非所有图书都可以在网上免费下载，能免费下载的是少数，一般而言，畅销书、计算机类图书比较多。但是这已经足够丰富自我的日常阅读，毕竟并不需要读所有书籍。第一种方法就是利用空间存储器寻找书籍。
首先找到优秀的外国的空间存储器。
http://rapidshare.de
http://rapidshare.com
http://mihd.net/
http://depositfiles.com/
http://megaupload.com
http:///
http:///
http:///
http:///
http://
http:///
http://sexupload.com
http://ultrashare.net
http://rapidupload.com
http://zshare.net
http://uploadspy.com
http://savefile.com
.http://mytempdir.com
http://upload.com
http://hyperupload.com
http://sendspace.com
http://
http://bestsharing.com
http://
http://
http://
http://upload.hostiran.net
http://
http://
http://
http://badongo.com
rapidshare的资源最丰富，包括电影，软件，书籍。对免费用户唯一的缺点就是等待的时间太长，下载一本书，等待一段时间。下载几本书，等待可能要几个小时。由于资源的丰富，又不得不依赖它，真是又爱又恨。网上有介绍破解流量限制的软件，个人试了很多，都不好用，有兴趣的在网上搜索一下学习。
直接用google搜索，书名+rapidshare.de/files、书名+inurl:rapidshare，rapidshare.com/users+关键词。
还有很多面向 rapidshare的搜索引擎：
http:///search/
http:///
http://shareminer.com/
http://filesbot.com/
http:///?q=users
GRE
http://rapidshare.com/users/S6NML7
http://rapidshare.com/users/URE983
http:///IELTS-SAT-TOEFL-GRE-GMAT.htm经济
http://rapidshare.com/users/RD4HZB
词汇
http://rapidshare.com/users/6CEKPE
计算机
http://rapidshare.com/users/T8Q8RB
rapidshare的搜索应用
http://rapidshare.com/users/S6NML7
http://mihd.net/
http://depositfiles.com/
这两个几乎没有限制，本人用得比较多。搜索方法与上面类似。http://megaupload.com
有用户数量限制，每次用都说用户已满，没有用过，不过很多人推荐。其它的存储空间没有用过，不好评价。
第二种方法就是BitTorrent，Emule等软件下载。
没有英语环境的人学习英语，并查找英文资料，就是要融入英语国家的生活氛围、生活习惯、生活圈子。这时候，多学习学习外国的相关文化等资料是有好处的。读书，就是一种学习的手段。
北美的图书资料异常丰富，往往你所想知道的信息都在某本书里。但是，如何找到这些书呢？
互联网的到来使得以前很多遥不可及的书籍唾手可得。这里我介绍的就是一种基于互联网的读书方式。
很多人已经知道如何用BitTorrent（BT，变态）、Emule（电驴）等p2p（点对点）的软件工具去下载电影、音乐，但是，其实它们也是可以用来下载书籍的。没事的时候，完全可以用它们的搜索功能（或其他搜索方式）去搜索相关的书籍。
重点推荐mininova：http:///e_magazine/ 这个地方主要书籍是杂志。
包括考研原材料来自于《The Economist》。
第三种方法就是论坛，博客收集的书籍上传的地址。
与“网上读书论坛”的专家找书版类似的地方，上面能够找到很多好书籍。http:///
报纸、杂志、电子书籍，种类齐全。
Ebooksclub
http://ebooksclub.org/?module=index
下载电子书最简单的办法就是找别人已经下载好的。
最值得推荐的就是渡岸学术网
http:///eb/index.htm
这里的书籍相当丰富，多为教材与学术性书籍，很适合研究用。大多数的书籍配有详细说明和图书封面，美观，赏心悦目。
推荐“海外选书系统”搜索书籍，可以结合http://books.google.com 与http:///
用。“海外选书系统”按中图法分类，很适合中国人。
http:///expert/index.php?toURI=useredit.php?curUser=1可以结合duxiu中西合璧。梦寐以求的学习方式来临
2.英文简易文章 篇二
1 开展英文简易读本活动的意义
(1) 激发阅读兴趣, 培养阅读能力
英文简易读本选取的都是经典文学读物, 既有古典名著又有近现代作品, 内容丰富充实, 故事情节曲折, 趣味浓厚, 可读性强。比如童话类故事《苏格兰玛丽女王》、《潘德尔的巫师》、《爱丽丝漫游奇境记》等, 它们情节生动, 人物形象各异, 内容充满新奇与独特;人物类简易读本有《威廉·莎士比亚》、《大卫·科波菲尔》等;历险记类读本如《格列弗游记》、《鲁宾孙漂流记》等, 内容跌宕起伏、引入注目;还有经典名著读物如《呼啸山庄》、《雾都孤儿》、《简爱》以及《傲慢与偏见》等等。这些简易读本思想性、文学性和故事性强, 极易激发学生的阅读兴趣和热情。因此, 开展英文简易读本活动, 对于培养学生热爱阅读的习惯, 训练阅读技巧, 拓展阅读视野, 提升阅读能力都有着极其重要的意义。
(2) 形成良好氛围, 创建外语特色学校
在初中生中开展阅读英文简易读本活动, 是我校创外语特色学校所开展的课外辅助活动之一。首先, 有趣的简易读本活动, 让学生们热爱阅读, 养成阅读的良好习惯, 在校园内形成良好的读书氛围。其次, 通过阅读简易读本, 可以拓展学生的知识范围, 开阔眼界和视野, 让学生足不出户就能了解到更多的跨文化知识, 对于提升学生的跨文化交流能力大有裨益。最后, 开展简易读本活动, 必然会带动出一系列的读书比赛、演讲比赛、经典话剧模拟表演、情景剧表演、英语角等活动, 这些活动无形中为学生学习英语营造出良好的语言环境。
2 开展英文简易读本活动的策略
如何在初中生中有效开展英文简易读本的读书活动呢?笔者认为, 可以从以下三方面思考:
(1) 课内合理引导
要想让学生在阅读简易读本过程中, 有所思有所悟有所获, 教师的合理引导和技巧指导至关重要。英语教师可以每周安排一堂课左右的时间专门指导学生如何阅读简易读本。以经典名著《简爱》为例, 教师可以选取其中的经典片段, 与学生一起阅读和欣赏。首先, 带领学生大声朗读片段, 培养语感和朗读兴趣, 获得对内容的初步认知。其次, 指导学生精读重点片段, 对于其中的重点单词、语法句义、习惯用语等进行重点理解记忆和掌握, 巩固英语基础知识。接着, 鼓励学生快速阅读, 注重对内容梗概的理解, 在较短的时间内吸收更多的语言信息量。最后, 在快速阅读完成之后, 用自己的语言, 简单概括《简爱》的故事情节和主要内容, 也可以写一写自己的读后感或读书笔记。
(2) 课外广泛阅读
阅读能力的培养是一项庞大工程, 短时间的课内指导显然是不够的, 学生需要在课余花费更多的时间去广泛阅读简易读本。在简易读本的选择上, 尽量多元化、多样化, 这样学生既能读到自己感兴趣的类型读物, 也可以了解更多其它方面的知识, 接触到地道的英文文学, 对于促进学生的英语综合能力很有帮助。
(3) 开展多元化活动
为了让简易读本活动开展得有声有色, 可以不定期地举办一些朗读比赛活动、经典名著的表演活动、电影欣赏活动等等。例如, 在全校范围内举行英文朗读比赛、英文辩论赛;开展表演活动, 学生们可以将《傲慢与偏见》、《五个孩子和沙精》等文学作品中的内容改编成话剧或情景剧, 进行表演和演绎;观看英文电影, 如《爱丽丝漫游奇境记》、《格列弗游记》、《海蒂》、《王子与贫儿》等电影。通过开展这些内容丰富、形式多样的活动, 一方面加深学生对简易读本内容的认识和理解, 了解更多英美国家的社会风俗及文化知识;另一方面训练学生的英语口语能力、应用能力和创造能力。
参考文献
[1]姜玉庆.读英文简易读物, 提高英语学习能力[J].文理导航, 2011 (32) .
[2]王芳.英语简易读物在高职英语教学中的作用[J].南昌高专学报, 2009 (2) .
3.文章英文摘要 篇三
On the morning of Monday March 16, shortly after my breakfast, I got a telephone call from Central Conservatory President Wang Cizhao, whose unusual voice suddenly upset me. I felt that something must have gone wrong. My suspicion was proved. He said with slight sobs, “I have just been to Prof. Lin Yaojis home and he died early this morning…” He told me in brief what had happened. “How come?” I never expected that what he told me was about the bad news of Prof. Lin, but then I could utter no more words. When President Wang said that he would go to his office, I said “ I will call his wife Hu Shixi immediately.” It took quite a long time to get through to her probably because there were too many calls to her at the time. I could feel her sorrow on the phone and I just said a few words to express my and my familys condolence to her on the death of Prof. Lin.
Hanging up the phone, I sat down on the chair, and was totally speechless. It was so sudden! As I live far from the conservatory, I could not get there very soon, but then I was wondering if his body would be transferred to the Baobaoshan Cemetery in a short while. My mind was in a terrible mess.
Lin and I had been schoolmates and more importantly, we had worked together as colleagues in the conservatory for the past fifty years. Apart from that, there was something unique between us. When I was living in the conservatory dormitory at Baojia Street about ten years ago, Lin had been my neighbour for many years as his apartment was just two stories lower than mine, in the same building. So every time I came home, I would pass his door. At that time, the conservatory was short of classrooms and practice rooms but Prof. Lin had so many students. So very often they had to come to his home for his lesson. When it was too hot in the summer and also the small space in the room caused some acoustic problems, sometimes he would have to open his door, so as to make his class a real “open class”. It is under such circumstances that Prof. Lin had brought up, with his extraordinary teaching methods and great care for his students, a few dozen internationally renowned violinists such as Hu Kun, Xue Wei, Chai Liang, Guo Chang, Li Chuanyun and Lu Wei, who won many prizes, including over ten gold prizes in national and international violin competitions. Prof. Lin and his students have won unprecedented reputation for China, and have also promoted the development of violin performing art in the country. Certainly, other teachers in the conservatory have also made their own contribution respectively as the teaching condition and teachers living condition have constantly been improved. I clearly remember that when I was acting as the conservatorys president in the 1980s, the violin major in the Orchestra Department had been the shining big star of the school, with highly frequent national and international competition participation and exchanges, which even attracted such great world violin maestros as Yehudi Menuhin and Isaac Stern who visit our school for several times just because they were interested in those young but truly talented violin students that we had. Very often Prof. Lin and I exchanged views over these matters by going upstairs or downstairs, and together with the teachers and students we shared the great joy of constantly made achievements and progress.
During that period I was also member of the Party Group of the Ministry of Culture, in charge of national and international music and dance competitions. In 1983, Chinese contestants made overwhelming results at the Mehuhin International Violin Competition. Among the 12 prizewinners in both the youth and junior categories, half of them were from China, and all in top ranks! Such unprecedented result made a real sensation in the British press. Later, Sir Yehudi Menuhin proposed to China that there should be international violin competitions for the youth in China. Finally, with his great help and support, and partly as result of the role I played in the Ministry of Culture, the first ever International Music Competition was organized in China with Sir Yehudi Menuhin as Artistic Advisor. Prof. Lin was at the time jury member in many major international competitions, and his teaching achievements won such high appraisal both at home and abroad that he was praised as “great violin educator”. Due to his powerful influence and support, the first China International Violin Competition turned out to be a great success.
The Modern and Contemporary Chinese
Music History Research in the 30 Years Since the Beginning of Reforms and Opening Up
The 30 years of modern and contemporary Chinese music history research since the beginning of the reforms and opening up can be best summarized in the following three aspects:
First of all, the modern and contemporary Chinese music history research in the 30 years since the reforms and opening up is characterized by the highly open-minded views, original perspectives and various research methods of the historians, who deal with music works and incidents in the history of modern and contemporary Chinese music as well as various music phenomena and issues in specific historical backgrounds and specific contexts in a realistic, objective and dialectical outlook while getting rid of the extreme leftism, and made remarkable achievements.
Secondly, the research in the field features active but not radical academic thoughts, academic exchanges and dialogues with equality and mutual respect, and diversified approached to probe issues. The researchers could find things in common through disputes, and could not only contend with and criticize each other, but also complement and learn from each other. The discipline of modern and contemporary Chinese music history has been established with considerably rich experience in training Ph.D., masters and bachelors in this major.
4.英文短篇哲理文章 篇四
宁静的早晨。
Sing a long song with my toddlers in the car.
与我的小宝贝在车里唱一首悠长的.歌。
Sunset and a beer with my wife.
夕阳，啤酒，爱人。
Runner’s high on a long run.
长跑后的酣畅淋漓。
Cuddling up and watching a DVD with the wife and kids.
蜷在沙发上，与妻子孩子一起看碟。
Walking outside with my son after it rains.
和我的儿子在雨中散步。
My “life” talks with my eldest daughter in the car.
在车里与我的大女儿谈论我的“人生”。
Writing a post for 50,000 people, in my pajamas.
穿着睡裤，写一篇文章，读者50, 000人。
Feeling sick and lying in bed all day without having to call my boss.
感觉不舒服，躺在床上一整天，不用给老板打电话。
Showing my 2-year-old the clear starry sky.
带我那两岁的孩子看布满星星的夜空。
Cheering my kids on in their soccer games.
为孩子们的足球赛加油喝彩。
Time alone with a good book.
独自一人，读一本好书。
Freshly brewed coffee.
喝一杯煮好的咖啡，精神饱满。
My hot veggie soup on a cold day.
寒冷冬日的一碗热蔬菜汤。
Writing before the sun rises.
在太阳升起前写作。
Fresh, cold berries.
新鲜，冰镇的浆果。
A long conversation with a friend.
和好友的一次促膝长谈。
Succumbing to a mid-afternoon nap.
午后禁不住打个小盹。
Playing kickball in the yard with my kids.
和我的孩子在花园里踢球。
The feeling of satisfaction after a workout.
经历考验后的满足感。
Waking up to a clean, uncluttered living room.
醒来发现躺在整洁的卧室里。
Laughing at my 4-year-old son’s wacky sense of humor.
对我四岁儿子独特的幽默感哈哈大笑。
Screaming my head off when my son scores a goal.
为我儿子的进球得分尖叫。
Collapsing after finishing a marathon, exhausted but in love with life.
在跑完马拉松后瘫倒在地，精疲力竭但挚爱着生活。
Spending time with my mom and sisters on a Saturday afternoon, baking sweets.
周六的午后与母亲和姐妹一起度过，烘培甜点。
Letting a warm chocolate chip cookie melt in my mouth with my eyes closed.
闭上眼睛，享受软软的巧克力曲奇在口中融化的感觉。
A long hot shower.
洗一个热水澡。
Walking with the sand between my toes as the sun goes down.
踩在沙滩上，感受沙子在脚趾间的触感，欣赏落日。
Listening to the sound of waves lapping a white sand beach.
听着海浪拍打白色沙滩的声音。
A hug when I need it.
在我需要时,给我一个拥抱。
Dew on the grass in the morning.
5.文章数字认证中英文 篇五
数字证书是一种数据文件，用来确定人们的身份和Internet上的电子资产。数字证书可以实现安全而加密的联机通信，并经常用来保护联机事务处理。
定义
随着电子交易的盛行，越来越需要第三方以数字证书的形式进行认证和授权。数字证书由被称为认证机构的可信任的第三方进行签发。认证机构对证书持有者的身份进行确认，并在证书上“签字”，来证明书该证书未曾被伪造或改变。
当某证书被认证机构进行数字化签名后，该证书的持有者就将其作为电子通行证来证明他的身份。持有者可以向要求安全访问的站点、网络或个人出示证书。
证书中的识别信息包括持有者的姓名、电子邮件地址、认机构的名称、序列号，以及证书的生效日期和失效日期。当用户的身份由认证机构确认后，证书就使用持有者的公钥来保护数据。
Web服务器也可以用使用公钥的证书来向用户的浏览器确认站点的真实性。当用户向某一个Web服务器发送机密信息，例如联机事务处理所需要的信用卡号，浏览器就会从服务器的数字证书中取出公钥来确认该服务器的身份。
公钥加密
公钥是公钥加密所使用的一对密钥中的一个，是数字认证的基础。
公钥加密利用一对公钥和私钥来进行加密和解密。这两种密钥都有数值，将该数值用于某种算法中，可将信息置乱，并只有拥有相应解密密钥的用户才能看懂信息。
一个人的公钥被其他人用来对只发给那个人的信息进行加密。当他收到信息时，就使用不被别人所知的相应密钥来对数据进行解密。一个人的公钥可以被分发给其他人，而不使私钥的保密性受到破坏。
数字证书采用公钥体制，即利用一对互相匹配的密钥进行加密、解密。每个用户自己设定一把特定的仅为本人所知的私有密钥（私钥），用它进行解密和签名；同时设定一把公共密钥（公钥）并由本人公开，为一组用户所共享，用于加密和验证签名。当发送一份保密文件时，发送方使用接收方的公钥对数据加密，而接收方则使用自己的私钥解密，这样信息就可以安全无误地到达目的地了。通过数字的手段保证加密过程是一个不可逆过程，即只有用私有密钥才能解密。在公开密钥密码体制中，常用的一种是RSA体制。其数学原理是将一个大数分解成两个质数的乘积，加密和解密用的是两个不同的密钥。即使已知明文、密文和加密密钥（公开密钥），想要推导出解密密钥（私密密钥），在计算上是不可能的。按现在的计算机技术水平，要破解目前采用的1024位RSA密钥，需要上千年的计算时间。公开密钥技术解决了密钥发布的管理问题，商户可以公开其公开密钥，而保留其私有密钥。购物者可以用人人皆知的公开密钥对发送的信息进行加密，安全地传送给商户，然后由商户用自己的私有密钥进行解密。
使用数字证书的Web服务器可以利用私钥，来确保只有它能对由Internet发给它的机密信息进行解密。Web服务器的证书是由自签的CA证书来确认，这种CA证书对发证机构进行标识。包括Microsoft Internet Explorer和Netscape Navigator在内的大多数主要的Web浏览器中，都提前安装了CA证书。
当某一Web服务器向浏览器出示时，CA证书就向用户表明该服务器证书是否可以信任。如果Web服务证书的有效性得到确认，对于采用SSL技术的服务器，该证书的公钥就可用于保护信息。
SSL安全协议使用数字证书为需求私下交流的双方创造一种安全的“通道”。在大多数主要的Web浏览器和商业Web服务器上都使用了SSL技术。
Digital Certificates
Digital certificates are data files used to establish the identity of people and electroic assets on the Internet.They for secure, encrypted online communication and are often used to protect online transactions.Definition
As electronic transactions proliferate, there’s an increasing need for third-party verification and authentication in the form of digital certificates.Digital certificates are issued by a trusted third party known as a certification authority.The CA validates the identiy of a certificate holder and “signs” the certificate to attest that it hasn’t been forged or altered.When a certificate is digitally signed by a CA ,its owner can use it as an electronic passport to prove his identity.It can be presented to Web sites, networks or individuals that require secure access.Identifying information embedded in the certificate includes the holder’s name and e-mail address, the name of the CA，a serial number and any activation or expiration data for the certificate.When a user’s identity is verified by the CA, the certificate uses the holder’s public key to protect data.Public keys are also employed by certificates that a Web server uses to confirm the authenticity of a Website for a user’s browser.When a user wants to send confidential information to a Web server, such as a credit-card number for an online transaction ,the browser will access the public key in the server’s digital certificate to verify its identity.Public-Key Cryptography
6.机械专业英语文章中英文对照 篇六
NUMERICAL CONTROL
Numerical control(N/C)is a form of programmable automation in which the processing equipment is controlled by means of numbers, letters, and other symbols, The numbers, letters, and symbols are coded in an appropriate format to define a program of instructions for a particular work part or job.When the job changes, the program of instructions is changed.The capability to change the program is what makes N/C suitable for low-and medium-volume production.It is much easier to write programs than to make major alterations of the processing equipment.There are two basic types of numerically controlled machine tools：point—to—point and continuous—path(also called contouring).Point—to—point machines use unsynchronized motors, with the result that the position of the machining head Can be assured only upon completion of a movement, or while only one motor is running.Machines of this type are principally used for straight—line cuts or for drilling or boring.The N/C system consists of the following components：data input, the tape reader with the control unit, feedback devices, and the metal—cutting machine tool or other type of N/C equipment.Data input, also called “man—to—control link”, may be provided to the machine tool manually, or entirely by automatic means.Manual methods when used as the sole source of input data are restricted to a relatively small number of inputs.Examples of manually operated devices are keyboard dials, pushbuttons, switches, or thumbwheel selectors.These are located on a console near the machine.Dials ale analog devices usually connected to a syn-chro-type resolver or potentiometer.In most cases, pushbuttons, switches, and other similar types of selectors are digital input devices.Manual input requires that the operator set the controls for each operation.It is a slow and tedious process and is seldom justified except in elementary machining applications or in special cases.In practically all cases, information is automatically supplied to the control unit and the machine tool by cards, punched tapes, or by magnetic tape.Eight—channel punched paper tape is the most commonly used form of data input for conventional N/C systems.The coded instructions on the tape consist of sections of punched holes called blocks.Each block represents a machine function, a machining operation, or a combination of the two.The entire N/C program on a tape is made up of an accumulation of these successive data blocks.Programs resulting in long tapes all wound on reels like motion-picture film.Programs on relatively short tapes may be continuously repeated by joining the two ends of the tape to form a loop.Once installed, the tape is used again and again without further handling.In this case, the operator simply loads and1
unloads the parts.Punched tapes ale prepared on type writers with special tape—punching attachments or in tape punching units connected directly to a computer system.Tape production is rarely error-free.Errors may be initially caused by the part programmer, in card punching or compilation, or as a result of physical damage to the tape during handling, etc.Several trial runs are often necessary to remove all errors and produce an acceptable working tape.While the data on the tape is fed automatically, the actual programming steps ale done manually.Before the coded tape may be prepared, the programmer, often working with a planner or a process engineer, must select the appropriate N/C machine tool, determine the kind of material to be machined, calculate the speeds and feeds, and decide upon the type of tooling needed.The dimensions on the part print are closely examined to determine a suitable zero reference point from which to start the program.A program manuscript is then written which gives coded numerical instructions describing the sequence of operations that the machine tool is required to follow to cut the part to the drawing specifications.The control unit receives and stores all coded data until a complete block of information has been accumulated.It then interprets the coded instruction and directs the machine tool through the required motions.The function of the control unit may be better understood by comparing it to the action of a dial telephone, where, as each digit is dialed, it is stored.When the entire number has been dialed, the equipment becomes activated and the call is completed.Silicon photo diodes, located in the tape reader head on the control unit, detect light as it passes through the holes in the moving tape.The light beams are converted to electrical energy, which is amplified to further strengthen the signal.The signals are then sent to registers in the control unit, where actuation signals are relayed to the machine tool drives.Some photoelectric devices are capable of reading at rates up to 1000 characters per second.High reading rates are necessary to maintain continuous machine—tool motion；otherwise dwell marks may be generated by the cutter on the part during contouring operations.The reading device must be capable of reading data blocks at a rate faster than the control system can process the data.A feedback device is a safeguard used on some N/C installations to constantly compensate for errors between the commanded position and the actual location of the moving slides of the machine tool.An N/C machine equipped with this kind of a direct feedback checking device has what is known as a closed-loop system.Positioning control is accomplished by a sensor which, during the actual operation, records the position of the slides and relays this information back to the control unit.Signals thus received ale compared to input signals on the tape, and any discrepancy between them is automatically rectified.In an alternative system, called an open—loop system, the machine is positioned solely by stepping motor drives in response to commands by a controllers.There is one basic type of NC motions.Point-to-point or Positional Control In point-to-point control the machine tool elements(tools, table, etc.)are moved to programmed locations and the machining operations performed
after the motions are completed.The path or speed of movement between locations is unimportant;only the coordinates of the end points of the motions are accurately controlled.This type of control is suitable for drill presses and some boring machines, where drilling, tapping, or boring operations must be performed at various locations on the work piece.Straight-Line or Linear Control Straight-Line control systems are able to move the cutting tool parallel to one of the major axes of the machine tool at a controlled rate suitable for machining.It is normally only possible to move in one direction at a time, so angular cuts on the work piece are not possible, consequently, for milling machines, only rectangular configurations can be machined or for lathes only surfaces parallel or perpendicular to the spindle axis can be machined.This type of controlled motion is often referred to as linear control or a half-axis of control.Machines with this form of control are also capable of point-to-point control.The original N/C used the closed—loop system.Of the two systems, closed and open loop, closed loop is more accurate and, as a consequence, is generally more expensive.Initially, open—loop systems were used almost entirely for light-duty applications because of inherent power limitations previously associated with conventional electric stepping motors.Recent advances in the development of electro hydraulic stepping motors have led to increasingly heavier machine load applications.中文译文
数控技术
数控是可编程自动化技术的一种形式,通过数字、字母和其他符号来控制加工设备。数字、字母和符号用适当的格式编码为一个特定工件定义指令程序。当工件改变时,指令程序就改变。这种改变程序的能力使数控适合于中、小批量生产,写一段新程序远比对加工设备做大的改动容易得多。
数控机床有两种基本形式：点位控制和连续控制(也称为轮廓控制)。点位控制机床采用异步电动机,因此,主轴的定位只能通过完成一个运动或一个电动机的转动来实现。这种机床主要用于直线切削或钻孔、镗孔等场合。
数控系统由下列组件组成：数据输入装置,带控制单元的磁带阅读机,反馈装置和切削机床或其他形式的数控设备。
数据输人装置,也称“人机联系装置”,可用人工或全自动方法向机床提供数据。人工方法作为输人数据唯一方法时,只限于少量输入。人工输入装置有键盘,拨号盘,按钮,开关或拨轮选择开关,这些都位于机床附近的一个控制台上。拨号盘通常连到一个同步解析器或电位计的模拟装置上。在大多数情况下,按钮、开关和其他类似的旋钮是数据输入元件。人工输入需要操作者控制每个操作,这是一个既慢又单调的过程,除了简单加工场合或特殊情况,已很少使用。
几乎所有情况下,信息都是通过卡片、穿孔纸带或磁带自动提供给控制单元。在传统的数控系统中,八信道穿孔纸带是最常用的数据输入形式,纸带上的编码指令由一系列称为程序块的穿孔组成。每一个程序块代表一种加工功能、一种操作或两者的组合。纸带上的整个数控程序由这些连续数据单元连接而成。带有程序的长带子像电影胶片一样绕在盘子上,相对较短的带子上的程序可通过将纸带两端连接形成一个循环而连续不断地重复使用。带子一旦安装好,就可反复使用而无需进一步处理。此时,操作者只是简单地上、下工件。穿孔纸带是在带有特制穿孔附件的打字机或直接连到计算机上的纸带穿孔装置上做成的。纸带制造很少不出错,错误可能由编程、卡片穿孔或编码、纸带穿孔时的物理损害等形成。通常,必须要试走几次来排除错误,才能得到一个可用的工作纸带。
虽然纸带上的数据是自动进给的,但实际编程却是手工完成的,在编码纸带做好前,编程者经常要和一个计划人员或工艺工程师一起工作,选择合适的数控机床,决定加工材料,计算切削速度和进给速度,决定所需刀具类型,仔细阅读零件图上尺寸,定下合适的程序开始的零参考点,然后写出程序清单,其上记载有描述加工顺序的编码数控指令,机床按顺序加工工件到图样要求。
控制单元接受和储存编码数据,直至形成一个完整的信息程序块,然后解释数控指令,并引导机床得到所需运动。
为更好理解控制单元的作用,可将它与拨号电话进行比较,即每拨一个数字,就储存一个,当整个数字拨好后,电话就被激活,也就完成了呼叫。
装在控制单元里的纸带阅读机,通过其内的硅光二极管,检测到穿过移动纸带上的孔漏
过的光线,将光束转变成电能,并通过放大来进一步加强信号,然后将信号送到控制单元里的寄存器,由它将动作信号传到机床驱动装置。
有些光电装置能以高达每秒1000个字节的速度阅读,这对保持机床连续动作是必须的,否则,在轮廓加工时,刀具可能在工件上产生划痕。阅读装置必须要能以比控制系统处理数据更快的速度来阅读数据程序块。
反馈装置是用在一些数控设备上的安全装置,它可连续补偿控制位置与机床运动滑台的实际位置之间的误差。装有这种直接反馈检查装置的数控机床有一个闭环系统装置。位置控制通过传感器实现,在实际工作时,记录下滑台的位置,并将这些信息送回控制单元。接受到的信号与纸带输入的信号相比较,它们之间的任何偏差都可得到纠正。
在另一个称为开环的系统中,机床仅由响应控制器命令的步进电动机驱动定位,工件的精度几乎完全取决于丝杠的精度和机床结构的刚度。有几个理由可以说明步进电机是一个自动化申请的非常有用的驱动装置。对于一件事物,它被不连续直流电压脉冲驱使,是来自数传计算机和其他的自动化的非常方便的输出控制系统。当多数是索引或其他的自动化申请所必备者的时候,步进电机对运行一个精确的有角进步也是理想的。因为控制系统不需要监听就提供特定的输出指令而且期待系统适当地反应的公开-环操作造成一个回应环,步进电机是理想的。一些工业的机械手使用高抬腿运步的马乘汽车驾驶员,而且步进电机是有用的在数字受约束的工作母机中。这些申请的大部分是公开-环 ,但是雇用回应环检测受到驱策的成份位置是可能的。环的一个分析者把真实的位置与需要的位置作比较,而且不同是考虑过的错误。那然后驾驶员能发行对步进电机的电脉冲,直到错误被减少对准零位。在这个系统中,没有信息反馈到控制单元的自矫正过程。出现误动作时,控制单元继续发出电脉冲。比如,一台数控铣床的工作台突然过载,阻力矩超过电机转矩时,将没有响应信号送回到控制器。因为,步进电机对载荷变化不敏感,所以许多数控系统设计允许电机停转。然而,尽管有可能损坏机床结构或机械传动系统,也有使用带有特高转矩步进电机的其他系统,此时,电动机有足够能力来应付系统中任何偶然事故。
7.英文简易文章 篇七
If time could be turned back
If time could be turned back, I would not waste so much time doing something just to pretend to be a good student.Back to myprimary school, we were always asked to copy the texts for so many times, it is so meaningless and boring, but every time I would complete it carefully even when I had the confidence to know every word in the texts and could recite it fluently.“What if the teacher thought me a bad student if I could not accomplish my homework?”
That` s what I thought then.What a foolish I am!If time could be turned back, I would just play games with my friends.Being “the children` s king “is surely better than a stupid student and I would be healthier now.Or I would just read some books I like instead of copying.It is shameful that I am far from learned now.And I would just tell the teacher my copying homework is undone becauseI could recite the whole texts.Then I entered my middle school and high school.There were so many subjects and I was so eager to be the NO·1，thus most of my time was spent on studying.And when I did have time to relax myself, I was so worried that I would fall behind because everyone else was still studying.So Iquitted my spare time and pushed a lot of my interests aside.Iwanted to play violin, but I still cannot now;I wanted to travel around the world, but the most distant way I travelled by far is the way from my hometown to my college.If time could be turned back, Iwould not be so anxious about what others were doing.I would concentrate on my study when it was the time for studying and truly enjoy my spare time doing something I like without thinking about studying.When you have a strong desire to do something and you push it aside, then you may never do it again, leaving endless regrets.Now I am a sophomore, I have learned a lot since entering the college and become mature.However while thinkingabout my freshman year, I felt that I lost something.I found myself walking on the wrong way to care too much about the gradeand was hampered much by that.I was busy doing a lot of homework, writing a lot of essays, reading some novels that I totally had no interests, and they took most of my time.And sometimes I had to attend some classes that I did not like.The eager curiosities for new knowledge become less and a feel of burden on shoulders took place.I should have lots of time to think more about my future, my life, my emotion, but till now they are still vague in my heart.And I surprisingly found,to some extent,that the teaching methods in college are so much alike what we had gone through in the primary school.I found myself so passive!If time could be turned back, I would take grades lighter;I am not here to just pursue a god grade but to learn something deep-rooted in my life, to receive new thoughts, to think more.If I were hampered now, maybe I could never fly freely in the sky.I would read more, think more and say“no” to something more.What is past is past, we must face the truth that time can never be turned back.The best way to say less “If time could be turned back” is to cherish the moment, to think more and judge more.人家学我也要学，不然落后