X62W万能铣床电控系统的改造与设计外文资料翻译.doc

淮 阴 工 学 院 毕业设计(论文)外文资料翻译 学 院： 机械工程学院 专 业： 机械设计制造及其自动化（数控方向） 姓 名： 周立勇 学 号： 1071104227 外文出处： Modern Control Engineering .Prentice Hall (用外文写) 附 件： 1.外文资料翻译译文；2.外文原文。 指导教师评语： 年 月 日 签名： （手写签名） 原文： Introductions to PLC and Intelligent Control Katsuhiko Ogata A PLC (i.e. Programmable Logic Controller) is a device that was invented to replace the necessary sequential relay circuits for machine control. The PLC works by looking at its inputs and depending upon their state, turning on/off its outputs. The user enters a program, usually via software or programmer that gives the desired results. PLC is used in many “real world” applications. If there is industry present, chances are good that there is a PLC present. If you are involved in machining, packaging, material handling, automated assembly or countless other industries, you are probably already using them. If you are not, you are wasting money and time. Almost any application that needs some type of electrical control has a need for a PLC. For example, let’s assume that when a switch turns on we want to turn a solenoid on for 5 seconds and then turn it off regardless of how long the switch is on for. We can do this with a simple external timer. But what if the process included 10 switches and solenoids? We would need 10 external timers. What if the process also needed to count how many times the switch individually turned on? We need a lot of external counters. As you can see, the bigger the process the more of a need we have for a PLC. We can simply program the PLC to count its inputs and turn the solenoids on for the specified time. We will take a look at what is considered to be the “top 20” PLC instructions. It can be safely estimated that with a firm understanding of these instructions one can solve more than 80% of the applications in existence. That’s right, more than 80%! Of course we’ll learn more than just these instructi