Uni证I lights,valves and many other devics.Both function repond to a custom,us pro ()rrts. and are typically Reduced Instruction Set (RISC) based.They are designed for real-time use.and often must withstand harsh environments on the shop floor.The programmable logic controller circuitry monitors the status of multiple snsor inputs.which control output actuators. which may be things like motor starters,solenoids,lights and displays.or valves. Most PLCs are programmed in a special language called Ladder Logi Ladder Logic ally a Bo olean logic-solving prograr m with a graphica to look ke an clementar ing diag A m rn prog to Basic or C.Typically on in a and then controller directly through a cable connection.The program is stored in the programmable logic controller in non-volatile memory. Words and Expressions ，计时器，定时器 hydnanmEtc[dhaitonrtik 油压[麦压]白动式的 互 gnate ['pet 以指花指出，任 GM 美通用汽车公 port [poa]
Unit 2 ■ CNC Machining you to control the motion of tools and computer programs that use numeric data.CNC machining can be used with nearly any traditional machine. CNC machining starts with a piece of metal,sometimes called a"billet". (Billet:pretentious word for"lump of metal".used by machinests and e oe naimorng only copu and motors on the control knobs installed.This is bsically iust a robot machinist.Youuse a rotating cutting tool to cut away all the metal that isn't your crank.3D metal etch-a-sketch.with the computer interpolating so the circles comeout looking pretty smooth. The down-side of CNC machinins There are a coupl of issucs.First,it wastes a lot of metal.The stuff removed is juist metal shvings,and can only be sold for scrp.By comparion. almost all of the metal. xoept for a little bit of "flash"that sccps int the k between the tooand the di.Thep can be tme melting things This is cially important for ing tool. severely weakened if you get it too hot,never mind near to melting).prt
Uni证2 that is“'sprawling”likc ed to th nd m technolooy that can measure to0 005 mm (o000 1")while covered in ail. CNC machine has a minimum of 6 motors (including some to change tools.and one or more to pump oil and coolant various places).This translates to running costs that may be well over $l/minute.(The computer is not a significant part of the cost any more.) it docsn't have the tightly comers that hav that crack Advantages of CNC machining omer it would cut rather than uush the metal into nlac CNC machinine doesn't impose sch restrictions,though to get nicely radiused corners.you might have to change tools.to make the last rass.(vou use a flat tool to get rid of the bulk of the mctal over the flat arcas,and se a round nosed tool to form the inside radius where needed.Soeliminating stress risers means more expensive machining time. Words and Expressions tik[saa.通用的，万能的|mmer在[nmmk]d.数字的 5
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Unit3 Unit 3 What is PID Control？ PID can be describd as a sct rules with which precise regulation of -loop control system is obta d.Closed loop control means a method i e me ement of the proc re tha red as the SETPOINT.The hbest way of a In its basic form.PID involyes three mathematical control functions working toeether.Pronortional-Inteeral-Derivative.The most important of these,Proportional Control,determines the magnitude of the difference between the SETPOINT and the PROCESS VARIABLE (known as ERROR). and then applies appropriate proportionl changes to the CONTROL VARIABLE to eliminate ERROR.Many control systems will.in fact,work quite well with ony Proportionl Control.Integral Control examines the offset of SETPOINT and the PROCESS VARIABLE over time and corrects it whe PROCES quently makes changes to the OUTPU A lal changes the ions is govemed by a uer- and. pre PID Tuning.although considered"black magic"by many.really is,of