2014年电大机电控制与可编程序控制器技术课程作业2.doc

专业好文档机电控制与可编程序控制器技术课程作业（二）1.简述机电设备电器控制线路的基本设计步骤。2.在选择机电设备拖动用的电动机时，应主要考虑哪些内容？3 试问下列控制线路是否合理（注：图中km1、km2为交流接触器，ya为直流电磁铁）？若不合理，应怎样改正？4现有三台电动机m1、m2、m3要求起动顺序为：先起动m3，经10s后起动m2，再经20s后起动m1。而停车时要求：首先停m1，经20s后停m2，再经10s后停m3。试设计该三电动机的起、停控制线路。 5设计一条由两台电动机拖动的装配车间的一输送机控制线路，应满足下列要求： （1）m1电动机与m2电动机均单向运转； （2）m1电动机起动工作后，m2电动机才能起动工作； （3）m2电动机先停机，而后m1电动机才能停机； （4）m1电动机过载时，两台电动机同时停机，m2电动机过载时，仅m2电动机停机； （5）要有必要的保护环节。试画出控制电路。 6设计组合机床的两台动力头的电气控制线路。设计要求如下： （1）加工时两台动力头电动机同时起动； （2）两台动力头电动机单向运转； （3）两台动力头电动机，在加工完成后各自停机； （4）若其中一台动力头电动机过载，另一台动力头电动机也应停机。画出其控制电路。 7. plc主要特点有哪些？plc的发展趋势如何？ 8.比较plc控制和继电接触器控制、微机控制的优缺点。 9.继电接触器控制系统，plc控制有哪些相同和不同之处？ 10plc基本硬件由哪几部分组成？ 11什么叫扫描工作方式？什么叫扫描周期？它主要受哪些因数影响？ 12.为什么称plc的内部继电器为软继电器？和硬件继电器相比，软继电器的触点在使用上有何特点？ 13.plc的工作过程分为哪几个工作阶段，各完成什么任务？ 14.什么是plc的输入输出滞后现象？造成这种现象的原因是什么？可采取哪些措施缩短输入输出滞后时间？ 15.plc的性能指标主要有那些？plc是怎样分类的？winger tuivasa-sheck, who scored two tries in the kiwis 20-18 semi-final win over england, has been passed fit after a lower-leg injury, while slater has been named at full-back but is still recovering from a knee injury aggravated against usa.both sides boast 100% records heading into the encounter but australia have not conceded a try since josh charnleys effort in their first pool match against england on the opening day.aussie winger jarryd hayne is the competitions top try scorer with nine, closely followed by tuivasa-sheck with eight.but it is recently named rugby league international federation player of the year sonny bill williams who has attracted the most interest in the tournament so far.the kiwi - with a tournament high 17 offloads - has the chance of becoming the first player to win the world cup in both rugby league and rugby union after triumphing with the all blacks in 2011.id give every award back in a heartbeat just to get across the line this weekend, said williams.the (lack of) air up there watch mcayman islands-based webb, the head of fifas anti-racism taskforce, is in london for the football associations 150th anniversary celebrations and will attend citys premier league match at chelsea on sunday.i am going to be at the match tomorrow and i have asked to meet yaya toure, he told bbc sport.for me its about how he felt and i would like to speak to him first to find out what his experience was.uefa hasopened disciplinary proceedings against cskafor the racist behaviour of their fans duringcitys 2-1 win.michel platini, president of european footballs governing body, has also ordered an immediate investigation into the referees actions.cska said they were surprised and disappointed by toures complaint. in a statement the russian side added: we found no racist insults from fans of cska. baumgartner the disappointing news: mission aborted.the supersonic descent could happen as early as sunda.the weather plays an important role in this mission. starting at the ground, conditions have to be very calm - winds less than 2 mph, with no precipitation or humidity and limited cloud cover. the balloon, with capsule attached, will move through the lower level of the atmosphere (the troposphere) where our day-to-day weather lives. it will climb higher than the tip of mount everest (5.5 miles/8.85 kilometers), drifting even higher than the cruising altitude of commercial airliners (5.6 miles/9.17 kilometers) and into the stratosphere. as he crosses the boundary layer (called the tropopause),e can expect a lot of turbulence.the balloon will slowly drift to the edge of space at 120,000 feet ( then, i would assume, he will slowly step out onto something resembling an olympic diving platform.they blew it in 2008 when they got caught cold in the final and they will not make the same mistake against the kiwis in manchester.five years ago they cruised through to the final and so far history has repeated itself here - the last try they conceded was scored by englands josh charnley in the opening game of the tournament.that could be classed as a weakness, a team under-cooked - but i have been impressed by the kangaroos focus in their games since then.they have been concentrating on the sort of stuff that wins you tough, even contests - strong defence, especially on their own goal-line, completing sets and a good kick-chase. theyve been great at all the unglamorous stuff that often goes unnoticed in the stands but not by your team-mates.it is as though their entire tournament has been preparation for the final.in johnathan thurston, cooper cronk, cameron smith and either billy slater or greg inglis at full-back they have a spine that is unmatched in rugby league. they have played in so many high-pressure games - a priceless asset going into saturday.the kiwis are a lot l