问题 问答题 简答题

什么是开环、闭环、半闭环伺服系统数控机床?它们之间有什么区别?

答案

参考答案:

(1)开环:这类机床没有来自位置传感器的反馈信号。数控系统将零件程序处理后,输出数字指令后给伺服系统,驱动机床运动;其结构简单、较为经济、维护方便,但是速度及精度低,适于精度要求不高的中小型机床,多用于对旧机床的数控化改造。

(2)闭环:这类机床上装有位置检测装置,直接对工件的位移量进行测量;其精度高,但系统设计和调整困难、结构复杂、成本高,主要用于一些精度要求很高的镗铣床、超精密车床、超精密铣床、加工中心等。

(3)半闭环:这类数控机床采用安装在进给丝杠或电动机端头上的转角测量元件测量丝杠旋转角度,来间接获得位置反馈信息;可获得较为满意的精度和速度,大多数数控机床采用它,如数控车床、数控铣床和加工中心等。

单项选择题

Modern liberal opinion is sensitive to problems of restriction of freedom and abuse of power. (1) , many hold that a man can be injured only by violating his will, but this view is much too (2) . It fails to (3) the great dangers we shall face in the (4) of biomedical technology that stems from an excess of freedom, from the unrestrained (5) of will. In my view, our greatest problems will be voluntary self-degradation, or willing dehumanization, as is the unintended yet often inescapable consequence of sternly and successfully pursuing our humanization (6) .

Certain (7) and perfected medical technologies have already had some dehumanizing consequences. Improved methods of resuscitation have made (8) heroic effort to "save" the severely ill and injured. Yet these efforts are sometimes only partly successful: They may succeed in (9) individuals, but these individuals may have sever brain damage and be capable of only a less-than-human, vegetating (10) . Such patients have been (11) a death with dignity. Families are forced to bear the burden of a (12) "death watch".

(13) the ordinary methods of treating disease and prolonging life have changed the (14) in which men die. Fewer and fewer people die in the familiar surroundings of home or in the (15) of family and friends. This loneliness, (16) , is not confined to the dying patient in the hospital bed. As a group, the elderly are the most alienated members of our society: Not yet (17) the world of the dead, not deemed fit for the world of the living, they are shunted (18) . We have learned how to increase their years, (19) we have not learned how to help them enjoy their days. Yet we continue to bravely and feverishly push back the frontiers (20) death.

20()

A.above

B.against

C.upon

D.with

单项选择题