简述误差补偿系统的组成及各组成部分的作用。
参考答案：
1）误差信号的检测
它是误差补偿控制的前提和基础，由误差检测系统来完成。误差信号检测的可行性和正确性直接影响误差补偿的成功与否。
2）误差信号的处理
由误差检测系统所测得的识差信号，其中必然包含着某些频率的噪声干扰信号。也会有几种误差信号混合在一起，这就需要进行一些处理，分离不需要的信号，提取所需要的误差信号，并能够满足误差补偿的要求。误差信号处职的关键是要有足够的处
3）误差信号的建模
建模就是要找出工件加工误差与在补偿作用点上补偿控制量之间的关系。
4）补偿控制
根据所建立的误差模型，并根据实际加工过程，用计算机计算欲补偿的误差值，输出补偿控制量。对于数控系统，补偿控制量就是正负脉冲数。
5）补偿执行机构
它是具体执行补偿动作的，设置在补偿点上。由于补偿是一个高速动态过程.要求位移精度和分辨率高，频响范围宽，结构刚度好，因此补偿执行机构多用微进机构来完成。
| It looks unlikely that medical science will abolish the process of ageing. But it no longer looks impossible. "In the long run," as John Maynard Keynes observed, "we are all dead." True. But can the short run be elongatedin a way that makes the long run longer And if so, how, and at what cost People have dreamt of immorality since ancient times. Now, with the growth of biological knowledge that has marked the past few decades, a few researchers believe it might be within reach. To think about the question, it is important to understand why organisms — people included —age in the first place. People are like machines, they wear out. That much is obvious. However, a machine can always be repaired. A good mechanic with a stock of spare parts can keep it going indefinitely. Eventually, no part of the original may remain, but it still carries on, like Lincoln’s famous axe that had three new handles and two new blades. The question, of course, is whether the machine is worth repairing. It is here that people and nature disagree. Or, to put it slightly differently, two bits of nature disagree with each other. From the individual’s point of view, survival is an imperative. A fear of death is a sensible evolved response and, since ageing is a sure way of dying, it is no surprise that people want to stop it in its tracks. Moreover, even the appearance of ageing can be harmful. It reduces the range of potential sexual partners who find you attractive and thus, again, curbs your reproduction. The paradox is that the individual’s evolved desire not to age is opposed by another evolutionary force, the disposable soma. The soma is all of a body’s cells apart from the sex cells. The soma’s role is to get those sex cells, and thus the organism’s genes, into the next generation. If the soma is a chicken, then it really is just an egg’s way of making another egg. And if evolutionary logic requires the soma to age and die in order for this to happen, so be it. Which is a pity, for evolutionary logic does, indeed, seem to require that. The argument is this. All organisms are going to die of something eventually. That something may be an accident, a fight, a disease or an encounter with a hungry predator. There is thus a premium on reproducing early rather than conserving resources for a future that may never come. The reason why repairs are not perfect is that they are costly and resources invested in them might be used for reproduction instead. Often, therefore, the body’s mechanics prefer lash-ups to complete rebuilds — or simply do not bother with the job at all. And if that is so, the place to start looking for longer life is in the repair shop. |
For whom does the author probably write this passage
A．( General readers
B．( Health service workers
C．( Medical scientists
D．( Elderly people