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C)is a of in is by of in an to a of a or of is to is C It is to to of of to of an be of a or is of or or C of or C be to or by as of to a of of or on a to a or In of It is a is in or in In is to by or by is of C on of of a a or a of C on a is up of an of in on on be by of to a is In on or in to a is be by in or or as a of to to an on is be a or a C of to be of on to a to A is of is to to to a of It of be by it to of a as is it is is in on as it in to is to to to of at up 000 to be by on be of at a A is a on C to of of C of a is as a is by a of to to on is In an an is by in to by a C as In to or of is of of of is or be at on to to of of at a It is to in at a so on be or or to be of is to as or a of of of In of or of so of be In be at a It is of in to of of to of is to as or a of C to as a of , Y, Z A or of of to or to of C an of is of . A is of of to is is to in , Y in to be at an be a 2CL C L . a in , Y, Z be be a or a 3c C of of of is no or of to In of an to of on a N C to no be to to C to to in in of of to or to In in of C Of is as a is of in of to is a in is by of of as it is to a in a to of In is to In a is so is is in a in is as a It of a on In or of it is of a in A is a an of of be of 1 In a is by in of is of of be by of to of is 2 In is at to is of of of on of of is by of a of 161 on is on be in by 16in up of in is in as As 16 2， of is in In up is at in a to it to of in of in a to so be In of on of In to at to of in be if is to be It be on of as in a at of is to up is of is to to be is or a of is of at of a as to an be is to on as 1 on by a of be or 2 In or of is an of as of by of of of is to of a so be on an or be in in a to of a or or on of is or in a at a a of is to or of be or in or on an to in an of to to as a to by to on on a in 32 16 to of 数控技术 数控是可编程自动化技术的一种形式，通过数字、字母和其他符号来控制加工设备。数字、字母和符号用适当的格式编码为一个特定工件定义指令程序。当工件改变时，指令程序就改变。这种改变程序的能力使数控适合于中、小批量生产，写一段新程序远比对加工设备做大的改动容易得多。 数控机床有两种基本形式：点位控制和连续控制 (也称为轮廓控制 )。点位控制机床采用异步电动机，因此，主轴的定位只能通过完成一个运动或一个电动机的转动 来实现。这种机床主要用于直线切削或钻 孔 、镗孔等场合。 数控系统由下列组件组成：数据输入装置，带控制单元的磁带阅读机，反馈装置和切削机床或其他形式的数控设备。 数据输人装置，也称“人机联系装置”，可用人工或全自动方法向机床提供数据。人工方法作为输人数据唯一方法时，只限于少量输入。人工输入装置有键盘，拨号盘，按钮，开关或拨轮选择开关，这些都位于机床附近的一个控制台上。拨号盘通常连到一个同步解析器或电位计的模拟装置上。在大多数情况下，按钮、开关和其他类似的旋钮是数据输入元件。人工输入需要操作者控制 每个操作，这是一个既慢又单调的过程，除了简单加工场合或特殊情况，已很少使用。 几乎所有情况下，信息都是通过卡片、穿孔纸带或磁带自动提供给控制单元。在传统的数控系统中，八信道穿孔纸带是最常用的数据输入形式，纸带上的编码指令由一系列称为程序块的穿 孔 组成。每一个程序块代表一种加工功能、一种操作或两者的组合。纸带上的整个数控程序由这些连续数据单元连接而成。带有程序的长带子像电影胶片一样绕在盘子上，相对较短的带子上的程序可通过将纸带两端连接形成一个循环而连续不断地重复使用。带子一旦安装好，就可反复使用而无需进 一步处理。此时，操作者只是简单地上、下工件。穿孔纸带是在带有特制穿孔附件的打字机或直接连到计算机上的纸带穿 孔 装置上做成的。纸带制造很少不出错，错误可能由编程、卡片穿孔或编码、纸带穿孔时的物理损害等形成。通常，必须要试走几次来排除错误，才能得到一个可用的工作纸带。 虽然纸带上的数据是自动进给的，但实际编程却是手工完成的，在编码纸带做好前，编程者经常要和一个计划人员或工艺工程师一起工作，选择合适的数控机床，决定加工材料，计算切削速度和进给速度，决定所需刀具类型，仔细阅读零件图上尺寸，定下合适的程序开始的 零参考点，然后写出程序清单，其上记载有描述加工顺序的编码数控指令，机床按顺序加工工件到图样要求。 控制单元接受和储存编码数据，直至形成一个完整的信息程序块，然后解释数控指令，并引导机床得到所需运动。 为更好理解控制单元的作用，可将它与拨号电话进行比较，即每拨一个数字，就储存一个，当整个数字拨好后，电话就被激活，也就完成了呼叫。 装在控制单元里的纸带阅读机，通过其内的硅光二极管，检测到穿过移动纸带上的孔漏过的光线，将光束转变成电能，并通过放大来进一步加强信号，然后将信号送到控制单元里 的寄存器，由它将动作信号传到机床驱动装置。 有些光电装置能以高达每秒 1000 个字节的速度阅读，这对保持机床连续动作是必须的，否则，在轮廓加工时，刀具可能在工件上产生划痕。阅读装置必须要能以比控制系统处理数据更快的速度来阅读数据程序块。 反馈装置是用在一些数控设备上的安全装置，它可连续补偿控制位置与机床运动滑台的实际位置之间的误差。装有这种直接反馈检查装置的数控机床有一个闭环系统装置。位置控制通过传感器实现，在实际工作时，记录下滑台的位置，并将这些信息送回控制单元。接受到的信号与纸带输入的信号 相比较，它们之间的任何偏差都可得到纠正。 在另一个称为开环的系统中，机床仅由响应控制器命令的步进电动机驱动定位，工件的精度几乎完全取决于丝杠的精度和机床结构的刚度。 有几个理由可以说明步进电机 是一个自动化申请的非常有用的 驱动装置 。对于一件事物，它被不连续直流电压脉 冲 驱使 ,是来自数传计算机和其他的自动化的非常方便的输出控制系统。 当多数是索引或其他的自动化申请所必备者的时候， 步进电机 对运行一个精确的有角进步也是理想的。因为控制系统不需要监听就提供特定的输出指令而且期待系统适当地反应的公开 - 环操作造成一 个回应环， 步进电机 是理想的。 一些工业的机械手使用高抬腿运步的马乘汽车驾驶员，而且 步进电机 是有用的在数字受约束的工作母机中。 这些申请的大部分是公开 - 环 ,但是雇用回应环检测受到驱策的成
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