In practically all cases，information is automatically supplied to the control unit and the machine tool by cards，punched tapes，or by magnetic tape．Eight—channel punched paper tape is the most commonly used form of data input for conventional N／C systems．The coded instructions on the tape consist of sections of punched holes called blocks．Each block represents a machine function，a machining operation，or a combination of the two．The entire N／C program on a tape is made up of an accumulation of these successive data blocks．Programs resulting in long tapes all wound on reels like motion-picture film．Programs on relatively short tapes may be continuously repeated by joining the two ends of the tape to form a loop．Once installed，the tape is used again and again without further handling．In this case，the operator simply loads and unloads the parts．Punched tapes ale prepared on type writers with special tape—punching attachments or in tape punching units connected directly to acomputer system．Tape production is rarely error-free．Errors may be initially caused by the part programmer，in card punching or compilation，or as a result of physical damage to the tape during handling，etc．Several trial runs are often necessary to remove all errors and produce an acceptable working tape．
While the data on the tape is fed automatically，the actual programming steps ale done manually．Before the coded tape may be prepared，the programmer，often working with a planner or a process engineer, must select the appropriate N／C machine tool，determine the kind of material to be machined，calculate the speeds and feeds，and decide upon the type of tooling needed. The dimensions on the part print are closely examined to determine a suitable zero reference point from which to start the program．A program manuscript is then written which gives coded numerical instructions describing the sequence of operations that the machine tool is required to follow to cut the part to the drawing specifications．
The control unit receives and stores all coded data until a complete block of information has been accumulated．It then interprets the coded instruction and directs the machine tool through the required motions．
The function of the control unit may be better understood by comparing it to the action of a dial telephone，where，as each digit is dialed，it is stored．When the entire number has been dialed，the equipment becomes activated and the call is completed．
Silicon photo diodes，located in the tape reader head on the control unit，detect light as it passes through the holes in the moving tape．The light beams are converted
to electrical energy，which is amplified to further strengthen the signal．The signals are then sent to registers in the control unit, where actuation signals are relayed to the machine tool drives．
Some photoelectric devices are capable of reading at rates up to 1000 characters per second．High reading rates are necessary to maintain continuous machine—tool motion；otherwise dwell marks may be generated by the cutter on the part during contouring operations．The reading device must be capable of reading data blocks at a rate faster than the control system can process the data．
A feedback device is a safeguard used on some N／C installations to constantly compensate for errors between the commanded position and the actual location of the moving slides of the machine tool．An N／C machine equipped with this kind of a direct feedback checking device has what is known as a closed-loop
system．Positioning control is accomplished by a sensor which，during the actual operation，records the position of the slides and relays this information back to the control unit．Signals thus received ale compared to input signals on the tape，and any discrepancy between them is automatically rectified．
In an alternative system，called an open—loop system，the machine is positioned solely by stepping motor drives in response to commands by a controllers．There are three basic types of NC motions, as follows:
Point-to-point or Positional Control In point-to-point control the machine tool elements (tools, table, etc.) are moved to programmed locations and the machining operations performed after the motions are completed. The path or speed of
movement between locations is unimportant; only the coordinates of the end points of the motions are accurately controlled. This type of control is suitable for drill presses and some boring machines, where drilling, tapping, or boring operations must be performed at various locations on the work piece. Straight-Line or Linear Control Straight-Line control systems are able to move the cutting tool parallel to one of the major axes of the machine tool at a controlled rate suitable for machining. It is normally only possible to move in one direction at a time, so angular cuts on the work piece are not possible, consequently, for milling machines, only rectangular
configurations can be machined or for lathes only surfaces parallel or perpendicular to the spindle axis can be machined. This type of controlled motion is often referred to
as linear control or a half-axis of control. Machines with this form of control are also capable of point-to-point control.
Continuous Path or Contouring Control In continuous path control the motions of two or more of the machine axes are controlled simultaneously, so that the position and velocity of the can be tool are changed continuously. In this way curves and surfaces can be machined at a controlled feed rate. It is the function of the interpolator in the controller to determine the increments of the individual controlled axes of the machines necessary to produce the desired motion. This type of control is referred to as continuous control or a full axis of control.
Some terminology concerning controlled motions for NC machines has been introduced. For example, some machines are referred to as four-or five-or even six-axis machines. For a vertical milling machine three axes of control are fairly obvious, these being the usual X, Y, Z coordinate directions. A fourth or fifth axis of control would imply some form of rotary table to index the work piece or possibly to provide angular motion of the work head. Thus, in NC terminology an axis of control is any controlled motion of the machine elements (spindles, tables, etc). A further complication is use of the term half-axis of control; for example, many milling machines are referred to as 2.5-axis machine. This means that continuous control is possible for two motions (axes) and only linear control is possible for the third axis. Applied to vertical milling machines, 2.5axis control means contouring in the X, Y plane and linear motion only in the Z direction. With these machines
three-dimensional objects have to be machined with water lines around the surface at different heights. With an alternative terminology the same machine could be called a 2CL machine (C for continuous, L for linear control). Thus, a milling machine with continuous control in the X, Y, Z directions could be termed be a three-axis machine or a 3c machine, Similarly, lathes are usually two axis or 2C machines. The degree of work precision depends almost entirely upon the accuracy of the lead screw and the rigidity of the machine structure．With this system．there is no self-correcting action or feedback of information to the control unit．In the event of an unexpected malfunction，the control unit continues to put out pulses of electrical current．If，for example，the table on a N／C milling machine were suddenly to become overloaded，no response would be sent back to the controller．Because stepping motors are not sensitive to load variations，many N／C systems are designed to permit the motors to stall when the resisting torque exceeds the motor torque．Other systems are in use，
however，which in spite of the possibility of damage to the machine structure or to the mechanical system，ale designed with special high—torque stepping motors．In this case，the motors have sufficient capacity to“overpower’’the system in the event of almost any contingency．
The original N／C used the closed—loop system．Of the two systems，closed and open loop，closed loop is more accurate and，as a consequence，is generally more expensive．Initially，open—loop systems were used almost entirely for light-duty applications because of inherent power limitations previously associated with conventional electric stepping motors．Recent advances in the development of electro hydraulic stepping motors have led to increasingly heavier machine load applications．
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带有自动换刀方法的加工中心配置合成
本文件的目的是出席一个自动换刀加工中心配置的综合设计方法，以满足所需的拓扑结构和运动特性。根据坐标系的概念，图论，概括，专业化，和运动合成，这种设计方法，提出和电脑，并与自动换刀多达8个环节的综合加工中心。作为结果，与鼓型刀库，6，7号的加工中心配置和8链接分别是2，13和20。同样，与线性型刀库的加工中心，5，6，7人数的加工中心配置和8联系分别为1，5，20和60。此外，这项工作提供了一个综合的空间开放与拓扑结构和运动的要求类型的机制系统的方法。 导言
加工中心运动学可以被看作是一个开放型的机制，他们与特定的拓扑结构特点的特殊功能。与平面机制的创新设计相关的问题一直是过去几年许多研究课题。然而，开放式的空间结构议案类型的机制设计方法合成不可用。在过去数年，只是在加工中心结构设计的重点几篇文章。杉村等。 （1981年）使用的分析方法，调查的机床设计。伊藤和信乃（1982年，1983年和1987年）产生的使用有向图的机床结构配置。列舍托夫和波特曼（1988）提出的合成与功能相同的成型机床配置的配置代码。的配置代码的概念被广泛采用的5配置合成轴机床（石泽等，1991;坂稻崎，1992年）。但是，自动换刀系统没有考虑。该系统自动执行之间的主轴和一个加工中心刀库工具的变化被称为自动换刀（ATC）的。空管在降低机器闲置时间了重要作用，因此，增加加工过程中的生产力。的建议本文是提出一个对加工中心的自动换刀可能的配置系统的一代，是开放式的设计方法，类型空间机制受拓扑和运动约束。 现有的机制
在设计过程的第一步是研究现有的机制和缔结的拓扑结构和运动特性，加工中心机床的4个基本组成部分：一轴，刀库，转变机制的工具组成，以及机床结构包括权力轴的议案。机床结构在很大程度上决定了加工表面，刚度准确性和动态品质。主轴旋转工具机到所需的工件表面。该工具杂志存储工具和行动为他们在加工操作使用适合的岗位。该工具的变化机制执行工具之间的杂志和主轴工具的变化。最简单的ATC是一个没有变化机制的设计工具，工具之间的杂志和
主轴实现相对运动换刀的议案。图3（a）和（b）显示2 3轴鼓型和直线型工具杂志，分别卧式加工中心。代表和分析的拓扑结构和加工中心，运动特色的坐标系统的定义来描述的每一项议案轴加工中心分配为基础的国际标准化组织（ISO，1974）命名。本标准坐标系是右手直角笛卡儿之一，相关的工件安装在一台机器，与校长的线性横向这台机器相一致。对机器的一个组成部分运动产生积极的方向是，这将导致越来越工件的积极方面。追加的卧式加工中心的ISO标准的原理图如图所示。 3。通过分析提供现有的3轴没有工具，改变机制卧式加工中心，我们可以得出结论的拓扑结构和运动特性（燕，陈，1995年）如下。 拓扑需求
拓扑要求结束根据现有机制的拓扑结构特点。在我们的例子，链接和3个关节的设计要求轴在其相应的树图的卧式加工中心是： 1、必须有一个为主轴吊坠顶点。
2、必须有一个顶点，那里的路径长度为4主轴，作为工作表。 3、必须有一个根，这是由主轴头路位于工作表中的帧。
4、必须有一个顶点，这是一个从顶点吊灯从帧路径主轴头位于顶点分支的分支为工具杂志。
5、与必须被看作是对分配的主轴转动边事件。
6、之间的主轴头和工作台的边缘，必须指定为棱镜对。
7、工具之间的杂志和分支顶点的边缘，必须指定为转动，棱柱形，或圆柱对。而且，如果有一个转动对或一对圆柱，它必须与工具的事件杂志。 链接分配规则
1、选择一个为主轴吊坠顶点。
2、选择一个顶点，那里的路径长度为主轴是4，如工作表。如果这个顶点不存在，删除此图并转到步骤6。
3、选择一个顶点，它是由主轴头路位于工作台，因为框架。
4、选择一个顶点，这是从挂件顶点从主轴头路径帧分行位于顶点分支，作为工具杂志。如果这个顶点不存在，删除此图并转到步骤6。 5、其他未分配的顶点分配的链接湖 6、完成连接任务。 联合分配规则
1、与主轴边缘事件被指定为一转动一对。
2、在从主轴头路的边缘，工作表中指定为棱镜对。
3、基于路径的长度从分支顶点工具杂志，边缘可分配根据的R，P和C中的专业化联合置换后，我们必须找出这些专门树图受该机制约束的拓扑结构加工中心，我们要建立。对于我们来说，拓扑约束列举如下： 1、该挂件顶点必须是主轴，工具杂志，或工作表。 2、该工具杂志顶点位于从主轴头支到框架。
3、在转动两人必须与主轴或刀库事件，以及圆柱对必须与工具杂志事件。
据联系和联合分配规则，我们可以专门树图的地图集，以获取专业树图。专业化过程可以通过电脑输入到程序树图相邻矩阵和邻接矩阵所需的联系和拓扑结构的数字结果。图7显示了计算机专业流程图和拓扑结构的号码，满足拓扑要求和限制，在表3中列出。
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