数字控制与计算机数字控制.doc

无锡职业技术学院毕业设计论文NC AND CNC数字控制与计算机数字控制1.1 The History of NC and CNC DevelopmentNumerical control (NC) is any machining process in which the operations are executed automatically in sequences as specified by the program that contains the information for the tool movements.The NC concept was proposed in the late 1940s by John Parsons of Traverrse City,Michigan.Parsons recommended a method of automatic machine control that would guide a milling cutter to produce a “thru-axis curve”in order to generate smooth profiles on work pieces.1.1数字控制与计算机数字控制的发展历史数字控制是按照含有机床（刀具）运动信息程序所指定的顺序自动执行操作的加工过程。数控这一概念是由密歇根洲特拉华诚的约翰 帕森于20世纪四十年代后期提出的。为了在工件上加工光滑的轮廓，帕森提出了一种自动的机床控制方式，它能够引导铣床刀具加工出一种“过轴曲线”。In 1949,The U.S. Air Force awarded Parsons a contract to develop a new type of machinetool that would be able to speed up production methods.Parsons commissioned the Massachusetts Institute of Technology (M.I.T) to develop a practical implementation of his concept.Scientists and engineers at M.I.T. built a control system for a two-axis milling machine that used a perforated paper tape as the input media. In a short period of time,all major machine tool manufacturers were producing some machines with NC, but it was not until the late 1970s that computer-based NC systems. 360毕业设计网 1949年，美国空军与帕森签署了合同，要求开发一种能够提高生产率的新型机床。帕森委托麻省理工学院（MIT）来开发一种新概念机床，麻省理工学院的科学家和工程师研制出了一种用穿孔纸带作为输入媒介的二轴联动铣床控制系统。在较短的时间内，当时所有主要的机床生产商都生产了一些数控机床，但直到20世纪七十年代后期，基于计算机的数字控制才被得到广泛的使用。只有价格低廉且功能强大的微处理芯片代替了计算机数控系统中的硬连线逻辑发生器后，NC才真正成为一门自动化技术。When Numerical Control is performed under computer supervision, it is called Computer Numerical Control (CNC). Computers are the control units of CNC machines, they are built in or linked to the machines via communications channels. When a programmer input some information in the programby tape and so on, the computer calculates all necessary data to get the job done.当数控机床在计算机监控下工作时，它就被称为计算机数控机床（CNC）。计算机是CNC机床的控制单元，它们内嵌于数控机床或者通过通讯渠道与数控机床联接，当程序员编程时，通过纸带或磁盘将一些信息输入，计算机将对一些必要的数据进行计算的完成工作。On the first Numerically controlled (NC) machines were controlled by tape,and because of that, the NC systems were known as tape-controlled machines.They were able to control a single operationentered into the machine by punched or magnetic tape. There was no possibility of editing the program on the machine. To change the program ,a new tape had to be made.由于第一台数控机床的数据是由纸带控制的，因此数控系统被成为纸带控制机床。它们只能控制由输入到机床内的纸带或磁带所规定的单一操作，输入到机床内的程序是不能被编辑的，要改变程序必须重做新纸带。Todays systems have computers to control data;they are called Computer Numerically controlled (CNC) machines. For both NC and CNC systems, work principles are the same. Only the way in which the execution is controlled is different. Normally, new systems are faster, more powerful, and more versatile.当今的系统都由计算机来控制数据，因而称之为计算机数控机床（简称CNC机床）。NC和CNC系统两者的工作原理一样，仅仅控制执行的方式不同。新型 的数控系统通常速度更快，功率更大，功能更齐全。2.2The Applications of NC/CNC Since its indroduction, NC technology has found many applications, including lathes and turning centers, milling machines and machining centers, punches, electrical discharge machines (EDM), flame cutters,grinders, and testing and inspection equipment. The most complex CNC machine tools are the turning center, (A modem turning center with a ten-station turret thar accepts quick-change tools.Each tool can be positioned in Seconds with the press of a button). And the machining center shown in (Vertical machining center, the tool magazine is on the left of the machine. The control panel on the right can be swiveled by the operator) and(Horizontal machining center, equipped with an automatic tool changer.Tool magazines can store 200 cutting tools).2.2数字控制与计算机数字控制的应用数控技术自创立以来就得到了广泛的应用，包括车床和车削中心、铣床和加工中心、冲床、电火花（EDM）加工机床、线切割机床、磨床以及测试检测装置等。最复杂的计算机数控机床是车削中心，一个具有十转位的刀架能进行快速换刀的现代车削中心，立式加工中心（刀具库在机床的左边。右边的控制面板可由操作者通过转臂转动），以及卧式加工中心，通过按下按钮每把刀可在数秒钟内定位。（配有自动换刀系统。刀具库储备有200把切削工具）。 When preparing a program for a particular operation, the programmer must select all cutting data using recommendations for conventional machining. This includes proper selection of cutting speeds, feedrate, tools and tool geometry,and so on. When the programmer has chosen all of the necessary information properly, the operater loads the program into the machine and presses a button to start the cutting cycle.The CNC machinemoves automatically from one machining operation to another, changing the cutting tools and applying the coolant. In a surprisingly short time, the workpiece is machined according to the highest quality standards. But that is not all. No matter how big the work series is ,all of the parts will be almost identical in size and surface finishing. At this time of advanced technology, with its high demands for surface finishing and tolerances of components in, for example, aerospace, nuclear, and medical equipment manufacturing, only CNC machines provide successful results.当为某项操作编程时，程序员必须选择传统的加工切削数据推荐值。这些切削数据包括切削速度、进给率、刀具和刀具几何形状等。当程序员正确选择所有必要信息后，操作人员将程序载入机床并按下按钮，切削循环开始。通过变换切削刀具及使用冷却液，计算机数控机床可以自动从一个加工工序转向另一个加工工序。在极短时间内，工件依据最佳质量标准被加工出来。但是那并不是全部，无论工件批量有多大，所有零部件在尺寸和表面精度上几乎是一致的。在当今先进技术时代，随着对零件表面精度和公差要求的提高，例如，航空业、核工业及医疗器械设备的制造，只有计算机数控机床才能胜任。2.3 The Advantages and Disadvantages of CNC MachinesCNC machines have many advantages over conventional machines, some of them are:(1) There is a possibility of performing multiple operations on the same machine in one setup.(2) Because of the possibility of simultaneous multi-axis tool movement,special profile tools are not necessary to cut unusual part shaps.(3) The scrap rate is significantly reduced because of the precision of the CNC machine and lesser operator impact.(4) It is easy to incorporate part design changes when CAD/CAM systems are used.(5) It is easier to perform quality assurance by a spot-check instead of checking all parts.(6) Productionis significantly increased.2.3计算机数控机床的优缺点1、计算机数控机床和传统机床相比具有很多优点，它们是：（1）在同一机床上，一次装夹可完成多个操作。（2）由于机床可以实现多轴联动，切削非常规的零件形状时，可以不必使用成形刀具。（3）由于计算机数控机床的精度高，受操作者影响小，废品率明显降低。（4）采用CAD/CAM系统后，对零配件装配设计的修改就变得很容易。（5）通过抽检代替全检，质量更容易保证。（6）生产率显著提高。2、CNC machines also have some disadvantages:(1) They are quite expensive.(2) They have to be programmed, set up, operated, and maintained by highly skilled personnel.2、计算机数控机床也有一些缺点：（1）价格昂贵。（2）必须由高级技术人员来编程、安装、操作与维护。Obviously,CNC machines have more advantages than disadvantages. The companies that adopt CNC technology increase their competitive edge. As always with new technology, the cost per CNC unit is being cut further and more companies can afford CNC equipment, which enables them to answer the incresingly strong requirements for production speed and quality that competitive markets demand. In the futhure the broader use of CNC machines will be one of the best ways to enhance automation in manufacturing.显然，计算机数控机床利大于弊。已经采用计算机数控机床的企业正在提高他们的竞争力。随着新技术的采用。每台计算机数控单元的价格正在进一步降低，更多的公司能够买得起计算机数控装备，使其能够满足竞争市场对产品生产速度和质量日益增强的需求。将来计算机数控机床的广泛使用成为制造业提高自动化程度的最佳选择之一。2.4The Construction of CNC Machines2.4计算机数控机床的结构 CNC machine tools are complex assemblies. However, in general, any CNC machine tool consists of the following units:CNC结构较为复杂。一般来说，任何CNC机床都包含以下几个单元组成： Computers 计算机Control systerms控制系统Drive motors驱动电机 Tool changers换刀机构 According to the construction of CNC machine tools, CNC machines work in the following manner根据CNC机床的结构，CNC机床以下列方式工作：(1) The CNC machine language, which is programming language of binary notation used on computuers, not on CNC machines.（1）CNC机床语言是一种用在计算机上的二进制符号编程语言，而不是用在CNC机床上。(2) When the operator starts the execution cycle the computer translates binary codes into electronic pulses which are automatically seent to the machines power units. The control units compare the number of pulses sent and received.（2）当操作者开始执行循环时，计算机将二进制代码翻译成电脉冲，并自动的送给机床的控制单元。控制单元将发出的脉冲数与接受的脉冲数加以比较。(3) When the motors receiveeach pulse, they automatically transform the pulses into rotations that drive the spindle and lead screw, causing the spindle rotation and slide or table movement. The part on the milling machine table or the tool in the lathe turret is driven to the position specified by the program.（3）电动机每接收一个脉冲，就自动的将脉冲信号转换成旋转信号从而驱动主轴和丝杠，带动主轴旋转和拖板或工作台的移动。铣床工作台上的零件或车床转塔刀架上的刀具被驱动到程序指定的位置。 1)、 Computers The computer reacts on. As with all computers, the CNC machine computer works on a binary principle using only two characters 1 and 0 for information processing precise time impulses form the circuit. There are two states,a steta with voltage, 1,and a state without voltage, 0 Series of ones and zeros are the only states that the computer distinguishes a called machine language, it is the only language the computer understands. When creating the program, the programmer does not care about the machine language. He or she simply uses a list of codes and keys in the meaningful information. Special built-in software compiles the program into machine language and the machine moves the tool by its servomotors. However, the programmability of the machine is dependent on whether there is a computer in the machines control.If there is a minicomputer programming,say a radius(which is a rather simple task), the computer will calculate all the pointson the tool path. On the machine without a minicomputer, this may prove to be a tedious task, since the programmer must calculate all the pointe of intersection on the tool path. Modern CNC machines use 32-bit processors in their computuers that allow fast and accurate processing of information.1)、计算机 如所有其它计算机，CNC机床的计算机也是根据二进制原理，只有两个字符1和0作为电路的时间脉冲信息，有两个状态，高电平为1，低电平为0，1和0的序列是计算机区别于所谓的机器语言的唯一状态，也是计算机理解的唯一语言。编程时程序员不必关心机器语言，只需简单的应用一系列代码和符号来表达有用的信息。机器内的特殊软件将程序翻译为机器语言，由伺服电动机带动刀具工作。然而，机床程序的可用性是依速于机床控制系统中是否有计算机，如果用一个微型计算机进行程序设计，例如，半径（一个相当简单的任务），计算机将计算刀具路径上所有的点坐标值，如果机床上没有微型计算机，这个计算将是一个繁琐的工作，因为程序员必须计算刀具路径上的所有交点位置。现代CNC机床的计算机使用32位处理器可以实现信息的快速准确处理。 2)、Control Systems There are two types of control systems on NC/CNC machines:open loop and closed loop. The type of control loop used determines the overall accuracy of the machine.2)、控制系统 在NC/CNC机床里有两种类型的控制系统：开环和闭环。控制环的类型决定机床的整体精度。 The open-loop control system does not provide positioning feedback to the control unit. The movement pulses are sent out by the control and they are received by a special type of servomotor called a stepper motor. The number of pulses that the control sends to the stepper motor controls the amount of the rotation of the motor. The stepper motor then proceeds with the next movementcommand. Since this control system only counts pulses and cannot identify discrepancies in positioning, the machine will continue this inaccuracy until somebody finds the error.开环控制系统不提供位置反馈信息给控制单元。移动脉冲由控制单元发出，并被一种称为步进电机的特殊伺服电动机所接收。控制单元发送给步进电机的脉冲数控制电机的旋转角度。然后步进电机接收下一个运动命令。由于这个控制系统只计算脉冲，不能识别位置偏差，所以机床将继续其不准确操作，直到有人发现错误为止。 The open-loop contorl can be used in applications in which there is no change in load conditions, such as the NC drilling mchine. The advantage of the open-loop contorl system is that it is less expensive,since it does not requir the additional hardware and electronics needed for positioning feedback. The disadvantage is the difficultyof detecting a positioning error.开环控制适用于载荷状态没有变化的场合下，例如，数控钻床。开环系统的好处是成本低，因为它不需要为位置反馈安装额外的硬件及电子装置，其缺点是很难检测位置误差。 In the closed-loop control system, the electronicmovement pulses are sent from the control to the servomotor, enabling the motor to rotate with each pulse. The movements are detected and counted by a feedback device called a transducer. With each step of movement,a transducer sends a signal back to the control, which compares the current position of the driven axis with the programmed position. When the number of pulses set and received match, the control starts sending out pulses for the next movement.在闭环控制系统中，由控制单元发出的电脉冲送给伺服电动机，使电机跟随每个脉冲旋转。这些运动能被一个成为传感器的反馈装置检测并统计下来。每移动一步，传感器就将信号送回到控制单元，并将当前驱动轴位置和程序中的设定位置相比较。当发出的脉冲数与接收的脉冲数相匹配时，控制单元开始为下一个运动发出脉冲。 Closed-loop systems are very accurate. Most has an automatic compensation for error, since the feedback device indicates the error and the control makes the necessary adjustments to bring the slide back to the position. They use AC, DC or hydraulic servomotors.闭环系统非常精确。大部分闭环系统具有误差的自动补偿功能，通过反馈装置指示误差并做出必要的调整，将拖板带回到准确位置。闭环控制系统通常采用交流、直流或液压伺服电动机。 Position measurement in NC machine can be accomplished through direct or indirect methods. In direct measuring system, a sensing device reads a graduated scale on the machine table or slide for linear movement. This system is the more accurate because the scale is built into the machine and backlash (the play between two adjacent mating gear teeth)in the mechanisms is not sinificant.在数控机床中，位置测量可通过直接或间接测量方式来实现。在直接测量系统中，传感器读取装在作直线运动的机床工作台或拖板上的标尺刻度数。这种系统比较准确，因为标尺是装在机床内，并且机构中的后座力（邻近啮合齿轮之间的作用）不是很明显。 In indirect measuring sysytems, rotary encoders or resolvers convert rotary movement to translation movement. In this system, backlash can significantly affect measurement accuracy. Position feedback mechanisms utilize various sansors that are based mainly on magnetic and photoclectric principles.在间接测量系统中，旋转编码器，将旋转运动转换为直线运动。在这种测量系统中，后座力在很大程度上会影响测量精度。采用多种传感器的位置反馈机构主要是基于磁和光电原理。 3)、Drive Motors The drive motors control the machine slide movement on NC/CNC equipment. They come in four basic types:3)、驱动电机 驱动电机控制NC/CNC设备上的拖板的运动，它们有四种基本类型： (1) Stepper motors 步进电机 (2) DC servomotors 直接伺服电机 (3) AC servomotors 间接伺服电机 (4) Fluid servomotors 液压伺服电机 Stepper motors convert a digital pulse generated by the microcomputer until (MCU) into a small step rotation. Stepper motors have a certain number of steps that they can travel. The number of pulses that the MCU sends to the stepper motor controls the amount of the rotation of the motor. Stepper motors are mostly used in applications where low torque is required.步进电机将由微机单元（MCU）发出的一个数字脉冲转换成一个小步转动，步进电机能够传递一定数量的步数，微机单元（MCU）送给步进电机的脉冲数控制步进电机的转动角度。步进电机常应用在传动扭矩要求较低的场合。 Stepper motors are used in open-loop cntrol systems. While AC, DC or hydraulic servomotors are used in closed-loop control systems.步进电机常使用在开环控制系统，而交流、直流或液压伺服电机常使用在闭环控制系统。 Direct current (DC) servomotors are variable speed motors that rotate in response to the applied voltage. They are used to drive a lead screw and gear mechanism. DC Servomotors provide higher-torque output than stepper motors.直流伺服电机是可以变速的电机，其转速随供给电压的变化而变化。它们常被用来驱动丝杠和齿轮传动机构。直流伺服电机能够提供比步进电机更大的传动扭矩。 Alternative current (AC) servomotors are controlled by varying the voltage frequency to control speed. They can develop more power than a DC servomotor. They are also used to drive a lead screw and gear mechanism.交流伺服电机是通过改变电压频率来控制转速的。交流伺服电机比直流伺服电机输出功率更大，它们也被用来驱动丝杠和齿轮机构。 Fluid or hydraulic servomotors are also variable speed motors. They are able to produce more power, or more speed in the case of pneumatic motors than electric servomotors. The hydraulic pump provides energy to valves that are controlled by the MCU.液压伺服电机也是速度可调电机。在应用气泵场合下，液压伺服电机能够产生的功率和速度要比电气伺服电机更大更高。液压泵将能量提供给由微机单元控制的阀门。 4)、Tool Changers Most of the time, several different cutting tools are used to produce a part. The tools must be replaced quickly for the next machining qperation. For this reason, the majority of NC/CNC machine tools are equipped with automatic tool changers,such as magazines on machining centers and turrets on turning centers. They allow tool changing without the intervention of the operator. Typically, an automatic tool changer grips the tool in the spindle, pulls it out, and replace it with another tool. On most machines with automatic tool changers, the turret or magazine can rotate in either direction, forward or reverse.4)、换刀机构 通常，加工一个零件需要使用几把不同的刀具。加工过程中必须为下一步加工工序迅速换刀。为此，大部分NC/CNC机床配备有自动换刀机构，如加工中心上的链式刀库和车削中心的转搭刀库。它们无须操作者干预，即可换刀。较为典型的是，一个自动换刀架夹住主轴上的刀具，将其拔出，然后用另一把刀代替。在大多数带有自动换刀机构的机床上，转搭刀库或链式刀库可以以任务方向旋转，或前或后。 Tool changers may be equipped for either random or sequential selection. In random tool selection, there is no specific pattern of tool selection. On the machining center, when the program calls for the tool, it is automatically indexed into waiting position, where it can be retrieved by the tool-handing device. On the turning center, the turret automatically rotates, bringing the tool into position.换刀机构有随机换刀和顺序换刀。在随机换刀中，没有刀具选择的具体路径。对于加工中心，当程序调用刀具时，刀具处理装置能自动检索到处于等待位置的刀具。对于车削中心，回转刀架能自动地旋转，将刀具带到指定位置。NC Operation数控机床操作2.5 Describing the Operation Panel2.5 操作面板的描述1、 EMERGENCY STOP The EMERGENCY STOP button is red and is located in the lower left corner of the control panel. If this button is pressed, the feed and rotation of the tool is stopped and the control system of the computer is turned off. The EMERGENCY STOP button is only used in special situations. Some of these are the overloading of the machine, a machined partis loose, or incorrect data in the program are causing a collision between the tool and the workpiece. To reset the EMERGENCY STOP button , push it in and turn it clockwise. Then you can turn the machine on, zero it, and eliminate the cause that forced the use of the EMERGENCY STOP button. Additionally, check whether any alarm signs appeared on the screen or whether the machine stopped during the execution of the cycle corresponding to a tool change or a table change. If such is the case, then repeat the same command (the cycle command) with the switch positioned on the MID (manual data input) to make sure that the cycle has been completed.1）、紧急制动 “紧急制动”按钮式红色的，位于控制面板的左下角。如果按下这个按钮，刀具进给和旋转将被停止，计算机的控制系统被关闭。紧急制动按钮只在特殊情况下使用。这些特殊情况有机床过载、被加工零件松动或者程序中的错误数据将导致刀具与工件之间发生的碰撞等。复位紧急制动按钮时，可按下并顺时针方向旋转此按钮，然后重新开机，按钮清零，排除被迫使用紧急制动按钮的原因。另外，在执行对应于换刀或工作台变位的循环过程中，检查屏幕上是否出现警戒信号或机床是否停止。如果是这样的话，那么将开关定位在MDI模式（人工数据输入模式），重复同样命令（循环命令）来确保循环能完成。2）MODE SELECT Use this switch (Fig.5-2) to specify the operational mode. The position of this switch determines whether the machine utilizes the computer or the manual control.2）、模式选择 使用这个开关可确定操作模式。该开关位置决定机床是由计算机控制还是由由人工控制