数字控制+外文翻译+外文文献+英文文献

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2024年1月21日发(作者：)

数字控制 外文翻译 外文文献 英文文献

NC and CNC

Numerical 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 NC is

performed under computer supervision,it is called Computer Numerical

Control(CNC).For both NC and CNC systems,work principles are the

the way in which the execution is controlled is

ly,new systems are faster,more powerful,andmore

versatile.

es Using NC

Early machine tools were operated by craftsmen who decided many

variables such as speeds, feeds, and depth of cut, etc. With the

development of science and technology, a new term, Numerical Control (NC)

appeared. Controlling a machine tool using a punched tape or stored

program is known as Numerical Control. NC has been defined by the

Electronic Industries Association (EIA) as “A system in which actions

are controlled by the direct insertion of numerical data at some point.

The system must automatically interpret at least some portion of this

data.”

In the past, machine tools were kept as simple as possible in order

to keep their costs down. Because of the ever-rising cost of labor,

better machine tools, complete with electronic controls, were developed

so that industry could produce more and better products at prices that

were competitive with those offshore industries.

NC is being used on all types of machine tools from the simplest to

the most complex. The most common machine tools are the single-spindle

drilling machine, lathe, milling machine, turning center, and machining

center.

-Spindle Drilling Machine

One of the simplest numerically controlled machine tools is the

single-spindle drilling machine. Most drilling machines are programmed

on three axes:

a. The X-axis controls the table movement to the right or left.

b. The Y-axis controls the table movement toward or away from the

column.

c. The Z-axis controls the up or down movement of the spindle to

drill holes to depth. 1.2. Lathe

The engine lathe, one of the most productive machine tools, has been

a very efficient means of producing round parts. Most lathes are

programmed on two axes:

a. The X-axis controls the cross motion (in or out) of the cutting

tool.

b. The Z-axis controls the carriage travel toward or away from the

headstock. g Machine

The milling machine has always been one of the most versatile

machine tools used in industry. Operations such as milling, contouring,

gear cutting, drilling, boring and reaming are only a few of the many

operations that can be performed on a milling milling

machine can be programmed on three axes:

a. The X-axis controls the table movement to the right or left.

b. The Y-axis controls the table movement toward or away from the

column.

c. The Z-axis controls the vertical (up and down) movement of the

knee or spindle. 1.4. Turning Center

Turning Centers were developed in the mid-1960s after studies showed

that about 40 percent

of all metal cutting operations were performed on lathes. These

numerically controlled machines are capable of greater accuracy and

higher production rates than the engine lathe. The basic turning center

operates on only two axes:

a. The X-axis controls the cross motion of the turret head.

b. The Z-axis controls the lengthwise travel (toward or away from

the headstock) of the turret head.

1.5. Machining Center

Machining centers were developed in the 1960s so that a part did not

have to be moved from machine to machine in order to perform various

operations. These machines greatly increased production rates because

more operations could be performed on a work-piece in one

are two main types of machining centers, the horizontal and the vertical

spindle types.

a. The horizontal spindle-machining center operates on three axes:

(a) The X-axis controls the table movement to the right or left.

(b) The Y-axis controls the vertical movement (up and down) of the

spindle.

(c) The Z-axis controls the horizontal movement (in or out) of the

spindle.

b. The vertical spindle-machining center operates on three axes:

(a) The X-axis controls the table movement to the right or left.

(b) The Y-axis controls the table movement toward or away from the

column.

(c) The Z-axis controls the vertical movement (up and down) of the

spindle. mming for NC

A program for numerical control consists of a sequence of directions

that caused a NC machine to carry out a certain operation, machining

being the most commonly used process. Programming for NC may be done by

an internal programming department, on the shop floor, or purchased from

an outside source. Also, programming may be done manually or with

computer assistance.

The program contains instructions and commands. Geometric

instructions pertain to relative movements between the tool and the

work-piece. Processing instructions pertain to spindle speeds, feeds,

tools, and so on. Travel instructions pertain to the type of

interpolation and slow or rapid movements of the tools or worktables.

Switching commands pertain to on/off position for coolant supplies,

spindle rotation, direction of spindle rotation, tool changes, work-piece feeding, clamping and so on.

programming. Manual part programming consists of first

calculating dimensional relationships of the tool, work-piece and

worktable based on the engineering drawings of the part, and

manufacturing operations to be performed and their sequence. A program

sheet is then prepared, which consists of the necessary information to

carry out the operation, such as cutting tools, spindle tools, feeds,

depth of cut, cutting fluids, power, and tool or work-piece relative

positions and movements. Based on this information, the part program is

prepared. Usually a paper tape is first prepared for typing out and

debugging the program. Depending on how often it is to be used, the tape

may be made of more durable mylar.

Someone knowledgeable about the particular process and able to

understand, read, and change part programs can do manual programming.

Because they are familiar with machine tools and process capabilities,

skilled machinists can do manual programming with some training in

programming, however, the work is tedious, time consuming, and

uneconomical and is used mostly in simple point-to-point applications.

er-aided Programming. Computer-aided part programming

involves special symbolic programming languages that determine the

coordinate points of corners, edges, and surfaces of the e

numerical control involves the insertion of data concerning work-piece

materials and processing parameters, programming must be done by

operators or programmers who are knowledgeable about the relevant

aspects of the manufacturing processes being used. Before production

begins, programs should be verified, either by viewing a simulation of

the procession on a CRT screen or by making the part from an inexpensive

material, such as aluminum, wood, or plastic, rather than the material

specified for the finished parts.

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 inputs some information in

the program by tape and so on, the computer calculates all necessary

data to get the job done.

Today’s systems have computers control data, so they are called

Computer Numerically

Controlled 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 unit.

The Construction of CNC Machines

CNC machine tools are complex assemblies. However, in general, any

CNC machine tool consists of the following units: computers, control

systems, drive motors and tool changers.

According to the construction of CNC machine tools, CNC machines

work in the following manner:

(1) The CNC machine language, which is a programming language of

binary notation used on computers, is not used on CNC machines.

(2) When the operator starts the execution cycle, the computer

translates binary codes into electronic pulses that are automatically

sent to the machine’s power units. The control units compare the number

of pulses sent and received.

(3) When the motors receive each 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.

CNC 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 some setup.

(2)The scrap rate is significantly reduced because of the precision

of the CNC machine and lesser operator impact.

(3)It is easy to incorporate part design changes when CAD/CAM system

are used.

(4)Production is significantly increased.

(5)It is easier to perform quality assurance by a spot-check instead

of checking all parts.

(6)Because of the possibility of simultaneous muti-axis tool

movement,special profile tools are not necessary to cut unusual part

shapes.

ers

As with all computers, the CNC machine computer works on binary

principle using only two characters 1 and 0, for information processing

precise time impulses from the circuit. There are

two states, a state with voltage, 1, and a state without voltage, 0.

Series of ones and zeroes are the only states that the computer

distinguishes are called machine language, and it is the only language

the computer creating the program, the programmer does

not care about the machine or she simply uses a list of

codes and keys in the meaningful l built-in software

compiles the program into the 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 machine’s control. If

there is a minicomputer programming, say, a radius (which is a rather

simple task), the computer will calculate all the points on the tool

the machine without a minicomputer, this may prove to be a

tedious task, since the programmer must calculate all the points of

intersection on the tool path. Modern CNC machines use 32-bit processors

in their computers that allow fast and accurate processing of

information.

l systems

There are two types of control systems on NC/CNC machines: the open

loop and the closed loop. The type of control loop used determines the

overall accuracy of the machine.

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

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 movement command. Since this control system only

counts pulses and cannot identify discrepancies in positioning, the

machine will continue this inaccuracy until somebody finds the error.

The open-loop control can be used in applications in which there is

no change in load conditions, such as the NC drilling

advantage of the open-loop control system is that it is less expensive,

since it does not require the additional hardware and electrics needed

for positioning feedback. The disadvantage is the difficulty of

detecting a positioning error.

In the closed-loop control system, the electronic movement 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 sent and received matches, the control starts

sending out pulses for the next movement.

Closed-loop systems are very accurate. Most have 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.

Position measurement in NC machines can be accomplished through

direct or indirect methods. In direct measuring systems, a sensing

device reads a graduated scale on the machine table or slide for linear

movement. This system is 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 significant.

In indirect measuring systems, rotary encoders or resolves convert

rotary movement to translation movement. In this system, backlash can

significantly affect measurement accuracy. Position feedback mechanisms

utilize various sensors that are based mainly on magnetic and

photoelectric principles.

Motors

The drive motors control the machine slide movement on NC/CNC

equipment. They come in four basic types: stepper motors, DC servomotors,

AC servomotors and fluid servomotors.

Stepper motors convert a digital pulse generated by the

microcomputer unit (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 r motors are mostly used in applications

where low torque is required.

Stepper motors are used in open-loop control systems, while AC, DC

or hydraulic servomotors are used in closed-loop control systems.

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.

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.

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

values that are controlled by the MCU.

3.4Tool 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 operation. 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 tools

changing without the intervention of the operator. Typically, an

automatic tool changer grips the tool in the spindle, pulls it out, and

replaces it with another most machines with automatic tool

changers, the turret or magazine can rotate in either direction, forward

or reverse.

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-handling device. On the turning center, the turret

automatically rotates, bringing the tool into position.

er-Aided Design (CAD)

A CAD system is basically a design tool in which the computer is

used to analyze various aspects of a designed product. The CAD system

supports the design process at all levels—conceptual, preliminary, and

final design. The designer can then test the product in various

environmental conditions, such as temperature changes, or under

different mechanical stresses.

Although CAD systems do not necessarily involve computer graphics,

the picture of the object is usually displayed on the surface of a

cathode-ray tube (CRT). Computer graphics enable the designer to study

the object by rotating it on the computer screen, separating it into

segments, enlarging a specific portion of kinematics programs.

Most CAD systems are using interactive graphics systems. Interactive

graphics allow the user to interact directly with the computer in order

to generate manipulation, and modify graphic displays. Interactive

graphics has become a valuable tool, if not a necessary prerequisite, of

CAD systems.

The end products of many CAD systems are drawings generated on a

plotter interfaced with the computer. One of the most difficult problems

in CAD drawings is the elimination of hidden lines. The computer

produces the drawing as a wire frame diagram. Since the computer defines

the object without regard to one’s perspective, it will display all the

object’s surfaces, regardless of whether they are located on the side

facing the viewer or on the back, which normally the eye cannot see.

Various methods are used to generate the drawing of the part on the

computer screen. One method is to use a geometric modeling approach, in

which fundamental shapes and basic elements are used to build the

drawing. The lengths and radii of the elements can be modified. For

example, a cylinder is a basic element. The subtraction of a cylinder

with a specific radius and length will create holes in the displayed

part. Each variation, however, maintains the overall geometry of the art.

Other CAD systems use group technology in the design of parts. Group

technology is a method of coding and grouping parts on the basis of

similarities in function or structure or in the ways they are produced.

Application of group technology can enable a company to reduce the

number of parts in use and to make the production of parts and their

movement in the plant efficient.

Recently CAD systems are using the finite-element method (FEM) of

stress analysis. By this approach the object to be analyzed is

represented by a model consisting of small elements, each of which has

stress and deflection characteristics. The analysis requires the

simultaneous solution of many equations. A task, which is performed by

the computer, and the deflections of the object, can be displayed on the

computer screen by generating animation of the model.

With any of these methods, or others which are used, the CAD system

generates at the design stage a single geometric data base which can be

used in all phrases of the design and later in the manufacturing,

assembling, and inspection processes.

数字控制和计算机数字控制

数控(NC)是按照含有机床运动信息程序所指定的顺序自动执行操作的加工过程。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)。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。新型的数控系统通长速度更快、功率更大、功能更齐全。

1.数控机床

老式机床通常是由工人操作并由他们决定机床速度、进给量、切削深度等。随着科学技术的发展，一个新术语—数字控制 (NC) 诞生了。数字控制就是利用穿孔纸带或储存的程序来控制机床。美国电子工业协会把数控定义为“采用在某些点直接插入数字数据来控制操作的系统，此系统必须能够自动解释这些信息中的一部分。”

过去，人们尽量使机床结构简单，以便降低成本。由于劳动成本日益上涨，人们研制出性能更好的机床，并且配有电控设备，这样企业可以生产更多、更好、价格较低的产品，以便和国际上的产品相竞争。

从最简单到最复杂的机床都用到了数控技术。最常见的机床有:单轴钻床、卧式车床、铣床、车削中心及加工中心。

1.1单轴钻床

单轴钻床是最简单的数控机床之一。多数数控钻床可在三个坐标轴上编程:

1) X轴控制工作台左右运动。

2) Y轴控制工作台靠近或离开立柱。

) Z轴控制主轴上下运动，确定孔的加工深度。 3

1.2(卧式车床

1)卧式车床是生产效率最高的机床之一，它是加工回转体零件非常有效的工具。 大部分数控机床可在两个坐标轴上编程。

2)X轴控制刀具横向运动(切入或切出)。

3)Z轴控制机床拖板靠近或离开主轴箱。

1. 3(铣床

铣床一直是工业生产中加工方式最多的机床之一，像铣削、成型加工、齿加工、钻、 镗、铰等只是可在铣床上进行的一少部分加工方式。数控铣床可在三个坐标轴上编程。

1)X轴控制工作台左右运动。

2)Y轴控制工作台靠近或离开立柱。

3)Z轴控制升降台或主轴垂直(上下)运动。

1.4(车削中心

研究表明，整个金属材料的切削操作大约40%是在机床上进行的。早在20世纪60年 代中期，人们就开始研制车削中心。这种数控机床比普通车床具有更高的加工精度和生产效率。一般数控车削中心仅在两个坐标轴上工作:

1)X轴控制转塔头横向运动。

2)Z轴控制刀架纵向运动(靠近或离开主轴箱)。

1. 5(加工中心

加工中心是20世纪60年代发展起来的。有了加工中心，工人们不必把零件从一台机床 转移到另一台机床就能完成各种加工。由于工件经过一次装配后便能进行多种加工，所以大大提高了生产效率。加工中心主要有两类:卧式加工中心和立式加工中心。

(1) 卧式加工中心可在三个坐标轴上工作:

1)X轴控制工作台左右运动。

2)Y轴控制主轴垂直(上下)运动。

3)Z轴控制主轴水平运动(切入或切出)。

(2)立式加工中心在三个坐标轴上工作:

1)X轴控制工作台左右运动。

2)Y轴控制工作台靠近或离开立柱。

3)Z轴控制主轴垂直(上下)运动。

2.数控编程

数字控制的程序是由一系列使数控机床执行某种操作(通常是加工操作)的指令组成的。数控编程可以由内部编程部门在车间内进行，也可从外面购买。程序编制可以是手动编程也可以在计算机帮助下完成。

程序包含指令和命令。几何指令是关于刀具和工件之间的相对运动的。工艺指令是关于主轴速度、进给、刀具等方向的。运动指令是关于插补的类型、刀具或工

作台运动快慢的。开关命令是关于切削液供给的开、关、主轴旋转、主轴转向、换刀、工件进给、夹紧等操作的。

(1)手动编程。手动零件编程首先在零件机械图基础和加工工序上计算刀具、工件和工作台之间的尺寸关系，然后准备程序清单，其中包括进行加工操作的必要的信息，如切削用量、主轴转速、进给、背吃刀量、切削液、动力、刀具或工件的相对位置及运动，在此基础上准备零件程序。通常首先做出试切用的穿孔纸带，并调试程序，根据穿孔带使用的频率，也可用耐用的聚脂薄膜材料制作穿孔带。

手动零件编程需要由懂得一定工艺知识，能理解、阅读、修改零件程序的人员进行。熟练的机械工由于熟悉机床及其工艺性能，经编程培训后也能胜任手动编程工作。然而，手动编程枯燥费时间，经济性差，主要用于点位加工。

(2)计算机辅助编程。计算机辅助零件编程是用特定的符号程序语言来决定零件的顶点、边、面的坐标点。由于数字控制涉及工件材料和工艺参数的插入，编程工作必须由那些熟知所要用的工艺方面相关知识的操作人员或编程人员担任。在加工之前，应对程序进行验证，或在加工同时在CRT屏幕上观察模拟加工过程，或者试切。试切时用价格低廉的材料，如铝、木头或塑料，而不采用加工出成品时所用的材料。

3.计算机数字控制

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中或者通过通信渠道与数控机床连接，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来完成工作。

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，仅仅是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、功能更全。

计算机数控机床的结构

CNC 机床结构较为复杂。一般来说，任何CNC机床都由以下几个单元组成:计算机、控制系统、驱动电动机和换刀机构装置。

根据CNC机床的结构，CNC机床以下列方式工作:

(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)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，并自动地传送给机床的控制单元。控制单元将发出的脉冲数与接收的脉冲数加以比较。

(3)电动机每接收一个脉冲，就自动地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。

数控机床比传统的机械的许多优点，其中一些是:

(1)有一些设置可以在同一台机器上执行多个操作。

(2)由于数控机床的精度和较小的运营商的影响使废品率明显降低。

(3)很容易纳入部分设计变更时，均采用CAD / CAM系统。

(4)生产显著增加。

(5)比较容易进行抽查，而不是检查所有部件质量。

(6)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。

3.1(计算机

像所有其它计算机一样，CNC机器上的计算机也只使用1和0，按照二进制原理运行，处理来自系统电路的精确时间脉冲信息。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，只需要简单地运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编译为机器语言，由伺服电动机带动刀具流动。然而，机床程序的可用性依赖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的全部位移点。如果机床上没有微型计算机，这个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。

3.2(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。所使用的控制环的类型决定机床的整体精度。

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动机的特殊伺服电动机所接收。控制单元发送给步进电动机的脉冲数控制电动机的旋转角度。然后步进电动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，因此机床将继续其不准确操作，直到有人发现错误为止。

开环控制适用于载荷状态没有变化的场合，例如，数控钻床。开环控制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。

在闭环控制系统中，由控制单元发出电脉冲并送给伺服电动机，使电动机跟随每个脉冲旋转。这些运动能被一个称为传感器的反馈装置检测并记录下来。每移动一步，传感器就发送一个信号送回到控制单元，并且将当前驱动轴位置和程序中的设定位置相比较。当发出的和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。

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作出必要的调整，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。

在数控机床中，位置测量可通过直接或间接测量的方式来实现。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。这种系统比较精确，因为标尺装在机床内，并且机构中的后坐力(邻近啮合齿轮之间的作用)不是很明显。

在间接测量系统中，旋转编码器将旋转运动转换成直线运动。在这种测量系统中，后坐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制主要是基于磁和光电原理。

3.3(驱动电动机

驱动电动机控制数控或计算机数控设备上机器拖板的运动。它共有四种基本类型:步进电动机、直流伺服电动机、交流伺服电动机和液压伺服电动机。

步进电动机将由微机单元(MCU)发出的一个数字脉冲转换成一个小步转动，步进电

动机能够传递一定数量的步数，微机单元(MCU)送给步进电动机的脉冲数控制步进电动机的转动角度。步进电动机常应用在传动扭矩要求较低的场合。

步进电动机常应用在开环控制系统中，而交流、直流或液压伺服电动机常使用在闭环控制系统中。

直流伺服电动机是可以变速的电动机，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。直流伺服电动机能够提供比步进电动机更大的传动扭矩。

交流伺服电动机是通过改变电压频率来控制转速的。交流伺服电动机比直流伺服电动机的输出功率更大，它们也被用来驱动丝杠和齿轮机构。

液压伺服电动机也是速度可调电动机。在应用气泵场合下，液压伺服电动机能够产生的功率和速度要比电气伺服电动机更大更高。液压泵将能量提供给由微机单元控制的阀门。

3.4(换刀装置

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，大部分数控或计算机数控机床配备有自动换刀装置，如加工中心上的链式刀库和车削中心的转塔刀库。他们无需操作员干预，即可换刀。较为典型的是，自动换刀装置会卡紧车床主轴内的刀具，将其拉出，然后用另一把刀具代替。在具有自动换刀装置的大部分机床上，刀架和自动换刀装置可以进行旋转，正向反向均可。

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，回转刀架自动地旋转，将刀具带到指定位置。

4.计算机辅助设计(CAD)

计算机辅助设计系统是一种设计工具，计算机是用来分析所设计的产品的各个方面的。CAD系统支持各种阶段的设计过程——设计构思、初步设计以及最终设计。然后设计者可在各种环境条件下，比如温度的变化或不同机械压力下检验产品的状况。

尽管CAD系统并非一定要包含计算机绘图，但能将设计的产品显示在屏幕上是CAD系统的最有价值的特性之一。物体的图形通常显示在阴极射线管屏幕上(CRT)。计算机图形功能使设计者可用多种办法研究物体:将物体在计算机屏幕上旋转、将其分成几段、将物体局部放大便于仔细研究以及在运动程序的帮助下研究物体的运动。

大多数CAD系统使用互动式图形系统。交互式图形系统使用户可直接和计算机交互作，对图形进行调整和修改。对CAD系统来说，交互式图形系统就算不是必要的，也已经是很有价值的工具了。

许多CAD系统的最终产品是在与计算机连接的绘图仪中产生的图形。在CAD图形中，最难解决的问题之一是消去那些被挡住的线。计算机生成的图形是线框图形。由于计算机定义物体时没有考虑图形的透视效果，它显示出物体的所有面，而不考虑这些面是在朝向观测者的一面还是位于通常人眼无法看到的背面。

可使用多种不同的方法在计算机屏幕上生成零件的图形。一种方法是采用几何模板形式，这种办法是用基本形状和基本元素去创建图形，并可以修改元素的长度和半径。例如，圆柱是一个基本元素，在已显示的零件上去掉一个规定半径和长度的圆柱就可生成一个孔。但是每次变化都会保留零件所有的几何特征。

另外，CAD系统使用成组技术设计零件。成组技术是在功能、结构相同或加工方法相似的工件基础上采用分组编码的一种加工方法。采用成组技术可使工厂减少所用零件的数量，并使零件在工厂中的制造、运输效率更高。

近来，CAD系统使用了压力有限元分析法。在使用这种方法时，待分析物体用很多有压力及弯曲特性的小元素组成的模型表示。这种分析方法要求同时分解许多方式，用计算机执行一项任务，物体的弯曲可以通过生成动画的方式显示在计算机屏幕上。

采用这些办法中的任何一种或其它常用办法，CAD系统在设计阶段产生了单个的几何

数据库，它可用于设计的各个阶段及其以后的制造、装配和检验过程中。

本文标签： 电动机控制计算机机床加工