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1、漆鹑割被稆豹崤侣伎孚则沼淝余呐恒秽论辜卡蠢悯嗟涵九、外文翻译鳃持瞒畛沭带詹翰厂挛扑计愿侉黔绍斓拐贿堑铣怀蟮菇NUMERICAL CONTROL OF PRODUCTION EQUIPMENTS粽要袅列遑墁哨躞凵叔蠛蛮Numerical control (NC) is a form of programmable automation in which the processing equipment is controlled by means of numbers, letters, and other symbols. The numbers, letters, and symbols a
2、re coded in an appropriate format to define a program of instructions for a particular workpart or job. When the job changes, the program of instructions is changed. The capability to change the program is what makes NC suitable for low-and medium-volume production. It is much easier to write new pr
3、ograms than to make major alterations of the processing equipment.嗒辕饲砌急蒿龃碜敲蕖太推BASIC COMPONENTS OF NC示魁埴钺咬亮猓耗尘输泰沅A numerical control system consists of the following three basic components:究忘谭挫颛份尉痴吒牢汽酝Program of instructions鸳支铽施环倏上韧珲阌故酷Machine control unit幄仍受很日牙沂傺旅挨皤鼓Processing equipment缙貌饪瀚蜷蹁题朊乡赕刻翟T
4、he general relationship among the three components is illustrated in Fig.2.1. The program is fed into the control unit, which directs the processing equipment accordingly.策喹犴漉答囝嘛策丁毪甜蒲The program of instructions is the detailed step-by-step commands that direct the processing equipment. In its most c
5、ommon form, the commands refer to positions of a machine tool spindle with respect to the worktable on which the part is fixtured. More advanced instructions include selection of spindle speeds, cutting tool, and other function. The most common medium in use over the last several decades has been 1-
6、in. -wide punched tape. Because of the widespread use of the punched tape, NC is sometimes called “tape control”. However, this is a misnomer in modern usage of numerical control. Coming into use more recently have been magnetic tape cassettes and floppy diskettes.熟躬涩箩咐腥耢嗤衷甩讫娈The machine control uni
7、t (MCU) consists of the electronics and control hardware that read and interpret the program of instruction and convert it into mechanical actions of the machine tool or other processing equipment.潍钡楱篡港削伤彳嗫敝圯双The processing equipment is the third basic component of an NC system. It is the component
8、that performs useful work. In the most common example of numerical control, one that performs machining operations, the processing equipment consists of the worktable and spindle as well as the motors and controls needed to drive them.禀褊虬播鸪锣呃歼荃嘶祧薪TYPES OF CONTROL SYSTEMS淫淤舛啷阗尺饩狳嗪雕殄赤There are two bas
9、ic types of control systems in numerical control: point-to-point and contouring. In the point-to-point system, also called positioning, each axis of the machine is driven separately by leadscrews and, depending on the type of operation, at different velocities. The machine moves initially at maximum
10、 velocity in order to reduce nonproductive time but decelerates as the tool reaches its numerically defined position. Thus in an potation such as drilling or punching, the positioning and cutting take place sequentially. After the hole is drilled or punched, the tool retracts, moves rapidly to anoth
11、er position, and repeats the operation. The path followed from one position to another is important in only one respect: The time required should be minimized for efficiency. Point-to-point systems are used mainly in drilling, punching, and straight milling operations.碳治彬菖珉掳隋钯杀炬鲳蓟In the contouring s
12、ystem, also known as the continuous path system, positioning and cutting operations are both along controlled paths but at different velocities. Because the tool cuts as it travels along a prescribed path, accurate control and synchronization of velocities and movements are important. The contouring
13、 system is used on lathes, milling machines, grinders, welding machinery, and machining centers.庞年莛嫂赶皇收砾乇垠堠当Movement along the path, or interpolation, occurs incrementally, by one of several basic methods. In all interpolations, the path controlled is that of the center of rotation of the tool. Comp
14、ensation for different tools, different diameter tools, or tool wear during machining, can be made in the NC program.逭悔嗄褶窠颢力麇佻咬泳琐There are a number of interpolation schemes that have been developed to deal with the various problems that are encountered in generating a smooth continuous path with a c
15、ontouring-type NC system. They include:肝簿镧偿溉雯岑瑙澄蚰烛虑Linear interpolation源淖高传菪笈坜茕帔描灭颧Circular interpolation吻挛坼耶躁谀箕混脍狷鄣组Helical interpolation帅含堞睡挲洄脚筷网癞蠹适Parabolic interpolation痈苓俱谅碹垆催斟摩恨妞鼎Cubic interpolation郐爰恕梧奄郧竖瞬畛涫色访Each of these interpolation procedures permits the programmer (or operator) to gener
16、ate machine instructions for linear or curvilinear paths, using a relatively few input parameters. The interpolation module in the MCU performs the calculations and directs the tool along the path.登嘀焘蝎遽郡樵碗础蒉辐肛Linear interpolation is the most basic and is used when a straight-line path is to be generated in continuous-path NC. Two-axis and three-axis linear interpolation routines are sometimes distinguished in practice, but conceptually
