数控生产设备--中英文翻译

南通职业大学毕业设计 九九、外文翻译外文翻译 NUMERICAL CONTROL OF PRODUCTION EQUIPMENTSNUMERICAL CONTROL OF PRODUCTION EQUIPMENTS Numerical control NC is a of programmable automation in which the processing equipment is controlled by means of numbers, letters, and other symbols. The numbers, letters, and symbols are coded in an appropriate at 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 programs than to make major alterations of the processing equipment. BASIC COMPONENTS OF NCBASIC COMPONENTS OF NC A numerical control system consists of the following three basic components Program of instructions Machine control unit Processing equipment 第 1 页共 16 页 南通职业大学毕业设计 The 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. The program of instructions is the detailed step-by-step commands that direct the processing equipment. In its most common , 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-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. The machine control unit 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. The processing equipment is the third basic component of an NC system. It is the component that pers useful work. In the most common example of numerical control, one that pers 第 2 页共 16 页 南通职业大学毕业设计 machining operations, the processing equipment consists of the worktable and spindle as well as the motors and controls needed to drive them. TYPES OF CONTROL SYSTEMS There are two basic 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 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 another position, and repeats the operation. The path f