数控技术概述

1、62956.Chapter 1 INTRODUCTION TO NUMERICAL CONTROL 1.1、Fundamental of NC Technology1.2、Classifications of NC Machines1.3、Features of Numerical Control and Its Application AreasCourse Description: NC is one of the most importantachievements in mechanical engineering field in20 century. It

2、 is a crossing and integrating technologycomprising of computer technology, automaticcontrol technology, information technology,sense technology, and machining technology. Numerical Control Technology has becameone of the important technical basic classes ofmechanical engineering specialty.Toshiba e

3、vents.Chapter 1 INTRODUCTION TO NUMERICAL CONTROL1.1.1、Development History of NC 1946-the first computer appeared in the world, which lift the curtain on the mankind into information time. 1948-Parsons Corporation brought forward using computer to control machinewhen they machined the surface contou

4、rs of airfoil shape. Parsons Corporation was a mini-helicopter manufacturer. The machining accuracy of the airfoil shape was 0.0381mm.Chapter 1 INTRODUCTION TO NUMERICAL CONTROL1.1.1、Development History of NC Under the support by the U.S Air ForceResponsed by the Servomechanisms Laboratory at the MI

5、T (Massachusetts Institute of Technology).Chapter 1 INTRODUCTION TO NUMERICAL CONTROL1.1.1、Development History of NC Three years later, in 1952 MIT and Parsons Corporation cooperated with each other, and developed the first NC machine which named Cincinnati Hydrotel milling machine.Background, time

6、and place.Chapter 1 INTRODUCTION TO NUMERICAL CONTROL1.1.1、Development History of NC The first generation,19521955 vacuum tubes, electrical relays and complicated machine control interfaces. The second generation,19551959 miniature electronic tubes, transistors. The third generation,19591965 small s

7、cale integrated circuits.Chapter 1 INTRODUCTION TO NUMERICAL CONTROL1.1.1、Development History of NC Above three generations, their NC functions were performed by hardware(electronic circuits), so we call them“hardwired NC”(硬线数硬线数控控) 1955 1959 1965.Chapter 1 INTRODUCTION TO NUMERICAL CONTROL1.1.1、Dev

8、elopment History of NC The fourth generation,1970s (19701974)minicomputers.(CNC) The fifth generation,1974- microprocessor.1979(VLIC)(MCNC)1994 PC-NC.Chapter 1 INTRODUCTION TO NUMERICAL CONTROL1.1.1、Development History of NC After the fourth generations, their NC functions were performed by software

9、(based on computer), so we call them“softwired NC” or “computer numerical control”(计算机数控计算机数控CNC) 1970 1974 1994.Chapter 1 INTRODUCTION TO NUMERICAL CONTROL1.1.2 Concept of NC and CNC 1、NC (Numerical Control,数字控制数字控制) Numerical Control（NC）is a form of programmable automation in which the mechanical

10、actions of a machine tool or other machines are controlled by a program containing coded alphanumeric data.Chapter 1 INTRODUCTION TO NUMERICAL CONTROL1.1.2 Concept of NC and CNC 2、Numerical Control Technology, (数控技术数控技术) It means the technology which adopts NC methods to control a work process to re

11、alize the automation.Chapter 1 INTRODUCTION TO NUMERICAL CONTROL1.1.2 Concept of NC and CNC 3、Numerical Control Machine Tools, (数控机床数控机床) It is a kind of machine tools which adopts the numerical control technology to realize the work process automation.It is a typical example of NC application.Chapt

12、er 1 INTRODUCTION TO NUMERICAL CONTROL1.1.2 Concept of NC and CNC 4、Numerical Control System, (数控系统数控系统) It is the equipment which can realize the numerical control.Chapter 1 INTRODUCTION TO NUMERICAL CONTROL1.1.2 Concept of NC and CNC 5、CNC(Computer Numerical Control, 计算机数控计算机数控) The machine contro

13、l units are based on computer technology.Chapter 1 INTRODUCTION TO NUMERICAL CONTROL1.1.3 Basic Components of NC Machine Tools The control system of a numerically controlled machine tool can handle many tasks commonly done by the operator of a conventional machine. The system has the ability to perf

14、orm the control functions through the numerical input information, which is the control program, also called the part program.Chapter 1 INTRODUCTION TO NUMERICAL CONTROL1.1.3 Basic Components of NC Machine Tools The work process of NC is shown as the right figure.Part drawingPart programControl comp

15、uterServo-drive unitMachine toolPartFirstly, the part programmer should study the part drawing and the process chart.Chapter 1 INTRODUCTION TO NUMERICAL CONTROL1.1.3 Basic Components of NC Machine Tools The work process of NC is shown in the right figure.Part drawingPart programControl computerServo

16、-drive unitMachine toolPartThen the part programmer should prepare the control program on a standard form in the specified format. It contains all the necessary control information.Chapter 1 INTRODUCTION TO NUMERICAL CONTROL1.1.3 Basic Components of NC Machine Tools The work process of NC is shown i

17、n the right figure.Part drawingPart programControl computerServo-drive unitMachine toolPartNext the part program is transferred into the control computer(MDI).the computer converts each command into the signal that the servo-drive unit needs.Chapter 1 INTRODUCTION TO NUMERICAL CONTROL1.1.3 Basic Com

18、ponents of NC Machine Tools The work process of NC is shown in the right figure.Part drawingPart programControl computerServo-drive unitMachine toolPartAt last , the servo-drive unit drives the machine tool to manufacture the finished part.Chapter 1 INTRODUCTION TO NUMERICAL CONTROL1.1.3 Basic Compo

19、nents of NC Machine Tools A typical NC machine tool has five fundamental units:(1)the input media;(2)the machine control unit;(3)the servo-drive unit;(4)the feedback transducer;(5)the mechanical machine tool unit.Chapter 1 INTRODUCTION TO NUMERICAL CONTROL1.1.3 Basic Components of NC Machine Tools T

20、he general relationship among the five components is illustrated in the below.Machine Control unitInput mediaServo- driveMachine toolFeedback Transducer.Chapter 1 INTRODUCTION TO NUMERICAL CONTROL1.1.3 Basic Components of NC Machine ToolsMachine Control unitInput mediaServo- driveMachine toolFeedbac

21、k Transducer The input media contains the program of instructions, it is the detailed step-by-step commands that direct the actions of the machine tool; the program of instructions is called a part program.Chapter 1 INTRODUCTION TO NUMERICAL CONTROL1.1.3 Basic Components of NC Machine ToolsMachine C

22、ontrol unitInput mediaServo- driveMachine toolFeedback Transducer The program is coded on a suitable medium for submission to the machine control unit.The common medium in the past is punched tape, magnetic tape:.Chapter 1 INTRODUCTION TO NUMERICAL CONTROL1.1.3 Basic Components of NC Machine ToolsMa

23、chine Control unitInput mediaServo- driveMachine toolFeedback Transducer Now, The common medium is diskette, electronic transfer from a computer(RS232C):.Chapter 1 INTRODUCTION TO NUMERICAL CONTROL1.1.3 Basic Components of NC Machine ToolsMachine Control unitInput mediaServo- driveMachine toolFeedba

24、ck Transducer MCU consists of a microcomputer and related control hardware that stores the program of instructions and executes it by converting each command into mechanical actions of machine tool, one command at a time.the MCU includes system software,calculation algorithm,and transition software

25、to covert the NC parts program into a usable format for the MCU.Chapter 1 INTRODUCTION TO NUMERICAL CONTROL1.1.3 Basic Components of NC Machine ToolsMachine Control unitInput mediaServo- driveMachine toolFeedback Transducer Spindle and feed drive motors and their servo-amplifiers are the components

26、of the servo-drive unit.The MCU processes the data and generates discrete numerical position commands for each feed drive and velocity command for the spindle drive.The numerical commands are converted into signal voltage by the MCU unit and sent to servo-amplifiers, which process and amplify them t

27、o the high voltage levels required by the drive motors. The drives in machine tools are classified as spindle and feed drive mechanisms.Chapter 1 INTRODUCTION TO NUMERICAL CONTROL1.2 CLASSIFICATIONS OF NC MACHINE Numerical control machines are classified in different way:(1)The types of NC motion co

28、ntrol system;(2)The type of servo-drive system;(3)Application of NC.Chapter 1 INTRODUCTION TO NUMERICAL CONTROL1.2.1 Types of NC Motion Control System Motion control systems for NC can be divided into two types:(1) Point-to-point control system (点位控制系统点位控制系统);(2) Continuous (Contouring)path control

29、system; （连续控制或连续控制或轮廓轮廓控制系统）控制系统）.Chapter 1 INTRODUCTION TO NUMERICAL CONTROL1.2.1 Types of NC Motion Control System1.2.1.1 Point-to-point control systemPoint to point (positioning) control in NC It is also called Positioning control system, Which moves the worktable to a programmed location without

30、 regard to the path taken to get to the location. That is to say ,the path between points is of little concern and is not particularly controlled. The program consists of a series of point locations at which operations are performed. Such as drilling or punching a hole.Chapter 1 INTRODUCTION TO NUME

31、RICAL CONTROL1.2.1 Types of NC Motion Control System1.2.1.1 point-to-point control system Many NC point to-point systems contain a more complex MCU. IN these servos, positioning commands are evaluated simultaneously so that vector motion in two axes is possible. The movements between points can be d

32、one along straight or 450 vectors paths determined by the machine ways or slides. Such systems are some times called straight-cut control system.（点位点位/直线）直线）.Chapter 1 INTRODUCTION TO NUMERICAL CONTROL1.2.1 Types of NC Motion Control System1.2.1.2 Contouring Control System It is also called continuo

33、us path control system, which manages the simultaneous motion (resultant motion)of the cutting tool in two, three, four, of five axes by interpolating(插补插补)the proper path between prescribed points. It enables the cutting tool to generate angular surfaces, two-dimensional curves, or three-dimensiona

34、l contours in the workpiece, such as milling and turning operations.Chapter 1 INTRODUCTION TO NUMERICAL CONTROL1.2.1 Types of NC Motion Control System1.2.1.3 Interpolation To cut along a circular path,the circle must be divided into a series of straight-line segments that approximate the circular pa

35、th.The tool is commanded to machine each line segment in succession so that the machined surface closely matches the desired shape.Chapter 1 INTRODUCTION TO NUMERICAL CONTROL1.2.2 Types of NC Servo-Drive System The principal function of NC is the positioning of the tool or the machine table in accor

36、dance with the programmed data. Industry has developed three different types of drives based on how the NC system accomplishes positioning. These are the open-loop（开环）开环）, the closed-loop（闭环）闭环） and half closed-loop（半闭环）半闭环） drive system.Chapter 1 INTRODUCTION TO NUMERICAL CONTROL1.2.2 Types of NC S

37、ervo-Drive System1.2.2.1 Open-Loop Servo-Drive It is the simplest and least cost form of servo-drive. It is characterized as a system that lacks feedback . That is , once an input control signal is sent , there is no sensing device to confirm the action of the control signal.Driving circuitStepping

38、motorWorktableLeadscrewPulse train.Chapter 1 INTRODUCTION TO NUMERICAL CONTROL1.2.2 Types of NC Servo-Drive System1.2.2.2 Half-Closed-Loop Servo-Drive It is characterized as a system that the indirect feedback monitors the output of servomotor.Although this method is popular with NC systems, it is n

39、ot as accurate as direct feedback, The half-closed-loop system compares the command position signal with the drive signal of the servomotor.Chapter 1 INTRODUCTION TO NUMERICAL CONTROL1.2.2 Types of NC Servo-Drive System1.2.2.2 Half-Closed-Loop Servo-DrivePosition compare circuitSpeed control circuit

40、WorktableInstructionSpeed feedback signalPosition feedback signal LeadscrewServomotor.Chapter 1 INTRODUCTION TO NUMERICAL CONTROL1.2.2 Types of NC Servo-Drive System1.2.2.3 Closed-Loop Servo-Drive It is characterized as a system that the direct feedback monitors the output of servomotor. A feedback

41、sensor directly measures the position of worktable. With its drive signal originated by the worktable, It is the preferred system because it monitors the actual position of the worktable on which the part is mounted. It is more accurate; however, its implementation costs are higher.Chapter 1 INTRODU

42、CTION TO NUMERICAL CONTROL1.2.2 Types of NC Servo-Drive System1.2.2.3 Closed-Loop Servo-DrivePosition compare circuitSpeed control circuitWorktableInstructionSpeed feedback signalPosition feedback signal LeadscrewServomotor.Chapter 1 INTRODUCTION TO NUMERICAL CONTROL1.2.3 Application of CNC The appl

43、ications of CNC are divided into two categories:(1)Machine tool applications;(2) non-machine tool applications. It should be noted that the applications are not always identified by the name “numerical control”, this term is used principally in the machine tool industry.Chapter 1 INTRODUCTION TO NUM

44、ERICAL CONTROL1.2.3 Application of CNC1.2.3.1 Machine Tool Application The most common applications of NC are in machine tool control, machining was the first application of NC . Machining is a manufacturing process in which the geometry of work is produced by removing excess material. By controllin

45、g the relative motion between a cutting tool and the workpiece, the desired geometry is created.Chapter 1 INTRODUCTION TO NUMERICAL CONTROL1.2.3 Application of CNC1.2.3.1 Machine Tool Application The common NC machine tools are listed in the following along with their typical features: NC lathe (数控车

46、床数控车床) Turning requires two-axis continuous path control, either to produce a straight cylindrical geometry or to create a profile.Chapter 1 INTRODUCTION TO NUMERICAL CONTROL1.2.3 Application of CNC1.2.3.1 Machine Tool Application NC boring mill (数控镗铣床数控镗铣床) horizontal or vertical spindle. Boring is

47、 similar to turning, except that an internal cylinder is created instead of an external cylinder. The operation requires continuous path, two-axis control.Chapter 1 INTRODUCTION TO NUMERICAL CONTROL1.2.3 Application of CNC1.2.3.1 Machine Tool Application NC drill press (数控钻床数控钻床) These machines use

48、point-to-point control of workhead and two axis control of the worktable. Some NC drill presses have turrets containing six or eight drill bits.Chapter 1 INTRODUCTION TO NUMERICAL CONTROL1.2.3 Application of CNC1.2.3.1 Machine Tool Application NC milling machine (数控铣床数控铣床) It requires continuous pat

49、h control to perform straight cut or contouring operations.Chapter 1 INTRODUCTION TO NUMERICAL CONTROL1.2.3 Application of CNC1.2.3.1 Machine Tool Application NC grinding machine (数控磨床数控磨床) It is intended for finishing treatment of workparts. The grinding machine includes cylindrical-, surface-, int

50、ernal-, spindle-,thread- ,gear-and tool-grinding machines.Chapter 1 INTRODUCTION TO NUMERICAL CONTROL1.2.3 Application of CNC1.2.3.1 Machine Tool ApplicationMachine center (加工中心加工中心) It is defined as multifunction NC machines with automatic tool changer and tool storage.It has the ability to perform

51、 drilling, turning, reaming, boring, milling, contouring, and threading operations on a single machine.Chapter 1 INTRODUCTION TO NUMERICAL CONTROL1.2.3 Application of CNC1.2.3.1 Machine Tool ApplicationMachine center (加工中心加工中心) Machining centers are classified as either vertical or horizontal. Verti

52、cal machining centers continue to be widely accepted and used, primarily for flat parts and where three-axis machining is required on the surface of a single part such as the mold and the die. Horizontal machining centers are particularly used for the large,boxy, and heavy parts.Chapter 1 INTRODUCTI

53、ON TO NUMERICAL CONTROL1.2.3 Application of CNC1.2.3.1 Machine Tool ApplicationMachine center (加工中心加工中心).Chapter 1 INTRODUCTION TO NUMERICAL CONTROL1.2.3 Application of CNC1.2.3.2 Non-Machine Tool ApplicationPunch presses for sheet metal hole punching (数控冲床数控冲床) The two-axis NC operation is similar

54、to that of a drill press except that holes are produced by punching rather than by drilling.Chapter 1 INTRODUCTION TO NUMERICAL CONTROL1.2.3 Application of CNC1.2.3.2 Non-Machine Tool ApplicationPresses for sheet metal bending (数控折弯机数控折弯机) Instead of cutting sheet metal, these systems bend sheet met

55、al according to programmed commands.Chapter 1 INTRODUCTION TO NUMERICAL CONTROL1.2.3 Application of CNC1.2.3.2 Non-Machine Tool ApplicationWelding machine (数控焊接机数控焊接机) Both spot welding and continuous arc welding machines are available with automatic controls based on NC.Chapter 1 INTRODUCTION TO NUMERICAL CONTROL1.2.3 Application of CNC1.2.3.2 Non-Machine Tool ApplicationThermal cutting machine (数控热切割机数控热切割机) Such as oxyfuel cutting(火火焰切割焰切割),laser cutting(激光切激光切割割), and pla