1、.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 is a crossing and i
2、ntegrating 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 events.Chapter 1 INTRODUC
3、TION 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 contours of airfoil shape.Parson
4、s 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 MIT(Massachusetts Institute of
5、 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 and place.Chapter 1 INTRODUCTION
6、 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 scale integrated circuits.Chapter 1 I
7、NTRODUCTION 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”(硬线数控硬线数控)1955 1959 1965.Chapter 1 INTRODUCTION TO NUMERICAL CONTROL1.1.1、Development History of NC The fourth gener
8、ation,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(based on computer),so we call them“softwir
9、ed NC”or“computer numerical control”(计算计算机数控机数控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 actions of a machine tool or other machines are c
10、ontrolled 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 realize the automation.Chapter 1 INTRODUCTION TO NUME
11、RICAL 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.Chapter 1 INTRODUCTION TO NUMERICAL CONTROL1.1.2 Concept o
12、f 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 control units are based on computer technology.Chapter 1 INTROD
13、UCTION 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 perform the control functions through the numerical input info
14、rmation,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 computerServo-drive unitMachine toolPartFirstly,the part program
15、mer 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-drive unitMachine toolPartThen the part programmer should pr
16、epare 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 in the right figure.Part drawingPart programControl computerSer
17、vo-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 Components of NC Machine Tools The work process of NC is shown in
18、 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 Components of NC Machine Tools A typical NC machine tool has five fun
19、damental 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 The general relationship among the five components is illustrated
20、 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 toolFeedback Transducer The input media contains the program of instructions,
21、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 Control unitInput mediaServo-driveMachine toolFeedback Transducer The
22、 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 ToolsMachine Control unitInput mediaServo-driveMachine toolFeedback Transduce
23、r 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 toolFeedback Transducer MCU consists of a microcomputer and related control hardware
24、 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 to covert the NC parts program into a usable format for the MCU.Chapter 1 I
25、NTRODUCTION 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 of the servo-drive unit.The MCU processes the data and generates discrete nu
26、merical 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 to the high voltage levels required by the drive motors.The drives in machine
27、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 control system;(2)The type of servo-drive system;(3)Application of NC.Chapter 1
28、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 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.
29、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 regard to the path taken to get to the location.That is to say,the path between poi
30、nts 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 NUMERICAL CONTROL1.2.1 Types of NC Motion Control System1.2.1.1 point-to-point control syste
31、m 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 done along straight or 450 vectors paths determined by the machine ways or slides.Such syste
32、ms 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 continuous path control system,which manages the simultaneous motion(resultant motion)of the cuttin
33、g 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-dimensional contours in the workpiece,such as milling and turning operations.Chapter 1 INTRODUCTION TO NUMERI
34、CAL 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 path.The tool is commanded to machine each line segment in succession so that the machined surface clo
35、sely 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 accordance with the programmed data.Industry has developed three different types of drives based on how t
36、he 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 Servo-Drive System1.2.2.1 Open-Loop Servo-Drive It is the simplest and least cost form of servo-drive.I
37、t 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 motorWorktableLeadscrewPulse train.Chapter 1 INTRODUCTION TO NUMERICAL CONTROL1.2.2 Types of NC Servo-Drive S
38、ystem1.2.2.2 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 not as accurate as direct feedback,The half-closed-loop system compares the command position signal with the dr
39、ive 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 circuitWorktableInstructionSpeed feedback signalPosition feedback signal LeadscrewServomotor.Chapter 1 INTRODUCTION TO
40、 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 sensor directly measures the position of worktable.With its drive signal originated by the worktable,It is the p
41、referred 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 INTRODUCTION TO NUMERICAL CONTROL1.2.2 Types of NC Servo-Drive System1.2.2.3 Closed-Loop Servo-DrivePosition compare circuit
42、Speed control circuitWorktableInstructionSpeed feedback signalPosition feedback signal LeadscrewServomotor.Chapter 1 INTRODUCTION TO NUMERICAL CONTROL1.2.3 Application of CNC The applications of CNC are divided into two categories:Machine tool applications;non-machine tool applications.It should be
43、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 NUMERICAL CONTROL1.2.3 Application of CNC1.2.3.1 Machine Tool Application The most common applications of NC are in machine tool c
44、ontrol,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 controlling the relative motion between a cutting tool and the workpiece,the desired geometry is created.Chapter 1 INTRODUCTION TO NUMERICAL
45、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(数控车床数控车床)Turning requires two-axis continuous path control,either to produce a straight cylindrical geometry or to create a profile.Chapt
46、er 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 similar to turning,except that an internal cylinder is created instead of an external cylinder.The operation requires continuous path,two-
47、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 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.C
48、hapter 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 path control to perform straight cut or contouring operations.Chapter 1 INTRODUCTION TO NUMERICAL CONTROL1.2.3 Application of CNC1.2.3.1 Machine Tool
49、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-,internal-,spindle-,thread-,gear-and tool-grinding machines.Chapter 1 INTRODUCTION TO NUMERICAL CONTROL1.2.3 Application of CNC1.2.3.1 Machine Tool Applicat
50、ionMachine 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 drilling,turning,reaming,boring,milling,contouring,and threading operations on a single machine.Chapter 1 INTRODUCTION TO NUMERICAL CONTROL1.2.3 Applicatio
