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1、NUMERICAL CONTROL TECHNOLOGYChapter 1Introduction to Numerical ControlTeacher Xu Cijun 13872082953 62956.Chapter 1INTRODUCTION TO NUMERICAL CONTROL1.1、FundamentalofNCTechnology1.2、ClassificationsofNCMachines1.3、FeaturesofNumericalControlandItsApplicationAreasCourse Description:NC is one of the most
2、importantachievements in mechanical engineering field in20 century.It 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 tec
3、hnical basic classes ofmechanical engineering specialty.Toshibaevents.Chapter 1INTRODUCTION TO NUMERICAL CONTROL1.1.1、DevelopmentHistoryofNC 1946-the first computer appeared in the world,which lift the curtain on the mankind into information time.1948-Parsons Corporation brought forward using comput
4、er to control machinewhen they machined the surface contours of airfoil shape.Parsons Corporation was a mini-helicopter manufacturer.The machining accuracy of the airfoil shape was 0.0381mm.Chapter 1INTRODUCTION TO NUMERICAL CONTROL1.1.1、DevelopmentHistoryofNC Under the support by the U.S Air ForceR
5、esponsed by the Servomechanisms Laboratory at the MIT(Massachusetts Institute of Technology).Chapter 1INTRODUCTION TO NUMERICAL CONTROL1.1.1、DevelopmentHistoryofNC Three years later,in 1952 MIT and Parsons Corporation cooperated with each other,and developed the first NC machine which named Cincinna
6、ti Hydrotel milling machine.Background,time and place.Chapter 1INTRODUCTION TO NUMERICAL CONTROL1.1.1、DevelopmentHistoryofNC The first generation,19521955 vacuum tubes,electrical relays and complicated machine control interfaces.The second generation,19551959 miniature electronic tubes,transistors.T
7、he third generation,19591965 small scale integrated circuits.Chapter 1INTRODUCTION TO NUMERICAL CONTROL1.1.1、DevelopmentHistoryofNC 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 1INTRODUCTION T
8、O NUMERICAL CONTROL1.1.1、DevelopmentHistoryofNC The fourth generation,1970s(19701974)minicomputers.(CNC)The fifth generation,1974-microprocessor.1979(VLIC)(MCNC)1994 PC-NC.Chapter 1INTRODUCTION TO NUMERICAL CONTROL1.1.1、DevelopmentHistoryofNC After the fourth generations,their NC functions were perf
9、ormed by software(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 1INTRODUCTION TO NUMERICAL CONTROL1.1.2ConceptofNCandCNC 1、NC(Numerical Control,数字控制数字控制)Numerical Control（NC）is a form of programmable automation in which the mechan
10、ical actions of a machine tool or other machines are controlled by a program containing coded alphanumeric data.Chapter 1INTRODUCTION TO NUMERICAL CONTROL1.1.2ConceptofNCandCNC 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 reali
11、ze the automation.Chapter 1INTRODUCTION TO NUMERICAL CONTROL1.1.2ConceptofNCandCNC 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 1INTRODU
12、CTION TO NUMERICAL CONTROL1.1.2ConceptofNCandCNC 4、Numerical Control System,(数控系统数控系统)It is the equipment which can realize the numerical control.Chapter 1INTRODUCTION TO NUMERICAL CONTROL1.1.2ConceptofNCandCNC 5、CNC(Computer Numerical Control,计算机数控计算机数控)The machine control units are based on comput
13、er technology.Chapter 1INTRODUCTION TO NUMERICAL CONTROL1.1.3BasicComponentsofNCMachineTools 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 t
14、he numerical input information,which is the control program,also called the part program.Chapter 1INTRODUCTION TO NUMERICAL CONTROL1.1.3BasicComponentsofNCMachineTools The work process of NC is shown as the right figure.PartdrawingPartprogramControlcomputerServo-driveunitMachinetoolPartFirstly,the p
15、art programmer should study the part drawing and the process chart.Chapter 1INTRODUCTION TO NUMERICAL CONTROL1.1.3BasicComponentsofNCMachineTools The work process of NC is shown in the right figure.PartdrawingPartprogramControlcomputerServo-driveunitMachinetoolPartThen the part programmer should pre
16、pare the control program on a standard form in the specified format.It contains all the necessary control information.Chapter 1INTRODUCTION TO NUMERICAL CONTROL1.1.3BasicComponentsofNCMachineTools The work process of NC is shown in the right figure.PartdrawingPartprogramControlcomputerServo-driveuni
17、tMachinetoolPartNext 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 1INTRODUCTION TO NUMERICAL CONTROL1.1.3BasicComponentsofNCMachineTools The work process of NC is shown in the right figure.Pa
18、rtdrawingPartprogramControlcomputerServo-driveunitMachinetoolPartAt last,the servo-drive unit drives the machine tool to manufacture the finished part.Chapter 1INTRODUCTION TO NUMERICAL CONTROL1.1.3BasicComponentsofNCMachineTools A typical NC machine tool has five fundamental units:(1)the input medi
19、a;(2)the machine control unit;(3)the servo-drive unit;(4)the feedback transducer;(5)the mechanical machine tool unit.Chapter 1INTRODUCTION TO NUMERICAL CONTROL1.1.3BasicComponentsofNCMachineTools The general relationship among the five components is illustrated in the below.Chapter 1INTRODUCTION TO
20、NUMERICAL CONTROL1.1.3BasicComponentsofNCMachineTools 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 1INTRODUCTION TO NUMERICAL CONTROL1.1.3BasicCom
21、ponentsofNCMachineTools 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 1INTRODUCTION TO NUMERICAL CONTROL1.1.3BasicComponentsofNCMachineTools Now,The common medium is diskette,electronic transf
22、er from a computer(RS232C):.Chapter 1INTRODUCTION TO NUMERICAL CONTROL1.1.3BasicComponentsofNCMachineTools 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 comma
23、nd 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 1INTRODUCTION TO NUMERICAL CONTROL1.1.3BasicComponentsofNCMachineTools Spindle and feed drive motors and their servo-amplifiers are the
24、components 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 ampl
25、ify them to the high voltage levels required by the drive motors.The drives in machine tools are classified as spindle and feed drive mechanisms.Chapter 1INTRODUCTION TO NUMERICAL CONTROL1.2CLASSIFICATIONSOFNCMACHINE Numerical control machines are classified in different way:(1)The types of NC motio
26、n control system;(2)The type of servo-drive system;(3)Application of NC.Chapter 1INTRODUCTION TO NUMERICAL CONTROL1.2.1TypesofNCMotionControlSystem 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
27、;（连续控制或（连续控制或轮廓轮廓控制系统）控制系统）.Chapter 1INTRODUCTION TO NUMERICAL CONTROL1.2.1TypesofNCMotionControlSystem1.2.1.1 Point-to-point control systemPointtopoint(positioning)controlinNC It is also called Positioning control system,Which moves the worktable to a programmed location without regard to the path
28、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 1INTRODUCTION TO NUMERICAL CONTROL1.2.1Typesof
29、NCMotionControlSystem1.2.1.1 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 done along straight or 450 vectors
30、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 1INTRODUCTION TO NUMERICAL CONTROL1.2.1TypesofNCMotionControlSystem1.2.1.2 Contouring Control System It is also called continuous path control system,which manages the
31、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-dimensional contours in the workpiece,such as milling and t
32、urning operations.Chapter 1INTRODUCTION TO NUMERICAL CONTROL1.2.1TypesofNCMotionControlSystem1.2.1.3 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
33、succession so that the machined surface closely matches the desired shape.Chapter 1INTRODUCTION TO NUMERICAL CONTROL1.2.2TypesofNCServo-DriveSystem 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 dif
34、ferent 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 1INTRODUCTION TO NUMERICAL CONTROL1.2.2TypesofNCServo-DriveSystem1.2.2.1 Open-Loop Servo-Drive It is the simplest and l
35、east 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 motorWorktableLeadscrewPulse train.Chapter 1INTRODUCTION TO NUMERICAL CONTROL1
36、.2.2TypesofNCServo-DriveSystem1.2.2.2 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 po
37、sition signal with the drive signal of the servomotor.Chapter 1INTRODUCTION TO NUMERICAL CONTROL1.2.2TypesofNCServo-DriveSystem1.2.2.2 Half-Closed-Loop Servo-DrivePosition compare circuitSpeed control circuitWorktableInstructionSpeed feedback signalPosition feedback signal LeadscrewServomotor.Chapte
38、r 1INTRODUCTION TO NUMERICAL CONTROL1.2.2TypesofNCServo-DriveSystem1.2.2.3 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 worktabl
39、e,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 1INTRODUCTION TO NUMERICAL CONTROL1.2.2TypesofNCServo-DriveSystem1.2.2.3 Closed-Loop Servo-DrivePosition compare
40、circuitSpeed control circuitWorktableInstructionSpeed feedback signalPosition feedback signal LeadscrewServomotor.Chapter 1INTRODUCTION TO NUMERICAL CONTROL1.2.3ApplicationofCNC The applications of CNC are divided into two categories:(1)Machine tool applications;(2)non-machine tool applications.It s
41、hould 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 1INTRODUCTION TO NUMERICAL CONTROL1.2.3ApplicationofCNC1.2.3.1 Machine Tool Application The most common applications of NC are in machine t
42、ool 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 controlling the relative motion between a cutting tool and the workpiece,the desired geometry is created.Chapter 1INTRODUCTION TO NUMERI
43、CAL CONTROL1.2.3ApplicationofCNC1.2.3.1 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.Chap
44、ter 1INTRODUCTION TO NUMERICAL CONTROL1.2.3ApplicationofCNC1.2.3.1 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-axi
45、s control.Chapter 1INTRODUCTION TO NUMERICAL CONTROL1.2.3ApplicationofCNC1.2.3.1 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.Chapter
46、1INTRODUCTION TO NUMERICAL CONTROL1.2.3ApplicationofCNC1.2.3.1 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 1INTRODUCTION TO NUMERICAL CONTROL1.2.3ApplicationofCNC1.2.3.1 Machine Tool Application NC
47、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 1INTRODUCTION TO NUMERICAL CONTROL1.2.3ApplicationofCNC1.2.3.1 Machine Tool ApplicationMachine center(加
48、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 1INTRODUCTION TO NUMERICAL CONTROL1.2.3ApplicationofCNC1.2.3.1 Machine
49、 Tool ApplicationMachine center(加工中心加工中心)Machining centers are classified as either vertical or horizontal.Vertical 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 d
50、ie.Horizontal machining centers are particularly used for the large,boxy,and heavy parts.Chapter 1INTRODUCTION TO NUMERICAL CONTROL1.2.3ApplicationofCNC1.2.3.1 Machine Tool ApplicationMachine center(加工中心加工中心).Chapter 1INTRODUCTION TO NUMERICAL CONTROL1.2.3ApplicationofCNC1.2.3.2 Non-Machine Tool App