1、書名：現代數控機床原理與結構（雙語） ISBN： 978-7-111-42403-1作者：郁元正出版社：機械工業出版社本書配有電子課件現代數控機床原理與結構（雙語） ppt 課件Chapter 2Motions & coordinate system of Machine tools2.1 Motions of machine tool 2.2 Machine tool drive 2.3 Coordinate systems 現代數控機床原理與結構（雙語） ppt 課件2.1 Motions of machine tool2.1.1 Purpose of motionsThe purpose

2、 of machine tool motions is to remove materials from workpieces to obtain required shapes, dimensions and surface quality.Motion essentials are tool motions, workpiece motions, and cutting motions.2.1.2 Surface forming motionSurface forming motion is the relative cutting motion between tool and work

3、piece. Types and quantity of surface forming motion determine shape of workpiece, machining method and tool constructions現代數控機床原理與結構（雙語） ppt 課件Outer circular surface turningSurface forming motion consists of :Primary motionFeeding motion現代數控機床原理與結構（雙語） ppt 課件1) Primary motionPrimary motion causes re

4、lative motion between cutting tool and workpiece, and remove material from workpiece.Examples of primary motions:Rotary motion of workpiece (turning)Rotary motion of cutting tools (drilling, milling, boring)Reciprocating motion of cutting tools (broaching, planing)Every machining process must have,

5、and only has a primary motion.現代數控機床原理與結構（雙語） ppt 課件2) Feeding motionFeeding motion causes an secondary relative motion between cutting tool and workpiece, and enables tool can continuously remove material from workpiece to form a desired shape.Examples of feeding motionAxial and radial motions of c

6、utting tool (turning)Step motions of cutting tool or workpiece (planing)Note:Feeding motion can be performed by both cutting tools or workpieces;Two or more feeding motions can co-exist (gear hobbing);Zero feeding motion is possible (broaching).現代數控機床原理與結構（雙語） ppt 課件Thinking Identify primary motions

7、 and feeding motions.PlaningBroachingMilling現代數控機床原理與結構（雙語） ppt 課件2.1.3 Assistant motionsAll motions other than surface forming motions, including plunge motion, indexing motion, alignment motion, fast moving, and other actions.1) Plunge motion Plunge cutting tool into workpiece to obtain a certain

8、dimension2) Indexing motion Periodical moving, rotating of worktable or tool post to machining each surfaces of workpiece, e.g. multi-thread screws turning, polygon machining, etc.現代數控機床原理與結構（雙語） ppt 課件3) Alignment motionIt is used to obtain correct relative positions between cutting tool and workpi

9、ece, e.g. aligning drill to hole center by moving rocker arm of the driller.4) Fast moving and other actionsFast moving improves machining efficiency.Other actions include direction change, clamping, releasing, etc.現代數控機床原理與結構（雙語） ppt 課件2.2Machine tool driveTo realize those necessary motions for mac

10、hining, each NC machine tool should have three basic units:(1) Actuators, e.g. spindle, tool post, worktable, etc. They direct perform machining(2) Drive system, e.g. AC/DC motors, step motors, etc. They produce mechanical motion for actuators. (3) Transmissions. They transfer motion and power from

11、drive system to actuators. Transmissions can be in mechanical, electric, hydraulic and pneumatic現代數控機床原理與結構（雙語） ppt 課件2.2.1 Transmission connectionConnection between actuator and power or between actuators by transmission components.Transmission diagram of CA6140 horizontal lathe2.2.2 Transmission c

12、hain A series of transmission components that consist a transmission connection is known as transmission chain.Two forms of transmission(1) Constant ratio and direction.(2) Variable and direction.Gears, worm gears-shaft, ball screw-nutAdjusting gears, clash gears, clutch gear shiftTransmission chain

13、s include external and internal relations:1) External relationConnecting power unit and actuatorsDriving actuators running at designed speedDetermining machining efficiency and surface roughness rather than shape of workpiece.2) Internal relationConnecting and regulating motions between actuators;Pr

14、ecise transmission ratio is important. Frictional transmission (e.g. clutch) or instantaneous variable ratio (chain drive) is unacceptable; Screw turning requires stringent transmission ratio between spindle rotation and tool post moving to ensure precise thread pitch.2.2.3 Transmission diagramTrans

15、mission diagram briefly represents relative motion paths of surface forming.Symbols for transmission diagramCutting toolSpindleMotorCombined unitConstant ratioHob（滾刀）Variable ratioTransmission diagram of screw turningGear ratio1(external relation)Gear ratio2(internal relation)MotorThread Cutting too

16、lLead screwSpindleFrom NC machine tools, spindle and tool post may be driven by their own motors.2.2.4 Transmission system diagram: XKA5750 milling machineCartesian coordinate (Right hand rules)Descartes (1596-1690)French philosopher, mathematician2.3.1 Standard coordinate system and direction1. ISO

17、 coordinate system2.3 Coordinate system for NC machine tools2. Directions of axes(1) All axes assume that tools move while worktables rest;When worktable moves, it moves along an axis marked with “;Notes: Worktable motion only be considered during machine tool design stage.(2) Positive direction- Th

18、e motion that makes tool and workpiece apart.(3) Positive rotation- Spindle screws into workpiece in right hand thread. 3. Axes1) Z-axisDefinition: Parallel to the axis of spindle, or for those machine tools that has no spindle (e.g. planers), vertical to clamping plane;Positive direction: tool move

19、s away from workpiece2) X-axisDefinition: Usually be horizontal, parallel to clamping plane, and parallel to main cutting direction;Positive direction:For horizontal Z-axis, positive X-axis pointing rightwards when looking from spindle to workpiece.For vertical Z-axis, positive X-axis pointing right

20、wards when looking from spindle to column.For machine tools that have no rotary cutting, X-axis parallel to the direction of main cutting force, and the direction is also defined as positive X-axis.Definitions of X, Y, Z-axis3) Y-axis-axis is vertical to both Z, X-axisPositive direction can be defin

21、ed by right hand rule with known Z, X-axis.Definitions of X, Y, Z-axis4. Additional axesFor complex machine tools, additional axes are introduced sometimes.Secondary linear axes: U, V, W-axis, more, P, Q, R-axisSecondary rotary axes: D, E, F-axisDouble column NC vertical lathe2.3.2 Coordinate system

22、s on machine tools1. Machine originAlso known as absolute origin or home position;A physical position on the machine tool set by manufacturer;Locates at ultimate positive positions of X, Y, Z-axis.2. Reference pointDetermined by stroke limiters;Constant relative position to machine origin (usually are not superposed);Precisely measured before leaving factory;For most machining centers, automatic tool changing is performed at reference point.Coordinate systems on machine toolsVertical axisHorizontal axis2.3.3 Workpiece coordinate system. Workpiece coordinate systemKnown as progr