1、书名：现代数控机床原理与结构（双语）ISBN：978-7-111-42403-1作者：郁元正出版社：机械工业出版社本书配有电子课件,现代数控机床原理与结构（双语）ppt 课件,Chapter 2Motions&coordinate system of Machine tools,2.1 Motions of machine tool 2.2 Machine tool drive 2.3 Coordinate systems,现代数控机床原理与结构（双语）ppt 课件,2.1 Motions of machine tool,2.1.1 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 workpiec
3、e.Types and quantity of surface forming motion determine shape of workpiece,machining method and tool constructions,现代数控机床原理与结构（双语）ppt 课件,Outer circular surface turning,Surface forming motion consists of:Primary motionFeeding motion,现代数控机床原理与结构（双语）ppt 课件,1)Primary motionPrimary motion causes relativ
4、e 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,and only has
5、 a primary motion.,现代数控机床原理与结构（双语）ppt 课件,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 cutting tool(t
6、urning)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).,现代数控机床原理与结构（双语）ppt 课件,Thinking,Identify primary motions and feeding mo
7、tions.,Planing,Broaching,Milling,现代数控机床原理与结构（双语）ppt 课件,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 dimension2)Indexi
8、ng motion Periodical moving,rotating of worktable or tool post to machining each surfaces of workpiece,e.g.multi-thread screws turning,polygon machining,etc.,现代数控机床原理与结构（双语）ppt 课件,3)Alignment motionIt is used to obtain correct relative positions between cutting tool and workpiece,e.g.aligning drill
9、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.,现代数控机床原理与结构（双语）ppt 课件,2.2Machine tool driveTo realize those necessary motions for machining,each NC machine tool
10、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 drive system to actuators.Transmissions can
11、be in mechanical,electric,hydraulic and pneumatic,现代数控机床原理与结构（双语）ppt 课件,2.2.1 Transmission connectionConnection between actuator and power or between actuators by transmission components.,Transmission diagram of CA6140 horizontal lathe,2.2.2 Transmission chain A series of transmission components tha
12、t consist a transmission connection is known as transmission chain.Two forms of transmissionConstant ratio and direction.Variable and direction.,Gears,worm gears-shaft,ball screw-nut,Adjusting gears,clash gears,clutch gear shift,Transmission chains include external and internal relations:1)External
13、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;Precise transmission ratio is important.Frictional trans
14、mission(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 diagramTransmission diagram briefly represents relative motion paths of
15、 surface forming.,Symbols for transmission diagram,Transmission diagram of screw turning,From NC machine tools,spindle and tool post may be driven by their own motors.,2.2.4 Transmission system diagram:XKA5750 milling machine,Cartesian coordinate(Right hand rules),Descartes(1596-1690)French philosop
16、her,mathematician,2.3.1 Standard coordinate system and direction1.ISO coordinate system,2.3 Coordinate system for NC machine tools,2.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 con
17、sidered during machine tool design stage.,(2)Positive direction-The 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)
18、,vertical to clamping plane;Positive direction:tool moves away from workpiece,2)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 workpiec
19、e.For vertical Z-axis,positive X-axis pointing rightwards 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-axis,3)Y-axis-axis is vertical
20、 to both Z,X-axisPositive direction can be defined by right hand rule with known Z,X-axis.,Definitions of X,Y,Z-axis,4.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-axis,Double column NC v
21、ertical lathe,2.3.2 Coordinate systems 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 pos
22、ition 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 tools,Vertical axis,Horizontal axis,2.3.3 Workpiece coordinate system.Workpiece coordinate s
23、ystemKnown as program coordinate.It gives a reference position of each point of a workpiece.Once the workpiece coordinate is determined,position of the workpiece on the worktable is determined as well.,2.Workpiece originAlso know as program origin.It is usually the datum point of the workpiece.Using instruction G92 or G54G59 to set workpiece origin.,2.3.4 Clamping originClamping origin is usually a constant point on worktable.The offset between clamping origin and machine origin can be precisely measured and stored in CNC system.For convenient,clamping origin sometimes locates on fixture.,
