Numerical Control NC

1
Numerical Control (NC)
2
Numerical Control (NC)

• ???????? ???????????????????????????????????????
  ???????????????????????????? ?????????????????????
  ????? (????????????????)

3
Numerical Control

• ??????? 1940s Parsons Corp ?????????????????????
  US Air force ????????????????????????????????????
  Cardamatic Milling machine
• 1948 US Air force ??? Parsons Corp ????????
• 1949 Parsons Corp ???? MIT ??? servomechnism Lab
  ????? ???????????????????????????????????????? 2.
  ??????????????????????????????? Cardamatic
• 1951 ???????????????? Numerical Control
  ?????????????????????????? NC machine tool
  ???????????????? ??????? Vertical Milling Machine
  ??? Cincinnati

4
Basic Components of an NC System

• A program of Instructions
• A machine control unit (MCU)
• Processing equipments

5
NC Coordinate Systems
6
Three-dimensional modeling Schemes

• Three Dimensional (3D) Coordinate System
• Right-handed
• Global Coordinate System (GCS)
• Work Coordinate System (WCS)

7
NC Coordinate Systems
8
Motion Control Systems

• 1.a Point-to-Point

9
Motion Control Systems

• 1. b Continue Path control

10
Motion Control Systems

• 2. Interpolation Methods

11
Motion Control Systems

• 2. Interpolation Methods
• Linear
• Circular
• Helical
• Parabolic

12
Motion Control Systems

• 3. Absolute VS Incremental Positioning

13
Computer NC (CNC)

• Feature
• Storage of more one part program
• Various forms of program input
• Program editing at the machine tool
• Fixed cycles and programming subroutines
• Interpolation

14
CNC

• Feature
• Positioning feature of set up
• Cutter length and size compensation
• Acceleration and deceleration calculation
• Communication interface
• Diagnostics
• Tool life Monitoring

15
(No Transcript)
16
?????????
17
(No Transcript)
18
NC Program

• ISO format G-M code
• Prefix
• N Line Number
• G G-code gt ?????????? position gtG01
• X Y Z Coordinate data gt x 75
• R Radius of arc
• I J K Coordinate arc
• F feed , S Spindle Speed
• T Tool no. , D tool dia.
• M M code ???Auxiliary Function ????
  ???????????????

19
Path-Program

• N10 G00 X100 Y100
• N20 G01 X110 Y120 F100 S1000
• N30 G02 R100 I50 J50

20
The machine Control Unit for CNC
21
CNC Auxiliary Function

• Coolant control
• Tool Change and Tool storage unit
• Fixture clamping device
• Emergency warning or stop
• Robot for part loading/unloading
• Times
• Counters

22
DNC

• Direct Numerical Control
• Distributed Numerical Control

23
Direct Numerical Control
24
Distributed Numerical Control
25
NC Characteristics

• Batch production
• Repeat orders
• Complex part geometry
• Much metal needs to be removed from the workpart
• Many separate machining operations on the part
• The part is expensive

26
Advantages of NC

• Nonproductive time is reduced
• Greater accuracy and repeatability
• Low scrap rates
• Inspection requirements are reduce
• More-complex part geometries are possible
• Engineering change can be accommodated more
  gracefully
• Simpler fixture are needed
• Shorter manufacturing lead time
• Reduced part inventory
• Less floorspace required
• Operation skill-level requirements are reduced

27
Engineering Analysis of NC positioning systems

• Open-Loop Positioning System
• Close-Loop Positioning System

28
Open-Loop Positioning System

• Leadscrew rotational speed (rev/min)
• N 60 fp
• ns rg
• fp Pulse train frequency (Hz, Pulse/sec)
• ns Steps per rev rg Gear ratio
• Table travel speed
• vt fr N p
• fr table feed rate N lead screw
  rotational speed
• p lead screw pitch
• fp vt ns rg
• 60p

29
Example 6.7 p.182

• The worktable of a positioning system is driven
  by a leadscrew whose pitch 6.0 mm. The
  leadscrew is connected to the output shaft of a
  stepping through gear box 51
• The step motor 48 step angles. Table distance
  250 mm. linear velocity 500 mm/min ?? a) np ?
  b)fp ?
• p 6.0 , rg 5, ns 48 x 250 mm
• vt 500 mm/min

30

• a) Lead screw ???? ??????
• 1??? gt 6 mm ??????????????????? 250 mm
• ??????? 250/6 41.6666 ???
• ??????????????? 41.6666 ??? x 360 ????
• 15,000 ????
• ???????????????? 51
• ??????????? 15000 x 5 75,000 ????
• ?????? ????????? 48 Pulse ???????????
• 1 Pulse 360/487.5 ????
• ????????????????????? 75000/7.5 10,000 Pulse

p
31

• b) Vt 500 mm/min 1 ??? 6 mm
• Lead screw ???????????? 500 / 6 83.333 rpm
• ???????????????? 51
• ??????????? 83.33 x 5 416.666 rpm
• ?????? ????????? 48 Pulse
• ??????????? 416.666 x 48
• 20,000 pulse/min
• ?????? Hz (Pulse/sec) 20,000/60
• 333.33 pulse/sec (Hz)

32
Close-Loop Positioning System
33
Precision in NC Positioning
34
Precision in NC Positioning

• Control resolution of the electromechnical
  components
• Open loop
• CR1 P .
• ns rg
• Close loop
• CR1 P .
• ns rg rge

35
Precision in NC Positioning

• Control resolution of the computer control system
  
• CR2 L .
• (2B 1)
• L axis range, B no. of bits

36
Precision in NC Positioning

• Control resolution
• CR Max CR1,CR2
• Accuracy CR 3?
• 2
• Repeatability 3?

37
Precision in NC Positioning

• Control resolution
• CR Max CR1,CR2
• Accuracy CR 3?
• 2
• Repeatability 3?

38
Example

• Standard Deviation 0.0005 mm The range of
  worktable axis is 500 mm There are 16 bits in the
  binary register. Pitch of leadscrew is 6.0 mm.
  rg. 5.0 and ns 192 step/rev
• Determine a) the control resolution b) accuracy
  and c) the repeatability for the positioning
  system

39

• Solution
• CR1 P . 6.0 /(192)(5.0)
  0.00625
• ns rg
• CR2 L 500
  0.00762 mm
• (2B 1) (216 1)
• CR Max 0.00625,0.00762 0.00762 mm
• b) Accuracy CR 3? 0.00762 3(0.0005)
• 2 2
• 0.00531mm
• c) Repeatability 3(0.0005) 0.0015 mm
  

40
Home work

• ??????????? CNC ???????? ??????????????? 32 bits
  ????? ???????????????????? 400 ??. ?????? lead
  screw ??????Pitch ??????? 4 ??. ?????????????????
  ????????? 31 ????? 96 Steps??????????????????????
  ???????????????????????????? 5 ?????
  ????????????
• 400.0001 400.0002 400.0000 400.0004 400.0002
• ??????? a) the control resolution b) accuracy and
  
• c) the repeatability for the
  positioning system

41
Home Work

• ???? 194-196
• ??? 6.24
• ??? 6.42