A New Measurement System for Active Compensation of Positioning Errors in Large Milling Machines

Transcription

1 A New Measurement System for Active Compensation of Positioning Errors in Large Milling Machines P. Bosetti Research funded by PAMA S.p.A., Italy 1

2 Contents Active error compensation in machine tools 2 m Deformation measurement system: the concept 9 m Design and development of the demonstrator Performance of the demonstrator 20 m Future developments 2

3 Università di Trento Active error compensation in Può essere più utile visualizzare l'intensità dell'errore globale (il modulo di EEe) a tre differenti qu montante (y=0,y=1000,y=2000): in questo caso, i tre assi del grafico rappresentano la posizio posizione z e il modulo dell'errore (in mm): machine tools norm@l_listd := Sqrt@Apply@Plus, Map@# ^ 2 &, lddd; 3

4 Error budget Positioning Errors Static errors Quasi-static errors Dynamic errors Squareness Form errors Kinematic errors Thermal def'ns Foundations Backlash Tool wear Dynamic loads Machining load Fixturing DC <1 Hz!1Hz 4

5 Error budget Positioning Errors Static errors Quasi-static errors Dynamic errors Squareness Form errors Kinematic errors Thermal def'ns Foundations Backlash Tool wear 70% of total error Dynamic loads Machining load Fixturing DC <1 Hz!1Hz 5

6 Active compensation Deterministic/Static errors Volumetric error compensation (HTM) Time-dependent errors Field values (temperature) Structural deformations 6

7 n 1 L 2 n 3 n i 2 L 2i 4 n i n m 1 L 1 L 3 L 2i 3 n 2 n i 1 n m 2 n m Deformation measurement system: the concept 7

8 The idea Direct measurement of the displacement field Reticular array of instrumented beams Real time computation of the nodal positions by triangulation 8

9 Triangulation n 1 L 2 n 3 n i 2 L 2i 4 n i n m 1 L 1 L 3 L 2i 3 n 2 n i 1 n m 2 n m { (xi x i 1 ) 2 + (y i y i 1 ) 2 = L 2 2i 3 (x i x i 2 ) 2 + (y i y i 2 ) 2 = L 2 2i 4 { xi = f x (x i 1, y i 1, x i 2, y i 2, L 2i 3, L 2i 4 ) y i = f y (x i 1, y i 1, x i 2, y i 2, L 2i 3, L 2i 4 ) i = 3... m Initial condition: { n1 = (x 1, y 1 ) = (0, 0) n 2 = (x 2, y 2 ) = (0, L 1 ) 9

10 n 1 L 3 L 2 n 3 Rigid rotation n i 2 n i L 2i 4 L 2i 3 n m 1 L 1 n i 1 n m 2 n m n 2 θ θ = tan 1 ( ym y 2 x m x 2 ) = tan 1 ( ym x m ) n i = ( cos θ sin θ sin θ cos θ ) n i 10

11 Prestressed bars with FBG Design and development of the demonstrator 11

12 Choice of strain sensors Requirements: no drift non need for re-calibration after system shutdown low- or no-sensitivity to EMF simple cabling choice: Fiber-optic Bragg Grating (FBG) strain sensors 12

13 Nominal FBG performance Wavelength Division Multiplexing measurement system Up to 4x128 FBG sensors Resolution: 0.5 pm (wavelength), 1 µstrain Wavelength stability: 2 pm Optical dynamic range: 15 db Acquisition frequency: 250 Hz 13

14 Is that enough? y [m] Ground x [m] Resolution: 1 µstrain 14

15 Yes. Vertical displacement [m] 5e-04-5e e-05 0 FEM! SDD Horizontal position [m] 15

16 Demonstrator 16

17 Hardware!"#$%&&'()#*%+%+,#-&".()#*%+/%0+/)1#-&"'&#"%+%+/%0+2"#&#&)2#+/ m x 0.3 m x 2.0 m reticular structure (Rexroth) supported on 2 rigid end blocks!"#$%&'()*'+",-./%&/-%0'1-2'344',-2/&/-5' + 60)+ '22#$$)+ -#*#+,#-&)&.)&)+ /'+ 70#,,8)+ )*+,%1%*&#9+,8%+ #::"#*#+ '0&'+ "%-,#12"%--)#*%+ 0)1)&'*/#+ '0+ 1)*)1#+ $0)+ -2#-&'1%*&)+ )*+ /)"%()#*%+ ;%"&),' %-&%"*)<++ 12 mesh measurement system 12 nodes 25 bars, 25 FBG sensors +!"#$%&'()*'+",-./%&/-%0'1-2'344',-2/&/-5' + 60)+ '22#$$)+ -#*#+,#-&)&.)&)+ /'+ 70#,,8)+ )*+,%1%*&#9+,8%+ #::"#*#+ '0&'+ "%-)-&%*(,#12"%--)#*%+ 0)1)&'*/#+ '0+ 1)*)1#+ $0)+ -2#-&'1%*&)+ )*+ /)"%()#*%+ ;%"&),'0%+ /%) %-&%"*)<++ + +!"#$%&'(6*'7&%/"1-8&%0'+0889&77-##"-'+08'+",-./%&/-%0'.$8'.$77-%/-5' + 17

18 Performance of the demonstrator 18

19 Measurement system FBG2 FBG1 FBG4 FBG3 Ethernet TCP/IP 19

20 Max displacement: ~20 µm 20

21 Performance!"#$%&&'()#*%+%+,#-&".()#*%+/%0+/)1#-&"'&#"%+%+/%0+2"#&#&)2#+/) Vertical displacement [µm] !"#$%&'(()'*&%+",-.&%/'0/.'*$1+-'0"'%"./2&3/1+-'0/#."'4*-4+&3/1+"'1-0&."5' µm Node number test 1 test 2 test 3 unload dial indicator + &#+/%0+,#12'"'&#"%+/%8%+%--%"%+2#-)()#*'&#+-.0+2'8)1%*&#+)*+1#/#+-&'9)0%:+ Repeatability < 2 µm +)+2)%/)*)+/)+'22#$$)#+)*+1#/#+/'+%8)&'"%+,;%+$0)+-2#-&'1%*&)+/%0+&"'0),,)#+ #8)1%*&)+ /% #"&#+ -&%--#:+,#*+,#*-%$.%*&%+ 2%"/)&'+ /)+ -)$*)<),'&)8)&=+."%+%-%$.)&%>+ Accuracy ~ 3 µm (w.r.t. digital dial indicator) &)(('+,;%+'+/)1#-&"'&#"%+-,'"),#+)+*#/)+/% )'*#+'00)*%'&)+%+0)8%00'&)+-.+ )11%&"),;%+")-2%&&#+'00?'--%+)/%'0%+/%0+/)1#-&"'&#"%@+)*+A.%-&'+-)&.'()#*%+-)+?'((%"'1%*&#+/%)+-%*-#")+/)+/%<#"1'()#*%+%+A.%-&'+,#*<)$."'()#*%+/)8%*&'+'+ %<<%&&)+ )0+ ")<%")1%*&#+ 2%"+ &.&&%+ 0%+ 1)-."'()#*)+ -.,,%--)8%>+ B'+ &'"'&."'+ 21

22 Future developments 22

23 Acquisition and computation Generalized N+1 geometries (simplex) Redundancy Failure detection Accuracy estimation Free Constrained Measured 23

24 Sensor array Industrialization Simplified design easy assembly robust and stable no backlash or mechanical hysteresis 24

25 Active compensation 3-D deformations SDD2 Integration on top of the machine tool structures SDD3 y Connection with the CNC and with other error compensation strategies x z SDD1 25

26 Conclusions Measurement system suitable for quasi-static and for dynamic structural deformations Accuracy: 3 span of 2 m Absolute measure (w.r.t. a given reference condition) Integrates with static errors compensation methods Patenting is in process 26

27 Contacts University of Trento: PAMA S.p.A.: 27

28 Thank you for your attention. 28