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
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
0 2000 X @mmd Università di Trento 4000 2000 1500 1000 Y @mmd 500 0 1000 500 Z @mmd 0 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
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
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
Active compensation Deterministic/Static errors Volumetric error compensation (HTM) Time-dependent errors Field values (temperature) Structural deformations 6
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
The idea Direct measurement of the displacement field Reticular array of instrumented beams Real time computation of the nodal positions by triangulation 8
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
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
Prestressed bars with FBG Design and development of the demonstrator 11
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
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
Is that enough? y [m] Ground x [m] Resolution: 1 µstrain 14
Yes. Vertical displacement [m] 5e-04-5e-05 0 5e-05 0 FEM! SDD 2 4 6 8 10 Horizontal position [m] 15
Demonstrator 16
Hardware!"#$%&&'()#*%+%+,#-&".()#*%+/%0+/)1#-&"'&#"%+%+/%0+2"#&#&)2#+/ + 0.3 m x 0.3 m x 2.0 m reticular structure (Rexroth) supported on 2 rigid end blocks!"#$%&'()*'+",-./%&/-%0'1-2'344',-2/&/-5' + 60)+ '22#$$)+ -#*#+,#-&)&.)&)+ /'+ 70#,,8)+ )*+,%1%*	+,8%+ #::"#*#+ '0&'+ "%-,#12"%--)#*%+ 0)1)&'*/#+ '0+ 1)*)1#+ $0)+ -2#-&'1%*&)+ )*+ /)"%()#*%+ ;%"&),' %-&%"*)<++ 12 mesh measurement system 12 nodes 25 bars, 25 FBG sensors +!"#$%&'()*'+",-./%&/-%0'1-2'344',-2/&/-5' + 60)+ '22#$$)+ -#*#+,#-&)&.)&)+ /'+ 70#,,8)+ )*+,%1%*	+,8%+ #::"#*#+ '0&'+ "%-)-&%*(,#12"%--)#*%+ 0)1)&'*/#+ '0+ 1)*)1#+ $0)+ -2#-&'1%*&)+ )*+ /)"%()#*%+ ;%"&),'0%+ /%) %-&%"*)<++ + +!"#$%&'(6*'7&%/"1-8&%0'+0889&77-##"-'+08'+",-./%&/-%0'.$8'.$77-%/-5' + 17
Performance of the demonstrator 18
Measurement system FBG2 FBG1 FBG4 FBG3 Ethernet TCP/IP 19
Max displacement: ~20 µm 20
Performance!"#$%&&'()#*%+%+,#-&".()#*%+/%0+/)1#-&"'&#"%+%+/%0+2"#&#&)2#+/)+344+ + 5.0 1-0.000006-6.000-0.000006-6.000-0.000006 3-0.000012-12.027-0.000011-11.386-0.000011 5-0.000020-19.632-0.000019-18.737-0.000019 7-0.000022-21.933-0.000022-21.918-0.000022 9-0.000017-16.694-0.000017-16.813-0.000017 11-0.000013-12.557-0.000012-11.558-0.000013 13-0.000001-1.000-0.000001-1.000-0.000001 Vertical displacement [µm] 0.0-5.0-10.0-15.0-20.0!"#$%&'(()'*&%+",-.&%/'0/.'*$1+-'0"'%"./2&3/1+-'0/#."'4*-4+&3/1+"'1-0&."5' + -25.0 1 3 5 7 9 11 13 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)&'"%+,;%+$0)+-2#-&'1%*&)+/%0+&"'0),,)#+ #8)1%*&)+ /%0+ -.22#"&#+ -&%--#:+,#*+,#*-%$.%*&%+ 2%"/)&'+ /)+ -)$*)<),'&)8)&=+."%+%-%$.)&%>+ Accuracy ~ 3 µm (w.r.t. digital dial indicator) &)(('+,;%+'+/)1#-&"'&#"%+-,'"),#+)+*#/)+/%0+344+-)'*#+'00)*%'&)+%+0)8%00'&)+-.+ )11%&"),;%+")-2%&&#+'00?'--%+)/%'0%+/%0+/)1#-&"'&#"%@+)*+A.%-&'+-)&.'()#*%+-)+?'((%"'1%*&#+/%)+-%*-#")+/)+/%<#"1'()#*%+%+A.%-&'+,#*<)$."'()#*%+/)8%*&'+'+ %<<%&&)+ )0+ ")<%")1%*&#+ 2%"+ &.&&%+ 0%+ 1)-."'()#*)+ -.,,%--)8%>+ B'+ &'"'&."'+ 21
Future developments 22
Acquisition and computation Generalized N+1 geometries (simplex) Redundancy Failure detection Accuracy estimation Free Constrained Measured 23
Sensor array Industrialization Simplified design easy assembly robust and stable no backlash or mechanical hysteresis 24
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
Conclusions Measurement system suitable for quasi-static and for dynamic structural deformations Accuracy: 3 µm @250Hz, span of 2 m Absolute measure (w.r.t. a given reference condition) Integrates with static errors compensation methods Patenting is in process 26
Contacts University of Trento: paolo.bosetti@ing.unitn.it PAMA S.p.A.: http://www.pama.it 27
Thank you for your attention. 28