Signal Processing Key Element in Designing an Accurate Machining Forces Measuring Device

Transcription

1 Proceedings of the 8th WSEAS Interntionl Conference on SIGNAL PROCESSING, ROBOTICS nd AUTOMATION Signl Processing Key Element in Designing n Accurte Mchining Forces Mesuring Device MIHAIELA ILIESCU, MAGDALENA ROŞU, PAULINA SPÂNU Mnufcturing Deprtment POLITEHNICA University of Buchrest Spliul Independenţei no. 1 Street ROMANIA iomi@clicknet.ro Abstrct: - When mnufcturing prts, specilly by mchining process, it is often necessry to hve relible informtion on mchining forces involved. So, systems nd devices for mesuring these forces hve to be used, this pper presenting n innovtive one, which, hs lso been ptented. One of the most importnt spects in designing such device is represented by good signl processing, so tht, for instnce, specific clibrting equtions to be pproprite determined. Checking obtined results into rel mchining conditions represents finl chllenge. Key-Words: - elstic element, resistive trnsducer, mesuring device, mchining force, dt cquisition. 1 Introduction Vrious kind of prts re used in nowdys production, being mde of vrious mterils type nd re hving, more or less, complicted geometricl fetures. One importnt procedure of their mnufcturing is represented by mchining processes, mening cutting ones (turning, milling, drilling, etc.) nd/or cold pressing ones (punching, bending, extrusion, etc.). Knowing mchining forces is importnt, when experimentl nd theoreticl reserch is crried out or, in rel mnufcturing production for choosing pproprite mnufcturing technologicl system components [4]. So, for these bove mentioned situtions, specific force mesuring devices hve to be used, so tht ech force component vlue cns be determined. Tht is becuse, there re mny fctors tht do influence it, such s mterils being unhomogeneous, cutting tools chrcteristics, including wer too, mchining prmeters vlues, etc. nd thus, most of mchining processes involve forces on rndom direction []. The most importnt prt of mchining forces mesuring device is represented by its elstic element nd the trnsducers fitted on it. Specific literture presents mthemticl reltions for determining specific deformtion nd elstic constnt vlues of vrious elstic elements type see tble 1. There re lso presented, some schemes of fitting trnsducers (resistive ones) on the elstic elements, so s to get mximum sensitivity see tble [1]. The most importnt disdvntge of the studied lredy existing mchining forces mesuring devices is tht they re specil or, specilized one mening cn be used only for one mchining procedure or, for more, if similrly. Thus, it hs been considered right to design nd mnufcture device to be used in mesuring both cutting processes forces nd cold pressing processes forces. The innovtive form of the elstic element, hs lredy been ptented nd the whole device ws designed, mnufctured nd tested into rel mchining conditions [5], [6]. Objective nd Reserch Directions Considering the spects presented bove, it cn be stted the objective of this pper s the pointing out of how importnt dt cquisition nd signl processing re in determining optimum elstic element s design, trnsducers position nd clibrting equtions when designing nd mnufcturing mchining forces mesuring device. As for reserch directions, there hve been followed some lines, s: - determining elstic element s shpe; - simulting elstic element s behvior in vrious loding conditions; - estblishing optimum position of resistive trnsducers; - mnufcturing the device; - clibrting the device; - testing the device into rel mchining processes. ISSN: ISBN:

2 Proceedings of the 8th WSEAS Interntionl Conference on SIGNAL PROCESSING, ROBOTICS nd AUTOMATION Loding Type Chrcteristics of vrious elstic elements type Scheme Specific Deformtion Elstic Constnt Tble 1 [1] 6Pl 1 = Bending = υ 1 4L Bending 1 ( 1) P = ± = υ 1 L Tensile P R 1 = Ee 1 1 e π P R = Ee e π Ee π 1 R 4 π Bending ( L) P 1 = ± = υ1 L Loding Type Tensile / Compression Resistive trnsducers position on elstic element Scheme Specific Deformtion 1 = Δl = l N EA ΔD = = ν 1 D Tble [1] 1 = 6Px Bending = ν1 Twisting 8M D 45 = t 4 4 πg( D d ) E where: G = (1 + ν) ISSN: ISBN:

3 Proceedings of the 8th WSEAS Interntionl Conference on SIGNAL PROCESSING, ROBOTICS nd AUTOMATION Designing the Elstic Element Bsed on the gol of hving device for mesuring vrious mchining forces, the shpe of elstic element hs been conceived so s to mke possible multiple loding types, ccording to ech of rel mchining processes [], [5].. In order to determine force s components, long estblished reference system s xes, there hve to be severl trnsducers, well positioned on the elstic element, such s the resulting signl represents the sum of ech trnsducer s signls. Thus, it hs been considered, s initil conditions, loding with nominl force vlues, up to 1, N, long ech of the min xes, nd with nominl torque vlues, up to 5 N m, round ech of the min direction (the reference system considered ws OXYZ). The overll dimensions, should be bout Φ 15 5 (mm). Elstic element s innovtive shpe is similr to two wheels, ech with two spokes nd the upper one rotted by 9 with respect to the lower one see figure 1. Becuse of the fcts tht elstic element s shpe cn t be correctly pproximted by ny of simple structures (plte, rod etc.) nd tht rel loding is complex, there hs been used ANSYS softwre for determining: mximum equivlent stresses nd deformtion vlues; resistive trnsducers position, reciprocl signls influence. So, there hs been considered ten points tetrhedron elements nd determined both, Von Misses equivlent stresses distribution nd specific deformtion distribution, for ech of the considered loding situtions mening, force horizontl components (F x = = 1, N), force verticl component (F y = 1, N), torque on horizontl xes (M x = M z = 5 N m ) nd torque on verticl xis (M y = 5 N m ). Becuse of elstic element symmetricl shpe, it ws considered only hlf, even qurter of its structure. An exmple of the obtined simultion results re shown in figure when loding with F x ( ) force,. F x Von Misses equivlent stresses View from C x specific deformtion [mm] Fig. 1 Elstic element s shpe Fig. Simultion of elstic element s behvior when loding with F x ( ) force ISSN: ISBN:

4 Proceedings of the 8th WSEAS Interntionl Conference on SIGNAL PROCESSING, ROBOTICS nd AUTOMATION Z Y X Fig. 4 Mchining forces mesuring device F x 1 C 1 chnnel exit 4 7 M x 1 1 C 4 Fig. Resistive trnsducers connection 9 F y chnnel exit C 6 chnnel exit 8 As result of ANSYS simultion, there hs been estblished resistive trnsducers position, right into the plces (direction) where specific deformtion hve mximum vlues. Their connection is complete Whetstone bridge one nd the trnsducers re connected so tht both force s nd torque s components vlues cn be mesured. The connection scheme, for trnsducers on the upper prt of the elstic element is presented in figure. The trnsducers used re Hottinger type one, with bse of mm nd electricl resistnce R = 1 Ω. Finlly, once ll components of the mchining forces mesuring device hve been designed, it hs been mnufctured see figure 4. It should be mentioned tht, there hve lso been designed nd mnufctured two dditionl elements necessry for connecting the device to mchine tools components one is of x type, for connection to lthe, in turning, nd the other is of round plte type for connection to milling mchine, drilling mchine, mechnicl press, etc. 4 Clibrting the Device There were crried out tests tht resulted in very good behvior of the device from rigidity point of view, in both, sttic nd dynmic lodings. [], [6]. So, it hs been considered right to use it, into rel mchining situtions but, before tht, clibrting equtions hd to be determined. Becuse of the vrious types of mchining forces to be mesured nd, becuse of the fct tht clibrtion should be done under conditions similr to rel ones, the lodings were done successively, with F x,, nd F y forces, whose vlues vried from to dn. The experimentl stnd, included the device equipped for turning type processes nd the electronic bridge used (ech chnnel connected for mesuring one force s or torque s component) ws Hottinger type one. Bsic principle of clibrtion is tht under ech force loding, F ρ (ρ = x, y, z) there re generted deformtions of the elstic element, which re trnslted into, se ρx, ρy, ρz signls t electronic bridge chnnels, C x, C y nd, respectively, C z. = f ( ), = f ( ), = f ( ) xx F x yx = f F y xy F x yy = f F y zy = f xz F x yz = f F y ( ), ( ), ( ) (1) zz = f = f ( ), ( ), ( ) zx Using specilized softwre, CurveExpert, there were determined liner regression models coefficieints ( nd b ) of : ρθ ρθ = ρθ Fρ + bρθ ρθ, ρ = x, y, z, θ = x, y, z () ISSN: ISBN:

5 Proceedings of the 8th WSEAS Interntionl Conference on SIGNAL PROCESSING, ROBOTICS nd AUTOMATION The simultneously ction of F x,, F y nd force s components is equivlent to the ction of sptil force, F. So, by dding ll the effects,, finl deformtions could be determined, s: x = xx + yx + zx y = xy + yy + zy () = + + z xz nd, the resulting clibrting eqution is: Fx Fy = Fz xx xy xz yx yy yz yz 1 zx zy zz x y z zz ( bxx + byx + bzx) ( b + b + b ) ( ) xy yy zy bxz + byz + bzz (4) The experiments scheme when force loding is presented in figure 5, nd n imge tken while experimenting is shown in figure Tble Experimentl results Deformtion [μm] [dn] I II m l ul zx A y A loding point 5 1 zy A O x z 1 zz Fig. 5 Scheme of clibrtion experiments Fig. 6 Clibrting when loding Exmples of results obtined while experimenting loding (l) nd unloding (ul) with force, re presented in Tble The resulting clibrting equtions in loding, re the ones in reltion (5): F x =,4 x,18 y,5 z 1,4849 F y =,1 x +,61 y,7 z + 1,45 =,9 x,181 y +,44 z 4,15 (5) ISSN: ISBN:

6 Proceedings of the 8th WSEAS Interntionl Conference on SIGNAL PROCESSING, ROBOTICS nd AUTOMATION zθ [μm/m] Fig. 7 Grphs for loding (l) F [dn] Series1 zx Series zz Series zy Grphs plotted out, from experimentl results shown in tble, re evidenced in figure 7. A turning process hs been performed on cylindricl smples nd forces hve been mesured, while mchining. For better nd more complex determintions, it ws used LbVIEW dt cquisition system, with smpling rte of 1, mesures/second, for 5 second. Imges of the experimentl stnd, s well s of turning force s components, s ppered on the computer screen, re presented in figure 8 nd, respectively, figure 9. Fig. 8 Experiments for turning process F x F y 5 Conclusion Designing nd mnufcturing device for mesuring forces, in vrious mchining processes hs proven to be dequte. The most importnt element, of it, is represented by elstic element, whose geometricl chrcteristics (shpe, dimensions) re innovtive nd ptented ones. There hs been used simultion, with ANSYS progrm, for testing elstic element s behvior nd, thus, determining the resistive trnsducer s position, s to get mximum sensitivity nd lowest signl s reciprocl influence. Signl processing, including dt cquisition, hd n importnt role in estblishing device s clibrtion equtions nd, in testing it for rel mchining process exterior cylindricl turning. Good results, in ccordnce to the ones obtined by lborious mthemticl clculi, hve been obtined. Further reserch should be developed, so s to integrte the forces mesuring device into n utomted system of dpted control, s to obtin optimum vlues of mchining process prmeters. References: [1] Constntinescu I. N., ş.., Măsurre mărimilor mecnice cu jutorul tensometriei, Editur Tehnică, Bucureşti, [] Iliescu M., Gheorghe M., Computer Aided Design Innovtive Design for Mesuring Mnufcturing Forces, 9 th WSEAS Interntionl Conference on Automtion nd Informtion, pg , ISSN , Buchrest, Romni, June, 8 [] Medel J De Jessus, Hernndez G., Guevre P., Rel Time Flexible Mnufcturing System, Proceedings of 1 th WSEAS on Automtic Control, Modeling & Simultion pg. 86, ISSN , Istnbul, 8. [4] Roy R., Chtelin J-F. t l., Progrmming of Mchining Procedure for Adptive Spirl Cutting Trjectories, Proceedings of 1 th WSEAS on Automtic Control, Modelling & Simultion pg. 17, ISSN , Istnbul, 8 [5] Turdenu E., Iliescu M., Găvn M, Mchinig Forces mesuring device, License Ptent, no. 1179/.4.8 [6] Turdenu, E., Contribuţii le dezvoltre cptorelor de măsurre forţelor de prelucrre, Teză de doctort, Bucureşti, 4. Fig. 9 Grphs of turning force s components ISSN: ISBN: