Beijing University of Technology, Beijing , China; Beijing University of Technology, Beijing , China;

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1 d Iteratoal Coferece o Machery, Materals Egeerg, Chemcal Egeerg ad Botechology (MMECEB 5) Research of error detecto ad compesato of CNC mache tools based o laser terferometer Yuemg Zhag, a, Xuxu Chu, b ad hechu Yag, c Bejg Uversty of Techology, Bejg 4, Cha; Bejg Uversty of Techology, Bejg 4, Cha; a zhagym@bjut.edu.c, bchuxx@emals.bjut.edu.c, cyagshechu@emals.but.edu.c Keywords: laser terferometer, postog accuracy, error compesato Abstract. Takg a certa type of precso ultra-precso CNC grdg mache as a expermetal platform, the research uses Reshaw XL-8 laser terferometer testg the mache tools postoal accuracy ad repeat postog accuracy the before ad after posto of error compesato. Through the establshmet of devato mathematcal model wth VDI stadard, the paper uses the Matlab powerful data aalyss fuctos to calculate mache movemet error value ad draws the error dstrbuto curve. Usg the error compesato mechasm of FANUC system for ptch compesato ad backlash compesato, so that the mache tools meet the requremets of precso ultra-precso machg accuracy. Itroducto Wth the rapd developmet of Cha's dustral 4., precso ultra-precso machg techology has become a mportat drecto of the trasformato of Cha's machery dustry. Precso ultra-precso machg s guarateed by the accuracy of CNC mache tools. At the same tme, t also put forward hgher requremets for the developmet ad applcato of domestc precso ultra-precso CNC mache tools. Postog accuracy s a mportat dcator of the precso of ultra-precso CNC mache, ad the ball screw ptch error ad the ball screw backlash error are mportat dcators to esure the postog accuracy of CNC mache tools. Although the level of precso of ball screw s hgher ad hgher, the log-term use of mache tools, due to the wear ad tear of the fuctoal compoets, ts accuracy wll be a sgfcat decle. Therefore, we eed to regularly test the postog accuracy of mache tools to esure the machg accuracy of the workpece. Ths paper, accordg to the posto accuracy problem of a model of precso ultra-precso CNC grdg mache, descrbes the prcple, stallato ad error compesato mechasm of the Reshaw XL-8 dual-frequecy laser terferometer. Ths paper uses the Matlab aalyss fuctos to calculate the errors. Ths artcle has detected ad compesated the mache ptch error ad backlash error to acheve the postog accuracy by the 9.μmto.7μm. XL-8 dual-frequecy laser terferometer Itroducto of laser terferometer. XL-8 laser terferometer produced by Reshaw s a hgh precso strumet of lear mache error measuremet ad calbrato. It has hgh measurg accuracy, good portablty ad error compesato fucto etc, so t s wdely used precso measuremet ad calbrato.xl-8 laser head performace dcators are show Table. 6. The authors - Publshed by Atlats Press 85

2 Table XL-8 Laser head performace dcators Idex tems Parameter ystem accuracy(ppm) ±.5 Laser precso(ppm).5 Resoluto(μm). Maxmum measuremet speed(m/m) 44 Maxmum samplg frequecy(khz) 5 Measurg rage(m) -8 Warm-up tme(m) ~5 Measurg prcple of laser terferometer. Reshaw XL-8 laser terferometer emtted se wave wavelegth of 633m. The laser has the followg characterstcs: wavelegth s precsely kow, log ad short of the wave s cosstet wth the phase of the wave. After the laser lght emtted from the laser head, t s dvded to two beams by spectroscope(a). Oe way laser s reflected to the fxed mrror(b) ad aother way laser hts the movg mrror(c). After reflecto, the measurg beam s formed. As show Fg.. Fg. The prcple dagram of laser terferometer measuremet Measurg beam ad referece beam terfere wth each other after through a spectroscope aga. If the two coheret beams the same phase, the let the two coheret beams peaks supermpose to form brght strpes. If the two coheret beams the opposte phase, the let the two coheret beams peaks ad troughs supermpose to form dark strpes.as show Fg.. Fg. Measurg beam ad referece beam These strpes are couted out to obta doppler dfferece of arrval( f ), so t ca calculate path dfferece of the two coheret beams. The calculatos are as follows: N t fdt () 86

3 f ( v / c) f () v dl/ dt (3) f c / (4) N t t fdt ( / ) dl L / (5) L ( / )N (6) I the formula: N: the cumulatve umber of pulses : a laser wavelegth c : the speed of lght The mathematcal model of error Accordg to the prcple of mathematcal statstcs: the paper uses the mea ad stadard devato (D) to aalyze the motorg data. I the followg formula, (=~m) s the measurg target locato, j(j=~) s the Number of measuremet, represets the forward movemet, represets the backward movemet. The average posto devato: X X P P (7) j j X j Pj P (8) X X j j (9) X X j j () X X X () The average stadard devato: j ( X j X ) () j ( X j X ) (3) (4) The average posto dsperso: P s Ps 6 (5) Ps P s (6) j The average reverse dfferece: U U X X (7) U X X (8) U max( X X ) (9) 87

4 U U () j Postog accuracy: P 3( ) U 3( ) U P max( X ) m( X ) () Repeat postog accuracy: R R max( P s ) () Postoal devato: M M max( X ) m( X ) (3) Data aalyss ad error correcto Icremetal compesato s a error compesato method, whch takes the adjacet error dfferece betwee two pots as compesato bass. Ths paper takes the mache Z axs as expermetal subject. Through aalyss of the data, t uses the cremetal method for error compesato.after a seres of data compesato, the precso of the mache tool of the Z axs s greatly mproved. The X axs ad Y axs ca use the same method for error compesato.the results are show Fg. 3 ad Fg. 4. Fg. 3 Precso before compesato Fg. 4 Precso after compesato ummary Ths artcle uses the laser terferometer to detect ad compesate a mache screw ptch error compesato. Mache accuracy s mproved greatly. Ths artcle acheve the postog accuracy by the 9.μmto.7μm. Practce ad data show that perodc precso detecto ad error proofg are very mportat to esure accuracy of mache tools. Through the ptch error compesato, the parts processg qualty ca be mproved. Ackowledgmets Ths work was facally supported by the Natoal cece ad Techology Major Project(ZX45) ad the Bejg Mucpal Educato Commsso cece ad Techology Iovato Platform(PXM ). Refereces [] W. Le, Y. Hsu, Error measyrmet of fve-axs CNC maches wth 3D probe-ball, Joural of Materals Processg Techology, 39(3)

5 [] A.C. Okafor, Y.M. Ertek, Dervato of mache tool error models ad error compesato procedurefor three axes vertcal machg ceter usg rgd body kematcs, Iteratoal Joural of Mache Tools & Maufacture, 4()-. [3] A.C. Okafor, Y.M. Ertek, Dervato of mache tool error models ad error compesato procedurefor three axes vertcal machg ceter usg rgd body kematcs, Iteratoal Joural of Mache Tools, 5()