Design and Realization of Open CNC System Based on Software Motion Controller

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Kristopher Kennedy
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1 Internatonal Forum on Management, Educaton and Informaton Technology Applcaton (IFMEITA 2016) Desgn and Realzaton of Open CNC System Based on Software Moton Controller Xu Ran1, a, Janqun Lu2, b, Weqang Gao3, c and Guoqang Huang4, d 1-4 Guangdong Unversty of Technology, Guangzhou, Chna a clarencerex@foxmal.com, bjqlu@sna.com, cwqgalt@139.com, dhuang_gq@qq.com Keywords: A3200; CNC system; Laser nterferometer; Error calbraton Abstract. The open CNC system based on A3200 has been desgned and realzed. Frstly, the hardware platform desgn of the system was ntroduced n the paper. Then, the HMI(Human Machne Interface) of the system has been ntroduced,whch was developed by Qt4.8. Afterwards, the process of the postonal accuracy measurement and error calbraton of the system has been llustrated. Fnally, the system has met the requrement of real-tme moton control and postonal accuracy, and t has worked well. Introducton An open CNC system s bult on an open platform, realzng the open ablty, nterchangeablty, transportablty and extendblty, and t has a modular structure [1,2]. A3200 s a software based moton controller that uses FreWre(IEEE-1394) to provde up to 32 axes of coordnated moton, networked wth ntellgent drves[3]. It allows the user to choose the controllng mode and the numbers of servo axes based on dffrent confgure to meet the practcal requrement of an open CNC system. Qt s a development framework of applcaton and user nterface. It makes t possble that the software developed by Qt can run on dfferent operatng system wthout repeatedly complng source codes[4]. The open CNC system has taken IPC(Industral Personal Computer) & SMC(Software based Moton Controller) as the structure of the system, and t s a full-closed loop system. The software system runnng under wndows operatng system has been developed wth Qt4.8 based on the object-orented program desgn and the module technques. After nstallaton, confgurng, measurement and calbraton, the system has met the desgn requrement. Desgn of the Hardware Platform IPC(ndustral personal computer) Wndows OS & INtme & HMI & A3200 frewre card frewre cable frewre cable frewre cable Lnear motor X Lnear motor Y1 Gratng Gratng Gantry frewre cable frewre cable frewre cable Nservo Lnear motor Y2 Lnear motor Z Lnear motor B ABB Drve Gratng Gratng Fg. 1. Hardware structure of the system The authors - Publshed by Atlants Press 298 Gratng Spndle

The system has been made up of software platform and hardware platform. It was the IPC that the connecton between software platform and hardware platform.

The machne tool platform and the electrc control cabnet are shown n Fg.2 and Fg.3. Ndrve dgtal drve s a hgh performance lnear amplfer. The communcaton transmsson rate s up to 3.

2 The system has been made up of software platform and hardware platform. It was the IPC that the connecton between software platform and hardware platform. The hardware platform has been composed of Ndrve dgtal drve, BLMX Seres lnear motor, Hedenhan gratng, Nservo, Ar bearng spndle and so on. The hardware structure of the system s shown n Fg.1. The machne tool platform and the electrc control cabnet are shown n Fg.2 and Fg.3. Ndrve dgtal drve s a hgh performance lnear amplfer. The communcaton transmsson rate s up to 3.2Gbps wth 1394 frewre so that t makes certan the feature of real-tme moton control. BLMX Seres lnear motors wth nonmagnetc forcer elmnates coggng and magnetc attracton to allow for extremely smooth moton, very tght velocty and poston control, whch are deal for applcatons demandng the ultmate n force output. LIP400 seres of the Hedenhan gratng s for meetng the hgh-precson measurement of the system. The system has worked for the fve-axes ultra-precson machne tool n our laboratory. Accordng to the layout of the machne tool, the Y-axs has taken the gantry mode, whch has used the force from ar cylnder to balance the weght of the prncpal axs. Wth the Nservo, the runnng mode of the spndle can be swtched between prncpal axs mode and C-axs mode. Fg. 2. Machne tool platform Fg. 3. Electrc control cabnet Desgn of the Software Platform The software platform has been composed of wndows operatng system, INtme real-tme extenson, A3200 software controller and the HMI of the system. The HMI s responsble for the functon of computer nteracton and real-tme dsplay. A3200 deals wth the real-tme tasks, such as the nterpolaton calculatng, poston control, cutter compensaton, velocty dealng and so on. A3200 runs under wndows operatng system n a real-tme kernel that runs ndependently of other programs runnng on the IPC, whch s responsble for the real-tme moton control tasks and data sharng by the shared memory wth the wndows operatng system [5]. Functon Module of the HMI. The moton control nterface of the CNC system s shown n Fg.4. Accordng to the desgn requrement, the applcaton had followng functon modules: 1)Product: enablng, homng and moton controllng of sngle axs or multple axes, loadng and edtng of NC program, dsplay of runnng status and other assstant functons. There are four moton controllng mode to satsfy dfferent applcaton, such as Auto Mode, Handle Feed Mode, Incremental Mode, Home Mode. When the system s n one mode, some functon buttons are unavalable for avodng msoperaton. 2)Edt: surface modelng of parts, post-processng and generatng the NC program. 3)Utlty: generatng the test program of error measurement, smulaton of machnng process. 4)Dagnose: montorng the runnng status of the open CNC system, dagnosng the fault of the system and fnshng the restoraton of the system. 5)Setup: managng the parameters of the open CNC system, workpece, cutter, processng craft and settng the coordnated system. 299

3 Fg. 4. Moton control nterface of the CNC system Measurement of Postonal Accuracy and Error Calbraton Measurement of Postonal Accuracy. Postonal accuracy s an mportant performance to evaluate the CNC system, t affects the processng qualty of the system. To meet the requrement of hgh velocty and hgh accuracy for the system, the postonal error has been measured and calbrated. Accordng to the measurement prncple of Dual-frequency Laser Interferometer [6], the measurement of the lnear postonal accuracy has been accomplshed wth RenShaw XL_80. The measurement and the calbraton of Z-axs were used to llustrate the whole process. Wthn the scope of travel(-85~+85mm), the 35 mark ponts selected randomly, 3mm for the skp dstance, 2mm/s for the feedrate, 4s for dwell tme and 5 double-drecton measurements have been chosen to generate the test program. The dwell tme made t sure that the Laser nterferometer had enough tme for collectng postonal error data of the mark ponts. The results of measurements before and after calbraton have been analyzed upon VDI/DGQ 3441 standard wth the analyss software provded by Laser Interferometer. The result of the measurements before calbraton s shown n Fg.5. Fg. 5. Result of the measurements before calbraton 300

4 Error Calbraton. There are two software error calbraton methods for CNC system. One s the backlash calbraton method, the other s the thread ptch error calbraton method. The former has been taken to calbrate the error of the system. 1D or 2D error calbraton fle s accepted by A3200 confguraton Manager provded by A3200. Accordng to the error measured by Dual-frequency Laser Interferometer, t has been generated that the error calbraton fle wth the format requred by A3200, and t has been loaded to A3200 confguraton Manager. Wthn the scope of travel, the travel has been dvded randomly for 35 mark ponts. The error of mark pont has been measured by Dual-frequency Laser Interferometer. And the average value of double drecton error has been calculated for. Wth the calbraton fle, the average value has been consdered by the system. The calbraton value of the error at the mark pont has been obtaned as below: 0 ( = 1,2,3,,35) (1) ' ' where : error of mark pont; calbraton value of mark pont. In order to get better postonal accuracy, more measurements of double drecton movement have been taken, and the average of the error at the same mark pont has been obtaned as below: 1 n (2) n 1 where : average of the error value at the same mark pont; n: tmes of measurng the same mark pont. After calbratng error of mark ponts, the fve double-drecton measurements have been done agan. The result of the measurements after calbraton s shown n Fg.6. The postonal accuracy and the repeated accuracy have been mproved obvously accordng to the contrast between Fg.5 and Fg.6, whch have been obtaned after calbraton. The contrast of analyss results before and after error calbraton s shown n Table 1. The system has met the requrement, whch the postonal accuracy was 1um. It has been proved effectve of the calbraton method accordng to the results. Fg. 6. Result of the measurements after calbraton 301

5 Table 1 Contrast of analyss results before and after error calbraton Items Before calbraton After calbraton Postonal uncertanty (P) [um] Maxmum scatter (P s max ) [um] Maxmum reversal (U max) [um] Postonal devaton (Pa) [um] Mean reversal (U mean) [um] Mean scatter (Ps mean) [um] Conclusons The open CNC system based on A3200 has been accomplshed, whch has a good nteracton nterface. Through calbratng the postonal error, the system has obtaned the hgh postonal accuracy and hgh repeated accuracy. The system has acheved P = 0.76um and P s max = 0.61um n Z-axs. The open CNC system not only has provded more choces and flexblty for users but also has reduced the amount of the hardware to mprove the stablty and relablty. It has been proved that the open CNC system has met the desgn requrement of the system and worked well. Further research wll focus on aspherc processng wth the system. Acknowledgements Ths work was supported by the Unversty Industry Scence Partnershp (UNISPAR) Project of Guangdong Provnce and Mnstry of Educaton of P.R. Chna (No.2013B , No.2013B ), the Scence and Technology Plannng Project of Guangdong Provnce (No.2015B , No.2015B ), the Postgraduate Demonstraton Base Project of Department of Educaton of Guangdong Provnce (No.2013JDXM29), and the Introducton of Innovatve R&D Team Program of Guangdong Provnce (No G ). Meanwhle, as the frst author, I would lke to express my grattude to all those who have helped me durng the wrtng of ths thess. References [1] Shucheng Zhang: Journal of Jamus Unversty(Natural Scence Edton), Vol.30 (2012) No.1, pp.83~85. (In Chnese) [2] Shu Zhang, Luqun Fan, Zhhao Zhu, Xu Jn: Manufacturng Technology & Machne Tool, (2012) No.2, pp.9~12. (In Chnese) [3] Informaton on [4] Yafe Huo, n: The Quck start of Qt Creator (second), edted by Behang Unversty Press, Bejng, Chna(2014). (In Chnese) [5] Informaton on [6] Janhu Zhang: Machne Tool & Hydraulcs, Vol.39 (2011) No.4, pp.114~115. (In Chnese) 302

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