This paper shows the guideway types of large machines and describes problems with their straightness measurement. A short description of straightness measurement methods and the results of investigation in straightness of 10 meter long guideways of a CNC machine by means of the XL-10 Renishaw interferometer are also presented.Rad prikazuje tipove vodilica velikih strojeva i opisuje probleme mjerenja njihove ravnosti. Dat je također i opis metoda mjerenja ravnosti, te rezultati ispitivanja ravnosti 10 metarskih vodilica CNC stroja pomoću XJ-10 Renishawovog interferometra

A. Gessner

P. Frąckowiak

R. Staniek

W. Ptaszyñski

Hrčak - Portal of scientific journals of Croatia

W. PTASZYÑSKI, A. GESSNER, P. FR¥CKOWIAK, R. STANIEKSTRAIGHTNESS MEASUREMENTOF LARGE MACHINE GUIDEWAYSReceived – Prispjelo: 2010-08-31Accepted – Prihva}eno: 2011-01-29Preliminary Note – Prethodno prop}enjeINTRODUCTIONIn case of small machine tools it is simple to machinethe base surfaces for the guideways correctly. Althoughthe structure of the body needs to be properly designed,it demands only precise milling and grinding.In case of large machine tools, with the guideways ofa few or more meters long, it is impossible to design andto machine a rigid body with straight slides. The ob-tained straightness of the slides depends mostly on theaccuracy of their assembly.There are several tools available for machine guidesstraightness measurement 1. The common methodsare not always suitable for measuring the straightness oflong guideways. This is the reason why sometimes cus-tomized tooling and programs have to be developed.GUIDEWAYS OF THELARGE SCALE MACHINE TOOLSTwo solutions for the body design of the longest axisof large scale machine tools are known:– monolithic body on which two guideways areplaced,– separated guideways – each guideway is a sepa-rate part.The monolithic bodies are used in gantry machinetools in which a table is placed on the longest slide andin horizontal mobile column machines in which the col-umn with headstock is moving on the longest slide, butthe table stays motionless.Separated guideways are applied in mobile gantryvertical machine tools in which the table is motionless,but the portal moves.Both the monolithic and the separated guidewayscan be assembled from individual segments, which en-able creating very long slides.Both kinds of slide design demand rigid foundationand fixing to the ground. They are fixed with specialscrews, usually arranged every 500 mm, with the possi-bility to adjust the guideway in 2 directions (horizon-tally and vertically). The screws are used for leveling aswell as for linear setting-up depicts the fixing of theguideway to the foundation (Figure 1).In case of the separated guideways, besides the pre-cise leveling, it is also required to set them on the samelevel. Setting them parallel is very important as well.METALURGIJA 50 (2011) 4, 281-284 281This paper shows the guideway types of large machines and describes problems with their straightness measu-rement. A short description of straightness measurement methods and the results of investigation in stra-ightness of 10 meter long guideways of a CNC machine by means of the XL-10 Renishaw interferometer arealso presented.Key words: machine, straightness measurement, machine guidewaysMjerenje ravnosti duga~kih strojnih vodilica. Rad prikazuje tipove vodilica velikih strojeva i opisuje pro-bleme mjerenja njihove ravnosti. Dat je tako|er i opis metoda mjerenja ravnosti, te rezultati ispitivanja ravnosti10 metarskih vodilica CNC stroja pomo}u XJ-10 Renishawovog interferometra.Klju~ne rije~i: strojevi, mjerenje ravnosti, strojne vodiliceISSN 0543-5846METABK 50(4) 281-284 (2011)UDC – UDK 621.9.002.53:621.81:513.3=111W. Ptaszyñski, A.Gessner, P.Fr¹ckowiak, R. Staniek, Institute of Me-chanical Engineering, Poznan University of Technology, Poznan, PolandFigure 1 The way of fixing the guideway to the groundand joining two segmentsThat could be complicated, when one considers the 7meter span and lack of suitable measuring instruments.THE METHODSOF STRAIGHTNESS MEASUREMENTAccording to the ISO-230 standard a line located ona plane is considered as straight within given length, ifevery of its points is enclosed between two lines at dis-tance equals tolerance, parallel to the main direction ofthe straight 1.The main direction of the line or the representativeline should be taken, so that the straightness error is min-imized. It can be determined by means of:– 2 points selected near the line that is being exam-ined,– a straight obtained on the basis of the measuredchart, e.g. with least squares method.There are two groups of methods for straightnessmeasurement that base on:– measuring the length,– measuring the angle.In the group based on length measuring there aremethods that use:– precise ruler and gauge,– string and microscope,– laser and photosensitive detector,– laser interferometer with optical set for straight-ness measuring.In the second group of methods that base on anglemeasurement one uses:– precise level,– autocollimator,– laser interferometer with optical set for angle mea-suring.The Institute of Mechanical Technology owns aRenishaw laser interferometer XL-10 with optical setfor straightness and angular measuring. The optical setfor straightness measurement is limited to 4 meters,that’s why in the presented investigation the methodbased on angle measurement was applied.Measuring the guideway straightness by means ofangular measurement is presented in Figure 2. The de-picted optical set enables measuring angular displace-ment in the range +/- 5 ° 1. In case of the angular re-flector rotation, the laser beam A2 from interferometer toreflector has longer distance than the beam A1. As a re-sult, a phase difference between A1 and A2 is noticed.Considering the known distance of A2 and A1, the angu-lar displacement can be calculated.The basic peripherals for that configuration (Figure2) are:– laser interferometer head,– angular interferometer,– angular reflector,– flatness base.A flatness measurement is carried out by taking a se-ries of incremental height readings as the angular reflec-tor is moved along the measurement path (Figure 3).On the basis of Figure 3 one can develop a roughequation for the straightness error in a given location:d d Ln n n  1 sin  (1)where: dn – straightness error in the n point,dn-1 – straightness error in the previous point,L – the distance between the measurements, n – the measured deflection error.Laser interferometer used in our investigation hasfollowing main parameters 3:– axial range: 0-15 m,– angular measurement range: ± 175 mm/m (± 10 °),– angular accuracy: ± 0,1M µm/m (M- measure-ment distance),– resolution: 0,1 µm/m (0,01 arc sec).RESULTS OF THE INVESTIGATIONINTO GUIDEWAY STRAIGHTNESSAs the investigated machine tool was a used one, theslide surfaces showed some wear. One could also noticea hard to remove dust layer. Every roughness of the slidesurface can influence the investigation results. Settingthe straightness of the slide top surface is presented inFigure 4.The Renishaw XL-10 measuring set includes mea-suring bases of lengths 50 mm, 100 mm and 150 mm.Considering the fact that the adjusting screws in thatparticular slide are arranged every 500 mm, a specialmeasuring base of 500 mm was prepared. Thanks tosuch a long foot it was possible to strongly limit the in-fluence of local roughness on the measurement 4-7.The foot and the measuring set are presented in Figure 5.Figure 6 presents the angular displacements for themeasured straightness of the slide top surface with the282 METALURGIJA 50 (2011) 4, 281-284W. PTASZYÑSKI et al.: STRAIGHTNESS MEASUREMENT OF LARGE MACHINE GUIDEWAYSFigure 2 Principle of straightness measurement 2Figure 3 Model for the straightness error calculation 2use of the 500 mm foot. On the basis of that chart and theequation (1) one can calculate the real straightness devi-ation. To that end a computer program was developed. Itcalculates the straightness deviation using the data ob-tained from the measuring system. The program win-dow is presented in Figure 7.The interferometer does not measure the absolute de-flection angle, so the absolute straightness error cannotbe obtained. For this reason the graph of the straightnesserror was compared to a straight line (the curve was ro-tated so that the start and the end of it were brought tozero). The table deflection calculated according to thedescribed method is presented in the Figure 8.The noticeable changes of the straightness, espe-cially in Figure 9, result from the imprecise connectionMETALURGIJA 50 (2011) 4, 281-284 283W. PTASZYÑSKI et al.: STRAIGHTNESS MEASUREMENT OF LARGE MACHINE GUIDEWAYSFigure 4 Setting the straightness of the slide top surfaceFigure 5 View of the measuring set: 1 – investigatedsurface (location of the carriage), 2 – prepared500 mm foot, 3 – measuring optical setFigure 6 Chart of the obtained angular displacementsfor the measured straightness of the slide topsurfaceFigure 7 Program for calculating straightness deviationon the basis of angular measurementFigure 8 Diagram for the calculated straightness devia-tion of the top slide surface in relation to thestraight lineFigure 9 Diagram for the calculated straightness devia-tion of the top slide surfaceof the slide segments. In that particular machine tool theslides are assembled from 3 m long segments.For measuring the straightness of the side slide sur-face an optical set presented in figure 5 was applied. Fig-ure 10 presents a diagram for straightness deviation inrelation to the straight line.RESULTS OF THE INVESTIGATIONINTO STRAIGHTNESS OF MOTIONAfter adjusting guideways and assembling the ma-chine tool an investigation into straightness of motionwas carried out. For the investigation the method de-scribed in chapter 3 was used, with that difference thatthe optical system was fixed to the movable part and itsangular displacement was measured. The machine toolportal moves on 2 carriages on each side arranged in2 500 mm distance. The side carriage is made of 4 parts.The straightness error of the slide results in angular de-viation of the portal. The Motion straightness investiga-tion was carried out every 50 mm.Figure 11 presents the calculated straightness devia-tion in the vertical plane within the whole range of mo-tion – 6 900 mm.SUMMARYThe accuracy of a machine tool is influenced notonly by the accuracy of the measuring system and theservo drives, but also by geometrical accuracy, particu-larly by guideways’ straightness. As already stated thestraightness of guideways of small machine tools isquite easy to achieve. However, in case of large machinetools the issue is more complicated. Longer guidewaysresult in lower rigidity of the body. Additionally, thelong guideways are assembled from segments that needto be very precisely arranged.Moreover, since the machine was used, the straight-ness measurement was influenced by roughness anddust on the slide surfaces.On the basis of the summarized results one can statethat the aim of the study was achieved. For that class andsize of machine tools the straightness deviation of 0,045mm within the whole range of motion is considered assufficient.REFERENCES1 ISO 230-1 1996: Test code for machine tools. Part 1: Geo-metric accuracy of machines operating under no-load or fi-nishing condition.2 XL laser measurement system manual. Renishaw.3 Ardelean F. A.: The measurement of the straightness in thecase of long guideways, using modern measurement met-hods, namely, the laser. Annals of the Oradea University.Fascicle of Management and Technological Engineering,Volume VII (XVII), 2008.4 Ptaszynski W.: Laser Interferometer Straightness Measure-ment of Machine Tool. The 8th International CarpathianControl Conference ICCC 2007, Strbske Pleso, Slovakia2007, pp. 579-582.5 Poniatowska M.: Methods of spatial data analysis in rese-arch on geometric deviations determined in coordinate mea-surements of freeform surfaces. Archives of MechanicalTechnology and Automation, Vol. 29/2, Poznan, pp. 63-72.6 Poniatowska M.: Characteristics of geometric errors deter-mined using discrete measurement data. Archives of Me-chanical Technology and Automation, Vol. 28/2, Poznan,pp. 51-58.7 Swornowski P. The optimum number and distribution ofmeasuring points for the circle with the shape deviation.Archives of Mechanical Technology and Automation, Vol.22/2, Poznan, pp. 79-86.NOTE: Responsible translator: Natalia Trawinska, The Poznan Collegeof Modern Languages, Poznan, Poland284 METALURGIJA 50 (2011) 4, 281-284W. PTASZYÑSKI et al.: STRAIGHTNESS MEASUREMENT OF LARGE MACHINE GUIDEWAYSFigure 10 Diagram of the calculated straightnessdeviation for the side slide surfacein relation to the straight lineFigure 11 Diagram for the calculated straightnessdeviation of the portal for motion in thevertical plane

Mjerenje ravnosti dugačkih strojnih vodilica

Abstract

Similar works

Full text

Available Versions

Hrčak - Portal of scientific journals of Croatia