1、01FTM5Traceability of Gears - New Ideas,Recent Developmentsby: F. Hrtig and F. Wldele, Physikalisch-TechnischeBundesanstaltTECHNICAL PAPERAmerican Gear ManufacturersAssociationTraceability of Gears - New Ideas, RecentDevelopmentsFrank Hrtig and Franz Wldele, Physikalisch-Technische BundesanstaltThes
2、tatementsandopinionscontainedhereinarethoseoftheauthorandshouldnotbeconstruedasanofficialactionoropinion of the American Gear Manufacturers Association.AbstractIn gear-cutting technique, some tolerances for cylindrical gears lie within the range of the national standardsmeasurement uncertainty. This
3、 situation is unsatisfactory. The Physikalisch-Technische Bundesanstalt (PTB) as thenationalmetrologyinstituteofGermanyhas,therefore,madeititsjobtoimprovethisstateofaffairs.Ithasdevelopedaconcept based on three fundamental goals: reduction of the uncertainty of measurement at PTB, construction ofpro
4、duct-like standards, and shortening of the calibration chain from PTB to the product. One of the focal points is thedevelopment of a standard measuring device. For this, additional metrological devices are integrated into a coordinatemeasuring machine. Thisallowsthe measured valuesto bedetermined wi
5、thinterferometric accuracy.Moreover, inthefuture, the flanks will be evaluated on the basis of a sculptured surface model. By this it will be possible to achieveconsiderably higher calibration accuracy, not only for spur gears, but also for internal gears and helical gears.CopyrightGe32001American G
6、ear Manufacturers Association1500 King Street, Suite 201Alexandria, Virginia, 22314October, 2001ISBN: 1-55589-784-31 Traceability of Gearings - New ideas, Recent Developments Frank Hrtig, Franz Wldele Physikalisch-Technische Bundesanstalt, Braunschweig, Germany 1 Introduction For a long time, involu
7、te gears have been amongst the most important elements of drive engineering. One of its essential applications is the transmission of great forces and the reduction and multiplication of rotations. In these processes, the gears are often subjected to high stresses. Errors on the flanks cause prematu
8、re wear. This leads to a shorter service time of the gears, a poorer efficiency of load transmission and an increase in the running noise. This is especially critical as the gears are typical replacement parts. Such parts which have been manufactured in different production facilities and by differe
9、nt production methods must later match with high precision. In the manufacture of mass-produced parts, such as gears for vehicles, it is, therefore, of great importance to monitor the production processes. This is normally done with the aid of suitable gear measuring instruments which allow manufact
10、uring defects to be determined. The results serve to evaluate the grade of the gear, and they can also be used to correct the manufacturing processes. Gear measurement is a particular metrological challenge. The complex geometry and the small manufacturing tolerances require reliable and traceable m
11、easuring processes. 2 Traceability of gearings today In addition to the surface qualities, such as roughness and waviness, inherent stability and dimensional accuracy are very important for the quality of gears. Today, they are realized with the aid of gearing standards 1. They allow the characteris
12、tic gearing parameters to be traced back. This traceability takes place within a calibration chain (Figure 1). At its top are the primary standards of the national metrological institutes. The characteristic parameters of the gears are treated independently of one another for profile, flank and pitc
13、h. For each of these characteristics a special standard is available which is calibrated on a standard measuring device. This procedure has been necessary up to the present, as the standard testing facilities have been optimized to the characteristic kinematics of the standards in order to achieve t
14、he highest accuracy of measurement. The measures are disseminated by comparison measurements, on coordinate measuring machines, primary standards and reference standards being measured in several positions under identical conditions. This allows systematic errors of the measuring instrument used to
15、be detected and corrected. In the ideal case, the measures are disseminated via accredited measurement laboratories. The Deutscher Kalibrierdienst (DKD, German Calibration Service) advocates and supports the establishment of such laboratories. Last year, the first calibration laboratory for gear mea
16、surands was accredited in Germany. Further laboratories have applied for accreditation or shown their interest in being accredited. In the next step of the calibration chain, the calibration laboratories calibrate industrial standards and working standards for industry. The industrial standards are
17、used for the calibration of gear measuring instruments in particular, whereas the working standards are used above all in precision measurement rooms. In a subsequent calibration process, they are used to calibrate master gears which serve to monitor the manufacturing processes. PTBGauge HierarchyNo
18、rmal-Measuring DeviceCMM- reference standardGear measuring machine / CMMworking standard / master gearunit meterProduct- national gear standardU=?industryDKDFigure 1 Calibration chain today 2 3 Limits of existing procedures The specified tolerances for the gears meanwhile lie within the ranges of th
19、e uncertainties of measurements (Table 1). It is, thus, no longer possible to state a reliable measurement result specifying the measured value and the associated uncertainty of measurement. Accuracy grade PTB (U=95%) DKD (U=95%) industry para- meter1 2 3 national stand-ard reference standard indust
20、rystand-ard work-pieceF 1.5 2.1 2.9 0.6 1.4 F 2.5 3.5 4.9 1.5 1.9 pF 4.6 6.5 9.0 0.2 1.3 ? ? Table 1 Comparison of tolerances according to ISO 1328 and measuring uncer-tainty of the calibration chain for a gear with d0= 100mm, mn= 2mm, b = 80mm (values in m) F : Total profile deviation F : Total hel
21、ix deviation pF : Total cumulative pitch deviation The relatively high uncertainties of measurement can be attributed to both, the existing technology and the procedures used to determine and disseminate the values. The shape of the primary standards, for example, usually differs consi-derably from
22、that of the workpieces. Direct traceability via comparison measurements is no longer possible. This is very clearly shown by the traceability of helical and internal gears for which no involute standards are available. But even the ranges covered by the existing gearing standards are no longer suffi
23、cient to meet the requirements in the field of micro gears or heavy gear construc-tion. On the contrary: a reliable estimate of the uncertainty of measurement is not possible at all. As to the procedures used today for the accept-ance of gear measuring instruments, the situation is even worse. Accep
24、tance is normally based on adjusting gauges. Normally, only one profile and one helix standard are adjusted. The uncertainties determined are valid only for gears, whose shape is in keeping with the standard and the place where the standard has been measured. The greater the deviation of the test pi
25、ece from these marginal conditions, the larger the uncertainty of the measurement result. A reliable statement of the uncertainty of measurement is no longer possible. The situation could be improved if several profile and helix standards were used for the acceptance with a view to defining measurin
26、g ranges within which the measurements could be carried out. This usually fails because of the high costs of the standards. 4 New concept Now activities are required to meet the require-ments already made by industry. This is why the Physikalisch-Technische Bundesanstalt has decid-ed to take the fol
27、lowing lines: Increase in the measurement accuracy within PTB Calibration of product-like standards Shortening of the calibration chain 4.1 Increase in the measurement accu-racy within PTB A new standard measuring device is developed on the basis of a coordinate measuring machine. It is to replace t
28、he existing measuring instruments for profile, helix and pitch by a universal and computer-aided measuring instrument (Figure 2). rotary tableCMMmeasuringplanelasertrackergeartargetmeasuringsphereFigure 2 Concept of the normal-measuring device The measuring instrument provides the required accuracy
29、owing to independent metrological devices which are integrated into the coordinate measuring machine 3. It consists of a laser tracker and a rotary table. When the gear-specific 3 characteristics are known, a measuring strategy can be selected which allows the profile, helix and pitch parameters to
30、be determined by a trans-latoric and a rotatoric motion, i.e. for translatoric motions an almost Abbe error-free measurement can be carried out. The accuracy of the rotational motion is obtained by the use of a high-precision rotary table . The measured values are evaluated with the aid of a softwar
31、e developed by PTB. The advantage of the new measuring device consists above all in a more flexible selection of the measuring strategy and, thus, in a more flexible shape of the primary standards. It is, for example, no longer necessary to provide the profile standards with high-precision discs of
32、the size of a base circle. This allows further barriers to be overcome. The measuring range today available, i.e. from 25 mm to 400 mm base diameter, can be extended to approx. 1 mm to 600 mm. 4.2 Calibration of workpiece-like standards The measuring device described above provides the basis for gre
33、ater national calibration accuracy for product-like standards. A prerequisite are standards with good surface characteristics, such as a small roughness, small waviness and small form errors. This allows the tracing uncertainties of repeat measurements to be kept small. These properties are not only
34、 valid for flank faces. They must also be valid for reference faces, as these are used to determine and specify the coordinates of the workpiece and thus exert a direct influence on the measurement results. The new standard testing device allows the PTB and the associated laboratories to calibrate i
35、nternal gearing standards for the first time on the highest metrological level. In addition it will be possible to calibrate modified profiles, i.e. profiles with crowning of profile and helix as well as profiles with root and tip relief (Figure 3). A prerequisite for this is the development of an e
36、valuation software and the specification of a data exchange format 4, 5. This ensures not only independence of purchased products. On the contrary: the software and the appertaining data interface can serve as a reference for the testing of commercial products with the self-developed programs. natio
37、nalstandardindustrystandardhelixpitchtoday futuretypes:characteristic parameters:- spur/helical gears- internal/external gears- modifications- profile- helix- pitch- tooth thicknessproduct-likeFigure 3 From special standards to product-like standards One of the greatest challenges to the PTB is the
38、introduction of a model of sculptured surfaces 6 for the determination of the flank defects (Figure 4). This will make the historical measuring sections of profile and helix as well as the point-by-point determination of the pitch parameters superfluous. The advantage of the method is that the invol
39、ute surface is also treated as a surface, just as its related and known geometries. The measurement points can be distributed over the whole flank. In contrast to the existing evaluations, this allows a more complete statement on the flank surface. Figure 4 Involute flank evaluated as a sculptured s
40、urface Measuring results of a micro gear (mn = 0.05mm) 4.3 Reduction of the calibration chain The universal character of the normal measuring device enables to calibrate product-like artifacts. This enables to transfer the measuring uncertainty which is achieved at PTB directly to be transferred on
41、the product (Figure 5). Inside the calibration chain the first step of the traceability will be omitted. The national standards ()bbbrF ,involute parameter br base diameter b lead angle b involute origin base cylinderinvolute surface Fdeviations 5 m4 will be replaced by normal measuring device. More
42、over, it will be possible to make tracable calibrations directly from all levels of the calibra-tion chain to PTB. PTBU = kuproductDKDindustryTraceabilityFigure 5 Future possibilities of traceable gear calibration 5 Outlook In the present contribution, a concept is described the PTB intends to use t
43、o reduce the uncertainty of measurement of gears. This step will be necessary to overcome the existing barriers for the gear-cutting industry and to considerably enhance the quality of future products. The decision to implement these concepts has already been made. Between the middle and the end of
44、2002, the new standard testing device of PTB will be taken into operation. Some months ago, work was started to prepare a specific PTB evaluation software. This will be completed by the end of 2001 and support a software interface which is at present being specified and adopted by VDI (Association o
45、f German Engineers). In addition, preparations are being made for the performance of a software test 7. The project will be carried out in cooperation with partners from the gear-cutting industry. 1 Beyer, W.: Traceable Calibration of Master Gears at PTB. AGMA Technical Meeting, Cincinnati, Ohio, IS
46、BN 1-55589-671-5; 1996 2 Beyer, W.: Limits in Gear Metrology; AGMA Technical Meeting 3 Verfahren zur Genauigkeitssteigerung von Koordinatenmessgerten und Werkzeug-maschinen; Patententwurf eingereicht Juni 2001 4 VDI/VDE 2607: Rechneruntersttzte Aus-wertung von Verzahnungsmessungen an Zylinderrdern m
47、it Evolventenprofil, 2000 5 VDI/VDE 2614: Austauschformat fr Verzah-nungsdaten; Entwurf 2001 6 Lotze, W., Rauth, H.-H. und Ertl, F.: Neue Wege und Systeme fr die wirtschaftliche 3D-Verzahnungsprfung. VDI-Berichte Nr. 1230, 1996 7 PTB-project: Softwaretest for validating profile-, lead- and pitch evaluation for involute gears. Project start Sept. 2001
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