A laser metroscope for the calibration of setting rings

Transcription

1 THE 0 th INTERNATIONAL SYMPOSIUM OF MEASUREMENT TECHNOLOGY AND INTELLIGENT INSTRUMENTS JUNE 29 JULY 2 20 / A laser metroscope for the of setting rings S.Zahwi,*, M.Amer 2, M.A.Abdo 3, A.El-Melegy 4 Professor, Tersa St., El haram, El Giza, Egypt Engineering and surface Metrology Lab., National Institute of s (NIS), Egypt 3 Alazhar University, Faculty of Engineering, Egypt. 4 Engineering and surface Metrology Lab., National Institute of s (NIS), Egypt. * Corresponding author: zahwi@nis.sci.eg TEL: Fax, Keywords: Calibration, Diameter, Laser, Metrology, Rings. Abstract: Calibration of setting rings could be an application of laser systems in dimensional measurements. In this investigation a commercial laser interferometer system Agilant has been used to upgrade a conventional metroscope. The aim is to improve resolution of measurement up to 0.0 µm while the conventional metroscope is µm. The conventional metroscope is a Carl Zeiss universal horizontal metroscope. This upgraded metroscope is named '' laser metroscope ''. The details of upgrading the metroscope are given in the full paper. The laser metroscope has been used to calibrate a setting ring of a nominally mm inner diameter. The same setting ring was calibrated using the conventional metroscope with its optical glass scale. Repeated results from the two methods of where carried out and presented in the paper. Uncertainties associated with the measurement results of each method have been estimated using the procedures mentioned in GUM. A comparison between these two methods of setting ring was carried out. The paper discusses the accuracies as well as difficults associated with each instrument. NOMENCLARURE: c i = sensitivity factor d = the diameter of the ball tip. k = a coverage factor S = the spindle displacement to touch two opposite sides of ring u (x i ) = uncertainty of quantity x i Δ = the correction due to temperature effects. Δ 2 = the correction due to non-coaxiality. Δ 3 = the correction due to tilting. Δ 4 = the correction due to elastic. Δ = the correction due to Abbe error. Δ s = the correction in S from of metroscope. ν i = degree of freedom Φ = the measured internal diameter of the setting ring.. Introduction: The progress in manufacturing process improved the accuracies of the products. A new issue of ISO code system for tolerances on linear sizes is being issued []. This called upon more accurate measurements for gauges. Setting rings are often used to set up measuring instruments. Accurate measurements for such setting rings are needed. Laser interferometer systems are applied in accurate length measurements [2]. Application of laser interferometer system in improving the accuracies of Abbe vertical metroscope has been reported [3]. In this investigation a laser metroscope with a resolution of 0.0 µm is developed and used in calibrating a precise setting ring of mm nominal inner diameter. 2. Setup: A laser metroscope has been developed to calibrate setting rings fig. A conventional metroscope having a measuring range of 00 mm and a resolution of 0. µm is upgraded by laser interferometer system. The retroreflector of the laser system is fixed to the measuring spindle of the metroscope; the interferometer is fixed to the bed of metroscope while the laser head is set on a tripod and aligned to the spindle motion. The resolution of the laser metroscope is improved to 0.0 µm. A setting ring of mm nominal internal diameter is calibrated by the two systems i.e. the laser and the conventional metroscope. The inner diameter of the setting ring is calibrated using a ball tip diameter of mm. The s are done under a measuring force of 200 mn and reported at 0 mn after corrected for the. The s have been carried under environmental conditions of 20 C ± C.

2 THE 0 th INTERNATIONAL SYMPOSIUM OF MEASUREMENT TECHNOLOGY AND INTELLIGENT INSTRUMENTS JUNE 29 JULY 2 20 / 2 Ф Ф = mm S(φ) = mm Diameter of setting ring, φ mm (a) Laser metroscope Figure : The developed laser metroscope Ф 3. Results Ф = mm 3. Repeated measurements: S(φ) = mm The basis of is to move the measuring spindle of metroscope with its ball tip a distance to touch one side of the ring and an initial reading of the displacement is taken then the spindle is moved manually backward a distance S to touch the other side of the ring gauge giving a second reading on the displacement measuring system figure 2. Diameter of setting ring, φ mm (b) Conventional metroscope Figure 3: Distribution of results for mm setting ring 3.2 Uncertainty Estimation Figure 2: Calibration of setting ring The estimation of uncertainties associated with of the setting ring is based on GUM [4]. The measured internal diameter Φ of the ring is the distance S plus the diameter of the ball tip and the necessary corrections, figure 4. Equation gives Φ. Φ = S + Δ s + d + Δ i..() The of the setting ring is repeated 0 times by each system. The results are summarized in table and figure 3. Table : Calibration results of the rotary table Calibration of setting ring Average diameter deviation S(φ), mm by Ф, mm Laser metroscope Conventional metroscope S Φ d Figure 4: Calibration basis of ring Coaxiality

3 THE 0 th INTERNATIONAL SYMPOSIUM OF MEASUREMENT TECHNOLOGY AND INTELLIGENT INSTRUMENTS JUNE 29 JULY 2 20 / 3 Where, Φ the measured internal diameter of the setting ring. S the spindle displacement to touch two opposite sides of ring Δ s the correction in S from of metroscope. d the diameter of the ball tip. Δ the correction due to temperature effects. Δ 2 the correction due to non-coaxiality. Δ 3 the correction due to tilting. Δ 4 the elastic correction due to measuring force. Δ the correction due to Abbe error. u 2 (Φ) = c 2 s u 2 (S)+c 2 s u 2 (Δ s )+ c 2 d u 2 (d)+ c i 2 u 2 (Δ i ). (2) Where, c s, c s, c d, c i and u(s), u(δ s ), u(d), u(δ i ) are the sensitivity coefficients and the uncertainties for the different influencing factors affecting the results of measurements, c s = Φ/ s ; c s = Φ/ Δ s ; c d = Φ/ d ; c i = Φ/ Δ i Thus; and c s = c s = c d = c i = u 2 (Φ) = u 2 (S)+ u 2 (Δ s )+ u 2 (d)+ u 2 (Δ i )....(3)...(4) The contributors affecting the results are; repeatability in measuring displacements u(s), uncertainty in metroscope u(δ s ), uncertainty in ball tip diameter u(d), uncertainty due to temperature effects u(δ ), uncertainty due to non-coaxiality u(δ 2 ), uncertainty due to tilting u(δ 3 ), elastic due to applied force u(δ 4 ) and Abbe error u(δ ). The uncertainty due to temperature effect is determined according to [,6] using thermal expansion coefficients of setting ring and metroscope scale of / º C ± 0-6 / º C and / º C ± 0-6 / º C respectively and temperature difference of ± º C. In the case of conventional metroscope the standard uncertainty due to temperature effect is found to be 0.29 µm. In the case of laser metroscope, the variation in temperature of the ring is measured continuously, instantaneously and corrected for automatically. The uncertainty in measuring the temperature of the ring is ± 0. º C. Also the weather unit of the laser system corrects the wave length instantaneously and continuously for the variation in temperature, pressure giving uncertainty in displacement to ± ppm. The thermal effects were computed separately and it was found to be within ± 0.04 µm A summary of uncertainties associated with the setting ring in each case are shown in tables 2 and 3. Table 2: Uncertainty budget of setting ring by laser metroscope Quantity x i Distribution Normal Uncertainty u(x i) μm ± 0.08 c i u 2 (Φ i) (0.08) 2 Table 3: Uncertainty budget of setting ring by conventional metroscope Quantity x i Distribution Normal Uncertainty u(x i) μm ± 0.09 c i u 2 (Φ i) (0.09) 2 Metroscope Normal 0.04 (0.04) 2 Diameter of ball tip Normal 0.3 (0.3) 2 Temperature effects Rectangular 0.04 (0.04) 2 Noncoaxiality Rectangular 0.06 (0.06) 2 Rectangular 0.06 (0.06) 2 Normal 0.40 (0.40) 2 24 Abbe error Rectangular 0.06 (0.06) 2 Combined Uncertainty (u c) = 0. ν eff = Expanded Uncertainty (U): U = k u c = 2 0. =.0 μm Where, k is a coverage factor, k=2 providing a level of confidence of approximately 9 %. Metroscope Normal 0.0 (0.0) 2 Diameter of ball tip Normal.00 (.00) 2 Temperature effects Rectangular 0.29 (0.29) 2 Noncoaxiality Rectangular 0.06 (0.06) 2 Rectangular 0.06 (0.06) 2 Normal 0.40 (0.40) 2 24 Abbe error Rectangular 0.06 (0.06) 2 Combined Uncertainty (u c) =.23 μm ν eff = Expanded Uncertainty (U): U = k u c = 2.23 = 2.46 μm Where, k is a coverage factor, k=2 providing a level of confidence of approximately 9 %. 3.3 Final results: A summary of the average measured diameter Ф and the uncertainty associated are shown in figures. ν i 9 ν i 9

4 measured diameter Ф mm Square uncertainty THE 0 th INTERNATIONAL SYMPOSIUM OF MEASUREMENT TECHNOLOGY AND INTELLIGENT INSTRUMENTS JUNE 29 JULY 2 20 / 4 nm 2 Expanded uncertainty Type B Type A laser metroscope, µm ±.0 µm conventional metroscope, µm ± 2. µm 0 Exp. uncertainty Ball tip Instrument Temperatu deformati re effect on Repeatabil ity Conventional M etroscope Laser M etroscope Figure 6: Contributors of uncertainty in results. Figure : Averages and uncertainties associated with. Laser Metroscope 4. Discussion Comparison between the average results obtained from the two systems is carried out. The normalizing error E n (number of consistency) [7] is used. Table 4 shows E n values for the calibrated setting ring by the different methods investigated. It was found that E n <. It can be said that according to the obtained results no significant difference in the average results is noticed. Table 4: E n values for the tested tables. Comparison between results of E n values Laser/Conventional Metroscope % Ball tip 39% Instrument Temp. effects 2% The uncertainty associated with the results of laser metroscope shows improvements. Values of the different contributors are shown in figure 6 and their percentages effects are shown in figures 7. The effect due to uncertainty in ball tip has a large percentage (39 % - 6 % of the combined uncertainty). The effect due to uncertainty in ball tip has improved by measuring the tip by the laser metroscope but not with the aimed target and is still a major contributor in the combined uncertainty. Although the effect due to elastic has the same value but their percentages effects on results are different in each case. Its effect is about % of the combined uncertainty in case of conventional metroscope while its effect is 0 % in case of laser metroscope. This effect can be minimized through minimizing the applied force in by using of electronic probes or through standardizing the applied force. The effect due to uncertainty in metroscope has been improved due to high accuracy of laser system. The uncertainty value due to temperature effect has also been improved due to using a weather unites having sensors for temperature, pressure, humidity and material temperatures for laser system and the continuous compensation of temperature variation during measurement process. The uncertainty due to repeatability, non-coaxiality, tilting, and Abbe error has about the same value for both cases i.e. conventional or laser metroscope. Their percentage effect is small compared with the other contributors (% - of the combined uncertainty). (a) Laser Metroscope (a) Conventional Metroscope Ball tip 6% % Instrument 7% Temp. effects 6% % 0% (b) Conventional (b) Metroscope Figure 7: Charts for different contributors of uncertainty. Practical experience showed that either of the two systems, is easy in use and nearly equally consuming time in measurements.

5 THE 0 th INTERNATIONAL SYMPOSIUM OF MEASUREMENT TECHNOLOGY AND INTELLIGENT INSTRUMENTS JUNE 29 JULY 2 20 /. Conclusions:. Insignificant difference in the averages of the results of the measurements; as obtained by either the conventional metroscope or the laser metroscope is found. 2. There is a good evidence that the uncertainty of results obtained by laser metroscope is less than that obtained by conventional metroscope. 3. The major uncertainty contributors in results of setting ring are due to uncertainties in ball tip diameter and in the correction for elastic due to the applied measuring force. 4. Both of laser metroscope and conventional metroscope are equally easy in applications. REFERANCES: [] ISO 286, ''Geometrical product specifications (GPS) ISO code system for tolerances on linear sizes part and 2''; 200. [2] H. Kunzmann, T. Pfeifer, J. Flügge, ''Scales vs. Laser Interferometers Performance and Comparison of Two Measuring Systems'', Annals of the CIRP, vol. 42, pp , 993. [3] S. Zahwi, M. Bahrawy, M. Amer and N. Farid, ''Improved Abbe Vertical Metroscope for the Calibration of Gauge Blocks, Key Engineering Materials, vols , pp , [4] ISO/IEC Guide 98-3,''Uncertainty of Measurement Part 3: Guide to the Expression of Uncertainty in Measurement (GUM: 99)'', [] EA-4/02, '' Expression of the Uncertainty of Measurement in Calibration SUPPLEMENT 2: Examples'', 999. [6] EAL-G29, "Extent of Calibration for Cylindrical diameter", 999. [7] ISO 328 ''Statistical Methods for use in Proficiency Testing by Interlaboratory Comparisons''; 200.