Different methods of measuring gauge rings.

Tasic, Tadej ; Acko, Bojan ; Godina, Andrej 等

1. 1D DEVICE

In this procedure we must fix the reference length (we are using internal probes), which is a dimension of gauge block for certain measurement range.

[FIGURE 1 OMITTED]

these five measurements. The "turning point" in horizontal as well as in vertical plane shall be found in each measurement. The calibration result is the difference between the measured and the nominal value of the gauge ring diameter.

The gauge block representing a reference length shall be rotated in horizontal and vertical plain in order to find minimal length. The gauge ring is diameter measured in the main probing direction lying in the plane P and oriented perpendicular to the ring axis (Figure 2). If such direction is not marked, than the measurement direction is perpendicular to the direction going through indication inscriptions and is marked with a waterproof marker.

* Additionally, two diameters in the plane P are measured in such a way, that the ring is turned around the cylinder axis for approximately [+ or -] 1 mm with respect to the main probing direction.

* After that two diameters are measured in the main probing direction parallel with the plane P shifted for approximately [+ or -] 1 mm.

* Probing in various directions shows us form error in the main direction surroundings. If the differences are significant (above the value of expanded uncertainty), the client is informed.

* The measurement in the main axis is repeated 5 times. The measurement result is calculated as an arithmetic mean of these five measurements. The "turning point" in horizontal as well as in vertical plane shall be found in each measurement. The calibration result is the difference between the measured and the nominal value of the gauge ring diameter.

According to EA coverage factor k=2 is used for the calculation of the expanded uncertainty. It is rounded up to:

U = 0.6 [micro]m + 0.8x[10.sup.-6]xL (1)

[FIGURE 2 OMITTED]

2. COORDINATE MEASURING MACHINE

In LTM we have CMM ZEISS UMC 850. We can measure distances from 2 mm up to 1000 mm and surfaces up to 500 mm x 500 mm. One surface is probed and set as an origin, and then the perpendicular distance into the center point of the second plane is measured. Measurement is repeated also in the surrounding points (Figure 2).

[FIGURE 3 OMITTED]

The whole procedure is repeated 3 x (15 points obtained). Measurement result ([bar.x]) and the uncertainty component is calculated by the CMM program (Calypso). Therefore, we apply uncertainty specified by the producer and verified with periodical verification tests. Expanded best measurement capability in one axis in a temperature range from 18[degrees]C to 20[degrees]C is:

[U.sub.KMN] = 2.1 [micro]m + 3.3 x [10.sup.-6] x L (2)

3. OPTICAL SCANER

This method is used when the measurement must be quickly done and must not be so precise. The ATOS(tm) system is based on the triangulation principle: The sensor unit projects different fringe patterns onto the object to be measured which are then recorded by two cameras (Figure 4). Each single measurement generates up to 4 million data points. In order to digitize an object completely, several individual measurements are required from different angles. Based on reference points (circular markers), which are applied to the object directly or to the measuring plate or a fixture, ATOS transforms these individual measurements fully automatically into a common global coordinate system (GOM 2007).

[FIGURE 4 OMITTED]

ATOS[TM] II three-dimensional scanner is equipped with three different projector and camera lenses setups that enable the scanning to be performed inside three different measuring volumes (135, 350 and 1200mm envelope). Using the larger measuring volume quickens the scanning of large parts by reducing the number of required consequent scans. However, the accuracy of scans falls with an increased volume envelope size. The results of our researches show the expected difference in accuracy between measuring volumes. Somewhat surprising is the accuracy difference of circle diameter and centre distances deviations in the same measuring volume. Deviations of diameters are 2 to 3 times bigger then deviation of centre distances. This can be seen as a consequence of optical scanning limitations in digitising holes, pockets and similar features. Also, bigger measuring volumes have problem scanning smaller details due to their smaller resolution. Because the scanner software enables the combination of different measuring volumes in a single project, the future research will be conducted in optimizing various measuring volume layouts, regarding to the scanned objects properties. If the uncertainy is estimated in the same simplified way as in the case of gauge block scanning, the expanded uncertainty at k = 2 is:

U = 5 [micro]m (3)

4. CONCLUSION

As it is shown in the article, we can offer few different methods for measuring gauge block diameter to our customers. The uncertainties show the difference in accuracy between measuring procedures. In most cases those measurement with best uncertainty needs more time and knowledge to be done, so they also cost more money.

5. REFERENCES

Acko, B. (1999). Industrial Measuring, Faculty of Mechanical Engineering Maribor, ISBN: 86-435-0261-8, Maribor

Brajlih, T. (2007). Testing the accuracy of Atos(tm) 3d optical scanner, Proceedings of 18th DAAAM Int. Spec. Conf, Valentan, B., Derstvensek, I., Pogacar, V., pp. 111-112, Croatia, Zadar

Acko, B. (1998). Calibration of coordinate measuring devices in the laboratory conditions, Strojniski vestnik, Vol. 44, No. 2, 41- 46

Quality control of injection moulded parts, Available from: http://www.gom.com/EN/B0C.html Accessed: 2007-31-05