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1 Open Access Repository eprint Terms and Conditions: Users may access, download, store, search and print a hard copy of the article. Copying must be limited to making a single printed copy or electronic copies of a reasonable number of individual articles or abstracts. Access is granted for internal research, testing or training purposes or for personal use in accordance with these terms and conditions. Printing for a for-fee-service purpose is prohibited. Title: Trinano N100 3D Measurements with Nanometer Repeatability and Effects of Probe-Surface Interaction Author(s): Bos, E.; Moers, A.; van Riel, M. Journal: Proceedings of the 27th Annual Meeting of the American Society for Precision Engineering Year: 2012, Volume: 54, Event name: 27th Annual Meeting of the American Society for Precision Engineering, place: San Diego, CA USA, date: October 2012 Funding programme: EMRP A169: Call 2010 Industry Project title: IND10: Form metrology: Optical and tactile metrology for absolute form characterization Copyright note: This article has been accepted for publication in the Proceedings of the 27th Annual Meeting of the American Society for Precision Engineering. Posting of the article to the EURAMET Open Access Repository has been permitted by the American Society for Precision Engineering. EURAMET Secretariat Bundesallee Braunschweig, Germany Phone: Fax: secretariat@euramet.org

TRINANO N100 3D MEASUREMENTS WITH NANOMETER REPEATABILITY AND EFFECTS OF PROBE-SURFACE INTERACTION Edwin J.C. Bos 1, A.J.M. Moers 1, M.C.J.M. van Riel 1 1 Xpress Precision Engineering B.V.

As the components are smaller, their weight and the required measurement volume also decrease.

The TriNano N100 design allows a 3D measurement uncertainty of 100 nanometers in a measurement range of 200 cubic centimeters, while greatly reducing manufacturing costs.

PARALLEL DRIVE CONCEPT In the TriNano, the workpiece is translated in 3 directions with respect to a stationary sensor, e.g. a tactile 3D probing system.

2 TRINANO N100 3D MEASUREMENTS WITH NANOMETER REPEATABILITY AND EFFECTS OF PROBE-SURFACE INTERACTION Edwin J.C. Bos 1, A.J.M. Moers 1, M.C.J.M. van Riel 1 1 Xpress Precision Engineering B.V. Eindhoven, The Netherlands INTRODUCTION In precision engineering, complex 3D components are developed and manufactured that are getting smaller and require increasingly tighter tolerances. As the components are smaller, their weight and the required measurement volume also decrease. In line with this trend, a novel coordinate measuring machine (CMM), the TriNano N100, has been developed, as shown in figures 1 and 2. The TriNano N100 design allows a 3D measurement uncertainty of 100 nanometers in a measurement range of 200 cubic centimeters, while greatly reducing manufacturing costs. This paper will discuss several important design aspects of this novel CMM as well as the results of the initial evaluation measurements that have been obtained. PARALLEL DRIVE CONCEPT In the TriNano, the workpiece is translated in 3 directions with respect to a stationary sensor, e.g. a tactile 3D probing system. This is achieved by three identical linear translation stages that support the workpiece table in a parallel configuration. Each of the 3 stages performs a linear motion only, whereby the position of each stage is measured using a linear encoder. The measurement axes of all 3 linear encoders remain aligned to the center of the probe tip over the whole measurement volume, i.e. the CMM complies with the Abbe principle in 3 dimensions throughout its measurement range. This is schematically shown in figure 3 for 2 dimensions. FIGURE 1. TriNano N100 CMM (artist impression). FIGURE 3. Schematic working principle 2D. FIGURE 2. Photo of TriNano N100 measuring an artifact using a Gannen XM probing system. The stages are positioned orthogonally and in parallel and support the work piece table via vacuum preloaded (VPL) air bearings, as shown in figure 4. A linear translation of a stage is transferred via its VPL air bearing to the work piece table. Translations of the work piece table perpendicular to the translation direction of the linear stage are decoupled by its VPL air bearing. Thus, each stage controls the position

3 of the workpiece table in one direction only, i.e. the stages are decoupled. As a result of the relatively simple operating principle, consisting of 3 identical stages and the use of linear encoders, this CMM is relatively cheap to manufacture and maintain. FIGURE 4. Schematic working principle 3D. The parallel configuration of the three identical stages supporting the workpiece stages results in superior dynamic behaviour of the TriNano. This configuration allows a low and equal actuated moving mass of each stage with short and stiff structural loops. On machine measurements show that the lowest natural frequency in the positioning loop is 75 Hz. This allows a high control bandwidth, required for scanning measurements of micro parts with a velocity of 1-2 mm/s, and reduces the influence of (external) vibrations on the measurement. THERMAL EFFECTS Thermally induced errors are often the largest contribution to the total error budget in precision measurement equipment despite the research efforts performed on the matter [1,2,3]. In the TriNano, thermal effects have been reduced by using low expansion materials for critical parts of the metrology loop. Also, the effect of heat sources is reduced. One example is in the heat generation of the actuators. Dynamic forces are minimized by the parallel layout of the machine, whereby each actuator only accelerates the mass of one stage and the work piece table. Static forces are minimized by the use of a frictionless pneumatic weight compensation mechanism. By adjusting the pressure, this mechanism can be adjusted to compensate for the mass of different work pieces as well. from low expansion materials like Zerodur or Invar. Therefore, these components are made from aluminium and compensation for their thermal expansion is used. NTC s are used to measure temperature variations in critical parts of the metrology loop. A linear compensation model is used to obtain an estimate for the thermal expansion. The main advantage of NTC s compared to other sensors like PT100 s is their resolution [4] which is better than 0.1 mk. MEASUREMENT RESULTS All measurements as discussed in this section are performed using a TriNano N100 CMM with a Gannen XP 3D probing system. The results include the disturbances of all parts of the metrology loop, e.g. thermally induced errors and the stability of the vacuum preloaded air bearings. The stability in the air gap of the vacuum preloaded air bearings is discussed in a previous publication [5]. Single point repeatability The single point repeatability is determined by repeatedly measuring the same point on a steel gauge block. Each position is recorded and the deviation between the measured positions is calculated, as shown in figure 5. FIGURE 5. Result of a single point repeatability measurement in vertical direction. The standard deviation over 50 points in this measurement was 2.4 nm. The standard deviation in the single point repeatability measurement shown in figure 5 is calculated to be 2.4 nm. This measurement was repeated at different position in the measurement volume, with similar results. The workpiece table and sensor support in the metrology loop are expensive to manufacture

Repeatability in distance To determine the repeatability in the distance measurement between points, two gauge blocks were placed in the CMM, as shown in figure 6.

From this graph, the standard deviation in the measurement of the distance between 2 points is calculated to be 4.1 nm.

4 Repeatability in distance To determine the repeatability in the distance measurement between points, two gauge blocks were placed in the CMM, as shown in figure 6. The result of the distance measurement between 2 positions on the gauge blocks is shown in figure 7. From this graph, the standard deviation in the measurement of the distance between 2 points is calculated to be 4.1 nm. thermal expansion, a top-top deviation of 28 nm is obtained, as shown in figure 9. As thermal shielding of the frame was not yet available, further improvements can be expected. FIGURE 8. Drift in the metrology loop over a 3 hour measurement. FIGURE 6. Photo of the repeatability measurement of the distance between 2 gauge blocks. FIGURE 9. Single point repeatability over a 3 hour measurement after thermal compensation is applied. FIGURE 7. Repeatability in the measurement of the distance between 2 gauge blocks at a nominal separation of mm. The standard deviation over 120 points in this measurement was 4.1 nm. Long term stability and temperature compensation Figure 8 shows the expansion in the metrology loop of the TriNano. During a 3 hour measurement a drift of 160 nm was observed. First results show that, after compensation for Repeatability of a scanning measurement To verify the dynamic behavior of all components in the metrology loop, including the Gannen XP probe, scanning tests are performed at a scanning velocity of 1 mm/s. The measurement object is an optical flat which is scanned using a Gannen XP probe with a ruby tip of 0.3 mm in diameter. The top surface of the optical flat is measured using two square patterns, as shown in figure 10. From this graph is can be seen that the optical flat was slightly tilted during the measurement.

uncertainty, while greatly reducing manufacturing costs. Initial verification measurements show a standard deviation in single point repeatability of 2.4 nm.

5 uncertainty, while greatly reducing manufacturing costs. Initial verification measurements show a standard deviation in single point repeatability of 2.4 nm. The standard deviation in the distance measurement between 2 gauge blocks is measured to be 4.1 nm. Furthermore, a thermal compensation algorithm has been implemented that allows long-term measurements to be performed with nanometer stability. Using this algorithm, a top-top deviation of 28 nm over a 3 hour measurement is obtained. FIGURE 10. Scanned pattern, consisting of 2 squares, on the top surface of an optical flat. The same pattern on the optical flat was measured twice. The difference between all corresponding measurement values of both scanning cycles, without averaging or filtering of data points, is within a band of ± 20 nm, as shown in figure 11. Finally, the CMM and probe dynamics have been investigated. The differences between repeated scanning cycles at 1 mm/s are shown to be within a band of ± 20 nm. ACKNOWLEDGEMENTS TriNano is a joint development of Eindhoven University of Technology, NTS Systence, TASS Software Professionals and Xpress Precision Engineering. The project is partially funded by the European Regional Development Fund, the Dutch government and the province of Noord- Brabant under the OP South Netherlands program. Scanning measurements and the influence of probe-workpiece interactions are performed under an EMRP Researcher Grant. The European Metrology Research Programme (EMRP) is jointly funded by the EMRP participating countries within EURAMET and the European Union. FIGURE 11. Deviations between the measured positions of individual data points for two scanning measurements on the top surface of an optical flat. CONCLUSION A novel CMM has been developed and manufactured. Its design allows nanometer REFERENCES [1] Bryan, International Status of Thermal Error Research, Annals of the CIRP, 39/2, 1990 [2] Ramesh et al., Error compensation in machine tools - a review, Part II: thermal errors, International Journal of Machine Tools & Manufacturing, 40, pp , 2000 [3] Van den Bergh, Reducing Thermal Errors of CMM Located on the Shop-Floor, PhD Thesis, Katholieke Universiteit Leuven, 2001 [4] Ruijl, Ultra Precision CMM, PhD thesis, Delft University of Technology, 2001 [5] Moers et al., Design and verification of the TriNano ultra precision CMM, IWK Ilmenau, 2011

Traceability of on-machine measurements under a wide range of working conditions

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