Research framework

This PhD study that has been undertaken by published works is comprised of seven research articles, five of them published in JCR international journals:

Traceability of On-Machine Tool Measurement: A Review

As a starting point of the research, the state of the art of traceable on-MT measurement is carefully presented within the first article. There are advantages and disadvantages to performing a measurement on an MT. The advantages include the reduction of the so-called quality losses for the manufacturing operation, because dimensional measurements can be employed at different stages of the manufacturing cycle: a) monitoring of the MT geometry performance by employing a calibrated standard; b) workpiece setup on the MT coordinate system; c) in-process measurements to provide correction values for the manufacturing process; and d) the performance of a final metrology validation of the finished product for final quality inspection as well as statistical trend analysis of the manufacturing process. Among the disadvantages, two main barriers limit traceable CMM measurements on MTs: a) Lack of volumetric MT accuracy; and b) a closed calibration chain for those measurements performed on an MT. This article also proposes a qualitative approach to the error sources that contribute to the uncertainty budget of on-MT measurement: the measurement system, the MT itself with the TTP and the measuring software, the component under measurement and the interaction between both of them.

Traceability of on-machine tool measurement: Uncertainty budget assessment on shop floor conditions The second article presents a quantitive approach to the uncertainty budget of on-MT measurement. Thus, a medium-size on-MT measurement uncertainty assessment is performed in shop floor conditions. A complete experimental test was performed according to the ISO 15530-3 technical specification on a medium-size MT. Five workpiece replica standards were manufactured and subsequently measured on an MT. To understand the systematic error of the on-MT measurement, these workpieces were calibrated on a CMM with the VCMM tool which permitted to realise a task-specific uncertainty assessment. Experimental results show that traceable CMM measurements can be performed on an MT. Furthermore, every expanded measurement result is within 20 µm and results also highlight the significance of each uncertainty contributor where the measurement procedure uncertainty is the main contributor to the uncertainty budget. It also demonstrates that the geometric error of the MT is the main error source within the systematic error contributor.

Uncertainty assessment for on-machine tool measurement: an alternative approach to the ISO 15530-3 technical specification

The third article proposes a new methodology for traceable on-MT uncertainty assessment without using a calibrated workpiece, assuming that previous research article concludes that geometric error of the MT is the main error source for the systematic error contributor. The ISO 15530-3 technical specification presented in the second article faces a strong limitation, it depends on a calibrated workpiece to understand how the systematic error contributor performs on the on-MT measurement uncertainty budget. For small batch production, mainly in large scale manufacture, the approach is not affordable because a calibrated workpiece similar to the manufactured part

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is needed, which makes the solution tedious and expensive. Therefore, the scalability of the solution is limited to a medium-size MT. In this scenario, this article proposes a volumetric error mapping of the MT immediately before the measurement process execution to avoid the use of a calibrated component on the systematic error contributor assessment. An experimental exercise shows that traceable on-MT measurements can be realised without the use of a calibrated workpiece. Obtained results are similar to those results obtained with the ISO 15530-3 technical specification.

Integrated multilateration for machine tool automatic verification

The fourth article presents an integrated MT volumetric error mapping solution that enables the scaling of traceable on-MT measurement to large MTs. The integration of a tracking interferometer measurement device on the MT spindle breaks with the typical multilateration approach, based on sequential measurement scheme, and allows to measure the geometric error of an MT automatically in the complete volume. It reduces (depending on the MT volume) the volumetric error mapping process time consumption and the measurement uncertainty. This article shows a complete simulation scheme of the proposed integrated solution and presents an initial validation exercise mounting a LEICA AT402 laser tracker on a KUKA KR60 industrial robot.

This integrated measurement procedure for automatic MT geometric verification is focused mainly on large MTs and therefore the measurement procedure is developed within the large scale metrology (LSM) field. It means that when it comes to large-scale manufacturing scenarios, the MTs face similar challenges to what the LSM does and therefore this measurement procedure considers the current LSM state of the art to select the suitable technologies and measurement sequences.

Integrated volumetric error mapping for large machine tools: An opportunity for more accurate and geometry connected machines

The fifth article demonstrates the integration exercise of the multilateration-based measurement solution on a large MT, conceptually presented in the previous article. The integration work was performed on a ZAYER MEMPHIS large MT and it was realised with a LEICA AT960 laser tracker. Obtained results were compared to the typical multilateration approach, realised with a laser tracer NG measurement device on the same MT and immediately after the integrated measurement approach. In this way, results show that the integrated measurement approach improves the typical volumetric error mapping measurement procedure.

3D Measurement Simulation and Relative Pointing Error Verification of the Telescope Mount Assembly Subsystem for the Large Synoptic Survey Telescope

The sixth research article proposes a new verification method for the RPE assessment of the TMA for the LSST project. At this point, this challenge benefits from the generated new knowledge within the LSM field for MTs and looks for a suitable measurement solution for the accuracy assessment of the LSST. The telescope size matches the size of extremely large MTs, and therefore some of the technologies and measurement techniques researched before are adapted for the LSST project.

The presented new measurement procedure, based on laser tracker technology and several fiducial points fixed to the floor, was designed and simulated within SA software thanks to the knowledge developed in the fourth and the fifth articles above-mentioned. The measurement scenario is up to 40 m in diameter and 10 m in height, so the

2. Presentation of the published work

measurement challenge is within the LSM field. Monte-Carlo-based simulation results show that the presented methodology is fit for purpose on the simulation stage, even if a floor movement occurs owing to a temperature variation during the measurement acquisition process.

Telescope mount assembly pointing accuracy assessment for the Large Synoptic Survey Telescope: A large-scale metrology challenge

Finally, the seventh article presents the TMA pointing accuracy survey performed in-situ for the LSST project. Following the custom engineered measurement procedure presented in the previous article, the RPE assessment measurements were performed at Asturfeito company premises, in the north of Spain during September of 2018. These measurements were realised on an engineering validation framework, where it is aimed to execute major performing tests at the subsystem level to verify the overall engineering performance of the observatory. Results demonstrate that the RPE assessment is similar to what previously obtained within the simulation model, so the survey uncertainty requirements were successfully fulfilled.