Project summary

The Traceability for contact probe and stylus instrument measurements project has been granted funding under the European Metrology Programme For Innovation and Research (EMPIR) with the project number and acronym of 18RPT01 Probe Trace. The project started in September 2019 and will continue for the following 3 years.

You may also reach the information given below from the publishable summary of the project maintained in the EURAMET website : https://www.euramet.org/research-innovation/search-research-projects/details/project/traceability-for-contact-probe-and-stylus-instrument-measurements

Objectives

The overall goal of this project is to develop traceable and cost-effective measurement capabilities for the calibration of form and surface roughness standards with uncertainties in the range 10 nm–100 nm. The specific objectives of the project are:

1. To calibrate reference stylus instruments for surface roughness measurements using novel portable displacement generators with uncertainties in the range 10 nm–100 nm and to evaluate the efficacy of displacement generators vs existing methods (e.g. depth setting standards) for calibration of stylus devices. Further, to develop novel software for the calibration of stylus devices using sphere standards.
2. To calibrate reference probes for form measurements in static and dynamic mode using novel portable displacement generators with uncertainties in the range 10 nm–100 nm and to evaluate the current state of the art for calibration of flick standards.
3. To investigate the traceable calibration of transducers to be used as portable displacement generators under static (+/-1000 µm) and dynamic (+/-100 µm) measurement conditions, including investigations into the set-up of the generators to be used as ‘portable’. Further, to prepare two best practice guides on their use in the calibration of stylus instruments and form measurement probes.
4. To develop noise reduction software, including the use of numerical methods for random noise bias reduction, that can be used to pre-process roughness and form profiles data to reduce the overall uncertainties down to a level of 10 nm in roughness and roundness measurements.
5. For each project partner, to develop an individual strategy for the long-term operation of the capacity developed, including regulatory support, research collaborations, quality schemes and accreditation. In addition, for partners to develop a strategy for offering calibration services from the established facilities to their own country and neighbouring countries. The individual strategies to be discussed within the consortium and with other EURAMET NMIs/DIs, to ensure that a coordinated and optimised approach to the development of traceability in this field is developed for Europe as a whole.

Need for the project

Surface finish and form parameters of products from manufacturing processes are important features to be examined for engineering and scientific purposes. Such characteristics of surface include wear resistance, bearing, sliding and lubricating properties, fatigue and corrosion resistance, functionality etc. These are important parameters for industries such as automotive, aerospace and energy (wind power electrical drive trains). Form and surface measurement devices with contact probes and stylus are used to characterise engineering surfaces. There is a need for traceable calibration of form and surface measuring standards in the uncertainty range 10-100 nm. These needs require NMIs to improve their scientific knowledge, instruments, methods and research capability in metrology for contact measurement probes and stylus instruments.

Form measuring devices utilise contact measurement probes in measurement of form parameters such as roundness, straightness, parallelism etc. The probe tip diameters are around a few millimetres long. Surface roughness measurement devices use stylus instruments with a tip of a few microns in radius. Both perform measurements in dynamic mode over an engineering surface i.e. while the tip or the surface is moving. They need to be calibrated for the same conditions as used for traceability.

Manufacturers provide simple samples for calibration of these devices. For example, gauge blocks are used to calibrate form measuring probes in static mode providing traceability. The dynamic performance of the probe (functional calibration of its sensitivity) is checked using so called flick standards or magnification standards. The probes are made of a cylinder with a flat part on the circumference and embody a well-defined roundness deviation. The application of flick standards is efficient and functional, since they allow calibration of the roundness instrument in its normal dynamic operational mode. Flick standards are primarily calibrated using fully characterised form measuring instruments. This raises the issue of traceability if no primarily calibrated flick standard is available. It is a typical problem for emerging NMIs as they seek traceability for the flick standards. In such cases they have to develop capability for full investigations of their form measuring device and then calibrate their own and customers’ flick standards to provide traceability. The same issues apply to any device utilising contact measurement probes for measurement of engineering surfaces in dynamic mode.

The calibration of flick standards (available in the last 20-30 years) is also an important issue for experienced NMIs. The results of a recent EURAMET comparison [5] between experienced NMIs revealed a partly unsatisfactory agreement between the measured values and strongly varying measurement uncertainties reported by the participating institutes, which do not seem to be consistent with the observed deviations. Furthermore, there were inconsistencies related to the filtered results. Related investigations [6] suggest that the reasons for variations in Calibration and Measurement Capabilities (CMCs) may be interpreted as a missing knowledge in establishing an uncertainty budget, having a reasonably good feeling for the achievable uncertainty but lacking detailed knowledge of all influence factors. Therefore, due to common needs this topic will bring experienced and new NMIs to work together.

Depth setting standards/spheres are utilised for provision of traceability to stylus instruments employed by surface roughness devices. Verification of the whole measurement system (mechanical-electronical parts, filtering process) with the software is carried out using surface roughness standards. Depth setting standards are primarily calibrated using special interference microscopes which are not available in most NMIs.

Currently, EURAMET.L-S26 comparison [9] is in progress for calibration of depth setting standards up to about 1000 µm which becomes a challenging work for most NMIs. These new depth setting standards (5-900 µm) have been very recently released to the market and seek traceability. To calibrate these standards by even comparing them to reference ones, stylus instruments have to be characterised very precisely since they suffer from non-linearities particularly in the large ranges.

An alternative approach uses piezo capacitive sensors traceable to laser displacement interferometers (available in most NMIs). However, this requires a good knowledge and understanding for traceable calibration of piezo capacitive sensors for the required uncertainty values. In addition, piezo capacitive sensors need to be developed to better address the issues related to the overall metrology path for the traceability including the actuator with its own on-board metrology, and the stylus instrument frame. Optimised Abbe offsets and drifts have to be considered with geometrical errors of the stage moving on the sample or of the moving head for calibration of stylus instruments.

Calibration of piezo capacitive sensors (micro actuators) for uncertainties down to a few nm is a critical issue and was studied in EURAMET Project 866, the final report of which was released recently [10]. Knowledge gained from this project must be used while designing the portable displacement generator which is required for calibration of stylus instruments and their performance in dynamic and static mode. A fully characterised stylus instrument (of form and surface roughness devices) can then be used to calibrate depth setting standards and also flick standards, demanded by customers.

Emerging NMIs need to improve their capability for traceable calibration of measurement probes and stylus instruments seeking optimised approaches. They have to develop new capabilities to provide traceability for their customers. In addition, good practice guides are required to ensure consistency for the evaluation of uncertainty parameters during calibration of form and surface roughness standards and this applies to all NMIs.

Economic impact:

By improving the surface texture and form measurements at a wider level reaching to the emerging NMIs and industries in Europe, this project will have positive wider impact on European industry. Most large European manufacturers (e.g. VW, BOSCH, Renault, Siemens, FIAT, Astron etc.) have manufacturing plants all over Europe (e.g. Turkey, Spain, Poland etc.) and even in Egypt (e.g. Renault, FIAT) with local suppliers of manufactured parts. This project will meet the demand of industry to obtain high accuracy calibration services throughout Europe, whilst making calibrations less time-consuming and less expensive.

Environmental impact:

In industrial manufacturing the vast majority of parts are made up of complex geometrical shapes requiring form and surface roughness measurements. Improvements in these measurement standards will lead to lower rejection rate of complex parts in the manufacturing process reducing waste and saving energy.

EU and US emission standards and the need for the reduction of fuel consumption can only be matched by even lower tolerances than the current ones. The realisation is explicitly dependent on very low measurement uncertainties in the production chain of the parts of fuel injection systems. Therefore, the manufacturing process of car fuel injection systems is an important and challenging precision engineering application. Most of the parts of fuel injection systems consist of precise cylindrical shapes with tolerances that are the most critical in mechanical manufacturing and concern small inner and outer diameters (typically 100 µm). The car fuel injection manufacturers will benefit from the new improvements in form and surface roughness standards and measurements by obtaining improved traceability.

The project outputs will help to lower Europe’s CO 2 footprint and to strengthen the competitiveness of the European automotive and supply industry by reducing waste and improving quality control.

Social impact:

The project will indirectly enhance consumer protection, particularly through an improvement of medical devices. The calibration of high accuracy pin gauges is vital to the medical device industry. Medical device companies use pin gauges to check the accuracy of their inspection equipment (i.e. laser micrometers). They are also used to carry out inspection of medical devices during the manufacturing process. The typical length of these pin gauges ranges from 25 mm–50 mm. Medical device companies are in need of reaching lower uncertainties for the calibration of pin gauges. Improvement in form and diameter measurements will positively influence the precision of medical devices which overall affects the healthcare industry.