Computer-Tomographie

• Forschungsstelle: METAS
• Projektnummer: F-5111.30053

Schlüsselwörter (Englisch)

Computed tomography, CT, micro-parts, dimensional metrology

Kurzbeschreibung (Englisch)

Measurements on delicate micro-parts are of great importance for many Swiss micro-technology companies and ever more complex micro-parts have to be measured reliably and in a traceable manner. Increasingly demanded are also measurements of points is space which are difficult to access or which are even within composed component groups such as a mechanical clock work, medical implants or HF- or fibre-optics couplers. Parts produced by 3D printing can have cavities with functional properties which have to comply with geometrical tolerances but which are inaccessible after production. Using tactile measuring methods, only structures accesible from the outside with a minimum structure size larger than 0.1 mm can be measured. The finite size of the probing sphere and the limited length of the stylus shaft limit the possibility to characterise surface elements which are difficult to access. Tactile coordinate measuring machines work very precisely but they acquire only a limited number of surface points and delicate parts can possibly become damaged by the tactile probing.

Computed tomography (CT) is an elegant solution to the problem of inaccessible part locations and offers thereby a large set of new measurement possibilities.
During a CT measurement many X-ray images are taken from different directions from which by extensive computer calculations a 3D model is produced. From the 3-D data model internal and external surfaces can be extracted and used for the determination of dimensional measurands. The advantage of this method lies in the complete, contact-free determination of all interfaces of an object. X-ray based computed tomography has made considerable progress during the last years and in near future it will become a standard method for precision production measurements.

The METAS laboratory for length, nano- and microtechnology is producing a considerable turnover through calibration and measurement services. With this project its strong position will be further strengthened and the Swiss high technology workplace will get continuing top measurement services. Computed tomography is an ideal extension of the currently present competences in the field of micro coordinate and photomask measurements. By this project the laboratory will also in future remain a competent and demanded contact partner for industry and an attractive partner for research and development projects.

The Swiss calibration labs (SCS) and research laboratories in many industry fields such as microtechnology, watches, medical, photonis will benefit from this project.

Projektziele (Englisch)

METAS has a micro CT instrument at disposition for dimensional measurements on artefacts and work pieces having the following specifications:

• Voxel-size:  < 1 µm³
• Measurement volume:  > 100 mm x 100 mm x 100 mm
• Measurement uncertainty: < 2 µm + 1 10^-5 L

Further project objectives:

• METAS acquires new competencies in the field of micro computed tomography.
• The implementation of computed tomography in the Swiss micro-technology industry is supported and promoted.
• Companies operating CT instruments receive traceability, validation and metrological guidance from METAS.
• METAS facilitates smaller companies the access to this expensive technology and offers appropriate measurement services.
• METAS is a sought-after partner for research and development projects in the field of dimensional measurements with micro CTs.

Abstract (Englisch)

The construction of the METAS-Computed-Tomography-System (METAS-CT) is finished. Control software for the X-ray tube, the flat panel detector, the positioning system, and the measurement system consisting of 8 interferometers, 5 straightness sensors, 3 index sensors, and 30 temperature probes, is in operation. A reconstruction and analysis workstation as well as commercial software for CT simulation (aRTist, BAM), reconstruction (CERA, Siemens) and data analysis (VG Studio MAX, Volume Graphics) are implemented and ready for use.

The planned specifications were met:

• Voxel-size: < 1 μm3
• Measurement volume: > 100 mm x 100 mm x 100 mm
• Uncertainty: < 2 μm + 1x10^-5 L (unidirectional)

Various demonstration measurements were performed. Project results were published.

METAS-CT enables new measurement capabilities, especially characterisation of small workpieces with internal geometries and nominal-actual comparisons with corresponding CAD models.

Umsetzung und Anwendungen (Englisch)

METAS has built competence in the field of micro-computed tomography and is a qualified and sought-after partner for research and development projects on dimensional measurements using micro-CT.

The introduction of computed tomography into the Swiss microtechnology industrie is supported and promoted. We have established contacts to various industrial partners and the calibration service providers that operate CT systems. Optimisation processes were initiated in close collaboration with CT component and software suppliers. We plan to provide traceability, validation, and metrological consulting to companies operating CT systems. Furthermore, METAS enables access to this expensive technology, especially for small companies, and will provide measurement services.

Publikationen / Ergebnisse (Englisch)

1. Bircher, B. A., Meli, F., Küng, A., & Thalmann, R. (2018). A geometry measurement system for a dimensional cone-beam CT. In 8th Conference on Industrial Computed Tomography, Wels, Austria (iCT 2018).
2. Meli, F., Bircher, B. A., Blankenberger, S., Küng, A., & Thalmann, R. (2018). A cone-beam CT geometry correction method based on intentional misalignments to render the projection images correctable. In 8th Conference on Industrial Computed Tomog-raphy, Wels, Austria (iCT 2018).
3. Bircher, B. A., Meli, F., Küng, A., & Thalmann, R. (2017). Characterising the Position-ing System of a Dimensional Computed Tomograph (CT). In MacroScale - Recent de-velopments in traceable dimensional measurements. https://doi.org/10.7795/810.20180323C
4. Bircher, B. A., Meli, F., Küng, A., & Thalmann, R. (2017). Towards metrological com-puted tomography at METAS. In euspen’s 17th International Conference & Exhibition.