# State of the Art of Tactile Micro Coordinate Metrology
## 6 State of the Art and Conclusions  
As outlined earlier there are actually a few types of machines for high precision tactile micro coordinate measurements available, which have full 3D measurement capability and are operational with a high-level software platform to provide industrial measurement services: the well established Zeiss F25 [8], from which about 25 machines were sold and are operating in research labs and institutes worldwide, but is unfortunately no longer commercially available; two more recent developments, the Isara 400 [30] and the TriNano [13; 23] are both in principle commercially available, but the market uptake did not really happen so far; the micro CMM at METAS [4] is a prototype development, which is fully operational since 2006 and almost daily used for providing calibration and measurement services to industry. Also to be mentioned is the commercially available SIOS nanopositioning and nanomeasuring machine [24; 25], which can be configured with a suitable probe to perform 3D coordinate measurements. Furthermore, micro CMMs were developed by Hefei University of Technology [26; 27], complemented by tactile micro probe developments [16; 17; 18; 19] to achieve 3D measurement capability. These latter laboratory instruments, however, are still in the developmentphase and have not proven yet their full measurement capability following standardized procedures as outlined in Section 4. Not discussed further in this context are multi-sensor CMMs, such as [6; 14], which have accuracies closer to conventional CMMs.  
State of the art probes of above mentioned instruments do achieve a repeatability of a few nanometers, but the best values reported for the 3D probing error according to standardized specification tests [31; 34] are around 50 nm, with similar performance for single point probing and scanning. The achievable probing errors are limited mainly by the form deviation and the roughness of the probing sphere, and the overall stability of the instrument during the test procedure. State of the art CMM stages were demonstrated to have maximum errors of indicated length according to a standardized specification test [38] in the entire volume and in arbitrary direction of about 60 nm, limited by the uncorrected flatness deviation of the reference mirrors, residual squareness errors and the errors of the probe, the latter being part of the mentioned specification test.  
In conclusion, in spite of the big research and development effort spent worldwide for tactile micro coordinate metrology, there are still very few results available for a comparable performance verification according to standardized procedures. The reason for this is partly that many instruments and probe systems are still in the development phase, but there is also a lack of generally accepted and widely available material standards and written standards dedicated to the particular characteristics of micro CMMs.  
This work was funded by the R & D-Program at METAS and the European Metrology Research Program EMRP.  
[PERSON], [PERSON] and [PERSON] conceived and designed the experiments; [PERSON] performed the experiments and analyzed the data; [PERSON] wrote the paper.  
The authors declare no conflict of interest.  
The following abbreviations are used in this manuscript:  
\begin{tabular}{p{42.7 pt} p{284.5 pt}} CMM & Coordinate measuring machine \\
3D & Three dimensional \\ \end{tabular}