# Impact of a Robot Manipulation on the Dimensional Measurements in an SPC-Based Robot Cell
## 5 Discussion
For this reason, more measuring sets were collected for the Magnet object than for the PKR object. The importance of the PKR object is that there are more added measurement codes. Furthermore, it served for the verification of the previously observed trends. The measurements on the PKR object confirmed the findings of the robot's manipulation influence on the dimensional measurements obtained with the Magnet object. Figure 10 shows measurements for the PKR object characteristic codes 10, 100, 130, and 140. The characteristic codes 10, 100, and 140 represent length measurements, and, by increasing the robot's degree of manipulation, the trend of the decrease of the \(C_{p}\) value and the increase of \(R\) and \(6\sigma\) can be observed for all three cases. In the case of the PKR object characteristic code 130, which represents the spherical geometry, a decrease of the \(C_{p}\) value is present but, in comparison with the other codes, to a much lesser extent. The \(R\) and \(6\sigma\) values, in this case, do not increase significantly. The similarity between the measurement results for the different measurement methods is not surprising. A comparable measurement uncertainty for TTM and SM was shown by [PERSON] [12] for rectangular and spherical geometries. They also showed that the measurement uncertainty decreases with an increasing number of sampling points. In our case, we could not prove a direct relationship between the number of sampling points and the factor \(C_{p}\), as the differences between the measurement sets, which have different numbers of sampling points, were practically negligible. From a statistical point of view, the measurement methods TTM and SM are equivalent, so, from the process measurements' point of view, SM is more desirable, as it enables shorter measurement cycles. Due to the Equator measurement device's comparative measurement principle, the absolute ambient temperature did not play a significant role. However, variations do play a more critical role. If the ambient temperature changes by more than the allowed temperature deviation, it is necessary to perform a re-master procedure, which \"re-calibrates\" the Equator. A direct relationship between the measurement uncertainty and the magnitude of the change in the ambient temperature was shown by [PERSON] et al. in Reference [21]. It turns out that, with a larger allowable temperature deviation between individual measurements, the measurement uncertainty increases exponentially and decreases with the implementation of the re-master procedure for relatively small temperature changes. The allowable temperature range in our study was defined as \(T_{a}=T_{m}\pm 1^{\circ}\), where \(T_{m}\) is the ambient temperature during the master procedure. Observing individual repetitions within the measurement sets, it can be argued that the ambient temperature was stable, since none of the repetitions triggered a request to perform a re-master procedure. By comparing Set 1, Set 2, and Set 3 (TTM, SM, and SM+) in Figure 8, as well as in Figure 9, it can be confirmed that different measurement methods and the number of sampling points do not play a significant role in the final dimensional measurements. Based on the used comparative method with frequent re-mastering, it can be stated that the ambient temperature and variation of it also have a minimal impact. Angular misalignment could be the reason for the increase of the \(6\sigma\) and \(R\) values and the consequent decrease in the value of the factor \(C_{p}\). The positional misalignment was not noticeable. This would happen by increasing the degree of the robot's manipulation. An angular misalignment represents the misalignment of the measurement object's orientation in the fixture between measurements compared to the object's orientation in the fixture during the re-master procedure. The misalignment error is manifested as a loose fit of the subjects in the pallet, in the re-gripping position and the fixture, as well.