# Selection of Optimal Path Control Algorithms for Probe Heads Used on Five-Axis Measuring Systems
## 4 Discussion  
The results of the investigations presented in this paper confirmed that it is possible to reduce the measurement errors (an error is taken as the difference between the measurement result and the reference value, represented as a result of the measured workpiece calibration) using a relevant path control algorithm for the probe head used on a five-axis coordinate measuring system. In the case of some measuring tasks (e.g., distance between planes and flatness deviation), the reduction of error is obvious and reaches up to 4 \(\upmu\)m; however, in the case of other (e.g., parallelism deviation and circularity deviation) it is not that significant, but the tendency to reduce the measurement error is still observed if the proper path control algorithm is used. When analyzing the values of standard deviations associated to each measuring task, it may also be observed that their values are smaller for measurements performed using the optimal path control algorithm (except one case, which is the measurement of distance between planes). It is hard to give one exact reason why there are such big differences in results obtained using different path control algorithms. As shown, the results of the previous research undertaken by the authors in [15] showed that the accuracy of the measurements performed using the probe heads used on five-axis CMMs is strongly dependent on the orientation (the A and B angles) of the probe head during point measurement. In the majority of the presented path control algorithms, with the change of the algorithm's control parameters (e.g., tilt, advance, and offset), the probe orientation during measurement is also changing, so this may be the main cause of the differences in results. The first  
Figure 8: The average deviations for the measurements of the multi-feature check using the default and the best path control algorithms. Figure 9: The standard deviations for the measurements of the multi-feature check using the default and the best path control algorithms. analysis confirmed this assumption; however, more detailed studies are now underway in order to unequivocally prove it. What is most important is that, as was mentioned above, it is possible to choose the best path control algorithm for each measuring task and thus reduce the measurement error. The next observation that can be made is that it is not as important to select the relevant path control algorithm for the type of measuring feature, but rather for the type of measuring task. Therefore, for some measuring tasks, which consist of measurements of the same features (e.g., distance between two planes and parallelism deviation between them--both of these tasks consist of measurement of the same planes) but also aim to determine the different relations between them, it may occur that the measurement errors for each task are smaller if both features are measured using different path control algorithms. The considerations presented in this paper provides guidance on the selection of the best possible path control algorithm for chosen measuring tasks (Table 2). Use of them may contribute to the general reduction of measurement error for measurements performed on five-axis systems, and the improvement of awareness of its users regarding how to run the measurements on them. This, in turn, could cause a decrease in the number of faulty classified parts during the assessment of the conformity with their geometrical specifications. The future works on this subject will involve the preparation of complete guidelines on the selection of the best path control algorithm for chosen metrological software (preferably Modus software, which is dedicated to be used on five-axis coordinate measuring systems). It will give guidance on the selection of proper algorithms during the measurement of all measuring tasks that are able to be evaluated using this software, including all possible combinations used for solving considered tasks.