# Selection of Optimal Path Control Algorithms for Probe Heads Used on Five-Axis Measuring Systems
## 3 Experiment and Results  
All measurements described in this article were performed on a five-axis measuring system, which was part of the LCM's equipment. It consisted of a CMM with a moving bridge, Zeiss WMM 850S (ZEISS International, Oberkochen, Germany), and the articulating probing system, PH20 by Renishaw \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Feature** & **Guide Point** & **Guide Rail** & **Guided Curve** & **Fixed Tilt and** \\  & **(GP)** & **(GR)** & **(GC)** & **Advance (FTAA)** & **Comments** \\ \hline Point & & & & \\ Line & & & & \\ Plane & & & & \\ Circle & & & & \\ Cylinder & & & & \\ Cone & & & & \\ Sphere & & & & \\ Surface & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Path control algorithms that can be applied for measurement of specified features. Figure 2: Path control algorithms used during five-axis measurements: (**a**) Guide point (GP); (**b**) guide rail (GR); (**c**) guided curve (GC); and (**d**) fixed tilt and advance (FTAA). (Wotton-under-Edge, UK), working with the TP20 STD probe. The whole system was located in an air-conditioned room, with constant ambient conditions that were monitored. The temperature during experiments varied between 19.8 to 20.4 \({}^{\circ}\)C. The experiments undertaken at the LCM consisted of two parts: The first part was conducted to assess the influence of the different methods used for path control on the measurement accuracy. It involved multiple measurements of standard objects; gauge block of 200 mm length and gauge ring of 28 mm diameter (Figure 3). The first step of the gauge block measurements was the determination of the local coordinate system, which was defined using three mutually perpendicular planes of gauge (the measurement of the planes that define the part coordinate system were performed using the standard three-axis mode, so only transitional movements of the machine were used during probing). After this step, the distance, angle between planes, parallelism, and flatness deviations were measured using different methods for inspection planning. Two methods were included in this part of the experiment, guide point and guide rail, as only these two were available for measurement of planes. Additionally, three different orientations of the guide point were utilized, marked as 0\({}^{\circ}\), 45\({}^{\circ}\), and 90\({}^{\circ}\) (denoted respectively as GP 0\({}^{\circ}\), GP 45\({}^{\circ}\), and GP 90\({}^{\circ}\) on Figures 4 and 5) with names corresponding to values around which A angle used during probing oscillated. Measurements performed with all mentioned methods were repeated 10 times and if it was possible in all cases the measurements were done with the same distribution of measured points. The results of measurements are presented in Figure 4 which shows average deviations from nominal values (taken from calibration certificate of gauge block) and in Figure 5 which gives information about standard deviation for each measurement task. The most noticeable differences between the results obtained for the different path planning methods during gauge block measurements can be seen for the measurements of the angle and parallelism deviation. The smallest difference was obtained for measurements of flatness. In most cases the lowest values of standard deviation can be observed for the path control algorithms that also gave the lowest values of deviations. Figure 3: Photographs of the Zeiss WMM 850S (right side), the Renishaw PH20 measuring head (upper left), and the mounting of gauges during measurements (lower left). The next part of the experiment involved measurements of the ring gauge using all possible methods of inspection path planning. The local coordinate system was created in the center of the ring, with the ring's axis determining the spatial alignment of the coordinate system. Again, the measurement needed for the coordinate system definition was performed in the three-axis mode of the measuring system. The ring was measured across half of its height, in 16 evenly-distributed points.