# High-Precision Roller Supported by Active Magnetic Bearings
## 5 Automatic Alignment Function Test of Precision Roller with Magnetic Bearings
### Automatic Alignment Test of Roller  
The basic automatic alignment method of the roller is shown in Table 2 and Figure 10. Figure 11 shows the simple schematic of the automatic alignment function test device using load cells. When the roller contacts the alignment reference surface, the contact forces at both ends of the roller are measured and these contact forces are compared to align the roller. Load cells, which can simultaneously measure the force applied at each end and play the role of the alignment reference, were installed at the left and right ends of the roller. Although both load cells have different distances from the origin of the roller, they are located within closer distances than the magnetic bearing air gap (0.2 mm), in which the roller can move. Figure 12 shows the experimental setup for the automatic alignment test. After levitating the roller to the origin with magnetic bearings, misalignment is forcibly formed by placing both load cells at different distances from the roller surface within the range of the air gap (\(\pm\)0.2 mm) of the radial magnetic bearings. The reference force used to determine whether the roller contacted the load cells (alignment reference surface) was set to 5 N, and the forces applied to the load cells were measured while the roller was moved toward the load cells with a constant fine displacement (here 5 \(\upmu\)m). The fine displacement movement of the magnetic bearings was stopped when contact forces exceeding 5 N were measured by both load cells. \begin{table}
\begin{tabular}{c c} \hline \hline  & **Step** \\ \hline
1 & A load cell for measuring the contact forces between the roller and counterpart surface is installed at each end of the roller. Here, each load cell is installed to create misalignment within the air gap (\(\pm\)0.2 mm) of the roller surface and radial magnetic bearings. \\ \hline
2 & The reference force used to determine whether the roller contacted the counterpart surface is set. \\ \hline
3 & The reference position of the roller shaft in the radial magnetic bearings is modified so that the roller can move toward the counterpart surface (load cell) at a constant displacement. Through this, the roller moves by a fine displacement. \\ \hline
4 & When the roller contacts a load cell, the load cell can measure the contact force. The fine displacement movement is repeated until the contact force is measured. \\ \hline
5 & The contact forces measured through the load cells at the magnetic bearings of both ends are compared with the reference force. If the contact forces are smaller than the reference force, the fine displacement movement is repeated. Otherwise, contact is determined and the movement is stopped. \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Sequence of steps for automatic alignment of roller. 120 \(\upmu\)m, completing automatic alignment. Through this, it could be predicted that the left-end and right-end misalignments of the roller for the load cells (counterpart surface) were approximately 60 \(\upmu\)m. The time spent for the automatic alignment was approximately 17 s. After alignment, the measured contact force was 7.4 N for the right end and 5.2 N for the left end. An approximate difference of 2.2 N was measured between both ends, which is 2.4 N over the reference value. Figure 14 shows the test results after setting the displacement at 10 \(\upmu\)m to reduce the time spent for alignment. Although the time spent for the automatic alignment decreased to 9 s, the measured contact force was 8.3 N for the right end and 6 N for the left end after the alignments. Under both conditions, a difference in the contact force between both ends occurred after the completion of the alignment, and the end that first reached the reference force showed a larger error than the other. This appears to be because a phenomenon similar to the principle of the lever occurring due to the force sensors being not located on the inside magnetic bearings.