## 4 Experimental Results  
To compare the analysis and experimental results with actual displacement measurements, a prototype PMSM model, including a rotor and a stator, is proposed. The displacement measurement concept is shown in Figure 9. The concept employs a gap sensor that measures shaft displacement. Figure 10 shows a system to measure vibration using two gap sensors. The displacements along the \(x\)- and \(y\)-axes were measured. The experimental results were validated by comparing them with the measurement results. The gap, torque, and speed sensors were connected to mechanically measure the displacement between the designed model and the sensor, torque, and speed of the continuous rotation of the designed model, namely, the PU-06A model of AEC, the CSA-1k model of CAS, and the MP-981 model of \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Parameter** & **9 Slot** & **12 Slot** & **Harmonics Order** \\ \hline Back-EMF THD & 20.10\% & 16.77\% & 1,3,5 \\ Cogging torque & 1.53 mNm & 311.53 mNm & 6 \\ Torque ripple & 2.53\% & 34.80\% & 6 \\ No-load UMF & 8.85 N & 0.01 N & 8 \\ On-load UMF & 72.42 N & 0.08 N & 8 \\ Deformations & 2.5 um & 0.04 um & 1,3,4,6,7,8 \\ Main harmonics & 1,3,4,6,7,8 & 1,3,4,6,7 & - \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The comparison of results of PMSMs according to slot. Figure 8: NVH characteristic analysis results of permanent magnet machines with two different pole/slot combinations: (**a**) 8-pole 12-slot and (**b**) 8-pole 9-slot. Figure 9: Schematic diagram of the displacement measurement concept. ONOSOKKI. An eddy-current-type gap sensor was used so that it can measure a maximum length of 1 mm. A magneto-type speed sensor was used so that it can be inserted into the desired position. The adopted indicator is the SS-130 model of CAS, which can work with both models. The servomotor and invertor, namely, the L7 SA model and the APM-FCL06A model of LS-mecapion, were connected to electrically operate at command rotational speed. The servomotor controller controls the motor with analog signals using a controller box configured using the supplied manual. It can be operated at maximum load conditions of 5000 rpm and 2 Nm. The servomotor was operated using a pulse-width modulation inverter with an analog signal control box, which can be operated based on user inputs. The designed model is operated by using an SPWM inverter that comprises an internal feedback loop. The rotational encoder is employed for position control. The experiment results are shown in Figure 11. It is observed that the displacement of the 9-slot model is 23% greater than that of the 12-slot model. In addition, comparing the harmonics of the displacement, the 9 th-order machine produces an 8 th-order harmonic caused by MPF and UMF, which affect the machines. This shows that MPF and UMF significantly influence the vibration of the motor. Table 2 lists the comparative results of the PM machines with two different pole/slot combinations. Compared with the electromechanical analysis, the results of the analysis model are derived by applying the motor unit. Therefore, it derives vibrations from the motor unit, resulting in an error when compared with the vibration test results of the entire system. For accurate analysis, it is necessary to assess the material characteristics and shapes of parts applied to the system, such as servomotors and housings, and the characteristics of the electromagnetic excitation source generated by the servomotor; however, the purchased parts are difficult to apply. Moreover, as the tendency of vibration harmonics that occur frequently is constant, the proposed method is considered to be effective in analyzing the tendency of vibration generated by the motor.