# Development of Piezoelectric Inertial Rotary Motor for Free-Space Optical Communication Systems
## 4 Experimental Investigation of Motor  
Experimental investigations were conducted to verify the operation principle as the well as mechanical, electromechanical, and thermal characteristics of the motor. A motor prototype was made with strict respect to the specified geometric parameters and material properties outlined in Figures 2 and 3 as well as Tables 1 and 2. The view of the prototype is shown in Figure 14.  
First, the impedance and phase characteristics of the motor at room temperature were measured by a SinePhase 1677K impedance analyzer (SinePhase, M\(\ddot{\mathrm{o}}\)dling, Austria). The results of the measurements are given in Figure 15.  
As can be found in Figure 15, the resonance frequency of the motor is at 11.93 kHz while the calculated value, under the same conditions, is 12.66 kHz, which results in a difference of 6.12%, while measured and calculated impedance values are 2939 \(\Omega\) and 2954 \(\Omega\); the difference in the is 0.51%. Finally, the calculations of the effective coupling coefficient have shown that the prototype has a \(k_{\mathit{eff}}\) of 0.163. Therefore, the results of the experimental investigations show that the numerical model and prototype are in acceptable agreement and further investigations can be performed. Figure 14: Prototype of the actuator: (a) side view; (b) top view. Figure 15: Impedance– and phase–frequency characteristics of the motor at room temperature. In order to perform experimental investigations of the motor, an experimental setup was assembled. The experimental setup is shown in Figure 16.  
Therefore, the experimental setup was based on a computer with data acquisition software, a function generator WW5064 (Tabor Electronics, Nesher, Israel), a power amplifier PX-200 (Piezo Drive, Shortland, Australia), an oscilloscope DL2000 (Yokogawa, Tokyo, Japan), a non-contact tachometer CA 1727 (Chauvin Arnoux, Paris, France), and a non-contact displacement sensor optoNCDT 1420 (Micro-Epsilon, Ortenburg, Germany). Therefore, on the basis of the experimental setup, the first experimental investigation was dedicated to measurements of angular motion speed characteristics, while different excitation signal amplitudes were used to drive the motor at its resonance frequency. The results of the measurements are given in Figure 17.  
As shown in Figure 17, the highest angular speed of 1178 RPM was achieved at a voltage of 180 V\({}_{\text{P-P}}\). This corresponds to an angular-speed-per-voltage ratio of 6.54 RPM/V\({}_{\text{P-P}}\). Figure 16: Schematic of experimental setup: (1)—a computer with data acquisition and switch control software; (2)—signal generator; (3)—power amplifier; (4)—oscilloscope; (5)—non-contact displacement sensor; (6)—non-contact tachometer; (7)—a prototype of the motor. Figure 17: Angular motion characteristics of motor under different excitation signal amplitudes at room temperature. Conversely, under the same conditions, but at an excitation voltage of 40 V\({}_{\text{p-p}}\), the angular speed reached 158 RPM, or 3.95 RPM/ V\({}_{\text{p-p}}\). When analyzing the deviations, it can be observed that at low voltage levels (e.g., 40 V\({}_{\text{p-p}}\)), the deviations are smaller due to lower thermal effects, which results in more-stable motor performance. As the voltage increases (e.g., 180 V\({}_{\text{p-p}}\)), the heat generated in the motor increases significantly, causing larger deviations. This increase in thermal load can affect the consistency of the motor's operation, leading to fluctuations in angular speed and greater measurement variability at higher voltage levels. Thus, these results indicate that the motor exhibits a stable and predictable angular speed across a wide range of voltage values, demonstrating its ability to maintain consistent performance under varying excitation conditions. The subsequent investigation focused on evaluating the resolution of the angular displacement of the motor under different excitation voltages.