This paper presents model-based hysteresis and cross-coupling compensators designed for precise control of a piezoelectric fast steering mirror (FSM). The hysteresis compensators are developed by inversely modeling the variation in the force constant relative to various excitation voltages, enabling the system to maintain linear response characteristics across a broad range of input amplitudes. The cross-coupling compensator is formulated by creating a decoupling matrix that cancels out coupling effects, generating signals of equal magnitude and opposite phase for each axis. The implementation of these compensators reduces the hysteresis band and magnitude uncertainty in the FSM dynamics by over 89.6% and 74.2%, respectively, while also significantly suppressing cross-coupling effects by more than 85.5%. Furthermore, the performance of the proposed compensators is validated in a closed-loop control system, demonstrating a notable reduction in cross-axis vibrations and improved tracking performance in response to step reference inputs and highfrequency sinusoidal trajectories.

Nonlinear hysteresis effects in piezoelectric fast steering mirrors (FSMs) are major culprits of deteriorating the servo performance and reducing the robustness of a control system. In order to compensate for such nonlinearities, this paper presents an identification and compensation method of piezoelectric hysteresis using frequency response measurements. The relationship between hysteresis curves and frequency response was analyzed using various amplitudes of input voltage and measured output displacements. Results proved that hysteresis curves could be reconstructed based on frequency response measurements. By utilizing an inverse function from reconstructed hysteresis curves, parameters for the compensation model were identified. Experimental results showed that the maximum range of output displacement at the nominal position due to hysteresis was significantly decreased by 76% when the hysteresis model identified by the proposed frequency-domain method was used. In addition, the compensated frequency response showed consistent results regardless of input amplitudes, implying that linear dynamics of the piezoelectric FSM could be separately measured.

Currently, the number of construction cases using large-diameter and high-strength steel and high-strength concrete is increasing due to the trend of large buildings. In the case of reinforcing bars that serve as the framework of a structure, the continuous state is the best in terms of structural stability. However, for convenience, it is transported and assembled to a predetermined standard. In this study, a coupler was developed applying SCM440 material with excellent mechanical properties, not S35C and S45C materials, generally used as coupler materials. To this end, high-frequency carburizing and heat treatment was applied to the element parts taking into account the taper angle and stress results, reflecting the results of low- and high-cycle fatigue tests and structural analysis for the applied material. Finally, in the case of a reinforced coupler fastened with hydraulic SD500 reinforcement bars with diameter D25, a reliability test was carried out using the mechanical joint inspection method of reinforced concrete reinforcement bars. Results were obtained that satisfied the characteristic performance values.

Superhydrophobicity and anisotropic wettability can be simultaneously achieved by simple groove pattern on a surface. To verify those characteristics experimentally, we fabricated the micro-grooved surfaces with four different groove widths. Static contact angles were measured with the sessile drop method to investigate the apparent wettability and wetting states. All four surfaces exhibited the static contact angles well fitted to those estimated on the Cassie-Baxter state in which favorable water-repellency was expected. The static contact angles measured perpendicular to grooves were higher than those measured parallel to grooves. This anisotropic wettability was also observed with the sliding angle at the onset of the droplet moving when the surfaces were tilted. The sliding angles measured perpendicular to grooves were much higher than those measured on the smooth surface without micro-grooves. Conversely, the sliding angles measured parallel to grooves were smaller than those measured on the smooth surface. Because the sliding angle as well as the contact angle hysteresis reflect the water-repellency, the micro-grooves clearly made the surfaces anisotropic water-repellent.

As per ISO376 : 2011, creep uncertainty can be measured directly or indirectly. In this regard, this paper seeks to provide a comparison between direct and indirect creeps computed from hysteresis. All computations for direct and indirect creeps were done using equations from ISO376 : 2011. Five force measuring devices were experimentally examined for this purpose. Results showed that the behaviors of direct and indirect creeps were quite different. The relative creep that was directly measured was constant. On the other hand, the relative creep that was indirectly estimated varied with the applying force. Therefore, the directly measured creep cannot be replaced by the indirect one. This paper proposes a method to use a representative value for indirect creep, as the maximum of the creep. For the force measuring devices that had good hysteresis characteristics, the directly and indirectly measured creeps were comparable. However, for the force measuring devices with poor hysteresis characteristics, the indirectly estimated creep was much higher than the directly measured creep. Therefore, it is highly recommended to measure the creep directly for the force measuring devices characterized by poor hysteresis.