## 5 Experiment  
### Experimental System Configuration  
The flying touch method cannot be applied to a general real hot rolling simulator because the vertical motion of the upper roller cannot be realized in a real system. Therefore, a downscaled simulator was designed for such an application. Different from the existing rolling system in which the upper roller is fixed, the upper roller of the designed simulator is capable of moving in the vertical direction. As shown in Figure 11, a single-axis actuator is designed to enable the upper roller to move vertically using a motor and a ball screw [22].  
The designed simulator, which uses an electric motor, is characterized by its inability to generate sufficient torque; consequently, rolling the actual steel plate is difficult. To mitigate this, the experiment was performed using a rubber belt instead of a metal slab. The overall structure of the 1/40 downscaled hot rolling simulator for implementing the scratch formation reduction algorithm is shown in Figure 12.  
A simulator with four motors was used for the rudimentary implementation of the rolling process. Motor M1, which allows the upper roller to move up and down in a vertical direction, is an actuator that implements the flying touch method. Motor M2 continuously rotates clockwise during rolling to transport the rubber belt, allowing it to pass between the upper and lower rollers. Motors M3 and M4 rotate the upper and lower rollers, respectively. These motors were used to implement the velocity synchronization algorithm. Each motor was appropriately selected by considering the expected load during rolling. In addition, all  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Properties**} & \multicolumn{3}{c}{**Constant Velocity of**} & \multicolumn{3}{c}{**Decelerating Velocity**} \\  & \multicolumn{3}{c}{**Descending Roller**} & \multicolumn{3}{c}{**of Descending Roller**} \\ \cline{2-5}  & **(MPa)** & **(MPa)** & **(MPa)** \\ \cline{2-5}  & **40 mm/s** & **20 mm/s** & **40 mm/s** & **20 mm/s** \\ \hline Total average stress on the steel plate & 290.24 & 289.47 & 284.80 & 284.29 \\ Maximum stress on the steel plate & 322.53 & 322.53 & 308.13 & 308.13 \\ Standard deviation stress after impact point & 23.29 & 24.40 & 12.46 & 13.54 \\ Stress on the steel plate at the moment & 269.49 & 163.53 & 181.68 & 181.16 \\ of impact & & & & \\ \hline \hline \end{tabular}
\end{table}
Table 2: Stress simulation results.  
Figure 11: Mechanism for vertical movement of upper roller.  
motors in this simulator were controlled by the robust control algorithm of the SMCSPO to overcome the disturbances and nonlinearities in the rolling process. The continuous torque and rated power of the motors, the size of the simulator, and the materials are listed in Table 3. Although the simulator shape reflects that of the POSCO hot rolling system, its size is 1/40 times that of the real system.  
The detailed control system configuration for the downscaled hot rolling simulator is shown in Figure 13. Each motor is connected to an alternating current (AC) servo driver that provides encoder data and control input to the motor. The personal computer affords control commands to the servo driver using an multi motion controller (MMC) board, which converts digital signals to analog signals.