## 4 Implementation
### Device Performance Optimization  
We measured the rotation angle interval, the movement direction, and the degree of force concentration of the proposed system using the DFF device. Overall, the motor's drive speed was shown to be slower than the programmed speed, and the real model was slower in reaching the maximum speed past the target point. A total of 36 datasets were created and analyzed (3 rotation angles \(\times\) 4 directions \(\times\) 3 levels of force concentration). Regarding the effect of adjusting the rotation angle interval, the maximum velocity occurs closer to the original target when a wide rotation angle interval is employed. When the rotation angle interval was set to \(\pm\)90 degrees, it was observed that the point at which the highest velocity occurred was pushed back by approximately 500 steps, which corresponds to a 45-degree angle difference (4096 steps \begin{table}
\begin{tabular}{c c c c} \hline \hline  & **AX-18A** & **MX-64R** & **MX-106R** \\ \hline Resolution (deg/step) & 0.2930 & 0.0879 & 0.0879 \\ Stall Torque (Nm) & 1.8 & 6.0 & 8.4 \\ Max Baud Rate (Mbps) & 1 & 4.5 & 4.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The comparisons on motor performance. Figure 6: DFF Device Design. of the 12-bit encoder; Figure 7). When the interval was \(\pm\)30 degrees, the difference was approximately 250 steps (22.5 degrees). In considering the directional force concentration, operation within a narrow rotation interval has advantages. As for the direction of rotation, by design, the acceleration direction is from downward to upward along the axis of rotation. To rotate in all four directions (forward, backward, up, down), additional force is required to compensate for the natural tendency and the weight attached to the device. On the other hand, acceleration is easily achieved in the upward and downward directions. As seen in Figure 8, the forward (Figure 8a) and backward (Figure 8c) directions show similar motor rotation behaviors, as do the upward (Figure 8b) and downward (Figure 8d) directions. Considering this, it is necessary to apply additional force when accelerating in the all four directions. Figure 8: Graph of programmed motor velocity and actual motor velocity of four directions (\(\pm\)60\({}^{\circ}\), 200 rpm): (**a**) forward; (**b**) upward; (**c**) backward; (**d**) downward. Figure 7: Graph of programmed motor velocity and actual motor velocity of rotation angle interval variation (300 rpm, front direction). Finally, in controlling the maximum speed of the rotation, we observed that it was more difficult to maintain higher target speeds of motor rotation (Figure 9). When the target speed was high, the motor acceleration was maximized but the motor deceleration was delayed longer. During the experiments with the actual DFF device, we identified a delay of 20 to 500 degrees in reaching the maximum velocity. Therefore, the directional sensation from the concentrated force did not correspond to the target direction. An actuator control equation was created to minimize this problem. The required target speed according to the rotation angle was derived as Equation (1). Where \(f_{v}(\theta)\) is function of target velocity of rotation angle. Theta is a relative rotation angle value set based on \(\overline{P_{target}}\). An additional weighting constant, \(R\), was added to \(Vmax\) (the maximum velocity) in Equation (2) to increase the initial acceleration. To solve the motor delay, it is necessary to set the inflection point of the motor's acceleration/deceleration function slightly ahead of \(\overline{P_{target}}\). At this time, the changed \(P\) correction value was defined as \(\overline{P_{offset}}\). Equation (2) thus reduces the overall values of rotation angle to solve the observed delay.