# Remote-Controlled Method with Force and Visual Assists Based on Time to Collision for Mobile Robot
## 4 Experiment
### Experimental Setup  
The specifications in this study that were decided based on the specifications of the mobile robot are shown in Table 1. The control parameters chosen by trial and error are listed in Table 2. In this experiment, 10 subjects who were not well acquainted with the operation of the mobile robot were dealt with.  
For exhibiting operability improvement, 10 subjects (A-J) with an average age of 22.5 years and a 0.81 year standard deviation took part in the experiments. The presence of the force assist depends on \(T_{th}\). There were four different types of remote-controlled experiments:  
* Case 1: Without force and visual assists;
* Case 2: With visual assist;
* Case 3: With force and visual assists with high presence of force assist (\(T_{th}=10\) s);
* Case 4: With force and visual assists with low presence of force assist (\(T_{th}=2\) s).  
The mobile robot was manipulated by the subjects who were notified as to which methods were applied before the operation. However, the order of the experiments was randomly selected to avoid experience of the operation. Before starting the experiments, the subjects were permitted to practice the operation of the mobile robot.  
To evaluate operability, the subjects needed to achieve straight and curved operations. Therefore, as shown in Figure 11, the mobile robot moved in the clockwise direction with some obstacles. Furthermore, the experimental environment was set with at least three obstacles and five turns as an initial setting. From start to finish, the subjects were required  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameters** & **Descriptions** & **Values** \\ \hline \(V^{max}\) & Maximum translational velocity & 0.45 (m/s) \\ \(V^{min}\) & Minimum translational velocity & 0.0 (m/s) \\ \(\Omega^{max}\) & Maximum angular velocity & 1.5 (rad/s) \\ \(\Omega^{min}\) & Minimum angular velocity & \(-1.5\) (rad/s) \\ \(\dot{V}^{max}\) & Maximum translational acceleration & 1.0 (m/s\({}^{2}\)) \\ \(\dot{\Omega}^{max}\) & Maximum angular acceleration & 2.0 (rad/s\({}^{2}\)) \\ \(D_{r}\) & Half width of mobile robot & 0.19 (m) \\ \(D_{w}\) & Diameter of wheel & 0.157 (m) \\ \(H\) & Height of mobile robot & 0.407 (m) \\ \hline \hline \end{tabular}
\end{table}
Table 1: Specifications of mobile robot.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameters** & **Descriptions** & **Values** \\ \hline \(K_{v}\) & Translational force feedback gain & \(3.0\times 10^{6}\) \\ \(K_{\omega}\) & Angular force feedback gain & 1.7 \\ \(R_{th}\) & Collision-free operating range & 0.7 (m) \\ \(P\) & Number of trajectories for searching & 21 \\ \(T_{th}\) & Time threshold for safe operation & 10.0 (s) (Case 3) \\  & & 2.0 (s) (Case 4) \\ \(G_{LPF}\) & Cut-off frequency of force command & 1.0 (rad/s) \\ \(T_{max}\) & Maximum time to collision & 5.0 (s) \\ \(N_{max}\) & Maximum number of dots & 50 \\ \(k_{x}\) & Lens distortion for \(x\)-axis & 1.0 \\ \(k_{y}\) & Lens distortion for \(y\)-axis & 1.0 \\ \(l_{f}\) & Focal length of camera & 200.0 (mm) \\ \(M_{L}^{\prime}L_{c}\) & Center point of monitor for \(U\)-axis & 320.0 (px) \\ \(MV_{c}\) & Center point of monitor for \(V\)-axis & 240.0 (px) \\ \(C_{r}\) & Color gain of gradation to increase intensity & 1.5 \\ \(C_{rs}\) & Color gain of gradation to decrease intensity & 0.9 \\ \(K_{res}\) & Resolution gain of gradation & 12.0 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Control parameters.  
to operate the mobile robot by achieving collision avoidance. Visual information on the monitor was used by each subject to manipulate the mobile robot.  
The experimental results were evaluated with three comparisons:  
* Comparison between Case 1 and Case 2 for evaluating the visual assist;
* Comparison between Case 3 and Case 4 for evaluating the presence of force assist;
* Comparison between Case 2 and Case 4 for evaluating the force and visual assists.