# A Review on the Prospects of Mobile Manipulators for Smart Maintenance of Railway Track
## 5 Case Study  
To examine the feasibility of mobile manipulators for railway track maintenance tasks, a robotic inspection and repair system (RIRS) has been developed by Cranfield University in conjunction with Network Rail Limited, UK. RIRS combines rail trolley, warthog UGV, and UR10e. These can navigate both off-track and on-track, as shown in Figure 17. Although the conversion between off-track and on-track navigation is performed manually, this is a unique capability of RIRS, which changes the kinematics of the whole system [145]. Moreover, different navigation strategies are required for off-track and on-track navigation [146]. RIRS has multiple sensors such as IMU, wheel encoder, PTZ environment camera, monocular wrist camera, RGB-D camera, LiDAR, and RTK-GPS. Table 4 lists the sensors and functions of RIRS. The monocular camera, attached to the manipulator end, can detect a range of defects. The manipulator enables it to inspect from different perspectives, providing comprehensive defect information. Combining the features from ROS, a UR10e industrial manipulator, and a monocular camera, RIRS can repeatedly and precisely inspect for defects [147]. The manipulator has a payload capacity of up to 10 kg, but the Warthog UGV has a higher capacity of 250 kg. Because of this, a RIRS can be equipped with additional auxiliary devices, such as ultrasonic track inspection instruments [148] or repair tools. Figure 17: Railway inspection and repair system (RIRS) in two different operational modes; (**a**) off-track navigation mode and (**b**) on-track navigation mode. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Application** & **Base Robot** & **Sensing Method** & **Key Technology and Contribution** \\ \hline \multirow{2}{*}{Garbage collection and sorting [140]} & Ground & RGB-D camera & Deep learning for garbage type identification \\ \hline \multirow{2}{*}{Bomb disposal [141]} & Ground & Two cameras & Teleoperation \\ \hline \multirow{2}{*}{Hydraulic manipulator for undersea environments [142]} & Underwater & Multiple cameras & Deep underwater operation \\ \hline \multirow{2}{*}{Transformable autonomous underwater vehicle [143]} & \multirow{2}{*}{Underwater} & \multirow{2}{*}{Camera} & Control system similar to \\  & & & spaceflight, user in the loop over \\ \cline{1-1}  & & & low-data transmission \\ \hline \multirow{2}{*}{Seabed inspection, repair [144]} & \multirow{2}{*}{Underwater} & \multirow{2}{*}{Camera} & Free-floating actuation, a \\ \cline{1-1}  & & & convolutional neural network for \\ \cline{1-1}  & & & object recognition \\ \hline \hline \end{tabular}
\end{table} 
Table 3: _Cont._Multiple experiments were conducted in the Northampton and Lamport Heritage Railway facilities to demonstrate the command-and-control system of RIRS and find the operational challenges for autonomous systems in the railway environment. Successful results showed the capability of RIRS in static and dynamic obstacle avoidance, short-range and long-range navigation, defect detection, and repair actuation. Furthermore, the testing facility provided standard gauge operational railway environments. Hence, a technology readiness level (TRL) of \(-7\)[149] was achieved after successful experiments. Moreover, as a mobile manipulator, RIRS can provide many flexibilities and cost-benefits in railway track maintenance. The attached RGB-D camera can provide 3D image of the target object, but it fails to capture information from the side and back of the object (Figure 18a). A 3D reconstruction method has been proposed and demonstrated with RIRS and sensor fusion technology to improve the track inspection technique as the reconstructed 3D model (Figure 18b) provides more dimensional and textural information than RGB-D camera output (Figure 18a) [150]. Additionally, the 3D reconstructed model can be fused with depth camera to provide better robot perception, with the LiDAR point cloud for environmental sensing and GPS data for geo-location.