# A Review on the Prospects of Mobile Manipulators for Smart Maintenance of Railway Track
## 7 Challenges and Requirements  
### Challenges for a Mobile Manipulator for Track Maintenance  
The mobile manipulator has a lot of potential uses in railway track maintenance. However, it has to overcome some challenges before successful deployment. These challenges arise from the railway track structure and maintenance systems, communication and localization methods, power, and weather conditions.  
1. Track structure and access points--Railway track surface condition is different than road or industrial setup. The railway track is an uneven terrain. Moreover, the workspace for the robot is limited inside the tunnel or bridge. Additionally, as the mobile manipulator cannot stay on track after finishing the tasks, it will need access points to use the track. Railway infrastructure such as platform, trackside furniture, overhead line equipment (OLE), and leftover material may cause navigational problems for autonomous robots [161].
2. Communication--Other challenges come from the communication perspective. Communication between the control or operation center and the mobile manipulator is required. With the advancement of teleoperation, human skills can be transferred to robots. However, stable communication between the human operator and the robot is a must in this scenario. Moreover, in the case of a fleet of robots, communication among mobile manipulators is required for safety and task collaboration. As railway track passes through mountains, forests, or remote locations, there is a lack of signal or weak signal along the track.
3. Location awareness--Localization of the robot is essential for defect location referencing and for re-locating the defect for repair tasks. Due to the remoteness of the track, overhead line equipment (OLE), nearby buildings, or dense forest interfere with the GPS signals. Additionally, tunnels are GPS-denied areas. Hence, in many places, the GPS positioning accuracy will be very low, or there will be no GPS signal. 4. Power--Most of the mobile manipulators are battery-powered, which is convenient. The mobile manipulator will need powerful batteries to perform many repair tasks, such as welding, grinding, drilling, and lifting heavy payloads. However, powerful batteries will increase the weight of the mobile robot and reduce the usable space on the robot. Although internal combustion (IC) engines can provide power instead of batteries, this is not feasible from an environmental perspective. Thus, power capacity and management are still challenging for mobile manipulators. 5. Data budget and management--The mobile manipulator will record sensor output for inspection. Depending on the control architecture, the mobile manipulator will analyze those data in real-time or save those for future usage. The data budget analyzes and estimates the requirements of data storage capacity and computational cost based on the sensor output. On the other hand, data management determines which data to store for future usage, the computation requirement for onboard data processing, and the data transfer process between the robot and the primary control system. As a portable machine, the mobile manipulator has limitations in processing large quantities of data, while the lack of internet connectivity in many places along the railway track will hinder the data transfer process.