# A Review on the Prospects of Mobile Manipulators for Smart Maintenance of Railway Track
## 7 Challenges and Requirements
### Requirements of a Mobile Manipulator for Track Maintenance  
As railway infrastructure is becoming smarter, robotic technologies are being gradually deployed. Mobile manipulators are particularly advantageous for use in inspection and repair. Based on the use case mentioned in Section 5 and the benefits mentioned in this section, mobile manipulators specifications for railway track maintenance include:  
1. Reduced track possession--Track possession is important to maintain the safety of the maintenance people. Usually, total possession time is the sum of 3 times: time from last train to start of work, work in progress time, and time from end of work to the first train. In the UK, the average time for the last train to start work was around 50 min and 20 min for AC-electrified and non-electrified routes, respectively [162]. Moreover, the end of work to the first train passing time was calculated as 25 min for AC-electrified routes and 100 min for non-electrified routes. Additionally, a minimum safety distance of 2 m is maintained between the staff and train in case of parallel tracks [162]. To ensure financial benefits and maximize asset utilization, mobile manipulators should have reduced track possession. 2. Safety and security--With the advancement of Industry 5.0, the collaboration between robots and humans is increasing gradually. Safety aspects of a robotic system should integrate both the autonomous and collaboration modes. Robotic systems should be capable of identifying static objects, dynamic objects, humans, or animals visible inside the workspace. Robotic systems should avoid any collision with objects. Lack of safety measures in robotic systems can cause fatalities in the workplace [163]. Security in a robotic system ensures that the environment does not create any harm to the robot or robot operation. Cybersecurity measures such as the security layer and authenticity of data communication are required to minimize the risk of hijacking or cyberattacks. Identifying the hazard; assuring safe design, safe operation, hazardous failure management; and verifying action are important tasks for any autonomous system working in complex environments [164]. 3. Design for maintenance--Design for maintenance is a guideline to enhance the maintainability, reliability, and supportability of a product to ensure maintenance of the product at less expense, less time, and less effort [165]. The mobile manipulator used for track maintenance will require regular maintenance such as sensor calibration, battery condition monitoring, links, and joint integrity. Easy maintainability will keep the robot ready for the next repair job and extend the life of the robot. Design for maintenance is also important to achieve overall cost-effectiveness [165]. * Task verification capability--finally, the mobile manipulator should be equipped with a task verification system. This will certify that the successful task completion is compliant with the railway's standards. This verification system will also capture any repair faults and save trains from any catastrophic accidents. * Using intelligence: Robots are becoming smarter gradually in terms of perception, object detection and control system with the usage of machine learning (ML), deep learning (DL) and artificial intelligence (AI). Although ML is used in many inspection tasks [46; 51; 52; 53; 54; 55; 56], more research is needed to ensure smart and intelligent robotic maintenance. Usage of ML, DL, AI can improve the efficiency of perception to differentiate between railway and foreign objects, detect humans, and identify faults. Moreover, robotic intelligence can improve the decision-making ability of control systems. Hence, the usage of robotic or machine intelligence is required in the future robots. * Legal and regulatory requirements: Railway is a highly regulated industry. As railway carries more people and freight than other mass transportation systems, policy makers give maximum priority to safety.