# A Review on the Prospects of Mobile Manipulators for Smart Maintenance of Railway Track
## 1 Introduction  
Railway infrastructure networks are among the most important transportation assets and have served the worldwide growth of industry and civilization for hundreds of years. The notion of asset management within a railway infrastructure context is developing to fulfill the needs of both users and owners for sustainable railway management. The railway infrastructure network can include vast numbers of tracks, bridges, tunnels, stations, track-side markers, overhead electric lines, etc. For example, the British railway network has approximately 20,000 miles of track, 30,000 bridges, and 2500 stations, some of which are almost 200 years old, as well as a plethora of signaling, electrification, and crossing systems that are geographically spread out [1]. Railway infrastructure operators are responsible for planning, controlling, and maintaining all asset-related hardware operations and maintenance. Railway track inspection and repair are fundamental requirements for ensuring safe transit and long-term growth [2]. The quality of the railway track also impacts both the reliability of pantograph-catenary interactions [3] and ride comforts [4]. Railways maintenance or repair tasks have primarily relied on human interventions for decades. Although many modern tools and machines have been introduced recently, human involvement is still essential. Currently, over 40,000 people are working in Britain to maintain theappropriate operation of infrastructures (e.g., signals and power supplies) and assets (e.g., tracks and bridges) [5]. Train services are considered among the safer, greener, and most reliable public transport systems. Construction of new railway infrastructure is time-consuming and costly. For example, the construction cost of the High Speed 2 (HS2) railway line of 330 miles may rise to more than GBP 100 billion [6]. Moreover, the construction cost per km of railway track is 12.5 to 30 times higher than per km per lane road [7]. Modern asset management systems ensure the life cycle of well-maintained railway assets, producing environmental and financial benefits by balancing maintenance, renewal, and enhancement activities [8]. Thus, governments and stakeholders strive to maximize the availability of railway networks by introducing enhanced asset management systems, including AI-based robotics [2]. As a result, there is avid demand for flexible and autonomous robots that can perform maintenance tasks effectively and which possess remote, reliable communication and sensing technology. Maintaining adequate track quality ensures a safe and comfortable journey for passengers and timely freight delivery. Railway maintenance tasks demand dexterity, quality, versatility, and speed. Some tasks can be repetitive and need to be performed out of hours or in adverse weather conditions. Smart maintenance is a concept which could revolutionize the available maintenance systems across different industries. It uses IoT, faster computing, sensor technologies, etc., to digitalize the maintenance process. Moreover, with the advancement of robotic technologies, it will include different solutions with which to optimize the existing maintenance tasks in order to minimize the whole life cycle cost and ensure the optimum usage of the assets. When used in railway inspection and maintenance tasks, robotics technologies will enable smart maintenance. During the inspection process, robotic technologies should detect any defects if provided with enough information, such as defect type, size and location, for the actuation tasks. In the maintenance tasks, robots should perform the repair tasks with or without human involvement based on the information from the inspection. A manipulator or robotic arm is a multipurpose mechanical device which is programmable for various tasks. Manipulators are articulated kinematic chains, linked with one another with flexible joints [9] and programmed to perform some motions in a designated workspace.