# A Review on the Prospects of Mobile Manipulators for Smart Maintenance of Railway Track
## 4 Robotic Maintenance Technology in Other Industries
### Mobile Manipulators for Inspection and Repair Tasks  
#### 4.2.1 Maintenance in High-Voltage Transmission Line and Substation  
High-voltage power transmission lines can be hazardous and unergonomic workspaces for a human operator because of heights and live electricity risks. Mobile manipulators require unique moving mechanisms to navigate along power transmission lines. A semi-autonomous teleoperated mobile manipulator was designed to inspect the aircraft warning spheres of the overhead power transmission lines [79]. A sensor arm was designed to be  
Figure 11: Classification of the mobile manipulator: (**a**) based on mobility features; (**b**) based on the area of application.  
a mobile manipulator that can move along the transmission line via sliding mechanism and perform inspection using a high-quality camera [80]. A robotic system was designed to inspect and repair the switch in the underground power transmission line, as shown in Figure 12a. The designed models consisted of a vehicle with a five DoFs hydraulic arm holding a six DoFs manipulator, a tool rack and a pneumatic tool changer [81; 82].  
LineScout, a teleoperated robot with a programmable pan and tilt camera, was proposed for live transmission lines with a rolling wheel for obstacle avoidance [83]. Another live transmission line inspection robot was proposed in [84] with two locomotion strategies to provide obstacle-crossing capability. Obstacles in a power transmission line include compression slices, vibration dampers, spacers, suspension clamps, etc., and the capability of crossing these obstacles is a desirable feature [85]. Simulations of and experiments using a mobile manipulator to adjust the vibration damper in the transmission line were performed in [14]. This robot hung on the line with the arm and moved along the line with the rolling wheel, as shown in Figure 12b.  
Apart from inspecting the power transmission line, mobile manipulators can perform various actuation and repair tasks. For example, an autonomous live-line maintenance robot (ALMR), shown in Figure 12c, stripped and clipped wire clips on a 10 kV transmission line [86]. [PERSON] et al. proposed a mobile manipulator with a creeping mechanism that moved along horizontal and suspended insulator strings via extra-high-voltage (EHV) lines [87].  
Apart from the ground, creeping, or crawling, an aerial mobile manipulator can be a feasible option for overhead transmission line maintenance. Aerial robots could easily reach different heights and navigate in the air without a special kinetic or driving mechanism [88; 89]. POSITRON, shown in Figure 12d, was a conceptual design and simulation for controlling the aerial mobile manipulator in a GPS-denied environment.  
Figure 12: Mobile manipulator for maintenance of power transmission line: (**a**) specially designed mobile manipulator for underground transmission line [79; 80]; (**b**) for vibration damper maintenance [12]; (**c**) autonomous live-line maintenance robot (ALMR) [84], (**d**) POSITRON [86; 87].  
A substation is an important part of electricity transmission. However, most of the equipment in the substation is installed outdoors, which is heavily affected by the environment and weather conditions. Research was carried out by [PERSON] et al. to find a suitable robotic technology for performing maintenance both in the indoor and outdoor environment [90]. [PERSON] et al. designed, fabricated, and experimented with a mobile manipulator to clean and remove ice from the insulator and repair broken wires [91; 92].