Abstract
This paper presents the current state of the art in mobile robots used on power transmission lines. Many theoretical and experimental studies have been conducted in order to develop autonomous machines to travel along transmission lines to perform inspection and/or repair work. These machines can improve efficiency, reduce labour costs and are expected to reduce the risk of injury to maintenance personnel. Despite there already being a number of pieces of theoretical research and technological developments in this area, problems related to stability, ability and autonomy still exist. As such, first this paper presents the main studies already carried out and the devices generally used on power transmission lines. After the latest trends have been presented, a new idea for module robots carrying out inspections/maintenance of power transmission lines is presented. Finally, the future of mobile robots applied to power transmission lines is discussed.
1. Introduction
Many theoretical and experimental studies have been carried out in order to develop autonomous machines which can travel along transmission lines to perform inspections and/or repair work. These machines can improve efficiency, reduce labour costs and are expected to reduce the risk of injury to maintenance personnel. Locomotion is essential for these machines and this can be achieved using several methods. Despite there already being a number of pieces of theoretical research and technological developments in this area, problems related to stability, ability and autonomy still exist.
Economic expansion and the development of urban centres have led to an increase in demand for electricity and the consumption of electricity, requiring the transmission of energy through an important power grid. Many transmission lines are installed higher than 150 metres above ground and therefore must be signalized for aerial security, principally those close to highways, airports, rivers, valleys and urban centres; these are regulated by specific norms for each country. These signalling devices must be inspected and maintenance must be carried out on them periodically. Other tasks include replacing ceramic insulators that support the conductor wire, opening and reclosing the circuits between the poles, and installing specific devices.
The operation close to and/or in contact with a high-voltage line represents risk of accident. Obtaining skilled workers to perform these tasks is quite difficult due to the high training and labour requirements of the job. Performing the maintenance while the lines are de-energized would alleviate some of the risks, but would also create other problems with a society that demands interruption-free service from electric power companies [1]. Moreover, the costs involved are high.
These devices require maintenance, cleaning and new parts to be exchanged and installed, something that is generally carried out by an electrician suspended from a helicopter or who moves along the cable. These methods of working have many disadvantages, such as the long inspection cycle, the high working intensity, the huge expense and the high level of danger [2]. Another method uses unmanned aerial vehicles (UAVs) and airplanes and is highly efficient compared to manual operations but it is more expensive and climate dependant. Thus, since the early 1990s many researchers have proposed mobile robots [1, 3–7], to assist or replace the people working on power transmission lines. The development of these robots is still an open research field.
One of the biggest problems is the design of the robot itself due to the diversity and size of devices used on transmission lines. Furthermore, the robot must be able to cross towers and have the autonomy to travel distances of as much as 100 km between cities.
As such, this paper presents the latest trends in mobile robots used on power transmission lines.
At the beginning of this work the usual devices used on transmission lines are presented. Then, the main studies carried out on these robots are presented and finally the future of mobile robots used on power transmission lines is discussed.
2. Devices Used on Transmission Tines
Transmission lines are exposed to a variety of factors, such as corrosion and wind induced vibrations, which cause different problems and limit the life span of the lines [5]. For example, the Brazilian Electric Sector has a transmission grid of over 100,000 kilometres of transmission lines with voltages of above 230kV which needs continuous inspection and maintenance.
Power lines are a complex and dangerous environment, with intense electric and magnetic fields, making the movement of robots difficult.
In Figure 1 several devices used in transmission lines are shown. The simplest transmission lines have one conductor per phase hung on insulator strings (3), which can be either suspension (4) or strain insulators. There are also vibration dampers (5), aircraft warning lights (7), and clamps. In bundle power lines, which have more than one conductor per phase (1), there are even more obstacles such as spacers and spacer dampers (2) [8].
Typical architecture and line components of power transmission lines [8].
Figure 2 shows the most common devices used in transmission lines.
Devices used in transmission lines, (a) Insulators; (b) Clamp; (c) Chain Suspension; (d) Signalizing Sphere; (e) Vibration Damper; (f) Spiral Bird Diverters; (g) Repair Sleeves; (h) Amendment; (i) Spacers.
Three typical obstacles can be identified on power lines that a mobile robot will have to overcome when used for repairing and/or inspecting the lines. The first is the counterweight (or vibration damper) which is the most common of the obstacles. The second type of obstacle is the aircraft warning sphere (or signalling sphere) and the third one is the tower that supports the wire. Each obstacle has a different spatial structure [9].
These devices are inspected by workers using binoculars moving along the transmission lines. Generally, maintenance procedures are performed when the problem has already occurred (corrective maintenance).
In Figure 3 examples of towers are shown in order to exemplify their variety and to illustrate the difficulty in developing a mobile robot to cross them.
Example of towers. (a) suspension bundled conductor; (b) Tension tower; (c) Tension tower with a change of horizontal direction.
3. Robots Used on Power Transmission Lines
The inspection and maintenance of power transmission lines can be carried out by an electrician working by him or herself or by using any of the following: helicopters, unmanned aerial vehicles, airplanes, boom trucks, trolleys and mobile robots suspended on the cable.
Generally, this operation is carried out by an electrician suspended from a helicopter or who moves along the cable using a trolley [3].
Unmanned aerial vehicles (UAVs) and airplanes are generally used for visual inspections, Fig. 4, the principle of which is to fly close to the transmission line to perform the visual inspection [7, 10]. These systems can use infrared and corona cameras to detect physical damage as well as some internal deterioration of the cable and devices. The use of such equipment does not allow for maintenance operations, due to the difficulty of installing a robotic arm or a mechanism for repairing.
Hornet H2 [11].
However, aerial inspection is costly and there is always the risk of contact with live lines and loss of life. Moreover, there are some critical aspects of the line such as internal corrosion of the steel reinforced aluminium conductors that must be precisely inspected from distances very close to the line that are not accessible from a mobile platform, a helicopter or even a UAV [5]. Another problem when using UAVs is government regulations, since every country has different regulations. For example, in Brazil, commercial UAVs are currently allowed to be used for experimental tests but there is not yet any regulation.
Rangel et al. [11] developed a complete Unmanned Aerial Vehicle (UAV) composed of navigation software, a ground station and an aircraft using Commercial Off-the-Shelf (COST) equipment (e.g., handheld GPS, high definition cameras, video and telemetry links and R/C equipment). The UAV can be remotely piloted from a ground station using a computer, with real-time video, telemetry, interface devices, flight controls (joystick), virtual reality glasses (VRG) and a dedicated software. The aircraft used is the Hornet H2, a complete man-portable UAV, Fig. 4.
Another way of inspecting/maintaining power transmission lines is to use lift vehicles (boom trucks), at the extremity of which a manipulator is installed. One of the first such systems to be developed was the TOMCAT (Teleoperator for Operations, Maintenance, and Construction using Advanced Technology). The TOMCAT is composed of an insulated bucket truck, a Kraft seven-function manipulator that is attached to the end of the truck boom, a television viewing system for human supervisory control and power supplies. The control components are installed on the back of the bucket truck and include a manipulator master with no force feedback [1, 12]. These systems cannot be used in inaccessible places such as valleys, rivers and mountainous regions, and lines higher than the operation range of the crane arm. They present problems related to mobility, controllability and accessibility. They are applied mainly for repairing and/or replacing insulators, components of the structure line and spacers [7, 13–16], Fig. 5.
Scheme of boom trucks with manipulator [17].
Power transmission lines located in coastal regions experience a strong process of degradation due to the weather. The main problem is the loss of the dielectric strength of the insulators due to the accumulation of salt. As a result, electrical current leakage between the lines and the ground might occur, triggering failures in the lines of distribution. To minimize this problem, maintenance services must be performed regularly by washing the insulators with tap water. Thus, in [16] an electro-hydraulic robot was developed, which was designed to clean the insulators of 13.8kV distribution network poles, by washing them with a water jet, Fig. 6. In the work, the authors analyse the workspace of the robot arm (crane) in such a way that the water jet reaches the two sides of the insulators.
System proposed by [16].
The suspended mobile robot is different from the ground-moving robot because it has to move stably, suspended on wire and, if possible, to have a low complexity control for tower transposition. Wheels are the simplest method of locomotion but wheeled robots encounter problems crossing obstacles along the cable such as clamps, signalizing spheres and vibration dampers. Several works have been developed involving algorithms for robot control and mechanical configuration. The first works were proposed by [18–21].
The sustained system can be composed of linkage mechanisms and wheels such as those proposed by [25] and [20] or by linkage mechanisms and grippers such as those proposed by [26] and [27]. Another type of locomotion, presented by [23], involves the mobile robot being suspended on wire by a linkage mechanism that creates a two or three-dimensional trajectory. In this case the robot feet are posed over the wire to sustain it, Fig. 7.
Sketch of the Mobile Robot presented by [22].
In [19] a balancer type robot was proposed which has a unique locomotion mechanism for the robot, equipped with four crawlers, two arms with pulleys, and four actuators that can pass over the towers with a stable motion.
Tsujimura et al. proposed a “legged robot” that walks suspended on telecommunication aerial cables. In this case, its own weight assures its equilibrium. The proposed robot has two pairs of legs, of the same leg length, where each leg is made of a slider-crank mechanism whereby one motor is coupled to the front legs and another to the rear ones [18, 22–23]. From kinematical and dynamical robot models they obtained the relationships between the length links of the mechanism leg in such a way that the robot can move stably at a regular speed, Fig. 7. The experimental results confirmed that the robot operates well when obstacles are placed at equal intervals and the maximum dimensions of the surmounted object are the function of the foot trajectory above the cable. If the obstacles are irregularly spaced, an algorithm is needed to control the motor motion in order to change the gait to avoid a collision between the foot and the obstacle [18].
Another robot had been studied by Sawada, called the self-guided type, which uses wheels for its normal motion and, as they wrote in their work: “but when the robot encounters a tower, it unfolds an arc-shaped arm and attaches it to the ground cable on opposite sides of the tower. The robot then travels along the arm to pass around to the other side of the tower. Once it is firmly affixed to the cable on the other side of the tower it detaches the arm and folds it up until it is needed again” [21].
In [24] a locomotion system resembling the motion of a cabbage worm was presented, which moves by expanding and contracting its own body but has low stability, Fig. 8. In [43–44] a variation of this robot was presented.
Locomotion of Mobile Robot presented by [24].
In [28] a robot was presented to inspect 500KV power transmission lines. The robot has two arms and a set of wheel-claw mechanisms is mounted on the end of each arm. The robot can climb on the wires with its arms and claws with a maximum inclination angle of 45°. Each arm has three degrees of freedom. The robot is 2m long, 1m high and weighs 60kg.
In [2, 10] a robot based on a new approach was presented which considers the catenary curve. The robot uses a line-walking mechanism (a biped structure supported by two feet which can keep their grip on wires). The mechanism design enables the centroid of the robot to be concentrated on the hip joint to minimize the drive torque of the hip joint and keep the robot stable during the single-support phase. This robot has not yet been tested on high voltage lines.
Another robot has been studied, which, like those proposed by [29], resembles a caterpillar. It adheres to and moves in the cable using a system of ridges and grooves that allows the robot to follow the elevations and depressions in the cable without falling, Fig 9.
Prototype of the Mobile Robot presented by [29].
In Brazil the first works on suspended mobile robots used on transmission lines were developed by [30], [25] and [31, 3].
[30] developed a simple but operational cable-climbing mechanism for the installation and removal of aircraft warning spheres, Fig. 10. The robot cannot cross obstacles and navigates on the line between two towers. Although this robot is not able to pass obstacles, it is simple and operational [5].
Prototype of the Mobile Robot suspended by wire presented by [30]. (a) Robot; (b) Detail robot.
In [25] a robot was developed that uses three wheels as a drive system, which swivel when it starts the process of transposing the towers, and is executed by insulator support. In this system, there is a screw which is responsible for balancing the masses, as well as during the procedure of transposing the towers. The robot has two cameras and they are located, one above the first wheel and another in the control box, this allows for the pan, tilt and zoom movements, Fig. 11.
Prototype built by [25].
In [30, 3] a mobile robot was presented which can surmount spherical obstacles. This robot was then later adapted to cross insulators [32, 33]. One alternative was proposed for providing the mobility necessary for Tsujimura's robot [18] in order to surmount certain kinds of obstacles present on cable, placed at any part of the cable, moved by only one motor. The robot is designed as shown in Fig. 12. It is composed of four slider-crank mechanisms, used as legs, sprockets, timing belts and only one motor to transmit a synchronized movement to the legs. It has two pairs of identical legs, one at the front and another at the rear that enable the robot to walk suspended from the cable hanging by hooks (feet) attached at the extremity of each leg. Each pair of legs is composed of two slider-crank mechanisms whereby each leg has one degree of freedom to change its length. Thus, the robot structure has two legs on the right and two on the left, and the legs on the same side have the same movement. Stability is assured by the feet of the same side maintaining continuous contact with the cable. The leg's motion can be divided into two modes: the first is the surmount mode where the foot describes a trajectory above the cable and the second mode, called contact mode, when the foot contacts the cable and supports the robot's weight and moves the robot forward. Each robot leg repeats these two modes in turn. The proposed robot's movements are like those of a sloth.
General configuration of the mobile robot suspended on cable [32].
In Figure 13 the side and top view of a graphical simulation are presented in which the mobile robot cross an insulator. In Figure 13(a) all the robot's feet are on the wire. From this condition, the robot starts its movement with the right feet leaving the wire, Fig. 13(b). After the right feet pass through the higher position and come back to the wire, the sensor identifies the obstacle, Fig. 13(c). From this position, the input crank turns back five degrees, Fig. 13(d). After the return position, the leg grows 30mm and simultaneously, the input crank goes forward and the sensor foot again identifies the insulator, Fig. 13(e). Then the input crank turns back five degrees and the feet are retracted, Fig. 13(f). The movement continues and the leg cross the insulator, Fig. 13(g). After the insulator transposition the feet return to their normal position to continue the robot's motion. In Figure 13(h) the feet are on the wire again.
Graphical Simulation of an insulator transposition [32].
In Figure 14 a constructed scaled prototype is presented which can surmount a signalizing sphere. The prototype was built in order to verify the validity of the proposed methodology. The control is based on a PC system by using a control board to control the four step motors used to vary the leg length, a dc motor that drives all the legs, and to verify the contact between feet and the obstacle. This contact is detected by a sensitive edge system (safety edge) placed at each foot. The mobile robot structure is made of aluminium and the synchronization of the motion legs is ensured by a dc motor, pulley and timing belt. Its weight is approximately 80N [3].
The constructed prototype surmounting a sphere [3].
In [34] a design for a robot for inspecting power transmission lines was presented with an emphasis on inspecting power cables using non-destructive techniques. Electromagnetic interference tests ensured that the system is capable of operating on energized lines, Fig. 15. This robot cannot cross any obstacles.
In Brazil, researchers at Furnas Central Electric have developed a robot able to install signalizing spheres, Fig. 16. The semi-autonomous robot carries the sphere to the point where it needs to be installed and then, with the aid of a screwdriver, attaches it to the cable. This same process can be done to remove the sphere [34]. The robot does not overcome obstacles and is specifically designed for sphere installation.
Robot to install signalizing spheres [34].
In [35] the robot Expliner was presented which is controlled by a remote control system. This robot uses pulleys to move along the transmission lines and has a two degree of freedom manipulator to move its centre of mass (counter-weight). The Expliner robot differs from most other robots in that it uses two cables for its locomotion, Fig. 17.
Prototype of the robot Expliner [35].
The EPRI (Electric Power Research Institute) has been developing a robot named Ti which has high-definition visual and infra-red spectrum cameras and many sensors. However, to cross obstacles it is necessary to install paths (bypass systems) that are permanently installed on the transmission lines [41–42].
4. Latest Trends in Robots Used on Power Transmission Lines
From the works presented here we can conclude that there are no complete solutions for inspecting and carrying out maintenance on power transmission lines. All the robots presented in this work are designed to cross/surmount some obstacles and/or inspect/ carry out maintenance on specific equipment.
The greatest obstacles to robots are the towers. In Brazil, for example, there are long stretches without cities, where it is essential to overcome the towers. Moreover, the design of robots for inspecting power transmission lines must take into account different types of obstacles and towers, as shown in section 2, to be able to move at least 100 km (the average distance between Brazilian cities) and if possible carry out inspections and maintenance of the lines.
To cross the towers, the robots that travel on the energized line can use the suspended insulator to perform the tower transposition as proposed by [32–33, 25, 8] or can form a path (bridge) over which the robot can travel as proposed by [9, 28] and the robot EPRI Ti.
In Figure 18 after identifying the tower (1), the robot climbs like a monkey from the overhead ground line to the adapted bridge (2) and walks along the bridge (3–4) and finally the robot holds onto the overhead ground line again (5–6) [9].
Transposition scheme of the tower using a bridge adapted [9].
The project LineScout was started in 2003 with the objective of developing a teleoperated platform that could travel along live transmission lines and cross most obstacles on the Hydro-Québec network. This robot has a weight of 110kg when equipped with a modular robotic arm. Figure 19 shows the steps that take place when the robot is crossing an obstacle, the suspended insulator and suspension clamp.
Demonstration of LineScout's capacity to cross obstacles [36].
A set of arms and grippers offer a temporarily grasp on both sides of the obstacle, allowing the wheels to disengage and flip down underneath the line prior to crossing to the other side. The operation is teleoperated from the ground [36] and cannot cross dead-end towers [37].
In [38] a robot named “Cable Crawler” was presented, a mobile teleoperated robot for the inspection of high-voltage power lines which rides on the topmost ground cable. It implements an innovative mechanism that allows it to cross a set of mast tops as well as smaller obstacles autonomously. The robot weighs 58kg and has six drives. Figure 20 shows the robot transposing the tower in the ground cable.
Sequence of passing a mast tip [38].
The robot proposed by [9, 28] can cross towers as in Fig 3(b) with a special bridge installed on it. However, for the practical application of this robot all the towers should be modified to include a path (ladder), or the robot will have to load and install the path which increases the complexity of the project as proposed by [21].
The major problem for all the robots is transposing the towers.
As such, the latest trends in mobile robots used on power transmission lines suggest a hybrid solution using a flying robot (UAV) and a mobile robot. The first to propose this idea were [6]. Katrasnik et al. [6] who have compared the three possibilities in the power lines inspection robot design: flying robot, mobile robot and flying/climbing (mobile robot). Their novel proposed mechanism is presented in Fig. 21 [6]. The authors concluded that the best project is the flying/climbing robot. The flying/climbing robot can be obtained by some modification to UAVs available in the market and this robot could cross any kind of obstacle [5].
Another solution has been studied by the authors. The idea consists of a modular robot that travels along the overground cable or the high voltage line, in which each module is compact, has its own motion and power system, and has its own function, Fig. 22. One module carries a UAV. As the modules are dedicated to one function, they are light, optimizing the electricity consumption. Thus, depending on the type of mission required, one or more modules can be selected or created. To increase the autonomy of the robot modules there are robot modules responsible for the exchange of the batteries. The module carrying the UAV will be used to cross larger and/or more complex obstacles, as large and complex as the signalizing spheres and towers. Thus, once the obstacle is identified, the UAV can carry each module of the robot to cross it, Fig. 23. In Figure 23(a) the UAV stands out from its module and addresses the module to be crossed, in the example it is the manipulator module, Fig. 23(a). Figure 23(b) shows the UAV connected to the manipulator module and Fig. 23(c) its transportation beyond the obstacle (signalizing sphere). In Figure 23(d) the UAV places the manipulator module on the cable and in Fig. 23(e) the UAV is shown returning to its transport module, Fig. 23(f). The modules can be designed for a variety of tasks, such as: inspection of cables and devices with cameras and sensors, maintenance/install signalizing spheres and another device, cleaning insulators and spheres (cleaning module), etc. If necessary, the UAV can be made to fly to take pictures of specific details of towers/devices and power transmission lines. This solution, when implemented, will be complete and viable for use worldwide. The analysis of the availability of this system considers that it is not possible to construct a multi-task robot in order to perform every kind of repair and/or maintenance operation. A multi-task robot will be very large and heavy, making it impossible to use in the power grid. The application of the modular robot starts by using an inspection module to travel along the cable to where all the defects are recorded by cameras and its position by GPS. Then, a specific robot module goes to execute the repair operation. The UAV module is used to place and remove the robot modules from the cable. In this case, the UAV can be controlled using a teleoperation system. An analysis of this system was carried out by considering its technical and financial feasibility.
A modular robot for repairing and maintaining power lines.
Sequence to cross obstacles.
5. Discussion
Economic expansion and the development of urban centres have increased the demand for electricity, requiring energy to be transmitted through an important power grid. Many power transmission lines are installed more than 150 meters above the ground and require detailed inspection to identify and repair defects to the cable, clamps and insulators. These power transmission lines also require the installation or exchange of signalized spheres, and the cables to be cleaned. Moreover, blackouts result in power companies being given fines. As such, regular checks and inspections are crucial for power supply security, reliability and the reduction of maintenance costs. The workers who maintain these cables not only face the constant risk of falling from a great height but also electric shocks. Thus, due to the difficulties of constructing and maintaining such transmission lines, automatic systems/machines are proposed and developed in order to reduce the danger of the work, with less need for human labour which will also reduce labour costs.
The inspection and maintenance of power transmission lines are carried out by an electrician by him or herself or by using any of the following: helicopters, unmanned aerial vehicles, airplanes, boom trucks, trolleys and mobile robots on the cable.
Traditional patrol inspections using helicopters are costly, do not provide a platform for the precise inspection of the line from close distances, and, due to the risk of contact with the live line in windy climates, are still not sufficiently safe for the operators [5].
The use of boom trucks, which have a manipulator installed at their extremity, cannot be used in inaccessible places such as valleys, rivers and mountain regions, and lines higher than the operating range of the crane arm. Although they are commonly used, they present problems related to mobility, controllability and accessibility, and basically are used to repair insulators.
Unmanned aerial vehicles (UAVs) and airplanes are generally used for visual inspection. The basic design principle for an aerial based robot is to perform visual inspection while flying near the transmission line conductor [2, 7]. The use of such equipment does not allow for maintenance operations, due to the difficulty of installing a robotic arm or mechanism for repairs.
Many theoretical and experimental studies have been carried out in order to develop autonomous machines to travel along power transmission lines, suspended on wire, to perform inspections and/or repair (maintenance) work. These robots are called mobile robots or climbing robots. Since the early 1990s, many researchers have investigated the development of inspection robots to assist people or to replace people on power transmission lines [2]. These machines can improve efficiency, reduce labour costs and are expected to reduce the risk of injury to maintenance personnel. Despite there being a lot of theoretical research and technological developments, problems related to stability, controllability, ability and autonomy still exist.
Obtaining a robot to travel along a cable and surmount/cross the different obstacles, including the towers, remains the main technical challenge. With regards to the obstacles' dimensions and the towers, presented in section 2, the dimensions and mass of the robots are important. Moreover, the robot must be equipped with sensors and devices that allow for the inspection and maintenance of power transmission lines. These devices increase the robot's mass. Due to these limitations of size and mass for the robot project, research in this area provides specific solutions that deal with the transposition of certain obstacles and individual maintenance/inspections tasks as discussed in sections 3 and 4.
Another problem for the design of mobiles robots used in power transmission lines is their power supply systems. These systems can be gasoline/diesel generators, batteries, using the power line's electric field and solar panels. The gasoline/diesel generators may provide 1000 to 2000 Watts, but, for example, a compact generator of 1000W has a mass of 15kg. Its advantage is its autonomy and the disadvantage, besides the weight, is safety issues. The Ti-ion battery remains the best choice, providing up to one day of energy autonomy [4], but several units are needed to provide the necessary power (1000 to 2000W) and autonomy. The batteries can be recharged using the power line's electric field or by installing solar panels to increase autonomy. Energy from the line could be extracted from the magnetic field of the line. This concept was presented in [39] where a magnetic iron core was placed around the conductor. The current induced in the secondary coil around the core was measured at different numbers of windings of the secondary coil. It was shown that the current reaches its maximum value at a certain number of secondary windings and that the power transferred to the secondary coil increases with the current of the power line. In [40] applying the power supply system to the robot RIOL was proposed. The power supply operating principle is based on the harvesting of the magnetic energy around the power supply lines by clamping a transformer around the line. A switching power rectifier, controlled to emulate a resistor, is then connected to the secondary coil of the transformer to obtain the robot's required voltages (55V±2.5%) and power (800W). The authors presented simulations in the MatLab environment.
Another problem is developing an autonomous robot. Given the complexity of the devices present in the power lines and the towers, see section 2, researchers have sought to develop teleoperated systems.
This paper does not discuss the problem of electromagnetic interference in robot design. This design constraint is discussed in [4].
The authors have focused on a modular robot because it is very difficult to design a small and light mobile robot to perform all the necessary tasks on a power grid. This idea facilitates inspection and maintenance operations. When inspecting, the robot obtains information, which is then analysed offline, using a variety of signals such as: visual, electrical, thermal, etc. Thus, the inspection module robot can carry all the necessary sensors in a compact module dedicated to this task. The maintenance tasks involve taking measurements, devices installation/replacement, cleaning devices, etc. The idea of modules permits the use of load robots which carry devices for installation and collect damaged devices, such as signalizing spheres, clamps, etc., Fig. 22.
6. Conclusions
As recounted in several works on robots used on power transmission lines, most problems are related to controllability and the ability to surmount obstacles. Although much work has been achieved in the past two decades, considerable developments still need to take place to obtain a reliable, low weight and autonomous robot to perform the inspection and maintenance of power transmission lines.
This paper reviewed and discussed some of the main efforts to obtain solutions to problems concerning the maintenance and inspection of power transmission.
Finally, a new modular robot was detailed, which provides a complete solution to inspection/maintenance, with the transposition of all obstacles (including towers), which can be applied in the future.
The next steps of this work are to design and construct the presented modular robots.
Footnotes
7. Acknowledgments
The authors are thankful to CAPES, UFU, FEMEC and FAPEMIG (process APQ-01999-10) for the partial financial support of this research.