This paper reviewed on several previous on work that have been done on the developed in pipe line inspection robot for the last few years. This type of inspection robots can be divided into several groups based on their locomotion. Each prototype inspection robot have its own advantages and disadvantages depending on their design requirements and purpose of robot. Each prototype have been tested on several experiments in order to verify its functionality and efficiency of inspection task.
Some of the researchers ran simulation to validate the kinetic and modelling mechanism of their own prototype. Pipe inspection is extremely essential to locate accurately the defects due to corrosion and third parties. By designing this type of robots to remove the human intervention from labour intensive and hazardous work environment, sometimes it is also used to explore inaccessible environment which are generally impossible to access by humans during repair and maintain inside the pipe line.
Keywords: Pipeline inspection robot, defects.
Robotics is one of the growing engineering fields of day to day in life. Robots are designed to remove the human factor from labour intensive or hazardous work and also to act in inaccessible environment. They are mostly used by the heavy industries. The visual inspection  in pipes such as gas pipe lines , water pipelines, chemical pipe lines, etc. For cracks, corrosion, blockages and leakages may be relevant for improving security and efficiency in industrial plants. The embedded system is use in robot for visual inspection by using camera, sensors and LED light, etc.
the underwater robot operations such as inspection, maintenance, cleaning etc. are done and thus, the application of the robots appeared to be one of the most attractive solution and effective one time investment. Pipelines which are used for transporting oils gases and other fluids such as chemical which are bound to be explosive at higher temperature have been used as major utilities in a number of industries for long time. Many defects occur in pipe lines as they become old and most of them caused by cracks, corrosion and mechanical damage from third parties. In pipe inspection robot can be classified into different categories based on their application. These named as pig type robot, wheel type robot, caterpillar type robot, wall-press type robot, inchworm type robot and screw type robot.
Figure 1: Different types of pipeline inspection robots
Jong-Hoon Kim, Gokarna Sharma, and S.Sitharama Iyenger have proposed the design and implementation of a fully autonomous mobile pipeline exploration robot, called FAMPER that can be used for the inspection of 150mm pipelines. This robot consists of four wall press caterpillars operated by two Dc motors each. The speed of each caterpillar is controlled independently to provide steering capability to go through 45-degree elbows, 90-degree elbow, T-branches and Y-branches. This paper is to show the opportunity of using 4 caterpillar configuration for superior performance in all types of complex networks of pipelines .
Atul Gargadel, Dhanraj Tambuskar, Gajanan Thokal have proposed that robot consists of a foreleg system, a rear leg system and a body. The fore and rear leg systems are constructed by using three worm gear system that is arranged at an angle of 120-degrees with respect to each other to operate inside a pipe of different diameters. The springs are attached to each leg and the robot body to operate in pipes of 140mm to 200mm diameter range .
Palwinder Kaur, Ravinder Kaur, Gurpreeth Singh have worked on innovative concept to handle the bore well rescue operations without human intervention and to inspect any type of leakage in the pipe. In this model they used wheeled leg mechanism. The legs are circumferentially and symmetrically spaced out 120-degrees apart. The robot made adaptive so that it can adjust its legs according to the pipeline dimensions. The structural design makes it possible to have the adaption to the diameter of the pipe and to have adjustable attractive force towards the walls of the pipe .
Ankit Nayak, S,K,Pradhan have designed robot in such way that they remove human intervention from labour intensive and hazardous work environment, sometimes they are also used to explore in accessible workplaces which are generally impossible to access by humans. The inspection of pipe comes in the same category because they carry toxic chemicals, fluids and the most of the time has small internal diameter or bends which become inaccessible to human. This paper proposed model is a screw driver type wall press adaptable wheeled in pipe inspection robot. It is move through vertical and horizontal pipes and it can easily pass through elbow of a pipeline. This model comprises of three modules rotor, stator and control unit. The rotor module has three wheels mounted on the outer periphery with helix angle of 15. Wheels of rotor follow the helical path on the internal surface of the pipeline and move in the longitudinal direction inside the pipe .
Edwin Dertien has discussed the design of mechanical structure of a miniature pipe inspection robot capable of moving through very small pipes (up to 41mm diameter). The main objective was to negotiate bends, T-joints and steep inclination. The proposed robot consists of a modular design (7 modules) with a relatively low number of active degrees of freedom. The system used a novel clamping mechanism with a series-elastic drive. The design of mechanism resulted in a high spreading factor allowing the system to operate in a wide diameter range (63mm to 125mm outer diameter). The mechanical design requirements and control system in the robot were also discussed and preliminary test results concluded that robot was found quite effective than the conventional inspection .
Numbers of related papers about in pipe inspection robots have been reviewed. The robots are divided into categories according to their types. A brief description about each one is given below.
Wheel robots are widely used in this application due to their simple and robust design, superior control methodologies and higher energy efficiencies. The simplest of to behave in a similar way as regular wheeled vehicles in which they depend on their own weight to maintain contact between and the pipe wall .
Figure 2: wheel type robot
Inchworm type robots are relatively simple to control and allow the robot to negative the various features inside the pipe. Each of these robots uses an actuation sources as the main driving force, coupled with a passive mechanical system that presses against the pipe wall. These robots use a form of linear actuation for propulsion, coupled with full control over the extensive and retraction of their limbs, which allows them to easily move forwards and backwards along the pipe .
Figure 3: inchworm type robot
Snake robots have many degrees of freedom, which permit a wide range of different motion covering large area. However, this results in robots using more actuators and having more complex robot design and control system than those found in robots using other locomotive types. This may or may not be acceptable to the industry owing to its high cost. These robots consist of several subassemblies connected together using actuated joints. Movement is primarily achieved through the use of travelling wave locomotion. This robot requires high power actuators and have limited pay load capacity but advantageous in situation where thorough inspection is required .
Figure 4: snake type robot
Spring loaded robots consists of three rotors, a compression spring with six wheels. Out of these six wheels three rare wheels are connected with the rotors. It works inside the pipe for inspection purpose. Due to spring mechanism, these robots can be adjust their height, hence it can work for inspection in pipes of various diameters. These have wireless camera to inspect the inside the pipe .
Figure5: spring type robot
Wall press robot consists of three or four track wheels, main body, extendable link system and other attached functions. The attached functions composed of different sensing, communication and actuation devices for the pipeline demand. Each track wheel consists of two DC motors. These robots are used for long distance pipeline inspection such as horizontal pipelines, vertical pipelines and bend pipelines with variable diameter .
Figure 6: Wall press type robot
The walking robot has eight legs arranged in the form of two stars. Each four time are attached to a central body which lies on a plane that contains the longitudinal axis of the crawler. These two planes are called leg planes. Each leg plane has two active joints and is driven by DC motors. Its axes of rotation are orthogonal to the leg plane so that it has full planar mobility. The legs are mounted to the central body with an additional passive joint, which allows compensation for small displacement to the leg plane .
Figure 7: Walking/leg type robot
All types of robots that have been discussed have the same general objectives, which is to do inspection inside pipelines. However, each of them has its own characteristics which adhere to its specific design requirements. Table 1 shows the comparisons between different types of in pipe line inspection robots .
Table 1 comparison between different types of robots.
Many researches and developments have been done in the in-pipe robot work field. Each design that has been produced is based on the design requirements set by developer in order to achieve their objective in building the prototype. Generally an in-pipe inspection robot consists of the main body, driven part, control device and inspection equipment. Based on the review it can be said for pipes having large internal diameter ranging from 500mm to 1000mm, a walking and wall press type inspection robot is the best mechanism to inspect for that size of pipe. For small medium internal diameter pipes ranging from 100mm to 400mm, the wheel and inchworm type inspection robot suitable to use for inspecting that kind of size of pipe. As further work, most of the researchers are working on optimizing the design in terms of power usage, the size of robot and minimizing the complexity of the robot mechanism. Looking at the current development of the robots, walking and spring type inspection robots seems to have a brighter future in having significant improvement in terms of the exterior design and controlling mechanism.