# Adapting Mechanisms for In-Pipe Inspection Robots: A Review
## 3 Analysis of Adapting Mechanisms
### Adapting Mechanisms Based on Slider-Crank Linkage  
The slider-crank linkage shown in Figure 1, can be the most straightforward constructive solution for the adapting mechanisms. As mentioned above, robots may have several rows of wheels/tracks arranged radially around the axis. In this case, a slider-crank linkage will be required for each of them. [PERSON] et al. in [32] proposed a pipe robot that is designed for internal weld seam processing of thick wall pipelines. The robot can move in pipes whose inner diameter has a range from 270 mm to 380 mm and according to the authors has a good ability to pass through bent and inclined pipes. It consists of several modules that include a mobile unit, a detection unit and a grinding unit. The main function of the mobile unit is to provide the traction needed to pull the entire robot through the pipe. Figure 4 shows the schematic diagram of the adapting mechanism for one of the three drive wheels. A single DC motor provides power to all three drive wheels through a worm gear and some gear trains. One of the elements of the adapting mechanism acts as a support for the robot's gear train. The pressing force against the pipe wall is provided by a spring acting on the slider 1. Thus, by the expansion and contraction of the slider-crank linkage under the action of the force exerted by the spring, the adaptation of the robot to different diameters of the pipe is ensured. The variation of friction force between the wheels and the pipe wall is compensated by the force of the spring. The mathematical model that describes the relationship between the maximum traction force of the mobile unit, the size of the linkage elements and the spring force is presented in [32]. Figure 4: Schematic diagram of the adapting mechanism. [PERSON] et al. in [33] and [PERSON] et al. in [34] present a wheeled pipe inspection robot designed to move in pipes with multiple elbows and an inclination of max. 35\({}^{\circ}\), with a diameter of 300 to 500 mm. The robot consists of two modules, one active and one passive. In both modules, each drive wheel is driven by its own gearmotor. The modules are connected with a universal joint to give the robot more flexibility. Figure 5 shows the schematic diagram of the adapting mechanism for the passive module. The only difference between the active and passive modules is the method in which the pressure force is obtained. In the active module, the slider \(I\) is moved by means of a screw driven by a motor and for the passive one by means of a spring. The slider's linear displacement determines the rotation of element 3 and also of the drive wheel, around the joint \(C\). Although the robot has an active adapting mechanism, the pressure on the pipe wall cannot be controlled. The active module, by means of a fuzzy controller, allows only the adaptation to predetermined pipe diameters [34]. A self-adaptive pipe inspection robot with a multi-axis differential system and an active adapting mechanism is proposed by [PERSON] et al. in [35]. The total length of the inspection robot is approx. 370 mm and was designed to move in horizontal multi-bend pipes. The robot consists mainly of an adaptation/propulsion unit and a three-axis differential drive mechanism used to prevent the drive wheels from slipping. After the differential output, a level gear and a transmission chain are used to provide the necessary torque to the drive wheel. Figure 6 presents the schematic diagram of the adapting mechanism. Figure 5: The adapting mechanism for passive module. Figure 6: Mechanism for a self-adaptive pipe inspection robot. The lengths of elements 2 and 3 are 130 mm and 120 mm, respectively. Slider 1 is moved by the lead screw's nut by means of a spring. A control system compares the pressure between the drive wheel and the inner wall of the pipe, which is measured indirectly by a force sensor mounted in the nut, with the required pressure value. Then, by means of the nut and spring, the preload motor transfers the necessary force to the adapting mechanism.