# Adapting Mechanisms for In-Pipe Inspection Robots: A Review
## 3 Analysis of Adapting Mechanisms
### Adapting Mechanisms Based on Slider-Crank Linkage
An inspection robot with independent underactuated parallelogram crawler modules is presented by [PERSON] et al. in [38]. The proposed robot has a passive adapting mechanism and three crawler modules. To accommodate variations in pipe diameter, each crawler module in the robot's structure is connected to a central unit via two identical slider-crank linkages as shown in Figure 9. The connection with the linkages is ensured through joints \(G\) and \(H\). As the adapting mechanism has 2 DOF, these joints can change their relative position which allows the crawler module to be tilted if necessary. The axial length of the robot is 235 mm and the diameters of the pipes that can be inspected vary between 136 and 226 mm. Figure 8: Adapting mechanism with 2 DOF. Figure 9: Adapting mechanism with crawler module. [PERSON] et al. in [39; 40] present a passive adapting mechanism with three pairs of driving wheels that can move asymmetrically in the radial direction. The proposed adapting mechanism consists of two identical sets of slider-crank linkages at the front and rear of the robot. The follower arms of the slider-crank linkages are connected to each other through an element (part of a driving module) and joints \(G\) and \(H\) as shown in Figure 10.  
The springs that preload the adapting mechanism are located inside which makes the robot have a compact structure and a total length of 150 mm. The proposed mechanism has been designed so that the wheels have good contact with the inside of the pipes and also to cope with the uncertain conditions inside the pipes. Thus, pipes with diameters between 85 and 109 mm can be inspected. Adaptation to different diameters and therefore the compensation of the friction force variation is based only on the springs force. The authors claim that the proposed robot can navigate in almost all types of pipe configurations, regardless of its position in the pipe or the direction of movement. A similar mechanism is used by [PERSON] et al. in [41]. In this case, the robot uses four pairs of interconnected slider-crank linkages. Each pair of linkages is connected to a track-based locomotion system, driven by two DC motors. The speed of each track is independently controlled to provide the ability to turn through any spatial pipe configuration involving any pipe fittings. When a track encounters obstacles, it also has the ability to tilt to increase the contact surface with the pipe wall. The length of the robot is 148 mm, and the outer diameter can vary between 127 mm at maximum shrinkage and 157 mm in a normal state. Another robot with a track-based locomotion system that uses the same type of adapting mechanisms is proposed by [PERSON] et al. in [42]. The robot consists mainly of two identical modules interconnected by a compression spring and can inspect pipes with diameters ranging from 80 to 100 mm. The track-based modules allow the robot to maintain contact with the pipe surface during movement. As each track is independently controlled, it can steer at the elbows or T-branches of the pipes. The total length of the robot, including both modules and the compression spring is 230 mm.