# Adapting Mechanisms for In-Pipe Inspection Robots: A Review
## 3 Analysis of Adapting Mechanisms
### Adapting Mechanisms Based on Combined Linkages  
These adapting mechanisms are obtained starting from the four-bar linkage as a basic unit to which a slider-crank linkage is added. As in the examples presented above, in this case, the mechanism can also be operated passively by means of springs or actively by means of actuators. [PERSON] et al. in [49] propose a three-axis differential drive pipe robot, which consists of a differential mechanism and a mechanism for adapting to variations in pipe diameter. The robot is equipped with three pairs of drive wheels. A 3-DOF tri-axial differential drive mechanism for steering allows the robot to easily adapt to any existing pipe configuration. After the differential output, a bevel gear and a set of synchronous belts are used to provide the required torque to the driving wheels. Figure 15 shows the schematic diagram of the adapting mechanism. Figure 14: Adapting mechanism based on pantograph linkage with one slider. Figure 15: Adapting mechanism based on combined linkages. The force required to adapt the robot to the inside diameter of the pipe is applied in the axial direction by means of a spring at which the pre-tightening can be adjusted. The movement of slider 1 causes the rotation of elements 3 and 5 together with the drive wheels around the joints \(D\) and \(H\). This ensures sufficient pressure on the pipe wall so that the diameters covered by the robot can vary from 275 to 300 mm. [PERSON] et al. in [50; 51] propose two inspection robots that use similar adapting mechanisms. In both cases, the robots have three identical adapting mechanisms with two pairs of wheels. The required force is generated by a helical spring also placed on the central axis. To drive the wheels, the first proposed robot uses a single DC motor and a combination of worm and cylindrical gears. One of the elements of the adapting mechanism also acts as a support for the robot's gear train. The first prototype of the inspection robot is shown in Figure 3b, and the schematic diagram of the adapting mechanism is presented in Figure 16.  
The total length of the robot is 140 mm and the pipe diameters that can be inspected are between 100 and 125 mm. The second prototype is shown in Figure 3c and has a gear motor for each drive wheel. It can inspect pipes with diameters between 140 and 200 mm and has a length of 280 mm. Both prototypes have good mobility and also the ability to overcome small obstacles when moving through horizontal or inclined pipes. The second prototype, because it has independently driven drive wheels, can easily move through bend pipes. [PERSON] et al. in [52] propose a novel pipeline inspection robot with a belt-driven ridged cone-shaped set of wheels. The three belt-driven wheels are connected to the main body through adapting mechanisms based on combined linkages. Figure 17 presents the schematic diagram of the proposed mechanism. Figure 16: Passive adapting mechanism. Figure 17: Adapting mechanism with belt-driven wheels. Each of the three adapting mechanisms contains an electric linear actuator for the longitudinal movement of slider \(1\). The active adapting mechanism does not allow the control of wall pressing force, but the mathematical model that describes the relationship between this force, the geometry of the mechanism and the force developed by the linear actuator is presented in [52]. To ensure sufficient frictional force and to overcome small obstacles the robot relies on wheel design. As the mechanisms can be operated individually the robot can easily adapt to variations in diameters or rough/irregular surfaces in the pipeline. As each wheel set is operated and controlled independently, the proposed inspection robot can pass through elbows and T-branches. The length of the robot is approx. 460 mm, and its outer diameter can be changed from 300 mm to 390 mm. A robot with a track-based locomotion system that uses the same type of adapting mechanism is proposed by [PERSON] et al. in [53].