Velocity analysis of tri-axial differential pipeline robot when getting across elbow

A wheel-type pipeline robot applying a tri-axial differential mechanism is presented in this paper, which is targeted for moving inside the elbow while the ratios of angular velocities of the driving wheels depend on their movement trajectories. The main features of the robot are illustrated and some details about the mechanism are provided. To confirm the differential effectiveness of the robot, a geometry model of the robot in the elbow is established, which makes it possible to calculate the wheel centers and the contact points between the wheels and the inner surface of the pipeline. On the basis of the geometry model, the velocity ratios of the driving wheels can be computed. Several virtual experiments are performed, and the differential function of the robot is validated through the comparisons of the results between the theoretical analysis and the experiments.