Abstract: In order to solve the problems of movement interference and transmission parts abrasion, the tri-axial differential mechanism is applied in the wheel-type pipeline robot. The output velocities of the driving wheels can be regulated by the tri-axial differential mechanism according to the external torques, and the robot can move in the elbow differentially. So the theory of bond graph is applied in the analysis of the transmission property of the mechanism. The bond graph model of the tri-axial differential mechanism is established based on the method of absolute speed, and then the corresponding equation of state can be obtained. As finding the non-equivalent phenomena of the output of the mechanism, the equivalent conditions of the mechanism can be get based on the equation of state and then the corresponding equivalent treatment is done. The mechanism is simulated under different conditions, and the results show that the tri-axial differential mechanism can achieve the differential output of movement according to the relations of the external torques.

Key words: Bond graph, Differential property, Equation of state, Tri-axial differential mechanism