Design and Control Method of a Coupled Loading–Damping Mechanism of Cable-Detecting Robots for Large Bridges

The climbing stability of cable-detecting robots holds important significance for bridge detection. To improve the climbing stability of robots under cable vibration, a loading mechanism coupling variable stiffness and damping and a control method were proposed for robots. At first, aiming at the slip of cable-detecting robots during climbing, the influences of cable vibration on the climbing stability of the robot and the damping mechanism of the variable-stiffness and variable-damping mechanism were assessed. Then, a new coupled loading mechanism was designed, and a mechanical model was established. The damping and stiffness were adjusted according to cable vibration, thus automatically adjusting the loading force of the robot. Afterwards, a fuzzy proportional–integral–derivative (PID) control strategy was devised and PID parameters were adjusted in accordance with cable vibration, thereby dynamically adjusting the clamping force of the coupled loading mechanism. Finally, a laboratory vibration test platform was established to conduct experiments on the output force of the coupled loading mechanism and on the robot climbing under vibration. Experimental results show that the maximum fluctuation amplitude of the climbing speed of the proposed robot decreases to 0.018 m/s, and the speed stability improves by 78.9% at the cable-vibration frequency of 10 Hz and amplitude of 4 mm, when compared with the original common helical-spring loading mechanism.