Modeling and control of TRDMR on a facade with thruster-driven adhesion

This paper presents posture control of a facade-cleaning robot called ”two-rope-driven mobile robot” (TRDMR) via two-degree-of-freedom (DOF) control method combining H∞ control with disturbance observer (DOB). The TRDMR utilizes two ropes fixed to the roof of building in order to move on the exterior wall of a building. Additionally, two propeller thrusters are added to the TRDMR not only to maintain its posture on the exterior wall of building but also to make it keep in contact with the exterior wall of building during its operation. However, the TRDMR may undesirably undergo the rotational oscillations along the yaw direction (axis perpendicular to the exterior wall) during its operation, which may be caused by the characteristics of the fiber rope and the structural characteristics of the TRDMR. Therefore, in order to cope with a posture problem of TRDMR caused by rotational oscillation, a 2-DOF control method consisting of H∞ control and a disturbance observer (DOB) is designed on the basis of dynamic analysis of the TRDMR. The comparative experiments are performed by using a well-known proportional–integral–derivative (PID) equipped with DOB control to evaluate the performance of proposed posture control. The experiments demonstrate that the control method using H∞ + DOB control is superior to that using PID + DOB control: when the rotational velocity of TRDMR along the yaw direction is 0.7 rad/s, the maximum amplitudes of rotational oscillation are attenuated to 3.89 and 4.6 by the H∞ + DOB control and the PID +DOB, respectively. The resulting settling times obtained by the H∞ + DOB control and the PID +DOB are 3.37 s and 3.62 s, respectively. With the rotational velocity of 1.0 m/s, the maximum amplitude of rotational oscillation attenuated by the H∞ + DOB control and the PID +DOB are 5.68 and 8.28, respectively. The resulting settling times obtained by the H∞ + DOB control and the PID +DOB are 1.47 s and 4.15 s, respectively.