Position Error Compensation of Façade-Cleaning Robot by Optimal Rope Winch Design

This study aimed to optimize the rope winch of a façade-cleaning robot, a system that travels vertically using the friction between ropes and pulleys. However, position errors can be caused by various factors during locomotion. This adversely affects the robot’s position accuracy. To solve this problem, an experiment was conducted to secure the repeatability of the robot position by optimizing it using the Taguchi method. Subsequently, an error compensation was designed by predicting slip errors of the rope, and accordingly the positional accuracy was determined through feedforward and feedforward + PI control. The experimental optimization confirmed that optimal repeatability can be obtained using a pressure module with the force of 45 N and an axial groove pitch angle of 6° of a pulley. The position accuracy was improved using an error prediction model based on weights, travel distances, and controllers. For a travel distance of 3.0 m, the position error could be reduced to 55%–81% and 72%–89% through feedforward control and feedforward + PI control, respectively, compared with that of the open-loop. The observations of this study could facilitate the control of the position of façade-cleaning robots and aid in the improvement of position accuracy.