This paper presents the design and force-tracking impedance control (FTIC) of a 2 degree-of-freedom (DOF) wall-cleaning manipulator. A novel 2-DOF wall-cleaning manipulator is designed not only to ensure good contact with different shapes of walls but also to avoid various obstacles on walls efficiently. By adopting two ball-screws, 2-DOF motions of the manipulator like translation by a maximum of 150 mm and tilting by 13 degrees are realized successfully. Then, the position-based FTIC is derived to enable the proposed manipulator to not only interact with walls in a desired impedance behavior but also maintain a desired contact force. The FTIC consists of a position-based impedance control (PIC) and a disturbance observer (DOB). While the PIC ensures the excellent force tracking capability of the proposed manipulator in the steady state, the DOB is combined with the PIC to enhance its transient response, i.e., to effectively reject the disturbances caused by various shapes of walls. The extensive experiments using the test bench successfully demonstrate that the proposed manipulator can maintain a desired contact force within 4.5 N with the help of the proposed FTIC against different types of roller brushes as well as varying shapes of walls.

This article presents the design and position-tracking control of a novel two-degree-of-freedom dual-rope winch robot. It is designed to be facilely installed at both corners of a building using two synthetic ropes and to move freely on the wall plane using the ropes to perform building maintenance work. This robot consists of a dual-rope winch system responsible for its movement on a plane and a thrust module that allows the robot to remain close to the wall through the force of the propeller. In the dual-rope winch system, ascending modules driven by two pulleys and connected by differential gears are arranged symmetrically; the position and posture on the plane can be determined by controlling the ropes. The robot winds a synthetic rope around the pulley to support the load with frictional force. Precise position control is difficult to implement because of the elasticity of the rope and the slip around the pulley. Therefore, in this article, a feedforward control to predict and compensate for the slip length of the rope and a proportional-integral controller to regulate the position error owing to the dynamic characteristics of the rope are proposed. Experiments to verify the performance of the controller for various trajectories were performed on the test bench. It was confirmed that the actual trajectory deviation is within 0.5% of the target trajectory.

In recent years, cable-driven-parallel robots (CDPRs) have been studied for façade operations. There are various types of CDPRs; however, underconstrained CDPRs are capable of wider operating in façade workspaces than overconstrained CDPRs. Therefore, in this article, a dual ascender robot (DAR) was used for façade operations. Herein, two suggestions for safe façade operations are presented. First, a flexible nylon fiber rope was modeled such that the vibration direction, natural frequency, and damping ratio of the DAR could be converted through a Jacobian matrix and modal decomposition from the rope model. Second, input shaping control was applied to reduce vibrations, based on the vibration model of a DAR using the rope model. Modal decomposition was verified using a verification experiment, and the effect of input shaping was evaluated by comparing the w/input shaping and w/o input shaping experiments. w/input shaping case was shown about 48% reducing robot vibration and about 35% shortening settling time compare with w/o input shaping case.

This study proposes a novel mechanical design of a cable-driven parallel robot (CDPR), called a dual ascender robot (DAR), which consists of two ascenders and two structures for rope-measuring sensors. Unlike other CDPRs that require external structures for winches, the DAR requires only two ropes because the traction pulleys of the ascenders allow the robot to climb on the ropes. Thus, this robot can be operated in any building. Because the ascender moves on the ropes using the friction between the rope and the traction pulley, length errors owing to rope slip are inevitable. Therefore, it is difficult to estimate the position of the robot by using the length data of the ascender. To minimize this error, a sensor-fusion method that combines the rope-length and angle-sensor data with weight factors was used. However, an optimal method of selecting the sensor resolution has not been developed yet. Therefore, this study proposes a method of selecting the sensor-reflection ratio according to sensor resolution and angle- and length-sensitivity data. The sensor-fusion method was verified to achieve excellence and resistance to rope slip through simulations and experiments. Moreover, it demonstrated improved stability of approximately 4-mm error in a 20 $\text{m}\times 20$ m space under the slip condition, compared to the position-estimation method that only used the rope-length data.

This paper presents a rope winch with high position repeatability using a differential gear mechanism. This winch is easy to apply to existing buildings using synthetic fiber ropes, which are generally used by building exterior maintenance workers, and can be widely utilized as a winch of a gondola or climbing robot. Multiple pulleys are used to achieve high payloads, and differential gear mechanisms are used to distribute the torque across each pulley evenly. Uniform torque distribution minimizes slipping on each pulley, which reduces the power loss due to friction. This is proven through an analysis using the capstan equation and an experiment on a test bench. In addition, a criterion for the position repeatability of the winch is designed, and its results show that one pressure roller achieves optimal performance when the roller at the free end is pressed to 37 N. Extensive experiments were carried out on the final model of the winch, and position repeatability of under 50 mm deviation per 10 m was achieved through stable torque distribution under various payloads.