Dual Ascender Robot With Position Estimation Using Angle and Length Sensors

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.