A Novel Friction Measuring Method and Its Application to Improve the Static Modeling Accuracy of Cable-Driven Continuum Manipulators

Cable-driven continuum manipulators exhibit high flexibility and dexterity, leading to their increased popularity in recent years. Friction analysis is a crucial problem for these ma- nipulators. Previous research has introduced friction models that are applicable to dynamic states where the direction of friction can be ascertained. However, in static states, the direction of internal friction remains undetermined. Additionally, previous studies have investigated the friction law within a single cable hole. However, as multiple cable holes exist along the manipulator, friction should be considered as a series of forces and examined across multiple cable holes. Measuring internal friction presents a challenge due to the unique structure of the manipulator. To our knowledge, no state-of-the-art research has studied how to measure the friction along the entire manipulator. In this letter, we propose a novel friction measuring method based on fiber Bragg grating (FBG) sensors. Experimental results show that the friction distribution can be fully measured. We apply this method to a static model and shape estimation experiments demonstrate that the accuracy of the static model is significantly improved, particularly when the fric- tion has inconsistent directions. Our proposed friction measuring method provides a valuable approach for mechanics analysis of cable-driven continuum manipulators.