Development of a cable-driven continuum robot having a large workspace (Mechanism design of a one-segment continuum robot focused on orientation workspace)

Abstract

In order to develop a cable-driven continuum robot having a large workspace without using a large number of segments, which leads to construction complexity and requires the use of many actuators, this paper presents a mechanism design for increasing the orientation workspace volume of a one-segment continuum robot by realizing multiple elastic rod shapes of different lengths, which have one inflection point. The proposed design is that an elastic rod of variable length is used as a backbone and two cables are routed in parallel to the elastic rod and the other two cables are connected to the tip of the elastic rod attachment point on the end disk. This design was obtained by deriving cable routings that meet the necessary conditions for the elastic rod to be in static equilibrium in the shape with one inflection point. Then, numerical analysis and experiments were performed to investigate the effectiveness of the proposed design on the increase of the orientation workspace volume. Considering that the length of the elastic rod is variable and the elastic rod deforms into the shape with one inflection point, the procedure for static analysis to derive the relationship between the length of the elastic rod, each cable tension and the position, orientation of the end disk, was presented. By this procedure, forward and inverse static analyses were conducted. Through the numerical calculation of the orientation workspace based on the static analysis, it was shown that the orientation workspace volume was increased by the proposed design. Furthermore, using the experimental apparatus based on the proposed design, a large orientation workspace was realized and measured configurations were in good agreement with the numerical calculation results.