An Analytical Variable-Stiffness Method for the Fine Control of Concentric Cable-Driven Manipulators

The concentric cable-driven manipulator (CCDM) has the characteristics of high dexterity, light weight, and safe movement, making them widely used in confined spaces. However, there are difficulties in the fine control with proper stiffness of CCDMs due to their flexible structures and various configurations. This article proposes an analytical variable-stiffness method for the fine control of CCDMs. First, the stiffness model is established by taking into account key factors, including the middle elastic backbone, cable tensions, configurations, and external loads. Then, the stiffness mesh is generated based on the stiffness model, which visually represents changing trends of its stiffness. Simultaneously, the stiffness of CCDMs can be accurately adjusted by optimizing their configurations and cable tensions. Therefore, the fine control with high or low stiffness of CCDMs can be realized in practical applications. Finally, experiments are conducted to verify the analytical variable-stiffness method of CCDMs. Results indicate that the average error of the stiffness model is 5.42%. It also confirms the effectiveness of the proposed method for achieving analytical variable-stiffness control of CCDMs. Furthermore, the proposed method is also applicable to cable-driven manipulators with similar structures.