Configuration design and analysis of a planar cable-driven higher pair inspired by human knee joints

Bionic joints have a wide range of applications in robotics and medical rehabilitation. However, most existing designs rely on lower pair mechanisms, which exhibit deficiencies such as insufficient motion precision and excessive mechanical complexity. Inspired by the structure and motion characteristics of the human knee joint, this paper proposes a novel configuration design method for a cable-driven parallel robot (CDPR) featuring two higher pairs and two cables. To address the challenges of unidirectional force transmission and wrench closure inherent in CDPR, a new graphical wrench closure criterion based on the instantaneous center is introduced. A boundary inversion method based on this criterion is proposed to guide the design process for selecting cable anchors, ensuring that the mechanism maintains wrench closure throughout its intended motion space. Finally, a prototype of a bionic knee joint is designed and constructed, and its motion performance and wrench closure capability are validated through motion and force analysis. The proposed approach offers a novel theoretical framework for CDPR configuration design, demonstrating significant potential for practical applications in bionic joints and related fields.