This study presents the design and motion analysis of a 14-link, single degree of freedom (DOF) mechanism for robotic legs and prosthetics. Through systematic number synthesis based on link mobility equations, 23 valid link combinations were generated that satisfy the condition of one DOF. Among these, the configuration consisting of 8 binary, 4 ternary, and 2 pentagonal links was selected because it is the only combination that incorporates pentagonal links, enabling a structurally rich, multi-loop architecture capable of coordinating complex hip, knee and ankle motion from a single actuator. The presence of two pentagonal links, each with five connection points, allows for strategic placement of joints and transmission elements, facilitating synchronized flexion and extension that closely mimic human gait kinematics. A 3D CAD model was developed in SOLIDWORKS and subjected to motion simulation, yielding a functional range of motion with 120° flexion and 37.6° extension. The mechanism achieves smooth articulation with a maximum angular velocity of 33.42 deg/s and acceleration of 33.04 deg/s², driven by a constant velocity rotor (300 deg/s). Simulink-based control system analysis confirmed stability, with an open-loop response exhibiting 10% overshoot and a 2-second settling time. A transfer function was derived from simulated input-output data, and system stability was further verified through pole-zero mapping, frequency response, and root locus analysis. By leveraging topological complexity rather than actuation redundancy, this work demonstrates that a single DOF mechanism can achieve biomimetic motion through intelligent link arrangement. The selected 14-link configuration provides a foundation for future integration of force analysis, lightweight materials, and experimental validation, offering a promising pathway toward adaptive, energy- efficient robotic leg systems.
Azaka et al. (Wed,) studied this question.