Structure design of fault-tolerant kinematically redundant parallel mechanisms for wave compensation

Abstract Wave compensation platforms are critical for ensuring offshore operational safety. However, existing designs often lack sufficient fault tolerance to withstand harsh marine environments. To facilitate the development of high-reliability compensation systems, a systematic seven-step structure design methodology utilizing screw theory is proposed in this paper. By embedding fault-tolerance verification within the synthesis phase, this methodology bypasses the repetitive trial-and-error iterations inherent in conventional intuitive approaches. Applying this methodology, a family of candidate structures is generated, among which a 3-PPSPR fault-tolerant kinematically redundant parallel mechanism (FTKRPM) is selected as a representative case for in-depth investigation. First, the kinematics is analysed and a geometric projection approach based on screw theory is employed to derive the analytical conditions for singularities. Subsequently, the fault-tolerant position workspace is analysed under single- and dual-actuator failure scenarios. Building upon these analytical foundations, a new Fault Tolerance Index is developed to quantitatively evaluate the mechanism's performance, thereby identifying the proposed structure as the optimal solution. Finally, a prototype is fabricated to qualitatively validate the kinematic feasibility and mobility retention under simulated fault conditions. The proposed methodology provides a practical and efficient structure design solution for marine engineering scenarios demanding high reliability, and the proposed PM demonstrates great potential for wave compensation.