Dynamic analysis and response experimental study of a 6-UPU-RRP serial-parallel wave compensation mechanism under micro-disturbance with 3-DOF excitations

This study addresses end-payload offset in offshore operations caused by a ship's pitch, yaw, and heave motions under low sea states (sea state 4 and below). a scaled 6-UPU-RRP serial-parallel wave compensation mechanism. Forward and inverse kinematics models are established, with small-amplitude nonlinear solutions simplified via equivalent infinitesimal substitution. A Newton-Euler-based dynamic model of the compensation chain is built to clarify correlations among excitation variables, compensation variables, and component accelerations. Scaled multi-parameter kinematic analysis explores the effects of excitation parameters on end-effector motion and compensation variables. An integrated test bench enables co-simulations and hardware-in-the-loop experiments under harmonic excitations representative of sea state 4, analyzing dynamic responses and joint bending moments, with PID parameters tuned to enhance performance. Quantitative experiments yield a normalized sensitivity ranking of pitch joint driving torque as β (1.00) > f (0.68) > Δz 0 (0.45) > γ (0.32). Under the tested harmonic excitations, the mechanism ensures high end-payload stability and precision, with position scatters within approximately ±15 mm, providing a validated experimental reference for scaled wave compensation under low-sea-state equivalent excitations. Extension of these findings to irregular wave conditions would require further investigation with realistic wave spectra.