Time-Varying Gain Disturbance Observer- and Ring-Coupled Sliding Mode-Based Multiaxis Synchronization Control for 4-PPR Parallel Platforms

The operational condition of mass transfer imposes high-speed and high-precision requirements on the motion control of aligning platforms with in-plane four-Prismatic-Prismatic-Revolute (PPR) parallel mechanism. However, the strong nonlinear coupling among multiple kinematic chains and time-varying system uncertainties pose substantial challenges for the design of platform motion controllers. To address these issues, this article proposes a synchronization control strategy based on time-varying gain disturbance observer (DOB) and ring-coupled sliding mode control (SMC) for a 4-PPR parallel platform. The time-varying gain DOB enhances the position tracking performance of kinematic chains by feed-forward compensation for external disturbances and system uncertainties. The observer convergence under a slow-varying disturbance is also well-proven. Additionally, considering the ring-coupled errors under nonlinear speed conditions, SMC is employed to improve the motion synchronization among the axes of the platform. Finally, numerical simulations and experimental validations of tracking control are conducted on the 4-PPR parallel platform test rig. The results demonstrate that this method exhibits superior interaxis synchronization control and dynamic response performance compared to other controllers.