Modified Synchronization Sliding Mode Control of a 6-DOF Closed-Kinematic Chain Mechanism Robot Manipulator

Abstract

This study addresses the motion control of a Closed-Kinematic Chain Mechanism (CKCM) robot manipulator possessing six degrees of freedom (DOF). A major challenge in controlling CKCM manipulators arises from errors in joint coordination, particularly during high accelerations or sudden changes in payload. These errors can lead to loss of accuracy and, in some cases, cause mechanical stress or even damage to the manipulator’s structure. To address these challenges, a synchronization-based control strategy integrating Nonsingular Fast Terminal Sliding Mode Control (NFTSMC) with Time-Delay Estimation (TDE) was developed, referred to here as Modified Synchronization Sliding Mode Control with Time-Delay Estimation (MSSMC). The NFTSMC component provides fast finite-time convergence without singularity, while the TDE mechanism utilizes past control inputs and delayed system data to estimate the lumped unknown dynamics, noise, and external disturbances, thereby reducing the need for large switching gains and mitigating chattering. In addition, a numerical forward-kinematics solution based on Jacobian inversion and numerical integration is developed to obtain the manipulator’s Cartesian motion in the absence of a closed-form solution. Overall, the MSSMC scheme is model-free and maintains synchronization among active joints while enhancing the robustness and efficiency of the manipulator’s motion. A Lyapunov-based stability analysis establishes the stability of the proposed controller under bounded uncertainties and demonstrates practical finite-time convergence of the tracking errors. Simulation results show that MSSMC achieves better control performance than existing control schemes.