Optimized Control of 3DOF Variable Stiffness Link Manipulator Using Feedback Linearization PD and Sliding Mode Approaches

Purpose: This study focuses on the control of a 3-degree-of-freedom (3DOF) variable stiffness flexible links manipulator, employing diverse control techniques to address the challenges associated with its inherent structural flexibilities. Variable Stiffness Link (VSL) manipulators offer enhanced adaptability and safety in various applications by dynamically adjusting their link stiffness. This feature allows them to optimize performance for different tasks, from delicate operations to robust industrial use. However, the variable stiffness introduces complex nonlinear dynamics, significantly complicating precise control and necessitating advanced control strategies. Methodology: The research investigates two advanced control methods: linearized feedback proportional-derivative (PD) control and sliding mode control (SMC). These techniques are employed for both position and trajectory control of the system, aiming to maintain precise joint angles while minimizing oscillations in the end effector. The controller designs for both linearized feedback PD and sliding mode control are presented, including stability analyses using Lyapunov theory. Experimental work is conducted to evaluate the effectiveness of both control strategies. Findings: The results demonstrate that both controllers achieve satisfactory performance in managing the complex dynamics of the flexible link system. The linearized feedback PD controller shows good tracking capabilities across the three joints while the sliding mode controller exhibits superior performance. Comparative analysis reveals that while both controllers effectively maintain stability and achieve precise trajectory tracking, the sliding mode controller displays marginally better performance in terms of steady-state errors and robustness to system nonlinearities. Unique contribution to theory, policy and practice: This research contributes to the advancement of control techniques for flexible manipulators, offering promising solutions for improving the performance and reliability of this manipulator for automation applications.