Fast and Precise Positioning With Coupling Torque Compensation for a Flexible Lightweight Two-Link Manipulator With Elastic Joints

This study presents an effective two-degrees-of-freedom controller, considering coupling torque compensation, with the aim of achieving fast and precise positioning of a flexible lightweight two-link robot with elastic joints. Coprime factorization-based feedforward control and
$H_\infty$
control are cooperatively applied to the quasi-full-closed-loop control structure, forming a fundamental control strategy with improved reference tracking and residual vibration suppression capability, compared with the original proportional–proportional integral control. However, satisfactory outcomes for control performance are not realized due to the coupling effect between the robot joints. Previous studies have often addressed the coupling issue for the semiclosed-loop control structure, based on the approximate rigid-body dynamics, but the existing methods are not applicable to the quasi-full-closed-loop control structure. In this research, a flexible three-mass model-based feedforward coupling torque compensation scheme appropriate for the quasi-full-closed-loop control structure is proposed, combined with a position reference filter design. The simulation and experimental results obtained confirm the superiority of the proposed method over the conventional methods, and the control specifications are consistent with those of the rigid manipulators. The proposed controller design is beneficial for industrial robotics applications that demand flexibility but without deterioration in control performance.