Dynamics and control of a 3-DOF planar parallel manipulator using visual servoing resolved acceleration control

Abstract

This paper proposes the visual servoing resolved acceleration control scheme applied to a 3-degree of freedom (DOF) planar manipulator, which aims to reduce computational loads of the feedback control loop and the tracking errors of the end-effector in the conventional resolved acceleration control scheme. The computation loads are increased due to the calculations of the direct kinematics and the velocity inversion in the feedback control loop. The tracking errors of the end-effector are increased due to low-accuracy encoders, gearbox backlashes, and manipulator flexibility, etc. The proposed scheme incorporates a visual system, which directly captures the position of the end-effector instead of calculating the direct kinematics and the velocity inversion. Due to the requirement of inverse dynamics in the proposed scheme, the transformation of the Jacobian matrices between the passive and active links is imposed to the Euler-Lagrange’s equation so as to derive dynamic equations. In order to show the control performances, three existing torque-based control schemes are also applied to the manipulator. This study investigates the numerical simulations and the experimental validations, and the results show that the proposed scheme can reduce the computation loads and the tracking errors of the end-effector to compare with the three existing schemes.